DC: Ways to Slow Brain Aging: Exercise, Estrogen, and Sleep?

18 Nov 2011

Aging brains slow down just as aging bodies do, but growing research indicates that people can influence the way their brains age. In a November 13 press conference at the Society for Neuroscience 2011 annual meeting, held 12-16 November in Washington, DC, scientists presented new evidence for the brain-protecting effects of several controllable factors: exercise, estrogen therapy, and sleep. Several studies employed structural brain imaging to detect preservation of the gray matter that normally shrinks with age, thus tying cognition to its physical underpinnings.

Claims for the cognitive benefits of exercise enjoy increasing research support. Numerous observational studies link physical activity to a lower risk of age-related cognitive decline and dementia (see AlzRisk analysis and ARF related news story). Some trial data support the relationship—for example, seniors who followed a regular exercise program for six months did better than non-exercisers on cognitive tests a year later (see ARF related news story). Recently, studies using structural MRI revealed that exercise can pump up brain volume. Older people who walked six to nine miles per week over a nine-year period ended up with more gray matter in several brain regions, including the hippocampus, than those who were more sedentary. The walkers also had a lower risk of cognitive impairment (see ARF related news story). In another study, the anterior hippocampus grew in seniors who walked three times per week for a year, but shrank in their sedentary peers (see ARF related news story).

Speaking at SfN, Gene Alexander at the University of Arizona, Tucson, described a different approach to testing the benefits of exercise. Rather than measuring the amount of exercise per se, he looked at physical fitness. As described in his poster, first author Krista Hanson and colleagues examined about 120 healthy, cognitively normal adults between the ages of 50 and 90 by structural MRI. In general, older participants showed a consistent pattern of smaller volumes in the lateral and medial frontal cortices, parietal and lateral temporal cortices, and cerebellum. Hippocampal size was relatively preserved with age. The researchers then tested the aerobic conditioning of the volunteers on an inclined treadmill. Those who scored the highest on fitness measures such as endurance and breathing efficiency also showed the least age-related brain changes. In effect, the most aerobically fit participants boasted “younger” brains than their less fit peers. They also scored better on tests of memory, processing speed, and executive function.

“Regions that are affected by aging are modulated by fitness,” Alexander concluded. He said the mechanism is not yet known, but suggested it might involve better vascularization or more brain-derived neurotrophic factor (BDNF), which is stimulated by exercise and plays a role in learning and memory (see, e.g., ARF related news story, ARF news story, and ARF story). The data add to accumulating evidence that exercise and fitness can preserve brain health. By focusing on specific fitness measures and how they correlate with brain volume, researchers may be able to pinpoint the best exercise interventions, Alexander suggested.

In contrast to the consensus on exercise, the benefits of estrogen for aging women have been hotly debated. (For the most recent analysis of this issue, see AlzRisk.) Though clinical trials showed health risks from long-term hormone replacement therapy, other studies suggest that estrogen helps the brain learn. Few studies have looked at the effect of the hormone on brain structure. One cross-sectional study found that postmenopausal women on hormone replacement therapy had more gray matter in prefrontal, parietal, and temporal cortices, and more white matter in medial temporal lobe, than non-users (see Erickson et al., 2005). The women who took hormones longest had more pronounced effects, suggesting that estrogen stems brain volume loss. However, this study did not follow women over time, so it could not demonstrate a causal relationship.

At SfN, Paul Newhouse at Vanderbilt University, Nashville, Tennessee, described a longitudinal estrogen study done in collaboration with Julie Dumas at the University of Vermont, Burlington. The authors gave either placebo or standard doses of 17β-estradiol, the primary human estrogen, to 24 healthy women around 60 years of age for three months. Each volunteer got structural MRI scans before and after treatment. Baseline scans showed no difference between placebo and treatment groups, but after treatment, women who had taken estradiol had more gray matter in several regions of the parietal, temporal, and prefrontal cortices than controls. In particular, the treatment enhanced frontal and temporal gyri, which play a role in attention, decision-making, and memory, Newhouse noted. These areas involve the cholinergic system, which degenerates in AD.

Newhouse said his data fit with primate work by John Morrison and colleagues at Mount Sinai School of Medicine in New York City that also shows volume loss in aged brains. Morrison found that aged, ovariectomized female rhesus monkeys lose dendritic spines from pyramidal cells in the prefrontal cortex, but that cyclical estrogen treatment restores spine density to the level seen in young monkeys (see Bailey et al., 2011). Spine density is closely tied to cognitive ability, as spines contain synapses.

One implication of the human study is that estrogen-induced neuroplasticity remains after menopause, Newhouse said. The women in this study were, on average, a few years past menopause, and some were as old as 70. Many researchers have advanced the idea of a “critical window” for estrogen treatment, saying brains that have been without the hormone for many years no longer respond to it (see, e.g., ARF related news story). In support of this idea, previous research by Newhouse and Dumas found that short-term estradiol treatment strengthens the cholinergic system in women in their fifties, but worsens performance in women over 70 (see Dumas et al., 2008).

A crucial question is whether these estrogen-related brain changes last, Newhouse said. If so, then perhaps short-term estrogen treatment could protect cognition in older women while avoiding the risk of stroke, breast cancer, and other health problems seen with long-term hormone therapy. “That’s the $64 million question,” Newhouse said, and he intends to address it if he can get funding, he told the crowd.

Sleep is another factor that has more recently begun to be tied to cognition and even Alzheimer’s disease (see, e.g., ARF related news story and ARF news story), as it plays a crucial role in memory consolidation (see ARF related news story). In her SfN press conference, Rebecca Spencer at the University of Massachusetts, Amherst, suggested that one culprit in age-related memory decline could be poor quality of sleep. It is believed that during sleep, the brain replays the day’s experiences to code them into the memory banks, but that this process becomes choppy in older brains (see Gerrard et al., 2008). Previously, Spencer’s group showed that sleep fails to consolidate motor learning in older adults (see Spencer et al., 2007). However, other studies have shown that episodic memories can be consolidated during sleep in older people (see Aly and Moscovitch, 2010).

For her current study, Spencer wondered whether the coding of a non-motor, sequential task would be affected by age. To test this, first author Laura Kurdziel taught 24 young adults and about 30 adults older than 50 to perform a computer task that required memorization of a sequence of colored doors in order to navigate through 10 virtual rooms. Kurdziel retested the participants 12 hours later. For half of each group, this time included a sleep interval during normal sleeping hours, while for the other half it did not. Kurdziel saw sharply divergent results for the young and old participants. Young adults who had had a chance to sleep made fewer errors on the task than those who had stayed awake. Older adults, however, got no cognitive benefit from sleep, and also made more errors overall than did younger participants. Spencer attributed this difference to the fragmented nature of sleep in older people, noting that seniors with more regular sleep patterns do better on memory tasks. She suggested that improving sleep quality could boost memory in aging adults. One hitch, however, is that researchers do not have a good way to “defragment” disordered sleep. Spencer said one possibility would be to use cognitive behavioral therapy to change sleep habits, as seniors who stay awake during the day and go to bed more tired sleep better than those who nap.—Madolyn Bowman Rogers.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Erickson KI, Colcombe SJ, Raz N, Korol DL, Scalf P, Webb A, Cohen NJ, McAuley E, Kramer AF. Selective sparing of brain tissue in postmenopausal women receiving hormone replacement therapy. Neurobiol Aging. 2005 Aug-Sep;26(8):1205-13. PubMed.
Bailey ME, Wang AC, Hao J, Janssen WG, Hara Y, Dumitriu D, Hof PR, Morrison JH. Interactive effects of age and estrogen on cortical neurons: implications for cognitive aging. Neuroscience. 2011 Sep 15;191:148-58. PubMed.
Dumas J, Hancur-Bucci C, Naylor M, Sites C, Newhouse P. Estradiol interacts with the cholinergic system to affect verbal memory in postmenopausal women: evidence for the critical period hypothesis. Horm Behav. 2008 Jan;53(1):159-69. PubMed.
Gerrard JL, Burke SN, McNaughton BL, Barnes CA. Sequence reactivation in the hippocampus is impaired in aged rats. J Neurosci. 2008 Jul 30;28(31):7883-90. PubMed.
Spencer RM, Gouw AM, Ivry RB. Age-related decline of sleep-dependent consolidation. Learn Mem. 2007 Jul;14(7):480-4. PubMed.
Aly M, Moscovitch M. The effects of sleep on episodic memory in older and younger adults. Memory. 2010 Apr;18(3):327-34. PubMed.

External Citations

DC: New ALS Genetics Hog the Limelight at Satellite Conference

18 Nov 2011

Researchers studying amyotrophic lateral sclerosis and other diseases related to RNA-binding proteins gathered in Arlington, Virginia, 10-11 November 2011, to revel in, amongst other things, widespread excitement about new genes recently identified in ALS. “The last two and a half months have been the most exciting time in the history of ALS,” said Don Cleveland of the University of California, San Diego, citing the discovery of ALS-linked variants in genes in ubiquilin 2 (see ARF related news story on Deng et al., 2011) and C9ORF72 (see ARF related news story on Renton et al., 2011 and Dejesus-Hernandez et al., 2011). This Society for Neuroscience satellite symposium titled RNA-Binding Proteins in Neurological Disease was convened by Paul Taylor of St. Jude Children’s Research Hospital in Memphis, Tennessee, and Fen-Biao Gao of the University of Massachusetts Medical School in Worcester.

Not surprisingly, the C9ORF72 work, presented at the meeting by Bryan Traynor of the National Institute on Aging in Bethesda, Maryland, and Rosa Rademakers of the Mayo Clinic in Jacksonville, Florida, made the biggest splash. The victory was all the sweeter because researchers had been hunting for the chromosome 9 mutation for five years (Morita et al., 2006). The repeat expansions in C9ORF72 found to cause disease probably come from a single founder, according to a paper published the week before the identification of the gene (Mok et al., 2011). This is remarkable, because this gene defect alone accounts for a sizable chunk of ALS cases. The anticipation continued with presentations by Aaron Gitler and James Shorter of the University of Pennsylvania in Philadelphia, who are sifting for new ALS gene candidates that are similar to already known genetic factors TAR DNA binding protein 43 (TDP-43; see ARF related news story on Sreedharan et al., 2008 and Gitcho et al., 2008) and Fused-in-Sarcoma (FUS; see ARF related news story on Kwiatkowski et al., 2009 and Vance et al., 2009).

Bob Brown of the University of Massachusetts Medical School in Worcester noted that there are now 22 genes or loci associated with familial as well as sporadic ALS. These account for approximately half of ALS cases with a clear inherited origin, as well as 4 to 5 percent of sporadic cases, Brown said. While superoxide dismutase 1 (SOD1) has long been the top gene—it explains one-fifth of familial ALS—TDP-43 and FUS appear to herald a new set of genes coding for RNA-binding proteins that relate to the disease. Genomewide association studies have yielded limited gene candidates (see ARF related news story on Chiò et al., 2009). In contrast, new hypothesis-driven approaches, in which scientists look for genes akin to those already implicated in ALS, are rapidly adding to the gene list. In this two-part series, Alzforum profiles the latest genes to capture attention for ALS and related diseases.

At the satellite meeting, Gitler, who works on yeast models of TDP-43 and FUS toxicity, and Shorter, who studies their propensity for aggregation (see ARF related news story on Sun et al., 2011), noted tantalizing similarities between the two disease proteins: Both bind RNA with prion-like sequences that form aggregates when expressed in yeast and in vitro (see ARF related news story on Johnson et al., 2008). Moreover, many other RNA-binding proteins share those "prion-esque" motifs. On a list of all known RNA-binding proteins with the most classical yeast prion-like regions, FUS is number 1 and TDP-43 falls in tenth place. Researchers have been wondering about numbers two through nine. Might they also be risk factors for ALS or other neurological diseases? Or as Shorter phrased it, “Are FUS and TDP-43 the tip of the iceberg?”

It is looking like they might be: Shorter reported on numbers 2 and 3 on that list: TAF15 (TAT box binding protein [TBP]-associated factor) and EWS (Ewing sarcoma protein), respectively. FUS, EWS, and TAF15 make up the FET family, with roles in RNA transcription, processing, and transport (Law et al., 2006; Tan and Manley, 2009; Kovar, 2011). Like TDP-43 and FUS, TAF15 and EWS aggregated in the cytoplasm of yeast, where they were toxic, and all four formed pore-shaped oligomers in vitro, Shorter reported. Perhaps, he suggested, all these RNA-binding proteins form self-templating aggregates based not on classical amyloid architecture, but on their prion domains. The infectious nature of prion particles could also explain why symptoms of ALS, in people, often move sequentially from one tissue to adjacent areas. “Is it possible,” Shorter asked, “that underlying this complexity is actually a very simple prion-based transfer mechanism?”

For his part, Gitler presented data published in the November 7 Proceedings of the National Academy of Sciences USA, which also points to TAF15 as an ALS gene. Julien Couthouis, Michael Hart, and Shorter, all at the University of Pennsylvania, were co-first authors. The group started out with the knowledge that there are 213 human RNA-binding proteins that contain an RNA recognition motif, or RRM, homologous to those in TDP-43 and FUS. Gitler obtained clones for 133 of the genes and gave them to a cadre of high school students he had recruited for the summer. The students inserted these genes into yeast expression vectors, fusing them to the gene for yellow fluorescent protein.

Then, the team put each gene through its paces, looking for those that would behave like TDP-43 and FUS. Using fluorescence microscopy, the researchers determined that 80 of their candidates localized to the cytoplasm, as do TDP-43 and FUS. Of that 80, 38 were toxic to yeast. Thirteen of those 38 proteins, including TDP-43, FUS, and TAF15, contain prion-like domains.

Gitler and colleagues then focused on that part of the TAF15 gene homologous to the two FUS regions where many disease-linked mutations concentrate: the arginine-glycine-glycine (RGG) domain required for aggregation, and the carboxyl-terminal proline-tyrosine-rich motif required for nuclear localization. They sequenced TAF15 DNA from 735 people with ALS and 1,328 healthy controls. The DNA samples came from mostly Caucasian libraries at the Coriell Institute for Medical Research in Camden, New Jersey; the University of Pennsylvania; and the Mayo Clinic in Jacksonville, Florida. The team discovered three mutations (glycine-391-glutamate; arginine-408-cysteine; and glycine-473-glutamate) that were present only in cases, not controls. They identified another variant (methionine-368-threonine) in a separate, Swedish cohort, and a fifth (glycine-452-glutamate) in Australian patients. The work jibes with two further TAF15 mutations (alanine-31-threonine and arginine-395-glutamine) that Brown reported at the meeting (Ticozzi et al., 2011). Brown also mentioned discovering potential ALS mutations in ubiquilin 1, a ubiquilin 2 homolog.

Furthermore, Gitler and colleagues transfected TAF15 into rat embryonic spinal cord neurons and discovered that the ALS-linked mutations promoted the formation of TAF15 cytoplasmic inclusions. TAF15 also aggregated in Shorter’s in-vitro assays, à la TDP-43 and FUS, with disease-linked mutations promoting aggregation. And in collaboration with Nancy Bonini, also at the University of Pennsylvania, the team determined that TAF15 upregulation caused neurodegeneration and death in fruit flies. Finally, working with UPenn colleagues Virginia Lee and John Trojanowski, the team showed that TAF15 is mislocalized to cytoplasmic inclusions in postmortem spinal cord tissue from people who had sporadic ALS. These inclusions were distinct from those that contain TDP-43. Mutations in RNA-binding proteins may work to dysregulate RNA metabolism and cause disease, Gitler suggested. Whether they do so individually or in concert is not clear yet. Gitler invited other researchers to investigate the RNA-binding proteins on his list that contain prion domains.

Gregory Petsko of Brandeis University in Waltham, Massachusetts, who attended the meeting and also works with yeast models of TDP-43 and FUS toxicity (see ARF related news story on Ju et al., 2011), commended the Gitler-Shorter approach to ALS gene discovery: “I think that RNA-binding proteins with prion-like domains are going to be potential genetic modifiers or causes of ALS. This makes a tremendous amount of sense,” Petsko told ARF.

While researchers such as Gitler are starting with a gene list, others are starting with ALS-linked protein aggregates to work backward to the genes involved in disease. Their hits include new RNA-binding proteins and players related to protein degradation. For that, read upcoming Part 2 of this report.—Amber Dance

This is Part 1 of a two-part series. See also Part 2.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Deng HX, Chen W, Hong ST, Boycott KM, Gorrie GH, Siddique N, Yang Y, Fecto F, Shi Y, Zhai H, Jiang H, Hirano M, Rampersaud E, Jansen GH, Donkervoort S, Bigio EH, Brooks BR, Ajroud K, Sufit RL, Haines JL, Mugnaini E, Pericak-Vance MA, Siddique T. Mutations in UBQLN2 cause dominant X-linked juvenile and adult-onset ALS and ALS/dementia. Nature. 2011 Sep 8;477(7363):211-5. PubMed.
Renton AE, Majounie E, Waite A, Simón-Sánchez J, Rollinson S, Gibbs JR, Schymick JC, Laaksovirta H, van Swieten JC, Myllykangas L, Kalimo H, Paetau A, Abramzon Y, Remes AM, Kaganovich A, Scholz SW, Duckworth J, Ding J, Harmer DW, Hernandez DG, Johnson JO, Mok K, Ryten M, Trabzuni D, Guerreiro RJ, Orrell RW, Neal J, Murray A, Pearson J, Jansen IE, Sondervan D, Seelaar H, Blake D, Young K, Halliwell N, Callister JB, Toulson G, Richardson A, Gerhard A, Snowden J, Mann D, Neary D, Nalls MA, Peuralinna T, Jansson L, Isoviita VM, Kaivorinne AL, Hölttä-Vuori M, Ikonen E, Sulkava R, Benatar M, Wuu J, Chiò A, Restagno G, Borghero G, Sabatelli M, ITALSGEN Consortium, Heckerman D, Rogaeva E, Zinman L, Rothstein JD, Sendtner M, Drepper C, Eichler EE, Alkan C, Abdullaev Z, Pack SD, Dutra A, Pak E, Hardy J, Singleton A, Williams NM, Heutink P, Pickering-Brown S, Morris HR, Tienari PJ, Traynor BJ. A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD. Neuron. 2011 Oct 20;72(2):257-68. Epub 2011 Sep 21 PubMed.
DeJesus-Hernandez M, Mackenzie IR, Boeve BF, Boxer AL, Baker M, Rutherford NJ, Nicholson AM, Finch NA, Flynn H, Adamson J, Kouri N, Wojtas A, Sengdy P, Hsiung GY, Karydas A, Seeley WW, Josephs KA, Coppola G, Geschwind DH, Wszolek ZK, Feldman H, Knopman DS, Petersen RC, Miller BL, Dickson DW, Boylan KB, Graff-Radford NR, Rademakers R. Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS. Neuron. 2011 Oct 20;72(2):245-56. Epub 2011 Sep 21 PubMed.
Morita M, Al-Chalabi A, Andersen PM, Hosler B, Sapp P, Englund E, Mitchell JE, Habgood JJ, de Belleroche J, Xi J, Jongjaroenprasert W, Horvitz HR, Gunnarsson LG, Brown RH. A locus on chromosome 9p confers susceptibility to ALS and frontotemporal dementia. Neurology. 2006 Mar 28;66(6):839-44. PubMed.
Mok K, Traynor BJ, Schymick J, Tienari PJ, Laaksovirta H, Peuralinna T, Myllykangas L, Chiò A, Shatunov A, Boeve BF, Boxer AL, Dejesus-Hernandez M, Mackenzie IR, Waite A, Williams N, Morris HR, Simón-Sánchez J, van Swieten JC, Heutink P, Restagno G, Mora G, Morrison KE, Shaw PJ, Rollinson PS, Al-Chalabi A, Rademakers R, Pickering-Brown S, Orrell RW, Nalls MA, Hardy J. The chromosome 9 ALS and FTD locus is probably derived from a single founder. Neurobiol Aging. 2012 Jan;33(1):209.e3-8. PubMed.
Sreedharan J, Blair IP, Tripathi VB, Hu X, Vance C, Rogelj B, Ackerley S, Durnall JC, Williams KL, Buratti E, Baralle F, de Belleroche J, Mitchell JD, Leigh PN, Al-Chalabi A, Miller CC, Nicholson G, Shaw CE. TDP-43 mutations in familial and sporadic amyotrophic lateral sclerosis. Science. 2008 Mar 21;319(5870):1668-72. Epub 2008 Feb 28 PubMed.
Gitcho MA, Baloh RH, Chakraverty S, Mayo K, Norton JB, Levitch D, Hatanpaa KJ, White CL 3rd, Bigio EH, Caselli R, Baker M, Al-Lozi MT, Morris JC, Pestronk A, Rademakers R, Goate AM, Cairns NJ. TDP-43 A315T mutation in familial motor neuron disease. Ann Neurol. 2008 Apr;63(4):535-8. PubMed.
Kwiatkowski TJ Jr, Bosco DA, Leclerc AL, Tamrazian E, Vanderburg CR, Russ C, Davis A, Gilchrist J, Kasarskis EJ, Munsat T, Valdmanis P, Rouleau GA, Hosler BA, Cortelli P, de Jong PJ, Yoshinaga Y, Haines JL, Pericak-Vance MA, Yan J, Ticozzi N, Siddique T, McKenna-Yasek D, Sapp PC, Horvitz HR, Landers JE, Brown RH Jr. Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis. Science. 2009 Feb 27;323(5918):1205-8. PubMed.
Vance C, Rogelj B, Hortobágyi T, De Vos KJ, Nishimura AL, Sreedharan J, Hu X, Smith B, Ruddy D, Wright P, Ganesalingam J, Williams KL, Tripathi V, Al-Saraj S, Al-Chalabi A, Leigh PN, Blair IP, Nicholson G, de Belleroche J, Gallo JM, Miller CC, Shaw CE. Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6. Science. 2009 Feb 27;323(5918):1208-11. PubMed.
Chiò A, Schymick JC, Restagno G, Scholz SW, Lombardo F, Lai SL, Mora G, Fung HC, Britton A, Arepalli S, Gibbs JR, Nalls M, Berger S, Kwee LC, Oddone EZ, Ding J, Crews C, Rafferty I, Washecka N, Hernandez D, Ferrucci L, Bandinelli S, Guralnik J, Macciardi F, Torri F, Lupoli S, Chanock SJ, Thomas G, Hunter DJ, Gieger C, Wichmann HE, Calvo A, Mutani R, Battistini S, Giannini F, Caponnetto C, Mancardi GL, La Bella V, Valentino F, Monsurrò MR, Tedeschi G, Marinou K, Sabatelli M, Conte A, Mandrioli J, Sola P, Salvi F, Bartolomei I, Siciliano G, Carlesi C, Orrell RW, Talbot K, Simmons Z, Connor J, Pioro EP, Dunkley T, Stephan DA, Kasperaviciute D, Fisher EM, Jabonka S, Sendtner M, Beck M, Bruijn L, Rothstein J, Schmidt S, Singleton A, Hardy J, Traynor BJ. A two-stage genome-wide association study of sporadic amyotrophic lateral sclerosis. Hum Mol Genet. 2009 Apr 15;18(8):1524-32. PubMed.
Sun Z, Diaz Z, Fang X, Hart MP, Chesi A, Shorter J, Gitler AD. Molecular determinants and genetic modifiers of aggregation and toxicity for the ALS disease protein FUS/TLS. PLoS Biol. 2011 Apr;9(4):e1000614. PubMed.
Johnson BS, McCaffery JM, Lindquist S, Gitler AD. A yeast TDP-43 proteinopathy model: Exploring the molecular determinants of TDP-43 aggregation and cellular toxicity. Proc Natl Acad Sci U S A. 2008 Apr 29;105(17):6439-44. PubMed.
Law WJ, Cann KL, Hicks GG. TLS, EWS and TAF15: a model for transcriptional integration of gene expression. Brief Funct Genomic Proteomic. 2006 Mar;5(1):8-14. PubMed.
Tan AY, Manley JL. The TET family of proteins: functions and roles in disease. J Mol Cell Biol. 2009 Dec;1(2):82-92. PubMed.
Kovar H. Dr. Jekyll and Mr. Hyde: The Two Faces of the FUS/EWS/TAF15 Protein Family. Sarcoma. 2011;2011:837474. PubMed.
Ticozzi N, Vance C, Leclerc AL, Keagle P, Glass JD, McKenna-Yasek D, Sapp PC, Silani V, Bosco DA, Shaw CE, Brown RH Jr, Landers JE. Mutational analysis reveals the FUS homolog TAF15 as a candidate gene for familial amyotrophic lateral sclerosis. Am J Med Genet B Neuropsychiatr Genet. 2011 Apr;156B(3):285-90. Epub 2011 Jan 13 PubMed.
Ju S, Tardiff DF, Han H, Divya K, Zhong Q, Maquat LE, Bosco DA, Hayward LJ, Brown RH, Lindquist S, Ringe D, Petsko GA. A Yeast Model of FUS/TLS-Dependent Cytotoxicity. PLoS Biol. 2011 Apr;9(4):e1001052. PubMed.

External Citations

DC: Do Measurable Changes in Brain Function Herald Dementia?

23 Nov 2011

Some successful Alzheimer’s disease treatments may hinge on predicting who will get disease before they present with symptoms. To that end, many research groups are exploring biomarkers, cognitive tests, and brain imaging as possible ways to spot at-risk individuals before they show neuronal damage or mental deficits. Two functional imaging studies presented at this year’s Society for Neuroscience meeting, held 12-16 November in Washington, DC, suggest that underlying brain function during working memory tasks could herald cognitive decline even while performance on cognitive tests still looks completely normal.

Julie Dumas and colleagues at the University of Vermont in Burlington reported at a November 14 SfN press conference that post-menopausal women with cognitive complaints activate larger portions of their working memory centers when performing a working memory task than those who do not complain of cognitive difficulties. Through a series of questionnaires, the research team categorized 23 post-menopausal women with an average age of 57 years as “complainers” or “non-complainers.” Functional magnetic resonance imaging (fMRI) revealed that, although the 12 complainers performed as well as their content counterparts on a visual/verbal test of working memory, more of the complainers’ dorsolateral prefrontal cortices and anterior cingulate cortices were active.

“We believe that this is a compensation response,” said Dumas. “These cognitive complainers are activating brain regions involved in working memory to a greater extent than non-complainers.” Previous work from Reisa Sperling’s lab at Brigham and Women’s Hospital, Boston, suggested a hyperactivation of the hippocampus, which may also reflect a compensatory mechanism (see Celone et al., 2006).

A previous longitudinal study on a mixed-gender sample of 213 people with an average age of 67 reported that 54 percent of people complaining of cognitive difficulties progressed to mild cognitive impairment (MCI) or dementia within seven years, even though they performed normally on initial cognitive testing. Only 15 percent of those without complaints showed such decline (see Reisberg et al., 2010). The results hint that subjective cognitive impairment is a risk factor for dementia—people may not just be imagining cognitive difficulties. While other factors can account for cognitive problems, Dumas said she controlled for depression, sleep deprivation, and hot flashes in her study and still found differences between groups.

Other studies suggest that the hippocampus in older adults is smaller in cognitive complainers compared to non-complainers (see Stewart et al., 2011 and van der Flier et al., 2004).

“We’re now showing that these cognitive complaints are important around the age of menopause. We suggest they may be related to future cognitive changes,” said Dumas. She plans to follow these women, half of whom will be treated for three months with estrogen and half with placebo, to see if estrogen mitigates the functional differences between the two groups.

In a related poster presentation by Lucas Broster, a graduate student in the lab of Yang Jiang at the University of Kentucky College of Medicine in Lexington, described a pilot study that used functional data to differentiate between people with MCI and healthy controls in a mixed-gender, older cohort. Broster reported that while people with MCI performed just like healthy controls on a working memory task, electroencephalography (EEG) measurements distinguished the two groups (see Part 1 of a two-part series on EEG).

The research team tested 46 people (average age, 76)—either normal controls or diagnosed with MCI or AD—on a delayed match-to-sample test. Participants memorized an image and then determined whether the following images matched. Cognitively healthy people took the same amount of effort to accept or reject an image. However, individuals with MCI had to work harder to reject an image than they did to accept it, as shown by EEG-measured event related potentials in the left frontal brain. Preliminary data suggest that those with AD also had to work harder to reject an image, though Broster cautioned that these data are not significant in the small number of AD patients studied so far. The team will collect more results to see if the trend holds up. “Differentiating healthy patients versus those with MCI is clinically challenging,” said Broster. “If we find that the task is as sensitive as our pilot data imply, it could have some translational potential for screening people for MCI.”—Gwyneth Dickey Zakaib.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Celone KA, Calhoun VD, Dickerson BC, Atri A, Chua EF, Miller SL, DePeau K, Rentz DM, Selkoe DJ, Blacker D, Albert MS, Sperling RA. Alterations in memory networks in mild cognitive impairment and Alzheimer's disease: an independent component analysis. J Neurosci. 2006 Oct 4;26(40):10222-31. PubMed.
Reisberg B, Shulman MB, Torossian C, Leng L, Zhu W. Outcome over seven years of healthy adults with and without subjective cognitive impairment. Alzheimers Dement. 2010 Jan;6(1):11-24. PubMed.
Stewart R, Godin O, Crivello F, Maillard P, Mazoyer B, Tzourio C, Dufouil C. Longitudinal neuroimaging correlates of subjective memory impairment: 4-year prospective community study. Br J Psychiatry. 2011 Mar;198(3):199-205. PubMed.
van der Flier WM, van Buchem MA, Weverling-Rijnsburger AW, Mutsaers ER, Bollen EL, Admiraal-Behloul F, Westendorp RG, Middelkoop HA. Memory complaints in patients with normal cognition are associated with smaller hippocampal volumes. J Neurol. 2004 Jun;251(6):671-5. PubMed.

DC: Anecdotes and Music Have Special Spots in the Brain

23 Nov 2011

Given a random date 30 years ago, most people could not recount exactly what they had for breakfast, the clothes they wore, or events in that evening’s news. But some people with an extraordinary ability known as highly superior autobiographical memory (HSAM) can recall such trivial facts with ease. What is going on in their brains? And could the answer to this question help researchers understand memory loss or dementia? New findings, presented at the 41st annual Society for Neuroscience meeting, held at the Walter E. Washington Convention Center in the nation’s capital on 12-16 November 2011, suggest that certain brain areas are structurally different in these rare mnemonic talents.

In 2006, Larry Cahill and colleagues at the University of California, Irvine, published a paper documenting the first known case of HSAM (see Parker et al., 2006). Since that case was publicized, more people came forward claiming this ability. Cahill’s group confirmed that 20 of them—ranging in age from 25 to 60, with a average age of about 43—have HSAM.

To see what sets people with HSAM apart from everyone else, Aurora Leport and colleagues in the Cahill lab conducted a structural magnetic resonance imaging (MRI) study of 11 of those individuals. She found that several brain areas were unique in people with HSAM. Their insula had a different shape, their lentiform nucleus was larger, and their parahippocampal gyrus and uncinate fascicule had a higher fractional anisotropy (FA) than in controls. The last could mean that white matter tracts are more robust and possibly able to communicate more easily. These brain areas are associated with both autobiographical memory (see Svoboda et al., 2006) and obsessive-compulsive disorder (see Radua and Mataix-Cols, 2009). This could explain why a majority of these volunteers, though they aren’t diagnosed with OCD, seem to have obsessive tendencies such as hoarding and germ-avoidance, said Aurora.

These HSAM regions are affected by atrophy or altered metabolism in Alzheimer’s disease. Even so, Leport and colleagues do not yet know whether these individuals are more or less resistant to Alzheimer’s neuropathology, or why these areas are different in their brains. Future studies will take a look at brain function to see how this unique group forms and retrieves autobiographical memories, as well as the genetics behind the condition.

Music memory, too, may have its own special place carved out in the brain. At SfN, a case study presented by Carsten Finke, Charité University Medicine Berlin, Germany, revealed that a 68-year-old former professional cellist with severe amnesia—both episodic and semantic—not only retained musical memory, but also the ability to learn music. The cellist’s dementia was not due to age or Alzheimer’s pathology. Rather, a bout of herpes encephalitis had destroyed his left temporal lobe, left orbitofrontal cortex, and parts of his right medial temporal lobe in 2005, permanently wiping his ability to name German landmarks, recall autobiographical or historical details, recognize most people, or encode new information.

But while the man, called P.M., could not name well-known composers or famous cellists, his semantic musical memory was substantially intact. He could identify rhythms and intervals in a test of amusia (the inability to recognize or reproduce musical tones). He distinguished orchestral pieces he had known from before his illness from others that were new, and even learned to recognize new musical pieces. The results suggest that semantic musical memory is likely separate from other areas of semantic memory in the brain, said Finke.

P.M.’s frail condition precludes functional brain imaging to examine how he processes music, said Finke, but the group will continue behavioral testing that may probe his abilities. For instance, the researchers want to know whether lyrics influence P.M.’s musical memory. They also want to see whether music therapy might help him, perhaps using his musical ability to compensate for other memory loss.

“Preserved musical memory may provide a window for rehabilitation and enhanced quality of life in patients suffering from memory disorders,” said Finke.

It is not immediately clear if these findings could help researchers studying Alzheimer’s. A recent paper reported that some AD patients fare better than those with semantic dementia at recognizing famous tunes, implicating the right temporal lobe in processing music (see Hsieh et al., 2011). Other studies suggest that the ability to play music remains intact for those with Alzheimer’s, but that patients have trouble recognizing familiar versus unfamiliar tunes (see Baird et al., 2009).
Other research suggests that Alzheimer’s patients respond positively to music, and suggest it as a therapeutic option (see Witzke et al., 2008), and anecdotally, caregivers frequently report that familiar music remains a way of reaching their loved one long after speech has been lost to advanced AD.—Gwyneth Dickey Zakaib.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

Paper Citations

Parker ES, Cahill L, McGaugh JL. A case of unusual autobiographical remembering. Neurocase. 2006 Feb;12(1):35-49. PubMed.
Svoboda E, McKinnon MC, Levine B. The functional neuroanatomy of autobiographical memory: a meta-analysis. Neuropsychologia. 2006;44(12):2189-208. PubMed.
Radua J, Mataix-Cols D. Voxel-wise meta-analysis of grey matter changes in obsessive-compulsive disorder. Br J Psychiatry. 2009 Nov;195(5):393-402. PubMed.
Hsieh S, Hornberger M, Piguet O, Hodges JR. Neural basis of music knowledge: evidence from the dementias. Brain. 2011 Sep;134(Pt 9):2523-34. PubMed.
Baird A, Samson S. Memory for music in Alzheimer's disease: unforgettable?. Neuropsychol Rev. 2009 Mar;19(1):85-101. PubMed.
Witzke J, Rhone RA, Backhaus D, Shaver NA. How sweet the sound: research evidence for the use of music in Alzheimer's dementia. J Gerontol Nurs. 2008 Oct;34(10):45-52. PubMed.

DC: Protein Work Expands ALS/FTD Genetics

25 Nov 2011

At RNA-Binding Proteins in Neurological Disease, a satellite of the annual meeting of the Society for Neuroscience, held 10-11 November 2011 in Arlington, Virginia, researchers reported big new discoveries in ALS genetics. Among the presenters who fingered potential new genes, many described a biochemical approach, examining disease-linked aggregates for promising candidates. “It may be that a good way to find ALS genes is to take these aggregates and ask what is in them,” said Robert Brown of the University of Massachusetts Medical School in Worcester. Gene variants that associate with ALS may illuminate the cause of related diseases, Brown added. Many labs are now beginning to tease apart aggregates to look for mutants that might be risk factors for disease.

Brown’s ideas bore out as the satellite meeting progressed and speakers rolled out a whole host of new proteins involved in these diseases (see also Part 1). Ian Mackenzie of the University of British Columbia in Vancouver, Canada, discussed one such related disease—frontotemporal lobar dementia. Mackenzie described an FTLD pathological aggregate that included new proteins related to ALS-linked Fused-in-Sarcoma (FUS): FUS’s close relatives TAF15 (TAT box binding protein (TBP)-associated factor 15) and EWS (Ewing sarcoma protein). Together with first author Manuela Neumann of the University Hospital Zurich, Switzerland, Mackenzie and colleagues reported the work in the September issue of the journal Brain. In another publication in the November Archives of Neurology, first author Faisal Fecto and senior author Teepu Siddique, of the Northwestern University Feinberg School of Medicine in Chicago, Illinois, looked beyond RNA binding proteins and reported that p62, a ubiquitin-binding protein involved in proteasomal and autophagic protein degradation, is mutated in some ALS cases. Paul Taylor of St. Jude Children’s Research Hospital in Memphis, Tennessee, who co-chaired the meeting with Fen-Biao Gao of the University of Massachusetts Medical School in Worcester, reported how a protein-based approach led him to new genes involved in human inclusion body myopathy with Paget’s frontotemporal dementia (IBMPFD), a disease that shares genetic risk factors, and sometimes symptoms, with ALS. Nicholas Seyfried of the Emory School of Medicine in Atlanta, Georgia, reported on a newly ALS-linked protein, PTB-associated splicing factor (PSF), which could provide fodder for a future gene hunt.

Mackenzie and Neumann theorized that if FUS appears in FTLD inclusions, then TAF15 and EWS might do the same. FUS, EWS, and TAF15 make up the FET family that shares homology and roles in RNA transcription, processing, and transport (Law et al., 2006; Tan and Manley, 2009; Kovar, 2011). And indeed, Mackenzie reported that cytoplasmic TAF15 inclusions appeared in postmortem tissue taken from both brain and spinal cord of patients who had FTLD with FUS pathology. EWS occasionally appeared in aggregates as well. TAF15 and EWS were absent from inclusions in the brain or spinal cord of ALS cases, Mackenzie said. All three proteins tended to be insoluble in FTLD-FUS cases, compared to healthy tissue, although for EWS, the difference was not statistically significant. TAF15 and EWS represent good candidates for FTLD genes, Mackenzie suggested. TAF15 has already been shown to be mutated in ALS (Ticozzi et al., 2011).

Further, Mackenzie proposed that defects in nuclear import of FET proteins could force them into the cytoplasm, causing disease. This protein family shares a proline-tyrosine (PY)-rich nuclear localization signal that is recognized by transportin, which ferries proteins into the nucleus. Mutations in the FUS PY region cause ALS. When the researchers transfected HeLa cervical cancer cells with a transportin inhibitor called M9M, TAF15 and EWS were forced into the cytoplasm, as happens for FUS (see ARF related news story). Barred from the nucleus, the TAF15 and EWS redistributed into stress granules, mimicking disease.

For their part, Fecto and Siddique also looked to previously implicated genes and proteins to form their hypothesis about p62. This protein is encoded by the gene sequestosome 1 (SQSTM1) and appears in inclusions in Alzheimer’s disease, Parkinson’s disease, ALS, and other neurodegenerative conditions (Kuusisto et al., 2001; Zatloukal et al., 2002; Gal et al., 2007; Mizuno et al., 2006). SQSTM1 is mutated in some cases of Paget’s disease of bone (Laurin et al., 2002). Given that so many inclusion body proteins—such as TAR DNA binding protein 43 (TDP-43) and FUS—have turned out to be genetically implicated in disease, p62 was a natural suspect, Fecto told ARF.

The researchers sequenced the gene from 546 people with ALS and 738 control subjects. They discovered 10 novel mutations among the ALS cases, including nine missense mutations and one deletion. The finding shows p62 is no mere “innocent bystander” that gets swept up into aggregates, but a real player in the disease, said Fecto, who speculated that the mutations might alter ubiquitin binding or make p62 more aggregation prone. Overall, genetic studies seem to be converging on two pathways, Fecto said. They are the RNA binding proteins and the protein degradation system. Perhaps not coincidentally, these pathways are intertwined, he noted. For example, p62 and ubiquilin 1 regulate TDP-43 stability and aggregation (Brady et al., 2011; Kim et al., 2009).

Both ALS and IBMPFD share mutations in p62. Another gene the two diseases have in common is valosin-containing protein (VCP; see ARF related news story on Johnson et al., 2010). VCP participates in a wide variety of cellular processes, including transcription and autophagy. It separates ubiquitinated proteins from complexes so they can be destroyed. At the meeting, Taylor presented new mutations in two RNA-binding proteins—the details are not yet available—that account for IBMPFD in two families. Like TDP-43 and FUS in ALS neurons, these mutant proteins exit the nucleus for the sarcoplasm of muscle cells.

Researchers at the University of Pennsylvania in Philadelphia have predicted that RNA-binding proteins with prion-like domains are also involved in ALS (see Part 1). Taylor’s two new IBMPFD proteins fit this profile. James Shorter of UPenn, who also spoke at the meeting, collaborated with Taylor to discover, via a computer algorithm, that the new proteins contain prion-like sequences. His lab also found that the proteins aggregate in vitro, especially when they contain the disease-linked mutations. “I think more and more of these RNA-binding proteins with prion-like domains will be revealed as crucial in neurodegenerative disease. Paul’s data…are extremely compelling, especially with the support from our prion-domain algorithm and pure protein studies,” Shorter wrote in an e-mail to ARF.

Finally, Seyfried presented PSF, which might be another potential candidate for a gene in ALS or related conditions. He reported that there is more PSF in insoluble fractions of frontal cortex from people who died of FTLD than from neurologically healthy controls. That protein functions in RNA transcription, splicing, and transport, Seyfried said. He found that PSF remained mostly nuclear, even in FTLD tissue, but occasionally filled the cytoplasm of oligodendrocytes. His team is now considering what role the protein might have in that cell type.—Amber Dance

This is Part 2 of a two-part series. See Part 1.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Law WJ, Cann KL, Hicks GG. TLS, EWS and TAF15: a model for transcriptional integration of gene expression. Brief Funct Genomic Proteomic. 2006 Mar;5(1):8-14. PubMed.
Tan AY, Manley JL. The TET family of proteins: functions and roles in disease. J Mol Cell Biol. 2009 Dec;1(2):82-92. PubMed.
Kovar H. Dr. Jekyll and Mr. Hyde: The Two Faces of the FUS/EWS/TAF15 Protein Family. Sarcoma. 2011;2011:837474. PubMed.
Ticozzi N, Vance C, Leclerc AL, Keagle P, Glass JD, McKenna-Yasek D, Sapp PC, Silani V, Bosco DA, Shaw CE, Brown RH Jr, Landers JE. Mutational analysis reveals the FUS homolog TAF15 as a candidate gene for familial amyotrophic lateral sclerosis. Am J Med Genet B Neuropsychiatr Genet. 2011 Apr;156B(3):285-90. Epub 2011 Jan 13 PubMed.
Kuusisto E, Salminen A, Alafuzoff I. Ubiquitin-binding protein p62 is present in neuronal and glial inclusions in human tauopathies and synucleinopathies. Neuroreport. 2001 Jul 20;12(10):2085-90. PubMed.
Zatloukal K, Stumptner C, Fuchsbichler A, Heid H, Schnoelzer M, Kenner L, Kleinert R, Prinz M, Aguzzi A, Denk H. p62 Is a common component of cytoplasmic inclusions in protein aggregation diseases. Am J Pathol. 2002 Jan;160(1):255-63. PubMed.
Gal J, Ström AL, Kilty R, Zhang F, Zhu H. p62 accumulates and enhances aggregate formation in model systems of familial amyotrophic lateral sclerosis. J Biol Chem. 2007 Apr 13;282(15):11068-77. PubMed.
Mizuno Y, Amari M, Takatama M, Aizawa H, Mihara B, Okamoto K. Immunoreactivities of p62, an ubiqutin-binding protein, in the spinal anterior horn cells of patients with amyotrophic lateral sclerosis. J Neurol Sci. 2006 Nov 1;249(1):13-8. PubMed.
Laurin N, Brown JP, Morissette J, Raymond V. Recurrent mutation of the gene encoding sequestosome 1 (SQSTM1/p62) in Paget disease of bone. Am J Hum Genet. 2002 Jun;70(6):1582-8. PubMed.
Brady OA, Meng P, Zheng Y, Mao Y, Hu F. Regulation of TDP-43 aggregation by phosphorylation and p62/SQSTM1. J Neurochem. 2011 Jan;116(2):248-59. PubMed.
Kim SH, Shi Y, Hanson KA, Williams LM, Sakasai R, Bowler MJ, Tibbetts RS. Potentiation of amyotrophic lateral sclerosis (ALS)-associated TDP-43 aggregation by the proteasome-targeting factor, ubiquilin 1. J Biol Chem. 2009 Mar 20;284(12):8083-92. PubMed.
Johnson JO, Mandrioli J, Benatar M, Abramzon Y, Van Deerlin VM, Trojanowski JQ, Gibbs JR, Brunetti M, Gronka S, Wuu J, Ding J, McCluskey L, Martinez-Lage M, Falcone D, Hernandez DG, Arepalli S, Chong S, Schymick JC, Rothstein J, Landi F, Wang YD, Calvo A, Mora G, Sabatelli M, Monsurrò MR, Battistini S, Salvi F, Spataro R, Sola P, Borghero G, , Galassi G, Scholz SW, Taylor JP, Restagno G, Chiò A, Traynor BJ. Exome sequencing reveals VCP mutations as a cause of familial ALS. Neuron. 2010 Dec 9;68(5):857-64. PubMed.

External Citations

DC: Where Does TDP-43’s Toxic End Really Come From?

25 Nov 2011

Clearly, the C-terminal of TDP-43 has something to do with amyotrophic lateral sclerosis (ALS). The toxic fragments appear as aggregating, 25- and 35-kiloDalton (kDa) species that supposedly result from cleavage by caspase 3 or another, still-unknown, protease. But there is a hole in this theory, according to Shangxi Xiao of the University of Toronto, Canada, who presented a poster at the Society for Neuroscience annual meeting, held in Washington, DC, 12-16 November 2011.

The hole is 8 kDa wide—the size of the amino-terminal stub that should be left behind when the 35-kDa piece is produced. That amino terminal peptide has not been observed. “If you cut TDP-43, you should get two parts,” said Xiao, who works with Janice Robertson at the University of Toronto, Canada. These scientists present a different theory. They propose that an alternative splice form of TDP-43 mRNA allows the ribosome to begin translation at a downstream start codon to make the carboxyl-terminal fragment of 35 kDa. Xiao cannot explain the provenance of the second 25-kDa C-terminal fragment, which could still be produced by caspase cleavage, he speculated.

In his poster, Xiao detailed the following scenario: TDP-43 has an alternatively spliced form that lacks 91 base pairs from exon 2. This deletion causes a frameshift, generating a premature stop codon and shortened open reading frame (ORF). It is unclear if this ORF is translated; however, the ribosome finds a second start codon farther down the transcript. This start codon normally encodes methionine 85 in full-length TDP-43, but in this alternate splice form acts as a second translational initiation site. That would then allow the ribosome to produce a protein of approximately 35 kDa. It is this product of alternative splicing and ribosomal scanning, not caspase cleavage, that accounts for the toxic C-terminal TDP-43 fragments, Xiao believes.

How did he get to this theory? While puzzling over the absence of the amino-terminal half of the supposedly cut-up protein, as well as a report that the fragment appears even in the absence of caspase 3 (Nishimoto et al., 2010), Xiao examined the mRNA sequences reported for TDP-43 in GenBank. He noticed the alternative splice form with the deletion and the premature stop codon. Xiao amplified and cloned this alternatively spliced mRNA from spinal cord samples donated by people who had amyotrophic lateral sclerosis (ALS). The splice variant was four times more prevalent in 12 ALS samples than in four control samples.

Xiao suspects that the first ORF of the alternatively spliced RNA is either not translated, or that the peptide product is rapidly degraded. To find evidence for the proposed C-terminal piece produced by the second start site, Xiao engineered an antibody specific for its amino end—MDETDASSA. He also generated an antibody to the amino end of the predicted caspase-cleaved 35kDA fragment—ASSAVKVKR. The antibodies clearly distinguished the fragments from each other, said Xiao, even though the two peptides share the ASSAVKVKR sequence. In patient tissue, the antibody to the translated fragment co-localized with a polyclonal full-length TDP-43 antibody, but the caspase-cleavage antibody did not. The researchers concluded that the cleavage-specific antibody does not recognize TDP-43 aggregates—and that the only fragments present were due to the alternative start site.

Next, Xiao transfected SH-SY5Y neuroblastoma cells and primary motor neurons with the code for the alternative start fragment. The cells formed toxic, ubiquitinated, insoluble aggregates in the cytoplasm; these recruited full-length TDP-43, matching what goes on in disease pathology. The scientists concluded that the 35-kDa TDP-43 fragment seen in people with ALS likely arises from alternative splicing and translation of an alternative open reading frame, not from caspase cleavage. But it remains possible that the 25-kDa fragment is a cleavage product, Xiao said.

The data are “convincing,” commented both Jean-Pierre Julien of Laval University in Québec City, Canada, and David Borchelt of the University of Florida in Gainesville, in e-mails to ARF. Both saw the data at the André-Delambre Foundation Symposium on ALS held 23-24 September 2011 in Québec City, Canada. “Their specific antibody is a very nice tool to study alternative splicing further,” emailed Mahmoud Kiaei of the University of Arkansas for Medical Sciences in Little Rock, who plans to collaborate with Xiao and Robertson.

Leonard Petrucelli of the Mayo Clinic in Jacksonville, Florida, noted that his and other groups have clearly seen a caspase-cleavage TDP-43 product (see ARF related news story; ARF news story; ARF story; and Dormann et al., 2009). If the enzyme cuts TDP-43 to make the 25-kDa piece, then it would also cut upstream to make the 35-kDa piece, he argued. As for the missing amino-terminal cleavage product, he said he has not specifically looked for it. The piece would be only 8 kDa and would run right off many standard gels. It could also be produced, but quickly degraded, he noted. But Petrucelli did not discount the possibility of alternative splicing: “Both mechanisms could exist,” he told ARF.—Amber Dance.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Nishimoto Y, Ito D, Yagi T, Nihei Y, Tsunoda Y, Suzuki N. Characterization of alternative isoforms and inclusion body of the TAR DNA-binding protein-43. J Biol Chem. 2010 Jan 1;285(1):608-19. PubMed.
Dormann D, Capell A, Carlson AM, Shankaran SS, Rodde R, Neumann M, Kremmer E, Matsuwaki T, Yamanouchi K, Nishihara M, Haass C. Proteolytic processing of TAR DNA binding protein-43 by caspases produces C-terminal fragments with disease defining properties independent of progranulin. J Neurochem. 2009 Aug;110(3):1082-94. Epub 2009 Jun 9 PubMed.

DC: Myriad Mice Mimic ALS, FTLD, Loss of TDP-43 Function

28 Nov 2011

The amyotrophic lateral sclerosis field is still searching for that super model. “There is no perfect mouse yet, but they all have interesting features,” said Amelie Gubitz, program director for research on ALS at the National Institute of Neurological Disorders and Stroke in Bethesda, Maryland. At RNA-Binding Proteins in Neurological Disease, a prelude to the Society for Neuroscience annual meeting held November 10-11 in Arlington, Virginia, attendees heard about four new mouse lines that produce various amounts of TAR DNA binding protein 43 (TDP-43).

Mutations in the RNA-binding protein TDP-43 cause amyotrophic lateral sclerosis (ALS) or frontotemporal lobar dementia (FTLD). In those diseases, TDP-43 exits the nucleus to form cytoplasmic aggregates. Philip Wong of Johns Hopkins University in Baltimore, Maryland, and Zuoshang Xu of the University of Massachusetts Medical School in Worcester each presented new model mice in which they attempted to mimic the loss of nuclear TDP-43 function by reducing or deleting the protein. Wong also described potential models for mild TDP-43 overexpression and for TDP-43 pathology in muscle tissue. And these four are not the only up-and-coming ALS mice out there: At the main Society meeting, held 12-16 November 2011 in Washington, DC, Peter Joyce of the Medical Research Council Mammalian Genetics Unit, Harwell, U.K., presented a new mouse based on superoxide dismutase 1, another aggregate-forming protein associated with ALS. The animals have a spontaneous mutation, in contrast to the usual SOD1 overexpressing strains.

At the Arlington meeting, chaired by Fen-Biao Gao of the University of Massachusetts Medical School in Worcester and Paul Taylor of St. Jude Children’s Research Hospital in Memphis, Tennessee, researchers noted that making ALS models by overexpressing TDP-43 might be the wrong way to go. “These overexpresser mice are pretty artificial,” Gubitz told ARF. Wong noted that most published TDP-43 mouse models make 2.5 to five times the normal amount of the protein (see ARF related news story on Wegorzewska et al., 2009; ARF news story on Wils et al., 2010; ARF news story on Xu et al., 2010; ARF related news story on Shan et al., 2010). Xu added, “We do not have credible evidence that TDP-43 [expression] is increased in humans.”

The problem in people, Xu and others believe, is nuclear depletion of TDP-43. One might assume, then, that a knockout model is appropriate—but Xu does not think there is absolutely no TDP-43 in the nucleus of ALS motor neurons. No null-TDP-43 mutations are associated with disease, he noted, and animals lacking any TDP-43 are not viable. He thinks instead there is less than normal TDP-43 in the nuclei of cells with ALS pathology. With this in mind, Xu set out to minimize, but not eliminate, TDP-43 expression using RNA interference. He introduced into mice a microRNA that interferes with TDP-43’s natural mRNA. By controlling the miRNA with the ubiquitous cytomegalovirus-chicken-β-actin promoter, Xu obtained a modest knockdown whereby TDP-43 mRNA dropped by half in the spinal cord and forebrain, and protein by some 20 percent in both the central nervous system and muscle tissue.

TDP-43 knockdown models are difficult to make, Xu told ARF, because TDP-43 regulates its own expression. Making a heterozygous mouse with one good and one bad copy of TDP-43 is ineffective because the protein simply upregulates its mRNA so that normal protein levels are still produced. The team’s RNA interference approach is a “creative” solution to this problem, commented Virginia Lee of the University of Pennsylvania in Philadelphia, who was not involved with the work.

Xu’s knockdowns started out normal—as do people who will go on to get ALS—but developed a wobbly gait around five to six weeks of age. This worsened to paralysis in some limbs by nine weeks. Internally, “there is exquisite selectivity to the motor neurons in terms of degeneration,” Xu said. Eventually, 60 percent of motor neurons were lost and the mice died around 100 days of age. “Because of the phenotypic resemblance to the human disease, this result suggests that a reduced function of TDP-43 may be the root of ALS and FTD,” Xu wrote in an e-mail to ARF. The model still needs further testing, he said.

Like Xu, researchers at the Wong lab worry that animals that highly overexpress TDP-43 make inaccurate models. These animals are so sick that they die too soon to properly mimic disease, said William Tsao, a student of Wong’s who presented a poster at the SfN conference. The animals do not even get paralysis. Even so, Tsao still thinks overexpression has some merit, saying that it needs to be done a little bit, instead of a lot. Tsao specifically selected transgenic mice that made slightly more of the protein than normal, using animals that carry either wild-type TDP-43 or the disease-linked mutant glycine-298-serine under the neural Thy1.2 promoter. His animals have approximately 1.5 times the normal amount of TDP-43 protein, including both the endogenous mouse version and the protein made from the human transgene. The mice did get sick, but Tsao had to be patient to see symptoms because they did not emerge until the mice were in their prime, Wong said. In this way, these animals model people with ALS, who do not develop symptoms until well into adulthood.

At one month, Tsao’s animals had abnormal reflexes in their hind limbs, and by one year of age they were not so much walking as paddling around their cages, with a swimming-like gait. By 18-20 months of age, many were paralyzed. The paralysis was frequently asymmetric, again akin to the human disease. At approximately two years old, the animals were so ill the researchers had to sacrifice them. The mice with mutant TDP-43 transgenes progressed in their disease a few months faster than those carrying wild-type TDP-43.

Looking postmortem, Tsao saw that neurons in these mice contained aggregates, but TDP-43 was not in them, leading Wong to conclude that TDP-43 inclusions may not be necessary for disease. He speculated that the aggregates may be made up of mitochondria, which have appeared in inclusions in other TDP-43 mice (see ARF related news story on Xu et al., 2010) . These animals offer a broader window in which to try treatments, Tsao said, and he thinks they might be better than other TDP-43 mice for testing drug treatments. Although the late-onset phenotypes are a practical challenge for researchers eager to obtain results, they may be more informative about the human disease, Gubitz said.

Wong also described his lab’s approach to selectively knock out TDP-43 to ask questions about the proteins’ role in particular tissues. The group uses the Cre-Lox system of gene deletion to knock out TDP-43 in specific cell types. “Does loss of TDP-43 in neurons contribute to disease?” Wong asked. Postdoctoral researcher Yun Ha Jeong aimed to answer this question in a poster at the Neuroscience meeting. She put Cre under control of the CaMKII promoter to ablate TDP-43 specifically in forebrain neurons. The researchers predicted that these mice should recapitulate the symptoms of frontotemporal lobar dementia caused by TDP-43 pathology in that part of the brain.

That prediction appears thus far to be right on. Although only two-thirds of the mice survived past their first month, those that did exhibited dramatic, age-dependent frontal atrophy, Wong told ARF. He is not sure why so many die young, but speculated that leaky Cre expression might knock out TDP-43 in more than forebrain neurons. Those that lived past their first month showed behavioral symptoms reminiscent of human FTLD. In mazes, they exhibited little anxiety or curiosity about their surroundings, unlike normal mice, Jeong said. She next plans to examine the social skills of the mutant animals, looking for a lack of interest in other mice. Apathy is a major FTLD symptom. “We have to be careful trying to assess [FTLD] in mouse models,” Wong noted. Nonetheless, he told ARF he thinks these mice are the best model for FTLD so far because others based on the genetic risk factors progranulin and tau have less frontal atrophy (Ghoshal et al., 2011; Kambe et al., 2011; Yin et al., 2010; Yin et al., 2010). Wong’s group is using the same approach to develop a line of mice lacking TDP-43 in motor neurons to mimic ALS.

In Arlington, Wong also asked if loss of TDP-43 in skeletal muscle could contribute to ALS. He presented a model designed to answer that query by expressing Cre under control of the myosin light chain promoter. These mice, made by graduate student Sophie Lin, consistently weighed less than controls, exhibited muscle degeneration, and died at four to five months of age. This suggests that some of the weakness in ALS could be due to problems in muscle rather than in motor neurons, Wong said. The TDP-43 knockout caused downregulation of Tbc1d1, which regulates glucose transporters on the cell surface (Chiang et al., 2010; Sakamoto and Holman, 2008). As a result, the mice have to obtain energy from fatty acids instead of glucose, limiting their caloric intake and weight gain. This metabolic phenotype may be relevant to human disease, where people with ALS have very little body fat, Gubitz commented (see ARF related news story).

Many labs are making TDP-43 mice, as well as mice that model pathology driven by FUS (see ARF related news story), another protein that is mutated in some ALS and FTLD cases. Together, they join the longtime favorite model in ALS research: mice that highly overexpress mutant human SOD1. However, those classic models have their own set of shortcomings; in particular, treatments that help SOD1 mice have not been successful in human trials (see ARF Webinar). The mice may have abnormalities related to the SOD1 overexpression that do not relate to human disease, said Joyce, who reported on a new breed of mSOD1 mice made by random mutagenesis. Among the 10,000 mutant mice archived at the MRC Mammalian Genetics Unit, one set had an aspartic acid-83-glycine mutation in SOD1. This corresponds to a human mutation (Millecamps et al., 2010) that interferes with the protein’s zinc binding, folding, and enzymatic activity (Krishnan et al., 2006).

Phenotypes for heterozygous mutant animals are mild. For homozygotes, “there seems to be a slowly progressive disease,” Joyce said. At 10-20 weeks of age, they developed hind limb tremors. Fifteen-week-old mice lost one-fifth of their spinal motor neurons. Shortly thereafter, Joyce observed the animals dropping their hips toward the ground. This behavior gradually worsened so that year-old animals—which were still alive, unlike many mSOD1 overexpression models—were jittery and did not move much about their enclosures. One-year-olds also showed gliosis. There were gender-specific phenotypes as well. Female mice were still alive at 18 months, but many of the males died of liver cancer starting around one year of age. This mimics a SOD1 knockout phenotype (Elchuri et al., 2005). Joyce next plans to look at the animals’ behavior and neuromuscular junctions.—Amber Dance.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Webinar Citations

Paper Citations

Wegorzewska I, Bell S, Cairns NJ, Miller TM, Baloh RH. TDP-43 mutant transgenic mice develop features of ALS and frontotemporal lobar degeneration. Proc Natl Acad Sci U S A. 2009 Nov 3;106(44):18809-14. Epub 2009 Oct 15 PubMed.
Wils H, Kleinberger G, Janssens J, Pereson S, Joris G, Cuijt I, Smits V, Ceuterick-de Groote C, Van Broeckhoven C, Kumar-Singh S. TDP-43 transgenic mice develop spastic paralysis and neuronal inclusions characteristic of ALS and frontotemporal lobar degeneration. Proc Natl Acad Sci U S A. 2010 Feb 23;107(8):3858-63. Epub 2010 Feb 3 PubMed.
Xu YF, Gendron TF, Zhang YJ, Lin WL, D'Alton S, Sheng H, Casey MC, Tong J, Knight J, Yu X, Rademakers R, Boylan K, Hutton M, McGowan E, Dickson DW, Lewis J, Petrucelli L. Wild-type human TDP-43 expression causes TDP-43 phosphorylation, mitochondrial aggregation, motor deficits, and early mortality in transgenic mice. J Neurosci. 2010 Aug 11;30(32):10851-9. PubMed.
Shan X, Chiang PM, Price DL, Wong PC. Altered distributions of Gemini of coiled bodies and mitochondria in motor neurons of TDP-43 transgenic mice. Proc Natl Acad Sci U S A. 2010 Sep 14;107(37):16325-30. Epub 2010 Aug 24 PubMed.
Ghoshal N, Dearborn JT, Wozniak DF, Cairns NJ. Core features of frontotemporal dementia recapitulated in progranulin knockout mice. Neurobiol Dis. 2012 Jan;45(1):395-408. PubMed.
Kambe T, Motoi Y, Inoue R, Kojima N, Tada N, Kimura T, Sahara N, Yamashita S, Mizoroki T, Takashima A, Shimada K, Ishiguro K, Mizuma H, Onoe H, Mizuno Y, Hattori N. Differential regional distribution of phosphorylated tau and synapse loss in the nucleus accumbens in tauopathy model mice. Neurobiol Dis. 2011 Jun;42(3):404-14. PubMed.
Yin F, Dumont M, Banerjee R, Ma Y, Li H, Lin MT, Beal MF, Nathan C, Thomas B, Ding A. Behavioral deficits and progressive neuropathology in progranulin-deficient mice: a mouse model of frontotemporal dementia. FASEB J. 2010 Dec;24(12):4639-47. PubMed.
Yin F, Banerjee R, Thomas B, Zhou P, Qian L, Jia T, Ma X, Ma Y, Iadecola C, Beal MF, Nathan C, Ding A. Exaggerated inflammation, impaired host defense, and neuropathology in progranulin-deficient mice. J Exp Med. 2010 Jan 18;207(1):117-28. PubMed.
Chiang PM, Ling J, Jeong YH, Price DL, Aja SM, Wong PC. Deletion of TDP-43 down-regulates Tbc1d1, a gene linked to obesity, and alters body fat metabolism. Proc Natl Acad Sci U S A. 2010 Sep 14;107(37):16320-4. PubMed.
Sakamoto K, Holman GD. Emerging role for AS160/TBC1D4 and TBC1D1 in the regulation of GLUT4 traffic. Am J Physiol Endocrinol Metab. 2008 Jul;295(1):E29-37. PubMed.
Millecamps S, Salachas F, Cazeneuve C, Gordon P, Bricka B, Camuzat A, Guillot-Noël L, Russaouen O, Bruneteau G, Pradat PF, Le Forestier N, Vandenberghe N, Danel-Brunaud V, Guy N, Thauvin-Robinet C, Lacomblez L, Couratier P, Hannequin D, Seilhean D, Le Ber I, Corcia P, Camu W, Brice A, Rouleau G, LeGuern E, Meininger V. SOD1, ANG, VAPB, TARDBP, and FUS mutations in familial amyotrophic lateral sclerosis: genotype-phenotype correlations. J Med Genet. 2010 Aug;47(8):554-60. Epub 2010 Jun 24 PubMed.
Krishnan U, Son M, Rajendran B, Elliott JL. Novel mutations that enhance or repress the aggregation potential of SOD1. Mol Cell Biochem. 2006 Jul;287(1-2):201-11. PubMed.
Elchuri S, Oberley TD, Qi W, Eisenstein RS, Jackson Roberts L, Van Remmen H, Epstein CJ, Huang TT. CuZnSOD deficiency leads to persistent and widespread oxidative damage and hepatocarcinogenesis later in life. Oncogene. 2005 Jan 13;24(3):367-80. PubMed.

DC: Does Estrogen Fine-Tune the Brain?

30 Nov 2011

Mounting evidence indicates that estrogens contribute to learning and memory, reported researchers at the Society for Neuroscience annual conference, held 12-16 November 2011 in Washington, DC. Estrogen signaling induces the rapid remodeling of spines and synapses, and amps up excitatory transmissions in the brain (see Smejkalova and Woolley, 2010), said Catherine Woolley at Northwestern University, Evanston, Illinois, in an SfN special lecture, although she added that researchers still need to clarify what physiological role these changes effect. In addition, estrogen acts through distinct mechanisms in male and female brains, Woolley noted, and these sex-specific differences deserve more study as they might shed light on gender differences in neurodegenerative and neuropsychiatric conditions. At an SfN mini-symposium, six scientists detailed some advances in this field, which may eventually yield therapeutic applications. As Woolley summed up, “We are at the beginning of a revolution in understanding how steroids act in the brain.”

Studies in rodents indicate estrogen plays a role in learning and memory. Mice that lack estrogen receptor (ER) β have a deficit in hippocampal long-term potentiation (LTP), a form of synaptic plasticity, while activation of ERβ enhances spatial working memory (see Liu et al., 2008). But how does estrogen produce these effects? In the classic steroid receptor model, estrogen binds nuclear ERα and ERβ, which act on DNA to alter transcription of target genes. The speakers noted that this model does not necessarily fit for all the cognitive actions of estrogen, however. Estrogen’s remodeling of spines and synapses is too rapid to be mediated by transcription, but instead seems to involve the activation of local signaling cascades. Supporting this idea, hippocampal estrogen receptors are mainly found in the plasma membrane around synapses, (see, e.g., Milner et al., 2001 and Mitterling et al., 2010). Estradiol, the main human estrogen, is also made locally at synapses by the enzyme aromatase (see e.g., Balthazart and Ball, 2006 and Saldanha et al., 2011), putting it in the right place to modulate neuronal circuitry. At SfN, speakers dug down into the detailed mechanisms of this rapid, synaptic estrogen action.

Adding estradiol to hippocampal slices from either male or female rodents amplifies excitatory synaptic transmission through the action of ERβ, Woolley said. Enikö Kramár at the University of California, Irvine, provided some clues as to how this works. In hippocampal tissue from adult male rats, she previously found that estradiol modulates the synaptic cytoskeleton by triggering actin polymerization through a second messenger pathway that involves the small GTPase RhoA and the actin-severing protein cofilin (see Kramár et al., 2009). Blocking actin assembly prevents the estrogen-induced increase in excitatory transmission, Kramár said. The question remained, however, as to how membrane-bound ERβ managed to activate intracellular RhoA. In new work, Kramár and colleagues report that ERβ can interact with and activate synaptic, membrane-bound integrin receptors of the β1 family, which can signal to RhoA. Neutralizing antibodies against β1 integrin blocked estrogen’s ability to pump up excitatory transmission, strengthening the case for this scenario.

By controlling the actin cytoskeleton, estrogen has the potential to remodel dendritic spines and to regulate neurotransmitter receptor trafficking. Deepak Srivastava at Northwestern described his research on cultured rat cortical neurons, in which estradiol treatment stimulates the growth of new dendritic spines within 30 minutes, and also leads to increased shuttling of AMPA glutamate receptors (see Srivastava et al., 2008). The new spines made contact with presynaptic terminals, suggesting they could form active synapses, but did not last, disappearing within 60 minutes after estradiol treatment. What is the purpose of such transient connections? Srivastava reported that when he followed estradiol treatment with a long-term potentiation protocol, the new spines stayed in place 24 hours later, and AMPA transmission was up as well. He suggested that estrogen acts to “prime” neuronal circuitry, creating increased connectivity that is then locked into place by brain activity and learning. He added that he does not know if this process is female-specific.

In her talk, Elizabeth Waters at Rockefeller University in New York City focused on estrogen’s effect in female rats. She noted that estrogen treatment increases spine number in young females, but not in aged ones. Searching for the reason, Waters found that estrogen treatment depletes synapses of ERα in young animals, but has no effect in old. By contrast, estrogen increases synaptic ERβ in both old and young females (see Waters et al., 2011). The changing ratio of synaptic ERα to ERβ in aged females may alter estrogen-induced plasticity, Waters suggested.

Paul Mermelstein at the University of Minnesota, Minneapolis, looked at sex-specific estrogen effects, using cultured female hippocampal neurons. He reported that within seconds, estradiol treatment causes a fourfold increase in CREB phosphorylation and CREB activity. CREB is a key protein implicated in learning and memory (see, e.g., ARF related news story). Dissecting the pathway, Mermelstein and colleagues found that ERα and ERβ interact with caveolin membrane proteins and metabotropic glutamate receptors (mGluRs) to activate downstream kinases and eventually CREB (see Boulware et al., 2005; Boulware et al., 2007; Meitzen et al., 2011). Depending on whether the estrogen receptor binds to caveolin 1 or 3, it activates distinct signaling pathways, Mermelstein added. He noted that this pathway is not the only mechanism of rapid estrogen action, but it seems to be a pervasive one, and is specific to female neurons. In addition, in different brain regions, estrogen receptors couple with distinct members of the mGluR family, allowing for a cell type-specific modulation of estrogen function, Mermelstein said. He pointed out that, depending on the particular mGluR activated, estrogen can play a role in behaviors such as sexual receptivity, drug-induced dopamine release, and pain perception, suggesting that this pathway may have broad-ranging effects.

Feng Liu at Pfizer Global Research and Development, Groton, Connecticut, also noted that estrogen is implicated in numerous conditions that show sex-specific differences. These include schizophrenia, which has delayed onset in women and symptoms that fluctuate across the menstrual cycle, and Alzheimer’s disease, where data suggests that lack of estrogens at menopause may increase the risk of cognitive decline (see Hughes et al., 2009). Estrogens may also play a role in depression, pain, and anxiety, Liu added. To try to target the central nervous system effects of estrogen without engaging its peripheral effects, Pfizer is focusing on ERβ, which is highly expressed in several brain structures. Liu said that Pfizer has developed a specific ERβ agonist, WAY200070, that replicates many of estrogen’s beneficial effects on memory, including increasing spine number, dendritic complexity, LTP, and learning (see ARF related news story). WAY200070 is an experimental compound that does not have good drug-like properties, Liu added. In addition to its other effects, the agonist quickly increases levels of critical synaptic proteins, which correlate with stronger LTP. Looking for the mechanism, Liu reported that ERβ activation decreases phosphorylation of the translation inhibitor EIF2α, thus allowing synaptic mRNAs to be quickly translated into proteins. Blocking EIF2α dephosphorylation abolished the effect of estrogen on synaptic protein levels, further supporting this mechanism.

Moving to a systems level, Tracey Shors at Rutgers University, Piscataway, New Jersey, provided a dramatic example of how male and female brains may be wired differently. Male and female rats respond in opposite ways to stress, Shors reported, which boosts spine density in the male hippocampus and depletes it in the female (see Shors et al., 2004). Stress also modulates subsequent learning in a sex-specific way. Shors subjected adult rats to a stressful experience, such as a 20 minute swim, allowed them to rest for a day, then trained them to blink in response to a tone. In unstressed rats, females learned this behavior more quickly than males. After a stress, however, females did not learn at all, while the performance of the male rats improved compared to their unstressed baseline. Impaired female learning depended on estrogen, as it did not happen in ovariectomized or prepubescent females.

Each sex uses different brain regions and circuitry for post-stress learning, Shors said. In males, the bed nucleus of the stria terminalis (BNST), a region that carries output from the amygdala and varies in males and females, mediates the enhanced learning after stress (see Bangasser et al., 2005). Lesions to this structure have no effect on female post-stress learning. Instead, females’ lack of learning after stress requires an active medial prefrontal cortex connected to the amygdala (see Maeng et al., 2010). Intriguingly, this wiring pattern is not set in stone, but changes across the lifespan and in response to experience, Shors said. Females who become mothers, or even mother another rat’s pups, no longer experience a drop in learning after stress, and this change seems to be permanent. Some of this work is slated for publication in Behavioral Neuroscience (see also Leuner and Shors, 2006). The experience of motherhood protects female rats from the negative effects of stress on learning, and implies that life experiences can affect brain circuitry, Shors concluded.

The data from this mini-symposium were also published in the November 9 Journal of Neuroscience. Commenting on the overall findings, Roberta Brinton at the University of Southern California, Los Angeles, noted that the data imply that estrogen is not needed for all types of learning, but is activated only in specific cells and pathways. Estrogen regulates synaptic plasticity for the most cognitively demanding tasks, Brinton suggested, such as delayed memory tests that require animals or people to encode information over time. Brinton pointed out that brain structures that develop hypometabolism after menopause, i.e., the prefrontal cortex and posterior cingulate, are also some of the first to exhibit deficits linked to mild cognitive impairment. Yet not all people develop age-related cognitive decline, and an estrogen-based therapy would probably not help everyone, Brinton said. In the future, scientists should focus on finding biomarkers that will identify those aging women who are candidates for hormone therapy, Brinton suggested. Other work presented at SfN found that post-menopausal women who complain of memory problems activate more of their brains during a memory task than those with no complaints, suggesting that this functional MRI signature could be such a biomarker (see ARF related news story).—Madolyn Bowman Rogers

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Smejkalova T, Woolley CS. Estradiol acutely potentiates hippocampal excitatory synaptic transmission through a presynaptic mechanism. J Neurosci. 2010 Dec 1;30(48):16137-48. PubMed.
Liu F, Day M, Muñiz LC, Bitran D, Arias R, Revilla-Sanchez R, Grauer S, Zhang G, Kelley C, Pulito V, Sung A, Mervis RF, Navarra R, Hirst WD, Reinhart PH, Marquis KL, Moss SJ, Pangalos MN, Brandon NJ. Activation of estrogen receptor-beta regulates hippocampal synaptic plasticity and improves memory. Nat Neurosci. 2008 Mar;11(3):334-43. PubMed.
Milner TA, McEwen BS, Hayashi S, Li CJ, Reagan LP, Alves SE. Ultrastructural evidence that hippocampal alpha estrogen receptors are located at extranuclear sites. J Comp Neurol. 2001 Jan 15;429(3):355-71. PubMed.
Mitterling KL, Spencer JL, Dziedzic N, Shenoy S, McCarthy K, Waters EM, McEwen BS, Milner TA. Cellular and subcellular localization of estrogen and progestin receptor immunoreactivities in the mouse hippocampus. J Comp Neurol. 2010 Jul 15;518(14):2729-43. PubMed.
Balthazart J, Ball GF. Is brain estradiol a hormone or a neurotransmitter?. Trends Neurosci. 2006 May;29(5):241-9. PubMed.
Saldanha CJ, Remage-Healey L, Schlinger BA. Synaptocrine signaling: steroid synthesis and action at the synapse. Endocr Rev. 2011 Aug;32(4):532-49. PubMed.
Kramár EA, Chen LY, Brandon NJ, Rex CS, Liu F, Gall CM, Lynch G. Cytoskeletal changes underlie estrogen's acute effects on synaptic transmission and plasticity. J Neurosci. 2009 Oct 14;29(41):12982-93. PubMed.
Srivastava DP, Woolfrey KM, Woolfrey K, Jones KA, Shum CY, Lash LL, Swanson GT, Penzes P. Rapid enhancement of two-step wiring plasticity by estrogen and NMDA receptor activity. Proc Natl Acad Sci U S A. 2008 Sep 23;105(38):14650-5. PubMed.
Waters EM, Yildirim M, Janssen WG, Lou WY, McEwen BS, Morrison JH, Milner TA. Estrogen and aging affect the synaptic distribution of estrogen receptor β-immunoreactivity in the CA1 region of female rat hippocampus. Brain Res. 2011 Mar 16;1379:86-97. PubMed.
Boulware MI, Weick JP, Becklund BR, Kuo SP, Groth RD, Mermelstein PG. Estradiol activates group I and II metabotropic glutamate receptor signaling, leading to opposing influences on cAMP response element-binding protein. J Neurosci. 2005 May 18;25(20):5066-78. PubMed.
Boulware MI, Kordasiewicz H, Mermelstein PG. Caveolin proteins are essential for distinct effects of membrane estrogen receptors in neurons. J Neurosci. 2007 Sep 12;27(37):9941-50. PubMed.
Meitzen J, Mermelstein PG. Estrogen receptors stimulate brain region specific metabotropic glutamate receptors to rapidly initiate signal transduction pathways. J Chem Neuroanat. 2011 Dec;42(4):236-41. PubMed.
Hughes ZA, Liu F, Marquis K, Muniz L, Pangalos MN, Ring RH, Whiteside GT, Brandon NJ. Estrogen receptor neurobiology and its potential for translation into broad spectrum therapeutics for CNS disorders. Curr Mol Pharmacol. 2009 Nov;2(3):215-36. PubMed.
Shors TJ, Falduto J, Leuner B. The opposite effects of stress on dendritic spines in male vs. female rats are NMDA receptor-dependent. Eur J Neurosci. 2004 Jan;19(1):145-50. PubMed.
Bangasser DA, Santollo J, Shors TJ. The bed nucleus of the stria terminalis is critically involved in enhancing associative learning after stressful experience. Behav Neurosci. 2005 Dec;119(6):1459-66. PubMed.
Maeng LY, Waddell J, Shors TJ. The prefrontal cortex communicates with the amygdala to impair learning after acute stress in females but not in males. J Neurosci. 2010 Dec 1;30(48):16188-96. PubMed.
Leuner B, Shors TJ. Learning during motherhood: A resistance to stress. Horm Behav. 2006 Jun;50(1):38-51. PubMed.

DC: ALS Treatment Possibilities Presented at SfN, Satellite

30 Nov 2011

While for patients, there is nothing but a void when it comes to effective treatments for amyotrophic lateral sclerosis (ALS), scientists have no shortage of ideas under development. Researchers presented several potential approaches at the Society for Neuroscience annual meeting, held 12-16 November 2011 in Washington, DC, and at RNA-Binding Proteins in Neurological Disease, a satellite conference held 10-11 November 2011 in Arlington, Virginia. Researchers at both meetings presented drug screens and other attempts to stymie ALS pathology by sidestepping or destroying toxic aggregates of the disease-linked proteins TDP-43 and FUS; blocking the destruction of protective molecules or the production of pathogenic ones; or silencing damaging genes. Fen-Biao Gao of the University of Massachusetts in Worcester and Paul Taylor of St. Jude Children’s Research Hospital in Memphis, Tennessee, chaired the satellite meeting.

Taming Toxicity
Gregory Petsko of Brandeis University in Waltham, Massachusetts, works with yeast models of TDP-43 and FUS. At the satellite meeting, he noted that FUS is “one of the more toxic proteins we have ever worked with.” In yeast, both wild-type and mutant FUS localize to the cytoplasm and form toxic aggregates. Looking for medicines that would ameliorate this toxicity, Petsko set up a screen to identify compounds with which yeast survive FUS induction. Even though the screen itself is simple, it took a year of tweaking to come up with a clean assay that has low signal-to-background noise but can still find small effects, Petsko said. His group has now screened some 150,000 compounds, of which 20 ameliorate FUS toxicity. The team is still working to discover what the drugs do, and whether their mechanism of action would be useful in human neurons suffering from ALS.

Petsko is also studying a suppressor of FUS toxicity called UPF1, a protein that is able to keep yeast alive in the presence of cytoplasmic aggregates of FUS or TDP-43 (see ARF related news story on Ju et al., 2011). UPF1 is an RNA-binding protein involved in degrading miscreant RNAs. Like TDP-43 and FUS, it has several functions, and Petsko’s team has not yet sorted out the protective mechanism. In collaboration with Steven Finkbeiner at the University of California in San Francisco, Petsko is studying the gene’s effects in motor neurons. As in yeast, FUS kills the neurons, and UPF1 rescues them. “We are pretty excited about this,” Petsko said. “This suggests that the yeast model is good enough and that the drug screen is worth doing.” At the same time, he wondered if perhaps UPF1, provided as a gene or a peptide, or upregulated or stabilized by medication, might be the treatment he is looking for.

TDP-43 Aggregate Busters
If aggregated TDP-43 and FUS are toxic to neurons, then some scientists argue that dissolving the aggregates should save the cells—and with that, perhaps people with ALS. Marisa Feiler in the Boston University laboratory of Ben Wolozin is taking that approach in her drug screen. Feiler presented a poster at the Neuroscience meeting and Wolozin discussed the work in a talk. Feiler transfected PC12 (rat adrenal cancer) cells with a green fluorescent protein-tagged TDP-43 construct and treated the cells with the stressor arsenite to cause the protein to aggregate in cytoplasmic stress granules (see related ARF Webinar on stress granules in disease). After screening more than 75,000 drugs, Feiler found 22 candidates that wipe away those TDP-43 clusters. On her poster, she focused on a drug known as “compound #8,” which cut the number of stress granule by 40 percent.

Feiler and Wolozin collaborated with Brian Kraemer of the University of Washington in Seattle to try out compound #8 in nematodes expressing both wild-type and mutant (alanine-315-threonine) TDP-43. These worms have movement phenotypes, but under the treatment they wriggled more quickly across their plates. “This was not a slam dunk…but it did increase their movement about twofold,” Wolozin told ARF. Worms with mutant TDP-43 normally lose five of their 19 motor neurons and three neuromuscular junctions; with treatment, they lost an average of 2.5 motor neurons and one junction. The researchers did not report if the treatment ablated aggregates. While the data suggest that dissolving TDP-43 aggregates is effective in this simple animal model, the investigators do not yet know how the drug acts.

At the South San Francisco biotechnology company iPierian, Ashkan Javaherian and colleagues are also working to do away with TDP-43 aggregates. The team, Javaherian reported at the Arlington symposium, has collected skin cells from 20 people with sporadic ALS and reprogrammed them into induced pluripotent stem cells, and then into motor neurons. “TDP-43 pathology seems to be a dominant type of pathology across sporadic ALS types,” said Javaherian, adding that TDP-43 aggregation is one among several potential disease mechanisms the company is targeting. In motor neurons derived from skin cells of healthy people, TDP-43 was nuclear and not aggregated, while three of the 20 sporadic ALS cases yielded motor neurons in which TDP-43 formed distinct nuclear aggregates. The company is looking for drugs that will block or destroy those TDP-43 globs. In a small screen of some 2,000 compounds, the team came up with 39 hits that decrease the percentage of cells with aggregates.

Virginia Lee of the University of Pennsylvania in Philadelphia questioned the pathology seen at iPierian, since most researchers have reported TDP-43 aggregation in the cytoplasm, not nucleus, of sick cells. “I worry that they are looking at an artifact,” she told ARF. In response, Javaherian noted that one of the three skin donors whose cells produced nuclear inclusions later died, and the researchers found the same kinds of nuclear aggregates in his spinal cord motor neurons. Thus, he thinks some scientists might have missed this nuclear pathology, or it might only be present in a subset of people with ALS.

Blocking Undesirable Pairings
Also at the Arlington satellite, Leonard Petrucelli of the Mayo Clinic in Jacksonville, Florida, discussed a potential treatment for frontotemporal lobar dementia (FTLD). This disease shares features with ALS, such as genetic mutations and pathology in TDP-43 and FUS. Petrucelli is interested in progranulin, which is mutated in some people with FTLD, leading to haploinsufficiency of the protein. Uptake of progranulin by the membrane receptor sortilin enhances progranulin clearance (see ARF related news story on Hu et al., 2010; reviewed in Ward and Miller, 2011), so Petrucelli hypothesized that blocking this process should boost progranulin levels and alleviate disease. His team screened for drugs that would interfere with the progranulin-sortilin interaction, and discovered compounds that boost extracellular progranulin levels in HeLa (cervical cancer) cells in culture.

Beka Solomon of Tel Aviv University in Israel also sought to block an undesirable interaction—in her case, between amyloid precursor protein (APP) and the β-secretase that cleaves it to form amyloid-β and soluble APP β (sAPPβ). At the Neuroscience meeting, Solomon described an antibody that shields the β-cleavage site on APP. She is testing this antibody in mouse models for Alzheimer’s disease (Arbel-Ornath et al., 2010), but some evidence indicates that sAPPβ may be involved in ALS as well (see ARF related news story; Steinacker et al., 2009; Koistinen et al., 2006). To look into this, Solomon treated 70-day-old ALS model mice overexpressing mutant human superoxide dismutase 1 (SOD1) with her APP antibody and observed a reduction in spinal cord sAPPβ levels. She reported seeing some improvement in the animals’ ability to balance on a rotating rod, as well as a two-week extension in lifespan. In male transgenics, the treatment tripled the number of motor neurons present at an age of 104 days, 14 days after treatment started, compared to untreated animals which lost neurons at a more rapid rate. At the same time point, the antibody treatment had reduced astrogliosis in both genders.

Gene Therapy
Gene therapy is another approach that Petsko and others are considering for ALS. This would require a reliable method to deliver nucleic acids to the motor neurons struggling in the spinal cord. Brian Kaspar of Nationwide Children’s Research Institute in Columbus, Ohio, is working on a vehicle, but as he said at the Arlington meeting, crossing the blood-brain barrier is ever the challenge. He has succeeded in getting adeno-associated virus (AAV) vectors to traverse the barrier (see ARF related news story on Foust et al., 2009), and at the meeting he discussed using the virus to deliver short hairpin RNA (shRNA) against SOD1. This approach is being trialed for familial ALS due to SOD1 mutations. Kaspar’s group recently reported that it also works on astrocytes derived from neural precursor cells from people with sporadic ALS, suggesting the treatment might have a broader reach (see ARF related news story on Haidet-Phillips et al., 2011). When Kaspar and colleagues used AAV9 to deliver the shRNA to three-week-old SOD1-G93A mice, it effectively knocked down the enzyme in astrocytes. Preliminary tests of grip strength indicated the treatment might delay disease onset, Kaspar said. While all of the treatment possibilities presented at the meeting are in preliminary stages of development, they offer varied approaches that may one day pan out as treatment options for ALS and related disorders.—Amber Dance.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Webinar Citations

Paper Citations

Ju S, Tardiff DF, Han H, Divya K, Zhong Q, Maquat LE, Bosco DA, Hayward LJ, Brown RH, Lindquist S, Ringe D, Petsko GA. A Yeast Model of FUS/TLS-Dependent Cytotoxicity. PLoS Biol. 2011 Apr;9(4):e1001052. PubMed.
Hu F, Padukkavidana T, Vægter CB, Brady OA, Zheng Y, Mackenzie IR, Feldman HH, Nykjaer A, Strittmatter SM. Sortilin-mediated endocytosis determines levels of the frontotemporal dementia protein, progranulin. Neuron. 2010 Nov 18;68(4):654-67. PubMed.
Ward ME, Miller BL. Potential mechanisms of progranulin-deficient FTLD. J Mol Neurosci. 2011 Nov;45(3):574-82. PubMed.
Arbel-Ornath M, Becker M, Rabinovich-Toidman P, Gartner M, Solomon B. Immunomodulation of AβPP processing alleviates amyloid-β-related pathology in Alzheimer's disease transgenic mice. J Alzheimers Dis. 2010;22(2):469-82. PubMed.
Steinacker P, Hendrich C, Sperfeld AD, Jesse S, Lehnert S, Pabst A, von Arnim CA, Mottaghy FM, Uttner I, Tumani H, Ludolph A, Otto M. Concentrations of beta-amyloid precursor protein processing products in cerebrospinal fluid of patients with amyotrophic lateral sclerosis and frontotemporal lobar degeneration. J Neural Transm. 2009 Sep;116(9):1169-78. PubMed.
Koistinen H, Prinjha R, Soden P, Harper A, Banner SJ, Pradat PF, Loeffler JP, Dingwall C. Elevated levels of amyloid precursor protein in muscle of patients with amyotrophic lateral sclerosis and a mouse model of the disease. Muscle Nerve. 2006 Oct;34(4):444-50. PubMed.
Foust KD, Nurre E, Montgomery CL, Hernandez A, Chan CM, Kaspar BK. Intravascular AAV9 preferentially targets neonatal neurons and adult astrocytes. Nat Biotechnol. 2009 Jan;27(1):59-65. PubMed.
Haidet-Phillips AM, Hester ME, Miranda CJ, Meyer K, Braun L, Frakes A, Song S, Likhite S, Murtha MJ, Foust KD, Rao M, Eagle A, Kammesheidt A, Christensen A, Mendell JR, Burghes AH, Kaspar BK. Astrocytes from familial and sporadic ALS patients are toxic to motor neurons. Nat Biotechnol. 2011 Sep;29(9):824-8. PubMed.

External Citations

DC: Is Alzheimer's Rooted in the Early Life?

02 Dec 2011

Could Alzheimer’s disease begin in the womb? One theory for the origin of some neurological diseases, such as schizophrenia (see Brown and Derkits, 2010) and autism (see Atladóttir et al., 2010), is that an infection in the mother alters fetal neurodevelopment, setting up offspring for disease brought on by another trigger later in life. Could the same be true for Alzheimer's disease? Irene Knuesel from the University of Zurich in Switzerland reported at the Society for Neuroscience annual meeting held 12-16 November 2011 in Washington, DC, that a two-hit immune challenge, one in late gestation and another one later in adult life, leads to amyloid plaques and hyperphosphorylated tau accumulation in wild-type mouse brains. The pathology follows a pattern that "strikingly" resembles that observed in humans with Alzheimer's disease, wrote the authors in their abstract. This new mouse model could allow study of late-onset sporadic Alzheimer's disease—as opposed to the familial form modeled by transgenic mice—and may implicate infection and inflammation as a driving force in AD, according to Knuesel.

"We have not studied the sporadic form of Alzheimer's disease sufficiently enough, and yet this makes up the major population of the patients," said Knuesel. "Now we have a model that would allow us to study, in a morphological context, the processing changes and upstream factors involved in initiation of plaque and tangle pathology—almost impossible to do in a transgenic mouse."

Knuesel and colleagues' work suggests that inflammation plays a prominent role in the sporadic form of the disease, perhaps even initiating it. They first found that in four-month-old triple-transgenic mice, a single systemic immune reaction—induced by injecting the viral mimic polyinosinic:polycytidylic acid (poly[I:C])—caused a dramatic boost in the plaque and tau pathology observed 11 months later. "I've never seen that much plaque deposition in triple-transgenic mice at that age," said Cindy Lemere, Brigham and Women's Hospital, Boston. "Giving that injection early in life led to very strong acceleration of AD-like pathology, showing that early exposure to an immune stimulus can fast-forward pathology."

Could an early immune challenge elicit AD-like pathology in wild-type mice as well? Knowing that some neurodevelopmental disorders might have their roots in gestation, the researchers wondered if the same might be true of Alzheimer's. The team found a window in late gestation when injecting mothers with poly(I:C), permanently altered their pups' immune systems. Circulating levels of several inflammatory cytokines remained elevated throughout the offspring's lives. The animals had more APP, and produced more Aβ42 and somatodendritic, hyperphosphorylated tau than controls, in which neuronal tau was predominantly axonal. A Y-maze test also demonstrated profound working memory deficits in these offspring at 22 months of age.

Knuesel and colleagues gave those same mice a second injection of poly(I:C) at 12 months of age, and looked at their brains three months later. Amyloid plaques—detected by an antibody against rodent Aβ40/42—were pronounced in the entorhinal (ERC) and piriform cortices. Relative to controls, there was also more Aβ immunoreactivity within the hippocampus, particularly in regions receiving projections from the ERC. The pattern suggests that the deposits started in the cortices and expanded to the hippocampus, much like they do in the early human form of Alzheimer's disease. The plaques resembled the diffuse ones found in humans, Knuesel said. Hyperphosphorylated tau also accumulated in the mouse neurons. While these aggregates were not similar to human neurofibrillary tangles (they were Gallyas silver stain-negative), Knuesel thought NFTs might form as the mice age. The mice also showed elevated microglial activation and some evidence of microglia degeneration. The researchers are conducting behavioral tests on the 12- to 15-month-old mice to test if they have cognitive deficits. The results suggest that an immune challenge early in development, followed by a second in adulthood, puts the brain at risk for AD-like pathology.

"The very early immune challenge seems to have long-term consequences for aging in the brain," said Lemere. "It appears that the brain is then set up so another immune challenge later in life makes the brain more susceptible to neurodegeneration."

Knuesel believes that the cytokines and chemokines produced by the mother as a result of infection cross the placental barrier, enter the fetus, and make their way across the underdeveloped blood-brain barrier to the central nervous system of the offspring. In late gestation, the fetus also contributes to the cytokine production. Knuesel thinks the elevated cytokines alter microglia and genes involved in early brain development and immune functions. Cytokines may also hamper division of microglial precursors so that there are fewer microglia in old age, making them less able to phagocytose protein deposits.

"I think it's a moderately low elevation of inflammatory cytokines that may damage the brain chronically," said Knuesel. Genetic factors and repeated infections in old age may also infer risk. "Then a systemic infection can be the last little kick that sends the system all the way downhill," Knuesel added.

Inflammation has long been thought to be involved in AD pathology, but it is not clear whether immune responses are a cause or a result of the disease (see ARF related news story). Microglia have been found to phagocytose plaques and clear them from the brain (see ARF related news story on Simard et al., 2006 and ARF related news story on El Khoury et al., 2007). But evidence that systemic inflammation in people with Alzheimer's disease speeds up cognitive decline suggests that some immune responses exacerbate AD (see Holmes et al., 2009). In addition, genomewide association studies reported that genes related to the innate immune system confer risk for AD (see ARF related news story on Harold et al., 2009 and Lambert et al., 2009).

There have been mixed reactions to Knuesel’s findings. At several conferences where she presented this work, scientists pointed out that rodent Aβ is not known to aggregate, leading them to question the nature of the amyloid deposits in these wild-type mice. "It would be helpful to clarify that they are extracellular versus intracellular, as well as the exact composition of β amyloid in these deposits, " said Lemere. Knuesel says she has done the biochemistry but is keeping the results under wraps until they are published, which she expects to be in the coming months.

This isn't the first time that Alzheimer's-like plaques have been induced in wild-type mice by infection. Chlamydia pneumoniae has been reported to induce amyloid plaques, for instance (see Little et al., 2004). Herpes simplex virus infection also causes Aβ42 to deposit in wild-type mice (see Wozniak et al., 2007 and recent ARF Webinar on herpes simplex virus as a possible trigger of AD). There is still much work to do before a link can be made between infection and the human form of Alzheimer's disease, including testing AD patients for immune markers and closely reviewing epidemiological data, Knuesel said.

"I don't think there's any epidemiology out there that has looked at that carefully," said Bruce Lamb of the Cleveland Clinic in Ohio. "But I think maybe it is time to do that kind of study." He added that the mechanism of how poly(I:C) works in these mice also needs further exploration.

"Knuesel’s two-hit strategy to develop a wild-type AD model has a sound scientific background because there is now genetic evidence for the role of innate immunity [in AD], and there is epidemiological and clinical evidence that systemic inflammatory mediators could contribute to the development of clinical Alzheimer’s," said Piet Eikelenboom of the Vrije Universiteit in Amsterdam, The Netherlands. But he is not yet convinced that the plaques seen in the rodents are comparable to the ones found in humans. He said he will reserve judgment until the new data are published.

Michael Chumley of the Texas Christian University in Fort Worth and his team are also looking into the effects of simulated bacterial infections on adult wild-type mice. In a poster presentation, graduate student Marielle Kahn reported that peripheral injections of lipopolysaccharide (LPS)—a bacterial coat component—over seven days in four- to six-month-old C57BL/6J mice (a common wild-type lab strain) led to immediate cognitive deficits. Animals had trouble with contextual fear learning and spent less time in the platform zone in the Morris water maze test. The mice were no longer sick at the time of testing, nor did they have elevated levels of some common pro-inflammatory cytokines left in their systems. However, their Aβ42 levels in the hippocampus were significantly elevated.

Taken together, these findings and Knuesel's support the idea that infection may trigger Alzheimer’s. "The implication could be that systemic inflammation is an instigating factor for Alzheimer's disease," said Chumley.

Chumley and colleagues do not yet know if mice fully recover cognitive function after the LPS injections, or if they continue to decline. The group will check for cognitive deficits a few weeks after injection, and will test the effects of repeated simulated infections on the mice. Recurring infections often occur in the older population, Chumley said, and the team wants to know if chronic infections and inflammation could drive Alzheimer's-like deficits and pathology.—Gwyneth Dickey Zakaib.

References

News Citations

Webinar Citations

Paper Citations

Brown AS, Derkits EJ. Prenatal infection and schizophrenia: a review of epidemiologic and translational studies. Am J Psychiatry. 2010 Mar;167(3):261-80. PubMed.
Atladóttir HO, Thorsen P, Østergaard L, Schendel DE, Lemcke S, Abdallah M, Parner ET. Maternal infection requiring hospitalization during pregnancy and autism spectrum disorders. J Autism Dev Disord. 2010 Dec;40(12):1423-30. PubMed.
Simard AR, Soulet D, Gowing G, Julien JP, Rivest S. Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease. Neuron. 2006 Feb 16;49(4):489-502. PubMed.
El Khoury J, Toft M, Hickman SE, Means TK, Terada K, Geula C, Luster AD. Ccr2 deficiency impairs microglial accumulation and accelerates progression of Alzheimer-like disease. Nat Med. 2007 Apr;13(4):432-8. PubMed.
Holmes C, Cunningham C, Zotova E, Woolford J, Dean C, Kerr S, Culliford D, Perry VH. Systemic inflammation and disease progression in Alzheimer disease. Neurology. 2009 Sep 8;73(10):768-74. PubMed.
Harold D, Abraham R, Hollingworth P, Sims R, Gerrish A, Hamshere ML, Pahwa JS, Moskvina V, Dowzell K, Williams A, Jones N, Thomas C, Stretton A, Morgan AR, Lovestone S, Powell J, Proitsi P, Lupton MK, Brayne C, Rubinsztein DC, Gill M, Lawlor B, Lynch A, Morgan K, Brown KS, Passmore PA, Craig D, McGuinness B, Todd S, Holmes C, Mann D, Smith AD, Love S, Kehoe PG, Hardy J, Mead S, Fox N, Rossor M, Collinge J, Maier W, Jessen F, Schürmann B, van den Bussche H, Heuser I, Kornhuber J, Wiltfang J, Dichgans M, Frölich L, Hampel H, Hüll M, Rujescu D, Goate AM, Kauwe JS, Cruchaga C, Nowotny P, Morris JC, Mayo K, Sleegers K, Bettens K, Engelborghs S, De Deyn PP, Van Broeckhoven C, Livingston G, Bass NJ, Gurling H, McQuillin A, Gwilliam R, Deloukas P, Al-Chalabi A, Shaw CE, Tsolaki M, Singleton AB, Guerreiro R, Mühleisen TW, Nöthen MM, Moebus S, Jöckel KH, Klopp N, Wichmann HE, Carrasquillo MM, Pankratz VS, Younkin SG, Holmans PA, O'Donovan M, Owen MJ, Williams J. Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease. Nat Genet. 2009 Oct;41(10):1088-93. PubMed.
Lambert JC, Heath S, Even G, Campion D, Sleegers K, Hiltunen M, Combarros O, Zelenika D, Bullido MJ, Tavernier B, Letenneur L, Bettens K, Berr C, Pasquier F, Fiévet N, Barberger-Gateau P, Engelborghs S, De Deyn P, Mateo I, Franck A, Helisalmi S, Porcellini E, Hanon O, , de Pancorbo MM, Lendon C, Dufouil C, Jaillard C, Leveillard T, Alvarez V, Bosco P, Mancuso M, Panza F, Nacmias B, Bossù P, Piccardi P, Annoni G, Seripa D, Galimberti D, Hannequin D, Licastro F, Soininen H, Ritchie K, Blanché H, Dartigues JF, Tzourio C, Gut I, Van Broeckhoven C, Alpérovitch A, Lathrop M, Amouyel P. Genome-wide association study identifies variants at CLU and CR1 associated with Alzheimer's disease. Nat Genet. 2009 Oct;41(10):1094-9. PubMed.
Little CS, Hammond CJ, MacIntyre A, Balin BJ, Appelt DM. Chlamydia pneumoniae induces Alzheimer-like amyloid plaques in brains of BALB/c mice. Neurobiol Aging. 2004 Apr;25(4):419-29. PubMed.
Wozniak MA, Itzhaki RF, Shipley SJ, Dobson CB. Herpes simplex virus infection causes cellular beta-amyloid accumulation and secretase upregulation. Neurosci Lett. 2007 Dec 18;429(2-3):95-100. PubMed.

Other Citations

DC: Targeting Toxic Extrasynaptic Signaling in HD and AD

02 Dec 2011

In neuronal transmission, as in real estate, location is everything. When N-methyl D-aspartate (NMDA) glutamate receptors sit in the synapse, they behave like good citizens, activating signaling pathways that promote memory formation and neuron survival. However, when the receptors loiter in the boondocks, they set off toxic signals that damage synapses and kill neurons. Extrasynaptic receptors fire particularly strongly in conditions like ischemia, Huntington’s disease (HD), and Alzheimer’s disease (AD), making them a promising therapeutic target (see Hardingham and Bading, 2010). In a symposium at the Society for Neuroscience annual meeting, held 12-16 November 2011 in Washington, DC, scientists discussed some of the latest research in this field. Session chair Stuart Lipton, from the Sanford-Burnham Medical Research Institute, La Jolla, California, pointed out that synaptic and extrasynaptic NMDA receptors vary in several ways, including their downstream targets, their subunit composition, and their firing patterns. Synaptic receptors fire in bursts, while extrasynaptic ones are continuously active. Speakers discussed these features in detail, as well as how extrasynaptic signaling might be targeted in HD and AD.

Synaptic and extrasynaptic NMDA receptors trigger antagonistic signaling pathways, emphasized Hilmar Bading at the University of Heidelberg, Germany. Synaptic signaling increases calcium levels in the nucleus, activates the transcription factor CREB, and leads to long-term learning and neuroprotection. By contrast, extrasynaptic signals shut off CREB, initiate apoptotic pathways, and cause breakdown of mitochondrial membranes. Bading’s group previously showed that the two types of NMDA signaling turn on distinct programs of gene expression (see ARF related news story on Zhang et al., 2007). Nuclear calcium may act as the master switch that controls adaptive responses such as neuronal plasticity and survival, Bading suggested. Of the nearly 200 genes regulated by nuclear calcium, about 10 of them make up the core neuroprotection program, Bading reported, and might be useful therapeutically. One of these, the transcription factor Atf3, reduces ischemic cell death by half in mice, Bading said.

Extrasynaptic NMDA receptors also vary from synaptic ones in their composition. All NMDA receptors consist of two GluN1 and two GluN2 subunits, but GluN2 subunits come in different forms. In the mature brain, GluN2A subunits predominate in synapses, while GluN2B preferentially populates extrasynaptic sites. This partitioning suggests that GluN2B plays the major role in excitotoxicity. The subunits also possess distinct C-terminal, cytoplasmic tails, allowing them to interact with different intracellular proteins. Interestingly, in early development, when GluN2B dominates at all NMDA receptor sites, synaptic signaling protects neurons from cell death, indicating that the GluN2B subunit does not necessarily activate cell death pathways (see Martel et al., 2009). Nonetheless, Giles Hardingham at the University of Edinburgh, U.K., wondered if subunit composition could help explain the differing toxicities of synaptic and extrasynaptic receptors.

To look more closely at the issue, Hardingham and colleagues made chimeric constructs, replacing the tail of GluN2B with that of 2A. Cultured neurons containing the chimeric receptor resisted excitotoxicity better than wild-type cells, Hardingham reported. Signaling by the GluN2B tail does play a role in harming cells, Hardingham concluded, and this difference is most noticeable in the context of a mild excitotoxic insult. Why is synaptic GluN2B less toxic than extrasynaptic? Hardingham noted that GluN2B toxicity only becomes apparent during chronic activation, such as that found in extrasynaptic sites. Looking for the downstream mechanism behind GluN2B excitotoxicity, Hardingham found that GluN2B signaling represses CREB, an important neuroprotective factor.

The difference between GluN2A and GluN2B excitotoxicity might have consequences for disease. Lynn Raymond at the University of British Columbia, Vancouver, pointed out that GluN2B is enriched in GABAergic medium spiny neurons of the striatum, which selectively degenerate in HD (see Raymond et al., 2011). Degeneration probably occurs through an excitotoxic mechanism, Raymond noted, as injecting glutamate and NMDA into the striatum can reproduce the symptoms of HD in mice. Raymond’s group found that HD mice have more extrasynaptic receptors than do wild-type mice (see ARF related news story on Milnerwood et al., 2010). In addition, overexpressing GluN2B in an HD mouse causes more atrophy, Raymond said.

Raymond compared HD mice (YAC128), which express mutant huntingtin protein containing 128 CAG repeats, with control mice that have normal huntingtin with 18 repeats. She reported that the YAC128 mice have more GluN2B at the cell surface than do controls, and that most of it is extrasynaptic. Looking for the mechanism, she found that the scaffold protein PSD-95, which stabilizes and maintains GluN2B in synaptic sites, shifts to extrasynaptic locales in HD mice. PSD-95 binds directly to huntingtin protein, and binds more tightly to the mutant form, Raymond noted, which may be linked to the relocation. In addition, striatal-enriched tyrosine phosphatase (STEP) is more active in HD mice than in wild-type. STEP dephosphorylates GluN2B, causing it to abandon the synapse and potentially freeing it up for incorporation into extrasynaptic receptors. Inhibiting STEP increases synaptic GluN2B, Raymond said. Downstream of GluN2B, Raymond found that the mitogen-activated protein kinase p38 was more active in the HD mice, and inhibiting it protected cultured HD neurons from death, suggesting that this protein could be a therapeutic target.

One sign of the importance of extrasynaptic signaling in HD is that memantine, an approved AD drug that selectively silences extrasynaptic signaling (see ARF related news story on Xia et al., 2010), reverses motor learning deficits in HD mice (see Okamoto et al., 2009). A UBC group led by Blair Leavitt is currently testing memantine in HD patients in a Phase 2 trial.

Memantine relieves symptoms in moderate AD, probably by dampening extrasynaptic signaling. In his talk, Lipton turned to the role that this type of signaling plays in AD. Recent work showed that Aβ can inhibit synaptic glutamate reuptake, causing the neurotransmitter to spill over and activate extrasynaptic sites (see ARF related news story on Li et al., 2011). Lipton reported that oligomeric Aβ also induces cultured astrocytes to spit out more glutamate. Lipton noted that this finding dovetails with data presented by Annalisa Scimemi at the National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, in a separate SfN session. The most abundant glutamate transporter in adult brain, GLT-1, is found mostly in astrocytes, and is responsible for mopping up extracellular glutamate. Scimemi reported that adding synthetic Aβ42 (oligomeric and monomeric) to hippocampal slices increased deposits of insoluble GLT-1 and doubled the time course of glutamate clearance by the transporter. This provides yet another mechanism behind elevated glutamate in AD brains.

Lipton, an author on worldwide memantine patents, said that the drug improves AD symptoms by acting as a low-affinity, transient NMDA channel blocker. This helps “turn down the volume” on NMDA transmission without silencing it, Lipton said. In addition, memantine blocks only open channels, allowing the drug to selectively block extrasynaptic receptors, which are chronically active, while largely sparing synaptic sites. However, memantine is not effective enough, Lipton said. He is developing a new version, nitro-memantine, that is even more selective for extrasynaptic sites. In addition to having the same effect as memantine in the NMDA receptor ion channel, nitro-memantine also nitrosylates the NMDA receptor, i.e., it transfers a nitric oxide group to a cysteine residue on the receptor, which desensitizes the channel. Lipton tested the drug in hippocampal slices from transgenic APP mice (J20), which show chronic extrasynaptic activity. In these mice, synaptic spine density is half that in wild-type mice. While memantine protects some spines, nitro-memantine restored spine density to virtually normal levels. Moving to an in-vivo system, Lipton reported that when 3xTg mice were treated with nitro-memantine for three months, levels of synaptophysin, a marker of synapses, returned to normal, and the mice improved in an object exploration test. In contrast, when treated with memantine, the mice showed no behavioral improvement. Lipton hopes the greater efficacy of nitro-memantine will eventually translate to people, although clinical trials are not yet scheduled.

Synaptic NMDA signaling not only protects neurons from insults, but also enables the encoding of long-term memories. In his talk, Bading noted that nuclear calcium may play a crucial role in learning, perhaps through the action of CREB, a key memory protein (see, e.g., ARF related news story). Using transgenic flies that express a neuronal calcium sensor, Bading found that calcium floods into the nucleus during learning. When he activated CaMBP4, an inhibitor of nuclear calcium signaling, the flies’ ability to remember an association 24 hours after learning dropped dramatically. Another gene stimulated by calcium signaling is vascular endothelial growth factor D (VEGF-D). Bading reported that VEGF-D maintains dendrite length and complexity, and is necessary for long-term memory in mice (see ARF related news story on Mauceri et al., 2011). Nuclear calcium signaling is not beneficial in all contexts, however. Blocking nuclear calcium signaling in the spinal cord dampens chronic inflammatory pain, Bading noted.—Madolyn Bowman Rogers.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

News Citations

Paper Citations

Hardingham GE, Bading H. Synaptic versus extrasynaptic NMDA receptor signalling: implications for neurodegenerative disorders. Nat Rev Neurosci. 2010 Oct;11(10):682-96. PubMed.
Zhang SJ, Steijaert MN, Lau D, Schütz G, Delucinge-Vivier C, Descombes P, Bading H. Decoding NMDA receptor signaling: identification of genomic programs specifying neuronal survival and death. Neuron. 2007 Feb 15;53(4):549-62. PubMed.
Martel MA, Wyllie DJ, Hardingham GE. In developing hippocampal neurons, NR2B-containing N-methyl-D-aspartate receptors (NMDARs) can mediate signaling to neuronal survival and synaptic potentiation, as well as neuronal death. Neuroscience. 2009 Jan 12;158(1):334-43. PubMed.
Raymond LA, André VM, Cepeda C, Gladding CM, Milnerwood AJ, Levine MS. Pathophysiology of Huntington's disease: time-dependent alterations in synaptic and receptor function. Neuroscience. 2011 Dec 15;198:252-73. PubMed.
Milnerwood AJ, Gladding CM, Pouladi MA, Kaufman AM, Hines RM, Boyd JD, Ko RW, Vasuta OC, Graham RK, Hayden MR, Murphy TH, Raymond LA. Early increase in extrasynaptic NMDA receptor signaling and expression contributes to phenotype onset in Huntington's disease mice. Neuron. 2010 Jan 28;65(2):178-90. PubMed.
Xia P, Chen HS, Zhang D, Lipton SA. Memantine preferentially blocks extrasynaptic over synaptic NMDA receptor currents in hippocampal autapses. J Neurosci. 2010 Aug 18;30(33):11246-50. PubMed.
Okamoto S, Pouladi MA, Talantova M, Yao D, Xia P, Ehrnhoefer DE, Zaidi R, Clemente A, Kaul M, Graham RK, Zhang D, Vincent Chen HS, Tong G, Hayden MR, Lipton SA. Balance between synaptic versus extrasynaptic NMDA receptor activity influences inclusions and neurotoxicity of mutant huntingtin. Nat Med. 2009 Dec;15(12):1407-13. PubMed.
Li S, Jin M, Koeglsperger T, Shepardson NE, Shankar GM, Selkoe DJ. Soluble Aβ oligomers inhibit long-term potentiation through a mechanism involving excessive activation of extrasynaptic NR2B-containing NMDA receptors. J Neurosci. 2011 May 4;31(18):6627-38. PubMed.
Mauceri D, Freitag HE, Oliveira AM, Bengtson CP, Bading H. Nuclear calcium-VEGFD signaling controls maintenance of dendrite arborization necessary for memory formation. Neuron. 2011 Jul 14;71(1):117-30. PubMed.

Other Citations

External Citations

DC: In a Scanner Made for Two, Dual Scan Shows Mental Coupling

08 Dec 2011

First, it was bicycles. Now, it’s magnetic resonance imagers. A dual-head functional magnetic resonance (fMRI) detection system developed by Ray Lee of Princeton University in New Jersey is the first to allow brain imaging of two people lying side by side in a single scanner. Lee presented some preliminary results at this year's Society for Neuroscience conference held 12-16 November in Washington, DC. The formidable instrument has turned up synchronized oscillations among certain brain areas—a buzz that happens only during social interaction. Which specific regions are coupled depends on the relationship between the two people being scanned and on the task they perform. The device could help researchers figure out how two brains interact with one another and what goes awry in the brains of people with social disorders.

Previous studies have attempted to get at the neural roots of social interaction by connecting two people in individual scanners via the Internet (see Montague et al., 2002) or by video conferencing (see Redcay et al., 2010). Data showed that regions such as the medial prefrontal cortex, the temporoparietal junction, and the anterior cingulate cortex are active when people communicate. But none of these studies captured an actual interaction between two people, said Lee; the interactions were only simulated. His device, which fits neatly inside any commercial MRI machine, contains two separate radiofrequency coils. The twin coils simultaneously pick up and transmit separate signals from both brains, allowing two people to be imaged while they directly interact in an fMRI scanner.

The twin coils surround each of two study participants’ heads. Subjects lie on their sides facing each other and make eye contact through a small transparent window between the two coils (see image below). Both keep their eyes open to steadily meet each other’s gaze or, as a control, alternately open and close their eyes so as not to make eye contact.

Scanner Made for Two
A twin-coil device accommodates a pair of volunteers in an MRI machine. The coils simultaneously pick up and transmit individual signals from each brain, allowing imaging of direct interactions, such as when the individuals gaze at each other through a small window. Image credit: Ray Lee

The study included 18 pairs of individuals—four romantically involved couples, 12 platonic female pairs and two male pairs. Lee found that between friends, the basal ganglia synchronize, meaning that the cells of that brain region oscillate together at the same rate. Between lovers, it’s the posterior cingulate cortex. In a separate experiment, one person gently touched the other. In that case, Lee found that the toucher’s motor and somatosensory cortex was coupled to the other person’s superior temporal sulcus and somatosensory cortex.

“This is direct evidence for how two people are communicating with each other—how their brains are synchronized,” said Lee. He suggested this new tool could help researchers uncover changes in brain coupling that underlie social disorders such as autism. The benefit for neurodegenerative disease research is not immediately clear. Conceivably, scientists could one day use the apparatus to understand why patients with Alzheimer’s disease stop recognizing friends, children, and spouses, or why people with frontotemporal dementia lose the ability to respond appropriately to social cues, Lee added. However, getting an AD patient that far advanced, or FTD patients, to lie in a scanner with someone else might be challenging. In addition, given the newfound synchronicity of basal ganglia in social interaction, his team is already thinking there may be some implications for Parkinson’s disease. Lee told ARF that motor symptoms worsen in people with PD when they are in certain social situations.

Despite the movement constraints inside an MRI scanner, the spatial resolution of this technique is much better than that of electroencephalography methods typically used to measure social interaction, said Joanna Saenger of the Max Planck Institute for Human Development in Berlin, Germany. The temporal resolution for EEG is superior to that of MRI. Even so, scientists will be able to use this new twin-coil device to help more precisely pinpoint individual brain regions that are associated with social interaction, she added.—Gwyneth Dickey Zakaib.

References

Paper Citations

Montague PR, Berns GS, Cohen JD, McClure SM, Pagnoni G, Dhamala M, Wiest MC, Karpov I, King RD, Apple N, Fisher RE. Hyperscanning: simultaneous fMRI during linked social interactions. Neuroimage. 2002 Aug;16(4):1159-64. PubMed.
Redcay E, Dodell-Feder D, Pearrow MJ, Mavros PL, Kleiner M, Gabrieli JD, Saxe R. Live face-to-face interaction during fMRI: a new tool for social cognitive neuroscience. Neuroimage. 2010 May 1;50(4):1639-47. PubMed.

DC: Anti-Aβ Treatments Old and New

09 Dec 2011

Despite clinical setbacks, lowering brain amyloid or soluble Aβ remains a popular approach for tackling Alzheimer’s disease. The main push comes in the form of small-molecule and immunotherapies developed in pharma companies. But at the Society for Neuroscience 2011 annual meeting, held 12-16 November in Washington, DC, numerous scientists also presented academic work in this area. Here follows a couple of strategies, including a new amyloid immunization strategy and an unusual attempt to clear brain amyloid with radiation.

The potential of the immune system to clear amyloid has caught the eye of many researchers, with more than a dozen anti-amyloid vaccination strategies currently in clinical trials. One potential drawback of active immunization is possible autoimmune side effects. At last year’s SfN, Charlie Glabe at the University of California, Irvine, talked about immunizing mice with a short peptide, called 3A, that forms β-sheet oligomers and stimulates an immune response specific for oligomeric forms of Aβ. Because 3A is not part of the human genome, it is unlikely to cause autoimmune effects, Glabe said. Back then, he reported that 3xTg mice vaccinated with 3A have fewer plaques and better cognitive function than unvaccinated ones. At this year’s meeting, Suhail Rasool, a postdoctoral researcher working with Glabe, presented new work extending the findings to Tg2576 mice. Rasool told ARF he chose these animals because, unlike the triple transgenics, they develop neuroinflammation and neuronal loss. This allowed the researchers to look more closely at the vaccine’s effect on inflammation.

Rasool compared vaccination with 3A peptide to vaccination with synthetic oligomers or fibrillar forms of Aβ. He injected the antigens subcutaneously every month from three to 14 months. The 3A oligomer was as effective as Aβ oligomers or fibrils in lowering soluble Aβ and amyloid plaque load, Rasool reported. At 14 months, immunized mice performed better in the water maze, object recognition tests, and passive inhibitory avoidance than unimmunized controls. Compared to controls, immunized mice produced less CD45, a marker of inflammation that is elevated in AD brain, and fewer activated astrocytes in the cortex and hippocampus, showing that the treatment quieted inflammation. Although most of these results were similar in all immunized animals, soluble Aβ42 fell only in mice immunized with 3A, not those treated with oligomeric or fibrillar Aβ. The data have been submitted for publication, Rasool noted. In future work, the authors would like to test 3A vaccination in an α-synuclein mouse model, as the immune response may also attack oligomeric forms of this protein.

If immunization approaches seem a dime a dozen, and you hunger for a new idea out of left field, then how about irradiating the skull? In a poster session, Daniel Michael at Beaumont Hospital, Royal Oak, Michigan, detailed early results from X radiation therapy in AD mouse models. If radiation seems far-fetched, it is in AD, but radiation has been used successfully to treat human systemic amyloidosis, Michael claimed (see Kurrus et al., 1998; Monroe et al., 2004; Poovaneswaran et al., 2008). Coauthor James Fontanesi, a radiation oncologist, wondered whether this treatment could also clear brain amyloid in APPSwe/PS1deltaE9 animals. They compared several different dosage amounts and protocols, from a single treatment of five, 10, or 15 grays (Gy), to a “fractionated” protocol where mice received one Gy for 10 days in a row, or two Gy for five consecutive days. (A “gray” is a unit of absorbed radiation equal to one joule of radiation absorbed by one kilogram of tissue, or 100 rad.) These dosages are similar to those used to treat the brains of children with leukemia who go on to have normal life expectancies, Michael told ARF, and, hence, are considered safe. In support of this, pathological examination showed little brain damage in the irradiated mice, and similar numbers of healthy neurons in treated and untreated brain regions.

The researchers irradiated one side of the brain and compared the number of amyloid plaques with those on the untreated side at two, four, and eight weeks after treatment. They reported that both the single and fractionated protocols reduced the number and size of plaques equally, with higher radiation doses being more effective than lower ones. Plaque number dropped further after eight weeks than after shorter intervals, implying that plaques continued to be cleared after dosing stopped. For example, mice treated with 15 Gy had an average of 40 percent fewer plaques in treated regions at two weeks post-treatment, and almost 70 percent fewer at eight weeks out. Michael said he does not know how radiation might reduce plaques, but hypothesizes that it stimulates local microglia and astrocytes, which then clear deposits. The researchers saw some evidence of increased levels of inflammatory mediators such as TNFα, IL10, and IL1β in treated brain regions, Michael said. In ongoing studies, the authors are testing cognition in treated mice and determining how long the effects they have seen to date will last.—Madolyn Bowman Rogers.

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

Paper Citations

Kurrus JA, Hayes JK, Hoidal JR, Menendez MM, Elstad MR. Radiation therapy for tracheobronchial amyloidosis. Chest. 1998 Nov;114(5):1489-92. PubMed.
Monroe AT, Walia R, Zlotecki RA, Jantz MA. Tracheobronchial amyloidosis: a case report of successful treatment with external beam radiation therapy. Chest. 2004 Feb;125(2):784-9. PubMed.
Poovaneswaran S, Razak AR, Lockman H, Bone M, Pollard K, Mazdai G. Tracheobronchial amyloidosis: utilization of radiotherapy as a treatment modality. Medscape J Med. 2008;10(2):42. PubMed.

Other Citations

External Citations

DC: What’s That New Stuff in and Around Nuclei of AD Cells?

09 Dec 2011

At this year’s annual meeting of the Society for Neuroscience, the number of mini- and nano-symposia dedicated to the molecular stalwarts of Alzheimer’s disease, Aβ and tau, was strikingly down. The trend may reflect both the field’s branching out toward other mechanisms and its shift toward more clinical and preclinical studies. In keeping with this shift, many of the Aβ presentations at the conference, held 12-16 November in Washington, DC, focused on treatment strategies or diagnostic potential. The former included a session on anti-Aβ strategies (see ARF related conference story), while the latter featured two posters from Charles Glabe’s lab that generated some hubbub and a novel tau correlate unveiled by Ben Wolozin’s group at Boston University.

Glabe, at the University of California, Irvine, has over the years generated a slew of antibodies to oligomeric forms of Aβ, notably the A11 and OC polyclonal antibodies that recognize a common structural conformation shared by different types of protein aggregates (see ARF related news story). At SfN, Glabe reported on a new monoclonal antibody whose properties raised eyebrows among other scientists. M78 recognizes a fibril-specific epitope in amino acids 6 to 12 of Aβ, but also binds large multimers and fibrils of α-synuclein and islet amyloid polypeptide. In that regard, it behaves similarly to A11, but in other aspects it seems unique. On his poster, Suhail Rasool in Glabe’s lab reported that M78 cross-reacts with some sort of inclusion in transgenic mice that is nuclear—not, as would be expected, extracellular, or even cytosolic. It also binds amyloid plaques. In another poster, Anna Pensalfini, in the same lab, reported that M78 similarly decorates cell nuclei and plaques in postmortem brain tissue taken from demented patients and cognitively normal people. The findings hint that the antibody may be detecting an early marker of pathology. Researchers with whom Alzforum at the meeting were intrigued while scratching their heads as to what this antibody might be picking up.

Probing the brains of six- to 14-month-old triple-transgenic (3xTg mice), Rasool found that M78 immunoreactivity appears in the nucleus at about 12 months of age. Scientists report variable pathology in these animals, but Glabe and colleagues find they accumulate intracellular Aβ (see ARF related Webinar) at about nine months and extracellular plaques at about 14 months. Rasool reported that M78 nuclear immunoreactivity coincides with cytosolic staining with the antibody 6E10, which recognizes the N-terminal of Aβ. Glabe told Alzforum that the new monoclonal seems to predominantly stain neurons, but also some oligodendrocytes and astrocytes. The researchers could not definitively say if it cross-reacts with any components in microglia. Most M78-positive nuclei lit up in the TUNEL test for DNA fragmentation, a marker of apoptotic cell death. M78 also recognized plaques that are not detected by 6E10 or by 4G8, another antibody that also binds the N-terminal of Aβ. It is unclear if M78-positive plaques are of a different kind. Rasool found thioflavin S-positive cores in only some of these plaques.

Pensalfini’s poster told a similar story about human tissue. She, too, found rampant nuclear M78 staining throughout the frontal cortex (Brodmann areas 4, 9, and 11) and in the hippocampus. Again, M78 correlated with 6E10 staining of the cytosol. In brain tissue from one non-demented person, Pensalfini used electron microscopy to confirm the M78 staining was indeed nuclear. The antibody also detected plaques in human tissue, though not necessarily in conjunction with the nuclear staining. In some tissue samples, M78 stained only nuclei; in others, it reacted only with plaques, and in yet others, it picked up both nuclei and plaques. Looking at tissue from 28 people with various levels of plaque deposition, Pensalfini found that M78-positive nuclei seem to appear before plaques, peak as plaque deposition ramps up, and then decline as plaques become widespread in the brain. Glabe told ARF that he thought this might indicate the antibody is detecting a marker of early- to mid-stage pathology, correlating with Braak plaque stages I and II.

As with the transgenic mice, M78-reactivity in human tissue seems to coincide with perturbations to DNA. Pensalfini found that DAPI staining for the latter goes down as M78 immunoreactivity goes up. Glabe suggested that these cells might be losing their nucleic acids because they are TUNEL positive, but other scientists were not so sure. For example, Dave Morgan, from the University of South Florida, Tampa, was intrigued by the posters, but thought DAPI might somehow be masked.

With what, exactly, does M78 react in transgenic mice and human brain? That’s the key question that Glabe said the lab is trying to answer. The researchers immunoprecipitated cell extracts with M78 and will employ mass spectrometry and other biophysical techniques to identify what the antibody pulled down. Morgan and some other scientists told Alzforum that M78 might actually bind some form of tau. Glabe is reserving judgment on that until more data come in, but he did tell ARF that of four transgenic AD models examined so far, M78 detects inclusions in nuclei of only 3xTg mice. These animals carry a tau mutation and develop tau pathology by six months of age and advanced neurofibrillary tangles by 20 months. The other three models have no tau pathology. Interestingly, Glabe also said that the most robust M78 staining seen so far in human tissue was from a patient with corticobasal degeneration, a tauopathy. In this initial sample, M78 did not bind brain tissue from people who had Parkinson’s disease or multiple system atrophy.

Ben Wolozin of Boston University was likewise intrigued by M78, but he had a different idea about what it binds. He suggested RNA-binding proteins. That might explain the antibody’s penchant for the nucleus, and it would fit with emerging work from Wolozin’s lab on stress granules. These cellular inclusions, which are laden with RNA-binding proteins, appear in response to “normal” stresses a cell might encounter and are reversible in this context; however, they also pop up in reaction to accumulating toxic proteins such as mutant huntingtin and TDP-43 (see ARF related Webinar). Wolozin has been looking to see if stress granules might be a common bellwether of neurodegeneration. At SfN, Tara Vanderweyde, a Ph.D. student in Wolozin’s lab, reported on her poster that stress granules coincide with tau pathology.

Vanderweyde used P301L tau mice (JPNL3) as a model system. She found that inclusions positive for the RNA-binding protein T cell internal antigen-1 (TIA-1), a common stress granule marker, accumulated in these animals as tau pathology progressed. The TIA-1 stress granules co-localized with tau and turned up predominantly in neurons, but some were also present in microglia early in the disease process, and in astrocytes at all stages. Interestingly, Vanderweyde reported that tristetraprolin (TTP), another stress granule marker, also accumulated in these animals but only associated with tau late in disease. Another stress granule marker that goes by the mouthful ras-GTPase-activating protein SH3-domain-binding protein (G3BP) identified granules that never associated with tau. The findings suggest that tauopathies could feature distinct forms of granules. In a related tau model (Tg4510), TIA-1, TTP, and G3BP accumulated with disease progression, and TIA-1 seemed to interact directly with tau, since the two co-immunoprecipitated.

Vanderweyde told Alzforum that she thinks G3BP could be an early marker of disease, accumulating in stress granules before tau pathology kicks in. “I think what is most striking is that people focus on tau, but doing that could miss an entire subset of neurons that may be sick,” she said. TTP, on the other hand, could mark late disease, which would be in keeping with its role in P-bodies, a type of granule that captures mRNAs for degradation.

Are these stress granules relevant to human conditions? As a first glimpse, Vanderweyde looked at tissue from six cases of Alzheimer’s and found the same scenario in human cells as in the mice. TIA-positive stress granules occurred predominantly in neurons and associated with tau in the perinuclear space. Wolozin told ARF that he is planning to look for stress granules in more samples of AD and other diseases. Vanderweyde said that they are also looking at Aβ mouse models. What, if anything, stress granules might mean in AD is something they plan to investigate. Whether Glabe’s M78 monoclonal recognizes tau, RNA-binding proteins, or something entirely different also remains to be seen.—Tom Fagan.

DC: Ways to Slow Brain Aging: Exercise, Estrogen, and Sleep?

Comments

Make a Comment

References

News Citations

Paper Citations

External Citations

Further Reading

News

DC: New ALS Genetics Hog the Limelight at Satellite Conference

Comments

Make a Comment

References

News Citations

Paper Citations

External Citations

Further Reading

Papers

News

DC: Do Measurable Changes in Brain Function Herald Dementia?

Comments

Make a Comment

References

News Citations

Paper Citations

Further Reading

News

DC: Anecdotes and Music Have Special Spots in the Brain

Comments

Make a Comment

References

Paper Citations

Further Reading

News

DC: Protein Work Expands ALS/FTD Genetics

Comments

Make a Comment

References

News Citations

Paper Citations

External Citations

Further Reading

Papers

News

DC: Where Does TDP-43’s Toxic End Really Come From?

Comments

Make a Comment

References

News Citations

Paper Citations

Further Reading

Papers

News

DC: Myriad Mice Mimic ALS, FTLD, Loss of TDP-43 Function

Comments

Make a Comment

References

News Citations

Webinar Citations

Paper Citations

Further Reading

Papers

News

DC: Does Estrogen Fine-Tune the Brain?

Comments

Make a Comment

References

News Citations

Paper Citations

Further Reading

News

DC: ALS Treatment Possibilities Presented at SfN, Satellite

Comments

Make a Comment

References

News Citations

Webinar Citations

Paper Citations

External Citations

Further Reading