Organization of Aβ Plaques and Tau Tangles Illuminated in AD Brain
Quick Links
Just as the Hubble space telescope’s ultra-deep field illuminated thousands of galaxies swirling within a tiny, dark, patch of the sky, the cryo-electron microscope has unveiled a striking array of Aβ and tau structures, all inhabiting one tiny section of a single human brain. Scientists led by René Frank of the University of Leeds, U.K., spied jumbles of different-sized Aβ fibrils in plaques, often intermixed with various vesicles and membrane parts, some of which may hail from inside dead cells. By contrast, tau aggregates were neatly ordered, with uniform, evenly spaced fibrils arranged into bundles. Many of these tau filaments resembled the paired helical filaments characteristic of AD. But surprisingly, others looked more like fibrils found in people with chronic traumatic encephalopathy (CTE). Different tau filament structures were spotted in separate cellular compartments, suggesting that subcellular environment shapes the formation of fibrils.
- Cryo-electron tomography reveals how plaques and tangles are arranged in brain tissue.
- Plaques comprise different-sized fibrils mixed with vesicles and other membrane detritus.
- Distinct tau fibril shapes were found in different subcellular compartments.
- Some tangles contain paired helical filaments and fibrils that resemble those found in CTE.
“The past several years of work from the labs of Michel Goedert and Sjors Scheres, among others, have shown us how the atomic structure of extracted fibrils correlates with histopathologic diagnosis,” wrote Andrew Stern and Dennis Selkoe of Brigham and Women’s Hospital in Boston (comment below). “These new findings from the Frank lab inch us closer to understanding how the atomic structure of amyloid fibrils relates to the adjacent subcellular disturbances underlying dementia.”
Previously, these researchers used similar methods to examine the in situ architecture of Aβ plaques within the brains of APP knock-in mice (May 2023 news). Cryo-ET exposed a mishmash of materials within plaques, including Aβ fibrils arranged in parallel bundles and lattices, along with short protofilament rods, some of which branched off from the fibrils. Intermixed within these amyloids were a menagerie of membrane parts, including extracellular vesicles and lipid droplets, multilamellar bodies, and bits of plasma membrane. Because APP knock-in mice do not develop extensive tau pathology or neurodegeneration, the mouse study was limited to the investigation of Aβ plaques.
The new study takes this “in-tissue” analysis to the next level, zooming in on the intricate molecular architecture of Aβ plaques and tau inclusions in the brain of a person who died with advanced AD. Co-first authors Madeleine Gilbert, Nayab Fatima, Joshua Jenkins, and Thomas O’Sullivan and colleagues obtained brain samples from the mid-temporal gyrus of this donor, who had developed AD symptoms at age 54 and died at age 70, as well as from a non-demented control who died at 90 years of age with no evidence of AD neuropathology. To preserve the original cytoarchitecture in the samples, both were rapidly flash-frozen, instead of chemically fixed in formalin, within six hours of death. Later, the researchers prepared thin slices from these frozen samples, and stained them with methoxy-04 to identify amyloids. They then selected regions rife with amyloid plaques or tau inclusions for deeper examination with cryo-electron tomography.
From among 25 tomograms taken in and around Aβ plaques, a scene emerged akin to what the researchers had seen in APP knock-in mice. Aβ plaques contained fibrils arranged in parallel arrays or lattices. About a third sprouted branches, which connected to each other, or thinner, protofilament-like rods. Interwoven into this fibrillar mix was a mishmash of membranes, including subcellular compartments such as extracellular vesicles and lipid droplets, as well as sheets of lipid membranes. This last feature had not been spotted in APP knock-in mice, and Frank proposed its presence in the AD brain could reflect remnants of dead cells. By contrast, neurodegeneration does not occur in the mouse model.
Anja Schneider of the German Center of Neurodegenerative Diseases in Bonn was intrigued by the presence of extracellular vesicles within the plaques. “It is unclear whether EVs just nonspecifically stick to pre-existing extracellular amyloid plaques, or if they play a role in seeding them,” she wrote. Schneider noted that previous studies indicate that EVs release Aβ from their surface, and may also seed plaques by virtue of their lipid composition.
Inside View of a Plaque. A tomographic slice of Aβ plaque reveals fibrils (cyan) arranged in different planes, extracellular lipid droplets (yellow) and vesicles (pink), subcellular compartments (dark green), and open membrane sheets (lighter green). [Courtesy of Gilbert et al., bioRxiv, 2023.]
How would tau filaments arrange themselves in the AD brain? Compared to the hodgepodge of amyloids and cellular odds and ends found within plaques, tau inclusions turned out to be extraordinarily tidy. The researchers spotted filaments within the cytoplasm of neurites and within myelinated axons. In one case, they found a bundle of tau fibrils stationed just outside of an axon, suggesting that it was extracellular, and could represent fibrillar leftovers from a dead cell, aka a “ghost tangle.” Regardless of their location, tau fibrils were always arranged in parallel bundles 300-800 nanometers wide. Within each bundle, filaments were evenly spaced, never had branches, and appeared structurally similar. This well-ordered arrangement likely speaks to the fact that tau filaments are formed by regulated, and spatially constrained, processes inside of cells, Frank said.
Zeroing in on the cross-section of tau fibrils within each bundle, the researchers observed a fold that was highly consistent with the paired, C-shaped protofilament core resolved by cryo-EM from the AD brain (Jul 2017 news). Fibrils in all but one bundle took this same core configuration, although the degree of helical twist differed from bundle to bundle.
Axonal Tau. In one tomogram, tau filaments (yellow) were oriented axially within a myelinated axon (brown). Subcellular membranes (green) and membrane-bound intracellular organelles (blue) appeared around the tau-laden axon. [Courtesy of Gilbert et al., bioRxiv, 2023.]
To examine fibrils at even higher resolution, the researchers deployed an alternative technique called cryo-focused ion beam scanning electron microscopy, in which an ion beam is used to carefully mill out a thin section of tissue. This avoids damage caused by mechanical cutting. From this analysis, they again spotted bundles of filaments that resembled AD PHFs. Surprisingly, they detected other bundles of filaments that took a different fold, in which the paired C-shaped protofilaments adopted a more open configuration. This fold was highly reminiscent of the atomic structure of tau filaments found in people with chronic traumatic encephalopathy (Mar 2019 news). Interestingly, although this bundle of CTE-like fibrils sat only one micron away from a bundle of AD PHF-like fibrils, the two bundles were separated by a membrane into different compartments.
Tsuneya Ikezu of the Mayo Clinic in Jacksonville, Florida, was fascinated by the detection of CTE-like tau fibrils in the AD brain. He noted that CTE tau pathology frequently arises in both neurons and glia, and wondered if the AD and CTE-like tau fibrils were found in distinct cell types.
Due to the thinness of the sections used for imaging and the lack of cell-type specific labeling, it is not possible to tell if the distinct structures reside within two different cells, or within separate compartments in the same cell, Frank said. However, he interprets the findings as convincing evidence that the subcellular environment in which a filament forms has a strong influence on its structure.
Segregated Bundles. In one bundle of tau filaments (gray, left), the cross-section of fibrils indicates a C-shaped protofilament core that resembles the cryo-EM structure of AD PHFs (left, yellow). Fibrils in another bundle (gray, right) had a more open C-shaped core structure resembling one seen in CTE (blue, right). [Courtesy of Gilbert et al., bioRxiv, 2023.]
Notably, the sample in Frank’s study came from a person with AD who had no neuropathological features of CTE, nor any history of head trauma. The findings jibe with recent reports of tau filaments striking a CTE pose in people with other conditions, including subacute sclerosing panencephalitis, an inflammatory condition that occurs in some individuals after measles infection, as well as in people with amyotrophic lateral sclerosis/parkinsonism dementia complex (Qi et al., 2023; Qi et al., 2023). The findings suggest that besides head trauma, other brain insults, such as environmental toxins or severe inflammation, might jostle tau into this configuration.
Michel Goedert and Sjors Scheres of the Medical Research Council Laboratory of Molecular Biology, Cambridge, U.K, who led those CTE studies, noted that most cases of Alzheimer’s disease lack CTE filaments, so it would therefore be important to demonstrate their presence in the brain of this individual using a complementary technique, such as cryo-EM of sarkosyl-insoluble tau filaments. They also suggested that future studies be performed in fresh human brain tissue, such as biopsy samples, to avoid potential biochemical changes introduced by the freezing process (comment below).
“The approach used here for targeted cryo-ET of amyloid pathology in human brain tissue has huge potential, including in the study of fresh tissue, for uncovering additional pathology in AD, and in other neurodegenerative diseases,” wrote Benjamin Ryskeldi-Falcon and Tiana Behr of the MRC in Cambridge (comment below). They recently used cryo-ET to reveal the arrangement of tau filaments nestled within extracellular vesicles (May 2023 news).
Frank agreed that applying the technique to fresh samples would be ideal, and emphasized that it will be important to analyze more brain samples, and in different regions of the brain. After all, if this much structural heterogeneity could be found within a tiny region of a single brain, it is tantalizing to imagine what future studies will unveil, he said.—Jessica Shugart
References
News Citations
- Amyloid Jungle: Plaque Fibrils Mesh With All Manner of Vesicles, Membranes
- Tau Filaments from the Alzheimer’s Brain Revealed at Atomic Resolution
- Traumatic Tau: Filaments from CTE Share Distinct Structure
- Tau Filaments Found Tethered Inside Alzheimer's Brain Exosomes
Paper Citations
- Qi C, Verheijen BM, Kokubo Y, Shi Y, Tetter S, Murzin AG, Nakahara A, Morimoto S, Vermulst M, Sasaki R, Aronica E, Hirokawa Y, Oyanagi K, Kakita A, Ryskeldi-Falcon B, Yoshida M, Hasegawa M, Scheres SH, Goedert M. Tau Filaments from Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex (ALS/PDC) adopt the CTE Fold. bioRxiv. 2023 Apr 28; PubMed.
- Qi C, Hasegawa M, Takao M, Sakai M, Sasaki M, Mizutani M, Akagi A, Iwasaki Y, Miyahara H, Yoshida M, Scheres SH, Goedert M. Identical tau filaments in subacute sclerosing panencephalitis and chronic traumatic encephalopathy. Acta Neuropathol Commun. 2023 May 5;11(1):74. PubMed.
Further Reading
No Available Further Reading
Primary Papers
- Gilbert MA, Fatima N, Jenkins J, O'Sullivan TJ, Schertel A, Halfon Y, Morrema TH, Geibel M, Radford SE, Hoozemans JJ, Frank RA. In situ cryo-electron tomography of beta-amyloid and tau in post-mortem Alzheimer's disease brain. 2023 Jul 18 10.1101/2023.07.17.549278 (version 1) bioRxiv.
Follow-On Reading
Papers
- Gilbert MA, Fatima N, Jenkins J, O'Sullivan TJ, Schertel A, Halfon Y, Wilkinson M, Morrema TH, Geibel M, Read RJ, Ranson NA, Radford SE, Hoozemans JJ, Frank RA. CryoET of β-amyloid and tau within postmortem Alzheimer's disease brain. Nature. 2024 Jul;631(8022):913-919. Epub 2024 Jul 10 PubMed.
Annotate
To make an annotation you must Login or Register.
Comments
Brigham and Women's Hospital, Harvard Medical School
Co-Director, Brigham and Women's Hospital's Ann Romney Center for Neurologic Diseases
Frank and colleagues now extend their beautiful cryo-ET work in mouse models to postmortem human Alzheimer’s disease brain with largely similar results. This work goes beyond the plastic-embedded, negative-staining EM begun in the last century to show us in three dimensions how Aβ and tau fibrils intertwine with cellular structures, and particularly for tau, details of how the atomic structure of fibrils correlates with their location. The past several years of work from the labs of Michel Goedert and Sjors Scheres, among others, have shown us how the atomic structure of extracted fibrils correlates with histopathologic diagnosis. These new findings from the Frank lab inch us closer to understanding how the atomic structure of amyloid fibrils relates to the adjacent subcellular disturbances underlying dementia.
It is tempting to conclude that the branching seen in some Aβ fibrils reflects secondary nucleation and that the narrower “protofilament-like rods” are indeed Aβ protofilaments (i.e., one stack of monomers without a pair as seen in all extracted Aβ fibrils to date). This may be the case. However, the resolution is not sufficient to exclude another explanation, such as a non-Aβ molecule interdigitated with and/or bound to the Aβ fibrils. If the fibril bundles and lattices can interdigitate with cellular structures so intimately, it would not be surprising that other molecules could interdigitate with individual fibrils, too. We look forward to the Frank group extending their already groundbreaking technological advancements to test this hypothesis.
MRC Laboratory of Molecular Biology
MRC Laboratory of Molecular Biology
This preprint by Gilbert, Fatima, Jenkins, O'Sullivan et al. from the group of René Frank at the University of Leeds describes the first-ever use of electron cryo-tomography (cryo-ET) on high-pressure frozen brain tissue (temporal cortex) from an individual with Alzheimer’s disease. It opens the way to future cryo-ET studies of diseased human brain tissues.
The work follows on from a recent study by the same group of cryo-ET of Aβ plaques from the cerebral cortices of AppNL-G-F knock-in mice (Leistner al., 2023). Similar to their previous findings, the authors now report that Aβ plaques from human brain contained abundant filaments that were intermingled with vesicles and droplets. It remains to be seen if Aβ 42 filaments were present other than those extracted from the brains of individuals with Alzheimer’s disease (Yang et al., 2022). Moreover, parallel clusters of unbranched filaments with the morphology of paired helical filaments (PHFs) were observed, indicating that PHFs can be identified in human brain samples by cryo-ET. It also remains to be seen if this is true of filaments with the chronic traumatic encephalopathy (CTE) fold, as suggested by the authors. Most cases of Alzheimer’s disease lack CTE filaments. It would therefore be important to demonstrate their presence in the brain of this individual using a complementary technique, such as cryo-EM of sarkosyl-insoluble tau filaments.
Even though these findings break new ground, they were not obtained using “fresh” tissue samples, contrary to what is being claimed. Traditionally, one distinguishes between fresh, frozen, and fixed tissues. The findings described here used frozen brain samples. Thus, following a postmortem delay of around six hours, the brain tissues were frozen in liquid nitrogen, which will have led to the formation of crystalline ice and subsequent tissue damage. Before cryo-ET, the tissues were thawed and frozen again under high pressure. To investigate deleterious effects of this process on Aβ plaques, the authors could perform control experiments using AppNL-G-F mice.
Many years ago, fixed brain tissues from individuals with Alzheimer’s disease were used to identify the abnormal filaments that were named PHFs (Kidd, 1963) and to visualize the ultrastructure of plaques and tangles (Terry et al., 1964). It will be interesting to see if cryo-ET on fresh brain samples from individuals with Alzheimer’s disease can provide fundamentally new insights.
It will be difficult to get around problems posed by the changes in brain chemistry that occur postmortem. For example, it was shown previously that non-assembled human tau is rapidly dephosphorylated after death (Matsuo et al., 1994). The future lies probably in the ability to perform cryo-ET on human brain biopsy samples or on fresh tissues obtained after very short postmortem delays.
References:
Kidd M. Paired helical filaments in electron microscopy of Alzheimer's disease. Nature. 1963 Jan;197:192-3.
Leistner C, Wilkinson M, Burgess A, Lovatt M, Goodbody S, Xu Y, Deuchars S, Radford SE, Ranson NA, Frank RA. The in-tissue molecular architecture of β-amyloid pathology in the mammalian brain. Nat Commun. 2023 May 17;14(1):2833. PubMed.
Matsuo ES, Shin RW, Billingsley ML, Van deVoorde A, O'Connor M, Trojanowski JQ, Lee VM. Biopsy-derived adult human brain tau is phosphorylated at many of the same sites as Alzheimer's disease paired helical filament tau. Neuron. 1994 Oct;13(4):989-1002. PubMed.
Terry RD, Gonatas NK, Weiss M. Ultrastructural studies in Alzheimer's presenile dementia. Am J Pathol. 1964 Feb;44:269-87.
Yang Y, Arseni D, Zhang W, Huang M, Lövestam S, Schweighauser M, Kotecha A, Murzin AG, Peak-Chew SY, Macdonald J, Lavenir I, Garringer HJ, Gelpi E, Newell KL, Kovacs GG, Vidal R, Ghetti B, Ryskeldi-Falcon B, Scheres SH, Goedert M. Cryo-EM structures of amyloid-β 42 filaments from human brains. Science. 2022 Jan 14;375(6577):167-172. Epub 2022 Jan 13 PubMed.
MRC Laboratory of Molecular Biology
MRC Laboratory of Molecular Biology
First authors Madeleine Gilbert, Nayab Fatima, Joshua Jenkins, and Thomas O’Sullivan, from the group of René Frank at the University of Leeds, have pioneered the use of electron cryo-tomography (cryo-ET) to image Aβ and tau pathology at molecular resolution in unfixed frozen human brain tissue.
This is a technical feat. The authors first used fluorescence cryo-microscopy to locate Aβ and tau pathology in high-pressure frozen tissue stained with the amyloidophilic dye methoxy-X04. This guided cryo-ultramicrotomy to produce ultra-thin tissue sections suitable for cryo-ET. To improve quality for a subset of tomograms, the authors also used focused ion beam cryo-milling to excise thin lamellae from the tissue.
Using this workflow, the authors imaged a parenchymal Aβ plaque, tau neuropil threads, and an extracellular tau deposit in tissue from the temporal cortex of an individual who had AD. They show in exquisite detail the presence of amyloid filaments and membranous structures, consistent with electron microscopy of Aβ deposits and tau inclusions in fixed human brain tissue (Kidd, 1963; Terry, 1963; Kidd, 1964; Terry et al., 1964). It will be fascinating to see what additional molecular pathology is revealed by the higher-resolution and better tissue preservation of cryo-ET.
The authors also performed sub-tomogram averaging of filaments in tau inclusions. The resulting reconstructions were of sufficient resolution to identify tau paired helical filaments (PHFs) by their protofilament ultrastructure. Filaments from one inclusion also produced a reconstruction that resembled the ultrastructure of type I CTE tau filaments (Falcon et al., 2019), raising the hypothesis that this individual may have suffered from a neuroinflammatory insult (Qi et al., 2023, 2023). Tau straight filaments (SFs) were not observed. We recently used cryo-ET and sub-tomogram averaging to identify PHFs and SFs tethered within extracellular vesicles from the brains of individuals with AD (Fowler et al., 2023). Implementing a three-dimensional classification step during sub-tomogram averaging enabled us to identify SFs.
The approach used here for targeted cryo-ET of amyloid pathology in human brain tissue has huge potential, including in the study of fresh tissue, for uncovering additional pathology in AD and in other neurodegenerative diseases.
References:
Falcon B, Zivanov J, Zhang W, Murzin AG, Garringer HJ, Vidal R, Crowther RA, Newell KL, Ghetti B, Goedert M, Scheres SH. Novel tau filament fold in chronic traumatic encephalopathy encloses hydrophobic molecules. Nature. 2019 Apr;568(7752):420-423. Epub 2019 Mar 20 PubMed.
Fowler SL, Behr TS, Turkes E, Cauhy PM, Foiani MS, Schaler A, Crowley G, Bez S, Ficulle E, Tsefou E, O'Brien DP, Fischer R, Geary B, Gaur P, Miller C, D'Acunzo P, Levy E, Duff KE, Ryskeldi-Falcon B. Tau filaments are tethered within brain extracellular vesicles in Alzheimer's disease. bioRxiv. 2023 Apr 30; PubMed.
Kidd M. Paired helical filaments in electron microscopy of Alzheimer's disease. Nature. 1963 Jan;197:192-3.
Kidd M. ALZHEIMER'S DISEASE--AN ELECTRON MICROSCOPICAL STUDY. Brain. 1964 Jun;87:307-20. PubMed.
Qi C, Hasegawa M, Takao M, Sakai M, Sasaki M, Mizutani M, Akagi A, Iwasaki Y, Miyahara H, Yoshida M, Scheres SH, Goedert M. Identical tau filaments in subacute sclerosing panencephalitis and chronic traumatic encephalopathy. Acta Neuropathol Commun. 2023 May 5;11(1):74. PubMed.
Qi C, Verheijen BM, Kokubo Y, Shi Y, Tetter S, Murzin AG, Nakahara A, Morimoto S, Vermulst M, Sasaki R, Aronica E, Hirokawa Y, Oyanagi K, Kakita A, Ryskeldi-Falcon B, Yoshida M, Hasegawa M, Scheres SH, Goedert M. Tau Filaments from Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex (ALS/PDC) adopt the CTE Fold. bioRxiv. 2023 Apr 28; PubMed.
TERRY RD. THE FINE STRUCTURE OF NEUROFIBRILLARY TANGLES IN ALZHEIMER'S DISEASE. J Neuropathol Exp Neurol. 1963 Oct;22:629-42. PubMed.
Terry RD, Gonatas NK, Weiss M. Ultrastructural studies in Alzheimer's presenile dementia. Am J Pathol. 1964 Feb;44:269-87.
Mayo Clinic Florida
This study is exciting because it reproduced in human postmortem AD brain tissue prior findings from mouse models, showing the accumulation of extracellular vesicles (EVs), as well as lipid droplets and different form of amyloid fibrils, in amyloid plaques. The authors also detected open lipid membranes in plaques, indicative of damaged cells, which can release intracellular vesicles.
APP NL-G-F mice do not develop tau pathology, but this study extends our understanding of the Cryo-EM structure to tau tangles, as well. The Cryo-electron tomography of tau fibril structures is very interesting, since they comprise not only AD-type tau misfolding but also CTE-like tau misfolding, suggesting a heterogenous origin of tau fibrils in AD brain. Since CTE tau pathology is frequently found in glial tangles as well as in neurofibrillary tangles, I was curious if there is any difference in origin of AD and CTE-like tau misfolding, such as one coming from neurons and another from glia. The difference in misfolding may also differentiate the pathological spread pattern of tau, which was shown previously in the tau seeding study in animal models (Narasimhan et al., 2017).
References:
Narasimhan S, Guo JL, Changolkar L, Stieber A, McBride JD, Silva LV, He Z, Zhang B, Gathagan RJ, Trojanowski JQ, Lee VM. Pathological Tau Strains from Human Brains Recapitulate the Diversity of Tauopathies in Nontransgenic Mouse Brain. J Neurosci. 2017 Nov 22;37(47):11406-11423. Epub 2017 Oct 20 PubMed.
German Center for Neurodegenerative Diseases, Bonn
I think this is an extremely important and exciting study. It would be great to see additional brains analyzed to learn more about earlier disease stages, in contrast to late-stage disease reported in this study, and to explore if these findings can be replicated in other AD patient brains. The presence of CTE-like tau filaments in AD brain, especially, warrants further study to address if these types of filaments are common in AD. In addition, it would be highly interesting to study other tauopathies as well, especially those where tau aggregation occurs in glial cells, since subcellular environments seem to impact tau filament structures. Another striking observation is the presence of extracellular vesicles (EVs), specifically in amyloid plaques. It is unclear whether EVs may just nonspecifically stick to pre-existing extracellular amyloid plaques, or if they play a role in seeding them. Previous research provided evidence that amyloid precursor protein (APP) and APP C-terminal fragments can be cleaved on the surface of EVs, thus releasing Aβ. In addition, the lipid composition of EV membranes has been implicated in facilitating aggregation of Aβ, supporting a possible role of EVs in seeding of plaques.
My lab is also very interested in EVs and their role in neurodegenerative diseases. We recently described the first molecular pathology-specific biomarker for ALS and FTD, which is easily accessible from blood and will have important implications for future diagnosis and therapy in ALS and FTD spectrum disorders (Chatterjee et al., 2023). One major obstacle for therapy trials in FTD is the lack of biomarkers for antemortem detection of underlying molecular pathology. Without such biomarkers, patient recruitment to TDP-43 or tau-directed therapy trials has so far been limited to rare genetic FTD cases. Biomarkers, especially less invasive ones, are therefore urgently needed for selecting appropriate patients for clinical trials and to determine target engagement.
In our work, we established a set of blood-based biomarkers that allow the reliable distinction between patients characterized by either tau or TDP-43 pathology. We show that plasma extracellular vesicles (EV) contain quantifiable amounts of TDP-43 as well as unfragmented tau which enables the quantification of 3-repeat (3R) and 4-repeat (4R) tau isoforms. We determined plasma EV TDP-43 levels and EV 3R/4R tau ratios in a large and deeply phenotyped cohort, comprising altogether 704 cases, including ALS as a TDP-43 proteinopathy, progressive supranuclear palsy (PSP) as a 4R tau predominant tauopathy, healthy controls and behavioral variant FTD (bvFTD) as a group which is associated with either tau or TDP-43 pathology.
Importantly, we found that the combination of plasma EV TDP-43 and plasma EV 3R/4R tau ratios discriminates FTD cases with underlying TDP-43 pathology from those with tau pathology, with high sensitivity and specificity. This was confirmed by 63 cases with neuropathologically and/or genetically proven molecular pathology. Furthermore, high plasma EV TDP-43 levels distinguished cases with ALS, and very low tau ratios cases distinguished PSP, from other diagnostic groups, both with high diagnostic accuracies (AUC > 0.9). In addition, both markers strongly correlated with disease severity as assessed by multiple clinical and neuropsychological scales. Thus, plasma EV TDP-43 and tau ratio could not only aid molecular diagnosis in ALS, FTD, and PSP, but may additionally bear the potential of a marker to monitor disease progression and target engagement.
References:
Chatterjee M, Özdemir S, Fritz C et al. Plasma extracellular vesicle Tau isoform ratios and TDP-43 inform about molecular pathology in Frontotemporal Dementia and Amyotrophic Lateral Sclerosis. https://doi.org/10.21203/rs.3.rs-3158170/v1 (version 1) Research Square
University of Leeds, England
Our published paper now also includes much-improved sub-tomogram averaging of in-tissue tau filaments, using Warp/M and Relion, developed by Dimitry Tegunov at Genentech and Sjors Scheres at the Medical Research Council Laboratory for Molecular Biology, respectively. This yielded an 8.7 Å resolution, in-tissue structure of paired-helical fragments (PHF) from a single cluster composed of 136 tau filaments from a single tomogram. At this resolution we could trace the polypeptide backbone and unambiguously identify the protein fold.
Mapping back this higher-resolution structure into the raw tomographic volume enabled us to identify the polarity orientation of each tau filament in tissue. Polarity orientation is an intrinsic property of all filamentous proteins. Because we found tau filaments are arranged in parallel clusters, the polarity of each filament could be oriented in one of two ways, top-to-bottom or bottom-to-top in the tomographic volume. We found that in the PHF only cluster, 114 filaments ran in one direction, but only 22 in the other. This highly skewed distribution of orientations was non-random. We think this indicates that the growth of one PHF filament has some degree of influence on the growth of the next, or that other factors within the cell control the polarity orientation of tau filaments.
We also applied the improved sub-tomogram averaging pipeline to eight additional tau filament clusters from distinct in-tissue locations. This improved most of the maps, including a cluster of straight filaments that previously and misleadingly appeared CTE-like. We think that this highlights the importance of Warp/M-Relion and validation software for comparing sub-tomogram average maps with atomic models. To validate the fit of atomic models in our maps we collaborated with Randy Read, Cambridge Institute for Medical Research at the University of Cambridge, who developed a “log likelihood gain” scoring tool called em_placement that provides an absolute score of the fit of an atomic model into EM maps (Millán et al., 2023).
References:
Millán C, McCoy AJ, Terwilliger TC, Read RJ. Likelihood-based docking of models into cryo-EM maps. Acta Crystallogr D Struct Biol. 2023 Apr 1;79(Pt 4):281-289. Epub 2023 Mar 15 PubMed.
Make a Comment
To make a comment you must login or register.