Comment by George Perry, Xiongwei Zhu, Akihiko Nunomura, Paula I. Moreira, Rudy J. Castellani, Mark A. Smith

Amyloid-β Protein Precursor at the Center of Iron and Redox Homeostasis: The Amyloid Reparative Cascade Hypothesis
It is an overused statement that the brain is poorly protected from oxidative stress. That statement is now put to rest by the elegant and meticulous work of Ashley Bush and colleagues (Duce et al., 2010). Bush has shown the amyloid-β protein precursor (AβPP) has ferroxidase activities comparable to ceruloplasmin or ferritin. Ferroxidase, by stabilizing Fe+3, is at the center of protecting cells from Fe+2/Fe+3 cycling, with consequent hydroxyl radical production. Additionally, ferroxidase activity is essential for iron transport and tissue response to injury. These findings explain why, in the face of increased oxidative damage and response, ceruloplasmin is not induced (Castellani et al., 1999). AβPP, therefore, represents a unique system, adapted to the brain, to cope with iron homeostasis. These results suggest that the iron deposits...  Read more

Comment by George Perry, Xiongwei Zhu, Akihiko Nunomura, Paula I. Moreira, Rudy J. Castellani, Mark A. Smith

Amyloid-β Protein Precursor at the Center of Iron and Redox Homeostasis: The Amyloid Reparative Cascade Hypothesis
It is an overused statement that the brain is poorly protected from oxidative stress. That statement is now put to rest by the elegant and meticulous work of Ashley Bush and colleagues (Duce et al., 2010). Bush has shown the amyloid-β protein precursor (AβPP) has ferroxidase activities comparable to ceruloplasmin or ferritin. Ferroxidase, by stabilizing Fe+3, is at the center of protecting cells from Fe+2/Fe+3 cycling, with consequent hydroxyl radical production. Additionally, ferroxidase activity is essential for iron transport and tissue response to injury. These findings explain why, in the face of increased oxidative damage and response, ceruloplasmin is not induced (Castellani et al., 1999). AβPP, therefore, represents a unique system, adapted to the brain, to cope with iron homeostasis. These results suggest that the iron deposits surrounding Aβ deposits are due to ferroxidase activity rather than iron binding (Dong et al., 2003). It is not surprising that AβPP is a critical marker of axonal injury (Cochran et al., 1991) and repair, as both ceruloplasmin and ferritin play similar roles. When seen together with the antioxidant role of Aβ through copper chelation (Hayashi et al., 2007), the reparative power of the amyloid pathway cannot be questioned (Rottkamp et al., 2001; Castellani et al., 2009).

References:
Castellani RJ, Lee HG, Siedlak SL, Nunomura A, Hayashi T, Nakamura M, Zhu X, Perry G, Smith MA (2009) Reexamining Alzheimer's disease: evidence for a protective role for amyloid-beta protein precursor and amyloid-beta. J Alzheimers Dis 18(2): 447-52. Abstract

Castellani RJ, Smith MA, Nunomura A, Harris PL, Perry G (1999) Is increased redox-active iron in Alzheimer disease a failure of the copper-binding protein ceruloplasmin? Free Radic Biol Med 26(11-12): 1508-12. Abstract

Cochran E, Bacci B, Chen Y, Patton A, Gambetti P, Autilio-Gambetti L (1991) Amyloid precursor protein and ubiquitin immunoreactivity in dystrophic axons is not unique to Alzheimer's disease. Am J Pathol 139(3): 485-9. Abstract

Dong J, Atwood CS, Anderson VE, Siedlak SL, Smith MA, Perry G, Carey PR (2003) Metal binding and oxidation of amyloid-beta within isolated senile plaque cores: Raman microscopic evidence. Biochemistry 42(10): 2768-73. Abstract

Duce JA, Tsatsanis A, Cater MA, James SA, Robb E, Wikhe K, Leong SL, Perez K, Johanssen T, Greenough MA, Cho HH, Galatis D, Moir RD, Masters CL, McLean C, Tanzi RE, Cappai R, Barnham KJ, Ciccotosto GD, Rogers JT, Bush AI (2010) Iron-Export Ferroxidase Activity of beta- Amyloid Precursor Protein Is Inhibited by Zinc in Alzheimer's Disease. Cell. Abstract

Hayashi T, Shishido N, Nakayama K, Nunomura A, Smith MA, Perry G, Nakamura M (2007) Lipid peroxidation and 4-hydroxy-2-nonenal formation by copper ion bound to amyloid-beta peptide. Free Radic Biol Med 43(11): 1552-9. Abstract

Rottkamp CA, Raina AK, Zhu X, Gaier E, Bush AI, Atwood CS, Chevion M, Perry G, Smith MA (2001) Redox-active iron mediates amyloid-beta toxicity. Free Radic Biol Med 30(4): 447-50. Abstract

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In September's issue of Cell, the report by Duce et al. (2010) describes the novel finding that the underlying biochemical function of the Alzheimer’s amyloid precursor protein (APP) incorporates a dual role in iron metabolism. First, APP displays ferroxidase activity, which detoxifies deleterious Fe2+ into the storage form of iron as Fe3+. Second, it shows that APP has a clear role in iron export, where APP is in association with the well-known iron export protein, ferroportin, also associated with hemachromatosis and iron-storage disease. Thus, APP helps ferroportin to export iron and detoxify neurons from potential iron-accelerated oxidative stress. This is the culmination of a highly productive collaboration between the Oxidation Biology Group led by Ashley Bush (University of Melbourne) and the Neurochemistry laboratory of myself, Jack Rogers (Psych-Neuroscience, Massachusetts General Hospital at Harvard).

It had long been suspected that APP expression and function is regulated by iron and iron metabolism. This paper finally pinpoints this function, attributable to a...  Read more

In September's issue of Cell, the report by Duce et al. (2010) describes the novel finding that the underlying biochemical function of the Alzheimer’s amyloid precursor protein (APP) incorporates a dual role in iron metabolism. First, APP displays ferroxidase activity, which detoxifies deleterious Fe2+ into the storage form of iron as Fe3+. Second, it shows that APP has a clear role in iron export, where APP is in association with the well-known iron export protein, ferroportin, also associated with hemachromatosis and iron-storage disease. Thus, APP helps ferroportin to export iron and detoxify neurons from potential iron-accelerated oxidative stress. This is the culmination of a highly productive collaboration between the Oxidation Biology Group led by Ashley Bush (University of Melbourne) and the Neurochemistry laboratory of myself, Jack Rogers (Psych-Neuroscience, Massachusetts General Hospital at Harvard).

It had long been suspected that APP expression and function is regulated by iron and iron metabolism. This paper finally pinpoints this function, attributable to a “tell-tale” iron binding REXXE site (at residues 401-417 in the E2 domain of APP-770), confirmed to be an iron oxidase site in the APP protein itself (see U.S. Patent WO/2002/034766; Rogers et al., 2002). Also, there is a uniquely configured iron-responsive element (IRE) RNA stem loop in the 5’ untranslated region of the APP transcript (Rogers et al., 2002). IRE stem loops on mRNAs can be viewed as a genetic tag linking the particular protein expressed to iron metabolism.

This key APP-ferroxidase paper is complemented by another contribution from my lab to J. Biol. Chem. (see Cho et al., 2010) that defines how iron metabolism controls APP expression.

View all comments by Jack T. Rogers

In August 2012, we published a paper in PLoS ONE entitled "A Synthetic Peptide with the Putative Iron Binding Motif of Amyloid Precursor Protein (APP) Does Not Catalytically Oxidize Iron." In this paper, we critically studied the ferroxidase activity of the FD1 peptide that was used by Duce et al. as part of their proof for ferroxidase activity in APP. Unlike Duce et al., we found that this peptide does not have ferroxidase activity. Moreover, we found several seminal inconsistencies in the data. We suggest that the ferroxidase activity of the APP should be re-evaluated.

References:
Honarmand Ebrahim K, Hagedoorn PL, Hagen WR. A Synthetic Peptide with the Putative Iron Binding Motif of Amyloid Precursor Protein (APP) Does Not Catalytically Oxidize Iron, PLoS ONE 7(8): e40287.

View all comments by Kourosh Honarmand Ebrahimi

There has been a longstanding curiosity in the field of Alzheimer's research regarding possible relationships between APP/Aβ and the process of apoptosis. Aβ oligomer toxicity is closely associated with neurotoxicity, but typical programmed cell death (aka apoptosis) has not been robustly indicated. Caspase cleavage of APP and PS2 have long stood as possible nexuses whereby APP metabolism and apoptosis might converge. Now Xu and colleagues discover a new protein, dubbed appoptosin, that bridges the gap between APP and mitochondrial physiology and apoptosis. Appoptosin levels are increased in AD brain and infarcted brain, and levels of any protein that buck the trend and rise during neuronal death are usually worth noting. Downregulation of appoptosin protects neurons from Aβ toxicity and glutamate toxicity, raising the possibility that therapeutic reduction of brain appoptosin becomes the latest novel strategy for protecting the brain besieged by AD.

View all comments by Samuel Gandy

Zhang et al. have identified further links between Alzheimer's disease and iron metabolism via their discovery of a role for appoptosin, which they reported to be a novel amyloid precursor protein (APP)-binding protein after yeast hybrid analysis.

Han Zhang's team collaborated with Huaxi Xu's team to conclusively show that appoptosin expression causes mitochondrial-driven apoptosis. However, more significantly, it can bind the C-terminal of the APP, tethered to the membrane. After damage, or even secretase cleavage, appoptosin moves to the mitochondria and is proposed to have a significant role in mitochondrial heme biosynthesis. Excess heme is known to generate reactive oxygen species by Fenton chemistry and thus cause neuronal death, as after hemorrhage, for example.

Intriguing links to iron metabolism yet again arise from this tour de force since the findings are consistent with the 2010 demonstration that APP also binds ferroportin and is considered an iron export ferroxidase via its N-terminus (see Duce et al., 2010).

Clearly, the APP/appoptosin partnership has...  Read more

Zhang et al. have identified further links between Alzheimer's disease and iron metabolism via their discovery of a role for appoptosin, which they reported to be a novel amyloid precursor protein (APP)-binding protein after yeast hybrid analysis.

Han Zhang's team collaborated with Huaxi Xu's team to conclusively show that appoptosin expression causes mitochondrial-driven apoptosis. However, more significantly, it can bind the C-terminal of the APP, tethered to the membrane. After damage, or even secretase cleavage, appoptosin moves to the mitochondria and is proposed to have a significant role in mitochondrial heme biosynthesis. Excess heme is known to generate reactive oxygen species by Fenton chemistry and thus cause neuronal death, as after hemorrhage, for example.

Intriguing links to iron metabolism yet again arise from this tour de force since the findings are consistent with the 2010 demonstration that APP also binds ferroportin and is considered an iron export ferroxidase via its N-terminus (see Duce et al., 2010).

Clearly, the APP/appoptosin partnership has a significant role in iron homeostasis.

This is particularly evident by the RNA binding protein iron-regulatory protein 1 (IRP1), which controls the rate of iron/heme-dependent translation of APP to thereby efflux excess iron from neural cells at risk from heme or iron overload (Cho et al., 2010).

The link between APP and heme/iron metabolism, and now apoptosis, is supported by more evidence that, like APP, appoptosin has a central role in iron homeostasis, and that mistakes in this homeostasis can kill neurons.

Indeed, genetic mutations to the appoptosin gene cause recessive congenital sideroblastic anemia (Guernsey et al., 2009, a reference in this paper).

References:
Duce JA, Tsatsanis A, Cater MA, James SA, Robb E, Wikhe K, Leong SL, Perez K, Johanssen T, Greenough MA, Cho HH, Galatis D, Moir RD, Masters CL, McLean C, Tanzi RE, Cappai R, Barnham KJ, Ciccotosto GD, Rogers JT, Bush AI. Iron-export ferroxidase activity of β-amyloid precursor protein is inhibited by zinc in Alzheimer's disease. Cell. 2010 Sep 17;142(6):857-67. Abstract

Cho HH, Cahill CM, Vanderburg CR, Scherzer CR, Wang B, Huang X, Rogers JT. Selective translational control of the Alzheimer amyloid precursor protein transcript by iron regulatory protein-1. J Biol Chem. 2010 Oct 8;285(41):31217-32. Abstract

Guernsey DL, Jiang H, Campagna DR, Evans SC, Ferguson M, Kellogg MD, Lachance M, Matsuoka M, Nightingale M, Rideout A, Saint-Amant L, Schmidt PJ, Orr A, Bottomley SS, Fleming MD, Ludman M, Dyack S, Fernandez CV, Samuels ME. Mutations in mitochondrial carrier family gene SLC25A38 cause nonsyndromic autosomal recessive congenital sideroblastic anemia. Nat Genet. 2009 Jun;41(6):651-3. Abstract

View all comments by Jack T. Rogers