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

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

View all comments by Rudy Castellani
View all comments by Paula Moreira
View all comments by Akihiko Nunomura
View all comments by George Perry
View all comments by Mark A. Smith
View all comments by Xiongwei Zhu