Toxicity of non‐Aβ component of Alzheimer's disease amyloid, and N‐terminal fragments thereof, correlates to formation of β‐sheet structure and fibrils

Abstract

The non-Ab component of Alzheimer's disease amyloid (NAC) and its precursor a-synuclein have been linked to amyloidogenesis in Alzheimer's disease (AD), Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Previously we have shown that NAC forms b-sheet structures and fibrils [El-Agnaf, O.M.A., Bodles, A.M., Guthrie, D.J.S., Harriott, P. & Irvine, G.B. (1998) Eur. J. Biochem. 258, 157±163]. As a measure of their neurotoxic potential we have examined the ability of fresh and aged NAC and fragments thereof to inhibit the reduction of the redox dye 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide by rat pheochromocytoma PC12 cells. Micromolar concentrations of NAC and fragments thereof display varying degrees of toxicity. On immediate dissolution and after an incubation period for 3 days at 37 8C the full-length peptide and fragments NAC(3±18) and NAC(1±18) scrambled sequence [NAC(1±18 s)] were toxic, whereas fragments NAC(1±13) and NAC(6±14) were not. CD indicates that NAC(3±18) and NAC(1±18 s) exhibit b-sheet secondary structure in aqueous solution, whereas NAC(1±13) and NAC(6±14) do not. NAC(3±18) aggregates, as indicated by concentration of peptide remaining in solution after 3 days measured by an HPLC assay, and forms fibrils, as determined by electron microscopy. However, although some fibrils were detected for NAC(1±18 s) it does not come out of solution to a significant degree. Fragments NAC(1±13) and NAC(6±14) form few fibrils and remain in solution. These findings indicate that the ability of the central region of NAC to form b-sheet secondary structures is important for determining the toxicity of the peptide. This contrasts with what has been reported previously for most Ab peptides as their toxicity appears to require the peptide to have formed fibrillary aggregates as well as displaying b-sheet. These results suggest that an intermediate, which exhibits b-sheet structure, may be responsible for the toxic properties of NAC and provides further evidence for the role of NAC in the pathogenesis of AD, PD and DLB.

αB-Crystallin inhibits the cell toxicity associated with amyloid fibril formation by κ-casein and the amyloid-β peptide

“…The fibrillar state of RCMκ-CN is cytotoxic to PC12 cells Previous research has shown that amyloid fibril-forming proteins are more toxic in an aggregated, fibrillar state compared to their native, non-fibrillar form (El-Agnaf et al 1998;Bodles et al 2000;Bucciantini et al 2002;Novitskaya et al 2006;Chimon et al 2007). To determine whether this was also the case for RCMκ-CN, PC12 cells were treated with RCMκ-CN in its native state and following incubation in phosphate buffer (50 mM, pH 7.4) at 37°C for 20 h (Thorn et al 2005;Ecroyd et al 2007Ecroyd et al , 2008, conditions under which it forms fibrils (i.e., fibrillar RCMκ-CN).…”

“…In cell models of AD, PD, and prion diseases, the amyloidogenic proteins associated with these diseases are toxic in their oligomeric and/or fibrillar form but not in their monomeric state (El-Agnaf et al 1998;Bodles et al 2000;Novitskaya et al 2006;Chimon et al 2007). Furthermore, fibrillar aggregates of non-disease-related proteins are toxic, which suggests that toxicity is related to the mechanism of fibril formation and/or the overall fibril structure (Bucciantini et al 2002) rather than the native state of the proteins that form them.…”

A simple algorithm locates β‐strands in the amyloid fibril core of α‐synuclein, Aβ, and tau using the amino acid sequence alone

“…However, peak III is absent from b-syn, which coincides with the difference at residues 71 and 72 and, most notably, the absence of the b-strand-favorable amino acids found in a-syn at residues 73-83. Peak III, which is the largest of the three peaks, locates to the region reported to dominate the fibrillogenic capacity of a-syn (Han et al 1995;Iwai et al 1995;El-Agnaf et al 1998a,b;Bodles et al 2000Bodles et al , 2001Giasson et al 2001;Du et al 2003). b-Syn is reproducibly nonfibrillogenic (Goedert 2001) and is absent from Lewy bodies (Spillantini et al 1997).…”

Oligomeric alpha‐synuclein and its role in neuronal death

“…The most common hypothesis for the mechanism of a-Syn oligomer toxicity is that oligomers can create pores in membranes, which increases cell permeability to ions from the extracellular space leading to cell death (21,27). This hypothesis is largely based on some species of a-Syn oligomers that are annular or pore-like with outer diameters of 10-12 nm and inner diameters of 2 nm, respectively (29,31). These features may lead to the increased but nonspecific ion permeability observed with a-Syn overexpressing cells (32).…”