Mechanistic Investigation of the Inhibition of Aβ42 Assembly and Neurotoxicity by Aβ42 C-Terminal Fragments

Abstract

Oligomeric forms of amyloid β-protein (Aβ) are key neurotoxins in Alzheimer's disease (AD). Previously, we found that C-terminal fragments (CTFs) of Aβ42 interfered with assembly of fulllength Aβ42 and inhibited Aβ42-induced toxicity. To decipher the mechanism(s) by which CTFs affect Aβ42 assembly and neurotoxicity, here, we investigated the interaction between Aβ42 and CTFs using photo-induced cross-linking and dynamic light scattering. The results demonstrate that distinct parameters control CTF inhibition of Aβ42 assembly and Aβ42-induced toxicity. Inhibition of Aβ42-induced toxicity was found to correlate with stabilization of oligomers with hydrodynamic radius (R H ) = 8-12 nm and attenuation of formation of oligomers with R H = 20-60 nm. In contrast, inhibition of Aβ42 paranucleus formation correlated with CTF solubility and the degree to which CTFs formed amyloid fibrils themselves but did not correlate with inhibition of Aβ42-induced toxicity. Our findings provide an important insight into the mechanisms by which different CTFs inhibit the toxic effect of Aβ42 and suggest that stabilization of non-toxic Aβ42 oligomers is a promising strategy for designing inhibitors of Aβ42 neurotoxicity. KeywordsAmyloid β-protein; aggregation; neurotoxicity; inhibitor; dynamic light scattering Alzheimer's Disease (AD) is the most common neurodegenerative disease, affecting over 35 million people worldwide (1). Abundant evidence suggests that oligomeric forms of amyloid * To whom correspondence should be addressed: Department of Neurology, David Geffen School of Medicine, University of California at Los Angeles, Neuroscience Research Building 1, Room 451, 635 Charles E. Young Drive South, Los Angeles, CA 90095-7334, USA. gbitan@mednet.ucla.edu. Tel.: +1-310-206-2082; Fax.: +1-310-206-1700 The sequences of such inhibitors were based on random selection (9), selfrecognition of the central hydrophobic cluster (CHC) of Aβ (10-13), or structural modifications of sequences from the CHC or C-terminal regions (14-17). As the hypothesis of the cause of AD shifted from Aβ fibril formation and deposition to oligomeric Aβ, the design strategy for peptide inhibitors for treatment of AD was adjusted to target Aβ oligomerization. In view of the important role of the C-terminus in Aβ42 assembly and toxicity, we hypothesized that the C-terminal fragments (CTFs) of Aβ42 might disrupt Aβ42 assembly and inhibit its neurotoxicity. In a previous study, we confirmed this hypothesis and found that Aβ42 CTFs, Recently, we reported a systematic characterization of biophysical properties of all the CTFs in the original series (19), to which we added for additional structural insight two Aβ40 CTFs, Aβ(34-40) and , and a fragment derived from the putative folding nucleus of Aβ, Aβ(21-30) (20). We found that most of Aβ42 CTFs longer than 8 residues readily formed β-sheet-rich fibrils, whereas the shorter CTFs did not. The two Aβ40 CTFs were substantially less prone to aggregation than their Aβ42 CTF counterparts (19). Surprisingly, Aβ(30-40)...

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