Elucidation of Amyloid-Beta's Gambit in Oligomerisation:Truncated Aβ fragments of residues Aβ1-23, Aβ1-24 and Aβ1-25 rapidly seed to form SDS-stable, low molecular weight Aβ oligomers that impair synaptic plasticity.

Abstract

In Alzheimers disease (AD), Amyloid-beta (A{beta}) oligomers are considered an appealing therapeutic- and diagnostic target. However, to date, the molecular mechanisms associated with the pathological accumulation or structure of A{beta} oligomers remains an enigma to the scientific community. Here we demonstrate the strong seeding properties of unique A{beta} fragment signatures and show that the truncated A{beta} peptides of residues A{beta}1-23, A{beta}1-24 and A{beta}1-25, rapidly seed to form small, SDS-PAGE stable assemblies of [~]5kDa to [~]14kDa molecular mass range. Mass spectrometry analysis of SDS-PAGE fractionated and gel extracted oligomers revealed that the truncated A{beta} isoforms of residues 1-23 to 1-25 form stable entities with low molecular weight (LMW) oligomers, which strongly resemble the regularly reported A{beta} entities of putative dimeric or trimeric assemblies found in human post-mortem AD and Tg mouse brain extracts. Furthermore, electrophysiological recordings in the mouse hippocampus indicate that LMW A{beta} assemblies formed by fragments A{beta}1-23 to A{beta}1-25 significantly impair long-term-potentiation (LTP) in the absence of full-length A{beta}1-42. Extensive antibody screening highlights the important observation, that the LMW A{beta} assemblies formed by these truncated A{beta} peptides escape immuno-detection using conventional, conformation specific antibodies but, more importantly, the clinical antibody aducanumab. Our novel findings suggest that there are new A{beta} target "loopholes" which can be exploited for the development of therapeutic antibodies with binding properties against stable target hotspots present in A{beta} oligomers. We provide here a first example of a new class of monoclonal antibody with unique binding properties against LMW A{beta} oligomers, in the absence of binding to large fibrillar A{beta} assemblies, or dense amyloid plaques. Our research supports a novel, unparalleled approach for targeting early, pathological A{beta} species during the insidious phase of AD and prior to the appearance of large oligomeric or protofibrilar assemblies.