Fibrillar seeds alleviate amyloid-ß cytotoxicity by omitting formation of higher-molecular-weight oligomers.

ABSTRACT

Amyloid-ß (Aß) peptides can exist in distinct forms including monomers, oligomers and fibrils, consisting of increased numbers of monomeric units. Among these, Aß oligomers are implicated as the primary toxic species as pointed by multiple lines of evidence. It has been suggested that toxicity could be rendered by the soluble higher-molecular-weight (high-n) Aß oligomers. Yet, the most culpable form in the pathogenesis of Alzheimer's disease (AD) remains elusive. Moreover, the potential interaction among the insoluble fibrils that have been excluded from the responsible aggregates in AD development, Aß monomers and high-n oligomers is undetermined. Here, we report that insoluble Aß fibrillar seeds can interact with Aß monomers at the stoichiometry of 12 (namely, each Aß molecule of seed can bind to two Aß monomers at a time) facilitating the fibrillization by omitting the otherwise mandatory formation of the toxic high-n oligomers during the fibril maturation. As a result, the addition of exogenous Aß fibrillar seeds is seen to rescue neuronal cells from Aß cytotoxicity presumably exerted by high-n oligomers, suggesting an unexpected protective role of Aß fibrillar seeds.