Strain-specific Fibril Propagation by an A\u03b2 Dodecamer

Dexter N Dean,Franklin Burg,Sarah E Morgan,Pratip Rana,Preetam Ghosh,Pradipta K Das,Yona Levites,Vijayaraghavan Rangachari

doi:10.1038/srep40787

Abstract

Low molecular weight oligomers of amyloid-β (Aβ) have emerged as the primary toxic agents in the etiology of Alzheimer disease (AD). Polymorphism observed within the aggregation end products of fibrils are known to arise due to microstructural differences among the oligomers. Diversity in aggregate morphology correlates with the differences in AD, cementing the idea that conformational strains of oligomers could be significant in phenotypic outcomes. Therefore, it is imperative to determine the ability of strains to faithfully propagate their structure. Here we report fibril propagation of an Aβ42 dodecamer called large fatty acid-derived oligomers (LFAOs). The LFAO oligomeric strain selectively induces acute cerebral amyloid angiopathy (CAA) in neonatally-injected transgenic CRND8 mice. Propagation in-vitro occurs as a three-step process involving the association of LFAO units. LFAO-seeded fibrils possess distinct morphology made of repeating LFAO units that could be regenerated upon sonication. Overall, these data bring forth an important mechanistic perspective into strain-specific propagation of oligomers that has remained elusive thus far.

Highlights

Biochemical analysis were performed on the frozen hemibrains by sequential fractionation in radioimmunoprecipitation assay (RIPA), SDS 2% and formic acid 70%, and Aβlevels were measured by sandwich ELISA
We have detailed the ability of LFAOs (12mers) to undergo a self-propagative replication mechanism in which LFAOs form quantitatively more of similar oligomers (12-24mers) upon interacting with monomer[11,12,13]
It is noteworthy that seeding of Aβwith high concentrations of LFAO seeds minimizes the emergence of on-pathway oligomers by altering the dynamics towards seeded aggregation

Summary

Introduction

To analyze whether the differences in sLFAO and sFib aggregation is manifested in the nature of fibrils formed, the samples were electrophoresed and immunoblotted after 14 days of incubation (Fig. 3b,c). This experiment confirms two things: i) the monomeric bands observed in denaturing gels are likely due to the dissociation of aggregates in 1% SDS contained in the sample buffer, and ii) sLFAOs contained a significant amount of soluble oligomers even after 14 days of incubation as opposed to sFib and Un samples, which could indicate a greater degree of fibril fragmentation in the sLFAO sample. Together the data reveal that LFAO-seeded aggregation behaves differently from the fibril-seeded control (Fig. 3f).

Results

Conclusion