Preparation of fibril nuclei of beta-amyloid peptides in reverse micelles.

We report the preparation of protofibrils from oligomeric Aß40 aggregates, which have been incubated under spatially constrained conditions. The molecular structure of the resultant protofibrils is highly homogeneous, suggesting that the phenomenon of structural polymorphism commonly observed in Aß40 fibrils may be largely due to multiple nucleation events.

Zinc ion rapidly induces toxic, off-pathway amyloid-ß oligomers distinct from amyloid-ß derived diffusible ligands in Alzheimer's disease.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the elderly. Zinc (Zn) ion interacts with the pathogenic hallmark, amyloid-ß (Aß), and is enriched in senile plaques in brain of AD patients. To understand Zn-chelated Aß (ZnAß) species, here we systematically characterized ZnAß aggregates by incubating equimolar Aß with Zn. We found ZnAß40 and ZnAß42 both form spherical oligomers with a diameter of ~12-14 nm composed of reduced ß-sheet content. Oligomer assembly examined by analytical ultracentrifugation, hydrophobic exposure by BisANS spectra, and immunoreactivity of ZnAß and Aß derived diffusible ligands (ADDLs) are distinct. The site-specific 13C labeled solid-state NMR spectra showed that ZnAß40 adopts ß-sheet structure as in Aß40 fibrils. Interestingly, removal of Zn by EDTA rapidly shifted the equilibrium back to fibrillization pathway with a faster kinetics. Moreover, ZnAß oligomers have stronger toxicity than ADDLs by cell viability and cytotoxicity assays. The ex vivo study showed that ZnAß oligomers potently inhibited hippocampal LTP in the wild-type C57BL/6JNarl mice. Finally, we demonstrated that ZnAß oligomers stimulate hippocampal microglia activation in an acute Aß-injected model. Overall, our study demonstrates that ZnAß rapidly form toxic and distinct off-pathway oligomers. The finding provides a potential target for AD therapeutic development.

Fibrillization of ß-Amyloid Peptides via Chemically Modulated Pathway.

The aggregation of ß-amyloid peptides is closely associated with Alzheimer's disease. We have used liposomes to modulate the early aggregation events of 40-residue ß-amyloid peptides. The spatial confinement provided by liposomes leads to the formation of nonfibrillar aggregates of ß-amyloid peptides. These on-pathway ß-sheet intermediates were used to seed the fibrillization of the monomer peptides. Solid-state NMR spectroscopy revealed that the resultant fibrils have a more uniform structure than those formed in liposome-free solution.