Rapidly progressive Alzheimer's disease features distinct structures of amyloid-β

Genetic and environmental factors that increase the risk of late-onset Alzheimer disease are now well recognized but the cause of variable progression rates and phenotypes of sporadic Alzheimer's disease is largely unknown. We aimed to investigate the relationship between diverse structural assemblies of amyloid-β and rates of clinical decline in Alzheimer's disease. Using novel biophysical methods, we analysed levels, particle size, and conformational characteristics of amyloid-β in the posterior cingulate cortex, hippocampus and cerebellum of 48 cases of Alzheimer's disease with distinctly different disease durations, and correlated the data with APOE gene polymorphism. In both hippocampus and posterior cingulate cortex we identified an extensive array of distinct amyloid-β₄₂ particles that differ in size, display of N-terminal and C-terminal domains, and conformational stability. In contrast, amyloid-β₄₀ present at low levels did not form a major particle with discernible size, and both N-terminal and C- terminal domains were largely exposed. Rapidly progressive Alzheimer's disease that is associated with a low frequency of APOE e4 allele demonstrates considerably expanded conformational heterogeneity of amyloid-β₄₂, with higher levels of distinctly structured amyloid-β₄₂ particles composed of 30-100 monomers, and fewer particles composed of < 30 monomers. The link between rapid clinical decline and levels of amyloid-β₄₂ with distinct structural characteristics suggests that different conformers may play an important role in the pathogenesis of distinct Alzheimer's disease phenotypes. These findings indicate that Alzheimer's disease exhibits a wide spectrum of amyloid-β₄₂ structural states and imply the existence of prion-like conformational strains.