Soluble high-molecular-weight amyloid-β species derived from amyloid-β-laden brains induce cerebral β-amyloidosis.

Spatiotemporal spreading of amyloid-β peptide deposition as senile plaques is a key pathogenic process in the brains of patients with Alzheimer's disease; however, the molecular properties of amyloid-β strains that initiate the spreading of amyloid-β peptide as aggregation seeds in vivo remain poorly understood. In this study, we discovered that the intrahippocampal injection of soluble amyloid-β species with a molecular weight of >150 kDa isolated from the brains of plaque-laden amyloid-β precursor protein transgenic mice or patients with Alzheimer's disease using size-exclusion chromatography, dramatically accelerated β-amyloidosis in the transgenic mice brains. In contrast, intrahippocampal injection of soluble amyloid-β species with 50-70 kDa or 10-20 kDa never induced β-amyloidosis. Moreover, injection of the soluble amyloid-β species with >150 kDa into cerebrospinal fluid of young transgenic mice via the cisterna magna predominantly induced amyloid-β deposition within the wall of leptomeningeal arteries surrounding the brain, reminiscent of cerebral amyloid angiopathy. The seeding activity of the soluble high-molecular-weight amyloid-β was prevented by the immunodepletion of amyloid-β and abolished by formic acid denaturation, suggesting that these amyloid-β oligomers are crucial in inducing β-amyloidosis. Furthermore, we have shown that the soluble high-molecular-weight amyloid-β is present in the brains of patients with Alzheimer's disease and induced β-amyloidosis. These results indicate that the soluble high-molecular-weight amyloid-β oligomers may play an important role in the spatiotemporal spreading of amyloid-β deposition in Alzheimer's disease brains.