Efficient Seeding of Cerebral Vascular Aβ-Amyloidosis by Recombinant AβM1-42 Amyloid Fibrils

Aβ-amyloid plaques and cerebral amyloid angiopathy (CAA) in the brain are pathological hallmarks of Alzheimer's disease (AD) and vascular dementia. The spreading of Aβ amyloidosis in the brain appears to be mediated by a seeding mechanism, where preformed fibrils (called seeds) accelerate Aβ fibril formation by bypassing the rate-determining nucleation step. Several studies have demonstrated that Aβ amyloidosis can be induced in transgenic mice, producing human Aβ, by injecting Aβ-rich brain extracts (seeds) derived from transgenic mice and human AD brains. However, studies on recombinant seeds are limited. Therefore, we investigated the seeding activity of pure recombinant human Aβ fibrils of different compositions. Seeds were inoculated into APP23 mice at the age of 3 months and were analyzed after 6 months of incubation. Recombinant fibril seeds made from Aβ-peptides with an N-terminal methionine (i.e. (preformed fibrils from AβM1-42, AβM1-40, and AβM1-40 + AβM1-42) accelerated Aβ-amyloid plaque formation in vivo compared to non-inoculated transgenic control mice of the same age. In addition, all seeds induced CAA pathology. Interestingly, AβM1-42 containing seeds produced significantly more CAA and amyloid plaques than seeds containing pure AβM1-40, which was surprising given that APP23 mice produce approximately four-fold more Aβ1-40 substrate than Aβ1-42. This study showed that AβM1-42 fibrils are highly potent in seeding CAA and implies that conformational templating occurs in amyloid plaque as deduced by comparative amyloid ligand staining. Our results verify that recombinant Aβ fibrils are transmissible amyloids, and that in vivo seeding can accelerate, and redirect Aβ amyloidosis patterns compared to spontaneous age dependent amyloidosis.