Morphometric analysis of the retina in a triple-transgenic model of Alzheimer's disease

Background: A major pathological hallmark of Alzheimer’s disease (AD) is the aggregation and deposition of amyloid-bpeptides (Ab) in the brain. According to the amyloid cascade hypothesis the accumulation of Abpeptide is an early and central event, which precedes the transition to the symptomatic phase of the disease. Thus, a great effort has been made to study the mechanisms of Abaggregation and pathogenicity. Due to the lack of satisfactory in vitro assays b-amyloidosis has mainly been studied in amyloidbprecursor protein (APP) transgenic mice. Here we report a long-term hippocampal slice culture model developing Abdeposits. We propose this system as a new tool to study b-amyloidosis. Methods: Hippocampal slice cultures from postnatal (P2-P3) wildtype micewere incubated with Ab-containing brain extracts from aged, plaque-bearing APP transgenic mice. The culture medium was supplemented with synthetic Abover the entire cultivation time. Subsequently, Abdepositions in the cultures were characterized by electron-microscopy and immunohistochemistry. To study the seeding activity of slice culture-aggregated Ab, extracts from slice cultures were prepared and intracerebral injected into the hippocampus of pre-depositing 3-4 month old APP transgenic mice.Results: b-Amyloid deposits started to develop in 4 week-old cultures and progressed up to 10 weeks in vitro. The morphotypes of the seeded b-amyloid deposits were dependent on the origin of the Abseed, i.e. brain extracts from either aged APP23 or APPPS1 transgenic mice as well as on the synthetic Abspecies applied to the culture medium (Ab1-40 or Ab1-42). Aggregated synthetic Abfrom these cultures, but not in vitro aggregated synthetic Ab of equal concentration,induced cerebral b-amyloidosis 4 months postinoculation in young APP transgenic mice. This observation suggests that synthetic Abcan be converted into in vivo active Abseeds in the hippocampal slice culture model. Conclusions: The here described ex vivo hippocampal slice culture model is a new approach to study b-amyloidosis and associated toxicities in a living system. It may open new opportunities to screen for inhibitory treatments under standardized conditions in vitro.