Increased amyloidogenic processing of APP in aged PS1/APP hippocampus. A) Representative western blots (n=4 for each age and animal group) for full-length APP (hAPPfl) (upper panel) and, APP-C terminal fragments (C99 and C83; middle panel) in 6, 12 and 18 month-old PS1/APP hippocampal samples. Quantitative analysis showed a significant increase in C99 from 6 to 18 months. APPfl also displayed a moderate (but significant) accumulation at 18 month-old. The amyloidogenic route was evaluated by testing the expression of BACE-1 (by western (B), n=5; and immunohistochermistry (C), n=3) and PS1 (n=6) (D) proteins. Dystrophic neurites surrounding plaques were positive for BACE-1 antibody. The enzymatic activities of BACE-1 (n=3) (E) and gamma-secretase (n=6) (F) were also assayed. Inset in panel F showed the accumulation of soluble AICD after 2 hours of incubation (at 37°C), in absence (minus) and in presence (plus) of 100 μM of the gamma-secretase inhibitor L-685-458, demonstrating that AICD production was dependent of the gamma-secretase activity. As shown, 18 month-old PS1/APP mice displayed an accumulation of both BACE-1 and PS1 (CTF fragment and full length) proteins paralleled by an increase in the corresponding enzymatic activities. Scale bar: 50 μm.