The effects of CD2AP expression on app processing

Our group has played a leading role in the discovery of >20 new susceptibility genes for AD. Several of these genes, including phosphatidylinositol binding clathrin assembly protein (PICALM), bridging integrator 1 (BIN1) and CD2-associated protein (CD2AP) are involved in endocytosis and intracellular trafficking. We have previously shown that the knockdown of PICALM and BIN1 in H4 cells has significant effects on the processing of amyloid beta precursor protein (APP). In this study, we investigated the effects of reduced CD2AP expression on APP processing. Knockdown of CD2AP was performed in H4 neuroglioma cell lines using siRNAs and confirmed by western blotting. Levels of APP, sAPPα, sAPPβ, β-CTF, Aβ40 and Aβ42 were determined by immunoprecipitation and/or enzyme-linked immunosorbent assays. Treatment of H4 cells with 50nM BIN1siRNA for 48 hours produced ∼90% reduction in CD2AP protein levels compared to controls (Figure 1). Treatment of H4 cells with CD2AP siRNA did not significantly alter APP levels compared to control cells. However, we did observe a significant increase in Aβ40 levels (∼40% p= 0.010, figure 2). These results suggest that while a reduction in CD2AP expression does not affect the overall levels of APP, the proportion of APP directed to the amyloidgenic pathway is increased.