The number of APP-GFP/cathepsin D co-localizing vesicles was scored and expressed as percentage of APP-GFP-containing vesicles ("Vesicular co-loc."). The co-localization coefficients ("Co-loc coefficient") represent the relative percentage between the number of APP-GFP/cathepsin D co-localizing pixels and the total number of pixels of the APP-GFP channel, upon single cell delimitation. Values are mean ± SEM (n = 20). (*), S655 mutant vs Wt data; (+), S655A vs S655E data. *, p < 0.05; ***/+++, p < 0.001.