APP and Alzheimer disease: Cathepsin D was also detected in our MS analysis of the aggregates isolated from astrocytes lacking stefin B. Cathepsin D was found to be increased in other two mouse models of AD [54] and it was shown in vitro that it can cleave both tau, APP [55] and the Swedish mutant of APP [56], thus possibly generating the pathogenic Aβ42 fragment [57], [58].