APP and Alzheimer disease: It has been demonstrated that amyloid plaques, which are the hallmark of the pathology, are characterized by the co-localization of lysosomal enzymes [55], and in a peripheral model of Alzheimer’s disease lysosomal glycohydrolases are upregulated, whereas cathepsin D, a lysosomal protease which has been also implicated in APP processing, is decreased [56,57].