To determine whether DNs contain hydrolase-active or -inactive lysosomes, we stained brain sections from three different AD mouse models, [6-month-old APP knock-in (APPNL-G-F), 4-month-old 5xFAD and 8-month-old APP/PS1ΔE9 (PA)], using antibodies specific to several lysosomal proteins including LAMP1 and LAMP2, lysosomal activator protein saposins (SAPs), the SAP precursor (PSAP), lysosomal hydrolases (cathepsin-B, cathepsin-D, β-glucosidase and β-galactosidase), as well as antibodies to the endosomal proteins EEA1, RAB4A/B, RAB5, RAB6A, RAB7, RAB9A, and RAB11. The gene discussed is PSAP; the disease is Alzheimer disease.