Cathepsin D is an aspartic endo-protease that is ubiquitously distributed in lysosomes. The main function of cathepsin D is to degrade proteins and activate precursors of bioactive proteins in pre-lysosomal compartments, including substrates of endocytosis, phagocytosis and autophagy. Consequently, cathespin D deficiency leads to a strong impairment of the lysosomal-autophagy machinery.

Mutations in the gene encoding cathespin D, CTSD, are associated with the pathogenesis of several diseases, including breast cancer and Alzheimer’s disease.