Cathepsin B (CTSB) and cathepsin D (CTSD) are the two most abundant cathepsins in lysosomes and have been reported to play profibrogenic roles in liver fibrosis37,38; therefore, we hypothesized that they might be the key to the mechanism underlying Prep knockout-induced exacerbated liver fibrosis. The gene discussed is CTSB; the disease is Hepatic fibrosis.