Cell Type-specific Functions of the Lysosomal Protease Cathepsin L in the Heart

The study explored the role of the lysosomal protease Cathepsin L (Ctsl) in heart function, particularly in Ctsl-deficient mice, which exhibited dilated cardiomyopathy (DCM) and myocardial fibrosis. The absence of Ctsl in cardiomyocytes was primarily responsible for the DCM phenotype, while transgenic expression of Ctsl in these cells improved cardiac function but did not resolve fibrosis. Expression in epithelial cells improved hair loss but not heart function. The findings suggested that Ctsl was crucial for maintaining cardiac structure and function, likely through its role in collagen turnover by cardiac fibroblasts, and its deficiency led to significant cardiac pathology and complex phenotypes, including hair loss.