Deficiency of CatK or CatL exacerbates lung and myocardial fibrosis and cardiomyopathy (Buhling et al., 2004, Petermann et al., 2006), whereas their overexpression reduces ECM deposition, cardiac hypertrophy, and cardiac and lung fibrosis (Tang et al., 2009, Zhang et al., 2011a, Zhang et al., 2011b). Here, CTSL is linked to pulmonary fibrosis.