As MAPK pathways play an important role in proliferation and differentiation in fibroblasts (36, 37) and targeting MAPK pathways has been proven to be a treatment for pulmonary and renal fibrosis (38, 39), we investigated the effect of secretory CTSC on the barrier function of AECs and differentiation of lung fibroblasts and MAPK pathways. Here, CTSC is linked to renal fibrosis.