SMAD3 and renal fibrosis: In particular, the activation of Smad3 plays an important role in various processes including cell growth, differentiation, apoptosis, and tissue repair (Yang et al. 1999; Roberts et al. 2003; Flanders 2004), and Smad3 serves as a key mediator of the TGF‐β signaling leading to renal fibrosis (Sato et al. 2003).