SMAD3 and renal fibrosis: In addition, polyamine depletion activates TGF-βsignaling (Patel et al., 1998; Rao et al., 2000; Liu et al., 2003) and our laboratory recently demonstrated that depletion of cellular polyamine levels by targeting Azin1 with a Smad3-dependent miR-433 exaggerates TGF-β-induced renal fibrosis (Li et al., 2013a).