SMAD3 and renal fibrosis: As Azin1 promotes polyamine synthesis and polyamine depletion can activate TGF-β signaling by increasing the expression levels of TGF-β1, TβRI, and Smad3 (Patel et al., 1998; Liu et al., 2003), elevation of miR-433 during renal fibrosis forms a positive feedback loop to amplify TGF-β signaling by suppressing Azin1 expression.