However, miR-21 may be also protective in kidney disease as miR-21-deficient TGF-β(1)-transgenic mice show increased proteinuria and glomerular injury in streptozotocin-induced diabetic mice, suggesting a diverse role of miR-21 as a feedback inhibitor of TGF-β/Smad3 signaling (Lai et al., 2015). Here, SMAD3 is linked to kidney disorder.