MiR-32-5p knockdown inhibits epithelial to mesenchymal transition and renal fibrosis by targeting SMAD7 in diabetic nephropathy.

Diabetic nephropathy (DN) is primary cause of end-stage renal disease. A previous study has shown that miR-32-5p (miR-32) is highly expressed in kidney tissue during chronic allograft dysfunction with interstitial fibrosis and tubular atrophy. However, the role of miR-32-5p (miR-32) in DN is still unclear. In this study, streptozotocin-induced DN rat models and high glucose (HG)-incubated human kidney proximal tubular epithelial (HK-2) cells were established to investigate the role and underlying mechanisms of miR-32 in DN. Results of real-time PCR revealed that miR-32 levels were greatly increased in DN rats and HG-incubated HK-2 cells. Downregulation of miR-32 effectively relieved HG-induced autophagy suppression, fibrosis, epithelial-mesenchymal transition (EMT) and inflammation in HK-2 cells. Besides, miR-32 overexpression significantly down-regulated the expression of mothers against decapentaplegic homolog 7 (SMAD7), whereas knockdown of miR-32 markedly up-regulated the level of SMAD7. Dual-luciferase reporter gene assay confirmed that SMAD7 was a target of miR-32. Reintroduction of SMAD7 expression rescued miR-32-induced HK-2 cells autophagy suppression, EMT and renal fibrosis. Our findings indicate that miR-32 may play roles in the progression of EMT and fibrosis in DN.