miR-133b and miR-199b knockdown attenuate TGF-β1-induced epithelial to mesenchymal transition and renal fibrosis by targeting SIRT1 in diabetic nephropathy.

Transforming growth factor-β1 (TGF-β1)-induced epithelial to mesenchymal transition (EMT) and renal fibrosis plays critical role in the development and progression of diabetic nephropathy (DN). Our study aimed to determine the detailed roles of miR-133b & miR-199b on TGF-β1-induced EMT & renal fibrosis in DN and its underlying mechanism. The expressions of miR-133b & miR-199b in OLETF rats, LETO rats & TGF-β1-treated human proximal tubule cell line (HK-2) were examined by qRT-PCR. Inhibition of miR-133b or miR-199b was realized in cells by transfection of lentivirus containing miR-133b inhibit or miR-199b inhibitor. The expression levels of collagen I (COL I), fibronectin (FN), α-smooth muscle actin (α-SMA), E-cadherin & sirtuin 1 (SIRT1) were detected by western blot and immunohistochemistry. Masson staining was conducted to estimate the degree of renal fibrosis. The interaction between SIRT1 and miR-133b, miR-199b was explored by luciferase reporter assay and RNA immunoprecipitation (RIP) assay. miR-133b and miR-199b were highly expressed in the renal cortex of diabetic OLETF rats and TGF-β1-treated HK-2 cells. EMT and renal fibrosis were induced in diabetic OLETF rats and TGF-β1-treated HK-2 cells. Inhibition of miR-133b and miR-199b attenuated EMT and renal fibrosis in diabetic OLETF rats and TGF-β1-treated HK-2 cells. In addition, SIRT1 was identified as a target of miR-133b & miR-199b in HK-2 cells. SIRT1 knockdown dramatically reversed the suppression on TGF-β1-induced EMT and renal fibrosis in HK-2 cells mediated by anti-miR-133b or anti-miR-199. Inhibition of miR-133b & miR-199b attenuated TGF-β1-induced EMT & renal fibrosis by upregulating SIRT1 shows that using different miRNAs is a potential strategy for the future treatment of DN.