Inhibition of miRNA‑135a‑5p ameliorates TGF‑β1‑induced human renal fibrosis by targeting SIRT1 in diabetic nephropathy

miRNA‑135a‑5p upregulation has been identified in renal fibrosis in diabetic nephropathy (DN) with an incompletely known mechanism. Previous data showed that Sirtuin 1 (SIRT1) serves as a novel therapeutic target for DN and interact with the transforming growth factor‑β/mothers against decapentaplegic homolog (TGF‑β/Smad) signaling pathway. The aim of this study was to investigate the regulatory relationship between miR‑135a‑5p and SIRT1. The expression of miR‑135a‑5p and SIRT1 was detected using reverse transcription‑quantitative PCR and western blotting. The renal fibrosis and SMAD3 signaling pathway were assessed by western blotting, by analyzing protein expression of collegen1A1, α‑smooth muscle actin (α‑SMA), fibronectin (FN), epithelial‑cadherin, SMAD3 and phosphorylated SMAD3 (p‑Smad3). The target binding between miR‑135a‑5p and SIRT1 was predicted on TargetScan Human software, and confirmed by dual‑luciferase reporter assay and RNA immunoprecipitation. The results demonstrated miR‑135a‑5p is upregulated and SIRT1 was downregulated in the serum and renal tissue of DN patients, and TGFβ1‑induced DN cell models in human HK‑2 and HMCs. Knockdown of miR‑135a‑5p and overexpression of SIRT1 could inhibit TGFβ1‑induced renal fibrosis in vitro. Moreover, SIRT1 was a downstream target for miR‑135a‑5p. Silencing of SIRT1 could abolish the suppressive role of miR‑135a‑5p knockdown in TGFβ1‑induced HK‑2 and HMCs. The TGFβ1 induced p‑Smad3 expression in HK‑2 and HMCs, which could be attenuated by miR‑135a‑5p knockdown via SIRT1. In conclusion, knockdown of miR‑135a‑5p inhibits TGFβ1‑induced renal fibrosis by targeting SIRT1 and inactivating SMAD3 signaling, providing a novel insight into miR‑135a‑5p as a potential therapeutic approach for DN.