Unveiling the mechanisms that drive the pathological phenotypes of diabetic nephropathy (DN) could help develop new effective therapeutics for this ailment. Transforming growth factor‐β1 (TGF‐β1)/Smad3 signaling is aberrantly induced in DN, leading to elevated microRNA‐21 (miR‐21) expression and tissue fibrosis. Ski‐related novel protein (SnoN) negatively regulates the TGF‐β pathway, but the relationship between SnoN and miR‐21 has not been described in the context of DN. In this study, this association was investigated in vivo (streptozotocin‐induced rat model of diabetes) and in vitro (NRK‐52E model system under high glucose conditions). In both model systems, we observed reduced amounts of the SnoN protein and elevated miR‐21 amounts, indicative of an inverse relationship. These changes in SnoN and miR‐21 amounts were accompanied by reduced E‐cadherin and elevated α‐smooth muscle actin and collagen III levels, consistent with epithelial to mesenchymal transition (EMT). In vitro overexpression of SnoN in NRK‐52E cells downregulated miR‐21 at the transcriptional and posttranscriptional levels and repressed EMT and extracellular matrix (ECM) deposition. In contrast, knockdown of SnoN resulted in miR‐21 upregulation, particularly at the transcriptional level. We further demonstrated that overexpression and inhibition of miR‐21 promoted and suppressed EMT and ECM deposition, respectively, without affecting SnoN levels. Our results indicated that SnoN suppresses the development of DN as well as renal fibrosis by downregulating miR‐21, and therefore represents a novel and promising therapeutic target for DN.
Diabetic nephropathy (DN) commonly causes end-stage renal disease (ESRD). Increasing evidence indicates that abnormal miRNA expression is tightly associated with chronic kidney disease (CKD). This work aimed to investigate whether miR-27a can promote the occurrence of renal fibrosis in DN by suppressing the expression of secreted frizzled-related protein 1 (Sfrp1) to activate Wnt/β-catenin signalling. Therefore, we assessed the expression levels of miR-27a, Sfrp1, Wnt signalling components, and extracellular matrix (ECM)-related molecules in vitro and in vivo. Sfrp1 was significantly down-regulated in a high-glucose environment, while miR-27a levels were markedly increased. A luciferase reporter assay confirmed that miR-27a down-regulated Sfrp1 by binding to the 3′ untranslated region directly. Further, NRK-52E cells under high-glucose conditions underwent transfection with miR-27a mimic or the corresponding negative control, miR-27a inhibitor or the corresponding negative control, si-Sfrp1, or combined miR-27a inhibitor and si-Sfrp1. Immunoblotting and immunofluorescence were performed to assess the relative expression levels of Wnt/β-catenin signalling and ECM components. The mRNA levels of Sfrp1, miR-27a, and ECM-related molecules were also detected by quantitative real-time PCR (qPCR). We found that miR-27a inhibitor inactivated Wnt/β-catenin signalling and reduced ECM deposition. Conversely, Wnt/β-catenin signalling was activated, while ECM deposition was increased after transfection with si-Sfrp1. Interestingly, miR-27a inhibitor attenuated the effects of si-Sfrp1. We concluded that miR-27a down-regulated Sfrp1 and activated Wnt/β-catenin signalling to promote renal fibrosis.
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