Ski-related novel protein suppresses the development of diabetic nephropathy by modulating transforming growth factor-β signaling and microRNA-21 expression.

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.

Wang Y ，Liu L ，Peng W ，Liu H ，Liang L ，Zhang X ，Mao Y ，Zhou X ，Shi M ，Xiao Y ，Zhang F ，Zhang Y ，Liu L ，Yan R ，Guo B ... -  《-》

Smad2 and Smad3 play antagonistic roles in high glucose-induced renal tubular fibrosis via the regulation of SnoN.

Diabetic nephropathy (DN) is a serious microvascular complication of diabetes mellitus.The main pathological features of DN include glomerular sclerosis and renal tubular interstitial fibrosis, which results in epithelial mesenchymal transition (EMT) and excessive extracellular matrix (ECM) deposition.Transforming growth factor-β1(TGF-β1) is a critical factor that regulates the manifestation of renal fibrosis.Smad2 and Smad3 are the main downstream of the TGF-β1 pathway. Ski-related novel protein N(SnoN) is a negative regulator of TGF-β1, and inhibits the activation of the TGF-β1/Smad2/3 signalling pathway. In this study, the expression of Smad2 and Smad3 proteins, SnoN mRNA, SnoN proteins, and the ubiquitination levels of SnoN were determined in DN rats and renal tubular epithelial cells(NRK52E cells). Knockdown and overexpression of Smad2 or Smad3 in NRK52E cells were used to investigate the specific roles of Smad2 and Smad3 in the development of high glucose-induced renal tubular fibrosis, with a specific focus on their effect on the regulation of SnoN expression. Our study demonstrated that Smad3 could inhibit SnoN expression and increase ECM deposition in NRK52E cells, to promote high glucose-induced renal tubular fibrosis. In contrast, Smad2 could induce SnoN expression and reduce ECM deposition, to inhibit high glucose-induced fibrosis. The underlying mechanism involves regulation of SnoN expression. These findings provide a novel mechanism to understanding the significant role of the TGF-β1/ Smad2/3 pathway in DN.

Wang Y ，Zhang X ，Mao Y ，Liang L ，Liu L ，Peng W ，Liu H ，Xiao Y ，Zhang Y ，Zhang F ，Shi M ，Liu L ，Guo B ... -  《-》

SnoN upregulation ameliorates renal fibrosis in diabetic nephropathy.

Liu L ，Shi M ，Wang Y ，Zhang C ，Su B ，Xiao Y ，Guo B ... -  《PLoS One》

BMP-7 inhibits renal fibrosis in diabetic nephropathy via miR-21 downregulation.

Epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) deposition in renal tubular epithelial cells are critical to diabetic nephropathy (DN) pathogenesis, but the underlying mechanisms remain undefined. Bone morphogenetic protein 7 (BMP-7) inhibits EMT and ECM accumulation in renal tubular epithelial cells cultured in presence of high glucose. Meanwhile, miRNA-21 (miR-21) downregulates Smad7, promoting EMT and ECM deposition. However, the association of BMP-7 with miR-21/Smad7 in DN is unknown. Here, NRK-52E cells incubated in presence of high glucose and STZ-induced C57BL diabetic mice were considered in vitro and in vivo models of DN, respectively. In both models, BMP-7 (mRNA/protein) amounts were decreased as well as Smad7 protein expression, while miR-21 expression and TGF-β1/Smad3 pathway activation were enhanced, accompanied by enhanced EMT and ECM deposition. Further, addition of BMP-7 human recombinant cytokine (rhBMP-7) and injection of the BMP-7 overexpression plasmid in diabetic mice markedly downregulated miR-21 and upregulated Smad7, reduced Smad3 activation without affecting TGF-β1 amounts, and prevented EMT and ECM accumulation. MiR-21 overexpression in the in vitro model downregulated Smad7, promoted EMT and ECM accumulation without affecting BMP-7 amounts, and miR-21 downregulation reversed it. By interfering with BMP-7 and miR-21 expression in high glucose conditions, miR-21 amounts and Smad3 phosphorylation were further decreased. Smad7 was then upregulated, and EMT and ECM deposition were inhibited; these effects were reversed after miR-21 overexpression. These findings suggest that BMP-7 decreases renal fibrosis in DN by regulating miR-21/Smad7 signaling, providing a theoretical basis for the development of novel and effective therapeutic drugs for DN.

Liu L ，Wang Y ，Yan R ，Liang L ，Zhou X ，Liu H ，Zhang X ，Mao Y ，Peng W ，Xiao Y ，Zhang F ，Liu L ，Shi M ，Guo B ... -  《-》

TAK1 may promote the development of diabetic nephropathy by reducing the stability of SnoN protein.

This study aimed to investigate the role of transforming growth factor-β-activated protein kinase 1(TAK1) in the development of diabetic nephropathy (DN) by regulating the protein stability of Ski-related novel protein N(SnoN). A combination of in vivo and in vitro model systems was used to investigate how TAK1 regulated the expression of SnoN protein in DN. The study determined the effects of modulating the expression or activity of TAK1 on the SnoN protein level and its influence on the epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) deposition. Under the high-glucose condition, the activation of TGF-β1/TAK1-induced phosphorylation and ubiquitination of SnoN protein resulted in reduced SnoN protein level as a consequence of enhanced SnoN degradation, which promoted EMT and ECM deposition in renal tubular epithelial cells. The study showed that TAK1 impaired SnoN protein level by decreasing the protein stability of SnoN. TAK1 mediated the phosphorylation of SnoN, resulting in SnoN ubiquitination and eventual degradation, which enhanced EMT and ECM deposition to promote renal fibrosis during DN.

Wang Y ，Mao Y ，Zhang X ，Liu H ，Peng W ，Liang L ，Shi M ，Xiao Y ，Zhang Y ，Zhang F ，Yan R ，Guo B ... -  《-》