Backgroud: Diabetic nephropathy is one of the most frequent causes of end-stage renal disease and is associated with proliferation of glomerular mesangial cells (MCs) and excessive production of the extracellular matrix (ECM). Several studies have shown that early growth response factor 1 (Egr1) plays a key role in renal fibrosis by regulating the expression of genes encoding ECM components. However, whether Egr1 also contributes to diabetic nephropathy is unclear. Methods: In the present study, we compared the expression of Egr1 in kidneys from OLETF rats with spontaneous type 2 diabetes and healthy LETO rats. We also examined whether high glucose and TGF-β1 signaling up-regulated Egr1 expression in cultured MCs, and whether Egr1 expression influenced MC proliferation and expression of ECM genes. Results: We found that higher expression of Egr1 and TGF-β1, at both the mRNA and protein levels, the kidneys from OLETF rats vs. LETO rats. High glucose or TGF-β1 signaling rapidly up-regulated expression of Egr1 mRNA and protein in cultured MCs. Overexpressing Egr1 in MCs by transfection with M61-Egr1 plasmid or treatment with high glucose up-regulated expression of fibronectin, type IV collagen and TGF-β1, and promoted MC proliferation. Conversely, siRNA-mediated silencing of Egr1 expression down-regulated these genes and inhibited MC proliferation. Chromatin immunoprecipitation (ChIP) assays revealed that Egr1 bound to the TGF-β1 promoter. Conclusion: Our results provide strong evidence that Egr1 contributes to diabetic nephropathy by enhancing MC proliferation and ECM production, in part by interacting with TGF-β1.

An imbalance between T helper 17 (Th17) and T regulatory (Treg) cell subsets contributes to the pathogenesis of diabetic kidney disease (DKD). However, the underlying regulatory mechanisms that cause this imbalance are unknown. Serum/glucocorticoid‐regulated kinase 1 (SGK1) has been suggested to affect Th17 polarization in a salt‐dependent manner, and sodium/glucose cotransporter 2 inhibitors (SGLT2i) have been demonstrated to regulate sodium‐mediated transportation in the renal tubules. This study aimed to evaluate the potential benefits of dapagliflozin (Dap) on DKD, as well as its influence on shifting renal T‐cell polarization and related cytokine secretion. We treated male db/db mice with Dap or voglibose (Vog) and measured blood and kidney levels of Th17 and Treg cells using flow cytometry. We found that Th17 cells were significantly increased, while Treg cells were significantly decreased in diabetic mice. Moreover, Dap suppressed the polarization of Th17/Treg cells by inhibiting SGK1 in diabetic kidneys, and this was accompanied by attenuation of albuminuria and tubulointerstitial fibrosis independent of glycemic control. Taken together, these results demonstrate that the imbalance of Th17/Treg cells plays an important role in the progression of DKD. Moreover, Dap protects against DKD by inhibiting SGK1 and reversing the T‐cell imbalance.