Development of the treatment of diabetic nephropathy by targeting the TGF-β signaling

糖尿病肾病的特点是细胞外基质（ECM）蛋白的积累。TGF-β是介导糖尿病肾病进展的关键细胞因子。在本研究中，我们研究了TGF-β诱导的ECM蛋白如纤连蛋白（肾小球中主要的ECM蛋白之一）在细胞内积累的机制。我们还研究了吡格列酮（新型胰岛素增敏剂）和n -乙酰-seryl-天冬氨酸-赖氨酸-脯氨酸（Ac-SDKP）对TGF-β诱导的ECM表达和细胞内信号通路的影响，Ac-SDKP通过血管紧张素转换酶抑制剂治疗而增加。在培养的系膜细胞中，TGF-β1刺激Smad2、3、4的核易位，激活ERK和JNK。TGF-β1诱导纤维连接蛋白mRNA表达，而这种表达被MEK特异性抑制剂PD98059抑制，而不影响Smad信号。这些结果提示，TGF-β诱导的纤维连接蛋白表达需要MEK-ERK通路。吡格列酮通过抑制TGF-β诱导的ap -1而非ERK激活来抑制TGF-β1诱导的纤维连接蛋白表达。Ac-SDKP抑制TGF-β诱导的PAI-1和I型胶原的表达。Ac-SDKP抑制TGF-β1激活Smad2、3和SBE报告基因活性。过表达的Smad7通过Ac-SDKP从细胞核转运到细胞质，表明Ac-SDKP通过Smad7转运抑制Smad信号转导。这些结果为吡格列酮和Ac-SDKP具有抗纤维化作用提供了新的证据，通过这些药物抑制TGF-β信号传导可能是治疗糖尿病肾病的有效方法。

Diabetic nephropathy is characterized by an accumulation of extracellular matrix (ECM) proteins. TGF-β is a key cytokine which mediates the progression of diabetic nephropathy. In this study, we examined the intracellular mechanism by which TGF-β-induced ECM proteins such as fibronectin, one of the major ECM proteins accumulated in renal glumeruli. We also examined the effects of pioglitazone, new insulin sensitizing agent, and N-Acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) which was increased by the treatment of angiotensin converting enzyme inhibitors on TGF-β-induced ECM expression and intracellular signaling pathways. In cultured mesangial cells, TGF-β1 stimulated nuclear translocation of Smad2, 3, 4 and activated ERK and JNK. TGF-β1 induced fibronectin mRNA expression, and this was inhibited by a specific MEK inhibitor, PD98059 without affecting Smad signaling. These results suggest that MEK-ERK pathway is required for TGF-β-induced fibronectin expression. Pioglitazone inhibited TGF-β1-induced fibronectin expression by inhibiting TGF-β-inducedAP-1 but not ERK activation. Ac-SDKP inhibited TGF-β-induced PAI-1 and type I collagen expressions. Ac-SDKP inhibited activation of Smad2, 3 and SBE reporter activity by TGF-β1. The overexpressed Smad7 was translocated from the nucleus to the cytosol by Ac-SDKP, suggesting that Ac-SDKP inhibited Smad signaling via Smad7 translocation. These results provide novel evidence that pioglitazone and Ac-SDKP has an antifibrotic effect, and inhibiting the TGF-β signaling by these agents could be a useful therapy to diabetic nephropathy.