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)蛋白积聚。转化生长因子-β是介导糖尿病肾病进展的关键细胞因子。在这项研究中，我们研究了转化生长因子-β诱导细胞外基质蛋白如纤维连接蛋白的细胞内机制，纤维连接蛋白是肾小球内积聚的主要细胞外基质蛋白之一。我们还观察了新型胰岛素增敏剂吡格列酮和经血管紧张素转换酶抑制剂处理后升高的N-乙酰丝氨酸天冬氨酰-赖氨酰脯氨酸对转化生长因子-β诱导的细胞外基质表达和细胞内信号转导途径的影响。在培养的肾小球系膜细胞中，转化生长因子-β-1刺激Smad2、3、4的核转位，并激活ERK和JNK1。转化生长因子-MEK1可诱导纤维连接蛋白β的表达，该作用可被特异性的MEK1抑制剂PD98059抑制，但不影响Smad信号转导。这些结果提示，在转化生长因子-β诱导的纤维连接蛋白表达中，MEK-ERK信号转导途径是必需的。吡格列酮通过抑制转化生长因子-β-1诱导的AP-1的表达而抑制转化生长因子-β诱导的纤维连接蛋白的表达，但不能抑制ERK的激活。AC-SDKP抑制转化生长因子-β诱导的纤溶酶原激活物-1和I型胶原的表达。Ac-β可抑制Smad2、3的激活和Smad7报告基因的活性。Ac-SdKP可将过表达的Smad7从胞核移位到胞浆中，提示Ac-SdKP通过Smad7转位抑制Smad7信号转位。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，通过抑制转化生长因子-β信号通路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.