足细胞PTEN减少导致脂质体吞噬增加引起肾小球硬化的机制研究

Diabetic nephropathy is the leading cause of end-stage renal disease. Type 2 diabetes usually accompanied with severe lipid metabolism disorders. Hyperlipidemia can cause kidney cell damage. When podocytes engulf excessive liposomes, it can trigger intracellular oxidative stress and cause podocytes damage resulting in proteinuria and glomerular sclerosis. Our previous studies have shown that in mice and patients with diabetic nephropathy, the expression of PTEN was suppressed in podocytes. When knockdown PTEN in cultured podocytes can stimulate endocytosis of lipids (ox-LDL), and this response was associated with dephosphorylation of cofilin-1. Becasue PTEN is a phosphatase and cofilin-1 is an important enzyme to control the dynamic of F-actin and the process of endocytosis, therefore, we hypothesized that a decrease in podocytes PTEN cause phosphorylation of cofilin-1 leading to excessive polarization of actin and increased endocytosis activity, as result increasing proteinuria and developing glomerulosclerosis. To examine our hypothesis, we plan to investigate the molecular mechanisms by knockdown and overexpress PTEN in vitro and in mice with podocyte-specific PTEN knockout. If we are correct, the results could help us to develop new therapeutic strategies to combat diabetic nephropathy.

糖尿病肾病是导致终末期肾病的主要原因之一，尤其是2型糖尿病伴有严重的脂代谢异常。高血脂可造成肾脏细胞损伤，和高血糖一起并列为糖尿病肾病主要诱因。足细胞异常吞噬脂质体可触发细胞内氧化应激反应，从而破坏其细胞完整性，导致蛋白尿产生和肾小球硬化。我们前期研究表明，糖尿病肾病时小鼠足细胞中PTEN 表达下降，而敲抑培养足细胞中PTEN能刺激其对脂质(ox-LDL)的吞噬作用。PTEN主要功能是去磷酸化，而去磷酸化的cofilin-1直接参与维持足细胞正常形态和吞噬功能。故我们推测：足细胞中PTEN表达下降直接导致cofilin-1磷酸化而丧失活性，进而F-actin紊乱、吞饮活动增强、脂质体堆积，最终引起足突融合、脱落和蛋白尿增加。本项目拟应用体外敲抑及过表达PTEN技术和PTEN敲除小鼠模型，证实以上假设，从而阐明导致蛋白尿和糖尿病肾病的发生和发展的分子生物学机制，为糖尿病肾病提供新的理论基础。

随着全球肥胖症的流行，肥胖相关性肾病（ORG）的患病率也逐年升高，目前已成为导致终末期肾病的主要病因之一。肥胖可以诱导足细胞中脂质体的积累并引起足细胞损伤。足细胞异常吞噬脂质体可触发细胞内氧化应激反应，从而破坏其细胞完整性，导致蛋白尿产生和肾小球硬化，但其具体分子机制尚不明确。我们的研究结果表明，ORG时人和小鼠足细胞中PTEN 表达下降。PTEN主要功能是去磷酸化，而去磷酸化的肌动蛋白解聚因子cofilin-1直接通过调节F-actin/G-actin的平衡参与维持足细胞正常形态和吞噬功能。因此我们应用体外敲抑及过表达PTEN技术和PTEN敲除小鼠模型等，得出结论：足细胞中PTEN表达下降直接导致cofilin-1磷酸化而丧失活性，进而F-actin紊乱、吞饮活动增强、脂质体堆积，最终引起足突融合、脱落和蛋白尿增加。本项目首次从足细胞对脂质体异常内吞的角度阐明了导致蛋白尿和ORG的发生和发展的分子生物学机制，为ORG提供新的理论基础。