支架蛋白IQGAP1介导nephrin内化在糖尿病肾病足细胞损伤中的作用及调控机制

Although the pathogenesis of diabetic nephropathy (DN) has not been fully delineated, an increasing number of studies have confirmed that podocyte injury is the primary cause of DN development. Nephrin behaves as the signaling hub of the podocyte slit-diaphragm domain, and its internalization mechanism has recently become a popular research topic. IQ domain GTPase-activating protein 1 (IQGAP1), a multifunctional scaffolding protein, is known to play a core regulatory role in cytomembrane molecule internalization. However, it is unknown whether IQGAP1 contributes to the pathogenesis of DN. Our preliminary study demonstrated that IQGAP1 was up-regulated in the renal tissue of streptozotocin-induced DN mice and was found to mainly localize in podocytes. Meanwhile, nephrin internalization was significantly increased in podocytes of DN mice and mediated podocyte injury. We further found that IQGAP1 interacts with nephrin through its poly-proline binding domain and RasGAP domain in the carboxyl terminus. These findings motivated us to determine whether IQGAP1 participates in nephrin internalization by interacting with each other, ultimately leading to podocyte injury. Therefore, the present study is designed to evaluate the role of IQGAP1 in DN podocyte injury and illuminate its regulatory mechanism in nephrin internalization both in cultured podocytes and IQGAP1-specific knock out mice. This study will provide insight into the molecular biological function of IQGAP1 and provide the scientific basis for future mechanistic studies and for designing DN prevention strategies.

糖尿病肾病发病机制的研究越来越关注于足细胞损伤，而足细胞膜上关键信号分子-nephrin的内化成为该领域的研究热点。IQGAP1是一种多功能支架蛋白，可在多种蛋白内化过程中发挥核心调控作用，但其在糖尿病肾病中的作用机制尚不清楚。本课题组前期研究首次证实IQGAP1在糖尿病肾病小鼠肾脏组织中表达显著增高，且局限于足细胞。而高糖刺激的nephrin内化参与足细胞损伤。进一步研究发现，IQGAP1通过其分子内WW以及RGCT区段与nephrin紧密相连。糖尿病肾病状态下表达增高的IQGAP1是否通过与nephrin相互作用，启动nephrin内化，进而导致足细胞损伤。为此，本课题将以IQGAP1为研究中心，运用细胞生物学、IQGAP1特异性敲除等技术方法深入探讨IQGAP1在糖尿病肾病中的作用并阐明其介导nephrin内化的分子调控机制，此研究将为糖尿病肾病的机制研究及防治策略提供新的理论依据。

糖尿病肾病是糖尿病最重要的微血管病变之一，居于发达国家慢性肾衰竭原发病的首位，在我国的发病率也在逐年上升，是终末期肾病和糖尿病患者死亡的重要原因。因此糖尿病肾病的防治工作至关重要。近年来对其发病机制的研究越来越关注于足细胞损伤，而足细胞膜上关键信号分子-nephrin 的内化成为该领域的研究热点。IQGAP1作为一种多功能支架蛋白，可在多种蛋白内化中发挥核心调控作用。本课题从体内外正反两方面，运用细胞生物学、基因工程等技术方法证实：IQGAP1在人类肾脏内区段特异性表达，而糖尿病肾病作为一种足细胞病，其足细胞内IQGAP1高表达，且糖尿病肾病的疾病状态使其表达部位从弥散分布于胞浆，逐渐向足细胞近胞膜处聚集，且与nephrin共定位明显增加，进一步应用基因工程技术调控内源性IQGAP1表达，证实IQGAP1通过与nephrin相互作用的增强参与介导糖尿病肾病时nephrin内吞从而导致足细胞损伤。进一步研究发现IQGAP1主要通过脂筏途径介导nephrin内吞，且糖尿病肾病时增高的PKCα所介导的nephrin磷酸化是其上游调控机制，同时nephrin内吞受到IQGAP1磷酸化以及细胞骨架稳态的影响。本研究详细阐明了IQGAP1在糖尿病肾病中的作用及其介导nephrin内吞的分子调控机制，进一步完善了糖尿病肾病发病的分子生物学机制，并为疾病的防治筛选有效的作用靶点，具有重要的理论意义和临床应用价值。