GPR124在糖尿病肾病足细胞损伤中的保护作用及分子机制

GPR124 is an orphan G protein–coupled receptor (GPCR) with a large ectodomain belonging to the adhesion GPCR subfamily. It has been reported that GPR124 plays vital role in angiogenesis and nervous system development. However, up to date, the expression and function of GPR124 in kidney remains unclear. Our preliminary studies showed that GPR124 was down-regulated in kidney biopsies from diabetic patients and the kidney from diabetic mice. In vitro, our studies showed overexpression of GPR124 reduced apoptosis in podocytes with high glucose treatment. Furthermore we found that GPR124 was essential for maintaining autophagy level in podocytes. These results indicate that GPR124 is a potentially important therapeutic target in diabetic nephropathy. Therefore, the present study was designed to elucidate the role of GPR124 in diabetic nephropathy and the regulatory mechanisms in podocytes homeostasis. Firstly, we investigate the expression pattern of GPR124 in both type I and II diabetic nephropathy. Secondly, we generate podocytes-specific GPR124 knockout mice by Cre-LOXP technology and assess the role of GPR124 in diabetes-induced podocyte injury. We then evaluate the possibility of overexpression of GPR124 in kidney by lentivirus transfection as a therapeutic strategy for the treatment of DN. This project may provide new insight into both the basic and clinical research on the pathogenesis and the potential theraputic targets of diabetic nephropathy.

GPR124是一种新发现粘附类G蛋白偶联受体(GPCR)，在肿瘤生长、血管生成及神经系统发育等过程中发挥重要作用，但GPR124是否在肾脏中表达及在糖尿病肾病中的作用尚不清楚。我们前期工作首次明确GPR124在肾脏及肾实质细胞中均表达，进一步发现其在糖尿病肾病病人及糖尿病小鼠肾脏中表达显著降低。体外在高糖条件下，相对其他肾脏实质细胞，足细胞GPR124的表达降低最为明显，提示GPR124表达变化可能是导致糖尿病足细胞损伤的重要因素之一。为此，本课题将通过临床标本、动物模型及体外细胞培养等方法明确GPR124在糖尿病肾病中的作用；运用Cre-LOXP技术构建足细胞特异性GPR124敲除小鼠，进一步应用电镜、激光共聚焦显微镜等技术深入探讨GPR124在糖尿病足细胞损伤中的作用及对足细胞自噬的调控机制。此研究将拓展对GPR124功能的认识，为寻找治疗糖尿病肾病的新靶点提供实验和理论依据。

糖尿病肾病发病机制的研究越来越关注于免疫平衡和细胞稳态的调控，而与之相关的炎性反应和衰老激活成为该领域的研究热点。GPR124是一种最新发现粘附类G蛋白偶联受体，在肿瘤生长、血管生成及神经系统发育等过程中发挥重要作用，但GPR124在肾脏中的表达及在糖尿病肾病(Diabetic Nephropathy, DN)中的作用尚不明确。本研究发现GPR124在DN小鼠肾脏组织及高糖培养条件下的足细胞中表达显著降低。通过Cre-loxp建立足细胞条件性GPR124敲除小鼠并构建DN模型，我们发现足细胞GPR124缺失加剧了DN足细胞自噬功能障碍及细胞凋亡，并且足细胞GPR124缺失促进了衰老进程。在DN的发生与发展过程中，肾脏固有细胞衰老现象导致肾功能的恢复及肾脏固有细胞再生潜能明显减低。同时，衰老细胞分泌多种衰老相关分泌表型因子（senescence-associated secretory phenotype，SASP）反馈性地加速肾脏固有细胞损伤。我们研究结果显示GPR124缺失加重了足细胞线粒体损伤，最终导致线粒体DNA(mitochondrial DNA, mtDNA)的泄露。mtDNA的释放是介导足细胞cGAS-STING信号通路激活的重要因素，我们发现GPR124足细胞特异性敲除加重了STING信号通路的激活，进而介导多种致炎因子的累积，促进衰老SASP炎症表型的产生。最后，我们在小鼠阿霉素诱导的局灶节段性肾小球硬化模型(FSGS)中验证了GPR124的作用，发现FSGS中GPR124的表达降低促进了足细胞衰老及SASP表型。此研究拓展了对GPR124功能的认识，并阐明了糖尿病肾病与肾脏衰老及STING激活介导的SASP炎症表型的关系，为多种足细胞病的治疗提供新的研究思路及干预策略。