Progranulin在糖尿病肾病足细胞损伤中的保护作用及分子机制

Although the pathogenesis of diabetic nephropathy (DN) is multifactorial, an increasing number of clinical and animal studies have implicated that the regulation of cellular homeostasis and the activation of innate immune system are of importance in the pathogenesis of DN. Therefore, inflammatory response and autophagy take center stage in the study of DN. Progranulin（PGRN）, a pleiotrophic growth factor, is known to play an important role in the maintenance and regulation of the homeostatic dynamics of normal tissue development, proliferation, regeneration, and the host-defense response. In addition, PGRN has also emerged as a multifaceted immune-regulatory molecule through regulating the signaling pathways known to be critical for immunology. However, it is unknown whether PGRN contributes to the regulation of renal functions. Our preliminary studies showed that PGRN was down-regulated in the kidney from streptozotocin-induced diabetic mice and kidney biopsies from diabetic patients. Exacerbation of inflammation and further reduced autophagy were detected in PGRN-/- diabetic mice. We further found that podocytes treated with high glucose selectively reduced PGRN expression. Recombinant PGRN can recover high glucose-reduced autophay and ameliorated inflammation. Therefore, the present study is designed to explore the protective role of PGRN in DN and investigate PGRN-autophagy-NLRP3 inflammasome activation signaling pathways in podocytes both in vitro and in vivo animal studies using podocyte-specific deletion of PGRN mice. We then evaluated the possibility of recombinant PGRN as a therapeutic drug for the treatment of DN. In this study, we postulate that PGRN-induced autophagy is a major protective mechanism against podocyte injury, representing a putative target to ameliorate human glomerular disease.

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自噬成为该领域的研究热点。Progranulin（PGRN）是一种多功能自分泌生长因子，在多种生理和疾病进程中发挥关键作用，但在糖尿病肾病中的作用机制尚不清楚。我们前期工作中首次证实PGRN在糖尿病肾病病人和糖尿病小鼠的肾脏中表达显著降低，同时发现PGRN在高糖条件下的表达变化具有细胞特异性并与足细胞自噬和炎性反应相关。为此，本课题将以PGRN为中心，运用细胞生物学、cre-loxp条件基因敲除技术构建特异性足细胞PGRN基因敲除小鼠等手段深入探讨PGRN在糖尿病肾病中的作用及探讨PGRN-自噬-NLRP3 炎性体在足细胞中的分子调控机制；并进一步以重组蛋白PGRN作为糖尿病肾病治疗手段的初步药效学研究。此研究将拓展对PGRN生物学功能的新认识，为糖尿病肾病的防治提供新靶点和思路，具有重要的理论价值。

糖尿病肾病是糖尿病重要的微血管病变，也是导致终末期肾病（end stage of renal disease, ESRD）的重要因素之一。肾小球硬化以及肾小管纤维化是糖尿病肾病的主要病理特征。颗粒蛋白前体（progranulin，PGRN）是一种自分泌型生长因子，广泛表达分布于体内各种组织与器官，具有诸多生物学功能，参与到多种病理生理过程中， 但在糖尿病肾病中的作用机制尚不清楚。本课题主要以糖尿病肾病为重点，探讨PGRN在肾脏中的作用机制。通过利用 Grn 基因敲除鼠 （B6(Cg)-Grn tm1.1Aidi /J）敲除小鼠构建糖尿病肾病模型发现，在糖尿病肾病组 PGRN的缺失导致了肾皮质中肾小球系膜基质增生加重。透射电镜结果显示 PGRN的缺失加重了肾小球足细胞损伤，导致足细胞足突的融合消失。进一步发现PGRN 的缺失导致肾皮质中炎性因子与趋化因子较野生型糖尿病肾病组更高。体外流式细胞术检测足细胞凋亡水平，特别是 Grn基因敲除鼠糖尿病肾病组较野生型糖尿病肾病组的线粒体的功能和线粒体自噬水平更低。加入重组 PGRN 后线粒体自噬水平恢复，细胞功能增强，表明与调控足细胞的线粒体自噬密切相关。在机制上， 我们发现PGRN通过调控组蛋白去乙酰化酶SIRT6的表达， 进而影响线粒体的合成和促进线粒体的自噬，从而对足细胞起到保护作用。在此基础上，我们进一步拓展PGRN在其他肾脏疾病中的作用。在急性肾损伤中发现PGRN敲除也可加重急性肾脏损伤, 外源性PGRN重组蛋白可有效地通过降低NOD2介导的炎性反应而减轻肾脏损伤。在高同型半胱氨酸血症(hHcy)介导的肾小球损伤中，高同型半胱氨酸血症野生型及Grn基因敲除小鼠肾脏中的β-catenin的明显活化。体外实验中， Hcy能够诱导 GEnC和HPC中β-catenin的活化，而加入外源重组PGRN则能抑制这一作用，说明PGRN可能通过抑制Wnt/β-catenin信号通路来保护hHcy诱导的肾脏损伤。总之，我们研究表明PGRN对于肾脏损伤具有显著的保护作用，可望成为治疗肾脏病的有效靶点。目前以通讯作者身份在本领域权威期刊如J Am Soc Nephrol、Kidney International、Hypertension 和Nature Communications等共发表标有本课题资助的SCI论文9篇，总影响因子60.3。