肥胖引起机体脂质代谢紊乱，肾脏脂质积聚引起肾小管上皮细胞结构和功能损害，是诱发终末肾脏疾病的重要因素。我们前期工作发现，在人肾近端小管上皮细胞中，Mas受体介导饱和脂肪酸棕榈酸诱导的细胞内质网应激及线粒体形态变化，因此提出假说：脂质通过肾小管上皮细胞Mas受体，引起内质网应激，干扰内质网与线粒体对话，诱发肾脏损伤。本项目拟研究（1）在肾脏近端小管细胞株及原代细胞模型中，研究Mas受体激活、抑制或Mas基因敲除是否影响棕榈酸诱导的细胞损害，特别是内质网、线粒体形态和功能变化及两者间的信息传递的改变；（2）利用特异性Mas受体激动剂和抑制剂，研究Mas受体在高脂诱导的小鼠肾小管细胞内质网、线粒体损伤中的作用及机制；（3）利用Mas受体基因敲除小鼠，研究Mas缺失是否缓解高脂饮食诱导的肾小管上皮细胞损害，着眼于内质网、线粒体以及内质网-线粒体之间相互作用的细胞分子机制，为可能的干预提供新的思路

Obesity has emerged as a leading cause of chronic kidney diseases. Chronic kidney damage may be caused by renal lipotoxicity, which involves the intracellular accumulation of free fatty acids, triglycerides, and modified cholesterol in renal glomerular and tubular epithelial cells. Of recent interest has been the interplay among lipid accumulation, endoplasmic reticulum (ER) and mitochondrial injury in the pathogenesis of obesity-related kidney disease. ER is the organelle where transmembrane, secretory, and ER resident proteins are folded and matured. Accumulation of unfolded or misfolded protein results in ER stress and ER-associated death. Our recent studies have demonstrated that palmitic acid (PA), a saturated fatty acid, induces ER stress in human proximal tubular cells. Recently dynamic interactions with the ER have been described for every cellular compartment. Among all of the ER partners, mitochondria is the most prominent with regard to regulating metabolism and cell survival. The two organelles physically interact, forming specialized contacts referred to as mitochondrial associated membranes (MAM), in which membrane and luminal components can intermix and exchange. ER, mitochondria, and MAM are important for maintaining energy balance and homeostasis in cells..Evidence has shown local renin-angiotensin system (RAS) in the kidney play an important role in development of obesity-associated kidney diseases. Angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARBs) have been indicated in the treatment of obesity-related kidney disease and can mitigate the progression of kidney disease. We have demonstrated a protective effect of RAS blockade with renin inhibitor or ARB in high-fat diet induced renal tubular injuries. Angiotensin II can be converted into angiotensin 1-7 by ACE2, which activates its G-protein coupled membrane Mas receptor in tubular epithelial cells. Generally activation of angiotensin 1-7--Mas axis may antagonize physiological effects of angiotensin II. .However, our preliminary data showed that Mas activation may be involved in palmitic acid-induced injuries of tubular cells. 1. In human proximal tubular HK2 cells, Ang1-7 or AVE0991, Mas agonists, aggravated PA-induced ER stress; whereas A779, a Mas antagonist, attenuated ER stress; 2. Mas receptor knockout in HK2 cells prevented ER stress induced by PA; 3. In wild type HK2 cells, PA caused elevated intracellular calcium levels, which was markedly prevented in cells with Mas deficiency, indicating an involvement of calcium signaling in PA-induced HK2 cell injury; Mas receptor deficiency was also associated with maintained MAM and improved mitochondrial morphology in HK2 cells treated with PA; 4. HK2 cells with Mas receptor deficiency showed improved cell vitality and proliferation after PA treatment; 5. In mice fed with high-fat diet for 12wk, Mas receptor blockade markedly inhibited ER stress in the kidney cortex. .We therefore hypothesize that activation of Mas receptor is involved in PA-induced epithelial cell injuries. In the current project, we aim to investigate 1) In HK2 cells and primary cultured proximal tubular cells, whether activation and suppression of Mas receptor signaling pathway is involved in PA-induced injuries, intracellular events e.g. ER stress, intracellular calcium oscillation, and a cross-talk between organelles will be evaluated; 2) In mice with high-fat diet, whether Mas receptor activation or inhibition is involved in tubular injuries induced by lipid accumulation; 3) In mice with Mas receptor deficiency, whether loss of Mas ameliorates high-fat diet-induced tubular epithelial injuries. A potential molecular mechanism will be examined, e.g. the cross-talk between ER and mitochondria. The current project is expected to provide evidence for therapeutic intervention of obesity-associated kidney diseases targeting to ER and mitochondria.