受体相互作用蛋白1（RIP1）介导的小肠上皮细胞增殖改变在肥胖发生中的作用及机制研究

Obesity is a major risk factor for type 2 diabetes and cardiovascular disease. Epidemiological studies have suggested that, excessive energy from food intake is the major cause of obesity. Intestinal absorption of nutrients is the initial and key step of energy intake, intestinal epithelial cell through constantly proliferation, differentiation, migration and apoptosis, to maintain the structure and absorptional function of epithelium throughout the lifetime. In previous studies, we found that nutrients could stimulate intestinal epithelial cell proliferation, intestinal villus elongation and increase absorptive capacity during obese development. In contrast, blocking of intestinal epithelial cell proliferation can prevent the occurrence of obesity. Receptor interacting-protein (RIP1), is an important molecular regulator of cell apoptosis and necrosis, the functional study of RIP1 mainly focused on the immune system, inflammation and tumor. Whether RIP1 is involved in the regulation of intestinal epithelial cell proliferation has not been reported. In our study, we found that RIP1 and its ubiquitination enzyme cIAP2 expression were significantly increased in obese mice intestine; intestinal epithelial cell specific RIP1 knockout mice shown significant weight loss, indicating that RIP1 may play an important role in regulating the proliferation of intestinal epithelial cells. In this study, we will use in vitro cell culture, the intestinal epithelial cell specific RIP1 knockout and transgenic mice, and high fat diet induced obese mice model, further investigate the mechanisms that how RIP1 is involved in the regulation of intestinal epithelial cell proliferation, epithelium structure and functional changes in mice and during high fat diet induced obese development.

肥胖是2型糖尿病和心血管疾病的主要危险因素。流行病学研究指出，过多摄取能量，是肥胖的罪魁祸首。小肠上皮营养物质的吸收是能量摄入的最关键环节。小肠上皮细胞不断地增殖、分化、迁移以及凋亡，维持小肠上皮的结构和吸收功能。我们发现，营养物质可使小肠上皮细胞增殖加快，绒毛变长，吸收能力增加而导致肥胖;阻断肠上皮细胞增殖，可阻止肥胖的发生。受体相互作用蛋白RIP1,是调节细胞凋亡和坏死的重要分子，其功能研究主要集中在免疫、炎症和肿瘤。RIP1是否参与调节小肠上皮细胞的增殖未见报道。我们发现，在肥胖小鼠肠道，RIP1及其泛素化酶cIAP2表达明显增高;而肠上皮细胞特异性RIP1敲除小鼠的体重明显减轻。说明RIP1可能在小肠上皮细胞增殖过程中发挥重要的调节作用。本课题将利用细胞、肠上皮细胞特异性RIP1敲出和转基因小鼠，结合高脂饮食模型，进一步研究RIP1对小肠上皮细胞增殖的调节及在肥胖发生中的作用机制。

肥胖影响着世界上大约30%的人口，肥胖可以造成包括血糖、血脂在内的多种代谢紊乱，是代谢综合征、慢性炎症、2型糖尿病和心血管疾病的主要危险因素。近年来的研究证明，肠道激素、肠道菌群及肠道的营养吸收在肥胖发生、发展过程中扮演着重要角色。以往的研究证明，受体相互作用蛋白 1 (receptor-interacting protein 1, RIP1) 是调节细胞凋亡和坏死的关键分子，在免疫性疾病、炎症和肿瘤发生、发展中都发挥着重要的作用。RIP1在肠道中主要表达在肠上皮细胞，参与调节肠道发育和炎症性疾病的发生、发展。但肠道上皮细胞中的RIP1是否影响肠道功能而参与肥胖的发生、发展尚未有研究。本课题利用肠上皮细胞特异性RIP1敲除小鼠，结合高脂饮食诱导的肥胖小鼠模型，研究了肠道上皮细胞RIP1在肥胖发生、发展过程中的作用及其作用机理。. 肠道上皮特异性RIP1纯合敲除导致小鼠出生后死亡。因此本课题使用了肠道上皮特异性RIP1杂合敲除小鼠。在正常饮食情况下，肠道上皮特异性RIP1杂合小鼠体重及其他代谢表型和野生型小鼠之间无明显差别。而在高脂饮食情况下，与野生型小鼠相比，肠道上皮特异性RIP1杂合雌性小鼠体重、体脂率、血清胆固醇水平均显著降低，肝脏脂肪沉积显著减少，胰岛素耐量和糖耐量均有明显改善。进一步研究发现，肠道上皮RIP1杂合小鼠回肠中，纤维母细胞生长因子(fibroblast growth factor 15, FGF15) mRNA以及蛋白水平均显著升高，同时血清中的FGF15水平也显著升高。FGF15/19主要由肠道上皮细胞产生和分泌后进入血液循环，作用于肝脏和其他脏器，可以调节能量代谢以及胆固醇、胆汁酸代谢。体外细胞试验也证明，当RIP1敲低后，FGF15/19 mRNA水平极显著升高，提示了肠道上皮特异性RIP1降低可能通过调节FGF15/19而参与了肥胖和代谢表型的调控。. 本研究首次发现了RIP1参与肥胖的发生和调控，并建立了RIP1与胆汁酸代谢通路的联系，进一步扩展了人们对肥胖的发生机理和肠道RIP1功能的认识，本研究也为未来将肠道RIP1作为治疗肥胖的潜在药物靶点提供了有力的理论依据。