短链脂肪酸通过调节固有免疫、内皮细胞和胰岛素靶组织介导肠道产丁酸菌改善胰岛素抵抗的分子机制

Obesity is an independent risk factor of Type 2 Diabetes. Obesity is characterized by inflammation of metabolic tissues (adipose, liver and skeletal muscle) that leads to insulin resistance (IR). It is now well recognized in the literature and from our previous work that innate immune cells and endothelial cells within these tissues and the circulation are involved in the presentation of inflammation and IR during obesity. Recently, the gut microbiota has been recognized to play a major role in the inflammation of metabolic tissues. It has been reported that a major change in the gut of obese rodents and humans is a reduction in butyrate-producing bacteria. Several strategies designed to improve IR, also increase the amount of butyrate-producing bacteria and their products, short-chain fatty acids (SCFAs). Gut-derived SCFAs enter the circulation to mediate the effect of gut microbiota on innate immune cells, endothelial cells and insulin target cells via G-protein coupled receptors (GPCRs). Therefore, we hypothesize that supplementation of butyrate-producing bacteria could relieve IR through their production of SCFAs. However, how the GPCR signaling pathways activated by SCFAs cross-talk with inflammation and insulin signaling pathways is not clear yet. In order to illustrate the molecular mechanisms of the relief of insulin resistance by SCFAs from butyrate-producing bacteria, we will administer different butyrate-producing bacteria or SCFAs to obese mice. The changes of gut microbiota, concentration of SCFAs and different signal pathways in the above tissues and cells will be studied by pyrosequencing, gas chromatopraphy and FACS analyses, respectively. Our study may provide new strategy for prevention and treatment of IR and could lay the foundation for clinical intervention study in the future.

肥胖是2型糖尿病的独立危险因素，表现为胰岛素抵抗（IR），炎症是其重要诱因。文献和我们的工作发现胰岛素靶组织以及固有免疫和内皮细胞这两个新因素与炎症和IR有关，近来报道肠道菌群也参与其中。肥胖个体肠道产丁酸菌减少，改善IR的不同干预方式大多能增加产丁酸菌及其产物短链脂肪酸（SCFAs）的量，肠道SCFAs可进入血循环，通过其G蛋白偶联受体（GPCR）作用于上述组织细胞等，介导肠道菌群与肠外的联系。我们推测，补充产丁酸菌可通过产生SCFAs缓解IR。但SCFAs如何通过GPCR信号通路与炎症及胰岛素信号通路cross-talk，相关的分子机制不明。本研究拟给予肥胖小鼠不同产丁酸菌或SCFA，借助焦磷酸测序、气相色谱、流式细胞术等分别检测肠道菌群结构、SCFAs浓度以及上述组织细胞的不同信号通路，明确SCFAs介导产丁酸菌改善IR的分子机制，寻求预防和治疗IR的新策略，为临床干预研究奠定基础。

糖尿病已成为全球性健康问题，超过90％的糖尿病为2型糖尿病，肥胖是其发病的独立危险因素，表现为胰岛素抵抗，慢性炎症与其密切相关。肠道菌群与肥胖和胰岛素抵抗有关，肥胖个体产丁酸菌减少，胰岛素抵抗的改善与产丁酸菌及其产物短链脂肪酸（SCFAs）的增加相关，从肠道进入血中的SCFAs通过GPCR作用于组织细胞，本研究探讨了产丁酸梭菌及其产物SCFAs对代谢紊乱的影响及机制。.高脂喂养雄性C57BL / 6小鼠造成肥胖的胰岛素抵抗模型，分别灌胃给予产丁酸梭菌CB337279悬液或NaCl对照悬液，免疫组织化学、流式细胞术和实时定量PCR评估全身性炎症，16S rRNA基因测序检测细菌群落的丰富度，Western blot检测胰岛素靶组织中GPR43、胰岛素信号通路和炎症信号通路分子，并用棕榈酸构建胰岛素抵抗的细胞模型检测上述信号分子。结果显示，相比于单纯高脂饮食小鼠，灌胃产丁酸梭菌小鼠体重减少，小肠和脂肪组织中GPR43表达升高，血中炎性细胞、炎性因子、LPS和LBP水平均降低，脂肪组织和肝脏炎症、糖脂代谢紊乱、胰岛素抵抗、肝脏脂质异位沉积均得到显著缓解。产丁酸梭菌显著改善高脂饮食小鼠的肠道微生物群丰富度，同时伴随肠道结构、屏障功能的改善及肠道炎症缓解。体外结果发现，SCFAs显著改善棕榈酸诱导的胰岛素抵抗并抑制炎症信号，其机制可能与激活AMPK有关。.运动以及能量限制激活的AMPK在胰岛素抵抗和代谢综合征相关疾病的治疗中发挥作用，本研究还明确了AMPKα2亚基具有缓解高脂饮食诱导的肝脏脂肪变性、炎症和纤维化的作用。.本项目的完成为治疗胰岛素抵抗提供了新策略，为临床干预研究提供了理论基础。