辣椒素通过调节肠道菌群-胆汁酸轴防治2型糖尿病的作用与机制研究

Type 2 diabetes mellitus (T2DM) is a challenging problem for public health worldwide. Recent studies suggest that the disorder of downstream bile acid metabolic pathways induced by gut microbiota dysfunction play important roles in the development and progression of T2DM. Capsaicin (CAP) has beneficial effects on anti-inflammation, lipid metabolism regulation and insulin sensitivity improvement. However, the effect and mechanism of CAP on T2DM is still unclear. Based on our previous findings that CAP can improve the glycemic control in gestational diabetic patients and regulate the gut microbiota and bile acid metabolism in healthy population, we hereby propose the hypothesis that dietary CAP can significantly improve the glycemic control of T2DM patients via the remodeling of gut microbiota-bile acid axis and subsequent regulation on its downstream pathways. Based on the population intervention and animal study, this project is designed to comprehensively evaluate the effects of dietary CAP on T2DM targeted on the regulation of gut microbiota-bile acid axon-TGR5 and FXR pathways, by using the techniques of high throughput sequencing, metagenomic detection, germ-free animal model, Cas9 transfection and predictive model establishment. Our study is of great significance in further clarifying the effects and mechanism of gut microbiota-bile acid axis remodeling on T2DM control, and also provides scientific evidence for the prevention and treatment of T2DM through the dietary management.

2型糖尿病（T2DM）是危害人类健康的重大疾病。新近研究表明，肠道菌群紊乱导致的胆汁酸代谢下游通路失调在T2DM发生发展中起重要作用。辣椒素（CAP）具有抗炎、调节血脂、增强胰岛素敏感性的作用，但对T2DM的防治效应及机制尚不明确。结合我们前期发现CAP能改善妊娠糖尿病患者的血糖水平并调节健康人群的肠道菌群组成及胆汁酸代谢，本项目提出“CAP可通过重塑肠道菌群-胆汁酸轴影响其下游血糖调控通路，进而抑制T2DM发生发展”的科学假说。通过人群研究和动物实验，运用高通量测序、宏基因组分析、无菌动物模型、Cas9转染、预测模型构建等技术，率先研究辣椒素干预诱导的肠道菌群和胆汁酸代谢的特征性变化，同时围绕肠道菌群-胆汁酸代谢-TGR5、FXR信号通路开展辣椒素的血糖调控效应机制研究。该课题旨在揭示辣椒素通过重塑肠道菌群-胆汁酸轴发挥血糖改善效应这一新机制，并为从膳食营养途径防治T2DM提供新策略。

本实验室前期人群试验研究结果显示，辣椒素可能对T2DM有潜在的防治作用，但其具体作用机制尚不清楚。本研究采用db/db糖尿病模型小鼠以及高脂诱导的C57BL/6J肥胖模型小鼠，通过广谱抗生素干预、菌群移植、拮抗剂和激动剂干预实验，并利用16S rRNA基因测序、宏基因组学测序、靶向代谢组学分析等生物信息学及分子生物学技术方法，阐明了辣椒素能够通过调节“肠道菌群-胆汁酸”轴改善小鼠糖代谢稳态及胰岛素敏感性。主要结论如下：.1、辣椒素重塑肠道菌群的结构和功能。门水平上，辣椒素显著降低厚壁菌门（Firmicutes）相对丰度，增加拟杆菌门（Bacteroidetes）相对丰度。属水平上，辣椒素显著降低乳酸菌属（Lactobacillus）相对丰度，同时增加拟杆菌属（Bacteroides），艾克曼氏菌属（Akkermansia muciniphila）及双歧杆菌属（Bifidobacterium）的相对丰度。种水平上，辣椒素显著提高Bacteroides_sp._CAG:927相对丰度。肠道菌群功能层面分析表明，辣椒素可以显著抑制肠道菌群胆盐水解酶（BSH）活性，提高7α-脱氢酶（7α-dehydrogenase）活性。.2、辣椒素通过调节胆汁酸谱及胆汁酸相关代谢通路，进而改善糖代谢稳态及胰岛素敏感性。一方面，辣椒素可显著提高结合胆汁酸TβMCA水平，进而抑制肠肝“FXR-FGF15”相关信号通路，最终促进胆汁酸重新合成，抑制肝脏糖异生，促进糖原合成及储存。另一方面，辣椒素通过促进次级胆汁酸LCA的合成，进而活化肠道GLP-1相关信号通路，刺激GLP-1的合成与分泌，最终改善糖代谢稳态及胰岛素敏感性。应用FXR激动剂可以削弱辣椒素对于胆汁酸代谢的调节效应，而使用GLP-1受体拮抗剂可逆转辣椒素对糖代谢稳态及胰岛素敏感性的有益效应。表明抑制“FXR-FGF15”或活化GLP-1相关信号通路可能是辣椒素改善胆汁酸代谢、糖代谢稳态及胰岛素敏感性的潜在机制。.3、肠道菌群在辣椒素改善机体代谢稳态过程中发挥关键作用。广谱抗生素干预可消除辣椒素对胆汁酸代谢、糖代谢稳态及胰岛素敏感性的改善效应。菌群移植实验进一步证明，辣椒素对糖代谢稳态及胰岛素敏感性的调节作用可以通过菌群移植的方式进行传递，表明肠道菌群可能是辣椒素发挥代谢调节效应中的关键靶点。