高脂肥胖对肠道区域树突状细胞的影响及相关机制研究

Mucosal dendritic cells (DCs) play vital roles in maintaining immune homeostasis and promoting inflammation in the gut. The biological functions and phenotypes of these DCs are largely depended on the resident microenvironment, especially tightly associated with intestinal flora and its metabolism. In recent decades, the population with obesity and its induced chronic inflammatory diseases dramatically increased and cost billions of dollars in China and other western countries. But, up to now, the roles of intestinal flora and mucosal dendritic cell subsets in obesity promoted inflammation are still not well explored. Here, we use high fat diet (HFD) feeding mice as obesity model to explore the effects of obesity on intestinal flora, its metabolites short chain fatty acids (SCFAs) and DC subsets by using highthroughput sequencing, gas chromatography-mass spectrometry and immunological methods. Moreover, we will study the contribution of SCFAs in regulating mucosal DCs by using HFD mice and dextran sulfate sodium induced colitis models. If this study were well done, it will demonstrated the potential mechanisms of gut microenvironment in regulating mucosal DCs, and its contribution in obesity induced inflammatory diseases. It will also be helpful in designing the strategies to treat these diseases.

肠道区域树突状细胞（dendritic cells, DCs）亚群在维持肠道免疫稳态、炎症发生等生理与病理过程中起着重要作用。DC细胞的功能、表型与定居的肠道微环境，尤其是肠道微生物代谢微环境密切相关。近年来，肥胖及其引起的慢性炎症疾病已成为我国乃至全球的重要社会问题，但肥胖如何通过影响肠道免疫微环境，尤其影响肠道DC细胞亚群稳态，从而引起炎症的机制仍不清楚。本课题拟利用高脂饮食（high fat diet, HFD）肥胖模型，通过气-质联用分析及相关免疫技术，分析肥胖对肠道内微生物代谢产物短链脂肪酸和DC细胞亚群的影响，探寻短链脂肪酸与肠道DC细胞亚群稳态间的关系，并结合免疫性肠炎模型，深入研究短链脂肪酸调控肠道DC细胞的作用及机制，以阐明肠道代谢微环境对肠道区域DC细胞独特的调节机制，及与肥胖相关炎症肠病的关系，为更好地了解肠道区域免疫特性及治疗相关疾病奠定理论基础。

肠道区域树突状细胞亚群在维持肠道免疫稳态、炎症发生中发挥着重要作用，本项目探讨了肥胖对DC细胞亚群的影响及相关机制，以期阐明肠道DC细胞在肥胖相关炎症肠病发生中的作用。研究发现，高脂摄入上调肠道固有层中定居性CD11c+CD103−CD11b+DC细胞群体，促进肠道CD11b+Gr-1hi 和CD11b+Gr-1int炎性髓系细胞的浸润，以及肠组织中炎症因子的上调。在DSS诱导肠炎的病理条件下，高脂摄入促进肠炎的进展并加重其严重程度，这一过程伴随着肠道内CD11c+CD103−CD11b+DC细胞亚群和CD11c+CD103+CD11b+DC细胞亚群的稳态紊乱。对肠道内短链脂肪酸的质谱分析和肠道菌群的RNA测序分析发现，高脂饮食可降低肠道内丁酸盐的水平，以及产丁酸盐菌群的丰度，下调参与CD11b+CD103+黏膜DC细胞发育所需视黄酸代谢限速酶视黄醛脱氢酶在肝和肠组织内的表达。而体外的研究表明，肠道菌群代谢物丁酸不但可调控成熟骨髓源树突状细胞（BMDC）的表型与功能，并且可协同视黄酸诱导骨髓前体细胞向表达CCR9、α4β7、CD103的低免疫应答性粘膜DC细胞分化。体外将丁酸与肠肿瘤细胞共培养的实验发现，丁酸不但抑制肠肿瘤细胞生长、促进其凋亡，并可上调肠肿瘤细胞表面TLR4和CD14的表达，上调肿瘤细胞TLR4介导的天然免疫应答，促进炎症因子TNF-α的分泌。综上所述，本研究发现肠道菌群代谢物丁酸可调控肠道定居性DC细胞亚群及肠道免疫稳态，而肥胖可通过影响肠道菌群谱，从而改变肠道局部代谢微环境，促进炎症性肠病的发生。本研究丰富了对肠道区域免疫特性的认知，也为炎症性肠病预防和治疗奠定了新的理论基础。