肠道菌群脂肪酸代谢功能基因fabs在肠易激综合征中的作用及机制研究

Gut microbial fatty acid biosynthesis functional genes fabs (including fabI, fabF, fabD, etc.) are the key enzymes of microbial fatty acid biosynthesis reaction. Our preliminary study found that irritable bowel syndrome (IBS) patients presented gut dysbiosis, accompanied with altered abundance of gut microbial fatty acid biosynthesis functional genes fabs and levels of intestinal short chain fatty acid (SCFA). According to literature and our preliminary results, we propose that “gut microbial fatty acid biosynthesis functional genes fabs might be involved in the pathogenesis of IBS”, including intestinal mucosal barrier and immune dysfunction, through the alteration of microbial SCFA synthesis. By using the metagenomics and metabolomics databases of IBS patients which were established by our group, the present project will verify above hypothesis through the following aspects: 1.Clarify the structural characteristics of the gut microbiota in IBS patients with altered gut microbial fatty acid biosynthesis functional genes fabs abundance; 2.Intervene the gut microbial fatty acid biosynthesis functional genes fabs abundance through germ-free rats fecal microbiota transplantation, in order to demonstrate the relationship of gut microbial fatty acid biosynthesis functional genes fabs and enteral SCFA levels, and the influence of intestinal mucosal barrier and immune function further; 3.Construct the genetically engineered microorganism with different expression of gut microbial fatty acid biosynthesis functional genes fabs to evaluate the mechanism that the influence of altered gut microbial fatty acid biosynthesis functional genes fabs to SCFA synthesis. This study will enrich the basic theory of the relationship between gut microbiota disturbance and pathogenesis of IBS, provide new clues for the precious medicine of IBS.

肠道菌群脂肪酸代谢功能基因fabs(fabF, fabD, fabI等)是微生物脂肪酸合成反应的关键调控酶。我们前期研究发现，肠易激综合征（IBS）患者存在肠道菌群紊乱，并伴有肠道菌群功能基因fabs表达丰度和肠道短链脂肪酸（SCFA）水平的变化。据此提出肠道菌群脂肪酸代谢功能基因fabs可能通过影响菌群SCFA合成，进而影响肠黏膜屏障和免疫功能，参与IBS发生。本项目利用前期已建立IBS患者肠菌宏基因组和代谢组学数据库研究上述假说：1.明确导致IBS患者肠道菌群功能基因fabs表达丰度改变的菌群结构特征；2.通过无菌大鼠粪菌移植干预功能基因fabs的丰度，明确其与菌群SCFA水平的关系以及对肠黏膜屏障和免疫功能的影响；3.建立功能基因fabs不同表达水平的基因工程菌，研究其调控菌群SCFA合成的机制。本研究将丰富肠菌紊乱与IBS发病关系的理论基础，为IBS的精准治疗提供新思路。

腹泻型肠易激综合征（IBS-D）患者存在显著的肠道菌群结构紊乱现象，是导致IBS-D发病的重要原因之一。本项目通过以下几方面对IBS-D患者肠道菌群功能的变化以及对肠-脑轴的影响和机制进行了深入研究。（1）临床研究：通过对IBS-D患者临床症状及生化指标检测，应用血浆代谢组学、粪便菌群宏基因组学等多组学方法，发现IBS-D患者内脏敏感性、全身及肠黏膜炎症水平显著升高，血浆中参与脂肪酸代谢和类固醇代谢的物质增加，粪便中丙酸水平显著高于健康对照。IBS-D患者肠道菌群结构及功能与健康对照存在显著差异，主要表现为IBS-D患者大肠杆菌和阴沟肠杆菌丰度显著增加，这可能是导致肠道菌群编码岩藻糖透性酶、海藻糖和麦芽糖水解酶基因丰度增加的主要原因。同时，IBS-D患者的肠道菌群互作模式较健康对照更为复杂。此外，IBS-D患者血浆代谢产物参与淀粉和蔗糖代谢、半乳糖代谢、果糖和甘露糖代谢途径有关的代谢产物增加，佐证了肠道菌群结构及功能的改变可以导致机体血浆代谢产物的改变。（2）动物实验：为了深入研究IBS-D患者肠道菌群结构改变对机体黏膜炎症水平及内脏敏感性的影响，本研究将IBS-D患者的粪菌移植给无菌大鼠。结果显示，移植IBS-D患者粪便菌群的无菌大鼠内脏敏感性、肠黏膜炎症水平显著增高，肠黏膜屏障功能受损。移植后IBS-D组大鼠粪便Roseburia丰度显著增加，与IBS-D患者肠道菌群结构特征相符。Roseburia丰度增加与粪菌移植大鼠内脏敏感性评分，结肠黏膜肥大细胞激活数目、血浆 IFNγ水平以及粪便中乙酸、丙酸水平呈显著正相关。（3）单菌干预实验：将Roseburia菌给予避水应激模型大鼠灌胃，结果显示Roseburia可减轻大鼠的内脏高敏感，降低循环中CRH水平，其产丁酸的功能可能在这一过程中发挥重要作用，相关机制仍需要进一步研究。本项目的完成，丰富了肠易激综合征的菌-肠-脑轴理论，发现了Roseburia改善机体应激状态、缓解内脏高敏感的作用，为IBS的治疗提供了新的靶点及潜在的益生菌种类。