Contribution of phytochemicals to gut symbiont colonization and synthesis of immunomodulatory sphingolipids

项目摘要 最近对人类微生物组的研究结果为研究影响增加了一层复杂性 饮食对健康的影响。虽然某些类别的饮食衍生分子的健康益处是很好的赞赏， 这些益处背后的分子机制仅得到部分阐明。饮食提供了 营养素不仅对宿主，而且对构成肠道微生物群的微生物。共生 宏基因组在数量上超过宿主基因组100倍， 营养代谢的多样性。已经确定了可归因于特定肠道微生物的膳食代谢物 作为宿主健康和疾病的关键效应分子。 在宿主、饮食和微生物群的三方结合点上，我们一直在研究一类独特的鞘脂 肠道脆弱拟杆菌（Bacteroides fragilis，BfaGCs）及其宿主免疫调节功能。BfaGC 调节宿主结肠中不变的自然杀伤T（NKT）细胞的增殖，这决定了疾病 NKT细胞介导的炎症性肠病小鼠模型的易感性。这个结肠NKT细胞 由B调节。脆裂体仅在小鼠生命的最初几天内发生定植时发生。这 观察表明，出生后早期肠道免疫系统暴露于微生物群对于 建立整个生命过程中肠道NKT细胞的数量。进一步的研究表明， 鞘糖脂结构在指导NKT细胞功能的激动或拮抗中是至关重要的。具有 膳食支链氨基酸（BCAA）可以决定BfaGCs的脂质结构，这一点引起了相当大的兴趣。 这一观察结果提出了一个新的概念，在共生介质的合成：直接纳入饮食因素 进入细菌生化途径，在那里它们进一步转化为生物活性介质。 支链氨基酸是人体必需的氨基酸，主要由植物产生。许多富含支链氨基酸的饮食， 植物来源也富含植物寡糖（PO），其中一些仅由B代谢。脆弱拟 并赋予这种有机体在肠道竞争环境中的生存优势。我们假设 这些植物化学物质（BCAA和PO）协同作用以帮助诱导B的定殖。脆弱拟杆菌和 促进NKT细胞调节性BfaGC的产生，保护宿主免受NKT细胞介导的结肠炎。 使用多管齐下的方法（细菌遗传学，gnotobiotic小鼠模型，和高灵敏度的分析， 平台），我们提出（1）描述BCAA衍生鞘脂生物合成途径中的关键基因 在B。fragilis，并研究其结肠NKT细胞调节功能，以及（2）确定 植物化学物质对免疫调节BfaGC产生、出生后NKT细胞发育和结肠炎抗性的影响 在成年期。我们希望获得分子水平的信息，了解饮食因素如何协同生长， 有益菌和细菌产生的共生因子。

Project summary Recent findings in studies of the human microbiome have added a layer of complexity to research on the impact of the diet on health. While the health benefits of certain classes of diet-derived molecules are well appreciated, the molecular mechanisms underlying these benefits have been only partially elucidated. The diet provides nutrients not only to the host but also to the microorganisms that make up the gut microbiota. The commensal metagenome, which numerically exceeds the host genome by >100-fold, contributes enormous chemical diversity to nutrient metabolism. Dietary metabolites attributable to specific gut commensals, have been identified as key effector molecules of host health and disease in several studies. At the tripartite juncture of host, diet, and microbiota, we have been investigating a unique class of sphingolipids of the gut commensal Bacteroides fragilis (BfaGCs) and their host immunomodulatory functions. BfaGCs regulate the proliferation of invariant natural killer T (NKT) cells in the host's colon, which determines disease susceptibility in the NKT cell–mediated murine model of inflammatory bowel disease. This colonic NKT-cell regulation by B. fragilis occurs only when colonization takes place during the first few days of life in mice. This observation indicates that early postnatal exposure of the gut immune system to the microbiota is crucial in establishing the number of gut NKT cells throughout life. Further studies have shown that terminal branching in the glycosphingolipid structure is crucial in directing either agonism or antagonism of NKT cells functions. It is of considerable interest that dietary branched-chain amino acids (BCAAs) can dictate the lipid structure of BfaGCs. This observation suggests a novel concept in symbiotic mediator synthesis: direct incorporation of dietary factors into bacterial biochemical pathways, where they are further converted into bioactive mediators. BCAAs are essential amino acids for humans and are primarily produced by plants. Many BCAA-rich diets of plant origin are also rich in plant oligosaccharides (POs), some of which are metabolized exclusively by B. fragilis and confer this a survival advantage to this organism in the competitive environment of the gut. We hypothesize that these phytochemicals (BCAAs and POs) act synergistically to help induce colonization by B. fragilis and promote the production of NKT cell–regulatory BfaGCs that protect the host from NKT cell–mediated colitis. Using multi-pronged approaches (bacterial genetics, gnotobiotic mouse models, and high-sensitivity analytical platforms), we propose (1) to characterize critical genes in the BCAA-derived sphingolipid biosynthetic pathway in B. fragilis and investigate their colonic NKT cell modulatory functions and (2) to determine the impact of phytochemicals on immunomodulatory BfaGC production, postnatal NKT cell development, and colitis resistance in adulthood. We expect to acquire molecular-level information on how dietary factors can synergize growth of beneficial bacteria and bacterial production of symbiotic factors.