Identifying novel mechanisms by which fermentable fibers modulate intestinal structure and function

我的NSERC资助的研究计划专注于定义各种饮食因素，如脂肪、益生菌和纤维，如何影响哺乳动物的肠道结构和功能。长期食用西式“高脂肪低纤维”饮食与肠道微生物区系的变化和肠道免疫功能受损有关。在我的NSERC资助的研究中(2005-2010)，我使用了几个啮齿动物模型来证明不同生命阶段饮食脂肪的摄入调节肠道上皮细胞的形态和功能、肠道微生物区系组成和肠道免疫反应。有趣的是，在高脂肪饮食中添加纤维可以部分逆转与高脂肪摄入有关的肠道功能障碍，这有助于我们理解不同来源、类型和剂量的纤维如何调节肠道微生物区系和粘膜免疫之间的相互作用。然而，我们还不了解哺乳动物肠道中纤维有益作用的复杂机制。在我目前的NSERC资助期间(2016-2022年)，我证明了富含纤维的饮食减少了基于微生物的结肠促炎免疫细胞的扩张，可能是因为众所周知，它有能力促进有益微生物代谢物的产生，如丁酸盐，以及它保护肠道粘液层免受微生物降解的能力。为了测试纤维是否通过其他机制发挥肠道保护作用，我在断奶小鼠中测试了一种可发酵的富含纤维的饮食，与无纤维饮食相比，这种饮食缺乏粘蛋白-2，因此缺乏肠道粘液层(Muc2-/-)。喂食无纤维食物的小鼠表现出局部免疫细胞的快速扩张，以及上皮细胞的恶化，这可能是由于共生肠道微生物与粘膜表面直接接触造成的。相比之下，喂食富纤维饲料的Muc2-/-小鼠没有免疫细胞增殖的迹象，也没有粘膜损伤的迹象，因为微生物群似乎仍然与粘膜表面隔离。值得注意的是，这种保护作用发生在没有增加丁酸盐的情况下(Muc2-/-小鼠的产生受到了损害)，也没有肠道粘液层。我建议探索新的宿主和微生物组机制，这些机制在阐明可发酵纤维对丁酸盐和粘液层以外的肠道内环境稳定具有保护作用方面发挥了作用。我将研究在断奶期间给予纤维如何影响：(1)野生型和MUC2-/-小鼠肠道微生物区系的结构、功能，以及关键保护性微生物的地理位置；(2)肠道上皮的功能；以及(3)这些影响的分子和细胞机制。总之，这些研究将定义可发酵纤维、肠道微生物和肠道粘膜之间的新的相互作用。

My NSERC-funded research program focuses on defining how various dietary factors, such as fat, prebiotics, and fiber, affect mammalian intestinal structure and function. Long-term consumption of a Western style "high-fat and low-fiber" diet has been associated with changes in the intestinal microbiota and impaired immune function in the gut1. In my NSERC-funded studies (2005-2010), I used several rodent models to show that the intake of dietary fat at different life stages modulates intestinal epithelial cell morphology and function, the intestinal microbiota composition, and intestinal immune responses. Interestingly, adding fiber to a high-fat diet partially reverses the intestinal dysfunction linked to high-fat intake, which has contributed to our understanding of how different sources, types, and dose of fibers modulate the interaction between intestinal microbiota and mucosal immunity. However, we do not yet understand the complex mechanisms underlying the beneficial effects of fibers in the mammalian gut. During my current NSERC funding period (2016-2022), I demonstrated that a fiber enriched diet reduced microbe-based expansion of colonic proinflammatory immune cells, potentially due to its well-known ability to promote production of beneficial microbial metabolites such as butyrate as well as its ability to preserve the intestinal mucus layer from microbe-based degradation. To test if fiber exerted intestinal protection via other mechanisms, I tested a fermentable fiber enriched diet in weanling mice deficient in Mucin-2 and thus lacking an intestinal mucus layer (Muc2-/-) as compared to a fiber-free diet. Mice fed the fiber-free diet showed a rapid expansion of local immune cells, as well as epithelial cell deterioration likely resulting from direct contact of commensal gut microbes with the mucosal surface. In contrast, Muc2-/- mice fed the fiber enriched diet showed no signs of immune cell proliferation, nor mucosal damage, as the microbiome appeared to remain segregated from the mucosal surface. Notably, this protection occurred in the absence of an increased in butyrate (Muc2-/- mice are impaired in its production) and in the absence of the intestinal mucus layer. I propose to explore novel host and microbiome mechanisms that are at play in elucidating the protective effect fermentable fiber has on intestinal homeostasis outside of butyrate and the mucus layer. I will investigate how fiber given at the weaning period affects: (1) the structure, function of the intestinal microbiota in wild type and Muc2-/- mice, as well as the geospatial location of key protective microbes; (2) the function of intestinal epithelium; and (3) the molecular and cellular mechanisms underlying these effects. Together, these studies will define novel interactions between fermentable fiber, gut microbes and the intestinal mucosa.