益生菌通过调控FXR受体下调NF-κB通路抑制溃疡性结肠炎炎症的机制研究

Our previous study has found that VSL#3 and Saccharomyces boulardii inhibited tumorigenesis by modulating inflammatory factors in ulcerative colitis carcinogenesis mice model, but the specific mechanism was still unclear. Some studies suggested that the interaction between intestinal microbiota, short chain fatty acids (SCFA) and bile acid metabolism could inhibit intestinal inflammation. Our study will further explore the mechanism of the probiotics’ maintaining UC remission and prevention of malignancy through up-regulating bile acid receptor FXR mediated by SCFA and/or methylation, and down-regulating NF-κB. In our study, the tumorigenesis as well as the relationship between expression of FXR and its methylation and SCFA will be detected in the AOM/DSS induced wild type and FXR-/- mice model. At the same time, in order to determine how probiotics regulate FXR expression, we’ll co-culture different colon cell lines with probiotics and treated with SCFA mimic and methylase inhibitor to detect FXR expression, inflammatory factors and NF-κB activation. All the above indicators will also be observed in UC patients who were given probiotics treatment. Our study will demongstrate the exact intermediate mechanism of inhibiting inflammation and carcinogenesis by probiotics.

我们前期在溃疡性结肠炎（UC）癌变小鼠模型中发现，VSL#3和布拉氏酵母菌通过调节炎症因子抑制成瘤，但具体机制未明。有研究认为肠道菌群与短链脂肪酸(SCFA)、胆汁酸代谢相互作用，抑制肠道炎症反应。本研究将进一步探讨益生菌通过SCFA和/或甲基化上调胆汁酸受体FXR，下调NF-κB，维持UC缓解，阻止恶变的相关机制。研究拟在野生型及FXR基因敲除的AOM/DSS小鼠动物模型中，检测益生菌干预后的成瘤情况，以及FXR表达与其甲基化水平和SCFA水平的相关性；同时选取不同结肠细胞株与益生菌共培养，并给予SCFA类似物和甲基化酶抑制剂处理，检测FXR表达，炎症因子以及NF-κB活化，明确益生菌调控FXR表达的机制；结合UC患者，观察益生菌治疗后上述各指标变化。本研究将明确益生菌抑制炎症和癌变的中间环节确切机制。

益生菌在维持溃疡性结肠炎（ulcerative colitis， UC）缓解及预防癌变中发挥重要作用，但具体机制未知。研究报道肠道菌群与宿主相互作用影响胆汁酸代谢，而胆汁酸代谢异常可调控胆汁酸受体FXR，与UC发病过程密切相关。我们前期研究结果发现益生菌VSL#3灌胃有效缓解肠道炎症，在溃疡性结肠炎癌变小鼠模型中发现，VSL#3和布拉氏酵母菌通过调节炎症因子抑制成瘤，但具体机制未明。本项目通过构建野生型及FXR敲除的急性炎症模型及炎癌小鼠模型，研究益生菌干预后的炎症程度及成瘤情况，从细胞水平、动物水平及临床水平研究益生菌通过FXR轴发挥其抑制炎症及癌变的作用及其具体机制。本项目发现婴儿双歧灌胃有效缓解小鼠肠道炎症，抑制成瘤；通过代谢组学、16s rRNA及宏基因组学分析发现益生菌恢复小鼠肠道菌群多样性，胆汁酸种类及数量发现显著改变。RNA-seq显示婴儿双歧杆菌对结肠炎小鼠肠道的免疫炎症相关信号传导途径产生了显著影响。通过检测FXR表达水平发现FXR在UC患者和结肠炎小鼠的结肠组织中均表达下调，婴儿双歧杆菌干预能上调结肠炎小鼠结肠FXR表达水平。进一步，通过构建FXR敲除小鼠发现，婴儿双歧杆菌介导的小鼠结肠炎缓解作用及抑制成瘤效果减弱，提示益生菌婴儿双歧杆菌通过FXR轴发挥其缓解肠道炎症并抑制成瘤的效应，本研究结果为益生菌的临床应用提供了理论依据。