肠道菌群预防空肠弯曲菌相关结直肠癌发生的作用及机制研究

Globally colorectal cancer (CRC) is the third most common cancer. Gut dysbiosis is associated with colorectal tumorigensis. Our previously publications proved that C. jejuni infection in gut promoted colorectal tumorigenesis and fecal microbiome transplantation (FMT) could alleviate C. jejuni-induced colitis through the action of bile acids metabolism. Our premilinary data showed FMT could prevent C. jejuni-induced CRC. Moreover, bile acids metabolism and PPARγ signaling pathway were not only associated with C. jejuni-induced CRC, but also with FMT-prevented C. jejuni-induced CRC. Therefore, we speculate that gut microbiota regulates bile acids metabolism and prevents C. jejuni-induced CRC through the activation of PPARγ signaling pathway. To verify this speculation, firstly we measure the quantity of bile acids by high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS) and detect the expression of bile acids transporter and PPARγ signaling pathway to confirm the relationship between gut microbiota-prevented colorectal tumorigenesis and bile acids metabolism and PPARγ signaling pathway. Finally, we try to prove that gut microbiome regulate bile acids metabolism and prevent C. jejuni-induced CRC through the activation of PPARγ signaling pathway in vitro and in vivo. This project can provide a new strategy for the prevention of C. jejuni-induced CRC.

结直肠癌的发病率在恶性肿瘤中位列第三。肠道菌群失调与结直肠癌的发生密切相关。我们前期发表的文章已证实，肠道空肠弯曲菌（Cj）感染可以促进结直肠癌的发生；肠道菌群移植通过影响肠道胆汁酸代谢，从而减轻Cj感染性肠炎。我们的预实验结果也显示，肠道菌群移植可以预防Cj相关结直肠癌的发生；胆汁酸代谢及PPARγ信号通路参与了Cj的致癌过程，并且肠道菌群移植预防Cj的致癌能力也与胆汁酸代谢及PPARγ信号通路有关。由此，我们猜想，肠道菌群可以通过调控胆汁酸代谢，激活PPARγ信号，从而抑制Cj的致癌能力。本项目拟进一步通过检测胆汁酸及其转运受体的含量和PPARγ信号通路的表达，证实胆汁酸代谢及PPARγ信号通路，与肠道菌群移植预防Cj相关结直肠癌发生的相关性；通过细胞和动物水平阐明，胆汁酸可通过激活PPARγ信号通路抑制空肠弯曲菌的致癌能力的因果关系。本项目可以为Cj相关结直肠癌的预防提供新的策略。

研究背景：炎症性肠病（Inflammatory bowel disease, IBD）被认为是肠炎相关肠癌（Colitis associated cancer, CAC）的易感因素，控制炎症对于预防和治疗CAC具有重要意义。.研究内容：本项目通过对溃疡性结肠炎（ulcerative colitis, UC）病人与健康对照结肠黏膜的转录组数据进行分析，发现BAs分泌通路与BAs代谢相关基因的表达在UC病人结肠黏膜中显著降低。动物实验表明，UDCA能缓解DSS诱导的肠道炎症。16S rRNA基因测序结果表明，UDCA处理可以改变小鼠肠道菌群组成，主要表现为拟杆菌门和变形菌门的丰度下降及疣微菌门的丰度增加。在属水平上，UDCA处理上调阿克曼菌（Akkermansia）的丰度。对使用UDCA治疗IBD的临床队列的宏基因组数据进行分析，得到与动物实验一致的结果：Akkermansia的增加及拟杆菌的下降与UDCA的使用相关。使用抗生素清除小鼠肠道菌群严重降低UDCA的治疗效果；而粪菌移植实验表明，移植UDCA调节菌群的受体小鼠的肠炎得到缓解，经检测发现，UDCA处理后的供体小鼠及接受其粪便移植的受体小鼠肠道内的Akkermansia丰度显著升高。.此外，UDCA的处理上调黏蛋白相关基因的表达，增加黏液层厚度，且肠道黏蛋基因Muc2的表达与Akkermansia的丰度呈正相关。在作用机制研究上，UDCA处理后的肠道菌群可显著上调巨噬细胞BAs受体（FXR，PXR）及其下游基因（SHP）的表达，抑制NF-κB信号通路，从而抑制肠上皮细胞的炎症水平，促进肠上皮细胞的迁移和愈合。.在肠炎相关肠癌模型中，UDCA的预防性和治疗性处理都抑制肠道炎症水平，减少肠道肿瘤的数量和大小。而抗生素清除肠道菌群后，UDCA的治疗作用降低。对小鼠粪便分析发现，UDCA能增加肠炎相关肠癌动物模型Akkermansia的丰度。.结论：本研究发现UDCA能显著改变小鼠肠道菌群结构，且依赖于肠道菌群缓解小鼠肠炎。UDCA通过增加肠道黏液层的厚度，富集益生菌Akkermansia，并通过上调BAs受体的表达和活化，促进肠上皮细胞的迁移和愈合，缓解小鼠炎症，进而预防和治疗肠炎相关肠癌。

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