Dectin-3/CARD9通路介导的免疫应答参与炎症相关结肠肿瘤发生发展的机制

Environmental difference and particularly alimentary customs, which probably affect the commensal microbita, are responsible for the geographical variation in colorectal cancer incidence. Although, the vast majority of studies on commensal microbiota have focused on gut bacteria, recent studies have begun to note the importance of commensal fungi in gut. A rich fungal community that interacts with the immune system was proved in mammalian gut. However, how commensal fungi interacts with immune system and whether this interaction affects colonic tumor development remains unknown. . In our preliminary studies, we found that Dectin-3 deficient mice had a higher tumor burden than wide type mice. The number of tumors was decreased after treatment of fluconazole. We also found that the level of M2 macrophage was increased in Dectin-3 knockout mice. Meanwhile, Dectin-3 and CARD9 knockout mice were both more susceptible to DSS-induced colitis than wild type mice. Based on our preliminary studies, we propose to characterize the molecular mechanism by which Dectin-3 and CARD9 deficiency leads to altered immunity to commensal fungi in the gut; to determine how interactions between commensal fungi and Dectin-3 influence colorectal cancer. . Together, these lines of investigation will reveal molecular mechanism by which host innate immune system affect colonic epithelial homeostasis in response to commensal fungal dysbiosis, which will provide the molecular basis of potential therapeutic targets for designing adjuvant and vaccine against microbial dysbiosis in gut. This project will also provide evidence for the relationship of commensal fungi with colitis-associated colon cancer for the first time.

肠道微生物引起的慢性炎症是影响肿瘤发生的重要因素，探索肠道炎-癌转化的机制对早期诊治结肠肿瘤有重要价值。研究发现，肠道真菌在哺乳动物中普遍存在且参与了肠道炎症反应，然而尚不清楚真菌是否参与了肠道肿瘤的恶性进程。我们前期建立了炎症相关结肠肿瘤模型，发现Dectin-3-/-鼠结肠肿瘤较野生鼠加重，而予氟康唑抗真菌治疗后肿瘤显著减少，且Dectin-3-/-鼠结肠淋巴细胞中M2型巨噬细胞增多。进一步在肠炎模型中发现CARD9-/-鼠与Dectin-3-/-鼠的表型一致，均比野生鼠严重。推测Dectin-3/CARD9通路介导了肠道巨噬细胞抗真菌的免疫应答能力和巨噬细胞极化的调控，参与了结肠肿瘤的发生发展。本课题拟通过体外细胞模型和活体动物模型分析真菌在炎-癌转化中的作用，探索Dectin-3/CARD9通路参与炎症恶性转化的机制，为临床控制结肠炎恶性转化提供理论基础。

肠道菌群是指在人体肠道中存在的种类繁多、数目惊人的微生物群体。普遍认为，肠道菌群参与炎症性肠病以及肥胖等代谢性疾病的发生，但关于肠道共生真菌介导的免疫应答是否影响结肠肿瘤的发生尚无报道。本项目研究发现胱天蛋白酶募集域蛋白（CARD9）敲除后，Card9-/-鼠比野生鼠易患炎症相关结肠肿瘤。值得关注的是Card9-/-鼠肠道中真菌的数量，尤其是条件致病真菌热带念珠菌（C. tropicalis）的数量显著高于正常鼠；Card9-/-鼠在肠道肿瘤诱导过程中予C. tropicalis灌胃可显著加重炎性病变及肿瘤负荷，而给予氟康唑抗真菌治疗后，Card9-/-鼠结肠肿瘤负荷显著减轻，提示我们在Card9-/-鼠中增多的肠道真菌促进了结肠肿瘤的进程。进一步研究发现在Card9-/-结肠肿瘤鼠中MDSCs的比例，尤其是粒样的髓系抑制细胞（G-MDSCs）显著增多，且MDSCs对CD4+ T细胞和CD8+ T细胞的抑制能力显著增强。肠道真菌的刺激可以促进髓系细胞向MDSCs的分化，并激活MDSCs的免疫抑制活性。该研究证实了CARD9介导的抗真菌免疫应答在维持肠道稳态和诱导肠道肿瘤中的重要作用，阐述了肠道共生真菌在结肠肿瘤发病中机制，对于临床结肠肿瘤的诊治具有重要的指导意义。