E3泛素连接酶FBXW7通过调控肠道炎性巨噬细胞促进炎症性肠病的作用机制研究

Intestinal macrophages play an important role in modulating the chronic intestinal inflammation, while the mechanisms for the regulation and function of the macrophage subsets are poorly understood. E3 ubiquitin-ligase FBXW7 is reported to modulate multiple biological processes such as tumor growth and lipid metabolism, but its roles in macrophages and related inflammatory diseases are still not clear. We found that compared with the normal control, the expression of FBXW7 was significantly increased in both IBD model mice intestinal tract and IBD patients’ intestinal tissue. We generated myeloid-specific deficiency of FBXW7 mice (Lysm-Cre+FBXW7f/f) and established the IBD mouse model. The results suggested that the intestinal inflammation was significantly reduced accompanying with lower levels of inflammatory factors in the KO mouse compared with the WT. Further, we found the deficiency of FBXW7 reduced the proportion of Ly6C+CX3CR1int proinflammatory macrophages and the expression of chemokines. Based on these, this project aims to study the role of FBXW7 in regulating the chemotaxis of intestinal macrophages and its molecular mechanism. Moreover, the expression of FBXW7 in the subsets of local immune cells will be observed in the peripheral blood and intestinal biopsies of IBD patients, as well as its correlation with IBD progression and drug sensitivity. Our results might offer new opinions to the occurrence and development of IBD, and more expectedly, to the strategies on IBD treatment and design of new therapeutic targets.

肠道巨噬细胞在炎症性肠病的发病中发挥着重要作用，但各个亚群的功能及调控机制尚不明确。E3泛素连接酶FBXW7参与调控肿瘤、脂类代谢等过程，但对巨噬细胞及炎症相关疾病的作用还不清楚。我们前期发现，与正常对照相比，IBD模型小鼠肠道固有层和IBD患者肠道组织中FBXW7表达明显上调。构建了髓系细胞特异性敲除FBXW7的小鼠并建立IBD模型。与WT小鼠相比，KO小鼠肠道炎症明显减轻，炎症因子下降。随后发现FBXW7的缺失显著降低了肠道固有层中Ly6C+CX3CR1int炎性巨噬细胞的比例以及趋化因子的表达。我们拟在此基础上，深入研究FBXW7对肠道炎性巨噬细胞的趋化聚集的调控作用及分子机制。并结合IBD患者样本，检测FBXW7在外周和肠道免疫细胞亚群中的表达特征，分析与疾病进展及药物敏感性的相关性。研究结果有望为进一步阐释IBD发生发展机制提供新的观点，并为IBD诊治提供新的思路和潜在靶点。

炎症性肠病是一种由遗传和环境因素造成的免疫细胞功能紊乱的慢性肠道炎症。巨噬细胞作为肠道组织的第一道免疫屏障，在肠道固有层中大量存在，发挥维持肠道稳态和清除病原菌的重要作用。肠道居住型巨噬细胞和炎症型单核样吞噬细胞（mononuclear phagocytes, MPhs）在固有层的平衡被打破，是诱发炎症性肠病的重要原因，但其具体机制尚不清楚。E3泛素连接酶FBXW7参与调控肿瘤、脂类代谢等过程，但对巨噬细胞及炎症相关疾病的作用还不清楚。本项目对临床炎症性肠病和小鼠肠道炎症模型的结肠组织进行免疫组化染色，发现FBXW7在巨噬细胞中的表达显著升高。同时，炎症性肠病患者外周血单核细胞中FBXW7的表达与肠道炎症的严重程度呈显著正相关。进一步地，利用右旋糖酐硫酸酯钠或2,4,6-三硝基苯磺酸构建小鼠肠道炎症模型，我们发现髓系特异性缺失FBXW7的小鼠（LysM-Cre+Fbxw7f/f）肠道炎症较野生型小鼠显著减轻。流式细胞术发现CX3CR1int MPhs在LysM-Cre+Fbxw7f/f小鼠中的聚集显著减少。之后，我们发现FBXW7特异性缺失的CX3CR1hi肠道居住型巨噬细胞分泌趋化因子CCL2和CCL7减少，体外实验证实其趋化单核细胞的作用明显减弱。我们通过机制筛选发现，巨噬细胞中FBXW7可通过K48位泛素化修饰，靶向降解组蛋白甲基转移酶EZH2，减少H3K27me3修饰及其在CCL2和CCL7基因启动子区域的富集，从而促进CCL2和CCL7的表达，正向调控小鼠肠道炎症进展。综上所述，本研究首次发现FBXW7可通过调控表观修饰酶EZH2的表达影响CX3CR1hi居住型巨噬细胞趋化因子CCL2和CCL7的表达，进而影响炎症型巨噬细胞的聚集，调控肠炎进展。本研究结果为进一步阐释炎症性肠病的发生发展机制提供了新的观点和视角，并为炎症性肠病的治疗方案提供新的思路和潜在靶点。

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