Tet家族蛋白对树突状细胞免疫功能的表观遗传调控机制研究

Tet family proteins which mediate active DNA demethylation through DNA oxidation play critical roles in regulating variety of pathophysiologic processes. Function of DNA methylation and Tet family proteins in regulating cell lineage commitment and pathogen infection-initiated immune response is largely unknown. However, this is a critical regulatory mechanism for establishing cell-specific function in innate immunity. Professional antigen presentation cells (APCs), such as dendritic cells, are critical in the initiation of immune responses and the maintenance of immune tolerance. These cells connect innate and adaptive immunity during pathogen infection. In this study, on the basis of our previous work for exploring regulatory roles of Tet family proteins in innate immunity and inflammation (Zhang Q, et al, Nature 2015), we will investigate the regulatory roles of Tet proteins in function of APCs. Using our well-established epigenomic technologies, such as genome-wide DNA methylome, we will screen DNA methylation variation during differentiation and maturation of APCs. Using knockout mice of Tet family proteins, we will investigate whether Tet family proteins play important roles in regulating function of APCs, such as antigen processing and presentation. Furthermore, molecular mechanism for Tet proteins-mediated regulation of APCs function will be also studied: whether Tet proteins act in a DNA modification-dependent manner, or whether new function of Tet proteins exists in regulating gene transcription.

Tet家族蛋白是介导DNA去甲基化的关键性DNA氧化酶，在多种生理病理过程中发挥关键的表观遗传调控作用。树突状细胞（DC）是专职抗原提呈细胞，能够启动免疫反应和维持免疫耐受，是连接天然和适应性免疫的桥梁，解析其分化发育及其介导的免疫反应的调控机制是免疫学的关键科学问题之一。Tet蛋白和DNA甲基化如何相互作用以调控DC细胞特异性功能的分子机制尚有待研究。本项目在筛选Tet家族蛋白调控炎症反应的基础上（Zhang Q, et al, Nature 2015），利用本课题组已建立的表观遗传组学体系，进一步筛选DC分化和成熟过程中染色质修饰变异和探索DC抗原加工和提呈功能的表观调控机制。结合Tet蛋白的基因敲除小鼠，观察Tet蛋白缺失是否影响DC抗原加工和提呈等特征性功能，并进一步探讨Tet蛋白基因表达调控的新机制，为免疫细胞特异性功能的表观遗传调控提出新的观点。

Tet家族蛋白是介导DNA、RNA去甲基化的关键性核酸氧化酶，在多种生理病理过程中发挥关键的表观遗传调控作用。我们前期研究发现Tet2能调控通过抑制促炎细胞因子IL-6的表达促进炎症的消退。本项目围绕Tet2在天然免疫中的功能进一步深入研究，我们发现DNA羟甲基化酶Tet2通过在转录后水平降低JAK-STAT信号通路的关键负调控分子Socs3的mRNA的稳定性，促进细胞因子如IL-3活化的信号通路，维持了病原体感染诱导的髓系天然免疫细胞的高效动员和分化。发现Tet2敲除，会显著降低小鼠脓毒症模型(CLP盲肠结扎穿孔)诱导的天然免疫细胞的数量，从而避免炎性细胞因子风暴，降低小鼠死亡率；Tet2敲除也能够抑制寄生虫感染诱导的肥大细胞的体内分化扩增。机制研究表明Tet2在mRNA水平抑制Socs3的表达，而非染色质水平，Tet2能够结合Socs3的3`-UTR，并抑制该区域5mC的水平，从而促进Socs3的mRNA的降解。提示了Tet2作为一种潜在的RNA结合蛋白在天然免疫中的新功能。. 同时我们建立了Tet2敲除和野生型对照树突状细胞的DNA甲基化和羟甲基化组，进一步分析Tet2是否能够在DNA甲基化水平调控树突状细胞的功能。我们发现Tet2敲除能够影响树突状细胞对T细胞的抗原提呈和活化。为下一步深入研究表观遗传因子如何调控树突状细胞经典功能打下数据基础。. 我们也关注其他表观酶在天然免疫中的调控作用，我们发现组蛋白去甲基化酶Kdm6a以经典模式通过去除启动子区H3K27me3，促进炎性细胞因子IL-6的表达；也可以通过非经典功能促进I型干扰素增强子的活性，来促进基因表达。

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