HPK1在Tfh细胞中所受的表观遗传学调控及其在系统性红斑狼疮发病机制中的作用

T follicular helper cells (Tfh cells) are a newly discovered subset of CD4+ T cells, which play a mainly role in inducing B cells to produce antibody. Tfh cells are over activated in systemic lupus erythematosus (SLE) patients, consequently bring about immune damages. Hematopoietic progenitor kinase 1 (HPK1) can inhibit T cell-mediated immune responses, but the role that HPK1 plays and the mechanisms that regulate HPK1 in Tfh cells from SLE patients remain elusive. In our previous work, we identified HPK1 levels were significantly decreased in Tfh cells from patients with SLE; down-regulating HPK1 activated control Tfh cells significantly, and overexpressing HPK1 caused a profoundly decrease in SLE Tfh cells reactivity. In addition, striking decreased histone H3 lysine 4 trimethylation (H3K4me3) and markedly increased histone H3 lysine 27 trimethylation (H3K27me3) enrichments were observed at the HPK1 promoter of SLE Tfh cells relative to controls. These results suggested that aberrant epigenetic alterations at the HPK1 promoter led to under-expression of HPK1 in SLE Tfh cells, as a result, Tfh cells were over activated. All these contribute to the onset of SLE in the end. This project aims to further unravel the expression, the role, and the epigenetic modifications of HPK1 in Tfh cells from SLE patients. We also plan to assess the role that HPK1 plays in SLE pathogenesis in vivo experiment by mouse model. This study will further reveal the pathogenesis of SLE, and provide a new idea for effective SLE therapy.

滤泡辅助性T细胞（Tfh细胞）是近年发现的一种主要的辅助B细胞产生抗体的CD4+ T细胞。在系统性红斑狼疮（SLE）患者中，其过度活化，进而导致免疫损害。定向造血干细胞激酶1（HPK1)可抑制T细胞免疫反应，然而其在SLE患者Tfh细胞中的作用及所受调控尚不清楚。我们前期实验发现SLE Tfh细胞HPK1表达降低；降低其表达可导致对照Tfh细胞过度活化，而升高其水平则可抑制SLE Tfh细胞活性；SLE Tfh细胞中HPK1启动子区H3K4me3水平下降，H3K27me3水平升高，提示SLE Tfh细胞HPK1启动子区有表观遗传学改变，导致HPK1表达下降，进而使Tfh细胞过度活化，促使SLE发病。本项目拟进一步证实HPK1在SLE Tfh细胞中的表达、作用及表观遗传学修饰，并通过小鼠模型在体内实验中研究HPK1在SLE发病中的作用，从而深入揭示SLE的发生机制，为SLE的治疗提供新思路。

滤泡辅助性T细胞（Tfh细胞）是主要的辅助B细胞产生抗体的CD4+ T细胞。在系统性红斑狼疮（SLE）患者中，其过度活化，进而导致免疫损害。定向造血干细胞激酶1（HPK1）可抑制T细胞免疫反应。我们研究发现SLE患者Tfh细胞的HPK1表达下降（mRNA：P < 0.001；蛋白：P < 0.001）。对正常外周血Tfh细胞转染HPK1-siRNA后，IL-21（P = 0.001）、BAFF（P = 0.007）、IFNγ（P = 0.002）升高，Tfh细胞明显增殖（P = 0.002），并刺激B细胞产生更多的IgG1（P = 0.002）、IgG2（P = 0.004）和IgG3（P = 0.001）。而转染了HPK1过表达质粒的SLE Tfh细胞则表现出相反的效应。我们又发现SLE Tfh细胞HPK1启动子区H3K27me3水平升高（P < 0.001），且该区H3K27去甲基化酶JMJD3降低（P < 0.001）。对正常对照Tfh细胞转染JMJD3-siRNA，可导致HPK1蛋白（P = 0.003）和HPK1启动子区的JMJD3（P = 0.001）降低，H3K27me3升高（P = 0.008），H3K4me3（P = 0.004）和H3K4甲基化酶MLL1（P = 0.003）下降，Tfh细胞增殖活性（P = 0.001）、Tfh细胞分泌的IL-21（P = 0.005）和IFNγ（P = 0.007）升高。Tfh细胞与自身B细胞共孵育后产生的IgG1（P = 0.003）和IgG3（P = 0.005）增加。而对SLE患者Tfh细胞转染JMJD3过表达质粒，则产生相反的效应。且SLE Tfh细胞HPK1启动子区H3K4me3（P < 0.001）和MLL1（P < 0.001）水平降低。.我们的研究表明SLE Tfh细胞HPK1启动子区JMJD3水平降低，从而导致该区H3K27me3水平升高，同时也减少了MLL1的招募，进而降低了H3K4me3的水平，这些因素致使HPK1表达受抑制，Tfh细胞被过度活化，B细胞被过度刺激，这些最终促使了SLE的发生与发展。这些结果提示HPK1和JMJD3在未来有可能成为SLE治疗的新靶点，而Tfh细胞则可成为更为精准的靶细胞。可据此开发新的药物或分子靶向治疗，同时对其他自身免疫性疾病的研究也具有重要的参考价值。