磷酸酶PP2A促进滤泡辅助性T细胞分化及相关自身免疫性疾病的作用和机制研究

T follicular helper cells(Tfh) activate B-cell-mediated humoral immunity and are essential for the induction of high-affinity antibodies and the formation of immune memory. It has been reported that the expression and activity of PP2A in peripheral blood T cells of patients with systemic lupus erythematosus are increased, and the proportion of circulating Tfh cells in peripheral blood is positively correlated with the activity of systemic lupus erythematosus. Whether PP2A promotes Tfh differentiation and subsequently leads to the overproduction of autoimmune antibodies by B cells is still unknown. To address this issue, we first constructed a PP2A peripheral T cell knockout mouse, and then analyzed Tfh differentiation with multiple Tfh inducing animal models. Preliminary data showed that the proportion of Tfh cells in PP2A cKO mice was significantly decreased as well as the proportion of germinal center B cells and the level of antigen-specific high-affinity antibodies. Moreover, the master transcription factor Bcl6 was resistant to be up-regulated with PP2A deficiency. Based on this, we will further reveal the molecular mechanism of Bcl6 induction defects in CD4+ T cells with PP2A ablation, explore the substrate proteins and dephosphorylation sites directly regulated by PP2A and their significance to related autoimmune diseases.

滤泡辅助性T细胞(T follicular helper cells, Tfh)可以激活B细胞介导的体液免疫，对诱导产生高亲和力抗体和形成免疫记忆至关重要。文献报道系统性红斑狼疮病人的外周血T细胞中PP2A的表达及活性增高，循环血中cTfh细胞比例与系统性红斑狼疮疾病的活动度呈正相关。磷酸酶PP2A是否通过促进Tfh细胞的分化介导B细胞产生大量自身免疫性抗体造成免疫损伤尚是研究空白。前期研究中，我们已构建了外周T细胞PP2A敲除小鼠，并分析了多个诱导Tfh细胞分化的动物模型。研究发现PP2A敲除后CD4+T细胞向Tfh细胞分化能力明显减弱，生发中心B细胞比例下降，抗原特异性高亲和力抗体水平减低，调控Tfh发育的主转录因子Bcl6上调不足。本课题将在此基础上进一步揭示PP2A敲除后Bcl6诱导缺陷的分子机制，寻找PP2A直接调控的底物蛋白和去磷酸化位点，探讨对相关自身免疫性疾病的影响。

滤泡辅助性T细胞(Tfh)可辅助B细胞形成生发中心和产生高亲和力抗体，对体液免疫反应至关重要。然而，Tfh细胞的异常扩增也会产生自身反应性抗体，诱发如系统性红斑狼疮为代表的，自身免疫抗体介导的自身免疫性疾病。文献显示，蛋白酶PP2A催化亚基的表达与外周自身抗体的滴度和狼疮活动度成正比。我们通过T细胞特异性PP2A敲除小鼠，发现PP2A在Tfh分化发育中起重要作用。我们在两个经典的Tfh分化诱导小鼠模型中都观察到PP2A缺乏，小鼠的Tfh分化和生发中心反应都受损。进一步机制研究发现，Tfh细胞PP2A缺陷下调Tfh调控转录因子Bcl6的转录。更重要的是，我们发现PP2A敲除小鼠和PP2A抑制剂处理小鼠在狼疮模型中均表现出疾病严重度下降。我们还发现在系统性狼疮病人CD4细胞中，PP2A催化亚基Cα的表达水平和Bcl6的表达呈正相关。综上，我们发现PP2A对调节Tfh细胞分化发育十分重要，可作为治疗系统性红斑狼疮的潜在靶点。

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