BAFF通过TRAF6/TAK1通路调控IgA肾病IgA类别转换与低糖基化IgA1产生机制研究

Primary IgA nephropathy (IgAN) is the most common form of idiopathic glomerulonephritis throughout the world and the main cause of end-stage renal disease in patients with primary glomerular disease. The disease is characterized by the predominant deposition of IgA1 in the mesangial area of the glomeruli. The excessive IgA production is due to the aberrant IgA class-switch recombination in B cells. B-cell-activation factor (BAFF) acts as a trigger in the pathogenic processes of IgAN. It may promote the generation of IgA1 by regulating immune responses in the B cells. But the regulatory mechanism is unclear. Applicants have found that IgA class switching is actived in patients with IgA nephropathy, and TRAF6 expression in peripheral blood mononuclear cells is increased. We speculate that BAFF may triggered IgA class-switch recombination and suppress IgA hinge region glycosylationby by activating TRAF6/TAK1 pathway, thus promote the production of under-glycosylated IgA1 in IgA nephropathy. The study via cell and animal experiments using magnetic bead sorting, flow cytometry, western blot, immunoprecipitation, fluorescence quantitative Real time PCR, RNA interference technology to explore the regulatory mechanism of TRAF6/TAK1 in IgA class-switch recombination and the under-glycosylated IgA1 generation. It will provide a new theoretical basis and therapeutic targets for the prevention and treatment of IgA nephropathy.

IgA肾病作为全球最常见的原发性肾小球疾病，是导致终末期肾病的主要病因之一。IgA肾病以低糖基化IgA1免疫复合物沉积于肾小球系膜区为病理特征，IgA1过度产生与B细胞IgA类别转换失调相关。B细胞活化因子是IgA肾病的重要致病因子，可能通过调节B细胞免疫应答促进IgA1的产生，但其具体机制未明。申请者已发现IgA肾病患者IgA类别转换活跃，外周血单个核细胞TRAF6表达上调。我们推测：IgA肾病中BAFF可能通过TRAF6/TAK1通路促进IgA类别转换，抑制 IgA1铰链区糖基化，导致大量低糖基化IgA1的产生。本项目通过细胞和动物实验，采用磁珠分选、流式细胞术、Western blot、免疫共沉淀、荧光定量Real time PCR、RNA干扰等技术，探索TRAF6/TAK1通路调控IgA类别转换及低糖基化IgA1产生的具体机制，为IgA肾病防治提供新的理论依据与治疗靶点。

IgA肾病是最常见的原发性肾小球疾病，为导致终末期肾病的重要病因。本课题组围绕“BAFF通过TRAF6/TAK1通路调控IgA肾病IgA类别转换与低糖基化IgA1产生机制研究”展开工作，按计划已完成三年预期研究目标，发现IgA 肾病患者血清BAFF含量增加，外周血单个核细胞 TRAF6/TAK1通路激活，与低糖基化IgA的表达量呈正相关；为了探究病毒感染在IgA肾病发病机制尤其是低糖基化IgA分泌中的作用，我们成果构建IgA肾病大鼠模型，以病毒dsRNA拟似物多聚次黄嘌呤多聚胞嘧啶核苷酸poly(I:C)作为干预刺激手段，通过体内、体外实验证实poly(I:C)通过TLR3/BAFF生物轴介导TACI/TLR3/TRIF/TRAF6通路激活，促进特异性IgA类别转换，加重肾脏病理损伤，首次揭示了黏膜组织病毒感染在IgA肾病发病机制中所起的作用；体外试验中，我们发现BAFF重组蛋白刺激B淋巴细胞，可以激活TRAF6/TAK1信号通路，上调AID、Iα1Cα1，抑制C1GALT1、COSMC，促进低糖基化IgA1产生；同时通过体内实验，初步探究了TRAF6/TAK1通路相关蛋白在动物模型中的表达情况；进一步的我们探究了维甲酸信号通路调控BAFF通路对IgA类别转换的影响，我们发现IgA肾病存在维甲酸信号通路的激活，经RA/BATFA通路促进IgA类别转换；我们也发现雷公藤甲素抑制NLRP3/TLR4通路，下调炎症水平，减轻IgA肾病病理损伤。上述研究为IgA肾病的防治提供了新的思路和潜在的治疗靶点。