CFHR1基因编码区遗传变异调控IgA肾病补体活化的机制研究

IgA nephropathy is the most common primary glomerulonephritis. Complement activation is common in patients with IgAN and further associated with disease severity and prognosis. Our recent IgAN-GWAS identified complement factor H related protein 1 gene (CFHR1), which encoded a complement regulatory protein, to be associated with IgAN susceptibility. Our previous study indicated that genetic deletion of CFHR1 regulated pathogenic IgA1 induced complement activation, and therefore contributed to IgAN susceptibility. Furthermore, our preliminary experiment observed the genetic association between the coding variants in CFHR1 (CFHR1*A/CFHR1*B) and IgA nephropathy. Recent important discovery of CFHR1 revealed its function of complement deregulation, induced by its competition binding to C3b with complement factor H (CFH), a complement inhibitor, and at last resulted in up-regulation of complement activation. Based on the deregulation function of CFHR1, as well as its genetic association with IgAN, we proposed the following pathogenic hypothesis of IgA nephropathy: compared to CFHR1*B, CFHR1*A has stronger function of complement deregulation (induced by more competition to CFH, therefore weakened the complement inhibition function of CFH), and resulted in more powerful complement activation. Therefore, under the challenge of pathogenic IgA molecules, individuals bearing the allele of CFHR1*A would be presented with more powerful complement activation and severer kidney injury, both of which contributed to the susceptibility of IgAN.

补体活化影响IgA肾病(IgAN)的肾损及预后。近期全基因组关联分析 (GWAS)揭示补体调节蛋白基因:H因子相关蛋白1(CFHR1)与IgAN发病易感。申请者前期研究证实CFHR1基因缺失通过影响IgA启动的补体活化参与IgAN发病。进一步预实验发现CFHR1编码区遗传变异(CFHR1*A/CFHR1*B)与IgAN的遗传关联。最近研究阐明CFHR1的补体活化去调节功能，即与补体H因子(CFH)竞争结合C3b，进而抑制CFH对补体活化的负调控，最终促进补体活化。基于CFHR1的功能发现及与IgAN的关联，申请者提出假设：CFHR1*A有较CFHR1*B蛋白更强的补体活化去调节功能，引起更显著的补体活化；携带CFHR1*A个体，在致病性IgA分子激发下，致更显著的补体活化和肾损，进而参与IgAN发病。本研究拟明确CFHR1基因编码区遗传变异参与IgAN的机制，并进一步在IgAN患者中验证。

IgA肾病是全球最常见的原发性肾小球肾炎，我国是IgA肾病高发国。补体激活影响IgA肾病的肾脏损伤及长期预后。已知补体H因子相关蛋白1(CFHR1)和补体H因子相关蛋白3(CFHR3)缺失是IgA肾病发病的保护因素。在本项目研究中，我们发现CFHR1基因编码区三个遗传变异形成的单倍型CFHR1*A是IgA肾病发病的易感因素，并与肾脏局部更高的补体激活强度相关。通过对CFHR1*A和CFHR1*B型的DNA序列进行生物信息学分析预测，我们发现CFHR1编码区遗传变异可能改变CFHR1蛋白SCR3~5功能域的空间构象。进一步通过重组表达CFHR1*A型和CFHR1*B型蛋白，并检测其功能，我们发现CFHR1*B蛋白通过影响与C3b及内皮细胞的结合，以及对CFH的竞争性抑制等机制，呈现出较CFHR1*A蛋白更强的促进补体激活的能力；另一方面，在独立于补体激活的功能方面，CFHR1*A蛋白具有较CFHR1*B蛋白更强的促进单核细胞释放炎症因子的功能。通过揭示CFHR1基因编码区遗传变异与IgA肾病发病与表型的关联，并进一步探究CFHR1*A和CFHR1*B蛋白的功能差异，我们的研究进一步丰富了IgA肾病中补体激活的复杂调控机制。在此基础上，我们还对IgA肾病中其它补体蛋白进行了分析，发现MBL在IgA肾病中具有多重作用机制，MBL缺失和MBL水平升高均与IgA肾病的不良预后相关；证实循环CFHR5水平在IgA肾病的疾病状态下升高，并对IgA肾病疾病严重性和预后具有独立的影响。