Genetic Basis of Non-Familial IgA Nephropathy

描述(申请人提供)：免疫球蛋白A(IgA)肾病(IgAN)或Berger病是一种自身免疫性疾病，由IgA在肾小球中的异常沉积引起。原发性IgAN是最常见的原发性肾小球肾炎，几乎三分之一的患者会导致进行性肾功能衰竭。大量研究表明，IgA_1的异常O-糖基化是导致IgAN的原因。正常的IgA1在免疫球蛋白中是独一无二的，因为它含有~5个Ser/Thr连接的O-糖链，具有单唾液酸化和双唾液酸化的核心1结构。IgAN的发病机制与O-糖链中半乳糖的缺乏以及伴随着TN抗原(GalNAc？-Ser/Thr)在其铰链区的表达有关。Tn抗原通常是通过T-合成酶添加半乳糖来掩盖的，以产生核心1结构(Gal(3GalNAc-R))。我们发现T-合成酶需要一个独特的分子伴侣，我们称之为Cosmc，它帮助T-合成酶在内质网的生物合成过程中折叠。Cosmc编码在Xq24上，是一种内质网伴侣，可防止T-合成酶的聚集/蛋白酶体降解。初步研究表明，Cosmc的体细胞突变导致Tn抗原的表达。我们现在假设，分泌IgA的B细胞中Cosmc的体细胞突变导致IgA1的半乳糖化不足，从而导致非家族性或散发性的IgAN。在这项提案中，我们将重点关注三个具体目标。目的1：分析IgAN患者外周血中TN/CD19(+)B淋巴细胞的COSMC。对于所有已发现的突变，将通过体外互补分析来检测COSMC伴侣对T-合酶的影响。我们将分离、永生化和建立IgAN患者的TN/CD19(+)或TN/IgA(+)B淋巴细胞，检测COSMc的基因和基因；将野生型COSMc导入B细胞以恢复T合酶活性；检测Cosmc的表达是否纠正细胞表面糖蛋白和IgA1的O-糖基化。目的2：我们将确定IgA铰链区每个位点上的O-糖链的结构。目的：利用包含多种糖链和代表IgA1铰链区的人工合成糖肽的糖链芯片，鉴定IgAN患者血清中的自身抗体，建立一种从血清样本中潜在诊断IgAN的ELISA方法。了解IgAN的遗传学基础将有助于开发新的IgAN诊断和治疗方法。公共卫生相关性我们这个项目的目标是研究非家族性IgA肾病(IgAN)的遗传基础或分子机制，非家族性IgA肾病是导致近三分之一患者进行性肾功能衰竭的最常见的原发肾小球肾炎形式。IGAN是由IgA1在肾小球中沉积引起的，因为IgA1携带着异常的O-糖链，如TN抗原。O-葡聚糖的生物合成受COSMC的调控，COSMC是核心1(3-半乳糖基转移酶特异性分子伴侣)，它通过辅助核心1(3-半乳糖基转移酶(T-Synthase))的折叠来调节O-糖链的生物合成。人类Cosmc基因由Xq24上的一个单外显子基因Cosmc编码。COSMC的体细胞突变是TN综合征患者外周血和肿瘤细胞中Tn和sialylTn抗原异常表达的原因。我们推测，分泌IgA1的B细胞X连锁Cosmc基因的体细胞突变与IgAN有关。为了验证我们的假设，我们将集中在三个目标上：1)检测从IgAN患者和匹配的健康对照组分离的TN(+)、分泌IgA1的B细胞或浆细胞中的Cosmc基因；检测永生化的TN(+)、分泌B细胞或浆细胞的IgA1中的Cosmc基因；通过将野生型Cosmc导入这些细胞来纠正IgA1上的O-糖链结构；2)确定IgA1铰链区每个部位的O-糖链结构；3)鉴定IgAN患者血清中的自身免疫抗体。这些研究将直接探讨IgAN的分子机制，对我们理解IgA1的发病机制有重要影响，并为散发性IgAN提供新的诊断和治疗或预防途径。

DESCRIPTION (provided by applicant): Immunoglobulin A (IgA) nephropathy (IgAN) or Berger's disease is an autoimmune disease resulting from the abnormal deposit of IgA in the glomerulus. Primary IgAN is the most common form of primary glomerulonephritis, leading to progressive renal failure in almost one third of the patients. Numerous studies have suggested that IgAN results from abnormal O-glycosylation of IgA1. Normal IgA1 is unique among immunoglobulins in that it contains ~5 Ser/Thr-linked O-glycans with mono-sialylated and di-sialylated core 1 structures. The pathogenesis of the IgAN is associated with a deficiency of galactose in O-glycans and concomitant expression of the Tn antigen (GalNAc?-Ser/Thr) in its hinge region of IgA1. Tn antigen is normally masked through addition of galactose by the T-synthase to generate the core 1 structure (Gal(3GalNAc-R). We discovered that T-synthase requires a unique molecular chaperone we termed Cosmc that helps to fold the T-synthase during its biosynthesis in the ER. Cosmc is encoded on Xq24 and is an ER chaperone that prevents the aggregation/proteasomal degradation of the T-synthase. Preliminary studies show that somatic mutations in Cosmc cause expression of the Tn antigen. We now hypothesize that somatic mutations of Cosmc in IgA-secreting B cells cause undergalactosylation of IgA1 and result in non-familial or sporadic IgAN. In this proposal, we will focus on three Specific Aims. Aim 1: We will analyze Cosmc in Tn/CD19(+) B lymphocytes from peripheral blood of patient with IgAN. For all mutations found, the effects of mutation on Cosmc chaperone toward the T-synthase will be examined by in vitro complementation assays. We will isolate, immortalize and establish the Tn/CD19(+) or Tn/IgA(+) Blymphocytes from patients with IgAN, examine the cDNA and gene for Cosmc; introduce wild type Cosmc into the B cells to restore T-synthase activity; and test whether Cosmc expression corrects O-glycosylation of cell surface glycoproteins and IgA1. Aim 2: We will define the structures of O-glycans on each site of the hinge region in IgA from patients with IgAN. Aim 3: We will characterize the autoantibodies in sera of patients with IgAN using a glycan microarray including various glycans and synthetic glycopeptides representing the IgA1 hinge region, and establish an ELISA method for potential diagnosis of IgAN from serum samples. Understanding the genetic basis for IgAN will shed light on developing new diagnostics and therapeutic treatments for IgAN. PUBLIC HEALTH RELEVANCE Our goal of this project is to investigate the genetic basis or molecular mechanism of non-familial IgA nephropathy (IgAN), the most common form of primary glomerulonephritis leading to progressive renal failure in almost one third of the patients. IgAN is caused by the deposit of IgA1 in glomerulus because the IgA1 carries aberrant O-glycans such as Tn antigen. O-glycan biosynthesis is regulated by Cosmc, core 1 (3-galactosyltransferase specific molecular chaperone, through assisting the folding of core 1 (3- galactosyltrasferase (T-synthase) which is a key enzyme guarding the pathway. Human Cosmc is encoded by a single-Exon gene Cosmc on Xq24. Somatic mutation in Cosmc is responsible for the abnormal expression of Tn and sialylTn antigens in human tumor cell lines and blood cells of patients with Tn syndrome. We hypothesize that the somatic mutation of X-linked Cosmc in IgA1 secreting B cell is associated with IgAN. To test our hypothesis, we will focus on three Aims for this proposal: 1) Examine Cosmc gene in Tn(+), IgA1 secreting B cells or plasma cells isolated from patients with IgAN and matched healthy controls; examine the Cosmc gene from immortalized Tn(+), IgA1 secreting B cells or plasma cells; correct the O-glycan structure on IgA1 by introducing the wild type Cosmc into these cells; 2) Define the O-glycan structure on each site of hinge region in IgA1; 3) Characterize the autoimmune antibody in sera of patients with IgAN. These studies will directly address the molecular mechanism of IgAN, which will have an important impact on our understanding of the pathogenesis of IgA1, and provide new diagnostics and avenues of treatment or prevention for sporadic IgAN.