Genetic Basis of Non-Familial IgA Nephropathy

非家族性 IgA 肾病的遗传基础

• 批准号: 7637963
• 负责人: Tongzhong Ju
• 金额: $ 30.6万
• 依托单位: EMORY UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-16 至 2013-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7637963
• 关键词: 7p13; Address; Amino Acids; Anabolism; Antibodies; Antigens; Autoantibodies; Autoimmune Diseases; B-Lymphocytes; Binding; Biological Assay; Blood Cells; Cell Line; Cell surface; Cells; Complementary DNA; Deposition; Diagnosis; Embryo; Enzyme-Linked Immunosorbent Assay; Enzymes; Evaluation; Exons; Galactose; Galactosyltransferases; Genes; Genetic; Glomerulonephritis; Glycopeptides; Glycoproteins; Goals; Hematopoietic stem cells; Human; IGA Glomerulonephritis; IgA1; Immunoglobulin A; Immunoglobulins; In Vitro; Inflammation; Kidney Diseases; Kidney Failure; Light; Link; Mammals; Maps; Masks; Membrane Glycoproteins; Methods; Molecular; Molecular Chaperones; Mono-S; Mus; Mutate; Mutation; O-Glycans Biosynthesis Pathway; Pathogenesis; Pathway interactions; Patients; Plasma Cells; Polysaccharides; Prevention; Proteins; Recombinants; Sampling; Serum; Severities; Site; Somatic Mutation; Structure; Syndrome; Testing; Therapeutic; Tn antigen; Tumor Cell Line; Xq24; base; glycosylation; in vivo; inhibitor/antagonist; insight; multicatalytic endopeptidase complex; novel; novel diagnostics; peripheral blood; prevent; public health relevance; sialosyl-Tn antigen

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.

描述（由申请人提供）：免疫球蛋白A （IgA）肾病（IgAN）或伯杰氏病是一种由肾小球中IgA异常沉积引起的自身免疫性疾病。原发性IgAN是原发性肾小球肾炎最常见的形式，几乎三分之一的患者会导致进行性肾衰竭。大量研究表明IgAN是由IgA1异常的o糖基化引起的。正常IgA1在免疫球蛋白中是独一无二的，因为它含有约5个丝氨酸/ thrr -连接的o-聚糖，具有单唾液化和双唾液化的核心1结构。IgAN的发病机制与o -聚糖中半乳糖的缺乏和伴随的Tn抗原的表达(GalNAc？-Ser/Thr)在IgA1的铰链区。Tn抗原通常通过添加半乳糖被t合酶掩盖，生成核心1结构（Gal(3GalNAc-R)）。我们发现t合酶需要一种独特的分子伴侣，我们称之为Cosmc，它有助于t合酶在内质网中的生物合成过程中折叠。Cosmc在Xq24上编码，是一种内质网伴侣，可阻止t合酶的聚集/蛋白酶体降解。初步研究表明，Cosmc的体细胞突变引起Tn抗原的表达。我们现在假设，IgA1分泌B细胞中Cosmc的体细胞突变导致IgA1半乳糖基化不足，并导致非家族性或散发性IgAN。在这一建议中，我们将重点关注三个具体目标。目的1：我们将分析IgAN患者外周血Tn/CD19(+) B淋巴细胞中的Cosmc。对于所有发现的突变，突变对Cosmc伴侣蛋白对t合酶的影响将通过体外互补试验进行检测。我们将分离、永生化和建立IgAN患者的Tn/CD19（+）或Tn/IgA（+）淋巴细胞，检测Cosmc的cDNA和基因；将野生型Cosmc引入B细胞，恢复t合酶活性；并检测Cosmc表达是否纠正了细胞表面糖蛋白和IgA1的o糖基化。目的2：我们将确定IgAN患者IgA中铰链区每个位点上o -聚糖的结构。目的3：我们将使用包括各种聚糖和代表IgA1铰链区域的合成糖肽在内的聚糖微阵列来表征IgAN患者血清中的自身抗体，并建立ELISA方法从血清样本中诊断IgAN。了解IgAN的遗传基础将有助于开发新的IgAN诊断和治疗方法。本项目的目的是研究非家族性IgA肾病（IgAN）的遗传基础或分子机制，IgAN是原发性肾小球肾炎最常见的形式，几乎三分之一的患者会导致进行性肾衰竭。IgAN是由肾小球中IgA1的沉积引起的，因为IgA1携带异常的o -聚糖，如Tn抗原。o -聚糖的生物合成受核心1(3-半乳糖基转移酶特异性分子伴侣Cosmc的调控，Cosmc通过协助核心1(3-半乳糖基转移酶（t合酶）的折叠，而核心1(3-半乳糖基转移酶是保护该途径的关键酶。人类Cosmc由Xq24上的一个单外显子基因Cosmc编码。Cosmc的体细胞突变导致Tn和sialylTn抗原在人肿瘤细胞系和Tn综合征患者血细胞中的异常表达。我们推测分泌IgA1的B细胞中x -连锁Cosmc的体细胞突变与IgAN有关。为了验证我们的假设，我们将关注本提案的三个目的：1)检测从IgAN患者和匹配的健康对照中分离的Tn(+)， IgA1分泌B细胞或浆细胞中的Cosmc基因；从永生化的分泌Tn（+）、IgA1的B细胞或浆细胞中检测Cosmc基因；通过将野生型Cosmc引入这些细胞来纠正IgA1上的o聚糖结构；2)确定IgA1中铰链区各位点上的o -聚糖结构；3) IgAN患者血清自身免疫抗体的特征。这些研究将直接揭示IgAN的分子机制，对我们了解IgA1的发病机制具有重要影响，并为散发性IgAN提供新的诊断和治疗或预防途径。