异常糖基化IgA1分子与IgA肾病的研究进展

IgA肾病是亚太地区最常见的原发性肾小球肾炎,其发病机制复杂,临床表现多样,以肾小球系膜区IgA1沉积为病理特征.IgA1分子异常糖基化既是导致肾脏IgA沉积的主要病理机制,也是IgA肾病进展的重要免疫异常因素.目前研究结果认为分子伴侣Cosmc表达下调是异常糖基化IgA1分子产生的重要原因,但其深层机制尚不清楚.异常糖基化IgA1分子致病机制仍未完全明确,以IgA1分子异常糖基化为基础的4次打击学说是其肾脏损伤机制的重要进展.对IgA1异常糖基化进一步深入研究,有助于了解IgA肾病的发病机制并为临床提供新的诊断治疗思路.     

IgA肾病患者IgA1糖基化异常及其致病机制

IgA肾病(IgAN)是导致终末期肾病最常见的原发性肾小球疾病。其病理特点为IgA1在肾小球系膜区沉积,IgA1分子的异常糖基化是导致IgAN发病的关键因素。多种与IgAN相关的基因位点已经被发现。这些基因编码的细胞因子参与了IgA1糖基化异常的发病机制。此外糖基化酶缺乏、分子伴侣甲基化异常都可能导致IgA1异常糖基化。异常糖基化的IgA1可通过自我聚集或形成免疫复合物沉积于系膜区,进而刺激系膜细胞增殖、分泌系膜基质、细胞因子、趋化因子、生长因子等,导致肾小球损伤。对IgA1异常糖基化的深入研究有助于了解IgA肾病的发病机制并提供新的诊断与治疗措施。     

低糖基化IgA1在IgA肾病中的作用

IgA肾病是最常见的一种原发性肾小球。肾炎,在我国是导致终末期肾衰竭的重要原因之一。IgA肾病是以多聚体IgA1（polymeride IgA1,pIgA1）为主,包括其他免疫球蛋白和补体沉积于肾小球系膜区,并引起肾小球损伤为特点的肾小球肾炎。IgA1是IgA的一个亚群,其结构特点是具有高度的糖基化,表现在铰链区同时存在N-连接和O-连接糖链。目前,对于IgA肾病的病因及发病机制仍然不明确,近年来,IgA1分子的异常糖基化结构在IgA肾病中的作用引起广泛关注,故本文就异常糖基化IgA1在IgA肾病中的发病机制进行综述。     

IgA肾病的诊治研究进展

IgA肾病经过50年的研究取得了不少进展,人们逐步认识到IgA肾病是一种慢性进展性的疾病。粘膜免疫异常,糖基化异常的IgA1及其抗体的产生以及免疫复合物在肾小球系膜区沉积并激活补体,肾小球的炎症、增殖和硬化,在疾病的发生发展中起着关键的作用。RAS阻断剂具有肾保护作用,但在很多方面还没有定论。本文主要从IgA肾病生物标志物、病理诊断、免疫抑制治疗和扁桃体摘除等方面,结合最新文献和笔者自己的体会,梳理总结其相关的研究进展,以飨读者。     

黏膜方对IgA肾病大鼠异常糖基化IgA1及肾间质纤维化的干预及机制研究

目的:研究血清和肾组织中的异常糖基化IgA1水平与IgA肾病的间质纤维化程度的相关性;阐明黏膜方治疗IgA肾病的作用机制。方法:采用口服牛血清白蛋白、四氯化碳皮下注射和尾静脉注射脂多糖免疫复合法建立IgA肾病大鼠模型,随机分为正常组、模型组、中药组(黏膜方)及西药组(福辛普利钠)、中西医结合组(黏膜方+福辛普利),观察治疗后各组血清和肾组织异常糖基化的IgA1水平、血清IgA-纤维连接蛋白(IgA-FN)、肾组织转化生长因子-β1(TGF-β1)和α-平滑肌肌动蛋白(α-SMA)及其mRNA的表达量。结果:血清IgA-FN,中药组及中西医结合组低于模型组(P<0.001);血清异常糖基化IgA1量,中药组及西药组均低于模型组(P<0.05);肾组织中的异常糖基化IgA1水平,模型组高于正常组(P<0.05),各治疗组低于模型组(P<0.05);肾组织中TGF-β1mRNA及蛋白表达量模型组均显著高于正常组(P<0.01),各治疗组TGF-β1mRNA及蛋白表达均低于模型组(P<0.05);模型组α-SMAmRNA高于正常组(P<0.05),各治疗组低于模型组(P<0.001),模型组α-SMA蛋白表达阳性面积高于正常组(P<0.001),中西医结合组和西药组阳性面积低于模型组(P<0.05);肾组织α-SMAmRNA及蛋白表达与血清及肾组织中异常糖基化IgA1呈正相关(P<0.005);肾组织TGF-β1mRNA与血清及肾组织异常糖基化IgA1呈正相关(P<0.005)。结论:血清中异常糖基化IgA1与肾间质纤维化程度密切相关,黏膜方能减轻实验性IgAN大鼠血清及肾脏异常糖基化的IgA1水平,改善肾间质纤维化。     

IgA1分子异常糖基化在IgA肾病中致病机理的研究

IgA肾病中IgA1分子铰链区O 连接糖基半乳糖基化的水平降低 ,该糖基化异常可通过多种途径引起IgA1分子在肾小球的沉积和肾小球的炎性损伤。B细胞内β1、3半乳糖基转移酶活性的缺乏可能是IgA1分子异常糖基化的原因。对该糖基化异常的深入研究将有利于进一步阐明IgA肾病的发病机制并有望对IgA肾病的治疗提供新的思路。     

IgA1 O-糖基化异常及其在IgAN中致病机制

IgA肾病（IgAN）又称Berger病,是以肾小球系膜区IgA沉积为特征的免疫复合物性肾小球肾炎,其发病机制尚不清楚,治疗上也无特异性方案。研究发现IgA1分子铰链区O-连接糖基化异常是其重要致病因素。本文主要对IgA1 O-糖基化异常及其在IgAN中致病机制的研究进展作一综述。     

IgA1分子异常糖基化在IgA肾病中致病机理的研究

IgA肾病中IgA1分子铰链区O-连接糖基半乳糖基化的水平降低，该糖基化异常可通过多种途径引起IgA1分子在肾小球的沉积和肾小球的炎性损伤。B细胞内β1、3半乳糖基转移酶活性的缺乏可能是IgA1分子异常糖基化的原因。对该糖基化异常的深入研究将有利于进一步阐明IgA肾病的发病机制并有望对IgA肾病的治疗提供新的思路。     

血清低半乳糖化IgA1测定对鉴别IgA肾病的临床价值

目的 确定血清低半乳糖化IgA1对鉴别诊断IgA肾病的临床价值。 方法 以原发性肾小球疾病患者91例为研究对象，接受肾活检并留取血清；以健康体检者20例血清作为对照。血清标本先用装有耦联蚕豆凝集素的微球进行微量离心柱法分离并洗脱，获得低半乳糖化IgA1。再以凝集素HAA（Helix aspersa）用ELISA法定量检测异常糖基化IgA1（HAA-IgA1）。分析血清低半乳糖IgA1升高在鉴别诊断IgA肾病方面的临床价值。 结果 48例IgA肾病患者HAA-IgA1水平[（83.7±41.0） U]高于健康对照组[（52.6±22.9） U]及43例其他原发性肾小球疾病患者组[（49.2±27.3） U]（均P < 0.01）。而该43例中，非IgA系膜增殖性肾炎患者22例（51%）的HAA-IgA1水平[（47.6±21.5） U]亦显著低于IgA肾病患者。以肾穿刺病理诊断为金标准，所绘制ROC曲线面积为0.797，面积的标准误为0.047（P < 0.01）；鉴别诊断IgA肾病的灵敏度为72.9%，特异度为72.1%，准确度为72.5%。 结论 应用微量离心柱法联合ELISA法检测IgA肾病患者血清低半乳糖IgA1对于鉴别诊断IgA肾病具有一定临床价值。     

各种细菌产生的IgA蛋白酶的结构、性质及作用

产IgA蛋白酶的细菌在危及生命的感染中占有很大比例,IgA蛋白酶可以裂解IgA,并使细菌免受各种免疫球蛋白的攻击,在感染中具有多种作用。IgA的糖基化异常影响其对IgA蛋白酶的敏感性,因此在最常见的肾小球肾炎IgAN中,IgA的糖基化异常可能为导致IgA升高的原因之一。近来,还有文献提出IgA蛋白酶可能具有治疗IgA肾病的潜在应用价值。可见IgA蛋白酶的研究具有重要意义。     

IgA serology in recurrent and non-recurrent IgA nephropathy after renal transplantation

BACKGROUND: This study investigated whether abnormal circulation of macromolecularIgA and IgA with altered glycosylation or electrical chargeplays a role in the recurrence of IgA nephropathy (IgAN) aftertransplantation. STUDY DESIGN: A total of 92 renal transplant patients were enrolled; 52 IgANpatients and 40 with other non-IgAN. The IgAN group included10 patients showing IgA mesangial deposits in the grafted kidneys(recurrent group) and 10 who did not (immunohistochemicallyproven non-recurrent group). In addition another 22 IgAN transplantpatients were clinically free of recurrent disease. METHODS: The analyses included macromolecular IgA (IgAIC) detected bythe conglutinin assay (K), heavy IgA precipitated in 2.5% polyethyleneglycol (PEG), IgA-fibronectin aggregates (IgA/F Aggr), mixedIgA/IgGIC, IgA binding to mesangial matrix components (fibronectin,laminin, type IV collagen) or polycations (poly-L-lysine) andIgA with altered glycosylation (Jacalin-binding assay). RESULTS: After transplantation, IgAN patients displayed significantlyhigher mean levels for each variable measured than non-IgAN(ANOVA, P <0.05). By stepwise regression analysis, the bindingof IgA to fibronectin had the highest coefficient. By comparingdata in recurrent and clinically non-recurrent IgAN, we observedthat two groups could be distinguished by the results of thetwo assays for macromolecular IgA (conglutinin IgAIC and IgA-fibronectinaggregates) and IgA with increased affinity for type IV collagen(P <0.05). When the selected group of immunohistochemicallyproven non-recurrent IgAN was compared to the recurrent one,a statistically significant difference was found only for thebinding of IgA to type IV collagen (P<0.05). Data from thistest were significantly related with proteinuria (P<0.05)and microscopic haematuria (P <0.04). CONCLUSION: Even though the IgA serology of renal transplant IgAN patientsshows peculiar features and recurrent and non-recurrent IgANdiffer in many aspects, the prevalence of positive data in thetwo groups had no predictive value. This suggests that the recurrenceof IgAN is modulated by factors affecting the interaction betweencirculating abnormal IgA and mesangial cells and/or matrix.     

Pathogenetic significance of aberrant glycosylation of IgA1 in IgA nephropathy

IgA nephropathy (IgAN), the most common form of primary glomerulonephritis worldwide, is defined by predominant IgA1 deposits in the glomerular mesangium. Among abnormalities of the IgA immune system reported so far in IgAN, aberrant O-linked glycosylation in the hinge region of IgA1 is the most consistent finding. IgA1 molecules bearing abnormal glycosylation have been found in serum, in tonsillar lymphocytes, and in eluate from mesangial deposits, and characterized by decreased O-linked N-acetylgalactosamine residues with or without alteration in the terminal sialylation of the O-linked sugars. IgA1 with incomplete galactosylation has a tendency to accumulate in glomerular mesangium by self-aggregation or immune complex formation. Glomerular mesangial cells exposed to immune complexes of these IgA1 can proliferate and secrete cytokines, chemokines, growth factors, and extracellular matrix components promoting inflammatory reactions in the glomeruli. Although genes encoding enzymes involved in the O-glycosylation process, such as C1GALT1, have been reported to be responsible for susceptibility to IgAN, recent evidence suggests that the abnormality is restricted to a small fraction of B cell populations and arises from dysregulated IgA1 production and secretion in mucosal immune system. This review will focus on and discuss the role of incompleteness of IgA1 O-galactosylation in the pathogenesis of IgAN and propose a possible mechanism in which abnormal IgA1 occurs in IgAN. Presented at the 37th Eastern Regional Meeting of the Japanese Society of Nephrology.     

The pathogenic role of IgA1 O-linked glycosylation in the pathogenesis of IgA nephropathy

Numerous abnormalities of the IgA immune system have been reported in IgAN but the most consistent finding remains aberrant IgA1 O-linked glycosylation of the IgA1 hinge region. The defect comprises reduced galactosylation of O-linked N-acetylgalactosamine residues with or without changes in the terminal sialylation of the O-linked sugars. Aberrant O-galactosylation has been found in serum IgA1, in IgA1 isolated from tonsillar lymphocytes, and in IgA1 eluted from mesangial deposits. There is evidence that changes in IgA1 O-galactosylation lead to IgA immune complex formation and mesangial IgA deposition. Mesangial cells exposed to these IgA immune complexes proliferate and adopt a pro-inflammatory phenotype; they secrete cytokines, chemokines, growth factors and extracellular matrix components promoting glomerular inflammation and glomerulosclerosis. Recent evidence suggests that the control of IgA1 O-glycosylation is linked to class switching from IgD to IgA1 synthesis and that the pattern of IgA1 O-glycosylation may be programmed at the time of initial antigen encounter. IgA1 glycosylation varies between systemic and mucosal sites and the association of aberrant IgA1 galactosylation with low affinity, polymeric IgA1 antibodies against mucosal antigens suggests undergalactosylated IgA1 may in fact be a mucosal glycoform of IgA1. Although suited to the mucosal compartment, when these IgA1 glycoforms enter the systemic circulation in appreciable quantities they deposit in the mesangium and trigger glomerular inflammation. This review will discuss the evidence for the role of IgA1 O-glycosylation in the pathogenesis of IgAN and propose an explanation for the presence of aberrantly O-glycosylated IgA1 in the circulation of patients with IgAN.     

Role of macromolecular IgA in IgA nephropathy

Primary IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis, leading to progressive renal failure in almost one third of the patients. The disease is characterized by mesangial deposits of IgA. The pathogenesis of IgAN remains incompletely understood. The basic abnormality of this disorder lies within the IgA immune system rather than in the kidney. Elevated levels of IgA and IgA-containing complexes are found in sera of most patients with IgAN, but increased levels alone are not sufficient to develop IgAN. Therefore abnormal physicochemical properties of circulating IgA, such as size, charge, and glycosylation may play a role. This is supported by the presence of altered glycosylation of serum and mesangial IgA in patients with IgAN. Although the precise origin and nature of the mesangial IgA deposits are still uncertain, they contain at least in part macromolecular IgA, which may be derived from circulating IgA-containing complexes. Recently, novel insights have been obtained in the molecular composition of circulating high-molecular-weight IgA, which might include complexes with underglycosylated IgA1 and IgA-CD89 complexes. In this review various aspects of macromolecular IgA in relation to IgAN will be discussed.     

炎症与IgA肾病

IgA肾病(IgAN)是目前全球范围内最为常见的原发性肾小球疾病,是导致终末期肾脏病(ESRD)常见原因之一。目前认为IgAN是一种自身免疫性疾病,但其具体发病机制并不清楚。既往的基础研究与临床观察均显示炎症与IgAN发病、加重及进展密切相关。本文将讨论炎症与IgAN发病机制的关系,并进一步讨论干预炎症对IgAN临床和预后的影响。     

Aberrant IgA1 glycosylation is inherited in familial and sporadic IgA nephropathy

IgA nephropathy (IgAN) is a complex trait determined by genetic and environmental factors. Most IgAN patients exhibit a characteristic undergalactosylation of the O-glycans of the IgA1 hinge region, which promotes formation and glomerular deposition of immune complexes. It is not known whether this aberrant glycosylation is the result of an acquired or inherited defect, or whether the presence of aberrant IgA1 glycoforms alone can produce IgAN. A newly validated lectin enzyme-linked immunosorbent assay (ELISA) was used to determine the serum level of galactose-deficient IgA1 (Gd-IgA1) in a cohort of 89 IgAN patients and 266 of their relatives. High Gd-IgA1 levels (> or =95th percentile for controls) were observed in all 5 available patients with familial IgAN, in 21 of 45 (47%) of their at-risk relatives (assuming autosomal dominant inheritance), and in only 1 of 19 (5%) of unrelated individuals who married into the family. This provides evidence that abnormal IgA1 glycosylation is an inherited rather than acquired trait. Similarly, Gd-IgA1 levels were high in 65 of 84 (78%) patients with sporadic IgAN and in 50 of 202 (25%) blood relatives. Heritability of Gd-IgA1 was estimated at 0.54 (P = 0.0001), and segregation analysis suggested the presence of a major dominant gene on a polygenic background. Because most relatives with abnormal IgA1 glycoforms were asymptomatic, additional cofactors must be required for IgAN to develop. The fact that abnormal IgA1 glycosylation clusters in most but not all families suggests that measuring Gd-IgA1 may help distinguish patients with different pathogenic mechanisms of disease.     

Interleukin-17 promotes the production of underglycosylated IgA1 in DAKIKI cells

Background: Interleukin 17 (IL-17) plays an important role in the pathogenesis of autoimmune diseases and might be associated with IgA nephropathy (IgAN). This study aimed to investigate the effect of IL-17 on autoimmune pathogenesis in IgA nephropathy.

Methods: DAKIKI cells were cultured and stimulated with IL-17 to perform dose-dependent and time-dependent experiments. Cell proliferation was examined by cell counting and the Cell Counting Kit-8 (CCK-8) assay. The IgA concentration and the degree of galactosylation in the supernatant were tested using ELISA and a helix aspersa (HAA) lectin binding assay, respectively. To study the mechanism of O-glycosylation, cells were stimulated with IL-17, lipopolysaccharide (LPS) or 5-azacytidine (5-AZA)?+?IL-17 for 48?h, and the levels of C1GALT1 and its molecular chaperone Cosmc were measured by western blot and real-time PCR.

Results: The cell counting and CCK-8 results suggested that B lymphocyte proliferation increased significantly with increased IL-17 concentration. IL-17 affected the quantity of IgA1 and its glycosylation status. HAA revealed that IL-17 promoted IgA1 underglycosylation. Mechanistically, the expression of C1GALT1 and Cosmc was significantly lower in cells stimulated by IL-17 or LPS than in the 5-AZA?+?IL-17 or the control group.

Conclusions: Our results suggested that IL-17 stimulates B lymphocyte to promote B-cell proliferation, which leads to increased IgA1 production in vitro accompanied by underglycosylation of IgA1. The molecular mechanism for the IgA1 underglycosylation induced by IL-17 was similar to that of LPS; however, 5-AZA inhibited IgA1 underglycosylation. IL-17 might participate in IgAN pathogenesis by influencing the production and glycosylation of IgA1 in B-cells.