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.     

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。     

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肾病免疫炎症发病机制研究进展

IgA肾病(IgA nephropathy,IgAN)是多基因、多因素参与的复杂疾病,其特征是糖基化异常的IgA1免疫复合物在肾小球系膜沉积并因此引起一系列炎性反应导致肾脏损伤。遗传和黏膜免疫异常在IgAN发病机制中起着关键作用,而免疫调节紊乱是该病发病机制的核心环节。近年来随着基因组高通量测序技术的进步,应用免疫组库测序技术分析T细胞受体或B细胞受体,初步揭示了IgAN相关免疫细胞的广泛激活和功能性克隆潜在的诊断和应用价值,为进一步探索干预IgAN新的靶标和精准个体化治疗奠定了基础。     

IgA肾病发病机理的研究进展

IgA肾病(IgA eanephrophathy，IgAN)是一组以IgA或IgA为主的免疫复合物在肾小球系膜区沉积为特征、临床和病理表现多样化，且不伴有系统性损害的最常见原发性肾小球疾病，其发病机制至今依然不清，当前对IgAN发病机制研究的两个重要切入点是对IgAN的分子遗传研究及其免疫学机制。     

IgA肾病中IgA1的异常糖基化及其在系膜区的沉积

人IgA1分子是IgA肾病中沉积于肾小球系膜区的主要亚型。IgA1的独特结构是其粘蛋白型的绞链区和绞链区上的O 聚糖。当O 聚糖出现异常 ,使IgA1通过相互聚合形成多聚体 ,诱发机体产生自身抗体 ,与系膜细胞及细胞外基质结合增多等不同途径和机制沉积于肾小球系膜区 ,可能参与了部分IgA肾病的发病     

IgA1异常糖基化致IgA肾病肾系膜细胞增殖

IgA肾病是一种常见的原发性肾小球肾炎。IgA肾病的确切发病机制仍不明确。目前的数据表明异常糖基化的IgA1(Gd-IgA1)生产过剩,进而形成循环免疫复合物（IgA1-IC、IgA1-IgG-IC）沉积于肾小球系膜,从而释放细胞因子、诱导炎症反应、激活补体系统导致系膜细胞的增殖以及细胞外基质的增加,进而造成肾小球损伤。     

IgA肾病中IgA1的异常糖基化及其在系膜区的沉积

人IgA1分子是IgA肾病中沉积于肾小球系膜区的主要亚型。IgA1的独特结构是其粘蛋白型的绞链区和绞链区上的O－聚糖。当O－聚糖出现异常，使IgA1通过相互聚合形成多聚体，诱发机体产生自身抗体，与系膜细胞及细胞外基质结合增多等不同途径和机制沉积于肾小球系膜区，可能参与了部分IgA肾病的发病。     

IgA-Ⅰ号对IgA肾病小鼠细胞因子及尿蛋白尿隐血的影响

IgA肾病（IgA nephropathy,IgAN）是以IgA为主的免疫球蛋白在肾小球系膜区沉积的一组临床症候群,其发病机制尚不完全清楚,但细胞因子在IgAN的发病中有重要作用。本文观察IgA-Ⅰ号对IgA肾病小鼠血清IL-4,IL-10和尿IL-6,TGF-β1含量及尿蛋白和尿隐血的影响,并探讨其作用机制。     

IgA肾病发病机制研究进展

IgA肾病（IgAnephropathy,IgAN）是全球范围内最常见的一种特殊类型的肾小球疾病,也是导致终末期肾衰竭一个主要原因,病理表现以IgA或IgA为主的免疫复合物在肾小球系膜区沉积为特征。尽管对IgAN的研究已取得不少进展,但确切的病因和发病机制仍未明,     

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.     

IgA肾病IgA1糖基化异常及相关中医药干预进展

IgA肾病是目前全球范围内最常见的原发性肾小球肾炎,病程进展快慢不一,临床表现多样,其中约10%～20%患者在10年内进展至终末期肾衰竭。IgA1异常糖基化与IgA肾病发病有着密切联系;减少异常糖基化IgA1可有效延缓IgA肾病的进展。对异常糖基化IgA1导致IgA肾病的病因机制、中医药对IgA肾病的治疗现况进行研究,有助于提供诊疗新途径、新思路。     

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.     

IgA glycosylation and IgA immune complexes in the pathogenesis of IgA nephropathy

Circulating immune complexes containing aberrantly glycosylated IgA1 play a pivotal role in the pathogenesis of IgA nephropathy (IgAN). A portion of IgA1 secreted by IgA1-producing cells in patients with IgAN is galactose-deficient and consequently recognized by anti-glycan IgG or IgA1 antibodies. Some of the resultant immune complexes in the circulation escape normal clearance mechanisms, deposit in the renal mesangium, and induce glomerular injury. Recent studies of the origin of these aberrant molecules, their glycosylation profiles, and mechanisms of biosynthesis have provided new insight into the autoimmune nature of the pathogenesis of this common renal disease. An imbalance in the activities of the pertinent glycosyltransferases in the IgA1-producing cells favors production of molecules with galactose-deficient O-linked glycans at specific sites in the hinge region of the alpha heavy chains. By using sophisticated analytic methods, it may be possible to define biomarkers for diagnostic purposes and identify new therapeutic targets for a future disease-specific therapy.     

Pathogenic role of the IgA molecule in IgA nephropathy

SUMMARY: Deposits of IgA together with complement in different body tissues support the hypothesis that IgA can trigger inflammatory mechanisms. IgA nephropathy (IgAN) is characterized by predominant mesangial IgA₁ deposits of a polymeric nature. So far, the mechanism of polymeric IgA₁ deposition in the kidney mesangium is poorly understood in IgAN. the exact pathophysiological sequel preceding renal fibrosis following the mesangial deposition of IgA immune complexes remains speculative. Recent in vitro studies revealed that binding of IgA to mesangial cells led to increased expression of growth factors, cytokines, and integrins. the release of these proinflammatory factors is likely to enhance inflammatory injury. In addition, the local renin-angiotensin system present in renal tissues also contributes to renal fibrosis through the activation of transforming growth factor-β. the question of whether polymeric IgA isolated from patients with IgAN exerted any upregulatory effect on the synthesis of macrophage migration inhibitory factor (MIF) and components of the renin-angiotensin system in human mesangial cells was explored. the in vitro studies revealed that polymeric IgA from IgAN patients upregulated the gene expression of renin and MIF in human mesangial cells in a dose-dependent manner. These findings further support the notion that glomerular deposition of IgA is not only a pathological epiphenomenon of IgAN, but that polymeric IgA exerts a pathophysiologic effect on the mesangial cells leading to renal fibrosis.     

IgA肾病诊疗进展

IgA肾病是全球最常见的原发性肾小球肾炎,亚洲人群中发病率高于其他人种。IgA肾病是目前导致终末期肾病的重要原因之一。临床上以血尿为特点,常伴随蛋白尿、高血压。其病理表现主要为IgA免疫复合物在肾小球系膜区的沉积、系膜细胞增生、毛细血管内皮细胞增生等。其发病机制可能为血液循环中半乳糖缺乏的IgA1增多,在內外界环境刺激下,产生过多的、能沉积于肾小球系膜区的免疫复合物。目前,对IgA肾病的诊断主要依靠病理检查。治疗方面,以肾素-血管紧张素系统阻断剂、控制血压为基础,恰当联合免疫抑制剂、细胞毒性药物、鱼油等或能延缓IgA肾病的进展。本文的目的是对IgA肾病的诊疗现状进行总结和分析,为临床工作及进一步科研提供指导和参考。     

Novel mechanisms of tubulointerstitial injury in IgA nephropathy: a new therapeutic paradigm in the prevention of progressive renal failure

IgA nephropathy (IgAN) runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. Notably, renal progression correlates more closely with the severity of tubulointerstitial lesions than with the degree of glomerular lesions In IgAN. Mesangial IgA deposition induces local release of cytokines, complement, and angiotensin II leading to glomerular inflammation. It remains unclear how mesangial IgA deposition leads to tubulointerstitial injury in IgAN. Moreover, IgA deposits are rarely detected in renal interstitium in IgAN. We hypothesize that mediators released from mesangial cells triggered by IgA deposition leads to activation of proximal tubular epithelial cells. Our preliminary findings implicate a glomerulotubular cross talk with mediators released from the mesangium contributing to the pathogenesis of tubulointerstitial damage in IgAN. We have also found the expression of angiotensin II subtype-1 receptor or angiotensin II subtype-2 receptor in proximal tubular epithelial cells differs from that of mesangial cells. One potential therapeutic approach is to counterbalance the growth-stimulatory effects of angiotensin II through subtype-1 receptor in tubular epithelial cells by subtype-2 receptor-mediated apoptosis and growth inhibition. These novel findings may provide clinicians new therapeutic approach for selective blockade of the RAS in IgAN.     

Structural features of IgA molecules which contribute to IgA nephropathy.

IgA nephropathy (IgAN) is characterised by the mesangial deposition of polymeric IgA1 (pIgA1). pIgA1 production is reduced in the mucosal immune system in IgAN and increased in the marrow; this switch may be secondary to a defect in gammadeltaT cell control of IgA production. However this does not explain the mechanism by which pIgA1 deposits in the mesangium. There is no direct evidence that classical immune complex deposition occurs in IgAN and alternative mechanisms resulting from physicochemical abnormalities of the IgA1 molecule, particular altered glycosylation, have been proposed. IgA1 has a distinctive hinge region which is a site for O-glycosylation. There is reduced terminal galactose on the hinge region O-glycans of circulating IgA1 in IgAN, perhaps due to a defect in B cell beta1,3 galactosyltransferase. A concomitant O-glycan defect in mesangial IgA1 has not yet been proven. Altered hinge O-glycosylation may have substantial impact on the quaternary structure of the IgA1 molecule influencing its capacity to interact with matrix proteins, IgA receptors on mesangial cells and leucocytes, and complement; it may therefore play a key role in the pathogenesis of mesangial deposition of IgA1 and subsequent glomerular injury in IgAN.     

Neutrophils in IgA nephropathy

Summary: Neutrophil participation is prominent in proliferative forms of glomerulonephritis. They are recruited by antibody-mediated chemoattractant complement fragments. Monocyte and endothelial derived cytokines or adhesion molecules may also recruit these cells. In most situations of inflammation, neutrophils induce injury by the release of reactive oxygen radicals and their production of lysosomal proteolytic enzymes. the clinical importance of neutrophils in mediating glomerular injury in IgA nephropathy (IgAN) has often been downplayed, although it has been recognized that IgA is involved in the initiation of intracellular oxidative metabolism in normal neutrophils. That disordered neutrophil activation could be relevant to the pathogenesis of IgAN seems likely from their prominent infiltration in glomerular capillaries in the acute phase of primary IgAN, increased expression of complement 3 receptors on neutrophils from patients with IgAN, and increased oxidative metabolism of neutrophils in these patients. Furthermore, recent data revealed heat-aggregated forms of IgA prepared from patients with IgAN exert an up-regulatory effect on calcium mobilization, inositol triphosphate production, and oxidative metabolism in human neutrophils. Interestingly, the plasma level of E-selectin, mainly derived from activated vascular endothelial cells upon interaction with neutrophil, was elevated following synpharyngitic macrohaematuria in patients with IgAN. There was also a significant stepwise increase in circulating E-selectin associated with increased histopathologic severity in these patients. These data tend to support the notion that neutrophils could be activated in IgAN despite lack of acute clinical exacerbation and may potentially be participating in the inflammatory process of glomerular and interstitial injury.     

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.