In situ hybridization studies of stromelysin and tissue inhibitor of metalloproteinase 1 in IgA nephropathy

Summary: Accumulation of the extracellular matrix (ECM) in IgA nephropathy (IgAN) is thought to cause deterioration of glomerular function. Stromelysin and tissue inhibitor of matrix proteinase 1 (TIMP1) may play an important role in the turnover of the glomerular ECM. However, the expression of these enzymes in human renal tissues remains undefined. In the present study, non-radioactive in situ mRNA hybridization, which permitted the analysis at a cellular level, was performed to localize stromelysin and TIMP1 in renal tissue of IgAN. We also determined the percentage of cells positive for stromelysin or TIMP1 mRNA among intraglomerular cells. A total of 16 patients with IgAN were examined, including eight patients with severe histopathological changes and eight with mild changes. Three patients without glomerular disease were also studied. Stromelysin and TIMP1 mRNA were weakly expressed in the mesangium of normal kidneys and IgAN renal tissues with mild damage. However, the expression of both mRNA was significantly increased in the area of mesangial proliferation, in glomerular epithelial cells and in Bowman's capsule of advanced lesions. Several cells in the area of mesangial proliferation were double positive for stromelysin and TIMP1 mRNA, while certain cells positive for stromelysin mRNA did not express TIMP1 mRNA. In the interstitium, epithelial cells of certain tubules and some mononuclear cells were positively stained for these mRNA, especially in advanced lesions. Our results indicated that stromelysin and TIMP1 genes were expressed in glomerular resident cells, tubular epithelial cells and infiltrated mononuclear cells in IgAN, and their expression was enhanced in advanced tissue damage. the demonstration of a co-expression and discordant expression of the genes indicates that each gene expression may be regulated in a cell type-specific manner and that it could also be altered by cellular environmental factors.     

Activation of mRNA expression of collagen,collagenase and its inhibitor on renal biopsy specimens in patients with IgA nephropathy

Summary: In situ hybridization of mRNA for collagen IV, collagen VI, stromelysin (MMP-3) and TIMP1 was examined in renal biopsy specimens from patients with IgA nephropathy (IgAN) or diabetic nephropathy with various degrees of tissue damage. The majority of cells in the glomeruli expressed these mRNA almost simultaneously, but a few cells demonstrated positive expression for only one of these probes. There was a parallel relationship between the degree of tissue damage and that of mRNA expressions of these probes in patients with IgAN, while patients with diabetic nephropathy showed a reverse relationship between these two parameters. It is concluded that patients with mesangial proliferative glomerulonephritis expressed mRNA for collagen collagenase and its inhibitor in the glomeruli in parallel with the progress of tissue damage. In contrast, glomerular samples from patients with diabetic nephropathy showed that there was an inverse relationship between tissue damage and expression of mRNA. It is concluded that expression of collagen, collagenase and its inhibitor parallels the progression of glomerular changes in IgAN, but such parallel expression was not observed in patients with diabetic nephropathy.     

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.     

Expression of connective tissue growth factor mRNA in human IgA nephropathy

Background. Connective tissue growth factor (CTGF) is a cysteine-rich member of a new family of growth regulators. Its upregulation is an important factor in the pathogenesis of mesangial matrix accumulation and progressive glomerulosclerosis. Methods. We evaluated the expression and localization of CTGF mRNA in renal tissues of 20 patients with IgA nephropathy (IgA-N) and 5 normal human kidneys (NHK), using high-resolution in situ hybridization with digoxigenin-labeled oligonucleotide. The expression level of CTGF mRNA was quantitated by counting all nuclei, as well as nuclei surrounded by CTGF mRNA-positive cytoplasm in at least ten randomly selected cross-sections of nonsclerotic glomeruli, and expressing the results as percentage of positive cells. Results. In both IgA-N and NHK, CTGF mRNA was mainly expressed in glomerular intrinsic cells, including mainly glomerular mesangial and epithelial cells, and some endothelial cells and cells of Bowman's capsule. CTGF mRNA-positive cells were abundant in tubulointerstitial fibrotic areas, especially in IgA-N with severe tissue damage. CTGF mRNA expression was also increased in vascular cells in IgA-N. The percentage of cells positive for CTGF mRNA was significantly higher in IgA-N than in NHK. Furthermore, the percentage of cells positive for CTGF mRNA was significantly greater in IgA-N with moderate mesangial proliferative lesions than in IgA-N with mild mesangial proliferative lesions and/or sclerotic lesions. Conclusions. Our study indicates that CTGF may play an important role in the development and progression of glomerulosclerosis and tubulointerstitial fibrosis in IgA-N. Received: July 17, 2000 / Accepted: October 21, 2000     

In situ hybridization analysis in IgA nephropathy

Summary: In situ hybridization provides much information on gene expression in renal biopsy specimens and is useful for detecting intrarenal cells producing molecules that are also present in the circulation. These molecules may deposit in the glomeruli. In situ hybridization is also useful for detecting cells producing cytokine that may be secreted immediately from such cells. Finally, in situ hybridization is useful for detecting extracellular matrix producing cells. Semiquantitative in situ hybridization is useful for assessing the retained RNA in the tissue and comparing the expression of specific mRNA in different tissues. This method may be useful in predicting the clinical outcome at the time of renal biopsy. In conclusion, in situ hybridization allows for the evaluation of cell function in human renal biopsy specimens. It not only provides information related to cell morphology, but also provides an estimation of functionality of human renal biopsy specimens.     

Pathogenesis of idiopathic IgA nephropathy

Despite a prodigious amount of work on the physiology of IgA production in man, and many studies on the immunopathology of IgA nephropathy, ranging from the immunogenetics to the immune response to chemical characteristics of the IgA, we are hardly any nearer to defining the pathogenesis of this disease. One of the main changes in our understanding has been to recognise that the bone marrow, now known to produce normally one-third of the body's IgA, overproduces this immunoglobulin in IgA nephropathy. This alters the previous notion that IgA nephropathy was due simply to IgA production in the mucosa, although a mucosal component is not excluded. Certain characteristics of the IgA in the diseased kidney and the circulation have been defined: it is of subclass IgA1 and has a higher proportion of light chains and negative charge than in normal subjects. The specificities of the IgA, either in the kidney or in complexes, have not helped to clarify the pathogenesis. They have been found for a wide range of endogenous and exogenous antigens, suggesting that the antibody activity represents polyclonal B cell activation. These findings have not helped to confirm the prevailing theory that IgA nephropathy is an immune complex disease. Other theories put forward are that IgA nephropathy is an autoimmune disease, glomerular components or IgA itself being among the candidate antigens, or that there is primary dysregulation of the IgA immune system. At this stage of development in our understanding of this common nephropathy, it is important to guard against the assumption that idiopathic IgA nephropathy is one disease and is the result of a single pathogenetic mechanism.     

Specific binding of circulating IgA antibodies in patients with IgA nephropathy

Detection of circulating IgA antibodies which are specific in patients with IgA nephropathy is described. Freeze and thawed extracts of pharyngeal cells obtained from patients with IgA nephropathy, other glomerular diseases, and healthy adults were cultured with fibroblasts such as Vero or Hel cells at 37 degrees C for 2 weeks. Serum samples were obtained from these patients and healthy adults. The cultured fibroblasts were fixed on slide glasses, and then incubated with the serum samples from the same or other patients with IgA nephropathy. The cells were stained with FITC-labeled heavy-chain specific anti-human IgA antiserum and then examined with a fluorescent microscope. It was demonstrated that the IgA antibodies in sera obtained from patients with IgA nephropathy or HSP nephritis were bound with the nuclear regions of such fibroblasts. It was suggested that IgA antibodies in sera could be bound with some antigenic substances which were transferred from pharyngeal cells of patients with IgA nephropathy to fibroblasts in vitro.     

Prognosis in IgA nephropathy

Summary: IgA nephropathy it is now widely recognized as the most common glomerulonephritis causing end-stage renal failure (ESRF) in many parts of the world. Large series of patients have been analysed in an attempt to identify prognostic clinical and histological features. Increasingly the importance of stage specific analysis of such factors has been reflected in the literature. Such analysis suggests that if therapeutic trials are to be conducted in an attempt to improve prognosis in IgA nephropathy these will need to be organized on a multicentre basis under the auspices of an international organization.     

Treatment of IgA nephropathy in children

SUMMARY: IgA nephropathy is the most common primary glomerulonephritis in the world, and about 20–50% of patients develop progressive renal failure. the pathogenesis is still unknown and treatment has not yet been established. Knowledge concerning childhood IgA nephropathy has expanded greatly in the last 10 years, and its importance as the major form of glomerulonephritis and major contributor to end-stage renal disease is also becoming apparent in children. This communication focuses on the treatment of IgA nephropathy in children.     

家族性IgA肾病--777例中国IgA肾病回顾性调查分析

目的报道中国家族性IgA肾病(FIgAN)发生情况以及临床病理特征,提高对家族性IgA肾病的认识。方法利用肾脏疾病数据库IgA肾病子库中我院1988～2001年收集的777例IgA肾病患者,进行家族史调查,以及部分家庭成员中行尿常规肾功能检查确定FIgAN发病情况,比较家族性与家族史阴性的IgA肾病患者临床表型的差异。结果(1)在调查的777例IgA肾病患者中,35例患者同时合并薄基底膜肾病,另外742例患者中,65例IgA肾病患者家族史阳性,占8.7%,其中10例(1.3%)患者为FIgAN,55例(7.4%)为可疑家族性IgA肾病。(2)与家族史阴性的患者相比,FIgAN患者在发病年龄、性别、肾穿时的血压、血尿、蛋白尿、肾功能上差异无显著性意义。结论FIgAN在中国人并非少见,加强家系调查特别是在IgA肾病患者亲属中常规进行尿检查将有助于发现该病。家族性IgA肾病诊断应强调同时电镜检查以除外薄基底膜肾病和早期Alport综合征。初步研究提示,本组患者与家族史阴性的IgAN患者相比,其临床病理表现不具有特征性。     

儿童IgA肾病的临床与病理分析

目的 探讨IgA肾病患儿临床表现和病理改变的关系及疾病转归.方法 分析30例IgA肾病患儿的临床和病理改变,病理分型采用改良Lee分型法,其中28例进行随访,4例重复肾活检.结果 临床表现孤立性血尿型10例,病理为Ⅰ、Ⅱ级;血尿和蛋白尿型11例,病理为Ⅰ～Ⅲ级;急性肾炎型2例,病理Ⅲ级;肾病综合征型7例,病理为Ⅱ～Ⅳ级,以Ⅱ、Ⅲ级为主.4例行重复肾活检,病理变化为改善、加重和无明显变化,但免疫复合物沉积均有加重.28例随访1年2个月～9年,其中9例预后不乐观;死亡1例;预后不良患儿7例治疗依从性差.结论 IgA肾病临床表现与病理有一定相关性,急性肾炎型、肾病综合征型患儿损伤重、预后欠佳,同时提示临床医师重视IgA肾病患儿随访和健康宣教,提高治疗依从性,以利疾病康复.     

Treatment of severe IgA nephropathy in children

We treated ten children with severe IgA nephropathy (IgAN) [proteinuria > 1g/day, hypertension, renal insufficiency, segmental sclerosis, crescent formation and/or glomerular basement membrane (GBM) deposition of IgA] with prednisone and azathioprine for 1 year. Following the year of therapy, seven of the ten children underwent a repeat kidney biopsy. All biopsies were scored for activity (percentage of glomeruli demonstrating crescent formation, degree of mesangial proliferation and interstitial infiltrate; maximum score = 9) and chronicity (percentage of glomeruli demonstrating fibrous crescents, segmental sclerosis, global sclerosis, and degree of tubular atrophy and interstitial fibrosis; maximum score = 12). After 1 year of therapy, the protein excretion of all the children decreased significantly (P<0.01) from 4052±3190 mg/day to 1692±1634 mg/day. The activity score decreased significantly (P<0.01) from 4.35±0.94 prior to therapy to 2.28±0.75 after therapy while the chronicity score was unchanged (5.42±1.7 vs 5.85±2.0). The percentage of glomeruli demonstrating cellular crescents decreased (P<0.05) from 21.2±21.7% prior to therapy to 0.94±2.4% after therapy. Mesangial deposition of IgA persisted but GBM deposition of IgA was less prominent after therapy. During the follow-up period (mean 2.6 years, range 9 months–7.5 years), one child required brief retreatment for biopsy-confirmed recurrence of active disease, two children have developed renal insufficiency due to progressive scarring in the absence of inflammation, while the remaining seven are stable. We suggest that treatment with prednisone and azathioprine may be beneficial in children with severe IgAN and that a controlled clinical trial is warranted.     

MicroRNAs in IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. It is considered that the pathogenesis of IgAN involves the ‘multiple hit theory’ and the immune-inflammatory mechanism; however, these theories have certain limitations. The gold standard for diagnosing IgAN is still renal biopsy. Although renal biopsy is accurate, it is traumatic and is associated with some risks and limitations, so there is a need for non-invasive diagnostic methods. According to recent studies, microRNAs (miRNAs) play important roles in the occurrence and development of IgAN; thus, they provide the possibility of the noninvasive diagnosis of IgAN and also have some value in predicting prognosis. This review summarizes the current research status of miRNAs in the occurrence, development, diagnosis, and prognosis of IgAN. We also highlight some interesting and challenging points that require further study.     

Urinary podocytes in childhood IgA nephropathy

SUMMARY: We have previously demonstrated the presence of detached podocytes in the urine in various glomerular diseases. In this study, we investigated the pathological significance of detachment of urinary podocytes (u-podocytes) in childhood IgA nephropathy. We investigated 28 children with IgA nephropathy. U-podocytes were detected in the urinary sediment by immunofluorescence. Renal pathological changes and urinalysis, including the u-podocyte test, were analysed. The expression of glomerular basement membrane (GBM) components, integrins and cytoskeleton components on urinary podocytes was investigated using dual immunofluorescence in 12 patients. The u-podocyte score paralleled the acute glomerular changes in renal biopsy samples. The infiltration of glomerular macrophages and polymorphonuclear leucocytes, and the number of urinary leucocytes, correlated highly with the u-podocyte score. Some of the u-podocytes expressed integrins and also components of the GBM. Detachment of podocytes reflects the presence of acute glomerular lesions. Infiltration of glomerular leucocytes is considered to be the cause of the detachment, partly because of the destruction of the GBM.     

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.