Development Of IgA Nephropathy Research Articles

Impact of gene polymorphisms of interleukin-18, transforming growth factor-β, and vascular endothelial growth factor on development of IgA nephropathy and thin glomerular basement membrane disease

BackgroundWe investigated the effects of gene polymorphisms on the development of IgA nephropathy and thin glomerular basement membrane (GBM) disease by analyzing polymorphisms in the interleukin (IL)-18, transforming growth factor (TGF)-β, and vascular endothelial growth factor (VEGF) genes in Korean patients. MethodsThis study included 146 normal individuals and 69 biopsy-proven IgA nephropathy and 44 thin GBM disease patients. The gene polymorphisms −607A/C and −137G/C in IL-18, −509C/T and T869C in TGF-β, and −2578C/A and 405C/G in VEGF were investigated in DNA extracted from peripheral blood. ResultsThe frequencies of the IL-18 −607CC genotype (43.5% vs. 21.2%, P=0.002, P corrected=0.012) and the VEGF 405GG genotype (37.7% vs. 21.2%, P=0.002, P corrected=0.012) were significantly increased in the IgA nephropathy group compared with the control group, whereas no significant differences in genotype frequency were observed between the thin GBM disease and control groups. However, there were no significant differences in genotype and allele frequencies between the IgA nephropathy and thin GBM disease groups. ConclusionThis study did not show any statistically significant differences of six selected gene polymorphisms of the IL-18, TGF-β, and VEGF genes between IgA nephropathy and thin GBM disease. Additional extensive studies are required to clarify the potential role of gene polymorphism to discriminate IgA nephropathy and thin GBM disease without renal biopsy.

Both IgA nephropathy and alcoholic cirrhosis feature abnormally glycosylated IgA1 and soluble CD89–IgA and IgG–IgA complexes: common mechanisms for distinct diseases

Abnormalities of IgA arise in alcoholic cirrhosis, including mesangial IgA deposits with possible development of secondary IgA nephropathy (IgAN). Since little is known about circulating immune complexes in cases of secondary IgAN, we analyzed IgA-associated parameters in the serum of 32 patients with compensated or advanced alcoholic cirrhosis. Galactose deficiency and decreased sialylation of IgA1, as well as increased amounts of abnormally glycosylated polymeric IgA1, were detected in the serum of patients with advanced alcoholic cirrhosis. Moreover, aberrant IgA1 formed complexes with IgG and soluble CD89 in serum of patients with advanced alcoholic cirrhosis, similar to those found in primary IgAN. The IgA1 of alcoholic cirrhosis, however, had a modified N-glycosylation, not found in primary IgAN. In patients with alcoholic cirrhosis and IgAN, IgA deposits were associated with CD71 overexpression in mesangial areas, suggesting that CD71 might be involved in deposit formation. Although the IgA1 found in alcoholic cirrhosis bound more extensively to human mesangial cells than control IgA1, they differ from primary IgAN by not inducing mesangial cell proliferation. Thus, abnormally glycosylated IgA1 and soluble CD89-IgA and IgA-IgG complexes, features of primary IgAN, are also present in alcoholic cirrhosis. Hence, common mechanisms appear to be shared by diseases of distinct origins, indicating that common environmental factors may influence the development of IgAN.

Search for genetic association between IgA nephropathy and candidate genes selected by function or by gene mapping at loci IGAN2 and IGAN3

IgA nephropathy (IgAN) is not generally considered a hereditary disease, even though extensive evidence suggests an undefined genetic influence. Linkage analysis identified a number of genome regions that could contain variations linked to IgAN. In this case-control association study, genes possibly involved in the development of IgAN were investigated. DNA samples from 460 North Italian patients with IgAN and 444 controls were collected. Candidate genes were selected based on their possible functional involvement (6 genes) or because of their location within linkage-identified genomic regions IGAN2 and IGAN3 (5 and 13 genes within chromosome 4q26-31 and 17q12-22, respectively). One hundred and ninety-two tag and functional single-nucleotide polymorphisms (SNPs) were typed with Veracode GoldenGate technology (Illumina). C1GALT1 showed an association with IgAN (rs1008898: P = 0.0019 and rs7790522: P = 0.0049). Associations were found when the population was stratified by gender (C1GALT1, CD300LG, GRN, ITGA2B, ITGB3 in males and C1GALT1, TRPC3, B4GALNT2 in females) and by age (TLR4, ITGB3 in patients aged <27 years). Furthermore, rs7873784 in TLR4 showed an association with proteinuria (G allele: P = 0.0091; GG genotype: P = 0.0077). Age and gender are likely to evidence distinct immunological and inflammatory reactions leading to individual susceptibility to IgAN. Overall, a genetic predisposition to sporadic IgAN was found. We might hypothesize that C1GALT1 and TLR4 polymorphisms influence the risk to develop IgAN and proteinuria, respectively.

Aberrantly Glycosylated IgA1 as a Factor in the Pathogenesis of IgA Nephropathy

Predominant or codominant immunoglobulin (Ig) A deposition in the glomerular mesangium characterizes IgA nephropathy (IgAN). Accumulated glomerular IgA is limited to the IgA1 subclass and usually galactose-deficient. This underglycosylated IgA may play an important role in the pathogenesis of IgAN. Recently, antibodies against galactose-deficient IgA1 were found to be well associated with the development of IgAN. Several therapeutic strategies based on corticosteroids or other immunosuppressive agents have been shown to at least partially suppress the progression of IgAN. On the other hand, several case reports of kidney transplantation or acquired IgA deficiency uncovered a remarkable ability of human kidney to remove mesangial IgA deposition, resulting in the long-term stabilization of kidney function. Continuous exposure to circulating immune complexes containing aberrantly glycosylated IgA1 and sequential immune response seems to be essential in the disease progression of IgAN. Removal of mesangial IgA deposition may be a challenging, but fundamental approach in the treatment of IgAN.

The Tetraspanin CD37 Protects Against Glomerular IgA Deposition and Renal Pathology

The tetraspanin protein CD37 is a leukocyte-specific transmembrane protein that is highly expressed on B cells. CD37-deficient (CD37(-/-)) mice exhibit a 15-fold increased level of immunoglobulin A (IgA) in serum and elevated numbers of IgA+ plasma cells in lymphoid organs. Here, we report that CD37(-/-) mice spontaneously develop renal pathology with characteristics of human IgA nephropathy. In young naïve CD37(-/-) mice, mild IgA deposition in glomeruli was observed. However, CD37(-/-) mice developed high titers of IgA immune complexes in serum during aging, which was associated with increased glomerular IgA deposition. Severe mesangial proliferation, fibrosis, and hyalinosis were apparent in aged CD37(-/-) mice, whereas albuminuria was mild. To further evaluate the role of CD37 in glomerular disease, we induced anti-glomerular basement membrane (GBM) nephritis in mice. CD37(-/-) mice developed higher IgA serum levels and glomerular deposits of anti-GBM IgA compared with wild-type mice. Importantly, glomerular macrophage and neutrophil influx was significantly higher in CD37(-/-) mice during both the heterologous and autologous phase of anti-GBM nephritis. Taken together, tetraspanin CD37 controls the formation of IgA-containing immune complexes and glomerular IgA deposition, which induces influx of inflammatory myeloid cells. Therefore, CD37 may protect against the development of IgA nephropathy.

Aberrantly glycosylated IgA1 in IgA nephropathy patients is recognized by IgG antibodies with restricted heterogeneity

IgA nephropathy (IgAN) is characterized by circulating immune complexes composed of galactose-deficient IgA1 and a glycan-specific IgG antibody. These immune complexes deposit in the glomerular mesangium and induce the mesangioproliferative glomerulonephritis characteristic of IgAN. To define the precise specificities and molecular properties of the IgG antibodies, we generated EBV-immortalized IgG-secreting lymphocytes from patients with IgAN and found that the secreted IgG formed complexes with galactose-deficient IgA1 in a glycan-dependent manner. We cloned and sequenced the heavy- and light-chain antigen-binding domains of IgG specific for galactose-deficient IgA1 and identified an A to S substitution in the complementarity-determining region 3 of the variable region of the gene encoding the IgG heavy chain in IgAN patients. Furthermore, site-directed mutagenesis that reverted the residue to alanine reduced the binding of recombinant IgG to galactose-deficient IgA1. Finally, we developed a dot-blot assay for the glycan-specific IgG antibody that differentiated patients with IgAN from healthy and disease controls with 88% specificity and 95% sensitivity and found that elevated levels of this antibody in the sera of patients with IgAN correlated with proteinuria. Collectively, these findings indicate that glycan-specific antibodies are associated with the development of IgAN and may represent a disease-specific marker and potential therapeutic target.

Altered production of IgE and IgA induced by IL-4 in peripheral blood mononuclear cells from patients with IgA nephropathy.

In order to elucidate the factors responsible for altered immunoglobulin production in patients with IgA nephropathy (IgAN), the in vitro effects of IL-4 and interferon-gamma (IFN-gamma) on the synthesis of IgE and IgA by peripheral blood mononuclear cells (PBMC) were studied. Spontaneous IgE and IgA synthesis by PBMC was significantly increased in patients with IgA nephropathy compared with controls. The maximum amounts of IgA and IgE synthesis by PBMC after stimulation with IL-4 were almost the same both in patients with IgAN and in controls. The enhancement rate of IL-4-induced IgE and IgA synthesis was significantly lower in IgAN than in the controls, suggesting in vivo preactivation of PBMC in IgAN patients. IFN-gamma suppressed IgA and IgE synthesis by PBMC from IgAN patients as well as controls. However, the suppressive effect on IgE synthesis was less prominent in patients with IgAN. These results suggested that altered IL-4 action might be involved in the development of IgA nephropathy.

Downregulated expression in high IgA (HIGA) mice and the renal protective role of meprinβ

This study discusses the critical role of the metalloproteinase meprinβ in the progression of glomerulonephritis. Using a microarray technique, the gene expression profiles in glomeruli isolated from high serum IgA (HIGA) mice with a purity of 97% or greater were examined. HIGA mice are a valid model of human IgA nephropathy (IgAN), with the typical pathological features of this condition, including a consistently high serum IgA level as well as dominant mesangial IgA deposition and mesangial enlargement. Among the many upregulated/downregulated genes after the development of IgAN, the downregulation of meprinβ was intriguing. The expression level of the meprinβ gene at 40 weeks of age was 52% of that observed at 8 weeks of age (prior to the development of IgAN), although in the control BALB/c mice, a 2.19-fold elevation was seen. These results were also confirmed by semi-quantitative RT-PCR and immunostaining analyses. As meprinβ is a subunit of metalloproteinase meprins (meprin A, meprin B) and meprins are capable of proteolytically degrading extracellular matrix (ECM) components and proteolytically processing bioactive peptides, the downregulation of meprinβ may contribute to the progression of glomerulonephritis and the eventual glomerular scarring. This working hypothesis was examined using an in vivo meprinβ inhibition study. The inhibition of meprins by actinonin exacerbated some parameters of renal injury in mice afflicted with anti-glomerular basement membrane (anti-GBM) antibody-associated nephritis. These in vitro and in vivo results suggest that meprinβ may play a protective role against the progression of renal injury through the degradation of ECM and bioactive peptides.

Mutations in the familial Mediterranean fever gene of patients with IgA nephropathy and other forms of glomerulonephritis

Glomerulonephritis, particularly IgA nephropathy (IgAN), seems to be more common in familial Mediterranean fever (FMF), an inherited disease caused by mutations in the MEditerranean FeVer gene (MEFV). The present study is aimed to determine, in populations not suffering from FMF, whether carriage of MEFV mutations may modify or precipitate IgAN and other forms of primary glomerulonephritis (PGN). Forty patients with biopsy proven IgAN and 40 with PGN were surveyed for the presence of the three most common MEFV mutations (M694V, V726A and E148Q), using polymerase chain reaction amplification and restriction enzyme analysis. The rate of MEFV mutations in the patients was related to the expected carrier rate in the general population of the same ethnic extraction. The effect of mutation carriage on the disease course was determined in the IgAN patient group. The frequency of MEFV mutations in IgAN or PGN was comparable to that found in ethnically adjusted general population (p = 0.1 and 0.5, respectively). Carriage of mutated MEFV was not associated with the course and severity of the disease or findings in kidney biopsy and urine analysis. In a population, mostly of Jewish extraction, MEFV mutations do not seem to predispose to the development of IgAN and other forms of PGN or affect the phenotype.

Sle3 and Sle5 can independently couple with Sle1 to mediate severe lupus nephritis

Genetic analyses of the lupus-prone NZM2410 mouse have identified multiple susceptibility loci on chromosome 7, termed Sle3 and Sle5. Both of these loci were contained within a large congenic interval, originally termed as Sle3 that strongly impacts a variety of myeloid and T-cell phenotypes and mediates fatal lupus nephritis when combined with Sle1. We have now produced two subcongenic strains, B6.Sle3 and B6.Sle5, carrying the Sle3 and Sle5 intervals separately and characterized their phenotypes as monocongenic strains and individually in combination with Sle1. Neither B6.Sle3 nor B6.Sle5 monocongenic strain develop severe autoimmunity; however, both of these intervals cause the development of severe glomerulonephritis when combined with Sle1. Thus, B6.Sle1Sle3 and B6.Sle1Sle5 exhibit splenomegaly, expansion of activated B and CD4+ T-cell populations and high levels of IgG and IgM autoantibodies targeting multiple nuclear antigens, intact glomeruli and various other autoantigens. In addition, B6.Sle1Sle3 mice also produced higher levels of IgA antinuclear autoantibodies, which were implicated in the development of IgA nephropathy. Our results indicate that Sle3 and Sle5 can independently complement with Sle1, through shared and unique mechanisms, to mediate the development of severe autoimmunity.

Enhanced intrarenal oxidative stress and angiotensinogen in IgA nephropathy patients

This study was performed to determine whether immunoreactivity of intrarenal hemeoxygenase-1 and angiotensinogen are increased in IgA nephropathy (IgAN) patients. Hemeoxygenase-1 and angiotensinogen immunoreactivity were determined by immunohistochemistry robot system in renal specimens from 39 patients with IgAN. Normal portions of surgically resected kidney served as controls. IgAN patients showed moderate proteinuria (1.1 ± 0.2 g/day); however, the control group did not show any proteinuria. Immunoreactivity of intrarenal hemeoxygenase-1 and angiotensinogen in IgAN were significantly increased compared to normal kidneys (2.42 ± 0.42 vs 1.00 ± 0.26 for hemeoxygenase-1 and 4.05 ± 0.40 vs 1.00 ± 0.21 for angiotensinogen, arbitrary unit). Even though these IgAN patients did not show massive renal damage, hemeoxygenase-1 and angiotensinogen immunoreactivity were increased in these patients at this time point. These data suggest that activated intrarenal reactive oxygen species-angiotensinogen axis plays some roles in development of IgAN at the early stage and will provide supportive foundation of effectiveness of the renin-angiotensin system blockade in IgAN.

Urinary neutrophil gelatinase-associated lipocalin (NGAL) is an early biomarker for renal tubulointerstitial injury in IgA nephropathy

Renal tubulointerstitial injury plays an important role in the development of IgA nephropathy (IgAN), the most common form of glomerulonephritis. Few currently in use biomarkers can sensitively detect the earliest signs of renal tubular injury, hindering our efforts to launch preventive and therapeutic measures for this disorder in a timely manner. Neutrophil gelatinase-associated lipocalin (NGAL) is an acute phase protein that is rapidly released from not only neutrophils but also a variety of cell types upon inflammation and tissue injury. Its small molecular size and protease resistance could render it an excellent biomarker of renal injury in IgAN. In this study, we tested this hypothesis by measuring urinary levels of NGAL, creatinine and N-acetyl-β- d-glucosaminidase (NAG) in 40 healthy individuals and 70 IgAN patients with various disease severities. The urinary NGAL levels and NGAL/creatinine values were significantly upregulated in Lee grade III IgAN patients, in correlation with progressive glomerular mesangial proliferation and tubulointerstitial injury. Compared with urinary NAG levels, the urinary NGAL levels elevated much more drastically and can be readily detected even in Lee grade II IgAN patients when their NAG levels showed almost no change. Our findings suggest the promising use of urinary NGAL as an early biomarker for tubulointerstitial injury of IgA nephropathy and perhaps other types of renal disease in general.

The genetic susceptibility to IgA nephropathy: A novel functional candidate gene for incomplete O-glycosylation of IgA1

Incompleteness of O-glycosylation in the IgA1 hinge has been implicated as a central mechanism in the development of IgA nephropathy. Although underglycosylation was reported to be an acquired abnormality, genes for enzymes of O-glycosylation, such as C1GALT1, may be responsible for susceptibility to IgA nephropathy.

Development of Immunoglobulin A Nephropathy- Like Disease in β-1,4-Galactosyltransferase-I-Deficient Mice

Beta4 galactosylation of glycoproteins plays important roles in protein conformation, stability, transport, and clearance from the circulation. Recent studies have revealed that aberrant glycosylation causes various human diseases. Here we report that mice lacking beta-1,4-galactosyltransferase (beta4GalT)-I, which transfers galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a beta-1,4 linkage, spontaneously developed human immunoglobulin A nephropathy (IgAN)-like glomerular lesions with IgA deposition and expanded mesangial matrix. beta4GalT-I-deficient mice also showed high serum IgA levels with increased polymeric forms as in human IgAN. IgAN is the most common form of glomerulonephritis, and a significant proportion of patients progress to renal failure. However, pathological molecular mechanisms of IgAN are poorly understood. In humans, abnormal character of serum IgA, especially serum IgA1 with aberrant galactosylation and sialylation of O-glycans in its hinge region is thought to contribute to the pathogenesis of IgAN. Mouse IgA has N-glycans but not O-glycans, and beta4-galactosylation and sialylation of the N-glycans on the serum IgA from beta4GalT-I-deficient mice was completely absent. This is the first report demonstrating that genetic remodeling of protein glycosylation causes IgAN. We propose that carbohydrates of serum IgA are involved in the development of IgAN, whether the carbohydrates are O-glycans or N-glycans.

Association between the Clara cell secretory protein (CC16) G38A polymorphism and the progression of IgA nephropathy

Clara cell secretory protein (CC16) is a protein with anti-inflammatory and immunomodulatory properties. Moreover, both CC16 gene knockout and antisense-transgenic mouse models developed glomerulonephritis resembling IgA nephropathy (IgAN). In the present study, we evaluated the influence of the G38A polymorphism in the CC16 gene exon 1 on the development and progression of IgAN. Korean patients with biopsy-proven IgAN (n=267) with a minimal follow-up of 4 years (mean +/- SD 103.8 +/- 52.6 months) were recruited. Healthy normal subjects (n=315) were included as controls. The G38A polymorphism was determined using the polymerase chain reaction-restriction fragment length polymorphism method. GG, GA and AA genotype frequencies were 36.3, 50.2 and 13.5% in IgAN patients, respectively, and 34.3, 50.2 and 15.5% in controls (chi2 = 0.596, p = 0.742). The G allele frequency was 0.614 in IgAN patients and 0.594 in controls (chi2 = 0.429, p = 0.512). Moreover, the GG genotype frequencies were 40.4% in patients showing stable disease course and 26.6% in those with progressive disease (chi2 = 4.029, p = 0.045). Patients with the GG genotype showed a better outcome by Kaplan-Meier analysis in terms of renal survival (p = 0.043). The CC16 polymorphism remained an independent risk factor for progression after multivariate analysis (Cox regression model, HR for CC16 AA genotype: 2.34, 95% CI 1.19-4.64, p = 0.014). Our results suggest that CC 16 gene G38A polymorphism is not associated with the development of IgAN, but that it is an important marker of progression in IgAN.

Association of liver cirrhosis related IgA nephropathy with portal hypertension

A high incidence of IgA nephropathy has been reported in patients with liver cirrhosis, though, clinically evident nephrotic syndrome is very uncommon. Impaired hepatic clearance of circulating IgA immune complexes and subsequent deposition in renal glomeruli has been considered principally in the pathogenesis of liver cirrhosis associated IgA nephropathy. Here we report on a patient with cryptogenic liver cirrhosis and splenic vein thrombosis, who presented with nephrotic syndrome. Renal biopsy showed findings consistent with IgA nephropathy. Lower endoscopy showed features of portal hypertensive colopathy. Following initiation of propranolol and anticoagulant treatment to reduce portal pressure, a gradual decrease of proteinuria and hematuria to normal range was noted. The potential pathogenetic role of portal hypertension in the development of IgA nephropathy in cirrhotic patients is discussed.

Role of obesity‐related factors in development of IgA nephropathy

Role of obesity‐related factors in development of IgA nephropathy

Detection and analysis of HBV antigen protein in kidney tissue and HBV DNA in serum and kidney tissue of patients with HBsAg+ IgA nephropathy.

To explore the relationship between hepatitis B virus (HBV) infection and development of IgA nephropathy. HBsAg and HBcAg protein in renal biopsy specimens of 32 cases was detected on frozen sections and HBV DNA was detected in paraffin section of renal biopsies and in serum of 42 HBsAg positive cases. The positive rate of HBAg in renal biopsies of IgA nephropathy was 59.1%, and 63.6% in non-IgA nephropathy, there was no significant difference between them. In 42 cases biopsies of renal tissues, only five were HBV-DNA positive (11.9%). The five cases were HBsAg, HBcAb and HBeAg positive, the pathological diagnosis of two cases were mesangial proliferative glomerulonephritis; one had minimal change of glomerulonephritis; and one had basement membrane change; and only one had IgA nephropathy. At the same time, in 42 HBsAg+ cases the serum specimens were detected; 12 cases were positive for HBsAg, HBcAg and HBeAg, in whom serum HBV-DNA was positive, but only 5 were positive for HBV-DNA in renal biopsy tissue, and HBV-DNA was negative in other 30 blood serum and tissue specimens. The difference in expression of HBsAg, HBcAb and HBeAg protein between IgA nephropathy and non-IgA nephropathy tissue from renal biopsy was not significant. There is no direct relationship between HBV infection and IgA nephropathy.

Self-aggregated deglycosylated IgA1 with or without IgG were associated with the development of IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, with various pathological phenotypes. Our previous study suggested that aberrant glycosylation of serum IgA1 was associated with different pathological phenotypes of IgAN, and substantial evidence indicated that deglycosylated IgA1 had an increased tendency to form macromolecules. The aim of the current study was to investigate the composition of IgA1-containing macromolecules in different pathological phenotypes of IgAN. Sera from 10 patients with mild mesangial proliferative IgAN (mIgAN), 10 with focal proliferative sclerosing IgAN (psIgAN) and 10 healthy blood donors were collected. The sera were applied and IgA1 binding proteins (IgA1-BP) were eluted from the columns immobilized with desialylated IgA1 (DesIgA1/Sepharose) or desialylated/degalactosylated IgA1 (DesDeGalIgA1/Sepharose), respectively. The amounts of IgA1 and IgG and the glycoform of IgA1 in the IgA1-BP were detected by enzyme-linked immunosorbent assays (ELISAs) and were compared between patients with different pathological phenotypes and normal controls. The amount of IgA1 in IgA1-BP eluted from both columns was significantly higher in patients with both pathological phenotypes of IgAN than in normal controls. In IgA1-BP eluted from DesDeGalIgA1/Sepharose, the desialylation of IgA1 was much more pronounced in patients with both pathological phenotypes of IgAN than in normal controls, while the degalactosylation of IgA1 was much more pronounced only in patients with psIgAN than in normal controls. Furthermore, the amount of IgG in IgA1-BP eluted from DesDeGalIgA1/Sepharose was significantly higher in patients with psIgAN than in normal controls. In patients with psIgAN, the amount of IgG eluted from DesDeGalIgA1/Sepharose was much greater than from DesIgA1/Sepharose. In conclusion, self-aggregated deglycosylated IgA1 with or without IgG were associated with the development of IgAN.

IgA Nephropathy

IgA Nephropathy