Differential expression of glycogenes in tonsillar B lymphocytes in association with proteinuria and renal dysfunction in IgA nephropathy

Effect of tonsillectomy combined with steroid pulse therapy upon IgA nephropathy depending on proteinuria status at diagnosis: a nationwide multicenter cohort study in Japan

BACKGROUND

The effects of tonsillectomy combined with steroid pulse (TSP) therapy for IgA nephropathy (IgAN) are little known. Therefore, we examined the effects of TSP therapy on the kidney outcomes of IgAN in a large, nationwide cohort study in Japan.

METHODS

Between 2002 and 2004, 632 IgAN patients with ≥ 0.5 g/day proteinuria at diagnosis were divided into three groups with mild (0.50-0.99 g/day; n = 264), moderate (1.00-1.99 g/day, n = 216), or severe (≥ 2.00 g/day; n = 153). Decline in kidney function and urinary remission were compared among the three groups after TSP therapy, corticosteroid (ST) therapy, or conservative therapy during a mean follow-up of 6.2 ± 3.3 years. 10.6% and 5.9% of patients in the ST and conservative therapy group underwent tonsillectomy.

RESULTS

The rate of urinary remission at the final observation was significantly higher in the TSP therapy group than in the ST or conservative therapy groups (mild proteinuria: 64%, 43%, and 41%; moderate proteinuria: 51%, 45%, and 28%; severe proteinuria: 48%, 30%, and 22%, respectively). In contrast, the rate of a 50% increase in serum creatinine was lower in groups TSP therapy, than ST or conservative therapy (mild proteinuria: 2.1%, 10.1% and 16.7%; moderate proteinuria: 4.8%, 8.8% and 27.7%; severe proteinuria: 12.0%, 28.9% and 43.1%, respectively). In multivariate analysis, TSP therapy significantly prevented a 50% increase in serum creatinine levels compared with conservative therapy in groups with moderate and severe proteinuria (hazard ratio, 0.12 and 0.22, respectively).

CONCLUSION

TSP significantly increased the rate of proteinuria disappearance and urinary remission in IgAN patients with mild-to-moderate urinary protein levels. It may also reduce the decline in kidney function in patients with moderate-to-severe urinary protein levels.

LIF/JAK2/STAT1 Signaling Enhances Production of Galactose-Deficient IgA1 by IgA1-Producing Cell Lines Derived From Tonsils of Patients With IgA Nephropathy

Introduction

Galactose-deficient IgA1 (Gd-IgA1) plays a key role in the pathogenesis of IgA nephropathy (IgAN). Tonsillectomy has been beneficial to some patients with IgAN, possibly due to the removal of tonsillar cytokine-activated cells producing Gd-IgA1. To test this hypothesis, we used immortalized IgA1-producing cell lines derived from tonsils of patients with IgAN or obstructive sleep apnea (OSA) and assessed the effect of leukemia inhibitory factor (LIF) or oncostatin M (OSM) on Gd-IgA1 production.

Methods

Gd-IgA1 production was measured by lectin enzyme-linked immunosorbent assay; JAK-STAT signaling in cultured cells was assessed by immunoblotting of cell lysates; and validated by using small interfering RNA (siRNA) knock-down and small-molecule inhibitors.

Results

IgAN-derived cells produced more Gd-IgA1 than the cells from patients with OSA, and exhibited elevated Gd-IgA1 production in response to LIF, but not OSM. This effect was associated with dysregulated STAT1 phosphorylation, as confirmed by STAT1 siRNA knock-down. JAK2 inhibitor, AZD1480 exhibited a dose-dependent inhibition of the LIF-induced Gd-IgA1 overproduction. Unexpectedly, high concentrations of AZD1480, but only in the presence of LIF, reduced Gd-IgA1 production in the cells derived from patients with IgAN to that of the control cells from patients with OSA. Based on modeling LIF-LIFR-gp130-JAK2 receptor complex, we postulate that LIF binding to LIFR may sequester gp130 and/or JAK2 from other pathways; and when combined with JAK2 inhibition, enables full blockade of the aberrant O-glycosylation pathways in IgAN.

Conclusion

In summary, IgAN cells exhibit LIF-mediated overproduction of Gd-IgA1 due to abnormal signaling. JAK2 inhibitors can counter these LIF-induced effects and block Gd-IgA1 synthesis in IgAN.

The nucleotide-sensing Toll-Like Receptor 9/Toll-Like Receptor 7 system is a potential therapeutic target for IgA nephropathy

The progression determinants of IgA nephropathy (IgAN) are still not fully elucidated. We have previously demonstrated that the mucosal activation of toll-like receptor (TLR) 9, which senses microbial unmethylated CpG DNA, influences progression by producing aberrantly glycosylated IgA. However, numerous recent reports of patients with IgAN presenting with gross hematuria after the mRNA vaccination for coronavirus disease 2019 suggest that the RNA-sensing system also exacerbates IgAN. Here, we investigated whether TLR7, which recognizes microbial RNA, is also involved in IgAN progression using a murine model and tonsil tissue from 53 patients with IgAN compared to samples from 40 patients with chronic tonsillitis and 12 patients with sleep apnea syndrome as controls. We nasally administered imiquimod, the ligand of TLR7, to IgAN-prone ddY mice and found that TLR7 stimulation elevated the serum levels of aberrantly glycosylated IgA and induced glomerular IgA depositions and proteinuria. Co-administered hydroxychloroquine, which inhibits TLRs, canceled the kidney injuries. In vitro, stimulating splenocytes from ddY mice with imiquimod increased interleukin-6 and aberrantly glycosylated IgA levels. The expression of TLR7 in the tonsils was elevated in patients with IgAN and positively correlated with that of a proliferation-inducing ligand (APRIL) involved in the production of aberrantly glycosylated IgA. Mechanistically, TLR7 stimulation enhanced the synthesis of aberrantly glycosylated IgA through the modulation of enzymes involved in the glycosylation of IgA. Thus, our findings suggest that nucleotide-sensing TLR9 and TLR7 play a crucial role in the pathogenesis of IgAN. Hence, nucleotide-sensing TLRs could be reasonably strong candidates for disease-specific therapeutic targets in IgAN.

Serum sCD40L and IL-31 in Association with Early Phase of IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a major cause of chronic glomerulonephritis worldwide. T cell dysregulation has been reported to contribute to the pathogenesis of IgAN. Methods We measured a broad range of Th1, Th2 and Th17 cytokines in the serum of IgAN patients. We searched for significant cytokines, which were associated with clinical parameters and histological scores in IgAN patients.

RESULTS

Among 15 cytokines, the levels of soluble CD40L (sCD40L) and IL-31 were higher in IgAN patients and were significantly associated with a higher estimated glomerular filtration rate (eGFR), a lower urinary protein to creatinine ratio (UPCR), and milder tubulointerstitial lesions (i.e., the early phase of IgAN). Multivariate analysis revealed that serum sCD40L was an independent determinant of a lower UPCR after adjustment for age, eGFR, and mean blood pressure (MBP). CD40, a receptor of sCD40L, has been reported to be upregulated on mesangial cells in IgAN. The sCD40L/CD40 interaction may directly induce inflammation in mesangial areas and may therefore be involved in the development of IgAN.

CONCLUSIONS

The present study demonstrated the significance of serum sCD40L and IL-31 in the early phase of IgAN. Serum sCD40L may be a marker of the beginning of inflammation in IgAN.

Mucosal Immune System Dysregulation in the Pathogenesis of IgA Nephropathy

The mucosal immune system, via a dynamic immune network, serves as the first line of defense against exogenous antigens. Mucosal immune system dysregulation is closely associated with the pathogenesis of immunoglobulin A nephropathy (IgAN), as illustrated by IgAN having the clinical feature of gross hematuria, often concurrent with mucosal infections. Notably, previous studies have demonstrated the efficacy of tonsillectomy and found that a targeted-release formulation of budesonide reduced proteinuria in patients with IgAN. However, it remains unclear how exogenous antigens interact with the mucosal immune system to induce or exacerbate IgAN. Thus, in this review, we focus on the dysregulation of mucosal immune response in the pathogenesis of IgAN.

Title IgA Nephropathy and Oral Bacterial Species Related to Dental Caries and Periodontitis

A relationship between IgA nephropathy (IgAN) and bacterial infection has been suspected. As IgAN is a chronic disease, bacteria that could cause chronic infection in oral areas might be pathogenetic bacteria candidates. Oral bacterial species related to dental caries and periodontitis should be candidates because these bacteria are well known to be pathogenic in chronic dental disease. Recently, several reports have indicated that collagen-binding protein (cnm)-(+) Streptococcs mutans is relate to the incidence of IgAN and the progression of IgAN. Among periodontal bacteria, Treponema denticola, Porphyromonas gingivalis and Campylobacte rectus were found to be related to the incidence of IgAN. These bacteria can cause IgAN-like histological findings in animal models. While the connection between oral bacterial infection, such as infection with S. mutans and periodontal bacteria, and the incidence of IgAN remains unclear, these bacterial infections might cause aberrantly glycosylated IgA1 in nasopharynx-associated lymphoid tissue, which has been reported to cause IgA deposition in mesangial areas in glomeruli, probably through the alteration of microRNAs related to the expression of glycosylation enzymes. The roles of other factors related to the incidence and progression of IgA, such as genes and cigarette smoking, can also be explained from the perspective of the relationship between these factors and oral bacteria. This review summarizes the relationship between IgAN and oral bacteria, such as cnm-(+) S. mutans and periodontal bacteria.

IgA glycosylation and immune complex formation in IgAN

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. This disease, discovered in 1968, is characterized by IgA-IgG glomerular immunodeposits with a mesangial pattern. It is thought that these immunodeposits originate from the immune complexes formed in the circulation. It is hypothesized that the pathogenesis of IgAN is driven by aberrant glycoforms of IgA1 (galactose-deficient IgA1, Gd-IgA1). Gd-IgA1, in genetically susceptible individuals, represents the initiating factor for the formation of circulating immune complexes due to its recognition by IgG autoantibodies and the subsequent formation of pathogenic IgA1-IgG immune complexes. Complement activation through alternative and/or lectin pathways is likely playing an important role in the pathogenic properties of these complexes and may further upregulate local inflammatory responses and glomerular injury.

Aberrantly Glycosylated IgA1 in IgA Nephropathy: What We Know and What We Don't Know

IgA nephropathy (IgAN), the most common primary glomerular disease worldwide, is characterized by glomerular deposition of IgA1-containing immune complexes. The IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine usually with β1,3-linked galactose and variable sialylation. Circulating levels of IgA1 with abnormally O-glycosylated HR, termed galactose-deficient IgA1 (Gd-IgA1), are increased in patients with IgAN. Current evidence suggests that IgAN is induced by multiple sequential pathogenic steps, and production of aberrantly glycosylated IgA1 is considered the initial step. Thus, the mechanisms of biosynthesis of aberrantly glycosylated IgA1 and the involvement of aberrant glycoforms of IgA1 in disease development have been studied. Furthermore, Gd-IgA1 represents an attractive biomarker for IgAN, and its clinical significance is still being evaluated. To elucidate the pathogenesis of IgAN, it is important to deconvolute the biosynthetic origins of Gd-IgA1 and characterize the pathogenic IgA1 HR O-glycoform(s), including the glycan structures and their sites of attachment. These efforts will likely lead to development of new biomarkers. Here, we review the IgA1 HR O-glycosylation in general and the role of aberrantly glycosylated IgA1 in the pathogenesis of IgAN in particular.

TLR7 in B cells promotes renal inflammation and Gd-IgA1 synthesis in IgA nephropathy

TLR7 has been linked to the pathogenesis of glomerulonephritis, but its precise roles are not clear. In this study, we evaluated the roles of TLR7 in IgA nephropathy (IgAN). TLR7 proteins were abundant in CD19+ B cells infiltrated in the kidneys of patients with IgAN. The intensities of both intrarenal TLR7 and CD19 proteins were closely associated with kidney function (estimated glomerular filtration rate [eGFR] and serum creatinine concentration) and renal histopathology (tubular atrophy, leukocyte infiltration, tubulointerstitial fibrosis, and global glomerulosclerosis) in patients with IgAN. Meanwhile, TLR7 mRNA levels were significantly increased in peripheral blood B cells of patients with IgAN. TLR7+CD19+ B cells expressed inflammatory cytokines (IL-6 and IL-12) in kidneys and produced high levels of IgA1 and galactose deficient-IgA1 (Gd-IgA1) in peripheral blood of patients with IgAN. Mechanistically, TLR7 activated B cells to produce high levels of Gd-IgA1 via the TLR7-GALNT2 axis in IgAN. Protein levels of GALNT2 were increased by overexpression of TLR7, while they were reduced by TLR7 knockdown in B cells. GALNT2 overexpression augmented Gd-IgA1 production in B cells derived from patients with IgAN. Taken together, high TLR7 expression in B cells has dual roles in the development and progression of IgAN, by facilitating renal inflammation and Gd-IgA1 antibody synthesis.

Podocyte autophagy is associated with foot process effacement and proteinuria in patients with minimal change nephrotic syndrome

Autophagy is a cellular mechanism involved in the bulk degradation of proteins and turnover of organelle. Several studies have shown the significance of autophagy of the renal tubular epithelium in rodent models of tubulointerstitial disorder. However, the role of autophagy in the regulation of human glomerular diseases is largely unknown. The current study aimed to demonstrate morphological evidence of autophagy and its association with the ultrastructural changes of podocytes and clinical data in patients with idiopathic nephrotic syndrome, a disease in which patients exhibit podocyte injury. The study population included 95 patients, including patients with glomerular disease (minimal change nephrotic syndrome [MCNS], n = 41; idiopathic membranous nephropathy [IMN], n = 37) and 17 control subjects who underwent percutaneous renal biopsy. The number of autophagic vacuoles and the grade of foot process effacement (FPE) in podocytes were examined by electron microscopy (EM). The relationships among the expression of autophagic vacuoles, the grade of FPE, and the clinical data were determined. Autophagic vacuoles were mainly detected in podocytes by EM. The microtubule-associated protein 1 light chain 3 (LC3)-positive area was co-localized with the Wilms tumor 1 (WT1)-positive area on immunofluorescence microscopy, which suggested that autophagy occurred in the podocytes of patients with MCNS. The number of autophagic vacuoles in the podocytes was significantly correlated with the podocyte FPE score (r = -0.443, p = 0.004), the amount of proteinuria (r = 0.334, p = 0.033), and the level of serum albumin (r = -0.317, p = 0.043) in patients with MCNS. The FPE score was a significant determinant for autophagy after adjusting for the age in a multiple regression analysis in MCNS patients (p = 0.0456). However, such correlations were not observed in patients with IMN or in control subjects. In conclusion, the results indicated that the autophagy of podocytes is associated with FPE and severe proteinuria in patients with MCNS. The mechanisms underlying the activation of autophagy in association with FPE in podocytes should be further investigated in order to elucidate the pathophysiology of MCNS.

C1GALT1 expression is associated with galactosylation of IgA1 in peripheral B lymphocyte in immunoglobulin a nephropathy

Background

More and more studies demonstrated that genetic variation at C1GALT1 influences Gd-IgA1 level in IgAN. However, whether the expression of β1, 3-galactosyltransferase (β1, 3Gal-T) was influenced may provide insights into how Gd-IgA1 levels are controlled in IgAN.

Methods

Thirty IgAN patients diagnosed in Tianjin Medical University General Hospital from April to September 2018 and 30 healthy volunteers whose age and gender matched with patients were enrolled in this study. Total Gd-IgA1 levels in plasma were determined by ELISA and C1GALT1 levels were determined by RT-PCR. Four databases (PubMed, EMBASE, CNKI, WanFang Medical Network) were searched to identify eligible studies that evaluated a difference in the expression of C1GALT1 in IgAN patients compared with total controls (non-IgAN and health controls). The C1GALT1C1 expression levels, which was indispensable to β1, 3Gal-T of IgA1, was also been compared.

Results

Gd-IgA1 levels were remarkable higher in IgAN patients compared with healthy control. The expression levels of C1GALT1 gene were remarkably down-regulated in IgAN patients compared with healthy control. And the mRNA level of C1GALT1 was inversely correlated to Gd-IgA1 levels. In meta-analysis, six articles including 316 participants that analyzed the expression of β1, 3Gal-T were met inclusion criteria. There was no significant difference in the expression of C1GALT1 between IgAN patients compared with controls. And we found patients with IgAN had lower levels of C1GALT1 gene expression in the B cells compared to controls. The C1GALT1C1 levels in the IgAN patients were not different from the levels in the control group, which were unchanged no matter according to different ethnic population, different control group and different cell source. Two studies including 46 persons compared enzymatic activity of β1, 3Gal-T in B cells, and the result showed the β1, 3Gal-T activity was decreased in B cells.

Conclusions

We found expression levels of C1GALT1 were remarkably downregulated in IgAN patients and negatively correlated with higher levels of Gd-IgA1. Subsequent meta-analysis validated the low expression and activity of β1, 3Gal-T in B cells in patients with IgAN. However, there was no apparent disparity in the aspect of C1GALT1C1 expression between IgAN and control groups.

Recent advances in the immunological understanding of association between tonsil and immunoglobulin A nephropathy as a tonsil-induced autoimmune/inflammatory syndrome

INTRODUCTION

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide. It is well known that upper respiratory tract infections, particularly acute tonsillitis, often worsen IgAN. Recent many clinical studies clearly show that tonsillectomy with steroid pulse therapy is the effective treatments for IgAN patients. Recently, the immunological evidence of association between tonsil and IgAN has been reported.

METHODS

In this review, the mechanism underlying the onset of IgAN, as a tonsil-induced autoimmune/inflammatory syndrome (TIAS), is outlined with the main focus on the authors' research results.

RESULTS

In the tonsils of patients with IgAN, hyperimmune response to the unmethylated deoxycytidyl-deoxyguanosine oligodeoxynucleotides (CpG-ODN) take place, resulting in hyperproduction of interferon-γ. The hyperproduction is followed by both overproduction of mutated IgA via B-cell activating factor (BAFF)/a proliferation-inducing ligand (APRIL)-mediated pathways and overexpression of T-cell receptor Vβ6, CXCR3, and CX3CR1 on tonsillar T cells. These IgA and T cells home to the kidney via the systemic circulation, resulting in nephritis of IgAN.

CONCLUSIONS

Scientific evidence supporting the use of tonsillectomy has gradually accumulated. We hope that many additional researchers will publish new evidence linking the tonsils and kidneys in the future.

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.

Comprehensive microbiome analysis of tonsillar crypts in IgA nephropathy

Background

Immunoglobulin A nephropathy (IgAN) is the most prevalent primary chronic glomerular disease, in which the mucosal immune response elicited particularly in the tonsils or intestine has been estimated to be involved in the development of the disease. To explore the relationship between IgAN and bacterial flora in the tonsils, we conducted a comprehensive microbiome analysis.

Methods

We enrolled 48 IgAN patients, 21 recurrent tonsillitis (RT) patients without urine abnormalities and 30 children with tonsillar hyperplasia (TH) who had undergone tonsillectomy previously. Genomic DNA from tonsillar crypts of each patient was extracted, and V4 regions of the 16S ribosomal RNA gene were amplified and analysed using a high-throughput multiplexed sequencing approach. Differences in genus composition among the three study groups were statistically analysed by permutational multivariate analysis of variance and visualized by principal component analysis (PCA).

Results

Substantial diversity in bacterial composition was detected in each sample. Prevotella spp., Fusobacterium spp., Sphingomonas spp. and Treponema spp. were predominant in IgAN patients. The percentage of abundance of Prevotella spp., Haemophilus spp., Porphyromonas spp. and Treponema spp. in IgAN patients was significantly different from that in TH patients. However, there was no significant difference in the percentage of abundance of any bacterial genus between IgAN and RT patients. PCA did not distinguish IgAN from RT, although it discriminated TH. No significant differences in microbiome composition among the groups of IgAN patients according to clinicopathological parameters were observed.

Conclusions

Similar patterns of bacteria are present in tonsillar crypts of both IgAN and RT patients, suggesting that the host response to these bacteria might be important in the development of IgAN.

Inhibition of STAT3 Signaling Reduces IgA1 Autoantigen Production in IgA Nephropathy

Introduction

IgA nephropathy is a chronic renal disease characterized by mesangial immunodeposits that contain autoantigen, which is aberrantly glycosylated IgA1 with some hinge-region O-glycans deficient in galactose. Macroscopic hematuria during an upper respiratory tract infection is common among patients with IgA nephropathy, which suggests a connection between inflammation and disease activity. Interleukin-6 (IL-6) is an inflammatory cytokine involved in IgA immune response. We previously showed that IL-6 selectively increases production of galactose-deficient IgA1 in IgA1-secreting cells from patients with IgA nephropathy.

Methods

We characterized IL-6 signaling pathways involved in the overproduction of galactose-deficient IgA1. To understand molecular mechanisms, IL-6 signaling was analyzed by kinomic activity profiling and Western blotting, followed by confirmation assays using siRNA knock-down and small-molecule inhibitors.

Results

STAT3 was differentially activated by IL-6 in IgA1-secreting cells from patients with IgA nephropathy compared with those from healthy control subjects. Specifically, IL-6 induced enhanced and prolonged phosphorylation of STAT3 in the cells from patients with IgA nephropathy, which resulted in overproduction of galactose-deficient IgA1. This IL-6−mediated overproduction of galactose-deficient IgA1 could be blocked by small molecule inhibitors of JAK/STAT signaling.

Discussion

Our results revealed that IL-6−induced aberrant activation of STAT3-mediated overproduction of galactose-deficient IgA1. STAT3 signaling pathway may thus represent a new target for disease-specific therapy of IgA nephropathy.

Circulating CD89-IgA complex does not predict deterioration of kidney function in Korean patients with IgA nephropathy

Background:

Soluble CD89 (sCD89)-IgA complex plays a key role in the pathogenesis of IgA nephropathy (IgAN). However, there is a lack of evidence supporting this complex as a good biomarker for disease progression. This study aimed to evaluate the usefulness of sCD89-IgA complex for risk stratification of IgAN.

Methods:

A total of 326 patients with biopsy-proven IgAN were included. sCD89-IgA complex was measured by sandwich-enzyme-linked immunosorbent assay. The study endpoints were a 30% decline in estimated glomerular filtration rate (eGFR).

Results:

sCD89-IgA complex levels were inversely and weakly associated with eGFR at the time of biopsy (r=−0.12, p=0.03). However, the significance between the two factors was lost in the multivariate linear regression after adjustment of clinical factors (β=0.35, p=0.75). In a multivariate Cox model, the highest (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.35–1.61; p=0.45) and middle (HR, 0.93; 95% CI, 0.46–1.89; p=0.84) tertiles of sCD89-IgA complex levels were not associated with an increased risk of developing a 30% decrease in eGFR. Furthermore, the decline rates in eGFR did not differ between groups and C-statistics revealed that the sCD89-IgA complex were not superior to clinical factors in predicting disease progression.

Conclusions:

This study found no association between sCD89-IgA complex levels and disease progression in IgAN. Although sCD89 can contribute to the formation of immune complexes, our findings suggest that the sCD89-IgA level is not a good predictor of adverse outcomes and has limited clinical utility as a biomarker for risk stratification in IgAN.

TGF-β1 mimics the effect of IL-4 on the glycosylation of IgA1 by downregulating core 1 β1, 3-galactosyltransferase and Cosmc

The aberrant glycosylation of IgA1 is pivotal in the pathogenesis of IgA nephropathy (IgAN). The aim of the present study was to investigate the effect of transforming growth factor‑β1 (TGF‑β1) on the glycosylation of IgA1 and the associated mechanism. The mRNA levels of core1 β1, 3-galactosyltransferase (C1GalT1) and its molecular chaperone, Cosmc, were analyzed, as was the subsequent O-glycosylation of IgA1, in a human B‑cell line stimulated with TGF‑β1. The IgA1‑positive human B‑cell line was cultured with different concentrations of recombinant human TGF‑β1 (5, 10, 15 and 30 ng/ml). The production and glycosylation of IgA1 were assayed using sandwich ELISA and enzyme‑linked lectin binding assays, respectively, and the mRNA levels of C1GalT1 and Cosmc were quantified using reverse transcription‑quantitative polymerase chain reaction analysis. The results showed that the production of IgA1 was stimulated by low concentrations of TGF‑β1 (5 or 10 ng/ml) and was suppressed by high concentrations (15 or 30 ng/ml). The terminal glycosylation of secreted IgA1 was altered in response to TGF‑β1. TGF‑β1 stimulation significantly decreased the mRNA levels of C1GalT1 and Cosmc. TGF‑β1 may be key in controlling the glycosylation of IgA1, in part via the downregulation of C1GalT1 and Cosmc.

Toll-Like Receptor 9 Stimulation Induces Aberrant Expression of a Proliferation-Inducing Ligand by Tonsillar Germinal Center B Cells in IgA Nephropathy

The TNF family member a proliferation-inducing ligand (APRIL; also known as TNFSF13), produced by myeloid cells, participates in the generation and survival of antibody-producing plasma cells. We studied the potential role of APRIL in the pathogenesis of IgA nephropathy (IgAN). We found that a significant proportion of germinal centers (GCs) in tonsils of patients with IgAN contained cells aberrantly producing APRIL, contributing to an overall upregulation of tonsillar APRIL expression compared with that in tonsils of control patients with tonsillitis. In IgAN GC, antigen-experienced IgD^-CD38^+/-CD19⁺ B cells expressing a switched IgG/IgA B cell receptor produced APRIL. Notably, these GC B cells expressed mRNA encoding the common cleavable APRIL-α but also, the less frequent APRIL-δ/ζ mRNA, which encodes a protein that lacks a furin cleavage site and is, thus, the uncleavable membrane-bound form. Significant correlation between TLR9 and APRIL expression levels existed in tonsils from patients with IgAN. In vitro, repeated TLR9 stimulation induced APRIL expression in tonsillar B cells from control patients with tonsillitis. Clinically, aberrant APRIL expression in tonsillar GC correlated with greater proteinuria, and patients with IgAN and aberrant APRIL overexpression in tonsillar GC responded well to tonsillectomy, with parallel decreases in serum levels of galactose-deficient IgA1. Taken together, our data indicate that antibody disorders in IgAN associate with TLR9-induced aberrant expression of APRIL in tonsillar GC B cells.

Promoters of Human Cosmc and T-synthase Genes Are Similar in Structure, Yet Different in Epigenetic Regulation

The T-synthase (core 1 β3-galactosyltransferase) and its molecular chaperone Cosmc regulate the biosynthesis of mucin type O-glycans on glycoproteins, and evidence suggests that both T-synthase and Cosmc are transcriptionally suppressed in several human diseases, although the transcriptional regulation of these two genes is not understood. Here, we characterized the promoters essential for human Cosmc and T-synthase transcription. The upstream regions of the genes lack a conventional TATA box but contain CpG islands, cCpG-I and cCpG-II for Cosmc and tCpG for T-synthase. Using luciferase reporter assays, site-directed mutagenesis, ChIP assays, and mithramycin A treatment, we identified the core promoters within cCpG-II and tCpG, which contain two binding sites for Krüppel-like transcription factors, including SP1/SP3, respectively. Methylome analysis of Tn4 B cells, which harbor a silenced Cosmc, confirmed the hypermethylation of the Cosmc core promoter but not for T-synthase. These results demonstrate that Cosmc and T-synthase are transcriptionally regulated at a basal level by the specificity protein/Krüppel-like transcription factor family of members, which explains their ubiquitous and coordinated expression, and also indicate that they are differentially epigenetically regulated beyond X chromosome imprinting. These results are important in understanding the regulation of these genes that have roles in human diseases, such as IgA nephropathy and cancer.

Role of let-7b in the regulation of N-acetylgalactosaminyltransferase 2 in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is characterized by aberrant O-glycosylation in the hinge region of IgA1. The early step in O-glycan formation is the attachment of N-acetylgalactosamine (GalNAc) to the serine/threonine of the hinge region; the process is catalysed by UDP-N-acetyl-α-d-galactosamine:polypeptide N-acetylgalactosaminyltransferase 2 (GALNT2). In our previous work, the microarray analysis on peripheral blood mononuclear cells (PBMCs) identified an upregulated miRNA called let-7b.

METHODS

To study the molecular mechanisms in which let-7b was involved, we performed a bioinformatic analysis to predict their target genes. To validate biologically let-7b targets, we performed transient transfection experiments ex vivo using PBMCs from an independent group of IgAN patients and healthy blood donors (HBDs).

RESULTS

Bioinformatic analysis revealed that GALNT2 is the potential target of let-7b. We found this miRNA significantly upregulated in PBMCs of IgAN patients compared with HBDs. Then, we demonstrated in ex-vivo experiments that let-7b decreased GALNT2 levels in PBMCs of IgAN patients, whereas the loss of let-7b function in PBMCs of HBDs led to an increase of GALNT2 mRNA and its protein level. Finally, we found that upregulation of let-7b occurred also in B-lymphocytes from IgAN patients.

CONCLUSIONS

Our results give novel additional information on the abnormal O-glycosylation process of IgA1 in IgAN patients. This study provides evidence for another important miRNA-based regulatory mechanism of the O-glycosylation process in which the deregulated expression of let-7b is associated with altered expression of GALNT2. This finding could be taken into consideration for new therapeutic approaches in IgAN because other serum glycosylated proteins do not display abnormal glycosylation.

Diagnosis and activity assessment of immunoglobulin A nephropathy: current perspectives on noninvasive testing with aberrantly glycosylated immunoglobulin A-related biomarkers

Immunoglobulin (Ig) A nephropathy (IgAN) is the most common form of glomerular disease worldwide and is associated with a poor prognosis. Thus, development of a curative treatment and strategies for early diagnosis and treatment are urgently needed. Pathological analysis of renal biopsy is the gold standard for the diagnosis and assessment of disease activity; however, immediate and frequent assessment based on biopsy specimens is difficult. Therefore, a simple and safe alternative is desirable. On the other hand, it is now widely accepted that multi-hit steps, including production of aberrantly glycosylated serum IgA1 (first hit), and IgG or IgA autoantibodies that recognize glycan containing epitopes on glycosylated serum IgA1 (second hit) and their subsequent immune complex formation (third hit) and glomerular deposition (fourth hit), are required for continued progression of IgAN. Although the prognostic and predictive values of several markers have been discussed elsewhere, we recently developed a highly sensitive and specific diagnostic method by measuring serum levels of glycosylated serum IgA1 and related IgA immune complex. In addition, we confirmed a significant correlation between serum levels of these essential effector molecules and disease activity after treatment, suggesting that each can be considered as a practical surrogate marker of therapeutic effects in this slowly progressive disease. Such a noninvasive diagnostic and activity assessment method using these disease-oriented specific biomarkers may be useful in the early diagnosis of and intervention in IgAN, with appropriate indication for treatment, and thus aid in the future development and dissemination of specific and curative treatments.

Identification of distinct glycoforms of IgA1 in plasma from patients with immunoglobulin A (IgA) nephropathy and healthy individuals

Immunoglobulin A nephropathy (IgAN) is the most common form of glomerulonephritis worldwide and is histologically characterized by the deposition of IgA1 and consequent inflammation in the glomerular mesangium. Prior studies suggested that serum IgA1 from IgAN patients contains aberrant, undergalactosylated O-glycans, for example, Tn antigen and its sialylated version, SialylTn (STn), but the mechanisms underlying aberrant O-glycosylation are not well understood. Here we have used serial lectin separation technologies, Western blot, enzymatic modifications, and mass spectrometry to explore whether there are different glycoforms of IgA1 in plasma from patients with IgAN and healthy individuals. Although total plasma IgA in IgAN patients was elevated ∼ 1.6-fold compared with that in healthy donors, IgA1 in all samples was unexpectedly separable into two distinct glycoforms: one with core 1 based O-glycans, and the other exclusively containing Tn/STn structures. Importantly, Tn antigen present on IgA1 from IgAN patients and controls was convertible into the core 1 structure in vitro by recombinant T-synthase. Our results demonstrate that undergalactosylation of O-glycans in IgA1 is not restricted to IgAN and suggest that in vivo inefficiency of T-synthase toward IgA1 in a subpopulation of B or plasma cells, as well as overall elevation of IgA, may contribute to IgAN pathogenesis.

Comparative Analysis of Glycogene Expression in Different Mouse Tissues Using RNA-Seq Data

Glycogenes regulate a wide array of biological processes in the development of organisms as well as different diseases such as cancer, primary open-angle glaucoma, and renal dysfunction. The objective of this study was to explore the role of differentially expressed glycogenes (DEGGs) in three major tissues such as brain, muscle, and liver using mouse RNA-seq data, and we identified 579, 501, and 442 DEGGs for brain versus liver (BvL579), brain versus muscle (BvM501), and liver versus muscle (LvM442) groups. DAVID functional analysis suggested inflammatory response, glycosaminoglycan metabolic process, and protein maturation as the enriched biological processes in BvL579, BvM501, and LvM442, respectively. These DEGGs were then used to construct three interaction networks by using GeneMANIA, from which we detected potential hub genes such as PEMT and HPXN (BvL579), IGF2 and NID2 (BvM501), and STAT6 and FLT1 (LvM442), having the highest degree. Additionally, our community analysis results suggest that the significance of immune system related processes in liver, glycosphingolipid metabolic processes in the development of brain, and the processes such as cell proliferation, adhesion, and growth are important for muscle development. Further studies are required to confirm the role of predicted hub genes as well as the significance of biological processes.

CagA, a major virulence factor of Helicobacter pylori, promotes the production and underglycosylation of IgA1 in DAKIKI cells

While Helicobacter pylori (Hp) infection is closely associated with IgA nephropathy (IgAN), the underlying molecular mechanisms remain to be elucidated. This study was to investigate the effect of cytotoxin associated gene A protein (CagA), a major virulence factor of Hp, on the production and underglycosylation of IgA1 in the B cell line DAKIKI cells. Cells were cultured and treated with recombinant CagA protein. We found that CagA stimulated cell proliferation and the production of IgA1 in a dose-dependent and time-dependent manner. Moreover, CagA promoted the underglycosylation of IgA1, which at least partly attributed to the downregulation of β1,3-galactosyltransferase (C1GALT1) and its chaperone Cosmc. In conclusion, we demonstrated that Hp infection, at least via CagA, may participate in the pathogenesis of IgAN by influencing the production and glycosylation of IgA1 in B cells.

Tn and sialyl-Tn antigens, aberrant O-glycomics as human disease markers

In many different human disorders, the cellular glycome is altered. An interesting but poorly understood alteration occurs in the mucin-type O-glycome, in which there is aberrant expression of the truncated O-glycans Tn (GalNAcα1-Ser/Thr) and its sialylated version sialyl-Tn (STn) (Neu5Acα2,6GalNAcα1-Ser/Thr). Both Tn and STn are tumor-associated carbohydrate antigens and tumor biomarkers, since they are not expressed normally and appear early in tumorigenesis. Moreover, their expression is strongly associated with poor prognosis and tumor metastasis. The Tn and STn antigens are also expressed in other human diseases and disorders, such as Tn syndrome and IgA nephropathy. The major pathological mechanism for expression of the Tn and STn antigens is compromised T-synthase activity, resulting from alteration of the X-linked gene that encodes for Cosmc, a molecular chaperone specifically required for the correct folding of T-synthase to form active enzyme. This review will summarize our current understanding of the Tn and STn antigens in terms of their biochemistry and role in pathology.

Activation of the interleukin-4/signal transducer and activator of transcription 6 signaling pathway and homeodomain-interacting protein kinase 2 production by tonsillar mononuclear cells in IgA nephropathy

BACKGROUND/AIM

Clinical development and exacerbation of IgA nephropathy (IgAN) are frequently preceded by episodes of upper respiratory tract infection such as tonsillitis. This study aimed to determine the role of the interleukin-4 (IL-4)/signal transducer and activator of transcription 6 (STAT6) signaling pathway and homeodomain-interacting protein kinase 2 (HIPK2) in aberrant IgA1 O-glycosylation production, and identify potential therapeutic targets in IgAN.

METHODS

Expression levels of IL-4, STAT6, core1β1,3-galactosyltransferase (C1GALT1C1), core1β3GalT-specific molecular chaperone (Cosmc) and HIPK2 in tonsil components were examined by immunohistochemical and immunofluorescence staining. Lymphocytes isolated from 22 patients with IgAN and 24 patients with chronic tonsillitis (CT) as controls were cultured for 72 h with or without IL-4, lipopolysaccharide (LPS) and α-hemolytic streptococcus (HS) stimulation. Expression levels of STAT6, C1GALT1C1, Cosmc, HIPK2-mRNA and protein were measured by real-time PCR and Western blot analysis, respectively. The concentration of IgA1 and level of O-glycosylation were determined by ELISA and Vicia villosa (VV) lectin-binding assay. To determine the contribution of HIPK2 in IgA secretion and O-glycosylation, cells were subjected to experiments for evaluation of HIPK2 silencing by Hipk2-siRNA transfection.

RESULTS

The IL-4/STAT6 signaling pathway was highly activated in all tonsil tissues (including the germinal center and tonsillar crypt epithelium) of IgAN patients, but the gene or protein expression of β1,3-Gal transferase (C1GALT1) and COSMC decreased significantly in patients with IgAN in comparison with those with CT. Hipk2 production in the tonsils derived from IgAN patients was significantly higher than that of CT patients. HIPK2-mRNA expression significantly negatively correlated with renal function as expressed by the estimated glomerular filtration rate, and also significantly positively correlated with daily proteinuria. The level of IL-4, STAT6 and HIPK2 were closely related with Lee's pathological grading system. The levels of mRNA and protein encoding STAT6 and Hipk2 in cells coincubated with IL-4, LPS and HS were significantly higher than those in the controls without stimulation; however, in the IgAN group the levels of mRNA and protein encoding C1GALT1 and Cosmc were significantly lower compared to the controls. IgA1 concentrations of supernatants in IgAN patients were remarkably higher under conditions of external stimulation. As expected, the optical density value of VV lectin binding to IgA1 increased after external stimulation in the IgAN group. By siRNA transfection, our results clearly indicate that Hipk2 negatively regulates C1GALT1 and Cosmc expression. Importantly, HIPK2-siRNA attenuates the aberrant glycosylation of IgA1 secretion.

CONCLUSION

We identified and confirmed that activation of the IL-4/STAT6 signaling pathway has a crucial role in aberrant glycosylation of IgA1 secretion. HIPK2, a protein kinase previously unrecognized in kidney disease, may mediate the glycosylation of IgA1. We believe that HIPK2 could be a new therapeutic target for IgAN, especially as protein kinases are 'drugable' targets.

A fluorescence-based assay for Core 1 β3galactosyltransferase (T-synthase) activity

Mucin-type O-glycans on glycoproteins in animal cells play important roles in many biological processes. Core 1 β3galactosyltransferase (Core 1 β3GalT, T-synthase) is a key enzyme in the O-glycan biosynthetic pathway. Emerging evidence has shown the importance of O-glycans and the absolute requirement of T-synthase in this pathway. The assessment of the T-synthase activity has historically been conducted using a radioactive method. Here we describe a fluorescence-based assay procedure for T-synthase activity. T-synthase utilizes the acceptor substrate 4-methylumbelliferone-α-GalNAc (GalNAcα-(4-MU)) and the donor substrate UDP-Gal to synthesize the disaccharide product Galβ1,3GalNAcα-(4-MU) structure. This product is specifically hydrolyzed by endo-α-N-acetylgalactosaminidase (O-glycosidase) releasing free 4-MU. Free 4-MU is highly fluorescent at pH 9.6-10 and can be easily measured by a fluorescent detector (Ex: 355 nm; Em: 460 nm). This fluorescence-based T-synthase assay is simple, sensitive, reproducible, not affected by enzyme source, and adaptable for high-throughput assays.

Epigenetic silencing of the chaperone Cosmc in human leukocytes expressing tn antigen

Cosmc is the specific molecular chaperone in the endoplasmic reticulum for T-synthase, a Golgi β3-galactosyltransferase that generates the core 1 O-glycan, Galβ1-3GalNAcα-Ser/Thr, in glycoproteins. Dysfunctional Cosmc results in the formation of inactive T-synthase and consequent expression of the Tn antigen (GalNAcα1-Ser/Thr), which is associated with several human diseases. However, the molecular regulation of expression of Cosmc, which is encoded by a single gene on Xq24, is poorly understood. Here we show that epigenetic silencing of Cosmc through hypermethylation of its promoter leads to loss of Cosmc transcripts in Tn4 cells, an immortalized B cell line from a male patient with a Tn-syndrome-like phenotype. These cells lack T-synthase activity and express the Tn antigen. Treatment of cells with 5-aza-2'-deoxycytidine causes restoration of Cosmc transcripts, restores T-synthase activity, and reduces Tn antigen expression. Bisulfite sequencing shows that CG dinucleotides in the Cosmc core promoter are hypermethylated. Interestingly, several other X-linked genes associated with glycosylation are not silenced in Tn4 cells, and we observed no correlation of a particular DNA methyltransferase to aberrant methylation of Cosmc in these cells. Thus, hypermethylation of the Cosmc promoter in Tn4 cells is relatively specific. Epigenetic silencing of Cosmc provides another mechanism underlying the abnormal expression of the Tn antigen, which may be important in understanding aberrant Tn antigen expression in human diseases, including IgA nephropathy and cancer.

Suppression of adiponectin by aberrantly glycosylated IgA1 in glomerular mesangial cells in vitro and in vivo

The pathogenesis of IgA nephropathy (IgAN) may be associated with the mesangial deposition of aberrantly glycosylated IgA1. To identify mediators affected by aberrantly glycosylated IgA1 in cultured human mesangial cells (HMCs), we generated enzymatically modified desialylated and degalactosylated (deSial/deGal) IgA1. The state of deglycosylated IgA1 was confirmed by lectin binding to Helix aspersa (HAA) and Sambucus nigra (SNA). In the cytokine array analysis, 52 proteins were upregulated and 34 were downregulated in HMCs after stimulation with deSial/deGal IgA1. Among them, the secretion of adiponectin was suppressed in HMCs after stimulation with deSial/deGal IgA1. HMCs expressed mRNAs for adiponectin and its type 1 receptor, but not the type 2 receptor. Moreover, we revealed a downregulation of adiponectin expression in the glomeruli of renal biopsy specimens from patients with IgAN compared to those with lupus nephritis. We also demonstrated that aberrantly glycosylated IgA1 was deposited in the mesangium of patients with IgAN by dual staining of HAA and IgA. Moreover, the urinary HAA/SNA ratio of lectin binding was significantly higher in IgAN compared to other kidney diseases. Since adiponectin has anti-inflammatory effects, including the inhibition of adhesion molecules and cytokines, these data suggest that the local suppression of this adipokine by aberrantly glycosylated IgA1 could be involved in the regulation of glomerular inflammation and sclerosis in IgAN.

Pathological role of tonsillar B cells in IgA nephropathy

Although impaired immune regulation along the mucosa-bone marrow axis has been postulated to play an important role, the pathogenesis of IgA nephropathy (IgAN) is unknown; thus, no disease-specific therapy for this disease exists. The therapeutic efficacy of tonsillectomy or tonsillectomy in combination with steroid pulse therapy for IgAN has been discussed. Although randomized control trials for these therapies are ongoing in Japan, the scientific rationale for these therapies remains obscure. It is now widely accepted that abnormally glycosylated IgA1 and its related immune complex (IC) are probably key molecules for the pathogenesis, and are thus considered possible noninvasive biomarkers for this disease. Emerging evidence indicates that B cells in mucosal infections, particularly in tonsillitis, may produce the nephritogenic IgA. In this paper, we briefly summarize characteristics of the nephritogenic IgA/IgA IC, responsible B cells, and underlying mechanisms. This clinical and experimental information may provide important clues for a therapeutic rationale.

The Tn antigen-structural simplicity and biological complexity

Glycoproteins in animal cells contain a variety of glycan structures that are added co- and/or posttranslationally to proteins. Of over 20 different types of sugar-amino acid linkages known, the two major types are N-glycans (Asn-linked) and O-glycans (Ser/Thr-linked). An abnormal mucin-type O-glycan whose expression is associated with cancer and several human disorders is the Tn antigen. It has a relatively simple structure composed of N-acetyl-D-galactosamine with a glycosidic α linkage to serine/threonine residues in glycoproteins (GalNAcα1-O-Ser/Thr), and was one of the first glycoconjugates to be chemically synthesized. The Tn antigen is normally modified by a specific galactosyltransferase (T-synthase) in the Golgi apparatus of cells. Expression of active T-synthase is uniquely dependent on the molecular chaperone Cosmc, which is encoded by a gene on the X chromosome. Expression of the Tn antigen can arise as a consequence of mutations in the genes for T-synthase or Cosmc, or genes affecting other steps of O-glycosylation pathways. Because of the association of the Tn antigen with disease, there is much interest in the development of Tn-based vaccines and other therapeutic approaches based on Tn expression.

A novel fluorescent assay for T-synthase activity

Loss of T-synthase (uridine diphosphate galactose:N-acetylgalactosaminyl-α1-Ser/Thr β3galactosyltransferase), a key enzyme required for the formation of mucin-type core 1 O-glycans, is observed in several human diseases, including cancer, Tn syndrome and IgA nephropathy, but current methods to assay the enzyme use radioactive substrates and complicated isolation of the product. Here we report the development of a novel fluorescent assay to measure its activity in a variety of tumor cell lines. Deficiencies in T-synthase activity correlate with mutations in the gene encoding the molecular chaperone Cosmc that is required for folding the T-synthase. This new high-throughput assay allows for facile screening of tumor specimens and other biological material for T-synthase activity and could be used diagnostically.