Inhibition of STAT3 Signaling Reduces IgA1 Autoantigen Production in IgA Nephropathy

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.

Deciphering roles of protein post-translational modifications in IgA nephropathy progression and potential therapy

Immunoglobulin A nephropathy (IgAN), one type of glomerulonephritis, displays the accumulation of glycosylated IgA in the mesangium. Studies have demonstrated that both genetics and epigenetics play a pivotal role in the occurrence and progression of IgAN. Post-translational modification (PTM) has been revealed to critically participate in IgAN development and progression because PTM dysregulation results in impaired degradation of proteins that regulate IgAN pathogenesis. A growing number of studies identify that PTMs, including sialylation, o-glycosylation, galactosylation, phosphorylation, ubiquitination and deubiquitination, modulate the initiation and progression of IgAN. Hence, in this review, we discuss the functions and mechanisms of PTMs in regulation of IgAN. Moreover, we outline numerous compounds that govern PTMs and attenuate IgAN progression. Targeting PTMs might be a useful strategy to ameliorate IgAN.

An Update on the Genetics of IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN), the most common form of glomerulonephritis, is one of the leading causes of end-stage kidney disease (ESKD). It is widely believed that genetic factors play a significant role in the development of IgAN. Previous studies of IgAN have provided important insights to unravel the genetic architecture of IgAN and its potential pathogenic mechanisms. The genome-wide association studies (GWASs) together have identified over 30 risk loci for IgAN, which emphasizes the importance of IgA production and regulation in the pathogenesis of IgAN. Follow-up fine-mapping studies help to elucidate the candidate causal variant and the potential pathogenic molecular pathway and provide new potential therapeutic targets. With the rapid development of next-generation sequencing technologies, linkage studies based on whole-genome sequencing (WGS)/whole-exome sequencing (WES) also identify rare variants associated with IgAN, accounting for some of the missing heritability. The complexity of pathogenesis and phenotypic variability may be better understood by integrating genetics, epigenetics, and environment. We have compiled a review summarizing the latest advancements in genetic studies on IgAN. We similarly summarized relevant studies examining the involvement of epigenetics in the pathogenesis of IgAN. Future directions and challenges in this field are also proposed.

Elevated levels of IL-6 in IgA nephropathy patients are induced by an epigenetically driven mechanism modulated by viral and bacterial RNA

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most frequent primary glomerulonephritis and the role of IL-6 in pathogenesis is becoming increasingly important. A recent whole genome DNA methylation screening in IgAN patients identified a hypermethylated region comprising the non-coding RNA Vault RNA 2-1 (VTRNA2-1) that could explain the high IL-6 levels.

METHODS

The pathway leading to IL-6 secretion controlled by VTRNA2-1, PKR, and CREB was analyzed in peripheral blood mononuclear cells (PBMCs) isolated from healthy subjects (HS), IgAN patients, transplanted patients with or without IgAN. The role of double and single-strand RNA in controlling the pathway was investigated.

RESULTS

VTRNA2-1 was downregulated in IgAN compared to HS and in transplanted IgAN patients (TP-IgAN) compared to non-IgAN transplanted (TP). The loss of the VTRNA2-1 natural restrain in IgAN patients caused PKR hyperphosphorylation, and consequently the activation of CREB by PKR, which, in turn, led to high IL-6 production, both in IgAN and in TP-IgAN patients. IL-6 levels could be decreased by the PKR inhibitor imoxin. In addition, PKR is normally activated by bacterial and viral RNA, and we found that both the RNA poly(I:C), and the COVID-19 RNA-vaccine stimulation significantly increased the IL-6 levels in PBMCs from HS but had an opposite effect in those from IgAN patients.

CONCLUSION

The discovery of the upregulated VTRNA2-1/PKR/CREB/IL-6 pathway in IgAN patients may provide a novel approach to treating the disease and may be useful for the development of precision nephrology and personalized therapy by checking the VTRNA2-1 methylation level in IgAN patients.

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.

The mechanism of Shenbing Decoction II against IgA nephropathy renal fibrosis revealed by UPLC-MS/MS, network pharmacology and experimental verification

Background

IgA nephropathy (IgAN) is a major and growing public health problem. Renal fibrosis plays a vital role in the progression of IgAN. This study is to investigate the mechanisms of action underlying the therapeutic effects of Shenbing Decoction II (SBDII) in IgAN renal fibrosis treatment based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), network pharmacology and experimental verification.

Method

We first used UPLC-MS/MS to explore the main compounds of SBDII, and then used network pharmacology to predict the targets and key pathways of SBDII in the treatment of IgAN renal fibrosis. Next, bovine serum albumin (BSA), lipopolysaccharide (LPS), and carbon tetrachloride (CCL4) were used to induce IgAN in rats, and then biochemical indicators, renal tissue pathology, and renal fibrosis-related indicators were examined. At the same time, part of the results predicted by network pharmacology were also verified.

Result

A total of 105 compounds were identified in SBDII by UPLC-MS/MS. Network pharmacology results showed that the active compounds such as acacetin, eupatilin, and galangin may mediate the therapeutic effects of SBDII in treating IgAN by targeting tumor protein p53 (TP53) and regulating phosphatidylinositol 3-kinase (PI3K)-Akt kinase (Akt) signaling pathway. Animal experiments showed that SBDII not only significantly improved renal function and fibrosis in IgAN rats, but also significantly downregulated the expressions of p53, p-PI3K and p-Akt.

Conclusion

This UPLC-MS/MS, network pharmacological and experimental study highlights that the TP53 as a target, and PI3K-Akt signaling pathway are the potential mechanism by which SBDII is involved in IgAN renal fibrosis treatment. Acacetin, eupatilin, and galangin are probable active compounds in SBDII, these results might provide valuable guidance for further studies of IgAN renal fibrosis treatment.

Causal relationships between circulating inflammatory factors and IgA vasculitis: a bidirectional Mendelian randomization study

Background

IgA vasculitis (IgAV) is an immune-associated vasculitis, yet its exact etiology remains unclear. Here, we explore the interaction between IgAV and inflammatory factors using bidirectional Mendelian randomization (MR).

Methods

We conducted a bidirectional summary-level MR analysis to delineate the causality of C-reactive protein (CRP), procalcitonin (PCT), and 41 circulating inflammatory regulators with IgAV. Data on genetic variants related to inflammation were obtained from three genome-wide association studies (GWASs) on CRP, PCT, and human cytokines, whereas data on IgAV was from large meta-analyses of GWAS among 216 569 FinnGen Biobank participants. The primary MR analysis was performed using the inverse-variance weighted (IVW) approach, and the sensitivity analyses were carried out using MR-Egger, weighted median, weighted mode, and MR-pleiotropy residual sum and outlier.

Results

This study revealed the association of CRP higher levels with increased risk of IgAV through IVW method (Estimate odds ratio [OR] = 1.41, 95% confidence interval [CI]: 1.01-1.98, P = 0.04), MR-Egger (OR = 1.87, CI: 1.15-3.02, P = 0.01), weighted median (OR = 2.00, CI: 1.21-3.30, P = 0.01) and weighted mode (OR = 1.74, CI: 1.13-2.68, P = 0.02). Furthermore, elevated IL-8 was strongly implicated with a higher risk of IgAV (IVW OR = 1.42, CI: 1.05-1.92; P = 0.02). Conversely, genetically predicted IgAV was associated with decreased levels of TNF-β (IVW estimate β = -0.093, CI: -0.178 - -0.007; P = 0.033). Additionally, no such significant statistical differences for other inflammatory factors were found.

Conclusion

Our current study using bidirectional MR analysis provides compelling evidence for a causal effect of CRP, PCT, and circulating inflammatory regulators on IgAV. These findings contribute to a better understanding of the pathogenesis of IgAV and emphasize the potential of targeting inflammatory factors for therapeutic interventions.

Novel insights into STAT3 in renal diseases

Signal transducer and activator of transcription 3 (STAT3) is a cell-signal transcription factor that has attracted considerable attention in recent years. The stimulation of cytokines and growth factors can result in the transcription of a wide range of genes that are crucial for several cellular biological processes involved in pro- and anti-inflammatory responses. STAT3 has attracted considerable interest as a result of a recent upsurge in study because of their role in directing the innate immune response and sustaining inflammatory pathways, which is a key feature in the pathogenesis of many diseases, including renal disorders. Several pathological conditions which may involve STAT3 include diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and renal cell carcinoma. STAT3 is expressed in various renal tissues under these pathological conditions. To better understand the role of STAT3 in the kidney and provide a theoretical foundation for STAT3-targeted therapy for renal disorders, this review covers the current work on the activities of STAT3 and its mechanisms in the pathophysiological processes of various types of renal diseases.

The therapeutic effect of Shenhua tablet against mesangial cell proliferation and renal inflammation in mesangial proliferative glomerulonephritis

Shenhua tablet (SH), a formulation of traditional Chinese medicine, exerts renoprotective effect on chronic kidney diseases, and it has been found to restrain inflammation, but the mechanism is still unclear. Here, we explored the potential renoprotection of SH in mesangial proliferative glomerulonephritis (MsPGN) rat model induced by anti-Thy1 antibody. Administration of SH reduced urinary albumin/creatinine ratio (UACR) and significantly attenuated mesangial cell proliferation and renal inflammation. Notably, SH protected rats against renal inflammation, which was associated with decreasing macrophage infiltration and promoting macrophage anti-inflammatory activity. Network analysis combined with arrays identified the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway as the main pathways of SH could target inflammation. Furthermore, it was confirmed that mesangial cell proliferation, which response to inflammation, were alleviated by ASS1 expression enhanced after SH administration both in vivo and in vitro. Collectively, SH has the beneficial on relieving the progression of MsPGN to alleviate inflammation and mesangial proliferation by inhibiting STAT3 phosphorylation and maintains the expression level of ASS1, might be an effective strategy for treating MsPGN.

Genome-wide association analyses define pathogenic signaling pathways and prioritize drug targets for IgA nephropathy

IgA nephropathy (IgAN) is a progressive form of kidney disease defined by glomerular deposition of IgA. Here we performed a genome-wide association study of 10,146 kidney-biopsy-diagnosed IgAN cases and 28,751 controls across 17 international cohorts. We defined 30 genome-wide significant risk loci explaining 11% of disease risk. A total of 16 loci were new, including TNFSF4/TNFSF18, REL, CD28, PF4V1, LY86, LYN, ANXA3, TNFSF8/TNFSF15, REEP3, ZMIZ1, OVOL1/RELA, ETS1, IGH, IRF8, TNFRSF13B and FCAR. The risk loci were enriched in gene orthologs causing abnormal IgA levels when genetically manipulated in mice. We also observed a positive genetic correlation between IgAN and serum IgA levels. High polygenic score for IgAN was associated with earlier onset of kidney failure. In a comprehensive functional annotation analysis of candidate causal genes, we observed convergence of biological candidates on a common set of inflammatory signaling pathways and cytokine ligand-receptor pairs, prioritizing potential new drug targets.

GalNAc-T14 may Contribute to Production of Galactose-Deficient Immunoglobulin A1, the Main Autoantigen in IgA Nephropathy

Introduction

Immunoglobulin A1 (IgA1) with galactose-deficient O-glycans (Gd-IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). Mucosal-tissue infections increase IL-6 production and, in patients with IgAN, are often associated with macroscopic hematuria. IgA1-secreting cell lines derived from the circulation of patients with IgAN, compared to those of healthy controls (HCs), produce more IgA1 that has O-glycans with terminal or sialylated N-acetylgalactosamine (GalNAc). GalNAc residues are added to IgA1 hinge region by some of the 20 GalNAc transferases, the O-glycosylation-initiating enzymes. Expression of GALNT2, encoding GalNAc-T2, the main enzyme initiating IgA1 O-glycosylation, is similar in cells derived from patients with IgAN and HCs. In this report, we extend our observations of GALNT14 overexpression in IgA1-producing cell lines from patients with IgAN.

Methods

GALNT14 expression was analyzed in peripheral blood mononuclear cells (PBMCs) from patients with IgAN and from HCs. Moreover, the effect of GALNT14 overexpression or knock-down on Gd-IgA1 production in Dakiki cells was assessed.

Results

GALNT14 was overexpressed in PBMCs from patients with IgAN. IL-6 increased GALNT14 expression in PBMCs from patients with IgAN and HCs. We used IgA1-producing cell line Dakiki, a previously reported model of Gd-IgA1-producing cells, and showed that overexpression of GalNAc-T14 enhanced galactose deficiency of IgA1, whereas siRNA-mediated GalNAc-T14 knock-down reduced it. GalNAc-T14 was localized in trans-Golgi network, as expected.

Conclusions

Overexpression of GALNT14 due to inflammatory signals during mucosal infections may contribute to overproduction of Gd-IgA1 in patients with IgAN.

Racial heterogeneity of IgA1 hinge-region O-glycoforms in patients with IgA nephropathy

Galactose (Gal)-deficient IgA1 (Gd-IgA1) is involved in IgA nephropathy (IgAN) pathogenesis. To reflect racial differences in clinical characteristics, we assessed disease- and race-specific heterogeneity in the O-glycosylation of the IgA1 hinge region (HR). We determined serum Gd-IgA1 levels in Caucasians (healthy controls [HCs], n = 31; IgAN patients, n = 63) and Asians (HCs, n = 20; IgAN patients, n = 60) and analyzed profiles of serum IgA1 HR O-glycoforms. Elevated serum Gd-IgA1 levels and reduced number of Gal residues per HR were observed in Caucasians. Reduced number of N-acetylgalactosamine (GalNAc) residues per HR and elevated relative abundance of IgA1 with three HR O-glycans were common features in IgAN patients; these features were associated with elevated blood pressure and reduced renal function. We speculate that the mechanisms underlying the reduced GalNAc content in IgA1 HR may be relevant to IgAN pathogenesis.

IgA vasculitis update: Epidemiology, pathogenesis, and biomarkers

Immunoglobulin A vasculitis (IgAV), formerly known as Henoch-Schönlein purpura, is the most common systemic vasculitis in children, characterized by diverse clinical manifestations with a wide spectrum ranging from isolated cutaneous vasculitis to systemic involvement. The incidence of IgAV is geographically and ethnically variable, with a prevalence in autumn and winter, suggesting a driving role that genetic and environmental factors play in the disease. Although IgAV has a certain degree of natural remission, it varies widely among individuals. Some patients can suffer from severe renal involvement and even progress to end-stage renal disease. Its pathogenesis is complex and has not been fully elucidated. The formation of galactose-deficient IgA1 (Gd-IgA1) and related immune complexes plays a vital role in promoting the occurrence and development of IgAV nephritis. In addition, neutrophil activation is stimulated through the binding of IgA to the Fc alpha receptor I expressed on its surface, resulting in systemic vascular inflammation and tissue damage. Starting from the epidemiological characteristics, this article will review the role of immunological factors such as Gd-IgA1, autoantibodies, circulating immune complexes, complement system, cellular immunization, and the contributions of environmental and genetic factors in the pathogenesis of IgAV, and conclude with the major biomarkers for IgAV.

Guben Tongluo Formula Protects LPS-induced Damage in Lamina Propria B Lymphocytes Through TLR4/MyD88/NF-κB Pathway

OBJECTIVE

The main pathological feature of immunoglobulin A nephropathy (IgAN), an autoimmune kidney disease, is the deposition of IgA immune complexes, accompanied by mesangial cell proliferation and elevated urine protein. The Guben Tongluo formula (GTF) is a traditional Chinese medicine prescription, which has predominant protective effects on IgAN. However, the therapeutic mechanism of the GTF in IgAN remains elusive. The present study aimed to determine the effects of GTF in treating IgAN via regulating the TLR4/MyD88/NF-κB pathway.

METHODS

In the present study, lamina propria B lymphocytes were treated with different concentrations of lipopolysaccharide (LPS) (0, 1, 5, 10 and 20 ng/mL). Flow cytometry was used to define positive CD86+CD19+ cells. CCK-8 assay was used to examine cell proliferation. RNAi was used to induce TLR4 silencing. qRT-PCR and Western blotting were used to determine gene expression.

RESULTS

It was found that the LPS dose-dependently increased the content of IgA and galactose-deficient IgA1 (Gd-IgA), the levels of TLR4, Cosmc, MyD88 and phosphorylated (p)-NF-κB, and the ratio of CD86+CD19+ and IgA-producing B cells. However, the TLR4 knockdown reversed the role of LPS. This suggests that TLR4 mediates the effects of LPS on lamina propria B lymphocytes. Furthermore, the GTF could dose-dependently counteract the effects of LPS and TLR4 overexpression on lamina propria B lymphocytes through the TLR4/MyD88/NF-κB pathway.

CONCLUSION

Collectively, these results demonstrate that the GTF can regulate the TLR4/MyD88/NF-κB pathway to treat IgAN model lamina propria B lymphocytes stimulated by LPS.

Advances in IgA glycosylation and its correlation with diseases

Immunoglobulin A (IgA) is the most abundant immunoglobulin synthesized in the human body. It has the highest concentration in the mucosa and is second only to IgG in serum. IgA plays an important role in mucosal immunity, and is the predominant antibody used to protect the mucosal surface from pathogens invasion and to maintain the homeostasis of intestinal flora. Moreover, The binding IgA to the FcαRI (Fc alpha Receptor I) in soluble or aggregated form can mediate anti- or pro- inflammatory responses, respectively. IgA is also known as one of the most heavily glycosylated antibodies among human immunoglobulins. The glycosylation of IgA has been shown to have a significant effect on its immune function. Variation in the glycoform of IgA is often the main characteration of autoimmune diseases such as IgA nephropathy (IgAN), IgA vasculitis (IgAV), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). However, compared with the confirmed glycosylation function of IgG, the pathogenic mechanism of IgA glycosylation involved in related diseases is still unclear. This paper mainly summarizes the recent reports on IgA’s glycan structure, its function, its relationship with the occurrence and development of diseases, and the potential application of glycoengineered IgA in clinical antibody therapeutics, in order to provide a potential reference for future research in this field.

Phosphatase control of cytokine-mediated overproduction of galactose-deficient IgA1, the main autoantigen in IgA nephropathy

IgA nephropathy (IgAN) is an autoimmune disease characterized by the deposition of galactose-deficient IgA1 (Gd-IgA1)-containing immune complexes in the kidneys. Elevated serum levels of Gd-IgA1, the main autoantigen in IgAN, are associated with mucosal infections and poor renal outcome in IgAN patients, but little is known about the activation of IgA1-secreting cells overproducing this autoantigen. We found that in peripheral blood mononuclear cells (PBMCs), cytokine stimulation elevated Gd-IgA1 production in B cells from IgAN patients but not in those from healthy controls (p < 0.01). These results were replicated in immortalized B cells derived from PBMCs of IgAN patients and healthy controls. Using single-cell transcriptomics, we identified subsets of IgA1-secreting cells from IgAN patients, but not from healthy controls, with decreased expression of C1GALT1 in response to cytokine stimulation. The C1GALT1-encoded glycosyltransferase is responsible for addition of galactose to IgA1 O-glycans, and its reduced activity is associated with elevated serum levels of Gd-IgA1. These newly identified subsets of IgA1-secreting cells with reduced C1GALT1 expression exhibited reduced expression of several genes related to cytokine-mediated signaling, including those encoding phosphatases, such as SOCS1. siRNA knock-down of SOCS1, and the related SOCS3, increased Gd-IgA1 production in cells derived from PBMCs of healthy controls, indicating a role of these regulators in abnormal cytokine signaling and Gd-IgA1 overproduction. These results revealed that specific subsets of IgA1-secreting cells may be responsible for autoantigen production in IgAN due to abnormal regulation of cytokine-mediated signaling, a process that may occur in inflammatory responses in IgAN patients.

IL-6 and its role in IgA nephropathy development

IL-6 is considered one of the well characterized cytokines exhibiting homeostatic, pro- and anti-inflammatory activities, depending on the receptor variant and the induced intracellular cis- or trans-signaling responses. IL-6-activated pathways are involved in the regulation of cell proliferation, survival, differentiation, and cell metabolism changes. Deviations in IL-6 levels or abnormal response to IL-6 signaling are associated with several autoimmune diseases including IgA nephropathy (IgAN), one of most frequent primary glomerulonephritis worldwide. IgAN is associated with increased plasma concentration of IL-6 and increased plasma concentration of aberrantly galactosylated IgA1 immunoglobulin (Gd-IgA1). Gd-IgA1 is specifically recognized by autoantibodies, leading to the formation of circulating immune complexes (CIC) with nephritogenic potential, since CIC deposited in the glomerular mesangium induce mesangial cells proliferation and glomerular injury. Infection of the upper respiratory or digestive tract enhances IL-6 production and in IgAN patients is often followed by the macroscopic hematuria. This review recapitulates general aspects of IL-6 signaling and summarizes experimental evidences about IL-6 involvement in the etiopathogenesis of IgA nephropathy through the production of Gd-IgA1 and regulation of mesangial cell proliferation.

Cytokines and Production of Aberrantly O-Glycosylated IgA1, the Main Autoantigen in IgA Nephropathy

Immunoglobulin A (IgA) nephropathy is the most common primary glomerulonephritis worldwide, with no disease-specific treatment and up to 40% of patients progressing to kidney failure. IgA nephropathy (IgAN), characterized by IgA1-containing immunodeposits in the glomeruli, is considered to be an autoimmune disease in which the kidneys are injured as innocent bystanders. Glomerular immunodeposits are thought to originate from the circulating immune complexes that contain aberrantly O-glycosylated IgA1, the main autoantigen in IgAN, bound by IgG autoantibodies. A common clinical manifestation associated with IgAN includes synpharyngitic hematuria at disease onset or during disease activity. This observation suggests a connection of disease pathogenesis with an activated mucosal immune system of the upper-respiratory and/or gastrointestinal tract and IgA1 glycosylation. In fact, some cytokines can enhance production of aberrantly O-glycosylated IgA1. This process involves abnormal cytokine signaling in IgA1-producing cells from patients with IgAN. In this article, we present our view of pathogenesis of IgAN and review how some cytokines can contribute to the disease process by enhancing production of aberrantly glycosylated IgA1. We also review current clinical trials of IgAN based on cytokine-targeting therapeutic approaches.

IgA vasculitis with nephritis: update of pathogenesis with clinical implications

IgA vasculitis with nephritis (IgAVN) shares many pathogenetic features with IgA nephropathy (IgAN). The purpose of this review is to describe our current understanding of the pathogenesis of pediatric IgAVN, particularly as it relates to the four-hit hypothesis for IgAN. These individual steps, i.e., hits, in the pathogenesis of IgAN are (1) elevated production of IgA1 glycoforms with some O-glycans deficient in galactose (galactose-deficient IgA1; Gd-IgA1), (2) generation of circulating IgG autoantibodies specific for Gd-IgA1, (3) formation of pathogenic circulating Gd-IgA1-containing immune complexes, and (4) kidney deposition of the Gd-IgA1-IgG immune complexes from the circulation and induction of glomerular injury. Evidence supporting the four-hit hypothesis in the pathogenesis of pediatric IgAVN is detailed. The genetics, pediatric outcomes, and kidney histopathologic features and the impact of these findings on future treatment and potential biomarkers are discussed. In summary, the evidence points to the critical roles of Gd-IgA1-IgG immune complexes and complement activation in the pathogenesis of IgAVN. Future studies are needed to characterize the features of the immune and autoimmune responses that enable progression of IgA vasculitis to IgAVN.

Tofacitinib combined with leflunomide for treatment of psoriatic arthritis with IgA nephropathy: a case report with literature review

Psoriasis is a systemic inflammatory disease that is associated with increased risk of several diseases, such as psoriatic arthritis (PsA), inflammatory bowel disease, and cardiovascular diseases. About 20 to 30% patients with psoriasis subsequently develop PsA. IgA nephropathy is the most common primary glomerular disease world-wide. Psoriasis and IgA nephropathy appear to be associated, but the mechanism underlying this connection is unclear. Tofacitinib and leflunomide are common treatments for psoriatic arthritis. We administered tofacitinib combined with leflunomide to a 38-year-old female patient who presented with PsA and IgA nephropathy. After treatment, she experienced significant reductions in the psoriatic lesions, pain in the right knee joint, and proteinuria. Administration of tofacitinib combined with leflunomide for treatment of a patient who had PsA complicated with IgA nephropathy led to significant resolution of the symptoms of both conditions. These results suggest similarities in the pathogenesis of PsA and IgA nephropathy and a possible new treatment for IgA nephropathy.

Galactose-Deficient IgA1 B cells in the Circulation of IgA Nephropathy Patients Carry Preferentially Lambda Light Chains and Mucosal Homing Receptors

Background: Immunoglobulin A nephropathy (IgAN) primary glomerulonephritis is characterized by the deposition of circulating immune complexes (CIC) composed of polymeric (p)IgA1 molecules with altered O-glycans (Gd-IgA1) and anti-glycan antibodies in the kidney mesangium. The mesangial IgA deposits and serum IgA1 contain predominantly lambda (λ) light (L) chain, but the nature and origin of such IgA remains enigmatic Methods: We analyzed λ L chain expression in peripheral blood B cells of 30 IgAN patients, 30 healthy controls (HC), and 18 membranous nephropathy patients selected as disease controls (Non-IgAN). Results: In comparison to HC and Non-IgAN, in peripheral blood surface/membrane bound (mb)-Gd-IgA1⁺ cells from IgAN patients express predominantly λ L chain. In contrast, total mb-IgA⁺, mb-IgG⁺, and mb-IgM⁺ cells were preferentially positive for kappa (κ) L chain, in all analyzed groups. Although minor in comparison to κ L chain, λ L chain subsets of mb-IgG⁺, mb-IgM,⁺ and mb-IgA⁺ cells were significantly enriched in IgAN in comparison to Non-IgAN and/or HC. In contrast to HC, the peripheral blood of IgAN patients was enriched for λ⁺ mb-Gd-IgA1,⁺ CCR10,⁺ and CCR9⁺ cells, which preferentially home to the upper respiratory and digestive tract, respectively. Furthermore, we observed that mb-Gd-IgA1⁺ cell populations comprise more CD138⁺ cells and plasmablasts (CD38⁺) in comparison to total mb-IgA⁺ cells. Conclusions: Peripheral blood of IgAN patients is enriched for migratory λ⁺ mb-GdIgA1⁺ B cells, with the potential to home to mucosal sites where Gd-IgA1 could be produced during local respiratory or digestive tract infections.

NSC828779 Alleviates Renal Tubulointerstitial Lesions Involving Interleukin-36 Signaling in Mice

Renal tubulointerstitial lesions (TILs), a common pathologic hallmark of chronic kidney disease that evolves to end-stage renal disease, is characterized by progressive inflammation and pronounced fibrosis of the kidney. However, current therapeutic approaches to treat these lesions remain largely ineffectual. Previously, we demonstrated that elevated IL-36α levels in human renal tissue and urine are implicated in impaired renal function, and IL-36 signaling enhances activation of NLRP3 inflammasome in a mouse model of TILs. Recently, we synthesized NSC828779, a salicylanilide derivative (protected by U.S. patents with US 8975255 B2 and US 9162993 B2), which inhibits activation of NF-κB signaling with high immunomodulatory potency and low IC50, and we hypothesized that it would be a potential drug candidate for renal TILs. The current study validated the therapeutic effects of NSC828779 on TILs using a mouse model of unilateral ureteral obstruction (UUO) and relevant cell models, including renal tubular epithelial cells under mechanically induced constant pressure. Treatment with NSC828779 improved renal lesions, as demonstrated by dramatically reduced severity of renal inflammation and fibrosis and decreased urinary cytokine levels in UUO mice. This small molecule specifically inhibits the IL-36α/NLRP3 inflammasome pathway. Based on these results, the beneficial outcome represents synergistic suppression of both the IL-36α-activated MAPK/NLRP3 inflammasome and STAT3- and Smad2/3-dependent fibrogenic signaling. NSC828779 appears justified as a new drug candidate to treat renal progressive inflammation and fibrosis.

Mesangioproliferative Kidney Diseases and Platelet-Derived Growth Factor-Mediated AXL Phosphorylation

RATIONALE & OBJECTIVE

Immunoglobulin A nephropathy (IgAN) is a common glomerular disease, with mesangial cell proliferation as a major feature. There is no disease-specific treatment. Platelet-derived growth factor (PDGF) contributes to the pathogenesis of IgAN. To better understand its pathogenic mechanisms, we assessed PDGF-mediated AXL phosphorylation in human mesangial cells and kidney tissue biopsy specimens.

STUDY DESIGN

Immunostaining using human kidney biopsy specimens and in vitro studies using primary human mesangial cells.

SETTING & PARTICIPANTS

Phosphorylation of AXL was assessed in cultured mesangial cells and 10 kidney-biopsy specimens from 5 patients with IgAN, 3 with minimal change disease, 1 with membranous nephropathy, and 1 with mesangioproliferative glomerulonephritis (GN).

PREDICTOR

Glomerular staining for phospho-AXL in kidney biopsy specimens of patients with mesangioproliferative diseases.

OUTCOMES

Phosphorylated AXL detected in biopsy tissues of patients with IgAN and mesangioproliferative GN and in cultured mesangial cells stimulated with PDGF.

ANALYTIC APPROACH

t test, Mann-Whitney test, and analysis of variance were used to assess the significance of mesangial cell proliferative changes.

RESULTS

Immunohistochemical staining revealed enhanced phosphorylation of glomerular AXL in IgAN and mesangioproliferative GN, but not in minimal change disease and membranous nephropathy. Confocal-microscopy immunofluorescence analysis indicated that mesangial cells rather than endothelial cells or podocytes expressed phospho-AXL. Kinomic profiling of primary mesangial cells treated with PDGF revealed activation of several protein-tyrosine kinases, including AXL. Immunoprecipitation experiments indicated association of AXL and PDGF receptor proteins. An AXL-specific inhibitor (bemcentinib) partially blocked PDGF-induced cellular proliferation and reduced phosphorylation of AXL and PDGF receptor and the downstream signals (AKT1 and ERK1/2).

LIMITATIONS

Small number of kidney biopsy specimens to correlate the activation of AXL with disease severity.

CONCLUSIONS

PDGF-mediated signaling in mesangial cells involves transactivation of AXL. Finding appropriate inhibitors to block PDGF-mediated transactivation of AXL may provide new therapeutic options for mesangioproliferative kidney diseases such as IgAN.

Pathogenesis of IgA Nephropathy: Current Understanding and Implications for Development of Disease-Specific Treatment

IgA nephropathy, initially described in 1968 as a kidney disease with glomerular “intercapillary deposits of IgA-IgG”, has no disease-specific treatment and is a common cause of kidney failure. Clinical observations and laboratory analyses suggest that IgA nephropathy is an autoimmune disease wherein the kidneys are damaged as innocent bystanders due to deposition of IgA1-IgG immune complexes from the circulation. A multi-hit hypothesis for the pathogenesis of IgA nephropathy describes four sequential steps in disease development. Specifically, patients with IgA nephropathy have elevated circulating levels of IgA1 with some O-glycans deficient in galactose (galactose-deficient IgA1) and these IgA1 glycoforms are recognized as autoantigens by unique IgG autoantibodies, resulting in formation of circulating immune complexes, some of which deposit in glomeruli and activate mesangial cells to induce kidney injury. This proposed mechanism is supported by observations that (i) glomerular immunodeposits in patients with IgA nephropathy are enriched for galactose-deficient IgA1 glycoforms and the corresponding IgG autoantibodies; (ii) circulatory levels of galactose-deficient IgA1 and IgG autoantibodies predict disease progression; and (iii) pathogenic potential of galactose-deficient IgA1 and IgG autoantibodies was demonstrated in vivo. Thus, a better understanding of the structure–function of these immunoglobulins as autoantibodies and autoantigens will enable development of disease-specific treatments.

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.

Targeting Canonical and Non-Canonical STAT Signaling Pathways in Renal Diseases

Signal transducer and activator of transcription (STAT) plays an essential role in the inflammatory reaction and immune response of numerous renal diseases. STATs can transmit the signals of cytokines, chemokines, and growth factors from the cell membrane to the nucleus. In the canonical STAT signaling pathways, upon binding with their cognate receptors, cytokines lead to a caspase of Janus kinases (JAKs) and STATs tyrosine phosphorylation and activation. Besides receptor-associated tyrosine kinases JAKs, receptors with intrinsic tyrosine kinase activities, G-protein coupled receptors, and non-receptor tyrosine kinases can also activate STATs through tyrosine phosphorylation or, alternatively, other post-translational modifications. Activated STATs translocate into the nucleus and mediate the transcription of specific genes, thus mediating the progression of various renal diseases. Non-canonical STAT pathways consist of preassembled receptor complexes, preformed STAT dimers, unphosphorylated STATs (U-STATs), and non-canonical functions including mitochondria modulation, microtubule regulation and heterochromatin stabilization. Most studies targeting STAT signaling pathways have focused on canonical pathways, but research extending into non-canonical STAT pathways would provide novel strategies for treating renal diseases. In this review, we will introduce both canonical and non-canonical STAT pathways and their roles in a variety of renal diseases.

A mouse model of prenatal exposure to Interleukin-6 to study the developmental origin of health and disease

Systemic inflammation in pregnant obese women is associated with 1.5- to 2-fold increase in serum Interleukin-6 (IL-6) and newborns with lower kidney/body weight ratio but the role of IL-6 in increased susceptibility to chronic kidney (CKD) in adult progeny is not known. Since IL-6 crosses the placental barrier, we administered recombinant IL-6 (10 pg/g) to pregnant mice starting at mid-gestation yielded newborns with lower body (p < 0.001) and kidney (p < 0.001) weights. Histomorphometry indicated decreased nephrogenic zone width (p = 0.039) with increased numbers of mature glomeruli (p = 0.002) and pre-tubular aggregates (p = 0.041). Accelerated maturation in IL-6 newborns was suggested by early expression of podocyte-specific protein podocin in glomeruli, increased 5-methyl-cytosine (LC–MS analysis for CpG DNA methylation) and altered expression of certain genes of cell-cycle and apoptosis (RT-qPCR array-analysis). Western blotting showed upregulated pJAK2/pSTAT3. Thus, treating dams with IL-6 as a surrogate provides newborns to study effects of maternal systemic inflammation on future susceptibility to CKD in adulthood.

Alternative Complement Pathway Is Activated and Associated with Galactose-Deficient IgA1 Antibody in IgA Nephropathy Patients

Background

Galactose-deficient IgA₁ (Gd-IgA₁) and alternative complement pathway activation are considered to be involved in the pathogenesis of IgA nephropathy (IgAN). Nevertheless, the relationships between alternative pathway activation and disease activity or Gd-IgA₁ level remains unclear.

Methods

Ninety-eight biopsy-diagnosed IgAN, twenty-five primary focal segmental sclerosis (FSGS) patients and forty-two healthy individuals were recruited in this study. Among them, fifty IgAN patients received immunosuppression. Follow-up blood samples at 1 and 3~6 months after immunosuppression were collected. Plasma levels of complement C5a, factor Ba and Gd-IgA₁ were measured and analyzed. Immunostaining for complement was performed in twenty-five IgAN and FSGS patients.

Results

At baseline, IgAN patients had higher levels of plasma C5a, factor Ba and Gd-IgA₁ than control subjects. Gd-IgA₁ levels positively correlated with plasma C5a and factor Ba. In addition, levels of factor Ba and Gd-IgA₁ were positively associated with proteinuria and negatively associated with renal function. Immunostaining revealed positive staining for factor Bb and C3c in glomeruli in IgAN patients, but not in FSGS patients. At baseline, patients receiving immunosuppression had more severe proteinuria and higher factor Ba. After 6 months, eGFR declined and proteinuria persisted in patients without immunosuppression. In contrast, patients who received immunosuppression exhibited decreased plasma levels of C5a, factor Ba, and Gd-IgA₁ as early as 1 month after treatment. Proteinuria decreased and renal function also remained stable 6 months after immunosuppression.

Conclusions

Our results indicate a close relationship between alternative complement pathway activation, Gd-IgA₁ concentration and clinical severity of IgAN. Level of complement factor B may be a potential marker for disease activity and therapeutic target in IgAN patients.

Mesangial C3 deposition and serum C3 levels predict renal outcome in IgA nephropathy

BACKGROUND

Complement activation plays an important role in the pathogenesis of IgA nephropathy (IgAN). We aimed to evaluate the relationship between mesangial C3 deposition and histologic lesions and to investigate the role of mesangial C3 deposition and serum C3 reduction in predicting renal outcome in IgAN children.

METHODS

We performed a retrospective cohort study in children with biopsy-proven IgAN. Mesangial C3 deposition (< 2+ vs. ≥ 2+) was detected by the immunofluorescence. Histopathologic kidney grades were determined by the Oxford classification. A decreased serum C3 concentration (hypoC3) was defined when C3 < 90 mg/dl. The endpoint was composite kidney outcome with either a 30% decline in glomerular filtration rates from baseline or kidney failure during the follow-up period.

RESULTS

A total of 98 children were analyzed. Mesangial hypercellularity (M) was an independent factor associated with mesangial C3 deposition (HR 3.267; 95% CI 1.028-10.389; P = 0.045). After a median follow-up period of 25 months (interquartile range 18-36 months), 6 (6.1%) children reached the endpoint. Compared with other children, a significantly higher proportion of children with composite kidney outcomes had mesangial C3 deposition ≥ 2+ and hypoC3 (3.4% versus 27.3%, P = 0.002). After adjustment for clinicopathologic risk factors, mesangial C3 deposition ≥ 2+ and hypoC3 were associated with renal outcome (HR 9.772; 95% CI 1.264-75.518; P = 0.029).

CONCLUSION

Mesangial C3 deposition was associated with M in IgAN. Mesangial C3 deposition and hypoC3 were risk factors for renal outcome in children with IgAN.

Exome Chip Analyses and Genetic Risk for IgA Nephropathy among Han Chinese

BACKGROUND AND OBJECTIVES

IgA nephropathy is the most common form of primary GN worldwide. The evidence of geographic and ethnic differences, as well as familial aggregation of the disease, supports a strong genetic contribution to IgA nephropathy. Evidence for genetic factors in IgA nephropathy comes also from genome-wide association patient-control studies. However, few studies have systematically evaluated the contribution of coding variation in IgA nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a two-stage exome chip-based association study in 13,242 samples, including 3363 patients with IgA nephropathy and 9879 healthy controls of Han Chinese ancestry. Common variant functional annotation, gene-based low-frequency variants analysis, differential mRNA expression, and gene network integration were also explored.

RESULTS

We identified three non-HLA gene regions (FBXL21, CCR6, and STAT3) and one HLA gene region (GABBR1) with suggestive significance (Pmeta <5×10-5) in single-variant associations. These novel non-HLA variants were annotated as expression-associated single-nucleotide polymorphisms and were located in enhancer regions enriched in histone marks H3K4me1 in primary B cells. Gene-based low-frequency variants analysis suggests CFB as another potential susceptibility gene. Further combined expression and network integration suggested that the five novel susceptibility genes, TGFBI, CCR6, STAT3, GABBR1, and CFB, were involved in IgA nephropathy.

CONCLUSIONS

Five novel gene regions with suggestive significance for IgA nephropathy were identified and shed new light for further mechanism investigation.

Assigning immunoglobulin class from single-cell transcriptomes in IgA1-secreting versus membrane subpopulations

IgA nephropathy (IgAN) is an autoimmune disease characterized by renal glomerular immunodeposits enriched for galactose-deficient IgA1 (Gd-IgA1; autoantigen) with the corresponding IgG autoantibodies. Despite the known contribution of Gd-IgA1 to IgAN, little is known concerning IgA1-secreting subpopulations responsible for autoantigen production. The goal of this study is to identify IgA1-secreting and membrane subpopulations from single-cell transcriptomic analysis. We developed a novel single-cell analytics workflow to discern cells expressing IgA1 secreted isoform or membrane-bound isoform. Multiple approaches were compared to assess immunoglobulin-isotype identity in single cells, and multiple immunoglobulin heavy-chain genes expressed in the same cells were found. To better identify specific immunoglobulin heavy-chain transcripts, we merged a software platform called Alteryx with the existing single-cell R toolkit program Seurat. This process allowed for improved calls on IgA1-secreting subpopulations based on secreting versus membrane splice-variant expression levels.

Immunoglobulin A Glycosylation and Its Role in Disease

Human IgA is comprised of two subclasses, IgA1 and IgA2. Monomeric IgA (mIgA), polymeric IgA (pIgA), and secretory IgA (SIgA) are the main molecular forms of IgA. The production of IgA rivals all other immunoglobulin isotypes. The large quantities of IgA reflect the fundamental roles it plays in immune defense, protecting vulnerable mucosal surfaces against invading pathogens. SIgA dominates mucosal surfaces, whereas IgA in circulation is predominately monomeric. All forms of IgA are glycosylated, and the glycans significantly influence its various roles, including antigen binding and the antibody effector functions, mediated by the Fab and Fc portions, respectively. In contrast to its protective role, the aberrant glycosylation of IgA1 has been implicated in the pathogenesis of autoimmune diseases, such as IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAVN). Furthermore, detailed characterization of IgA glycosylation, including its diverse range of heterogeneity, is of emerging interest. We provide an overview of the glycosylation observed for each subclass and molecular form of IgA as well as the range of heterogeneity for each site of glycosylation. In many ways, the role of IgA glycosylation is in its early stages of being elucidated. This chapter provides an overview of the current knowledge and research directions.

Compound K inhibits priming and mitochondria-associated activating signals of NLRP3 inflammasome in renal tubulointerstitial lesions

BACKGROUND

Renal tubulointerstitial lesions (TILs), a key pathological hallmark for chronic kidney disease to progress to end-stage renal disease, feature renal tubular atrophy, interstitial mononuclear leukocyte infiltration and fibrosis in the kidney. Our study tested the renoprotective and therapeutic effects of compound K (CK), as described in our US patent (US7932057B2), on renal TILs using a mouse unilateral ureteral obstruction (UUO) model.

METHODS

Renal pathology was performed and renal draining lymph nodes were subjected to flow cytometry analysis. Mechanism-based experiments included the analysis of mitochondrial dysfunction, a model of tubular epithelial cells (TECs) under mechanically induced constant pressure (MICP) and tandem mass tags (TMT)-based proteomics analysis.

RESULTS

Administration of CK ameliorated renal TILs by reducing urine levels of proinflammatory cytokines, and preventing mononuclear leukocyte infiltration and fibrosis in the kidney. The beneficial effects clearly correlated with its inhibition of: (i) NF-κB-associated priming and the mitochondria-associated activating signals of the NLRP3 inflammasome; (ii) STAT3 signalling, which in part prevents NLRP3 inflammasome activation; and (iii) the TGF-β-dependent Smad2/Smad3 fibrotic pathway, in renal tissues, renal TECs under MICP and/or activated macrophages, the latter as a major inflammatory player contributing to renal TILs. Meanwhile, TMT-based proteomics analysis revealed downregulated renal NLRP3 inflammasome activation-associated signalling pathways in CK-treated UUO mice.

CONCLUSIONS

The present study, for the first time, presents the potent renoprotective and therapeutic effects of CK on renal TILs by targeting the NLRP3 inflammasome and STAT3 signalling.

Tonsillar immunology in IgA nephropathy

As one of the most common types of primary glomerulonephritis, IgA nephropathy (IgAN) is often characterized by the immunoprecipitation of IgA1 in mesangial area. In clinical terms, IgA nephropathy can be treated with tonsillectomy or conservative treatment, basing on modern immunology knowledge in which the mucosa immune system (MIS), especially the widely distributed mucosa-associated lymphoid tissue (MALT) is focused accordingly In terms of basic research, IgAN has been shown correlated with multiple factors, including serum Gd-IgA1 level, IgA-IgG immunity, tonsil-associated bacteria,GADD34, CX3CR1, FOXP3 and the expression of other related intrinsic immune antibody. Therefore, it is reasonable there could be mutual correlation among IgAN-associated factors. The purpose of this study is to review the new progress on the treatment and prevention of IgAN diseases and related mechanisms of IgAN tonsils, which will be of great significance for the therapy of IgAN patients.

JAK-STAT Activity in Peripheral Blood Cells and Kidney Tissue in IgA Nephropathy

BACKGROUND AND OBJECTIVES

IgA nephropathy is the most common primary glomerular disease in the world. Marked by mesangial inflammation and proliferation, it generally leads to progressive kidney fibrosis. As the Janus kinase signal transducer and activator of transcription pathway has been implicated as an important mediator of diabetic kidney disease and FSGS, detailed investigation of this pathway in IgA nephropathy was undertaken to establish the basis for targeting this pathway across glomerular diseases.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Well characterized patients with IgA nephropathy and controls were studied, allowing us to compare 77 patients with biopsy-proven IgA nephropathy with 45 healthy subjects. STAT phosphorylation was assessed in peripheral blood monocytes (PBMCs) by phosphoflow before and after cytokine stimulation. Kidney Janus kinase signal transducer and activator of transcription activity was studied by immunofluorescence and by transcriptomic studies. An STAT1 activity score was established using downstream transcriptional targets of pSTAT1 and associated with disease and clinical outcomes.

RESULTS

We found PBMCs to have upregulated pSTAT production at baseline in patients with IgA nephropathy with a limited reserve to respond to cytokine stimulation compared with controls. Increased staining in glomerular mesangium and endothelium was seen for Jak-2 and pSTAT1 and in the tubulointerstitial for JAK2, pSTAT1, and pSTAT3. Activation of the Janus kinase signal transducer and activator of transcription pathway was further supported by increased pSTAT1 and pSTAT3 scores in glomerular and tubulointerstitial sections of the kidney (glomerular activation Z scores: 7.1 and 4.5, respectively; P values: <0.001 and <0.001, respectively). Clinically, phosphoflow results associated with proteinuria and kidney function, and STAT1 activation associated with proteinuria but was not associated with progression.

CONCLUSIONS

Janus kinase signal transducer and activator of transcription signaling was activated in patients with IgA nephropathy compared with controls. There were altered responses in peripheral immune cells and increased message and activated proteins in the kidney. These changes variably related to proteinuria and kidney function.

Leukemia Inhibitory Factor Signaling Enhances Production of Galactose-Deficient IgA1 in IgA Nephropathy

Objectives

IgA nephropathy (IgAN) is thought to involve an autoimmune process wherein galactose-deficient IgA1 (Gd-IgA1), recognized as autoantigen by autoantibodies, forms pathogenic immune complexes. Mounting evidence has implicated abnormal activation of some protein-tyrosine kinases (PTKs) in IgAN. Furthermore, genome-wide association studies (GWAS) of IgAN provided insight into disease pathobiology and genetics. A GWAS locus on chromosome 22q12 contains genes encoding leukemia inhibitory factor (LIF) and oncostatin M, interleukin (IL)-6-related cytokines implicated in mucosal immunity and inflammation. We have previously shown that IL-6 mediates overproduction of Gd-IgA1 through aberrant STAT3 activation. Here, we show that LIF enhanced production of Gd-IgA1 in IgA1-secreting cells of patients with IgAN and provide initial analyses of LIF signaling.

Methods

We characterized LIF signaling that is involved in the overproduction of Gd-IgA1, using IgA1-secreting cell lines derived from peripheral blood of patients with IgAN and healthy controls (HC). We used global PTK activity profiling, immunoblotting, lectin ELISA, and siRNA knock-down.

Results

LIF stimulation did not significantly affect production of total IgA1 in IgA1-secreting cells from patients with IgAN or HC. However, LIF increased production of Gd-IgA1, but only in the cells from patients with IgAN. LIF stimulation enhanced phosphorylation of STAT1 in IgA1-secreting cells from patients with IgAN to a higher degree than in the cells from HC. siRNA knock-down of STAT1 blocked LIF-mediated overproduction of Gd-IgA1. Unexpectedly, this abnormal phosphorylation of STAT1 in IgA1-secreting cells from patients with IgAN was not mediated by JAK, but rather involved activation of Src-family PTKs (SFKs).

Conclusion

Abnormal LIF/STAT1 signaling represents another pathway potentially leading to overproduction of Gd-IgA1 in IgAN, providing possible explanation for the phenotype associated with chromosome 22q12 GWAS locus. Abnormal LIF/STAT1 signaling and the associated SFKs may represent potential diagnostic and/or therapeutic targets in IgAN.

Towards a personalized treatment for IgA nephropathy considering pathology and pathogenesis

The search of personalized treatment for a subject with immunoglobulin A nephropathy (IgAN) is appealing since the individual long-term outcome is highly variable in spite of common mild clinical signs such as microscopic haematuria, moderate proteinuria and slightly reduced glomerular filtration rate (GFR). The only risk factor considered by the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines to target corticosteroid/immunosuppressive treatment in IgAN is proteinuria persistently >1 g/day despite 3-6 months of optimized supportive care. However, proteinuria in IgAN may result not only from active lesions but also from sclerotic glomerular lesions with hyperfiltration and tubular damage. The Oxford classification study and subsequent investigations have indicated the value of pathology risk factors for progression independent of proteinuria, blood pressure and GFR at renal biopsy. Meanwhile new studies have provided an improved understanding of the pathogenetic mechanisms operating in IgAN leading to kidney tissue damage. These findings suggest the possibility for the individual patient with IgAN of using a pathology-based therapy, taking into consideration the pathogenetic mechanisms operating at the time of renal biopsy. This review is largely opinion based, since evidence-based reports are mostly incomplete: hypotheses are suggested based on interesting published investigations. The clinician faces a daily challenge: find the best management for his/her patient, modelling a rather general indication as obtained by the guidelines to the needs of the patient. This review offers some considerations that hopefully will be useful in this difficult choice.

C-X-C motif chemokine receptor 4 aggravates renal fibrosis through activating JAK/STAT/GSK3β/β-catenin pathway

Chronic kidney disease (CKD) has a high prevalence worldwide. Renal fibrosis is the common pathological feature in various types of CKD. However, the underlying mechanisms are not determined. Here, we adopted different CKD mouse models and cultured human proximal tubular cell line (HKC-8) to examine the expression of C-X-C motif chemokine receptor 4 (CXCR4) and β-catenin signalling, as well as their relationship in renal fibrosis. In CKD mice and humans with a variety of nephropathies, CXCR4 was dramatically up-regulated in tubules, with a concomitant activation of β-catenin. CXCR4 expression level was positively correlated with the expression of β-catenin target MMP-7. AMD3100, a CXCR4 receptor blocker, and gene knockdown of CXCR4 significantly inhibited the activation of JAK/STAT and β-catenin signalling, protected against tubular injury and renal fibrosis. CXCR4-induced renal fibrosis was inhibited by treatment with ICG-001, an inhibitor of β-catenin signalling. In HKC-8 cells, overexpression of CXCR4 induced activation of β-catenin and deteriorated cell injury. These effects were inhibited by ICG-001. Stromal cell-derived factor (SDF)-1α, the ligand of CXCR4, stimulated the activation of JAK2/STAT3 and JAK3/STAT6 signalling in HKC-8 cells. Overexpression of STAT3 or STAT6 decreased the abundance of GSK3β mRNA. Silencing of STAT3 or STAT6 significantly blocked SDF-1α-induced activation of β-catenin and fibrotic lesions. These results uncover a novel mechanistic linkage between CXCR4 and β-catenin activation in renal fibrosis in association with JAK/STAT/GSK3β pathway. Our studies also suggest that targeted inhibition of CXCR4 may provide better therapeutic effects on renal fibrosis by inhibiting multiple downstream signalling cascades.

The upregulation of miR-98-5p affects the glycosylation of IgA1 through cytokines in IgA nephropathy

OBJECTIVE

Increases in galactose-deficient IgA1 (Gd-IgA1) play a crucial role in the pathogenesis of IgA nephropathy (IgAN), and several recent experiments have shown that microRNAs (miRNAs) are involved in regulating the development and physiological function of the kidney. The aims of this study were to identify miRNAs that can affect the pathogenesis of IgAN and reveal the underlying regulatory mechanism of IgA1 glycosylation in peripheral blood.

METHODS

The differentially expressed miRNAs in peripheral blood mononuclear cells (PBMCs) between IgAN patients and healthy controls were screened by high-throughput sequencing, and the targets of these miRNAs were predicted and verified by dual-luciferase reporter assays. We also explored the miRNA regulation of Gd-IgA1 through the transfection of miRNA mimics and related plasmids.

RESULTS

The high-throughput sequencing results showed that miR-98-5p was more highly expressed in the PBMCs of IgAN patients compared with healthy controls, and the luciferase reporter gene system confirmed that miR-98-5p might target chemokine ligand 3 (CCL3). The transfection of si-CCL3 confirmed that a decrease in CCL3 can affect the expression of interleukin-6 (IL-6) and C1GALT1. The overexpression of miR-98-5p in PBMCs through the transfection of miR-98-5p mimic reduced the CCL3 and C1GALT1 levels and increased the IL-6 levels, and these changes in PBMCs were attenuated by cotransfection with the CCL3 plasmid.

CONCLUSION

The results showed that in PBMCs, miR-98-5p can target CCL3 to decrease its expression and thereby increase the IL-6 levels, and the resulting increase in IL-6 can decrease C1GALT1 expression. Therefore, miR-98-5p might be involved in the development of IgAN.

Comprehensive analysis of aberrantly expressed profiles of mRNA and its relationship with serum galactose-deficient IgA1 level in IgA nephropathy

Background

Immunoglobulin A nephropathy (IgAN) is the leading cause of end-stage kidney disease. Previous mRNA microarray profiling studies of IgAN revealed inconsistent data. We sought to identify the aberrantly expressed genes and biological pathways by integrating IgAN gene expression datasets in blood cells and performing systematically experimental validation. We also explored the relationship between target genes and galactose-deficient IgA1 (Gd-IgA1) in IgAN.

Methods

We retrieved Gene Expression Omnibus (GEO) datasets of IgAN. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used for functional analysis. Deep sequencing on RNA isolated from B cells was used for microarray validation. The relationship between target mRNA expressions and Gd-IgA1 levels in serum were also studied.

Results

Three studies with microarray expression profiling datasets met our inclusion criteria. We identified 655 dyregulated genes, including 319 up-regulated and 336 down-regulated genes in three GEO datasets with a total of 35 patients of IgAN and 19 healthy controls. Based on biological process in GO term, these dyregulated genes are mainly related to pentose-phosphate shunt, non-oxidative branch, post-embryonic camera-type eye development and leukocyte activation. KEGG pathway analysis of microarray data revealed that these aberrantly expressed genes were enriched in human T-cell leukemia virus 1 infection, proteoglycans in cancer, intestinal immune network for IgA production and autophagy. We further performed deep sequencing on mRNAs isolated from B cells of an independent set of five patients with IgAN and three healthy persons with the same clinical and demographic characteristics. Seventy-seven genes overlapped with 655 differentially regulated genes mentioned above, including 43 up-regulated and thirty-four down-regulated genes. We next investigated whether these genes expression correlated with Gd-IgA1 levels in IgAN patients. Pearson correlation analyses showed PTEN (phosphatase and tensin homolog) was the most powerful gene negatively correlated with Gd-IgA1 levels.

Conclusions

These results demonstrated that dyregulated genes in patients with IgAN were enriched in intestinal immune network for IgA production and autophagy process, and PTEN in B cells might be involved in the mechanism of Gd-IgA1 production.

TLR9 activation induces aberrant IgA glycosylation via APRIL- and IL-6-mediated pathways in IgA nephropathy

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of IgA nephropathy (IgAN). However, the pathogenic mechanisms driving Gd-IgA1 production have not been fully elucidated. Innate-immune activation via Toll-like receptor 9 (TLR9) is known to be involved in Gd-IgA1 production. A proliferation inducing ligand (APRIL) and IL-6 are also known to enhance Gd-IgA1 synthesis in IgAN. With this as background, we investigated how TLR9 activation in IgA secreting cells results in overproduction of nephritogenic IgA in the IgAN-prone ddY mouse and in human IgA1-secreting cells. Injection of the TLR9 ligand CpG-oligonucleotides increased production of aberrantly glycosylated IgA and IgG-IgA immune complexes in ddY mice that, in turn, exacerbated kidney injury. CpG-oligonucleotide-stimulated mice had elevated serum levels of APRIL that correlated with those of aberrantly glycosylated IgA and IgG-IgA immune complexes. In vitro, TLR9 activation enhanced production of the nephritogenic IgA as well as APRIL and IL-6 in splenocytes of ddY mice and in human IgA1-secreting cells. However, siRNA knock-down of APRIL completely suppressed overproduction of Gd-IgA1 induced by IL-6. Neutralization of IL-6 decreased CpG-oligonucleotide-induced overproduction of Gd-IgA1. Furthermore, APRIL and IL-6 pathways each independently mediated TLR9-induced overproduction of Gd-IgA1. Thus, TLR9 activation enhanced synthesis of aberrantly glycosylated IgA that, in a mouse model of IgAN, further enhanced kidney injury. Hence, APRIL and IL-6 synergistically, as well as independently, enhance synthesis of Gd-IgA1.

The role of complement in IgA nephropathy

IgA nephropathy (IgAN) is common and often progresses to end stage renal disease. IgAN encompasses a wide range of histology and clinical features. IgAN pathogenesis is incompletely understood; the current multi-hit hypothesis of IgAN pathogenesis does not explain the range of glomerular inflammation and renal injury associated with mesangial IgA deposition. Although associations between IgAN and glomerular and circulating markers of complement activation are established, the mechanism of complement activation and contribution to glomerular inflammation and injury are not defined. Recent identification of specific complement pathways and proteins in severe IgAN cases had advanced our understanding of complement in IgAN pathogenesis. In particular, a growing body of evidence implicates the complement factor H related proteins 1 and 5 and lectin pathway as pathogenic in a subset of patients with severe disease. These data suggest complement deregulation and activity may be dominant drivers of renal injury in IgAN. Thereby, markers of complement activation may identify IgAN patients likely to progress to significant renal impairment and complement inhibition may emerge as an effective method of preventing and reducing glomerular injury in IgAN.

IgA nephropathy: clearance kinetics of IgA-containing immune complexes

IgA nephropathy (IgAN) is associated predominantly IgA deposition in the affected glomeruli and has been shown to be the most common glomerular disorder among young people in the world. Although the exact pathogenic mechanism underlying IgAN remains largely unknown, circulating IgA-containing immune complexes (IgA ICs) is considered to play a major role in initiating the development and evolution of the renal disorder. In this review article, we discuss the fundamental mechanisms of clearance kinetics of IgA ICs and related issues, covering the following: (1) role of circulating IgA ICs in the pathogenesis of IgAN and (2) elimination of IgA ICs from the body, with emphasis of the role of the liver and Fc receptors in immune cells.

Aberrant Glycosylation of the IgA1 Molecule in IgA Nephropathy

IgA nephropathy, the most common primary glomerulonephritis in the world and a frequent cause of end-stage renal disease, is characterized by typical mesangial deposits of IgA1, as described by Berger and Hinglaise in 1968. Since then, it has been discovered that aberrant IgA1 O-glycosylation is involved in disease pathogenesis. Progress in glycomic, genomic, clinical, analytical, and biochemical studies has shown autoimmune features of IgA nephropathy. The autoimmune character of the disease is explained by a multihit pathogenesis model, wherein overproduction of aberrantly glycosylated IgA1, galactose-deficient in some O-glycans, by IgA1-secreting cells leads to increased levels of circulatory galactose-deficient IgA1. These glycoforms induce production of autoantibodies that subsequently bind hinge-region of galactose-deficient IgA1 molecules, resulting in the formation of nephritogenic immune complexes. Some of these complexes deposit in the kidney, activate mesangial cells, and incite glomerular injury. Thus, galactose-deficient IgA1 is central to the disease process. In this article, we review studies concerning IgA1 O-glycosylation that have contributed to the current understanding of the role of IgA1 in the pathogenesis of IgA nephropathy.

Assay for galactose-deficient IgA1 enables mechanistic studies with primary cells from IgA nephropathy patients

AIMS

IgA nephropathy, the most common primary glomerulonephritis worldwide, is characterized by glomerular deposition of galactose-deficient IgA1 and elevated serum levels of this IgA1 glycoform. Current ELISA methods lack sensitivity to assess galactose deficiency using small amounts of IgA1, which limits studies in primary cells due to modest IgA1 production in isolated peripheral-blood lymphocytes.

METHODS

Lectin from Helix pomatia was conjugated to biotin or acridinium ester and used in ELISA to detect galactose deficiency of IgA1 using small amounts of IgA1.

RESULTS

Lectin conjugated to acridinium had an approximately a log-fold increased sensitivity compared with biotin-labeled lectin.

CONCLUSIONS

The new method of using lectin from Helix pomatia conjugated to acridinium increased assay sensitivity, allowing future mechanistic studies with cultured primary cells.

Glucocorticoids Reduce Aberrant O-Glycosylation of IgA1 in IgA Nephropathy Patients

BACKGROUND/AIMS

IgA nephropathy is associated with aberrant O-glycosylation of IgA1, which is recognized by autoantibodies leading to the formation of circulating immune complexes. Some of them, after deposition into kidney mesangium, trigger glomerular injury. In patients with active disease nonresponding to angiotensin-converting enzyme inhibitors or angiotensin II blockers, corticosteroids are recommended.

METHODS

The relationship between the corticosteroid therapy and serum levels of IgA, aberrantly O-glycosylated IgA1, IgA-containing immune complexes and their mesangioproliferative activity was analyzed in IgA nephropathy patients and disease and healthy controls.

RESULTS

Prednisone therapy significantly reduced proteinuria and levels of serum IgA, galactose-deficient IgA1, and IgA-IgG immune complexes in IgA nephropathy patients and thus reduced differences in all of the above parameters between IgAN patients and control groups. A moderate but not significant reduction of mesangioproliferative potential of IgA-IgG immune complexes and IgA sialylation was detected.

CONCLUSION

The prednisone therapy reduces overall aberrancy in IgA1 O-glycosylation in IgA nephropathy patients, but the measurement of IgA1 parameters does not allow us to predict the prednisone therapy outcome in individual patients.