Synergistic effect of mesangial cell-induced CXCL1 and TGF-β1 in promoting podocyte loss in IgA nephropathy. PLoS One. 2013;8:e73425. [PMID: 24023680 PMCID: PMC3758267 DOI: 10.1371/journal.pone.0073425]

Replication kinetics of pathogenic Eurasian orthohantaviruses in human mesangial cells

BACKGROUND

Eurasian pathogenic orthohantaviruses cause hemorrhagic fever with renal syndrome (HFRS) characterized by acute kidney injury (AKI). The virulence of orthohantaviruses varies enormously and direct infection of different renal cell types contribute to pathogenesis. Glomerular mesangial cells play an essential role in the interplay between kidney cells and proper kidney function. Therefore, we analyzed the replication competence of different orthohantavirus species in primary mesangial cells and a mesangial cell line.

METHODS

We tested the suitability of the mesangial cell line CIHGM-1 (conditionally immortalized human glomerular mesangial cells) as cell culture model for orthohantavirus kidney infection by comparison with primary human renal mesangial cells (HRMCs). We analyzed infection with high pathogenic Hantaan virus (HTNV), moderate pathogenic Puumala virus (PUUV) and non-/low-pathogenic Tula virus (TULV).

RESULTS

Effective viral spread was observed for PUUV only, whereas infection with HTNV and TULV was abortive. However, in contrast to TULV, HTNV exhibits an initially high infection rate and declines afterwards. This replication pattern was observed in HRMCs and CIHGM-1 cells. Viability or adhesion was neither impaired for PUUV-infected CIHGM-1 nor HRMCs. A loss of migration capacity was observed in PUUV-infected CIHGM-1 cells, but not in HRMCs.

CONCLUSIONS

The identification of differences in the replication competence of pathogenic orthohantavirus strains in renal mesangial cells is of special interest and may provide useful insights in the virus-specific mechanisms of orthohantavirus induced AKI. The use of CIHGM-1 cells will facilitate the research in a relevant cell culture system.

The successful use of rituximab in IgA nephropathy patients with podocytopathy: a case series

Background

Immunoglobulin A nephropathy (IgAN) with podocytopathy is a rare pathological type of glomerular disease. The use of rituximab (RTX) in the treatment of glomerular diseases has increased in recent decades, but the efficacy of RTX in the treatment of patients with IgAN and podocytopathy has rarely been reported.

Methods

This was a single-centre retrospective study of IgAN patients with podocytopathy who were treated with RTX as second-line therapy was conducted at our centre from 2019 to 2022. The aim of this study was to investigate the efficacy and safety of RTX in IgAN patients with podocytopathy.

Results

Seven out of eight patients met the criteria for complete remission following RTX therapy. Only one patient experienced adverse events (infectious diarrhoea and pulmonary infection) and experienced relapse 6 months after RTX therapy. The maximum relapse-free time after RTX therapy was 20 months, while the maximum relapse-free time before RTX therapy was only 6 months. The number of relapses before RTX therapy (per year) was one to four; moreover, seven patients did not relapse and maintained remission at the last follow-up despite steroid withdrawal after RTX therapy.

Conclusion

Overall, RTX effectively reduced proteinuria, increased the maximum relapse-free time, reduced the number of relapses per year and helped patients stop steroid use as soon as possible. RTX also helped most patients achieve clinical remission. RTX appears to be an effective and safe alternative for treating IgAN patients with podocytopathy with steroid dependence or frequent relapse.

IgA Nephropathy: Emerging Mechanisms of Disease

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis reported across the world and is characterized by immunoglobulin A (IgA) dominant mesangial deposits, which are poorly O-glycosylated. This deposition leads to a cascade of glomerular and tubulointerstitial inflammation and fibrosis, which can progress to chronic kidney disease. The variability in rate of progression reflects the many genetic and environmental factors that drive IgAN. Here, we summarize the contemporary understanding of the disease mechanisms that drive IgAN and provide an overview of new and emerging therapies, which target these mechanisms.

The role of the mesangium in glomerular function

When discussing glomerular function, one cell type is often left out, the mesangial cell (MC), probably since it is not a part of the filtration barrier per se. The MCs are instead found between the glomerular capillaries, embedded in their mesangial matrix. They are in direct contact with the endothelial cells and in close contact with the podocytes and together they form the glomerulus. The MCs can produce and react to a multitude of growth factors, cytokines, and other signaling molecules and are in the perfect position to be a central hub for crosstalk communication between the cells in the glomerulus. In certain glomerular diseases, for example, in diabetic kidney disease or IgA nephropathy, the MCs become activated resulting in mesangial expansion. The expansion is normally due to matrix expansion in combination with either proliferation or hypertrophy. With time, this expansion can lead to fibrosis and decreased glomerular function. In addition, signs of complement activation are often seen in biopsies from patients with glomerular disease affecting the mesangium. This review aims to give a better understanding of the MCs in health and disease and their role in glomerular crosstalk and inflammation.

Role of abnormal glycosylated IgA1 and interstitial transformation of glomerular endothelial cells in the development and progression of IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a common primary renal disease in childhood.

METHODS

Twenty blood samples and renal tissue from patients with IgAN, 20 blood samples from healthy children and 10 normal renal tissue were collected. Serum Gd-IgA1 and renal Gd-IgA1, CD31, α-SMA and vimentin were measured.

RESULTS

The serum Gd-IgA1 concentration in the IgAN group was significantly higher. Gd-IgA1 was not expressed in normal kidneys, which was positive in the IgAN group. Gd-IgA1 levels in serum and renal tissue were not related. The expression of CD31 decreased significantly in IgAN group, while the expression of α-SMA and vimentin increased significantly. There was no significant correlation between the renal concentration of Gd-IgA1 and CD31, α-SMA and vimentin.

CONCLUSION

The increased Gd-IgA1 in the serum and kidney may promote the pathogenesis of IgAN. The serum Gd-IgA1 cannot predict the extent of its deposition in the kidney. Endothelial mesenchymal transition (EndMT) may be involved in the pathogenesis of renal fibrosis in IgAN.

Chemokine (C-C motif) receptor 2 is associated with the pathological grade and inflammatory response in IgAN children

Background

Chemokine (C–C motif) receptor 2 (CCR2) is involved in important physiological and pathological processes, such as inflammation and autoimmune diseases. Abnormal immune and inflammatory responses play a critical role in the development and progression of IgA nephritis (IgAN). However, the role of CCR2 in IgAN is unknown.

Methods

Fifteen IgAN children who were diagnosed by kidney biopsy provided kidney biopsy tissue, blood and urine samples, and age-matched healthy control subjects (blood donators n = 12; tissue donators n = 8) were included. Immunohistochemical analysis was used to detect the expression of CCR2, MCP-1, IL-6, IL-17, and TNF-α in the kidney tissues. Relative optical density (OD) was calculated by Image J software, and the correlation between CCR2 expression and pathological grade in IgAN children was analyzed.

Results

The expression of CCR2 significantly increased in mesangial cells of children with IgAN compared to that in control group (P < 0.001), especially in IgAN patients with Lee’s grade III to IV (P < 0.001). Interestingly, CCR2 expression was positively correlated with Lee’s grade (r = 0.9152, P = 0.0001) in IgAN children. The expression levels of inflammatory factors were markedly increased in IgAN children, and importantly CCR2 expression was positively correlated with it’s expression level.

Conclusions

The results suggest that CCR2 signaling might be involved in pathological process and inflammatory responses of children IgAN, and could potentially be an intervention target in children IgAN.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02839-y.

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Immune Characteristics of IgA Nephropathy With Minimal Change Disease

Background: IgA nephropathy (IgAN) has a high degree of heterogeneity in clinical and pathological features. Among all subsets of IgAN, the pathogenesis of IgAN with minimal change disease (MCD-IgAN) remained controversial.

Methods: We analyzed the clinical and pathological characteristics of MCD-IgAN patients in a retrospective cohort. Patients diagnosed with IgAN, excluding MCD-IgAN, were randomly selected as controls. Levels of plasma galactose-deficient IgA1 (GdIgA1), IgG autoantibodies against GdIgA1, GdIgA1 deposition in the glomerulus, and inflammatory reactivity of circulating poly-IgA1 complexes to cultured mesangial cells were evaluated.

Results: Patients with MCD-IgAN had significantly higher levels of proteinuria and estimated glomerular filtration rate (eGFR), lower levels of albumin and urine blood cells, and milder histological lesions by a light microscope compared to IgAN patients, which bears a resemblance to MCD. Lower levels of GdIgA1 (3.41 ± 1.68 vs. 4.92 ± 2.30 μg/ml, p = 0.009) and IgG antiglycan autoantibodies (23.25 ± 22.59 vs. 76.58 ± 71.22 IU/ml, p < 0.001) were found in MCD-IgAN patients than those in IgAN controls. Meanwhile, weaker fluorescence intensities of both IgA and GdIgA1 were observed in the glomerulus of MCD-IgAN patients compared to those in IgAN patients. Furthermore, poly-IgA1 complexes from MCD-IgAN patients induced weaker inflammatory effects on cultured mesangial cells than those from IgAN patients in vitro.

Conclusion: The results demonstrated that MCD-IgAN cases represent a dual glomerulopathy, namely, mild IgAN with superimposed MCD, which furthermore provides substantial evidence for the corticosteroids therapy in MCD-IgAN patients as the guidelines recommended.

Collectin11 and Complement Activation in IgA Nephropathy

BACKGROUND AND OBJECTIVES

IgA nephropathy is the most common primary GN worldwide. Previous research demonstrated that collectin11, an initiator of the complement lectin pathway, was involved in both AKI and chronic tubulointerstitial fibrosis. Here, we investigated the potential role of collectin11 in the pathogenesis of IgA nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The deposition of collectin11 and other complement proteins was detected in glomeruli of 60 participants with IgA nephropathy by immunofluorescence. In vitro, human mesangial cells were treated with IgA1-containing immune complexes derived from participants with IgA nephropathy. Then, the expression of collectin11 in mesangial cells was examined by quantitative RT-PCR and immunofluorescence. The codeposition of collectin11 with IgA1 or C3 on mesangial cells was detected by immunofluorescence and proximity ligation assays.

RESULTS

In total, 37% of participants with IgA nephropathy (22 of 60) showed codeposition of collectin11 with IgA in the glomerular mesangium. Using an injury model of mesangial cells, we demonstrated that IgA1-immune complexes derived from participants with IgA nephropathy increased the secretion of collectin11 in mesangial cells with the subsequent deposition of collectin11 on the cell surface via the interaction with deposited IgA1-immune complexes. In vitro, we found that collectin11 bound to IgA1-immune complexes in a dose-dependent but calcium-independent manner. Furthermore, deposited collectin11 initiated the activation of complement and accelerated the deposition of C3 on mesangial cells.

CONCLUSIONS

In situ-produced collectin11 by mesangial cells might play an essential role in kidney injury in a subset of patients with IgA nephropathy through the induction of complement activation.

Mass spectrometry-based screening identifies circulating immunoglobulinA-α1-microglobulin complex as potential biomarker in immunoglobulin A nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is characterized by predominant IgA deposition in the glomerular mesangium. Previous studies have proved that renal-deposited IgA in IgAN came from circulating IgA1-containing complexes (CICs).

METHODS

To explore the composition of CICs in IgAN, we isolated CICs from IgAN patients and healthy controls and then quantitatively analyzed them by mass spectrometry. Meanwhile, the isolated CICs were used to treat human mesangial cells to monitor mesangial cell injury. Using the protein content and injury effects, the key constituent in CICs was identified. Then the circulating levels of identified key constituent-IgA complex were detected in an independent population by an in-house-developed enzyme-linked immunosorbent assay.

RESULTS

By comparing the proteins of CICs between IgAN patients and controls, we found that 14 proteins showed significantly different levels. Among them, α1-microglobulin content in CICs was associated with not only in vitro mesangial cell proliferation and monocyte chemoattractant protein 1 secretion, but also in vivo estimated glomerular filtration rate (eGFR) levels and tubulointerstitial lesions in IgAN patients. Moreover, we found α1-microglobulin was prone to bind aberrant glycosylated IgA1. Additionally, elevated circulating IgA-α1-microglobulin complex levels were detected in an independent IgAN population and IgA-α1-microglobulin complex levels were correlated with hypertension, eGFR levels and Oxford T- scores in these IgAN patients.

CONCLUSIONS

Our results suggest that the IgA-α1-microglobulin complex is an important constituent in CICs and that circulating IgA-α1-microglobulin complex detection might serve as a potential noninvasive biomarker detection method for IgAN.

Renal deposition and clearance of recombinant poly-IgA complexes in a model of IgA nephropathy

IgA nephropathy (IgAN) is the most common type of glomerulonephritis worldwide, which follows a chronic but nonetheless highly variable course of progression. IgA immune complexes are the primary source of renal deposits in IgAN. Apart from the presence of granular IgA1 deposits in the glomerular mesangium and mesangial hypercellularity as common features, the detailed process of IgA1 deposition and clearance in the kidney remains unclear. We sought to examine the dynamics of IgA deposition and tissue plasticity in response to deposits including their intrarenal clearance. We followed a synthetic approach to produce a recombinant fusion between IgA Fc (rIgA) and a biotin tag, which was subsequently induced with streptavidin (SA) to form an oligomeric poly-IgA mimic. Both uninduced rIgA (mono-rIgA) and polymeric SA-rIgA (poly-rIgA) were injected intravenously into Wistar rats. Plasma IgA levels and renal and liver histology were examined in a time series. In contrast to mono-rIgA, this synthetic poly-rIgA analog formed renal deposits exclusively in the glomerulus and were mostly cleared in 3 h. However, repeated daily injections for 12 days caused long-lasting and stronger glomerular IgA deposition together with IgG and complement C3, in association with mesangial cell proliferation, matrix expansion, and variable degrees of albuminuria and hematuria that phenocopied IgAN. Ex vivo, poly-rIgA bound cultured mesangial cells and elicited cytokine production, in addition to activating plasma C3 that was consistent with the actions of IgA immune complexes in IgAN pathogenesis. Remarkably, the kidneys were able to reverse all pathologic manifestations and restore normal glomerular histology 2 weeks after injections were halted. The synthetic model showed the kinetics between the intricate balance of renal deposition and clearance, as well as glomerular plasticity towards healing. Together, the results revealed a priming effect of existing deposits in promoting stronger and longer-lasting IgA deposition to cause renal damage. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Huangkui Capsule in Combination with Leflunomide Improves Immunoglobulin A Nephropathy by Inhibiting the TGF-β1/Smad3 Signaling Pathway

OBJECTIVES

To investigate the efficacy and potential molecular mechanism of Huangkui capsule in combination with leflunomide (HKL) for the treatment of immunoglobulin A nephropathy (IgAN).

METHODS

IgAN rat models were constructed by treating rats with bovine serum albumin, lipopolysaccharide, and tetrachloromethane. Th22 cells were isolated from the blood samples of patients with IgAN using a CD4+ T cell isolation kit. The expression levels of the components of the TGF-β1/Smad3 signaling pathway, namely, TGF-β1, Smad2, Smad3, Smad4, and Smad7, were detected using quantitative reverse transcription polymerase chain reaction. Cell proliferation was determined using the MTT assay, cell viability was determined using the WST 1 method, and the chemotaxis of Th22 cells was observed using the wound healing assay. Changes in the histology of the kidney tissues were analyzed using hematoxylin and eosin staining.

RESULTS

Compared with IgAN rats, the rats subjected to HKL treatment showed good improvement in kidney injuries, and the combined drug treatment performed much better than the single-drug treatment. In addition, following HKL treatment, the viability, proliferation, and chemotaxis of Th22 cells dramatically decreased (*p<0.05, **p<0.01, and ***p<0.001). In addition, CCL20, CCL22, and CCL27 levels decreased and the expression of the key components of the TGF-β1/Smad3 signaling pathway was downregulated in IgAN rats and Th22 cells (*p<0.05, ***p<0.001).

CONCLUSIONS

By targeting the TGF-β1/Smad3 signaling pathway, HKL treatment can improve kidney injury in IgAN rats as well as the excessive proliferation and metastasis of Th22 cells.

Monozygotic Twins Discordant for Immunoglobulin A Nephropathy Display Differences in DNA Methylation and Gene Expression

Introduction

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis. It involves both genetic and environmental factors, among which DNA methylation, the most studied epigenetic modification, was shown to play a role. Here, we assessed genome-wide DNA methylation and gene expression profiles in 2 pairs of IgAN-discordant monozygotic (MZ) twins, in order to characterize methylation changes and their potential influences on gene expression in IgAN.

Methods

Genome-wide DNA methylation and gene expression profiles were evaluated in peripheral blood mononuclear cells obtained from 2 IgAN-discordant MZ twins. Differentially methylated regions (DMRs) and differentially expressed genes (DEGs) were detected, and an integrated analysis was performed. Finally, functional enrichment analysis was done for DMR-associated genes and DEGs.

Results

Totally 521 DMRs were detected for 2 IgAN-discordant MZ twins. Among them, 9 DMRs were found to be mapped to genes that differentially expressed in 2 MZ twins, indicating the potential regulatory mechanisms of expression for these 9 genes (MNDA, DYSF, IL1R2, TLR6, TREML2, TREM1, IL32, S1PR5, and ADGRE3) in IgAN. Biological process analysis of them showed that they were mostly involved in the immune system process. Functional enrichment analysis of DEGs and DMR-associated genes both identified multiple pathways relevant to inflammatory and immune responses. And DMR-associated genes were significantly enriched in terms related to T-cell function.

Conclusions

Our findings indicate that changes in DNA methylation patterns were involved in the pathogenesis of IgAN. Nine target genes detected in our study may provide new ideas for the exploration of molecular mechanisms of IgAN.

The implications of focal segmental glomerulosclerosis in children with IgA nephropathy

Focal segmental glomerular sclerotic lesions in IgA nephropathy (IgAN), considered for years a chronic histologic feature related to proteinuria in remnant nephrons without any active role in the pathogenesis and progression of glomerular damage of IgAN, have been recently reconsidered. The Oxford classification of IgAN reported it as the "S" score and found it to be an independent risk factor for progression of IgAN. Its prognostic value was confirmed also in children. The identification of some histologic subvariants of the S lesion has produced interesting insights into different pathogenetic mechanisms of glomerular damage in IgAN. Tip lesion and podocyte hypertrophy are considered secondary to active podocytopathy and are correlated with higher levels of proteinuria and a faster decline in glomerular filtration rate. Moreover, endocapillary and mesangial hypercellularity might contribute in children with IgAN to formation and progression of S lesions. Considering the pathophysiology of these processes, children with some S features may benefit not only from nephroprotective measures but also from immunosuppression.

The soluble VEGF receptor sFlt-1 contributes to endothelial dysfunction in IgA nephropathy

Endothelial injury is a common manifestation in IgA nephropathy (IgAN). After the previous identification of the upregulated soluble fms-like tyrosine kinase-1 (sFlt-1) correlated with endothelial injury in IgAN, in the present study, we further explored the role of sFlt-1 in endothelial injury in IgAN. We enrolled 72 patients with IgAN and detected the sFlt-1 levels. The polymeric IgA1 (pIgA1) complexes were isolated from the pooled plasma samples of another 10 patients with IgAN. Apoptosis proteins were detected in cultured human umbilical vein endothelial cells (HUVECs) with the stimulation of recombinant sFlt-1 or the caspase-9 inhibitor Z-LEHD-FMK. We identified there were positive correlations between sFlt-1 and IgA-IgG complex as well as vWF levels in patients with IgAN. The sFlt-1 levels in HUVECs were significantly upregulated by pIgA1 complex derived from IgAN patients in a concentration-dependent manner. The proliferation ability of HUVECs was damaged when stimulated with sFlt-1 protein in a time- and dose- dependent manner. And the apoptosis rate was up-regulated significantly as the stimulation concentrations of sFlt-1 increased. We found sFlt-1 challenge could significantly increase the expression of vWF. In addition, sFlt-1 increased the levels of caspase-9, caspase-3, Bax and mitochondrial membrane potential; facilitated the release of cytochrome C from mitochondria to cytoplasma. In contrast, Z-LEHD-FMK attenuated high sFlt-1-induced HUVECs apoptosis. In conclusion, our study demonstrated that sFlt-1 expression was up-regulated by the challenge of pIgA1 complex derived from patients with IgAN. Furthermore, increased sFlt-1 facilitated human umbilical vein endothelial cells apoptosis via the mitochondrial-dependent pathway.

The TLR4-MyD88-NF-κB pathway is involved in sIgA-mediated IgA nephropathy

Previous studies have shown that secretory IgA (sIgA) was critically involved in IgA nephropathy (IgAN) immune responses. Toll-like receptors (TLRs), especially TLR4 which participates in mucosal immunity, may be involved in the pathogenesis of IgAN. The purpose of this study was to investigate whether sIgA and TLR4 interact to mediate kidney damage in IgAN patients. IgAN patients with positive sIgA deposition in renal tissues were screened by immunofluorescence assay. Patient salivary sIgA (P-sIgA) was collected and purified by jacalin affinity chromatography. Salivary sIgA from healthy volunteers was used as a control (N-sIgA). Expression of TLR4, MyD88, NF-κB, TNF-α, IL-6, and MCP-1 were detected in the mesangial area of IgAN patients by immunohistochemistry, the expression levels in patients with positive sIgA deposition were higher than that with negative sIgA deposition. Human renal mesangial cells (HRMCs) were cultured in vitro, flow cytometry showed that P-sIgA bound HRMCs significantly better than N-sIgA. HRMCs were cultured in the presence of sIgA (400 μg/mL) for 24 h, compared with cells cultured with N-sIgA, HRMCs cultured in vitro with P-sIgA showed enhanced expression of TLR4, increased secretion of TNF-α, IL-6, and MCP-1, and increased expression of MyD88/NF-κB. TLR4 shRNA silencing and NF-κB inhibition both reduced the ability of HRMCs to synthesize TNF-α, IL-6, and MCP-1. Our results indicate that sIgA may induce high expression of TLR4 in HRMCs and further activate downstream signalling pathways, prompting HRMCs to secrete multiple cytokines and thereby mediating kidney damage in IgAN patients.

The Role of Immune Modulation in Pathogenesis of IgA Nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide, with diverse clinical manifestations characterized by recurrent gross hematuria or microscopic hematuria, and pathological changes featuring poorly O-galactosylated IgA1 deposition in the glomerular mesangium. Pathogenesis has always been the focus of IgAN studies. After 50 years of research, most scholars agree that IgAN is a group of clinicopathological syndromes with certain common immunopathological characteristics, and multiple mechanisms are involved in its pathogenesis, including immunology, genetics, and environmental or nutritional factors. However, the precise pathogenetic mechanisms have not been fully determined. One hypothesis about the pathogenesis of IgAN suggests that immunological factors are engaged in all aspects of IgAN development and play a critical role. A variety of immune cells (e.g., dendritic cells, NK cells, macrophages, T-lymphocyte subsets, and B-lymphocytes, etc.) and molecules (e.g., IgA receptors, Toll-like receptors, complements, etc.) in innate and adaptive immunity are involved in the pathogenesis of IgAN. Moreover, the abnormality of mucosal immune regulation is the core of IgAN immunopathogenesis. The roles of tonsil immunity or intestinal mucosal immunity, which have received more attention in recent years, are supported by mounting evidence. In this review, we will explore the latest research insights on the role of immune modulation in the pathogenesis of IgAN. With a better understanding of immunopathogenesis of IgAN, emerging therapies will soon become realized.

The Role of Chemokine Receptors in Renal Fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. Renal fibrosis is considered to be closely related to various cell types, such as fibroblasts, myofibroblasts, T cells, and other inflammatory cells. Multiple types of cells regulate renal fibrosis through the recruitment, proliferation, and activation of fibroblasts, and the production of the extracellular matrix. Cell trafficking is orchestrated by a family of small proteins called chemokines. Chemokines are cytokines with chemotactic properties, which are classified into 4 groups: CXCL, CCL, CX3CL, and XCL. Similarly, chemokine receptors are G protein-coupled seven-transmembrane receptors classified into 4 groups: XCR, CCR, CXCR, and CX3CR. Chemokine receptors are also implicated in the infiltration, differentiation, and survival of functional cells, triggering inflammation that leads to fibrosis development. In this review, we summarize the different chemokine receptors involved in the processes of fibrosis in different cell types. Further studies are required to identify the molecular mechanisms of chemokine signaling that contribute to renal fibrosis.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Podocytopathy in the mesangial proliferative immunoglobulin A nephropathy: new insights into the mechanisms of damage and progression

Immunoglobulin A nephropathy (IgAN) was defined as a mesangiopathic disease, since the primary site of deposition of IgA immune material is the mesangium, and proliferation of mesangial cells and matrix excess deposition are the first histopathologic lesions. However, the relentless silent progression of IgAN is mostly due to the development of persistent proteinuria, and recent studies indicate that a major role is played by previous damage of function and anatomy of podocytes. In IgAN, the podocytopathic changes are the consequence of initial alterations in the mesangial area with accumulation of IgA containing immune material. Podocytes are therefore affected by interactions of messages originally driven from the mesangium. After continuous insult, podocytes detach from the glomerular basement membrane. This podocytopathy favours not only the development of glomerular focal and segmental sclerosis, but also the progressive renal function loss. It is still debated whether these lesions can be prevented or cured by corticosteroid/immunosuppressive treatment. We aimed to review recent data on the mechanisms implicated in the podocytopathy present in IgAN, showing new molecular risk factors for progression of this disease. Moreover, these observations may indicate that the target for new drugs is not only focused on decreasing the activity of mesangial cells and inflammatory reactions in IgAN, but also on improving podocyte function and survival.

Acteoside relieves mesangial cell injury by regulating Th22 cell chemotaxis and proliferation in IgA nephropathy

The existing therapies of IgA nephropathy are unsatisfying. Acteoside, the main component of Rehmannia glutinosa with anti-inflammatory and anti-immune effects, can improve urinary protein excretion and immune disorder. Th22 cell is involved in IgA nephropathy progression. This study was determined to explore the effect of acteoside on mesangial injury underlying Th22 cell disorder in IgA nephropathy. Serum Th22 cells and urine total protein of patients with IgA nephropathy were measured before and after six months treatment of Rehmannia glutinosa acteoside or valsartan. Chemotactic assay and co-culture assay were performed to investigate the effect of acteoside on Th22 cell chemotaxis and differentiation. The expression of CCL20, CCL22 and CCL27 were analyzed. To explore the effect of acteoside on mesangial cell injury induced by inflammation, IL-1, IL-6, TNF-α and TGF-β1 were tested. Results showed that the proteinuria and Th22 lymphocytosis of patients with IgA nephropathy significantly improved after combination treatment of Rehmannia glutinosa acteoside and valsartan, compared with valsartan monotherapy. In vitro study further demonstrated that acteoside inhibit Th22 cell chemotaxis by suppressing the production of Th22 cell attractive chemokines, i.e., CCL20, CCL22 and CCL27. In addition, acteoside inhibited the Th22 cell proliferation. Co-culture assay proved that acteoside could relieve the overexpression of pro-inflammatory cytokines, and prevent the synthesis of TGF-β1. TGF-β1 level in mesangial cells was positively correlated with the Th22 cell. This research demonstrated that acteoside can alleviate mesangial cell inflammatory injury by modulating Th22 lymphocytes chemotaxis and proliferation.

Triptolide protects podocytes via autophagy in immunoglobulin A nephropathy

Triptolide is often used to treat patients with immunoglobulin A nephropathy (IgAN), especially in Asia. However, its detailed mechanism remains unclear. In vitro experiments were conducted with podocytes exposed to aggregated IgA (aIgA)-MSC1097-conditioned media. A total of four groups were compared in this study: A control group (CON); a healthy supernatant group (HEAs); an IgAN supernatant group (IgANs); and a triptolide group (TRI). First, aggregated IgA1 (aIgA1) was generated by heating monomeric IgA1 (mIgA1) from IgAN patients or healthy subjects. Next, the conditioned supernatant of MSC-1097 cells cultured with aIgA1 (100 mg/l) from IgAN patients (IgANs) or healthy subjects (HEAs) or without aIgA1 (CON) were harvested and used to incubate MPC5 cells. MPC5 cells in the TRI group were cultured with triptolide (10 ng/ml) and conditioned media from MSC-1097 cells cultured with aIgA1 from IgAN patients. After 24 h of treatment, MPC5 cells were collected to measure autophagy-related protein levels, including microtubule-associated protein light chain 3 (LC3), p62, cluster of differentiation (CD)63, phosphorylated-protein kinase B (Akt), Akt, p-mammalian target of rapamycin (mTOR), and mTOR, via western blotting, immunofluorescence or both, and to determine apoptosis by flow cytometry. All the results showed no difference between the CON and the HEAs. Compared to the CON and the HEAs, MPC5 cells in the IgANs group showed reduced autophagy, which was presented as decreased levels of LC3-II and CD63, as well as accumulation of p62, and an increased podocyte apoptosis rate. This was partly rescued by the addition of triptolide. Moreover, the p-mTOR/mTOR ratio increased in the IgANs group and decreased in the TRI group. Therefore, these results suggest that triptolide protects podocyte autophagy in IgAN patients.

Toll-Like Receptor 3 Signaling Contributes to Regional Neutrophil Recruitment in Cultured Human Glomerular Endothelial Cells

BACKGROUND

Given the importance of neutrophil recruitment in the pathogenesis of glomerulonephritis (GN), the representative neutrophil chemoattractant C-X-C motif chemokine 1 (CXCL1)/GROα and the adhesion molecule E-selectin in glomerular endothelial cells (GECs) play a pivotal role in the development of GN. Endothelial Toll-like receptor 3 (TLR3) is thought to be involved in the inflammatory response via innate immunity. However, the role of endothelial TLR3 signaling in the expression of neutrophil chemoattractants and adhesion molecules remains to be elucidated. Thus, we aimed to examine this issue.

METHODS

We treated normal human GECs with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expressions of CXCL1 and E-selectin using quantitative real-time reverse transcription-polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assay. To further elucidate the poly IC-induced signaling pathway, we subjected the cells to RNA interference against TLR3, interferon (IFN)-β, nuclear factor (NF)-κB p65, and IFN regulatory factor (IRF) 3. We also used immunofluorescence to examine the endothelial expression of CXCL1 in biopsy specimens from patients with crescentic and non-crescentic purpura nephritis (PN).

RESULTS

We found that the activation of TLR3 induced the endothelial expression of CXCL1 and E-selectin, and that this involved TLR3, -NF-κB, IRF3, and IFN-β. Intense endothelial CXCL1 expression was observed in biopsy specimens from patients with crescentic PN.

CONCLUSION

These findings support a role for glomerular antiviral innate immunity in the pathogenesis of GN. Intervention of glomerular TLR3 signaling may therefore be a suitable therapeutic strategy for treating GN in the future.

TREM-1 Contributes to Inflammation in IgA Nephropathy

Background

Circulating IgA1-containing immune complexes (cIgA1) were shown to play important roles in IgA nephropathy (IgAN). They could induce the release of multiple inflammatory factors, including MCP-1 and IL-6, and elevated urinary inflammatory factors were also reported in patients with IgAN, which suggested that inflammation is a major contributor to kidney injury in IgAN. After the previous identification of the upregulated release of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) by mesangial cells under cIgA1 challenge using cytokine array, in the present study, we further explored the role of TREM-1, an amplifier of inflammation, in cIgA1-induced kidney injury.

Methods

In total, 35 patients with IgAN and 17 healthy controls were enrolled. The cIgA1 was isolated from plasma and used to treat cultured mesangial cells. The mRNA expression of TREM-1 as well as levels of sTREM-1, MCP-1, and IL-6 in the mesangial cell supernatant and urine samples were detected.

Results

We found that cIgA1 from patients with IgAN could significantly upregulate the expression of TREM-1 in mesangial cells compared to healthy controls. The levels of ΔsTREM-1 were positively correlated with MCP-1 levels in the mesangial supernatant. Similarly, higher urinary levels of sTREM-1 were also observed in patients with IgAN compared to healthy controls. Moreover, IgAN patients with detectable urinary sTREM-1 presented with severe clinical and pathological manifestations, including higher IgA and lower eGFR levels, compared to patients whose urinary sTREM-1 levels were below the limit of quantification.

Conclusion

Our present study suggested that TREM-1 in cIgA1 induced inflammatory kidney injury in IgAN.

Pathogenic role of glycan-specific IgG antibodies in IgA nephropathy

Background

Accumulating evidences proved the important roles of circulating IgA1-containing immune complexes (cIgA1) in IgA nephropathy (IgAN). Galactose-deficient IgA1 (Gd-IgA1) and glycan-specific IgG antibody have been identified as major components in cIgA1. Before, Gd-IgA1 was reported as a vital factor in IgAN, partly via of its pathogenic role to induce mesangial cells activation. However, we still lack direct evidences to clarify the biological effect of glycan-specific IgG antibody in IgAN.

Methods

In the present study, we enrolled 35 IgAN patients and 17 age- and sex-matched healthy controls. Using uniform aberrant glycosylated IgA1 molecules, and IgG from different individuals, we in vitro prepared IgG-ddIgA1 complexes, and compared the biological differences among these immune complexes regarding their proliferative and inflammatory effects on mesangial cells.

Results

IgG-ddIgA1 complexes from both patients with IgA nephropathy (IgAN-IgG-dd-IgA1) and healthy controls (HC-IgG-dd-IgA1) could induce the proliferation of mesangial cells and up-regulate expression of MCP-1, IL-6 and CXCL1. The levels of mesangial cells proliferation induced by IgAN-IgG-dd-IgA1 were significantly higher than those induced by HC-IgG-dd-IgA1 (1.10 ± 0.05 vs. 1.03 ± 0.03; p < 0.001). However, the levels of secreted MCP-1, IL-6 and CXCL1 from mesangial cells challenged by IgAN-IgG-dd-IgA1 and HC-IgG-dd-IgA1 were comparable.

Conclusions

We found that glycan-specific IgG antibodies derived from patients with IgAN had the biological effect to induce mesangial cells proliferation. Moreover, in the present study we also established a method for in vitro preparation of pathogenic IgG-ddIgA1 complexes, which could be applied in future studies exploring IgAN pathogenesis.

CCL20 secreted from IgA1-stimulated human mesangial cells recruits inflammatory Th17 cells in IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis characterized by human mesangial cells (HMC) proliferation and extracellular matrix expansion associated with immune deposits consisting of galactose-deficient IgA1. However, how IgA1 contributes to IgAN has yet to be completely elucidated. In this study, the expression profile of chemokines was more altered in IgA1-treated HMC than in the control group. CCL20 was significantly higher either in the serum of IgAN patients or in IgA1-treated HMC. Further experiments demonstrated that CCR6, the only receptor of CCL20, was highly expressed in activated T cells. Intracellular staining assay and cytokine expression profile implied that CCR6⁺ T cells produced high IL-17 levels. Transwell experiment immunohistochemistry and immunofluorescence experiments extensively demonstrated that CCL20 could recruit inflammatory Th17 cells to the kidneys. These phenomena caused a series of immune inflammatory responses and further damaged the kidneys. Therefore, HMC stimulated by IgA1 could produce CCL20 and consequently recruit inflammatory Th17 cells to the kidneys to induce further lesion in IgA nephropathy.

Rapamycin Induces Autophagy and Reduces the Apoptosis of Podocytes Under a Stimulated Condition of Immunoglobulin A Nephropathy

Backgroud/Aims: The aim of this study was to investigate the potential renoprotective effect of rapamycin on the autophagy of podocytes treated with the supernatant of mesangial cells cultured with aggregated IgA1 (aIgA1) from immunoglobulin A nephropathy (IgAN) patients.

METHODS

Monomeric IgA1 (mIgA1) was isolated from the serum of IgAN patients or healthy volunteers, and then transformed to aIgA1 by heating. Subsequently, the aIgA1-mesangial cell supernatant was prepared by collecting the medium of mouse mesangial cells (MSC1097) cultured with aIgA1 (100 mg/L) from different IgAN patients or healthy volunteers for 48 h. Subsequently mouse podocytes (MPC5) were exposed to the supernatant of the aIgA1-mesangial cells for 24 h, using 100 mg/L aIgA1 from healthy volunteers as the control group or 100 mg/L aIgA1 from IgAN patients as the IgANs group, in RPMI 1640 medium. The MPC5 cells in the IgANs+Rap group were cultured with rapamycin (10 nmol/L) and the supernatant of MSC-1097 cells cultured with aIgA1 from IgAN patients in RPMI 1640 medium. Autophagy was assessed by western blot analysis (LC3, p62), electron microscopy, and immunofluorescence staining (LC3, p62, and CD63). The apoptosis of podocytes was evaluated by flow cytometry, and the expression of apoptosis-associated proteins cleaved-caspase-3 and caspase-3 were determined by western blot analysis.

RESULTS

Deficient autophagy, which was evident by decreased LC3-II and CD63 levels, caused accumulation of p62, and fewer autophagosomes were observed in the MPC5 cells cultured with the IgAN supernatant, along with stronger expression of cleaved caspase-3 and a higher apoptosis rate. Inhibition of autophagy was alleviated in the IgANs+Rap group. The LC3-II/LC3-I ratio increased by almost 30%, the accumulated p62 amount was reduced by 50%, and the number of autophagosomes per podocyte increased to about 7 times that of the IgAN groups. These results were confirmed by immunofluorescence staining. In addition, the apoptosis rate of MPC5 cells decreased from 19.88% in the IgAN group to 16.78% in the IgANs+Rap group, which was accompanied by a weaker expression level of cleaved caspase-3.

CONCLUSIONS

Rapamycin can reduce the apoptosis of podocytes by inducing autophagy in IgAN.

Original Research: Potential of urinary nephrin as a biomarker reflecting podocyte dysfunction in various kidney disease models

Urinary nephrin is a potential non-invasive biomarker of disease. To date, however, most studies of urinary nephrin have been conducted in animal models of diabetic nephropathy, and correlations between urinary nephrin-to-creatinine ratio and other parameters have yet to be evaluated in animal models or patients of kidney disease with podocyte dysfunction. We hypothesized that urinary nephrin-to-creatinine ratio can be up-regulated and is negatively correlated with renal nephrin mRNA levels in animal models of kidney disease, and that increased urinary nephrin-to-creatinine ratio levels are attenuated following administration of glucocorticoids. In the present study, renal nephrin mRNA, urinary nephrin-to-creatinine ratio, urinary protein-to-creatinine ratio, and creatinine clearance ratio were measured in animal models of adriamycin nephropathy, puromycin aminonucleoside nephropathy, anti-glomerular basement membrane glomerulonephritis, and 5/6 nephrectomy. The effects of prednisolone on urinary nephrin-to-creatinine ratio and other parameters in puromycin aminonucleoside (single injection) nephropathy rats were also investigated. In all models tested, urinary nephrin-to-creatinine ratio and urinary protein-to-creatinine ratio increased, while renal nephrin mRNA and creatinine clearance ratio decreased. Urinary nephrin-to-creatinine ratio exhibited a significant negative correlation with renal nephrin mRNA in almost all models, as well as a significant positive correlation with urinary protein-to-creatinine ratio and a significant negative correlation with creatinine clearance ratio. Urinary protein-to-creatinine ratio exhibited a significant negative correlation with renal nephrin mRNA. Following the administration of prednisolone to puromycin aminonucleoside (single injection) nephropathy rats, urinary nephrin-to-creatinine ratio was significantly suppressed and exhibited a significant positive correlation with urinary protein-to-creatinine ratio. In addition, the decrease in number of glomerular Wilms tumor antigen-1-positive cells was attenuated, and urinary nephrin-to-creatinine ratio exhibited a significant negative correlation in these cells. In conclusion, these results suggest that urinary nephrin-to-creatinine ratio level is a useful and reliable biomarker for predicting the amelioration of podocyte dysfunction by candidate drugs in various kidney disease models with podocyte dysfunction. This suggestion will also be validated in a clinical setting in future studies.

Toll-like receptor 4 is involved in a protective effect of rhein on immunoglobulin A nephropathy

OBJECTIVES

The objective was to investigate the protective effects of rhein on renal histology change and the effects of rhein on renal tissue toll-like receptor (TLR) 4, TLR9, transforming growth factor-β1 (TGF-β1) expression in immunoglobulin A nephropathy (IgAN) rats.

MATERIALS AND METHODS

Bovine serum albumin-lipopolysaccharide-carbon tetrachloride 4 method was used to establish IgAN model. Thirty-two male sprague dawley rats were randomly divided into the control group, IgAN model group, rhein-prevented group, and rhein-treated group. 24-h urinary protein (UP), creatinine, urea, alanine aminotransferase (ALT), total protein (TP) contents in the serum of rats were detected with automatic biochemical analyzer and renal pathological changes were observed by the hematoxylin and eosin and periodic acid-Schiff staining. The glomerular deposition of IgA was measured by immunofluorescence staining. Real-time polymerase chain reaction and immunohistochemistry were used to detect renal tissue contents of TLR4, TLR9, TGF-β1 messenger ribonucleic acid and protein expression.

RESULTS

The biochemical parameters results of IgAN model rats showed that the 24-h UP excretion and ALT concentration were much higher, and TP concentration was much lower than those of the control group (P < 0.05). Granule-like or mass-like IgA depositions in the mesangial area, glomerular hypercellularity, hyperplasia of mesangial matrix, and tubulointerstitial fibrosis were found in IgAN group. Rhein-prevented and rhein-treated both improved the biochemical parameters and relieved renal pathological injury. The expressions of renal tissue TLR4, TGF-β1, but not TLR9 were significantly elevated in IgAN model rats (P < 0.05). Rhein-prevented and rhein-treated both inhibited TLR4 and TGF-β1 expressions.

CONCLUSION

Rhein significantly improved the serum and urine biochemical parameters, and attenuated the glomerular pathological changes and tubulointerstitial fibrosis in IgAN rats. The mechanism may involve inhibition of renal TLR4 and TGF-β1 secretion.

IgA nephropathy in Brazil: apropos of 600 cases

IgA nephropathy (IgAN) is th e commonest primary glomerular disease worldwide. Studies on its prevalence in Brazil are however scarce. Databases and clinical records from 10 reference centres were retrospectively reviewed. Clinical and laboratory features at the moment of the biopsy were retrieved (age, gender, presence of hematuria, serum creatinine [mg/dL], proteinuria [g/24 h]). Renal biopsy findings were classified according to Haas single grade classification scheme and the Oxford Classification of IgAN. 600 cases of IgAN were identified, of which 568 (94.7 %) were on native kidneys. Male to female ratio was 1.24:1. Patients averaged 32.76 ± 15.12 years old (range 4–89, median 32). Proteinuria and hematuria were observed, respectively in 56.63 and 72.29 % of patients. The association of both these findings occurred in 37.95 % of the cases. Serum creatinine averaged 1.65 ± 0.67 mg/dL (median 1.5 mg/dL) at diagnosis. Segmental sclerosis and mesangial hypercellularity were the main glomerular findings (47.6 and 46.2 %) The commonest combination by Oxford Classification of IgAN, was M0 E0 S0 T0 (22.4 %). Chronic tubulo-interstitial lesions with an extension wider than 25 % of the renal cortex could be identified in 32.2 % of the cases. Tubular atrophy and interstitial fibrosis were more strongly associated with higher 24-h proteinuria and serum creatinine levels. Segmental sclerosis (S1) showed a stronger tendency of association with the presence of tubulo-interstitial lesions (T1 and T2) than other glomerular variables. To the best of our knowledge this is the largest series of IgAN in Brazil. It depicts the main biopsy findings and their possible clinical correlates. Our set of data is comparable to previous reports.

Update on immunoglobulin A nephropathy, Part I: Pathophysiology

Immunoglobulin A (IgA) nephropathy is one of the most common glomerulonephritis and its frequency is probably underestimated because in most patients the disease has an indolent course and the kidney biopsy is essential for the diagnosis. In the last years its pathogenesis has been better identified even if still now several questions remain to be answered. The genetic wide association studies have allowed to identifying the relevance of genetics and several putative genes have been identified. The genetics has also allowed explaining why some ancestral groups are affected with higher frequency. To date is clear that IgA nephropathy is related to auto antibodies against immunoglobulin A1 (IgA1) with poor O-glycosylation. The role of mucosal infections is confirmed, but which are the pathogens involved and which is the role of Toll-like receptor polymorphism is less clear. Similarly to date whether the disease is due to the circulating immunocomplexes deposition on the mesangium or whether the antigen is already present on the mesangial cell as a “lanthanic” deposition remains to be clarified. Finally also the link between the mesangial and the podocyte injury and the tubulointerstitial scarring, as well as the mechanisms involved need to be better clarified.

Pentoxifylline Attenuates Proteinuria in Anti-Thy1 Glomerulonephritis via Downregulation of Nuclear Factor-κB and Smad2/3 Signaling

Anti-Thy1 glomerulonephritis is a rat nephritis model closely simulating human mesangial proliferative glomerulonephritis. It affects primarily the mesangium, yet displays substantial proteinuria during the course. This study investigated the molecular signals underlying proteinuria in this disease and the modulation of which by the known antiproteinuric agent, pentoxifylline. Male Wistar rats were randomly divided into a control group and nephritic groups with or without treatment with IMD-0354 (an IκB kinase inhibitor), SB431542 (an activin receptor-like kinase inhibitor) or pentoxifylline. Kidney sections were prepared for histological examinations. Glomeruli were isolated for mRNA and protein analysis. Urine samples were collected for protein and nephrin quantitation. One day after nephritis induction, proteinuria developed together with ultrastructural changes of the podocyte and downregulation of podocyte mRNA and protein expression. These were associated with upregulation of tumor necrosis factor (TNF)-α and transforming growth factor (TGF)-β/activins mRNAs and activation of nuclear factor (NF)-κB p65 and Smad2/3. IMD-0354 attenuated proteinuria on d 1, whereas SB431542 decreased proteinuria on d 3 and 5, in association with partial restoration of downregulated podocyte mRNA and protein expression. Pentoxifylline attenuated proteinuria and nephrinuria through the course, plus inhibition of p-NF-κB p65 (d 1) and p-Smad2/3 (d 5) and partial reversal of downregulated podocyte mRNA and protein. Our data show that the pathogenesis of proteinuria in anti-Thy1 glomerulonephritis involves TNF-α and TGF-β/activin pathways, and the evolution of this process can be attenuated by pentoxifylline via downregulation of NF-κB and Smad signals and restoration of the podocyte component of the glomerular filtration barrier.

Urinary CXCL1: a novel predictor of IgA nephropathy progression

BACKGROUND

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide. In recent years, consistent efforts have been made to develop new non-invasive biomarkers for IgAN progression. In our previous in vitro study we found mesangial derived CXCL1 as a contributor for kidney injury, and observed higher urinary CXCL1 levels in patients with IgAN. It implied that the urinary CXCL1 might be a potential biomarker.

METHODS

In the present study, we enrolled 425 IgAN patients with follow-up data and detected their urinary CXCL1 levels at the time of renal biopsy, to explore the predictive value of urinary CXCL1 in IgAN progression. Urinary CXCL1 levels were measured using enzyme-linked immunosorbent assay.

RESULTS

Urinary CXCL1 levels were associated with presently well established predictors of IgAN progression, including SBP (r = 0.138, p = 0.004), DBP (r = 0.114, p = 0.019), proteinuria (r = 0.155, p = 0.001), eGFR (r = -0.259, p<0.001) and tubular atrophy and interstitial fibrosis (r = 0.181, p<0.001). After adjusted for them, higher levels of urinary CXCL1 were independently associated with a greater risk of deterioration in renal function (HR, per s.d. increment of natural log-transformed CXCL1: 1.748; 95% CI: 1.222-2.499, P = 0.002). Furthermore, time-dependent receiver operating characteristic (ROC) curve showed that urinary CXCL1, when combined with proteinuria and eGFR, could enhance the prognostic value of these traditional predictors for IgAN progression.

CONCLUSIONS

The results in our present study suggested urinary CXCL1 as a new non-invasive predictor of IgAN progression.

Toll-like receptor 3 signaling contributes to the expression of a neutrophil chemoattractant, CXCL1 in human mesangial cells

BACKGROUND

Mesangial proinflammatory chemokine/cytokine expressions via innate immunity play a pivotal role in the pathogenesis of glomerulonephritis. CXCL1/GROα is a strong neutrophil chemoattractant cytokine and reportedly plays an important role in regional inflammatory reactions. However, detailed signaling of mesangial CXCL1 expression induced by viral or "pseudoviral" immunity remains to be determined.

METHODS

We treated normal human mesangial cells (MCs) in culture with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expression of CXCL1 by reverse transcription-polymerase chain reaction (RT-PCR), real-time quantitative RT-PCR and enzyme-linked immunosorbent assay. To elucidate the poly IC-induced signaling pathway for CXCL1 expression, we subjected the cells to RNA interference against Toll-like receptor (TLR) 3, retinoic acid-inducible gene-I (RIG-I), melanoma differentiation-associated gene 5 (MDA5), interferon (IFN)-β, nuclear factor (NF)-κB p65 and IFN regulatory factor (IRF) 3. We also conducted an immunofluorescence study to examine mesangial CXCL1 expression in biopsy specimens from patients with lupus nephritis (LN) and IgA nephropathy (IgAN).

RESULTS

We found that activation of TLR3 signaling could induce the expression of CXCL1 in MCs. NF-κB, IRF3 and IFN-β, but neither RIG-I nor MDA5, were found to be involved in mesangial CXCL1 expression in this setting. Induction of CXCL1 by poly IC was inhibited by pretreatment of cells with dexamethasone. Intense glomerular CXCL1 expression was observed in biopsy specimens from patients with LN, whereas only a trace staining occurred in specimens from patients with IgAN.

CONCLUSION

TLR3 signaling also contributes to the CXCL1 expression in MCs. These observations further support the implication of viral and "pseudoviral" immunity in the pathogenesis of inflammatory renal diseases, especially in LN.

Variants in Complement Factor H and Complement Factor H-Related Protein Genes, CFHR3 and CFHR1, Affect Complement Activation in IgA Nephropathy

Complement activation is common in patients with IgA nephropathy (IgAN) and associated with disease severity. Our recent genome-wide association study of IgAN identified susceptibility loci on 1q32 containing the complement regulatory protein-encoding genes CFH and CFHR1-5, with rs6677604 in CFH as the top single-nucleotide polymorphism and CFHR3-1 deletion (CFHR3-1∆) as the top signal for copy number variation. In this study, to explore the clinical effects of variation in CFH, CFHR3, and CFHR1 on IgAN susceptibility and progression, we enrolled two populations. Group 1 included 1178 subjects with IgAN and available genome-wide association study data. Group 2 included 365 subjects with IgAN and available clinical follow-up data. In group 1, rs6677604 was associated with mesangial C3 deposition by genotype-phenotype correlation analysis. In group 2, we detected a linkage between the rs6677604-A allele and CFHR3-1∆ and found that the rs6677604-A allele was associated with higher serum levels of CFH and lower levels of the complement activation split product C3a. Furthermore, CFH levels were positively associated with circulating C3 levels and negatively associated with mesangial C3 deposition. Moreover, serum levels of the pathogenic galactose-deficient glycoform of IgA1 were also associated with the degree of mesangial C3 deposition in patients with IgAN. Our findings suggest that genetic variants in CFH, CFHR3, and CFHR1 affect complement activation and thereby, predispose patients to develop IgAN.