Association of phospholipase A2 receptor 1 polymorphisms with idiopathic membranous nephropathy in Chinese patients in Taiwan

A review of progress on complement and primary membranous nephropathy

Primary membranous nephropathy (PMN) is a predominant cause of adult nephrotic syndrome, with its incidence witnessing a progressive surge over time. Approximately 35% to 47% of patients progress to renal failure within 10 years, causing a huge social burden. Within China, the proportion of PMN in primary glomerular disease exhibits a gradual ascension. Recent studies have shown that the 3 activation pathways of complement: the classical pathway, mannose-binding lectin pathway, and alternative pathway, are all involved in the pathogenesis of PMN. Despite historical limitations in detecting C1q deposits on the glomeruli of PMN in the past, recent studies have confirmed the classical pathway is implicated in patients with PMN. Considering the dysregulation of the complement system has been observed in PMN, complement inhibitors become increasingly promising. Several clinical trials are presently underway to evaluate the efficacy of complement inhibitors, such as MASP2 antagonists (OMS721), C3 and C3b antagonists (APL2), FD inhibitors (BCX9930), C3aR antagonists (SB290157 and JR14a), FB inhibitors (LNP023). This article reviews the recent research progress on the role of the complement pathway in the pathogenesis of PMN, and underscores the importance of continued research into the complement pathway and its inhibitors, which may pave the way for groundbreaking advancements in the management of PMN.

Association of 10 Polymorphisms in PLA2R1 and HLA DQA1 Genes with Primary Membranous Nephropathy Risk: A Meta-Analysis and a Meta-Regression

Background

Although, several studies have assessed the association of the phospholipase A2 receptor (PLA2R) and HLA-DQA1 SNPs with primary membranous nephropathy (PMN), results were inconsistent and between-studies heterogeneity needs to be investigated.

Objectives

The aim of this review was to summarize existing data on the contribution of 10 SNPs in the PLA2R and HLA-DQA1 genes to PMN susceptibility and to investigate the between-studies heterogeneity by subgroup analyses and meta-regressions.

Design

This study was performed according to the PRISMA guidelines for systematic reviews and meta-analyses.

Data sources and methods

An electronic literature search for eligible studies among all papers published prior to January 10, 2024, was conducted through PubMed, EMBASE, Web of science and Scopus databases. Meta-analyses together with subgroup analyses and meta-regressions were performed for the 10 following SNPs: rs4664308, rs3749117, rs3749119, rs35771982, rs3828323, rs16844715, rs1511223, rs6757188, rs2715918, and rs2187668.

Results

Combined analyses revealed a significant increase in PMN risk conferred by the following alleles: rs4664308*A, rs3749117*T, rs3749119*C, rs35771982*G, rs3828323*C, rs16844715*C, rs1511223*A, rs2715918*A, and rs2187668*A, all P-values < .001. Moreover, the PLA2R-rs4664308/HLA-DQA1-rs2187668 interaction was significantly associated with an increased PMN risk, P < .001. However, there was a substantial between-studies heterogeneity for some SNPs. Subgroup analyses by ethnicity for the 9 PLA2R SNPs did not show any cross-ethnic disparity. Inversely, the risk conferred by the HLA-DQA1 rs2187668*A allele was significantly higher in Caucasians (OR [95% CI] = 3.929 [3.251-4.748]) than in Asians (OR [95% CI] = 2.537 [1.94-3.318], P = .007. Besides, meta-regressions revealed for the majority of investigated SNPs significant correlations of the effect size with albumin, 24-hours proteinuria, serum creatinine, and eGFR levels. Hence, the influence on PMN risk conferred by the PLA2R and HLA-DQA1 SNPs was rather noted in patients with a severe disease.

Conclusion

This meta-analysis showed that 9 out of the 10 investigated SNPs in PLA2R and HLA-DQA1 genes were associated with increased PMN risk. Heterogeneity could be due to disparate patient groups in terms of disease presentation for almost all SNPs, and ethnicity for the HLA-DQA1 rs2187668 SNP.

Registration

This review has been registered on PROSPERO: CRD42024506729. Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42024506729.

Association between PLA2R gene polymorphism and idiopathic membranous nephropathy in Heilongjiang Chinese

Background

The aim of this study was to investigate the correlation between the phospholipase A2 receptor (PLA2R) gene polymorphism and idiopathic membranous nephropathy (IMN) in Heilongjiang Chinese.

Methods

Thirty-five patients with IMN confirmed by renal biopsy attending the Heilongjiang Hospital of Traditional Chinese Medicine between June 2021 and December of 2021 were selected as the IMN group, and a group of 25 healthy participants from the Physical Examination Center of Heilongjiang Hospital of Traditional Chinese Medicine were enrolled as healthy controls. Polymerase chain reaction (PCR) was used to identify and genotype 8 single-nucleotide polymorphism (SNP) loci (rs16844715, rs2715918, rs2715928, rs35771982, rs3749119, rs3828323, rs4665143, and rs6757188) of PLA2R and to analyze the PLA2R gene polymorphisms that correlated with IMN. SPSS 26.0 statistical software was used for data analysis, and the chi-squared (χ²) goodness-of-fit test was used to determine whether each SNP genotype and allele in the PLA2R gene complied with the Hardy-Weinberg equilibrium. The qualitative data were analyzed via χ² or Fisher exact probability method. Logistic regression was used to analyze risk factors, and the odds ratios (ORs) values and 95% confidence intervals (CIs) were calculated. α=0.05 was taken as the test level, and P<0.05 was considered statistically significant.

Results

Statistically significant differences were found in the genotype and allele frequencies of rs35771982 and rs3749119 between the IMN and control groups (P<0.05). Logistic regression analysis showed that the genotypes rs35771982 GG and rs3749119 CC were associated with IMN susceptibility. Statistically significant differences in uric acid level were found between the rs35771982 GG and CG + CC genotypes (P<0.05), while statistically significant differences in serum albumin were detected between rs3749119 CC and the CT + TT genotypes (P<0.05). Multivariate logistic regression analysis showed that gender, age, and triglyceride levels affected the occurrence of IMN (P<0.05).

Conclusions

The PLA2R gene polymorphisms rs35771982 and rs3749119 in Heilongjiang Chinese may be related to IMN susceptibility and correlated with clinical indicators of IMN. Gender, age, and triglyceride levels may influence the occurrence of IMN.

Membranous nephropathy: new pathogenic mechanisms and their clinical implications

Membranous nephropathy (MN) is characterized histomorphologically by the presence of immune deposits in the subepithelial space of the glomerular filtration barrier; its clinical hallmarks are nephrotic range proteinuria with oedema. In patients with primary MN, autoimmunity is driven by circulating autoantibodies that bind to one or more antigens on the surface of glomerular podocytes. Compared with other autoimmune kidney diseases, the understanding of the pathogenesis of MN has substantially improved in the past decade, thanks to the discovery of pathogenic circulating autoantibodies against phospholipase A₂ receptor 1 (PLA₂R1) and thrombospondin type 1 domain-containing protein 7A (THSD7A). The subsequent identification of more proteins associated with MN, some of which are also endogenous podocyte antigens, might further advance the clinical characterization of MN, including its diagnosis, treatment and prognosis. Insights from studies in patients with MN, combined with the development of novel in vivo and in vitro experimental models, have potential to improve the management of patients with MN. Characterizing the interaction between autoimmunity and local glomerular lesions provides an opportunity to develop more specific, pathogenesis-based treatments.

Revisiting immunological and clinical aspects of membranous nephropathy

Idiopathic or primary membranous nephropathy (IMN) is one of the most frequent causes of nephrotic syndrome in adults and the elderly. It is characterized by a thickening of the wall of the glomerular capillaries due to the presence of immune complex deposits. 85% of membranous nephropathy cases are classified as primary or idiopathic (IMN). The rest are of secondary origin (SMN), caused by autoimmune conditions or malignant tumors as lung cancer, colon and melanomas. It is an organ-specific autoimmune disease in which the complement system plays an important role with the formation of the membrane attack complex (MAC; C5b-9), which produces an alteration of the podocyte structure. The antigen responsible for 70-80% of IMN is a podocyte protein called M-type phospholipase A2 receptor (PLA2R). More recently, another podocyte antigen has been identified, the "Thrombospondin type-1 domain-containing 7A" (THSD7A), which is responsible for 10% of the cases of negative IMN for anti- PLA2R.

How Times Have Changed! A Cornucopia of Antigens for Membranous Nephropathy

The identification of the major target antigen phospholipase A2 receptor (PLA2R) in the majority of primary (idiopathic) cases of membranous nephropathy (MN) has been followed by the rapid identification of numerous minor antigens that appear to define phenotypically distinct forms of disease. This article serves to review all the known antigens that have been shown to localize to subepithelial deposits in MN, as well as the distinctive characteristics associated with each subtype of MN. We will also shed light on the novel proteomic approaches that have allowed identification of the most recent antigens. The paradigm of an antigen normally expressed on the podocyte cell surface leading to in-situ immune complex formation, complement activation, and subsequent podocyte injury will be discussed and challenged in light of the current repertoire of multiple MN antigens. Since disease phenotypes associated with each individual target antigens can often blur the distinction between primary and secondary disease, we encourage the use of antigen-based classification of membranous nephropathy.

Associations between m-type phospholipase A2 receptor,human leukocyte antigen gene polymorphisms and idiopathic membranous nephropathy

Primary membranous nephropathy, also known as idiopathic membranous nephropathy, is an autoimmune disease. As an autoimmune disease, genetic factors are essential in the pathogenesis of IMN. People pay more and more attention to genetics and bioinformatics. With the continuous improvement and development of high-throughput gene sequencing and genotyping technology, it has been confirmed that many genes and their single nucleotide polymorphisms are strongly correlated with IMN disease susceptibility. However, there are few studies on HLA-DQA1 and PLA2R gene polymorphisms and IMN susceptibility in China. The purpose of this study was to investigate whether PLA2R rs2715928 and rs16844715 are related to IMN, the correlation between five SNP loci of PLA2R and HLA-DQA1 and IMN, and the effect of gene-gene interaction among different genotypes of each locus on disease. In this study, 86 patients with IMN confirmed by renal biopsy in the first hospital of Harbin Medical University and 90 healthy controls were selected. All subjects were excluded from secondary membranous nephropathy, pregnant or breastfeeding women, severe primary disease of vital organs, severe infection, major surgery, and severe trauma. Seven selected SNP loci were genotyped using the IMLDR multiple SNP typing kit. Chi-square test and logistic regression were used to analyze the correlation between each SNP and IMN. The general clinical data and laboratory indicators of each subject were recorded, and the relationship between different genotypes and clinical manifestations was analyzed. Among the 7 SNP loci included in the study, except HLA-DQA1 rs2187668, the other 6 loci all met Hardy-Weiberg equilibrium test (P > 0.05). The allele distribution of PLA2R rs2715928 and rs16844715 was significantly different between the IMN group and the healthy control group, and it was closely related to IMN (P < 0.05). There was no statistical difference in the distribution of alleles of rs2715918 between the IMN group and the control group (P* > 0.05), and there was also statistical difference in the distribution of alleles of rs35771982, rs3749117, and rs4664308 between the IMN group and the healthy control group (P < 0.05).The C allele of rs16844715 (OR = 2.03, 95%CI: 1.29–3.19, P* = 0.0140) and the A allele of rs2715928 (OR = 3.18, 95%CI: 1.94–5.24, P* = 3.54E-5), G allele of rs35771982 (OR = 4.07, 95%CI: 2.34–7.08, P* = 4.96E-6), T allele of rs3749117 (OR = 4.07, 95%CI: 2.34–7.08, P* = 4.96E-6), the A allele of rs4664308 (OR = 2.63, 95%CI: 1.54–4.49, P* = 0.0028) was the risk gene of IMN.Through the establishment of different genetic models, we found that,in the additive model, the three SNPs of PLA2R rs2715928 (OR = 5.40, 95%CI: 1.77–16.50, P* = 0.0217) and rs35771982 (OR = 15.15, 95%CI: 2.92–78.48, P* = 0.0084), rs3749117 (OR = 15.15, 95%CI: 2.92–78.48, P* = 0.0084) had a strong correlation with IMN. In the stealth model,homozygous gene risk type of the five SNPs,PLA2R rs16844715 (OR = 2.52, 95%CI: 1.38–4.61, P* = 0.0189) and rs2715928 (OR = 4.30, 95%CI: 2.31–8.03, P* = 3.14E-5), rs35771982 (OR = 4.85, 95%CI: 5.53–9.31, P* = 1.42E-5), rs3749117 (OR = 4.85, 95%CI: 5.53–9.31, P* = 1.42E-5) and rs4664308 (OR = 3.16, 95%CI: 1.67–5.97, P* = 0.0028) had a strong correlation with IMN. The distribution of GT haplotypes and CC haplotypes of rs35771982 and rs3749117 and CA haplotypes and TG haplotypes of rs16844715 and rs4664308 were significantly different between IMN group and control group (P < 0.05). When GMDR software was used to establish a model to analyze the interaction between various SNP sites, it was found that the combination of GG genotype at rs35771982 and AA genotype at rs2715928 was the highest risk of disease. The risk genotypes of rs16844715, rs2715928 and rs4664308 had no effect on the clinical manifestations of IMN (P > 0.05). PLA2R rs2715928 and rs16844715 are associated with susceptibility to IMN. The C allele of rs16844715, the A allele of rs2715928, the G allele of rs35771982, the T allele of rs3749117, and the A allele of rs4664308 are the dangerous genes of IMN. The combination of GG genotype at rs35771982 and AA genotype at rs2715928 poses the greatest risk of disease. Haplotype may affect susceptibility to IMN. The risk genotype had no effect on the clinical manifestations of IMN.

The association between variants in PLA2R and HLA-DQA1 and renal outcomes in patients with primary membranous nephropathy in Western China

BACKGROUND

Both Genome-wide associations and our previous study have shown that single nucleotide polymorphisms (SNPs) of M-type phospholipase A2 receptor (PLA2R) and human leukocyte antigen complex class II HLA-DQα-chain 1 (HLA-DQA1) gene were identified to be associated with primary membranous nephropathy (PMN). However, whether these SNPs affect clinical manifestation and renal outcome for PMN patients is poorly defined. Here, we evaluated whether there is an association between these SNPs and clinical manifestations and renal outcomes of PMN in a western Chinese cohort.

METHODS

Seven SNPs within PLA2R and one SNP in HLA-DQA1 were selected in our study. Clinical data from 314 patients with PMN were collected and the relationship between the genotype and phenotype was evaluated. A total of 186 patients had follow-up data. We assessed the treatment responses and renal outcomes between patients with these gene polymorphisms after a median follow-up of 18.6 months.

RESULTS

Eight SNPs were not associated with clinical manifestations of PMN patients (Pc < 0.05). rs3828323 T allele was marginally significantly associated with hypertension (P = 0.008, Pc = 0.064, OR = 1.821). After treatment for PMN, the SR group (including CR and PR) had lower serum creatinine level (68.4 ± 18.8 μmol/L vs. 122.8 ± 126.6 μmol/L, P < 0.001), urea (5.5 ± 1.9 mmol/L vs. 8.0 ± 4.0 mmol/L, P < 0.001), uric acid (358.5 ± 95.1 μmol/L vs. 392.8 ± 118.1 μmol/L, P = 0.037) and urinary protein (0.23 (0.76,1.05) g/d vs. 3.01 (2.06,7.95) g/d, P < 0.001), higher eGFR (100.0 ± 20.1 ml/min/1.73m2 vs. 77.1 ± 35.3 ml/min/1.73m2, P < 0.001) and albumin (41.1 ± 5.1 g/L vs.30.4 ± 8.2 g/L, P < 0.001). We also identified that PMN patients with CT/TT genotype for rs3828323 achieved higher cumulative survival rate than patients with CC genotype.

CONCLUSIONS

Rs3828323 may influence hypertension and renal outcome in patients with PMN. Further research is needed to explore the mechanism for this genotype-disease phenotype association.

Primary membranous nephropathy in the era of autoantibodies and biological therapies

Primary membranous nephropathy is an autoimmune kidney disease and the most common cause of nephrotic syndrome in adults. About 70%-80% of cases are caused by anti-PLA2R antibodies. Its association with anti-THSD7A antibodies and other autoantibodies has also been described. Recent pilot studies and clinical trials have shown that several biological agents targeting autoantibody-producing cells are effective in controlling the disease with an acceptable safety profile. In this narrative review, we update key concepts about the pathogenesis, autoantibody-based diagnosis, and kidney biopsy findings in primary membranous nephropathy. In addition, we propose a diagnostic and therapeutic algorithm, including guidance on monitoring the response to therapy. We compare the efficacy and safety of currently available treatments, including rituximab and new biological agents, and identify unmet clinical needs.

PLA2R1 and HLA-DQA1 gene variations in idiopathic membranous nephropathy in South China

INTRODUCTION

Associations of variations in PLA2R1 and HLA-DQA1 genes with susceptibility to idiopathic membranous nephropathy (IMN) have been well documented. Association with spontaneous remission, however, is poorly defined in the Chinese Han population.

METHODS

A Chinese cohort of 117 IMN patients and 138 healthy controls were recruited between July 2009 and November 2019. Case-control studies for single-nucleotide polymorphisms (SNPs) within HLA-DQA1 (rs2187668) and PLA2R1 (rs35771982, rs4664308, rs3749117, rs3749119) genes were performed. The contributions of these polymorphisms to predict susceptibility, titre of autoantibodies against the M-type phospholipase A2 receptor (anti-PLA2R1), glomerular PLA2R1 expression, and spontaneous remission were analysed.

RESULTS

We found that variations in PLA2R1 (SNPs rs35771982, rs4664308, rs3749117) were strongly associated with IMN susceptibility, while SNP (rs2187668) within HLA-DQA1 did not increase the risk of IMN. All SNPs in PLA2R1 and HLA-DQA1 were not statistically associated with anti-PLA2R1 titre, glomerular PLA2R1 expression and spontaneous remission after Bonferroni correction (P>0.0167). Clinical and pathological parameters such as lower levels of serum albumin, higher levels of anti-PLA2R1 and glomerular PLA2R1 expression were independent risk factors for non-spontaneous remission.

CONCLUSION

This study confirms that variations in PLA2R1 (SNPs rs35771982, rs4664308, rs3749117) are risk factors for IMN. We found excellent association of serum albumin level, anti-PLA2R1 titre and glomerular PLA2R1 positivity with non-spontaneous remission in IMN.

PLA2R antibody, PLA2R rs4664308 polymorphism and PLA2R mRNA levels in Tunisian patients with primary membranous nephritis

BACKGROUND

Primary membranous nephritis (PMN) is an autoimmune disease induced by the deposit of antibodies (Ab) to the phospholipase receptor A2 receptor (PLA2R) on podocytes. In this context, we aimed to assess the relationships between anti-PLA2R Ab, PLA2R rs4664308 SNP, PLA2R mRNA levels and PMN susceptibility and outcome.

METHODS

Sixty-eight PMN patients, 30 systemic lupus erythematosus (SLE) patients with secondary MN and 30 healthy control subjects served for anti-PLA2R Ab measurement by ELISA and PLA2R rs4664308 SNP genotyping by a commercial real-time PCR. Twenty patients with tubulo-interstitial nephritis (TIN) were used as controls for renal PLA2R mRNA quantification in PMN patients from kidney biopsies. PLA2R mRNA quantification was carried-out by real-time PCR after RNA extraction.

RESULTS

Forty-three (63.2%) PMN patients received initial therapy consisting of alternating monthly cycles of corticosteroids and cyclophosphamide. Twelve (17.6%) patients had resistant PMN to initial therapy and were consecutively treated by cyclosporine or tacrolimus. Anti-PLA2R Ab were positive in 54 (79.4%) PMN patients, while all SLE patients and controls were negative, p<0.0001. Moreover, anti-PLA2R Ab levels were significantly higher in PMN patients (134.85 [41.25-256.97] RU/ml) than in SLE patients (3.35 [2.3-4.35] RU/ml) and controls (2 [2-2.3]), p<0.0001. Consequently, a ROC curve showed for 100% specificity a sensitivity of 94.1% at a threshold of 2.6 RU/ml. Besides, Anti-PLA2R antibodies levels were significantly associated to non-remission; p = 0.002. The rs4664308*A wild-type allele was significantly more frequent in PMN patients (0.809) than in controls (0.633) and SLE patients (0.65); p = 0.008, OR [95% CI] = 2.44 [1.24-4.82] and p = 0.016, OR [95% CI] = 2.27 [1.15-4.5], respectively. Renal PLA2R mRNA levels were significantly higher in PMN patients (218.29 [66.05-486.07]) than in TIN patients (22.09 [13.62-43.34]), p<0.0001. Moreover, PLA2R mRNA levels were significantly higher in non-remission patients (fold-factor vs. partial remission = 2.46 and fold-factor vs. complete remission = 12.25); p = 1.56 10E-8. In addition, PLA2R mRNA and anti-PLA2R Ab levels were significantly correlated, Spearman Rho = 0.958, p<0.0001.

CONCLUSION

Anti-PLA2R Ab and renal PLA2R mRNA could be useful markers for PMN outcome predicting. The PLA2R rs6446308 SNP is associated with PMN susceptibility in Tunisians.

Single-nucleotide polymorphism rs4664308 in PLA2R1 gene is associated with the risk of idiopathic membranous nephropathy: a meta-analysis

Although many studies investigated the associations between single-nucleotide polymorphisms (SNPs) in the M-type phospholipase A2 receptor-1 (PLA2R1) gene and susceptibility to idiopathic membranous nephropathy (IMN), some showed inconsistent results. Here, we conducted a meta-analysis examining the associations between PLA2R1 SNPs and IMN susceptibility after systematic searches in the PubMed and Web of Science databases. Our meta-analysis for rs4664308 A>G including 2,542 IMN patients and 4,396 controls in seven studies showed a significant association between the G allele and a lower risk of IMN, as determined using an allelic model (odds ratio, 0.45; 95% confidence interval [0.41–0.50]), an additive model (for GG vs. AA: 0.26; [0.21–0.33]; for AG vs. AA: 0.40; [0.36–0.45]), a dominant model (0.37; [0.34–0.42]) and a recessive model (0.38; [0.31–0.48]). Our meta-analysis also suggested associations between rs3828323, rs35771982, rs3749117 and rs3749119 and IMN susceptibility although high heterogeneities and/or publication biases were observed. We did not study in our meta-analysis, but other studies indicated that high-risk genotype combinations of rs2187668 in the human leucocyte antigen-DQ a-chain 1 gene and rs4664308 in the PLA2R1 gene had even stronger associations and could affect the formation of anti-PLA2R1 antibodies, suggesting these SNPs could be novel therapeutic targets.

Mutational analysis on predicting the impact of high-risk SNPs in human secretary phospholipase A2 receptor (PLA2R1)

PLA2R1 is a transmembrane glycoprotein that acts as an endogenous ligand which stimulates the processes including cell proliferation and cell migration. The SNPs in PLA2R1 is associated with idiopathic membranous nephropathy which is an autoimmune kidney disorder. The present study aimed to explore the structure-function analysis of high risk SNPs in PLA2R1 by using 12 different computational tools. First the functional annotation of SNPs were carried out by sequence based tools which were further subjected to evolutionary conservation analysis. Those SNPs which were predicted as deleterious in both categories were further considered for structure based analysis. The resultant SNPs were C1096S, C545S, C664S, F1257L, F734S, I1174T, I1114T, P177S, P384S, W1198G, W1328G, W692C, W692L, W962R, Y499H. One functional domain of PLA2R1 is already modelled in PDB (6JLI), the full 3D structure of the protein was predicted using I-TASSER homology modelling tool. The stability analysis, structure superimposition, RMSD calculation and docking studies were carried out. The structural analysis predicted four mutations F734S, F1246L, I1174T, W1198G as damaging to the structure of the protein. All these mutations are occurring at the conserved region of CTL domain hence are more likely to abolish the function of the protein. Up to the best of our knowledge, this is the first study that provides in-depth and in-silico analysis of deleterious mutations on structure and function of PLA2R1.

Clinicopathological features and prognosis in patients with idiopathic membranous nephropathy with hypertension

The present study analyzed the clinicopathological features and prognosis in patients with idiopathic membranous nephropathy (IMN) with hypertension. In the hypertension group, significant differences were found in the age, hypertension history, systolic blood pressure, diastolic blood pressure (DBP), mean arterial pressure, albumin, serum creatinine, low-density lipoprotein, 24 h urine protein levels, calculated estimated glomerular filtration rate (e-GFR), glomerular sclerosis, segmental sclerosis, ischemic sclerosis, interstitial fibrosis, tubular atrophy and vascular lesion compared with the non-hypertension group (P<0.05). The average follow-up time was 35.70 months (5.10-103.77 months). In total, 54 patients reported a 50% decline in e-GFR, eight patients reported progression of disease to end-stage renal disease (ESRD) and nine cases of mortality were reported. Survival analysis results suggested that patients with hypertension had a lower cumulative renal survival rate than those without hypertension (P=0.034). Multivariate Cox hazards regression analysis results suggested that DBP [hazard ratio (H), 5.160; CI, 0.865-0.989; P=0.023], age (H, 4.839; CI, 1.008-1.142; P=0.028), sex (H, 5.680; CI, 0.031-0.714; P=0.017), serum creatinine (H, 20.920; CI, 1.035-1.089; P<0.001), uric acid (H, 4.783; CI, 0.982-0.0.999; P=0.029), 24 h urine protein (H, 6.318; CI, 1.079-1.850; P=0.012), e-GFR (H, 4.008; CI, 1.001-1.062; P=0.045) and glomerular sclerosis (H, 8.722; CI, 1.860-21.559; P=0.003), segmental sclerosis (H, 7.737; CI, 7.770-13.219; P=0.005), percentage of ischemic sclerosis (H, 4.729; CI, 1.444-11.945; P=0.030), crescents (H, 5.938; CI, 0.003-0.526; P=0.015), interstitial fibrosis and tubular atrophy (H, 8.128; CI, 0.005-1.052; P=0.043), and vascular lesion (H, 4.049; CI, 1.030-9.766; P=0.044) were risk factors for the development of IMN into ESRD. The results suggested that DBP may be an independent risk factor for the development of IMN with hypertension.

The anti-PLA2R antibody in membranous nephropathy: what we know and what remains a decade after its discovery

The discovery in 2009 of the M-type phospholipase A2 receptor (PLA2R) as the primary target in membranous nephropathy (MN) greatly advanced basic and clinical research. Primary MN is now considered a renal-limited autoimmune disease, with antibodies against PLA2R (aPLA2Rab) identified in 70-80 % of patients of various ethnic groups. Although the use of aPLA2Rab as a diagnostic and prognostic biomarker is now widely accepted, many questions related to the development of the auto-immune response, the role of IgG subclasses and antigenic epitopes, and the pathways to podocyte injury remain unresolved. PLA2R-associated MN most likely develops governed by factors such as genetic susceptibility, loss of tolerance, alterations in antigen expression with a role for environmental factors like air pollution, smoking, and infections. More detailed knowledge of genetic factors, the relevant B- and T-cell epitopes, and the mechanisms of podocyte injury is needed to identify patients at risk for disease progression and to develop optimized, targeted treatment strategies. In this review we highlight unresolved issues, addressing initiation of antibody formation, the timeline of antibody production, the role of IgG subclass, and the pathogenicity of the antibodies in concert with complement to produce glomerular pathology and proteinuria.

Unmet challenges in membranous nephropathy

PURPOSE OF REVIEW

Despite major advances in since the discovery of the phospholipase A2 receptor (PLA2R) as the major autoantigen on podocytes in primary membranous nephropathy, there are still several unanswered questions as highlighted here.

RECENT FINDINGS

A substantial body of literature, included in more than 680 articles since 2009, has documented genetic susceptibility to primary membranous nephropathy involving PLA2R1 and class II MHC alleles, the clinical value of anti-PLA2R assays, the significance of epitope spreading of the anti-PLA2R response, discovery of thrombospondin type I domain-containing 7A (THSD7A) as a minor antigen in primary membranous nephropathy, and the ability to transfer disease into mice by infusion of anti-THSD7A sera. However, the normal physiology and pathophysiology of PLA2R and THSD7A in podocytes is still unknown and the genetic influence on disease susceptibility is unexplained. We still do not know what causes loss of self-tolerance to PLA2R and THSD7A or how the autoantibodies, which are predominantly of the IgG4 subclass, cause podocyte injury and proteinuria. Complement deposits are prominent in membranous nephropathy but we are still uncertain how the complement system is activated and whether or not it plays a role in podocyte damage. Notwithstanding the advances over the past decade, our treatments have not changed substantially.

SUMMARY

This review identifies opportunities to extend the advances that have been made to better understand the immunopathogenesis and genetic basis of primary membranous nephropathy and apply the knowledge to design more specific therapies.

Genetics of membranous nephropathy

An HLA-DR3 association with membranous nephropathy (MN) was described in 1979 and additional evidence for a genetic component to MN was suggested in 1984 in reports of familial MN. In 2009, a pathogenic autoantibody was identified against the phospholipase A2 receptor 1 (PLA2R1). Here we discuss the genetic studies that have proven the association of human leucocyte antigen class II and PLA2R1 variants and disease in MN. The common variants in PLA2R1 form a haplotype that is associated with disease incidence. The combination of the variants in both genes significantly increases the risk of disease by 78.5-fold. There are important genetic ethnic differences in MN. Disease outcome is difficult to predict and attempts to correlate the genetic association to outcome have so far not been helpful in a reproducible manner. The role of genetic variants may not only extend beyond the risk of disease development, but can also help us understand the underlying molecular biology of the PLA2R1 and its resultant pathogenicity. The genetic variants identified thus far have an association with disease and could therefore become useful biomarkers to stratify disease risk, as well as possibly identifying novel drug targets in the near future.

The Genetic and Environmental Factors of Primary Membranous Nephropathy: An Overview from China

Background

Primary membranous nephropathy (pMN) is the most common cause of nephrotic syndrome in adults. The discovery of the 2 autoantigens, M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A), has defined pMN as an autoimmune disease. A remarkable increase in the frequency of pMN in primary glomerular disease was witnessed in China. The genetic and environmental contributors to disease susceptibility have been investigated in these patients.

Summary

We reviewed recent publications in genetic and environmental studies of pMN, focusing mainly on those undertaken in China. Following a genome-wide association study, the gene-gene interaction between the 2 most significant risk factors, PLA2R1 and DQA1, was validated in Chinese patients with MN. Fine mapping on human leukocyte antigen (HLA) locus found that DRB1*1501 and DRB1*0301 were risk alleles. Three amino acid residues on positions 13 and 71 of HLA-DRβ1 chain may confer the susceptibility to pMN by presenting T-cell epitopes on PLA2R. Another study found that DRB3*0202 was the most likely culprit allele for the signal at DRB1*0301. One environmental risk factor for pMN has been identified as the long-term exposure to high levels of PM_2.5 in Chinese patients with MN. Each 10 μg/m³ increase in PM_2.5 concentration was associated with 14% higher odds for pMN in the regions with PM_2.5 above 70 μg/m³.

Key Message

A gene-environment interaction is suspected as an underlying mechanism for the increasing trend of pMN in China.

Membranous Nephropathy and Anti-Podocytes Antibodies: Implications for the Diagnostic Workup and Disease Management

The discovery of circulating antibodies specific for native podocyte antigens has transformed the diagnostic workup and greatly improved management of idiopathic membranous nephropathy (iMN). In addition, their identification has clearly characterized iMN as a largely autoimmune disorder. Anti-PLA2R1 antibodies are detected in approximately 70% to 80% and anti-THSD7A antibodies in only 2% of adult patients with iMN. The presence of anti-THSD7A antibodies is associated with increased risk of malignancy. The assessment of PLA2R1 and THSD7A antigen expression in glomerular immune deposits has a better sensitivity than measurement of the corresponding autoantibodies. Therefore, in the presence of circulating anti-podocytes autoantibodies and/or enhanced expression of PLA2R1 and THSD7A antigens MN should be considered as primary MN (pMN). Anti-PLA2R1 or anti-THSD7A autoantibodies have been proposed as biomarkers of autoimmune disease activity and their blood levels should be regularly monitored in pMN to evaluate disease activity and predict outcomes. We propose a revised clinical workup flow for patients with MN that recommends assessment of kidney biopsy for PLA2R1 and THSD7A antigen expression, screening for circulating anti-podocytes antibodies, and assessment for secondary causes, especially cancer, in patients with THSD7A antibodies. Persistence of anti-podocyte antibodies for 6 months or their increase in association with nephrotic proteinuria should lead to the introduction of immunosuppressive therapies. Recent data have reported the efficacy and safety of new specific therapies targeting B cells (anti-CD20 antibodies, inhibitors of proteasome) in pMN which should lead to an update of currently outdated treatment guidelines.

Urine anti-PLA2R antibody is a novel biomarker of idiopathic membranous nephropathy

Since urine samples more directly reflect kidney alterations and damage than blood samples, we investigated whether urine anti-PLA₂R antibody (uPLA₂R-Ab) could be utilized similarly to serum anti-PLA₂R antibody (sPLA₂R-Ab) as a noninvasive biomarker of idiopathic membranous nephropathy (IMN). In this study, we performed a qualitative analysis using an indirect immunofluorescence test (IIFT) and measured uPLA₂R-Ab and sPLA₂R-Ab concentrations using an enzyme-linked immunosorbent assay (ELISA) in 28 patients with biopsy-proven IMN and 12 patients with secondary membranous nephropathy (SMN). Overall, 64.3% (n=18) of patients with IMN had IIFT-positive sPLA₂R-Ab, 67.9% (n=19) of patients with IMN had IIFT-positive uPLA₂R-Ab, and none of the SMN patients had IIFT-positive sPLA₂R-Ab or uPLA₂R-Ab. The titers of the anti-PLA₂R antibody from the IMN patients in the urine (10.72±22.24 RU/μmol, presented as uPLA₂R-Ab/urine creatinine) and serum (107.36±140.93 RU/ml) were higher than those from the SMN patients (0.51±0.46 RU/μmol, 0.008±0.029 RU/ml, respectively, p<0.05). Statistical analyses indicated that there were positive correlations between uPLA₂R-Ab and gPLA₂R, sPLA₂R-Ab or urinary protein and negative correlations between uPLA₂R-Ab and serum albumin in patients with IMN. In conclusion, uPLA₂R-Ab is a novel biomarker of IMN. sPLA₂R-Ab combined with uPLA₂R-Ab might be more helpful for diagnosis and activity in PLA₂R associated MN.

High-density Association Mapping and Interaction Analysis of PLA2R1 and HLA Regions with Idiopathic Membranous Nephropathy in Japanese

Although recent studies showed anti-PLA2R antibody plays a crucial role in idiopathic membranous nephropathy (IMN), detailed HLA mapping and interaction between the HLA genes and PLA2R1 have not been investigated in IMN. We genotyped across the PLA2R1 gene and the HLA region, using 183 IMN patients and 811 healthy controls. Five SNPs around the PLA2R1 gene were significantly associated with IMN. In addition to the two SNPs previously reported to be strongly associated with IMN, rs3749119 and rs35771982 (OR 3.02 and 2.93, P = 3.24E-14 and 4.64E-14, respectively), two novel intronic SNPs (rs2715928 and rs16844715) were also identified as IMN-associated SNPs (OR = 2.30 and 2.51, P = 3.15E-10 and 5.66E-13, respectively). In the HLA gene analysis, DRB1*1501 and DQB1*0602 were strongly associated with IMN (P = 1.14E-11 and 1.25E-11, respectively). The interaction was strongest between HLA-DRB1*15:01 - HLA-DQB1*06:02 and the intronic SNP rs2715928 (OR = 17.53, P = 4.26E-26). Furthermore, positive interaction was also observed between HLA-DRB1*15:01 - HLA-DQB1*06:02 and the missense SNP rs35771982 (OR = 15.91, P = 2.76E-29), which is in strong linkage disequilibrium with 5′UTR SNP rs3749119, and intronic SNP rs16844715 (OR = 15.91, P = 2.30E-26) for IMN. Neither HLA-DRB1*15:01 nor HLA-DQB1*06:02 was associated with steroid responsiveness, overall survival and renal survival during the observation period of mean 11 years though limited number of analysis.

Membranous Nephropathy: A Journey From Bench to Bedside

Lessons from an animal model that faithfully resembles human membranous nephropathy (MN) have informed our understanding of the pathogenesis of this organ-specific autoimmune disease and common cause of nephrotic syndrome. After it was established that the subepithelial immune deposits that characterize experimental MN form in situ when circulating antibodies bind to an intrinsic podocyte antigen, it was merely a matter of time before the human antigen was identified. The M-type phospholipase A2 receptor 1 (PLA2R) represents the major target antigen in primary MN, and thrombospondin type 1 domain-containing 7A (THSD7A) was more recently identified as a minor antigen. Serologic tests for anti-PLA2R and kidney biopsy specimen staining for PLA2R show >90% specificity and 70% to 80% sensitivity for the diagnosis of primary MN in most populations. The assays distinguish most cases of primary MN from MN associated with other systemic diseases, and sequential anti-PLA2R titers are useful to monitor treatment response. A positive pretransplantation test result for anti-PLA2R is also helpful for predicting the risk for posttransplantation recurrence. Identification of target epitopes within PLA2R and the genetic association of primary MN with class II major histocompatibility and PLA2R1 variants are 2 additional examples of our evolving understanding of this disease.

Phospholipase A2 Receptor Gene Polymorphisms Alter its Functions and Present a Genetic Risk of an Increased Intima-Media Thickness of the Carotid Artery

Aims: Phospholipase A₂ receptor 1 (PLA₂R) has multiple biological functions other than functioning as a receptor for secretory PLA_2s. Two nonsynonymous polymorphisms in the C-type lectin-like domains (CTLD) 1 of PLA₂R gene have been associated with idiopathic membranous nephropathy. This study examined whether the same PLA₂R polymorphisms may alter functions of PLA₂R in cells expressing the variant PLA₂R. In addition, the clinical relevance of the experiment was examined.

Methods: Two nonsynonymous polymorphisms (T/C at rs3749117 and G/C at rs35771982) in CTLD1 of PLA₂R gene were completely linked. HEK293 cells expressing human wild-type PLA₂R (T at rs3749117 and G at rs35771982) or human mutant PLA₂R that had double mutations (C at rs3749117 and C at rs35771982) were constructed.

Results: HEK293 cells expressing mutant PLA₂R had lower migratory and proliferative responses to collagen I compared with cells expressing wild-type PLA₂R. In 580 male patients, PLA₂R gene polymorphisms were associated with an increase in maximum intima-media thickness (maxIMT) of the carotid artery. The multivariate regression model showed that PLA₂R gene polymorphisms were a risk factor of an increased maxIMT that was independent of conventional risk factors (OR = 1.93, 95% CI: 1.17–3.19, p < 0.01).

Conclusions: The nonsynonymous common variants of PLA₂R gene altered biological functions in cells expressing variant PLA₂R. PLA₂R gene polymorphisms present a genetic risk of an increased IMT of the carotid artery in male. The functional changes in the variant PLA₂R may potentially be responsible for its association with an increased IMT of the carotid artery.

OXA-Carbapenemases Present in Clinical Acinetobacter baumannii-calcoaceticus Complex Isolates from Patients in Kurdistan Region, Iraq

In addition to intrinsic resistance in Acinetobacter baumannii, many different types of acquired resistance mechanisms have been reported, including the presence of VIM and IMP metallo β-lactamases and also of bla_OXA-23-like and bla_OXA-58-like enzymes. In the Kurdistan region of Iraq, the multiresistant A. baumannii-calcoaceticus complex is prevalent. We characterized the different mechanisms of resistance present in clinical isolates collected from different wards and different hospitals from the Kurdistan region. One hundred twenty clinical nonduplicate A. baumannii-calcoaceticus complex isolates were collected from four hospitals between January 2012 and October 2013. The identification of the isolates was confirmed by MALDI-TOF. The susceptibility to different antibiotics was determined by disk diffusion and analyzed in accordance to EUCAST guidelines. By PCR, the presence of bla_OXA-51-like, bla_OXA-23-like, bla_OXA-24-like, and bla_OXA-58-like genes was determined as well as the presence of the insertion element ISAba1. Clonal diversity was analyzed by pulsed-field gel electrophoresis (PFGE) using the restriction enzyme ApaI and, in addition, multilocus sequence typing (MLST) was performed on a selected subset of 15 isolates. All 120 A. baumannii isolates harbored bla_OXA-51-like genes. One hundred one out of 110 (92%) imipenem (IMP)-resistant A. baumannii-calcoaceticus complex isolates additionally carried the bla_OXA-23-like gene and four isolates (3%) were positive for bla_OXA-24-like. All 101 bla_OXA-23-like-positive isolates had the ISAba1 insertion sequence, 1,600 bp upstream of the bla_OXA-23-like gene. The bla_OXA-58-like gene was not detected in any of the 110 IMP-resistant strains. Eight different PFGE clusters were identified and distributed over the different hospitals. MLST analysis performed on a subset of 15 representative isolates revealed the presence of the international clone ST2 (Pasteur). Besides ST2 (Pasteur), also many other STs (Pasteur) were encountered such as ST136, ST94, ST623, ST792, and ST793, all carrying the bla_OXA-23 gene. In clinical A. baumannii-calcoaceticus complex isolates from Kurdistan-Iraq, the bla_OXA-23 gene in combination with the upstream ISAba1 insertion element is largely responsible for carbapenem resistance. Several small clusters of identical genotypes were found from patients admitted to the same ward and during overlapping time periods, suggesting transmission within the hospital. Identification of source(s) and limiting the transmission of these strains to patients needs to be prioritized.

Membranous nephropathy: A fairy tale for immunopathologists, nephrologists and patients

This article reviews the considerable progress which has been made in the recent years in the understanding of the pathophysiology of membranous nephropathy, a model of organ-specific auto-immune disease. It shows how experimental models developed more than 30 years ago have led to the identification of several human antigens including neutral endopeptidase in the neonate, phospholipase A2 receptor, and thrombospondin 1 domain 7A in the adult, and cationic bovine serum albumin in children. Thanks to a successful GWAS performed in European Caucasians, the genetics of the disease begins to be understood. These groundbreaking findings already have a major impact on patients' care owing to the development of reliable ELISA and immunofluorescence test for the detection of PLA2R antibodies and of PLA2R antigen screening in biopsies. This review will tell the story from the careful clinical observation of cases to the most recent therapeutic perspectives which have been made possible by these advances. Advances in medical science often proceed by steps which are highly interdependent. New, groundbreaking findings with important clinical implications often result from the combination of faithful experimental models and careful clinical observations. This is well illustrated by the story of membranous nephropathy which started more than 50 years ago. It is remarkable that in this disease, the experimental models predicted the pathophysiology of the human glomerulopathy. The stories that we will tell in this article are aimed at young clinical investigators who are sometimes reluctant to embark on research projects. We hope that they will convince them that bedside research performed with intellectual curiosity and a bit of chance can lead to significant progress in clinical medicine.

Pathophysiological advances in membranous nephropathy: time for a shift in patient's care

Membranous nephropathy is a major cause of nephrotic syndrome of non-diabetic origin in adults. It is the second or third leading cause of end-stage renal disease in patients with primary glomerulonephritis, and is the leading glomerulopathy that recurs after kidney transplantation (occurring in about 40% of patients). Treatment with costly and potentially toxic drugs remains controversial and challenging, partly because of insufficient insight into the pathogenesis of the disease and absence of sensitive biomarkers of disease activity. The disease is caused by the formation of immune deposits on the outer aspect of the glomerular basement membrane, which contain podocyte or planted antigens and circulating antibodies specific to those antigens, resulting in complement activation. In 2002, podocyte neutral endopeptidase was identified as an antigenic target of circulating antibodies in alloimmune neonatal nephropathy, and in 2009, podocyte phospholipase A2 receptor (PLA2R) was reported as an antigenic target in autoimmune adult membranous nephropathy. These major breakthroughs were translated to clinical practice very quickly. Measurement of anti-PLA2R antibodies in serum and detection of PLA2R antigen in glomerular deposits can now be done routinely. Anti-PLA2R antibodies have high specificity (close to 100%), sensitivity (70-80%), and predictive value. PLA2R detection in immune deposits allows for retrospective diagnosis of PLA2R-related membranous nephropathy in archival kidney biopsies. These tests already have a major effect on diagnosis and monitoring of treatment, including after transplantation.

Idiopathic membranous nephropathy and IgG4: an interesting relationship

Idiopathic membranous nephropathy (iMN) is a single-organ autoimmune disease characterized by subepithelial deposition of immune complexes containing IgG4 resulting in proteinuria, nephrotic syndrome, and, in some, end-stage renal disease. The pathogenesis involves a chronic IgG4 response against specific podocyte antigens which have now been at least partially defined in the neonatal, early childhood, and adult varieties. More has recently been learned about the genetic predisposition as well. This review discusses the pathophysiology of iMN in light of these discoveries and what is known about the genesis and potential clinical ramifications of an antigen-specific IgG4 response.

Membranous nephropathy: from models to man

As recently as 2002, most cases of primary membranous nephropathy (MN), a relatively common cause of nephrotic syndrome in adults, were considered idiopathic. We now recognize that MN is an organ-specific autoimmune disease in which circulating autoantibodies bind to an intrinsic antigen on glomerular podocytes and form deposits of immune complexes in situ in the glomerular capillary walls. Here we define the clinical and pathological features of MN and describe the experimental models that enabled the discovery of the major target antigen, the M-type phospholipase A2 receptor 1 (PLA2R). We review the pathophysiology of experimental MN and compare and contrast it with the human disease. We discuss the diagnostic value of serological testing for anti-PLA2R and tissue staining for the redistributed antigen, and their utility for differentiating between primary and secondary MN, and between recurrent MN after kidney transplant and de novo MN. We end with consideration of how knowledge of the antigen might direct future therapeutic strategies.

Immunopathogenesis of membranous nephropathy: an update

Membranous nephropathy (MN) is a non-inflammatory organ-specific autoimmune disease which affects the kidney glomerulus, resulting in the formation of immune deposits on the outer aspect of the glomerular basement membrane, complement-mediated proteinuria, and severe renal failure in 30% of patients. In the last 10 years, substantial advances have been made in the understanding of the molecular bases of MN, with the identification of several antigens and predisposing genes in children and adults. These ground-breaking findings already have a major impact on diagnosis and monitoring and to some extent on therapies. However, there is evidence that the disease is more complex and involves a variety of antigen-antibody systems and genes involved in immune response, progression, recovery, and protective mechanisms. We herein review these recent findings which open new perspectives of research. Understanding the complex pathogenesis of MN will offer many opportunities for future therapeutic interventions and will hopefully have a major impact on patient care. New insights into the molecular mechanisms of MN may also enlighten the pathogenesis of organ-specific autoimmune diseases.

HLA-DQA1 and PLA2R1 polymorphisms and risk of idiopathic membranous nephropathy

BACKGROUND AND OBJECTIVES

Single nucleotide polymorphisms (SNPs) within HLA complex class II HLA-DQ α-chain 1 (HLA-DQA1) and M-type phospholipase A2 receptor (PLA2R1) genes were identified as strong risk factors for idiopathic membranous nephropathy (IMN) development in a recent genome-wide association study. Copy number variants (CNVs) within the Fc gamma receptor III (FCGR3) locus have been associated with several autoimmune diseases, but their role in IMN has not been studied. This study aimed to validate the association of HLA-DQA1 and PLA2R1 risk alleles with IMN in a Spanish cohort, test the putative association of FCGR3A and FCGR3B CNVs with IMN, and assess the use of these genetic factors to predict the clinical outcome of the disease.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

A Spanish cohort of 89 IMN patients and 286 matched controls without nephropathy was recruited between October of 2009 and July of 2012. Case-control studies for SNPs within HLA-DQA1 (rs2187668) and PLA2R1 (rs4664308) genes and CNVs for FCGR3A and FCGR3B genes were performed. The contribution of these polymorphisms to predict clinical outcome and renal function decline was analyzed.

RESULTS

This study validated the association of these HLA-DQA1 and PLA2R1 SNPs with IMN in a Spanish cohort and its increased risk when combining both risk genotypes. No significant association was found between FCGR3 CNVs and IMN. These results revealed that HLA-DQA1 and PLA2R1 genotype combination adjusted for baseline proteinuria strongly predicted response to immunosuppressive therapy. HLA-DQA1 genotype adjusted for proteinuria was also linked with renal function decline.

CONCLUSION

This study confirms that HLA-DQA1 and PLA2R1 genotypes are risk factors for IMN, whereas no association was identified for FCGR3 CNVs. This study provides, for the first time, evidence of the contribution of these HLA-DQA1 and PLA2R1 polymorphisms in predicting IMN response to immunosuppressors and disease progression. Future studies are needed to validate and identify prognostic markers.

Diagnostic tests and treatment options in glomerular disease: 2014 update

Glomerular diseases historically have been challenging disorders to comprehend and treat for patients and physicians alike. Kidney biopsy is the gold standard of diagnosis, but the link between pathophysiology and the histologic representation of kidney injury has remained elusive in many of these diseases. As a result, treatment of glomerular disease usually involves therapies that are not specific to disease pathogenesis, such as blockade of the renin-angiotensin-aldosterone system and various immunosuppression regimens. Recent research has resulted in greater insight into some glomerular diseases, leading to the hope that new diagnostic tests and treatments targeting disease-specific mechanisms are on the horizon. We review recent progress on the understanding, diagnosis, and treatment of 4 glomerular diseases: immunoglobulin A nephropathy, focal segmental glomerulosclerosis, the C3 glomerulopathies, and idiopathic membranous nephropathy.

Interaction between PLA2R1 and HLA-DQA1 variants associates with anti-PLA2R antibodies and membranous nephropathy

Risk alleles at genome loci containing phospholipase A2 receptor 1 (PLA2R1) and HLA-DQA1 closely associate with idiopathic membranous nephropathy (IMN) in the European population, but it is unknown whether a similar association exists in the Chinese population and whether high-risk alleles promote the development of anti-PLA2R antibodies. Here, we genotyped 2132 Chinese individuals, including 1112 patients with IMN and 1020 healthy controls, for three single nucleotide polymorphisms (SNPs) within PLA2R1 and three SNPs within HLA genes. We also selected 71 patients, with varying genotypes, to assess for circulating anti-PLA2R antibody and for PLA2R expression in glomeruli. Three SNPs within PLA2R1 and one SNP within HLA-DQA1 strongly associated with IMN, and we noted gene-gene interactions involving these SNPs. Furthermore, these risk alleles strongly associated with the presence of anti-PLA2R antibodies and glomerular PLA2R expression. Among individuals who carried risk alleles for both genes, 73% had anti-PLA2R antibodies and 75% expressed PLA2R in glomeruli. In contrast, among individuals who carried protective genotypes of both genes, none had anti-PLA2R antibodies and glomerular expression of PLA2R was weak or absent. In conclusion, the interaction between PLA2R1 and HLA-DQA1 risk alleles associates with the development of IMN in the Chinese population. Individuals carrying risk alleles are predisposed to the generation of circulating anti-PLA2R autoantibodies, which may contribute to the development of IMN.

Phospholipase A2 receptor (PLA2R1) sequence variants in idiopathic membranous nephropathy

The M-type receptor for phospholipase A2 (PLA2R1) is the major target antigen in idiopathic membranous nephropathy (iMN). Our recent genome-wide association study showed that genetic variants in an HLA-DQA1 and phospholipase A2 receptor (PLA2R1) allele associate most significantly with biopsy-proven iMN, suggesting that rare genetic variants within the coding region of the PLA2R1 gene may contribute to antibody formation. Here, we sequenced PLA2R1 in a cohort of 95 white patients with biopsy-proven iMN and assessed all 30 exons of PLA2R1, including canonical (GT-AG) splice sites, by Sanger sequencing. Sixty patients had anti-PLA2R1 in serum or detectable PLA2R1 antigen in kidney tissue. We identified 18 sequence variants, comprising 2 not previously described, 7 reported as rare variants (<1%) in the Single Nucleotide Polymorphism Database or the 1000 Genomes project, and 9 known to be common polymorphisms. Although we confirmed significant associations among 6 of the identified common variants and iMN, only 9 patients had the private or rare variants, and only 4 of these patients were among the 60 who were PLA2R positive. In conclusion, rare variants in the coding sequence of PLA2R1, including splice sites, are unlikely to explain the pathogenesis of iMN.

Membranous nephropathy: the start of a paradigm shift

PURPOSE OF REVIEW

Primary membranous nephropathy is a common glomerular disease characterized by sub-epithelial immune deposits that has become the prototype of an autoimmune glomerular disease. The purpose of this review is to highlight recent advances regarding the pathogenesis of membranous nephropathy as well as potential new therapies.

RECENT FINDINGS

The discovery of two major podocyte antigens, neutral endopeptidase (NEP), involved in rare cases of neonatal membranous nephropathy, and the M-type phospholipase A2 receptor 1 (PLA2R1), the first antigen discovered in adults, have been major 'breakthroughs' in our understanding of the pathogenesis of human membranous nephropathy. Anti-PLA2R antibodies appear to predict activity of the disease as well as response to therapy. Pediatric and adult cases of membranous nephropathy occurring in the presence of circulating cationic bovine serum album (BSA) and anti-BSA antibodies have also been described, raising the possibility that food antigens may be involved in the development of membranous nephropathy. Moreover, the results of genetic susceptibility have become available. Exciting progress has also been made in the treatment of this disease including therapy with adrenocorticotropic hormone and rituximab.

SUMMARY

Understanding disease pathogenesis is crucial in guiding patient evaluation and designing appropriate therapy. Recent discoveries have helped to elucidate the pathophysiology of membranous nephropathy and may facilitate a more patient-specific treatment approach in these patients.

Searching for new biomarkers of renal diseases through proteomics

BACKGROUND

Technological advances have resulted in a renaissance of proteomic studies directed at finding markers of disease progression, diagnosis, or responsiveness to therapy. Renal diseases are ideally suited for such research, given that urine is an easily accessible biofluid and its protein content is derived mainly from the kidney. Current renal prognostic markers have limited value, and renal biopsy remains the sole method for establishing a diagnosis. Mass spectrometry instruments, which can detect thousands of proteins at nanomolar (or even femtomolar) concentrations, may be expected to allow the discovery of improved markers of progression, diagnosis, or treatment responsiveness.

CONTENT

In this review we describe the strengths and limitations of proteomic methods and the drawbacks of existing biomarkers, and provide an overview of opportunities in the field. We also highlight several proteomic studies of biomarkers of renal diseases selected from the plethora of studies performed.

SUMMARY

It is clear that the field of proteomics has not yet fulfilled its promise. However, ongoing efforts to standardize sample collection and preparation, improve study designs, perform multicenter validations, and create joint industry-regulatory bodies offer promise for the recognition of novel molecules that could change clinical nephrology forever.

Autoantibodies specific for the phospholipase A2 receptor in recurrent and De Novo membranous nephropathy

Recent findings in idiopathic membranous nephropathy (MN) suggest that in most patients, the disease is because of anti-phospholipase A(2) receptor (PLA(2) R1) autoantibodies. Our aim was to analyze the prevalence and significance of anti-PLA(2) R1 antibodies in recurrent and de novo MN after transplantation. We assessed circulating PLA(2) R1 autoantibodies by a direct immunofluorescence assay based on human embryonic kidney cells transfected with a PLA(2) R1 cDNA, and the presence of PLA(2) R1 antigen in immune deposits. We showed that PLA(2) R1 was involved in 5 of 10 patients with recurrent MN, but in none of the 9 patients with de novo MN. We also showed a marked heterogeneity in the kinetics and titers of anti-PLA(2) R1, which may relate to different pathogenic potential. We provide evidence that some patients with PLA(2) R1-related idiopathic MN and anti-PLA(2) R1 antibodies at the time of transplantation will not develop recurrence. Because PLA(2) R1 autoantibody was not always associated with recurrence, its predictive value should be carefully analyzed in prospective studies.

Genetics of kidney failure and the evolving story of APOL1

Chronic kidney disease (CKD) results from a wide array of processes that impair the kidney's ability to perform its major functions. As many as 20 million Americans suffer from CKD and nearly a half million from end-stage renal disease, but there are also examples of centenarians with adequate renal function. Family-based and genome-wide studies suggest that genetic differences substantially influence an individual's lifetime risk for kidney disease. One emerging theme is that evolution of genes related to host defense against pathogens may limit kidney longevity. The identification of these genetic factors will be critical for expanding our understanding of renal development and function as well as for the design of novel therapeutics for kidney disease.

Biomarkers in chronic kidney disease: a review

Chronic kidney disease (CKD) is a major public health problem. The classification of CKD by KDOQI and KDIGO and the routine eGFR reporting have resulted in increased identification of CKD. It is important to be able to identify those at high risk of CKD progression and its associated cardiovascular disease (CVD). Proteinuria is the most sensitive marker of CKD progression in clinical practice, especially when combined with eGFR, but these have limitations. Hence, early, more sensitive, biomarkers are required. Recently, promising biomarkers have been identified for CKD progression and its associated CVD morbidity and mortality. These may be more sensitive biomarkers of kidney function, the underlying pathophysiological processes, and/or cardiovascular risk. Although there are some common pathways to CKD progression, there are many primary causes, each with its own specific pathophysiological mechanism. Hence, a panel measuring multiple biomarkers including disease-specific biomarkers may be required. Large, longitudinal observational studies are needed to validate candidate biomarkers in a broad range of populations prior to implementation into routine CKD management. Recent renal biomarkers discovered include neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and liver-type fatty acid-binding protein. Although none are ready for use in clinical practice, it is timely to review the role of such biomarkers in predicting CKD progression and/or CVD risk in CKD.