Impact of plasminogen activator inhibitor-1 gene polymorphisms on primary membranous nephropathy

Advances in Pathogenesis of Idiopathic Membranous Nephropathy

BACKGROUND

Membranous nephropathy (MN), a major cause of nephrotic syndrome, has attracted people's attention in recent years for its growing prevalence. It is the second or third leading cause of ESRD in patients with primary glomerulonephritis and is the leading glomerulopathy that recurs after kidney transplantation.

SUMMARY

MN can be classified as idiopathic membranous nephropathy (IMN) and secondary MN. The discovery of the M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) provides the new diagnostic methods and treatment strategies for IMN on the molecular level. The study on single nucleotide polymorphism of IMN genes, such as the single M-type phospholipase A2 receptor 1 (PLA2R1) gene and human leukocyte antigen (HLA) gene, explains the pathogenesis of the disease from the perspective of genetics and conforms to the trend of the era of precision medicine.

KEY MESSAGES

This review focuses on advances in the pathogenesis of IMN, including molecular and genetic pathogenesis, as well as discussing the diagnostic and treatment guiding value brought by these new discoveries.

Relationship between plasminogen activator inhibitor-1 gene alterations and fibrosis in peritoneal dialysis patients

Peritoneal fibrosis (PF) is a pathological change that occurs mostly long-term peritoneal dialysis (PD) patients, as a result of triggering the inflammatory response. Plasminogen activator inhibitor-1 (PAI-1) is an important molecule featured in the development of fibrosis. It has been shown in literature that PAI-1 gene alterations are associated with fibrosis in many tissues and organs. However, PAI-1 gene alterations in long-term PD patients have not yet been investigated. In this study, PAI-1 4G/5G polymorphism was examined by reverse hybridization, and all coding exons of the PAI-1 gene were examined by sequence analysis to provide treatment modification in patients with predisposition before fibrosis develops. The patients were divided into two groups according to ultrafiltration failure test and duration of PD treatment: those with suspected PF or a high probability of developing PF (36%) and those with a low probability of developing PF (64%). There was no significant difference between the two groups in findings such as peritoneal equilibration test (PET), Kt/V, the content of the PD solution used, peritonitis, and PAI-1 4G/5G polymorphism (P > .05). A total of eight gene alterations (rs2227660, rs2227668, rs2854233, rs41281004, rs61553169, rs368413856, rs2227684) were detected by sequence analysis, one of which was exonic (rs6092). When the genotype distributions of these variants were examined, no significant difference was found between the two groups. PAI-1 gene changes were not detected in patients with the probability of developing PF. There is a need for further studies involving other molecules responsible for predisposing to PF with larger patient populations in patients undergoing long-term PD treatment.

Biomarker prediction for membranous nephropathy prognosis by microarray analysis

AIM

This study aimed to explore biomarkers for membranous nephropathy (MN) diagnosis and to provide novel insights into the pathogenesis of this disease.

METHODS

A microarray data set, GSE73953, was used, which contained 15 immunoglobulin A nephropathy (IgAN) samples, 8 MN samples and 2 healthy controls. Pretreatments were performed for the raw data, and then, the differentially expressed genes (DEG) were screened out using the limma package. The function and pathways of these genes were demonstrated through enrichment analysis. Protein-protein interaction (PPI) network analysis was performed to uncover interactions of DEG from the protein level. MN-related genes were further selected, integrating the Comparative Toxicogenomics Database (CTD).

RESULTS

In total, 446 and 231 DEG were identified in the comparisons of MN versus control and MN versus IgAN, respectively. JUN, NFKB1, TGFB1 and PPBP were the predominant DEG, and the latter two were especially differentially expressed between the MN and IgAN groups. UBL4A and EIF4G1 were the two most important DEG for MN because they were downregulated compared with both control and IgAN groups. The above-mentioned genes were highlighted in the PPI networks and mainly enriched the ribosome- and platelet-related function/pathways.

CONCLUSION

Several potential biomarkers were identified in MN, and some of them could well distinguish the MN from IgAN. Disruption of ribosome- and platelet-related function or pathways might contribute to MN progression. EIF4F and UBL4A might be two novel biomarkers for MN prognosis. Nevertheless, more experimental validations are needed.

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.

Long-Term Exposure to Air Pollution and Increased Risk of Membranous Nephropathy in China

The effect of air pollution on the changing pattern of glomerulopathy has not been studied. We estimated the profile of and temporal change in glomerular diseases in an 11-year renal biopsy series including 71,151 native biopsies at 938 hospitals spanning 282 cities in China from 2004 to 2014, and examined the association of long-term exposure to fine particulate matter of <2.5 μm (PM_2.5) with glomerulopathy. After age and region standardization, we identified IgA nephropathy as the leading type of glomerulopathy, with a frequency of 28.1%, followed by membranous nephropathy (MN), with a frequency of 23.4%. Notably, the adjusted odds for MN increased 13% annually over the 11-year study period, whereas the proportions of other major glomerulopathies remained stable. During the study period, 3-year average PM_2.5 exposure varied among the 282 cities, ranging from 6 to 114 μg/m³ (mean, 52.6 μg/m³). Each 10 μg/m³ increase in PM_2.5 concentration associated with 14% higher odds for MN (odds ratio, 1.14; 95% confidence interval, 1.10 to 1.18) in regions with PM_2.5 concentration >70 μg/m³ We also found that higher 3-year average air quality index was associated with increased risk of MN. In conclusion, in this large renal biopsy series, the frequency of MN increased over the study period, and long-term exposure to high levels of PM_2.5 was associated with an increased risk of MN.

Membranous nephropathy: a review on the pathogenesis, diagnosis, and treatment

In adults, membranous nephropathy (MN) is a major cause of nephrotic syndrome. However, the etiology of approximately 75% of MN cases is idiopathic. Secondary causes of MN are autoimmune diseases, infection, drugs, and malignancy. The pathogenesis of MN involves formation of immune complex in subepithelial sites, but the definite mechanism is still unknown. There are three hypotheses about the formation of immune complex, including preformed immune complex, in situ immune-complex formation, and autoantibody against podocyte membrane antigen. The formation of immune complex initiates complement activation, which subsequently leads to glomerular damage. Recently, the antiphospholipase A2 receptor antibody was found to be associated with idiopathic MN. This finding may be useful in the diagnosis and prognosis of MN. The current treatment includes best supportive care, which consists of the use of angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers, lipid-lowering agents, and optimal control of blood pressure. Immunosuppressive agents should be used for patients who suffer from refractory proteinuria or complications associated with nephrotic syndrome. Existing evidence supports the use of a combination of steroid and alkylating agents. This article reviews the epidemiology, pathogenesis, diagnosis, and the treatment of MN.

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.

Urokinase gene 3'-UTR T/C polymorphism is associated with malignancy and ESRD in idiopathic membranous nephropathy

Idiopathic membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults, and 25% of MN patients proceed to ESRD. Urokinase plasminogen activator (uPA) may play an important role in reducing renal fibrosis. This study was conducted to clarify the relationship between uPA gene polymorphisms and clinical manifestations of MN. We recruited 91 biopsy-diagnosed MN patients and 105 healthy subjects. Genotyping of uPA gene 3'-UTR T/C polymorphism was performed by polymerase chain reaction methods. The genotype distribution had no effect on the development of MN. Thirteen patients (15.9%; P = 0.008) acquired malignancies and seventeen (20.7%; P = 0.006) patients progressed to ESRD with the C/C genotype, but no patients with the T/C genotype did. In conclusion, we demonstrated that the presence of the uPA gene 3'-UTR C/C genotype was associated with ESRD as well as acquired malignancies in MN patients. These findings should prompt specific considerations for the treatment of MN patients to maintain a balance between treating disease entities and protecting the immune system from cancers.

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.

Toll-like receptor 9 SNPs are susceptible to the development and progression of membranous glomerulonephritis: 27 years follow-up in Taiwan

The purpose of this study was to determine whether toll-like receptors 9 (TLR9) gene polymorphisms (rs352139 and rs352140) were markers of susceptibility to the development and progression of membranous nephropathy (MGN) in Taiwanese patients. The polymorphisms were investigated by polymerase chain reaction in 397 Taiwanese individuals (134 MGN patients and 263 controls). Patients with malignancy, chronic infectious diseases, lupus nephritis, or drug-induced secondary MGN were excluded from the study. Data showed AA genotype at rs352139 SNP or GG genotype at rs352140 SNP may indicate higher risk for MGN (odds ratio [OR] = 1.55; 95% confidence interval [CI] = 1.02-2.35, at rs352139 SNP; OR = 1.57; 95% CI = 1.03-2.39, at rs352140 SNP). However, MGN patients with A-G haplotype were susceptible for decreased creatinine clearance rate and for seriously tubule-interstitial fibrosis. The result suggests for the first time that TLR9 (rs352139 and rs352140) polymorphisms may contribute to the development and progression of MGN.

Impact of the -675 4G/5G polymorphism of the plasminogen activator inhibitor-1 gene on childhood IgA nephropathy

Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of the fibrinolytic pathway and extracellular matrix (ECM) turnover. The -675 4G/5G polymorphism in the PAI-1 promoter is associated with altered PAI-1 transcription, suggesting that this polymorphism may be a candidate risk factor for diseases characterized by ECM accumulation, such as immunoglobulin A nephropathy (IgAN) and mesangial proliferative glomerulonephritis (MesPGN). We genotyped childhood patients with biopsy-confirmed IgAN (n=111) and MesPGN (n=47), and healthy control subjects (n=230) for the -675 4G/5G PAI-1 polymorphism by polymerase chain reaction-restriction fragment length polymorphism methods. The distribution of the 4G/4G (27.9%), 4G/5G (45.1%) and 5G/5G (27.0%) genotypes in IgAN patients was significantly different from the healthy controls (32.2, 54.3 and 13.5%, respectively) (p=0.0092). There was no significant difference in the genotype distributions of the 4G/5G polymorphism between MesPGN patients and the healthy controls. Regarding the impact of the polymorphism on IgAN, the 4G/4G genotype was markedly increased in patients with proteinuria (≥1,000 mg/day) and/or hypertension when compared to patients without proteinuria and hypertension (OR=5.23, 95% CI 1.34-20.38, P=0.0183). These findings indicate that the PAI-1 gene polymorphism may affect the susceptibility of childhood IgAN.

Association of STAT4 polymorphisms with susceptibility to primary membranous glomerulonephritis and renal failure

BACKGROUND

Membranous glomerulonephritis (MGN) is one of common causes of idiopathic nephrotic syndrome in adults, and 25% of MGN patients proceed to end-stage renal disease. STAT4 gene polymorphisms have been reported to be associated with many inflammatory diseases. The objective of this study was to clarify the relationship between STAT4 gene polymorphisms and the pathogenesis of MGN.

METHODS

We investigated the association of three STAT4 gene polymorphisms (rs3024912, rs3024908, and rs3024877) with the susceptibility to MGN in 403 Taiwanese populations (138 MGN patients and 265 controls).

RESULTS

The results indicated that the statistically significant difference in genotype frequency distribution was found at rs3024908 SNP in MGN patients and control groups (p=0.014). In addition, the individuals with the GG genotype at rs3024912 SNP may have a higher risk in kidney failure of MGN patients (adjusted odds ratio [OR]=3.255; 95% confidence interval [CI]=1.155-9.176, p=0.026).

CONCLUSIONS

Our data provide a new information that the STAT4 (rs3024912 and rs3024908) polymorphisms may be the underlying cause of MGN, and these polymorphisms revealed by this study warrant further investigation.

Effect of IL-6 C-572G polymorphism on idiopathic membranous nephropathy risk in a Han Chinese population

Membranous glomerulonephritis (MGN) is viewed as an immune-mediated glomerular disease, with immunologic expression occurring in genetically susceptible persons. The cytokine interleukin-6 (IL-6) gene polymorphism is known to impair intracellular signaling pathways following adaptive immune response. Our study gauged the effects of IL-6 C-572G (rs1800796) single nucleotide polymorphism (SNP) on MGN among Taiwan's Han Chinese population, as analyzed in 265 controls and 106 MGN patients. Genotyping for IL-6 C-572G SNP was performed by restriction fragment length polymorphism assay. Data showed stark differences in genotype and allele frequency distributions at IL-6 C-572G SNP between MGN patients and controls (p = 1.6E-04 and 1.7E-04, respectively). People with C allele or with CC genotype at IL-6 C-572G SNP showed higher risk of MGN (odds ratio = 2.42 and 2.71, respectively; 95% confidence interval = 1.51-3.87 and 1.60-4.60, respectively). These point to IL-6 C-572G polymorphism as the underlying cause of MGN; polymorphism merits further investigation.

Lack of association between transient receptor potential cation channel 6 polymorphisms and primary membranous glomerulonephritis

Membranous glomerulonephritis (MGN) is one common cause of idiopathic nephrotic syndrome. Transient receptor potential cation channel 6 (TRPC6) has been identified as causing a familial form of progressive focal and segmental glomerulosclerosis. The objective was to clarify the relationship between TRPC6 polymorphisms and MGN. We recruited a cohort of 134 biopsy-diagnosed MGN patients and 265 healthy subjects. Genotyping of TRPC6 polymorphisms was performed using allele-specific polymerase chain reaction methods. We then analyzed associations between TRPC6 gene polymorphisms and clinical manifestations and pathogenesis of MGN. There was no statistically significant difference of TRPC6 gene rs3824935 C/T, rs17096918 C/T, and rs4326755 A/G polymorphisms between controls and patients with MGN. There was no statistical significance of allele frequencies in these two groups. The characteristics of clinical parameters in TRPC6 gene (rs3284935) C/T polymorphism revealed no difference except proteinuria (p < 0.0005) between CC and non-CC genotype in MGN patients. Besides, no apparent statistically significant differences of rs17096918 C/T (TT and non-TT) and rs4326755 A/G (AA and non-AA) polymorphisms between genotypes were found in the clinical parameters. There is no different genotype distribution between normal controls and patients with MGN of TRPC6 gene. The data also show that TRPC6 gene may not be associated with disease clinical course of MGN.

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

Background

Idiopathic membranous nephropathy (IMN) is one of the most common forms of autoimmune nephritic syndrome in adults. The purpose of this study is to evaluate whether polymorphisms of PLA2R1 affect the development of IMN.

Methods

Taiwanese-Chinese individuals (129 patients with IMN and 106 healthy controls) were enrolled in this study. The selected single nucleotide polymorphisms (SNPs) in PLA2R1 were genotyped by real-time polymerase chain reaction using TaqMan fluorescent probes, and were further confirmed by polymerase chain reaction-restriction fragment length polymorphism. The roles of the SNPs in disease progression were analyzed.

Results

Genotype distribution was significantly different between patients with IMN and controls for PLA2R1 SNP rs35771982 (p = 0.015). The frequency of G allele at rs35771982 was significantly higher in patients with IMN as compared with controls (p = 0.005). In addition, haplotypes of PLA2R1 may be used to predict the risk of IMN (p = 0.004). Haplotype H1 plays a role in an increased risk of IMN while haplotype H3 plays a protective role against this disease. None of these polymorphisms showed a significant and independent influence on the progression of IMN and the risk of end-stage renal failure and death (ESRF/death). High disease progression in patients having C/T genotype at rs6757188 and C/G genotype at rs35771982 were associated with a low rate of remission.

Conclusions

Our results provide new evidence that genetic polymorphisms of PLA2R1 may be the underlying cause of IMN, and the polymorphisms revealed by this study warrant further investigation.

Association between genetic polymorphisms of the NPHS1 gene and membranous glomerulonephritis in the Taiwanese population

BACKGROUND

Membranous glomerulonephritis (MGN) is one of the most common causes of nephrotic syndrome in adults. NPHS1 encoding nephrin is a transmembrane protein of the immunoglobulin family. We clarified the relationship between NPHS1 gene polymorphisms and the susceptibility or progression of MGN.

METHODS

We recruited a cohort of 132 biopsy-diagnosed MGN patients and 257 healthy subjects. Genotyping of three SNPs (rs401824, rs437168 and rs3814995) at chromosome positions 41034749 (5'UTR), 41026259(exon17) and 41034052 (exon 3) was performed using a Taqman SNP genotyping assay.

RESULTS

There was a significant difference in genotype frequency distribution of rs437168 polymorphism between MGN patients and controls. The results also showed that the frequency of the G allele was significantly higher in the patient group. Among the polymorphisms rs437168, rs401824 and rs3814995, no significant haplotype was shown in MGN patients. A stratified analysis revealed that a high disease progression in the AA genotype of rs401824 and GG genotype of rs437168 patients were associated with a low rate of remission.

CONCLUSIONS

The presence of the different genotypes of NPHS1 was associated with susceptibility of MGN and the remission of proteinuria during disease progression after the therapy.