The CTLA-4 +49GG genotype is associated with susceptibility for nephrotic kidney diseases

What did we learn from CTLA-4 insufficiency on the human immune system?

Cytotoxic-T-lymphocyte-antigen-4 (CTLA-4) is a negative immune regulator constitutively expressed on regulatory T (Treg) cells and upregulated on activated T cells. CTLA-4 inhibits T cell activation by various suppressive functions including competition with CD28, regulation of the inhibitory function of Treg cells, such as transendocytosis, and the control of adhesion and motility. Intrinsic CTLA-4 signaling has been controversially discussed, but so far no distinct signaling pathway has been identified. The CTLA-4-mediated Treg suppression plays an important role in the maintenance of peripheral tolerance and the prevention of autoimmune diseases. Human CTLA-4 insufficiency is caused by heterozygous germline mutations in CTLA4 and characterized by a complex immune dysregulation syndrome. Clinical studies on CTLA4 mutation carriers showed a reduced penetrance and variable expressivity, suggesting modifying factor(s). One hundred and forty-eight CTLA4 mutation carriers have been reported; patients showed hypogammaglobulinemia, recurrent infectious diseases, various autoimmune diseases, and lymphocytic infiltration into multiple organs. The CTLA-4 expression level in Treg cells was reduced, while the frequency of Treg cells was increased in CTLA-4-insufficient patients. The transendocytosis assay is a specific functional test for the assessment of newly identified CTLA4 gene variants. Immunoglobulin substitution, corticosteroids, immunosuppressive therapy, and targeted therapy such as with CTLA-4 fusion proteins and mechanistic target of rapamycin (mTOR) inhibitors were applied; patients with life-threatening, treatment-resistant symptoms underwent hematopoietic stem cell transplantation. The fact that in humans CTLA-4 insufficiency causes severe disease taught us that the amount of CTLA-4 molecules present in/on T cells matters for immune homeostasis. However, whether the pathology-causing activated T lymphocytes in CTLA-4-insufficient patients are antigen-specific is an unsolved question. CTLA-4, in addition, has a role in autoimmune diseases and cancer. Anti-CTLA-4 drugs are employed as checkpoint inhibitors to target various forms of cancer. Thus, clinical research on human CTLA-4 insufficiency might provide us a deeper understanding of the mechanism(s) of the CTLA-4 molecule and immune dysregulation disorders.

CTLA-4 Expression Inversely Correlates with Kidney Function and Serum Immunoglobulin Concentration in Patients with Primary Glomerulonephritides

Major causes of chronic kidney disease are primary proliferative and nonproliferative glomerulonephritides (PGN and NPGN). However, the pathogenesis of PGN and NPGN is still not fully understood. Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) is a T-cell membrane receptor that plays a key role in T-cell inhibition. Despite its role in autoimmunological diseases, little is known about the involvement of CTLA-4 in the pathogenesis of PGN and NPGN. The objective of this study was to determine the role of CTLA-4 in the pathogenesis of PGN and NPGN by evaluating the frequencies of T and B lymphocytes expressing CTLA-4 and the serum concentration of the sCTLA-4 isoform in patients with PGN and NPGN in relation to clinical parameters. The study included peripheral blood (PB) samples from 40 PGN and NPGN patients and 20 healthy age- and sex-matched volunteers (control group). The viable PB lymphocytes were labeled with fluorochrome-conjugated monoclonal anti-CTLA-4 antibodies and analyzed using flow cytometry. The serum concentration of sCTLA-4 was measured using ELISA. The frequencies and absolute counts of CD4+/CTLA-4+ T lymphocytes, CD8+/CTLA-4+ T lymphocytes and CD19+/CTLA-4+ B lymphocytes and the serum sCTLA-4 concentration were lower in PGN and NPGN patients that in the control group. Reduced sCTLA-4 expression was associated with a lower concentration of serum immunoglobulins. Our results indicate that deregulation of CTLA-4 expression may result in continuous activation of T cells and contribute to the pathogenesis of PGN and NPGN.

Lipid metabolism participates in human membranous nephropathy identified by whole-genome gene expression profiling

A genomics approach is an effective way to understand the possible mechanisms underlying the onset and progression of disease. However, very limited results have been published regarding whole-genome expression analysis of human idiopathic membranous nephropathy (iMN) using renal tissue. In the present study, gene expression profiling using renal cortex tissue from iMN patients and healthy controls was conducted; differentially expressed genes (DEGs) were filtered out, and 167 up- and 291 down-regulated genes were identified as overlapping DEGs (ODEGs). Moreover, enrichment analysis and protein-protein network construction were performed, revealing enrichment of genes mainly in cholesterol metabolism and arachidonic acid metabolism, among others, with 38 hub genes obtained. Furthermore, we found several associations between circulating lipid concentrations and hub gene signal intensities in the renal cortex. Our findings indicate that lipid metabolism, including cholesterol metabolism and arachidonic acid metabolism, may participate in iMN pathogenesis through key genes, including apolipoprotein A1 (APOA1), apolipoprotein B (APOB), apolipoprotein C3 (APOC3), cholesteryl ester transfer protein (CETP), and phospholipase A2 group XIIB (PLA2G12B).

Cytotoxic T- Lymphocyte Antigen-4 (CTLA4) Gene Expression and Urinary CTLA4 Levels in Idiopathic Nephrotic Syndrome

OBJECTIVES

To detect Cytotoxic T- Lymphocyte Antigen-4 (CTLA4) single nucleotide polymorphisms (SNPs) at +49A/G (rs231775) and -318C/T (rs5742909) positions in children with idiopathic nephrotic syndrome (INS) and also assay urinary soluble CTLA4 (sCTLA4) levels in children with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS) and steroid sensitive nephrotic syndrome (SSNS) in remission.

METHODS

The study included 59 patients of INS (MCD-23, FSGS-15 and SSNS in remission-21) and 35 healthy controls. The CTLA4 SNPs profiling was done in peripheral blood mononuclear cells and urinary sCTLA4 level was assayed by ELISA kit.

RESULTS

Although frequency of homozygous +49 GG (rs4553808) genotype (26.3% vs. 11.4%; p = 0.231) and G allele (52.6% vs. 40%; p = 0.216) were found to be higher in INS as compared to controls, the differences were statistically non-significant. Genotypes GG, AG, AA and alleles A and G frequencies were comparable among MCD, FSGS and controls. SNP at -318 C/T (rs5742909) did not show homozygous TT genotype both in INS as well as controls. Median urinary sCTLA4/creatinine level was significantly higher in MCD as compared to FSGS (p = 0.027), SSNS in remission (p = 0.001) and controls (p = 0.003).

CONCLUSIONS

The positive associations of +49 GG genotype and G allele in patients with nephrotic syndrome were not observed. The frequencies did not differ significantly among MCD, FSGS and controls. Urinary sCTLA4 level was significantly increased in MCD; suggesting its possible role in the pathogenesis of disease.

CTLA-4 Polymorphisms in Patients with IgA Nephropathy Correlate with Proteinuria

BACKGROUND/AIMS

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis and still constitutes one of the most important causes of end-stage renal disease. Abnormal T cell responses may play a role in IgAN pathogenesis. Co-stimulatory molecules such as cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) are important for naive T cells to initiate and terminate immune responses. Single nucleotide polymorphisms (SNPs) in the CTLA4 gene locus are associated with several autoimmune diseases.

METHODS

We aimed to investigate the occurrence of the SNPs -318C/T, +49A/G and CT60 G/A within the CTLA4 locus in healthy blood donors (n=455) and IgAN patients (n=252) recruited from the recently published STOP-IgAN trial. The presence of these SNPs was then associated with baseline proteinuria in IgAN patients.

RESULTS

We observed a significantly increased frequency of the CTLA4 -318C/T genotype in IgAN patients as compared to controls (CC vs. CT+TT: OR 1.65, 95%-CI 1.03-2.65, p=0.035). No significant associations, neither with the +49A/G nor for the CT60 G/A SNP, were detected. However, when we stratified for proteinuria at time of inclusion into the STOP-IgAN trial (<1 g/day vs. >1 g/day), we observed significant differences in the frequencies of the CT60 G/A genotype, i.e. a significantly increased risk for higher proteinuria in patients carrying the G allele (OR 2.81, 95%-CI 1.03-7.64, p=0.042).

CONCLUSION

The CTLA4 -318/C/T SNP was associated with an increased risk to develop IgAN, while the CT60 G/A genotype significantly associated with the risk for higher proteinuria suggesting a possible role for CTLA-4 in IgAN.

Remaining Physiological Barriers in Porcine Kidney Xenotransplantation: Potential Pathways behind Proteinuria as well as Factors Related to Growth Discrepancies following Pig-to-Kidney Xenotransplantation

Considerable shortages in the supply of available organs continue to plague the field of solid organ transplantation. Despite changes in allocation, as well as the utilization of extended criteria and living donors, the number of patients waiting for organs continues to grow at an alarming pace. Xenotransplantation, cross-species solid organ transplantation, offers one potential solution to this dilemma. Previous extensive research dedicated to this field has allowed for resolution of xenograft failure due to acute rejection, leaving new areas of unresolved challenges as barriers to success in large animal models. Specific to kidney xenotransplantation, recent data seems to indicate that graft compromise can occur due to discrepancies in growth between breeds of donors and significant proteinuria leading to nephrotic syndrome in the recipient. Given these potential limitations, herein, we review potential pathways behind proteinuria, as well as potential causative factors related to growth discrepancies. Control of both of these has the potential to allow xenotransplantation to become clinically applicable in an effort to resolve this organ shortage crisis.

The glomerular permeability factors in idiopathic nephrotic syndrome

It is currently postulated that steroid-sensitive idiopathic nephrotic syndrome (SSNS) and steroid-resistant idiopathic nephrotic syndrome (SRNS), which are not related to the mutation of a gene coding for podocyte structures or for glomerular basement membrane proteins, result from a circulating factor affecting podocyte shape and function. T lymphocytes have for a long time been suspected to be involved in the pathophysiology of these diseases. The successful treatment of steroid-dependant nephrotic syndrome with rituximab suggests a potential role for B lymphocytes. Clinical and experimental data indicate roles for cytokines IL-13, TNFα, circulating cardiotrophin-like cytokine factor 1 (member of the IL-6 family), circulating hemopexin, radical oxygen species, and the soluble urokinase-type plasminogen activator receptor (suPAR) in the development of nephrotic syndrome. Podocyte metabolism modifications-leading to the overexpression of the podocyte B7-1antigen (CD 80), hypoactivity of the podocyte enzyme sphingomyelin phosphodiesterase acid-like 3 b (SMPDL3b), and to the podocyte production of a hyposialylated form of the angiopoietin-like 4 (Angptl4)-are mechanisms possibly involved in the changes in the podocyte cytoskeleton leading to SSNS and or SRNS. Different multifactorial pathophysiological mechanisms can be advocated for SSNS and SRNS. The present paper reviews the experimental and clinical data upon which the different hypotheses are based and reports their possible clinical applications.

Case series: CTLA4-IgG1 therapy in minimal change disease and focal segmental glomerulosclerosis

BACKGROUND

Minimal Change Disease (MCD) in relapse is associated with increased podocyte CD80 expression and elevated urinary CD80 excretion, whereas focal segmental glomerulosclerosis (FSGS) has mild or absent CD80 podocyte expression and normal urinary CD80 excretion.

METHODS

One patient with MCD, one patient with primary FSGS and three patients with recurrent FSGS after transplantation received CD80 blocking antibodies (abatacept or belatacept). Urinary CD80 and CTLA-4 levels were measured by ELISA. Glomeruli were stained for CD80.

RESULTS

After abatacept therapy, urinary CD80 became undetectable with a concomitant transient resolution of proteinuria in the MCD patient. In contrast, proteinuria remained unchanged after abatacept or belatacept therapy in the one patient with primary FSGS and in two of the three patients with recurrent FSGS despite the presence of mild CD80 glomerular expression but normal urinary CD80 excretion. The third patient with recurrent FSGS after transplantation had elevated urinary CD80 excretion immediately after surgery which fell spontaneously before the initiation of abatacept therapy; after abatacept therapy, his proteinuria remained unchanged for 5 days despite normal urinary CD80 excretion.

CONCLUSION

These observations are consistent with a role of podocyte CD80 in the development of proteinuria in MCD. In contrast, CD80 may not play a role in recurrent FSGS since the urinary CD80 of our three patients with recurrent FSGS was only increased transiently after surgery and normalization of urinary CD80 did not result in resolution of proteinuria.

Pathogenesis of childhood idiopathic nephrotic syndrome: a paradigm shift from T-cells to podocytes

BACKGROUND

Nephrotic syndrome is the most common cause of kidney disease in children, but its pathogenesis remains unclear. This article reviews the novel aspects of the mechanisms underlying massive proteinuria in minimal-change disease, which is the most common form of childhood nephrotic syndrome.

DATA SOURCES

This article integrates the findings of a PubMed database search for English language articles published in the past 40 years (from September 1974 to February 2014) using the key words "pathogenesis", "minimal change nephrotic syndrome" or "idiopathic nephrotic syndrome".

RESULTS

Unknown humoral factors associated with T-cell dysfunction have been thought to play an important role in the pathogenesis of minimal-change disease. However, recent findings are changing this paradigm, i.e., visceral glomerular epithelial cells (podocytes) may be involved via expression of molecules such as CD80 and angiopoietin-like 4.

CONCLUSIONS

Recent evidence suggests that minimal-change disease results from interactions between humoral factors and dysfunctional podocytes. In addition to immunosuppressant drugs that target lymphocytes, a biological agent such as an antibody against the abnormal molecule(s) expressed by podocytes may provide novel drug treatment for minimal-change disease.

Minimal change disease: a dysregulation of the podocyte CD80-CTLA-4 axis?

BACKGROUND

Minimal Change Disease (MCD) is associated with CD80 expression in podocytes and elevated urinary CD80 excretion during active renal disease. We have evaluated the urinary excretion of CTLA-4 and CD80 during different stages of the nephrotic syndrome in patients with MCD to test the hypothesis that persistent increased urinary CD80 excretion in patients with MCD in relapse is due to an ineffectual CTLA-4 response of the host to curtail the activation of CD80.

METHODS

Thirty-two children with biopsy-proven MCD were studied during relapse and/or remission. Eleven healthy subjects served as controls.

RESULTS

Urinary CD80 excretion was significantly increased in MCD patients in relapse relative to that in MCD patients in remission (p < 0.001) and controls (p < 0.001). Although urinary CTLA-4 excretion was higher in MCD patients in relapse than in MCD patients in remission (p = 0.01) and controls (p = 0.03), no significant correlation was observed between urinary CD80 excretion and urinary CTLA-4 level in MCD patients at the time of relapse (p = 0.06). At the time of remission, CD80 had decreased significantly in all patients, but CTLA-4 levels either decreased or remained unchanged in all but five patients, and no correlation was observed between urinary CD80 excretion and CTLA-4 level (p = 0.7).

CONCLUSIONS

Urinary CTLA-4 levels do not correlate with urinary CD80 excretion, suggesting the possibility that the CTLA4 response may be suboptimal in this disease during relapse.

The association of PTPN22 rs2476601 polymorphism and CTLA-4 rs231775 polymorphism with LADA risks: a systematic review and meta-analysis

Although the polymorphisms of PTPN22 and the variants of CTLA-4 have been reported to be the susceptibility genes, which increased risk of latent autoimmune diabetes in adults (LADA), the results remained inconclusive. The aim of this meta-analysis was to evaluate the association between the polymorphisms of two genes and LADA. We performed a systematic review by identifying relevant studies and applied meta-analysis to pool gene effects. Data from ten studies published between 2001 and 2013 were pooled for two polymorphisms: rs2476601 in the PTPN22 gene and rs231775 in the CTLA-4 gene. Data extraction and assessments for risk of bias were independently performed by two reviewers. Fixed-effect model and random-effect model were used to pool the odds ratios; meanwhile, heterogeneity test, publication bias and sensitive analysis were explored. The minor T allele at rs2476601 and the minor G at rs231775 carried estimated relative risks (odds ratio) of 1.52 (95 % CI 1.29-1.79) and 1.39 (95 % CI 1.11-1.74), respectively. These alleles contributed to an absolute lowering of the risk of all LADA by 4.88 and 14.93 % when individuals do not carry these alleles. The estimated lambdas were 0.49 and 0.63, suggesting a codominant model of effects was most likely for two genes. In summary, our systematic review has demonstrated that PTPN22 rs2476601 and CTLA-4 rs231775 are potential risk factors for LADA. An updated meta-analysis is required when more studies are published to increase the power of these polymorphisms and LADA.

Familial clustering of ESRD in the Norwegian population

BACKGROUND AND OBJECTIVES

Studies and clinical experience suggest that kidney disease clusters in families, but few population-based studies have been performed. This study investigates risks and causes of ESRD in Norwegians with and without a first-degree relative with ESRD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

On the basis of data from the Norwegian Population Registry, first-degree relatives for most Norwegians were identified. All Norwegians with ESRD (defined as chronic RRT) since 1980 have been registered in the Norwegian Renal Registry. All Norwegians born in Norway who were alive in 1980 and had at least one registered relative were included. For this study, data on ESRD were available through 2009, and individuals without ESRD were censored at December 31, 2009. Data were analyzed in a cohort design, with ESRD in a first-degree relative of the included person as the main explanatory variable. Risks of ESRD and different causes of ESRD were analyzed using Cox regression statistics.

RESULTS

In total, 5,119,134 individuals were included, of whom 8203 individuals developed ESRD during follow-up and 27,046 individuals had a first-degree relative with ESRD. Compared with individuals without a first-degree relative with ESRD, individuals with a first-degree relative with ESRD had a relative risk of ESRD of 7.2 (95% confidence interval, 6.5 to 8.1). Similar analyses showed that relative risk of ESRD caused by nonhereditary causes was 3.7 (95% confidence interval, 3.1 to 4.4), relative risk of ESRD caused by glomerular disease was 5.2 (95% confidence interval, 4.1 to 6.6), relative risk of ESRD caused by interstitial disease was 4.7 (95% confidence interval, 3.1 to 7.3), relative risk of ESRD caused by diabetic nephropathy was 2.6 (95% confidence interval, 1.6 to 4.1), and relative risk of ESRD caused by hypertensive nephrosclerosis was 2.6 (95% confidence interval, 1.6 to 4.1). Relative risk of nonhereditary parenchymal renal disease was 3.8 (95% confidence interval, 3.1 to 4.7).

CONCLUSIONS

As expected, ESRD clusters in families. Interestingly, ESRD without known hereditary cause also clusters in families.

The association between cytotoxic T lymphocyte-associated antigen-4 and cervical cancer

Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) gene polymorphisms have been associated with many autoimmune diseases and malignancy susceptibility, but the relationship between CTLA-4 and cervical cancer is still controversial. Hence, a meta-analysis of the published studies for the CTLA-4 gene polymorphisms and the risk of cervical cancer was performed to evaluate the association between them. Odds ratios (ORs) and 95% confidence intervals (CIs) for the codominant, dominant, and recessive genetic models were assessed. The fixed or random effect pooled measure was selected on the basis of the heterogeneity test among studies. The heterogeneity among studies was evaluated using the I (2). Eight studies with 2,835 cases and 2,560 controls were included. In seven studies for the CTLA-4 +49A/G polymorphism, a significant association was showed between the A allele and the increased risk of cervical cancer in the codominant (OR 1.16, 95% CI 1.05-1.29), dominant (OR 1.18, 95% CI 1.03-1.36), and recessive (OR 1.24, 95% CI 1.05-1.56) models. In five studies for the CTLA-4 -318C/T polymorphism, the meta-analysis showed a significant association of the C allele with the reduced risk of cervical cancer in the codominant (OR 0.79, 95% CI 0.66-0.94) and recessive (OR 0.76, 95% CI 0.63-0.93) models. This meta-analysis suggested that +49A/G and -318C/T polymorphisms of the CTLA-4 gene were significantly associated with the risk of cervical cancer. However, further studies are required to draw a solid conclusion on the relation between the CTLA-4 polymorphism and the risk of cervical cancer.