Chemokine (CCR) and fractalkine (CX3CR) receptors and end stage renal disease

Role of the CX3CL1-CX3CR1 axis in renal disease

Excessive infiltration of immune cells into the kidney is a key feature of acute and chronic kidney diseases. The family of chemokines comprises key drivers of this process. Fractalkine [chemokine (C-X3-C motif) ligand 1 (CX3CL1)] is one of two unique chemokines synthesized as a transmembrane protein that undergoes proteolytic cleavage to generate a soluble species. Through interacting with its cognate receptor, chemokine (C-X3-C motif) receptor 1 (CX3CR1), CX3CL1 was originally shown to act as a conventional chemoattractant in the soluble form and as an adhesion molecule in the transmembrane form. Since then, other functions of CX3CL1 beyond leukocyte recruitment have been described, including cell survival, immunosurveillance, and cell-mediated cytotoxicity. This review summarizes diverse roles of CX3CL1 in kidney disease and potential uses as a therapeutic target and novel biomarker. As the CX3CL1-CX3CR1 axis has been shown to contribute to both detrimental and protective effects in various kidney diseases, a thorough understanding of how the expression and function of CX3CL1 are regulated is needed to unlock its therapeutic potential.

Fractalkine (CX3CL1) and Its Receptor CX3CR1: A Promising Therapeutic Target in Chronic Kidney Disease?

Innate immune cells are key contributors to kidney inflammation and fibrosis. Infiltration of the renal parenchyma by innate immune cells is governed by multiple signalling pathways. Since the discovery of the chemokine fractalkine (CX3CL1) and its receptor, CX3CR1 over twenty years ago, a wealth of evidence has emerged linking CX3CL1-CX3CR1 signalling to renal pathologies in both acute and chronic kidney diseases (CKD). However, despite the extent of data indicating a pathogenic role for this pathway in kidney disease and its complications, no human trials of targeted therapeutic agents have been reported. Although acute autoimmune kidney disease is often successfully treated with immunomodulatory medications, there is a notable lack of treatment options for patients with progressive fibrotic CKD. In this article we revisit the CX3CL1-CX3CR1 axis and its functional roles. Furthermore we review the accumulating evidence that CX3CL1-CX3CR1 interactions mediate important events in the intra-renal pathophysiology of CKD progression, particularly via recruitment of innate immune cells into the kidney. We also consider the role that systemic activation of the CX3CL1-CX3CR1 axis in renal disease contributes to CKD-associated cardiovascular disease. Based on this evidence, we highlight the potential for therapies targeting CX3CL1 or CX3CR1 to benefit people living with CKD.

CX3CR1 at V249M and T280M Gene Polymorphism and Its Potential Risk for End-Stage Renal Diseases in Egyptian Patients

CX3CL1-CX3CR1 pathway may be one of the future treatment targets to delay the progression of end-stage renal diseases. This study aimed to evaluate the CX3CR gene polymorphism in Egyptian patients with ESRD and its relation to fractalkine blood level. The study included 100 patients with ESRD on dialysis, 61 males and 39 females with mean age 51.02 ± 7.8 years. The V2491 genotype revealed a significant increase in the frequency of GG genotype in healthy control (83%) compared to patients [69%] with a significant increase in GA in patients [30%] compared to control subjects [15%], P = 0.03. T280M study showed a statistically significant prevalence of TT genotype in healthy control subjects [86%-OR 95% CI 1.7] compared to patients [70%] with a significant increase in the prevalence of TA in patients [29%] compared to control subjects [13%], P = 0.01. There was a significant increase in fractalkine levels in genotypes GA + AA [503.04±224.1] pg/ml compared to genotype GG [423.6 210.3], P = 0.03. Moreover, there was a significant increase in the blood level of fractalkine in genotype TA + AA [498.8 219.6] compared to genotype TT [426.8±212.8], P = 0.05. In conclusion, our study showed that both V2491-GA genotype and T280M-TA are associated with potential risk for end-stage renal disease in Egyptian patients.

Association of CX3CR1 Gene Polymorphisms with Fractalkine, Fractalkine Receptor, and C-Reactive Protein Levels in Patients with Kidney Failure

Fractalkine (CX3CL1) is a chemokine that plays a significant role in inflammation, one of the pathophysiological processes underlying end-stage renal disease (ESRD). Genetic factors are significantly involved in cytokine expression and have been studied as potential risk factors for chronic kidney disease (CKD). Objectives: We aimed to elucidate the association of CX3CR1 gene polymorphisms rs3732378 and rs3732379 with the levels of CX3CL1, CX3CL1 receptor (CX3CR1), as well as C-reactive protein (CRP). Patients and methods: We enrolled 198 participants, including 106 patients with ESRD and 92 controls. Peripheral blood samples were collected from each patient for genetic (rs3732378 and rs3732379 polymorphisms) and immunoenzymatic (fractalkine, CX3CR1, CRP) tests. Results: CX3CR1 and CRP levels were higher in patients with ESRD than in controls (p < 0.05). Fractalkine levels were significantly higher in ESRD patients who were homozygous for the G allele of the rs3732378 polymorphism and for the C allele of the rs3732379 polymorphism than in homozygous controls. Moreover, carriers of these alleles among patients with ESRD had significantly higher CX3CR1 levels than controls. Conclusions: The G allele of the rs3732378 polymorphism and the C allele of the rs3732379 polymorphism of the CX3CR1 gene are associated with higher CX3CL1 and CX3CR1 levels. Our study suggests that CX3CR1 gene polymorphisms could be potentially involved in the pathogenesis of ESRD, but the study needs to be replicated in a larger population with a longitudinal follow-up study. Identification of genetic factors associated with inflammation in ESRD may contribute to the development of targeted gene therapies in the future.

Association of chemokine receptor CX3CR1 V249I and T280M polymorphisms with chronic kidney disease

The chemokine fractalkine (CX3CL1) and its receptor CX3CR1 are involved in the activation of leukocytes. Two common single-nucleotide polymorphisms of the CX3CR1 gene, V249I and T280M, have been associated with reduced fractalkine signaling, leading to decreased adhesive function and leukocyte chemotaxis. We hypothesized that variation in the CX3CR1 gene could be associated with chronic kidney disease (CKD), a disease of inflammatory activation. We studied the association between CX3CR1 V249I and T280M polymorphisms, and fractalkine and highly sensitive C-reactive protein (hs-CRP) levels in 123 patients with CKD and 100 healthy controls (HCs). Genotype analysis was done by polymerase chain reaction-restriction fragment length polymorphism, and fractalkine and hs-CRP levels were analyzed by enzyme-linked immunosorbent assay. MM genotype of T280M was absent in CKD patients, while in controls it was seen in 1% of the individuals. The allele frequencies in both the groups were similar (P = 0.059). Compared to HC, M280M + T280M genotype was more frequent in CKD (P = 0.041). The frequency of II genotype of V249I was 0.8% in CKD, whereas in HC, it was 2%. I249I + V249I genotype was more frequent in CKD as compared to HC (P = 0.034). No difference in allelic frequency of V249I was noted between the two groups (P = 0.061, odds ratios = 1.74, 95% confidence intervals = 0.96–3.12). Plasma fractalkine and serum hs-CRP levels were higher in CKD subjects (P = 0.004 and P < 0.0001). No association of either genotype was found with fractalkine and hs-CRP levels. Polymorphisms at I249 and M280 genotype in CX3CR1 gene are associated with CKD; however, there was no association of fractalkine or inflammatory marker with these genotypes.

Associations of fractalkine receptor (CX3CR1) and CCR5 gene variants with hypertension, diabetes and atherosclerosis in chronic renal failure patients undergoing hemodialysis

PURPOSE

We aimed to investigate the associations of fractalkine receptor (CX3CR1) V249I, T280M and CCR5-59029 A/G gene polymorphisms in chronic renal failure (CRF) subjects undergoing hemodialysis and to evaluate possible associations of these polymorphisms with hypertension (HT), diabetes mellitus (DM) and atherosclerosis (AS).

METHODS

A total of 225 CRF subjects undergoing hemodialysis and 201 healthy controls were enrolled in the study. CRF subjects were divided into three major subgroups according to comorbidities including HT (n = 127), DM (n = 65) and AS (n = 33). Genotyping was done using polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

The II genotype and I allele frequencies of CX3CR1 V249I polymorphism were found significantly more frequent in CRF subjects, CRF subjects with DM and CRF subjects with AS compared with controls (p < 0.05 for all comparisons). G allele frequency of CCR5 polymorphism was found significantly more prevalent in CRF subjects with DM than that of controls. Further, GG genotype and G allele frequencies of CCR5 polymorphism were significantly more prevalent in CRF subjects with AS compared with controls (p < 0.05). We also explored these polymorphisms among CRF subjects with and without following comorbidities: HT, DM, AS. We found significant association between CRF subjects with HT and without HT in terms of genotype and allele frequencies of V249I polymorphism (p < 0.05). CX3CR1 T280M polymorphism was not found significantly different in none of the comparisons.

CONCLUSION

These data demonstrate possible associations between CX3CR1 V249I and CCR5-59029 A/G polymorphisms and/or HT, DM and AS in CRF subjects.

Association of RAC1 Gene Polymorphisms with Primary End-Stage Renal Disease in Chinese Renal Recipients

BACKGROUND/OBJECTIVE

RAC1 gene could influence susceptibility to renal failure by altering the activity and expression of Rac1, which is a member of the Rho family of small GTP-binding proteins. In clinical practice, renal transplantation provides the optimal treatment for people with end-stage renal disease (ESRD). The objective of this present study was to determine whether the RAC1 gene polymorphisms were associated with primary ESRD susceptibility in Chinese renal recipients.

METHODS

Six single nucleotide polymorphisms (SNPs) of RAC1 gene, including rs836488 T>C, rs702482 A>T, rs10951982 G>A, rs702483 A>G, rs6954996 G>A, and rs9374 G>A, were genotyped in 300 renal transplant recipients (cases) and 998 healthy Chinese subjects (controls) by using TaqMan SNP genotyping assay. Allele, genotype, and haplotype frequencies of the six SNPs were compared between cases and controls. Odds ratios (OR) and 95% confidence intervals (CI) were calculated in logistic regression models to evaluate the associations of the six SNPs with ESRD risk.

RESULTS

The genotype distributions for the six SNPs in controls were consistent with Hardy-Weinberg equilibrium (P > 0.05). Association analysis revealed that three SNPs were significantly associated with ESRD risk. Positive associations with ESRD risk were found for the rs836488, rs702482, and rs702483 in the co-dominant model (minor allele homozygotes versus major allele homozygotes); specifically, the frequencies of the minor allele homozygotes and the minor allele for the three SNPs were higher in the cases than in the controls. In addition, these three SNPs also had associations with increased ESRD risk under the additive model (P < 0.05), and positive associations were also found for the rs836488 in the dominant model (P < 0.05) and for the rs702483 in the recessive model (P < 0.05). All these associations were independent of confounding factors. The other three SNPs (rs10951982, rs6954996, and rs9374), in all comparison models, were not associated with ESRD risk (P > 0.05). In haplotype analysis, carriers with "C-T-G-G-G-G" haplotype had a significantly higher risk of ESRD compared with the most common haplotype "T-A-G-A-G-G" (P = 0.011, OR = 1.46, 95% CI = 1.09-1.94).

CONCLUSION

This study suggested that polymorphisms of RAC1 gene might influence the susceptibility to ESRD in Chinese Han population. Further studies are necessary to confirm our findings.

Prediction of susceptible biomarkers for end stage renal disease among North Indians

AIM

Involvement of pro-inflammatory genes has been correlated with basic kidney diseases and end stage renal disease (ESRD). However, results at odds were often noted from such independent association studies. This study proposes a genome wide analysis approach to predict ESRD risk associated genes.

METHODS

We included 42 single nucleotide polymorphisms (SNPs) showing association among north Indian ESRD cases and controls. ESRD cases comprised chronic glomerulonephritis (CGN), chronic interstitial nephritis (CIN), hypertension (HTN) and autosomal dominant polycystic kidney disease (ADPKD). Genotyping data obtained from our prior published reports were compared with Genome-Wide Association Studies (GWAS) SNPs retrieved from HapMap and GWASCentral databases using R-statistical package SNPAssoc. Linkage disequilibrium (LD), gene-gene interaction, classification and regression tree (CART) and pathway analysis were carried out in the present study supplemented with IL-6 and TNF-α levels estimation using enzyme linked immunosorbent assay (ELISA).

RESULTS

Comparison of genotyping data with GWAS SNPs revealed significant associations for interleukin (IL)1-RN, IL-6, MTHFR, tumour necrosis factor-α (TNF-α) and CCR3 genes with ESRD. Nine SNPs were commonly associated with CGN, CIN, HTN, ADPKD and ESRD. LD (D = 0.9) and gene-gene interaction (P = 0.0002) analyses revealed significant associations for IL-6 and TNF-α genes. In a consistent manner, CART analysis and functional analysis servers predict predisposing effects for TNF-α and IL-6 with ESRD. Finally, higher body circulating levels were observed for mutant TNF-α and IL-6 alleles among ESRD.

CONCLUSION

The study indicates significance for IL-6 and TNF-α gene with basic kidney diseases and ESRD. Extensive statistical tests, pathway analysis and functional assays also reflect attenuated level of significance for these SNPs. In future these may be brought from bench side to clinical practice as diagnostic biomarkers upon external and prospective replication and confirmation among other cohorts.

Association between the CX3CR1 gene V249I polymorphism and delayed kidney allograft function

BACKGROUND

Fractalkine is a member of the chemokine family that acts as an adhesion molecule and as an extracellular chemoattractant promoting cellular migration. In this study, we analysed the association between the CX3CR1 gene V249I (rs3732379) SNP and renal allograft function.

METHODS

The study enrolled 270 Caucasian kidney allograft recipients. The following parameters were recorded in each case: the recipient's age and gender, delayed graft function (DGF) defined as the need for dialysis in the first 7 days after transplantation, occurrence and number of episodes of acute rejection (AR), and chronic allograft dysfunction (CAD).

RESULTS

Delayed graft function was diagnosed in 39.2% of individuals with the CC genotype, 22.7% with CT and 23.5% of those with the TT genotype. The differences were statistically significant (CC vs. TT+CT: OR = 2.17; 95% CI = 1.28-3.70, p = 0.0042). In multivariate analysis the CC genotype was an independent and significant predictor of higher risk of DGF. The distribution of genotypes and alleles of the CX3CR1 gene polymorphism among patients with and without AR as well as CAD did not differ significantly.

CONCLUSIONS

The results of this study suggest that the CX3CR1 gene V249I (rs3732379) SNP CC genotype is associated with increased risk of DGF.

Expression of chemokine receptors on peripheral blood T cells in children with chronic kidney disease

Chemokine receptors play a role in leukocyte recruitment, activation, and maintaining effector functions and regulate adaptive immune response and angiogenesis. The study aimed at flow cytometric analysis of T cell subsets with selected surface chemokine receptors (CCR4, CCR5, CCR7, CXCR3, and CXCR4) or receptor combination in peripheral blood of children with chronic kidney disease (CKD) on hemodialysis (HD). The percentage of T lymphocytes with CD8 and combined CD28,CCR7 expression was higher in HD children. The percentage of T lymphocytes expressing CCR7, CD28,CCR7, and CXCR4,CD8 was increased in children on conservative treatment. Total number (tn) of CXCR4+ cells was reduced in children on hemodialysis. The tn of T CXCR3+ cells was lower in children on conservative treatment. During HD the percentage of T CD4+ cells was higher and of T CXCR3+ lymphocytes was lower after HD session as compared to 15 min of session duration. During HD tn of T cells with expression of CCR4, CCR5, CCR7, CXCR3, and CXCR4 was constant. The alteration of chemokine receptors expression in children with CKD occurs early in the development. Diminished expression of CXCR3, CXCR4 on T cells in patients with CKD on HD might result in impaired inflammatory response. Increased CCR7+ T cell percentage could be responsible for the alteration of migration of cells into secondary lymphatic organs.

Variations in CCR5, but not HFE, ELMO1, or SLC12A3, are associated with susceptibility to kidney disease in north Indian individuals with type 2 diabetes

BACKGROUND

Diabetic nephropathy (DN), the leading cause of end-stage renal disease worldwide, may have a genetic component. In the present study, we investigated variations in a set of genes with susceptibility to DN in a north Indian population.

METHODS

Four genes (HFE, ELMO1, SLC12A3, and CCR5) were selected on the basis of reported association with type 2 diabetes and nephropathy. In all, 417 diabetic subjects (215 without kidney disease [DM] and 202 with DN) and 197 healthy controls (HC) were evaluated for variations in HFE (845 G>A and 187G>C), SLC12A3 (g.34372G>A), CCR5 (59029A>G), and ELMO1 (+9170 G>A). Polymorphism analysis was performed by polymerase chain reaction-restriction fragment length polymorphism and Taqman allele discrimination assays.

RESULTS

Significant differences were found in genotype and allelic frequency in SLC12A3 (g.34372G>A) between diabetic subjects and HC (P < 0.03). There were no differences in the SLC12A3 g.34372G>A (AA+GA) genotype between diabetic subjects with and without nephropathy. However, the CCR5 59029AA genotype and A allele were significantly more frequent in diabetics compared with the HC (P = 0.01 and 0.03, respectively) and subjects with DN versus DM (P = 0.002 and 0.01, respectively). For ELMO1 (+9170 G>A), the GG genotype frequency was higher in the diabetic versus HC group. There were no differences in the frequency of HFE-845 G>A and HFE-187G>C among the groups.

CONCLUSION

This study shows that the CCR5 AA genotype is over-represented in subjects with kidney disease due to type 2 diabetes. The CCR5 59029G>A and ELMO1 (+9170 G>A) loci are more frequent, and the SLC12A3 34372 AA genotype is associated with a reduced risk of diabetes.

Lack of association of angiotensin II type 1 receptor A1166C gene polymorphism with the risk of end-stage renal disease

The association between angiotensin II type 1 receptor (AT1R) A 1166C (rs5186) gene polymorphism and end-stage renal disease (ESRD) risk remains controversial. We aimed to assess the association between AT1R A1166C gene polymorphism and ESRD susceptibility by performing a meta-analysis. Eligible studies were searched according to a predefined criterion using electronic databases. Eight articles were identified for the analysis of the association between AT1R A1166C gene polymorphism and ESRD risk. A allele and AA genotype were not associated with ESRD risk in overall populations, Caucasians and Asians (overall populations: p = 0.834 and 0.832, Caucasians: p = 0.853 and 0.884, Asians: p = 0.243 and 0.982). CC and AC genotype were not associated with ESRD risk in overall populations, Caucasians and Asians (overall populations: p = 0.304 and 0.712, Caucasians: p = 0.510 and 0.987, Asians: p = 0.319 and 0.225). In conclusion, AT1R A1166C gene polymorphism may not be correlated with ESRD risk in overall populations, Caucasians and Asians. However, more studies should be performed in the future.

Lack of an association between vitamin D receptor BsmI gene polymorphism and the risk of end-stage renal disease: a meta-analysis

OBJECTIVE

To evaluate the association between vitamin D receptor (VDR) BsmI gene polymorphism and the risk of end-stage renal disease (ESRD).

METHODS

All eligible studies were included in our meta-analysis of a search of the PubMed, Embase, Cochrane and China National Knowledge Infrastructure (CNKI) databases according to predefined criteria. The fixed-effects or, in the presence of heterogeneity, random-effects models were used to calculate the pooled odds ratio (OR) and corresponding 95% confidence interval (CI).

MATERIALS

Six studies including 863 patients and 1,063 controls were recruited for the analysis of the association between the VDR BsmI gene polymorphism and the risk of ESRD.

RESULTS

The B allele/BB genotype was not associated with the ESRD risk in the overall population, Caucasians or Asians (overall population: p=0.492 and 0.382, Caucasians: p=0.765 and 0.522, Asians: p=0.607 and 0.481). The Bb/bb genotype was also not associated with the risk of ESRD in the overall population, Caucasians or Asians (overall population: p=0.556 and 0.166, Caucasians: p=0.770 and 0.965, Asians: p=0.411 and 0.098). The exclusion of any single study had little impact on the p value in the overall population. No evidence of publication bias was observed.

CONCLUSION

VDR BsmI gene polymorphism appears to not be associated with the risk of ESRD in the overall population, Caucasians or Asians. However, more studies should be performed in the future.