Most common single-nucleotide polymorphisms associated with rheumatoid arthritis in persons of European ancestry confer risk of rheumatoid arthritis in African Americans

Single Nucleotide Polymorphisms Associated with Rheumatoid Arthritis in Saudi Patients

Rheumatoid arthritis (RA) is a complex, multifactorial disorder with an autoimmune etiology. RA is highly heritable and is associated with both human leucocyte antigen (HLA) and non-HLA genes. We investigated the associations of 33 single nucleotide polymorphisms (SNPs) with RA in the Saudi population.

METHODS

This study included 105 patients with RA and an equal number of age- and sex-matched controls. The patients with RA attended outpatient clinics at King Khalid University Hospital in Riyadh, Saudi Arabia. Blood samples were collected, and DNA was extracted using Qiagen kits. Primers were designed for the 33 selected SNPs using the MassEXTEND primers program, and samples were genotyped on the Sequenom MassARRAY iPLEX platform. The allele frequencies and genotypes were determined for each SNP, and the results obtained for the patients were compared to those for the controls.

RESULTS

The allele and genotype frequencies of six SNPs were significantly associated with RA: rs1188934, rs10919563, rs3087243, rs1980422, rs10499194, and rs629326. The minor alleles of rs1188934, rs10919563, rs10499194, and rs629326 were protective, with odds ratios of 0.542, 0.597, 0.589, and 0.625, and p-values of 0.002, 0.023, 0.013 and 0.036, respectively. In addition, the heterozygote frequencies of two SNPs (rs6859219 and rs11586238) were significantly higher in the controls than in the patients.

CONCLUSIONS

There is considerable heterogeneity in the genetics of RA in different populations, and the SNPs that are associated with RA in some populations are not in others. We studied 33 SNPs and only eight were associated with RA. The remaining SNPs showed no allelic or genotypic associations with RA.

Polymorphism of protein tyrosine phosphatase non-receptor type 22 and protein arginine deiminase 4 gene among Ghanaian rheumatoid arthritis patients: A case-control study

AIM

Rheumatoid arthritis (RA) is an autoimmune disease which affects millions of lives globally characterized by chronic inflammation in the joints of the body. There is no known cause for RA; however, genetic predisposition has been associated with its occurrence. The association between genetic predisposition and RA has been reported largely among Caucasians and Asians. However, few studies with limited data have reported genome-wide association studies of RA in Africa, especially in Ghana. In addition, there is genetic heterogeneity that exists geographically among different populations. This study therefore investigated the association of protein arginine deiminase type 4 (PAD4) and protein tyrosine phosphatase non-receptor type 22 (PTPN22) single nucleotide polymorphisms with susceptibility of RA among Ghanaians.

METHODS

This case-control study included 75 RA patients and 75 healthy controls from the Komfo Anokye Teaching Hospital in Ghana. Validated questionnaires were used to obtain demographic data, and blood samples were collected and processed for DNA and polymerase chain reaction analysis. Statistical analysis was done using SPSS version 25.0.

RESULTS

PTPN22 demonstrated a 100% minor allele frequency (GG) in both cases and healthy controls; however, an association could not be made for PTPN22 polymorphism with susceptibility of RA when comparing cases to controls. The homozygous minor allele (GG) of PAD4 was absent in the population.

CONCLUSION

PAD4 polymorphism was absent, while PTPN22 was present in the Ghanaian population. The association between PTPN22 (rs2476601) and PAD4 (rs2240340) with RA susceptibility could not be established, thus may not contribute as risk factors for RA in the Ghanaian population.

A20 Inhibits Intraocular Inflammation in Mice by Regulating the Function of CD4+T Cells and RPE Cells

A20 is a negative regulator of inflammation and immunity and plays a role in several autoimmune and inflammatory diseases. Here, we demonstrate that A20 overexpression significantly ameliorates severity of EAU by inhibiting the infiltration of Th1 and Th17 cells, and by protecting integrity of the blood retinal barrier. In vitro studies showed that A20 silencing could promote CD4+T cells toward a Th1 and Th17 phenotype. A decreased expression of A20 in CD4+T cells was noticed in active BD patients but not in VKH patients. Furthermore, silencing of A20 in hRPE cells induced the production of IL-6, IL-8, and MCP-1 and downregulated ZO-1 and occludin expression which is mediated by inhibition of MAPK and NF-κB pathways. This study reveals a mechanism by which A20 prevents autoimmune uveitis.

A comparison of risk factors for osteo- and rheumatoid arthritis using NHANES data

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Both osteo- and rheumatoid arthritis increase with age.

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Osteoarthritis is more common in whites, but rheumatoid arthritis is in blacks.

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Obesity and female sex increase risk of risk of both osteo- and rheumatoid arthritis.

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Smoking increases risk of both forms of arthritis in women.

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These two forms of arthritis have many common risk factors.

Osteoarthritis and rheumatoid arthritis are both diseases of joints, but they have very different etiologies. Osteoarthritis is a disease assumed to result from wear and tear over time, whereas rheumatoid arthritis is an autoimmune disease where the body’s immune system attacks joint tissues. Using NHANES data (1999–2015), we have compared the influence of age, sex, ethnicity, body mass index and smoking on these two very different forms of arthritis. Incidence of both increases with age and are more frequent in females than males. There is little apparent difference between osteoarthritis and rheumatoid arthritis in women of normal as comparted to overweight, but both are more frequent in obese women, especially those over the age of 60. While osteoarthritis is more frequent in whites, blacks have more rheumatoid arthritis, and Hispanics show an intermediate prevalence. Smoking significantly increased the incidence of both osteoarthritis and rheumatoid arthritis in women, but increased prevalence of only RA in men. There was no effect of smoking on OA prevalence in males. It is remarkable that two diseases of joints, which have quite different causes, should have so many commonalities. The differences that exist appear to be due to a combination of inflammatory markers and access to health care.

Genetic influences on susceptibility to rheumatoid arthritis in African-Americans

Large meta-analyses of rheumatoid arthritis (RA) susceptibility in European (EUR) and East Asian (EAS) populations have identified >100 RA risk loci, but genome-wide studies of RA in African-Americans (AAs) are absent. To address this disparity, we performed an analysis of 916 AA RA patients and 1392 controls and aggregated our data with genotyping data from >100 000 EUR and Asian RA patients and controls. We identified two novel risk loci that appear to be specific to AAs: GPC5 and RBFOX1 (PAA < 5 × 10-9). Most RA risk loci are shared across different ethnicities, but among discordant loci, we observed strong enrichment of variants having large effect sizes. We found strong evidence of effect concordance for only 3 of the 21 largest effect index variants in EURs. We used the trans-ethnic fine-mapping algorithm PAINTOR3 to prioritize risk variants in >90 RA risk loci. Addition of AA data to those of EUR and EAS descent enabled identification of seven novel high-confidence candidate pathogenic variants (defined by posterior probability > 0.8). In summary, our trans-ethnic analyses are the first to include AAs, identified several new RA risk loci and point to candidate pathogenic variants that may underlie this common autoimmune disease. These findings may lead to better ways to diagnose or stratify treatment approaches in RA.

Association of Signal Transducer and Activator of Transcription 4 rs10181656 Polymorphism With Rheumatoid Arthritis and Systemic Sclerosis in Khuzestan Province in Southwestern Iran

Objectives

This study aims to investigate the association of polymorphism rs10181656 (C>G) of signal transducer and activator of transcription 4 (STAT4) gene with rheumatoid arthritis (RA) and systemic sclerosis (SSc) in the southwest of Iran as well as the probable relationship between the polymorphism with clinical features and disease activity parameters in both diseases.

Patients and methods

A total of 200 patients (120 with RA [21 males, 99 females; mean age 44.83 years; range, 16 to 75 years] and 80 with SSc [13 males, 67 females; mean age 44.3 years; range, 30 to 75 years]) and 120 healthy controls (25 males, 95 females; mean age 46.93 years; range, 30 to 75 years) were recruited in this study. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism. A set of genotypes was confirmed by sequencing.

Results

A statistically significant association was detected between STAT4 rs10181656 polymorphism and RA (p=0.007). No significant correlation was detected between STAT4 rs10181656 polymorphism and SSc (p=0.357). None of the clinical features (anti-cyclic citrullinated peptide, rheumatoid factor) or disease activity parameters (limited cutaneous SSc, diffuse cutaneous SSc) showed any correlation with the genotype distribution of the STAT4 rs10181656 polymorphism in RA or SSc patients.

Conclusion

Our findings suggest an association between RA susceptibility and STAT4 rs10181656 polymorphism. However, no significant association was found between the mentioned polymorphism and SSc. Clinical features and disease activity parameters did not show any association with the polymorphism.

CCR6 controls autoimmune but not innate immunity-driven experimental arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease, characterized by synovial infiltration of various inflammatory cells. Chemokines are involved in controlling the recruitment of different cell types into the synovial membrane. The role of CCR6 in the development of arthritis so far remains unclear. In this study, we investigated the role of CCR6 in the pathogenesis of arthritis using three different murine arthritis models. Compared to WT animals, CCR6^−/− mice developed less clinical signs of arthritis in the collagen‐induced arthritis model but not in the K/BxN serum transfer arthritis model and in the human tumour necrosis factor transgenic arthritis model, suggesting a defect in adaptive effector functions but intact innate effector functions in the development of arthritis in CCR6^−/− animals. In line with this, anti‐collagen antibody levels were significantly reduced in CCR6^−/− mice compared with WT mice. Moreover, we demonstrate enhanced osteoclastogenesis in vitro in CCR6^−/− mice compared with WT mice. However, we did not detect differences in bone mass under steady state conditions in vivo between WT and CCR6‐deficient mice. These data suggest that CCR6 is crucially involved in adaptive but not in innate immunity‐driven arthritis. CCR6 or its chemokine ligand CCL20 might represent a possible new target for the treatment of RA.

Intracellular B Lymphocyte Signalling and the Regulation of Humoral Immunity and Autoimmunity

B lymphocytes are critical for effective immunity; they produce antibodies and cytokines, present antigens to T lymphocytes and regulate immune responses. However, because of the inherent randomness in the process of generating their vast repertoire of antigen-specific receptors, B cells can also cause diseases through recognizing and reacting to self. Therefore, B lymphocyte selection and responses require tight regulation at multiple levels and at all stages of their development and activation to avoid diseases. Indeed, newly generated B lymphocytes undergo rigorous tolerance mechanisms in the bone marrow and, subsequently, in the periphery after their migration. Furthermore, activation of mature B cells is regulated through controlled expression of co-stimulatory receptors and intracellular signalling thresholds. All these regulatory events determine whether and how B lymphocytes respond to antigens, by undergoing apoptosis or proliferation. However, defects that alter regulated co-stimulatory receptor expression or intracellular signalling thresholds can lead to diseases. For example, autoimmune diseases can result from altered regulation of B cell responses leading to the emergence of high-affinity autoreactive B cells, autoantibody production and tissue damage. The exact cause(s) of defective B cell responses in autoimmune diseases remains unknown. However, there is evidence that defects or mutations in genes that encode individual intracellular signalling proteins lead to autoimmune diseases, thus confirming that defects in intracellular pathways mediate autoimmune diseases. This review provides a synopsis of current knowledge of signalling proteins and pathways that regulate B lymphocyte responses and how defects in these could promote autoimmune diseases. Most of the evidence comes from studies of mouse models of disease and from genetically engineered mice. Some, however, also come from studying B lymphocytes from patients and from genome-wide association studies. Defining proteins and signalling pathways that underpin atypical B cell response in diseases will help in understanding disease mechanisms and provide new therapeutic avenues for precision therapy.

Three single nucleotide polymorphisms of TNFAIP3 gene increase the risk of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic destructive inflammation in synovial joints. To date, many studies explored the associations between tumor necrosis factor alpha inducible protein 3 (TNFAIP3) gene rs6920220, rs2230926, and rs5029937 polymorphisms and the risk of rheumatoid arthritis (RA), but with contradictory results. We therefore conducted a comprehensive meta-analysis to address the associations. We searched in the databases of PubMed and Embase. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by the Stata 11.0 software. A total of 21 case-control studies for these three single nucleotide polymorphisms (SNPs) were included in this meta-analysis. Meta-analysis indicated that TNFAIP3 gene rs6920220, rs2230926, and rs5029937 polymorphisms were associated with the increased risk of RA. Stratification analysis of ethnicity found that rs6920220 and rs5029937 polymorphisms increased the risk of RA among Caucasians, while rs2230926 polymorphism increased the risk of RA among Asians. In summary, this meta-analysis confirms that TNFAIP3 gene polymorphisms may play important roles in the pathogenesis of RA.

Dense Genotyping of Immune-Related Regions Identifies Loci for Rheumatoid Arthritis Risk and Damage in African Americans

Over 100 risk loci for rheumatoid arthritis (RA) have been identified in individuals of European and Asian descent, but the genetic basis for RA in African Americans is less well understood. We genotyped 610 African Americans with autoantibody positive RA and 933 African American controls on the ImmunoChip (iChip) array. Using multivariable regression we evaluated the association between iChip markers and the risk of RA and radiographic severity. The single nucleotide polymorphism (SNP) rs1964995 (OR = 1.97, p = 1.28 × 10^-15) near HLA-DRB1 was the most strongly associated risk SNP for RA susceptibility; SNPs in AFF3, TNFSF11, and TNFSF18 loci were suggestively associated (10^-4 < p < 3.1 × 10^-6). Trans-ethnic fine mapping of AFF3 identified a 90% credible set containing previously studied variants including rs9653442, rs7608424, and rs6712515 as well as the novel candidate variant rs11681966; several of these likely influence AFF3 gene expression level. Variants in TNFRSF9, CTLA4, IL2RA, C5/TRAF1, and ETS1 - but no variants within the major histocompatibility complex - were associated with RA radiographic severity. Conditional regression and pairwise linkage disequilibrium (LD) analyses suggest that additional pathogenic variants may be found in ETS1 and IL2RA beyond those found in other ethnicities. In summary, we use the dense genotyping of the iChip array and unique LD structure of African Americans to validate known risk loci for RA susceptibility and radiographic severity, and to better characterize the associations of AFF3, ETS1, and IL2RA.

In vitro and in vivo evaluation of anti-arthritic, antioxidant efficacy of fucoidan from Undaria pinnatifida (Harvey) Suringar

Seaweed and their constituents have been traditionally employed for the management of various human pathologic conditions such as edema, urinary disorders and inflammatory anomalies. The current study was performed to investigate the antioxidant and anti-arthritic effects of fucoidan from Undaria pinnatifida. A noteworthy in vitro antioxidant potential at 500μg/ml in 2, 2-diphenyl-1-picrylhydrazyl scavenging assay (80% inhibition), nitrogen oxide inhibition assay (71.83%), hydroxyl scavenging assay (71.92%), iron chelating assay (73.55%) and a substantial ascorbic acid equivalent reducing power (399.35μg/mg ascorbic acid equivalent) and total antioxidant capacity (402.29μg/mg AAE) suggested fucoidan a good antioxidant agent. Down regulation of COX-2 expression in rabbit articular chondrocytes in a dose (0-100μg) and time (0-48h) dependent manner, unveiled its in vitro anti-inflammatory significance. In vivo carrageenan induced inflammatory rat model demonstrated a 68.19% inhibition of inflammation whereas an inflammation inhibition potential of 79.38% was recorded in anti-arthritic complete Freund's adjuvant-induced arthritic rat model. A substantial ameliorating effect on altered hematological and biochemical parameters in arthritic rats was also observed. Therefore, findings of the present study prospects fucoidan as a potential antioxidant that can effectively abrogate oxidative stress, edema and arthritis-mediated inflammation and mechanistic studies are recommended for observed activities.

TNFAIP3 gene rs10499194, rs13207033 polymorphisms decrease the risk of rheumatoid arthritis

Accumulating evidences suggested that tumor necrosis factor alpha inducible protein 3 (TNFAIP3) gene rs10499194, rs13207033 polymorphisms may be associated with the risk of rheumatoid arthritis (RA). However, these studies yielded contradictory findings. To clarify convincing associations, we conducted a comprehensive meta-analysis by searching in PubMed, Embase, and the China Knowledge Resource Integrated Database. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by using fixed-effect or random-effect models. A total of 13 case-control studies for rs10499194 polymorphism and 6 studies for rs13207033 polymorphism were included. Our data indicated that TNFAIP3 gene rs10499194, rs13207033 polymorphisms were associated with the decreased risk of RA. Stratification analyses of ethnicity indicated rs10499194, rs13207033 polymorphisms decreased the risk of RA among Caucasian populations, but not among Asian populations. In conclusion, this meta-analysis indicates that TNFAIP3 gene rs10499194, rs13207033 polymorphisms decrease the risk of RA, especially among Caucasian populations.

Mutation-Induced Functional Alterations of CCR6

The Cys-Cys chemokine receptor 6 (CCR6) is a well-established modulator of inflammation. Although several genetic associations have been identified between CCR6 polymorphisms and immune system disorders (e.g., rheumatoid arthritis and Crohn's disease), the pharmacological effects of naturally occurring missense mutations in this receptor have yet to be characterized. In this study, we initially assessed G protein-mediated signaling and observed that wild-type (WT) CCR6 exhibited ligand-independent activity. In addition, we found that the five most frequent CCR6 missense variants (A89T, A150V, R155W, G345S, and A369V) exhibited decreased basal and/or ligand induced Gαi protein signaling. To complement the study of these loss-of-function variants, we engineered a set of constitutively active CCR6 receptors. Selected mutations enhanced basal G protein-mediated signaling up to 3-fold relative to the WT value. Using a bioluminescence resonance energy transfer assay we investigated the ability of each naturally occurring and engineered CCR6 receptor mutant to recruit β-arrestin. In contrast to G protein-mediated signaling, β-arrestin mobilization was largely unperturbed by the naturally occurring loss-of-function CCR6 variants. Elevated recruitment of β-arrestin was observed in one of the engineered constitutively active mutants (T98P). Our results demonstrate that point mutations in CCR6 can result in either a gain or loss of receptor function. These observations underscore the need to explore how CCR6 natural variants may influence immune cell physiology and human disease.

Tumor necrosis factor α-induced protein-3 protects zinc transporter 8 against proinflammatory cytokine-induced downregulation

Zinc transporter 8 (ZnT8) is exclusively expressed in the pancreatic islet and is essential for insulin crystallization, hexamerization and secretion. Tumor necrosis factor α-induced protein-3 (TNFAIP3) is a zinc finger protein that serves a major role in the negative feedback regulation of NF-κB signaling in response to multiple stimuli, and is a central regulator of immunopathology. Although the role of TNFAIP3 in diabetes has been extensively studied, its effect on ZnT8 has not been fully elucidated. The present study aimed to verify whether proinflammatory cytokines, tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), are able to affect ZnT8 expression in islet cells. In addition, the study aimed to determine the effect of TNFAIP3 overexpression on cytokine-altered ZnT8 activity, considering its effect on NF-κB signaling. Cell-based studies using NIT-1 cells overexpressing TNFAIP3 were used to assess the effect of cytokines on ZnT8 and NF-κB activation, as well as the effect of TNFAIP3 on ZnT8 expression. Western blot analysis and immunofluorescence staining were employed to determine the protein expression and NF-κB activation, respectively. The results indicated that cytokine stimulation led to TNFAIP3 upregulation, ZnT8 downregulation and NF-κB activation. Furthermore, TNFAIP3 overexpression protected ZnT8 from cytokine-induced downregulation. In conclusion, the current results suggest that inflammation or TNFAIP3 dysfunction may be involved in the pathogenesis of diabetes via ZnT8 expression, besides from islet cell apoptosis. In addition, restricting inflammation and enhancing TNFAIP3 expression may exert a positive effect in diabetes prevention, treatment and pancreatic cell transplantation.

T Cell Migration in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints, associated with synovial hyperplasia and with bone and cartilage destruction. Although the primacy of T cell-related events early in the disease continues to be debated, there is strong evidence that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. In addition, T cells are key components of the immune cell infiltrate detected in the joints of RA patients. Initial analysis of the cytokines released into the synovial membrane showed an imbalance, with a predominance of proinflammatory mediators, indicating a deleterious effect of Th1 T cells. There is nonetheless evidence that Th17 cells also play an important role in RA. T cells migrate from the bloodstream to the synovial tissue via their interactions with the endothelial cells that line synovial postcapillary venules. At this stage, selectins, integrins, and chemokines have a central role in blood cell invasion of synovial tissue, and therefore in the intensity of the inflammatory response. In this review, we will focus on the mechanisms involved in T cell attraction to the joint, the proteins involved in their extravasation from blood vessels, and the signaling pathways activated. Knowledge of these processes will lead to a better understanding of the mechanism by which the systemic immune response causes local joint disorders and will help to provide a molecular basis for therapeutic strategies.

Association between CCR6 and rheumatoid arthritis: a meta-analysis

OBJECTIVE

Chemokine (C-C motif) receptor 6 gene (CCR6) polymorphism has been reported to be associated with rheumatoid arthritis (RA) in different ethnic populations. Moreover, its inhibition by monoclonal antibody in mouse model has suppressed arthritis. However, few replication studies have reported conflicting results about this association. Therefore, to establish that CCR6 indeed is a risk factor associated with RA among different ethnic populations, a comprehensive meta-analysis study was conducted.

METHODS

PubMed and MEDLINE databases were searched using the term 'CCR6' for all articles published before May 2014. All the replication studies examining the association between CCR6 and RA were reviewed for meta-analysis. Data were summarized using random-effects meta-analysis. The heterogeneity and publication bias among studies were examined by χ(2) -based Q statistic test and Egger's test, respectively.

RESULTS

A total of 24955 RA patients and 56129 controls from seven articles were included in the meta-analysis. While CCR6 was a risk factor in Asian (OR = 1.19, 95% CI: 1.14-1.24) and European (OR = 1.14, 95% CI: 1.08-1.21) populations, it was indicated as a protective factor in African Americans (OR = 0.79, 95% CI: 0.62-0.96).

CONCLUSIONS

Our meta-analysis study concludes that there is a significant association between CCR6 and RA in all racial groups except African-American subgroup, which require a large sample size for concrete prediction.

HLA-DRB1-associated rheumatoid arthritis risk at multiple levels in African Americans: hierarchical classification systems, amino acid positions, and residues

OBJECTIVE

To evaluate HLA-DRB1 genetic risk of rheumatoid arthritis (RA) in African Americans by 3 validated allele classification systems and by amino acid position and residue, and to compare genetic risk between African American and European ancestries.

METHODS

Four-digit HLA-DRB1 genotyping was performed on 561 autoantibody-positive African American cases and 776 African American controls. Association analysis was performed on Tezenas du Montcel (TdM), de Vries (DV), and Mattey classification system alleles and separately by amino acid position and individual residues.

RESULTS

TdM S2 and S3P alleles were associated with RA (odds ratio [95% confidence interval] 2.8 [2.0-3.9] and 2.1 [1.7-2.7], respectively). The DV (P = 3.2 × 10(-12)) and Mattey (P = 6.5 × 10(-13)) system alleles were both protective in African Americans. Amino acid position 11 (permutation P < 0.00001) accounted for nearly all variability explained by HLA-DRB1, although conditional analysis demonstrated that position 57 was also significant (0.01 ≤ permutation P ≤ 0.05). The valine and aspartic acid residues at position 11 conferred the highest risk of RA in African Americans.

CONCLUSION

With some exceptions, the genetic risk conferred by HLA-DRB1 in African Americans is similar to that in individuals of European ancestry at multiple levels: classification system (e.g., TdM), amino acid position (e.g., 11), and residue (Val11). Unlike that reported for individuals of European ancestry, amino acid position 57 was associated with RA in African Americans, but positions 71 and 74 were not. Asp11 (odds ratio 1 in European ancestry) corresponds to the 4-digit classical allele *09:01, which is also a risk allele for RA in Koreans.

Identification of rheumatoid arthritis biomarkers based on single nucleotide polymorphisms and haplotype blocks: A systematic review and meta-analysis

Genetics of autoimmune diseases represent a growing domain with surpassing biomarker results with rapid progress. The exact cause of Rheumatoid Arthritis (RA) is unknown, but it is thought to have both a genetic and an environmental bases. Genetic biomarkers are capable of changing the supervision of RA by allowing not only the detection of susceptible individuals, but also early diagnosis, evaluation of disease severity, selection of therapy, and monitoring of response to therapy. This review is concerned with not only the genetic biomarkers of RA but also the methods of identifying them. Many of the identified genetic biomarkers of RA were identified in populations of European and Asian ancestries. The study of additional human populations may yield novel results. Most of the researchers in the field of identifying RA biomarkers use single nucleotide polymorphism (SNP) approaches to express the significance of their results. Although, haplotype block methods are expected to play a complementary role in the future of that field.

Decreased A20 mRNA and protein expression in peripheral blood mononuclear cells in patients with type 2 diabetes and latent autoimmune diabetes in adults

AIMS

A20 is a negative regulator of nuclear factor kappa B activation and the central gatekeeper in inflammation and immunity. While its role in type 1 diabetes has been widely studied, its expression level in immune cells from type 2 diabetes (T2D) and latent autoimmune diabetes in adult (LADA) patients remains unclear. This study aimed to clarify whether the expression of A20 is altered in patients with T2D or LADA.

METHODS

Quantitative real-time polymerase chain reaction and western blotting were utilized to determine the expression of A20 mRNA and protein respectively in peripheral blood mononuclear cells (PBMCs) from patients with T2D (n=36) or LADA (n=17) and sex- and age-matched healthy controls (n=34).

RESULTS

The mRNA and protein expression of A20 in PBMCs from T2D and LADA patients was significantly decreased compared with healthy controls (P<0.05). Furthermore, A20 mRNA and protein expression was significantly lower in newly diagnosed T2D patients (≤1 year since diagnosis) than in patients with a long T2D duration (>1 year since diagnosis) (P<0.05).

CONCLUSIONS

Our results suggest that decreased expression of A20 in PBMCs may be involved in the pathogenesis of diabetes, and targeting A20 may offer a potential therapeutic tool in the treatment of diabetes.

TNFAIP3 gene polymorphisms associated with differential susceptibility to rheumatoid arthritis and systemic lupus erythematosus in the Korean population

OBJECTIVE

We investigated the relationship between polymorphisms in the TNF-a-induced protein 3 (TNFAIP3) gene and genetic susceptibility to SLE and RA in the Korean population.

METHODS

The present case control study included 422 patients with RA, 133 patients with SLE and 422 healthy controls. Genotyping for TNFAIP3 gene polymorphisms rs5029941 (C>T), rs2230926 (T>G), rs5029930 (C>A), rs5029937 (G>T) and rs5029939 (G>C) in TNFAIP3 gene polymorphisms was performed. The status of RA-related autoantibodies, including RF and anti-CCP, in RA and the presence of arthritis and nephritis in SLE were assessed.

RESULTS

Significantly different frequencies of minor alleles in two TNFAIP3 polymorphisms were found in patients with SLE compared with healthy controls [odds ratio (OR) 2.13, 95% CI 1.25, 3.65, P= 0.02 for rs5029937; OR 2.17, 95% CI 1.27, 3.72, P= 0.01 for rs5029939). Moreover, patients with SLE showed different frequencies of haplotypes compared with healthy controls (P<0.001). However, no association was found between RA susceptibility and TNFAIP3 polymorphisms (P= 0.28). Interactions between RA-related autoantibody status and TNFAIP3 polymorphisms were not associated with RA susceptibility. Interestingly, arthritis in patients with SLE was marginally associated with TNFAIP3 polymorphisms (P= 0.04).

CONCLUSION

The results suggest that TNFAIP3 gene polymorphisms are associated with differential susceptibility to SLE and RA in the Korean population. The relationship between TNFAIP3 gene polymorphisms and RA susceptibility may be dependent on ethnic background.

Immunochip identifies novel, and replicates known, genetic risk loci for rheumatoid arthritis in black South Africans

The aim of this study was to identify genetic variants associated with rheumatoid arthritis (RA) risk in black South Africans. Black South African RA patients (n = 263) were compared with healthy controls (n = 374). Genotyping was performed using the Immunochip, and four-digit high-resolution human leukocyte antigen (HLA) typing was performed by DNA sequencing of exon 2. Standard quality control measures were implemented on the data. The strongest associations were in the intergenic region between the HLA-DRB1 and HLA-DQA1 loci. After conditioning on HLA-DRB1 alleles, the effect in the rest of the extended major histocompatibility (MHC) diminished. Non-HLA single nucleotide polymorphisms (SNPs) in the intergenic regions LOC389203|RBPJ, LOC100131131|IL1R1, KIAA1919|REV3L, LOC643749|TRAF3IP2, and SNPs in the intron and untranslated regions (UTR) of IRF1 and the intronic region of ICOS and KIAA1542 showed association with RA (p < 5 × 10(-5)). Of the SNPs previously associated with RA in Caucasians, one SNP, rs874040, locating to the intergenic region LOC389203|RBPJ was replicated in this study. None of the variants in the PTPN22 gene was significantly associated. The seropositive subgroups showed similar results to the overall cohort. The effects observed across the HLA region are most likely due to HLA-DRB1, and secondary effects in the extended MHC cannot be detected. Seven non-HLA loci are associated with RA in black South Africans. Similar to Caucasians, the intergenic region between LOC38920 and RBPJ is associated with RA in this population. The strong association of the R620W variant of the PTPN22 gene with RA in Caucasians was not replicated since this variant was monomorphic in our study, but other SNP variants of the PTPN22 gene were also not associated with RA in black South Africans, suggesting that this locus does not play a major role in RA in this population.

Genome-wide association studies to advance our understanding of critical cell types and pathways in rheumatoid arthritis: recent findings and challenges

PURPOSE OF REVIEW

A significant number of loci implicated in rheumatoid arthritis (RA) susceptibility have been highlighted by genome-wide association studies (GWAS). Here, we review the recent advances of GWAS in understanding the genetic architecture of RA, and place these findings in the context of RA pathogenesis.

RECENT FINDINGS

Although the interpretation of GWAS findings in the context of the disease biology remains challenging, interesting observations can be highlighted. Integration of GWAS results with cell-type specific gene expression or epigenetic marks have highlighted regulatory T cells and CD4 memory T cells as critical cell types in RA. In addition, many genes in RA loci are involved in the nuclear factor-kappaB signaling pathway or the Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signaling pathway. The observation that these pathways are targeted by several approved drugs used to treat the symptoms of RA highlights the promises of human genetics to provide insights in the disease biology, and help identify new therapeutic targets.

SUMMARY

These findings highlight the promises and need of future studies investigating causal genes and underlined mechanisms in GWAS loci to advance our understanding of RA.

Single nucleotide polymorphisms in TNFAIP3 were associated with the risks of rheumatoid arthritis in northern Chinese Han population

BACKGROUND

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic destructive inflammation in synovial joints. It is well known that genetic and environmental risk factors and their interaction contribute to RA pathogenesis. This study aimed to investigate the association between the critical polymorphisms in the tumor necrosis factor α (TNFα)-induced protein 3(TNFAIP3) gene and the risk of RA in a large northern Chinese Han population.

METHODS

A case-control study of 1280 RA patients and 1280 matched healthy controls was conducted.

RESULTS

This study showed that carriers of the rs2230926 TG genotype or rs10499194 CT genotype had an increased risk for RA compared with those carrying the wild genotype (rs2230926: OR = 1.48, 95% CI = 1.17-1.86, p = 0.001; rs10499194: OR = 2.00, 95% CI = 1.46-2.74, p < 0.001). The combined rs2230926TG/GG or rs10499194 CT/TT were associated with an increased risk of RA (ORs were 1.50 and 2.01, 95% CIs were 1.19-1.88 and 1.47-2.74, respectively, both p < 0.001). There was not significant association between rs13207033 polymorphism and RA risk. Subset analysis stratified to gender showed that the increased risks were significant among the genotypes TG, TG/GG of rs2230926 and CT, CT/TT of rs10499194 and the corresponding ORs were 1.42 (95%  CI = 1.10-1.83, p = 0.006), 1.44(95% CI = 1.12-1.85, p = 0.004), 1.52(95% CI = 1.05-2.20, p = 0.026) and 1.52(95% CI = 1.06-2.19, p = 0.023) in the female population. Stratified analyses by age found that rs2230926(TG, TG/GG) and rs10499194(CT, CT/TT) polymorphisms were associated with RA risks in population ≤53 years old and among >53 years old only rs10499194(CT, TT, CT/TT) polymorphism had significant results. The interaction analysis suggested that individuals with both risk genotypes of the two SNPs have a higher elevated risk of RA than those with only one of them (ORs were 3.44 compared to 1.74 and 1.35). The haplotype results showed that individuals with the rs2230926G-rs13207033G-rs10499194C haplotype were associated with increased risks of RA (OR = 1.37, 95% CI = 1.08-1.74, p = 0.010).

CONCLUSIONS

Rs10499194 and rs2230926 polymorphisms in the TNFAIP3 gene region may be susceptibility factors for rheumatoid arthritis in the northern Chinese Han population.

The deubiquitinase A20 in immunopathology of autoimmune diseases

Deubiquitination-mediated regulation is important for homeostatic NF-κB activation. Aberrant NF-κB activation associated with various inflammatory and autoimmune disorders is linked with defects in the deubiquitinase A20. A20 is an important anti-inflammatory molecule that is induced by multiple signals and has numerous targets. Polymorphisms within the A20 locus or its altered expression are thought to contribute in development of autoimmune disorders. Further various studies in mice models underscore the biological importance of A20 in prevention of inflammatory conditions. Dysregulated A20 is also been suggested as a link between prolonged inflammation and cancer by preliminary reports. This review summarizes the existing understanding and focuses on the new developments in the field of A20 biology. These developments highlight the importance of A20 in pathophysiology of autoimmune disorders and its scope as therapeutics and a biomarker.

Differentiation of follicular helper T cells by salivary gland epithelial cells in primary Sjögren's syndrome

Follicular helper T cells (Tfh), which play a pivotal role in B cell activation and differentiation in lymphoid structures, secrete IL-21 whose augmented secretion is a hallmark of several autoimmune diseases. To decipher the cellular and molecular interactions occurring in salivary glands of patients suffering from primary Sjögren's syndrome (pSS), we investigated whether salivary gland epithelial cells (SGECs) were capable to induce Tfh differentiation. Co-cultures of naïve CD4(+) T cells and SGECs from both patients with pSS and controls were performed. Here, we report that IL-6 and ICOSL expression by SGECs contributes to naïve CD4(+) T differentiation into Tfh cells, as evidenced by their acquisition of a specific phenotype, characterized by Bcl-6, ICOS and CXCR5 expression and IL-21 secretion, but also but by their main functional feature: the capacity to enhance B lymphocytes survival. We demonstrated an increase of serum IL-21 with systemic activity. Finally, we analyzed the potential occurrence of a genetic association between IL-21 or IL-21R gene polymorphisms and pSS or elevated IL-21 secretion. This study, which demonstrates a direct induction of Tfh differentiation by SGECs, emphasizes a yet unknown pathogenic role of SGECs and suggests that Tfh and IL-21 might be relevant biomarkers and/or therapeutic targets in primary Sjögren's syndrome.

Single nucleotide polymorphisms at the TNFAIP3/A20 locus and susceptibility/resistance to inflammatory and autoimmune diseases

The anti-inflammatory and immune regulatory functions of the ubiquitin-editing and NF-kappaB inhibitory protein A20 are well documented in vitro, and in multiple animal models. The high rank held by A20 in the cell's physiologic anti-inflammatory defense mechanisms is highlighted by the striking phenotype of A20 knockout mice, characterized by cachexia, multi-organ failure, and premature death. Even partial depletion of A20, as in A20 heterozygous mice, significantly alters NF-kappaB activation in response to pro-inflammatory activators, even though these mice are phenotypically unremarkable at baseline. A recent burst of genome wide association studies (GWAS), fueled by advances in genomic technologies and analysis tools, uncovered associations between single nucleotide polymorphisms (SNPs) at the TNFAIP3/A20 gene locus and multiple autoimmune and inflammatory diseases in humans. Interestingly, some of these studies emphasized significant associations between TNFAIP3/A20 SNPs imparting decreased expression or loss of NF-kappaB inhibitory function, and susceptibility to systemic lupus erythematosus (SLE) and coronary artery disease (CAD). These clinical data phenocopy partial loss of A20 in mouse models of inflammatory diseases, thereby incriminating TNFAIP3/A20 deficiency as a pathogenic culprit in autoimmune and inflammatory diseases. In this chapter, we undertook a thorough review of studies that explored association between TNFAIP3/A20 SNPs and human autoimmune and inflammatory diseases. Beyond the prognostic value of TNFAIP3/ A20 SNPs for assessing disease risk, their implication in the pathogenic processes of these maladies prompts the pursuit of A20-targeted therapies for disease prevention/treatment in patients harboring susceptibility haplotypes.

The anti-arthritic and immune-modulatory effects of NHAG: a novel glucosamine analogue in adjuvant-induced arthritis

Rheumatoid arthritis (RA) is potentially devastating condition which lacks good treatment options. Pro-inflammatory cytokines interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and oxidative stress markers such as nitric oxide (NO) and peroxide (PO) are mediators of RA pathogenesis. In the present study N-[2,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-3-yl]acrylamide (NHAG), analogue of glucosamine, was evaluated in adjuvant-induced arthritic model of rats. The disease progression was monitored by analysing arthritis scoring, loss of body weight, paw oedema, and histological changes in joints. RA associated hyperalgesia was evaluated by gait analysis. The serum or plasma levels of NO, PO, glutathione (GSH) superoxide dismutase (SOD) IL-1β and TNF-α were analyzed to monitor the state of disease severity. The arthritic control animals exhibited significant increase in arthritic score (P < 0.003) and paw oedema (P < 0.001) with parallel loss in body weight (P < 0.04). The NHAG-treated arthritic animals exhibited refinement in the gait changes associated with arthritis. NHAG also significantly decreased the NO (P < 0.02) and PO (P < 0.03) with concurrent increased in GSH (P < 0.04) and SOD (P < 0.007). Both IL-1β (P < 0.001) and TNF-α (P < 0.001), were significantly decreased in NHAG-treated group. Thus NHAG might have a therapeutic potential for arthritis by exerting antioxidative and immunomodulatory effects.

TRAF1-C5 affects quality of life in patients with primary biliary cirrhosis

BACKGROUND

Previous studies reported associations between specific alleles of non-HLA immunoregulatory genes and higher fatigue scores in patients with primary biliary cirrhosis (PBC).

AIM

To study the relationship between variables of health-related quality of life (HRQoL) and single nucleotide polymorphisms of TRAF1-C5, a member of the tumor necrosis factor receptor family.

PATIENTS AND METHODS

TRAF1-C5 gene polymorphisms, rs2900180 and rs3761847, were analysed in 120 Caucasian PBCs. The HRQoL was assessed with SF-36, PBC-40, and PBC-27 questionnaires.

RESULTS

We found a negative association between TT genotype of rs2900180 and SF-36's domains vitality (P < 0.05), mental health (P < 0.05), and mental component summary score (P < 0.05). GG homozygotes of rs3761847 had lower vitality (P < 0.05), mental health (P < 0.05), mental component summary score (P < 0.05) and impairment of social functioning (P < 0.01). Allelic analysis has shown that T allele of rs2900180 and G allele of rs3761847 related to SF-36's vitality (P < 0.05 and P < 0.01), social functioning (P < 0.05 and P < 0.05), mental health (P < 0.01 and P < 0.05), and mental component summary score (P < 0.01 and P < 0.05), respectively. Genotyping and allelic analysis did not reveal correlation with PBC-40 and PBC-27 domains.

CONCLUSION

The association between rs2900180 and rs3761847 polymorphisms and HRQoL variables indicates that TRAF1 is involved in the induction of impaired QoL in PBC.

Racial and ethnic disparities in rheumatoid arthritis

Racial and ethnic health disparities are a national health issue. They are well described in other chronic diseases, but in rheumatoid arthritis (RA), research into their causes, outcomes, and elimination is in its early stages. Health disparities occur in a complex milieu, with system-level, provider-level, and individual-level factors playing roles. Dissecting the overlapping aspects of race/ethnicity, socioeconomic variables, and how their individual components combine to explain the magnitude of disparities in RA can be challenging. Recent research has focused on the extent to which treatment preferences, adherence, trust in physicians, patient-physician communication, health literacy, and depression have contributed to observed disparities in RA. Practicing evidence-based medicine, improving patient-physician communication skills, reducing language and literacy barriers, improving adherence to therapies, raising awareness of racial/ethnic disparities, and recognizing comorbidities such as depression are steps clinicians may take to help eliminate racial/ethnic disparities in RA.

Gene expression patterns in peripheral blood cells associated with radiographic severity in African Americans with early rheumatoid arthritis

Gene expression profiling may be used to stratify patients by disease severity to test the hypothesis that variable disease outcome has a genetic component. In order to define unique expression signatures in African American rheumatoid arthritis (RA) patients with severe erosive disease, we undertook a gene expression study using samples of RNA from peripheral blood mononuclear cells (PBMCs). RNA from baseline PBMC samples of 96 African American RA patients with early RA (<2 years disease duration) was hybridized to cDNA probes of the Illumina Human HT-V3 expression array. Expression analyses were performed using the ca. 25,000 cDNA probes, and then expression levels were compared to the total number of erosions in radiographs of the hands and feet at baseline and 36 months. Using a false discovery rate cutoff of Q = 0.30, 1,138 genes at baseline and 680 genes at 36 months significantly correlated with total erosions. No evidence of a signal differentiating disease progression, or change in erosion scores between baseline and 36 months, was found. Further analyses demonstrated that the differential gene expression signature was localized to the patients with the most erosive disease (>10 erosions). Ingenuity Pathway Analysis demonstrated that genes with fold change greater than 1.5 implicated immune pathways such as CTLA signaling in cytotoxic T lymphocytes. These results demonstrate that CLEAR patients with early RA having the most severe erosive disease, as compared to more mild cases (<10 erosions), may be characterized by a set of differentially expressed genes that represent biological pathways with relevance to autoimmune disease.

Non-MHC risk alleles in rheumatoid arthritis and in the syntenic chromosome regions of corresponding animal models

Rheumatoid arthritis (RA) is a polygenic autoimmune disease primarily affecting the synovial joints. Numerous animal models show similarities to RA in humans; some of them not only mimic the clinical phenotypes but also demonstrate the involvement of homologous genomic regions in RA. This paper compares corresponding non-MHC genomic regions identified in rodent and human genome-wide association studies (GWAS). To date, over 30 non-MHC RA-associated loci have been identified in humans, and over 100 arthritis-associated loci have been identified in rodent models of RA. The genomic regions associated with the disease are designated by the name(s) of the gene having the most frequent and consistent RA-associated SNPs or a function suggesting their involvement in inflammatory or autoimmune processes. Animal studies on rats and mice preferentially have used single sequence length polymorphism (SSLP) markers to identify disease-associated qualitative and quantitative trait loci (QTLs) in the genome of F2 hybrids of arthritis-susceptible and arthritis-resistant rodent strains. Mouse GWAS appear to be far ahead of rat studies, and significantly more mouse QTLs correspond to human RA risk alleles.

Study of association of CD40-CD154 gene polymorphisms with disease susceptibility and cardiovascular risk in Spanish rheumatoid arthritis patients

Objective

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with increased cardiovascular (CV) mortality. Since CD40-CD154 binding has direct consequences on inflammation process initiation, we aimed to replicate previous findings related to disease susceptibility in Spanish RA population. Furthermore, as the major complication in RA disease patients is the development of CV events due to accelerated atherosclerosis, and elevated levels of CD40L/CD154 are present in patients with acute myocardial infarction, we assessed the potential association of CD40 and CD154/CD40L gene variants with CV risk in Spanish RA patients.

Methods

One thousand five hundred and seventy-five patients fulfilling the 1987 ACR classification criteria for RA and 1600 matched controls were genotyped for the CD40 rs1883832, rs4810485 and rs1535045 and CD154 rs3092952 and rs3092920 gene polymorphisms, using predesigned TaqMan single nucleotide polymorphism genotyping assays. Afterwards, we investigated the influence of CD40-CD154 gene variants in the development of CV events. Also, in a subgroup of 273 patients without history of CV events, we assessed the influence of these polymorphisms in the risk of subclinical atherosclerosis determined by carotid ultrasonography.

Results

Nominally significant differences in the allele frequencies for the rs1883832 CD40 gene polymorphism between RA patients and controls were found (p = 0.038). Although we did not observe a significant association of CD40-CD154 gene variants with the development of CV events, an ANCOVA model adjusted for sex, age at the time of the ultrasonography assessment, follow-up time, traditional CV risk factors and anti-cyclic citrullinated peptide antibodies disclosed a significant association (p = 0.0047) between CD40 rs1535045 polymorphism and carotid intima media thickness, a surrogate marker of atherosclerosis.

Conclusion

Data from our pilot study indicate a potential association of rs1883832 CD40 gene polymorphism with susceptibility to RA. Also, the CD40 rs1535045 gene variant may influence development of subclinical atherosclerosis in RA patients.

Investigation of Caucasian rheumatoid arthritis susceptibility loci in African patients with the same disease

INTRODUCTION

The largest genetic risk to develop rheumatoid arthritis (RA) arises from a group of alleles of the HLA DRB1 locus ('shared epitope', SE). Over 30 non-HLA single nucleotide polymorphisms (SNPs) predisposing to disease have been identified in Caucasians, but they have never been investigated in West/Central Africa. We previously reported a lower prevalence of the SE in RA patients in Cameroon compared to European patients and aimed in the present study to investigate the contribution of Caucasian non-HLA RA SNPs to disease susceptibility in Black Africans.

METHODS

RA cases and controls from Cameroon were genotyped for Caucasian RA susceptibility SNPs using Sequenom MassArray technology. Genotype data were also available for 5024 UK cases and 4281 UK controls and for 119 Yoruba individuals in Ibadan, Nigeria (YRI, HapMap). A Caucasian aggregate genetic-risk score (GRS) was calculated as the sum of the weighted risk-allele counts.

RESULTS

After genotyping quality control procedures were performed, data on 28 Caucasian non-HLA susceptibility SNPs were available in 43 Cameroonian RA cases and 44 controls. The minor allele frequencies (MAF) were tightly correlated between Cameroonian controls and YRI individuals (correlation coefficient 93.8%, p = 1.7E-13), and they were pooled together. There was no correlation between MAF of UK and African controls; 13 markers differed by more than 20%. The MAF for markers at PTPN22, IL2RA, FCGR2A and IL2/IL21 was below 2% in Africans. The GRS showed a strong association with RA in the UK. However, the GRS did not predict RA in Africans (OR = 0.71, 95% CI 0.29 - 1.74, p = 0.456). Random sampling from the UK cohort showed that this difference in association is unlikely to be explained by small sample size or chance, but is statistically significant with p<0.001.

CONCLUSIONS

The MAFs of non-HLA Caucasian RA susceptibility SNPs are different between Caucasians and Africans, and several polymorphisms are barely detectable in West/Central Africa. The genetic risk of developing RA conferred by a set of 28 Caucasian susceptibility SNPs is significantly different between the UK and Africa with p<0.001. Taken together, these observations strengthen the hypothesis that the genetic architecture of RA susceptibility is different in different ethnic backgrounds.

A20: linking a complex regulator of ubiquitylation to immunity and human disease

A20 (also known as TNFAIP3) is a potent anti-inflammatory signalling molecule that restricts multiple intracellular signalling cascades. Recent studies in three general areas have converged to highlight the clinical and biological importance of A20. First, human genetic studies have strongly linked polymorphisms and mutations in the gene encoding A20 to inflammatory, autoimmune and malignant diseases. Second, studies in gene-targeted mice have revealed that A20 regulates multiple immune cell functions and prevents experimental diseases that closely mimic human conditions. Third, biochemical studies have unveiled complex mechanisms by which A20 regulates ubiquitin-dependent nuclear factor-κB and cell-survival signals. Taken together, these studies are revealing the importance of A20-mediated regulation of ubiquitin-dependent signalling in human disease.

TRAF1 gene polymorphism correlates with the titre of Gp210 antibody in patients with primary biliary cirrhosis

Background. Polymorphisms of TRAF1 (Tumor necrosis factor receptor-associated factor 1) are associated with rheumatoid arthritis (RA). Whether TRAF1 polymorphisms confer increased risk for primary biliary cirrhosis (PBC), an autoimmune liver disease which can co-exist with RA, is unknown. Aim of the Study. To assess the frequency of the RA-conferring susceptibility TRAF1 polymorphisms rs3761847 and rs2900180 in a cohort of PBC patients. The association of TRAF1 polymorphisms with clinical features and autoantibody markers was also analyzed. Methods. We studied 179 PBC patients and 300 controls. Samples were genotyped for TRAF1 gene polymorphisms by real-time PCR. Autoantibodies were tested by ELISA. Results. The frequency of rs3761847 and rs2900180 polymorphisms did not differ between patients and controls. Laboratory or clinical features were not associated with specific polymorphisms. Gp210 autoantibody titres were conspicuously higher among GG homozygotes of rs3761847 as compared with AA homozygotes (P = 0.02). In contrast, antichromatin titers were higher in AA compared to GG rs3761847 homozygotes (P = 0.04). Rheumatoid factor IgG titres were significantly higher in rs2900180 TT homozygotes than CC homozygotes (P = 0.02). Conclusions. TRAF1 polymorphisms occur with the similar frequency in PBC patients and in the general population, but their presence is probably involved in the regulation of specific PBC-related autoantibodies.

A20: linking a complex regulator of ubiquitylation to immunity and human disease

A20 (also known as TNFAIP3) is a potent anti-inflammatory signalling molecule that restricts multiple intracellular signalling cascades. Recent studies in three general areas have converged to highlight the clinical and biological importance of A20. First, human genetic studies have strongly linked polymorphisms and mutations in the gene encoding A20 to inflammatory, autoimmune and malignant diseases. Second, studies in gene-targeted mice have revealed that A20 regulates multiple immune cell functions and prevents experimental diseases that closely mimic human conditions. Third, biochemical studies have unveiled complex mechanisms by which A20 regulates ubiquitin-dependent nuclear factor-κB and cell-survival signals. Taken together, these studies are revealing the importance of A20-mediated regulation of ubiquitin-dependent signalling in human disease.

Association of single-nucleotide polymorphisms in CCR6, TAGAP, and TNFAIP3 with rheumatoid arthritis in African Americans

OBJECTIVE

We previously reported an analysis of single-nucleotide polymorphisms (SNPs) in 3 validated European rheumatoid arthritis (RA) susceptibility loci, TAGAP, TNFAIP3, and CCR6, in African American patients with RA. Unexpectedly, the disease-associated alleles were different in African Americans from those in Europeans. In an effort to better define their contribution, we performed additional SNP genotyping in these genes.

METHODS

Seven SNPs were genotyped in 446 African American patients with RA and in 733 African American control subjects. Differences in minor allele frequency between the RA cases and controls were analyzed after controlling for the global proportion of European admixture, and pairwise linkage disequilibrium (LD) was estimated among the SNPs.

RESULTS

Three SNPs were significantly associated with RA: the TNFAIP3 rs719149 A allele (OR 1.22 [95% confidence interval (95% CI) 1.03-1.44], P = 0.02), the TAGAP rs1738074 G allele (OR 0.75 [95% CI 0.63-0.89, P = 0.0012), and the TAGAP rs4709267 G allele (OR 0.74 [95% CI 0.60-0.91], P = 0.004). Pairwise LD between the TAGAP SNPs was low (r(2) = 0.034). The haplotype containing minor alleles for both TAGAP SNPs was uncommon (4.5%). After conditional analysis of each TAGAP SNP, its counterpart remained significantly associated with RA (rs1738074 for rs4709267 P = 0.00001 and rs4709267 for rs1738074 P = 0.00005), suggesting independent effects.

CONCLUSION

SNPs in regulatory regions of TAGAP and an intronic SNP (TNFAIP3) are potential susceptibility loci in African Americans. Pairwise LD, haplotype analysis, and SNP conditioning analysis suggest that these 2 SNPs in TAGAP are independent susceptibility alleles. Additional fine-mapping of this gene and functional genomic studies of these SNPs should provide further insight into the role of these genes in RA.

Precipitating and perpetuating factors of rheumatoid arthritis immunopathology: linking the triad of genetic predisposition, environmental risk factors and autoimmunity to disease pathogenesis

Rheumatoid arthritis (RA) is considered to occur when genetic and environmental factors interact to trigger immunopathological changes and consequently an inflammatory arthritis. Over the last few decades, epidemiological and genetic studies have identified a large number of risk factors for RA development, the most prominent of which comprise cigarette smoking and the shared epitope alleles. These risks appear to differ substantially between anti-cyclic citrullinated peptide (ACPA)-positive and ACPA-negative disease. In this article, we will summarise the risk factors for RA development that have currently been identified, outlining the specific gene-environment and gene-gene interactions that may occur to precipitate and perpetuate autoimmunity and RA. We will also focus on how this knowledge of risk factors for RA may be implemented in the future to identify individuals at a high risk of disease development in whom preventative strategies may be undertaken.

PTPN22.6, a dominant negative isoform of PTPN22 and potential biomarker of rheumatoid arthritis

PTPN22 is a tyrosine phosphatase and functions as a damper of TCR signals. A C-to-T single nucleotide polymorphism (SNP) located at position 1858 of human PTPN22 cDNA and converting an arginine (R620) to tryptophan (W620) confers the highest risk of rheumatoid arthritis among non-HLA genetic variations that are known to be associated with this disease. The effect of the R-to-W conversion on the phosphatase activity of PTPN22 protein and the impact of the minor T allele of the C1858T SNP on the activation of T cells has remained controversial. In addition, how the overall activity of PTPN22 is regulated and how the R-to-W conversion contributes to rheumatoid arthritis is still poorly understood. Here we report the identification of an alternative splice form of human PTPN22, namely PTPN22.6. It lacks the nearly entire phosphatase domain and can function as a dominant negative isoform of the full length PTPN22. Although conversion of R620 to W620 in the context of PTPN22.1 attenuated T cell activation, expression of the tryptophan variant of PTPN22.6 reciprocally led to hyperactivation of human T cells. More importantly, the level of PTPN22.6 in peripheral blood correlates with disease activity of rheumatoid arthritis. Our data depict a model that can reconcile the conflicting observations on the functional impact of the C1858T SNP and also suggest that PTPN22.6 is a novel biomarker of rheumatoid arthritis.

Associations between TNFAIP3 gene polymorphisms and rheumatoid arthritis: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether tumor necrosis factor alpha inducible protein 3 (TNFAIP3) polymorphisms confer susceptibility to rheumatoid arthritis (RA) in ethnically different populations.

METHODS

The authors conducted meta-analyses on associations between the TNFAIP3 polymorphisms and RA susceptibility.

RESULT

A total of ten comparative studies were included in this meta-analysis, which showed an association between the two allele of rs6920220 and RA in all study subjects [odds ratio (OR) 1.216, 95% confidence interval (CI) 1.166-1.269, p < 1.0 × 10(-9)]. The two allele of rs6920220 was also significantly associated with RA in Europeans only (OR 1.227, 95% CI 1.175-1.282, p < 1.0 × 10(-9)). Meta-analysis revealed no association between the two allele of the rs10499194 polymorphism and RA in Europeans, but a significant association was found in Asians (OR 1.254, 95% CI 1.101-1.429, p=6.7 × 10(-4)). Furthermore, an association was found between the two allele of rs2230926 and RA in all study subjects (OR 1.390, 95% CI 1.214-2.331, p=1.9 × 10(-6)).

CONCLUSIONS

This meta-analysis confirms that the TNFAIP3 polymorphisms are associated with RA susceptibility in different ethnic groups, namely, in Europeans for rs6920220 and in Asians for rs10499194.

Use of a multiethnic approach to identify rheumatoid- arthritis-susceptibility loci, 1p36 and 17q12

We have previously shown that rheumatoid arthritis (RA) risk alleles overlap between different ethnic groups. Here, we utilize a multiethnic approach to show that we can effectively discover RA risk alleles. Thirteen putatively associated SNPs that had not yet exceeded genome-wide significance (p < 5 × 10(-8)) in our previous RA genome-wide association study (GWAS) were analyzed in independent sample sets consisting of 4,366 cases and 17,765 controls of European, African American, and East Asian ancestry. Additionally, we conducted an overall association test across all 65,833 samples (a GWAS meta-analysis plus the replication samples). Of the 13 SNPs investigated, four were significantly below the study-wide Bonferroni corrected p value threshold (p < 0.0038) in the replication samples. Two SNPs (rs3890745 at the 1p36 locus [p = 2.3 × 10(-12)] and rs2872507 at the 17q12 locus [p = 1.7 × 10(-9)]) surpassed genome-wide significance in all 16,659 RA cases and 49,174 controls combined. We used available GWAS data to fine map these two loci in Europeans and East Asians, and we found that the same allele conferred risk in both ethnic groups. A series of bioinformatic analyses identified TNFRSF14-MMEL1 at the 1p36 locus and IKZF3-ORMDL3-GSDMB at the 17q12 locus as the genes most likely associated with RA. These findings demonstrate empirically that a multiethnic approach is an effective strategy for discovering RA risk loci, and they suggest that combining GWASs across ethnic groups represents an efficient strategy for gaining statistical power.

Disease-promoting and -protective genomic loci on mouse chromosomes 3 and 19 control the incidence and severity of autoimmune arthritis

Proteoglycan (PG)-induced arthritis (PGIA) is a murine model of rheumatoid arthritis. Arthritis-prone BALB/c mice are 100% susceptible, whereas the major histocompatibility complex-matched DBA/2 strain is completely resistant to PGIA. To reduce the size of the disease-suppressive loci for sequencing and to find causative genes of arthritis, we created a set of BALB/c.DBA/2-congenic/subcongenic strains carrying DBA/2 genomic intervals overlapping the entire Pgia26 locus on chromosome 3 (chr3) and Pgia23/Pgia12 loci on chr19 in the arthritis-susceptible BALB/c background. Upon immunization of these subcongenic strains and their wild-type (BALB/c) littermates, we identified a major Pgia26a sublocus on chr3 that suppressed disease onset, incidence and severity via controlling the complex trait of T-cell responses. The region was reduced to 3 Mbp (11.8 Mbp with flanking regions) in size and contained gene(s) influencing the production of a number of proinflammatory cytokines. Additionally, two independent loci (Pgia26b and Pgia26c) suppressed the clinical scores of arthritis. The Pgia23 locus (∼3 Mbp in size) on chr19 reduced arthritis susceptibility and onset, and the Pgia12 locus (6 Mbp) associated with low arthritis severity. Thus, we have reached the critical sizes of arthritis-associated genomic loci on mouse chr3 and chr19, which are ready for high-throughput sequencing of genomic DNA.

Dampened ERK signaling in hematopoietic progenitor cells in rheumatoid arthritis

In rheumatoid arthritis (RA), hematopoietic progenitor cells (HPC) have age-inappropriate telomeric shortening suggesting premature senescence and possible restriction of proliferative capacity. In response to hematopoietic growth factors RA-derived CD34(+) HPC expanded significantly less than age-matched controls. Cell surface receptors for stem cell factor (SCF), Flt 3-Ligand, IL-3 and IL-6 were intact in RA HPC but the cells had lower transcript levels of cell cycle genes, compatible with insufficient signal strength in the ERK pathway. Cytokine-induced phosphorylation of ERK1/2 was diminished in RA HPC whereas phosphorylated STAT3 and STAT5 molecules accumulated to a similar extent as in controls. Confocal microscopy demonstrated that the membrane-proximal colocalization of K-Ras and B-Raf was less efficient in RA-derived CD34(+) cells. Thus, hyporesponsiveness of RA HPC to growth factors results from dampening of the ERK signaling pathways; with a defect localized in the very early steps of the ERK signaling cascade.