Rheumatoid Arthritis Susceptibility Genes Research Articles

Protein citrullination and NET formation do not contribute to the pathology of A20/TNFAIP3 mutant mice

A20 serves as a critical brake on NF-κB-dependent inflammation. In humans, polymorphisms in or near the TNFAIP3/A20 gene have been linked to various inflammatory disorders, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Experimental gene knockout studies in mice have confirmed A20 as a susceptibility gene for SLE and RA. Here, we examine the significance of protein citrullination and NET formation in the autoimmune pathology of A20 mutant mice because autoimmunity directed against citrullinated antigens released by neutrophil extracellular traps (NETs) is central to the pathogenesis of RA and SLE. Furthermore, genetic variants impairing the deubiquitinase (DUB) function of A20 have been shown to contribute to autoimmune susceptibility. Our findings demonstrate that genetic disruption of A20 DUB function in A20 C103R knockin mice does not result in autoimmune pathology. Moreover, we show that PAD4 deficiency, which abolishes protein citrullination and NET formation, does not prevent the development of autoimmunity in A20 deficient mice. Collectively, these findings provide experimental confirmation that PAD4-dependent protein citrullination and NET formation do not serve as pathogenic mechanisms in the development of RA and SLE pathology in mice with A20 mutations.

Effects of Human Leukocyte Antigen DRB1 Genetic Polymorphism on Anti-Cyclic Citrullinated Peptide (ANTI-CCP) and Rheumatoid Factor (RF) Expression in Rheumatoid Arthritis (RA) Patients.

Rheumatoid arthritis (RA) is a systemic disease characterized by non-infectious inflammation of the joints and surrounding tissues, which can cause severe health problems, affect the patient's daily life, and even cause death. RA can be clinically diagnosed by the occurrence of blood serological markers, rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (anti-CCP). However, about 20% of RA patients exhibit negative results for both markers, which makes RA diagnosis difficult and, therefore, may delay the effective treatment. Previous studies found some evidence that human leukocyte antigen (HLA)-related genes might be the susceptibility genes for RA and their polymorphisms might contribute to varieties of susceptibility and disease severity. This study aimed for the genetic polymorphisms of the RA patient genome and their effects on the RA patient's serological makers, RF and anti-CCP. A total of 4580 patients' electronic medical records from 1992 to 2020 were retrieved from the China Medical University Hospital database. The most representative single-nucleotide polymorphisms (SNPs) were identified through a genome-wide association study (GWAS) followed by enzyme-linked immunosorbent assay (ELISA) validation using the blood from 30 additional RA patients. The results showed significant changes at the position of chromosome 6 with rs9270481 being the most significant locus, which indicated the location of the HLA-DRB1 gene. Further, patients with the CC genotype at this locus were more likely to exhibit negative results for RF and anti-CCP than those with the TT genotype. The C allele was also more likely to be associated with negative results for RF and anti-CCP. The results demonstrated that a genetic polymorphism at rs9270481 affected the expression of RF and anti-CCP in RA patients, which might indicate the necessity to develop a personalized treatment plan for each individual patient based on the genetic profile.

Exploration of the association between the single-nucleotide polymorphism of co-stimulatory system and rheumatoid arthritis.

The human leukocyte antigen (HLA) has been linked to the majority of autoimmune diseases (ADs). However, non-HLA genes may be risk factors for ADs. A number of genes encoding proteins involved in regulating T-cell and B-cell function have been identified as rheumatoid arthritis (RA) susceptibility genes. In this study, we investigated the association between RA and single-nucleotide polymorphisms (SNPs) of co-stimulatory or co-inhibitory molecules in 124 RA cases and 100 healthy controls without immune-related diseases [including tumor necrosis factor superfamily member 4 (TNFSF4), CD28, cytotoxic T-lymphocyte-associated protein 4 (CTLA4), and programmed cell death protein 1 (PDCD1)]. The results showed that there were 13 SNPs associated with RA, including rs181758110 of TNFSF4 (CC vs. CT, p = 0.038); rs3181096 of CD28 (TT vs. CC + CT, p = 0.035; CC vs. TT, p = 0.047); rs11571315 (TT vs. CT, p = 0.045), rs733618 (CC vs. TT + CT, p = 0.043), rs4553808 (AA vs. AG vs. GG, p = 0.035), rs11571316 (GG vs. AG vs. AA, p = 0.048; GG vs. AG + AA, p = 0.026; GG vs. AG, p = 0.014), rs16840252 (CC vs. CT vs. TT, p = 0.007; CC vs. CT, p = 0.011), rs5742909 (CC vs. CT vs. TT, p = 0.040), and rs11571319 of CTLA4 (GG vs. AG vs. AA, p < 0.001; GG vs. AG + AA, p = 0.048; AA vs. GG + AG, p = 0.001; GG vs. AA, p = 0.008; GG vs. AG, p ≤ 0.001); and rs10204525 (TT vs. CT + CC, p = 0.024; TT vs. CT, p = 0.021), rs2227982 (AA vs. GG, p = 0.047), rs36084323 (TT vs. CT vs. CC, p = 0.022; TT vs. CT + CC, p = 0.013; CC vs. TT + CT, p = 0.048; TT vs. CC, p = 0.008), and rs5839828 of PDCD1 (DEL vs. DEL/G vs. GG, p = 0.014; DEL vs. DEL/G + GG, p = 0.014; GG vs. DEL + DEL/G, p = 0.025; DEL vs. GG, p = 0.007). Consequently, these SNPs may play an important role in immune regulation, and further research into the role of these SNPs of immune regulatory genes in the pathogenesis of RA is required.

Genome-wide identification of RNA modification-related single nucleotide polymorphisms associated with rheumatoid arthritis

BackgroundRNA modification plays important roles in many biological processes, such as gene expression control. The aim of this study was to identify single nucleotide polymorphisms related to RNA modification (RNAm-SNPs) for rheumatoid arthritis (RA) as putative functional variants.MethodsWe examined the association of RNAm-SNPs with RA in summary data from a genome-wide association study of 19,234 RA cases and 61,565 controls. We performed eQTL and pQTL analyses for the RNAm-SNPs to find associated gene expression and protein levels. Furthermore, we examined the associations of gene expression and circulating protein levels with RA using two-sample Mendelian randomization analysis methods.ResultsA total of 160 RNAm-SNPs related to m6A, m1A, A-to-I, m7G, m5C, m5U and m6Am modifications were identified to be significantly associated with RA. These RNAm-SNPs were located in 62 protein-coding genes, which were significantly enriched in immune-related pathways. RNAm-SNPs in important RA susceptibility genes, such as PADI2, SPRED2, PLCL2, HLA-A, HLA-B, HLA-DRB1, HLA-DPB1, TRAF1 and TXNDC11, were identified. Most of these RNAm-SNPs showed eQTL effects, and the expression levels of 26 of the modifiable genes (e.g., PADI2, TRAF1, HLA-A, HLA-DRB1, HLA-DPB1 and HLA-B) in blood cells were associated with RA. Circulating protein levels, such as CFB, GZMA, HLA-DQA2, IL21, LRPAP1 and TFF3, were affected by RNAm-SNPs and were associated with RA.ConclusionThe present study identified RNAm-SNPs in the reported RA susceptibility genes and suggested that RNAm-SNPs may affect RA risk by affecting the expression levels of corresponding genes and proteins.

Understanding the function of the GABAergic system and its potential role in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a highly disabling chronic autoimmune disease. Multiple factors contribute to the complex pathological process of RA, in which an abnormal autoimmune response, high survival of inflammatory cells, and excessive release of inflammatory factors lead to a severe chronic inflammatory response. Clinical management of RA remains limited; therefore, exploring and discovering new mechanisms of action could enhance clinical benefits for patients with RA. Important bidirectional communication occurs between the brain and immune system in inflammatory diseases such as RA, and circulating immune complexes can cause neuroinflammatory responses in the brain. The gamma-aminobutyric acid (GABA)ergic system is a part of the nervous system that primarily comprises GABA, GABA-related receptors, and GABA transporter (GAT) systems. GABA is an inhibitory neurotransmitter that binds to GABA receptors in the presence of GATs to exert a variety of pathophysiological regulatory effects, with its predominant role being neural signaling. Nonetheless, the GABAergic system may also have immunomodulatory effects. GABA/GABA-A receptors may inhibit the progression of inflammation in RA and GATs may promote inflammation. GABA-B receptors may also act as susceptibility genes for RA, regulating the inflammatory response of RA via immune cells. Furthermore, the GABAergic system may modulate the abnormal pain response in RA patients. We also summarized the latest clinical applications of the GABAergic system and provided an outlook on its clinical application in RA. However, direct studies on the GABAergic system and RA are still lacking; therefore, we hope to provide potential therapeutic options and a theoretical basis for RA treatment by summarizing any potential associations.

Circulating methylation level of HTR2A is associated with inflammation and disease activity in rheumatoid arthritis.

HTR2A is previously identified as a susceptibility gene for rheumatoid arthritis (RA). In this study, we performed the association analysis between DNA methylation of HTR2A with RA within peripheral blood samples. We enrolled peripheral blood samples from 235 patients with RA, 30 osteoarthritis (OA) patients, and 30 healthy controls. The DNA methylation levels of about 218 bp from chr13: 46898190 to chr13: 46897973 (GRCh38/hg38) around HTR2A cg15692052 from patients were analyzed by targeted methylation sequencing. We measured methylation status for 7 CpGs in the promoter region of HTR2A and obseved overall methylation status are signficantly increased in RA compared with normal inviduals (FDR= 9.05 x 10-5). The average cg15692052 methylation levels (methylation score) showed a positive correlation with CRP (r=0.15, P=0.023). Compared with the OA group or HC group, the proportion of haplotypes CCCCCCC (FDR=0.02 and 2.81 x 10-6) is signficantly increased while TTTTTCC (FDR =0.01) and TTTTTTT(FDR =6.92 x 10-3) are significantly decreased in RA. We find methylation haplotypes combining with RF and CCP could signficantly enhance the performance of the diagnosing RA and its comorbidities (hypertension, interstitial lung disease, and osteoporosis), especially in interstitial lung disease. In our study, we found signficant hypermethylation of promoter region of HTR2A which indicates the potential clinical diagnostic role in rheumatoid arthritis.

Correlation between an intronic SNP genotype and ARL15 level in rheumatoid arthritis

ADP ribosylation factor like protein 15 (ARL15) was identified as a novel susceptibility gene for rheumatoid arthritis (RA) based on a genomewide association study in a north Indian cohort. Mechanism of its action and functional relevance in RA biology remain largely unknown. In this study, we aimed to establish (i) ARL15 protein level in sera samples of RA patients; and (ii) its correlation, if any, with the RA associated ARL15 intronic single-nucleotide polymorphism (SNP) rs255758 (A>C). DNA, RNA and sera were isolated from blood samples of 117 RA patients and 25 age-matched healthy controls recruited at All India Institute of Medical Sciences, New Delhi with institutional ethical committee clearance. SNP rs255758 (A>C) was genotyped by Sanger sequencing; ARL15 RNA and protein levels were estimated by quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively; and genotype-phenotype correlation established using Mann-Whitney nonparametric test. Very low level of ARL15 expression in human blood was confirmed at both RNA and protein levels. Genotype-wise distribution showed increased levels (P = 0.05) of ARL15 protein in RA patients with the homozygous variant (CC) as compared to AA + AC genotypes of rs255758. This first-ever correlation between higher ARL15 protein levels and the intronic susceptibility genotype (CC; rs255758) in RA patients may be of diagnostic and therapeutic relevance encouraging additional investigations.

Computational insight into the three-dimensional structure of ADP ribosylation factor like protein 15, a novel susceptibility gene for rheumatoid arthritis

The ARL15 gene (ADP ribosylation factor like protein 15) encodes for an uncharacterized small GTP-binding protein. Its exact role in human physiology remains unknown, but a number of genetic association studies have recognised different variants in this gene to be statistically associated with numerous traits and complex diseases. We have previously reported a novel association of ARL15 with rheumatoid arthritis (RA) based on a genome-wide association study in a north Indian cohort. Subsequent investigations have provided leads for its involvement in RA pathophysiology, especially its potential as a novel therapeutic target. However, the absence of an experimentally determined tertiary structure for ARL15 significantly hinders the understanding of its biochemical and physiological functions, as well as development of potential lead molecules. We, therefore, aimed to derive a high quality, refined model of the three dimensional structure of human ARL15 protein using two different computational protein structure prediction methods – template-based threading and ab initio modelling. The best model each from among the five each derived from both the approaches was selected based on stringent quality assessment and refinement. Molecular dynamics simulations over long timescales revealed the ab initio model to be relatively more stable, and it marginally outperformed the template-based model in the quality assessment as well. A putative GTP-binding site was also predicted using homology for the ARL15 protein, where potential competitive inhibitors can be targeted. This high quality predicted model may provide insights to the biological role(s) of ARL15 and inform and guide further experimental, structural and biochemical characterization efforts. Communicated by Ramaswamy H. Sarma

Association of NCF2, NCF4, and CYBA Gene Polymorphisms with Rheumatoid Arthritis in a Chinese Population.

Objective Recent studies have focused on the special roles of NADPH-oxidase in multiple autoimmune diseases. Nevertheless, the association of genetic variation in NADPH-oxidase genes with rheumatoid arthritis (RA) was not extensively studied in a Chinese population. We performed this study to examine the association of NCF2, NCF4, and CYBA gene polymorphisms with RA susceptibility in a Chinese population. Methods Six single nucleotide polymorphisms (SNPs) (NCF2 rs10911363, NCF4 rs1883112, rs4821544, rs729749, CYBA rs3794624, and rs4673) were genotyped in a cohort composed of 593 RA patients and 596 normal controls. Improved multiple ligase detection reaction (iMLDR) was used for genotyping. Results We observed that NCF4 rs4821544 CT genotype and C allele frequencies in RA patients were significantly decreased when compared to controls (CT vs. TT: P = 0.043; C vs. T: P = 0.031), and rs4821544 polymorphism was significantly associated with an increased RA risk under the dominant model (TT vs. CT+CC: P = 0.031). Our results also indicated that rs729749 CT genotype frequency was significantly lower in RA patients than that in controls (CT vs. CC: P = 0.033). Moreover, the rs729749 CT genotype frequency was also significantly decreased in RA patients in males (CT vs. CC: P = 0.024). No significant association between NCF2 and CYBA gene polymorphisms and RA susceptibility was observed. There were significant associations between rs4821544 TT genotype and T allele frequencies and anti-CCP in male RA patients. Conclusions In summary, NCF4 rs4821544 and rs729749 polymorphisms might contribute to RA susceptibility, while NCF2 and CYBA gene polymorphisms were not associated with RA susceptibility.

Features of functional annotation of rheumatoid arthritis susceptibility genes by Cytoscape

Aim. To evaluate the functional annotation of genes associated with rheumatoid arthritis with different parameters of the ClueGO Cytoscape tool. Materials and methods. Genes of susceptibility to rheumatoid arthritis were extracted from publicly available database GWAS (catalog of associations of single nucleotide polymorphisms with diseases). The Gene Ontology (GO), the functional annotation of genes, was performed using Cytoscape ClueGO. The features of the functional annotation using the plugin ClueGO Cytoscape were analyzed. Results. Depending on the initial parameters specified in the plugin, the grouping of terms according to the gene ontology was carried out with a different degree of generalization. A smaller minimum number of genes in a group allows to form a larger number of groups, which makes it possible to obtain more detailed functional characteristics. Conclusion. The results obtained with different grouping options can be useful for further studies of genetic mechanisms of rheumatoid arthritis.

Human leukocyte antigen (HLA)-Cw0303, HLA-Cw04, and HLA-Cw07 polymorphisms are associated with susceptibility of rheumatoid arthritis in Chinese Han patients from Southern China.

This study aimed to investigate the association between human leukocyte antigen Cw (HLA-Cw) polymorphisms and rheumatoid arthritis (RA) in Chinese Han patients in the Jiangsu area (Southern China). Polymerase chain reaction-sequence specific primers were used to detect HLA-Cw01-08 of 201 RA patients and 211 healthy individuals from Zhongda Hospital (China). The allele frequency distribution of HLA-Cw and genotypic differences between the two groups were analyzed. The frequency of HLA-Cw0303 in patients with RA was significantly higher than that in controls, while the frequency of HLA-Cw04 was lower than that in controls (P<0.05). The gene frequency of HLA-Cw07 in anti-cyclic citrullinated peptide (anti-CCP)-negative patients was higher than that in controls (P=0.044). The frequency of HLA-Cw04 was decreased in the short duration subgroup and increased in the long duration subgroup (P<0.05). Compared to controls, the frequency of HLA-Cw0303 in patients with RA and morning stiffness was increased (P=0.004), while the frequency of HLA-Cw04 was decreased ( 0.005). These results suggest that HLA-Cw0303 is a susceptibility gene for RA in Chinese Han patients in the Jiangsu area of southern China. The HLA-Cw04 gene may be a protective factor against RA, while HLA-Cw07 might play a protective role in the production of anti-CCP in the long-term course in patients with RA.

Role of ADAMTS-12 in Protecting Against Inflammatory Arthritis in Mice By Interacting With and Inactivating Proinflammatory Connective Tissue Growth Factor.

It has been reported that ADAMTS-12 is a susceptibility gene for rheumatoid arthritis (RA) development, and its level is significantly increased in RA patients. In addition, ADAMTS-12 is reported to be required for inflammation in otherwise healthy subjects. This study was undertaken to determine the role of ADAMTS-12 and the underlying mechanisms in the pathogenesis of inflammatory arthritis. The collagen-induced arthritis (CIA) model was established in ADAMTS-12-deficient mice and their control littermates to determine the role of ADAMTS-12 invivo. Micro-computed tomography scanning was used to demonstrate the destruction of the ankle joint; histologic analysis illustrated synovitis, pannus formation, and bone and cartilage destruction; enzyme-linked immunosorbent assay was performed to measure serum levels of inflammatory cytokines; and protein-protein interaction assays were performed to detect the interactions of ADAMTS-12 and its various deletion mutants with connective tissue growth factor (CTGF). Deficiency of ADAMTS-12 led to accelerated inflammatory arthritis in the CIA mouse model. Loss of ADAMTS-12 caused enhanced osteoclastogenesis. In vitro and invivo protein-protein interaction assays demonstrated that ADAMTS-12 bound and processed CTGF, a previously unrecognized substrate of ADAMTS-12. In addition, deletion of ADAMTS-12 enhanced, while overexpression of ADMATS-12 reduced, CTGF-mediated inflammation. Furthermore, ADAMTS-12 regulation of inflammation was largely lost in CTGF-deficient macrophages. Importantly, blocking of CTGF attenuated elevated inflammatory arthritis seen in the ADAMTS-12-deficient CIA mouse model. This study provides evidence that ADAMTS-12 is a critical regulator of inflammatory arthritis and that this is mediated, at least in part, through control of CTGF turnover.

Polymorphisms of RAD51B are associated with rheumatoid arthritis and erosion in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a common, chronic autoimmune disease affecting 0.5–1.0% of adults worldwide, including approximately 4.5–5.0 million patients in China. The genetic etiology and pathogenesis of RA have not yet been fully elucidated. Recently, one new RA susceptibility gene (RAD51B) has been identified in Korean and European populations. In this study, we designed a two-stage case-control study to further assess the relationship of common variants in the RAD51B gene with increased risk of RA in a total of 965 RA patients and 2,511 unrelated healthy controls of Han Chinese ancestry. We successfully identified a common variant, rs911263, as being significantly associated with the disease status of RA (P = 4.8 × 10−5, OR = 0.64). In addition, this SNP was shown to be related to erosion, a clinical assessment of disease severity in RA (P = 2.89 × 10−5, OR = 0.52). These findings shed light on the role of RAD51B in the onset and severity of RA. More research in the future is needed to clarify the underlying functional link between rs911263 and the disease.

No association between ITGAV rs3738919 and rs3768777 polymorphisms and rheumatoid arthritis susceptibility in Iranian population

Abstract Background: Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by angiogenesis, cell proliferation and bone and cartilage damage in the affected joint. Many genetic and environmental factors contribute to RA susceptibility. ITGAV is a member of the integrin family, which plays a major role in bone destruction, angiogenesis and macrophage-dependent inflammation and has been suggested that it may be an RA susceptibility gene. In this study, we investigated association of two single nucleotide polymorphisms in ITGAV (rs3738919 and rs3768777) with susceptibility to RA. Methods: Iranian patients with confirmed RA, aged over 50 years, were compared with healthy controls for allelic and genotypic frequencies of these polymorphisms. The subjects and controls were matched through their race, age and sex. After whole genome extraction, we compared genotype frequencies of analyzed alleles in RA patients and controls using a polymerase chain reaction (PCR)-restriction fragment length polymorphism assay. Association of rs3738919 and rs3768777 with RA was tested in these two sample sets using the χ2-test. Results: Statistical analysis indicated no association between RA and rs3738919 allele frequencies (C and A alleles), single genotype frequencies (AA, AC, CC) and combined genotype frequencies of (AC+CC vs. AA). We also found no evidence of association between rs3768777 SNP allele frequencies, single genotype frequencies and combined genotype frequencies and RA susceptibility. Conclusions: This study did not find any association between RA and ITGAV rs3738919 and rs3768777 polymorphisms in Iranian patients. However, this finding is not conclusive due to the limited sample size. A subsequent study with a larger sample size is recommended.

Decreased severity of experimental autoimmune arthritis in peptidylarginine deiminase type 4 knockout mice.

BackgroundPeptidylarginine deiminase type 4 (PADI4) has been identified as a susceptibility gene for rheumatoid arthritis (RA) by genome-wide association studies. PADI4 is highly expressed in the bone marrow, macrophages, neutrophils, and monocytes. Peptidyl citrulline is an interesting molecule in RA because it is a target antigen for anti-citrullinated peptide antibodies, and only PADs (translated proteins from PADI genes) can provide peptidyl citrulline via the modification of protein substrates. The aim of this study was to evaluate the importance of the PADI4 gene in the progression of RA.MethodsWe generated Padi4 knockout (Padi4−/−) DBA1J mice. The Padi4−/− DBA1J and wild-type mice were immunized with bovine type II collagen (CII) to develop collagen-induced arthritis (CIA). The expression of various inflammatory cytokines and Padi genes in immune cells was detected by the real-time TaqMan assay. Cytokine concentrations in sera were measured by enzyme-linked immunosorbent assays. Localization of the PAD4 and PAD2 proteins was indicated by immunohistochemistry.ResultsWe demonstrated that the clinical disease score was significantly decreased in the Padi4−/− mice and Padi4 expression was induced by CII immunization. In the Padi4−/− mice, serum anti-type II collagen (CII) immunoglobulin M (IgM), IgG, and inflammatory cytokine levels were significantly decreased compared with those in the wild-type mice. Padi2 expression was induced in the immune cells of the Padi4−/− mice as a compensation for the defect in Padi4.ConclusionsPadi4 affected disease severity in the CIA mice and was involved in the enhancement of the collagen-initiated inflammatory responses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-016-1055-2) contains supplementary material, which is available to authorized users.

A twin study of rheumatoid arthritis in the Japanese population

Objectives: Rheumatoid arthritis (RA) is the most common immune-related inflammatory arthritis affecting 0.5–1.0% of the population. Both genetic and environmental factors are associated with RA onset. Twin studies reported from European countries estimated heritability of RA as 53–65%. However, no twin studies have been reported from Asian countries.Methods: We collected a total of 43 monozygotic and 43 dizygotic twins from 7550 patients with RA and obtained information of RA status in the twin pairs. We characterized RA patients whose twin siblings had RA. Variance components analysis was performed to estimate heritability in RA in the Japanese population.Results: Four and one patients with RA over 43 monozygotic (9.3%) and 43 dizygotic twins (2.3%), respectively, had twin siblings with RA. All the patients whose information of sero-positivity was available and whose twin siblings had RA were sero-positive. Heritability of RA was estimated as 62.2% and 56.1% in the AE and ACE models, respectively. The estimated heritability was comparable with those reported in the Europeans, compatible with previous overlap of RA susceptibility genes between Japanese and European populations.Conclusions: Heritability of RA onset in the Japanese population is estimated to be comparable with that in European populations.

CYB5A polymorphism increases androgens and reduces risk of rheumatoid arthritis in women.

IntroductionRheumatoid arthritis (RA) is characterized by decreased androgen levels, which was the first hormonal abnormality described. Several studies indicated that steroidogenesis is directed towards endogenous glucocorticoids at the expense of androgens. The decisive step governing androgen synthesis is the 17,20-lyase activity of the CYP17A1 gene-encoded enzyme cytochrome P450 17A1. Here, we focused on the role in RA of the critical cofactor for 17,20-lyase activity, cytochrome b5, encoded by the CYB5A gene.MethodsData sets of two genome wide RA association studies (GWAS) were screened for single nucleotide polymorphisms (SNP) in the CYB5A gene. Candidate SNPs in CYB5A were studied in a case–control study population of Slovakia. Expression analyses were done in synovial fibroblasts from RA patients by quantitative real-time polymerase chain reaction, and cytochrome b5–expression was detected by immunohistochemistry. Real-life androgen production after steroid conversion was measured using radiolabeled substrates.ResultsThe study identified the RA-associated intronic SNP rs1790834 in the CYB5A gene in one GWAS and confirmed the same SNP in our study. The minor allele reduced RA risk selectively in women (P = 4.1*10−3; OR = 0.63, 95% CI [0.46-0.86]). The protective effect was confined to rheumatoid factor-positive (OR = 0.53, [0.37-0.75]) and anti-cyclic citrullinated peptide-positive (OR = 0.58, [0.41-0.83]) cases, respectively. The protective allele doubles CYB5A mRNA-expression resulting in 2-3fold activation of steroid 17,20-lyase activity, and protective allele was accompanied by a higher density of cytochrome b5-positive cells in synovial tissue.ConclusionsCYB5A is the first RA susceptibility gene involved in androgen synthesis. Our functional analysis of SNP rs1790834 indicates that it contributes to the sex bias observed in RA.

Genetics of rheumatoid arthritis in Asia--present and future.

Genome-wide association studies (GWAS) have uncovered numerous susceptibility genes for rheumatoid arthritis (RA) in patients of European, Asian and other ethnic ancestries. Although previous transethnic GWAS meta-analyses enabled the identification of several novel loci, the genetic heterogeneity observed in the PADI4 and PTPN22 genes suggests that ethnic variation should be considered. In addition, the effects of genetic polymorphisms on gene expression profiles are important when assessing the association of genetic information with disease pathogenesis and will influence the development of personalized medicine. Gene expression is controlled by epigenetic modifications, which in turn can be affected by environmental stimuli. Altogether, genetic and epigenetic information of Asian populations will contribute considerably to future rheumatology research.

Negative regulation of the NLRP3 inflammasome by A20 protects against arthritis.

Rheumatoid arthritis (RA) is a chronic autoinflammatory disease that affects 1-2% of the world population and is characterized by widespread joint inflammation. IL-1 is an important mediator of cartilage destruction in rheumatic diseases1, but our understanding of the upstream mechanisms leading to IL-1β production in rheumatoid arthritis is limited by the absence of suitable RA mouse models in which inflammasomes contribute to pathology. Myeloid-cell-specific deletion of the RA-susceptibility gene A20/TNFAIP3 in mice (A20myel-KO mice) triggers a spontaneous erosive polyarthritis that resembles RA in patients2. Notably, RA in A20myel-KO mice was not rescued by tumor necrosis factor receptor 1 (TNF-R1) deletion, but we showed it to crucially rely on interleukin-1 receptor (IL-1R) signaling. Macrophages lacking A20 had increased basal and LPS-induced expression levels of the inflammasome adaptor Nlrp3 and proIL-1β. As a result, A20-deficiency in macrophages significantly enhanced Nlrp3 inflammasome-mediated caspase-1 activation, pyroptosis and IL-1β secretion by soluble and crystalline Nlrp3 stimuli. In contrast, activation of the Nlrc4 and AIM2 inflammasomes was not altered. Importantly, increased Nlrp3 inflammasome activation contributed to RA pathology in vivo, because deletion of Nlrp3 and caspase-1 markedly protected against RA-associated inflammation and cartilage destruction in A20myel-KO mice. These results reveal A20 as a novel negative regulator of Nlrp3 inflammasome activation, and describe A20myel-KO mice as the first experimental model to study the role of inflammasomes in RA pathology.

AB0017 Impact of Disease Susceptibility Genes on Progression of Joint Destruction in Japanese Patients with Rheumatoid Arthritis

BackgroundDisease severity of rheumatoid arthritis (RA) is objectively measured by radiographic joint damage, which is reflective of the cumulative burden of inflammation. To date, several genetic risk loci for progression...