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Functional analysis of a complement polymorphism (rs17611) associated with rheumatoid arthritis.

ABSTRACT: Complement is implicated in the pathogenesis of rheumatoid arthritis (RA); elevated levels of complement activation products have been measured in plasma, synovial fluid, and synovial tissues of patients. Complement polymorphisms are associated with RA in genome-wide association studies. Coding-region polymorphisms may directly impact protein activity; indeed, we have shown that complement polymorphisms affecting a single amino acid change cause subtle changes in individual component function that in combination have dramatic effects on complement activity and disease risk. In this study, we explore the functional consequences of a single nucleotide polymorphism (SNP) (rs17611) encoding a V802I polymorphism in C5 and propose a mechanism for its link to RA pathology. Plasma levels of C5, C5a, and terminal complement complex were measured in healthy and RA donors and correlated to rs17611 polymorphic status. Impact of the SNP on C5 functionality was assessed. Plasma C5a levels were significantly increased and C5 levels significantly lower with higher copy number of the RA risk allele for rs17611, suggesting increased turnover of C5 V802. Functional assays using purified C5 variants revealed no significant differences in lytic activity, suggesting that increased C5 V802 turnover was not mediated by complement convertase enzymes. C5 is also cleaved in vivo by proteases; the C5 V802 variant was more sensitive to cleavage with elastase and the "C5a" generated was biologically active. We hypothesize that this SNP in C5 alters the rate at which elastase generates active C5a in rheumatoid joints, hence recruiting neutrophils to the site thus maintaining a state of inflammation in arthritic joints.

SUBMITTER: Giles JL

PROVIDER: S-EPMC4367161 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Functional analysis of a complement polymorphism (rs17611) associated with rheumatoid arthritis.

Giles Joanna L JL Choy Ernest E van den Berg Carmen C Morgan B Paul BP Harris Claire L CL

Journal of immunology (Baltimore, Md. : 1950) 20150227 7

Complement is implicated in the pathogenesis of rheumatoid arthritis (RA); elevated levels of complement activation products have been measured in plasma, synovial fluid, and synovial tissues of patients. Complement polymorphisms are associated with RA in genome-wide association studies. Coding-region polymorphisms may directly impact protein activity; indeed, we have shown that complement polymorphisms affecting a single amino acid change cause subtle changes in individual component function th ...[more]

PMID: 25725109

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Project description:ObjectiveWe previously observed the association of the co-occurrence of the HLA-DRB1 shared epitope (SE) and RANKL single-nucleotide polymorphisms (SNPs) with younger age at the onset of rheumatoid arthritis (RA) in 182 rheumatoid factor (RF)-positive European American patients with early-onset RA. The aim of this study was to fine-map the 48-kb RANKL region in the extended cohort of 210 European American RF-positive patients with early RA, to seek replication of RA-associated SNPs in additional RA cohorts of 501 European Americans and 298 African Americans, and to explore the functional consequences of RA-associated SNPs.MethodsSNP genotyping was conducted using pyrosequencing or TaqMan polymerase chain reaction (PCR) assays. Associations of rs7984870 with RANKL expression in plasma, peripheral blood mononuclear cells, and isolated T cells were quantified using enzyme-linked immunosorbent assay and reverse transcription-PCR. Site-directed mutagenesis of rs7984870 within the 2-kb RANKL promoter was performed to drive the luciferase reporter gene in osteoblast and stromal cell lines. Interaction of DNA and protein was determined by electrophoretic mobility shift assay.ResultsA single promoter SNP, rs7984870, was consistently significantly associated with earlier age at the onset of RA in 3 independent seropositive (RF or anti-cyclic citrullinated peptide antibody) RA cohorts but not in seronegative RA patients. The C risk allele of rs7984870 conferred 2-fold higher plasma RANKL levels in RF-positive patients with RA, significantly elevated RANKL messenger RNA expression in activated normal T cells, and increased promoter activity after stimulation in vitro via differential binding to the transcription factor SOX5.ConclusionThe RANKL promoter allele that increased transcription levels upon stimulation might promote interaction between activated T cells and dendritic cells, predisposing to a younger age at the onset of RA in seropositive European American and African American patients.

Project description:BackgroundThe complement system plays an important role in pathophysiology of cardiovascular disease (CVD), and might be involved in accelerated atherogenesis in rheumatoid arthritis (RA). The role of complement activation in response to treatment, and in development of premature CVD in RA, is limited. Therefore, we examined the effects of methotrexate (MTX) and tumor necrosis factor inhibitors (TNFi) on complement activation using soluble terminal complement complex (TCC) levels in RA; and assessed associations between TCC and inflammatory and cardiovascular biomarkers.MethodsWe assessed 64 RA patients starting with MTX monotherapy (n = 34) or TNFi with or without MTX co-medication (TNFi±MTX, n = 30). ELISA was used to measure TCC in EDTA plasma. The patients were examined at baseline, after 6 weeks and 6 months of treatment.ResultsMedian TCC was 1.10 CAU/mL, and 57 (89%) patients had TCC above the estimated upper reference limit (<0.70). Compared to baseline, TCC levels were significantly lower at 6-week visit (0.85 CAU/mL, p<0.0001), without significant differences between the two treatment regimens. Notably, sustained reduction in TCC was only achieved after 6 months on TNFi±MTX (0.80 CAU/mL, p = 0.006). Reductions in TCC after treatment were related to decreased C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and interleukin 6, and increased levels of total, high and low-density lipoprotein cholesterol. Similarly, baseline TCC was significantly related to baseline CRP, ESR and interleukin 6. Patients with endothelial dysfunction had higher baseline TCC than those without (median 1.4 versus 1.0 CAU/mL, p = 0.023).ConclusionsPatients with active RA had elevated TCC, indicating increased complement activation. TCC decreased with antirheumatic treatment already after 6 weeks. However, only treatment with TNFi±MTX led to sustained reduction in TCC during the 6-month follow-up period. RA patients with endothelial dysfunction had higher baseline TCC compared to those without, possibly reflecting involvement of complement in the atherosclerotic process in RA.

Project description:Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder affecting the joints. Many patients carry anti-citrullinated protein autoantibodies (ACPA). Overactivation of the complement system seems to be part of the pathogenesis of RA, and autoantibodies against the pathway initiators C1q and MBL, and the regulator of the complement alternative pathway, factor H (FH), were previously reported. Our aim was to analyze the presence and role of autoantibodies against complement proteins in a Hungarian RA cohort. To this end, serum samples of 97 ACPA-positive RA patients and 117 healthy controls were analyzed for autoantibodies against FH, factor B (FB), C3b, C3-convertase (C3bBbP), C1q, MBL and factor I. In this cohort, we did not detect any patient with FH autoantibodies but detected C1q autoantibodies in four patients, MBL autoantibodies in two patients and FB autoantibodies in five patients. Since the latter autoantibodies were previously reported in patients with kidney diseases but not in RA, we set out to further characterize such FB autoantibodies. The isotypes of the analyzed autoantibodies were IgG2, IgG3, IgGκ, IgGλ and their binding site was localized in the Bb part of FB. We detected in vivo formed FB-autoanti-FB complexes by Western blot. The effect of the autoantibodies on the formation, activity and FH-mediated decay of the C3 convertase in solid phase convertase assays was determined. In order to investigate the effect of the autoantibodies on complement functions, hemolysis assays and fluid phase complement activation assays were performed. The autoantibodies partially inhibited the complement-mediated hemolysis of rabbit red blood cells, inhibited the activity of the solid phase C3-convertase and C3 and C5b-9 deposition on complement activating surfaces. In summary, in ACPA-positive RA patients we identified FB autoantibodies. The characterized FB autoantibodies did not enhance complement activation, rather, they had inhibitory effect on complement. These results support the involvement of the complement system in the pathomechanism of RA and raise the possibility that protective autoantibodies may be generated in some patients against the alternative pathway C3 convertase. However, further analyses are needed to assess the exact role of such autoantibodies.

Dataset Information

Functional analysis of a complement polymorphism (rs17611) associated with rheumatoid arthritis.

Publications

Functional analysis of a complement polymorphism (rs17611) associated with rheumatoid arthritis.

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