Genetic Variants of the NLRP3 Inflammasome Are Associated with Stroke in Patients with Rheumatoid Arthritis
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Genetic Variants of the NLRP3 Inflammasome Are Associated with Stroke in Patients with Rheumatoid Arthritis Alf Kastbom, Lisbeth Ärlestig, and Solbritt Rantapää-Dahlqvist ABSTRACT. Objective. Inflammasomes are intracellular protein complexes important for the production of pro- inflammatory cytokines. Studies have suggested that the NLRP3 inflammasome influences both the severity of rheumatoid arthritis (RA) and development of atherosclerosis. Therefore, we investigated whether functional genetic variants related to the NLRP3 inflammasome influence the risk of cardio- vascular (CV) disease (CVD) in patients with RA. Methods. The incidence of CVD was assessed in 522 patients with established RA by a retrospective survey of medical records in combination with a 6-year prospective followup. NLRP3-Q705K and CARD8-C10X genotypes were analyzed in relation to CVD by logistic regression, adjusting for tradi- tional risk factors, antirheumatic treatment, and age at the onset of RA. Results. Carriage of the NLRP3-Q705K minor allele was associated with an increased risk of stroke/transient ischemic attack (TIA; OR 2.01, 95% CI 1.0–4.1, p = 0.05), while CARD8-C10X was not associated with any type of CV event. Patients with ≥ 1 variant allele in both polymorphisms had an increased risk of CVD when compared with patients without variant alleles present in both polymor- phisms (adjusted OR 3.05, 95% CI 1.42–6.54, p = 0.004). Stratification showed that this risk was confined to stroke/TIA (adjusted OR 5.09, 95% CI 2.27–11.44, p < 0.0001) and not to myocardial infarction (MI)/angina pectoris (adjusted OR 1.58, 95% CI 0.67–3.73). Risk estimates were consis- tently higher among female patients. Conclusion. Genetic variants of the NLRP3 inflammasome influence the risk of stroke/TIA, but not of MI/angina pectoris in Swedish patients with established RA. (First Release July 15 2015; J Rheumatol 2015;42:1740–5; doi:10.3899/jrheum.141529) Key Indexing Terms: RHEUMATOID ARTHRITIS INFLAMMASOMES GENETICS CARDIOVASCULAR DISEASE Cardiovascular (CV) disease (CVD) is significantly overrep- It is well established that local inflammation in vessel resented among patients with rheumatoid arthritis (RA). It is walls is crucial in the development of atherosclerotic lesions, a major cause of the increased risk of premature death consis- and in patients without a concurrent inflammatory disease tently associated with established RA1,2. Apart from tradi- such as RA7. However, understanding of the mechanisms by tional proatherosclerotic risk factors, inflammatory activity which systemic inflammation increases the risk of clinical enhances the risk of CV events3,4 and may possibly be CVD in patients with RA remains incomplete. We have modified by antirheumatic therapy5,6. previously suggested a role for the interleukin 1β (IL-1β)-regulating NLRP3 inflammasome in the disease From the Department of Rheumatology, and Department of Clinical and course of early RA because functional single-nucleotide Experimental Medicine, Linköping University, Linköping; the Department of Public Health and Clinical Medicine/Rheumatology, Umeå University, polymorphisms (SNP) in the genes encoding NLRP3 and Umeå, Sweden. CARD8 were found to be associated with inflammatory Supported by grants from the County Council of Östergötland, the activity and the subsequent need for therapy with tumor Reinhold Sund Foundation, the Swedish Society of Medicine, the Swedish 8,9 Research Council (K2011–68X–20611–04–3 and Dnr 825-2010-5986), necrosis factor inhibitors (TNFi) . Intriguingly, there is also King Gustaf V’s 80–Year Fund, King Gustaf V’s and Queen Victoria’s increasing evidence for a role of the NLRP3 inflammasome Fund, the Swedish Rheumatism Association, the Swedish COMBINE in the development of atherosclerotic lesions. First, it was program, the Department of Research, Västerbotten county council, and shown that the NLRP3 inflammasome was activated by the Swedish Foundation for Strategic Research. 10,11 A. Kastbom, MD, PhD, Department of Rheumatology, and Department of cholesterol crystals, resulting in the secretion of IL-1β , Clinical and Experimental Medicine, Linköping University; L. Ärlestig, and that this mechanism significantly contributed to athero- PhD; S. Rantapää-Dahlqvist, Department of Public Health and Clinical genesis in a mouse model11. Second, activation of the NLRP3 Medicine/Rheumatology, Umeå University. inflammasome was shown to accelerate macrophage lipid Address correspondence to Dr. A. Kastbom, AIR/Rheumatology, 12 Department of Clinical and Experimental Medicine, Linköping University, deposition and foam cell development . SE-581 85 Linköping, Sweden. E-mail: [email protected] Mutations in the gene encoding NLRP3 are associated Accepted for publication June 3, 2015. with rare autoinflammatory diseases [e.g., cryopyrin-associ- Personal non-commercial use only. The Journal of Rheumatology Copyright © 2015. All rights reserved. 1740 The Journal of Rheumatology 2015; 42:10; doi:10.3899/jrheum.141529 Downloaded on September 25, 2021 from www.jrheum.org ated periodic syndromes (CAPS)] and dysregulated IL-1β The study protocol was approved by the Research Ethics Committee in production13. The Q705K variant (rs35829419), however, is Umeå, Sweden. All patients gave informed consent to participate in the study that was performed according to the principles of the Helsinki Declaration. a polymorphism with about 10% of the Swedish population 8,9,14 Laboratory analyses. Genomic DNA was extracted from buffy-coat cells being carriers of a minor allele . NLRP3-Q705K causes using standard methods. HLA-DRB1 genotyping was performed using PCR significantly increased inflammasome-mediated release of sequence-specific primers from DR low-resolution kit and DRB1*04 IL-1β in vitro, although to a more moderate degree compared subtyping kit (Olerup SSP AB). Shared epitope was defined as 26 with the mutations causing CAPS15. CARD8 is an adaptor DRB1*0401/0404/0405/0408, as previously described in detail . protein that both interacts with inflammasome components NLRP3-Q705K and CARD8-C10X were genotyped using commercially κ κ 16,17 available TaqMan assays (Applied Biosystems) according to the manufac- and inhibits nuclear factor- B (NF- B) transcription . The turer’s instructions. The genotyping success rate was 99% for the CARD8-C10X polymorphism (rs2043211), which introduces CARD8-C10X polymorphism and 100% for NLRP3-Q705K. IgG-class anti- an early stop codon, has been shown to impair the citrullinated protein antibodies were analyzed by ELISA with second-gener- κ NF- B–inhibiting properties of the protein17, but functional ation cyclic citrullinated peptides as antigen (Axis Shield Diagnostics; cutoff studies in relation to inflammasomes are lacking. A number 5 U/ml). of reports have described interacting effects between Statistical methods. The chi-squared test or Fisher’s exact test, when appro- priate, was used for testing categorical data between groups, and logistic NLRP3-Q705K and CARD8-C10X, for example, regarding 8 18 regression analyses were used to estimate OR for predicting variables for RA , aortic abdominal aneurysms , inflammatory bowel the dependent variable. For analysis of continuous data, the independent 19,20 disease , and plasma levels of IL-1β in healthy Student t test was used. All p values are 2-sided, and p values ≤ 0.05 were individuals14. considered statistically significant. Calculations were performed using SPSS Given that CVD is overrepresented among patients with 22 software. Adjustments in the multiple logistic analyses were based on those factors that were significantly associated in simple logistic regression RA, and that the NLRP3 inflammasome has been linked to analyses. Empirical p values were calculated with Haploview 4.2, using both RA severity and the development of atherosclerosis, we 10,000 permutations. hypothesized that the NLRP3-Q705K and CARD8-C10X polymorphisms increase the risk of CVD in patients with RA. RESULTS Genotype frequencies were in Hardy-Weinberg equilibrium MATERIALS AND METHODS for both SNP (p > 0.1), and comparable with previous Subjects. The study subjects were 560 patients with established RA from 8,9,14 northern Sweden fulfilling the 1987 American College of Rheumatology RA findings from Swedish datasets . Table 1 shows classification criteria21, consecutively recruited into the study during the first demographic and clinical characteristics of the patients. From 4 months of 1995, 2000, and 200122. Of these, 522 patients (382 women and the onset of RA to the 6-year followup, 121 patients were 140 men) donated blood samples for DNA analysis. A thorough survey of recorded as undergoing a CV event(s): 74 had an MI, 20 had all the available patient records from the onset of RA until inclusion in the angina pectoris with intervention, and 50 experienced a study was performed retrospectively according to a structured study regis- stroke/TIA. Patients with registered CV event(s) after the tration form. All patients were followed prospectively for 6 years from the inclusion date. CV events after the onset of RA were registered retrospec- onset of RA were older, had a longer duration of the disease, tively according to the following definitions: (1) a myocardial infarction and had more often survived a CV event before the onset of (MI) diagnosed by a clinical physiologist or cardiologist based upon typical RA as compared with those without a CV event(s). They were 23 changes in electrocardiograms according to the Minnesota code