New insights into RA genetics from GWAS meta-analysis

Interleukin-18 Gene Polymorphisms and Rheumatoid Arthritis Susceptibility: An Umbrella Review of Meta-Analyses

This study systematically analyzes the association between interleukin-18 (IL-18) gene polymorphisms and rheumatoid arthritis (RA) susceptibility. The electronic databases Ovid MEDLINE, Ovid Excerpta Medica Database, and Cochrane Library were searched to identify meta-analyses that included case-control studies reporting IL-18 gene polymorphisms and RA susceptibility. Data were reanalyzed using Review Manager Software 5.1, and Mantel-Haenszel random effects were applied for the five genetic models: allelic, recessive, dominant, homozygote, and heterozygote. The effect size of odds ratios (ORs) and their corresponding 95% confidence interval (CI) were calculated. A total of seven meta-analyses with poor quality were included. The IL-18 polymorphisms -607 A/C, -137 C/G, -920 T/C, and -105 C/A have been reported. With weak evidence, IL-18 -607 A/C polymorphisms were associated with a reduced risk of RA susceptibility using the allele model (OR = 0.76, 95% CI: 0.61 - 0.93, p=0.01), dominant model (OR = 0.67, 95% CI: 0.50 - 0.90, p=0.008), homozygote model (OR = 0.57, 95% CI: 0.35 - 0.91, p=0.02), and heterozygote model (OR = 0.71, 95% CI: 0.54 - 0.93, p=0.01) in the overall population. IL-18 gene polymorphisms and RA susceptibility are affected by ethnicity: With weak evidence, IL-18 -137 C/G polymorphisms were related to reduce RA susceptibility in the Asian population (allele model: OR = 0.59, 95% CI: 0.40 - 0.88, p=0.01; dominant model: OR = 0.57, 95% CI: 0.37 - 0.89, p=0.01; heterozygote model: OR = 0.60, 95% CI: 0.38 - 0.94, p=0.03). IL-18 -607 A/C gene polymorphisms are a protective factor for RA susceptibility in the overall population, and IL-18 -137 C/G gene polymorphisms are a protective factor for RA susceptibility in the Asian population. Further studies are needed to confirm these results owing to the limitations of the included studies.

Sinomenine ameliorates rheumatoid arthritis by modulating tryptophan metabolism and activating aryl hydrocarbon receptor via gut microbiota regulation

Gut microbiota dysbiosis is associated with the development of rheumatoid arthritis (RA). Sinomenine (SIN) is an effective immunosuppressive and anti-inflammatory drug used for treating RA, but how SIN regulates gut microbiota to alleviate RA remains underexplored. To identify the critical gut microbial species and microbial metabolites associated with the RA-protective effects of SIN, the microbiota-dependent anti-RA effects of SIN were assessed by 16S rRNA gene sequencing, antibiotic treatment, and fecal microbiota transplantation. Metabolomics analysis, transcriptional analysis, and targeted bacteria/metabolites gavage were conducted to explore how SIN regulates gut microbiota to reduce the severity of RA. SIN could restore intestinal microbial balance by mainly modulating the abundance of Lactobacillus, and significantly relieve collagen-induced arthritis (CIA) symptoms in a gut microbiota-dependent manner. SIN significantly elevated microbial tryptophan metabolites indole-3-acrylic acid (IA), indole-3-propionic acid (IPA), and indole-3-acetic acid (IAA). Tryptophan metabolites supplementation could activate aryl hydrocarbon receptor (AhR) and regulate Th17/Treg balance in CIA rats. Intriguingly, SIN relieved the arthritis symptoms involving the enrichment of two beneficial anti-CIA Lactobacillus species, L. paracasei and L. casei by mono-colonization. The promising therapeutic function of SIN was mostly attributed to the activation of AhR by explicitly targeting the Lactobacillus and microbial tryptophan metabolites. The intestinal bacterium L. paracasei and L. casei may be used to reduce the severity of CIA.

Genetic susceptibility to autoimmunity-Current status and challenges

Autoimmune diseases (ADs) often arise from a combination of genetic and environmental triggers that disrupt the immune system's capability to properly tolerate body self-antigens. Familial studies provided the earliest insights into the risk loci of such diseases, while genome-wide association studies (GWAS) significantly broadened the horizons. A drug targeting a prominent pathological pathway can be applied to multiple indications sharing overlapping mechanisms. Advances in genomic technologies used in genetic studies provide critical insights into future research on gene-environment interactions in autoimmunity. This Review summarizes the history and recent advances in the understanding of genetic susceptibility to ADs and related immune disorders, including coronavirus disease 2019 (COVID-19), and their indications for the development of diagnostic or prognostic markers for translational applications.

Assessment of the association between TNIP1 polymorphism with clinical features and risk of systemic lupus erythematosus

OBJECTIVE

Over the past decades, TNIP1 has been identified as a strong risk locus in multiple genome-wide association studies (GWAS), spanning multiple populations and various autoimmune diseases. TNIP1 is a polyubiquitin-binding protein that works as a physiological inhibitor of NF-κB and maintains immune homeostasis. Some studies have confirmed that TNIP1 is downregulated in autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). In the current study, for the first time, we evaluated the possible association between rs6889239 polymorphism in the TNIP1 gene with the risk and clinical characteristics of RA and SLE in the Iranian population.

METHOD

In this case-control study, 115 patients with RA, 115 patients with SLE, and 115 unrelated healthy subjects were enrolled to estimate rs6889239 genotypes with real-time PCR high resolution melting (HRM) method.

RESULTS

Our results demonstrated considerable associations between CC genotype and C allele of rs6889239 with augmented risk of SLE (OR for CC genotype= 2.23; 95%CI [1.175-4.307], OR for C allele= 1.84; 95%CI [1.254-2.720]). However, there was an insignificant association between genotypes and allele frequencies of rs6889239 with the occurrence risk of RA in the population under study (p > 0.05). Additionally, stratification analysis specified that the C allele in rs6889239 was linked with the incidence of renal involvement in SLE patients and lower age of onset in the RA group (p < 0.05).

CONCLUSION

These findings propose a significant association between TNIP1 polymorphism and higher risk of SLE and some clinical characteristics of RA and SLE.

Prediction of New Risk Genes and Potential Drugs for Rheumatoid Arthritis from Multiomics Data

Rheumatoid arthritis (RA) is an autoimmune and inflammatory disease for which there is a lack of therapeutic options. Genome-wide association studies (GWASs) have identified over 100 genetic loci associated with RA susceptibility; however, the most causal risk genes (RGs) associated with, and molecular mechanism underlying, RA remain unknown. In this study, we collected 95 RA-associated loci from multiple GWASs and detected 87 candidate high-confidence risk genes (HRGs) from these loci via integrated multiomics data (the genome-scale chromosome conformation capture data, enhancer-promoter linkage data, and gene expression data) using the Bayesian integrative risk gene selector (iRIGS). Analysis of these HRGs indicates that these genes were indeed, markedly associated with different aspects of RA. Among these, 36 and 46 HRGs have been reported to be related to RA and autoimmunity, respectively. Meanwhile, most novel HRGs were also involved in the significantly enriched RA-related biological functions and pathways. Furthermore, drug repositioning prediction of the HRGs revealed three potential targets (ERBB2, IL6ST, and MAPK1) and nine possible drugs for RA treatment, of which two IL-6 receptor antagonists (tocilizumab and sarilumab) have been approved for RA treatment and four drugs (trastuzumab, lapatinib, masoprocol, and arsenic trioxide) have been reported to have a high potential to ameliorate RA. In summary, we believe that this study provides new clues for understanding the pathogenesis of RA and is important for research regarding the mechanisms underlying RA and the development of therapeutics for this condition.