Genetics of RA susceptibility, what comes next?

(5R)-5-Hydroxytriptolide (LLDT-8) induces substantial epigenetic mediated immune response network changes in fibroblast-like synoviocytes from rheumatoid arthritis patients

Tripterygium is a traditional Chinese medicine that has widely been used in the treatment of rheumatic disease. (5R)-5-hydroxytriptolide (LLDT-8) is an extracted compound from Tripterygium, which has been shown to have lower cytotoxicity and relatively higher immunosuppressive activity when compared to Tripterygium. However, our understanding of LLDT-8-induced epigenomic impact and overall regulatory changes in key cell types remains limited. Doing so will provide critically important mechanistic information about how LLDT-8 wields its immunosuppressive activity. The purpose of this study was to assess the effects of LLDT-8 on transcriptome including mRNAs and long non-coding RNA (lncRNAs) in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) by a custom genome-wide microarray assay. Significant differential expressed genes were validated by QPCR. Our work shows that 394 genes (281 down- and 113 up-regulated) were significantly differentially expressed in FLS responding to the treatment of LLDT-8. KEGG pathway analysis showed 20 pathways were significantly enriched and the most significantly enriched pathways were relevant to Immune reaction, including cytokine-cytokine receptor interaction (P = 4.61 × 10⁻¹³), chemokine signaling pathway (P = 1.01 × 10⁻⁵) and TNF signaling pathway (P = 2.79 × 10⁻⁴). Furthermore, we identified 618 highly negatively correlated lncRNA-mRNA pairs from the selected significantly differential lncRNA and mRNA including 27 cis-regulated and 591 trans-regulated lncRNA-mRNAs modules. KEGG and GO based function analysis to differential lncRNA also shown the enrichment of immune response. Finally, lncRNA-transcription factor (TF) and lncRNA-TF-mRNA co-expression network were constructed with high specific network characteristics, indicating LLDT-8 would influence the expression network within the whole FLS cells. The results indicated that the LLDT-8 would mainly influence the FLS cells systemically and specially in the process of immune related pathways.

A noncanonical role for the engulfment gene ELMO1 in neutrophils that promotes inflammatory arthritis

Rheumatoid arthritis is characterized by progressive joint inflammation and affects ~1% of the human population. We noted single nucleotide polymorphisms (SNPs) in the apoptotic cell engulfment genes ELMO1, DOCK2, and RAC1 linked to rheumatoid arthritis. As ELMO1 promotes cytoskeletal reorganization during engulfment, we hypothesized that ELMO1 loss would worsen inflammatory arthritis. Surprisingly, Elmo1-deficient mice showed reduced joint inflammation in acute and chronic arthritis models. Genetic and cell biological studies revealed that ELMO1 associates with receptors linked to neutrophil function in arthritis and regulates activation and early neutrophil recruitment to the joints, without general inhibition of inflammatory responses. Further, neutrophils from peripheral blood of human donors that carry the SNP in ELMO1 associated with arthritis display increased migratory capacity, whereas ELMO1 knockdown reduces human neutrophil migration to chemokines linked to arthritis. These data identify ‘non-canonical’ roles for ELMO1 as an important cytoplasmic regulator of specific neutrophil receptors and promoter of arthritis.

DNA Damage Response Signals Transduce Stress From Rheumatoid Arthritis Risk Factors Into T Cell Dysfunction

Rheumatoid arthritis (RA) is an autoimmune-mediated disease that is associated with significant cartilage damage and immunosenescence. Despite decades of research, the major signal pathways that initiate RA are still unclear. The DNA damage response (DDR) is a specific and hierarchical network that includes cell cycle checkpoints, DNA repair, and DNA-damage tolerance pathways. Recent studies suggest that this condition is associated with deficits in telomere maintenance and overall genomic instability in the T cells of RA patients. Analysis of the underlying mechanisms has revealed defects in DDR pathways. Particularly, the DNA repair enzyme, ataxia telangiectasia mutated (ATM), is downregulated, which leaves the damaged DNA breaks in RA-associated T cells unrepaired and pushes them to apoptosis, exhausts the T cell pool, and promotes the arthritogenesis effector function of T cells. This review discusses recent advancements and illustrates that risk factors for RA, such as viral infections, environmental events, and genetic risk loci are combat with DDR signals, and the impaired DDR response of RA-associated T cells, in turn, triggers disease-related phenotypes. Therefore, DDR is the dominant signal that converts genetic and environmental stress to RA-related immune dysfunction. Understanding the orchestration of RA pathogenesis by DDR signals would further our current knowledge of RA and provide novel avenues in RA therapy.

Association of PTPN22 Haplotypes (-1123G>C/+1858C>T) with Rheumatoid Arthritis in Western Mexican Population

Rheumatoid arthritis (RA) is an autoimmune disease characterized by the presence of antibodies against cyclic citrullinated peptide (anti-CCP), a consequence of the breakdown of immune tolerance. The lymphoid tyrosine phosphatase (Lyp) protein has significant effects on maintenance of peripheral immune tolerance. Two polymorphic variants (-1123G>C and +1858C>T) at PTPN22 gene that encodes this protein have been associated with autoimmune disorders and found in strong linkage disequilibrium in Caucasian population. We evaluated whether PTPN22 haplotypes (-1123G>C/+1858C>T) are associated with anti-CCP antibodies, as well as susceptibility to RA in a Western Mexican population. A total of 315 RA patients and 315 control subjects (CS) were included. The polymorphisms were genotyped by PCR-RFLP and the anti-CCP antibodies were determined by ELISA. The PTPN22 polymorphisms were in strong linkage disequilibrium (D' = 1.00 in CS). The susceptibility haplotype CT was significantly more frequent in RA patients than in CS (OR 2.18, 95% CI 1.15-4.16, p = 0.01). No association between haplotypes and anti-CCP antibodies levels was observed. In conclusion, this study confirmed that -1123G>C and +1858C>T PTPN22 polymorphisms are in strong linkage disequilibrium and the CT haplotype is a susceptibility marker to RA in Western Mexico. However, the PTPN22 haplotypes are not associated with anti-CCP antibodies.

Genetic markers as therapeutic target in rheumatoid arthritis: A game changer in clinical therapy?

Rheumatoid arthritis (RA) is a chronic, inflammatory, multi-systemic autoimmune disease unremitted by genetic and environmental factors. The factors are crucial but inadequate in the development of disease; however, these factors can be representative of potential therapeutic targets and response to clinical therapy. Insights into the contribution of genetic risk factors are currently in progress with studies querying the genetic variation, their role in gene expression of coding and non-coding genes and other mechanisms of disease. In this review, we describe the significance of genetic markers architecture of RA through genome-wide association studies and meta-analysis studies. Further, it also reveals the mechanism of disease pathogenesis investigated through the mutual findings of functional and genetic studies of individual RA-associated genes, which includes HLA-DRB1, HLA-DQB1, HLA-DPB1, PADI4, PTPN22, TRAF1-C5, STAT4 and C5orf30. However, the genetic background of RA remains to be clearly depicted. Prospective efforts of the post-genomic and functional genomic period can travel toward real possible assessment of the genetic effect on RA. The discovery of novel genes associated with the disease can be appropriate in identifying potential biomarkers, which could assist in early diagnosis and aggressive treatment.

A novel long non-coding RNA in the rheumatoid arthritis risk locus TRAF1-C5 influences C5 mRNA levels

Long non-coding RNAs (lncRNAs) can regulate the transcript levels of genes in the same genomic region. These locally acting lncRNAs have been found deregulated in human disease and some have been shown to harbour quantitative trait loci (eQTLs) in autoimmune diseases. However, lncRNAs linked to the transcription of candidate risk genes in loci associated to rheumatoid arthritis (RA) have not yet been identified. The TRAF1 and C5 risk locus shows evidence of multiple eQTLs and transcription of intergenic non-coding sequences. Here, we identified a non-coding transcript (C5T1lncRNA) starting in the 3' untranslated region (UTR) of C5. RA-relevant cell types express C5T1lncRNA and RNA levels are further enhanced by specific immune stimuli. C5T1lncRNA is expressed predominantly in the nucleus and its expression correlates positively with C5 mRNA in various tissues (P=0.001) and in peripheral blood mononuclear cells (P=0.02) indicating transcriptional co-regulation. Knockdown results in a concurrent decrease in C5 mRNA levels but not of other neighbouring genes. Overall, our data show the identification of a novel lncRNA C5T1lncRNA that is fully located in the associated region and influences transcript levels of C5, a gene previously linked to RA pathogenesis.