Rheumatoid arthritis (RA) is a complex disease triggered by the interaction between genetics and environment, especially through the shared epitope (SE) and cell surface calreticulin (CSC) theory. However, the available evidence shows that genetic diversity and environmental exposure cannot explain all the clinical characteristics and heterogeneity of RA. In contrast, recent studies demonstrate that epigenetics play important roles in the pathogenesis of RA, especially DNA methylation and histone modification. DNA methylation and histone methylation are involved in innate and adaptive immune cell differentiation, and migration, proliferation, apoptosis, and mesenchymal characteristics of fibroblast-like synoviocytes (FLS). Epigenetic-mediated regulation of immune-related genes and inflammation pathways explains the dynamic expression network of RA. In this review, we summarized the comprehensive evidence to show that methylation of DNA and histones is significantly involved in the pathogenesis of RA and could be applied as a promising biomarker in the disease progression and drug response prediction. We also explained the advantages and challenges of the current epigenetics research in RA. In summary, epigenetic modules provide a possible interface, through which genetic and environmental risk factors connect to contribute to the susceptibility and pathogenesis of RA. Additionally, epigenetic regulators provide promising drug targets to develop novel therapeutic drugs for RA. Finally, DNA methylation and histone modifications could be important features for providing a better RA subtype identification, to accelerate personalized treatment and precision medicine.

MicroRNAs (miRNAs) play crucial roles in the regulation of the transcriptome and development of diseases including cancer and autoimmune diseases, such as rheumatoid arthritis (RA). Currently, a comprehensive map, illustrating how miRNAs regulate transcripts, pathways, immune system differentiation, and their interaction with terminal cells, such as T cells, fibroblast-like synoviocytes (FLS), osteoblasts, and osteoclasts, is still missing. In this review, we provide a thorough summary of the roles of miRNAs in the susceptibility to pathogenesis, diagnosis, therapeutic intervention, and prognosis of RA. Numerous miRNAs are abnormally expressed in cells involved in RA, and regulate target genes and pathways including the NF-κB, Fas-FasL, JAK-STAT, IRE1-RIDD, and mTOR pathways. By regulating gene expression, miRNAs affect T cell differentiation to diverse cell types, including Th17 and T-reg cells, and thus constitute promising gene therapy targets to modulate the immune system in RA. We summarize the diagnostic and prognostic potential of blood-circulating and cell-free miRNAs, highlighting the novel opportunities to combine these with rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) to provide accurate diagnosis and prognosis, especially for seronegative patients. Furthermore, we outline how functional genetic variants of miR-499 and miR-146a partly explain the unmet susceptibility to RA. Additionally, we review the evidence implicating miRNAs as promising biomarkers of efficiency, response, and resistance to disease-modifying anti-rheumatic drugs (DMRDs) and immunotherapy. Finally, we discuss the autotherapeutic effect of miRNA intervention as a step toward the development of miRNA-based anti-RA drugs. Collectively, the current evidence supports miRNAs as interesting targets to better understand the pathogenetic mechanisms of RA and design more efficient therapeutic interventions.

Rheumatoid arthritis (RA) is a chronic, systemic, abnormal inflammatory immune response. It is characterized by the involvement of the synovium and multiple organs and the destruction of joints and articular cartilage. Over the past 30 years, several promising novel compounds and antibodies have been developed for the treatment of RA. The introduction of new drugs and precision medicine for all forms of RA raises several issues related to access to novel treatments by patients, optimal regimen selection, cost-effectiveness, prognosis monitoring and outcome surveillance, particularly with regarding to the development of low drug response rates, drug resistance and adverse side effects. Tremendous attention has been given to the identification of optimized drug combinations for the treatment of RA, particularly in early high-risk vulnerable and early individuals. Addressing these issues requires novel therapeutic approaches with new mechanisms and the establishment of accurate guidelines for drug selection, drug recombination, and non-chemical therapeutic efforts. In this study, we reviewed the most exciting recently established or ongoing novel drugs and methods according to the clinical trial database maintained by the United States National Library of Medicine and discussed the trends in RA drug development and challenges in the treatment, providing a reference significant for the accurate treatment of RA and the research direction in the future.