Research of the methylation status of miR-124a gene promoter among rheumatoid arthritis patients

Exploring regulatory mechanisms on miRNAs and their implications in inflammation-related diseases

This comprehensive exploration delves into the pivotal role of microRNAs (miRNAs) within the intricate tapestry of cellular regulation. As potent orchestrators of gene expression, miRNAs exhibit diverse functions in cellular processes, extending their influence from the nucleus to the cytoplasm. The complex journey of miRNA biogenesis, involving transcription, processing, and integration into the RNA-induced silencing complex, showcases their versatility. In the cytoplasm, mature miRNAs finely tune cellular functions by modulating target mRNA expression, while their reach extends into the nucleus, influencing transcriptional regulation and epigenetic modifications. Dysregulation of miRNAs becomes apparent in various pathologies, such as cancer, autoimmune diseases, and inflammatory conditions. The adaptability of miRNAs to environmental signals, interactions with transcription factors, and involvement in intricate regulatory networks underscore their significance. DNA methylation and histone modifications adds depth to understanding the dynamic regulation of miRNAs. Mechanisms like competition with RNA-binding proteins, sponging, and the control of miRNA levels through degradation and editing contribute to this complex regulation process. In this review, we mainly focus on how dysregulation of miRNA expression can be related with skin-related autoimmune and autoinflammatory diseases, arthritis, cardiovascular diseases, inflammatory bowel disease, autoimmune and autoinflammatory diseases, and neurodegenerative disorders. We also emphasize the multifaceted roles of miRNAs, urging continued research to unravel their complexities. The mechanisms governing miRNA functions promise advancements in therapeutic interventions and enhanced insights into cellular dynamics in health and disease.

Study of MicroRNA-124 in Patients with Lupus Nephritis

BACKGROUND

Lupus nephritis is associated with a six-fold increase in mortality compared with the general population. MicroRNAs studies revealed that increased MicroRNA -21 and MicroRNA -155 levels represent risk factors for active LN patients. MicroRNAs can be used as biomarkers in the diagnosis of clinical stages of LN.

OBJECTIVES

The present study aimed to determine the level of miR-124 in patients with lupus nephritis by reverse transcriptase real-time polymerase chain reaction compared to healthy control and correlate its levels with biochemical findings in those patients.

METHODS

The study was a case-control study that included fifty patients with lupus nephritis in addition to fifty healthy controls. Blood samples from the participants were subjected to the determination of serological markers of SLE. Moreover, real-time PCR was used for the determination of miR-124.

RESULTS

The comparison of Micro-RNA124 between patients and control subjects revealed a statistically significant decrease in Micro-RNA124 in patients (1.193 ± 0.56) compared to the control (3.36 ± 0.50, p <0.001); the comparison of the level of MicroRNA 124 in the patients with different clinical and serological findings of SLE revealed a significant decrease in the level of MicroRNA 124 in patients with muscular findings (1.02 ± 0.5) compared to the patients with negative manifestations (1.47 ± 0.5, p =0.005).

CONCLUSION

In the present study, a comparison of MicroRNA-124 in LN patients with different stages compared to normal control showed a statistically significant decrease in Micro-RNA124 in patients with lupus nephritis p <0.001 with significant correlation to the patients' different clinical and serological findings of SLE. Therefore, it may be used as a new noninvasive therapeutic approach to monitor response to therapy, predict relapses, and identify the degree of the activity of the disease or the progression to the chronic stage.

Obefazimod: A First-in-class Drug for the Treatment of Ulcerative Colitis

Biologic agents and oral small molecules are the mainstays of inflammatory bowel disease [IBD] management. However, an unmet clinical need remains for additional agents with novel mechanism of action which are effective, safe, and disease-modifying; this is due to the substantial proportion of patients who do not respond, lose response, or develop intolerance to currently marketed products. microRNAs [miRNAs] that play a role in the modulation of signal transduction pathways implicated in the development of IBD hold the potential to be used as therapeutic targets. Recently, a novel first-in-class compound, obefazimod, originally conceived as a human immunodeficiency virus [HIV] infection drug, has shown great promise in phase II induction trials for ulcerative colitis [UC] patients. Findings from the maintenance phases of trials showed that long-term obefazimod treatment provides continued improvement in clinical symptoms of disease, with a substantial proportion of patients in clinical remission, and an overall good safety profile. With a novel mechanism of action, obefazimod is an orally available small molecule with anti-inflammatory properties through the specific and selective upregulation of miR-124 expression. The aim of this paper is to critically review the available evidence related to pharmacokinetics and pharmacodynamics, and to discuss the potential clinical implications of this first-in-class oral small molecule.

Comprehensive overview of microRNA function in rheumatoid arthritis

MicroRNAs (miRNAs), a class of endogenous single-stranded short noncoding RNAs, have emerged as vital epigenetic regulators of both pathological and physiological processes in animals. They direct fundamental cellular pathways and processes by fine-tuning the expression of multiple genes at the posttranscriptional level. Growing evidence suggests that miRNAs are implicated in the onset and development of rheumatoid arthritis (RA). RA is a chronic inflammatory disease that mainly affects synovial joints. This common autoimmune disorder is characterized by a complex and multifaceted pathogenesis, and its morbidity, disability and mortality rates remain consistently high. More in-depth insights into the underlying mechanisms of RA are required to address unmet clinical needs and optimize treatment. Herein, we comprehensively review the deregulated miRNAs and impaired cellular functions in RA to shed light on several aspects of RA pathogenesis, with a focus on excessive inflammation, synovial hyperplasia and progressive joint damage. This review also provides promising targets for innovative therapies of RA. In addition, we discuss the regulatory roles and clinical potential of extracellular miRNAs in RA, highlighting their prospective applications as diagnostic and predictive biomarkers.

The Epigenetic Role of miR-124 in HIV-1 Tat- and Cocaine-Mediated Microglial Activation

HIV-1 and drug abuse have been indissolubly allied as entwined epidemics. It is well-known that drug abuse can hasten the progression of HIV-1 and its consequences, especially in the brain, causing neuroinflammation. This study reports the combined effects of HIV-1 Transactivator of Transcription (Tat) protein and cocaine on miR-124 promoter DNA methylation and its role in microglial activation and neuroinflammation. The exposure of mouse primary microglial cells to HIV-1 Tat (25 ng/mL) and/or cocaine (10 μM) resulted in the significantly decreased expression of primary (pri)-miR-124-1, pri-miR-124-2, and mature miR-124 with a concomitant upregulation in DNMT1 expression as well as global DNA methylation. Our bisulfite-converted genomic DNA sequencing also revealed significant promoter DNA methylation in the pri-miR-124-1 and pri-miR-124-2 in HIV-1 Tat- and cocaine-exposed mouse primary microglial cells. We also found the increased expression of proinflammatory cytokines such as IL1β, IL6 and TNF in the mouse primary microglia exposed to HIV-1 Tat and cocaine correlated with microglial activation. Overall, our findings demonstrate that the exposure of mouse primary microglia to both HIV-1 Tat and cocaine could result in intensified microglial activation via the promoter DNA hypermethylation of miR-124, leading to the exacerbated release of proinflammatory cytokines, ultimately culminating in neuroinflammation.

Transformation of fibroblast-like synoviocytes in rheumatoid arthritis; from a friend to foe

Swelling and the progressive destruction of articular cartilage are major characteristics of rheumatoid arthritis (RA), a systemic autoimmune disease that directly affects the synovial joints and often causes severe disability in the affected positions. Recent studies have shown that type B synoviocytes, which are also called fibroblast-like synoviocytes (FLSs), as the most commonly and chiefly resident cells, play a crucial role in early-onset and disease progression by producing various mediators. During the pathogenesis of RA, the FLSs' phenotype is altered, and represent invasive behavior similar to that observed in tumor conditions. Modified and stressful microenvironment by FLSs leads to the recruitment of other immune cells and, eventually, pannus formation. The origins of this cancerous phenotype stem fundamentally from the significant metabolic changes in glucose, lipids, and oxygen metabolism pathways. Moreover, the genetic abnormalities and epigenetic alterations have recently been implicated in cancer-like behaviors of RA FLSs. In this review, we will focus on the mechanisms underlying the transformation of FLSs to a cancer-like phenotype during RA. A comprehensive understanding of these mechanisms may lead to devising more effective and targeted treatment strategies.

MicroRNA-124: An emerging therapeutic target in cancer

MicroRNAs (miRNAs) are noncoding single-stranded RNAs, approximately 20-24 nucleotides in length, known as powerful posttranscriptional regulators. miRNAs play important regulatory roles in cellular processes by changing messenger RNA expression and are widely involved in human diseases, including tumors. It has been reported in the literature that miRNAs have a precise role in cell proliferation, programmed cell death, differentiation, and expression of coding genes. MicroRNA-124 (miR-124) has reduced exparession in various human neoplasms and is believed to be related to the occurrence, development, and prognosis of malignant tumors. In our review, we focus on the specific molecular functions of miR-124 and the downstream gene targets in major cancers, which provide preclinical evidence for the treatment of human cancer. Although some obstacles exist, miR-124 is still attracting intensive research focus as a promising and effective anticancer weapon.

MicroRNA-124 represents a novel diagnostic marker in human lupus nephritis and plays an inhibitory effect on the growth and inflammation of renal mesangial cells by targeting TRAF6

microRNAs (miRs) are short non-coding RNAs that function as guide molecules in RNA silencing by inducing mRNA degradation or blocking protein translation. Increasing evidence has shown that miRNAs play an important role in regulating the pathological process of lupus nephritis (LN), but the precise role of miR-124 in LN is still unknown. Here, we found that miR-124 expression is significantly reduced in patients with active LN compared with those patients with non-active LN and the absence of LN. Additionally, the miR-124 level was negatively correlated with serum IL-1β, IL-6, TNF-α, and TRAF6 mRNA expressions in active LN patients. Receiver operating characteristic and logistic regression analyses revealed miR-124 is a significant diagnostic biomarker for active LN. Furthermore, transfection of the miR-124 mimic into human renal mesangial cells (HRMCs) resulted in significantly reduced cell proliferation, induced cell apoptosis, and decreased synthesis of inflammatory factors. Moreover, a dual luciferase assay showed that TRAF6 was a direct target of miR-124, and the expression of TRAF6 was suppressed by miR-124 through direct binding to the 3'-UTR of mRNA. Mechanistic studies demonstrated that the over-expression of TRAF6 could abrogate miR-124-related effects on cell proliferation, apoptosis and the synthesis of inflammatory factors in HRMCs. Taken together, these findings indicate that downregulated miR-124 represents a novel diagnostic marker in human LN and plays an inhibitory effect on the growth and inflammation of renal mesangial cells by targeting TRAF6.

Serum microRNA Profiles Serve as Novel Biomarkers for Autoimmune Diseases

Autoimmune diseases involve a complex dysregulation of immunity. Autoimmune diseases include many members [e.g., rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE)], and most of them are classified according to what organs and tissues are targeted by the damaging immune response. Many studies have focused on finding specific biomarkers for single autoimmune diseases, but so far, there are no universal biomarkers for detecting almost all autoimmune diseases. Serum miRNAs have served as potential biomarkers for detecting various diseases. The purpose of this study was to find a universal biomarker for diagnosing autoimmune diseases. Regulatory T cells (Tregs) play a crucial role in protecting an individual from autoimmunity, and depletion of Tregs in mice is considered a representative animal model of autoimmune disease. Two mouse models for Treg depletion, in which Treg was depleted by CD25mAb (in C57 mice) or by diphtheria toxin (DT) (in Foxp3^DTR mice), were investigated, and 381 miRNAs were identified in the serum of mice with Treg depletion. A distinctive circulating miRNA profile was identified in Treg-depleted mice and in patients with autoimmune disease. QRT-PCR confirmation and ROC curve analysis determined that six miRNAs (miR-551b, miR-448, miR-9, miR-124, miR-148, and miR-34c) in the Treg-depleted mouse models and three miRNAs [miR-551b (specificity 73.5%, sensitivity 88.4%), miR-448 (specificity 82.4%, sensitivity 91.3%), and miR-124 (specificity 76.5%, sensitivity 91.3%)] in patients with RA, SLE, Sjogren's syndrome (SS), and ulcerative colitis (UC) could serve as valuable specific biomarkers. These circulating miRNAs may represent potential universal biomarkers for autoimmune diseases diagnosis and prognosis.

Epigenetic Promoter DNA Methylation of miR-124 Promotes HIV-1 Tat-Mediated Microglial Activation via MECP2-STAT3 Axis

The present study demonstrates HIV-1 Tat-mediated epigenetic downregulation of microglial miR-124 and its association with microglial activation. Exposure of mouse primary microglia isolated from newborn pups of either sex to HIV-1 Tat resulted in decreased expression of primary miR-124-1, primary miR-124-2 as well as the mature miR-124. In parallel, HIV-1 Tat exposure to mouse primary microglial cells resulted in increased expression of DNA methylation enzymes, such as DNMT1, DNMT3A, and DNMT3B, which were also accompanied by increased global DNA methylation. Bisulfite-converted genomic DNA sequencing in the HIV-1 Tat-exposed mouse primary microglial cells further confirmed increased DNA methylation of the primary miR-124-1 and primary miR-124-2 promoters. Bioinformatic analyses identified MECP2 as a novel 3'-UTR target of miR-124. This was further validated in mouse primary microglial cells wherein HIV-1 Tat-mediated downregulation of miR-124 resulted in increased expression of MECP2, leading in turn to further repression of miR-124 via the feedback loop. In addition to MECP2, miR-124 also modulated the levels of STAT3 through its binding to the 3'-UTR, leading to microglial activation. Luciferase assays and Ago2 immunoprecipitation determined the direct binding between miR-124 and 3'-UTR of both MECP2 and STAT3. Gene silencing of MECP2 and DNMT1 and overexpression of miR-124 blocked HIV-1 Tat-mediated downregulation of miR-124 and microglial activation. In vitro findings were also confirmed in the basal ganglia of SIV-infected rhesus macaques (both sexes). In summary, our findings demonstrate a novel mechanism of HIV-1 Tat-mediated activation of microglia via downregulation of miR-124, leading ultimately to increased MECP2 and STAT3 signaling.SIGNIFICANCE STATEMENT Despite the effectiveness of combination antiretroviral therapy in controlling viremia, the CNS continues to harbor viral reservoirs. The persistence of low-level virus replication leads to the accumulation of early viral proteins, including HIV-1 Tat protein. Understanding the epigenetic/molecular mechanism(s) by which viral proteins, such as HIV-1 Tat, can activate microglia is thus of paramount importance. This study demonstrated that HIV-1 Tat-mediated DNA methylation of the miR-124 promoter leads to its downregulation with a concomitant upregulation of the MECP2-STAT3-IL6, resulting in microglial activation. These findings reveal an unexplored epigenetic/molecular mechanism(s) underlying HIV-1 Tat-mediated microglial activation, thereby providing a potential target for the development of therapeutics aimed at ameliorating microglial activation and neuroinflammation in the context of HIV-1 infection.

Rheumatoid Arthritis and miRNAs: A Critical Review through a Functional View

Rheumatoid arthritis (RA) is a systemic autoimmune disease with severe joint inflammation and destruction associated with an inflammatory environment. The etiology behind RA remains to be elucidated; most updated concepts include the participation of environmental, proteomic, epigenetic, and genetic factors. Epigenetic is considered the missing link to explain genetic diversification among RA patients. Within epigenetic factors participating in RA, miRNAs are defined as small noncoding molecules with a length of approximately 22 nucleotides, capable of gene expression modulation, either negatively through inhibition of translation and degradation of the mRNA or positively through increasing the translation rate. Over the last decade and due to the feasibility of the identification of miRNAs among different tissues and compartments, they have been proposed as biomarkers for diagnosis, prognosis, and response to treatment in different pathologies. Nevertheless, miRNAs seem to be important regulators of networks instead of single genes; their hypothetical use as biomarkers needs to rely on a functional integrative description of their effects in the biological process of autoimmune conditions which until now is missing. Therefore, we underwent a bibliographic search for review and original articles related to miRNAs and their possible implications in rheumatoid arthritis. We found 48 different studies using the key words “miRNAs” or “micro-RNAs” and “rheumatoid arthritis” with restriction of publication dates from 2011 to 2016, in humans, using the English language. After a critical reading, we provide in this paper a functional view with respect to miRNA biogenesis, interaction with targets that are expressed in specific cells and tissues, during different stages of inflammatory responses associated with RA, and recognized specific areas where miRNAs might also have a pathogenic role but remain undescribed. Our results will be useful in designing future research projects that can support miRNAs as biomarkers or therapeutic targets in RA.

A time-course microarray data analysis reveals consistent dysregulated genes and upstream microRNAs in autoantibody-mediated arthritis

Background

The purpose of this study is to identify key genes and microRNAs (miRNAs) involved in autoantibody-mediated arthritis (AMA).

Methods

A time-course microarray data (ID: GSE27492) of peripheral blood leukocytes, ankle tissue, and synovial fluid from K/BxN mouse serum-transferred mice were downloaded from Gene Expression Omnibus. Those samples were collected at days 0, 1, 3, 7, 12, and 18 after serum injection. Limma of R was employed to identify differentially expressed genes (DEGs) in samples collected at days 1–18 compared with those collected at day 0. Consistent DEGs were obtained by taking the interaction of DEGs from different time points, followed by functional enrichment analysis. MiRNAs were screened out and constructed into regulatory network with DEGs using Cytoscape.

Results

In total, 17 consistent DEGs were obtained, including downregulated Ephx1 and upregulated AF251705, Adam8, Arg1, Basp1, Ccl2, Ccl7, Ccl9, Ccr2, Clec4a2, Clec4d, Cxcl1, Fabp5, Fcgr1, Gp49a, Il1rn, and Saa3. Those DEGs were associated with biological processes of immune response, inflammatory response, and defense response; chemokine signaling pathway; cytokine-cytokine receptor interaction; and NOD-like receptor signaling pathway. Additionally, 202 miRNAs were identified to have a regulatory effect on 9 of the 17 DEGs. Notably, miR-944, miR-374a, and miR374b were found to regulate the expression of Cxcl1, Ccl7, and Ccl2. Clec4d was targeted by 78 miRNAs.

Conclusions

Our study reveals that 17 DEGs and 202 miRNAs may be associated with autoimmune disorder in the progression of AMA, which could guide future researches.

Reconstruction and analysis of the lncRNA–miRNA–mRNA network based on competitive endogenous RNA reveal functional lncRNAs in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease with an unknown etiology, occurring in approximately 1.0% of general population.

Demethylation of MicroRNA-124a Genes Attenuated Proliferation of Rheumatoid Arthritis Derived Fibroblast-Like Synoviocytes and Synthesis of Tumor Necrosis Factor-α

Objective

To examine the impact of 5-Aza-2ʹ-deoxycytidine (5-AzadC) on methylation status of miR-124a genes in rheumatoid arthritis (RA) associated fibroblast-like synoviocytes (FLS) and its effect on RA-FLS proliferation and TNF-α expression.

Materials and Methods

FLS were isolated from seven RA-derived synovial tissues and cultured in vitro. The expression of miR-124a was measured by real time quantitative polymerase chain reaction (PCR) in FLS with or without 5-AzadC treatment. MiR-124a gene methylation was detected by methylation-specific PCR. FLS were divided into three groups as control, IL-1β and IL-1β/5-AzadC, respectively. The cells in the IL-1β group were treated with 5 μg/L of IL-1β for 24 hours, whereas the cells in the IL-1β/5-AzadC group were first treated with IL-1β exactly as those in the IL-1β group for 24 h but further treated with 1μM 5-AzadC for additional 3 days. The cell growth was estimated based on absorbance at UV450nm. Secreted TNF-α from the cells was evaluated by enzyme-linked immunosorbent assay. After that, RA-FLS treated with IL-1β plus 5-AzadC were further transfected with miR-124a inhibitor or scrambled control. After culturing for 3 days, cell growth and TNF-α concentrations were measured.

Results

After 5-AzadC treatment, the expression of miR-124a was significantly increased compared with the control group (1.545 ± 0.189 vs 0.836 ± 0.166, p = 0.001). On the other hand, 5-AzadC significantly reduced IL-1β-mediated cell proliferation by nearly 2.5 fold (p = 0.006). Also, the level of TNF-α secreted from the cells treated with IL-1β plus 5-AzadC was considerably less than that from the cells treated with IL-1β alone (324.99 ± 22.73 ng/L vs 387.91 ± 58.51 ng/L, p = 0.022). After transfection with miR-124a inhibitor in RA-FLS treated with IL-1β plus 5-AzadC, the cell proliferation was increased by 18.2% and the TNF-α expression was increased by 19.0% (p = 0.001 and 0.011, respectively).

Conclusion

Methylation of miR-124a genes contributed to IL-1β-mediated RA-FLS proliferation and TNF-α expression.

miRNA-124 in Immune System and Immune Disorders

In recent years, miR-124 has emerged as a critical modulator of immunity and inflammation. Here, we summarize studies on the function and mechanism of miR-124 in the immune system and immunity-related diseases. They indicated that miR-124 exerts a crucial role in the development of immune system, regulation of immune responses, and inflammatory disorders. It is evident that miR-124 may serve as an informative diagnostic biomarker and therapeutic target in the future.

Influence of hydrogen sulfide on zymogen activation of homocysteine-induced matrix metalloproteinase-2 in H9C2 cardiocytes

OBJECTIVE

To observe the influence of different concentrations of homocysteine (Hcy) and hydrogen sulfide (H2S) on the secretion and activation of matrix metalloproteinase-2 (MMP-2) in cardiocytes so as to search for new ways to fight against myocardial tissue fibrosis.

METHODS

Cardiocytes H9C2 was cultured in vitro and different concentrations of Hcy and H2S were added for 6-h and 24-h cultivation. MTT cell proliferation assay was applied to test the activation change of cardiocytes H9C2 after affecting by different concentrations of Hcy and H2S. ELISA and MTT were employed to detect the expression and enzymatic activity of MMP-2.

RESULTS

The H9C2 cell inhibition of activity was more significant with 1000 μmol/L of Hcy as compared with other concentrations (P < 0.001). With 2.5-100.0 μmol/L Hcy and 0.1, 1.0 and 10.0 mmol/L H2S, the activity of H9C2 did not change significantly (P > 0.05). Hcy with concentrations of 10, 50 and 100 μmol/L could increase the quantity of MMP-2 secreted by cardiocytes H9C2, and the interaction strength was concentration-dependent (P < 0.05). After interacting with 100 μmol/L of Hcy for 6 h, the zymogen activation effect of MMP-2 was stronger than that of the 2.5-25 μmol/L group (P < 0.05). After interacting with Hcy and H2S (1.0 mmol/L) for 6 h and 24 h, the activation effect of MMP-2 was stronger than those interacted with 10, 25, 50 and 100 μmol/L of Hcy (P < 0.05).

CONCLUSIONS

Hcy can increase the production of MMP-2 secreted by H9C2 cell and improve its zymogen activation. Besides, the interaction strength is concentration-dependent; while H2S can up-regulate the activation of MMP-2 and co-promote the activation of MMP-2 with Hcy as well.

MicroRNA variants as genetic determinants of bone mass

Single nucleotide polymorphisms (SNPs) are the most abundant genetic variants that contribute to the heritability of bone mass. MicroRNAs (miRNAs, miRs) are key post-transcriptional regulators that modulate the differentiation and function of skeletal cells by targeting multiple genes in the same or distinct signaling pathways. SNPs in miRNA genes and miRNA binding sites can alter miRNA abundance and mRNA targeting. This review describes the potential impact of miRNA-related SNPs on skeletal phenotype. Although many associations between SNPs and bone mass have been described, this review is limited to gene variants for which a function has been experimentally validated. SNPs in miRNA genes (miR-SNPs) that impair miRNA processing and alter the abundance of mature miRNA are discussed for miR-146a, miR-125a, miR-196a, miR-149 and miR-27a. SNPs in miRNA targeting sites (miR-TS-SNPs) that alter miRNA binding are described for the bone remodeling genes bone morphogenetic protein receptor 1 (Bmpr1), fibroblast growth factor 2 (Fgf2), osteonectin (Sparc) and histone deacetylase 5 (Hdac5). The review highlights two aspects of miRNA-associated SNPs: the mechanism for altering miRNA mediated gene regulation and the potential of miR-associated SNPs to alter osteoblast, osteoclast or chondrocyte differentiation and function. Given the polygenic nature of skeletal diseases like osteoporosis and osteoarthritis, validating the function of additional miRNA-associated SNPs has the potential to enhance our understanding of the genetic determinants of bone mass and predisposition to selected skeletal diseases.

Deregulation and therapeutic potential of microRNAs in arthritic diseases

Epigenetic abnormalities are part of the pathogenetic alterations involved in the development of rheumatic disorders. In this context, the main musculoskeletal cell lineages, which are generated from the pool of mesenchymal stromal cells (MSCs), and the immune cells that participate in rheumatic diseases are deregulated. In this Review, we focus on microRNA (miRNA)-mediated regulatory pathways that control cell proliferation, drive the production of proinflammatory mediators and modulate bone remodelling. The main studies that identify miRNAs as regulators of immune cell fate, MSC differentiation and immunomodulatory properties - parameters that are altered in rheumatoid arthritis (RA) and osteoarthritis (OA) - are also discussed, with emphasis on the importance of miRNAs in the regulation of cellular machinery, extracellular matrix remodelling and cytokine release. A deeper understanding of the involvement of miRNAs in rheumatic diseases is needed before these regulatory pathways can be explored as therapeutic approaches for patients with RA or OA.

Epigenetics in rheumatoid arthritis

PURPOSE OF REVIEW

To give an overview of recently published articles addressing the role of epigenetic modifications in rheumatoid arthritis (RA). Here we focused on DNA methylation and posttranslational histone modifications.

RECENT FINDINGS

Recent studies attempted to link epigenetic modifications with genetic or environmental risk factors for RA. There is evidence that histone deacetylases confer effects of environmental triggers such as smoking, diet or therapy on expression levels of target genes. Additionally, disturbed methylation patterns and cell-type specific histone methylation marks were identified as potential mediators of genetic risk in RA. Altered methylome signatures were found in several cell types in RA, first of all RA synovial fibroblasts, and contribute to the intrinsic fibroblast activation. The reversal of DNA hypomethylation by inhibiting the polyamine recycling pathway was suggested as new epigenetic therapy in RA. Moreover, targeting epigenetic reader proteins, such as bromodomain proteins, emerged as a new field in drug development and the first studies underscored the potential of these drugs not only in malignant and inflammatory conditions but also in autoimmune diseases.

SUMMARY

Epigenetic factors represent a promising area to link genetics, regulation of gene expression and environmental risk factors.

DNA methylation profiling of synovial fluid FLS in rheumatoid arthritis reveals changes common with tissue-derived FLS

Aim: Alterations in DNA methylation contribute to the abnormal phenotype of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA). We profiled genome-wide DNA methylation in these cells from synovial fluid, a more readily accessible source of disease-associated cells. Patients & methods: Genome-wide DNA methylation was interrogated in fluid-derived FLS from five RA and six osteoarthritis patients using Human Methylation 450 Bead Chip and bisulfite pyrosequencing. Results: Array analysis identified 328 CpGs, representing 195 genes, that were differentially methylated between RA and osteoarthritis fluid-derived FLS. Comparison with the genes identified in two independent studies of tissue-derived FLS revealed 73 genes in common (˜40%), of which 22 shared identity with both studies. Pyrosequencing confirmed altered methylation of these genes. Conclusion: Synovial fluid-derived RA FLS show methylation changes common with tissue-derived FLS, supporting the use of fluid-derived FLS for future investigations.

MicroRNAs in rheumatoid arthritis

The role of genetic and epigenetic factors in the development of rheumatic diseases has been an interesting field of research over the past decades all around the world. Research on the role of microRNAs (miRNAs) in rheumatoid arthritis (RA) has been active and ongoing, and investigations have attempted to use miRNAs as biomarkers in disease diagnosis, prognosis, and treatment. This review focuses on experimental researches in the field of miRNAs and RA to present the data available up to this date and includes researches searched by keywords "microRNA" and "rheumatoid arthritis" in PubMed from 2008 to January 2015. All references were also searched for related papers. miRNAs are shown to act as proinflammatory or anti-inflammatory agents in diverse cell types, and their role seems to be regulatory in most instances. Researchers have evaluated miRNAs in patients compared to controls or have investigated their role by overexpressing or silencing them. Multiple targets have been identified in vivo, in vitro, or in silico, and the researches still continue to show their efficacy in clinical settings.

MicroRNA-152 modulates the canonical Wnt pathway activation by targeting DNA methyltransferase 1 in arthritic rat model

Rheumatoid arthritis (RA) is an autoimmune and progressive systemic disease of unknown etiology. Research shows that fibroblast-like synoviocytes (FLS) participate in the cartilage erosion, synovial hyperplasia, inflammatory cytokine secretion and suggests that fibroblast-like synoviocytes (FLS) display a crucial role in RA pathogenesis. Recent studies have suggested the role of the Wnt signaling pathway in the pathogenesis of RA. In previous study, we identified that increased methyl-CpG-binding protein 2 (MeCP2) reduced the secreted frizzled-related protein 4 (SFRP4) expression in FLS in Arthritic rat model and the DNA methyltransferase (DNMT) inhibitor 5-Aza-2'-deoxycytidine (5-azadC) could induce the SFRP4 expression, indicating that DNMT has a key role in the differential expression of SFRP4. MicroRNAs (MiRNAs), which are small non-coding RNAs, are involved in diverse biological functions, regulation of gene expression, pathogenesis of autoimmune disease and carcinogenesis. In light of the directly down-regulation of miR-152 on DNMT1 expression by targeting the 3' untranslated regions of its transcript in nickel sulfide (NiS)-transformed human bronchial epithelial cells, we investigated whether miR-152 is aberrantly expressed and targets DNMT1 in FLS in Arthritic rat model. Our results demonstrated that the expression of miR-152 was specifically down-regulated in Arthritic rat model, whereas up-regulation of miR-152 in FLS resulted in a marked reduction of DNMT1 expression. Further experiments revealed that increased miR-152 indirectly up-regulated the SFRP4 expression, a negative regulator of WNT signaling pathway, by targeting the DNMT1. Moreover, activation of miR-152 expression in FLS could inhibit the canonical Wnt pathway activation and result in a significant decrease of FLS proliferation. MiR-152 and DNA methylation may provide molecular mechanisms for the activation of canonical Wnt pathway in RA. Combination of miR-152 and DNMT1 may be a promising treatment strategy for RA patients in which SFRP4 is inactivated.