Rheumatoid arthritis and p53: how oxidative stress might alter the course of inflammatory diseases

Antioxidant Potential of Vespa affinis L., a Traditional Edible Insect Species of North East India

Introduction

Elevated oxidative stress plays an important role in the pathogenesis of health disorders, like arthritis. Traditionally, Vespa affinis L., a common edible insect among many tribes in North-East India, is believed to have a beneficial role in extenuating health disorders, such as arthritis. The present study investigated the molecular mechanism underlying medicinal benefit of the Aqueous Extract of Vespa affinis L. (AEVA) against oxidative stress pathophysiology.

Methods

The free radical scavenging activities of AEVA were examined against DPPH, hydroxyl, and superoxide radicals and the effect on the activities of antioxidant enzyme (GST and CAT) was determined using both recombinant proteins and human plasma. The antioxidant potential of AEVA was again investigated using THP-1 monocytes.

Results

AEVA possesses a significant free radical scavenging activity as evident from the DPPH, superoxide, and hydroxyl radical scavenging assay. Incubation of AEVA (2.5, 5, 7.5, and 10 μg/μL) with the recombinant antioxidant enzymes, rGST and rCAT significantly increased the enzyme activities compared to those observed in corresponding enzyme alone or AEVA itself. AEVA supplementation (5, 7.5, and 10 μg/μL) also stimulates the activities of GST and CAT when incubated with human plasma. A cell culture study also confirmed the beneficial role of AEVA (0.8 and 1.2 μg/μL) which enhances the activities of GST and CAT, and also reduces the intercellular ROS production in monocytes treated with or without H₂O₂ and the effects are at par with what is observed in N-acetyl cysteine-treated cells.

Conclusion

The antioxidant potential of the aqueous extract of Vespa affinis L. may mediate its therapeutic activities in oxidative stress-associated health disorders.

Abnormal PTPN11 enhancer methylation promotes rheumatoid arthritis fibroblast-like synoviocyte aggressiveness and joint inflammation

The PTPN11 gene, encoding the tyrosine phosphatase SHP-2, is overexpressed in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) compared with osteoarthritis (OA) FLS and promotes RA FLS invasiveness. Here, we explored the molecular basis for PTPN11 overexpression in RA FLS and the role of SHP-2 in RA pathogenesis. Using computational methods, we identified a putative enhancer in PTPN11 intron 1, which contained a glucocorticoid receptor- binding (GR-binding) motif. This region displayed enhancer function in RA FLS and contained 2 hypermethylation sites in RA compared with OA FLS. RA FLS stimulation with the glucocorticoid dexamethasone induced GR binding to the enhancer and PTPN11 expression. Glucocorticoid responsiveness of PTPN11 was significantly higher in RA FLS than OA FLS and required the differentially methylated CpGs for full enhancer function. SHP-2 expression was enriched in the RA synovial lining, and heterozygous Ptpn11 deletion in radioresistant or innate immune cells attenuated K/BxN serum transfer arthritis in mice. Treatment with SHP-2 inhibitor 11a-1 reduced RA FLS migration and responsiveness to TNF and IL-1β stimulation and reduced arthritis severity in mice. Our findings demonstrate how abnormal epigenetic regulation of a pathogenic gene determines FLS behavior and demonstrate that targeting SHP-2 or the SHP-2 pathway could be a therapeutic strategy for RA.

Antioxidant-guided isolation and mass spectrometric identification of the major polyphenols in barley (Hordeum vulgare) grain

In the present study, the relative contribution of individual/classes of polyphenols in barley, to its antioxidant properties, was evaluated. Flash chromatography was used to fractionate the total polyphenol extract of Irish barley cultivar 'Irina', and fractions with highest antioxidant properties were identified using total phenolic content and three in vitro antioxidant assays: DPPH, FRAP, and ORAC. Flavanols (catechin, procyanidin B, prodelphinidin B, procyanidin C) and a novel substituted flavanol (catechin dihexoside, C27H33O16(-), m/z 613.17), were identified as constituents of the fraction with highest antioxidant capacity. Upon identification of phenolics in the other active fractions, the order of most potent contributors to observed antioxidant capacity of barley extract were, flavanols>flavonols (quercetin)>hydroxycinnamic acids (ferulic, caffeic, coumaric acids). The most abundant polyphenol in the overall extract was ferulic acid (277.7μg/gdw barley), followed by procyanidin B (73.7μg/gdw barley).

Plasma and Synovial Fluid TrxR Levels are Correlated With Disease Risk and Severity in Patients With Rheumatoid Arthritis

This study was designed and performed to establish the relationship between plasma and synovial fluid (SF) levels of thioredoxin reductase (TrxR) and disease activity in Chinese patients with rheumatoid arthritis (RA).This study consisted of a total of 224 patients diagnosed with RA, 224 age and sex-matched healthy controls, and 156 patient controls. The disease activity of RA patients was calculated as diseases activity score that include 28-joint counts (DAS 28), which was divided into low-diseases activity (LDA) and high-diseases activity (HDA) groups.Increased plasma TrxR was detected in patients with RA than healthy controls (P < 0.0001). With an area under the curve (AUC) of 0.874, plasma TrxR showed a evidently greater discriminatory ability than C-reactive protein (CRP; AUC, 0.815), antistreptolysin-O (ASO; AUC, 0.631), rheumatoid factor (RF, AUC, 0.793), and erythrocyte sedimentation rate (ESR, AUC, 0.789) in diagnosing RA. RA patients with HDA had significantly elevated TrxR levels in plasma and SF than did those with LDA (P < 0.0001). With an AUC of 0.874, plasma TrxR levels as an indicator for screening of HDA showed a significantly greater discriminatory ability than CRP (AUC, 0.690), ASO (AUC, 0.597), RF (AUC, 0.657), and ESR (AUC, 0.603). Similarly, SF TrxR levels as an indicator for screening of HDA also showed a significantly greater discriminatory ability as compared with above biomarkers.TrxR levels in plasma and SF were positively correlated with the severity of RA. TrxR levels may therefore serve as a new biomarker in addition of the traditional biomarkers for assessing the risk and severity of RA. Further analysis of TrxR release machinery may give us a new understanding of pathogenesis of RA.

Epigenetic mechanisms and drug discovery in rheumatology

There is a growing understanding of the epigenetic mechanisms that regulate gene expression in healthy conditions and a realisation that dysregulation of these mechanisms is an underlying factor in many human diseases. We discuss studies demonstrating that small molecule inhibitors of epigenetic regulatory proteins can block pathogenic mechanisms associated with rheumatoid arthritis, focusing on the effects of these inhibitors on synovial fibroblasts-fibroblast-like synoviocytes.

Discovery of serum proteomic biomarkers for prediction of response to moxibustion treatment in rats with collagen-induced arthritis: an exploratory analysis

OBJECTIVE

To examine the possible impact of moxibustion on the serum proteome of the collagen-induced arthritis (CIA) rat model.

MATERIALS AND METHODS

Thirty-six male Sprague-Dawley rats were included in this experiment. The CIA animal model was prepared by injection of type II bovine collagen in Freund's adjuvant on the first and seventh day. The 36 rats were randomly divided into two groups: the untreated CIA group (control), and the CIA plus treatment with moxibustion (CIA+moxi) group. Moxibustion was administered daily at ST36 and BL23 for 7, 14 or 21 days (n=12 rats each). Arthritis score was used to assess the severity of arthritis. At the end of each 7 day treatment, blood samples from the control group and the CIA+moxi group were collected. After removal of high abundance proteins from serum samples, two-dimensional gel combined with matrix-assisted laser desorption ionisation time-of-flight MS/MS (MALDI-TOF-MS/MS) techniques were performed to examine serum protein expression patterns of the CIA rat model with and without moxibustion treatment. In addition, the relevant proteins were further analysed with the use of bioinformatics analysis.

RESULTS

Moxibustion significantly decreased arthritis severity in the rats in the CIA+moxi group, when compared with the rats in the CIA group 35 days after the first immunisation (p=0.001). Seventeen protein spots which changed >1.33 or <0.77 at p<0.05 using Bonferonni correction for multiple testing were found to be common to all three comparisons, and these proteins were used for classification of functions using the Gene Ontology method. Consequently, with the use of the Ingenuity Pathway Analysis, the top canonical pathways and a predicted proteomic network related to the moxibustion effect of CIA were established.

CONCLUSIONS

Using the proteomics technique, we have identified novel candidate proteins that may be involved in the mechanisms of action underlying the beneficial effects of moxibustion in rats with CIA. Our findings suggest that immune responses and metabolic processes may be involved in mediating the effects of moxibustion. Moreover, periodxiredoxin I (PRDX1) and inositol 1,4,5-triphosphate receptor (IP3R) may be potential targets.

JNK-dependent downregulation of FoxO1 is required to promote the survival of fibroblast-like synoviocytes in rheumatoid arthritis

BACKGROUND

Forkhead box O (FoxO) transcription factors integrate environmental signals to modulate cell proliferation and survival, and alterations in FoxO function have been reported in rheumatoid arthritis (RA).

OBJECTIVES

To examine the relationship between inflammation and FoxO expression in RA, and to analyse the mechanisms and biological consequences of FoxO regulation in RA fibroblast-like synoviocytes (FLS).

METHODS

RNA was isolated from RA patient and healthy donor (HD) peripheral blood and RA synovial tissue. Expression of FoxO1, FoxO3a and FoxO4 was measured by quantitative PCR. FoxO1 DNA binding, expression and mRNA stability in RA FLS were measured by ELISA-based assays, immunoblotting and quantitative PCR. FLS were transduced with adenovirus encoding constitutively active FoxO1 (FoxO1ADA) or transfected with small interfering RNA targeting FoxO1 to examine the effects on cell viability and gene expression.

RESULTS

FoxO1 mRNA levels were reduced in RA patient peripheral blood compared with HD blood, and RA synovial tissue FoxO1 expression correlated negatively with disease activity. RA FLS stimulation with interleukin 1β or tumour necrosis factor caused rapid downregulation of FoxO1. This effect was independent of protein kinase B (PKB), but dependent on c-Jun N-terminal kinase (JNK)-mediated acceleration of FoxO1 mRNA degradation. FoxO1ADA overexpression in RA FLS induced apoptosis associated with altered expression of genes regulating cell cycle and survival, including BIM, p27(Kip1) and Bcl-XL.

CONCLUSIONS

Our findings identify JNK-dependent modulation of mRNA stability as an important PKB-independent mechanism underlying FoxO1 regulation by cytokines, and suggest that reduced FoxO1 expression is required to promote FLS survival in RA.

Decoy receptor 3 regulates the expression of tryptophan hydroxylase 1 in rheumatoid synovial fibroblasts

Decoy receptor 3 (DcR3) is expressed in rheumatoid arthritis fibroblast‑like synoviocytes (RA‑FLS) and downregulates the expression of tryptophan hydroxylase 1 (TPH1), which is the rate‑limiting enzyme in serotonin synthesis. The aim of the present study was to determine the specificity of the effects of DcR3 on TPH1 in RA‑FLS, and therefore determine whether DcR3 had the potential to modulate the pathogenesis of RA. The present study also aimed to compare the effects of DcR3 and inflammatory cytokines on the expression of TPH1 in RA‑FLS and osteoarthritis (OA)‑FLS. Primary cultured RA‑ or OA‑FLS were incubated with 1.0 µg/ml DcR3‑Fc protein or 1.0 µg/ml control immunoglobulin G (IgG)1 for 12 h, or with 1.0 ng/ml tumor necrosis factor (TNF)α, 1.0 ng/ml interleukin (IL)‑1β or serum‑free Opti‑MEM only, for 24 h. The relative mRNA expression levels of TPH1 were subsequently quantified using reverse transcription‑polymerase chain reaction. The expression of serotonin in RA or OA synovial tissue was detected using immunohistochemistry. The mRNA expression of TPH1 was observed in both RA‑ and OA‑FLS and was significantly decreased following treatment with DcR3 in the RA‑FLS, however, not in the OA‑FLS. The mRNA expression of TPH1 was significantly decreased following treatment with TNFα or IL‑1β in both the RA‑ and OA‑FLS. The expression of serotonin in the multi‑layered lining synovial cells of RA and the outer layer lining synovial cells of OA was detected using immunohistochemistry. The present study is the first, to the best of our knowledge, to demonstrate that the expression of TPH1 in FLS is downregulated by inflammatory cytokines, and that DcR3 suppressed the expression of TPH1 in RA‑FLS in a disease‑specific manner. These results suggested that synovial serotonin may be involved in the pathogenesis of RA, and that TPH1 and DcR3 may be potential therapeutic targets for the treatment of RA.

Energy Metabolism Disorder as a Contributing Factor of Rheumatoid Arthritis: A Comparative Proteomic and Metabolomic Study

Objectives

To explore the pathogenesis of rheumatoid arthritis (RA), the different metabolites were screened in synovial fluid by metabolomics.

Methods

Synovial fluid from 25 RA patients and 10 normal subjects were analyzed by GC/TOF MS analysis so as to give a broad overview of synovial fluid metabolites. The metabolic profiles of RA patients and normal subjects were compared using multivariate statistical analysis. Different proteins were verified by qPCR and western blot. Different metabolites were verified by colorimetric assay kit in 25 inactive RA patients, 25 active RA patients and 20 normal subjects. The influence of hypoxia-inducible factor (HIF)-1α pathway on catabolism was detected by HIF-1α knockdown.

Results

A subset of 58 metabolites was identified, in which the concentrations of 7 metabolites related to energy metabolism were significantly different as shown by importance in the projection (VIP) (VIP≥1) and Student’s t-test (p<0.05). In the 7 metabolites, the concentration of glucose was decreased, and the concentration of lactic acid was increased in the synovial fluid of RA patients than normal subjects verified by colorimetric assay Kit. Receiver operator characteristic (ROC) analysis shows that the concentration of glucose and lactic acid in synovial fluid could be used as dependable biomarkers for the diagnosis of active RA, provided an AUC of 0.906 and 0.922. Sensitivity and specificity, which were determined by cut-off points, reached 84% and 96% in sensitivity and 95% and 85% in specificity, respectively. The verification of different proteins identified in our previous proteomic study shows that the enzymes of anaerobic catabolism were up-regulated (PFKP and LDHA), and the enzymes of aerobic oxidation and fatty acid oxidation were down-regulated (CS, DLST, PGD, ACSL4, ACADVL and HADHA) in RA patients. The expression of HIF-1α and the enzymes of aerobic oxidation and fatty acid oxidation were decreased and the enzymes of anaerobic catabolism were increased in FLS cells after HIF-1α knockdown.

Conclusion

It was found that enhanced anaerobic catabolism and reduced aerobic oxidation regulated by HIF pathway are newly recognized factors contributing to the progression of RA, and low glucose and high lactic acid concentration in synovial fluid may be the potential biomarker of RA.

New perspective on targeting the tumor suppressor p53 pathway in the tumor microenvironment to enhance the efficacy of immunotherapy

About 50% of human cancers harbor somatic mutations of the tumor suppressor p53 (p53 or Trp53) gene. Many of those mutations result in the inactivation of the p53 pathway and are often associated with the stabilization and accumulation of mutant p53 proteins. Therefore, increased p53 expression in tumors is frequently used as a surrogate marker for p53 mutation and inactivation. Moreover, this elevated p53 expression also makes it an ideal tumor associated antigen (TAA) for cancer vaccines. Recent advances in our understanding of p53 as a crucial transcription factor reveal that p53 is an important sensor of cellular stress under genotoxic, chemotoxic, pathological, and even normal physiological conditions. Experimental and clinical observations by our laboratory and others have demonstrated that p53 also participates in immune regulation as p53 dysfunction skews host immune responses towards pro-inflammation, which further promotes tumor progression. Furthermore, recent studies using a genetic approach revealed that p53-restoration or re-activation led to tumor regression and clearance, which were at least partially caused by the activation of innate antitumor immunity. Since many of the currently used cancer therapeutics, including radiotherapy and chemotherapy, disrupt tumor growth by inducing DNA damage via genotoxic or chemotoxic stress, which activates the p53 pathway in the tumor microenvironment, we postulate that some of those observed therapeutic benefits might also be partially mediated through their immune stimulatory effects. Here, we briefly review our current understanding of the potential cellular and molecular mechanisms by which p53 participates in immune regulation and, subsequently, extend our discussion to the immunostimulatory potential of existing and new approaches of targeting the p53-pathway to alter the immunological landscape of tumors for maximizing immunotherapy outcome.

Central pathways causing fatigue in neuro-inflammatory and autoimmune illnesses

BACKGROUND

The genesis of severe fatigue and disability in people following acute pathogen invasion involves the activation of Toll-like receptors followed by the upregulation of proinflammatory cytokines and the activation of microglia and astrocytes. Many patients suffering from neuroinflammatory and autoimmune diseases, such as multiple sclerosis, Parkinson's disease and systemic lupus erythematosus, also commonly suffer from severe disabling fatigue. Such patients also present with chronic peripheral immune activation and systemic inflammation in the guise of elevated proinflammtory cytokines, oxidative stress and activated Toll-like receptors. This is also true of many patients presenting with severe, apparently idiopathic, fatigue accompanied by profound levels of physical and cognitive disability often afforded the non-specific diagnosis of chronic fatigue syndrome.

DISCUSSION

Multiple lines of evidence demonstrate a positive association between the degree of peripheral immune activation, inflammation and oxidative stress, gray matter atrophy, glucose hypometabolism and cerebral hypoperfusion in illness, such as multiple sclerosis, Parkinson's disease and chronic fatigue syndrome. Most, if not all, of these abnormalities can be explained by a reduction in the numbers and function of astrocytes secondary to peripheral immune activation and inflammation. This is also true of the widespread mitochondrial dysfunction seen in otherwise normal tissue in neuroinflammatory, neurodegenerative and autoimmune diseases and in many patients with disabling, apparently idiopathic, fatigue. Given the strong association between peripheral immune activation and neuroinflammation with the genesis of fatigue the latter group of patients should be examined using FLAIR magnetic resonance imaging (MRI) and tested for the presence of peripheral immune activation.

SUMMARY

It is concluded that peripheral inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in many patients with neuroimmune and autoimmune diseases.This would also appear to be the case for many patients afforded a diagnosis of Chronic Fatigue Syndrome.

Macrophage-mediated response to hypoxia in disease

Hypoxia plays a critical role in the pathobiology of various inflamed, diseased tissues, including malignant tumors, atherosclerotic plaques, myocardial infarcts, the synovia of rheumatoid arthritic joints, healing wounds, and sites of bacterial infection. These areas of hypoxia form when the blood supply is occluded and/or the oxygen supply is unable to keep pace with cell growth and/or infiltration of inflammatory cells. Macrophages are ubiquitous in all tissues of the body and exhibit great plasticity, allowing them to perform divergent functions, including, among others, patrolling tissue, combating invading pathogens and tumor cells, orchestrating wound healing, and restoring homeostasis after an inflammatory response. The number of tissue macrophages increases markedly with the onset and progression of many pathological states, with many macrophages accumulating in avascular and necrotic areas, where they are exposed to hypoxia. Recent studies show that these highly versatile cells then respond rapidly to the hypoxia present by altering their expression of a wide array of genes. Here we review the evidence for hypoxia-driven macrophage inflammatory responses in various disease states, and how this influences disease progression and treatment.

Anti-inflammatory and antioxidant activities of Costus afer Ker Gawl. hexane leaf fraction in arthritic rat models

ETHNOPHARMACOLOGICAL RELEVANCE

Costus afer Ker Gawl is an indigenous tropical African medicinal plant used as therapy in the treatment of inflammatory ailments such as rheumatoid arthritis. This study was designed to evaluate the anti-inflammatory and antioxidant activities of the hexane fraction of C. afer leaves (CAHLF).

MATERIALS AND METHODS

The anti-inflammatory effect of varying doses of CAHLF on carrageenan, arachidonic acid, and formaldehyde induced arthritis in male albino rats׳ models were investigated in order to study the acute inflammatory phase. Complete Freund׳s Adjuvant (CFA)-induced arthritis model was used to study the chronic inflammatory phase. Two known anti-inflammatory drugs, Diclofenac sodium (non-steroidal anti-inflammatory drug [NSAID]) and prednisolone (glucocorticoid [steroidal drug]) were used as standards for comparison. Various biochemical indices viz. superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), reduced glutathione (GSH) and malondialdehyde (MDA), aspartate amino transferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), total bilirubin (TB), total protein (TP), globulin and albumin levels were assayed using spectrophotometric methods.

RESULTS

Control animals in which arthritis have been induced using carrageenan, arachidonic acid, formaldehyde or CFA showed significant increases (P<0.05) in paw edema when compared with normal animals. Treatment of the arthritis induced rats with CAHLF significantly (P<0.05) suppressed the edema. in vivo antioxidant study showed that CAHLF treated animals had a significantly (P<0.05) elevated GSH level, SOD, CAT and GST activities while MDA levels were significantly (P<0.05) reduced in the plasma, liver, kidney and brain. CAHLF treated rats had a significantly (P<0.05) reduced plasma AST, ALT and ALP. Plasma TP, globulin, TB levels were reduced while albumin levels were elevated in CAHLF treated animals.

CONCLUSIONS

CAHLF possesses substantial anti-inflammatory and antioxidant activities against inflammatory diseases especially arthritis. It could be considered as a choice candidate in pharmaceutical anti-inflammatory drug development.

Nigella sativa Pretreatment in Guinea Pigs Exposed to Cigarette Smoke Modulates In Vitro Tracheal Responsiveness

BACKGROUND

In previous studies, the bronchodilator and antitussive effects of Nigella sativa have been demonstrated on guinea pigs.

OBJECTIVES

In the present study, the effect of the hydroethanolic extract of N. sativa on tracheal responsiveness in guinea pigs exposed to cigarette smoke was examined.

MATERIALS AND METHODS

Three groups of guinea pig models of COPD were given drinking water alone (COPD group), drinking water containing vitamin C (COPD + VC group), and N. sativa (COPD + NS group). Tracheal responses to methacholine were measured as effective concentration causing 50% of maximum response (EC50 M) in control animals (group C) and three groups of guinea pigs with COPD (n = 7, for all groups). Tracheal responses to 0.1% ovalbumin in comparison to contraction obtained by 10 µM methacholine were also examined.

RESULTS

The tracheal responsiveness to both methacholine and ovalbumin in guinea pigs with COPD were significantly higher than those of controls (P < 0.001 for both cases). The tracheal responsiveness in the COPD + VC and the COPD + NS groups to both methacholine and ovalbumin were significantly decreased in comparison to the COPD group (P < 0.05 and P < 0.001, respectively).

CONCLUSIONS

These results showed the preventive effect of hydroethanolic extract of N. sativa on tracheal responsiveness of guinea pig model of COPD, which was as effective as vitamin C.

Stress, oxidative injury and disease

The living system on earth is largely using oxygen for burning metabolic fuel for energy. The toxicity of oxygen is largely due to the formation of free radicals in living systems. Stress is also responsible for the generation of free radicals. The evidence for the involvement of free radicals and oxidative injury in producing metabolic disturbance, maladjustment and many diseases has been accumulating since long. It is largely believed that the root cause of many chronic diseases is stress induced free radicals and resultant oxidative injury.

Molecular hydrogen: new antioxidant and anti-inflammatory therapy for rheumatoid arthritis and related diseases

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which the progressive destruction of joint causes morbidity. It is also associated with an increased risk of atherosclerosis, which can result in cardiovascular disease and mortality. The therapeutic goal is to control the systemic inflammation to obtain not only the remission of symptoms, but also improve general state of health. Although recent biologic immunosuppressive therapies targeting pro-inflammatory cytokines have spawned a paradigm shift regarding the prognosis of RA, these therapies possess inherent side effects. Also, early diagnosis of the disease remains confounded by uncertainty. While the mechanisms responsible for the onset of RA remain unclear, reactive oxygen species (ROS) play a significant role in the pathogenesis of RA. ROS play a central role both upstream and downstream of NF-κB and TNFα pathways, which are located at the center of the inflammatory response. Among the ROS, the hydroxyl radical is the most harmful, and molecular hydrogen (H2) is a selective scavenger for this species. Recently, it has been shown that H2 is useful when administered along with the conventional therapy in RA as it acts to reduce oxidative stress in the patients. Especially in the early stage, H2 showed significant therapeutic potential, which also seemed to assist diagnosis and treatment decisions of RA. The possible expectations regarding the potential benefits of H2 by reducing the oxidative stress, resulting from inflammatory factors, are raised and discussed here. They include prevention of RA and related atherosclerosis, as well as therapeutic validity for RA

Identification of clinical parameters associated with serum oxidative stress in patients with rheumatoid arthritis

OBJECTIVES

Reactive oxygen species (ROS) are considered to be involved in the pathobiology of rheumatoid arthritis (RA); however, their association with disease activity has not been elucidated. In this study, we measured reactive oxygen metabolites (ROM) in patients with RA using a new Free Radical Analytical System and determined clinical parameters associated with ROM.

METHODS

One hundred and fifty-two patients with RA and 80 patients with diabetes mellitus (DM) were included in this observational study. To measure ROM, the d-ROM test was performed on blood samples drawn from all subjects. The correlation between ROM and biomarkers, disease activity, doses of methotrexate (MTX), and prednisolone (PSL) were investigated.

RESULTS

There were significant, positive correlations between ROM and CRP, matrix metalloproteinase 3 (MMP3), Disease Activity Score 28-erythrocyte sedimentation rate (DAS28-ESR), Clinical Disease Activity Index (CDAI), and the Simplified Disease Activity Index (SDAI). Multiple regression analysis revealed that CRP and DAS28-ESR were correlated with ROM.

CONCLUSIONS

The serum level of ROM was associated with CRP and DAS28-ESR, suggesting that ROM, in conjunction with CRP and MMP3, may be able to be used as a new biological disease marker to evaluate the disease activity of RA.

MiR-146a regulates SOD2 expression in H2O2 stimulated PC12 cells

SOD2 (superoxide dismutase 2) is one of the endogenous antioxidant enzymes that protect against reactive oxygen species. While explorations of SOD2 expression regulation are mainly focused on transcriptional and post-translational activation, there are few reports about the post-transcriptional regulation of SOD2. MicroRNAs (miRNAs) are 21nt-25nt (nucleotide) small noncoding RNAs that have emerged as indispensable regulators of gene expression. Here we show that miR-146a, a widely expressed miRNA, is up-regulated by H2O2-induced stress. By sequence analysis we found a binding site for miR-146a in the sod2 mRNA 3'UTR, and a luciferase reporter assay confirmed that miR-146a can interact with this sod2 regulatory region. Our results further show that miR-146a could down-regulate the SOD2 protein expression, and antisense-miR-146a could reverse the decrease of both the SOD2 level and cell viability in H2O2 treated PC12 cells. In conclusion, here we have identified a novel function of miR-146a in the post-transcriptional regulation of SOD2 expression.

Regulation of DNA methylation in rheumatoid arthritis synoviocytes

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which fibroblast-like synoviocytes (FLS) exhibit an aggressive phenotype. Although the mechanisms responsible are not well defined, epigenetic determinants such as DNA methylation might contribute. DNA methyltransferases (DNMTs) are critical enzymes that establish and maintain DNA methylation. We evaluated whether proinflammatory cytokines might contribute to differential DNA methylation previously described in RA FLS through altered DNMT expression. FLS were obtained from RA and osteoarthritis (OA) synovium at the time of total joint replacement. Gene expression was determined by quantitative real-time PCR and protein expression by Western blot analysis. DNMT activity was measured with a functional assay, and global methylation was determined by an immunoassay that detects methylcytosine. Resting expression of DNMT1, -3a, and -3b mRNA were similar in RA and OA FLS. Western blot showed abundant DNMT1 and DNMT3a protein. Exposure to IL-1 decreased DNMT1 and DNMT3a mRNA expression in FLS. Dose responses demonstrated decreased DNMT expression at concentrations as low as 1 pg/ml of IL-1. DNMT mRNA levels decreased rapidly, with significant suppression after 2-8 h of IL-1 stimulation. IL-1 stimulation of OA FLS did not affect methylation of LINE1 sites but led to demethylation of a CHI3L1 locus that is hypomethylated in RA FLS. Chronic IL-1 stimulation also mimicked the effect of a DNMT inhibitor on FLS gene expression. Exposure to proinflammatory mediators reversibly alters DNA methylation in FLS by decreasing DNMT expression and function. These data suggest that IL-1 can potentially imprint cells in chronic inflammatory diseases.

A microfluidic systems biology approach for live single-cell mitochondrial ROS imaging

Most current studies of reactive oxygen species (ROS) production report globally averaged measurements within the cell; however, ROS can be produced in distinct subcellular locations and have local effects in their immediate vicinity. A microfluidic platform for high-throughput single-cell imaging allows mitochondrial ROS production to be monitored as varying in both space and time. Using this systems biology approach, single-cell variability can be viewed within a population. We discuss single-cell monitoring of contributors to mitochondrial redox state-mitochondrial hydrogen peroxide or superoxide-through the use of a small molecule probe or targeted fluorescent reporter protein. Jurkat T lymphoma cells were stimulated with antimycin A and imaged in an arrayed microfluidic device over time. Differences in single-cell responses were observed as a function of both inhibitor concentration and type of ROS measurement used.

DNA methylome signature in rheumatoid arthritis

OBJECTIVES

Epigenetics can influence disease susceptibility and severity. While DNA methylation of individual genes has been explored in autoimmunity, no unbiased systematic analyses have been reported. Therefore, a genome-wide evaluation of DNA methylation loci in fibroblast-like synoviocytes (FLS) isolated from the site of disease in rheumatoid arthritis (RA) was performed.

METHODS

Genomic DNA was isolated from six RA and five osteoarthritis (OA) FLS lines and evaluated using the Illumina HumanMethylation450 chip. Cluster analysis of data was performed and corrected using Benjamini-Hochberg adjustment for multiple comparisons. Methylation was confirmed by pyrosequencing and gene expression was determined by qPCR. Pathway analysis was performed using the Kyoto Encyclopedia of Genes and Genomes.

RESULTS

RA and control FLS segregated based on DNA methylation, with 1859 differentially methylated loci. Hypomethylated loci were identified in key genes relevant to RA, such as CHI3L1, CASP1, STAT3, MAP3K5, MEFV and WISP3. Hypermethylation was also observed, including TGFBR2 and FOXO1. Hypomethylation of individual genes was associated with increased gene expression. Grouped analysis identified 207 hypermethylated or hypomethylated genes with multiple differentially methylated loci, including COL1A1, MEFV and TNF. Hypomethylation was increased in multiple pathways related to cell migration, including focal adhesion, cell adhesion, transendothelial migration and extracellular matrix interactions. Confirmatory studies with OA and normal FLS also demonstrated segregation of RA from control FLS based on methylation pattern.

CONCLUSIONS

Differentially methylated genes could alter FLS gene expression and contribute to the pathogenesis of RA. DNA methylation of critical genes suggests that RA FLS are imprinted and implicate epigenetic contributions to inflammatory arthritis.

The resolution of inflammation

In 2012, Nature Reviews Immunology organized a conference that brought together scientists and clinicians from both academia and industry to discuss one of the most pressing questions in medicine--how do we turn off rampant, undesirable inflammation? There is a growing appreciation that, similarly to the initiation of inflammation, the resolution of inflammation is an intricate and active process. Can we therefore harness the mediators involved in resolution responses to treat patients with chronic inflammatory or autoimmune diseases? Here, we ask five of the speakers from the conference to share their thoughts on this emerging field.

Duality of fibroblast-like synoviocytes in RA: passive responders and imprinted aggressors

Rheumatoid arthritis (RA) is characterized by hyperplastic synovial pannus tissue, which mediates destruction of cartilage and bone. Fibroblast-like synoviocytes (FLS) are a key component of this invasive synovium and have a major role in the initiation and perpetuation of destructive joint inflammation. The pathogenic potential of FLS in RA stems from their ability to express immunomodulating cytokines and mediators as well as a wide array of adhesion molecule and matrix-modelling enzymes. FLS can be viewed as 'passive responders' to the immunoreactive process in RA, their activated phenotype reflecting the proinflammatory milieu. However, FLS from patients with RA also display unique aggressive features that are autonomous and vertically transmitted, and these cells can behave as primary promoters of inflammation. The molecular bases of this 'imprinted aggressor' phenotype are being clarified through genetic and epigenetic studies. The dual behaviour of FLS in RA suggests that FLS-directed therapies could become a complementary approach to immune-directed therapies in this disease. Pathophysiological characteristics of FLS in RA, as well as progress in targeting these cells, are reviewed in this manuscript.

Oxidative stress and calcium-phosphorus levels in Rheumatoid arthritis

Generation of reactive oxygen species is an important factor in the development and maintenance of rheumatoid arthritis (RA) in humans. This study was undertaken to investigate interplay among oxidants, antioxidants and pathogenesis of Rheumatoid arthritis. Serum levels of lipid peroxides, nitric oxide, vitamin E and ratio of calcium/phosphorus in RA patients were determined and compared with normal healthy controls. Significant increases in lipid peroxides (p<0.001) and nitric oxide (p<0.001) levels were found in patients presenting with RA as compared to controls. Whereas significant decrease in vitamin E (P<0.001) and calcium/phosphorus ratio (p<0.001) were found in Rheumatoid arthritis patients as compared to controls. Positive correlation was found between lipid peroxides and nitric oxide as well as between vitamin E and calcium. While lipid peroxides and nitric oxide were correlated negatively with vitamin E. whereas negative correlation was observed between MDA and Calcium/Phosphorus ratio in patients with rheumatoid arthritis. Our findings suggest that there is a close association between bone loss and oxidative threat in patients presenting with Rheumatoid arthritis.

PBEF/NAMPT/visfatin: a promising drug target for treating rheumatoid arthritis?

NAMPT, also known as pre-B-cell colony-enhancing factor and visfatin, has been proposed to be involved in preventing apoptosis in cancer cells and, as such, has received a great deal of attention in recent years and stimulated the development to specific inhibitors for treating cancer. The role of NAMPT inhibitors as potential therapeutic agents for other diseases has not been studied extensively. Here, we describe their applicability for treating rheumatoid arthritis. We summarize current knowledge of NAMPT expression in healthy and diseased tissues, thereafter, we focus on pathological mechanisms relevant to rheumatoid arthritis that involve the NAMPT pathway and review the current status of NAMPT inhibitors being evaluated in clinical trials.

Characteristics of synovial inflammation in early arthritis analysed by pixel-by-pixel time-intensity curve shape analysis

OBJECTIVE

Dynamic contrast-enhanced (DCE-MRI) time-intensity curve (TIC) shape analysis has previously been used in oncology, where fast initial enhancement and early washout are associated with malignancy. As RA synovium has some tumour-like features, we investigated DCE-MRI TIC shape expression in early arthritis in relationship to diagnosis.

METHODS

Twenty-eight DMARD-naïve, early arthritis patients (<1 year) with inflammation of at least one knee joint were included. At baseline DCE-MRI of the inflamed knee joint was performed, and the TIC shape type expression, maximal enhancement, maximum slope of increase and total volume of enhancing pixels were calculated. In addition, disease activity parameters were determined. At 2 years of follow-up, patients were classified as RA or non-RA according to established classification criteria.

RESULTS

Type 4 TIC shape, characterized by fast initial enhancement followed by a quick washout phase, was significantly higher in patients fulfilling classification criteria for RA after 2 years of follow-up compared with non-RA patients (15.6 and 7.9%, respectively, P = 0.02). All other DCE-MRI parameters showed no differences between the groups, highlighting the specificity of this observation.

CONCLUSION

A high expression of aggressive DCE-MRI TIC shape Type 4 is associated with RA. Our results are consistent with the view that increased vascularity plays a key role in the pathogenesis of RA. This study underlines the rationale for further studies investigating the prospect of DCE-MRI TIC shape analysis as a diagnostic tool in early arthritis and the relationship with development of destructive disease.

Hypoxia induces mitochondrial mutagenesis and dysfunction in inflammatory arthritis

OBJECTIVE

To assess the levels and spectrum of mitochondrial DNA (mtDNA) point mutations in synovial tissue from patients with inflammatory arthritis in relation to in vivo hypoxia and oxidative stress levels.

METHODS

Random Mutation Capture assay was used to quantitatively evaluate alterations of the synovial mitochondrial genome. In vivo tissue oxygen levels (tPO(2)) were measured at arthroscopy using a Licox probe. Synovial expression of lipid peroxidation (4-hydroxynonenal [4-HNE]) and mitochondrial cytochrome c oxidase subunit II (CytcO II) deficiency were assessed by immunohistochemistry. In vitro levels of mtDNA point mutations, reactive oxygen species (ROS), mitochondrial membrane potential, and markers of oxidative DNA damage (8-oxo-7,8-dihydro-2'-deoxyguanine [8-oxodG]) and lipid peroxidation (4-HNE) were determined in human synoviocytes under normoxia and hypoxia (1%) in the presence or absence of superoxide dismutase (SOD) or N-acetylcysteine (NAC) or a hydroxylase inhibitor (dimethyloxalylglycine [DMOG]). Patients were categorized according to their in vivo tPO(2) level (<20 mm Hg or >20 mm Hg), and mtDNA point mutations, immunochemistry features, and stress markers were compared between groups.

RESULTS

The median tPO(2) level in synovial tissue indicated significant hypoxia (25.47 mm Hg). Higher frequency of mtDNA mutations was associated with reduced in vivo oxygen tension (P = 0.05) and with higher synovial 4-HNE cytoplasmic expression (P = 0.04). Synovial expression of CytcO II correlated with in vivo tPO(2) levels (P = 0.03), and levels were lower in patients with tPO(2) <20 mm Hg (P < 0.05). In vitro levels of mtDNA mutations, ROS, mitochondrial membrane potential, 8-oxo-dG, and 4-HNE were higher in synoviocytes exposed to 1% hypoxia (P < 0.05); all of these increased levels were rescued by SOD and DMOG and, with the exception of ROS, by NAC.

CONCLUSION

These findings demonstrate that hypoxia-induced mitochondrial dysfunction drives mitochondrial genome mutagenesis, and antioxidants significantly rescue these events.

Serum level of oxidative stress marker is dramatically low in patients with rheumatoid arthritis treated with tocilizumab

Regarding the pathobiology of rheumatoid arthritis, oxidative stress induced by reactive oxygen species is an important mechanism that underlies destructive and proliferative synovitis. Abundant amounts of reactive oxygen species have been detected in the synovial fluid of inflamed rheumatoid joints. It is reported that drugs that block tumor necrosis factor-α reduce the oxidative stress marker levels in patients with rheumatoid arthritis. In this study, we measured reactive oxygen species using a free radical analytical system in patients with rheumatoid arthritis treated with disease-modifying antirheumatic drugs, tumor necrosis factor-α-blocking drugs (infliximab, etanercept), and an interleukin-6-blocking drug (tocilizumab). The serum level of oxidative stress was drastically low in patients with rheumatoid arthritis treated with tocilizumab, suggesting that interleukin-6 blocking therapy reduces not only joint damage, but also vascular degeneration in patients with rheumatoid arthritis. We believe that such a drastic effect would reduce the incidence of cardiovascular events and mortality in patients with rheumatoid arthritis.

Successful tumour necrosis factor (TNF) blocking therapy suppresses oxidative stress and hypoxia-induced mitochondrial mutagenesis in inflammatory arthritis

Introduction

To examine the effects of tumour necrosis factor (TNF) blocking therapy on the levels of early mitochondrial genome alterations and oxidative stress.

Methods

Eighteen inflammatory arthritis patients underwent synovial tissue oxygen (tpO₂) measurements and clinical assessment of disease activity (DAS28-CRP) at baseline (T0) and three months (T3) after starting biologic therapy. Synovial tissue lipid peroxidation (4-HNE), T and B cell specific markers and synovial vascular endothelial growth factor (VEGF) were quantified by immunohistochemistry. Synovial levels of random mitochondrial DNA (mtDNA) mutations were assessed using Random Mutation Capture (RMC) assay.

Results

4-HNE levels pre/post anti TNF-α therapy were inversely correlated with in vivo tpO₂ (P < 0.008; r = -0.60). Biologic therapy responders showed a significantly reduced 4-HNE expression (P < 0.05). High 4-HNE expression correlated with high DAS28-CRP (P = 0.02; r = 0.53), tender joint count for 28 joints (TJC-28) (P = 0.03; r = 0.49), swollen joint count for 28 joints (SJC-28) (P = 0.03; r = 0.50) and visual analogue scale (VAS) (P = 0.04; r = 0.48). Strong positive association was found between the number of 4-HNE positive cells and CD4+ cells (P = 0.04; r = 0.60), CD8+ cells (P = 0.001; r = 0.70), CD20+ cells (P = 0.04; r = 0.68), CD68+ cells (P = 0.04; r = 0.47) and synovial VEGF expression (P = 0.01; r = 063). In patients whose in vivo tpO₂ levels improved post treatment, significant reduction in mtDNA mutations and DAS28-CRP was observed (P < 0.05). In contrast in those patients whose tpO₂ levels remained the same or reduced at T3, no significant changes for mtDNA mutations and DAS28-CRP were found.

Conclusions

High levels of synovial oxidative stress and mitochondrial mutation burden are strongly associated with low in vivo oxygen tension and synovial inflammation. Furthermore these significant mitochondrial genome alterations are rescued following successful anti TNF-α treatment.

Increase in CpG DNA-induced inflammatory responses by DNA oxidation in macrophages and mice

Unmethylated CpG dinucleotide (CpG motif) is involved in the exacerbation of DNA-associated autoimmune diseases. We investigated the effect of DNA containing 8-hydroxydeoxyguanosine (oxo-dG), a representative DNA biomarker for oxidative stress in the diseases, on CpG motif-dependent inflammatory responses. ODN1668 and ODN1720 were selected as CpG-DNA and non-CpG DNA, respectively. Deoxyguanosine in the CpG motif (G9) or outside the motif (G15) of ODN1668 was substituted with oxo-dG to obtain oxo(G9)-1668 and oxo(G15)-1668, respectively. Oxo(G15)-1668 induced a significantly higher amount of tumor necrosis factor (TNF)-α from RAW264.7 macrophage-like cells than ODN1668, whereas oxo(G9)-1668, oxo(G8)-1720, or oxo(G15)-1720 hardly did. CpG DNA-induced TNF-α production was significantly increased by addition of oxo(G8)-1720 or oxo(G15)-1720, but not of ODN1720. This oxo-dG-containing DNA-induced increase in TNF-α production was also observed in primary cultured macrophages isolated from wild-type mice, but not observed in those from Toll-like receptor (TLR)-9 knockout mice. In addition, TNF-α production by ligands for TLR3, TLR4, or TLR7 was not affected by oxo-dG-containing DNA. Then, the footpad swelling induced by subcutaneous injection of ODN1668 into mice was increased by coinjection with oxo(G8)-1720, but not with ODN1720. These results indicate that oxo-dG-containing DNA increases the CpG motif-dependent inflammatory responses, which would exacerbate DNA-related autoimmune diseases.

Trp53 negatively regulates autoimmunity via the STAT3-Th17 axis

Emerging evidence suggests that the tumor suppressor p53 is also a crucial regulator for many physiological processes. Previous observations indicate that p53 suppresses inflammation by inhibiting inflammatory antigen-presenting cells. To investigate the potential role of p53 in autoimmune effector T cells, we generated p53(null)CD45.1 mice by crossing p53(null)CD45.2 and CD45.1 mice. We demonstrate that p53(null)CD45.1 mice spontaneously developed autoimmunity, with a significant increase in IL-17-producing Th17 effectors in their lymph nodes (4.7 ± 1.0%) compared to the age-matched counterparts (1.9 ± 0.8% for p53(null)CD45.2, 1.1 ± 0.2% for CD45.1, and 0.5 ± 0.1% for CD45.2 mice). Likewise, p53(null)CD45.1 mice possess highly elevated serum levels of inflammatory cytokines IL-17 and IL-6. This enhanced Th17 response results largely from an increased sensitivity of p53(null)CD45.1 T cells to IL-6-induced STAT3 phosphorylation. Administration of STAT3 inhibitor S31-201 (IC50 of 38.0 ± 7.2 μM for IL-6-induced STAT3 phosphorylation), but not PBS control, to p53(null)CD45.1 mice suppressed Th17 effectors and alleviated autoimmune pathology. This is the first report revealing that p53 activity in T cells suppresses autoimmunity by controlling Th17 effectors. This study suggests that p53 serves as a guardian of immunological functions and that the p53-STAT3-Th17 axis might be a therapeutic target for autoimmunity.

A short overview of vitamin C and selected cells of the immune system

Vitamin C (ascorbic acid) is an essential water-soluble nutrient that primarily exerts its effect on a host defense mechanisms and immune homeostasis and is the most important physiological antioxidant. Stable intake of vitamin C is essential for life in humans because the body does not synthesize it. Even the numerous studies have demonstrated that vitamin C supplementation stimulates the immune system, prevents DNA damage and significantly decreases the risk of a wide range of pathologies; the potential protective mechanisms are still largely unknown. This review summarizes the recently known facts about the role of vitamin C on the selected cells of the immune system and potential molecular mechanisms involved. Further, in this review, many new data about the positive effects of vitamin C on the immune system, potential toxicological effects, vitamin C supplementation in disease development, as well as some proposed mechanisms of vitamin C activity, are discussed.

Possible involvement of peptidylprolyl isomerase Pin1 in rheumatoid arthritis

The peptidylprolyl isomerase Pin1 is over-expressed in some human diseases including malignancies and chronic inflammatory diseases, this suggests that it contributes to the constitutive activation of certain intracellular signaling pathways that promote cell proliferation and cell invasion. Here, we investigate the possible role of Pin1 in rheumatoid arthritis (RA). Pin1 expression was immunohistochemically analyzed in synovial tissue (ST) obtained from patients with RA and osteoarthritis (OA). To investigate the correlation between Pin1 and motility and proliferation of synovial cells, Pin1 localization was immunohistochemically compared with matrix metalloproteinase (MMP)-1, MMP-3, and proliferating cell nuclear antigen (PCNA). Double immunofluorescent staining for Pin1 and p65 was performed to determine whether Pin1 is involved in nuclear factor κB (NF-κB) activation in RA-ST. Results showed Pin1 expression was significantly higher in RA-ST than in OA-ST. The expression of MMP-1, MMP-3, and PCNA was also significantly elevated in RA-ST. Double immunofluorescent staining revealed colocalization of Pin1 and p65 in the nuclei of RA-ST. These results suggest that Pin1 may be involved in the pathogenesis of RA binding with p65 to activate the proteins MMP-1, MMP-3, and PCNA. Therefore, Pin1 may play a pivotal role in the pathogenesis of RA.

Silencing the expression of Ras family GTPase homologues decreases inflammation and joint destruction in experimental arthritis

Changes in the expression and activation status of Ras proteins are thought to contribute to the pathological phenotype of stromal fibroblast-like synoviocytes (FLS) in rheumatoid arthritis, a prototypical immune-mediated inflammatory disease. Broad inhibition of Ras and related proteins has shown protective effects in animal models of arthritis, but each of the Ras family homologues (ie, H-, K-, and N-Ras) makes distinct contributions to cellular activation. We examined the expression of each Ras protein in synovial tissue and FLS obtained from patients with rheumatoid arthritis and other forms of inflammatory arthritis. Each Ras protein was expressed in synovial tissue and cultured FLS. Each homolog was also activated following FLS stimulation with tumor necrosis factor-α or interleukin (IL)-1β. Constitutively active mutants of each Ras protein enhanced IL-1β-induced FLS matrix metalloproteinase-3 production, while only active H-Ras enhanced IL-8 production. Gene silencing demonstrated that each Ras protein contributed to IL-1β-dependent IL-6 production, while H-Ras and N-Ras supported IL-1β-dependent matrix metalloproteinase-3 and IL-8 production, respectively. The overlap in contributions of Ras homologues to FLS activation suggests that broad targeting of Ras GTPases in vivo suppresses global inflammation and joint destruction in arthritis. Consistent with this, simultaneous silencing of H-Ras, K-Ras, and N-Ras expression significantly reduces inflammation and joint destruction in murine collagen-induced arthritis, while specific targeting of N-Ras alone is less effective in providing clinical benefits.

MDM4 overexpression contributes to synoviocyte proliferation in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease with features of inflammatory cell infiltration, synovial cell invasive proliferation, and ultimately, irreversible joint destruction. It has been reported that the p53 pathway is involved in RA pathogenesis. MDM4/MDMX is a major negative regulator of p53. To determine whether MDM4 contributes to RA pathogenesis, MDM4 mRNA and protein expression were assessed in fibroblast-like synoviocytes (FLS) by real-time PCR, western blotting, and in synovial tissues by immunohistochemistry. Furthermore, MDM4 was knocked down and overexpressed by lentivirus-mediated expression, and the proliferative capacity of FLS was determined by MTS assay. We found that cultured FLS from RA and osteoarthritis (OA) patients exhibited higher levels of MDM4 mRNA and protein expression than those from trauma controls. MDM4 protein was highly expressed in the synovial lining and sublining cells from both types of arthritis. Finally, MDM4 knockdown inhibited the proliferation of RA FLS by enhancing functional p53 levels while MDM4 overexpression promoted the growth of RA FLS by inhibiting p53 effects. Taken together, our results suggest that the abundant expression of MDM4 in FLS may contribute to the hyperplasia phenotype of RA synovial tissues.

Slug suppression induces apoptosis via Puma transactivation in rheumatoid arthritis fibroblast-like synoviocytes treated with hydrogen peroxide

Inadequate apoptosis contributes to synovial hyperplasia in rheumatoid arthritis (RA). Recent study shows that low expression of Puma might be partially responsible for the decreased apoptosis of fibroblast-like synoviocytes (FLS). Slug, a highly conserved zinc finger transcriptional repressor, is known to antagonize apoptosis of hematopoietic progenitor cells by repressing Puma transactivation. In this study, we examined the expression and function of Slug in RA FLS. Slug mRNA expression was measured in the synovial tissue (ST) and FLS obtained from RA and osteoarthritis patients. Slug and Puma mRNA expression in FLS by apoptotic stimuli were measured by real-time PCR analysis. FLS were transfected with control siRNA or Slug siRNA. Apoptosis was quantified by trypan blue exclusion, DNA fragmentation and caspase-3 assay. RA ST expressed higher level of Slug mRNA compared with osteoarthritis ST. Slug was significantly induced by hydrogen peroxide (H2O2) but not by exogenous p53 in RA FLS. Puma induction by H2O2 stimulation was significantly higher in Slug siRNA-transfected FLS compared with control siRNA-transfected FLS. After H2O2 stimulation, viable cell number was significantly lower in Slug siRNA-transfected FLS compared with control siRNA-transfected FLS. Apoptosis enhancing effect of Slug siRNA was further confirmed by ELISA that detects cytoplasmic histone-associated DNA fragments and caspase-3 assay. These data demonstrate that Slug is overexpressed in RA ST and that suppression of Slug gene facilitates apoptosis of FLS by increasing Puma transactivation. Slug may therefore represent a potential therapeutic target in RA.