Posttranscriptional regulation of collagenase-1 gene expression in synoviocytes by adenosine receptor stimulation

Targeting fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-like synoviocytes (FLS) are mesenchymal-derived cells that play an important role in the physiology of the synovium by producing certain components of the synovial fluid and articular cartilage. In rheumatoid arthritis (RA), however, fibroblasts become a key driver of synovial inflammation and joint damage. Because of this, there has been recent interest in FLS as a therapeutic target in RA to avoid side effects such as systemic immune suppression associated with many existing RA treatments. In this review, we describe how approved treatments for RA affect FLS signaling and function and discuss the effects of investigational FLS-targeted drugs for RA.

The implication of adenosine receptor expression in prediction of methotrexate clinical response in Egyptian rheumatoid arthritis patients

Background

Adenosine signaling is now an accepted explanation for the therapeutic mechanism of Methotrexate (MTX) in rheumatoid arthritis (RA). Adenosine receptors categorized into four subclasses: adenosine A1 receptor (ADORA1), adenosine 2a receptor (ADORA2a), adenosine 2b receptor (ADORA2B), and adenosine 3 receptor (ADORA3). Our aim is to check the mRNA expression of two adenosine receptors; ADORA2a and ADORA3 in whole blood cell of RA patients and its relation in prediction of MTX clinical response in Egyptian patients.

Results

There was significant correlation between both ADORA2a and ADORA3 gene expression in RA patients as compared with healthy controls. The expression of ADORA2a and ADORA3 was increased in good and moderate response groups compared to no response group. There was significant correlation between both genes in mRNA expression before and after MTX treatment. Matrix metalloproteinase-3 (MMP3) concentration was significantly decreased after treatment in good and moderate response groups in comparison to non-responder group.

Conclusion

The inflammatory and clinical responses in RA patients which is demonstrated by DAS28 and suppression of MMP3 were regulated by ADORA2a and ADORA3. Their level of expression can predict MTX response and their agonists may offer a novel and effective therapeutic option for RA patients.

Ras-guanine-nucleotide-releasing factors 1 and 2 interact with PLCγ at focal adhesions to enable IL-1-induced Ca(2+) signalling, ERK activation and MMP-3 expression

IL (interleukin)-1 signalling in anchorage-dependent cells involves focal-adhesion-restricted and Ca2+-dependent Ras and ERK (extracellular-signal-regulated kinase) activation that leads to MMP (matrix metalloproteinase) release and extracellular matrix remodelling. Ras activity is regulated, in part, by the Ca2+-responsive Ras GRFs (guanine-nucleotide-releasing factors) 1 and 2, but the mechanisms that link and localize IL-1-induced Ca2+ signalling to focal adhesions are not defined. In the present study we characterized the role of Ras-GRF1/2 in Ca2+ and Ras→ERK signalling after IL-1 stimulation. By immunoprecipitation we found that Ras-GRF1/2 associates with PLCγ1 (phospholipase Cγ1). This association enables PLCγ1 recruitment to focal adhesions and is required for Ras signalling, ERK activation and MMP-3 release downstream of IL-1 stimulation. Depletion of PLCγ1 by siRNA (small interfering RNA) abolished IL-1-induced Ras activation and MMP-3 expression. Buffering of cytosolic Ca2+ reduced Ras interactions with Ras-GRF1/2 and blocked MMP-3 release. The results of the present study show that, in addition to their functions as Ras-exchange factors, Ras-GRF1 and -GRF2 may act as adaptors that bind PLCγ1 and restrict Ca2+ signalling to the vicinity of focal adhesions, indicating a new role for these GRFs that is required for IL-1 induction of the Ras→ERK pathway and MMP-3 expression.

IL-1β enhances cell adhesion to degraded fibronectin

IL-1β is a prominent proinflammatory cytokine that mediates degradation of extracellular matrix proteins through increased expression of matrix metalloproteinases, which involves a signaling pathway in adherent cells that is restricted by focal adhesions. Currently, the mechanism by which IL-1β affects cell adhesion to matrix proteins is not defined, and it is not known whether degraded matrix proteins affect IL-1β signaling. We examined adhesion-related IL-1β signaling in fibroblasts attaching to native or MMP3-degraded fibronectin. IL-1β increased cell attachment, resistance to shear force and the numbers of focal adhesions containing activated β(1) integrins. IL-1β-enhanced attachment required FAK, kindlins 1/2, and talin. MMP3-degraded fibronectin-inhibited IL-1β-enhanced cell adhesion and promoted spontaneous ERK activation that was independent of IL-1β treatment. We conclude that IL-1β enhances the adhesion of anchorage-dependent cells to MMP3-degraded fibronectin, which, in turn, is associated with deregulated cellular responses to IL-1β. These data point to a novel role of IL-1β as a proadhesive signaling molecule in inflammation that employs kindlins and talin to regulate adhesion.

A2A and A3 adenosine receptor expression in rheumatoid arthritis: upregulation, inverse correlation with disease activity score and suppression of inflammatory cytokine and metalloproteinase release

INTRODUCTION

The reduction of the inflammatory status represents one of the most important targets in rheumatoid arthritis (RA). A central role of A2A and A3 adenosine receptors (ARs) in mechanisms of inflammation has been reported in different pathologies. The primary aim of this study was to investigate the A2A and A3ARs and their involvement in RA progression measured by Disease Activity Score in 28 or 44 joints (DAS28 or DAS).

METHODS

ARs were analyzed by saturation binding assays, mRNA and Western blotting analysis in lymphocytes from early and established RA patients. The effect of A2A and A3AR agonists in nuclear factor kB (NF-kB) pathway was evaluated. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) release was carried out by A2A and A3AR activation. AR pharmacological regulation in matrix metalloproteinase-1 (MMP-1) and metalloproteinase-3 (MMP-3) release was also studied.

RESULTS

In lymphocytes obtained from RA patients, A2A and A3ARs were up-regulated if compared with healthy controls. A2A and A3AR activation inhibited the NF-kB pathway and diminished inflammatory cytokines such as TNF-α, IL-1β and IL-6. A2A and A3AR agonists mediated a reduction of MMP-1 and MMP-3 release. A2A and A3AR density inversely correlated with DAS28 and DAS suggesting a direct role of the endogenous activation of these receptors in the control of RA joint inflammation.

CONCLUSIONS

Taken together these data demonstrate that the inflammatory and clinical responses in RA are regulated by A2A and A3ARs and support the use of A2A and/or A3AR agonists as novel and effective pharmacological treatment in RA patients.

Protein-tyrosine phosphatase-alpha and Src functionally link focal adhesions to the endoplasmic reticulum to mediate interleukin-1-induced Ca2+ signaling

Calcium (Ca2+) signaling by the pro-inflammatory cytokine interleukin-1 (IL-1) is dependent on focal adhesions, which contain diverse structural and signaling proteins including protein phosphatases. We examined here the role of protein-tyrosine phosphatase (PTP) alpha in regulating IL-1-induced Ca2+ signaling in fibroblasts. IL-1 promoted recruitment of PTPalpha to focal adhesions and endoplasmic reticulum (ER) fractions, as well as tyrosine phosphorylation of the ER Ca2+ release channel IP3R. In response to IL-1, catalytically active PTPalpha was required for Ca2+ release from the ER, Src-dependent phosphorylation of IP3R1 and accumulation of IP3R1 in focal adhesions. In pulldown assays and immunoprecipitations PTPalpha was required for the association of PTPalpha with IP3R1 and c-Src, and this association was increased by IL-1. Collectively, these data indicate that PTPalpha acts as an adaptor to mediate functional links between focal adhesions and the ER that enable IL-1-induced Ca2+ signaling.

Characterization of adenosine receptors in bovine chondrocytes and fibroblast-like synoviocytes exposed to low frequency low energy pulsed electromagnetic fields

OBJECTIVE

The present study describes the presence and binding parameters of the A1, A2A, A2B and A3 adenosine receptors in bovine chondrocytes and fibroblast-like synoviocytes. The effect of low frequency low energy pulsed electromagnetic fields (PEMFs) on the adenosine receptor affinity and density was studied.

METHODS

Saturation, competition binding experiments and Western blotting assays in the absence and in the presence of PEMFs on the adenosine receptors in bovine chondrocytes or fibroblast-like synoviocytes were performed. Thermodynamic analysis of the A2A or A3 binding was studied to investigate the forces driving drug-receptor coupling. In the adenylyl cyclase and proliferation assays the potency of typical high-affinity A2A or A3 agonists in the absence and in the presence of PEMFs was evaluated.

RESULTS

Bovine chondrocytes and fibroblast-like synoviocytes expressed all adenosine receptors. PEMFs evoked an up-regulation of A2A and A3 receptors and thermodynamic parameters indicate that adenosine binding is enthalpy and entropy driven. In PEMF-treated cells the potency of typical A2A or A3 agonists on cyclic AMP assays was significantly increased when compared with the untreated cells. PEMFs potentiated the effect of A2A or A3 agonists on cell proliferation in both cell types.

CONCLUSIONS

PEMFs mediate an up-regulation of A2A and A3 receptors related to an increase of their functional activities in bovine chondrocytes and fibroblast-like synoviocytes. No differences are present in adenosine affinity and in the drug-receptor interactions. Our data could be used as a trigger to future studies addressed to PEMFs and adenosine therapeutic intervention in inflammatory joint diseases.

Phosphorylation of SHP-2 Regulates Interactions between the Endoplasmic Reticulum and Focal Adhesions to Restrict Interleukin-1-induced Ca2+ Signaling

Interleukin-1 (IL-1)-induced Ca2+ signaling in fibroblasts is constrained by focal adhesions. This process involves the proteintyrosine phosphatase SHP-2, which is critical for IL-1-induced phosphorylation of phospholipase Cgamma1, thereby enhancing IL-1-induced Ca2+ release and ERK activation. Currently, the mechanisms by which SHP-2 modulates Ca2+ release from the endoplasmic reticulum are not defined. We used immunoprecipitation and fluorescence protein-tagged SHP-2 or endoplasmic reticulum (ER)-protein expression vectors, and an ER-specific calcium indicator, to examine the functional relationships between SHP-2, focal adhesions, and IL-1-induced Ca2+ release from the ER. By total internal reflection fluorescence microscopy to image subplasma membrane compartments, SHP-2 co-localized with the ER-associated proteins calnexin and calreticulin at sites of focal adhesion formation in fibroblasts. IL-1beta promoted time-dependent recruitment of SHP-2 and ER proteins to focal adhesions; this process was blocked in cells treated with small interfering RNA for SHP-2 and in cells expressing a Y542F SHP-2 mutant. IL-1 stimulated inositol 1,4,5-trisphosphate receptor-mediated Ca2+ release from the ER subjacent to the plasma membrane that was tightly localized around fibronectin-coated beads and was reduced 4-fold in cells expressing Tyr-542 SHP-2 mutant. In subcellular fractions enriched for ER proteins, immunoprecipitation demonstrated that IL-1-enhanced association of SHP-2 with the type 1 inositol 1,4,5-trisphosphate receptor was dependent on Tyr-542 of SHP-2. We conclude that Tyr-542 of SHP-2 modulates IL-1-induced Ca2+ signals and association of the ER with focal adhesions.

Tyrosine phosphatase SHP-2 regulates IL-1 signaling in fibroblasts through focal adhesions

Interleukin-1beta (IL-1beta) mediates destruction of matrix collagens in diverse inflammatory diseases including arthritis, periodontitis, and pulmonary fibrosis by activating fibroblasts, cells that interact with matrix proteins through integrin-based adhesions. In vitro, IL-1beta signaling is modulated by focal adhesions, supramolecular protein complexes that are enriched with tyrosine kinases and phosphatases. We assessed the importance of tyrosine phosphatases in regulating cell-matrix interactions and IL-1beta signaling. In human gingival fibroblasts plated on fibronectin, IL-1beta enhanced the maturation of focal adhesions as defined by morphology and enrichment with paxillin and alpha-actinin. IL-1beta also induced activation of ERK and recruitment of phospho-ERK to focal complexes/adhesions. Treatment with the potent tyrosine phosphatase inhibitor pervanadate, in the absence of IL-1beta, recapitulated many of these responses indicating the importance of tyrosine phosphatases. Immunoblotting of collagen bead-associated complexes revealed that the tyrosine phosphatase, SHP-2, was also enriched in focal complexes/adhesions. Depletion of SHP-2 by siRNA or by homologous recombination markedly altered IL-1beta-induced ERK activation and maturation of focal adhesions. IL-1beta-induced tyrosine phosphorylation of SHP-2 on residue Y542 promoted focal adhesion maturation. Association of Gab1 with SHP-2 in focal adhesions correlated temporally with activation of ERK and was abrogated in cells expressing mutant (Y542F) SHP-2. We conclude that IL-1beta mediated maturation of focal adhesions is dependent on tyrosine phosphorylation of SHP-2 at Y542, leading to recruitment of Gab1, a process that may influence the downstream activation of ERK.

Mitochondrial function is a critical determinant of IL-1-induced ERK activation

Interleukin-1 (IL-1) is a potent, proinflammatory cytokine, but local environmental factors in inflamed sites or in sepsis may affect cell metabolism and energetics, including the amplitude and duration of IL-1-induced signals, thereby leading to loss of tissue homeostasis. Currently, the mechanisms by which disruption of cell energetics affects inflammatory signaling are incompletely understood. Here, we examined the impact of cell energetics and mitochondrial function on the regulation of IL-1-induced Ca2+ signals and ERK activation in human gingival fibroblasts, cells that are important targets for IL-1-induced destruction of extracellular matrix in inflamed connective tissues. In untreated cells, IL-1 induced a prolonged increase of free intracellular calcium, which was required for ERK activation. Inhibition of cellular energetics by selective depolarization of mitochondria blocked Ca2+ uptake and almost completely abolished IL-1-induced cytosolic Ca2+ signals and ERK activation. IL-1 caused rapid Ca2+ release from the endoplasmic reticulum (ER), concomitant with mitochondrial Ca2+ uptake from ER and non-ER stores. Disruption of mitochondrial energetics abrogated IL-1 induced Ca2+ release from the ER but left other vital cellular functions intact. The negative effect of mitochondrial depolarization on ER release was bypassed by BAPTA/AM, indicating that mitochondrial Ca2+ buffering is the key mechanism in regulating ER release. Thus, in gingival fibroblasts, mitochondrial Ca2+ uptake is essential not only for shaping the kinetics and duration, but also the generation of, IL-1-induced Ca2+ signals. Consequently, mitochondria regulate key downstream effectors of IL-1, including MAP kinases.

SHP-2 modulates interleukin-1-induced Ca2+ flux and ERK activation via phosphorylation of phospholipase Cgamma1

Interleukin-1 (IL-1) signaling is dependent on focal adhesions, structures that are enriched with tyrosine kinases and phosphatases. Because the non-receptor tyrosine phosphatase Src homology 2 domain-containing protein tyrosine phosphatase-2 (SHP-2) is enriched in focal adhesions and IL-1-induced ERK activation requires increased Ca(2+), we determined whether SHP-2 modulates IL-1-induced Ca(2+) signaling. In SHP-2-deficient fibroblasts, IL-1-induced Ca(2+) signaling and ERK activation were markedly diminished compared with cells expressing SHP-2. IL-1-induced Ca(2+) release from the endoplasmic reticulum occurred in the vicinity of focal adhesions and was strongly inhibited by the blockage of phospholipase C (PLC) catalytic activity. Immunoprecipitation and immunostaining showed that SHP-2, the endoplasmic reticulum-specific protein calnexin, and PLCgamma1 were associated with focal adhesions; however, these associations and IL-1-induced ERK activation dissipated after cells were plated on non-integrin substrates. IL-1 promoted phosphorylation of SHP-2 and PLCgamma1. IL-1-induced phosphorylation of PLCgamma1 was diminished in SHP-2-deficient cells but was restored by stable transfection with SHP-2. BAPTA/AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester)) blocked IL-1-induced phosphorylation of SHP-2 and PLCgamma1, indicating mutually dependent interactive roles for Ca(2+), SHP-2, and PLCgamma1 in IL-1 signaling. We conclude that SHP-2 is critical for IL-1-induced phosphorylation of PLCgamma1 and thereby enhances IL-1-induced Ca(2+) release and ERK activation. Focal adhesions co-localizing with the endoplasmic reticulum may provide molecular staging sites required for ERK activation.

Spinal adenosine receptor activation inhibits inflammation and joint destruction in rat adjuvant-induced arthritis

OBJECTIVE

To examine the effect of spinal cord adenosine (Ado) receptor stimulation on rat adjuvant-induced arthritis (AIA).

METHODS

Long-term intrathecal (IT) catheters were implanted into rats to provide spinal access for drug delivery. Animals were immunized with complete Freund's adjuvant at the tail base. Eight days later and every other day thereafter until day 20, rats were treated IT with the selective Ado A1 receptor agonist cyclohexyladenosine (CHA) or vehicle. In some experiments, animals received an additional daily intraperitoneal injection of the nonselective Ado antagonist theophylline. Paw swelling was measured by water displacement plethysmometry. The effect of IT CHA on the activation of activator protein 1 (AP-1) was determined by electromobility shift assay. Spinal cord c-Fos expression was determined by immunohistochemistry.

RESULTS

Spinal CHA significantly inhibited inflammation in AIA, with a mean +/- SEM 20.9 +/- 16.9% increase in paw swelling in the IT CHA group compared with 81.3 +/- 10.6% in the saline group. The antiinflammatory effect of CHA was mediated through Ado receptors since the effect was reversed by coadministration of systemic theophylline. In addition, radiographs showed significantly less bone and cartilage destruction in the CHA-treated animals. Synovial expression of AP-1, which is a key regulator of metalloproteinase expression, was lower in IT CHA-treated animals. C-Fos expression was localized to spinal laminae I-VI, with a modest decrease observed in the superficial laminae in IT CHA-treated rats.

CONCLUSION

These data demonstrate that the spinal cord can regulate peripheral inflammation. Therapeutic strategies that target the central nervous system might be useful in arthritis.

Pathogenesis of rheumatoid arthritis: the role of synoviocytes

Considering the characteristics of RA synovial tissues such as marked proliferation and invasion to adjacent tissues, comparisons with transformed or neoplastic tissue are natural. RA synovial tissues or cells are not truly malignant, but they have many features of transformation, denoted as "partial transformation" in this article. These features include anchorage-independent growth, loss of contact inhibition, oncogene activation, monoclonal or oligoclonal expansion, detectable telomerase activity, and somatic gene mutations. Although it is not possible to conclude whether most of these cells are permanently changed in association with some genetic alterations or are passively changed by virtue of environmental factors (i.e., cytokine-mediated imprinting), the presence of p53 mutations in RA synovial tissues is especially persuasive. A number of transcription factors play a critical role in the activation, differentiation, and proliferation of RA synovial cells. In particular, the roles of AP-1, MAPKs, and NF-kappa B have been investigated carefully because of their ability to regulate numerous inflammation-related genes. These transcription factors also control expression and activation of matrix-degrading enzymes, including MMPs, aggrecanase, and cysteine proteases, which are the primary enzymes responsible for joint destruction. Elucidation of gene mutations and detailed signal transduction pathways that are specific to RA as well as mechanisms of action of matrix-degrading enzymes may lead to development of a novel therapy for RA. Careful mapping of cytokine networks a decade ago led to groundbreaking advances in therapy. Similarly, methodical evaluation and prioritization of intracellular targets might provide the basis for therapeutic interventions.