Valproic acid suppresses interleukin-1ß-induced microsomal prostaglandin E2 synthase-1 expression in chondrocytes through upregulation of NAB1.

OBJECTIVE: Microsomal prostaglandin E(2) synthase-1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE(2). Early growth response factor-1 (Egr-1) is a key transcription factor in the regulation of mPGES-1, and its activity is negatively regulated by the corepressor NGF1-A-binding protein-1 (NAB1). We examined the effects of valproic acid (VA), a histone deacetylase inhibitor, on interleukin 1ß (IL-1ß)-induced mPGES-1 expression in human chondrocytes, and evaluated the roles of Egr-1 and NAB1 in these effects. METHODS: Chondrocytes were stimulated with IL-1 in the absence or presence of VA, and the level of mPGES-1 protein and mRNA expression were evaluated using Western blotting and real-time reverse-transcription polymerase chain reaction (PCR), respectively. mPGES-1 promoter activity was analyzed in transient transfection experiments. Egr-1 and NAB1 recruitment to the mPGES-1 promoter was evaluated using chromatin immunoprecipitation assays. Small interfering RNA (siRNA) approaches were used to silence NAB1 expression. RESULTS: VA dose-dependently suppressed IL-1-induced mPGES-1 protein and mRNA expression as well as its promoter activation. Treatment with VA did not alter IL-1-induced Egr-1 expression, or its recruitment to the mPGES-1 promoter, but prevented its transcriptional activity. The suppressive effect of VA requires de novo protein synthesis. VA induced the expression of NAB1, and its recruitment to the mPGES-1 promoter, suggesting that NAB1 may mediate the suppressive effect of VA. Indeed, NAB1 silencing with siRNA blocked VA-mediated suppression of IL-1-induced mPGES-1 expression. CONCLUSION: VA inhibited IL-1-induced mPGES-1 expression in chondrocytes. The suppressive effect of VA was not due to reduced expression or recruitment of Egr-1 to the mPGES-1 promoter and involved upregulation of NAB1.

Contribution of H3K4 methylation by SET-1A to interleukin-1-induced cyclooxygenase 2 and inducible nitric oxide synthase expression in human osteoarthritis chondrocytes.

OBJECTIVE: To investigate the role of histone H3 lysine 4 (H3K4) methylation in interleukin-1ß (IL-1ß)-induced cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) expression in human osteoarthritic (OA) chondrocytes. METHODS: Chondrocytes were stimulated with IL-1, and the expression of iNOS and COX-2 messenger RNA and proteins was evaluated by real-time reverse transcriptase-polymerase chain reaction analysis and Western blotting, respectively. H3K4 methylation and the recruitment of the histone methyltransferases SET-1A and MLL-1 to the iNOS and COX-2 promoters were evaluated using chromatin immunoprecipitation assays. The role of SET-1A was further evaluated using the methyltransferase inhibitor 5'-deoxy-5'-(methylthio)adenosine (MTA) and gene silencing experiments. SET-1A level in cartilage was determined using immunohistochemistry. RESULTS: The induction of iNOS and COX-2 expression by IL-1 was associated with H3K4 di- and trimethylation at the iNOS and COX-2 promoters. These changes were temporally correlated with the recruitment of the histone methyltransferase SET-1A, suggesting an implication of SET-1A in these modifications. Treatment with MTA inhibited IL-1-induced H3K4 methylation as well as IL-1-induced iNOS and COX-2 expression. Similarly, SET-1A gene silencing with small interfering RNA prevented IL-1-induced H3K4 methylation at the iNOS and COX-2 promoters as well as iNOS and COX-2 expression. Finally, we showed that the level of SET-1A expression was elevated in OA cartilage as compared with normal cartilage. CONCLUSION: These results indicate that H3K4 methylation by SET-1A contributes to IL-1-induced iNOS and COX-2 expression and suggest that this pathway could be a potential target for pharmacologic intervention in the treatment of OA and possibly other arthritic diseases.

Human articular chondrocytes express 15-lipoxygenase-1 and -2: potential role in osteoarthritis.

INTRODUCTION: 15-Lipoxygenases and their metabolites have been shown to exhibit anti-inflammatory and immunomodulatory properties, but little is known regarding their expression and function in chondrocytes. The objective of this study was to evaluate the expression of 15-lipoxygenase-1 and -2 in human articular chondrocytes, and to investigate the effects of their metabolites 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids on IL-1beta-induced matrix metalloproteinase (MMP)-1 and MMP-13 expression. METHODS: The expression levels of 15-lipoxygenase-1 and -2 were analyzed by reverse transcription PCR and Western blotting in chondrocytes, and by immunohistochemistry in cartilage. Chondrocytes or cartilage explants were stimulated with IL-1beta in the absence or presence of 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, and the levels of MMP-1 and MMP-13 protein production and type II collagen cleavage were evaluated using immunoassays. The role of peroxisome proliferator-activated receptor (PPAR)gamma was evaluated using transient transfection experiments and the PPARgamma antagonist GW9662. RESULTS: Articular chondrocytes express 15-lipoxygenase-1 and -2 at the mRNA and protein levels. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids dose dependently decreased IL-1beta-induced MMP-1 and MMP-13 protein and mRNA expression as well as type II collagen cleavage. The effect on MMP-1 and MMP-13 expression does not require de novo protein synthesis. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids activated endogenous PPARgamma, and GW9662 prevented their suppressive effect on MMP-1 and MMP-13 production, suggesting the involvement of PPARgamma in these effects. CONCLUSIONS: This study is the first to demonstrate the expression of 15-lipoxygenase-1 and -2 in articular chondrocytes. Their respective metabolites, namely 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, suppressed IL-1beta-induced MMP-1 and MMP-13 expression in a PPARgamma-dependent pathway. These data suggest that 15-lipoxygenases may have chondroprotective properties by reducing MMP-1 and MMP-13 expression.

HDAC4 contributes to IL-1-induced mPGES-1 expression in human synovial fibroblasts through up-regulation of Egr-1 transcriptional activity.

Microsomal prostaglandin E synthase-1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE(2), which contributes to many physiopathological processes. We show here that inhibitors of histone deacetylase (HDAC) activity, trichostatin A (TSA), butyric acid (BA), and valproic acid (BA) prevented IL-1-induced mPGES-1 protein expression in human synovial fibroblasts. TSA also inhibited IL-1-induced mPGES-1 mRNA expression and promoter activation. Overexpression of HDAC4, but not of HDAC1, 2, 3, 5, or 6 enhanced, whereas HDAC4 silencing with small interfering RNA (siRNA) reduced, IL-1-induced mPGES-1 promoter activation, implying that HDAC4 contributes to mPGES-1 gene expression. Consistently, IL-1-induced mPGES-1 protein expression was prevented by siRNA for HDAC4. We also demonstrate that IL-1-induced HDAC4 recruitment to the mPGES-1 promoter. This recruitment was not accompanied by deacetylation of histones H3 and H4, suggesting that HDAC4 contributes to mPGES-1 induction independently of local deacetylation of histones H3 and H4. We then investigated whether HDAC4 regulates mPGES-1 expression by modulating the activity of Egr-1, a key transcription factor in IL-1-induced mPGES-1 expression. We found that HDAC4 overexpression enhances, whereas HDAC4 knockdown by siRNA reduces Egr-1-mediated activation of the mPGES-1 promoter. Together these data indicate that HDAC4 contributes to transcriptional induction of mPGES-1 by IL-1 through a mechanism involving up-regulation of Egr-1 transcriptional activity.

Increased expression of lipocalin-type prostaglandin D2 synthase in osteoarthritic cartilage.

INTRODUCTION: Prostaglandin D synthase (PGDS) is responsible for the biosynthesis of PGD and J series, which have been shown to exhibit anti-inflammatory and anticatabolic effects. Two isoforms have been identified: hematopoietic- and lipocalin-type PGDS (H-PGDS and L-PGDS, respectively). The aims of this study were to investigate the expressions of H-PGDS and L-PGDS in cartilage from healthy donors and from patients with osteoarthritis (OA) and to characterize their regulation by interleukin-1-beta (IL-1beta) in cultured OA chondrocytes. METHODS: The expressions of H-PGDS and L-PGDS mRNA and protein in cartilage were analyzed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Chondrocytes were stimulated with IL-1beta, and the expression of L-PGDS was evaluated by real-time RT-PCR and Western blotting. The roles of de novo protein synthesis and of the signalling pathways mitogen-activated protein kinases (MAPKs), nuclear factor-kappa-B (NF-kappaB), and Notch were evaluated using specific pharmacological inhibitors. RESULTS: L-PGDS and H-PGDS mRNAs were present in both healthy and OA cartilage, with higher levels of L-PGDS than H-PGDS (> 20-fold). The levels of L-PGDS mRNA and protein were increased in OA compared with healthy cartilage. Treatment of chondrocytes with IL-1beta upregulated L-PGDS mRNA and protein expressions as well as PGD2 production in a dose- and time-dependent manner. The upregulation of L-PGDS by IL-1beta was blocked by the translational inhibitor cycloheximide, indicating that this effect is indirect, requiring de novo protein synthesis. Specific inhibitors of the MAPK p38 (SB 203580) and c-jun N-terminal kinase (JNK) (SP600125) and of the NF-kappaB (SN-50) and Notch (DAPT) signalling pathways suppressed IL-1beta-induced upregulation of L-PGDS expression. In contrast, an inhibitor of the extracellular signal-regulated kinase (ERK/MAPK) (PD98059) demonstrated no significant influence. We also found that PGD2 prevented IL-1beta-induced upregulation of L-PGDS expression. CONCLUSIONS: This is the first report demonstrating increased levels of L-PGDS in OA cartilage. IL-1beta may be responsible for this upregulation through activation of the JNK and p38 MAPK and NF-kappaB signalling pathways. These data suggest that L-PGDS might have an important role in the pathophysiology of OA.

Inhibition of interleukin-1beta-induced matrix metalloproteinases 1 and 13 production in human osteoarthritic chondrocytes by prostaglandin D2.

OBJECTIVE: To investigate the effects of prostaglandin D2 (PGD2) on interleukin-1beta (IL-1beta)-induced matrix metalloproteinase 1 (MMP-1) and MMP-13 expression in human chondrocytes and the signaling pathways involved in these effects. METHODS: Chondrocytes were stimulated with IL-1 in the presence or absence of PGD2, and expression of MMP-1 and MMP-13 proteins was evaluated by enzyme-linked immunosorbent assay. Messenger RNA (mRNA) expression and promoter activity were analyzed by real-time reverse transcription-polymerase chain reaction and transient transfections, respectively. The role of the PGD2 receptors D prostanoid receptor 1 (DP1) and chemoattractant receptor-like molecule expressed on Th2 cells (CRTH2) was evaluated using specific agonists and antibody-blocking experiments. The contribution of the cAMP/protein kinase A (PKA) pathway was determined using cAMP-elevating agents and PKA inhibitors. RESULTS: PGD2 decreased in a dose-dependent manner IL-1-induced MMP-1 and MMP-13 protein and mRNA expression as well as their promoter activation. DP1 and CRTH2 were expressed and functional in chondrocytes. The effect of PGD2 was mimicked by BW245C, a selective agonist of DP1, but not by 13,14-dihydro-15-keto-PGD2, a selective agonist of CRTH2. Furthermore, treatment with an anti-DP1 antibody reversed the effect of PGD2, indicating that the inhibitory effect of PGD2 is mediated by DP1. The cAMP-elevating agents 8-Br-cAMP and forskolin suppressed IL-1-induced MMP-1 and MMP-13 expression, and the PKA inhibitors KT5720 and H89 reversed the inhibitory effect of PGD2, suggesting that the effect of PGD2 is mediated by the cAMP/PKA pathway. CONCLUSION: PGD2 inhibits IL-1-induced production of MMP-1 and MMP-13 by chondrocytes through the DP1/cAMP/PKA signaling pathway. These data also suggest that modulation of PGD2 levels in the joint may have therapeutic potential in the prevention of cartilage degradation.