Cyclooxygenase 2-dependent prostaglandin E2 modulates cartilage proteoglycan degradation in human osteoarthritis explants

Endoplasmic reticulum stress (ER-stress) by 2-deoxy-D-glucose (2DG) reduces cyclooxygenase-2 (COX-2) expression and N-glycosylation and induces a loss of COX-2 activity via a Src kinase-dependent pathway in rabbit articular chondrocytes

Endoplasmic reticulum (ER) stress regulates a wide range of cellular responses including apoptosis, proliferation, inflammation, and differentiation in mammalian cells. In this study, we observed the role of 2-deoxy-D-glucose (2DG) on inflammation of chondrocytes. 2DG is well known as an inducer of ER stress, via inhibition of glycolysis and glycosylation. Treatment of 2DG in chondrocytes considerably induced ER stress in a dose- and time-dependent manner, which was demonstrated by a reduction of glucose regulated protein of 94 kDa (grp94), an ER stress-inducible protein, as determined by a Western blot analysis. In addition, induction of ER stress by 2DG led to the expression of COX-2 protein with an apparent molecular mass of 66-70kDa as compared with the normally expressed 72-74 kDa protein. The suppression of ER stress with salubrinal (Salub), a selective inhibitor of eif2-alpha dephosphorylation, successfully prevented grp94 induction and efficiently recovered 2DG- modified COX-2 molecular mass and COX-2 activity might be associated with COX-2 N-glycosylation. Also, treatment of 2DG increased phosphorylation of Src in chondrocytes. The inhibition of the Src signaling pathway with PP2 (Src tyrosine kinase inhibitor) suppressed grp94 expression and restored COX-2 expression, N-glycosylation, and PGE2 production, as determined by a Western blot analysis and PGE2 assay. Taken together, our results indicate that the ER stress induced by 2DG results in a decrease of the transcription level, the molecular mass, and the activity of COX-2 in rabbit articular chondrocytes via a Src kinase-dependent pathway.

Interleukin-1 beta affects cyclooxygenase-2 expression and cartilage metabolism in mandibular condyle

Extracellular matrix degradation in mandibular condylar cartilage is mediated by various cytokines in the temporomandibular joint (TMJ). Interleukin-1 beta (IL-1β) is detected in joint structures with pathologic status, and participates in catabolic action in the extracellular matrix. The purpose of this study was to investigate the effects of IL-1β on cyclooxygenase-2 (COX-2) expression and cartilage metabolism using cultured chondrocytes from mandibular condyle. Articular chondrocytes from the porcine mandibular condylar cartilage around the surface were cultured and treated with 0-10 ng/ml IL-1β or 0-1000 ng/ml prostaglandin (PGE(2)) for 0-24h. The mRNA levels of COX-2, MMP-1, -3, and -13 were evaluated by real-time PCR analysis. The protein levels of PGE(2) and MMPs were examined by ELISA and Western blot analysis, respectively. The expression levels of COX-2 and PGE(2) were enhanced by exogenous IL-1β in chondrocytes. The mRNA levels of MMP-1, -3, and -13 were up-regulated by PGE(2) treatment dose-dependently. It is shown that the expression of COX-2/PGE(2) was enhanced by IL-1β in articular chondrocytes from mandibular condyle, and that MMP-1, -3, and -13 were induced by PGE(2), suggesting that IL-1β-induced COX-2/PGE(2) play a crucial role in catabolic processes of mandibular condylar cartilage under inflammatory conditions.

Effect of Phellodendron amurense in protecting human osteoarthritic cartilage and chondrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional medicine has been widely using Phellodendron amurense Rupr. (Rutaceae) to treat various inflammatory diseases including arthritis.

AIM OF THE STUDY

This study investigated the effects of Phellodendron amurense in protecting cartilage, including regulating the levels of aggrecanases, matrix metalloproteinases (MMPs)/tissue inhibitor of metalloproteinase (TIMP), proinflammatory cytokines and signaling of the mitogen activated protein kinase (MAPK) pathway in human osteoarticular cartilage and chondrocytes.

MATERIALS AND METHODS

Explants from human osteoarthritis cartilage were cultured alone or in IL-1α for 7 days with or without Phellodendron amurense ethanol extract or celecoxib (40, 100, 200μg/ml). The effect of Phellodendron amurense on matrix degradation induced by IL-1α in human articular cartilage was assessed by staining, and the quantities of sulfated glycosaminoglycan (GAG) and type II collagen were calculated from the culture media. The levels of aggrecanases, MMPs, TIMP, and PGE(2) in the culture media were investigated using an enzyme-linked immunosorbent assay (ELISA). In addition, reverse transcription polymerase chain reaction (RT-PCR) evaluated the mRNA expression of aggrecanases, MMPs and TIMP. Furthermore, Western blot analysis was performed to identify the roles that Phellodendron amurense played in the ERK, JNK and p38 signaling pathways.

RESULTS

Phellodendron amurense showed no evident cytotoxicity on human articular cartilage. Phellodendron amurense significantly inhibited the IL-1α-induced degradation of GAG and type II collagen from human osteoarticular cartilage in a concentration-dependent manner. Celecoxib did not significantly inhibit IL-1α-induced release of GAG and only slightly reduced type II collagen. Phellodendron amurense also dose-dependently decreased the levels of aggrecanase-1 and -2, MMP-1, -3, and -13, whereas it increased TIMP-1 expression in human osteoarticular cartilage. Celecoxib only decreased MMP-1 and MMP-13 levels in human osteoarticular cartilage. In addition, Phellodendron amurense reduced the phosphorylation of extracellular signal regulated kinase (ERK)1/2, Jun NH2-terminal kinase (JNK) and activated phospho-p38 MAPK in a dose-dependent manner in human osteoarthritic chondrocytes.

CONCLUSIONS

Phellodendron amurense inhibited osteoarticular cartilage and chondrocyte destruction by inhibiting proteoglycan release and type II collagen degradation, down-regulating aggrecanases, MMP activities and phospho-ERK1/2, JNK and p38 MAP kinase signaling, and up-regulating TIMP-1 activity. Therefore, our results suggest that Phellodendron amurense is a potential therapeutic agent to protect cartilage against OA progression.

Multiple phospholipase A2 enzymes participate in the inflammatory process in osteoarthritic cartilage

OBJECTIVE

The aim of this study was to determine the involvement of pro-inflammatory phospholipase A2 (PLA2) enzymes in human chondrocytes from patients with osteoarthritis (OA).

METHODS

PLA2 involvement in OA chondrocytes was analysed by (a) arachidonic acid (AA) and oleic acid release, (b) PLA2 mRNA analysis, and (c) prostaglandin E2 (PGE2) production in cultured OA chondrocytes in response to various cytokines and platelet activating factor (PAF).

RESULTS

Pro-inflammatory cytokines and PAF stimulation led to increased AA release, interleukin (IL)-1β and tumour necrosis factor (TNF) being the strongest inducers. The pattern of oleic acid release was similar to but less prominent than AA release, suggesting that predominantly arachidonyl selective enzymes were activated. IL-1β, TNF, IL-6, and IL-8 upregulated secretory group IIA, IID, and V phospholipase A2 (sPLA2-IIA, -IID, -V) and cytosolic group IVA phospholipase A2 (cPLA2-IVA) expression, where induction of chondrocyte sPLA2-IID is a novel finding. Furthermore, IL-1β, TNF, and IL-6 also induced COX2 expression. PAF induced expression of group IIA, IID and IVA PLA2, and COX2. In line with its anti-inflammatory properties, IL-4 was unable to induce either AA release or expression of PLA2s or COX2. IL-1β and TNF strongly increased PGE2 production, with IL-1β as the most prominent inducer.

CONCLUSION

Multiple PLA2 isoforms are expressed and influenced by pro-inflammatory stimuli in OA chondrocytes. Hence, several PLA2 enzymes may contribute to chondrocyte function by their upregulation and activation, and increased AA release and PGE2 production may therefore be important effectors in OA pathophysiology. PLA2 enzymes and cPLA2-IVA in particular are thus possible therapeutic targets in OA.

In vitro inhibition of compression-induced catabolic gene expression in meniscal explants following treatment with IL-1 receptor antagonist

BACKGROUND

Damage to the knee meniscus may result in tears that are difficult or unable to heal, and are often treated by partial removal of the damaged tissue. In vitro, 20% dynamic compressive strains on meniscal tissue explants have resulted in an increase in the release of sulfated glycosaminoglycans (GAG) and nitric oxide (NO) from the tissue explants and increased expression of matrix metalloproteinases (MMP) and interleukin-1α (IL-1α). The objective of this study was to explore the efficacy of IL-1 blockade on the expression of a wide range of genes, as well as NO and GAG release, following dynamic compression of porcine meniscal explants.

METHODS

Explants were dynamically compressed for 2 h at 1 Hz to 0, 10, or 20% strain with and without a pre-treatment of 500 ng/ml interleukin-1 receptor antagonist (IL-1RA). Relative changes in gene expression of IL-1α, MMP-1, -3, -13, A Disintegrin and Metalloproteinase with ThromboSpondin 4 (ADAMTS-4), ADAMTS-5, iNOS, aggrecan, and COX-2, as well as changes in NO and GAG release, were measured with standard biochemical assays.

RESULTS

Expression of IL-1α, MMP-3, MMP-13, and ADAMTS-4 in superficial explants was significantly downregulated at 20% dynamic strain compared to 10% strain following treatment with IL-1RA. GAG and NO release were not significantly influenced by IL-1RA treatment.

CONCLUSIONS

Treatment of meniscal explants with IL-1RA inhibited the expression of many catabolic genes following a single bout of high dynamic strain. IL-1RA may therefore be a potential therapy option during the acute phase of meniscal tear or meniscectomy treatment.

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-1β (IL-1β)-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.

Valproic Acid Suppresses Interleukin-1ß-induced Microsomal Prostaglandin E2 Synthase-1 Expression in Chondrocytes Through Upregulation of NAB1

Objective.

Microsomal prostaglandin E2 synthase-1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE2. 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.

Prostaglandin EP2 receptor signalling inhibits the expression of matrix metalloproteinase 13 in human osteoarthritic chondrocytes

OBJECTIVES

Matrix metalloproteinase (MMP) 13 is a pathogenic collagenase that causes cartilage destruction and plays a leading role in causing osteoarthritis. This study focused on 114 genes that are differentially expressed between intact and damaged osteoarthritis cartilage, in order to determine which molecules are involved in suppressing MMP-13 expression.

METHODS

MMP-13 concentrations were measured in the supernatant of human osteoarthritis chondrocyte cultures transfected with small interfering RNA (siRNA) against the 114 genes. MMP-13 levels changed most dramatically in response to siRNA against prostaglandin EP2 receptor. The authors performed further measurements of MMP-13 production in osteoarthritis chondrocytes stimulated by the EP2 agonist butaprost in the presence or absence of interleukin-1β (IL-1β) and/or cyclooxygenase-2 (COX-2) inhibitor. They also assessed the effect of butaprost on chondrocyte viability, and investigated the involvement of the cAMP-protein kinase A (PKA) pathway on EP2 signalling using inhibitors. Cartilage-related gene expression was examined in chondrocytes treated with butaprost. The authors also investigated which E series of prostaglandin (EP) receptors are expressed in osteoarthritis cartilage.

RESULTS

MMP-13 messenger RNA expression was significantly affected by two molecules, EP2 receptor and SLC14A1, a urea transporter. In IL-1β-treated osteoarthritis chondrocytes, butaprost suppressed MMP-13 production, which was further decreased by COX-2 inhibitor. EP2 signalling downregulated MMP-13 mRNA expression via the cAMP-PKA pathway without affecting cell viability. Although EP2 signalling enhanced IL-6 expression, the expressions of several catabolic factors (MMP-1, MMP-3, MMP-13, ADAMTS5, IL-1β and tumour necrosis factor alpha) were inhibited. EP2 receptor was the major EP receptor in osteoarthritis cartilage.

CONCLUSION

The results suggest that EP2 signalling has 'anti-catabolic' effects in osteoarthritis chondrocytes.

Mechanical loading, cartilage degradation, and arthritis

Joint tissues are exquisitely sensitive to their mechanical environment, and mechanical loading may be the most important external factor regulating the development and long-term maintenance of joint tissues. Moderate mechanical loading maintains the integrity of articular cartilage; however, both disuse and overuse can result in cartilage degradation. The irreversible destruction of cartilage is the hallmark of osteoarthritis and rheumatoid arthritis. In these instances of cartilage breakdown, inflammatory cytokines such as interleukin-1 beta and tumor necrosis factor-alpha stimulate the production of matrix metalloproteinases (MMPs) and aggrecanases (ADAMTSs), enzymes that can degrade components of the cartilage extracellular matrix. In order to prevent cartilage destruction, tremendous effort has been expended to design inhibitors of MMP/ADAMTS activity and/or synthesis. To date, however, no effective clinical inhibitors exist. Accumulating evidence suggests that physiologic joint loading helps maintain cartilage integrity; however, the mechanisms by which these mechanical stimuli regulate joint homeostasis are still being elucidated. Identifying mechanosensitive chondroprotective pathways may reveal novel targets or therapeutic strategies in preventing cartilage destruction in joint disease.

Age-related differences in prostaglandin E2 synthesis by equine cartilage explants and synoviocytes

Time- and concentration-related actions of lipopolysaccharide (LPS) on the synthesis of prostaglandin E(2) (PGE(2)) were investigated in cartilage explants and synoviocytes harvested from 3 age groups of horses, all with clinically normal joint function: group A <10 years; group B 11-20 years and group C >20 years. Cartilage explants from group A horses were least and those from group C were most sensitive to LPS. Significant increases in PGE(2) concentration (P <or= 0.01) were obtained in group C horses in response to LPS concentrations of 1.0 microg/mL (and higher) after exposure for 24, 36 and 48 h, whereas explants from group A horses failed to respond to LPS at concentrations up to 100 microg/mL after exposure times up to 48 h. In contrast, synoviocytes from group A horses were most and those from group C horses were least sensitive to LPS stimulation. Synoviocytes from group A horses responded to LPS concentrations of 1 microg/mL (and higher) with significantly increased concentrations of PGE(2) at 24 and 36 h. Significant but numerically smaller increases in PGE(2) concentration were induced by LPS in synoviocytes from groups B and C. As the effects of high PGE(2) concentrations are catabolic for cartilage, these observations suggest that both synoviocytes and chondrocytes might exert roles in the degenerative changes which occur in cartilage in horses with osteoarthritis.

Dynamic loading enhances integrative meniscal repair in the presence of interleukin-1

OBJECTIVE

Meniscal tears are a common knee injury and increased levels of interleukin-1 (IL-1) have been measured in injured and degenerated joints. Studies have shown that IL-1 decreases the shear strength, cell accumulation, and tissue formation in meniscal repair interfaces. While mechanical stress and IL-1 modulate meniscal biosynthesis and degradation, the effects of dynamic loading on meniscal repair are unknown. The purpose of this study was to determine the effects of mechanical compression on meniscal repair under normal and inflammatory conditions.

EXPERIMENTAL DESIGN

Explants were harvested from porcine medial menisci. To simulate a full-thickness defect, a central core was removed and reinserted. Explants were loaded for 4h/day at 1 Hz and 0%-26% strain for 14 days in the presence of 0 or 100 pg/mL of IL-1. Media were assessed for matrix metalloproteinase (MMP) activity, aggrecanase activity, sulfated glycosaminoglycan (S-GAG) release, and nitric oxide (NO) production. After 14 days, biomechanical testing and histological analyses were performed.

RESULTS

IL-1 increased MMP activity, S-GAG release, and NO production, while decreasing the shear strength and tissue repair in the interface. Dynamic loading antagonized IL-1-mediated inhibition of repair at all strain amplitudes. Neither IL-1 treatment nor strain altered aggrecanase activity. Additionally, strain alone did not alter meniscal healing, except at the highest strain magnitude (26%), a level that enhanced the strength of repair.

CONCLUSIONS

Dynamic loading blocked the catabolic effects of IL-1 on meniscal repair, suggesting that joint loading through physical therapy may be beneficial in promoting healing of meniscal lesions under inflammatory conditions.

Prostaglandin E2 induces interleukin-6 expression in human chondrocytes via cAMP/protein kinase A- and phosphatidylinositol 3-kinase-dependent NF-kappaB activation

Elevated levels of prostaglandin (PG)E(2) and interleukin (IL)-6 have been reported in the cartilage and synovial fluid from patients with arthritic disorders. PGE(2) regulates IL-6 production in numerous different cells including macrophages and synovial fibroblasts. Although PGE(2) stimulates IL-6 expression in human chondrocytes, the underlying signaling pathway of this process has yet to be delineated. Here, we investigate the mechanism of IL-6 induction in human T/C-28a2 chondrocytes treated with exogenously added PGE(2). PGE(2) induces IL-6 mRNA and protein expression via a cAMP-dependent pathway, reaching maximal levels after 60 min of stimulation before declining to baseline levels at 6 h. Forskolin, an adenylyl cyclase activator, also stimulates IL-6 expression in human chondrocytes in a dose- and time-dependent fashion. Inhibition of downstream effectors of cAMP activity such as protein kinase A (PKA) or phosphatidylinositol 3 kinase (PI3K) blocks PGE(2)- and forskolin-induced IL-6 upregulation. Simultaneous inhibition of PKA and PI3K reduces IL-6 expression in stimulated chondrocytes well below the basal levels of untreated cells. Gel shift, supershift, and chromatin immunoprecipitation assays reveal the activation and binding of the nuclear factor (NF)-kappaB p65 subunit to the IL-6 promoter, which is markedly suppressed by selective PI3K or PKA pharmacological inhibitors. p65 knockdown completely abrogates IL-6 mRNA synthesis in PGE(2)- and forskolin-primed chondrocytes. Cumulatively, our data show that PGE(2) and forskolin induce IL-6 expression in human chondrocytes via cAMP/PKA and PI3K-dependent pathways, which in turn regulate the activation and binding of p65 to the IL-6 promoter.

Arthritis and cannabinoids: HU-210 and Win-55,212–2 prevent IL-1 α-induced matrix degradation in bovine articular chondrocytes in-vitro

Cannabinoids have analgesic, immunomodulatory and anti-inflammatory properties and attenuate joint damage in animal models of arthritis. In this study the mechanisms of action of the synthetic cannabinoid agonists, HU-210 and Win-55,212–2, were studied to determine if they affected interleukin-1 alpha (IL-1α)-induced proteoglycan and collagen degradation in bovine nasal cartilage explant cultures and prostaglandin E2 (PGE2) production in primary cultures of bovine articular chondrocytes. The effects of the inactive enantiomer, Win-55,212–3, were compared with those of the active enantiomer, Win-55,212–2, to determine if the effects were cannabinoid (CB)-receptor mediated. The chondrocytes and explants were stimulated by IL-1α (100 U mL−1 ≡ 0.06 nm and 500 U mL−1 ≡ 0.3 nm, respectively). Proteoglycan breakdown was determined as sulfated glycosaminoglycan (sGAG) release using the dimethylmethylene blue assay. Collagen degradation was determined as hydroxyproline in the conditioned culture media and cartilage digests. PGE2 was determined by ELISA. Expression of cannabinoid receptors, CB1 and CB2; cyclooxygenase-1 and −2 (COX-1 and COX-2); inducible nitric oxide synthase (iNOS); as well as activation of nuclear factor-kappa B (NF-κB) in chondrocytes were studied using immunoblotting techniques and immunofluorescence. The results showed that HU-210 and Win-55,212–2 (5–15 μm) significantly inhibited IL-1α-stimulated proteoglycan (P &lt; 0.001) and collagen degradation (P &lt; 0.001). Win-55,212–2 (5–10 μm) also significantly inhibited PGE2 production (P &lt; 0.01). At 5 μm, Win-55,212–2 inhibited the expression of iNOS and COX-2 and activation of NF-κB. Chondrocytes appeared to constitutively express cannabinoid receptors CB1 and CB2. It is concluded that biologically stable synthetic cannabinoids protect cartilage matrix from degradation induced by cytokines and this effect is possibly CB-receptor mediated and involves effects on prostaglandin and nitric oxide metabolism. Cannabinoids could also be producing these effects via inhibition of NF-κB activation.

Regulation of microsomal prostaglandin E2 synthase-1 and 5-lipoxygenase-activating protein/5-lipoxygenase by 4-hydroxynonenal in human osteoarthritic chondrocytes

INTRODUCTION

This study aimed to investigate whether hydroxynonenal (HNE) depletion is responsible for the switch from cyclooxygenase-2 (COX-2) and microsomal prostaglandin E2 synthase-1 (mPGES-1) to 5-lipoxygenase-activating protein (FLAP) and 5-lipoxygenase (5-LOX).

METHODS

For COX-2 and mPGES-1 studies, human osteoarthritic chondrocytes were stimulated at different incubation times (up to 24 hours) with a single or repetitive addition of 10 muM HNE to the cultures at 2-hour intervals, up to 14 hours. For 5-LOX and FLAP studies, cells were treated with a single addition of 10 muM HNE for 24 hours, 48 hours, and 72 hours in the presence or absence of naproxen (a nonspecific COX-2 inhibitor) or antibody anti-transforming growth factor-beta 1 (TGF-beta1). The protein levels of COX-2, mPGES-1 and early growth response factor-1 (Egr-1) transcription factor were evaluated by western blot, and those of prostaglandin E2 (PGE2), leukotriene B4 (LTB4) and TGF-beta1 were determined with commercial kits. The levels of mPGES-1, FLAP and 5-LOX mRNA were measured by real-time RT-PCR. Transient transfection was performed to determine promoter activities of mPGES-1 and 5-LOX.

RESULTS

Single addition of 10 muM HNE to cultured chondrocytes induced PGE2 release as well as COX-2 and mPGES-1 expression at the protein and mRNA levels, with a plateau reached respectively at 8 and 16 hours of incubation, followed by a subsequent decline. However, repeated treatments with HNE prevented the decline of COX-2 and mPGES-1 expression that occurred with a single aldehyde addition. HNE induced mPGES-1 promoter activity, possibly through transcription factor Egr-1 activation. After 48 hours, when COX-2 expression decreased, the LTB4 level rose through 5-LOX and FLAP upregulation. The addition of naproxen to cultured chondrocytes revealed that FLAP and 5-LOX regulation by HNE required PGE2 production. Furthermore, our data showed that HNE significantly induced TGF-beta1 production. The addition of anti-TGF-beta1 antibody reduced HNE-induced 5-LOX and FLAP expression by 40%, indicating the partial involvement of a TGF-beta1-dependent mechanism.

CONCLUSIONS

Our data demonstrate that the shunt to the FLAP and 5-LOX pathway in HNE-induced human osteoarthritic chondrocytes is attributed to COX-2 and mPGES-1 inhibition, probably due to HNE depletion. PGE2 and TGF-beta1 are suggested to be involved in this regulation.

Cytokine receptor-like factor 1 is highly expressed in damaged human knee osteoarthritic cartilage and involved in osteoarthritis downstream of TGF-beta

Osteoarthritis (OA) is the most prevalent joint disease and is characterized by pain and functional loss of the joint. However, the pathogenic mechanism of OA remains unclear, and no drug therapy for preventing its progress has been established. To identify genes related to the progress of OA, the gene expression profiles of paired intact and damaged cartilage obtained from OA patients undergoing joint substitution were compared using oligo microarrays. Using functional categorization combined with gene ontology and a statistical analysis, five genes were found to be highly expressed in damaged cartilage (HBEGF, ASUS, CRLF1, LOX, CDA), whereas three genes were highly expressed in intact tissues (CHST2, PTPRD, CPAN6). Among these genes, the upregulated expression of CRLF1 was reconfirmed using real-time PCR, and the in vivo expression of CRLF1 was detected in clusters of chondrocytes and fibrocartilage-like cells in damaged OA cartilages using in situ hybridization. In vitro, the transcriptional level of CRLF1 was positively regulated by TGF-beta1 in the mouse chondrogenic cell line ATDC5. Additionally, the CRLF1/CLC complex promoted the proliferation of ATDC5 cells and suppressed the expression level of aggrecan and type II collagen. Our data suggest that the CRLF1/CLC complex disrupts cartilage homeostasis and promotes the progress of OA by enhancing the proliferation of chondrocytes and suppressing the production of cartilage matrix. A component of the complex, CRLF1, may be useful as a biomarker of OA; and the corresponding receptor is a potential new drug target for OA.

SHP-1, a novel peptide isolated from seahorse inhibits collagen release through the suppression of collagenases 1 and 3, nitric oxide products regulated by NF-kappaB/p38 kinase

Considerable efforts have been taken to identify natural peptides as potential bioactive substances. In this study, novel peptide (SHP-1) derived from seahorse (Hippocampus, Syngnathidae) hydrolysate was explored for its inhibitory effects on collagen release in arthritis with the investigation of its underlying mechanism of action. The efficacy of SHP-1 was determined on cartilage protective effects such as inhibition of collagen and GAG release. SHP-1 was able to suppress not only the expression of collagenases 1 and 3, but also the production of NO via down-regulation of iNOS. However, it presented an irrelevant effect on the level of GAG release in chondrocytic and osteoblastic cells. Inhibition of collagen release by SHP-1 is associated with restraining the phosphorylation of NF-kappaB and p38 kinase cascade. Therefore, it could be suggested that SHP-1 has a potential to be used in arthritis treatment.

Therapeutic effect of Aralia cordata extracts on cartilage protection in collagenase-induced inflammatory arthritis rabbit model

AIM OF THIS STUDY

Aralia cordata has been used to alleviate symptoms of osteoarthritis (OA) in traditional medicine. However, there is no in vivo study related with the therapeutic effects and mechanisms of Aralia cordata. On the basis of this background, our study was designed to examine the cartilage protective and proliferative effects of Aralia cordata by using a collagenase-induced osteoarthritis (CIA) rabbit model.

MATERIALS AND METHODS

The right knees of rabbits were injected intra-articularly with collagenase, and rabbits were orally administered with distilled water (vehicle), Aralia cordata (200mg/kg) and celecoxib (100mg/kg) once a day for 28 days after the initiation of the CIA.

RESULTS

In histopathologic studying by using H&E and Safranin O staining, Aralia cordata showed a cartilage protective effect in CIA rabbit femoral condyle. However, celecoxib had no effect on cartilage protection in CIA. The inflammatory mediators involved in cartilage destruction, such as COX-2 and PGE(2), were inhibited in the Aralia cordata-treated group. Aralia cordata also showed an anti-apoptotic effect through suppression of caspase-3 activity and chondrocyte proliferation induction in both in vivo and in vitro.

CONCLUSION

These results indicate that Aralia cordata showed cartilage protective effects through the down-regulations of COX-2 expression, PGE(2) production, caspase-3 activity, and chondrocyte proliferation in the CIA rabbit model.

Regulation of prostaglandin E(2) synthesis in cells derived from chondrocytes of patients with osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a disorder that causes pain and degeneration of the joint over a chronic time course. Chondrocytes in OA play important roles in maintaining the homeostasis of the joint while they produce many cytokines and pathological mediators, including interleukin-1beta (IL-1beta), cyclooxygenases (COX), and prostaglandin E(2) (PGE(2)). To elucidate the mechanisms of pain due to OA, the pathway of PGE(2) synthesis was analyzed using cells derived from chondrocytes obtained from patients with OA.

METHODS

Chondrocytes were isolated from cartilage samples obtained at the time of joint replacement surgery from patients with OA. The chondrocytes at the second passage were cultured with or without IL-1beta, dexamethasone (DEX), or COX inhibitors such as NS-398, meloxicam, and indomethacin. Reverse transcription-polymerase chain reaction and Western blotting analysis were performed to study the levels of mRNA and protein, respectively. An enzyme-linked immunosorbent assay was performed to investigate the translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus, and Western blotting analysis was performed to study the phosphorylation of mitogen-activated protein kinases.

RESULTS

IL-1beta markedly enhanced the expression of COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) at both the mRNA and protein levels. The up-regulation was suppressed by DEX or COX inhibitors. IL-1beta strongly increased the translocation of NF-kappaB to the nucleus and the phosphorylation of extracellular-signal-regulated kinase, p38, and c-Jun amino-terminal kinase; but the up-regulation was not inhibited by DEX or COX inhibitors. Interestingly, in a dose-dependent manner, PGE(2) recovered mPGES-1 expression from suppression by DEX, whereas it did not restore the expression of COX-2 in the presence of DEX and IL-1beta.

CONCLUSIONS

These results suggested that in cells derived from OA chondrocytes different mechanisms of regulation exist between mPGES-1 and COX-2, and the expression of mPGES-1 was, at least partially, regulated through the autocrine positive feedback by PGE(2).

Glutamate signaling in chondrocytes and the potential involvement of NMDA receptors in cell proliferation and inflammatory gene expression

OBJECTIVE

Increased levels of glutamate, the main excitatory neurotransmitter, are found in the synovial fluid of osteoarthritis (OA) patients. Our aim was to study glutamate signaling in chondrocytes, focusing on the composition, pharmacology, and functional role of N-methyl-d-aspartate (NMDA) glutamate receptors.

METHODS

We used the human chondrocyte cell line SW1353 and, in parallel, primary rat articular chondrocytes. Glutamate release and uptake were measured by fluorimetric and radiometric methods, respectively. Gene expression was analyzed by quantitative polymerase chain reaction. NMDA receptor pharmacology was studied in binding experiments with [3H]MK-801, a specific NMDA receptor antagonist. RNA interference was used to knock-down the expression of NR1, a subunit of NMDA receptors.

RESULTS

Glutamate release, sodium- and calcium-dependent glutamate uptake, and the expression of a glutamate transporter were observed in chondrocytes. NR2D was the most abundant NMDA receptor subunit in these cells. Consistent with this observation, the binding affinity of [3H]MK-801 was much lower in chondrocytes than in rat brain membranes (mean K(d) values of 700 and 2.6 nM, respectively). NR1 knock-down, as well as NMDA receptor blockade with MK-801, reduced chondrocyte proliferation. Interleukin (IL)-1beta significantly altered glutamate release and uptake (about 90% increase and 50% decrease, respectively, in SW1353 cells). Moreover, IL-1beta induced the gene expression of cytokines and enzymes involved in cartilage degradation, and MK-801 significantly inhibited this response.

CONCLUSIONS

Our findings suggest that chondrocytes express a self-sufficient machinery for glutamate signaling, including a peripheral NMDA receptor with unique properties. This receptor may have a role in the inflammatory process associated with cartilage degradation, thus emerging as a potential pharmacological target in OA.

Protective effects of butanol fraction from Betula platyphyla var. japonica on cartilage alterations in a rabbit collagenase-induced osteoarthritis

AIM OF THIS STUDY

Many cartilage protective agents have been developed from natural products, and they have resulted in the development of treatments for osteoarthritis. In this study, we determined the osteoarthritic efficacy and mechanism of butanol fraction from the bark of Betula platyphylla var. japonica (BFBP) in collagenase-induced rabbit model of osteoarthritis (CIA).

MATERIALS AND METHODS

The right knees of rabbits were injected intra-articularly with collagenase, and rabbits were orally administrated with distilled water (vehicle), BFBP (50, 100 and 200 mg/kg) or celecoxib (100 mg/kg) once a day for 28 days after the initiation of the CIA.

RESULTS

Oral administration of BFBP dose-dependently suppressed the stiffness and global histologic score. Proteoglycan intensity was considerably increased in a dose-dependent manner. As well, the mRNA expression of MMP-1, and MMP-3 was decreased. On the contrary, the level of TIMP-1 in the synovial fluids was significantly increased in the BFBP treated group. The pathologic inflammatory molecules such as PGE2 and COX-2 were inhibited by BFBP, but COX-1 expression not affected.

CONCLUSION

We suggest that BFBP has shown the protective effect on cartilage alternations through balance of MMPs/TIMP-1 and regulates inflammatory-related molecules in vivo model of osteoarthritis, and great candidate for development of osteoarthritis treatment.

Cyclic AMP regulates extracellular matrix gene expression and metabolism in cultured primary rat chondrocytes

In osteo- and rheumatoid arthritis, the synovial fluid surrounding chondrocytes contains increased levels of prostaglandin E(2) (PGE(2)), an agent known to elevate intracellular cyclic AMP (cAMP). However, the effect of PGE(2)/cAMP on mRNA expression in chondrocytes is largely unknown. In this report, we assess the effect of the cell-permeable cAMP analog adenosine 8-(4-chloro-phenylthio)-3',5'-cyclic monophosphate (CPT-cAMP) and PGE(2) on mRNA expression in primary neonatal rat chondrocytes. CPT-cAMP decreased type II collagen, link protein, parathyroid hormone/parathyroid hormone-related peptide receptor and alkaline phosphatase, increased glyceraldehyde-3-phosphate dehydrogenase mRNA and lactate efflux, but did not alter type X collagen or aggrecan mRNA. The effect of CPT-cAMP on type II collagen and link protein mRNAs and chondrocyte metabolism were attenuated by the transcriptional inhibitor actinomycin D, indicating that the ability of CPT-cAMP to suppress mRNA expression was not due to alterations in mRNA stability, but were instead likely due to transcriptional mechanisms. CPT-cAMP-treatment induced GSK3 beta phosphorylation and beta-catenin-mediated transcriptional activity. Pharmacological inhibition of GSK3 beta paralleled the effects of CPT-cAMP on type II collagen, link protein and chondrocyte metabolism, suggesting that the effect of CPT-cAMP on chondrocytes may be GSK3 beta/beta-catenin-dependent. The effects of CPT-cAMP on beta-catenin-mediated transcription, cell metabolism and mRNA expression were mimicked by the cAMP-elevating agent PGE(2), providing a physiologically relevant context for our studies. Collectively, these results suggest that agents that elevate cAMP signaling may impair chondrocyte function in conditions such as arthritis.

Tophaceous pseudogout of the femorotibial joint in a painted turtle (Chrysemys picta)

A 5-year-old painted turtle (Chrysemys picta) presented with a 1cm nodular enlargement of the right femorotibial joint. The right leg was amputated, because the nodule continued to grow and motor problems appeared. The cut surface of the nodule was yellowish white, and had a colloidal to chalky gross appearance. Microscopically, a multinodular foreign-body granuloma was observed around the joint capsule. Morphological and histochemical examination showed that the foreign body consisted of calcium pyrophosphate. Histological findings revealed that the articular cartilage was mainly involved in the pathological onset of the disease, and was therefore diagnosed as tophaceous pseudogout. This disease is generic in elderly people, but is rare in animals. Also, there are only three reports in reptiles.

Meniscal tissue explants response depends on level of dynamic compressive strain

OBJECTIVE

Following partial meniscectomy, the remaining meniscus is exposed to an altered loading environment. In vitro 20% dynamic compressive strains on meniscal tissue explants has been shown to lead to an increase in release of glycosaminoglycans from the tissue and increased expression of interleukin-1alpha (IL-1alpha). The goal of this study was to determine if compressive loading which induces endogenously expressed IL-1 results in downstream changes in gene expression of anabolic and catabolic molecules in meniscal tissue, such as MMP expression.

METHOD

Relative changes in gene expression of MMP-1, MMP-3, MMP-9, MMP-13, A Disintegrin and Metalloproteinase with ThromboSpondin 4 (ADAMTS4), ADAMTS5, TNFalpha, TGFbeta, COX-2, Type I collagen (COL-1) and aggrecan and subsequent changes in the concentration of prostaglandin E(2) released by meniscal tissue in response to varying levels of dynamic compression (0%, 10%, and 20%) were measured. Porcine meniscal explants were dynamically compressed for 2h at 1Hz.

RESULTS

20% dynamic compressive strains upregulated MMP-1, MMP-3, MMP-13 and ADAMTS4 compared to no dynamic loading. Aggrecan, COX-2, and ADAMTS5 gene expression were upregulated under 10% strain compared to no dynamic loading while COL-1, TIMP-1, and TGFbeta gene expression were not dependent on the magnitude of loading.

CONCLUSION

This data suggests that changes in mechanical loading of the knee joint meniscus from 10% to 20% dynamic strain can increase the catabolic activity of the meniscus.

Liposomal dexamethasone-diclofenac combinations for local osteoarthritis treatment

Conventional chronic and acute treatments for osteoarthritis (OA) are by oral NSAIDs (such as diclofenac) and intra-articular injected glucocorticosteroids (such as dexamethasone). In free form, diclofenac and dexamethasone generate severe adverse effects with risks of toxicity. To reduce these drawbacks, we investigated local injections of liposomal formulations for diclofenac and dexamethasone (each alone, and their combination). Bioadhesive liposomes carrying hyaluronan (HA-BAL) or collagen (COL-BAL) as their surface-anchored ligand were used for the task. Each drug alone or their combination showed high efficiency encapsulations (> or =80%) and performance as slow-release depots (half-lives in the range of 1-3 days under the fastest conditions). Employing RIA and immunoblot assay techniques, it was verified that the encapsulated drugs retained their biological activities: inhibitions of Cyclooxygenases enzyme-activity (diclofenac) and of Cyclooxygenases protein-expression (dexamethasone). Using live-animal MRI, a single intra-articular injection of each liposome-drug(s) formulation sufficed to reduce knee joint inflammation in OA rats over a time span of 17 days, HA-BAL better than COL-BAL. The most effective treatment was by the combination of both drugs in HA-BAL, a single dose reducing the inflammation volume down to 12.9% from initial over that time span. We find all three HA-BAL formulations worthy of further studies.

A suppressive effect of prostaglandin E2 on the expression of SERPINE1/plasminogen activator inhibitor-1 in human articular chondrocytes: An in vitro pilot study

Prostaglandin E₂ (PGE₂) is expressed in articular joints with inflammatory arthropathy and may exert catabolic effects leading to cartilage degradation. As we observed in a preliminary experiment that PGE₂ suppressed the expression of SERPINE1/plasminogen activator inhibitor (PAI)-1 mRNA in chondrocytes, we focused on the effect of PGE₂ on PAI-1 in a panel of cultured chondrocytes obtained from osteoarthritic patients. Specifically, articular cartilage specimens were obtained from patients with osteoarthritis who underwent joint surgery. Isolated chondrocytes were cultured in vitro as a monolayer and stimulated with PGE₂. Stimulated cells and culture supernatants were analyzed using Western blotting and enzyme-linked immunosorbent assay. The results confirmed that the in vitro PGE₂ stimulation suppressed the expression of PAI-1 in the tested chondrocyte samples. The inhibitory effect was partly abrogated by an antagonist of EP4 receptor of PGE₂, but not by an EP2 antagonist. Although PGE₂ induced activations of mitogen-activated protein kinases (MAPK), blocking of the MAPK did not abrogate the suppressive effect of PGE₂, implying a distinct signaling pathway. In summary, prostaglandin is suggested to modulate the plasminogen system in chondrocytes. Further elucidation of the interaction might open a new avenue to understand the degradative process of cartilage.

Heme oxygenase-1 induction modulates microsomal prostaglandin E synthase-1 expression and prostaglandin E(2) production in osteoarthritic chondrocytes

Pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) may participate in the pathogenesis of cartilage damage in osteoarthritis (OA) through the production of catabolic enzymes and inflammatory mediators. Induction of heme oxygenase-1 (HO-1) has previously been shown to exert anti-inflammatory effects in different cell types. We have investigated whether HO-1 induction may modify chondrocyte viability and the production of relevant mediators such as oxidative stress and prostaglandin E(2) (PGE(2)) elicited by IL-1beta in OA chondrocytes. Chondrocytes were isolated from OA cartilage and used in primary culture. Cells were stimulated with IL-1beta in the absence or presence of the HO-1 inducer cobalt protoporphyrin IX (CoPP). Gene expression was assessed by quantitative real-time PCR, protein levels by ELISA and Western blot, apoptosis by laser scanning cytometry using annexin V-FITC and TUNEL assays, and oxidative stress by LSC with dihydrorhodamine 123. HO-1 induction by CoPP enhanced chondrocyte viability and aggrecan content while inhibiting apoptosis and oxidative stress generation. PGE(2) is produced in OA chondrocytes stimulated by IL-1beta by the coordinated induction of cyclooxygenase-2 and microsomal PGE synthase 1 (mPGES-1). The production of PGE(2) was decreased by HO-1 induction as a result of diminished mPGES-1 protein and mRNA expression. Transfection with HO-1 small interfering RNA counteracted CoPP effects. In addition, the activation of nuclear factor-kappaB and early growth response-1 was significantly reduced by CoPP providing a basis for its anti-inflammatory effects. These results confirm the protective role of HO-1 induction in OA chondrocytes and suggest the potential interest of this strategy in degenerative joint diseases.

Prostaglandin E2 and its cognate EP receptors control human adult articular cartilage homeostasis and are linked to the pathophysiology of osteoarthritis

OBJECTIVE

To elucidate the pathophysiologic links between prostaglandin E(2) (PGE(2)) and osteoarthritis (OA) by characterizing the catabolic effects of PGE(2) and its unique receptors in human adult articular chondrocytes.

METHODS

Human adult articular chondrocytes were cultured in monolayer or alginate beads with and without PGE(2) and/or agonists of EP receptors, antagonists of EP receptors, and cytokines. Cell survival, proliferation, and total proteoglycan synthesis and accumulation were measured in alginate beads. Chondrocyte-related gene expression and phosphatidylinositol 3-kinase/Akt signaling were assessed by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively, using a monolayer cell culture model.

RESULTS

Stimulation of human articular chondrocytes with PGE(2) through the EP2 receptor suppressed proteoglycan accumulation and synthesis, suppressed aggrecan gene expression, did not appreciably affect expression of matrix-degrading enzymes, and decreased the type II collagen:type I collagen ratio. EP2 and EP4 receptors were expressed at higher levels in knee cartilage than in ankle cartilage and in a grade-dependent manner. PGE(2) titration combined with interleukin-1 (IL-1) synergistically accelerated expression of pain-associated molecules such as inducible nitric oxide synthase and IL-6. Finally, stimulation with exogenous PGE(2) or an EP2 receptor-specific agonist inhibited activation of Akt that was induced by insulin-like growth factor 1.

CONCLUSION

PGE(2) exerts an antianabolic effect on human adult articular cartilage in vitro, and EP2 and EP4 receptor antagonists may represent effective therapeutic agents for the treatment of OA.

Inhibition of cyclooxygenase 2 expression by diallyl sulfide on joint inflammation induced by urate crystal and IL-1beta

OBJECTIVE

Investigation of the effects of diallyl sulfide (DAS), a garlic sulfur compound, on joint tissue inflammatory responses induced by monosodium urate (MSU) crystals and interleukin-1beta (IL-1beta).

DESIGN

The HIG-82 synovial cell line was used to establish the experimental model and DAS regime. Primary cultures of articular chondrocytes and synovial fibroblasts obtained from patients undergoing joint replacement for osteoarthritis were used in experimental studies. Cyclooxygenase (COX) expression following MSU crystal and IL-1beta stimulation with/without DAS co-incubation was assessed by reverse transcription-polymerase chain reaction (RT-PCR), western blotting, and immunocytochemistry and nuclear factor-kappa B (NF-kappaB) activation determined by electrophoretic mobility shift assay. Prostaglandin E2 (PGE(2)) production was measured by enzyme-linked immunosorbent assay (ELISA). DAS effects on COX gene expression in an MSU crystal-induced acute arthritis in rats were assessed by RT-PCR.

RESULTS

MSU crystals upregulated COX-2 expression in HIG-82 cells and this was inhibited by co-incubation with DAS. DAS inhibited MSU crystal and IL-1beta induced elevation of COX-2 expression in primary synovial cells and chondrocytes. Production of PGE(2) induced by crystals was suppressed by DAS and celecoxib. MSU crystals had no effect on expression of COX-1 in synovial cells. NF-kappaB was activated by MSU crystals and this was blocked by DAS. Increased expression of COX-2 in synovium following intraarticular injection of MSU crystals in a rat model was inhibited by co-administration of DAS.

CONCLUSIONS

DAS prevents IL-1beta and MSU crystal induced COX-2 upregulation in synovial cells and chondrocytes and ameliorates crystal induced synovitis potentially through a mechanism involving NF-kappaB. Anti-inflammatory actions of DAS may be of value in treatment of joint inflammation.

Prostaglandin E2 exerts catabolic effects in osteoarthritis cartilage: evidence for signaling via the EP4 receptor

Elevated levels of PGE(2) have been reported in synovial fluid and cartilage from patients with osteoarthritis (OA). However, the functions of PGE(2) in cartilage metabolism have not previously been studied in detail. To do so, we cultured cartilage explants, obtained from patients undergoing knee replacement surgery for advanced OA, with PGE(2) (0.1-10 muM). PGE(2) inhibited proteoglycan synthesis in a dose-dependent manner (maximum 25% inhibition (p < 0.01)). PGE(2) also induced collagen degradation, in a manner inhibitable by the matrix metalloproteinase (MMP) inhibitor ilomastat. PGE(2) inhibited spontaneous MMP-1, but augmented MMP-13 secretion by OA cartilage explant cultures. PCR analysis of OA chondrocytes treated with PGE(2) with or without IL-1 revealed that IL-1-induced MMP-13 expression was augmented by PGE(2) and significantly inhibited by the cycolooygenase 2 selective inhibitor celecoxib. Conversely, MMP-1 expression was inhibited by PGE(2), while celecoxib enhanced both spontaneous and IL-1-induced expression. IL-1 induction of aggrecanase 5 (ADAMTS-5), but not ADAMTS-4, was also enhanced by PGE(2) (10 muM) and reversed by celecoxib (2 muM). Quantitative PCR screening of nondiseased and end-stage human knee OA articular cartilage specimens revealed that the PGE(2) receptor EP4 was up-regulated in OA cartilage. Moreover, blocking the EP4 receptor (EP4 antagonist, AH23848) mimicked celecoxib by inhibiting MMP-13, ADAMST-5 expression, and proteoglycan degradation. These results suggest that PGE(2) inhibits proteoglycan synthesis and stimulates matrix degradation in OA chondrocytes via the EP4 receptor. Targeting EP4, rather than cyclooxygenase 2, could represent a future strategy for OA disease modification.

Long-term NSAID treatment directly decreases COX-2 and mPGES-1 production in the articular cartilage of patients with osteoarthritis

OBJECTIVE

To simultaneously study the effect of a selective cyclooxygenase-2 (COX-2) inhibitor and that of a classic non-steroidal anti-inflammatory drug (NSAID) on the expression of pro-inflammatory genes in the cartilage of patients with severe knee osteoarthritis (OA) and in cultured human OA chondrocytes.

METHODS

A 3-month clinical trial was carried out on 30 patients with severe knee OA scheduled for knee replacement surgery. Patients were randomized into two groups: patients treated with celecoxib (CBX) and patients treated with aceclofenac (ACF). OA patients who did not want to be treated served as the control group. After surgery, cartilage was processed for molecular biology studies. We also employed cultured chondrocytes from different OA patients to examine NSAID effects on pro-inflammatory gene expression in cells stimulated with interleukin (IL)-1beta.

RESULTS

Both CBX and ACF inhibited COX-2, microsomal prostaglandin E synthase-1 (mPGES-1) and inducible nitric oxide synthase (iNOS) synthesis in the articular cartilage of OA patients. In cultured chondrocytes, both NSAID decreased COX-2 and mPGES-1 synthesis and prostaglandin E2 (PGE2) release induced by IL-1beta, while no effect was observed on nitric oxide or iNOS synthesis. In OA patients, only CBX decreased tumor necrosis factor alpha and IL-1beta expression in the cartilage, while both NSAID diminished IL-1beta induced cytokine synthesis in cultured OA chondrocytes.

CONCLUSIONS

Both NSAID diminished PGE2 release and induced a decrease in COX-2 and mPGES-1 synthesis in the cartilage from OA patients and in OA chondrocytes. These data suggest that prolonged therapy with PGE2 blocking agents decreases PGE2 production not only by direct inhibition of COX-2 activity, but also by down-regulating COX-2 and mPGES-1 synthesis in the cartilage. However, CBX and ACF seem to have a different anti-inflammatory profile in controlling pro-inflammatory gene expression in the cartilage.

Mechanism of basic calcium phosphate crystal-stimulated matrix metalloproteinase-13 expression by osteoarthritic synovial fibroblasts: inhibition by prostaglandin E2

OBJECTIVE

To determine the mechanism of matrix metalloproteinase (MMP)-13 upregulation in osteoarthritic synovial fibroblasts (OASF) in response to stimulation with basic calcium phosphate (BCP) crystals and to investigate the effect of prostaglandin (PG)E2 on BCP crystal-stimulated MMP expression.

METHODS

Primary OASF were stimulated with BCP crystals; mRNA expression was measured by real-time reverse transcription-polymerase chain reaction and protein levels were assessed by Western blotting.

RESULTS

BCP crystals upregulated MMP-13 mRNA expression over 20-fold and increased MMP-13 protein production in OASF. BCP crystal-stimulated MMP-13 mRNA expression was blocked by inhibition of the extracellular regulated kinase (ERK1/2) and p38 mitogen activated protein kinase (MAPK) pathways and inhibition of the activation of nuclear factor kappaB. Addition of exogenous PGE2 downregulated BCP crystal-stimulated MMP-13 expression. In contrast, PGE2 upregulated, and had no effect, on BCP crystal stimulated MMP-3 and MMP-1 mRNA expression, respectively. These effects of PGE2 were diminished by L-161,982, a selective EP4 receptor antagonist, and mimicked by CAY10399, a selective EP2 receptor agonist, and forskolin, an adenylate cyclase activator.

CONCLUSIONS

These data suggest that BCP crystal induction of MMP-13 expression may involve the ERK1/2 and p38 MAPK pathways and activation of nuclear factor kappaB; this upregulation of MMP-13 may contribute to the accelerated cartilage breakdown in BCP crystal-associated osteoarthritis. PGE2 had contrasting effects on BCP crystal-stimulated MMP-3 and MMP-13 mRNA expression, mediated in an EP2/EP4/cAMP-dependent manner, suggesting that PGE2 may have beneficial as well as deleterious effects in BCP crystal-associated osteoarthritis.

Histone deacetylase inhibitors suppress interleukin-1beta-induced nitric oxide and prostaglandin E2 production in human chondrocytes

OBJECTIVE

Overproduction of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) plays an important role in the pathogenesis of osteoarthritis (OA). In the present study, we determined the effect of trichostatin A (TSA) and butyric acid (BA), two histone deacetylase (HDAC) inhibitors, on NO and PGE(2) synthesis, inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 expression, and nuclear factor (NF)-kappaB DNA-binding activity, in interleukin-1beta (IL-1)-stimulated human OA chondrocytes, and on IL-1-induced proteoglycan degradation in cartilage explants.

METHODS

Chondrocytes were stimulated with IL-1 in the absence or presence of increasing concentrations of TSA or BA. The production of NO and PGE(2) was evaluated using Griess reagent and an enzyme immunoassay, respectively. The expression of iNOS and COX-2 proteins and mRNAs was evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), respectively. Proteoglycan degradation was measured with dimethymethylene blue assay. Electrophoretic mobility shift assay (EMSA) was utilized to analyze the DNA-binding activity of NF-kappaB.

RESULTS

HDAC inhibition with TSA or BA resulted in a dose-dependent inhibition of IL-1-induced NO and PGE(2) production. IL-17- and tumor necrosis factor-alpha (TNF-alpha)-induced NO and PGE(2) production was also inhibited by TSA and BA. This inhibition correlated with the suppression of iNOS and COX-2 protein and mRNA expression. TSA and BA also prevented IL-1-induced proteoglycan release from cartilage explants. Finally, we demonstrate that the DNA-binding activity of NF-kappaB, was induced by IL-1, but was not affected by treatment with HDAC inhibitors.

CONCLUSIONS

These data indicate that HDAC inhibitors suppressed IL-1-induced NO and PGE(2) synthesis, iNOS and COX-2 expression, as well as proteoglycan degradation. The suppressive effect of HDAC inhibitors is not due to impaired DNA-binding activity of NF-kappaB. These findings also suggest that HDAC inhibitors may be of potential therapeutic value in the treatment of OA.

IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains

OBJECTIVE

Partial meniscectomy is known to cause osteoarthritis (OA) of the underlying cartilage as well as alter the load on the remaining meniscus. Removal of 30-60% of the medial meniscus increases compressive strains from a maximum of approximately 10% to almost 20%. The goal of this study is to determine if meniscal cells produce catabolic molecules in response to the altered loading that results from a partial meniscectomy.

METHOD

Relative changes in gene expression of interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and subsequent changes in the concentration of nitric oxide (NO) released by meniscal tissue in response to compression were measured. Porcine meniscal explants were dynamically compressed for 2 h at 1 Hz to simulate physiological stimulation at either 10% strain or 0.05 MPa stress. Additional explants were pathologically stimulated to either 0% strain, 20% strain or, 0.1 MPa stress.

RESULTS

iNOS and IL-1 gene expression and NO release into the surrounding media were increased at 20% compressive strain compared to other conditions. Pathological unloading (0% compressive strain) of meniscal explants did not significantly change expression of IL-1 or iNOS genes, but did result in an increased amount of NO released compared to physiological strain of 10%.

CONCLUSION

These data suggest that meniscectomies which reduce the surface area of the meniscus by 30-60% will increase the catabolic activity of the meniscus which may contribute to the progression of OA.

Role of fibroblast growth factor 8 (FGF8) in animal models of osteoarthritis

INTRODUCTION

Fibroblast growth factor 8 (FGF8) is isolated as an androgen-induced growth factor, and has recently been shown to contribute to limb morphogenesis. The aim of the present study was to clarify the role of FGF8 in animal models of osteoarthritis (OA).

METHODS

The expression of FGF8 in the partial meniscectomy model of OA in the rabbit knee was examined by immunohistochemistry. The effect of intraperitoneal administration of anti-FGF8 antibody was tested in a model of OA that employed injection of monoiodoacetic acid or FGF8 into the knee joint of rats. The effect of FGF8 was also tested using cultured chondrocytes. Rabbit articular chondrocytes were treated with FGF8 for 48 hours, and the production of matrix metalloproteinase and the degradation of sulfated glycosaminoglycan in the extracellular matrix (ECM) were measured.

RESULTS

The expression of FGF8 in hyperplastic synovial cells and fibroblasts was induced in the meniscectomized OA model, whereas little or no expression was detected in normal synovium. Injection of FGF8 into rat knee joints induced the degradation of the ECM, which was suppressed by anti-FGF8 antibody. In the monoiodoacetic acid-induced arthritis model, anti-FGF8 antibody reduced ECM release into the synovial cavity. In cultured chondrocytes, FGF8 induced the release of matrix metalloproteinase 3 and prostaglandin E2, and caused degradation of the ECM. The combination of FGF8 and IL-1alpha accelerated the degradation of the ECM. Anti-FGF8 antibody suppressed the effects of FGF8 on the cells.

CONCLUSION

FGF8 is produced by injured synovium and enhances the production of protease and prostaglandin E2 from inflamed synoviocytes. Degradation of the ECM is enhanced by FGF8. FGF8 may therefore participate in the degradation of cartilage and exacerbation of osteoarthritis.

The CO-releasing molecule CORM-2 is a novel regulator of the inflammatory process in osteoarthritic chondrocytes

OBJECTIVES

Previous work has shown that the CO-releasing molecule CORM-2 protects against cartilage degradation. The aim of this study was to examine whether CORM-2 can control the production of inflammatory mediators in osteoarthritic chondrocytes and determine the mechanisms involved.

METHODS

Primary cultures of chondrocytes from OA patients were stimulated with IL-1beta. The production of reactive oxygen species, nitrite, PGE(2), TNF-alpha and IL-1 receptor antagonist (IL-1Ra) were measured in the presence or absence of CORM-2. The expression of nitric oxide synthase-2 (NOS-2), cyclo-oxygenase-2 (COX-2) and microsomal PG E synthase-1 (mPGES-1) was followed by western blot and real-time PCR. Activation of nuclear factor-kappaB (NF-kappaB) and hypoxia inducible factor-1alpha (HIF-1alpha), and phosphorylation of NF-kappaB inhibitory protein alpha (IkappaBalpha) were determined by ELISA.

RESULTS

CORM-2 decreased the production of oxidative stress, nitrite and PGE(2). In addition, CORM-2 inhibited IL-1beta-induced TNF-alpha but enhanced IL-1Ra production. Treatment of chondrocytes with CORM-2 strongly down-regulated NOS-2 and mPGES-1 protein expression, whereas COX-2 was reduced to a lesser extent. These changes were accompanied by a significant decrease in mRNA expression for NOS-2 and mPGES-1. CORM-2 showed a concentration-dependent inhibition of DNA-binding activity for p65 NF-kappaB and HIF-1alpha. IkappaBalpha phosphorylation was also reduced by CORM-2 treatment.

CONCLUSIONS

These data have opened new mechanisms of action for CORM-2, raising the prospect that CO-releasing molecules are an interesting strategy for the development of new treatments in articular conditions.

Genome-wide association scan identifies a prostaglandin-endoperoxide synthase 2 variant involved in risk of knee osteoarthritis

Osteoarthritis (OA), the most prevalent form of arthritis in the elderly, is characterized by the degradation of articular cartilage and has a strong genetic component. Our aim was to identify genetic variants involved in risk of knee OA in women. A pooled genome-wide association scan with the Illumina550 Duo array was performed in 255 controls and 387 cases. Twenty-eight variants with p < 1 x 10(-5) were estimated to have probabilities of being false positives Collapse

Key Words Collapse

MESH Headings

• Aged
• Aged, 80 and over
• Alleles
• Base Sequence
• Case-Control Studies
• Chondrocytes/enzymology
• Cohort Studies
• Cyclooxygenase 2/genetics
• DNA Primers/genetics
• Female
• Genetic Predisposition to Disease
• Genetic Variation
• Genomics
• Group IV Phospholipases A2/genetics
• Humans
• Linkage Disequilibrium
• Middle Aged
• Oligonucleotide Array Sequence Analysis
• Osteoarthritis, Knee/enzymology
• Osteoarthritis, Knee/genetics
• Polymorphism, Single Nucleotide
• RNA, Messenger/genetics
• Risk Factors

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Grants

• Wellcome Trust
• 17489 Arthritis Research UK

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Affiliation(s)

Ana M Valdes Twin Research Unit, St. Thomas' Hospital Campus, Kings College London School of Medicine, London SE1 7EH, UK.
John Loughlin
Kirsten M Timms
Joyce J B van Meurs
Lorraine Southam
Scott G Wilson
Sally Doherty
Rik J Lories
Frank P Luyten
Alexander Gutin
Victor Abkevich
Dongliang Ge
Albert Hofman
André G Uitterlinden
Deborah J Hart
Feng Zhang
Guangju Zhai
Rainer J Egli
Michael Doherty
Jerry Lanchbury
Tim D Spector

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Collaborators Collapse

Involvement of the p38 MAPK-NF-kappaB signal transduction pathway and COX-2 in the pathobiology of meniscus degeneration in humans

Meniscal tears are attributed to either trauma or degeneration processes. Clinical data suggest that meniscal degeneration (MD) is associated with knee osteoarthritis; however, the molecular events underpinning the pathogenesis of MD in humans remain elusive. Here we immunohistochemically examined the expression of p38 MAPK, its phosphorylated/activated form (p-p38), its target NF-kappaB (p50-p65 dimer), and COX-2 in ruptured menisci and investigated their involvement in MD development. Our findings demonstrate increased expression of the p38-NF-kappaB axis elements and COX-2 in disintegrated fibrocartilage, suggesting a role of these molecules in the pathobiochemistry of MD and consequential rupture.

The multicomponent phytopharmaceutical SKI306X inhibits in vitro cartilage degradation and the production of inflammatory mediators

Clinical studies have demonstrated that SKI306X, a purified preparation of three medicinal plants, relieves joint pain and improves functionality in osteoarthritis patients. To study the biological action of SKI306X, bovine cartilage explants and human peripheral blood mononuclear cells (PBMC) were stimulated with IL-1 beta and lipopolysaccharide (LPS) respectively, in the presence or absence of SKI306X and its individual composites. All tested compounds inhibited dose-dependently IL-1 beta-induced proteoglycan release and nitric oxide production by cartilage, indicating cartilage protective activity. SKI306X and two of its compounds inhibited PGE(2), TNF-alpha and IL-1 beta production by LPS-stimulated PBMC, indicating anti-inflammatory activity. These results demonstrate that the biological effect of SKI306X is at least bipartite: (1) cartilage protective and (2) anti-inflammatory. The observed anti-inflammatory effects may provide an explanation for the outcome of the clinical studies. Long-term clinical trails are necessary to elucidate whether the in vitro cartilage protective activity results in disease-modifying effects.

Aurothiomalate inhibits COX-2 expression in chondrocytes and in human cartilage possibly through its effects on COX-2 mRNA stability

Cyclooxygenase-2 (COX-2) is expressed in rheumatoid and osteoarthritic cartilage and produces pro-inflammatory prostanoids in the joint. In the present study, we investigated the effects of disease modifying anti-rheumatic drugs on COX-2 expression in chondrocytes. Unlike the other tested drugs, aurothiomalate was found to inhibit COX-2 expression in chondrocytes. In the further studies, effects and mechanisms of action of aurothiomalate were investigated in more detail. Aurothiomalate inhibited IL-1beta-induced COX-2 protein expression and PGE(2) production in chondrocytes in a dose-dependent manner. Because aurothiomalate did not alter IL-1beta-induced mRNA levels when measured 0-3 h after addition of IL-1beta, its effects on COX-2 mRNA degradation were tested by Actinomycin D assay. The half-life of COX-2 mRNA was reduced from 3 h to less than 1.5 h in aurothiomalate-treated cells. The 3'-untranslated region (3'-UTR) of COX-2 mRNA contains an ARE element which has been shown to bind mRNA stabilizing factor HuR. Interestingly, aurothiomalate inhibited HuR expression which may explain its destabilizing effect on COX-2 mRNA. Aurothiomalate reduced COX-2 expression and PGE(2) production also in human cartilage at drug concentrations which have been measured in serum and synovial fluid during treatment with aurothiomalate. The results show that aurothiomalate reduces COX-2 expression and PGE(2) production in chondrocyte cultures and in human cartilage. The action is likely mediated by enhanced COX-2 mRNA degradation possibly through a mechanism related to reduced expression of HuR. The results provide a novel mechanism of action for aurothiomalate which may be important in the treatment of arthritis.

Cyclooxygenase inhibition lowers prostaglandin E2 release from articular cartilage and reduces apoptosis but not proteoglycan degradation following an impact load in vitro

This study investigated the release of prostaglandin E₂ (PGE₂) from cartilage following an impact load in vitro and the possible chondroprotective effect of cyclooxygenase-2 (COX-2) inhibition using non-steroidal anti-inflammatory drugs (NSAIDs).

Explants of human articular cartilage were subjected to a single impact load in a drop tower, and then cultured for 6 days in the presence of either a selective COX-2 inhibitor (celecoxib; 0.01, 0.1, 1.0 and 10 μM) or a non-selective COX inhibitor (indomethacin; 0.1 and 10 μM). The concentrations of PGE₂ and glycosaminoglycans (GAGs), a measure of cartilage breakdown, were measured in the explant culture medium at 3 and 6 days post-impact. Apoptotic cell death was measured in frozen explant sections by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) method.

PGE₂ levels were increased by more than 20-fold in the medium of explants at both 3 (p = 0.012) and 6 days (p = 0.004) following impact, compared with unloaded controls. In the presence of celecoxib and indomethacin, the PGE₂ levels were reduced in a dose-related manner. These inhibitors, however, had no effect in reducing the impact-induced release of GAGs from the cartilage matrix. Addition of celecoxib and indomethacin significantly reduced the number of trauma-induced apoptotic chondrocytes in cartilage explant sections.

In this study, a marked increase in PGE₂ was measured in the medium following an impact load on articular cartilage, which was abolished by the selective COX-2 inhibitor, celecoxib, and non-selective indomethacin. These inhibitors reduced chondrocyte apoptosis but no change was observed in the release of GAGs from the explants, suggesting that the COX/PGE₂ pathway is not directly responsible for cartilage breakdown following traumatic injury. Our in vitro study demonstrates that it is unlikely that COX-2 inhibition alone would slow down or prevent the development of secondary osteoarthritis.

Association of microsomal prostaglandin E synthase 1 deficiency with impaired fracture healing, but not with bone loss or osteoarthritis, in mouse models of skeletal disorders

OBJECTIVE

Prostaglandin E synthase (PGES) functions as the terminal enzyme in the biosynthesis of prostaglandin E(2) (PGE(2)) and is a potent regulator of bone and cartilage metabolism. Among the 3 isozymes of PGES, microsomal PGES-1 (mPGES-1) is known to play the most critical role in the production of PGE(2) in pathophysiologic events. This study investigated the roles of mPGES-1 under normal physiologic and pathophysiologic conditions in the skeletons of mPGES-1-deficient (mPGES-1(-/-)) mice.

METHODS

Skeletons of mPGES-1(-/-) mice and their wild-type littermates were compared by radiologic and histologic analyses. Four models of skeletal disorders were created: bone loss induced by ovariectomy, bone loss induced by hind limb unloading, osteoarthritis (OA) induced by instability in the knee joint, and bone fracture by osteotomy at the tibial midshaft. Expression of the PGES enzymes was examined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction. The cellular mechanism of fracture healing was examined in ex vivo cultures of costal cartilage chondrocytes.

RESULTS

Microsomal PGES-1(-/-) mice had unaffected skeletal phenotypes under normal physiologic conditions. In the bone fracture model, fracture healing was impaired by the mPGES-1 deficiency, with half of the mice remaining in a non-bone union state even after 21 days; normal fracture healing was restored by adenoviral reintroduction of mPGES-1. The other skeletal disorders were not affected by the mPGES-1 deficiency. In vivo and ex vivo analyses revealed an impaired proliferation of chondrocytes in cartilage with the mPGES-1 deficiency, at an early stage of fracture healing.

CONCLUSION

In these mouse models of skeletal disorders, mPGES-1 was indispensable for bone repair through chondrocyte proliferation, but was not essential for the skeleton under normal physiologic conditions, nor did it play a role in the pathophysiologic conditions of bone loss due to ovariectomy, bone loss due to unloading, or stress-induced OA.

Synthesis and release of human cartilage matrix proteoglycans are differently regulated by nitric oxide and prostaglandin-E2

OBJECTIVES

Recent studies showed beneficial effects of COX-2 inhibition on proteoglycan turnover of both IL-1beta/tumour necrosis factor alpha (TNFalpha) damaged cartilage and of osteoarthritic cartilage. Although proteoglycan release and content were normalised, proteoglycan synthesis was only partially influenced. Prostaglandin-E2 is the main product formed by COX-2. We therefore evaluate the role of prostaglandin-E2 in relation to nitric oxide in disturbing cartilage proteoglycan turnover.

METHODS

Human healthy cartilage, alone or in the presence of IL-1beta+TNFalpha, was cultured for 7 days with or without prostaglandin-E2 or the selective COX-2 inhibitor (celecoxib 10 microM). Changes in cartilage matrix proteoglycan turnover, levels of prostaglandin-E2 and nitric oxide were determined.

RESULTS

Proteoglycan synthesis and release of the cartilage were not affected by prostaglandin-E2 alone. Addition of IL-1beta+TNFalpha to healthy cartilage resulted in inhibition of proteoglycan synthesis and increase in proteoglycan release. When prostaglandin-E2 was added, in addition to IL-1beta+TNFalpha, proteoglycan release increased further, but proteoglycan synthesis was not influenced further. Addition of a selective COX-2 inhibitor to the IL-1beta+TNFalpha treated cartilage inhibited the enhanced prostaglandin-E2 production and almost completely normalised proteoglycan release, whereas synthesis remained unaffected. Also, the enhanced NO-levels remained elevated. Prostaglandin-E2 levels correlated significantly with proteoglycan release, whereas NO levels correlated significantly with proteoglycan synthesis.

CONCLUSION

The present results suggest involvement of prostaglandin-E2 in enhanced cartilage proteoglycan release but not synthesis, although healthy cartilage has to be sensitised by IL-1beta+tumour necrosis factor alpha (TNFalpha). IL-1beta+TNFalpha induced NO seems to be involved in inhibition of proteoglycan synthesis, independent of prostaglandin-E2, and thus seems insensitive to regulation by (selective) COX-2 inhibitors.

Transforming growth factor alpha suppression of articular chondrocyte phenotype and Sox9 expression in a rat model of osteoarthritis

OBJECTIVE

To define the roles of transforming growth factor alpha (TGFalpha) in cartilage degradation.

METHODS

Primary rat articular chondrocytes and articular osteochondral explants were cultured with TGFalpha to assess the effects of TGFalpha on chondrocyte physiology and phenotype.

RESULTS

TGFalpha altered chondrocyte morphology through reorganization of the actin cytoskeleton and formation of stress fibers. Expression of anabolic genes, including aggrecan, type II collagen, and cartilage link protein, was reduced in response to TGFalpha. Proliferation of chondrocytes and formation of articular chondrocyte clusters was stimulated by TGFalpha. Expression of matrix metalloproteinase 13 and cathepsin C was increased by TGFalpha. We demonstrated the down-regulation of Sox9 messenger RNA and protein levels by TGFalpha. This was associated with reduced levels of phosphorylated and total SOX9 in cartilage explants upon TGFalpha treatment. In contrast, another growth factor identified in our microarrays, Kitl, had no effects on the chondrocyte parameters tested. To examine correlations between the increased levels of TGFalpha in experimental knee osteoarthritis (OA) with the levels of TGFalpha in humans with knee OA, a microarray analysis of mRNA from 13 normal and 12 late-stage OA cartilage samples was performed. Seven OA samples showed TGFA mRNA levels similar to those in the normal controls, but expression was markedly increased in the other 5 OA samples. These data confirm that TGFA transcript levels are increased in a subset of patients with OA.

CONCLUSION

This study adds TGFalpha to the list of dysregulated cytokines present in degrading cartilage in OA. Since TGFalpha inhibits articular chondrocyte anabolic capacity, increases catabolic factors, and contributes to the development of chondrocyte clusters, TGFalpha may be a potential target for therapeutic strategies in the treatment of OA.