Excessive release of basic fibroblast growth factor (bFGF) during loading and/or injury of the cartilage matrix may contribute to the onset or progression of osteoarthritis. This pathological role may be related to the ability of bFGF to decrease proteoglycan synthesis and to antagonize the activity of anabolic growth factors in cartilage such as insulin-like growth factor-1 and bone morphogenetic protein 7 (BMP7 or OP-1). Matrix metalloproteinase-13 (MMP-13), a catabolic cartilage-degrading enzyme, is dramatically up-regulated by inflammatory cytokines or by fibronectin fragments in articular chondrocytes. In this study, we investigated MMP-13 production by bFGF using human articular chondrocytes. Endogenous concentration of bFGF in synovial fluids collected from arthritis patients and asymptomatic subjects showed a good linear correlation with the endogenous levels of MMP-13. bFGF stimulation of MMP-13 was mediated at the transcriptional level and, at least in part, by stimulation of interleukin-1 production. Also, our findings suggest that bFGF stimulation of MMP-13 required the activation of multiple MAPKs (ERK, p38, and JNK) by bFGF, and more importantly, bFGF activation of protein kinase C (PKC) ␦ played a key role in the MMP-13 stimulation. Indeed, PKC␦ is the only isoform associated with MMP-13 stimulation among the PKC isoforms tested. PKC␦ controls the bFGF response by regulating multiple MAPK pathways. Our results suggest that PKC␦ activation is a principal rate-limiting event in the bFGF-dependent stimulation of MMP-13 in human adult articular chondrocytes. We propose that deregulation of cross-talk between MAPK and PKC␦ signaling may contribute to the etiology of osteoarthritis in human patients. Osteoarthritis (OA)2 involves the progressive destruction of the cartilage extracellular matrix (ECM) by a pathological imbalance in the normal metabolic functions of articular chondrocytes. Under normal conditions, chondrocytes maintain a dynamic equilibrium between synthesis and degradation of ECM components. Although the causative events in the etiology of OA remain to be clearly defined, OA is characterized by a disruption of matrix equilibrium leading to progressive loss of cartilage tissue and clonal expansion of cells in the depleted regions. In the early stages of OA, cells respond with a transient induction of matrix synthesis (e.g. increases in the expression and/or protein secretion of insulin-like growth factor-1 (IGF-1) and bone morphogenetic protein 7 (BMP7 or OP-1)). This de novo ECM synthesis cannot overcome the concurrent catabolic processes (1, 2) that involve the excess production of matrixdegrading enzymes, including matrix metalloproteinases (MMPs), aggrecanases, and other proteinases by chondrocytes. The resulting degradation of cartilage ECM may exacerbate the imbalance by enhancing the local activity of systemic regulatory factors, including growth factors and cytokines.Matrix metalloproteinase-13 (MMP-13 or collagenase-3) is the most potent enzyme that degrades type II collagen (the...

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 realtime 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 painassociated 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.

The pathology of joint destruction is associated with elevated production of basic fibroblast growth factor (bFGF) and matrix metalloproteinase-13 (MMP-13). In osteoarthritic joint disease, expression of bFGF and MMP-13 in chondrocytes and their release into the synovial fluid are significantly increased. We have previously found that the capacity for cartilage repair in human adult articular chondrocytes is severely compromised by minimal exposure to bFGF because bFGF reduces responsiveness to bone morphogenetic protein-7 and insulin-like growth factor-1 and induces MMP-13 through protein kinase C␦-dependent activation of multiple mitogen-activated protein kinase (MAPK) signaling pathways. Here we show using biochemical and molecular approaches that transcription factor Elk-1, a direct downstream target of MAPK, is a critical transcriptional activator of of MMP-13 by bFGF in human articular chondrocytes. We also provide evidence that Elk-1 is a direct target of NFB and induces MMP-13 expression upon activation of the NFB signaling pathway. Taken together, our results suggest that elevated expression of MMP-13 occurs through Elk-1 activation of both MAPK and NFB signaling pathways, thus revealing a two-pronged biological mechanism by which bFGF controls the production of catabolic enzymes that are associated with excessive degradation of the cartilage matrix in degenerative joint diseases such as osteoarthritis.

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Pain-related neuropeptides released from synovial fibroblasts, such as substance P, have been implicated in joint destruction. Substance P-induced inflammatory processes are mediated via signaling through a G-protein-coupled receptor, that is, neurokinin-1 tachykinin receptor (NK(1)-R). We determined the pathophysiological link between substance P and its receptor in human adult articular cartilage homeostasis. We further examined if catabolic growth factors such as basic fibroblast growth factor (bFGF or FGF-2) or IL-1beta accelerate matrix degradation via a neural pathway upregulation of substance P and NK(1)-R. We show here that substance P stimulates the production of cartilage-degrading enzymes, such as matrix metalloproteinase-13 (MMP-13), and suppresses proteoglycan deposition in human adult articular chondrocytes via NK(1)-R. Furthermore, we have demonstrated that substance P negates proteoglycan stimulation promoted by bone morphogenetic protein-7, suggesting the dual role of substance P as both a pro-catabolic and anti-anabolic mediator of cartilage homeostasis. We report that bFGF-mediated stimulation of substance P and its receptor NK(1)-R is, in part, through an IL-1beta-dependent pathway.

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