Faculty Bibliography

While research in osteoarthritis has focused on the events that lead to the destruction of articular cartilage, recent evidence suggests that two other components of the joints-bone and synovium-also play key roles in pathogenesis. All three tissues undergo alterations in concert at the structural levels in response to mechanical stress and joint malalignment. Advanced imaging studies such as MRI support this interdependence, revealing the classical changes of joint space narrowing and cartilage degeneration as well as the more recently appreciated bone marrow lesions and synovitis that may correlate with clinical symptoms. Molecular evidence also points to a coordinated release of cytokines and other inflammatory mediators from each of the three tissues together in progression of disease, although we are still in search of biochemical signatures that will predict the subset of patients who progress more quickly-and who will provide key clues to successful molecular targets in future therapies. At this time we lack definitive evidence pointing to which, if any, of the three tissues should serve as the main target for disease modification or structure protection, although most efforts have focused on cartilage. Thus current therapies focus on controlling symptoms, while research efforts search for reliable imaging and molecular biomarkers to help guide future trials of potential disease-modifying agents

Annexins are intracellular molecules implicated in the down-regulation of inflammation. Recently, annexin-1 has also been identified as a secreted molecule, suggesting it may have more complex effects on inflammation than previously appreciated. We studied the role of annexin-1 in mediating MMP-1 secretion from rheumatoid arthritis (RA) synovial fibroblasts (SF) stimulated with TNF-alpha. TNF-alpha induced a biphasic secretion of annexin-1 from RA SF. Early (< or = 60 min), cycloheximide-independent secretion from preformed intracellular pools was followed by late (24 h) cycloheximide-inhibitable secretion requiring new protein synthesis. Exogenous annexin-1 N-terminal peptide Ac2-26 stimulated MMP-1 secretion in a dose- (EC(50) approximately 25 microM) and time- (8-24 h) dependent manner; full-length annexin-1 had a similar effect. Down-regulation of annexin-1 using small interfering RNA resulted in decreased secretion of both annexin-1 and MMP-1, confirming that annexin-1 mediates TNF-alpha-stimulated MMP-1 secretion. Erk, Jnk, and NF-kappaB have been implicated in MMP-1 secretion. Erk, Jnk, and NF-kappaB inhibitors had no effect on annexin-1 secretion stimulated by TNF-alpha but inhibited MMP-1 secretion in response to Ac2-26, indicating that these molecules signal downstream of annexin-1. Annexin-1 stimulation of MMP-1 secretion was inhibited by both a formyl peptide receptor antagonist and pertussis toxin, suggesting that secreted annexin-1 acts via formyl peptide family receptors, most likely FPLR-1. In contrast to its commonly appreciated anti-inflammatory roles, our data indicate that annexin-1 is secreted by RA SF in response to TNF-alpha and acts in an autacoid manner to engage FPRL-1, activate Erk, Jnk, and NF-kappaB, and stimulate MMP-1 secretion

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

Osteoarthritis (OA) is caused by both biochemical and mechanical factors. While the mechanisms that underlie the disease are not completely understood, investigators have characterized a number of catabolic and protective factors that have a role in the disease process. Nitric oxide (NO) and its redox derivatives appear to have a number of different functions in both normal and pathophysiological joint conditions. Until recently, NO was considered a catabolic factor that was responsible for perpetuating the OA disease process by mediating the expression of proinflammatory cytokines, inhibiting the synthesis of collagen and proteoglycans and inducing apoptosis. However, recent studies suggest that NO and its redox derivatives may also have protective effects on cartilage. This review will summarize the literature on the effects of NO on cartilage and chondrocytes as well as discuss some evidence that suggests potential protective effects of NO and/or its derivatives on other cell types. More research is needed to elucidate the role of NO and its derivatives on both normal and osteoarthritis cartilage

Osteoarthritis (OA) is a degenerative disease involving chondrocytes, cartilage and other joint tissues, and has a number of underlying causes, including both biochemical and mechanical factors. Although proinflammatory factors including nitric oxide (NO) are associated with OA, there is recent evidence suggesting that NO and its redox derivatives may also play protective roles in the joint. However, the mechanisms that underlie the development and progression of OA are not completely understood. Experiments have demonstrated that NO plays a catabolic role in the development of OA and mediates the inflammatory response, is involved in the degradation of matrix metalloproteinases, inhibits the synthesis of both collagen and proteoglycans, and helps to mediate apoptosis. However, there is also evidence that in cultured chondrocytes the addition of exogenous NO may inhibit proinflammatory activation by preventing the nuclear localization of the transcription factor nuclear factor-kappaB, whereas the presence of peroxynitrite--a redox derivative of NO--appears to enhance the inflammatory response by sustaining the nuclear localization of nuclear factor-kappaB. In addition, under some conditions exogenous NO can stimulate collagen synthesis in cultured rat fibroblasts and human tendon cells. The protective roles of NO in multiple cell types, along with the opposing activities in cultured chondrocytes, suggest that NO may play additional protective roles in chondrocyte function. NO and its derivatives have a similarly complicated involvement in nociception and pain, which may contribute to the functional disability of OA. Further research may help to elucidate a potential role for NO-donating agents in the management of OA

OBJECTIVE: To determine the effects of the antioxidant resveratrol on the functions of human chondrocytes in osteoarthritis (OA). METHODS: Chondrocytes and cartilage explants were isolated from OA patients undergoing knee replacement surgery. Effects of resveratrol in the presence or absence of interleukin-1beta (IL-1beta) stimulation were assessed by measurement of prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)) synthesis, cyclooxygenase (COX) activity, matrix metalloproteinase (MMP) expression, and proteoglycan production. To explore the mechanisms of action of resveratrol, its effects on mitochondrial function and apoptosis were examined by assessing mitochondrial membrane potential, ATP levels, cytochrome c release, and annexin V staining. RESULTS: Resveratrol inhibited both spontaneous and IL-1beta-induced PGE(2) production by >20% (P < 0.05) and by 80% (P < 0.001), respectively; similarly, LTB(4) production was reduced by >50% (P < 0.05). The production of PGE(2) was inhibited via a 70-90% suppression of COX-2 expression and enzyme activity (P < 0.05). Resveratrol also promoted anabolic effects in OA explant cultures, by elevating proteoglycan synthesis and decreasing production of MMPs 1, 3, and 13. Pretreatment of OA chondrocytes with resveratrol blocked mitochondrial membrane depolarization, loss of mitochondrial biomass, and IL-1beta-induced ATP depletion. Similarly, IL-1beta-mediated induction of the apoptotic markers cytochrome c and annexin V was also inhibited by resveratrol. Exogenous addition of PGE(2) abolished the protective effects of resveratrol on mitochondrial membrane integrity, ATP levels, expression of apoptotic markers, and DNA fragmentation. CONCLUSION: Resveratrol protects against IL-1beta-induced catabolic effects and prevents chondrocyte apoptosis via its inhibition of mitochondrial membrane depolarization and ATP depletion. These beneficial effects of resveratrol are due, in part, to its capacity to inhibit COX-2-derived PGE(2) synthesis. Resveratrol may therefore protect against oxidant injury and apoptosis, which are main features of progressive OA