Even with current treatments of acute joint injuries, more than 40% of people who suffer significant ligament or meniscus tears, or articular surface injuries, will develop osteoarthritis (OA). Correspondingly, 12% or more of all patients with lower extremity OA have a history of joint injury. Recent research suggests that acute joint damage that occurs at the time of an injury initiates a sequence of events that can lead to progressive articular surface damage. New molecular interventions, combined with evolving surgical methods, aim to minimize or prevent progressive tissue damage triggered by joint injury. Seizing the potential for progress in the treatment of joint injuries to forestall OA will depend on advances in (1) quantitative methods of assessing the injury severity, including both structural damage and biologic responses, (2) understanding of the pathogenesis of post-traumatic OA, taking into account potential interactions among the different tissues and the role of post-traumatic incongruity and instability, and (3) application of engineering and molecular research to develop new methods of treating injured joints. This paper highlights recent advances in understanding of the structural damage and the acute biological response following joint injury, and it identifies important directions for future research. ß

Objective. To assess the presence of fibroblast collagenase (MMP-l), neutrophil collagenase (MMP-8), and collagenase 3 (MMP-13) in osteoarthritic (OA) cartilage, with particular emphasis on areas of macroscopic cartilage erosion.Methods. Messenger RNA (mRNA) levels were assessed by reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridization, and Northern blot analysis.Results. MMP-1 and MMP-13 were expressed at higher levels by OA chondrocytes than by normal chondrocytes. In addition, mRNA for MMP-8 was present in OA cartilage but not normal cartilage by PCR and Northern blot analyses. Chondrocytes from areas surrounding the OA lesion expressed greater quantities of MMP-1 and MMP-13 compared with normal chondrocytes, suggesting local modulation by mechanical and inflammatory factors. Tumor necrosis factor a stimulated the expression of all 3 collagenases. Retinoic acid, an agent which induces autodigestion of cartilage in vitro, stimulated only the expression of MMP-13.Conclusion. These findings suggest a key role of MMP-13 and MMP-8, as well as MMP-1 in osteoarthritis.The matrix metalloproteinase (MMP) family of enzymes consists of at least 15 distinct entities, including

Matrix metalloproteinase-13 (collagenase-3), a member of the family of matrix metalloproteinases (MMPs), plays a major pathological role in the cartilage destruction of arthritis. A dramatic up-regulation of MMP-13 by inflammatory cytokines such as interleukin (IL)-1␤ or by fibronectin fragments has been observed in chondrocytes. In this study, we investigated the inhibitory effects of insulin-like growth factor-1 (IGF-1) and osteogenic protein-1 (OP-1) on the expression of MMP-13, which was induced by fibronectin fragment or IL-1␤ in human immortalized or human primary chondrocytes. IGF-1 and OP-1 each significantly reduced the basal level as well as fibronectin fragment-or IL-1␤-stimulated transcription of the MMP-13 gene in a dosedependent fashion with the corresponding decreases in the protein level of MMP-13. The most prominent suppressive effect was observed by the combination of IGF-1 and OP-1, which decreased the basal promoter activity by 60% and almost completely abrogated the fibronectin fragmentstimulated MMP-13 promoter activity. OP-1 was found to enhance mRNA levels of IGF-1 and the IGF-1 receptor, the latter of which appeared to be responsible for the combined effect of IGF-1 and OP-1. The suppressive effect of IGF-1 and OP-1 on MMP-13 expression was due in part to downregulation of the expression of pro-inflammatory cytokines and the activity of their intermediate molecules, including NF-B and AP-1 factors. We propose that IGF-1 and OP-1 could be key physiological regulators of MMP-13 gene expression and that the combination of IGF-1 and OP-1 may be useful in controlling the excess catabolic activity in arthritis.Cartilage homeostasis is a well synchronized balance between anabolic and catabolic processes. During the development of osteoarthritis, this balance is disrupted resulting in progressive degradation of the articular cartilage (1). Studies have demonstrated that members of the matrix metalloproteinase (MMP) 1 family are the major pathophysiological mediators of the cartilage destruction process in osteoarthritis (2). Recently, in vitro, clinical, and transgenic studies have provided evidence that chondrocyte MMP-13 (collagenase-3) is a leading candidate enzyme mediating the degradation of type II collagen in osteoarthritis (2-4). A dramatic up-regulation of MMP-13 gene expression in response to inflammatory cytokines, such as interleukin-1␤ (IL-1␤) (5), or by fibronectin fragment (Fn-f) (6) has been observed in chondrocytes. However, there is limited knowledge of the cellular mechanisms that regulate MMP-13 gene expression in chondrocytes. Accumulating evidence demonstrates that the bone morphogenetic proteins (BMPs), a subfamily of the transforming growth factor-␤ superfamily, are inhibitors of MMP-13 expression in human fetal chondrocytes (7) or rat osteoblast-enriched cells (8, 9). Upon ligand binding, the specific serine/threonine kinase activity of BMP receptors (type I or II) transduce signals (10) by allowing the association of Smad1 and Smad4 in the cytoplasm followed by the tran...

Three years ago we published a book chapter on the role of bone morphogenetic proteins (BMPs) in cartilage repair. Since that time our understanding of the function of osteogenic protein-1 (OP-1) or BMP-7 in cartilage homeostasis and repair has substantially improved and therefore we decided to devote a current review solely to this BMP. Here we summarise the information accumulated on OP-1 from in vitro and ex vivo studies with cartilage cells and tissues as well as from in vivo studies of cartilage repair in various animal models. The primary focus is on articular chondrocytes and cartilage, but data will also be presented on nonarticular cartilage, particularly from the intervertebral disc. The data show that OP-1 is a unique growth factor which, unlike other members of the same BMP family, exhibits in addition to its strong pro-anabolic activity very prominent anti-catabolic properties. Animal studies have demonstrated that OP-1 has the ability to repair cartilage in vivo in various models of articular cartilage degradation, including focal osteochondral and chondral defects and osteoarthritis, as well as models of degeneration in intervertebral disc cartilage. Together our findings indicate a significant promise for OP-1 as therapeutic in cartilage repair.

Objective. Although growth factor therapy could be an attractive method for stimulating the repair of damaged cartilage matrix, there is evidence that with aging and/or with the development of osteoarthritis (OA), articular chondrocytes may become unresponsive to growth factor stimulation. The aim of the current study was to compare the ability of insulin-like growth factor 1 (IGF-1) and osteogenic protein 1 (OP-1), alone and in combination, to stimulate human normal and OA chondrocytes in culture.Methods. Chondrocytes isolated by enzymatic digestion of cartilage obtained from subjects undergoing knee replacement for OA (n ‫؍‬ 6) or from normal ankle joints of tissue donors (n ‫؍‬ 7) were cultured in alginate beads in serum-free medium and treated for 21 days with 100 ng/ml IGF-1, 100 ng/ml OP-1, or both. Controls were treated with vehicle alone. The cultures were evaluated for cell survival, cell number by DNA analysis, matrix production by particle exclusion assay, and level of accumulated proteoglycan by dimethylmethylene blue assay.Results. After 21 days in serum-free alginate culture, survival of cells from OA cartilage was 65 ؎ 2% (mean ؎ SEM), while survival of cells from normal cartilage was significantly greater (82 ؎ 3%). Treatment with either IGF-1 or OP-1 alone minimally improved survival, while the combination IGF ؉ OP significantly improved survival, to 87 ؎ 2% for OA cells and 95 ؎ 1% for normal cells. Cell proliferation was noted only in the IGF ؉ OP group; this was significant for both normal and OA cells (ϳ2-fold increase in DNA levels). Matrix production, assessed by particle exclusion and by proteoglycan accumulation, was greatest in the cells treated with IGF ؉ OP in both normal and OA cultures. When proteoglycan levels were corrected for cell numbers (g proteoglycan/ng DNA), a significant increase over control was noted with OP-1 alone and IGF ؉ OP, but not IGF-1 alone, in both normal and OA cultures, with the greatest levels in the combination group (3-fold increase over control).Conclusion. OP-1 was more potent than IGF-1 in stimulating proteoglycan production in both normal and OA cells. However, the best results were obtained with the combination, suggesting that combined therapy with IGF-1 and OP-1 may be an effective strategy for treating OA cartilage damage.

Objective. To determine the effects of basic fibroblast growth factor (bFGF) on the chondrocyte anabolic activity promoted by insulin-like growth factor 1 (IGF-1) and osteogenic protein 1 (OP-1).Methods. Human articular chondrocytes were cultured in alginate beads or as cartilage explants in serum-free medium with or without IGF-1 (100 ng/ml), OP-1 (100 ng/ml), or bFGF (0-100 ng/ml). Cell survival, proliferation, proteoglycan synthesis, and total proteoglycan accumulation were measured after 21 days of culture in alginate beads, and proteoglycan synthesis was measured in explants.Results. Cell survival was not altered by bFGF at any dose, and chondrocyte proliferation was stimulated only at doses above 1 ng/ml. When combined with IGF-1, 1 ng/ml of bFGF stimulated proliferation to 170% of control, but when combined with IGF-1 and OP-1, proliferation increased to 373% of control. Doses of bFGF of 100 ng/ml decreased total proteoglycan levels accumulated per cell by 60% compared with control and also inhibited the ability of IGF-1 or OP-1 to increase proteoglycan production. Likewise, sulfate incorporation in response to IGF-1 and OP-1 alone or together was completely inhibited by 50 ng/ml bFGF in both alginate and explant cultures.Conclusion. The anabolic activity of IGF-1 and OP-1, alone and in combination, is significantly inhibited by bFGF. The results suggest that excessive release of bFGF from the cartilage matrix during injury, with loading, or in arthritis could contribute to increased proliferation and reduced anabolic activity in articular cartilage.

Oxidative stress-mediated post-translational modifications of redox-sensitive proteins are postulated as a key mechanism underlying age-related cellular dysfunction and disease progression. Peroxiredoxins (PRX) are critical intracellular antioxidants that also regulate redox signaling events. Age-related osteoarthritis is a common form of arthritis that has been associated with mitochondrial dysfunction and oxidative stress. The objective of this study was to determine the effect of aging and oxidative stress on chondrocyte intracellular signaling, with a specific focus on oxidation of cytosolic PRX2 and mitochondrial PRX3. Menadione was used as a model to induce cellular oxidative stress. Compared with chondrocytes isolated from young adult humans, chondrocytes from older adults exhibited higher levels of PRX1-3 hyperoxidation basally and under conditions of oxidative stress. Peroxiredoxin hyperoxidation was associated with inhibition of pro-survival Akt signaling and stimulation of pro-death p38 signaling. These changes were prevented in cultured human chondrocytes by adenoviral expression of catalase targeted to the mitochondria (MCAT) and in cartilage explants from MCAT transgenic mice. Peroxiredoxin hyperoxidation was observed in situ in human cartilage sections from older adults and in osteoarthritic cartilage. MCAT transgenic mice exhibited less age-related osteoarthritis. These findings demonstrate that age-related oxidative stress can disrupt normal physiological signaling and contribute to osteoarthritis and suggest peroxiredoxin hyperoxidation as a potential mechanism.Aging is characterized by an inability to maintain homeostasis resulting in a progressive loss of function and is associated with many chronic conditions including cancer, type II diabetes, neurodegenerative disease, cardiovascular disease, and osteoarthritis (1, 2). Although several theories aimed at explaining the aging phenotype have been suggested, an age-related imbalance between the production of reactive oxygen species (ROS) 2 and the antioxidant capacity of the cell has been identified as a contributing factor (3-5). Although the original free radical theory of aging focused on accumulation of cellular damage from excessive ROS as a cause for aging and age-related conditions, more recent studies suggest that disturbances in redox signaling that result from age-related oxidative stress are likely to play a key role (5-7). Increased levels of ROS caused by mitochondrial dysfunction, one of the hallmarks of aging, have been proposed to contribute to age-related oxidative stress, but the underlying mechanisms for how this increase causes a disruption in cell signaling leading to cell and tissue dysfunction is poorly understood (1, 4, 8).Recent advances in redox signaling recognize that reversible post-translational oxidative modifications of reactive protein cysteine thiols mediated by controlled production of H 2 O 2 regulate key signal transduction events (9, 10). The cysteine-dependent peroxiredoxins (PRXs), which display high rea...

Objective Traumatic joint injury can initiate early cartilage degeneration in the presence of elevated inflammatory cytokines (e.g., TNF-α and IL-6). The positive/negative effects of post-injury dynamic loading on cartilage degradation and repair in vivo is not well-understood. This study examined the effects of dynamic strain on immature bovine cartilage in vitro challenged with TNF-α + IL-6 and its soluble receptor (sIL-6R) with/without initial mechanical injury. Methods Groups of mechanically injured or non-injured explants were cultured in TNF-α + IL-6/sIL-6R for 8 days. Intermittent dynamic compression was applied concurrently at 10%, 20%, or 30% strain amplitude. Outcome measures included sGAG loss (DMMB), aggrecan biosynthesis (35S-incorporation), aggrecanase activity (Western blot), chondrocyte viability (fluorescence staining) and apoptosis (nuclear blebbing via light microscopy), and gene expression (qPCR). Results In bovine explants, cytokine-alone and injury-plus-cytokine treatments markedly increased sGAG loss and aggrecanase activity, and induced chondrocyte apoptosis. These effects were abolished by moderate 10% and 20% strains. However, 30% strain-amplitude greatly increased apoptosis and had no inhibitory effect on aggrecanase activity. TNF+IL-6/sIL-6R downregulated matrix gene expression and upregulated expression of inflammatory genes, effects that were rescued by moderate dynamic strains but not by 30% strain. Conclusions Moderate dynamic compression inhibits the pro-catabolic response of cartilage to mechanical injury and cytokine challenge, but there is a threshold strain-amplitude above which loading becomes detrimental to cartilage. Our findings support the concept of appropriate loading for post-injury rehabilitation.