While many proteases in articular cartilage have been described, current studies indicate that members of two families of metalloproteases – MMPs and the ADAMTSs – are responsible for the degradation of the major components of this tissue. Collagenases (MMPs) make the first cleavage in triple-helical collagen, allowing its further degradation by other proteases. Aggrecanases (ADAMTSs), in conjunction with other MMPs, degrade aggrecan, a component of the proteoglycan aggregate. Anti-neoepitope antibodies that recognize the cleavage products of collagen and aggrecan generated by these enzymes are now available and are being used to detect the sites of action and to quantitate degradation products.

The reaction patterns of chondrocytes in osteoarthritis can be summarized in five categories: (1) proliferation and cell death (apoptosis); changes in (2) synthetic activity and (3) degradation; (4) phenotypic modulation of the articular chondrocytes; and (5) formation of osteophytes. In osteoarthritis, the primary responses are reinitiation of synthesis of cartilage macromolecules, the initiation of synthesis of types IIA and III procollagens as markers of a more primitive phenotype, and synthesis of active proteolytic enzymes. Reversion to a fibroblast-like phenotype, known as 'dedifferentiation', does not appear to be an important component. Proliferation plays a role in forming characteristic chondrocyte clusters near the surface, while apoptosis probably occurs primarily in the calcified cartilage.

Matrix metalloproteinase (MMP)-1, MMP-8 and MMP-13 are interstitial collagenases that degrade type II collagen in cartilage; this is a committed step in the progression of rheumatoid arthritis and osteoarthritis. Of these enzymes, the expression of MMP-1 and MMP-13 is substantially increased in response to IL-1 and tumor necrosis factor-α, and elevated levels of these collagenases are observed in arthritic tissues. Therefore, cytokine-mediated MMP-1 and MMP-13 gene regulation is an important issue in arthritis research. In this review, we discuss current models of MMP-1 and MMP-13 transcriptional regulation, with a focus on signaling intermediates and transcription factors that may be future targets for the development of new arthritis drugs.

Rheumatoid arthritis represents an excellent model in which to gain insights into the local and systemic effects of joint inflammation on skeletal tissues. Three forms of bone disease have been described in rheumatoid arthritis. These include: focal bone loss affecting the immediate subchondral bone and bone at the joint margins; periarticular osteopenia adjacent to inflamed joints; and generalized osteoporosis involving the axial and appendicular skeleton. Although these three forms of bone loss have several features in common, careful histomorphometric and histopathological analysis of bone tissues from different skeletal sites, as well as the use of urinary and serum biochemical markers of bone remodeling, provide compelling evidence that different mechanisms are involved in their pathogenesis. An understanding of these distinct pathological forms of bone loss has relevance not only with respect to gaining insights into the different pathological mechanisms, but also for developing specific and effective strategies for preventing the different forms of bone loss in rheumatoid arthritis.

There is mounting evidence for a role of the growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF) in inflammatory disease, including arthritis. In the present study, we examined the effectiveness of treatment of collagen-induced arthritis (CIA) with a neutralizing mAb to GM-CSF. DBA/1 mice were immunized for the development of CIA and treated at different times, and with different doses, with neutralizing mAb to GM-CSF or isotype control mAb. Anti-GM-CSF mAb treatment prior to the onset of arthritis, at the time of antigen challenge, was effective at ameliorating the ensuing disease. Modulation of arthritis was seen predominantly as a reduction in overall disease severity, both in terms of the number of limbs affected per mouse and the clinical score of affected limbs. Importantly, anti-GM-CSF mAb treatment ameliorated existing disease, seen both as a reduction in the number of initially affected limbs progressing and lower numbers of additional limbs becoming affected. By histology, both inflammation and cartilage destruction were reduced in anti-GM-CSF-treated mice, and the levels of tumor necrosis factor-a and IL-1? were also reduced in joint tissue washouts of these mice. Neither humoral nor cellular immunity to type II collagen, however, was affected by anti-GM-CSF mAb treatment. These results suggest that the major effect of GM-CSF in CIA is on mediating the effector phase of the inflammatory reaction to type II collagen. The results also highlight the essential role of GM-CSF in the ongoing development of inflammation and arthritis in CIA, with possible therapeutic implications for rheumatoid arthritis.

We have analyzed the pattern of procoagulant and fibrinolytic gene expression in affected joints during the course of arthritis in two murine models. In both models, we found an increased expression of tissue factor, tissue factor pathway inhibitor, urokinase plasminogen activator, and plasminogen activator inhibitor 1, as well as thrombin receptor. The observed pattern of gene expression tended to favor procoagulant activity, and this pattern was confirmed by functional assays. These alterations would account for persistence of fibrin within the inflamed joint, as is seen in rheumatoid arthritis.

The origin and role of IL-17, a T-cell derived cytokine, in cartilage and bone destruction during rheumatoid arthritis (RA) remain to be clarified. In human ex vivo models, addition of IL-17 enhanced IL-6 production and collagen destruction, and inhibited collagen synthesis by RA synovium explants. On mouse cartilage, IL-17 enhanced cartilage proteoglycan loss and inhibited its synthesis. On human RA bone explants, IL-17 also increased bone resorption and decreased formation. Addition of IL-1 in these conditions increased the effect of IL-17. Blocking of bone-derived endogenous IL-17 with specific inhibitors resulted in a protective inhibition of bone destruction. Conversely, intra-articular administration of IL-17 into a normal mouse joint induced cartilage degradation. In conclusion, the contribution of IL-17 derived from synovium and bone marrow T cells to joint destruction suggests the control of IL-17 for the treatment of RA.

To determine whether IL-4 is therapeutic in treating established experimental arthritis, a recombinant adenovirus carrying the gene that encodes murine IL-4 (Ad-mIL-4) was used for periarticular injection into the ankle joints into mice with established collagen-induced arthritis (CIA). Periarticular injection of Ad-mIL-4 resulted in a reduction in the severity of arthritis and joint swelling compared with saline- and adenoviral control groups. Local expression of IL-4 also reduced macroscopic signs of joint inflammation and bone erosion. Moreover, injection of Ad-mIL-4 into the hind ankle joints resulted in a decrease in disease severity in the untreated front paws. Systemic delivery of murine IL-4 by intravenous injection of Ad-mIL-4 resulted in a significant reduction in the severity of early-stage arthritis.

Background Inflammatory cells are believed to play a prominent role during tissue repair and remodeling. Since repair processes develop and mature over extended time frames, the present study was designed to evaluate the effect of monocytes and fibroblasts in prolonged culture in three-dimensional collagen gels. Methods Blood monocytes from healthy donors and human fetal lung fibroblasts were cast into type I collagen gels and maintained in floating cultures for three weeks. Results Fibroblast-mediated gel contraction was initially inhibited by the presence of monocytes (P < 0.01). However, with extended co-culture, contraction of the collagen gels was greatly augmented (P < 0.01). In addition, with extended co-culture, degradation of collagen in the gels occurred. The addition of neutrophil elastase to the medium augmented both contraction and degradation (P < 0.01). Prostaglandin E2 production was significantly increased by co-culture and its presence attenuated collagen degradation. Conclusion The current study, therefore, demonstrates that interaction between monocytes and fibroblasts can contract and degrade extracellular matrix in extended culture.

Background The tissue accumulation of protein-bound advanced glycation endproducts (AGE) may be involved in the etiology of diabetic chronic complications, including osteopenia. The aim of this study was to investigate the effect of an AGE-modified type I collagen substratum on the adhesion, spreading, proliferation and differentiation of rat osteosarcoma UMR106 and mouse non-transformed MC3T3E1 osteoblastic cells. We also studied the role of reactive oxygen species (ROS) and nitric oxide synthase (NOS) expression on these AGE-collagen mediated effects. Results AGE-collagen decreased the adhesion of UMR106 cells, but had no effect on the attachment of MC3T3E1 cells. In the UMR106 cell line, AGE-collagen also inhibited cellular proliferation, spreading and alkaline phosphatase (ALP) activity. In preosteoblastic MC3T3E1 cells (24-hour culture), proliferation and spreading were significantly increased by AGE-collagen. After one week of culture (differentiated MC3T3E1 osteoblasts) AGE-collagen inhibited ALP activity, but had no effect on cell number. In mineralizing MC3T3E1 cells (3-week culture) AGE-collagen induced a decrease in the number of surviving cells and of extracellular nodules of mineralization, without modifying their ALP activity. Intracellular ROS production, measured after a 48-hour culture, was decreased by AGE-collagen in MC3T3E1 cells, but was increased by AGE-collagen in UMR106 cells. After a 24-hour culture, AGE-collagen increased the expression of endothelial and inducible NOS, in both osteoblastic cell lines. Conclusions These results suggest that the accumulation of AGE on bone extracellular matrix could regulate the proliferation and differentiation of osteoblastic cells. These effects appear to depend on the stage of osteoblastic development, and possibly involve the modulation of NOS expression and intracellular ROS pathways.