Synovial fibroblasts (SFs) play a critical role in the pathogenesis of rheumatoid arthritis (RA) and are directly involved in joint destruction. Both SF-resident matrix metalloproteases and cathepsins have been implicated in cartilage degradation although their identities and individual contributions remain unclear. The aims of this study were to investigate the expression of cathepsin K in SFs, the correlation between cathepsin K expression and disease severity, and the contribution of cathepsin K to fibroblast-mediated collagen degradation. Immunostaining of joint specimens of 21 patients revealed high expression of cathepsin K in SFs in the synovial lining and the stroma of synovial villi, and to a lesser extent in CD68-positive cells of the synovial lining. Cathepsin K-positive SFs were consistently observed at sites of cartilage and bone degradation. Expression levels of cathepsin K in the sublining and vascularized areas of inflamed synovia showed a highly significant negative correlation with results derived from the Hannover Functional Capacity Questionnaire (r = 0.78, P = 0.003; and r = 0.70, P = 0.012, respectively) as a measure of the severity of RA in individual patients. For comparison, there was no correlation between Hannover Functional Capacity Questionnaire and cathepsin S whose expression is limited to CD-68-positive macrophage-like synoviocytes. The expression of cathepsin K was also demonstrated in primary cell cultures of RA-SFs. Co-cultures of SFs on cartilage disks revealed the ability of fibroblast-like cells to phagocytose collagen fibrils whose intralysosomal hydrolysis was prevented in the presence of a potent cathepsin K inhibitor but not by an inhibitor effective against cathepsins L, B, and S. The selective and critical role of cathepsin K in articular cartilage and subchondral bone erosion was further corroborated by the finding that cathepsin K has a potent aggrecan-degrading activity and that cathepsin K-generated aggrecan cleavage products specifically potentiate the collagenolytic activity of cathepsin K toward type I and II collagens. This study demonstrates for the first time a critical role of cathepsin K in cartilage degradation by SFs in RA that is comparable to its well-known activity in osteoclasts.

Objective. To determine and compare the expression of cathepsins K and S proteins in joints with rheumatoid arthritis (RA) and osteoarthritis (OA) and to determine the effect of interleukin-1␤ (IL-1␤) and tumor necrosis factor ␣ (TNF␣) on the expression of cathepsin K in fibroblast-like synoviocytes.Method. Expression and localization of cathepsins K and S were determined by immunohistochemistry in the synovium of 10 RA-and 8 OA-affected joints. Northern and Western blot analyses were performed to analyze cathepsin K and S expression in primary fibroblast-like synoviocyte cultures from RA and OA patients. The effect of IL-1␤ and TNF␣ on the expression and secretion of cathepsin K in primary cultures of synoviocytes was determined by real-time polymerase chain reaction and Western blot analysis. Staining of in situ activity was used to identify active cathepsin K enzyme in primary synovial fibroblast cultures.Results. Cathepsin K and S protein expression was identified in the synovium from patients with RA and OA. Cathepsin K protein was localized in synovial fibroblasts, stromal multinucleated giant cells, and, to a lesser degree, in CD68؉ macrophage-like synoviocytes. Of note is the expression of cathepsin K in synovial fibroblasts and mononuclear macrophage-like cells at sites of cartilage erosion in RA and in interdigitating cells of lymphocyterich areas. In contrast, cathepsin S expression was restricted to CD68؉ macrophage-like synoviocytes, interdigitating cells, and endothelial cells of blood vessels. Cathepsin K protein expression in the interstitial areas and perivascular regions of RA-derived synovial specimens was 2-5 times higher than in OA samples (P < 0.001), whereas the expression of cathepsin S did not significantly differ in these diseases. Cathepsin K expression levels in normal synovium were low and restricted to fibroblast-like cells. Of note, cathepsin K also was expressed in repairing fibrocartilage in 1 OA specimen. Primary cell cultures of RA-and OA-derived synovial fibroblasts expressed comparable amounts of cathepsin K at the transcript and protein levels. Both cell cultures secreted mature cathepsin K as well as procathepsin K, and expressed active cathepsin K in cytosolic vesicles. In contrast, neither RA-nor OA-derived fibroblasts expressed detectable levels of cathepsin S. IL-1␤ and TNF␣ stimulated the transcript (7-8-fold) and protein expression (2-fold) of cathepsin K (P < 0.05) in primary synovial fibroblast cultures, without differences in expression between RA-and OA-derived synovial fibroblasts.Conclusion. The presence of cathepsin K polypeptide in synovial fibroblasts and macrophage-like cells in normal, OA, and RA synovia suggests a constitutive expression of this protease and a role in synovial remodeling. The comparable increase in cathepsin K expression after stimulation of RA-and OA-derived synovial fibroblasts with IL-1␤ and TNF␣ further suggests that the expression of cathepsin K is independent of cellular alterations leading to the invasive phenotype of RA-synovial fi...

Summary Background : Osteonecrosis is a major complication of inflammatory bowel disease usually associated with steroid use. There are few large series available detailing the specifics of affected patients. Aim : To identify any specific characteristics of osteonecrosis in this cohort. A major focus was placed on steroid dose, the average time between diagnosis of IBD and appearance of osteonecrosis and the frequency of multiple joint involvement. Methods : Our study identified 23 patients in the practices of five gastroenterologists at the Mount Sinai Medical Center. We retrospectively reviewed their clinical history, as well as imaging studies. We classified osteonecrosis according to the Association Research Circulation Osseous (ARCO) staging system. Results : Although our prednisone dosing data could not be used as an accurate predictor of onset or joint distribution, there was a tendency for correlation between the average daily dosing and the ARCO score. The ARCO scoring system was consistent for patients with bilateral hip involvement. The distribution of affected joints in IBD is similar to other conditions associated with osteonecrosis, with hips being the most frequently involved joints. Data showed bilateral involvement in most hips, but usually unilateral disease in the shoulders and knees. Treatment options include core decompression for early stages, whereas joint replacement surgery is required for stages 3 and 4. Conclusion : IBD predisposes patients to corticosteroid induced osteonecrosis. An exact threshold dose has not been determined. The data suggests that either long term therapy or short term high dose treatment increases the risk of osteonecrosis. Even if symptoms are limited to one joint, multiple joints are often involved and comprehensive testing with MRI is indicated in all cases.

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