Chondrocyte apoptosis determined by caspase-3 expression varies with fibronectin distribution in equine articular cartilage.

AIM: The purpose of this study was to investigate associations between the extent of chondrocyte apoptosis and expression of the articular cartilage (AC) extracellular matrix (ECM) molecules, cartilage oligomeric matrix protein (COMP) and fibronectin. METHOD: Cartilage from four sites (when available) on equine left middle carpal joints (n = 12) were used. Expression of COMP and fibronectin was determined using specific polyclonal antibodies and a biotin-streptavidin/peroxidase method. The intensity of staining for matrix molecules was graded (none, mild, moderate, strong) in each cartilage zone. Apoptosis of chondrocytes in AC sections was assessed by their expression of active caspase-3 using immunohistochemistry. RESULTS: The intensity of fibronectin expression varied significantly according to cartilage depth, with greater expression in the deep zone than in either the superficial or middle layers (P < 0.001). A significant positive association was found overall between intensity of fibronectin expression and chondrocyte apoptosis (r = 0.44, P = 0.0187). The data were also significant for superficial and deep zones (r = 0.44, P = 0.0239 and r = 0.42, P = 0.0279 respectively). Conversely, intensity of COMP expression did not show zonal differences and was un-associated with degree of apoptosis. However, COMP expression was significantly more intense in cartilage than fibronectin (P = 0.0007), and the correlation between overall intensity of COMP and fibronectin was statistically significant (r = 0.56, P = 0.0018). CONCLUSION: The positive correlation between the incidence of apoptosis and expression of fibronectin, a key ECM molecule involved in communication between the chondrocyte and surrounding matrix, suggests that chondrocyte death by apoptosis may alter cartilage metabolism, supporting the role of this process in the pathogenesis of osteoarthritis.

Chondrocyte death by apoptosis is associated with the initiation and severity of articular cartilage degradation.

AIM: To investigate the role of chondrocyte apoptosis in the initiation and severity of articular cartilage (AC) damage. METHODS: Articular cartilage from equine metacarpophalangeal (MCP) (n = 13) and metatarsophalangeal (MTP) (n = 16) joints was used and each graded macroscopically for cartilage degradation (macroscopic osteoarthritis [OA] grade). Cartilage was sampled from six regions on the articular surface of both joint types and graded using a 'modified' Mankin scoring system. Apoptosis of chondrocytes in cartilage sections was assessed by expression of active caspase-3 using indirect immunohistochemistry. RESULTS: Apoptosis was found to increase significantly with macroscopic OA grade (P < 0.0001). There was a significant trend for increasing 'modified' Mankin score with increasing macroscopic OA grade (P < 0.0009). Apoptosis was significantly higher in the superficial zone than in the middle or deep zones (P < 0.01 and P < 0.001, respectively). The incidence of apoptosis correlated significantly with the early stages of microscopic cartilage damage ('modified' Mankin scores 0-3). Significant differences in overall apoptosis were noted when cartilage specimens with a 'modified' Mankin score of 3 were compared to grade 2 (P < 0.001), grade 1 (P < 0.001) and grade 0 (P < 0.05) specimens. However, no significant difference in overall apoptosis was noted between grade 3, 4 and 5 samples. CONCLUSIONS: The positive correlations of chondrocyte apoptosis with early stages of OA and severity of cartilage damage in the joints, suggest that this process is intrinsically linked to cartilage damage and may be associated with the initiation of cartilage degradation in OA.