Ultrastructural quantification of cell death after injurious compression of bovine calf articular cartilage

Abstract Objective: It has been suggested that chondrocyte death by apoptosis may play a role in the pathogenesis of cartilage destruction in osteoarthritis, but the results of in-vivo and in-vitro investigations have been conflicting. To investigate further the cell death in our in-vitro model for traumatic joint injury, we performed a quantitative analysis by electron microscopy (EM) of cell morphology after injurious compression. For comparison, the TUNEL assay was also performed. Design: Articular cartilage explant disks were harvested from newborn calf femoropatellar groove. The disks were subjected to injurious compression (50% strain at a strain rate of 100%/s), incubated for 3 days, and then fixed for quantitative morphological analysis. Results: By TUNEL, the cell apoptosis rate increased from 7±2% in unloaded controls to 33±6% after injury ( P =0.01; N =8 animals). By EM, the apoptosis rate increased from 5±1% in unloaded controls to 62±10% in injured cartilage ( P =0.02, N =5 animals). Analysis by EM also identified that of the dead cells in injured disks, 97% were apoptotic by morphology. Conclusions: These results confirm a significant increase in cell death after injurious compression and suggest that most cell death observed here was by an apoptotic process.