Osteoarthritis chondrocytes die by apoptosis. A possible pathway for osteoarthritis pathology

To determine which kind of cell death occurs in cartilage from patients with osteoarthritis (OA).

Seven normal and 16 OA cartilage samples were collected at autopsy or during joint replacement surgery, respectively. A piece of cartilage was cryopreserved until histologic studies were done. The rest of the cartilage was used to isolate chondrocytes. Apoptotic chondrocytes were analyzed by light and fluorescence microscopy using nuclear 4',6-diamidino-2-phenylindole dihydrochloride stain. Apoptotic chondrocytes were quantified by fluorescence-activated cell sorter (FACS) analysis. The TUNEL technique was used to study histologic apoptosis in situ. Superficial cartilage was processed for ultrastructural study by electron microscopy.

OA chondrocytes displayed nuclear and cytoplasmic changes consistent with apoptotic cell death. FACS analysis showed that the OA cartilage had a higher proportion of apoptotic chondrocytes than did normal tissue (51% versus 11%; P < 0.01). In situ study of DNA fragmentation in the cartilage showed that apoptotic cells were located in the superficial and middle zones. Ultrastructural analysis of the superficial OA cartilage revealed some empty lacunae, lysosomal-like structures, matrix vesicle-like structures, fragmented chondrocytes, and nuclear condensation.

Chondrocytes in OA cartilage demonstrated morphologic changes that are characteristic features of apoptosis. This mechanism of cell death plays an important role in the pathogenesis of OA and could be targeted for new treatment strategies.