Apoptosis in human osteoarthritic cartilage: A microscopy report

Knee articular cartilage samples obtained by arthroscopy from four patients with well defined knee osteoarthritis (OA) and four obtained after corrective surgery from non-osteoarthritic patients (normal) were studied by light, confocal and transmission electron microscopy. Samples were processed by morphological and cytochemical (acid phosphatase) methods as well as by a histoenzymatic TUNEL technique for DNA fragmentation. The electron microscopy study showed degenerating cells characterised by fragmentation of the nuclei and cytoplasm, all typical of programmed cell death. The TUNEL technique also demonstrated DNA fragmentation in the nuclei of chondrocytes from the deep zone of the cartilage from OA patients. 'Clonal' cells displayed fine granular labels. There were different numbers of labelled nuclei in the four patients. In non-AO patients, normal cartilage displayed labels mainly in chondrocytes from the superficial zone of the tissue. There was lysosomal activity (acid phosphatase) in the OA cartilage, mainly in the non-clonal cells. This activity could be related to the mechanism of cell degeneration in apoptotic chondrocytes.