Pathogenesis of Osteoarthritis: Chondrocyte Replicative Senescence or Apoptosis?

Background: The aim of this study was to investigate by flow cytometry cellular viability and apoptosis of human chondrocytes isolated from osteoarthritic cartilage and to correlate replicative senescence with apoptosis of these cells. Methods: To understand the mechanisms underlying the process of cell death in cartilage destruction, we investigated by flow cytometry cellular viability (Cell viability calcein-AM assay) and apoptosis (Light scattering properties of chondrocytes, study of chondrocyte death using Annexin-V-FITC and propidium iodide double-labeling, caspase-3 activity determination) of human chondrocytes isolated from osteoarthritic and nonosteoarthritic cartilage. Senescent cells were characterized using the senescence-associated-beta-galactosidase marker (SA-P-Gal marker) by staining with chromogenic substrate (X-Gal) to produce blue coloration of SA-P-Gal-positive cells and microscopy analysis. Results: The results we obtained show that between 25 and 40% of chondrocytes were in apoptosis and all of them were SA-beta-Gal-positive. Conclusions: These results demonstrate that the death of osteoarthritic chondrocytes is an apoptotic phenomenon which is preceded by an accelerated mechanism of replicative senescence. (C) 2008 Clinical Cytometry Society