Catabolic stress induces features of chondrocyte senescence through overexpression of caveolin 1 - Possible involvement of caveolin 1-induced down-regulation of articular chondrocytes in the pathogenesis of osteoarthritis

Objective. Articular chondrocyte senescence is responsible, at least in part, for the increased incidence of osteoarthritis (OA) with increased age. Recently, it was suggested that caveolin. 1, a 21-24-kd membrane protein, participates in premature cellular senescence. Caveolin 1 is the principal structural component of caveolae, vesicular invaginations of the plasma membrane. This study was undertaken to investigate whether the catabolic factors oxidative stress and interleukin-1 beta (IL-1 beta) induce features of premature senescence of articular chondrocytes through up-regulation of caveolin 1 expression. Methods. Caveolin 1 expression was investigated in human OA cartilage by real-time polymerase chain reaction and in rat OA cartilage by immunohistologic analysis. We studied whether IL-1 beta and H2O2 induce caveolin 1 expression in OA chondrocytes and analyzed the relationship between cellular senescent phenotypes and caveolin 1 expression in human chondrocytes. Results. In human and rat OA articular cartilage, caveolin 1 positivity was associated with cartilage degeneration. Both IL-1 beta and H2O2 up-regulated caveolin 1 messenger RNA and protein levels, and both treatments induced marked expression of senescent phenotypes: altered cellular morphology, cell growth arrest, telomere erosion, and specific senescence-associated beta-galactosidase activity. Caveolin 1 overexpression induced p38 MAPK activation and impaired the ability of chondrocytes to produce type II collagen and aggrecan. In contrast, down-regulation of caveolin 1 with antisense oligonucleotide significantly inhibited the features of chondrocyte senescence induced by catabolic factors. Caveolin 1I induction and stresses with both IL-1 beta and H2O2 up-regulated p53. and p21 and down-regulated phosphorylated retinoblastoma (Rb), suggesting that the p53/p21/Rb phosphorylation pathway, as well as prolonged p38 MAPK activation, may mediate the features of chondrocyte senescence induced by stress. Conclusion. Our findings suggest that IL-1 beta and oxidative stress induce features of premature senescence in OA chondrocytes, mediated, at least in part, by stress-induced caveolin 1 expression. This indicates that caveolin 1 plays a role in the pathogenesis of OA via promotion of chondrocyte down-regulation.