Regulation of nitric oxide and bcl-2 expression by shear stress in human osteoarthritic chondrocytes in vitro

Onset and progression of cartilage degeneration is associated with shear stress occurring in diarthrodial joints subjected to inappropriate loading. This study tested the hypothesis that shear stress induced nitric oxide is associated with altered expression of regulatory onco-proteins, bcl-2, and Fas (APO-1/CD95) and apoptosis in primary human osteoarthritic chondrocyte cultures. Shear stress induced membrane phosphatidylserine and nucleosomal degradation were taken as evidence of chondrocyte apoptosis. Application of shear stress upregulated nitric oxide in a dose-dependent manner and was associated with increases in membrane phosphatidylserine and nucleosomal degradation. Increasing levels of shear stress decreased expression of the anti-apoptotic factor, bcl-2, from 44 to 10 U/ml. Addition of the nitric oxide antagonists, L-N⁵-(1-iminoethyl) ornithine and Nω-nitro-L-arginine methyl ester (L-NAME), reduced shear stress induced nucleosomal degradation by 62% and 74%, respectively. Inhibition of shear stress induced nitric oxide release by L-NAME coincided with a 2.7-fold increase of bcl-2, when compared to chondrocytes exposed to shear stress in the absence of L-NAME. These data suggest that shear stress induced nitric oxide is associated with changes in apoptotic regulatory factors that alter chondrocyte metabolism and may contribute to joint degeneration.