Mitochondrial Dysfunction Increases Inflammatory Responsiveness to Cytokines in Normal Human Chondrocytes

Objective. Alterations in mitochondria play a key role in the pathogenesis of osteoarthritis (OA). The role of inflammation in the progression of OA has also acquired important new dimensions. This study was undertaken to evaluate the potential role of mitochondrial dysfunction in increasing the inflammatory response of normal human chondrocytes to cytokines. Methods. Mitochondrial dysfunction was induced by commonly used inhibitors. Interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) were used as inflammatory mediators. IL-8 and cyclooxygenase 2 (COX-2) protein and messenger RNA (mRNA) expression and prostaglandin E-2 (PGE(2)) levels were assessed. The chemotactic activity of neutrophils was assayed. Additionally, inhibitors of reactive oxygen species (ROS) and NF-kappa B were used to identify possible inflammatory response pathways induced by mitochondrial dysfunction, and the effects of the natural antioxidant resveratrol were tested. Results. Pretreatment with antimycin A or oligomycin (inhibitors of mitochondrial respiratory chain complexes III and V, respectively) triggered a strong potentiation of IL-1 beta-induced IL-8 mRNA and protein expression (mean +/- SEM at 18 hours 5,932 +/- 1,995 pg/50,000 cells for IL-1 beta alone versus 16,241 +/- 5,843 pg/50,000 cells for antimycin A plus IL-1 beta and 20,087 +/- 5,407 pg/50,000 cells for oligomycin plus IL-1 beta; P < 0.05). Similar results were observed with TNF alpha or when expression of the inflammatory mediator COX-2 or PGE(2) production was assessed. Mitochondrial dysfunction increased the chemotactic activity induced by cytokines, and ROS and NF-kappa B inhibitors decreased the production of IL-8. Resveratrol significantly reduced the inflammatory response. Conclusion. Our findings indicate that mitochondrial dysfunction could amplify the responsiveness to cytokine-induced chondrocyte inflammation through ROS production and NF-kappa B activation. This pathway might lead to the impairment of cartilage and joint function in OA.