Mitochondrial dysfunction promotes and aggravates the inflammatory response in normal human synoviocytes.

Objectives: In RA, synoviocytes cause increased oxidative stress, leading to mitochondrial alterations that may participate in the pathogenesis of RA. Here we investigated whether mitochondrial dysfunction induces inflammatory responses in cultured normal human synoviocytes, a hallmark of RA.

Methods: Mitochondrial dysfunction was induced with the inhibitor oligomycin. The effects of mitochondrial dysfunction on cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2) and IL-8 expression; cellular and mitochondrial reactive oxygen species (ROS) production; nuclear factor-κB (NF-κB) activation and p65 translocation were studied. ROS scavengers (N-acetylcysteine and mitoTEMPO) and an NF-κB inhibitor (BAY-117085) were used to investigate the pathways involved. The natural anti-inflammatory antioxidant resveratrol was also tested.

Results: Mitochondrial dysfunction per se significantly stimulated mitochondrial ROS production as well as low-grade expressions of COX-2, PGE2 and IL-8. Interestingly, mitochondrial dysfunction induced by pretreatment of synoviocytes with oligomycin synergized with IL-1β to increase the expression of these inflammatory mediators. The inflammatory effects of mitochondrial damage appeared to be dependent on ROS production and NF-κB activation since the inflammatory response was counteracted by both N-acetylcysteine and mitoTEMPO and it was also reduced by BAY-117085. Antimycin A and paraquat (inhibitors of mitochondrial function) also induced inflammatory responses. Furthermore, resveratrol significantly reduced the inflammatory response by decreasing ROS production and NF-κB activation.

Conclusion: These data suggest that mitochondrial dysfunction could induce an inflammatory response in normal human synoviocytes and sensitize these cells, causing a significant amplification of the inflammatory response induced by IL-1β. Resveratrol may represent a promising strategy in controlling the synovial inflammatory response.