Combined Effects of TNF-α, IL-1β, and HIF-1α on MMP-2 Production in ACL Fibroblasts under Mechanical Stretch: An In Vitro Study

The dynamics between inflammatory factors, mechanical stress, and healing factors, in an intra-articular joint, are very complex after injury. Injury to intra-articular tissue [anterior cruciate ligament (ACL), synovium] results in hypoxia, accumulation of various pro-inflammatory factors, cytokines, and metalloproteases. Although the presence of increased amounts of matrix-metalloproteinases (MMP) in the joint fluid after knee injury is considered the key factor for ACL poor healing ability; however, the exact role of collective participants of the joint fluid on MMP-2 activity and production has not been fully studied yet. To investigate the combined effects of mechanical injury, inflammation and hypoxia induced factor-1 alpha (HIF-1 alpha) on induction of MMP-2; we mimicked the microenvironment of joint cavity after ACL injury. The results show that TNF-alpha and IL-1 beta elevate the activity of MMP-2 in a dose-and time-dependent manner. In addition, mechanical stretch further enhances the MMP-2 protein levels with TNF-alpha, IL-1 beta, and their mixture. CoCl(2)-induced HIF-1 alpha (100 and 500 mu M) also increases the levels and activity of MMP-2. Mechanical stretch has a strong additional effect on MMP-2 production with HIF-1 alpha. Our results conclude that mechanical injury, HIF-1 alpha and inflammatory factors collectively induce increased MMP-2 production in ACL fibroblasts, which was inhibited by NF-kappa B pathway inhibitor (Bay-11-7082). (C) 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29: 1008-1014, 2011