ABSTRACT: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-1a (HIF-1a) on induction of MMP-2; we mimicked the microenvironment of joint cavity after ACL injury. The results show that TNF-a and IL-1b 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-a, IL-1b, and their mixture. CoCl 2 -induced HIF-1a (100 and 500 mM) also increases the levels and activity of MMP-2. Mechanical stretch has a strong additional effect on MMP-2 production with HIF-1a. Our results conclude that mechanical injury, HIF-1a and inflammatory factors collectively induce increased MMP-2 production in ACL fibroblasts, which was inhibited by NF-kB pathway inhibitor . ß