Regulation of Plasminogen Activator Inhibitor 1 Expression in Human Osteoarthritic Chondrocytes by Fluid Shear Stress Role of Protein Kinase Cα

Objective. To test a fluid flow system for the investigation of the influence of shear stress on expression of plasminogen activator inhibitor 1 (PAI-1) in human osteoarthritic (OA) articular chondrocytes (from lesional and nonlesional sites) and human SW-1353 chondrocytes. Methods. Human SW-1353 chondrocytes and OA and normal human articular chondrocytes were cultured on type II collagen-coated glass plates under static conditions or placed in a flow chamber to form a closed fluid-circulation system for exposure to different levels of shear stress (2-20 dyn/cm(2)). Real-time polymerase chain reaction was used to analyze PAI-1 gene expression, and protein kinase C (PKC) inhibitors and small interfering RNA were used to investigate the mechanism of shear stress-induced signal transduction in SW-1353 and OA (lesional and nonlesional) articular chondrocytes. Results. There was a significant reduction in PAI-1 expression in CIA chondrocytes obtained from lesional sites compared with those obtained from nonlesional sites. In SW-1353 chondrocytes subjected to 2 hours of shear flow, moderate shear stresses (5 and 10 dyn/cm(2)) generated significant PAI-1 expression, which was regulated through PKC alpha phosphorylation and Sp-1 activation. These levels of shear stress also increased PAI-1 expression in articular chondrocytes from nonlesional sites and from normal healthy cartilage through the activation of PKC alpha and Sp-1 signal transduction, but no effect of these levels of fluid shear stress was observed on OA chondrocytes from lesional sites. Conclusion. OA chondrocytes from lesional sites and those from nonlesional sites of human cartilage have differential responses to shear stress with regard to PAI-1 gene expression, and therefore diverse functional consequences can be observed.