Hemodynamic forces modulate the effects of cytokines on fibrinolytic activity of endothelial cells

We investigated the effects of hemodynamic force on fibrinolytic activity of cultured human umbilical vein endothelial cells stimulated by cytokines, using a modified cone-plate viscometer in which well-controlled and -defined sheer forces were generated. Treatment of the cells with interleukin (IL)-β or tumor necrosis factor α (TNFα) under static conditions had no effect on tissue plasminogen activator (t-PA) secretion, while release of plasminogen activator inhibitor-1 (PAI-1) increased. When cells were exposed to increasing shear stress up to 24 dynes/cm², levels of t-PA and t-PA/PAI-1 complex significantly increased relative to shear stress, while total PAI-1 and active PAI-1 secretion decreased gradually. In the presence of IL-1β or TNFα, the increase in production of t-PA and the t-PA/PAI-1 complex was further augmented. Dot blot hybridization analysis of cultured cells in similar experimental conditions using t-PA and PAI-1 cDNA probes revealed no t-PA mRNA in 3 μg total RNA from static endothelial cells under resting or cytokine-stimulated conditions, but abundant t-PA mRNA was detected in cells subjected to a shear force of 18 dynes/cm², and the increase was further augmented by addition of cytokines. In contrast, PAI-1 mRNA was detected in resting and cytokine-stimulated, nonsheared endothelial cells, but levels decreased after exposure to shear stress, even in the presence of cytokines. These results indicate a role for hemodynamic forces in regulating fibrinolytic activity with or without cytokine stimulation.