We studied the effects of fibrinogen degradation product (FDP) fragment D on endothelial monolayer integrity and the mechanisms of fragment D-induced endothelial cell detachment from the substratum. Incubation of bovine pulmonary artery endothelial cells (BPAEC) with fragment D caused concentration- and time-dependent cell detachment from the substratum. The optimal response occurred at fragment D concentrations of 2 microM and required an incubation time of 24 h. BPAEC challenged with fragment D increased the concentration and activity of urokinase-type plasminogen activator (uPA) in the conditioned medium within 2 to 4 h of incubation. Fragment D also induced the release of tissue-type plasminogen activator, but to a lesser extent than uPA. Fragment D concurrently increased plasminogen activator (PA) activity in a concentration-dependent manner. Increased PA activity was followed by augmentation of cell-associated plasmin activity and subsequent increase in the degradation of 125I-fibrinogen and 125I-vitronectin precoated in the subendothelial matrix. Pretreatment of BPAEC with anti-uPA antibody, and inhibitors of uPA (dansyl-GGACK) and plasmin (aprotinin) prevented approximately 60% of the fragment D-induced endothelial cell detachment. We conclude that FDP fragment D increases secretion of endothelial PAs and enhances the generation of plasmin, thereby contributing to proteolysis of extracellular matrix and endothelial cell detachment. Fragment D may be a critical mediator linking activation of fibrinolysis to vascular endothelial injury in inflammatory disorders.
M Ge, G Tang, T J Ryan, A B Malik