APOPTOTIC VASCULAR ENDOTHELIAL-CELLS BECOME PROCOAGULANT

Whereas unperturbed endothelial cells provide potent anticoagulant pro perties, exposure to inflammatory and atherogenic stimuli can rapidly lead to a procoagulant behavior. Because recent studies provide eviden ce that apoptosis of vascular cells may occur under conditions such as atherosclerosis and inflammation, we investigated whether apoptotic e ndothelial cells may contribute to the development of a prothrombotic state. In this report, it is shown that both adherent and detached apo ptotic human umbilical vein endothelial cells (HUVECs) become procoagu lant. Apoptosis was induced by staurosporine, a nonspecific protein ki nase inhibitor, or by culture in suspension with serum deprivation. Bo th methods resulted in similar findings. As assessed by flow cytometri c determination of annexin V binding, HUVECs undergoing cell death exh ibited typically a more rapid exposure of membrane phosphatidylserine (PS) than DNA fragmentation. Depending on the stage of apoptosis, this redistribution of phospholipids was found to induce an increase of th e activity of the intrinsic tenase complex by 25% to 60%. Although apo ptotic cells did not show antigenic or functional tissue factor (if) a ctivity, when preactivated with lipopolysaccharide, TF procoagulant ac tivity increased by 50% to 70%. At 8 hours after apoptosis induction, antigenic thrombomodulin, heparan sulfates, and TF pathway inhibitor d ecreased by about 83%, 80%, and 59%, respectively. The functional acti vity of these components was reduced by about 36%, 52%, and 39%, respe ctively. Moreover, the presence of apoptotic HUVECs led to a significa nt increase of thrombin formation in recalcified citrated plasma. In c onclusion, apoptotic HUVECs, either adherent or in suspension, become procoagulant by increased expression of PS and the loss of anticoagula nt membrane components. (C) 1997 by The American Society of Hematology .