Endothelial cells undergoing apoptosis become proadhesive for nonactivatedplatelets

Under normal conditions, platelets do not adhere to endothelium. However, w hen platelets or endothelial cells are stimulated by thrombin or cytokines, respectively, platelets bind avidly to endothelium. Because there is accum ulating evidence that endothelial cells may become apoptotic under certain proinflammatory or prothrombotic conditions, we investigated whether endoth elial cells undergoing apoptosis may become proadhesive for nonactivated pl atelets, Human umbilical vein endothelial cells (HUVEC) were induced to und ergo apoptosis by staurosporine, a nonspecific protein kinase inhibitor, or by culture in suspension with serum-deprivation. After treatment of HUVEC or platelets with different receptor antagonists, nonactivated, washed huma n platelets were allowed to adhere to HUVEC for 20 minutes. To exclude matr ix involvement, platelet binding was measured in suspension by using flow c ytometry. Independent of the method of apoptosis induction, there was a mar ked increase in platelet binding to apoptotic HUVEC. Although HUVEC exhibit ed maximal adhesiveness for platelets after 2 to 4 hours, complete DNA frag mentation of HUVEC occurred only several hours later. Adhesion assays after blockade of different platelet receptors showed only involvement of beta(1 )-integrins. Platelet binding to apoptotic HUVEC was inhibited by more than 70% when platelets were treated with blocking anti-beta(1) antibodies. Tre atment of apoptotic HUVEC with blocking antibodies to different potential p latelet receptors, including known ligands for beta(1)-integrins, did not a ffect platelet binding. As assessed by determination of beta-thromboglobuli n and platelet factor 4 in the supernatants, platelets bound to apoptotic H UVEC became slightly activated. However, significant expression of platelet P-selectin (CD62P) was not found. These data provide further evidence that endothelial cells undergoing apoptosis may contribute to thrombotic events . (C) 1999 by The American Society of Hematology.