The impact of the endothelial protein C receptor on thrombin generation and clot lysis

INTRODUCTION: When thrombin is bound to thrombomodulin (TM), it becomes a potent activator of protein C (PC) and thrombin-activable fibrinolysis inhibitor (TAFI). Activation of PC is enhanced when PC is bound to the endothelial protein C receptor (EPCR). Activated protein C (APC) inhibits thrombin generation while activated TAFI (TAFIa) attenuates fibrinolysis. To determine the impact of diminished EPCR function on thrombin generation and fibrinolysis we generated cells that expressed TM and a variant of EPCR (R96C) that does not bind PC. METHODS: To determine the impact of EPCR on the generation of APC and TAFIa and how this affects thrombin generation and fibrinolysis we performed thrombin generation and clot lysis assays in the presence of cells expressing wild-type TM and EPCR (WT cells) or wild-type TM and the R96C variant of EPCR (R96C cells). RESULTS: In the presence of R96C cells, thrombin generation in normal plasma is increased, as a result of impaired PC activation when compared to WT cells. In addition, clot lysis is delayed in normal plasma in the presence of R96C cells, despite no increase in TAFI activation. In PC deficient plasma, clot lysis is delayed in the presence of WT and R96C cells as a result of increased TAFI activation. CONCLUSIONS: We demonstrate that impaired EPCR function can be detected by thrombin generation and clot lysis assays on cells expressing TM and EPCR. We also demonstrated that deficiency in EPCR has procoagulant effects that lead to a delay in clot lysis.