Endothelial microparticles induce formation of platelet aggregates via a von Willebrand factor/ristocetin dependent pathway, rendering them resistant to dissociation

Abstract

Summary. Endothelial microparticles (EMP) released from activated or apoptotic endothelial cells (EC) are emerging as useful markers for detection of EC dysfunction. Our recent observation that EMP carry von Willebrand factor (vWf) led us to investigate their interaction with platelets. EMP were incubated with normal washed platelets in the presence or absence of ristocetin, then platelet aggregates were measured by flow cytometry. In the absence of ristocetin, negligible EMP conjugated with platelets (< 5%) but in the presence of ristocetin (1 mg mL), EMP induced up to 95% of platelets to aggregate. EMP-platelet interaction was 80% blocked by anti-CD42b, or by 0.1 lm filtration to remove EMP. Platelet aggregates induced by normal plasma or high molecular weight vWf (Humate-P) dissociated 50% within 15-25 min following 1 : 20 dilution. In contrast, aggregates formed with EMP persisted two-to threefold longer with the same treatment, indicating greater stability. A similar degree of prolongation of dissociation was observed using plasma from thrombotic thrombocytopenic purpura (TTP) patients compared with normal plasma. Addition of EMP to plasma from severe von Willebrand disease restored his ristocetin-induced platelet aggregation. Multimer analysis of vWf on EMP showed unusually large vWf (ULvWf). In summary, EMP carries ULvWf multimers, promote platelet aggregates, and increase the stability of the aggregates thus formed.

Dynamic Release and Clearance of Circulating Microparticles During Cardiac Stress

“…20 We found that, within 1 hour, elevated circulating procoagulant, platelet, and EMPs are significantly reduced. Clearance rate differed by cellular origin so that erythrocyte-derived microparticles had not declined as much and 21 they present a potential thrombotic risk, which might explain their apparently more rapid clearance mechanism. However, EMP response to cardiac stress, in general, differed.…”

Endothelial microparticles: a universal marker of vascular health?

“…6 In addition, EMPs carry von Willebrand factor promoting platelet aggregation. 7 Levels of EMP-platelet aggregates have been found to be significantly higher in patients with stable coronary artery disease but diminished in acute phase of myocardial infarction, typical condition of platelet-dependent thrombosis. 8 EMPs and EMP-monocyte conjugates are elevated in patients with venous thromboembolism and are believed to play important role in thrombogenesis and reflect marked activation of endothelium, platelets and leukocytes which occurs in relation to thrombotic disorders.…”

Role of extracellular membrane vesicles in the pathogenesis of various diseases, including cancer, renal diseases, atherosclerosis, and arthritis

“…They usually measure from 100 to 500 nm in diameter, and are released by budding from the surface membranes of activated platelets, after platelet attachment to endothelial-lined inner surfaces of the vessel wall, during normal hemostasis 62 (Table 2). First referred to as 'platelet dust,' circulating MVs are CD 42 positive (indicating their origin from platelets) and contain platelet-derived tissue factor (TF) and von Willebrand's factor (VWF), 30,63 which are the major initiators of intravascular coagulation in normal processes and in thromboembolic diseases. 30 Platelet release of extracellular MPs also increases during the tightly regulated process of platelet apoptosis, and is dependent on the formation of mitochondrial permeability transition pore.…”