Different Potential of Extracellular Vesicles to Support Thrombin Generation: Contributions of Phosphatidylserine, Tissue Factor, and Cellular Origin

Abstract

Cells release diverse types of vesicles constitutively or in response to proliferation, injury, inflammation, or stress. Extracellular vesicles (EVs) are crucial in intercellular communication, and there is emerging evidence for their roles in inflammation, cancer, and thrombosis. We investigated the thrombogenicity of platelet-derived EVs, which constitute the majority of circulating EVs in human blood, and assessed the contributions of phosphatidylserine and tissue factor exposure on thrombin generation. Addition of platelet EVs to vesicle-free human plasma induced thrombin generation in a dose-dependent manner, which was efficiently inhibited by annexin V, but not by anti-tissue factor antibodies, indicating that it was primarily due to the exposure of phosphatidylserine on platelet EVs. Platelet EVs exhibited higher thrombogenicity than EVs from unstimulated monocytic THP-1 cells, but blockade of contact activation significantly reduced thrombin generation by platelet EVs. Stimulation of monocytic cells with lipopolysaccharide enhanced their thrombogenicity both in the presence and in the absence of contact activation, and thrombin generation was efficiently blocked by anti-tissue factor antibodies. Our study provides evidence that irrespective of their cellular origin, EVs support the propagation of coagulation via the exposure of phosphatidylserine, while the expression of functional tissue factor on EVs appears to be limited to pathological conditions.

Extracellular vesicles in cardiovascular homeostasis and disease

“…Progression of the coagulation cascade requires the presence and activation of several enzymes that aid in the generation of thrombin, and many of the rate limiting enzymatic reactions begin at the surface of EVs [24]. Tissue factor, a key enzyme that initiates the coagulation cascade, is found on subpopulations of EVs derived from vascular SMCs [25*], endothelial cells [26], monocytes/macrophages [27], and platelets [28]. Further, the charged phospholipid profile (e.g., enrichment of phosphatidylserine) characteristic of many EV populations may also aid in the generation of thrombin [28].…”

“…Tissue factor, a key enzyme that initiates the coagulation cascade, is found on subpopulations of EVs derived from vascular SMCs [25*], endothelial cells [26], monocytes/macrophages [27], and platelets [28]. Further, the charged phospholipid profile (e.g., enrichment of phosphatidylserine) characteristic of many EV populations may also aid in the generation of thrombin [28]. In response to the generation of thrombin, local platelets release exosomal EVs that mediate paracrine signaling to endothelial cells [29].…”

Microvesicles and Cancer Associated Thrombosis

“…Platelet MVs (PMVs), the main subset of MVs, present in the blood circulation 21,22 are natively lacking TF-dependent procoagulant activity. 23 When observed, the TF activity on PMVs may result from the fusion of endothelial or monocyte-derived TF þ MVs with activated platelets as described above. Moreover, the PS-rich environment generated by PMVs may amplify the TF þ MVs activity from MVs from another source.…”

Platelet, erythrocyte, endothelial, and monocyte microparticles in coagulation activation and propagation

“…The stronger activation from TF-bearing MMPs and EMPs compared to TF-negative PMPs, ErMPs, and neutrophil MPs was demonstrated in the recalcification test in works [28–30]. The importance of PS in the procoagulant effect of PMPs [25] and the amplification of TF-initiated thrombin generation by PMPs [24] and ErMPs [27] indirectly indicate their participation in coagulation propagation. However, all these works were performed with homogeneous tests that do not allow for direct separation of the activation and propagation phases.…”