Role of Extracellular Vesicles in the Pathogenesis of Venous Thromboembolism

Venous thromboembolism (VTE) is a common disease with an incidence of 1–2 per 1000 individuals. VTE is a collective term for deep vein thrombosis and pulmonary embolism. Extracellular vesicles (EVs) are lipid-membrane-bound spherical vesicles that bud off from the cells upon activation and apoptosis. Their size varies between 30 nm and 1 μm. Recent advances in experimental and observational studies suggest a pivotal role of EVs in VTE. The main goals of the present thesis were to assess plasma levels, the cellular origin and the morphological characteristics of P-selectin Glycoprotein Ligand-1 (PSGL-1) positive microvesicles (MVs) in patients with unprovoked VTE. We investigated the potential of microRNA (miRNA) plasma levels as biomarkers for unprovoked VTE, as well as the impact of pre-analyses handling and fasting status on plasma EVs. We also developed a cost-effective modified assay to measure procoagulant phospholipid activity. In the study described in Paper I, we evaluated plasma levels and parental origins of PSGL-1+ MVs in patients with unprovoked VTE. The results showed that high plasma PSGL-1+ MV levels were associated with an increased risk of unprovoked VTE. In Paper II, we analyzed the effect of anticoagulant choice on EVs, and found no difference between anticoagulants in terms of total EVs plasma concentrations and size distribution. Postprandial lipidemia was not accompanied by apparent changes in plasma EVs concentration, but an increase in the mean size of VLDL particles interfered with EV measurements in the postprandial phase. The results of the study described in Paper III revealed that plasma miRNA profiling could provide novel biomarkers for unprovoked VTE. In Paper IV, we showed that a modified PPL assay performed as well as a commercial competitor, with advantages of being insensitive to postprandial lipoproteins and tissue factor positive (TF+) EVs and lower cost, making it suitable for large-scale studies.