Activation of plasminogen into plasmin at the surface of endothelial microparticles: a mechanism that modulates angiogenic properties of endothelial progenitor cells in vitro.
Résumé
The regulation of plasmin generation on cell surfaces is of critical importance in the control of vascular homeostasis. Cell-derived microparticles participate in the dissemination of biological activities. However their capacity to promote plasmin generation has not been documented. In this study, we show that endothelial microparticles (EMP) from TNFalpha-stimulated endothelial cells, served as a surface for the generation of plasmin. The generation of plasmin involved expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) at the surface of EMP and was further increased by their ability to bind exogenous uPA on uPAR. Plasminogen was activated at the surface of EMP in a dose-dependent, saturable and specific manner as indicated by the inhibition of plasmin formation by epsilon-amino-caproic acid (epsilon-ACA) and carboxypeptidase B. EMP-induced plasmin generation affects tube formation mediated by endothelial progenitor cells. However, low amounts of EMP increased tube formation whereas higher concentrations inhibited it. Prevention of these effects by inhibitors of either uPA or plasmin, underscore the key role of EMP-induced plasmin generation. In conclusion, we demonstrated that EMP act as vectors supporting efficient plasmin generation and dissemination, a new pathway in the regulation of endothelial proteolytic activities with potential involvement in inflammation, angiogenesis and atherosclerosis.