Granulocyte microvesicles with a high plasmin generation capacity promote clot lysis and improve outcome in septic shock

Microvesicles (MVs) have previously been shown to exert profibrinolytic capacity, which is increased in patients with septic shock (SS) with a favorable outcome. We therefore hypothesized that the plasmin generation capacity (PGC) could confer to MVs a protective effect supported by their capacity to lyse a thrombus, and we investigated the mechanisms involved. Using a MV-PGC kinetic assay, ELISA and flow cytometry, we found that granulocyte MVs (Gran-MVs) from SS patients display a heterogeneous PGC profile driven by the uPA (urokinase)/uPAR system. In vitro, these MVs lyse a thrombus according to their MV-PGC levels in a uPA/uPAR-dependent manner, as shown in a fluorescent clot lysis test and a lysis front retraction assay. Fibrinolytic activators conveyed by MVs contribute to approximately 30% of the plasma plasminogenolytic capacity of SS patients. In a murine model of SS, the injection of high PGC Gran-MVs significantly improved mouse survival and reduced the number of thrombi in vital organs. This was associated with a modification of the mouse coagulation and fibrinolysis properties toward a more fibrinolytic profile. Interestingly, mouse survival was not improved when soluble uPA was injected. Finally, using a multiplex array on plasma from SS patients, we found that neutrophil elastase correlates with the effect of high-PGC-capacity plasma and modulates the Gran-MV plasmin generation capacity by cleaving uPA-PAI-1 complexes. In conclusion, we show that high PGC level displayed by Gran-MVs reduce thrombus formation and improve survival conferring to Gran-MVs a protective role in a murine model of sepsis.