Pathways regulating the levels of tissue factor–positive extracellular vesicles and activation of coagulation in endotoxemic mice

Background: Sepsis and endotoxemia are associated with activation of coagulation as part of the host response to infection, but this can lead to disseminated intravascular coagulation. Lipopolysaccharide (LPS) is detected by the cell surface receptor toll-like receptor (TLR)4 and the intracellular receptor caspase 11. Objectives: This study aimed to determine the roles of TLR4, caspase 11, and the NOD-, LRR-, and pyrin domain-containing protein (NLRP)3 inflammasome in increases of extracellular vesicle (EV) tissue factor (TF) activity and activation of coagulation in a mouse endotoxemia model. Methods: LPS was injected intraperitoneally into control mice and Tlr4^−/−, Casp11^−/−, Nlrp3^−/−, or Casp1^−/− mice or wild-type mice treated with the TLR4 inhibitor TAK-242 or the NLRP3 inhibitor MCC950. Blood samples were collected at 3 and 8 hours for analysis of cells, tumor necrosis factor α, interleukin (IL)-6, IL-1β, soluble intercellular adhesion molecule 1, EV TF activity, and thrombin–antithrombin (TAT) complexes. Results: LPS induced IL-1β at 3 and 8 hours, indicating inflammasome activation at these times. Tlr4 deficiency was associated with a significant decrease in tumor necrosis factor α and IL-6 but not soluble intercellular adhesion molecule 1 in endotoxemic mice. LPS induction of EV TF activity and TAT reduced significantly in Tlr4^−/− mice at both 3 and 8 hours postinjection. In contrast, EV TF activity and TAT were only reduced in Casp11^−/− mice at 8 hours post-LPS injection. Conclusion: Our results indicate that TLR4 plays a major role whereas caspase 11 and the NLRP3 inflammasome play minor roles in the generation of TF-positive EVs and activation of coagulation in a mouse model of endotoxemia.