Septic shock is invariably associated with systemic coagulation leading to thrombus formation. Sepsis-related organ dysfunction has been attributed to microvascular thrombosis. Mortality rate doubles in septic patients with disseminated intravascular coagulation (DIC). DIC is even considered as a sign that ?death is coming?. Previous studies have demonstrated the important roles of tissue factor (TF) in sepsis-associated DIC. However, the mechanism leading to TF release, which triggers systemic coagulation in sepsis, is unknown. Recent in vitro studies revealed that bacterial components (flagellin, the rod protein of the type III secretion system (T3SS), or LPS) induce programmed cell death (called pyroptosis) of macrophages through activation of inflammasome pathways. We show that intravenous injection of a T3SS rod protein E. coli, EprJ, induced depletion of peripheral monocytes and macrophages in tissues. Importantly, injection of EprJ or LPS, which elicit canonical and noncanonical inflammasome activation, respectively, induced systemic coagulation activation, as evident by prolonged prothrombin time (PT) due to increased consumption of coagulation factors, thrombocytopenia, increased plasma levels of thrombin-antithrombin complex (TAT), and reduced plasma fibrinogen levels. Thus, our findings made connections between the in vitro and in vivo observations and suggested monocyte/macrophage pyroptosis as a trigger of DIC in sepsis. The goal of this application is to delineate the underlying mechanisms by which inflammasome activation and pyroptosis trigger DIC in sepsis.
Specific Aim 1 will establish inflammasome activation and pyroptosis as a common mechanism for DIC induced by bacterial infection. The working hypothesis is that bacteria and bacterial components from different strains elicit DIC through Inflammasome activation and pyroptosis. We will use a combination of various deficient mice to elucidate the role of inflammasome activation and pyroptosis in DIC elicited by Gram-negative bacteria.
Specific Aim 2 is to identify the molecular mechanism of TF release from macrophages following inflammasome activation. We will also use the myeloid-specific TF knockout mice and a low TF mouse model to elucidate whether DIC elicited by the bacterial components depends on release of TF from macrophages.
Specific Aim 3 will demonstrate the role of inflammasome activation in sepsis-associated coagulopathy. We will use the cecal ligation and puncture (CLP) sepsis model and bacterial infusion sepsis model to investigate the role of inflammasome activation and pyroptosis in coagulation. Completion of the proposed studies will demonstrate the molecular mechanism of systemic coagulation is sepsis. Such findings would have profound ramifications for the identification of new drug targets for DIC, the deadly complication of sepsis.
Systemic coagulation is a major driving force for morbidity and mortality in sepsis. This research project seeks to understand the mechanism of coagulation in sepsis. Completion of this work will provide new insights into the molecular mechanisms eliciting coagulation during sepsis that could lead to targeted therapies to treat this deadly disease.