The burden of trauma-related diseases is considerable. Following exsanguination and/or brain injury that commonly result in early phase death, more than 60% of surviving patients later die of causes related to the development of systemic inflammatory response syndrome (SIRS) and acute lung injury (ALI). This patient population is well suited for prophylactic interventions aimed at preventing these occurrences because of the time lag before the onset of organ inflammation and failure. Nonetheless, few specific targets have been identified that predispose to SIRS and ALI. Since endothelial cells (ECs) play important and broad roles in hemorrhagic shock (HS)-induced inflammation, and programed EC death significantly influence the progress of inflammation, an insight of the mechanism of HS-induced EC pyroptosis, a caspase-1-dependent programmed cell death, will provide us novel potential therapeutic targets for post-HS SIRS and ALI. In a broader sense, the proposed studies will contribute to a greater understanding of the pathogenesis of a number of human inflammatory diseases in which endothelium is involved in the inflammatory process. Pyroptosis is a recently identified host cell death that is stimulated by a range of microbial infections and non-infectious stimuli, including stroke, heart attack, or cancer. Pyroptosis features rapid plasma-membrane rupture and release of proinflammatory intracellular contents. Our published and preliminary findings demonstrate an important role for pyroptosis in the development of inflammation following HS. We observed that: 1) HS induces lung EC pyroptosis following inflammasome activation, and this induction requires HMGB1- TLR4 signaling; 2) Lung EC pyroptosis results in pro-inflammatory cytokines release from the ECs and induces cytokines expression in alveolar macrophages; 3) Pyroptotic ECs increase polymorphonuclear neutrophils (PMN) adhesion to the ECs; 4) Pyroptotic ECs increases endothelial permeability; 5) Prevention of HS-induced EC pyroptosis by EC-specific TLR4 knockout reduces lung permeability following HS; and 6) TLR4- upregulated TLR2 signaling augments HS-induced lung EC pyroptosis. These results suggest a novel and important role of lung EC pyroptosis in the development of post-HS ALI. Based on our findings, we hypothesize that: 1) HS through danger molecules activates inflammasome and/or pyroptosome, and thereby induces lung EC pyroptosis; 2) Lung EC pyroptosis serves an important role in the development of ALI after HS; and 3) Interactions between TLR4 and TLR2 serve as an important mechanism mediating HS-primed EC pyroptosis. We propose three specific aims to test our hypotheses:
Aim 1. To determine the mechanism by which HS induces pyroptosis in the lung and lung EC;
Aim 2. To determine the role of EC pyroptosis in the development of ALI following HS;
and Aim 3. To determine the mechanisms of HS-primed induction of pyroptosis in the lung and lung EC in response to TLR2 ligands.
Acute lung injury (ALI) is a major component of post-hemorrhagic shock (HS)/trauma systemic inflammatory response syndrome (SIRS); however, few specific targets have yet been identified that predispose to SIRS and ALI, rendering mortality rates high and effective treatment lacking. Lung endothelial cells (ECs) play a crucial role in the development of lung inflammation, and cell pyroptosis is a recently identified programmed cell death pathway with proinflammatory features that importantly influence inflammation progression. Gaining Insight into the mechanism of HS-induced EC pyroptosis will provide us with novel potential therapeutic targets for post- HS SIRS and ALI.
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