Caspase-1 and Inflammasome Activation in Traumahemorrhagic Shock

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DESCRIPTION (provided by applicant): Controlling inflammation and cellular damage is the key to preventing and treating multiple organ failure (MOF) following trauma. However, many of the mechanisms that regulate inflammation and cell death in specific organs remain unknown. This means that despite advances in supportive measures for patients with MOF, there have been few advances in MOF treatments, or in our ability to adequately prevent the onset of MOF. Our overarching goal is to ultimately develop new therapeutics for trauma patients based on regulating the inflammatory response and its effects on cellular death and survival pathways following trauma and hemorrhagic shock (HS). In this proposal we will continue to investigate molecular pathways following HS that lead to activation of caspase-1 in end-organs, particularly liver. We will also determine how caspase-1 activation regulates autophagy and apoptosis, which in turn determines organ cell survival. Knowing how these cell-signaling pathways function and interact may help us to find future therapeutic targets for prevention and treatment of MOF after trauma. Our preliminary data suggest novel roles for caspase-1 in the liver during trauma/HS and during oxidative stresses. We have found that caspase-1 is a central regulator of autophagy in the liver following trauma/HS. Importantly, we have shown that caspase-1 activation is hepatoprotective after trauma/HS, in a manner independent of caspase-1-activated cytokines (IL1b/IL18) or a main inflammasome component, NLRP3. These findings challenge the paradigm that activation of caspase-1 by danger signals such as reactive oxygen species (ROS) occurs via the NLRP3-inflammasome. These preliminary findings lead us to our main hypothesis that caspase-1 activation occurs by cell-type specific mechanisms, and that caspase-1 function also differs in these cell types. We have shown that caspase-1 is central to the regulation of liver cell survival pathways during oxidative stress induced by HS. Without caspase-1, or where caspase-1 activation is inhibited, hepatocytes are less able to initiate cell survival strategies such as autophagy in response to HS. This results in increased apoptotic or necrotic cell death and increased levels of organ damage and failure. We expect to show that caspase-1 activation pathways differ after HS and are cell-type dependent. We also expect to show that caspase-1 has multiple novel functions in cells where production of IL1b/IL18 inflammatory cytokines is not the primary response to trauma. Understanding these novel pathways of inflammatory activation and function in individual cell types and organs may help us find new ways to treat and prevent MOF in trauma patients in the future.