DESCRIPTION (provided by applicant): Abstract Sepsis affects more than 800,000 people annually with a mortality rate as high as 30% in the US. Severe sepsis complicated with multiple organ dysfunction syndrome (MODS) is a leading cause of death in intensive therapy units with a mortality rate exceeding 50%. Acute lung injury (ALI) is an important component of MODS and often serves as a direct cause of patient death. Nonetheless, few effective therapeutic targets have been identified that predispose an individual to MODS and ALI in sepsis. Alveolar macrophages (AM) are at the center of the pathogenesis of ALI triggered by sepsis. Macrophage (M�pyroptosis is a recently identified caspase-1-dependent programmed cell death, which features rapid plasma-membrane rupture and release of pro-inflammatory intracellular contents. However, the in vivo role of M�yroptosis in the progression of sepsis and the mechanism underlying M�yroptosis remain unclear. We now demonstrate in our preliminary studies that sepsis induces AM and circulating monocytes pyroptosis in a mouse polymicrobial sepsis model of cecal ligation and puncture (CLP). This sepsis-induced pyroptosis is mediated by a novel signaling pathway, in which (RAGE)-dependent endocytosis of HMGB1) activates pyroptosome assembly and cell pyroptosis. Our further observations suggest that induction of AM pyroptosis enhances inflammation by releasing or promoting healthy AM to release pro-inflammatory cytokines and chemokines, augmenting polymorphonuclear neutrophil (PMN) chemotaxis and suppressing T lymphocyte migration. receptor for advanced glycation end products high mobility group box 1 ( Moreover, we have also shown in our previous and preliminary studies that LPS and HMGB1 throughTLR4 upregulate TLR2 in AM, which in turn augments AM pyroptosis in response to bacteria-derived TLR2 ligands. Based on these findings, we hypothesize that: 1) AM pyroptosis may promote the development of ALI in sepsis by amplifying the inflammatory process; 2) HMGB1-RAGE signaling serves as a novel mechanism that induces AM pyroptosis in sepsis; and 3) TLR4 signaling-upregulated TLR2 serves as an important mechanism for augmented AM pyroptosis in sepsis. In order to test these hypotheses, we propose the following three specific aims: Specific Aim #1: to determine the role of AM pyroptosis in the development of ALI following sepsis. Specific Aim #2: to determine the molecular mechanism through which sepsis induces AM pyroptosis. Specific Aim #3: to determine the mechanism of TLR2 signaling-primed AM pyroptosis in sepsis.