PROJECT SUMMARY ABSTRACT Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection, and acute lung injury (ALI) is a leading cause of death associated with sepsis. An emerging mechanism of sepsis induced-ALI (sepsis-ALI) involves neutrophils/macrophages undergoing cell death, releasing nuclear histones and citrullinated histone H3 (CitH3) to cause tissue damage and exacerbate pulmonary injury. CitH3 is catalyzed by peptidylarginine deiminase 2 and 4 (PAD2 and PAD4). We found that CitH3 is elevated in serum of patients with sepsis-ALI, but not in ALI patients due to non-infectious causes, suggesting that CitH3 could be a biomarker, as well as a potential causative factor for sepsis-ALI. Significant elevations of CitH3 and PAD2 in bronchoalveolar lavage fluid (BALF), not PAD4, are detected in septic patients. While Pad4-/- mice do not show a clear septic phenotype compared with wild type littermates, the Pad2-/- mice are strikingly more resistant to sepsis-ALI and other organ dysfunctions. The improved survival of the Pad2-/- septic mice is linked to enhanced bacterial clearance due to enhanced function of macrophages. We have data to show that chemical inhibition of PAD2 and antibody sequestration of CitH3 have therapeutic benefits to treat sepsis- ALI in mice. Combining our expertise in cell and molecular biology, animal models of and clinical research in sepsis, and chemical biology, our team-based research aims to dissect the physiological actions of PAD2 and CitH3 in modulating macrophage function associated with sepsis (Aim 1), and to conduct proof-of-concept studies targeting PAD2 and CitH3 as novel means to treat sepsis-ALI in mice (Aim 2). Circulating CitH3 could act as a signaling molecule and bind to membrane receptor(s) to fulfill its biological function; or CitH3 can enter the host cells via endocytosis to directly interfere with their survival or death pathways. Thus, knowledge on the membrane delimited interaction between CitH3 and macrophages will add significant insight into the pathogenesis and potential treatment of sepsis-ALI and other multi-organ dysfunctions.

PROJECT NARRATIVE Sepsis-induced acute lung injury (sepsis-ALI) is a pulmonary dysfunction caused by dysregulated host response to infection. This project aims to establish novel approaches to ameliorate sepsis-ALI through selective inhibition of peptidylarginine deiminase 2 (PAD2) and/or sequestration of citrullinated H3 (CitH3).