Activation and Evasion of the Inflammasome by Noncytotoxic Staphylococcus aureus

PROJECT SUMMARY/ABSTRACT The bacterium Staphylococcus aureus (S. aureus) is the second-leading infectious cause of death in the world. S. aureus spreads through the bloodstream, causing disseminated infections that can persist for weeks and are associated with high mortality. The ability of S. aureus to evade clearance by the immune system is a major barrier to the treatment of disseminated S. aureus infections. Upon dissemination, S. aureus can adopt a noncytotoxic phenotype. The presence of noncytotoxic bacteria is associated with non-resolving infections and with increased patient mortality during bloodstream infections. Despite mounting evidence that noncytotoxic S. aureus plays a major role during infection of humans, most research on S. aureus-immune interactions has focused on cytotoxic bacteria. It not clear how noncytotoxic S. aureus restricts immune responses, and how these activities impact the outcomes of infection. The research detailed in this proposal aims to determine how noncytotoxic S. aureus evades detection by the innate immune system. To address this knowledge gap, Dr. Jastrab developed a macrophage infection model using noncytotoxic S. aureus. This model demonstrated that a cell wall modification previously implicated in immune evasion, peptidoglycan (PGN) O-acetylation, blunts release of the inflammatory cytokine IL-1b. Release of IL-1b required a second cell wall modification, glycosylation of the cell wall component wall teichoic acid (WTA). Thus, these cell wall modifications have competing effects on immune signaling during noncytotoxic S. aureus infection. IL-1b release required activation of the cytosolic DNA receptor Absent in Melanoma 2 (AIM2). These data support the hypothesis that PGN O-acetylation and WTA glycosylation alter the availability of cytosolic DNA within macrophages to modulate immunity. The research described in this proposal explores key features of this hypothesis by defining the origin of AIM2-associated DNA, determining how cell wall modifications impact immunity during bloodstream infection, and identifying host factors that regulate AIM2 activation. Dr. Jastrab’s research will be supported by a team of mentors committed to fostering his scientific development. His primary mentor, Dr. Jonathan Kagan, is a world-renowned immunologist who will provide hands-on scholarly and technical training in molecular immunology. Dr. Kagan has a proven track record of successful mentorship, having supervised numerous trainees currently in tenure-track faculty positions. Drs. Jastrab and Kagan have devised a Career Development Plan that will ensure important professional benchmarks are met. To augment Dr. Kagan’s mentorship, Dr. Jastrab has assembled an Advisory Committee of scientists with expertise in microbiology, immunology, and clinical infectious diseases to provide scientific and professional guidance. The support of this K08 award will facilitate Dr. Jastrab’s transition to a role as an independent investigator characterizing molecular mechanisms of bacteria-immune interactions during infection.