Innate Recognition of Bacterial Sugars

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SUMMARY/ABSTRACT IL-1β production is essential for effective host defense against many pathogens, but can also be a source of significant pathological inflammation. As such, the mechanisms by which IL-1β is produced are an intense area of research interest. Secretion of IL-1β (and related cytokines such as IL-18) by phagocytes including macrophages and dendritic cells is regulated by the formation of “inflammasome” complexes that activate cytosolic caspase-1 to process pro-cytokine into the mature form and allow its release from the cell. This project has been investigating the innate immune mechanisms by which peptidoglycan from gram-positive bacterial cell walls activates the NLRP3 inflammasome. We have recently discovered that when peptidoglycan is eaten by phagocytes, degradation and release of monomeric n-acetylglucosamine is necessary to stimulate IL-1β release. Further, we have developed evidence that this sugar is detected in the cytosol by hexokinase II, an enzyme involved in the first step of glycolysis. This finding suggests a new link between mechanisms of cellular metabolism and innate sensing of microbial pathogens. In this project, we will investigate the role of hexokinase in macrophage responses to infection with Staphylococcus aureus in vitro and in vivo, the mechanisms by which hexokinase regulation activates the NLRP3 inflammasome, and the role of mitochondrial permeability in the process.