Oxysterol Regulation of Microbial Pathogenesis

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Project Summary The proposed project focuses on our recent discovery that immunological production of the oxysterol 25- Hydroxycholesterol (25HC) potently inhibits the cellular dissemination of two globally important bacterial pathogens, Listeria monocytogenes and Shigella flexneri. The anti-bacterial activity of 25HC is mediated through mobilization of the accessible cholesterol pool from the plasma membrane (PM). Accessible cholesterol is one of three pools into which PM cholesterol is sub-divided and this pool regulates cellular signaling pathways that control lipid homeostasis and cell growth. By first characterizing the molecular mechanism by which 25HC induces internalization of accessible cholesterol (Aim 1), these studies will reveal how cholesterol can be rapidly transported in response to cytokine stimulation. Second, we will determine how remodeling of PM cholesterol suppresses Listeria and Shigella from penetrating the cell-to-cell contact junctions of the mucosal epithelium (Aim 2). This work will reveal how mammals enhance the barrier function of mucosal surfaces through cholesterol metabolic pathways and will identify points of weakness in the mucosal immune system that may be exploited by numerous microbial pathogens. Third, we will develop new technologies for monitoring cholesterol dynamics in the living organism and use these technologies to determine the tissues and cell types that mobilize accessible cholesterol in response to bacterial infection (Aim 3). Finally, the physiological significance of oxysterol-mediated immune pathways will be investigated in mammalian model organisms using three complementary mouse models that disrupt 25HC activation, production, and downstream activity (Aim 4). Insights gleaned from these studies, which range from basic biochemistry to mouse models of infection, will explain how the human immune system has adapted fundamental aspects of cholesterol metabolism to protect barrier cells from intracellular bacterial infection. Developing new drugs that mimic the molecular activity of 25HC as determined in this proposal would be an innovative approach to combat human infectious disease associated with pathogens that exploit host cholesterol metabolism. These studies will also provide new insights into the pathogenic mechanisms of an important infectious disease-causing agent and also into the biology of the human inflammatory response.