Role of non-myeloid cells' pyroptosis in melioidosis

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Activation of caspase-1 and caspase-11 in the context of inflammasomes leads to processing and secretion of IL-1β and IL-18 and triggers a lytic cell death termed pyroptosis. Inflammasome activation and pyroptosis have been shown to protect the host from infection with a range of pathogens including Burkholderia pseudomallei, a gram-negative bacterium used as a mouse model of melioidosis. However, it is also becoming clear that inflammasome activation and pyroptosis can be deleterious to the host by triggering lethal eicosanoid storm, mediating lethal endotoxic shock, and causing disseminated intravascular coagulation (DIC). We have recently shown that the only functional inflammasome expressed by epithelial and endothelial cells is caspase-11, and that in a model of melioidosis caspase-11-dependent pyroptosis of lung epithelial cells is protective. Based on our preliminary results and the published literature we hypothesize that activation of caspase-11 in epithelial cells will protect the host from pneumonic melioidosis through induction of pyroptosis and preferential production of anti-inflammatory eicosanoids like prostaglandin E2. In contrast, caspase-11 activation in endothelial cells may prove deleterious because it may damage barrier integrity, induce DIC and excessive inflammation through release of Tissue Factor and LTB4. Thus, studying the function of caspase-11 selectively in epithelial or endothelial cells will allow us to identify the deleterious and the beneficial responses and therefore potentially indicate therapeutic avenues to inhibit the former and encourage the latter. In aim 1 we will focus on the role of caspase-11 in epithelial cells. We will test the role of caspase-11 and gasdermin D in the production of eicosanoids by lung epithelial cells. We will also test the susceptibility to melioidosis of mice that lack expression of caspase-11 in lung epithelial cells and determine the role of epithelial-derived eicosanoids in melioidosis. In aim 2 we will study the role of caspase-11 in endothelial cells. We will examine how caspase-11 controls production of eicosanoids and release of Tissue Factor in endothelial cells. We will test the susceptibility to melioidosis of mice that lack expression of caspase-11 in endothelial cells and establish the role of Tissue Factor, Platelet Activating Factor, and DIC in the pathogenesis of melioidosis.