A New IFN-? Activated Cell Death Pathway in Salmonella-infected Non-Phagocytic Cells

PROJECT SUMMARY/ABSTRACTSalmonella species (especially the S. enterica serotypes typhi and typhimurium) cause disease in ~90 millionpeople every year worldwide. Salmonella infects both phagocytic immune cells (such as macrophages), as wellas non-phagocytic cells. When Salmonella infects macrophages, it triggers a rapid, pro-inflammatory form ofdeath called pyroptosis. Unlike the case with macrophages, less is known about Salmonella-triggered cell deathresponses in non-phagocytic cells, such as intestinal epithelial cells and fibroblasts. As these are the some ofthe first cell types infected by Salmonella, understanding how they respond to this bacterium, and whetherpyroptotic clearance mechanisms are at play in these cells, is an important objective. Our preliminary datademonstrate that infecting epithelial and fibroblastic cells with Salmonella and later exposing them to IFN-?, mimicking the environment of infection in the intestine, induces a novel form of cell death that is neitherpyroptosis nor any of the other reported mechanisms of programmed cell death, including apoptosis, necroptosis,or autophagy. Mechanistically, we find that IFN-? ruptures the Salmonella-containing vacuole in non-phagocyticcells, releasing Salmonella into the cytosol, from where the bacterium induces cell death. Results from a CRISPRscreen suggest that such cell death is the consequence of toxified mitochondria. Based on these and otherobservations, we hypothesize that IFN-?-induced cell death in non-phagocytic cells is a host defense mechanismthat destroys infected intestinal epithelial cells to limit Samonella spread in vivo. To test this hypothesis, we havegenerated mice in which IFN-? signaling can be selectively ablated in either intestinal epithelial cells orphagocytes. The Aims of this proposal are to (1) elucidate the mechanism by which Salmonella kills non-phagocytic cells upon IFN-? exposure; and (2) test the in vivo role of IFN-? signaling and cell death in Salmonella-infected intestinal epithelial cells during acute Salmonella infection. The successful completion of these Aims willreveal the mechanism and in vivo role of a IFN-?-driven new death pathway engaged by the host during anti-Salmonella immune responses.