Radiation exposure can have detrimental effects to human health. Exposure to high doses of radiation can provoke acute radiation syndrome within days and often results in death of the exposed. Exposure to suboptimal doses of radiation does not result in acute radiation syndrome but can significantly increase the risk of cancer in humans. Human activities such as medical treatment (x-rays, CT scans, radiotherapy), nuclear power plant jobs, space explorations and warfare (atomic bombs) have made radiation exposure inevitable. Most importantly relevant to this project, military personnel are directly involved in a number of these activities and are at high risk for getting exposed to high levels of radiation that are detrimental to health. Thus, understanding cellular and molecular mechanisms that proceed radiation exposure is critical for developing new targeted therapies to treat radiation-induced illness. Specifically, how cytoplasmic sensors are involved in radiation-induced illness is understudied. Our preliminary data demonstrate that RIPK2, independently of its known receptors NLRC1 and NLRC2, provoke radiation-induced acute illness. WT mice succumb to 6.5-7Gy lethal radiation within 2-4 weeks of exposure, whereas mice deficient in RIPK2 show not only delay in onset of disease, but also significant protection from death with more than 50% mice surviving the endpoint of the experiment. Interestingly, mice deficient in NLRC1 and NLRC2, the only known sensors upstream of RIPK2, are hypersusceptible to the same 6.5-7Gy radiation dose when compared to WT mice. These NLRC1 and NLRC2-deficient mice show early onset of disease, morbidity and mortality when compared to WT controls. Furthermore, WT and RIPK2-deficient mice co-housing experiments suggest a potential role for microbiota in radiation-induced lethality. These data highlight a central role for RIPK2 in promoting radiation-induced lethality. In aim 1 – first, we will examine the distinct and opposite role of NLRC1 and NLRC2 vs. RIPK2 during radiation-induced lethality in mice; second, we will determine gut epithelium intrinsic role for RIPK2 in radiation- induced lethality; and third, we will investigate cell death pathways that are induced upon radiation and examine the cell death pathways regulated by RIPK2 during radiation exposure. In aim 2 – first, we will examine the effect of antibiotics and fecal microbiome transfer on the outcome of radiation-induced lethality in WT and RIPK2-deficient mice; second, we will examine the effect of colonization of recipient host with WT- or RIPK2-enriched bacteria; third, we will elucidate the fecal microbial landscape in WT and RIPK2-deficient mice before and after radiation using 16S rRNA sequencing; and fourth, we will test the hypothesis that RIPK2 supports specific gut microbiota observed. Successful completion of these projects will elucidate cellular and molecular mechanisms involving RIPK2-mediated illness observed in radiation exposed mice and...