F"avin-containing monooxygenases (FMOs) are conserved intrace""u"ar enzymes that oxidize organic mo"e- cu"es, such as xenobiotics, and promote their export by p"asma membrane transporters. We recent"y discov- ered that FMOs are important innate host defense effectors. This project uses an in vivo reductionist approach with Caenorhabditis e5egans as mode5 organism to improve understanding of the host defense functions of FMOs. The "ong-term goa" of this project is to understand how C. e5egans and mamma"ian FMOs are regu- "ated and how they promote host defense during infection. Our prior research supports the idea that C. e5e- gans FMO-D, human FMOE, and other FMOs may possess evo"utionari"y conserved functions in host-microbe interactions. What these functions are and how they are regu5ated is current5y unknown. This is an important fundamenta" know"edge gap that impedes understanding of homeostasis and host defense in anima"s, and that obscures therapeutic opportunities to treat infections or inf"ammatory diseases. The overa"" objective of this deve"opmenta" app"ication is to increase mechanistic understanding of FMO-D/FMOE function in the con- text of host defense against bacteria" infection and to deve"op nove" approaches and mode" organisms, thus enab"ing future studies to e"ucidate the ro"es and regu"ation of FMOs in C. e5egans and mamma"ian innate im- munity. This project’s centra" hypothesis is that HLH-CD/TFEB and NHR-JK/PPAR-α induce expression of FMO-P/FMOQ for host defense via FMO-P activity-dependent antimicrobia5 mechanisms. To test this hypothe- sis, we wi"" Define upstream mechanisms of fmo-P/FMOQ gene regu"ation and downstream mechanisms of FMO-D/FMOE-mediated host defense. The proposed research is technica""y innovative because of innovations in the app"ication of new methods to determine peroxidized "ipids in C. e5egans, for the use of synthetic "etha"- ity to uncover specific and genetica""y redundant tissues of action, and for use of genetic comp"ementation for in vivo functiona" eva"uation of reconstructed ancient mamma"ian FMOs in C. e5egans. Additiona""y, the pro- posed work is conceptua""y innovative for connecting HLH-MN/TFEB to NHR-ST/PPAR-α for the regu"ation of FMO-D/FMOE (revea"ing a nove" connection between metabo"ism and innate immunity) and for its proposed ro"e for FMO-D/FMOE as source of ROS and oxidized signa"ing "ipids during infection. This proposa" is high"y re"evant to human hea"th because it focuses on genes and pathways that are conserved in humans. This pro- posa" is high"y significant because it direct"y addresses the important gap in fundamenta" know"edge of FMO ro"es and regu"ation as innate immunity effectors. Moreover, the reagents, assays, new mode" organisms, and know"edge gained through this deve"opmenta" project wi"" open new avenues of research into innate immunity and FMO function and he"p create a path forward for the rationa" design of host-directed therapeutics against bacteria" infections a...