The Fatty Acid Oleate in the C. elegans Innate Immune Response

Abstract

Host metabolism is profoundly altered during bacterial infection, both as a consequence of immune activation and secondary to virulence strategies of invading pathogens. As a result, the metabolic pathways that regulate nutrient acquisition, energy storage, and resource allocation in host cells must adapt to pathogen stress in order to meet the physiological demands of the host during infection. In this work, we uncover that the synthesis of the monounsaturated fatty acid (MUFA) oleate is necessary for the pathogen-mediated induction of immune defense genes. Accordingly, C. elegans deficient in oleate production are hypersusceptible to infection with diverse human pathogens, which can be rescued by the addition of exogenous oleate. However, oleate is not sufficient to drive protective immune activation. Oleate is also important for proper lipid storage and abundance. We found that exposure to pathogenic bacteria drives rapid somatic depletion of lipid stores in C. elegans. Activating the p38/MAPK immune signaling pathway in the absence of pathogens was also sufficient to drive loss of somatic fat. In addition, we found that transcriptional suppression of MUFA synthesis occurs during P. aeruginosa infection, in a manner dependent on pathogen virulence. Finally, we showed that the host compensates for the pathogen-induced depletion of fatty acids by promoting the redistribution of oleate from non-intestinal tissues to support immune function in the intestine. Together, these data add to the known health-promoting effects of MUFAs, and suggest an ancient link between nutrient stores, metabolism, and host responses to bacterial infection.