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Background Acyl-Homoserine Lactones (AHLs) are Quorum Sensing molecules involved in the communication network of bacteria and can also have an impact on the host’s cells. We recently showed, in the human gut ecosystem, the presence of AHLs. Among them, we identified one that has never been described: 3-oxo-C12:2. This molecule was decreased in Inflammatory Bowel Disease (IBD) patients, and its presence was correlated to normobiosis. Interestingly, 3-oxo-C12:2 is structurally close to an AHL well described and synthesized by P. aeruginosa, 3-oxo-C12. We intent to describe 3-oxo-C12:2 effects on gut inflammation and to identified which signalling pathways are involved. Given its analogous structure to 3-oxo-C12, we hypothesized that 3-oxo-C12:2 can interact with the same cellular partners, in particular a bitter taste receptor (BTR), called T2R138, which is a GPCR expressed by immune and epithelial gut cells. Methods To test our hypothesis, we used murine macrophages cell line RAW264.7, stimulated by interferon-γ (IFN-γ, 20U/mL) and lipopolysaccharide (LPS, 10ng/mL). Inflammatory response was monitored by measuring cytokine secretion via ELISA We performed a transcriptome analysis to identify inflammatory pathways involved in the effects and analyse pathways by capillary Western blot. Probenecid, a known allosteric inhibitor for T2R138, was used to study T2R138 role in AHL signalling. BTR screening assay was performed to extend search for 3-oxo-C12:2 receptors. Results After LPS/IFN-γ activation, we observed a decrease of secreted TNFα when cells were exposed to 3-oxo-C12:2, in a dose dependent manner: 15μM (-30%, p&amp;lt;0.05), 25μM (-50%, p&amp;lt;0.001) et 50μM (-65%, p&amp;lt;0.0001) while no change were observed in steady state. This reflects an anti-inflammatory effect, in absence of cytotoxicity. By transcriptomic analysis, we identified the JAK-STAT pathway as differentially down-regulated. Exposing cells to 3-oxo-C12:2 prevented JAK1 and STAT1 protein phosphorylation. In addition, the observed anti-inflammatory effects were lost in presence of Probenecid, a T2R138 inhibitor. In a BTR screening assay, we confirmed that 3-oxo-C12:2 activates T2R38, but also five other BTR (T2R13, T2R8, T2R14, T2R1, T2R10). Conclusion 3-oxo-C12:2 exerts a dose dependent anti-inflammatory effect on murine immune cells by preventing the activation of the JAK-STAT pathway. This response is partly mediated by the bitter taste receptor T2R138. This receptor is a potential target of our AHL of interest. Studying the signalling between the receptor and the anti-inflammatory response would allow us to better understand the inter-kingdom dialogue between microbiota involving AHL in IBD.

P043 3-oxo-C12:2, a Quorum Sensing molecule from the gut, exerts anti-inflammatory effects through a bitter taste receptor