Abstract
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 gut ecosystems, the presence AHLs and among them we identified one that has never been described: 3-oxo-C12:2. This molecule was decreased in Inflammatory Bowel Disease (IBD) patients, especially during flare, 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-ɣ (IFN-g, 20U/mL) and lipopolysaccharide (LPS, 10ng/mL). We performed a transcriptome analysis using RNAseq to identify inflammatory pathways involved in the effects. Inflammatory response was monitored by measuring cytokine secretion TFNα via ELISA. 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. Cytotoxicity was measured via Lactate Dehydrogenase release.
Results
After LPS/IFN-γ activation, we observed a decrease of secreted TNFα when cells are exposed to 3-oxo-C12:2, in a dose dependent manner: 15μM (-30%, p<0.05), 25μM (-50%, p<0.001) et 50μM (-65%, p<0.0001), no change were observed in steady state. Itreflects an anti-inflammatory effect, without increasing cytotoxicity. To identify mechanisms behind those effects, we analysed the transcriptome of RAW264.7 cells exposed to AHL. JAK-STAT and NF-κB pathways were differentially down-regulated in presence of 3-oxo-C12:2. In addition, the 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. This response is partly mediated by the bitter taste receptor T2R138. This receptor is a potential target of our AHL of interest and we are currently studying the inflammatory pathways involved behind those effects. 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.
Isolation of Anti-Inflammatory and Epithelium Reinforcing Bacteroides and Parabacteroides Spp. from A Healthy Fecal Donor