Background Crohn's disease (CD) associated dysbiosis is characterized by a loss of Faecalibacterium prausnitzii, whose culture supernatant exerts an anti-inflammatory effect both in vitro and in vivo. However, the chemical nature of the anti-inflammatory compounds has not yet been determined. Methods Peptidomic analysis using mass spectrometry was applied to F. prausnitzii supernatant. Anti-inflammatory effects of identified peptides were tested in vitro directly on intestinal epithelial cell lines and on cell lines transfected with a plasmid construction coding for the candidate protein encompassing these peptides. In vivo, the cDNA of the candidate protein was delivered to the gut by recombinant Lactic Acid Bacteria to prevent DNBS-colitis in mice. Results The seven peptides, identified in the F. prausnitzii culture supernatants, derived from a single Microbial Anti-inflammatory Molecule (MAM), a protein of 15 kDa and comprising 53% of nonpolar residues. This last feature prevented the direct characterization of the putative anti-inflammatory activity of MAM-derived peptides. Transfection of MAM cDNA in epithelial cells led to a significant decrease in the activation of the NF-κB pathway with a dose-dependent effect. Finally, the use of a food-grade bacterium, Lactococcus lactis, delivering a plasmid encoding MAM was able to alleviate DNBS-induced colitis in mice. Conclusion A 15kDa protein with anti-inflammatory properties is produced by F. prausnitzii, a commensal bacterium involved in CD pathogenesis. This protein is able to inhibit the NF-κB pathway in intestinal epithelial cells and to prevent colitis in an animal model.

Metabolism of tryptophan by the gut microbiota into derivatives that activate the aryl hydrocarbon receptor (AhR) contributes to intestinal homeostasis. Many chronic inflammatory conditions, including celiac disease involving a loss of tolerance to dietary gluten, are influenced by cues from the gut microbiota. We investigated whether AhR ligand production by the gut microbiota could influence gluten immunopathology in nonobese diabetic (NOD) mice expressing DQ8, a celiac disease susceptibility gene. NOD/DQ8 mice, exposed or not exposed to gluten, were subjected to three interventions directed at enhancing AhR pathway activation. These included a high-tryptophan diet, gavage with Lactobacillus reuteri that produces AhR ligands or treatment with an AhR agonist. We investigated intestinal permeability, gut microbiota composition determined by 16S rRNA gene sequencing, AhR pathway activation in intestinal contents, and small intestinal pathology and inflammatory markers. In NOD/DQ8 mice, a high-tryptophan diet modulated gut microbiota composition and enhanced AhR ligand production. AhR pathway activation by an enriched tryptophan diet, treatment with the AhR ligand producer L. reuteri, or pharmacological stimulation using 6-formylindolo (3,2-b) carbazole (Ficz) decreased immunopathology in NOD/DQ8 mice exposed to gluten. We then determined AhR ligand production by the fecal microbiota and AhR activation in patients with active celiac disease compared to nonceliac control individuals. Patients with active celiac disease demonstrated reduced AhR ligand production and lower intestinal AhR pathway activation. These results highlight gut microbiota-dependent modulation of the AhR pathway in celiac disease and suggest a new therapeutic strategy for treating this disorder.

Faecalibacterium prausnitzii and its supernatant showed protective effects in different chemically-induced colitis models in mice. Recently, we described 7 peptides found in the F. prausnitzii supernatant, all belonging to a protein called Microbial Anti-inflammatory Molecule (MAM). These peptides were able to inhibit NF-κB pathway in vitro and showed anti-inflammatory properties in vivo in a DiNitroBenzene Sulfate (DNBS)-induced colitis model. In this current proof we tested MAM effect on NF-κB pathway in vivo, using a transgenic model of mice producing luciferase under the control of NF-κB promoter. Moreover, we tested this protein on Dextran Sodium Sulfate (DSS)-induced colitis in mice. To study the effect of MAM we orally administered to the mice a Lactococcus lactis strain carrying a plasmid containing the cDNA of MAM under the control of a eukaryotic promoter. L. lactis delivered plasmids in epithelial cells of the intestinal membrane allowing thus the production of MAM directly by host. We showed that MAM administration inhibits NF-κB pathway in vivo. We confirmed the anti-inflammatory properties of MAM in DNBS-induced colitis but also in DSS model. In DSS model MAM was able to inhibit Th1 and Th17 immune response while in DNBS model MAM reduced Th1, Th2, and Th17 immune response and increased TGFβ production.