Gut - brain communications disorders in irritable bowel syndrome (IBS) are associated with intestinal microbiota composition, increased gut permeability, and psychosocial disturbances. Symptoms of IBS are difficult to medicate, and hence much research is being made into alternative approaches. This study assesses the potential of a treatment with pasteurized Akkermansia muciniphila for alleviating IBS-like symptoms in two mouse models of IBS with different etiologies. Two clinically relevant animal models were used to mimic IBS-like symptoms in C57BL6/J mice: the neonatal maternal separation (NMS) paradigm and the Citrobacter rodentium infection model. In both models, gut permeability, colonic sensitivity, fecal microbiota composition and colonic IL-22 expression were evaluated. The cognitive performance and emotional state of the animals were also assessed by several tests in the C. rodentium infection model. The neuromodulation ability of pasteurized A. muciniphila was assessed on primary neuronal cells from mice dorsal root ganglia using a ratiometric calcium imaging approach. The administration of pasteurized A. muciniphila significantly reduced colonic hypersensitivity in both IBS mouse models, accompanied by a reinforcement of the intestinal barrier function. Beneficial effects of pasteurized A. muciniphila treatment have also been observed on anxiety-like behavior and memory defects in the C. rodentium infection model. Finally, a neuroinhibitory effect exerted by pasteurized A. muciniphila was observed on neuronal cells stimulated with two algogenic substances such as capsaicin and inflammatory soup. Our findings demonstrate novel anti-hyperalgesic and neuroinhibitory properties of pasteurized A. muciniphila, which therefore may have beneficial effects in relieving pain and anxiety in subjects with IBS.

The potential role of gut microbiota in pain modulation is arousing an emerging interest since recent years. This study investigated neuromodulatory properties of gut microbiota to identify next-generation probiotics to propose alternative therapies for visceral pain management. Neuromodulation ability of 10 bacterial strains isolated from a healthy donor was assessed both on ND7/23 immortalized cell line and primary neuronal cells from rat dorsal root ganglia. This screening highlighted the neuroinhibitory property of Parabacteroides distasonis (F1-2) strain, supported both by its intracellular content and membrane fraction, which was further investigated in visceral pain mouse models. Oral administration of F1-2 resulted in a significant decrease of colonic hypersensitivity (CHS) in dextran sulfate sodium (0.5%) model associated with low-grade inflammation and a significant decrease of CHS in Citrobacter rodentium postinfectious models. No effect of F1-2 oral administration on CHS was observed in a neonatal maternal separation stress model. Antihyperalgesic effect unlikely involved modulation of inflammatory processes or restoration of intestinal barrier. Exploration of direct dialogue mechanisms between this strain and nervous system, assessed by calcium imaging experiments, revealed that F1-2 interacts directly with nociceptors by reducing activation level on capsaicin, inflammatory soup, and bradykinin stimulations. Our study provides new insights about bacteria–host interaction and places P distasonis as a potential therapeutic strategy in the treatment of visceral pain observed in leaky gut–associated pathologies.

Experimental and clinical evidence has demonstrated the potential of probiotic strains in the prevention or treatment of inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). However, there is little data on what the methodology leading to the identification of such strains should be. In this work, we propose a new flowchart to identify strains with probiotic potential for the management of IBS and IBD, which we tested on a collection of 39 lactic acid bacteria and Bifidobacteria strains. This flowchart included in vitro tests of immunomodulatory properties on intestinal and peripheral blood mononuclear cells (PBMCs), assessment of the barrier-strengthening effect by measuring transepithelial electric resistance (TEER) and quantification of short-chain fatty acids (SCFAs) and aryl hydrocarbon receptor (AhR) agonists produced by the strains. The in vitro results were then combined in a principal component analysis (PCA) to identify strains associated with an anti-inflammatory profile. To validate our flowchart, we tested the two most promising strains identified in the PCA in mouse models of post-infectious IBS or chemically induced colitis to mimic IBD. Our results show that this screening strategy allows the identification of strains with potential beneficial effects on colonic inflammation and colonic hypersensitivity.

Acid-sensing ion channels (ASICs) are members of the DEG/ENaC family that includes the only known peptide-gated ion channels. While ASICs are gated by protons, they are also sensitive to peptides and are modulated by the molluscan FMRFamide and other mammalian neuropeptides ending by the RFamide motif. We identified a set of synthetic short amidated hexapeptides, which not only end by the RFamide motif but also by CFamide and FCamide, as potent positive modulators of ASIC3 acid-induced activity. We focused on two of them, a RFamide peptide (FRCC‾RFamide) and a CFamide peptide (FRCRC‾Famide), demonstrating that they have similar specificity for and effects on ASIC3. The potentiating effects of the two peptides are due to a strong slow-down of desensitization, leading to an increase in the amount of current induced by acid pH (≤pH6.6), with apparent affinities ranging from 1 to 5 μM. Surprisingly, the washout kinetic of FRCC‾RFamide peptide was much slower than those of FRCRC‾Famide and other known RFamide peptides, suggesting potential differences in their mechanisms of action. Computational modeling and structure-function analysis reveal interactions of both peptides with the non-proton binding site of ASIC3 as already reported before for other RFamide peptides, but our data also suggest possible additional effects of FRCC‾RFamide involving directly or indirectly the proton binding domain. These findings expand our understanding of ASICs' modulation by peptides, identifying novel short modulators of ASIC3, including peptides with new CFamide and FCamide ending motifs, and showing differences between these peptides using their washout kinetic as a new parameter.

Les perturbations de l'axe cerveau-intestin-microbiote font l’objet de nombreuses études afin de mettre au point de nouveaux traitements pour les pathologies intestinales chroniques telles que le syndrome de l’intestin irritable (SII). Dans certains cas, à la suite d’une infection gastro-intestinale par des Entérobactéries et malgré l'élimination de l'agent pathogène, des troubles du transit et des douleurs abdominales chroniques persistent et peuvent favoriser le développement de symptômes anxio-dépressifs. Ceci est alors appelé SII post-infectieux (SII-PI). En développant un modèle préclinique d'infection à Citrobacter rodentium, mes travaux se sont focalisés sur (1) l’étude de l'impact de la cytokine IL-22 sur les symptômes associés au SII-PI, (2) l’étude du métabolisme du tryptophane (Trp), en particulier l'expression d’AhR induite par ses ligands dérivés du microbiote et, (3) l’étude du microbiote et du métabolome fécal sur les troubles de l'homéostasie suite à la résolution d’une infection gastro-intestinale. Ainsi, nous avons montré que le modèle murin d'infection à C. rodentium développe en période post-infectieuse, une hypersensibilité viscérale d’origine colique (HSVC) persistante, un comportement de type anxieux ainsi que des altérations cognitivo-émotionnelles, associés à une dysbiose, une inflammation à bas bruit et à une perméabilité intestinale augmentée montrant qu’il s’agit d’un modèle pertinent pour étudier les mécanismes physiopathologiques du SII-PI. Dans un premier temps, des analyses de métabolomique dirigée ont dévoilé des perturbations fonctionnelles au niveau fécal en phase post-infectieuse. Le métabolisme du Trp est altéré avec une diminution de la voie indole et de l'activité d’AhR ainsi qu’une diminution de la production du tryptophol. La production de la cytokine IL-22 peut être activée par la voie AhR et représente un acteur essentiel de l’homéostasie intestinale. Ainsi l’efficacité de la vectorisation d’IL-22 à l’aide d’une souche de Lactococcus lactis portant un plasmide d'expression eucaryote pour l’IL-22 murine (L. lactisIL-22) a été testée dans ce modèle animal de SII-PI. Le traitement avec L. lactisIL-22 permet d’améliorer les perturbations associées à l’infection par C. rodentium durant la phase post-infectieuse. Nos résultats suggèrent que le ciblage de la voie de signalisation AhR/IL-22 atténue les symptômes du SII-PI en agissant sur l'intégrité de la barrière épithéliale intestinale et les métabolites du Trp dérivés du microbiote. Les études de métabolomique ont été élargies afin d’identifier les perturbations fonctionnelles du microbiote fécal induite par l’infection. Ces travaux ont permis de préciser la physiopathologie du SII-PI et d’identifier de nouvelles cibles thérapeutiques potentielles telle que la voie AhR/IL-22. De plus, le rôle d’autres infections sur les comportements cognitivo-émotionnels de l’hôte a été étudié dans deux modèles animaux. Une infection chronique parasitaire à Blastocystis chez le rat a été utilisé afin de mimer un SII, ainsi qu’une infection chronique aux Escherichia coli producteurs de colibactine (CoPEC), Entérobactéries associées au cancer colorectal (CCR).

Acid-sensing ion channels (ASICs) are members of the DEG/ENaC family that includes the only known peptide-gated ion channels. While ASICs are gated by protons, they have kept sensitivity to peptides and are notably modulated by the molluscan FMRFamide and other related mammalian neuropeptides ending by the RFamide motif. Screening efforts have been made to identify and characterize natural peptides able to modulate ASICs’ activity, and some peptides from different species are already known to modulate ASIC1a, ASIC1b and ASIC3. We identified here a set of synthetic short amidated hexapeptides, initially designed thirty years ago for their ability to inhibit the Na/Ca exchanger, as potent and selective positive modulators of the ASIC3 acid-induced activity. We focused on two of them, a RFamide peptide (FR CC RFamide) and a CFamide peptide (FRC̄R̄C̄Famide), demonstrating that they have similar specificity for and effects on ASIC3. The potentiating effects of the two peptides are due to a strong slow-down of the current desensitization, leading to an increase in the amount of current induced by acid pH (≤pH6.6), with apparent affinities ranging from 1 to 5 µM. Surprisingly, the washout kinetic for the FRC̄C̄RFamide peptide was much slower than those of FRC̄R̄C̄Famide and other known RFamide peptides, suggesting potential differences in their mechanisms of action. Computational modeling and structure-function analysis reveal interactions of both peptides with the non-proton binding site of ASIC3 initially identified for the synthetic compound GMQ (2-guanidine-4-methylquinazoline), as already reported before for other RFamide peptides, but our data also suggest possible additional effects of FRC̄C̄RFamide involving directly or indirectly the proton binding domain. These findings expand our understanding of peptide modulation of ASIC channels and identify novel pharmacological tools selective among ASICs for investigating ASIC3 function.