“pVill-hCC6”: A NEW MOUSE MODEL MIMICKING ILEAL COLONIZATION BY AIEC BACTERIA TO EVALUATE MICROBIOTA-TARGETING STRATEGIES IN CROHN’S DISEASE

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Sivignon, Adeline | Chervy, Mélissa | Chevarin, Caroline | Billard, Elisabeth | Denizot, Jérémy | Barnich, Nicolas

Edité par CCSD -

International audience. Introduction: Adherent-invasive Escherichia coli (AIEC) pathobiont bacteria are highly prevalent in ileal lesions of Crohn’s Disease (CD) patients. These bacteria play an important role in the induction and/or maintenance of intestinal inflammation. Adhesion ability of AIEC to intestinal epithelial cells mainly relies on FimH adhesin, a mannose-binding lectin located at the tip of type 1 pili. The CEACAM6 glycoprotein, abnormally expressed in ileal mucosa of CD patients, harbors mannosides recognized by FimH and favors AIEC encroachment. This study proposes a novel transgenic mouse model named “pVill-hCC6” allowing AIEC-CEACAM6 interaction in ileum as observed in CD patients. In this model, the Villin promoter drives the expression of the human CEACAM6 transgene in epithelial cells of ileal mucosa. Mat&Met: The human CEACAM6 cDNA under the control of the Villin promoter was introduced into the murine Hprt locus to generate the transgenic mouse model ‘pVill-hCC6’. Mucosal CEACAM6 expression was assessed by qRT-PCR and western blotting in various sections of the intestine. CEACAM6 localization in the intestinal tissue was visualized by immunohistochemical analysis. Glycosylation pattern of CEACAM6 was studied on isolated enterocytes using fluorescent lectins. AIEC interaction with intestine from Vill-hCC6 mice was studied ex vivo on isolated enterocytes and in vivo after oral administration of AIEC pathobiont to mice. Results: Expression of CEACAM6 is high and limited to the small intestine in pVill-hCC6 mice, from the duodenum to the ileum. IHC experiments indicate that CEACAM6 expression is restricted to intestinal epithelial cells. A strong binding of concanavalin A lectin at the brush border of ileal enterocytes from pVill-hCC6 mice indicates that intestinal mucosa of transgenic mice exhibits high levels of glycosylation/mannosylation compared to their WT littermates. AIEC bacteria highly adhere to the brush border of enterocytes from pVill-hCC6 compared to enterocytes from WT mice and this adhesion is abrogated in the presence of mannose. In vivo, gut colonization by AIEC was greater in pVill-hCC6 mice than in their WT littermates, particularly in the small intestine. Finally, AIEC strain deleted for fimH, compared to WT AIEC strain, shows altered implantation capacity in gut mucosa of pVill-hCC6 mice, suggesting that intestinal encroachment of AIEC pathobiont is dependent of FimH expression. Conclusion: In this work, we have developed a new murine model reproducing abnormal over-expression of mannosylated receptor CEACAM6 allowing ileal colonization by AIEC, as observed in CD patients. This model will be of particular interest to evaluate innovative strategies targeting the gut microbiota, and more specifically the AIEC pathobiont, one possible trigger of intestinal inflammation.

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