Epithelial Ido1 Modulates Ahr And Notch Signaling To Enhance Secretory Cell Differentiation And Alters Mucus-Associated Microbiota

Inflammation, injury, and infection upregulate intestinal expression of the tryptophan metabolizing enzyme indoleamine 2,3-dioxygenase 1 (IDO1). In most disease models, IDO1 activity dampens inflammatory responses, reduces host injury and promotes recovery. Although epithelial cells are the predominant source of IDO1 during intestinal inflammation recovery and repair, the specific role of epithelial IDO1 has not been examined. We generated a novel transgenic mouse model that overexpresses EGFP-tagged IDO1 in the intestinal epithelium under the villin promoter (IDO1-TG). Using primary intestinal spheroid culture, we quantified stem cell and differentiation markers by qRT-PCR and immunofluorescence. Mucus thickness and luminal microbiota were assessed in vivo. A published database from Crohn’s disease patients were interrogated for secretory lineage genes. IDO1-TG small intestine demonstrated increased secretory cells by histology. Stem, goblet, Paneth, and enteroendocrine cell markers in IDO1-TG enteroids were increased compared to wild-type enteroids, with a concomitant decrease in absorptive cell markers. IDO1 interacted non-enzymatically with the aryl hydrocarbon receptor to inhibit Notch1 activation. In vivo, IDO1-TG mice possessed an enhanced mucus layer thickness (2.0-fold, P=0.01) and increased proportions of mucinophilic Akkermansia muciniphila (3.0-fold, P=0.03) and Mucispirillum schaedleri (11.3-fold, P=0.008). When challenged with enteropathogenic E. coli, IDO1-TG mice demonstrated reduced bacteria in the ileum (~85% reduction, P=0.03). In patients with active Crohn’s disease, high IDO1 expression correlates with reduced SLC2A5 (r=-0.35, P=0.01) and increased MUC5B (r=0.26, P=0.07), LYZ1 (r=0.38, P=0.006), and AHR (r=0.73, P<0.001). Intestinal epithelial IDO1 promotes secretory cell differentiation and mucus production, identifying a novel mechanism by which epithelial IDO1 may contribute to intestinal homeostasis.