The gut microbiota influences intestinal barrier integrity through mechanisms that are incompletely understood. Here we show that the commensal microbiota weakens the intestinal barrier by suppressing epithelial neuropilin-1 (NRP1) and Hedgehog (Hh) signaling. Microbial colonization of germ-free mice dampens signaling of the intestinal Hh pathway through epithelial Toll-like receptor (TLR)-2, resulting in decreased epithelial NRP1 protein levels. Following activation via TLR2/TLR6, epithelial NRP1, a positive-feedback regulator of Hh signaling, is lysosomally degraded. Conversely, elevated epithelial NRP1 levels in germ-free mice are associated with a strengthened gut barrier. Functionally, intestinal epithelial cell-specific Nrp1 deficiency (Nrp1ΔIEC) results in decreased Hh pathway activity and a weakened gut barrier. In addition, Nrp1ΔIEC mice have a reduced density of capillary networks in their small intestinal villus structures. Collectively, our results reveal a role for the commensal microbiota and epithelial NRP1 signaling in the regulation of intestinal barrier function through postnatal control of Hh signaling.

Aims:The mammalian gut is the largest endocrine organ. Dozens of hormones secreted by enteroendocrine cells regulate a variety of physiological functions of the gut but also of the pancreas and brain. Here, we examined the role of the helix-loop-helix transcription factor ID2 during the differentiation of intestinal stem cells along the enteroendocrine lineage. Methods:To assess the functions of ID2 in the adult mouse small intestine, we used single-cell RNA sequencing, genetically modified mice, and organoid assays. Results:We found that in the adult intestinal epithelium Id2 is predominantly expressed in enterochromaffin and peptidergic enteroendocrine cells.Consistently, the loss of Id2 leads to the reduction of Chromogranin A-positive enteroendocrine cells. In contrast, the numbers of tuft cells are increased in Id2 mutant small intestine. Moreover, ablation of Id2 elevates the numbers of Serotonin + enterochromaffin cells and Ghrelin + X-cells in the posterior part of the small intestine. Finally, ID2 acts downstream of BMP signalling during the differentiation of Glucagon-like peptide-1 + L-cells and Cholecystokinin + I-cells towards Neurotensin + PYY + N-cells. Conclusion: ID2 plays an important role in cell fate decisions in the adult small intestine. First, ID2 is essential for establishing a differentiation gradient for enterochromaffin and X-cells along the anterior-posterior axis of the gut. Next, ID2 is necessary for the differentiation of N-cells thus ensuring a differentiation gradient along the crypt-villi axis. Finally, ID2 suppresses the commitment of secretory intestinal epithelial progenitors towards tuft cell lineage and thus controls host immune response to commensal and parasitic microbiota.

Continuous and rapid renewal of the intestinal epithelium depends on intestinal stem cells (ISCs). A large repertoire of transcription factors mediates the correct maintenance and differentiation of ISCs along either absorptive or secretory lineages. In the present study, we addressed the role of TCF7L1, a negative regulator of WNT signalling, in embryonic and adult intestinal epithelium using conditional mouse mutants. We found that TCF7L1 prevents precocious differentiation of the embryonic intestinal epithelial progenitors towards enterocytes and ISCs. We show that Tcf7l1 deficiency leads to upregulation of the Notch effector Rbp-J, resulting in a subsequent loss of embryonic secretory progenitors. In the adult small intestine, TCF7L1 is required for the differentiation of secretory epithelial progenitors along the tuft cell lineage. Furthermore, we show that Tcf7l1 promotes the differentiation of enteroendocrine D- and L-cells in the anterior small intestine. We conclude that TCF7L1-mediated repression of both Notch and WNT pathways is essential for the correct differentiation of intestinal secretory progenitors.