Enteroendocrine Cells Protect the Stem Cell Niche by Regulating Crypt Metabolism in Response to Nutrients

In this study, loss of enteroendocrine cells recapitulated many aspects of fasting, including increased stem and progenitor activity, increased fatty acid oxidation, and loss of activity of mammalian target of rapamycin signaling in intestinal crypts. These data suggest that enteroendocrine cells are essential regulators of intestinal metabolism and crypt homeostasis. BACKGROUND & AIMS: The intestinal stem cell niche is exqui-sitely sensitive to changes in diet, with high-fat diet, caloric re-striction, and fasting resulting in altered crypt metabolism and intestinal stem cell function. Unlike cells on the villus, cells in the crypt are not immediately exposed to the dynamically changing contents of the lumen. We hypothesized that enteroendocrine cells (EECs), which sense environmental cues and in response release hormones and metabolites, are essential for relaying the luminal and nutritional status of the animal to cells deep in the crypt. METHODS: We used the tamoxifen-inducible VillinCreERT2 mouse model to deplete EECs (Neurog3(fl/fl)) from adult intestinal epithelium and we generated human intestinal organoids from wild-type and NEUROGENIN 3 (NEUROG3)-null human pluripo-tent stem cells. We used indirect calorimetry, H-1-Nuclear Magnetic Resonance (NMR) metabolomics, mitochondrial live imaging, and the Seahorse bioanalyzer (Agilent Technologies) to assess meta-bolism. Intestinal stem cell activity was measured by proliferation and enteroid-forming capacity. Transcriptional changes were assessed using 10x Genomics single-cell sequencing. RESULTS: Loss of EECs resulted in increased energy expendi-ture in mice, an abundance of active mitochondria, and a shift of crypt metabolism to fatty acid oxidation. Crypts from mouse and human intestinal organoids lacking EECs displayed increased intestinal stem cell activity and failed to activate phosphorylation of downstream target S6 kinase ribosomal protein, a marker for activity of the master metabolic regulator mammalian target of rapamycin (mTOR). These phenotypes were similar to those observed when control mice were deprived of nutrients. CONCLUSIONS: EECs are essential regulators of crypt meta-bolism. Depletion of EECs recapitulated a fasting metabolic phenotype despite normal levels of ingested nutrients. These data suggest that EECs are required to relay nutritional infor-mation to the stem cell niche and are essential regulators of intestinal metabolism.