RET Signaling Persists in the Adult Intestine and Stimulates Motility by Limiting PYY Release from Enteroendocrine Cells

Background & Aims RET receptor tyrosine kinase is necessary for enteric nervous system (ENS) development. Loss-of-function RET mutations cause Hirschsprung disease (HSCR), in which infants are born with aganglionic bowel. Despite surgical correction, HSCR patients often experience chronic defecatory dysfunction and enterocolitis, suggesting that RET is important after development. To test this hypothesis, we determined the location of postnatal RET and its significance in gastrointestinal (GI) motility. Methods Ret CFP/+ mice and human transcriptional profiling data were studied to identify the enteric neuronal and epithelial cells that express RET. To determine whether RET signaling in these cells regulates adult gut motility in vivo , genetic and pharmacologic approaches were used to disrupt RET in either all RET-expressing cells, a major subset of enteric neurons, or intestinal epithelial cells. Results Distinct subsets of enteric neurons and enteroendocrine cells expressed RET in the adult intestine. RET disruption in the intestinal epithelium, rather than in enteric neurons, slowed GI motility selectively in adult male mice. This effect was phenocopied by RET kinase inhibition. Most RET+ epithelial cells were either enterochromaffin cells that release serotonin (5-HT) or L-cells that release peptide YY (PYY), both of which can alter motility. RET kinase inhibition exaggerated PYY release in a nutrient-dependent manner without altering 5-HT secretion. PYY receptor blockade fully rescued dysmotility in mice lacking epithelial RET. Conclusion RET signaling normally limits nutrient-dependent PYY release from L-cells and this activity is necessary for normal intestinal motility in male mice. These effects could contribute to post-operative dysmotility in HSCR, which predominantly affects males, and uncovers a mechanism that could be targeted to treat post-prandial GI dysfunction. ![Figure][1] ### Competing Interest Statement This study received partial funding support from sponsored research agreements with GlaxoSmithKline and Boston Pharmaceuticals. M.R. receives research support from Takeda Pharmaceuticals for unrelated studies and has consulted for 89Bio. M.R's spouse is an employee of Takeda. All other authors declare no competing interests. * CFP : cyan fluorescent protein CMMC : colonic migrating motor complex dpt : days post treatment EEC : enteroendocrine cell ENS : enteric nervous system FPO : fecal pellet output GE/SITT : gastric emptying/small intestinal transit time GI : gastrointestinal GITT : gastrointestinal transit time HSCR : Hirschsprung’s Disease IBS : irritable bowel syndrome IPAN : intrinsic primary afferent neuron LC/MS : liquid chromatography/mass spectrometry MEN2 : multiple endocrine neoplasia type 2 MP : myenteric plexus PYY : peptide YY scRNA-SEQ : single cell RNA sequencing SMP : submucosal plexus UMAP : uniform manifold approximation and projection WT : wildtype 5-HT : serotonin [1]: pending:yes