Expression of odorant receptor Olfr78 in enteroendocrine cells of the colon.

The precise regulation of digestive and other physiological processes in the gastrointestinal tract in accordance with the food ingested requires continuous monitoring of the luminal content by chemosensory cells. With regard to the detection of chemical compounds in the lumen of the gastrointestinal tract, G-protein-coupled receptors (GPCRs) are interesting signaling proteins, since some of them are well known to bind to macronutrients, including sugars, amino acids and lipids. We report that Olfr78, a member of the odorant receptor (OR) class of GPCRs, is expressed in the murine gut. Our results support the concept that Olfr78 is activated by propionate, an important nutrient generated in the colon by microbiota. In situ hybridization and immunohistochemical approaches show that Olfr78 is expressed in the colon but is absent from other gastrointestinal compartments, such as the stomach and small intestine. In the colon, Olfr78 is expressed by a subset of epithelial cells lining the crypts; these cells are endowed with an apical process protruding towards the crypt lumen. The Olfr78-positive cells in the colon co-express the hormonal peptide YY (PYY), a marker for given enteroendocrine cells. The expression of the propionate receptor Olfr78 in epithelial enteroendocrine cells of the colon suggests that Olfr78 is involved in the regulation of hormone secretion from such cells, as evoked by nutritional compounds.