Overview of Intestinal Bitter Taste Receptors: Gene Expression in Human, Pig and Mouse

Bitter taste receptors (TAS2Rs) are new targets for the pharmaceutical market as they were found to be players in several important metabolic and physiological processes outside the oral cavity. Lately, it has been studied how intestinal TAS2Rs recognize bitter compounds and elicit secretion of energy- and appetite- controlling hormone peptides, e.g. GLP-1 (Glucagon-like peptide-1). Although TAS2Rs have been reported to be expressed on intestinal enteroendocrine cells, such as I, K, L, and enterochromaffin cells, the expression of these receptors along the entire intestinal tract (i.e., Duodenum, Jejunum, Ileum, and Colon) is not yet fully elucidated. Studying their expression pattern could provide insight into the functioning of TAS2Rs in the intestine. Thus, we aimed to evaluate the gene expression profile of the TAS2Rs at different locations in the intestine across species: in human and relevant models, such as pig and mouse. By employing microarray analysis of biopsies and mucosal scrapings, we examined the gene expression levels of TAS2Rs in the three mammalian species along the intestinal tracts. We compared their expression pattern to other functional markers in the intestine. The evaluation of TAS2Rs gene expression shows that intestinal tissue contains a large number of bitter receptor family members in the three species: at the least, 24/29 in humans, 11/14 in pigs and 35/35 in mice. TAS2Rs throughout all intestinal sections show low expression levels compared to the enterocyte marker Villin 1 and the enteroendocrine marker Chromogranin A, and with comparable expression level to other taste receptors. We conclude that human, pig, and mouse TAS2R orthologs are, overall, equally distributed along intestinal sections. However, per species, TAS2Rs show orthology-independent profiles.