Regulation of α-Transducin and α-Gustducin Expression by a High Protein Diet in the Pig Gastrointestinal Tract

Background The expression of taste receptors (TASRs) and their signalling molecules in the gastrointestinal (GI) epithelial cells, including enteroendocrine cells (EECs), suggests they participate in chemosensing mechanisms influencing GI physiology via the release of endocrine messengers. TASRs mediate gustatory signalling by interacting with different transducers, including α-gustducin (G αgust ) and α-transducin (G αtran ) G protein subunits. This study tested whether G αtran and G αgust immunoreactive (-IR) cells are affected by a short-term (3 days) and long-term (30 days) high protein (Hp) diet in the pig GI tract. Result In the stomach, G αgust and G αtran -IR cells contained serotonin (5-HT) and ghrelin (GHR), while in the small and large intestine, G αgust and G αtran -IR colocalized with 5-HT-, cholecystokinin (CCK)- and peptide YY (PYY)-IR. There was a significant increase in the density of G αtran -IR cells in the pyloric mucosa in both short- and long-term Hp diet groups (Hp3 and Hp30) vs. the control group (Ctr) ( P <0.05), while the increase of G αgust -IR cells in the pyloric mucosa was significant in Hp30 group vs. Ctr and vs. Hp3 ( P <0.05); these cells included G αtran / 5HT-IR and G αtran / GHR-IR cells ( P <0.05 and P <0.001 vs. Ctr, respectively) as well as G αgust /5-HT-IR or G αgust / GHR-IR cells ( P <0.05 and P <0.01 vs. Ctr, respectively). In the small intestine, we recorded a significant increase in G αtran -IR cells in the duodenal crypts and a significant increase of G αgust -IR cells in the jejunal crypts in Hp3 group compared to HP30 ( P <0.05). With regard to the number of G αtran -G αgust IR cells colocalized with CCK or 5-HT, there was only a significant increase of G αtran / CCK-IR cells in Hp3 group compared to Ctr ( P = 0.01). Conclusion This study showed an upregulation of selected subpopulations of G αgust / G αtran -IR cells in distinct regions of the pig GI tract by short- and long-term Hp diet lending support to TASR-mediated effects in metabolic homeostasis and satiety mechanisms.