Chemosensing of fat digestion by the expression pattern of GPR40, GPR120, CD36 and enteroendocrine profile in sheep

Abstract

Gastrointestinal tract (GIT) epithelial cells detect nutrients in the lumen via G-protein coupled receptors (GPRs) located in the gut epithelial cells especially in enteroendocrine cells. Dietary free fatty acids (FFA) are the major energy source and also acts as signalling molecules for FFA receptors. Long chain fatty acids (LCFA) activate LCFA receptors, GPR40/FFAR1 and GPR120/FFAR4 which trigger intracellular signalling and release gut hormones or modifies gene expression that facilitate fat digestion and absorption. However, there is a paucity of information on chemosensing of nutrients and digestion in ruminants. Hence, present study was aimed to evaluate chemosensing of fat digestion and absorption by the expression pattern of GPR40, GPR120, chylomicron forming genes, fatty acid translocase (CD36/FAT), microsomal triglyceride transfer protein (MTTP) and apolipoprotein B (APOB) in the various segments of GIT in sheep supplemented with calcium salts of long chain fatty acids (CSLCFAs) along with the secretory patterns of gut peptides cholecystokinin (CCK) and peptide tyrosine tyrosine (PYY). The study was carried out for a period 60 days with eighteen adult ewes of 8–12 months of age and they were divided into three groups with six animals each as group-I, group-II and group-III. All the experimental animals were stall fed with a basal diet and maintained as per animal husbandry standards. Group-II and group-III were supplemented additionally with 3% and 5% CSLCFAs, respectively on dry matter intake. The results from the study indicated that the supplementation of CSLCFAs upregulated (P < 0.05) the relative mRNA expression of GPR40 and GPR120 in the various segments of GIT of sheep in correspondence to level of dietary fat. Abundance of mRNA expression of CD36, MTTP and APOB increased (P < 0.05) in the GIT of sheep in accordance to quantity of LCFAs in the diet where these genes facilitate fatty acid uptake. Feeding of CSLCFAs enhanced (P < 0.05) pre-feeding level of CCK from day 15 onwards, whereas, post-feeding CCK and PYY increased in all the experimental sheep. However, the increase was higher (P < 0.05) in sheep supplemented with CSLCFAs by 10.80 ± 1.45% and 14.25 ± 1.17%, respectively in comparison to group-I. The comprehensive results of the study concluded that feeding of additional CSLCFAs upregulated the expression of GPR40, GPR120, CD36, and chemosensing of LCFAs by these genes triggered the signalling transduction that enhanced CCK and PYY levels to facilitate fat digestion and absorption in accordance with quantity of dietary fat. This was further evident from the significant upregulation of MTTP and APOB in the various segments of GIT supported the high content of dietary fat at cellular fat metabolism in the gut that regulates the fatty acid uptake.