Enterohormones Down-Regulated in High-Fat Diet

Abstract

Introduction: To investigate the role of microbes upon the regulation of enteroendocrine hormones. Methods: Germ-free and specific pathogen-free (SPF) mice were caged under a 12-hour light-dark cycle and fed a high- or low-fat diet for 10 weeks. Animals were then humanely anesthetized with a mixture of ketamine and xylazine. Then, ileal mucosal scrapes were collected for RNA. cDNA was synthesized and qRT-PCR was performed with GiP, PYY, CCK primers, and normalized to GAPDH as a housekeeping gene. Results: More than 1/3 of U.S. adults are obese, and evidence suggests that inappropriate responsiveness to the intestinal microbiome plays a role. Obesity is a multivariable disease resulting in prolonged imbalance of energy input and energy expenditure. Since evidence suggests that changes in the gut microbiome influence energy metabolism and play an important role in the pathogenesis of obesity, we hypothesized that microbes influence enteroendocrine hormones in the intesitne. CCK is produced by I cells, and was the first gut hormone identified to regulate appetite. GiP is produced by K cells and is an incretin that regulates fatty acid metabolism. PYY is produced by L cells and regulates appetite and gastric emptying. Our results show that CCK, GiP, and PYY expression is unchanged in germ-free animals regardless of the diet (high-fat vs low-fat). However, in SPF animals, high-fat diets significantly up-regulate CCK by twofold and GiP by three-fold compared with animals on low-fat diet. No changes were observed in PYY expression in SPF regardless of the diet. In addition, no diurnal patterns were observed when examining CCK or GIP in circadian time, suggesting feeding patterns do not drive the changes in expression. Conclusion: Under germ-free conditions, diet has no influence upon CCK, GiP, or PYY expression in the small intestine. In SPF mice, CCK and GiP are up-regulated in the ileum under high fat diet. It appears microbes are required for the dietary regulation of CCK and GiP expression. There is no circardian variation of CCK and GiP ileal expression in animals fed with high-fat versus low-fat diet. Therefore, the effect of the different diets is not due to diurnal variation. Our study will add to our mechanistic insight into the regulation of obesity by the microbiome and further elucidate how changes in the microbiome lead to obesity.