Abstract
AIMS/INTRODUCTION: Incretin hormone glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) plays a key role in high-fat diet-induced obesity and insulin resistance. GIP is strongly secreted from enteroendocrine K cells by oil ingestion. G protein-coupled receptor (GPR)120 and GPR40 are two major receptors for long chain fatty acids, and are expressed in enteroendocrine K cells. In the present study, we investigated the effect of the two receptors on oil-induced GIP secretion using GPR120- and GPR40-double knockout (DKO) mice. MATERIALS AND METHODS: Global knockout mice of GPR120 and GPR40 were crossbred to generate DKO mice. Oral glucose tolerance test and oral corn oil tolerance test were carried out. For analysis of the number of K cells and gene expression in K cells, DKO mice were crossbred with GIP-green fluorescent protein knock-in mice in which visualization and isolation of K cells can be achieved. RESULTS: Double knockout mice showed normal glucose-induced GIP secretion, but no GIP secretion by oil. We then investigated the number of K cells and gene characteristics in K cells isolated from GIP-green fluorescent protein knock-in mice. Deficiency of both receptors did not affect the number of K cells in the small intestine or expression of GIP messenger ribonucleic acid in K cells. Furthermore, there was no significant difference in the expression of the genes associated with lipid absorption or GIP secretion in K cells between wild-type and DKO mice. CONCLUSIONS: Oil-induced GIP secretion is triggered by the two major fatty acid receptors, GPR120 and GPR40, without changing K-cell number or K-cell characteristics.