The G-protein-coupled receptor GPR40 directly mediates long-chain fatty acid-induced secretion of cholecystokinin.
OBJECTIVE
Long-chain fatty acid receptors G-protein-coupled receptor 40 (GPR40) (FFAR1) and GPR120 have been implicated in the chemosensation of dietary fats. I cells in the intestine secrete cholecystokinin (CCK), a peptide hormone that stimulates digestion of fat and protein, but these cells are rare and hard to identify. We sought to determine whether dietary fat-induced secretion of CCK is directly mediated by GPR40 expressed on I cells.


METHODS
We used fluorescence-activated cell sorting to isolate a pure population of I cells from duodenal mucosa in transgenic mice that expressed green fluorescent protein under the control of the CCK promoter (CCK-enhanced green fluorescent protein [eGFP] bacterial artificial chromosome mice). CCK-eGFP cells were evaluated for GPR40 expression by quantitative reverse transcription polymerase chain reaction and immunostaining. GPR40(-/-) mice were bred with CCK-eGFP mice to evaluate functional relevance of GPR40 on long-chain fatty acid-stimulated increases in [Ca(2+)]i and CCK secretion in isolated CCK-eGFP cells. Plasma levels of CCK after olive oil gavage were compared between GPR40(+/+) and GPR40(-/-) mice.


RESULTS
Cells that expressed eGFP also expressed GPR40; expression of GPR40 was 100-fold greater than that of cells that did not express eGFP. In vitro, linoleic, oleic, and linolenic acids increased [Ca(2+)]i; linolenic acid increased CCK secretion by 53% in isolated GPR40(+/+) cells that expressed eGFP. In contrast, in GPR40(-/-) that expressed eGFP, [Ca(2+)]i response to linoleic acid was reduced by 50% and there was no significant CCK secretion in response to linolenic acid. In mice, olive oil gavage significantly increased plasma levels of CCK compared with pregavage levels: 5.7-fold in GPR40(+/+) mice and 3.1-fold in GPR40(-/-) mice.


CONCLUSIONS
Long-chain fatty acid receptor GPR40 induces secretion of CCK by I cells in response to dietary fat.
Digestive Diseases Branch, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Alice P
AP
Liou
Xinping
X
Lu
Yoshitatsu
Y
Sei
Xilin
X
Zhao
Susanne
S
Pechhold
Ricardo J
RJ
Carrero
Helen E
HE
Raybould
Stephen
S
Wank
D000818:Animals; D002469:Cell Separation / Q000379:methods; D002766:Cholecystokinin / Q000235:genetics / Q000378:metabolism*; D022202:Chromosomes, Artificial, Bacterial; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D019858:Enteroendocrine Cells / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D005434:Flow Cytometry; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D007441:Intubation, Gastrointestinal; D019787:Linoleic Acid / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D019301:Oleic Acid / Q000378:metabolism; D000069463:Olive Oil; D010938:Plant Oils / Q000008:administration & dosage / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D043562:Receptors, G-Protein-Coupled / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation; D017962:alpha-Linolenic Acid / Q000378:metabolism
D005227:Fatty Acids; C473036:Ffar1 protein, mouse; D000069463:Olive Oil; D010938:Plant Oils; D043562:Receptors, G-Protein-Coupled; C485184:enhanced green fluorescent protein; D017962:alpha-Linolenic Acid; D049452:Green Fluorescent Proteins; D019301:Oleic Acid; D002766:Cholecystokinin; D019787:Linoleic Acid