Free fatty acid receptor 1 (FFA1R/GPR40) and its involvement in fatty-acid-stimulated insulin secretion
Free fatty acids (FFA) have generally been proposed to regulate pancreatic insulin release by an intracellular mechanism involving inhibition of CPT-1. The recently de-orphanized G-protein coupled receptor, FFA1R/GPR40, has been shown to be essential for fatty-acid-stimulated insulin release in MIN6 mouse insulinoma cells. The CPT-1 inhibitor, 2-bromo palmitate (2BrP), was investigated for its ability to interact with mouse FFA1R/GPR40. It was found to inhibit phosphatidyl inositol hydrolysis induced by linoleic acid (LA) (100 μM in all experiments) in HEK293 cells transfected with FFA1R/GPR40 and in the MIN6 subclone, MIN6c4. 2BrP also inhibited LA-stimulated insulin release from mouse pancreatic islets. Mouse islets were subjected to antisense intervention by treatment with a FFA1R/GPR40-specific morpholino oligonucleotide for 48 h. Antisense treatment of islets suppressed LA-stimulated insulin release by 50% and by almost 100% when islets were pretreated with LA for 30 min before applying the antisense. Antisense treatment had no effect on tolbutamide-stimulated insulin release. Confocal microscopy using an FFA1R/GPR40-specific antibody revealed receptor expression largely localized to the plasma membrane of insulin-producing cells. Pretreating the islets with LA for 30 min followed by antisense oligonucleotide treatment for 48 h reduced the FFA1R/GPR40 immunoreactivity to background levels. The results demonstrate that FFA1R/GPR40 is inhibited by the CPT-1 inhibitor, 2BrP, and confirm that FFA1R/GPR40 is indeed necessary, at least in part, for fatty-acid-stimulated insulin release.
KeywordsGPR40 Free fatty acid Insulin Pancreatic islet 2-bromo palmitate Mouse (NMRI)
The technical help of Britt-Marie Nilsson is greatly appreciated. We also thank professor Patrik Rorsman for making available the confocal microscope. This work was supported in part by grants from the Swedish Segerfalk Foundation, GS Development, Crafoord Foundation, Kock Foundation, Royal Physiographic Society, Lund, The Swedish Diabetes Foundation, The Diabetes Programme at the Medical Faculty of Lund University, and the Swedish National Council for Medical Research.
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