Abstract
The long-chain fatty acid receptor FFAR1 is highly expressed in pancreatic β-cells. Synthetic FFAR1 agonists can be used as antidiabetic drugs to promote glucose-stimulated insulin secretion (GSIS). However, the physiological role of FFAR1 in β-cells remains poorly understood. Here we show that 20-HETE activates FFAR1 and promotes GSIS via FFAR1 with higher potency and efficacy than dietary fatty acids such as palmitic, linoleic, and α-linolenic acid. Murine and human β-cells produce 20-HETE, and the ω-hydroxylase-mediated formation and release of 20-HETE is strongly stimulated by glucose. Pharmacological inhibition of 20-HETE formation and blockade of FFAR1 in islets inhibits GSIS. In islets from type-2 diabetic humans and mice, glucose-stimulated 20-HETE formation and 20-HETE-dependent stimulation of GSIS are strongly reduced. We show that 20-HETE is an FFAR1 agonist, which functions as an autocrine positive feed-forward regulator of GSIS, and that a reduced glucose-induced 20-HETE formation contributes to inefficient GSIS in type-2 diabetes.
Highlights
The long-chain fatty acid receptor FFAR1 is highly expressed in pancreatic β-cells
In addition to a reduced glucose-stimulated 20HETE formation in diabetic islets, we found that stimulation of glucose-stimulated insulin secretion (GSIS) by the selective FFAR1 agonist TAK-875 was reduced in islets from HFD-fed diabetic mice compared to non-diabetic animals fed a normal chow diet (Fig. 5d)
In a search for lipid mediators which function as physiological FFAR1 agonists in the regulation of insulin secretion, we identified 20-hydroxyeicosatetraenoic acid (20-HETE) as a new regulator of pancreatic β-cells. 20-HETE turned out to be a highly efficacious agonist of FFAR1, which is produced by phospholipase A2 (PLA2) and ω-hydroxylases after uptake of glucose by β-cells
Summary
Reagents. 20-HETE and related HETEs, PGE2, PGD2, U46619, cicaprost, cloprostenol, α-linolenic, linoleic, γ-linolenic acids, GW1100, HET0016, and TAK-875 were from Cayman Chemicals. COS-1 cells, obtained from ATCC, were seeded in 96-well plates with white walls and transparent bottom and transfected with plasmids containing cDNAs encoding a calcium-sensitive bioluminescent fusion protein consisting of aequorin and GFP68 and the indicated receptors by using Lipofectamine 2000 (Life Technologies) following the manufacturer’s instructions. To determine equilibrium binding of [9,10-3H(N)]palmitic acid (Hartmann-Analytik, 27 Ci/mmol) to FFAR1 receptor, COS-1 cells seeded in 24-well plates were transfected with an eukaryotic expression plasmid carrying the FFAR1 cDNA. Forty-eight hours later cells were rinsed with ice-cold binding buffer (PBS + 0.5% fatty acid-free BSA) and competition binding assay was performed by incubating transfected cells in binding buffer containing 100 nM 3Hpalmitic acid and the indicated compounds for 90 min at +4 °C. Cells were stimulated in 20 μl fresh KRB medium containing the indicated glucose concentrations and other test compounds for 1 h at 37 °C. All relevant data are available from the authors upon reasonable request
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