Increased Glucose Metabolism and Glycerolipid Formation by Fatty Acids and GPR40 Receptor Signaling Underlies the Fatty Acid Potentiation of Insulin Secretion

Background: Pathways underlying fatty acid potentiation of glucose-stimulated insulin secretion have not been fully elucidated. Results: In INS-1 cells, fatty acids increase de novo production of glycerolipids and simultaneously increase glucose utilization. GPR40 receptor activation increases these activities. Conclusion: Fatty acids enhance the production of multiple signals supporting glucose-stimulated insulin secretion. Significance: The studies clarify the effects of fatty acids and GPR40 activity in cell insulin secretion. Acute fatty acid (FA) exposure potentiates glucose-stimulated insulin secretion in cells through metabolic and receptor-mediated effects. We assessed the effect of fatty acids on the dynamics of the metabolome in INS-1 cells following exposure to [U-C-13]glucose to assess flux through metabolic pathways. Metabolite profiling showed a fatty acid-induced increase in long chain acyl-CoAs that were rapidly esterified with glucose-derived glycerol-3-phosphate to form lysophosphatidic acid, mono- and diacylglycerols, and other glycerolipids, some implicated in augmenting insulin secretion. Glucose utilization and glycolytic flux increased, along with a reduction in the NADH/NAD(+) ratio, presumably by an increase in conversion of dihydroxyacetone phosphate to glycerol-3-phosphate. The fatty acid-induced increase in glycolysis also resulted in increases in tricarboxylic cycle flux and oxygen consumption. Inhibition of fatty acid activation of FFAR1/GPR40 by an antagonist decreased glycerolipid formation, attenuated fatty acid increases in glucose oxidation, and increased mitochondrial FA flux, as evidenced by increased acylcarnitine levels. Conversely, FFAR1/GPR40 activation in the presence of low FA increased flux into glycerolipids and enhanced glucose oxidation. These results suggest that, by remodeling glucose and lipid metabolism, fatty acid significantly increases the formation of both lipid- and TCA cycle-derived intermediates that augment insulin secretion, increasing our understanding of mechanisms underlying cell insulin secretion.