Endogenous Fatty Acids Are Essential Signaling Factors of Pancreatic β-Cells and Insulin Secretion

The secretion of insulin from β-cells depends on extracellular factors, in particular glucose and other small molecules, some of which act on G-protein–coupled receptors. Fatty acids (FAs) have been discussed as exogenous secretagogues of insulin for decades, especially after the FA receptor GPR40 (G-protein–coupled receptor 40) was discovered. However, the role of FAs as endogenous signaling factors has not been investigated until now. In the present work, we demonstrate that lowering endogenous FA levels in β-cell medium by stringent washing or by the application of FA-free (FAF) BSA immediately reduced glucose-induced oscillations of cytosolic Ca2+ ([Ca2+]i oscillations) in MIN6 cells and mouse primary β-cells, as well as insulin secretion. Mass spectrometry confirmed BSA-mediated removal of FAs, with palmitic, stearic, oleic, and elaidic acid being the most abundant species. [Ca2+]i oscillations in MIN6 cells recovered when BSA was replaced by buffer or as FA levels in the supernatant were restored. This was achieved by recombinant lipase–mediated FA liberation from membrane lipids, by the addition of FA-preloaded FAF-BSA, or by the photolysis of cell-impermeant caged FAs. Our combined data support the hypothesis of FAs as essential endogenous signaling factors for β-cell activity and insulin secretion.

[1]  D. Trauner,et al.  Optical control of GPR40 signalling in pancreatic β-cells† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc01475a , 2017, Chemical science.

[2]  Sean J. Humphrey,et al.  Glucose-regulated and drug-perturbed phosphoproteome reveals molecular mechanisms controlling insulin secretion , 2016, Nature Communications.

[3]  G. Patti,et al.  Inaccurate quantitation of palmitate in metabolomics and isotope tracer studies due to plastics , 2016, Metabolomics.

[4]  C. Mulle,et al.  Exclusive photorelease of signalling lipids at the plasma membrane , 2015, Nature Communications.

[5]  D. Longnecker Anatomy and Histology of the Pancreas , 2014 .

[6]  Johannes E. Schindelin,et al.  Fiji: an open-source platform for biological-image analysis , 2012, Nature Methods.

[7]  Fredrik Karpe,et al.  Quantification of PtdInsP3 molecular species in cells and tissues by mass spectrometry , 2011, Nature Methods.

[8]  P. Rorsman,et al.  γ-Aminobutyric Acid (GABA) Is an Autocrine Excitatory Transmitter in Human Pancreatic β-Cells , 2010, Diabetes.

[9]  M. Ravier,et al.  Isolation and culture of mouse pancreatic islets for ex vivo imaging studies with trappable or recombinant fluorescent probes. , 2010, Methods in molecular biology.

[10]  Richard D. Smith,et al.  Deletion of GPR40 Impairs Glucose-Induced Insulin Secretion In Vivo in Mice Without Affecting Intracellular Fuel Metabolism in Islets , 2009, Diabetes.

[11]  K. Takeuchi,et al.  Overexpression of GPR40 in Pancreatic β-Cells Augments Glucose-Stimulated Insulin Secretion and Improves Glucose Tolerance in Normal and Diabetic Mice , 2009, Diabetes.

[12]  A. Tengholm,et al.  Oscillatory control of insulin secretion , 2009, Molecular and Cellular Endocrinology.

[13]  L. Noriega,et al.  Nutrient modulation of insulin secretion. , 2009, Vitamins and hormones.

[14]  M. Wilmanns,et al.  Probing lipid- and drug-binding domains with fluorescent dyes. , 2008, Bioorganic & medicinal chemistry.

[15]  Christopher R. Weber,et al.  Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate* , 2007, Journal of Biological Chemistry.

[16]  S. Schnell,et al.  Free fatty acids increase cytosolic free calcium and stimulate insulin secretion from β-cells through activation of GPR40 , 2007, Molecular and Cellular Endocrinology.

[17]  F. Wei Fatty Acid Signaling in the β-cell and Insulin Secretion , 2007 .

[18]  M. Prentki,et al.  Fatty Acid Signaling in the β-Cell and Insulin Secretion , 2006, Diabetes.

[19]  J. Fornwald,et al.  Pharmacological regulation of insulin secretion in MIN6 cells through the fatty acid receptor GPR40: identification of agonist and antagonist small molecules , 2006, British journal of pharmacology.

[20]  S. Roh,et al.  Reduction in voltage-gated K+ currents in primary cultured rat pancreatic beta-cells by linoleic acids. , 2006, Endocrinology.

[21]  H. Shapiro,et al.  Role of GPR40 in fatty acid action on the β cell line INS-1E , 2005 .

[22]  B. Hellman,et al.  External ATP triggers Ca2+ signals suited for synchronization of pancreatic beta-cells. , 2005, The Journal of endocrinology.

[23]  J. Miyazaki,et al.  Pancreatic beta cell line MIN6 exhibits characteristics of glucose metabolism and glucose-stimulated insulin secretion similar to those of normal islets , 1993, Diabetologia.

[24]  Angel Nadal,et al.  Widespread synchronous [Ca2+]i oscillations due to bursting electrical activity in single pancreatic islets , 1991, Pflügers Archiv.

[25]  J. Chambers,et al.  The Orphan G Protein-coupled Receptor GPR40 Is Activated by Medium and Long Chain Fatty Acids* , 2003, The Journal of Biological Chemistry.

[26]  Masataka Harada,et al.  Free fatty acids regulate insulin secretion from pancreatic β cells through GPR40 , 2003, Nature.

[27]  B. Olde,et al.  A human cell surface receptor activated by free fatty acids and thiazolidinedione drugs. , 2003, Biochemical and biophysical research communications.

[28]  Min Zhang,et al.  Connexin 36 controls synchronization of Ca2+ oscillations and insulin secretion in MIN6 cells. , 2003, Diabetes.

[29]  D. Ramji,et al.  Lipoprotein lipase: structure, function, regulation, and role in disease , 2002, Journal of Molecular Medicine.

[30]  M. Ravier,et al.  Disorganization of cytoplasmic Ca(2+) oscillations and pulsatile insulin secretion in islets from ob/ obmice. , 2002, Diabetologia.

[31]  I. Johnson,et al.  Chemical and physiological characterization of fluo-4 Ca(2+)-indicator dyes. , 2000, Cell calcium.

[32]  M. Komatsu,et al.  Augmentation of Ca2+-stimulated insulin release by glucose and long-chain fatty acids in rat pancreatic islets: free fatty acids mimic ATP-sensitive K+ channel-independent insulinotropic action of glucose. , 1999, Diabetes.

[33]  G. Boden,et al.  Acute lowering of plasma fatty acids lowers basal insulin secretion in diabetic and nondiabetic subjects. , 1998, Diabetes.

[34]  J. McGarry,et al.  Circulating fatty acids are essential for efficient glucose-stimulated insulin secretion after prolonged fasting in humans. , 1998, Diabetes.

[35]  P. Gilon,et al.  Temporal and Quantitative Correlations Between Insulin Secretion and Stably Elevated or Oscillatory Cytoplasmic Ca2+ in Mouse Pancreatic β-Cells , 1998, Diabetes.

[36]  J. Leahy,et al.  Beta-cell hypersensitivity to glucose following 24-h exposure of rat islets to fatty acids , 1997, Diabetologia.

[37]  J. McGarry,et al.  Essentiality of circulating fatty acids for glucose-stimulated insulin secretion in the fasted rat. , 1996, The Journal of clinical investigation.

[38]  P. Bergsten,et al.  Slow and fast oscillations of cytoplasmic Ca2+ in pancreatic islets correspond to pulsatile insulin release. , 1995, The American journal of physiology.

[39]  C. Newgard,et al.  Metabolic coupling factors in pancreatic beta-cell signal transduction. , 1995, Annual review of biochemistry.

[40]  S. Bloom,et al.  Evidence of a paracrine role of neuropeptide-Y in the regulation of insulin release from pancreatic islets of normal and dexamethasone-treated rats. , 1994, Endocrinology.

[41]  P. Gilon,et al.  Oscillations of secretion driven by oscillations of cytoplasmic Ca2+ as evidences in single pancreatic islets. , 1993, The Journal of biological chemistry.

[42]  J. Hamilton,et al.  Locations of the three primary binding sites for long-chain fatty acids on bovine serum albumin. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[43]  J. Miyazaki,et al.  Establishment of a pancreatic beta cell line that retains glucose-inducible insulin secretion: special reference to expression of glucose transporter isoforms. , 1990, Endocrinology.

[44]  G. Paolisso,et al.  Pulsatile insulin delivery is more efficient than continuous infusion in modulating islet cell function in normal subjects and patients with type 1 diabetes. , 1988, The Journal of clinical endocrinology and metabolism.

[45]  S. Fowler,et al.  Spectrofluorometric studies of the lipid probe, nile red. , 1985, Journal of lipid research.

[46]  I. Sjöholm,et al.  The binding sites on human serum albumin for some nonsteroidal antiinflammatory drugs. , 1980, Molecular pharmacology.

[47]  M. J. Crooks,et al.  Binding of nonsteroidal anti-inflammatory agents to proteins--I. Ibuprofen-serum albumin interaction. , 1979, Biochemical pharmacology.

[48]  A. A. Spector,et al.  Long chain fatty acid binding to human plasma albumin. , 1975, The Journal of biological chemistry.

[49]  D. Steinberg,et al.  Stimulation of insulin secretion by long-chain free fatty acids. A direct pancreatic effect. , 1973, The Journal of clinical investigation.

[50]  J. Fletcher,et al.  Medium chain fatty acid binding to human plasma albumin. , 1972, The Journal of biological chemistry.

[51]  J. Oncley,et al.  The specific binding of L-tryptophan to serum albumin. , 1958, The Journal of biological chemistry.