Activation of ATP-sensitive potassium channels in rat pancreatic β-cells by linoleic acid through both intracellular metabolites and membrane receptor signalling pathway

ATP-sensitive potassium channels (KATP channels) determine the excitability of pancreatic β-cells and importantly regulate glucose-stimulated insulin secretion (GSIS). Long-chain free fatty acids (FFAs) decrease GSIS after long-term exposure to β-cells, but the effects of exogenous FFAs on KATP channels are not yet well clarified. In this study, the effects of linoleic acid (LA) on membrane potential (MP) and KATP channels were observed in primary cultured rat pancreatic β-cells. LA (20 μM) induced hyperpolarization of MP and opening of KATP channels, which was totally reversed and inhibited by tolbutamide, a KATP channel blocker. Inhibition of LA metabolism by acyl-CoA synthetase inhibitor, triacsin C (10 μM), partially inhibited LA-induced opening of KATP channels by 64%. The non-FFA G protein-coupled receptor (GPR) 40 agonist, GW9508 (40 μM), induced an opening of KATP channels, which was similar to that induced by LA under triacsin C treatment. Blockade of protein kinases A and C did not influence the opening of KATP channels induced by LA and GW9508, indicating that these two protein kinase pathways are not involved in the action of LA on KATP channels. The present study demonstrates that LA induces hyperpolarization of MP by activating KATP channels via both intracellular metabolites and activation of GPR40. It indicates that not only intracellular metabolites of FFAs but also GPR40-mediated pathways take part in the inhibition of GSIS and β-cell dysfunction induced by FFAs.

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Linoleic acid induces Ca2+-induced inactivation of voltage-dependent Ca2+ currents in rat pancreatic β-cells

Journal of Endocrinology ◽

10.1677/joe-07-0426 ◽

2007 ◽

Vol 196 (2) ◽

pp. 377-384 ◽

Cited By ~ 10

Author(s):

Dan-Dan Feng ◽

Yu-Feng Zhao ◽

Zi-Qiang Luo ◽

Damien J Keating ◽

Chen Chen

Keyword(s):

Insulin Secretion ◽

Linoleic Acid ◽

Specific Protein ◽

Β Cells ◽

Pancreatic Β Cells ◽

Cell Dysfunction ◽

Cell Recording ◽

Voltage Dependent ◽

Intracellular Ca ◽

G Protein Coupled

Free fatty acids (FFAs) regulate insulin secretion in a complex pattern and induce pancreatic β-cell dysfunction in type 2 diabetes. Voltage-dependent Ca2+ channels (VDCC) in β-cells play a major role in regulating insulin secretion. The aim of present study is to clarify the action of the FFA, linoleic acid, on VDCC in β-cells. The VDCC current in primary cultured rat β-cells were recorded under nystatin-perforated whole-cell recording configuration. The VDCC was identified as high-voltage-gated Ca2+ channels due to there being no difference in current amplitude under holding potential between −70 and −40 mV. Linoleic acid (10 μM) significantly inhibited VDCC currents in β-cells, an effect which was fully reversible upon washout. Methyl-linoleic acid, which does not activate G protein coupled receptor (GPR)40, neither did alter VDCC current in rat β-cells nor did influence linoleic acid-induced inhibition of VDCC currents. Linoleic acid-induced inhibition of VDCC current was not blocked by preincubation of β-cells with either the specific protein kinase A (PKA) inhibitor, H89, or the PKC inhibitor, chelerythrine. However, pretreatment of β-cells with thapsigargin, which depletes intracellular Ca2+ stores, completely abolished linoleic acid-induced decrease in VDCC current. Measurement of intracellular Ca2+ concentration ([Ca2+]i) illustrated that linoleic acid induced an increase in [Ca2+]i and that thapsigargin pretreatment inhibited this increase. Methyl-linoleic acid neither did induce increase in [Ca2+]i nor did it block linoleic acid-induced increase in [Ca2+]i. These results suggest that linoleic acid stimulates Ca2+ release from intracellular Ca2+ stores and inhibits VDCC currents in rat pancreatic β-cells via Ca2+-induced inactivation of VDCC.

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Pancreatic β-cells respond to fuel pressure with an early metabolic switch

Scientific Reports ◽

10.1038/s41598-020-72348-1 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Ronja M. Malinowski ◽

Seyed M. Ghiasi ◽

Thomas Mandrup-Poulsen ◽

Sebastian Meier ◽

Mathilde H. Lerche ◽

...

Keyword(s):

Cell Metabolism ◽

Polyol Pathway ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Metabolic Switch ◽

Cell Dysfunction ◽

Similar Quantity ◽

Glucose Stimulated Insulin Secretion

Abstract Pancreatic β-cells become irreversibly damaged by long-term exposure to excessive glucose concentrations and lose their ability to carry out glucose stimulated insulin secretion (GSIS) upon damage. The β-cells are not able to control glucose uptake and they are therefore left vulnerable for endogenous toxicity from metabolites produced in excess amounts upon increased glucose availability. In order to handle excess fuel, the β-cells possess specific metabolic pathways, but little is known about these pathways. We present a study of β-cell metabolism under increased fuel pressure using a stable isotope resolved NMR approach to investigate early metabolic events leading up to β-cell dysfunction. The approach is based on a recently described combination of 13C metabolomics combined with signal enhanced NMR via dissolution dynamic nuclear polarization (dDNP). Glucose-responsive INS-1 β-cells were incubated with increasing concentrations of [U-13C] glucose under conditions where GSIS was not affected (2–8 h). We find that pyruvate and DHAP were the metabolites that responded most strongly to increasing fuel pressure. The two major divergence pathways for fuel excess, the glycerolipid/fatty acid metabolism and the polyol pathway, were found not only to operate at unchanged rate but also with similar quantity.

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Peroxisome Proliferator-Activated Receptor α (PPARα) Potentiates, whereas PPARγ Attenuates, Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells

Endocrinology ◽

10.1210/en.2004-1430 ◽

2005 ◽

Vol 146 (8) ◽

pp. 3266-3276 ◽

Cited By ~ 71

Author(s):

Kim Ravnskjaer ◽

Michael Boergesen ◽

Blanca Rubi ◽

Jan K. Larsen ◽

Tina Nielsen ◽

...

Keyword(s):

Insulin Secretion ◽

Mitochondrial Membrane ◽

Uncoupling Protein ◽

Peroxisome Proliferator ◽

Dependent Manner ◽

Β Cells ◽

Pancreatic Β Cells ◽

Peroxisome Proliferator Activated Receptor ◽

Glucose Stimulated Insulin Secretion

Abstract Fatty acids (FAs) are known to be important regulators of insulin secretion from pancreatic β-cells. FA-coenzyme A esters have been shown to directly stimulate the secretion process, whereas long-term exposure of β-cells to FAs compromises glucose-stimulated insulin secretion (GSIS) by mechanisms unknown to date. It has been speculated that some of these long-term effects are mediated by members of the peroxisome proliferator-activated receptor (PPAR) family via an induction of uncoupling protein-2 (UCP2). In this study we show that adenoviral coexpression of PPARα and retinoid X receptor α (RXRα) in INS-1E β-cells synergistically and in a dose- and ligand-dependent manner increases the expression of known PPARα target genes and enhances FA uptake and β-oxidation. In contrast, ectopic expression of PPARγ/RXRα increases FA uptake and deposition as triacylglycerides. Although the expression of PPARα/RXRα leads to the induction of UCP2 mRNA and protein, this is not accompanied by reduced hyperpolarization of the mitochondrial membrane, indicating that under these conditions, increased UCP2 expression is insufficient for dissipation of the mitochondrial proton gradient. Importantly, whereas expression of PPARγ/RXRα attenuates GSIS, the expression of PPARα/RXRα potentiates GSIS in rat islets and INS-1E cells without affecting the mitochondrial membrane potential. These results show a strong subtype specificity of the two PPAR subtypes α and γ on lipid partitioning and insulin secretion when systematically compared in a β-cell context.

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Kisspeptin-Activated Autophagy Independently Suppresses Non-Glucose-Stimulated Insulin Secretion from Pancreatic β-Cells

Scientific Reports ◽

10.1038/s41598-019-53826-7 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 3

Author(s):

Chien Huang ◽

Hao-Yi Wang ◽

Mu-En Wang ◽

Meng-Chieh Hsu ◽

Yi-Hsieng Samuel Wu ◽

...

Keyword(s):

Insulin Secretion ◽

Β Cells ◽

Pancreatic Β Cells ◽

Insulin Granules ◽

Autophagic Degradation ◽

Basal Insulin Secretion ◽

Glucose Stimulated Insulin Secretion

AbstractPrevious studies have demonstrated the important role of kisspeptin in impaired glucose-stimulated insulin secretion (GSIS). In addition, it was reported that the activation of autophagy in pancreatic β-cells decreases insulin secretion by selectively degrading insulin granules. However, it is currently unknown whether kisspeptin suppresses GSIS in β-cells by activating autophagy. To investigate the involvement of autophagy in kisspeptin–regulated insulin secretion, we overexpressed Kiss1 in NIT-1 cells to mimic the long-term exposure of pancreatic β-cells to kisspeptin during type 2 diabetes (T2D). Interestingly, our data showed that although kisspeptin potently decreases the intracellular proinsulin and insulin ((pro)insulin) content and insulin secretion of NIT-1 cells, autophagy inhibition using bafilomycin A1 and Atg5 siRNAs only rescues basal insulin secretion, not kisspeptin-impaired GSIS. We also generated a novel in vivo model to investigate the long-term exposure of kisspeptin by osmotic pump. The in vivo data demonstrated that kisspeptin lowers GSIS and (pro)insulin levels and also activated pancreatic autophagy in mice. Collectively, our data demonstrated that kisspeptin suppresses both GSIS and non-glucose-stimulated insulin secretion of pancreatic β-cells, but only non-glucose-stimulated insulin secretion depends on activated autophagic degradation of (pro)insulin. Our study provides novel insights for the development of impaired insulin secretion during T2D progression.

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Oleic acid interacts with GPR40 to induce Ca2+ signaling in rat islet β-cells: mediation by PLC and L-type Ca2+ channel and link to insulin release

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00035.2005 ◽

2005 ◽

Vol 289 (4) ◽

pp. E670-E677 ◽

Cited By ~ 167

Author(s):

Ken Fujiwara ◽

Fumihiko Maekawa ◽

Toshihiko Yada

Keyword(s):

Insulin Secretion ◽

Oleic Acid ◽

Insulin Release ◽

Β Cells ◽

Pancreatic Β Cells ◽

Insulinoma Cell ◽

Transduction Mechanisms ◽

Glucose Stimulated Insulin Secretion ◽

Interfering Rna ◽

G Protein Coupled

It has long been thought that long-chain free fatty acids (FFAs) stimulate insulin secretion via mechanisms involving their metabolism in pancreatic β-cells. Recently, it was reported that FFAs function as endogenous ligands for GPR40, a G protein-coupled receptor, to amplify glucose-stimulated insulin secretion in an insulinoma cell line and rat islets. However, signal transduction mechanisms for GPR40 in β-cells are little known. The present study was aimed at elucidating GPR40-linked Ca2+ signaling mechanisms in rat pancreatic β-cells. We employed oleic acid (OA), an FFA that has a high affinity for the rat GPR40, and examined its effect on cytosolic Ca2+ concentration ([Ca2+]i) in single β-cells by fura 2 fluorescence imaging. OA at 1–10 μM concentration-dependently increased [Ca2+]i in the presence of 5.6, 8.3, and 11.2 mM, but not 2.8 mM, glucose. OA-induced [Ca2+]i increases at 11.2 mM glucose were inhibited in β-cells transfected with small interfering RNA targeted to rat GPR40 mRNA. OA-induced [Ca2+]i increases were also inhibited by phospholipase C (PLC) inhibitors, U73122 and neomycin, Ca2+-free conditions, and an L-type Ca2+ channel blocker, nitrendipine. Furthermore, OA increased insulin release from isolated islets at 8.3 mM glucose, and it was markedly attenuated by PLC and L-type Ca2+ channel inhibitors. These results demonstrate that OA interacts with GPR40 to increase [Ca2+]i via PLC- and L-type Ca2+ channel-mediated pathway in rat islet β-cells, which may be link to insulin release.

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SIRT6 protects against palmitate-induced pancreatic β-cell dysfunction and apoptosis

Journal of Endocrinology ◽

10.1530/joe-16-0317 ◽

2016 ◽

Vol 231 (2) ◽

pp. 159-165 ◽

Cited By ~ 25

Author(s):

Xiwen Xiong ◽

Xupeng Sun ◽

Qingzhi Wang ◽

Xinlai Qian ◽

Yang Zhang ◽

...

Keyword(s):

Insulin Secretion ◽

Mrna Levels ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Glucose Stimulation ◽

Cell Dysfunction ◽

High Concentrations ◽

Glucose Stimulated Insulin Secretion

Chronic exposure of pancreatic β-cells to abnormally elevated levels of free fatty acids can lead to β-cell dysfunction and even apoptosis, contributing to type 2 diabetes pathogenesis. In pancreatic β-cells, sirtuin 6 (SIRT6) has been shown to regulate insulin secretion in response to glucose stimulation. However, the roles played by SIRT6 in β-cells in response to lipotoxicity remain poorly understood. Our data indicated that SIRT6 protein and mRNA levels were reduced in islets from diabetic and aged mice. High concentrations of palmitate (PA) also led to a decrease in SIRT6 expression in MIN6 β-cells and resulted in cell dysfunction and apoptosis. Knockdown of Sirt6 caused an increase in cell apoptosis and impairment in insulin secretion in response to glucose in MIN6 cells even in the absence of PA exposure. Furthermore, overexpression of SIRT6 alleviated the palmitate-induced lipotoxicity with improved cell viability and increased glucose-stimulated insulin secretion. In summary, our data suggest that SIRT6 can protect against palmitate-induced β-cell dysfunction and apoptosis.

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GW9508 inhibits insulin secretion by activating ATP-sensitive potassium channels in rat pancreatic β-cells

Journal of Molecular Endocrinology ◽

10.1530/jme-13-0019 ◽

2013 ◽

Vol 51 (1) ◽

pp. 69-77 ◽

Cited By ~ 7

Author(s):

Yu-Feng Zhao ◽

Li Wang ◽

Dingjun Zha ◽

Li Qiao ◽

Lianjun Lu ◽

...

Keyword(s):

Insulin Secretion ◽

Membrane Potential ◽

Primary Culture ◽

Acute Effects ◽

Β Cells ◽

Pancreatic Β Cells ◽

Intracellular Ca ◽

Glucose Stimulated Insulin Secretion ◽

G Protein Coupled ◽

Inhibit Insulin Secretion

GW9508 is an agonist of G protein-coupled receptor 40 (GPR40) that is expressed in pancreatic β-cells and is reported to regulate insulin secretion. However, the effects of GW9508 on pancreatic β-cells in primary culture have not been well investigated. This study measured the acute effects of GW9508 on insulin secretion from rat pancreatic islets in primary culture, and the insulin secretion-related events such as the changes in membrane potential, ATP-sensitive potassium currents (KATP currents), and intracellular Ca2+ concentrations ([Ca2+]i) of rat islet β-cells were also recorded. GW9508 (10–40 μM) did not influence basal insulin levels at 2 mM glucose, but it (above 20 μM) significantly inhibited 5 and 15 mM glucose-stimulated insulin secretion (GSIS). GW9508 did not inhibit insulin secretion stimulated by tolbutamide, the closer of KATP channels. GW9508 activated KATP channels and blocked the membrane depolarization and the increase in [Ca2+]i that were stimulated by glucose. GW9508 itself stimulated a transient increase in [Ca2+]i, which was fully blocked by depletion of intracellular Ca2+ stores with thapsigargin or by inhibition of phospholipase C (PLC) activity with U73122. GW9508-induced activation of KATP channels was only partly inhibited by U73122 treatment. In conclusion, although it stimulates a transient release of Ca2+ from intracellular Ca2+ stores via activation of PLC, GW9508 inhibits GSIS by activating KATP channels probably in a distal step to GPR40 activation in rat β-cells.

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5-Bromoprotocatechualdehyde Combats against Palmitate Toxicity by Inhibiting Parkin Degradation and Reducing ROS-Induced Mitochondrial Damage in Pancreatic β-Cells

Antioxidants ◽

10.3390/antiox10020264 ◽

2021 ◽

Vol 10 (2) ◽

pp. 264

Author(s):

Seon-Heui Cha ◽

Chunying Zhang ◽

Soo-Jin Heo ◽

Hee-Sook Jun

Keyword(s):

Cell Loss ◽

Cellular Damage ◽

Mitochondrial Morphology ◽

Protective Effects ◽

Β Cells ◽

Β Cell ◽

Zebrafish Model ◽

Cell Dysfunction ◽

Glucose Stimulated Insulin Secretion

Pancreatic β-cell loss is critical in diabetes pathogenesis. Up to now, no effective treatment has become available for β-cell loss. A polyphenol recently isolated from Polysiphonia japonica, 5-Bromoprotocatechualdehyde (BPCA), is considered as a potential compound for the protection of β-cells. In this study, we examined palmitate (PA)-induced lipotoxicity in Ins-1 cells to test the protective effects of BPCA on insulin-secreting β-cells. Our results demonstrated that BPCA can protect β-cells from PA-induced lipotoxicity by reducing cellular damage, preventing reactive oxygen species (ROS) overproduction, and enhancing glucose-stimulated insulin secretion (GSIS). BPCA also improved mitochondrial morphology by preserving parkin protein expression. Moreover, BPCA exhibited a protective effect against PA-induced β-cell dysfunction in vivo in a zebrafish model. Our results provide strong evidence that BPCA could be a potential therapeutic agent for the management of diabetes.

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