P2Y receptor activation enhances insulin release from pancreatic β-cells by triggering the cyclic AMP/protein kinase A pathway

Abstract Glucagon-like peptide-1 (GLP-1)-based medicines have recently been widely used to treat type 2 diabetic patients, whereas adverse effects of nausea and vomiting have been documented. Inhibition of voltage-gated K+ channel subtype Kv2.1 in pancreatic β-cells has been suggested to contribute to mild depolarization and promotion of insulin release. This study aimed to determine whether the blockade of Kv2.1 channels potentiates the insulinotropic effect of GLP-1 agonists. Kv2.1 channel blocker guangxitoxin-1E (GxTx) and GLP-1 agonist exendin-4 at subthreshold concentrations, when combined, markedly increased the insulin release and cytosolic Ca2+ concentration ([Ca2+]i) in a glucose-dependent manner in mouse islets and β-cells. Exendin-4 at subthreshold concentration alone increased islet insulin release and β-cell [Ca2+]i in Kv2.1+/− mice. The [Ca2+]i response to subthreshold exendin-4 and GxTx in combination was attenuated by pretreatment with protein kinase A inhibitor H-89, indicating the protein kinase A dependency of the cooperative effect. Furthermore, subthreshold doses of GxTx and GLP-1 agonist liraglutide in combination markedly increased plasma insulin and improved glucose tolerance in diabetic db/db mice and NSY mice. These results demonstrate that a modest suppression of Kv2.1 channels dramatically raises insulinotropic potency of GLP-1-based drugs, which opens a new avenue to reduce their doses and associated adverse effects while achieving the same glycemic control in type 2 diabetes.

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Reduction in Voltage-Gated K+ Currents in Primary Cultured Rat Pancreatic β-Cells by Linoleic Acids

Endocrinology ◽

10.1210/en.2005-0225 ◽

2006 ◽

Vol 147 (2) ◽

pp. 674-682 ◽

Cited By ~ 85

Author(s):

Dan Dan Feng ◽

Ziqiang Luo ◽

Sang-gun Roh ◽

Maria Hernandez ◽

Neveen Tawadros ◽

...

Keyword(s):

Insulin Secretion ◽

Linoleic Acid ◽

Protein Kinase ◽

Protein Kinase A ◽

Β Cells ◽

Pancreatic Β Cells ◽

Voltage Gated ◽

K Current ◽

K Currents ◽

Kinase A

Free fatty acids (FFAs), in addition to glucose, have been shown to stimulate insulin release through the G protein-coupled receptor (GPCR)40 receptor in pancreatic β-cells. Intracellular free calcium concentration ([Ca2+]i) in β-cells is elevated by FFAs, although the mechanism underlying the [Ca2+]i increase is still unknown. In this study, we investigated the action of linoleic acid on voltage-gated K+ currents. Nystatin-perforated recordings were performed on identified rat β-cells. In the presence of nifedipine, tetrodotoxin, and tolbutamide, voltage-gated K+ currents were observed. The transient current represents less than 5%, whereas the delayed rectifier current comprises more than 95%, of the total K+ currents. A long-chain unsaturated FFA, linoleic acid (10 μm), reversibly decreased the amplitude of K+ currents (to less than 10%). This reduction was abolished by the cAMP/protein kinase A system inhibitors H89 (1 μm) and Rp-cAMP (10 μm) but was not affected by protein kinase C inhibitor. In addition, forskolin and 8′-bromo-cAMP induced a similar reduction in the K+ current as that evoked by linoleic acid. Insulin secretion and cAMP accumulation in β-cells were also increased by linoleic acid. Methyl linoleate, which has a similar structure to linoleic acid but no binding affinity to GPR40, did not change K+ currents. Treatment of cultured cells with GPR40-specific small interfering RNA significantly reduced the decrease in K+ current induced by linoleic acid, whereas the cAMP-induced reduction of K+ current was not affected. We conclude that linoleic acid reduces the voltage-gated K+ current in rat β-cells through GPR40 and the cAMP-protein kinase A system, leading to an increase in [Ca2+]i and insulin secretion.

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Melanocortin 4 receptor activation induces brain-derived neurotrophic factor expression in rat astrocytes through cyclic AMP – Protein kinase A pathway

Molecular and Cellular Endocrinology ◽

10.1016/j.mce.2011.07.036 ◽

2012 ◽

Vol 348 (1) ◽

pp. 47-54 ◽

Cited By ~ 43

Author(s):

Carla Caruso ◽

Lila Carniglia ◽

Daniela Durand ◽

Patricia V. Gonzalez ◽

Teresa N. Scimonelli ◽

...

Keyword(s):

Protein Kinase ◽

Cyclic Amp ◽

Protein Kinase A ◽

Neurotrophic Factor ◽

Brain Derived Neurotrophic Factor ◽

Receptor Activation ◽

Melanocortin 4 Receptor ◽

Factor Expression ◽

Rat Astrocytes ◽

Kinase A

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GLP-1 Analog Liraglutide Enhances Proinsulin Processing in Pancreatic β-Cells via a PKA-Dependent Pathway

Endocrinology ◽

10.1210/en.2014-1218 ◽

2014 ◽

Vol 155 (10) ◽

pp. 3817-3828 ◽

Cited By ~ 8

Author(s):

Liang Wang ◽

Ye Liu ◽

Jin Yang ◽

Hejun Zhao ◽

Jing Ke ◽

...

Keyword(s):

Type 2 Diabetes ◽

Protein Kinase ◽

Protein Kinase A ◽

Pancreatic Β Cell ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Proinsulin Processing ◽

Kinase A

Abstract Hyperproinsulinemia has gained increasing attention in the development of type 2 diabetes. Clinical studies have demonstrated that glucagon-like peptide-1 (GLP-1)-based therapies significantly decrease plasma proinsulin/insulin ratio in patients with type 2 diabetes. However, the underlying mechanism remains unclear. Prohormone convertase (PC)-1/3 and PC2 are primarily responsible for processing proinsulin to insulin in pancreatic β-cells. We have recently reported that Pax6 mutation down-regulated PC1/3 and PC2 expression, resulting in defective proinsulin processing in Pax6 heterozygous mutant (Pax6m/+) mice. In this study, we investigated whether and how liraglutide, a novel GLP-1 analog, modulated proinsulin processing. Our results showed that liraglutide significantly up-regulated PC1/3 expression and decreased the proinsulin to insulin ratio in both Pax6m/+ and db/db diabetic mice. In the cultured mouse pancreatic β-cell line, Min6, liraglutide stimulated PC1/3 and PC2 expression and lowered the proinsulin to insulin ratio in a dose- and time-dependent manner. Moreover, the beneficial effects of liraglutide on PC1/3 and PC2 expression and proinsulin processing were dependent on the GLP-1 receptor-mediated cAMP/protein kinase A signaling pathway. The same mechanism was recapitulated in isolated mouse islets. In conclusion, liraglutide enhanced PC1/3- and PC2-dependent proinsulin processing in pancreatic β-cells through the activation of the GLP-1 receptor/cAMP/protein kinase A signaling pathway. Our study provides a new mechanism for improvement of pancreatic β-cell function by the GLP-1-based therapy.

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Chronic hyperglycemia downregulates GLP-1 receptor signaling in pancreatic β-cells via protein kinase A

Molecular Metabolism ◽

10.1016/j.molmet.2015.01.010 ◽

2015 ◽

Vol 4 (4) ◽

pp. 265-276 ◽

Cited By ~ 38

Author(s):

Sindhu Rajan ◽

Lorna M. Dickson ◽

Elizabeth Mathew ◽

Caitlin M.O. Orr ◽

Johanne H. Ellenbroek ◽

...

Keyword(s):

Protein Kinase ◽

Protein Kinase A ◽

Receptor Signaling ◽

Β Cells ◽

Pancreatic Β Cells ◽

Chronic Hyperglycemia ◽

Kinase A

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Abstract 34: Apolipoprotein A-I Increases Insulin Secretion from β-cells via a Protein Kinase A Dependent Mechanism

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.32.suppl_1.a34 ◽

2012 ◽

Vol 32 (suppl_1) ◽

Author(s):

Blake J Cochran ◽

Kerry-Anne Rye

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Protein Kinase ◽

Protein Kinase A ◽

Adenyl Cyclase ◽

Β Cells ◽

Pancreatic Β Cells ◽

Kinase A ◽

Dependent Mechanism

Introduction: The progression to hyperglycaemia in type 2 diabetes is marked by β-cell insulin secretory dysfunction and cell loss. We have previously demonstrated that apolipoprotein (apo) A-I, the major protein constituent of high density lipoproteins (HDL) increases insulin expression and secretion from β-cells. Clinical data also suggests that pharmacological elevation of HDL levels is associated with improved glycemic control in patients with type 2 diabetes. With the current interest in HDL raising therapeutics, defining the mechanism by which apoA-I acts on insulin secretion is of importance. Objective: To elucidate the cell signalling events responsible for increasing insulin secretion from pancreatic β-cells treated with lipid-free apoA-I. Methods: Ins-1E (rat insulinoma) cells were pre-treated for 30 min with the Protein kinase A (PKA) specific inhibitor H89 (20 μM), soluble and transmembrane adenyl cyclase specific inhibitors (KH7, 30 μM and 2’5’ dideoxyadenosine, 50 μM, respectively) or vehicle control, then incubated for 1 h with lipid-free apoA-I (final concentration 1 mg/mL) under both basal (2.8 mM) and high (25 mM) glucose conditions. The insulin concentration in the culture supernatants was determined by radioimmunoassay and the cells were either lysed for protein analysis by western blotting or treated with 0.1 M HCl for determining cAMP by enzyme immunoassay. Results: Incubation of Ins-1E cells with apoA-I increased insulin secretion up to 3-fold. This increase was no longer apparent when the cells were pre-treated with H89. Incubation with apoA-I increased cAMP accumulation in Ins-1E cells 2.5-fold. This increase was totally inhibited when the cells were pre-incubated with 2’5’ dideoxyadenosine but not by KH7, indicating that transmembrane adenyl cyclase(s) are responsible for this response. ApoA-I also activated the small GTPase Cdc42, which may link cell surface apoA-I receptors with transmembrane adenyl cyclases. Conclusion: ApoA-I increases insulin secretion from pancreatic β-cells via a PKA-dependent mechanism involving transmembrane, but not soluble, adenyl cyclases and possibly Cdc42. This provides a possible explanation of the clinical observations that increased HDL may be beneficial in type 2 diabetes.

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Ca2+-induced Ca2+ Release via Inositol 1,4,5-trisphosphate Receptors Is Amplified by Protein Kinase A and Triggers Exocytosis in Pancreatic β-Cells

Journal of Biological Chemistry ◽

10.1074/jbc.m407673200 ◽

2004 ◽

Vol 279 (44) ◽

pp. 45455-45461 ◽

Cited By ~ 72

Author(s):

Oleg Dyachok ◽

Erik Gylfe

Keyword(s):

Protein Kinase ◽

Protein Kinase A ◽

Ryanodine Receptors ◽

Nucleotide Exchange ◽

High Concentration ◽

Β Cells ◽

Pancreatic Β Cells ◽

Inositol 1,4,5 Trisphosphate ◽

Glucagon Like Peptide 1 ◽

Kinase A

Hormones, such as glucagon and glucagon-like peptide-1, potently amplify nutrient stimulated insulin secretion by raising cAMP. We have studied how cAMP affects Ca2+-induced Ca2+release (CICR) in pancreatic β-cells from mice and rats and the role of CICR in secretion. CICR was observed as pronounced Ca2+spikes on top of glucose- or depolarization-dependent rise of the cytoplasmic Ca2+concentration ([Ca2+]i). cAMP-elevating agents strongly promoted CICR. This effect involved sensitization of the receptors underlying CICR, because many cells exhibited the characteristic Ca2+spiking at low or even in the absence of depolarization-dependent elevation of [Ca2+]i. The cAMP effect was mimicked by a specific activator of protein kinase A in cells unresponsive to activators of cAMP-regulated guanine nucleotide exchange factor. Ryanodine pretreatment, which abolishes CICR mediated by ryanodine receptors, did not prevent CICR. Moreover, a high concentration of caffeine, known to activate ryanodine receptors independently of Ca2+, failed to mobilize intracellular Ca2+. On the contrary, a high caffeine concentration abolished CICR by interfering with inositol 1,4,5-trisphosphate receptors (IP3Rs). Therefore, the cell-permeable IP3R antagonist 2-aminoethoxydiphenyl borate blocked the cAMP-promoted CICR. Individual CICR events in pancreatic β-cells were followed by [Ca2+]ispikes in neighboring human erythroleukemia cells, used to report secretory events in the β-cells. The results indicate that protein kinase A-mediated promotion of CICR via IP3Rs is part of the mechanism by which cAMP amplifies insulin release.

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