Uncoupling protein-2 contributes significantly to high mitochondrial proton leak in INS-1E insulinoma cells and attenuates glucose-stimulated insulin secretion

2007 ◽  
Vol 409 (1) ◽  
pp. 199-204 ◽  
Author(s):  
Charles Affourtit ◽  
Martin D. Brand
Keyword(s):  
Insulin Secretion ◽  
Uncoupling Protein ◽  
Proton Leak ◽  
Cell Physiology ◽  
Uncoupling Protein 2 ◽  
Proton Conductance ◽  
Β Cells ◽  
Knock Down ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells

Proton leak exerts stronger control over ATP/ADP in mitochondria from clonal pancreatic β-cells (INS-1E) than in those from rat skeletal muscle, due to the higher proton conductance of INS-1E mitochondria [Affourtit and Brand (2006) Biochem. J. 393, 151–159]. In the present study, we demonstrate that high proton leak manifests itself at the cellular level too: the leak rate (measured as myxothiazol-sensitive, oligomycin-resistant respiration) was nearly four times higher in INS-1E cells than in myoblasts. This relatively high leak activity was decreased more than 30% upon knock-down of UCP2 (uncoupling protein-2) by RNAi (RNA interference). The high contribution of UCP2 to leak suggests that proton conductance through UCP2 accounts for approx. 20% of INS-1E respiration. UCP2 knock-down enhanced GSIS (glucose-stimulated insulin secretion), consistent with a role for UCP2 in β-cell physiology. We propose that the high mitochondrial proton leak in β-cells is a mechanism which amplifies the effect of physiological UCP2 regulators on cytoplasmic ATP/ADP and hence on insulin secretion.

scholarly journals Increased Uncoupling Protein-2 Levels in β-cells Are Associated With Impaired Glucose-Stimulated Insulin Secretion

Diabetes ◽  
2001 ◽  
Vol 50 (6) ◽  
pp. 1302-1310 ◽  
Author(s):  
Catherine B. Chan ◽  
Domenica De Leo ◽  
Jamie W. Joseph ◽  
Timothy S. McQuaid ◽  
Xiao Fang Ha ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Uncoupling Protein ◽  
Uncoupling Protein 2 ◽  
Β Cells ◽  
Glucose Stimulated Insulin Secretion

scholarly journals cAMP-mediated signaling normalizes glucose-stimulated insulin secretion in uncoupling protein-2 overexpressing β-cells

2006 ◽  
Vol 190 (3) ◽  
pp. 669-680 ◽  
Author(s):  
T S McQuaid ◽  
M C Saleh ◽  
J W Joseph ◽  
A Gyulkhandanyan ◽  
J E Manning-Fox ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Uncoupling Protein ◽  
Uncoupling Protein 2 ◽  
Β Cells ◽  
Camp Content ◽  
Rat Islets ◽  
Mediated Effects ◽  
Intracellular Ca ◽  
Glucose Stimulated Insulin Secretion ◽  
Glucose Responsiveness

We investigated whether an increase in cAMP could normalize glucose-stimulated insulin secretion (GSIS) in uncoupling protein-2 (UCP2) overexpressing (ucp2-OE) β-cells. Indices of β-cell (β-TC-6f7 cells and rodent islets) function were measured after induction of ucp2, in the presence or absence of cAMP-stimulating agents, analogs, or inhibitors. Islets of ob/ob mice had improved glucose-responsiveness in the presence of forskolin. Rat islets overexpressing ucp2 had significantly lower GSIS than controls. Acutely, the protein kinase A (PKA) and epac pathway stimulant forskolin normalized insulin secretion in ucp2-OE rat islets and β-TC-6f7 β-cells, an effect blocked by specific PKA inhibitors but not mimicked by epac agonists. However, there was no effect of ucp2-OE on cAMP concentrations or PKA activity. In ucp2-OE islets, forskolin inhibited ATP-dependent potassium (KATP) channel currents and 86Rb+ efflux, indicative of KATP block. Likewise, forskolin application increased intracellular Ca2+, which could account for its stimulatory effects on insulin secretion. Chronic exposure to forskolin increased ucp2 mRNA and exaggerated basal secretion but not GSIS. In mice deficient in UCP2, there was no augmentation of either cAMP content or cAMP-dependent insulin secretion. Thus, elevating cellular cAMP can reverse the deficiency in GSIS invoked by ucp2-OE, at least partly through PKA-mediated effects on the KATP channel.

scholarly journals Glutathionylation State of Uncoupling Protein-2 and the Control of Glucose-stimulated Insulin Secretion

2012 ◽  
Vol 287 (47) ◽  
pp. 39673-39685 ◽  
Author(s):  
Ryan J. Mailloux ◽  
Accalia Fu ◽  
Christine Robson-Doucette ◽  
Emma M. Allister ◽  
Michael B. Wheeler ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Uncoupling Protein ◽  
Uncoupling Protein 2 ◽  
Glucose Stimulated Insulin Secretion

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

Endocrinology ◽  
2005 ◽  
Vol 146 (8) ◽  
pp. 3266-3276 ◽  
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.

scholarly journals Chronic fructose renders pancreatic β-cells hyper-responsive to glucose-stimulated insulin secretion through extracellular ATP signaling

2019 ◽  
Vol 317 (1) ◽  
pp. E25-E41 ◽  
Author(s):  
Clarissa Bartley ◽  
Thierry Brun ◽  
Lucie Oberhauser ◽  
Mariagrazia Grimaldi ◽  
Filippo Molica ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Atp Release ◽  
Extracellular Atp ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Cellular Mechanisms ◽  
Kinase Activation ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells ◽  
Atp Signaling

Fructose is widely used as a sweetener in processed food and is also associated with metabolic disorders, such as obesity. However, the underlying cellular mechanisms remain unclear, in particular, regarding the pancreatic β-cell. Here, we investigated the effects of chronic exposure to fructose on the function of insulinoma cells and isolated mouse and human pancreatic islets. Although fructose per se did not acutely stimulate insulin exocytosis, our data show that chronic fructose rendered rodent and human β-cells hyper-responsive to intermediate physiological glucose concentrations. Fructose exposure reduced intracellular ATP levels without affecting mitochondrial function, induced AMP-activated protein kinase activation, and favored ATP release from the β-cells upon acute glucose stimulation. The resulting increase in extracellular ATP, mediated by pannexin1 (Panx1) channels, activated the calcium-mobilizer P2Y purinergic receptors. Immunodetection revealed the presence of both Panx1 channels and P2Y1 receptors in β-cells. Addition of an ectonucleotidase inhibitor or P2Y1 agonists to naïve β-cells potentiated insulin secretion stimulated by intermediate glucose, mimicking the fructose treatment. Conversely, the P2Y1 antagonist and Panx1 inhibitor reversed the effects of fructose, as confirmed using Panx1-null islets and by the clearance of extracellular ATP by apyrase. These results reveal an important function of ATP signaling in pancreatic β-cells mediating fructose-induced hyper-responsiveness.

scholarly journals In pancreatic β-cells myosin 1b regulates glucose-stimulated insulin secretion by modulating an early step in insulin granule trafficking from the Golgi

2021 ◽  
pp. mbc.E21-03-0094
Author(s):  
Hiroshi Tokuo ◽  
Shigeru Komaba ◽  
Lynne M. Coluccio
Keyword(s):  
Insulin Secretion ◽  
Islet Cells ◽  
Early Stage ◽  
Secretory Granules ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Levels ◽  
Insulin Granule ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells

Pancreatic β-cells secrete insulin, which controls blood glucose levels, and defects in insulin secretion are responsible for diabetes mellitus. The actin cytoskeleton and some myosins support insulin granule trafficking and release, although a role for the class I myosin Myo1b, an actin- and membrane-associated load-sensitive motor, in insulin biology is unknown. We found by immunohistochemistry that Myo1b is expressed in islet cells of rat pancreas. In cultured rat insulinoma 832/13 cells Myo1b localized near actin patches, the trans-Golgi network (TGN) marker TGN38, and insulin granules in the perinuclear region. Myo1b depletion by siRNA in 832/13 cells reduced intracellular proinsulin and insulin content and glucose-stimulated insulin secretion (GSIS), and led to the accumulation of (pro)insulin SGs at the TGN. Using an in situ fluorescent pulse-chase strategy to track nascent proinsulin (Bearrows et al., 2019), Myo1b depletion in insulinoma cells reduced the number of (pro)insulin-containing secretory granules budding from the TGN. The studies indicate for the first time that in pancreatic β-cells Myo1b controls GSIS at least in part by mediating an early stage in insulin granule trafficking from the TGN.

Members of the Kv1 and Kv2 Voltage-Dependent K+ Channel Families Regulate Insulin Secretion

2001 ◽  
Vol 15 (8) ◽  
pp. 1423-1435 ◽  
Author(s):  
Patrick E. MacDonald ◽  
Xiao Fang Ha ◽  
Jing Wang ◽  
Simon R. Smukler ◽  
Anthony M. Sun ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
K Channel ◽  
Delayed Rectifier ◽  
Β Cells ◽  
Rat Islets ◽  
Kv Channels ◽  
Delayed Rectifier Current ◽  
Voltage Dependent ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells

Abstract In pancreatic β-cells, voltage-dependent K+ (Kv) channels are potential mediators of repolarization, closure of Ca2+ channels, and limitation of insulin secretion. The specific Kv channels expressed in β-cells and their contribution to the delayed rectifier current and regulation of insulin secretion in these cells are unclear. High-level protein expression and mRNA transcripts for Kv1.4, 1.6, and 2.1 were detected in rat islets and insulinoma cells. Inhibition of these channels with tetraethylammonium decreased IDR by approximately 85% and enhanced glucose-stimulated insulin secretion by 2- to 4-fold. Adenovirus-mediated expression of a C-terminal truncated Kv2.1 subunit, specifically eliminating Kv2 family currents, reduced delayed rectifier currents in these cells by 60–70% and enhanced glucose-stimulated insulin secretion from rat islets by 60%. Expression of a C-terminal truncated Kv1.4 subunit, abolishing Kv1 channel family currents, reduced delayed rectifier currents by approximately 25% and enhanced glucose-stimulated insulin secretion from rat islets by 40%. This study establishes that Kv2 and 1 channel homologs mediate the majority of repolarizing delayed rectifier current in rat β-cells and that antagonism of Kv2.1 may prove to be a novel glucose-dependent therapeutic treatment for type 2 diabetes.

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