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.

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.

Overexpression of uncoupling protein 2 inhibits glucose-stimulated insulin secretion from rat islets

Diabetes ◽  
1999 ◽  
Vol 48 (7) ◽  
pp. 1482-1486 ◽  
Author(s):  
C. B. Chan ◽  
P. E. MacDonald ◽  
M. C. Saleh ◽  
D. C. Johns ◽  
E. Marban ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Uncoupling Protein ◽  
Uncoupling Protein 2 ◽  
Rat Islets ◽  
Glucose Stimulated 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 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 Intragranular targeting of syncollin, but not a syncollinGFP chimera, inhibits regulated insulin exocytosis in pancreatic β-cells

2005 ◽  
Vol 185 (1) ◽  
pp. 57-67 ◽  
Author(s):  
L B Hays ◽  
B Wicksteed ◽  
Y Wang ◽  
J F McCuaig ◽  
L H Philipson ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Fluorescent Protein ◽  
Zymogen Granule ◽  
Β Cells ◽  
Rat Islets ◽  
Intracellular Ca ◽  
Specific Localization ◽  
Glucagon Like Peptide 1 ◽  
Green Fluorescent ◽  
Insulin Exocytosis

Several proteins play a role in the mechanism of insulin exocytosis. However, these ‘exocytotic proteins’ have yet to account for the regulated aspect of insulin exocytosis, and other factors are involved. In pancreatic exocrine cells, the intralumenal zymogen granule protein, syncollin, is required for efficient regulated exocytosis, but it is not known whether intragranular peptides similarly influence regulated insulin exocytosis. Here, this issue has been addressed using expression of syncollin and a syncollin-green fluorescent protein (syncollinGFP) chimera in rat islet β-cells as experimental tools. Syncollin is not normally expressed in β-cells but adenoviral-mediated expression of both syncollin and syncollinGFP indicated that these were specifically targeted to the lumen of β-granules. Syncollin expression in isolated rat islets had no effect on basal insulin secretion but significantly inhibited regulated insulin secretion stimulated by glucose (16.7 mM), glucagon-like peptide-1 (GLP-1) (10 nM) and glyburide (5μM). Consistent with specific localization of syncollin to β-granules, constitutive secretion was unchanged by syncollin expression in rat islets. Syncollin-mediated inhibition of insulin secretion was not due to inadequate insulin production. Moreover, secretagogue-induced increases in cytosolic intracellular Ca2+, which is a prerequisite for triggering insulin exocytosis, were unaffected in syncollin-expressing islets. Therefore, syncollin was most likely acting downstream of secondary signals at the level of insulin exocytosis. Thus, syncollin expression in β-cells has highlighted the importance of intralumenal β-granule peptide factors playing a role in the control of insulin exocytosis. In contrast to syncollin, syncollinGFP had no effect on insulin secretion, underlining its usefulness as a ‘fluorescent tag’ to track β-granule transport and exocytosis in real time.

scholarly journals Inhibition of Forkhead Box O1 Protects Pancreatic β-Cells against Dexamethasone-Induced Dysfunction

Endocrinology ◽  
2009 ◽  
Vol 150 (9) ◽  
pp. 4065-4073 ◽  
Author(s):  
Xiongfei Zhang ◽  
Wei Yong ◽  
Jinghuan Lv ◽  
Yunxia Zhu ◽  
Jingjing Zhang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Cell Types ◽  
Pancreatic Β Cell ◽  
Rinm5f Cells ◽  
Β Cells ◽  
Β Cell ◽  
Rat Islets ◽  
Cell Dysfunction ◽  
Forkhead Box ◽  
Glucose Stimulated Insulin Secretion

Abstract Forkhead Box O1 (FoxO1) is a key transcription regulator of insulin/IGF-I signaling pathway, and its activity can be increased by dexamethasone (DEX) in several cell types. However, the role of FoxO1 in DEX-induced pancreatic β-cell dysfunction has not been fully understood. Therefore, in this study, we investigated whether FoxO1 could mediate DEX-induced β-cell dysfunction and the possible underlying mechanisms in pancreatic β-cell line RINm5F cells and primary rat islet. We found that DEX markedly increased FoxO1 mRNA and protein expression and decreased FoxO1 phosphorylation through the Akt pathway, which resulted in an increase in active FoxO1 in RINm5F cells and isolated rat islets. Activated FoxO1 subsequently inhibited pancreatic duodenal homeobox-1 expression and induced nuclear exclusion of pancreatic duodenal homeobox-1. Knockdown of FoxO1 by RNA interference restored the expression of pancreatic duodenal homeobox-1 and prevented DEX-induced dysfunction of glucose-stimulated insulin secretion in rat islets. Together, the results of present study demonstrate that FoxO1 is integrally involved in DEX-induced inhibition of pancreatic duodenal homeobox-1 and glucose-stimulated insulin secretion dysfunction in pancreatic islet β-cells. Inhibition of FoxO1 can effectively protect β-cells against DEX-induced dysfunction.

Increased glucose sensitivity of both triggering and amplifying pathways of insulin secretion in rat islets cultured for 1 wk in high glucose

2004 ◽  
Vol 287 (2) ◽  
pp. E207-E217 ◽  
Author(s):  
M. Z. Khaldi ◽  
Y. Guiot ◽  
P. Gilon ◽  
J. C. Henquin ◽  
J. C. Jonas
Keyword(s):  
Insulin Secretion ◽  
High Glucose ◽  
Uncoupling Protein ◽  
Glucose Stimulation ◽  
Rat Islets ◽  
Chronic Hyperglycemia ◽  
Intracellular Ca ◽  
Increased Sensitivity ◽  
Glucose Sensitivity ◽  
Stimulation Of

Chronic hyperglycemia has been shown to induce either a lack of response or an increased sensitivity to glucose in pancreatic β-cells. We reinvestigated this controversial issue in a single experimental model by culturing rat islets for 1 wk in 10 or 30 mmol/l glucose (G10, Controls; or G30, High-glucose islets) before testing the effect of stepwise glucose stimulation from G0.5 to G20 on key β-cell stimulus-secretion coupling events. Compared with Controls, the glucose sensitivity of High-glucose islets was markedly increased, leading to maximal stimulation of oxidative metabolism and both triggering and amplifying pathways of insulin secretion in G6 rather than G20, hence to loss of glucose effect above G6. This enhanced glucose sensitivity occurred despite an approximately twofold increase in islet uncoupling protein 2 mRNA expression. Besides this increased glucose sensitivity, the maximal glucose stimulation of insulin secretion in High-glucose islets was reduced by ∼50%, proportionally to the reduction of insulin content. In High-glucose islets, changes in 45Ca2+ influx induced by glucose and diazoxide were qualitatively similar but quantitatively smaller than in Control islets and, paradoxically, did not lead to detectable changes in the intracellular Ca2+ concentration measured by microspectrofluorimetry (fura PE 3). In conclusion, after 1 wk of culture in G30, the loss of glucose stimulation of insulin secretion in the physiological range of glucose concentrations (G5–G10) results from the combination of an increased sensitivity to glucose of both triggering and amplifying pathways of insulin secretion and an ∼50% reduction in the maximal glucose stimulation of insulin secretion.

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