| 1. |
- Zhang, Q., et al.
(författare)
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Na+ current properties in islet alpha- and beta-cells reflect cell-specific Scn3a and Scn9a expression
- 2014
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Ingår i: Journal of Physiology-London. - : Wiley. - 0022-3751 .- 1469-7793. ; 592:21, s. 4677-4696
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Tidskriftsartikel (refereegranskat)abstract
- - and -cells express both Na(v)1.3 and Na(v)1.7 Na+ channels but in different relative amounts. The differential expression explains the different properties of Na+ currents in - and -cells. Na(v)1.3 is the functionally important Na+ channel subunit in both - and -cells. Islet Na(v)1.7 channels are locked in an inactive state due to an islet cell-specific factor. Mouse pancreatic - and -cells are equipped with voltage-gated Na+ currents that inactivate over widely different membrane potentials (half-maximal inactivation (V-0.5) at -100mV and -50mV in - and -cells, respectively). Single-cell PCR analyses show that both - and -cells have Na(v)1.3 (Scn3) and Na(v)1.7 (Scn9a) subunits, but their relative proportions differ: -cells principally express Na(v)1.7 and -cells Na(v)1.3. In -cells, genetically ablating Scn3a reduces the Na+ current by 80%. In -cells, knockout of Scn9a lowers the Na+ current by >85%, unveiling a small Scn3a-dependent component. Glucagon and insulin secretion are inhibited in Scn3a(-/-) islets but unaffected in Scn9a-deficient islets. Thus, Na(v)1.3 is the functionally important Na+ channel subunit in both - and -cells because Na(v)1.7 is largely inactive at physiological membrane potentials due to its unusually negative voltage dependence of inactivation. Interestingly, the Na(v)1.7 sequence in brain and islets is identical and yet the V-0.5 for inactivation is >30mV more negative in -cells. This may indicate the presence of an intracellular factor that modulates the voltage dependence of inactivation.
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| 2. |
- Amisten, Stefan, et al.
(författare)
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An atlas and functional analysis of G-protein coupled receptors in human islets of Langerhans
- 2013
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Ingår i: Pharmacology and Therapeutics. - : Elsevier BV. - 0163-7258. ; 139:3, s. 359-391
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Forskningsöversikt (refereegranskat)abstract
- G-protein coupled receptors (GPCRs) regulate hormone secretion from islets of Langerhans, and recently developed therapies for type-2 diabetes target islet GLP-1 receptors. However, the total number of GPCRs expressed by human islets, as well as their function and interactions with drugs, is poorly understood. In this review we have constructed an atlas of all GPCRs expressed by human islets: the 'islet GPCRome'. We have used this atlas to describe how islet GPCRs interact with their endogenous ligands, regulate islet hormone secretion, and interact with drugs known to target GPCRs, with a focus on drug/receptor interactions that may affect insulin secretion. The islet GPCRome consists of 293 GPCRs, a majority of which have unknown effects on insulin, glucagon and somatostatin secretion. The islet GPCRs are activated by 271 different endogenous ligands, at least 131 of which are present in islet cells. A large signalling redundancy was also found, with 119 ligands activating more than one islet receptor. Islet GPCRs are also the targets of a large number of clinically used drugs, and based on their coupling characteristics and effects on receptor signalling we identified 107 drugs predicted to stimulate and 184 drugs predicted to inhibit insulin secretion. The islet GPCRome highlights knowledge gaps in the current understanding of islet GPCR function, and identifies GPCR/ligand/drug interactions that might affect insulin secretion, which are important for understanding the metabolic side effects of drugs. This approach may aid in the design of new safer therapeutic agents with fewer detrimental effects on islet hormone secretion. (C) 2013 Elsevier Inc. All rights reserved.
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| 3. |
- De Marinis, Yang, et al.
(författare)
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Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCalpha and PKCdelta.
- 2010
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 53:4, s. 717-729
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Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESIS: Protein kinase C (PKC) regulates exocytosis in various secretory cells. Here we studied intracellular translocation of the PKC isoenzymes PKCalpha and PKCdelta, and investigated how activation of PKC influences glucagon secretion in mouse and human pancreatic alpha cells. METHODS: Glucagon release from intact islets was measured in static incubations, and the amounts released were determined by RIA. Exocytosis was monitored as increases in membrane capacitance using the patch-clamp technique. The expression of genes encoding PKC isoforms was analysed by real-time PCR. Intracellular PKC distribution was assessed by confocal microscopy. RESULTS: The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated glucagon secretion from mouse and human islets about fivefold (p < 0.01). This stimulation was abolished by the PKC inhibitor bisindolylmaleimide (BIM). Whereas PMA potentiated exocytosis more than threefold (p < 0.001), BIM inhibited alpha cell exocytosis by 60% (p < 0.05). In mouse islets, the PKC isoenzymes, PKCalpha and PKCbeta1, were highly abundant, while in human islets PKCeta, PKCepsilon and PKCzeta were the dominant variants. PMA stimulation of human alpha cells correlated with the translocation of PKCalpha and PKCdelta from the cytosol to the cell periphery. In the mouse alpha cells, PKCdelta was similarly affected by PMA, whereas PKCalpha was already present at the cell membrane in the absence of PMA. This association of PKCalpha in alpha cells was principally dependent on Ca(2+) influx through the L-type Ca(2+) channel. CONCLUSIONS/INTERPRETATION: PKC activation augments glucagon secretion in mouse and human alpha cells. This effect involves translocation of PKCalpha and PKCdelta to the plasma membrane, culminating in increased Ca(2+)-dependent exocytosis. In addition, we demonstrated that PKCalpha translocation and exocytosis exhibit differential Ca(2+) channel dependence.
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| 4. |
- De Marinis, Yang, et al.
(författare)
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GLP-1 inhibits and adrenaline stimulates glucagon release by differential modulation of N- and L-type Ca2+ channel-dependent exocytosis.
- 2010
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 11:6, s. 543-553
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Tidskriftsartikel (refereegranskat)abstract
- Glucagon secretion is inhibited by glucagon-like peptide-1 (GLP-1) and stimulated by adrenaline. These opposing effects on glucagon secretion are mimicked by low (1-10 nM) and high (10 muM) concentrations of forskolin, respectively. The expression of GLP-1 receptors in alpha cells is <0.2% of that in beta cells. The GLP-1-induced suppression of glucagon secretion is PKA dependent, is glucose independent, and does not involve paracrine effects mediated by insulin or somatostatin. GLP-1 is without much effect on alpha cell electrical activity but selectively inhibits N-type Ca(2+) channels and exocytosis. Adrenaline stimulates alpha cell electrical activity, increases [Ca(2+)](i), enhances L-type Ca(2+) channel activity, and accelerates exocytosis. The stimulatory effect is partially PKA independent and reduced in Epac2-deficient islets. We propose that GLP-1 inhibits glucagon secretion by PKA-dependent inhibition of the N-type Ca(2+) channels via a small increase in intracellular cAMP ([cAMP](i)). Adrenaline stimulates L-type Ca(2+) channel-dependent exocytosis by activation of the low-affinity cAMP sensor Epac2 via a large increase in [cAMP](i).
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| 5. |
- Latreille, Mathieu, et al.
(författare)
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MicroRNA-7a regulates pancreatic beta cell function
- 2014
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Ingår i: Journal of Clinical Investigation. - 0021-9738. ; 124:6, s. 2722-2735
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Tidskriftsartikel (refereegranskat)abstract
- Dysfunctional microRNA (miRNA) networks contribute to inappropriate responses following pathological stress and are the underlying cause of several disease conditions. In pancreatic beta cells, miRNAs have been largely unstudied and little is known about how specific miRNAs regulate glucose-stimulated insulin secretion (GSIS) or impact the adaptation of beta cell function to metabolic stress. In this study, we determined that miR-7 is a negative regulator of GSIS in beta cells. Using Mir7a2 deficient mice, we revealed that miR-7a2 regulates beta cell function by directly regulating genes that control late stages of insulin granule fusion with the plasma membrane and ternary SNARE complex activity. Transgenic mice overexpressing miR-7a in beta cells developed diabetes due to impaired insulin secretion and beta cell dedifferentiation. Interestingly, perturbation of miR-7a expression in beta cells did not affect proliferation and apoptosis, indicating that miR-7 is dispensable for the maintenance of endocrine beta cell mass. Furthermore, we found that miR-7a levels are decreased in obese/ diabetic mouse models and human islets from obese and moderately diabetic individuals with compensated beta cell function. Our results reveal an interconnecting miR-7 genomic circuit that regulates insulin granule exocytosis in pancreatic beta cells and support a role for miR-7 in the adaptation of pancreatic p cell function in obesity and type 2 diabetes.
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| 6. |
- Obermüller, Stefanie, et al.
(författare)
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Defective secretion of islet hormones in chromogranin-B deficient mice
- 2010
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:1, s. e8936-
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Tidskriftsartikel (refereegranskat)abstract
- Granins are major constituents of dense-core secretory granules in neuroendocrine cells, but their function is still a matter of debate. Work in cell lines has suggested that the most abundant and ubiquitously expressed granins, chromogranin A and B (CgA and CgB), are involved in granulogenesis and protein sorting. Here we report the generation and characterization of mice lacking chromogranin B (CgB-ko), which were viable and fertile. Unlike neuroendocrine tissues, pancreatic islets of these animals lacked compensatory changes in other granins and were therefore analyzed in detail. Stimulated secretion of insulin, glucagon and somatostatin was reduced in CgB-ko islets, in parallel with somewhat impaired glucose clearance and reduced insulin release, but normal insulin sensitivity in vivo. CgB-ko islets lacked specifically the rapid initial phase of stimulated secretion, had elevated basal insulin release, and stored and released twice as much proinsulin as wildtype (wt) islets. Stimulated release of glucagon and somatostatin was reduced as well. Surprisingly, biogenesis, morphology and function of insulin granules were normal, and no differences were found with regard to beta-cell stimulus-secretion coupling. We conclude that CgB is not required for normal insulin granule biogenesis or maintenance in vivo, but is essential for adequate secretion of islet hormones. Consequentially CgB-ko animals display some, but not all, hallmarks of human type-2 diabetes. However, the molecular mechanisms underlying this defect remain to be determined.
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| 7. |
- Rorsman, Patrik, et al.
(författare)
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Electrophysiology of pancreatic beta-cells in intact mouse islets of Langerhans
- 2011
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Ingår i: Progress in Biophysics and Molecular Biology. - : Elsevier BV. - 1873-1732 .- 0079-6107. ; 107:2, s. 224-235
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Forskningsöversikt (refereegranskat)abstract
- When exposed to intermediate glucose concentrations (6-16 mol/l), pancreatic beta-cells in intact islets generate bursts of action potentials (superimposed on depolarised plateaux) separated by repolarised electrically silent intervals. First described more than 40 years ago, these oscillations have continued to intrigue beta-cell electrophysiologists. To date, most studies of beta-cell ion channels have been performed on isolated cells maintained in tissue culture (that do not burst). Here we will review the electrophysiological properties of beta-cells in intact, freshly isolated, mouse pancreatic islets. We will consider the role of ATP-regulated K+-channels (K-ATP-channels), small-conductance Ca2+-activated K+-channels and voltage-gated Ca2+-channels in the generation of the bursts. Our data indicate that K-ATP-channels not only constitute the glucose-regulated resting conductance in the beta-cell but also provide a variable K+- conductance that influence the duration of the bursts of action potentials and the silent intervals. We show that inactivation of the voltage-gated Ca2+-current is negligible at voltages corresponding to the plateau potential and consequently unlikely to play a major role in the termination of the burst. Finally, we propose a model for glucose-induced beta-cell electrical activity based on observations made in intact pancreatic islets. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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| 8. |
- Rosengren, Anders, et al.
(författare)
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Overexpression of alpha2A-adrenergic receptors contributes to type 2 diabetes
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 327:5962, s. 217-20
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Tidskriftsartikel (refereegranskat)abstract
- Several common genetic variations have been associated with type 2 diabetes, but the exact disease mechanisms are still poorly elucidated. Using congenic strains from the diabetic Goto-Kakizaki rat, we identified a 1.4-megabase genomic locus that was linked to impaired insulin granule docking at the plasma membrane and reduced beta cell exocytosis. In this locus, Adra2a, encoding the alpha2A-adrenergic receptor [alpha(2A)AR], was significantly overexpressed. Alpha(2A)AR mediates adrenergic suppression of insulin secretion. Pharmacological receptor antagonism, silencing of receptor expression, or blockade of downstream effectors rescued insulin secretion in congenic islets. Furthermore, we identified a single-nucleotide polymorphism in the human ADRA2A gene for which risk allele carriers exhibited overexpression of alpha(2A)AR, reduced insulin secretion, and increased type 2 diabetes risk. Human pancreatic islets from risk allele carriers exhibited reduced granule docking and secreted less insulin in response to glucose; both effects were counteracted by pharmacological alpha(2A)AR antagonists.
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| 9. |
- Rosengren, Anders, et al.
(författare)
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Reduced Insulin Exocytosis in Human Pancreatic β-cells With Gene Variants Linked to Type 2 Diabetes.
- 2012
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 61:7, s. 1726-1733
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Tidskriftsartikel (refereegranskat)abstract
- The majority of genetic risk variants for type 2 diabetes (T2D) affect insulin secretion, but the mechanisms through which they influence pancreatic islet function remain largely unknown. We functionally characterized human islets to determine secretory, biophysical, and ultrastructural features in relation to genetic risk profiles in diabetic and nondiabetic donors. Islets from donors with T2D exhibited impaired insulin secretion, which was more pronounced in lean than obese diabetic donors. We assessed the impact of 14 disease susceptibility variants on measures of glucose sensing, exocytosis, and structure. Variants near TCF7L2 and ADRA2A were associated with reduced glucose-induced insulin secretion, whereas susceptibility variants near ADRA2A, KCNJ11, KCNQ1, and TCF7L2 were associated with reduced depolarization-evoked insulin exocytosis. KCNQ1, ADRA2A, KCNJ11, HHEX/IDE, and SLC2A2 variants affected granule docking. We combined our results to create a novel genetic risk score for β-cell dysfunction that includes aberrant granule docking, decreased Ca(2+) sensitivity of exocytosis, and reduced insulin release. Individuals with a high risk score displayed an impaired response to intravenous glucose and deteriorating insulin secretion over time. Our results underscore the importance of defects in β-cell exocytosis in T2D and demonstrate the potential of cellular phenotypic characterization in the elucidation of complex genetic disorders.
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| 10. |
- Salehi, S Albert, et al.
(författare)
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The insulinogenic effect of whey protein is partially mediated by a direct effect of amino acids and GIP on beta-cells
- 2012
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Ingår i: Nutrition & Metabolism. - : Springer Science and Business Media LLC. - 1743-7075. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Whey protein increases postprandial serum insulin levels. This has been associated with increased serum levels of leucine, isoleucine, valine, lysine, threonine and the incretin hormone glucose-dependent insulinotropic polypeptide (GIP). We have examined the effects of these putative mediators of whey's action on insulin secretion from isolated mouse Langerhans islets. Methods: Mouse pancreatic islets were incubated with serum drawn from healthy individuals after ingestion of carbohydrate equivalent meals of whey protein (whey serum), or white wheat bread (control serum). In addition the effect of individual amino acid combinations on insulin secretion was also tested. Furthermore, the stimulatory effects of whey serum on insulin secretion was tested in vitro in the absence and presence of a GIP receptor antagonist ((Pro(3)) GIP[mPEG]). Results: Postprandial amino acids, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) responses were higher after whey compared to white wheat bread. A stimulatory effect on insulin release from isolated islets was observed with serum after whey obtained at 15 min (+87%, P < 0.05) and 30 min (+139%, P < 0.05) postprandially, compared with control serum. The combination of isoleucine, leucine, valine, lysine and threonine exerted strong stimulatory effect on insulin secretion (+270%, P < 0.05), which was further augmented by GIP (+558% compared to that produced by glucose, P < 0.05). The stimulatory action of whey on insulin secretion was reduced by the GIP-receptor antagonist (Pro(3)) GIP[mPEG]) at both 15 and 30 min (-56% and -59%, P < 0.05). Conclusions: Compared with white wheat bread meal, whey causes an increase of postprandial insulin, plasma amino acids, GIP and GLP-1 responses. The in vitro data suggest that whey protein exerts its insulinogenic effect by preferential elevation of the plasma concentrations of certain amino acids, GIP and GLP-1.
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