| 1. |
- Wendt, Anna, et al.
(author)
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Synapsins I and II Are Not Required for Insulin Secretion from Mouse Pancreatic beta-cells
- 2012
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In: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 153:5, s. 2112-2119
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Journal article (peer-reviewed)abstract
- Synapsins are a family of phosphoproteins that modulate the release of neurotransmitters from synaptic vesicles. The release of insulin from pancreatic beta-cells has also been suggested to be regulated by synapsins. In this study, we have utilized a knock out mouse model with general disruptions of the synapsin I and II genes [synapsin double knockout (DKO)]. Stimulation with 20 mM glucose increased insulin secretion 9-fold in both wild-type (WT) and synapsin DKO islets, whereas secretion in the presence of 70 mM K+ and 1mM glucose was significantly enhanced in the synapsin DKO mice compared to WT. Exocytosis in single beta-cells was investigated using patch clamp. The exocytotic response, measured by capacitance measurements and elicited by a depolarization protocol designed to visualize exocytosis of vesicles from the readily releasable pool and from the reserve pool, was of the same size in synapsin DKO and WT beta-cells. The increase in membrane capacitance corresponding to readily releasable pool was approximately 50fF in both genotypes. We next investigated the voltage-dependent Ca2+ influx. In both WT and synapsin DKO beta-cells the Ca2+ current peaked at 0 mV and measured peak current (I-p) and net charge (Q) were of similar magnitude. Finally, ultrastructural data showed no variation in total number of granules (N-v) or number of docked granules (N-s) between the beta-cells from synapsin DKO mice and WT control. We conclude that neither synapsin I nor synapsin II are directly involved in the regulation of glucose-stimulated insulin secretion and Ca-2-dependent exocytosis in mouse pancreatic beta-cells. (Endocrinology 153: 2112-2119, 2012)
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| 2. |
- Andersson, Sofia A, et al.
(author)
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Reduced insulin secretion correlates with decreased expression of exocytotic genes in pancreatic islets from patients with type 2 diabetes.
- 2012
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In: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 364:1-2, s. 36-45
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Journal article (peer-reviewed)abstract
- Reduced insulin release has been linked to defect exocytosis in β-cells. However, whether expression of genes suggested to be involved in the exocytotic process (exocytotic genes) is altered in pancreatic islets from patients with type 2 diabetes (T2D), and correlate to insulin secretion, needs to be further investigated. Analysing expression levels of 23 exocytotic genes using microarray revealed reduced expression of five genes in human T2D islets (χ(2)=13.25; p<0.001). Gene expression of STX1A, SYT4, SYT7, SYT11, SYT13, SNAP25 and STXBP1 correlated negatively to in vivo measurements of HbA1c levels and positively to glucose stimulated insulin secretion (GSIS) in vitro in human islets. STX1A, SYT4 and SYT11 protein levels correspondingly decreased in human T2D islets. Moreover, silencing of SYT4 and SYT13 reduced GSIS in INS1-832/13 cells. Our data support that reduced expression of exocytotic genes contributes to impaired insulin secretion, and suggest decreased expression of these genes as part of T2D pathogenesis.
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| 3. |
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| 4. |
- Ahmed Khandker, Meftun, et al.
(author)
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Mitochondrial proteome analysis reveals altered expression of voltage dependent anion channels in pancreatic beta-cells exposed to high glucose
- 2010
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In: Islets. - : Informa UK Limited. - 1938-2022 .- 1938-2014. ; 2:5, s. 283-292
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Journal article (peer-reviewed)abstract
- Chronic hyperglycemia leads to deterioration of insulin release from pancreatic beta-cells as well as insulin action on peripheral tissues. However, the mechanism underlying beta-cell dysfunction resulting from glucose toxicity has not been fully elucidated. The aim of the present study was to define a set of alterations in mitochondrial protein profiles of pancreatic beta-cell line in response to glucotoxic condition using 2-DE and tandem mass spectrometry. INS1E cells were incubated in the presence of 5.5 and 20 mM glucose for 72 hrs and mitochondria were isolated. Approximately 75 protein spots displayed significant changes (p < 0.05) in relative abundance in the presence of 20 mM glucose compared to controls. Mitochondrial proteins downregulated under glucotoxic conditions includes ATP synthase a chain and delta chain, malate dehydrogenase, aconitase, trifunctional enzyme beta subunit, NADH-cytochrome b5 reductase and voltage-dependent anion-selective channel protein (VDAC) 2. VDAC 1, 75 kDa glucose-regulated protein, heat shock protein (HSP) 60 and HSP10 were found to be upregulated. The orchestrated changes in expression of VDACs and multiple other proteins involved in nutrient metabolism, ATP synthesis, cellular defense, glycoprotein folding and mitochondrial DNA stability may explain cellular dysfunction in glucotoxicity resulting in altered insulin secretion.
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| 5. |
- Alonso-Magdalena, Paloma, et al.
(author)
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Antidiabetic Actions of an Estrogen Receptor beta Selective Agonist
- 2013
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In: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 62:6, s. 2015-2025
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Journal article (peer-reviewed)abstract
- The estrogen receptor beta (ER beta) is emerging as an important player in the physiology of the endocrine pancreas. We evaluated the role and antidiabetic actions of the ER beta selective agonist WAY200070 as an insulinotropic molecule. We demonstrate that WAY200070 enhances glucose-stimulated insulin secretion both in mouse and human islets. In vivo experiments showed that a single administration of WAY200070 leads to an increase in plasma insulin levels with a concomitant improved response to a glucose load. Two-week treatment administration increased glucose-induced insulin release and pancreatic beta-cell mass and improved glucose and insulin sensitivity. In addition, streptozotocin-nicotinamide-induced diabetic mice treated with WAY200070 exhibited a significant improvement in plasma insulin levels and glucose tolerance as well as a regeneration of pancreatic beta-cell mass. Studies performed in db/db mice demonstrated that this compound restored first-phase insulin secretion and enhanced pancreatic beta-cell mass. We conclude that ER beta agonists should be considered as new targets for the treatment of diabetes.
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| 6. |
- Amisten, Stefan, et al.
(author)
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ADP mediates inhibition of insulin secretion by activation of P2Y13 receptors in mice.
- 2010
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In: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; Jul 1, s. 1927-1934
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Journal article (peer-reviewed)abstract
- AIMS/HYPOTHESES: To investigate the effects of extracellular purines on insulin secretion from mouse pancreatic islets. METHODS: Mouse islets and beta cells were isolated and examined with mRNA real-time quantification, cAMP quantification and insulin and glucagon secretion. ATP release was measured in MIN6c4 cells. Insulin and glucagon secretion were measured in vivo after glucose injection. RESULTS: Enzymatic removal of extracellular ATP at low glucose levels increased the secretion of both insulin and glucagon, while at high glucose levels insulin secretion was reduced and glucagon secretion was stimulated, indicating an autocrine effect of purines. In MIN6c4 cells it was shown that glucose does induce release of ATP into the extracellular space. Quantitative real-time PCR demonstrated the expression of the ADP receptors P2Y(1) and P2Y(13) in both intact mouse pancreatic islets and isolated beta cells. The stable ADP analogue 2-MeSADP had no effect on insulin secretion. However, co-incubation with the P2Y(1) antagonist MRS2179 inhibited insulin secretion, while co-incubation with the P2Y(13) antagonist MRS2211 stimulated insulin secretion, indicating that ADP acting via P2Y(1) stimulates insulin secretion, while signalling via P2Y(13) inhibits the secretion of insulin. P2Y(13) antagonism through MRS2211 per se increased the secretion of both insulin and glucagon at intermediate (8.3 mmol/l) and high (20 mmol/l) glucose levels, confirming an autocrine role for ADP. Administration of MRS2211 during glucose injection in vivo resulted in both increased secretion of insulin and reduced glucose levels. CONCLUSIONS/INTERPRETATION: In conclusion, ADP acting on the P2Y(13) receptors inhibits insulin release. An antagonist to P2Y(13) increases insulin release and could be evaluated for the treatment of diabetes.
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| 7. |
- Amisten, Stefan, et al.
(author)
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An atlas and functional analysis of G-protein coupled receptors in human islets of Langerhans
- 2013
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In: Pharmacology and Therapeutics. - : Elsevier BV. - 0163-7258. ; 139:3, s. 359-391
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Research review (peer-reviewed)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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| 8. |
- Balhuizen, Alexander, et al.
(author)
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Activation of G protein-coupled receptor 30 modulates hormone secretion and counteracts cytokine-induced apoptosis in pancreatic islets of female mice.
- 2010
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In: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 320, s. 16-24
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Journal article (peer-reviewed)abstract
- The role of the newly discovered estrogen receptor GPR30 in islet physiology and pathophysiology is unclear. We examined GPR30 expression in relation to hormone secretion and possible anti-apoptotic effects in isolated mouse islets using the synthetic GPR30 ligand G-1. The mRNA and protein expression of GPR30 was analyzed by qPCR, Western blot and confocal microscopy. Hormone secretion and cAMP content were determined with RIA and apoptosis in islet cells with the Annexin-V method. GPR30 mRNA and protein expression was markedly higher in islets from females compared to male. This gender difference was not found for the genomic estrogen receptors ERalpha and ERbeta, the ERalpha expression being 10-fold higher than ERbeta in both genders. Confocal microscopy revealed abounden GPR30 expression in insulin, glucagon and somatostatin cells. Dose-response studies of G-1 vs 17beta-estradiol in isolated islets at 1 or 12mM glucose showed an almost identical pattern in that both compounds increased insulin and inhibited glucagon and somatostatin secretion. ICI-182,780 and EM-652, potent antagonists of the 17beta-estradiol receptors (ERalpha and ERbeta) did not influence the amplifying effect of G-1 or 17beta-estradiol on cAMP content or insulin secretion from isolated islets. Cytokine-induced (IL-1beta+TNFalpha+INFgamma) apoptosis in islets, cultured for 24h at 5mM glucose, was almost abolished by G-1 or 17beta-estradiol treatment. Addition of ICI-182,780 or EM-652 did not affect this beneficial effect of G-1 or 17beta-estradiol. Taken together, our findings show that GPR30 is expressed in most islet endocrine cells. The synthetic GPR30 ligand G-1 mimics the non-genomic effects of 17beta-estradiol on islet hormone secretion, cAMP content in islets and its anti-apoptotic effects. G-1 or analogs thereof might be new potential candidates in the therapeutic strategy for type 2 diabetes in women.
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