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1.
  • Collins, S. C., et al. (författare)
  • Long-term exposure of mouse pancreatic islets to oleate or palmitate results in reduced glucose-induced somatostatin and oversecretion of glucagon
  • 2008
  • Ingår i: Diabetologia. - Springer. - 1432-0428. ; 51:9, s. 1689-1693
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims/hypothesis Long-term exposure to NEFAs leads to inhibition of glucose-induced insulin secretion. We tested whether the release of somatostatin and glucagon, the two other major islet hormones, is also affected. Methods Mouse pancreatic islets were cultured for 72 h at 4.5 or 15 mmol/l glucose with or without 0.5 mmol/l oleate or palmitate. The release of glucagon and somatostatin during subsequent 1 h incubations at 1 or 20 mmol/l glucose as well as the islet content of the two hormones were determined. Lipid-induced changes in islet cell ultrastructure were assessed by electron microscopy. Results Culture at 15 mmol/l glucose increased islet glucagon content by similar to 50% relative to that observed following culture at 4.5 mmol/l glucose. Inclusion of oleate or palmitate reduced islet glucagon content by 25% (at 4.5 mmol/l glucose) to 50% (at 15 mmol/l glucose). Long-term exposure to the NEFA increased glucagon secretion at 1 mmol/l glucose by 50% (when islets had been cultured at 15 mmol/l glucose) to 100% (with 4.5 mmol/l glucose in the culture medium) and abolished the inhibitory effect of 20 mmol/l glucose on glucagon secretion. Somatostatin content was unaffected by glucose and lipids, but glucose-induced somatostatin secretion was reduced by similar to 50% following long-term exposure to either of the NEFA, regardless of whether the culture medium contained 4.5 or 15 mmol/l glucose. Ultrastructural evidence of lipid deposition was seen in < 10% of non-beta cells but in > 80% of the beta cells. Conclusions/interpretation Long-term exposure to high glucose and/or NEFA affects the release of somatostatin and glucagon. The effects on glucagon secretion are very pronounced and in type 2 diabetes in vivo may aggravate the hyperglycaemic effects due to lack of insulin.
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2.
  • Lundquist, Ingmar, et al. (författare)
  • Metformin ameliorates dysfunctional traits of glibenclamide- and glucose-induced insulin secretion by suppression of imposed overactivity of the islet nitric oxide synthase-no system
  • 2016
  • Ingår i: PLoS ONE. - Public Library of Science. - 1932-6203. ; 11:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Metformin lowers diabetic blood glucose primarily by reducing hepatic gluconeogenesis and increasing peripheral glucose uptake. However, possible effects by metformin on beta-cell function are incompletely understood. We speculated that metformin might positively influence insulin secretion through impacting the beta-cell nitric oxide synthase (NOS)-NO system, a negative modulator of glucose-stimulated insulin release. In short-time incubations with isolated murine islets either glibenclamide or high glucose augmented insulin release associated with increased NO production from both neural and inducible NOS. Metformin addition suppressed the augmented NO generation coinciding with amplified insulin release. Islet culturing with glibenclamide or high glucose revealed pronounced fluorescence of inducible NOS in the beta-cells being abolished by metformin co-culturing. These findings were reflected in medium nitrite-nitrate levels. A glucose challenge following islet culturing with glibenclamide or high glucose revealed markedly impaired insulin response. Metformin coculturing restored this response. Culturing murine islets and human islets from controls and type 2 diabetics with high glucose or high glucose + glibenclamide induced a pronounced decrease of cell viability being remarkably restored by metformin co-culturing. We show here, that imposed overactivity of the beta-cell NOS-NO system by glibenclamide or high glucose leads to insulin secretory dysfunction and reduced cell viability and also, importantly, that these effects are relieved by metformin inhibiting beta-cell NO overproduction from both neural and inducible NOS thus ameliorating a concealed negative influence by NO induced by sulfonylurea treatment and/or high glucose levels. This double-edged effect of glibenclamide on the beta-cellsuggests sulfonylurea monotherapy in type 2 diabetes being avoided.
3.
  • Rosengren, Anders, et al. (författare)
  • Overexpression of Alpha2A-Adrenergic Receptors Contributes to Type 2 Diabetes.
  • 2010
  • Ingår i: Science (New York, N.Y.). - American Association for the Advancement of Science. - 1095-9203. ; 327, s. 217-220
  • Tidskriftsartikel (refereegranskat)abstract
    • Several common genetic variations have been associated with type 2 diabetes, but the exact disease mechanisms are still poorly elucidated. Here, using congenic strains from the diabetic GK-rat, we identified a 1.4-Mb 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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4.
  • Alonso-Magdalena, Paloma, et al. (författare)
  • Antidiabetic Actions of an Estrogen Receptor beta Selective Agonist
  • 2013
  • Ingår i: Diabetes. - American Diabetes Association Inc.. - 1939-327X. ; 62:6, s. 2015-2025
  • Tidskriftsartikel (refereegranskat)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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5.
  • Amisten, Stefan, et al. (författare)
  • Anti-diabetic action of all-trans retinoic acid and the orphan G protein coupled receptor GPRC5C in pancreatic β-cells
  • 2017
  • Ingår i: Endocrine Journal. - Japan Endocrine Society. - 0918-8959. ; 64:3, s. 325-338
  • Tidskriftsartikel (refereegranskat)abstract
    • Pancreatic islets express high levels of the orphan G-protein coupled receptor C5C (GPRC5C), the function of which remains to be established. Here we have examined the role of GPRC5C in the regulation of insulin secretion and β-cell survival and proliferation using human and mouse pancreatic islets. The expression of GPRC5C was analysed by RNA-sequencing, qPCR, western blotting and confocal microscopy. Insulin secretion and cell viability were determined by RIA and MTS assays, respectively. GPRC5C mRNA expression and protein level were reduced in the islets from type-2 diabetic donors. RNA sequencing in human islets revealed GPRC5C expression correlated with the expression of genes controlling apoptosis, cell survival and proliferation. A reduction in Gprc5c mRNA and protein expression was observed in islets isolated from old mice (>46 weeks of age) compared to that in islets from newborn (<3 weeks) mice. Down-regulation of Gprc5c led to both moderately reduced glucose-stimulated insulin release and also reduced cAMP content in mouse islets. Potentiation of glucose-stimulated insulin secretion concomitant with enhanced islet cAMP level by all-trans retinoic acid (ATRA) was attenuated upon Gprc5c-KD. ATRA also increased [Ca+2 ]i in Huh7-cells. Gprc5c over expression in Huh7 cells was associated with increased ERK1/2 activity. Gprc5c-KD in clonal MIN6c4 cells reduced cell proliferation and in murine islets increased apoptosis and the sensitivity of primary islet cells to a cocktail of pro-apoptotic cytokines. Our results demonstrate that agents activating GPRC5C represent a novel modality for the treatment and/or prevention of diabetes by restoring and/or maintaining functional β-cell mass.
6.
  • Collins, Stephan C., et al. (författare)
  • Increased expression of the diabetes gene SOX4 reduces insulin secretion by impaired fusion pore expansion
  • 2016
  • Ingår i: Diabetes. - American Diabetes Association Inc.. - 0012-1797. ; 65:7, s. 1952-1961
  • Tidskriftsartikel (refereegranskat)abstract
    • The transcription factor Sox4 has been proposed to underlie the increased type 2 diabetes risk linked to an intronic single nucleotide polymorphism in CDKAL1. In a mouse model expressing a mutant form of Sox4, glucose-induced insulin secretion is reduced by 40% despite normal intracellular Ca2+ signaling and depolarization-evoked exocytosis. This paradox is explained by a fourfold increase in kiss-and-run exocytosis (as determined by single-granule exocytosis measurements) in which the fusion pore connecting the granule lumen to the exterior expands to a diameter of only 2 nm, which does not allow the exit of insulin. Microarray analysis indicated that this correlated with an increased expression of the exocytosis-regulating protein Stxbp6. In a large collection of human islet preparations (n = 63), STXBP6 expression and glucose-induced insulin secretion correlated positively and negatively with SOX4 expression, respectively. Overexpression of SOX4 in the human insulin-secreting cell EndoC-βH2 interfered with granule emptying and inhibited hormone release, the latter effect reversed by silencing STXBP6. These data suggest that increased SOX4 expression inhibits insulin secretion and increased diabetes risk by the upregulation of STXBP6 and an increase in kissand-run exocytosis at the expense of full fusion. We propose that pharmacological interventions promoting fusion pore expansion may be effective in diabetes therapy.
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7.
  • Dunér, Pontus, et al. (författare)
  • Adhesion G protein-coupled receptor G1 (ADGRG1/GPR56) and pancreatic β-cell function
  • 2016
  • Ingår i: Journal of Clinical Endocrinology and Metabolism. - Oxford University Press. - 0021-972X. ; 101:12, s. 4637-4645
  • Tidskriftsartikel (refereegranskat)abstract
    • Context: Adhesion G protein-coupled receptor (GPCR)-G1 (ADGRG1) is the most abundant GPCR in human pancreatic islets, but its role in islet function is unclear. Objective: Investigate how ADGRG1 expression and activation by its ligand, collagen III, impacts β-cell function in normal and type 2 diabetic (T2D) islets. Design: Genes associated with the ADGRG1 in human islets was probed by RNA-sequencing of human pancreatic islet isolated from cadaveric donors, followed by functional studies on β-cell proliferation, apoptosis, and insulin secretion in human and mouse islets and in INS-1 cells. Main Outcome Measures: Changes in β-cell gene expression, proliferation, apoptosis, and insulin secretion were quantified by RNA-sequencing, qPCR, Thymidine incorporation, Western blotting, and RIA, respectively. Results: ADGRG1 is the most abundant GPCR mRNA in both human and mouse islets, and its expression inhumanislets strongly correlates with genes important for β-cell function and T2 Drisk. Theexpression ofADGRG1wasreduced in islets ofT2Ddonors, in db/dbmouseislets,andin isolated human islets exposed to chronic hyperglycemia. Beneficial effects of collagen type III on β-cell function via activation of the cAMP/protein kinase A pathway, suppression of RhoA and caspase-3 activity, increased β-cell viability, and proliferation were abolished when ADGRG1 was downregulated in β-cells. Conclusions:Wedemonstrate a mechanistic link between ADGRG1 expression andβ-cell function. Pharmacological agents that promote expression or activation of the ADGRG1 receptor may represent a novel approach for the treatment of T2D.
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8.
  • Eliasson, Lena, et al. (författare)
  • SUR1 Regulates PKA-independent cAMP-induced Granule Priming in Mouse Pancreatic B-cells.
  • 2003
  • Ingår i: Journal of General Physiology. - Rockefeller Institute for Medical Research. - 0022-1295. ; 121:3, s. 181-197
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of membrane capacitance were applied to dissect the cellular mechanisms underlying PKA-dependent and -independent stimulation of insulin secretion by cyclic AMP. Whereas the PKA-independent (Rp-cAMPS–insensitive) component correlated with a rapid increase in membrane capacitance of ~80 fF that plateaued within ~200 ms, the PKA-dependent component became prominent during depolarizations >450 ms. The PKA-dependent and -independent components of cAMP-stimulated exocytosis differed with regard to cAMP concentration dependence; the Kd values were 6 and 29 µM for the PKA-dependent and -independent mechanisms, respectively. The ability of cAMP to elicit exocytosis independently of PKA activation was mimicked by the selective cAMP-GEFII agonist 8CPT-2Me-cAMP. Moreover, treatment of B-cells with antisense oligodeoxynucleotides against cAMP-GEFII resulted in partial (50%) suppression of PKA-independent exocytosis. Surprisingly, B-cells in islets isolated from SUR1-deficient mice (SUR1-/- mice) lacked the PKA-independent component of exocytosis. Measurements of insulin release in response to GLP-1 stimulation in isolated islets from SUR1-/- mice confirmed the complete loss of the PKA-independent component. This was not attributable to a reduced capacity of GLP-1 to elevate intracellular cAMP but instead associated with the inability of cAMP to stimulate influx of Cl- into the granules, a step important for granule priming. We conclude that the role of SUR1 in the B cell extends beyond being a subunit of the plasma membrane KATP-channel and that it also plays an unexpected but important role in the cAMP-dependent regulation of Ca2+-induced exocytosis.
9.
  • Li, Dai-Qing, et al. (författare)
  • Suppression of sulfonylurea- and glucose-induced insulin secretion in vitro and in vivo in mice lacking the chloride transport protein ClC-3.
  • 2009
  • Ingår i: Cell Metabolism. - Cell Press. - 1550-4131. ; 10:4, s. 309-315
  • Tidskriftsartikel (refereegranskat)abstract
    • Priming of insulin secretory granules for release requires intragranular acidification and depends on vesicular Cl(-)-fluxes, but the identity of the chloride transporter/ion channel involved is unknown. We tested the hypothesis that the chloride transport protein ClC-3 fulfills these actions in pancreatic beta cells. In ClC-3(-/-) mice, insulin secretion evoked by membrane depolarization (high extracellular K(+), sulfonylureas), or glucose was >60% reduced compared to WT animals. This effect was mirrored by a approximately 80% reduction in depolarization-evoked beta cell exocytosis (monitored as increases in cell capacitance) in single ClC-3(-/-) beta cells, as well as a 44% reduction in proton transport across the granule membrane. ClC-3 expression in the insulin granule was demonstrated by immunoblotting, immunostaining, and negative immuno-EM in a high-purification fraction of large dense-core vesicles (LDCVs) obtained by phogrin-EGFP labeling. The data establish the importance of granular Cl(-) fluxes in granule priming and provide direct evidence for the involvement of ClC-3 in the process.
10.
  • Mosén, Henrik, et al. (författare)
  • Impaired glucose-stimulated insulin secretion in the GK rat is associated with abnormalities in islet nitric oxide production.
  • 2008
  • Ingår i: Regulatory Peptides. - Elsevier. - 1873-1686. ; 151, s. 139-146
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated implications of nitric oxide (NO) derived from islet neuronal constitutive NO synthase (ncNOS) and inducible NOS (iNOS) on insulin secretory mechanisms in the mildly diabetic GK rat. Islets from GK rats and Wistar controls were analysed for ncNOS and iNOS by HPLC, immunoblotting and immunocytochemistry in relation to insulin secretion stimulated by glucose or l-arginine in vitro and in vivo. No obvious difference in ncNOS fluorescence in GK vs control islets was seen but freshly isolated GK islets displayed a marked iNOS expression and activity. After incubation at low glucose GK islets showed an abnormal increase in both iNOS and ncNOS activities. At high glucose the impaired glucose-stimulated insulin release was associated with an increased iNOS expression and activity and NOS inhibition dose-dependently amplified insulin secretion in both GK and control islets. This effect by NOS inhibition was also evident in depolarized islets at low glucose, where forskolin had a further amplifying effect in GK but not in control islets. NOS inhibition increased basal insulin release in perfused GK pancreata and amplified insulin release after glucose stimulation in both GK and control pancreata, almost abrogating the nadir separating first and second phase in controls. A defective insulin response to l-arginine was seen in GK rats in vitro and in vivo, being partially restored by NOS inhibition. The results suggest that increased islet NOS activities might contribute to the defective insulin response to glucose and l-arginine in the GK rat. Excessive iNOS expression and activity might be deleterious for the beta-cells over time.
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