| 1. |
- Adam, J., et al.
(författare)
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Fumarate Hydratase Deletion in Pancreatic beta Cells Leads to Progressive Diabetes
- 2017
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Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 20:13, s. 3135-3148
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Tidskriftsartikel (refereegranskat)abstract
- We explored the role of the Krebs cycle enzyme fumarate hydratase (FH) in glucose-stimulated insulin secretion (GSIS). Mice lacking Fh1 in pancreatic beta cells (Fh1 beta KO mice) appear normal for 6-8 weeks but then develop progressive glucose intolerance and diabetes. Glucose tolerance is rescued by expression of mitochondrial or cytosolic FH but not by deletion of Hif1 alpha or Nrf2. Progressive hyperglycemia in Fh1bKO mice led to dysregulated metabolism in b cells, a decrease in glucose-induced ATP production, electrical activity, cytoplasmic [Ca2+](i) elevation, and GSIS. Fh1 loss resulted in elevated intracellular fumarate, promoting succination of critical cysteines in GAPDH, GMPR, and PARK 7/DJ-1 and cytoplasmic acidification. Intracellular fumarate levels were increased in islets exposed to high glucose and in islets from human donors with type 2 diabetes (T2D). The impaired GSIS in islets from diabetic Fh1bKO mice was ameliorated after culture under normoglycemic conditions. These studies highlight the role of FH and dysregulated mitochondrial metabolism in T2D.
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| 2. |
- 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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| 3. |
- Briant, L., et al.
(författare)
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Glucagon secretion from pancreatic alpha-cells
- 2016
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Ingår i: Upsala Journal of Medical Sciences. - : Uppsala Medical Society. - 0300-9734 .- 2000-1967. ; 121:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- Type 2 diabetes involves a menage a trois of impaired glucose regulation of pancreatic hormone release: in addition to impaired glucose-induced insulin secretion, the release of the hyperglycaemic hormone glucagon becomes dysregulated; these last-mentioned defects exacerbate the metabolic consequences of hypoinsulinaemia and are compounded further by hypersecretion of somatostatin (which inhibits both insulin and glucagon secretion). Glucagon secretion has been proposed to be regulated by either intrinsic or paracrine mechanisms, but their relative significance and the conditions under which they operate are debated. Importantly, the paracrine and intrinsic modes of regulation are not mutually exclusive; they could operate in parallel to control glucagon secretion. Here we have applied mathematical modelling of alpha-cell electrical activity as a novel means of dissecting the processes that underlie metabolic regulation of glucagon secretion. Our analyses indicate that basal hypersecretion of somatostatin and/or increased activity of somatostatin receptors may explain the loss of adequate counter regulation under hypoglycaemic conditions, as well as the physiologically inappropriate stimulation of glucagon secretion during hyperglycaemia seen in diabetic patients. We therefore advocate studying the interaction of the paracrine and intrinsic mechanisms; unifying these processes may give a more complete picture of the regulation of glucagon secretion from alpha-cells than studying the individual parts.
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| 4. |
- Briant, L. J. B., et al.
(författare)
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Functional identification of islet cell types by electrophysiological fingerprinting
- 2017
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 14:128
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Tidskriftsartikel (refereegranskat)abstract
- The alpha-, beta- and delta-cells of the pancreatic islet exhibit different electrophysiological features. We used a large dataset of whole- cell patch- clamp recordings from cells in intactmouse islets (N = 288 recordings) to investigatewhether it is possible to reliably identify cell type (alpha,beta or gamma) based on their electrophysiological characteristics. We quantified 15 electrophysiological variables in each recorded cell. Individually, none of the variables could reliably distinguish the cell types. We therefore constructed a logistic regressionmodel that included all quantified variables, to determine whether they could together identify cell type. The model identified cell typewith 94% accuracy. Thismodelwas applied to a dataset of cells recorded from hyperglycaemic bV59M mice; it correctly identified cell type in all cells and was able to distinguish cells that co-expressed insulin and glucagon. Based on this revised functional identification, we were able to improve conductance-based models of the electrical activity in alpha-cells and generate a model of gamma-cell electrical activity. These new models could faithfully emulate alpha- and gamma-cell electrical activity recorded experimentally.
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| 5. |
- Denwood, G., et al.
(författare)
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Glucose stimulates somatostatin secretion in pancreatic delta-cells by cAMP-dependent intracellular Ca-2+ release
- 2019
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Ingår i: Journal of General Physiology. - : Rockefeller University Press. - 0022-1295 .- 1540-7748. ; 151:9, s. 1094-1115
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Tidskriftsartikel (refereegranskat)abstract
- Somatostatin secretion from pancreatic islet delta-cells is stimulated by elevated glucose levels, but the underlying mechanisms have only partially been elucidated. Here we show that glucose-induced somatostatin secretion (GISS) involves both membrane potential-dependent and -independent pathways. Although glucose-induced electrical activity triggers somatostatin release, the sugar also stimulates GISS via a cAMP-dependent stimulation of CICR and exocytosis of somatostatin. The latter effect is more quantitatively important and in mouse islets depolarized by 70 mM extracellular K+, increasing glucose from 1 mM to 20 mM produced an similar to 3.5-fold stimulation of somatostatin secretion, an effect that was mimicked by the application of the adenylyl cyclase activator forskolin. Inhibiting cAMP-dependent pathways with PKI or ESI-05, which inhibit PKA and exchange protein directly activated by cAMP 2 (Epac2), respectively, reduced glucose/forskolin-induced somatostatin secretion. Ryanodine produced a similar effect that was not additive to that of the PKA or Epac2 inhibitors. Intracellular application of cAMP produced a concentration-dependent stimulation of somatostatin exocytosis and elevation of cytoplasmic Ca2+ ([Ca2+](i)). Both effects were inhibited by ESI-05 and thapsigargin (an inhibitor of SERCA). By contrast, inhibition of PKA suppressed delta-cell exocytosis without affecting [Ca2+](i) . Simultaneous recordings of electrical activity and [Ca2+](i) in delta-cells expressing the genetically encoded Ca2+ indicator GCaMP3 revealed that the majority of glucose-induced [Ca2+](i) spikes did not correlate with delta-cell electrical activity but instead reflected Cat' release from the ER. These spontaneous [Ca2+](i) spikes are resistant to PKI but sensitive to ESI-05 or thapsigargin. We propose that cAMP links an increase in plasma glucose to stimulation of somatostatin secretion by promoting CICR, thus evoking exocytosis of somatostatin-containing secretory vesicles in the delta-cell.
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| 6. |
- Hamilton, A., et al.
(författare)
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Adrenaline stimulates glucagon secretion by Tpc2-Dependent ca2+ mobilization from acidic stores in pancreatic a-Cells
- 2018
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 67:6, s. 1128-1139
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Tidskriftsartikel (refereegranskat)abstract
- Adrenaline is a powerful stimulus of glucagon secretion. It acts by activation of b-adrenergic receptors, but the downstream mechanisms have only been partially elucidated. Here, we have examined the effects of adrenaline in mouse and human a-cells by a combination of electrophysiology, imaging of Ca2+ and PKA activity, and hormone release measurements. We found that stimulation of glucagon secretion correlated with a PKA- and EPAC2-dependent (inhibited by PKI and ESI-05, respectively) elevation of [Ca2+]i in a-cells, which occurred without stimulation of electrical activity and persisted in the absence of extracellular Ca2+ but was sensitive to ryanodine, bafilomycin, and thapsigargin. Adrenaline also increased [Ca2+]i in a-cells in human islets. Genetic or pharmacological inhibition of the Tpc2 channel (that mediates Ca2+ release from acidic intracellular stores) abolished the stimulatory effect of adrenaline on glucagon secretion and reduced the elevation of [Ca2+]i. Furthermore, in Tpc2-deficient islets, ryanodine exerted no additive inhibitory effect. These data suggest that b-adrenergic stimulation of glucagon secretion is controlled by a hierarchy of [Ca2+]i signaling in the a-cell that is initiated by cAMP-induced Tpc2-dependent Ca2+ release from the acidic stores and further amplified by Ca2+-induced Ca2+ release from the sarco/endoplasmic reticulum. © 2018 by the American Diabetes Association.
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| 7. |
- Knudsen, J. G., et al.
(författare)
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Dysregulation of Glucagon Secretion by Hyperglycemia-Induced Sodium-Dependent Reduction of ATP Production
- 2019
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 29:2, s. 430-
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Tidskriftsartikel (refereegranskat)abstract
- Diabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their beta cells (Fh1 beta KO mice) develop progressive hyperglycemia and dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na+ accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in alpha cells from hyperglycemic Fh1 beta KO and beta-V59M gain-of-function K-ATP channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1 beta KO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.
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| 8. |
- Oduori, O. S., et al.
(författare)
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Gs/Gq signaling switch in beta cells defines incretin effectiveness in diabetes
- 2020
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Ingår i: Journal of Clinical Investigation. - : American Society for Clinical Investigation. - 0021-9738 .- 1558-8238. ; 130:12, s. 6639-6655
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Tidskriftsartikel (refereegranskat)abstract
- By restoring glucose-regulated insulin secretion, glucagon-like peptide-1-based (GLP-1-based) therapies are becoming increasingly important in diabetes care. Normally, the incretins GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) jointly maintain normal blood glucose levels by stimulation of insulin secretion in pancreatic beta cells. However, the reason why only GLP-1-based drugs are effective in improving insulin secretion after presentation of diabetes has not been resolved. ATP-sensitive K+ (K-ATP) channels play a crucial role in coupling the systemic metabolic status to beta cell electrical activity for insulin secretion. Here, we have shown that persistent membrane depolarization of beta cells due to genetic cell-specific Kcnj11(-/-)mice) or pharmacological (long-term exposure to sulfonylureas) inhibition of the K-ATP channel led to a switch from Gs to Gq in a major amplifying pathway of insulin secretion. The switch determined the relative insulinotropic effectiveness of GLP-1 and GIP, as GLP-1 can activate both Gq and Gs, while GIP only activates Gs. The findings were corroborated in other models of persistent depolarization: a spontaneous diabetic KK-Ay mouse and nondiabetic human and mouse beta cells of pancreatic islets chronically treated with high glucose. Thus, a Gs/Gq signaling switch in beta cells exposed to chronic hyperglycemia underlies the differential insulinotropic potential of incretins in diabetes.
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| 9. |
- Ramracheya, R., et al.
(författare)
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GLP-1 suppresses glucagon secretion in human pancreatic alpha-cells by inhibition of P/Q-type Ca2+ channels
- 2018
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Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 6:17
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Tidskriftsartikel (refereegranskat)abstract
- Glucagon is the body's main hyperglycemic hormone, and its secretion is dysregulated in type 2 diabetes mellitus (T2DM). The incretin hormone glucagon-like peptide-1 (GLP-1) is released from the gut and is used in T2DM therapy. Uniquely, it both stimulates insulin and inhibits glucagon secretion and thereby lowers plasma glucose levels. In this study, we have investigated the action of GLP-1 on glucagon release from human pancreatic islets. Immunocytochemistry revealed that only <0.5% of the alpha-cells possess detectable GLP-1R immunoreactivity. Despite this, GLP-1 inhibited glucagon secretion by 50-70%. This was due to a direct effect on alpha-cells, rather than paracrine signaling, because the inhibition was not reversed by the insulin receptor antagonist S961 or the somatostatin receptor-2 antagonist CYN154806. The inhibitory effect of GLP-1 on glucagon secretion was prevented by the PKA-inhibitor Rp-cAMPS and mimicked by the adenylate cyclase activator forskolin. Electrophysiological measurements revealed that GLP-1 decreased action potential height and depolarized interspike membrane potential. Mathematical modeling suggests both effects could result from inhibition of P/Q-type Ca2+ channels. In agreement with this, GLP-1 and omega-aga-toxin (a blocker of P/Q-type channels) inhibited glucagon secretion in islets depolarized by 70 mmol/L [K+](o), and these effects were not additive. Intracellular application of cAMP inhibited depolarization-evoked exocytosis in individual alpha-cells by a PKA-dependent (Rp-cAMPS-sensitive) mechanism. We propose that inhibition of glucagon secretion by GLP-1 involves activation of the few GLP-1 receptors present in the alpha-cell membrane. The resulting small elevation of cAMP leads to PKA-dependent inhibition of P/Q-type Ca2+ channels and suppression of glucagon exocytosis.
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| 10. |
- Satin, L. S., et al.
(författare)
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"Take Me To Your Leader": An Electrophysiological Appraisal of the Role of Hub Cells in Pancreatic Islets
- 2020
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 69:5, s. 830-836
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Tidskriftsartikel (refereegranskat)abstract
- The coordinated electrical activity of beta-cells within the pancreatic islet drives oscillatory insulin secretion. A recent hypothesis postulates that specially equipped "hub" or "leader" cells within the beta-cell network drive islet oscillations and that electrically silencing or optically ablating these cells suppresses coordinated electrical activity (and thus insulin secretion) in the rest of the islet. In this Perspective, we discuss this hypothesis in relation to established principles of electrophysiological theory. We conclude that whereas electrical coupling between beta-cells is sufficient for the propagation of excitation across the islet, there is no obvious electrophysiological mechanism that explains how hyperpolarizing a hub cell results in widespread inhibition of islet electrical activity and disruption of their coordination. Thus, intraislet diffusible factors should perhaps be considered as an alternate mechanism.
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