| 1. |
- Adam, J., et al.
(författare)
-
Fumarate Hydratase Deletion in Pancreatic beta Cells Leads to Progressive Diabetes
- 2017
-
Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 20:13, s. 3135-3148
-
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.
|
|
| 2. |
- Adam, Julie, et al.
(författare)
-
Fumarate Hydratase Deletion in Pancreatic β Cells Leads to Progressive Diabetes
- 2017
-
Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 20:13, s. 3135-3148
-
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 β cells (Fh1βKO 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 Hif1α or Nrf2. Progressive hyperglycemia in Fh1βKO mice led to dysregulated metabolism in β 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 Fh1βKO mice was ameliorated after culture under normoglycemic conditions. These studies highlight the role of FH and dysregulated mitochondrial metabolism in T2D. Adam et al. have shown that progressive diabetes develops if fumarate hydratase is deleted in mouse pancreatic β cells. Such β cells exhibit elevated fumarate and protein succination and show progressively reduced ATP production and insulin secretion. The depleted insulin response to glucose recovers when diabetic islets are cultured in reduced glucose.
|
|
| 3. |
- Tarasov, A. I., et al.
(författare)
-
Monitoring real-time hormone release kinetics: Via high-content 3-D imaging of compensatory endocytosis
- 2018
-
Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 18:18, s. 2838-2848
-
Tidskriftsartikel (refereegranskat)abstract
- High-content real-time imaging of hormone secretion in tissues or cell populations is a challenging task, which is unlikely to be resolved directly, despite immense translational value. We approach this problem indirectly, using compensatory endocytosis, a process that closely follows exocytosis in the cell, as a surrogate read-out for secretion. The tissue is immobilized in an open-air perifusion chamber and imaged using a two-photon microscope. A fluorescent polar tracer, perifused through the experimental circuit, gets trapped into the cells via endocytosis, and is quantified using a feature-detection algorithm. The signal of the tracer that accumulates into the endocytotic system reliably reflects stimulated exocytosis, which is demonstrated via co-imaging of the latter using existing reporters. A high signal-to-noise ratio and compatibility with multisensor imaging affords the real-time quantification of the secretion at the tissue/population level, whereas the cumulative nature of the signal allows imprinting of the “secretory history” within each cell. The technology works for several cell types, reflects disease progression and can be used for human tissue.
|
|
| 4. |
- Vergari, Elisa, et al.
(författare)
-
Insulin inhibits glucagon release by SGLT2-induced stimulation of somatostatin secretion
- 2019
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Hypoglycaemia (low plasma glucose) is a serious and potentially fatal complication of insulin-treated diabetes. In healthy individuals, hypoglycaemia triggers glucagon secretion, which restores normal plasma glucose levels by stimulation of hepatic glucose production. This counterregulatory mechanism is impaired in diabetes. Here we show in mice that therapeutic concentrations of insulin inhibit glucagon secretion by an indirect (paracrine) mechanism mediated by stimulation of intra-islet somatostatin release. Insulin's capacity to inhibit glucagon secretion is lost following genetic ablation of insulin receptors in the somatostatin-secreting δ-cells, when insulin-induced somatostatin secretion is suppressed by dapagliflozin (an inhibitor of sodium-glucose co-tranporter-2; SGLT2) or when the action of secreted somatostatin is prevented by somatostatin receptor (SSTR) antagonists. Administration of these compounds in vivo antagonises insulin's hypoglycaemic effect. We extend these data to isolated human islets. We propose that SSTR or SGLT2 antagonists should be considered as adjuncts to insulin in diabetes therapy.
|
|
| 5. |
- Zhang, Q., et al.
(författare)
-
Na+ current properties in islet alpha- and beta-cells reflect cell-specific Scn3a and Scn9a expression
- 2014
-
Ingår i: Journal of Physiology-London. - : Wiley. - 0022-3751 .- 1469-7793. ; 592:21, s. 4677-4696
-
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.
|
|
| 6. |
- Briant, L. J. B., et al.
(författare)
-
Functional identification of islet cell types by electrophysiological fingerprinting
- 2017
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 14:128
-
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.
|
|
| 7. |
- Haythorne, E., et al.
(författare)
-
Diabetes causes marked inhibition of mitochondrial metabolism in pancreatic beta-cells
- 2019
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Diabetes is a global health problem caused primarily by the inability of pancreatic beta-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of beta-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic beta V59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 beta-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in beta-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of beta-cells in diabetes.
|
|
| 8. |
- Zhang, Quan, et al.
(författare)
-
R-type Ca2+-channel-evoked CICR regulates glucose-induced somatostatin secretion
- 2007
-
Ingår i: Nature Cell Biology. - : Springer Science and Business Media LLC. - 1465-7392 .- 1476-4679. ; 9:4, s. 171-453
-
Tidskriftsartikel (refereegranskat)abstract
- Pancreatic islets have a central role in blood glucose homeostasis. In addition to insulin-producing beta-cells and glucagon-secreting alpha-cells, the islets contain somatostatin-releasing delta-cells(1). Somatostatin is a powerful inhibitor of insulin and glucagon secretion(2). It is normally secreted in response to glucose(3) and there is evidence suggesting its release becomes perturbed in diabetes(4). Little is known about the control of somatostatin release. Closure of ATP-regulated K+-channels (K-ATP-channels)(5) and a depolarization-evoked increase in cytoplasmic free Ca2+ concentration ([Ca2+](i))(6-8) have been proposed to be essential. Here, we report that somatostatin release evoked by high glucose (>= 10 mM) is unaffected by the K-ATP-channel activator diazoxide and proceeds normally in K-ATP-channel-deficient islets. Glucose-induced somatostatin secretion is instead primarily dependent on Ca2+-induced Ca2+-release (CICR). This constitutes a novel mechanism for K-ATP-channel-independent metabolic control of pancreatic hormone secretion.
|
|
