| 1. |
- Amisten, Stefan, et al.
(författare)
-
An atlas and functional analysis of G-protein coupled receptors in human islets of Langerhans
- 2013
-
Ingår i: Pharmacology and Therapeutics. - : Elsevier BV. - 0163-7258. ; 139:3, s. 359-391
-
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.
|
|
| 2. |
- De Marinis, Yang, et al.
(författare)
-
GLP-1 inhibits and adrenaline stimulates glucagon release by differential modulation of N- and L-type Ca2+ channel-dependent exocytosis.
- 2010
-
Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 11:6, s. 543-553
-
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).
|
|
| 3. |
- MacDonald, Patrick E., et al.
(författare)
-
A K-ATP channel-dependent pathway within alpha cells regulates glucagon release from both rodent and human islets of langerhans
- 2007
-
Ingår i: PLoS Biology. - : Public Library of Science (PLoS). - 1545-7885. ; 5:6, s. 1236-1247
-
Tidskriftsartikel (refereegranskat)abstract
- Glucagon, secreted from pancreatic islet a cells, stimulates gluconeogenesis and liver glycogen breakdown. The mechanism regulating glucagon release is debated, and variously attributed to neuronal control, paracrine control by neighbouring beta cells, or to an intrinsic glucose sensing by the a cells themselves. We examined hormone secretion and Ca2+ responses of a and b cells within intact rodent and human islets. Glucose-dependent suppression of glucagon release persisted when paracrine GABA or Zn (2+) signalling was blocked, but was reversed by low concentrations (1-20 mu M) of the ATP-sensitive K+ (K-ATP) channel opener diazoxide, which had no effect on insulin release or b cell responses. This effect was prevented by the K-ATP channel blocker tolbutamide (100 mu M). Higher diazoxide concentrations (>= 30 mu M) decreased glucagon and insulin secretion, and alpha-and beta-cell Ca2+ responses, in parallel. In the absence of glucose, tolbutamide at low concentrations (< 1 mu M) stimulated glucagon secretion, whereas high concentrations (> 10 mu M) were inhibitory. In the presence of a maximally inhibitory concentration of tolbutamide (0.5 mM), glucose had no additional suppressive effect. Downstream of the K-ATP channel, inhibition of voltage-gated Na+ (TTX) and N-type Ca2+ channels (omega-conotoxin), but not L-type Ca2+ channels (nifedipine), prevented glucagon secretion. Both the N-type Ca2+ channels and alpha-cell exocytosis were inactivated at depolarised membrane potentials. Rodent and human glucagon secretion is regulated by an a-cell K-ATP channel-dependent mechanism. We propose that elevated glucose reduces electrical activity and exocytosis via depolarisation-induced inactivation of ion channels involved in action potential firing and secretion.
|
|
| 4. |
- Mårtensson, Ulrika, et al.
(författare)
-
Deletion of the G protein-coupled receptor 30 impairs glucose tolerance, reduces bone growth, increases blood pressure, and eliminates estradiol-stimulated insulin release in female mice.
- 2009
-
Ingår i: Endocrinology. - : The Endocrine Society. - 1945-7170 .- 0013-7227. ; 150:2, s. 687-98
-
Tidskriftsartikel (refereegranskat)abstract
- In vitro studies suggest that the G protein-coupled receptor (GPR) 30 is a functional estrogen receptor. However, the physiological role of GPR30 in vivo is unknown, and it remains to be determined whether GPR30 is an estrogen receptor also in vivo. To this end, we studied the effects of disrupting the GPR30 gene in female and male mice. Female GPR30((-/-)) mice had hyperglycemia and impaired glucose tolerance, reduced body growth, increased blood pressure, and reduced serum IGF-I levels. The reduced growth correlated with a proportional decrease in skeletal development. The elevated blood pressure was associated with an increased vascular resistance manifested as an increased media to lumen ratio of the resistance arteries. The hyperglycemia and impaired glucose tolerance in vivo were associated with decreased insulin expression and release in vivo and in vitro in isolated pancreatic islets. GPR30 is expressed in islets, and GPR30 deletion abolished estradiol-stimulated insulin release both in vivo in ovariectomized adult mice and in vitro in isolated islets. Our findings show that GPR30 is important for several metabolic functions in female mice, including estradiol-stimulated insulin release.
|
|
| 5. |
- Obermüller, Stefanie, et al.
(författare)
-
Defective secretion of islet hormones in chromogranin-B deficient mice
- 2010
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:1, s. e8936-
-
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.
|
|
| 6. |
- Olofsson, Charlotta, et al.
(författare)
-
Long-term exposure to glucose and lipids inhibits glucose-induced insulin secretion downstream of granule fusion with plasma membrane.
- 2007
-
Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 56:7, s. 1888-1897
-
Tidskriftsartikel (refereegranskat)abstract
- Mouse beta-cells cultured at 15 mmol/l glucose for 72 h had reduced ATP-sensitive K+ (K-ATP) channel activity (-30%), increased voltage-gated Ca2+ currents, higher intracellular free Ca2+ concentration ([Ca-i(2+]) +160%), more exocytosis (monitored by capacitance measurements, +100%), and greater insulin content (+230%) than those cultured at 4.5 mmol/l glucose. However, they released 20% less insulin when challenged with 20 mmol/l glucose. Glucose-induced (20 mmol/l) insulin secretion was reduced by 60-90% in islets cocultured at 4.5 or 15 mmol/l glucose and either oleate or palmitate (0.5 mmol/l). Free fatty acid (FFA)induced inhibition of secretion was not associated with any major changes in [Ca2+](i) or islet ATP content. Palmitate stimulated exocytosis by twofold or more but reduced V-induced secretion by up to 60%. Basal (1 mmol/l glucose) K-ATP channel activity was 40% lower in islets cultured at 4.5 mmol/l glucose plus palmitate and 60% lower in islets cultured at 15 mmol/l glucose plus either of the FFAs. Insulin content decreased by 75% in islets exposed to FFAs in the presence of high (15 mmol/l), but not low (4.5 mmol/l), glucose concentrations, but the number of secre tory granules was unchanged. FFA-induced inhibition of insulin secretion was not associated with increased tran script levels of the apoptosis markers Bax (BclII-associated X protein) and caspase-3. We conclude that glucose and FFAs reduce insulin secretion by interference with the exit of insulin via the fusion pore.
|
|
| 7. |
- Rorsman, Patrik, et al.
(författare)
-
K-ATP-channels and glucagon secretion glucose-regulated
- 2008
-
Ingår i: Trends in Endocrinology and Metabolism. - : Elsevier BV. - 1879-3061 .- 1043-2760. ; 19:8, s. 277-284
-
Forskningsöversikt (refereegranskat)abstract
- Glucagon, secreted by the a-cells of the pancreatic islets, is the most important glucose-increasing hormone of the body. The precise regulation of glucagon release remains incompletely defined but has been proposed to involve release of inhibitory factors from neighbouring P-cells (paracrine control). However, the observation that glucose can regulate glucagon secretion under conditions when insulin secretion does not occur argues that the a-cell is also equipped with its own intrinsic (exerted within the a-cell itself) glucose sensing. Here we consider the possible mechanisms involved with a focus on ATP-regulated K+-channels and changes in a-cell membrane potential.
|
|
| 8. |
|
|
| 9. |
- Rosengren, Anders, et al.
(författare)
-
Reduced Insulin Exocytosis in Human Pancreatic β-cells With Gene Variants Linked to Type 2 Diabetes.
- 2012
-
Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 61:7, s. 1726-1733
-
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.
|
|
| 10. |
- Salehi, S Albert, et al.
(författare)
-
Secretory and electrophysiological characteristics of insulin cells from gastrectomized mice: Evidence for the existence of insulinotropic agents in the stomach.
- 2007
-
Ingår i: Regulatory Peptides. - : Elsevier BV. - 1873-1686 .- 0167-0115. ; 139:1-3, s. 31-38
-
Tidskriftsartikel (refereegranskat)abstract
- Mice were subjected to gastrectomy (GX) or sham operation (controls). Four to six weeks later the pancreatic islets were isolated and analysed for cAMP or alternatively incubated in a Krebs-Ringer based medium in an effort to study insulin secretion and cAMP accumulation in response to glucose or the adenylate cyclase activator forskolin. Freshly isolated islets from GX mice had higher cAMP content than islets from control mice, a difference that persisted after incubation for I h at a glucose concentration of 4 mmol/l. Addition of forskolin to this medium induced much greater cAMP and insulin responses in islets from GX mice than in islets from control mice. In contrast, the insulin response to high glucose (16.7 mmol/l) was much weaker in GX islets than in control islets. Glucose-induced insulin release was associated with a 2-fold rise in the cAMP content in control islets. Surprisingly no rise in cAMP was noted in GX islets incubated at high glucose. Capacitance measurements conducted on isolated insulin cells from GX mice revealed a much lower exocytotic response to a single 500 ms depolarisation (from -70 mV to zero) than in control insulin cells. Addition of cAMP to the cytosol enhanced the exocytotic response in insulin cells from control mice but not from GX mice. The depolarisation-triggered inward Ca2+ current in insulin cells from GX mice did not differ from that in control mice, and hence the reduced exocytotic response following GX cannot be ascribed to a decreased Ca2+ influx. Experiments involving a train of ten 500 ms depolarisations revealed that the exocytotic response was prominent in control insulin cells but modest in GX insulin cells. It seems that cAMP is capable of eliciting insulin release from insulin cells of GX mice only when cAMP is generated in a specific microdomain conceivably through the intervention of membrane-associated adenylate cyclases that can be activated by forskolin. The GX-evoked impairment of depolarisation-induced exocytosis and glucose-stimulated insulin release may reflect the lack of a gastric agent that serves to maintain an appropriate insulin response to glucose and an appropriate exocytotic response to depolarisation by raising cAMP in a special glucose-sensitive compartment possibly regulated by a soluble adenylate cyclase. (c) 2006 Elsevier B.V. All rights reserved.
|
|
