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Greitzer-Antes D, Xie L, Qin T, Xie H, Zhu D, Dolai S, Liang T, Kang F, Hardy AB, He Y, Kang Y, Gaisano HY. K v2.1 clusters on β-cell plasma membrane act as reservoirs that replenish pools of newcomer insulin granule through their interaction with syntaxin-3. J Biol Chem 2018; 293:6893-6904. [PMID: 29549124 DOI: 10.1074/jbc.ra118.002703] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Revised: 03/09/2018] [Indexed: 01/22/2023] Open
Abstract
The voltage-dependent K+ (Kv) channel Kv2.1 is a major delayed rectifier in many secretory cells, including pancreatic β cells. In addition, Kv2.1 has a direct role in exocytosis at an undefined step, involving SNARE proteins, that is independent of its ion-conducting pore function. Here, we elucidated the precise step in exocytosis. We previously reported that syntaxin-3 (Syn-3) is the key syntaxin that mediates exocytosis of newcomer secretory granules that spend minimal residence time on the plasma membrane before fusion. Using high-resolution total internal reflection fluorescence microscopy, we now show that Kv2.1 forms reservoir clusters on the β-cell plasma membrane and binds Syn-3 via its C-terminal C1b domain, which recruits newcomer insulin secretory granules into this large reservoir. Upon glucose stimulation, secretory granules were released from this reservoir to replenish the pool of newcomer secretory granules for subsequent fusion, occurring just adjacent to the plasma membrane Kv2.1 clusters. C1b deletion blocked the aforementioned Kv2.1-Syn-3-mediated events and reduced fusion of newcomer secretory granules. These insights have therapeutic implications, as Kv2.1 overexpression in type-2 diabetes rat islets restored biphasic insulin secretion.
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Affiliation(s)
- Dafna Greitzer-Antes
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Li Xie
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Tairan Qin
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Huanli Xie
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Dan Zhu
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Subhankar Dolai
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Tao Liang
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Fei Kang
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Alexandre B Hardy
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Yan He
- the Department of Epidemiology and Health Statistics, School of Public Health and Family Medicine, Capital Medical University, Beijing 100050, China
| | - Youhou Kang
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Herbert Y Gaisano
- From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
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Wheeler SE, Stacey HM, Nahaei Y, Hale SJ, Hardy AB, Reimann F, Gribble FM, Larraufie P, Gaisano HY, Brubaker PL. The SNARE Protein Syntaxin-1a Plays an Essential Role in Biphasic Exocytosis of the Incretin Hormone Glucagon-Like Peptide 1. Diabetes 2017; 66:2327-2338. [PMID: 28596237 PMCID: PMC6237272 DOI: 10.2337/db16-1403] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 06/01/2017] [Indexed: 02/02/2023]
Abstract
Exocytosis of the hormone glucagon-like peptide 1 (GLP-1) by the intestinal L cell is essential for the incretin effect after nutrient ingestion and is critical for the actions of dipeptidyl peptidase 4 inhibitors that enhance GLP-1 levels in patients with type 2 diabetes. Two-photon microscopy revealed that exocytosis of GLP-1 is biphasic, with a first peak at 1-6 min and a second peak at 7-12 min after stimulation with forskolin. Approximately 75% of the exocytotic events were represented by compound granule fusion, and the remainder were accounted for by full fusion of single granules under basal and stimulated conditions. The core SNARE protein syntaxin-1a (syn1a) was expressed by murine ileal L cells. At the single L-cell level, first-phase forskolin-induced exocytosis was reduced to basal (P < 0.05) and second-phase exocytosis abolished (P < 0.05) by syn1a knockout. L cells from intestinal-epithelial syn1a-deficient mice demonstrated a 63% reduction in forskolin-induced GLP-1 release in vitro (P < 0.001) and a 23% reduction in oral glucose-stimulated GLP-1 secretion (P < 0.05) in association with impairments in glucose-stimulated insulin release (by 60%; P < 0.01) and glucose tolerance (by 20%; P < 0.01). The findings identify an exquisite mechanism of metered secretory output that precisely regulates release of the incretin hormone GLP-1 and hence insulin secretion after a meal.
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Affiliation(s)
- Sarah E Wheeler
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Holly M Stacey
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Yasaman Nahaei
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Stephen J Hale
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Frank Reimann
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Fiona M Gribble
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Pierre Larraufie
- Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, U.K
| | - Herbert Y Gaisano
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Patricia L Brubaker
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
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Hardy AB, Cowdell S, Griffiths P. M14 Surgical interventions for emphysema: The experience of a community based COPD service. Thorax 2015. [DOI: 10.1136/thoraxjnl-2015-207770.441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Fu A, Robitaille K, Faubert B, Reeks C, Dai XQ, Hardy AB, Sankar KS, Ogrel S, Al-Dirbashi OY, Rocheleau JV, Wheeler MB, MacDonald PE, Jones R, Screaton RA. LKB1 couples glucose metabolism to insulin secretion in mice. Diabetologia 2015; 58:1513-22. [PMID: 25874445 DOI: 10.1007/s00125-015-3579-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Accepted: 03/13/2015] [Indexed: 01/05/2023]
Abstract
AIMS/HYPOTHESIS Precise regulation of insulin secretion by the pancreatic beta cell is essential for the maintenance of glucose homeostasis. Insulin secretory activity is initiated by the stepwise breakdown of ambient glucose to increase cellular ATP via glycolysis and mitochondrial respiration. Knockout of Lkb1, the gene encoding liver kinase B1 (LKB1) from the beta cell in mice enhances insulin secretory activity by an undefined mechanism. Here, we sought to determine the molecular basis for how deletion of Lkb1 promotes insulin secretion. METHODS To explore the role of LKB1 on individual steps in the insulin secretion pathway, we used mitochondrial functional analyses, electrophysiology and metabolic tracing coupled with by gas chromatography and mass spectrometry. RESULTS Beta cells lacking LKB1 surprisingly display impaired mitochondrial metabolism and lower ATP levels following glucose stimulation, yet compensate for this by upregulating both uptake and synthesis of glutamine, leading to increased production of citrate. Furthermore, under low glucose conditions, Lkb1(-/-) beta cells fail to inhibit acetyl-CoA carboxylase 1 (ACC1), the rate-limiting enzyme in lipid synthesis, and consequently accumulate NEFA and display increased membrane excitability. CONCLUSIONS/INTERPRETATION Taken together, our data show that LKB1 plays a critical role in coupling glucose metabolism to insulin secretion, and factors in addition to ATP act as coupling intermediates between feeding cues and secretion. Our data suggest that beta cells lacking LKB1 could be used as a system to identify additional molecular events that connect metabolism to cellular excitation in the insulin secretion pathway.
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Affiliation(s)
- Accalia Fu
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, K1H 8L1, Canada
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Liu Y, Batchuluun B, Ho L, Zhu D, Prentice KJ, Bhattacharjee A, Zhang M, Pourasgari F, Hardy AB, Taylor KM, Gaisano H, Dai FF, Wheeler MB. Characterization of Zinc Influx Transporters (ZIPs) in Pancreatic β Cells: ROLES IN REGULATING CYTOSOLIC ZINC HOMEOSTASIS AND INSULIN SECRETION. J Biol Chem 2015; 290:18757-69. [PMID: 25969539 PMCID: PMC4513131 DOI: 10.1074/jbc.m115.640524] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Indexed: 12/12/2022] Open
Abstract
Zinc plays an essential role in the regulation of pancreatic β cell function, affecting important processes including insulin biosynthesis, glucose-stimulated insulin secretion, and cell viability. Mutations in the zinc efflux transport protein ZnT8 have been linked with both type 1 and type 2 diabetes, further supporting an important role for zinc in glucose homeostasis. However, very little is known about how cytosolic zinc is controlled by zinc influx transporters (ZIPs). In this study, we examined the β cell and islet ZIP transcriptome and show consistent high expression of ZIP6 (Slc39a6) and ZIP7 (Slc39a7) genes across human and mouse islets and MIN6 β cells. Modulation of ZIP6 and ZIP7 expression significantly altered cytosolic zinc influx in pancreatic β cells, indicating an important role for ZIP6 and ZIP7 in regulating cellular zinc homeostasis. Functionally, this dysregulated cytosolic zinc homeostasis led to impaired insulin secretion. In parallel studies, we identified both ZIP6 and ZIP7 as potential interacting proteins with GLP-1R by a membrane yeast two-hybrid assay. Knock-down of ZIP6 but not ZIP7 in MIN6 β cells impaired the protective effects of GLP-1 on fatty acid-induced cell apoptosis, possibly via reduced activation of the p-ERK pathway. Therefore, our data suggest that ZIP6 and ZIP7 function as two important zinc influx transporters to regulate cytosolic zinc concentrations and insulin secretion in β cells. In particular, ZIP6 is also capable of directly interacting with GLP-1R to facilitate the protective effect of GLP-1 on β cell survival.
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Affiliation(s)
- Ying Liu
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Battsetseg Batchuluun
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Louisa Ho
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Dan Zhu
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Kacey J Prentice
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Alpana Bhattacharjee
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Ming Zhang
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Farzaneh Pourasgari
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Alexandre B Hardy
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Kathryn M Taylor
- the Breast Cancer Molecular Pharmacology Unit, School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Redwood Building, King Edward VIIth Avenue, Cardiff CF10 3NB United Kingdom
| | - Herbert Gaisano
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Feihan F Dai
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Michael B Wheeler
- From the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
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Luu L, Dai FF, Prentice KJ, Huang X, Hardy AB, Hansen JB, Liu Y, Joseph JW, Wheeler MB. The loss of Sirt1 in mouse pancreatic beta cells impairs insulin secretion by disrupting glucose sensing. Diabetologia 2013; 56:2010-20. [PMID: 23783352 DOI: 10.1007/s00125-013-2946-5] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 04/29/2013] [Indexed: 10/26/2022]
Abstract
AIMS/HYPOTHESIS Sirtuin 1 (SIRT1) has emerged as a key metabolic regulator of glucose homeostasis and insulin secretion. Enhanced SIRT1 activity has been shown to be protective against diabetes, although the mechanisms remain largely unknown. The aim of this study was to determine how SIRT1 regulates insulin secretion in the pancreatic beta cell. METHODS Pancreatic beta cell-specific Sirt1 deletion was induced by tamoxifen injection in 9-week-old Pdx1CreER:floxSirt1 mice (Sirt1BKO). Controls were injected with vehicle. Mice were assessed metabolically via glucose challenge, insulin tolerance tests and physical variables. In parallel, Sirt1 short interfering RNA-treated MIN6 cells (SIRT1KD) and isolated Sirt1BKO islets were used to investigate the effect of SIRT1 inactivation on insulin secretion and gene expression. RESULTS OGTTs showed impaired glucose disposal in Sirt1BKO mice due to insufficient insulin secretion. Isolated Sirt1BKO islets and SIRT1KD MIN6 cells also exhibited impaired glucose-stimulated insulin secretion. Subsequent analyses revealed impaired α-ketoisocaproic acid-induced insulin secretion and attenuated glucose-induced Ca(2+) influx, but normal insulin granule exocytosis in Sirt1BKO beta cells. Microarray studies revealed a large cluster of mitochondria-related genes, the expression of which was dysregulated in SIRT1KD MIN6 cells. Upon further analysis, we demonstrated an explicit defect in mitochondrial function: the inability to couple nutrient metabolism to mitochondrial membrane hyperpolarisation and reduced oxygen consumption rates. CONCLUSIONS/INTERPRETATION Taken together, these findings indicate that in beta cells the deacetylase SIRT1 regulates the expression of specific mitochondria-related genes that control metabolic coupling, and that a decrease in beta cell Sirt1 expression impairs glucose sensing and insulin secretion.
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Affiliation(s)
- L Luu
- Department of Physiology, University of Toronto, 1 King's College Circle Room 3352, Toronto, ON M5S 1A8, Canada
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Allister EM, Robson-Doucette CA, Prentice KJ, Hardy AB, Sultan S, Gaisano HY, Kong D, Gilon P, Herrera PL, Lowell BB, Wheeler MB. UCP2 regulates the glucagon response to fasting and starvation. Diabetes 2013; 62:1623-33. [PMID: 23434936 PMCID: PMC3636632 DOI: 10.2337/db12-0981] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Glucagon is important for maintaining euglycemia during fasting/starvation, and abnormal glucagon secretion is associated with type 1 and type 2 diabetes; however, the mechanisms of hypoglycemia-induced glucagon secretion are poorly understood. We previously demonstrated that global deletion of mitochondrial uncoupling protein 2 (UCP2(-/-)) in mice impaired glucagon secretion from isolated islets. Therefore, UCP2 may contribute to the regulation of hypoglycemia-induced glucagon secretion, which is supported by our current finding that UCP2 expression is increased in nutrient-deprived murine and human islets. Further to this, we created α-cell-specific UCP2 knockout (UCP2AKO) mice, which we used to demonstrate that blood glucose recovery in response to hypoglycemia is impaired owing to attenuated glucagon secretion. UCP2-deleted α-cells have higher levels of intracellular reactive oxygen species (ROS) due to enhanced mitochondrial coupling, which translated into defective stimulus/secretion coupling. The effects of UCP2 deletion were mimicked by the UCP2 inhibitor genipin on both murine and human islets and also by application of exogenous ROS, confirming that changes in oxidative status and electrical activity directly reduce glucagon secretion. Therefore, α-cell UCP2 deletion perturbs the fasting/hypoglycemic glucagon response and shows that UCP2 is necessary for normal α-cell glucose sensing and the maintenance of euglycemia.
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Affiliation(s)
- Emma M. Allister
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Kacey J. Prentice
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Alexandre B. Hardy
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Sobia Sultan
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Herbert Y. Gaisano
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Dong Kong
- Division of Endocrinology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts
| | - Patrick Gilon
- Pôle d’endocrinologie, diabète et nutrition, Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium
| | - Pedro L. Herrera
- Department of Genetic Medicine and Development, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Bradford B. Lowell
- Division of Endocrinology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts
| | - Michael B. Wheeler
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Corresponding author: Michael B. Wheeler,
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Haataja L, Snapp E, Wright J, Liu M, Hardy AB, Wheeler MB, Markwardt ML, Rizzo M, Arvan P. Proinsulin intermolecular interactions during secretory trafficking in pancreatic β cells. J Biol Chem 2012; 288:1896-906. [PMID: 23223446 DOI: 10.1074/jbc.m112.420018] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Classically, exit from the endoplasmic reticulum (ER) is rate-limiting for secretory protein trafficking because protein folding/assembly occurs there. In this study, we have exploited "hPro-CpepSfGFP," a human proinsulin bearing "superfolder" green fluorescent C-peptide expressed in pancreatic β cells where it is processed to human insulin and CpepSfGFP. Remarkably, steady-state accumulation of hPro-CpepSfGFP and endogenous proinsulin is in the Golgi region, as if final stages of protein folding/assembly were occurring there. The Golgi regional distribution of proinsulin is dynamic, influenced by fasting/refeeding, and increased with β cell zinc deficiency. However, coexpression of ER-entrapped mutant proinsulin-C(A7)Y shifts the steady-state distribution of wild-type proinsulin to the ER. Endogenous proinsulin coprecipitates with hPro-CpepSfGFP and even more so with hProC(A7)Y-CpepSfGFP. Using Cerulean and Venus-tagged proinsulins, we find that both WT-WT and WT-mutant proinsulin pairs exhibit FRET. The data demonstrate that wild-type proinsulin dimerizes within the ER but accumulates at a poorly recognized slow step within the Golgi region, reflecting either slow kinetics of proinsulin hexamerization, steps in formation of nascent secretory granules, or other unknown molecular events. However, in the presence of ongoing misfolding of a subpopulation of proinsulin in β cells, the rate-limiting step in transport of the remaining proinsulin shifts to the ER.
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Affiliation(s)
- Leena Haataja
- Division of Metabolism, Endocrinology, and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, USA
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Abstract
Serotonin [or 5-hydroxytryptamine or (5-HT)] has been implicated as a key modulator in energy homeostasis and a primary focus in the treatment of obesity. There is growing evidence that 5-HT, acting through the 5-HT 1B receptor (5-HT(1B)R) in the paraventricular nucleus of the hypothalamus (PVN), is important to this regulation. However, there is some contention as to whether 5-HT(1B)R action occurs directly on PVN neurons or indirectly via inhibitory inputs into the PVN. To address these questions, we used a novel clonal, hypothalamic neuronal cell model, adult mouse hypothalamic-2/30 (mHypoA-2/30), expressing a PVN-specific marker, single-minded homolog 1, as well as a complement of PVN neuropeptides, including TRH, vasopressin, ghrelin, nucleobindin-2, and galanin. Adult mouse hypothalamic-2/30 neurons were also found to express the 5-HT(1B)R and 5-HT 6 receptor, but not 2C, all previously linked to feeding regulation. Direct serotonergic stimulation (100 nm to 10 μm) of these neurons resulted in dose-dependent cFos activation. 5-HT (10 μm) suppressed forskolin-induced cAMP levels and induced a rise in intracellular Ca(2+) through ER Ca(2+) release, effects that were mimicked by the 5-HT(1B)R agonists, CGS12066B and CP93129, and that were attenuated in the presence of the 5-HT(1B)R-specific inhibitors, GR55562 and isamoltane hemifumarate. Modest transcriptional changes in ghrelin and nucleobindin-2 were also observed in response to 100 nm and 10 μm 5-HT, respectively. These findings support the model wherein 5-HT action through the 1B receptor subtype occurs directly on PVN neurons, leading to potential modification of neuronal transcriptional and secretory machinery.
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Affiliation(s)
- Stephanie Tung
- Departments of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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11
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Basford CL, Prentice KJ, Hardy AB, Sarangi F, Micallef SJ, Li X, Guo Q, Elefanty AG, Stanley EG, Keller G, Allister EM, Nostro MC, Wheeler MB. The functional and molecular characterisation of human embryonic stem cell-derived insulin-positive cells compared with adult pancreatic beta cells. Diabetologia 2012; 55:358-71. [PMID: 22075915 DOI: 10.1007/s00125-011-2335-x] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 09/05/2011] [Indexed: 12/26/2022]
Abstract
AIMS/HYPOTHESIS Using a novel directed differentiation protocol, we recently generated up to 25% insulin-producing cells from human embryonic stem cells (hESCs) (insulin(+) cells). At this juncture, it was important to functionally and molecularly characterise these hESC-derived insulin(+) cells and identify key differences and similarities between them and primary beta cells. METHODS We used a new reporter hESC line with green fluorescent protein (GFP) cDNA targeted to the INS locus by homologous recombination (INS (GFP/w)) and an untargeted hESC line (HES2). INS (GFP/w) allowed efficient identification and purification of GFP-producing (INS:GFP(+)) cells. Insulin(+) cells were examined for key features of adult beta cells using microarray, quantitative PCR, secretion assays, imaging and electrophysiology. RESULTS Immunofluorescent staining showed complete co-localisation of insulin with GFP; however, cells were often multihormonal, many with granules containing insulin and glucagon. Electrophysiological recordings revealed variable K(ATP) and voltage-gated Ca(2+) channel activity, and reduced glucose-induced cytosolic Ca(2+) uptake. This translated into defective glucose-stimulated insulin secretion but, intriguingly, appropriate glucagon responses. Gene profiling revealed differences in global gene expression between INS:GFP(+) cells and adult human islets; however, INS:GFP(+) cells had remarkably similar expression of endocrine-lineage transcription factors and genes involved in glucose sensing and exocytosis. CONCLUSIONS/INTERPRETATION INS:GFP(+) cells can be purified from differentiated hESCs, providing a superior source of insulin-producing cells. Genomic analyses revealed that INS:GFP(+) cells collectively resemble immature endocrine cells. However, insulin(+) cells were heterogeneous, a fact that translated into important functional differences within this population. The information gained from this study may now be used to generate new iterations of functioning beta cells that can be purified for transplant.
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Affiliation(s)
- C L Basford
- Division of Cellular and Molecular Biology, Toronto General Research Institute, TMDT, Toronto, ON, Canada
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Hardy AB, Serino AS, Wijesekara N, Chimienti F, Wheeler MB. Regulation of glucagon secretion by zinc: lessons from the β cell-specific Znt8 knockout mouse model. Diabetes Obes Metab 2011; 13 Suppl 1:112-7. [PMID: 21824264 DOI: 10.1111/j.1463-1326.2011.01451.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In type-2 diabetes, hyperglucagonaemia aggravates elevated blood glucose levels. Relative to our knowledge of the β-cell and insulin secretion, there remains a limited understanding of glucagon secretion in α-cells. Regulation of glucagon may be dependent on a combination of factors, which include direct glucose sensing by the α-cell, innervations from the autonomic nervous system and potential 'paracrine' actions by hormones and factors that are released by adjacent endocrine cells within the islets. The list of potential 'paracrine' regulators within the islet includes insulin, somatostatin, γ-aminobutyric acid, glutamate and zinc. Zinc crystallises with insulin in β-cells and is co-secreted with insulin. In the scientific literature, the effect of exogeneous zinc on glucagon secretion has been debated. Here, we confirm that an increase in exogeneous zinc does inhibit glucagon secretion. To determine if there are physiological effects of zinc on glucagon secretion we used a β-cell-specific ZnT8 knockout (Znt8BKO) mouse model. Znt8BKO mice, despite showing lower granular zinc content in β-cells, showed no changes in fasted plasma glucagon levels and glucose regulated glucagon secretion. These findings suggest that zinc secreted from β-cell does not regulate glucagon secretion.
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Affiliation(s)
- A B Hardy
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
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Wijesekara N, Dai FF, Hardy AB, Giglou PR, Bhattacharjee A, Koshkin V, Chimienti F, Gaisano HY, Rutter GA, Wheeler MB. Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion. Diabetologia 2010; 53:1656-68. [PMID: 20424817 PMCID: PMC6101216 DOI: 10.1007/s00125-010-1733-9] [Citation(s) in RCA: 219] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Accepted: 02/05/2010] [Indexed: 02/01/2023]
Abstract
AIMS/HYPOTHESIS Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage and may regulate glucagon secretion from alpha cells. Zinc transport family member 8 (ZnT8) is a zinc efflux transporter that is highly abundant in beta cells. Polymorphisms of ZnT8 (also known as SLC30A8) gene in man are associated with increased risk of type 2 diabetes. While global Znt8 knockout (Znt8KO) mice have been characterised, ZnT8 is also present in other islet cell types and extra-pancreatic tissues. Therefore, it is important to find ways of understanding the role of ZnT8 in beta and alpha cells without the difficulties caused by the confounding effects of ZnT8 in these other tissues. METHODS We generated mice with beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout of Znt8, and performed in vivo and in vitro characterisation of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis. RESULTS Znt8BKO mice are glucose-intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first-phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, Znt8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis. CONCLUSIONS/INTERPRETATION This is the first report of specific beta and alpha cell deletion of Znt8. Our data indicate that while, under the conditions studied, ZnT8 is absolutely essential for proper beta cell function, it is largely dispensable for alpha cell function.
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Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, 1 King's College Circle Room 3352, Toronto, ON, Canada M5S 1A8
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Hardy AB, Varma R, Collyns T, Moffitt SJ, Mullarkey C, Watson JP. Cost-effectiveness of the NICE guidelines for screening for latent tuberculosis infection: the QuantiFERON-TB Gold IGRA alone is more cost-effective for immigrants from high burden countries. Thorax 2009; 65:178-80. [PMID: 19996345 DOI: 10.1136/thx.2009.119677] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Affiliation(s)
- A B Hardy
- Leeds Teaching Hospitals NHS Trust, Department of Respiratory Machine, Beckett Street, Leeds LS9 7TF, UK.
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Delaney KR, Qnais EY, Hardy AB. Short-term synaptic plasticity at the main and vomeronasal olfactory receptor to mitral cell synapse in frog. Eur J Neurosci 2009; 30:2077-88. [PMID: 20128846 DOI: 10.1111/j.1460-9568.2009.06997.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Synaptic responses resulting from stimulation of the main olfactory and vomeronasal (VN) nerves were measured in main and accessory olfactory bulb (AOB) of frog, Rana pipiens, to test the hypothesis that properties of these synapses would reflect the distinct differences in the time course of odour delivery to each of these olfactory structures. Paired-pulse depression dominated responses to repetitive stimulation of the main olfactory nerve for interstimulus intervals (ISI) up to several seconds. Inhibition of voltage-gated Ca(2+) channels by GABAb receptors contributes significantly to this inhibition of transmitter release, particularly for ISI > 0.5 s. In contrast, the monosynaptic connection between VN sensory neurons and mitral cells in the AOB showed enhancement with pairs or short trains of stimuli for ISI of 0.5 to > 10 s. A small inhibitory effect of GABAb receptors on presynaptic Ca(2+) influx and release was only evident when a large proportion of the VN axons were stimulated simultaneously but even with inhibition present an overall enhancement of release was observed. Increasing the number of conditioning stimuli from one to five increased residual [Ca(2+)] and enhancement but a direct correlation between residual [Ca(2+)] and either the magnitude or the time course of enhancement was not observed. Enhanced transmitter release from VN afferent terminals results in effective integration of sustained low-frequency activity, which may play a role in the detection of low-intensity odourant stimuli by the VN system.
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Affiliation(s)
- K R Delaney
- Department of Biology, University of Victoria, Victoria, BC V8W 3N5, Canada.
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Hardy AB, Fox JEM, Giglou PR, Wijesekara N, Bhattacharjee A, Sultan S, Gyulkhandanyan AV, Gaisano HY, MacDonald PE, Wheeler MB. Characterization of Erg K+ channels in alpha- and beta-cells of mouse and human islets. J Biol Chem 2009; 284:30441-52. [PMID: 19690348 DOI: 10.1074/jbc.m109.040659] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated eag-related gene (Erg) K(+) channels regulate the electrical activity of many cell types. Data regarding Erg channel expression and function in electrically excitable glucagon and insulin producing cells of the pancreas is limited. In the present study Erg1 mRNA and protein were shown to be highly expressed in human and mouse islets and in alpha-TC6 and Min6 cells alpha- and beta-cell lines, respectively. Whole cell patch clamp recordings demonstrated the functional expression of Erg1 in alpha- and beta-cells, with rBeKm1, an Erg1 antagonist, blocking inward tail currents elicited by a double pulse protocol. Additionally, a small interference RNA approach targeting the kcnh2 gene (Erg1) induced a significant decrease of Erg1 inward tail current in Min6 cells. To investigate further the role of Erg channels in mouse and human islets, ratiometric Fura-2 AM Ca(2+)-imaging experiments were performed on isolated alpha- and beta-cells. Blocking Erg channels with rBeKm1 induced a transient cytoplasmic Ca(2+) increase in both alpha- and beta-cells. This resulted in an increased glucose-dependent insulin secretion, but conversely impaired glucagon secretion under low glucose conditions. Together, these data present Erg1 channels as new mediators of alpha- and beta-cell repolarization. However, antagonism of Erg1 has divergent effects in these cells; to augment glucose-dependent insulin secretion and inhibit low glucose stimulated glucagon secretion.
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Affiliation(s)
- Alexandre B Hardy
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Abstract
Two-photon laser scanning microscopy was used to correlate electrical events detected with whole-cell somatic recordings to Ca2+ transients in dendrites of olfactory bulb granule cells. A subset of spontaneous subthreshold depolarizing events recorded at the soma were shown to correspond to suprathreshold dendritic, Na-dependent action potentials [APs; dendritic spikes (D-spikes)]. These potentials were blocked by intracellular QX-314 (lidocaine N-ethyl bromide), hyperpolarizing current injection at the soma, and by partial inhibition of AMPA/kainate receptors with 0.75 microM DNQX. They were affected only slightly by 100 microM NiCl2. The majority of D-spikes recorded at the soma had a time to peak of <4 ms, comparable with somatic APs, a nonexponential decay, and amplitudes between 3 and 21 mV. Somatically recorded APs produced Ca2+ transients that were observed in spines and dendrites in all parts of the cell. Ca2+ transients from D-spikes were restricted to subsets of distal dendrites and their associated spines but were absent from the soma and dendrite within approximately 50-80 microm of the soma. Ca2+ transients in different branches could be correlated with different-sized D-spikes. D-spike and backpropagating AP-induced Ca2+ transients summed in dendrites, provided the interval between them was >5-6 ms. Generation of a D-spike in a particular dendrite <5-6 ms before a somatic AP blocked backpropagation of the somatic AP into that dendrite. The temporally specific interplay between D-spikes and backpropagating APs may play a role in regulating feedback and feedforward inhibition of groups of mitral cells synapsing on different granule cell dendrites.
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Affiliation(s)
- Tibor Zelles
- Department of Biology, University of Victoria, Victoria, British Columbia V8W 3N5, Canada
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Hardy AB, Aïoun J, Baly C, Julliard KA, Caillol M, Salesse R, Duchamp-Viret P. Orexin A modulates mitral cell activity in the rat olfactory bulb: patch-clamp study on slices and immunocytochemical localization of orexin receptors. Endocrinology 2005; 146:4042-53. [PMID: 15976062 DOI: 10.1210/en.2005-0020] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Orexin A and B are involved in feeding behaviors, and recently fibers containing these peptides were found in the rat olfactory bulb. These fibers, which originate from the lateral and posterior hypothalamus and the perifornical area, are distributed in the glomerular, mitral cell, and granule cell layers. Orexin receptors are mainly expressed by mitral cells. In the present study, RT-PCR experiments were done to determine orexin receptor expression during the early postnatal life of rats, and immunocytochemical experiments were performed to further clarify the structural and ultrastructural localization of orexin receptors in the olfactory bulb. Furthermore, a functional electrophysiological approach examined the action of orexin A on mitral cell excitability and spontaneous activity using in vitro patch-clamp techniques. RT-PCR results show that mRNA of the two type receptors, type 1 orexin receptors and type 2 orexin receptors, are expressed in the olfactory bulb of rat from 10 d to the adult stage. At the same ages, immunocytochemical data show that orexin 1 receptors are localized in the cell bodies of periglomerular, mitral/tufted, and granule cells. Immunoreactivity was also demonstrated in mitral/tufted cell dendrites arborizing in the glomerulus and mitral/tufted and granule cell processes running in the external plexiform layer. Functionally, orexin A produced either a direct, tetrodotoxin-insensitive depolarization in one group of mitral cells (7%), or, in another group (30%), an indirect, tetrodotoxin-sensitive hyperpolarization. Both actions were mediated by type 1 orexin receptors because the response was antagonized by SB-334867-A, a selective antagonist. Mitral cell recordings performed under bicuculline [gamma-aminobutyric acid (GABA)A receptor antagonist], indicate that the orexin-induced indirect hyperpolarization was partly mediated through GABA(A) receptors. Because granule cells and periglomerular cells express orexin receptors and are GABAergic cells, they could be both involved in this hyperpolarization. Other mechanisms, which could support an indirect hyperpolarization of mitral cells through dopamine interneuron solicitation, are proposed. Our results provide data that should allow us to better understand neural communication and regulation mechanisms between the hypothalamic feeding centers and the olfactory bulb.
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Affiliation(s)
- Alexandre B Hardy
- Laboratoire de Neurosciences et Systèmes Sensoriels, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5020, Université Claude Bernard, 50 Avenue Tony Garnier, 69366 Lyon cedex 07, France
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Palouzier-Paulignan B, Duchamp-Viret P, Hardy AB, Duchamp A. GABA(B) receptor-mediated inhibition of mitral/tufted cell activity in the rat olfactory bulb: a whole-cell patch-clamp study in vitro. Neuroscience 2002; 111:241-50. [PMID: 11983311 DOI: 10.1016/s0306-4522(02)00003-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
GABA, the major inhibitory neurotransmitter involved in information processing in the olfactory bulb, is hypothesized to act through GABA(B) receptors by depressing primary neurotransmitter release at the level of olfactory nerve axon endings. The present study was designed to analyze GABA(B) receptor-mediated inhibition mechanisms by performing whole-cell patch-clamp recordings of mitral/tufted cell activity in the rat in vitro. To do so, GABA(B) receptor-mediated action was mimicked by baclofen and antagonized by saclofen. Our protocol led us to provide an original description of GABA(B) receptor-mediated inhibition exerted on mitral/tufted cells. First, their spontaneous activity was shown to be drastically abolished by baclofen. Second, their responses to olfactory nerve electrical stimulation were graded by GABA(B) receptor-mediated inhibition. Indeed, this inhibition may be described as inducing effects ranked from a slight increase in response latency to a complete response suppression.Altogether, our results corroborate the hypothesis of a presynaptic extrasynaptic GABA(B) receptor-mediated inhibition influencing mitral/tufted cell olfactory nerve responsivity. However, the involvement of postsynaptic receptors, with different properties or with different anatomical locations, cannot be ruled out, particularly in the control of spontaneous activity. In conclusion, we underline that, in the vertebrate olfactory bulb, GABA(B) receptor-mediated action appears to contribute to make mitral/tufted cell responses more salient by reducing their resting activity.
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Affiliation(s)
- B Palouzier-Paulignan
- Laboratoire de Neurosciences et Systèmes Sensoriels, CNRS, UMR 5020, Université Claude Bernard, 50 avenue Tony Garnier, 69366 Lyon Cedex 07, France.
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