1
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Bisht S, Singh MF. The triggering pathway, the metabolic amplifying pathway, and cellular transduction in regulation of glucose-dependent biphasic insulin secretion. Arch Physiol Biochem 2024:1-12. [PMID: 38196246 DOI: 10.1080/13813455.2023.2299920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 12/16/2023] [Indexed: 01/11/2024]
Abstract
Introduction: Insulin secretion is a highly regulated process critical for maintaining glucose homeostasis. This abstract explores the intricate interplay between three essential pathways: The Triggering Pathway, The Metabolic Amplifying Pathway, and Cellular Transduction, in orchestrating glucose-dependent biphasic insulin secretion.Mechanism: During the triggering pathway, glucose metabolism in pancreatic beta-cells leads to ATP production, closing ATP-sensitive potassium channels and initiating insulin exocytosis. The metabolic amplifying pathway enhances insulin secretion via key metabolites like NADH and glutamate, enhancing calcium influx and insulin granule exocytosis. Additionally, the cellular transduction pathway involves G-protein coupled receptors and cyclic AMP, modulating insulin secretion.Result and Conclusion: These interconnected pathways ensure a dynamic insulin response to fluctuating glucose levels, with the initial rapid phase and the subsequent sustained phase. Understanding these pathways' complexities provides crucial insights into insulin dysregulation in diabetes and highlights potential therapeutic targets to restore glucose-dependent insulin secretion.
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Affiliation(s)
- Shradha Bisht
- Amity Institute of Pharmacy, Amity University, Lucknow, Uttar Pradesh, India
| | - Mamta F Singh
- School of Pharmaceutical Sciences, SBS University, Balawala, Uttarakhand, India
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2
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Ouassou H, Elhouda Daoudi N, Bouknana S, Abdnim R, Bnouham M. A Review of Antidiabetic Medicinal Plants as a Novel Source of Phosphodiesterase Inhibitors: Future Perspective of New Challenges Against Diabetes Mellitus. Med Chem 2024; 20:467-486. [PMID: 38265379 DOI: 10.2174/0115734064255060231116192839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Revised: 07/31/2023] [Accepted: 09/25/2023] [Indexed: 01/25/2024]
Abstract
Intracellular glucose concentration plays a crucial role in initiating the molecular secretory process of pancreatic β-cells through multiple messengers and signaling pathways. Cyclic nucleotides are key physiological regulators that modulate pathway interactions in β -cells. An increase of cyclic nucleotides is controled by hydrolysed phosphodiesterases (PDEs), which degrades cyclic nucleotides into inactive metabolites. Despite the undeniable therapeutic potential of PDE inhibitors, they are associated with several side effects. The treatment strategy for diabetes based on PDE inhibitors has been proposed for a long time. Hence, the world of natural antidiabetic medicinal plants represents an ideal source of phosphodiesterase inhibitors as a new strategy for developing novel agents to treat diabetes mellitus. This review highlights medicinal plants traditionally used in the treatment of diabetes mellitus that have been proven to have inhibitory effects on PDE activity. The contents of this review were sourced from electronic databases, including Science Direct, PubMed, Springer Link, Web of Science, Scopus, Wiley Online, Scifinder and Google Scholar. These databases were consulted to collect information without any limitation date. After comprehensive literature screening, this paper identified 27 medicinal plants that have been reported to exhibit anti-phosphodiesterase activities. The selection of these plants was based on their traditional uses in the treatment of diabetes mellitus. The review emphasizes the antiphosphodiesterase properties of 31 bioactive components derived from these plant extracts. Many phenolic compounds have been identified as PDE inhibitors: Brazilin, mesozygin, artonin I, chalcomaracin, norartocarpetin, moracin L, moracin M, moracin C, curcumin, gallic acid, caffeic acid, rutin, quercitrin, quercetin, catechin, kaempferol, chlorogenic acid, and ellagic acid. Moreover, smome lignans have reported as PDE inhibitors: (+)-Medioresinol di-O-β-d-glucopyranoside, (+)- Pinoresinol di-O-β-d-glucopyranoside, (+)-Pinoresinol-4-O-β-d-glucopyranosyl (1→6)-β-dglucopyranoside, Liriodendrin, (+)-Pinoresinol 4'-O-β-d-glucopyranoside, and forsythin. This review provides a promising starting point of medicinal plants, which could be further studied for the development of natural phosphodiesterase inhibitors to treat diabetes mellitus. Therefore, it is important to consider clinical studies for the identification of new targets for the treatment of diabetes.
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Affiliation(s)
- Hayat Ouassou
- Higher Institute of Nurses Professions and Health Techniques, Oujda 60000, Morocco
- Laboratory of Bioresources, Biotechnology, Ethnopharmacology and Health, Department of Biology, Faculty of Sciences, Mohammed First University, BP. 717, Oujda 60040, Morocco
| | - Nour Elhouda Daoudi
- Laboratory of Bioresources, Biotechnology, Ethnopharmacology and Health, Department of Biology, Faculty of Sciences, Mohammed First University, BP. 717, Oujda 60040, Morocco
| | - Saliha Bouknana
- Department of Biology, Faculty of Sciences, University Mohammed First, Boulevard Mohamed VI BP 717, Oujda 60040, Morocco
| | - Rhizlan Abdnim
- Laboratory of Bioresources, Biotechnology, Ethnopharmacology and Health, Department of Biology, Faculty of Sciences, Mohammed First University, BP. 717, Oujda 60040, Morocco
| | - Mohamed Bnouham
- Laboratory of Bioresources, Biotechnology, Ethnopharmacology and Health, Department of Biology, Faculty of Sciences, Mohammed First University, BP. 717, Oujda 60040, Morocco
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Mohammad Al-Amily I, Sjögren M, Duner P, Tariq M, Wollheim CB, Salehi A. Ablation of GPR56 Causes β-Cell Dysfunction by ATP Loss through Mistargeting of Mitochondrial VDAC1 to the Plasma Membrane. Biomolecules 2023; 13:biom13030557. [PMID: 36979492 PMCID: PMC10046417 DOI: 10.3390/biom13030557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 03/02/2023] [Accepted: 03/15/2023] [Indexed: 03/30/2023] Open
Abstract
The activation of G Protein-Coupled Receptor 56 (GPR56), also referred to as Adhesion G-Protein-Coupled Ceceptor G1 (ADGRG1), by Collagen Type III (Coll III) prompts cell growth, proliferation, and survival, among other attributes. We investigated the signaling cascades mediating this functional effect in relation to the mitochondrial outer membrane voltage-dependent anion Channel-1 (VDAC1) expression in pancreatic β-cells. GPR56KD attenuated the Coll III-induced suppression of P70S6K, JNK, AKT, NFκB, STAT3, and STAT5 phosphorylation/activity in INS-1 cells cultured at 20 mM glucose (glucotoxicity) for 72 h. GPR56-KD also increased Chrebp, Txnip, and Vdac1 while decreasing Vdac2 mRNA expression. In GPR56-KD islet β-cells, Vdac1 was co-localized with SNAP-25, demonstrating its plasma membrane translocation. This resulted in ATP loss, reduced cAMP production and impaired glucose-stimulated insulin secretion (GSIS) in INS-1 and human EndoC βH1 cells. The latter defects were reversed by an acute inhibition of VDAC1 with an antibody or the VDAC1 inhibitor VBIT-4. We demonstrate that Coll III potentiates GSIS by increasing cAMP and preserving β-cell functionality under glucotoxic conditions in a GPR56-dependent manner by attenuating the inflammatory response. These results emphasize GPR56 and VDAC1 as drug targets in conditions with impaired β-cell function.
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Affiliation(s)
- Israa Mohammad Al-Amily
- Department of Clinical Science, SUS, Division of Islet Cell Physiology, University of Lund, SE-205 02 Malmö, Sweden
| | - Marie Sjögren
- Department of Clinical Science, SUS, Division of Islet Cell Physiology, University of Lund, SE-205 02 Malmö, Sweden
| | - Pontus Duner
- Department of Clinical Science, SUS, Division of Experimental Cardiovascular Research, Lund University, SE-221 00 Lund, Sweden
| | - Mohammad Tariq
- Department of Clinical Science, SUS, Division of Islet Cell Physiology, University of Lund, SE-205 02 Malmö, Sweden
| | - Claes B Wollheim
- Department of Clinical Science, SUS, Division of Islet Cell Physiology, University of Lund, SE-205 02 Malmö, Sweden
| | - Albert Salehi
- Department of Clinical Science, SUS, Division of Islet Cell Physiology, University of Lund, SE-205 02 Malmö, Sweden
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4
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Mukai E, Fujimoto S, Inagaki N. Role of Reactive Oxygen Species in Glucose Metabolism Disorder in Diabetic Pancreatic β-Cells. Biomolecules 2022; 12:biom12091228. [PMID: 36139067 PMCID: PMC9496160 DOI: 10.3390/biom12091228] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 08/28/2022] [Accepted: 08/31/2022] [Indexed: 11/18/2022] Open
Abstract
The dysfunction of pancreatic β-cells plays a central role in the onset and progression of type 2 diabetes mellitus (T2DM). Insulin secretory defects in β-cells are characterized by a selective impairment of glucose stimulation, and a reduction in glucose-induced ATP production, which is essential for insulin secretion. High glucose metabolism for insulin secretion generates reactive oxygen species (ROS) in mitochondria. In addition, the expression of antioxidant enzymes is very low in β-cells. Therefore, β-cells are easily exposed to oxidative stress. In islet studies using a nonobese T2DM animal model that exhibits selective impairment of glucose-induced insulin secretion (GSIS), quenching ROS generated by glucose stimulation and accumulated under glucose toxicity can improve impaired GSIS. Acute ROS generation and toxicity cause glucose metabolism disorders through different molecular mechanisms. Nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor, is a master regulator of antioxidant defense and a potential therapeutic target in oxidative stress-related diseases, suggesting the possible involvement of Nrf2 in β-cell dysfunction caused by ROS. In this review, we describe the mechanisms of insulin secretory defects induced by oxidative stress in diabetic β-cells.
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Affiliation(s)
- Eri Mukai
- Medical Physiology and Metabolism Laboratory, Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, Kusatsu 5258577, Japan
- Correspondence:
| | - Shimpei Fujimoto
- Department of Endocrinology, Metabolism, and Nephrology, Kochi Medical School, Kochi University, Kochi 7838505, Japan
| | - Nobuya Inagaki
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto 6068507, Japan
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5
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Foster HR, Ho T, Potapenko E, Sdao SM, Huang SM, Lewandowski SL, VanDeusen HR, Davidson SM, Cardone RL, Prentki M, Kibbey RG, Merrins MJ. β-cell deletion of the PKm1 and PKm2 isoforms of pyruvate kinase in mice reveals their essential role as nutrient sensors for the K ATP channel. eLife 2022; 11:79422. [PMID: 35997256 PMCID: PMC9444242 DOI: 10.7554/elife.79422] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 08/23/2022] [Indexed: 02/03/2023] Open
Abstract
Pyruvate kinase (PK) and the phosphoenolpyruvate (PEP) cycle play key roles in nutrient-stimulated KATP channel closure and insulin secretion. To identify the PK isoforms involved, we generated mice lacking β-cell PKm1, PKm2, and mitochondrial PEP carboxykinase (PCK2) that generates mitochondrial PEP. Glucose metabolism was found to generate both glycolytic and mitochondrially derived PEP, which triggers KATP closure through local PKm1 and PKm2 signaling at the plasma membrane. Amino acids, which generate mitochondrial PEP without producing glycolytic fructose 1,6-bisphosphate to allosterically activate PKm2, signal through PKm1 to raise ATP/ADP, close KATP channels, and stimulate insulin secretion. Raising cytosolic ATP/ADP with amino acids is insufficient to close KATP channels in the absence of PK activity or PCK2, indicating that KATP channels are primarily regulated by PEP that provides ATP via plasma membrane-associated PK, rather than mitochondrially derived ATP. Following membrane depolarization, the PEP cycle is involved in an 'off-switch' that facilitates KATP channel reopening and Ca2+ extrusion, as shown by PK activation experiments and β-cell PCK2 deletion, which prolongs Ca2+ oscillations and increases insulin secretion. In conclusion, the differential response of PKm1 and PKm2 to the glycolytic and mitochondrial sources of PEP influences the β-cell nutrient response, and controls the oscillatory cycle regulating insulin secretion.
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Affiliation(s)
- Hannah R Foster
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Thuong Ho
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Evgeniy Potapenko
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Sophia M Sdao
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Shih Ming Huang
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Sophie L Lewandowski
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Halena R VanDeusen
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States
| | - Shawn M Davidson
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of TechnologyCambridgeUnited States,Lewis-Sigler Institute for Integrative Genomics, Princeton UniversityPrincetonUnited States
| | - Rebecca L Cardone
- Department of Internal Medicine, Yale UniversityNew HavenUnited States
| | - Marc Prentki
- Molecular Nutrition Unit and Montreal Diabetes Research Center, CRCHUM, and Departments of Nutrition, Biochemistry and Molecular Medicine, Université de MontréalMontréalCanada
| | - Richard G Kibbey
- Department of Internal Medicine, Yale UniversityNew HavenUnited States,Department of Cellular & Molecular Physiology, Yale UniversityNew HavenUnited States
| | - Matthew J Merrins
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-MadisonMadisonUnited States,William S. Middleton Memorial Veterans HospitalMadisonUnited States
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6
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Thapaliya ER, Mony L, Sanchez R, Serraz B, Paoletti P, Ellis-Davies GCR. Photochemical control of drug efficacy - a comparison of uncaging and photoswitching ifenprodil on NMDA receptors. CHEMPHOTOCHEM 2021; 5:445-454. [PMID: 36540756 PMCID: PMC9762817 DOI: 10.1002/cptc.202000240] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Indexed: 09/29/2023]
Abstract
Ifenprodil is an important negative allosteric modulator of the N-methyl-D-aspartate (NMDA) receptors. We have synthesized caged and photoswitchable derivatives of this small molecule drug. Caged ifenprodil was biologically inert before photolysis, UV irradiation efficiently released the drug allowing selective inhibition of GluN2B-containing NMDA receptors. Azobenzene-modified ifenprodil, on the other hand, is inert in both its trans and cis configurations, although in silico modeling predicted the trans form to be able to bind to the receptor. The disparity in effectiveness between the two compounds reflects, in part, the inherent ability of each method in manipulating the binding properties of drugs. With appropriate structure-activity relationship uncaging enables binary control of effector binding, whereas photoswitching using feely diffusable chromophores shifts the dose-response curve of drug-receptor interaction. Our data suggest that the efficacy of pharmacophores having a confined binding site such as ifenprodil can be controlled more easily by uncaging in comparison to photoswitching.
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Affiliation(s)
- Ek Raj Thapaliya
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029, USA
- Equal contribution
| | - Laetitia Mony
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), École Normale Supérieure, CNRS, INSERM, Université PSL, Paris 75005, France
- Equal contribution
| | - Roberto Sanchez
- Department of Pharmacological Sciences and Drug Discovery Institute, Mount Sinai School of Medicine, New York, NY 10029, USA
| | - Benjamin Serraz
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), École Normale Supérieure, CNRS, INSERM, Université PSL, Paris 75005, France
| | - Pierre Paoletti
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), École Normale Supérieure, CNRS, INSERM, Université PSL, Paris 75005, France
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Lewandowski SL, Cardone RL, Foster HR, Ho T, Potapenko E, Poudel C, VanDeusen HR, Sdao SM, Alves TC, Zhao X, Capozzi ME, de Souza AH, Jahan I, Thomas CJ, Nunemaker CS, Davis DB, Campbell JE, Kibbey RG, Merrins MJ. Pyruvate Kinase Controls Signal Strength in the Insulin Secretory Pathway. Cell Metab 2020; 32:736-750.e5. [PMID: 33147484 PMCID: PMC7685238 DOI: 10.1016/j.cmet.2020.10.007] [Citation(s) in RCA: 85] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 06/30/2020] [Accepted: 10/09/2020] [Indexed: 12/14/2022]
Abstract
Pancreatic β cells couple nutrient metabolism with appropriate insulin secretion. Here, we show that pyruvate kinase (PK), which converts ADP and phosphoenolpyruvate (PEP) into ATP and pyruvate, underlies β cell sensing of both glycolytic and mitochondrial fuels. Plasma membrane-localized PK is sufficient to close KATP channels and initiate calcium influx. Small-molecule PK activators increase the frequency of ATP/ADP and calcium oscillations and potently amplify insulin secretion. PK restricts respiration by cyclically depriving mitochondria of ADP, which accelerates PEP cycling until membrane depolarization restores ADP and oxidative phosphorylation. Our findings support a compartmentalized model of β cell metabolism in which PK locally generates the ATP/ADP required for insulin secretion. Oscillatory PK activity allows mitochondria to perform synthetic and oxidative functions without any net impact on glucose oxidation. These findings suggest a potential therapeutic route for diabetes based on PK activation that would not be predicted by the current consensus single-state model of β cell function.
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Affiliation(s)
- Sophie L Lewandowski
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Rebecca L Cardone
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Hannah R Foster
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Thuong Ho
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Evgeniy Potapenko
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Chetan Poudel
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Halena R VanDeusen
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Sophia M Sdao
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Tiago C Alves
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Xiaojian Zhao
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Megan E Capozzi
- Duke Molecular Physiology Institute, Duke University, Durham, NC 27701, USA
| | - Arnaldo H de Souza
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Ishrat Jahan
- Department of Biomedical Sciences, Ohio University, Athens, OH 45701, USA
| | - Craig J Thomas
- National Center for Advancing Translational Sciences, Rockville, MD 20850, USA
| | - Craig S Nunemaker
- Department of Biomedical Sciences, Ohio University, Athens, OH 45701, USA
| | - Dawn Belt Davis
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA
| | | | - Richard G Kibbey
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA; Department of Cellular & Molecular Physiology, Yale University, New Haven, CT 06520, USA.
| | - Matthew J Merrins
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism, University of Wisconsin-Madison, Madison, WI 53705, USA; William S. Middleton Memorial Veterans Hospital, Madison, WI 53705, USA.
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Abstract
Light has been instrumental in the study of living cells since its use helped in their discovery in the late 17th century. Further, combining chemical technology with light microscopy was an essential part of the Nobel Prize for Physiology in 1906. Such landmark scientific findings involved passive observation of cells. However, over the past 50 years, a "second use" of light has emerged in cell physiology, namely one of rational control. The seminal method for this emerged in late 1970s with the invention of caged compounds. This was the point when "caged compounds" were defined as optical probes in which the active functionality of a physiological signaling molecule was blocked with a photochemical protecting group. Caged compounds are analogous to prodrugs; in both, the activity of the effector is latent. However, caged compounds, unlike prodrugs, use a trigger that confers the power of full temporal and spatial manipulation of the effects of release of its latent biological cargo. Light is distinct because it is bio-orthogonal, passes through living tissue (even into the cell interior), and initiates rapid release of the "caged" biomolecule. Further, because light can be directed to broad areas or focused to small points, caged compounds offer an array of timing scenarios for physiologists to dissect virtually any type of cellular process.The collaborative interaction between chemists and physiologists plays a fundamental role in the development of caged compounds. First, the physiologists must define the problem to be addressed; then, with the help of chemists, decide if a caged compound would be useful. For this, structure-activity relationships of the potential optical probe and receptor must be determined. If rational targets seem feasible, synthetic organic chemistry is used to make the caged compound. The crucial property of prephotolysis bio-inertness relies on physiological or biochemical assays. Second, detailed optical characterization of the caged compound requires the skill of photochemists because the rate and efficiency of uncaging are also crucial properties for a useful caged compound. Often, these studies reveal limitations in the caged compound which has been developed; thus, chemists and physiologists use their abilities for iterative development of even more powerful optical probes. A similar dynamic will be familiar to scientists in the pharmaceutical industry. Therefore, caged compound development provides an excellent training framework for (young) chemists both intellectually and professionally. In this Account, I draw on my long experience in the field of making useful caged compounds for cell physiology by showing how each probe I have developed has been defined by an important physiological problem. Fundamental to this process has been my initial training by the pioneers in aromatic photochemistry, Derek Bryce-Smith and Andrew Gilbert. I discuss making a range of "caged calcium" probes, ones which went on to be the most widely used of all caged compounds. Then, I describe the development of caged neurotransmitters for two-photon uncaging microscopy. Finally, I survey recent work on making new photochemical protecting groups for wavelength orthogonal, two-color, and ultraefficient two-photon uncaging.
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Affiliation(s)
- Graham C R Ellis-Davies
- Department of Neuroscience, Mount Sinai School of Medicine, New York, New York 10029, United States
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9
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Kahancová A, Sklenář F, Ježek P, Dlasková A. Regulation of glucose-stimulated insulin secretion by ATPase Inhibitory Factor 1 (IF1). FEBS Lett 2018; 592:999-1009. [PMID: 29380352 DOI: 10.1002/1873-3468.12991] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 01/16/2018] [Accepted: 01/22/2018] [Indexed: 12/13/2022]
Abstract
ATPase Inhibitory factor 1 (IF1) is an endogenous regulator of mitochondrial ATP synthase, which is involved in cellular metabolism. Although great progress has been made, biological roles of IF1 and molecular mechanisms of its action are still to be elucidated. Here, we show that IF1 is present in pancreatic β-cells, bound to the ATP synthase also under normal physiological conditions. IF1 silencing in model pancreatic β-cells (INS-1E) increases insulin secretion over a range of glucose concentrations. The left-shifted dose-response curve reveals excessive insulin secretion even under low glucose, corresponding to fasting conditions. A parallel increase in cellular respiration and ATP levels is observed. To conclude, our results indicate that IF1 is a negative regulator of insulin secretion involved in pancreatic β-cell glucose sensing.
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Affiliation(s)
- Anežka Kahancová
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Filip Sklenář
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Petr Ježek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Andrea Dlasková
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
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10
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Kukushkin NV. Taking memory beyond the brain: Does tobacco dream of the mosaic virus? Neurobiol Learn Mem 2018; 153:111-116. [PMID: 29396326 DOI: 10.1016/j.nlm.2018.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 01/05/2018] [Accepted: 01/21/2018] [Indexed: 10/18/2022]
Abstract
Memory is typically defined through animal behavior, but this point of view may limit our understanding of many related processes in diverse biological systems. The concept of memory can be broadened meaningfully by considering it from the perspective of time and homeostasis. On the one hand, this theoretical angle can help explain and predict the behavior of various non-neural systems such as insulin-secreting cells, plants, or signaling cascades. On the other hand, it emphasizes biological continuity between neural phenomena, such as synaptic plasticity, and their evolutionary precursors in cellular signaling.
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Affiliation(s)
- Nikolay V Kukushkin
- Center for Neural Science, New York University, 4 Washington Pl, New York, NY 10003, USA.
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11
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Rorsman P, Ashcroft FM. Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men. Physiol Rev 2018; 98:117-214. [PMID: 29212789 PMCID: PMC5866358 DOI: 10.1152/physrev.00008.2017] [Citation(s) in RCA: 456] [Impact Index Per Article: 76.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 05/30/2017] [Accepted: 06/18/2017] [Indexed: 12/14/2022] Open
Abstract
The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca2+ concentration and initiation of Ca2+-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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12
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Fong R, Khokhar S, Chowdhury AN, Xie KG, Wong JHY, Fox AP, Xie Z. Caffeine accelerates recovery from general anesthesia via multiple pathways. J Neurophysiol 2017; 118:1591-1597. [PMID: 28659466 PMCID: PMC5596131 DOI: 10.1152/jn.00393.2017] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 06/22/2017] [Accepted: 06/22/2017] [Indexed: 12/19/2022] Open
Abstract
Various studies have explored different ways to speed emergence from anesthesia. Previously, we have shown that three drugs that elevate intracellular cAMP (forskolin, theophylline, and caffeine) accelerate emergence from anesthesia in rats. However, our earlier studies left two main questions unanswered. First, were cAMP-elevating drugs effective at all anesthetic concentrations? Second, given that caffeine was the most effective of the drugs tested, why was caffeine more effective than forskolin since both drugs elevate cAMP? In our current study, emergence time from anesthesia was measured in adult rats exposed to 3% isoflurane for 60 min. Caffeine dramatically accelerated emergence from anesthesia, even at the high level of anesthetic employed. Caffeine has multiple actions including blockade of adenosine receptors. We show that the selective A2a adenosine receptor antagonist preladenant or the intracellular cAMP ([cAMP]i)-elevating drug forskolin, accelerated recovery from anesthesia. When preladenant and forskolin were tested together, the effect on anesthesia recovery time was additive indicating that these drugs operate via different pathways. Furthermore, the combination of preladenant and forskolin was about as effective as caffeine suggesting that both A2A receptor blockade and [cAMP]i elevation play a role in caffeine's ability to accelerate emergence from anesthesia. Because anesthesia in rodents is thought to be similar to that in humans, these results suggest that caffeine might allow for rapid and uniform emergence from general anesthesia in humans at all anesthetic concentrations and that both the elevation of [cAMP]i and adenosine receptor blockade play a role in this response.NEW & NOTEWORTHY Currently, there is no method to accelerate emergence from anesthesia. Patients "wake" when they clear the anesthetic from their systems. Previously, we have shown that caffeine can accelerate emergence from anesthesia. In this study, we show that caffeine is effective even at high levels of anesthetic. We also show that caffeine operates by both elevating intracellular cAMP levels and by blocking adenosine receptors. This complicated pharmacology makes caffeine especially effective in accelerating emergence from anesthesia.
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Affiliation(s)
- Robert Fong
- Department of Anesthesia and Critical Care, The University of Chicago, Chicago, Illinois
| | - Suhail Khokhar
- College of Medicine, University of Illinois, School of Life Sciences, Chicago, Illinois
| | - Atif N Chowdhury
- Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts
| | - Kelvin G Xie
- School of Engineering and Applied Science, Washington University, St Louis, Missouri
| | | | - Aaron P Fox
- Department of Neurobiology, Pharmacology and Physiology, The University of Chicago, Chicago, Illinois
| | - Zheng Xie
- Department of Anesthesia and Critical Care, The University of Chicago, Chicago, Illinois;
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13
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Abstract
Pancreatic islet β cells secrete insulin in response to nutrient secretagogues, like glucose, dependent on calcium influx and nutrient metabolism. One of the most intriguing qualities of β cells is their ability to use metabolism to amplify the amount of secreted insulin independent of further alterations in intracellular calcium. Many years studying this amplifying process have shaped our current understanding of β cell stimulus-secretion coupling; yet, the exact mechanisms of amplification have been elusive. Recent studies utilizing metabolomics, computational modeling, and animal models have progressed our understanding of the metabolic amplifying pathway of insulin secretion from the β cell. New approaches will be discussed which offer in-roads to a more complete model of β cell function. The development of β cell therapeutics may be aided by such a model, facilitating the targeting of aspects of the metabolic amplifying pathway which are unique to the β cell.
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Affiliation(s)
- Michael A Kalwat
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, United States.
| | - Melanie H Cobb
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, United States
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14
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Eliasson L, Esguerra JLS, Wendt A. Lessons from basic pancreatic beta cell research in type-2 diabetes and vascular complications. Diabetol Int 2017; 8:139-152. [PMID: 30603317 DOI: 10.1007/s13340-017-0304-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 01/08/2017] [Indexed: 12/14/2022]
Abstract
The changes in life-style with increased access of food and reduced physical activity have resulted in the global epidemic of obesity. Consequently, individuals with type 2 diabetes and cardiovascular disease have also escalated. A central organ in the development of diabetes is the pancreas, and more specifically the pancreatic beta cells within the islets of Langerhans. Beta cells have been assigned the important task of secreting insulin when blood glucose is increased to lower the glucose level. An early sign of diabetes pathogenesis is lack of first phase insulin response and reduced second phase secretion. In this review, which is based on the foreign investigator award lecture given at the JSDC meeting in Sendai in October 2016, we discuss a possible cellular explanation for the reduced first phase insulin response and how this can be influenced by lipids. Moreover, since patients with cardiovascular disease and high levels of cholesterol are often treated with statins, we summarize recent data regarding effects on statins on glucose homeostasis and insulin secretion. Finally, we suggest microRNAs (miRNAs) as central players in the adjustment of beta cell function during the development of diabetes. We specifically discuss miRNAs regarding their involvement in insulin secretion regulation, differential expression in type 2 diabetes, and potential as biomarkers for prediction of diabetes and cardiovascular complications.
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Affiliation(s)
- Lena Eliasson
- Islet Cell Exocytosis, Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Lund University, Clinical Research Centre, SUS 91-11, Box 50332, 202 13 Malmö, Sweden
| | - Jonathan Lou S Esguerra
- Islet Cell Exocytosis, Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Lund University, Clinical Research Centre, SUS 91-11, Box 50332, 202 13 Malmö, Sweden
| | - Anna Wendt
- Islet Cell Exocytosis, Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Lund University, Clinical Research Centre, SUS 91-11, Box 50332, 202 13 Malmö, Sweden
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15
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Mitochondrial Calcium Handling in Physiology and Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 982:25-47. [PMID: 28551780 DOI: 10.1007/978-3-319-55330-6_2] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Calcium (Ca2+) accumulation inside mitochondria represents a pleiotropic signal controlling a wide range of cellular functions, including key metabolic pathways and life/death decisions. This phenomenon has been first described in the 1960s, but the identity of the molecules controlling this process remained a mystery until just few years ago, when both mitochondrial Ca2+ uptake and release systems were genetically dissected. This finally opened the possibility to develop genetic models to directly test the contribution of mitochondrial Ca2+ homeostasis to cellular functions. Here we summarize our current understanding of the molecular machinery that controls mitochondrial Ca2+ handling and critically evaluate the physiopathological role of mitochondrial Ca2+ signaling, based on recent evidences obtained through in vitro and in vivo models.
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16
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Ferdaoussi M, MacDonald PE. Toward Connecting Metabolism to the Exocytotic Site. Trends Cell Biol 2016; 27:163-171. [PMID: 27932063 DOI: 10.1016/j.tcb.2016.10.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 10/28/2016] [Accepted: 10/31/2016] [Indexed: 12/14/2022]
Abstract
Within cells the regulated exocytosis of secretory granules controls multiple physiological functions, including endocrine hormone secretion. Release of the glucose-regulating hormone insulin from pancreatic islet β cells is critical for whole-body metabolic homeostasis. Impaired insulin secretion appears early in the progression to type 2 diabetes (T2D). Key mechanisms that control the β-cell exocytotic response, mediating the long-known but little understood metabolic amplification of insulin secretion, are becoming clearer. Recent insights indicate a convergence of metabolism-driven signals, such as lipid-derived messengers and redox-dependent deSUMOylation, at the plasma membrane to augment Ca2+-dependent insulin exocytosis. These pathways have important implications for the metabolic control of hormone secretion, for the functional compensation that occurs in obesity, and for impaired insulin secretion in diabetes.
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Affiliation(s)
- Mourad Ferdaoussi
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada T6G 2E1
| | - Patrick E MacDonald
- Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada T6G 2E1.
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17
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Type II PKAs are anchored to mature insulin secretory granules in INS-1 β-cells and required for cAMP-dependent potentiation of exocytosis. Biochimie 2016; 125:32-41. [PMID: 26898328 DOI: 10.1016/j.biochi.2016.02.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 02/13/2016] [Indexed: 11/23/2022]
Abstract
Specificity of the cAMP-dependent protein kinase (PKA) pathway relies on an extremely sophisticated compartmentalization mechanism of the kinase within a given cell, based on high-affinity binding of PKA tetramer pools to different A-Kinase Anchoring Proteins (AKAPs). We and others have previously shown that AKAPs-dependent PKA subcellular targeting is a requisite for optimal cAMP-dependent potentiation of insulin exocytosis. We thus hypothesized that a PKA pool may directly anchor to the secretory compartment to potentiate insulin exocytosis. Here, using immunofluorescence analyses combined to subcellular fractionations and purification of insulin secretory granules (ISGs), we identified discrete subpools of type II PKAs, RIIα and RIIβ PKAs, along with the catalytic subunit, physically associated with ISGs within pancreatic insulin-secreting β-cells. Ultrastructural analysis of native rodent β-cells confirmed in vivo the occurrence of PKA on dense-core ISGs. Isoform-selective disruption of binding of PKAs to AKAPs reinforced the requirement of type II PKA isoforms for cAMP potentiation of insulin exocytosis. This granular localization of PKA was of critical importance since siRNA-mediated depletion of either RIIα or RIIβ PKAs resulted in a significant reduction of cAMP-dependent potentiation of insulin release. The present work provides evidence for a previously unrecognized pool of type II PKAs physically anchored to the β-cell ISGs compartment and supports a non-redundant function for type II PKAs during cAMP potentiation of exocytosis.
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18
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Castiello FR, Heileman K, Tabrizian M. Microfluidic perfusion systems for secretion fingerprint analysis of pancreatic islets: applications, challenges and opportunities. LAB ON A CHIP 2016; 16:409-31. [PMID: 26732665 DOI: 10.1039/c5lc01046b] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
A secretome signature is a heterogeneous profile of secretions present in a single cell type. From the secretome signature a smaller panel of proteins, namely a secretion fingerprint, can be chosen to feasibly monitor specific cellular activity. Based on a thorough appraisal of the literature, this review explores the possibility of defining and using a secretion fingerprint to gauge the functionality of pancreatic islets of Langerhans. It covers the state of the art regarding microfluidic perfusion systems used in pancreatic islet research. Candidate analytical tools to be integrated within microfluidic perfusion systems for dynamic secretory fingerprint monitoring were identified. These analytical tools include patch clamp, amperometry/voltametry, impedance spectroscopy, field effect transistors and surface plasmon resonance. Coupled with these tools, microfluidic devices can ultimately find applications in determining islet quality for transplantation, islet regeneration and drug screening of therapeutic agents for the treatment of diabetes.
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Affiliation(s)
- F Rafael Castiello
- Biomedical Engineering Department, McGill University, Montreal, QC H3A 2B4, Canada.
| | - Khalil Heileman
- Biomedical Engineering Department, McGill University, Montreal, QC H3A 2B4, Canada.
| | - Maryam Tabrizian
- Biomedical Engineering Department, McGill University, Montreal, QC H3A 2B4, Canada.
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19
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Pizarro-Delgado J, Deeney JT, Martín-del-Río R, Corkey BE, Tamarit-Rodriguez J. KCl -Permeabilized Pancreatic Islets: An Experimental Model to Explore the Messenger Role of ATP in the Mechanism of Insulin Secretion. PLoS One 2015; 10:e0140096. [PMID: 26444014 PMCID: PMC4596849 DOI: 10.1371/journal.pone.0140096] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 09/22/2015] [Indexed: 11/18/2022] Open
Abstract
Our previous work has demonstrated that islet depolarization with KCl opens connexin36 hemichannels in β-cells of mouse pancreatic islets allowing the exchange of small metabolites with the extracellular medium. In this study, the opening of these hemichannels has been further characterized in rat islets and INS-1 cells. Taking advantage of hemicannels'opening, the uptake of extracellular ATP and its effect on insulin release were investigated. 70 mM KCl stimulated light emission by luciferin in dispersed rat islets cells transduced with the fire-fly luciferase gene: it was suppressed by 20 mM glucose and 50 μM mefloquine, a specific connexin36 inhibitor. Extracellular ATP was taken up or released by islets depolarized with 70 mM KCl at 5 mM glucose, depending on the external ATP concentration. 1 mM ATP restored the loss of ATP induced by the depolarization itself. ATP concentrations above 5 mM increased islet ATP content and the ATP/ADP ratio. No ATP uptake occurred in non-depolarized or KCl-depolarized islets simultaneously incubated with 50 μM mefloquine or 20 mM glucose. Extracellular ATP potentiated the secretory response induced by 70 mM KCl at 5 mM glucose in perifused rat islets: 5 mM ATP triggered a second phase of insulin release after the initial peak triggered by KCl-depolarization itself; at 10 mM, it increased both the initial, KCl-dependent, peak and stimulated a greater second phase of secretion than at 5 mM. These stimulatory effects of extracellular ATP were almost completely suppressed by 50 μM mefloquine. The magnitude of the second phase of insulin release due to 5 mM extracellular ATP was decreased by addition of 5 mM ADP (extracellular ATP/ADP ratio = 1). ATP acts independently of KATP channels closure and its intracellular concentration and its ATP/ADP ratio seems to regulate the magnitude of both the first (triggering) and second (amplifying) phases of glucose-induced insulin secretion.
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Affiliation(s)
| | - Jude T. Deeney
- Obesity Research Center, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America
| | | | - Barbara E. Corkey
- Obesity Research Center, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America
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20
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Schwede F, Chepurny OG, Kaufholz M, Bertinetti D, Leech CA, Cabrera O, Zhu Y, Mei F, Cheng X, Manning Fox JE, MacDonald PE, Genieser HG, Herberg FW, Holz GG. Rp-cAMPS Prodrugs Reveal the cAMP Dependence of First-Phase Glucose-Stimulated Insulin Secretion. Mol Endocrinol 2015; 29:988-1005. [PMID: 26061564 DOI: 10.1210/me.2014-1330] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
cAMP-elevating agents such as the incretin hormone glucagon-like peptide-1 potentiate glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. However, a debate has existed since the 1970s concerning whether or not cAMP signaling is essential for glucose alone to stimulate insulin secretion. Here, we report that the first-phase kinetic component of GSIS is cAMP-dependent, as revealed through the use of a novel highly membrane permeable para-acetoxybenzyl (pAB) ester prodrug that is a bioactivatable derivative of the cAMP antagonist adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS). In dynamic perifusion assays of human or rat islets, a step-wise increase of glucose concentration leads to biphasic insulin secretion, and under these conditions, 8-bromoadenosine-3',5'-cyclic monophosphorothioate, Rp-isomer, 4-acetoxybenzyl ester (Rp-8-Br-cAMPS-pAB) inhibits first-phase GSIS by up to 80%. Surprisingly, second-phase GSIS is inhibited to a much smaller extent (≤20%). Using luciferase, fluorescence resonance energy transfer, and bioluminescence resonance energy transfer assays performed in living cells, we validate that Rp-8-Br-cAMPS-pAB does in fact block cAMP-dependent protein kinase activation. Novel effects of Rp-8-Br-cAMPS-pAB to block the activation of cAMP-regulated guanine nucleotide exchange factors (Epac1, Epac2) are also validated using genetically encoded Epac biosensors, and are independently confirmed in an in vitro Rap1 activation assay using Rp-cAMPS and Rp-8-Br-cAMPS. Thus, in addition to revealing the cAMP dependence of first-phase GSIS from human and rat islets, these findings establish a pAB-based chemistry for the synthesis of highly membrane permeable prodrug derivatives of Rp-cAMPS that act with micromolar or even nanomolar potency to inhibit cAMP signaling in living cells.
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Affiliation(s)
- Frank Schwede
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Oleg G Chepurny
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Melanie Kaufholz
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Daniela Bertinetti
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Colin A Leech
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Over Cabrera
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Yingmin Zhu
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Fang Mei
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Xiaodong Cheng
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Jocelyn E Manning Fox
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Patrick E MacDonald
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Hans-G Genieser
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - Friedrich W Herberg
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
| | - George G Holz
- BIOLOG Life Science Institute (F.S., H.-G.G.), 28199 Bremen, Germany; Departments of Medicine (O.G.C., C.A.L., G.G.H.) and Pharmacology (G.G.H.), State University of New York, Upstate Medical University, Syracuse, New York 13210; Department of Biochemistry (M.K., D.B., F.W.H.), University of Kassel, 34132 Kassel, Germany; Eli Lilly and Company (O.C.), Indianapolis, Indiana 46225; Department of Integrative Biology and Pharmacology (Y.Z., F.M., X.C.), Texas Therapeutics Institute, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, Texas 77030; Department of Pharmacology and the Alberta Diabetes Institute (J.E.M.F., P.E.M.), University of Alberta, Edmonton, Canada AB T6G 2E1
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21
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Schumacher K, Matz M, Brüning D, Baumann K, Rustenbeck I. Granule mobility, fusion frequency and insulin secretion are differentially affected by insulinotropic stimuli. Traffic 2015; 16:493-509. [PMID: 25615411 DOI: 10.1111/tra.12261] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 01/05/2015] [Accepted: 01/09/2015] [Indexed: 01/01/2023]
Abstract
The pre-exocytotic behavior of insulin granules was studied against the background of the entirety of submembrane granules in MIN6 cells, and the characteristics were compared with the macroscopic secretion pattern and the cytosolic Ca(2+) concentration of MIN6 pseudo-islets at 22°C, 32°C and 37°C. The mobility of granules labeled by insulin-EGFP and the fusion events were assessed by TIRF microscopy utilizing an observer-independent algorithm. In the z-dimension, 40 mm K(+) or 30 mm glucose increased the granule turnover. The effect of high K(+) was quickly reversible. The increase by glucose was more sustained and modified the efficacy of a subsequent K(+) stimulus. The effect size of glucose increased with physiological temperature whereas that of high K(+) did not. The mobility in the x/y-dimension and the fusion rates were little affected by the stimuli, in contrast to secretion. Fusion and secretion, however, had the same temperature dependence. Granules that appeared and fused within one image sequence had significantly larger caging diameters than pre-existent granules that underwent fusion. These in turn had a different mobility than residence-matched non-fusing granules. In conclusion, delivery to the membrane, tethering and fusion of granules are differently affected by insulinotropic stimuli. Fusion rates and secretion do not appear to be tightly coupled.
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Affiliation(s)
- Kirstin Schumacher
- Institute of Pharmacology and Toxicology, University of Braunschweig, Braunschweig, Germany
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22
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Hendricks BK, Shi R. Mechanisms of neuronal membrane sealing following mechanical trauma. Neurosci Bull 2014; 30:627-44. [PMID: 24993771 DOI: 10.1007/s12264-013-1446-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Accepted: 09/20/2013] [Indexed: 12/11/2022] Open
Abstract
Membrane integrity is crucial for maintaining the intricate signaling and chemically-isolated intracellular environment of neurons; disruption risks deleterious effects, such as unregulated ionic flux, neuronal apoptosis, and oxidative radical damage as observed in spinal cord injury and traumatic brain injury. This paper, in addition to a discussion of the current understanding of cellular tactics to seal membranes, describes two major factors involved in membrane repair. These are line tension, the hydrophobic attractive force between two lipid free-edges, and membrane tension, the rigidity of the lipid bilayer with respect to the tethered cortical cytoskeleton. Ca(2+), a major mechanistic trigger for repair processes, increases following flux through a membrane injury site, and activates phospholipase enzymes, calpain-mediated cortical cytoskeletal proteolysis, protein kinase cascades, and lipid bilayer microdomain modification. The membrane tension appears to be largely modulated through vesicle dynamics, cytoskeletal organization, membrane curvature, and phospholipase manipulation. Dehydration of the phospholipid gap edge and modification of membrane packaging, as in temperature variation, experimentally impact line tension. Due to the time-sensitive nature of axonal sealing, increasing the efficacy of axolemmal sealing through therapeutic modification would be of great clinical value, to deter secondary neurodegenerative effects. Better therapeutic enhancement of membrane sealing requires a complete understanding of its intricate underlying neuronal mechanism.
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Affiliation(s)
- Benjamin K Hendricks
- Department of Basic Medical Sciences, College of Veterinary Medicine, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA
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23
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Holz GG, Leech CA, Chepurny OG. New insights concerning the molecular basis for defective glucoregulation in soluble adenylyl cyclase knockout mice. Biochim Biophys Acta Mol Basis Dis 2014; 1842:2593-600. [PMID: 24980705 DOI: 10.1016/j.bbadis.2014.06.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 06/17/2014] [Accepted: 06/18/2014] [Indexed: 01/09/2023]
Abstract
Recently published findings indicate that a knockout (KO) of soluble adenylyl cyclase (sAC, also known as AC-10) gene expression in mice leads to defective glucoregulation that is characterized by reduced pancreatic insulin secretion and reduced intraperitoneal glucose tolerance. Summarized here are current concepts regarding the molecular basis for this phenotype, with special emphasis on the potential role of sAC as a determinant of glucose-stimulated insulin secretion. Highlighted is new evidence that in pancreatic beta cells, oxidative glucose metabolism stimulates mitochondrial CO₂production that in turn generates bicarbonate ion (HCO(3)(-)). Since HCO(3)(-) binds to and directly stimulates the activity of sAC, we propose that glucose-stimulated cAMP production in beta cells is mediated not simply by transmembrane adenylyl cyclases (TMACs), but also by sAC. Based on evidence that sAC is expressed in mitochondria, there exists the possibility that beta-cell glucose metabolism is linked to mitochondrial cAMP production with consequent facilitation of oxidative phosphorylation. Since sAC is also expressed in the cytoplasm, sAC catalyzed cAMP production may activate cAMP sensors such as PKA and Epac2 to control ion channel function, intracellular Ca²⁺ handling, and Ca²⁺-dependent exocytosis. Thus, we propose that the existence of sAC in beta cells provides a new and unexpected explanation for previously reported actions of glucose metabolism to stimulate cAMP production. It seems possible that alterations of sAC activity might be of importance when evaluating new strategies for the treatment of type 2 diabetes (T2DM), or when evaluating why glucose metabolism fails to stimulate insulin secretion in patients diagnosed with T2DM. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.
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Affiliation(s)
- George G Holz
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA; Department of Pharmacology, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA.
| | - Colin A Leech
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA
| | - Oleg G Chepurny
- Department of Medicine, State University of New York (SUNY), Upstate Medical University, Syracuse, NY 13210, USA
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24
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Wang Q, Fong R, Mason P, Fox AP, Xie Z. Caffeine accelerates recovery from general anesthesia. J Neurophysiol 2014; 111:1331-40. [PMID: 24375022 PMCID: PMC3949308 DOI: 10.1152/jn.00792.2013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Accepted: 12/26/2013] [Indexed: 11/22/2022] Open
Abstract
General anesthetics inhibit neurotransmitter release from both neurons and secretory cells. If inhibition of neurotransmitter release is part of an anesthetic mechanism of action, then drugs that facilitate neurotransmitter release may aid in reversing general anesthesia. Drugs that elevate intracellular cAMP levels are known to facilitate neurotransmitter release. Three cAMP elevating drugs (forskolin, theophylline, and caffeine) were tested; all three drugs reversed the inhibition of neurotransmitter release produced by isoflurane in PC12 cells in vitro. The drugs were tested in isoflurane-anesthetized rats. Animals were injected with either saline or saline containing drug. All three drugs dramatically accelerated recovery from isoflurane anesthesia, but caffeine was most effective. None of the drugs, at the concentrations tested, had significant effects on breathing rates, O2 saturation, heart rate, or blood pressure in anesthetized animals. Caffeine alone was tested on propofol-anesthetized rats where it dramatically accelerated recovery from anesthesia. The ability of caffeine to accelerate recovery from anesthesia for different chemical classes of anesthetics, isoflurane and propofol, opens the possibility that it will do so for all commonly used general anesthetics, although additional studies will be required to determine whether this is in fact the case. Because anesthesia in rodents is thought to be similar to that in humans, these results suggest that caffeine might allow for rapid and uniform emergence from general anesthesia in human patients.
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Affiliation(s)
- Qiang Wang
- Department of Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, Illinois
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Abstract
Mathematical modeling of the electrical activity of the pancreatic β-cell has been extremely important for understanding the cellular mechanisms involved in glucose-stimulated insulin secretion. Several models have been proposed over the last 30 y, growing in complexity as experimental evidence of the cellular mechanisms involved has become available. Almost all the models have been developed based on experimental data from rodents. However, given the many important differences between species, models of human β-cells have recently been developed. This review summarizes how modeling of β-cells has evolved, highlighting the proposed physiological mechanisms underlying β-cell electrical activity.
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Key Words
- ADP, adenosine diphosphate
- ATP, adenosine triphosphate
- CK, Chay-Keizer
- CRAC, calcium release-activated current
- Ca2+, calcium ions
- DOM, dual oscillator model
- ER, endoplasmic reticulum
- F6P, fructose-6-phosphate
- FBP, fructose-1,6-bisphosphate
- GLUT, glucose transporter
- GSIS, glucose-stimulated insulin secretion
- HERG, human eter à-go-go related gene
- IP3R, inositol-1,4,5-trisphosphate receptors
- KATP, ATP-sensitive K+ channels
- KCa, Ca2+-dependent K+ channels
- Kv, voltage-dependent K+ channels
- MCU, mitochondrial Ca2+ uniporter
- NCX, Na+/Ca2+ exchanger
- PFK, phosphofructokinase
- PMCA, plasma membrane Ca2+-ATPase
- ROS, reactive oxygen species
- RyR, ryanodine receptors
- SERCA, sarco-endoplasmic reticulum Ca2+-ATPase
- T2D, Type 2 Diabetes
- TCA, trycarboxylic acid cycle
- TRP, transient receptor potential
- VDCC, voltage-dependent Ca2+ channels
- Vm, membrane potential
- [ATP]i, cytosolic ATP
- [Ca2+]i, intracellular calcium concentration
- [Ca2+]m, mitochondrial calcium
- [Na+], Na+ concentration
- action potentials
- bursting
- cAMP, cyclic AMP
- calcium
- electrical activity
- ion channels
- mNCX, mitochondrial Na+/Ca2+ exchanger
- mathematical model
- β-cell
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Affiliation(s)
- Gerardo J Félix-Martínez
- Department of Electrical Engineering; Universidad
Autónoma Metropolitana-Iztapalapa; México, DF,
México
- Correspondence to: Gerardo J
Félix-Martínez;
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26
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Guay C, Joly É, Pepin É, Barbeau A, Hentsch L, Pineda M, Madiraju SRM, Brunengraber H, Prentki M. A role for cytosolic isocitrate dehydrogenase as a negative regulator of glucose signaling for insulin secretion in pancreatic ß-cells. PLoS One 2013; 8:e77097. [PMID: 24130841 PMCID: PMC3795013 DOI: 10.1371/journal.pone.0077097] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 08/30/2013] [Indexed: 01/24/2023] Open
Abstract
Cytosolic NADPH may act as one of the signals that couple glucose metabolism to insulin secretion in the pancreatic ß-cell. NADPH levels in the cytoplasm are largely controlled by the cytosolic isoforms of malic enzyme and isocitrate dehydrogenase (IDHc). Some studies have provided evidence for a role of malic enzyme in glucose-induced insulin secretion (GIIS) via pyruvate cycling, but the role of IDHc in ß-cell signaling is unsettled. IDHc is an established component of the isocitrate/α-ketoglutarate shuttle that transfers reducing equivalents (NADPH) from the mitochondrion to the cytosol. This shuttle is energy consuming since it is coupled to nicotinamide nucleotide transhydrogenase that uses the mitochondrial proton gradient to produce mitochondrial NADPH and NAD(+) from NADP(+) and NADH. To determine whether flux through IDHc is positively or negatively linked to GIIS, we performed RNAi knockdown experiments in ß-cells. Reduced IDHc expression in INS 832/13 cells and isolated rat islet ß-cells resulted in enhanced GIIS. This effect was mediated at least in part via the KATP-independent amplification arm of GIIS. IDHc knockdown in INS 832/13 cells did not alter glucose oxidation but it reduced fatty acid oxidation and increased lipogenesis from glucose. Metabolome profiling in INS 832/13 cells showed that IDHc knockdown increased isocitrate and NADP(+) levels. It also increased the cellular contents of several metabolites linked to GIIS, in particular some Krebs cycle intermediates, acetyl-CoA, glutamate, cAMP and ATP. The results identify IDHc as a component of the emerging pathways that negatively regulate GIIS.
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Affiliation(s)
- Claudiane Guay
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Érik Joly
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Émilie Pepin
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Annie Barbeau
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Lisa Hentsch
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Marco Pineda
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - S. R. Murthy Madiraju
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
| | - Henri Brunengraber
- Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, Ohio, United State of America
| | - Marc Prentki
- Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada
- Departments of Nutrition and Biochemistry, University of Montreal, Montreal, Quebec, Canada
- * E-mail:
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27
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Abstract
The pancreatic islet β cell senses circulating levels of calorigenic nutrients to secrete insulin according to the needs of the organism. Altered insulin secretion is linked to various disorders such as diabetes, hypoglycemic states, and cardiometabolic diseases. Fuel stimuli, including glucose, free fatty acids, and amino acids, promote insulin granule exocytosis primarily via their metabolism in β cells and the production of key signaling metabolites. This paper reviews our current knowledge of the pathways involved in both positive and negative metabolic signaling for insulin secretion and assesses the role of established and candidate metabolic coupling factors, keeping recent developments in focus.
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Affiliation(s)
- Marc Prentki
- Molecular Nutrition Unit, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, QC, Canada.
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28
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Li J, Shuai HY, Gylfe E, Tengholm A. Oscillations of sub-membrane ATP in glucose-stimulated beta cells depend on negative feedback from Ca(2+). Diabetologia 2013; 56:1577-86. [PMID: 23536115 PMCID: PMC3671113 DOI: 10.1007/s00125-013-2894-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Accepted: 03/04/2013] [Indexed: 10/27/2022]
Abstract
AIMS/HYPOTHESIS ATP links changes in glucose metabolism to electrical activity, Ca(2+) signalling and insulin secretion in pancreatic beta cells. There is evidence that beta cell metabolism oscillates, but little is known about ATP dynamics at the plasma membrane, where regulation of ion channels and exocytosis occur. METHODS The sub-plasma-membrane ATP concentration ([ATP]pm) was recorded in beta cells in intact mouse and human islets using total internal reflection microscopy and the fluorescent reporter Perceval. RESULTS Glucose dose-dependently increased [ATP]pm with half-maximal and maximal effects at 5.2 and 9 mmol/l, respectively. Additional elevations of glucose to 11 to 20 mmol/l promoted pronounced [ATP]pm oscillations that were synchronised between neighbouring beta cells. [ATP]pm increased further and the oscillations disappeared when voltage-dependent Ca(2+) influx was prevented. In contrast, K(+)-depolarisation induced prompt lowering of [ATP]pm. Simultaneous recordings of [ATP]pm and the sub-plasma-membrane Ca(2+) concentration ([Ca(2+)]pm) during the early glucose-induced response revealed that the initial [ATP]pm elevation preceded, and was temporarily interrupted by the rise of [Ca(2+)]pm. During subsequent glucose-induced oscillations, the increases of [Ca(2+)]pm correlated with lowering of [ATP]pm. CONCLUSIONS/INTERPRETATION In beta cells, glucose promotes pronounced oscillations of [ATP]pm, which depend on negative feedback from Ca(2+) . The bidirectional interplay between these messengers in the sub-membrane space generates the metabolic and ionic oscillations that underlie pulsatile insulin secretion.
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Affiliation(s)
- J. Li
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - H. Y. Shuai
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - E. Gylfe
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
| | - A. Tengholm
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University, Box 571, 75123 Uppsala, Sweden
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29
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Kaihara KA, Dickson LM, Jacobson DA, Tamarina N, Roe MW, Philipson LH, Wicksteed B. β-Cell-specific protein kinase A activation enhances the efficiency of glucose control by increasing acute-phase insulin secretion. Diabetes 2013; 62:1527-36. [PMID: 23349500 PMCID: PMC3636652 DOI: 10.2337/db12-1013] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Acute insulin secretion determines the efficiency of glucose clearance. Moreover, impaired acute insulin release is characteristic of reduced glucose control in the prediabetic state. Incretin hormones, which increase β-cell cAMP, restore acute-phase insulin secretion and improve glucose control. To determine the physiological role of the cAMP-dependent protein kinase (PKA), a mouse model was developed to increase PKA activity specifically in the pancreatic β-cells. In response to sustained hyperglycemia, PKA activity potentiated both acute and sustained insulin release. In contrast, a glucose bolus enhanced acute-phase insulin secretion alone. Acute-phase insulin secretion was increased 3.5-fold, reducing circulating glucose to 58% of levels in controls. Exendin-4 increased acute-phase insulin release to a similar degree as PKA activation. However, incretins did not augment the effects of PKA on acute-phase insulin secretion, consistent with incretins acting primarily via PKA to potentiate acute-phase insulin secretion. Intracellular calcium signaling was unaffected by PKA activation, suggesting that the effects of PKA on acute-phase insulin secretion are mediated by the phosphorylation of proteins involved in β-cell exocytosis. Thus, β-cell PKA activity transduces the cAMP signal to dramatically increase acute-phase insulin secretion, thereby enhancing the efficiency of insulin to control circulating glucose.
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Affiliation(s)
- Kelly A. Kaihara
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Lorna M. Dickson
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - David A. Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Natalia Tamarina
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Michael W. Roe
- Department of Medicine, Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York
| | - Louis H. Philipson
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
| | - Barton Wicksteed
- Kovler Diabetes Center, Section of Adult and Pediatric Endocrinology, Diabetes and Metabolism, Department of Medicine, The University of Chicago, Chicago, Illinois
- Corresponding author: Barton Wicksteed,
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30
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Abstract
Membrane microparticles are submicron fragments of membrane shed into extracellular space from cells under conditions of stress/injury. They may be distinguished from other classes of extracellular vesicles (i.e. exosomes) on the basis of size, content and mechanism of formation. Microparticles are found in plasma and other biological fluids from healthy individuals and their levels are altered in various diseases, including diabetes, chronic kidney disease, pre-eclampsia and hypertension among others. Accordingly, they have been considered biomarkers of vascular injury and pro-thrombotic or pro-inflammatory conditions. In addition to this, emerging evidence suggests that microparticles are not simply a consequence of disease, but that they themselves may contribute to pathological processes. Thus microparticles appear to serve as both markers and mediators of pathology. The present review examines the evidence for microparticles as both biomarkers of, and contributors to, the progression of disease. Approaches for the detection of microparticles are summarized and novel concepts relating to the formation of microparticles and their biological effects are examined.
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31
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Almassy J, Yule DI. Photolysis of caged compounds: studying Ca(2+) signaling and activation of Ca(2+)-dependent ion channels. Cold Spring Harb Protoc 2013; 2013:2013/1/pdb.top066076. [PMID: 23282631 DOI: 10.1101/pdb.top066076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
A wide variety of signaling molecules have been chemically modified by conjugation to a photolabile chromophore to render the substance temporarily biologically inert. Subsequent exposure to ultraviolet (UV) light can release the active moiety from the "caged" precursor in an experimentally controlled manner. This allows the concentration of active molecule to be precisely manipulated in both time and space. These techniques are particularly useful in experimental protocols designed to investigate the mechanisms underlying Ca(2+) signaling and the activation of Ca(2+)-dependent effectors.
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Affiliation(s)
- Janos Almassy
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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32
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Abstract
Insulin secretion from pancreatic β-cells is tightly regulated by glucose and other nutrients, hormones, and neural factors. The exocytosis of insulin granules is triggered by an elevation of the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and is further amplified by cyclic AMP (cAMP). Cyclic AMP is formed primarily in response to glucoincretin hormones and other G(s)-coupled receptor agonists, but generation of the nucleotide is critical also for an optimal insulin secretory response to glucose. Nutrient and receptor stimuli trigger oscillations of the cAMP concentration in β-cells. The oscillations arise from variations in adenylyl cyclase-mediated cAMP production and phosphodiesterase-mediated degradation, processes controlled by factors like cell metabolism and [Ca(2+)](i). Protein kinase A and the guanine nucleotide exchange factor Epac2 mediate the actions of cAMP in β-cells and operate at multiple levels to promote exocytosis and pulsatile insulin secretion. The cAMP signaling system contains important targets for pharmacological improvement of insulin secretion in type 2 diabetes.
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Affiliation(s)
- Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre , Box 571, SE-751 23 Uppsala, Sweden.
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33
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Mourad NI, Nenquin M, Henquin JC. cAMP-mediated and metabolic amplification of insulin secretion are distinct pathways sharing independence of β-cell microfilaments. Endocrinology 2012; 153:4644-54. [PMID: 22948217 DOI: 10.1210/en.2012-1450] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Insulin secretion is triggered by an increase in the cytosolic calcium concentration ([Ca(2+)](c)) in β-cells. Ca(2+)-induced exocytosis of insulin granules can be augmented by metabolic amplification (unknown signals generated through glucose metabolism) or neurohormonal amplification (in particular cAMP mediated). Functional actin microfilaments are not required for metabolic amplification, but their possible role in cAMP-mediated amplification is unknown. It is also uncertain whether cAMP (generated in response to glucose) is implicated in metabolic amplification. These questions were addressed using isolated mouse islets. cAMP levels were increased by phosphodiesterase inhibition (with isobutylmethylxanthine) and adenylate-cyclase stimulation (with forskolin or glucagon-like peptide-1, 7-36 amide). Raising cAMP levels had no steady-state impact on actin polymerization in control islets. Neither disruption (depolymerization by latrunculin) nor stabilization (polymerization by jasplakinolide) of actin microfilaments was counteracted by cAMP. Both changes increased both phases of glucose- or tolbutamide-induced insulin secretion but did not prevent further amplification by cAMP. These large changes in secretion were not caused by changes in [Ca(2+)](c), which was only slightly increased by cAMP. Both phases of insulin secretion were larger in response to glucose than tolbutamide, although [Ca(2+)](c) was lower. This difference in secretion, which reflects metabolic amplification, was independent of microfilaments, was not attributable to differences in cAMP, and persisted in presence of dibutyryl-cAMP or when cAMP levels were variably raised by isobutylmethylxanthine + forskolin or glucagon-like peptide-1, 7-36 amide. We conclude that metabolic and cAMP-mediated amplification of insulin secretion are distinct pathways that accelerate acquisition of release competence by insulin granules that can access exocytotic sites without intervention of microfilaments.
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Affiliation(s)
- Nizar I Mourad
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, B-1200 Brussels, Belgium
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34
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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35
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Seino S. Cell signalling in insulin secretion: the molecular targets of ATP, cAMP and sulfonylurea. Diabetologia 2012; 55:2096-108. [PMID: 22555472 DOI: 10.1007/s00125-012-2562-9] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 03/09/2012] [Indexed: 12/25/2022]
Abstract
Clarification of the molecular mechanisms of insulin secretion is crucial for understanding the pathogenesis and pathophysiology of diabetes and for development of novel therapeutic strategies for the disease. Insulin secretion is regulated by various intracellular signals generated by nutrients and hormonal and neural inputs. In addition, a variety of glucose-lowering drugs including sulfonylureas, glinide-derivatives, and incretin-related drugs such as dipeptidyl peptidase IV (DPP-4) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists are used for glycaemic control by targeting beta cell signalling for improved insulin secretion. There has been a remarkable increase in our understanding of the basis of beta cell signalling over the past two decades following the application of molecular biology, gene technology, electrophysiology and bioimaging to beta cell research. This review discusses cell signalling in insulin secretion, focusing on the molecular targets of ATP, cAMP and sulfonylurea, an essential metabolic signal in glucose-induced insulin secretion (GIIS), a critical signal in the potentiation of GIIS, and the commonly used glucose-lowering drug, respectively.
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Affiliation(s)
- S Seino
- Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, 650-0017, Japan.
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Tarasov AI, Semplici F, Ravier MA, Bellomo EA, Pullen TJ, Gilon P, Sekler I, Rizzuto R, Rutter GA. The mitochondrial Ca2+ uniporter MCU is essential for glucose-induced ATP increases in pancreatic β-cells. PLoS One 2012; 7:e39722. [PMID: 22829870 PMCID: PMC3400633 DOI: 10.1371/journal.pone.0039722] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 05/25/2012] [Indexed: 01/09/2023] Open
Abstract
Glucose induces insulin release from pancreatic β-cells by stimulating ATP synthesis, membrane depolarisation and Ca2+ influx. As well as activating ATP-consuming processes, cytosolic Ca2+ increases may also potentiate mitochondrial ATP synthesis. Until recently, the ability to study the role of mitochondrial Ca2+ transport in glucose-stimulated insulin secretion has been hindered by the absence of suitable approaches either to suppress Ca2+ uptake into these organelles, or to examine the impact on β-cell excitability. Here, we have combined patch-clamp electrophysiology with simultaneous real-time imaging of compartmentalised changes in Ca2+ and ATP/ADP ratio in single primary mouse β-cells, using recombinant targeted (Pericam or Perceval, respectively) as well as entrapped intracellular (Fura-Red), probes. Through shRNA-mediated silencing we show that the recently-identified mitochondrial Ca2+ uniporter, MCU, is required for depolarisation-induced mitochondrial Ca2+ increases, and for a sustained increase in cytosolic ATP/ADP ratio. By contrast, silencing of the mitochondrial Na+-Ca2+ exchanger NCLX affected the kinetics of glucose-induced changes in, but not steady state values of, cytosolic ATP/ADP. Exposure to gluco-lipotoxic conditions delayed both mitochondrial Ca2+ uptake and cytosolic ATP/ADP ratio increases without affecting the expression of either gene. Mitochondrial Ca2+ accumulation, mediated by MCU and modulated by NCLX, is thus required for normal glucose sensing by pancreatic β-cells, and becomes defective in conditions mimicking the diabetic milieu.
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Affiliation(s)
- Andrei I. Tarasov
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Francesca Semplici
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Magalie A. Ravier
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- Institut de Génomique Fonctionnelle, INSERM U661, CNRS UMR5203, Université Montpellier I et II, Montpellier, France
| | - Elisa A. Bellomo
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Timothy J. Pullen
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
| | - Patrick Gilon
- Pole of Endocrinology, Diabetes and Nutrition, Faculty of Medicine, Université Catholique de Louvain, Brussels, Belgium
| | - Israel Sekler
- Department of Physiology, Faculty of Health Sciences, Ben Gurion University, Beer-Sheva, Israel
| | - Rosario Rizzuto
- Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Guy A. Rutter
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, United Kingdom
- * E-mail:
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Tarasov AI, Griffiths EJ, Rutter GA. Regulation of ATP production by mitochondrial Ca(2+). Cell Calcium 2012; 52:28-35. [PMID: 22502861 PMCID: PMC3396849 DOI: 10.1016/j.ceca.2012.03.003] [Citation(s) in RCA: 187] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Revised: 03/10/2012] [Accepted: 03/14/2012] [Indexed: 01/09/2023]
Abstract
Stimulation of mitochondrial oxidative metabolism by Ca(2+) is now generally recognised as important for the control of cellular ATP homeostasis. Here, we review the mechanisms through which Ca(2+) regulates mitochondrial ATP synthesis. We focus on cardiac myocytes and pancreatic β-cells, where tight control of this process is likely to play an important role in the response to rapid changes in workload and to nutrient stimulation, respectively. We also describe a novel approach for imaging the Ca(2+)-dependent regulation of ATP levels dynamically in single cells.
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Affiliation(s)
- Andrei I Tarasov
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Imperial College London, SW7 2AZ, London, UK
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Fujimoto S, Mukai E, Inagaki N. Role of endogenous ROS production in impaired metabolism-secretion coupling of diabetic pancreatic β cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:304-10. [PMID: 21839765 DOI: 10.1016/j.pbiomolbio.2011.07.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 07/30/2011] [Accepted: 07/31/2011] [Indexed: 12/25/2022]
Abstract
One of the characteristics of type 2 diabetes is that the insulin secretory response of β cells is selectively impaired to glucose. In the Goto-Kakizaki (GK) rat, a genetic model of type 2 diabetes mellitus, glucose-induced insulin secretion is selectively impaired due to deficient ATP production derived from impaired glucose metabolism. In addition, islets in GK rat and human type 2 diabetes are oxidatively stressed. In this issue, role of endogenous reactive oxygen species (ROS) production in impaired metabolism-secretion coupling of diabetic pancreatic β cells is reviewed. In β cells, ROS is endogenously produced by activation of Src, a non-receptor tyrosine kinase. Src inhibitors restore the impaired insulin release and impaired ATP elevation by reduction in ROS production in diabetic islets. Src is endogenously activated in diabetic islets, since the level of Src pY416 in GK islets is higher than that in control islets. In addition, exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, decreases Src pY416 and glucose-induced ROS production and ameliorates impaired ATP production dependently on Epac in GK islets. These results indicate that GLP-1 signaling regulates endogenous ROS production due to Src activation and that incretin has unique therapeutic effects on impaired glucose metabolism in diabetic β cells.
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Affiliation(s)
- Shimpei Fujimoto
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
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Bonfleur ML, Ribeiro RA, Balbo SL, Vanzela EC, Carneiro EM, de Oliveira HCF, Boschero AC. Lower expression of PKAα impairs insulin secretion in islets isolated from low-density lipoprotein receptor (LDLR(-/-)) knockout mice. Metabolism 2011; 60:1158-64. [PMID: 21306750 DOI: 10.1016/j.metabol.2010.12.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Revised: 12/08/2010] [Accepted: 12/16/2010] [Indexed: 11/19/2022]
Abstract
Hypercholesterolemic low-density lipoprotein receptor knockout mice (LDLR(-/-)) show normal whole-body insulin sensitivity, but impaired glucose tolerance due to a reduced insulin secretion in response to glucose. Here, we investigate the possible mechanisms involved in such a defect in isolated LDLR(-/-) mice islets. Low-fat chow-fed female and male mice aged 20 weeks, LDLR(-/-) mice, and wild-type (WT) mice were used in this study. Static insulin secretion, cytoplasmatic Ca(2+) analysis, and protein expression were measured in islets isolated from LDLR(-/-) and WT mice. At basal (2.8 mmol/L) and stimulatory (11.1 mmol/L) glucose concentrations, the insulin secretion rates induced by depolarizing agents such as KCl, L-arginine, and tolbutamide were significantly reduced in LDLR(-/-) when compared with control (WT) islets. In addition, KCl-induced Ca(2+) influx at 2.8 mmol/L glucose was lower in LDLR(-/-) islets, suggesting a defect downstream of the substrate metabolism step of the insulin secretion pathway. Insulin secretion induced by the protein kinase A (PKA) activators forskolin and 3-isobutyl-1-methyl-xanthine, in the presence of 11.1 mmol/L glucose, was lower in LDLR(-/-) islets and was normalized in the presence of the protein kinase C pathway activators carbachol and phorbol 12-myristate 13-acetate. Western blotting analysis showed that phospholipase Cβ(2) expression was increased and PKAα was decreased in LDLR(-/-) compared with WT islets. Results indicate that the lower insulin secretion observed in islets from LDLR(-/-) mice at postprandial levels of glucose can be explained, at least in part, by the reduced expression of PKAα in these islets.
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Affiliation(s)
- Maria Lúcia Bonfleur
- Centro de Ciências Biológicas e da Saúde, Universidade Estadual do Oeste do Paraná (UNIOESTE), 85810-119 Cascavel, PR, Brazil
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Leech CA, Dzhura I, Chepurny OG, Kang G, Schwede F, Genieser HG, Holz GG. Molecular physiology of glucagon-like peptide-1 insulin secretagogue action in pancreatic β cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:236-47. [PMID: 21782840 DOI: 10.1016/j.pbiomolbio.2011.07.005] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Accepted: 07/08/2011] [Indexed: 10/18/2022]
Abstract
Insulin secretion from pancreatic β cells is stimulated by glucagon-like peptide-1 (GLP-1), a blood glucose-lowering hormone that is released from enteroendocrine L cells of the distal intestine after the ingestion of a meal. GLP-1 mimetics (e.g., Byetta) and GLP-1 analogs (e.g., Victoza) activate the β cell GLP-1 receptor (GLP-1R), and these compounds stimulate insulin secretion while also lowering levels of blood glucose in patients diagnosed with type 2 diabetes mellitus (T2DM). An additional option for the treatment of T2DM involves the administration of dipeptidyl peptidase-IV (DPP-IV) inhibitors (e.g., Januvia, Galvus). These compounds slow metabolic degradation of intestinally released GLP-1, thereby raising post-prandial levels of circulating GLP-1 substantially. Investigational compounds that stimulate GLP-1 secretion also exist, and in this regard a noteworthy advance is the demonstration that small molecule GPR119 agonists (e.g., AR231453) stimulate L cell GLP-1 secretion while also directly stimulating β cell insulin release. In this review, we summarize what is currently known concerning the signal transduction properties of the β cell GLP-1R as they relate to insulin secretion. Emphasized are the cyclic AMP, protein kinase A, and Epac2-mediated actions of GLP-1 to regulate ATP-sensitive K⁺ channels, voltage-dependent K⁺ channels, TRPM2 cation channels, intracellular Ca⁺ release channels, and Ca⁺-dependent exocytosis. We also discuss new evidence that provides a conceptual framework with which to understand why GLP-1R agonists are less likely to induce hypoglycemia when they are administered for the treatment of T2DM.
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Affiliation(s)
- Colin A Leech
- Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY, USA.
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Li CY, Shi HB, Wang J, Ye HB, Song NY, Yin SK. Bilirubin facilitates depolarizing GABA/glycinergic synaptic transmission in the ventral cochlear nucleus of rats. Eur J Pharmacol 2011; 660:310-7. [DOI: 10.1016/j.ejphar.2011.03.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2010] [Revised: 02/22/2011] [Accepted: 03/15/2011] [Indexed: 12/22/2022]
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Dzhura I, Chepurny OG, Leech CA, Roe MW, Dzhura E, Xu X, Lu Y, Schwede F, Genieser HG, Smrcka AV, Holz GG. Phospholipase C-ε links Epac2 activation to the potentiation of glucose-stimulated insulin secretion from mouse islets of Langerhans. Islets 2011; 3:121-8. [PMID: 21478675 PMCID: PMC3116928 DOI: 10.4161/isl.3.3.15507] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells is potentiated by cAMP-elevating agents, such as the incretin hormone glucagon-like peptide-1 (GLP-1), and cAMP exerts its insulin secretagogue action by activating both protein kinase A (PKA) and the cAMP-regulated guanine nucleotide exchange factor designated as Epac2. Although prior studies of mouse islets demonstrated that Epac2 acts via Rap1 GTPase to potentiate GSIS, it is not understood which downstream targets of Rap1 promote the exocytosis of insulin. Here, we measured insulin secretion stimulated by a cAMP analog that is a selective activator of Epac proteins in order to demonstrate that a Rap1-regulated phospholipase C-epsilon (PLC-ε) links Epac2 activation to the potentiation of GSIS. Our analysis demonstrates that the Epac activator 8-pCPT-2'-O-Me-cAMP-AM potentiates GSIS from the islets of wild-type (WT) mice, whereas it has a greatly reduced insulin secretagogue action in the islets of Epac2 (-/-) and PLC-ε (-/-) knockout (KO) mice. Importantly, the insulin secretagogue action of 8-pCPT-2'-O-Me-cAMP-AM in WT mouse islets cannot be explained by an unexpected action of this cAMP analog to activate PKA, as verified through the use of a FRET-based A-kinase activity reporter (AKAR3) that reports PKA activation. Since the KO of PLC-ε disrupts the ability of 8-pCPT-2'-O-Me-cAMP-AM to potentiate GSIS, while also disrupting its ability to stimulate an increase of β-cell [Ca2+]i, the available evidence indicates that it is a Rap1-regulated PLC-ε that links Epac2 activation to Ca2+-dependent exocytosis of insulin.
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Affiliation(s)
- Igor Dzhura
- Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY, USA
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Ravier MA, Cheng-Xue R, Palmer AE, Henquin JC, Gilon P. Subplasmalemmal Ca(2+) measurements in mouse pancreatic beta cells support the existence of an amplifying effect of glucose on insulin secretion. Diabetologia 2010; 53:1947-57. [PMID: 20461354 PMCID: PMC3297670 DOI: 10.1007/s00125-010-1775-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Accepted: 04/07/2010] [Indexed: 10/19/2022]
Abstract
AIMS/HYPOTHESIS Glucose-induced insulin secretion is attributed to a rise of beta cell cytosolic free [Ca(2+)] ([Ca(2+)](c)) (triggering pathway) and amplification of the action of Ca(2+). This concept of amplification rests on observations that glucose can increase Ca(2+)-induced insulin secretion without further elevating an imposed already high [Ca(2+)](c). However, it remains possible that this amplification results from an increase in [Ca(2+)] just under the plasma membrane ([Ca(2+)](SM)), which escaped detection by previous measurements of global [Ca(2+)](c). This was the hypothesis that we tested here by measuring [Ca(2+)](SM). METHODS The genetically encoded Ca(2+) indicators D3-cpv (untargeted) and LynD3-cpv (targeted to plasma membrane) were expressed in clusters of mouse beta cells. LynD3-cpv was also expressed in beta cells within intact islets. [Ca(2+)](SM) changes were monitored using total internal reflection fluorescence microscopy. Insulin secretion was measured in parallel. RESULTS Beta cells expressing D3cpv or LynD3cpv displayed normal [Ca(2+)] changes and insulin secretion in response to glucose. Distinct [Ca(2+)](SM) fluctuations were detected during repetitive variations of KCl between 30 and 32-35 mmol/l, attesting to the adequate sensitivity of our system. When the amplifying pathway was evaluated (high KCl + diazoxide), increasing glucose from 3 to 15 mmol/l consistently lowered [Ca(2+)](SM) while stimulating insulin secretion approximately two fold. Blocking Ca(2+) uptake by the endoplasmic reticulum largely attenuated the [Ca(2+)](SM) decrease produced by high glucose but did not unmask localised [Ca(2+)](SM) increases. CONCLUSIONS/INTERPRETATION Glucose can increase Ca(2+)-induced insulin secretion without causing further elevation of beta cell [Ca(2+)](SM). The phenomenon is therefore a true amplification of the triggering action of Ca(2+).
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Affiliation(s)
- M. A. Ravier
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - R. Cheng-Xue
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - A. E. Palmer
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
| | - J. C. Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
| | - P. Gilon
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, 1200 Brussels, Belgium
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Takahashi N, Hatakeyama H, Okado H, Noguchi J, Ohno M, Kasai H. SNARE conformational changes that prepare vesicles for exocytosis. Cell Metab 2010; 12:19-29. [PMID: 20620992 DOI: 10.1016/j.cmet.2010.05.013] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 04/28/2010] [Accepted: 05/26/2010] [Indexed: 11/25/2022]
Abstract
When cells release hormones and neurotransmitters through exocytosis, cytosolic Ca(2+) triggers the fusion of secretory vesicles with the plasma membrane. It is well known that this fusion requires assembly of a SNARE protein complex. However, the timing of SNARE assembly relative to vesicle fusion--essential for understanding exocytosis--has not been demonstrated. To investigate this timing, we constructed a probe that detects the assembly of two plasma membrane SNAREs, SNAP25 and syntaxin-1A, through fluorescence resonance energy transfer (FRET). With two-photon imaging, we simultaneously measured FRET signals and insulin exocytosis in beta cells from the pancreatic islet of Langerhans. In some regions of the cell, we found that the SNARE complex was preassembled, which enabled rapid exocytosis. In other regions, SNARE assembly followed Ca(2+) influx, and exocytosis was slower. Thus, SNARE proteins exist in multiple stable preparatory configurations, from which Ca(2+) may trigger exocytosis through distinct mechanisms and with distinct kinetics.
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Affiliation(s)
- Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
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Idevall-Hagren O, Barg S, Gylfe E, Tengholm A. cAMP mediators of pulsatile insulin secretion from glucose-stimulated single beta-cells. J Biol Chem 2010; 285:23007-18. [PMID: 20498366 DOI: 10.1074/jbc.m109.095992] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Pulsatile insulin release from glucose-stimulated beta-cells is driven by oscillations of the Ca(2+) and cAMP concentrations in the subplasma membrane space ([Ca(2+)](pm) and [cAMP](pm)). To clarify mechanisms by which cAMP regulates insulin secretion, we performed parallel evanescent wave fluorescence imaging of [cAMP](pm), [Ca(2+)](pm), and phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) in the plasma membrane. This lipid is formed by autocrine insulin receptor activation and was used to monitor insulin release kinetics from single MIN6 beta-cells. Elevation of the glucose concentration from 3 to 11 mm induced, after a 2.7-min delay, coordinated oscillations of [Ca(2+)](pm), [cAMP](pm), and PIP(3). Inhibitors of protein kinase A (PKA) markedly diminished the PIP(3) response when applied before glucose stimulation, but did not affect already manifested PIP(3) oscillations. The reduced PIP(3) response could be attributed to accelerated depolarization causing early rise of [Ca(2+)](pm) that preceded the elevation of [cAMP](pm). However, the amplitude of the PIP(3) response after PKA inhibition was restored by a specific agonist to the cAMP-dependent guanine nucleotide exchange factor Epac. Suppression of cAMP formation with adenylyl cyclase inhibitors reduced already established PIP(3) oscillations in glucose-stimulated cells, and this effect was almost completely counteracted by the Epac agonist. In cells treated with small interfering RNA targeting Epac2, the amplitudes of the glucose-induced PIP(3) oscillations were reduced, and the Epac agonist was without effect. The data indicate that temporal coordination of the triggering [Ca(2+)](pm) and amplifying [cAMP](pm) signals is important for glucose-induced pulsatile insulin release. Although both PKA and Epac2 partake in initiating insulin secretion, the cAMP dependence of established pulsatility is mediated by Epac2.
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Affiliation(s)
- Olof Idevall-Hagren
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-75123 Uppsala, Sweden
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Chepurny OG, Kelley GG, Dzhura I, Leech CA, Roe MW, Dzhura E, Li X, Schwede F, Genieser HG, Holz GG. PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM in human islets of Langerhans. Am J Physiol Endocrinol Metab 2010; 298:E622-33. [PMID: 20009023 PMCID: PMC2838523 DOI: 10.1152/ajpendo.00630.2009] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Potential insulin secretagogue properties of an acetoxymethyl ester of a cAMP analog (8-pCPT-2'-O-Me-cAMP-AM) that activates the guanine nucleotide exchange factors Epac1 and Epac2 were assessed using isolated human islets of Langerhans. RT-QPCR demonstrated that the predominant variant of Epac expressed in human islets was Epac2, although Epac1 was detectable. Under conditions of islet perifusion, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) potentiated first- and second-phase 10 mM glucose-stimulated insulin secretion (GSIS) while failing to influence insulin secretion measured in the presence of 3 mM glucose. The insulin secretagogue action of 8-pCPT-2'-O-Me-cAMP-AM was associated with depolarization and an increase of [Ca(2+)](i) that reflected both Ca(2+) influx and intracellular Ca(2+) mobilization in islet beta-cells. As expected for an Epac-selective cAMP analog, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) failed to stimulate phosphorylation of PKA substrates CREB and Kemptide in human islets. Furthermore, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) had no significant ability to activate AKAR3, a PKA-regulated biosensor expressed in human islet cells by viral transduction. Unexpectedly, treatment of human islets with an inhibitor of PKA activity (H-89) or treatment with a cAMP antagonist that blocks PKA activation (Rp-8-CPT-cAMPS) nearly abolished the action of 8-pCPT-2'-O-Me-cAMP-AM to potentiate GSIS. It is concluded that there exists a permissive role for PKA activity in support of human islet insulin secretion that is both glucose dependent and Epac regulated. This permissive action of PKA may be operative at the insulin secretory granule recruitment, priming, and/or postpriming steps of Ca(2+)-dependent exocytosis.
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Affiliation(s)
- Oleg G Chepurny
- Departments of Medicine, State University of New York, Syracuse, 13210, USA
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Kasai H, Hatakeyama H, Ohno M, Takahashi N. Exocytosis in islet beta-cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:305-38. [PMID: 20217504 DOI: 10.1007/978-90-481-3271-3_14] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The development of technologies that allow for live optical imaging of exocytosis from beta-cells has greatly improved our understanding of insulin secretion. Two-photon imaging, in particular, has enabled researchers to visualize the exocytosis of large dense-core vesicles (LDCVs) containing insulin from beta-cells in intact islets of Langerhans. These studies have revealed that high glucose levels induce two phases of insulin secretion and that this release is dependent upon cytosolic Ca(2+) and cAMP. This technology has also made it possible to examine the spatial profile of insulin exocytosis in these tissues and compare that profile with those of other secretory glands. Such studies have led to the discovery of the massive exocytosis of synaptic-like microvesicles (SLMVs) in beta-cells. These imaging studies have also helped clarify facets of insulin exocytosis that cannot be properly addressed using the currently available electrophysiological techniques. This chapter provides a concise introduction to the field of optical imaging for those researchers who wish to characterize exocytosis from beta-cells in the islets of Langerhans.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, The University of Tokyo, Hongo, Tokyo 113-0033, Japan.
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Kelley GG, Chepurny OG, Schwede F, Genieser HG, Leech CA, Roe MW, Li X, Dzhura I, Dzhura E, Afshari P, Holz GG. Glucose-dependent potentiation of mouse islet insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM. Islets 2009; 1:260-5. [PMID: 21099281 PMCID: PMC2859731 DOI: 10.4161/isl.1.3.9645] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Epac2 is a cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF) that is proposed to mediate stimulatory actions of the second messenger cAMP on mouse islet insulin secretion. Here we have used methods of islet perifusion to demonstrate that the acetoxymethyl ester (AM-ester) of an Epac-selective cAMP analog (ESCA) penetrates into mouse islets and is capable of potentiating both first and second phases of glucose-stimulated insulin secretion (GSIS). When used at low concentrations (1-10 μM), 8-pCPT-2'-O-Me-cAMP-AM activates Rap1 GTPase but exhibits little or no ability to activate protein kinase A (PKA), as validated in assays of in vitro PKA activity (phosphorylation of Kemptide), Ser (133) CREB phosphorylation status, RIP1-CRE-Luc reporter gene activity, and PKA-dependent AKAR3 biosensor activation. Since quantitative PCR demonstrates Epac2 mRNA to be expressed at levels ca. 5.3-fold greater than that of Epac1, available evidence indicates that Epac2 does in fact mediate stimulatory actions of cAMP on mouse islet GSIS.
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Affiliation(s)
- Grant G. Kelley
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | - Oleg G. Chepurny
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | | | | | - Colin A. Leech
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | - Michael W. Roe
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
- Department of Cell and Developmental Biology; State University of New York Upstate Medical University; Syracuse, NY USA
| | - Xiangquan Li
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | - Igor Dzhura
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | - Elvira Dzhura
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
| | - Parisa Afshari
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
- Department of Pharmacology, State University of New York Upstate Medical University; Syracuse, NY USA
| | - George G. Holz
- Department of Medicine, State University of New York Upstate Medical University; Syracuse, NY USA
- Department of Pharmacology, State University of New York Upstate Medical University; Syracuse, NY USA
- Correspondence to: George G. Holz;
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49
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Hatlapatka K, Willenborg M, Rustenbeck I. Plasma membrane depolarization as a determinant of the first phase of insulin secretion. Am J Physiol Endocrinol Metab 2009; 297:E315-22. [PMID: 19470830 DOI: 10.1152/ajpendo.90981.2008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of plasma membrane depolarization as a determinant of the initial phase of insulin secretion was investigated. NMRI mouse islets and beta-cells were used to measure the kinetics of insulin secretion, ATP and ADP content, membrane potential, and cytosolic free Ca(2+) concentration ([Ca(2+)](i)). The depolarization of metabolically intact beta-cells by KCl corresponded closely to the theoretical values. In contrast to physiological (glucose) or pharmacological (tolbutamide) ATP-sensitive K(+) (K(ATP)) channel block, KCl depolarization did not induce action potential spiking. The depolarization by 15 mM K(+) (21 mV) corresponded to the plateau depolarization by 50 or 500 microM tolbutamide; that by 40 mM K(+) (41 mV) corresponded to the action potential peaks. Nifedipine and diazoxide abolished action potentials but not KCl depolarization, suggesting that the depolarizing strength of 15, but not 40 mM K(+) corresponds to that of K(ATP) channel closure. K(+) (40 mM) induced a massive secretory response in the presence of 5 mM glucose, whereas 15 mM K(+), like 50 microM tolbutamide, was only slightly effective, even though a marked increase in [Ca(2+)](i) was produced. Raising glucose from 5 to 10 mM in the continued presence of 15 mM K(+) resulted in a strongly enhanced biphasic response. The depolarization pattern of this combination could be mimicked by combining basal glucose with 15 mM K(+) and 50 microM tolbutamide; however, the secretory response to these nonnutrients was much weaker. In conclusion, the initial secretory response to nutrient secretagogues is largely influenced by signaling mechanisms that do not involve depolarization.
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Affiliation(s)
- K Hatlapatka
- Institute of Pharmacology and Toxicology, Technical University of Braunschweig, Braunschweig, Germany
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50
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Henquin JC. Regulation of insulin secretion: a matter of phase control and amplitude modulation. Diabetologia 2009; 52:739-51. [PMID: 19288076 DOI: 10.1007/s00125-009-1314-y] [Citation(s) in RCA: 343] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Accepted: 02/05/2009] [Indexed: 12/14/2022]
Abstract
The consensus model of stimulus-secretion coupling in beta cells attributes glucose-induced insulin secretion to a sequence of events involving acceleration of metabolism, closure of ATP-sensitive K(+) channels, depolarisation, influx of Ca(2+) and a rise in cytosolic free Ca(2+) concentration ([Ca(2+)](c)). This triggering pathway is essential, but would not be very efficient if glucose did not also activate a metabolic amplifying pathway that does not raise [Ca(2+)](c) further but augments the action of triggering Ca(2+) on exocytosis. This review discusses how both pathways interact to achieve temporal control and amplitude modulation of biphasic insulin secretion. First-phase insulin secretion is triggered by the rise in [Ca(2+)](c) that occurs synchronously in all beta cells of every islet in response to a sudden increase in the glucose concentration. Its time course and duration are shaped by those of the Ca(2+) signal, and its amplitude is modulated by the magnitude of the [Ca(2+)](c) rise and, substantially, by amplifying mechanisms. During the second phase, synchronous [Ca(2+)](c) oscillations in all beta cells of an individual islet induce pulsatile insulin secretion, but these features of the signal and response are dampened in groups of intrinsically asynchronous islets. Glucose has hardly any influence on the amplitude of [Ca(2+)](c) oscillations and mainly controls the time course of triggering signal. Amplitude modulation of insulin secretion pulses largely depends on the amplifying pathway. There are more similarities than differences between the two phases of glucose-induced insulin secretion. Both are subject to the same dual, hierarchical control over time and amplitude by triggering and amplifying pathways, suggesting that the second phase is a sequence of iterations of the first phase.
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Affiliation(s)
- J C Henquin
- Faculty of Medicine, University of Louvain, Brussels, Belgium.
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