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Rizwan MZ, Kamstra K, Pretz D, Shepherd PR, Tups A, Grattan DR. Conditional Deletion of β-Catenin in the Mediobasal Hypothalamus Impairs Adaptive Energy Expenditure in Response to High-Fat Diet and Exacerbates Diet-Induced Obesity. J Neurosci 2024; 44:e1666232024. [PMID: 38395612 PMCID: PMC10993030 DOI: 10.1523/jneurosci.1666-23.2024] [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: 09/04/2023] [Revised: 01/23/2024] [Accepted: 02/08/2024] [Indexed: 02/25/2024] Open
Abstract
β-Catenin is a bifunctional molecule that is an effector of the wingless-related integration site (Wnt) signaling to control gene expression and contributes to the regulation of cytoskeleton and neurotransmitter vesicle trafficking. In its former role, β-catenin binds transcription factor 7-like 2 (TCF7L2), which shows strong genetic associations with the pathogenesis of obesity and type-2 diabetes. Here, we sought to determine whether β-catenin plays a role in the neuroendocrine regulation of body weight and glucose homeostasis. Bilateral injections of adeno-associated virus type-2 (AAV2)-mCherry-Cre were placed into the arcuate nucleus of adult male and female β-catenin flox mice, to specifically delete β-catenin expression in the mediobasal hypothalamus (MBH-β-cat KO). Metabolic parameters were then monitored under conditions of low-fat (LFD) and high-fat diet (HFD). On LFD, MBH-β-cat KO mice showed minimal metabolic disturbances, but on HFD, despite having only a small difference in weekly caloric intake, the MBH-β-cat KO mice were significantly heavier than the control mice in both sexes (p < 0.05). This deficit seemed to be due to a failure to show an adaptive increase in energy expenditure seen in controls, which served to offset the increased calories by HFD. Both male and female MBH-β-cat KO mice were highly glucose intolerant when on HFD and displayed a significant reduction in both leptin and insulin sensitivity compared with controls. This study highlights a critical role for β-catenin in the hypothalamic circuits regulating body weight and glucose homeostasis and reveals potential mechanisms by which genetic variation in this pathway could impact on development of metabolic disease.
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Affiliation(s)
- Mohammed Z Rizwan
- Centre for Neuroendocrinology and Department of Anatomy, University of Otago School of Biomedical Sciences, Dunedin 9016, New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery, Auckland 1010, New Zealand
| | - Kaj Kamstra
- Centre for Neuroendocrinology and Department of Physiology, University of Otago School of Biomedical Sciences, Dunedin 9016, New Zealand
| | - Dominik Pretz
- Centre for Neuroendocrinology and Department of Physiology, University of Otago School of Biomedical Sciences, Dunedin 9016, New Zealand
| | - Peter R Shepherd
- Maurice Wilkins Centre for Molecular Biodiscovery, Auckland 1010, New Zealand
- Faculty of Medical and Health Sciences, University of Auckland, Auckland 1010, New Zealand
| | - Alexander Tups
- Maurice Wilkins Centre for Molecular Biodiscovery, Auckland 1010, New Zealand
- Centre for Neuroendocrinology and Department of Physiology, University of Otago School of Biomedical Sciences, Dunedin 9016, New Zealand
| | - David R Grattan
- Centre for Neuroendocrinology and Department of Anatomy, University of Otago School of Biomedical Sciences, Dunedin 9016, New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery, Auckland 1010, New Zealand
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2
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Yammine L, Picatoste B, Abdullah N, Leahey RA, Johnson EF, Gómez-Banoy N, Rosselot C, Wen J, Hossain T, Goncalves MD, Lo JC, Garcia-Ocaña A, McGraw TE. Spatiotemporal regulation of GIPR signaling impacts glucose homeostasis as revealed in studies of a common GIPR variant. Mol Metab 2023; 78:101831. [PMID: 37925022 PMCID: PMC10665708 DOI: 10.1016/j.molmet.2023.101831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 10/20/2023] [Accepted: 10/23/2023] [Indexed: 11/06/2023] Open
Abstract
OBJECTIVE Glucose-dependent insulinotropic polypeptide (GIP) has a role in controlling postprandial metabolic tone. In humans, a GIP receptor (GIPR) variant (Q354, rs1800437) is associated with a lower body mass index (BMI) and increased risk for Type 2 Diabetes. To better understand the impacts of GIPR-Q354 on metabolism, it is necessary to study it in an isogeneic background to the predominant GIPR isoform, E354. To accomplish this objective, we used CRISPR-CAS9 editing to generate mouse models of GIPR-Q354 and GIPR-E354. Here we characterize the metabolic effects of GIPR-Q354 variant in a mouse model (GIPR-Q350). METHODS We generated the GIPR-Q350 mice for in vivo studies of metabolic impact of the variant. We isolated pancreatic islets from GIPR-Q350 mice to study insulin secretion ex vivo. We used a β-cell cell line to understand the impact of the GIPR-Q354 variant on the receptor traffic. RESULTS We found that female GIPR-Q350 mice are leaner than littermate controls, and male GIPR-Q350 mice are resistant to diet-induced obesity, in line with the association of the variant with reduced BMI in humans. GIPR-Q350 mice of both sexes are more glucose tolerant and exhibit an increased sensitivity to GIP. Postprandial GIP levels are reduced in GIPR-Q350 mice, revealing feedback regulation that balances the increased sensitivity of GIP target tissues to secretion of GIP from intestinal endocrine cells. The increased GIP sensitivity is recapitulated ex vivo during glucose stimulated insulin secretion assays in islets. Generation of cAMP in islets downstream of GIPR activation is not affected by the Q354 substitution. However, post-activation traffic of GIPR-Q354 variant in β-cells is altered, characterized by enhanced intracellular dwell time and increased localization to the Trans-Golgi Network (TGN). CONCLUSIONS Our data link altered intracellular traffic of the GIPR-Q354 variant with GIP control of metabolism. We propose that this change in spatiotemporal signaling underlies the physiologic effects of GIPR-Q350/4 and GIPR-E350/4 in mice and humans. These findings contribute to a more complete understanding of the impact of GIPR-Q354 variant on glucose homeostasis that could perhaps be leveraged to enhance pharmacologic targeting of GIPR for the treatment of metabolic disease.
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Affiliation(s)
- Lucie Yammine
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Belén Picatoste
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Nazish Abdullah
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Rosemary A Leahey
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Emma F Johnson
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Nicolás Gómez-Banoy
- Weill Center for Metabolic Health and Division of Cardiology, Department of Medicine, Weill Cornell Medicine, New York, NY, 10021, USA
| | - Carolina Rosselot
- Diabetes, Obesity, and Metabolism Institute, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA
| | - Jennifer Wen
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Tahmina Hossain
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | | | - James C Lo
- Weill Center for Metabolic Health and Division of Cardiology, Department of Medicine, Weill Cornell Medicine, New York, NY, 10021, USA
| | - Adolfo Garcia-Ocaña
- Department of Molecular and Cellular Endocrinology, Arthur Riggs Diabetes and Metabolism Research Institute, City of Hope, Duarte, CA 91010, USA
| | - Timothy E McGraw
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA; Weill Center for Metabolic Health and Division of Cardiology, Department of Medicine, Weill Cornell Medicine, New York, NY, 10021, USA; Department of Cardiothoracic Surgery, Weill Cornell Medical College, New York, NY, 10065, USA.
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3
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Dissanayake WC, Shepherd PR. β-cells retain a pool of insulin-containing secretory vesicles regulated by adherens junctions and the cadherin binding protein p120 catenin. J Biol Chem 2022; 298:102240. [PMID: 35809641 PMCID: PMC9358467 DOI: 10.1016/j.jbc.2022.102240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 06/16/2022] [Accepted: 06/17/2022] [Indexed: 11/03/2022] Open
Abstract
The β-cells of the islets of Langerhans are the sole producers of insulin in the human body. In response to rising glucose levels, insulin-containing vesicles inside β-cells fuse with the plasma membrane and release their cargo. However, the mechanisms regulating this process are only partly understood. Previous evidence indicated reductions in α-catenin elevate insulin release, while reductions in β-catenin decrease insulin release. α- and β-catenin contribute to cellular regulation in a range of ways but one is as members of the adherens junction complex and these contribute to the development of cell polarity in b-cells. Therefore, we investigated the effects of adherens junctions on insulin release. We show in INS-1E β-cells knockdown of either E- or N-cadherin had only small effects on insulin secretion, but simultaneous knockout of both cadherins resulted in a significant increase in basal insulin release to the same level as glucose-stimulated release. This double knockdown also significantly attenuated levels of p120 catenin, a cadherin binding partner involved in regulating cadherin turnover. Conversely, reducing p120 catenin levels with siRNA destabilized both E- and N-cadherin, and this was also associated with an increase in levels of insulin secreted from INS-1E cells. Furthermore, there were also changes in these cells consistent with higher insulin release, namely reductions in levels of F-actin and increased intracellular free Ca2+ levels in response to KCl-induced membrane depolarization. Taken together, these data provide evidence that adherens junctions play important roles in retaining a pool of insulin secretory vesicles within the cell and establish a role for p120 catenin in regulating this process.
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Affiliation(s)
- Waruni C Dissanayake
- Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Peter R Shepherd
- Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
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4
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Andersen RC, Schmidt JH, Rombach J, Lycas MD, Christensen NR, Lund VK, Stapleton DS, Pedersen SS, Olsen MA, Stoklund M, Noes-Holt G, Nielsen TT, Keller MP, Jansen AM, Herlo R, Pietropaolo M, Simonsen JB, Kjærulff O, Holst B, Attie AD, Gether U, Madsen KL. Coding variants identified in diabetic patients alter PICK1 BAR domain function in insulin granule biogenesis. J Clin Invest 2022; 132:144904. [PMID: 35077398 PMCID: PMC8884907 DOI: 10.1172/jci144904] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 01/14/2022] [Indexed: 11/17/2022] Open
Abstract
Bin/amphiphysin/Rvs (BAR) domains are positively charged crescent-shaped modules that mediate curvature of negatively charged lipid membranes during remodeling processes. The BAR domain proteins PICK1, ICA69, and the arfaptins have recently been demonstrated to coordinate the budding and formation of immature secretory granules (ISGs) at the trans-Golgi network. Here, we identify 4 coding variants in the PICK1 gene from a whole-exome screening of Danish patients with diabetes that each involve a change in positively charged residues in the PICK1 BAR domain. All 4 coding variants failed to rescue insulin content in INS-1E cells upon knock down of endogenous PICK1. Moreover, 2 variants showed dominant-negative properties. In vitro assays addressing BAR domain function suggested that the coding variants compromised BAR domain function but increased the capacity to cause fission of liposomes. Live confocal microscopy and super-resolution microscopy further revealed that PICK1 resides transiently on ISGs before egress via vesicular budding events. Interestingly, this egress of PICK1 was accelerated in the coding variants. We propose that PICK1 assists in or complements the removal of excess membrane and generic membrane trafficking proteins, and possibly also insulin, from ISGs during the maturation process; and that the coding variants may cause premature budding, possibly explaining their dominant-negative function.
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Affiliation(s)
- Rita C. Andersen
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jan H. Schmidt
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Joscha Rombach
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Matthew D. Lycas
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Nikolaj R. Christensen
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Viktor K. Lund
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Donnie S. Stapleton
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
| | - Signe S. Pedersen
- Beta Cell Biology Group, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mathias A. Olsen
- Beta Cell Biology Group, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mikkel Stoklund
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gith Noes-Holt
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Tommas T.E. Nielsen
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Mark P. Keller
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
| | - Anna M. Jansen
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rasmus Herlo
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Massimo Pietropaolo
- Diabetes Research Center, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Jens B. Simonsen
- Department of Health Technology, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Ole Kjærulff
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Birgitte Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Alan D. Attie
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin, USA
| | - Ulrik Gether
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kenneth L. Madsen
- Molecular Neuropharmacology and Genetics Laboratory, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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5
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Zhao YF. Free fatty acid receptors in the endocrine regulation of glucose metabolism: Insight from gastrointestinal-pancreatic-adipose interactions. Front Endocrinol (Lausanne) 2022; 13:956277. [PMID: 36246919 PMCID: PMC9554507 DOI: 10.3389/fendo.2022.956277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 09/14/2022] [Indexed: 11/25/2022] Open
Abstract
Glucose metabolism is primarily controlled by pancreatic hormones, with the coordinated assistance of the hormones from gastrointestine and adipose tissue. Studies have unfolded a sophisticated hormonal gastrointestinal-pancreatic-adipose interaction network, which essentially maintains glucose homeostasis in response to the changes in substrates and nutrients. Free fatty acids (FFAs) are the important substrates that are involved in glucose metabolism. FFAs are able to activate the G-protein coupled membrane receptors including GPR40, GPR120, GPR41 and GPR43, which are specifically expressed in pancreatic islet cells, enteroendocrine cells as well as adipocytes. The activation of FFA receptors regulates the secretion of hormones from pancreas, gastrointestine and adipose tissue to influence glucose metabolism. This review presents the effects of the FFA receptors on glucose metabolism via the hormonal gastrointestinal-pancreatic-adipose interactions and the underlying intracellular mechanisms. Furthermore, the development of therapeutic drugs targeting FFA receptors for the treatment of abnormal glucose metabolism such as type 2 diabetes mellitus is summarized.
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6
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Gheibi S, Ghasemi A. Insulin secretion: The nitric oxide controversy. EXCLI JOURNAL 2020; 19:1227-1245. [PMID: 33088259 PMCID: PMC7573190 DOI: 10.17179/excli2020-2711] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 08/31/2020] [Indexed: 12/14/2022]
Abstract
Nitric oxide (NO) is a gas that serves as a ubiquitous signaling molecule participating in physiological activities of various organ systems. Nitric oxide is produced in the endocrine pancreas and contributes to synthesis and secretion of insulin. The potential role of NO in insulin secretion is disputable - both stimulatory and inhibitory effects have been reported. Available data indicate that effects of NO critically depend on its concentration. Different isoforms of NO synthase (NOS) control this and have the potential to decrease or increase insulin secretion. In this review, the role of NO in insulin secretion as well as the possible reasons for discrepant findings are discussed. A better understanding of the role of NO system in the regulation of insulin secretion may facilitate the development of new therapeutic strategies in the management of diabetes.
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Affiliation(s)
- Sevda Gheibi
- Department of Clinical Sciences in Malmö, Unit of Molecular Metabolism, Lund University Diabetes Centre, Clinical Research Center, Malmö University Hospital, Lund University, Malmö, Sweden
| | - Asghar Ghasemi
- Endocrine Physiology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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7
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Nguyen TTN, Koerdt SN, Gerke V. Plasma membrane phosphatidylinositol (4,5)-bisphosphate promotes Weibel-Palade body exocytosis. Life Sci Alliance 2020; 3:3/11/e202000788. [PMID: 32826291 PMCID: PMC7442956 DOI: 10.26508/lsa.202000788] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 08/14/2020] [Accepted: 08/14/2020] [Indexed: 01/26/2023] Open
Abstract
Phosphatidylinositol (4,5)-bisphosphate transiently accumulates at sites of Weibel–Palade body–plasma membrane fusion and promotes agonist-evoked exocytosis of endothelial von-Willebrand factor. Weibel–Palade bodies (WPB) are specialized secretory organelles of endothelial cells that control vascular hemostasis by regulated, Ca2+-dependent exocytosis of the coagulation-promoting von-Willebrand factor. Some proteins of the WPB docking and fusion machinery have been identified but a role of membrane lipids in regulated WPB exocytosis has so far remained elusive. We show here that the plasma membrane phospholipid composition affects Ca2+-dependent WPB exocytosis and von-Willebrand factor release. Phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] becomes enriched at WPB–plasma membrane contact sites at the time of fusion, most likely downstream of phospholipase D1-mediated production of phosphatidic acid (PA) that activates phosphatidylinositol 4-phosphate (PI4P) 5-kinase γ. Depletion of plasma membrane PI(4,5)P2 or down-regulation of PI4P 5-kinase γ interferes with histamine-evoked and Ca2+-dependent WPB exocytosis and a mutant PI4P 5-kinase γ incapable of binding PA affects WPB exocytosis in a dominant-negative manner. This indicates that a unique PI(4,5)P2-rich environment in the plasma membrane governs WPB fusion possibly by providing interaction sites for WPB-associated docking factors.
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Affiliation(s)
- Tu Thi Ngoc Nguyen
- Institute of Medical Biochemistry, Center for Molecular Biology of Inflammation, University of Münster, Münster, Germany
| | - Sophia N Koerdt
- Institute of Medical Biochemistry, Center for Molecular Biology of Inflammation, University of Münster, Münster, Germany
| | - Volker Gerke
- Institute of Medical Biochemistry, Center for Molecular Biology of Inflammation, University of Münster, Münster, Germany
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8
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α-catenin isoforms are regulated by glucose and involved in regulating insulin secretion in rat clonal β-cell models. Biochem J 2020; 477:763-772. [PMID: 32003420 PMCID: PMC7036346 DOI: 10.1042/bcj20190832] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 01/29/2020] [Accepted: 01/30/2020] [Indexed: 12/19/2022]
Abstract
The recent finding that β-catenin levels play an important rate-limiting role in processes regulating insulin secretion lead us to investigate whether its binding partner α-catenin also plays a role in this process. We find that levels of both α-E-catenin and α-N-catenin are rapidly up-regulated as levels of glucose are increased in rat clonal β-cell models INS-1E and INS-832/3. Lowering in levels of either α-catenin isoform using siRNA resulted in significant increases in glucose stimulated insulin secretion (GSIS) and this effect was attenuated when β-catenin levels were lowered indicating these proteins have opposing effects on insulin release. This effect of α-catenin knockdown on GSIS was not due to increases in insulin expression but was associated with increases in calcium influx into cells. Moreover, simultaneous depletion of α-E catenin and α-N catenin decreased the actin polymerisation to a similar degree as latrunculin treatment and inhibition of ARP 2/3 mediated actin branching with CK666 attenuated the α-catenin depletion effect on GSIS. This suggests α-catenin mediated actin remodelling may be involved in the regulation of insulin secretion. Together this indicates that α-catenin and β-catenin can play opposing roles in regulating insulin secretion, with some degree of functional redundancy in roles of α-E-catenin and α-N-catenin. The finding that, at least in β-cell models, the levels of each can be regulated in the longer term by glucose also provides a potential mechanism by which sustained changes in glucose levels might impact on the magnitude of GSIS.
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Bittner T, Wittwer C, Hauke S, Wohlwend D, Mundinger S, Dutta AK, Bezold D, Dürr T, Friedrich T, Schultz C, Jessen HJ. Photolysis of Caged Inositol Pyrophosphate InsP 8 Directly Modulates Intracellular Ca 2+ Oscillations and Controls C2AB Domain Localization. J Am Chem Soc 2020; 142:10606-10611. [PMID: 32459478 DOI: 10.1021/jacs.0c01697] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Inositol pyrophosphates constitute a family of hyperphosphorylated signaling molecules involved in the regulation of glucose uptake and insulin sensitivity. While our understanding of the biological roles of inositol heptaphosphates (PP-InsP5) has greatly improved, the functions of the inositol octaphosphates ((PP)2-InsP4) have remained unclear. Here we present the synthesis of two enantiomeric cell-permeant and photocaged (PP)2-InsP4 derivatives and apply them to study the functions in living β-cells. Photorelease of the naturally occurring isomer 1,5-(PP)2-InsP4 led to an immediate and concentration-dependent reduction of intracellular calcium oscillations, while other caged inositol pyrophosphates (3,5-(PP)2-InsP4, 5-PP-InsP5, 1-PP-InsP5, 3-PP-InsP5) showed no immediate effect. Furthermore, uncaging of 1,5-(PP)2-InsP4 but not 3,5-(PP)2-InsP4 induced translocation of the C2AB domain of granuphilin from the plasma membrane to the cytosol. Granuphilin is involved in membrane docking of secretory vesicles. This suggests that 1,5-(PP)2-InsP4 impacts β-cell activity by regulating granule localization and/or priming and calcium signaling in concert.
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Affiliation(s)
- Tamara Bittner
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Christopher Wittwer
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Sebastian Hauke
- Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Daniel Wohlwend
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Stephan Mundinger
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Amit K Dutta
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Dominik Bezold
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Tobias Dürr
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Thorsten Friedrich
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany
| | - Carsten Schultz
- Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany.,Department of Chemical Physiology and Biochemistry, Oregon Health & Science University (OHSU), Sam Jackson Park Road, Portland, Oregon 97239-3098, United States
| | - Henning J Jessen
- Department of Chemistry and Pharmacy, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104 Freiburg i.B., Germany.,CIBSS-Centre for Integrative Biological Signalling Studies, 79104 Freiburg i.B., Germany.,Freiburg Research Institute for Advanced Studies (FRIAS), Albert-Ludwigs University Freiburg, Albertstrasse 19, 79104 Freiburg i.B., Germany
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10
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Nguyen PM, Gandasi NR, Xie B, Sugahara S, Xu Y, Idevall-Hagren O. The PI(4)P phosphatase Sac2 controls insulin granule docking and release. J Cell Biol 2019; 218:3714-3729. [PMID: 31533953 PMCID: PMC6829663 DOI: 10.1083/jcb.201903121] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 06/20/2019] [Accepted: 08/08/2019] [Indexed: 12/12/2022] Open
Abstract
Insulin granule biogenesis involves transport to, and stable docking at, the plasma membrane before priming and fusion. Defects in this pathway result in impaired insulin secretion and are a hallmark of type 2 diabetes. We now show that the phosphatidylinositol 4-phosphate phosphatase Sac2 localizes to insulin granules in a substrate-dependent manner and that loss of Sac2 results in impaired insulin secretion. Sac2 operates upstream of granule docking, since loss of Sac2 prevented granule tethering to the plasma membrane and resulted in both reduced granule density and number of exocytic events. Sac2 levels correlated positively with the number of docked granules and exocytic events in clonal β cells and with insulin secretion in human pancreatic islets, and Sac2 expression was reduced in islets from type 2 diabetic subjects. Taken together, we identified a phosphoinositide switch on the surface on insulin granules that is required for stable granule docking at the plasma membrane and impaired in human type 2 diabetes.
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Affiliation(s)
- Phuoc My Nguyen
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Nikhil R Gandasi
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Beichen Xie
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Sari Sugahara
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.,Laboratory of Health Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan
| | - Yingke Xu
- Department of Biomedical Engineering, Key Laboratory of Biomedical Engineering of Ministry of Education, Zhejiang Provincial Key Laboratory of Cardio-Cerebral Vascular Detection Technology and Medicinal Effectiveness Appraisal, Zhejiang University, Hangzhou, China
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11
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METTL14 is essential for β-cell survival and insulin secretion. Biochim Biophys Acta Mol Basis Dis 2019; 1865:2138-2148. [PMID: 31029827 DOI: 10.1016/j.bbadis.2019.04.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 12/20/2018] [Accepted: 01/06/2019] [Indexed: 12/14/2022]
Abstract
Defects in the development, maintenance or expansion of β-cell mass can result in impaired glucose metabolism and diabetes. N6-methyladenosine affects mRNA stability and translation efficiency, and impacts cell differentiation and stress response. To determine if there is a role for m6A in β-cells, we investigated the effect of Mettl14, a key component of the m6A methyltransferase complex, on β-cell survival and function using rat insulin-2 promoter-Cre-mediated deletion of Mettl14 mouse line (βKO). We found that βKO mice with normal chow exhibited glucose intolerance, lower levels of glucose-stimulated insulin secretion, increased β-cell death and decreased β-cell mass. In addition, HFD-fed βKO mice developed glucose intolerance, decreased β-cell mass and proliferation, exhibited lower body weight, increased adipose tissue mass, and enhanced insulin sensitivity due to enhanced AKT signaling and decreased gluconeogenesis in the liver. HFD-fed βKO mice also showed a decrease in de novo lipogenesis, and an increase in lipolysis in the liver. RNA sequencing in islets revealed that Mettl14 deficiency in β-cells altered mRNA expression levels of some genes related to cell death and inflammation. Together, we showed that Mettl14 in β-cells plays a key role in β-cell survival, insulin secretion and glucose homeostasis.
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12
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The role of adherens junction proteins in the regulation of insulin secretion. Biosci Rep 2018; 38:BSR20170989. [PMID: 29459424 PMCID: PMC5861323 DOI: 10.1042/bsr20170989] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 02/17/2018] [Accepted: 02/19/2018] [Indexed: 12/16/2022] Open
Abstract
In healthy individuals, any rise in blood glucose levels is rapidly countered by the release of insulin from the β-cells of the pancreas which in turn promotes the uptake and storage of the glucose in peripheral tissues. The β-cells possess exquisite mechanisms regulating the secretion of insulin to ensure that the correct amount of insulin is released. These mechanisms involve tight control of the movement of insulin containing secretory vesicles within the β-cells, initially preventing most vesicles being able to move to the plasma membrane. Elevated glucose levels trigger an influx of Ca2+ that allows fusion of the small number of insulin containing vesicles that are pre-docked at the plasma membrane but glucose also stimulates processes that allow other insulin containing vesicles located further in the cell to move to and fuse with the plasma membrane. The mechanisms controlling these processes are complex and not fully understood but it is clear that the interaction of the β-cells with other β-cells in the islets is very important for their ability to develop the appropriate machinery for proper regulation of insulin secretion. Emerging evidence indicates one factor that is key for this is the formation of homotypic cadherin mediated adherens junctions between β-cells. Here, we review the evidence for this and discuss the mechanisms by which these adherens junctions might regulate insulin vesicle trafficking as well as the implications this has for understanding the dysregulation of insulin secretion seen in pathogenic states.
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Lambert C, Cubedo J, Padró T, Vilahur G, López-Bernal S, Rocha M, Hernández-Mijares A, Badimon L. Effects of a Carob-Pod-Derived Sweetener on Glucose Metabolism. Nutrients 2018; 10:E271. [PMID: 29495516 PMCID: PMC5872689 DOI: 10.3390/nu10030271] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/16/2018] [Accepted: 02/16/2018] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Patients with type 2 diabetes mellitus (T2DM) have a higher incidence of cardiovascular (CV) events. The ingestion of high-glycemic index (GI) diets, specially sweetened beverage consumption, has been associated with the development of T2DM and CV disease. OBJECTIVE We investigated the effects of the intake of a sweetened beverage, obtained from natural carbohydrates containing pinitol (PEB) compared to a sucrose-enriched beverage (SEB) in the context of impaired glucose tolerance (IGT) and diabetes. METHODS The study was divided in three different phases: (1) a discovery phase where the plasma proteomic profile was investigated by 2-DE (two-dimensional electrophoresis) followed by mass spectrometry (matrix-assisted laser desorption/ionization time-of-flight-MALDI-TOF/TOF) in healthy and IGT volunteers; (2) a verification phase where the potential mechanisms behind the observed protein changes were investigated in the discovery cohort and in an additional group of T2DM volunteers; and (3) the results were validated in a proof-of-concept interventional study in an animal model of diabetic rats with complementary methodologies. RESULTS Six weeks of pinitol-enriched beverage (PEB) intake induced a significant increase in two proteins involved in the insulin secretion pathway, insulin-like growth factor acid labile subunit (IGF1BP-ALS; 1.3-fold increase; P = 0.200) and complement C4A (1.83-fold increase; P = 0.007) in IGT subjects but not in healthy volunteers. Changes in C4A were also found in the serum samples of Zucker diabetic fatty (ZDF) rats after four weeks of PEB intake compared to basal levels (P = 0.042). In addition, an increased expression of the glucose transporter-2 (GLUT2) gene was observed in the jejunum (P = 0.003) of inositol-supplemented rats when compared to sucrose supplementation. This change was correlated with the observed change in C4A (P = 0.002). CONCLUSIONS Our results suggest that the substitution of a common sugar source, such as sucrose, by a naturally-based, pinitol-enriched beverage induces changes in the insulin secretion pathway that could help to reduce blood glucose levels by protecting β-cells and by stimulating the insulin secretion pathway. This mechanism of action could have a relevant role in the prevention of insulin resistance and diabetes progression.
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Affiliation(s)
- Carmen Lambert
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
| | - Judit Cubedo
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
- Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares, Ciber CV, Instituto de Salud Carlos III, 28029 Madrid, Spain.
| | - Teresa Padró
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
- Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares, Ciber CV, Instituto de Salud Carlos III, 28029 Madrid, Spain.
| | - Gemma Vilahur
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
- Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares, Ciber CV, Instituto de Salud Carlos III, 28029 Madrid, Spain.
| | - Sergi López-Bernal
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
| | - Milagros Rocha
- Service of Endocrinology, University Hospital Dr Peset, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), 46020 Valencia, Spain.
| | - Antonio Hernández-Mijares
- Service of Endocrinology, University Hospital Dr Peset, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), 46020 Valencia, Spain.
- Department of Medicine, University of Valencia, 46010 Valencia, Spain.
| | - Lina Badimon
- Program ICCC-Cardiovascular Research Center, Institut de Reserca, Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, 08025 Barcelona, Spain.
- Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares, Ciber CV, Instituto de Salud Carlos III, 28029 Madrid, Spain.
- Cardiovascular Research Chair, UAB, 08025 Barcelona, Spain.
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14
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Ashe S, Malhotra V, Raghu P. Protein kinase D regulates metabolism and growth by controlling secretion of insulin like peptide. Dev Biol 2018; 434:175-185. [PMID: 29247620 DOI: 10.1016/j.ydbio.2017.12.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Revised: 12/08/2017] [Accepted: 12/10/2017] [Indexed: 12/21/2022]
Abstract
Mechanisms coupling growth and metabolism are conserved in Drosophila and mammals. In metazoans, such coupling is achieved across tissue scales through the regulated secretion of chemical messengers such as insulin that control the metabolism and growth of cells. Although the regulated secretion of Insulin like peptide (dILP) is key to normal growth and metabolism in Drosophila, the sub-cellular mechanisms that regulate dILP release remain poorly understood. We find that reduced function of the only protein kinase D in Drosophila (dPKDH) results in delayed larval growth and development associated with abnormal sugar and lipid metabolism, reduced insulin signalling and accumulation of dILP2 in the neurosecretory IPCs of the larval brain. These phenotypes are rescued by tissue-selective reconstitution of dPKD in the neurosecretory cells of dPKDH. Selective downregulation of dPKD activity in the neurosecretory IPCs phenocopies the growth defects, metabolic abnormalities and dILP2 accumulation seen in dPKDH. Thus, dPKD mediated secretion of dILP2 from neurosecretory cells during development is necessary for normal larval growth.
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Affiliation(s)
- Sudipta Ashe
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India; Manipal University, Madhav Nagar, Manipal 576104, Karnataka, India
| | - Vivek Malhotra
- Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), 08002 Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India.
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15
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Watabe K, Yokawa S, Inoh Y, Suzuki T, Furuno T. Decreased intracellular granule movement and glucagon secretion in pancreatic α cells attached to superior cervical ganglion neurites. Mol Cell Biochem 2018; 446:83-89. [PMID: 29318457 DOI: 10.1007/s11010-018-3275-2] [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: 10/11/2017] [Accepted: 01/04/2018] [Indexed: 11/25/2022]
Abstract
Autonomic neurons innervate pancreatic islets of Langerhans and participate in the maintenance of blood glucose concentrations by controlling hormone levels through attachment with islet cells. We previously found that stimulated superior cervical ganglia (SCG) could induce Ca2+ oscillation in α cells via neuropeptide substance P using an in vitro co-culture model. In this study, we studied the effect of SCG neurite adhesion on intracellular secretory granule movement and glucagon secretion in α cells stimulated by low glucose concentration. Spinning disk microscopic analysis revealed that the mean velocity of intracellular granules was significantly lower in α cells attached to SCG neurites than that in those without neurites under low (2 mM), middle (10 mM), and high (20 mM) glucose concentrations. Stimulation by a low (2 mM) glucose concentration significantly increased glucagon secretion in α cells lacking neurites but not in those bound to neurites. These results suggest that adhesion to SCG neurites decreases low glucose-induced glucagon secretion in pancreatic α cells by attenuating intracellular granule movement activity.
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Affiliation(s)
- Kiyoto Watabe
- School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, 464-8650, Japan
| | - Satoru Yokawa
- School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, 464-8650, Japan
| | - Yoshikazu Inoh
- School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, 464-8650, Japan
| | - Takahiro Suzuki
- School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, 464-8650, Japan
| | - Tadahide Furuno
- School of Pharmacy, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya, 464-8650, Japan.
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16
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Lorincz R, Emfinger CH, Walcher A, Giolai M, Krautgasser C, Remedi MS, Nichols CG, Meyer D. In vivo monitoring of intracellular Ca 2+ dynamics in the pancreatic β-cells of zebrafish embryos. Islets 2018; 10:221-238. [PMID: 30521410 PMCID: PMC6300091 DOI: 10.1080/19382014.2018.1540234] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Assessing the response of pancreatic islet cells to glucose stimulation is important for understanding β-cell function. Zebrafish are a promising model for studies of metabolism in general, including stimulus-secretion coupling in the pancreas. We used transgenic zebrafish embryos expressing a genetically-encoded Ca2+ sensor in pancreatic β-cells to monitor a key step in glucose induced insulin secretion; the elevations of intracellular [Ca2+]i. In vivo and ex vivo analyses of [Ca2+]i demonstrate that β-cell responsiveness to glucose is well established in late embryogenesis and that embryonic β-cells also respond to free fatty acid and amino acid challenges. In vivo imaging of whole embryos further shows that indirect glucose administration, for example by yolk injection, results in a slow and asynchronous induction of β-cell [Ca2+]i responses, while intravenous glucose injections cause immediate and islet-wide synchronized [Ca2+]i fluctuations. Finally, we demonstrate that embryos with disrupted mutation of the CaV1.2 channel gene cacna1c are hyperglycemic and that this phenotype is associated with glucose-independent [Ca2+]i fluctuation in β-cells. The data reveal a novel central role of cacna1c in β-cell specific stimulus-secretion coupling in zebrafish and demonstrate that the novel approach we propose - to monitor the [Ca2+]i dynamics in embryonic β-cells in vivo - will help to expand the understanding of β-cell physiological functions in healthy and diseased states.
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Affiliation(s)
- Reka Lorincz
- Institute of Molecular Biology/CMBI, University of Innsbruck, Innsbruck, Austria
| | - Christopher H. Emfinger
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases (CIMED), Washington University School of Medicine, St. Louis, MO, USA
- Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Andrea Walcher
- Institute of Molecular Biology/CMBI, University of Innsbruck, Innsbruck, Austria
| | - Michael Giolai
- Institute of Molecular Biology/CMBI, University of Innsbruck, Innsbruck, Austria
| | - Claudia Krautgasser
- Institute of Molecular Biology/CMBI, University of Innsbruck, Innsbruck, Austria
| | - Maria S. Remedi
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, USA
- Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases (CIMED), Washington University School of Medicine, St. Louis, MO, USA
| | - Dirk Meyer
- Institute of Molecular Biology/CMBI, University of Innsbruck, Innsbruck, Austria
- CONTACT Dirk Meyer Institute of Molecular Biology/CMBI, University of Innsbruck, Technikerstrasse 25, Innsbruck 6020, Austria
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17
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Hastoy B, Clark A, Rorsman P, Lang J. Fusion pore in exocytosis: More than an exit gate? A β-cell perspective. Cell Calcium 2017; 68:45-61. [PMID: 29129207 DOI: 10.1016/j.ceca.2017.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 10/17/2017] [Accepted: 10/24/2017] [Indexed: 12/14/2022]
Abstract
Secretory vesicle exocytosis is a fundamental biological event and the process by which hormones (like insulin) are released into the blood. Considerable progress has been made in understanding this precisely orchestrated sequence of events from secretory vesicle docked at the cell membrane, hemifusion, to the opening of a membrane fusion pore. The exact biophysical and physiological regulation of these events implies a close interaction between membrane proteins and lipids in a confined space and constrained geometry to ensure appropriate delivery of cargo. We consider some of the still open questions such as the nature of the initiation of the fusion pore, the structure and the role of the Soluble N-ethylmaleimide-sensitive-factor Attachment protein REceptor (SNARE) transmembrane domains and their influence on the dynamics and regulation of exocytosis. We discuss how the membrane composition and protein-lipid interactions influence the likelihood of the nascent fusion pore forming. We relate these factors to the hypothesis that fusion pore expansion could be affected in type-2 diabetes via changes in disease-related gene transcription and alterations in the circulating lipid profile. Detailed characterisation of the dynamics of the fusion pore in vitro will contribute to understanding the larger issue of insulin secretory defects in diabetes.
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Affiliation(s)
- Benoit Hastoy
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK.
| | - Anne Clark
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK; Metabolic Research, Institute of Neuroscience and Physiology, University of Goteborg, Medicinaregatan 11, S-41309 Göteborg, Sweden
| | - Jochen Lang
- Laboratoire de Chimie et Biologie des Membranes et Nano-objets (CBMN), CNRS UMR 5248, Université de Bordeaux, Allée de Geoffrey St Hilaire, 33600 Pessac, France.
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18
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Makhmutova M, Liang T, Gaisano H, Caicedo A, Almaça J. Confocal Imaging of Neuropeptide Y-pHluorin: A Technique to Visualize Insulin Granule Exocytosis in Intact Murine and Human Islets. J Vis Exp 2017. [PMID: 28930993 DOI: 10.3791/56089] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Insulin secretion plays a central role in glucose homeostasis under normal physiological conditions as well as in disease. Current approaches to study insulin granule exocytosis either use electrophysiology or microscopy coupled to the expression of fluorescent reporters. However most of these techniques have been optimized for clonal cell lines or require dissociating pancreatic islets. In contrast, the method presented here allows for real time visualization of insulin granule exocytosis in intact pancreatic islets. In this protocol, we first describe the viral infection of isolated pancreatic islets with adenovirus that encodes a pH-sensitive green fluorescent protein (GFP), pHluorin, coupled to neuropeptide Y (NPY). Second, we describe the confocal imaging of islets five days after viral infection and how to monitor the insulin granule secretion. Briefly, the infected islets are placed on a coverslip on an imaging chamber and imaged under an upright laser-scanning confocal microscope while being continuously perfused with extracellular solution containing various stimuli. Confocal images spanning 50 µm of the islet are acquired as time-lapse recordings using a fast-resonant scanner. The fusion of insulin granules with the plasma membrane can be followed over time. This procedure also allows for testing a battery of stimuli in a single experiment, is compatible with both mouse and human islets, and can be combined with various dyes for functional imaging (e.g., membrane potential or cytosolic calcium dyes).
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Affiliation(s)
| | - Tao Liang
- Department of Medicine, University of Toronto
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19
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Kaur H, Sparvoli D, Osakada H, Iwamoto M, Haraguchi T, Turkewitz AP. An endosomal syntaxin and the AP-3 complex are required for formation and maturation of candidate lysosome-related secretory organelles (mucocysts) in Tetrahymena thermophila. Mol Biol Cell 2017; 28:1551-1564. [PMID: 28381425 PMCID: PMC5449153 DOI: 10.1091/mbc.e17-01-0018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 03/22/2017] [Accepted: 03/28/2017] [Indexed: 12/14/2022] Open
Abstract
Lysosome-related organelles (LROs) are secretory organelles formed by convergence between secretory and endosomal trafficking pathways. In Tetrahymena, secretory vesicles that resemble dense core granules are a new class of LROs whose synthesis depends on a conserved syntaxin required for heterotypic fusion and AP-3 for maturation. The ciliate Tetrahymena thermophila synthesizes large secretory vesicles called mucocysts. Mucocyst biosynthesis shares features with dense core granules (DCGs) in animal cells, including proteolytic processing of cargo proteins during maturation. However, other molecular features have suggested relatedness to lysosome-related organelles (LROs). LROs, which include diverse organelles in animals, are formed via convergence of secretory and endocytic trafficking. Here we analyzed Tetrahymena syntaxin 7-like 1 (Stx7l1p), a Qa-SNARE whose homologues in other lineages are linked with vacuoles/LROs. Stx7l1p is targeted to both immature and mature mucocysts and is essential in mucocyst formation. In STX7L1-knockout cells, the two major classes of mucocyst cargo proteins localize independently, accumulating in largely nonoverlapping vesicles. Thus initial formation of immature mucocysts involves heterotypic fusion, in which a subset of mucocyst proteins is delivered via an endolysosomal compartment. Further, we show that subsequent maturation requires AP-3, a complex widely implicated in LRO formation. Knockout of the µ-subunit gene does not impede delivery of any known mucocyst cargo but nonetheless arrests mucocyst maturation. Our data argue that secretory organelles in ciliates may represent a new class of LROs and reveal key roles of an endosomal syntaxin and AP-3 in the assembly of this complex compartment.
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Affiliation(s)
- Harsimran Kaur
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
| | - Daniela Sparvoli
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
| | - Hiroko Osakada
- Advanced ICT Research Institute, National Institute of Information and Communications Technology, Kobe 651-2492, Japan
| | - Masaaki Iwamoto
- Advanced ICT Research Institute, National Institute of Information and Communications Technology, Kobe 651-2492, Japan
| | - Tokuko Haraguchi
- Advanced ICT Research Institute, National Institute of Information and Communications Technology, Kobe 651-2492, Japan.,Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
| | - Aaron P Turkewitz
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
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