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Yi H, Gong D, Daddysman MK, Renn M, Scherer NF. Distinct Sub- to Superdiffuse Insulin Granule Transport Behaviors in β-Cells Are Strongly Affected by Granule Age. J Phys Chem B 2024; 128:6246-6256. [PMID: 38861346 DOI: 10.1021/acs.jpcb.4c01403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2024]
Abstract
Intracellular transport is a complex process that is difficult to describe by a single general model for motion. Here, we study the transport of insulin containing vesicles, termed granules, in live MIN6 cells. We characterize how the observed heterogeneity is affected by different intracellular factors by constructing a MIN6 cell line by CRISPR-CAS9 that constitutively expresses mCherry fused to insulin and is thus packaged in granules. Confocal microscopy imaging and single particle tracking of the granule transport provide long trajectories of thousands of single granule trajectories for statistical analysis. Mean squared displacement (MSD), angle correlation distribution, and step size distribution analysis allowed identifying five distinct granule transport subpopulations, from nearly immobile and subdiffusive to run-pause and superdiffusive. The subdiffusive subpopulation recapitulates the subordinated random walk we reported earlier (Tabei, 2013; ref 18). We show that the transport characteristics of the five subpopulations have a strong dependence on the age of insulin granules. The five subpopulations also reflect the effect of local microtubule and actin networks on transport in different cellular regions. Our results provide robust metrics to clarify the heterogeneity of granule transport and demonstrate the roles of microtubule versus actin networks with granule age since initial packaging in the Golgi.
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Affiliation(s)
- Hannah Yi
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Daozheng Gong
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
- Graduate Program in Biophysical Science, University of Chicago, Chicago, Illinois 60637, United States
| | - Matthew K Daddysman
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Martha Renn
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Norbert F Scherer
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
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2
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Suckert C, Zosel C, Schaefer M. Simultaneous TIRF imaging of subplasmalemmal Ca 2+ dynamics and granule fusions in insulin-secreting INS-1 cells reveals coexistent synchronized and asynchronous release. Cell Calcium 2024; 120:102883. [PMID: 38643716 DOI: 10.1016/j.ceca.2024.102883] [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: 01/04/2024] [Revised: 03/21/2024] [Accepted: 03/29/2024] [Indexed: 04/23/2024]
Abstract
The basal and glucose-induced insulin secretion from pancreatic beta cells is a tightly regulated process that is triggered in a Ca2+-dependent fashion and further positively modulated by substances that raise intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) or by certain antidiabetic drugs. In a previous study, we have temporally resolved the subplasmalemmal [Ca2+]i dynamics in beta cells that are characterized by trains of sharply delimited spikes, reaching peak values up to 5 µM. Applying total internal reflection fluorescence (TIRF) microscopy and synaptopHluorin to visualize fusion events of individual granules, we found that several fusion events can coincide within 50 to 150 ms. To test whether subplasmalemmal [Ca2+]i microdomains around single or clustered Ca2+ channels may cause a synchronized release of insulin-containing vesicles, we applied simultaneous dual-color TIRF microscopy and monitored Ca2+ fluctuations and exocytotic events in INS-1 cells at high frame rates. The results indicate that fusions can be triggered by subplasmalemmal Ca2+ spiking. This, however, does account for a minority of fusion events. About 90 %-95 % of fusion events either happen between Ca2+ spikes or incidentally overlap with subplasmalemmal Ca2+ spikes. We conclude that only a fraction of exocytotic events in glucose-induced and tolbutamide- or forskolin-enhanced insulin release from INS-1 cells is tightly coupled to Ca2+ microdomains around voltage-gated Ca2+ channels.
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Affiliation(s)
- Charlotte Suckert
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Carolin Zosel
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Michael Schaefer
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany.
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3
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Woolley L, Burbidge A, Vermant J, Christakopoulos F. A microrheological examination of insulin-secreting β-cells in healthy and diabetic-like conditions. SOFT MATTER 2024; 20:3464-3472. [PMID: 38573072 DOI: 10.1039/d3sm01141k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/05/2024]
Abstract
Pancreatic β-cells regulate glucose homeostasis through glucose-stimulated insulin secretion, which is hindered in type-2 diabetes. Transport of the insulin vesicles is expected to be affected by changes in the viscoelastic and transport properties of the cytoplasm. These are evaluated in situ through particle-tracking measurements using a rat insulinoma β-cell line. The use of inert probes assists in decoupling the material properties of the cytoplasm from the active transport through cellular processes. The effect of glucose-stimulated insulin secretion is examined, and the subsequent remodeling of the cytoskeleton, at constant effects of cell activity, is shown to result in reduced mobility of the tracer particles. Induction of diabetic-like conditions is identified to alter the mean-squared displacement of the passive particles in the cytoplasm and diminish its reaction to glucose stimulation.
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Affiliation(s)
- Lukas Woolley
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.
| | - Adam Burbidge
- Nestlé Research, Route de Jorat 57, vers-chez-les Blanc, 1000 Lausanne, Switzerland
| | - Jan Vermant
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.
| | - Fotis Christakopoulos
- Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.
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4
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Gaus B, Brüning D, Groß S, Müller M, Rustenbeck I. The changing view of insulin granule mobility: From conveyor belt to signaling hub. Front Endocrinol (Lausanne) 2022; 13:983152. [PMID: 36120467 PMCID: PMC9478610 DOI: 10.3389/fendo.2022.983152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 08/11/2022] [Indexed: 11/28/2022] Open
Abstract
Before the advent of TIRF microscopy the fate of the insulin granule prior to secretion was deduced from biochemical investigations, electron microscopy and electrophysiological measurements. Since Calcium-triggered granule fusion is indisputably necessary to release insulin into the extracellular space, much effort was directed to the measure this event at the single granule level. This has also been the major application of the TIRF microscopy of the pancreatic beta cell when it became available about 20 years ago. To better understand the metabolic modulation of secretion, we were interested to characterize the entirety of the insulin granules which are localized in the vicinity of the plasma membrane to identify the characteristics which predispose to fusion. In this review we concentrate on how the description of granule mobility in the submembrane space has evolved as a result of progress in methodology. The granules are in a state of constant turnover with widely different periods of residence in this space. While granule fusion is associated +with prolonged residence and decreased lateral mobility, these characteristics may not only result from binding to the plasma membrane but also from binding to the cortical actin web, which is present in the immediate submembrane space. While granule age as such affects granule mobility and fusion probability, the preceding functional states of the beta cell leave their mark on these parameters, too. In summary, the submembrane granules form a highly dynamic heterogeneous population and contribute to the metabolic memory of the beta cells.
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Affiliation(s)
- Bastian Gaus
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Dennis Brüning
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Sofie Groß
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
| | - Michael Müller
- Institute of Dynamics and Vibrations, Technische Universität Braunschweig, Braunschweig, Germany
| | - Ingo Rustenbeck
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Braunschweig, Germany
- *Correspondence: Ingo Rustenbeck,
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5
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Ferri G, Pesce L, Tesi M, Marchetti P, Cardarelli F. β-Cell Pathophysiology: A Review of Advanced Optical Microscopy Applications. Int J Mol Sci 2021; 22:ijms222312820. [PMID: 34884624 PMCID: PMC8657725 DOI: 10.3390/ijms222312820] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 11/24/2021] [Accepted: 11/24/2021] [Indexed: 11/30/2022] Open
Abstract
β-cells convert glucose (input) resulting in the controlled release of insulin (output), which in turn has the role to maintain glucose homeostasis. β-cell function is regulated by a complex interplay between the metabolic processing of the input, its transformation into second-messenger signals, and final mobilization of insulin-containing granules towards secretion of the output. Failure at any level in this process marks β-cell dysfunction in diabetes, thus making β-cells obvious potential targets for therapeutic purposes. Addressing quantitatively β-cell (dys)function at the molecular level in living samples requires probing simultaneously the spatial and temporal dimensions at the proper resolution. To this aim, an increasing amount of research efforts are exploiting the potentiality of biophysical techniques. In particular, using excitation light in the visible/infrared range, a number of optical-microscopy-based approaches have been tailored to the study of β-cell-(dys)function at the molecular level, either in label-free mode (i.e., exploiting intrinsic autofluorescence of cells) or by the use of organic/genetically-encoded fluorescent probes. Here, relevant examples from the literature are reviewed and discussed. Based on this, new potential lines of development in the field are drawn.
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Affiliation(s)
- Gianmarco Ferri
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
| | - Luca Pesce
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
| | - Marta Tesi
- Islet Cell Laboratory, Department of Clinical and Experimental Medicine, University of Pisa, 56127 Pisa, Italy; (M.T.); (P.M.)
| | - Piero Marchetti
- Islet Cell Laboratory, Department of Clinical and Experimental Medicine, University of Pisa, 56127 Pisa, Italy; (M.T.); (P.M.)
| | - Francesco Cardarelli
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy; (G.F.); (L.P.)
- Correspondence:
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Yau B, Hocking S, Andrikopoulos S, Kebede MA. Targeting the insulin granule for modulation of insulin exocytosis. Biochem Pharmacol 2021; 194:114821. [PMID: 34748819 DOI: 10.1016/j.bcp.2021.114821] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 10/29/2021] [Accepted: 11/02/2021] [Indexed: 02/08/2023]
Abstract
The pancreatic β-cells control insulin secretion in the body to regulate glucose homeostasis, and β-cell stress and dysfunction is characteristic of Type 2 Diabetes. Pharmacological targeting of the β-cell to increase insulin secretion is typically utilised, however, extended use of common drugs such as sulfonylureas are known to result in secondary failure. Moreover, there is evidence they may induce β-cell failure in the long term. Within β-cells, insulin secretory granules (ISG) serve as compartments to store, process and traffic insulin for exocytosis. There is now growing evidence that ISG exist in multiple populations, distinct in their protein composition, motility, age, and capacity for secretion. In this review, we discuss the implications of a heterogenous ISG population in β-cells and highlight the need for more understanding into how unique ISG populations may be targeted in anti-diabetic therapies.
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Affiliation(s)
- Belinda Yau
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Camperdown, NSW, Australia; Charles Perkins Centre, The University of Sydney, Camperdown, NSW, Australia.
| | - Samantha Hocking
- Charles Perkins Centre, The University of Sydney, Camperdown, NSW, Australia; Central Clinical School, Faculty of Medicine and Health and Department of Endocrinology Royal Prince Alfred Hospital, NSW, Australia
| | | | - Melkam A Kebede
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Camperdown, NSW, Australia; Charles Perkins Centre, The University of Sydney, Camperdown, NSW, Australia
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7
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Hu R, Zhu X, Yuan M, Ho KH, Kaverina I, Gu G. Microtubules and Gαo-signaling modulate the preferential secretion of young insulin secretory granules in islet β cells via independent pathways. PLoS One 2021; 16:e0241939. [PMID: 34292976 PMCID: PMC8297875 DOI: 10.1371/journal.pone.0241939] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 06/15/2021] [Indexed: 12/24/2022] Open
Abstract
For sustainable function, each pancreatic islet β cell maintains thousands of insulin secretory granules (SGs) at all times. Glucose stimulation induces the secretion of a small portion of these SGs and simultaneously boosts SG biosynthesis to sustain this stock. The failure of these processes, often induced by sustained high-insulin output, results in type 2 diabetes. Intriguingly, young insulin SGs are more likely secreted during glucose-stimulated insulin secretion (GSIS) for unknown reasons, while older SGs tend to lose releasability and be degraded. Here, we examine the roles of microtubule (MT) and Gαo-signaling in regulating the preferential secretion of young versus old SGs. We show that both MT-destabilization and Gαo inactivation results in more SGs localization near plasma membrane (PM) despite higher levels of GSIS and reduced SG biosynthesis. Intriguingly, MT-destabilization or Gαo-inactivation results in higher secretion probabilities of older SGs, while combining both having additive effects on boosting GSIS. Lastly, Gαo inactivation does not detectably destabilize the β-cell MT network. These findings suggest that Gαo and MT can modulate the preferential release of younger insulin SGs via largely parallel pathways.
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Affiliation(s)
- Ruiying Hu
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Xiaodong Zhu
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Mingyang Yuan
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Kung-Hsien Ho
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Irina Kaverina
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
- * E-mail: (GG); (IK)
| | - Guoqiang Gu
- Department of Cell and Developmental Biology, The Program of Developmental Biology and the Center for Stem Cell Biology, Vanderbilt University, Nashville, TN, United States of America
- * E-mail: (GG); (IK)
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8
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Isolation and Proteomics of the Insulin Secretory Granule. Metabolites 2021; 11:metabo11050288. [PMID: 33946444 PMCID: PMC8147143 DOI: 10.3390/metabo11050288] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 04/28/2021] [Accepted: 04/28/2021] [Indexed: 12/21/2022] Open
Abstract
Insulin, a vital hormone for glucose homeostasis is produced by pancreatic beta-cells and when secreted, stimulates the uptake and storage of glucose from the blood. In the pancreas, insulin is stored in vesicles termed insulin secretory granules (ISGs). In Type 2 diabetes (T2D), defects in insulin action results in peripheral insulin resistance and beta-cell compensation, ultimately leading to dysfunctional ISG production and secretion. ISGs are functionally dynamic and many proteins present either on the membrane or in the lumen of the ISG may modulate and affect different stages of ISG trafficking and secretion. Previously, studies have identified few ISG proteins and more recently, proteomics analyses of purified ISGs have uncovered potential novel ISG proteins. This review summarizes the proteins identified in the current ISG proteomes from rat insulinoma INS-1 and INS-1E cell lines. Here, we also discuss techniques of ISG isolation and purification, its challenges and potential future directions.
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9
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Pratt EP, Anson KJ, Tapper JK, Simpson DM, Palmer AE. Systematic Comparison of Vesicular Targeting Signals Leads to the Development of Genetically Encoded Vesicular Fluorescent Zn 2+ and pH Sensors. ACS Sens 2020; 5:3879-3891. [PMID: 33305939 DOI: 10.1021/acssensors.0c01231] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Genetically encoded fluorescent sensors have been widely used to illuminate secretory vesicle dynamics and the vesicular lumen, including Zn2+ and pH, in living cells. However, vesicular sensors have a tendency to mislocalize and are susceptible to the acidic intraluminal pH. In this study, we performed a systematic comparison of five different vesicular proteins to target the fluorescent protein mCherry and a Zn2+ Förster resonance energy transfer (FRET) sensor to secretory vesicles. We found that motifs derived from vesicular cargo proteins, including chromogranin A (CgA), target vesicular puncta with greater efficacy than transmembrane proteins. To characterize vesicular Zn2+ levels, we developed CgA-Zn2+ FRET sensor fusions with existing sensors ZapCY1 and eCALWY-4 and characterized subcellular localization and the influence of pH on sensor performance. We simultaneously monitored Zn2+ and pH in individual secretory vesicles by leveraging the acceptor fluorescent protein as a pH sensor and found that pH influenced FRET measurements in situ. While unable to characterize vesicular Zn2+ at the single-vesicle level, we were able to monitor Zn2+ dynamics in populations of vesicles and detected high vesicular Zn2+ in MIN6 cells compared to lower levels in the prostate cancer cell line LnCaP. The combination of CgA-ZapCY1 and CgA-eCALWY-4 allows for measurement of Zn2+ from pM to nM ranges.
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Affiliation(s)
- Evan P.S. Pratt
- Department of Biochemistry and BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Ave, UCB 596, Boulder, Colorado 80309-0401, United States
| | - Kelsie J. Anson
- Department of Biochemistry and BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Ave, UCB 596, Boulder, Colorado 80309-0401, United States
| | - Justin K. Tapper
- Department of Biochemistry and BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Ave, UCB 596, Boulder, Colorado 80309-0401, United States
| | - David M. Simpson
- Department of Biochemistry and BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Ave, UCB 596, Boulder, Colorado 80309-0401, United States
| | - Amy E. Palmer
- Department of Biochemistry and BioFrontiers Institute, University of Colorado Boulder, 3415 Colorado Ave, UCB 596, Boulder, Colorado 80309-0401, United States
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10
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Ho KH, Yang X, Osipovich AB, Cabrera O, Hayashi ML, Magnuson MA, Gu G, Kaverina I. Glucose Regulates Microtubule Disassembly and the Dose of Insulin Secretion via Tau Phosphorylation. Diabetes 2020; 69:1936-1947. [PMID: 32540877 PMCID: PMC7458041 DOI: 10.2337/db19-1186] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 06/07/2020] [Indexed: 12/16/2022]
Abstract
The microtubule cytoskeleton of pancreatic islet β-cells regulates glucose-stimulated insulin secretion (GSIS). We have reported that the microtubule-mediated movement of insulin vesicles away from the plasma membrane limits insulin secretion. High glucose-induced remodeling of microtubule network facilitates robust GSIS. This remodeling involves disassembly of old microtubules and nucleation of new microtubules. Here, we examine the mechanisms whereby glucose stimulation decreases microtubule lifetimes in β-cells. Using real-time imaging of photoconverted microtubules, we demonstrate that high levels of glucose induce rapid microtubule disassembly preferentially in the periphery of individual β-cells, and this process is mediated by the phosphorylation of microtubule-associated protein tau. Specifically, high glucose induces tau hyper-phosphorylation via glucose-responsive kinases GSK3, PKA, PKC, and CDK5. This causes dissociation of tau from and subsequent destabilization of microtubules. Consequently, tau knockdown in mouse islet β-cells facilitates microtubule turnover, causing increased basal insulin secretion, depleting insulin vesicles from the cytoplasm, and impairing GSIS. More importantly, tau knockdown uncouples microtubule destabilization from glucose stimulation. These findings suggest that tau suppresses peripheral microtubules turning over to restrict insulin oversecretion in basal conditions and preserve the insulin pool that can be released following stimulation; high glucose promotes tau phosphorylation to enhance microtubule disassembly to acutely enhance GSIS.
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Affiliation(s)
- Kung-Hsien Ho
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
| | - Xiaodun Yang
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
| | - Anna B Osipovich
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | | | | | - Mark A Magnuson
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | - Guoqiang Gu
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
| | - Irina Kaverina
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN
- Program of Developmental Biology and Vanderbilt Center for Stem Cell Biology, Vanderbilt University, Nashville, TN
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11
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Yau B, Hays L, Liang C, Laybutt DR, Thomas HE, Gunton JE, Williams L, Hawthorne WJ, Thorn P, Rhodes CJ, Kebede MA. A fluorescent timer reporter enables sorting of insulin secretory granules by age. J Biol Chem 2020; 295:8901-8911. [PMID: 32341128 PMCID: PMC7335792 DOI: 10.1074/jbc.ra120.012432] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2020] [Revised: 03/21/2020] [Indexed: 01/03/2023] Open
Abstract
Within the pancreatic β-cells, insulin secretory granules (SGs) exist in functionally distinct pools, displaying variations in motility as well as docking and fusion capability. Current therapies that increase insulin secretion do not consider the existence of these distinct SG pools. Accordingly, these approaches are effective only for a short period, with a worsening of glycemia associated with continued decline in β-cell function. Insulin granule age is underappreciated as a determinant for why an insulin granule is selected for secretion and may explain why newly synthesized insulin is preferentially secreted from β-cells. Here, using a novel fluorescent timer protein, we aimed to investigate the preferential secretion model of insulin secretion and identify how granule aging is affected by variation in the β-cell environment, such as hyperglycemia. We demonstrate the use of a fluorescent timer construct, syncollin-dsRedE5TIMER, which changes its fluorescence from green to red over 18 h, in both microscopy and fluorescence-assisted organelle-sorting techniques. We confirm that the SG-targeting construct localizes to insulin granules in β-cells and does not interfere with normal insulin SG behavior. We visualize insulin SG aging behavior in MIN6 and INS1 β-cell lines and in primary C57BL/6J mouse and nondiabetic human islet cells. Finally, we separated young and old insulin SGs, revealing that preferential secretion of younger granules occurs in glucose-stimulated insulin secretion. We also show that SG population age is modulated by the β-cell environment in vivo in the db/db mouse islets and ex vivo in C57BL/6J islets exposed to different glucose environments.
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Affiliation(s)
- Belinda Yau
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; School of Life and Environmental Sciences, Faculty of Science, University of Sydney, Sydney, New South Wales, Australia
| | - Lori Hays
- STEM-Department of Biology, Edmonds Community College, Lynnwood, Washington, USA
| | - Cassandra Liang
- Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - D Ross Laybutt
- Garvan Institute of Medical Research, Sydney, New South Wales, Australia; St. Vincent's Clinical School, University of New South Wales Sydney, Sydney, New South Wales, Australia
| | - Helen E Thomas
- St. Vincent's Institute, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia
| | - Jenny E Gunton
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; The Westmead Institute for Medical Research, University of Sydney, Westmead, New South Wales, Australia
| | - Lindy Williams
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; National Pancreas and Islet Transplant Unit (NPITU), Westmead Hospital, Sydney, New South Wales, Australia
| | - Wayne J Hawthorne
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; National Pancreas and Islet Transplant Unit (NPITU), Westmead Hospital, Sydney, New South Wales, Australia
| | - Peter Thorn
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; Discipline of Physiology, School of Medical Sciences, Faculty of Medicine and Health, Charles Perkins Centre, University of Sydney, Camperdown, New South Wales, Australia
| | - Christopher J Rhodes
- Research and Early Development, Cardiovascular, Renal and Metabolic Diseases, BioPharmaceuticals R&D, AstraZeneca Ltd, Gaithersburg, Maryland, USA; Pacific Northwest Research Institute, Seattle, Washington, USA
| | - Melkam A Kebede
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; School of Life and Environmental Sciences, Faculty of Science, University of Sydney, Sydney, New South Wales, Australia.
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12
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Bearrows SC, Bauchle CJ, Becker M, Haldeman JM, Swaminathan S, Stephens SB. Chromogranin B regulates early-stage insulin granule trafficking from the Golgi in pancreatic islet β-cells. J Cell Sci 2019; 132:jcs.231373. [PMID: 31182646 DOI: 10.1242/jcs.231373] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 05/31/2019] [Indexed: 12/12/2022] Open
Abstract
Chromogranin B (CgB, also known as CHGB) is abundantly expressed in dense core secretory granules of multiple endocrine tissues and has been suggested to regulate granule biogenesis in some cell types, including the pancreatic islet β-cell, though the mechanisms are poorly understood. Here, we demonstrate a critical role for CgB in regulating secretory granule trafficking in the β-cell. Loss of CgB impairs glucose-stimulated insulin secretion, impedes proinsulin processing to yield increased proinsulin content, and alters the density of insulin-containing granules. Using an in situ fluorescent pulse-chase strategy to track nascent proinsulin, we show that loss of CgB impairs Golgi budding of proinsulin-containing secretory granules, resulting in a substantial delay in trafficking of nascent granules to the plasma membrane with an overall decrease in total plasma membrane-associated granules. These studies demonstrate that CgB is necessary for efficient trafficking of secretory proteins into the budding granule, which impacts the availability of insulin-containing secretory granules for exocytic release.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Shelby C Bearrows
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52246, USA.,Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA 52246, USA
| | - Casey J Bauchle
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52246, USA.,Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA 52246, USA
| | - McKenzie Becker
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52246, USA.,Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA 52246, USA
| | - Jonathan M Haldeman
- Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC 27710, USA.,Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA
| | - Svetha Swaminathan
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52246, USA.,Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA 52246, USA
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52246, USA .,Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Iowa, Iowa City, IA 52246, USA
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13
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Insulin secretory granules labelled with phogrin-fluorescent proteins show alterations in size, mobility and responsiveness to glucose stimulation in living β-cells. Sci Rep 2019; 9:2890. [PMID: 30814595 PMCID: PMC6393586 DOI: 10.1038/s41598-019-39329-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 01/15/2019] [Indexed: 11/13/2022] Open
Abstract
The intracellular life of insulin secretory granules (ISGs) from biogenesis to secretion depends on their structural (e.g. size) and dynamic (e.g. diffusivity, mode of motion) properties. Thus, it would be useful to have rapid and robust measurements of such parameters in living β-cells. To provide such measurements, we have developed a fast spatiotemporal fluctuation spectroscopy. We calculate an imaging-derived Mean Squared Displacement (iMSD), which simultaneously provides the size, average diffusivity, and anomalous coefficient of ISGs, without the need to extract individual trajectories. Clustering of structural and dynamic quantities in a multidimensional parametric space defines the ISGs’ properties for different conditions. First, we create a reference using INS-1E cells expressing proinsulin fused to a fluorescent protein (FP) under basal culture conditions and validate our analysis by testing well-established stimuli, such as glucose intake, cytoskeleton disruption, or cholesterol overload. After, we investigate the effect of FP-tagged ISG protein markers on the structural and dynamic properties of the granule. While iMSD analysis produces similar results for most of the lumenal markers, the transmembrane marker phogrin-FP shows a clearly altered result. Phogrin overexpression induces a substantial granule enlargement and higher mobility, together with a partial de-polymerization of the actin cytoskeleton, and reduced cell responsiveness to glucose stimulation. Our data suggest a more careful interpretation of many previous ISG-based reports in living β-cells. The presented data pave the way to high-throughput cell-based screening of ISG structure and dynamics under various physiological and pathological conditions.
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14
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Firlar E, Ouy M, Covnot L, Xing Y, Lee D, Chan A, He Y, Song B, Afelik S, Wang Y, Shahbazian-Yassar R, Oberholzer J, Shokuhfar T. In situ graphene liquid cell-transmission electron microscopy study of insulin secretion in pancreatic islet cells. Int J Nanomedicine 2019; 14:371-382. [PMID: 30662261 PMCID: PMC6327893 DOI: 10.2147/ijn.s169506] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Islet cell transplantation is one of the key treatments for type 1 diabetes. Understanding the mechanisms of insulin fusion and exocytosis are of utmost importance for the improvement of the current islet cell transplantation and treatment of diabetes. These phenomena have not been fully evaluated due either to the lack of proper dynamic imaging, or the lack of proper cell preservation during imaging at nanoscales. METHODS By maintaining the native environment of pancreatic β-cells between two graphene monolayer sheets, we were able to monitor the subcellular events using in situ graphene liquid cell (GLC)-transmission electron microscopy (TEM) with both high temporal and high spatial resolution. RESULTS For the first time, the nucleation and growth of insulin particles until the later stages of fusion were imaged at nanometer scales. The release of insulin from plasma membrane involves the degradation of plasma membrane and drastic reductions in the shorter axis of the insulin particles. Sequential exocytosis results indicated the nucleation, growth and attachment of the new insulin particles to the already anchored ones, which is thermodynamically favorable due to the reduction in total surface, further reducing the Gibbs free energy. The retraction of the already anchored insulin toward the cell is also monitored for the first time live at nanoscale resolution. CONCLUSION Investigation of insulin granule dynamics in β-cells can be investigated via GLC-TEM. Our findings with this technology open new realms for the development of novel drugs on pathological pancreatic β-cells, because this approach facilitates observing the effects of the stimuli on the live cells and insulin granules.
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Affiliation(s)
- Emre Firlar
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
- University of Illinois at Chicago, Department of Mechanical and Industrial Engineering, Chicago, IL, USA,
| | - Meagan Ouy
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
| | - Leigha Covnot
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
| | - Yuan Xing
- University of Virginia, Department of Surgery, Charlottesville, VA, USA
| | - Daniel Lee
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
- University of Illinois at Chicago, Department of Surgery, Chicago, IL, USA
| | - Alessandro Chan
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
- University of Illinois at Chicago, Department of Surgery, Chicago, IL, USA
| | - Yi He
- University of Virginia, Department of Surgery, Charlottesville, VA, USA
| | - Boao Song
- University of Illinois at Chicago, Department of Mechanical and Industrial Engineering, Chicago, IL, USA,
| | - Solomon Afelik
- University of Illinois at Chicago, Department of Surgery, Chicago, IL, USA
| | - Yong Wang
- University of Virginia, Department of Surgery, Charlottesville, VA, USA
| | - Reza Shahbazian-Yassar
- University of Illinois at Chicago, Department of Mechanical and Industrial Engineering, Chicago, IL, USA,
| | - Jose Oberholzer
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
- University of Virginia, Department of Surgery, Charlottesville, VA, USA
| | - Tolou Shokuhfar
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA,
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15
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Scavuzzo MA, Chmielowiec J, Yang D, Wamble K, Chaboub LS, Duraine L, Tepe B, Glasgow SM, Arenkiel BR, Brou C, Deneen B, Borowiak M. Pancreatic Cell Fate Determination Relies on Notch Ligand Trafficking by NFIA. Cell Rep 2018; 25:3811-3827.e7. [PMID: 30590051 DOI: 10.1016/j.celrep.2018.11.078] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Revised: 09/28/2018] [Accepted: 11/20/2018] [Indexed: 12/24/2022] Open
Abstract
Notch is activated globally in pancreatic progenitors; however, for progenitors to differentiate into endocrine cells, they must escape Notch activation to express Neurogenin-3. Here, we find that the transcription factor nuclear factor I/A (NFIA) promotes endocrine development by regulating Notch ligand Dll1 trafficking. Pancreatic deletion of NFIA leads to cell fate defects, with increased duct and decreased endocrine formation, while ectopic expression promotes endocrine formation in mice and human pancreatic progenitors. NFIA-deficient mice exhibit dysregulation of trafficking-related genes including increased expression of Mib1, which acts to target Dll1 for endocytosis. We find that NFIA binds to the Mib1 promoter, with loss of NFIA leading to an increase in Dll1 internalization and enhanced Notch activation with rescue of the cell fate defects after Mib1 knockdown. This study reveals NFIA as a pro-endocrine factor in the pancreas, acting to repress Mib1, inhibit Dll1 endocytosis and thus promote escape from Notch activation.
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Affiliation(s)
- Marissa A Scavuzzo
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jolanta Chmielowiec
- Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, TX 77030, USA; Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, Houston, TX 77030, USA
| | - Diane Yang
- Molecular and Cellular Biology Department, Baylor College of Medicine, Houston, TX 77030, USA
| | - Katrina Wamble
- Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, TX 77030, USA; Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, Houston, TX 77030, USA
| | - Lesley S Chaboub
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Lita Duraine
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA
| | - Burak Tepe
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Stacey M Glasgow
- Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, TX 77030, USA; Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Benjamin R Arenkiel
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; McNair Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Christel Brou
- Department of Cell Biology and Infection, Institute Pasteur, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France
| | - Benjamin Deneen
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA; Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, TX 77030, USA; Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Malgorzata Borowiak
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA; Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, and Houston Methodist Hospital, Houston, TX 77030, USA; Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, Houston, TX 77030, USA; Molecular and Cellular Biology Department, Baylor College of Medicine, Houston, TX 77030, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; McNair Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA.
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16
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Ferri G, Bugliani M, Marchetti P, Cardarelli F. Probing the light scattering properties of insulin secretory granules in single live cells. Biochem Biophys Res Commun 2018; 503:2710-2714. [PMID: 30119894 DOI: 10.1016/j.bbrc.2018.08.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 08/03/2018] [Indexed: 11/22/2022]
Abstract
Light scattering was recently demonstrated to serve as an intrinsic indicator for pancreatic islet cell mass and secretion. The insulin secretory granule (ISG), in particular, was proposed to be a reasonable candidate as the main intracellular source of scattered light due to the densely-packed insulin semi-crystal in the granule lumen. This scenario, if confirmed, would in principle open new perspectives for label-free single-granule imaging, tracking, and analysis. Contrary to such expectations, here we demonstrate that ISGs are not a primary source of scattering in primary human β-cells, as well as in immortalized β-like cells, quantitatively not superior to other intracellular organelles/structures, such as lysosomes and internal membranes. This result is achieved through multi-channel imaging of scattered light along with fluorescence arising from selectively-labelled ISGs. Co-localization and spatiotemporal cross-correlation analysis is performed on these signals, and compared among different cell lines. Obtained results suggest a careful re-thinking of the possibility to exploit intrinsic optical properties originating from ISGs for single-granule imaging purposes.
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Affiliation(s)
- Gianmarco Ferri
- NEST - Scuola Normale Superiore, Istituto Nanoscienze - CNR (CNR NANO), Pisa, Italy; Nanoscopy, Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, Genova, 16163 Italy
| | - Marco Bugliani
- Department of Clinical and Experimental Medicine, Islet Cell Laboratory, University of Pisa, Pisa, Italy
| | - Piero Marchetti
- Department of Clinical and Experimental Medicine, Islet Cell Laboratory, University of Pisa, Pisa, Italy
| | - Francesco Cardarelli
- NEST - Scuola Normale Superiore, Istituto Nanoscienze - CNR (CNR NANO), Pisa, Italy.
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17
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Stephens SB, Edwards RJ, Sadahiro M, Lin WJ, Jiang C, Salton SR, Newgard CB. The Prohormone VGF Regulates β Cell Function via Insulin Secretory Granule Biogenesis. Cell Rep 2018; 20:2480-2489. [PMID: 28877479 DOI: 10.1016/j.celrep.2017.08.050] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 07/25/2017] [Accepted: 08/15/2017] [Indexed: 12/18/2022] Open
Abstract
The prohormone VGF is expressed in neuroendocrine and endocrine tissues and regulates nutrient and energy status both centrally and peripherally. We and others have shown that VGF-derived peptides have direct action on the islet β cell as secretagogues and cytoprotective agents; however, the endogenous function of VGF in the β cell has not been described. Here, we demonstrate that VGF regulates secretory granule formation. VGF loss-of-function studies in both isolated islets and conditional knockout mice reveal a profound decrease in stimulus-coupled insulin secretion. Moreover, VGF is necessary to facilitate efficient exit of granule cargo from the trans-Golgi network and proinsulin processing. It also functions to replenish insulin granule stores following nutrient stimulation. Our data support a model in which VGF operates at a critical node of granule biogenesis in the islet β cell to coordinate insulin biosynthesis with β cell secretory capacity.
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Affiliation(s)
- Samuel B Stephens
- Sarah W. Stedman Nutrition and Metabolism Center, Duke University Medical Center, Durham, NC 27704, USA; Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC 27704, USA; Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27704, USA.
| | - Robert J Edwards
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27704, USA
| | - Masato Sadahiro
- Department of Neuroscience, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA
| | - Wei-Jye Lin
- Department of Neuroscience, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA
| | - Cheng Jiang
- Department of Neuroscience, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA
| | - Stephen R Salton
- Department of Neuroscience, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA; Friedman Brain Institute, Icahn School of Medicine at Mt. Sinai, New York, NY 10029, USA
| | - Christopher B Newgard
- Sarah W. Stedman Nutrition and Metabolism Center, Duke University Medical Center, Durham, NC 27704, USA; Duke Molecular Physiology Institute, Duke University Medical Center, Durham, NC 27704, USA; Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27704, USA; Department of Medicine, Division of Endocrinology, Duke University Medical Center, Durham, NC 27704, USA
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18
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Mollet IG, Malm HA, Wendt A, Orho-Melander M, Eliasson L. Integrator of Stress Responses Calmodulin Binding Transcription Activator 1 (Camta1) Regulates miR-212/miR-132 Expression and Insulin Secretion. J Biol Chem 2016; 291:18440-52. [PMID: 27402838 DOI: 10.1074/jbc.m116.716860] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Indexed: 01/04/2023] Open
Abstract
Altered microRNA profiles have been demonstrated in experimental models of type 2 diabetes, including in islets of the diabetic Goto-Kakizaki (GK) rat. Our bioinformatic analysis of conserved sequences in promoters of microRNAs, previously observed to be up-regulated in GK rat islets, revealed putative CGCG-core motifs on the promoter of the miR-212/miR-132 cluster, overexpression of which has been shown to increase insulin secretion. These motifs are possible targets of calmodulin binding transcription activators Camta1 and Camta2 that have been recognized as integrators of stress responses. We also identified putative NKE elements, possible targets of NK2 homeobox proteins like the essential islet transcription factor Nkx2-2. As Camtas can function as co-activators with NK2 proteins in other tissues, we explored the role of Camta1, Camta2, and Nkx2-2 in the regulation of the miR-212/miR-132 cluster and insulin secretion. We demonstrate that exposure of control Wistar or GK rat islets to 16.7 mm glucose increases miR-212/miR-132 expression but significantly less so in the GK rat. In addition, Camta1, Camta2, and Nkx2-2 were down-regulated in GK rat islets, and knockdown of Camta1 reduced miR-212/miR-132 promoter activity and miR-212/miR-132 expression, even under cAMP elevation. Knockdown of Camta1 decreased insulin secretion in INS-1 832/13 cells and Wistar rat islets but increased insulin content. Furthermore, knockdown of Camta1 reduced K(+)-induced insulin secretion and voltage-dependent Ca(2+) currents. We also demonstrate Camta1 and Nkx2-2 protein interaction. These results indicate that Camta1 is required not only for expression of the miR-212/miR-132 cluster but at multiple levels for regulating beta cell insulin content and secretion.
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Affiliation(s)
- Inês Guerra Mollet
- From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden
| | - Helena Anna Malm
- From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden
| | - Anna Wendt
- From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden
| | - Marju Orho-Melander
- From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden
| | - Lena Eliasson
- From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden
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19
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Nemet I, Ropelewski P, Imanishi Y. Applications of phototransformable fluorescent proteins for tracking the dynamics of cellular components. Photochem Photobiol Sci 2016; 14:1787-806. [PMID: 26345171 DOI: 10.1039/c5pp00174a] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In the past few decades, fluorescent proteins have revolutionized the field of cell biology. Phototransformable fluorescent proteins are capable of changing their excitation and emission spectra after being exposed to specific wavelength(s) of light. The majority of phototransformable fluorescent proteins have originated from marine organisms. Genetic engineering of these proteins has made available many choices for different colors, modes of conversion, and other biophysical properties. Their phototransformative property has allowed the highlighting and tracking of subpopulations of cells, organelles, and proteins in living systems. Furthermore, phototransformable fluorescent proteins have offered new methods for superresolution fluorescence microscopy and optogenetics manipulation of proteins. One of the major advantages of phototransformable fluorescent proteins is their applicability for visualizing newly synthesized proteins that are en route to their final destinations. In this paper, we will discuss the biological applications of phototransformable fluorescent proteins with special emphasis on the application of tracking membrane proteins in vertebrate photoreceptor cells.
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Affiliation(s)
- Ina Nemet
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA.
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20
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Röder PV, Wu B, Liu Y, Han W. Pancreatic regulation of glucose homeostasis. Exp Mol Med 2016; 48:e219. [PMID: 26964835 PMCID: PMC4892884 DOI: 10.1038/emm.2016.6] [Citation(s) in RCA: 448] [Impact Index Per Article: 56.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 12/03/2015] [Accepted: 12/06/2015] [Indexed: 12/11/2022] Open
Abstract
In order to ensure normal body function, the human body is dependent on a tight control of its blood glucose levels. This is accomplished by a highly sophisticated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissue. Within this network, the pancreas represents a key player by secreting the blood sugar-lowering hormone insulin and its opponent glucagon. However, disturbances in the interplay of the hormones and peptides involved may lead to metabolic disorders such as type 2 diabetes mellitus (T2DM) whose prevalence, comorbidities and medical costs take on a dramatic scale. Therefore, it is of utmost importance to uncover and understand the mechanisms underlying the various interactions to improve existing anti-diabetic therapies and drugs on the one hand and to develop new therapeutic approaches on the other. This review summarizes the interplay of the pancreas with various other organs and tissues that maintain glucose homeostasis. Furthermore, anti-diabetic drugs and their impact on signaling pathways underlying the network will be discussed.
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Affiliation(s)
- Pia V Röder
- Metabolism in Human Diseases Unit, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- Metabolism in Human Diseases Unit, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore 138673, Singapore. E-mail: or
| | - Bingbing Wu
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, A*STAR, Singapore, Singapore
| | - Yixian Liu
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, A*STAR, Singapore, Singapore
| | - Weiping Han
- Metabolism in Human Diseases Unit, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, A*STAR, Singapore, Singapore
- Metabolism in Human Diseases Unit, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore 138673, Singapore. E-mail: or
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21
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Yi NY, He Q, Caligan TB, Smith GR, Forsberg LJ, Brenman JE, Sexton JZ. Development of a Cell-Based Fluorescence Polarization Biosensor Using Preproinsulin to Identify Compounds That Alter Insulin Granule Dynamics. Assay Drug Dev Technol 2015; 13:558-69. [PMID: 26505612 PMCID: PMC4955689 DOI: 10.1089/adt.2015.665] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Diabetes currently affects 9.3% of the U.S. population totaling $245 billion annually in U.S. direct and indirect healthcare costs. Current therapies for diabetes are limited in their ability to control blood glucose and/or enhance insulin sensitivity. Therefore, innovative and efficacious therapies for diabetes are urgently needed. Herein we describe a fluorescent insulin reporter system (preproinsulin-mCherry, PPI-mCherry) that tracks live-cell insulin dynamics and secretion in pancreatic β-cells with utility for high-content assessment of real-time insulin dynamics. Additionally, we report a new modality for sensing insulin granule packaging in conventional high-throughput screening (HTS), using a hybrid cell-based fluorescence polarization (FP)/internal FRET biosensor using the PPI-mCherry reporter system. We observed that bafilomycin, a vacuolar H(+) ATPase inhibitor and inhibitor of insulin granule formation, significantly increased mCherry FP in INS-1 cells with PPI-mCherry. Partial least squares regression analysis demonstrated that an increase of FP by bafilomycin is significantly correlated with a decrease in granularity of PPI-mCherry signal in the cells. The increased FP by bafilomycin is due to inhibition of self-Förster resonant energy transfer (homo-FRET) caused by the increased mCherry intermolecular distance. FP substantially decreases when insulin is tightly packaged in the granules, and the homo-FRET decreases when insulin granule packaging is inhibited, resulting in increased FP. We performed pilot HTS of 1782 FDA-approved small molecules and natural products from Prestwick and Enzo chemical libraries resulting in an overall Z'-factor of 0.52 ± 0.03, indicating the suitability of this biosensor for HTS. This novel biosensor enables live-cell assessment of protein-protein interaction/protein aggregation in live cells and is compatible with conventional FP plate readers.
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Affiliation(s)
- Na Young Yi
- Biomanufacturing Research Institute and Technology Enterprise, Department of Pharmaceutical Sciences, North Carolina Central University, Durham, North Carolina
| | - Qingping He
- Biomanufacturing Research Institute and Technology Enterprise, Department of Pharmaceutical Sciences, North Carolina Central University, Durham, North Carolina
| | - Thomas B. Caligan
- Biomanufacturing Research Institute and Technology Enterprise, Department of Pharmaceutical Sciences, North Carolina Central University, Durham, North Carolina
| | - Ginger R. Smith
- Biomanufacturing Research Institute and Technology Enterprise, Department of Pharmaceutical Sciences, North Carolina Central University, Durham, North Carolina
| | - Lawrence J. Forsberg
- The Neuroscience Center and Department of Cell Biology & Physiology, UNC Chapel Hill School of Medicine, Chapel Hill, North Carolina
| | - Jay E. Brenman
- The Neuroscience Center and Department of Cell Biology & Physiology, UNC Chapel Hill School of Medicine, Chapel Hill, North Carolina
| | - Jonathan Z. Sexton
- Biomanufacturing Research Institute and Technology Enterprise, Department of Pharmaceutical Sciences, North Carolina Central University, Durham, North Carolina
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22
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Arous C, Halban PA. The skeleton in the closet: actin cytoskeletal remodeling in β-cell function. Am J Physiol Endocrinol Metab 2015; 309:E611-20. [PMID: 26286869 DOI: 10.1152/ajpendo.00268.2015] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 08/11/2015] [Indexed: 01/13/2023]
Abstract
Over the last few decades, biomedical research has considered not only the function of single cells but also the importance of the physical environment within a whole tissue, including cell-cell and cell-extracellular matrix interactions. Cytoskeleton organization and focal adhesions are crucial sensors for cells that enable them to rapidly communicate with the physical extracellular environment in response to extracellular stimuli, ensuring proper function and adaptation. The involvement of the microtubular-microfilamentous cytoskeleton in secretion mechanisms was proposed almost 50 years ago, since when the evolution of ever more sensitive and sophisticated methods in microscopy and in cell and molecular biology have led us to become aware of the importance of cytoskeleton remodeling for cell shape regulation and its crucial link with signaling pathways leading to β-cell function. Emerging evidence suggests that dysfunction of cytoskeletal components or extracellular matrix modification influences a number of disorders through potential actin cytoskeleton disruption that could be involved in the initiation of multiple cellular functions. Perturbation of β-cell actin cytoskeleton remodeling could arise secondarily to islet inflammation and fibrosis, possibly accounting in part for impaired β-cell function in type 2 diabetes. This review focuses on the role of actin remodeling in insulin secretion mechanisms and its close relationship with focal adhesions and myosin II.
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Affiliation(s)
- Caroline Arous
- Department of Genetic Medicine and Development, University of Geneva Medical Center, Geneva, Switzerland
| | - Philippe A Halban
- Department of Genetic Medicine and Development, University of Geneva Medical Center, Geneva, Switzerland
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23
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Dehghany J, Hoboth P, Ivanova A, Mziaut H, Müller A, Kalaidzidis Y, Solimena M, Meyer-Hermann M. A Spatial Model of Insulin-Granule Dynamics in Pancreatic β-Cells. Traffic 2015; 16:797-813. [DOI: 10.1111/tra.12286] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Revised: 03/18/2015] [Accepted: 03/20/2015] [Indexed: 01/19/2023]
Affiliation(s)
- Jaber Dehghany
- Department of Systems Immunology and Braunschweig Integrated Centre of Systems Biology; Helmholtz Centre for Infection Research; Braunschweig Germany
| | - Peter Hoboth
- Paul Langerhans Institute Dresden of Helmholtz Centre Munich at University Clinic Carl Gustav Carus of TU Dresden and Faculty of Medicine; Technische Universität Dresden; Dresden Germany
- German Center for Diabetes Research (DZD e.V.); Neuherberg Germany
| | - Anna Ivanova
- Paul Langerhans Institute Dresden of Helmholtz Centre Munich at University Clinic Carl Gustav Carus of TU Dresden and Faculty of Medicine; Technische Universität Dresden; Dresden Germany
- German Center for Diabetes Research (DZD e.V.); Neuherberg Germany
| | - Hassan Mziaut
- Paul Langerhans Institute Dresden of Helmholtz Centre Munich at University Clinic Carl Gustav Carus of TU Dresden and Faculty of Medicine; Technische Universität Dresden; Dresden Germany
- German Center for Diabetes Research (DZD e.V.); Neuherberg Germany
| | - Andreas Müller
- Paul Langerhans Institute Dresden of Helmholtz Centre Munich at University Clinic Carl Gustav Carus of TU Dresden and Faculty of Medicine; Technische Universität Dresden; Dresden Germany
- German Center for Diabetes Research (DZD e.V.); Neuherberg Germany
| | - Yannis Kalaidzidis
- Max Planck Institute of Molecular Cell Biology and Genetics; Dresden Germany
- Faculty of Bioengineering and Bioinformatics; Moscow State University; Moscow Russia
| | - Michele Solimena
- Paul Langerhans Institute Dresden of Helmholtz Centre Munich at University Clinic Carl Gustav Carus of TU Dresden and Faculty of Medicine; Technische Universität Dresden; Dresden Germany
- German Center for Diabetes Research (DZD e.V.); Neuherberg Germany
- Max Planck Institute of Molecular Cell Biology and Genetics; Dresden Germany
| | - Michael Meyer-Hermann
- Department of Systems Immunology and Braunschweig Integrated Centre of Systems Biology; Helmholtz Centre for Infection Research; Braunschweig Germany
- Institute for Biochemistry, Biotechnology and Bioinformatics; Technische Universität Braunschweig; Braunschweig Germany
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Aged insulin granules display reduced microtubule-dependent mobility and are disposed within actin-positive multigranular bodies. Proc Natl Acad Sci U S A 2015; 112:E667-76. [PMID: 25646459 DOI: 10.1073/pnas.1409542112] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Insulin secretion is key for glucose homeostasis. Insulin secretory granules (SGs) exist in different functional pools, with young SGs being more mobile and preferentially secreted. However, the principles governing the mobility of age-distinct SGs remain undefined. Using the time-reporter insulin-SNAP to track age-distinct SGs we now show that their dynamics can be classified into three components: highly dynamic, restricted, and nearly immobile. Young SGs display all three components, whereas old SGs are either restricted or nearly immobile. Both glucose stimulation and F-actin depolymerization recruit a fraction of nearly immobile young, but not old, SGs for highly dynamic, microtubule-dependent transport. Moreover, F-actin marks multigranular bodies/lysosomes containing aged SGs. These data demonstrate that SGs lose their responsiveness to glucose stimulation and competence for microtubule-mediated transport over time while changing their relationship with F-actin.
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Li L, Trifunovic A, Köhler M, Wang Y, Petrovic Berglund J, Illies C, Juntti-Berggren L, Larsson NG, Berggren PO. Defects in β-cell Ca2+ dynamics in age-induced diabetes. Diabetes 2014; 63:4100-14. [PMID: 24985350 DOI: 10.2337/db13-1855] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Little is known about the molecular mechanisms underlying age-dependent deterioration in β-cell function. We now demonstrate that age-dependent impairment in insulin release, and thereby glucose homeostasis, is associated with subtle changes in Ca(2+) dynamics in mouse β-cells. We show that these changes are likely to be accounted for by impaired mitochondrial function and to involve phospholipase C/inositol 1,4,5-trisphosphate-mediated Ca(2+) mobilization from intracellular stores as well as decreased β-cell Ca(2+) influx over the plasma membrane. We use three mouse models, namely, a premature aging phenotype, a mature aging phenotype, and an aging-resistant phenotype. Premature aging is studied in a genetically modified mouse model with an age-dependent accumulation of mitochondrial DNA mutations. Mature aging is studied in the C57BL/6 mouse, whereas the 129 mouse represents a model that is more resistant to age-induced deterioration. Our data suggest that aging is associated with a progressive decline in β-cell mitochondrial function that negatively impacts on the fine tuning of Ca(2+) dynamics. This is conceptually important since it emphasizes that even relatively modest changes in β-cell signal transduction over time lead to compromised insulin release and a diabetic phenotype.
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Affiliation(s)
- Luosheng Li
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Aleksandra Trifunovic
- Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Martin Köhler
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Yixin Wang
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Jelena Petrovic Berglund
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Christopher Illies
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Lisa Juntti-Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Nils-Göran Larsson
- Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden Lee Kong Chian School of Medicine, Nanyang Technological University/Imperial College London, Novena Campus, Singapore
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Heaslip AT, Nelson SR, Lombardo AT, Beck Previs S, Armstrong J, Warshaw DM. Cytoskeletal dependence of insulin granule movement dynamics in INS-1 beta-cells in response to glucose. PLoS One 2014; 9:e109082. [PMID: 25310693 PMCID: PMC4195697 DOI: 10.1371/journal.pone.0109082] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 09/01/2014] [Indexed: 02/03/2023] Open
Abstract
For pancreatic β-cells to secrete insulin in response to elevated blood glucose, insulin granules retained within the subplasmalemmal space must be transported to sites of secretion on the plasma membrane. Using a combination of super-resolution STORM imaging and live cell TIRF microscopy we investigate how the organization and dynamics of the actin and microtubule cytoskeletons in INS-1 β-cells contribute to this process. GFP-labeled insulin granules display 3 different modes of motion (stationary, diffusive-like, and directed). Diffusive-like motion dominates in basal, low glucose conditions. Upon glucose stimulation no gross rearrangement of the actin cytoskeleton is observed but there are increases in the 1) rate of microtubule polymerization; 2) rate of diffusive-like motion; and 3) proportion of granules undergoing microtubule-based directed motion. By pharmacologically perturbing the actin and microtubule cytoskeletons, we determine that microtubule-dependent granule transport occurs within the subplasmalemmal space and that the actin cytoskeleton limits this transport in basal conditions, when insulin secretion needs to be inhibited.
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Affiliation(s)
- Aoife T. Heaslip
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Shane R. Nelson
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Andrew T. Lombardo
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Samantha Beck Previs
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - Jessica Armstrong
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
| | - David M. Warshaw
- University of Vermont, Department of Molecular Physiology and Biophysics, Health Sciences Research Facility, Burlington, Vermont, United States of America
- * E-mail:
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Barker CJ, Li L, Köhler M, Berggren PO. β-Cell Ca(2+) dynamics and function are compromised in aging. Adv Biol Regul 2014; 57:112-9. [PMID: 25282681 DOI: 10.1016/j.jbior.2014.09.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 09/13/2014] [Indexed: 10/24/2022]
Abstract
Defects in pancreatic β-cell function and survival are key components in type 2 diabetes (T2D). An age-dependent deterioration in β-cell function has also been observed, but little is known about the molecular mechanisms behind this phenomenon. Our previous studies indicate that the regulation of cytoplasmic free Ca(2+) concentration ([Ca(2+)]i) may be critical and that this is dependent on the proper function of the mitochondria. The [Ca(2+)]i dynamics of the pancreatic β-cell are driven by an interplay between glucose-induced influx of extracellular Ca(2+) via voltage-dependent Ca(2+) channels and the inositol 1,4,5-trisphosphate (Ins(1,4,5)P3)-mediated liberation of Ca(2+) from intracellular stores. Our previous work has indicated a direct relationship between disruption of Ins(1,4,5)P3-mediated Ca(2+) regulation and loss of β-cell function, including disturbed [Ca(2+)]i dynamics and compromised insulin secretion. To investigate these processes in aging we used three mouse models, a premature aging mitochondrial mutator mouse, a mature aging phenotype (C57BL/6) and an aging-resistant phenotype (129). Our data suggest that age-dependent impairment in mitochondrial function leads to modest changes in [Ca(2+)]i dynamics in mouse β-cells, particularly in the pattern of [Ca(2+)]i oscillations. These changes are driven by modifications in both PLC/Ins(1,4,5)P3-mediated Ca(2+) mobilization from intracellular stores and decreased β-cell Ca(2+) influx over the plasma membrane. Our findings underscore an important concept, namely that even relatively small, time-dependent changes in β-cell signal-transduction result in compromised insulin release and in a diabetic phenotype.
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Affiliation(s)
- Christopher J Barker
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, SE-171 76 Stockholm, Sweden
| | - Luosheng Li
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, SE-171 76 Stockholm, Sweden
| | - Martin Köhler
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, SE-171 76 Stockholm, Sweden
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital L1, SE-171 76 Stockholm, Sweden; Lee Kong Chian School of Medicine, Nangyang Technological University, Imperial College London, Novena Campus, Singapore 637 553.
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Yu H, Zheng X, Zhang Z. Mechanism of Roux-en-Y gastric bypass treatment for type 2 diabetes in rats. J Gastrointest Surg 2013; 17:1073-83. [PMID: 23580087 PMCID: PMC3653054 DOI: 10.1007/s11605-013-2188-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 03/18/2013] [Indexed: 02/07/2023]
Abstract
OBJECTIVES Roux-en-Y gastric bypass (RYGB) is a novel therapy for diabetes. We aimed to explore the therapeutic mechanism of RYGB. METHODS After RYGB, animal models were established, and gene expression profile of islets was assessed. Additionally, gastrointestinal hormones were measured using enzyme-linked immunosorbent assays. Ca(2+) was studied using confocal microscopy and patch-clamp technique. The morphology of islets and beta cells was observed using optical microscopy and electron microscopy. RESULTS RYGB was an effective treatment in diabetic rats. Expression profiling data showed that RYGB produced a new metabolic environment and that gene expression changed to adapt to the new environment. The differential expression of genes associated with hormones, Ca(2+) and cellular proliferation was closely related to RYGB and diabetes metabolism. Furthermore, the data verified that RYGB led to changes in hormone level and enhanced Ca(2+) concentration changes and Ca(2+) channel activity. Morphological data showed that RYGB induced the proliferation of islets and improved the function of beta cells. CONCLUSIONS RYGB promoted a new metabolic environment while triggering changes to adapt to the new environment. These changes promoted the cellular proliferation of islets and improved the function of beta cells. The quantity of beta cells increased, and their quality improved, ultimately leading to insulin secretion enhancement.
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Affiliation(s)
- Hongwei Yu
- School of Medicine, Tsinghua University, Beijing, People’s Republic of China
| | - Xiyan Zheng
- School of Medicine, Tsinghua University, Beijing, People’s Republic of China
| | - Zongming Zhang
- School of Medicine, Tsinghua University, Beijing, People’s Republic of China
- Department of Hepatobiliary Surgery, Futian Hospital, Guangdong Medical College, Shenzhen, People’s Republic of China
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29
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Arous C, Rondas D, Halban PA. Non-muscle myosin IIA is involved in focal adhesion and actin remodelling controlling glucose-stimulated insulin secretion. Diabetologia 2013; 56:792-802. [PMID: 23354122 DOI: 10.1007/s00125-012-2800-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Accepted: 11/19/2012] [Indexed: 12/22/2022]
Abstract
AIMS/HYPOTHESIS Actin and focal adhesion (FA) remodelling are essential for glucose-stimulated insulin secretion (GSIS). Non-muscle myosin II (NM II) isoforms have been implicated in such remodelling in other cell types, and myosin light chain kinase (MLCK) and Rho-associated coiled-coil-containing kinase (ROCK) are upstream regulators of NM II, which is known to be involved in GSIS. The aim of this work was to elucidate the implication and regulation of NM IIA and IIB in beta cell actin and FA remodelling, granule trafficking and GSIS. METHODS Inhibitors of MLCK, ROCK and NM II were used to study NM II activity, and knockdown of NM IIA and IIB to determine isoform specificity, using sorted primary rat beta cells. Insulin was measured by radioimmunoassay. Protein phosphorylation and subcellular distribution were determined by western blot and confocal immunofluorescence. Dynamic changes were monitored by live cell imaging and total internal reflection fluorescence microscopy using MIN6B1 cells. RESULTS NM II and MLCK inhibition decreased GSIS, associated with shortening of peripheral actin stress fibres, and reduced numbers of FAs and insulin granules in close proximity to the basal membrane. By contrast, ROCK inhibition increased GSIS and caused disassembly of glucose-induced central actin stress fibres, resulting in large FAs without any effect on FA number. Only glucose-induced NM IIA reorganisation was blunted by MLCK inhibition. NM IIA knockdown decreased GSIS, levels of FA proteins and glucose-induced extracellular signal-regulated kinase 1/2 phosphorylation. CONCLUSIONS/INTERPRETATION Our data indicate that MLCK-NM IIA may modulate translocation of secretory granules, resulting in enhanced insulin secretion through actin and FA remodelling, and regulation of FA protein levels.
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Affiliation(s)
- C Arous
- Department of Genetic Medicine and Development, University Medical Centre, University of Geneva, 1 Michel Servet, 1211 Geneva 4, Switzerland.
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Bogan JS, Xu Y, Hao M. Cholesterol accumulation increases insulin granule size and impairs membrane trafficking. Traffic 2012; 13:1466-80. [PMID: 22889194 DOI: 10.1111/j.1600-0854.2012.01407.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 08/09/2012] [Accepted: 08/13/2012] [Indexed: 11/28/2022]
Abstract
The formation of mature secretory granules is essential for proper storage and regulated release of hormones and neuropeptides. In pancreatic β cells, cholesterol accumulation causes defects in insulin secretion and may participate in the pathogenesis of type 2 diabetes. Using a novel cholesterol analog, we show for the first time that insulin granules are the major sites of intracellular cholesterol accumulation in live β cells. This is distinct from other, non-secretory cell types, in which cholesterol is concentrated in the recycling endosomes and the trans-Golgi network. Excess cholesterol was delivered specifically to insulin granules, which caused granule enlargement and retention of syntaxin 6 and VAMP4 in granule membranes, with concurrent depletion of these proteins from the trans-Golgi network. Clathrin also accumulated in the granules of cholesterol-overloaded cells, consistent with a possible defect in the last stage of granule maturation, during which clathrin-coated vesicles bud from the immature granules. Excess cholesterol also reduced the docking and fusion of insulin granules at the plasma membrane. Together, the data support a model in which cholesterol accumulation in insulin secretory granules impairs the ability of these vesicles to respond to stimuli, and thus reduces insulin secretion.
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Affiliation(s)
- Jonathan S Bogan
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA
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31
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Elias S, Delestre C, Ory S, Marais S, Courel M, Vazquez-Martinez R, Bernard S, Coquet L, Malagon MM, Driouich A, Chan P, Gasman S, Anouar Y, Montero-Hadjadje M. Chromogranin A induces the biogenesis of granules with calcium- and actin-dependent dynamics and exocytosis in constitutively secreting cells. Endocrinology 2012; 153:4444-56. [PMID: 22851679 DOI: 10.1210/en.2012-1436] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Chromogranins are a family of acidic glycoproteins that play an active role in hormone and neuropeptide secretion through their crucial role in secretory granule biogenesis in neuroendocrine cells. However, the molecular mechanisms underlying their granulogenic activity are still not fully understood. Because we previously demonstrated that the expression of the major component of secretory granules, chromogranin A (CgA), is able to induce the formation of secretory granules in nonendocrine COS-7 cells, we decided to use this model to dissect the mechanisms triggered by CgA leading to the biogenesis and trafficking of such granules. Using quantitative live cell imaging, we first show that CgA-induced organelles exhibit a Ca(2+)-dependent trafficking, in contrast to native vesicle stomatitis virus G protein-containing constitutive vesicles. To identify the proteins that confer such properties to the newly formed granules, we developed CgA-stably-expressing COS-7 cells, purified their CgA-containing granules by subcellular fractionation, and analyzed the granule proteome by liquid chromatography-tandem mass spectrometry. This analysis revealed the association of several cytosolic proteins to the granule membrane, including GTPases, cytoskeleton-based molecular motors, and other proteins with actin- and/or Ca(2+)-binding properties. Furthermore, disruption of cytoskeleton affects not only the distribution and the transport but also the Ca(2+)-evoked exocytosis of the CgA-containing granules, indicating that these granules interact with microtubules and cortical actin for the regulated release of their content. These data demonstrate for the first time that the neuroendocrine factor CgA induces the recruitment of cytoskeleton-, GTP-, and Ca(2+)-binding proteins in constitutively secreting COS-7 cells to generate vesicles endowed with typical dynamics and exocytotic properties of neuroendocrine secretory granules.
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Affiliation(s)
- Salah Elias
- Institut National de la Santé et de la Recherche Médicale (Inserm) U982, University of Rouen, Mont-Saint-Aignan 76821, France
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Hatlapatka K, Matz M, Schumacher K, Baumann K, Rustenbeck I. Bidirectional insulin granule turnover in the submembrane space during K(+) depolarization-induced secretion. Traffic 2011; 12:1166-78. [PMID: 21668594 DOI: 10.1111/j.1600-0854.2011.01231.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Like primary mouse islets, MIN6 pseudoislets responded to the depolarization by 40 mm KCl and the resulting increase in the free cytosolic Ca(2+) concentration ([Ca(2+) ](i) ) with a massive increase in insulin secretion, whereas 15 mm KCl had little effect in spite of a clear increase in [Ca(2+) ](i) . Analysis of insulin-enhanced green fluorescent protein (EGFP)-labeled granules in MIN6 cells by total internal reflection fluorescence (TIRF) microscopy showed that 40 mm KCl increased the number of short-term resident granules (<1 second presence in the submembrane space), while the total granule number and the number of long-term resident granules decreased. The rates of granule arrival at and departure from the submembrane space changed in parallel and were two orders of magnitude higher than the release rates, suggesting a back-and-forth movement of the granules as the primary determinant of the submembrane granule number. The effect of 15 mm KCl resembled that of 40 mm but did not achieve significance. Both 15 and 40 mm KCl evoked a [Ca(2+) ](i) increase, which was antagonized by 10 µm nifedipine. Nifedipine also antagonized the effect on secretion and on granule number and mobility. In conclusion, during KCl depolarization L-type Ca(2+) channels seem to regulate two processes, insulin granule turnover in the submembrane space and granule exocytosis.
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Affiliation(s)
- Kathrin Hatlapatka
- Institute of Pharmacology and Toxicology, University of Braunschweig, Mendelssohnstr. 1, 38106 Braunschweig, Germany
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Epac2-dependent rap1 activation and the control of islet insulin secretion by glucagon-like peptide-1. VITAMINS AND HORMONES 2011; 84:279-302. [PMID: 21094904 DOI: 10.1016/b978-0-12-381517-0.00010-2] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) binds its Class II G protein-coupled receptor to stimulate cyclic adenosine monophosphate (cAMP) production and to potentiate the glucose metabolism-dependent secretion of insulin from pancreatic β cells located within the islets of Langerhans. Prior clinical studies demonstrate that this cAMP-mediated action of GLP-1 to potentiate glucose-stimulated insulin secretion (GSIS) is of major therapeutic importance when evaluating the abilities of GLP-1 receptor (GLP-1R) agonists to lower levels of blood glucose in type 2 diabetic subjects. Surprisingly, recent in vitro studies of human or rodent islets of Langerhans provide evidence for the existence of a noncanonical mechanism of β cell cAMP signal transduction, one that may explain how GLP-1R agonists potentiate GSIS. What these studies demonstrate is that a cAMP-regulated guanine nucleotide exchange factor designated as Epac2 couples β cell cAMP production to the protein kinase A-independent stimulation of insulin exocytosis. Provided here is an overview of the Epac2 signal transduction system in β cells, with special emphasis on Rap1, a Ras-related GTPase that is an established target of Epac2.
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Mourad NI, Nenquin M, Henquin JC. Metabolic amplification of insulin secretion by glucose is independent of β-cell microtubules. Am J Physiol Cell Physiol 2011; 300:C697-706. [DOI: 10.1152/ajpcell.00329.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glucose-induced insulin secretion (IS) by β-cells is controlled by two pathways. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and rise in the cytosolic Ca2+ concentration ([Ca2+]c), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca2+]c. After exclusion of the contribution of actin microfilaments, we here tested whether amplification implicates microtubule-dependent granule mobilization. Mouse islets were treated with nocodazole or taxol, which completely depolymerized and polymerized tubulin. They were then perifused to measure [Ca2+]c and IS. Metabolic amplification was studied during imposed steady elevation of [Ca2+]c by tolbutamide or KCl or by comparing [Ca2+]c and IS responses to glucose and tolbutamide. Nocodazole did not alter [Ca2+]c or IS changes induced by the three secretagogues, whereas taxol caused a small inhibition of IS that is partly ascribed to a decrease in [Ca2+]c. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was unaffected by microtubule disruption or stabilization. Both phases of IS were larger in response to glucose than tolbutamide, although triggering [Ca2+]c was lower. This difference, due to amplification, persisted in nocodazole- or taxol-treated islets, even when IS was augmented fourfold by microfilament disruption with cytochalasin B or latrunculin B. In conclusion, metabolic amplification rapidly augments first and second phases of IS independently of insulin granule translocation along microtubules. We therefore extend our previous proposal that it does not implicate the cytoskeleton but corresponds to acceleration of the priming process conferring release competence to insulin granules.
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Affiliation(s)
- Nizar I. Mourad
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Myriam Nenquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
| | - Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, Brussels, Belgium
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Kang N, Won JH, Park YM. Annexin I stimulates insulin secretion through regulation of cytoskeleton and PKC activity. Anim Cells Syst (Seoul) 2010. [DOI: 10.1080/19768354.2009.9647190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Affiliation(s)
- Na‐na Kang
- a Department of Biological Sciences and Institute for Basic Sciences , Sungkyunkwan University , Suwon, 440–746, Korea
| | - Jong Hak Won
- b Department of Pharmacology and Physiology , University of Rochester , Rochester, New York, 14642, USA
| | - Young Min Park
- c Department of Biological Sciences and Institute for Basic Sciences , Sungkyunkwan University , Suwon, 440–746, Korea Phone: Fax: E-mail:
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36
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Harada S, Fujita-Hamabe W, Kamiya K, Mizushina Y, Satake T, Tokuyama S. Morinda citrifolia fruit juice prevents ischemic neuronal damage through suppression of the development of post-ischemic glucose intolerance. J Nat Med 2010; 64:468-73. [PMID: 20574728 DOI: 10.1007/s11418-010-0437-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Accepted: 05/26/2010] [Indexed: 11/30/2022]
Abstract
Fruit juice of Morinda citrifolia (Noni juice) is a well-known health drink and has various pharmacological properties including antioxidant and anti-inflammatory effects. We have hitherto found the protective effect of Noni juice on brain damage caused by ischemic stress in mice. In addition, we also recently reported that regulation of post-ischemic glucose intolerance might be important for good prognosis. Here, we focused on the effect of Noni juice on the development of the post-ischemic glucose intolerance as a cerebral protective mechanism. Noni juice was obtained from the mature fruit grown in Okinawa (about 1.5 L/4 kg of fruit; 100% ONJ). Male ddY mice were given 10% ONJ in drinking water for 7 days. Then, mice were subjected to 2 h of middle cerebral artery occlusion (MCAO). Ingestion of 10% ONJ suppressed the development of neuronal damage after MCAO. Interestingly, glucose intolerance observed on the 1st day after MCAO completely disappeared after 10% ONJ administration. Furthermore, ONJ treatment significantly increased serum insulin levels much further than the control group on the 1st day, while serum adiponectin levels were not affected at all. These results suggest that ONJ could facilitate insulin secretion after ischemic stress and may attenuate the development of glucose intolerance. These mechanisms may contribute to the neuronal protective effect of ONJ against ischemic stress.
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Affiliation(s)
- Shinichi Harada
- Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Kobe Gakuin University, 1-1-3 Minatojima, Chuo-ku, Kobe, Hyogo, 650-8586, Japan
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Ku TC, Kao LS, Lin CC, Tsai YS. Morphological filter improve the efficiency of automated tracking of secretory vesicles with various dynamic properties. Microsc Res Tech 2009; 72:639-49. [PMID: 19350659 DOI: 10.1002/jemt.20711] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Membrane trafficking is a very important physiological process involved in protein transport, endocytosis, and exocytosis. The functions of vesicles are strongly correlated with various spatial dynamic properties of vesicles, including their types of movements and morphology. Several methods are used to quantify such dynamic properties, but most of them are specific to particular populations of vesicles. We previously developed the so-called PTrack system for quantifying the dynamics of secretory vesicles near the cell surface, which are small and move slowly. To improve the system performance in quantifying large and fast-moving vesicles, we firstly combined morphological filter with two-threshold image processing techniques to locate granules of various sizes. Next, Kalman filtering was used to improve the performance in tracking fast-moving and large granules. Performance evaluation by using simulation image sequences shown that the new system, called PTrack II, yields better tracking accuracy. The tracking system was validated using time-lapse images of insulin granules in betaTC3 cells, which revealed that PTrack II could track better than PTrack, averaged accuracy up to 56%. The overall tracking results indicate that PTrack II is better at tracking vesicles with various dynamic properties, which will facilitate the acquisition of more-complete information on vesicle dynamics.
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Affiliation(s)
- Tien-Chuan Ku
- Department of Biomedical Engineering, Chung Yuan Christian University, Jhongli, Taiwan, Republic of China
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Insulin granule biogenesis, trafficking and exocytosis. VITAMINS AND HORMONES 2009; 80:473-506. [PMID: 19251047 DOI: 10.1016/s0083-6729(08)00616-x] [Citation(s) in RCA: 142] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
It is becoming increasingly apparent that beta cell dysfunction resulting in abnormal insulin secretion is the essential element in the progression of patients from a state of impaired glucose tolerance to frank type 2 diabetes (Del Prato, 2003; Del Prato and Tiengo, 2001). Although extensive studies have examined the molecular, cellular and physiologic mechanisms of insulin granule biogenesis, sorting, and exocytosis the precise mechanisms controlling these processes and their dysregulation in the developed of diabetes remains an area of important investigation. We now know that insulin biogenesis initiates with the synthesis of preproinsulin in rough endoplastic reticulum and conversion of preproinsulin to proinsulin. Proinsulin begins to be packaged in the Trans-Golgi Network and is sorting into immature secretory granules. These immature granules become acidic via ATP-dependent proton pump and proinsulin undergoes proteolytic cleavage resulting the formation of insulin and C-peptide. During the granule maturation process, insulin is crystallized with zinc and calcium in the form of dense-core granules and unwanted cargo and membrane proteins undergo selective retrograde trafficking to either the constitutive trafficking pathway for secretion or to degradative pathways. The newly formed mature dense-core insulin granules populate two different intracellular pools, the readily releasable pools (RRP) and the reserved pool. These two distinct populations are thought to be responsible for the biphasic nature of insulin release in which the RRP granules are associated with the plasma membrane and undergo an acute calcium-dependent release accounting for first phase insulin secretion. In contrast, second phase insulin secretion requires the trafficking of the reserved granule pool to the plasma membrane. The initial trigger for insulin granule fusion with the plasma membrane is a rise in intracellular calcium and in the case of glucose stimulation results from increased production of ATP, closure of the ATP-sensitive potassium channel and cellular depolarization. In turn, this opens voltage-dependent calcium channels allowing increased influx of extracellular calcium. Calcium is thought to bind to members of the fusion regulatory proteins synaptogamin that functionally repressors the fusion inhibitory protein complexin. Both complexin and synaptogamin interact as well as several other regulatory proteins interact with the core fusion machinery composed of the Q- or t-SNARE proteins syntaxin 1 and SNAP25 in the plasma membrane that assembles with the R- or v-SNARE protein VAMP2 in insulin granules. In this chapter we will review the current progress of insulin granule biogenesis, sorting, trafficking, exocytosis and signaling pathways that comprise the molecular basis of glucose-dependent insulin secretion.
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Jung SR, Kim MH, Hille B, Koh DS. Control of granule mobility and exocytosis by Ca2+ -dependent formation of F-actin in pancreatic duct epithelial cells. Traffic 2009; 10:392-410. [PMID: 19192247 DOI: 10.1111/j.1600-0854.2009.00884.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) triggers exocytosis of secretory granules in pancreatic duct epithelia. In this study, we find that the signal also controls granule movement. Motions of fluorescently labeled granules stopped abruptly after a [Ca(2+)](i) increase, kinetically coincident with formation of filamentous actin (F-actin) in the whole cytoplasm. At high resolution, the new F-actin meshwork was so dense that cellular structures of granule size appeared physically trapped in it. Depolymerization of F-actin with latrunculin B blocked both the F-actin formation and the arrest of granules. Interestingly, when monitored with total internal reflection fluorescence microscopy, the immobilized granules still moved slowly and concertedly toward the plasma membrane. This group translocation was abolished by blockers of myosin. Exocytosis measured by microamperometry suggested that formation of a dense F-actin meshwork inhibited exocytosis at small Ca(2+) rises <1 microm. Larger [Ca(2+)](i) rises increased exocytosis because of the co-ordinate translocation of granules and fusion to the membrane. We propose that the Ca(2+)-dependent freezing of granules filters out weak inputs but allows exocytosis under stronger inputs by controlling granule movements.
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Affiliation(s)
- Seung-Ryoung Jung
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA
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Baltrusch S, Lenzen S. Monitoring of glucose-regulated single insulin secretory granule movement by selective photoactivation. Diabetologia 2008; 51:989-96. [PMID: 18389213 DOI: 10.1007/s00125-008-0979-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Accepted: 02/07/2008] [Indexed: 10/22/2022]
Abstract
AIMS/HYPOTHESIS Fluorescence microscopy opens new perspectives for the analysis of insulin secretory granule movement. In this study, we examined whether recently developed photoactivatable/photoconvertible proteins are a useful tool for studying this process at the single granule level in insulin-secreting cells after glucose stimulation. METHODS Plasmids were generated for expression of fusion proteins of the granule membrane phosphatase phogrin or the granule cargo protein neuropeptide Y (NPY) with the photoactivatable green fluorescent protein mutant A206K (PA-GFP-A206K), the photoconvertible protein Dendra2 and the fluorescent protein mCherry. Transfected insulin-secreting MIN6 cells were analysed by fluorescence microscopy. RESULTS Point-resolved 405 nm light exposure during image acquisition of MIN6 cells transiently transfected with Phogrin-PA-GFP-A206K or NPY-PA-GFP-A206K as well as of stable MIN6-Phogrin-Dendra2 cells resulted in selective visualisation of few granules by green or red fluorescence, respectively. Movement of these granules was analysed by an automated tracking method from confocal 3D image series. The high spatiotemporal resolution facilitated an elongated tracking of single granules. Interestingly, the track speed and track displacement of granules after 1 h starvation and subsequent glucose stimulation was lower in cells pre-cultured for 48 h at 3 mmol/l glucose than in cells pre-cultured at 25 mmol/l glucose. CONCLUSIONS/INTERPRETATION Targeting of the granule membrane or its cargo with a photoactivatable/photoconvertible protein allows in-depth visualisation and tracking of single insulin granules in dependence upon glucose. This technique may also open the way to elucidating the regulation of granule movement velocity within the pancreatic beta cell with respect to secretory defects in type 2 diabetes.
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Affiliation(s)
- S Baltrusch
- Institute of Clinical Biochemistry, Hannover Medical School, 30623, Hannover, Germany.
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Abstract
Biphasic insulin secretion is required for proper insulin action and is observed not only in vivo, but also in isolated pancreatic islets and even single β-cells. Late events in the granule life cycle are thought to underlie this temporal pattern. In the last few years, we have therefore combined live cell imaging and electrophysiology to study insulin secretion at the level of individual granules, as they approach the plasma membrane, undergo exocytosis and finally release their insulin cargo. In the present paper, we review evidence for two emerging concepts that affect insulin secretion at the level of individual granules: (i) the existence of specialized sites where granules dock in preparation for exocytosis; and (ii) post-exocytotic regulation of cargo release by the fusion pore.
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Hao M, Head WS, Gunawardana SC, Hasty AH, Piston DW. Direct effect of cholesterol on insulin secretion: a novel mechanism for pancreatic beta-cell dysfunction. Diabetes 2007; 56:2328-38. [PMID: 17575085 DOI: 10.2337/db07-0056] [Citation(s) in RCA: 231] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Type 2 diabetes is often accompanied by abnormal blood lipid and lipoprotein levels, but most studies on the link between hyperlipidemia and diabetes have focused on free fatty acids (FFAs). In this study, we examined the relationship between cholesterol and insulin secretion from pancreatic beta-cells that is independent of the effects of FFAs. RESEARCH DESIGN AND METHODS Several methods were used to modulate cholesterol levels in intact islets and cultured beta-cells, including a recently developed mouse model that exhibits elevated cholesterol but normal FFA levels. Acute and metabolic alteration of cholesterol was done using pharmacological reagents. RESULTS We found a direct link between elevated serum cholesterol and reduced insulin secretion, with normal secretion restored by cholesterol depletion. We further demonstrate that excess cholesterol inhibits secretion by downregulation of metabolism through increased neuronal nitric oxide synthase dimerization. CONCLUSIONS This direct effect of cholesterol on beta-cell metabolism opens a novel set of mechanisms that may contribute to beta-cell dysfunction and the onset of diabetes in obese patients.
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Affiliation(s)
- Mingming Hao
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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Tamkun MM, O'connell KMS, Rolig AS. A cytoskeletal-based perimeter fence selectively corrals a sub-population of cell surface Kv2.1 channels. J Cell Sci 2007; 120:2413-23. [PMID: 17606996 DOI: 10.1242/jcs.007351] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Kv2.1 delayed-rectifier channel trafficks to 1-3 μm2 clusters on the surface of neurons and transfected HEK cells. Single quantum dot (Qdot) tracking and FRAP approaches were used to quantify the diffusion of GFP-labeled Kv2.1 channels on the cell surface and address the mechanisms underlying the formation of these unique membrane structures. Mean square displacement analysis of single Kv2.1 channel tracks inside or outside the surface clusters yielded mean diffusion coefficients of 0.03±0.02 μm2/second and 0.06±0.05 μm2/second, respectively. Kv2.1 channels outside the clusters effectively ignore the cluster boundary, readily diffusing through these microdomains. However, in 5% of the tracks analyzed, single, non-clustered channels were observed to cross into a cluster and become corralled within the cluster perimeter. Alexa Fluor 594-labelled phalloidin staining and mCherry-Kv2.1 co-expression with GFP-actin indicated that the Kv2.1 surface clusters form where the cortical actin cytoskeleton is reduced. Kv2.1 channels lacking the C-terminus do not form clusters, freely diffusing over the cell surface with a mean diffusion coefficient of 0.07±0.04 μm2/second. These data support a model whereby the Kv2.1 clusters are formed by sub-membrane cytoskeletal structures that limit the lateral diffusion of only the sub-population of Kv2.1 channels carrying the appropriate modifications on the Kv2.1 C-terminus.
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Affiliation(s)
- Michael M Tamkun
- Department of Biomedical Sciences, Colorado State University, Ft. Collins, CO 80523, USA
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