1
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Xue R, Zhang E, Wang Y. Pre-fusion motion state determines the heterogeneity of membrane fusion dynamics for large dense-core vesicles. Acta Physiol (Oxf) 2024; 240:e14115. [PMID: 38353019 DOI: 10.1111/apha.14115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 11/30/2023] [Accepted: 02/02/2024] [Indexed: 04/17/2024]
Abstract
AIM In neuroendocrine cells, large dense-core vesicles (LDCVs) undergo highly regulated pre-fusion processes before releasing hormones via membrane fusion. Significant heterogeneity has been found for LDCV population based on the dynamics of membrane fusion. However, how the pre-fusion status impacts the heterogeneity of LDCVs still remains unclear. Hence, we explored pre-fusion determinants of heterogeneous membrane fusion procedure of LDCV subpopulations. METHODS We assessed the pre-fusion motion of two LDCV subpopulations with distinct membrane fusion dynamics individually, using total internal reflection fluorescence microscopy. These two subpopulations were isolated by blocking Rho GTPase-dependent actin reorganization using Clostridium difficile toxin B (ToxB), which selectively targets the fast fusion vesicle pool. RESULTS We found that the fast fusion subpopulation was in an active motion mode prior to release, termed "active" LDCV pool, while vesicles from the slow fusion subpopulation were also moving but in a significantly more confined status, forming an "inert" pool. The depletion of the active pool by ToxB also eliminated fast fusion vesicles and was not rescued by pre-treatment with phorbol ester. A mild actin reorganization blocker, latrunculin A, that partially disrupted the active pool, only slightly attenuated the fast fusion subpopulation. CONCLUSION The pre-fusion motion state of LDCVs also exhibits heterogeneity and dictates the heterogeneous fusion pore dynamics. Rearrangement of F-actin network mediates vesicle pre-fusion motion and subsequently determines the membrane fusion kinetics.
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Affiliation(s)
- Renhao Xue
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center of Shanghai First Maternity and Infant Hospital, School of Life Sciences and Technology, Tongji University, Shanghai, China
- Department of Gynecology, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Enming Zhang
- Department of Clinical Sciences in Malmö, Lund University Diabetes Centre, Lund University, Malmö, Sweden
| | - Yu Wang
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center of Shanghai First Maternity and Infant Hospital, School of Life Sciences and Technology, Tongji University, Shanghai, China
- Department of Gynecology, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai, China
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2
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Krishnan P, Branco RCS, Weaver SA, Chang G, Lee CC, Syed F, Evans-Molina C. miR-146a-5p mediates inflammation-induced β cell mitochondrial dysfunction and apoptosis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.18.585543. [PMID: 38562689 PMCID: PMC10983918 DOI: 10.1101/2024.03.18.585543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
We previously showed that miR-146a-5p is upregulated in pancreatic islets treated with pro-inflammatory cytokines. Others have reported that miR-146a-5p overexpression is associated with β cell apoptosis and impaired insulin secretion. However, the molecular mechanisms mediating these effects remain elusive. To investigate the role of miR-146a-5p in β cell function, we developed stable MIN6 cell lines to either overexpress or inhibit the expression of miR-146a-5p. Monoclonal cell populations were treated with pro-inflammatory cytokines (IL-1β, IFNγ, and TNFα) to model T1D in vitro. We found that overexpression of miR-146a-5p increased cell death under conditions of inflammatory stress, whereas inhibition of miR-146a-5p reversed these effects. Additionally, inhibition of miR-146a-5p increased mitochondrial DNA copy number, respiration rate, and ATP production. Further, RNA sequencing data showed enrichment of pathways related to insulin secretion, apoptosis, and mitochondrial function when the expression levels of miR-146a-5p were altered. Finally, a temporal increase in miR-146a-5p expression levels and a decrease in mitochondria function markers was observed in islets derived from NOD mice. Collectively, these data suggest that miR-146a-5p may promote β cell dysfunction and death during inflammatory stress by suppressing mitochondrial function.
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Affiliation(s)
- Preethi Krishnan
- Department of Medicine, Indiana University School of Medicine
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
| | - Renato Chaves Souto Branco
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
- Department of Pediatrics, Indiana University School of Medicine
| | - Staci A Weaver
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine
| | - Garrick Chang
- Department of Physics, Indiana University School of Medicine
| | - Chih-Chun Lee
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
- Department of Pediatrics, Indiana University School of Medicine
| | - Farooq Syed
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
- Department of Pediatrics, Indiana University School of Medicine
| | - Carmella Evans-Molina
- Department of Medicine, Indiana University School of Medicine
- Department of Herman B Wells Center for Pediatric Research, Indiana University School of Medicine
- Department of Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine
- Department of Pediatrics, Indiana University School of Medicine
- Department of Roudebush VA Medical Center, Indianapolis, IN 46202, USA
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3
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Wang H, Li Q, Yuan YC, Han XC, Cao YT, Yang JK. KCNH6 channel promotes insulin exocytosis via interaction with Munc18-1 independent of electrophysiological processes. Cell Mol Life Sci 2024; 81:86. [PMID: 38349432 PMCID: PMC10864572 DOI: 10.1007/s00018-024-05134-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 12/23/2023] [Accepted: 01/19/2024] [Indexed: 02/15/2024]
Abstract
Glucose-stimulated insulin secretion (GSIS) in pancreatic islet β-cells primarily relies on electrophysiological processes. Previous research highlighted the regulatory role of KCNH6, a member of the Kv channel family, in governing GSIS through its influence on β-cell electrophysiology. In this study, we unveil a novel facet of KCNH6's function concerning insulin granule exocytosis, independent of its conventional electrical role. Young mice with β-cell-specific KCNH6 knockout (βKO) exhibited impaired glucose tolerance and reduced insulin secretion, a phenomenon not explained by electrophysiological processes alone. Consistently, islets from KCNH6-βKO mice exhibited reduced insulin secretion, conversely, the overexpression of KCNH6 in murine pancreatic islets significantly enhanced insulin release. Moreover, insulin granules lacking KCNH6 demonstrated compromised docking capabilities and a reduced fusion response upon glucose stimulation. Crucially, our investigation unveiled a significant interaction between KCNH6 and the SNARE protein regulator, Munc18-1, a key mediator of insulin granule exocytosis. These findings underscore the critical role of KCNH6 in the regulation of insulin secretion through its interaction with Munc18-1, providing a promising and novel avenue for enhancing our understanding of the Kv channel in diabetes mechanisms.
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Affiliation(s)
- Hao Wang
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China.
- Laboratory for Clinical Medicine, Capital Medical University, Beijing, 100069, China.
| | - Qi Li
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China
- Laboratory for Clinical Medicine, Capital Medical University, Beijing, 100069, China
| | - Ying-Chao Yuan
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China
| | - Xue-Chun Han
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China
| | - Yong-Ting Cao
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China
- Department of Endocrinology, Beijing Mentougou District Hospital, Beijing, 102399, China
| | - Jin-Kui Yang
- Beijing Key Laboratory of Diabetes Research and Care, Department of Endocrinology and Metabolism, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, 100730, China.
- Laboratory for Clinical Medicine, Capital Medical University, Beijing, 100069, China.
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4
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Harada K, Takashima M, Kitaguchi T, Tsuboi T. F-actin determines the time-dependent shift in docking dynamics of glucagon-like peptide-1 granules upon stimulation of secretion. FEBS Lett 2023; 597:657-671. [PMID: 36694275 DOI: 10.1002/1873-3468.14580] [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: 12/08/2022] [Revised: 01/09/2023] [Accepted: 01/09/2023] [Indexed: 01/26/2023]
Abstract
Although exocytosis can be categorized into several forms based on docking dynamics, temporal regulatory mechanisms of the exocytotic forms are unclear. We explored the dynamics of glucagon-like peptide-1 (GLP-1) exocytosis in murine GLUTag cells (GLP-1-secreting enteroendocrine L-cells) upon stimulation with deoxycholic acid (DCA) or high K+ to elucidate the mechanisms regulating the balance between the different types of exocytotic forms (pre-docked with the plasma membrane before stimulation; docked after stimulation and subsequently fused; or rapidly recruited and fused after stimulation, without stable docking). GLP-1 exocytosis showed a biphasic pattern, and we found that most exocytosis was from the pre-docked granules with the plasma membrane before stimulation, or granules rapidly fused to the plasma membrane without docking after stimulation. In contrast, granules docked with the plasma membrane after stimuli and eventually fused were predominant thereafter. Inhibition of actin polymerization suppressed exocytosis of the pre-docked granules. These results suggest that the docking dynamics of GLP-1 granules shows a time-dependent biphasic shift, which is determined by interaction with F-actin.
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Affiliation(s)
- Kazuki Harada
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Japan
| | - Maoko Takashima
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Japan
| | - Tetsuya Kitaguchi
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan
| | - Takashi Tsuboi
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Japan
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5
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Zhao K, Matsunaga K, Mizuno K, Wang H, Okunishi K, Izumi T. Functional hierarchy among different Rab27 effectors involved in secretory granule exocytosis. eLife 2023; 12:82821. [PMID: 36803984 PMCID: PMC9988257 DOI: 10.7554/elife.82821] [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: 08/18/2022] [Accepted: 02/21/2023] [Indexed: 02/23/2023] Open
Abstract
The Rab27 effectors are known to play versatile roles in regulated exocytosis. In pancreatic beta cells, exophilin-8 anchors granules in the peripheral actin cortex, whereas granuphilin and melanophilin mediate granule fusion with and without stable docking to the plasma membrane, respectively. However, it is unknown whether these coexisting effectors function in parallel or in sequence to support the whole insulin secretory process. Here, we investigate their functional relationships by comparing the exocytic phenotypes in mouse beta cells simultaneously lacking two effectors with those lacking just one of them. Analyses of prefusion profiles by total internal reflection fluorescence microscopy suggest that melanophilin exclusively functions downstream of exophilin-8 to mobilize granules for fusion from the actin network to the plasma membrane after stimulation. The two effectors are physically linked via the exocyst complex. Downregulation of the exocyst component affects granule exocytosis only in the presence of exophilin-8. The exocyst and exophilin-8 also promote fusion of granules residing beneath the plasma membrane prior to stimulation, although they differentially act on freely diffusible granules and those stably docked to the plasma membrane by granuphilin, respectively. This is the first study to diagram the multiple intracellular pathways of granule exocytosis and the functional hierarchy among different Rab27 effectors within the same cell.
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Affiliation(s)
- Kunli Zhao
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Kohichi Matsunaga
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Kouichi Mizuno
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Hao Wang
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Katsuhide Okunishi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma UniversityMaebashiJapan
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6
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Wang H, Yuan YC, Chang C, Izumi T, Wang HH, Yang JK. The signaling protein GIV/Girdin mediates the Nephrin-dependent insulin secretion of pancreatic islet β cells in response to high glucose. J Biol Chem 2023; 299:103045. [PMID: 36822326 PMCID: PMC10040812 DOI: 10.1016/j.jbc.2023.103045] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 02/10/2023] [Accepted: 02/12/2023] [Indexed: 02/23/2023] Open
Abstract
Glucose-stimulated insulin secretion of pancreatic β cells is essential in maintaining glucose homeostasis. Recent evidence suggests that the Nephrin-mediated intercellular junction between β cells is implicated in the regulation of insulin secretion. However, the underlying mechanisms are only partially characterized. Herein we report that GIV is a signaling mediator coordinating glucose-stimulated Nephrin phosphorylation and endocytosis with insulin secretion. We demonstrate that GIV is expressed in mouse islets and cultured β cells. The loss of function study suggests that GIV is essential for the second phase of glucose-stimulated insulin secretion. Next, we demonstrate that GIV mediates the high glucose-stimulated tyrosine phosphorylation of GIV and Nephrin by recruiting Src kinase, which leads to the endocytosis of Nephrin. Subsequently, the glucose-induced GIV/Nephrin/Src signaling events trigger downstream Akt phosphorylation, which activates Rac1-mediated cytoskeleton reorganization, allowing insulin secretory granules to access the plasma membrane for the second-phase secretion. Finally, we found that GIV is downregulated in the islets isolated from diabetic mice, and rescue of GIV ameliorates the β-cell dysfunction to restore the glucose-stimulated insulin secretion. We conclude that the GIV/Nephrin/Akt signaling axis is vital to regulate glucose-stimulated insulin secretion. This mechanism might be further targeted for therapeutic intervention of diabetic mellitus.
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Affiliation(s)
- Hao Wang
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
| | - Ying-Chao Yuan
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Cong Chang
- College of Biology, Hunan University, Changsha, Hunan, China; Hunan Food and Drug Vocational College, Changsha, Hunan, China
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, Japan
| | - Hong-Hui Wang
- College of Biology, Hunan University, Changsha, Hunan, China.
| | - Jin-Kui Yang
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
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7
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Mizuno K, Izumi T. Munc13b stimulus-dependently accumulates on granuphilin-mediated, docked granules prior to fusion. Cell Struct Funct 2022; 47:31-41. [PMID: 35387942 PMCID: PMC10511056 DOI: 10.1247/csf.22005] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 03/30/2022] [Indexed: 11/11/2022] Open
Abstract
The Rab27 effector granuphilin plays an indispensable role in stable docking of secretory granules to the plasma membrane by interacting with the complex of Munc18-1 and the fusion-incompetent, closed form of syntaxins-1~3. Although this process prevents spontaneous granule exocytosis, those docked granules actively fuse in parallel with other undocked granules after stimulation. Therefore, it is postulated that the closed form of syntaxins must be converted into the fusion-competent open form in a stimulus-dependent manner. Although Munc13 family proteins are generally thought to prime docked vesicles by facilitating conformational change in syntaxins, it is unknown which isoform acts in granuphilin-mediated, docked granule exocytosis. In the present study, we show that, although both Munc13a and Munc13b are expressed in mouse pancreatic islets and their beta-cell line MIN6, the silencing of Munc13b, but not that of Munc13a, severely affects glucose-induced insulin secretion. Furthermore, Munc13b accumulates on a subset of granules beneath the plasma membrane just prior to fusion during stimulation, whereas Munc13a is translocated to the plasma membrane where granules do not exist. When fluorescently labeled granuphilin was introduced to discriminate between molecularly docked granules and other undocked granules in living cells, Munc13b downregulation was observed to preferentially decrease the fusion of granuphilin-positive granules immobilized to the plasma membrane. These findings suggest that Munc13b promotes insulin exocytosis by clustering on molecularly docked granules in a stimulus-dependent manner.Key words: docking, insulin, live cell imaging, priming, TIRF microscopy.
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Affiliation(s)
- Kouichi Mizuno
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan
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8
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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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9
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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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Izumi T. In vivo Roles of Rab27 and Its Effectors in Exocytosis. Cell Struct Funct 2021; 46:79-94. [PMID: 34483204 PMCID: PMC10511049 DOI: 10.1247/csf.21043] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 08/31/2021] [Indexed: 11/11/2022] Open
Abstract
The monomeric GTPase Rab27 regulates exocytosis of a broad range of vesicles in multicellular organisms. Several effectors bind GTP-bound Rab27a and/or Rab27b on secretory vesicles to execute a series of exocytic steps, such as vesicle maturation, movement along microtubules, anchoring within the peripheral F-actin network, and tethering to the plasma membrane, via interactions with specific proteins and membrane lipids in a local milieu. Although Rab27 effectors generally promote exocytosis, they can also temporarily restrict it when they are involved in the rate-limiting step. Genetic alterations in Rab27-related molecules cause discrete diseases manifesting pigment dilution and immunodeficiency, and can also affect common diseases such as diabetes and cancer in complex ways. Although the function and mechanism of action of these effectors have been explored, it is unclear how multiple effectors act in coordination within a cell to regulate the secretory process as a whole. It seems that Rab27 and various effectors constitutively reside on individual vesicles to perform consecutive exocytic steps. The present review describes the unique properties and in vivo roles of the Rab27 system, and the functional relationship among different effectors coexpressed in single cells, with pancreatic beta cells used as an example.Key words: membrane trafficking, regulated exocytosis, insulin granules, pancreatic beta cells.
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Affiliation(s)
- Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
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11
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Zhao MM, Lu J, Li S, Wang H, Cao X, Li Q, Shi TT, Matsunaga K, Chen C, Huang H, Izumi T, Yang JK. Berberine is an insulin secretagogue targeting the KCNH6 potassium channel. Nat Commun 2021; 12:5616. [PMID: 34556670 PMCID: PMC8460738 DOI: 10.1038/s41467-021-25952-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 09/08/2021] [Indexed: 11/09/2022] Open
Abstract
Coptis chinensis is an ancient Chinese herb treating diabetes in China for thousands of years. However, its underlying mechanism remains poorly understood. Here, we report the effects of its main active component, berberine (BBR), on stimulating insulin secretion. In mice with hyperglycemia induced by a high-fat diet, BBR significantly increases insulin secretion and reduced blood glucose levels. However, in mice with hyperglycemia induced by global or pancreatic islet β-cell-specific Kcnh6 knockout, BBR does not exert beneficial effects. BBR directly binds KCNH6 potassium channels, significantly accelerates channel closure, and subsequently reduces KCNH6 currents. Consequently, blocking KCNH6 currents prolongs high glucose-dependent cell membrane depolarization and increases insulin secretion. Finally, to assess the effect of BBR on insulin secretion in humans, a randomized, double-blind, placebo-controlled, two-period crossover, single-dose, phase 1 clinical trial (NCT03972215) including 15 healthy men receiving a 160-min hyperglycemic clamp experiment is performed. The pre-specified primary outcomes are assessment of the differences of serum insulin and C-peptide levels between BBR and placebo treatment groups during the hyperglycemic clamp study. BBR significantly promotes insulin secretion under hyperglycemic state comparing with placebo treatment, while does not affect basal insulin secretion in humans. All subjects tolerate BBR well, and we observe no side effects in the 14-day follow up period. In this study, we identify BBR as a glucose-dependent insulin secretagogue for treating diabetes without causing hypoglycemia that targets KCNH6 channels.
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Affiliation(s)
- Miao-Miao Zhao
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Jing Lu
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Sen Li
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Hao Wang
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Xi Cao
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Qi Li
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Ting-Ting Shi
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China
| | - Kohichi Matsunaga
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Chen Chen
- School of Biomedical Sciences, University of Queensland, Brisbane, QLD, 4072, Australia
| | - Haixia Huang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, 100069, Beijing, China
| | - Tetsuro Izumi
- Laboratory of Molecular Endocrinology and Metabolism, Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
| | - Jin-Kui Yang
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, 100730, Beijing, China.
- Beijing Key Laboratory of Diabetes Research and Care, Beijing Diabetes Institute, 100730, Beijing, China.
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