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Bhat S, Rousseau J, Michaud C, Lourenço CM, Stoler JM, Louie RJ, Clarkson LK, Lichty A, Koboldt DC, Reshmi SC, Sisodiya SM, Hoytema van Konijnenburg EMM, Koop K, van Hasselt PM, Démurger F, Dubourg C, Sullivan BR, Hughes SS, Thiffault I, Tremblay ES, Accogli A, Srour M, Blunck R, Campeau PM. Mono-allelic KCNB2 variants lead to a neurodevelopmental syndrome caused by altered channel inactivation. Am J Hum Genet 2024; 111:761-777. [PMID: 38503299 PMCID: PMC11023922 DOI: 10.1016/j.ajhg.2024.02.014] [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: 07/28/2023] [Revised: 02/23/2024] [Accepted: 02/25/2024] [Indexed: 03/21/2024] Open
Abstract
Ion channels mediate voltage fluxes or action potentials that are central to the functioning of excitable cells such as neurons. The KCNB family of voltage-gated potassium channels (Kv) consists of two members (KCNB1 and KCNB2) encoded by KCNB1 and KCNB2, respectively. These channels are major contributors to delayed rectifier potassium currents arising from the neuronal soma which modulate overall excitability of neurons. In this study, we identified several mono-allelic pathogenic missense variants in KCNB2, in individuals with a neurodevelopmental syndrome with epilepsy and autism in some individuals. Recurrent dysmorphisms included a broad forehead, synophrys, and digital anomalies. Additionally, we selected three variants where genetic transmission has not been assessed, from two epilepsy studies, for inclusion in our experiments. We characterized channel properties of these variants by expressing them in oocytes of Xenopus laevis and conducting cut-open oocyte voltage clamp electrophysiology. Our datasets indicate no significant change in absolute conductance and conductance-voltage relationships of most disease variants as compared to wild type (WT), when expressed either alone or co-expressed with WT-KCNB2. However, variants c.1141A>G (p.Thr381Ala) and c.641C>T (p.Thr214Met) show complete abrogation of currents when expressed alone with the former exhibiting a left shift in activation midpoint when expressed alone or with WT-KCNB2. The variants we studied, nevertheless, show collective features of increased inactivation shifted to hyperpolarized potentials. We suggest that the effects of the variants on channel inactivation result in hyper-excitability of neurons, which contributes to disease manifestations.
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Affiliation(s)
- Shreyas Bhat
- Center for Interdisciplinary Research on Brain and Learning (CIRCA), Department of Physics and Department of Pharmacology and Physiology, Université de Montréal, Montréal, QC, Canada
| | - Justine Rousseau
- Centre de Recherche Du Centre Hospitalier Universitaire Sainte-Justine, Université de Montréal, Montréal, QC H3T 1C5, Canada
| | - Coralie Michaud
- Centre de Recherche Du Centre Hospitalier Universitaire Sainte-Justine, Université de Montréal, Montréal, QC H3T 1C5, Canada
| | | | - Joan M Stoler
- Division of Genetics and Genomics, Boston Children's Hospital, Boston, MA, USA
| | | | | | - Angie Lichty
- Greenwood Genetic Center, Greenwood, SC 29646, USA
| | - Daniel C Koboldt
- Steve and Cindy Rasmussen Institute for Genomic Medicine at Nationwide Children's Hospital, Columbus, OH, USA
| | - Shalini C Reshmi
- Steve and Cindy Rasmussen Institute for Genomic Medicine at Nationwide Children's Hospital, Columbus, OH, USA; Department of Pathology and Laboratory Medicine, Nationwide Children's Hospital, Columbus, OH, USA
| | - Sanjay M Sisodiya
- Department of Clinical and Experimental Epilepsy, University College London Queen Square Institute of Neurology, London WC1N 3BG, UK
| | | | - Klaas Koop
- Department of Metabolic Diseases, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Peter M van Hasselt
- Department of Genetics, Section Metabolic Diagnostics, University Medical Center Utrecht, Utrecht, the Netherlands
| | | | - Christèle Dubourg
- Department of Molecular Genetics and Genomics, Rennes University Hospital, Rennes, France; Université de Rennes, CNRS, IGDR, UMR 6290 Rennes, France
| | - Bonnie R Sullivan
- Division of Clinical Genetics, Department of Pediatrics, Children's Mercy Kansas City, Kansas City, MO, USA
| | - Susan S Hughes
- Division of Clinical Genetics, Department of Pediatrics, Children's Mercy Kansas City, Kansas City, MO, USA
| | - Isabelle Thiffault
- Departments of Pediatrics and of Pathology and Laboratory Medicine, Children's Mercy Kansas City, Kansas City, MO, USA
| | - Elisabeth Simard Tremblay
- Department of Neurology and Neurosurgery, McGill University Health Centre, Montréal, QC, Canada; Department of Pediatrics, Division of Pediatric Neurology, McGill University, Montréal, QC, Canada
| | - Andrea Accogli
- Department of Specialized Medicine, Division of Medical Genetics, McGill University Health Centre, Montréal, QC, Canada; Department of Human Genetics, Faculty of Medicine, McGill University, Montral, QC H3A 1B1, Canada
| | - Myriam Srour
- Department of Pediatrics, Division of Pediatric Neurology, McGill University, Montréal, QC, Canada; Department of Human Genetics, Faculty of Medicine, McGill University, Montral, QC H3A 1B1, Canada
| | - Rikard Blunck
- Center for Interdisciplinary Research on Brain and Learning (CIRCA), Department of Physics and Department of Pharmacology and Physiology, Université de Montréal, Montréal, QC, Canada.
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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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Wang J, Yan D, Cui H, Zhang R, Ma X, Chen L, Hu C, Wu J. Identification of eight genomic protective alleles for mitochondrial diabetes by Kinship-graph convolutional network. J Diabetes Investig 2024; 15:52-62. [PMID: 38157301 PMCID: PMC10759726 DOI: 10.1111/jdi.14125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 11/16/2023] [Accepted: 11/21/2023] [Indexed: 01/03/2024] Open
Abstract
AIMS Nearly 85% of maternally inherited diabetes and deafness (MIDD) are caused by the m.3243A>G mutation in the mitochondrial DNA. However, the clinical phenotypes of MIDD may also be influenced by the nuclear genome, this study aimed to investigate nuclear genome variants that influence clinical phenotypes associated with m.3243A>G mutation in MIDD based on whole-genome sequencing of the patients belonging to pedigrees. MATERIALS AND METHODS We analyzed a whole-genome sequencing (WGS) dataset from blood samples of 38 MIDD patients with the m.3243A > G mutation belonging to 10 pedigrees, by developing a Kinship-graph convolutional network approach, called Ki-GCN, integrated with the conventional genome-wide association study (GWAS) methods. RESULTS We identified eight protective alleles in the nuclear genome that have protective effects against the onset of MIDD, related deafness, and also type 2 diabetes. Based on these eight protective alleles, we constructed an effective logistic regression model to predict the early or late onset of MIDD patients. CONCLUSIONS There are protective alleles in the nuclear genome that are associated with the onset-age of MIDD patients and might also provide protective effects on the deafness derived from MIDD patients.
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Affiliation(s)
- Jiahao Wang
- CAS Key Laboratory of Systems Biology, Center for Excellence in Molecular Cell ScienceChinese Academy of SciencesShanghaiChina
- College of Life SciencesUniversity of Chinese Academy of SciencesBeijingChina
| | - Dandan Yan
- Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Centre for Diabetes, Shanghai Diabetes InstituteShanghai Jiao Tong University Affiliated Sixth People's HospitalShanghaiChina
| | - Haoyue Cui
- School of Life Science and TechnologyShanghaiTech UniversityShanghaiChina
| | - Rong Zhang
- Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Centre for Diabetes, Shanghai Diabetes InstituteShanghai Jiao Tong University Affiliated Sixth People's HospitalShanghaiChina
| | - Xiaojing Ma
- Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Centre for Diabetes, Shanghai Diabetes InstituteShanghai Jiao Tong University Affiliated Sixth People's HospitalShanghaiChina
| | - Luonan Chen
- CAS Key Laboratory of Systems Biology, Center for Excellence in Molecular Cell ScienceChinese Academy of SciencesShanghaiChina
- School of Life Science and TechnologyShanghaiTech UniversityShanghaiChina
- Key Laboratory of Systems Health Science of Zhejiang Province, Hangzhou Institute for Advanced StudyUniversity of Chinese Academy of SciencesHangzhouZhejiangChina
| | - Cheng Hu
- Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Centre for Diabetes, Shanghai Diabetes InstituteShanghai Jiao Tong University Affiliated Sixth People's HospitalShanghaiChina
- Institute for Metabolic DiseaseFengxian Central Hospital Affiliated to Southern Medical UniversityShanghaiChina
| | - Jiarui Wu
- CAS Key Laboratory of Systems Biology, Center for Excellence in Molecular Cell ScienceChinese Academy of SciencesShanghaiChina
- School of Life Science and TechnologyShanghaiTech UniversityShanghaiChina
- Key Laboratory of Systems Health Science of Zhejiang Province, Hangzhou Institute for Advanced StudyUniversity of Chinese Academy of SciencesHangzhouZhejiangChina
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Ramanadham S, Turk J, Bhatnagar S. Noncanonical Regulation of cAMP-Dependent Insulin Secretion and Its Implications in Type 2 Diabetes. Compr Physiol 2023; 13:5023-5049. [PMID: 37358504 PMCID: PMC10809800 DOI: 10.1002/cphy.c220031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
Impaired glucose tolerance (IGT) and β-cell dysfunction in insulin resistance associated with obesity lead to type 2 diabetes (T2D). Glucose-stimulated insulin secretion (GSIS) from β-cells occurs via a canonical pathway that involves glucose metabolism, ATP generation, inactivation of K ATP channels, plasma membrane depolarization, and increases in cytosolic concentrations of [Ca 2+ ] c . However, optimal insulin secretion requires amplification of GSIS by increases in cyclic adenosine monophosphate (cAMP) signaling. The cAMP effectors protein kinase A (PKA) and exchange factor activated by cyclic-AMP (Epac) regulate membrane depolarization, gene expression, and trafficking and fusion of insulin granules to the plasma membrane for amplifying GSIS. The widely recognized lipid signaling generated within β-cells by the β-isoform of Ca 2+ -independent phospholipase A 2 enzyme (iPLA 2 β) participates in cAMP-stimulated insulin secretion (cSIS). Recent work has identified the role of a G-protein coupled receptor (GPCR) activated signaling by the complement 1q like-3 (C1ql3) secreted protein in inhibiting cSIS. In the IGT state, cSIS is attenuated, and the β-cell function is reduced. Interestingly, while β-cell-specific deletion of iPLA 2 β reduces cAMP-mediated amplification of GSIS, the loss of iPLA 2 β in macrophages (MØ) confers protection against the development of glucose intolerance associated with diet-induced obesity (DIO). In this article, we discuss canonical (glucose and cAMP) and novel noncanonical (iPLA 2 β and C1ql3) pathways and how they may affect β-cell (dys)function in the context of impaired glucose intolerance associated with obesity and T2D. In conclusion, we provide a perspective that in IGT states, targeting noncanonical pathways along with canonical pathways could be a more comprehensive approach for restoring β-cell function in T2D. © 2023 American Physiological Society. Compr Physiol 13:5023-5049, 2023.
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Affiliation(s)
- Sasanka Ramanadham
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Alabama, USA
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
| | - John Turk
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Sushant Bhatnagar
- Comprehensive Diabetes Center, University of Alabama at Birmingham, Alabama, USA
- Department of Medicine, University of Alabama at Birmingham, Alabama, USA
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Inhibitory Effectiveness in Delayed-Rectifier Potassium Current Caused by Vortioxetine, Known to Be a Novel Antidepressant. Biomedicines 2022; 10:biomedicines10061318. [PMID: 35740340 PMCID: PMC9220334 DOI: 10.3390/biomedicines10061318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 05/25/2022] [Accepted: 06/01/2022] [Indexed: 01/27/2023] Open
Abstract
Vortioxetine (VOR) is recognized to exert antidepressant actions. However, whether this drug modifies ionic currents in excitable cells remains unclear. The aim of this study was to explore the electrophysiological effects of VOR and other related compounds in pituitary GH3 cells and in Neuro-2a cells. VOR suppressed the delayed-rectifier K+ current (IK(DR)) in a concentration-, time-, and state-dependent manner. Effective IC50 values needed to inhibit peak and sustained IK(DR) were computed to be 31.2 and 8.5 μM, respectively, while the KD value estimated from minimal binding scheme was 7.9 μM. Cell exposure to serotonin (10 μM) alone failed to alter IK(DR), while fluoxetine (10 μM), a compound structurally similar to VOR, mildly suppressed current amplitude. In continued presence of VOR, neither further addition of propranolol nor risperidone reversed VOR-mediated inhibition of IK(DR). Increasing VOR concentration not only depressed IK(DR) conductance but also shifted toward the hyperpolarized potential. As the VOR concentration was raised, the recovery of IK(DR) block became slowed. The IK(DR) activated by a downsloping ramp was suppressed by its presence. The inhibition of IK(DR) by a train pulse was enhanced during exposure to VOR. In Neuro-2a cells, this drug decreased IK(DR). Overall, inhibitory effects of VOR on ionic currents might constitute another underlying mechanism of its actions.
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Lubberding AF, Juhl CR, Skovhøj EZ, Kanters JK, Mandrup‐Poulsen T, Torekov SS. Celebrities in the heart, strangers in the pancreatic beta cell: Voltage-gated potassium channels K v 7.1 and K v 11.1 bridge long QT syndrome with hyperinsulinaemia as well as type 2 diabetes. Acta Physiol (Oxf) 2022; 234:e13781. [PMID: 34990074 PMCID: PMC9286829 DOI: 10.1111/apha.13781] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 12/20/2021] [Accepted: 01/02/2022] [Indexed: 12/13/2022]
Abstract
Voltage‐gated potassium (Kv) channels play an important role in the repolarization of a variety of excitable tissues, including in the cardiomyocyte and the pancreatic beta cell. Recently, individuals carrying loss‐of‐function (LoF) mutations in KCNQ1, encoding Kv7.1, and KCNH2 (hERG), encoding Kv11.1, were found to exhibit post‐prandial hyperinsulinaemia and episodes of hypoglycaemia. These LoF mutations also cause the cardiac disorder long QT syndrome (LQTS), which can be aggravated by hypoglycaemia. Interestingly, patients with LQTS also have a higher burden of diabetes compared to the background population, an apparent paradox in relation to the hyperinsulinaemic phenotype, and KCNQ1 has been identified as a type 2 diabetes risk gene. This review article summarizes the involvement of delayed rectifier K+ channels in pancreatic beta cell function, with emphasis on Kv7.1 and Kv11.1, using the cardiomyocyte for context. The functional and clinical consequences of LoF mutations and polymorphisms in these channels on blood glucose homeostasis are explored using evidence from pre‐clinical, clinical and genome‐wide association studies, thereby evaluating the link between LQTS, hyperinsulinaemia and type 2 diabetes.
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Affiliation(s)
- Anniek F. Lubberding
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Christian R. Juhl
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Emil Z. Skovhøj
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Jørgen K. Kanters
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Thomas Mandrup‐Poulsen
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
| | - Signe S. Torekov
- Department of Biomedical Sciences Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark
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Munjal NS, Sapra D, Parthasarathi KTS, Goyal A, Pandey A, Banerjee M, Sharma J. Deciphering the Interactions of SARS-CoV-2 Proteins with Human Ion Channels Using Machine-Learning-Based Methods. Pathogens 2022; 11:pathogens11020259. [PMID: 35215201 PMCID: PMC8874499 DOI: 10.3390/pathogens11020259] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 01/31/2022] [Accepted: 02/08/2022] [Indexed: 01/04/2023] Open
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is accountable for the protracted COVID-19 pandemic. Its high transmission rate and pathogenicity led to health emergencies and economic crisis. Recent studies pertaining to the understanding of the molecular pathogenesis of SARS-CoV-2 infection exhibited the indispensable role of ion channels in viral infection inside the host. Moreover, machine learning (ML)-based algorithms are providing a higher accuracy for host-SARS-CoV-2 protein–protein interactions (PPIs). In this study, PPIs of SARS-CoV-2 proteins with human ion channels (HICs) were trained on the PPI-MetaGO algorithm. PPI networks (PPINs) and a signaling pathway map of HICs with SARS-CoV-2 proteins were generated. Additionally, various U.S. food and drug administration (FDA)-approved drugs interacting with the potential HICs were identified. The PPIs were predicted with 82.71% accuracy, 84.09% precision, 84.09% sensitivity, 0.89 AUC-ROC, 65.17% Matthews correlation coefficient score (MCC) and 84.09% F1 score. Several host pathways were found to be altered, including calcium signaling and taste transduction pathway. Potential HICs could serve as an initial set to the experimentalists for further validation. The study also reinforces the drug repurposing approach for the development of host directed antiviral drugs that may provide a better therapeutic management strategy for infection caused by SARS-CoV-2.
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Affiliation(s)
- Nupur S. Munjal
- Institute of Bioinformatics, International Technology Park, Bangalore 560066, India; (N.S.M.); (D.S.); (K.T.S.P.); (A.G.)
| | - Dikscha Sapra
- Institute of Bioinformatics, International Technology Park, Bangalore 560066, India; (N.S.M.); (D.S.); (K.T.S.P.); (A.G.)
| | - K. T. Shreya Parthasarathi
- Institute of Bioinformatics, International Technology Park, Bangalore 560066, India; (N.S.M.); (D.S.); (K.T.S.P.); (A.G.)
| | - Abhishek Goyal
- Institute of Bioinformatics, International Technology Park, Bangalore 560066, India; (N.S.M.); (D.S.); (K.T.S.P.); (A.G.)
| | - Akhilesh Pandey
- Center for Molecular Medicine, National Institute of Mental Health and Neurosciences (NIMHANS), Hosur Road, Bangalore 560029, India;
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 55905, USA
- Center for Individualized Medicine, Mayo Clinic, Rochester, MN 55905, USA
| | - Manidipa Banerjee
- Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India;
| | - Jyoti Sharma
- Institute of Bioinformatics, International Technology Park, Bangalore 560066, India; (N.S.M.); (D.S.); (K.T.S.P.); (A.G.)
- Manipal Academy of Higher Education (MAHE), Udupi 576104, India
- Correspondence:
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Olmos-Ortiz A, Flores-Espinosa P, Díaz L, Velázquez P, Ramírez-Isarraraz C, Zaga-Clavellina V. Immunoendocrine Dysregulation during Gestational Diabetes Mellitus: The Central Role of the Placenta. Int J Mol Sci 2021; 22:8087. [PMID: 34360849 PMCID: PMC8348825 DOI: 10.3390/ijms22158087] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 07/15/2021] [Accepted: 07/26/2021] [Indexed: 02/07/2023] Open
Abstract
Gestational Diabetes Mellitus (GDM) is a transitory metabolic condition caused by dysregulation triggered by intolerance to carbohydrates, dysfunction of beta-pancreatic and endothelial cells, and insulin resistance during pregnancy. However, this disease includes not only changes related to metabolic distress but also placental immunoendocrine adaptations, resulting in harmful effects to the mother and fetus. In this review, we focus on the placenta as an immuno-endocrine organ that can recognize and respond to the hyperglycemic environment. It synthesizes diverse chemicals that play a role in inflammation, innate defense, endocrine response, oxidative stress, and angiogenesis, all associated with different perinatal outcomes.
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Affiliation(s)
- Andrea Olmos-Ortiz
- Departamento de Inmunobioquímica, Instituto Nacional de Perinatología Isidro Espinosa de los Reyes (INPer), Ciudad de México 11000, Mexico; (A.O.-O.); (P.F.-E.)
| | - Pilar Flores-Espinosa
- Departamento de Inmunobioquímica, Instituto Nacional de Perinatología Isidro Espinosa de los Reyes (INPer), Ciudad de México 11000, Mexico; (A.O.-O.); (P.F.-E.)
| | - Lorenza Díaz
- Departamento de Biología de la Reproducción, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Ciudad de México 14080, Mexico;
| | - Pilar Velázquez
- Departamento de Ginecología y Obstetricia, Hospital Ángeles México, Ciudad de México 11800, Mexico;
| | - Carlos Ramírez-Isarraraz
- Clínica de Urología Ginecológica, Instituto Nacional de Perinatología Isidro Espinosa de los Reyes (INPer), Ciudad de México 11000, Mexico;
| | - Verónica Zaga-Clavellina
- Departamento de Fisiología y Desarrollo Celular, Instituto Nacional de Perinatología Isidro Espinosa de los Reyes (INPer), Ciudad de México 11000, Mexico
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Stožer A, Paradiž Leitgeb E, Pohorec V, Dolenšek J, Križančić Bombek L, Gosak M, Skelin Klemen M. The Role of cAMP in Beta Cell Stimulus-Secretion and Intercellular Coupling. Cells 2021; 10:1658. [PMID: 34359828 PMCID: PMC8304079 DOI: 10.3390/cells10071658] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 06/18/2021] [Accepted: 06/28/2021] [Indexed: 12/22/2022] Open
Abstract
Pancreatic beta cells secrete insulin in response to stimulation with glucose and other nutrients, and impaired insulin secretion plays a central role in development of diabetes mellitus. Pharmacological management of diabetes includes various antidiabetic drugs, including incretins. The incretin hormones, glucagon-like peptide-1 and gastric inhibitory polypeptide, potentiate glucose-stimulated insulin secretion by binding to G protein-coupled receptors, resulting in stimulation of adenylate cyclase and production of the secondary messenger cAMP, which exerts its intracellular effects through activation of protein kinase A or the guanine nucleotide exchange protein 2A. The molecular mechanisms behind these two downstream signaling arms are still not fully elucidated and involve many steps in the stimulus-secretion coupling cascade, ranging from the proximal regulation of ion channel activity to the central Ca2+ signal and the most distal exocytosis. In addition to modifying intracellular coupling, the effect of cAMP on insulin secretion could also be at least partly explained by the impact on intercellular coupling. In this review, we systematically describe the possible roles of cAMP at these intra- and inter-cellular signaling nodes, keeping in mind the relevance for the whole organism and translation to humans.
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Affiliation(s)
- Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Eva Paradiž Leitgeb
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Viljem Pohorec
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
- Faculty of Natural Sciences and Mathematics, University of Maribor, SI-2000 Maribor, Slovenia
| | - Lidija Križančić Bombek
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
| | - Marko Gosak
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
- Faculty of Natural Sciences and Mathematics, University of Maribor, SI-2000 Maribor, Slovenia
| | - Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, SI-2000 Maribor, Slovenia; (A.S.); (E.P.L.); (V.P.); (J.D.); (L.K.B.); (M.G.)
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MicroRNA Sequences Modulated by Beta Cell Lipid Metabolism: Implications for Type 2 Diabetes Mellitus. BIOLOGY 2021; 10:biology10060534. [PMID: 34203703 PMCID: PMC8232095 DOI: 10.3390/biology10060534] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Revised: 06/08/2021] [Accepted: 06/09/2021] [Indexed: 12/23/2022]
Abstract
Alterations in lipid metabolism within beta cells and islets contributes to dysfunction and apoptosis of beta cells, leading to loss of insulin secretion and the onset of type 2 diabetes. Over the last decade, there has been an explosion of interest in understanding the landscape of gene expression which influences beta cell function, including the importance of small non-coding microRNA sequences in this context. This review sought to identify the microRNA sequences regulated by metabolic challenges in beta cells and islets, their targets, highlight their function and assess their possible relevance as biomarkers of disease progression in diabetic individuals. Predictive analysis was used to explore networks of genes targeted by these microRNA sequences, which may offer new therapeutic strategies to protect beta cell function and delay the onset of type 2 diabetes.
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11
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Félix-Martínez GJ, González-Vélez V, Godínez-Fernández JR, Gil A. Electrophysiological models of the human pancreatic δ-cell: From single channels to the firing of action potentials. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2020; 36:e3296. [PMID: 31833669 DOI: 10.1002/cnm.3296] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 12/05/2019] [Accepted: 12/05/2019] [Indexed: 06/10/2023]
Abstract
Minimal mathematical models were developed to describe the electrophysiological properties of human δ-cells. Markov models of single channels were first developed based on the analysis of electrophysiological data. Monte Carlo simulations of voltage-clamp experiments were performed in an iteratively optimization procedure to estimate the number of channels required to reproduce the main characteristics of the macroscopic currents recorded experimentally. A membrane model of the firing of action potentials was then developed based on the kinetic schemes of single channels and the number of channels estimated. We showed that macroscopic currents of human δ-cells can be reproduced by minimal models of single channels when the appropriate number of channels is considered. In addition, our simulations suggest that human δ-cells are capable of generating action potentials through the interaction of the ionic currents involved. Finally, we determined the relative contribution of the currents underlying the firing of action potentials in human pancreatic δ-cells, which allowed us to propose a qualitative model of an action potential in terms of the underlying ionic currents.
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Affiliation(s)
- Gerardo J Félix-Martínez
- Cátedras CONACYT, Consejo Nacional de Ciencia y Tecnología, Mexico City, Mexico
- Departamento de Ingeniería Eléctrica, Universidad Autónoma Metropolitana, Mexico City, Mexico
| | | | | | - Amparo Gil
- Departamento de Matemática Aplicada y Ciencias de la Computación, Universidad de Cantabria, Santander, Spain
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12
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Bozic I, Savic D, Milosevic A, Janjic M, Laketa D, Tesovic K, Bjelobaba I, Jakovljevic M, Nedeljkovic N, Pekovic S, Lavrnja I. The Potassium Channel Kv1.5 Expression Alters During Experimental Autoimmune Encephalomyelitis. Neurochem Res 2019; 44:2733-2745. [PMID: 31624998 DOI: 10.1007/s11064-019-02892-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/23/2019] [Accepted: 10/11/2019] [Indexed: 12/29/2022]
Abstract
Multiple sclerosis (MS) is a chronic, inflammatory, neurodegenerative disease with an autoimmune component. It was suggested that potassium channels, which are involved in crucial biological functions may have a role in different diseases, including MS and its animal model, experimental autoimmune encephalomyelitis (EAE). It was shown that voltage-gated potassium channels Kv1.5 are responsible for fine-tuning in the immune physiology and influence proliferation and differentiation in microglia and astrocytes. Here, we explored the cellular distribution of the Kv1.5 channel, together with its transcript and protein expression in the male rat spinal cord during different stages of EAE. Our results reveal a decrease of Kv1.5 transcript and protein level at the peak of disease, where massive infiltration of myeloid cells occurs, together with reactive astrogliosis and demyelination. Also, we revealed that the presence of this channel is not found in infiltrating macrophages/microglia during EAE. It is interesting to note that Kv1.5 channel is expressed only in resting microglia in the naïve animals. Predominant expression of Kv1.5 channel was found in the astrocytes in all experimental groups, while some vimentin+ cells, resembling macrophages, are devoid of Kv1.5 expression. Our results point to the possible link between Kv1.5 channel and the pathophysiological processes in EAE.
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Affiliation(s)
- I Bozic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - D Savic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - A Milosevic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - M Janjic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - D Laketa
- Department for General Physiology and Biophysics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - K Tesovic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - I Bjelobaba
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - M Jakovljevic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - N Nedeljkovic
- Department for General Physiology and Biophysics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - S Pekovic
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - I Lavrnja
- Department of Neurobiology, Institute for Biological Research "Siniša Stanković"- National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia.
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13
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Mawla AM, Huising MO. Navigating the Depths and Avoiding the Shallows of Pancreatic Islet Cell Transcriptomes. Diabetes 2019; 68:1380-1393. [PMID: 31221802 PMCID: PMC6609986 DOI: 10.2337/dbi18-0019] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2018] [Accepted: 04/29/2019] [Indexed: 12/24/2022]
Abstract
Islet gene expression has been widely studied to better understand the transcriptional features that define a healthy β-cell. Transcriptomes of FACS-purified α-, β-, and δ-cells using bulk RNA-sequencing have facilitated our understanding of the complex network of cross talk between islet cells and its effects on β-cell function. However, these approaches were by design not intended to resolve heterogeneity between individual cells. Several recent studies used single-cell RNA sequencing (scRNA-Seq) to report considerable heterogeneity within mouse and human β-cells. In this Perspective, we assess how this newfound ability to assess gene expression at single-cell resolution has enhanced our understanding of β-cell heterogeneity. We conduct a comprehensive assessment of several single human β-cell transcriptome data sets and ask if the heterogeneity reported by these studies showed overlap and concurred with previously known examples of β-cell heterogeneity. We also illustrate the impact of the inevitable limitations of working at or below the limit of detection of gene expression at single cell resolution and their consequences for the quality of single-islet cell transcriptome data. Finally, we offer some guidance on when to opt for scRNA-Seq and when bulk sequencing approaches may be better suited.
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Affiliation(s)
- Alex M Mawla
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, Davis, CA
| | - Mark O Huising
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, Davis, CA
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, CA
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14
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Yoon S, Kim J, Kim SK, Baik B, Chi SM, Kim SY, Nam D. GScluster: network-weighted gene-set clustering analysis. BMC Genomics 2019; 20:352. [PMID: 31072324 PMCID: PMC6507172 DOI: 10.1186/s12864-019-5738-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Accepted: 04/25/2019] [Indexed: 12/29/2022] Open
Abstract
Background Gene-set analysis (GSA) has been commonly used to identify significantly altered pathways or functions from omics data. However, GSA often yields a long list of gene-sets, necessitating efficient post-processing for improved interpretation. Existing methods cluster the gene-sets based on the extent of their overlap to summarize the GSA results without considering interactions between gene-sets. Results Here, we presented a novel network-weighted gene-set clustering that incorporates both the gene-set overlap and protein-protein interaction (PPI) networks. Three examples were demonstrated for microarray gene expression, GWAS summary, and RNA-sequencing data to which different GSA methods were applied. These examples as well as a global analysis show that the proposed method increases PPI densities and functional relevance of the resulting clusters. Additionally, distinct properties of gene-set distance measures were compared. The methods are implemented as an R/Shiny package GScluster that provides gene-set clustering and diverse functions for visualization of gene-sets and PPI networks. Conclusions Network-weighted gene-set clustering provides functionally more relevant gene-set clusters and related network analysis. Electronic supplementary material The online version of this article (10.1186/s12864-019-5738-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Sora Yoon
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Jinhwan Kim
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Seon-Kyu Kim
- Epigenomics Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea.,Genome Structure Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
| | - Bukyung Baik
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Sang-Mun Chi
- School of Computer Science and Engineering, Kyungsung University, Busan, Republic of Korea
| | - Seon-Young Kim
- Department of Functional Genomics, University of Science and Technology (UST), Daejeon, 34141, Republic of Korea. .,Genome Editing Research Center, Personalized Genomic Medicine Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34141, Republic of Korea.
| | - Dougu Nam
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea. .,Department of Mathematical Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea.
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15
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Raph SM, Bhatnagar A, Nystoriak MA. Biochemical and physiological properties of K + channel-associated AKR6A (Kvβ) proteins. Chem Biol Interact 2019; 305:21-27. [PMID: 30926318 DOI: 10.1016/j.cbi.2019.03.023] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 03/14/2019] [Accepted: 03/25/2019] [Indexed: 11/16/2022]
Abstract
Voltage-gated potassium (Kv) channels play an essential role in the regulation of membrane excitability and thereby control physiological processes such as cardiac excitability, neural communication, muscle contraction, and hormone secretion. Members of the Kv1 and Kv4 families are known to associate with auxiliary intracellular Kvβ subunits, which belong to the aldo-keto reductase superfamily. Electrophysiological studies have shown that these proteins regulate the gating properties of Kv channels. Although the three gene products encoding Kvβ proteins are functional enzymes in that they catalyze the nicotinamide adenine dinucleotide phosphate (NAD[P]H)-dependent reduction of a wide range of aldehyde and ketone substrates, the physiological role for these proteins and how each subtype may perform unique roles in coupling membrane excitability with cellular metabolic processes remains unclear. Here, we discuss current knowledge of the enzymatic properties of Kvβ proteins from biochemical studies with their described and purported physiological and pathophysiological influences.
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Affiliation(s)
- Sean M Raph
- Department of Pharmacology and Toxicology, University of Louisville, Louisville, KY, 40202, USA
| | - Aruni Bhatnagar
- Department of Medicine, Diabetes and Obesity Center, University of Louisville, Louisville, KY, 40202, USA
| | - Matthew A Nystoriak
- Department of Medicine, Diabetes and Obesity Center, University of Louisville, Louisville, KY, 40202, USA.
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16
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Tanner MR, Beeton C. Differences in ion channel phenotype and function between humans and animal models. FRONT BIOSCI-LANDMRK 2018; 23:43-64. [PMID: 28930537 PMCID: PMC5626566 DOI: 10.2741/4581] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ion channels play crucial roles in regulating a broad range of physiological processes. They form a very large family of transmembrane proteins. Their diversity results from not only a large number of different genes encoding for ion channel subunits but also the ability of subunits to assemble into homo- or heteromultimers, the existence of splice variants, and the expression of different regulatory subunits. These characteristics and the existence of very selective modulators make ion channels very attractive targets for therapy in a wide variety of pathologies. Some ion channels are already being targeted in the clinic while many more are being evaluated as novel drug targets in both clinical and preclinical studies. Advancing ion channel modulators from the bench to the clinic requires their assessment for safety and efficacy in animal models. While extrapolating results from one species to another is tempting, doing such without careful evaluation of the ion channels in different species presents a risk as the translation is not always straightforward. Here, we discuss differences between species in terms of ion channels expressed in selected tissues, differing roles of ion channels in some cell types, variable response to pharmacological agents, and human channelopathies that cannot fully be replicated in animal models.
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Affiliation(s)
- Mark R Tanner
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston TX 77030, and Interdepartmental Graduate Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston TX 77030
| | - Christine Beeton
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston TX 77030, and Center for Drug Discovery and Biology of Inflammation Center, Baylor College of Medicine, Houston TX 77030,
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17
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Lee CH, Chu CS, Tsai HJ, Ke LY, Lee HC, Yeh JL, Chen CH, Wu BN. Xanthine-derived KMUP-1 reverses glucotoxicity-activated Kv channels through the cAMP/PKA signaling pathway in rat pancreatic β cells. Chem Biol Interact 2017; 279:171-176. [PMID: 29183753 DOI: 10.1016/j.cbi.2017.11.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 11/23/2017] [Indexed: 10/18/2022]
Abstract
Hyperglycemia-associated glucotoxicity induces β-cell dysfunction and a reduction in insulin secretion. Voltage-dependent K+ (Kv) channels in pancreatic β-cells play a key role in glucose-dependent insulin secretion. KMUP-1, a xanthine derivative, has been demonstrated to modulate Kv channel activity in smooth muscles; however, the role of KMUP-1 in glucotoxicity-activated Kv channels in pancreatic β-cells remains unclear. In this study we examined the mechanisms by which KMUP-1 could inhibit high glucose (25 mM) activated Kv currents (IKv) in pancreatic β-cells. Pancreatic β-cells were isolated from Wistar rats and IKv was monitored by perforated patch-clamp recording. The peak IKv in high glucose-treated β-cells was ∼1.4-fold greater than for normal glucose (5.6 mM). KMUP-1 (1, 10, 30 μM) prevented high glucose-stimulated IKv in a concentration-dependent manner. Reduction of high glucose-activated IKv was also found for protein kinase A (PKA) activator 8-Br-cAMP (100 μM). Additionally, KMUP-1 (30 μM) current inhibition was reversed by the PKA inhibitor H-89 (1 μM). Otherwise, pretreatment with the PKC activator or inhibitor had no effect on IKv in high glucose exposure. In conclusion, glucotoxicity-diminished insulin secretion was due to IKv activation. KMUP-1 attenuated high glucose-stimulated IKv via the PKA but not the PKC signaling pathway. This finding provides evidence that KMUP-1 might be a promising agent for treating hyperglycemia-induced insulin resistance.
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Affiliation(s)
- Chien-Hsing Lee
- Department of Pharmacology, Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan
| | - Chih-Sheng Chu
- Division of Cardiology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan; Lipid Science and Aging Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan
| | - Han-Jie Tsai
- Department of Pharmacology, Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan
| | - Liang-Yin Ke
- Lipid Science and Aging Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan; Department of Medical Laboratory Science and Biotechnology, College of Health Sciences, Kaohsiung Medical University, Kaohsiung 807, Taiwan
| | - Hsiang-Chun Lee
- Division of Cardiology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan; Lipid Science and Aging Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan
| | - Jwu-Lai Yeh
- Department of Pharmacology, Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan; Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan
| | - Chu-Huang Chen
- Lipid Science and Aging Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan; Vascular and Medicinal Research, Texas Heart Institute, Houston, TX 77030, USA
| | - Bin-Nan Wu
- Department of Pharmacology, Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan; Lipid Science and Aging Research Center, Kaohsiung Medical University, Kaohsiung 807, Taiwan; Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan.
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18
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Robinson SD, Safavi-Hemami H. Venom peptides as pharmacological tools and therapeutics for diabetes. Neuropharmacology 2017; 127:79-86. [PMID: 28689026 DOI: 10.1016/j.neuropharm.2017.07.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 06/24/2017] [Accepted: 07/04/2017] [Indexed: 12/31/2022]
Abstract
Diabetes mellitus is a chronic disease caused by a deficiency in production of insulin by the beta cells of the pancreas (type 1 diabetes, T1D), or by partial deficiency of insulin production and the ineffectiveness of the insulin produced (type 2 diabetes, T2D). Animal venoms are a unique source of compounds targeting ion channels and receptors in the nervous and cardiovascular systems. In recent years, several venom peptides have also emerged as pharmacological tools and therapeutics for T1D and T2D. Some of these peptides act directly as mimics of endogenous metabolic hormones while others act on ion channels expressed in pancreatic beta cells. Here, we provide an overview of the discovery of these venom peptides, their mechanisms of action in the context of diabetes, and their therapeutic potential for the treatment of this disease. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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Affiliation(s)
- Samuel D Robinson
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
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19
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Fu J, Dai X, Plummer G, Suzuki K, Bautista A, Githaka JM, Senior L, Jensen M, Greitzer-Antes D, Manning Fox JE, Gaisano HY, Newgard CB, Touret N, MacDonald PE. Kv2.1 Clustering Contributes to Insulin Exocytosis and Rescues Human β-Cell Dysfunction. Diabetes 2017; 66:1890-1900. [PMID: 28607108 PMCID: PMC5482075 DOI: 10.2337/db16-1170] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 04/15/2017] [Indexed: 12/12/2022]
Abstract
Insulin exocytosis is regulated by ion channels that control excitability and Ca2+ influx. Channels also play an increasingly appreciated role in microdomain structure. In this study, we examine the mechanism by which the voltage-dependent K+ (Kv) channel Kv2.1 (KCNB1) facilitates depolarization-induced exocytosis in INS 832/13 cells and β-cells from human donors with and without type 2 diabetes (T2D). We find that Kv2.1, but not Kv2.2 (KCNB2), forms clusters of 6-12 tetrameric channels at the plasma membrane and facilitates insulin exocytosis. Knockdown of Kv2.1 expression reduces secretory granule targeting to the plasma membrane. Expression of the full-length channel (Kv2.1-wild-type) supports the glucose-dependent recruitment of secretory granules. However, a truncated channel (Kv2.1-ΔC318) that retains electrical function and syntaxin 1A binding, but lacks the ability to form clusters, does not enhance granule recruitment or exocytosis. Expression of KCNB1 appears reduced in T2D islets, and further knockdown of KCNB1 does not inhibit Kv current in T2D β-cells. Upregulation of Kv2.1-wild-type, but not Kv2.1-ΔC318, rescues the exocytotic phenotype in T2D β-cells and increases insulin secretion from T2D islets. Thus, the ability of Kv2.1 to directly facilitate insulin exocytosis depends on channel clustering. Loss of this structural role for the channel might contribute to impaired insulin secretion in diabetes.
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Affiliation(s)
- Jianyang Fu
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Xiaoqing Dai
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Gregory Plummer
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Kunimasa Suzuki
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Austin Bautista
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - John M Githaka
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Laura Senior
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Mette Jensen
- Sarah W. Stedman Nutrition and Metabolism Center and Duke Molecular Physiology Institute, Departments of Pharmacology & Cancer Biology and Medicine, Duke University, Durham, NC
| | - Dafna Greitzer-Antes
- Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Jocelyn E Manning Fox
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Herbert Y Gaisano
- Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Christopher B Newgard
- Sarah W. Stedman Nutrition and Metabolism Center and Duke Molecular Physiology Institute, Departments of Pharmacology & Cancer Biology and Medicine, Duke University, Durham, NC
| | - Nicolas Touret
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Patrick E MacDonald
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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20
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Sesti F. Oxidation of K(+) Channels in Aging and Neurodegeneration. Aging Dis 2016; 7:130-5. [PMID: 27114846 PMCID: PMC4809605 DOI: 10.14336/ad.2015.0901] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 09/01/2015] [Indexed: 01/26/2023] Open
Abstract
Reversible regulation of proteins by reactive oxygen species (ROS) is an important mechanism of neuronal plasticity. In particular, ROS have been shown to act as modulatory molecules of ion channels-which are key to neuronal excitability-in several physiological processes. However ROS are also fundamental contributors to aging vulnerability. When the level of excess ROS increases in the cell during aging, DNA is damaged, proteins are oxidized, lipids are degraded and more ROS are produced, all culminating in significant cell injury. From this arose the idea that oxidation of ion channels by ROS is one of the culprits for neuronal aging. Aging-dependent oxidative modification of voltage-gated potassium (K(+)) channels was initially demonstrated in the nematode Caenorhabditis elegans and more recently in the mammalian brain. Specifically, oxidation of the delayed rectifier KCNB1 (Kv2.1) and of Ca(2+)- and voltage sensitive K(+) channels have been established suggesting that their redox sensitivity contributes to altered excitability, progression of healthy aging and of neurodegenerative disease. Here I discuss the implications that oxidation of K(+) channels by ROS may have for normal aging, as well as for neurodegenerative disease.
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Affiliation(s)
- Federico Sesti
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
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21
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Bocksteins E. Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders. J Gen Physiol 2016; 147:105-25. [PMID: 26755771 PMCID: PMC4727947 DOI: 10.1085/jgp.201511507] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 12/11/2015] [Indexed: 12/19/2022] Open
Abstract
Members of the electrically silent voltage-gated K(+) (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K(+) channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department for Biomedical Sciences, University of Antwerp, 2610 Antwerp, Belgium
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22
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Qiu HY, Yuan SS, Yang FY, Shi TT, Yang JK. HERG Protein Plays a Role in Moxifloxacin-Induced Hypoglycemia. J Diabetes Res 2016; 2016:6741745. [PMID: 26649323 PMCID: PMC4663361 DOI: 10.1155/2016/6741745] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 08/06/2015] [Indexed: 11/17/2022] Open
Abstract
The purpose of this study was to investigate the effect of moxifloxacin on HERG channel protein and glucose metabolism. HERG expression was investigated using immunohistochemistry. The whole-cell patch clamp method was used to examine the effect of moxifloxacin on HERG channel currents. A glucose tolerance test was used to analyze the effects of moxifloxacin on blood glucose and insulin concentrations in mice. Results show that HERG protein was expressed in human pancreatic β-cells. Moxifloxacin inhibited HERG time-dependent and tail currents in HEK293 cells in a concentration-dependent manner. The IC50 of moxifloxacin inhibition was 36.65 μmol/L. Moxifloxacin (200 mg/kg) reduced blood glucose levels and increased insulin secretion in wild-type mice at 60 min after the start of the glucose tolerance test. In contrast, moxifloxacin did not significantly alter blood glucose and insulin levels in HERG knockout mice. Serum glucose levels increased and insulin concentrations decreased in HERG knockout mice when compared to wild-type mice. The moxifloxacin-induced decrease in blood glucose and increase in insulin secretion occurred via the HERG protein; thus, HERG protein plays a role in insulin secretion.
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Affiliation(s)
- Hai-Yan Qiu
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing 100730, China
| | - Sha-Sha Yuan
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing 100730, China
| | - Fang-Yuan Yang
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing 100730, China
| | - Ting-Ting Shi
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing 100730, China
| | - Jin-Kui Yang
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
- Beijing Key Laboratory of Diabetes Research and Care, Beijing 100730, China
- *Jin-Kui Yang:
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Peltola MA, Kuja-Panula J, Liuhanen J, Võikar V, Piepponen P, Hiekkalinna T, Taira T, Lauri SE, Suvisaari J, Kulesskaya N, Paunio T, Rauvala H. AMIGO-Kv2.1 Potassium Channel Complex Is Associated With Schizophrenia-Related Phenotypes. Schizophr Bull 2016; 42:191-201. [PMID: 26240432 PMCID: PMC4681558 DOI: 10.1093/schbul/sbv105] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The enormous variability in electrical properties of neurons is largely affected by a multitude of potassium channel subunits. Kv2.1 is a widely expressed voltage-dependent potassium channel and an important regulator of neuronal excitability. The Kv2.1 auxiliary subunit AMIGO constitutes an integral part of the Kv2.1 channel complex in brain and regulates the activity of the channel. AMIGO and Kv2.1 localize to the distinct somatodendritic clusters at the neuronal plasma membrane. Here we have created and characterized a mouse line lacking the AMIGO gene. Absence of AMIGO clearly reduced the amount of the Kv2.1 channel protein in mouse brain and altered the electrophysiological properties of neurons. These changes were accompanied by behavioral and pharmacological abnormalities reminiscent of those identified in schizophrenia. Concomitantly, we have detected an association of a rare, population-specific polymorphism of KV2.1 (KCNB1) with human schizophrenia in a genetic isolate enriched with schizophrenia. Our study demonstrates the involvement of AMIGO-Kv2.1 channel complex in schizophrenia-related behavioral domains in mice and identifies KV2.1 (KCNB1) as a strong susceptibility gene for schizophrenia spectrum disorders in humans.
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Affiliation(s)
- Marjaana A. Peltola
- Neuroscience Center, University of Helsinki, Helsinki, Finland;,*To whom correspondence should be addressed; Neuroscience Center, PO Box 56 (Viikinkaari 4), FI-00014 University of Helsinki, Helsinki, Finland; tel: +358-2941-57649, fax: +358-2941-57620, e-mail:
| | | | - Johanna Liuhanen
- Public Health Genomics Unit, National Institute for Health and Welfare, Helsinki, Finland
| | - Vootele Võikar
- Neuroscience Center, University of Helsinki, Helsinki, Finland
| | - Petteri Piepponen
- Division of Pharmacology and Toxicology, University of Helsinki, Helsinki, Finland
| | - Tero Hiekkalinna
- Public Health Genomics Unit, National Institute for Health and Welfare, Helsinki, Finland;,Institute for Molecular Medicine Finland, University of Helsinki, Helsinki, Finland
| | - Tomi Taira
- Neuroscience Center, University of Helsinki, Helsinki, Finland;,Department of Biosciences, University of Helsinki, Helsinki, Finland;,Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland
| | - Sari E. Lauri
- Neuroscience Center, University of Helsinki, Helsinki, Finland;,Department of Biosciences, University of Helsinki, Helsinki, Finland
| | - Jaana Suvisaari
- Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare, Helsinki, Finland
| | | | - Tiina Paunio
- Public Health Genomics Unit, National Institute for Health and Welfare, Helsinki, Finland;,Institute for Molecular Medicine Finland, University of Helsinki, Helsinki, Finland;,Department of Psychiatry, Institute of Clinical Medicine, University of Helsinki, Helsinki, Finland
| | - Heikki Rauvala
- Neuroscience Center, University of Helsinki, Helsinki, Finland
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Wu Y, Shyng SL, Chen PC. Concerted Trafficking Regulation of Kv2.1 and KATP Channels by Leptin in Pancreatic β-Cells. J Biol Chem 2015; 290:29676-90. [PMID: 26453299 DOI: 10.1074/jbc.m115.670877] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Indexed: 11/06/2022] Open
Abstract
In pancreatic β-cells, voltage-gated potassium 2.1 (Kv2.1) channels are the dominant delayed rectifier potassium channels responsible for action potential repolarization. Here, we report that leptin, a hormone secreted by adipocytes known to inhibit insulin secretion, causes a transient increase in surface expression of Kv2.1 channels in rodent and human β-cells. The effect of leptin on Kv2.1 surface expression is mediated by the AMP-activated protein kinase (AMPK). Activation of AMPK mimics whereas inhibition of AMPK occludes the effect of leptin. Inhibition of Ca(2+)/calmodulin-dependent protein kinase kinase β, a known upstream kinase of AMPK, also blocks the effect of leptin. In addition, the cAMP-dependent protein kinase (PKA) is involved in Kv2.1 channel trafficking regulation. Inhibition of PKA prevents leptin or AMPK activators from increasing Kv2.1 channel density, whereas stimulation of PKA is sufficient to promote Kv2.1 channel surface expression. The increased Kv2.1 surface expression by leptin is dependent on actin depolymerization, and pharmacologically induced actin depolymerization is sufficient to enhance Kv2.1 surface expression. The signaling and cellular mechanisms underlying Kv2.1 channel trafficking regulation by leptin mirror those reported recently for ATP-sensitive potassium (KATP) channels, which are critical for coupling glucose stimulation with membrane depolarization. We show that the leptin-induced increase in surface KATP channels results in more hyperpolarized membrane potentials than control cells at stimulating glucose concentrations, and the increase in Kv2.1 channels leads to a more rapid repolarization of membrane potential in cells firing action potentials. This study supports a model in which leptin exerts concerted trafficking regulation of KATP and Kv2.1 channels to coordinately inhibit insulin secretion.
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Affiliation(s)
- Yi Wu
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Show-Ling Shyng
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Pei-Chun Chen
- the Department of Physiology, College of Medicine, National Cheng Kung University, Tainan 701, Taiwan
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25
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Kim Y, Park T. Robust Gene-Gene Interaction Analysis in Genome Wide Association Studies. PLoS One 2015; 10:e0135016. [PMID: 26267341 PMCID: PMC4534386 DOI: 10.1371/journal.pone.0135016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 07/17/2015] [Indexed: 11/19/2022] Open
Abstract
Genome-wide association studies (GWAS) have successfully discovered hundreds of associations between genetic variants and complex traits. Most GWAS have focused on the identification of single variants. It has been shown that most of the variants that were discovered by GWAS could only partially explain disease heritability. The explanation for this missing heritability is generally believed to be gene-gene (GG) or gene-environment (GE) interactions and other structural variants. Generalized multifactor dimensionality reduction (GMDR) has been proven to be reasonably powerful in detecting GG and GE interactions; however, its performance has been found to decline when outlying quantitative traits are present. This paper proposes a robust GMDR estimation method (based on the L-estimator and M-estimator estimation methods) in an attempt to reduce the effects caused by outlying traits. A comparison of robust GMDR with the original MDR based on simulation studies showed the former method to outperform the latter. The performance of robust GMDR is illustrated through a real GWA example consisting of 8,577 samples from the Korean population using the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) level as a phenotype. Robust GMDR identified the KCNH1 gene to have strong interaction effects with other genes on the function of insulin secretion.
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Affiliation(s)
- Yongkang Kim
- Department of Statistics, Seoul National University, Seoul, South Korea
| | - Taesung Park
- Department of Statistics, Seoul National University, Seoul, South Korea
- Interdisciplinary Program in Bioinformatics, Seoul National University, Seoul, 151–741, South Korea
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Manning Fox JE, Lyon J, Dai XQ, Wright RC, Hayward J, van de Bunt M, Kin T, Shapiro AMJ, McCarthy MI, Gloyn AL, Ungrin MD, Lakey JR, Kneteman NM, Warnock GL, Korbutt GS, Rajotte RV, MacDonald PE. Human islet function following 20 years of cryogenic biobanking. Diabetologia 2015; 58:1503-12. [PMID: 25930156 PMCID: PMC4472956 DOI: 10.1007/s00125-015-3598-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Accepted: 04/07/2015] [Indexed: 02/07/2023]
Abstract
AIMS/HYPOTHESIS There are potential advantages to the low-temperature (-196 °C) banking of isolated islets, including the maintenance of viable islets for future research. We therefore assessed the in vitro and in vivo function of islets cryopreserved for nearly 20 years. METHODS Human islets were cryopreserved from 1991 to 2001 and thawed between 2012 and 2014. These were characterised by immunostaining, patch-clamp electrophysiology, insulin secretion, transcriptome analysis and transplantation into a streptozotocin (STZ)-induced mouse model of diabetes. RESULTS The cryopreservation time was 17.6 ± 0.4 years (n = 43). The thawed islets stained positive with dithizone, contained insulin-positive and glucagon-positive cells, and displayed levels of apoptosis and transcriptome profiles similar to those of freshly isolated islets, although their insulin content was lower. The cryopreserved beta cells possessed ion channels and exocytotic responses identical to those of freshly isolated beta cells. Cells from a subset of five donors demonstrated similar perifusion insulin secretion profiles pre- and post-cryopreservation. The transplantation of cryopreserved islets into the diabetic mice improved their glucose tolerance but did not completely normalise their blood glucose levels. Circulating human insulin and insulin-positive grafts were detectable at 10 weeks post-transplantation. CONCLUSIONS/INTERPRETATION We have demonstrated the potential for long-term banking of human islets for research, which could enable the use of tissue from a large number of donors with future technologies to gain new insight into diabetes.
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Affiliation(s)
- Jocelyn E. Manning Fox
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Pharmacology, University of Alberta, Edmonton, Canada
| | - James Lyon
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Pharmacology, University of Alberta, Edmonton, Canada
| | - Xiao Qing Dai
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Pharmacology, University of Alberta, Edmonton, Canada
| | - Robert C. Wright
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Pharmacology, University of Alberta, Edmonton, Canada
| | - Julie Hayward
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Surgery, University of Alberta, Edmonton, Canada
| | - Martijn van de Bunt
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Oxford, UK
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Tatsuya Kin
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Surgery, University of Alberta, Edmonton, Canada
| | - A. M. James Shapiro
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Surgery, University of Alberta, Edmonton, Canada
| | - Mark I. McCarthy
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Oxford, UK
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Anna L. Gloyn
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Oxford, UK
- Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Mark D. Ungrin
- Faculty of Veterinary Medicine, University of Calgary, Calgary, Canada
| | - Jonathan R. Lakey
- Departments of Surgery and Biomedical Engineering, University of California, Irvine, USA
| | | | - Garth L. Warnock
- Department of Surgery, University of British Columbia, Vancouver, Canada
| | - Gregory S. Korbutt
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Surgery, University of Alberta, Edmonton, Canada
| | - Raymond V. Rajotte
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Surgery, Surgical Medical Research Institute, HMRC, University of Alberta, Edmonton, AB Canada T6G 2S2
| | - Patrick E. MacDonald
- Alberta Diabetes Institute, University of Alberta, LKS Centre, Edmonton, AB Canada T6G 2R3
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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Sukma Rita R, Dezaki K, Kurashina T, Kakei M, Yada T. Partial blockade of Kv2.1 channel potentiates GLP-1's insulinotropic effects in islets and reduces its dose required for improving glucose tolerance in type 2 diabetic male mice. Endocrinology 2015; 156:114-23. [PMID: 25337656 DOI: 10.1210/en.2014-1728] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Glucagon-like peptide-1 (GLP-1)-based medicines have recently been widely used to treat type 2 diabetic patients, whereas adverse effects of nausea and vomiting have been documented. Inhibition of voltage-gated K(+) channel subtype Kv2.1 in pancreatic β-cells has been suggested to contribute to mild depolarization and promotion of insulin release. This study aimed to determine whether the blockade of Kv2.1 channels potentiates the insulinotropic effect of GLP-1 agonists. Kv2.1 channel blocker guangxitoxin-1E (GxTx) and GLP-1 agonist exendin-4 at subthreshold concentrations, when combined, markedly increased the insulin release and cytosolic Ca(2+) concentration ([Ca(2+)]i) in a glucose-dependent manner in mouse islets and β-cells. Exendin-4 at subthreshold concentration alone increased islet insulin release and β-cell [Ca(2+)]i in Kv2.1(+/-) mice. The [Ca(2+)]i response to subthreshold exendin-4 and GxTx in combination was attenuated by pretreatment with protein kinase A inhibitor H-89, indicating the protein kinase A dependency of the cooperative effect. Furthermore, subthreshold doses of GxTx and GLP-1 agonist liraglutide in combination markedly increased plasma insulin and improved glucose tolerance in diabetic db/db mice and NSY mice. These results demonstrate that a modest suppression of Kv2.1 channels dramatically raises insulinotropic potency of GLP-1-based drugs, which opens a new avenue to reduce their doses and associated adverse effects while achieving the same glycemic control in type 2 diabetes.
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Affiliation(s)
- Rauza Sukma Rita
- Division of Integrative Physiology (R.S.R., K.D., T.K., T.Y.), Department of Physiology, Jichi Medical University School of Medicine, Shimotsuke, Tochigi 329-0498, Japan; Department of Internal Medicine (M.K.), Saitama Medical Center, Jichi Medical University School of Medicine, Saitama 337-8503, Japan; and Department of Development Physiology (T.Y.), Division of Adaptation Development, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan
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28
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Yang SN, Shi Y, Yang G, Li Y, Yu J, Berggren PO. Ionic mechanisms in pancreatic β cell signaling. Cell Mol Life Sci 2014; 71:4149-77. [PMID: 25052376 PMCID: PMC11113777 DOI: 10.1007/s00018-014-1680-6] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2014] [Revised: 07/03/2014] [Accepted: 07/10/2014] [Indexed: 01/07/2023]
Abstract
The function and survival of pancreatic β cells critically rely on complex electrical signaling systems composed of a series of ionic events, namely fluxes of K(+), Na(+), Ca(2+) and Cl(-) across the β cell membranes. These electrical signaling systems not only sense events occurring in the extracellular space and intracellular milieu of pancreatic islet cells, but also control different β cell activities, most notably glucose-stimulated insulin secretion. Three major ion fluxes including K(+) efflux through ATP-sensitive K(+) (KATP) channels, the voltage-gated Ca(2+) (CaV) channel-mediated Ca(2+) influx and K(+) efflux through voltage-gated K(+) (KV) channels operate in the β cell. These ion fluxes set the resting membrane potential and the shape, rate and pattern of firing of action potentials under different metabolic conditions. The KATP channel-mediated K(+) efflux determines the resting membrane potential and keeps the excitability of the β cell at low levels. Ca(2+) influx through CaV1 channels, a major type of β cell CaV channels, causes the upstroke or depolarization phase of the action potential and regulates a wide range of β cell functions including the most elementary β cell function, insulin secretion. K(+) efflux mediated by KV2.1 delayed rectifier K(+) channels, a predominant form of β cell KV channels, brings about the downstroke or repolarization phase of the action potential, which acts as a brake for insulin secretion owing to shutting down the CaV channel-mediated Ca(2+) entry. These three ion channel-mediated ion fluxes are the most important ionic events in β cell signaling. This review concisely discusses various ionic mechanisms in β cell signaling and highlights KATP channel-, CaV1 channel- and KV2.1 channel-mediated ion fluxes.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, SE-171 76, Stockholm, Sweden,
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29
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Venglovecz V, Rakonczay Z, Gray MA, Hegyi P. Potassium channels in pancreatic duct epithelial cells: their role, function and pathophysiological relevance. Pflugers Arch 2014; 467:625-40. [PMID: 25074489 DOI: 10.1007/s00424-014-1585-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 07/09/2014] [Accepted: 07/18/2014] [Indexed: 12/14/2022]
Abstract
Pancreatic ductal epithelial cells play a fundamental role in HCO3 (-) secretion, a process which is essential for maintaining the integrity of the pancreas. Although several studies have implicated impaired HCO3 (-) and fluid secretion as a triggering factor in the development of pancreatitis, the mechanism and regulation of HCO3 (-) secretion is still not completely understood. To date, most studies on the ion transporters that orchestrate ductal HCO3 (-) secretion have focussed on the role of Cl(-)/HCO3 (-) exchangers and Cl(-) channels, whereas much less is known about the role of K(+) channels. However, there is growing evidence that many types of K(+) channels are present in ductal cells where they have an essential role in establishing and maintaining the electrochemical driving force for anion secretion. For this reason, strategies that increase K(+) channel function may help to restore impaired HCO3 (-) and fluid secretion, such as in pancreatitis, and therefore provide novel directions for future pancreatic therapy. In this review, our aims are to summarize the types of K(+) channels found in pancreatic ductal cells and to discuss their individual roles in ductal HCO3 (-) secretion. We will also describe how K(+) channels are involved in pathophysiological conditions and discuss how they could act as new molecular targets for the development of therapeutic approaches to treat pancreatic diseases.
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Affiliation(s)
- Viktória Venglovecz
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary,
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30
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Sesti F, Wu X, Liu S. Oxidation of KCNB1 K(+) channels in central nervous system and beyond. World J Biol Chem 2014; 5:85-92. [PMID: 24921000 PMCID: PMC4050120 DOI: 10.4331/wjbc.v5.i2.85] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 01/26/2014] [Accepted: 03/03/2014] [Indexed: 02/05/2023] Open
Abstract
KCNB1, a voltage-gated potassium (K(+)) channel that conducts a major delayed rectifier current in the brain, pancreas and cardiovascular system is a key player in apoptotic programs associated with oxidative stress. As a result, this protein represents a bona fide drug target for limiting the toxic effects of oxygen radicals. Until recently the consensus view was that reactive oxygen species trigger a pro-apoptotic surge in KCNB1 current via phosphorylation and SNARE-dependent incorporation of KCNB1 channels into the plasma membrane. However, new evidence shows that KCNB1 can be modified by oxidants and that oxidized KCNB1 channels can directly activate pro-apoptotic signaling pathways. Hence, a more articulated picture of the pro-apoptotic role of KCNB1 is emerging in which the protein induces cell's death through distinct molecular mechanisms and activation of multiple pathways. In this review article we discuss the diverse functional, toxic and protective roles that KCNB1 channels play in the major organs where they are expressed.
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31
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Frolov RV, Singh S. Celecoxib and ion channels: a story of unexpected discoveries. Eur J Pharmacol 2014; 730:61-71. [PMID: 24630832 DOI: 10.1016/j.ejphar.2014.02.032] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2013] [Revised: 01/28/2014] [Accepted: 02/18/2014] [Indexed: 10/25/2022]
Abstract
Celecoxib (Celebrex), a highly popular selective inhibitor of cyclooxygenase-2, can modulate ion channels and alter functioning of neurons and myocytes at clinically relevant concentrations independently of cyclooxygenase inhibition. In experimental systems varying from Drosophila to primary mammalian and human cell lines, celecoxib inhibits many voltage-activated Na(+), Ca(2+), and K(+) channels, including NaV1.5, L- and T-type Ca(2+) channels, KV1.5, KV2.1, KV4.3, KV7.1, KV11.1 (hERG), while stimulating other K(+) channels-KV7.2-5 and, possibly, KV11.1 (hERG) channels under certain conditions. In this review, we summarize the information currently available on the effects of celecoxib on ion channels, examine mechanistic aspects of drug action and the concomitant changes at the cellular and organ levels, and discuss these findings in the therapeutic context.
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Affiliation(s)
- Roman V Frolov
- Department of Physical Sciences, Division of Biophysics, University of Oulu, PO Box 3000, 90014 Oulun Yliopisto, Finland.
| | - Satpal Singh
- Department of Pharmacology and Toxicology, State University of New York at Buffalo, Buffalo, NY 14214, USA
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32
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Nguyen TTN, Folch B, Létourneau M, Truong NH, Doucet N, Fournier A, Chatenet D. Design of a truncated cardiotoxin-I analogue with potent insulinotropic activity. J Med Chem 2014; 57:2623-33. [PMID: 24552570 DOI: 10.1021/jm401904q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Insulin secretion by pancreatic β-cells in response to glucose or other secretagogues is tightly coupled to membrane potential. Various studies have highlighted the prospect of enhancing insulin secretion in a glucose-dependent manner by blocking voltage-gated potassium channels (K(v)) and calcium-activated potassium channels (K(Ca)). Such strategy is expected to present a lower risk for hypoglycemic events compared to KATP channel blockers. Our group recently reported the discovery of a new insulinotropic agent, cardiotoxin-I (CTX-I), from the Naja kaouthia snake venom. In the present study, we report the design and synthesis of [Lys(52)]CTX-I(41-60) via structure-guided modification, a truncated, equipotent analogue of CTX-I, and demonstrate, using various pharmacological inhibitors, that this derivative probably exerts its action through Kv channels. This new analogue could represent a useful pharmacological tool to study β-cell physiology or even open a new therapeutic avenue for the treatment of type 2 diabetes.
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Affiliation(s)
- Thi Tuyet Nhung Nguyen
- INRS-Institut Armand-Frappier , Université du Québec , 531 Boulevard des Prairies Ville de Laval, Québec H7 V 1B7, Québec Canada
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Jia X, Zheng S, Xie X, Zhang Y, Wang W, Wang Z, Zhang Y, Wang J, Gao M, Hou Y. MicroRNA-1 accelerates the shortening of atrial effective refractory period by regulating KCNE1 and KCNB2 expression: an atrial tachypacing rabbit model. PLoS One 2013; 8:e85639. [PMID: 24386485 PMCID: PMC3875574 DOI: 10.1371/journal.pone.0085639] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 12/05/2013] [Indexed: 01/08/2023] Open
Abstract
Background The potential mechanisms of microRNA-1 (miR-1) in the electrical remodeling of atrial fibrillation remain unclear. The purpose of this study was to evaluate the effects of miR-1 on the atrial effective refractory period (AERP) in a right atrial tachypacing model and to elucidate the potential mechanisms. Methods and Results QRT-PCR and western blot were used to detect the expression of the miR-1, KCNE1, and KCNB2 genes after 1-week of right atrial tachypacing in New Zealand white rabbits. The AERP was measured using a programmable multichannel stimulator, and atrial fibrillation was induced by burst stimulation invivo. The slowly activating delayed rectifier potassium current (IKs) and AERP in atrial cells were measured by whole cell patch clamp invitro. Right atrial tachypacing upregulated miR-1 expression and downregulated KCNE1 and KCNB2 in this study, while the AERP was decreased and the atrial IKs increased. The downregulation of KCNE1 and KCNB2 levels was greater when miR-1 was further upregulated through invivo lentiviral infection. Electrophysiological tests indicated a shorter AERP, a great increase in the IKs and a higher atrial fibrillation inducibility. In addition, similar results were found when the levels of KCNE1 and KCNB2 were downregulated by smallinterferingRNA while keeping miR-1 level unaltered. Conversely, knockdown of miR-1 by anti-miR-1 inhibitor oligonucleotides alleviated the downregulation of KCNE1 and KCNB2, the shortening of AERP, and the increase in the IKs. KCNE1 and KCNB2 as the target genes for miR-1 were confirmed by luciferase activity assay. Conclusions These results indicate that miR-1 accelerates right atrial tachypacing-induced AERP shortening by targeting potassium channel genes, which further suggests that miR-1 plays an important role in the electrical remodeling of atrial fibrillation and exhibits significant clinical relevance as a potential therapeutic target for atrial fibrillation.
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Affiliation(s)
- Xiaomeng Jia
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Shaohua Zheng
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Xinxing Xie
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Yujiao Zhang
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Weizong Wang
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Zhongsu Wang
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Yong Zhang
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Jiangrong Wang
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Mei Gao
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
| | - Yinglong Hou
- Department of Cardiology, Shandong Provincial Qianfoshan Hospital, Shandong University, Jinan, Shandong, China
- * E-mail:
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Jensen MV, Haldeman JM, Zhang H, Lu D, Huising MO, Vale WW, Hohmeier HE, Rosenberg P, Newgard CB. Control of voltage-gated potassium channel Kv2.2 expression by pyruvate-isocitrate cycling regulates glucose-stimulated insulin secretion. J Biol Chem 2013; 288:23128-40. [PMID: 23788641 DOI: 10.1074/jbc.m113.491654] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Recent studies have shown that the pyruvate-isocitrate cycling pathway, involving the mitochondrial citrate/isocitrate carrier and the cytosolic NADP-dependent isocitrate dehydrogenase (ICDc), is involved in control of glucose-stimulated insulin secretion (GSIS). Here we demonstrate that pyruvate-isocitrate cycling regulates expression of the voltage-gated potassium channel family member Kv2.2 in islet β-cells. siRNA-mediated suppression of ICDc, citrate/isocitrate carrier, or Kv2.2 expression impaired GSIS, and the effect of ICDc knockdown was rescued by re-expression of Kv2.2. Moreover, chronic exposure of β-cells to elevated fatty acids, which impairs GSIS, resulted in decreased expression of Kv2.2. Surprisingly, knockdown of ICDc or Kv2.2 increased rather than decreased outward K(+) current in the 832/13 β-cell line. Immunoprecipitation studies demonstrated interaction of Kv2.1 and Kv2.2, and co-overexpression of the two channels reduced outward K(+) current compared with overexpression of Kv2.1 alone. Also, siRNA-mediated knockdown of ICDc enhanced the suppressive effect of the Kv2.1-selective inhibitor stromatoxin1 on K(+) currents. Our data support a model in which a key function of the pyruvate-isocitrate cycle is to maintain levels of Kv2.2 expression sufficient to allow it to serve as a negative regulator of Kv channel activity.
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Affiliation(s)
- Mette V Jensen
- Duke Institute of Molecular Physiology, Duke University Medical Center, Durham, North Carolina 27704, USA
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35
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Frolov RV, Bagati A, Casino B, Singh S. Potassium channels in Drosophila: historical breakthroughs, significance, and perspectives. J Neurogenet 2013. [PMID: 23181728 DOI: 10.3109/01677063.2012.744990] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Drosophila has enabled important breakthroughs in K(+) channel research, including identification and fi rst cloning of a voltage-activated K(+) channel, Shaker, a founding member of the K(V)1 family. Drosophila has also helped in discovering other K(+) channels, such as Shab, Shaw, Shal, Eag, Sei, Elk, and also Slo, a Ca(2+) - and voltage-dependent K(+) channel. These findings have contributed significantly to our understanding of ion channels and their role in physiology. Drosophila continues to play an important role in ion channel studies, benefiting from an unparalleled arsenal of genetic tools and availability of tens of thousands of genetically modified strains. These tools allow deletion, expression, or misexpression of almost any gene in question with temporal and spatial control. The combination of these tools and resources with the use of forward genetic approach in Drosophila further enhances its strength as a model system. There are many areas in which Drosophila can further help our understanding of ion channels and their function. These include signaling pathways involved in regulating and modulating ion channels, basic information on channels and currents where very little is currently known, and the role of ion channels in physiology and pathology.
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Affiliation(s)
- Roman V Frolov
- Department of Pharmacology and Toxicology, State University of New York at Buffalo, Buffalo, New York 14214-3000, USA
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36
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Kodera SY, Yoshida M, Dezaki K, Yada T, Murayama T, Kawakami M, Kakei M. Inhibition of insulin secretion from rat pancreatic islets by dexmedetomidine and medetomidine, two sedatives frequently used in clinical settings. Endocr J 2013; 60:337-46. [PMID: 23171706 DOI: 10.1507/endocrj.ej12-0308] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The aim of this study was to determine whether dexmedetomidine (DEX) and medetomidine (MED), α2-adrenergic agonists clinically used as sedatives, influence insulin secretion from rat pancreatic islets. Islets were isolated from adult male Wistar rats after collagenase digestion. Static incubation was used to determine effects of DEX or MED on insulin secretion and ionic-channel currents of β-cells. Results indicate that both drugs dose-dependently inhibit insulin secretion, DEX more potently than MED. The inhibitory effects were attenuated by addition of yohimbine or by pretreatment of rats with pertussis toxin (PTX). 10 nM DEX decreased the current amplitude of voltage-dependent Ca2+ channels, but this did not occur when the N-type Ca2+ channel blocker ω-conotoxin was added. In the presence of tetraethylammonium, a classical voltage-gated K+ channel (Kv channel) blocker, the magnitude of inhibition of insulin secretion by MED was reduced. However, when tolbutamide, a specific blocker of the ATP-sensitive K+ channel (KATP channel), was present, the magnitude of MED inhibition of insulin secretion was not influenced, suggesting that Kv-channel activity alteration, but not that of KATP channels, is involved in MED-associated insulin secretory inhibition. The Kv-channel currents were increased during 1 nM MED exposure at membrane potentials ranging from -30 mV to -10 mV, where action potentials were generated in response to glucose stimulation. These results indicate that DEX and MED inhibit insulin secretion through an α2-adrenoceptor and PTX-sensitive GTP-binding protein pathway that eventually involves Kv channel activation and Ca2+ channel inhibition.
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Affiliation(s)
- Shiho Yamato Kodera
- Division of Anesthesiology, Second Department of General Medicine, Saitama Medical Center, Jichi Medical University School of Medicine, Omiya 330-8503, Japan
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Fridlyand LE, Jacobson DA, Philipson LH. Ion channels and regulation of insulin secretion in human β-cells: a computational systems analysis. Islets 2013; 5:1-15. [PMID: 23624892 PMCID: PMC3662377 DOI: 10.4161/isl.24166] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In mammals an increase in glucose leads to block of ATP dependent potassium channels in pancreatic β cells leading to membrane depolarization. This leads to the repetitive firing of action potentials that increases calcium influx and triggers insulin granule exocytosis. Several important differences between species in this process suggest that a dedicated human-oriented approach is advantageous as extrapolating from rodent data may be misleading in several respects. We examined depolarization-induced spike activity in pancreatic human islet-attached β-cells employing whole-cell patch-clamp methods. We also reviewed the literature concerning regulation of insulin secretion by channel activity and constructed a data-based computer model of human β cell function. The model couples the Hodgkin-Huxley-type ionic equations to the equations describing intracellular Ca²⁺ homeostasis and insulin release. On the basis of this model we employed computational simulations to better understand the behavior of action potentials, calcium handling and insulin secretion in human β cells under a wide range of experimental conditions. This computational system approach provides a framework to analyze the mechanisms of human β cell insulin secretion.
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Li XN, Herrington J, Petrov A, Ge L, Eiermann G, Xiong Y, Jensen MV, Hohmeier HE, Newgard CB, Garcia ML, Wagner M, Zhang BB, Thornberry NA, Howard AD, Kaczorowski GJ, Zhou YP. The role of voltage-gated potassium channels Kv2.1 and Kv2.2 in the regulation of insulin and somatostatin release from pancreatic islets. J Pharmacol Exp Ther 2012; 344:407-16. [PMID: 23161216 DOI: 10.1124/jpet.112.199083] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The voltage-gated potassium channels Kv2.1 and Kv2.2 are highly expressed in pancreatic islets, yet their contribution to islet hormone secretion is not fully understood. Here we investigate the role of Kv2 channels in pancreatic islets using a combination of genetic and pharmacologic approaches. Pancreatic β-cells from Kv2.1(-/-) mice possess reduced Kv current and display greater glucose-stimulated insulin secretion (GSIS) relative to WT β-cells. Inhibition of Kv2.x channels with selective peptidyl [guangxitoxin-1E (GxTX-1E)] or small molecule (RY796) inhibitors enhances GSIS in isolated wild-type (WT) mouse and human islets, but not in islets from Kv2.1(-/-) mice. However, in WT mice neither inhibitor improved glucose tolerance in vivo. GxTX-1E and RY796 enhanced somatostatin release in isolated human and mouse islets and in situ perfused pancreata from WT and Kv2.1(-/-) mice. Kv2.2 silencing in mouse islets by adenovirus-small hairpin RNA (shRNA) specifically enhanced islet somatostatin, but not insulin, secretion. In mice lacking somatostatin receptor 5, GxTX-1E stimulated insulin secretion and improved glucose tolerance. Collectively, these data show that Kv2.1 regulates insulin secretion in β-cells and Kv2.2 modulates somatostatin release in δ-cells. Development of selective Kv2.1 inhibitors without cross inhibition of Kv2.2 may provide new avenues to promote GSIS for the treatment of type 2 diabetes.
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Affiliation(s)
- Xiaoyan Nina Li
- Department of Metabolic Disorders, Merck Research Laboratories, Rahway, New Jersey, USA
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Dai XQ, Manning Fox JE, Chikvashvili D, Casimir M, Plummer G, Hajmrle C, Spigelman AF, Kin T, Singer-Lahat D, Kang Y, Shapiro AMJ, Gaisano HY, Lotan I, Macdonald PE. The voltage-dependent potassium channel subunit Kv2.1 regulates insulin secretion from rodent and human islets independently of its electrical function. Diabetologia 2012; 55:1709-20. [PMID: 22411134 DOI: 10.1007/s00125-012-2512-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 01/24/2012] [Indexed: 02/07/2023]
Abstract
AIMS/HYPOTHESIS It is thought that the voltage-dependent potassium channel subunit Kv2.1 (Kv2.1) regulates insulin secretion by controlling beta cell electrical excitability. However, this role of Kv2.1 in human insulin secretion has been questioned. Interestingly, Kv2.1 can also regulate exocytosis through direct interaction of its C-terminus with the soluble NSF attachment receptor (SNARE) protein, syntaxin 1A. We hypothesised that this interaction mediates insulin secretion independently of Kv2.1 electrical function. METHODS Wild-type Kv2.1 or mutants lacking electrical function and syntaxin 1A binding were studied in rodent and human beta cells, and in INS-1 cells. Small intracellular fragments of the channel were used to disrupt native Kv2.1-syntaxin 1A complexes. Single-cell exocytosis and ion channel currents were monitored by patch-clamp electrophysiology. Interaction between Kv2.1, syntaxin 1A and other SNARE proteins was probed by immunoprecipitation. Whole-islet Ca(2+)-responses were monitored by ratiometric Fura red fluorescence and insulin secretion was measured. RESULTS Upregulation of Kv2.1 directly augmented beta cell exocytosis. This happened independently of channel electrical function, but was dependent on the Kv2.1 C-terminal syntaxin 1A-binding domain. Intracellular fragments of the Kv2.1 C-terminus disrupted native Kv2.1-syntaxin 1A interaction and impaired glucose-stimulated insulin secretion. This was not due to altered ion channel activity or impaired Ca(2+)-responses to glucose, but to reduced SNARE complex formation and Ca(2+)-dependent exocytosis. CONCLUSIONS/INTERPRETATION Direct interaction between syntaxin 1A and the Kv2.1 C-terminus is required for efficient insulin exocytosis and glucose-stimulated insulin secretion. This demonstrates that native Kv2.1-syntaxin 1A interaction plays a key role in human insulin secretion, which is separate from the channel's electrical function.
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Affiliation(s)
- X Q Dai
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada T6G 2E1
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DeSUMOylation Controls Insulin Exocytosis in Response to Metabolic Signals. Biomolecules 2012; 2:269-81. [PMID: 24970137 PMCID: PMC4030845 DOI: 10.3390/biom2020269] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 05/14/2012] [Accepted: 05/16/2012] [Indexed: 12/25/2022] Open
Abstract
The secretion of insulin by pancreatic islet β-cells plays a pivotal role in glucose homeostasis and diabetes. Recent work suggests an important role for SUMOylation in the control of insulin secretion from β-cells. In this paper we discuss mechanisms whereby (de)SUMOylation may control insulin release by modulating β-cell function at one or more key points; and particularly through the acute and reversible regulation of the exocytotic machinery. Furthermore, we postulate that the SUMO-specific protease SENP1 is an important mediator of insulin exocytosis in response to NADPH, a metabolic secretory signal and major determinant of β-cell redox state. Dialysis of mouse β-cells with NADPH efficiently amplifies β-cell exocytosis even when extracellular glucose is low; an effect that is lost upon knockdown of SENP1. Conversely, over-expression of SENP1 itself augments β-cell exocytosis in a redox-dependent manner. Taken together, we suggest that (de)SUMOylation represents an important mechanism that acutely regulates insulin secretion and that SENP1 can act as an amplifier of insulin exocytosis.
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41
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Finol-Urdaneta RK, Remedi MS, Raasch W, Becker S, Clark RB, Strüver N, Pavlov E, Nichols CG, French RJ, Terlau H. Block of Kv1.7 potassium currents increases glucose-stimulated insulin secretion. EMBO Mol Med 2012; 4:424-34. [PMID: 22438204 PMCID: PMC3403299 DOI: 10.1002/emmm.201200218] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 01/12/2012] [Accepted: 01/13/2012] [Indexed: 01/26/2023] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) relies on repetitive, electrical spiking activity of the beta cell membrane. Cyclic activation of voltage-gated potassium channels (Kv) generates an outward, ‘delayed rectifier’ potassium current, which drives the repolarizing phase of each spike and modulates insulin release. Although several Kv channels are expressed in pancreatic islets, their individual contributions to GSIS remain incompletely understood. We take advantage of a naturally occurring cone-snail peptide toxin, Conkunitzin-S1 (Conk-S1), which selectively blocks Kv1.7 channels to provide an intrinsically limited, finely graded control of total beta cell delayed rectifier current and hence of GSIS. Conk-S1 increases GSIS in isolated rat islets, likely by reducing Kv1.7-mediated delayed rectifier currents in beta cells, which yields increases in action potential firing and cytoplasmic free calcium. In rats, Conk-S1 increases glucose-dependent insulin secretion without decreasing basal glucose. Thus, we conclude that Kv1.7 contributes to the membrane-repolarizing current of beta cells during GSIS and that block of this specific component of beta cell Kv current offers a potential strategy for enhancing GSIS with minimal risk of hypoglycaemia during metabolic disorders such as Type 2 diabetes.
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Affiliation(s)
- Rocio K Finol-Urdaneta
- Department of Physiology and Pharmacology, and HBI, University of Calgary, Calgary, AB, Canada
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Zhuang JL, Wang CY, Zhou MH, Duan KZ, Mei YA. TGF-β1 enhances Kv2.1 potassium channel protein expression and promotes maturation of cerebellar granule neurons. J Cell Physiol 2011; 227:297-307. [PMID: 21412780 DOI: 10.1002/jcp.22735] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Members of the transforming growth factor-β (TGF-β) family of cytokines are involved in diverse physiological processes. Although TGF-β is known to play multiple roles in the mammalian central nervous system (CNS), its role in neuronal development has not been explored. We have studied the effects of TGF-β1 on the electrophysiological properties and maturation of rat primary cerebellar granule neurons (CGNs). We report that incubation with TGF-β1 increased delayed rectifier potassium current (I(K) ) amplitudes in a dose- and time-dependent manner, but did not affect the kinetic properties of the channel. Exposure to TGF-β1 (20 ng/ml) for 36 h led to a 37.2% increase in I(K) amplitudes. There was no significant change in mRNA levels for the key Kv2.1 channel protein, but translation blockade abolished the increase in protein levels and channel activity, arguing that TGF-β1 increases I(K) amplitudes by upregulating translation of the Kv2.1 channel protein. Although TGF-β1 treatment did not affect the activity of protein kinase A (PKA), and constitutive activation of PKA with forskolin failed to increase I(K) amplitudes, inhibition of PKA prevented channel upregulation, demonstrating that basal PKA activity is required for TGF-β1 stimulation of I(K) channel activity. TGF-β1 also promoted the expression of the γ-aminobutyric acid (GABA(A) ) receptor α6 subunit, a marker of mature CGNs, and calcium influx during depolarizing stimuli was reduced by TGF-β1. The effects of TGF-β1 were only observed during a narrow developmental time-window, and were lost as CGNs matured. These findings suggest that TGF-β1 upregulates K(+) channel expression and I(K) currents and thereby promotes CGN maturation.
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Affiliation(s)
- Jia-Li Zhuang
- Institutes of Brain Science, School of Life Sciences and State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, China
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Herrington J, Solly K, Ratliff KS, Li N, Zhou YP, Howard A, Kiss L, Garcia ML, McManus OB, Deng Q, Desai R, Xiong Y, Kaczorowski GJ. Identification of novel and selective Kv2 channel inhibitors. Mol Pharmacol 2011; 80:959-64. [PMID: 21948463 DOI: 10.1124/mol.111.074831] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Identification of selective ion channel inhibitors represents a critical step for understanding the physiological role that these proteins play in native systems. In particular, voltage-gated potassium (K(V)2) channels are widely expressed in tissues such as central nervous system, pancreas, and smooth muscle, but their particular contributions to cell function are not well understood. Although potent and selective peptide inhibitors of K(V)2 channels have been characterized, selective small molecule K(V)2 inhibitors have not been reported. For this purpose, high-throughput automated electrophysiology (IonWorks Quattro; Molecular Devices, Sunnyvale, CA) was used to screen a 200,000-compound mixture (10 compounds per sample) library for inhibitors of K(V)2.1 channels. After deconvolution of 190 active samples, two compounds (A1 and B1) were identified that potently inhibit K(V)2.1 and the other member of the K(V)2 family, K(V)2.2 (IC(50), 0.1-0.2 μM), and that possess good selectivity over K(V)1.2 (IC(50) >10 μM). Modeling studies suggest that these compounds possess a similar three-dimensional conformation. Compounds A1 and B1 are >10-fold selective over Na(V) channels and other K(V) channels and display weak activity (5-9 μM) on Ca(V) channels. The biological activity of compound A1 on native K(V)2 channels was confirmed in electrophysiological recordings of rat insulinoma cells, which are known to express K(V)2 channels. Medicinal chemistry efforts revealed a defined structure-activity relationship and led to the identification of two compounds (RY785 and RY796) without significant Ca(V) channel activity. Taken together, these newly identified channel inhibitors represent important tools for the study of K(V)2 channels in biological systems.
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Affiliation(s)
- James Herrington
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey 07065, USA
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Ma Z, Lavebratt C, Almgren M, Portwood N, Forsberg LE, Bränström R, Berglund E, Falkmer S, Sundler F, Wierup N, Björklund A. Evidence for presence and functional effects of Kv1.1 channels in β-cells: general survey and results from mceph/mceph mice. PLoS One 2011; 6:e18213. [PMID: 21483673 PMCID: PMC3071710 DOI: 10.1371/journal.pone.0018213] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Accepted: 03/01/2011] [Indexed: 01/26/2023] Open
Abstract
Background Voltage-dependent K+ channels (Kv) mediate repolarisation of β-cell action potentials, and thereby abrogate insulin secretion. The role of the Kv1.1 K+ channel in this process is however unclear. We tested for presence of Kv1.1 in different species and tested for a functional role of Kv1.1 by assessing pancreatic islet function in BALB/cByJ (wild-type) and megencephaly (mceph/mceph) mice, the latter having a deletion in the Kv1.1 gene. Methodology/Principal Findings Kv1.1 expression was detected in islets from wild-type mice, SD rats and humans, and expression of truncated Kv1.1 was detected in mceph/mceph islets. Full-length Kv1.1 protein was present in islets from wild-type mice, but, as expected, not in those from mceph/mceph mice. Kv1.1 expression was localized to the β-cell population and also to α- and δ-cells, with evidence of over-expression of truncated Kv1.1 in mceph/mceph islets. Blood glucose, insulin content, and islet morphology were normal in mceph/mceph mice, but glucose-induced insulin release from batch-incubated islets was (moderately) higher than that from wild-type islets. Reciprocal blocking of Kv1.1 by dendrotoxin-K increased insulin secretion from wild-type but not mceph/mceph islets. Glucose-induced action potential duration, as well as firing frequency, was increased in mceph/mceph mouse β-cells. This duration effect on action potential in β-cells from mceph/mceph mice was mimicked by dendrotoxin-K in β-cells from wild-type mice. Observations concerning the effects of both the mceph mutation, and of dendrotoxin-K, on glucose-induced insulin release were confirmed in pancreatic islets from Kv1.1 null mice. Conclusion/Significance Kv1.1 channels are expressed in the β-cells of several species, and these channels can influence glucose-stimulated insulin release.
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Affiliation(s)
- Zuheng Ma
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Catharina Lavebratt
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Malin Almgren
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Neil Portwood
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Lars E. Forsberg
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Robert Bränström
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Erik Berglund
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Sture Falkmer
- Laboratory of Pathology and Clinical Cytology, Ryhov Hospital, Jönköping, Sweden
| | - Frank Sundler
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Nils Wierup
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Anneli Björklund
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
- * E-mail:
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Mechanism of Kv2.1 channel inhibition by a selective COX-2 inhibitor SC-791—modification of gating. Brain Res 2010; 1359:67-74. [DOI: 10.1016/j.brainres.2010.08.062] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2010] [Revised: 08/18/2010] [Accepted: 08/20/2010] [Indexed: 11/22/2022]
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Spigelman AF, Dai X, MacDonald PE. Voltage-dependent K(+) channels are positive regulators of alpha cell action potential generation and glucagon secretion in mice and humans. Diabetologia 2010; 53:1917-26. [PMID: 20446079 DOI: 10.1007/s00125-010-1759-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 03/23/2010] [Indexed: 01/22/2023]
Abstract
AIMS/HYPOTHESIS The regulation of glucagon secretion from alpha cells is poorly understood. Since action potential firing at low glucose is required for glucagon secretion, we hypothesised that voltage-dependent K(+) (Kv) currents limit glucagon secretion under these conditions, similarly to their role in insulin secretion. METHODS Kv currents and action potential firing of mouse and human alpha cells, identified by immunostaining, were examined by whole-cell patch-clamp. Glucagon secretion from mouse and human islets was measured by ELISA. RESULTS Kv current density was 35% larger in alpha than in beta cells. Alpha cell Kv channels were sensitive to block by tetraethylammonium (TEA) and 4-aminopyridine. Surprisingly, Kv channel inhibition reduced glucagon release to the same extent as glucose. Robust action potential firing was observed in beta cells when ATP-sensitive K(+) channels were closed, but in alpha cells a negative current (-8 pA) injection was required for action potential firing. TEA (0.5 mmol/l) impaired alpha cell action potential firing, which could be restored by further hyperpolarising current injection (-16 pA). Kv currents were more sensitive to the Kv2 inhibitor stromatoxin (100 nmol/l) in mouse (80%) than in human (45%) alpha cells. Finally, the maxi-K (BK) channel inhibitor iberiotoxin (100 nmol/l) blocked 55% of the current in human alpha cells and inhibited glucagon release from human islets. CONCLUSIONS/INTERPRETATION Kv currents in alpha cells are positive regulators of glucagon secretion. These currents, mediated by Kv2 and BK channels, limit membrane depolarisation, and prevent inactivation of alpha cell action potentials and suppression of glucagon release.
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Affiliation(s)
- A F Spigelman
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
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Jacobson DA, Mendez F, Thompson M, Torres J, Cochet O, Philipson LH. Calcium-activated and voltage-gated potassium channels of the pancreatic islet impart distinct and complementary roles during secretagogue induced electrical responses. J Physiol 2010; 588:3525-37. [PMID: 20643768 DOI: 10.1113/jphysiol.2010.190207] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Glucose-induced β-cell action potential (AP) repolarization is regulated by potassium efflux through voltage gated (Kv) and calcium activated (K(Ca)) potassium channels. Thus, ablation of the primary Kv channel of the β-cell, Kv2.1, causes increased AP duration. However, Kv2.1(-/-) islet electrical activity still remains sensitive to the potassium channel inhibitor tetraethylammonium. Therefore, we utilized Kv2.1(-/-) islets to characterize Kv and K(Ca) channels and their respective roles in modulating the β-cell AP. The remaining Kv current present in Kv2.1(-/-) β-cells is inhibited with 5 μM CP 339818. Inhibition of the remaining Kv current in Kv2.1(-/-) mouse β-cells increased AP firing frequency by 39.6% but did not significantly enhance glucose stimulated insulin secretion (GSIS). The modest regulation of islet AP frequency by CP 339818 implicates other K(+) channels, possibly K(Ca) channels, in regulating AP repolarization. Blockade of the K(Ca) channel BK with slotoxin increased β-cell AP amplitude by 28.2%, whereas activation of BK channels with isopimaric acid decreased β-cell AP amplitude by 30.6%. Interestingly, the K(Ca) channel SK significantly contributes to Kv2.1(-/-) mouse islet AP repolarization. Inhibition of SK channels decreased AP firing frequency by 66% and increased AP duration by 67% only when Kv2.1 is ablated or inhibited and enhanced GSIS by 2.7-fold. Human islets also express SK3 channels and their β-cell AP frequency is significantly accelerated by 4.8-fold with apamin. These results uncover important repolarizing roles for both Kv and K(Ca) channels and identify distinct roles for SK channel activity in regulating calcium- versus sodium-dependent AP firing.
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Affiliation(s)
- David A Jacobson
- Deparment of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232-0615, USA.
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Drews G, Krippeit-Drews P, Düfer M. Electrophysiology of islet cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:115-63. [PMID: 20217497 DOI: 10.1007/978-90-481-3271-3_7] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Stimulus-Secretion Coupling (SSC) of pancreatic islet cells comprises electrical activity. Changes of the membrane potential (V(m)) are regulated by metabolism-dependent alterations in ion channel activity. This coupling is best explored in beta-cells. The effect of glucose is directly linked to mitochondrial metabolism as the ATP/ADP ratio determines the open probability of ATP-sensitive K(+) channels (K(ATP) channels). Nucleotide sensitivity and concentration in the direct vicinity of the channels are controlled by several factors including phospholipids, fatty acids, and kinases, e.g., creatine and adenylate kinase. Closure of K(ATP) channels leads to depolarization of beta-cells via a yet unknown depolarizing current. Ca(2+) influx during action potentials (APs) results in an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that triggers exocytosis. APs are elicited by the opening of voltage-dependent Na(+) and/or Ca(2+) channels and repolarized by voltage- and/or Ca(2+)-dependent K(+) channels. At a constant stimulatory glucose concentration APs are clustered in bursts that are interrupted by hyperpolarized interburst phases. Bursting electrical activity induces parallel fluctuations in [Ca(2+)](c) and insulin secretion. Bursts are terminated by I(Kslow) consisting of currents through Ca(2+)-dependent K(+) channels and K(ATP) channels. This review focuses on structure, characteristics, physiological function, and regulation of ion channels in beta-cells. Information about pharmacological drugs acting on K(ATP) channels, K(ATP) channelopathies, and influence of oxidative stress on K(ATP) channel function is provided. One focus is the outstanding significance of L-type Ca(2+) channels for insulin secretion. The role of less well characterized beta-cell channels including voltage-dependent Na(+) channels, volume sensitive anion channels (VSACs), transient receptor potential (TRP)-related channels, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is discussed. A model of beta-cell oscillations provides insight in the interplay of the different channels to induce and maintain electrical activity. Regulation of beta-cell electrical activity by hormones and the autonomous nervous system is discussed. alpha- and delta-cells are also equipped with K(ATP) channels, voltage-dependent Na(+), K(+), and Ca(2+) channels. Yet the SSC of these cells is less clear and is not necessarily dependent on K(ATP) channel closure. Different ion channels of alpha- and delta-cells are introduced and SSC in alpha-cells is described in special respect of paracrine effects of insulin and GABA secreted from beta-cells.
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Affiliation(s)
- Gisela Drews
- Institute of Pharmacy, Department of Pharmacology and Clinical Pharmacy, University of Tübingen, 72076 Tübingen, Germany.
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Frolov RV, Bondarenko VE, Singh S. Mechanisms of Kv2.1 channel inhibition by celecoxib--modification of gating and channel block. Br J Pharmacol 2009; 159:405-18. [PMID: 20015088 DOI: 10.1111/j.1476-5381.2009.00539.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Selective cyclooxygenase-2 (COX-2) inhibitors such as rofecoxib (Vioxx) and celecoxib (Celebrex) were developed as NSAIDs with reduced gastric side effects. Celecoxib has now been shown to affect cellular physiology via an unexpected, COX-independent, pathway - by inhibiting K(v)2.1 and other ion channels. In this study, we investigated the mechanism of the action of celecoxib on K(v)2.1 channels. EXPERIMENTAL APPROACH The mode of action of celecoxib on rat K(v)2.1 channels was studied by whole-cell patch-clamping to record currents from channels expressed in HEK-293 cells. KEY RESULTS Celecoxib reduced current through K(v)2.1 channels when applied from the extracellular side. At low concentrations (<or=3 microM), celecoxib accelerated kinetics of activation, deactivation and inactivation. Recovery of rat K(v)2.1 channels from inactivation could be characterized by two components, with celecoxib selectively accelerating the slow component of recovery at <or=10 microM. At >3 microM, celecoxib led to closed-channel block with relative slowing of activation. At 30 microM, it additionally induced open-channel block that manifested in use-dependent inhibition and slower recovery from inactivation. CONCLUSIONS AND IMPLICATIONS Celecoxib reduced current through K(v)2.1 channels by modifying gating and inducing closed- and open-channel block, with the three effects manifesting at different concentrations. These data will help to elucidate the mechanisms of action of this widely prescribed drug on ion channels and those underlying its neurological, cardiovascular and other effects.
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Affiliation(s)
- R V Frolov
- Department of Pharmacology and Toxicology, State University of New York, Buffalo, New York 14214-3000, USA
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Souren NY, Zeegers MP, Janssen RGJH, Steyls A, Gielen M, Loos RJF, Beunen G, Fagard R, Stassen APM, Aerssens J, Derom C, Vlietinck R, Paulussen ADC. Anthropometry, carbohydrate and lipid metabolism in the East Flanders Prospective Twin Survey: linkage of candidate genes using two sib-pair based variance components analyses. Twin Res Hum Genet 2009; 11:505-16. [PMID: 18828733 DOI: 10.1375/twin.11.5.505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Insulin resistance and obesity are underlying causes of type 2 diabetes and therefore much interest is focused on the potential genes involved. A series of anthropometric and metabolic characteristic were measured in 240 MZ and 112 DZ twin pairs recruited from the East Flanders Prospective Twin Survey. Microsatellite markers located close to ABCC8, ADIPOQ, GCK, IGF1, IGFBP1, INSR, LEP, LEPR, PPARgamma and the RETN gene were genotyped. Univariate single point variance components linkage analyses were performed using two methods: (1) the standard method, only comprising the phenotypic and genotypic data of the DZ twin pairs and (2) the extended method, also incorporating the phenotypic data of the MZ twin pairs. Suggestive linkages (LOD > 1) were observed between the ABCC8 marker and waist-to-hip ratio and HDL-cholesterol levels. Both markers flanking ADIPOQ showed suggestive linkage with triglycerides levels, the upstream marker also with body mass and HDL-cholesterol levels. The IGFBP1 marker showed suggestive linkage with fat mass, fasting insulin and leptin levels and the LEP marker showed suggestive linkage with birth weight. This study suggests that DNA variants in ABCC8, ADIPOQ, IGFBP1 and LEP gene region may predispose to type 2 diabetes. In addition, the two methods used to perform linkage analyses yielded similar results. This was however not the case for birth weight where chorionicity seems to be an important confounder.
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Affiliation(s)
- Nicole Y Souren
- Department of Complex Genetics, Maastricht University, the Netherlands.
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