1
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Rödström KEJ, Cloake A, Sörmann J, Baronina A, Smith KHM, Pike ACW, Ang J, Proks P, Schewe M, Holland-Kaye I, Bushell SR, Elliott J, Pardon E, Baukrowitz T, Owens RJ, Newstead S, Steyaert J, Carpenter EP, Tucker SJ. Extracellular modulation of TREK-2 activity with nanobodies provides insight into the mechanisms of K2P channel regulation. Nat Commun 2024; 15:4173. [PMID: 38755204 PMCID: PMC11099193 DOI: 10.1038/s41467-024-48536-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 05/03/2024] [Indexed: 05/18/2024] Open
Abstract
Potassium channels of the Two-Pore Domain (K2P) subfamily, KCNK1-KCNK18, play crucial roles in controlling the electrical activity of many different cell types and represent attractive therapeutic targets. However, the identification of highly selective small molecule drugs against these channels has been challenging due to the high degree of structural and functional conservation that exists not only between K2P channels, but across the whole K+ channel superfamily. To address the issue of selectivity, here we generate camelid antibody fragments (nanobodies) against the TREK-2 (KCNK10) K2P K+ channel and identify selective binders including several that directly modulate channel activity. X-ray crystallography and CryoEM data of these nanobodies in complex with TREK-2 also reveal insights into their mechanisms of activation and inhibition via binding to the extracellular loops and Cap domain, as well as their suitability for immunodetection. These structures facilitate design of a biparatropic inhibitory nanobody with markedly improved sensitivity. Together, these results provide important insights into TREK channel gating and provide an alternative, more selective approach to modulation of K2P channel activity via their extracellular domains.
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Affiliation(s)
- Karin E J Rödström
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Alexander Cloake
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - Janina Sörmann
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Agnese Baronina
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
| | - Kathryn H M Smith
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Ashley C W Pike
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
| | - Jackie Ang
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
| | - Peter Proks
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Marcus Schewe
- Institute of Physiology, Medical Faculty, Kiel University, Kiel, Germany
| | | | - Simon R Bushell
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
| | - Jenna Elliott
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
| | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Thomas Baukrowitz
- Institute of Physiology, Medical Faculty, Kiel University, Kiel, Germany
| | - Raymond J Owens
- The Rosalind Franklin Institute, Harwell Campus, Didcot, UK
- Division of Structural Biology, University of Oxford, Oxford, UK
| | - Simon Newstead
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
- Department of Biochemistry, University of Oxford, Oxford, UK
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Elisabeth P Carpenter
- Centre for Medicines Discovery, University of Oxford, Oxford, UK.
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK.
| | - Stephen J Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK.
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK.
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2
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Ceplecha V, Shea A, Frances M, Proks P, Williams J, Irving J, Rehakova K, Vlasin M, Mala B, Miller A. Auricular myoclonus associated with intra-abdominal botryomycosis in a dog. J Small Anim Pract 2023; 64:806. [PMID: 37661781 DOI: 10.1111/jsap.13658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 05/08/2023] [Accepted: 06/10/2023] [Indexed: 09/05/2023]
Affiliation(s)
- V Ceplecha
- Vale Referrals, Stinchcombe, Dursley, Gloucestershire, GL11 6HF, UK
| | - A Shea
- School of Veterinary Science, Massey University, Palmerston North, New Zealand
- VetCT, Broers Building, 21 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
| | - M Frances
- VetCT, Broers Building, 21 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
| | - P Proks
- Faculty of Veterinary Medicine, University of Veterinary Sciences Brno, Brno, 612 42, Czech Republic
| | - J Williams
- Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hatfield, Hertfordshire, AL9 7TA, UK
| | - J Irving
- Harper & Keele Veterinary School, Keele, Newcastle, Staffordshire, ST5 5NS, UK
| | - K Rehakova
- Faculty of Veterinary Medicine, University of Veterinary Sciences Brno, Brno, 612 42, Czech Republic
| | - M Vlasin
- Vale Referrals, Stinchcombe, Dursley, Gloucestershire, GL11 6HF, UK
| | - B Mala
- Vale Referrals, Stinchcombe, Dursley, Gloucestershire, GL11 6HF, UK
| | - A Miller
- Department of Biomedical Sciences, Section of Anatomic Pathology, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14850-6401, USA
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3
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Proks P, Ceplecha V, Černá P. Duplication and hypoplasia of obturator foramina in a dog. J Small Anim Pract 2022; 64:310. [PMID: 36447330 DOI: 10.1111/jsap.13578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2022] [Accepted: 10/13/2022] [Indexed: 12/05/2022]
Affiliation(s)
- P. Proks
- Small Animal Clinic, Faculty of Veterinary Medicine University of Veterinary Sciences Brno Brno 61242 Czech Republic
| | | | - P. Černá
- Small Animal Clinic, Faculty of Veterinary Medicine University of Veterinary Sciences Brno Brno 61242 Czech Republic
- Department of Clinical Sciences Colorado State University Fort Collins Colorado 80523 USA
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4
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Sörmann J, Schewe M, Proks P, Jouen-Tachoire T, Rao S, Riel EB, Agre KE, Begtrup A, Dean J, Descartes M, Fischer J, Gardham A, Lahner C, Mark PR, Muppidi S, Pichurin PN, Porrmann J, Schallner J, Smith K, Straub V, Vasudevan P, Willaert R, Carpenter EP, Rödström KEJ, Hahn MG, Müller T, Baukrowitz T, Hurles ME, Wright CF, Tucker SJ. Gain-of-function mutations in KCNK3 cause a developmental disorder with sleep apnea. Nat Genet 2022; 54:1534-1543. [PMID: 36195757 PMCID: PMC9534757 DOI: 10.1038/s41588-022-01185-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Accepted: 08/09/2022] [Indexed: 11/07/2022]
Abstract
Sleep apnea is a common disorder that represents a global public health burden. KCNK3 encodes TASK-1, a K+ channel implicated in the control of breathing, but its link with sleep apnea remains poorly understood. Here we describe a new developmental disorder with associated sleep apnea (developmental delay with sleep apnea, or DDSA) caused by rare de novo gain-of-function mutations in KCNK3. The mutations cluster around the 'X-gate', a gating motif that controls channel opening, and produce overactive channels that no longer respond to inhibition by G-protein-coupled receptor pathways. However, despite their defective X-gating, these mutant channels can still be inhibited by a range of known TASK channel inhibitors. These results not only highlight an important new role for TASK-1 K+ channels and their link with sleep apnea but also identify possible therapeutic strategies.
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Affiliation(s)
- Janina Sörmann
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Marcus Schewe
- Institute of Physiology, Faculty of Medicine, Kiel University, Kiel, Germany
| | - Peter Proks
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
| | - Thibault Jouen-Tachoire
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK
- Department of Pharmacology, University of Oxford, Oxford, UK
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | - Shanlin Rao
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Elena B Riel
- Institute of Physiology, Faculty of Medicine, Kiel University, Kiel, Germany
| | | | | | - John Dean
- Department of Medical Genetics, NHS Grampian, Aberdeen, UK
| | - Maria Descartes
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jan Fischer
- Institute for Clinical Genetics, Universitätsklinikum, Technischen Universität Dresden, Dresden, Germany
| | - Alice Gardham
- North West Thames Regional Genetics Service, London North West Healthcare NHS Trust, London, UK
| | | | - Paul R Mark
- Spectrum Health Medical Genetics, Grand Rapids, MI, USA
| | | | | | - Joseph Porrmann
- Institute for Clinical Genetics, Universitätsklinikum, Technischen Universität Dresden, Dresden, Germany
| | - Jens Schallner
- Department of Neuropediatrics, Universitätsklinikum, Technischen Universität Dresden, Dresden, Germany
| | - Kirstin Smith
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Volker Straub
- Institute of Translational and Clinical Research, Newcastle University, Newcastle upon Tyne, UK
| | - Pradeep Vasudevan
- University Hospitals of Leicester NHS Trust, Leicester Royal Infirmary, Leicester, UK
| | | | - Elisabeth P Carpenter
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
- Centre for Medicines Discovery, University of Oxford, Oxford, UK
| | | | - Michael G Hahn
- Bayer AG, Research & Development, Pharmaceuticals, Wuppertal, Germany
| | - Thomas Müller
- Bayer AG, Research & Development, Pharmaceuticals, Wuppertal, Germany
| | - Thomas Baukrowitz
- Institute of Physiology, Faculty of Medicine, Kiel University, Kiel, Germany
| | - Matthew E Hurles
- Human Genetics Programme, Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, UK
| | - Caroline F Wright
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK.
| | - Stephen J Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, UK.
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK.
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5
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Conrad LJ, Proks P, Tucker SJ. Effects of ionic strength on gating and permeation of TREK-2 K2P channels. PLoS One 2021; 16:e0258275. [PMID: 34618865 PMCID: PMC8496810 DOI: 10.1371/journal.pone.0258275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 09/22/2021] [Indexed: 11/26/2022] Open
Abstract
In addition to the classical voltage-dependent behavior mediated by the voltage-sensing-domains (VSD) of ion channels, a growing number of voltage-dependent gating behaviors are being described in channels that lack canonical VSDs. A common thread in their mechanism of action is the contribution of the permeating ion to this voltage sensing process. The polymodal K2P K+ channel, TREK2 responds to membrane voltage through a gating process mediated by the interaction of K+ with its selectivity filter. Recently, we found that this action can be modulated by small molecule agonists (e.g. BL1249) which appear to have an electrostatic influence on K+ binding within the inner cavity and produce an increase in the single-channel conductance of TREK-2 channels. Here, we directly probed this K+-dependent gating process by recording both macroscopic and single-channel currents of TREK-2 in the presence of high concentrations of internal K+. Surprisingly we found TREK-2 is inhibited by high internal K+ concentrations and that this is mediated by the concomitant increase in ionic-strength. However, we were still able to determine that the increase in single channel conductance in the presence of BL1249 was blunted in high ionic-strength, whilst its activatory effect (on channel open probability) persisted. These effects are consistent with an electrostatic mechanism of action of negatively charged activators such as BL1249 on permeation, but also suggest that their influence on channel gating is complex.
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Affiliation(s)
- Linus J. Conrad
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, United Kingdom
| | - Peter Proks
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, United Kingdom
| | - Stephen J. Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, United Kingdom
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford, United Kingdom
- * E-mail:
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6
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Proks P, Schewe M, Conrad LJ, Rao S, Rathje K, Rödström KEJ, Carpenter EP, Baukrowitz T, Tucker SJ. Norfluoxetine inhibits TREK-2 K2P channels by multiple mechanisms including state-independent effects on the selectivity filter gate. J Gen Physiol 2021; 153:212184. [PMID: 34032848 PMCID: PMC8155809 DOI: 10.1085/jgp.202012812] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 05/06/2021] [Indexed: 12/25/2022] Open
Abstract
The TREK subfamily of two-pore domain K+ (K2P) channels are inhibited by fluoxetine and its metabolite, norfluoxetine (NFx). Although not the principal targets of this antidepressant, TREK channel inhibition by NFx has provided important insights into the conformational changes associated with channel gating and highlighted the role of the selectivity filter in this process. However, despite the availability of TREK-2 crystal structures with NFx bound, the precise mechanisms underlying NFx inhibition remain elusive. NFx has previously been proposed to be a state-dependent inhibitor, but its binding site suggests many possible ways in which this positively charged drug might inhibit channel activity. Here we show that NFx exerts multiple effects on single-channel behavior that influence both the open and closed states of the channel and that the channel can become highly activated by 2-APB while remaining in the down conformation. We also show that the inhibitory effects of NFx are unrelated to its positive charge but can be influenced by agonists which alter filter stability, such as ML335, as well as by an intrinsic voltage-dependent gating process within the filter. NFx therefore not only inhibits channel activity by altering the equilibrium between up and down conformations but also can directly influence filter gating. These results provide further insight into the complex allosteric mechanisms that modulate filter gating in TREK K2P channels and highlight the different ways in which filter gating can be regulated to permit polymodal regulation.
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Affiliation(s)
- Peter Proks
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.,OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | - Marcus Schewe
- Department of Physiology, University of Kiel, Kiel, Germany
| | - Linus J Conrad
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.,OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
| | - Shanlin Rao
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Kristin Rathje
- Department of Physiology, University of Kiel, Kiel, Germany
| | | | - Elisabeth P Carpenter
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK.,Centre for Medicines Discovery, University of Oxford, UK
| | | | - Stephen J Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK.,OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, UK
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7
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Sachse G, Haythorne E, Hill T, Proks P, Joynson R, Terrón-Expósito R, Bentley L, Tucker SJ, Cox RD, Ashcroft FM. The KCNJ11-E23K Gene Variant Hastens Diabetes Progression by Impairing Glucose-Induced Insulin Secretion. Diabetes 2021; 70:1145-1156. [PMID: 33568422 DOI: 10.2337/db20-0691] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 02/05/2021] [Indexed: 11/13/2022]
Abstract
The ATP-sensitive K+ (KATP) channel controls blood glucose levels by coupling glucose metabolism to insulin secretion in pancreatic β-cells. E23K, a common polymorphism in the pore-forming KATP channel subunit (KCNJ11) gene, has been linked to increased risk of type 2 diabetes. Understanding the risk-allele-specific pathogenesis has the potential to improve personalized diabetes treatment, but the underlying mechanism has remained elusive. Using a genetically engineered mouse model, we now show that the K23 variant impairs glucose-induced insulin secretion and increases diabetes risk when combined with a high-fat diet (HFD) and obesity. KATP-channels in β-cells with two K23 risk alleles (KK) showed decreased ATP inhibition, and the threshold for glucose-stimulated insulin secretion from KK islets was increased. Consequently, the insulin response to glucose and glycemic control was impaired in KK mice fed a standard diet. On an HFD, the effects of the KK genotype were exacerbated, accelerating diet-induced diabetes progression and causing β-cell failure. We conclude that the K23 variant increases diabetes risk by impairing insulin secretion at threshold glucose levels, thus accelerating loss of β-cell function in the early stages of diabetes progression.
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Affiliation(s)
- Gregor Sachse
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K.
| | - Elizabeth Haythorne
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Thomas Hill
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
- Department of Physics, University of Oxford, Oxford, U.K
| | - Russell Joynson
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Oxfordshire, U.K
| | - Raul Terrón-Expósito
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Liz Bentley
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Oxfordshire, U.K
| | | | - Roger D Cox
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Oxfordshire, U.K
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
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8
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Sachse G, Haythorne E, Proks P, Stewart M, Cater H, Ellard S, Davies B, Ashcroft FM. Phenotype of a transient neonatal diabetes point mutation (SUR1-R1183W) in mice. Wellcome Open Res 2021; 5:15. [PMID: 34368464 PMCID: PMC8323074 DOI: 10.12688/wellcomeopenres.15529.2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/21/2020] [Indexed: 01/12/2023] Open
Abstract
Background: The K ATP channel plays a key role in glucose homeostasis by coupling metabolically generated changes in ATP to insulin secretion from pancreatic beta-cells. Gain-of-function mutations in either the pore-forming (Kir6.2) or regulatory (SUR1) subunit of this channel are a common cause of transient neonatal diabetes mellitus (TNDM), in which diabetes presents shortly after birth but remits within the first few years of life, only to return in later life. The reasons behind this time dependence are unclear. Methods: In an attempt to understand the mechanism behind diabetes remission and relapse, we generated mice expressing the common TNDM mutation SUR1-R1183W. We employed Cre/LoxP technology for both inducible and constitutive expression of SUR1-R1183W specifically in mouse beta-cells, followed by investigation of their phenotype using glucose tolerance tests and insulin secretion from isolated islets. Results: We found that the R1183W mutation impaired inhibition of K ATP channels by ATP when heterologously expressed in human embryonic kidney cells. However, neither induced nor constitutive expression of SUR1-R1183W in mice resulted in changes in blood glucose homeostasis, compared to littermate controls. When challenged with a high fat diet, female mice expressing SUR1-R1183W showed increased weight gain, elevated blood glucose and impaired glycaemic control, but glucose-stimulated insulin secretion from pancreatic islets appeared unchanged. Conclusions: The mouse model of TNDM did not recapitulate the human phenotype. We discuss multiple potential reasons why this might be the case. Based on our findings, we recommend future TNDM mouse models employing a gain-of-function SUR1 mutation should be created using the minimally invasive CRISPR/Cas technology, which avoids many potential pitfalls associated with the Cre/LoxP system.
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Affiliation(s)
- Gregor Sachse
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
| | - Elizabeth Haythorne
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
| | - Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
- Department of Physics, University of Oxford, Oxford, OX1 3PJ, UK
| | - Michelle Stewart
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Harwell Campus, Oxfordshire, OX11 0RD, UK
| | - Heather Cater
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Harwell Campus, Oxfordshire, OX11 0RD, UK
| | - Sian Ellard
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Barrack Road, Exeter, EX2 5DW, UK
| | - Ben Davies
- Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK
| | - Frances M. Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
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9
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Pipatpolkai T, Corey RA, Proks P, Ashcroft FM, Stansfeld PJ. Evaluating inositol phospholipid interactions with inward rectifier potassium channels and characterising their role in disease. Commun Chem 2020; 3:147. [PMID: 36703430 PMCID: PMC9814360 DOI: 10.1038/s42004-020-00391-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Accepted: 09/17/2020] [Indexed: 01/29/2023] Open
Abstract
Membrane proteins are frequently modulated by specific protein-lipid interactions. The activation of human inward rectifying potassium (hKir) channels by phosphoinositides (PI) has been well characterised. Here, we apply a coarse-grained molecular dynamics free-energy perturbation (CG-FEP) protocol to capture the energetics of binding of PI lipids to hKir channels. By using either a single- or multi-step approach, we establish a consistent value for the binding of PIP2 to hKir channels, relative to the binding of the bulk phosphatidylcholine phospholipid. Furthermore, by perturbing amino acid side chains on hKir6.2, we show that the neonatal diabetes mutation E179K increases PIP2 affinity, while the congenital hyperinsulinism mutation K67N results in a reduced affinity. We show good agreement with electrophysiological data where E179K exhibits a reduction in neomycin sensitivity, implying that PIP2 binds more tightly E179K channels. This illustrates the application of CG-FEP to compare affinities between lipid species, and for annotating amino acid residues.
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Affiliation(s)
- Tanadet Pipatpolkai
- Department of Physiology Anatomy and Genetics, Parks Road, Oxford, OX1 3PT, UK
- Department of Biochemistry, South Parks Road, Oxford, OX1 3QU, UK
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, OX1 3PT, UK
| | - Robin A Corey
- Department of Biochemistry, South Parks Road, Oxford, OX1 3QU, UK
| | - Peter Proks
- Department of Physiology Anatomy and Genetics, Parks Road, Oxford, OX1 3PT, UK
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, OX1 3PT, UK
| | - Frances M Ashcroft
- Department of Physiology Anatomy and Genetics, Parks Road, Oxford, OX1 3PT, UK.
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, OX1 3PT, UK.
| | - Phillip J Stansfeld
- Department of Biochemistry, South Parks Road, Oxford, OX1 3QU, UK.
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, OX1 3PT, UK.
- Department of Chemistry, School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.
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10
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Sachse G, Haythorne E, Proks P, Stewart M, Cater H, Ellard S, Davies B, Ashcroft FM. Phenotype of a transient neonatal diabetes point mutation (SUR1-R1183W) in mice. Wellcome Open Res 2020; 5:15. [PMID: 34368464 PMCID: PMC8323074 DOI: 10.12688/wellcomeopenres.15529.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/17/2020] [Indexed: 11/20/2022] Open
Abstract
Background: The K ATP channel plays a key role in glucose homeostasis by coupling metabolically generated changes in ATP to insulin secretion from pancreatic beta-cells. Gain-of-function mutations in either the pore-forming (Kir6.2) or regulatory (SUR1) subunit of this channel are a common cause of transient neonatal diabetes mellitus (TNDM), in which diabetes presents shortly after birth but remits within the first few years of life, only to return in later life. The reasons behind this time dependence are unclear. Methods: In an attempt to understand the mechanism behind diabetes remission and relapse, we generated mice expressing the common TNDM mutation SUR1-R1183W. We employed Cre/LoxP technology for both inducible and constitutive expression of SUR1-R1183W specifically in mouse beta-cells, followed by investigation of their phenotype using glucose tolerance tests and insulin secretion from isolated islets. Results: We found that the R1183W mutation impaired inhibition of K ATP channels by ATP when heterologously expressed in human embryonic kidney cells. However, neither induced nor constitutive expression of SUR1-R1183W in mice resulted in changes in blood glucose homeostasis, compared to littermate controls. When challenged with a high fat diet, female mice expressing SUR1-R1183W showed increased weight gain, elevated blood glucose and impaired glycaemic control, but glucose-stimulated insulin secretion from pancreatic islets appeared unchanged. Conclusions: The mouse model of TNDM did not recapitulate the human phenotype. We discuss multiple potential reasons why this might be the case. Based on our findings, we recommend future TNDM mouse models employing a gain-of-function SUR1 mutation should be created using the minimally invasive CRISPR/Cas technology, which avoids many potential pitfalls associated with the Cre/LoxP system.
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Affiliation(s)
- Gregor Sachse
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
| | - Elizabeth Haythorne
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
| | - Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
- Department of Physics, University of Oxford, Oxford, OX1 3PJ, UK
| | - Michelle Stewart
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Harwell Campus, Oxfordshire, OX11 0RD, UK
| | - Heather Cater
- Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell Institute, Harwell Campus, Oxfordshire, OX11 0RD, UK
| | - Sian Ellard
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Barrack Road, Exeter, EX2 5DW, UK
| | - Ben Davies
- Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK
| | - Frances M. Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK
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Vedovato N, Rorsman O, Hennis K, Ashcroft FM, Proks P. Role of the C-terminus of SUR in the differential regulation of β-cell and cardiac K ATP channels by MgADP and metabolism. J Physiol 2018; 596:6205-6217. [PMID: 30179258 PMCID: PMC6292810 DOI: 10.1113/jp276708] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Accepted: 08/29/2018] [Indexed: 12/14/2022] Open
Abstract
Key points β‐Cell KATP channels are partially open in the absence of metabolic substrates, whereas cardiac KATP channels are closed. Using cloned channels heterologously expressed in Xenopus oocytes we measured the effect of MgADP on the MgATP concentration–inhibition curve immediately after patch excision. MgADP caused a far more striking reduction in ATP inhibition of Kir6.2/SUR1 channels than Kir6.2/SUR2A channels; this effect declined rapidly after patch excision. Exchanging the final 42 amino acids of SUR was sufficient to switch the Mg‐nucleotide regulation of Kir6.2/SUR1 and Kir6.2/SUR2A channels, and partially switch their sensitivity to metabolic inhibition. Deletion of the C‐terminal 42 residues of SUR abolished MgADP activation of both Kir6.2/SUR1 and Kir6.2/SUR2A channels. We conclude that the different metabolic sensitivity of Kir6.2/SUR1 and Kir6.2/SUR2A channels is at least partially due to their different regulation by Mg‐nucleotides, which is determined by the final 42 amino acids.
Abstract ATP‐sensitive potassium (KATP) channels couple the metabolic state of a cell to its electrical activity and play important physiological roles in many tissues. In contrast to β‐cell (Kir6.2/SUR1) channels, which open when extracellular glucose levels fall, cardiac (Kir6.2/SUR2A) channels remain closed. This is due to differences in the SUR subunit rather than cell metabolism. As ATP inhibition and MgADP activation are similar for both types of channels, we investigated channel inhibition by MgATP in the presence of 100 μm MgADP immediately after patch excision [when the channel open probability (PO) is near maximal]. The results were strikingly different: 100 μm MgADP substantially reduced MgATP inhibition of Kir6.2/SUR1, but had no effect on MgATP inhibition of Kir6.2/SUR2A. Exchanging the final 42 residues of SUR2A with that of SUR1 switched the channel phenotype (and vice versa), and deleting this region abolished Mg‐nucleotide activation. This suggests the C‐terminal 42 residues are important for the ability of MgADP to influence ATP inhibition at Kir6.2. This region was also necessary, but not sufficient, for activation of the KATP channel in intact cells by metabolic inhibition (azide). We conclude that the ability of MgADP to impair ATP inhibition at Kir6.2 accounts, in part, for the differential metabolic sensitivities of β‐cell and cardiac KATP channels. β‐Cell KATP channels are partially open in the absence of metabolic substrates, whereas cardiac KATP channels are closed. Using cloned channels heterologously expressed in Xenopus oocytes we measured the effect of MgADP on the MgATP concentration–inhibition curve immediately after patch excision. MgADP caused a far more striking reduction in ATP inhibition of Kir6.2/SUR1 channels than Kir6.2/SUR2A channels; this effect declined rapidly after patch excision. Exchanging the final 42 amino acids of SUR was sufficient to switch the Mg‐nucleotide regulation of Kir6.2/SUR1 and Kir6.2/SUR2A channels, and partially switch their sensitivity to metabolic inhibition. Deletion of the C‐terminal 42 residues of SUR abolished MgADP activation of both Kir6.2/SUR1 and Kir6.2/SUR2A channels. We conclude that the different metabolic sensitivity of Kir6.2/SUR1 and Kir6.2/SUR2A channels is at least partially due to their different regulation by Mg‐nucleotides, which is determined by the final 42 amino acids.
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Affiliation(s)
- Natascia Vedovato
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Olof Rorsman
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Konstantin Hennis
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
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Abstract
Sulphonylurea drugs stimulate insulin secretion from pancreatic β-cells primarily by inhibiting ATP sensitive potassium (KATP) channels in the β-cell membrane. The effective sulphonylurea concentration at its site of action is significantly attenuated by binding to serum albumin, which makes it difficult to compare in vitro and in vivo data. We therefore measured the ability of gliclazide and glibenclamide to inhibit KATP channels and stimulate insulin secretion in the presence of serum albumin. We used this data, together with estimates of free drug concentrations from binding studies, to predict the extent of sulphonylurea inhibition of KATP channels at therapeutic concentrations in vivo. KATP currents from mouse pancreatic β-cells and Xenopus oocytes were measured using the patch-clamp technique. Gliclazide and glibenclamide binding to human plasma were determined in spiked plasma samples using an ultrafiltration-mass spectrometry approach. Bovine serum albumin (60g/l) produced a mild, non-significant reduction of gliclazide block of KATP currents in pancreatic β-cells and Xenopus oocytes. In contrast, glibenclamide inhibition of recombinant KATP channels was dramatically suppressed by albumin (predicted free drug concentration <0.1%). Insulin secretion was also reduced. Free concentrations of gliclazide and glibenclamide in the presence of human plasma measured in binding experiments were 15% and 0.05%, respectively. Our data suggest the free concentration of glibenclamide in plasma is too low to account for the drug’s therapeutic effect. In contrast, the free gliclazide concentration in plasma is high enough to close KATP channels and stimulate insulin secretion.
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Affiliation(s)
- Peter Proks
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Holger Kramer
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Elizabeth Haythorne
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M. Ashcroft
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
- * E-mail:
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Proks P, Stehlik L, Nyvltova I, Necas A, Vignoli M, Jekl V. Vertebral formula and congenital abnormalities of the vertebral column in rabbits. Vet J 2018; 236:80-88. [PMID: 29871755 DOI: 10.1016/j.tvjl.2018.04.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 04/21/2018] [Accepted: 04/23/2018] [Indexed: 11/16/2022]
Abstract
The aim of this retrospective study of 330 rabbits (164 males, 166 females) was to determine different vertebral formulas and prevalence of congenital vertebral anomalies in rabbits from radiographs of the cervical (C), thoracic (Th), lumbar (L) and sacral (S) segments of the vertebral column. The number of vertebrae in each segment of vertebral column, position of anticlinal vertebra and localisation and type of congenital abnormalities were recorded. In 280/330 rabbits (84.8%) with normal vertebral morphology, seven vertebral formulas were identified: C7/Th12/L7/S4 (252/330, 76.4%), C7/Th12/L6/S4 (11/330, 3.3%), C7/Th13/L7/S4 (8/330, 2.4%), C7/Th12/L7/S5 (4/330, 1.2%), C7/Th12/L8/S4 (3/330, 0.9%), C7/Th12/L7/S6 (1/330, 0.3%) and C7/Th11/L7/S4 (1/330, 0.3%). The anticlinal vertebra was identified as Th10 in 56.4% of rabbits and Th11 in 42.4% of rabbits. Congenital spinal abnormalities were identified in 50/330 (15.2%) rabbits, predominantly as a single pathology (n=44). Transitional vertebrae represented the most common abnormalities (n=41 rabbits) in the thoracolumbar (n=35) and lumbosacral segments (n=6). Five variants of thoracolumbar transitional vertebrae were identified. Cervical butterfly vertebrae were detected in three rabbits. One rabbit exhibited three congenital vertebral anomalies: cervical block vertebra, thoracic hemivertebra and thoracolumbar transitional vertebra. Five rabbits exhibited congenital vertebral abnormalities with concurrent malalignment, specifically cervical kyphosis/short vertebra (n=1), thoracic lordoscoliosis/thoracolumbar transitional vertebrae (n=1), thoracic kyphoscoliosis/wedge vertebrae (n=2) and thoracolumbar lordoscoliosis/thoracolumbar transitional vertebrae/lumbosacral transitional vertebrae (n=1). These findings suggest that vertebral columns in rabbits display a wide range of morphologies, with occasional congenital malformations.
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Affiliation(s)
- P Proks
- Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic; Central European Institute of Technology (CEITEC), Brno, Czech Republic.
| | - L Stehlik
- Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic
| | - I Nyvltova
- Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic
| | - A Necas
- Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic
| | - M Vignoli
- Faculty of Veterinary Medicine, University of Teramo, Piano D́Accio, 641 00, Teramo, Italy
| | - V Jekl
- Avian and Exotic Animal Clinics, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic
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Vedovato N, Proks P, Rorsman OH, Hennis K, Ashcroft FM. Differential Metabolic and Nucleotide Sensitivity of Beta-Cell and Cardiac KATP Channels. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.1136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Proks P, Puljung MC, Vedovato N, Sachse G, Mulvaney R, Ashcroft FM. Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0426. [PMID: 27377720 PMCID: PMC4938026 DOI: 10.1098/rstb.2015.0426] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/17/2016] [Indexed: 11/29/2022] Open
Abstract
KATP channels act as key regulators of electrical excitability by coupling metabolic cues—mainly intracellular adenine nucleotide concentrations—to cellular potassium ion efflux. However, their study has been hindered by their rapid loss of activity in excised membrane patches (rundown), and by a second phenomenon, the decline of activation by Mg-nucleotides (DAMN). Degradation of PI(4,5)P2 and other phosphoinositides is the strongest candidate for the molecular cause of rundown. Broad evidence indicates that most other determinants of rundown (e.g. phosphorylation, intracellular calcium, channel mutations that affect rundown) also act by influencing KATP channel regulation by phosphoinositides. Unfortunately, experimental conditions that reproducibly prevent rundown have remained elusive, necessitating post hoc data compensation. Rundown is clearly distinct from DAMN. While the former is associated with pore-forming Kir6.2 subunits, DAMN is generally a slower process involving the regulatory sulfonylurea receptor (SUR) subunits. We speculate that it arises when SUR subunits enter non-physiological conformational states associated with the loss of SUR nucleotide-binding domain dimerization following prolonged exposure to nucleotide-free conditions. This review presents new information on both rundown and DAMN, summarizes our current understanding of these processes and considers their physiological roles. This article is part of the themed issue ‘Evolution brings Ca2+ and ATP together to control life and death’.
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Affiliation(s)
- Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | - Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | - Gregor Sachse
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | - Rachel Mulvaney
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
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Bąkowska J, Proks P, Stehlik L, Irova K, Bugyiova K. Pectus Excavatum in Seven Dogs. J Comp Pathol 2017. [DOI: 10.1016/j.jcpa.2016.11.105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Snášil R, Proks P, Nečasová A, Michalčáková K, Nečas A. [Canine Elbow Humeroulnar Incongruity Measurements Using Computed Tomography]. Acta Chir Orthop Traumatol Cech 2017; 84:299-303. [PMID: 28933333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
PURPOSE OF THE STUDY The purpose of the study is to compare the repeatability and reproducibility of quantitative and subjective evaluation of elbow humeroulnar incongruity (HUI) using computed tomography (CT) on an in vivo canine model. MATERIAL AND METHODS HUI was evaluated on canine (n = 50) elbow joints (n = 100). The computed tomography of elbow joints was performed under intravenous sedation. Multiplanar reconstructions (MPR) were produced. HUI was evaluated on sagittal MPR images subjectively and by measuring the subluxation index (SI). The SI was defined by measuring the distance between the centres of two circles, the shape of which corresponded the most with the shape of the trochlear notch of the ulna at sagittal crest and the shape of humeral trochlea. This distance was divided by the radius of the circle (r) defining the humeral trochlea. HUI was subjectively evaluated based on the width of the joint space at the greatest caudal convexity of the trochlear notch of the ulna. Three categories of HUI were established: 0 (congruent), 1 (moderately incongruent), 2 (strongly incongruent). Measurement and evaluation of HUI was conducted by two evaluators twice at a one-month interval between the first and second measurement. The statistical analysis was carried out using the repeated measures ANOVA and the Cohen s kappa coefficient. RESULTS The mean SI was 11.14 (SD 8.703). The SI values measured by two evaluators were statistically significantly different (p < 0.05). Contrarily, there was no statistically significant difference between the two measurements of the same evaluator (p > 0.05). The subjective evaluation of HUI done by two evaluators showed a mean to substantial agreement (Kappa = 0.53-0.79). There was a substantial to almost perfect agreement between the results of two evaluations carried out by a single evaluator (Kappa = 0.79-0.83). DISCUSSION The radiographic detection of moderate incongruity is unreliable, especially on account of wrongly positioned elbow joint, superposition of bone structures and due to the evaluation of three-dimensional bone structure through a two-dimensional image. Evaluation of humeroulnar congruity by computed tomography (CT) enables to assess the congruity of joints without the superposition of neighbouring bone structures. The quantification of humeroulnar incongruity using the SI does not show a higher degree of agreement between two evaluators as against the subjective evaluation of HUI. On the contrary, the agreement between two measurements of a single evaluator was high in both the cases. CONCLUSIONS Dog is a suitable model animal for evaluation of HUI of elbow joints due to frequent incidence of elbow dysplasia associated with HUI. The quantification of HUI at the expense of subjective evaluation of HUI is often overrated in radiological studies. Key words: dog, elbow, humeroulnar incongruity.
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Affiliation(s)
- R Snášil
- Oddělení chirurgie a ortopedie, Klinika chorob psů a koček, Fakulta veterinárního lékařství, Veterinární a farmaceutická univerzita Brno
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Proks P, Puljung MC, Vedovato N, Sachse G, Mulvaney R, Ashcroft FM. Correction to ‘Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels’. Philos Trans R Soc Lond B Biol Sci 2016; 371:rstb.2016.0330. [PMID: 27481794 PMCID: PMC4971194 DOI: 10.1098/rstb.2016.0330] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Vedovato N, Cliff E, Proks P, Poovazhagi V, Flanagan SE, Ellard S, Hattersley AT, Ashcroft FM. Neonatal diabetes caused by a homozygous KCNJ11 mutation demonstrates that tiny changes in ATP sensitivity markedly affect diabetes risk. Diabetologia 2016; 59:1430-1436. [PMID: 27118464 PMCID: PMC4901145 DOI: 10.1007/s00125-016-3964-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 03/23/2016] [Indexed: 11/16/2022]
Abstract
AIMS/HYPOTHESIS The pancreatic ATP-sensitive potassium (KATP) channel plays a pivotal role in linking beta cell metabolism to insulin secretion. Mutations in KATP channel genes can result in hypo- or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, respectively. To date, all patients affected by neonatal diabetes due to a mutation in the pore-forming subunit of the channel (Kir6.2, KCNJ11) are heterozygous for the mutation. Here, we report the first clinical case of neonatal diabetes caused by a homozygous KCNJ11 mutation. METHODS A male patient was diagnosed with diabetes shortly after birth. At 5 months of age, genetic testing revealed he carried a homozygous KCNJ11 mutation, G324R, (Kir6.2-G324R) and he was successfully transferred to sulfonylurea therapy (0.2 mg kg(-1) day(-1)). Neither heterozygous parent was affected. Functional properties of wild-type, heterozygous and homozygous mutant KATP channels were examined after heterologous expression in Xenopus oocytes. RESULTS Functional studies indicated that the Kir6.2-G324R mutation reduces the channel ATP sensitivity but that the difference in ATP inhibition between homozygous and heterozygous channels is remarkably small. Nevertheless, the homozygous patient developed neonatal diabetes, whereas the heterozygous parents were, and remain, unaffected. Kir6.2-G324R channels were fully shut by the sulfonylurea tolbutamide, which explains why the patient's diabetes was well controlled by sulfonylurea therapy. CONCLUSIONS/INTERPRETATION The data demonstrate that tiny changes in KATP channel activity can alter beta cell electrical activity and insulin secretion sufficiently to cause diabetes. They also aid our understanding of how the Kir6.2-E23K variant predisposes to type 2 diabetes.
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Affiliation(s)
- Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Edward Cliff
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
- Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, VIC, Australia
| | - Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | | | - Sarah E Flanagan
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK
| | - Sian Ellard
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK
| | - Andrew T Hattersley
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
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O'Connell SM, Proks P, Kramer H, Mattis KK, Sachse G, Joyce C, Houghton JAL, Ellard S, Hattersley AT, Ashcroft FM, O'Riordan SMP. The value of in vitro studies in a case of neonatal diabetes with a novel Kir6.2-W68G mutation. Clin Case Rep 2015; 3:884-7. [PMID: 26509030 PMCID: PMC4614663 DOI: 10.1002/ccr3.370] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Revised: 06/19/2015] [Accepted: 08/06/2015] [Indexed: 11/20/2022] Open
Abstract
In infants, especially with novel previously undescribed mutations of the KATP channel causing neonatal diabetes, in vitro studies can be used to both predict the response to sulphonylurea treatment and support a second trial of glibenclamide at higher than standard doses if the expected response is not observed.
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Affiliation(s)
- Susan M O'Connell
- Department of Paediatrics and Child Health, Cork University Hospital Cork, Ireland
| | - Peter Proks
- Department of Physiology Anatomy & Genetics Parks Road, University of Oxford Oxford, OX1 3PT, UK
| | - Holger Kramer
- Department of Physiology Anatomy & Genetics Parks Road, University of Oxford Oxford, OX1 3PT, UK
| | - Katia K Mattis
- Department of Physiology Anatomy & Genetics Parks Road, University of Oxford Oxford, OX1 3PT, UK
| | - Gregor Sachse
- Department of Physiology Anatomy & Genetics Parks Road, University of Oxford Oxford, OX1 3PT, UK
| | - Caroline Joyce
- Department of Biochemistry, Cork University Hospital Cork, Ireland
| | - Jayne A L Houghton
- Institute of Biomedical and Clinical Science, University of Exeter Medical School Exeter, EX2 5AD, UK
| | - Sian Ellard
- Institute of Biomedical and Clinical Science, University of Exeter Medical School Exeter, EX2 5AD, UK
| | - Andrew T Hattersley
- Institute of Biomedical and Clinical Science, University of Exeter Medical School Exeter, EX2 5AD, UK
| | - Frances M Ashcroft
- Department of Physiology Anatomy & Genetics Parks Road, University of Oxford Oxford, OX1 3PT, UK
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Proks P, de Wet H, Ashcroft FM. Sulfonylureas suppress the stimulatory action of Mg-nucleotides on Kir6.2/SUR1 but not Kir6.2/SUR2A KATP channels: a mechanistic study. ACTA ACUST UNITED AC 2015; 144:469-86. [PMID: 25348414 PMCID: PMC4210431 DOI: 10.1085/jgp.201411222] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Sulfonylureas suppress the stimulatory effect of Mg-nucleotides on recombinant β-cell (Kir6.2/SUR1) but not cardiac (Kir6.2/SUR2A) KATP channels. Sulfonylureas, which stimulate insulin secretion from pancreatic β-cells, are widely used to treat both type 2 diabetes and neonatal diabetes. These drugs mediate their effects by binding to the sulfonylurea receptor subunit (SUR) of the ATP-sensitive K+ (KATP) channel and inducing channel closure. The mechanism of channel inhibition is unusually complex. First, sulfonylureas act as partial antagonists of channel activity, and second, their effect is modulated by MgADP. We analyzed the molecular basis of the interactions between the sulfonylurea gliclazide and Mg-nucleotides on β-cell and cardiac types of KATP channel (Kir6.2/SUR1 and Kir6.2/SUR2A, respectively) heterologously expressed in Xenopus laevis oocytes. The SUR2A-Y1206S mutation was used to confer gliclazide sensitivity on SUR2A. We found that both MgATP and MgADP increased gliclazide inhibition of Kir6.2/SUR1 channels and reduced inhibition of Kir6.2/SUR2A-Y1206S. The latter effect can be attributed to stabilization of the cardiac channel open state by Mg-nucleotides. Using a Kir6.2 mutation that renders the KATP channel insensitive to nucleotide inhibition (Kir6.2-G334D), we showed that gliclazide abolishes the stimulatory effects of MgADP and MgATP on β-cell KATP channels. Detailed analysis suggests that the drug both reduces nucleotide binding to SUR1 and impairs the efficacy with which nucleotide binding is translated into pore opening. Mutation of one (or both) of the Walker A lysines in the catalytic site of the nucleotide-binding domains of SUR1 may have a similar effect to gliclazide on MgADP binding and transduction, but it does not appear to impair MgATP binding. Our results have implications for the therapeutic use of sulfonylureas.
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Affiliation(s)
- Peter Proks
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
| | - Heidi de Wet
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
| | - Frances M Ashcroft
- Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK Oxford Centre for Gene Function and Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, England, UK
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Negishi M, Shimomura K, Proks P, Nakahara R, Murakami M, Shimomura Y, Kobayashi I. Development of postpartum Graves' disease and type 1 diabetes after delivery in a patient with gestational diabetes. J Diabetes Investig 2014; 2:328-30. [PMID: 24843507 PMCID: PMC4014976 DOI: 10.1111/j.2040-1124.2010.00089.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Pregnancy and the postpartum period are associated with changes of the immune system. These changes might eventually result in autoimmune diseases, such as Graves’ disease and type 1 diabetes mellitus, in the postpartum period. We describe a case of a patient with gestational diabetes who developed both Graves’ disease and type 1 diabetes mellitus in the postpartum period. The pathology of gestational diabetes (GDM) is close to that of type 2 diabetes mellitus. However, the present case emphasizes the importance of screening and monitoring high‐risk GDM patients for all available autoimmune antibodies throughout pregnancy and the postpartum period, as GDM has a risk of developing into type 1 diabetes and multiple autoimmune diseases. In addition, only Graves’ disease was transient, whereas type 1 diabetes mellitus remained permanent in the present case. Thus, the present case shows etiological differences between these two autoimmune diseases. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00089.x,2011)
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Affiliation(s)
- Mayumi Negishi
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Takasaki, Japan
| | - Kenju Shimomura
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK ; Institute of Molecular Physiology and Genetics, Slovak Academy of Science, Bratislava, Slovakia
| | | | - Masami Murakami
- Department of Clinical Laboratory, Gunma University School of Medicine, Maebashi
| | - Yohnosuke Shimomura
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Takasaki, Japan
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Shimomura K, Tusa M, Iberl M, Brereton MF, Kaizik S, Proks P, Lahmann C, Yaluri N, Modi S, Huopio H, Ustinov J, Otonkoski T, Laakso M, Ashcroft FM. A mouse model of human hyperinsulinism produced by the E1506K mutation in the sulphonylurea receptor SUR1. Diabetes 2013; 62:3797-806. [PMID: 23903354 PMCID: PMC3806602 DOI: 10.2337/db12-1611] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Loss-of-function mutations in the KATP channel genes KCNJ11 and ABCC8 cause neonatal hyperinsulinism in humans. Dominantly inherited mutations cause less severe disease, which may progress to glucose intolerance and diabetes in later life (e.g., SUR1-E1506K). We generated a mouse expressing SUR1-E1506K in place of SUR1. KATP channel inhibition by MgATP was enhanced in both homozygous (homE1506K) and heterozygous (hetE1506K) mutant mice, due to impaired channel activation by MgADP. As a consequence, mutant β-cells showed less on-cell KATP channel activity and fired action potentials in glucose-free solution. HomE1506K mice exhibited enhanced insulin secretion and lower fasting blood glucose within 8 weeks of birth, but reduced insulin secretion and impaired glucose tolerance at 6 months of age. These changes correlated with a lower insulin content; unlike wild-type or hetE1506K mice, insulin content did not increase with age in homE1506K mice. There was no difference in the number and size of islets or β-cells in the three types of mice, or evidence of β-cell proliferation. We conclude that the gradual development of glucose intolerance in patients with the SUR1-E1506K mutation might, as in the mouse model, result from impaired insulin secretion due a failure of insulin content to increase with age.
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Affiliation(s)
- Kenju Shimomura
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Maija Tusa
- Department of Medicine, University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland
| | - Michaela Iberl
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Melissa F. Brereton
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Stephan Kaizik
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Carolina Lahmann
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
| | - Nagendra Yaluri
- Department of Medicine, University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland
| | - Shalem Modi
- Department of Medicine, University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland
| | - Hanna Huopio
- Department of Pediatrics, University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland
| | - Jarkko Ustinov
- Research Programs Unit, Molecular Neurology, Biomedicum Stem Cell Centre, University of Helsinki, Helsinki, Finland
| | - Timo Otonkoski
- Research Programs Unit, Molecular Neurology, Biomedicum Stem Cell Centre, University of Helsinki, Helsinki, Finland
- Children’s Hospital, Helsinki University Central Hospital, Helsinki, Finland
| | - Markku Laakso
- Department of Medicine, University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland
| | - Frances M. Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, U.K
- Corresponding author: Frances M. Ashcroft,
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Abstract
Sulphonylurea drugs are the therapy of choice for treating neonatal diabetes (ND) caused by mutations in the ATP-sensitive K(+) channel (KATP channel). We investigated the interactions between MgATP, MgADP, and the sulphonylurea gliclazide with KATP channels expressed in Xenopus oocytes. In the absence of MgATP, gliclazide block was similar for wild-type channels and those carrying the Kir6.2 ND mutations R210C, G334D, I296L, and V59M. Gliclazide abolished the stimulatory effect of MgATP on all channels. Conversely, high MgATP concentrations reduced the gliclazide concentration, producing a half-maximal block of G334D and R201C channels and suggesting a mutual antagonism between nucleotide and gliclazide binding. The maximal extent of high-affinity gliclazide block of wild-type channels was increased by MgATP, but this effect was smaller for ND channels; channels that were least sensitive to ATP inhibition showed the smallest increase in sulphonylurea block. Consequently, G334D and I296L channels were not fully blocked, even at physiological MgATP concentrations (1 mmol/L). Glibenclamide block was also reduced in β-cells expressing Kir6.2-V59M channels. These data help to explain why patients with some mutations (e.g., G334D, I296L) are insensitive to sulphonylurea therapy, why higher drug concentrations are needed to treat ND than type 2 diabetes, and why patients with severe ND mutations are less prone to drug-induced hypoglycemia.
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Abstract
Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic β-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory subunit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment.
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Affiliation(s)
- Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
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Abstract
The mechanism of adenosine triphosphate (ATP)-sensitive potassium (KATP) channel activation by Mg-nucleotides was studied using a mutation (G334D) in the Kir6.2 subunit of the channel that renders KATP channels insensitive to nucleotide inhibition and has no apparent effect on their gating. KATP channels carrying this mutation (Kir6.2-G334D/SUR1 channels) were activated by MgATP and MgADP with an EC50 of 112 and 8 µM, respectively. This activation was largely suppressed by mutation of the Walker A lysines in the nucleotide-binding domains of SUR1: the remaining small (∼10%), slowly developing component of MgATP activation was fully inhibited by the lipid kinase inhibitor LY294002. The EC50 for activation of Kir6.2-G334D/SUR1 currents by MgADP was lower than that for MgATP, and the time course of activation was faster. The poorly hydrolyzable analogue MgATPγS also activated Kir6.2-G334D/SUR1. AMPPCP both failed to activate Kir6.2-G334D/SUR1 and to prevent its activation by MgATP. Maximal stimulatory concentrations of MgATP (10 mM) and MgADP (1 mM) exerted identical effects on the single-channel kinetics: they dramatically elevated the open probability (PO > 0.8), increased the mean open time and the mean burst duration, reduced the frequency and number of interburst closed states, and eliminated the short burst states. By comparing our results with those obtained for wild-type KATP channels, we conclude that the MgADP sensitivity of the wild-type KATP channel can be described quantitatively by a combination of inhibition at Kir6.2 (measured for wild-type channels in the absence of Mg2+) and activation via SUR1 (determined for Kir6.2-G334D/SUR1 channels). However, this is not the case for the effects of MgATP.
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Affiliation(s)
- Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, England, UK
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Plánka L, Nečas A, Crha M, Proks P, Vojtová L, Gál P. [Treatment of a bone bridge by transplantation of mesenchymal stem cells and chondrocytes in a composite scaffold in pigs: experimental study]. Acta Chir Orthop Traumatol Cech 2011; 78:528-536. [PMID: 22217406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
PURPOSE OF THE STUDY The presented experimental study describes the results of using a combination of allogeneic mesenchymal cells (MSCs) with chondrocytes (CHCs) and a novel scaffold based on type I collagen and chitosan fibres. This biocomposite was transplanted into a defect produced by excision of a bone bridge to induce new cartilaginous tissue formation. The left femur was treated by transplantation into a defect of distal epiphysis; the right femur with implantation of the scaffold only served as control. A better therapeutic result was therefore expected in the left femur - the reduction of growth and angular deformities, and the histological finding of a tissue similar to the cartilage excised from the left femur.. MATERIAL AND METHODS The miniature pig was selected as an experimental model and 10 pigs were used. Mesenchymal stem cells derived from femoral bone marrow and chondrocytes derived from a sample harvested from the non-weight-bearing articular surface of the distal end of the femur were cultured in medium. The novel scaffold was based on collagen containing chitosan nanofibres. To make manipulation during implantation easier, the cilindrical scaffolds after lyophilisation were again placed in 96-well plates for seeding. The scaffolds before implantation were seeded with 2x106 allogeneic MSCs and 1x106 allogeneic CHCs. The outcomes of treatment were assessed by measuring the length of bone and the degree of distal femoral valgus deformity, and by the histological findings obtained (properties and maturity of the newly-formed tissue, detection of type II collagen, PAS reaction). RESULTS The right and left legs were examined for longitudinal bone growth and the valgus angle and compared. The treated left leg showed a higher average value for longitudinal growth than the untreated right leg (p = 0.004). The average degree of angular deformity was lower in the left leg than in the right leg (p = 0.008). The microscopic findings showed that a tissue similar to hyaline cartilage was more frequently present in the femoral bone defect of the left leg, as compared with that of the right leg. Type II collagen was detected more frequently and at higher amounts on the left than the right side (p = 0.033). The PAS reaction was positive in all left limbs, with a high degree of positivity in 80 % of them, while this was not achieved in any of the right limbs (p = 0.001). DISCUSSION The use of stem cells in the indication reported here has only been the matter of time since the information on encouraging results in neurology and cardiology was published. First studies with positive results have soon been reported. The initial hydrogel scaffolds were based on tissue adhesives. However, they were not stable enough and were difficult to handle during surgery. In further studies, therefore, the use was made of a three-dimensional scaffold with a self-supporting structure of collagen fibres. This structure also facilitated its hydrodynamic seeding with MSCs and CHCs, which is an effective and sparing procedure for the transplanted cells. Studies concerned with MSCs and/or CHCs transplantation for re - pair of a physeal defect following bone bridge excision, i.e. for bone bridge treatment, in a broader experimental design, however, are still missing. CONCLUSION Transplantation of a composite scaffold seeded with mesenchymal stem cells and chondrocytes into a physeal defect following bone bridge excision prevented growth disturbance and angular deformity development in the distal femoral epi - physis. In comparison with the control group, it resulted in a more frequent production of a tissue similar to hyaline cartilage, with a cell formation reminiscent of a typical columnar arrangement of the growth plate. Key words: mesenchymal stem cells, growth plate, bone bridge, scaffold.
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Affiliation(s)
- L Plánka
- Klinika dětské chirurgie, ortopedie a traumatologie
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Imamura M, Shimomura K, Watanabe A, Negishi M, Akuzawa M, Takahashi M, Proks P, Shimomura Y. Sepsis and gas-forming splenic abscess by Clostridium septicum in a patient with type 2 diabetes. J Diabetes Complications 2010; 24:142-4. [PMID: 19285435 DOI: 10.1016/j.jdiacomp.2009.02.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2008] [Accepted: 02/04/2009] [Indexed: 11/21/2022]
Abstract
Clostridium infections are rare but frequently associated with malignancy, and mortality approaches 100% if care is not rendered within 12 to 24 h. These infections are associated with various medical problems including diabetes mellitus. In this report, we describe a unique case of sepsis and a gas-forming splenic abscess caused by Clostridium septicum in a type 2 diabetes patient which was treatable solely with antibiotics.
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Affiliation(s)
- Makoto Imamura
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Japan
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Negishi M, Shimomura K, Proks P, Akuzawa M, Takahashi M, Mori M, Shimomura Y, Kobayashi I. An obese patient with slowly progressive type 1 diabetes diagnosed by ketoacidosis. Intern Med 2010; 49:393-5. [PMID: 20190471 DOI: 10.2169/internalmedicine.49.2843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The patient was a 69-year-old woman with a family history of type 2 diabetes. Her body mass index was 31.5. She was diagnosed as type 2 diabetes 32 years previously, and treated with insulin for 8 years. She had no episode of weight loss. She was hospitalized with diabetic ketoacidosis for the first time. Her GAD antibodies were not detected. However, ICA antibodies and insulin antibodies were positively detected. She was diagnosed with type 1 diabetes. Interestingly, her diabetes state was controlled to the same level after recovery from ketoacidosis.
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Affiliation(s)
- Mayumi Negishi
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Takasaki.
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Abstract
The ATP-sensitive potassium (K(ATP)) channel plays a crucial role in insulin secretion and thus glucose homeostasis. K(ATP) channel activity in the pancreatic beta-cell is finely balanced; increased activity prevents insulin secretion, whereas reduced activity stimulates insulin release. The beta-cell metabolism tightly regulates K(ATP) channel gating, and if this coupling is perturbed, two distinct disease states can result. Diabetes occurs when the K(ATP) channel fails to close in response to increased metabolism, whereas congenital hyperinsulinism results when K(ATP) channels remain closed even at very low blood glucose levels. In general there is a good correlation between the magnitude of K(ATP) current and disease severity. Mutations that cause a complete loss of K(ATP) channels in the beta-cell plasma membrane produce a severe form of congenital hyperinsulinism, whereas mutations that partially impair channel function produce a milder phenotype. Similarly mutations that greatly reduce the ATP sensitivity of the K(ATP) channel lead to a severe form of neonatal diabetes with associated neurological complications, whilst mutations that cause smaller shifts in ATP sensitivity cause neonatal diabetes alone. This chapter reviews our current understanding of the pancreatic beta-cell K(ATP) channel and highlights recent structural, functional and clinical advances.
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Affiliation(s)
- Rebecca Clark
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK.
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Aittoniemi J, Fotinou C, Craig TJ, de Wet H, Proks P, Ashcroft FM. Review. SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator. Philos Trans R Soc Lond B Biol Sci 2009; 364:257-67. [PMID: 18990670 DOI: 10.1098/rstb.2008.0142] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
SUR1 is an ATP-binding cassette (ABC) transporter with a novel function. In contrast to other ABC proteins, it serves as the regulatory subunit of an ion channel. The ATP-sensitive (KATP) channel is an octameric complex of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits, and it links cell metabolism to electrical activity in many cell types. ATPase activity at the nucleotide-binding domains of SUR results in an increase in KATP channel open probability. Conversely, ATP binding to Kir6.2 closes the channel. Metabolic regulation is achieved by the balance between these two opposing effects. Precisely how SUR1 talks to Kir6.2 remains unclear, but recent studies have identified some residues and domains that are involved in both physical and functional interactions between the two proteins. The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes. This paper reviews recent data on the regulation of Kir6.2 by SUR1 and considers the molecular mechanisms by which SUR1 mutations produce disease.
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Affiliation(s)
- Jussi Aittoniemi
- Department of Physiology, Henry Wellcome Centre for Gene Function, University of Oxford, Parks Road, Oxford, UK
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Abstract
BACKGROUND Disopyramide, an antiarrhythmia drug, has been reported to cause hypoglycaemia. Pre-existing factors that increase the concentration of the drug in the blood increase the risk of hypoglycaemia. Furthermore, other factors can also increase the risk of hypoglycaemia even when disopyramide levels are in the therapeutic range. It has been proposed that disopyramide-induced hypoglycaemia is caused by inhibition of the pancreatic B-cell K(ATP) channels. CASE REPORT We report a case of severe disopyramide-induced hypoglycaemia in a 62-year-old woman with Type 2 diabetes taking low-dose glimepiride treatment. She had not experienced hypoglycaemia prior to the start of disopyramide therapy. No further hypoglycaemic episodes occurred following withdrawal of disopyramide therapy. FUNCTIONAL STUDY: Current recordings of K(ATP) channels expressed in Xenopus oocytes showed that at their estimated therapeutic concentrations, disopyramide and glimepiride inhibited K(ATP) channels by about 50-60%. However, when both drugs were applied together, K(ATP) channels were almost completely closed (approximately 95%). Such dramatic inhibition of K(ATP) channels is sufficient to cause B-cell membrane depolarization and stimulate insulin secretion. CONCLUSIONS Disopyramide therapy is not recommended for patients treated with K(ATP) channel inhibitors.
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Affiliation(s)
- M Negishi
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Gunma, Japan.
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Takahashi M, Shimomura K, Proks P, Craig TJ, Negishi M, Akuzawa M, Hayashi R, Shimomura Y, Kobayashi I. A proposal of combined evaluation of waist circumference and BMI for the diagnosis of metabolic syndrome. Endocr J 2009; 56:1079-82. [PMID: 19734693 DOI: 10.1507/endocrj.k09e-197] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
We performed a receiver operator characteristic (ROC) curve analysis of 3915 men and 2032 women. Subjects who were diagnosed with two or more factors among high blood pressure, hyperglycaemia or high triglyceride and/or low HDL were classified as the metabolic syndrome group. By performing a ROC curve analysis, we have determined the cut-off point of waist circumference (WC) and BMI to define metabolic syndrome and further calculated the sensitivity and specificity of these two factors for the diagnosis. Cut-off point for the diagnosis of metabolic syndrome was 85 cm (men) and 80 cm (women) in WC and 24 (men) and 23 (women) in BMI. By combining these two factors, the sensitivity for the diagnosis increased to more than 80%. We conclude that it is beneficial to combine both WC and BMI for diagnosis of metabolic syndrome.
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Affiliation(s)
- Masaki Takahashi
- Diabetes and Metabolic Disease Research Centre, Hidaka Hospital, Gunma, Japan
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Girard CA, Wunderlich FT, Shimomura K, Collins S, Kaizik S, Proks P, Abdulkader F, Clark A, Ball V, Zubcevic L, Bentley L, Clark R, Church C, Hugill A, Galvanovskis J, Cox R, Rorsman P, Brüning JC, Ashcroft FM. Expression of an activating mutation in the gene encoding the KATP channel subunit Kir6.2 in mouse pancreatic beta cells recapitulates neonatal diabetes. J Clin Invest 2008; 119:80-90. [PMID: 19065048 PMCID: PMC2613450 DOI: 10.1172/jci35772] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Accepted: 10/29/2008] [Indexed: 12/25/2022] Open
Abstract
Neonatal diabetes is a rare monogenic form of diabetes that usually presents within the first six months of life. It is commonly caused by gain-of-function mutations in the genes encoding the Kir6.2 and SUR1 subunits of the plasmalemmal ATP-sensitive K+ (KATP) channel. To better understand this disease, we generated a mouse expressing a Kir6.2 mutation (V59M) that causes neonatal diabetes in humans and we used Cre-lox technology to express the mutation specifically in pancreatic beta cells. These beta-V59M mice developed severe diabetes soon after birth, and by 5 weeks of age, blood glucose levels were markedly increased and insulin was undetectable. Islets isolated from beta-V59M mice secreted substantially less insulin and showed a smaller increase in intracellular calcium in response to glucose. This was due to a reduced sensitivity of KATP channels in pancreatic beta cells to inhibition by ATP or glucose. In contrast, the sulfonylurea tolbutamide, a specific blocker of KATP channels, closed KATP channels, elevated intracellular calcium levels, and stimulated insulin release in beta-V59M beta cells, indicating that events downstream of KATP channel closure remained intact. Expression of the V59M Kir6.2 mutation in pancreatic beta cells alone is thus sufficient to recapitulate the neonatal diabetes observed in humans. beta-V59M islets also displayed a reduced percentage of beta cells, abnormal morphology, lower insulin content, and decreased expression of Kir6.2, SUR1, and insulin mRNA. All these changes are expected to contribute to the diabetes of beta-V59M mice. Their cause requires further investigation.
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Affiliation(s)
- Christophe A Girard
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
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Abstract
ATP-sensitive potassium (KATP) channels are composed of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits. Binding of ATP to Kir6.2 leads to inhibition of channel activity. Because there are four subunits and thus four ATP-binding sites, four binding events are possible. ATP binds to both the open and closed states of the channel and produces a decrease in the mean open time, a reduction in the mean burst duration, and an increase in the frequency and duration of the interburst closed states. Here, we investigate the mechanism of interaction of ATP with the open state of the channel by analyzing the single-channel kinetics of concatenated Kir6.2 tetramers containing from zero to four mutated Kir6.2 subunits that possess an impaired ATP-binding site. We show that the ATP-dependent decrease in the mean burst duration is well described by a Monod-Wyman-Changeux model in which channel closing is produced by all four subunits acting in a single concerted step. The data are inconsistent with a Hodgkin-Huxley model (four independent steps) or a dimer model (two independent dimers). When the channel is open, ATP binds to a single ATP-binding site with a dissociation constant of 300 μM.
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Affiliation(s)
- Tim J Craig
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
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36
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de Wet H, Proks P, Lafond M, Aittoniemi J, Sansom MSP, Flanagan SE, Pearson ER, Hattersley AT, Ashcroft FM. A mutation (R826W) in nucleotide-binding domain 1 of ABCC8 reduces ATPase activity and causes transient neonatal diabetes. EMBO Rep 2008; 9:648-54. [PMID: 18497752 PMCID: PMC2475326 DOI: 10.1038/embor.2008.71] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 03/17/2008] [Accepted: 04/02/2008] [Indexed: 12/13/2022] Open
Abstract
Activating mutations in the pore-forming Kir6.2 (KCNJ11) and regulatory sulphonylurea receptor SUR1 (ABCC8) subunits of the K(ATP) channel are a common cause of transient neonatal diabetes mellitus (TNDM). We identified a new TNDM mutation (R826W) in the first nucleotide-binding domain (NBD1) of SUR1. The mutation was found in a region that heterodimerizes with NBD2 to form catalytic site 2. Functional analysis showed that this mutation decreases MgATP hydrolysis by purified maltose-binding protein MBP-NBD1 fusion proteins. Inhibition of ATP hydrolysis by MgADP or BeF was not changed. The results indicate that the ATPase cycle lingers in the post-hydrolytic MgADP.P(i)-bound state, which is associated with channel activation. The extent of MgADP-dependent activation of K(ATP) channel activity was unaffected by the R826W mutation, but the time course of deactivation was slowed. Channel inhibition by MgATP was reduced, leading to an increase in resting whole-cell currents. In pancreatic beta cells, this would lead to less insulin secretion and thereby diabetes.
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MESH Headings
- ATP-Binding Cassette Transporters/chemistry
- ATP-Binding Cassette Transporters/genetics
- Adenosine Diphosphate/pharmacology
- Adenosine Triphosphatases/chemistry
- Adenosine Triphosphatases/metabolism
- Adenosine Triphosphate/pharmacology
- Amino Acid Sequence
- Amino Acid Substitution
- Arginine/genetics
- Child
- Diabetes Mellitus/enzymology
- Diabetes Mellitus/genetics
- Humans
- Infant, Newborn
- Infant, Newborn, Diseases/enzymology
- Infant, Newborn, Diseases/genetics
- Ion Channel Gating/drug effects
- Kinetics
- Male
- Molecular Sequence Data
- Mutant Proteins/chemistry
- Mutation/genetics
- Potassium Channels, Inwardly Rectifying/chemistry
- Potassium Channels, Inwardly Rectifying/genetics
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, Drug/chemistry
- Receptors, Drug/genetics
- Sulfonylurea Receptors
- Tryptophan/genetics
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Affiliation(s)
- Heidi de Wet
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
| | - Peter Proks
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
| | - Mathilde Lafond
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
| | - Jussi Aittoniemi
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
- Department of Biochemistry, University of Oxford, Oxford OX1 3PT, UK
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, Oxford OX1 3PT, UK
| | - Sarah E Flanagan
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, UK
| | - Ewan R Pearson
- Division of Medicine and Therapeutics, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
| | - Andrew T Hattersley
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
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Negishi M, Shimomura K, Proks P, Shimomura Y, Mori M. Alpha glucosidase inhibitor voglibose can prevent pioglitazone-induced body weight gain in Type 2 diabetic patients. Br J Clin Pharmacol 2008; 66:318-9. [PMID: 18507653 DOI: 10.1111/j.1365-2125.2008.03216.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
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Tammaro P, Shimomura K, Proks P. Xenopus oocytes as a heterologous expression system for studying ion channels with the patch-clamp technique. Methods Mol Biol 2008; 491:127-39. [PMID: 18998089 DOI: 10.1007/978-1-59745-526-8_10] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Oocytes from the Xenopus laevis represent one of the most widely used expression systems for functional characterization of ion channels. Their large size facilitates both injection of heterologous cRNA and subsequent electrophysiological recordings of ion channel currents. Furthermore, Xenopus oocytes translate cRNA very efficiently, resulting in the generation of a large number of ion channels in the plasma membrane. In this chapter, we outline methods for oocyte preparation and maintenance and describe procedures for patch-clamping of oocytes, with a special focus on the macropatch technique. We discuss some common problems associated with patch-clamping of oocytes and their use as an expression system for ion channels.
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Affiliation(s)
- Paolo Tammaro
- Department of Physiology, Anatomy and Genetics, University of Oxford, UK
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Shield JPH, Flanagan SE, Mackay DJ, Harries LW, Proks P, Girard C, Ashcroft FM, Temple IK, Ellard S. Mosaic paternal uniparental isodisomy and an ABCC8 gene mutation in a patient with permanent neonatal diabetes and hemihypertrophy. Diabetes 2008; 57:255-8. [PMID: 17942821 DOI: 10.2337/db07-0999] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Activating mutations in the KCNJ11 and ABCC8 genes encoding the Kir6.2 and SUR1 subunits of the pancreatic ATP-sensitive K(+) channel are the most common cause of permanent neonatal diabetes. In contrast to KCNJ11, where only dominant heterozygous mutations have been identified, recessively acting ABCC8 mutations have recently been found in some patients with neonatal diabetes. These genes are co-located on chromosome 11p15.1, centromeric to the imprinted Beckwith-Wiedemann syndrome (BWS) locus at 11p15.5. We investigated a male with hemihypertrophy, a condition classically associated with neonatal hyperinsulinemia and hypoglycemia, who developed neonatal diabetes at age 5 weeks. RESEARCH DESIGN AND METHODS The KCNJ11 and ABCC8 genes and microsatellite markers on chromosome 11 were analyzed in DNA samples from the patient and his parents. RESULTS A paternally inherited activating mutation (N72S) in the ABCC8 gene was identified in the proband. The mutation was present at 70% in the patient's leukocytes and 50% in buccal cells. Microsatellite analysis demonstrated mosaic segmental paternal uniparental isodisomy (UPD) of 11pter-11p14 in the proband that encompassed the ABCC8 gene and the BWS locus. CONCLUSIONS We report a patient with neonatal diabetes, hemihypertrophy, and relatively high birth weight resulting from telomeric segmental paternal UPD of chromosome 11, which unmasks a recessively acting gain-of-function mutation in the ABCC8 gene and causes deregulation of imprinted genes at the BWS locus on 11p15.5.
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Affiliation(s)
- Julian P H Shield
- Department of Endocrinology and Diabetes, Bristol Royal Hospital for Children and University of Bristol, Bristol, UK
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Ellard S, Flanagan SE, Girard CA, Patch AM, Harries LW, Parrish A, Edghill EL, Mackay DJG, Proks P, Shimomura K, Haberland H, Carson DJ, Shield JPH, Hattersley AT, Ashcroft FM. Permanent neonatal diabetes caused by dominant, recessive, or compound heterozygous SUR1 mutations with opposite functional effects. Am J Hum Genet 2007; 81:375-82. [PMID: 17668386 PMCID: PMC1950816 DOI: 10.1086/519174] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2006] [Accepted: 04/20/2007] [Indexed: 11/03/2022] Open
Abstract
Heterozygous activating mutations in the KCNJ11 gene encoding the pore-forming Kir6.2 subunit of the pancreatic beta cell K(ATP) channel are the most common cause of permanent neonatal diabetes (PNDM). Patients with PNDM due to a heterozygous activating mutation in the ABCC8 gene encoding the SUR1 regulatory subunit of the K(ATP) channel have recently been reported. We studied a cohort of 59 patients with permanent diabetes who received a diagnosis before 6 mo of age and who did not have a KCNJ11 mutation. ABCC8 gene mutations were identified in 16 of 59 patients and included 8 patients with heterozygous de novo mutations. A recessive mode of inheritance was observed in eight patients with homozygous, mosaic, or compound heterozygous mutations. Functional studies of selected mutations showed a reduced response to ATP consistent with an activating mutation that results in reduced insulin secretion. A novel mutational mechanism was observed in which a heterozygous activating mutation resulted in PNDM only when a second, loss-of-function mutation was also present.
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Affiliation(s)
- Sian Ellard
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter, EX2 5DW, and Wessex Regional Genetics Labs, Salisbury District Hospital, UK
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41
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Proks P, Shimomura K, Craig TJ, Girard CAJ, Ashcroft FM. Mechanism of action of a sulphonylurea receptor SUR1 mutation (F132L) that causes DEND syndrome. Hum Mol Genet 2007; 16:2011-9. [PMID: 17584766 DOI: 10.1093/hmg/ddm149] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Activating mutations in the genes encoding the ATP-sensitive potassium (K(ATP)) channel subunits Kir6.2 and SUR1 are a common cause of neonatal diabetes. Here, we analyse the molecular mechanism of action of the heterozygous mutation F132L, which lies in the first set of transmembrane helices (TMD0) of SUR1. This mutation causes severe developmental delay, epilepsy and permanent neonatal diabetes (DEND syndrome). We show that the F132L mutation reduces the ATP sensitivity of K(ATP) channels indirectly, by altering the intrinsic gating of the channel. Thus, the open probability is markedly increased when Kir6.2 is co-expressed with mutant TMD0 alone or with mutant SUR1. The F132L mutation disrupts the physical interaction between Kir6.2 and TMD0, but does not alter the plasmalemma channel density. Our results explain how a mutation in an accessory subunit can produce enhanced activity of the K(ATP) channel pore (formed by Kir6.2). They also provide further evidence that interactions between TMD0 of SUR1 and Kir6.2 are critical for K(ATP) channel gating and identify a residue crucial for this interaction at both physical and functional levels.
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Affiliation(s)
- Peter Proks
- University Laboratory of Physiology, Oxford University, Oxford, UK
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42
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Krupa P, Krsek P, Javorník M, Dostál O, Srnec R, Usvald D, Proks P, Kecová H, Amler E, Jancár J, Gál P, Plánka L, Necas A. Use of 3D geometry modeling of osteochondrosis-like iatrogenic lesions as a template for press-and-fit scaffold seeded with mesenchymal stem cells. Physiol Res 2007; 56 Suppl 1:S107-S114. [PMID: 17552888 DOI: 10.33549/physiolres.931308] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Computed tomography (CT) is an effective diagnostic modality for three-dimensional imaging of bone structures, including the geometry of their defects. The aim of the study was to create and optimize 3D geometrical and real plastic models of the distal femoral component of the knee with joint surface defects. Input data included CT images of stifle joints in twenty miniature pigs with iatrogenic osteochondrosis-like lesions in medial femoral condyle of the left knee. The animals were examined eight and sixteen weeks after surgery. Philips MX 8000 MX and View workstation were used for scanning parallel plane cross section slices and Cartesian discrete volume creation. On the average, 100 slices were performed in each stifle joint. Slice matrices size was 512 x 512 with slice thickness of 1 mm. Pixel (voxel) size in the slice plane was 0.5 mm (with average accuracy of +/-0.5 mm and typical volume size 512 x 512 x 100 voxels). Three-dimensional processing of CT data and 3D geometrical modelling, using interactive computer graphic system MediTools formerly developed here, consisted of tissue segmentation (raster based method combination and 5 % of manual correction), vectorization by the marching-cubes method, smoothing and decimation. Stifle- joint CT images of three individuals of different body size (small, medium and large) were selected to make the real plastic models of their distal femurs from plaster composite using rapid prototyping technology of Zcorporation. Accuracy of the modeling was +/- 0.5 mm. The real plastic models of distal femurs can be used as a template for developing custom made press and fit scaffold implants seeded with mesenchymal stem cells that might be subsequently implanted into iatrogenic joint surface defects for articular cartilage-repair enhancement.
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Affiliation(s)
- P Krupa
- Department of Medical Imaging Radiology, St Anne's University Hospital, Masaryk University, Brno, Czech Republic
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Shimomura K, Ikeda M, Ariyama Y, Proks P, Shimomura Y, Mori M, Matsumoto S. Effect of peroxisome proliferator-activated receptor alpha ligand fenofibrate on K(v) channels in the insulin-secreting cell line HIT-T15. Gen Physiol Biophys 2006; 25:455-60. [PMID: 17356236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Ligands for peroxisome proliferator-activated receptors alpha (PPARalpha) are clinically used for the treatment of patients with hyperlipidemia. As we have previously shown, a synthetic ligand of PPARalpha, fenofibrate, has a stimulatory effect on insulin secretion in clonal hamster insulinoma beta-cell line HIT-T15 cells. We have also demonstrated that fenofibrate directly inhibits ATP-sensitive potassium (K(ATP)) channels, an effect independent of PPARalpha. In this study, fenofibrate was shown to be able to reduce voltage-dependent K(+) (K(v)) channel currents in voltage-independent manner. Therefore, fenofibrate may modulate insulin secretion not only via inhibition of K(ATP) channels but also via reduction of the K(v) channel current.
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Affiliation(s)
- K Shimomura
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, United Kingdom.
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44
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Girard CAJ, Shimomura K, Proks P, Absalom N, Castano L, Perez de Nanclares G, Ashcroft FM. Functional analysis of six Kir6.2 (KCNJ11) mutations causing neonatal diabetes. Pflugers Arch 2006; 453:323-32. [PMID: 17021801 DOI: 10.1007/s00424-006-0112-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Accepted: 06/05/2006] [Indexed: 12/25/2022]
Abstract
ATP-sensitive potassium (K(ATP)) channels, composed of pore-forming Kir6.2 and regulatory sulphonylurea receptor (SUR) subunits, play an essential role in insulin secretion from pancreatic beta cells. Binding of ATP to Kir6.2 inhibits, whereas interaction of Mg-nucleotides with SUR, activates the channel. Heterozygous activating mutations in Kir6.2 (KCNJ11) are a common cause of neonatal diabetes (ND). We assessed the functional effects of six novel Kir6.2 mutations associated with ND: H46Y, N48D, E227K, E229K, E292G, and V252A. K(ATP) channels were expressed in Xenopus oocytes and the heterozygous state was simulated by coexpression of wild-type and mutant Kir6.2 with SUR1 (the beta cell type of SUR). All mutations reduced the sensitivity of the K(ATP) channel to inhibition by MgATP, and enhanced whole-cell K(ATP) currents. Two mutations (E227K, E229K) also enhanced the intrinsic open probability of the channel, thereby indirectly reducing the channel ATP sensitivity. The other four mutations lie close to the predicted ATP-binding site and thus may affect ATP binding. In pancreatic beta cells, an increase in the K(ATP) current is expected to reduce insulin secretion and thereby cause diabetes. None of the mutations substantially affected the sensitivity of the channel to inhibition by the sulphonylurea tolbutamide, suggesting patients carrying these mutations may respond to these drugs.
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45
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Proks P, Girard C, Baevre H, Njølstad PR, Ashcroft FM. Functional effects of mutations at F35 in the NH2-terminus of Kir6.2 (KCNJ11), causing neonatal diabetes, and response to sulfonylurea therapy. Diabetes 2006; 55:1731-7. [PMID: 16731836 DOI: 10.2337/db05-1420] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Heterozygous mutations in the human Kir6.2 gene (KCNJ11), the pore-forming subunit of the ATP-sensitive K(+) channel (K(ATP) channel), cause neonatal diabetes. To date, all mutations increase whole-cell K(ATP) channel currents by reducing channel inhibition by MgATP. Here, we provide functional characterization of two mutations (F35L and F35V) at residue F35 of Kir6.2, which lies within the NH(2)-terminus. We further show that the F35V patient can be successfully transferred from insulin to sulfonylurea therapy. The patient has been off insulin for 24 months and shows improved metabolic control (mean HbA(1c) 7.58 before and 6.18% after sulfonylurea treatment; P < 0.007). Wild-type and mutant Kir6.2 were heterologously coexpressed with SUR1 in Xenopus oocytes. Whole-cell K(ATP) channel currents through homomeric and heterozygous F35V and F35L channels were increased due to a reduced sensitivity to inhibition by MgATP. The mutation also increased the open probability (P(O)) of homomeric F35 mutant channels in the absence of ATP. These effects on P(O) and ATP sensitivity were abolished in the absence of SUR1. Our results suggest that mutations at F35 cause permanent neonatal diabetes by affecting K(ATP) channel gating and thereby, indirectly, ATP inhibition. Heterozygous F35V channels were markedly inhibited by the sulfonylurea tolbutamide, accounting for the efficacy of sulfonylurea therapy in the patient.
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Affiliation(s)
- Peter Proks
- University Laboratory of Physiology, Oxford University, Parks Road, Oxford OX1 3PT, UK
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Shimomura K, Girard CAJ, Proks P, Nazim J, Lippiat JD, Cerutti F, Lorini R, Ellard S, Hattersley AT, Barbetti F, Ashcroft FM. Mutations at the same residue (R50) of Kir6.2 (KCNJ11) that cause neonatal diabetes produce different functional effects. Diabetes 2006; 55:1705-12. [PMID: 16731833 DOI: 10.2337/db05-1640] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Heterozygous mutations in the human Kir6.2 gene (KCNJ11), the pore-forming subunit of the ATP-sensitive K(+) channel (K(ATP) channel), are a common cause of neonatal diabetes. We identified a novel KCNJ11 mutation, R50Q, that causes permanent neonatal diabetes (PNDM) without neurological problems. We investigated the functional effects this mutation and another at the same residue (R50P) that led to PNDM in association with developmental delay. Wild-type or mutant Kir6.2/SUR1 channels were examined by heterologous expression in Xenopus oocytes. Both mutations increased resting whole-cell currents through homomeric and heterozygous K(ATP) channels by reducing channel inhibition by ATP, an effect that was larger in the presence of Mg(2+). However the magnitude of the reduction in ATP sensitivity (and the increase in the whole-cell current) was substantially larger for the R50P mutation. This is consistent with the more severe phenotype. Single-R50P channel kinetics (in the absence of ATP) did not differ from wild type, indicating that the mutation primarily affects ATP binding and/or transduction. This supports the idea that R50 lies in the ATP-binding site of Kir6.2. The sulfonylurea tolbutamide blocked heterozygous R50Q (89%) and R50P (84%) channels only slightly less than wild-type channels (98%), suggesting that sulfonylurea therapy may be of benefit for patients with either mutation.
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Affiliation(s)
- Kenju Shimomura
- University Laboratory of Physiology, Oxford University, Parks Road, Oxford OX1 3PT, UK
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Proks P, Arnold AL, Bruining J, Girard C, Flanagan SE, Larkin B, Colclough K, Hattersley AT, Ashcroft FM, Ellard S. A heterozygous activating mutation in the sulphonylurea receptor SUR1 (ABCC8) causes neonatal diabetes. Hum Mol Genet 2006; 15:1793-800. [PMID: 16613899 DOI: 10.1093/hmg/ddl101] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Neonatal diabetes is a genetically heterogeneous disorder with nine different genetic aetiologies reported to date. Heterozygous activating mutations in the KCNJ11 gene encoding Kir6.2, the pore-forming subunit of the ATP-sensitive potassium (K(ATP)) channel, are the most common cause of permanent neonatal diabetes. The sulphonylurea receptor (SUR) SUR1 serves as the regulatory subunit of the K(ATP) channel in pancreatic beta cells. We therefore hypothesized that activating mutations in the ABCC8 gene, which encodes SUR1, might cause neonatal diabetes. We identified a novel heterozygous mutation, F132L, in the ABCC8 gene of a patient with severe developmental delay, epilepsy and neonatal diabetes (DEND syndrome). This mutation had arisen de novo and was not present in 150 control chromosomes. Residue F132 shows evolutionary conservation across species and is located in the first set of transmembrane helices (TMD0) of SUR1, which is proposed to interact with Kir6.2. Functional studies of recombinant K(ATP) channels demonstrated that F132L markedly reduces the sensitivity of the K(ATP) channel to inhibition by MgATP and this increases the whole-cell K(ATP) current. The functional consequence of this ABCC8 mutation mirrors that of KCNJ11 mutations causing neonatal diabetes and provides new insights into the interaction of Kir6.2 and SUR1. As SUR1 is expressed in neurones as well as in beta cells, this mutation can account for both neonatal diabetes and the neurological phenotype. Our results demonstrate that SUR1 mutations constitute a new genetic aetiology for neonatal diabetes and that they act by reducing the K(ATP) channel's ATP sensitivity.
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Affiliation(s)
- Peter Proks
- Department of Molecular Genetics, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, UK
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Abstract
Type-2, or non-insulin-dependent diabetes mellitus is a serious disease that is now widespread throughout Western society. Glucose intolerance, or failure of glucose to stimulate insulin secretion, is a primary factor in the manifestation of this disease and is likely to be due to the failure of glucose metabolism to stimulate pancreatic beta-cell electrical activity, calcium influx, and insulin secretion. In this review we describe how ion channels regulate the electrical behaviour of the beta-cell and how the membrane potential depolarises in response to a rise in glucose metabolism. Central to these electrical events is the inhibition of ATP-sensitive potassium channel by ATP, and we summarise recent advances in our understanding of the properties of this ion channel in coupling beta-cell metabolism to electrical activity. We discuss the mechanism, specificity, and clinical implications of the pharmacological inhibition of KATP channels by sulphonyureas and other antidiabetic drugs. The roles of other ion channels in regulating electrical activity are considered, and also their potential use as targets for drug action in treating beta-cell disorders.
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Affiliation(s)
- P Proks
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovakia.
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49
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Tammaro P, Proks P, Ashcroft FM. Functional effects of naturally occurring KCNJ11 mutations causing neonatal diabetes on cloned cardiac KATP channels. J Physiol 2005; 571:3-14. [PMID: 16339180 PMCID: PMC1805653 DOI: 10.1113/jphysiol.2005.099168] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
ATP-sensitive K+ (K(ATP)) channels are hetero-octamers of inwardly rectifying K+ channel (Kir6.2) and sulphonylurea receptor subunits (SUR1 in pancreatic beta-cells, SUR2A in heart). Heterozygous gain-of-function mutations in Kir6.2 cause neonatal diabetes, which may be accompanied by epilepsy and developmental delay. However, despite the importance of K(ATP) channels in the heart, patients have no obvious cardiac problems. We examined the effects of adenine nucleotides on K(ATP) channels containing wild-type or mutant (Q52R, R201H) Kir6.2 plus either SUR1 or SUR2A. In the absence of Mg2+, both mutations reduced ATP inhibition of SUR1- and SUR2A-containing channels to similar extents, but when Mg2+ was present ATP blocked mutant channels containing SUR1 much less than SUR2A channels. Mg-nucleotide activation of SUR1, but not SUR2A, channels was markedly increased by the R201H mutation. Both mutations also increased resting whole-cell K(ATP) currents through heterozygous SUR1-containing channels to a greater extent than for heterozygous SUR2A-containing channels. The greater ATP inhibition of mutant Kir6.2/SUR2A than of Kir6.2/SUR1 can explain why gain-of-function Kir6.2 mutations manifest effects in brain and beta-cells but not in the heart.
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Affiliation(s)
- Paolo Tammaro
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK
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Haider S, Antcliff JF, Proks P, Sansom MSP, Ashcroft FM. Focus on Kir6.2: a key component of the ATP-sensitive potassium channel. J Mol Cell Cardiol 2005; 38:927-36. [PMID: 15910877 DOI: 10.1016/j.yjmcc.2005.01.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Accepted: 01/24/2005] [Indexed: 11/24/2022]
Abstract
ATP-sensitive potassium (K(ATP)) channels are found in a wide variety of cell types where they couple cell metabolism to electrical activity. In glucose-sensing tissues, these channels respond to fluctuating changes in blood glucose concentration, but in other tissues they are activated only under ischemic conditions or in response to hormonal stimulation. Although K(ATP) channels in different tissues have different regulatory subunits, in almost all cases (except vascular smooth muscle) the pore-forming subunit is the inwardly rectifying K(+) channel Kir6.2. This article reviews recent studies of Kir6.2, focussing on the relation between channel structure and function, and on naturally occurring mutations in Kir6.2 that lead to human disease. New insights into the location of the ATP-binding site, the permeation pathway for K(+), and the gating of the pore provided by homology modelling are discussed in relation to functional studies. Gain-of-function mutations in Kir6.2 cause permanent neonatal diabetes mellitus (PNDM) by reducing the ATP sensitivity of the K(ATP) channel and increasing the K(ATP) current, which is predicted to inhibit beta-cell electrical activity and insulin secretion. Mutations at specific residues, that cause a greater decrease in ATP sensitivity, are associated with additional neurological symptoms. The molecular mechanism underlying the differences in ATP sensitivity produced by these two classes of mutations is discussed. We speculate on how some mutations lead to neurological disease and why no obvious cardiac symptoms are observed. We also consider the implications of these studies for type-2 diabetes.
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Affiliation(s)
- Shozeb Haider
- Department of Biochemistry, University of Oxford, UK
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