1
|
Rodríguez-Rivera NS, Barrera-Oviedo D. Exploring the Pathophysiology of ATP-Dependent Potassium Channels in Insulin Resistance. Int J Mol Sci 2024; 25:4079. [PMID: 38612888 PMCID: PMC11012456 DOI: 10.3390/ijms25074079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Revised: 03/15/2024] [Accepted: 03/29/2024] [Indexed: 04/14/2024] Open
Abstract
Ionic channels are present in eucaryotic plasma and intracellular membranes. They coordinate and control several functions. Potassium channels belong to the most diverse family of ionic channels that includes ATP-dependent potassium (KATP) channels in the potassium rectifier channel subfamily. These channels were initially described in heart muscle and then in other tissues such as pancreatic, skeletal muscle, brain, and vascular and non-vascular smooth muscle tissues. In pancreatic beta cells, KATP channels are primarily responsible for maintaining the membrane potential and for depolarization-mediated insulin release, and their decreased density and activity may be related to insulin resistance. KATP channels' relationship with insulin resistance is beginning to be explored in extra-pancreatic beta tissues like the skeletal muscle, where KATP channels are involved in insulin-dependent glucose recapture and their activation may lead to insulin resistance. In adipose tissues, KATP channels containing Kir6.2 protein subunits could be related to the increase in free fatty acids and insulin resistance; therefore, pathological processes that promote prolonged adipocyte KATP channel inhibition might lead to obesity due to insulin resistance. In the central nervous system, KATP channel activation can regulate peripheric glycemia and lead to brain insulin resistance, an early peripheral alteration that can lead to the development of pathologies such as obesity and Type 2 Diabetes Mellitus (T2DM). In this review, we aim to discuss the characteristics of KATP channels, their relationship with clinical disorders, and their mechanisms and potential associations with peripheral and central insulin resistance.
Collapse
Affiliation(s)
- Nidia Samara Rodríguez-Rivera
- Laboratorio de Farmacología y Bioquímica Clínica, Departamento de Farmacología, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico;
| | | |
Collapse
|
2
|
Lee CT, Tsai WH, Chang CC, Chen PC, Fann CSJ, Chang HK, Liu SY, Wu MZ, Chiu PC, Hsu WM, Yang WS, Lai LP, Tsai WY, Yang SB, Chen PL. Genotype-phenotype correlation in Taiwanese children with diazoxide-unresponsive congenital hyperinsulinism. Front Endocrinol (Lausanne) 2023; 14:1283907. [PMID: 38033998 PMCID: PMC10687152 DOI: 10.3389/fendo.2023.1283907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2023] [Accepted: 10/23/2023] [Indexed: 12/02/2023] Open
Abstract
Objective Congenital hyperinsulinism (CHI) is a group of clinically and genetically heterogeneous disorders characterized by dysregulated insulin secretion. The aim of the study was to elucidate genetic etiologies of Taiwanese children with the most severe diazoxide-unresponsive CHI and analyze their genotype-phenotype correlations. Methods We combined Sanger with whole exome sequencing (WES) to analyze CHI-related genes. The allele frequency of the most common variant was estimated by single-nucleotide polymorphism haplotype analysis. The functional effects of the ATP-sensitive potassium (KATP) channel variants were assessed using patch clamp recording and Western blot. Results Nine of 13 (69%) patients with ten different pathogenic variants (7 in ABCC8, 2 in KCNJ11 and 1 in GCK) were identified by the combined sequencing. The variant ABCC8 p.T1042QfsX75 identified in three probands was located in a specific haplotype. Functional study revealed the human SUR1 (hSUR1)-L366F KATP channels failed to respond to intracellular MgADP and diazoxide while hSUR1-R797Q and hSUR1-R1393C KATP channels were defective in trafficking. One patient had a de novo dominant mutation in the GCK gene (p.I211F), and WES revealed mosaicism of this variant from another patient. Conclusion Pathogenic variants in KATP channels are the most common underlying cause of diazoxide-unresponsive CHI in the Taiwanese cohort. The p.T1042QfsX75 variant in the ABCC8 gene is highly suggestive of a founder effect. The I211F mutation in the GCK gene and three rare SUR1 variants associated with defective gating (p.L366F) or traffic (p.R797Q and p.R1393C) KATP channels are also associated with the diazoxide-unresponsive phenotype.
Collapse
Affiliation(s)
- Cheng-Ting Lee
- Department of Pediatrics, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
- Graduate Institute of Clinical Medicine, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Wen-Hao Tsai
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | | | - Pei-Chun Chen
- Department of Physiology, National Cheng-Kung University, Tainan, Taiwan
| | | | - Hsueh-Kai Chang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Shih-Yao Liu
- Department of Pediatrics, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Mu-Zon Wu
- Department of Pathology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Pao-Chin Chiu
- Department of Pediatrics, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan
| | - Wen-Ming Hsu
- Department of Surgery, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Wei-Shiung Yang
- Graduate Institute of Clinical Medicine, National Taiwan University College of Medicine, Taipei, Taiwan
- Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
- Graduate Institute of Medical Genomics and Proteomics, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Ling-Ping Lai
- Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Wen-Yu Tsai
- Department of Pediatrics, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Shi-Bing Yang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Pei-Lung Chen
- Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
- Graduate Institute of Medical Genomics and Proteomics, National Taiwan University College of Medicine, Taipei, Taiwan
- Department of Medical Genetics, National Taiwan University Hospital, Taipei, Taiwan
| |
Collapse
|
3
|
Ferreira G, Santander A, Cardozo R, Chavarría L, Domínguez L, Mujica N, Benítez M, Sastre S, Sobrevia L, Nicolson GL. Nutrigenomics of inward rectifier potassium channels. Biochim Biophys Acta Mol Basis Dis 2023:166803. [PMID: 37406972 DOI: 10.1016/j.bbadis.2023.166803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 06/27/2023] [Accepted: 06/30/2023] [Indexed: 07/07/2023]
Abstract
Inwardly rectifying potassium (Kir) channels play a key role in maintaining the resting membrane potential and supporting potassium homeostasis. There are many variants of Kir channels, which are usually tetramers in which the main subunit has two trans-membrane helices attached to two N- and C-terminal cytoplasmic tails with a pore-forming loop in between that contains the selectivity filter. These channels have domains that are strongly modulated by molecules present in nutrients found in different diets, such as phosphoinositols, polyamines and Mg2+. These molecules can impact these channels directly or indirectly, either allosterically by modulation of enzymes or via the regulation of channel expression. A particular type of these channels is coupled to cell metabolism and inhibited by ATP (KATP channels, essential for insulin release and for the pathogenesis of metabolic diseases like diabetes mellitus). Genomic changes in Kir channels have a significant impact on metabolism, such as conditioning the nutrients and electrolytes that an individual can take. Thus, the nutrigenomics of ion channels is an important emerging field in which we are attempting to understand how nutrients and diets can affect the activity and expression of ion channels and how genomic changes in such channels may be the basis for pathological conditions that limit nutrition and electrolyte intake. In this contribution we briefly review Kir channels, discuss their nutrigenomics, characterize how different components in the diet affect their function and expression, and suggest how their genomic changes lead to pathological phenotypes that affect diet and electrolyte intake.
Collapse
Affiliation(s)
- Gonzalo Ferreira
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay.
| | - Axel Santander
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Romina Cardozo
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Luisina Chavarría
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Lucía Domínguez
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Nicolás Mujica
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Milagros Benítez
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay
| | - Santiago Sastre
- Laboratory of Ion Channels, Biological Membranes and Cell Signaling, Dept. of Biophysics, Facultad de Medicina, CP 11800, Universidad de la Republica, Montevideo, Uruguay; Centro de Investigaciones Biomédicas (CEINBIO), Universidad de la República, Montevideo CP 11800, Uruguay
| | - Luis Sobrevia
- Cellular and Molecular Physiology Laboratory (CMPL), Department of Obstetrics, Division of Obstetrics and Gynaecology, School of Medicine, Faculty of Medicine, Pontificia Universidad Católica de Chile, Santiago 8330024, Chile; Department of Physiology, Faculty of Pharmacy, Universidad de Sevilla, Seville E-41012, Spain; Medical School (Faculty of Medicine), Sao Paulo State University (UNESP), Brazil; University of Queensland, Centre for Clinical Research (UQCCR), Faculty of Medicine and Biomedical Sciences, University of Queensland, Herston, 4029, Queensland, Australia; Tecnologico de Monterrey, Eutra, The Institute for Obesity Research (IOR), School of Medicine and Health Sciences, Monterrey, Nuevo León, Mexico
| | - Garth L Nicolson
- Department of Molecular Pathology, The Institute for Molecular Medicine, Huntington Beach, CA, USA
| |
Collapse
|
4
|
Ježek P, Holendová B, Jabůrek M, Dlasková A, Plecitá-Hlavatá L. Contribution of Mitochondria to Insulin Secretion by Various Secretagogues. Antioxid Redox Signal 2022; 36:920-952. [PMID: 34180254 PMCID: PMC9125579 DOI: 10.1089/ars.2021.0113] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca2+ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca2+ influx was found to enhance GSIS, reflecting cytosolic Ca2+ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca2+ and K+ channels) or the superimposed Ca2+ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca2+ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.
Collapse
Affiliation(s)
- Petr Ježek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Blanka Holendová
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Martin Jabůrek
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Andrea Dlasková
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Lydie Plecitá-Hlavatá
- Department of Mitochondrial Physiology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| |
Collapse
|
5
|
Ježek P, Holendová B, Jabůrek M, Tauber J, Dlasková A, Plecitá-Hlavatá L. The Pancreatic β-Cell: The Perfect Redox System. Antioxidants (Basel) 2021; 10:antiox10020197. [PMID: 33572903 PMCID: PMC7912581 DOI: 10.3390/antiox10020197] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 01/20/2021] [Accepted: 01/25/2021] [Indexed: 12/12/2022] Open
Abstract
Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H2O2 production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K+ channel (KATP) can only be closed when both ATP and H2O2 are elevated. Otherwise ATP would block KATP, while H2O2 would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed KATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca2+ channels. Open synergic NSCCs or Cl- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca2+-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca2+-influx (fortified by endoplasmic reticulum Ca2+). ATP plus H2O2 are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H2O2 diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.
Collapse
|
6
|
Hariharan A, Weir N, Robertson C, He L, Betsholtz C, Longden TA. The Ion Channel and GPCR Toolkit of Brain Capillary Pericytes. Front Cell Neurosci 2020; 14:601324. [PMID: 33390906 PMCID: PMC7775489 DOI: 10.3389/fncel.2020.601324] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/13/2020] [Indexed: 12/14/2022] Open
Abstract
Brain pericytes reside on the abluminal surface of capillaries, and their processes cover ~90% of the length of the capillary bed. These cells were first described almost 150 years ago (Eberth, 1871; Rouget, 1873) and have been the subject of intense experimental scrutiny in recent years, but their physiological roles remain uncertain and little is known of the complement of signaling elements that they employ to carry out their functions. In this review, we synthesize functional data with single-cell RNAseq screens to explore the ion channel and G protein-coupled receptor (GPCR) toolkit of mesh and thin-strand pericytes of the brain, with the aim of providing a framework for deeper explorations of the molecular mechanisms that govern pericyte physiology. We argue that their complement of channels and receptors ideally positions capillary pericytes to play a central role in adapting blood flow to meet the challenge of satisfying neuronal energy requirements from deep within the capillary bed, by enabling dynamic regulation of their membrane potential to influence the electrical output of the cell. In particular, we outline how genetic and functional evidence suggest an important role for Gs-coupled GPCRs and ATP-sensitive potassium (KATP) channels in this context. We put forth a predictive model for long-range hyperpolarizing electrical signaling from pericytes to upstream arterioles, and detail the TRP and Ca2+ channels and Gq, Gi/o, and G12/13 signaling processes that counterbalance this. We underscore critical questions that need to be addressed to further advance our understanding of the signaling topology of capillary pericytes, and how this contributes to their physiological roles and their dysfunction in disease.
Collapse
Affiliation(s)
- Ashwini Hariharan
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States
| | - Nick Weir
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States
| | - Colin Robertson
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States
| | - Liqun He
- Rudbeck Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Christer Betsholtz
- Rudbeck Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.,Department of Medicine Huddinge (MedH), Karolinska Institutet & Integrated Cardio Metabolic Centre, Huddinge, Sweden
| | - Thomas A Longden
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, United States
| |
Collapse
|
7
|
Taylor-Miller T, Houghton J, Munyard P, Kumar Y, Puvirajasinghe C, Giri D. Congenital hyperinsulinism due to compound heterozygous mutations in ABCC8 responsive to diazoxide therapy. J Pediatr Endocrinol Metab 2020; 33:671-674. [PMID: 32267248 DOI: 10.1515/jpem-2019-0457] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 02/18/2020] [Indexed: 11/15/2022]
Abstract
Background Congenital hyperinsulinism (CHI), a condition characterized by dysregulation of insulin secretion from the pancreatic β cells, remains one of the most common causes of hyperinsulinemic, hypoketotic hypoglycemia in the newborn period. Mutations in ABCC8 and KCNJ11 constitute the majority of genetic forms of CHI. Case presentation A term macrosomic male baby, birth weight 4.81 kg, born to non-consanguineous parents, presented on day 1 of life with severe and persistent hypoglycemia. The biochemical investigations confirmed a diagnosis of CHI. Diazoxide was started and progressively increased to 15 mg/kg/day to maintain normoglycemia. Sequence analysis identified compound heterozygous mutations in ABCC8 c.4076C>T and c.4119+1G>A inherited from the unaffected father and mother, respectively. The mutations are reported pathogenic. The patient is currently 7 months old with a sustained response to diazoxide. Conclusions Biallelic ABCC8 mutations are known to result in severe, diffuse, diazoxide-unresponsive hypoglycemia. We report a rare patient with CHI due to compound heterozygous mutations in ABCC8 responsive to diazoxide.
Collapse
Affiliation(s)
- Tashunka Taylor-Miller
- Department of Paediatric Endocrinology, Bristol Royal Hospital for Children, Bristol, UK
| | - Jayne Houghton
- Department of Molecular Genetics, University of Exeter Medical School, Exeter, UK
| | - Paul Munyard
- Department of Paediatrics, Royal Cornwall Hospitals NHS Trust, Truro, UK
| | - Yadlapalli Kumar
- Department of Paediatrics, Royal Cornwall Hospitals NHS Trust, Truro, UK
| | - Clinda Puvirajasinghe
- Great Ormond Street Hospital for Children NHS Foundation Trust, Rare and Inherited Disease Laboratory, North London Genomic Laboratory Hub, London, UK
| | - Dinesh Giri
- Consultant Paediatric Endocrinologist and Honorary Senior Lecturer, Bristol Royal Hospital for Children and University of Bristol, Bristol BS2 8BJ, UK.,Department of Paediatric Endocrinology, Department of Translational Health Sciences, University of Bristol, Bristol, UK
| |
Collapse
|
8
|
Huang Y, Hu D, Huang C, Nichols CG. Genetic Discovery of ATP-Sensitive K + Channels in Cardiovascular Diseases. Circ Arrhythm Electrophysiol 2020; 12:e007322. [PMID: 31030551 DOI: 10.1161/circep.119.007322] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The ATP-sensitive K+ (KATP) channels are hetero-octameric protein complexes comprising 4 pore-forming (Kir6.x) subunits and 4 regulatory sulfonylurea receptor (SURx) subunits. They are prominent in myocytes, pancreatic β cells, and neurons and link cellular metabolism with membrane excitability. Using genetically modified animals and genomic analysis in patients, recent studies have implicated certain ATP-sensitive K+ channel subtypes in physiological and pathological processes in a variety of cardiovascular diseases. In this review, we focus on the causal relationship between ATP-sensitive K+ channel activity and pathophysiology in the cardiovascular system, particularly from the perspective of genetic changes in human and animal models.
Collapse
Affiliation(s)
- Yan Huang
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Dan Hu
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Congxin Huang
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Colin G Nichols
- Center for the Investigation of Membrane Excitability Diseases and Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO (C.G.N.)
| |
Collapse
|
9
|
De Bernardis Murat C, Leão RM. A voltage-dependent depolarization induced by low external glucose in neurons of the nucleus of the tractus solitarius: interaction with K ATP channels. J Physiol 2019; 597:2515-2532. [PMID: 30927460 DOI: 10.1113/jp277729] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 03/21/2019] [Indexed: 12/18/2022] Open
Abstract
KEY POINTS Neurons from the brainstem nucleus of the tractus solitarius (NTS) participate in the counter-regulatory mechanisms in response to hypoglycaemia. ATP-sensitive potassium (KATP ) channels are expressed in NTS neurons, and are partially open at rest in normoglycaemic 5 mM glucose. In normoglycaemic conditions, most NTS neurons depolarize in response to low external glucose (0.5 mM), via a voltage-dependent mechanism. Conversely, most NTS neurons incubated in hyperglycaemic 10 mM glucose do not respond to low glucose due to a more positive resting membrane potential caused by the closure of KATP channels following increased intracellular metabolic ATP. Our findings show that in hyperglycaemic conditions, NTS neurons failed to sense rapid changes in external glucose, which could be related to hypoglycaemia-associated autonomic failure. ABSTRACT The nucleus of the tractus solitarius (NTS) is an integrative centre for autonomic counter-regulatory responses to hypoglycaemia. KATP channels link the metabolic status of the neuron to its excitability. Here we investigated the influence of KATP channels on the membrane potential of NTS neurons in normo- and hyperglycaemic external glucose concentrations, and after switching to a hypoglycaemic concentration, using in vitro electrophysiological recordings in brainstem slices. We found that in normoglycaemic (5 mM) glucose, tolbutamide, a KATP channel antagonist, depolarized the membrane of most neurons, and this effect was observed in more hyperpolarized neurons. All neurons hyperpolarized after pharmacological activation of KATP channels. Most NTS neurons depolarized in the presence of low glucose (0.5 mM), and this effect was only seen in hyperpolarized neurons. The effect of glucose was caused by a cationic current with a reversal potential around -50 mV. In the presence of hyperglycaemic glucose (10 mM), neurons were more depolarized, and fewer neurons responded to KATP blockage. Application of 0.5 mM glucose solution to these neurons depolarized the membrane only in more hyperpolarized neurons. We conclude that NTS neurons present with KATP channels open at rest in normoglycaemic conditions, and their membrane potential is affected by extracellular glucose. Moreover, NTS neurons depolarize the membrane in response to the application of a low glucose solution, but this effect is occluded by membrane depolarization triggered by KATP blockage. Our data suggest a homeostatic regulation of the membrane potential by external glucose, and a possible mechanism related to the hypoglycaemia-associated autonomic failure.
Collapse
Affiliation(s)
- Cahuê De Bernardis Murat
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Ricardo Mauricio Leão
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
| |
Collapse
|
10
|
Galcheva S, Demirbilek H, Al-Khawaga S, Hussain K. The Genetic and Molecular Mechanisms of Congenital Hyperinsulinism. Front Endocrinol (Lausanne) 2019; 10:111. [PMID: 30873120 PMCID: PMC6401612 DOI: 10.3389/fendo.2019.00111] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Accepted: 02/06/2019] [Indexed: 12/13/2022] Open
Abstract
Congenital hyperinsulinism (CHI) is a heterogenous and complex disorder in which the unregulated insulin secretion from pancreatic beta-cells leads to hyperinsulinaemic hypoglycaemia. The severity of hypoglycaemia varies depending on the underlying molecular mechanism and genetic defects. The genetic and molecular causes of CHI include defects in pivotal pathways regulating the secretion of insulin from the beta-cell. Broadly these genetic defects leading to unregulated insulin secretion can be grouped into four main categories. The first group consists of defects in the pancreatic KATP channel genes (ABCC8 and KCNJ11). The second and third categories of conditions are enzymatic defects (such as GDH, GCK, HADH) and defects in transcription factors (for example HNF1α, HNF4α) leading to changes in nutrient flux into metabolic pathways which converge on insulin secretion. Lastly, a large number of genetic syndromes are now linked to hyperinsulinaemic hypoglycaemia. As the molecular and genetic basis of CHI has expanded over the last few years, this review aims to provide an up-to-date knowledge on the genetic causes of CHI.
Collapse
Affiliation(s)
- Sonya Galcheva
- Department of Paediatrics, University Hospital St. Marina, Varna Medical University, Varna, Bulgaria
| | - Hüseyin Demirbilek
- Department of Paediatric Endocrinology, Hacettepe University Faculty of Medicine, Ankara, Turkey
| | - Sara Al-Khawaga
- Division of Endocrinology, Department of Paediatric Medicine, Sidra Medicine, Doha, Qatar
| | - Khalid Hussain
- Division of Endocrinology, Department of Paediatric Medicine, Sidra Medicine, Doha, Qatar
- *Correspondence: Khalid Hussain
| |
Collapse
|
11
|
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] [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.
Collapse
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
| |
Collapse
|
12
|
Tinker A, Aziz Q, Li Y, Specterman M. ATP‐Sensitive Potassium Channels and Their Physiological and Pathophysiological Roles. Compr Physiol 2018; 8:1463-1511. [DOI: 10.1002/cphy.c170048] [Citation(s) in RCA: 72] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
|
13
|
Page MM, Johnson JD. Mild Suppression of Hyperinsulinemia to Treat Obesity and Insulin Resistance. Trends Endocrinol Metab 2018; 29:389-399. [PMID: 29665988 DOI: 10.1016/j.tem.2018.03.018] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 03/23/2018] [Accepted: 03/27/2018] [Indexed: 12/14/2022]
Abstract
Insulin plays roles in lipid uptake, lipolysis, and lipogenesis, in addition to controlling blood glucose levels. Excessive circulating insulin is associated with adipose tissue expansion and obesity, yet a causal role for hyperinsulinemia in the development of mammalian obesity has proven controversial, with many researchers suggesting it as a consequence of insulin resistance. Recently, evidence that specifically reducing hyperinsulinemia can prevent and reverse obesity in animal models has been presented. Our experiments, and others in this field, question the current dogma that hyperinsulinemia is a response to obesity and/or insulin resistance. In this review, we discuss preclinical evidence in the context of the broader literature and speculate on the possibility of clinical translation of alternative approaches for treating obesity.
Collapse
Affiliation(s)
- Melissa M Page
- Life Sciences Institute Diabetes Research Group and the Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada; Louvain Institute of Biomolecular Science and Technology, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - James D Johnson
- Life Sciences Institute Diabetes Research Group and the Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada. https://twitter.com/JimJohnsonSci
| |
Collapse
|
14
|
Ligand binding and conformational changes of SUR1 subunit in pancreatic ATP-sensitive potassium channels. Protein Cell 2018; 9:553-567. [PMID: 29594720 PMCID: PMC5966361 DOI: 10.1007/s13238-018-0530-y] [Citation(s) in RCA: 76] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 03/14/2018] [Indexed: 01/19/2023] Open
Abstract
ATP-sensitive potassium channels (KATP) are energy sensors on the plasma membrane. By sensing the intracellular ADP/ATP ratio of β-cells, pancreatic KATP channels control insulin release and regulate metabolism at the whole body level. They are implicated in many metabolic disorders and diseases and are therefore important drug targets. Here, we present three structures of pancreatic KATP channels solved by cryo-electron microscopy (cryo-EM), at resolutions ranging from 4.1 to 4.5 Å. These structures depict the binding site of the antidiabetic drug glibenclamide, indicate how Kir6.2 (inward-rectifying potassium channel 6.2) N-terminus participates in the coupling between the peripheral SUR1 (sulfonylurea receptor 1) subunit and the central Kir6.2 channel, reveal the binding mode of activating nucleotides, and suggest the mechanism of how Mg-ADP binding on nucleotide binding domains (NBDs) drives a conformational change of the SUR1 subunit.
Collapse
|
15
|
Heeley N, Kirwan P, Darwish T, Arnaud M, Evans ML, Merkle FT, Reimann F, Gribble FM, Blouet C. Rapid sensing of l-leucine by human and murine hypothalamic neurons: Neurochemical and mechanistic insights. Mol Metab 2018; 10:14-27. [PMID: 29439854 PMCID: PMC5985239 DOI: 10.1016/j.molmet.2018.01.021] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 11/27/2022] Open
Abstract
Objective Dietary proteins are sensed by hypothalamic neurons and strongly influence multiple aspects of metabolic health, including appetite, weight gain, and adiposity. However, little is known about the mechanisms by which hypothalamic neural circuits controlling behavior and metabolism sense protein availability. The aim of this study is to characterize how neurons from the mediobasal hypothalamus respond to a signal of protein availability: the amino acid l-leucine. Methods We used primary cultures of post-weaning murine mediobasal hypothalamic neurons, hypothalamic neurons derived from human induced pluripotent stem cells, and calcium imaging to characterize rapid neuronal responses to physiological changes in extracellular l-Leucine concentration. Results A neurochemically diverse subset of both mouse and human hypothalamic neurons responded rapidly to l-leucine. Consistent with l-leucine's anorexigenic role, we found that 25% of mouse MBH POMC neurons were activated by l-leucine. 10% of MBH NPY neurons were inhibited by l-leucine, and leucine rapidly reduced AGRP secretion, providing a mechanism for the rapid leucine-induced inhibition of foraging behavior in rodents. Surprisingly, none of the candidate mechanisms previously implicated in hypothalamic leucine sensing (KATP channels, mTORC1 signaling, amino-acid decarboxylation) were involved in the acute activity changes produced by l-leucine. Instead, our data indicate that leucine-induced neuronal activation involves a plasma membrane Ca2+ channel, whereas leucine-induced neuronal inhibition is mediated by inhibition of a store-operated Ca2+ current. Conclusions A subset of neurons in the mediobasal hypothalamus rapidly respond to physiological changes in extracellular leucine concentration. Leucine can produce both increases and decreases in neuronal Ca2+ concentrations in a neurochemically-diverse group of neurons, including some POMC and NPY/AGRP neurons. Our data reveal that leucine can signal through novel mechanisms to rapidly affect neuronal activity. A neurochemically diverse group of mouse and human hypothalamic neurons rapidly sense and respond to l-leucine. Leucine can produce neuronal activation or neuronal inhibition via distinct and novel Ca2+ signaling mechanisms. Leucine activates 25% ARH POMC neurons. Leucine inhibits 10% ARH NPY/AGRP neurons and reduces AGRP secretion from fasted mediobasal hypothalamic slices.
Collapse
Affiliation(s)
- Nicholas Heeley
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Peter Kirwan
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Tamana Darwish
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Marion Arnaud
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Mark L Evans
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Florian T Merkle
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Frank Reimann
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Fiona M Gribble
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK
| | - Clemence Blouet
- MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK.
| |
Collapse
|
16
|
Rorsman P, Ashcroft FM. Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men. Physiol Rev 2018; 98:117-214. [PMID: 29212789 PMCID: PMC5866358 DOI: 10.1152/physrev.00008.2017] [Citation(s) in RCA: 424] [Impact Index Per Article: 70.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 05/30/2017] [Accepted: 06/18/2017] [Indexed: 12/14/2022] Open
Abstract
The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca2+ concentration and initiation of Ca2+-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.
Collapse
Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| |
Collapse
|
17
|
Pashynska V, Stepanian S, Gömöry Á, Vékey K, Adamowicz L. New cardioprotective agent flokalin and its supramolecular complexes with target amino acids: An integrated mass-spectrometry and quantum-chemical study. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.06.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
18
|
Abstract
Pancreatic islet β cells secrete insulin in response to nutrient secretagogues, like glucose, dependent on calcium influx and nutrient metabolism. One of the most intriguing qualities of β cells is their ability to use metabolism to amplify the amount of secreted insulin independent of further alterations in intracellular calcium. Many years studying this amplifying process have shaped our current understanding of β cell stimulus-secretion coupling; yet, the exact mechanisms of amplification have been elusive. Recent studies utilizing metabolomics, computational modeling, and animal models have progressed our understanding of the metabolic amplifying pathway of insulin secretion from the β cell. New approaches will be discussed which offer in-roads to a more complete model of β cell function. The development of β cell therapeutics may be aided by such a model, facilitating the targeting of aspects of the metabolic amplifying pathway which are unique to the β cell.
Collapse
Affiliation(s)
- Michael A Kalwat
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, United States.
| | - Melanie H Cobb
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, United States
| |
Collapse
|
19
|
Borschel WF, Wang S, Lee S, Nichols CG. Control of Kir channel gating by cytoplasmic domain interface interactions. J Gen Physiol 2017; 149:561-576. [PMID: 28389584 PMCID: PMC5412532 DOI: 10.1085/jgp.201611719] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 12/29/2016] [Accepted: 03/01/2017] [Indexed: 12/19/2022] Open
Abstract
The pore-forming unit of ATP-sensitive K channels is composed of four Kir6.2 subunits. Borschel et al. show that salt bridges between the cytoplasmic domain of adjacent Kir6.2 subunits determine the degree to which channels inactivate after removal of ATP. Inward rectifier potassium (Kir) channels are expressed in almost all mammalian tissues and play critical roles in the control of excitability. Pancreatic ATP-sensitive K (KATP) channels are key regulators of insulin secretion and comprise Kir6.2 subunits coupled to sulfonylurea receptors. Because these channels are reversibly inhibited by cytoplasmic ATP, they link cellular metabolism with membrane excitability. Loss-of-function mutations in the pore-forming Kir6.2 subunit cause congenital hyperinsulinism as a result of diminished channel activity. Here, we show that several disease mutations, which disrupt intersubunit salt bridges at the interface of the cytoplasmic domains (CD-I) of adjacent subunits, induce loss of channel activity via a novel channel behavior: after ATP removal, channels open but then rapidly inactivate. Re-exposure to inhibitory ATP causes recovery from this inactivation. Inactivation can be abolished by application of phosphatidylinositol-4,5-bisphosphate (PIP2) to the cytoplasmic face of the membrane, an effect that can be explained by a simple kinetic model in which PIP2 binding competes with the inactivation process. Kir2.1 channels contain homologous salt bridges, and we find that mutations that disrupt CD-I interactions in Kir2.1 also reduce channel activity and PIP2 sensitivity. Kir2.1 channels also contain an additional CD-I salt bridge that is not present in Kir6.2 channels. Introduction of this salt bridge into Kir6.2 partially rescues inactivating mutants from the phenotype. These results indicate that the stability of the intersubunit CD-I is a major determinant of the inactivation process in Kir6.2 and may control gating in other Kir channels.
Collapse
Affiliation(s)
- William F Borschel
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Shizhen Wang
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Sunjoo Lee
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110.,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 .,Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| |
Collapse
|
20
|
Emfinger CH, Welscher A, Yan Z, Wang Y, Conway H, Moss JB, Moss LG, Remedi MS, Nichols CG. Expression and function of ATP-dependent potassium channels in zebrafish islet β-cells. ROYAL SOCIETY OPEN SCIENCE 2017; 4:160808. [PMID: 28386438 PMCID: PMC5367309 DOI: 10.1098/rsos.160808] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 01/06/2017] [Indexed: 05/04/2023]
Abstract
ATP-sensitive potassium channels (KATP channels) are critical nutrient sensors in many mammalian tissues. In the pancreas, KATP channels are essential for coupling glucose metabolism to insulin secretion. While orthologous genes for many components of metabolism-secretion coupling in mammals are present in lower vertebrates, their expression, functionality and ultimate impact on body glucose homeostasis are unclear. In this paper, we demonstrate that zebrafish islet β-cells express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. We further show that pharmacological activation of native zebrafish KATP using diazoxide, a specific KATP channel opener, is sufficient to disturb glucose tolerance in adult zebrafish. That β-cell KATP channel expression and function are conserved between zebrafish and mammals illustrates the evolutionary conservation of islet metabolic sensing from fish to humans, and lends relevance to the use of zebrafish to model islet glucose sensing and diseases of membrane excitability such as neonatal diabetes.
Collapse
Affiliation(s)
- Christopher H. Emfinger
- Department of Cell Biology and Physiology, Washington University in St Louis, St Louis, MO, USA
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| | - Alecia Welscher
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| | - Zihan Yan
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| | - Yixi Wang
- Department of Cell Biology and Physiology, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| | - Hannah Conway
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University in St Louis, St Louis, MO, USA
| | - Jennifer B. Moss
- Division of Endocrinology, Metabolism, and Nutrition and DMPI, Duke University Medical Center, Durham, NC, USA
| | - Larry G. Moss
- Division of Endocrinology, Metabolism, and Nutrition and DMPI, Duke University Medical Center, Durham, NC, USA
| | - Maria S. Remedi
- Department of Cell Biology and Physiology, Washington University in St Louis, St Louis, MO, USA
- Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology, Washington University in St Louis, St Louis, MO, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, MO, USA
| |
Collapse
|
21
|
Vedovato N, Ashcroft FM, Puljung MC. The Nucleotide-Binding Sites of SUR1: A Mechanistic Model. Biophys J 2016; 109:2452-2460. [PMID: 26682803 PMCID: PMC4699857 DOI: 10.1016/j.bpj.2015.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels comprise four pore-forming Kir6.2 subunits and four modulatory sulfonylurea receptor (SUR) subunits. The latter belong to the ATP-binding cassette family of transporters. KATP channels are inhibited by ATP (or ADP) binding to Kir6.2 and activated by Mg-nucleotide interactions with SUR. This dual regulation enables the KATP channel to couple the metabolic state of a cell to its electrical excitability and is crucial for the KATP channel’s role in regulating insulin secretion, cardiac and neuronal excitability, and vascular tone. Here, we review the regulation of the KATP channel by adenine nucleotides and present an equilibrium allosteric model for nucleotide activation and inhibition. The model can account for many experimental observations in the literature and provides testable predictions for future experiments.
Collapse
Affiliation(s)
- Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
| |
Collapse
|
22
|
Esterson YB, Carey M, Boucai L, Goyal A, Raghavan P, Zhang K, Mehta D, Feng D, Wu L, Kehlenbrink S, Koppaka S, Kishore P, Hawkins M. Central Regulation of Glucose Production May Be Impaired in Type 2 Diabetes. Diabetes 2016; 65:2569-79. [PMID: 27207526 PMCID: PMC5001178 DOI: 10.2337/db15-1465] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 04/19/2016] [Indexed: 12/21/2022]
Abstract
The challenges of achieving optimal glycemic control in type 2 diabetes highlight the need for new therapies. Inappropriately elevated endogenous glucose production (EGP) is the main source of hyperglycemia in type 2 diabetes. Because activation of central ATP-sensitive potassium (KATP) channels suppresses EGP in nondiabetic rodents and humans, this study examined whether type 2 diabetic humans and rodents retain central regulation of EGP. The KATP channel activator diazoxide was administered in a randomized, placebo-controlled crossover design to eight type 2 diabetic subjects and seven age- and BMI-matched healthy control subjects. Comprehensive measures of glucose turnover and insulin sensitivity were performed during euglycemic pancreatic clamp studies following diazoxide and placebo administration. Complementary rodent clamp studies were performed in Zucker Diabetic Fatty rats. In type 2 diabetic subjects, extrapancreatic KATP channel activation with diazoxide under fixed hormonal conditions failed to suppress EGP, whereas matched control subjects demonstrated a 27% reduction in EGP (P = 0.002) with diazoxide. Diazoxide also failed to suppress EGP in diabetic rats. These results suggest that suppression of EGP by central KATP channel activation may be lost in type 2 diabetes. Restoration of central regulation of glucose metabolism could be a promising therapeutic target to reduce hyperglycemia in type 2 diabetes.
Collapse
Affiliation(s)
- Yonah B Esterson
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Michelle Carey
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Laura Boucai
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Akankasha Goyal
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Pooja Raghavan
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Kehao Zhang
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Deeksha Mehta
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Daorong Feng
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Licheng Wu
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Sylvia Kehlenbrink
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Sudha Koppaka
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Preeti Kishore
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| | - Meredith Hawkins
- Diabetes Research and Training Center and Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY
| |
Collapse
|
23
|
Vetterli L, Carobbio S, Frigerio F, Karaca M, Maechler P. The Amplifying Pathway of the β-Cell Contributes to Diet-induced Obesity. J Biol Chem 2016; 291:13063-75. [PMID: 27137930 DOI: 10.1074/jbc.m115.707448] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Indexed: 12/24/2022] Open
Abstract
Efficient energy storage in adipose tissues requires optimal function of the insulin-producing β-cell, whereas its dysfunction promotes diabetes. The associated paradox related to β-cell efficiency is that excessive accumulation of fat in adipose tissue predisposes for type 2 diabetes. Insulin exocytosis is regulated by intracellular metabolic signal transduction, with glutamate dehydrogenase playing a key role in the amplification of the secretory response. Here, we used mice with β-cell-selective glutamate dehydrogenase deletion (βGlud1(-/-)), lacking an amplifying pathway of insulin secretion. As opposed to control mice, βGlud1(-/-) animals fed a high calorie diet maintained glucose tolerance and did not develop diet-induced obesity. Islets of βGlud1(-/-) mice did not increase their secretory response upon high calorie feeding, as did islets of control mice. Inhibited adipose tissue expansion observed in knock-out mice correlated with lower expression of genes responsible for adipogenesis. Rather than being efficiently stored, lipids were consumed at a higher rate in βGlud1(-/-) mice compared with controls, in particular during food intake periods. These results show that reduced β-cell function prior to high calorie feeding prevented diet-induced obesity.
Collapse
Affiliation(s)
- Laurène Vetterli
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Stefania Carobbio
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Francesca Frigerio
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Melis Karaca
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| | - Pierre Maechler
- From the Department of Cell Physiology and Metabolism and Faculty Diabetes Center, Geneva University Medical Centre, 1211 Geneva 4, Switzerland
| |
Collapse
|
24
|
Gao Z, Sierra A, Zhu Z, Koganti SRK, Subbotina E, Maheshwari A, Anderson ME, Zingman LV, Hodgson-Zingman DM. Loss of ATP-Sensitive Potassium Channel Surface Expression in Heart Failure Underlies Dysregulation of Action Potential Duration and Myocardial Vulnerability to Injury. PLoS One 2016; 11:e0151337. [PMID: 26964104 PMCID: PMC4786327 DOI: 10.1371/journal.pone.0151337] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Accepted: 02/26/2016] [Indexed: 11/18/2022] Open
Abstract
The search for new approaches to treatment and prevention of heart failure is a major challenge in medicine. The adenosine triphosphate-sensitive potassium (KATP) channel has been long associated with the ability to preserve myocardial function and viability under stress. High surface expression of membrane KATP channels ensures a rapid energy-sparing reduction in action potential duration (APD) in response to metabolic challenges, while cellular signaling that reduces surface KATP channel expression blunts APD shortening, thus sacrificing energetic efficiency in exchange for greater cellular calcium entry and increased contractile force. In healthy hearts, calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylates the Kir6.2 KATP channel subunit initiating a cascade responsible for KATP channel endocytosis. Here, activation of CaMKII in a transaortic banding (TAB) model of heart failure is coupled with a 35–40% reduction in surface expression of KATP channels compared to hearts from sham-operated mice. Linkage between KATP channel expression and CaMKII is verified in isolated cardiomyocytes in which activation of CaMKII results in downregulation of KATP channel current. Accordingly, shortening of monophasic APD is slowed in response to hypoxia or heart rate acceleration in failing compared to non-failing hearts, a phenomenon previously shown to result in significant increases in oxygen consumption. Even in the absence of coronary artery disease, failing myocardium can be further injured by ischemia due to a mismatch between metabolic supply and demand. Ischemia-reperfusion injury, following ischemic preconditioning, is diminished in hearts with CaMKII inhibition compared to wild-type hearts and this advantage is largely eliminated when myocardial KATP channel expression is absent, supporting that the myocardial protective benefit of CaMKII inhibition in heart failure may be substantially mediated by KATP channels. Recognition of CaMKII-dependent downregulation of KATP channel expression as a mechanism for vulnerability to injury in failing hearts points to strategies targeting this interaction for potential preventives or treatments.
Collapse
Affiliation(s)
- Zhan Gao
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Ana Sierra
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Zhiyong Zhu
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Siva Rama Krishna Koganti
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Ekaterina Subbotina
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Ankit Maheshwari
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Mark E. Anderson
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- François Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa, United States of America
| | - Leonid V. Zingman
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- François Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa, United States of America
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States of America
- Veterans Affairs Medical Center, Iowa City, Iowa, United States of America
| | - Denice M. Hodgson-Zingman
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- François Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
| |
Collapse
|
25
|
Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
Collapse
Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| |
Collapse
|
26
|
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] [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.
Collapse
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
| |
Collapse
|
27
|
Fan ZC, Ni JW, Yang L, Hu LY, Ma SM, Mei M, Sun BJ, Wang HJ, Zhou WH. Uncovering the molecular pathogenesis of congenital hyperinsulinism by panel gene sequencing in 32 Chinese patients. Mol Genet Genomic Med 2015; 3:526-36. [PMID: 26740944 PMCID: PMC4694131 DOI: 10.1002/mgg3.162] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 06/05/2015] [Accepted: 06/09/2015] [Indexed: 01/06/2023] Open
Abstract
Congenital hyperinsulinism (CHI) has been mostly associated with mutations in seven major genes. We retrospectively reviewed a cohort of 32 patients with CHI. Extensive mutational analysis (ABCC8,KCNJ11,GCK,GLUD1,HADH,HNF4A, and UCP2) was performed on Ion torrent platform, which could analyze hundreds of genes simultaneously with ultrahigh-multiplex PCR using up to 6144 primer pairs in a single primer pool and address time-sensitive samples with single-day assays, from samples to annotated variants, to identify the genetic etiology of this disease. Thirty-seven sequence changes were identified, including in ABCC8/KCNJ11 (n = 25, 65.7%), GCK (n = 2), HNF4A (n = 3), GLUD1 (n = 2), HADH (n = 4), and UCP2 (n = 1); these mutations included 14 disease-causing mutations, eight rare SNPs, 14 common SNPs, and one novel mutation. Mutations were identified in 21 of 32 patients (65.6%). Among the patients with an identified mutation, 14 had mutations in ABCC8, one of which was combined with a GLUD1 mutation. Four patients had mutations in KCNJ11, 1 had a GCK mutation, 1 had a mutation in HADH, and two had a mutation in HNF4A. Among the 32 patients, the age at the onset of hyperinsulinemia ranged from the neonatal period to 1 year of age; five patients underwent a pancreatectomy due to intractable hyperinsulinemia. This study describes novel and previously identified mutations in patients with CHI. The spectrum of mutations in CHI patients represents an important tool for the diagnosis and prognosis of CHI patients in the Chinese population as well as for the genetic counseling of CHI families.
Collapse
Affiliation(s)
- Zi-Chuan Fan
- Department of NeonatologyChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Birth DefectChildren's Hospital of Fudan UniversityShanghaiChina
| | - Jin-Wen Ni
- Department of Neonatology Children's Hospital of Fudan University Shanghai China
| | - Lin Yang
- Key Laboratory of Birth DefectChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Neonatal DiseasesMinistry of HealthChildren's HospitalFudan UniversityShanghaiChina
| | - Li-Yuan Hu
- Department of Neonatology Children's Hospital of Fudan University Shanghai China
| | - Si-Min Ma
- Department of Neonatology Children's Hospital of Fudan University Shanghai China
| | - Mei Mei
- Department of Neonatology Children's Hospital of Fudan University Shanghai China
| | - Bi-Jun Sun
- Department of NeonatologyChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Birth DefectChildren's Hospital of Fudan UniversityShanghaiChina
| | - Hui-Jun Wang
- Key Laboratory of Birth DefectChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Neonatal DiseasesMinistry of HealthChildren's HospitalFudan UniversityShanghaiChina
| | - Wen-Hao Zhou
- Department of NeonatologyChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Birth DefectChildren's Hospital of Fudan UniversityShanghaiChina; Key Laboratory of Neonatal DiseasesMinistry of HealthChildren's HospitalFudan UniversityShanghaiChina
| |
Collapse
|
28
|
Nessa A, Aziz QH, Thomas AM, Harmer SC, Tinker A, Hussain K. Molecular mechanisms of congenital hyperinsulinism due to autosomal dominant mutations in ABCC8. Hum Mol Genet 2015; 24:5142-53. [PMID: 26092864 DOI: 10.1093/hmg/ddv233] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 06/16/2015] [Indexed: 11/12/2022] Open
Abstract
Congenital Hyperinsulinism (CHI) is a rare heterogeneous disease characterized by unregulated insulin secretion. Dominant mutations in ABCC8 causing medically unresponsive CHI have been reported; however, the molecular mechanisms are not clear. The molecular basis of medically unresponsive CHI due to dominant ABCC8 mutations has been studied in 10 patients, who were medically unresponsive to diazoxide (DZX), and nine of whom required a near-total pancreatectomy, and one partial pancreatectomy. DNA sequencing revealed seven dominant inactivating heterozygous missense mutations in ABCC8, including one novel and six previously reported but uncharacterized mutations. Two groups of mutations with different cellular mechanisms were characterized. Mutations in the transmembrane domain (TMD) were more responsive to channel activators such as DZX, MgADP and metabolic inhibition. The trafficking analysis has shown that nucleotide-binding domain two (NBD2) mutations are not retained in the endoplasmic reticulum (ER) and are present on the membrane. However, the TMD mutations were retained in the ER. D1506E was the most severe SUR1-NBD2 mutation. Homologous expression of D1506E revealed a near absence of KATP currents in the presence of DZX and intracellular MgADP. Heterozygous expression of D1506E showed a strong dominant-negative effect on SUR1\Kir6.2 currents. Overall, we define two groups of mutation with different cellular mechanisms. In the first group, channel complexes with mutations in NBD2 of SUR1 traffic normally but are unable to be activated by MgADP. In the second group, channels mutations in the TMD of SUR1 are retained in the ER and have variable functional impairment.
Collapse
Affiliation(s)
- Azizun Nessa
- Genetics and Genomic Medicine, UCL Institute of Child Health, London WC1N 1EH, UK
| | - Qadeer H Aziz
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK and
| | - Alison M Thomas
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK and
| | - Stephen C Harmer
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK and
| | - Andrew Tinker
- The Heart Centre, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK and
| | - Khalid Hussain
- Genetics and Genomic Medicine, UCL Institute of Child Health, London WC1N 1EH, UK, Genetics and Genomic Medicine, UCL Institute of Child Health, London Centre for Paediatric Endocrinology and Metabolism, Great Ormond Street Hospital for Children NHS, London WC1N 1EH, UK
| |
Collapse
|
29
|
Tinker A, Aziz Q, Thomas A. The role of ATP-sensitive potassium channels in cellular function and protection in the cardiovascular system. Br J Pharmacol 2014; 171:12-23. [PMID: 24102106 DOI: 10.1111/bph.12407] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 07/30/2013] [Accepted: 08/26/2013] [Indexed: 12/14/2022] Open
Abstract
ATP-sensitive potassium channels (K(ATP)) are widely distributed and present in a number of tissues including muscle, pancreatic beta cells and the brain. Their activity is regulated by adenine nucleotides, characteristically being activated by falling ATP and rising ADP levels. Thus, they link cellular metabolism with membrane excitability. Recent studies using genetically modified mice and genomic studies in patients have implicated K(ATP) channels in a number of physiological and pathological processes. In this review, we focus on their role in cellular function and protection particularly in the cardiovascular system.
Collapse
Affiliation(s)
- Andrew Tinker
- William Harvey Heart Centre, Barts and The London School of Medicine and Dentistry, London, UK
| | | | | |
Collapse
|
30
|
Zhu Z, Sierra A, Burnett CML, Chen B, Subbotina E, Koganti SRK, Gao Z, Wu Y, Anderson ME, Song LS, Goldhamer DJ, Coetzee WA, Hodgson-Zingman DM, Zingman LV. Sarcolemmal ATP-sensitive potassium channels modulate skeletal muscle function under low-intensity workloads. ACTA ACUST UNITED AC 2013; 143:119-34. [PMID: 24344248 PMCID: PMC3874572 DOI: 10.1085/jgp.201311063] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
ATP-sensitive potassium (KATP) channels have the unique ability to adjust membrane excitability and functions in accordance with the metabolic status of the cell. Skeletal muscles are primary sites of activity-related energy consumption and have KATP channels expressed in very high density. Previously, we demonstrated that transgenic mice with skeletal muscle–specific disruption of KATP channel function consume more energy than wild-type littermates. However, how KATP channel activation modulates skeletal muscle resting and action potentials under physiological conditions, particularly low-intensity workloads, and how this can be translated to muscle energy expenditure are yet to be determined. Here, we developed a technique that allows evaluation of skeletal muscle excitability in situ, with minimal disruption of the physiological environment. Isometric twitching of the tibialis anterior muscle at 1 Hz was used as a model of low-intensity physical activity in mice with normal and genetically disrupted KATP channel function. This workload was sufficient to induce KATP channel opening, resulting in membrane hyperpolarization as well as reduction in action potential overshoot and duration. Loss of KATP channel function resulted in increased calcium release and aggravated activity-induced heat production. Thus, this study identifies low-intensity workload as a trigger for opening skeletal muscle KATP channels and establishes that this coupling is important for regulation of myocyte function and thermogenesis. These mechanisms may provide a foundation for novel strategies to combat metabolic derangements when energy conservation or dissipation is required.
Collapse
Affiliation(s)
- Zhiyong Zhu
- Department of Internal Medicine and 2 Fraternal Order of Eagles Diabetes Research Center, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Abstract
ATP-sensitive potassium channels (K(ATP) channels) link cell metabolism to electrical activity by controlling the cell membrane potential. They participate in many physiological processes but have a particularly important role in systemic glucose homeostasis by regulating hormone secretion from pancreatic islet cells. Glucose-induced closure of K(ATP) channels is crucial for insulin secretion. Emerging data suggest that K(ATP) channels also play a key part in glucagon secretion, although precisely how they do so remains controversial. This Review highlights the role of K(ATP) channels in insulin and glucagon secretion. We discuss how K(ATP) channels might contribute not only to the initiation of insulin release but also to the graded stimulation of insulin secretion that occurs with increasing glucose concentrations. The various hypotheses concerning the role of K(ATP) channels in glucagon release are also reviewed. Furthermore, we illustrate how mutations in K(ATP) channel genes can cause hyposecretion or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, and how defective metabolic regulation of the channel may underlie the hypoinsulinaemia and the hyperglucagonaemia that characterize type 2 diabetes mellitus. Finally, we outline how sulphonylureas, which inhibit K(ATP) channels, stimulate insulin secretion in patients with neonatal diabetes mellitus or type 2 diabetes mellitus, and suggest their potential use to target the glucagon secretory defects found in diabetes mellitus.
Collapse
Affiliation(s)
- Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
| | | |
Collapse
|
32
|
Proks P, de Wet H, Ashcroft FM. Molecular mechanism of sulphonylurea block of K(ATP) channels carrying mutations that impair ATP inhibition and cause neonatal diabetes. Diabetes 2013; 62:3909-19. [PMID: 23835339 PMCID: PMC3806600 DOI: 10.2337/db13-0531] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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.
Collapse
|
33
|
Targeting microglial K(ATP) channels to treat neurodegenerative diseases: a mitochondrial issue. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:194546. [PMID: 23844272 PMCID: PMC3697773 DOI: 10.1155/2013/194546] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 03/26/2013] [Accepted: 05/08/2013] [Indexed: 12/11/2022]
Abstract
Neurodegeneration is a complex process involving different cell types and neurotransmitters. A common characteristic of neurodegenerative disorders is the occurrence of a neuroinflammatory reaction in which cellular processes involving glial cells, mainly microglia and astrocytes, are activated in response to neuronal death. Microglia do not constitute a unique cell population but rather present a range of phenotypes closely related to the evolution of neurodegeneration. In a dynamic equilibrium with the lesion microenvironment, microglia phenotypes cover from a proinflammatory activation state to a neurotrophic one directly involved in cell repair and extracellular matrix remodeling. At each moment, the microglial phenotype is likely to depend on the diversity of signals from the environment and of its response capacity. As a consequence, microglia present a high energy demand, for which the mitochondria activity determines the microglia participation in the neurodegenerative process. As such, modulation of microglia activity by controlling microglia mitochondrial activity constitutes an innovative approach to interfere in the neurodegenerative process. In this review, we discuss the mitochondrial KATP channel as a new target to control microglia activity, avoid its toxic phenotype, and facilitate a positive disease outcome.
Collapse
|
34
|
Zhou Q, Pratt EB, Shyng SL. Engineered Kir6.2 mutations that correct the trafficking defect of K(ATP) channels caused by specific SUR1 mutations. Channels (Austin) 2013; 7:313-7. [PMID: 23695995 DOI: 10.4161/chan.25003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
KATP channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. The molecular interactions between SUR1 and Kir6.2 that govern channel gating and biogenesis are incompletely understood. In a recent study, we showed that a SUR1 and Kir6.2 mutation pair, E203K-SUR1 and Q52E-Kir6.2, at the SUR1/Kir6.2 interface near the plasma membrane increases the ATP-sensitivity of the channel by nearly 100-fold. Here, we report the finding that the same mutation pair also suppresses channel folding/trafficking defects caused by select SUR1 mutations in the first transmembrane domain of SUR1. Analysis of the contributions from individual mutations, however, revealed that the correction effect is attributed largely to Q52E-Kir6.2 alone. Moreover, the correction is dependent on the negative charge of the substituting amino acid at the Q52 position in Kir6.2. Our study demonstrates for the first time that engineered mutations in Kir6.2 can correct the biogenesis defect caused by specific mutations in the SUR1 subunit.
Collapse
Affiliation(s)
- Qing Zhou
- Department of Biochemistry and Molecular Biology; Oregon Health & Science University; Portland, OR USA
| | | | | |
Collapse
|
35
|
Kapoor RR, Flanagan SE, Arya VB, Shield JP, Ellard S, Hussain K. Clinical and molecular characterisation of 300 patients with congenital hyperinsulinism. Eur J Endocrinol 2013; 168:557-64. [PMID: 23345197 PMCID: PMC3599069 DOI: 10.1530/eje-12-0673] [Citation(s) in RCA: 158] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Congenital hyperinsulinism (CHI) is a clinically heterogeneous condition. Mutations in eight genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, HNF4A and HNF1A) are known to cause CHI. AIM To characterise the clinical and molecular aspects of a large cohort of patients with CHI. METHODOLOGY Three hundred patients were recruited and clinical information was collected before genotyping. ABCC8 and KCNJ11 genes were analysed in all patients. Mutations in GLUD1, HADH, GCK and HNF4A genes were sought in patients with diazoxide-responsive CHI with hyperammonaemia (GLUD1), raised 3-hydroxybutyrylcarnitine and/or consanguinity (HADH), positive family history (GCK) or when CHI was diagnosed within the first week of life (HNF4A). RESULTS Mutations were identified in 136/300 patients (45.3%). Mutations in ABCC8/KCNJ11 were the commonest genetic cause identified (n=109, 36.3%). Among diazoxide-unresponsive patients (n=105), mutations in ABCC8/KCNJ11 were identified in 92 (87.6%) patients, of whom 63 patients had recessively inherited mutations while four patients had dominantly inherited mutations. A paternal mutation in the ABCC8/KCNJ11 genes was identified in 23 diazoxide-unresponsive patients, of whom six had diffuse disease. Among the diazoxide-responsive patients (n=183), mutations were identified in 41 patients (22.4%). These include mutations in ABCC8/KCNJ11 (n=15), HNF4A (n=7), GLUD1 (n=16) and HADH (n=3). CONCLUSIONS A genetic diagnosis was made for 45.3% of patients in this large series. Mutations in the ABCC8 gene were the commonest identifiable cause. The vast majority of patients with diazoxide-responsive CHI (77.6%) had no identifiable mutations, suggesting other genetic and/or environmental mechanisms.
Collapse
Affiliation(s)
| | - Sarah E Flanagan
- Institute of Biomedical and Clinical Science, University of Exeter Medical SchoolExeter, EX2 5DWUK
| | | | - Julian P Shield
- Department of Child Health, Bristol Royal Hospital for ChildrenBristol, BS2 8BJUK
| | - Sian Ellard
- Institute of Biomedical and Clinical Science, University of Exeter Medical SchoolExeter, EX2 5DWUK
| | - Khalid Hussain
- (Correspondence should be addressed to K Hussain who is now at Molecular Genetics Unit, Developmental Endocrinology Research Group, Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK; )
| |
Collapse
|
36
|
Woo SK, Kwon MS, Ivanov A, Gerzanich V, Simard JM. The sulfonylurea receptor 1 (Sur1)-transient receptor potential melastatin 4 (Trpm4) channel. J Biol Chem 2012; 288:3655-67. [PMID: 23255597 PMCID: PMC3561583 DOI: 10.1074/jbc.m112.428219] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The sulfonylurea receptor 1 (Sur1)-NCCa-ATP channel plays a central role in necrotic cell death in central nervous system (CNS) injury, including ischemic stroke, and traumatic brain and spinal cord injury. Here, we show that Sur1-NCCa-ATP channels are formed by co-assembly of Sur1 and transient receptor potential melastatin 4 (Trpm4). Co-expression of Sur1 and Trpm4 yielded Sur1-Trpm4 heteromers, as shown in experiments with Förster resonance energy transfer (FRET) and co-immunoprecipitation. Co-expression of Sur1 and Trpm4 also yielded functional Sur1-Trpm4 channels with biophysical properties of Trpm4 and pharmacological properties of Sur1. Co-assembly with Sur1 doubled the affinity of Trpm4 for calmodulin and doubled its sensitivity to intracellular calcium. Experiments with FRET and co-immunoprecipitation showed de novo appearance of Sur1-Trpm4 heteromers after spinal cord injury in rats. Our findings depart from the long-held view of an exclusive association between Sur1 and KATP channels and reveal an unexpected molecular partnership with far-ranging implications for CNS injury.
Collapse
Affiliation(s)
- Seung Kyoon Woo
- Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | | | | | | | | |
Collapse
|
37
|
Sierra A, Zhu Z, Sapay N, Sharotri V, Kline CF, Luczak ED, Subbotina E, Sivaprasadarao A, Snyder PM, Mohler PJ, Anderson ME, Vivaudou M, Zingman LV, Hodgson-Zingman DM. Regulation of cardiac ATP-sensitive potassium channel surface expression by calcium/calmodulin-dependent protein kinase II. J Biol Chem 2012; 288:1568-81. [PMID: 23223335 DOI: 10.1074/jbc.m112.429548] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Cardiac ATP-sensitive potassium (K(ATP)) channels are key sensors and effectors of the metabolic status of cardiomyocytes. Alteration in their expression impacts their effectiveness in maintaining cellular energy homeostasis and resistance to injury. We sought to determine how activation of calcium/calmodulin-dependent protein kinase II (CaMKII), a central regulator of calcium signaling, translates into reduced membrane expression and current capacity of cardiac K(ATP) channels. We used real-time monitoring of K(ATP) channel current density, immunohistochemistry, and biotinylation studies in isolated hearts and cardiomyocytes from wild-type and transgenic mice as well as HEK cells expressing wild-type and mutant K(ATP) channel subunits to track the dynamics of K(ATP) channel surface expression. Results showed that activation of CaMKII triggered dynamin-dependent internalization of K(ATP) channels. This process required phosphorylation of threonine at 180 and 224 and an intact (330)YSKF(333) endocytosis motif of the K(ATP) channel Kir6.2 pore-forming subunit. A molecular model of the μ2 subunit of the endocytosis adaptor protein, AP2, complexed with Kir6.2 predicted that μ2 docks by interaction with (330)YSKF(333) and Thr-180 on one and Thr-224 on the adjacent Kir6.2 subunit. Phosphorylation of Thr-180 and Thr-224 would favor interactions with the corresponding arginine- and lysine-rich loops on μ2. We concluded that calcium-dependent activation of CaMKII results in phosphorylation of Kir6.2, which promotes endocytosis of cardiac K(ATP) channel subunits. This mechanism couples the surface expression of cardiac K(ATP) channels with calcium signaling and reveals new targets to improve cardiac energy efficiency and stress resistance.
Collapse
Affiliation(s)
- Ana Sierra
- Department of Internal Medicine, University of Iowa, Carver College of Medicine, Iowa City, Iowa 52242, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
38
|
Mohamed Z, Arya VB, Hussain K. Hyperinsulinaemic hypoglycaemia:genetic mechanisms, diagnosis and management. J Clin Res Pediatr Endocrinol 2012; 4:169-81. [PMID: 23032149 PMCID: PMC3537282 DOI: 10.4274/jcrpe.821] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Hyperinsulinaemic hypoglycaemia (HH) is characterized by unregulated insulin secretion from pancreatic β-cells. Untreated hypoglycaemia in infants can lead to seizures, developmental delay, and subsequent permanent brain injury. Early identification and meticulous managementof these patients is vital to prevent neurological insult. Mutations in eight different genes (ABCC8, KCNJ11, GLUD1, CGK, HADH, SLC16A1, HNF4A and UCP2) have been identified to date in patients with congenital forms of hyperinsulinism (CHI). The most severe forms of CHI are due to mutations in ABCC8 and KCJN11, which encode the two components of pancreatic β-cell ATP-sensitive potassium channel. Recent advancement in understanding the genetic aetiology, histological characterisation into focal and diffuse variety combined with improved imaging (such as fluorine 18 L-3, 4-dihydroxyphenylalanine positron emission tomography 18F-DOPA-PET scanning) and laparoscopic surgical techniques have greatly improved management. In adults, HH can be due to an insulinoma, pancreatogenous hypoglycaemic syndrome, post gastric-bypass surgery for morbid obesity as well as to mutations in insulin receptor gene. This review provides an overview of the molecular basis of CHI and outlines the clinical presentation, diagnostic criteria, and management of these patients.
Collapse
Affiliation(s)
- Zainaba Mohamed
- University College London, Institue of Child Health, Developmental Endocrinology Research Clinical, Molecular Genetics Unit, London, United Kingdom
| | - Ved Bhushan Arya
- University College London, Institue of Child Health, Developmental Endocrinology Research Clinical, Molecular Genetics Unit, London, United Kingdom
| | - Khalid Hussain
- University College London, Institue of Child Health, Developmental Endocrinology Research Clinical, Molecular Genetics Unit, London, United Kingdom
,* Address for Correspondence: Khalid Hussain MD, University College London, Institue of Child Health, Developmental Endocrinology Research Clinical, Molecular Genetics Unit, London, United Kingdom Phone: +44 207 905 2128 E-mail:
| |
Collapse
|
39
|
Abstract
Hyperglycaemia has multiple effects on β-cells, some clearly prosecretory, including hyperplasia and elevated insulin content, but eventually, a 'glucotoxic' effect which leads to pancreatic β-cell dysfunction, reduced β-cell mass and insulin deficiency, is an important part of diabetes pathophysiology. Myriad underlying cellular and molecular processes could lead to such dysfunction. High glucose will stimulate glycolysis and oxidative phosphorylation, which will in turn increase β-cell membrane excitability through K(ATP) channel closure. Chronic hyperexcitability will then lead to persistently elevated [Ca(2+)](i), a key trigger to insulin secretion. Thus, at least a part of the consequence of 'hyperstimulation' by glucose has been suggested to be a result of 'hyperexcitability' and chronically elevated [Ca(2+)](i). This link is lost when the [glucose], K(ATP) -channel activity link is broken, either pharmacologically or genetically. In isolated islets, such studies reveal that hyperexcitability causes a largely reversible chronic loss of insulin content, but in vivo chronic hyperexcitability per se does not lead to β-cell death or loss of insulin content. On the other hand, chronic inexcitability in vivo leads to systemic diabetes and consequential β-cell death, even while [Ca(2+)](i) remains low.
Collapse
Affiliation(s)
- C G Nichols
- Department of Cell Biology and Physiology and Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA.
| | | |
Collapse
|
40
|
Fatima N, Schooley JF, Claycomb WC, Flagg TP. Promoter DNA methylation regulates murine SUR1 (Abcc8) and SUR2 (Abcc9) expression in HL-1 cardiomyocytes. PLoS One 2012; 7:e41533. [PMID: 22844491 PMCID: PMC3402388 DOI: 10.1371/journal.pone.0041533] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 06/27/2012] [Indexed: 01/28/2023] Open
Abstract
Two mammalian genes encode the SURx (SUR1, Abcc8 and SUR2, Abcc9) subunits that combine with Kir6.2 (Kcnj11) subunits to form the ATP-sensitive potassium (KATP) channel in cardiac myocytes. Different isoform combinations endow the channel with distinct physiological and pharmacological properties, and we have recently reported that the molecular composition of sarcolemmal KATP channels is chamber specific in the mouse heart. KATP channel composition is determined by what subunits are expressed in a cell or tissue. In the present study, we explore the role of CpG methylation in regulating SUR1 and SUR2 expression. In HL-1 cardiomyocytes, as in atrial myocytes, SUR1 expression is markedly greater than SUR2. Consistent with CpG methylation-dependent silencing of SUR2 expression, bisulfite sequencing of genomic DNA isolated from HL-1 cells demonstrates that 57.6% of the CpGs in the promoter region of the SUR2 gene are methylated, compared with 0.14% of the the CpG residues in the SUR1 sequence. Moreover, treatment with 10 µM 5-aza-2'-deoxycytidine (Aza-dC) significantly increased both the unmethylated fraction of the SUR2 CpG island and mRNA expression. However, we cannot rule out additional mechanisms of Aza-dC action, as Aza-dC also causes a decrease in SUR1 expression and lower doses of Aza-dC do not alter the unmethylated DNA fraction but do elicit a small increase in SUR2 expression. The conclusion that DNA methylation alone is not the only regulator of SUR subunit expression is also consistent with observations in native myocytes, where the CpG islands of both SUR genes are essentially unmethylated in both atrial and ventricular myocytes. Collectively, these data demonstrate the potential for CpG methylation to regulate SURx subunit expression and raises the possibility that regulated or aberrant CpG methylation might play a role in controlling channel structure and function under different physiological conditions or different species.
Collapse
Affiliation(s)
- Naheed Fatima
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Hebert School of Medicine, Bethesda, Maryland, United States of America
| | - James F. Schooley
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Hebert School of Medicine, Bethesda, Maryland, United States of America
| | - Willliam C. Claycomb
- Department of Biochemistry and Molecular Biology, LSU Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Thomas P. Flagg
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Hebert School of Medicine, Bethesda, Maryland, United States of America
- * E-mail:
| |
Collapse
|
41
|
Pratt EB, Zhou Q, Gay JW, Shyng SL. Engineered interaction between SUR1 and Kir6.2 that enhances ATP sensitivity in KATP channels. ACTA ACUST UNITED AC 2012; 140:175-87. [PMID: 22802363 PMCID: PMC3409095 DOI: 10.1085/jgp.201210803] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ATP-sensitive potassium (KATP) channel consisting of the inward rectifier Kir6.2 and SUR1 (sulfonylurea receptor 1) couples cell metabolism to membrane excitability and regulates insulin secretion. Inhibition by intracellular ATP is a hallmark feature of the channel. ATP sensitivity is conferred by Kir6.2 but enhanced by SUR1. The mechanism by which SUR1 increases channel ATP sensitivity is not understood. In this study, we report molecular interactions between SUR1 and Kir6.2 that markedly alter channel ATP sensitivity. Channels bearing an E203K mutation in SUR1 and a Q52E in Kir6.2 exhibit ATP sensitivity ∼100-fold higher than wild-type channels. Cross-linking of E203C in SUR1 and Q52C in Kir6.2 locks the channel in a closed state and is reversible by reducing agents, demonstrating close proximity of the two residues. Our results reveal that ATP sensitivity in KATP channels is a dynamic parameter dictated by interactions between SUR1 and Kir6.2.
Collapse
Affiliation(s)
- Emily B Pratt
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA.
| | | | | | | |
Collapse
|
42
|
de Wet H, Shimomura K, Aittoniemi J, Ahmad N, Lafond M, Sansom MSP, Ashcroft FM. A universally conserved residue in the SUR1 subunit of the KATP channel is essential for translating nucleotide binding at SUR1 into channel opening. J Physiol 2012; 590:5025-36. [PMID: 22802590 PMCID: PMC3495298 DOI: 10.1113/jphysiol.2012.236075] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The sulphonylurea receptor (SUR1) subunit of the ATP-sensitive potassium (KATP) channel is a member of the ATP-binding cassette (ABC) protein family. Binding of MgADP to nucleotide-binding domain 2 (NBD2) is critical for channel activation.We identified a residue in NBD2 (G1401) that is fully conserved among ABC proteins and whose functional importance is unknown. Homology modelling places G1401 on the outer surface of the protein, distant from the nucleotide-binding site. The ATPase activity of purified SUR1-NBD2-G1410R (bound to maltose-binding protein) was slightly inhibited when compared to the wild-type protein, but its inhibition by MgADP was unchanged, indicating that MgADP binding is not altered. However, MgADP activation of channel activity was abolished. This implies that the G1401R mutation impairs the mechanism by which MgADP binding to NBD2 is translated into opening of the KATP channel pore. The location of G1401 would be consistent with interaction of this residue with the pore-forming Kir6.2 subunit. Channel activity in the presence of MgATP reflects the balance between the stimulatory (at SUR1) and inhibitory (at Kir6.2) effects of nucleotides. Mutant channels were 2.5-fold less sensitive to MgATP inhibition and not activated by MgATP. This suggests that ATP block of the channel is reduced by the SUR1 mutation. Interestingly, this effect was dependent on the functional integrity of the NBDs. These results therefore suggest that SUR1 modulates both nucleotide inhibition and activation of the KATP channel.
Collapse
Affiliation(s)
- Heidi de Wet
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK
| | | | | | | | | | | | | |
Collapse
|
43
|
Effects of Single Nucleotide Polymorphisms in KATP Channel Genes on Type 2 Diabetes in a Turkish Population. Arch Med Res 2012; 43:317-23. [DOI: 10.1016/j.arcmed.2012.06.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 05/24/2012] [Indexed: 01/12/2023]
|
44
|
Clark R, Männikkö R, Stuckey DJ, Iberl M, Clarke K, Ashcroft FM. Mice expressing a human K(ATP) channel mutation have altered channel ATP sensitivity but no cardiac abnormalities. Diabetologia 2012; 55:1195-204. [PMID: 22252471 PMCID: PMC3296019 DOI: 10.1007/s00125-011-2428-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Accepted: 11/28/2011] [Indexed: 11/29/2022]
Abstract
AIMS/HYPOTHESIS Patients with severe gain-of-function mutations in the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, have neonatal diabetes, muscle hypotonia and mental and motor developmental delay-a condition known as iDEND syndrome. However, despite the fact that Kir6.2 forms the pore of the cardiac K(ATP) channel, patients show no obvious cardiac symptoms. The aim of this project was to use a mouse model of iDEND syndrome to determine whether iDEND mutations affect cardiac function and cardiac K(ATP) channel ATP sensitivity. METHODS We performed patch-clamp and in vivo cine-MRI studies on mice in which the most common iDEND mutation (Kir6.2-V59M) was targeted to cardiac muscle using Cre-lox technology (m-V59M mice). RESULTS Patch-clamp studies of isolated cardiac myocytes revealed a markedly reduced K(ATP) channel sensitivity to MgATP inhibition in m-V59M mice (IC(50) 62 μmol/l compared with 13 μmol/l for littermate controls). In vivo cine-MRI revealed there were no gross morphological differences and no differences in heart rate, end diastolic volume, end systolic volume, stroke volume, ejection fraction, cardiac output or wall thickening between m-V59M and control hearts, either under resting conditions or under dobutamine stress. CONCLUSIONS/INTERPRETATION The common iDEND mutation Kir6.2-V59M decreases ATP block of cardiac K(ATP) channels but was without obvious effect on heart function, suggesting that metabolic changes fail to open the mutated channel to an extent that affects function (at least in the absence of ischaemia). This may have implications for the choice of sulfonylurea used to treat neonatal diabetes.
Collapse
Affiliation(s)
- R. Clark
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - R. Männikkö
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
- Present Address: Molecular Neuroscience, Institute of Neurology, UCL, London, UK
| | - D. J. Stuckey
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- Present Address: Biological Imaging Centre, National Heart and Lung Institute, Imperial College, Hammersmith Hospital, London, UK
| | - M. Iberl
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - K. Clarke
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - F. M. Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| |
Collapse
|
45
|
Ortiz D, Voyvodic P, Gossack L, Quast U, Bryan J. Two neonatal diabetes mutations on transmembrane helix 15 of SUR1 increase affinity for ATP and ADP at nucleotide binding domain 2. J Biol Chem 2012; 287:17985-95. [PMID: 22451668 DOI: 10.1074/jbc.m112.349019] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
K(ATP) channels, (SUR1/Kir6.2)(4) (sulfonylurea receptor type 1/potassium inward rectifier type 6.2) respond to the metabolic state of pancreatic β-cells, modulating membrane potential and insulin exocytosis. Mutations in both subunits cause neonatal diabetes by overactivating the pore. Hyperactive channels fail to close appropriately with increased glucose metabolism; thus, β-cell hyperpolarization limits insulin release. K(ATP) channels are inhibited by ATP binding to the Kir6.2 pore and stimulated, via an uncertain mechanism, by magnesium nucleotides at SUR1. Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. GBC binds with high affinity to aporeceptors, presumably in the inward facing ATP-binding cassette configuration; MgATP reduces binding affinity via a shift to the outward facing conformation. To determine nucleotide affinities under equilibrium, non-hydrolytic conditions, Mg(2+) was eliminated. A four-state equilibrium model describes the allosteric linkage. The K(D) for ATP(4-) is ~1 versus 12 mM, Q1178R versus wild type, respectively. The linkage constant is ~10, implying that outward facing conformations bind GBC with a lower affinity, 9-10 nM for Q1178R. Thus, nucleotides cannot completely inhibit GBC binding. Binding of channel openers is reported to require ATP hydrolysis, but diazoxide, a SUR1-selective agonist, concentration-dependently augments ATP(4-) action. An eight-state model describes linkage between diazoxide and ATP(4-) binding; diazoxide markedly increases the affinity of Q1178R for ATP(4-) and ATP(4-) augments diazoxide binding. NBD2, but not NBD1, has a higher affinity for ATP (and ADP) in mutant versus wild type (with or without Mg(2+)). Thus, the mutants spend more time in nucleotide-bound conformations, with reduced affinity for GBC, that activate the pore.
Collapse
Affiliation(s)
- David Ortiz
- Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
| | | | | | | | | |
Collapse
|
46
|
Lin YW, Akrouh A, Hsu Y, Hughes N, Nichols CG, De León DD. Compound heterozygous mutations in the SUR1 (ABCC 8) subunit of pancreatic K(ATP) channels cause neonatal diabetes by perturbing the coupling between Kir6.2 and SUR1 subunits. Channels (Austin) 2012; 6:133-8. [PMID: 22562119 DOI: 10.4161/chan.19980] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
KATP channels regulate insulin secretion by coupling β-cell metabolism to membrane excitability. These channels are comprised of a pore-forming Kir6.2 tetramer which is enveloped by four regulatory SUR1 subunits. ATP acts on Kir6.2 to stabilize the channel closed state while ADP (coordinated with Mg(2+)) activates channels via the SUR1 domains. Aberrations in nucleotide-binding or in coupling binding to gating can lead to hyperinsulinism or diabetes. Here, we report a case of diabetes in a 7-mo old child with compound heterozygous mutations in ABCC8 (SUR1[A30V] and SUR1[G296R]). In unison, these mutations lead to a gain of KATP channel function, which will attenuate the β-cell response to increased metabolism and will thereby decrease insulin secretion. (86)Rb(+) flux assays on COSm6 cells coexpressing the mutant subunits (to recapitulate the compound heterozygous state) show a 2-fold increase in basal rate of (86)Rb(+) efflux relative to WT channels. Experiments on excised inside-out patches also reveal a slight increase in activity, manifested as an enhancement in stimulation by MgADP in channels expressing the compound heterozygous mutations or homozygous G296R mutation. In addition, the IC 50 for ATP inhibition of homomeric A30V channels was increased ~6-fold, and was increased ~3-fold for both heteromeric A30V+WT channels or compound heterozygous (A30V +G296R) channels. Thus, each mutation makes a mechanistically distinct contribution to the channel gain-of-function that results in neonatal diabetes, and which we predict may contribute to diabetes in related carrier individuals.
Collapse
Affiliation(s)
- Yu-Wen Lin
- Department of Cell Biology and Physiology and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St Louis, MO, USA
| | | | | | | | | | | |
Collapse
|
47
|
Schmid D, Stolzlechner M, Sorgner A, Bentele C, Assinger A, Chiba P, Moeslinger T. An abundant, truncated human sulfonylurea receptor 1 splice variant has prodiabetic properties and impairs sulfonylurea action. Cell Mol Life Sci 2012; 69:129-48. [PMID: 21671119 PMCID: PMC11114697 DOI: 10.1007/s00018-011-0739-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2010] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 12/20/2022]
Abstract
An alternatively spliced form of human sulfonylurea receptor (SUR) 1 mRNA lacking exon 2 (SUR1Δ2) has been identified. The omission of exon 2 caused a frame shift and an immediate stop codon in exon 3 leading to translation of a 5.6-kDa peptide that comprises the N-terminal extracellular domain and the first transmembrane helix of SUR1. Based on a weak first splice acceptor site in the human SUR1 gene (ABCC8), RT-PCR revealed a concurrent expression of SUR1Δ2 and SUR1. The SUR1Δ2/(SUR1 + SUR1Δ2) mRNA ratio differed between tissues, and was lowest in pancreas (46%), highest in heart (88%) and negatively correlated with alternative splice factor/splicing factor 2 (ASF/SF2) expression. In COS-7 cells triple transfected with SUR1Δ2/SUR1/Kir6.2, the SUR1Δ2 peptide co-immunoprecipitated with Kir6.2, thereby displacing two of four SUR1 subunits on the cell surface. The ATP sensitivity of these hybrid ATP-sensitive potassium channels (K(ATP)) channels was reduced by about sixfold, as shown with single-channel recordings. RINm5f rat insulinoma cells, which genuinely express SUR1 but not SUR1Δ2, exhibited a strongly increased K(ATP) channel current upon transfection with SUR1Δ2. This led to inhibition of glucose-induced depolarization, calcium flux, insulin release and glibenclamide action. A non-mutagenic SNP on nucleotide position 333 (Pro69Pro) added another exonic splicing enhancer sequence detected by ASF/SF2, reduced relative abundance of SUR1Δ2 and slightly protected from non-insulin dependent diabetes in homozygotic individuals. Thus, SUR1Δ2 represents an endogenous K(ATP)-channel modulator with prodiabetic properties in islet cells. Its predominance in heart may explain why high-affinity sulfonylurea receptors are not found in human cardiac tissue.
Collapse
MESH Headings
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Alternative Splicing/physiology
- Animals
- COS Cells
- Calcium/metabolism
- Chlorocebus aethiops
- Diabetes Mellitus, Type 2/genetics
- Diabetes Mellitus, Type 2/metabolism
- Diabetes Mellitus, Type 2/physiopathology
- Exons/physiology
- Glyburide/pharmacology
- Humans
- Hypoglycemic Agents/pharmacology
- Insulin/metabolism
- Islets of Langerhans/metabolism
- KATP Channels/drug effects
- KATP Channels/metabolism
- Myocardium/metabolism
- Organ Specificity/genetics
- Pancreas/metabolism
- Polymorphism, Single Nucleotide
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Receptors, Drug/genetics
- Receptors, Drug/metabolism
- Species Specificity
- Sulfonylurea Receptors
Collapse
Affiliation(s)
- Diethart Schmid
- Institute of Physiology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.
| | | | | | | | | | | | | |
Collapse
|
48
|
Zhu Z, Burnett CML, Maksymov G, Stepniak E, Sierra A, Subbotina E, Anderson ME, Coetzee WA, Hodgson-Zingman DM, Zingman LV. Reduction in number of sarcolemmal KATP channels slows cardiac action potential duration shortening under hypoxia. Biochem Biophys Res Commun 2011; 415:637-41. [PMID: 22079630 DOI: 10.1016/j.bbrc.2011.10.125] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Accepted: 10/26/2011] [Indexed: 12/25/2022]
Abstract
The cardiovascular system operates under demands ranging from conditions of rest to extreme stress. One mechanism of cardiac stress tolerance is action potential duration shortening driven by ATP-sensitive potassium (K(ATP)) channels. K(ATP) channel expression has a significant physiologic impact on action potential duration shortening and myocardial energy consumption in response to physiologic heart rate acceleration. However, the effect of reduced channel expression on action potential duration shortening in response to severe metabolic stress is yet to be established. Here, transgenic mice with myocardium-specific expression of a dominant negative K(ATP) channel subunit were compared with littermate controls. Evaluation of K(ATP) channel whole cell current and channel number/patch was assessed by patch clamp in isolated ventricular cardiomyocytes. Monophasic action potentials were monitored in retrogradely perfused, isolated hearts during the transition to hypoxic perfusate. An 80-85% reduction in cardiac K(ATP) channel current density results in a similar magnitude, but significantly slower rate, of shortening of the ventricular action potential duration in response to severe hypoxia, despite no significant difference in coronary flow. Therefore, the number of functional cardiac sarcolemmal K(ATP) channels is a critical determinant of the rate of adaptation of myocardial membrane excitability, with implications for optimization of cardiac energy consumption and consequent cardioprotection under conditions of severe metabolic stress.
Collapse
Affiliation(s)
- Zhiyong Zhu
- Department of Internal Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA 52242, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
49
|
Patel JC, Witkovsky P, Coetzee WA, Rice ME. Subsecond regulation of striatal dopamine release by pre-synaptic KATP channels. J Neurochem 2011; 118:721-36. [PMID: 21689107 DOI: 10.1111/j.1471-4159.2011.07358.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
ATP-sensitive K(+) (K(ATP)) channels are composed of pore-forming subunits, typically Kir6.2 in neurons, and regulatory sulfonylurea receptor subunits. In dorsal striatum, activity-dependent H(2)O(2) produced from glutamate receptor activation inhibits dopamine release via K(ATP) channels. Sources of modulatory H(2)O(2) include striatal medium spiny neurons, but not dopaminergic axons. Using fast-scan cyclic voltammetry in guinea-pig striatal slices and immunohistochemistry, we determined the time window for H(2)O(2)/K(ATP)-channel-mediated inhibition and assessed whether modulatory K(ATP) channels are on dopaminergic axons. Comparison of paired-pulse suppression of dopamine release in the absence and presence of glibenclamide, a K(ATP)-channel blocker, or mercaptosuccinate, a glutathione peroxidase inhibitor that enhances endogenous H(2)O(2) levels, revealed a time window for inhibition of 500-1000 ms after stimulation. Immunohistochemistry demonstrated localization of Kir6.2 K(ATP)-channel subunits on dopaminergic axons. Consistent with the presence of functional K(ATP) channels on dopaminergic axons, K(ATP)-channel openers, diazoxide and cromakalim, suppressed single-pulse evoked dopamine release. Although cholinergic interneurons that tonically regulate dopamine release also express K(ATP) channels, diazoxide did not induce the enhanced frequency responsiveness of dopamine release seen with nicotinic-receptor blockade. Together, these studies reveal subsecond regulation of striatal dopamine release by endogenous H(2)O(2) acting at K(ATP) channels on dopaminergic axons, including a role in paired-pulse suppression.
Collapse
Affiliation(s)
- Jyoti C Patel
- Department of Neurosurgery, New York University School of Medicine, New York, New York 10016, USA.
| | | | | | | |
Collapse
|
50
|
Pratt EB, Shyng SL. ATP activates ATP-sensitive potassium channels composed of mutant sulfonylurea receptor 1 and Kir6.2 with diminished PIP2 sensitivity. Channels (Austin) 2011; 5:314-9. [PMID: 21654216 DOI: 10.4161/chan.5.4.16510] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are inhibited by ATP and activated by phosphatidylinositol 4,5-bisphosphate (PIP(2)). Both channel subunits Kir6.2 and sulfonylurea receptor 1 (SUR1) contribute to gating: while Kir6.2 interacts with ATP and PIP(2), SUR1 enhances sensitivity to both ligands. Recently, we showed that a mutation, E128K, in the N-terminal transmembrane domain of SUR1 disrupts functional coupling between SUR1 and Kir6.2, leading to reduced ATP and PIP(2) sensitivities resembling channels formed by Kir6.2 alone. We show here that when E128K SUR1 was co-expressed with Kir6.2 mutants known to disrupt PIP(2) gating, the resulting channels were surprisingly stimulated rather than inhibited by ATP. To explain this paradoxical gating behavior, we propose a model in which the open state of doubly mutant channels is highly unstable; ATP binding induces a conformational change in ATP-unbound closed channels that is conducive to brief opening when ATP unbinds, giving rise to the appearance of ATP-induced stimulation.
Collapse
Affiliation(s)
- Emily B Pratt
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, USA
| | | |
Collapse
|