1
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Walczewska-Szewc K, Nowak W. Structural Determinants of Insulin Release: Disordered N-Terminal Tail of Kir6.2 Affects Potassium Channel Dynamics through Interactions with Sulfonylurea Binding Region in a SUR1 Partner. J Phys Chem B 2020; 124:6198-6211. [PMID: 32598150 PMCID: PMC7467719 DOI: 10.1021/acs.jpcb.0c02720] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
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Inward rectifying
potassium ion channels (KATP), sensitive to the
ATP/ADP concentration ratio, play an important, control role in pancreatic
β cells. The channels close upon the increase of this ratio,
which, in turn, triggers insulin release to blood. Numerous mutations
in KATP lead to severe and widespread medical conditions such as diabetes.
The KATP system consists of a pore made of four Kir6.2 subunits and
four accompanying large SUR1 proteins belonging to the ABCC transporters
group. How SUR1 affects KATP function is not yet known; therefore,
we created simplified models of the Kir6.2 tetramer based on recently
determined cryo-EM KATP structures. Using all-atom molecular dynamics
(MD) with the CHARMM36 force field, targeted MD, and molecular docking,
we revealed functionally important rearrangements in the Kir6.2 pore,
induced by the presence of the SUR1 protein. The cytoplasmic domain
of Kir6.2 (CTD) is brought closer to the membrane due to interactions
with SUR1. Each Kir6.2 subunit has a conserved, functionally important,
disordered N-terminal tail. Using molecular docking, we found that
the Kir6.2 tail easily docks to the sulfonylurea drug binding region
located in the adjacent SUR1 protein. We reveal, for the first time,
dynamical behavior of the Kir6.2/SUR1 system, confirming a physiological
role of the Kir6.2 disordered tail, and we indicate structural determinants
of KATP-dependent insulin release from pancreatic β cells.
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Affiliation(s)
- Katarzyna Walczewska-Szewc
- Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5, 87-100 Toruń, Poland.,Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University, Wileńska 4, 87-100 Toruń, Poland
| | - Wiesław Nowak
- Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5, 87-100 Toruń, Poland
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2
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Pipatpolkai T, Usher S, Stansfeld PJ, Ashcroft FM. New insights into K ATP channel gene mutations and neonatal diabetes mellitus. Nat Rev Endocrinol 2020; 16:378-393. [PMID: 32376986 DOI: 10.1038/s41574-020-0351-y] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/17/2020] [Indexed: 12/12/2022]
Abstract
The ATP-sensitive potassium channel (KATP channel) couples blood levels of glucose to insulin secretion from pancreatic β-cells. KATP channel closure triggers a cascade of events that results in insulin release. Metabolically generated changes in the intracellular concentrations of adenosine nucleotides are integral to this regulation, with ATP and ADP closing the channel and MgATP and MgADP increasing channel activity. Activating mutations in the genes encoding either of the two types of KATP channel subunit (Kir6.2 and SUR1) result in neonatal diabetes mellitus, whereas loss-of-function mutations cause hyperinsulinaemic hypoglycaemia of infancy. Sulfonylurea and glinide drugs, which bind to SUR1, close the channel through a pathway independent of ATP and are now the primary therapy for neonatal diabetes mellitus caused by mutations in the genes encoding KATP channel subunits. Insight into the molecular details of drug and nucleotide regulation of channel activity has been illuminated by cryo-electron microscopy structures that reveal the atomic-level organization of the KATP channel complex. Here we review how these structures aid our understanding of how the various mutations in the genes encoding Kir6.2 (KCNJ11) and SUR1 (ABCC8) lead to a reduction in ATP inhibition and thereby neonatal diabetes mellitus. We also provide an update on known mutations and sulfonylurea therapy in neonatal diabetes mellitus.
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Affiliation(s)
- Tanadet Pipatpolkai
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Samuel Usher
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Phillip J Stansfeld
- Department of Biochemistry, University of Oxford, Oxford, UK
- School of Life Sciences, University of Warwick, Coventry, UK
- Department of Chemistry, University of Warwick, Coventry, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.
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3
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Cooper PE, McClenaghan C, Chen X, Stary-Weinzinger A, Nichols CG. Conserved functional consequences of disease-associated mutations in the slide helix of Kir6.1 and Kir6.2 subunits of the ATP-sensitive potassium channel. J Biol Chem 2017; 292:17387-17398. [PMID: 28842488 DOI: 10.1074/jbc.m117.804971] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 08/04/2017] [Indexed: 11/06/2022] Open
Abstract
Cantu syndrome (CS) is a condition characterized by a range of anatomical defects, including cardiomegaly, hyperflexibility of the joints, hypertrichosis, and craniofacial dysmorphology. CS is associated with multiple missense mutations in the genes encoding the regulatory sulfonylurea receptor 2 (SUR2) subunits of the ATP-sensitive K+ (KATP) channel as well as two mutations (V65M and C176S) in the Kir6.1 (KCNJ8) subunit. Previous analysis of leucine and alanine substitutions at the Val-65-equivalent site (Val-64) in Kir6.2 indicated no major effects on channel function. In this study, we characterized the effects of both valine-to-methionine and valine-to-leucine substitutions at this position in both Kir6.1 and Kir6.2 using ion flux and patch clamp techniques. We report that methionine substitution, but not leucine substitution, results in increased open state stability and hence significantly reduced ATP sensitivity and a marked increase of channel activity in the intact cell irrespective of the identity of the coassembled SUR subunit. Sulfonylurea inhibitors, such as glibenclamide, are potential therapies for CS. However, as a consequence of the increased open state stability, both Kir6.1(V65M) and Kir6.2(V64M) mutations essentially abolish high-affinity sensitivity to the KATP blocker glibenclamide in both intact cells and excised patches. This raises the possibility that, at least for some CS mutations, sulfonylurea therapy may not prove to be successful and highlights the need for detailed pharmacogenomic analyses of CS mutations.
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Affiliation(s)
- Paige E Cooper
- From the Department of Cell Biology and Physiology and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110 and
| | - Conor McClenaghan
- From the Department of Cell Biology and Physiology and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110 and
| | - Xingyu Chen
- Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
| | - Colin G Nichols
- From the Department of Cell Biology and Physiology and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110 and
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4
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Notary AM, Westacott MJ, Hraha TH, Pozzoli M, Benninger RKP. Decreases in Gap Junction Coupling Recovers Ca2+ and Insulin Secretion in Neonatal Diabetes Mellitus, Dependent on Beta Cell Heterogeneity and Noise. PLoS Comput Biol 2016; 12:e1005116. [PMID: 27681078 PMCID: PMC5040430 DOI: 10.1371/journal.pcbi.1005116] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 08/23/2016] [Indexed: 11/29/2022] Open
Abstract
Diabetes is caused by dysfunction to β-cells in the islets of Langerhans, disrupting insulin secretion and glucose homeostasis. Gap junction-mediated electrical coupling between β-cells in the islet plays a major role in coordinating a pulsatile secretory response at elevated glucose and suppressing insulin secretion at basal glucose. Previously, we demonstrated that a critical number of inexcitable cells can rapidly suppress the overall islet response, as a result of gap junction coupling. This was demonstrated in a murine model of Neonatal Diabetes Mellitus (NDM) involving expression of ATP-insensitive KATP channels, and by a multi-cellular computational model of islet electrical activity. Here we examined the mechanisms by which gap junction coupling contributes to islet dysfunction in NDM. We first verified the computational model against [Ca2+] and insulin secretion measurements in islets expressing ATP-insensitive KATP channels under different levels of gap junction coupling. We then applied this model to predict how different KATP channel mutations found in NDM suppress [Ca2+], and the role of gap junction coupling in this suppression. We further extended the model to account for stochastic noise and insulin secretion dynamics. We found experimentally and in the islet model that reductions in gap junction coupling allow progressively greater glucose-stimulated [Ca2+] and insulin secretion following expression of ATP-insensitive KATP channels. The model demonstrated good correspondence between suppression of [Ca2+] and clinical presentation of different NDM mutations. Significant recoveries in [Ca2+] and insulin secretion were predicted for many mutations upon reductions in gap junction coupling, where stochastic noise played a significant role in the recoveries. These findings provide new understanding how the islet functions as a multicellular system and for the role of gap junction channels in exacerbating the effects of decreased cellular excitability. They further suggest novel therapeutic options for NDM and other monogenic forms of diabetes. Diabetes is a disease reaching a global epidemic, which results from dysfunction to the islets of Langerhans in the pancreas and their ability to secrete the hormone insulin to regulate glucose homeostasis. Islets are multicellular structures that show extensive coupling between heterogeneous cellular units; and central to the causes of diabetes is a dysfunction to these cellular units and their interactions. Understanding the inter-relationship between structure and function is challenging in biological systems, but is crucial to the cause of disease and discovering therapeutic targets. With the goal of further characterizing the islet of Langerhans and its excitable behavior, we examined the role of important channels in the islet where dysfunction is linked to or causes diabetes. Advances in our ability to computationally model perturbations in physiological systems has allowed for the testing of hypothesis quickly, in systems that are not experimentally accessible. Using an experimentally validated model and modeling human mutations, we discover that monogenic forms of diabetes may be remedied by a reduction in electrical coupling between cells; either alone or in conjunction with pharmacological intervention. Knowledge of biological systems in general is also helped by these findings, in that small changes to cellular elements may lead to major disruptions in the overall system. This may then be overcome by allowing the system components to function independently in the presence of dysfunction to individual cells.
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Affiliation(s)
- Aleena M. Notary
- Department of Bioengineering, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
| | - Matthew J. Westacott
- Department of Bioengineering, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
| | - Thomas H. Hraha
- Department of Bioengineering, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
| | - Marina Pozzoli
- Department of Bioengineering, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
| | - Richard K. P. Benninger
- Department of Bioengineering, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
- Barbara Davis Center for Diabetes, University of Colorado, Anschutz Medical campus, Aurora, Colorado, United States of America
- * E-mail:
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5
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Wang S, Vafabakhsh R, Borschel WF, Ha T, Nichols CG. Structural dynamics of potassium-channel gating revealed by single-molecule FRET. Nat Struct Mol Biol 2015; 23:31-36. [PMID: 26641713 PMCID: PMC4833211 DOI: 10.1038/nsmb.3138] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 11/06/2015] [Indexed: 01/06/2023]
Abstract
Crystallography has provided invaluable insights to ion channel selectivity and gating, but to advance understanding to a new level, dynamic views of channel structures within membranes are essential. We labeled tetrameric KirBac1.1 potassium channels with single donor and acceptor fluorophores at different sites, and examined structural dynamics within lipid membranes by single molecule FRET. We found that the extracellular region is structurally rigid in both closed and open states, whereas the N-terminal slide helix undergoes marked conformational fluctuations. The cytoplasmic C-terminal domain fluctuates between two major structural states both of which become less dynamic and move away from the pore axis and away from the membrane in closed channels. Our results reveal mobile and rigid conformations of functionally relevant KirBac1.1 channel motifs, implying similar dynamics for similar motifs in eukaryotic Kir channels and for cation channels in general.
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Affiliation(s)
- Shizhen Wang
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
| | - Reza Vafabakhsh
- Department of Physics and the Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL
| | - William F Borschel
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
| | - Taekjip Ha
- Department of Physics and the Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL.,Howard Hughes Medical Institute, Baltimore, MD.,Department of Biophysics and Biophysical Chemistry, Department of Biophysics, Department of Biomedical Engineering, Baltimore, MD
| | - Colin G Nichols
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
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6
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Quinn JC. Complex Membrane Channel Blockade: A Unifying Hypothesis for the Prodromal and Acute Neuropsychiatric Sequelae Resulting from Exposure to the Antimalarial Drug Mefloquine. J Parasitol Res 2015; 2015:368064. [PMID: 26576290 PMCID: PMC4630403 DOI: 10.1155/2015/368064] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 09/28/2015] [Indexed: 12/18/2022] Open
Abstract
The alkaloid toxin quinine and its derivative compounds have been used for many centuries as effective medications for the prevention and treatment of malaria. More recently, synthetic derivatives, such as the quinoline derivative mefloquine (bis(trifluoromethyl)-(2-piperidyl)-4-quinolinemethanol), have been widely used to combat disease caused by chloroquine-resistant strains of the malaria parasite, Plasmodium falciparum. However, the parent compound quinine, as well as its more recent counterparts, suffers from an incidence of adverse neuropsychiatric side effects ranging from mild mood disturbances and anxiety to hallucinations, seizures, and psychosis. This review considers how the pharmacology, cellular neurobiology, and membrane channel kinetics of mefloquine could lead to the significant and sometimes life-threatening neurotoxicity associated with mefloquine exposure. A key role for mefloquine blockade of ATP-sensitive potassium channels and connexins in the substantia nigra is considered as a unifying hypothesis for the pathogenesis of severe neuropsychiatric events after mefloquine exposure in humans.
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Affiliation(s)
- Jane C. Quinn
- Plant and Animal Toxicology Group, School of Animal and Veterinary Sciences, Graham Centre for Agricultural Innovation, Charles Sturt University, Boorooma Street, Wagga Wagga, NSW 2650, Australia
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7
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Li JBW, Huang X, Zhang RS, Kim RY, Yang R, Kurata HT. Decomposition of slide helix contributions to ATP-dependent inhibition of Kir6.2 channels. J Biol Chem 2013; 288:23038-49. [PMID: 23798684 DOI: 10.1074/jbc.m113.485789] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Regulation of inwardly rectifying potassium channels by intracellular ligands couples cell membrane excitability to important signaling cascades and metabolic pathways. We investigated the molecular mechanisms that link ligand binding to the channel gate in ATP-sensitive Kir6.2 channels. In these channels, the "slide helix" forms an interface between the cytoplasmic (ligand-binding) domain and the transmembrane pore, and many slide helix mutations cause loss of function. Using a novel approach to rescue electrically silent channels, we decomposed the contribution of each interface residue to ATP-dependent gating. We demonstrate that effective inhibition by ATP relies on an essential aspartate at residue 58. Characterization of the functional importance of this conserved aspartate, relative to other residues in the slide helix, has been impossible because of loss-of-function of Asp-58 mutant channels. The Asp-58 position exhibits an extremely stringent requirement for aspartate because even a highly conservative mutation to glutamate is insufficient to restore normal channel function. These findings reveal unrecognized slide helix elements that are required for functional channel expression and control of Kir6.2 gating by intracellular ATP.
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Affiliation(s)
- Jenny B W Li
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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8
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9
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Denton JS, Jacobson DA. Channeling dysglycemia: ion-channel variations perturbing glucose homeostasis. Trends Endocrinol Metab 2012; 23:41-8. [PMID: 22134088 PMCID: PMC3733341 DOI: 10.1016/j.tem.2011.09.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Revised: 09/22/2011] [Accepted: 09/23/2011] [Indexed: 01/26/2023]
Abstract
Maintaining blood glucose homeostasis is a complex process that depends on pancreatic islet hormone secretion. Hormone secretion from islets is coupled to calcium entry which results from regenerative islet cell electrical activity. Therefore, the ionic mechanisms that regulate calcium entry into islet cells are crucial for maintaining normal glucose homeostasis. Genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs), including five located in or near ion-channel or associated subunit genes, which show an association with human diseases characterized by dysglycemia. This review focuses on polymorphisms and mutations in ion-channel genes that are associated with perturbations in human glucose homeostasis and discusses their potential roles in modulating pancreatic islet hormone secretion.
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Affiliation(s)
- Jerod Scott Denton
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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10
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Paynter JJ, Andres-Enguix I, Fowler PW, Tottey S, Cheng W, Enkvetchakul D, Bavro VN, Kusakabe Y, Sansom MSP, Robinson NJ, Nichols CG, Tucker SJ. Functional complementation and genetic deletion studies of KirBac channels: activatory mutations highlight gating-sensitive domains. J Biol Chem 2010; 285:40754-61. [PMID: 20876570 PMCID: PMC3003375 DOI: 10.1074/jbc.m110.175687] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 09/27/2010] [Indexed: 12/16/2022] Open
Abstract
The superfamily of prokaryotic inwardly rectifying (KirBac) potassium channels is homologous to mammalian Kir channels. However, relatively little is known about their regulation or about their physiological role in vivo. In this study, we have used random mutagenesis and genetic complementation in K(+)-auxotrophic Escherichia coli and Saccharomyces cerevisiae to identify activatory mutations in a range of different KirBac channels. We also show that the KirBac6.1 gene (slr5078) is necessary for normal growth of the cyanobacterium Synechocystis PCC6803. Functional analysis and molecular dynamics simulations of selected activatory mutations identified regions within the slide helix, transmembrane helices, and C terminus that function as important regulators of KirBac channel activity, as well as a region close to the selectivity filter of KirBac3.1 that may have an effect on gating. In particular, the mutations identified in TM2 favor a model of KirBac channel gating in which opening of the pore at the helix-bundle crossing plays a far more important role than has recently been proposed.
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Affiliation(s)
| | | | - Philip W. Fowler
- the Structural Bioinformatics and Computational Biochemistry Unit, Department of Biochemistry
| | - Stephen Tottey
- the Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle NE1 7RU, United Kingdom
| | - Wayland Cheng
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Decha Enkvetchakul
- the Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104, and
| | | | | | - Mark S. P. Sansom
- the Structural Bioinformatics and Computational Biochemistry Unit, Department of Biochemistry
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Nigel J. Robinson
- the Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle NE1 7RU, United Kingdom
| | - Colin G. Nichols
- the Department of Cell Biology and Physiology, and Center for Investigation of Membrane Excitability Disorders, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Stephen J. Tucker
- the Department of Physics, Clarendon Laboratory, and
- the OXION Initiative, University of Oxford, Oxford OX1 3PU, United Kingdom
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11
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Lang V, Light PE. The molecular mechanisms and pharmacotherapy of ATP-sensitive potassium channel gene mutations underlying neonatal diabetes. Pharmgenomics Pers Med 2010; 3:145-61. [PMID: 23226049 PMCID: PMC3513215 DOI: 10.2147/pgpm.s6969] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Indexed: 12/14/2022] Open
Abstract
Neonatal diabetes mellitus (NDM) is a monogenic disorder caused by mutations in genes involved in regulation of insulin secretion from pancreatic β-cells. Mutations in the KCNJ11 and ABCC8 genes, encoding the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel Kir6.2 and SUR1 subunits, respectively, are found in ∼50% of NDM patients. In the pancreatic β-cell, K(ATP) channel activity couples glucose metabolism to insulin secretion via cellular excitability and mutations in either KCNJ11 or ABCC8 genes alter K(ATP) channel activity, leading to faulty insulin secretion. Inactivation mutations decrease K(ATP) channel activity and stimulate excessive insulin secretion, leading to hyperinsulinism of infancy. In direct contrast, activation mutations increase K(ATP) channel activity, resulting in impaired insulin secretion, NDM, and in severe cases, developmental delay and epilepsy. Many NDM patients with KCNJ11 and ABCC8 mutations can be successfully treated with sulfonylureas (SUs) that inhibit the K(ATP) channel, thus replacing the need for daily insulin injections. There is also strong evidence indicating that SU therapy ameliorates some of the neurological defects observed in patients with more severe forms of NDM. This review focuses on the molecular and cellular mechanisms of mutations in the K(ATP) channel that underlie NDM. SU pharmacogenomics is also discussed with respect to evaluating whether patients with certain K(ATP) channel activation mutations can be successfully switched to SU therapy.
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Affiliation(s)
- Veronica Lang
- Department of Pharmacology and Alberta Diabetes Institute, Faculty of Medicine and Dentistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada
| | - Peter E Light
- Department of Pharmacology and Alberta Diabetes Institute, Faculty of Medicine and Dentistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada
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12
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Morales A, Pinto JR, Siegfried JD, Li D, Norton N, Hofmeyer M, Vallin M, Morales AR, Potter JD, Hershberger RE. Late onset sporadic dilated cardiomyopathy caused by a cardiac troponin T mutation. Clin Transl Sci 2010; 3:219-26. [PMID: 20973921 PMCID: PMC2965560 DOI: 10.1111/j.1752-8062.2010.00228.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Mutations in TNNT2, encoding cardiac troponin T, commonly shows early onset, aggressive dilated cardiomyopathy (DCM). This observation may influence the decision of whether to undertake clinical genetic testing for TNNT2 in later onset DCM. Further, the trigger for late onset DCM remains enigmatic. A 70-year-old woman, previously healthy with a left ventricular ejection fraction of 50%-55% at age 69, presented with DCM of unknown cause and a 4-month history progressive heart failure requiring cardiac transplantation. Clinical genetic testing revealed a novel TNNT2 R139H mutation but no relevant variants in 18 other DCM genes. Her explanted heart showed partial fatty replacement in the right ventricle. Sequencing for five arrhythmogenic right ventricular dysplasia genes was negative. Functional studies in porcine cardiac skinned fibers reconstituted with the mutant R139H troponin T protein showed decreased Ca(2+) sensitivity at pH 7, characteristic of DCM. Because fatty infiltration may acidify the myocellular environment, maximal force development examined at pH 6.5 was diminished, suggesting a possible environmental trigger. We conclude that the TNNT2 R139H mutation was likely to be disease causing. Further, later age of onset may not be relevant to exclude genetic testing for TNNT2 mutations.
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Affiliation(s)
- Ana Morales
- Cardiovascular Division, Department of Medicine, University of Miami Miller School of Medicine, USA
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