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Johnsen LØ, Friis KA, Møller-Madsen MK, Damkier HH. Mechanisms of cerebrospinal fluid secretion by the choroid plexus epithelium: Application to various intracranial pathologies. Clin Anat 2024. [PMID: 38894645 DOI: 10.1002/ca.24199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2024] [Revised: 06/02/2024] [Accepted: 06/06/2024] [Indexed: 06/21/2024]
Abstract
The choroid plexus (CP) is a small yet highly active epithelial tissue located in the ventricles of the brain. It secretes most of the CSF that envelops the brain and spinal cord. The epithelial cells of the CP have a high fluid secretion rate and differ from many other secretory epithelia in the organization of several key ion transporters. One striking difference is the luminal location of, for example, the vital Na+-K+-ATPase. In recent years, there has been a renewed focus on the role of ion transporters in CP secretion. Several studies have indicated that increased membrane transport activity is implicated in disorders such as hydrocephalus, idiopathic intracranial hypertension, and posthemorrhagic sequelae. The importance of the CP membrane transporters in regulating the composition of the CSF has also been a focus in research in recent years, particularly as a regulator of breathing and hemodynamic parameters such as blood pressure. This review focuses on the role of the fundamental ion transporters involved in CSF secretion and its ion composition. It gives a brief overview of the established factors and controversies concerning ion transporters, and finally discusses future perspectives related to the role of these transporters in the CP epithelium.
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Barlow IL, Mackay E, Wheater E, Goel A, Lim S, Zimmerman S, Woods I, Prober DA, Rihel J. The zebrafish mutant dreammist implicates sodium homeostasis in sleep regulation. eLife 2023; 12:RP87521. [PMID: 37548652 PMCID: PMC10406431 DOI: 10.7554/elife.87521] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/08/2023] Open
Abstract
Sleep is a nearly universal feature of animal behaviour, yet many of the molecular, genetic, and neuronal substrates that orchestrate sleep/wake transitions lie undiscovered. Employing a viral insertion sleep screen in larval zebrafish, we identified a novel gene, dreammist (dmist), whose loss results in behavioural hyperactivity and reduced sleep at night. The neuronally expressed dmist gene is conserved across vertebrates and encodes a small single-pass transmembrane protein that is structurally similar to the Na+,K+-ATPase regulator, FXYD1/Phospholemman. Disruption of either fxyd1 or atp1a3a, a Na+,K+-ATPase alpha-3 subunit associated with several heritable movement disorders in humans, led to decreased night-time sleep. Since atpa1a3a and dmist mutants have elevated intracellular Na+ levels and non-additive effects on sleep amount at night, we propose that Dmist-dependent enhancement of Na+ pump function modulates neuronal excitability to maintain normal sleep behaviour.
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Affiliation(s)
- Ida L Barlow
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
| | - Eirinn Mackay
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
| | - Emily Wheater
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
| | - Aimee Goel
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
| | - Sumi Lim
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
| | - Steve Zimmerman
- Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
| | | | - David A Prober
- Division of Biology and Biological Engineering, California Institute of TechnologyPasadenaUnited States
| | - Jason Rihel
- Department of Cell and Developmental Biology, University College LondonLondonUnited Kingdom
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3
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Skogestad J, Aronsen JM. Regulation of Cardiac Contractility by the Alpha 2 Subunit of the Na+/K+-ATPase. Front Physiol 2022; 13:827334. [PMID: 35812308 PMCID: PMC9258780 DOI: 10.3389/fphys.2022.827334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 05/16/2022] [Indexed: 11/14/2022] Open
Abstract
Cytosolic Na + concentrations regulate cardiac excitation-contraction coupling and contractility. Inhibition of the Na+/K+-ATPase (NKA) activity increases cardiac contractility by increasing cytosolic Ca2+ levels, as increased cytosolic Na+ levels are coupled to less Ca2+ extrusion and/or increased Ca2+ influx from the Na+/Ca2+-exchanger. NKA consists of one α subunit and one β subunit, with α1 and α2 being the main α isoforms in cardiomyocytes. Substantial evidence suggests that NKAα2 is the primary regulator of cardiac contractility despite being outnumbered by NKAα1 in cardiomyocytes. This review will mainly focus on differential regulation and subcellular localization of the NKAα1 and NKAα2 isoforms, and their relation to the proposed concept of subcellular gradients of Na+ in cardiomyocytes. We will also discuss the potential roles of NKAα2 in mediating cardiac hypertrophy and ventricular arrhythmias.
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Affiliation(s)
- Jonas Skogestad
- Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Oslo, Norway
- Department of Pharmacology, Oslo University Hospital, Oslo, Norway
| | - Jan Magnus Aronsen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Oslo, Norway
- Department of Pharmacology, Oslo University Hospital, Oslo, Norway
- *Correspondence: Jan Magnus Aronsen,
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Meyer DJ, Bijlani S, de Sautu M, Spontarelli K, Young VC, Gatto C, Artigas P. FXYD protein isoforms differentially modulate human Na/K pump function. J Gen Physiol 2021; 152:211559. [PMID: 33231612 PMCID: PMC7690937 DOI: 10.1085/jgp.202012660] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 10/29/2020] [Indexed: 12/28/2022] Open
Abstract
Tight regulation of the Na/K pump is essential for cellular function because this heteromeric protein builds and maintains the electrochemical gradients for Na+ and K+ that energize electrical signaling and secondary active transport. We studied the regulation of the ubiquitous human α1β1 pump isoform by five human FXYD proteins normally located in muscle, kidney, and neurons. The function of Na/K pump α1β1 expressed in Xenopus oocytes with or without FXYD isoforms was evaluated using two-electrode voltage clamp and patch clamp. Through evaluation of the partial reactions in the absence of K+ but presence of Na+ in the external milieu, we demonstrate that each FXYD subunit alters the equilibrium between E1P(3Na) and E2P, the phosphorylated conformations with Na+ occluded and free from Na+, respectively, thereby altering the apparent affinity for Na+. This modification of Na+ interaction shapes the small effects of FXYD proteins on the apparent affinity for external K+ at physiological Na+. FXYD6 distinctively accelerated both the Na+-deocclusion and the pump-turnover rates. All FXYD isoforms altered the apparent affinity for intracellular Na+ in patches, an effect that was observed only in the presence of intracellular K+. Therefore, FXYD proteins alter the selectivity of the pump for intracellular ions, an effect that could be due to the altered equilibrium between E1 and E2, the two major pump conformations, and/or to small changes in ion affinities that are exacerbated when both ions are present. Lastly, we observed a drastic reduction of Na/K pump surface expression when it was coexpressed with FXYD1 or FXYD6, with the former being relieved by injection of PKA's catalytic subunit into the oocyte. Our results indicate that a prominent effect of FXYD1 and FXYD6, and plausibly other FXYDs, is the regulation of Na/K pump trafficking.
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Affiliation(s)
- Dylan J Meyer
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Sharan Bijlani
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Marilina de Sautu
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Victoria C Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Craig Gatto
- School of Biological Sciences, Illinois State University. Normal, IL
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
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5
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Yap JQ, Seflova J, Sweazey R, Artigas P, Robia SL. FXYD proteins and sodium pump regulatory mechanisms. J Gen Physiol 2021; 153:211866. [PMID: 33688925 PMCID: PMC7953255 DOI: 10.1085/jgp.202012633] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 02/03/2021] [Indexed: 12/12/2022] Open
Abstract
The sodium/potassium-ATPase (NKA) is the enzyme that establishes gradients of sodium and potassium across the plasma membrane. NKA activity is tightly regulated for different physiological contexts through interactions with single-span transmembrane peptides, the FXYD proteins. This diverse family of regulators has in common a domain containing a Phe-X-Tyr-Asp (FXYD) motif, two conserved glycines, and one serine residue. In humans, there are seven tissue-specific FXYD proteins that differentially modulate NKA kinetics as appropriate for each system, providing dynamic responsiveness to changing physiological conditions. Our understanding of how FXYD proteins contribute to homeostasis has benefitted from recent advances described in this review: biochemical and biophysical studies have provided insight into regulatory mechanisms, genetic models have uncovered remarkable complexity of FXYD function in integrated physiological systems, new posttranslational modifications have been identified, high-resolution structural studies have revealed new details of the regulatory interaction with NKA, and new clinical correlations have been uncovered. In this review, we address the structural determinants of diverse FXYD functions and the special roles of FXYDs in various physiological systems. We also discuss the possible roles of FXYDs in protein trafficking and regulation of non-NKA targets.
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Affiliation(s)
- John Q Yap
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Ryan Sweazey
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
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Baasch Christensen I, Cheng L, Brewer JR, Bartsch U, Fenton RA, Damkier HH, Praetorius J. Multiple Na,K-ATPase Subunits Colocalize in the Brush Border of Mouse Choroid Plexus Epithelial Cells. Int J Mol Sci 2021; 22:ijms22041569. [PMID: 33557294 PMCID: PMC7915972 DOI: 10.3390/ijms22041569] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2021] [Accepted: 01/29/2021] [Indexed: 01/24/2023] Open
Abstract
(1) Background: The unusual accumulation of Na,K-ATPase complexes in the brush border membrane of choroid plexus epithelial cells have intrigued researchers for decades. However, the full range of the expressed Na,K-ATPase subunits and their relation to the microvillus cytoskeleton remains unknown. (2) Methods: RT-PCR analysis, co-immunoprecipitation, native PAGE, mass spectrometry, and differential centrifugation were combined with high-resolution immunofluorescence histochemistry, proximity ligase assays, and stimulated emission depletion (STED) microscopy on mouse choroid plexus cells or tissues in order to resolve these issues. (3) Results: The choroid plexus epithelium expresses Na,K-ATPase subunits α1, α2, β1, β2, β3, and phospholemman. The α1, α2, β1, and β2, subunits are all localized to the brush border membrane, where they appear to form a complex. The ATPase complexes may stabilize in the brush border membrane via anchoring to microvillar actin indirectly through ankyrin-3 or directly via other co-precipitated proteins. Aquaporin 1 (AQP1) may form part of the proposed multi-protein complexes in contrast to another membrane protein, the Na-K-2Cl cotransporter 1 (NKCC1). NKCC1 expression seems necessary for full brush border membrane accumulation of the Na,K-ATPase in the choroid plexus. (4) Conclusion: A multitude of Na,K-ATPase subunits form molecular complexes in the choroid plexus brush border, which may bind to the cytoskeleton by various alternative actin binding proteins.
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Affiliation(s)
- Inga Baasch Christensen
- Department of Biomedicine, Faculty of Health Science, Aarhus University, 8000 Aarhus, Denmark; (I.B.C.); (L.C.); (R.A.F.); (H.H.D.)
| | - Lei Cheng
- Department of Biomedicine, Faculty of Health Science, Aarhus University, 8000 Aarhus, Denmark; (I.B.C.); (L.C.); (R.A.F.); (H.H.D.)
| | - Jonathan R. Brewer
- Department of Biochemistry and Molecular Biology, Faculty of Science, University of Southern Denmark, 5230 Odense, Denmark;
| | - Udo Bartsch
- Department of Ophthalmology, Experimental Ophthalmology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany;
| | - Robert A. Fenton
- Department of Biomedicine, Faculty of Health Science, Aarhus University, 8000 Aarhus, Denmark; (I.B.C.); (L.C.); (R.A.F.); (H.H.D.)
| | - Helle H. Damkier
- Department of Biomedicine, Faculty of Health Science, Aarhus University, 8000 Aarhus, Denmark; (I.B.C.); (L.C.); (R.A.F.); (H.H.D.)
| | - Jeppe Praetorius
- Department of Biomedicine, Faculty of Health Science, Aarhus University, 8000 Aarhus, Denmark; (I.B.C.); (L.C.); (R.A.F.); (H.H.D.)
- Correspondence: ; Tel.: +45-61820576
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Upmanyu N, Dietze R, Bulldan A, Scheiner-Bobis G. Cardiotonic steroid ouabain stimulates steroidogenesis in Leydig cells via the α3 isoform of the sodium pump. J Steroid Biochem Mol Biol 2019; 191:105372. [PMID: 31042565 DOI: 10.1016/j.jsbmb.2019.04.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/29/2019] [Accepted: 04/26/2019] [Indexed: 11/28/2022]
Abstract
Cardiotonic steroids such as ouabain are potent inhibitors of the sodium pump and have been widely used for centuries in the treatment of congestive heart failure. In recent decades, however, they have also been identified as hormone-like molecules that trigger signaling cascades of physiological relevance by using the various sodium pump α subunit isoforms as receptors. The murine Leydig cell line MLTC-1 expresses both the ubiquitous, relatively ouabain-insensitive α1 isoform of the sodium pump and the ouabain-sensitive α3 isoform that is normally found in neuronal cells. The physiological relevance of the simultaneous presence of the two isoforms in Leydig cells has not been previously addressed. MLTC-1 Leydig cells contain lipid droplets (LDs) and are capable of progesterone biosynthesis when stimulated by luteinizing hormone (LH). When exposed to low nanomolar concentrations of ouabain, they respond with stimulation of Erk1/2, CREB, and ATF-1 phosphorylation, LD enlargement, and perilipin2 mobilization to the LDs. As a result, progesterone biosynthesis is augmented. Abrogation of α3 isoform expression by siRNA prevents all of the above responses, indicating that it is the hormone/receptor-like interaction of ouabain exclusively with this isoform that triggers the signaling events that normally occur when LH binds to its receptor. Considering that ouabain is produced endogenously and is found in seminal fluid, one can speculate that effects of this substance on germ and somatic cells of the testis might play a role in male reproductive physiology.
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Affiliation(s)
- Neha Upmanyu
- Institut für Veterinär-Physiologie und -Biochemie, Fachbereich Veterinärmedizin, Justus-Liebig Universität Giessen, Giessen, Germany
| | - Raimund Dietze
- Institut für Veterinär-Physiologie und -Biochemie, Fachbereich Veterinärmedizin, Justus-Liebig Universität Giessen, Giessen, Germany
| | - Ahmed Bulldan
- Institut für Veterinär-Physiologie und -Biochemie, Fachbereich Veterinärmedizin, Justus-Liebig Universität Giessen, Giessen, Germany
| | - Georgios Scheiner-Bobis
- Institut für Veterinär-Physiologie und -Biochemie, Fachbereich Veterinärmedizin, Justus-Liebig Universität Giessen, Giessen, Germany.
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8
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Gross NB, Abad N, Lichtstein D, Taron S, Aparicio L, Fonteh AN, Arakaki X, Cowan RP, Grant SC, Harrington MG. Endogenous Na+, K+-ATPase inhibitors and CSF [Na+] contribute to migraine formation. PLoS One 2019; 14:e0218041. [PMID: 31173612 PMCID: PMC6555523 DOI: 10.1371/journal.pone.0218041] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2019] [Accepted: 05/24/2019] [Indexed: 12/24/2022] Open
Abstract
There is strong evidence that neuronal hyper-excitability underlies migraine, and may or may not be preceded by cortical spreading depression. However, the mechanisms for cortical spreading depression and/or migraine are not established. Previous studies reported that cerebrospinal fluid (CSF) [Na+] is higher during migraine, and that higher extracellular [Na+] leads to hyper-excitability. We raise the hypothesis that altered choroid plexus Na+, K+-ATPase activity can cause both migraine phenomena: inhibition raises CSF [K+] and initiates cortical spreading depression, while activation raises CSF [Na+] and causes migraine. In this study, we examined levels of specific Na+, K+-ATPase inhibitors, endogenous ouabain-like compounds (EOLC), in CSF from migraineurs and controls. CSF EOLC levels were significantly lower during ictal migraine (0.4 nM +/- 0.09) than from either controls (1.8 nM +/- 0.4) or interictal migraineurs (3.1 nM +/- 1.9). Blood plasma EOLC levels were higher in migraineurs than controls, but did not differ between ictal and interictal states. In a Sprague-Dawley rat model of nitroglycerin-triggered central sensitization, we changed the concentrations of EOLC and CSF sodium, and measured aversive mechanical threshold (von Frey hairs), trigeminal nucleus caudalis activation (cFos), and CSF [Na+] (ultra-high field 23Na MRI). Animals were sensitized by three independent treatments: intraperitoneal nitroglycerin, immunodepleting EOLC from cerebral ventricles, or cerebroventricular infusion of higher CSF [Na+]. Conversely, nitroglycerin-triggered sensitization was prevented by either vascular or cerebroventricular delivery of the specific Na+, K+-ATPase inhibitor, ouabain. These results affirm our hypothesis that higher CSF [Na+] is linked to human migraine and to a rodent migraine model, and demonstrate that EOLC regulates them both. Our data suggest that altered choroid plexus Na+, K+-ATPase activity is a common source of these changes, and may be the initiating mechanism in migraine.
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Affiliation(s)
- Noah B. Gross
- Huntington Medical Research Institutes, Pasadena, California, United States of America
| | - Nastaren Abad
- Department of Chemical & Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, Florida, United States of America
- Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States of America
| | - David Lichtstein
- Department of Medical Neurobiology, Institute for Medical Research, Israel-Canada, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Shiri Taron
- Department of Medical Neurobiology, Institute for Medical Research, Israel-Canada, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Lorena Aparicio
- Huntington Medical Research Institutes, Pasadena, California, United States of America
| | - Alfred N. Fonteh
- Huntington Medical Research Institutes, Pasadena, California, United States of America
| | - Xianghong Arakaki
- Huntington Medical Research Institutes, Pasadena, California, United States of America
| | - Robert P. Cowan
- Department of Neurology, Stanford University, Palo Alto, California, United States of America
| | - Samuel C. Grant
- Department of Chemical & Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, Florida, United States of America
- Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States of America
| | - Michael G. Harrington
- Huntington Medical Research Institutes, Pasadena, California, United States of America
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Hormonal regulation of Na +-K +-ATPase from the evolutionary perspective. CURRENT TOPICS IN MEMBRANES 2019; 83:315-351. [PMID: 31196608 DOI: 10.1016/bs.ctm.2019.01.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Na+-K+-ATPase, an α/β heterodimer, is an ancient enzyme that maintains Na+ and K+ gradients, thus preserving cellular ion homeostasis. In multicellular organisms, this basic housekeeping function is integrated to fulfill the needs of specialized organs and preserve whole-body homeostasis. In vertebrates, Na+-K+-ATPase is essential for many fundamental physiological processes, such as nerve conduction, muscle contraction, nutrient absorption, and urine excretion. During vertebrate evolution, three key developments contributed to diversification and integration of Na+-K+-ATPase functions. Generation of novel α- and β-subunits led to formation of multiple Na+-K+-ATPase isoenyzmes with distinct functional characteristics. Development of a complex endocrine system enabled efficient coordination of diverse Na+-K+-ATPase functions. Emergence of FXYDs, small transmembrane proteins that regulate Na+-K+-ATPase, opened new ways to modulate its function. FXYDs are a vertebrate innovation and an important site of hormonal action, suggesting they played an especially prominent role in evolving interaction between Na+-K+-ATPase and the endocrine system in vertebrates.
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Matagne V, Wondolowski J, Frerking M, Shahidullah M, Delamere NA, Sandau US, Budden S, Ojeda SR. Correcting deregulated Fxyd1 expression rescues deficits in neuronal arborization and potassium homeostasis in MeCP2 deficient male mice. Brain Res 2018; 1697:45-52. [PMID: 29902467 DOI: 10.1016/j.brainres.2018.06.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 05/22/2018] [Accepted: 06/11/2018] [Indexed: 12/26/2022]
Abstract
Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the MECP2 gene. In the absence of MeCP2, expression of FXYD domain-containing transport regulator 1 (FXYD1) is deregulated in the frontal cortex (FC) of mice and humans. Because Fxyd1 is a membrane protein that controls cell excitability by modulating Na+, K+-ATPase activity (NKA), an excess of Fxyd1 may reduce NKA activity and contribute to the neuronal phenotype of Mecp2 deficient (KO) mice. To determine if Fxyd1 can rescue these RTT deficits, we studied the male progeny of Fxyd1 null males bred to heterozygous Mecp2 female mice. Maximal NKA enzymatic activity was not altered by the loss of MeCP2, but it increased in mice lacking one Fxyd1 allele, suggesting that NKA activity is under Fxyd1 inhibitory control. Deletion of one Fxyd1 allele also prevented the increased extracellular potassium (K+) accumulation observed in cerebro-cortical neurons from Mecp2 KO animals in response to the NKA inhibitor ouabain, and rescued the loss of dendritic arborization observed in FC neurons of Mecp2 KO mice. These effects were gene-dose dependent, because the absence of Fxyd1 failed to rescue the MeCP2-dependent deficits, and mimicked the effect of MeCP2 deficiency in wild-type animals. These results indicate that excess of Fxyd1 in the absence of MeCP2 results in deregulation of endogenous K+ conductances functionally associated with NKA and leads to stunted neuronal growth.
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Affiliation(s)
- Valerie Matagne
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, OR 97006, USA.
| | - Joyce Wondolowski
- Neuroscience Graduate Program, Oregon Health and Sciences University, Portland, OR 97239, USA.
| | - Matthew Frerking
- Departments of Behavioral Neuroscience, Oregon Health & Science University, Portland, OR 97239, USA.
| | | | | | - Ursula S Sandau
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, OR 97006, USA.
| | - Sarojini Budden
- Division of Developmental Pediatrics, Oregon Health & Science University, Portland, OR 97239, USA.
| | - Sergio R Ojeda
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, OR 97006, USA.
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11
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Arystarkhova E, Bouley R, Liu YB, Sweadner KJ. Impaired AQP2 trafficking in Fxyd1 knockout mice: A role for FXYD1 in regulated vesicular transport. PLoS One 2017; 12:e0188006. [PMID: 29155857 PMCID: PMC5695786 DOI: 10.1371/journal.pone.0188006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Accepted: 10/30/2017] [Indexed: 01/08/2023] Open
Abstract
The final adjustment of urine volume occurs in the inner medullary collecting duct (IMCD), chiefly mediated by the water channel aquaporin 2 (AQP2). With vasopressin stimulation, AQP2 accumulation in the apical plasma membrane of principal cells allows water reabsorption from the lumen. We report that FXYD1 (phospholemman), better known as a regulator of Na,K-ATPase, has a role in AQP2 trafficking. Daytime urine of Fxyd1 knockout mice was more dilute than WT despite similar serum vasopressin, but both genotypes could concentrate urine during water deprivation. FXYD1 was found in IMCD. In WT mice, phosphorylated FXYD1 was detected intracellularly, and vasopressin induced its dephosphorylation. We tested the hypothesis that the dilute urine in knockouts was caused by alteration of AQP2 trafficking. In WT mice at baseline, FXYD1 and AQP2 were not strongly co-localized, but elevation of vasopressin produced translocation of both FXYD1 and AQP2 to the apical plasma membrane. In kidney slices, baseline AQP2 distribution was more scattered in the Fxyd1 knockout than in WT. Apical recruitment of AQP2 occurred in vasopressin-treated Fxyd1 knockout slices, but upon vasopressin washout, there was more rapid reversal of apical AQP2 localization and more heterogeneous cytoplasmic distribution of AQP2. Notably, in sucrose gradients, AQP2 was present in a detergent-resistant membrane domain that had lower sedimentation density in the knockout than in WT, and vasopressin treatment normalized its density. We propose that FXYD1 plays a role in regulating AQP2 retention in apical membrane, and that this involves transfers between raft-like membrane domains in endosomes and plasma membranes.
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Affiliation(s)
- Elena Arystarkhova
- Laboratory of Membrane Biology, Dept. of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, Unites States of America
- * E-mail: (EA); (KJS)
| | - Richard Bouley
- Center for Systems Biology, Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Yi Bessie Liu
- Laboratory of Membrane Biology, Dept. of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, Unites States of America
| | - Kathleen J. Sweadner
- Laboratory of Membrane Biology, Dept. of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, Unites States of America
- * E-mail: (EA); (KJS)
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12
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Praetorius J, Damkier HH. Transport across the choroid plexus epithelium. Am J Physiol Cell Physiol 2017; 312:C673-C686. [PMID: 28330845 DOI: 10.1152/ajpcell.00041.2017] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 11/22/2022]
Abstract
The choroid plexus epithelium is a secretory epithelium par excellence. However, this is perhaps not the most prominent reason for the massive interest in this modest-sized tissue residing inside the brain ventricles. Most likely, the dominant reason for extensive studies of the choroid plexus is the identification of this epithelium as the source of the majority of intraventricular cerebrospinal fluid. This finding has direct relevance for studies of diseases and conditions with deranged central fluid volume or ionic balance. While the concept is supported by the vast majority of the literature, the implication of the choroid plexus in secretion of the cerebrospinal fluid was recently challenged once again. Three newer and promising areas of current choroid plexus-related investigations are as follows: 1) the choroid plexus epithelium as the source of mediators necessary for central nervous system development, 2) the choroid plexus as a route for microorganisms and immune cells into the central nervous system, and 3) the choroid plexus as a potential route for drug delivery into the central nervous system, bypassing the blood-brain barrier. Thus, the purpose of this review is to highlight current active areas of research in the choroid plexus physiology and a few matters of continuous controversy.
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Affiliation(s)
- Jeppe Praetorius
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and
| | - Helle Hasager Damkier
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and.,Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Development of a high-affinity peptide that prevents phospholemman (PLM) inhibition of the sodium/calcium exchanger 1 (NCX1). Biochem J 2016; 473:2413-23. [PMID: 27247424 PMCID: PMC4964977 DOI: 10.1042/bcj20160465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 05/31/2016] [Indexed: 11/17/2022]
Abstract
NCX1 (Na+/Ca2+ exchanger 1) is an important regulator of intracellular Ca2+ and a potential therapeutic target for brain ischaemia and for diastolic heart failure with preserved ejection fraction. PLM (phospholemman), a substrate for protein kinases A and C, has been suggested to regulate NCX1 activity. However, although several studies have demonstrated that binding of phosphorylated PLM (pSer68-PLM) leads to NCX1 inhibition, other studies have failed to demonstrate a functional interaction of these proteins. In the present study, we aimed to analyse the biological function of the pSer68-PLM–NCX1 interaction by developing high-affinity blocking peptides. PLM was observed to co-fractionate and co-immunoprecipitate with NCX1 in rat left ventricle, and in co-transfected HEK (human embryonic kidney)-293 cells. For the first time, the NCX1–PLM interaction was also demonstrated in the brain. PLM binding sites on NCX1 were mapped to two regions by peptide array assays, containing the previously reported PASKT and QKHPD motifs. Conversely, the two NCX1 regions bound identical sequences in the cytoplasmic domain of PLM, suggesting that NCX1-PASKT and NCX1-QKHPD might bind to each PLM monomer. Using two-dimensional peptide arrays of the native NCX1 sequence KHPDKEIEQLIELANYQVLS revealed that double substitution of tyrosine for positions 1 and 4 (K1Y and D4Y) enhanced pSer68-PLM binding 8-fold. The optimized peptide blocked binding of NCX1-PASKT and NCX1-QKHPD to PLM and reversed PLM(S68D) inhibition of NCX1 activity (both forward and reverse mode) in HEK-293 cells. Altogether our data indicate that PLM interacts directly with NCX1 and inhibits NCX1 activity when phosphorylated at Ser68.
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Mishra NK, Habeck M, Kirchner C, Haviv H, Peleg Y, Eisenstein M, Apell HJ, Karlish SJD. Molecular Mechanisms and Kinetic Effects of FXYD1 and Phosphomimetic Mutants on Purified Human Na,K-ATPase. J Biol Chem 2015; 290:28746-59. [PMID: 26429909 DOI: 10.1074/jbc.m115.687913] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (FXYD1) is a single-transmembrane protein regulator of Na,K-ATPase, expressed strongly in heart, skeletal muscle, and brain and phosphorylated by protein kinases A and C at Ser-68 and Ser-63, respectively. Binding of FXYD1 reduces Na,K-ATPase activity, and phosphorylation at Ser-68 or Ser-63 relieves the inhibition. Despite the accumulated information on physiological effects, whole cell studies provide only limited information on molecular mechanisms. As a complementary approach, we utilized purified human Na,K-ATPase (α1β1 and α2β1) reconstituted with FXYD1 or mutants S63E, S68E, and S63E,S68E that mimic phosphorylation at Ser-63 and Ser-68. Compared with control α1β1, FXYD1 reduces Vmax and turnover rate and raises K0.5Na. The phosphomimetic mutants reverse these effects and reduce K0.5Na below control K0.5Na. Effects on α2β1 are similar but smaller. Experiments in proteoliposomes reconstituted with α1β1 show analogous effects of FXYD1 on K0.5Na, which are abolished by phosphomimetic mutants and also by increasing mole fractions of DOPS in the proteoliposomes. Stopped-flow experiments using the dye RH421 show that FXYD1 slows the conformational transition E2(2K)ATP → E1(3Na)ATP but does not affect 3NaE1P → E2P3Na. This regulatory effect is explained simply by molecular modeling, which indicates that a cytoplasmic helix (residues 60-70) docks between the αN and αP domains in the E2 conformation, but docking is weaker in E1 (also for phosphomimetic mutants). Taken together with previous work showing that FXYD1 also raises binding affinity for the Na(+)-selective site III, these results provide a rather comprehensive picture of the regulatory mechanism of FXYD1 that complements the physiological studies.
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Affiliation(s)
| | | | - Corinna Kirchner
- the Department of Biology, University of Konstanz, 78464 Konstanz, Germany
| | - Haim Haviv
- From the Department of Biological Chemistry
| | - Yoav Peleg
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot 7610001, Israel and
| | | | - Hans Juergen Apell
- the Department of Biology, University of Konstanz, 78464 Konstanz, Germany
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Pejchinovski M, Hrnjez D, Ramirez-Torres A, Bitsika V, Mermelekas G, Vlahou A, Zürbig P, Mischak H, Metzger J, Koeck T. Capillary zone electrophoresis on-line coupled to mass spectrometry: A perspective application for clinical proteomics. Proteomics Clin Appl 2015; 9:453-68. [DOI: 10.1002/prca.201400113] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 11/21/2014] [Accepted: 01/14/2015] [Indexed: 12/21/2022]
Affiliation(s)
| | | | | | - Vasiliki Bitsika
- Biotechnology Division; Biomedical Research Foundation, Academy of Athens; Athens Greece
| | - George Mermelekas
- Biotechnology Division; Biomedical Research Foundation, Academy of Athens; Athens Greece
| | - Antonia Vlahou
- Biotechnology Division; Biomedical Research Foundation, Academy of Athens; Athens Greece
- School of Biomedical and Healthcare Sciences; Plymouth University, Plymouth; UK
| | | | - Harald Mischak
- Mosaiques Diagnostics GmbH; Hanover Germany
- Institute of Cardiovascular and Medical Sciences; University of Glasgow; UK
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Changes in the Distribution of the α 3 Na(+)/K(+) ATPase Subunit in Heterozygous Lurcher Purkinje Cells as a Genetic Model of Chronic Depolarization during Development. Int J Cell Biol 2014; 2014:152645. [PMID: 24719618 PMCID: PMC3955620 DOI: 10.1155/2014/152645] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 12/28/2013] [Accepted: 01/13/2014] [Indexed: 11/30/2022] Open
Abstract
A common assumption of excitotoxic mechanisms in the nervous system is that the ionic imbalance resulting from overstimulation of glutamate receptors and increased Na+ and Ca++ influx overwhelms cellular energy metabolic systems leading to cell death. The goal of this study was to examine how a chronic Na+ channel leak current in developing Purkinje cells in the heterozygous Lurcher mutant (+/Lc) affects the expression and distribution of the α3 subunit of the Na+/K+ ATPase pump, a key component of the homeostasis system that maintains ionic equilibrium in neurons. The expression pattern of the catalytic α3 Na+/K+ ATPase subunit was analyzed by immunohistochemistry, histochemistry, and Western Blots in wild type (WT) and +/Lc cerebella at postnatal days P10, P15, and P25 to determine if there are changes in the distribution of active Na+/K+ ATPase subunits in degenerating Purkinje cells. The results suggest that the expression of the catalytic α3 subunit is altered in chronically depolarized +/Lc Purkinje cells, although the density of active Na+/K+ ATPase pumps is not significantly altered compared with WT in the cerebellar cortex at P15, and then declines from P15 to P25 in the +/Lc cerebellum as the +/Lc Purkinje cells degenerate.
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Cirri E, Kirchner C, Becker S, Katz A, Karlish SJ, Apell HJ. Surface charges of the membrane crucially affect regulation of Na,K-ATPase by phospholemman (FXYD1). J Membr Biol 2013; 246:967-79. [PMID: 24105627 DOI: 10.1007/s00232-013-9600-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 09/24/2013] [Indexed: 01/02/2023]
Abstract
The human α1/His10-β1 isoform of Na,K-ATPase has been reconstituted as a complex with and without FXYD1 into proteoliposomes of various lipid compositions in order to study the effect of the regulatory subunit on the half-saturating Na⁺ concentration (K(½)) of Na⁺ ions for activation of the ion pump. It has been shown that the fraction of negatively charged lipid in the bilayer crucially affects the regulatory properties. At low concentrations of the negatively charged lipid DOPS (<10 %), FXYD1 increases K(½) of Na⁺ ions for activation of the ion pump. Phosphorylation of FXYD1 by protein kinase A at Ser68 abrogates this effect. Conversely, for proteoliposomes made with high concentrations of DOPS (>10 %), little or no effect of FXYD1 on the K(½) of Na⁺ ions is observed. Depending on ionic strength and lipid composition of the proteoliposomes, FXYD1 can alter the K(½) of Na⁺ ions by up to twofold. We propose possible molecular mechanisms to explain the regulatory effects of FXYD1 and the influence of charged lipid and protein phosphorylation. In particular, the positively charged C-terminal helix of FXYD1 appears to be highly mobile and may interact with the cytoplasmic N domain of the α-subunit, the interaction being strongly affected by phosphorylation at Ser68 and the surface charge of the membrane.
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Affiliation(s)
- Erica Cirri
- Department of Biology and Graduate School of Chemical Biology, University of Konstanz, 78464, Constance, Germany
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Damkier HH, Brown PD, Praetorius J. Cerebrospinal Fluid Secretion by the Choroid Plexus. Physiol Rev 2013; 93:1847-92. [DOI: 10.1152/physrev.00004.2013] [Citation(s) in RCA: 291] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.
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Affiliation(s)
- Helle H. Damkier
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and Faculty of Life Sciences, Michael Smith Building, Manchester University, Manchester, United Kingdom
| | - Peter D. Brown
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and Faculty of Life Sciences, Michael Smith Building, Manchester University, Manchester, United Kingdom
| | - Jeppe Praetorius
- Department of Biomedicine, Health, Aarhus University, Aarhus, Denmark; and Faculty of Life Sciences, Michael Smith Building, Manchester University, Manchester, United Kingdom
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Pavlovic D, Fuller W, Shattock MJ. Novel regulation of cardiac Na pump via phospholemman. J Mol Cell Cardiol 2013; 61:83-93. [PMID: 23672825 DOI: 10.1016/j.yjmcc.2013.05.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 04/30/2013] [Accepted: 05/03/2013] [Indexed: 12/19/2022]
Abstract
As the only quantitatively significant Na efflux pathway from cardiac cells, the Na/K ATPase (Na pump) is the primary regulator of intracellular Na. The transmembrane Na gradient it establishes is essential for normal electrical excitability, numerous coupled-transport processes and, as the driving force for Na/Ca exchange, thus setting cardiac Ca load and contractility. As Na influx varies with electrical excitation, heart rate and pathology, the dynamic regulation of Na efflux is essential. It is now widely recognized that phospholemman, a 72 amino acid accessory protein which forms part of the Na pump complex, is the key nexus linking cellular signaling to pump regulation. Phospholemman is the target of a variety of post-translational modifications (including phosphorylation, palmitoylation and glutathionation) and these can dynamically alter the activity of the Na pump. This review summarizes our current understanding of the multiple regulatory mechanisms that converge on phospholemman and govern NA pump activity in the heart. The corrected Fig. 4 is reproduced below. The publisher would like to apologize for any inconvenience caused. [corrected].
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Affiliation(s)
- Davor Pavlovic
- Cardiovascular Division, King's College London, The Rayne Institute, St Thomas' Hospital, London, UK.
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20
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Arakaki X, McCleary P, Techy M, Chiang J, Kuo L, Fonteh AN, Armstrong B, Levy D, Harrington MG. Na,K-ATPase alpha isoforms at the blood-cerebrospinal fluid-trigeminal nerve and blood-retina interfaces in the rat. Fluids Barriers CNS 2013; 10:14. [PMID: 23497725 PMCID: PMC3636111 DOI: 10.1186/2045-8118-10-14] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2012] [Accepted: 03/07/2013] [Indexed: 01/12/2023] Open
Abstract
Background Cerebrospinal fluid (CSF) sodium concentration increases during migraine attacks, and both CSF and vitreous humor sodium increase in the rat migraine model. The Na,K-ATPase is a probable source of these sodium fluxes. Since Na,K-ATPase isoforms have different locations and physiological roles, our objective was to establish which alpha isoforms are present at sites where sodium homeostasis is disrupted. Methods Specific Na,K-ATPase alpha isoforms were identified in rat tissues by immunohistochemistry at the blood-CSF barrier at the choroid plexus, at the blood-CSF-trigeminal barrier at the meninges, at the blood-retina barrier, and at the blood-aqueous barrier at the ciliary body. Calcitonin gene-related peptide (CGRP), occludin, or von Willibrand factor (vWF) were co-localized with Na,K-ATPase to identify trigeminal nociceptor fibers, tight junctions, and capillary endothelial cells respectively. Results The Na,K-ATPase alpha-2 isoform is located on capillaries and intensely at nociceptive trigeminal nerve fibers at the meningeal blood-CSF-trigeminal barrier. Alpha-1 and −3 are lightly expressed on the trigeminal nerve fibers but not at capillaries. Alpha-2 is expressed at the blood-retina barriers and, with alpha-1, at the ciliary body blood aqueous barrier. Intense apical membrane alpha-1 was associated with moderate cytoplasmic alpha-2 expression at the choroid plexus blood-CSF barrier. Conclusion Na,K-ATPase alpha isoforms are present at the meningeal, choroid plexus, and retinal barriers. Alpha-2 predominates at the capillary endothelial cells in the meninges and retinal ganglion cell layer.
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Affiliation(s)
- Xianghong Arakaki
- Molecular Neurology Program, Huntington Medical Research Institutes, 99 N, El Molino Avenue, Pasadena, CA, 91101, USA.
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Expression profiles of branchial FXYD proteins in the brackish medaka Oryzias dancena: a potential saltwater fish model for studies of osmoregulation. PLoS One 2013; 8:e55470. [PMID: 23383199 PMCID: PMC3561181 DOI: 10.1371/journal.pone.0055470] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Accepted: 12/23/2012] [Indexed: 12/03/2022] Open
Abstract
FXYD proteins are novel regulators of Na+-K+-ATPase (NKA). In fish subjected to salinity challenges, NKA activity in osmoregulatory organs (e.g., gills) is a primary driving force for the many ion transport systems that act in concert to maintain a stable internal environment. Although teleostean FXYD proteins have been identified and investigated, previous studies focused on only a limited group of species. The purposes of the present study were to establish the brackish medaka (Oryzias dancena) as a potential saltwater fish model for osmoregulatory studies and to investigate the diversity of teleostean FXYD expression profiles by comparing two closely related euryhaline model teleosts, brackish medaka and Japanese medaka (O. latipes), upon exposure to salinity changes. Seven members of the FXYD protein family were identified in each medaka species, and the expression of most branchial fxyd genes was salinity-dependent. Among the cloned genes, fxyd11 was expressed specifically in the gills and at a significantly higher level than the other fxyd genes. In the brackish medaka, branchial fxyd11 expression was localized to the NKA-immunoreactive cells in gill epithelia. Furthermore, the FXYD11 protein interacted with the NKA α-subunit and was expressed at a higher level in freshwater-acclimated individuals relative to fish in other salinity groups. The protein sequences and tissue distributions of the FXYD proteins were very similar between the two medaka species, but different expression profiles were observed upon salinity challenge for most branchial fxyd genes. Salinity changes produced different effects on the FXYD11 and NKA α-subunit expression patterns in the gills of the brackish medaka. To our knowledge, this report is the first to focus on FXYD expression in the gills of closely related euryhaline teleosts. Given the advantages conferred by the well-developed Japanese medaka system, we propose the brackish medaka as a saltwater fish model for osmoregulatory studies.
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Chang JT, Lowery LA, Sive H. Multiple roles for the Na,K-ATPase subunits, Atp1a1 and Fxyd1, during brain ventricle development. Dev Biol 2012; 368:312-22. [PMID: 22683378 DOI: 10.1016/j.ydbio.2012.05.034] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Revised: 05/29/2012] [Accepted: 05/29/2012] [Indexed: 01/26/2023]
Abstract
Formation of the vertebrate brain ventricles requires both production of cerebrospinal fluid (CSF), and its retention in the ventricles. The Na,K-ATPase is required for brain ventricle development, and we show here that this protein complex impacts three associated processes. The first requires both the alpha subunit (Atp1a1) and the regulatory subunit, Fxyd1, and leads to formation of a cohesive neuroepithelium, with continuous apical junctions. The second process leads to modulation of neuroepithelial permeability, and requires Atp1a1, which increases permeability with partial loss of function and decreases it with overexpression. In contrast, fxyd1 overexpression does not alter neuroepithelial permeability, suggesting that its activity is limited to neuroepithelium formation. RhoA regulates both neuroepithelium formation and permeability, downstream of the Na,K-ATPase. A third process, likely to be CSF production, is RhoA-independent, requiring Atp1a1, but not Fxyd1. Consistent with a role for Na,K-ATPase pump function, the inhibitor ouabain prevents neuroepithelium formation, while intracellular Na(+) increases after Atp1a1 and Fxyd1 loss of function. These data include the first reported role for Fxyd1 in the developing brain, and indicate that the Na,K-ATPase regulates three aspects of brain ventricle development essential for normal function: formation of a cohesive neuroepithelium, restriction of neuroepithelial permeability, and production of CSF.
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Affiliation(s)
- Jessica T Chang
- Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA 02142, United States
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Dawson J, Walters M, Delles C, Mischak H, Mullen W. Urinary proteomics to support diagnosis of stroke. PLoS One 2012; 7:e35879. [PMID: 22615742 PMCID: PMC3353991 DOI: 10.1371/journal.pone.0035879] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Accepted: 03/23/2012] [Indexed: 01/17/2023] Open
Abstract
Accurate diagnosis in suspected ischaemic stroke can be difficult. We explored the urinary proteome in patients with stroke (n = 69), compared to controls (n = 33), and developed a biomarker model for the diagnosis of stroke. We performed capillary electrophoresis online coupled to micro-time-of-flight mass spectrometry. Potentially disease-specific peptides were identified and a classifier based on these was generated using support vector machine-based software. Candidate biomarkers were sequenced by liquid chromatography-tandem mass spectrometry. We developed two biomarker-based classifiers, employing 14 biomarkers (nominal p-value <0.004) or 35 biomarkers (nominal p-value <0.01). When tested on a blinded test set of 47 independent samples, the classification factor was significantly different between groups; for the 35 biomarker model, median value of the classifier was 0.49 (−0.30 to 1.25) in cases compared to −1.04 (IQR −1.86 to −0.09) in controls, p<0.001. The 35 biomarker classifier gave sensitivity of 56%, specificity was 93% and the AUC on ROC analysis was 0.86. This study supports the potential for urinary proteomic biomarker models to assist with the diagnosis of acute stroke in those with mild symptoms. We now plan to refine further and explore the clinical utility of such a test in large prospective clinical trials.
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Affiliation(s)
- Jesse Dawson
- Institute of Cardiovascular and Medical Sciences, College of Medicine, Veterinary & Life Sciences, University of Glasgow, Glasgow, United Kingdom.
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Role of protein kinase C in phospholemman mediated regulation of α2β1 isozyme of Na+/K+-ATPase in caveolae of pulmonary artery smooth muscle cells. Biochimie 2012; 94:991-1000. [DOI: 10.1016/j.biochi.2011.12.020] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 12/22/2011] [Indexed: 11/19/2022]
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Bøttger P, Doğanlı C, Lykke-Hartmann K. Migraine- and dystonia-related disease-mutations of Na+/K+-ATPases: relevance of behavioral studies in mice to disease symptoms and neurological manifestations in humans. Neurosci Biobehav Rev 2011; 36:855-71. [PMID: 22067897 DOI: 10.1016/j.neubiorev.2011.10.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 10/20/2011] [Accepted: 10/26/2011] [Indexed: 10/15/2022]
Abstract
The two autosomal dominantly inherited neurological diseases: familial hemiplegic migraine type 2 (FHM2) and familial rapid-onset of dystonia-parkinsonism (Familial RDP) are caused by in vivo mutations of specific alpha subunits of the sodium-potassium pump (Na(+)/K(+)-ATPase). Intriguingly, patients with classical FHM2 and RDP symptoms additionally suffer from other manifestations, such as epilepsy/seizures and developmental disabilities. Recent studies of FHM2 and RDP mouse models provide valuable tools for dissecting the vital roles of the Na(+)/K(+)-ATPases, and we discuss their relevance to the complex patient symptoms and manifestations. Thus, it is interesting that mouse models targeting a specific α-isoform cause different, although still comparable, phenotypes consistent with classical symptoms and other manifestations observed in FHM2 and RDP patients. This review highlights that use of mouse models have broad potentials for future research concerning migraine and dystonia-related diseases, which will contribute towards understanding the, yet unknown, pathophysiologies.
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Affiliation(s)
- Pernille Bøttger
- Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Denmark; Department of Biomedicine, Aarhus University, Ole Worms Allé 3, Aarhus C, Denmark
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Benziane B, Widegren U, Pirkmajer S, Henriksson J, Stepto NK, Chibalin AV. Effect of exercise and training on phospholemman phosphorylation in human skeletal muscle. Am J Physiol Endocrinol Metab 2011; 301:E456-66. [PMID: 21653224 DOI: 10.1152/ajpendo.00533.2010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Phospholemman (PLM, FXYD1) is a partner protein and regulator of the Na(+)-K(+)-ATPase (Na(+)-K(+) pump). We explored the impact of acute and short-term training exercise on PLM physiology in human skeletal muscle. A group of moderately trained males (n = 8) performed a 1-h acute bout of exercise by utilizing a one-legged cycling protocol. Muscle biopsies were taken from vastus lateralis at 0 and 63 min (non-exercised leg) and 30 and 60 min (exercised leg). In a group of sedentary males (n = 9), we determined the effect of a 10-day intense aerobic cycle training on Na(+)-K(+)-ATPase subunit expression, PLM phosphorylation, and total PLM expression as well as PLM phosphorylation in response to acute exercise (1 h at ∼72% Vo(2peak)). Biopsies were taken at rest, immediately following, and 3 h after an acute exercise bout before and at the conclusion of the 10-day training study. PLM phosphorylation was increased both at Ser(63) and Ser(68) immediately after acute exercise (75%, P < 0.05, and 30%, P < 0.05, respectively). Short-term training had no adaptive effect on PLM phosphorylation at Ser(63) and Ser(68), nor was the total amount of PLM altered posttraining. The protein expressions of α(1)-, α(2)-,and β(1)-subunits of Na(+)-K(+)-ATPase were increased after training (113%, P < 0.05, 49%, P < 0.05, and 27%, P < 0.05, respectively). Whereas an acute bout of exercise increased the phosphorylation of PKCα/βII on Thr(638/641) pre- and posttraining, phosphorylation of PKCζ/λ on Thr(403/410) was increased in response to acute exercise only after the 10-day training. In conclusion, we show that only acute exercise, and not short-term training, increases phosphorylation of PLM on Ser(63) and Ser(68), and data from one-legged cycling indicate that this effect of exercise on PLM phosphorylation is not due to systemic factors. Our results provide evidence that phosphorylation of PLM may play a role in the acute regulation of the Na(+)-K(+)-ATPase response to exercise.
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Affiliation(s)
- Boubacar Benziane
- Dept. of Molecular Medicine and Surgery, Integrative Physiology, Karolinska Institutet, Stockholm, Sweden
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Cirri E, Katz A, Mishra NK, Belogus T, Lifshitz Y, Garty H, Karlish SJD, Apell HJ. Phospholemman (FXYD1) raises the affinity of the human α1β1 isoform of Na,K-ATPase for Na ions. Biochemistry 2011; 50:3736-48. [PMID: 21449573 DOI: 10.1021/bi2001714] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The human α(1)/His(10)-β(1) isoform of the Na,K-ATPase has been expressed in Pichia pastoris, solubilized in n-dodecyl-β-maltoside, and purified by metal chelate chromatography. The α(1)β(1) complex spontaneously associates in vitro with the detergent-solubilized purified human FXYD1 (phospholemman) expressed in Escherichia coli. It has been confirmed that FXYD1 spontaneously associates in vitro with the α(1)/His(10)-β(1) complex and stabilizes it in an active mode. The functional properties of the α(1)/His(10)-β(1) and α(1)/His(10)-β(1)/FXYD1 complexes have been investigated by fluorescence methods. The electrochromic dye RH421 which monitors binding to and release of ions from the binding sites has been applied in equilibrium titration experiments to determine ion binding affinities and revealed that FXYD1 induces an ∼30% increase of the Na(+)-binding affinity in both the E(1) and P-E(2) conformations. By contrast, it does not affect the affinities for K(+) and Rb(+) ions. Phosphorylation induced partial reactions of the enzyme have been studied as backdoor phosphorylation by inorganic phosphate and in kinetic experiments with caged ATP in order to evaluate the ATP-binding affinity and the time constant of the conformational transition, Na(3)E(1)-P → P-E(2)Na(3). No significant differences with or without FXYD1 could be detected. Rate constants of the conformational transitions Rb(2)E(1) → E(2)(Rb(2)) and E(2)(Rb(2)) → Na(3)E(1), investigated with fluorescein-labeled Na,K-ATPase, showed only minor or no effects of FXYD1, respectively. The conclusion from all these experiments is that FXYD1 raises the binding affinity of α(1)β(1) for Na ions, presumably at the third Na-selective binding site. In whole cell expression studies FXYD1 reduces the apparent affinity for Na ions. Possible reasons for the difference from this study using the purified recombinant Na,K-ATPase are discussed.
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Affiliation(s)
- Erica Cirri
- Department of Biology, University of Konstanz, 78464 Konstanz, Germany
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Banine F, Matagne V, Sherman LS, Ojeda SR. Brain region-specific expression of Fxyd1, an Mecp2 target gene, is regulated by epigenetic mechanisms. J Neurosci Res 2011; 89:840-51. [PMID: 21394759 DOI: 10.1002/jnr.22608] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Revised: 12/23/2010] [Accepted: 01/13/2011] [Indexed: 12/25/2022]
Abstract
Fxyd1 encodes a trans-membrane protein that modulates Na(+) ,K(+) -ATPase activity and is a substrate for multiple protein kinases. Fxyd1 expression is repressed by methyl CpG-binding protein 2 (Mecp2) in the frontal cortex (FC) but not in the cerebellum (CB) of the mouse brain. Consistently with these observations, FXYD1 mRNA abundance is increased in the FC of Rett syndrome (RTT) patients with MECP2 mutations. Because Fxyd1 is implicated in the regulation of neuronal excitability, understanding how Fxyd1 expression is controlled is important. Here we report that basal expression of Fxyd1a and Fxyd1b, the two main alternatively spliced forms of Fxyd1 mRNA, is lower in the FC than in the CB. This difference is accompanied by increased Mecp2 recruitment to the promoter region of these two Fxyd1 mRNA forms. DNA methylation of both promoters is more frequent in the FC than in the CB, and in both cases the most frequently methylated CpG dinucleotides are adjacent to [A/T](4) sequences required for high-affinity Mecp2 binding. Consistently with these features of epigenetic silencing, histone 3 acetylated at lysines 9 and 14 (H3K9/14ac) and histone 3 methylated at lysine 4 (H3K4me3), both activating histone marks, were associated with the Fxyd1 promoter to a lesser degree in the FC than in the CB. These results indicate that differential Fxyd1 expression in these two brain regions is, at least in part, regulated by an epigenetic mechanism involving increased DNA methylation of the two alternative Fxyd1 promoters, enhanced Mecp2 recruitment, and reduced association of activating histones.
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Affiliation(s)
- Fatima Banine
- Division of Neuroscience, Oregon National Primate Research Center, Beaverton, Oregon, USA
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Damkier HH, Brown PD, Praetorius J. Epithelial pathways in choroid plexus electrolyte transport. Physiology (Bethesda) 2010; 25:239-49. [PMID: 20699470 DOI: 10.1152/physiol.00011.2010] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A stable intraventricular milieu is crucial for maintaining normal neuronal function. The choroid plexus epithelium produces the cerebrospinal fluid and in doing so influences the chemical composition of the interstitial fluid of the brain. Here, we review the molecular pathways involved in transport of the electrolytes Na+, K+, Cl-, and HCO3(-)across the choroid plexus epithelium.
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Affiliation(s)
- Helle H Damkier
- Department of Anatomy and the Water and Salt Research Center, Aarhus University, Aarhus C, Denmark
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30
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Lingrel JB. The physiological significance of the cardiotonic steroid/ouabain-binding site of the Na,K-ATPase. Annu Rev Physiol 2010; 72:395-412. [PMID: 20148682 DOI: 10.1146/annurev-physiol-021909-135725] [Citation(s) in RCA: 226] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The Na,K-ATPase is the membrane "pump" that generates the Na(+) and K(+) gradients across the plasma membrane that drives many physiological processes. This enzyme is highly sensitive to inhibition by cardiotonic steroids, most notably the digitalis/ouabain class of compounds, which have been used for centuries to treat congestive heart failure and arrhythmias. The amino acids that constitute the ouabain-binding site are highly conserved across the evolutionary spectrum. This could be fortuitous or could result from this site being conserved because it has an important biological function. New physiological approaches using genetically engineered mice are being used to define the biological significance of the "receptor function" of the Na,K-ATPase and its regulation by potential endogenous cardiotonic steroid-like compounds. These studies extend the reach of earlier studies involving the biochemical purification of endogenous regulatory ligands.
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Affiliation(s)
- Jerry B Lingrel
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA.
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Xue Z, Li B, Gu L, Hu X, Li M, Butterworth RF, Peng L. Increased Na, K-ATPase alpha2 isoform gene expression by ammonia in astrocytes and in brain in vivo. Neurochem Int 2010; 57:395-403. [PMID: 20447429 DOI: 10.1016/j.neuint.2010.04.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2009] [Revised: 03/28/2010] [Accepted: 04/27/2010] [Indexed: 10/19/2022]
Abstract
In mouse astrocyte cultures identical to those used in the present study ammonia increases the production of ouabain-like compounds and Na, K-ATPase activity (Kala et al., 2000). Increased activity of Na, K-ATPase could be the result of enhanced production of ouabain-like compounds, since cultured rat astrocytes react to prolonged exposure to a high concentration of ouabain with an upregulation of the Na, K-ATPase alpha(1) isoform (Hosoi et al., 1997). However, unlike astrocytes in brain in vivo and mouse primary cultures, cultured rat astrocytes do not express the astrocyte-specific alpha(2) isoform, which shows a higher affinity for ouabain (EC(50) approximately 0.1 microM) than the alpha(1) isoform (EC(50) approximately 10 microM). In the present study we have investigated (i) effects of ammonia on mRNA and protein expression of alpha(1) and alpha(2) isoforms in primary cultures of mouse astrocytes; (ii) effects of hyperammonia obtained by urease injection on mRNA and protein expression of alpha(1) and alpha(2) isoforms in the brain in vivo; and (iii) effect on observed upregulation of gene expression of AG1478, an inhibitor of the EGF receptor-tyrosine kinase, PP1, an inhibitor of Src, and GM6001, an inhibitor of Zn(2+)-dependent metalloproteinases in the cultured cells. It was established that alpha(2) mRNA and protein expression, but not alpha(1) expression, was upregulated in cultured astrocytes by 1-4 days of exposure to 3 or 5 mM ammonia and that similar upregulation, contrasted by a downregulation of the neuronal alpha(3) subunit occurred in the hyperammonemic brain. Based on the effects of the inhibitors and literature data it is concluded that ammonia activates formation of an endogenous ouabain-like compound, which binds to the Na, K-ATPase, activating Src, which in turn stimulates the receptor-tyrosine kinase of the EGF receptor, leading to activation of the Ras, Raf, MEK pathway and phosphorylation of ERK(1/2), which eventually causes upregulation of alpha(2) gene expression.
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Affiliation(s)
- Zhanxia Xue
- Department of Clinical Pharmacology, China Medical University, Shenyang, PR China
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Sørensen DM, Buch-Pedersen MJ, Palmgren MG. Structural divergence between the two subgroups of P5 ATPases. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:846-55. [PMID: 20416272 DOI: 10.1016/j.bbabio.2010.04.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 04/09/2010] [Accepted: 04/09/2010] [Indexed: 10/19/2022]
Abstract
Evolution of P5 type ATPases marks the origin of eukaryotes but still they remain the least characterized pumps in the superfamily of P-type ATPases. Phylogenetic analysis of available sequences suggests that P5 ATPases should be divided into at least two subgroups, P5A and P5B. P5A ATPases have been identified in the endoplasmic reticulum and seem to have basic functions in protein maturation and secretion. P5B ATPases localize to vacuolar/lysosomal or apical membranes and in animals play a role in hereditary neuronal diseases. Here we have used a bioinformatical approach to identify differences in the primary sequences between the two subgroups. P5A and P5B ATPases appear have a very different membrane topology from other P-type ATPases with two and one, respectively, additional transmembrane segments inserted in the N-terminal end. Based on conservation of residues in the transmembrane region, the two P5 subgroups most likely have different substrate specificities although these cannot be predicted from their sequences. Furthermore, sequence differences between P5A and P5B ATPases are identified in the catalytic domains that could influence key kinetic properties differentially. Together these findings indicate that P5A and P5B ATPases are structurally and functionally different.
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Affiliation(s)
- Danny Mollerup Sørensen
- Centre for Membrane Pumps in Cells and Disease, PUMPKIN, Danish National Research Foundation, Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
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Harrington MG, Fonteh AN, Arakaki X, Cowan RP, Ecke LE, Foster H, Hühmer AF, Biringer RG. Capillary endothelial Na(+), K(+), ATPase transporter homeostasis and a new theory for migraine pathophysiology. Headache 2010; 50:459-78. [PMID: 19845787 PMCID: PMC8020446 DOI: 10.1111/j.1526-4610.2009.01551.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Cerebrospinal fluid sodium concentration ([Na(+)](csf)) increases during migraine, but the cause of the increase is not known. OBJECTIVE Analyze biochemical pathways that influence [Na(+)](csf) to identify mechanisms that are consistent with migraine. METHOD We reviewed sodium physiology and biochemistry publications for links to migraine and pain. RESULTS Increased capillary endothelial cell (CEC) Na(+), K(+), -ATPase transporter (NKAT) activity is probably the primary cause of increased [Na(+)](csf). Physiological fluctuations of all NKAT regulators in blood, many known to be involved in migraine, are monitored by receptors on the luminal wall of brain CECs; signals are then transduced to their abluminal NKATs that alter brain extracellular sodium ([Na(+)](e)) and potassium ([K(+)](e)). CONCLUSIONS We propose a theoretical mechanism for aura and migraine when NKAT activity shifts outside normal limits: (1) CEC NKAT activity below a lower limit increases [K(+)](e), facilitates cortical spreading depression, and causes aura; (2) CEC NKAT activity above an upper limit elevates [Na(+)](e), increases neuronal excitability, and causes migraine; (3) migraine-without-aura may arise from CEC NKAT over-activity without requiring a prior decrease in activity and its consequent spreading depression; (4) migraine triggers disturb, and treatments improve, CEC NKAT homeostasis; (5) CEC NKAT-induced regulation of neural and vasomotor excitability coordinates vascular and neuronal activities, and includes occasional pathology from CEC NKAT-induced apoptosis or cerebral infarction.
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Affiliation(s)
- Michael G Harrington
- Huntington Medical Research Institutes - Molecular Neurology, Pasadena, CA 91101, USA
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Abstract
During activation of the sympathetic nervous system, cardiac performance is increased as part of the fight-or-flight stress response. The increase in contractility with sympathetic stimulation is an orchestrated combination of intrinsic inotropic, lusitropic, and chronotropic effects, mediated in part by activation of beta-adrenergic receptors and protein kinase A. This causes phosphorylation of several Ca cycling proteins in cardiac myocytes (increasing Ca entry via L-type Ca channels, sarcoplasmic reticulum Ca pumping, and the dissociation rate of Ca from the myofilaments). Here, we discuss how stimulation of the Na/K-ATPase, mediated by phosphorylation of phospholemman (a small sarcolemmal protein that associates with and modulates Na/K-ATPase), is an additional important player in the sympathetic fight-or-flight response. Enhancement of Na/K- ATPase activity limits the rise in [Na](i) caused by the higher level of Na influx and by doing so limits the rise in cellular and sarcoplasmic reticulum Ca load by favoring Ca extrusion via the Na/Ca exchanger. Thus, phospholemman-mediated activation of the Na/K-ATPase may prevent Ca overload and triggered arrhythmias during stress.
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35
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Floyd RV, Wray S, Martín-Vasallo P, Mobasheri A. Differential cellular expression of FXYD1 (phospholemman) and FXYD2 (gamma subunit of Na, K-ATPase) in normal human tissues: a study using high density human tissue microarrays. Ann Anat 2009; 192:7-16. [PMID: 19879113 DOI: 10.1016/j.aanat.2009.09.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Revised: 08/03/2009] [Accepted: 09/15/2009] [Indexed: 01/02/2023]
Abstract
FXYD proteins have been proposed to function as regulators of Na, K-ATPase function by lowering affinities of the system for potassium and sodium. However, their distribution in normal human tissues has not been studied. We have therefore used immunohistochemistry and semi-quantitative histomorphometric analysis to determine the relative expression at the protein level and distribution of FXYD1 (phospholemman) and FXYD2 (gamma subunit of Na, K-ATPase) in human Tissue MicroArrays (TMAs). Expression of FXYD1 was abundant in heart, kidney, placenta, skeletal muscle, gastric and anal mucosa, small intestine and colon. Lower FXYD1 expression was detected in uterine, intestinal and bladder smooth muscle, choroid plexus, liver, gallbladder, spleen, breast, prostate and epididymis. The tissue distribution of FXYD2 was less extensive compared to that of FXYD1. There was an abundant expression in kidney and choroid plexus and moderate expression in placenta, amniotic membranes, breast epithelium, salivary glands, pancreas and uterine endometrium. Weaker FXYD2 expression was detected in the adrenal medulla, liver, gallbladder, bladder and pancreas. The common denominator in the distribution of FXYD1 and FXYD2 was expression in highly active transport epithelia of the kidney, choroid plexus, placenta and salivary glands. This study reveals, in human tissues, the specific expression of FXYD proteins, which may associate with Na, K-ATPase in selected cell types and modulate its catalytic properties.
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Affiliation(s)
- Rachel V Floyd
- Physiological Laboratory, Department of Physiology, School of Biomedical Sciences, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, UK
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36
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Bossuyt J, Despa S, Han F, Hou Z, Robia SL, Lingrel JB, Bers DM. Isoform specificity of the Na/K-ATPase association and regulation by phospholemman. J Biol Chem 2009; 284:26749-57. [PMID: 19638348 DOI: 10.1074/jbc.m109.047357] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM) phosphorylation mediates enhanced Na/K-ATPase (NKA) function during adrenergic stimulation of the heart. Multiple NKA isoforms exist, and their function/regulation may differ. We combined fluorescence resonance energy transfer (FRET) and functional measurements to investigate isoform specificity of the NKA-PLM interaction. FRET was measured as the increase in the donor fluorescence (CFP-NKA-alpha1 or CFP-NKA-alpha2) during progressive acceptor (PLM-YFP) photobleach in HEK-293 cells. Both pairs exhibited robust FRET (maximum of 23.6 +/- 3.4% for NKA-alpha1 and 27.5 +/- 2.5% for NKA-alpha2). Donor fluorescence depended linearly on acceptor fluorescence, indicating a 1:1 PLM:NKA stoichiometry for both isoforms. PLM phosphorylation induced by cAMP-dependent protein kinase and protein kinase C activation drastically reduced the FRET with both NKA isoforms. However, submaximal cAMP-dependent protein kinase activation had less effect on PLM-NKA-alpha2 versus PLM-NKA-alpha1. Surprisingly, ouabain virtually abolished NKA-PLM FRET but only partially reduced co-immunoprecipitation. PLM-CFP also showed FRET to PLM-YFP, but the relationship during progressive photobleach was highly nonlinear, indicating oligomers involving >or=3 monomers. Using cardiac myocytes from wild-type mice and mice where NKA-alpha1 is ouabain-sensitive and NKA-alpha2 is ouabain-resistant, we assessed the effects of PLM phosphorylation on NKA-alpha1 and NKA-alpha2 function. Isoproterenol enhanced internal Na(+) affinity of both isoforms (K((1/2)) decreased from 18.1 +/- 2.0 to 11.5 +/- 1.9 mm for NKA-alpha1 and from 16.4 +/- 2.5 to 10.4 +/- 1.5 mm for NKA-alpha2) without altering maximum transport rate (V(max)). Protein kinase C activation also decreased K((1/2)) for both NKA-alpha1 and NKA-alpha2 (to 9.4 +/- 1.0 and 9.1 +/- 1.1 mm, respectively) but increased V(max) only for NKA-alpha2 (1.9 +/- 0.4 versus 1.2 +/- 0.5 mm/min). In conclusion, PLM associates with and modulates both NKA-alpha1 and NKA-alpha2 in a comparable but not identical manner.
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Affiliation(s)
- Julie Bossuyt
- Department of Pharmacology, University of California, Davis, California 95616, USA
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Wang PJ, Lin CH, Hwang HH, Lee TH. Branchial FXYD protein expression in response to salinity change and its interaction with Na+/K+-ATPase of the euryhaline teleost Tetraodon nigroviridis. ACTA ACUST UNITED AC 2009; 211:3750-8. [PMID: 19011216 DOI: 10.1242/jeb.018440] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Na+/K+-ATPase (NKA) is a ubiquitous membrane-bound protein crucial for teleost osmoregulation. The enzyme is composed of two essential subunits, a catalytic alpha subunit and a glycosylated beta subunit which is responsible for membrane targeting of the enzyme. In mammals, seven FXYD members have been found. FXYD proteins have been identified as the regulatory protein of NKA in mammals and elasmobranchs, it is thus interesting to examine the expression and functions of FXYD protein in the euryhaline teleosts with salinity-dependent changes of gill NKA activity. The present study investigated the expression and distribution of the FXYD protein in gills of seawater (SW)- or freshwater (FW)-acclimated euryhaline pufferfish (Tetraodon nigroviridis). The full-length pufferfish FXYD gene (pFXYD) was confirmed by RT-PCR. pFXYD was found to be expressed in many organs including gills of both SW and FW pufferfish. pFXYD mRNA abundance in gills, determined by real-time PCR, was significantly higher in FW fish than in SW fish. An antiserum raised against a partial amino acid sequence of pFXYD was used for the immunoblots of gill homogenates and a major band at 13 kDa was detected. The relative amounts of pFXYD protein and mRNA in gills of SW and FW pufferfish were identical, but opposite to the expression levels of NKA. Immunofluorescent staining of frozen sections demonstrated that pFXYD was colocalized to NKA-immunoreactive cells in the gill filaments. In addition, interaction between pFXYD and NKA was demonstrated by co-immunoprecipitation. Taken together, salinity-dependent expression of pFXYD protein and NKA, as well as the evidence for their colocalization and interaction in pufferfish gills suggested that pFXYD regulates NKA activity in gills of euryhaline teleosts upon salinity challenge.
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Affiliation(s)
- Pei-Jen Wang
- Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan
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Garcia-Rudaz C, Deng V, Matagne V, Ronnekleiv O, Bosch M, Han V, Percy AK, Ojeda SR. FXYD1, a modulator of Na,K-ATPase activity, facilitates female sexual development by maintaining gonadotrophin-releasing hormone neuronal excitability. J Neuroendocrinol 2009; 21:108-22. [PMID: 19187398 PMCID: PMC2934895 DOI: 10.1111/j.1365-2826.2008.01812.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The excitatory tone to gonadotrophin-releasing hormone (GnRH) neurones is a critical component underlying the pubertal increase in GnRH secretion. However, the homeostatic mechanisms modulating the response of GnRH neurones to excitatory inputs remain poorly understood. A basic mechanism of neuronal homeostasis is the Na(+),K(+)-ATPase-dependent restoration of Na(+) and K(+) transmembrane gradients after neuronal excitation. This activity is reduced in a mouse model of Rett syndrome (RTT), a neurodevelopmental disorder in which expression of FXYD1, a modulator of Na(+),K(+)-ATPase activity, is increased. We now report that the initiation, but not the completion of puberty, is advanced in girls with RTT, and that, in rodents, FXYD1 may contribute to the neuroendocrine regulation of female puberty by modulating GnRH neuronal excitability. Fxyd1 mRNA abundance reaches maximal levels in the female rat hypothalamus by the fourth postnatal week of life (i.e., around the time when the mode of GnRH secretion acquires an adult pattern of release). Although Fxyd1 mRNA expression is low in the hypothalamus, approximately 50% of GnRH neurones contain Fxyd1 transcripts. Whole-cell patch recording of GnRH-EGFP neurones revealed that the neurones of Fxyd1-null female mice respond to somatic current injections with a lower number of action potentials than wild-type cells. Both the age at vaginal opening and at first oestrous were delayed in Fxyd1(-/-) mice, but adult reproductive capacity was normal. These results suggest that FXYD1 contributes to facilitating the advent of puberty by maintaining GnRH neuronal excitability to incoming transsynaptic stimulatory inputs.
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Affiliation(s)
- Cecilia Garcia-Rudaz
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, Oregon
| | - Vivianne Deng
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, Oregon
| | - Valerie Matagne
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, Oregon
| | - Oline Ronnekleiv
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
| | - Martha Bosch
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon
| | - Victor Han
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, Oregon
| | - Alan K. Percy
- Department of Pediatrics University of Alabama at Birmingham, Birmingham, Alabama
| | - Sergio R. Ojeda
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health & Science University, Beaverton, Oregon
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Sharma D, Sethi P, Hussain E, Singh R. Curcumin counteracts the aluminium-induced ageing-related alterations in oxidative stress, Na+, K+ ATPase and protein kinase C in adult and old rat brain regions. Biogerontology 2008; 10:489-502. [DOI: 10.1007/s10522-008-9195-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 10/28/2008] [Indexed: 12/23/2022]
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40
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Rasmussen MK, Kristensen M, Juel C. Exercise-induced regulation of phospholemman (FXYD1) in rat skeletal muscle: implications for Na+/K+-ATPase activity. Acta Physiol (Oxf) 2008; 194:67-79. [PMID: 18373741 DOI: 10.1111/j.1748-1716.2008.01857.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Na(+)/K(+)-ATPase activity is upregulated during muscle exercise to maintain ionic homeostasis. One mechanism may involve movement of alpha-subunits to the outer membrane (translocation). AIM We investigated the existence of exercise-induced translocation and phosphorylation of phospholemman (PLM, FXYD1) protein in rat skeletal muscle and exercise-induced changes in V(max) and K(m) for Na(+) of the Na(+)/K(+)-ATPase. METHODS Two membrane fractionation methods and immunoprecipitation were used. RESULTS Both fractionation methods revealed a 200-350% increase in PLM in the sarcolemma after 30 min of treadmill running, while the phosphorylation of Ser-68 of PLM appeared to be unchanged. Exercise did not change V(max) or K(m) for Na(+) of the Na(+)/K(+)-ATPase in muscle homogenate, but induced a 67% increase in V(max) in the sarcolemmal giant vesicle preparation; K(m) for Na(+) remained constant. The main part of the increase in V(max) is related to a 36-53% increase in the level of alpha-subunits; the remainder may be related to increased PLM content. Similar results were obtained with another membrane purification method. In resting muscle, 29% and 32% of alpha(1)- and alpha(2)-subunits, respectively, were co-immunoprecipitated by PLM antibodies. In muscle homogenate prepared after exercise, immunoprecipitation of alpha(1)-subunits was increased to 227%, whereas the fraction of precipitated alpha(2) remained constant. CONCLUSION Exercise translocates PLM to the muscle outer membrane and increases its association with mainly the alpha(1)-subunit, which may contribute to the increased V(max) of the Na(+)/K(+)-ATPase.
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Affiliation(s)
- M K Rasmussen
- Department of Molecular Biology, Copenhagen Muscle Research Centre, University of Copenhagen, Denmark
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41
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Despa S, Tucker AL, Bers DM. Phospholemman-mediated activation of Na/K-ATPase limits [Na]i and inotropic state during beta-adrenergic stimulation in mouse ventricular myocytes. Circulation 2008; 117:1849-55. [PMID: 18362230 DOI: 10.1161/circulationaha.107.754051] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Cardiac Na/K-ATPase (NKA) regulates intracellular Na ([Na](i)), which in turn affects intracellular Ca and thus contractility via Na/Ca exchange. Recent evidence shows that phosphorylation of the NKA-associated small transmembrane protein phospholemman (PLM) mediates beta-adrenergic-induced NKA stimulation. METHODS AND RESULTS Here, we tested whether PLM phosphorylation during beta-adrenergic activation limits the rise in [Na](i), Ca transient amplitude, and triggered arrhythmias in mouse ventricular myocytes. In myocytes from wild-type (WT) mice, [Na](i) increased on field stimulation at 2 Hz from 11.1+/-1.8 mmol/L to a plateau of 15.2+/-1.5 mmol/L. Isoproterenol induced a decrease in [Na](i) to 12.0+/-1.2 mmol/L. In PLM knockout (PLM-KO) mice in which beta-adrenergic stimulation does not activate NKA, [Na](i) also increased at 2 Hz (from 10.4+/-1.2 to 17.0+/-1.5 mmol/L) but was unaltered by isoproterenol. The PLM-mediated decrease in [Na](i) in WT mice could limit the isoproterenol-induced inotropic state. Indeed, the isoproterenol-induced increase in the amplitude of Ca transients was significantly smaller in the WT mice (5.2+/-0.4- versus 7.1+/-0.5-fold in PLM-KO mice). This also was the case for the sarcoplasmic reticulum Ca content, which increased by 1.27+/-0.09-fold in WT mice versus 1.53+/-0.09-fold in PLM-KO mice. The higher sarcoplasmic reticulum Ca content in PLM-KO versus WT mice was associated with an increased propensity for spontaneous Ca transients and contractions in PLM-KO mice. CONCLUSIONS These data suggest that PLM phosphorylation and NKA stimulation are an integral part of the sympathetic fight-or-flight response, tempering the rise in [Na](i) and cellular Ca loading and perhaps limiting Ca overload-induced arrhythmias.
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Affiliation(s)
- Sanda Despa
- Department of Physiology, Loyola University Chicago, Maywood, Ill, USA
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Zougman A, Pilch B, Podtelejnikov A, Kiehntopf M, Schnabel C, Kumar C, Mann M. Integrated Analysis of the Cerebrospinal Fluid Peptidome and Proteome. J Proteome Res 2008; 7:386-99. [DOI: 10.1021/pr070501k] [Citation(s) in RCA: 151] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Bibert S, Roy S, Schaer D, Horisberger JD, Geering K. Phosphorylation of phospholemman (FXYD1) by protein kinases A and C modulates distinct Na,K-ATPase isozymes. J Biol Chem 2007; 283:476-486. [PMID: 17991751 DOI: 10.1074/jbc.m705830200] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (FXYD1), mainly expressed in heart and skeletal muscle, is a member of the FXYD protein family, which has been shown to decrease the apparent K(+) and Na(+) affinity of Na,K-ATPase ( Crambert, G., Fuzesi, M., Garty, H., Karlish, S., and Geering, K. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 11476-11481 ). In this study, we use the Xenopus oocyte expression system to study the role of phospholemman phosphorylation by protein kinases A and C in the modulation of different Na,K-ATPase isozymes present in the heart. Phosphorylation of phospholemman by protein kinase A has no effect on the maximal transport activity or on the apparent K(+) affinity of Na,K-ATPase alpha1/beta1 and alpha2/beta1 isozymes but increases their apparent Na(+) affinity, dependent on phospholemman phosphorylation at Ser(68). Phosphorylation of phospholemman by protein kinase C affects neither the maximal transport activity of alpha1/beta1 isozymes nor the K(+) affinity of alpha1/beta1 and alpha2/beta1 isozymes. However, protein kinase C phosphorylation of phospholemman increases the maximal Na,K-pump current of alpha2/beta1 isozymes by an increase in their turnover number. Thus, our results indicate that protein kinase A phosphorylation of phospholemman has similar functional effects on Na,K-ATPase alpha1/beta and alpha2/beta isozymes and increases their apparent Na(+) affinity, whereas protein kinase C phosphorylation of phospholemman modulates the transport activity of Na,K-ATPase alpha2/beta but not of alpha1/beta isozymes. The complex and distinct regulation of Na,K-ATPase isozymes by phosphorylation of phospholemman may be important for the efficient control of heart contractility and excitability.
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Affiliation(s)
- Stéphanie Bibert
- Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland
| | - Sophie Roy
- Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland
| | - Danièle Schaer
- Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland
| | - Jean-Daniel Horisberger
- Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland
| | - Käthi Geering
- Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland.
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Jordan C, Li HH, Kwan HC, Francke U. Cerebellar gene expression profiles of mouse models for Rett syndrome reveal novel MeCP2 targets. BMC MEDICAL GENETICS 2007; 8:36. [PMID: 17584923 PMCID: PMC1931432 DOI: 10.1186/1471-2350-8-36] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/13/2007] [Accepted: 06/20/2007] [Indexed: 01/01/2023]
Abstract
Background MeCP2, methyl-CpG-binding protein 2, binds to methylated cytosines at CpG dinucleotides, as well as to unmethylated DNA, and affects chromatin condensation. MECP2 mutations in females lead to Rett syndrome, a neurological disorder characterized by developmental stagnation and regression, loss of purposeful hand movements and speech, stereotypic hand movements, deceleration of brain growth, autonomic dysfunction and seizures. Most mutations occur de novo during spermatogenesis. Located at Xq28, MECP2 is subject to X inactivation, and affected females are mosaic. Rare hemizygous males suffer from a severe congenital encephalopathy. Methods To identify the pathways mis-regulated by MeCP2 deficiency, microarray-based global gene expression studies were carried out in cerebellum of Mecp2 mutant mice. We compared transcript levels in mutant/wildtype male sibs of two different MeCP2-deficient mouse models at 2, 4 and 8 weeks of age. Increased transcript levels were evaluated by real-time quantitative RT-PCR. Chromatin immunoprecipitation assays were used to document in vivo MeCP2 binding to promoter regions of candidate target genes. Results Of several hundred genes with altered expression levels in the mutants, twice as many were increased than decreased, and only 27 were differentially expressed at more than one time point. The number of misregulated genes was 30% lower in mice with the exon 3 deletion (Mecp2tm1.1Jae) than in mice with the larger deletion (Mecp2tm1.1Bird). Between the mutants, few genes overlapped at each time point. Real-time quantitative RT-PCR assays validated increased transcript levels for four genes: Irak1, interleukin-1 receptor-associated kinase 1; Fxyd1, phospholemman, associated with Na, K-ATPase;Reln, encoding an extracellular signaling molecule essential for neuronal lamination and synaptic plasticity; and Gtl2/Meg3, an imprinted maternally expressed non-translated RNA that serves as a host gene for C/D box snoRNAs and microRNAs. Chromatin immunoprecipitation assays documented in vivo MeCP2 binding to promoter regions of Fxyd1, Reln, and Gtl2. Conclusion Transcriptional profiling of cerebellum failed to detect significant global changes in Mecp2-mutant mice. Increased transcript levels of Irak1, Fxyd1, Reln, and Gtl2 may contribute to the neuronal dysfunction in MeCP2-deficient mice and individuals with Rett syndrome. Our data provide testable hypotheses for future studies of the regulatory or signaling pathways that these genes act on.
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Affiliation(s)
- ChaRandle Jordan
- Department of Genetics, Stanford University School of Medicine, Stanford CA 94305-5323, USA
| | - Hong Hua Li
- Department of Genetics, Stanford University School of Medicine, Stanford CA 94305-5323, USA
| | - Helen C Kwan
- Department of Genetics, Stanford University School of Medicine, Stanford CA 94305-5323, USA
| | - Uta Francke
- Department of Genetics, Stanford University School of Medicine, Stanford CA 94305-5323, USA
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Shimizu H, Watanabe E, Hiyama TY, Nagakura A, Fujikawa A, Okado H, Yanagawa Y, Obata K, Noda M. Glial Nax Channels Control Lactate Signaling to Neurons for Brain [Na+] Sensing. Neuron 2007; 54:59-72. [PMID: 17408578 DOI: 10.1016/j.neuron.2007.03.014] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2006] [Revised: 02/08/2007] [Accepted: 03/19/2007] [Indexed: 11/25/2022]
Abstract
Sodium (Na) homeostasis is crucial for life, and Na levels in body fluids are constantly monitored in the brain. The subfornical organ (SFO) is the center of the sensing responsible for the control of salt-intake behavior, where Na(x) channels are expressed in specific glial cells as the Na-level sensor. Here, we show direct interaction between Na(x) channels and alpha subunits of Na(+)/K(+)-ATPase, which brings about Na-dependent activation of the metabolic state of the glial cells. The metabolic enhancement leading to extensive lactate production was observed in the SFO of wild-type mice, but not of the Na(x)-knockout mice. Furthermore, lactate, as well as Na, stimulated the activity of GABAergic neurons in the SFO. These results suggest that the information on a physiological increase of the Na level in body fluids sensed by Na(x) in glial cells is transmitted to neurons by lactate as a mediator to regulate neural activities of the SFO.
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Affiliation(s)
- Hidetada Shimizu
- Division of Molecular Neurobiology, National Institute for Basic Biology, Okazaki, Aichi 444-8787, Japan
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Vanagas L, Rossi RC, Caride AJ, Filoteo AG, Strehler EE, Rossi JPF. Plasma membrane calcium pump activity is affected by the membrane protein concentration: evidence for the involvement of the actin cytoskeleton. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1641-9. [PMID: 17481573 PMCID: PMC2041878 DOI: 10.1016/j.bbamem.2007.03.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Revised: 03/08/2007] [Accepted: 03/17/2007] [Indexed: 11/23/2022]
Abstract
Plasma membrane calcium pumps (PMCAs) are integral membrane proteins that actively expel Ca(2+) from the cell. Specific Ca(2+)-ATPase activity of erythrocyte membranes increased steeply up to 1.5-5 times when the membrane protein concentration decreased from 50 microg/ml to 1 microg/ml. The activation by dilution was also observed for ATP-dependent Ca(2+) uptake into vesicles from Sf9 cells over-expressing the PMCA 4b isoform, confirming that it is a property of the PMCA. Dilution of the protein did not modify the activation by ATP, Ca(2+) or Ca(2+)-calmodulin. Treatment with non-ionic detergents did not abolish the dilution effect, suggesting that it was not due to resealing of the membrane vesicles. Pre-incubation of erythrocyte membranes with Cytochalasin D under conditions that promote actin polymerization abolished the dilution effect. Highly-purified, micellar PMCA showed no dilution effect and was not affected by Cytochalasin D. Taken together, these results suggest that the concentration-dependent behavior of the PMCA activity was due to interactions with cytoskeletal proteins. The dilution effect was also observed with different PMCA isoforms, indicating that this is a general phenomenon for all PMCAs.
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Affiliation(s)
- Laura Vanagas
- IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 (1113) Buenos Aires, Argentina
| | - Rolando C. Rossi
- IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 (1113) Buenos Aires, Argentina
| | - Ariel J. Caride
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
| | - Adelaida G. Filoteo
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
| | - Emanuel E. Strehler
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
| | - Juan Pablo F.C. Rossi
- IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 (1113) Buenos Aires, Argentina
- Corresponding author: Address mail:
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Deng V, Matagne V, Banine F, Frerking M, Ohliger P, Budden S, Pevsner J, Dissen GA, Sherman LS, Ojeda SR. FXYD1 is an MeCP2 target gene overexpressed in the brains of Rett syndrome patients and Mecp2-null mice. Hum Mol Genet 2007; 16:640-50. [PMID: 17309881 DOI: 10.1093/hmg/ddm007] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Rett syndrome (RTT) is an X-linked neurodevelopmental disorder linked to heterozygous de novo mutations in the MECP2 gene. MECP2 encodes methyl-CpG-binding protein 2 (MeCP2), which represses gene transcription by binding to 5-methylcytosine residues in symmetrically positioned CpG dinucleotides. Direct MeCP2 targets underlying RTT pathogenesis remain largely unknown. Here, we report that FXYD1, which encodes a transmembrane modulator of Na(+), K(+) -ATPase activity, is elevated in frontal cortex (FC) neurons of RTT patients and Mecp2-null mice. Increasing neuronal FXDY1 expression is sufficient to reduce dendritic arborization and spine formation, hallmarks of RTT neuropathology. Mecp2-null mouse cortical neurons have diminished Na(+),K(+)-ATPase activity, suggesting that aberrant FXYD1 expression contributes to abnormal neuronal activity in RTT. MeCP2 represses Fxyd1 transcription through direct interactions with sequences in the Fxyd1 promoter that are methylated in FC neurons. FXYD1 is therefore a MeCP2 target gene whose de-repression may directly contribute to RTT neuronal pathogenesis.
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Affiliation(s)
- Vivianne Deng
- Division of Neuroscience, Oregon National Primate Research Center, Beaverton, OR 97006, USA
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Praetorius J. Water and solute secretion by the choroid plexus. Pflugers Arch 2006; 454:1-18. [PMID: 17120021 DOI: 10.1007/s00424-006-0170-6] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 09/12/2006] [Indexed: 12/23/2022]
Abstract
The cerebrospinal fluid (CSF) provides mechanical and chemical protection of the brain and spinal cord. This review focusses on the contribution of the choroid plexus epithelium to the water and salt homeostasis of the CSF, i.e. the secretory processes involved in CSF formation. The choroid plexus epithelium is situated in the ventricular system and is believed to be the major site of CSF production. Numerous studies have identified transport processes involved in this secretion, and recently, the underlying molecular background for some of the mechanisms have emerged. The nascent CSF consists mainly of NaCl and NaHCO(3), and the production rate is strictly coupled to the rate of Na(+) secretion. In contrast to other secreting epithelia, Na(+) is actively pumped across the luminal surface by the Na(+),K(+)-ATPase with possible contributions by other Na(+) transporters, e.g. the luminal Na(+),K(+),2Cl(-) cotransporter. The Cl(-) and HCO(3) (-) ions are likely transported by a luminal cAMP activated inward rectified anion conductance, although the responsible proteins have not been identified. Whereas Cl(-) most likely enters the cells through anion exchange, the functional as well as the molecular basis for the basolateral Na(+) entry are not yet well-defined. Water molecules follow across the epithelium mainly through the water channel, AQP1, driven by the created ionic gradient. In this article, the implications of the recent findings for the current model of CSF secretion are discussed. Finally, the clinical implications and the prospects of future advances in understanding CSF production are briefly outlined.
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Affiliation(s)
- Jeppe Praetorius
- The Water and Salt Research Center & Institute of Anatomy, University of Aarhus, Wilhelm Meyers Allé, 8000 Aarhus, Denmark.
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Han F, Bossuyt J, Despa S, Tucker AL, Bers DM. Phospholemman phosphorylation mediates the protein kinase C-dependent effects on Na+/K+ pump function in cardiac myocytes. Circ Res 2006; 99:1376-83. [PMID: 17095720 DOI: 10.1161/01.res.0000251667.73461.fb] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Because phospholemman (PLM) regulates the Na(+)/K(+) pump (NKA) and is a major cardiac phosphorylation target for both protein kinase A (at Ser68) and protein kinase C (PKC) (at both Ser63 and Ser68), we evaluated whether PLM mediates the PKC-dependent regulation of NKA function and protein kinase A/PKC crosstalk in ventricular myocytes. PKC was activated by PDBu (300 nmol/L), and we measured NKA-mediated [Na(+)](i) decline (fluorescence measurements) and current (I(pump)) (voltage clamp). In wild-type mouse myocytes, PDBu increased PLM phosphorylation at Ser63 and Ser68, I(pump) (both at 10 and 100 mmol/L Na(+) in the pipette solution) and maximal NKA-mediated Na(+) extrusion rate (V(max)) from 7.9+/-1.1 to 12.7+/-1.9 mmol.L(-1) per minute without altering NKA affinity for internal Na(+) (K(0.5)). In PLM knockout mice, PDBu had no effect on either V(max) or K(0.5). After pretreatment with isoproterenol (ISO) (1 mumol/L), PDBu still increased the NKA V(max) and PLM phosphorylation at Ser63 and Ser68. Conversely, after pretreatment with PDBu, ISO further increased the Na(+) affinity of NKA and phosphorylation at Ser68, as it did alone without PDBu. The final NKA activity was independent of the application sequence. The NKA activity in PLM knockout myocytes, after normalizing the protein level, was similar to that after PDBu and ISO treatment. We conclude that (1) PLM mediates the PKC-dependent activation of NKA function in cardiac myocytes, (2) PDBu and ISO effects are additive in the mouse (affecting mainly V(max) and K(0.5), respectively), and (3) PDBu and ISO combine to activate NKA in wild-type to the level found in the PLM knockout mouse.
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Affiliation(s)
- Fei Han
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 S First Ave, Maywood, IL 60153, USA
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Arystarkhova E, Donnet C, Muñoz-Matta A, Specht SC, Sweadner KJ. Multiplicity of expression of FXYD proteins in mammalian cells: dynamic exchange of phospholemman and gamma-subunit in response to stress. Am J Physiol Cell Physiol 2006; 292:C1179-91. [PMID: 17050615 DOI: 10.1152/ajpcell.00328.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Functional properties of Na-K-ATPase can be modified by association with FXYD proteins, expressed in a tissue-specific manner. Here we show that expression of FXYDs in cell lines does not necessarily parallel the expression pattern of FXYDs in the tissue(s) from which the cells originate. While being expressed only in lacis cells in the juxtaglomerular apparatus and in blood vessels in kidney, FXYD1 was abundant in renal cell lines of proximal tubule origin (NRK-52E, LLC-PK1, and OK cells). Authenticity of FXYD1 as a part of Na-K-ATPase in NRK-52E cells was demonstrated by co-purification, co-immunoprecipitation, and co-localization. Induction of FXYD2 by hypertonicity (500 mosmol/kgH(2)O with NaCl for 48 h or adaptation to 700 mosmol/kgH(2)O) correlated with downregulation of FXYD1 at mRNA and protein levels. The response to hypertonicity was influenced by serum factors and entailed, first, dephosphorylation of FXYD1 at Ser(68) (1-5 h) and, second, induction of FXYD2a and a decrease in FXYD1 with longer exposure. FXYD1 was completely replaced with FXYD2a in cells adapted to 700 mosmol/kgH(2)O and showed a significantly decreased sodium affinity. Thus dephosphorylation of FXYD1 followed by exchange of regulatory subunits is utilized to make a smooth transition of properties of Na-K-ATPase. We also observed expression of mRNA for multiple FXYDs in various cell lines. The expression was dynamic and responsive to physiological stimuli. Moreover, we demonstrated expression of FXYD5 protein in HEK-293 and HeLa cells. The data imply that FXYDs are obligatory rather than auxiliary components of Na-K-ATPase, and their interchangeability underlies responses of Na-K-ATPase to cellular stress.
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Affiliation(s)
- Elena Arystarkhova
- Laboratory of Membrane Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
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