1
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Theparambil SM, Begum G, Rose CR. pH regulating mechanisms of astrocytes: A critical component in physiology and disease of the brain. Cell Calcium 2024; 120:102882. [PMID: 38631162 DOI: 10.1016/j.ceca.2024.102882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Revised: 03/28/2024] [Accepted: 03/28/2024] [Indexed: 04/19/2024]
Abstract
Strict homeostatic control of pH in both intra- and extracellular compartments of the brain is fundamentally important, primarily due to the profound impact of free protons ([H+]) on neuronal activity and overall brain function. Astrocytes, crucial players in the homeostasis of various ions in the brain, actively regulate their intracellular [H+] (pHi) through multiple membrane transporters and carbonic anhydrases. The activation of astroglial pHi regulating mechanisms also leads to corresponding alterations in the acid-base status of the extracellular fluid. Notably, astrocyte pH regulators are modulated by various neuronal signals, suggesting their pivotal role in regulating brain acid-base balance in both health and disease. This review presents the mechanisms involved in pH regulation in astrocytes and discusses their potential impact on extracellular pH under physiological conditions and in brain disorders. Targeting astrocytic pH regulatory mechanisms represents a promising therapeutic approach for modulating brain acid-base balance in diseases, offering a potential critical contribution to neuroprotection.
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Affiliation(s)
- Shefeeq M Theparambil
- Faculty of Health and Medicine, Department of Biomedical and Life Sciences, Lancaster University, Lancaster, LA1 4YW, Lancaster, UK.
| | - Gulnaz Begum
- Department of Neurology, The Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA, USA
| | - Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
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2
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Pandya VA, Patani R. The role of glial cells in amyotrophic lateral sclerosis. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2024; 176:381-450. [PMID: 38802179 DOI: 10.1016/bs.irn.2024.04.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
Amyotrophic lateral sclerosis (ALS) has traditionally been considered a neuron-centric disease. This view is now outdated, with increasing recognition of cell autonomous and non-cell autonomous contributions of central and peripheral nervous system glia to ALS pathomechanisms. With glial research rapidly accelerating, we comprehensively interrogate the roles of astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells and satellite glia in nervous system physiology and ALS-associated pathology. Moreover, we highlight the inter-glial, glial-neuronal and inter-system polylogue which constitutes the healthy nervous system and destabilises in disease. We also propose classification based on function for complex glial reactive phenotypes and discuss the pre-requisite for integrative modelling to advance translation. Given the paucity of life-enhancing therapies currently available for ALS patients, we discuss the promising potential of harnessing glia in driving ALS therapeutic discovery.
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Affiliation(s)
- Virenkumar A Pandya
- University College London Medical School, London, United Kingdom; The Francis Crick Institute, London, United Kingdom.
| | - Rickie Patani
- The Francis Crick Institute, London, United Kingdom; Department of Neuromuscular Diseases, University College London Queen Square Institute of Neurology, Queen Square, London, United Kingdom.
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3
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Pethe A, Hamze M, Giannaki M, Heimrich B, Medina I, Hartmann AM, Roussa E. K +/Cl - cotransporter 2 (KCC2) and Na +/ HCO3- cotransporter 1 (NBCe1) interaction modulates profile of KCC2 phosphorylation. Front Cell Neurosci 2023; 17:1253424. [PMID: 37881493 PMCID: PMC10595033 DOI: 10.3389/fncel.2023.1253424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/07/2023] [Indexed: 10/27/2023] Open
Abstract
K+/Cl- cotransporter 2 (KCC2) is a major Cl- extruder in mature neurons and is responsible for the establishment of low intracellular [Cl-], necessary for fast hyperpolarizing GABAA-receptor mediated synaptic inhibition. Electrogenic sodium bicarbonate cotransporter 1 (NBCe1) is a pH regulatory protein expressed in neurons and glial cells. An interactome study identified NBCe1 as a possible interaction partner of KCC2. In this study, we investigated the putative effect of KCC2/NBCe1 interaction in baseline and the stimulus-induced phosphorylation pattern and function of KCC2. Primary mouse hippocampal neuronal cultures from wildtype (WT) and Nbce1-deficient mice, as well as HEK-293 cells stably transfected with KCC2WT, were used. The results show that KCC2 and NBCe1 are interaction partners in the mouse brain. In HEKKCC2 cells, pharmacological inhibition of NBCs with S0859 prevented staurosporine- and 4-aminopyridine (4AP)-induced KCC2 activation. In mature cultures of hippocampal neurons, however, S0859 completely inhibited postsynaptic GABAAR and, thus, could not be used as a tool to investigate the role of NBCs in GABA-dependent neuronal networks. In Nbce1-deficient immature hippocampal neurons, baseline phosphorylation of KCC2 at S940 was downregulated, compared to WT, and exposure to staurosporine failed to reduce pKCC2 S940 and T1007. In Nbce1-deficient mature neurons, baseline levels of pKCC2 S940 and T1007 were upregulated compared to WT, whereas after 4AP treatment, pKCC2 S940 was downregulated, and pKCC2 T1007 was further upregulated. Functional experiments showed that the levels of GABAAR reversal potential, baseline intracellular [Cl-], Cl- extrusion, and baseline intracellular pH were similar between WT and Nbce1-deficient neurons. Altogether, our data provide a primary description of the properties of KCC2/NBCe1 protein-protein interaction and implicate modulation of stimulus-mediated phosphorylation of KCC2 by NBCe1/KCC2 interaction-a mechanism with putative pathophysiological relevance.
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Affiliation(s)
- Abhishek Pethe
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Mira Hamze
- INMED, INSERM, Aix-Marseille University, Marseille, France
| | - Marina Giannaki
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Bernd Heimrich
- Department of Neuroanatomy, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Igor Medina
- INMED, INSERM, Aix-Marseille University, Marseille, France
| | - Anna-Maria Hartmann
- Division of Neurogenetics, Faculty VI, School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
- Research Center for Neurosensory Science, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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4
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Giannaki M, Ruf DE, Pfeifer E, Everaerts K, Heiland DH, Schnell O, Rose CR, Roussa E. Cell-Type Dependent Regulation of the Electrogenic Na+/HCO3- Cotransporter 1 (NBCe1) by Hypoxia and Acidosis in Glioblastoma. Int J Mol Sci 2022; 23:ijms23168975. [PMID: 36012235 PMCID: PMC9408864 DOI: 10.3390/ijms23168975] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 08/05/2022] [Accepted: 08/08/2022] [Indexed: 11/16/2022] Open
Abstract
Glioblastoma multiforme (GBM) is the most common and malignant brain tumour. It is characterised by transcriptionally distinct cell populations. In tumour cells, physiological pH gradients between the intracellular and extracellular compartments are reversed, compared to non-cancer cells. Intracellular pH in tumour cells is alkaline, whereas extracellular pH is acidic. Consequently, the function and/or expression of pH regulating transporters might be altered. Here, we investigated protein expression and regulation of the electrogenic sodium/bicarbonate cotransporter 1 (NBCe1) in mesenchymal (MES)-like hypoxia-dependent and -independent cells, as well as in astrocyte-like glioblastoma cells following chemical hypoxia, acidosis and elucidated putative underlying molecular pathways. Immunoblotting, immunocytochemistry, and intracellular pH recording with the H+-sensitive dye 2′,7′-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein were applied. The results show NBCe1 protein abundance and active NBCe1 transport. Hypoxia upregulated NBCe1 protein and activity in MES-like hypoxia-dependent GBM cells. This effect was positively correlated with HIF-1α protein levels, was mediated by TGF-β signalling, and was prevented by extracellular acidosis. In MES-like hypoxia-independent GBM cells, acidosis (but not hypoxia) regulated NBCe1 activity in an HIF-1α-independent manner. These results demonstrate a cell-specific adaptation of NBCe1 expression and activity to the microenvironment challenge of hypoxia and acidosis that depends on their transcriptional signature in GBM.
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Affiliation(s)
- Marina Giannaki
- Department of Molecular Embryology, Faculty of Medicine, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany
| | - Debora E. Ruf
- Department of Molecular Embryology, Faculty of Medicine, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany
| | - Emilie Pfeifer
- Department of Molecular Embryology, Faculty of Medicine, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany
| | - Katharina Everaerts
- Institute of Neurobiology, Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Dieter H. Heiland
- Department of Neurosurgery, Faculty of Medicine, Medical Center, University of Freiburg, D-79106 Freiburg, Germany
- Microenvironment and Immunology Research Laboratory, Medical Center, University of Freiburg, D-79106 Freiburg, Germany
| | - Oliver Schnell
- Department of Neurosurgery, Faculty of Medicine, Medical Center, University of Freiburg, D-79106 Freiburg, Germany
| | - Christine R. Rose
- Institute of Neurobiology, Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Faculty of Medicine, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany
- Correspondence: ; Tel.: +49-761-203-5114
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5
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Saint-Criq V, Guequén A, Philp AR, Villanueva S, Apablaza T, Fernández-Moncada I, Mansilla A, Delpiano L, Ruminot I, Carrasco C, Gray MA, Flores CA. Inhibition of the sodium-dependent HCO 3- transporter SLC4A4, produces a cystic fibrosis-like airway disease phenotype. eLife 2022; 11:e75871. [PMID: 35635440 PMCID: PMC9173743 DOI: 10.7554/elife.75871] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 05/27/2022] [Indexed: 11/30/2022] Open
Abstract
Bicarbonate secretion is a fundamental process involved in maintaining acid-base homeostasis. Disruption of bicarbonate entry into airway lumen, as has been observed in cystic fibrosis, produces several defects in lung function due to thick mucus accumulation. Bicarbonate is critical for correct mucin deployment and there is increasing interest in understanding its role in airway physiology, particularly in the initiation of lung disease in children affected by cystic fibrosis, in the absence of detectable bacterial infection. The current model of anion secretion in mammalian airways consists of CFTR and TMEM16A as apical anion exit channels, with limited capacity for bicarbonate transport compared to chloride. However, both channels can couple to SLC26A4 anion exchanger to maximise bicarbonate secretion. Nevertheless, current models lack any details about the identity of the basolateral protein(s) responsible for bicarbonate uptake into airway epithelial cells. We report herein that the electrogenic, sodium-dependent, bicarbonate cotransporter, SLC4A4, is expressed in the basolateral membrane of human and mouse airways, and that it's pharmacological inhibition or genetic silencing reduces bicarbonate secretion. In fully differentiated primary human airway cells cultures, SLC4A4 inhibition induced an acidification of the airways surface liquid and markedly reduced the capacity of cells to recover from an acid load. Studies in the Slc4a4-null mice revealed a previously unreported lung phenotype, characterized by mucus accumulation and reduced mucociliary clearance. Collectively, our results demonstrate that the reduction of SLC4A4 function induced a CF-like phenotype, even when chloride secretion remained intact, highlighting the important role SLC4A4 plays in bicarbonate secretion and mammalian airway function.
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Affiliation(s)
- Vinciane Saint-Criq
- Biosciences Institute, The Medical School, Newcastle UniversityNewcastle upon TyneUnited Kingdom
| | - Anita Guequén
- Centro de Estudios CientíficosValdiviaChile
- Universidad Austral de ChileValdiviaChile
| | - Amber R Philp
- Centro de Estudios CientíficosValdiviaChile
- Universidad Austral de ChileValdiviaChile
| | | | - Tábata Apablaza
- Centro de Estudios CientíficosValdiviaChile
- Universidad Austral de ChileValdiviaChile
| | | | - Agustín Mansilla
- Centro de Estudios CientíficosValdiviaChile
- Universidad Austral de ChileValdiviaChile
| | - Livia Delpiano
- Biosciences Institute, The Medical School, Newcastle UniversityNewcastle upon TyneUnited Kingdom
| | - Iván Ruminot
- Centro de Estudios CientíficosValdiviaChile
- Universidad San SebastiánValdiviaChile
| | - Cristian Carrasco
- Subdepartamento de Anatomía Patológica, Hospital Base de ValdiviaValdiviaChile
| | - Michael A Gray
- Biosciences Institute, The Medical School, Newcastle UniversityNewcastle upon TyneUnited Kingdom
| | - Carlos A Flores
- Centro de Estudios CientíficosValdiviaChile
- Universidad San SebastiánValdiviaChile
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6
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Giannaki M, Ludwig C, Heermann S, Roussa E. Regulation of electrogenic Na + /HCO 3 - cotransporter 1 (NBCe1) function and its dependence on m-TOR mediated phosphorylation of Ser 245. J Cell Physiol 2021; 237:1372-1388. [PMID: 34642952 DOI: 10.1002/jcp.30601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 09/09/2021] [Accepted: 10/01/2021] [Indexed: 11/09/2022]
Abstract
Astrocytes are pivotal responders to alterations of extracellular pH, primarily by regulation of their principal acid-base transporter, the membrane-bound electrogenic Na+ /bicarbonate cotransporter 1 (NBCe1). Here, we describe amammalian target of rapamycin (mTOR)-dependent and NBCe1-mediated astroglial response to extracellular acidosis. Using primary mouse cortical astrocytes, we investigated the effect of long-term extracellular metabolic acidosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant increase of NBCe1-mediated recovery of intracellular pH from acidification in WT astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Acidosis-induced upregulation of NBCe1 activity was prevented following inhibition of mTOR signaling by rapamycin. Yet, during acidosis or following exposure of astrocytes to rapamycin, surface protein abundance of NBCe1 remained -unchanged. Mutational analysis in HeLa cells suggested that NBCe1 activity was dependent on phosphorylation state of Ser245 , a residue conserved in all NBCe1 variants. Moreover, phosphorylation state of Ser245 is regulated by mTOR and is inversely correlated with NBCe1 transport activity. Our results identify pSer245 as a novel regulator of NBCe1 functional expression. We propose that context-dependent and mTOR-mediated multisite phosphorylation of serine residues of NBCe1 is likely to be a potent mechanism contributing to the response of astrocytes to acid/base challenges during pathophysiological conditions.
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Affiliation(s)
- Marina Giannaki
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Christina Ludwig
- Bavarian Center for Biomolecular Mass Spectrometry (BayBioMS), Technical University of Munich (TUM), Freising, Germany
| | - Stephan Heermann
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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7
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Choi JIV, Tchernookova BK, Kumar W, Kiedrowski L, Goeke C, Guizzetti M, Larson J, Kreitzer MA, Malchow RP. Extracellular ATP-Induced Alterations in Extracellular H + Fluxes From Cultured Cortical and Hippocampal Astrocytes. Front Cell Neurosci 2021; 15:640217. [PMID: 33994945 PMCID: PMC8120152 DOI: 10.3389/fncel.2021.640217] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/19/2021] [Indexed: 12/18/2022] Open
Abstract
Small alterations in the level of extracellular H+ can profoundly alter neuronal activity throughout the nervous system. In this study, self-referencing H+-selective microelectrodes were used to examine extracellular H+ fluxes from individual astrocytes. Activation of astrocytes cultured from mouse hippocampus and rat cortex with extracellular ATP produced a pronounced increase in extracellular H+ flux. The ATP-elicited increase in H+ flux appeared to be independent of bicarbonate transport, as ATP increased H+ flux regardless of whether the primary extracellular pH buffer was 26 mM bicarbonate or 1 mM HEPES, and persisted when atmospheric levels of CO2 were replaced by oxygen. Adenosine failed to elicit any change in extracellular H+ fluxes, and ATP-mediated increases in H+ flux were inhibited by the P2 inhibitors suramin and PPADS suggesting direct activation of ATP receptors. Extracellular ATP also induced an intracellular rise in calcium in cultured astrocytes, and ATP-induced rises in both calcium and H+ efflux were significantly attenuated when calcium re-loading into the endoplasmic reticulum was inhibited by thapsigargin. Replacement of extracellular sodium with choline did not significantly reduce the size of the ATP-induced increases in H+ flux, and the increases in H+ flux were not significantly affected by addition of EIPA, suggesting little involvement of Na+/H+ exchangers in ATP-elicited increases in H+ flux. Given the high sensitivity of voltage-sensitive calcium channels on neurons to small changes in levels of free H+, we hypothesize that the ATP-mediated extrusion of H+ from astrocytes may play a key role in regulating signaling at synapses within the nervous system.
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Affiliation(s)
- Ji-In Vivien Choi
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States.,Stritch School of Medicine, Loyola University, Maywood, IL, United States
| | - Boriana K Tchernookova
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States
| | - Wasan Kumar
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States
| | - Lech Kiedrowski
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States.,Spot Cells LLC, Chicago, IL, United States
| | - Calla Goeke
- VA Portland Health Care System, Portland, OR, United States.,Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, OR, United States
| | - Marina Guizzetti
- VA Portland Health Care System, Portland, OR, United States.,Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, OR, United States
| | - John Larson
- Department of Psychiatry, University of Illinois at Chicago, Chicago, IL, United States
| | - Matthew A Kreitzer
- Department of Biology, Indiana Wesleyan University, Marion, IN, United States
| | - Robert Paul Malchow
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States.,Department Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, United States
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8
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Becker HM, Deitmer JW. Proton Transport in Cancer Cells: The Role of Carbonic Anhydrases. Int J Mol Sci 2021; 22:ijms22063171. [PMID: 33804674 PMCID: PMC8003680 DOI: 10.3390/ijms22063171] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 03/16/2021] [Accepted: 03/17/2021] [Indexed: 02/06/2023] Open
Abstract
Intra- and extracellular pH regulation is a pivotal function of all cells and tissues. Net outward transport of H+ is a prerequisite for normal physiological function, since a number of intracellular processes, such as metabolism and energy supply, produce acid. In tumor tissues, distorted pH regulation results in extracellular acidification and the formation of a hostile environment in which cancer cells can outcompete healthy local host cells. Cancer cells employ a variety of H+/HCO3−-coupled transporters in combination with intra- and extracellular carbonic anhydrase (CA) isoforms, to alter intra- and extracellular pH to values that promote tumor progression. Many of the transporters could closely associate to CAs, to form a protein complex coined “transport metabolon”. While transport metabolons built with HCO3−-coupled transporters require CA catalytic activity, transport metabolons with monocarboxylate transporters (MCTs) operate independently from CA catalytic function. In this article, we assess some of the processes and functions of CAs for tumor pH regulation and discuss the role of intra- and extracellular pH regulation for cancer pathogenesis and therapeutic intervention.
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Affiliation(s)
- Holger M. Becker
- Zoology and Animal Physiology, Institute of Zoology, TU Dresden, D-01217 Dresden, Germany
- Correspondence:
| | - Joachim W. Deitmer
- Department of Biology, University of Kaiserslautern, D-67653 Kaiserslautern, Germany;
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9
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Giannaki M, Schrödl-Häußel M, Khakipoor S, Kirsch M, Roussa E. STAT3-dependent regulation of the electrogenic Na +/ HCO 3- cotransporter 1 (NBCe1) functional expression in cortical astrocytes. J Cell Physiol 2021; 236:2036-2050. [PMID: 32761631 DOI: 10.1002/jcp.29990] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 07/03/2020] [Accepted: 07/21/2020] [Indexed: 01/10/2023]
Abstract
The electrogenic Na+ /HCO3- cotransporter (NBCe1) in astrocytes is crucial in regulation of acid-base homeostasis in the brain. Since many pathophysiological conditions in the brain have been associated with pH shifts we exposed primary mouse cortical and hippocampal astrocytes to prolonged low or high extracellular pH (pHo ) at constant extracellular bicarbonate concentration and investigated activation of astrocytes and regulation of NBCe1 by immunoblotting, biotinylation of surface proteins, and intracellular H+ recordings. High pHo at constant extracellular bicarbonate caused upregulation of NBCe1 protein, surface expression and activity via upregulation of the astrocytic activation markers signal transducer and activator of transcription 3 (STAT3) signaling and glial fibrillary acidic protein expression. High pHo -induced increased NBCe1 protein expression was prevented in astrocytes from Stat3flox/flox ::GfapCre/+ mice. In vitro, basal and high pHo -induced increased NBCe1 functional expression was impaired following inhibition of STAT3 phosphorylation. These results provide a novel regulation mode of NBCe1 protein and activity, highlight the importance of astrocyte reactivity on regulation of NBCe1 and implicate roles for NBCe1 in altering/modulating extracellular pH during development as well as of the microenvironment at sites of brain injuries and other pathophysiological conditions.
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Affiliation(s)
- Marina Giannaki
- Department of Molecular Embryology, Medical Faculty, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Magdalena Schrödl-Häußel
- Department of Molecular Embryology, Medical Faculty, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Shokoufeh Khakipoor
- Department of Molecular Embryology, Medical Faculty, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Matthias Kirsch
- Department of Neuroanatomy, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Medical Faculty, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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10
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Tchernookova BK, Gongwer MW, George A, Goeglein B, Powell AM, Caringal HL, Leuschner T, Phillips AG, Schantz AW, Kiedrowski L, Chappell R, Kreitzer MA, Malchow RP. ATP-mediated increase in H + flux from retinal Müller cells: a role for Na +/H + exchange. J Neurophysiol 2020; 125:184-198. [PMID: 33206577 DOI: 10.1152/jn.00546.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Small alterations in extracellular H+ can profoundly alter neurotransmitter release by neurons. We examined mechanisms by which extracellular ATP induces an extracellular H+ flux from Müller glial cells, which surround synaptic connections throughout the vertebrate retina. Müller glia were isolated from tiger salamander retinae and H+ fluxes examined using self-referencing H+-selective microelectrodes. Experiments were performed in 1 mM HEPES with no bicarbonate present. Replacement of extracellular sodium by choline decreased H+ efflux induced by 10 µM ATP by 75%. ATP-induced H+ efflux was also reduced by Na+/H+ exchange inhibitors. Amiloride reduced H+ efflux initiated by 10 µM ATP by 60%, while 10 µM cariporide decreased H+ flux by 37%, and 25 µM zoniporide reduced H+ flux by 32%. ATP-induced H+ fluxes were not significantly altered by the K+/H+ pump blockers SCH28080 or TAK438, and replacement of all extracellular chloride with gluconate was without effect on H+ fluxes. Recordings of ATP-induced H+ efflux from cells that were simultaneously whole cell voltage clamped revealed no effect of membrane potential from -70 mV to 0 mV. Restoration of extracellular potassium after cells were bathed in 0 mM potassium produced a transient alteration in ATP-dependent H+ efflux. The transient response to extracellular potassium occurred only when extracellular sodium was present and was abolished by 1 mM ouabain, suggesting that alterations in sodium gradients were mediated by Na+/K+-ATPase activity. Our data indicate that the majority of H+ efflux elicited by extracellular ATP from isolated Müller cells is mediated by Na+/H+ exchange.NEW & NOTEWORTHY Glial cells are known to regulate neuronal activity, but the exact mechanism(s) whereby these "support" cells modulate synaptic transmission remains unclear. Small changes in extracellular levels of acidity are known to be particularly powerful regulators of neurotransmitter release. Here, we show that extracellular ATP, known to be a potent activator of glial cells, induces H+ efflux from retinal Müller (glial) cells and that the bulk of the H+ efflux is mediated by Na+/H+ exchange.
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Affiliation(s)
| | | | - Alexis George
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Brock Goeglein
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Alyssa M Powell
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | | | - Thomas Leuschner
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Anna G Phillips
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Adam W Schantz
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Lech Kiedrowski
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois.,Spot Cells LLC, Chicago, Illinois
| | - Richard Chappell
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York.,Eugene Bell Center, Marine Biological Laboratory, Woods Hole, Massachusetts
| | | | - Robert Paul Malchow
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois.,Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois
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11
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Theparambil SM, Hosford PS, Ruminot I, Kopach O, Reynolds JR, Sandoval PY, Rusakov DA, Barros LF, Gourine AV. Astrocytes regulate brain extracellular pH via a neuronal activity-dependent bicarbonate shuttle. Nat Commun 2020; 11:5073. [PMID: 33033238 PMCID: PMC7545092 DOI: 10.1038/s41467-020-18756-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 09/09/2020] [Indexed: 12/19/2022] Open
Abstract
Brain cells continuously produce and release protons into the extracellular space, with the rate of acid production corresponding to the levels of neuronal activity and metabolism. Efficient buffering and removal of excess H+ is essential for brain function, not least because all the electrogenic and biochemical machinery of synaptic transmission is highly sensitive to changes in pH. Here, we describe an astroglial mechanism that contributes to the protection of the brain milieu from acidification. In vivo and in vitro experiments conducted in rodent models show that at least one third of all astrocytes release bicarbonate to buffer extracellular H+ loads associated with increases in neuronal activity. The underlying signalling mechanism involves activity-dependent release of ATP triggering bicarbonate secretion by astrocytes via activation of metabotropic P2Y1 receptors, recruitment of phospholipase C, release of Ca2+ from the internal stores, and facilitated outward HCO3- transport by the electrogenic sodium bicarbonate cotransporter 1, NBCe1. These results show that astrocytes maintain local brain extracellular pH homeostasis via a neuronal activity-dependent release of bicarbonate. The data provide evidence of another important metabolic housekeeping function of these glial cells.
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Affiliation(s)
- Shefeeq M Theparambil
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Patrick S Hosford
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Iván Ruminot
- Centro de Estudios Científicos (CECs), Valdivia, Chile
| | - Olga Kopach
- Institute of Neurology, University College London, London, UK
| | | | | | | | | | - Alexander V Gourine
- Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, London, UK.
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12
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Toft-Bertelsen TL, Larsen BR, Christensen SK, Khandelia H, Waagepetersen HS, MacAulay N. Clearance of activity-evoked K + transients and associated glia cell swelling occur independently of AQP4: A study with an isoform-selective AQP4 inhibitor. Glia 2020; 69:28-41. [PMID: 32506554 DOI: 10.1002/glia.23851] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 05/11/2020] [Accepted: 05/13/2020] [Indexed: 12/29/2022]
Abstract
The mammalian brain consists of 80% water, which is continuously shifted between different compartments and cellular structures by mechanisms that are, to a large extent, unresolved. Aquaporin 4 (AQP4) is abundantly expressed in glia and ependymal cells of the mammalian brain and has been proposed to act as a gatekeeper for brain water dynamics, predominantly based on studies utilizing AQP4-deficient mice. However, these mice have a range of secondary effects due to the gene deletion. An efficient and selective AQP4 inhibitor has thus been sorely needed to validate the results obtained in the AQP4-/- mice to quantify the contribution of AQP4 to brain fluid dynamics. In AQP4-expressing Xenopus laevis oocytes monitored by a high-resolution volume recording system, we here demonstrate that the compound TGN-020 is such a selective AQP4 inhibitor. TGN-020 targets the tested species of AQP4 with an IC50 of ~3.5 μM, but displays no inhibitory effect on the other AQPs (AQP1-AQP9). With this tool, we employed rat hippocampal slices and ion-sensitive microelectrodes to determine the role of AQP4 in glia cell swelling following neuronal activity. TGN-020-mediated inhibition of AQP4 did not prevent stimulus-induced extracellular space shrinkage, nor did it slow clearance of the activity-evoked K+ transient. These data, obtained with a verified isoform-selective AQP4 inhibitor, indicate that AQP4 is not required for the astrocytic contribution to the K+ clearance or the associated extracellular space shrinkage.
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Affiliation(s)
- Trine Lisberg Toft-Bertelsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Brian Roland Larsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sofie Kjellerup Christensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Himanshu Khandelia
- Department of Physics, Chemistry and Pharmacy, Faculty of Science, University of Southern Denmark, Odense, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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13
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MacAulay N. Molecular mechanisms of K + clearance and extracellular space shrinkage-Glia cells as the stars. Glia 2020; 68:2192-2211. [PMID: 32181522 DOI: 10.1002/glia.23824] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/28/2020] [Accepted: 03/04/2020] [Indexed: 12/17/2022]
Abstract
Neuronal signaling in the central nervous system (CNS) associates with release of K+ into the extracellular space resulting in transient increases in [K+ ]o . This elevated K+ is swiftly removed, in part, via uptake by neighboring glia cells. This process occurs in parallel to the [K+ ]o elevation and glia cells thus act as K+ sinks during the neuronal activity, while releasing it at the termination of the pulse. The molecular transport mechanisms governing this glial K+ absorption remain a point of debate. Passive distribution of K+ via Kir4.1-mediated spatial buffering of K+ has become a favorite within the glial field, although evidence for a quantitatively significant contribution from this ion channel to K+ clearance from the extracellular space is sparse. The Na+ /K+ -ATPase, but not the Na+ /K+ /Cl- cotransporter, NKCC1, shapes the activity-evoked K+ transient. The different isoform combinations of the Na+ /K+ -ATPase expressed in glia cells and neurons display different kinetic characteristics and are thereby distinctly geared toward their temporal and quantitative contribution to K+ clearance. The glia cell swelling occurring with the K+ transient was long assumed to be directly associated with K+ uptake and/or AQP4, although accumulating evidence suggests that they are not. Rather, activation of bicarbonate- and lactate transporters appear to lead to glial cell swelling via the activity-evoked alkaline transient, K+ -mediated glial depolarization, and metabolic demand. This review covers evidence, or lack thereof, accumulated over the last half century on the molecular mechanisms supporting activity-evoked K+ and extracellular space dynamics.
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Affiliation(s)
- Nanna MacAulay
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
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14
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Deitmer JW, Theparambil SM, Ruminot I, Noor SI, Becker HM. Energy Dynamics in the Brain: Contributions of Astrocytes to Metabolism and pH Homeostasis. Front Neurosci 2019; 13:1301. [PMID: 31866811 PMCID: PMC6909239 DOI: 10.3389/fnins.2019.01301] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Accepted: 11/20/2019] [Indexed: 12/17/2022] Open
Abstract
Regulation of metabolism is complex and involves enzymes and membrane transporters, which form networks to support energy dynamics. Lactate, as a metabolic intermediate from glucose or glycogen breakdown, appears to play a major role as additional energetic substrate, which is shuttled between glycolytic and oxidative cells, both under hypoxic and normoxic conditions. Transport of lactate across the cell membrane is mediated by monocarboxylate transporters (MCTs) in cotransport with H+, which is a substrate, a signal and a modulator of metabolic processes. MCTs form a “transport metabolon” with carbonic anhydrases (CAs), which not only provide a rapid equilibrium between CO2, HCO3– and H+, but, in addition, enhances lactate transport, as found in Xenopus oocytes, employed as heterologous expression system, as well as in astrocytes and cancer cells. Functional interactions between different CA isoforms and MCTs have been found to be isoform-specific, independent of the enzyme’s catalytic activity, and they require physical interaction between the proteins. CAs mediate between different states of metabolic acidosis, induced by glycolysis and oxidative phosphorylation, and play a relay function in coupling pH regulation and metabolism. In the brain, metabolic processes in astrocytes appear to be linked to bicarbonate transport and to neuronal activity. Here, we focus on physiological processes of energy dynamics in astrocytes as well as on the transfer of energetic substrates to neurons.
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Affiliation(s)
- Joachim W Deitmer
- Department of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Shefeeq M Theparambil
- Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
| | | | - Sina I Noor
- Centre for Organismal Studies, Heidelberg University, Heidelberg, Germany
| | - Holger M Becker
- Institute of Physiological Chemistry, University of Veterinary Medicine Hanover, Hanover, Germany
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15
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Burggren W, Bautista N. Invited review: Development of acid-base regulation in vertebrates. Comp Biochem Physiol A Mol Integr Physiol 2019; 236:110518. [DOI: 10.1016/j.cbpa.2019.06.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2019] [Revised: 06/24/2019] [Accepted: 06/25/2019] [Indexed: 12/26/2022]
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16
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Song S, Luo L, Sun B, Sun D. Roles of glial ion transporters in brain diseases. Glia 2019; 68:472-494. [PMID: 31418931 DOI: 10.1002/glia.23699] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 07/22/2019] [Accepted: 07/26/2019] [Indexed: 12/21/2022]
Abstract
Glial ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions of the central nervous system (CNS). In response to acute or chronic brain injuries, these ion transporters can be activated and differentially regulate glial functions, which has subsequent impact on brain injury or tissue repair and functional recovery. In this review, we summarized the current knowledge about major glial ion transporters, including Na+ /H+ exchangers (NHE), Na+ /Ca2+ exchangers (NCX), Na+ -K+ -Cl- cotransporters (NKCC), and Na+ -HCO3 - cotransporters (NBC). In acute neurological diseases, such as ischemic stroke and traumatic brain injury (TBI), these ion transporters are rapidly activated and play significant roles in regulation of the intra- and extracellular pH, Na+ , K+ , and Ca2+ homeostasis, synaptic plasticity, and myelin formation. However, overstimulation of these ion transporters can contribute to glial apoptosis, demyelination, inflammation, and excitotoxicity. In chronic brain diseases, such as glioma, Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), glial ion transporters are involved in the glioma Warburg effect, glial activation, neuroinflammation, and neuronal damages. These findings suggest that glial ion transporters are involved in tissue structural and functional restoration, or brain injury and neurological disease development and progression. A better understanding of these ion transporters in acute and chronic neurological diseases will provide insights for their potential as therapeutic targets.
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Affiliation(s)
- Shanshan Song
- Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania.,Pittsburgh Institute for Neurodegenerative Disorders, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Lanxin Luo
- Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania.,Pittsburgh Institute for Neurodegenerative Disorders, University of Pittsburgh, Pittsburgh, Pennsylvania.,School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang, China.,School of Functional Food and Wine, Shenyang Pharmaceutical University, Shenyang, China
| | - Baoshan Sun
- School of Functional Food and Wine, Shenyang Pharmaceutical University, Shenyang, China.,Pólo Dois Portos, Instituto National de Investigação Agrária e Veterinária, Dois Portos, Portugal
| | - Dandan Sun
- Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania.,Pittsburgh Institute for Neurodegenerative Disorders, University of Pittsburgh, Pittsburgh, Pennsylvania.,Veterans Affairs Pittsburgh Health Care System, Geriatric Research, Educational and Clinical Center, Pittsburgh, Pennsylvania
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17
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Khakipoor S, Giannaki M, Theparambil SM, Zecha J, Küster B, Heermann S, Deitmer JW, Roussa E. Functional expression of electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse cortical astrocytes is dependent on S255‐257 and regulated by mTOR. Glia 2019; 67:2264-2278. [DOI: 10.1002/glia.23682] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 06/23/2019] [Accepted: 07/03/2019] [Indexed: 01/14/2023]
Affiliation(s)
- Shokoufeh Khakipoor
- Department of Molecular Embryology, Faculty of Medicine Institute of Anatomy and Cell Biology, Albert‐Ludwigs‐Universität Freiburg Freiburg Germany
| | - Marina Giannaki
- Department of Molecular Embryology, Faculty of Medicine Institute of Anatomy and Cell Biology, Albert‐Ludwigs‐Universität Freiburg Freiburg Germany
| | - Shefeeq M. Theparambil
- Department of General Zoology, FB Biology University of Kaiserslautern Kaiserslautern Germany
| | - Jana Zecha
- Chair of Proteomics and Bioanalytics Technical University of Munich Freising Germany
| | - Bernhard Küster
- Chair of Proteomics and Bioanalytics Technical University of Munich Freising Germany
- Bavarian Biomolecular Mass Spectrometry Center (BayBioMS) Technical University of Munich Freising Germany
| | - Stephan Heermann
- Department of Molecular Embryology, Faculty of Medicine Institute of Anatomy and Cell Biology, Albert‐Ludwigs‐Universität Freiburg Freiburg Germany
| | - Joachim W. Deitmer
- Department of General Zoology, FB Biology University of Kaiserslautern Kaiserslautern Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Faculty of Medicine Institute of Anatomy and Cell Biology, Albert‐Ludwigs‐Universität Freiburg Freiburg Germany
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18
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Verkhratsky A, Untiet V, Rose CR. Ionic signalling in astroglia beyond calcium. J Physiol 2019; 598:1655-1670. [PMID: 30734296 DOI: 10.1113/jp277478] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 01/15/2019] [Indexed: 12/18/2022] Open
Abstract
Astrocytes are homeostatic and protective cells of the central nervous system. Astroglial homeostatic responses are tightly coordinated with neuronal activity. Astrocytes maintain neuronal excitability through regulation of extracellular ion concentrations, as well as assisting and modulating synaptic transmission by uptake and catabolism of major neurotransmitters. Moreover, they support neuronal metabolism and detoxify ammonium and reactive oxygen species. Astroglial homeostatic actions are initiated and controlled by intercellular signalling of ions, including Ca2+ , Na+ , Cl- , H+ and possibly K+ . This review summarises current knowledge on ionic signals mediated by the major monovalent ions, which occur in microdomains, as global events, or as propagating intercellular waves and thereby represent the substrate for astroglial excitability.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Biology, Medicine and Health, The University of Manchester, M13 9PT, Manchester, UK.,Centre for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark.,Achucarro Centre for Neuroscience, IKERBASQUE, Basque Foundation for Science, 48011, Bilbao, Spain
| | - Verena Untiet
- Centre for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Universitätsstrasse 1, D-40225, Düsseldorf, Germany
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19
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Larsen BR, Stoica A, MacAulay N. Developmental maturation of activity-induced K + and pH transients and the associated extracellular space dynamics in the rat hippocampus. J Physiol 2019; 597:583-597. [PMID: 30357826 PMCID: PMC6332761 DOI: 10.1113/jp276768] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Accepted: 10/22/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Neuronal activity induces fluctuation in extracellular space volume, [K+ ]o and pHo , the management of which influences neuronal function The neighbour astrocytes buffer the K+ and pH and swell during the process, causing shrinkage of the extracellular space In the present study, we report the developmental rise of the homeostatic control of the extracellular space dynamics, for which regulation becomes tighter with maturation and thus is proposed to ensure efficient synaptic transmission in the mature animals The extracellular space dynamics of volume, [K+ ]o and pHo evolve independently with developmental maturation and, although all of them are inextricably tied to neuronal activity, they do not couple directly. ABSTRACT Neuronal activity in the mammalian central nervous system associates with transient extracellular space (ECS) dynamics involving elevated K+ and pH and shrinkage of the ECS. These ECS properties affect membrane potentials, neurotransmitter concentrations and protein function and are thus anticipated to be under tight regulatory control. It remains unresolved to what extent these ECS dynamics are developmentally regulated as synaptic precision arises and whether they are directly or indirectly coupled. To resolve the development of homeostatic control of [K+ ]o , pH, and ECS and their interaction, we utilized ion-sensitive microelectrodes in electrically stimulated rat hippocampal slices from rats of different developmental stages (postnatal days 3-28). With the employed stimulation paradigm, the stimulus-evoked peak [K+ ]o and pHo transients were stable across age groups, until normalized to neuronal activity (field potential amplitude), in which case the K+ and pH shifted significantly more in the younger animals. By contrast, ECS dynamics increased with age until normalized to the field potential, and thus correlated with neuronal activity. With age, the animals not only managed the peak [K+ ]o better, but also displayed swifter post-stimulus removal of [K+ ]o , in correlation with the increased expression of the α1-3 isoforms of the Na+ /K+ -ATPase, and a swifter return of ECS volume. The different ECS dynamics approached a near-identical temporal pattern in the more mature animals. In conclusion, although these phenomena are inextricably tied to neuronal activity, our data suggest that they do not couple directly.
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Affiliation(s)
- Brian Roland Larsen
- Department of NeuroscienceFaculty of Health and Medical SciencesUniversity of CopenhagenCopenhagenDenmark
| | - Anca Stoica
- Department of NeuroscienceFaculty of Health and Medical SciencesUniversity of CopenhagenCopenhagenDenmark
| | - Nanna MacAulay
- Department of NeuroscienceFaculty of Health and Medical SciencesUniversity of CopenhagenCopenhagenDenmark
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20
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Khakipoor S, Ophoven C, Schrödl‐Häußel M, Feuerstein M, Heimrich B, Deitmer JW, Roussa E. TGF-β signaling directly regulates transcription and functional expression of the electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), via Smad4 in mouse astrocytes. Glia 2017; 65:1361-1375. [PMID: 28568893 PMCID: PMC5518200 DOI: 10.1002/glia.23168] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 04/27/2017] [Accepted: 05/04/2017] [Indexed: 02/06/2023]
Abstract
The electrogenic sodium bicarbonate cotransporter NBCe1 (SLC4A4) expressed in astrocytes regulates intracellular and extracellular pH. Here, we introduce transforming growth factor beta (TGF-β) as a novel regulator of NBCe1 transcription and functional expression. Using hippocampal slices and primary hippocampal and cortical astrocyte cultures, we investigated regulation of NBCe1 and elucidated the underlying signaling pathways by RT-PCR, immunoblotting, immunofluorescence, intracellular H(+ ) recording using the H(+ ) -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, mink lung epithelial cell (MLEC) assay, and chromatin immunoprecipitation. Activation of TGF-β signaling significantly upregulated transcript, protein, and surface expression of NBCe1. These effects were TGF-β receptor-mediated and suppressed following inhibition of JNK and Smad signaling. Moreover, 4-aminopyridine (4AP)-dependent NBCe1 regulation requires TGF-β. TGF-β increased the rate and amplitude of intracellular H+ changes upon challenging NBCe1 in wild-type astrocytes but not in cortical astrocytes from Slc4a4-deficient mice. A Smad4 binding sequence was identified in the NBCe1 promoter and Smad4 binding increased after activation of TGF-β signaling. The data show for the first time that NBCe1 is a direct target of TGF-β/Smad4 signaling. Through activation of the canonical pathway TGF-β acts directly on NBCe1 by binding of Smad4 to the NBCe1 promoter and regulating its transcription, followed by increased protein expression and transport activity.
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Affiliation(s)
- Shokoufeh Khakipoor
- Department of Molecular EmbryologyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
| | - Christian Ophoven
- Department of Molecular EmbryologyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
| | - Magdalena Schrödl‐Häußel
- Department of Molecular EmbryologyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
| | - Melanie Feuerstein
- Department of Molecular EmbryologyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
| | - Bernd Heimrich
- Department of NeuroanatomyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
| | - Joachim W. Deitmer
- Department of General ZoologyFB Biology, University of KaiserslauternP.B. 3049D‐67653KaiserslauternGermany
| | - Eleni Roussa
- Department of Molecular EmbryologyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
- Department of NeuroanatomyInstitute for Anatomy and Cell Biology, Faculty of Medicine, University of FreiburgAlbertstrasse 17D‐79104FreiburgGermany
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21
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Larsen BR, MacAulay N. Activity-dependent astrocyte swelling is mediated by pH-regulating mechanisms. Glia 2017; 65:1668-1681. [PMID: 28744903 DOI: 10.1002/glia.23187] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 06/09/2017] [Accepted: 06/23/2017] [Indexed: 11/09/2022]
Abstract
During neuronal activity in the mammalian brain, the K+ released into the synaptic space is initially buffered by the astrocytic compartment. In parallel, the extracellular space (ECS) shrinks, presumably due to astrocytic cell swelling. With the Na+ /K+ /2Cl- cotransporter and the Kir4.1/AQP4 complex not required for the astrocytic cell swelling in the hippocampus, the molecular mechanisms underlying the activity-dependent ECS shrinkage have remained unresolved. To identify these molecular mechanisms, we employed ion-sensitive microelectrodes to measure changes in ECS, [K+ ]o and [H+ ]o /pHo during electrical stimulation of rat hippocampal slices. Transporters and receptors responding directly to the K+ and glutamate released into the extracellular space (the K+ /Cl- cotransporter, KCC, glutamate transporters and G protein-coupled receptors) did not modulate the extracellular space dynamics. The HCO3--transporting mechanism, which in astrocytes mainly constitutes the electrogenic Na+ / HCO3- cotransporter 1 (NBCe1), is activated by the K+ -mediated depolarization of the astrocytic membrane. Inhibition of this transporter reduced the ECS shrinkage by ∼25% without affecting the K+ transients, pointing to NBCe1 as a key contributor to the stimulus-induced astrocytic cell swelling. Inhibition of the monocarboxylate cotransporters (MCT), like-wise, reduced the ECS shrinkage by ∼25% without compromising the K+ transients. Isosmotic reduction of extracellular Cl- revealed a requirement for this ion in parts of the ECS shrinkage. Taken together, the stimulus-evoked astrocytic cell swelling does not appear to occur as a direct effect of the K+ clearance, as earlier proposed, but partly via the pH-regulating transport mechanisms activated by the K+ -induced astrocytic depolarization and the activity-dependent metabolism.
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Affiliation(s)
- Brian Roland Larsen
- Faculty of Health and Medical Sciences, Center for Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Nanna MacAulay
- Faculty of Health and Medical Sciences, Center for Neuroscience, University of Copenhagen, Copenhagen, Denmark
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22
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Mechanisms of CO2/H+ Sensitivity of Astrocytes. J Neurosci 2017; 36:10750-10758. [PMID: 27798130 DOI: 10.1523/jneurosci.1281-16.2016] [Citation(s) in RCA: 93] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 08/18/2016] [Indexed: 11/21/2022] Open
Abstract
Ventral regions of the medulla oblongata of the brainstem are populated by astrocytes sensitive to physiological changes in PCO2/[H+]. These astrocytes respond to decreases in pH with elevations in intracellular Ca2+ and facilitated exocytosis of ATP-containing vesicles. Released ATP propagates Ca2+ excitation among neighboring astrocytes and activates neurons of the brainstem respiratory network triggering adaptive increases in breathing. The mechanisms linking increases in extracellular and/or intracellular PCO2/[H+] with Ca2+ responses in chemosensitive astrocytes remain unknown. Fluorescent imaging of changes in [Na+]i and/or [Ca2+]i in individual astrocytes was performed in organotypic brainstem slice cultures and acute brainstem slices of adult rats. It was found that astroglial [Ca2+]i responses triggered by decreases in pH are preceded by Na+ entry, markedly reduced by inhibition of Na+/HCO3- cotransport (NBC) or Na+/Ca2+ exchange (NCX), and abolished in Na+-free medium or by combined NBC/NCX blockade. Acidification-induced [Ca2+]i responses were also dramatically reduced in brainstem astrocytes of mice deficient in the electrogenic Na+/HCO3- cotransporter NBCe1. Sensitivity of astrocytes to changes in pH was not affected by inhibition of Na+/H+ exchange or blockade of phospholipase C. These results suggest that in pH-sensitive astrocytes, acidification activates NBCe1, which brings Na+ inside the cell. Raising [Na+]i activates NCX to operate in a reverse mode, leading to Ca2+ entry followed by activation of downstream signaling pathways. Coupled NBC and NCX activities are, therefore, suggested to be responsible for functional CO2/H+ sensitivity of astrocytes that contribute to homeostatic regulation of brain parenchymal pH and control of breathing. SIGNIFICANCE STATEMENT Brainstem astrocytes detect physiological changes in pH, activate neurons of the neighboring respiratory network, and contribute to the development of adaptive respiratory responses to the increases in the level of blood and brain PCO2/[H+]. The mechanisms underlying astroglial pH sensitivity remained unknown and here we show that in brainstem astrocytes acidification activates Na+/HCO3- cotransport, which brings Na+ inside the cell. Raising [Na+]i activates the Na+/Ca2+ exchanger to operate in a reverse mode leading to Ca2+ entry. This identifies a plausible mechanism of functional CO2/H+ sensitivity of brainstem astrocytes, which play an important role in homeostatic regulation of brain pH and control of breathing.
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Todd AC, Marx MC, Hulme SR, Bröer S, Billups B. SNAT3-mediated glutamine transport in perisynaptic astrocytesin situis regulated by intracellular sodium. Glia 2017; 65:900-916. [DOI: 10.1002/glia.23133] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 01/12/2017] [Accepted: 02/08/2017] [Indexed: 01/16/2023]
Affiliation(s)
- Alison C. Todd
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
- Centre for Integrative Physiology, School of Biomedical Sciences; University of Edinburgh; Edinburgh EH8 9XD United Kingdom
| | - Mari-Carmen Marx
- Department of Pharmacology; University of Cambridge; Tennis Court Road Cambridge CB2 1BT United Kingdom
| | - Sarah R. Hulme
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
| | - Stefan Bröer
- Research School of Biology; The Australian National University; Linnaeus Way 134 Canberra ACT 2601 Australia
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
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Theparambil SM, Naoshin Z, Defren S, Schmaelzle J, Weber T, Schneider HP, Deitmer JW. Bicarbonate sensing in mouse cortical astrocytes during extracellular acid/base disturbances. J Physiol 2017; 595:2569-2585. [PMID: 27981578 DOI: 10.1113/jp273394] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 11/30/2016] [Indexed: 12/18/2022] Open
Abstract
KEY POINTS The present study suggests that the electrogenic sodium-bicarbonate cotransporter, NBCe1, supported by carbonic anhydrase II, CAII, provides an efficient mechanism of bicarbonate sensing in cortical astrocytes. This mechanism is proposed to play a major role in setting the pHi responses to extracellular acid/base challenges in astrocytes. A decrease in extracellular [HCO3- ] during isocapnic acidosis and isohydric hypocapnia, or an increase in intracellular [HCO3- ] during hypercapnic acidosis, was effectively sensed by NBCe1, which carried bicarbonate out of the cells under these conditions, and caused an acidification and sodium fall in WT astrocytes, but not in NBCe1-knockout astrocytes. Isocapnic acidosis, hypercapnic acidosis and isohydric hypocapnia evoked inward currents in NBCe1- and CAII-expressing Xenopus laevis oocytes, but not in native oocytes, suggesting that NBCe1 operates in the outwardly directed mode under these conditions consistent with our findings in astrocytes. We propose that bicarbonate sensing of astrocytes may have functional significance during extracellular acid/base disturbances in the brain, as it not only alters intracellular pH/[HCO3- ]-dependent functions of astrocytes, but also modulates the extracellular pH/[HCO3- ] in brain tissue. ABSTRACT Extracellular acid/base status of the mammalian brain undergoes dynamic changes during many physiological and pathological events. Although intracellular pH (pHi ) of astrocytes responds to extracellular acid/base changes, the mechanisms mediating these changes have remained unresolved. We have previously shown that the electrogenic sodium-bicarbonate cotransporter, NBCe1, is a high-affinity bicarbonate carrier in cortical astrocytes. In the present study, we investigated whether NBCe1 plays a role in bicarbonate sensing in astrocytes, and in determining the pHi responses to extracellular acid/base challenges. We measured changes in intracellular H+ and Na+ in astrocytes from wild-type (WT) and from NBCe1-knockout (KO) mice, using ion-selective dyes, during isocapnic acidosis, hypercapnic acidosis and hypocapnia. We also analysed NBCe1-mediated membrane currents in Xenopus laevis oocytes under similar conditions. Comparing WT and NBCe1-KO astrocytes, we could dissect the contribution of NBCe1, of diffusion of CO2 across the cell membrane and, after blocking carbonic anhydrase (CA) activity with ethoxyzolamide, of the role of CA, for the amplitude and rate of acid/base fluxes. Our results suggest that NBCe1 transport activity in astrocytes, supported by CA activity, renders astrocytes bicarbonate sensors in the mouse cortex. NBCe1 carried bicarbonate into and out of the cell by sensing the variations of transmembrane [HCO3- ], irrespective of the changes in intra- and extracellular pH, and played a major role in setting pHi responses to the extracellular acid/base challenges. We propose that bicarbonate sensing of astrocytes may have potential functional significance during extracellular acid/base alterations in the brain.
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Affiliation(s)
- Shefeeq M Theparambil
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Zinnia Naoshin
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Sabrina Defren
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Jana Schmaelzle
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Tobias Weber
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Hans-Peter Schneider
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
| | - Joachim W Deitmer
- Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Pb 3049, D-67653, Kaiserslautern, Germany
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Expression of Carbonic Anhydrase I in Motor Neurons and Alterations in ALS. Int J Mol Sci 2016; 17:ijms17111820. [PMID: 27809276 PMCID: PMC5133821 DOI: 10.3390/ijms17111820] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/20/2016] [Accepted: 10/24/2016] [Indexed: 12/27/2022] Open
Abstract
Carbonic anhydrase I (CA1) is the cytosolic isoform of mammalian α-CA family members which are responsible for maintaining pH homeostasis in the physiology and pathology of organisms. A subset of CA isoforms are known to be expressed and function in the central nervous system (CNS). CA1 has not been extensively characterized in the CNS. In this study, we demonstrate that CA1 is expressed in the motor neurons in human spinal cord. Unexpectedly, a subpopulation of CA1 appears to be associated with endoplasmic reticulum (ER) membranes. In addition, the membrane-associated CA1s are preferentially upregulated in amyotrophic lateral sclerosis (ALS) and exhibit altered distribution in motor neurons. Furthermore, long-term expression of CA1 in mammalian cells activates apoptosis. Our results suggest a previously unknown role for CA1 function in the CNS and its potential involvement in motor neuron degeneration in ALS.
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Theparambil SM, Weber T, Schmälzle J, Ruminot I, Deitmer JW. Proton Fall or Bicarbonate Rise: GLYCOLYTIC RATE IN MOUSE ASTROCYTES IS PAVED BY INTRACELLULAR ALKALINIZATION. J Biol Chem 2016; 291:19108-17. [PMID: 27422823 PMCID: PMC5009280 DOI: 10.1074/jbc.m116.730143] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 07/12/2016] [Indexed: 01/08/2023] Open
Abstract
Glycolysis is the primary step for major energy production in the cell. There is strong evidence suggesting that glucose consumption and rate of glycolysis are highly modulated by cytosolic pH/[H(+)], but those can also be stimulated by an increase in the intracellular [HCO3 (-)]. Because proton and bicarbonate shift concomitantly, it remained unclear whether enhanced glucose consumption and glycolytic rate were mediated by the changes in intracellular [H(+)] or [HCO3 (-)]. We have asked whether glucose metabolism is enhanced by either a fall in intracellular [H(+)] or a rise in intracellular [HCO3 (-)], or by both, in mammalian astrocytes. We have recorded intracellular glucose in mouse astrocytes using a FRET-based nanosensor, while imposing different intracellular [H(+)] and [CO2]/[HCO3 (-)]. Glucose consumption and glycolytic rate were augmented by a fall in intracellular [H(+)], irrespective of a concomitant rise or fall in intracellular [HCO3 (-)]. Transport of HCO3 (-) into and out of astrocytes by the electrogenic sodium bicarbonate cotransporter (NBCe1) played a crucial role in causing changes in intracellular pH and [HCO3 (-)], but was not obligatory for the pH-dependent changes in glucose metabolism. Our results clearly show that it is the cytosolic pH that modulates glucose metabolism in cortical astrocytes, and possibly also in other cell types.
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Affiliation(s)
- Shefeeq M Theparambil
- From the Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserlautern, P. B. 3049, D-67653 Kaiserslautern, Germany and
| | - Tobias Weber
- From the Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserlautern, P. B. 3049, D-67653 Kaiserslautern, Germany and
| | - Jana Schmälzle
- From the Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserlautern, P. B. 3049, D-67653 Kaiserslautern, Germany and
| | - Ivàn Ruminot
- From the Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserlautern, P. B. 3049, D-67653 Kaiserslautern, Germany and the Centro de Estudios Científicos (CECs), Valdivia 5110466, Chile
| | - Joachim W Deitmer
- From the Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserlautern, P. B. 3049, D-67653 Kaiserslautern, Germany and
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Theparambil SM, Naoshin Z, Thyssen A, Deitmer JW. Reversed electrogenic sodium bicarbonate cotransporter 1 is the major acid loader during recovery from cytosolic alkalosis in mouse cortical astrocytes. J Physiol 2015; 593:3533-47. [PMID: 25990710 DOI: 10.1113/jp270086] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 05/17/2015] [Indexed: 12/29/2022] Open
Abstract
KEY POINTS The regulation of H(+) i from cytosolic alkalosis has generally been attributed to the activity of Cl(-) -coupled acid loaders/base extruders in most cell types, including brain cells. The present study demonstrates that outwardly-directed sodium bicarbonate cotransport via electrogenic sodium bicarbonate cotransporter 1 (NBCe1) mediates the major fraction of H(+) i regulation from cytosolic alkalosis in mouse cortical astrocytes. Cl(-) -coupled acid-loading transporters play only a minor role in the regulation of H(+) i from alkalosis in mouse cortical astrocytes. NBCe1-mediated H(+) i regulation from alkalosis was dominant, with the support of intracellular carbonic anhydrase II, even when the intra- and extracellular [HCO3 (-) ] was very low (<1mM), as in nominally CO2 /HCO3 (-) free condition. A reversed NBCe1 in astrocytes may also be significant for stabilizing extracellular pH in brain tissue. ABSTRACT Recovery of intracellular pH from cytosolic alkalosis has been attributed primarily to Cl(-) coupled acid loaders/base extruders such as Cl(-) /HCO3 (-) or Cl(-) /OH(-) exchangers. We have studied this process in cortical astrocytes from wild-type and transgenic mouse models with gene deletion for the electrogenic sodium bicarbonate cotransporter 1 (NBCe1) and for carbonic anhydrase (CA) isoform II. An acute cytosolic alkalosis was induced by the removal of either CO2 /HCO3 (-) or butyric acid, and the subsequent acid loading was analysed by monitoring changes in cytosolic H(+) or Na(+) using ion-sensitive fluorescent dyes. We have identified that NBCe1 reverses during alkalosis and contributes more than 70% to the rate of recovery from alkalosis by extruding Na(+) and HCO3 (-) . After CA inhibition or in CAII-knockout (KO) cells, the rate of recovery was reduced by 40%, and even by 70% in the nominal absence of CO2 /HCO3 (-) . Increasing the extracellular K(+) concentration modulated the rate of acid loading in wild-type cells, but not in NBCe1-KO cells. Removing chloride had only a minor effect on the recovery from alkalosis. Reversal of NBCe1 by reducing pH/[HCO3 (-) ] was demonstrated in astrocytes and in Xenopus oocytes, in which human NBCe1 was heterologously expressed. The results obtained suggest that reversed NBCe1, supported by CAII activity, plays a major role in acid-loading cortical astrocytes to support recovery from cytosolic alkalosis.
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Affiliation(s)
- Shefeeq M Theparambil
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Zinnia Naoshin
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Anne Thyssen
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Joachim W Deitmer
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
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