1
|
Xiong M, Li C, Wang W, Yang B. Protein Structure and Modification of Aquaporins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1398:15-38. [PMID: 36717484 DOI: 10.1007/978-981-19-7415-1_2] [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: 02/01/2023]
Abstract
Aquaporins (AQPs) allow water molecules and other small, neutral solutes to quickly pass through membrane. The protein structures of AQPs solved by crystallographic methods or cryo-electron microscopy technology show that AQP monomer consists of six membrane-spanning alpha-helices that form the central water-transporting pore. AQP monomers assemble to form tetramers, forming the functional units in the membrane, to transport water or other small molecules. The biological functions of AQPs are regulated by posttranslational modifications, e.g., phosphorylation, ubiquitination, glycosylation, subcellular distribution, degradation and protein interactions. Modifications of AQP combined with structural properties contribute to a better functional mechanism of AQPs. Insight into the molecular mechanisms responsible for AQP modifications as well as gating and transport properties proved to be fundamental to the development of new therapeutic targets or reliable diagnostic and prognostic biomarkers.
Collapse
Affiliation(s)
- Mengyao Xiong
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Chunling Li
- Institute of Hypertension and Kidney Research, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China
| | - Weidong Wang
- Institute of Hypertension and Kidney Research, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China.
| | - Baoxue Yang
- School of Basic Medical Sciences, Peking University, Beijing, China.
| |
Collapse
|
2
|
Zhao Z, He J, Chen Y, Wang Y, Wang C, Tan C, Liao J, Xiao G. The pathogenesis of idiopathic normal pressure hydrocephalus based on the understanding of AQP1 and AQP4. Front Mol Neurosci 2022; 15:952036. [PMID: 36204139 PMCID: PMC9530743 DOI: 10.3389/fnmol.2022.952036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 08/12/2022] [Indexed: 11/21/2022] Open
Abstract
Idiopathic normal pressure hydrocephalus (iNPH) is a neurological disorder without a recognized cause. Aquaporins (AQPs) are transmembrane channels that carry water through cell membranes and are critical for cerebrospinal fluid circulation and cerebral water balance. The function of AQPs in developing and maintaining hydrocephalus should be studied in greater detail as a possible diagnostic and therapeutic tool. Recent research indicates that patients with iNPH exhibited high levels of aquaporin 1 and low levels of aquaporin 4 expression, suggesting that these AQPs are essential in iNPH pathogenesis. To determine the source of iNPH and diagnose and treat it, it is necessary to examine and appreciate their function in the genesis and maintenance of hydrocephalus. The expression, function, and regulation of AQPs in iNPH are reviewed in this article, in order to provide fresh targets and suggestions for future research.
Collapse
Affiliation(s)
- Zitong Zhao
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Jian He
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China
| | - Yibing Chen
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Yuchang Wang
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Chuansen Wang
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Changwu Tan
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Junbo Liao
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
| | - Gelei Xiao
- Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, China
- Diagnosis and Treatment Center for Hydrocephalus, Xiangya Hospital, Central South University, Changsha, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, China
- *Correspondence: Gelei Xiao
| |
Collapse
|
3
|
Abe Y, Yasui M. Aquaporin-4 in Neuromyelitis Optica Spectrum Disorders: A Target of Autoimmunity in the Central Nervous System. Biomolecules 2022; 12:biom12040591. [PMID: 35454180 PMCID: PMC9030581 DOI: 10.3390/biom12040591] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 04/11/2022] [Accepted: 04/12/2022] [Indexed: 12/20/2022] Open
Abstract
Since the discovery of a specific autoantibody in patients with neuromyelitis optica spectrum disorder (NMOSD) in 2004, the water channel aquaporin-4 (AQP4) has attracted attention as a target of autoimmune diseases of the central nervous system. In NMOSD, the autoantibody (NMO-IgG) binds to the extracellular loops of AQP4 as expressed in perivascular astrocytic end-feet and disrupts astrocytes in a complement-dependent manner. NMO-IgG is an excellent marker for distinguishing the disease from other inflammatory demyelinating diseases, such as multiple sclerosis. The unique higher-order structure of AQP4—called orthogonal arrays of particles (OAPs)—as well as its subcellular localization may play a crucial role in the pathogenesis of the disease. Recent studies have also demonstrated complement-independent cytotoxic effects of NMO-IgG. Antibody-induced endocytosis of AQP4 has been suggested to be involved in this mechanism. This review focuses on the binding properties of antibodies that recognize the extracellular region of AQP4 and the characteristics of AQP4 that are implicated in the pathogenesis of NMOSD.
Collapse
Affiliation(s)
- Yoichiro Abe
- Department of Pharmacology, Keio University School of Medicine, Tokyo 160-8582, Japan
- Keio University Global Research Institute, Tokyo 108-8345, Japan
- Correspondence: (Y.A.); (M.Y.); Tel.: +81-3-5363-3751 (M.Y.)
| | - Masato Yasui
- Department of Pharmacology, Keio University School of Medicine, Tokyo 160-8582, Japan
- Keio University Global Research Institute, Tokyo 108-8345, Japan
- Correspondence: (Y.A.); (M.Y.); Tel.: +81-3-5363-3751 (M.Y.)
| |
Collapse
|
4
|
Abstract
Our brains consist of 80% water, which is continuously shifted between different compartments and cell types during physiological and pathophysiological processes. Disturbances in brain water homeostasis occur with pathologies such as brain oedema and hydrocephalus, in which fluid accumulation leads to elevated intracranial pressure. Targeted pharmacological treatments do not exist for these conditions owing to our incomplete understanding of the molecular mechanisms governing brain water transport. Historically, the transmembrane movement of brain water was assumed to occur as passive movement of water along the osmotic gradient, greatly accelerated by water channels termed aquaporins. Although aquaporins govern the majority of fluid handling in the kidney, they do not suffice to explain the overall brain water movement: either they are not present in the membranes across which water flows or they appear not to be required for the observed flow of water. Notably, brain fluid can be secreted against an osmotic gradient, suggesting that conventional osmotic water flow may not describe all transmembrane fluid transport in the brain. The cotransport of water is an unconventional molecular mechanism that is introduced in this Review as a missing link to bridge the gap in our understanding of cellular and barrier brain water transport.
Collapse
Affiliation(s)
- Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| |
Collapse
|
5
|
Zeneyedpour L, Sten-van `t Hoff J, Luider T. Using phosphoproteomics and next generation sequencing to discover novel therapeutic targets in patient antibodies. Expert Rev Proteomics 2020; 17:675-684. [DOI: 10.1080/14789450.2020.1845147] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Lona Zeneyedpour
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| | - Jenny Sten-van `t Hoff
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| | - Theo Luider
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| |
Collapse
|
6
|
Vandebroek A, Yasui M. Regulation of AQP4 in the Central Nervous System. Int J Mol Sci 2020; 21:E1603. [PMID: 32111087 PMCID: PMC7084855 DOI: 10.3390/ijms21051603] [Citation(s) in RCA: 86] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 02/21/2020] [Accepted: 02/21/2020] [Indexed: 12/26/2022] Open
Abstract
Aquaporin-4 (AQP4) is the main water channel protein expressed in the central nervous system (CNS). AQP4 is densely expressed in astrocyte end-feet, and is an important factor in CNS water and potassium homeostasis. Changes in AQP4 activity and expression have been implicated in several CNS disorders, including (but not limited to) epilepsy, edema, stroke, and glioblastoma. For this reason, many studies have been done to understand the various ways in which AQP4 is regulated endogenously, and could be regulated pharmaceutically. In particular, four regulatory methods have been thoroughly studied; regulation of gene expression via microRNAs, regulation of AQP4 channel gating/trafficking via phosphorylation, regulation of water permeability using heavy metal ions, and regulation of water permeability using small molecule inhibitors. A major challenge when studying AQP4 regulation is inter-method variability. A compound or phosphorylation which shows an inhibitory effect in vitro may show no effect in a different in vitro method, or even show an increase in AQP4 expression in vivo. Although a large amount of variability exists between in vitro methods, some microRNAs, heavy metal ions, and two small molecule inhibitors, acetazolamide and TGN-020, have shown promise in the field of AQP4 regulation.
Collapse
Affiliation(s)
- Arno Vandebroek
- Department of Pharmacology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan;
| | | |
Collapse
|
7
|
Deshpande V, Kao A, Raghuram V, Datta A, Chou CL, Knepper MA. Phosphoproteomic identification of vasopressin V2 receptor-dependent signaling in the renal collecting duct. Am J Physiol Renal Physiol 2019; 317:F789-F804. [PMID: 31313956 PMCID: PMC6843035 DOI: 10.1152/ajprenal.00281.2019] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 06/28/2019] [Accepted: 07/04/2019] [Indexed: 12/15/2022] Open
Abstract
Vasopressin controls water balance largely through PKA-dependent effects to regulate the collecting duct water channel aquaporin-2 (AQP2). Although considerable information has accrued regarding the regulation of water and solute transport in collecting duct cells, information is sparse regarding the signaling connections between PKA and transport responses. Here, we exploited recent advancements in protein mass spectrometry to perform a comprehensive, multiple-replicate analysis of changes in the phosphoproteome of native rat inner medullary collecting duct cells in response to the vasopressin V2 receptor-selective agonist 1-desamino-8D-arginine vasopressin. Of the 10,738 phosphopeptides quantified, only 156 phosphopeptides were significantly increased in abundance, and only 63 phosphopeptides were decreased, indicative of a highly selective response to vasopressin. The list of upregulated phosphosites showed several general characteristics: 1) a preponderance of sites with basic (positively charged) amino acids arginine (R) and lysine (K) in position -2 and -3 relative to the phosphorylated amino acid, consistent with phosphorylation by PKA and/or other basophilic kinases; 2) a greater-than-random likelihood of sites previously demonstrated to be phosphorylated by PKA; 3) a preponderance of sites in membrane proteins, consistent with regulation by membrane association; and 4) a greater-than-random likelihood of sites in proteins with class I COOH-terminal PDZ ligand motifs. The list of downregulated phosphosites showed a preponderance of those with proline in position +1 relative to the phosphorylated amino acid, consistent with either downregulation of proline-directed kinases (e.g., MAPKs or cyclin-dependent kinases) or upregulation of one or more protein phosphatases that selectively dephosphorylate such sites (e.g., protein phosphatase 2A). The phosphoproteomic data were used to create a web resource for the investigation of G protein-coupled receptor signaling and regulation of AQP2-mediated water transport.
Collapse
Affiliation(s)
- Venkatesh Deshpande
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Anika Kao
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Viswanathan Raghuram
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Arnab Datta
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Chung-Lin Chou
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Mark A Knepper
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| |
Collapse
|
8
|
Nesverova V, Törnroth-Horsefield S. Phosphorylation-Dependent Regulation of Mammalian Aquaporins. Cells 2019; 8:cells8020082. [PMID: 30678081 PMCID: PMC6406877 DOI: 10.3390/cells8020082] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 01/17/2019] [Accepted: 01/21/2019] [Indexed: 12/26/2022] Open
Abstract
Water homeostasis is fundamental for cell survival. Transport of water across cellular membranes is governed by aquaporins—tetrameric integral membrane channels that are highly conserved throughout the prokaryotic and eukaryotic kingdoms. In eukaryotes, specific regulation of these channels is required and is most commonly carried out by shuttling the protein between cellular compartments (trafficking) or by opening and closing the channel (gating). Structural and functional studies have revealed phosphorylation as a ubiquitous mechanism in aquaporin regulation by both regulatory processes. In this review we summarize what is currently known about the phosphorylation-dependent regulation of mammalian aquaporins. Focusing on the water-specific aquaporins (AQP0–AQP5), we discuss how gating and trafficking are controlled by phosphorylation and how phosphorylation affects the binding of aquaporins to regulatory proteins, thereby highlighting structural details and dissecting the contribution of individual phosphorylated residues when possible. Our aim is to provide an overview of the mechanisms behind how aquaporin phosphorylation controls cellular water balance and to identify key areas where further studies are needed.
Collapse
Affiliation(s)
- Veronika Nesverova
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Box 124, 221 00 Lund, Sweden.
| | - Susanna Törnroth-Horsefield
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Box 124, 221 00 Lund, Sweden.
| |
Collapse
|
9
|
Ferrer I, García MA, González IL, Lucena DD, Villalonga AR, Tech MC, Llorens F, Garcia‐Esparcia P, Martinez‐Maldonado A, Mendez MF, Escribano BT, Bech‐Serra JJ, Sabido E, de la Torre Gómez C, del Rio JA. Aging-related tau astrogliopathy (ARTAG): not only tau phosphorylation in astrocytes. Brain Pathol 2018; 28:965-985. [PMID: 29396893 PMCID: PMC8028270 DOI: 10.1111/bpa.12593] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 01/26/2018] [Indexed: 12/12/2022] Open
Abstract
Aging-related tau astrogliopathy (ARTAG) is defined by the presence of two types of tau-bearing astrocytes: thorn-shaped astrocytes (TSAs) and granular/fuzzy astrocytes in the brain of old-aged individuals. The present study is focused on TSAs in rare forms of ARTAG with no neuronal tau pathology or restricted to entorhinal and transentorhinal cortices, to avoid bias from associated tauopathies. TSAs show 4Rtau phosphorylation at several specific sites and abnormal tau conformation, but they lack ubiquitin and they are not immunostained with tau-C3 antibodies which recognize truncated tau at Asp421. Astrocytes in ARTAG have atrophic processes, reduced glial fibrillary acidic protein (GFAP) and increased superoxide dismutase 2 (SOD2) immunoreactivity. Gel electrophoresis and western blotting of sarkosyl-insoluble fractions reveal a pattern of phospho-tau in ARTAG characterized by two bands of 68 and 64 kDa, and several middle bands between 35 and 50 kDa which differ from what is seen in AD. Phosphoproteomics of dissected vulnerable regions identifies an increase of phosphorylation marks in a large number of proteins in ARTAG compared with controls. GFAP, aquaporin 4, several serine-threonine kinases, microtubule associated proteins and other neuronal proteins are among the differentially phosphorylated proteins in ARTAG thus suggesting a hyper-phosphorylation background that affects several molecules, including many kinases and proteins from several cell compartments and various cell types. Finally, present results show for the first time that tau seeding is produced in neurons of the hippocampal complex, astrocytes, oligodendroglia and along fibers of the corpus callosum, fimbria and fornix following inoculation into the hippocampus of wild type mice of sarkosyl-insoluble fractions enriched in hyper-phosphorylated tau from selected ARTAG cases. These findings show astrocytes as crucial players of tau seeding in tauopathies.
Collapse
Affiliation(s)
- Isidro Ferrer
- Department of Pathology and Experimental TherapeuticsUniversity of BarcelonaBarcelonaSpain
- Bellvitge University Hospital, IDIBELL (Bellvitge Biomedical Research Centre)BarcelonaSpain
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
- Institute of Neurosciences, University of BarcelonaBarcelonaSpain
| | - Meritxell Aguiló García
- Department of Pathology and Experimental TherapeuticsUniversity of BarcelonaBarcelonaSpain
- Laboratory of Molecular Biology and BiochemistryInstitute for Molecular Biosciences, Karl‐Franzens University of GrazAustria
| | - Irene López González
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
| | - Daniela Diaz Lucena
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
| | - Aina Roig Villalonga
- Department of Pathology and Experimental TherapeuticsUniversity of BarcelonaBarcelonaSpain
| | - Margarita Carmona Tech
- Department of Pathology and Experimental TherapeuticsUniversity of BarcelonaBarcelonaSpain
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
| | - Franc Llorens
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
| | - Paula Garcia‐Esparcia
- Bellvitge University Hospital, IDIBELL (Bellvitge Biomedical Research Centre)BarcelonaSpain
| | | | - Margalida Frau Mendez
- Department of Pathology and Experimental TherapeuticsUniversity of BarcelonaBarcelonaSpain
| | - Benjamín Torrejón Escribano
- Biology Unit, Scientific and Technical ServicesUniversity of Barcelona, Hospitalet de LlobregatBarcelonaSpain
| | | | - Eduard Sabido
- Proteomics Unit, Centre de Regulació GenòmicaBarcelona Institute of Science and TechnologyBarcelonaSpain
| | | | - José Antonio del Rio
- Ministry of Economy and CompetitivenessCIBERNED (Network Centre of Biomedical Research of Neurodegenerative Diseases), Institute of Health Carlos IIIBarcelonaSpain
- Institute of Neurosciences, University of BarcelonaBarcelonaSpain
- Molecular and Cellular NeurobiotechnologyInstitute of Bioengineering of Catalonia (IBEC), Barcelona Institute for Science and Technology, Parc Científic de BarcelonaBarcelonaSpain
| |
Collapse
|
10
|
Berland S, Toft-Bertelsen TL, Aukrust I, Byska J, Vaudel M, Bindoff LA, MacAulay N, Houge G. A de novo Ser111Thr variant in aquaporin-4 in a patient with intellectual disability, transient signs of brain ischemia, transient cardiac hypertrophy, and progressive gait disturbance. Cold Spring Harb Mol Case Stud 2018; 4:mcs.a002303. [PMID: 29437797 PMCID: PMC5793774 DOI: 10.1101/mcs.a002303] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 11/06/2017] [Indexed: 11/25/2022] Open
Abstract
Aquaporin-4, encoded by AQP4, is the major water channel in the central nervous system and plays an important role in the brain's water balance, including edema formation and clearance. Using genomic copy-number analysis and trio-exome sequencing, we investigated a male patient with intellectual disability, hearing loss, and progressive gait dysfunction and found a de novo missense change Ser111Thr in AQP4 as the only suspicious finding. Perinatally, signs of brain ischemia were detected in relation to acute collapse 2 h after birth that resolved a few days later. At the age of 3 mo, cardiac hypertrophy was detected that persisted through childhood but was completely resolved by age 16. In theory, this neurodevelopmental disorder with transient cardiomyopathy could be caused by a disturbance of cellular water balance. Ser111 is an extremely conserved residue in the short cytoplasmic loop between AQP4 transmembrane helix 2 and 3, present across all AQP isoforms from plants to mammals, and it does not appear to be a phosphorylation site. We found that the Ser111Thr change does not affect water permeability or protein stability, suggesting another and possibly regulatory role. Although causality remains unproven, this case study draws attention to AQP4 as a candidate gene for a unique developmental disorder and to a specific serine as a residue of possibly great functional importance in many AQPs.
Collapse
Affiliation(s)
- Siren Berland
- Department of Medical Genetics, Haukeland University Hospital, Bergen N-5021, Norway
| | | | - Ingvild Aukrust
- Department of Medical Genetics, Haukeland University Hospital, Bergen N-5021, Norway
| | - Jan Byska
- Department of Informatics, University of Bergen, Bergen N-5020, Norway
| | - Marc Vaudel
- Department of Medical Genetics, Haukeland University Hospital, Bergen N-5021, Norway.,KG Jebsen Center for Diabetes Research, Department of Clinical Science, Faculty of Medicine and Dentistry, University of Bergen, Bergen N-5020, Norway
| | - Laurence A Bindoff
- Department of Neurology, Haukeland University Hospital, Bergen N-5021, Norway.,Department of Clinical Medicine (K1), University of Bergen, Bergen N-5020, Norway
| | - Nanna MacAulay
- Department of Neuroscience, University of Copenhagen, Copenhagen DK-2200, Denmark
| | - Gunnar Houge
- Department of Medical Genetics, Haukeland University Hospital, Bergen N-5021, Norway
| |
Collapse
|
11
|
Wambo TO, Rodriguez RA, Chen LY. Computing osmotic permeabilities of aquaporins AQP4, AQP5, and GlpF from near-equilibrium simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1310-1316. [PMID: 28455098 DOI: 10.1016/j.bbamem.2017.04.022] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2017] [Revised: 04/23/2017] [Accepted: 04/24/2017] [Indexed: 12/01/2022]
Abstract
Measuring or computing the single-channel permeability of aquaporins/aquaglyceroporins (AQPs) has long been a challenge. The measured values scatter over an order of magnitude but the corresponding Arrhenius activation energies converge in the current literature. Osmotic flux through an AQP was simulated as water current forced through the channel by kilobar hydraulic pressure or theoretically approximated as single-file diffusion. In this paper, we report large scale simulations of osmotic current under sub M gradient through three AQPs (water channels AQP4 and AQP5 and glycerol-water channel GlpF) using the mature particle mesh Ewald technique (PME) for which the established force fields have been optimized with known accuracy. These simulations were implemented with hybrid periodic boundary conditions devised to avoid the artifactitious mixing across the membrane in a regular PME simulation. The computed single-channel permeabilities at 5°C and 25°C are in agreement with recently refined experiments on GlpF. The Arrhenius activation energies extracted from our simulations for all the three AQPs agree with the in vitro measurements. The single-file diffusion approximations from our large-scale simulations are consistent with the current literature on smaller systems. From these unambiguous agreements among the in vitro and in silico studies, we observe the quantitative accuracy of the all-atom force fields of the current literature for water-channel biology. We also observe that AQP4, that is particularly rich in the central nervous system, is more efficient in water conduction and more temperature-sensitive than other water-only channels (excluding glycerol channels that also conduct water when not inhibited by glycerol).
Collapse
Affiliation(s)
- Thierry O Wambo
- Department of Physics, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Roberto A Rodriguez
- Department of Physics, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Liao Y Chen
- Department of Physics, University of Texas at San Antonio, San Antonio, TX 78249, USA.
| |
Collapse
|
12
|
Turning down the volume: Astrocyte volume change in the generation and termination of epileptic seizures. Neurobiol Dis 2017; 104:24-32. [PMID: 28438505 DOI: 10.1016/j.nbd.2017.04.016] [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: 03/16/2017] [Revised: 04/18/2017] [Accepted: 04/20/2017] [Indexed: 12/20/2022] Open
Abstract
Approximately 1% of the global population suffers from epilepsy, a class of disorders characterized by recurrent and unpredictable seizures. Of these cases roughly one-third are refractory to current antiepileptic drugs, which typically target neuronal excitability directly. The events leading to seizure generation and epileptogenesis remain largely unknown, hindering development of new treatments. Some recent experimental models of epilepsy have provided compelling evidence that glial cells, especially astrocytes, could be central to seizure development. One of the proposed mechanisms for astrocyte involvement in seizures is astrocyte swelling, which may promote pathological neuronal firing and synchrony through reduction of the extracellular space and elevated glutamate concentrations. In this review, we discuss the common conditions under which astrocytes swell, the resultant effects on neural excitability, and how seizure development may ultimately be influenced by these effects.
Collapse
|
13
|
Abstract
Aquaporins (AQPs ) are a family of membrane water channels that basically function as regulators of intracellular and intercellular water flow. To date, thirteen AQPs , which are distributed widely in specific cell types in various organs and tissues, have been characterized in humans. Four AQP monomers, each of which consists of six membrane-spanning alpha-helices that have a central water-transporting pore, assemble to form tetramers, forming the functional units in the membrane. AQP facilitates osmotic water transport across plasma membranes and thus transcellular fluid movement. The cellular functions of aquaporins are regulated by posttranslational modifications , e.g. phosphorylation, ubiquitination, glycosylation, subcellular distribution, degradation, and protein interactions. Insight into the molecular mechanisms responsible for regulated aquaporin trafficking and synthesis is proving to be fundamental for development of novel therapeutic targets or reliable diagnostic and prognostic biomarkers.
Collapse
Affiliation(s)
- Chunling Li
- Institute of Hypertension, Zhongshan School of Medicine, Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China
| | - Weidong Wang
- Institute of Hypertension, Zhongshan School of Medicine, Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China.
| |
Collapse
|
14
|
Yu L, Rodriguez RA, Chen LL, Chen LY, Perry G, McHardy SF, Yeh CK. 1,3-propanediol binds deep inside the channel to inhibit water permeation through aquaporins. Protein Sci 2016; 25:433-41. [PMID: 26481430 DOI: 10.1002/pro.2832] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Revised: 10/15/2015] [Accepted: 10/16/2015] [Indexed: 01/10/2023]
Abstract
Aquaporins and aquaglyceroporins (AQPs) are membrane channel proteins responsible for transport of water and for transport of glycerol in addition to water across the cell membrane, respectively. They are expressed throughout the human body and also in other forms of life. Inhibitors of human AQPs have been sought for therapeutic treatment for various medical conditions including hypertension, refractory edema, neurotoxic brain edema, and so forth. Conducting all-atom molecular dynamics simulations, we computed the binding affinity of acetazolamide to human AQP4 that agrees closely with in vitro experiments. Using this validated computational method, we found that 1,3-propanediol (PDO) binds deep inside the AQP4 channel to inhibit that particular aquaporin efficaciously. Furthermore, we used the same method to compute the affinities of PDO binding to four other AQPs and one aquaglyceroporin whose atomic coordinates are available from the protein data bank (PDB). For bovine AQP1, human AQP2, AQP4, AQP5, and Plasmodium falciparum PfAQP whose structures were resolved with high resolution, we obtained definitive predictions on the PDO dissociation constant. For human AQP1 whose PDB coordinates are less accurate, we estimated the dissociation constant with a rather large error bar. Taking into account the fact that PDO is generally recognized as safe by the US FDA, we predict that PDO can be an effective diuretic which directly modulates water flow through the protein channels. It should be free from the serious side effects associated with other diuretics that change the hydro-homeostasis indirectly by altering the osmotic gradients.
Collapse
Affiliation(s)
- Lili Yu
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas, 78249
| | - Roberto A Rodriguez
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas, 78249
| | - L Laurie Chen
- Medical School, University of Texas Southwestern Medical Center, Dallas, Texas, 75390
| | - Liao Y Chen
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas, 78249
| | - George Perry
- Department of Biology, University of Texas at San Antonio, San Antonio, Texas, 78249
| | - Stanton F McHardy
- Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas, 78249
| | - Chih-Ko Yeh
- Department of Comprehensive Dentistry, University of Texas Health Science Center at San Antonio & GRECC, South Texas Veterans Health Care System, San Antonio, Texas 78229
| |
Collapse
|
15
|
Ximenes-da-Silva A. Metal Ion Toxins and Brain Aquaporin-4 Expression: An Overview. Front Neurosci 2016; 10:233. [PMID: 27313504 PMCID: PMC4887506 DOI: 10.3389/fnins.2016.00233] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 05/11/2016] [Indexed: 01/15/2023] Open
Abstract
Metal ions such as iron, zinc, and manganese are essential to metabolic functions, protein synthesis, neurotransmission, and antioxidant neuroprotective mechanisms. Conversely, non-essential metals such as mercury and lead are sources of human intoxication due to occupational activities or environmental contamination. Essential or non-essential metal accumulation in the central nervous system (CNS) results in changes in blood-brain barrier (BBB) permeability, as well as triggering microglia activation and astrocyte reactivity and changing water transport through the cells, which could result in brain swelling. Aquaporin-4 is the main water channel in the CNS, is expressed in astrocyte foot processes in brain capillaries and along the circumventricular epithelium in the ventricles, and has important physiological functions in maintaining brain osmotic homeostasis and supporting brain excitability through regulation of the extracellular space. Some evidence has pointed to a role of AQP4 during metal intoxication in the brain, where it may act in a dual form as a neuroprotector or a mediator of the development of oxidative stress in neurons and astrocytes, resulting in brain swelling and neuronal damage. This mini-review presents the way some metal ions affect changes in AQP4 expression in the CNS and discuss the ways in which water transport in brain cells can be involved in brain damage.
Collapse
Affiliation(s)
- Adriana Ximenes-da-Silva
- Setor de Fisiologia, Instituto de Ciências Biológicas e da Saúde, Universidade Federal de Alagoas Maceió, Brazil
| |
Collapse
|
16
|
Yu L, Villarreal OD, Chen LL, Chen LY. 1,3-Propanediol binds inside the water-conducting pore of aquaporin 4: Does this efficacious inhibitor have sufficient potency? ACTA ACUST UNITED AC 2016; 2:91-98. [PMID: 27213050 DOI: 10.15761/jsin.1000117] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Among the thirteen types of water channel proteins, aquaporins (AQPs), which play various essential roles in human physiology, AQP4 is richly expressed in cells of the central nervous system and implicated in pathological conditions such as brain edema. Therefore, researchers have been looking for ways to inhibit AQP4's water-conducting function. Many small molecules have been investigated for their interactions with the residues that form the AQP4 channel entry vestibule on the extracellular side and their interruption of waters entering into the conducting pore. Conducting all-atom simulations on the basis of CHARMM 36 force field, we study one such inhibitor, 5-acetamido-1,3,4-thiadiazole-2-sulfonamide (AZM), to achieve quantitative agreement between the computed and the experimentally measured values of AZM-AQP4 binding affinity. Using the same method, we examine the possibility of plugging up the AQP4 channel around the Asn-Pro-Ala motifs located near the channel center because a small molecule bound there would totally occlude water conduction through AQP4. We compute the binding affinities of 1,2-ethanediol (EDO) and 1,3-propanediol (PDO) inside the AQP4 conducting pore and identify the specificities of the interactions. The EDO-AQP4 interaction is weak with a dissociation constant of 80 mM. The PDO-AQP4 interaction is rather strong with a dissociation constant of 328 μM, which indicates that PDO is an efficacious AQP4 inhibitor with sufficiently high potency. Considering the fact that PDO is classified by the US Food and Drug Administration as generally safe, we predict that 1,3-propanediol could be an effective drug for brain edema and other AQP4-correlated neurological conditions.
Collapse
Affiliation(s)
- Lili Yu
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas 78249, USA
| | - Oscar D Villarreal
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas 78249, USA
| | - L Laurie Chen
- Medical School, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Liao Y Chen
- Department of Physics, University of Texas at San Antonio, San Antonio, Texas 78249, USA
| |
Collapse
|
17
|
H95 Is a pH-Dependent Gate in Aquaporin 4. Structure 2015; 23:2309-2318. [PMID: 26585511 DOI: 10.1016/j.str.2015.08.020] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Revised: 07/17/2015] [Accepted: 08/19/2015] [Indexed: 11/21/2022]
Abstract
Aquaporin 4 (AQP4) is a transmembrane protein from the aquaporin family and is the predominant water channel in the mammalian brain. The regulation of permeability of this protein could be of potential therapeutic use to treat various forms of damage to the nervous tissue. In this work, based on data obtained from in silico and in vitro studies, a pH sensitivity that regulates the osmotic water permeability of AQP4 is demonstrated. The results indicate that AQP4 has increased water permeability at conditions of low pH in atomistic computer simulations and experiments carried out on Xenopus oocytes expressing AQP4. With molecular dynamics simulations, this effect was traced to a histidine residue (H95) located in the cytoplasmic lumen of AQP4. A mutant form of AQP4, in which H95 was replaced with an alanine (H95A), loses sensitivity to cytoplasmic pH changes in in vitro osmotic water permeability, thereby substantiating the in silico work.
Collapse
|
18
|
He ZP, Lu H. Aquaporin-4 gene silencing protects injured neurons after early cerebral infarction. Neural Regen Res 2015; 10:1082-7. [PMID: 26330830 PMCID: PMC4541238 DOI: 10.4103/1673-5374.160099] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2015] [Indexed: 02/04/2023] Open
Abstract
Aquaporin-4 regulates water molecule channels and is important in tissue regulation and water transportation in the brain. Upregulation of aquaporin-4 expression is closely related to cellular edema after early cerebral infarction. Cellular edema and aquaporin-4 expression can be determined by measuring cerebral infarct area and apparent diffusion coefficient using diffusion-weighted imaging (DWI). We examined the effects of silencing aquaporin-4 on cerebral infarction. Rat models of cerebral infarction were established by occlusion of the right middle cerebral artery and siRNA-aquaporin-4 was immediately injected via the right basal ganglia. In control animals, the area of high signal intensity and relative apparent diffusion coefficient value on T2-weighted imaging (T2WI) and DWI gradually increased within 0.5-6 hours after cerebral infarction. After aquaporin-4 gene silencing, the area of high signal intensity on T2WI and DWI reduced, relative apparent diffusion coefficient value was increased, and cellular edema was obviously alleviated. At 6 hours after cerebral infarction, the apparent diffusion coefficient value was similar between treatment and model groups, but angioedema was still obvious in the treatment group. These results indicate that aquaporin-4 gene silencing can effectively relieve cellular edema after early cerebral infarction; and when conducted accurately and on time, the diffusion coefficient value and the area of high signal intensity on T2WI and DWI can reflect therapeutic effects of aquaporin-4 gene silencing on cellular edema.
Collapse
Affiliation(s)
- Zhan-ping He
- Department of Radiology, Affiliated Haikou Hospital of Xiangya School of Medicine, Central South University (Department of Radiology, Haikou Municipal People's Hospital), Haikou, Hainan Province, China
| | - Hong Lu
- Department of Radiology, Affiliated Haikou Hospital of Xiangya School of Medicine, Central South University (Department of Radiology, Haikou Municipal People's Hospital), Haikou, Hainan Province, China
| |
Collapse
|
19
|
Kitchen P, Day RE, Taylor LHJ, Salman MM, Bill RM, Conner MT, Conner AC. Identification and Molecular Mechanisms of the Rapid Tonicity-induced Relocalization of the Aquaporin 4 Channel. J Biol Chem 2015; 290:16873-81. [PMID: 26013827 PMCID: PMC4505433 DOI: 10.1074/jbc.m115.646034] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Indexed: 11/06/2022] Open
Abstract
The aquaporin family of integral membrane proteins is composed of channels that mediate cellular water flow. Aquaporin 4 (AQP4) is highly expressed in the glial cells of the central nervous system and facilitates the osmotically driven pathological brain swelling associated with stroke and traumatic brain injury. Here we show that AQP4 cell surface expression can be rapidly and reversibly regulated in response to changes of tonicity in primary cortical rat astrocytes and in transfected HEK293 cells. The translocation mechanism involves PKA activation, influx of extracellular calcium, and activation of calmodulin. We identify five putative PKA phosphorylation sites and use site-directed mutagenesis to show that only phosphorylation at one of these sites, serine 276, is necessary for the translocation response. We discuss our findings in the context of the identification of new therapeutic approaches to treating brain edema.
Collapse
Affiliation(s)
- Philip Kitchen
- From the Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL
| | - Rebecca E Day
- the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB
| | - Luke H J Taylor
- From the Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL
| | - Mootaz M Salman
- the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB
| | - Roslyn M Bill
- the School of Life & Health Sciences and Aston Research Centre for Healthy Ageing, Aston University, Aston Triangle, Birmingham B4 7ET, and
| | - Matthew T Conner
- the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB,
| | - Alex C Conner
- the School of Clinical and Experimental Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| |
Collapse
|
20
|
Assentoft M, Larsen BR, MacAulay N. Regulation and Function of AQP4 in the Central Nervous System. Neurochem Res 2015; 40:2615-27. [PMID: 25630715 DOI: 10.1007/s11064-015-1519-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 01/08/2015] [Accepted: 01/12/2015] [Indexed: 01/09/2023]
Abstract
Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain-blood interface. Based on studies on AQP4(-/-) mice, AQP4 has been assigned physiological roles in stimulus-induced K(+) clearance, paravascular fluid flow, and brain edema formation. Conflicting data have been presented on the role of AQP4 in K(+) clearance and associated extracellular space shrinkage and on the stroke-induced alterations of AQP4 expression levels during edema formation, raising questions about the functional importance of AQP4 in these (patho)physiological aspects. Phosphorylation-dependent gating of AQP4 has been proposed as a regulatory mechanism for AQP4-mediated osmotic water transport. This paradigm was, however, recently challenged by experimental evidence and molecular dynamics simulations. Regulatory patterns and physiological roles for AQP4 thus remain to be fully explored.
Collapse
Affiliation(s)
- Mette Assentoft
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, Bldg. 12.6, 2200, Copenhagen, Denmark
| | - Brian Roland Larsen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, Bldg. 12.6, 2200, Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, Bldg. 12.6, 2200, Copenhagen, Denmark.
| |
Collapse
|