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Houser A, Baconguis I. Structural Insights into Subunit-Dependent Functional Regulation in Epithelial Sodium Channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.28.595834. [PMID: 38853903 PMCID: PMC11160588 DOI: 10.1101/2024.05.28.595834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
Epithelial sodium channels (ENaC) play a crucial role in Na + reabsorption in mammals. To date, four subunits have been identified-α, β, γ, and δ-believed to form different heteromeric complexes. Currently, only the structure of the αβγ complex is known. To understand how these channels form with varying subunit compositions and define the contribution of each subunit to distinct properties, we co-expressed human δ, β, and γ. Using single-particle cryo-electron microscopy, we observed three distinct ENaC complexes. The structures unveil a pattern in which β and γ positions are conserved among the different complexes while the α position in αβγ trimer is occupied by either δ or another β. The presence of δ induces structural rearrangements in the γ subunit explaining the differences in channel activity observed between αβγ and δβγ channels. These structures define the mechanism by which ENaC subunit composition tunes ENaC function.
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Kashlan OB, Wang XP, Sheng S, Kleyman TR. Epithelial Na + Channels Function as Extracellular Sensors. Compr Physiol 2024; 14:1-41. [PMID: 39109974 PMCID: PMC11309579 DOI: 10.1002/cphy.c230015] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2024]
Abstract
The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.
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Affiliation(s)
- Ossama B. Kashlan
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Computational and Systems Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
| | - Xue-Ping Wang
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaohu Sheng
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R. Kleyman
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh,
Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
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3
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Lysikova DV, Vasileva VY, Chubinskiy-Nadezhdin VI, Morachevskaya EA, Sudarikova AV. Capsazepine activates amiloride-insensitive ENaC-like channels in human leukemia cells. Biochem Biophys Res Commun 2023; 687:149187. [PMID: 37944472 DOI: 10.1016/j.bbrc.2023.149187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Revised: 10/27/2023] [Accepted: 10/30/2023] [Indexed: 11/12/2023]
Abstract
Sodium influx carried out by ion channels is one of the main regulators of water-salt and volume balance in cells of blood origin. Previously, we described amiloride-insensitive ENaC-like channels in human myeloid leukemia K562 cells; the intracellular regulatory mechanisms of the channels are associated with actin cytoskeleton dynamics. Recently, an extracellular mechanism of ENaC-like channels activation in K562 cells by the action of serine protease trypsin has been revealed. The other extracellular pathways that modulate ENaC (epithelial Na+ channel) activity and sodium permeability in transformed blood cells are not yet fully investigated. Here, we study the action of capsazepine (CPZ), as δ-ENaC activator, on single channel activity in K562 cells in whole-cell patch clamp experiments. Addition of CPZ (2 μM) to the extracellular solution caused an activation of sodium channels with typical features; unitary conductance was 15.1 ± 0.8 pS. Amiloride derivative benzamil (50 μM) did not inhibit their activity. Unitary currents and conductance of CPZ-activated channels were higher in Na+-containing extracellular solution than in Li+, that is one of the main fingerprints of δ-ENaC. The results of RT-PCR analysis and immunofluorescence staining also confirmed the expression of δ-hENaC (as well as α-, β-, γ-ENaC) at the mRNA and protein level. These findings allow us to speculate that CPZ activates amiloride-insensitive ENaC-like channels that contain δ-ENaC in К562 cells. Our data reveal a novel extracellular mechanism for ENaC-like activation in human leukemia cells.
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Affiliation(s)
- Daria V Lysikova
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | - Valeria Y Vasileva
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | | | - Elena A Morachevskaya
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | - Anastasia V Sudarikova
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia.
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4
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Oz M, Lorke DE, Howarth FC. Transient receptor potential vanilloid 1 (TRPV1)-independent actions of capsaicin on cellular excitability and ion transport. Med Res Rev 2023. [PMID: 36916676 DOI: 10.1002/med.21945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 01/17/2023] [Accepted: 02/26/2023] [Indexed: 03/15/2023]
Abstract
Capsaicin is a naturally occurring alkaloid derived from chili pepper that is responsible for its hot pungent taste. Capsaicin is known to exert multiple pharmacological actions, including analgesia, anticancer, anti-inflammatory, antiobesity, and antioxidant effects. The transient receptor potential vanilloid subfamily member 1 (TRPV1) is the main receptor mediating the majority of the capsaicin effects. However, numerous studies suggest that the TRPV1 receptor is not the only target for capsaicin. An increasing number of studies indicates that capsaicin, at low to mid µM ranges, not only indirectly through TRPV1-mediated Ca2+ increases, but also directly modulates the functions of voltage-gated Na+ , K+ , and Ca2+ channels, as well as ligand-gated ion channels and other ion transporters and enzymes involved in cellular excitability. These TRPV1-independent effects are mediated by alterations of the biophysical properties of the lipid membrane and subsequent modulation of the functional properties of ion channels and by direct binding of capsaicin to the channels. The present study, for the first time, systematically categorizes this diverse range of non-TRPV1 targets and discusses cellular and molecular mechanisms mediating TRPV1-independent effects of capsaicin in excitable, as well as nonexcitable cells.
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Affiliation(s)
- Murat Oz
- Department of Pharmacology and Therapeutics, Faculty of Pharmacy, Kuwait University, Safat, Kuwait
| | - Dietrich E Lorke
- Department of Anatomy and Cellular Biology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates.,Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Frank C Howarth
- Department of Physiology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates
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Gettings SM, Maxeiner S, Tzika M, Cobain MRD, Ruf I, Benseler F, Brose N, Krasteva-Christ G, Vande Velde G, Schönberger M, Althaus M. Two functional epithelial sodium channel isoforms are present in rodents despite pronounced evolutionary pseudogenisation and exon fusion. Mol Biol Evol 2021; 38:5704-5725. [PMID: 34491346 PMCID: PMC8662647 DOI: 10.1093/molbev/msab271] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The epithelial sodium channel (ENaC) plays a key role in salt and water homeostasis in
tetrapod vertebrates. There are four ENaC subunits (α, β, γ, δ), forming heterotrimeric
αβγ- or δβγ-ENaCs. Although the physiology of αβγ-ENaC is well understood, for decades the
field has stalled with respect to δβγ-ENaC due to the lack of mammalian model organisms.
The SCNN1D gene coding for δ-ENaC was previously believed to be absent in
rodents, hindering studies using standard laboratory animals. We analyzed all currently
available rodent genomes and discovered that SCNN1D is present in rodents
but was independently lost in five rodent lineages, including the Muridae (mice and rats).
The independent loss of SCNN1D in rodent lineages may be constrained by
phylogeny and taxon-specific adaptation to dry habitats, however habitat aridity does not
provide a selection pressure for maintenance of SCNN1D across Rodentia. A
fusion of two exons coding for a structurally flexible region in the extracellular domain
of δ-ENaC appeared in the Hystricognathi (a group that includes guinea pigs). This
conserved pattern evolved at least 41 Ma and represents a new autapomorphic feature for
this clade. Exon fusion does not impair functionality of guinea pig (Cavia
porcellus) δβγ-ENaC expressed in Xenopus oocytes.
Electrophysiological characterization at the whole-cell and single-channel level revealed
conserved biophysical features and mechanisms controlling guinea pig αβγ- and δβγ-ENaC
function as compared with human orthologs. Guinea pigs therefore represent commercially
available mammalian model animals that will help shed light on the physiological function
of δ-ENaC.
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Affiliation(s)
- Sean M Gettings
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.,Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Stephan Maxeiner
- Institute for Anatomy and Cell Biology, Saarland University School of Medicine, Homburg, Germany
| | - Maria Tzika
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Matthew R D Cobain
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Irina Ruf
- Division of Messel Research and Mammalogy, Senckenberg Research Institute and Natural History Museum Frankfurt, Frankfurt am Main, Germany
| | - Fritz Benseler
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Gabriela Krasteva-Christ
- Institute for Anatomy and Cell Biology, Saarland University School of Medicine, Homburg, Germany
| | - Greetje Vande Velde
- Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Matthias Schönberger
- Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Mike Althaus
- Institute for Functional Gene Analytics, Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, Rheinbach, Germany
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Abstract
The Epithelial Na+ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na+ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.
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Affiliation(s)
- Daniela Rotin
- The Hospital for Sick Children, and The University of Toronto, Toronto, Canada
| | - Olivier Staub
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
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Mukherjee A, MacDonald KD, Kim J, Henderson MI, Eygeris Y, Sahay G. Engineered mutant α-ENaC subunit mRNA delivered by lipid nanoparticles reduces amiloride currents in cystic fibrosis-based cell and mice models. SCIENCE ADVANCES 2020; 6:6/47/eabc5911. [PMID: 33208364 PMCID: PMC7673816 DOI: 10.1126/sciadv.abc5911] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 10/05/2020] [Indexed: 05/02/2023]
Abstract
Cystic fibrosis (CF) results from mutations in the chloride-conducting CF transmembrane conductance regulator (CFTR) gene. Airway dehydration and impaired mucociliary clearance in CF is proposed to result in tonic epithelial sodium channel (ENaC) activity, which drives amiloride-sensitive electrogenic sodium absorption. Decreasing sodium absorption by inhibiting ENaC can reverse airway surface liquid dehydration. Here, we inhibit endogenous heterotrimeric ENaC channels by introducing inactivating mutant ENaC α mRNA (αmutENaC). Lipid nanoparticles carrying αmutENaC were transfected in CF-based airway cells in vitro and in vivo. We observed a significant decrease in macroscopic as well as amiloride-sensitive ENaC currents and an increase in airway surface liquid height in CF airway cells. Similarly, intranasal transfection of αmutENaC mRNA decreased amiloride-sensitive nasal potential difference in CFTRKO mice. These data suggest that mRNA-based ENaC inhibition is a powerful strategy for reducing mucus dehydration and has therapeutic potential for treating CF in all patients, independent of genotype.
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Affiliation(s)
- Anindit Mukherjee
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Kelvin D MacDonald
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
- Department of Pediatrics, School of Medicine, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jeonghwan Kim
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Michael I Henderson
- Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, OR 97201, USA
| | - Yulia Eygeris
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Gaurav Sahay
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA.
- Department of Biomedical Engineering, Robertson Life Sciences Building, Oregon Health & Science University, Portland, OR 97239, USA
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Zhao R, Ali G, Chang J, Komatsu S, Tsukasaki Y, Nie HG, Chang Y, Zhang M, Liu Y, Jain K, Jung BG, Samten B, Jiang D, Liang J, Ikebe M, Matthay MA, Ji HL. Proliferative regulation of alveolar epithelial type 2 progenitor cells by human Scnn1d gene. Am J Cancer Res 2019; 9:8155-8170. [PMID: 31754387 PMCID: PMC6857051 DOI: 10.7150/thno.37023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 09/16/2019] [Indexed: 01/03/2023] Open
Abstract
Lung epithelial sodium channel (ENaC) encoded by Scnn1 genes is essential for maintaining transepithelial salt and fluid homeostasis in the airway and the lung. Compared to α, β, and γ subunits, the role of respiratory δ-ENaC has not been studied in vivo due to the lack of animal models. Methods: We characterized full-length human δ802-ENaC expressed in both Xenopus oocytes and humanized transgenic mice. AT2 proliferation and differentiation in 3D organoids were analysed with FACS and a confocal microscope. Both two-electrode voltage clamp and Ussing chamber systems were applied to digitize δ802-ENaC channel activity. Immunoblotting was utilized to analyse δ802-ENaC protein. Transcripts of individual ENaC subunits in human lung tissues were quantitated with qPCR. Results: The results indicate that δ802-ENaC functions as an amiloride-inhibitable Na+ channel. Inhibitory peptide α-13 distinguishes δ802- from α-type ENaC channels. Modified proteolysis of γ-ENaC by plasmin and aprotinin did not alter the inhibition of amiloride and α-13 peptide. Expression of δ802-ENaC at the apical membrane of respiratory epithelium was detected with biophysical features similar to those of heterologously expressed channels in oocytes. δ802-ENaC regulated alveologenesis through facilitating the proliferation of alveolar type 2 epithelial cells. Conclusion: The humanized mouse line conditionally expressing human δ802-ENaC is a novel model for studying the expression and function of this protein in vivo .
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Downs CA, Johnson NM, Coca C, Helms MN. Angiotensin II regulates δ-ENaC in human umbilical vein endothelial cells. Microvasc Res 2018; 116:26-33. [DOI: 10.1016/j.mvr.2017.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 09/19/2017] [Accepted: 10/15/2017] [Indexed: 11/24/2022]
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Agrawal PB, Wang R, Li HL, Schmitz-Abe K, Simone-Roach C, Chen J, Shi J, Louie T, Sheng S, Towne MC, Brainson CF, Matthay MA, Kim CF, Bamshad M, Emond MJ, Gerard NP, Kleyman TR, Gerard C. The Epithelial Sodium Channel Is a Modifier of the Long-Term Nonprogressive Phenotype Associated with F508del CFTR Mutations. Am J Respir Cell Mol Biol 2017; 57:711-720. [PMID: 28708422 PMCID: PMC5765421 DOI: 10.1165/rcmb.2017-0166oc] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Accepted: 07/05/2017] [Indexed: 12/11/2022] Open
Abstract
Cystic fibrosis (CF) remains the most lethal genetic disease in the Caucasian population. However, there is great variability in clinical phenotypes and survival times, even among patients harboring the same genotype. We identified five patients with CF and a homozygous F508del mutation in the CFTR gene who were in their fifth or sixth decade of life and had shown minimal changes in lung function over a longitudinal period of more than 20 years. Because of the rarity of this long-term nonprogressive phenotype, we hypothesized these individuals may carry rare genetic variants in modifier genes that ameliorate disease severity. Individuals at the extremes of survival time and lung-function trajectory underwent whole-exome sequencing, and the sequencing data were filtered to include rare missense, stopgain, indel, and splicing variants present with a mean allele frequency of <0.2% in general population databases. Epithelial sodium channel (ENaC) mutants were generated via site-directed mutagenesis and expressed for Xenopus oocyte assays. Four of the five individuals carried extremely rare or never reported variants in the SCNN1D and SCNN1B genes of the ENaC. Separately, an independently enriched rare variant in SCNN1D was identified in the Exome Variant Server database associated with a milder pulmonary disease phenotype. Functional analysis using Xenopus oocytes revealed that two of the three variants in δ-ENaC encoded by SCNN1D exhibited hypomorphic channel activity. Our data suggest a potential role for δ-ENaC in controlling sodium reabsorption in the airways, and advance the plausibility of ENaC as a therapeutic target in CF.
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Affiliation(s)
- Pankaj B. Agrawal
- Divisions of Newborn Medicine
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | - Hongmei Lisa Li
- Stem Cell Program, Division of Hematology/Oncology, Boston Children’s Hospital, Boston, Massachusetts
- Harvard Stem Cell Institute, Cambridge, Massachusetts
- Department of Genetics, and
| | - Klaus Schmitz-Abe
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | | | - Jiahai Shi
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong SAR
| | - Tin Louie
- Biostatistics and Center for Biomedical Statistics
| | | | - Meghan C. Towne
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | - Michael A. Matthay
- Departments of Medicine and
- Anesthesia, Cardiovascular Research Institute, University of California–San Francisco, San Francisco, California
| | - Carla F. Kim
- Pulmonary and Respiratory Diseases, and
- Stem Cell Program, Division of Hematology/Oncology, Boston Children’s Hospital, Boston, Massachusetts
- Harvard Stem Cell Institute, Cambridge, Massachusetts
- Department of Genetics, and
| | - Michael Bamshad
- Pediatrics and Genome Sciences, University of Washington, Seattle, Washington
| | | | - Norma P. Gerard
- Pulmonary and Respiratory Diseases, and
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
| | - Thomas R. Kleyman
- Departments of Medicine
- Cell Biology, and Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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Londino JD, Lazrak A, Collawn JF, Bebok Z, Harrod KS, Matalon S. Influenza virus infection alters ion channel function of airway and alveolar cells: mechanisms and physiological sequelae. Am J Physiol Lung Cell Mol Physiol 2017; 313:L845-L858. [PMID: 28775098 DOI: 10.1152/ajplung.00244.2017] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Revised: 07/25/2017] [Accepted: 07/27/2017] [Indexed: 02/07/2023] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) and the amiloride-sensitive epithelial sodium channels (ENaC) are located in the apical membranes of airway and alveolar epithelial cells. These transporters play an important role in the regulation of lung fluid balance across airway and alveolar epithelia by being the conduits for chloride (Cl-) and bicarbonate ([Formula: see text]) secretion and sodium (Na+) ion absorption, respectively. The functional role of these channels in the respiratory tract is to maintain the optimum volume and ionic composition of the bronchial periciliary fluid (PCL) and alveolar lining fluid (ALF) layers. The PCL is required for proper mucociliary clearance of pathogens and debris, and the ALF is necessary for surfactant homeostasis and optimum gas exchange. Dysregulation of ion transport may lead to mucus accumulation, bacterial infections, inflammation, pulmonary edema, and compromised respiratory function. Influenza (or flu) in mammals is caused by influenza A and B viruses. Symptoms include dry cough, sore throat, and is often followed by secondary bacterial infections, accumulation of fluid in the alveolar spaces and acute lung injury. The underlying mechanisms of flu symptoms are not fully understood. This review summarizes our present knowledge of how influenza virus infections alter airway and alveolar epithelial cell CFTR and ENaC function in vivo and in vitro and the role of these changes in influenza pathogenesis.
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Affiliation(s)
- James David Londino
- Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Ahmed Lazrak
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - James F Collawn
- Department of Cell, Developmental and Integrative Biology School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Zsuzsanna Bebok
- Department of Cell, Developmental and Integrative Biology School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Kevin S Harrod
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Sadis Matalon
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
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Rauh R, Hoerner C, Korbmacher C. δβγ-ENaC is inhibited by CFTR but stimulated by cAMP in Xenopus laevis oocytes. Am J Physiol Lung Cell Mol Physiol 2016; 312:L277-L287. [PMID: 27941075 DOI: 10.1152/ajplung.00375.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 12/05/2016] [Accepted: 12/05/2016] [Indexed: 11/22/2022] Open
Abstract
The epithelial sodium channel (ENaC) and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel critically regulate airway surface liquid by driving fluid absorption and secretion, respectively. Their functional interplay is complex and incompletely understood. ENaC is a heteromeric channel with three well-characterized subunits (α, β, and γ). In humans, an additional δ-ENaC subunit exists in lung and several other tissues, where it may replace the α-subunit to form δβγ-ENaC. Little is known about the physiological role of δβγ-ENaC and its possible interaction with CFTR. The aim of the present study was to investigate the effect of human CFTR on human δβγ-ENaC heterologously expressed in Xenopus laevis oocytes. In oocytes coexpressing δβγ-ENaC and CFTR the ENaC-mediated amiloride-sensitive whole cell current (ΔIami) was reduced by ~50% compared with that measured in oocytes expressing δβγ-ENaC alone. Moreover, basal level of proteolytic ENaC activation was reduced in the presence of CFTR. The inhibitory effect of CFTR on δβγ-ENaC was due to a combination of decreased average open probability (Po) and reduced channel expression at the cell surface. Interestingly, in oocytes expressing δβγ-ENaC, increasing intracellular [cAMP] by IBMX and forskolin increased ΔIami by ~50%. This stimulatory effect was not observed for human and rat αβγ-ENaC and was independent of CFTR coexpression and coactivation. Experiments with a mutant channel (δβS520Cγ-ENaC) which can be converted to a channel with a Po of nearly 1 suggested that cAMP activates δβγ-ENaC by increasing Po In conclusion, our results demonstrate that δβγ-ENaC is inhibited by CFTR but activated by cAMP.
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Affiliation(s)
- Robert Rauh
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christian Hoerner
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
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13
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Hanukoglu I. ASIC and ENaC type sodium channels: conformational states and the structures of the ion selectivity filters. FEBS J 2016; 284:525-545. [DOI: 10.1111/febs.13840] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 08/04/2016] [Accepted: 08/26/2016] [Indexed: 12/18/2022]
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Liu Y, Jiang BJ, Zhao RZ, Ji HL. Epithelial Sodium Channels in Pulmonary Epithelial Progenitor and Stem Cells. Int J Biol Sci 2016; 12:1150-4. [PMID: 27570489 PMCID: PMC4997059 DOI: 10.7150/ijbs.15747] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 07/11/2016] [Indexed: 11/05/2022] Open
Abstract
Regeneration of the epithelium of mammalian lungs is essential for restoring normal function following injury, and various cells and mechanisms contribute to this regeneration and repair. Club cells, bronchioalveolar stem cells (BASCs), and alveolar type II epithelial cells (ATII) are dominant stem/progenitor cells for maintaining epithelial turnover and repair. Epithelial Na(+) channels (ENaC), a critical pathway for transapical salt and fluid transport, are expressed in lung epithelial progenitors, including club and ATII cells. Since ENaC activity and expression are development- and differentiation-dependent, apically located ENaC activity has therefore been used as a functional biomarker of lung injury repair. ENaC activity may be involved in the migration and differentiation of local and circulating stem/progenitor cells with diverse functions, eventually benefiting stem cells spreading to re-epithelialize injured lungs. This review summarizes the potential roles of ENaC expressed in native progenitor and stem cells in the development and regeneration of the respiratory epithelium.
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Affiliation(s)
- Yang Liu
- Institute of Lung and Molecular Therapy, Xinxiang Medical University, Xinxiang, Henan 453003, China
| | - Bi-Jie Jiang
- School of Public Health, Xinxiang Medical University, Xinxiang, Henan 453003, China
| | - Run-Zhen Zhao
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
- Texas Lung Injury Institute, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
- Texas Lung Injury Institute, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
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Ji HL, Nie HG, Chang Y, Lian Q, Liu SL. CPT-cGMP Is A New Ligand of Epithelial Sodium Channels. Int J Biol Sci 2016; 12:359-66. [PMID: 27019621 PMCID: PMC4807156 DOI: 10.7150/ijbs.13764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Accepted: 11/11/2015] [Indexed: 12/28/2022] Open
Abstract
Epithelial sodium channels (ENaC) are localized at the apical membrane of the epithelium, and are responsible for salt and fluid reabsorption. Renal ENaC takes up salt, thereby controlling salt content in serum. Loss-of-function ENaC mutations lead to low blood pressure due to salt-wasting, while gain-of-function mutations cause impaired sodium excretion and subsequent hypertension as well as hypokalemia. ENaC activity is regulated by intracellular and extracellular signals, including hormones, neurotransmitters, protein kinases, and small compounds. Cyclic nucleotides are broadly involved in stimulating protein kinase A and protein kinase G signaling pathways, and, surprisingly, also appear to have a role in regulating ENaC. Increasing evidence suggests that the cGMP analog, CPT-cGMP, activates αβγ-ENaC activity reversibly through an extracellular pathway in a dose-dependent manner. Furthermore, the parachlorophenylthio moiety and ribose 2'-hydroxy group of CPT-cGMP are essential for facilitating the opening of ENaC channels by this compound. Serving as an extracellular ligand, CPT-cGMP eliminates sodium self-inhibition, which is a novel mechanism for stimulating salt reabsorption in parallel to the traditional NO/cGMP/PKG signal pathway. In conclusion, ENaC may be a druggable target for CPT-cGMP, leading to treatments for kidney malfunctions in salt reabsorption.
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Affiliation(s)
- Hong-Long Ji
- 1. Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Hong-Guang Nie
- 2. Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110001, China
| | - Yongchang Chang
- 3. Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, Arizona, 85013, USA
| | - Qizhou Lian
- 4. Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Shan-Lu Liu
- 5. Department of Molecular Microbiology and Immunology, Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
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Matalon S, Bartoszewski R, Collawn JF. Role of epithelial sodium channels in the regulation of lung fluid homeostasis. Am J Physiol Lung Cell Mol Physiol 2015; 309:L1229-38. [PMID: 26432872 DOI: 10.1152/ajplung.00319.2015] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 09/25/2015] [Indexed: 01/11/2023] Open
Abstract
In utero, fetal lung epithelial cells actively secrete Cl(-) ions into the lung air spaces while Na(+) ions follow passively to maintain electroneutrality. This process, driven by an electrochemical gradient generated by the Na(+)-K(+)-ATPase, is responsible for the secretion of fetal fluid that is essential for normal lung development. Shortly before birth, a significant upregulation of amiloride-sensitive epithelial channels (ENaCs) on the apical side of the lung epithelial cells results in upregulation of active Na(+) transport. This process is critical for the reabsorption of fetal lung fluid and the establishment of optimum gas exchange. In the adult lung, active Na(+) reabsorption across distal lung epithelial cells limits the degree of alveolar edema in patients with acute lung injury and cardiogenic edema. Cl(-) ions are transported either paracellularly or transcellularly to preserve electroneutrality. An increase in Cl(-) secretion across the distal lung epithelium has been reported following an acute increase in left atrial pressure and may result in pulmonary edema. In contrast, airway epithelial cells secrete Cl(-) through apical cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels and absorb Na(+). Thus the coordinated action of Cl(-) secretion and Na(+) absorption is essential for maintenance of the volume of epithelial lining fluid that, in turn, maximizes mucociliary clearance and facilitates clearance of bacteria and debris from the lungs. Any factor that interferes with Na(+) or Cl(-) transport or dramatically upregulates ENaC activity in airway epithelial cells has been associated with lung diseases such as cystic fibrosis or chronic obstructive lung disease. In this review we focus on the role of the ENaC, the mechanisms involved in ENaC regulation, and how ENaC dysregulation can lead to lung pathology.
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Affiliation(s)
- Sadis Matalon
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Department of Cell, Developmental, and Integrative Biology, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Pulmonary Injury and Repair Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Gregory Fleming James Cystic Fibrosis Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Rafal Bartoszewski
- Department of Biology and Pharmaceutical Botany, Medical University of Gdansk, Gdansk, Poland
| | - James F Collawn
- Department of Cell, Developmental, and Integrative Biology, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Pulmonary Injury and Repair Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Gregory Fleming James Cystic Fibrosis Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
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Downs CA, Kreiner LH, Johnson NM, Brown LA, Helms MN. Receptor for advanced glycation end-products regulates lung fluid balance via protein kinase C-gp91(phox) signaling to epithelial sodium channels. Am J Respir Cell Mol Biol 2015; 52:75-87. [PMID: 24978055 DOI: 10.1165/rcmb.2014-0002oc] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The receptor for advanced glycation end-products (RAGE), a multiligand member of the Ig family, may play a crucial role in the regulation of lung fluid balance. We quantified soluble RAGE (sRAGE), a decoy isoform, and advanced glycation end-products (AGEs) from the bronchoalveolar lavage fluid of smokers and nonsmokers, and tested the hypothesis that AGEs regulate lung fluid balance through protein kinase C (PKC)-gp91(phox) signaling to the epithelial sodium channel (ENaC). Human bronchoalveolar lavage samples from smokers showed increased AGEs (9.02 ± 3.03 μg versus 2.48 ± 0.53 μg), lower sRAGE (1,205 ± 292 pg/ml versus 1,910 ± 263 pg/ml), and lower volume(s) of epithelial lining fluid (97 ± 14 ml versus 133 ± 17 ml). sRAGE levels did not predict ELF volumes in nonsmokers; however, in smokers, higher volumes of ELF were predicted with higher levels of sRAGE. Single-channel patch clamp analysis of rat alveolar epithelial type 1 cells showed that AGEs increased ENaC activity measured as the product of the number of channels (N) and the open probability (Po) (NPo) from 0.19 ± 0.08 to 0.83 ± 0.22 (P = 0.017) and the subsequent addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.15 ± 0.07 (P = 0.01). In type 2 cells, human AGEs increased ENaC NPo from 0.12 ± 0.05 to 0.53 ± 0.16 (P = 0.025) and the addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.10 ± 0.03 (P = 0.013). Using molecular and biochemical techniques, we observed that inhibition of RAGE and PKC activity attenuated AGE-induced activation of ENaC. AGEs induced phosphorylation of p47(phox) and increased gp91(phox)-dependent reactive oxygen species production, a response that was abrogated with RAGE or PKC inhibition. Finally, tracheal instillation of AGEs promoted clearance of lung fluid, whereas concomitant inhibition of RAGE, PKC, and gp91(phox) abrogated the response.
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Schwagerus E, Sladek S, Buckley ST, Armas-Capote N, de la Rosa DA, Harvey BJ, Fischer H, Illek B, Huwer H, Schneider-Daum N, Lehr CM, Ehrhardt C. Expression and function of the epithelial sodium channel δ-subunit in human respiratory epithelial cells in vitro. Pflugers Arch 2015; 467:2257-73. [DOI: 10.1007/s00424-015-1693-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/02/2015] [Accepted: 02/03/2015] [Indexed: 11/24/2022]
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Chen Z, Zhao R, Zhao M, Liang X, Bhattarai D, Dhiman R, Shetty S, Idell S, Ji HL. Regulation of epithelial sodium channels in urokinase plasminogen activator deficiency. Am J Physiol Lung Cell Mol Physiol 2014; 307:L609-17. [PMID: 25172911 DOI: 10.1152/ajplung.00126.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaC) govern transepithelial salt and fluid homeostasis. ENaC contributes to polarization, apoptosis, epithelial-mesenchymal transformation, etc. Fibrinolytic proteases play a crucial role in virtually all of these processes and are elaborated by the airway epithelium. We hypothesized that urokinase-like plasminogen activator (uPA) regulates ENaC function in airway epithelial cells and tested that possibility in primary murine tracheal epithelial cells (MTE). Both basal and cAMP-activated Na(+) flow through ENaC were significantly reduced in monolayers of uPA-deficient cells. The reduction in ENaC activity was further confirmed in basolateral membrane-permeabilized cells. A decrease in the Na(+)-K(+)-ATPase activity in the basolateral membrane could contribute to the attenuation of ENaC function in intact monolayer cells. Dysfunctional fluid resolution was seen in uPA-disrupted cells. Administration of uPA and plasmin partially restores ENaC activity and fluid reabsorption by MTEs. ERK1/2, but not Akt, phosphorylation was observed in the cells and lungs of uPA-deficient mice. On the other hand, cleavage of γ ENaC is significantly depressed in the lungs of uPA knockout mice vs. those of wild-type controls. Expression of caspase 8, however, did not differ between wild-type and uPA(-/-) mice. In addition, uPA deficiency did not alter transepithelial resistance. Taken together, the mechanisms for the regulation of ENaC by uPA in MTEs include augmentation of Na(+)-K(+)-ATPase, proteolysis, and restriction of ERK1/2 phosphorylation. We demonstrate for the first time that ENaC may serve as a downstream signaling target by which uPA controls the biophysical profiles of airway fluid and epithelial function.
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Affiliation(s)
- Zaixing Chen
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Runzhen Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Meimi Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Xinrong Liang
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Deepa Bhattarai
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Rohan Dhiman
- Department of Pulmonary Immunology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Sreerama Shetty
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Steven Idell
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and Department of Medicine, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and
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Herold S, Gabrielli NM, Vadász I. Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction. Am J Physiol Lung Cell Mol Physiol 2013; 305:L665-81. [PMID: 24039257 DOI: 10.1152/ajplung.00232.2013] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In this review we summarize recent major advances in our understanding on the molecular mechanisms, mediators, and biomarkers of acute lung injury (ALI) and alveolar-capillary barrier dysfunction, highlighting the role of immune cells, inflammatory and noninflammatory signaling events, mechanical noxae, and the affected cellular and molecular entities and functions. Furthermore, we address novel aspects of resolution and repair of ALI, as well as putative candidates for treatment of ALI, including pharmacological and cellular therapeutic means.
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Affiliation(s)
- Susanne Herold
- Dept. of Internal Medicine, Justus Liebig Univ., Universities of Giessen and Marburg Lung Center, Klinikstrasse 33, 35392 Giessen, Germany.
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21
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Abstract
Ion channels perform a variety of cellular functions in lung epithelia. Oxidant- and antioxidant-mediated mechanisms (that is, redox regulation) of ion channels are areas of intense research. Significant progress has been made in our understanding of redox regulation of ion channels since the last Experimental Biology report in 2003. Advancements include: 1) identification of nonphagocytic NADPH oxidases as sources of regulated reactive species (RS) production in epithelia, 2) an understanding that excessive treatment with antioxidants can result in greater oxidative stress, and 3) characterization of novel RS signaling pathways that converge upon ion channel regulation. These advancements, as discussed at the 2013 Experimental Biology Meeting in Boston, MA, impact our understanding of oxidative stress in the lung, and, in particular, illustrate that the redox state has profound effects on ion channel and cellular function.
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Ji HL, Zhao RZ, Chen ZX, Shetty S, Idell S, Matalon S. δ ENaC: a novel divergent amiloride-inhibitable sodium channel. Am J Physiol Lung Cell Mol Physiol 2012; 303:L1013-26. [PMID: 22983350 DOI: 10.1152/ajplung.00206.2012] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The fourth subunit of the epithelial sodium channel, termed delta subunit (δ ENaC), was cloned in human and monkey. Increasing evidence shows that this unique subunit and its splice variants exhibit biophysical and pharmacological properties that are divergent from those of α ENaC channels. The widespread distribution of epithelial sodium channels in both epithelial and nonepithelial tissues implies a range of physiological functions. The altered expression of SCNN1D is associated with numerous pathological conditions. Genetic studies link SCNN1D deficiency with rare genetic diseases with developmental and functional disorders in the brain, heart, and respiratory systems. Here, we review the progress of research on δ ENaC in genomics, biophysics, proteomics, physiology, pharmacology, and clinical medicine.
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Affiliation(s)
- Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
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Giraldez T, Rojas P, Jou J, Flores C, Alvarez de la Rosa D. The epithelial sodium channel δ-subunit: new notes for an old song. Am J Physiol Renal Physiol 2012; 303:F328-38. [PMID: 22573384 DOI: 10.1152/ajprenal.00116.2012] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Amiloride-sensitive epithelial Na(+) channels (ENaCs) can be formed by different combinations of four homologous subunits, named α, β, γ, and δ. In addition to providing an apical entry pathway for transepithelial Na(+) reabsorption in tight epithelia such as the kidney distal tubule and collecting duct, ENaCs are also expressed in nonepithelial cells, where they may play different functional roles. The δ-subunit of ENaC was originally identified in humans and is able to form amiloride-sensitive Na(+) channels alone or in combination with β and γ, generally resembling the canonical kidney ENaC formed by α, β, and γ. However, δ differs from α in its tissue distribution and channel properties. Despite the low sequence conservation between α and δ (37% identity), their similar functional characteristics provide an excellent model for exploring structural correlates of specific ENaC biophysical and pharmacological properties. Moreover, the study of cellular mechanisms modulating the activity of different ENaC subunit combinations provides an opportunity to gain insight into the regulation of the channel. In this review, we examine the evolution of ENaC genes, channel subunit composition, the distinct functional and pharmacological features that δ confers to ENaC, and how this can be exploited to better understand this ion channel. Finally, we briefly consider possible functional roles of the ENaC δ-subunit.
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Affiliation(s)
- Teresa Giraldez
- Research Division, University Hospital N.S. Candelaria, Santa Cruz de Tenerife, Tenerife, Spain
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