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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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Hu M, Bogoyevitch MA, Jans DA. Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies. Physiol Rev 2020; 100:1527-1594. [PMID: 32216549 DOI: 10.1152/physrev.00030.2019] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.
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Affiliation(s)
- MengJie Hu
- Department of Biochemistry and Molecular Biology, University of Melbourne, Melbourne, Victoria, Australia; and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia
| | - Marie A Bogoyevitch
- Department of Biochemistry and Molecular Biology, University of Melbourne, Melbourne, Victoria, Australia; and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia
| | - David A Jans
- Department of Biochemistry and Molecular Biology, University of Melbourne, Melbourne, Victoria, Australia; and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia
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Dey I, Bradbury NA. Physiology of the Gut: Experimental Models for Investigating Intestinal Fluid and Electrolyte Transport. CURRENT TOPICS IN MEMBRANES 2018; 81:337-381. [PMID: 30243437 DOI: 10.1016/bs.ctm.2018.08.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Once thought to be exclusively an absorptive tissue, the intestine is now recognized as an important secretory tissue, playing a key role in body ion and fluid homeostasis. Given the intestine's role in fluid homeostasis, it is not surprising that important clinical pathologies arise from imbalances in fluid absorption and secretion. Perhaps the most important examples of this can be seen in enterotoxigenic secretory diarrheas with extreme fluid secretion, and Cystic Fibrosis with little or no fluid secretion. A mechanistic understanding of the cellular pathways regulating ion and fluid transport has been obtained from a variety of approaches and model systems. These have ranged from the intact intestine to a single intestinal epithelial cell type. Although for many years a reductionist approach has held sway for investigating intestinal transport, the growing realization that physiologic processes should really be examined within a physiological context has seen a marked increase in studies using models that are essentially mini-intestines in a dish. The aim of this chapter is to provide a historical context for our understanding of intestinal ion and fluid transport, and to highlight the model systems that have been used to acquire this knowledge.
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Affiliation(s)
- Isha Dey
- Department of Physiology and Biophysics, Chicago Medical School, North Chicago, IL, United States
| | - Neil A Bradbury
- Department of Physiology and Biophysics, Chicago Medical School, North Chicago, IL, United States
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Woods PS, Doolittle LM, Hickman-Davis JM, Davis IC. ATP catabolism by tissue nonspecific alkaline phosphatase contributes to development of ARDS in influenza-infected mice. Am J Physiol Lung Cell Mol Physiol 2017; 314:L83-L92. [PMID: 28982733 DOI: 10.1152/ajplung.00149.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Influenza A viruses are highly contagious respiratory pathogens that are responsible for significant morbidity and mortality worldwide on an annual basis. We have shown previously that influenza infection of mice leads to increased ATP and adenosine accumulation in the airway lumen. Moreover, we demonstrated that A1-adenosine receptor activation contributes significantly to influenza-induced acute respiratory distress syndrome (ARDS). However, we found that development of ARDS in influenza-infected mice does not require catabolism of ATP to adenosine by ecto-5'-nucleotidase (CD73). Hence, we hypothesized that increased adenosine generation in response to infection is mediated by tissue nonspecific alkaline phosphatase (TNAP), which is a low-affinity, high-capacity enzyme that catabolizes nucleotides in a nonspecific manner. In the current study, we found that whole lung and BALF TNAP expression and alkaline phosphatase enzymatic activity increased as early as 2 days postinfection (dpi) of C57BL/6 mice with 10,000 pfu/mouse of influenza A/WSN/33 (H1N1). Treatment at 2 and 4 dpi with a highly specific quinolinyl-benzenesulfonamide TNAP inhibitor (TNAPi) significantly reduced whole lung alkaline phosphatase activity at 6 dpi but did not alter TNAP gene or protein expression. TNAPi treatment attenuated hypoxemia, lung dysfunction, histopathology, and pulmonary edema at 6 dpi without impacting viral replication or BALF adenosine. Treatment also improved epithelial barrier function and attenuated cellular and humoral immune responses to influenza infection. These data indicate that TNAP inhibition can attenuate influenza-induced ARDS by reducing inflammation and fluid accumulation within the lung. They also further emphasize the importance of adenosine generation for development of ARDS in influenza-infected mice.
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Affiliation(s)
- Parker S Woods
- Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University , Columbus, Ohio
| | - Lauren M Doolittle
- Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University , Columbus, Ohio
| | - Judy M Hickman-Davis
- Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University , Columbus, Ohio
| | - Ian C Davis
- Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University , Columbus, Ohio
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Measurement of ion fluxes across epithelia. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017; 127:1-11. [DOI: 10.1016/j.pbiomolbio.2017.03.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 03/13/2017] [Accepted: 03/18/2017] [Indexed: 12/23/2022]
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Hasan D, Blankman P, Nieman GF. Purinergic signalling links mechanical breath profile and alveolar mechanics with the pro-inflammatory innate immune response causing ventilation-induced lung injury. Purinergic Signal 2017; 13:363-386. [PMID: 28547381 PMCID: PMC5563293 DOI: 10.1007/s11302-017-9564-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 04/26/2017] [Indexed: 02/06/2023] Open
Abstract
Severe pulmonary infection or vigorous cyclic deformation of the alveolar epithelial type I (AT I) cells by mechanical ventilation leads to massive extracellular ATP release. High levels of extracellular ATP saturate the ATP hydrolysis enzymes CD39 and CD73 resulting in persistent high ATP levels despite the conversion to adenosine. Above a certain level, extracellular ATP molecules act as danger-associated molecular patterns (DAMPs) and activate the pro-inflammatory response of the innate immunity through purinergic receptors on the surface of the immune cells. This results in lung tissue inflammation, capillary leakage, interstitial and alveolar oedema and lung injury reducing the production of surfactant by the damaged AT II cells and deactivating the surfactant function by the concomitant extravasated serum proteins through capillary leakage followed by a substantial increase in alveolar surface tension and alveolar collapse. The resulting inhomogeneous ventilation of the lungs is an important mechanism in the development of ventilation-induced lung injury. The high levels of extracellular ATP and the upregulation of ecto-enzymes and soluble enzymes that hydrolyse ATP to adenosine (CD39 and CD73) increase the extracellular adenosine levels that inhibit the innate and adaptive immune responses rendering the host susceptible to infection by invading microorganisms. Moreover, high levels of extracellular adenosine increase the expression, the production and the activation of pro-fibrotic proteins (such as TGF-β, α-SMA, etc.) followed by the establishment of lung fibrosis.
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Affiliation(s)
- Djo Hasan
- Department of Adult ICU, University Hospital Erasmus MC Rotterdam, 's-Gravendijkwal 230 3015 CE, Rotterdam, the Netherlands.
| | - Paul Blankman
- Department of Adult ICU, University Hospital Erasmus MC Rotterdam, 's-Gravendijkwal 230 3015 CE, Rotterdam, the Netherlands
| | - Gary F Nieman
- Department of Surgery, Upstate Medical University, 750 E Adams St, Syracuse, NY, 13210, USA
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Hover S, Foster B, Barr JN, Mankouri J. Viral dependence on cellular ion channels - an emerging anti-viral target? J Gen Virol 2017; 98:345-351. [PMID: 28113044 DOI: 10.1099/jgv.0.000712] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The broad range of cellular functions governed by ion channels represents an attractive target for viral manipulation. Indeed, modulation of host cell ion channel activity by viral proteins is being increasingly identified as an important virus-host interaction. Recent examples have demonstrated that virion entry, virus egress and the maintenance of a cellular environment conducive to virus persistence are, in part, dependent on virus manipulation of ion channel activity. Most excitingly, evidence has emerged that targeting ion channels pharmacologically can impede virus life cycles. Here, we discuss current examples of virus-ion channel interactions and the potential of targeting ion channel function as a new, pharmacologically safe and broad-ranging anti-viral therapeutic strategy.
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Affiliation(s)
- Samantha Hover
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Becky Foster
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - John N Barr
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Jamel Mankouri
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
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Aeffner F, Woods PS, Davis IC. Ecto-5'-nucleotidase CD73 modulates the innate immune response to influenza infection but is not required for development of influenza-induced acute lung injury. Am J Physiol Lung Cell Mol Physiol 2015; 309:L1313-22. [PMID: 26432867 PMCID: PMC4669338 DOI: 10.1152/ajplung.00130.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Accepted: 09/27/2015] [Indexed: 11/22/2022] Open
Abstract
Extracellular nucleotides and nucleosides are important signaling molecules in the lung. Nucleotide and nucleoside concentrations in alveolar lining fluid are controlled by a complex network of surface ectonucleotidases. Previously, we demonstrated that influenza A/WSN/33 (H1N1) virus resulted in increased levels of the nucleotide ATP and the nucleoside adenosine in bronchoalveolar lavage fluid (BALF) of wild-type (WT) C57BL/6 mice. Influenza-induced acute lung injury (ALI) was highly attenuated in A1-adenosine receptor-knockout mice. Because AMP hydrolysis by the ecto-5'-nucleotidase (CD73) plays a central role in and is rate-limiting for generation of adenosine in the normal lung, we hypothesized that ALI would be attenuated in C57BL/6-congenic CD73-knockout (CD73-KO) mice. Infection-induced hypoxemia, bradycardia, viral replication, and bronchoconstriction were moderately increased in CD73-KO mice relative to WT controls. However, postinfection weight loss, pulmonary edema, and parenchymal dysfunction were not altered. Treatment of WT mice with the CD73 inhibitor 5'-(α,β-methylene) diphosphate (APCP) also had no effect on infection-induced pulmonary edema but modestly attenuated hypoxemia. BALF from CD73-KO and APCP-treated WT mice contained more IL-6 and CXCL-10/IFN-γ-induced protein 10, less CXCL-1/keratinocyte chemoattractant, and fewer neutrophils than BALF from untreated WT controls. BALF from APCP-treated WT mice also contained fewer alveolar macrophages and more transforming growth factor-β than BALF from untreated WT mice. These results indicate that CD73 is not necessary for development of ALI following influenza A virus infection and suggest that tissue-nonspecific alkaline phosphatase may be responsible for increased adenosine generation in the infected lung. However, they do suggest that CD73 has a previously unrecognized immunomodulatory role in influenza.
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Affiliation(s)
- Famke Aeffner
- Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio
| | - Parker S Woods
- Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio
| | - Ian C Davis
- Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio
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Brealey JC, Sly PD, Young PR, Chappell KJ. Viral bacterial co-infection of the respiratory tract during early childhood. FEMS Microbiol Lett 2015; 362:fnv062. [PMID: 25877546 DOI: 10.1093/femsle/fnv062] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2015] [Indexed: 12/21/2022] Open
Abstract
Acute respiratory infection (ARI) is an important cause of morbidity in children. Mixed aetiology is frequent, with pathogenic viruses and bacteria co-detected in respiratory secretions. However, the clinical significance of these viral/bacterial co-infections has long been a controversial topic. While severe bacterial pneumonia following influenza infection has been well described, associations are less clear among infections caused by viruses that are more common in young children, such as respiratory syncytial virus. Although assessing the overall contribution of bacteria to disease severity is complicated by the presence of many confounding factors in clinical studies, understanding the role of viral/bacterial co-infections in defining the outcome of paediatric ARI will potentially reveal novel treatment and prevention strategies, improving patient outcomes. This review summarizes current evidence for the clinical significance of respiratory viral/bacterial co-infections in young children, discusses possible mechanisms of cooperative interaction between these pathogens and highlights areas that require further investigation.
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Affiliation(s)
- Jaelle C Brealey
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Peter D Sly
- Queensland Children's Medical Research Institute, The University of Queensland, Brisbane, QLD 4006, Australia Australian Infectious Diseases Research Centre, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Paul R Young
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia Australian Infectious Diseases Research Centre, The University of Queensland, St Lucia, QLD 4072, Australia Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Keith J Chappell
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia Australian Infectious Diseases Research Centre, The University of Queensland, St Lucia, QLD 4072, Australia
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10
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Abstract
Acute respiratory tract infection (RTI) is a leading cause of morbidity and mortality worldwide and the majority of RTIs are caused by viruses, among which respiratory syncytial virus (RSV) and the closely related human metapneumovirus (hMPV) figure prominently. Host innate immune response has been implicated in recognition, protection and immune pathological mechanisms. Host-viral interactions are generally initiated via host recognition of pathogen-associated molecular patterns (PAMPs) of the virus. This recognition occurs through host pattern recognition receptors (PRRs) which are expressed on innate immune cells such as epithelial cells, dendritic cells, macrophages and neutrophils. Multiple PRR families, including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs) and NOD-like receptors (NLRs), contribute significantly to viral detection, leading to induction of cytokines, chemokines and type I interferons (IFNs), which subsequently facilitate the eradication of the virus. This review focuses on the current literature on RSV and hMPV infection and the role of PRRs in establishing/mediating the infection in both in vitro and in vivo models. A better understanding of the complex interplay between these two viruses and host PRRs might lead to efficient prophylactic and therapeutic treatments, as well as the development of adequate vaccines.
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Cholesterol-rich microdomains as docking platforms for respiratory syncytial virus in normal human bronchial epithelial cells. J Virol 2011; 86:1832-43. [PMID: 22090136 DOI: 10.1128/jvi.06274-11] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Respiratory syncytial virus (RSV) is one of the major causes of respiratory infections in children, and it is the main pathogen causing bronchiolitis in infants. The binding and entry mechanism by which RSV infects respiratory epithelial cells has not yet been determined. In this study, the earliest stages of RSV infection in normal human bronchial epithelial cells were probed by tracking virions with fluorescent lipophilic dyes in their membranes. Virions colocalized with cholesterol-containing plasma membrane microdomains, identified by their ability to bind cholera toxin subunit B. Consistent with an important role for cholesterol in RSV infection, cholesterol depletion profoundly inhibited RSV infection, while cholesterol repletion reversed this inhibition. Merger of the outer leaflets of the viral envelope and the cell membrane appeared to be triggered at these sites. Using small-molecule inhibitors, RSV infection was found to be sensitive to Pak1 inhibition, suggesting the requirement of a subsequent step of cytoskeletal reorganization that could involve plasma membrane rearrangements or endocytosis. It appears that RSV entry depends on its ability to dock to cholesterol-rich microdomains (lipid rafts) in the plasma membrane where hemifusion events begin, assisted by a Pak1-dependent process.
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Ousingsawat J, Mirza M, Tian Y, Roussa E, Schreiber R, Cook DI, Kunzelmann K. Rotavirus toxin NSP4 induces diarrhea by activation of TMEM16A and inhibition of Na+ absorption. Pflugers Arch 2011; 461:579-89. [PMID: 21399895 DOI: 10.1007/s00424-011-0947-0] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2010] [Revised: 02/18/2011] [Accepted: 02/21/2011] [Indexed: 01/05/2023]
Abstract
Rotavirus infection is the most frequent cause for severe diarrhea in infants, killing more than 600,000 every year. The nonstructural protein NSP4 acts as a rotavirus enterotoxin, inducing secretory diarrhea without any structural organ damage. Electrolyte transport was assessed in the colonic epithelium from pups and adult mice using Ussing chamber recordings. Western blots and immunocytochemistry was performed in intestinal tissues from wild-type and TMEM16A knockout mice. Ion channel currents were recorded using patch clamp techniques. We show that the synthetic NSP4(114-135) peptide uses multiple pro-secretory pathways to induce diarrhea, by activating the recently identified Ca2+ -activated Cl- channel TMEM16A, and by inhibiting Na+ absorption by the epithelial Na+ channel ENaC and the Na+ /glucose cotransporter SGLT1. Activation of secretion and inhibition of Na+ absorption by NSP4(114-135), respectively, could be potently suppressed by wheat germ agglutinin which probably competes with NSP4(114-135) for binding to an unknown glycolipid receptor. The present paper gives a clue as to mechanisms of rotavirus-induced diarrhea and suggests wheat germ agglutinin as a simple and effective therapy.
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Affiliation(s)
- Jiraporn Ousingsawat
- Institut für Physiologie, Universität Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany
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Dodrill MW, Fedan JS. Lipopolysaccharide hyperpolarizes guinea pig airway epithelium by increasing the activities of the epithelial Na(+) channel and the Na(+)-K(+) pump. Am J Physiol Lung Cell Mol Physiol 2010; 299:L550-8. [PMID: 20639350 DOI: 10.1152/ajplung.00123.2010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Earlier, we found that systemic administration of lipopolysaccharide (LPS; 4 mg/kg) hyperpolarized the transepithelial potential difference (V(t)) of tracheal epithelium in the isolated, perfused trachea (IPT) of the guinea pig 18 h after injection. As well, LPS increased the hyperpolarization component of the response to basolateral methacholine, and potentiated the epithelium-derived relaxing factor-mediated relaxation responses to hyperosmolar solutions applied to the apical membrane. We hypothesized that LPS stimulates the transepithelial movement of Na(+) via the epithelial sodium channel (ENaC)/Na(+)-K(+) pump axis, leading to hyperpolarization of V(t). LPS increased the V(t)-depolarizing response to amiloride (10 μM), i.e., offset the effect of LPS, indicating that Na(+) transport activity was increased. The functional activity of ENaC was measured in the IPT after short-circuiting the Na(+)-K(+) pump with basolateral amphotericin B (7.5 μM). LPS had no effect on the hyperpolarization response to apical trypsin (100 U/ml) in the Ussing chamber, indicating that channel-activating proteases are not involved in the LPS-induced activation of ENaC. To assess Na(+)-K(+) pump activity in the IPT, ENaC was short-circuited with apical amphotericin B. The greater V(t) in the presence of amphotericin B in tracheas from LPS-treated animals compared with controls revealed that LPS increased Na(+)-K(+) pump activity. This finding was confirmed in the Ussing chamber by inhibiting the Na(+)-K(+) pump via extracellular K(+) removal, loading the epithelium with Na(+), and observing a greater hyperpolarization response to K(+) restoration. Together, the findings of this study reveal that LPS hyperpolarizes the airway epithelium by increasing the activities of ENaC and the Na(+)-K(+) pump.
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Affiliation(s)
- Michael W Dodrill
- Department of Basic Pharmaceutical Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, USA
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Regulation of the epithelial Na+ channel and airway surface liquid volume by serine proteases. Pflugers Arch 2010; 460:1-17. [PMID: 20401730 DOI: 10.1007/s00424-010-0827-z] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/10/2010] [Accepted: 03/12/2010] [Indexed: 01/11/2023]
Abstract
Mammalian airways are protected from infection by a thin film of airway surface liquid (ASL) which covers airway epithelial surfaces and acts as a lubricant to keep mucus from adhering to the epithelial surface. Precise regulation of ASL volume is essential for efficient mucus clearance and too great a reduction in ASL volume causes mucus dehydration and mucus stasis which contributes to chronic airway infection. The epithelial Na(+) channel (ENaC) is the rate-limiting step that governs Na(+) absorption in the airways. Recent in vitro and in vivo data have demonstrated that ENaC is a critical determinant of ASL volume and hence mucus clearance. ENaC must be cleaved by either intracellular furin-type proteases or extracellular serine proteases to be active and conduct Na(+), and this process can be inhibited by protease inhibitors. ENaC can be regulated by multiple pathways, and once proteolytically cleaved ENaC may then be inhibited by intracellular second messengers such as cAMP and PIP(2). In the airways, however, regulation of ENaC by proteases seems to be the predominant mode of regulation since knockdown of either endogenous serine proteases such as prostasin, or inhibitors of ENaC proteolysis such as SPLUNC1, has large effects on ENaC activity in airway epithelia. In this review, we shall discuss how ENaC is proteolytically cleaved, how this process can regulate ASL volume, and how its failure to operate correctly may contribute to chronic airway disease.
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Song JJ, Kown SK, Kim EJ, Lee YS, Kim BY, Chae SW. Mucosal expression of ENaC and AQP in experimental otitis media induced by Eustachian tube obstruction. Int J Pediatr Otorhinolaryngol 2009; 73:1589-93. [PMID: 19732969 DOI: 10.1016/j.ijporl.2009.08.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2009] [Revised: 08/10/2009] [Accepted: 08/10/2009] [Indexed: 01/24/2023]
Abstract
OBJECTIVE We investigated the expression of the epithelial sodium channel (ENaC) and aquaporins (AQPs) in the middle ear mucosa of a rat model of otitis media with effusion caused by surgical obstruction of the Eustachian tube. METHODS Sixty-four rats were randomly assigned to either undergo unilateral Eustachian tube obstruction (groups 1, 2, and 3) or to undergo no procedure (control group). Bony Eustachian tubes were approached through ventral incisions and obstructed with electrocautery. On days 14, 28, and 56, the ears were evaluated, and the rats were sacrificed for otoscopic evaluation and real-time RT-PCR. Immunohistochemistry was done for ENaC-alpha and AQP-1. RESULTS The level of ENaC-alpha expression decreased 0.28- and 0.73-fold at 2 and 4 weeks, respectively, but increased 1.48-fold at 8 weeks (p<0.05). The change in ENaC-beta expression at 2 weeks was insignificant. However, the level of ENaC-beta expression increased 3.17- and 7.85-fold at 4 and 8 weeks, respectively (p<0.05). The level of ENaC-gamma expression increased 1.51-, 4.82- and 14.79-fold at 2, 4 and 8 weeks, respectively (p<0.05). The level of AQP-1 expression decreased 0.10- and 0.04-fold at 4 and 8 weeks, respectively (p<0.05). The change in AQP4 expression at 4 and 8 weeks was insignificant (p>0.05). The pattern of immunoreactivity of ENaC-alpha and AQP-1 was similar with that of gene expression. CONCLUSION The experimental methods provoked reproducible otitis media with effusion. This model is well suited for studies of middle ear homeostasis during disease pathogenesis. Middle ear mucosa homeostasis is altered significantly by ETO, and the subunits of AQP proteins show a characteristic expression pattern over time.
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Affiliation(s)
- Jae-Jun Song
- Department of Otorhinolaryngology-Head and Neck Surgery, Dongguk University International Hospital, Goyang, Gyeonggi, Republic of Korea
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Oshansky CM, Zhang W, Moore E, Tripp RA. The host response and molecular pathogenesis associated with respiratory syncytial virus infection. Future Microbiol 2009; 4:279-97. [PMID: 19327115 DOI: 10.2217/fmb.09.1] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Since the isolation of respiratory syncytial virus (RSV) in 1956, its significance as an important human pathogen in infants, the elderly and the immunocompromised has been established. Many important mechanisms contributing to RSV infection, replication and disease pathogenesis have been uncovered; however, there is still insufficient knowledge in these and related areas, which must be addressed to facilitate the development of safe and effective vaccines and therapeutic treatments. A better understanding of the molecular pathogenesis of RSV infection, particularly the host-cell response and transcription profiles to RSV infection, is required to advance disease intervention strategies. Substantial information is accumulating regarding how RSV proteins modulate molecular signaling and regulation of cytokine and chemokine responses to infection, molecular signals regulating programmed cell death, and innate and adaptive immune responses to infection. This review discusses RSV manipulation of the host response to infection and related disease pathogenesis.
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Affiliation(s)
- Christine M Oshansky
- Department of Infectious Diseases, University of Georgia, Athens, GA 30602, USA.
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Song W, Liu G, Bosworth CA, Walker JR, Megaw GA, Lazrak A, Abraham E, Sullender WM, Matalon S. Respiratory syncytial virus inhibits lung epithelial Na+ channels by up-regulating inducible nitric-oxide synthase. J Biol Chem 2009; 284:7294-306. [PMID: 19131335 PMCID: PMC2652346 DOI: 10.1074/jbc.m806816200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 01/06/2009] [Indexed: 12/13/2022] Open
Abstract
Respiratory syncytial virus (RSV) infection has been shown to reduce Na+-driven alveolar fluid clearance in BALB/c mice in vivo. To investigate the cellular mechanisms by which RSV inhibits amiloride-sensitive epithelial Na+ channels (ENaC), the main pathways through which Na+ ions enter lung epithelial cells, we infected human Clara-like lung (H441) cells with RSV that expresses green fluorescent protein (rRA2). 3-6 days later patch clamp recordings showed that infected cells (i.e. cells expressing green fluorescence; GFP+) had significantly lower whole-cell amiloride-sensitive currents and single channel activity (NPo) as compared with non-infected (GFP-), non-inoculated, or cells infected with UV-inactivated RSV. Both alpha and beta ENaC mRNA levels were significantly reduced in GFP+ cells as measured by real-time reverse transcription-PCR. Infection with RSV increased expression of the inducible nitric-oxide synthase (iNOS) and nitrite concentration in the culture medium; nuclear translocation of NF-kappaB p65 subunit and NF-kappaB activation were also up-regulated. iNOS up-regulation in GFP+ cells was prevented by knocking down IkappaB kinase gamma before infection. Furthermore, pretreatment of H441 cells with the specific iNOS inhibitor 1400W (1 microM) resulted in a doubling of the amiloride-sensitive Na+ current in GFP+ cells. Additionally, preincubation of H441 cells with A77-1726 (20 microM), a de novo UTP synthesis inhibitor, and 1400W completely reversed the RSV inhibition of amiloride-sensitive currents in GFP+ cells. Thus, both UTP- and iNOS-generated reactive species contribute to ENaC down-regulation in RSV-infected airway epithelial cells.
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Affiliation(s)
- Weifeng Song
- Department of Anesthesiology, Center for Free Radical Biology, University of Alabama at Birmingham, Birmingham, Alabama 35233, USA
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Abstract
Human metapneumovirus (hMPV) is a recently described paramyxovirus that causes lower respiratory infections in children and adults worldwide. The hMPV fusion (F) protein is a membrane-anchored glycoprotein and major protective antigen. All hMPV F protein sequences determined to date contain an Arg-Gly-Asp (RGD) sequence, suggesting that F engages RGD-binding integrins to mediate cell entry. The divalent cation chelator EDTA, which disrupts heterodimeric integrin interactions, inhibits infectivity of hMPV but not the closely related respiratory syncytial virus (RSV), which lacks an RGD motif. Function-blocking antibodies specific for alphavbeta1 integrin inhibit infectivity of hMPV but not RSV. Transfection of nonpermissive cells with alphav or beta1 cDNAs confers hMPV infectivity, whereas reduction of alphav and beta1 integrin expression by siRNA inhibits hMPV infection. Recombinant hMPV F protein binds to cells, whereas Arg-Gly-Glu (RGE)-mutant F protein does not. These data suggest that alphavbeta1 integrin is a functional receptor for hMPV.
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Ji HL, Song W, Gao Z, Su XF, Nie HG, Jiang Y, Peng JB, He YX, Liao Y, Zhou YJ, Tousson A, Matalon S. SARS-CoV proteins decrease levels and activity of human ENaC via activation of distinct PKC isoforms. Am J Physiol Lung Cell Mol Physiol 2008; 296:L372-83. [PMID: 19112100 DOI: 10.1152/ajplung.90437.2008] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Among the multiple organ disorders caused by the severe acute respiratory syndrome coronavirus (SARS-CoV), acute lung failure following atypical pneumonia is the most serious and often fatal event. We hypothesized that two of the hydrophilic structural coronoviral proteins (S and E) would regulate alveolar fluid clearance by decreasing the cell surface expression and activity of amiloride-sensitive epithelial sodium (Na(+)) channels (ENaC), the rate-limiting protein in transepithelial Na(+) vectorial transport across distal lung epithelial cells. Coexpression of either S or E protein with human alpha-, beta-, and gamma-ENaC in Xenopus oocytes led to significant decreases of both amiloride-sensitive Na(+) currents and gamma-ENaC protein levels at their plasma membranes. S and E proteins decreased the rate of ENaC exocytosis and either had no effect (S) or decreased (E) rates of endocytosis. No direct interactions among SARS-CoV E protein with either alpha- or gamma-ENaC were indentified. Instead, the downregulation of ENaC activity by SARS proteins was partially or completely restored by administration of inhibitors of PKCalpha/beta1 and PKCzeta. Consistent with the whole cell data, expression of S and E proteins decreased ENaC single-channel activity in oocytes, and these effects were partially abrogated by PKCalpha/beta1 inhibitors. Finally, transfection of human airway epithelial (H441) cells with SARS E protein decreased whole cell amiloride-sensitive currents. These findings indicate that lung edema in SARS infection may be due at least in part to activation of PKC by SARS proteins, leading to decreasing levels and activity of ENaC at the apical surfaces of lung epithelial cells.
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Affiliation(s)
- Hong-Long Ji
- Department of Anesthesiology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama 35233-6810, USA
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Chen L, Song W, Davis IC, Shrestha K, Schwiebert E, Sullender WM, Matalon S. Inhibition of Na+ transport in lung epithelial cells by respiratory syncytial virus infection. Am J Respir Cell Mol Biol 2008; 40:588-600. [PMID: 18952569 DOI: 10.1165/rcmb.2008-0034oc] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
We investigated the mechanisms by which respiratory syncytial virus (RSV) infection decreases vectorial Na+ transport across respiratory epithelial cells. Mouse tracheal epithelial (MTE) cells from either BALB/c or C57BL/6 mice and human airway H441 cells were grown on semipermeable supports under an air-liquid interface. Cells were infected with RSV-A2 and mounted in Ussing chambers for measurements of short-circuit currents (I(sc)). Infection with RSV for 24 hours (multiplicity of infection = 1) resulted in positive immunofluorescence for RSV antigen in less than 10% of MTE or H441 cells. In spite of the limited number of cells infected, RSV reduced both basal and amiloride-sensitive I(sc) in both MTE and H441 cells by approximately 50%, without causing a concomitant reduction in transepithelial resistance. Agents that increased intracellular cAMP (forskolin, cpt-CAMP, and IBMX) increased mainly Cl(-) secretion in MTE cells and Na+ absorption in H441 cells. RSV infection for 24 hours blunted both variables. In contrast, ouabain sensitive I(sc), measured across apically permeabilized H441 monolayers, remained unchanged. Western blot analysis of H441 cell lysates demonstrated reductions in alpha- but not gamma-ENaC subunit protein levels at 24 hours after RSV infection. The reduction in amiloride-sensitive I(sc) in H441 cells was prevented by pretreatment with inhibitors of de novo pyrimidine or purine synthesis (A77-1726 and 6-MP, respectively, 50 microM). Our results suggest that infection of both murine and human respiratory epithelial cells with RSV inhibits vectorial Na+ transport via nucleotide release. These findings are consistent with our previous studies showing reduced alveolar fluid clearance after RSV infection of BALB/c mice.
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Affiliation(s)
- Lan Chen
- Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, AL 35205-3703, USA
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Viral and host factors in human respiratory syncytial virus pathogenesis. J Virol 2007; 82:2040-55. [PMID: 17928346 DOI: 10.1128/jvi.01625-07] [Citation(s) in RCA: 351] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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Singh D, McCann KL, Imani F. MAPK and heat shock protein 27 activation are associated with respiratory syncytial virus induction of human bronchial epithelial monolayer disruption. Am J Physiol Lung Cell Mol Physiol 2007; 293:L436-45. [PMID: 17557802 PMCID: PMC2231338 DOI: 10.1152/ajplung.00097.2007] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Respiratory syncytial virus (RSV) is the major cause of bronchiolitis in infants, and a common feature of RSV infections is increased lung permeability. The accumulation of fluid in the infected lungs is caused by changes in the endothelial and epithelial membrane integrity. However, the exact mechanisms of viral-induced fluid extravasation remain unclear. Here, we report that infection of human epithelial cells with RSV results in significant epithelial membrane barrier disruption as assessed by a decrease in transepithelial electrical resistance (TEpR). This decrease in TEpR, which indicates changes in paracellular permeability, was mediated by marked cellular cytoskeletal rearrangement. Importantly, the decrease in TEpR was attenuated by using p38 MAPK inhibitors (SB-203580) but was partially affected by JNK inhibitor SP-600125. Interestingly, treatment of A549 cells with MEK1/2 inhibitor (U-0126) led to a decrease in TEpR in the absence of RSV infection. The changes in TEpR were concomitant with an increase in heat shock protein 27 (Hsp27) phosphorylation and with actin microfilament rearrangement. Thus our data suggest that p38 MAPK and Hsp27 are required for RSV induction of human epithelial membrane permeability.
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Affiliation(s)
- Divyendu Singh
- Laboratory of Respiratory Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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