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Vidović A, Dolinar K, Chibalin AV, Pirkmajer S. AMPK and glucose deprivation exert an isoform-specific effect on the expression of Na +,K +-ATPase subunits in cultured myotubes. J Muscle Res Cell Motil 2024; 45:139-154. [PMID: 38709429 DOI: 10.1007/s10974-024-09673-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Accepted: 04/24/2024] [Indexed: 05/07/2024]
Abstract
In skeletal muscle, Na+,K+-ATPase (NKA), a heterodimeric (α/β) P-type ATPase, has an essential role in maintenance of Na+ and K+ homeostasis, excitability, and contractility. AMP-activated protein kinase (AMPK), an energy sensor, increases the membrane abundance and activity of NKA in L6 myotubes, but its potential role in regulation of NKA content in skeletal muscle, which determines maximum capacity for Na+ and K+ transport, has not been clearly delineated. We examined whether energy stress and/or AMPK affect expression of NKA subunits in rat L6 and primary human myotubes. Energy stress, induced by glucose deprivation, increased protein content of NKAα1 and NKAα2 in L6 myotubes, while decreasing the content of NKAα1 in human myotubes. Pharmacological AMPK activators (AICAR, A-769662, and diflunisal) modulated expression of NKA subunits, but their effects only partially mimicked those that occurred in response to glucose deprivation, indicating that AMPK does not mediate all effects of energy stress on NKA expression. Gene silencing of AMPKα1/α2 increased protein levels of NKAα1 in L6 myotubes and NKAα1 mRNA levels in human myotubes, while decreasing NKAα2 protein levels in L6 myotubes. Collectively, our results suggest a role for energy stress and AMPK in modulation of NKA expression in skeletal muscle. However, their modulatory effects were not conserved between L6 myotubes and primary human myotubes, which suggests that coupling between energy stress, AMPK, and regulation of NKA expression in vitro depends on skeletal muscle cell model.
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Affiliation(s)
- Anja Vidović
- Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | - Klemen Dolinar
- Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | - Alexander V Chibalin
- Department of Molecular Medicine and Surgery, Integrative Physiology, Karolinska Institutet, Stockholm, Sweden
- National Research Tomsk State University, Tomsk, Russia
| | - Sergej Pirkmajer
- Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia.
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2
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Mansley MK, Niklas C, Nacken R, Mandery K, Glaeser H, Fromm MF, Korbmacher C, Bertog M. Prostaglandin E2 stimulates the epithelial sodium channel (ENaC) in cultured mouse cortical collecting duct cells in an autocrine manner. J Gen Physiol 2021; 152:151804. [PMID: 32442241 PMCID: PMC7398144 DOI: 10.1085/jgp.201912525] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Revised: 03/30/2020] [Accepted: 04/21/2020] [Indexed: 12/26/2022] Open
Abstract
Prostaglandin E2 (PGE2) is the most abundant prostanoid in the kidney, affecting a wide range of renal functions. Conflicting data have been reported regarding the effects of PGE2 on tubular water and ion transport. The amiloride-sensitive epithelial sodium channel (ENaC) is rate limiting for transepithelial sodium transport in the aldosterone-sensitive distal nephron. The aim of the present study was to explore a potential role of PGE2 in regulating ENaC in cortical collecting duct (CCD) cells. Short-circuit current (ISC) measurements were performed using the murine mCCDcl1 cell line known to express characteristic properties of CCD principal cells and to be responsive to physiological concentrations of aldosterone and vasopressin. PGE2 stimulated amiloride-sensitive ISC via basolateral prostaglandin E receptors type 4 (EP4) with an EC50 of ∼7.1 nM. The rapid stimulatory effect of PGE2 on ISC resembled that of vasopressin. A maximum response was reached within minutes, coinciding with an increased abundance of β-ENaC at the apical plasma membrane and elevated cytosolic cAMP levels. The effects of PGE2 and vasopressin were nonadditive, indicating similar signaling cascades. Exposing mCCDcl1 cells to aldosterone caused a much slower (∼2 h) increase of the amiloride-sensitive ISC. Interestingly, the rapid effect of PGE2 was preserved even after aldosterone stimulation. Furthermore, application of arachidonic acid also increased the amiloride-sensitive ISC involving basolateral EP4 receptors. Exposure to arachidonic acid resulted in elevated PGE2 in the basolateral medium in a cyclooxygenase 1 (COX-1)–dependent manner. These data suggest that in the cortical collecting duct, locally produced and secreted PGE2 can stimulate ENaC-mediated transepithelial sodium transport.
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Affiliation(s)
- Morag K Mansley
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Christian Niklas
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Regina Nacken
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Kathrin Mandery
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Hartmut Glaeser
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Martin F Fromm
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Marko Bertog
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
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3
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Baldassi D, Gabold B, Merkel O. Air-liquid interface cultures of the healthy and diseased human respiratory tract: promises, challenges and future directions. ADVANCED NANOBIOMED RESEARCH 2021; 1:2000111. [PMID: 34345878 PMCID: PMC7611446 DOI: 10.1002/anbr.202000111] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Air-liquid interface (ALI) culture models currently represent a valid instrument to recreate the typical aspects of the respiratory tract in vitro in both healthy and diseased state. They can help reducing the number of animal experiments, therefore, supporting the 3R principle. This review discusses ALI cultures and co-cultures derived from immortalized as well as primary cells, which are used to study the most common disorders of the respiratory tract, in terms of both pathophysiology and drug screening. The article displays ALI models used to simulate inflammatory lung diseases such as chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis, lung cancer, and viral infections. It also includes a focus on ALI cultures described in literature studying respiratory viruses such as SARS-CoV-2 causing the global Covid-19 pandemic at the time of writing this review. Additionally, commercially available models of ALI cultures are presented. Ultimately, the aim of this review is to provide a detailed overview of ALI models currently available and to critically discuss them in the context of the most prevalent diseases of the respiratory tract.
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Affiliation(s)
- Domizia Baldassi
- Pharmaceutical Technology and Biopharmacy, LMU Munich Butenandtstr. 5-13, 81377 Munich, Germany
| | - Bettina Gabold
- Pharmaceutical Technology and Biopharmacy, LMU Munich Butenandtstr. 5-13, 81377 Munich, Germany
| | - Olivia Merkel
- Pharmaceutical Technology and Biopharmacy, LMU Munich Butenandtstr. 5-13, 81377 Munich, Germany
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4
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Rooj AK, Cormet-Boyaka E, Clark EB, Qadri YJ, Lee W, Boddu R, Agarwal A, Tambi R, Uddin M, Parpura V, Sorscher EJ, Fuller CM, Berdiev BK. Association of cystic fibrosis transmembrane conductance regulator with epithelial sodium channel subunits carrying Liddle's syndrome mutations. Am J Physiol Lung Cell Mol Physiol 2021; 321:L308-L320. [PMID: 34037494 DOI: 10.1152/ajplung.00298.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The association of the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) in the pathophysiology of cystic fibrosis (CF) is controversial. Previously, we demonstrated a close physical association between wild-type (WT) CFTR and WT ENaC. We have also shown that the F508del CFTR fails to associate with ENaC unless the mutant protein is rescued pharmacologically or by low temperature. In this study, we present the evidence for a direct physical association between WT CFTR and ENaC subunits carrying Liddle's syndrome mutations. We show that all three ENaC subunits bearing Liddle's syndrome mutations (both point mutations and the complete truncation of the carboxy terminus), could be coimmunoprecipitated with WT CFTR. The biochemical studies were complemented by fluorescence lifetime imaging microscopy (FLIM), a distance-dependent approach that monitors protein-protein interactions between fluorescently labeled molecules. Our measurements revealed significantly increased fluorescence resonance energy transfer between CFTR and all tested ENaC combinations as compared with controls (ECFP and EYFP cotransfected cells). Our findings are consistent with the notion that CFTR and ENaC are within reach of each other even in the setting of Liddle's syndrome mutations, suggestive of a direct intermolecular interaction between these two proteins.
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Affiliation(s)
- Arun K Rooj
- Department of Cell, Developmental & Integrative Biology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | | | - Edlira B Clark
- Department of Cell, Developmental & Integrative Biology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Yawar J Qadri
- Department of Anesthesiology, The Emory University School of Medicine, Atlanta, Georgia
| | - William Lee
- Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Ravindra Boddu
- Department of Medicine, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Anupam Agarwal
- Department of Medicine, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Richa Tambi
- College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates
| | - Mohammed Uddin
- College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates
| | - Vladimir Parpura
- Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Eric J Sorscher
- Department of Pediatrics, The Emory University School of Medicine, Atlanta, Georgia
| | - Cathy M Fuller
- Department of Cell, Developmental & Integrative Biology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama
| | - Bakhrom K Berdiev
- Department of Cell, Developmental & Integrative Biology, The University of Alabama at Birmingham School of Medicine, Birmingham, Alabama.,College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates
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Moore PJ, Reidel B, Ghosh A, Sesma J, Kesimer M, Tarran R. Cigarette smoke modifies and inactivates SPLUNC1, leading to airway dehydration. FASEB J 2018; 32:fj201800345R. [PMID: 29890087 PMCID: PMC6219833 DOI: 10.1096/fj.201800345r] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 05/21/2018] [Indexed: 01/14/2023]
Abstract
Chronic obstructive pulmonary disease (COPD) is a growing cause of morbidity and mortality worldwide. Cigarette smoke (CS) exposure, a major cause of COPD, dysregulates airway epithelial ion transport and diminishes airway surface liquid (ASL) volume. Short palate lung and nasal epithelial clone 1 (SPLUNC1) is secreted into the airway lumen where it maintains airway hydration via interactions with the epithelial Na+ channel (ENaC). Although ASL hydration is dysregulated in CS-exposed/COPD airways, effects of CS on SPLUNC1 have not been elucidated. We hypothesized that CS alters SPLUNC1 activity, therefore contributing to ASL dehydration. CS exposure caused irreversible SPLUNC1 aggregation and prevented SPLUNC1 from internalizing ENaC and maintaining ASL hydration. Proteomic analysis revealed αβ-unsaturated aldehyde modifications to SPLUNC1's cysteine residues. Removal of these cysteines prevented SPLUNC1 from regulating ENaC/ASL volume. In contrast, SPX-101, a peptide mimetic of natural SPLUNC1, that internalizes ENaC, but does not contain cysteines was unaffected by CS. SPX-101 increased ASL hydration and attenuated ENaC activity in airway cultures after CS exposure and prolonged survival in a chronic airway disease model. These findings suggest that the CS-induced defects in SPLUNC1 can be circumvented, thus making SPX-101 a novel candidate for the treatment of mucus dehydration in COPD. -Moore, P. J., Reidel, B., Ghosh, A., Sesma, J., Kesimer, M., Tarran, R. Cigarette smoke modifies and inactivates SPLUNC1, leading to airway dehydration.
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Affiliation(s)
- Patrick J. Moore
- Marsico Lung Institute, University of North Carolina at Chapel Hill, North Carolina, USA
| | - Boris Reidel
- Marsico Lung Institute, University of North Carolina at Chapel Hill, North Carolina, USA
| | - Arunava Ghosh
- Marsico Lung Institute, University of North Carolina at Chapel Hill, North Carolina, USA
| | | | - Mehmet Kesimer
- Marsico Lung Institute, University of North Carolina at Chapel Hill, North Carolina, USA
| | - Robert Tarran
- Marsico Lung Institute, University of North Carolina at Chapel Hill, North Carolina, USA
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, North Carolina, USA
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Kim CS, Ahmad S, Wu T, Walton WG, Redinbo MR, Tarran R. SPLUNC1 is an allosteric modulator of the epithelial sodium channel. FASEB J 2018; 32:2478-2491. [PMID: 29295861 PMCID: PMC5901381 DOI: 10.1096/fj.201701126r] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Accepted: 12/04/2017] [Indexed: 01/20/2023]
Abstract
Cystic fibrosis (CF) is a common genetic disease with significantly increased mortality. CF airways exhibit ion transport abnormalities, including hyperactivity of the epithelial Na+ channel (ENaC). Short-palate lung and nasal epithelial clone 1 (SPLUNC1) is a multifunctional innate defense protein that is secreted into the airway lumen. We have previously demonstrated that SPLUNC1 binds to and inhibits ENaC to maintain fluid homeostasis in airway epithelia and that this process fails in CF airways. Despite this, how SPLUNC1 actually regulates ENaC is unknown. Here, we found that SPLUNC1 caused αγ-ENaC to internalize, whereas SPLUNC1 and β-ENaC remained at the plasma membrane. Additional studies revealed that SPLUNC1 increased neural precursor cell-expressed developmentally down-regulated protein 4-2-dependent ubiquitination of α- but not β- or γ-ENaC. We also labeled intracellular ENaC termini with green fluorescent protein and mCherry, and found that extracellular SPLUNC1 altered intracellular ENaC Forster resonance energy transfer. Taken together, our data indicate that SPLUNC1 is an allosteric regulator of ENaC that dissociates αβγ-ENaC to generate a new SPLUNC1-β-ENaC complex. These data indicate a novel mode for regulating ENaC at the plasma membrane.-Kim, C. S., Ahmad, S., Wu, T., Walton, W. G., Redinbo, M. R., Tarran, R. SPLUNC1 is an allosteric modulator of the epithelial sodium channel.
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Affiliation(s)
- Christine Seulki Kim
- Cystic Fibrosis Center, Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Saira Ahmad
- Cystic Fibrosis Center, Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Tongde Wu
- Cystic Fibrosis Center, Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - William G. Walton
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Matthew R. Redinbo
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Robert Tarran
- Cystic Fibrosis Center, Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
- Department of Cell Biology and Physiology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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7
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Lee KW, Nam MH, Lee HR, Hong CO, Lee KW. Protective effects of chebulic acid on alveolar epithelial damage induced by urban particulate matter. BMC COMPLEMENTARY AND ALTERNATIVE MEDICINE 2017; 17:373. [PMID: 28724416 PMCID: PMC5518117 DOI: 10.1186/s12906-017-1870-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 07/04/2017] [Indexed: 11/10/2022]
Abstract
BACKGROUND Chebulic acid (CA) isolated from T. chebula, which has been reported for treating asthma, as a potent anti-oxidant resources. Exposure to ambient urban particulate matter (UPM) considered as a risk for cardiopulmonary vascular dysfunction. To investigate the protective effect of CA against UPM-mediated collapse of the pulmonary alveolar epithelial (PAE) cell (NCI-H441), barrier integrity parameters, and their elements were evaluated in PAE. METHODS CA was acquired from the laboratory previous reports. UPM was obtained from the National Institutes of Standards and Technology, and these were collected in St. Louis, MO, over a 24-month period and used as a standard reference. To confirm the protection of PAE barrier integrity, paracellular permeability and the junctional molecules were estimated with determination of transepithelial electrical resistance, Western Blotting, RT-PCR, and fluorescent staining. RESULTS UPM aggravated the generation of reactive oxygen species (ROS) in PAE and also decreased mRNA and protein levels of junction molecules and barrier integrity in NCI-H441. However, CA repressed the ROS in PAE, also improved barrier integrity by protecting the junctional parameters in NCI-H411. CONCLUSIONS These data showed that CA resulted in decreased UPM-induced ROS formation, and the protected the integrity of the tight junctions against UPM exposure to PAE barrier.
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8
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Castellani S, Orlando C, Carbone A, Di Gioia S, Conese M. Magnetofection Enhances Lentiviral-Mediated Transduction of Airway Epithelial Cells through Extracellular and Cellular Barriers. Genes (Basel) 2016; 7:genes7110103. [PMID: 27886077 PMCID: PMC5126789 DOI: 10.3390/genes7110103] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 11/04/2016] [Accepted: 11/15/2016] [Indexed: 02/03/2023] Open
Abstract
Gene transfer to airway epithelial cells is hampered by extracellular (mainly mucus) and cellular (tight junctions) barriers. Magnetofection has been used to increase retention time of lentiviral vectors (LV) on the cellular surface. In this study, magnetofection was investigated in airway epithelial cell models mimicking extracellular and cellular barriers. Bronchiolar epithelial cells (H441 line) were evaluated for LV-mediated transduction after polarization onto filters and dexamethasone (dex) treatment, which induced hemicyst formation, with or without magnetofection. Sputum from cystic fibrosis (CF) patients was overlaid onto cells, and LV-mediated transduction was evaluated in the absence or presence of magnetofection. Magnetofection of unpolarized H441 cells increased the transduction with 50 MOI (multiplicity of infection, i.e., transducing units/cell) up to the transduction obtained with 500 MOI in the absence of magnetofection. Magnetofection well-enhanced LV-mediated transduction in mucus-layered cells by 20.3-fold. LV-mediated transduction efficiency decreased in dex-induced hemicysts in a time-dependent fashion. In dome-forming cells, zonula occludens-1 (ZO-1) localization at the cell borders was increased by dex treatment. Under these experimental conditions, magnetofection significantly increased LV transduction by 5.3-fold. In conclusion, these results show that magnetofection can enhance LV-mediated gene transfer into airway epithelial cells in the presence of extracellular (sputum) and cellular (tight junctions) barriers, representing CF-like conditions.
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Affiliation(s)
- Stefano Castellani
- Department of Medical and Surgical Sciences, University of Foggia, V. L. Pinto 1, 71122 Foggia, Italy.
| | - Clara Orlando
- Brainlab AG, Kapellenstrasse 12, 85622 Feldkirchen, Germany.
| | - Annalucia Carbone
- Department of Medical and Surgical Sciences, University of Foggia, V. L. Pinto 1, 71122 Foggia, Italy.
| | - Sante Di Gioia
- Department of Medical and Surgical Sciences, University of Foggia, V. L. Pinto 1, 71122 Foggia, Italy.
| | - Massimo Conese
- Department of Medical and Surgical Sciences, University of Foggia, V. L. Pinto 1, 71122 Foggia, Italy.
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Papazian D, Würtzen PA, Hansen SWK. Polarized Airway Epithelial Models for Immunological Co-Culture Studies. Int Arch Allergy Immunol 2016; 170:1-21. [PMID: 27240620 DOI: 10.1159/000445833] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Epithelial cells line all cavities and surfaces throughout the body and play a substantial role in maintaining tissue homeostasis. Asthma and other atopic diseases are increasing worldwide and allergic disorders are hypothesized to be a consequence of a combination of dysregulation of the epithelial response towards environmental antigens and genetic susceptibility, resulting in inflammation and T cell-derived immune responses. In vivo animal models have long been used to study immune homeostasis of the airways but are limited by species restriction and lack of exposure to a natural environment of both potential allergens and microflora. Limitations of these models prompt a need to develop new human cell-based in vitro models. A variety of co-culture systems for modelling the respiratory epithelium exist and are available to the scientific community. The models have become increasingly sophisticated and specific care needs to be taken with regard to cell types, culture medium and culture models, depending on the aim of the study. Although great strides have been made, there is still a need for further optimization, and optimally also for standardization, in order for in vitro co-culture models to become powerful tools in the discovery of key molecules dictating immunity and/or tolerance, and for understanding the complex interplay that takes place between mucosa, airway epithelium and resident or infiltrating immune cells. This review focuses on current knowledge and the advantages and limitations of the different cell types and culture methods used in co-culture models of the human airways.
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Affiliation(s)
- Dick Papazian
- Department of Cancer and Inflammation Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
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10
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Hittinger M, Juntke J, Kletting S, Schneider-Daum N, de Souza Carvalho C, Lehr CM. Preclinical safety and efficacy models for pulmonary drug delivery of antimicrobials with focus on in vitro models. Adv Drug Deliv Rev 2015; 85:44-56. [PMID: 25453270 DOI: 10.1016/j.addr.2014.10.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 09/30/2014] [Accepted: 10/07/2014] [Indexed: 12/11/2022]
Abstract
New pharmaceutical formulations must be proven as safe and effective before entering clinical trials. Also in the context of pulmonary drug delivery, preclinical models allow testing of novel antimicrobials, reducing risks and costs during their development. Such models allow reducing the complexity of the human lung, but still need to reflect relevant (patho-) physiological features. This review focuses on preclinical pulmonary models, mainly in vitro models, to assess drug safety and efficacy of antimicrobials. Furthermore, approaches to investigate common infectious diseases of the respiratory tract, are emphasized. Pneumonia, tuberculosis and infections occurring due to cystic fibrosis are in focus of this review. We conclude that especially in vitro models offer the chance of an efficient and detailed analysis of new antimicrobials, but also draw attention to the advantages and limitations of such currently available models and critically discuss the necessary steps for their future development.
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11
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Agné AM, Baldin JP, Benjamin AR, Orogo-Wenn MC, Wichmann L, Olson KR, Walters DV, Althaus M. Hydrogen sulfide decreases β-adrenergic agonist-stimulated lung liquid clearance by inhibiting ENaC-mediated transepithelial sodium absorption. Am J Physiol Regul Integr Comp Physiol 2015; 308:R636-49. [PMID: 25632025 DOI: 10.1152/ajpregu.00489.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 01/19/2015] [Indexed: 01/11/2023]
Abstract
In pulmonary epithelia, β-adrenergic agonists regulate the membrane abundance of the epithelial sodium channel (ENaC) and, thereby, control the rate of transepithelial electrolyte absorption. This is a crucial regulatory mechanism for lung liquid clearance at birth and thereafter. This study investigated the influence of the gaseous signaling molecule hydrogen sulfide (H2S) on β-adrenergic agonist-regulated pulmonary sodium and liquid absorption. Application of the H2S-liberating molecule Na2S (50 μM) to the alveolar compartment of rat lungs in situ decreased baseline liquid absorption and abrogated the stimulation of liquid absorption by the β-adrenergic agonist terbutaline. There was no additional effect of Na2S over that of the ENaC inhibitor amiloride. In electrophysiological Ussing chamber experiments with native lung epithelia (Xenopus laevis), Na2S inhibited the stimulation of amiloride-sensitive current by terbutaline. β-adrenergic agonists generally increase ENaC abundance by cAMP formation and activation of PKA. Activation of this pathway by forskolin and 3-isobutyl-1-methylxanthine increased amiloride-sensitive currents in H441 pulmonary epithelial cells. This effect was inhibited by Na2S in a dose-dependent manner (5-50 μM). Na2S had no effect on cellular ATP concentration, cAMP formation, and activation of PKA. By contrast, Na2S prevented the cAMP-induced increase in ENaC activity in the apical membrane of H441 cells. H441 cells expressed the H2S-generating enzymes cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, and they produced H2S amounts within the employed concentration range. These data demonstrate that H2S prevents the stimulation of ENaC by cAMP/PKA and, thereby, inhibits the proabsorptive effect of β-adrenergic agonists on lung liquid clearance.
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Affiliation(s)
- Alisa M Agné
- Institute of Animal Physiology, Department of Molecular Cell Physiology, Justus-Liebig University, Giessen, Germany
| | - Jan-Peter Baldin
- Institute of Animal Physiology, Department of Molecular Cell Physiology, Justus-Liebig University, Giessen, Germany
| | - Audra R Benjamin
- Division of Clinical Sciences, St. George's University of London, London, United Kingdom
| | - Maria C Orogo-Wenn
- Division of Clinical Sciences, St. George's University of London, London, United Kingdom
| | - Lukas Wichmann
- Institute of Animal Physiology, Department of Molecular Cell Physiology, Justus-Liebig University, Giessen, Germany
| | - Kenneth R Olson
- Department of Physiology, Indiana University School of Medicine-South Bend, South Bend, Indiana; and
| | - Dafydd V Walters
- Division of Clinical Sciences, St. George's University of London, London, United Kingdom
| | - Mike Althaus
- Institute of Animal Physiology, Department of Molecular Cell Physiology, Justus-Liebig University, Giessen, Germany;
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12
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Haghi M, Ong HX, Traini D, Young P. Across the pulmonary epithelial barrier: Integration of physicochemical properties and human cell models to study pulmonary drug formulations. Pharmacol Ther 2014; 144:235-52. [DOI: 10.1016/j.pharmthera.2014.05.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 04/30/2014] [Indexed: 11/16/2022]
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13
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Jeong JH, Joo NS, Hwang PH, Wine JJ. Mucociliary clearance and submucosal gland secretion in the ex vivo ferret trachea. Am J Physiol Lung Cell Mol Physiol 2014; 307:L83-93. [PMID: 24793168 DOI: 10.1152/ajplung.00009.2014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
In many species submucosal glands are an important source of tracheal mucus, but the extent to which mucociliary clearance (MCC) depends on gland secretion is unknown. To explore this relationship, we measured basal and agonist-stimulated MCC velocities in ex vivo tracheas from adult ferrets and compared the velocities with previously measured rates of ferret glandular mucus secretion (Cho HJ, Joo NS, Wine JJ. Am J Physiol Lung Cell Mol Physiol 299: L124-L136, 2010). Stimulated MCC velocities (mm/min, means ± SE for 10- to 35-min period poststimulation) were as follows: 1 μM carbachol: 19.1 ± 3.3 > 10 μM phenylephrine: 15.3 ± 2.4 ≈ 10 μM isoproterenol: 15.0 ± 1.9 ≈ 10 μM forskolin: 14.6 ± 3.1 > 1 μM vasoactive intestinal peptide (VIP): 10.2 ± 2.2 >> basal (t15): 1.8 ± 0.3; n = 5-10 for each condition. Synergistic stimulation of MCC was observed between low concentrations of carbachol (100 nM) and isoproterenol (300 nM). Bumetanide inhibited carbachol-stimulated MCC by ~70% and abolished the increase in MCC stimulated by forskolin + VIP, whereas HCO3 (-)-free solutions did not significantly inhibit MCC to either intracellular Ca(2+) concentration or intracellular cAMP concentration ([cAMP]i)-elevating agonists. Stimulation and inhibition of MCC and gland secretion differed in several respects: most importantly, elevating [cAMP]i increased MCC much more effectively than expected from its effects on gland secretion, and bumetanide almost completely inhibited [cAMP]i-stimulated MCC while it had a smaller effect on gland secretion. We conclude that changes in glandular fluid secretion are complexly related to MCC and discuss possible reasons for this.
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Affiliation(s)
- Jin Hyeok Jeong
- Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California; Department of Otolaryngology-Head and Neck Surgery, Hanyang University School of Medicine, Seoul, Korea; and
| | - Nam Soo Joo
- Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California
| | - Peter H Hwang
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, California
| | - Jeffrey J Wine
- Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California;
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Korbmacher JP, Michel C, Neubauer D, Thompson K, Mizaikoff B, Frick M, Dietl P, Wittekindt OH. Amiloride-sensitive fluid resorption in NCI-H441 lung epithelia depends on an apical Cl(-) conductance. Physiol Rep 2014; 2:e00201. [PMID: 24744880 PMCID: PMC3967684 DOI: 10.1002/phy2.201] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 12/12/2013] [Accepted: 12/21/2013] [Indexed: 01/12/2023] Open
Abstract
Proper apical airway surface hydration is essential to maintain lung function. This hydration depends on well‐balanced water resorption and secretion. The mechanisms involved in resorption are still a matter of debate, especially as the measurement of transepithelial water transport remains challenging. In this study, we combined classical short circuit current (ISC) measurements with a novel D2O dilution method to correlate ion and water transport in order to reveal basic transport mechanisms in lung epithelia. D2O dilution method enabled precise analysis of water resorption with an unprecedented resolution. NCI‐H441 cells cultured at an air–liquid interface resorbed water at a rate of 1.5 ± 0.4 μL/(h cm2). Water resorption and ISC were reduced by almost 80% in the presence of the bulk Cl− channel inhibitor 5‐nitro‐2‐(3‐phenylpropylamino)benzoic acid (NPPB) or amiloride, a specific inhibitor of epithelial sodium channel (ENaC). However, water resorption and ISC were only moderately affected by forskolin or cystic fibrosis transmembrane regulator (CFTR) channel inhibitors (CFTRinh‐172 and glybenclamide). In line with previous studies, we demonstrate that water resorption depends on ENaC, and CFTR channels have only a minor but probably modulating effect on water resorption. However, the major ENaC‐mediated water resorption depends on an apical non‐CFTR Cl− conductance. We investigated water transport across lung epithelia, using a novel D2O dilution method in combination with Ussing chamber experiments. Our results revealed that CFTR channels have a minor modulating effect on water resorption. The major ENaC‐mediated resorption depends on non‐CFTR channels.
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Affiliation(s)
- Jonas P Korbmacher
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Christiane Michel
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Daniel Neubauer
- Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Kristin Thompson
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Boris Mizaikoff
- Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Manfred Frick
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Paul Dietl
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Oliver H Wittekindt
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
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15
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Hobbs CA, Da Tan C, Tarran R. Does epithelial sodium channel hyperactivity contribute to cystic fibrosis lung disease? J Physiol 2013; 591:4377-87. [PMID: 23878362 DOI: 10.1113/jphysiol.2012.240861] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Airway epithelia absorb Na+ through the epithelial Na+ channel (ENaC) and secrete Cl- through the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. This balance maintains sufficient airway surface liquid hydration to permit efficient mucus clearance, which is needed to maintain sterility of the lung. Cystic fibrosis (CF) is a common autosomal recessive inherited disease caused by mutations in the CFTR gene that lead to the reduction or elimination of the CFTR protein. CF is a multi-organ disease that affects epithelia lining the intestines, lungs, pancreas, sweat ducts and vas deferens, among others. CF lungs are characterized by viscous, dehydrated mucus, persistent neutrophilia and chronic infections. ENaC is negatively regulated by CFTR and, in patients with CF, the absence of CFTR results in a double hit of reduced Cl-/HCO3- and H2O secretion as well as ENaC hyperactivity and increased Na+ and H2O absorption. Together, these effects are hypothesized to trigger mucus dehydration, resulting in a failure to clear mucus. Rehydrating CF mucus has become a recent clinical focus and yields important end-points for clinical trials. However, while ENaC hyperactivity in CF airways has been detected in vivo and in vitro, recent data have brought the role of ENaC in CF lung disease pathogenesis into question. This review will focus on our current understanding of the contribution of ENaC to CF pathogenesis.
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Affiliation(s)
- Carey A Hobbs
- R. Tarran: 7125 Thurston Bowles Building, UNC, Chapel Hill, NC 27599-7248, USA.
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16
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Aarbiou J, Copreni E, Buijs-Offerman RM, van der Wegen P, Castellani S, Carbone A, Tilesi F, Fradiani P, Hiemstra PS, Yueksekdag G, Diana A, Rosenecker J, Ascenzioni F, Conese M, Scholte BJ. Lentiviral small hairpin RNA delivery reduces apical sodium channel activity in differentiated human airway epithelial cells. J Gene Med 2013; 14:733-45. [PMID: 23074129 DOI: 10.1002/jgm.2672] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Revised: 09/27/2012] [Accepted: 10/07/2012] [Indexed: 01/23/2023] Open
Abstract
BACKGROUND Epithelial sodium channel (ENaC) hyperactivity has been implicated in the pathogenesis of cystic fibrosis (CF) by dysregulation of fluid and electrolytes in the airways. In the present study, we show proof-of-principle for ENaC inhibition by lentiviral-mediated RNA interference. METHODS Immortalized normal (H441) and CF mutant (CFBE) airway cells, and differentiated human bronchial epithelial cells in air liquid interface culture (HBEC-ALI) were transduced with a vesicular stomatitis virus G glycoprotein pseudotyped lentiviral (LV) vector expressing a short hairpin RNA (shRNA) targeting the α subunit of ENaC (ENaCα), and a marker gene. Efficacy of ENaCα down-regulation was assayed by the real-time polymerase chain reaction (PCR), membrane potential assay, western blotting, short-circuit currents and fluid absorption. Off-target effects were investigated by a lab-on-a-chip quantitative PCR array. RESULTS Transduction to near one hundred percentage efficiency of H441, CFBE and HBEC-ALI was achieved by the addition of the LV vector before differentiation and polarization. Transduction resulted in the inhibition of ENaCα mRNA and antigen expression, and a proportional decrease in ENaC-dependent short circuit current and fluid transport. No effect on transepithelial resistance or cAMP-induced secretion responses was observed in HBEC-ALI. The production of interferon α and pro-inflammatory cytokine mRNA, indicating Toll-like receptor 3 or RNA-induced silencing complex mediated off-target effects, was not observed in HBEC-ALI transduced with this vector. CONCLUSIONS We have established a generic method for studying the effect of RNA interference in HBEC-ALI using standard lentiviral vectors. Down-regulation of ENaCα by lentiviral shRNA expression vectors as shown in the absence off-target effects has potential therapeutic value in the treatment of cystic fibrosis.
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Affiliation(s)
- Jamil Aarbiou
- Department of Cell Biology, Erasmus MC, Rotterdam, The Netherlands
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Yang HY, Charles RP, Hummler E, Baines DL, Isseroff RR. The epithelial sodium channel mediates the directionality of galvanotaxis in human keratinocytes. J Cell Sci 2013; 126:1942-51. [PMID: 23447677 DOI: 10.1242/jcs.113225] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Cellular directional migration in an electric field (galvanotaxis) is one of the mechanisms guiding cell movement in embryogenesis and in skin epidermal repair. The epithelial sodium channel (ENaC), in addition to its function of regulating sodium transport in kidney, has recently been found to modulate cell locomotory speed. Here we tested whether ENaC has an additional function of mediating the directional migration of galvanotaxis in keratinocytes. Genetic depletion of ENaC completely blocks only galvanotaxis and does not decrease migration speed. Overexpression of ENaC is sufficient to drive galvanotaxis in otherwise unresponsive cells. Pharmacologic blockade or maintenance of the open state of ENaC also decreases or increases, respectively, galvanotaxis, suggesting that the channel open state is responsible for the response. Stable lamellipodial extensions formed at the cathodal sides of wild-type cells at the start of galvanotaxis; these were absent in the ENaC knockout keratinocytes, suggesting that ENaC mediates galvanotaxis by generating stable lamellipodia that steer cell migration. We provide evidence that ENaC is required for directional migration of keratinocytes in an electric field, supporting a role for ENaC in skin wound healing.
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Affiliation(s)
- Hsin-Ya Yang
- Department of Dermatology, University of California, Davis, CA 95616, USA
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18
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Cleavage of endogenous γENaC and elevated abundance of αENaC are associated with increased Na⁺ transport in response to apical fluid volume expansion in human H441 airway epithelial cells. Pflugers Arch 2011; 462:431-41. [PMID: 21667229 PMCID: PMC3155050 DOI: 10.1007/s00424-011-0982-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2011] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 10/31/2022]
Abstract
Using human H441 airway epithelial cells cultured at air-liquid interface (ALI), we have uniquely correlated the functional response to apical fluid volume expansion with the abundance and cleavage of endogenous α- and γENaC proteins in the apical membrane. Monolayers cultured at ALI rapidly elevated I (sc) when inserted into fluid-filled Ussing chambers. The increase in I (sc) was not significantly augmented by the apical addition of trypsin, and elevation was abolished by the protease inhibitor aprotinin and an inhibitor of the proprotein convertase, furin. These treatments also increased the IC₅₀ amiloride indicating that the effect was via inhibition of highly Na⁺-selective ENaC channels. Apical fluid, 5-500 μl for 1 h in culture, increased the spontaneous starting I (sc) in a dose-dependent manner, whilst maximal fluid-induced I (sc) in the Ussing chamber was unchanged. Apical fluid expansion increased the abundance of 63-65-kDa αENaC proteins in the apical membrane. However, this could not be attributed to increased cleavage as protease inhibitors had no effect on the ratio of cleaved to non-cleaved (90 kDa) αENaC proteins. Instead, fluid expansion increased αENaC abundance in the membrane. In contrast, function correlated well with γENaC cleavage at known sites by furin and extracellular proteases. Interestingly, cleavage of γENaC was associated with increased retrieval from the membrane via the proteosomal pathway. Thus, the response to apical fluid volume expansion in H441 airway epithelial cells involves cleavage of γENaC, and changes in α- and γENaC protein abundance at the apical membrane.
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Dodrill MW, Beezhold DH, Meighan T, Kashon ML, Fedan JS. Lipopolysaccharide increases Na+,K+-pump, but not ENaC, expression in guinea-pig airway epithelium. Eur J Pharmacol 2011; 651:176-86. [DOI: 10.1016/j.ejphar.2010.10.088] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 10/18/2010] [Accepted: 10/31/2010] [Indexed: 10/18/2022]
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20
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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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21
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Han DY, Nie HG, Gu X, Nayak RC, Su XF, Fu J, Chang Y, Rao V, Ji HL. K+ channel openers restore verapamil-inhibited lung fluid resolution and transepithelial ion transport. Respir Res 2010; 11:65. [PMID: 20507598 PMCID: PMC2889873 DOI: 10.1186/1465-9921-11-65] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Accepted: 05/27/2010] [Indexed: 12/19/2022] Open
Abstract
Background Lung epithelial Na+ channels (ENaC) are regulated by cell Ca2+ signal, which may contribute to calcium antagonist-induced noncardiogenic lung edema. Although K+ channel modulators regulate ENaC activity in normal lungs, the therapeutical relevance and the underlying mechanisms have not been completely explored. We hypothesized that K+ channel openers may restore calcium channel blocker-inhibited alveolar fluid clearance (AFC) by up-regulating both apical and basolateral ion transport. Methods Verapamil-induced depression of heterologously expressed human αβγ ENaC in Xenopus oocytes, apical and basolateral ion transport in monolayers of human lung epithelial cells (H441), and in vivo alveolar fluid clearance were measured, respectively, using the two-electrode voltage clamp, Ussing chamber, and BSA protein assays. Ca2+ signal in H441 cells was analyzed using Fluo 4AM. Results The rate of in vivo AFC was reduced significantly (40.6 ± 6.3% of control, P < 0.05, n = 12) in mice intratracheally administrated verapamil. KCa3.1 (1-EBIO) and KATP (minoxidil) channel openers significantly recovered AFC. In addition to short-circuit current (Isc) in intact H441 monolayers, both apical and basolateral Isc levels were reduced by verapamil in permeabilized monolayers. Moreover, verapamil significantly altered Ca2+ signal evoked by ionomycin in H441 cells. Depletion of cytosolic Ca2+ in αβγ ENaC-expressing oocytes completely abolished verapamil-induced inhibition. Intriguingly, KV (pyrithione-Na), K Ca3.1 (1-EBIO), and KATP (minoxidil) channel openers almost completely restored the verapamil-induced decrease in Isc levels by diversely up-regulating apical and basolateral Na+ and K+ transport pathways. Conclusions Our observations demonstrate that K+ channel openers are capable of rescuing reduced vectorial Na+ transport across lung epithelial cells with impaired Ca2+ signal.
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Affiliation(s)
- Dong-Yun Han
- Department of Biochemistry, University of Texas Health Science Center at Tyler, Tyler, TX 75708, USA
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Althaus M, Pichl A, Clauss WG, Seeger W, Fronius M, Morty RE. Nitric oxide inhibits highly selective sodium channels and the Na+/K+-ATPase in H441 cells. Am J Respir Cell Mol Biol 2010; 44:53-65. [PMID: 20139350 DOI: 10.1165/2009-0335oc] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Nitric oxide (NO) is an important regulator of Na(+) reabsorption by pulmonary epithelial cells and therefore of alveolar fluid clearance. The mechanisms by which NO affects epithelial ion transport are poorly understood and vary from model to model. In this study, the effects of NO on sodium reabsorption by H441 cell monolayers were studied in an Ussing chamber. Two NO donors, (Z)-1-[N-(3-aminopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate and diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate, rapidly, reversibly, and dose-dependently reduced amiloride-sensitive, short-circuit currents across H441 cell monolayers. This effect was neutralized by the NO scavenger hemoglobin and was not observed with inactive NO donors. The effects of NO were not blocked by 8-bromoguanosine-3',5'-cyclic monophosphate or by soluble guanylate cyclase inhibitors (methylene blue and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) and were therefore independent of soluble guanylate cyclase signaling. NO targeted apical, highly selective, amiloride-sensitive Na(+) channels in basolaterally permeabilized H441 cell monolayers. NO had no effect on the activity of the human epithelial sodium channel heterologously expressed in Xenopus oocytes. NO decreased Na(+)/K(+)-ATPase activity in apically permeabilized H441 cell monolayers. The inhibition of Na(+)/K(+)-ATPase activity by NO was reversed by mercury and was mimicked by N-ethylmaleimide, which are agents that reverse and mimic, respectively, the reaction of NO with thiol groups. Consistent with these data, S-NO groups were detected on the Na(+)/K(+)-ATPase α subunit in response to NO-donor application, using a biotin-switch approach coupled to a Western blot. These data demonstrate that, in the H441 cell model, NO impairs Na(+) reabsorption by interfering with the activity of highly selective Na(+) channels and the Na(+)/K(+)-ATPase.
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Affiliation(s)
- Mike Althaus
- Department of Internal Medicine (Pulmonology), University of Giessen Lung Center, Justus Liebig University, Giessen, Germany
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23
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Rahman MS, Gandhi S, Otulakowski G, Duan W, Sarangapani A, O'Brodovich H. Long-term terbutaline exposure stimulates alpha1-Na+-K+-ATPase expression at posttranscriptional level in rat fetal distal lung epithelial cells. Am J Physiol Lung Cell Mol Physiol 2009; 298:L96-L104. [PMID: 19880505 DOI: 10.1152/ajplung.00158.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Transepithelial Na(+) transport through epithelial Na(+) channels (ENaC) on the apical membrane and Na(+)-K(+)-ATPase activity on the basolateral membrane of distal lung epithelial cells are critical for alveolar fluid clearance. Acute exposure to beta-adrenergic agonists stimulates lung fluid clearance by increasing Na(+) transport. We investigated the effects of chronic exposure to the beta(2)-adrenergic agonist terbutaline on the transepithelial Na(+) transport in rat fetal distal lung epithelia (FDLE). FDLE monolayers exposed to 10(-4) M terbutaline for 48 h had significantly increased propanolol-blockable transepithelial total and amiloride-sensitive short-circuit current (I(sc)); however, when these chronically exposed monolayers were acutely exposed to additional beta-agonists and intracellular cAMP upregulators, there was no further increase in I(sc). Monolayers exposed to terbutaline for >48 h had I(sc) similar to control cells. Ouabain-sensitive Na(+)-K(+)-ATPase activity was increased in 48-h terbutaline-exposed FDLE whose apical membranes were permeabilized with nystatin. In contrast, terbutaline did not increase amiloride-sensitive apical membrane I(sc) in FDLE whose basolateral membranes were permeabilized with nystatin. Terbutaline treatment did not affect alpha-, beta-, or gamma-ENaC mRNA or alpha-ENaC protein steady-state levels, but increased total cellular levels and rate of synthesis of alpha(1)-Na(+)-K(+)-ATPase protein in FDLE in the absence of any change in alpha(1)-Na(+)-K(+)-ATPase mRNA. Total cellular beta(1)-Na(+)-K(+)-ATPase mRNA and protein levels were not affected by terbutaline. These data suggest that FDLE have different responses from adult type II epithelial cells when chronically exposed to terbutaline, and their increased transepithelial Na(+) transport occurs via a posttranscriptional increase in alpha(1)-Na(+)-K(+)-ATPase expression.
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Affiliation(s)
- Muhammad S Rahman
- Program in Physiology and Experimental Medicine, Hospital for Sick Children Research Institute, 555 Univ. Ave., Toronto, Ontario, Canada M5G 1X8
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Baines DL, Albert AP, Hazell MJ, Gambling L, Woollhead AM, Dockrell MEC. Lipopolysaccharide modifies amiloride-sensitive Na+ transport processes across human airway cells: role of mitogen-activated protein kinases ERK 1/2 and 5. Pflugers Arch 2009; 459:451-63. [PMID: 19823867 PMCID: PMC2810363 DOI: 10.1007/s00424-009-0717-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Accepted: 08/14/2009] [Indexed: 02/08/2023]
Abstract
Bacterial lipopolysaccharides (LPS) are potent inducers of proinflammatory signaling pathways via the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK), causing changes in the processes that control lung fluid homeostasis and contributing to the pathogenesis of lung disease. In human H441 airway epithelial cells, incubation of cells with 15 µg ml−1 LPS caused a significant reduction in amiloride-sensitive Isc from 15 ± 2 to 8 ± 2 µA cm−2 (p = 0.01, n = 13) and a shift in IC50 amiloride of currents from 6.8 × 10−7 to 6.4 × 10−6 M. This effect was associated with a decrease in the activity of 5 pS, highly Na+ selective, amiloride-sensitive <1 µM channels (HSC) and an increase in the activity of ∼18 pS, nonselective, amiloride-sensitive >10 µM cation channels (NSC) in the apical membrane. LPS decreased αENaC mRNA and protein abundance, inferring that LPS inhibited αENaC gene expression. This correlated with the decrease in HSC activity, indicating that these channels, but not NSCs, were comprised of at least αENaC protein. LPS increased NF-κB DNA binding activity and phosphorylation of extracellular signal-related kinase (ERK)1/2, but decreased phosphorylation of ERK5 in H441 cells. Pretreatment of monolayers with PD98059 (20 µM) inhibited ERK1/2 phosphorylation, promoted phosphorylation of ERK5, increased αENaC protein abundance, and reversed the effect of LPS on Isc and the shift in amiloride sensitivity. Inhibitors of NF-κB activation were without effect. Taken together, our data indicate that LPS acts via ERK signaling pathways to decrease αENaC transcription, reducing HSC/ENaC channel abundance, activity, and transepithelial Na+ transport in H441 airway epithelial cells.
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Affiliation(s)
- D L Baines
- St. George's, University of London, Tooting, London SW17 0RE, UK.
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Scharl M, Paul G, Barrett KE, McCole DF. AMP-activated protein kinase mediates the interferon-gamma-induced decrease in intestinal epithelial barrier function. J Biol Chem 2009; 284:27952-27963. [PMID: 19654324 DOI: 10.1074/jbc.m109.046292] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Impaired epithelial barrier function plays a crucial role in the pathogenesis of inflammatory bowel disease. Elevated levels of the pro-inflammatory cytokine, interferon-gamma (IFNgamma), are believed to be prominently involved in the pathogenesis of Crohn disease. Treatment of T(84) intestinal epithelial cells with IFNgamma severely impairs their barrier properties measured as transepithelial electrical resistance (TER) or permeability and reduces the expression of tight junction proteins such as occludin and zonula occludens-1 (ZO-1). However, little is known about the signaling events that are involved. The cellular energy sensor, AMP-activated protein kinase (AMPK), is activated in response to cellular stress, as occurs during inflammation. The aim of this study was to investigate a possible role for AMPK in mediating IFNgamma-induced effects on the intestinal epithelial barrier. We found that IFNgamma activates AMPK by phosphorylation, independent of intracellular energy levels. Inhibition of AMPK prevents, at least in part, the IFNgamma-induced decrease in TER. Furthermore, AMPK knockdown prevented the increased epithelial permeability, the decreased TER, and the decrease in occludin and ZO-1 caused by IFNgamma treatment of T(84) cells. However, AMPK activity alone was not sufficient to cause alterations in epithelial barrier function. These data show a novel role for AMPK, in concert with other signals induced by IFNgamma, in mediating reduced epithelial barrier function in a cell model of chronic intestinal inflammation. These findings may implicate AMPK in the pathogenesis of chronic intestinal inflammatory conditions, such as inflammatory bowel disease.
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Affiliation(s)
- Michael Scharl
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Gisela Paul
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Kim E Barrett
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093
| | - Declan F McCole
- Department of Medicine, University of California, San Diego, School of Medicine, La Jolla, California 92093.
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Kong XB, Ma HG, Li HG, Xiong CL. Blockade of epithelial sodium channels improves sperm motility in asthenospermia patients. ACTA ACUST UNITED AC 2009; 32:330-6. [DOI: 10.1111/j.1365-2605.2008.00864.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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27
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Namkoong S, Kim CK, Cho YL, Kim JH, Lee H, Ha KS, Choe J, Kim PH, Won MH, Kwon YG, Shim EB, Kim YM. Forskolin increases angiogenesis through the coordinated cross-talk of PKA-dependent VEGF expression and Epac-mediated PI3K/Akt/eNOS signaling. Cell Signal 2009; 21:906-15. [PMID: 19385062 DOI: 10.1016/j.cellsig.2009.01.038] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Forskolin, a potent activator of adenylyl cyclases, has been implicated in modulating angiogenesis, but the underlying mechanism has not been clearly elucidated. We investigated the signal mechanism by which forskolin regulates angiogenesis. Forskolin stimulated angiogenesis of human endothelial cells and in vivo neovascularization, which was accompanied by phosphorylation of CREB, ERK, Akt, and endothelial nitric oxide synthase (eNOS) as well as NO production and VEGF expression. Forskolin-induced CREB phosphorylation, VEGF promoter activity, and VEGF expression were blocked by the PKA inhibitor PKI.Moreover, phosphorylation of ERK by forskolin was inhibited by the MEK inhibitor PD98059, but not PKI. The forskolin-induced Akt/eNOS/NO pathway was completely inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, but not significantly suppressed by PKI. These inhibitors and a NOS inhibitor partially inhibited forskolin-induced angiogenesis. The exchange protein directly activated by cAMP (Epac) activator, 8CPT-2Me-cAMP, promoted the Akt/eNOS/NO pathway and ERK phosphorylation,but did not induce CREB phosphorylation and VEGF expression. The angiogenic effect of the Epac activator was diminished by the inhibition of PI3K and MEK, but not by the PKA inhibitor. Small interfering RNA-mediated knockdown of Epac1 suppressed forskolin-induced angiogenesis and phosphorylation of ERK, Akt, and eNOS, but not CREB phosphorylation and VEGF expression. These results suggest that forskolin stimulates angiogenesis through coordinated cross-talk between two distinct pathways, PKA-dependent VEGF expression and Epac-dependent ERKactivation and PI3K/Akt/eNOS/NO signaling.
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Affiliation(s)
- Seung Namkoong
- Vascular System Research Center, School of Medicine, Kangwon National University, Chunchon, Kangwon-do, Republic of Korea
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Bhalla V, Hallows KR. Mechanisms of ENaC regulation and clinical implications. J Am Soc Nephrol 2008; 19:1845-54. [PMID: 18753254 DOI: 10.1681/asn.2008020225] [Citation(s) in RCA: 180] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The epithelial Na+ channel (ENaC) transports Na+ across tight epithelia, including the distal nephron. Different paradigms of ENaC regulation include extrinsic and intrinsic factors that affect the expression, single-channel properties, and intracellular trafficking of the channel. In particular, recent discoveries highlight new findings regarding proteolytic processing, ubiquitination, and recycling of the channel. Understanding the regulation of this channel is critical to the understanding of various clinical phenomena, including normal physiology and several diseases of kidney and lung epithelia, such as blood pressure (BP) control, edema, and airway fluid clearance. Significant progress has been achieved in this active field of research. Although ENaC is classically thought to be a mediator of BP and volume status through Na+ reabsorption in the distal nephron, several studies in animal models highlight important roles for ENaC in lung pathophysiology, including in cystic fibrosis. The purpose of this review is to highlight the various modes and mechanisms of ENaC regulation, with a focus on more recent studies and their clinical implications.
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Affiliation(s)
- Vivek Bhalla
- Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, California, USA
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Albert AP, Woollhead AM, Mace OJ, Baines DL. AICAR decreases the activity of two distinct amiloride-sensitive Na+-permeable channels in H441 human lung epithelial cell monolayers. Am J Physiol Lung Cell Mol Physiol 2008; 295:L837-48. [PMID: 18723760 PMCID: PMC2584878 DOI: 10.1152/ajplung.90353.2008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Transepithelial transport of Na+ across the lung epithelium via amiloride-sensitive Na+ channels (ENaC) regulates fluid volume in the lung lumen. Activators of AMP-activated protein kinase (AMPK), the adenosine monophosphate mimetic AICAR, and the biguanide metformin decreased amiloride-sensitive apical Na+ conductance (GNa+) in human H441 airway epithelial cell monolayers. Cell-attached patch-clamp recordings identified two distinct constitutively active cation channels in the apical membrane that were likely to contribute to GNa+: a 5-pS highly Na+ selective ENaC-like channel (HSC) and an 18-pS nonselective cation channel (NSC). Substituting NaCl with NMDG-Cl in the patch pipette solution shifted the reversal potentials of HSC and NSC, respectively, from +23 mV to −38 mV and 0 mV to −35 mV. Amiloride at 1 μM inhibited HSC activity and 56% of short-circuit current (Isc), whereas 10 μM amiloride partially reduced NSC activity and inhibited a further 30% of Isc. Neither conductance was associated with CNG channels as there was no effect of 10 μM pimoside on Isc, HSC, or NSC activity, and 8-bromo-cGMP (0.3–0.1 mM) did not induce or increase HSC or NSC activity. Pretreatment of H441 monolayers with 2 mM AICAR inhibited HSC/NSC activity by 90%, and this effect was reversed by the AMPK inhibitor Compound C. All three ENaC proteins were identified in the apical membrane of H441 monolayers, but no change in their abundance was detected after treatment with AICAR. In conclusion, activation of AMPK with AICAR in H441 cell monolayers is associated with inhibition of two distinct amiloride-sensitive Na+-permeable channels by a mechanism that likely reduces channel open probability.
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Affiliation(s)
- A P Albert
- Centre for Ion Channels and Cell Signalling, Division of Basic Medical Sciences, St. George's, University of London, London, UK
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30
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Mace OJ, Woollhead AM, Baines DL. AICAR activates AMPK and alters PIP2 association with the epithelial sodium channel ENaC to inhibit Na+ transport in H441 lung epithelial cells. J Physiol 2008; 586:4541-57. [PMID: 18669532 DOI: 10.1113/jphysiol.2008.158253] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Changes in amiloride-sensitive epithelial Na(+) channel (ENaC) activity (NP(o)) in the lung lead to pathologies associated with dysregulation of lung fluid balance. UTP activation of purinergic receptors and hydrolysis of PIP(2) via activation of phospholipase C (PLC) or AICAR activation of AMP-activated protein kinase (AMPK) inhibited amiloride-sensitive Na(+) transport across human H441 epithelial cell monolayers. Neither treatment altered alpha, beta or gamma ENaC subunit abundance (N) in the apical membrane indicating that the mechanism of inhibition was via a change in channel open state probability (P(o)). We found that UTP depleted PIP(2) abundance in the apical membrane whilst activation of AMPK prevented the binding of beta and gamma ENaC subunits to PIP(2.) The association of PIP(2) with the ENaC subunits is required to maintain channel activity via P(o). Thus, these data show for the first time that AICAR activation of AMPK inhibits Na(+) transport via a mechanism that perturbs the PIP(2)-ENaC channel interaction to alter P(o). In addition, we show that dissociation of PIP(2) from ENaC together with activation of AMPK further reduced Na(+) transport by a secondary effect that correlated with ENaC subunit internalization. Thus, when PIP(2)-ENaC subunit interactions were compromised, ENaC protein retrieval was initiated, indicating that AMPK can modulate ENaC P(o) and N.
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Affiliation(s)
- Oliver J Mace
- Division of Basic Medical Sciences, St George's University of London, Cranmer Terrace, London SW17 0RE, UK.
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31
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Greenwood IA, Yeung SYM, Hettiarachi S, Andersson M, Baines DL. KCNQ-encoded channels regulate Na+ transport across H441 lung epithelial cells. Pflugers Arch 2008; 457:785-94. [PMID: 18663467 DOI: 10.1007/s00424-008-0557-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 07/09/2008] [Accepted: 07/09/2008] [Indexed: 12/11/2022]
Abstract
H441 cells are a model of absorptive airway epithelia that are characterised by a pronounced apical Na+ flux through amiloride-sensitive Na+ channels. The flux of Na+ is intimately linked to Na+ handling by the cell as well as the membrane potential across the apical membrane. As KCNQ-encoded K+ channels influence chloride secretion in gastrointestinal epithelia, the goal of the present study was to ascertain the expression of KCNQ genes in H441 cells and determine the functional role of the expression products. Message for KCNQ3 and KCNQ5 was detected by RT-polymerase chain reaction and the translated proteins were observed by immunocytochemistry. Ussing experiments showed that the pan-KCNQ channel blocker XE991, but not KCNQ1 selective blockers, reduced the short circuit current and the amiloride-sensitive component. These data show for the first time that potassium channels encoded by KCNQ3 or KCNQ5 are crucial determinants of epithelial Na+ flux.
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Affiliation(s)
- I A Greenwood
- Division of Basic Medical Sciences, St. George's, University of London, London, SW17 0RE, UK
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Sporty JL, Horálková L, Ehrhardt C. In vitrocell culture models for the assessment of pulmonary drug disposition. Expert Opin Drug Metab Toxicol 2008; 4:333-45. [DOI: 10.1517/17425255.4.4.333] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Kalsi KK, Baker EH, Medina RA, Rice S, Wood DM, Ratoff JC, Philips BJ, Baines DL. Apical and basolateral localisation of GLUT2 transporters in human lung epithelial cells. Pflugers Arch 2008; 456:991-1003. [PMID: 18239936 PMCID: PMC2480509 DOI: 10.1007/s00424-008-0459-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 01/11/2008] [Accepted: 01/15/2008] [Indexed: 12/15/2022]
Abstract
Glucose concentrations of normal human airway surface liquid are ~12.5 times lower than blood glucose concentrations indicating that glucose uptake by epithelial cells may play a role in maintaining lung glucose homeostasis. We have therefore investigated potential glucose uptake mechanisms in non-polarised and polarised H441 human airway epithelial cells and bronchial biopsies. We detected mRNA and protein for glucose transporter type 2 (GLUT2) and glucose transporter type 4 (GLUT4) in non-polarised cells but GLUT4 was not detected in the plasma membrane. In polarised cells, GLUT2 protein was detected in both apical and basolateral membranes. Furthermore, GLUT2 protein was localised to epithelial cells of human bronchial mucosa biopsies. In non-polarised H441 cells, uptake of d-glucose and deoxyglucose was similar. Uptake of both was inhibited by phloretin indicating that glucose uptake was via GLUT-mediated transport. Phloretin-sensitive transport remained the predominant route for glucose uptake across apical and basolateral membranes of polarised cells and was maximal at 5–10 mM glucose. We could not conclusively demonstrate sodium/glucose transporter-mediated transport in non-polarised or polarised cells. Our study provides the first evidence that glucose transport in human airway epithelial cells in vitro and in vivo utilises GLUT2 transporters. We speculate that these transporters could contribute to glucose uptake/homeostasis in the human airway.
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Affiliation(s)
- Kameljit K Kalsi
- Centre for Ion Channel and Cell Signalling, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London, SW17 0RE, UK
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