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Laselva O, Guerra L, Castellani S, Favia M, Di Gioia S, Conese M. Small-molecule drugs for cystic fibrosis: Where are we now? Pulm Pharmacol Ther 2021; 72:102098. [PMID: 34793977 DOI: 10.1016/j.pupt.2021.102098] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2021] [Revised: 10/24/2021] [Accepted: 11/12/2021] [Indexed: 01/05/2023]
Abstract
The cystic fibrosis (CF) lung disease is due to the lack/dysfunction of the CF Transmembrane Conductance Regulator (CFTR), a chloride channel expressed by epithelial cells as the main regulator of ion and fluid homeostasis. More than 2000 genetic variation in the CFTR gene are known, among which those with identified pathomechanism have been divided into six VI mutation classes. A major advancement in the pharmacotherapy of CF has been the development of small-molecule drugs hitting the root of the disease, i.e. the altered ion and fluid transport through the airway epithelium. These drugs, called CFTR modulators, have been advanced to the clinics to treat nearly 90% of CF patients, including the CFTR potentiator ivacaftor, approved for residual function mutations (Classes III and IV), and combinations of correctors (lumacaftor, tezacaftor, elexacaftor) and ivacaftor for patients bearing at least one the F508del mutation, the most frequent mutation belonging to class II. To cover the 10% of CF patients without etiological therapies, other novel small-molecule CFTR modulators are in evaluation of their effectiveness in all the CFTR mutation classes: read-through agents for Class I, correctors, potentiators and amplifiers from different companies for Class II-V, stabilizers for Class VI. In alternative, other solute carriers, such as SLC26A9 and SLC6A14, are the focus of intensive investigation. Finally, other molecular targets are being evaluated for patients with no approved CFTR modulator therapy or as means of enhancing CFTR modulatory therapy, including small molecules forming ion channels, inhibitors of the ENaC sodium channel and potentiators of the calcium-activated chloride channel TMEM16A. This paper aims to give an up-to-date overview of old and novel CFTR modulators as well as of novel strategies based on small-molecule drugs. Further investigations in in-vivo and cell-based models as well as carrying out large prospective studies will be required to determine if novel CFTR modulators, stabilizers, amplifiers, and the ENaC inhibitors or TMEM16A potentiators will further improve the clinical outcomes in CF management.
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Affiliation(s)
- Onofrio Laselva
- Department of Medical and Surgical Sciences, University of Foggia, Foggia, Italy
| | - Lorenzo Guerra
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Stefano Castellani
- Department of Medical Sciences and Human Oncology, University of Bari, Bari, Italy
| | - Maria Favia
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Sante Di Gioia
- Department of Medical and Surgical Sciences, University of Foggia, Foggia, Italy
| | - Massimo Conese
- Department of Medical and Surgical Sciences, University of Foggia, Foggia, Italy.
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2
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Combined agonists act synergistically to increase mucociliary clearance in a cystic fibrosis airway model. Sci Rep 2021; 11:18828. [PMID: 34552115 PMCID: PMC8458446 DOI: 10.1038/s41598-021-98122-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 09/03/2021] [Indexed: 11/30/2022] Open
Abstract
Mucus clearance, a primary innate defense mechanism of airways, is defective in patients with cystic fibrosis (CF) and CF animals. In previous work, the combination of a low dose of the cholinergic agonist, carbachol with forskolin or a β adrenergic agonist, isoproterenol synergistically increased mucociliary clearance velocity (MCCV) in ferret tracheas. Importantly, the present study shows that synergistic MCCV can also be produced in CF ferrets, with increases ~ 55% of WT. Synergistic MCCV was also produced in pigs. The combined agonists increased MCCV by increasing surface fluid via multiple mechanisms: increased fluid secretion from submucosal glands, increased anion secretion across surface epithelia and decreased Na+ absorption. To avoid bronchoconstriction, the cAMP agonist was applied 30 min before carbachol. This approach to increasing mucus clearance warrants testing for safety and efficacy in humans as a potential therapeutic for muco-obstructive diseases.
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Danahay HL, Lilley S, Fox R, Charlton H, Sabater J, Button B, McCarthy C, Collingwood SP, Gosling M. TMEM16A Potentiation: A Novel Therapeutic Approach for the Treatment of Cystic Fibrosis. Am J Respir Crit Care Med 2020; 201:946-954. [PMID: 31898911 PMCID: PMC7159426 DOI: 10.1164/rccm.201908-1641oc] [Citation(s) in RCA: 56] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Rationale: Enhancing non–CFTR (cystic fibrosis transmembrane conductance regulator)-mediated anion secretion is an attractive therapeutic approach for the treatment of cystic fibrosis (CF) and other mucoobstructive diseases. Objectives: To determine the effects of TMEM16A potentiation on epithelial fluid secretion and mucociliary clearance. Methods: The effects of a novel low-molecular-weight TMEM16A potentiator (ETX001) were evaluated in human cell and animal models of airway epithelial function and mucus transport. Measurements and Main Results: Potentiating the activity of TMEM16A with ETX001 increased the Ca2+-activated Cl− channel activity and anion secretion in human bronchial epithelial (HBE) cells from patients with CF without impacting calcium signaling. ETX001 rapidly increased fluid secretion and airway surface liquid height in CF-HBE cells under both static conditions and conditions designed to mimic the shear stress associated with tidal breathing. In ovine models of mucus clearance (tracheal mucus velocity and mucociliary clearance), inhaled ETX001 was able to accelerate clearance both when CFTR function was reduced by administration of a pharmacological blocker and when CFTR was fully functional. Conclusions: Enhancing the activity of TMEM16A increases epithelial fluid secretion and enhances mucus clearance independent of CFTR function. TMEM16A potentiation is a novel approach for the treatment of patients with CF and non-CF mucoobstructive diseases.
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Affiliation(s)
| | - Sarah Lilley
- Sussex Drug Discovery Centre, University of Sussex, Brighton, United Kingdom
| | - Roy Fox
- Sussex Drug Discovery Centre, University of Sussex, Brighton, United Kingdom
| | - Holly Charlton
- Sussex Drug Discovery Centre, University of Sussex, Brighton, United Kingdom
| | - Juan Sabater
- Mount Sinai Medical Center of Florida, Miami, Florida; and
| | - Brian Button
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | | | | | - Martin Gosling
- Enterprise Therapeutics, Brighton, United Kingdom.,Sussex Drug Discovery Centre, University of Sussex, Brighton, United Kingdom
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TMEM16A: An Alternative Approach to Restoring Airway Anion Secretion in Cystic Fibrosis? Int J Mol Sci 2020; 21:ijms21072386. [PMID: 32235608 PMCID: PMC7177896 DOI: 10.3390/ijms21072386] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 03/26/2020] [Accepted: 03/27/2020] [Indexed: 12/18/2022] Open
Abstract
The concept that increasing airway hydration leads to improvements in mucus clearance and lung function in cystic fibrosis has been clinically validated with osmotic agents such as hypertonic saline and more convincingly with cystic fibrosis transmembrane conductance regulator (CFTR) repair therapies. Although rapidly becoming the standard of care in cystic fibrosis (CF), current CFTR modulators do not treat all patients nor do they restore the rate of decline in lung function to normal levels. As such, novel approaches are still required to ensure all with CF have effective therapies. Although CFTR plays a fundamental role in the regulation of fluid secretion across the airway mucosa, there are other ion channels and transporters that represent viable targets for future therapeutics. In this review article we will summarise the current progress with CFTR-independent approaches to restoring mucosal hydration, including epithelial sodium channel (ENaC) blockade and modulators of SLC26A9. A particular emphasis is given to modulation of the airway epithelial calcium-activated chloride channel (CaCC), TMEM16A, as there is controversy regarding whether it should be positively or negatively modulated. This is discussed in light of a recent report describing for the first time bona fide TMEM16A potentiators and their positive effects upon epithelial fluid secretion and mucus clearance.
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Olotu C, Lehmensiek F, Koch B, Kiefmann M, Riegel AK, Hammerschmidt S, Kiefmann R. Streptococcus pneumoniae inhibits purinergic signaling and promotes purinergic receptor P2Y 2 internalization in alveolar epithelial cells. J Biol Chem 2019; 294:12795-12806. [PMID: 31289122 DOI: 10.1074/jbc.ra118.007236] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 06/28/2019] [Indexed: 12/14/2022] Open
Abstract
Bacterial pneumonia is a global health challenge that causes up to 2 million deaths each year. Purinergic signaling plays a pivotal role in healthy alveolar epithelium. Here, we used fluorophore-based analysis and live-cell calcium imaging to address the question of whether the bacterial pathogen Streptococcus pneumoniae directly interferes with purinergic signaling in alveolar epithelial cells. Disturbed purinergic signaling might result in pathophysiologic changes like edema formation and atelectasis, which are commonly seen in bacterial pneumonia. Purine receptors are mainly activated by ATP, mediating a cytosolic calcium response. We found that this purinergic receptor P2Y2-mediated response is suppressed in the presence of S. pneumoniae in A549 and isolated primary alveolar cells in a temperature-dependent manner. Downstream inositol 3-phosphate (IP3) signaling appeared to be unaffected, as calcium signaling via protease-activated receptor 2 remained unaltered. S. pneumoniae-induced suppression of the P2Y2-mediated calcium response depended on the P2Y2 phosphorylation sites Ser-243, Thr-344, and Ser-356, which are involved in receptor desensitization and internalization. Spinning-disk live-cell imaging revealed that S. pneumoniae induces P2Y2 translocation into the cytosol. In conclusion, our results show that S. pneumoniae directly inhibits purinergic signaling by inducing P2Y2 phosphorylation and internalization, resulting in the suppression of the calcium response of alveolar epithelial cells to ATP, thereby affecting cellular integrity and function.
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Affiliation(s)
- Cynthia Olotu
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
| | - Felix Lehmensiek
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
| | - Bastian Koch
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
| | - Martina Kiefmann
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
| | - Ann-Kathrin Riegel
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
| | - Sven Hammerschmidt
- Institute of Genetics and Functional Genomics, Department of Molecular Genetics and Infection Biology, University of Greifswald, Felix-Hausdorff-Strasse 8, 17489 Greifswald, Germany
| | - Rainer Kiefmann
- Center for Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 22051 Hamburg, Germany
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Webster MJ, Tarran R. Slippery When Wet: Airway Surface Liquid Homeostasis and Mucus Hydration. CURRENT TOPICS IN MEMBRANES 2018; 81:293-335. [PMID: 30243435 DOI: 10.1016/bs.ctm.2018.08.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The ability to regulate cell volume is crucial for normal physiology; equally the regulation of extracellular fluid homeostasis is of great importance. Alteration of normal extracellular fluid homeostasis contributes to the development of several diseases including cystic fibrosis. With regard to the airway surface liquid (ASL), which lies apically on top of airway epithelia, ion content, pH, mucin and protein abundance must be tightly regulated. Furthermore, airway epithelia must be able to switch from an absorptive to a secretory state as required. A heterogeneous population of airway epithelial cells regulate ASL solute and solvent composition, and directly secrete large mucin molecules, antimicrobials, proteases and soluble mediators into the airway lumen. This review focuses on how epithelial ion transport influences ASL hydration and ASL pH, with a specific focus on the roles of anion and cation channels and exchangers. The role of ions and pH in mucin expansion is also addressed. With regard to fluid volume regulation, we discuss the roles of nucleotides, adenosine and the short palate lung and nasal epithelial clone 1 (SPLUNC1) as soluble ASL mediators. Together, these mechanisms directly influence ciliary beating and in turn mucociliary clearance to maintain sterility and to detoxify the airways. Whilst all of these components are regulated in normal airways, defective ion transport and/or mucin secretion proves detrimental to lung homeostasis as such we address how defective ion and fluid transport, and a loss of homeostatic mechanisms, contributes to the development of pathophysiologies associated with cystic fibrosis.
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Affiliation(s)
- Megan J Webster
- Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Robert Tarran
- Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States; Department of Cell Biology & Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
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Bertrand CA, Mitra S, Mishra SK, Wang X, Zhao Y, Pilewski JM, Madden DR, Frizzell RA. The CFTR trafficking mutation F508del inhibits the constitutive activity of SLC26A9. Am J Physiol Lung Cell Mol Physiol 2017; 312:L912-L925. [PMID: 28360110 PMCID: PMC5495941 DOI: 10.1152/ajplung.00178.2016] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 03/22/2017] [Accepted: 03/22/2017] [Indexed: 11/22/2022] Open
Abstract
Several members of the SLC26A family of anion transporters associate with CFTR, forming complexes in which CFTR and SLC26A functions are reciprocally regulated. These associations are thought to be facilitated by PDZ scaffolding interactions. CFTR has been shown to be positively regulated by NHERF-1, and negatively regulated by CAL in airway epithelia. However, it is unclear which PDZ-domain protein(s) interact with SLC26A9, a SLC26A family member found in airway epithelia. We have previously shown that primary, human bronchial epithelia (HBE) from non-CF donors exhibit constitutive anion secretion attributable to SLC26A9. However, constitutive anion secretion is absent in HBE from CF donors. We examined whether changes in SLC26A9 constitutive activity could be attributed to a loss of CFTR trafficking, and what role PDZ interactions played. HEK293 coexpressing SLC26A9 with the trafficking mutant F508del CFTR exhibited a significant reduction in constitutive current compared with cells coexpressing SLC26A9 and wt CFTR. We found that SLC26A9 exhibits complex glycosylation when coexpressed with F508del CFTR, but its expression at the plasma membrane is decreased. SLC26A9 interacted with both NHERF-1 and CAL, and its interaction with both significantly increased with coexpression of wt CFTR. However, coexpression with F508del CFTR only increased SLC26A9's interaction with CAL. Mutation of SLC26A9's PDZ motif decreased this association with CAL, and restored its constitutive activity. Correcting aberrant F508del CFTR trafficking in CF HBE with corrector VX-809 also restored SLC26A9 activity. We conclude that when SLC26A9 is coexpressed with F508del CFTR, its trafficking defect leads to a PDZ motif-sensitive intracellular retention of SLC26A9.
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Affiliation(s)
- Carol A Bertrand
- Departments of Pediatrics and Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania;
| | - Shalini Mitra
- Departments of Pediatrics and Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Sanjay K Mishra
- Departments of Pediatrics and Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Xiaohui Wang
- Departments of Pediatrics and Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Yu Zhao
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
| | - Joseph M Pilewski
- Department of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Dean R Madden
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
| | - Raymond A Frizzell
- Departments of Pediatrics and Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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8
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Abstract
Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.
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Affiliation(s)
- Jonathan H Widdicombe
- Department of Physiology and Membrane Biology, University of California-Davis, Davis, California; and Department of Psychology and Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California
| | - Jeffrey J Wine
- Department of Physiology and Membrane Biology, University of California-Davis, Davis, California; and Department of Psychology and Cystic Fibrosis Research Laboratory, Stanford University, Stanford, California
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Higgins G, Buchanan P, Perriere M, Al-Alawi M, Costello RW, Verriere V, McNally P, Harvey BJ, Urbach V. Activation of P2RY11 and ATP release by lipoxin A4 restores the airway surface liquid layer and epithelial repair in cystic fibrosis. Am J Respir Cell Mol Biol 2014; 51:178-90. [PMID: 24588705 DOI: 10.1165/rcmb.2012-0424oc] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In cystic fibrosis (CF), the airway surface liquid (ASL) height is reduced as a result of impaired ion transport, which favors bacterial colonization and inflammation of the airway and leads to progressive lung destruction. Lipoxin (LX)A4, which promotes resolution of inflammation, is inadequately produced in the airways of patients with CF. We previously demonstrated that LXA4 stimulates an ASL height increase and epithelial repair. Here we report the molecular mechanisms involved in these processes. We found that LXA4 (1 nM) induced an apical ATP release from non-CF (NuLi-1) and CF (CuFi-1) airway epithelial cell lines and CF primary cultures. The ATP release induced by LXA4 was completely inhibited by antagonists of the ALX/FPR2 receptor and Pannexin-1 channels. LXA4 induced an increase in intracellular cAMP and calcium, which were abolished by the selective inhibition of the P2RY11 purinoreceptor. Pannexin-1 and ATP hydrolysis inhibition and P2RY11 purinoreceptor knockdown all abolished the increase of ASL height induced by LXA4. Inhibition of the A2b adenosine receptor did not affect the ASL height increase induced by LXA4, whereas the PKA inhibitor partially inhibited this response. The stimulation of NuLi-1 and CuFi-1 cell proliferation, migration, and wound repair by LXA4 was inhibited by the antagonists of Pannexin-1 channel and P2RY11 purinoreceptor. Taken together, our results provide evidence for a novel role of LXA4 in stimulating apical ATP secretion via Pannexin-1 channels and P2RY11 purinoreceptors activation leading to an ASL height increase and epithelial repair.
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Souza-Menezes J, da Silva Feltran G, Morales MM. CFTR and TNR-CFTR expression and function in the kidney. Biophys Rev 2014; 6:227-236. [PMID: 28510183 PMCID: PMC5425698 DOI: 10.1007/s12551-014-0140-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 03/04/2014] [Indexed: 10/25/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is abundantly expressed in the kidney. CFTR mRNA is detected in all nephron segments of rats and humans and its expression is higher in the renal cortex and outer medulla than in the inner medulla. CFTR protein is detected at the apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. The localization of CFTR in the proximal tubules is compatible with that of endosomes, suggesting that CFTR might regulate pH in endocytic vesicles by equilibrating H+ accumulation due to H+-ATPase activity. Many studies have also demonstrated that CFTR also regulates channel pore opening and the transport of sodium, chloride and potassium. The kidneys also express a CFTR splicing variant, called TNR-CFTR, in a tissue-specific manner, primarily in the renal medulla. This splicing variant conserves the functional characteristics of wild-type CFTR. The functional significance of TNR-CFTR remains to be elucidated, but our group proposes that TNR-CFTR may have a basic function in intracellular organelles, rather than in the plasma membrane. Also, this splicing variant is able to partially substitute CFTR functions in the renal medulla of Cftr-/- mice and CF patients. In this review we discuss the major functions that have been proposed for CFTR and TNR-CFTR in the kidney.
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Affiliation(s)
- Jackson Souza-Menezes
- Laboratório Integrado de Ciências Morfofuncionais, Núcleo em Ecologia e Desenvolvimento Sócio-Ambiental, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Av. São José do Barreto, 764, Barreto, Macaé, 27965-045 RJ Brazil
- Laboratório de Fisiologia Celular e Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902 Brazil
| | - Geórgia da Silva Feltran
- Laboratório Integrado de Ciências Morfofuncionais, Núcleo em Ecologia e Desenvolvimento Sócio-Ambiental, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Av. São José do Barreto, 764, Barreto, Macaé, 27965-045 RJ Brazil
| | - Marcelo M. Morales
- Laboratório de Fisiologia Celular e Molecular, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902 Brazil
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Locke LW, Myerburg MM, Markovetz MR, Parker RS, Weber L, Czachowski MR, Harding TJ, Brown SL, Nero JA, Pilewski JM, Corcoran TE. Quantitative imaging of airway liquid absorption in cystic fibrosis. Eur Respir J 2014; 44:675-84. [PMID: 24743971 DOI: 10.1183/09031936.00220513] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
New measures are needed to rapidly assess emerging treatments for cystic fibrosis (CF) lung disease. Using an imaging approach, we evaluated the absorptive clearance of the radiolabeled small molecule probe diethylene triamine penta-acetic acid (DTPA) as an in vivo indicator of changes in airway liquid absorption. DTPA absorption and mucociliary clearance rates were measured in 21 patients with CF (12 adults and nine children) and nine adult controls using nuclear imaging. The effect of hypertonic saline on DTPA absorption was also studied. In addition, in vitro studies were conducted to identify the determinants of transepithelial DTPA absorption. CF patients had significantly increased rates of DTPA absorption compared with control subjects but had similar mucociliary clearance rates. Treatment with hypertonic saline resulted in a decrease in DTPA absorption and an increase in mucociliary clearance in 11 out of 11 adult CF patients compared with treatment with isotonic saline. In vitro studies revealed that ∼ 50% of DTPA absorption can be attributed to transepithelial fluid transport. Apically applied mucus impedes liquid and DTPA absorption. However, mucus effects become negligible in the presence of an osmotic stimulus. Functional imaging of DTPA absorption provides a quantifiable marker of immediate response to treatments that promote airway surface liquid hydration.
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Affiliation(s)
- Landon W Locke
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Michael M Myerburg
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | | | - Robert S Parker
- Dept of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Lawrence Weber
- Dept of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Michael R Czachowski
- Dept of Radiology, Children's Hospital of Pittsburgh, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Thomas J Harding
- Dept of Radiology, Children's Hospital of Pittsburgh, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Stefanie L Brown
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Joseph A Nero
- Dept of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Joseph M Pilewski
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA Dept of Cell Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Timothy E Corcoran
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA
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Corcoran TE, Thomas KM, Brown S, Myerburg MM, Locke LW, Pilewski JM. Liquid hyper-absorption as a cause of increased DTPA clearance in the cystic fibrosis airway. EJNMMI Res 2013; 3:14. [PMID: 23446051 PMCID: PMC3600668 DOI: 10.1186/2191-219x-3-14] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Accepted: 02/15/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Airway liquid hyper-absorption is a key pathophysiological link between the genetic mutations of cystic fibrosis (CF) and the development of lung disease. Here we consider whether the clearance of radiolabeled diethylene triamine pentaacetic acid (DTPA) might be used to detect changes in airway liquid absorption. METHODS Tc99m-DTPA was added to the apical (luminal) surface of primary human bronchial epithelial cell cultures from CF and non-CF lungs. Liquid absorption rates were assessed using an optical method and compared to DTPA absorption rates. Measurements of transepithelial electrical resistance (TER) were made to determine the effect of epithelial permeability. DTPA absorption was assessed after stimuli known to influence liquid absorption (volume addition and osmotic gradients) and in cultures containing different proportions of CF and non-CF cells. RESULTS DTPA absorption rate was increased in CF cultures matching previous in vivo studies in individuals with CF. DTPA and liquid absorption rates were proportional. There was no relationship between TER and DTPA absorption rate when measured in individual cultures. Apical volume addition increased both DTPA and liquid absorption rates. DTPA absorption increased in a dose-dependent manner after basolateral mannitol addition was used to create transepithelial osmotic gradients favoring liquid absorption. Conversely, apical mannitol (a candidate therapy) slowed DTPA absorption in CF cultures. CONCLUSIONS These results imply that DTPA absorption is directly related to liquid absorption, consistent with increased rates of airway surface liquid absorption in the CF airway, and that modification of liquid absorption from osmotic therapies might be detectable through DTPA absorption measurements in vivo. TRIAL REGISTRATION none.
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Affiliation(s)
- Timothy E Corcoran
- Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, UPMC MUH NW628, 3459 Fifth Ave, Pittsburgh, PA 15213, USA.
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13
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Balut CM, Hamilton KL, Devor DC. Trafficking of intermediate (KCa3.1) and small (KCa2.x) conductance, Ca(2+)-activated K(+) channels: a novel target for medicinal chemistry efforts? ChemMedChem 2012; 7:1741-55. [PMID: 22887933 DOI: 10.1002/cmdc.201200226] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Revised: 07/09/2012] [Indexed: 12/22/2022]
Abstract
Ca(2+)-activated K(+) (KCa) channels play a pivotal role in the physiology of a wide variety of tissues and disease states, including vascular endothelia, secretory epithelia, certain cancers, red blood cells (RBC), neurons, and immune cells. Such widespread involvement has generated an intense interest in elucidating the function and regulation of these channels, with the goal of developing pharmacological strategies aimed at selective modulation of KCa channels in various disease states. Herein we give an overview of the molecular and functional properties of these channels and their therapeutic importance. We discuss the achievements made in designing pharmacological tools that control the function of KCa channels by modulating their gating properties. Moreover, this review discusses the recent advances in our understanding of KCa channel assembly and anterograde trafficking toward the plasma membrane, the micro-domains in which these channels are expressed within the cell, and finally the retrograde trafficking routes these channels take following endocytosis. As the regulation of intracellular trafficking by agonists as well as the protein-protein interactions that modify these events continue to be explored, we anticipate this will open new therapeutic avenues for the targeting of these channels based on the pharmacological modulation of KCa channel density at the plasma membrane.
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Affiliation(s)
- Corina M Balut
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA 15261, USA
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14
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Cystic fibrosis: insight into CFTR pathophysiology and pharmacotherapy. Clin Biochem 2012; 45:1132-44. [PMID: 22698459 DOI: 10.1016/j.clinbiochem.2012.05.034] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2012] [Revised: 05/15/2012] [Accepted: 05/28/2012] [Indexed: 12/14/2022]
Abstract
Cystic fibrosis is the most common life-threatening recessively inherited disease in Caucasians. Due to early provision of care in specialized reference centers and more comprehensive care, survival has improved over time. Despite great advances in supportive care and in our understanding of its pathophysiology, there is still no cure for the disease. Therapeutic strategies aimed at rescuing the abnormal protein are either being sought after or under investigation. This review highlights salient insights into pathophysiology and candidate molecules suitable for CFTR pharmacotherapy. Clinical trials using Ataluren, VX-809 and ivacaftor have provided encouraging data. Preclinical data with inhibitors of phosphodiesterase type 5, such as sildenafil and analogs, have highlighted their potential for CFTR pharmacotherapy. Because sildenafil and analogs are in clinical use for other clinical applications, research on this class of drugs might speed up the development of new therapies for CF.
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15
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Yoo JC, Kim HY, Han KH, Oh SH, Chang SO, Marcus DC, Lee JH. Na+ absorption by Claudius' cells is regulated by purinergic signaling in the cochlea. Acta Otolaryngol 2012; 132 Suppl 1:S103-8. [PMID: 22582771 DOI: 10.3109/00016489.2012.664285] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
CONCLUSION Claudius' cells absorb Na(+) through the amiloride-sensitive epithelial sodium channel (ENaC). Transepithelial ion transport through ENaC and possibly a Cl(-) secretory pathway is regulated by P2Y purinergic signaling. OBJECTIVES The purpose of this study was to investigate ion transport in Claudius' cells and its purinergic regulation. METHODS Young adult Sprague-Dawley rats and gerbils were studied. The Claudius' cell layer on the basilar membrane was dissected from the basal turn of the cochlea. A voltage-sensitive vibrating probe was used to measure transepithelial short circuit current (I(sc) ). The baseline I(sc) of Claudius' cells was measured in the perilymph-like control solution and the change of I(sc) after application of amiloride (10 μM) or uridine triphosphate (UTP, 100 μM). RESULTS A negative baseline I(sc) was observed in the control solution (-12.50 ± 3.95 μA/cm(2), n = 8) and the addition of amiloride resulted in a decrease of I(sc) by 75.8%. The application of UTP, an agonist for P2Y purinergic receptors, led to a partial inhibition of I(sc) (by 38.2 ± 3.2%, n = 5), and subsequent addition of amiloride abolished the remaining I(sc).
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Affiliation(s)
- Jae Chul Yoo
- Department of Otorhinolaryngology, National Medical Center, Seoul, Korea
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16
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Öhman J, Erlinge D. The touching story of purinergic signaling in epithelial and endothelial cells. Purinergic Signal 2012; 8:599-608. [PMID: 22528685 DOI: 10.1007/s11302-012-9316-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 01/20/2012] [Indexed: 11/26/2022] Open
Affiliation(s)
- Jenny Öhman
- Faculty of Medicine, Lund University, Box 117, 221 00, Lund, Sweden.
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17
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Abstract
Cystic fibrosis (CF) is a lethal, recessive, genetic disease affecting approximately 1 in 2500 live births among Caucasians. The CF gene codes for a cAMP/PKA-dependent, ATP-requiring, membrane chloride ion channel, generally found in the apical membranes of many secreting epithelia and known as CFTR (cystic fibrosis transmembrane conductance regulator). There are currently over 1700 known mutations affecting CFTR, many of which give rise to a disease phenotype. Around 75% of CF alleles contain the ΔF508 mutation in which a triplet codon has been lost, leading to a missing phenylalanine at position 508 in the protein. This altered protein fails to be trafficked to the correct location in the cell and is generally destroyed by the proteasome. The small amount that does reach the correct location functions poorly. Clearly the cohort of patients with at least one ΔF508 allele are a major target for therapeutic intervention. It is now over two decades since the CF gene was discovered and during this time the properties of CFTR have been intensely investigated. At long last there appears to be progress with the pharmaco-therapeutic approach. Ongoing clinical trials have produced fascinating results in which clinical benefit appears to have been achieved. To arrive at this point ingenious ways have been devised to screen very large chemical libraries for one of two properties: (i) agents promoting trafficking of mutant CFTR to, and insertion into the membrane, and known as correctors or (ii) agents which activate appropriately located mutant CFTR, known as potentiators. The best compounds emerging from these programmes are then used as chemical scaffolds to synthesize other compounds with appropriate pharmaceutical properties, hopefully with their pharmacological activity maintained or even enhanced. In summary, this approach attempts to make the mutant CFTR function in place of the real CFTR. A major function of CFTR in healthy airways is to maintain an adequate airway surface liquid (ASL) layer. In CF the position is further confounded since epithelial sodium channels (ENaC) are no longer regulated and transport salt and water out of the airways to exacerbate the lack of ASL. Thus an additional possibility for treatment of CF is to use agents that inhibit ENaC either alone or as adjuncts to CFTR correctors and/or potentiators. Yet a further way in which a pharmacological approach to CF can be considered is to recruit alternative chloride channels, such as calcium-activated chloride channel (CaCC), to act as surrogates for CFTR. A number of P2Y(2) receptor agonists have been investigated that operate by increasing Ca(2+)(i) which in turn activates CaCC. Some of these compounds are currently in clinical trials. The knowledge base surrounding the structure and function of CFTR that has accumulated in the last 20 years is impressive. Translational research feeding from this is now yielding compounds that provide real prospects for a pharmacotherapy for this disease.
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Affiliation(s)
- A W Cuthbert
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, UK.
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18
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Novak I. Purinergic signalling in epithelial ion transport: regulation of secretion and absorption. Acta Physiol (Oxf) 2011; 202:501-22. [PMID: 21073662 DOI: 10.1111/j.1748-1716.2010.02225.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular ATP, the energy source for many reactions, is crucial for the activity of plasma membrane pumps and, thus, for the maintenance of transmembrane ion gradients. Nevertheless, ATP and other nucleotides/nucleosides are also extracellular molecules that regulate diverse cellular functions, including ion transport. In this review, I will first introduce the main components of the extracellular ATP signalling, which have become known as the purinergic signalling system. With more than 50 components or processes, just at cell membranes, it ranks as one of the most versatile signalling systems. This multitude of system components may enable differentiated regulation of diverse epithelial functions. As epithelia probably face the widest variety of potential ATP-releasing stimuli, a special attention will be given to stimuli and mechanisms of ATP release with a focus on exocytosis. Subsequently, I will consider membrane transport of major ions (Cl(-) , HCO(3)(-) , K(+) and Na(+) ) and integrate possible regulatory functions of P2Y2, P2Y4, P2Y6, P2Y11, P2X4, P2X7 and adenosine receptors in some selected epithelia at the cellular level. Some purinergic receptors have noteworthy roles. For example, many studies to date indicate that the P2Y2 receptor is one common denominator in regulating ion channels on both the luminal and basolateral membranes of both secretory and absorptive epithelia. In exocrine glands though, P2X4 and P2X7 receptors act as cation channels and, possibly, as co-regulators of secretion. On an organ level, both receptor types can exert physiological functions and together with other partners in the purinergic signalling, integrated models for epithelial secretion and absorption are emerging.
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Affiliation(s)
- I Novak
- Department of Biology, August Krogh Building, University of Copenhagen, Denmark.
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19
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Seminario-Vidal L, Okada SF, Sesma JI, Kreda SM, van Heusden CA, Zhu Y, Jones LC, O'Neal WK, Penuela S, Laird DW, Boucher RC, Lazarowski ER. Rho signaling regulates pannexin 1-mediated ATP release from airway epithelia. J Biol Chem 2011; 286:26277-86. [PMID: 21606493 DOI: 10.1074/jbc.m111.260562] [Citation(s) in RCA: 171] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP released from airway epithelial cells promotes purinergic receptor-regulated mucociliary clearance activities necessary for innate lung defense. Cell swelling-induced membrane stretch/strain is a common stimulus that promotes airway epithelial ATP release, but the mechanisms transducing cell swelling into ATP release are incompletely understood. Using knockdown and knockout approaches, we tested the hypothesis that pannexin 1 mediates ATP release from hypotonically swollen airway epithelia and investigated mechanisms regulating this activity. Well differentiated primary cultures of human bronchial epithelial cells subjected to hypotonic challenge exhibited enhanced ATP release, which was paralleled by the uptake of the pannexin probe propidium iodide. Both responses were reduced by pannexin 1 inhibitors and by knocking down pannexin 1. Importantly, hypotonicity-evoked ATP release from freshly excised tracheas and dye uptake in primary tracheal epithelial cells were impaired in pannexin 1 knockout mice. Hypotonicity-promoted ATP release and dye uptake in primary well differentiated human bronchial epithelial cells was accompanied by RhoA activation and myosin light chain phosphorylation and was reduced by the RhoA dominant negative mutant RhoA(T19N) and Rho and myosin light chain kinase inhibitors. ATP release and Rho activation were reduced by highly selective inhibitors of transient receptor potential vanilloid 4 (TRPV4). Lastly, knocking down TRPV4 impaired hypotonicity-evoked airway epithelial ATP release. Our data suggest that TRPV4 and Rho transduce cell membrane stretch/strain into pannexin 1-mediated ATP release in airway epithelia.
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Affiliation(s)
- Lucia Seminario-Vidal
- Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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20
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Harvey PR, Tarran R, Garoff S, Myerburg MM. Measurement of the airway surface liquid volume with simple light refraction microscopy. Am J Respir Cell Mol Biol 2011; 45:592-9. [PMID: 21239602 DOI: 10.1165/rcmb.2010-0484oc] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In the cystic fibrosis (CF) lung, the airway surface liquid (ASL) volume is depleted, impairing mucus clearance from the lung and leading to chronic airway infection and obstruction. Several therapeutics have been developed that aim to restore normal airway surface hydration to the CF airway, yet preclinical evaluation of these agents is hindered by the paucity of methods available to directly measure the ASL. Therefore, we sought to develop a straightforward approach to measure the ASL volume that would serve as the basis for a standardized method to assess mucosal hydration using readily available resources. Primary human bronchial epithelial (HBE) cells cultured at an air-liquid interface develop a liquid meniscus at the edge of the culture. We hypothesized that the size of the fluid meniscus is determined by the ASL volume, and could be measured as an index of the epithelial surface hydration status. A simple method was developed to measure the volume of fluid present in meniscus by imaging the refraction of light at the ASL interface with the culture wall using low-magnification microscopy. Using this method, we found that primary CF HBE cells had a reduced ASL volume compared with non-CF HBE cells, and that known modulators of ASL volume caused the predicted responses. Thus, we have demonstrated that this method can detect physiologically relevant changes in the ASL volume, and propose that this novel approach may be used to rapidly assess the effects of airway hydration therapies in high-throughput screening assays.
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Affiliation(s)
- Peter R Harvey
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
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21
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Lazarowski ER, Sesma JI, Seminario L, Esther CR, Kreda SM. Nucleotide release by airway epithelia. Subcell Biochem 2011; 55:1-15. [PMID: 21560042 DOI: 10.1007/978-94-007-1217-1_1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The purinergic events regulating the airways' innate defenses are initiated by the release of purines from the epithelium, which occurs constitutively and is enhanced by chemical or mechanical stimulation. While the external triggers have been reviewed exhaustively, this chapter focuses on current knowledge of the receptors and signaling cascades mediating nucleotide release. The list of secreted purines now includes ATP, ADP, AMP and nucleotide sugars, and involves at least three distinct mechanisms reflecting the complexity of airway epithelia. First, the constitutive mechanism involves ATP translocation to the ER/Golgi complex as energy source for protein folding, and fusion of Golgi-derived vesicles with the plasma membrane. Second, goblet cells package ATP with mucins into granules, which are discharged in response to P2Y(2)R activation and Ca(2+)-dependent signaling pathways. Finally, non-mucous cells support a regulated mechanism of ATP release involving protease activated receptor (PAR)-elicited G(12/13) activation, leading to the RhoGEF-mediated exchange of GDP for GTP on RhoA, and cytoskeleton rearrangement. Together, these pathways provide fine tuning of epithelial responses regulated by purinergic signaling events.
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Affiliation(s)
- Eduardo R Lazarowski
- Cystic Fibrosis Pulmonary Research and Treatment Center, University of North Carolina, 7011 Thurston-Bowles building, Chapel Hill, NC, 27599, USA,
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22
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Passero CJ, Carattino MD, Kashlan OB, Myerburg MM, Hughey RP, Kleyman TR. Defining an inhibitory domain in the gamma subunit of the epithelial sodium channel. Am J Physiol Renal Physiol 2010; 299:F854-61. [PMID: 20630937 DOI: 10.1152/ajprenal.00316.2010] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proteases activate the epithelial sodium channel (ENaC) by cleaving the large extracellular domains of the α- and γ-subunits and releasing peptides with inhibitory properties. Furin and prostasin activate mouse ENaC by cleaving the γ-subunit at sites flanking a 43 residue inhibitory tract (γE144-K186). To determine whether there is a minimal inhibitory region within this 43 residue tract, we generated serial deletions in the inhibitory tract of the γ-subunit in channels resistant to cleavage by furin and prostasin. We found that partial or complete deletion of a short segment in the γ-subunit, R158-N171, enhanced channel activity. Synthetic peptides overlapping this segment in the γ-subunit further identified a key 11-mer tract, R158-F168 (RFLNLIPLLVF), which inhibited wild-type ENaC expressed in Xenopus laevis oocytes, and endogenous channels in mpkCCD cells and human airway epithelia. Further studies with amino acid-substituted peptides defined residues that are required for inhibition in this key 11-mer tract. The presence of the native γ inhibitory tract in ENaC weakened the intrinsic binding constant of the 11-mer peptide inhibitor, suggesting that the γ inhibitory tract and the 11-mer peptide interact at overlapping sites within the channel.
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Affiliation(s)
- Christopher J Passero
- Renal Electrolyte Div., Dept. of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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23
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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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24
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Abstract
The epithelial cells of Reissner's membrane (RM) are capable of transporting Na(+) out of endolymph via epithelial Na(+) channel (ENaC). However, much remains to be known as to mechanism of regulation of Na(+) absorption in RM. We investigated P2Y signaling as a possible regulatory mechanism of ENaC in gerbil RM using voltage-sensitive vibrating probe technique and immunohistochemistry. Results showed that UTP induced partial inhibition of the amiloride-sensitive short-circuit current but did not change short-circuit current when applied in the presence of amiloride. The inhibitory effect of UTP was not completely reversible in minutes. The response to UTP was inhibited by reactive blue-2 and 2',3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate but not by suramin or pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid, which indicates this P2Y receptor as the P2Y(4) subtype. The phospholipase C (PLC) inhibitors 1-[6[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine markedly inhibited the effect of UTP on ENaC. In contrast, neither modulation of protein kinase C nor application of 2-aminoehoxydiphenyl borate affected P2Y(4)-mediated inhibition of ENaC. Immunoreactive staining for P2Y(4) was observed in the RM, apical membrane of stria vascularis, spiral ligament, and organ of Corti, including outer hair cell, inner hair cell, outer pillar cell, Deiters' cell, and Hensen cell. These results suggest that the physiological role of P2Y(4) receptor in RM is likely to regulate Na(+) homeostasis in the endolymph. The acute inhibition of ENaC activity by activation of P2Y(4) receptor is possibly mediated by decrease of phosphatidylinositol 4,5-biphosphate in the plasma membrane through PLC activation.
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25
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Myerburg MM, Harvey PR, Heidrich EM, Pilewski JM, Butterworth MB. Acute regulation of the epithelial sodium channel in airway epithelia by proteases and trafficking. Am J Respir Cell Mol Biol 2010; 43:712-9. [PMID: 20097829 DOI: 10.1165/rcmb.2009-0348oc] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Effective clearance of inhaled pathogens is the primary innate defense mechanism in the lung, and requires the maintenance of a proper airway surface liquid (ASL) volume to facilitate ciliary beat and optimize mucociliary clearance. Na(+) absorption via the epithelial sodium channel (ENaC) is tightly regulated and, together with chloride movement, provides the optimal osmotic gradients to absorb excessive fluid in the airway lumen while preventing excessive ASL dehydration, which would compromise mucus clearance from the lung. To absorb excessive fluid from the luminal surface, a local mechanism of ENaC activation allows for an increase in Na(+) absorption at times when the ASL volume is expanded. To help define these regulatory mechanisms, we examined the effects of ASL volume expansion on ENaC activity in primary human bronchial epithelial (HBE) cell cultures. We found that ENaC activity increases dramatically after rapid dilution of endogenous ASL. Approximately 35% of the increase in Na(+) absorption was attributable to activation of ENaC by proteases. The remainder of the increase in Na(+) current was prevented when membrane trafficking was disrupted with brefeldin A, nocodazole, or myosin light chain kinase inhibitors, demonstrating that trafficking is involved with ENaC regulation in the airway. These findings demonstrate that Na(+) absorption in the airway is acutely modulated by the coordinated trafficking of channels to the luminal surface and by the proteolytic activation of ENaC in response to ASL volume expansion.
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Affiliation(s)
- Michael M Myerburg
- Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh Medical Center, Montefiore University Hospital, 3459 Fifth Ave., Pittsburgh, PA 15213, USA.
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26
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Wildman SS, Kang ESK, King BF. ENaC, renal sodium excretion and extracellular ATP. Purinergic Signal 2009; 5:481-9. [PMID: 19306075 PMCID: PMC2776138 DOI: 10.1007/s11302-009-9150-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2007] [Accepted: 03/15/2008] [Indexed: 11/30/2022] Open
Abstract
Sodium balance determines the extracellular fluid volume and sets arterial blood pressure (BP). Chronically raised BP (hypertension) represents a major health risk in Western societies. The relationship between BP and renal sodium excretion (the pressure/natriuresis relationship) represents the key element in defining the BP homeostatic set point. The renin-angiotensin-aldosterone system (RAAS) makes major adjustments to the rates of renal sodium secretion, but this system works slowly over a period of hours to days. More rapid adjustments can be made by the sympathetic nervous system, although the kidney can function well without sympathetic nerves. Attention has now focussed on regulatory mechanisms within the kidney, including extracellular nucleotides and the P2 receptor system. Here, we discuss how extracellular ATP can control renal sodium excretion by altering the activity of epithelial sodium channels (ENaC) present in the apical membrane of principal cells. There remains considerable controversy over the molecular targets for released ATP, although the P2Y(2) receptor has received much attention. We review the available data and reflect on our own findings in which ATP-activated P2Y and P2X receptors make adjustments to ENaC activity and therefore sodium excretion.
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Affiliation(s)
- Scott Sp Wildman
- Department of Veterinary Basic Sciences, Royal Veterinary College, Royal College Street, London, NW1 0TU, UK,
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27
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Savitski AN, Mesaros C, Blair IA, Cohen NA, Kreindler JL. Secondhand smoke inhibits both Cl- and K+ conductances in normal human bronchial epithelial cells. Respir Res 2009; 10:120. [PMID: 19943936 PMCID: PMC2792224 DOI: 10.1186/1465-9921-10-120] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Accepted: 11/27/2009] [Indexed: 11/21/2022] Open
Abstract
Secondhand smoke (SHS) exposure is an independent risk factor for asthma, rhinosinusitis, and more severe respiratory tract infections in children and adults. Impaired mucociliary clearance with subsequent mucus retention contributes to the pathophysiology of each of these diseases, suggesting that altered epithelial salt and water transport may play an etiological role. To test the hypothesis that SHS would alter epithelial ion transport, we designed a system for in vitro exposure of mature, well-differentiated human bronchial epithelial cells to SHS. We show that SHS exposure inhibits cAMP-stimulated, bumetanide-sensitive anion secretion by 25 to 40% in a time-dependent fashion in these cells. Increasing the amount of carbon monoxide to 100 ppm from 5 ppm did not increase the amount of inhibition, and filtering SHS reduced inhibition significantly. It was determined that SHS inhibited cAMP-dependent apical membrane chloride conductance by 25% and Ba2+-sensitive basolateral membrane potassium conductance by 50%. These data confirm previous findings that cigarette smoke inhibits chloride secretion in a novel model of smoke exposure designed to mimic SHS exposure. They also extend previous findings to demonstrate an effect on basolateral K+ conductance. Therefore, pharmacological agents that increase either apical membrane chloride conductance or basolateral membrane potassium conductance might be of therapeutic benefit in patients with diseases related to SHS exposure.
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Affiliation(s)
- Amy N Savitski
- Division of Pulmonary Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
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28
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Kreindler JL. Cystic fibrosis: exploiting its genetic basis in the hunt for new therapies. Pharmacol Ther 2009; 125:219-29. [PMID: 19903491 DOI: 10.1016/j.pharmthera.2009.10.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 10/16/2009] [Indexed: 01/11/2023]
Abstract
Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel expressed in epithelial cells throughout the body. In the lungs, absence or dysfunction of CFTR results in altered epithelial salt and water transport eventuating in impaired mucociliary clearance, chronic infection and inflammation, and tissue damage. CF lung disease is the major cause of morbidity and mortality in CF despite the many therapies aimed at reducing it. However, recent technological advances combined with two decades of research driven by the discovery of the CFTR gene have resulted in the development and clinical testing of novel therapies aimed at the principal underlying defect in CF, thereby ushering in a new age of therapy for CF.
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Affiliation(s)
- James L Kreindler
- Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, 3615 Civic Center Boulevard, Abramson Research Center, Rm 1016-D, Philadelphia, PA 19104, USA.
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29
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Myerburg MM, King JD, Oyster NM, Fitch AC, Magill A, Baty CJ, Watkins SC, Kolls JK, Pilewski JM, Hallows KR. AMPK agonists ameliorate sodium and fluid transport and inflammation in cystic fibrosis airway epithelial cells. Am J Respir Cell Mol Biol 2009; 42:676-84. [PMID: 19617399 DOI: 10.1165/2009-0147oc] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The metabolic sensor AMP-activated kinase (AMPK) inhibits both the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) Cl(-) channel and epithelial Na(+) channel (ENaC), and may inhibit secretion of proinflammatory cytokines in epithelia. Here we have tested in primary polarized CF and non-CF human bronchial epithelial (HBE) cells the effects of AMPK activators, metformin and 5-aminoimidazole-4-carboxamide-1-beta-D-riboside (AICAR), on various parameters that contribute to CF lung disease: ENaC-dependent short-circuit currents (I(sc)), airway surface liquid (ASL) height, and proinflammatory cytokine secretion. AMPK activation after overnight treatment with either metformin (2-5 mM) or AICAR (1 mM) substantially inhibited ENaC-dependent I(sc) in both CF and non-CF airway cultures. Live-cell confocal images acquired 60 minutes after apical addition of Texas Red-dextran-containing fluid revealed significantly greater ASL heights after AICAR and metformin treatment relative to controls, suggesting that AMPK-dependent ENaC inhibition slows apical fluid reabsorption. Both metformin and AICAR decreased secretion of various proinflammatory cytokines, both with and without prior LPS stimulation. Finally, prolonged exposure to more physiologically relevant concentrations of metformin (0.03-1 mM) inhibited ENaC currents and decreased proinflammatory cytokine levels in CF HBE cells in a dose-dependent manner. These findings suggest that novel therapies to activate AMPK in the CF airway may be beneficial by blunting excessive sodium and ASL absorption and by reducing excessive airway inflammation, which are major contributors to CF lung disease.
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Affiliation(s)
- Michael M Myerburg
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, S976 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261, USA
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O'Mullane LM, Cook DI, Dinudom A. Purinergic regulation of the epithelial Na+ channel. Clin Exp Pharmacol Physiol 2009; 36:1016-22. [PMID: 19566815 DOI: 10.1111/j.1440-1681.2009.05256.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
1. The epithelial Na(+) channel (ENaC) is a major conductive pathway that transports Na(+) across the apical membrane of the distal nephron, the respiratory tract, the distal colon and the ducts of exocrine glands. The ENaC is regulated by hormonal and humoral factors, including extracellular nucleotides that are available from the epithelial cells themselves. 2. Extracellular nucleotides, via the P2Y2 receptors (P2Y2Rs) at the basolateral and apical membrane of the epithelia, trigger signalling systems that inhibit the activity of the ENaC and activate Ca(2+) -dependent Cl(-) secretion. 3. Recent data from our laboratory suggest that stimulation of the P2Y2Rs at the basolateral membrane inhibits ENaC activity by a signalling mechanism that involves G beta gamma subunits freed from a pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) beta 4. A similar signalling mechanism is also partially responsible for inhibition of the ENaC during activation of apical P2Y2Rs. 4. Stimulation of apical P2Y2Rs also activates an additional signalling mechanism that inhibits the ENaC and involves the activated Galpha subunit of a PTX-insensitive G-protein and activation of an unidentified PLC. The effect of this PTX-insensitive system requires the activity of the basolateral Na(+)/K(+)/2Cl(-) cotransporter.
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Affiliation(s)
- Lauren M O'Mullane
- Discipline of Physiology, The Bosch Institute, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, Australia
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Yang C, Su L, Wang Y, Liu L. UTP regulation of ion transport in alveolar epithelial cells involves distinct mechanisms. Am J Physiol Lung Cell Mol Physiol 2009; 297:L439-54. [PMID: 19542245 DOI: 10.1152/ajplung.90268.2008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
UTP is known to regulate alveolar fluid clearance. However, the relative contribution of alveolar type I cells and type II cells to this process is unknown. In this study, we investigated the effects of UTP on ion transport in type I-like cell (AEC I) and type II-like cell (AEC II) monolayers. Luminal treatment of cell monolayers with UTP increased short-circuit current (I(sc)) of AEC II but decreased I(sc) of AEC I. The Cl(-) channel blockers NPPB and DIDS inhibited the UTP-induced changes in I(sc) (DeltaIsc) in both types of cells. Amiloride, an inhibitor of epithelial Na(+) channels (ENaC), abolished the UTP-induced DeltaI(sc) in AEC I, but not in AEC II. The general blocker of K(+) channels, BaCl(2), eliminated the UTP-induced DeltaI(sc) in AEC II, but not in AEC I. The intermediate conductance (IK(Ca)) blocker, clofilium, also blocked the UTP effect in AEC II. The signal transduction pathways mediated by UTP were the same in AEC I and AEC II. Furthermore, UTP increased Cl(-) secretion in AEC II and Cl(-) absorption in AEC I. Our results suggest that UTP induces opposite changes in I(sc) in AEC I and AEC II, likely due to the reversed Cl(-) flux and different contributions of ENaC and IK(Ca). Our results further imply a new concept that type II cells contribute to UTP-induced fluid secretion and type I cells contribute to UTP-induced fluid absorption in alveoli.
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Affiliation(s)
- Chuanxiu Yang
- Lundberg-Kienlen Lung Biology and Toxicology Laboratory, Department of Physiological Sciences, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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Seminario-Vidal L, Kreda S, Jones L, O'Neal W, Trejo J, Boucher RC, Lazarowski ER. Thrombin promotes release of ATP from lung epithelial cells through coordinated activation of rho- and Ca2+-dependent signaling pathways. J Biol Chem 2009; 284:20638-48. [PMID: 19439413 DOI: 10.1074/jbc.m109.004762] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Extracellular ATP controls key aspects of lung function via activation of epithelial cell purinergic receptors, but how ATP is released from cells remains poorly understood. To identify mechanistic components upstream of ATP release, we examined the effect of selected G protein coupled-receptor activation on ATP release from lung epithelial cells. The protease-activated receptor (PAR) agonist thrombin elicited a rapid Ca(2+)-dependent release of ATP from A549 cells. In contrast, the P2Y(2) receptor agonist UTP caused negligible ATP release, despite promoting a robust Ca(2+) response. Agonist-elicited ATP release was associated with Rho activation and was reduced in cells transfected with dominant negative mutants of p115-Rho GEF or RhoA, and by inhibitors of Rho kinase (ROCK). However, RhoA activation alone did not promote ATP release if temporally separated from Ca(2+) mobilization. PAR3 was the only PAR subtype detected in A549 cells by reverse transcription-PCR. Transfection of cells with human PAR3 cDNA increased thrombin-promoted ATP release, inositol phosphate formation, and RhoA activation. Conversely, small interference RNA against PAR3 diminished thrombin-evoked responses. Thrombin-elicited ATP release was accompanied by an enhanced cellular uptake of propidium iodide in a Ca(2+)- and ROCK-dependent manner and was inhibited by connexin/pannexin hemichannel blockers. Our data suggest that thrombin promotes ATP release from A549 cells via Rho- and Ca(2+)-dependent activation of connexin/pannexin hemichannels. The relevance of these findings is highlighted by the observation that exposure of primary cultures of well differentiated human bronchial epithelial cells to thrombin resulted in robust ATP release, which was inhibited by ROCK inhibitors and by connexin/pannexin hemichannel blockers.
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Affiliation(s)
- Lucia Seminario-Vidal
- Department of Cell and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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Namkung W, Song Y, Mills AD, Padmawar P, Finkbeiner WE, Verkman AS. In situ measurement of airway surface liquid [K+] using a ratioable K+-sensitive fluorescent dye. J Biol Chem 2009; 284:15916-26. [PMID: 19364771 DOI: 10.1074/jbc.m808021200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The airway surface liquid (ASL) is the thin fluid layer lining airway surface epithelial cells, whose volume and composition are tightly regulated and may be abnormal in cystic fibrosis (CF). We synthesized a two-color fluorescent dextran to measure ASL [K(+)], TAC-Lime-dextran-TMR, consisting of a green-fluorescing triazacryptand K(+) ionophore-Bodipy conjugate, coupled to dextran, together with a red fluorescing tetramethylrhodamine reference chromophore. TAC-Lime-dextran-TMR fluorescence was K(+)-selective, increasing >4-fold with increasing [K(+)] from 0 to 40 mm. In well differentiated human airway epithelial cells, ASL [K(+)] was 20.8 +/- 0.3 mm and decreased by inhibition of the Na(+)/K(+) pump (ouabain), ENaC (amiloride), CF transmembrane conductance regulator (CFTR(inh)-172), or K(+) channels (TEA or XE991). ASL [K(+)] was increased by forskolin but not affected by Na(+)/K(+)/2Cl(-) cotransporter inhibition (bumetanide). Functional and expression studies indicated the involvement of [K(+)] channels KCNQ1, KCNQ3, and KCNQ5 as determinants of ASL [K(+)]. [K(+)] in CF cultures was similar to that in non-CF cultures, suggesting that abnormal ASL [K(+)] is not a factor in CF lung disease. In intact airways, ASL [K(+)] was also well above extracellular [K(+)]: 22 +/- 1 mm in pig trachea ex vivo and 16 +/- 1 mm in mouse trachea in vivo. Our results provide the first noninvasive measurements of [K(+)] in the ASL and indicate the involvement of apical and basolateral membrane ion transporters in maintaining a high ASL [K(+)].
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Affiliation(s)
- Wan Namkung
- Departments of Medicine and Physiology, University of California, San Francisco, California 94143, USA
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Bertrand CA, Zhang R, Pilewski JM, Frizzell RA. SLC26A9 is a constitutively active, CFTR-regulated anion conductance in human bronchial epithelia. J Gen Physiol 2009; 133:421-38. [PMID: 19289574 PMCID: PMC2664976 DOI: 10.1085/jgp.200810097] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Accepted: 02/23/2009] [Indexed: 12/25/2022] Open
Abstract
Human bronchial epithelial (HBE) cells exhibit constitutive anion secretion that is absent in cells from cystic fibrosis (CF) patients. The identity of this conductance is unknown, but SLC26A9, a member of the SLC26 family of CF transmembrane conductance regulator (CFTR)-interacting transporters, is found in the human airway and exhibits chloride channel behavior. We sought differences in the properties of SLC26A9 and CFTR expressed in HEK 293 (HEK) cells as a fingerprint to identify HBE apical anion conductances. HEK cells expressing SLC26A9 displayed a constitutive chloride current that was inhibited by the CFTR blocker GlyH-101 (71 +/- 4%, 50 microM) and exhibited a near-linear current-voltage (I-V) relation during block, while GlyH-101-inhibited wild-type (wt)CFTR exhibited a strong inward-rectified (IR) I-V relation. We tested polarized HBE cells endogenously expressing either wt or DeltaF508-CFTR for similar activity. After electrical isolation of the apical membrane using basolateral alpha-toxin permeabilization, wtCFTR monolayers displayed constitutive chloride currents that were inhibited by GlyH-101 (68 +/- 6%) while maintaining a near-linear I-V relation. In the absence of blocker, the addition of forskolin stimulated a current increase having a linear I-V; GlyH-101 blocked 69 +/- 7% of the current and shifted the I-V relation IR, consistent with CFTR activation. HEK cells coexpressing SLC26A9 and wtCFTR displayed similar properties, as well as forskolin-stimulated currents that exceeded the sum of those in cells separately expressing SLC26A9 or wtCFTR, and an I-V relation during GlyH-101 inhibition that was moderately IR, indicating that SLC26A9 contributed to the stimulated current. HBE cells from CF patients expressed SLC26A9 mRNA, but no constitutive chloride currents. HEK cells coexpressing SLC26A9 with DeltaF508-CFTR also failed to exhibit SLC26A9 current. We conclude that SLC26A9 functions as an anion conductance in the apical membranes of HBE cells, it contributes to transepithelial chloride currents under basal and cAMP/protein kinase A-stimulated conditions, and its activity in HBE cells requires functional CFTR.
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Affiliation(s)
- Carol A Bertrand
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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Souza-Menezes J, Morales MM. CFTR structure and function: is there a role in the kidney? Biophys Rev 2009; 1:3-12. [PMID: 28510151 PMCID: PMC5387792 DOI: 10.1007/s12551-008-0002-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 12/19/2008] [Indexed: 12/27/2022] Open
Abstract
Cystic fibrosis (CF) is a lethal autosomal recessive genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR). Mutations in the CFTR gene may result in a defective protein processing that leads to changes in function and regulation of this chloride channel. Despite of the expression of CFTR in the kidney, patients with CF do not present major renal dysfunction, but it is known that both the urinary excretion of proteins and renal capacity to concentrate and dilute urine are altered in these patients. CFTR mRNA is expressed in all nephron segments of rat and human, and this abundance is more prominent in renal cortex and outer medulla renal areas. CFTR protein was detected in apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. Studies have demonstrated that CFTR does not only transport Cl- but also ATP. ATP transport by CFTR could be involved in the control of other ion transporters such as Na+ (ENaC) and K+ (renal outer medullary potassium) channels, especially in TAL and CCD. In the kidney, CFTR also might be involved in the endocytosis of low-molecular-weight proteins by proximal tubules. This review is focused on the CFTR function and structure, its role in the renal physiology, and its modulation by hormones involved in the control of extracellular fluid volume.
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Affiliation(s)
- J. Souza-Menezes
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Macaé, Brazil
| | - M. M. Morales
- Instituto de Biofísica Carlos Chagas Filho, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- Av Carlos Chagas Filho 373, Centro de Ciências da Saúde Bloco G Sala 48, Cidade Universitária, Rio de Janeiro, 21941-902 Brazil
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Coote KJ, Atherton H, Young A, Sugar R, Burrows R, Smith NJ, Schlaeppi JM, Groot-Kormelink PJ, Gosling M, Danahay H. The guinea-pig tracheal potential difference as an in vivo model for the study of epithelial sodium channel function in the airways. Br J Pharmacol 2008; 155:1025-33. [PMID: 18806814 DOI: 10.1038/bjp.2008.363] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE The epithelial sodium channel (ENaC) is a key regulator of airway mucosal hydration and mucus clearance. Negative regulation of airway ENaC function is predicted to be of clinical benefit in the cystic fibrosis lung. The aim of this study was to develop a small animal model to enable the direct assessment of airway ENaC function in vivo. EXPERIMENTAL APPROACH Tracheal potential difference (TPD) was utilized as a measure of airway epithelial ion transport in the guinea-pig. ENaC activity in the trachea was established with a dose-response assessment to a panel of well-characterized direct and indirect pharmacological modulators of ENaC function, delivered by intra-tracheal (i.t.) instillation. KEY RESULTS The TPD in anaesthetized guinea-pigs was attenuated by the direct ENaC blockers: amiloride, benzamil and CF552 with ED(50) values of 16, 14 and 0.2 microg kg(-1) (i.t.), respectively. 5-(N-Ethyl-N-isopropyl) amiloride, a structurally related compound but devoid of activity on ENaC, was without effect on the TPD. Intra-tracheal dosing of the Kunitz-type serine protease inhibitors aprotinin and placental bikunin, which have previously been demonstrated to inhibit proteolytic activation of ENaC, likewise potently attenuated TPD in guinea-pigs, whereas alpha(1)-antitrypsin and soya bean trypsin inhibitor were without effect. CONCLUSIONS AND IMPLICATIONS The pharmacological sensitivity of the TPD to amiloride analogues and also to serine protease inhibitors are both consistent with that of ENaC activity in the guinea-pig trachea. The guinea-pig TPD therefore represents a suitable in vivo model of human airway epithelial ion transport.
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Affiliation(s)
- K J Coote
- Novartis Institutes for BioMedical Research, Horsham, West Sussex, UK
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Button B, Boucher RC. Role of mechanical stress in regulating airway surface hydration and mucus clearance rates. Respir Physiol Neurobiol 2008; 163:189-201. [PMID: 18585484 DOI: 10.1016/j.resp.2008.04.020] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Revised: 04/11/2008] [Accepted: 04/11/2008] [Indexed: 11/16/2022]
Abstract
Effective clearance of mucus is a critical innate airway defense mechanism, and under appropriate conditions, can be stimulated to enhance clearance of inhaled pathogens. It has become increasingly clear that extracellular nucleotides (ATP and UTP) and nucleosides (adenosine) are important regulators of mucus clearance in the airways as a result of their ability to stimulate fluid secretion, mucus hydration, and cilia beat frequency (CBF). One ubiquitous mechanism to stimulate ATP release is through external mechanical stress. This article addresses the role of physiologically relevant mechanical forces in the lung and their effects on regulating mucociliary clearance (MCC). The effects of mechanical forces on the stimulating ATP release, fluid secretion, CBF, and MCC are discussed. Also discussed is evidence suggesting that airway hydration and stimulation of MCC by stress-mediated ATP release may play a role in several therapeutic strategies directed at improving mucus clearance in patients with obstructive lung diseases, including cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD).
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Affiliation(s)
- Brian Button
- Cystic Fibrosis Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7248, USA.
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Feghali-Bostwick CA, Gadgil AS, Otterbein LE, Pilewski JM, Stoner MW, Csizmadia E, Zhang Y, Sciurba FC, Duncan SR. Autoantibodies in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2008; 177:156-63. [PMID: 17975205 PMCID: PMC2204079 DOI: 10.1164/rccm.200701-014oc] [Citation(s) in RCA: 185] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2006] [Accepted: 10/22/2007] [Indexed: 11/16/2022] Open
Abstract
RATIONALE Adaptive immune responses are present in patients with chronic obstructive pulmonary disease (COPD), and it has been postulated that these processes could be autoreactive. OBJECTIVES To ascertain if humoral autoimmunity could play a role in COPD pathogenesis. METHODS Circulating IgG autoantibodies were detected by immunofluorescence and immunoprecipitation. Immunohistochemistry and immunofluorescence were used to evaluate intrapulmonary IgG and complement (C3) deposition in human lung explants. Autoantibody pathogenicity was also investigated with an antibody-dependent cell-mediated cytotoxicity assay. MEASUREMENTS AND MAIN RESULTS The prevalence of anti-HEp-2 epithelial cell autoantibodies in 47 smokers/former smokers with COPD (GOLD stages 1-4) was greater than among 8 subjects with a smoking history but normal spirometry and 21 healthy control subjects who had never smoked (68 vs. 13 vs. 10%, respectively; P < 0.0001). Antibodies against primary pulmonary epithelial cells were found in 12 of 12 patients with COPD versus 3 of 12 never-smoked control subjects (P < 0.001). Self-antigens immunoprecipitated from 34 of 35 (97%) of COPD plasmas (vs. 0/12 never-smoked controls). Antibodies against a particular 130-kD autoantigen (n = 7) were associated with decreased body mass index (23.2 +/- 2.1 vs. 29.5 +/- 1.0 kg/m(2), P = 0.007). Intrapulmonary immune complexes were present in six of six and C3 was seen in five of six COPD lung explants, unlike zero of six and one of six normals, respectively. Cytotoxicity of pulmonary epithelial cells by allogeneic mononuclear cells also increased 46% after incubation with COPD plasmas (n = 10), compared with identical treatments with eight normal specimens (P = 0.03). CONCLUSIONS IgG autoantibodies with avidity for pulmonary epithelium, and the potential to mediate cytotoxicity, are prevalent in patients with COPD. Autoreactive adaptive immune responses may be important in the etiology of this disease.
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Affiliation(s)
- Carol A Feghali-Bostwick
- Division of Pulmonary, Allergy, and Critical Care, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA
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Abstract
The epithelial sodium channel (ENaC) represents the rate-limiting step of sodium absorption across airway epithelia and thereby constitutes the major pathway for volume absorption from the airway surface liquid compartment. ENaC dysregulation leads to dehydration of airway surfaces in patients with cystic fibrosis, which in turn disrupts the primary innate lung defense mechanism, mucus clearance. The development of treatment strategies that address this defect is a logical and promising means of preventing or delaying the onset of this lethal lung disease.
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Affiliation(s)
- Scott H Donaldson
- Cystic Fibrosis Research and Treatment Center, 6007B Thurston Bowles Building, CB# 7248, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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40
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Abstract
In summary, there is a significant interplay between the pulmonary manifestations and nutritional status of CF patients. The advances in CF clinical care in the past 2 decades are mainly attributed to anti-infective therapy as well as aggressive nutritional management. Currently, there are multiple therapeutic agents that are in clinical trial that target either the underlying CFTR defect or the downstream effects of CFTR. The broad spectrum of therapeutic agents being studied as well as the advances in therapies that target the underlying CFTR defect are exciting, making it likely that at least one of the treatments will make a major difference in how we will treat CF in the future.
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Affiliation(s)
- Reshma Amin
- Division of Respiratory Medicine, Department of Pediatrics, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, ON, M5G 1X8, Canada
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Köles L, Gerevich Z, Oliveira JF, Zadori ZS, Wirkner K, Illes P. Interaction of P2 purinergic receptors with cellular macromolecules. Naunyn Schmiedebergs Arch Pharmacol 2007; 377:1-33. [DOI: 10.1007/s00210-007-0222-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Accepted: 11/12/2007] [Indexed: 02/04/2023]
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Carattino MD, Passero CJ, Steren CA, Maarouf AB, Pilewski JM, Myerburg MM, Hughey RP, Kleyman TR. Defining an inhibitory domain in the alpha-subunit of the epithelial sodium channel. Am J Physiol Renal Physiol 2007; 294:F47-52. [PMID: 18032549 DOI: 10.1152/ajprenal.00399.2007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaC) are processed by proteases as they transit the biosynthetic pathway. We recently observed that furin-dependent processing of the alpha-subunit of ENaC at two sites within its extracellular domain is required for channel activation due to release of a 26-residue inhibitory domain. While channels with alpha-subunits lacking the furin sites are not cleaved and have very low activity, channels lacking the furin consensus sites as well as the tract between these sites (alphaD206-R231) are active. We analyzed channels with a series of deletions in the tract alphaD206-R231 and lacking the alpha-subunit furin consensus sites in Xenopus laevis oocytes. We found an eight-residue tract that, when deleted, restored channel activity to the level found in oocytes expressing wild-type ENaC. A synthetic peptide, LPHPLQRL, representing the tract alphaL211-L218, inhibited wild-type ENaC expressed in oocytes with an IC(50) of 0.9 microM, and inhibited channels expressed in collecting duct cells and human primary airway epithelial cells with an IC(50)s of between approximately 50 and 100 microM. Analyses of peptides with deletions within this inhibitory tract indicate that eight residues is the minimal backbone length that is required for ENaC inhibition. Analyses of 8-mer peptides with conserved and nonconserved substitutions suggest that L(1), P(2), H(3), P(4), and L(8) are required for inhibitory activity. Our findings suggest that this eight-residue tract is a key conserved inhibitory domain that provides epithelial cells with a reserve of inactive channels that can be activated as required by proteases.
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Affiliation(s)
- Marcelo D Carattino
- Renal-Electrolyte Division, University of Pittsburgh, S931 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261, USA.
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Milano PM, Douillet CD, Riesenman PJ, Robinson WP, Beidler SK, Zarzaur BL, Rich PB. Intestinal ischemia-reperfusion injury alters purinergic receptor expression in clinically relevant extraintestinal organs. J Surg Res 2007; 145:272-8. [PMID: 17688885 PMCID: PMC2323452 DOI: 10.1016/j.jss.2007.03.028] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2007] [Revised: 03/01/2007] [Accepted: 03/13/2007] [Indexed: 01/21/2023]
Abstract
BACKGROUND Intestinal ischemia-reperfusion (IIR) injury is known to initiate the systemic inflammatory response syndrome, which often progresses to multiple organ failure. We investigated changes in purinoceptor expression in clinically relevant extra-intestinal organs following IIR injury. MATERIALS AND METHODS Anesthetized adult male BalbC mice were randomized to sham laparotomy (control, n = 5), or 15 min of superior mesenteric artery occlusion. Experimental ischemia was followed by a period of reperfusion [1 min (n = 6) or 1 h (n = 6)]. Mice were then sacrificed and lung, kidney, and intestinal tissues were harvested. Following RNA extraction, purinoceptor mRNA expression for P2Y2, A3, P2X7, A2b, P2Y4, and P2Y6 was analyzed using real-time RT-PCR. RESULTS Significant differences in purinoceptor expression were observed in the lungs and kidneys of mice exposed to IIR injury when compared to controls. Pulmonary P2Y2 receptor expression was increased in the 1 h IIR group when compared to control, while pulmonary A3 receptor expression was incrementally elevated following IIR injury. In the kidney, P2Y2 receptor expression was increased in the 1 h IIR group compared to both 1 min IIR and control, and A3 receptor expression was decreased in the 1 h IIR group compared to the 1 min IIR group. No significant changes were observed in the intestinal purinoceptor profiles. CONCLUSION Purinoceptor expression is altered in the murine lung and kidney, but not intestine following experimental IIR injury. These findings may implicate extracellular nucleotides and purinoceptors as possible mediators of the extra-intestinal organ dysfunction associated with IIR injury.
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Affiliation(s)
- Peter M. Milano
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Christelle D. Douillet
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Paul J. Riesenman
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - William P. Robinson
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Stephanie K. Beidler
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Ben L. Zarzaur
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Preston B. Rich
- Department of Surgery, Division of Trauma and Critical Care. The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
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An Inositol Phosphate Analog, INO-4995, Normalizes Electrophysiology in CF Airway Epithelia. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007. [DOI: 10.1007/0-387-23250-8_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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45
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Is Intervention in Inositol Phosphate Signaling a Useful Therapeutic Option for Cystic Fibrosis? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007. [DOI: 10.1007/0-387-23250-8_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Kunzelmann K, Bachhuber T, Adam G, Voelcker T, Murle B, Mall M, Schreiber R. Role of CFTR and Other Ion Channels in Cystic Fibrosis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007. [DOI: 10.1007/0-387-23250-8_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Deterding RR, Lavange LM, Engels JM, Mathews DW, Coquillette SJ, Brody AS, Millard SP, Ramsey BW. Phase 2 randomized safety and efficacy trial of nebulized denufosol tetrasodium in cystic fibrosis. Am J Respir Crit Care Med 2007; 176:362-9. [PMID: 17446337 DOI: 10.1164/rccm.200608-1238oc] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
RATIONALE Denufosol tetrasodium is a selective P2Y(2) agonist that enhances mucosal hydration and mucus clearance by activating Cl(-) secretion and inhibiting epithelial Na(+) transport through a non-cystic fibrosis transmembrane conductance regulator mechanism in the lung. OBJECTIVES To examine the safety and efficacy of 28 days of treatment with denufosol compared with placebo in patients with mild cystic fibrosis. METHODS The study was a randomized, double-blind, multi-center, 28-day, phase 2 clinical trial of denufosol tetrasodium inhalation solution (20, 40, or 60 mg) versus placebo (normal saline). Patients with screening FEV(1) >or= 75% of predicted normal value and not treated with inhaled antibiotics for the past 30 days were randomized to receive one of three doses of denufosol or placebo administered three times daily. MEASUREMENTS AND MAIN RESULTS Eighty-nine patients were randomized and received the study drug, 94% completed the study, and 98% were compliant with dosing. All treatments were generally well tolerated, with no dose-response trends observed with respect to safety parameters. The most common adverse event was cough (52% of placebo patients and 47% of denufosol patients). Five patients discontinued early due to adverse events, two on placebo and three on denufosol. Denufosol patients (pooling active doses) had significantly higher changes from baseline in FEV(1) (P = 0.006), FEF(25%-75%) (P = 0.008), FVC (P = 0.022), and FEV(1)/FVC (P = 0.047) than placebo patients at the end of the study. CONCLUSIONS Denufosol administered three times daily for 28 days appeared to be safe and well tolerated in this population with mild cystic fibrosis and provided preliminary evidence of potential benefit in lung function.
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Affiliation(s)
- Robin R Deterding
- The Children's Hospital, 1056 East 19th Avenue, B395, Denver, CO 80218, USA.
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Reynolds SD, Shen H, Reynolds PR, Betsuyaku T, Pilewski JM, Gambelli F, Di Giuseppe M, DeGuiseppe M, Ortiz LA, Stripp BR. Molecular and functional properties of lung SP cells. Am J Physiol Lung Cell Mol Physiol 2007; 292:L972-83. [PMID: 17142352 DOI: 10.1152/ajplung.00090.2006] [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: 11/22/2022] Open
Abstract
Previous analysis of lung injury and repair has provided evidence for region-specific stem cells that maintain proximal and distal epithelial compartments. However, redundant expression of lineage markers by cells at several levels of the stem cell hierarchy has complicated phenotypic and functional characterization of clonogenic airway cells. Based on the demonstration that rapid efflux of the DNA dye Hoechst 33342 can be used to prospectively purify long-term repopulating hematopoietic stem cells, we hypothesized that lung cells with similar biochemical properties would be enriched for clonogenic progenitors. We demonstrate that Hoechst-dim side population (SP) cells isolated from proximal and distal compartments of the mouse lung were relatively small and agranular, exhibited low red and green autofluorescence, and that the SP fraction was highly enriched in clonogenic cells. Quantitative RT-PCR indicated that vimentin mRNA was enriched and that epithelial markers were depleted in these preparations of SP cells. Bleomycin exposure was associated with decreased clonogenicity among alveolar SP and suggested that SP cell function was compromised under profibrotic conditions. We conclude that the SP phenotype is common to clonogenic cells at multiple airway locations and suggest that Hoechst efflux is a property of cells expressing a wound-repair phenotype.
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Affiliation(s)
- Susan D Reynolds
- Center for Lung Regeneration, Department of Environmental and Occupational Health, University of Pittsburgh, USA.
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Matos JE, Sorensen MV, Geyti CS, Robaye B, Boeynaems JM, Leipziger J. Distal colonic Na(+) absorption inhibited by luminal P2Y(2) receptors. Pflugers Arch 2007; 454:977-87. [PMID: 17356885 DOI: 10.1007/s00424-007-0248-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2007] [Accepted: 02/28/2007] [Indexed: 10/23/2022]
Abstract
Luminal P2 receptors are ubiquitously expressed in transporting epithelia. In steroid-sensitive epithelia (e.g., lung, distal nephron) epithelial Na(+) channel (ENaC)-mediated Na(+) absorption is inhibited via luminal P2 receptors. In distal mouse colon, we have identified that both, a luminal P2Y(2) and a luminal P2Y(4) receptor, stimulate K(+) secretion. In this study, we investigate the effect of luminal adenosine triphosphate/uridine triphosphate (ATP/UTP) on electrogenic Na(+) absorption in distal colonic mucosa of mice treated on a low Na(+) diet for more than 2 weeks. Transepithelial electrical parameters were recorded in an Ussing chamber. Baseline parameters: transepithelial voltage (V (te)): -13.7 +/- 1.9 mV (lumen negative), transepithelial resistance (R (te)): 24.1 +/- 1.8 Omega cm(2), equivalent short circuit current (I (sc)): -563.9 +/- 63.8 microA/cm(2) (n = 21). Amiloride completely inhibited I (sc) to -0.5 +/- 8.5 microA/cm(2). Luminal ATP induced a slowly on-setting and persistent inhibition of the amiloride-sensitive I (sc) by 160.7 +/- 29.7 microA/cm(2) (n = 12, NMRI mice). Luminal ATP and UTP were almost equipotent with IC(50) values of 10 microM and 3 microM respectively. In P2Y(2) knock-out (KO) mice, the effect of luminal UTP on amiloride-sensitve Na(+) absorption was absent. In contrast, in P2Y(4) KO mice the inhibitory effect of luminal UTP on Na(+) absorption remained present. Semiquantitative polymerase chain reaction did not indicate regulation of the P2Y receptors under low Na(+) diet, but it revealed a pronounced axial expression of both receptors with highest abundance in surface epithelia. Thus, luminal P2Y(2) and P2Y(4) receptors and ENaC channels co-localize in surface epithelium. Intriguingly, only the stimulation of the P2Y(2) receptor mediates inhibition of electrogenic Na(+) absorption.
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Affiliation(s)
- J E Matos
- Institute of Physiology and Biophysics, The Water and Salt Research Center, University of Aarhus, Aarhus, Denmark
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Xie Y, Schafer JA. Endogenous ATP release inhibits electrogenic Na⁺ absorption and stimulates Cl⁻ secretion in MDCK cells. Purinergic Signal 2007; 4:125-37. [PMID: 18368527 PMCID: PMC2377323 DOI: 10.1007/s11302-007-9053-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Accepted: 02/02/2007] [Indexed: 11/30/2022] Open
Abstract
Our previous studies with a line of Madin-Darby canine kidney (MDCK) cells (FL-MDCK) transfected with FLAG-labeled alpha, beta, and gamma subunits of epithelial Na(+) channel (ENaC) showed that, although most of the short-circuit current (I (sc)) was amiloride sensitive (AS-I (sc)), there was also an amiloride-insensitive component (NS-I (sc)) due to Cl(-) secretion (Morris and Schafer, J Gen Physiol 120:71-85, 2002). In the present studies, we observed a progressive increase in NS-I (sc) and a corresponding decrease in AS-I (sc) during experiments. There was a significant negative correlation between AS-I (sc) and NS-I (sc) both in the presence and absence of treatment with cyclic adenosine monophosphate (cAMP). NS-I (sc) could be attributed to both cystic fibrosis transmembrane conductance regulator (CFTR) and a 4, 4'-diisothiocyano-2, 2'-disulfonic acid stilbene (DIDS)-sensitive Ca(2+)-activated Cl(-) channel (CaCC). Continuous perfusion of both sides of the Ussing chamber with fresh rather than recirculated bathing solutions, or addition of hexokinase (6 U/ml), prevented the time-dependent changes and increased AS-I (sc) by 40-60%, with a proportional decrease in NS-I (sc). Addition of 100 muM adenosine triphosphate (ATP) in the presence of luminal amiloride produced a transient four-fold increase in NS-I (sc) that was followed by a sustained increase of 50-60% above the basal level. ATP release from the monolayers, measured by bioluminescence, was found to occur across the apical but not the basolateral membrane, and the apical release was tripled by cAMP treatment. These data show that constitutive apical ATP release, which occurs under both basal and cAMP-stimulated conditions, underlies the time-dependent rise in Cl(-) secretion and the proportional fall in ENaC-mediated Na(+) absorption in FL-MDCK cells. Thus, endogenous ATP release can introduce a significant confounding variable in experiments with this and similar epithelial cells, and it may underlie at least some of the observed interaction between Cl(-) secretion and Na(+) absorption.
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Affiliation(s)
- Yi Xie
- Department of Physiology and Biophysics, and Medicine, University of Alabama at Birmingham, Birmingham, AL 35294 USA
- Department of Physiology, UCLA School of Medicine, 650 Charles Young Dr. S. 3-609 MRL, Los Angeles, CA 90095-1751 USA
| | - James A. Schafer
- Department of Physiology and Biophysics, and Medicine, University of Alabama at Birmingham, Birmingham, AL 35294 USA
- Departments of Physiology and Biophysics, University of Alabama at Birmingham, 1918 University Blvd., Rm. 834 MCLM, Birmingham, AL 35294-0005 USA
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