1
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Liu X, Li Z, Shan J, Wang F, Li Z, Luo S, Wu J. PM 2.5 Exposure Inhibits Transepithelial Anion Short-circuit Current by Downregulating P2Y2 Receptor/CFTR Pathway. Int J Med Sci 2024; 21:1929-1944. [PMID: 39113893 PMCID: PMC11302563 DOI: 10.7150/ijms.96777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Accepted: 07/06/2024] [Indexed: 08/10/2024] Open
Abstract
Fine particulate matter (PM2.5) can damage airway epithelial barriers. The anion transport system plays a crucial role in airway epithelial barriers. However, the detrimental effect and mechanism of PM2.5 on the anion transport system are still unclear. In this study, airway epithelial cells and ovalbumin (OVA)-induced asthmatic mice were used. In transwell model, the adenosine triphosphate (ATP)-induced transepithelial anion short-circuit current (Isc) and airway surface liquid (ASL) significantly decreased after PM2.5 exposure. In addition, PM2.5 exposure decreased the expression levels of P2Y2R, CFTR and cytoplasmic free-calcium, but ATP can increase the expressions of these proteins. PM2.5 exposure increased the levels of Th2-related cytokines of bronchoalveolar lavage fluid, lung inflammation, collagen deposition and hyperplasisa of goblet cells. Interestingly, the administration of ATP showed an inhibitory effect on lung inflammation induced by PM2.5. Together, our study reveals that PM2.5 impairs the ATP-induced transepithelial anion Isc through downregulating P2Y2R/CFTR pathway, and this process may participate in aggravating airway hyperresponsiveness and airway inflammation. These findings may provide important insights on PM2.5-mediated airway epithelial injury.
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Affiliation(s)
- Xiaolong Liu
- Second Department of Elderly Respiratory, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, 510080, Guangzhou, China
| | - Zhangwen Li
- School of Medicine, South China University of Technology, Guangzhou, 510000, China
| | - Jiajie Shan
- School of Medicine, South China University of Technology, Guangzhou, 510000, China
| | - Fang Wang
- Second Department of Elderly Respiratory, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, 510080, Guangzhou, China
- School of Medicine, South China University of Technology, Guangzhou, 510000, China
| | - Zhongpeng Li
- Second Department of Elderly Respiratory, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, 510080, Guangzhou, China
| | - Shaohua Luo
- Second Department of Elderly Respiratory, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, 510080, Guangzhou, China
| | - Jian Wu
- Second Department of Elderly Respiratory, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, 510080, Guangzhou, China
- School of Medicine, South China University of Technology, Guangzhou, 510000, China
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2
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Zhong J, Dong J, Ruan W, Duan X. Potential Theranostic Roles of SLC4 Molecules in Human Diseases. Int J Mol Sci 2023; 24:15166. [PMID: 37894847 PMCID: PMC10606849 DOI: 10.3390/ijms242015166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 09/28/2023] [Accepted: 10/03/2023] [Indexed: 10/29/2023] Open
Abstract
The solute carrier family 4 (SLC4) is an important protein responsible for the transport of various ions across the cell membrane and mediating diverse physiological functions, such as the ion transporting function, protein-to-protein interactions, and molecular transduction. The deficiencies in SLC4 molecules may cause multisystem disease involving, particularly, the respiratory system, digestive, urinary, endocrine, hematopoietic, and central nervous systems. Currently, there are no effective strategies to treat these diseases. SLC4 proteins are also found to contribute to tumorigenesis and development, and some of them are regarded as therapeutic targets in quite a few clinical trials. This indicates that SLC4 proteins have potential clinical prospects. In view of their functional characteristics, there is a critical need to review the specific functions of bicarbonate transporters, their related diseases, and the involved pathological mechanisms. We summarize the diseases caused by the mutations in SLC4 family genes and briefly introduce the clinical manifestations of these diseases as well as the current treatment strategies. Additionally, we illustrate their roles in terms of the physiology and pathogenesis that has been currently researched, which might be the future therapeutic and diagnostic targets of diseases and a new direction for drug research and development.
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Affiliation(s)
| | | | | | - Xiaohong Duan
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Disease, Shaanxi Key Laboratory of Stomatology, Department of Oral Biology & Clinic of Oral Rare Diseases and Genetic Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an 710032, China; (J.Z.); (J.D.); (W.R.)
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3
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Zajac M, Dreano E, Edwards A, Planelles G, Sermet-Gaudelus I. Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge. Int J Mol Sci 2021; 22:3384. [PMID: 33806154 PMCID: PMC8037888 DOI: 10.3390/ijms22073384] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 03/08/2021] [Accepted: 03/08/2021] [Indexed: 12/22/2022] Open
Abstract
Knowledge on the mechanisms of acid and base secretion in airways has progressed recently. The aim of this review is to summarize the known mechanisms of airway surface liquid (ASL) pH regulation and their implication in lung diseases. Normal ASL is slightly acidic relative to the interstitium, and defects in ASL pH regulation are associated with various respiratory diseases, such as cystic fibrosis. Basolateral bicarbonate (HCO3-) entry occurs via the electrogenic, coupled transport of sodium (Na+) and HCO3-, and, together with carbonic anhydrase enzymatic activity, provides HCO3- for apical secretion. The latter mainly involves CFTR, the apical chloride/bicarbonate exchanger pendrin and paracellular transport. Proton (H+) secretion into ASL is crucial to maintain its relative acidity compared to the blood. This is enabled by H+ apical secretion, mainly involving H+/K+ ATPase and vacuolar H+-ATPase that carry H+ against the electrochemical potential gradient. Paracellular HCO3- transport, the direction of which depends on the ASL pH value, acts as an ASL protective buffering mechanism. How the transepithelial transport of H+ and HCO3- is coordinated to tightly regulate ASL pH remains poorly understood, and should be the focus of new studies.
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Affiliation(s)
- Miroslaw Zajac
- Department of Physics and Biophysics, Institute of Biology, Warsaw University of Life Sciences, 02-776 Warsaw, Poland;
| | - Elise Dreano
- Institut Necker Enfants Malades, INSERM U1151, 75015 Paris, France;
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, 75006 Paris, France;
| | - Aurelie Edwards
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA;
| | - Gabrielle Planelles
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, 75006 Paris, France;
- Laboratoire de Physiologie rénale et Tubulopathies, CNRS ERL 8228, 75006 Paris, France
| | - Isabelle Sermet-Gaudelus
- Institut Necker Enfants Malades, INSERM U1151, 75015 Paris, France;
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, 75006 Paris, France;
- Centre de Référence Maladies Rares, Mucoviscidose et Maladies de CFTR, Hôpital Necker Enfants Malades, 75015 Paris, France
- Clinical Trial Network, European Cystic Fibrosis Society, BT2 Belfast, Ireland
- European Respiratory Network Lung, 75006 Paris, France
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4
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Kouthouridis S, Goepp J, Martini C, Matthes E, Hanrahan JW, Moraes C. Oxygenation as a driving factor in epithelial differentiation at the air-liquid interface. Integr Biol (Camb) 2021; 13:61-72. [PMID: 33677549 PMCID: PMC7965686 DOI: 10.1093/intbio/zyab002] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 12/13/2020] [Accepted: 01/12/2021] [Indexed: 01/05/2023]
Abstract
Culture at the air-liquid interface is broadly accepted as necessary for differentiation of cultured epithelial cells towards an in vivo-like phenotype. However, air-liquid interface cultures are expensive, laborious and challenging to scale for increased throughput applications. Deconstructing the microenvironmental parameters that drive these differentiation processes could circumvent these limitations, and here we hypothesize that reduced oxygenation due to diffusion limitations in liquid media limits differentiation in submerged cultures; and that this phenotype can be rescued by recreating normoxic conditions at the epithelial monolayer, even under submerged conditions. Guided by computational models, hyperoxygenation of atmospheric conditions was applied to manipulate oxygenation at the monolayer surface. The impact of this rescue condition was confirmed by assessing protein expression of hypoxia-sensitive markers. Differentiation of primary human bronchial epithelial cells isolated from healthy patients was then assessed in air-liquid interface, submerged and hyperoxygenated submerged culture conditions. Markers of differentiation, including epithelial layer thickness, tight junction formation, ciliated surface area and functional capacity for mucociliary clearance, were assessed and found to improve significantly in hyperoxygenated submerged cultures, beyond standard air-liquid interface or submerged culture conditions. These results demonstrate that an air-liquid interface is not necessary to produce highly differentiated epithelial structures, and that increased availability of oxygen and nutrient media can be leveraged as important strategies to improve epithelial differentiation for applications in respiratory toxicology and therapeutic development.
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Affiliation(s)
- Sonya Kouthouridis
- Department of Chemical Engineering, McGill University, Montreal, Canada
- Department of Chemical Engineering, McMaster University, Hamilton, Canada
| | - Julie Goepp
- Department of Physiology, Cystic Fibrosis Translational Research Centre, McGill University, Montreal, Canada
| | | | | | - John W Hanrahan
- Department of Physiology, Cystic Fibrosis Translational Research Centre, McGill University, Montreal, Canada
- Department of Physiology, McGill University, Montreal, Canada
| | - Christopher Moraes
- Department of Chemical Engineering, McGill University, Montreal, Canada
- Department of Physiology, Cystic Fibrosis Translational Research Centre, McGill University, Montreal, Canada
- Department of Biological and Biomedical Engineering, McGill University, Montreal, Canada
- Faculty of Medicine, Rosalind and Morris Goodman Cancer Research Center, Montreal, Canada
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5
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Grebert C, Becq F, Vandebrouck C. Phospholipase C controls chloride-dependent short-circuit current in human bronchial epithelial cells. Am J Physiol Lung Cell Mol Physiol 2020; 320:L205-L219. [PMID: 33236921 DOI: 10.1152/ajplung.00437.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chloride secretion by airway epithelial cells is primordial for water and ion homeostasis and airways surface prevention of infections. This secretion is impaired in several human diseases, including cystic fibrosis, a genetic pathology due to CFTR gene mutations leading to chloride channel defects. A potential therapeutic approach is aiming at increasing chloride secretion either by correcting the mutated CFTR itself or by stimulating non-CFTR chloride channels at the plasma membrane. Here, we studied the role of phospholipase C in regulating the transepithelial chloride secretion in human airway epithelial 16HBE14o- and CFBE cells over-expressing wild type (WT)- or F508del-CFTR. Western blot analysis shows expression of the three endogenous phospholipase C (PLC) isoforms, namely, PLCδ1, PLCγ1, and PLCβ3 in 16HBE14o- cells. In 16HBE14o- cells, we performed Ussing chamber experiments after silencing each of these PLC isoforms or using the PLC inhibitor U73122 or its inactive analogue U73343. Our results show the involvement of PLCβ3 and PLCγ1 in CFTR-dependent short-circuit current activated by forskolin, but not of PLCδ1. In CFBE-WT CFTR and corrected CFBE-F508del CFTR cells, PLCβ3 silencing also inhibits CFTR-dependent current activated by forskolin and UTP-activated calcium-dependent chloride channels (CaCC). Our study supports the importance of PLC in maintaining CFTR-dependent chloride secretion over time, getting maximal CFTR-dependent current and increasing CaCC activation in bronchial epithelial cells.
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Affiliation(s)
- Chloé Grebert
- Laboratoire Signalisation et Transports Ioniques Membranaires, Université de Poitiers, Poitiers, France
| | - Frédéric Becq
- Laboratoire Signalisation et Transports Ioniques Membranaires, Université de Poitiers, Poitiers, France
| | - Clarisse Vandebrouck
- Laboratoire Signalisation et Transports Ioniques Membranaires, Université de Poitiers, Poitiers, France
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6
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Kim D, Huang J, Billet A, Abu-Arish A, Goepp J, Matthes E, Tewfik MA, Frenkiel S, Hanrahan JW. Pendrin Mediates Bicarbonate Secretion and Enhances Cystic Fibrosis Transmembrane Conductance Regulator Function in Airway Surface Epithelia. Am J Respir Cell Mol Biol 2020; 60:705-716. [PMID: 30742493 DOI: 10.1165/rcmb.2018-0158oc] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Bicarbonate facilitates mucin unpacking and bacterial killing; however, its transport mechanisms in the airways are not well understood. cAMP stimulates anion efflux through the cystic fibrosis (CF) transmembrane conductance regulator (CFTR; ABCC7) anion channel, and this is defective in CF. The anion exchanger pendrin (SLC26A4) also mediates HCO3- efflux and is upregulated by proinflammatory cytokines. Here, we examined pendrin and CFTR expression and their contributions to HCO3- secretion by human nasal and bronchial epithelia. In native tissue, both proteins were most abundant at the apical pole of ciliated surface cells with little expression in submucosal glands. In well-differentiated primary nasal and bronchial cell cultures, IL-4 dramatically increased pendrin mRNA levels and apical immunostaining. Exposure to low-Cl- apical solution caused intracellular alkalinization (ΔpHi) that was enhanced fourfold by IL-4 pretreatment. ΔpHi was unaffected by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) or CFTR inhibitor CFTRinh-172, but was reduced by adenoviral shRNA targeting pendrin. Forskolin increased ΔpHi, and this stimulation was prevented by CFTRinh-172, implicating CFTR, yet forskolin only increased ΔpHi after pendrin expression had been induced by IL-4. The dependence of ΔpHi on pendrin suggests there is minimal electrical coupling between Cl- and HCO3- fluxes and that CFTR activation increases anion exchange-mediated HCO3- influx. Conversely, inducing pendrin expression increased forskolin-stimulated, CFTRinh-172-sensitive current by approximately twofold in epithelial and nonepithelial cells. We conclude that pendrin mediates most HCO3- secretion across airway surface epithelium during inflammation and enhances electrogenic Cl- secretion via CFTR, as described for other SLC26A transporters.
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Affiliation(s)
- Dusik Kim
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Junwei Huang
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Arnaud Billet
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Asmahan Abu-Arish
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Julie Goepp
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Elizabeth Matthes
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and
| | - Marc A Tewfik
- 2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and.,3 Department of Otolaryngology-Head and Neck Surgery and
| | - Saul Frenkiel
- 2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and.,3 Department of Otolaryngology-Head and Neck Surgery and
| | - John W Hanrahan
- 1 Department of Physiology and.,2 Cystic Fibrosis Translational Research Centre, McGill University, Montréal, Québec, Canada; and.,4 Research Institute, McGill University Health Centre, Montréal, Québec, Canada
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7
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Huang J, Kim D, Shan J, Abu‐Arish A, Luo Y, Hanrahan JW. Most bicarbonate secretion by Calu-3 cells is mediated by CFTR and independent of pendrin. Physiol Rep 2018; 6:e13641. [PMID: 29536650 PMCID: PMC5849580 DOI: 10.14814/phy2.13641] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2018] [Revised: 02/10/2018] [Accepted: 02/12/2018] [Indexed: 11/24/2022] Open
Abstract
Bicarbonate plays an important role in airway host defense, however, its transport mechanisms remain uncertain. Here we examined the relative contributions of the anion channel CFTR (cystic fibrosis transmembrane conductance regulator, ABCC7) and the anion exchanger pendrin (SLC26A4) to HCO3- secretion by the human airway cell line Calu-3. Pendrin and CFTR were both detected in parental Calu-3 cells, although mRNA and protein expression appeared higher for CFTR than for pendrin. Targeting pendrin transcripts with lentiviral shRNA reduced pendrin detection by immunofluorescence staining but did not alter the rates of HCO3- or fluid secretion, HCO3- transport under pH-stat conditions, or net HCO3- flux across basolaterally permeabilized monolayers. Intracellular pH varied with step changes in apical Cl- and HCO3- concentrations in control and pendrin knockdown Calu-3 cells, but not in CFTR deficient cells. Exposure to the proinflammatory cytokine IL-4, which strongly upregulates pendrin expression in airway surface epithelia, had little effect on Calu-3 pendrin expression and did not alter fluid or HCO3- secretion. Similar results were obtained using air-liquid interface and submerged cultures, although CFTR and pendrin mRNA expression were both lower when cells were cultured under submerged conditions. While the conclusions cannot be extrapolated to other airway epithelia, the present results demonstrate that most HCO3- secretion by Calu-3 cells is mediated by CFTR.
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Affiliation(s)
- Junwei Huang
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
- Present address:
AbbVie Bioresearch CenterAbbVie Inc.381 Plantation St.WorcesterMA01605
| | - Dusik Kim
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
| | - Jiajie Shan
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
- Present address:
School of MedicineSouth China University of TechnologyGuangzhou University TownPanyu DistrictGuangzhouChina
| | - Asmahan Abu‐Arish
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
| | - Yishan Luo
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
| | - John W. Hanrahan
- Department of PhysiologyMcGill UniversityMontréalQuébecCanada
- Cystic Fibrosis Translational Research CenterMcGill UniversityMontréalQuébecCanada
- Research Institute‐McGill University Health CentreMontréalQuébecCanada
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8
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CK2 is a key regulator of SLC4A2-mediated Cl -/HCO 3- exchange in human airway epithelia. Pflugers Arch 2017; 469:1073-1091. [PMID: 28455748 PMCID: PMC5554290 DOI: 10.1007/s00424-017-1981-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/27/2017] [Accepted: 04/10/2017] [Indexed: 12/17/2022]
Abstract
Transepithelial bicarbonate secretion by human airway submucosal glands and surface epithelial cells is crucial to maintain the pH-sensitive innate defence mechanisms of the lung. cAMP agonists stimulate HCO3- secretion via coordinated increases in basolateral HCO3- influx and accumulation, as well as CFTR-dependent HCO3- efflux at the luminal membrane of airway epithelial cells. Here, we investigated the regulation of a basolateral located, DIDS-sensitive, Cl-/HCO3- exchanger, anion exchanger 2 (AE2; SLC4A2) which is postulated to act as an acid loader, and therefore potential regulator of HCO3- secretion, in human airway epithelial cells. Using intracellular pH measurements performed on Calu-3 cells, we demonstrate that the activity of the basolateral Cl-/HCO3- exchanger was significantly downregulated by cAMP agonists, via a PKA-independent mechanism and also required Ca2+ and calmodulin under resting conditions. AE2 contains potential phosphorylation sites by a calmodulin substrate, protein kinase CK2, and we demonstrated that AE2 activity was reduced in the presence of CK2 inhibition. Moreover, CK2 inhibition abolished the activity of AE2 in primary human nasal epithelia. Studies performed on mouse AE2 transfected into HEK-293T cells confirmed almost identical Ca2+/calmodulin and CK2 regulation to that observed in Calu-3 and primary human nasal cells. Furthermore, mouse AE2 activity was reduced by genetic knockout of CK2, an effect which was rescued by exogenous CK2 expression. Together, these findings are the first to demonstrate that CK2 is a key regulator of Cl--dependent HCO3- export at the serosal membrane of human airway epithelial cells.
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9
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Saint-Criq V, Gray MA. Role of CFTR in epithelial physiology. Cell Mol Life Sci 2016; 74:93-115. [PMID: 27714410 PMCID: PMC5209439 DOI: 10.1007/s00018-016-2391-y] [Citation(s) in RCA: 243] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 12/20/2022]
Abstract
Salt and fluid absorption and secretion are two processes that are fundamental to epithelial function and whole body fluid homeostasis, and as such are tightly regulated in epithelial tissues. The CFTR anion channel plays a major role in regulating both secretion and absorption in a diverse range of epithelial tissues, including the airways, the GI and reproductive tracts, sweat and salivary glands. It is not surprising then that defects in CFTR function are linked to disease, including life-threatening secretory diarrhoeas, such as cholera, as well as the inherited disease, cystic fibrosis (CF), one of the most common life-limiting genetic diseases in Caucasian populations. More recently, CFTR dysfunction has also been implicated in the pathogenesis of acute pancreatitis, chronic obstructive pulmonary disease (COPD), and the hyper-responsiveness in asthma, underscoring its fundamental role in whole body health and disease. CFTR regulates many mechanisms in epithelial physiology, such as maintaining epithelial surface hydration and regulating luminal pH. Indeed, recent studies have identified luminal pH as an important arbiter of epithelial barrier function and innate defence, particularly in the airways and GI tract. In this chapter, we will illustrate the different operational roles of CFTR in epithelial function by describing its characteristics in three different tissues: the airways, the pancreas, and the sweat gland.
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Affiliation(s)
- Vinciane Saint-Criq
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, University Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH UK
| | - Michael A. Gray
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, University Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH UK
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10
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Walker NM, Liu J, Stein SR, Stefanski CD, Strubberg AM, Clarke LL. Cellular chloride and bicarbonate retention alters intracellular pH regulation in Cftr KO crypt epithelium. Am J Physiol Gastrointest Liver Physiol 2016; 310:G70-80. [PMID: 26542396 PMCID: PMC4719062 DOI: 10.1152/ajpgi.00236.2015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 10/29/2015] [Indexed: 01/31/2023]
Abstract
Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR), an anion channel providing a major pathway for Cl(-) and HCO3 (-) efflux across the apical membrane of the epithelium. In the intestine, CF manifests as obstructive syndromes, dysbiosis, inflammation, and an increased risk for gastrointestinal cancer. Cftr knockout (KO) mice recapitulate CF intestinal disease, including intestinal hyperproliferation. Previous studies using Cftr KO intestinal organoids (enteroids) indicate that crypt epithelium maintains an alkaline intracellular pH (pHi). We hypothesized that Cftr has a cell-autonomous role in downregulating pHi that is incompletely compensated by acid-base regulation in its absence. Here, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein microfluorimetry of enteroids showed that Cftr KO crypt epithelium sustains an alkaline pHi and resistance to cell acidification relative to wild-type. Quantitative real-time PCR revealed that Cftr KO enteroids exhibit downregulated transcription of base (HCO3 (-))-loading proteins and upregulation of the basolateral membrane HCO3 (-)-unloader anion exchanger 2 (Ae2). Although Cftr KO crypt epithelium had increased Ae2 expression and Ae2-mediated Cl(-)/HCO3 (-) exchange with maximized gradients, it also had increased intracellular Cl(-) concentration relative to wild-type. Pharmacological reduction of intracellular Cl(-) concentration in Cftr KO crypt epithelium normalized pHi, which was largely Ae2-dependent. We conclude that Cftr KO crypt epithelium maintains an alkaline pHi as a consequence of losing both Cl(-) and HCO3 (-) efflux, which impairs pHi regulation by Ae2. Retention of Cl(-) and an alkaline pHi in crypt epithelium may alter several cellular processes in the proliferative compartment of Cftr KO intestine.
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Affiliation(s)
- Nancy M. Walker
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and
| | - Jinghua Liu
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and
| | - Sydney R. Stein
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and
| | - Casey D. Stefanski
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and ,2Department of Biomedical Sciences, University of Missouri, Columbia, Missouri
| | - Ashlee M. Strubberg
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and ,2Department of Biomedical Sciences, University of Missouri, Columbia, Missouri
| | - Lane L. Clarke
- 1Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri; and ,2Department of Biomedical Sciences, University of Missouri, Columbia, Missouri
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11
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Jeong YS, Hong JH. Governing effect of regulatory proteins for Cl(-)/HCO3(-) exchanger 2 activity. Channels (Austin) 2015; 10:214-24. [PMID: 26716707 DOI: 10.1080/19336950.2015.1134068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Anion exchanger 2 (AE2) has a critical role in epithelial cells and is involved in the ionic homeostasis such as Cl(-) uptake and HCO3(-) secretion. However, little is known about the regulatory mechanism of AE2. The main goal of the present study was to investigate potential regulators, such as spinophilin (SPL), inositol-1,4,5-trisphosphate [IP3] receptors binding protein released with IP3 (IRBIT), STE20/SPS1-related proline/alanine-rich kinase (SPAK) kinase, and carbonic anhydrase XII (CA XII). We found that SPL binds to AE2 and markedly increased the Cl(-)/HCO3(-) exchange activity of AE2. Especially SPL 1-480 domain is required for enhancing AE2 activity. For other regulatory components that affect the fidelity of fluid and HCO3(-) secretion, IRBIT and SPAK had no effect on the activity of AE2 and no protein-protein interaction with AE2. It has been proposed that CA activity is closely associated with AE activity. In this study, we provide evidence that the basolateral membrane-associated CA isoform CA XII significantly increased the activity of AE2 and co-localized with AE2 to the plasma membrane. Collectively, SPL and CA XII enhanced the Cl(-)/HCO3(-) exchange activity of AE2. The modulating action of these regulatory proteins could serve as potential therapeutic targets for secretory diseases mediated by AE2.
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Affiliation(s)
- Yon Soo Jeong
- a Department of Physiology , Graduate School of Medicine, Gachon University , South Korea
| | - Jeong Hee Hong
- a Department of Physiology , Graduate School of Medicine, Gachon University , South Korea
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Turner MJ, Saint-Criq V, Patel W, Ibrahim SH, Verdon B, Ward C, Garnett JP, Tarran R, Cann MJ, Gray MA. Hypercapnia modulates cAMP signalling and cystic fibrosis transmembrane conductance regulator-dependent anion and fluid secretion in airway epithelia. J Physiol 2015; 594:1643-61. [PMID: 26574187 PMCID: PMC4799982 DOI: 10.1113/jp271309] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 11/05/2015] [Indexed: 12/20/2022] Open
Abstract
Hypercapnia is clinically defined as an arterial blood partial pressure of CO2 of above 40 mmHg and is a feature of chronic lung disease. In previous studies we have demonstrated that hypercapnia modulates agonist-stimulated cAMP levels through effects on transmembrane adenylyl cyclase activity. In the airways, cAMP is known to regulate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated anion and fluid secretion, which contributes to airway surface liquid homeostasis. The aim of the current work was to investigate if hypercapnia could modulate cAMP-regulated ion and fluid transport in human airway epithelial cells. We found that acute exposure to hypercapnia significantly reduced forskolin-stimulated elevations in intracellular cAMP as well as both adenosine- and forskolin-stimulated increases in CFTR-dependent transepithelial short-circuit current, in polarised cultures of Calu-3 human airway cells. This CO2 -induced reduction in anion secretion was not due to a decrease in HCO3 (-) transport given that neither a change in CFTR-dependent HCO3 (-) efflux nor Na(+) /HCO3 (-) cotransporter-dependent HCO3 (-) influx were CO2 -sensitive. Hypercapnia also reduced the volume of forskolin-stimulated fluid secretion over 24 h, yet had no effect on the HCO3 (-) content of the secreted fluid. Our data reveal that hypercapnia reduces CFTR-dependent, electrogenic Cl(-) and fluid secretion, but not CFTR-dependent HCO3 (-) secretion, which highlights a differential sensitivity of Cl(-) and HCO3 (-) transporters to raised CO2 in Calu-3 cells. Hypercapnia also reduced forskolin-stimulated CFTR-dependent anion secretion in primary human airway epithelia. Based on current models of airways biology, a reduction in fluid secretion, associated with hypercapnia, would be predicted to have important consequences for airways hydration and the innate defence mechanisms of the lungs.
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Affiliation(s)
- Mark J Turner
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.,Department of Physiology, McIntyre Medical Sciences Building, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada, H3G 1Y6
| | - Vinciane Saint-Criq
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - Waseema Patel
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - Salam H Ibrahim
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - Bernard Verdon
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - Christopher Ward
- Institute for Cellular Medicine, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - James P Garnett
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
| | - Robert Tarran
- Marsico Lung Institute, University of North Carolina, Chapel Hill, NC, 27599, USA
| | - Martin J Cann
- School of Biological and Biomedical Sciences, Durham University, South Road, Durham, DH1 3LE, UK
| | - Michael A Gray
- Institute for Cell & Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
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Hong JH, Muhammad E, Zheng C, Hershkovitz E, Alkrinawi S, Loewenthal N, Parvari R, Muallem S. Essential role of carbonic anhydrase XII in secretory gland fluid and HCO3 (-) secretion revealed by disease causing human mutation. J Physiol 2015; 593:5299-312. [PMID: 26486891 DOI: 10.1113/jp271378] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 10/12/2015] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS Fluid and HCO3 (-) secretion is essential for all epithelia; aberrant secretion is associated with several diseases. Carbonic anhydrase XII (CA12) is the key carbonic anhydrase in epithelial fluid and HCO3 (-) secretion and works by activating the ductal Cl(-) -HCO3 (-) exchanger AE2. Delivery of CA12 to salivary glands increases salivation in mice and of the human mutation CA12(E143K) markedly inhibits it. The human mutation CA12(E143K) causes disease due to aberrant CA12 glycosylation, and misfolding resulting in loss of AE2 activity. ABSTRACT Aberrant epithelial fluid and HCO3 (-) secretion is associated with many diseases. The activity of HCO3 (-) transporters depends of HCO3 (-) availability that is determined by carbonic anhydrases (CAs). Which CAs are essential for epithelial function is unknown. CA12 stands out since the CA12(E143K) mutation causes salt wasting in sweat and dehydration in humans. Here, we report that expression of CA12 and of CA12(E143K) in mice salivary glands respectively increased and prominently inhibited ductal fluid secretion and salivation in vivo. CA12 markedly increases the activity and is the major HCO3 (-) supplier of ductal Cl(-) -HCO3 (-) exchanger AE2, but not of NBCe1-B. The E143K mutation alters CA12 glycosylation at N28 and N80, resulting in retention of the basolateral CA12 in the ER. Knockdown of AE2 and of CA12 inhibited pancreatic and salivary gland ductal AE2 activity and fluid secretion. Accordingly, patients homozygous for the CA12(E143K) mutation have a dry mouth, dry tongue phenotype. These findings reveal an unsuspected prominent role of CA12 in epithelial function, explain the disease and call for caution in the use of CA12 inhibitors in cancer treatment.
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Affiliation(s)
- Jeong Hee Hong
- Epithelial Signalling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, 20892, USA.,Department of Physiology, College of Medicine, Gachon University, 191 Hambakmeoro, Yeonsu-gu, Incheon, 406-799, South Korea
| | - Emad Muhammad
- Shraga Segal Department of Microbiology, Immunology and Genetics, Faculty of Health Sciences and National Institute for Biotechnology in the Negev, Beer Sheva, Israel
| | - Changyu Zheng
- Epithelial Signalling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Eli Hershkovitz
- Pediatric Endocrinology Unit, Soroka Medical Centre and Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel
| | - Soliman Alkrinawi
- Pediatric Endocrinology Unit, Soroka Medical Centre and Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel
| | - Neta Loewenthal
- Pediatric Endocrinology Unit, Soroka Medical Centre and Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel
| | - Ruti Parvari
- Shraga Segal Department of Microbiology, Immunology and Genetics, Faculty of Health Sciences and National Institute for Biotechnology in the Negev, Beer Sheva, Israel
| | - Shmuel Muallem
- Epithelial Signalling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, 20892, USA
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14
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Garnett JP, Hickman E, Tunkamnerdthai O, Cuthbert AW, Gray MA. Protein phosphatase 1 coordinates CFTR-dependent airway epithelial HCO3- secretion by reciprocal regulation of apical and basolateral membrane Cl(-)-HCO3- exchangers. Br J Pharmacol 2015; 168:1946-60. [PMID: 23215877 DOI: 10.1111/bph.12085] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 11/14/2012] [Accepted: 12/01/2012] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND AND PURPOSE Our recent studies on human airway serous-like Calu-3 cells showed that cAMP agonists stimulated a HCO3(-) rich secretion containing up to 80 mM HCO3(-). This alkaline secretion relied on a coordinated switch in the activity of distinct Cl(-)-HCO3(-) anion exchangers (AE) located at different regions of the cell. At the apical membrane, cAMP agonists activated the electroneutral AE pendrin (SLC26A4), together with cystic fibrosis transmembrane conductance regulator (CFTR), while at the basolateral membrane the agonists inhibited AE2 (SLC4A2). However, the underlying mechanism(s) that orchestrates this cAMP-dependent switch in AE activity has not been elucidated. EXPERIMENTAL APPROACH Apical and basolateral Cl(-)-HCO3(-) exchange was assessed by measuring Cl(-)-dependent changes in intracellular pH (pH(i)). KEY RESULTS We show that protein phosphatase 1 (PP1), together with CFTR, play central roles in this reciprocal regulation of AE activity. Activation of pendrin by cAMP agonists, but not inhibition of the basolateral exchanger, was protein kinase A-dependent. Knocking down CFTR expression, or blocking its activity with GlyH-101, led to incomplete inhibition of the basolateral AE by cAMP, supporting a role for CFTR in this process. Addition of the PP1/2A inhibitor, okadaic acid, but not the PP2A specific inhibitor fostreicin, mimicked the effect of cAMP stimulation. Furthermore, okadaic acid-treated Calu-3 monolayers produced a more alkaline fluid than untreated cells, which was comparable with that produced by cAMP stimulation. CONCLUSIONS AND IMPLICATIONS These results identify PP1 as a novel regulator of AE activity which, in concert with CFTR, coordinates events at both apical and basolateral membranes, crucial for efficient HCO3(-) secretion from Calu-3 cells.
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Affiliation(s)
- James P Garnett
- Institute for Cell & Molecular Biosciences, Newcastle University, Newcastle upon Tyne, UK
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15
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Kim D, Kim J, Burghardt B, Best L, Steward MC. Role of anion exchangers in Cl− and HCO3− secretion by the human airway epithelial cell line Calu-3. Am J Physiol Cell Physiol 2014; 307:C208-19. [DOI: 10.1152/ajpcell.00083.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Despite the importance of airway surface liquid pH in the lung's defenses against infection, the mechanism of airway HCO3− secretion remains unclear. Our aim was to assess the contribution of apical and basolateral Cl−/HCO3− exchangers to Cl− and HCO3− transport in the Calu-3 cell line, derived from human airway submucosal glands. Changes in intracellular pH (pHi) were measured following substitution of Cl− with gluconate. Apical Cl− substitution led to an alkalinization in forskolin-stimulated cells, indicative of Cl−/HCO3− exchange. This was unaffected by the anion exchange inhibitor DIDS but inhibited by the CFTR blocker CFTRinh-172, suggesting that the HCO3− influx might occur via CFTR, rather than a solute carrier family 26 (SLC26) exchanger, as recently proposed. The anion selectivity of the recovery process more closely resembled that of CFTR than an SLC26 exchanger, and quantitative RT-PCR showed only low levels of SLC26 exchanger transcripts relative to CFTR and anion exchanger 2 (AE2). For pHi to rise to observed values (∼7.8) through HCO3− entry via CFTR, the apical membrane potential must reverse to at least +20 mV following Cl− substitution; this was confirmed by perforated-patch recordings. Substitution of basolateral Cl− evoked a DIDS-sensitive alkalinization, attributed to Cl−/HCO3− exchange via AE2. This appeared to be abolished in forskolin-stimulated cells but was unmasked by blocking apical efflux of HCO3− via CFTR. We conclude that Calu-3 cells secrete HCO3− predominantly via CFTR, and, contrary to previous reports, the basolateral anion exchanger AE2 remains active during stimulation, providing an important pathway for basolateral Cl− uptake.
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Affiliation(s)
- Dusik Kim
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Juyeon Kim
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Beáta Burghardt
- Department of Oral Biology, Semmelweis University, Budapest, Hungary; and
| | - Len Best
- Faculty of Medicine and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - Martin C. Steward
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
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16
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Frizzell RA, Hanrahan JW. Physiology of epithelial chloride and fluid secretion. Cold Spring Harb Perspect Med 2013; 2:a009563. [PMID: 22675668 DOI: 10.1101/cshperspect.a009563] [Citation(s) in RCA: 154] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Epithelial salt and water secretion serves a variety of functions in different organ systems, such as the airways, intestines, pancreas, and salivary glands. In cystic fibrosis (CF), the volume and/or composition of secreted luminal fluids are compromised owing to mutations in the gene encoding CFTR, the apical membrane anion channel that is responsible for salt secretion in response to cAMP/PKA stimulation. This article examines CFTR and related cellular transport processes that underlie epithelial anion and fluid secretion, their regulation, and how these processes are altered in CF disease to account for organ-specific secretory phenotypes.
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Affiliation(s)
- Raymond A Frizzell
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
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17
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Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
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Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
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18
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Affiliation(s)
- Bruce D Schultz
- Department of Anatomy & Physiology, Kansas State University, Coles Hall Room 228, 1600 Denison Avenue, Manhattan, KS 66506, USA.
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19
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Huang J, Shan J, Kim D, Liao J, Evagelidis A, Alper SL, Hanrahan JW. Basolateral chloride loading by the anion exchanger type 2: role in fluid secretion by the human airway epithelial cell line Calu-3. J Physiol 2012; 590:5299-316. [PMID: 22802585 DOI: 10.1113/jphysiol.2012.236919] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Anion exchanger type 2 (AE2 or SLC4A2) is an electroneutral Cl(-)/HCO(3)(-) exchanger expressed at the basolateral membrane of many epithelia. It is thought to participate in fluid secretion by airway epithelia. However, the role of AE2 in fluid secretion remains uncertain, due to the lack of specific pharmacological inhibitors, and because it is electrically silent and therefore does not contribute directly to short-circuit current (I(sc)). We have studied the role of AE2 in Cl(-) and fluid secretion by the airway epithelial cell line Calu-3. After confirming expression of its mRNA and protein, a knock-down cell line called AE2-KD was generated by lentivirus-mediated RNA interference in which AE2 mRNA and protein levels were reduced 90%. Suppressing AE2 increased the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) by ∼70% without affecting the levels of NKCC1 (Na(+)-K(+)-2Cl(-) cotransporter) or NBCe1 (Na(+)-nHCO(3)(-) cotransporter). cAMP agonists stimulated fluid secretion by parental Calu-3 and scrambled shRNA cells >6.5-fold. In AE2-KD cells this response was reduced by ∼70%, and the secreted fluid exhibited elevated pH and [HCO(3)(-)] as compared with the control lines. Unstimulated equivalent short-circuit current (I(eq)) was elevated in AE2-KD cells, but the incremental response to forskolin was unaffected. The modest bumetanide-induced reductions in both I(eq) and fluid secretion were more pronounced in AE2-KD cells. Basolateral Cl(-)/HCO(3)(-) exchange measured by basolateral pH-stat in cells with permeabilized apical membranes was abolished in AE2-KD monolayers, and the intracellular alkalinization resulting from basolateral Cl(-) removal was reduced by ∼80% in AE2-KD cells. These results identify AE2 as a major pathway for basolateral Cl(-) loading during cAMP-stimulated secretion of Cl(-) and fluid by Calu-3 cells, and help explain the large bumetanide-insensitive component of fluid secretion reported previously in airway submucosal glands and some other epithelia.
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Affiliation(s)
- Junwei Huang
- Department of Physiology, McGill University, Montr´eal, QC, Canada
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20
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Shan J, Liao J, Huang J, Robert R, Palmer ML, Fahrenkrug SC, O'Grady SM, Hanrahan JW. Bicarbonate-dependent chloride transport drives fluid secretion by the human airway epithelial cell line Calu-3. J Physiol 2012; 590:5273-97. [PMID: 22777674 DOI: 10.1113/jphysiol.2012.236893] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Anion and fluid secretion are both defective in cystic fibrosis (CF); however, the transport mechanisms are not well understood. In this study, Cl(-) and HCO(3)(-) secretion was measured using genetically matched CF transmembrane conductance regulator (CFTR)-deficient and CFTR-expressing cell lines derived from the human airway epithelial cell line Calu-3. Forskolin stimulated the short-circuit current (I(sc)) across voltage-clamped monolayers, and also increased the equivalent short-circuit current (I(eq)) calculated under open-circuit conditions. I(sc) was equivalent to the HCO(3)(-) net flux measured using the pH-stat technique, whereas I(eq) was the sum of the Cl(-) and HCO(3)(-) net fluxes. I(eq) and HCO(3)(-) fluxes were increased by bafilomycin and ZnCl(2), suggesting that some secreted HCO(3)(-) is neutralized by parallel electrogenic H(+) secretion. I(eq) and fluid secretion were dependent on the presence of both Na(+) and HCO(3)(-). The carbonic anhydrase inhibitor acetazolamide abolished forskolin stimulation of I(eq) and HCO(3)(-) secretion, suggesting that HCO(3)(-) transport under these conditions requires catalysed synthesis of carbonic acid. Cl(-) was the predominant anion in secretions under all conditions studied and thus drives most of the fluid transport. Nevertheless, 50-70% of Cl(-) and fluid transport was bumetanide-insensitive, suggesting basolateral Cl(-) loading by a sodium-potassium-chloride cotransporter 1 (NKCC1)-independent mechanism. Imposing a transepithelial HCO(3)(-) gradient across basolaterally permeabilized Calu-3 cells sustained a forskolin-stimulated current, which was sensitive to CFTR inhibitors and drastically reduced in CFTR-deficient cells. Net HCO(3)(-) secretion was increased by bilateral Cl(-) removal and therefore did not require apical Cl(-)/HCO(3)(-) exchange. The results suggest a model in which most HCO(3)(-) is recycled basolaterally by exchange with Cl(-), and the resulting HCO(3)(-)-dependent Cl(-) transport provides an osmotic driving force for fluid secretion.
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Affiliation(s)
- Jiajie Shan
- Department of Physiology, McGill University, Montr´eal, QC H3G 1Y6, Canada
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