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Lysikova DV, Vasileva VY, Chubinskiy-Nadezhdin VI, Morachevskaya EA, Sudarikova AV. Capsazepine activates amiloride-insensitive ENaC-like channels in human leukemia cells. Biochem Biophys Res Commun 2023; 687:149187. [PMID: 37944472 DOI: 10.1016/j.bbrc.2023.149187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Revised: 10/27/2023] [Accepted: 10/30/2023] [Indexed: 11/12/2023]
Abstract
Sodium influx carried out by ion channels is one of the main regulators of water-salt and volume balance in cells of blood origin. Previously, we described amiloride-insensitive ENaC-like channels in human myeloid leukemia K562 cells; the intracellular regulatory mechanisms of the channels are associated with actin cytoskeleton dynamics. Recently, an extracellular mechanism of ENaC-like channels activation in K562 cells by the action of serine protease trypsin has been revealed. The other extracellular pathways that modulate ENaC (epithelial Na+ channel) activity and sodium permeability in transformed blood cells are not yet fully investigated. Here, we study the action of capsazepine (CPZ), as δ-ENaC activator, on single channel activity in K562 cells in whole-cell patch clamp experiments. Addition of CPZ (2 μM) to the extracellular solution caused an activation of sodium channels with typical features; unitary conductance was 15.1 ± 0.8 pS. Amiloride derivative benzamil (50 μM) did not inhibit their activity. Unitary currents and conductance of CPZ-activated channels were higher in Na+-containing extracellular solution than in Li+, that is one of the main fingerprints of δ-ENaC. The results of RT-PCR analysis and immunofluorescence staining also confirmed the expression of δ-hENaC (as well as α-, β-, γ-ENaC) at the mRNA and protein level. These findings allow us to speculate that CPZ activates amiloride-insensitive ENaC-like channels that contain δ-ENaC in К562 cells. Our data reveal a novel extracellular mechanism for ENaC-like activation in human leukemia cells.
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Affiliation(s)
- Daria V Lysikova
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | - Valeria Y Vasileva
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | | | - Elena A Morachevskaya
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia
| | - Anastasia V Sudarikova
- Institute of Cytology, Russian Academy of Sciences, 194064 Tikhoretsky Ave. 4, St. Petersburg, Russia.
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2
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Blaconà G, Raso R, Castellani S, Pierandrei S, Del Porto P, Ferraguti G, Ascenzioni F, Conese M, Lucarelli M. Downregulation of epithelial sodium channel (ENaC) activity in cystic fibrosis cells by epigenetic targeting. Cell Mol Life Sci 2022; 79:257. [PMID: 35462606 PMCID: PMC9035428 DOI: 10.1007/s00018-022-04190-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 01/28/2022] [Accepted: 02/02/2022] [Indexed: 12/31/2022]
Abstract
The pathogenic mechanism of cystic fibrosis (CF) includes the functional interaction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein with the epithelial sodium channel (ENaC). The reduction of ENaC activity may constitute a therapeutic option for CF. This hypothesis was evaluated using drugs that target the protease-dependent activation of the ENaC channel and the transcriptional activity of its coding genes. To this aim we used: camostat, a protease inhibitor; S-adenosyl methionine (SAM), showed to induce DNA hypermethylation; curcumin, known to produce chromatin condensation. SAM and camostat are drugs already clinically used in other pathologies, while curcumin is a common dietary compound. The experimental systems used were CF and non-CF immortalized human bronchial epithelial cell lines as well as human bronchial primary epithelial cells. ENaC activity and SCNN1A, SCNN1B and SCNN1G gene expression were analyzed, in addition to SCNN1B promoter methylation. In both immortalized and primary cells, the inhibition of extracellular peptidases and the epigenetic manipulations reduced ENaC activity. Notably, the reduction in primary cells was much more effective. The SCNN1B appeared to be the best target to reduce ENaC activity, in respect to SCNN1A and SCNN1G. Indeed, SAM treatment resulted to be effective in inducing hypermethylation of SCNN1B gene promoter and in lowering its expression. Importantly, CFTR expression was unaffected, or even upregulated, after treatments. These results open the possibility of CF patients’ treatment by epigenetic targeting.
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Affiliation(s)
- Giovanna Blaconà
- Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy
| | - Roberto Raso
- Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy
| | - Stefano Castellani
- Department of Biomedical Sciences and Human Oncology, University of Bari, Bari, Italy
| | - Silvia Pierandrei
- Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy
| | - Paola Del Porto
- Department of Biology and Biotechnology "Charles Darwin", Sapienza University of Rome, Rome, Italy
| | - Giampiero Ferraguti
- Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy
| | - Fiorentina Ascenzioni
- Department of Biology and Biotechnology "Charles Darwin", Sapienza University of Rome, Rome, Italy
| | - Massimo Conese
- Department of Medical and Surgical Sciences, University of Foggia, Foggia, Italy.
| | - Marco Lucarelli
- Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy. .,Pasteur Institute, Cenci Bolognetti Foundation, Sapienza University of Rome, Rome, Italy.
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3
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Palma AG, Kotsias BA. The Effect of Dynasore Upon the Negative Interaction Between ENaC and CFTR Channels in Xenopus laevis Oocytes. J Membr Biol 2022; 255:61-69. [DOI: 10.1007/s00232-021-00212-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2021] [Accepted: 12/22/2021] [Indexed: 11/29/2022]
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4
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Zhang J, Yuan HK, Chen S, Zhang ZR. Detrimental or beneficial: Role of endothelial ENaC in vascular function. J Cell Physiol 2021; 237:29-48. [PMID: 34279047 DOI: 10.1002/jcp.30505] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 06/29/2021] [Accepted: 07/01/2021] [Indexed: 12/19/2022]
Abstract
In the past, it was believed that the expression of the epithelial sodium channel (ENaC) was restricted to epithelial tissues, such as the distal nephron, airway, sweat glands, and colon, where it is critical for sodium homeostasis. Over the past two decades, this paradigm has shifted due to the finding that ENaC is also expressed in various nonepithelial tissues, notably in vascular endothelial cells. In this review, the recent findings of the expression, regulation, and function of the endothelial ENaC (EnNaC) are discussed. The expression of EnNaC subunits is reported in a variety of endothelial cell lines and vasculatures, but this is controversial across different species and vessels and is not a universal finding in all vascular beds. The expression density of EnNaC is very faint compared to ENaC in the epithelium. To date, little is known about the regulatory mechanism of EnNaC. Through it can be regulated by aldosterone, the detailed downstream signaling remains elusive. EnNaC responds to increased extracellular sodium with the feedforward activation mechanism, which is quite different from the Na+ self-inhibition mechanism of ENaC. Functionally, EnNaC was shown to be a determinant of cellular mechanics and vascular tone as it can sense shear stress, and its activation or insertion into plasma membrane causes endothelial stiffness and reduced nitric oxide production. However, in some blood vessels, EnNaC is essential for maintaining the integrity of endothelial barrier function. In this context, we discuss the possible reasons for the distinct role of EnNaC in vasculatures.
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Affiliation(s)
- Jun Zhang
- School of Biomedical Sciences and Li Ka Shing Institute of Health Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Hui-Kai Yuan
- Department of General Surgery, The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Shuo Chen
- Department of Biopharmaceutical Sciences, School of Pharmacy, Harbin Medical University (Daqing), Daqing, China
| | - Zhi-Ren Zhang
- Departments of Pharmacy and Cardiology, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Heilongjiang Key Laboratory for Metabolic Disorder & Cancer Related Cardiovascular Diseases, NHC Key Laboratory of Cell Transplantation, Harbin Medical University & Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and Treatment, Harbin, China
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5
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Pierandrei S, Truglio G, Ceci F, Del Porto P, Bruno SM, Castellani S, Conese M, Ascenzioni F, Lucarelli M. DNA Methylation Patterns Correlate with the Expression of SCNN1A, SCNN1B, and SCNN1G (Epithelial Sodium Channel, ENaC) Genes. Int J Mol Sci 2021; 22:ijms22073754. [PMID: 33916525 PMCID: PMC8038451 DOI: 10.3390/ijms22073754] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 03/12/2021] [Accepted: 03/23/2021] [Indexed: 12/17/2022] Open
Abstract
The interplay between the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial sodium channel (ENaC) in respiratory epithelia has a crucial role in the pathogenesis of cystic fibrosis (CF). The comprehension of the mechanisms of transcriptional regulation of ENaC genes is pivotal to better detail the pathogenic mechanism and the genotype-phenotype relationship in CF, as well as to realize therapeutic approaches based on the transcriptional downregulation of ENaC genes. Since we aimed to study the epigenetic transcriptional control of ENaC genes, an assessment of their expression and DNA methylation patterns in different human cell lines, nasal brushing samples, and leucocytes was performed. The mRNA expression of CFTR and ENaC subunits α, β and γ (respectively SCNN1A, SCNN1B, and SCNN1G genes) was studied by real time PCR. DNA methylation of 5'-flanking region of SCNN1A, SCNN1B, and SCNN1G genes was studied by HpaII/PCR. The levels of expression and DNA methylation of ENaC genes in the different cell lines, brushing samples, and leukocytes were very variable. The DNA regions studied of each ENaC gene showed different methylation patterns. A general inverse correlation between expression and DNA methylation was evidenced. Leukocytes showed very low expression of all the 3 ENaC genes corresponding to a DNA methylated pattern. The SCNN1A gene resulted to be the most expressed in some cell lines that, accordingly, showed a completely demethylated pattern. Coherently, a heavy and moderate methylated pattern of, respectively, SCNN1B and SCNN1G genes corresponded to low levels of expression. As exceptions, we found that dexamethasone treatment appeared to stimulate the expression of all the 3 ENaC genes, without an evident modulation of the DNA methylation pattern, and that in nasal brushing a considerable expression of all the 3 ENaC genes were found despite an apparent methylated pattern. At least part of the expression modulation of ENaC genes seems to depend on the DNA methylation patterns of specific DNA regions. This points to epigenetics as a controlling mechanism of ENaC function and as a possible therapeutic approach for CF.
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Affiliation(s)
- Silvia Pierandrei
- Department of Experimental Medicine, Sapienza University of Rome, Viale Regina Elena 324, 00161 Roma, Italy; (S.P.); (G.T.); (F.C.); (S.M.B.)
| | - Gessica Truglio
- Department of Experimental Medicine, Sapienza University of Rome, Viale Regina Elena 324, 00161 Roma, Italy; (S.P.); (G.T.); (F.C.); (S.M.B.)
| | - Fabrizio Ceci
- Department of Experimental Medicine, Sapienza University of Rome, Viale Regina Elena 324, 00161 Roma, Italy; (S.P.); (G.T.); (F.C.); (S.M.B.)
| | - Paola Del Porto
- Department of Biology and Biotechnology “Charles Darwin”, Sapienza University of Rome, Via dei Sardi 70, 00185 Roma, Italy;
| | - Sabina Maria Bruno
- Department of Experimental Medicine, Sapienza University of Rome, Viale Regina Elena 324, 00161 Roma, Italy; (S.P.); (G.T.); (F.C.); (S.M.B.)
| | - Stefano Castellani
- Department of Biomedical Sciences and Human Oncology, University of Bari, Piazza Giulio Cesare 11, 70124 Bari, Italy;
| | - Massimo Conese
- Department of Medical and Surgical Sciences, University of Foggia, Via Napoli 121, 71122 Foggia, Italy;
| | - Fiorentina Ascenzioni
- Department of Biology and Biotechnology “Charles Darwin”, Sapienza University of Rome, Via dei Sardi 70, 00185 Roma, Italy;
- Correspondence: (F.A.); (M.L.)
| | - Marco Lucarelli
- Department of Experimental Medicine, Sapienza University of Rome, Viale Regina Elena 324, 00161 Roma, Italy; (S.P.); (G.T.); (F.C.); (S.M.B.)
- Pasteur Institute, Cenci Bolognetti Foundation, Sapienza University of Rome, Viale Regina Elena 291, 00161 Roma, Italy
- Correspondence: (F.A.); (M.L.)
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Mukherjee A, MacDonald KD, Kim J, Henderson MI, Eygeris Y, Sahay G. Engineered mutant α-ENaC subunit mRNA delivered by lipid nanoparticles reduces amiloride currents in cystic fibrosis-based cell and mice models. SCIENCE ADVANCES 2020; 6:6/47/eabc5911. [PMID: 33208364 PMCID: PMC7673816 DOI: 10.1126/sciadv.abc5911] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 10/05/2020] [Indexed: 05/02/2023]
Abstract
Cystic fibrosis (CF) results from mutations in the chloride-conducting CF transmembrane conductance regulator (CFTR) gene. Airway dehydration and impaired mucociliary clearance in CF is proposed to result in tonic epithelial sodium channel (ENaC) activity, which drives amiloride-sensitive electrogenic sodium absorption. Decreasing sodium absorption by inhibiting ENaC can reverse airway surface liquid dehydration. Here, we inhibit endogenous heterotrimeric ENaC channels by introducing inactivating mutant ENaC α mRNA (αmutENaC). Lipid nanoparticles carrying αmutENaC were transfected in CF-based airway cells in vitro and in vivo. We observed a significant decrease in macroscopic as well as amiloride-sensitive ENaC currents and an increase in airway surface liquid height in CF airway cells. Similarly, intranasal transfection of αmutENaC mRNA decreased amiloride-sensitive nasal potential difference in CFTRKO mice. These data suggest that mRNA-based ENaC inhibition is a powerful strategy for reducing mucus dehydration and has therapeutic potential for treating CF in all patients, independent of genotype.
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Affiliation(s)
- Anindit Mukherjee
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Kelvin D MacDonald
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
- Department of Pediatrics, School of Medicine, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jeonghwan Kim
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Michael I Henderson
- Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, OR 97201, USA
| | - Yulia Eygeris
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA
| | - Gaurav Sahay
- Department of Pharmaceutical Sciences, College of Pharmacy, Robertson Life Sciences Building, Oregon State University, Portland, OR 97201, USA.
- Department of Biomedical Engineering, Robertson Life Sciences Building, Oregon Health & Science University, Portland, OR 97239, USA
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7
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Effects of syntaxins 2, 3, and 4 on rat and human epithelial sodium channel (ENaC) in Xenopus laevis oocytes. Pflugers Arch 2020; 472:461-471. [PMID: 32221667 PMCID: PMC7165155 DOI: 10.1007/s00424-020-02365-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 03/09/2020] [Accepted: 03/12/2020] [Indexed: 01/20/2023]
Abstract
Syntaxins are SNARE proteins and may play a role in epithelial sodium channel (ENaC) trafficking. The aim of the present study was to investigate the effects of syntaxin 2 (STX2), syntaxin 3 (STX3), and syntaxin 4 (STX4) on rat (rENaC) and human ENaC (hENaC). Co-expression of rENaC and STX3 or STX4 in Xenopus laevis oocytes increased amiloride-sensitive whole-cell currents (ΔIami) on average by 50% and 135%, respectively, compared to oocytes expressing rENaC alone. In contrast, STX2 had no significant effect on rENaC. Similar to its effect on rENaC, STX3 stimulated hENaC by 48%. In contrast, STX2 and STX4 inhibited hENaC by 51% and 44%, respectively. Using rENaC carrying a FLAG tag in the extracellular loop of the β-subunit, we demonstrated that the stimulatory effects of STX3 and STX4 on ΔIami were associated with an increased expression of the channel at the cell surface. Co-expression of STX3 or STX4 did not significantly alter the degree of proteolytic channel activation by chymotrypsin. STX3 had no effect on the inhibition of rENaC by brefeldin A, and the stimulatory effect of STX3 was preserved in the presence of dominant negative Rab11. This indicates that the stimulatory effect of STX3 is not mediated by inhibiting channel retrieval or by stimulating fusion of recycling endosomes. Our results suggest that the effects of syntaxins on ENaC are isoform and species dependent. Furthermore, our results demonstrate that STX3 increases ENaC expression at the cell surface, probably by enhancing insertion of vesicles carrying newly synthesized channels.
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8
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Sharma S, Kumaran GK, Hanukoglu I. High-resolution imaging of the actin cytoskeleton and epithelial sodium channel, CFTR, and aquaporin-9 localization in the vas deferens. Mol Reprod Dev 2020; 87:305-319. [PMID: 31950584 DOI: 10.1002/mrd.23317] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 01/05/2020] [Indexed: 12/30/2022]
Abstract
Vas deferens is a conduit for sperm and fluid from the epididymis to the urethra. The duct is surrounded by a thick smooth muscle layer. To map the actin cytoskeleton of the duct and its epithelium, we reacted sections of the proximal and distal regions with fluorescent phalloidin. Confocal microscopic imaging showed that the cylinder-shaped epithelium of the proximal region has a thick apical border of actin filaments that form microvilli. The epithelium of the distal region is covered with tall stereocilia (13-18 µm) that extend from the apical border into the lumen. In both regions, the lateral and basal cell borders showed a thin lining of actin cytoskeleton. The vas deferens epithelium contains various channels to regulate the fluid composition in the lumen. We mapped the localization of the epithelial sodium channel (ENaC), aquaporin-9 (AQP9), and cystic fibrosis transmembrane conductance regulator (CFTR) in the rat and mouse vas deferens. ENaC and AQP9 immunofluorescence were localized on the luminal surface and stereocilia and also in the basal and smooth muscle layers. CFTR immunofluorescence appeared only on the luminal surface and in smooth muscle layers. The localization of all three channels on the apical surface of the columnar epithelial cells provides clear evidence that these channels are involved concurrently in the regulation of fluid and electrolyte balance in the lumen of the vas deferens. ENaC allows the flow of Na+ ions from the lumen into the cytoplasm, and the osmotic gradient generated provides the driving force for the passive flow of water through AQP channels.
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Affiliation(s)
- Sachin Sharma
- Laboratory of Cell Biology, Ariel University, Ariel, Israel
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Zhao R, Ali G, Chang J, Komatsu S, Tsukasaki Y, Nie HG, Chang Y, Zhang M, Liu Y, Jain K, Jung BG, Samten B, Jiang D, Liang J, Ikebe M, Matthay MA, Ji HL. Proliferative regulation of alveolar epithelial type 2 progenitor cells by human Scnn1d gene. Am J Cancer Res 2019; 9:8155-8170. [PMID: 31754387 PMCID: PMC6857051 DOI: 10.7150/thno.37023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 09/16/2019] [Indexed: 01/03/2023] Open
Abstract
Lung epithelial sodium channel (ENaC) encoded by Scnn1 genes is essential for maintaining transepithelial salt and fluid homeostasis in the airway and the lung. Compared to α, β, and γ subunits, the role of respiratory δ-ENaC has not been studied in vivo due to the lack of animal models. Methods: We characterized full-length human δ802-ENaC expressed in both Xenopus oocytes and humanized transgenic mice. AT2 proliferation and differentiation in 3D organoids were analysed with FACS and a confocal microscope. Both two-electrode voltage clamp and Ussing chamber systems were applied to digitize δ802-ENaC channel activity. Immunoblotting was utilized to analyse δ802-ENaC protein. Transcripts of individual ENaC subunits in human lung tissues were quantitated with qPCR. Results: The results indicate that δ802-ENaC functions as an amiloride-inhibitable Na+ channel. Inhibitory peptide α-13 distinguishes δ802- from α-type ENaC channels. Modified proteolysis of γ-ENaC by plasmin and aprotinin did not alter the inhibition of amiloride and α-13 peptide. Expression of δ802-ENaC at the apical membrane of respiratory epithelium was detected with biophysical features similar to those of heterologously expressed channels in oocytes. δ802-ENaC regulated alveologenesis through facilitating the proliferation of alveolar type 2 epithelial cells. Conclusion: The humanized mouse line conditionally expressing human δ802-ENaC is a novel model for studying the expression and function of this protein in vivo .
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Pouokam E, Diener M. Segmental differences in ion transport in rat cecum. Pflugers Arch 2019; 471:1007-1023. [PMID: 31093757 DOI: 10.1007/s00424-019-02276-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 03/21/2019] [Accepted: 04/09/2019] [Indexed: 12/30/2022]
Abstract
Ion-transport properties of the epithelium of the cecum, the biggest fermental chamber in non-ruminant species, are largely unknown. Recently, in Ussing chamber experiments, segmental differences in basal short-circuit current (Isc) in rat corpus ceci were observed. The oral segment usually exhibited a much lower or even negative basal Isc in comparison with the aboral segment. The aim of the present study was the closer characterization of these differences. Basal Isc was inhibited by bumetanide and tetrodotoxin in both segments, whereas indomethacin reduced basal Isc only in the aboral corpus. Amiloride did not inhibit basal Isc suggesting that spontaneous anion secretion (but not electrogenic Na+ absorption via ENaC) contributes to the baseline current. In both segments, mucosally applied K+ channel blockers increased Isc indicating a spontaneous K+ secretion. Basolateral depolarization was used to characterize the ion conductances in the apical membrane. When a Cl- gradient was applied, apical Cl- conductance stimulated by carbachol and by forskolin was revealed. When the Cl- gradient was omitted and instead a K+ gradient was used to drive currents across apical K+ channels, a Ba2+-sensititve K+ conductance was observed in both segments, and carbachol stimulated this conductance leading to a negative Isc. Conversely, forskolin induced a positive Isc under these conditions which was dependent on the presence of mucosal Na+ consistent with electrogenic Na+ absorption. This current was reduced by amiloride and several blockers of members of the TRP channel superfamily. These results indicate that similar transport mechanisms are involved in electrogenic ion transport across cecal oral and aboral segments, but with a higher spontaneous prostaglandin production in the aboral segment responsible for higher basal transport rates of both anions and cations.
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Affiliation(s)
- Ervice Pouokam
- Institute for Veterinary Physiology and Biochemistry, Justus Liebig University Giessen, Giessen, Germany
| | - Martin Diener
- Institute for Veterinary Physiology and Biochemistry, Justus Liebig University Giessen, Giessen, Germany.
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11
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Agrawal PB, Wang R, Li HL, Schmitz-Abe K, Simone-Roach C, Chen J, Shi J, Louie T, Sheng S, Towne MC, Brainson CF, Matthay MA, Kim CF, Bamshad M, Emond MJ, Gerard NP, Kleyman TR, Gerard C. The Epithelial Sodium Channel Is a Modifier of the Long-Term Nonprogressive Phenotype Associated with F508del CFTR Mutations. Am J Respir Cell Mol Biol 2017; 57:711-720. [PMID: 28708422 PMCID: PMC5765421 DOI: 10.1165/rcmb.2017-0166oc] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Accepted: 07/05/2017] [Indexed: 12/11/2022] Open
Abstract
Cystic fibrosis (CF) remains the most lethal genetic disease in the Caucasian population. However, there is great variability in clinical phenotypes and survival times, even among patients harboring the same genotype. We identified five patients with CF and a homozygous F508del mutation in the CFTR gene who were in their fifth or sixth decade of life and had shown minimal changes in lung function over a longitudinal period of more than 20 years. Because of the rarity of this long-term nonprogressive phenotype, we hypothesized these individuals may carry rare genetic variants in modifier genes that ameliorate disease severity. Individuals at the extremes of survival time and lung-function trajectory underwent whole-exome sequencing, and the sequencing data were filtered to include rare missense, stopgain, indel, and splicing variants present with a mean allele frequency of <0.2% in general population databases. Epithelial sodium channel (ENaC) mutants were generated via site-directed mutagenesis and expressed for Xenopus oocyte assays. Four of the five individuals carried extremely rare or never reported variants in the SCNN1D and SCNN1B genes of the ENaC. Separately, an independently enriched rare variant in SCNN1D was identified in the Exome Variant Server database associated with a milder pulmonary disease phenotype. Functional analysis using Xenopus oocytes revealed that two of the three variants in δ-ENaC encoded by SCNN1D exhibited hypomorphic channel activity. Our data suggest a potential role for δ-ENaC in controlling sodium reabsorption in the airways, and advance the plausibility of ENaC as a therapeutic target in CF.
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Affiliation(s)
- Pankaj B. Agrawal
- Divisions of Newborn Medicine
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | - Hongmei Lisa Li
- Stem Cell Program, Division of Hematology/Oncology, Boston Children’s Hospital, Boston, Massachusetts
- Harvard Stem Cell Institute, Cambridge, Massachusetts
- Department of Genetics, and
| | - Klaus Schmitz-Abe
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | | | - Jiahai Shi
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong SAR
| | - Tin Louie
- Biostatistics and Center for Biomedical Statistics
| | | | - Meghan C. Towne
- Genetics and Genomics
- Gene Discovery Core, Manton Center for Orphan Disease Research
| | | | - Michael A. Matthay
- Departments of Medicine and
- Anesthesia, Cardiovascular Research Institute, University of California–San Francisco, San Francisco, California
| | - Carla F. Kim
- Pulmonary and Respiratory Diseases, and
- Stem Cell Program, Division of Hematology/Oncology, Boston Children’s Hospital, Boston, Massachusetts
- Harvard Stem Cell Institute, Cambridge, Massachusetts
- Department of Genetics, and
| | - Michael Bamshad
- Pediatrics and Genome Sciences, University of Washington, Seattle, Washington
| | | | - Norma P. Gerard
- Pulmonary and Respiratory Diseases, and
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
| | - Thomas R. Kleyman
- Departments of Medicine
- Cell Biology, and Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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