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Wang XP, Srinivasan P, El Hamdaoui M, Blobner BM, Grytz R, Kashlan OB. Varying Selection Pressure for a Na+ Sensing Site in Epithelial Na+ Channel Subunits Reflect Divergent Roles in Na+ Homeostasis. Mol Biol Evol 2024; 41:msae162. [PMID: 39101592 PMCID: PMC11331422 DOI: 10.1093/molbev/msae162] [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: 02/21/2024] [Revised: 06/10/2024] [Accepted: 07/29/2024] [Indexed: 08/06/2024] Open
Abstract
The epithelial Na+ channel (ENaC) emerged early in vertebrates and has played a role in Na+ and fluid homeostasis throughout vertebrate evolution. We previously showed that proteolytic activation of the channel evolved at the water-to-land transition of vertebrates. Sensitivity to extracellular Na+, known as Na+ self-inhibition, reduces ENaC function when Na+ concentrations are high and is a distinctive feature of the channel. A fourth ENaC subunit, δ, emerged in jawed fishes from an α subunit gene duplication. Here, we analyzed 849 α and δ subunit sequences and found that a key Asp in a postulated Na+ binding site was nearly always present in the α subunit, but frequently lost in the δ subunit (e.g. human). Analysis of site evolution and codon substitution rates provide evidence that the ancestral α subunit had the site and that purifying selection for the site relaxed in the δ subunit after its divergence from the α subunit, coinciding with a loss of δ subunit expression in renal tissues. We also show that the proposed Na+ binding site in the α subunit is a bona fide site by conferring novel function to channels comprising human δ subunits. Together, our findings provide evidence that ENaC Na+ self-inhibition improves fitness through its role in Na+ homeostasis in vertebrates.
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Affiliation(s)
- Xue-Ping Wang
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Priyanka Srinivasan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Mustapha El Hamdaoui
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | | | - Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Ossama B Kashlan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA, USA
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2
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Houser A, Baconguis I. Structural Insights into Subunit-Dependent Functional Regulation in Epithelial Sodium Channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.28.595834. [PMID: 38853903 PMCID: PMC11160588 DOI: 10.1101/2024.05.28.595834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
Epithelial sodium channels (ENaC) play a crucial role in Na + reabsorption in mammals. To date, four subunits have been identified-α, β, γ, and δ-believed to form different heteromeric complexes. Currently, only the structure of the αβγ complex is known. To understand how these channels form with varying subunit compositions and define the contribution of each subunit to distinct properties, we co-expressed human δ, β, and γ. Using single-particle cryo-electron microscopy, we observed three distinct ENaC complexes. The structures unveil a pattern in which β and γ positions are conserved among the different complexes while the α position in αβγ trimer is occupied by either δ or another β. The presence of δ induces structural rearrangements in the γ subunit explaining the differences in channel activity observed between αβγ and δβγ channels. These structures define the mechanism by which ENaC subunit composition tunes ENaC function.
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Kashlan OB, Wang XP, Sheng S, Kleyman TR. Epithelial Na + Channels Function as Extracellular Sensors. Compr Physiol 2024; 14:1-41. [PMID: 39109974 PMCID: PMC11309579 DOI: 10.1002/cphy.c230015] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2024]
Abstract
The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.
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Affiliation(s)
- Ossama B. Kashlan
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Computational and Systems Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
| | - Xue-Ping Wang
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaohu Sheng
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R. Kleyman
- Department of Medicine, Renal-Electrolyte Division,
University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh,
Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University
of Pittsburgh, Pittsburgh, Pennsylvania
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4
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Aufy M, Hussein AM, Stojanovic T, Studenik CR, Kotob MH. Proteolytic Activation of the Epithelial Sodium Channel (ENaC): Its Mechanisms and Implications. Int J Mol Sci 2023; 24:17563. [PMID: 38139392 PMCID: PMC10743461 DOI: 10.3390/ijms242417563] [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: 11/20/2023] [Revised: 12/10/2023] [Accepted: 12/14/2023] [Indexed: 12/24/2023] Open
Abstract
Epithelial sodium channel (ENaC) are integral to maintaining salt and water homeostasis in various biological tissues, including the kidney, lung, and colon. They enable the selective reabsorption of sodium ions, which is a process critical for controlling blood pressure, electrolyte balance, and overall fluid volume. ENaC activity is finely controlled through proteolytic activation, a process wherein specific enzymes, or proteases, cleave ENaC subunits, resulting in channel activation and increased sodium reabsorption. This regulatory mechanism plays a pivotal role in adapting sodium transport to different physiological conditions. In this review article, we provide an in-depth exploration of the role of proteolytic activation in regulating ENaC activity. We elucidate the involvement of various proteases, including furin-like convertases, cysteine, and serine proteases, and detail the precise cleavage sites and regulatory mechanisms underlying ENaC activation by these proteases. We also discuss the physiological implications of proteolytic ENaC activation, focusing on its involvement in blood pressure regulation, pulmonary function, and intestinal sodium absorption. Understanding the mechanisms and consequences of ENaC proteolytic activation provides valuable insights into the pathophysiology of various diseases, including hypertension, pulmonary disorders, and various gastrointestinal conditions. Moreover, we discuss the potential therapeutic avenues that emerge from understanding these mechanisms, offering new possibilities for managing diseases associated with ENaC dysfunction. In summary, this review provides a comprehensive discussion of the intricate interplay between proteases and ENaC, emphasizing the significance of proteolytic activation in maintaining sodium and fluid balance in both health and disease.
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Affiliation(s)
- Mohammed Aufy
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
| | - Ahmed M. Hussein
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
- Department of Zoology, Faculty of Science, Al-Azhar University, Assiut 71524, Egypt
| | - Tamara Stojanovic
- Programme for Proteomics, Paracelsus Medical University, 5020 Salzburg, Austria;
| | - Christian R. Studenik
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
| | - Mohamed H. Kotob
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
- Department of Pathology, Faculty of Veterinary Medicine, Assiut University, Assiut 71515, Egypt
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Nickerson AJ, Mutchler SM, Sheng S, Cox NA, Ray EC, Kashlan OB, Carattino MD, Marciszyn AL, Winfrey A, Gingras S, Kirabo A, Hughey RP, Kleyman TR. Mice lacking γENaC palmitoylation sites maintain benzamil-sensitive Na+ transport despite reduced channel activity. JCI Insight 2023; 8:e172051. [PMID: 37707951 PMCID: PMC10721255 DOI: 10.1172/jci.insight.172051] [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: 05/08/2023] [Accepted: 09/12/2023] [Indexed: 09/16/2023] Open
Abstract
Epithelial Na+ channels (ENaCs) control extracellular fluid volume by facilitating Na+ absorption across transporting epithelia. In vitro studies showed that Cys-palmitoylation of the γENaC subunit is a major regulator of channel activity. We tested whether γ subunit palmitoylation sites are necessary for channel function in vivo by generating mice lacking the palmitoylated cysteines (γC33A,C41A) using CRISPR/Cas9 technology. ENaCs in dissected kidney tubules from γC33A,C41A mice had reduced open probability compared with wild-type (WT) littermates maintained on either standard or Na+-deficient diets. Male mutant mice also had higher aldosterone levels than WT littermates following Na+ restriction. However, γC33A,C41A mice did not have reduced amiloride-sensitive Na+ currents in the distal colon or benzamil-induced natriuresis compared to WT mice. We identified a second, larger conductance cation channel in the distal nephron with biophysical properties distinct from ENaC. The activity of this channel was higher in Na+-restricted γC33A,C41A versus WT mice and was blocked by benzamil, providing a possible compensatory mechanism for reduced prototypic ENaC function. We conclude that γ subunit palmitoylation sites are required for prototypic ENaC activity in vivo but are not necessary for amiloride/benzamil-sensitive Na+ transport in the distal nephron or colon.
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Affiliation(s)
| | | | | | | | | | - Ossama B. Kashlan
- Department of Medicine
- Department of Computational and Systems Biology
| | | | | | | | - Sebastien Gingras
- Department of Immunology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Annet Kirabo
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | | | - Thomas R. Kleyman
- Department of Medicine
- Department of Cell Biology, and
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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6
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Lemmens-Gruber R, Tzotzos S. The Epithelial Sodium Channel-An Underestimated Drug Target. Int J Mol Sci 2023; 24:ijms24097775. [PMID: 37175488 PMCID: PMC10178586 DOI: 10.3390/ijms24097775] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 04/14/2023] [Accepted: 04/15/2023] [Indexed: 05/15/2023] Open
Abstract
Epithelial sodium channels (ENaC) are part of a complex network of interacting biochemical pathways and as such are involved in several disease states. Dependent on site and type of mutation, gain- or loss-of-function generated symptoms occur which span from asymptomatic to life-threatening disorders such as Liddle syndrome, cystic fibrosis or generalized pseudohypoaldosteronism type 1. Variants of ENaC which are implicated in disease assist further understanding of their molecular mechanisms in order to create models for specific pharmacological targeting. Identification and characterization of ENaC modifiers not only furthers our basic understanding of how these regulatory processes interact, but also enables discovery of new therapeutic targets for the disease conditions caused by ENaC dysfunction. Numerous test compounds have revealed encouraging results in vitro and in animal models but less in clinical settings. The EMA- and FDA-designated orphan drug solnatide is currently being tested in phase 2 clinical trials in the setting of acute respiratory distress syndrome, and the NOX1/ NOX4 inhibitor setanaxib is undergoing clinical phase 2 and 3 trials for therapy of primary biliary cholangitis, liver stiffness, and carcinoma. The established ENaC blocker amiloride is mainly used as an add-on drug in the therapy of resistant hypertension and is being studied in ongoing clinical phase 3 and 4 trials for special applications. This review focuses on discussing some recent developments in the search for novel therapeutic agents.
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Affiliation(s)
- Rosa Lemmens-Gruber
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, A-1090 Vienna, Austria
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7
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Yangchen T, Koraishy FM, Xu C, Hou W, Rohatgi R. Initial mean arterial blood pressure (MABP) measurement is a risk factor for mortality in hypertensive COVID-19 positive hospitalized patients. PLoS One 2023; 18:e0283331. [PMID: 36996126 PMCID: PMC10062544 DOI: 10.1371/journal.pone.0283331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 03/07/2023] [Indexed: 03/31/2023] Open
Abstract
BACKGROUND Hypertension (HTN) is associated with severe COVID-19 infection; however, it remains unknown if the level of blood pressure (BP) predicts mortality. We tested whether the initial BP in the emergency department of hospitalized patients portends mortality in COVID-19 positive(+) patients. METHODS Data from COVID-19(+) and negative (-) hospitalized patients at Stony Brook University Hospital from March to July 2020 were included. The initial mean arterial BPs (MABPs) were categorized into tertiles (T) of MABP (65-85 [T1], 86-97 [T2] and ≥98 [T3] mmHg). Differences were evaluated using univariable (t-tests, chi-squared) tests. Multivariable (MV) logistic regression analyses were computed to assess links between MABP and mortality in hypertensive COVID-19 patients. RESULTS 1549 adults were diagnosed with COVID-19 (+) and 2577 tested negative (-). Mortality of COVID-19(+) was 4.4-fold greater than COVID-19(-) patients. Though HTN prevalance did not differ between COVID-19 groups, the presenting systolic BP, diastolic BP, and MABP were lower in the COVID-19(+) vs (-) cohort. When subjects were categorized into tertiles of MABP, T2 tertile of MABP had the lowest mortality and the T1 tertile of MABP had greatest mortality compared to T2; however, no difference in mortality was noted across tertiles of MABP in COVID-19 (-). MV analysis of COVID-19 (+) subjects exposed death as a risk factor for T1 MABP. Next, the mortality of those with a historic diagnosis of hypertension or normotension were studied. On MV analysis, T1 MABP, gender, age, and first respiratory rate correlated with mortality while lymphocyte count inversely correlated with death in hypertensive COVID-19 (+) patients while neither T1 nor T3 categories of MABP predicted death in non-hypertensives. CONCLUSIONS Low-normal admitting MABP in COVID-19 (+) subjects with a historical diagnosis of HTN is associated with mortality and may assist in identifying those at greatest mortality risk.
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Affiliation(s)
- Tenzin Yangchen
- Stony Brook University School of Medicine, Stony Brook, NY, United States of America
| | - Farrukh M. Koraishy
- Stony Brook University School of Medicine, Stony Brook, NY, United States of America
- Northport VAMC, Northport, NY, United States of America
| | - Chang Xu
- James J. Peters VAMC, Bronx, NY, United States of America
- Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY, United States of America
| | - Wei Hou
- Vertex Pharmaceuticals Inc., Boston, MA, United States of America
| | - Rajeev Rohatgi
- James J. Peters VAMC, Bronx, NY, United States of America
- Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY, United States of America
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8
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Wang T, Zhai Y, Xue H, Zhou W, Ding Y, Nie H. Regulation of Epithelial Sodium Transport by SARS-CoV-2 Is Closely Related with Fibrinolytic System-Associated Proteins. Biomolecules 2023; 13:biom13040578. [PMID: 37189326 DOI: 10.3390/biom13040578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 03/08/2023] [Accepted: 03/21/2023] [Indexed: 05/17/2023] Open
Abstract
Dyspnea and progressive hypoxemia are the main clinical features of patients with coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pulmonary pathology shows diffuse alveolar damage with edema, hemorrhage, and the deposition of fibrinogens in the alveolar space, which are consistent with the Berlin Acute Respiratory Distress Syndrome Criteria. The epithelial sodium channel (ENaC) is a key channel protein in alveolar ion transport and the rate-limiting step for pulmonary edema fluid clearance, the dysregulation of which is associated with acute lung injury/acute respiratory distress syndrome. The main protein of the fibrinolysis system, plasmin, can bind to the furin site of γ-ENaC and induce it to an activation state, facilitating pulmonary fluid reabsorption. Intriguingly, the unique feature of SARS-CoV-2 from other β-coronaviruses is that the spike protein of the former has the same furin site (RRAR) with ENaC, suggesting that a potential competition exists between SARS-CoV-2 and ENaC for the cleavage by plasmin. Extensive pulmonary microthrombosis caused by disorders of the coagulation and fibrinolysis system has also been seen in COVID-19 patients. To some extent, high plasmin (ogen) is a common risk factor for SARS-CoV-2 infection since an increased cleavage by plasmin accelerates virus invasion. This review elaborates on the closely related relationship between SARS-CoV-2 and ENaC for fibrinolysis system-related proteins, aiming to clarify the regulation of ENaC under SARS-CoV-2 infection and provide a novel reference for the treatment of COVID-19 from the view of sodium transport regulation in the lung epithelium.
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Affiliation(s)
- Tingyu Wang
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
| | - Yiman Zhai
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
| | - Hao Xue
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
| | - Wei Zhou
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
| | - Yan Ding
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
| | - Hongguang Nie
- Department of Stem Cells and Regenerative Medicine, College of Basic Medical Science, China Medical University, Shenyang 110122, China
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9
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Zhang L, Wang X, Chen J, Sheng S, Kleyman TR. Extracellular intersubunit interactions modulate epithelial Na + channel gating. J Biol Chem 2023; 299:102914. [PMID: 36649907 PMCID: PMC9975279 DOI: 10.1016/j.jbc.2023.102914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 12/13/2022] [Accepted: 01/12/2023] [Indexed: 01/15/2023] Open
Abstract
Epithelial Na+ channels (ENaCs) and related channels have large extracellular domains where specific factors interact and induce conformational changes, leading to altered channel activity. However, extracellular structural transitions associated with changes in ENaC activity are not well defined. Using crosslinking and two-electrode voltage clamp in Xenopus oocytes, we identified several pairs of functional intersubunit contacts where mouse ENaC activity was modulated by inducing or breaking a disulfide bond between introduced Cys residues. Specifically, crosslinking E499C in the β-subunit palm domain and N510C in the α-subunit palm domain activated ENaC, whereas crosslinking βE499C with αQ441C in the α-subunit thumb domain inhibited ENaC. We determined that bridging βE499C to αN510C or αQ441C altered the Na+ self-inhibition response via distinct mechanisms. Similar to bridging βE499C and αQ441C, we found that crosslinking palm domain αE557C with thumb domain γQ398C strongly inhibited ENaC activity. In conclusion, we propose that certain residues at specific subunit interfaces form microswitches that convey a conformational wave during ENaC gating and its regulation.
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Affiliation(s)
- Lei Zhang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xueqi Wang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Jingxin Chen
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Shaohu Sheng
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
| | - Thomas R Kleyman
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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10
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Lugo CI, Liu LP, Bala N, Morales AG, Gholam MF, Abchee JC, Elmoujahid N, Elshikha AS, Avdiaj R, Searcy LA, Denslow ND, Song S, Alli AA. Human Alpha-1 Antitrypsin Attenuates ENaC and MARCKS and Lowers Blood Pressure in Hypertensive Diabetic db/db Mice. Biomolecules 2022; 13:66. [PMID: 36671451 PMCID: PMC9856210 DOI: 10.3390/biom13010066] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/17/2022] [Accepted: 12/22/2022] [Indexed: 12/31/2022] Open
Abstract
Hypertension may develop before or after the onset of diabetes and it is known to increase the risk of developing diabetic nephropathy. Alpha-1 antitrypsin (AAT) is a multi-functional protein with beneficial effects in various diseases but its role in reducing blood pressure in the diabetic kidney has not been thoroughly studied. Like blood pressure, epithelial sodium channels (ENaC) and its adaptor protein myristoylated alanine-rich C-kinase substrate (MARCKS) are regulated by circadian rhythms. Our hypothesis is that administration of human AAT (hAAT) reduces blood pressure in hypertensive diabetic mice by attenuating membrane expression of ENaC and its association with the actin cytoskeleton. First, we show hAAT administration results in reduced blood pressure in diabetic db/db mice compared to vehicle treatment in both the inactive and active cycles. Western blotting and immunohistochemistry analyses showed a reduction of ENaC and the actin cytoskeleton protein, MARCKS in the kidneys of diabetic db/db mice treated with hAAT compared to vehicle. hAAT treatment resulted in elevated amounts of extracellular vesicles present in the urine of diabetic db/db mice compared to vehicle treatment both in the inactive and active cycles. Multiple hexosylceramides, among other lipid classes increased in urinary EVs released from hAAT treated hypertensive diabetic mice compared to vehicle treated mice. Taken together, these data suggest hAAT treatment could normalize blood pressure in the diabetic kidney in a mechanism involving attenuation of renal ENaC and MARCKS protein expression and possibly ceramide metabolism to hexosylceramide in kidney cells.
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Affiliation(s)
- Carlos I. Lugo
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Lauren P. Liu
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Niharika Bala
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Angelica G. Morales
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Mohammed F. Gholam
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
- Department of Basic Medical Sciences, College of Medicine, King Saud bin Abdulaziz University for Health Sciences, Jeddah 21423, Saudi Arabia
| | - Julia C. Abchee
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Nasseem Elmoujahid
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
| | - Ahmed Samir Elshikha
- Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, Gainesville, FL 32610, USA
- Department of Pharmaceutics, University of Florida College of Pharmacy, Gainesville, FL 32610, USA
| | - Rigena Avdiaj
- Department of Pharmaceutics, University of Florida College of Pharmacy, Gainesville, FL 32610, USA
| | - Louis A. Searcy
- Department of Physiological Sciences and Center for Environmental and Human Toxicology, University of Florida College of Veterinary Medicine, Gainesville, FL 32610, USA
| | - Nancy D. Denslow
- Department of Physiological Sciences and Center for Environmental and Human Toxicology, University of Florida College of Veterinary Medicine, Gainesville, FL 32610, USA
| | - Sihong Song
- Department of Pharmaceutics, University of Florida College of Pharmacy, Gainesville, FL 32610, USA
| | - Abdel A. Alli
- Department of Physiology and Aging, University of Florida College of Medicine, Gainesville, FL 32610, USA
- Department of Medicine Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, FL 32610, USA
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11
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Wang XP, Tomilin V, Nickerson AJ, Tian R, Ertem M, McKernan A, Lei X, Pochynyuk O, Kashlan OB. Bile acids regulate the epithelial Na + channel in native tissues through direct binding at multiple sites. J Physiol 2022; 600:4695-4711. [PMID: 36071685 PMCID: PMC9633555 DOI: 10.1113/jp283318] [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: 05/17/2022] [Accepted: 09/01/2022] [Indexed: 11/08/2022] Open
Abstract
Bile acids, originally known to emulsify dietary lipids, are now established signalling molecules that regulate physiological processes. Signalling targets several proteins that include the ion channels involved in regulating intestinal motility and bile viscosity. Studies show that bile acids regulate the epithelial sodium channel (ENaC) in cultured cell models and heterologous expression systems. ENaC plays both local and systemic roles in regulating extracellular fluids. Here we investigated whether bile acids regulate ENaC expressed in native tissues. We found that taurocholic acid and taurohyodeoxycholic acid regulated ENaC in both the distal nephron and distal colon. We also tested the hypothesis that regulation occurs through direct binding. Using photoaffinity labelling, we found evidence for specific binding to both the β and γ subunits of the channel. In functional experiments, we found that the α subunit was sufficient for regulation. We also found that regulation by at least one bile acid was voltage-sensitive, suggesting that one binding site may be closely associated with the pore-forming helices of the channel. Our data provide evidence that bile acids regulate ENaC by binding to multiple sites to influence the open probability of the channel. KEY POINTS: Recent studies have shown that bile acids regulate the epithelial sodium channel (ENaC) in vitro. Here we investigated whether bile acids regulate ENaC in native tissues and whether bile acids directly bind the channel. We found that bile acids regulate ENaC expressed in the mouse cortical collecting duct and mouse colon by modulating open probability. Photoaffinity labelling experiments showed specific binding to the β and γ subunits of the channel, while channels comprising only α subunits were sensitive to taurocholic acid in functional experiments using Xenopus oocytes. Taurocholic acid regulation of ENaC was voltage-dependent, providing evidence for binding to pore-forming helices. Our data indicate that bile acids are ENaC regulatory effectors that may have a role in the physiology and pathophysiology of several systems.
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Affiliation(s)
- Xue-Ping Wang
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Viktor Tomilin
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Andrew J Nickerson
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Runze Tian
- Beijing National Laboratory for Molecular Sciences, Department of Chemical Biology, College of Chemistry and Molecular Engineering, and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Merve Ertem
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Abagail McKernan
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Xiaoguang Lei
- Beijing National Laboratory for Molecular Sciences, Department of Chemical Biology, College of Chemistry and Molecular Engineering, and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Ossama B Kashlan
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Departments of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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12
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Mutengo KH, Masenga SK, Mwesigwa N, Patel KP, Kirabo A. Hypertension and human immunodeficiency virus: A paradigm for epithelial sodium channels? Front Cardiovasc Med 2022; 9:968184. [PMID: 36093171 PMCID: PMC9452753 DOI: 10.3389/fcvm.2022.968184] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 08/10/2022] [Indexed: 02/03/2023] Open
Abstract
Hypertension is a risk factor for end organ damage and death and is more common in persons with HIV compared to the general population. Several mechanisms have been studied in the pathogenesis of hypertension. Current evidence suggests that the epithelial sodium channel (ENaC) plays a key role in regulating blood pressure through the transport of sodium and water across membranes in the kidney tubules, resulting in retention of sodium and water and an altered fluid balance. However, there is scarcity of information that elucidates the role of ENaC in HIV as it relates to increasing the risk for development or pathogenesis of hypertension. This review summarized the evidence to date implicating a potential role for altered ENaC activity in contributing to hypertension in patients with HIV.
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Affiliation(s)
- Katongo H. Mutengo
- School of Medicine and Health Sciences, HAND Research Group, Mulungushi University, Livingstone Campus, Livingstone, Zambia,School of Public Health and Medicine, University of Zambia, Lusaka, Zambia
| | - Sepiso K. Masenga
- School of Medicine and Health Sciences, HAND Research Group, Mulungushi University, Livingstone Campus, Livingstone, Zambia,School of Public Health and Medicine, University of Zambia, Lusaka, Zambia
| | - Naome Mwesigwa
- Department of Medicine and Dentistry, Kampala International University, Kampala, Uganda
| | - Kaushik P. Patel
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, NE, United States
| | - Annet Kirabo
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, United States,*Correspondence: Annet Kirabo,
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13
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Elevated intracellular Na + and osmolarity stimulate catalytic activity of the ubiquitin ligase Nedd4-2. Proc Natl Acad Sci U S A 2022; 119:e2122495119. [PMID: 35858421 PMCID: PMC9335340 DOI: 10.1073/pnas.2122495119] [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] [Indexed: 01/21/2023] Open
Abstract
Regulation of catalytic activity of E3 ubiquitin ligases is critical for their cellular functions. We identified an unexpected mode of regulation of E3 catalytic activity by ions and osmolarity; enzymatic activity of the HECT family E3 Nedd4-2/Nedd4L is enhanced by increased intracellular Na+ ([Na+]i) and by hyperosmolarity. This stimulated activity is mediated by activation of p38-MAPK and is inhibited by WNKs. Moreover, protease (Furin)-mediated activation of the epithelial Na+ channel ENaC (a bona fide Nedd4-2 substrate), which leads to increased [Na+]i and osmolarity, results in enhanced Nedd4-2 catalytic activity. This enhancement is inhibited by a Furin inhibitor, by a protease-resistant ENaC mutant, or by treatment with the ENaC inhibitor amiloride. Moreover, WNK inhibition, which stimulates catalytic activity of Nedd4-2, leads to reduced levels of cell-surface ENaC and reduced channel activity. ENaC activity does not affect Nedd4-2:ENaC binding. Therefore, these results demonstrate activation of a ubiquitin ligase by Na+ and osmotic changes. Importantly, they reveal a negative feedback loop in which active ENaC leads to stimulation of catalytic activity of its own suppressor, Nedd4-2, to protect cells from excessive Na+ loading and hyperosmotic stress and to protect the animal from hypertension.
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14
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Zhang L, Wang X, Chen J, Kleyman TR, Sheng S. Accessibility of ENaC extracellular domain central core residues. J Biol Chem 2022; 298:101860. [PMID: 35339489 PMCID: PMC9052164 DOI: 10.1016/j.jbc.2022.101860] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 03/16/2022] [Accepted: 03/21/2022] [Indexed: 11/20/2022] Open
Abstract
The epithelial Na+ channel (ENaC)/degenerin family has a similar extracellular architecture, where specific regulatory factors interact and alter channel gating behavior. The extracellular palm domain serves as a key link to the channel pore. In this study, we used cysteine-scanning mutagenesis to assess the functional effects of Cys-modifying reagents on palm domain β10 strand residues in mouse ENaC. Of the 13 ENaC α subunit mutants with Cys substitutions examined, only mutants at sites in the proximal region of β10 exhibited changes in channel activity in response to methanethiosulfonate reagents. Additionally, Cys substitutions at three proximal sites of β and γ subunit β10 strands also rendered mutant channels methanethiosulfonate-responsive. Moreover, multiple Cys mutants were activated by low concentrations of thiophilic Cd2+. Using the Na+ self-inhibition response to assess ENaC gating behavior, we identified four α, two β, and two γ subunit β10 strand mutations that changed the Na+ self-inhibition response. Our results suggest that the proximal regions of β10 strands in all three subunits are accessible to small aqueous compounds and Cd2+ and have a role in modulating ENaC gating. These results are consistent with a structural model of mouse ENaC that predicts the presence of aqueous tunnels adjacent to the proximal part of β10 and with previously resolved structures of a related family member where palm domain structural transitions were observed with channels in an open or closed state.
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Affiliation(s)
- Lei Zhang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Xueqi Wang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Jingxin Chen
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Thomas R Kleyman
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
| | - Shaohu Sheng
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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15
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Mutchler SM, Kleyman TR. Effects of amiloride on acetylcholine-dependent arterial vasodilation evolve over time in mice on a high salt diet. Physiol Rep 2022; 10:e15255. [PMID: 35384364 PMCID: PMC8984245 DOI: 10.14814/phy2.15255] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2022] [Revised: 03/17/2022] [Accepted: 03/21/2022] [Indexed: 12/28/2022] Open
Abstract
The maintenance of endothelial health is required for normal vascular function and blood pressure regulation. The epithelial Na+ channel (ENaC) in endothelial cells has emerged as a new molecular player in the regulation of endothelial nitric oxide production and vascular stiffness. While ENaC expression in the kidney is negatively regulated by high [Na+ ], ENaC expression in isolated endothelial cells has been shown to increase in response to a high extracellular [Na+ ]. In culture, this increased expression leads to cellular stiffening and decreased nitric oxide release. In vivo, the effects of high salt diet on endothelial ENaC expression and activity have varied depending on the animal model utilized. Our aim in the present study was to examine the role of endothelial ENaC in mediating vasorelaxation in the C57Bl/6 mouse strain. We utilized pressure myography to test the responsiveness of thoracodorsal arteries to acetylcholine in mice with increased sodium consumption both in the presence and absence of increased aldosterone. ENaC's contribution was assessed with the use of the specific inhibitor amiloride. We found that while aldosterone had very little effect on ENaC's contribution to acetylcholine sensitivity, a high salt diet led to an amiloride-dependent shift in the acetylcholine response of vessels. However, the direction of this shift was dependent on the length of high salt diet administration. Overall, our studies reveal that ENaC's role in the endothelium may be more complicated than previously thought. The channel does not simply inhibit nitric oxide generation, but instead helps preserve a homeostatic response.
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Affiliation(s)
| | - Thomas R Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.,Departments of Cell Biology and of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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16
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Wang XP, Balchak DM, Gentilcore C, Clark NL, Kashlan OB. Activation by cleavage of the epithelial Na + channel α and γ subunits independently coevolved with the vertebrate terrestrial migration. eLife 2022; 11:75796. [PMID: 34984981 PMCID: PMC8791634 DOI: 10.7554/elife.75796] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 12/28/2021] [Indexed: 12/17/2022] Open
Abstract
Vertebrates evolved mechanisms for sodium conservation and gas exchange in conjunction with migration from aquatic to terrestrial habitats. Epithelial Na+ channel (ENaC) function is critical to systems responsible for extracellular fluid homeostasis and gas exchange. ENaC is activated by cleavage at multiple specific extracellular polybasic sites, releasing inhibitory tracts from the channel’s α and γ subunits. We found that proximal and distal polybasic tracts in ENaC subunits coevolved, consistent with the dual cleavage requirement for activation observed in mammals. Polybasic tract pairs evolved with the terrestrial migration and the appearance of lungs, coincident with the ENaC activator aldosterone, and appeared independently in the α and γ subunits. In summary, sites within ENaC for protease activation developed in vertebrates when renal Na+ conservation and alveolar gas exchange were required for terrestrial survival.
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Affiliation(s)
- Xue-Ping Wang
- Department of Medicine, University of Pittsburgh, Pittsburgh, United States
| | - Deidra M Balchak
- Department of Medicine, University of Pittsburgh, Pittsburgh, United States
| | - Clayton Gentilcore
- Department of Medicine, University of Pittsburgh, Pittsburgh, United States
| | - Nathan L Clark
- Department of Human Genetics, University of Utah, Salt Lake City, United States
| | - Ossama B Kashlan
- Department of Medicine, University of Pittsburgh, Pittsburgh, United States.,Computational and Systems Biology, University of Pittsburgh, Pittsburgh, United States
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17
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Rickert-Zacharias V, Schultz M, Mall MA, Schultz C. Visualization of Ectopic Serine Protease Activity by Förster Resonance Energy Transfer-Based Reporters. ACS Chem Biol 2021; 16:2174-2184. [PMID: 34726893 DOI: 10.1021/acschembio.1c00168] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Channel-activating proteases (CAPs) play a fundamental role in the regulation of sodium transport across epithelial tissues mainly via cleavage-mediated fine-tuning of the activity of the epithelial sodium channel (ENaC). Hyperactivity of CAPs and subsequently increased ENaC activity have been associated with various diseases, including cystic fibrosis (CF). To date, there is only a limited number of tools available to investigate CAP activity. Here, we developed ratiometric, peptide-based Förster resonance energy transfer (FRET) reporters useful to visualize and quantify the activity of ectopic serine proteases including the CAPs prostasin and matriptase in human and murine samples in a temporally and spatially resolved manner. Lipidated varieties were inserted into the outer leaflet of the plasma membrane to detect enzyme activity on the surface of individual cells, that is, close to the protease substrates. The FRET reporters (termed CAPRee) selectively detected the activity of ectopic serine proteases such as CAPs in solution and on the surface of human and murine cells. We found increased CAP activity on the surface of cells with a genetic background of CF. The new reporters will contribute to a better understanding of ectopic serine protease activity and their regulation under physiological and pathophysiological conditions.
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Affiliation(s)
- Verena Rickert-Zacharias
- Molecular Medicine Partnership Unit (MMPU), European Molecular Biology Laboratory (EMBL) and University of Heidelberg, 69117 Heidelberg, Germany
- Faculty of Biosciences, Collaboration for Joint Ph.D. Degree between EMBL and Heidelberg University, 69117 Heidelberg, Germany
- Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), 69120 Heidelberg, Germany
- Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Madeleine Schultz
- Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Marcus A. Mall
- Molecular Medicine Partnership Unit (MMPU), European Molecular Biology Laboratory (EMBL) and University of Heidelberg, 69117 Heidelberg, Germany
- Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), 69120 Heidelberg, Germany
- Department of Pediatric Pulmonology, Immunology and Critical Care Medicine, Charité─Universitätsmedizin Berlin, 13353 Berlin, Germany
- Berlin Institute of Health, 10178 Berlin, Germany
- German Center for Lung Research (DZL), Associated
Partner Site, 13353 Berlin, Germany
| | - Carsten Schultz
- Molecular Medicine Partnership Unit (MMPU), European Molecular Biology Laboratory (EMBL) and University of Heidelberg, 69117 Heidelberg, Germany
- Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), 69120 Heidelberg, Germany
- Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon 97239, United States
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18
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Gettings SM, Maxeiner S, Tzika M, Cobain MRD, Ruf I, Benseler F, Brose N, Krasteva-Christ G, Vande Velde G, Schönberger M, Althaus M. Two functional epithelial sodium channel isoforms are present in rodents despite pronounced evolutionary pseudogenisation and exon fusion. Mol Biol Evol 2021; 38:5704-5725. [PMID: 34491346 PMCID: PMC8662647 DOI: 10.1093/molbev/msab271] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The epithelial sodium channel (ENaC) plays a key role in salt and water homeostasis in
tetrapod vertebrates. There are four ENaC subunits (α, β, γ, δ), forming heterotrimeric
αβγ- or δβγ-ENaCs. Although the physiology of αβγ-ENaC is well understood, for decades the
field has stalled with respect to δβγ-ENaC due to the lack of mammalian model organisms.
The SCNN1D gene coding for δ-ENaC was previously believed to be absent in
rodents, hindering studies using standard laboratory animals. We analyzed all currently
available rodent genomes and discovered that SCNN1D is present in rodents
but was independently lost in five rodent lineages, including the Muridae (mice and rats).
The independent loss of SCNN1D in rodent lineages may be constrained by
phylogeny and taxon-specific adaptation to dry habitats, however habitat aridity does not
provide a selection pressure for maintenance of SCNN1D across Rodentia. A
fusion of two exons coding for a structurally flexible region in the extracellular domain
of δ-ENaC appeared in the Hystricognathi (a group that includes guinea pigs). This
conserved pattern evolved at least 41 Ma and represents a new autapomorphic feature for
this clade. Exon fusion does not impair functionality of guinea pig (Cavia
porcellus) δβγ-ENaC expressed in Xenopus oocytes.
Electrophysiological characterization at the whole-cell and single-channel level revealed
conserved biophysical features and mechanisms controlling guinea pig αβγ- and δβγ-ENaC
function as compared with human orthologs. Guinea pigs therefore represent commercially
available mammalian model animals that will help shed light on the physiological function
of δ-ENaC.
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Affiliation(s)
- Sean M Gettings
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.,Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Stephan Maxeiner
- Institute for Anatomy and Cell Biology, Saarland University School of Medicine, Homburg, Germany
| | - Maria Tzika
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Matthew R D Cobain
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Irina Ruf
- Division of Messel Research and Mammalogy, Senckenberg Research Institute and Natural History Museum Frankfurt, Frankfurt am Main, Germany
| | - Fritz Benseler
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Gabriela Krasteva-Christ
- Institute for Anatomy and Cell Biology, Saarland University School of Medicine, Homburg, Germany
| | - Greetje Vande Velde
- Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Matthias Schönberger
- Biomedical Imaging, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Belgium
| | - Mike Althaus
- Institute for Functional Gene Analytics, Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, Rheinbach, Germany
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19
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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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20
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Abstract
The Epithelial Na+ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na+ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.
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Affiliation(s)
- Daniela Rotin
- The Hospital for Sick Children, and The University of Toronto, Toronto, Canada
| | - Olivier Staub
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
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21
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Madhur MS, Elijovich F, Alexander MR, Pitzer A, Ishimwe J, Van Beusecum JP, Patrick DM, Smart CD, Kleyman TR, Kingery J, Peck RN, Laffer CL, Kirabo A. Hypertension: Do Inflammation and Immunity Hold the Key to Solving this Epidemic? Circ Res 2021; 128:908-933. [PMID: 33793336 PMCID: PMC8023750 DOI: 10.1161/circresaha.121.318052] [Citation(s) in RCA: 69] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Elevated cardiovascular risk including stroke, heart failure, and heart attack is present even after normalization of blood pressure in patients with hypertension. Underlying immune cell activation is a likely culprit. Although immune cells are important for protection against invading pathogens, their chronic overactivation may lead to tissue damage and high blood pressure. Triggers that may initiate immune activation include viral infections, autoimmunity, and lifestyle factors such as excess dietary salt. These conditions activate the immune system either directly or through their impact on the gut microbiome, which ultimately produces chronic inflammation and hypertension. T cells are central to the immune responses contributing to hypertension. They are activated in part by binding specific antigens that are presented in major histocompatibility complex molecules on professional antigen-presenting cells, and they generate repertoires of rearranged T-cell receptors. Activated T cells infiltrate tissues and produce cytokines including interleukin 17A, which promote renal and vascular dysfunction and end-organ damage leading to hypertension. In this comprehensive review, we highlight environmental, genetic, and microbial associated mechanisms contributing to both innate and adaptive immune cell activation leading to hypertension. Targeting the underlying chronic immune cell activation in hypertension has the potential to mitigate the excess cardiovascular risk associated with this common and deadly disease.
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Affiliation(s)
- Meena S. Madhur
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center
- Department of Molecular Physiology and Biophysics, Vanderbilt University
| | - Fernando Elijovich
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Matthew R. Alexander
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center
| | - Ashley Pitzer
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Jeanne Ishimwe
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Justin P. Van Beusecum
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - David M. Patrick
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center
| | - Charles D. Smart
- Department of Molecular Physiology and Biophysics, Vanderbilt University
| | - Thomas R. Kleyman
- Departments of Medicine, Cell Biology, Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Justin Kingery
- Center for Global Health, Weill Cornell Medical College, New York, NY, USA
- Department of Medicine, Weill Bugando School of Medicine, Mwanza, Tanzania
| | - Robert N. Peck
- Center for Global Health, Weill Cornell Medical College, New York, NY, USA
- Department of Medicine, Weill Bugando School of Medicine, Mwanza, Tanzania
- Mwanza Intervention Trials Unit (MITU), Mwanza, Tanzania
| | - Cheryl L. Laffer
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Annet Kirabo
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Molecular Physiology and Biophysics, Vanderbilt University
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22
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Abstract
The development of high blood pressure is influenced by genetic and environmental factors, with high salt intake being a known environmental contributor. Humans display a spectrum of sodium-sensitivity, with some individuals displaying a significant blood pressure rise in response to increased sodium intake while others experience almost no change. These differences are, in part, attributable to genetic variation in pathways involved in sodium handling and excretion. ENaC (epithelial sodium channel) is one of the key transporters responsible for the reabsorption of sodium in the distal nephron. This channel has an important role in the regulation of extracellular fluid volume and consequently blood pressure. Herein, we review the role of ENaC in the development of salt-sensitive hypertension, and present mechanistic insights into the regulation of ENaC activity and how it may accelerate sodium-induced damage and dysfunction. We discuss the traditional role of ENaC in renal sodium reabsorption and review work addressing ENaC expression and function in the brain, vasculature, and immune cells, and how this has expanded the implications for its role in the initiation and progression of salt-sensitive hypertension.
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Affiliation(s)
| | - Annet Kirabo
- Division of Clinical Pharmacology, Department of Medicine, and Department of Molecular Physiology and Biophysics Vanderbilt University, Nashville, TN (A.K.)
| | - Thomas R Kleyman
- From the Department of Medicine (S.M.M., T.R.K.), University of Pittsburgh, PA.,Department of Cell Biology (T.R.K.), University of Pittsburgh, PA.,Department of Pharmacology and Chemical Biology (T.R.K.), University of Pittsburgh, PA
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23
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Hou Y, Ding Y, Nie H, Ji HL. Fibrinolysis influences SARS-CoV-2 infection in ciliated cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2021:2021.01.07.425801. [PMID: 33442688 PMCID: PMC7805445 DOI: 10.1101/2021.01.07.425801] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Rapid spread of COVID-19 has caused an unprecedented pandemic worldwide, and an inserted furin site in SARS-CoV-2 spike protein (S) may account for increased transmissibility. Plasmin, and other host proteases, may cleave the furin site of SARS-CoV-2 S protein and γ subunits of epithelial sodium channels (γ ENaC), resulting in an increment in virus infectivity and channel activity. As for the importance of ENaC in the regulation of airway surface and alveolar fluid homeostasis, whether SARS-CoV-2 will share and strengthen the cleavage network with ENaC proteins at the single-cell level is urgently worthy of consideration. To address this issue, we analyzed single-cell RNA sequence (scRNA-seq) datasets, and found the PLAU (encoding urokinase plasminogen activator), SCNN1G (γENaC), and ACE2 (SARS-CoV-2 receptor) were co-expressed in alveolar epithelial, basal, club, and ciliated epithelial cells. The relative expression level of PLAU, TMPRSS2, and ACE2 were significantly upregulated in severe COVID-19 patients and SARS-CoV-2 infected cell lines using Seurat and DESeq2 R packages. Moreover, the increments in PLAU, FURIN, TMPRSS2, and ACE2 were predominately observed in different epithelial cells and leukocytes. Accordingly, SARS-CoV-2 may share and strengthen the ENaC fibrinolytic proteases network in ACE2 positive airway and alveolar epithelial cells, which may expedite virus infusion into the susceptible cells and bring about ENaC associated edematous respiratory condition.
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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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Abstract
PURPOSE OF REVIEW The main goal of this article is to discuss the role of the epithelial sodium channel (ENaC) in extracellular fluid and blood pressure regulation. RECENT FINDINGS Besides its role in sodium handling in the kidney, recent studies have found that ENaC expressed in other cells including immune cells can influence blood pressure via extra-renal mechanisms. Dendritic cells (DCs) are activated and contribute to salt-sensitive hypertension in an ENaC-dependent manner. We discuss recent studies on how ENaC is regulated in both the kidney and other sites including the vascular smooth muscles, endothelial cells, and immune cells. We also discuss how this extra-renal ENaC can play a role in salt-sensitive hypertension and its promise as a novel therapeutic target. The role of ENaC in blood pressure regulation in the kidney has been well studied. Recent human gene sequencing efforts have identified thousands of variants among the genes encoding ENaC, and research efforts to determine if these variants and their expression in extra-renal tissue play a role in hypertension will advance our understanding of the pathogenesis of ENaC-mediated cardiovascular disease and lead to novel therapeutic targets.
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Affiliation(s)
- Ashley L Pitzer
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, 2215 Garland Avenue, P415C Medical Research Building IV, Nashville, TN, 37232, USA
| | - Justin P Van Beusecum
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, 2215 Garland Avenue, P415C Medical Research Building IV, Nashville, TN, 37232, USA
| | - Thomas R Kleyman
- Departments of Medicine, Cell Biology, Pharmacology, and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Annet Kirabo
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, 2215 Garland Avenue, P415C Medical Research Building IV, Nashville, TN, 37232, USA. .,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.
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Wichmann L, Althaus M. Evolution of epithelial sodium channels: current concepts and hypotheses. Am J Physiol Regul Integr Comp Physiol 2020; 319:R387-R400. [PMID: 32783689 DOI: 10.1152/ajpregu.00144.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The conquest of freshwater and terrestrial habitats was a key event during vertebrate evolution. Occupation of low-salinity and dry environments required significant osmoregulatory adaptations enabling stable ion and water homeostasis. Sodium is one of the most important ions within the extracellular liquid of vertebrates, and molecular machinery for urinary reabsorption of this electrolyte is critical for the maintenance of body osmoregulation. Key ion channels involved in the fine-tuning of sodium homeostasis in tetrapod vertebrates are epithelial sodium channels (ENaCs), which allow the selective influx of sodium ions across the apical membrane of epithelial cells lining the distal nephron or the colon. Furthermore, ENaC-mediated sodium absorption across tetrapod lung epithelia is crucial for the control of liquid volumes lining the pulmonary surfaces. ENaCs are vertebrate-specific members of the degenerin/ENaC family of cation channels; however, there is limited knowledge on the evolution of ENaC within this ion channel family. This review outlines current concepts and hypotheses on ENaC phylogeny and discusses the emergence of regulation-defining sequence motifs in the context of osmoregulatory adaptations during tetrapod terrestrialization. In light of the distinct regulation and expression of ENaC isoforms in tetrapod vertebrates, we discuss the potential significance of ENaC orthologs in osmoregulation of fishes as well as the putative fates of atypical channel isoforms in mammals. We hypothesize that ancestral proton-sensitive ENaC orthologs might have aided the osmoregulatory adaptation to freshwater environments whereas channel regulation by proteases evolved as a molecular adaptation to lung liquid homeostasis in terrestrial tetrapods.
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Affiliation(s)
- Lukas Wichmann
- Institute for Animal Physiology, Justus Liebig University, Giessen, Germany
| | - Mike Althaus
- Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, Rheinbach, Germany
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Noreng S, Posert R, Bharadwaj A, Houser A, Baconguis I. Molecular principles of assembly, activation, and inhibition in epithelial sodium channel. eLife 2020; 9:59038. [PMID: 32729833 PMCID: PMC7413742 DOI: 10.7554/elife.59038] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 07/29/2020] [Indexed: 12/11/2022] Open
Abstract
The molecular bases of heteromeric assembly and link between Na+ self-inhibition and protease-sensitivity in epithelial sodium channels (ENaCs) are not fully understood. Previously, we demonstrated that ENaC subunits – α, β, and γ – assemble in a counterclockwise configuration when viewed from outside the cell with the protease-sensitive GRIP domains in the periphery (Noreng et al., 2018). Here we describe the structure of ENaC resolved by cryo-electron microscopy at 3 Å. We find that a combination of precise domain arrangement and complementary hydrogen bonding network defines the subunit arrangement. Furthermore, we determined that the α subunit has a primary functional module consisting of the finger and GRIP domains. The module is bifurcated by the α2 helix dividing two distinct regulatory sites: Na+ and the inhibitory peptide. Removal of the inhibitory peptide perturbs the Na+ site via the α2 helix highlighting the critical role of the α2 helix in regulating ENaC function.
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Affiliation(s)
- Sigrid Noreng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Richard Posert
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Arpita Bharadwaj
- Vollum Institute, Oregon Health & Science University, Portland, United States
| | - Alexandra Houser
- Neuroscience Graduate Program, Oregon Health & Science University, Portland, United States
| | - Isabelle Baconguis
- Vollum Institute, Oregon Health & Science University, Portland, United States
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28
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Kleyman TR, Eaton DC. Regulating ENaC's gate. Am J Physiol Cell Physiol 2020; 318:C150-C162. [PMID: 31721612 PMCID: PMC6985836 DOI: 10.1152/ajpcell.00418.2019] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 10/24/2019] [Accepted: 10/24/2019] [Indexed: 02/07/2023]
Abstract
Epithelial Na+ channels (ENaCs) are members of a family of cation channels that function as sensors of the extracellular environment. ENaCs are activated by specific proteases in the biosynthetic pathway and at the cell surface and remove embedded inhibitory tracts, which allows channels to transition to higher open-probability states. Resolved structures of ENaC and an acid-sensing ion channel revealed highly organized extracellular regions. Within the periphery of ENaC subunits are unique domains formed by antiparallel β-strands containing the inhibitory tracts and protease cleavage sites. ENaCs are inhibited by Na+ binding to specific extracellular site(s), which promotes channel transition to a lower open-probability state. Specific inositol phospholipids and channel modification by Cys-palmitoylation enhance channel open probability. How these regulatory factors interact in a concerted manner to influence channel open probability is an important question that has not been resolved. These various factors are reviewed, and the impact of specific factors on human disorders is discussed.
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Affiliation(s)
- Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, and Departments of Cell Biology and of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Douglas C Eaton
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
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29
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Ware AW, Rasulov SR, Cheung TT, Lott JS, McDonald FJ. Membrane trafficking pathways regulating the epithelial Na + channel. Am J Physiol Renal Physiol 2019; 318:F1-F13. [PMID: 31657249 DOI: 10.1152/ajprenal.00277.2019] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Renal Na+ reabsorption, facilitated by the epithelial Na+ channel (ENaC), is subject to multiple forms of control to ensure optimal body blood volume and pressure through altering both the ENaC population and activity at the cell surface. Here, the focus is on regulating the number of ENaCs present in the apical membrane domain through pathways of ENaC synthesis and targeting to the apical membrane as well as ENaC removal, recycling, and degradation. Finally, the mechanisms by which ENaC trafficking pathways are regulated are summarized.
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Affiliation(s)
- Adam W Ware
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Sahib R Rasulov
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Tanya T Cheung
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - J Shaun Lott
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Fiona J McDonald
- Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
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30
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Wang X, Chen J, Shi S, Sheng S, Kleyman TR. Analyses of epithelial Na + channel variants reveal that an extracellular β-ball domain critically regulates ENaC gating. J Biol Chem 2019; 294:16765-16775. [PMID: 31551351 DOI: 10.1074/jbc.ra119.010001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 09/19/2019] [Indexed: 11/06/2022] Open
Abstract
Epithelial Na+ channel (ENaC)-mediated Na+ transport has a key role in the regulation of extracellular fluid volume, blood pressure, and extracellular [K+]. Among the thousands of human ENaC variants, only a few exist whose functional consequences have been experimentally tested. Here, we used the Xenopus oocyte expression system to investigate the functional roles of four nonsynonymous human ENaC variants located within the β7-strand and its adjacent loop of the α-subunit extracellular β-ball domain. αR350Wβγ and αG355Rβγ channels exhibited 2.5- and 1.8-fold greater amiloride-sensitive currents than WT αβγ human ENaCs, respectively, whereas αV351Aβγ channels conducted significantly less current than WT. Currents in αH354Rβγ-expressing oocytes were similar to those expressing WT. Surface expression levels of three mutants (αR350Wβγ, αV351Aβγ, and αG355Rβγ) were similar to that of WT. However, three mutant channels (αR350Wβγ, αH354Rβγ, and αG355Rβγ) exhibited a reduced Na+ self-inhibition response. Open probability of αR350Wβγ was significantly greater than that of WT. Moreover, other Arg-350 variants, including αR350G, αR350L, and αR350Q, also had significantly increased channel activity. A direct comparison of αR350W and two previously reported gain-of-function variants revealed that αR350W increases ENaC activity similarly to αW493R, but to a much greater degree than does αC479R. Our results indicate that αR350W along with αR350G, αR350L, and αR350Q, and αG355R are novel gain-of-function variants that function as gating modifiers. The location of these multiple functional variants suggests that the αENaC β-ball domain portion that interfaces with the palm domain of βENaC critically regulates ENaC gating.
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Affiliation(s)
- Xueqi Wang
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Nephrology, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, China.,The Third Xiangya Hospital of Central South University, Changsha, Hunan 410013, China
| | - Jingxin Chen
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shujie Shi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shaohu Sheng
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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31
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Wu M, Liang C, Yu X, Song B, Yue Q, Zhai Y, Linck V, Cai Y, Niu N, Yang X, Zhang B, Wang Q, Zou L, Zhang S, Thai TL, Ma J, Sutliff RL, Zhang Z, Ma H. Lovastatin attenuates hypertension induced by renal tubule-specific knockout of ATP-binding cassette transporter A1, by inhibiting epithelial sodium channels. Br J Pharmacol 2019; 176:3695-3711. [PMID: 31222723 PMCID: PMC6715779 DOI: 10.1111/bph.14775] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2018] [Revised: 05/12/2019] [Accepted: 06/08/2019] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND AND PURPOSE We have shown that cholesterol is synthesized in the principal cells of renal cortical collecting ducts (CCD) and stimulates the epithelial sodium channels (ENaC). Here we have determined whether lovastatin, a cholesterol synthesis inhibitor, can antagonize the hypertension induced by activated ENaC, following deletion of the cholesterol transporter (ATP-binding cassette transporter A1; ABCA1). EXPERIMENTAL APPROACH We selectively deleted ABCA1 in the principal cells of mouse CCD and used the cell-attached patch-clamp technique to record ENaC activity. Western blot and immunofluorescence staining were used to evaluate protein expression levels. Systolic BP was measured with the tail-cuff method. KEY RESULTS Specific deletion of ABCA1 elevated BP and ENaC single-channel activity in the principal cells of CCD in mice. These effects were antagonized by lovastatin. ABCA1 deletion elevated intracellular cholesterol levels, which was accompanied by elevated ROS, increased expression of serum/glucocorticoid regulated kinase 1 (Sgk1), phosphorylated neural precursor cell-expressed developmentally down-regulated protein 4-2 (Nedd4-2) and furin, along with shorten the primary cilium, and reduced ATP levels in urine. CONCLUSIONS AND IMPLICATIONS These data suggest that specific deletion of ABCA1 in principal cells increases BP by stimulating ENaC channels via a cholesterol-dependent pathway which induces several secondary responses associated with oxidative stress, activated Sgk1/Nedd4-2, increased furin expression, and reduced cilium-mediated release of ATP. As ABCA1 can be blocked by cyclosporine A, these results suggest further investigation of the possible use of statins to treat CsA-induced hypertension.
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Affiliation(s)
- Ming‐Ming Wu
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Chen Liang
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Xiao‐Di Yu
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Bin‐Lin Song
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Qiang Yue
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Yu‐Jia Zhai
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Valerie Linck
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Yong‐Xu Cai
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Na Niu
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Xu Yang
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Bao‐Long Zhang
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Qiu‐Shi Wang
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - Li Zou
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Shuai Zhang
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Tiffany L. Thai
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
| | - Jing Ma
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of MedicineAtlanta Veterans Affairs Medical CenterDecaturGeorgia
| | - Roy L. Sutliff
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of MedicineAtlanta Veterans Affairs Medical CenterDecaturGeorgia
| | - Zhi‐Ren Zhang
- Departments of Cardiology and Clinic Pharmacy, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Key Laboratories of Education Ministry for Myocardial Ischemia Mechanism and TreatmentHarbin Medical University Cancer HospitalHarbinChina
| | - He‐Ping Ma
- Department of PhysiologyEmory University School of MedicineAtlantaGeorgia
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32
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Wichmann L, Dulai JS, Marles-Wright J, Maxeiner S, Szczesniak PP, Manzini I, Althaus M. An extracellular acidic cleft confers profound H +-sensitivity to epithelial sodium channels containing the δ-subunit in Xenopus laevis. J Biol Chem 2019; 294:12507-12520. [PMID: 31248986 DOI: 10.1074/jbc.ra119.008255] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Revised: 06/27/2019] [Indexed: 11/06/2022] Open
Abstract
The limited sodium availability of freshwater and terrestrial environments was a major physiological challenge during vertebrate evolution. The epithelial sodium channel (ENaC) is present in the apical membrane of sodium-absorbing vertebrate epithelia and evolved as part of a machinery for efficient sodium conservation. ENaC belongs to the degenerin/ENaC protein family and is the only member that opens without an external stimulus. We hypothesized that ENaC evolved from a proton-activated sodium channel present in ionocytes of freshwater vertebrates and therefore investigated whether such ancestral traits are present in ENaC isoforms of the aquatic pipid frog Xenopus laevis Using whole-cell and single-channel electrophysiology of Xenopus oocytes expressing ENaC isoforms assembled from αβγ- or δβγ-subunit combinations, we demonstrate that Xenopus δβγ-ENaC is profoundly activated by extracellular acidification within biologically relevant ranges (pH 8.0-6.0). This effect was not observed in Xenopus αβγ-ENaC or human ENaC orthologs. We show that protons interfere with allosteric ENaC inhibition by extracellular sodium ions, thereby increasing the probability of channel opening. Using homology modeling of ENaC structure and site-directed mutagenesis, we identified a cleft region within the extracellular loop of the δ-subunit that contains several acidic amino acid residues that confer proton-sensitivity and enable allosteric inhibition by extracellular sodium ions. We propose that Xenopus δβγ-ENaC can serve as a model for investigating ENaC transformation from a proton-activated toward a constitutively-active ion channel. Such transformation might have occurred during the evolution of tetrapod vertebrates to enable bulk sodium absorption during the water-to-land transition.
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Affiliation(s)
- Lukas Wichmann
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom; Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University Giessen, 35390 Giessen, Germany
| | - Jasdip Singh Dulai
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Jon Marles-Wright
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Stephan Maxeiner
- Institute of Anatomy and Cell Biology, Saarland University, 66421 Homburg, Germany
| | - Pawel Piotr Szczesniak
- Department of Medicine, Haematology/Oncology, Johann-Wolfgang-Goethe University Frankfurt, 60323 Frankfurt, Germany
| | - Ivan Manzini
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University Giessen, 35390 Giessen, Germany
| | - Mike Althaus
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom.
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Mutchler SM, Kleyman TR. New insights regarding epithelial Na+ channel regulation and its role in the kidney, immune system and vasculature. Curr Opin Nephrol Hypertens 2019; 28:113-119. [PMID: 30585851 PMCID: PMC6349474 DOI: 10.1097/mnh.0000000000000479] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE OF REVIEW This review describes recent findings regarding the epithelial Na channel (ENaC) and its roles in physiologic and pathophysiologic states. We discuss new insights regarding ENaC's structure, its regulation by various factors, its potential role in hypertension and nephrotic syndrome, and its roles in the immune system and vasculature. RECENT FINDINGS A recently resolved structure of ENaC provides clues regarding mechanisms of ENaC activation by proteases. The use of amiloride in nephrotic syndrome, and associated complications are discussed. ENaC is expressed in dendritic cells and contributes to immune system activation and increases in blood pressure in response to NaCl. ENaC is expressed in endothelial ENaC and has a role in regulating vascular tone. SUMMARY New findings have emerged regarding ENaC and its role in the kidney, immune system, and vasculature.
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Affiliation(s)
- Stephanie M. Mutchler
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA
| | - Thomas R. Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA
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34
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Cheung TT, Ismail NAS, Moir R, Arora N, McDonald FJ, Condliffe SB. Annexin II Light Chain p11 Interacts With ENaC to Increase Functional Activity at the Membrane. Front Physiol 2019; 10:7. [PMID: 30800070 PMCID: PMC6375906 DOI: 10.3389/fphys.2019.00007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2018] [Accepted: 01/07/2019] [Indexed: 11/13/2022] Open
Abstract
The epithelial Na+ channel (ENaC) provides for Na+ absorption in various types of epithelia including the kidney, lung, and colon where ENaC is localized to the apical membrane to enable Na+ entry into the cell. The degree of Na+ entry via ENaC largely depends on the number of active channels localized to the cell membrane, and is tightly controlled by interactions with ubiquitin ligases, kinases, and G-proteins. While regulation of ENaC endocytosis has been well-studied, relatively little is understood of the proteins that govern ENaC exocytosis. We hypothesized that the annexin II light chain, p11, could participate in the transport of ENaC along the exocytic pathway. Our results demonstrate that all three ENaC channel subunits interacted with p11 in an in vitro binding assay. Furthermore, p11 was able to immunoprecipitate ENaC in epithelial cells. Quantitative mass spectrometry of affinity-purified ENaC-p11 complexes recovered several other trafficking proteins including HSP-90 and annexin A6. We also report that p11 exhibits a robust protein expression in cortical collecting duct epithelial cells. However, the expression of p11 in these cells was not influenced by either short-term or long-term exposure to aldosterone. To determine whether the p11 interaction affected ENaC function, we measured amiloride sensitive Na+ currents in Xenopus oocytes or mammalian epithelia co-expressing ENaC and p11 or a siRNA to p11. Results from these experiments showed that p11 significantly augmented ENaC current, whereas knockdown of p11 decreased current. Further, knockdown of p11 reduced ENaC cell surface population suggesting p11 promotes membrane insertion of ENaC. Overall, our findings reveal a novel protein interaction that controls the number of ENaC channels inserted at the membrane via the exocytic pathway.
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Affiliation(s)
- Tanya T Cheung
- Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Noor A S Ismail
- Department of Physiology, University of Otago, Dunedin, New Zealand.,Biochemistry Department, Faculty of Medicine, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
| | - Rachel Moir
- Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Nikhil Arora
- Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Fiona J McDonald
- Department of Physiology, University of Otago, Dunedin, New Zealand
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35
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Gupta S, Pepper RJ, Ashman N, Walsh SB. Nephrotic Syndrome: Oedema Formation and Its Treatment With Diuretics. Front Physiol 2019; 9:1868. [PMID: 30697163 PMCID: PMC6341062 DOI: 10.3389/fphys.2018.01868] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 12/11/2018] [Indexed: 01/01/2023] Open
Abstract
Oedema is a defining element of the nephrotic syndrome. Its' management varies considerably between clinicians, with no national or international clinical guidelines, and hence variable outcomes. Oedema may have serious sequelae such as immobility, skin breakdown and local or systemic infection. Treatment of nephrotic oedema is often of limited efficacy, with frequent side-effects and interactions with other pharmacotherapy. Here, we describe the current paradigms of oedema in nephrosis, including insights into emerging mechanisms such as the role of the abnormal activation of the epithelial sodium channel in the collecting duct. We then discuss the physiological basis for traditional and novel therapies for the treatment of nephrotic oedema. Despite being the cardinal symptom of nephrosis, few clinical studies guide clinicians to the rational use of therapy. This is reflected in the scarcity of publications in this field; it is time to undertake new clinical trials to direct clinical practice.
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Affiliation(s)
- Sanjana Gupta
- UCL Centre for Nephrology, University College London, London, United Kingdom.,Renal Unit, The Royal London Hospital, Bart's Health NHS Trust, London, United Kingdom
| | - Ruth J Pepper
- UCL Centre for Nephrology, University College London, London, United Kingdom
| | - Neil Ashman
- Renal Unit, The Royal London Hospital, Bart's Health NHS Trust, London, United Kingdom
| | - Stephen B Walsh
- UCL Centre for Nephrology, University College London, London, United Kingdom
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36
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Sheng S, Chen J, Mukherjee A, Yates ME, Buck TM, Brodsky JL, Tolino MA, Hughey RP, Kleyman TR. Thumb domains of the three epithelial Na + channel subunits have distinct functions. J Biol Chem 2018; 293:17582-17592. [PMID: 30228189 PMCID: PMC6231141 DOI: 10.1074/jbc.ra118.003618] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 09/13/2018] [Indexed: 01/10/2023] Open
Abstract
The epithelial Na+ channel (ENaC) possesses a large extracellular domain formed by a β-strand core enclosed by three peripheral α-helical subdomains, which have been dubbed thumb, finger, and knuckle. Here we asked whether the ENaC thumb domains play specific roles in channel function. To this end, we examined the characteristics of channels lacking a thumb domain in an individual ENaC subunit (α, β, or γ). Removing the γ subunit thumb domain had no effect on Na+ currents when expressed in Xenopus oocytes, but moderately reduced channel surface expression. In contrast, ENaCs lacking the α or β subunit thumb domain exhibited significantly reduced Na+ currents along with a large reduction in channel surface expression. Moreover, channels lacking an α or γ thumb domain exhibited a diminished Na+ self-inhibition response, whereas this response was retained in channels lacking a β thumb domain. In turn, deletion of the α thumb domain had no effect on the degradation rate of the immature α subunit as assessed by cycloheximide chase analysis. However, accelerated degradation of the immature β subunit and mature γ subunit was observed when the β or γ thumb domain was deleted, respectively. Our results suggest that the thumb domains in each ENaC subunit are required for optimal surface expression in oocytes and that the α and γ thumb domains both have important roles in the channel's inhibitory response to external Na+ Our findings support the notion that the extracellular helical domains serve as functional modules that regulate ENaC biogenesis and activity.
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Affiliation(s)
- Shaohu Sheng
- From the Renal-Electrolyte Division, Department of Medicine and
| | - Jingxin Chen
- From the Renal-Electrolyte Division, Department of Medicine and
| | | | | | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Microbiology and Molecular Genetics, and
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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37
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Balchak DM, Thompson RN, Kashlan OB. The epithelial Na + channel γ subunit autoinhibitory tract suppresses channel activity by binding the γ subunit's finger-thumb domain interface. J Biol Chem 2018; 293:16217-16225. [PMID: 30131333 DOI: 10.1074/jbc.ra118.004362] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 08/21/2018] [Indexed: 01/11/2023] Open
Abstract
Epithelial Na+ channel (ENaC) maturation and activation require proteolysis of both the α and γ subunits. Cleavage at multiple sites in the finger domain of each subunit liberates their autoinhibitory tracts. Synthetic peptides derived from the proteolytically released fragments inhibit the channel, likely by reconstituting key interactions removed by the proteolysis. We previously showed that a peptide derived from the α subunit's autoinhibitory sequence (α-8) binds at the α subunit's finger-thumb domain interface. Despite low sequence similarity between the α and γ subunit finger domains, we hypothesized that a peptide derived from the γ subunit's autoinhibitory sequence (γ-11) inhibits the channel through an analogous mechanism. Using Xenopus oocytes, we found here that channels lacking a γ subunit thumb domain were no longer sensitive to γ-11, but remained sensitive to α-8. We identified finger domain sites in the γ subunit that dramatically reduced γ-11 inhibition. Using cysteines and sulfhydryl reactive cross-linkers introduced into both the peptide and the subunit, we also could cross-link γ-11 to both the finger domain and the thumb domain of the γ subunit. Our results suggest that α-8 and γ-11 occupy similar binding pockets within their respective subunits, and that proteolysis of the α and γ subunits activate the channel through analogous mechanisms.
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Affiliation(s)
| | | | - Ossama B Kashlan
- From the Department of Medicine, Renal-Electrolyte Division and .,the Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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38
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Wichmann L, Vowinkel KS, Perniss A, Manzini I, Althaus M. Incorporation of the δ-subunit into the epithelial sodium channel (ENaC) generates protease-resistant ENaCs in Xenopus laevis. J Biol Chem 2018; 293:6647-6658. [PMID: 29576549 DOI: 10.1074/jbc.ra118.002543] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 03/14/2018] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is a critical regulator of vertebrate electrolyte homeostasis. ENaC is the only constitutively open ion channel in the degenerin/ENaC protein family, and its expression, membrane abundance, and open probability therefore are tightly controlled. The canonical ENaC is composed of three subunits (α, β, and γ), but a fourth δ-subunit may replace α and form atypical δβγ-ENaCs. Using Xenopus laevis as a model, here we found that mRNAs of the α- and δ-subunits are differentially expressed in different tissues and that δ-ENaC predominantly is present in the urogenital tract. Using whole-cell and single-channel electrophysiology of oocytes expressing Xenopus αβγ- or δβγ-ENaC, we demonstrate that the presence of the δ-subunit enhances the amount of current generated by ENaC due to an increased open probability, but also changes current into a transient form. Activity of canonical ENaCs is critically dependent on proteolytic processing of the α- and γ-subunits, and immunoblotting with epitope-tagged ENaC subunits indicated that, unlike α-ENaC, the δ-subunit does not undergo proteolytic maturation by the endogenous protease furin. Furthermore, currents generated by δβγ-ENaC were insensitive to activation by extracellular chymotrypsin, and presence of the δ-subunit prevented cleavage of γ-ENaC at the cell surface. Our findings suggest that subunit composition constitutes an additional level of ENaC regulation, and we propose that the Xenopus δ-ENaC subunit represents a functional example that demonstrates the importance of proteolytic maturation during ENaC evolution.
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Affiliation(s)
- Lukas Wichmann
- From the School of Natural and Environmental Sciences, Newcastle University, Ridley Building 2, Newcastle upon Tyne NE1 7RU, United Kingdom and.,the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Kirsty Sophia Vowinkel
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Alexander Perniss
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Ivan Manzini
- the Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig University, 35392 Giessen, Germany
| | - Mike Althaus
- From the School of Natural and Environmental Sciences, Newcastle University, Ridley Building 2, Newcastle upon Tyne NE1 7RU, United Kingdom and
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39
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Hachem A, Hariri E, Saoud P, Lteif C, Lteif L, Welty F. The Role of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in Cardiovascular Homeostasis: A Non-Systematic Literature Review. Curr Cardiol Rev 2018; 13:274-282. [PMID: 28782494 PMCID: PMC5730960 DOI: 10.2174/1573403x13666170804150954] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 07/09/2017] [Accepted: 07/17/2017] [Indexed: 01/10/2023] Open
Affiliation(s)
- Ahmad Hachem
- Department of Pediatrics and Adolescent Medicine, American University of Beirut Medical Center, Cairo St., Hamra, Beirut. Lebanon
| | - Essa Hariri
- University of Massachusetts Medical School, Department of Cardiovascular Medicine, Worcester, MA. United States
| | - Perla Saoud
- School of Pharmacy, Lebanese American University, P.O. Box 36, Byblos. Lebanon
| | - Christelle Lteif
- School of Pharmacy, Lebanese American University, P.O. Box 36, Byblos. Lebanon
| | - Louis Lteif
- Department of Pharmacy Practice, The Daniel K. Inouye College of Pharmacy, University of Hawaii at Hilo, Hawaii, HI. United States
| | - Francine Welty
- Division of Cardiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA. United States
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40
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Hamacher J, Hadizamani Y, Borgmann M, Mohaupt M, Männel DN, Moehrlen U, Lucas R, Stammberger U. Cytokine-Ion Channel Interactions in Pulmonary Inflammation. Front Immunol 2018; 8:1644. [PMID: 29354115 PMCID: PMC5758508 DOI: 10.3389/fimmu.2017.01644] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/10/2017] [Indexed: 12/12/2022] Open
Abstract
The lungs conceptually represent a sponge that is interposed in series in the bodies’ systemic circulation to take up oxygen and eliminate carbon dioxide. As such, it matches the huge surface areas of the alveolar epithelium to the pulmonary blood capillaries. The lung’s constant exposure to the exterior necessitates a competent immune system, as evidenced by the association of clinical immunodeficiencies with pulmonary infections. From the in utero to the postnatal and adult situation, there is an inherent vital need to manage alveolar fluid reabsorption, be it postnatally, or in case of hydrostatic or permeability edema. Whereas a wealth of literature exists on the physiological basis of fluid and solute reabsorption by ion channels and water pores, only sparse knowledge is available so far on pathological situations, such as in microbial infection, acute lung injury or acute respiratory distress syndrome, and in the pulmonary reimplantation response in transplanted lungs. The aim of this review is to discuss alveolar liquid clearance in a selection of lung injury models, thereby especially focusing on cytokines and mediators that modulate ion channels. Inflammation is characterized by complex and probably time-dependent co-signaling, interactions between the involved cell types, as well as by cell demise and barrier dysfunction, which may not uniquely determine a clinical picture. This review, therefore, aims to give integrative thoughts and wants to foster the unraveling of unmet needs in future research.
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Affiliation(s)
- Jürg Hamacher
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Internal Medicine V - Pneumology, Allergology, Respiratory and Environmental Medicine, Faculty of Medicine, Saarland University, Saarbrücken, Germany.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Yalda Hadizamani
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Michèle Borgmann
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Markus Mohaupt
- Internal Medicine, Sonnenhofspital Bern, Bern, Switzerland
| | | | - Ueli Moehrlen
- Paediatric Visceral Surgery, Universitäts-Kinderspital Zürich, Zürich, Switzerland
| | - Rudolf Lucas
- Department of Pharmacology and Toxicology, Vascular Biology Center, Medical College of Georgia, Augusta, GA, United States
| | - Uz Stammberger
- Lungen- und Atmungsstiftung Bern, Bern, Switzerland.,Novartis Institutes for Biomedical Research, Translational Clinical Oncology, Novartis Pharma AG, Basel, Switzerland
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41
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Kashlan OB, Kinlough CL, Myerburg MM, Shi S, Chen J, Blobner BM, Buck TM, Brodsky JL, Hughey RP, Kleyman TR. N-linked glycans are required on epithelial Na + channel subunits for maturation and surface expression. Am J Physiol Renal Physiol 2017; 314:F483-F492. [PMID: 29187368 DOI: 10.1152/ajprenal.00195.2017] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial Na+ channel (ENaC) subunits undergo N-linked glycosylation in the endoplasmic reticulum where they assemble into an αβγ complex. Six, 13, and 5 consensus sites (Asn-X-Ser/Thr) for N-glycosylation reside in the extracellular domains of the mouse α-, β-, and γ-subunits, respectively. Because the importance of ENaC N-linked glycans has not been fully addressed, we examined the effect of preventing N-glycosylation of specific subunits on channel function, expression, maturation, and folding. Heterologous expression in Xenopus oocytes or Fischer rat thyroid cells with αβγ-ENaC lacking N-linked glycans on a single subunit reduced ENaC activity as well as the inhibitory response to extracellular Na+. The lack of N-linked glycans on the β-subunit also precluded channel activation by trypsin. However, channel activation by shear stress was N-linked glycan independent, regardless of which subunit was modified. We also discovered that the lack of N-linked glycans on any one subunit reduced the total and surface levels of cognate subunits. The lack of N-linked glycans on the β-subunit had the largest effect on total levels, with the lack of N-linked glycans on the γ- and α-subunits having intermediate and modest effects, respectively. Finally, channels with wild-type β-subunits were more sensitive to limited trypsin proteolysis than channels lacking N-linked glycans on the β-subunit. Our results indicate that N-linked glycans on each subunit are required for proper folding, maturation, surface expression, and function of the channel.
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Affiliation(s)
- Ossama B Kashlan
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.,Department of Computational and Systems Biology, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Carol L Kinlough
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Michael M Myerburg
- Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Shujie Shi
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Jingxin Chen
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Brandon M Blobner
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Teresa M Buck
- Department of Biological Sciences, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Rebecca P Hughey
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.,Department of Cell Biology, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Thomas R Kleyman
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.,Department of Cell Biology, University of Pittsburgh , Pittsburgh, Pennsylvania.,Department of Pharmacology and Chemical Biology, University of Pittsburgh , Pittsburgh, Pennsylvania
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42
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Kleyman TR, Kashlan OB, Hughey RP. Epithelial Na + Channel Regulation by Extracellular and Intracellular Factors. Annu Rev Physiol 2017; 80:263-281. [PMID: 29120692 DOI: 10.1146/annurev-physiol-021317-121143] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Epithelial Na+ channels (ENaCs) are members of the ENaC/degenerin family of ion channels that evolved to respond to extracellular factors. In addition to being expressed in the distal aspects of the nephron, where ENaCs couple the absorption of filtered Na+ to K+ secretion, these channels are found in other epithelia as well as nonepithelial tissues. This review addresses mechanisms by which ENaC activity is regulated by extracellular factors, including proteases, Na+, and shear stress. It also addresses other factors, including acidic phospholipids and modification of ENaC cytoplasmic cysteine residues by palmitoylation, which enhance channel activity by altering interactions of the channel with the plasma membrane.
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Affiliation(s)
- Thomas R Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA; .,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA
| | - Ossama B Kashlan
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA; .,Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Rebecca P Hughey
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA; .,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.,Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15219, USA
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43
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Reihill JA, Walker B, Hamilton RA, Ferguson TEG, Elborn JS, Stutts MJ, Harvey BJ, Saint-Criq V, Hendrick SM, Martin SL. Inhibition of Protease-Epithelial Sodium Channel Signaling Improves Mucociliary Function in Cystic Fibrosis Airways. Am J Respir Crit Care Med 2017; 194:701-10. [PMID: 27014936 DOI: 10.1164/rccm.201511-2216oc] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
RATIONALE In cystic fibrosis (CF) a reduction in airway surface liquid (ASL) height compromises mucociliary clearance, favoring mucus plugging and chronic bacterial infection. Inhibitors of the epithelial sodium channel (ENaC) have therapeutic potential in CF airways to reduce hyperstimulated sodium and fluid absorption to levels that can restore airway hydration. OBJECTIVES To determine whether a novel compound (QUB-TL1) designed to inhibit protease/ENaC signaling in CF airways restores ASL volume and mucociliary function. METHODS Protease activity was measured using fluorogenic activity assays. Differentiated primary airway epithelial cell cultures (F508del homozygotes) were used to determined ENaC activity (Ussing chamber recordings), ASL height (confocal microscopy), and mucociliary function (by tracking the surface flow of apically applied microbeads). Cell toxicity was measured using a lactate dehydrogenase assay. MEASUREMENTS AND MAIN RESULTS QUB-TL1 inhibits extracellularly located channel activating proteases (CAPs), including prostasin, matriptase, and furin, the activities of which are observed at excessive levels at the apical surface of CF airway epithelial cells. QUB-TL1-mediated CAP inhibition results in diminished ENaC-mediated Na(+) absorption in CF airway epithelial cells caused by internalization of a prominent pool of cleaved (active) ENaCγ from the cell surface. Importantly, diminished ENaC activity correlates with improved airway hydration status and mucociliary clearance. We further demonstrate QUB-TL1-mediated furin inhibition, which is in contrast to other serine protease inhibitors (camostat mesylate and aprotinin), affords protection against neutrophil elastase-mediated ENaC activation and Pseudomonas aeruginosa exotoxin A-induced cell death. CONCLUSIONS QUB-TL1 corrects aberrant CAP activities, providing a mechanism to delay or prevent the development of CF lung disease in a manner independent of CF transmembrane conductance regulator mutation.
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Affiliation(s)
- James A Reihill
- 1 Biomolecular Sciences Research Group, School of Pharmacy, and
| | - Brian Walker
- 1 Biomolecular Sciences Research Group, School of Pharmacy, and
| | | | | | - J Stuart Elborn
- 2 School of Medicine, Dentistry & Biomedical Sciences, Queen's University, Belfast, Northern Ireland, United Kingdom
| | - M Jackson Stutts
- 3 Marsico Lung Institute and Cystic Fibrosis Center, University of North Carolina, Chapel Hill, North Carolina; and
| | - Brian J Harvey
- 4 Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI-ERC Beaumont Hospital, Dublin, Ireland
| | - Vinciane Saint-Criq
- 4 Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI-ERC Beaumont Hospital, Dublin, Ireland
| | - Siobhan M Hendrick
- 4 Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI-ERC Beaumont Hospital, Dublin, Ireland
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44
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Ray EC, Chen J, Kelly TN, He J, Hamm LL, Gu D, Shimmin LC, Hixson JE, Rao DC, Sheng S, Kleyman TR. Human epithelial Na+ channel missense variants identified in the GenSalt study alter channel activity. Am J Physiol Renal Physiol 2016; 311:F908-F914. [PMID: 27582106 PMCID: PMC5130461 DOI: 10.1152/ajprenal.00426.2016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 08/22/2016] [Indexed: 12/31/2022] Open
Abstract
Mutations in genes encoding subunits of the epithelial Na+ channel (ENaC) can cause early onset familial hypertension, demonstrating the importance of this channel in modulating blood pressure. It remains unclear whether other genetic variants resulting in subtler alterations of channel function result in hypertension or altered sensitivity of blood pressure to dietary salt. This study sought to identify functional human ENaC variants to examine how these variants alter channel activity and to explore whether these variants are associated with altered sensitivity of blood pressure to dietary salt. Six-hundred participants of the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study with salt-sensitive or salt-resistant blood pressure underwent sequencing of the genes encoding ENaC subunits. Functional effects of identified variants were examined in a Xenopus oocyte expression system. Variants that increased channel activity included three in the gene encoding the α-subunit (αS115N, αR476W, and αV481M), one in the β-subunit (βS635N), and one in the γ-subunit (γL438Q). One α-subunit variant (αA334T) and one γ-subunit variant (βD31N) decreased channel activity. Several α-subunit extracellular domain variants altered channel inhibition by extracellular Na+ (Na+ self-inhibition). One variant (αA334T) decreased and one (αV481M) increased cell surface expression. Association between these variants and salt sensitivity did not reach statistical significance. This study identifies novel functional human ENaC variants and demonstrates that some variants alter channel cell surface expression and/or Na+ self-inhibition.
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Affiliation(s)
- Evan C Ray
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Jingxin Chen
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Tanika N Kelly
- Department of Epidemiology, Tulane University, New Orleans, Louisiana
| | - Jiang He
- Department of Epidemiology, Tulane University, New Orleans, Louisiana.,Department of Medicine, Tulane University, New Orleans, Louisiana
| | - L Lee Hamm
- Department of Medicine, Tulane University, New Orleans, Louisiana
| | - Dongfeng Gu
- State Key Laboratory of Cardiovascular Disease, Division of Population Genetics, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Lawrence C Shimmin
- Human Genetics Center, University of Texas School of Public Health, Houston, Texas
| | - James E Hixson
- Human Genetics Center, University of Texas School of Public Health, Houston, Texas
| | - Dabeeru C Rao
- Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri
| | - Shaohu Sheng
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania;
| | - Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.,Departments of Cell Biology and Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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45
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Boscardin E, Alijevic O, Hummler E, Frateschi S, Kellenberger S. The function and regulation of acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC): IUPHAR Review 19. Br J Pharmacol 2016; 173:2671-701. [PMID: 27278329 DOI: 10.1111/bph.13533] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 05/19/2016] [Accepted: 06/02/2016] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC) are both members of the ENaC/degenerin family of amiloride-sensitive Na(+) channels. ASICs act as proton sensors in the nervous system where they contribute, besides other roles, to fear behaviour, learning and pain sensation. ENaC mediates Na(+) reabsorption across epithelia of the distal kidney and colon and of the airways. ENaC is a clinically used drug target in the context of hypertension and cystic fibrosis, while ASIC is an interesting potential target. Following a brief introduction, here we will review selected aspects of ASIC and ENaC function. We discuss the origin and nature of pH changes in the brain and the involvement of ASICs in synaptic signalling. We expose how in the peripheral nervous system, ASICs cover together with other ion channels a wide pH range as proton sensors. We introduce the mechanisms of aldosterone-dependent ENaC regulation and the evidence for an aldosterone-independent control of ENaC activity, such as regulation by dietary K(+) . We then provide an overview of the regulation of ENaC by proteases, a topic of increasing interest over the past few years. In spite of the profound differences in the physiological and pathological roles of ASICs and ENaC, these channels share many basic functional and structural properties. It is likely that further research will identify physiological contexts in which ASICs and ENaC have similar or overlapping roles.
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Affiliation(s)
- Emilie Boscardin
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Omar Alijevic
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
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46
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The Epithelial Sodium Channel and the Processes of Wound Healing. BIOMED RESEARCH INTERNATIONAL 2016; 2016:5675047. [PMID: 27493961 PMCID: PMC4963570 DOI: 10.1155/2016/5675047] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 06/15/2016] [Indexed: 12/19/2022]
Abstract
The epithelial sodium channel (ENaC) mediates passive sodium transport across the apical membranes of sodium absorbing epithelia, like the distal nephron, the intestine, and the lung airways. Additionally, the channel has been involved in the transduction of mechanical stimuli, such as hydrostatic pressure, membrane stretch, and shear stress from fluid flow. Thus, in vascular endothelium, it participates in the control of the vascular tone via its activity both as a sodium channel and as a shear stress transducer. Rather recently, ENaC has been shown to participate in the processes of wound healing, a role that may also involve its activities as sodium transporter and as mechanotransducer. Its presence as the sole channel mediating sodium transport in many tissues and the diversity of its functions probably underlie the complexity of its regulation. This brief review describes some aspects of ENaC regulation, comments on evidence about ENaC participation in wound healing, and suggests possible regulatory mechanisms involved in this participation.
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Hanukoglu I, Hanukoglu A. Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases. Gene 2016; 579:95-132. [PMID: 26772908 PMCID: PMC4756657 DOI: 10.1016/j.gene.2015.12.061] [Citation(s) in RCA: 250] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Revised: 12/20/2015] [Accepted: 12/22/2015] [Indexed: 01/24/2023]
Abstract
The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.
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Affiliation(s)
- Israel Hanukoglu
- Laboratory of Cell Biology, Faculty of Natural Sciences, Ariel University, Ariel, Israel.
| | - Aaron Hanukoglu
- Division of Pediatric Endocrinology, E. Wolfson Medical Center, Holon, Israel; Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel
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Larsen CK, Jensen IS, Sorensen MV, de Bruijn PI, Bleich M, Praetorius HA, Leipziger J. Hyperaldosteronism after decreased renal K+ excretion in KCNMB2 knockout mice. Am J Physiol Renal Physiol 2016; 310:F1035-46. [PMID: 26962098 DOI: 10.1152/ajprenal.00010.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/08/2016] [Indexed: 11/22/2022] Open
Abstract
The kidney is the primary organ ensuring K(+) homeostasis. K(+) is secreted into the urine in the distal tubule by two mechanisms: by the renal outer medullary K(+) channel (Kir1.1) and by the Ca(2+)-activated K(+) channel (KCa1.1). Here, we report a novel knockout mouse of the β2-subunit of the KCa1.1 channel (KCNMB2), which displays hyperaldosteronism after decreased renal K(+) excretion. KCNMB2(-/-) mice displayed hyperaldosteronism, normal plasma K(+) concentration, and produced dilute urine with decreased K(+) concentration. The normokalemia indicated that hyperaldosteronism did not result from primary aldosteronism. Activation of the renin-angiotensin-aldosterone system was also ruled out as renal renin mRNA expression was reduced in KCNMB2(-/-) mice. Renal K(+) excretion rates were similar in the two genotypes; however, KCNMB2(-/-) mice required elevated plasma aldosterone to achieve K(+) balance. Blockade of the mineralocorticoid receptor with eplerenone triggered mild hyperkalemia and unmasked reduced renal K(+) excretion in KCNMB2(-/-) mice. Knockout mice for the α-subunit of the KCa1.1 channel (KCNMA1(-/-) mice) have hyperaldosteronism, are hypertensive, and lack flow-induced K(+) secretion. KCNMB2(-/-) mice share the phenotypic traits of normokalemia and hyperaldosteronism with KCNMA1(-/-) mice but were normotensive and displayed intact flow-induced K(+) secretion. Despite elevated plasma aldosterone, KNCMB2(-/-) mice did not display salt-sensitive hypertension and were able to decrease plasma aldosterone on a high-Na(+) diet, although plasma aldosterone remained elevated in KCNMB2(-/-) mice. In summary, KCNMB2(-/-) mice have a reduced ability to excrete K(+) into the urine but achieve K(+) balance through an aldosterone-mediated, β2-independent mechanism. The phenotype of KCNMB2 mice was similar but milder than the phenotype of KCNMA1(-/-) mice.
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Affiliation(s)
- Casper K Larsen
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark
| | - Iben S Jensen
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark
| | - Mads V Sorensen
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark; Aarhus Institute for Advanced Studies, Aarhus University, Aarhus, Denmark; and
| | - Pauline I de Bruijn
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark
| | - Markus Bleich
- Institute of Physiology, Christian-Albrechts-University, Kiel, Germany
| | - Helle A Praetorius
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark
| | - Jens Leipziger
- Department of Biomedicine, Physiology, and Health, Aarhus University, Aarhus, Denmark;
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Ji HL, Nie HG, Chang Y, Lian Q, Liu SL. CPT-cGMP Is A New Ligand of Epithelial Sodium Channels. Int J Biol Sci 2016; 12:359-66. [PMID: 27019621 PMCID: PMC4807156 DOI: 10.7150/ijbs.13764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Accepted: 11/11/2015] [Indexed: 12/28/2022] Open
Abstract
Epithelial sodium channels (ENaC) are localized at the apical membrane of the epithelium, and are responsible for salt and fluid reabsorption. Renal ENaC takes up salt, thereby controlling salt content in serum. Loss-of-function ENaC mutations lead to low blood pressure due to salt-wasting, while gain-of-function mutations cause impaired sodium excretion and subsequent hypertension as well as hypokalemia. ENaC activity is regulated by intracellular and extracellular signals, including hormones, neurotransmitters, protein kinases, and small compounds. Cyclic nucleotides are broadly involved in stimulating protein kinase A and protein kinase G signaling pathways, and, surprisingly, also appear to have a role in regulating ENaC. Increasing evidence suggests that the cGMP analog, CPT-cGMP, activates αβγ-ENaC activity reversibly through an extracellular pathway in a dose-dependent manner. Furthermore, the parachlorophenylthio moiety and ribose 2'-hydroxy group of CPT-cGMP are essential for facilitating the opening of ENaC channels by this compound. Serving as an extracellular ligand, CPT-cGMP eliminates sodium self-inhibition, which is a novel mechanism for stimulating salt reabsorption in parallel to the traditional NO/cGMP/PKG signal pathway. In conclusion, ENaC may be a druggable target for CPT-cGMP, leading to treatments for kidney malfunctions in salt reabsorption.
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Affiliation(s)
- Hong-Long Ji
- 1. Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Hong-Guang Nie
- 2. Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110001, China
| | - Yongchang Chang
- 3. Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, Arizona, 85013, USA
| | - Qizhou Lian
- 4. Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Shan-Lu Liu
- 5. Department of Molecular Microbiology and Immunology, Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
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Shobair M, Dagliyan O, Kota P, Dang YL, He H, Stutts MJ, Dokholyan NV. Gain-of-Function Mutation W493R in the Epithelial Sodium Channel Allosterically Reconfigures Intersubunit Coupling. J Biol Chem 2015; 291:3682-92. [PMID: 26668308 DOI: 10.1074/jbc.m115.678052] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Indexed: 12/21/2022] Open
Abstract
Sodium absorption in epithelial cells is rate-limited by the epithelial sodium channel (ENaC) activity in lung, kidney, and the distal colon. Pathophysiological conditions, such as cystic fibrosis and Liddle syndrome, result from water-electrolyte imbalance partly due to malfunction of ENaC regulation. Because the quaternary structure of ENaC is yet undetermined, the bases of pathologically linked mutations in ENaC subunits α, β, and γ are largely unknown. Here, we present a structural model of heterotetrameric ENaC α1βα2γ that is consistent with previous cross-linking results and site-directed mutagenesis experiments. By using this model, we show that the disease-causing mutation αW493R rewires structural dynamics of the intersubunit interfaces α1β and α2γ. Changes in dynamics can allosterically propagate to the channel gate. We demonstrate that cleavage of the γ-subunit, which is critical for full channel activation, does not mediate activation of ENaC by αW493R. Our molecular dynamics simulations led us to identify a channel-activating electrostatic interaction between α2Arg-493 and γGlu-348 at the α2γ interface. By neutralizing a sodium-binding acidic patch at the α1β interface, we reduced ENaC activation of αW493R by more than 2-fold. By combining homology modeling, molecular dynamics, cysteine cross-linking, and voltage clamp experiments, we propose a dynamics-driven model for the gain-of-function in ENaC by αW493R. Our integrated computational and experimental approach advances our understanding of structure, dynamics, and function of ENaC in its disease-causing state.
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Affiliation(s)
- Mahmoud Shobair
- From the Program in Molecular and Cellular Biophysics, Curriculum in Bioinformatics and Computational Biology, Department of Biochemistry and Biophysics, and
| | - Onur Dagliyan
- From the Program in Molecular and Cellular Biophysics, Department of Biochemistry and Biophysics, and
| | - Pradeep Kota
- From the Program in Molecular and Cellular Biophysics, Department of Biochemistry and Biophysics, and
| | - Yan L Dang
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Hong He
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - M Jackson Stutts
- Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Nikolay V Dokholyan
- From the Program in Molecular and Cellular Biophysics, Curriculum in Bioinformatics and Computational Biology, Department of Biochemistry and Biophysics, and Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
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