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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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2
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Diakov A, Nesterov V, Dahlmann A, Korbmacher C. Two adjacent phosphorylation sites in the C-terminus of the channel's α-subunit have opposing effects on epithelial sodium channel (ENaC) activity. Pflugers Arch 2022; 474:681-697. [PMID: 35525869 PMCID: PMC9192390 DOI: 10.1007/s00424-022-02693-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 04/25/2022] [Indexed: 02/07/2023]
Abstract
How phosphorylation of the epithelial sodium channel (ENaC) contributes to its regulation is incompletely understood. Previously, we demonstrated that in outside-out patches ENaC activation by serum- and glucocorticoid-inducible kinase isoform 1 (SGK1) was abolished by mutating a serine residue in a putative SGK1 consensus motif RXRXX(S/T) in the channel’s α-subunit (S621 in rat). Interestingly, this serine residue is followed by a highly conserved proline residue rather than by a hydrophobic amino acid thought to be required for a functional SGK1 consensus motif according to invitro data. This suggests that this serine residue is a potential phosphorylation site for the dual-specificity tyrosine phosphorylated and regulated kinase 2 (DYRK2), a prototypical proline-directed kinase. Its phosphorylation may prime a highly conserved preceding serine residue (S617 in rat) to be phosphorylated by glycogen synthase kinase 3 β (GSK3β). Therefore, we investigated the effect of DYRK2 on ENaC activity in outside-out patches of Xenopus laevis oocytes heterologously expressing rat ENaC. DYRK2 included in the pipette solution significantly increased ENaC activity. In contrast, GSK3β had an inhibitory effect. Replacing S621 in αENaC with alanine (S621A) abolished the effects of both kinases. A S617A mutation reduced the inhibitory effect of GKS3β but did not prevent ENaC activation by DYRK2. Our findings suggest that phosphorylation of S621 activates ENaC and primes S617 for subsequent phosphorylation by GSK3β resulting in channel inhibition. In proof-of-concept experiments, we demonstrated that DYRK2 can also stimulate ENaC currents in microdissected mouse distal nephron, whereas GSK3β inhibits the currents.
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Affiliation(s)
- Alexei Diakov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr, 6, 91054, Erlangen, Germany
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr, 6, 91054, Erlangen, Germany
| | - Anke Dahlmann
- Medizinische Klinik 4 - Nephrologie und Hypertensiologie, Universitätsklinikum Erlangen, Ulmenweg 18, 91054, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr, 6, 91054, Erlangen, Germany.
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3
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Anand D, Hummler E, Rickman OJ. ENaC activation by proteases. Acta Physiol (Oxf) 2022; 235:e13811. [PMID: 35276025 PMCID: PMC9540061 DOI: 10.1111/apha.13811] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/04/2022] [Accepted: 03/08/2022] [Indexed: 12/13/2022]
Abstract
Proteases are fundamental for a plethora of biological processes, including signalling and tissue remodelling, and dysregulated proteolytic activity can result in pathogenesis. In this review, we focus on a subclass of membrane‐bound and soluble proteases that are defined as channel‐activating proteases (CAPs), since they induce Na+ ion transport through an autocrine mechanism when co‐expressed with the highly amiloride‐sensitive epithelial sodium channel (ENaC) in Xenopus oocytes. These experiments first identified CAP1 (channel‐activating protease 1, prostasin) followed by CAP2 (channel‐activating protease 2, TMPRSS4) and CAP3 (channel‐activating protease 3, matriptase) as in vitro mediators of ENaC current. Since then, more serine‐, cysteine‐ and metalloproteases were confirmed as in vitro CAPs that potentially cleave and regulate ENaC, and thus this nomenclature was not further followed, but is accepted as functional term or alias. The precise mechanism of ENaC modulation by proteases has not been fully elucidated. Studies in organ‐specific protease knockout models revealed evidence for their role in increasing ENaC activity, although the proteases responsible for ENaC activation are yet to be identified. We summarize recent findings in animal models of these CAPs with respect to their implication in ENaC activation. We discuss the consequences of dysregulated CAPs underlying epithelial phenotypes in pathophysiological conditions, and the role of selected protease inhibitors. We believe that these proteases may present interesting therapeutic targets for diseases with aberrant sodium homoeostasis.
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Affiliation(s)
- Deepika Anand
- Department of Biomedical Sciences University of Lausanne Lausanne Switzerland
- National Center of Competence in Research, Kidney.CH Lausanne Switzerland
| | - Edith Hummler
- Department of Biomedical Sciences University of Lausanne Lausanne Switzerland
- National Center of Competence in Research, Kidney.CH Lausanne Switzerland
| | - Olivia J. Rickman
- Department of Biomedical Sciences University of Lausanne Lausanne Switzerland
- National Center of Competence in Research, Kidney.CH Lausanne Switzerland
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4
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Sure F, Bertog M, Afonso S, Diakov A, Rinke R, Madej MG, Wittmann S, Gramberg T, Korbmacher C, Ilyaskin AV. Transmembrane serine protease 2 (TMPRSS2) proteolytically activates the epithelial sodium channel (ENaC) by cleaving the channel's γ-subunit. J Biol Chem 2022; 298:102004. [PMID: 35504352 PMCID: PMC9163703 DOI: 10.1016/j.jbc.2022.102004] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 04/21/2022] [Accepted: 04/27/2022] [Indexed: 01/09/2023] Open
Abstract
The epithelial sodium channel (ENaC) is a heterotrimer consisting of α-, β-, and γ-subunits. Channel activation requires proteolytic release of inhibitory tracts from the extracellular domains of α-ENaC and γ-ENaC; however, the proteases involved in the removal of the γ-inhibitory tract remain unclear. In several epithelial tissues, ENaC is coexpressed with the transmembrane serine protease 2 (TMPRSS2). Here, we explored the effect of human TMPRSS2 on human αβγ-ENaC heterologously expressed in Xenopus laevis oocytes. We found that coexpression of TMPRSS2 stimulated ENaC-mediated whole-cell currents by approximately threefold, likely because of an increase in average channel open probability. Furthermore, TMPRSS2-dependent ENaC stimulation was not observed using a catalytically inactive TMPRSS2 mutant and was associated with fully cleaved γ-ENaC in the intracellular and cell surface protein fractions. This stimulatory effect of TMPRSS2 on ENaC was partially preserved when inhibiting its proteolytic activity at the cell surface using aprotinin but was abolished when the γ-inhibitory tract remained attached to its binding site following introduction of two cysteine residues (S155C–Q426C) to form a disulfide bridge. In addition, computer simulations and site-directed mutagenesis experiments indicated that TMPRSS2 can cleave γ-ENaC at sites both proximal and distal to the γ-inhibitory tract. This suggests a dual role of TMPRSS2 in the proteolytic release of the γ-inhibitory tract. Finally, we demonstrated that TMPRSS2 knockdown in cultured human airway epithelial cells (H441) reduced baseline proteolytic activation of endogenously expressed ENaC. Thus, we conclude that TMPRSS2 is likely to contribute to proteolytic ENaC activation in epithelial tissues in vivo.
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Affiliation(s)
- Florian Sure
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
| | - Marko Bertog
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
| | - Sara Afonso
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
| | - Alexei Diakov
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
| | - Ralf Rinke
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
| | - M Gregor Madej
- Department of Biophysics II/Structural Biology, University of Regensburg, Regensburg, Germany
| | - Sabine Wittmann
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsklinikum Erlangen, Institute of Clinical and Molecular Virology, Erlangen, Germany
| | - Thomas Gramberg
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Universitätsklinikum Erlangen, Institute of Clinical and Molecular Virology, Erlangen, Germany
| | - Christoph Korbmacher
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany.
| | - Alexandr V Ilyaskin
- Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Cellular and Molecular Physiology, Erlangen, Germany
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5
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Artunc F, Bohnert BN, Schneider JC, Staudner T, Sure F, Ilyaskin AV, Wörn M, Essigke D, Janessa A, Nielsen NV, Birkenfeld AL, Etscheid M, Haerteis S, Korbmacher C, Kanse SM. Proteolytic activation of the epithelial sodium channel (ENaC) by factor VII activating protease (FSAP) and its relevance for sodium retention in nephrotic mice. Pflugers Arch 2021; 474:217-229. [PMID: 34870751 PMCID: PMC8766372 DOI: 10.1007/s00424-021-02639-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 10/05/2021] [Accepted: 10/18/2021] [Indexed: 12/18/2022]
Abstract
Proteolytic activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases is thought to contribute to renal sodium retention in nephrotic syndrome. However, the identity of the responsible proteases remains elusive. This study evaluated factor VII activating protease (FSAP) as a candidate in this context. We analyzed FSAP in the urine of patients with nephrotic syndrome and nephrotic mice and investigated its ability to activate human ENaC expressed in Xenopus laevis oocytes. Moreover, we studied sodium retention in FSAP-deficient mice (Habp2−/−) with experimental nephrotic syndrome induced by doxorubicin. In urine samples from nephrotic humans, high concentrations of FSAP were detected both as zymogen and in its active state. Recombinant serine protease domain of FSAP stimulated ENaC-mediated whole-cell currents in a time- and concentration-dependent manner. Mutating the putative prostasin cleavage site in γ-ENaC (γRKRK178AAAA) prevented channel stimulation by the serine protease domain of FSAP. In a mouse model for nephrotic syndrome, active FSAP was present in nephrotic urine of Habp2+/+ but not of Habp2−/− mice. However, Habp2−/− mice were not protected from sodium retention compared to nephrotic Habp2+/+ mice. Western blot analysis revealed that in nephrotic Habp2−/− mice, proteolytic cleavage of α- and γ-ENaC was similar to that in nephrotic Habp2+/+ animals. In conclusion, active FSAP is excreted in the urine of nephrotic patients and mice and activates ENaC in vitro involving the putative prostasin cleavage site of γ-ENaC. However, endogenous FSAP is not essential for sodium retention in nephrotic mice.
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Affiliation(s)
- Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany. .,Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen, Tubingen, Germany. .,German Center for Diabetes Research (DZD) at the University Tübingen, Tubingen, Germany.
| | - Bernhard N Bohnert
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany.,Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen, Tubingen, Germany.,German Center for Diabetes Research (DZD) at the University Tübingen, Tubingen, Germany
| | - Jonas C Schneider
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany
| | - Tobias Staudner
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Florian Sure
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Alexandr V Ilyaskin
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Matthias Wörn
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany
| | - Daniel Essigke
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany.,Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen, Tubingen, Germany.,German Center for Diabetes Research (DZD) at the University Tübingen, Tubingen, Germany
| | - Andrea Janessa
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany
| | - Nis V Nielsen
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Andreas L Birkenfeld
- Department of Internal Medicine, Division of Endocrinology, Diabetology and Nephrology, University Hospital Tübingen, Tubingen, Germany.,Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen, Tubingen, Germany.,German Center for Diabetes Research (DZD) at the University Tübingen, Tubingen, Germany
| | | | - Silke Haerteis
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany.,Institute of Anatomy, University of Regensburg, Regensburg, Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Sandip M Kanse
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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6
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Bohnert BN, Essigke D, Janessa A, Schneider JC, Wörn M, Kalo MZ, Xiao M, Kong L, Omage K, Hennenlotter J, Amend B, Birkenfeld AL, Artunc F. Experimental nephrotic syndrome leads to proteolytic activation of the epithelial Na + channel in the mouse kidney. Am J Physiol Renal Physiol 2021; 321:F480-F493. [PMID: 34423678 DOI: 10.1152/ajprenal.00199.2021] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proteolytic activation of the renal epithelial Na+ channel (ENaC) involves cleavage events in its α- and γ-subunits and is thought to mediate Na+ retention in nephrotic syndrome (NS). However, the detection of proteolytically processed ENaC in kidney tissue from nephrotic mice has been elusive so far. We used a refined Western blot technique to reliably discriminate full-length α-ENaC and γ-ENaC and their cleavage products after proteolysis at their proximal and distal cleavage sites (designated from the NH2-terminus), respectively. Proteolytic ENaC activation was investigated in kidneys from mice with experimental NS induced by doxorubicin or inducible podocin deficiency with or without treatment with the serine protease inhibitor aprotinin. Nephrotic mice developed Na+ retention and increased expression of fragments of α-ENaC and γ-ENaC cleaved at both the proximal cleavage site and, more prominently, the distal cleavage site, respectively. Treatment with aprotinin but not with the mineralocorticoid receptor antagonist canrenoate prevented Na+ retention and upregulation of the cleavage products in nephrotic mice. Increased expression of cleavage products of α-ENaC and γ-ENaC was similarly found in healthy mice treated with a low-salt diet, sensitive to mineralocorticoid receptor blockade. In human nephrectomy specimens, γ-ENaC was found in the full-length form and predominantly cleaved at its distal cleavage site. In conclusion, murine experimental NS leads to aprotinin-sensitive proteolytic activation of ENaC at both proximal and, more prominently, distal cleavage sites of its α- and γ-subunit, most likely by urinary serine protease activity or proteasuria.NEW & NOTEWORTHY This study demonstrates that murine experimental nephrotic syndrome leads to aprotinin-sensitive proteolytic activation of the epithelial Na+ channel at both the α- and γ-subunit, most likely by urinary serine protease activity or proteasuria.
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Affiliation(s)
- Bernhard N Bohnert
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany.,Institute of Diabetes Research and Metabolic Diseases, Helmholtz Center Munich, University Tübingen, Tübingen, Germany.,German Center for Diabetes Research, University Tübingen, Tübingen, Germany
| | - Daniel Essigke
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Andrea Janessa
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Jonas C Schneider
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Matthias Wörn
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - M Zaher Kalo
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Mengyun Xiao
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Lingsi Kong
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Kingsley Omage
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany
| | - Jörg Hennenlotter
- Department of Urology, University Hospital Tübingen, Tübingen, Germany
| | - Bastian Amend
- Department of Urology, University Hospital Tübingen, Tübingen, Germany
| | - Andreas L Birkenfeld
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany.,Institute of Diabetes Research and Metabolic Diseases, Helmholtz Center Munich, University Tübingen, Tübingen, Germany.,German Center for Diabetes Research, University Tübingen, Tübingen, Germany
| | - Ferruh Artunc
- Division of Endocrinology, Diabetology and Nephrology, Department of Internal Medicine, University Hospital Tübingen, Tübingen, Germany.,Institute of Diabetes Research and Metabolic Diseases, Helmholtz Center Munich, University Tübingen, Tübingen, Germany.,German Center for Diabetes Research, University Tübingen, Tübingen, Germany
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7
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Essigke D, Ilyaskin AV, Wörn M, Bohnert BN, Xiao M, Daniel C, Amann K, Birkenfeld AL, Szabo R, Bugge TH, Korbmacher C, Artunc F. Zymogen-locked mutant prostasin (Prss8) leads to incomplete proteolytic activation of the epithelial sodium channel (ENaC) and severely compromises triamterene tolerance in mice. Acta Physiol (Oxf) 2021; 232:e13640. [PMID: 33650216 DOI: 10.1111/apha.13640] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/15/2021] [Accepted: 02/26/2021] [Indexed: 02/06/2023]
Abstract
AIM The serine protease prostasin (Prss8) is expressed in the distal tubule and stimulates proteolytic activation of the epithelial sodium channel (ENaC) in co-expression experiments in vitro. The aim of this study was to explore the role of prostasin in proteolytic ENaC activation in the kidney in vivo. METHODS We used genetically modified knockin mice carrying a Prss8 mutation abolishing proteolytic activity (Prss8-S238A) or a mutation leading to a zymogen-locked state (Prss8-R44Q). Mice were challenged with low sodium diet and diuretics. Regulation of ENaC activity by Prss8-S238A and Prss8-R44Q was studied in vitro using the Xenopus laevis oocyte expression system. RESULTS Co-expression of murine ENaC with Prss8-wt or Prss8-S238A in oocytes caused maximal proteolytic ENaC activation, whereas ENaC was activated only partially in oocytes co-expressing Prss8-R44Q. This was paralleled by a reduced proteolytic activity at the cell surface of Prss8-R44Q expressing oocytes. Sodium conservation under low sodium diet was preserved in Prss8-S238A and Prss8-R44Q mice but with higher plasma aldosterone concentrations in Prss8-R44Q mice. Treatment with the ENaC inhibitor triamterene over four days was tolerated in Prss8-wt and Prss8-S238A mice, whereas Prss8-R44Q mice developed salt wasting and severe weight loss associated with hyperkalemia and acidosis consistent with impaired ENaC function and renal failure. CONCLUSION Unlike proteolytically inactive Prss8-S238A, zymogen-locked Prss8-R44Q produces incomplete proteolytic ENaC activation in vitro and causes a severe renal phenotype in mice treated with the ENaC inhibitor triamterene. This indicates that Prss8 plays a role in proteolytic ENaC activation and renal function independent of its proteolytic activity.
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Affiliation(s)
- Daniel Essigke
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
| | - Alexandr V. Ilyaskin
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Matthias Wörn
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
| | - Bernhard N. Bohnert
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tuebingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tuebingen Germany
| | - Mengyun Xiao
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
| | - Christoph Daniel
- Institute of Pathology Department of Nephropathology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Kerstin Amann
- Institute of Pathology Department of Nephropathology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Andreas L. Birkenfeld
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tuebingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tuebingen Germany
| | - Roman Szabo
- Proteases and Tissue Remodeling Section National Institute of Dental and Craniofacial ResearchNational Institutes of Health Bethesda MD USA
| | - Thomas H. Bugge
- Proteases and Tissue Remodeling Section National Institute of Dental and Craniofacial ResearchNational Institutes of Health Bethesda MD USA
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Ferruh Artunc
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tuebingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tuebingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tuebingen Germany
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8
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Xiao M, Bohnert BN, Aypek H, Kretz O, Grahammer F, Aukschun U, Wörn M, Janessa A, Essigke D, Daniel C, Amann K, Huber TB, Plow EF, Birkenfeld AL, Artunc F. Plasminogen deficiency does not prevent sodium retention in a genetic mouse model of experimental nephrotic syndrome. Acta Physiol (Oxf) 2021; 231:e13512. [PMID: 32455507 DOI: 10.1111/apha.13512] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 05/15/2020] [Accepted: 05/19/2020] [Indexed: 12/19/2022]
Abstract
AIM Sodium retention is the hallmark of nephrotic syndrome (NS) and mediated by the proteolytic activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases. Plasmin is highly abundant in nephrotic urine and has been proposed to be the principal serine protease responsible for ENaC activation in NS. However, a proof of the essential role of plasmin in experimental NS is lacking. METHODS We used a genetic mouse model of NS based on an inducible podocin knockout (Bl6-Nphs2tm3.1Antc *Tg(Nphs1-rtTA*3G)8Jhm *Tg(tetO-cre)1Jaw or nphs2Δipod ). These mice were crossed with plasminogen deficient mice (Bl6-Plgtm1Jld or plg-/- ) to generate double knockout mice (nphs2Δipod *plg-/- ). NS was induced after oral doxycycline treatment for 14 days and mice were followed for subsequent 14 days. RESULTS Uninduced nphs2Δipod *plg-/- mice had normal kidney function and sodium handling. After induction, proteinuria increased similarly in both nphs2Δipod *plg+/+ and nphs2Δipod *plg-/- mice. Western blot revealed the urinary excretion of plasminogen and plasmin in nphs2Δipod *plg+/+ mice which were absent in nphs2Δipod *plg-/- mice. After the onset of proteinuria, amiloride-sensitive natriuresis was increased compared to the uninduced state in both genotypes. Subsequently, urinary sodium excretion dropped in both genotypes leading to an increase in body weight and development of ascites. Treatment with the serine protease inhibitor aprotinin prevented sodium retention in both genotypes. CONCLUSIONS This study shows that mice lacking urinary plasminogen are not protected from ENaC-mediated sodium retention in experimental NS. This points to an essential role of other urinary serine proteases in the absence of plasminogen.
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Affiliation(s)
- Mengyun Xiao
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
| | - Bernhard N. Bohnert
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Hande Aypek
- III. Department of Medicine University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Oliver Kretz
- III. Department of Medicine University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Florian Grahammer
- III. Department of Medicine University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Ute Aukschun
- IV. Department of Medicine, Faculty and University Medical Center Freiburg Freiburg Germany
| | - Matthias Wörn
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
| | - Andrea Janessa
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
| | - Daniel Essigke
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
| | - Christoph Daniel
- Institute of Nephropathology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Kerstin Amann
- Institute of Nephropathology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Tobias B. Huber
- III. Department of Medicine University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Edward F. Plow
- Lerner Research InstituteCleveland Clinic Cleveland OH USA
| | - Andreas L. Birkenfeld
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Ferruh Artunc
- Department of Internal Medicine Division of Endocrinology, Diabetology and Nephrology University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
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9
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Zhao R, Ali G, Nie HG, Chang Y, Bhattarai D, Su X, Zhao X, Matthay MA, Ji HL. Plasmin improves blood-gas barrier function in oedematous lungs by cleaving epithelial sodium channels. Br J Pharmacol 2020; 177:3091-3106. [PMID: 32133621 DOI: 10.1111/bph.15038] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Revised: 02/11/2020] [Accepted: 02/25/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND AND PURPOSE Lung oedema in association with suppressed fibrinolysis is a hallmark of lung injury. Here, we have tested whether plasmin cleaves epithelial sodium channels (ENaC) to resolve lung oedema fluid. EXPERIMENTAL APPROACH Human lungs and airway acid-instilled mice were used for analysing fluid resolution. In silico prediction, mutagenesis, Xenopus oocytes, immunoblotting, voltage clamp, mass spectrometry, and protein docking were combined for identifying plasmin cleavage sites. KEY RESULTS Plasmin improved lung fluid resolution in both human lungs ex vivo and injured mice. Plasmin activated αβγENaC channels in oocytes in a time-dependent manner. Deletion of four consensus proteolysis tracts (αΔ432-444, γΔ131-138, γΔ178-193, and γΔ410-422) eliminated plasmin-induced activation significantly. Further, immunoblotting assays identified 7 cleavage sites (K126, R135, K136, R153, K168, R178, K179) for plasmin to trim both furin-cleaved C-terminal fragments and full-length human γENaC proteins. In addition, 9 new sites (R122, R137, R138, K150, K170, R172, R180, K181, K189) in synthesized peptides were found to be cleaved by plasmin. These cleavage sites were located in the finger and the thumb, particularly the GRIP domain of human ENaC 3D model composed of two proteolytic centres for plasmin. Novel uncleaved sites beyond the GRIP domain in both α and γ subunits were identified to interrupt the plasmin cleavage-induced conformational change in ENaC channel complexes. Additionally, plasmin could regulate ENaC activity via the G protein signal. CONCLUSION AND IMPLICATIONS Plasmin can cleave ENaC to improve blood-gas exchange by resolving oedema fluid and could be a potent therapy for oedematous lungs.
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Affiliation(s)
- Runzhen Zhao
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas
| | - Gibran Ali
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas
| | - Hong-Guang Nie
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas.,College of Basic Medical Science, China Medical University, Shenyang, Liaoning, China
| | - Yongchang Chang
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona
| | - Deepa Bhattarai
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas
| | - Xuefeng Su
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas
| | - Xiaoli Zhao
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia
| | - Michael A Matthay
- Department of Medicine and Anesthesia, University of California San Francisco, San Francisco, California
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Centre at Tyler, Tyler, Texas.,Texas Lung Injury Institute, University of Texas Health Science Centre at Tyler, Tyler, Texas
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10
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Bohnert BN, Kanse S, Haerteis S, Korbmacher C, Artunc F. Rebuttal to editorial: Sodium retention by uPA in nephrotic syndrome? Acta Physiol (Oxf) 2020; 228:e13427. [PMID: 31794131 DOI: 10.1111/apha.13427] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Accepted: 12/02/2019] [Indexed: 12/31/2022]
Affiliation(s)
- Bernhard N. Bohnert
- Department of Internal Medicine Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Germany
| | - Sandip Kanse
- Institute of Basic Medical Sciences University of Oslo Oslo Norway
| | - Silke Haerteis
- Institute of Anatomy University of Regensburg Regensburg Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Erlangen Germany
| | - Ferruh Artunc
- Department of Internal Medicine Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Germany
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11
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Frindt G, Bertog M, Korbmacher C, Palmer LG. Ubiquitination of renal ENaC subunits in vivo. Am J Physiol Renal Physiol 2020; 318:F1113-F1121. [PMID: 32174140 DOI: 10.1152/ajprenal.00609.2019] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ubiquitination of the epithelial Na+ channel (ENaC) in epithelial cells may influence trafficking and hormonal regulation of the channels. We assessed ENaC ubiquitination (ub-ENaC) in mouse and rat kidneys using affinity beads to capture ubiquitinated proteins from tissue homogenates and Western blot analysis with anti-ENaC antibodies. Ub-αENaC was observed primarily as a series of proteins of apparent molecular mass of 40-70 kDa, consistent with the addition of variable numbers of ubiquitin molecules primarily to the NH2-terminal cleaved fragment (~30 kDa) of the subunit. No significant Ub-βENaC was detected, indicating that ubiquitination of this subunit is minimal. For γENaC, the protein eluted from the affinity beads had the same apparent molecular mass as the cleaved COOH-terminal fragment of the subunit (~65 kDa). This suggests that the ubiquitinated NH2 terminus remains attached to the COOH-terminal moiety during isolation through disulfide bonds. Consistent with this, under nonreducing conditions, eluates contained material with increased molecular mass (90-150 kDa). In mice with a Liddle syndrome mutation (β566X) deleting a putative binding site for the ubiquitin ligase neural precursor cell expressed developmentally downregulated 4-2, the amount of ub-γENaC was reduced as expected. To assess aldosterone dependence of ubiquitination, we fed rats either control or low-Na+ diets for 7 days before kidney harvest. Na+ depletion increased the amounts of ub-αENaC and ub-γENaC by three- to fivefold, probably reflecting increased amounts of fully cleaved ENaC. We conclude that ubiquitination occurs after complete proteolytic processing of the subunits, contributing to retrieval and/or disposal of channels expressed at the cell surface. Diminished ubiquitination does not appear to be a major factor in aldosterone-dependent ENaC upregulation.
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Affiliation(s)
- Gustavo Frindt
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, New York
| | - Marko Bertog
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, New York
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12
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Bohnert BN, Daiminger S, Wörn M, Sure F, Staudner T, Ilyaskin AV, Batbouta F, Janessa A, Schneider JC, Essigke D, Kanse S, Haerteis S, Korbmacher C, Artunc F. Urokinase-type plasminogen activator (uPA) is not essential for epithelial sodium channel (ENaC)-mediated sodium retention in experimental nephrotic syndrome. Acta Physiol (Oxf) 2019; 227:e13286. [PMID: 31006168 DOI: 10.1111/apha.13286] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/10/2019] [Accepted: 04/15/2019] [Indexed: 12/17/2022]
Abstract
AIM In nephrotic syndrome, aberrantly filtered plasminogen (plg) is converted to active plasmin by tubular urokinase-type plasminogen activator (uPA) and thought to lead to sodium retention by proteolytic activation of the epithelial sodium channel (ENaC). This concept predicts that uPA is an important factor for sodium retention and that inhibition of uPA might be protective in nephrotic syndrome. METHODS Activation of amiloride-sensitive currents by uPA and plg were studied in Xenopus laevis oocytes expressing murine ENaC. In doxorubicin-induced nephrotic mice, uPA was inhibited pharmacologically by amiloride and genetically by the use of uPA-deficient mice (uPA-/- ). RESULTS Experiments in Xenopus laevis oocytes expressing murine ENaC confirmed proteolytic ENaC activation by a combination of plg and uPA which stimulated amiloride-sensitive currents with concomitant cleavage of the ENaC γ-subunit at the cell surface. Treatment of nephrotic wild-type mice with amiloride inhibited urinary uPA activity, prevented urinary plasmin formation and sodium retention. In nephrotic mice lacking uPA (uPA-/- ), urinary plasmin formation from plg was suppressed and urinary uPA activity absent. However, in nephrotic uPA-/- mice, sodium retention was not reduced compared to nephrotic uPA+/+ mice. Amiloride prevented sodium retention in nephrotic uPA-/- mice which confirmed the critical role of ENaC in sodium retention. CONCLUSION uPA is responsible for the conversion of aberrantly filtered plasminogen to plasmin in the tubular lumen in vivo. However, uPA-dependent plasmin generation is not essential for ENaC-mediated sodium retention in experimental nephrotic syndrome.
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Affiliation(s)
- Bernhard N. Bohnert
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Sophie Daiminger
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Matthias Wörn
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Florian Sure
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Tobias Staudner
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Alexandr V. Ilyaskin
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Firas Batbouta
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Andrea Janessa
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Jonas C. Schneider
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Daniel Essigke
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Sandip Kanse
- Institute of Basic Medical Sciences University of Oslo Oslo Norway
| | - Silke Haerteis
- Institute of Anatomy University of Regensburg Regensburg Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology Friedrich‐Alexander University Erlangen‐Nürnberg (FAU) Bayern Germany
| | - Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
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13
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Zhao R, Ali G, Chang J, Komatsu S, Tsukasaki Y, Nie HG, Chang Y, Zhang M, Liu Y, Jain K, Jung BG, Samten B, Jiang D, Liang J, Ikebe M, Matthay MA, Ji HL. Proliferative regulation of alveolar epithelial type 2 progenitor cells by human Scnn1d gene. Am J Cancer Res 2019; 9:8155-8170. [PMID: 31754387 PMCID: PMC6857051 DOI: 10.7150/thno.37023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 09/16/2019] [Indexed: 01/03/2023] Open
Abstract
Lung epithelial sodium channel (ENaC) encoded by Scnn1 genes is essential for maintaining transepithelial salt and fluid homeostasis in the airway and the lung. Compared to α, β, and γ subunits, the role of respiratory δ-ENaC has not been studied in vivo due to the lack of animal models. Methods: We characterized full-length human δ802-ENaC expressed in both Xenopus oocytes and humanized transgenic mice. AT2 proliferation and differentiation in 3D organoids were analysed with FACS and a confocal microscope. Both two-electrode voltage clamp and Ussing chamber systems were applied to digitize δ802-ENaC channel activity. Immunoblotting was utilized to analyse δ802-ENaC protein. Transcripts of individual ENaC subunits in human lung tissues were quantitated with qPCR. Results: The results indicate that δ802-ENaC functions as an amiloride-inhibitable Na+ channel. Inhibitory peptide α-13 distinguishes δ802- from α-type ENaC channels. Modified proteolysis of γ-ENaC by plasmin and aprotinin did not alter the inhibition of amiloride and α-13 peptide. Expression of δ802-ENaC at the apical membrane of respiratory epithelium was detected with biophysical features similar to those of heterologously expressed channels in oocytes. δ802-ENaC regulated alveologenesis through facilitating the proliferation of alveolar type 2 epithelial cells. Conclusion: The humanized mouse line conditionally expressing human δ802-ENaC is a novel model for studying the expression and function of this protein in vivo .
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14
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Artunc F, Wörn M, Schork A, Bohnert BN. Proteasuria-The impact of active urinary proteases on sodium retention in nephrotic syndrome. Acta Physiol (Oxf) 2019; 225:e13249. [PMID: 30597733 DOI: 10.1111/apha.13249] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 11/30/2018] [Accepted: 12/03/2018] [Indexed: 12/14/2022]
Abstract
Sodium retention and extracellular volume expansion are typical features of patients with nephrotic syndrome. In recent years, from in vitro data, endoluminal activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases has been proposed as an underlying mechanism. Recently, this concept was supported in vivo in nephrotic mice that were protected from proteolytic ENaC activation and sodium retention by the use of aprotinin for the pharmacological inhibition of urinary serine protease activity. These and other findings from studies in both rodents and humans highlight the impact of active proteases in the urine, or proteasuria, on ENaC-mediated sodium retention and edema formation in nephrotic syndrome. Targeting proteasuria could become a therapeutic approach to treat patients with nephrotic syndrome. However, pathophysiologically relevant proteases remain to be identified. In this review, we introduce the concept of proteasuria to explain tubular sodium avidity and conclude that proteasuria can be considered as a key mechanism of sodium retention in patients with nephrotic syndrome.
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Affiliation(s)
- Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Matthias Wörn
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
| | - Anja Schork
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
| | - Bernhard N. Bohnert
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry University Hospital Tübingen Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen Tübingen Germany
- German Center for Diabetes Research (DZD) at the University Tübingen Tübingen Germany
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15
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Haerteis S, Schork A, Dörffel T, Bohnert BN, Nacken R, Wörn M, Xiao M, Essigke D, Janessa A, Schmaier AH, Feener EP, Häring HU, Bertog M, Korbmacher C, Artunc F. Plasma kallikrein activates the epithelial sodium channel in vitro but is not essential for volume retention in nephrotic mice. Acta Physiol (Oxf) 2018; 224:e13060. [PMID: 29489063 DOI: 10.1111/apha.13060] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2017] [Revised: 02/20/2018] [Accepted: 02/22/2018] [Indexed: 01/04/2023]
Abstract
AIM Recent work has demonstrated that activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases causes sodium retention in nephrotic syndrome. The aim of this study was to elucidate a potential role of plasma kallikrein (PKLK) as a candidate serine protease in this context. METHODS We analysed PKLK in the urine of patients with chronic kidney disease (CKD, n = 171) and investigated its ability to activate human ENaC expressed in Xenopus laevis oocytes. Moreover, we studied sodium retention in PKLK-deficient mice (klkb1-/- ) with experimental nephrotic syndrome induced by doxorubicin injection. RESULTS In patients with CKD, we found that PKLK is excreted in the urine up to a concentration of 2 μg mL-1 which was correlated with albuminuria (r = .71) and overhydration as assessed by bioimpedance spectroscopy (r = .44). PKLK increased ENaC-mediated whole-cell currents, which was associated with the appearance of a 67 kDa γ-ENaC cleavage product at the cell surface consistent with proteolytic activation. Mutating a putative prostasin cleavage site in γ-ENaC prevented channel stimulation by PKLK. In a mouse model for nephrotic syndrome, active PKLK was present in nephrotic urine of klkb1+/+ but not of klkb1-/- mice. However, klkb1-/- mice were not protected from ENaC activation and sodium retention compared to nephrotic klkb1+/+ mice. CONCLUSION Plasma kallikrein is detected in the urine of proteinuric patients and mice and activates ENaC in vitro involving the putative prostasin cleavage site. However, PKLK is not essential for volume retention in nephrotic mice.
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Affiliation(s)
- S. Haerteis
- Institute of Cellular and Molecular Physiology; Friedrich-Alexander University Erlangen-Nürnberg; Erlangen Germany
| | - A. Schork
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich; University of Tübingen; Tübingen Germany
- German Center for Diabetes Research (DZD); University of Tübingen; Tübingen Germany
| | - T. Dörffel
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
| | - B. N. Bohnert
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich; University of Tübingen; Tübingen Germany
- German Center for Diabetes Research (DZD); University of Tübingen; Tübingen Germany
| | - R. Nacken
- Institute of Cellular and Molecular Physiology; Friedrich-Alexander University Erlangen-Nürnberg; Erlangen Germany
| | - M. Wörn
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
| | - M. Xiao
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
| | - D. Essigke
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
| | - A. Janessa
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
| | - A. H. Schmaier
- Division of Hematology and Oncology; University Hospitals Cleveland Medical Center; Cleveland OH USA
- Case Western Reserve University; Cleveland OH USA
| | | | - H.-U. Häring
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich; University of Tübingen; Tübingen Germany
- German Center for Diabetes Research (DZD); University of Tübingen; Tübingen Germany
| | - M. Bertog
- Institute of Cellular and Molecular Physiology; Friedrich-Alexander University Erlangen-Nürnberg; Erlangen Germany
| | - C. Korbmacher
- Institute of Cellular and Molecular Physiology; Friedrich-Alexander University Erlangen-Nürnberg; Erlangen Germany
| | - F. Artunc
- Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry; Department of Internal Medicine; University Hospital Tübingen; Tübingen Germany
- Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich; University of Tübingen; Tübingen Germany
- German Center for Diabetes Research (DZD); University of Tübingen; Tübingen Germany
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16
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Bohnert BN, Menacher M, Janessa A, Wörn M, Schork A, Daiminger S, Kalbacher H, Häring HU, Daniel C, Amann K, Sure F, Bertog M, Haerteis S, Korbmacher C, Artunc F. Aprotinin prevents proteolytic epithelial sodium channel (ENaC) activation and volume retention in nephrotic syndrome. Kidney Int 2018; 93:159-172. [DOI: 10.1016/j.kint.2017.07.023] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2017] [Revised: 07/24/2017] [Accepted: 07/27/2017] [Indexed: 10/18/2022]
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17
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Abstract
JGP hosts key papers that shaped the epithelial transport field. Epithelia define the boundaries of the body and often transfer solutes and water from outside to inside (absorption) or from inside to outside (secretion). Those processes involve dual plasma membranes with different transport components that interact with each other. Understanding those functions has entailed breaking down the problem to analyze properties of individual membranes (apical vs. basolateral) and individual transport proteins. It also requires understanding of how those components interact and how they are regulated. This article outlines the modern history of this research as reflected by publications in The Journal of General Physiology.
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Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill-Cornell Medical College, New York, NY
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Rauh R, Hoerner C, Korbmacher C. δβγ-ENaC is inhibited by CFTR but stimulated by cAMP in Xenopus laevis oocytes. Am J Physiol Lung Cell Mol Physiol 2016; 312:L277-L287. [PMID: 27941075 DOI: 10.1152/ajplung.00375.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 12/05/2016] [Accepted: 12/05/2016] [Indexed: 11/22/2022] Open
Abstract
The epithelial sodium channel (ENaC) and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel critically regulate airway surface liquid by driving fluid absorption and secretion, respectively. Their functional interplay is complex and incompletely understood. ENaC is a heteromeric channel with three well-characterized subunits (α, β, and γ). In humans, an additional δ-ENaC subunit exists in lung and several other tissues, where it may replace the α-subunit to form δβγ-ENaC. Little is known about the physiological role of δβγ-ENaC and its possible interaction with CFTR. The aim of the present study was to investigate the effect of human CFTR on human δβγ-ENaC heterologously expressed in Xenopus laevis oocytes. In oocytes coexpressing δβγ-ENaC and CFTR the ENaC-mediated amiloride-sensitive whole cell current (ΔIami) was reduced by ~50% compared with that measured in oocytes expressing δβγ-ENaC alone. Moreover, basal level of proteolytic ENaC activation was reduced in the presence of CFTR. The inhibitory effect of CFTR on δβγ-ENaC was due to a combination of decreased average open probability (Po) and reduced channel expression at the cell surface. Interestingly, in oocytes expressing δβγ-ENaC, increasing intracellular [cAMP] by IBMX and forskolin increased ΔIami by ~50%. This stimulatory effect was not observed for human and rat αβγ-ENaC and was independent of CFTR coexpression and coactivation. Experiments with a mutant channel (δβS520Cγ-ENaC) which can be converted to a channel with a Po of nearly 1 suggested that cAMP activates δβγ-ENaC by increasing Po In conclusion, our results demonstrate that δβγ-ENaC is inhibited by CFTR but activated by cAMP.
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Affiliation(s)
- Robert Rauh
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christian Hoerner
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
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19
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Ramachandran R, Altier C, Oikonomopoulou K, Hollenberg MD. Proteinases, Their Extracellular Targets, and Inflammatory Signaling. Pharmacol Rev 2016; 68:1110-1142. [PMID: 27677721 DOI: 10.1124/pr.115.010991] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Given that over 2% of the human genome codes for proteolytic enzymes and their inhibitors, it is not surprising that proteinases serve many physiologic-pathophysiological roles. In this context, we provide an overview of proteolytic mechanisms regulating inflammation, with a focus on cell signaling stimulated by the generation of inflammatory peptides; activation of the proteinase-activated receptor (PAR) family of G protein-coupled receptors (GPCR), with a mechanism in common with adhesion-triggered GPCRs (ADGRs); and by proteolytic ion channel regulation. These mechanisms are considered in the much wider context that proteolytic mechanisms serve, including the processing of growth factors and their receptors, the regulation of matrix-integrin signaling, and the generation and release of membrane-tethered receptor ligands. These signaling mechanisms are relevant for inflammatory, neurodegenerative, and cardiovascular diseases as well as for cancer. We propose that the inflammation-triggering proteinases and their proteolytically generated substrates represent attractive therapeutic targets and we discuss appropriate targeting strategies.
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Affiliation(s)
- Rithwik Ramachandran
- Inflammation Research Network-Snyder Institute for Chronic Disease, Department of Physiology & Pharmacology (R.R., C.A., M.D.H.) and Department of Medicine (M.D.H.),University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada; Department of Pathology and Laboratory Medicine, Toronto Western Hospital, Toronto, Ontario, Canada (K.O.); and Department of Physiology and Pharmacology, Western University, London, Ontario, Canada (R.R.)
| | - Christophe Altier
- Inflammation Research Network-Snyder Institute for Chronic Disease, Department of Physiology & Pharmacology (R.R., C.A., M.D.H.) and Department of Medicine (M.D.H.),University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada; Department of Pathology and Laboratory Medicine, Toronto Western Hospital, Toronto, Ontario, Canada (K.O.); and Department of Physiology and Pharmacology, Western University, London, Ontario, Canada (R.R.)
| | - Katerina Oikonomopoulou
- Inflammation Research Network-Snyder Institute for Chronic Disease, Department of Physiology & Pharmacology (R.R., C.A., M.D.H.) and Department of Medicine (M.D.H.),University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada; Department of Pathology and Laboratory Medicine, Toronto Western Hospital, Toronto, Ontario, Canada (K.O.); and Department of Physiology and Pharmacology, Western University, London, Ontario, Canada (R.R.)
| | - Morley D Hollenberg
- Inflammation Research Network-Snyder Institute for Chronic Disease, Department of Physiology & Pharmacology (R.R., C.A., M.D.H.) and Department of Medicine (M.D.H.),University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada; Department of Pathology and Laboratory Medicine, Toronto Western Hospital, Toronto, Ontario, Canada (K.O.); and Department of Physiology and Pharmacology, Western University, London, Ontario, Canada (R.R.)
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20
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Ilyaskin AV, Diakov A, Korbmacher C, Haerteis S. Activation of the Human Epithelial Sodium Channel (ENaC) by Bile Acids Involves the Degenerin Site. J Biol Chem 2016; 291:19835-47. [PMID: 27489102 DOI: 10.1074/jbc.m116.726471] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Indexed: 12/22/2022] Open
Abstract
The epithelial sodium channel (ENaC) is a member of the ENaC/degenerin ion channel family, which also includes the bile acid-sensitive ion channel (BASIC). So far little is known about the effects of bile acids on ENaC function. ENaC is probably a heterotrimer consisting of three well characterized subunits (αβγ). In humans, but not in mice and rats, an additional δ-subunit exists. The aim of this study was to investigate the effects of chenodeoxycholic, cholic, and deoxycholic acid in unconjugated (CDCA, CA, and DCA) and tauro-conjugated (t-CDCA, t-CA, t-DCA) form on human ENaC in its αβγ- and δβγ-configuration. We demonstrated that tauro-conjugated bile acids significantly stimulate ENaC in the αβγ- and in the δβγ-configuration. In contrast, non-conjugated bile acids have a robust stimulatory effect only on δβγENaC. Bile acids stimulate ENaC-mediated currents by increasing the open probability of active channels without recruiting additional near-silent channels known to be activated by proteases. Stimulation of ENaC activity by bile acids is accompanied by a significant reduction of the single-channel current amplitude, indicating an interaction of bile acids with a region close to the channel pore. Analysis of the known ASIC1 (acid-sensing ion channel) crystal structure suggested that bile acids may bind to the pore region at the degenerin site of ENaC. Substitution of a single amino acid residue within the degenerin region of βENaC (N521C or N521A) significantly reduced the stimulatory effect of bile acids on ENaC, suggesting that this site is critical for the functional interaction of bile acids with the channel.
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Affiliation(s)
- Alexandr V Ilyaskin
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Alexei Diakov
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Christoph Korbmacher
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
| | - Silke Haerteis
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054 Erlangen, Germany
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21
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Schork A, Woern M, Kalbacher H, Voelter W, Nacken R, Bertog M, Haerteis S, Korbmacher C, Heyne N, Peter A, Häring HU, Artunc F. Association of Plasminuria with Overhydration in Patients with CKD. Clin J Am Soc Nephrol 2016; 11:761-769. [PMID: 26933188 PMCID: PMC4858495 DOI: 10.2215/cjn.12261115] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 01/27/2016] [Indexed: 01/13/2023]
Abstract
BACKGROUND AND OBJECTIVES Hypervolemia is a common feature of patients with CKD and associated with hypertension. Recent work has shown stimulation of sodium retention by urinary plasmin during nephrotic syndrome. However, it is unclear whether plasminuria plays a role in patients with stable CKD and non-nephrotic proteinuria. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In this cross-sectional study, we analyzed the fluid status of 171 patients with CKD consecutively presenting to our outpatient clinic from 2012 to 2013 using bioimpedance spectroscopy (Body Composition Monitor [BCM]; Fresenius Medical Care, Germany) and its associations to the urinary excretion of plasminogen and plasmin from a spot urine sample. Two-electrode voltage clamp measurements were performed in Xenopus laevis oocytes expressing human epithelial sodium channel to investigate whether plasmin in concentrations found in urine can activate the channel. RESULTS Overhydration >5% and overhydration >10% of the extracellular volume were found in 29% and 17% of the patients, respectively, and overhydration was associated with edema, hypertension, higher stages of CKD, and proteinuria. Proteinuria was the strongest independent predictor for overhydration (+0.58 L/1.73 m(2) per 10-fold increase; P<0.001). Urinary excretion of plasmin(ogen) quantified by ELISA correlated strongly with proteinuria (r=0.87) and overhydration (r=0.47). Using a chromogenic substrate, active plasmin was found in 44% of patients and correlated with proteinuria and overhydration. Estimated urinary plasmin concentrations were in a range sufficient to activate epithelial sodium channel currents in vitro. In multivariable analysis, urinary excretion of plasmin(ogen) was associated with overhydration similar to proteinuria. CONCLUSIONS Hypervolemia in patients with CKD is strongly associated with proteinuria, even in the non-nephrotic range. Protein-rich urine contains high amounts of plasminogen and active plasmin, rendering plasminuria as a possible link between proteinuria and hypervolemia.
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Affiliation(s)
- Anja Schork
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
| | - Matthias Woern
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
| | - Hubert Kalbacher
- Interfacultary Institute of Biochemistry, University Tuebingen, Tuebingen, Germany; and
| | - Wolfgang Voelter
- Interfacultary Institute of Biochemistry, University Tuebingen, Tuebingen, Germany; and
| | - Regina Nacken
- Institute of Cellular and Molecular Physiology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Marko Bertog
- Institute of Cellular and Molecular Physiology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Silke Haerteis
- Institute of Cellular and Molecular Physiology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institute of Cellular and Molecular Physiology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Nils Heyne
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
| | - Andreas Peter
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
| | - Hans-Ulrich Häring
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
| | - Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital of Tuebingen, Tuebingen, Germany
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Sensitisation of TRPV4 by PAR2 is independent of intracellular calcium signalling and can be mediated by the biased agonist neutrophil elastase. Pflugers Arch 2015; 467:687-701. [PMID: 24906497 DOI: 10.1007/s00424-014-1539-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Revised: 05/14/2014] [Accepted: 05/15/2014] [Indexed: 12/21/2022]
Abstract
Proteolytic activation of protease-activated receptor 2 (PAR2) may represent a major mechanism of regulating the transient receptor potential vanilloid 4 (TRPV4) non-selective cation channel in pathophysiological conditions associated with protease activation (e.g. during inflammation). To provide electrophysiological evidence for PAR2-mediated TRPV4 regulation, we characterised the properties of human TRPV4 heterologously expressed in Xenopus laevis oocytes in the presence and absence of co-expressed human PAR2. In outside-out patches from TRPV4 expressing oocytes, we detected single-channel activity typical for TRPV4 with a single-channel conductance of about 100 pS for outward and 55 pS for inward currents. The synthetic TRPV4 activator GSK1016790A stimulated TRPV4 mainly by converting previously silent channels into active channels with an open probability of nearly one. In oocytes co-expressing TRPV4 and PAR2, PAR2 activation by trypsin or by specific PAR2 agonist SLIGRL-NH2 potentiated the GSK1016790A-stimulated TRPV4 whole-cell currents several fold, indicative of channel sensitisation. Pre-incubation of oocytes with the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM did not reduce the stimulatory effect of PAR2 activation on TRPV4, which indicates that the effect is independent of intracellular calcium signalling. Neutrophil elastase, a biased agonist of PAR2 that does not induce intracellular calcium signalling, also caused a PAR2-dependent sensitisation of TRPV4. The Rho-kinase inhibitor Y27362 abolished elastase-stimulated sensitisation of TRPV4, which indicates that Rho-kinase signalling plays a critical role in PAR2-mediated TRPV4 sensitisation by the biased agonist neutrophil elastase. During acute inflammation, neutrophil elastase may sensitise TRPV4 by a mechanism involving biased agonism of PAR2 and activation of Rho-kinase.
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Ji HL, Zhao R, Komissarov AA, Chang Y, Liu Y, Matthay MA. Proteolytic regulation of epithelial sodium channels by urokinase plasminogen activator: cutting edge and cleavage sites. J Biol Chem 2015; 290:5241-55. [PMID: 25555911 DOI: 10.1074/jbc.m114.623496] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Plasminogen activator inhibitor 1 (PAI-1) level is extremely elevated in the edematous fluid of acutely injured lungs and pleurae. Elevated PAI-1 specifically inactivates pulmonary urokinase-type (uPA) and tissue-type plasminogen activators (tPA). We hypothesized that plasminogen activation and fibrinolysis may alter epithelial sodium channel (ENaC) activity, a key player in clearing edematous fluid. Two-chain urokinase (tcuPA) has been found to strongly stimulate heterologous human αβγ ENaC activity in a dose- and time-dependent manner. This activity of tcuPA was completely ablated by PAI-1. Furthermore, a mutation (S195A) of the active site of the enzyme also prevented ENaC activation. By comparison, three truncation mutants of the amino-terminal fragment of tcuPA still activated ENaC. uPA enzymatic activity was positively correlated with ENaC current amplitude prior to reaching the maximal level. In sharp contrast to uPA, neither single-chain tPA nor derivatives, including two-chain tPA and tenecteplase, affected ENaC activity. Furthermore, γ but not α subunit of ENaC was proteolytically cleaved at ((177)GR↓KR(180)) by tcuPA. In summary, the underlying mechanisms of urokinase-mediated activation of ENaC include release of self-inhibition, proteolysis of γ ENaC, incremental increase in opening rate, and activation of closed (electrically "silent") channels. This study for the first time demonstrates multifaceted mechanisms for uPA-mediated up-regulation of ENaC, which form the cellular and molecular rationale for the beneficial effects of urokinase in mitigating mortal pulmonary edema and pleural effusions.
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Affiliation(s)
- Hong-Long Ji
- From the Department of Cellular and Molecular Biology and the Texas Lung Injury Institute, University of Texas Health Science Center, Tyler, Texas 75708,
| | - Runzhen Zhao
- From the Department of Cellular and Molecular Biology and
| | | | - Yongchang Chang
- the Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013
| | - Yongfeng Liu
- the College of Public Health, Xinxiang Medical University, Xinxiang, Henan 453100, China, and
| | - Michael A Matthay
- the Departments of Medicine and Anesthesia, Cardiovascular Research Institute, University of California, San Francisco, California 94143
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Svenningsen P, Andersen H, Nielsen LH, Jensen BL. Urinary serine proteases and activation of ENaC in kidney--implications for physiological renal salt handling and hypertensive disorders with albuminuria. Pflugers Arch 2014; 467:531-42. [PMID: 25482671 DOI: 10.1007/s00424-014-1661-5] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 11/21/2014] [Accepted: 11/25/2014] [Indexed: 12/21/2022]
Abstract
Serine proteases, both soluble and cell-attached, can activate the epithelial sodium channel (ENaC) proteolytically through release of a putative 43-mer inhibitory tract from the ectodomain of the γ-subunit. ENaC controls renal Na(+) excretion and loss-of-function mutations lead to low blood pressure, while gain-of-function mutations lead to impaired Na(+) excretion, hypertension, and hypokalemia. We review an emerging pathophysiological concept that aberrant glomerular filtration of plasma proteases, e.g., plasmin, prostasin, and kallikrein, contributes to proteolytic activation of ENaC, both in acute conditions with proteinuria, like nephrotic syndrome and preeclampsia, and in chronic diseases, such as diabetes with microalbuminuria. A vast literature on renin-angiotensin-aldosterone system and volume homeostasis from the last four decades show a number of common characteristics for conditions with albuminuria compatible with impaired renal Na(+) excretion: hypertension and volume retention is secondary to proteinuria in, e.g., preeclampsia and nephrotic syndrome; plasma concentrations of renin, angiotensin II, and aldosterone are frequently suppressed in proteinuric conditions, e.g., preeclampsia and diabetic nephropathy; blood pressure is salt-sensitive in conditions with microalbuminuria/proteinuria; and extracellular volume is expanded, plasma atrial natriuretic peptide (ANP) concentration is increased, and diuretics, like amiloride and spironolactone, are effective blood pressure-reducing add-ons. Active plasmin in urine has been demonstrated in diabetes, preeclampsia, and nephrosis. Urine from these patients activates, plasmin-dependently, amiloride-sensitive inward current in vitro. The concept predicts that patients with albuminuria may benefit particularly from reduced salt intake with RAS blockers; that distally acting diuretics, in particular amiloride, are warranted in low-renin/albuminuric conditions; and that urine serine proteases and their activators may be pharmacological targets.
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Affiliation(s)
- Per Svenningsen
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
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25
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Lieu T, Jayaweera G, Zhao P, Poole DP, Jensen D, Grace M, McIntyre P, Bron R, Wilson YM, Krappitz M, Haerteis S, Korbmacher C, Steinhoff MS, Nassini R, Materazzi S, Geppetti P, Corvera CU, Bunnett NW. The bile acid receptor TGR5 activates the TRPA1 channel to induce itch in mice. Gastroenterology 2014; 147:1417-28. [PMID: 25194674 PMCID: PMC4821165 DOI: 10.1053/j.gastro.2014.08.042] [Citation(s) in RCA: 159] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Revised: 08/19/2014] [Accepted: 08/26/2014] [Indexed: 12/11/2022]
Abstract
BACKGROUND & AIMS Patients with cholestatic disease have increased systemic concentrations of bile acids (BAs) and profound pruritus. The G-protein-coupled BA receptor 1 TGR5 (encoded by GPBAR1) is expressed by primary sensory neurons; its activation induces neuronal hyperexcitability and scratching by unknown mechanisms. We investigated whether the transient receptor potential ankyrin 1 (TRPA1) is involved in BA-evoked, TGR5-dependent pruritus in mice. METHODS Co-expression of TGR5 and TRPA1 in cutaneous afferent neurons isolated from mice was analyzed by immunofluorescence, in situ hybridization, and single-cell polymerase chain reaction. TGR5-induced activation of TRPA1 was studied in in HEK293 cells, Xenopus laevis oocytes, and primary sensory neurons by measuring Ca(2+) signals. The contribution of TRPA1 to TGR5-induced release of pruritogenic neuropeptides, activation of spinal neurons, and scratching behavior were studied using TRPA1 antagonists or Trpa1(-/-) mice. RESULTS TGR5 and TRPA1 protein and messenger RNA were expressed by cutaneous afferent neurons. In HEK cells, oocytes, and neurons co-expressing TGR5 and TRPA1, BAs caused TGR5-dependent activation and sensitization of TRPA1 by mechanisms that required Gβγ, protein kinase C, and Ca(2+). Antagonists or deletion of TRPA1 prevented BA-stimulated release of the pruritogenic neuropeptides gastrin-releasing peptide and atrial natriuretic peptide B in the spinal cord. Disruption of Trpa1 in mice blocked BA-induced expression of Fos in spinal neurons and prevented BA-stimulated scratching. Spontaneous scratching was exacerbated in transgenic mice that overexpressed TRG5. Administration of a TRPA1 antagonist or the BA sequestrant colestipol, which lowered circulating levels of BAs, prevented exacerbated spontaneous scratching in TGR5 overexpressing mice. CONCLUSIONS BAs induce pruritus in mice by co-activation of TGR5 and TRPA1. Antagonists of TGR5 and TRPA1, or inhibitors of the signaling mechanism by which TGR5 activates TRPA1, might be developed for treatment of cholestatic pruritus.
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Affiliation(s)
- TinaMarie Lieu
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia
| | - Gihan Jayaweera
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia
| | - Peishen Zhao
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia
| | - Daniel P. Poole
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia,Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria, Australia
| | - Dane Jensen
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia
| | - Megan Grace
- Health Innovations Research Institute and School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia
| | - Peter McIntyre
- Health Innovations Research Institute and School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia
| | - Romke Bron
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria, Australia
| | - Yvette M. Wilson
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria, Australia
| | - Matteus Krappitz
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Martin S. Steinhoff
- Charles Institute for Translational Dermatology, University College Dublin, Dublin, Ireland
| | - Romina Nassini
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence, Florence, Italy
| | - Serena Materazzi
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence, Florence, Italy
| | - Pierangelo Geppetti
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence, Florence, Italy
| | - Carlos U. Corvera
- Department of Surgery, University of California, San Francisco, San Francisco, California
| | - Nigel W. Bunnett
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia,Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia
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Chen Z, Zhao R, Zhao M, Liang X, Bhattarai D, Dhiman R, Shetty S, Idell S, Ji HL. Regulation of epithelial sodium channels in urokinase plasminogen activator deficiency. Am J Physiol Lung Cell Mol Physiol 2014; 307:L609-17. [PMID: 25172911 DOI: 10.1152/ajplung.00126.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaC) govern transepithelial salt and fluid homeostasis. ENaC contributes to polarization, apoptosis, epithelial-mesenchymal transformation, etc. Fibrinolytic proteases play a crucial role in virtually all of these processes and are elaborated by the airway epithelium. We hypothesized that urokinase-like plasminogen activator (uPA) regulates ENaC function in airway epithelial cells and tested that possibility in primary murine tracheal epithelial cells (MTE). Both basal and cAMP-activated Na(+) flow through ENaC were significantly reduced in monolayers of uPA-deficient cells. The reduction in ENaC activity was further confirmed in basolateral membrane-permeabilized cells. A decrease in the Na(+)-K(+)-ATPase activity in the basolateral membrane could contribute to the attenuation of ENaC function in intact monolayer cells. Dysfunctional fluid resolution was seen in uPA-disrupted cells. Administration of uPA and plasmin partially restores ENaC activity and fluid reabsorption by MTEs. ERK1/2, but not Akt, phosphorylation was observed in the cells and lungs of uPA-deficient mice. On the other hand, cleavage of γ ENaC is significantly depressed in the lungs of uPA knockout mice vs. those of wild-type controls. Expression of caspase 8, however, did not differ between wild-type and uPA(-/-) mice. In addition, uPA deficiency did not alter transepithelial resistance. Taken together, the mechanisms for the regulation of ENaC by uPA in MTEs include augmentation of Na(+)-K(+)-ATPase, proteolysis, and restriction of ERK1/2 phosphorylation. We demonstrate for the first time that ENaC may serve as a downstream signaling target by which uPA controls the biophysical profiles of airway fluid and epithelial function.
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Affiliation(s)
- Zaixing Chen
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Runzhen Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Meimi Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Xinrong Liang
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Deepa Bhattarai
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Rohan Dhiman
- Department of Pulmonary Immunology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Sreerama Shetty
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Steven Idell
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and Department of Medicine, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and
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Krappitz M, Korbmacher C, Haerteis S. Demonstration of proteolytic activation of the epithelial sodium channel (ENaC) by combining current measurements with detection of cleavage fragments. J Vis Exp 2014. [PMID: 25045853 PMCID: PMC4211894 DOI: 10.3791/51582] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The described methods can be used to investigate the effect of proteases on ion channels, receptors, and other plasma membrane proteins heterologously expressed in Xenopus laevis oocytes. In combination with site-directed mutagenesis, this approach provides a powerful tool to identify functionally relevant cleavage sites. Proteolytic activation is a characteristic feature of the amiloride-sensitive epithelial sodium channel (ENaC). The final activating step involves cleavage of the channel’s γ-subunit in a critical region potentially targeted by several proteases including chymotrypsin and plasmin. To determine the stimulatory effect of these serine proteases on ENaC, the amiloride-sensitive whole-cell current (ΔIami) was measured twice in the same oocyte before and after exposure to the protease using the two-electrode voltage-clamp technique. In parallel to the electrophysiological experiments, a biotinylation approach was used to monitor the appearance of γENaC cleavage fragments at the cell surface. Using the methods described, it was demonstrated that the time course of proteolytic activation of ENaC-mediated whole-cell currents correlates with the appearance of a γENaC cleavage product at the cell surface. These results suggest a causal link between channel cleavage and channel activation. Moreover, they confirm the concept that a cleavage event in γENaC is required as a final step in proteolytic channel activation. The methods described here may well be applicable to address similar questions for other types of ion channels or membrane proteins.
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Affiliation(s)
- Matteus Krappitz
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
| | - Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU);
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28
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Kota P, Buchner G, Chakraborty H, Dang YL, He H, Garcia GJM, Kubelka J, Gentzsch M, Stutts MJ, Dokholyan NV. The N-terminal domain allosterically regulates cleavage and activation of the epithelial sodium channel. J Biol Chem 2014; 289:23029-23042. [PMID: 24973914 DOI: 10.1074/jbc.m114.570952] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The epithelial sodium channel (ENaC) is activated upon endoproteolytic cleavage of specific segments in the extracellular domains of the α- and γ-subunits. Cleavage is accomplished by intracellular proteases prior to membrane insertion and by surface-expressed or extracellular soluble proteases once ENaC resides at the cell surface. These cleavage events are partially regulated by intracellular signaling through an unknown allosteric mechanism. Here, using a combination of computational and experimental techniques, we show that the intracellular N terminus of γ-ENaC undergoes secondary structural transitions upon interaction with phosphoinositides. From ab initio folding simulations of the N termini in the presence and absence of phosphatidylinositol 4,5-bisphosphate (PIP2), we found that PIP2 increases α-helical propensity in the N terminus of γ-ENaC. Electrophysiology and mutation experiments revealed that a highly conserved cluster of lysines in the γ-ENaC N terminus regulates accessibility of extracellular cleavage sites in γ-ENaC. We also show that conditions that decrease PIP2 or enhance ubiquitination sharply limit access of the γ-ENaC extracellular domain to proteases. Further, the efficiency of allosteric control of ENaC proteolysis is dependent on Tyr(370) in γ-ENaC. Our findings provide an allosteric mechanism for ENaC activation regulated by the N termini and sheds light on a potential general mechanism of channel and receptor activation.
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Affiliation(s)
- Pradeep Kota
- Departments of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599; Departments of Molecular and Cellular Biophysics, and University of North Carolina, Chapel Hill, North Carolina 27599
| | - Ginka Buchner
- Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071, and
| | - Hirak Chakraborty
- Departments of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Yan L Dang
- Departments of Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Hong He
- Departments of Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Guilherme J M Garcia
- Biotechnology & Bioengineering Center, Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Jan Kubelka
- Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071, and
| | - Martina Gentzsch
- Departments of Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599,; Departments of Cell Biology and Physiology and University of North Carolina, Chapel Hill, North Carolina 27599
| | - M Jackson Stutts
- Departments of Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Nikolay V Dokholyan
- Departments of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599; Departments of Molecular and Cellular Biophysics, and University of North Carolina, Chapel Hill, North Carolina 27599; Departments of Cystic Fibrosis and Pulmonary Diseases Research and Treatment Center, University of North Carolina, Chapel Hill, North Carolina 27599,.
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29
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Haerteis S, Krappitz A, Krappitz M, Murphy JE, Bertog M, Krueger B, Nacken R, Chung H, Hollenberg MD, Knecht W, Bunnett NW, Korbmacher C. Proteolytic activation of the human epithelial sodium channel by trypsin IV and trypsin I involves distinct cleavage sites. J Biol Chem 2014; 289:19067-78. [PMID: 24841206 DOI: 10.1074/jbc.m113.538470] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Proteolytic activation is a unique feature of the epithelial sodium channel (ENaC). However, the underlying molecular mechanisms and the physiologically relevant proteases remain to be identified. The serine protease trypsin I can activate ENaC in vitro but is unlikely to be the physiologically relevant activating protease in ENaC-expressing tissues in vivo. Herein, we investigated whether human trypsin IV, a form of trypsin that is co-expressed in several extrapancreatic epithelial cells with ENaC, can activate human ENaC. In Xenopus laevis oocytes, we monitored proteolytic activation of ENaC currents and the appearance of γENaC cleavage products at the cell surface. We demonstrated that trypsin IV and trypsin I can stimulate ENaC heterologously expressed in oocytes. ENaC cleavage and activation by trypsin IV but not by trypsin I required a critical cleavage site (Lys-189) in the extracellular domain of the γ-subunit. In contrast, channel activation by trypsin I was prevented by mutating three putative cleavage sites (Lys-168, Lys-170, and Arg-172) in addition to mutating previously described prostasin (RKRK(178)), plasmin (Lys-189), and neutrophil elastase (Val-182 and Val-193) sites. Moreover, we found that trypsin IV is expressed in human renal epithelial cells and can increase ENaC-mediated sodium transport in cultured human airway epithelial cells. Thus, trypsin IV may regulate ENaC function in epithelial tissues. Our results show, for the first time, that trypsin IV can stimulate ENaC and that trypsin IV and trypsin I activate ENaC by cleavage at distinct sites. The presence of distinct cleavage sites may be important for ENaC regulation by tissue-specific proteases.
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Affiliation(s)
- Silke Haerteis
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Annabel Krappitz
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Matteus Krappitz
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Jane E Murphy
- the UCSF Center for the Neurobiology of Digestive Diseases, Department of Surgery, University of California, San Francisco, California
| | - Marko Bertog
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Bettina Krueger
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Regina Nacken
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany
| | - Hyunjae Chung
- the Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - Morley D Hollenberg
- the Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta T2N 4N1, Canada
| | - Wolfgang Knecht
- Bioscience, CVGI iMed, AstraZeneca Research and Development, 43181 Mölndal, Sweden
| | - Nigel W Bunnett
- the Monash Institute of Pharmaceutical Sciences, 381 Royal Parade, Parkville, Victoria 3052, Australia, and the Department of Pharmacology, University of Melbourne, Melbourne, Victoria 3010, Australia
| | - Christoph Korbmacher
- From the Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Waldstrasse 6, 91054 Erlangen, Germany,
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30
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Nguitragool W, Rayavara K, Desai SA. Proteolysis at a specific extracellular residue implicates integral membrane CLAG3 in malaria parasite nutrient channels. PLoS One 2014; 9:e93759. [PMID: 24699906 PMCID: PMC3974804 DOI: 10.1371/journal.pone.0093759] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 03/09/2014] [Indexed: 11/24/2022] Open
Abstract
The plasmodial surface anion channel mediates uptake of nutrients and other solutes into erythrocytes infected with malaria parasites. The clag3 genes of P. falciparum determine this channel’s activity in human malaria, but how the encoded proteins contribute to transport is unknown. Here, we used proteases to examine the channel’s composition and function. While proteases with distinct specificities all cleaved within an extracellular domain of CLAG3, they produced differing degrees of transport inhibition. Chymotrypsin-induced inhibition depended on parasite genotype, with channels induced by the HB3 parasite affected to a greater extent than those of the Dd2 clone. Inheritance of functional proteolysis in the HB3×Dd2 genetic cross, DNA transfection, and gene silencing experiments all pointed to the clag3 genes, providing independent evidence for a role of these genes. Protease protection assays with a Dd2-specific inhibitor and site-directed mutagenesis revealed that a variant L1115F residue on a CLAG3 extracellular loop contributes to inhibitor binding and accounts for differences in functional proteolysis. These findings indicate that surface-exposed CLAG3 is the relevant pool of this protein for channel function. They also suggest structural models for how exposed CLAG3 domains contribute to pore formation and parasite nutrient uptake.
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Affiliation(s)
- Wang Nguitragool
- The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America
- * E-mail: (WN); (SAD)
| | - Kempaiah Rayavara
- The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America
| | - Sanjay A. Desai
- The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America
- * E-mail: (WN); (SAD)
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31
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Galea CA, Nguyen HM, George Chandy K, Smith BJ, Norton RS. Domain structure and function of matrix metalloprotease 23 (MMP23): role in potassium channel trafficking. Cell Mol Life Sci 2014; 71:1191-210. [PMID: 23912897 PMCID: PMC11113776 DOI: 10.1007/s00018-013-1431-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 07/17/2013] [Accepted: 07/18/2013] [Indexed: 10/26/2022]
Abstract
MMP23 is a member of the matrix metalloprotease family of zinc- and calcium-dependent endopeptidases, which are involved in a wide variety of cellular functions. Its catalytic domain displays a high degree of structural homology with those of other metalloproteases, but its atypical domain architecture suggests that it may possess unique functional properties. The N-terminal MMP23 pro-domain contains a type-II transmembrane domain that anchors the protein to the plasma membrane and lacks the cysteine-switch motif that is required to maintain other MMPs in a latent state during passage to the cell surface. Instead of the C-terminal hemopexin domain common to other MMPs, MMP23 contains a small toxin-like domain (TxD) and an immunoglobulin-like cell adhesion molecule (IgCAM) domain. The MMP23 pro-domain can trap Kv1.3 but not closely-related Kv1.2 channels in the endoplasmic reticulum, preventing their passage to the cell surface, while the TxD can bind to the channel pore and block the passage of potassium ions. The MMP23 C-terminal IgCAM domain displays some similarity to Ig-like C2-type domains found in IgCAMs of the immunoglobulin superfamily, which are known to mediate protein-protein and protein-lipid interactions. MMP23 and Kv1.3 are co-expressed in a variety of tissues and together are implicated in diseases including cancer and inflammatory disorders. Further studies are required to elucidate the mechanism of action of this unique member of the MMP family.
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Affiliation(s)
- Charles A Galea
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia,
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32
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The phosphorylation of endogenous Nedd4-2 In Na(+)-absorbing human airway epithelial cells. Eur J Pharmacol 2014; 732:32-42. [PMID: 24657276 PMCID: PMC4022840 DOI: 10.1016/j.ejphar.2014.03.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 03/03/2014] [Accepted: 03/10/2014] [Indexed: 11/24/2022]
Abstract
Neural precursor cell expressed, developmentally down-regulated protein 4-2 (Nedd4-2) mediates the internalisation / degradation of epithelial Na+ channel subunits (α-, β- and γ-ENaC). Serum / glucocorticoid inducible kinase 1 (SGK1) and protein kinase A (PKA) both appear to inhibit this process by phosphorylating Nedd4-2-Ser221, -Ser327 and -Thr246. This Nedd4-2 inactivation process is thought to be central to the hormonal control of Na+ absorption. The present study of H441 human airway epithelial cells therefore explores the effects of SGK1 and / or PKA upon the phosphorylation / abundance of endogenous Nedd4-2; the surface expression of ENaC subunits, and electrogenic Na+ transport. Effects on Nedd4-2 phosphorylation/abundance and the surface expression of ENaC were monitored by western analysis, whilst Na+ absorption was quantified electrometrically. Acutely (20 min) activating PKA in glucocorticoid-deprived (24 h) cells increased the abundance of Ser221-phosphorylated, Ser327-phosphorylated and total Nedd4-2 without altering the abundance of Thr246-phosphorylated Nedd4-2. Activating PKA under these conditions did not cause a co-ordinated increase in the surface abundance of α-, β- and γ-ENaC and had only a very small effect upon electrogenic Na+ absorption. Activating PKA (20 min) in glucocorticoid-treated (0.2 µM dexamethasone, 24 h) cells, on the other hand, increased the abundance of Ser221-, Ser327- and Thr246-phosphorylated and total Nedd4-2; increased the surface abundance of α-, β- and γ-ENaC and evoked a clear stimulation of Na+ transport. Chronic glucocorticoid stimulation therefore appears to allow cAMP-dependent control of Na+ absorption by facilitating the effects of PKA upon the Nedd4-2 and ENaC subunits.
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33
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Büsst CJ. Blood pressure regulation via the epithelial sodium channel: from gene to kidney and beyond. Clin Exp Pharmacol Physiol 2014; 40:495-503. [PMID: 23710770 DOI: 10.1111/1440-1681.12124] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 05/17/2013] [Accepted: 05/20/2013] [Indexed: 01/11/2023]
Abstract
The epithelial sodium channel (ENaC) has long been recognized as playing a vital role in blood pressure (BP) regulation due to its involvement in fluid balance. The genes encoding the three ENaC subunits are likewise important contributors to hypertension, both in rare monogenic diseases and in the general population. The unusually high numbers of genetic variants associated with complex traits, including BP, that are located in non-coding areas suggest an involvement of these variants in regulatory functions. This may involve differential regulation of expression in different tissues. Emerging evidence indicates that the ENaC plays an important role in BP determination not only via its actions in the kidney, but also in other tissues commonly involved in BP regulation. The ENaC in the central nervous system is proposed to regulate BP via sympathetic nervous system activity. Recent evidence suggests that the ENaC contributes to vascular function and the myogenic response. Additional roles potentially include initiation of the baroreceptor reflex via ENaC in the baroreceptors and driving high salt intake with a 'taste for salt' via ENaC in the tongue. The present review describes the involvement of the ENaC in the determination of BP at a genetic and physiological level, detailing recent evidence for its role in the kidney and in other pertinent tissues.
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Affiliation(s)
- Cara J Büsst
- Departments of Physiology, The University of Melbourne and Monash University, Melbourne, Vic., Australia.
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34
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Warnock DG, Kusche-Vihrog K, Tarjus A, Sheng S, Oberleithner H, Kleyman TR, Jaisser F. Blood pressure and amiloride-sensitive sodium channels in vascular and renal cells. Nat Rev Nephrol 2014; 10:146-57. [PMID: 24419567 DOI: 10.1038/nrneph.2013.275] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Sodium transport in the distal nephron is mediated by epithelial sodium channel activity. Proteolytic processing of external domains and inhibition with increased sodium concentrations are important regulatory features of epithelial sodium channel complexes expressed in the distal nephron. By contrast, sodium channels expressed in the vascular system are activated by increased external sodium concentrations, which results in changes in the mechanical properties and function of endothelial cells. Mechanosensitivity and shear stress affect both epithelial and vascular sodium channel activity. Guyton's hypothesis stated that blood pressure control is critically dependent on vascular tone and fluid handling by the kidney. The synergistic effects, and complementary regulation, of the epithelial and vascular systems are consistent with the Guytonian model of volume and blood pressure regulation, and probably reflect sequential evolution of the two systems. The integration of vascular tone, renal perfusion and regulation of renal sodium reabsorption is the central underpinning of the Guytonian model. In this Review, we focus on the expression and regulation of sodium channels, and we outline the emerging evidence that describes the central role of amiloride-sensitive sodium channels in the efferent (vascular) and afferent (epithelial) arms of this homeostatic system.
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Affiliation(s)
- David G Warnock
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, 1720 2nd Avenue South, Birmingham, AL 34294-0007, USA
| | - Kristina Kusche-Vihrog
- Institut für Physiologie II, Westfälische Wilhelms Universität, Robert-Koch-Straße 27, 48149 Münster, Germany
| | - Antoine Tarjus
- INSERM U872 Team 1, Centre de Recherche des Cordeliers, Université René Descartes, Université Pierre et Marie Curie, 15 rue de l'Ecole de Médecine, 75006 Paris, France
| | - Shaohu Sheng
- Renal and Electrolyte Division, Department of Medicine, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, PA 15261, USA
| | - Hans Oberleithner
- Institut für Physiologie II, Westfälische Wilhelms Universität, Robert-Koch-Straße 27, 48149 Münster, Germany
| | - Thomas R Kleyman
- Renal and Electrolyte Division, Department of Medicine, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, PA 15261, USA
| | - Frederic Jaisser
- INSERM U872 Team 1, Centre de Recherche des Cordeliers, Université René Descartes, Université Pierre et Marie Curie, 15 rue de l'Ecole de Médecine, 75006 Paris, France
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35
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Pharmacological and electrophysiological characterization of the human bile acid-sensitive ion channel (hBASIC). Pflugers Arch 2013; 466:253-63. [PMID: 23842738 DOI: 10.1007/s00424-013-1310-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/07/2013] [Accepted: 06/10/2013] [Indexed: 01/23/2023]
Abstract
The human bile acid-sensitive ion channel (hBASIC) is a cation channel of the degenerin/epithelial Na(+) channel gene family that is expressed in the intestinal tract and can be activated by bile acids. Here, we show that in addition to its sensitivity for bile acids, hBASIC shares further key features with its rat ortholog: it is blocked by extracellular divalent cations, is inhibited by micromolar concentrations of the diarylamidine diminazene, and activated by millimolar concentrations of flufenamic acid. Furthermore, we demonstrate that two major bile acids present in human bile, chenodeoxycholic acid and deoxycholic acid, activate hBASIC in a synergistic manner. In addition, we determined the single-channel properties of hBASIC in outside-out patch clamp recordings, revealing a single-channel conductance of about 11 pS and a high Na(+) selectivity. Deoxycholic acid activates hBASIC in patch clamp recordings mainly by reducing the single-channel closed time. In summary, we provide a thorough functional characterization of hBASIC.
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36
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Svenningsen P, Friis UG, Versland JB, Buhl KB, Møller Frederiksen B, Andersen H, Zachar RM, Bistrup C, Skøtt O, Jørgensen JS, Andersen RF, Jensen BL. Mechanisms of renal NaCl retention in proteinuric disease. Acta Physiol (Oxf) 2013; 207:536-45. [PMID: 23216619 DOI: 10.1111/apha.12047] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Revised: 11/27/2012] [Accepted: 12/03/2012] [Indexed: 02/06/2023]
Abstract
In diseases with proteinuria, for example nephrotic syndrome and pre-eclampsia, there often are suppression of plasma renin-angiotensin-aldosterone system components, expansion of extracellular volume and avid renal sodium retention. Mechanisms of sodium retention in proteinuria are reviewed. In animal models of nephrotic syndrome, the amiloride-sensitive epithelial sodium channel ENaC is activated while more proximal renal Na(+) transporters are down-regulated. With suppressed plasma aldosterone concentration and little change in ENaC abundance in nephrotic syndrome, the alternative modality of proteolytic activation of ENaC has been explored. Proteolysis leads to putative release of an inhibitory peptide from the extracellular domain of the γ ENaC subunit. This leads to full activation of the channel. Plasminogen has been demonstrated in urine from patients with nephrotic syndrome and pre-eclampsia. Urine plasminogen correlates with urine albumin and is activated to plasmin within the urinary space by urokinase-type plasminogen activator. This agrees with aberrant filtration across an injured glomerular barrier independent of the primary disease. Pure plasmin and urine samples containing plasmin activate inward current in single murine collecting duct cells. In this study, it is shown that human lymphocytes may be used to uncover the effect of urine plasmin on amiloride- and aprotinin-sensitive inward currents. Data from hypertensive rat models show that protease inhibitors may attenuate blood pressure. Aberrant filtration of plasminogen and conversion within the urinary space to plasmin may activate γ ENaC proteolytically and contribute to inappropriate NaCl retention and oedema in acute proteinuric conditions and to hypertension in diseases with chronic microalbuminuria/proteinuria.
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Affiliation(s)
- P. Svenningsen
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - U. G. Friis
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - J. B. Versland
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - K. B. Buhl
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - B. Møller Frederiksen
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - H. Andersen
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - R. M. Zachar
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - C. Bistrup
- Department of Nephrology; Odense University Hospital; Odense; Denmark
| | - O. Skøtt
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - J. S. Jørgensen
- Department of Obstetrics and Gynecology; Odense University Hospital; Odense; Denmark
| | - R. F. Andersen
- Department of Pediatrics; Aarhus University Hospital; Skejby; Aarhus; Denmark
| | - B. L. Jensen
- Cardiovascular and Renal Research; Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
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37
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Rauh R, Soell D, Haerteis S, Diakov A, Nesterov V, Krueger B, Sticht H, Korbmacher C. A mutation in the β-subunit of ENaC identified in a patient with cystic fibrosis-like symptoms has a gain-of-function effect. Am J Physiol Lung Cell Mol Physiol 2012; 304:L43-55. [PMID: 23087020 DOI: 10.1152/ajplung.00093.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
In some patients with atypical cystic fibrosis (CF), only one allele of the CF transmembrane conductance regulator (CFTR) gene is affected. Mutations of the epithelial sodium channel (ENaC) may contribute to the pathophysiology of the disease in these patients. To functionally characterize a mutation in the β-subunit of ENaC (βV348M) recently identified in a patient with severe CF-like symptoms (Mutesa et al. 2009), we expressed wild-type (wt) αβγENaC or mutant αβV348MγENaC in Xenopus laevis oocytes. The βV348M mutation stimulated amiloride-sensitive whole-cell current (ΔI(ami)) by ∼40% but had no effect on surface expression or single-channel conductance of ENaC. Instead the mutation increased channel open probability (P(o)). Proteolytic activation of mutant ENaC by chymotrypsin was reduced compared with that of wt ENaC (∼3.0-fold vs. ∼4.2-fold), which is consistent with the increased baseline P(o) of mutant ENaC. Similarly, the ENaC activator S3969 stimulated mutant ENaC currents to a lesser degree (by ∼2.6-fold) than wt ENaC currents (by ∼3.5-fold). The gain-of-function effect of the βV348M mutation was confirmed by whole-cell current measurements in HEK293 cells transiently transfected with wt or mutant ENaC. Computational channel modeling in combination with functional expression of different βV348 mutants in oocytes suggests that the βV348M mutation increases channel P(o) by destabilizing the closed channel state. Our findings indicate that the gain-of-function effect of the βV348M mutation may contribute to CF pathophysiology by inappropriately increasing sodium and fluid absorption in the respiratory tract.
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Affiliation(s)
- Robert Rauh
- Institut für Zelluläre und Molekulare Physiologie, Erlangen, Germany.
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