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Nickerson AJ, Mutchler SM, Sheng S, Cox NA, Ray EC, Kashlan OB, Carattino MD, Marciszyn AL, Winfrey A, Gingras S, Kirabo A, Hughey RP, Kleyman TR. Mice lacking γENaC palmitoylation sites maintain benzamil-sensitive Na+ transport despite reduced channel activity. JCI Insight 2023; 8:e172051. [PMID: 37707951 PMCID: PMC10721255 DOI: 10.1172/jci.insight.172051] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Accepted: 09/12/2023] [Indexed: 09/16/2023] Open
Abstract
Epithelial Na+ channels (ENaCs) control extracellular fluid volume by facilitating Na+ absorption across transporting epithelia. In vitro studies showed that Cys-palmitoylation of the γENaC subunit is a major regulator of channel activity. We tested whether γ subunit palmitoylation sites are necessary for channel function in vivo by generating mice lacking the palmitoylated cysteines (γC33A,C41A) using CRISPR/Cas9 technology. ENaCs in dissected kidney tubules from γC33A,C41A mice had reduced open probability compared with wild-type (WT) littermates maintained on either standard or Na+-deficient diets. Male mutant mice also had higher aldosterone levels than WT littermates following Na+ restriction. However, γC33A,C41A mice did not have reduced amiloride-sensitive Na+ currents in the distal colon or benzamil-induced natriuresis compared to WT mice. We identified a second, larger conductance cation channel in the distal nephron with biophysical properties distinct from ENaC. The activity of this channel was higher in Na+-restricted γC33A,C41A versus WT mice and was blocked by benzamil, providing a possible compensatory mechanism for reduced prototypic ENaC function. We conclude that γ subunit palmitoylation sites are required for prototypic ENaC activity in vivo but are not necessary for amiloride/benzamil-sensitive Na+ transport in the distal nephron or colon.
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Affiliation(s)
| | | | | | | | | | - Ossama B. Kashlan
- Department of Medicine
- Department of Computational and Systems Biology
| | | | | | | | - Sebastien Gingras
- Department of Immunology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Annet Kirabo
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | | | - Thomas R. Kleyman
- Department of Medicine
- Department of Cell Biology, and
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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2
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Launonen H, Luiskari L, Linden J, Siltari A, Salmenkari H, Korpela R, Vapaatalo H. Adverse effects of an aldosterone synthase (CYP11B2) inhibitor, fadrozole (FAD286), on inflamed rat colon. Basic Clin Pharmacol Toxicol 2023; 133:211-225. [PMID: 37345281 DOI: 10.1111/bcpt.13918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 05/01/2023] [Accepted: 05/08/2023] [Indexed: 06/23/2023]
Abstract
Recently, we described local aldosterone production in the murine large intestine. Upregulated local aldosterone synthesis in different tissues has been linked with inflammatory conditions, which have been attenuated by the aldosterone synthase (CYP11B2) inhibitor, fadrozole (FAD286). Therefore, we investigated the effect of inhibition of intestinal aldosterone synthesis on the development of intestinal inflammation. Sprague-Dawley rats were administered 5% (v/w) dextran sodium sulphate (DSS) for 7 days with or without daily FAD286 (30 mg/kg/d) subcutaneous injections on 3 days before, during and one day after DSS. Tissue aldosterone concentrations were evaluated by ELISA, CYP11B2 by Western blot and RT-qPCR. FAD286 halved adrenal aldosterone production but, intriguingly, increased the colonic aldosterone concentration. The lack of inhibitory effect of FAD286 in the colon might have been affected by the smaller size of colonic vs. adrenal CYP11B2, as seen in Western blot. When combined with DSS, FAD286 aggravated the macroscopic and histological signs of intestinal inflammation, lowered the animals' body weight gain and increased the incidence of gastrointestinal bleeding and the permeability to iohexol in comparison to DSS-animals. To conclude, FAD286 exerted harmful effects during intestinal inflammation. Local intestinal aldosterone did not seem to play any role in the inflammatory pathogenesis occurring in the intestine.
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Affiliation(s)
- Hanna Launonen
- Faculty of Medicine, Pharmacology, University of Helsinki, Helsinki, Finland
| | - Lotta Luiskari
- Faculty of Medicine, Pharmacology, University of Helsinki, Helsinki, Finland
| | - Jere Linden
- Faculty of Veterinary Medicine, Department of Veterinary Biosciences and Finnish Centre for Laboratory Animal Pathology (FCLAP), HiLIFE, University of Helsinki, Helsinki, Finland
| | - Aino Siltari
- Faculty of Medicine, Pharmacology, University of Helsinki, Helsinki, Finland
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Hanne Salmenkari
- Folkhälsan Research Center, Folkhälsan Institute of Genetics, Helsinki, Finland
- Abdominal Center, Nephrology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
- Research Program for Clinical and Molecular Metabolism, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Riitta Korpela
- Faculty of Medicine, Pharmacology, University of Helsinki, Helsinki, Finland
- Faculty of Medicine, Human Microbiome Research Program, University of Helsinki, Helsinki, Finland
| | - Heikki Vapaatalo
- Faculty of Medicine, Pharmacology, University of Helsinki, Helsinki, Finland
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3
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Loffing J, Pech V, Loffing-Cueni D, Abood DC, Kim YH, Chen C, Pham TD, Verlander JW, Wall SM. Pendrin abundance, subcellular distribution, and function are unaffected by either αENaC gene ablation or by increasing ENaC channel activity. Pflugers Arch 2023; 475:607-620. [PMID: 36977894 PMCID: PMC10105674 DOI: 10.1007/s00424-023-02797-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 01/20/2023] [Accepted: 02/13/2023] [Indexed: 03/30/2023]
Abstract
The intercalated cell Cl-/HCO3- exchanger, pendrin, modulates ENaC subunit abundance and function. Whether ENaC modulates pendrin abundance and function is however unknown. Because αENaC mRNA has been detected in pendrin-positive intercalated cells, we hypothesized that ENaC, or more specifically the αENaC subunit, modulates intercalated cell function. The purpose of this study was therefore to determine if αENaC is expressed at the protein level in pendrin-positive intercalated cells and to determine if αENaC gene ablation or constitutively upregulating ENaC activity changes pendrin abundance, subcellular distribution, and/or function. We observed diffuse, cytoplasmic αENaC label in pendrin-positive intercalated cells from both mice and rats, with much lower label intensity in pendrin-negative, type A intercalated cells. However, while αENaC gene ablation within principal and intercalated cells of the CCD reduced Cl- absorption, it did not change pendrin abundance or subcellular distribution in aldosterone-treated mice. Further experiments used a mouse model of Liddle's syndrome to explore the effect of increasing ENaC channel activity on pendrin abundance and function. The Liddle's variant did not increase either total or apical plasma membrane pendrin abundance in aldosterone-treated or in NaCl-restricted mice. Similarly, while the Liddle's mutation increased total Cl- absorption in CCDs from aldosterone-treated mice, it did not significantly affect the change in Cl- absorption seen with pendrin gene ablation. We conclude that in rats and mice, αENaC localizes to pendrin-positive ICs where its physiological role remains to be determined. While pendrin modulates ENaC abundance, subcellular distribution, and function, ENaC does not have a similar effect on pendrin.
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Affiliation(s)
- Johannes Loffing
- Institute of Anatomy, University of Zurich, Zurich, Switzerland.
| | - Vladimir Pech
- Division of Renal Medicine, Department of Medicine, Emory University, Atlanta, GA, 30322, USA
| | | | - Delaney C Abood
- Division of Renal Medicine, Department of Medicine, Emory University, Atlanta, GA, 30322, USA
| | - Young Hee Kim
- Division of Renal Medicine, Department of Medicine, Emory University, Atlanta, GA, 30322, USA
| | - Chao Chen
- The Division of Nephrology, Hypertension and Renal Transplantation, The University of Florida College of Medicine, Gainesville, FL, USA
| | - Truyen D Pham
- Division of Renal Medicine, Department of Medicine, Emory University, Atlanta, GA, 30322, USA
| | - Jill W Verlander
- The Division of Nephrology, Hypertension and Renal Transplantation, The University of Florida College of Medicine, Gainesville, FL, USA
| | - Susan M Wall
- Division of Renal Medicine, Department of Medicine, Emory University, Atlanta, GA, 30322, USA.
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4
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Loughlin S, Costello HM, Roe AJ, Buckley C, Wilson SM, Bailey MA, Mansley MK. Mapping the Transcriptome Underpinning Acute Corticosteroid Action within the Cortical Collecting Duct. KIDNEY360 2023; 4:226-240. [PMID: 36821614 PMCID: PMC10103384 DOI: 10.34067/kid.0003582022] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Accepted: 11/08/2022] [Indexed: 11/10/2022]
Abstract
Key Points We report the transcriptomes associated with acute corticosteroid regulation of ENaC activity in polarized mCCDcl1 collecting duct cells. Nine genes were regulated by aldosterone (ALDO), 0 with corticosterone alone, and 151 with corticosterone when 11βHSD2 activity was inhibited. We validated three novel ALDO-induced genes, Rasd1 , Sult1d1 , and Gm43305 , in primary cells isolated from a novel principal cell reporter mouse. Background Corticosteroids regulate distal nephron and collecting duct (CD) Na+ reabsorption, contributing to fluid-volume and blood pressure homeostasis. The transcriptional landscape underpinning the acute stimulation of the epithelial sodium channel (ENaC) by physiological concentrations of corticosteroids remains unclear. Methods Transcriptomic profiles underlying corticosteroid-stimulated ENaC activity in polarized mCCDcl1 cells were generated by coupling electrophysiological measurements of amiloride-sensitive currents with RNAseq. Generation of a principal cell-specific reporter mouse line, mT/mG -Aqp2Cre, enabled isolation of primary CD principal cells by FACS, and ENaC activity was measured in cultured primary cells after acute application of corticosteroids. Expression of target genes was assessed by qRT-PCR in cultured cells or freshly isolated cells after the acute elevation of steroid hormones in mT/mG -Aqp2Cre mice. Results Physiological relevance of the mCCDcl1 model was confirmed with aldosterone (ALDO)-specific stimulation of SGK1 and ENaC activity. Corticosterone (CORT) only modulated these responses at supraphysiological concentrations or when 11βHSD2 was inhibited. When 11βHSD2 protection was intact, CORT caused no significant change in transcripts. We identified a small number of ALDO-induced transcripts associated with stimulated ENaC activity in mCCDcl1 cells and a much larger number with CORT in the absence of 11βHSD2 activity. Principal cells isolated from mT/mG -Aqp2Cre mice were validated and assessment of identified ALDO-induced genes revealed that Sgk1 , Zbtbt16 , Sult1d1 , Rasd1 , and Gm43305 are acutely upregulated by corticosteroids both in vitro and in vivo . Conclusions This study reports the transcriptome of mCCDcl1 cells and identifies a small number of ALDO-induced genes associated with acute stimulation of ENaC, including three previously undescribed genes.
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Affiliation(s)
- Struan Loughlin
- Cellular Medicine Research Division, University of St Andrews, St Andrews, United Kingdom
- Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom
| | - Hannah M. Costello
- Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom
| | - Andrew J. Roe
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, United Kingdom
| | - Charlotte Buckley
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Stuart M. Wilson
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, United Kingdom
| | - Matthew A. Bailey
- Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom
| | - Morag K. Mansley
- Cellular Medicine Research Division, University of St Andrews, St Andrews, United Kingdom
- Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, United Kingdom
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5
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Wang XP, Tomilin V, Nickerson AJ, Tian R, Ertem M, McKernan A, Lei X, Pochynyuk O, Kashlan OB. Bile acids regulate the epithelial Na + channel in native tissues through direct binding at multiple sites. J Physiol 2022; 600:4695-4711. [PMID: 36071685 PMCID: PMC9633555 DOI: 10.1113/jp283318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 09/01/2022] [Indexed: 11/08/2022] Open
Abstract
Bile acids, originally known to emulsify dietary lipids, are now established signalling molecules that regulate physiological processes. Signalling targets several proteins that include the ion channels involved in regulating intestinal motility and bile viscosity. Studies show that bile acids regulate the epithelial sodium channel (ENaC) in cultured cell models and heterologous expression systems. ENaC plays both local and systemic roles in regulating extracellular fluids. Here we investigated whether bile acids regulate ENaC expressed in native tissues. We found that taurocholic acid and taurohyodeoxycholic acid regulated ENaC in both the distal nephron and distal colon. We also tested the hypothesis that regulation occurs through direct binding. Using photoaffinity labelling, we found evidence for specific binding to both the β and γ subunits of the channel. In functional experiments, we found that the α subunit was sufficient for regulation. We also found that regulation by at least one bile acid was voltage-sensitive, suggesting that one binding site may be closely associated with the pore-forming helices of the channel. Our data provide evidence that bile acids regulate ENaC by binding to multiple sites to influence the open probability of the channel. KEY POINTS: Recent studies have shown that bile acids regulate the epithelial sodium channel (ENaC) in vitro. Here we investigated whether bile acids regulate ENaC in native tissues and whether bile acids directly bind the channel. We found that bile acids regulate ENaC expressed in the mouse cortical collecting duct and mouse colon by modulating open probability. Photoaffinity labelling experiments showed specific binding to the β and γ subunits of the channel, while channels comprising only α subunits were sensitive to taurocholic acid in functional experiments using Xenopus oocytes. Taurocholic acid regulation of ENaC was voltage-dependent, providing evidence for binding to pore-forming helices. Our data indicate that bile acids are ENaC regulatory effectors that may have a role in the physiology and pathophysiology of several systems.
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Affiliation(s)
- Xue-Ping Wang
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Viktor Tomilin
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Andrew J Nickerson
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Runze Tian
- Beijing National Laboratory for Molecular Sciences, Department of Chemical Biology, College of Chemistry and Molecular Engineering, and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Merve Ertem
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Abagail McKernan
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Xiaoguang Lei
- Beijing National Laboratory for Molecular Sciences, Department of Chemical Biology, College of Chemistry and Molecular Engineering, and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Ossama B Kashlan
- Departments of Medicine, Renal-electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Departments of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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6
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Pearce D, Manis AD, Nesterov V, Korbmacher C. Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology. Pflugers Arch 2022; 474:869-884. [PMID: 35895103 PMCID: PMC9338908 DOI: 10.1007/s00424-022-02732-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 02/03/2023]
Abstract
Regulated Na+ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na+ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na+ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K+, Ca++, Mg++, Cl-, and HCO3-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na+ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na+ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na+ and K+ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K+ concentrations are involved in the reciprocal regulation of Na+-Cl- cotransporter (NCC) and ENaC activity to adjust renal K+ secretion to dietary intake.
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Affiliation(s)
- David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Anna D. Manis
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
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7
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Mansley MK, Niklas C, Nacken R, Mandery K, Glaeser H, Fromm MF, Korbmacher C, Bertog M. Prostaglandin E2 stimulates the epithelial sodium channel (ENaC) in cultured mouse cortical collecting duct cells in an autocrine manner. J Gen Physiol 2021; 152:151804. [PMID: 32442241 PMCID: PMC7398144 DOI: 10.1085/jgp.201912525] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Revised: 03/30/2020] [Accepted: 04/21/2020] [Indexed: 12/26/2022] Open
Abstract
Prostaglandin E2 (PGE2) is the most abundant prostanoid in the kidney, affecting a wide range of renal functions. Conflicting data have been reported regarding the effects of PGE2 on tubular water and ion transport. The amiloride-sensitive epithelial sodium channel (ENaC) is rate limiting for transepithelial sodium transport in the aldosterone-sensitive distal nephron. The aim of the present study was to explore a potential role of PGE2 in regulating ENaC in cortical collecting duct (CCD) cells. Short-circuit current (ISC) measurements were performed using the murine mCCDcl1 cell line known to express characteristic properties of CCD principal cells and to be responsive to physiological concentrations of aldosterone and vasopressin. PGE2 stimulated amiloride-sensitive ISC via basolateral prostaglandin E receptors type 4 (EP4) with an EC50 of ∼7.1 nM. The rapid stimulatory effect of PGE2 on ISC resembled that of vasopressin. A maximum response was reached within minutes, coinciding with an increased abundance of β-ENaC at the apical plasma membrane and elevated cytosolic cAMP levels. The effects of PGE2 and vasopressin were nonadditive, indicating similar signaling cascades. Exposing mCCDcl1 cells to aldosterone caused a much slower (∼2 h) increase of the amiloride-sensitive ISC. Interestingly, the rapid effect of PGE2 was preserved even after aldosterone stimulation. Furthermore, application of arachidonic acid also increased the amiloride-sensitive ISC involving basolateral EP4 receptors. Exposure to arachidonic acid resulted in elevated PGE2 in the basolateral medium in a cyclooxygenase 1 (COX-1)–dependent manner. These data suggest that in the cortical collecting duct, locally produced and secreted PGE2 can stimulate ENaC-mediated transepithelial sodium transport.
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Affiliation(s)
- Morag K Mansley
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Christian Niklas
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Regina Nacken
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Kathrin Mandery
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Hartmut Glaeser
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Martin F Fromm
- Institute of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- 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
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8
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Abstract
The Epithelial Na+ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na+ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.
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Affiliation(s)
- Daniela Rotin
- The Hospital for Sick Children, and The University of Toronto, Toronto, Canada
| | - Olivier Staub
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
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9
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Gray Z, Tu W, Chertow GM, Bhalla V. Aldosterone sensitivity: an opportunity to explore the pathogenesis of hypertension. Am J Physiol Renal Physiol 2021; 320:F325-F335. [PMID: 33491565 DOI: 10.1152/ajprenal.00415.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Aldosterone sensitivity is defined as an outcome variable for a given circulating level of aldosterone. In basic and translational studies, aldosterone sensitivity has been measured in differential tissue responses, e.g., lower urine sodium and higher urine potassium, as an index of the renal response; in clinical studies, aldosterone sensitivity has been measured in differential blood pressure responses. The concept of aldosterone sensitivity disrupts the conventional wisdom of the renin-angiotensin-aldosterone system and has the potential to uncover novel mechanisms of hypertension. Here, we review basic and translational science studies that uncovered differential renal responses to aldosterone and connect this earlier work to more recent observational studies and randomized trials that have demonstrated differential blood pressure responses for a given level of aldosterone in healthy and hypertensive persons. Black race and older age are associated with higher aldosterone sensitivity and blood pressure. We also discuss gaps in the field and how future basic and clinical studies might inform mechanisms of differential sensitivity.
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Affiliation(s)
- Zachary Gray
- Stanford Hypertension Center, Stanford University School of Medicine, Stanford, California
| | - Wanzhu Tu
- Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana
| | - Glenn M Chertow
- Stanford Hypertension Center, Stanford University School of Medicine, Stanford, California.,Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, California
| | - Vivek Bhalla
- Stanford Hypertension Center, Stanford University School of Medicine, Stanford, California.,Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, California
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10
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Increased colonic K + excretion through inhibition of the H,K-ATPase type 2 helps reduce plasma K + level in a murine model of nephronic reduction. Sci Rep 2021; 11:1833. [PMID: 33469051 PMCID: PMC7815745 DOI: 10.1038/s41598-021-81388-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 12/21/2020] [Indexed: 11/09/2022] Open
Abstract
Hyperkalemia is frequently observed in patients at the end-stage of chronic kidney disease (CKD), and has possible harmful consequences on cardiac function. Many strategies are currently used to manage hyperkalemia, one consisting of increasing fecal K+ excretion through the administration of cation-exchange resins. In this study, we explored another more specific method of increasing intestinal K+ secretion by inhibiting the H,K-ATPase type 2 (HKA2), which is the main colonic K+ reabsorptive pathway. We hypothetised that the absence of this pump could impede the increase of plasma K+ levels following nephronic reduction (N5/6) by favoring fecal K+ secretion. In N5/6 WT and HKA2KO mice under normal K+ intake, the plasma K+ level remained within the normal range, however, a load of K+ induced strong hyperkalemia in N5/6 WT mice (9.1 ± 0.5 mM), which was significantly less pronounced in N5/6 HKA2KO mice (7.9 ± 0.4 mM, p < 0.01). This was correlated to a higher capacity of HKA2KO mice to excrete K+ in their feces. The absence of HKA2 also increased fecal Na+ excretion by inhibiting its colonic ENaC-dependent absorption. We also showed that angiotensin-converting-enzyme inhibitor like enalapril, used to treat hypertension during CKD, induced a less severe hyperkalemia in N5/6 HKA2KO than in N5/6 WT mice. This study therefore provides the proof of concept that the targeted inhibition of HKA2 could be a specific therapeutic maneuver to reduce plasma K+ levels in CKD patients.
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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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Bukhari AAS, Zhang X, Li M, Zhao A, Dong H, Liang X. Cofilin participates in regulating alpha-epithelial sodium channel by interaction with 14-3-3 isoforms. J Biomed Res 2020; 34:351-360. [PMID: 32981895 PMCID: PMC7540242 DOI: 10.7555/jbr.34.20190155] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Renal epithelial sodium channel (ENaC) plays a crucial role in maintaining homeostasis and sodium absorption. While insulin participates in controlling sodium transport across the renal epithelium, the underlying molecular mechanism remain unclear. In this study, we found that insulin increased the expression and function of alpha-epithelial sodium channel (α-ENaC) as well as phosphorylation of cofilin, a family of actin-binding proteins which disassembles actin filaments, in mouse cortical collecting duct (mpkCCDc14) cells. The wild-type (WT) cofilin and its constitutively phosphorylated form (S3D), but not its constitutively non-phosphorylable form (S3A), contributed to the elevated expression on α-ENaC. Overexpression of 14-3-3ε, β, or γ increased the expression of α-ENaC and cofilin phosphorylation, which was blunted by knockdown of 14-3-3ε, β, or γ. Moreover, it was found that insulin increased the interaction between cofilin and 14-3-3 isoforms, which indicated relevance of 14-3-3 isoforms with cofilin. Furthermore, LIMK1/SSH1 pathway was involved in regulation of cofilin and α-ENaC expression by insulin. The results from this work indicate that cofilin participates in the regulation of α-ENaC by interaction with 14-3-3 isoforms.
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Affiliation(s)
| | | | | | | | | | - Xiubin Liang
- Department of Pathophysiology;Department of Nephrology, the Affiliated Sir Run Run Hospital of Nanjing Medical University, Nanjing, Jiangsu 211166, China
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13
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Mansley MK, Roe AJ, Francis SL, Gill JH, Bailey MA, Wilson SM. Trichostatin A blocks aldosterone-induced Na + transport and control of serum- and glucocorticoid-inducible kinase 1 in cortical collecting duct cells. Br J Pharmacol 2019; 176:4708-4719. [PMID: 31423568 DOI: 10.1111/bph.14837] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Revised: 06/30/2019] [Accepted: 07/26/2019] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND AND PURPOSE Aldosterone stimulates epithelial Na+ channel (ENaC)-dependent Na+ retention in the cortical collecting duct (CCD) of the kidney by activating mineralocorticoid receptors that promote expression of serum and glucocorticoid-inducible kinase 1 (SGK1). This response is critical to BP homeostasis. It has previously been suggested that inhibiting lysine deacetylases (KDACs) can post-transcriptionally disrupt this response by promoting acetylation of the mineralocorticoid receptor. The present study critically evaluates this hypothesis. EXPERIMENTAL APPROACH Electrometric and molecular methods were used to define the effects of a pan-KDAC inhibitor, trichostatin A, on the responses to a physiologically relevant concentration of aldosterone (3 nM) in murine mCCDcl1 cells. KEY RESULTS Aldosterone augmented ENaC-induced Na+ absorption and increased SGK1 activity and abundance, as expected. In the presence of trichostatin A, these responses were suppressed. Trichostatin A-induced inhibition of KDAC was confirmed by increased acetylation of histone H3, H4, and α-tubulin. Trichostatin A did not block the electrometric response to insulin, a hormone that activates SGK1 independently of increased transcription, indicating that trichostatin A has no direct effect upon the SGK1/ENaC pathway. CONCLUSIONS AND IMPLICATIONS Inhibition of lysine de-acetylation suppresses aldosterone-dependent control over the SGK1-ENaC pathway but does not perturb post-transcriptional signalling, providing a physiological basis for the anti-hypertensive action of KDAC inhibition seen in vivo.
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Affiliation(s)
- Morag K Mansley
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK.,Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK
| | - Andrew J Roe
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
| | - Sarah L Francis
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
| | - Jason H Gill
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
| | - Matthew A Bailey
- Centre for Cardiovascular Science, Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, UK
| | - Stuart M Wilson
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
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14
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van der Wijst J, Belge H, Bindels RJM, Devuyst O. Learning Physiology From Inherited Kidney Disorders. Physiol Rev 2019; 99:1575-1653. [PMID: 31215303 DOI: 10.1152/physrev.00008.2018] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.
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Affiliation(s)
- Jenny van der Wijst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Hendrica Belge
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - René J M Bindels
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Olivier Devuyst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
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15
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Abstract
Since its discovery, aldosterone and ion modulation have been entwined. While scientific investigations throughout the decades have emphasized aldosterone's connection to Na+, K+, and H+ homeostasis, more recent research has demonstrated a relationship between aldosterone and Mg2+, Ca2+, and Cl- homeostasis. The mechanisms connecting aldosterone to ion regulation frequently involve ion channels; the membrane localized proteins containing at least one aqueous pore for ion conduction. In order to precisely control intracellular or intraorganelle ion concentrations, ion channels have evolved highly specific regions within the conduction pore that select ions by charge, size, and/or dehydration energy requirement, meaning aldosterone must be able to modulate multiple ion channels to regulate the many ions described above. The list of ion channels presently connected to aldosterone includes ENaC (Na+), ROMK/BK (K+), TRPV4/5/6 (Ca2+), TRPM7/6 (Mg2+), and ClC-K/CFTR (Cl-), among others. This list is only expected to grow over time, as the promiscuity of aldosterone becomes more understood.
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Affiliation(s)
| | - Rhian M Touyz
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Alvin Shrier
- Department of Physiology, McGill University, Montreal, QC, Canada.
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16
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Nakamura T, Kurihara I, Kobayashi S, Yokota K, Murai-Takeda A, Mitsuishi Y, Morisaki M, Kohata N, Oshima Y, Minami Y, Shibata H, Itoh H. Intestinal Mineralocorticoid Receptor Contributes to Epithelial Sodium Channel-Mediated Intestinal Sodium Absorption and Blood Pressure Regulation. J Am Heart Assoc 2018; 7:JAHA.117.008259. [PMID: 29929989 PMCID: PMC6064907 DOI: 10.1161/jaha.117.008259] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Background Mineralocorticoid receptor (MR) has pathological roles in various cell types, including renal tubule cells, myocytes, and smooth muscle cells; however, the role of MR in intestinal epithelial cells (IECs) has not been sufficiently evaluated. The intestine is the sensing organ of ingested sodium; accordingly, intestinal MR is expected to have essential roles in blood pressure (BP) regulation. Methods and Results We generated IEC‐specific MR knockout (IEC‐MR‐KO) mice. With a standard diet, fecal sodium excretion was 1.5‐fold higher in IEC‐MR‐KO mice, with markedly decreased colonic expression of β‐ and γ‐epithelial sodium channel, than in control mice. Urinary sodium excretion in IEC‐MR‐KO mice decreased by 30%, maintaining sodium balance; however, a low‐salt diet caused significant reductions in body weight and BP in IEC‐MR‐KO mice, and plasma aldosterone exhibited a compensatory increase. With a high‐salt diet, intestinal sodium absorption markedly increased to similar levels in both genotypes, without an elevation in BP. Deoxycorticosterone/salt treatment elevated BP and increased intestinal sodium absorption in both genotypes. Notably, the increase in BP was significantly smaller in IEC‐MR‐KO mice than in control mice. The addition of the MR antagonist spironolactone to deoxycorticosterone/salt treatment eliminated the differences in BP and intestinal sodium absorption between genotypes. Conclusions Intestinal MR regulates intestinal sodium absorption in the colon and contributes to BP regulation. These regulatory effects are associated with variation in epithelial sodium channel expression. These findings suggest that intestinal MR is a new target for studying the molecular mechanism of hypertension and cardiovascular diseases.
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Affiliation(s)
- Toshifumi Nakamura
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Isao Kurihara
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Sakiko Kobayashi
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Kenichi Yokota
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Ayano Murai-Takeda
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Yuko Mitsuishi
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Mitsuha Morisaki
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Nao Kohata
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Yosuke Oshima
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Yukiko Minami
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
| | - Hirotaka Shibata
- Department of Endocrinology, Metabolism, Rheumatology and Nephrology, Faculty of Medicine, Oita University, Oita, Japan
| | - Hiroshi Itoh
- Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
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17
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Development and Characterization of a Human and Mouse Intestinal Epithelial Cell Monolayer Platform. Stem Cell Reports 2017; 9:1976-1990. [PMID: 29153987 PMCID: PMC5785676 DOI: 10.1016/j.stemcr.2017.10.013] [Citation(s) in RCA: 118] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2017] [Revised: 10/13/2017] [Accepted: 10/15/2017] [Indexed: 12/13/2022] Open
Abstract
We describe the development and characterization of a mouse and human epithelial cell monolayer platform of the small and large intestines, with a broad range of potential applications including the discovery and development of minimally systemic drug candidates. Culture conditions for each intestinal segment were optimized by correlating monolayer global gene expression with the corresponding tissue segment. The monolayers polarized, formed tight junctions, and contained a diversity of intestinal epithelial cell lineages. Ion transport phenotypes of monolayers from the proximal and distal colon and small intestine matched the known and unique physiology of these intestinal segments. The cultures secreted serotonin, GLP-1, and FGF19 and upregulated the epithelial sodium channel in response to known biologically active agents, suggesting intact secretory and absorptive functions. A screen of over 2,000 pharmacologically active compounds for inhibition of potassium ion transport in the mouse distal colon cultures led to the identification of a tool compound. Epithelial cell monolayer growth conditions developed for all intestinal segments Monolayer gene expression is consistent with tissue from each intestinal segment Ion transport, secretory, and absorptive functions match intestinal physiology Compound screen identified inhibitor of mouse distal colon potassium transport
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18
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Inhibitors of the proteasome stimulate the epithelial sodium channel (ENaC) through SGK1 and mimic the effect of aldosterone. Pflugers Arch 2017; 470:295-304. [DOI: 10.1007/s00424-017-2060-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 08/17/2017] [Accepted: 08/21/2017] [Indexed: 10/19/2022]
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19
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Trac PT, Thai TL, Linck V, Zou L, Greenlee M, Yue Q, Al-Khalili O, Alli AA, Eaton AF, Eaton DC. Alveolar nonselective channels are ASIC1a/α-ENaC channels and contribute to AFC. Am J Physiol Lung Cell Mol Physiol 2017; 312:L797-L811. [PMID: 28283476 DOI: 10.1152/ajplung.00379.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 03/01/2017] [Accepted: 03/02/2017] [Indexed: 12/13/2022] Open
Abstract
A thin fluid layer in alveoli is normal and results from a balance of fluid entry and fluid uptake by transepithelial salt and water reabsorption. Conventional wisdom suggests the reabsorption is via epithelial Na+ channels (ENaC), but if all Na+ reabsorption were via ENaC, then amiloride, an ENaC inhibitor, should block alveolar fluid clearance (AFC). However, amiloride blocks only half of AFC. The reason for failure to block is clear from single-channel measurements from alveolar epithelial cells: ENaC channels are observed, but another channel is present at the same frequency that is nonselective for Na+ over K+, has a larger conductance, and has shorter open and closed times. These two channel types are known as highly selective channels (HSC) and nonselective cation channels (NSC). HSC channels are made up of three ENaC subunits since knocking down any of the subunits reduces HSC number. NSC channels contain α-ENaC since knocking down α-ENaC reduces the number of NSC (knocking down β- or γ-ENaC has no effect on NSC, but the molecular composition of NSC channels remains unclear). We show that NSC channels consist of at least one α-ENaC and one or more acid-sensing ion channel 1a (ASIC1a) proteins. Knocking down either α-ENaC or ASIC1a reduces both NSC and HSC number, and no NSC channels are observable in single-channel patches on lung slices from ASIC1a knockout mice. AFC is reduced in knockout mice, and wet wt-to-dry wt ratio is increased, but the percentage increase in wet wt-to-dry wt ratio is larger than expected based on the reduction in AFC.
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Affiliation(s)
- Phi T Trac
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Tiffany L Thai
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Valerie Linck
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Li Zou
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Megan Greenlee
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Qiang Yue
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Otor Al-Khalili
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Abdel A Alli
- Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida
| | - Amity F Eaton
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
| | - Douglas C Eaton
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and
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20
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Altered Prostasin (CAP1/Prss8) Expression Favors Inflammation and Tissue Remodeling in DSS-induced Colitis. Inflamm Bowel Dis 2016; 22:2824-2839. [PMID: 27755216 DOI: 10.1097/mib.0000000000000940] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
BACKGROUND Inflammatory bowel diseases (IBD) including ulcerative colitis and Crohn's disease are diseases with impaired epithelial barrier function. We aimed to investigate whether mutated prostasin and thus, reduced colonic epithelial sodium channel activity predisposes to develop an experimentally dextran sodium sulfate (DSS)-induced colitis. METHODS Wildtype, heterozygous (fr/+), and homozygous (fr/fr) prostasin-mutant rats were treated 7 days with DSS followed by 7 days of recovery and analyzed with respect to histology, clinicopathological parameters, inflammatory marker mRNA transcript expression, and sodium transporter protein expression. RESULTS In this study, a more detailed analysis on rat fr/fr colons revealed reduced numbers of crypt and goblet cells, and local angiodysplasia, as compared with heterozygous (fr/+) and wildtype littermates. Following 2% DSS treatment for 7 days followed by 7 days recovery, fr/fr animals lost body weight, and reached maximal diarrhea score and highest disease activity after only 3 days, and strongly increased cytokine levels. The histology score significantly increased in all groups, but fr/fr colons further displayed pronounced histological alterations with near absence of goblet cells, rearrangement of the lamina propria, and presence of neutrophils, eosinophils, and macrophages. Additionally, fr/fr colons showed ulcerations and edemas that were absent in fr/+ and wildtype littermates. Following recovery, fr/fr rats reached, although significantly delayed, near-normal diarrhea score and disease activity, but exhibited severe architectural remodeling, despite unchanged sodium transporter protein expression. CONCLUSIONS In summary, our results demonstrate a protective role of colonic prostasin expression against experimental colitis, and thus represent a susceptibility gene in the development of inflammatory bowel disease.
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21
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Boscardin E, Alijevic O, Hummler E, Frateschi S, Kellenberger S. The function and regulation of acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC): IUPHAR Review 19. Br J Pharmacol 2016; 173:2671-701. [PMID: 27278329 DOI: 10.1111/bph.13533] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 05/19/2016] [Accepted: 06/02/2016] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC) are both members of the ENaC/degenerin family of amiloride-sensitive Na(+) channels. ASICs act as proton sensors in the nervous system where they contribute, besides other roles, to fear behaviour, learning and pain sensation. ENaC mediates Na(+) reabsorption across epithelia of the distal kidney and colon and of the airways. ENaC is a clinically used drug target in the context of hypertension and cystic fibrosis, while ASIC is an interesting potential target. Following a brief introduction, here we will review selected aspects of ASIC and ENaC function. We discuss the origin and nature of pH changes in the brain and the involvement of ASICs in synaptic signalling. We expose how in the peripheral nervous system, ASICs cover together with other ion channels a wide pH range as proton sensors. We introduce the mechanisms of aldosterone-dependent ENaC regulation and the evidence for an aldosterone-independent control of ENaC activity, such as regulation by dietary K(+) . We then provide an overview of the regulation of ENaC by proteases, a topic of increasing interest over the past few years. In spite of the profound differences in the physiological and pathological roles of ASICs and ENaC, these channels share many basic functional and structural properties. It is likely that further research will identify physiological contexts in which ASICs and ENaC have similar or overlapping roles.
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Affiliation(s)
- Emilie Boscardin
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Omar Alijevic
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
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22
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Lou Y, Zhang F, Luo Y, Wang L, Huang S, Jin F. Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis. Int J Mol Sci 2016; 17:ijms17081307. [PMID: 27517916 PMCID: PMC5000704 DOI: 10.3390/ijms17081307] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 08/02/2016] [Accepted: 08/03/2016] [Indexed: 12/13/2022] Open
Abstract
The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na+/K+-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na+ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na+ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na+ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.
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Affiliation(s)
- Yiyun Lou
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Department of Gynaecology, Hangzhou Hospital of Traditional Chinese Medicine, Hangzhou 310007, Zhejiang, China.
| | - Fan Zhang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Yuqin Luo
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Liya Wang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Shisi Huang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Fan Jin
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Key Laboratory of Reproductive Genetics, National Ministry of Education (Zhejiang University), Women's Reproductive Healthy Laboratory of Zhejiang Province, Hangzhou 310058, Zhejiang, China.
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23
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Nesterov V, Krueger B, Bertog M, Dahlmann A, Palmisano R, Korbmacher C. In Liddle Syndrome, Epithelial Sodium Channel Is Hyperactive Mainly in the Early Part of the Aldosterone-Sensitive Distal Nephron. Hypertension 2016; 67:1256-62. [DOI: 10.1161/hypertensionaha.115.07061] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 03/16/2016] [Indexed: 11/16/2022]
Affiliation(s)
- Viatcheslav Nesterov
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Bettina Krueger
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Marko Bertog
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Anke Dahlmann
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Ralf Palmisano
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christoph Korbmacher
- From the Institut für Zelluläre und Molekulare Physiologie (V.N., B.K., M.B., C.K.), Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie (A.D.), and Optical Imaging Center Erlangen (OICE) (R.P.), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
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Jeggle P, Hofschröer V, Maase M, Bertog M, Kusche‐Vihrog K. Aldosterone synthase knockout mouse as a model for sodium‐induced endothelial sodium channel up‐regulation in vascular endothelium. FASEB J 2015; 30:45-53. [DOI: 10.1096/fj.14-259606] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 08/13/2015] [Indexed: 12/31/2022]
Affiliation(s)
- Pia Jeggle
- Institute of Physiology II, University of MunsterMunsterGermany
| | | | - Martina Maase
- Institute of Physiology II, University of MunsterMunsterGermany
| | - Marko Bertog
- Institut für Zelluläre und Molekulare Physiologie, Friedrich‐Alexander Universität Erlangen‐NürnbergErlangenGermany
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25
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Luo L, Deng J, Wang DX, He J, Deng W. Regulation of epithelial sodium channel expression by oestradiol and progestogen in alveolar epithelial cells. Respir Physiol Neurobiol 2015; 216:52-62. [PMID: 26051998 DOI: 10.1016/j.resp.2015.06.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Revised: 05/15/2015] [Accepted: 06/01/2015] [Indexed: 01/11/2023]
Abstract
Oestrogen (E) and progestogen (P) exert regulatory effects on the epithelial Na(+) channel (ENaC) in the kidneys and the colon. However, the effects of E and P on the ENaC and on alveolar fluid clearance (AFC) remain unclear, and the mechanisms of action of these hormones are unknown. In this study, we showed that E and/or P administration increased AFC by more than 25% and increased the expression of the α and γ subunits of ENaC by approximately 35% in rats subjected to oleic acid-induced acute lung injury (ALI). A similar effect was observed in the dexamethasone-treated group. Furthermore, E and/or P treatment inhibited 11β-hydroxysteroid dehydrogenase (HSD) type 2 (11β-HSD2) activity, increased corticosterone expression and decreased the serum adrenocorticotrophic hormone (ACTH) levels. These effects were similar to those observed following treatment with carbenoxolone (CBX), a nonspecific HSD inhibitor. Further investigation showed that CBX further significantly increased AFC and α-ENaC expression after treatment with a low dose of E and/or P. In vitro, E or P alone inhibited 11β-HSD2 activity in a dose-dependent manner and increased α-ENaC expression by at least 50%, and E combined with P increased α-ENaC expression by more than 80%. Thus, E and P may augment the expression of α-ENaC, enhance AFC, attenuate pulmonary oedema by inhibiting 11β-HSD2 activity, and increase the active glucocorticoid levels in vivo and in vitro.
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Affiliation(s)
- Ling Luo
- Department of Respiratory Medicine, Second Affiliated Hospital of Chongqing Medical University, Chongqing, China
| | - Jia Deng
- First Department of Internal Medicine, Traditional Chinese Medical Hospital of Jiangbei District, Chongqing, China
| | - Dao-xin Wang
- Department of Respiratory Medicine, Second Affiliated Hospital of Chongqing Medical University, Chongqing, China.
| | - Jing He
- Department of Respiratory Medicine, Second Affiliated Hospital of Chongqing Medical University, Chongqing, China
| | - Wang Deng
- Department of Respiratory Medicine, Second Affiliated Hospital of Chongqing Medical University, Chongqing, China
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26
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Ronzaud C, Staub O. Ubiquitylation and control of renal Na+ balance and blood pressure. Physiology (Bethesda) 2014; 29:16-26. [PMID: 24382868 DOI: 10.1152/physiol.00021.2013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ubiquitylation is crucial for regulating numerous cellular functions. In the kidney, ubiquitylation regulates the epithelial Na(+) channel ENaC. The importance of this process is highlighted in Liddle's syndrome, where mutations interfere with ENaC ubiquitylation, resulting in constitutive Na(+) reabsorption and hypertension. There is emerging evidence that NCC, involved in hypertensive diseases, is also regulated by ubiquitylation. Here, we discuss the current knowledge and recent findings in this field.
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Affiliation(s)
- Caroline Ronzaud
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
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27
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Molecular genetics of Liddle's syndrome. Clin Chim Acta 2014; 436:202-6. [PMID: 24882431 DOI: 10.1016/j.cca.2014.05.015] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Revised: 05/11/2014] [Accepted: 05/15/2014] [Indexed: 01/04/2023]
Abstract
Liddle's syndrome, an autosomal dominant form of monogenic hypertension, is characterized by salt-sensitive hypertension with early penetrance, hypokalemia, metabolic alkalosis, suppression of plasma rennin activity and aldosterone secretion, and a clear-cut response to epithelial sodium channel (ENaC) blockers but not spironolactone therapy. Our understanding of ENaCs and Na(+) transport defects has expanded greatly over the past two decades and provides detailed insight into the molecular basis of Liddle's syndrome. In this review, we offer an overview of recent advances in understanding the molecular genetics of Liddle's syndrome, involving mutation analysis, molecular mechanisms and genetic testing. The ENaC in the distal nephron is composed of α, β and γ subunits that share similar structures. Mutations associated with Liddle's syndrome are positioned in either β or γ subunits and disturb or truncate a conserved proline-rich sequence (i.e., PY motif), leading to constitutive activation of the ENaC. Genetic testing has made it possible to make accurate diagnoses and develop tailored therapies for mutation carriers.
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28
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Malsure S, Wang Q, Charles RP, Sergi C, Perrier R, Christensen BM, Maillard M, Rossier BC, Hummler E. Colon-specific deletion of epithelial sodium channel causes sodium loss and aldosterone resistance. J Am Soc Nephrol 2014; 25:1453-64. [PMID: 24480829 DOI: 10.1681/asn.2013090936] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Aldosterone promotes electrogenic sodium reabsorption through the amiloride-sensitive epithelial sodium channel (ENaC). Here, we investigated the importance of ENaC and its positive regulator channel-activating protease 1 (CAP1/Prss8) in colon. Mice lacking the αENaC subunit in colonic superficial cells (Scnn1a(KO)) were viable, without fetal or perinatal lethality. Control mice fed a regular or low-salt diet had a significantly higher amiloride-sensitive rectal potential difference (∆PDamil) than control mice fed a high-salt diet. In Scnn1a(KO) mice, however, this salt restriction-induced increase in ∆PDamil did not occur, and the circadian rhythm of ∆PDamil was blunted. Plasma and urinary sodium and potassium did not change with regular or high-salt diets or potassium loading in control or Scnn1a(KO) mice. However, Scnn1a(KO) mice fed a low-salt diet lost significant amounts of sodium in their feces and exhibited high plasma aldosterone and increased urinary sodium retention. Mice lacking the CAP1/Prss8 in colonic superficial cells (Prss8(KO)) were viable, without fetal or perinatal lethality. Compared with controls, Prss8(KO) mice fed regular or low-salt diets exhibited significantly reduced ∆PDamil in the afternoon, but the circadian rhythm was maintained. Prss8(KO) mice fed a low-salt diet also exhibited sodium loss through feces and higher plasma aldosterone levels. Thus, we identified CAP1/Prss8 as an in vivo regulator of ENaC in colon. We conclude that, under salt restriction, activation of the renin-angiotensin-aldosterone system in the kidney compensated for the absence of ENaC in colonic surface epithelium, leading to colon-specific pseudohypoaldosteronism type 1 with mineralocorticoid resistance without evidence of impaired potassium balance.
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Affiliation(s)
- Sumedha Malsure
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Qing Wang
- Service of Nephrology, University Hospital of Lausanne (CHUV), Lausanne, Switzerland; and Division of Physiology, Department of Medicine, University of Fribourg, Fribourg, Switzerland
| | - Roch-Philippe Charles
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Chloe Sergi
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Romain Perrier
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | | | - Marc Maillard
- Service of Nephrology, University Hospital of Lausanne (CHUV), Lausanne, Switzerland; and
| | - Bernard C Rossier
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland;
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29
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Yu L, Cai H, Yue Q, Alli AA, Wang D, Al-Khalili O, Bao HF, Eaton DC. WNK4 inhibition of ENaC is independent of Nedd4-2-mediated ENaC ubiquitination. Am J Physiol Renal Physiol 2013; 305:F31-41. [PMID: 23594824 DOI: 10.1152/ajprenal.00652.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
A serine-threonine protein kinase, WNK4, reduces Na⁺ reabsorption and K⁺ secretion in the distal convoluted tubule by reducing trafficking of the thiazide-sensitive Na-Cl cotransporter to and enhancing renal outer medullary potassium channel retrieval from the apical membrane. Epithelial sodium channels (ENaC) in the distal nephron also play a role in regulating Na⁺ reabsorption and are also regulated by WNK4, but the mechanism is unclear. In A6 distal nephron cells, transepithelial current measurement and single channel recording show that WNK4 inhibits ENaC activity. Analysis of the number of channel per patch shows that WNK4 reduces channel number but has no effect on channel open probability. Western blots of apical and total ENaC provide additional evidence that WNK4 reduces apical as well as total ENaC expression. WNK4 enhances ENaC internalization independent of Nedd4-2-mediated ENaC ubiquitination. WNK4 also reduced the amount of ENaC available for recycling but has no effect on the rate of transepithelial current increase to forskolin. In contrast, Nedd4-2 not only reduced ENaC in the recycling pool but also decreased the rate of increase of current after forskolin. WNK4 associates with wild-type as well as Liddle's mutated ENaC, and WNK4 reduces both wild-type and mutated ENaC expressed in HEK293 cells.
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Affiliation(s)
- Ling Yu
- Center for Cell and Molecular Signaling, Department of Physiology, Emory University School of Medicine, Atlanta, GA, USA.
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30
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Jeggle P, Callies C, Tarjus A, Fassot C, Fels J, Oberleithner H, Jaisser F, Kusche-Vihrog K. Epithelial sodium channel stiffens the vascular endothelium in vitro and in Liddle mice. Hypertension 2013; 61:1053-9. [PMID: 23460285 DOI: 10.1161/hypertensionaha.111.199455] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Liddle syndrome, an inherited form of hypertension, is caused by gain-of-function mutations in the epithelial Na(+) channel (ENaC), the principal mediator of Na(+) reabsorption in the kidney. Accordingly, the disease pathology was ascribed to a primary renal mechanism. Whether this is the sole responsible mechanism, however, remains uncertain as dysregulation of ENaC in other tissues may also be involved. Previous work indicates that ENaC in the vascular endothelium is crucial for the regulation of cellular mechanics and thus vascular function. The hormone aldosterone has been shown to concomitantly increase ENaC surface expression and stiffness of the cell cortex in vascular endothelial cells. The latter entails a reduced release of the vasodilator nitric oxide, which eventually leads to an increase in vascular tone and blood pressure. Using atomic force microscopy, we have found a direct correlation between ENaC surface expression and the formation of cortical stiffness in endothelial cells. Stable knockdown of αENaC in endothelial cells evoked a reduced channel surface density and a lower cortical stiffness compared with the mock control. In turn, an increased αENaC expression induced an elevated cortical stiffness. More importantly, using ex vivo preparations from a mouse model for Liddle syndrome, we show that this disorder evokes enhanced ENaC expression and increased cortical stiffness in vascular endothelial cells in situ. We conclude that ENaC in the vascular endothelium determines cellular mechanics and hence might participate in the control of vascular function.
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Affiliation(s)
- Pia Jeggle
- Institute of Physiology II, University of Muenster, Muenster, Germany
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Abstract
Liddle syndrome is monogenic hypertension caused by mutations in the epithelial Na+ channel (ENaC) that interfere with its ubiquitylation by Nedd4-2. In this issue, Ronzaud and colleagues found that deleting Nedd4-2 from kidney tubules in adult mice led to ENaC accumulation, but not at the plasma membrane, as predicted from current models. Instead, abundance of the sodium chloride transporter NCC increased at the plasma membrane, and the mice have some features of increased NCC activity. Together, the results suggest that defective ubiquitylation of ENaC by Nedd4-2 may not fully explain Liddle syndrome and that Nedd4-2 modulates NCC more strongly.
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Affiliation(s)
- David H Ellison
- Division of Nephrology and Hypertension, CH12R, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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Nesterov V, Dahlmann A, Krueger B, Bertog M, Loffing J, Korbmacher C. Aldosterone-dependent and -independent regulation of the epithelial sodium channel (ENaC) in mouse distal nephron. Am J Physiol Renal Physiol 2012; 303:F1289-99. [DOI: 10.1152/ajprenal.00247.2012] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Aldosterone is thought to be the main hormone to stimulate the epithelial sodium channel (ENaC) in the aldosterone-sensitive distal nephron (ASDN) comprising the late distal convoluted tubule (DCT2), the connecting tubule (CNT) and the entire collecting duct (CD). There is immunohistochemical evidence for an axial gradient of ENaC expression along the ASDN with highest expression in the DCT2 and CNT. However, most of our knowledge about renal ENaC function stems from studies in the cortical collecting duct (CCD). Here we investigated ENaC function in the transition zone of DCT2/CNT or CNT/CCD microdissected from mice maintained on different sodium diets to vary plasma aldosterone levels. Single-channel recordings demonstrated amiloride-sensitive Na+ channels in DCT2/CNT with biophysical properties typical for ENaC previously described in CNT/CCD. In animals maintained on a standard salt diet, the average ENaC-mediated whole cell current (Δ Iami) was higher in DCT2/CNT than in CNT/CCD. A low salt diet increased Δ Iami in CNT/CCD but had little effect on Δ Iami in DCT2/CNT. To investigate whether aldosterone is necessary for ENaC activity in the DCT2/CNT, we used aldosterone synthase knockout (AS−/−) mice that lack aldosterone. In CNT/CCD of AS−/− mice, Δ Iami was lower than that in wild-type (WT) animals and was not stimulated by a low salt diet. In contrast, in DCT2/CNT of AS−/− mice, Δ Iami was similar to that in DCT2/CNT of WT animals both on a standard and on a low salt diet. We conclude that ENaC function in the DCT2/CNT is largely independent of aldosterone which is in contrast to its known aldosterone sensitivity in CNT/CCD.
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Affiliation(s)
- Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
| | - Anke Dahlmann
- Universitätsklinikum Erlangen, Medizinische Klinik 4–Nephrologie und Hypertensiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany; and
| | - Bettina Krueger
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
| | - Marko Bertog
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
| | | | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
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33
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Alli AA, Song JZ, Al-Khalili O, Bao HF, Ma HP, Alli AA, Eaton DC. Cathepsin B is secreted apically from Xenopus 2F3 cells and cleaves the epithelial sodium channel (ENaC) to increase its activity. J Biol Chem 2012; 287:30073-83. [PMID: 22782900 DOI: 10.1074/jbc.m111.338574] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) plays an important role in regulating sodium balance, extracellular volume, and blood pressure. Evidence suggests the α and γ subunits of ENaC are cleaved during assembly before they are inserted into the apical membranes of epithelial cells, and maximal activity of ENaC depends on cleavage of the extracellular loops of α and γ subunits. Here, we report that Xenopus 2F3 cells apically express the cysteine protease cathepsin B, as indicated by two-dimensional gel electrophoresis and mass spectrometry analysis. Recombinant GST ENaC α, β, and γ subunit fusion proteins were expressed in Escherichia coli and then purified and recovered from bacterial inclusion bodies. In vitro cleavage studies revealed the full-length ENaC α subunit fusion protein was cleaved by active cathepsin B but not the full-length β or γ subunit fusion proteins. Both single channel patch clamp studies and short circuit current experiments show ENaC activity decreases with the application of a cathepsin B inhibitor directly onto the apical side of 2F3 cells. We suggest a role for the proteolytic cleavage of ENaC by cathepsin B, and we suggest two possible mechanisms by which cathepsin B could regulate ENaC. Cathepsin B may cleave ENaC extracellularly after being secreted or intracellularly, while ENaC is present in the Golgi or in recycling endosomes.
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Affiliation(s)
- Abdel A Alli
- Department of Physiology, Emory University School of Medicine and the Center for Cell and Molecular Signaling, Atlanta, GA 30345, USA.
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Palmer LG, Patel A, Frindt G. Regulation and dysregulation of epithelial Na+ channels. Clin Exp Nephrol 2011; 16:35-43. [PMID: 22038262 DOI: 10.1007/s10157-011-0496-z] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Accepted: 03/25/2011] [Indexed: 12/15/2022]
Affiliation(s)
- Lawrence G Palmer
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA.
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35
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Thomas SV, Kathpalia PP, Rajagopal M, Charlton C, Zhang J, Eaton DC, Helms MN, Pao AC. Epithelial sodium channel regulation by cell surface-associated serum- and glucocorticoid-regulated kinase 1. J Biol Chem 2011; 286:32074-85. [PMID: 21784856 PMCID: PMC3173222 DOI: 10.1074/jbc.m111.278283] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Revised: 07/20/2011] [Indexed: 11/06/2022] Open
Abstract
Serum- and glucocorticoid-regulated kinase 1 (sgk1) participates in diverse biological processes, including cell growth, apoptosis, and sodium homeostasis. In the cortical collecting duct of the kidney, sgk1 regulates sodium transport by stimulating the epithelial sodium channel (ENaC). Control of subcellular localization of sgk1 may be an important mechanism for modulating specificity of sgk1 function; however, which subcellular locations are required for sgk1-regulated ENaC activity in collecting duct cells has yet to be established. Using cell surface biotinylation studies, we detected endogenous sgk1 at the apical cell membrane of aldosterone-stimulated mpkCCD(c14) collecting duct cells. The association of sgk1 with the cell membrane was enhanced when ENaC was co-transfected with sgk1 in kidney cells, suggesting that ENaC brings sgk1 to the cell surface. Furthermore, association of endogenous sgk1 with the apical cell membrane of mpkCCD(c14) cells could be modulated by treatments that increase or decrease ENaC expression at the apical membrane; forskolin increased the association of sgk1 with the apical surface, whereas methyl-β-cyclodextrin decreased the association of sgk1 with the apical surface. Single channel recordings of excised inside-out patches from the apical membrane of aldosterone-stimulated A6 collecting duct cells revealed that the open probability of ENaC was sensitive to the sgk1 inhibitor GSK650394, indicating that endogenous sgk1 is functionally active at the apical cell membrane. We propose that the association of sgk1 with the apical cell membrane, where it interacts with ENaC, is a novel means by which sgk1 specifically enhances ENaC activity in aldosterone-stimulated collecting duct cells.
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Affiliation(s)
- Sheela V. Thomas
- From the Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305
| | - Paru P. Kathpalia
- From the Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305
| | - Madhumitha Rajagopal
- From the Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305
| | - Carol Charlton
- From the Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305
| | - Jianning Zhang
- the Department of Medicine, Division of Nephrology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390, and
| | - Douglas C. Eaton
- the Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322
| | - My N. Helms
- the Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Alan C. Pao
- From the Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305
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36
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Could mineralocorticoids play a role in the pathophysiology of open angle glaucoma? J Ophthalmol 2011; 2012:196418. [PMID: 21876784 PMCID: PMC3163018 DOI: 10.1155/2012/196418] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Accepted: 07/02/2011] [Indexed: 11/25/2022] Open
Abstract
Since the pathomechanisms of primary open angle glaucoma are still not defined, different aspects related to this topic have to be discussed and further investigated. Possible candidates are the mineralocorticoids, which are known to lower intraocular pressure. A data search and personal investigations assume a limited role of mineralocorticoids for the development of glaucoma. Specific experiments for a final conclusion are, however, not yet performed.
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37
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Schild L. The epithelial sodium channel and the control of sodium balance. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1159-65. [PMID: 20600867 DOI: 10.1016/j.bbadis.2010.06.014] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 06/17/2010] [Accepted: 06/19/2010] [Indexed: 12/30/2022]
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Abstract
PURPOSE OF REVIEW We integrate recent evidence that demonstrates the importance of the gastric (HKalpha1) and nongastric (HKalpha2)-containing hydrogen potassium adenosine triphosphatases (H,K-ATPases) on physiological function and their role in potassium (K), sodium (Na), and acid-base balance. RECENT FINDINGS Previous studies focused on the primary role of H,K-ATPases as a mechanism of K conservation during states of K deprivation. Both isoforms function in H secretion and K absorption in vivo during K deprivation, but recent findings show that these pumps also function in acid secretion in animals fed normal K-replete diets. The complicated pharmacological inhibition of both pumps is reviewed. Interestingly, HKalpha2-null mice have a reduced expression and activity of the renal epithelial Na channel alpha subunit in the colon. When the human nongastric isoform was studied in a heterologous expression system with its cognate beta subunit (NaKbeta1), the pump exhibited substantial Na affinity at the 'K'-binding site. Evidence cited herein raises the possibility that either directly or indirectly the renal HKalpha2-containing H,K-ATPase may affect Na balance. SUMMARY Both H,K-ATPase isoforms are active in normal animals and not just under conditions of K depletion. The possibility that either one or both isoforms contribute to Na absorption, particularly in humans, raises important clinical implications for these pumps in the kidney.
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Role of the ubiquitin system in regulating ion transport. Pflugers Arch 2010; 461:1-21. [PMID: 20972579 DOI: 10.1007/s00424-010-0893-2] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2010] [Revised: 10/04/2010] [Accepted: 10/04/2010] [Indexed: 12/22/2022]
Abstract
Ion channels and transporters play a critical role in ion and fluid homeostasis and thus in normal animal physiology and pathology. Tight regulation of these transmembrane proteins is therefore essential. In recent years, many studies have focused their attention on the role of the ubiquitin system in regulating ion channels and transporters, initialed by the discoveries of the role of this system in processing of Cystic Fibrosis Transmembrane Regulator (CFTR), and in regulating endocytosis of the epithelial Na(+) channel (ENaC) by the Nedd4 family of ubiquitin ligases (mainly Nedd4-2). In this review, we discuss the role of the ubiquitin system in ER Associated Degradation (ERAD) of ion channels, and in the regulation of endocytosis and lysosomal sorting of ion channels and transporters, focusing primarily in mammalian cells. We also briefly discuss the role of ubiquitin like molecules (such as SUMO) in such regulation, for which much less is known so far.
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40
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Tapolyai M, Uysal A, Dossabhoy NR, Zsom L, Szarvas T, Lengvárszky Z, Fülöp T. High Prevalence of Liddle Syndrome Phenotype Among Hypertensive US Veterans in Northwest Louisiana. J Clin Hypertens (Greenwich) 2010; 12:856-60. [DOI: 10.1111/j.1751-7176.2010.00359.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Mall MA, Button B, Johannesson B, Zhou Z, Livraghi A, Caldwell RA, Schubert SC, Schultz C, O'Neal WK, Pradervand S, Hummler E, Rossier BC, Grubb BR, Boucher RC. Airway surface liquid volume regulation determines different airway phenotypes in liddle compared with betaENaC-overexpressing mice. J Biol Chem 2010; 285:26945-26955. [PMID: 20566636 DOI: 10.1074/jbc.m110.151803] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Studies in cystic fibrosis patients and mice overexpressing the epithelial Na(+) channel beta-subunit (betaENaC-Tg) suggest that raised airway Na(+) transport and airway surface liquid (ASL) depletion are central to the pathogenesis of cystic fibrosis lung disease. However, patients or mice with Liddle gain-of-function betaENaC mutations exhibit hypertension but no lung disease. To investigate this apparent paradox, we compared the airway phenotype (nasal versus tracheal) of Liddle with CFTR-null, betaENaC-Tg, and double mutant mice. In mouse nasal epithelium, the region that functionally mimics human airways, high levels of CFTR expression inhibited Liddle epithelial Nat channel (ENaC) hyperfunction. Conversely, in mouse trachea, low levels of CFTR failed to suppress Liddle ENaC hyperfunction. Indeed, Na(+) transport measured in Ussing chambers ("flooded" conditions) was raised in both Liddle and betaENaC-Tg mice. Because enhanced Na(+) transport did not correlate with lung disease in these mutant mice, measurements in tracheal cultures under physiologic "thin film" conditions and in vivo were performed. Regulation of ASL volume and ENaC-mediated Na(+) absorption were intact in Liddle but defective in betaENaC-Tg mice. We conclude that the capacity to regulate Na(+) transport and ASL volume, not absolute Na(+) transport rates in Ussing chambers, is the key physiologic function protecting airways from dehydration-induced lung disease.
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Affiliation(s)
- Marcus A Mall
- Division of Pediatric Pulmonology and Cystic Fibrosis Center, Department of Pediatrics III, University of Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany; Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Im Neuenheimer Feld 350, 69120 Heidelberg, Germany.
| | - Brian Button
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
| | - Bjarki Johannesson
- Division of Pediatric Pulmonology and Cystic Fibrosis Center, Department of Pediatrics III, University of Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany; Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Im Neuenheimer Feld 350, 69120 Heidelberg, Germany
| | - Zhe Zhou
- Division of Pediatric Pulmonology and Cystic Fibrosis Center, Department of Pediatrics III, University of Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Alessandra Livraghi
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
| | - Ray A Caldwell
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
| | - Susanne C Schubert
- Division of Pediatric Pulmonology and Cystic Fibrosis Center, Department of Pediatrics III, University of Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Carsten Schultz
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Im Neuenheimer Feld 350, 69120 Heidelberg, Germany; Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Wanda K O'Neal
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
| | - Sylvain Pradervand
- Department of Pharmacology and Toxicology, University of Lausanne, Bugnon 27, CH-1005 Lausanne, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Bugnon 27, CH-1005 Lausanne, Switzerland
| | - Bernard C Rossier
- Department of Pharmacology and Toxicology, University of Lausanne, Bugnon 27, CH-1005 Lausanne, Switzerland
| | - Barbara R Grubb
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
| | - Richard C Boucher
- Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7248, Switzerland
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Abstract
Compelling evidence is accumulating indicating a pathophysiological role of the serum-and-glucocorticoid-inducible-kinase-1 (SGK1) in the development and complications of diabetes. SGK1 is ubiquitously expressed with exquisitely high transcriptional volatility. Stimulators of SGK1 expression include hyperglycemia, cell shrinkage, ischemia, glucocorticoids and mineralocorticoids. SGK1 is activated by insulin and growth factors via PI3K, 3-phosphoinositide dependent kinase PDK1 and mTOR. SGK1 activates ion channels (including ENaC, TRPV5, ROMK, KCNE1/KCNQ1 and CLCKa/Barttin), carriers (including NCC, NKCC, NHE3, SGLT1 and EAAT3), and the Na(+)/K(+)-ATPase. It regulates the activity of several enzymes (e.g., glycogen-synthase-kinase-3, ubiquitin-ligase Nedd4-2, phosphomannose-mutase-2), and transcription factors (e.g., forkhead-transcription-factor FOXO3a, beta-catenin and NF-kappaB). A common SGK1 gene variant ( approximately 3 - 5% prevalence in Caucasians, approximately 10% in Africans) is associated with increased blood pressure, obesity and type 2 diabetes. In patients suffering from type 2 diabetes, SGK1 presumably contributes to fluid retention and hypertension, enhanced coagulation and increased deposition of matrix proteins leading to tissue fibrosis such as diabetic nephropathy. Accordingly, targeting SGK1 may favourably influence occurrence and course of type 2 diabetes.
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Affiliation(s)
- Florian Lang
- Eberhard-Karls-University of Tuebingen, Department of Physiology, Gmelinstrasse 5, Tuebingen 72076, Germany.
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The physiological impact of the serum and glucocorticoid-inducible kinase SGK1. Curr Opin Nephrol Hypertens 2009; 18:439-48. [PMID: 19584721 DOI: 10.1097/mnh.0b013e32832f125e] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW The role of serum and glucocorticoid-inducible kinase 1 (SGK1) in renal physiology and pathophysiology is reviewed with particular emphasis on recent advances. RECENT FINDINGS The mammalian target of rapamycin complex 2 has been shown to phosphorylate SGK1 at Ser422 (the so-called hydrophobic motif). Ser397 and Ser401 are two additional SGK1-phosphorylation sites required for maximal SGK1 activity. A 5' variant alternate transcript of human Sgk1 has been identified that is widely expressed and shows improved stability, enhanced membrane association, and greater stimulation of epithelial Na+ transport. SGK1 is essential for optimal processing of the epithelial sodium channel and also regulates the expression of the Na+-Cl- cotransporter. With regard to pathophysiology, SGK1 participates in the stimulation of renal tubular glucose transport in diabetes, the renal profibrotic effect of both angiotensin II and aldosterone, and in fetal programing of arterial hypertension. SUMMARY The outlined recent findings advanced our understanding of the molecular regulation of SGK1 as well as the role of the kinase in renal physiology and the pathophysiology of renal disease and hypertension. Future studies using pharmacological inhibitors of SGK1 will reveal the utility of the kinase as a new therapeutic target.
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Current world literature. Curr Opin Endocrinol Diabetes Obes 2009; 16:260-77. [PMID: 19390324 DOI: 10.1097/med.0b013e32832c937e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Loffing J, Korbmacher C. Regulated sodium transport in the renal connecting tubule (CNT) via the epithelial sodium channel (ENaC). Pflugers Arch 2009; 458:111-35. [PMID: 19277701 DOI: 10.1007/s00424-009-0656-0] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 02/18/2009] [Accepted: 02/22/2009] [Indexed: 12/29/2022]
Abstract
The aldosterone-sensitive distal nephron (ASDN) includes the late distal convoluted tubule 2, the connecting tubule (CNT) and the collecting duct. The appropriate regulation of sodium (Na(+)) absorption in the ASDN is essential to precisely match urinary Na(+) excretion to dietary Na(+) intake whilst taking extra-renal Na(+) losses into account. There is increasing evidence that Na(+) transport in the CNT is of particular importance for the maintenance of body Na(+) balance and for the long-term control of extra-cellular fluid volume and arterial blood pressure. Na(+) transport in the CNT critically depends on the activity and abundance of the amiloride-sensitive epithelial sodium channel (ENaC) in the luminal membrane of the CNT cells. As a rate-limiting step for transepithelial Na(+) transport, ENaC is the main target of hormones (e.g. aldosterone, angiotensin II, vasopressin and insulin/insulin-like growth factor 1) to adjust transepithelial Na(+) transport in this tubular segment. In this review, we highlight the structural and functional properties of the CNT that contribute to the high Na(+) transport capacity of this segment. Moreover, we discuss some aspects of the complex pathways and molecular mechanisms involved in ENaC regulation by hormones, kinases, proteases and associated proteins that control its function. Whilst cultured cells and heterologous expression systems have greatly advanced our knowledge about some of these regulatory mechanisms, future studies will have to determine the relative importance of the various pathways in the native tubule and in particular in the CNT.
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Affiliation(s)
- Bernard C. Rossier
- From the Department of Pharmacology and Toxicology, University of Lausanne, Switzerland
| | - Laurent Schild
- From the Department of Pharmacology and Toxicology, University of Lausanne, Switzerland
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Nesterov V, Dahlmann A, Bertog M, Korbmacher C. Trypsin can activate the epithelial sodium channel (ENaC) in microdissected mouse distal nephron. Am J Physiol Renal Physiol 2008; 295:F1052-62. [PMID: 18653483 DOI: 10.1152/ajprenal.00031.2008] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Proteases are involved in the processing and activation of the epithelial sodium channel (ENaC). The aim of the present study was to investigate whether the prototypical serine protease trypsin can activate ENaC in microdissected, split-open mouse renal distal tubules. Whole-cell patch-clamp recordings from principal cells of connecting tubules (CNT) or cortical collecting ducts (CCD) demonstrated that addition of trypsin (20 microg/ml) to the bath solution increased the ENaC-mediated amiloride-sensitive whole cell current (DeltaIAmi) in the majority of cells. In contrast, trypsin applied in the presence of an excess of soybean trypsin inhibitor had no stimulatory effect. The DeltaIAmi response to trypsin was variable, ranging from no apparent effect to a twofold increase in DeltaI(Ami) with an average stimulatory effect of 31 or 37% in mice on low-Na+ or standard Na+ diet, respectively. In cultured M-1 mouse collecting duct cells, a robust stimulatory effect of trypsin on DeltaIAmi was only observed in cells pretreated with protease inhibitors. This suggests that endogenous proteases contribute to ENaC activation in renal tubular cells and that the degree of ENaC prestimulation by endogenous proteases determines the magnitude of the stimulatory response to exogenous trypsin. In conclusion, we provide electrophysiological evidence that trypsin can stimulate ENaC activity in native renal mouse tubules. Thus, in the kidney, ENaC stimulation by extracellular proteases may be a relevant regulatory mechanism in vivo.
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Affiliation(s)
- Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
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