1
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Ortmann LA, Nandi S, Li YL, Zheng H, Patel KP. Activation of renal epithelial Na + channels (ENaC) in infants with congenital heart disease. Front Pediatr 2024; 12:1338672. [PMID: 38379911 PMCID: PMC10876900 DOI: 10.3389/fped.2024.1338672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 01/25/2024] [Indexed: 02/22/2024] Open
Abstract
Introduction This study was designed to measure the concentration and activity of urinary proteases that activate renal epithelial sodium channel (ENaC) mediated Na+ transport in infants with congenital heart disease, a potential mechanism for fluid retention. Methods Urine samples from infants undergoing cardiac surgery were collected at three time points: T1) pre-operatively, T2) 6-8 h after surgery, and T3) 24 h after diuretics. Urine was collected from five heathy infant controls. The urine was tested for four proteases and whole-cell patch-clamp testing was conducted in renal collecting duct M-1 cells to test whether patient urine increased Na+ currents consistent with ENaC activation. Results Heavy chain of plasminogen, furin, and prostasin were significantly higher in cardiac patients prior to surgery compared to controls. There was no difference in most proteases before and after surgery. Urine from cardiac patients produced a significantly greater increase in Na+ inward currents compared to healthy controls. Conclusion Urine from infants with congenital heart disease is richer in proteases and has the potential to increase activation of ENaC in the nephron to enhance Na+ reabsorption, which may lead to fluid retention in this population.
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Affiliation(s)
- Laura A. Ortmann
- Department of Pediatrics, University of Nebraska Medical Center, Omaha, NE, United States
| | - Shyam Nandi
- Department of Integrative and Cellular Physiology, University of Nebraska Medical Center, Omaha, NE, United States
| | - Yu-long Li
- Department of Emergency Medicine, University of Nebraska Medical Center, Omaha, NE, United States
| | - Hong Zheng
- Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD, United States
| | - Kaushik P. Patel
- Department of Integrative and Cellular Physiology, University of Nebraska Medical Center, Omaha, NE, United States
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2
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Aufy M, Hussein AM, Stojanovic T, Studenik CR, Kotob MH. Proteolytic Activation of the Epithelial Sodium Channel (ENaC): Its Mechanisms and Implications. Int J Mol Sci 2023; 24:17563. [PMID: 38139392 PMCID: PMC10743461 DOI: 10.3390/ijms242417563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 12/10/2023] [Accepted: 12/14/2023] [Indexed: 12/24/2023] Open
Abstract
Epithelial sodium channel (ENaC) are integral to maintaining salt and water homeostasis in various biological tissues, including the kidney, lung, and colon. They enable the selective reabsorption of sodium ions, which is a process critical for controlling blood pressure, electrolyte balance, and overall fluid volume. ENaC activity is finely controlled through proteolytic activation, a process wherein specific enzymes, or proteases, cleave ENaC subunits, resulting in channel activation and increased sodium reabsorption. This regulatory mechanism plays a pivotal role in adapting sodium transport to different physiological conditions. In this review article, we provide an in-depth exploration of the role of proteolytic activation in regulating ENaC activity. We elucidate the involvement of various proteases, including furin-like convertases, cysteine, and serine proteases, and detail the precise cleavage sites and regulatory mechanisms underlying ENaC activation by these proteases. We also discuss the physiological implications of proteolytic ENaC activation, focusing on its involvement in blood pressure regulation, pulmonary function, and intestinal sodium absorption. Understanding the mechanisms and consequences of ENaC proteolytic activation provides valuable insights into the pathophysiology of various diseases, including hypertension, pulmonary disorders, and various gastrointestinal conditions. Moreover, we discuss the potential therapeutic avenues that emerge from understanding these mechanisms, offering new possibilities for managing diseases associated with ENaC dysfunction. In summary, this review provides a comprehensive discussion of the intricate interplay between proteases and ENaC, emphasizing the significance of proteolytic activation in maintaining sodium and fluid balance in both health and disease.
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Affiliation(s)
- Mohammed Aufy
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
| | - Ahmed M. Hussein
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
- Department of Zoology, Faculty of Science, Al-Azhar University, Assiut 71524, Egypt
| | - Tamara Stojanovic
- Programme for Proteomics, Paracelsus Medical University, 5020 Salzburg, Austria;
| | - Christian R. Studenik
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
| | - Mohamed H. Kotob
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, 1090 Vienna, Austria; (A.M.H.); (M.H.K.)
- Department of Pathology, Faculty of Veterinary Medicine, Assiut University, Assiut 71515, Egypt
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3
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Douglas LEJ, Reihill JA, Montgomery BM, Martin SL. Furin as a therapeutic target in cystic fibrosis airways disease. Eur Respir Rev 2023; 32:32/168/220256. [PMID: 37137509 PMCID: PMC10155048 DOI: 10.1183/16000617.0256-2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 02/22/2023] [Indexed: 05/05/2023] Open
Abstract
Clinical management of cystic fibrosis (CF) has been greatly improved by the development of small molecule modulators of the CF transmembrane conductance regulator (CFTR). These drugs help to address some of the basic genetic defects of CFTR; however, no suitable CFTR modulators exist for 10% of people with CF (PWCF). An alternative, mutation-agnostic therapeutic approach is therefore still required. In CF airways, elevated levels of the proprotein convertase furin contribute to the dysregulation of key processes that drive disease pathogenesis. Furin plays a critical role in the proteolytic activation of the epithelial sodium channel; hyperactivity of which causes airways dehydration and loss of effective mucociliary clearance. Furin is also responsible for the processing of transforming growth factor-β, which is increased in bronchoalveolar lavage fluid from PWCF and is associated with neutrophilic inflammation and reduced pulmonary function. Pathogenic substrates of furin include Pseudomonas exotoxin A, a major toxic product associated with Pseudomonas aeruginosa infection and the spike glycoprotein of severe acute respiratory syndrome coronavirus 2, the causative pathogen for coronavirus disease 2019. In this review we discuss the importance of furin substrates in the progression of CF airways disease and highlight selective furin inhibition as a therapeutic strategy to provide clinical benefit to all PWCF.
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Affiliation(s)
- Lisa E J Douglas
- School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
| | - James A Reihill
- School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
| | | | - S Lorraine Martin
- School of Pharmacy, Queen's University Belfast, Belfast, Northern Ireland, UK
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4
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Bigiani A, Rhyu M. Effect of kokumi taste-active γ-glutamyl peptides on amiloride-sensitive epithelial Na+ channels in rat fungiform taste cells. Biochem Biophys Rep 2023; 33:101400. [DOI: 10.1016/j.bbrep.2022.101400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 11/17/2022] [Accepted: 11/27/2022] [Indexed: 12/03/2022] Open
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5
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Montalbetti N, Przepiorski AJ, Shi S, Sheng S, Baty CJ, Maggiore JC, Carattino MD, Vanichapol T, Davidson AJ, Hukriede NA, Kleyman TR. Functional characterization of ion channels expressed in kidney organoids derived from human induced pluripotent stem cells. Am J Physiol Renal Physiol 2022; 323:F479-F491. [PMID: 35979965 PMCID: PMC9529267 DOI: 10.1152/ajprenal.00365.2021] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 08/15/2022] [Accepted: 08/16/2022] [Indexed: 02/04/2023] Open
Abstract
Kidney organoids derived from human or rodent pluripotent stem cells have glomerular structures and differentiated/polarized nephron segments. Although there is an increasing understanding of the patterns of expression of transcripts and proteins within kidney organoids, there is a paucity of data regarding functional protein expression, in particular on transporters that mediate the vectorial transport of solutes. Using cells derived from kidney organoids, we examined the functional expression of key ion channels that are expressed in distal nephron segments: the large-conductance Ca2+-activated K+ (BKCa) channel, the renal outer medullary K+ (ROMK, Kir1.1) channel, and the epithelial Na+ channel (ENaC). RNA-sequencing analyses showed that genes encoding the pore-forming subunits of these transporters, and for BKCa channels, key accessory subunits, are expressed in kidney organoids. Expression and localization of selected ion channels was confirmed by immunofluorescence microscopy and immunoblot analysis. Electrophysiological analysis showed that BKCa and ROMK channels are expressed in different cell populations. These two cell populations also expressed other unidentified Ba2+-sensitive K+ channels. BKCa expression was confirmed at a single channel level, based on its high conductance and voltage dependence of activation. We also found a population of cells expressing amiloride-sensitive ENaC currents. In summary, our results show that human kidney organoids functionally produce key distal nephron K+ and Na+ channels.NEW & NOTEWORTHY Our results show that human kidney organoids express key K+ and Na+ channels that are expressed on the apical membranes of cells in the aldosterone-sensitive distal nephron, including the large-conductance Ca2+-activated K+ channel, renal outer medullary K+ channel, and epithelial Na+ channel.
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Affiliation(s)
| | - Aneta J Przepiorski
- Department of Developmental Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shujie Shi
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaohu Sheng
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Catherine J Baty
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Joseph C Maggiore
- Department of Developmental Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Marcelo D Carattino
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thitinee Vanichapol
- Department of Molecular Medicine and Pathology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Alan J Davidson
- Department of Molecular Medicine and Pathology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Neil A Hukriede
- Department of Developmental Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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6
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Cox ZL, Sarrell BA, Cella MK, Tucker B, Arroyo JP, Umanath K, Tidwell W, Guide A, Testani JM, Lewis JB, Dwyer JP. Multinephron Segment Diuretic Therapy to Overcome Diuretic Resistance in Acute Heart Failure: A Single-Center Experience. J Card Fail 2021; 28:21-31. [PMID: 34403831 DOI: 10.1016/j.cardfail.2021.07.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 07/14/2021] [Accepted: 07/19/2021] [Indexed: 12/17/2022]
Abstract
BACKGROUND The concept of multinephron segment diuretic therapy (MSDT) has been recommended in severe diuretic resistance with only expert opinion and case-level evidence. The purpose of this study was to investigate the safety and efficacy of MSDT, combining 4 diuretic classes, in acute heart failure (AHF) complicated by diuretic resistance. METHODS AND RESULTS A retrospective analysis was conducted in patients hospitalized with AHF at a single medical center who received MSDT, including concomitant carbonic anhydrase inhibitor, loop, thiazide, and mineralocorticoid receptor antagonist diuretics. Subjects served as their own controls with efficacy evaluated as urine output and weight change before and after MSDT. Serum chemistries, renal replacement therapies, and in-hospital mortality were evaluated for safety. Patients with severe diuretic resistance before MSDT were analyzed as a subcohort. A total of 167 patients with AHF and diuretic resistance received MSDT. MSDT was associated with increased median 24-hour urine output in the first day of therapy compared with the previous day (2.16 L [0.95-4.14 L] to 3.08 L [1.74-4.86 L], P = .003) in the total cohort and in the Severe diuretic resistance cohort (0.91 L [0.43-1.43 L] to 2.08 L [1.13-3.96 L], P < .001). The median cumulative weight loss at day 7 or discharge was -7.4 kg (-15.3 to -3.4 kg) (P = .02). Neither serum sodium, chloride, potassium, bicarbonate, or creatinine changed significantly relative to baseline (P > .05 for all). CONCLUSIONS In an AHF cohort with diuretic resistance, MSDT was associated with increased diuresis without changes in serum chemistries or kidney function. Prospective studies of MSDT in AHF and diuretic resistance are warranted.
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Affiliation(s)
- Zachary L Cox
- Department of Pharmacy Practice, Lipscomb University College of Pharmacy, Nashville, Tennessee; Department of Pharmacy, Vanderbilt University Medical Center, Nashville, Tennessee.
| | - Bonnie Ann Sarrell
- Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Mary Katherine Cella
- Department of Pharmacy Practice, Lipscomb University College of Pharmacy, Nashville, Tennessee
| | - Brent Tucker
- Department of Pharmacy Practice, Lipscomb University College of Pharmacy, Nashville, Tennessee
| | - Juan P Arroyo
- Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Kausik Umanath
- Division of Nephrology and Hypertension, Henry Ford Hospital, Detroit, Michigan; Division of Nephrology and Hypertension, Wayne State University, Detroit, Michigan
| | - William Tidwell
- Department of Pharmacy, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Andrew Guide
- Department of Biostatistics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Jeffrey M Testani
- Division of Internal Medicine, Section of Cardiovascular Medicine, Yale University School of Medicine, New Haven, Connecticut
| | - Julia B Lewis
- Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Jamie P Dwyer
- Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, Tennessee
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7
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Wang X, Ullah N, Shen Y, Sun Z, Wang X, Feng T, Zhang X, Huang Q, Xia S. Emulsion delivery of sodium chloride: A promising approach for modulating saltiness perception and sodium reduction. Trends Food Sci Technol 2021. [DOI: 10.1016/j.tifs.2021.02.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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8
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Does ENaC Work as Sodium Taste Receptor in Humans? Nutrients 2020; 12:nu12041195. [PMID: 32344597 PMCID: PMC7230849 DOI: 10.3390/nu12041195] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Revised: 04/14/2020] [Accepted: 04/21/2020] [Indexed: 12/17/2022] Open
Abstract
Taste reception is fundamental for the proper selection of food and beverages. Among the several chemicals recognized by the human taste system, sodium ions (Na+) are of particular relevance. Na+ represents the main extracellular cation and is a key factor in many physiological processes. Na+ elicits a specific sensation, called salty taste, and low-medium concentrations of table salt (NaCl, the common sodium-containing chemical we use to season foods) are perceived as pleasant and appetitive. How we detect this cation in foodstuffs is scarcely understood. In animal models, such as the mouse and the rat, the epithelial sodium channel (ENaC) has been proposed as a key protein for recognizing Na+ and for mediating preference responses to low-medium salt concentrations. Here, I will review our current understanding regarding the possible involvement of ENaC in the detection of food Na+ by the human taste system.
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9
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Zheng H, Liu X, Katsurada K, Patel KP. Renal denervation improves sodium excretion in rats with chronic heart failure: effects on expression of renal ENaC and AQP2. Am J Physiol Heart Circ Physiol 2019; 317:H958-H968. [PMID: 31490733 DOI: 10.1152/ajpheart.00299.2019] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Previously we have shown that increased expression of renal epithelial sodium channels (ENaC) may contribute to the renal sodium and water retention observed during chronic heart failure (CHF). The goal of this study was to examine whether renal denervation (RDN) changed the expressions of renal sodium transporters ENaC, sodium-hydrogen exchanger-3 proteins (NHE3), and water channel aquaporin 2 (AQP2) in rats with CHF. CHF was produced by left coronary artery ligation in rats. Four weeks after ligation surgery, surgical bilateral RDN was performed. The expression of ENaC, NHE3, and AQP2 in both renal cortex and medulla were measured. As a functional test for ENaC activation, diuretic and natriuretic responses to ENaC inhibitor benzamil were monitored in four groups of rats (Sham, Sham+RDN, CHF, CHF+RDN). Western blot analysis indicated that RDN (1 wk later) significantly reduced protein levels of α-ENaC, β-ENaC, γ-ENaC, and AQP2 in the renal cortex of CHF rats. RDN had no significant effects on the protein expression of kidney NHE3 in both Sham and CHF rats. Immunofluorescence studies of kidney sections confirmed the reduced signaling of ENaC and AQP2 in the CHF+RDN rats compared with the CHF rats. There were increases in diuretic and natriuretic responses to ENaC inhibitor benzamil in rats with CHF. RDN reduced the diuretic and natriuretic responses to benzamil in CHF rats. These findings suggest a critical role for renal nerves in the enhanced expression of ENaC and AQP2 and subsequent pathophysiology of renal sodium and water retention associated with CHF.NEW & NOTEWORTHY This is the first study to show in a comprehensive way that renal denervation initiated after a period of chronic heart failure reduces the expression of epithelial sodium channels and aquaporin 2 leading to reduced epithelial sodium channel function and sodium retention.
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Affiliation(s)
- Hong Zheng
- Division of Basic Biomedical Sciences, Sanford School of Medicine of the University of South Dakota, Vermillion, South Dakota
| | - Xuefei Liu
- Division of Basic Biomedical Sciences, Sanford School of Medicine of the University of South Dakota, Vermillion, South Dakota
| | - Kenichi Katsurada
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Kaushik P Patel
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska
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10
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Niu F, Xu X, Zhang R, Sun L, Gan N, Wang A. Ursodeoxycholic acid stimulates alveolar fluid clearance in LPS-induced pulmonary edema via ALX/cAMP/PI3K pathway. J Cell Physiol 2019; 234:20057-20065. [PMID: 30972764 DOI: 10.1002/jcp.28602] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 02/27/2019] [Accepted: 03/06/2019] [Indexed: 12/18/2022]
Abstract
This study aims to examine the impact of ursodeoxycholic acid (UDCA) on pulmonary edema and explore the underlying molecular mechanisms. The effects of UDCA on pulmonary edema were assessed through hematoxylin and eosin (H&E) staining, lung dry/wet (W/D) ratio, TNF-α/IL-1β levels of bronchoalveolar lavage fluid (BALF), protein expression of epithelial sodium channel (ENaC), and Na+ /K+ -ATPase. Besides, the detailed mechanisms were explored in primary rat alveolar type (AT) II epithelial cells by determining the effects of BOC-2 (ALX [lipoxin A4 receptor] inhibitor), Rp-cAMP (cAMP inhibitor), LY294002 (PI3K inhibitor), and H89 (PKA inhibitor) on the therapeutic effects of UDCA against lipopolysaccharide (LPS)-induced changes. Histological examination suggested that LPS-induced lung injury was obviously attenuated by UDCA. BALF TNF-α/IL-1β levels and lung W/D ratios were decreased by UDCA in LPS model rats. UDCA stimulated alveolar fluid clearance (AFC) though the upregulation of ENaC and Na+ /K+ -ATPase. BOC-2, Rp-cAMP, and LY294002 largely suppressed the therapeutic effects of UDCA. Significant attenuation of pulmonary edema and lung inflammation was revealed in LPS-challenged rats after the UDCA treatment. The therapeutic efficacy of UDCA against LPS was mainly achieved through the ALX/cAMP/PI3K pathway. Our results suggested that UDCA might be a potential drug for the treatment of pulmonary edema induced by LPS.
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Affiliation(s)
- Fangfang Niu
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Xiaotao Xu
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Rong Zhang
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Lingling Sun
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Ning Gan
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Aizhong Wang
- Department of Anesthesiology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
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Stolle T, Grondinger F, Dunkel A, Hofmann T. Quantitative proteomics and SWATH-MS to elucidate peri-receptor mechanisms in human salt taste sensitivity. Food Chem 2018; 254:95-102. [DOI: 10.1016/j.foodchem.2018.01.160] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 01/18/2018] [Accepted: 01/23/2018] [Indexed: 12/23/2022]
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12
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Ayasse N, de Bruijn PIA, Berg P, Sørensen MV, Leipziger J. Hydrochlorothiazide and acute urinary acidification: The "voltage hypothesis" of ENaC-dependent H + secretion refuted. Acta Physiol (Oxf) 2018; 223:e13013. [PMID: 29226589 DOI: 10.1111/apha.13013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 11/20/2017] [Accepted: 12/04/2017] [Indexed: 11/26/2022]
Abstract
AIM The "voltage hypothesis" of H+ secretion states that urinary acidification following increased Na+ delivery to the collecting duct (CD) is ENaC dependent leading to transepithelial voltage-dependent increase in H+ secretion. We recently showed that furosemide acidifies the urine independently of ENaC activity. If the voltage hypothesis holds, hydrochlorothiazide (HCT) must acidify the urine. We here tested the acute effect of HCT on urine pH under normal and high ENaC expression. METHODS Mice subjected to a control or a low-Na+ diet were anesthetized and infused (0.5 mL h-1 ) with saline. Catheterization of the urinary bladder allowed real-time measurement of diuresis and urine pH. Mice received either HCT (1 mg mL-1 ) or vehicle. Urinary Na+ and K+ excretions were determined by flame photometry. ENaC expression levels were measured by semi-quantitative Western blotting. RESULTS (1) HCT increased diuresis and natriuresis in both diet groups. (2) K+ excretion rates increased after HCT administration from 18.6 ± 1.3 to 31.7 ± 2.5 μmol h-1 in the control diet group and from 23.0 ± 1.3 to 48.7 ± 3.0 μmol h-1 in the low-Na+ diet group. (3) Mice fed a low-Na+ diet showed a marked upregulation of ENaC. (4) Importantly, no acute changes in urine pH were observed after the administration of HCT in either group. CONCLUSION Acute administration of HCT has no effect on urine pH. Similarly, substantial functional and molecular upregulation of ENaC did not cause HCT to acutely change urine pH. Thus, an increased Na+ load to the CD does not alter urine pH. This supports our previous finding and likely falsifies the voltage hypothesis of H+ secretion.
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Affiliation(s)
- N. Ayasse
- Department of Biomedicine, Physiology and Biophysics; Aarhus University; Aarhus C Denmark
| | - P. I. A. de Bruijn
- Department of Biomedicine, Physiology and Biophysics; Aarhus University; Aarhus C Denmark
| | - P. Berg
- Department of Biomedicine, Physiology and Biophysics; Aarhus University; Aarhus C Denmark
| | - M. V. Sørensen
- Department of Biomedicine, Physiology and Biophysics; Aarhus University; Aarhus C Denmark
- Aarhus Institute of Advanced Studies; Aarhus University; Aarhus C Denmark
| | - J. Leipziger
- Department of Biomedicine, Physiology and Biophysics; Aarhus University; Aarhus C Denmark
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13
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Wynne BM, Zou L, Linck V, Hoover RS, Ma HP, Eaton DC. Regulation of Lung Epithelial Sodium Channels by Cytokines and Chemokines. Front Immunol 2017; 8:766. [PMID: 28791006 PMCID: PMC5524836 DOI: 10.3389/fimmu.2017.00766] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Accepted: 06/16/2017] [Indexed: 12/20/2022] Open
Abstract
Acute lung injury leading to acute respiratory distress (ARDS) is a global health concern. ARDS patients have significant pulmonary inflammation leading to flooding of the pulmonary alveoli. This prevents normal gas exchange with consequent hypoxemia and causes mortality. A thin fluid layer in the alveoli is normal. The maintenance of this thin layer results from fluid movement out of the pulmonary capillaries into the alveolar interstitium driven by vascular hydrostatic pressure and then through alveolar tight junctions. This is then balanced by fluid reabsorption from the alveolar space mediated by transepithelial salt and water transport through alveolar cells. Reabsorption is a two-step process: first, sodium enters via sodium-permeable channels in the apical membranes of alveolar type 1 and 2 cells followed by active extrusion of sodium into the interstitium by the basolateral Na+, K+-ATPase. Anions follow the cationic charge gradient and water follows the salt-induced osmotic gradient. The proximate cause of alveolar flooding is the result of a failure to reabsorb sufficient salt and water or a failure of the tight junctions to prevent excessive movement of fluid from the interstitium to alveolar lumen. Cytokine- and chemokine-induced inflammation can have a particularly profound effect on lung sodium transport since they can alter both ion channel and barrier function. Cytokines and chemokines affect alveolar amiloride-sensitive epithelial sodium channels (ENaCs), which play a crucial role in sodium transport and fluid reabsorption in the lung. This review discusses the regulation of ENaC via local and systemic cytokines during inflammatory disease and the effect on lung fluid balance.
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Affiliation(s)
- Brandi M Wynne
- Department of Medicine, Nephrology, Emory University, Atlanta, GA, United States.,Department of Physiology, Emory University, Atlanta, GA, United States.,The Center for Cell and Molecular Signaling, Emory University, Atlanta, GA, United States
| | - Li Zou
- Department of Physiology, Emory University, Atlanta, GA, United States
| | - Valerie Linck
- Department of Physiology, Emory University, Atlanta, GA, United States
| | - Robert S Hoover
- Department of Medicine, Nephrology, Emory University, Atlanta, GA, United States.,Department of Physiology, Emory University, Atlanta, GA, United States.,Research Service, Atlanta Veteran's Administration Medical Center, Decatur, GA, United States
| | - He-Ping Ma
- Department of Physiology, Emory University, Atlanta, GA, United States.,The Center for Cell and Molecular Signaling, Emory University, Atlanta, GA, United States
| | - Douglas C Eaton
- Department of Physiology, Emory University, Atlanta, GA, United States.,The Center for Cell and Molecular Signaling, Emory University, Atlanta, GA, United States
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Lucas R, Yue Q, Alli A, Duke BJ, Al-Khalili O, Thai TL, Hamacher J, Sridhar S, Lebedyeva I, Su H, Tzotzos S, Fischer B, Gameiro AF, Loose M, Chakraborty T, Shabbir W, Aufy M, Lemmens-Gruber R, Eaton DC, Czikora I. The Lectin-like Domain of TNF Increases ENaC Open Probability through a Novel Site at the Interface between the Second Transmembrane and C-terminal Domains of the α-Subunit. J Biol Chem 2016; 291:23440-23451. [PMID: 27645999 DOI: 10.1074/jbc.m116.718163] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Indexed: 12/29/2022] Open
Abstract
Regulation of the epithelial sodium channel (ENaC), which regulates fluid homeostasis and blood pressure, is complex and remains incompletely understood. The TIP peptide, a mimic of the lectin-like domain of TNF, activates ENaC by binding to glycosylated residues in the extracellular loop of ENaC-α, as well as to a hitherto uncharacterized internal site. Molecular docking studies suggested three residues, Val567, Glu568, and Glu571, located at the interface between the second transmembrane and C-terminal domains of ENaC-α, as a critical site for binding of the TIP peptide. We generated Ala replacement mutants in this region of ENaC-α and examined its interaction with TIP peptide (3M, V567A/E568A/E571A; 2M, V567A/E568A; and 1M, E571A). 3M and 2M ENaC-α, but not 1M ENaC-α, displayed significantly reduced binding capacity to TIP peptide and to TNF. When overexpressed in H441 cells, 3M mutant ENaC-α formed functional channels with similar gating and density characteristics as the WT subunit and efficiently associated with the β and γ subunits in the plasma membrane. We subsequently assayed for increased open probability time and membrane expression, both of which define ENaC activity, following addition of TIP peptide. TIP peptide increased open probability time in H441 cells overexpressing wild type and 1M ENaC-α channels, but not 3M or 2M ENaC-α channels. On the other hand, TIP peptide-mediated reduction in ENaC ubiquitination was similar in cells overexpressing either WT or 3M ENaC-α subunits. In summary, this study has identified a novel site in ENaC-α that is crucial for activation of the open probability of the channel, but not membrane expression, by the lectin-like domain of TNF.
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Affiliation(s)
- Rudolf Lucas
- From the Vascular Biology Center, .,the Department of Pharmacology and Toxicology, and.,the Division of Pulmonary and Critical Care Medicine, Medical College of Georgia, Augusta, Georgia 30912
| | - Qiang Yue
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Abdel Alli
- the Department of Physiology, Emory University, Atlanta, Georgia 30322.,the Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida 32610
| | | | - Otor Al-Khalili
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Tiffany L Thai
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Jürg Hamacher
- the Department of Pulmonology, Saarland University, D-66421 Homburg, Germany
| | | | - Iryna Lebedyeva
- the Department of Chemistry, Augusta University, Augusta, Georgia 30912
| | - Huabo Su
- From the Vascular Biology Center
| | - Susan Tzotzos
- Apeptico Research and Development, 1150 Vienna, Austria
| | | | | | - Maria Loose
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Trinad Chakraborty
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Waheed Shabbir
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Mohammed Aufy
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Rosa Lemmens-Gruber
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Douglas C Eaton
- the Department of Physiology, Emory University, Atlanta, Georgia 30322,
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15
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Ji HL, Nie HG, Chang Y, Lian Q, Liu SL. CPT-cGMP Is A New Ligand of Epithelial Sodium Channels. Int J Biol Sci 2016; 12:359-66. [PMID: 27019621 PMCID: PMC4807156 DOI: 10.7150/ijbs.13764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Accepted: 11/11/2015] [Indexed: 12/28/2022] Open
Abstract
Epithelial sodium channels (ENaC) are localized at the apical membrane of the epithelium, and are responsible for salt and fluid reabsorption. Renal ENaC takes up salt, thereby controlling salt content in serum. Loss-of-function ENaC mutations lead to low blood pressure due to salt-wasting, while gain-of-function mutations cause impaired sodium excretion and subsequent hypertension as well as hypokalemia. ENaC activity is regulated by intracellular and extracellular signals, including hormones, neurotransmitters, protein kinases, and small compounds. Cyclic nucleotides are broadly involved in stimulating protein kinase A and protein kinase G signaling pathways, and, surprisingly, also appear to have a role in regulating ENaC. Increasing evidence suggests that the cGMP analog, CPT-cGMP, activates αβγ-ENaC activity reversibly through an extracellular pathway in a dose-dependent manner. Furthermore, the parachlorophenylthio moiety and ribose 2'-hydroxy group of CPT-cGMP are essential for facilitating the opening of ENaC channels by this compound. Serving as an extracellular ligand, CPT-cGMP eliminates sodium self-inhibition, which is a novel mechanism for stimulating salt reabsorption in parallel to the traditional NO/cGMP/PKG signal pathway. In conclusion, ENaC may be a druggable target for CPT-cGMP, leading to treatments for kidney malfunctions in salt reabsorption.
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Affiliation(s)
- Hong-Long Ji
- 1. Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Hong-Guang Nie
- 2. Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110001, China
| | - Yongchang Chang
- 3. Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, Arizona, 85013, USA
| | - Qizhou Lian
- 4. Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Shan-Lu Liu
- 5. Department of Molecular Microbiology and Immunology, Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
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16
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Zheng H, Liu X, Sharma NM, Li Y, Pliquett RU, Patel KP. Urinary Proteolytic Activation of Renal Epithelial Na+ Channels in Chronic Heart Failure. Hypertension 2015; 67:197-205. [PMID: 26628676 DOI: 10.1161/hypertensionaha.115.05838] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Accepted: 10/30/2015] [Indexed: 12/31/2022]
Abstract
One of the key mechanisms involved in renal Na(+) retention in chronic heart failure (CHF) is activation of epithelial Na(+) channels (ENaC) in collecting tubules. Proteolytic cleavage has an important role in activating ENaC. We hypothesized that enhanced levels of proteases in renal tubular fluid activate ENaC, resulting in renal Na(+) retention in rats with CHF. CHF was produced by left coronary artery ligation in rats. By immunoblotting, we found that several urinary serine proteases were significantly increased in CHF rats compared with sham rats (fold increases: furin 6.7, prostasin 23.6, plasminogen 2.06, and plasmin 3.57 versus sham). Similar increases were observed in urinary samples from patients with CHF. Whole-cell patch clamp was conducted in cultured renal collecting duct M-1 cells to record Na(+) currents. Protease-rich urine (from rats and patients with CHF) significantly increased the Na(+) inward current in M-1 cells. Two weeks of protease inhibitor treatment significantly abrogated the enhanced diuretic and natriuretic responses to ENaC inhibitor benzamil in rats with CHF. Increased podocyte lesions were observed in the kidneys of rats with CHF by transmission electron microscopy. Consistent with these results, podocyte damage markers desmin and podocin expressions were also increased in rats with CHF (increased ≈2-folds). These findings suggest that podocyte damage may lead to increased proteases in the tubular fluid, which in turn contributes to the enhanced renal ENaC activity, providing a novel mechanistic insight for Na(+) retention commonly observed in CHF.
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Affiliation(s)
- Hong Zheng
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.)
| | - Xuefei Liu
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.)
| | - Neeru M Sharma
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.)
| | - Yulong Li
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.)
| | - Rainer U Pliquett
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.)
| | - Kaushik P Patel
- From the Department of Cellular and Integrative Physiology (H.Z., X.L., N.M.S., K.P.P.) and Department of Emergency Medicine (Y.L.), University of Nebraska Medical Center, Omaha; and Department of Internal Medicine II, University Hospital Halle, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany (R.U.P.).
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17
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Teoh CW, Robinson LA, Noone D. Perspectives on edema in childhood nephrotic syndrome. Am J Physiol Renal Physiol 2015; 309:F575-82. [PMID: 26290369 DOI: 10.1152/ajprenal.00229.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 08/11/2015] [Indexed: 12/21/2022] Open
Abstract
There have been two major theories surrounding the development of edema in nephrotic syndrome (NS), namely, the under- and overfill hypotheses. Edema is one of the cardinal features of NS and remains one of the principal reasons for admission of children to the hospital. Recently, the discovery that proteases in the glomerular filtrate of patients with NS are activating the epithelial sodium channel (ENaC), resulting in intrarenal salt retention and thereby contributing to edema, might suggest that targeting ENaC with amiloride might be a suitable strategy to manage the edema of NS. Other potential agents, particularly urearetics and aquaretics, might also prove useful in NS. Recent evidence also suggests that there may be other areas involved in salt storage, especially the skin, and it will be intriguing to study the implications of this in NS.
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Affiliation(s)
- Chia Wei Teoh
- Division of Nephrology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Lisa A Robinson
- Division of Nephrology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Damien Noone
- Division of Nephrology, The Hospital for Sick Children, Toronto, Ontario, Canada
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18
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Ellis D. Pathophysiology, Evaluation, and Management of Edema in Childhood Nephrotic Syndrome. Front Pediatr 2015; 3:111. [PMID: 26793696 PMCID: PMC4707228 DOI: 10.3389/fped.2015.00111] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 12/07/2015] [Indexed: 01/22/2023] Open
Abstract
Generalized edema is a major presenting clinical feature of children with nephrotic syndrome (NS) exemplified by such primary conditions as minimal change disease (MCD). In these children with classical NS and marked proteinuria and hypoalbuminemia, the ensuing tendency to hypovolemia triggers compensatory physiological mechanisms, which enhance renal sodium (Na(+)) and water retention; this is known as the "underfill hypothesis." Edema can also occur in secondary forms of NS and several other glomerulonephritides, in which the degree of proteinuria and hypoalbuminemia, are variable. In contrast to MCD, in these latter conditions, the predominant mechanism of edema formation is "primary" or "pathophysiological," Na(+) and water retention; this is known as the "overfill hypothesis." A major clinical challenge in children with these disorders is to distinguish the predominant mechanism of edema formation, identify other potential contributing factors, and prevent the deleterious effects of diuretic regimens in those with unsuspected reduced effective circulatory volume (i.e., underfill). This article reviews the Starling forces that become altered in NS so as to tip the balance of fluid movement in favor of edema formation. An understanding of these pathomechanisms then serves to formulate a more rational approach to prevention, evaluation, and management of such edema.
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Affiliation(s)
- Demetrius Ellis
- Division of Pediatric Nephrology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA
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19
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Tarran R, Redinbo MR. Mammalian short palate lung and nasal epithelial clone 1 (SPLUNC1) in pH-dependent airway hydration. Int J Biochem Cell Biol 2014; 52:130-5. [PMID: 24631954 PMCID: PMC4048990 DOI: 10.1016/j.biocel.2014.03.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 02/22/2014] [Accepted: 03/03/2014] [Indexed: 12/12/2022]
Abstract
The epithelia that line the conducting airways are the lung's first point of contact with inhaled pathogens and toxicants. As such, they are known to play an important role in the lung's innate defense system, which includes (i) the production of airway surface liquid (ASL) that helps cleanse the airways through the physical removal of pathogens and toxicants on the mucociliary escalator and (ii) the secretion of anti-microbial proteins into the ASL to kill inhaled pathogens. Interestingly, the recently crystallized short palate lung and nasal epithelial clone 1 (SPLUNC1) protein appears to be a multi-functional protein. That is, it not only acts as an anti-microbial agent, but also modulates ASL homeostasis by acting as an endogenous inhibitor of the epithelial Na(+) channel (ENaC). This review will focus on the latter function of SPLUNC1, and will discuss new structural and physiological data regarding SPLUNC1's failure to function as a regulator of ASL hydration in CF airways.
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Affiliation(s)
- Robert Tarran
- Cystic Fibrosis/Pulmonary Research and Treatment Center, Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC 27599, USA.
| | - Matthew R Redinbo
- Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599, USA; Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA; Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599, USA.
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20
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Sorensen MV, Grossmann S, Roesinger M, Gresko N, Todkar AP, Barmettler G, Ziegler U, Odermatt A, Loffing-Cueni D, Loffing J. Rapid dephosphorylation of the renal sodium chloride cotransporter in response to oral potassium intake in mice. Kidney Int 2013; 83:811-24. [DOI: 10.1038/ki.2013.14] [Citation(s) in RCA: 241] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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21
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Edinger RS, Bertrand CA, Rondandino C, Apodaca GA, Johnson JP, Butterworth MB. The epithelial sodium channel (ENaC) establishes a trafficking vesicle pool responsible for its regulation. PLoS One 2012; 7:e46593. [PMID: 23029554 PMCID: PMC3460899 DOI: 10.1371/journal.pone.0046593] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 09/05/2012] [Indexed: 12/16/2022] Open
Abstract
The epithelial sodium channel (ENaC) is the rate-limiting step for sodium reabsorption across tight epithelia. Cyclic-AMP (cAMP) stimulation promotes ENaC trafficking to the apical surface to increase channel number and transcellular Na(+) transport. Removal of corticosteroid supplementation in a cultured cortical collecting duct cell line reduced ENaC expression. Concurrently, the number of vesicles trafficked in response to cAMP stimulation, as measured by a change in membrane capacitance, also decreased. Stimulation with aldosterone restored both the basal and cAMP-stimulated ENaC activity and increased the number of exocytosed vesicles. Knocking down ENaC directly decreased both the cAMP-stimulated short-circuit current and capacitance response in the presence of aldosterone. However, constitutive apical recycling of the Immunoglobulin A receptor was unaffected by alterations in ENaC expression or trafficking. Fischer Rat Thyroid cells, transfected with α,β,γ-mENaC had a significantly greater membrane capacitance response to cAMP stimulation compared to non-ENaC controls. Finally, immunofluorescent labeling and quantitation revealed a smaller number of vesicles in cells where ENaC expression was reduced. These findings indicate that ENaC is not a passive passenger in regulated epithelial vesicle trafficking, but plays a role in establishing and maintaining the pool of vesicles that respond to cAMP stimulation.
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Affiliation(s)
- Robert S. Edinger
- Department of Medicine, Renal-Electrolyte Division, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Carol A. Bertrand
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Christine Rondandino
- Department of Medicine, Renal-Electrolyte Division, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Gerard A. Apodaca
- Department of Medicine, Renal-Electrolyte Division, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - John P. Johnson
- Department of Medicine, Renal-Electrolyte Division, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Michael B. Butterworth
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- * E-mail:
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22
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Haerteis S, Krappitz M, Diakov A, Krappitz A, Rauh R, Korbmacher C. Plasmin and chymotrypsin have distinct preferences for channel activating cleavage sites in the γ subunit of the human epithelial sodium channel. ACTA ACUST UNITED AC 2012; 140:375-89. [PMID: 22966015 PMCID: PMC3457690 DOI: 10.1085/jgp.201110763] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Proteolytic activation of the epithelial sodium channel (ENaC) involves cleavage of its γ subunit in a critical region targeted by several proteases. Our aim was to identify cleavage sites in this region that are functionally important for activation of human ENaC by plasmin and chymotrypsin. Sequence alignment revealed a putative plasmin cleavage site in human γENaC (K189) that corresponds to a plasmin cleavage site (K194) in mouse γENaC. We mutated this site to alanine (K189A) and expressed human wild-type (wt) αβγENaC and αβγK189AENaC in Xenopus laevis oocytes. The γK189A mutation reduced but did not abolish activation of ENaC whole cell currents by plasmin. Mutating a putative prostasin site (γRKRK178AAAA) had no effect on the stimulatory response to plasmin. In contrast, a double mutation (γRKRK178AAAA;K189A) prevented the stimulatory effect of plasmin. We conclude that in addition to the preferential plasmin cleavage site K189, the putative prostasin cleavage site RKRK178 may serve as an alternative site for proteolytic channel activation by plasmin. Interestingly, the double mutation delayed but did not abolish ENaC activation by chymotrypsin. The time-dependent appearance of cleavage products at the cell surface nicely correlated with the stimulatory effect of chymotrypsin on ENaC currents in oocytes expressing wt or double mutant ENaC. Delayed proteolytic activation of the double mutant channel with a stepwise recruitment of so-called near-silent channels was confirmed in single-channel recordings from outside-out patches. Mutating two phenylalanines (FF174) in the vicinity of the prostasin cleavage site prevented proteolytic activation by chymotrypsin. This indicates that chymotrypsin preferentially cleaves at FF174. The close proximity of FF174 to the prostasin site may explain why mutating the prostasin site impedes channel activation by chymotrypsin. In conclusion, this study supports the concept that different proteases have distinct preferences for certain cleavage sites in γENaC, which may be relevant for tissue-specific proteolytic ENaC activation.
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Affiliation(s)
- Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
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23
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Haerteis S, Krappitz M, Bertog M, Krappitz A, Baraznenok V, Henderson I, Lindström E, Murphy JE, Bunnett NW, Korbmacher C. Proteolytic activation of the epithelial sodium channel (ENaC) by the cysteine protease cathepsin-S. Pflugers Arch 2012; 464:353-65. [PMID: 22864553 PMCID: PMC3448907 DOI: 10.1007/s00424-012-1138-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 07/10/2012] [Accepted: 07/10/2012] [Indexed: 01/16/2023]
Abstract
Proteolytic processing of the amiloride-sensitive epithelial sodium channel (ENaC) by serine proteases is known to be important for channel activation. Inappropriate ENaC activation by proteases may contribute to the pathophysiology of cystic fibrosis and could be involved in sodium retention and the pathogenesis of arterial hypertension in the context of renal disease. We hypothesized that in addition to serine proteases, cathepsin proteases may activate ENaC. Cathepsin proteases belong to the group of cysteine proteases and play a pathophysiological role in inflammatory diseases. Under pathophysiological conditions, cathepsin-S (Cat-S) may reach ENaC in the apical membrane of epithelial cells. The aim of this study was to investigate the effect of purified Cat-S on human ENaC heterologously expressed in Xenopus laevis oocytes and on ENaC-mediated sodium transport in cultured M-1 mouse renal collecting duct cells. We demonstrated that Cat-S activates amiloride-sensitive whole-cell currents in ENaC-expressing oocytes. The stimulatory effect of Cat-S was preserved at pH 5. ENaC stimulation by Cat-S was associated with the appearance of a γENaC cleavage fragment at the plasma membrane indicating proteolytic channel activation. Mutating two valine residues (V182 and V193) in the critical region of γENaC prevented proteolytic activation of ENaC by Cat-S. Pre-incubation of the oocytes with the Cat-S inhibitor morpholinurea-leucine-homophenylalanine-vinylsulfone-phenyl (LHVS) prevented the stimulatory effect of Cat-S on ENaC. In contrast, LHVS had no effect on ENaC activation by the prototypical serine proteases trypsin and chymotrypsin. Cat-S also stimulated ENaC in differentiated renal epithelial cells. These findings demonstrate that the cysteine protease Cat-S can activate ENaC which may be relevant under pathophysiological conditions.
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Affiliation(s)
- Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
| | - Matteus Krappitz
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
| | - Marko Bertog
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
| | - Annabel Krappitz
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
| | | | | | | | - Jane E. Murphy
- Center for the Neurobiology of Digestive Diseases, Department of Surgery, University of California San Francisco, San Francisco, CA USA
| | - Nigel W. Bunnett
- Monash Institute of Pharmaceutical Sciences, 381 Royal Parade, Parkville, VIC 3052 Australia
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstr. 6, 91054 Erlangen, Germany
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24
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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: 35] [Impact Index Per Article: 2.9] [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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25
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Abstract
The mechanism of edema formation in the nephrotic syndrome has long been a source of controversy. In this review, through the construct of Starling's forces, we examine the roles of albumin, intravascular volume, and neurohormones on edema formation and highlight the evolving literature on the role of primary sodium absorption in edema formation. We propose that a unifying mechanism of sodium retention is present in the nephrotic syndrome regardless of intravascular volume status and is due to the activation of epithelial sodium channel by serine proteases in the glomerular filtrate of nephrotic patients. Finally, we assert that mechanisms in addition to sodium retention are likely operant in the formation of nephrotic edema.
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26
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Thibodeau PH, Butterworth MB. Proteases, cystic fibrosis and the epithelial sodium channel (ENaC). Cell Tissue Res 2012; 351:309-23. [PMID: 22729487 DOI: 10.1007/s00441-012-1439-z] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 04/20/2012] [Indexed: 02/06/2023]
Abstract
Proteases perform a diverse array of biological functions. From simple peptide digestion for nutrient absorption to complex signaling cascades, proteases are found in organisms from prokaryotes to humans. In the human airway, proteases are associated with the regulation of the airway surface liquid layer, tissue remodeling, host defense and pathogenic infection and inflammation. A number of proteases are released in the airways under both physiological and pathophysiological states by both the host and invading pathogens. In airway diseases such as cystic fibrosis, proteases have been shown to be associated with increased morbidity and airway disease progression. In this review, we focus on the regulation of proteases and discuss specifically those proteases found in human airways. Attention then shifts to the epithelial sodium channel (ENaC), which is regulated by proteolytic cleavage and that is considered to be an important component of cystic fibrosis disease. Finally, we discuss bacterial proteases, in particular, those of the most prevalent bacterial pathogen found in cystic fibrosis, Pseudomonas aeruginosa.
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Affiliation(s)
- P H Thibodeau
- Department of Cell Biology, University of Pittsburgh School of Medicine, 3500 Terrace Street, S327 Biomedical Science Tower, Pittsburgh, PA 15261, USA
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Abstract
The central goal of this overview article is to summarize recent findings in renal epithelial transport,focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD).Mammalian CCD and CNT are involved in fine-tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, for example, aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades.Recent studies shed new light on several key questions concerning the regulation of renal transport.Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will also be covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD.
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Affiliation(s)
- Alexander Staruschenko
- Department of Physiology and Kidney Disease Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
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Abstract
PURPOSE OF REVIEW Activation of epithelial sodium channel (ENaC) by proteolysis appears to be relevant for day-to-day physiological regulation of channel activity in kidney and other epithelial tissues. Pathophysiogical, proteolytic activation of ENaC in kidney has been demonstrated in proteinuric disease. RECENT FINDINGS A variation in sodium and potassium intake or plasma aldosterone changes the number of cleaved α and γ-ENaC subunits and is associated with changes in ENaC currents. The protease furin mediates intracellular cleavage, whereas the channel-activating protease prostasin (CAP-1), which is glycophosphatidylinositol-anchored to the apical cell surface, mediates important extracellular cleavage. Soluble protease activity is very low in urine under physiological conditions but rises in proteinuria. In nephrotic syndrome, the dominant soluble protease activity is plasmin, which is formed from filtered plasminogen via urokinase-type plasminogen activator. Plasmin activates ENaC directly at high concentrations and through prostasin at lower concentrations. SUMMARY The discovery of serine protease-mediated activation of renal ENaC in physiological and pathophysiological conditions opens the way for new understanding of the pathogenesis of proteinuric sodium retention, which may involve plasmin and present several potential new drug targets.
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Lazrak A, Jurkuvenaite A, Chen L, Keeling KM, Collawn JF, Bedwell DM, Matalon S. Enhancement of alveolar epithelial sodium channel activity with decreased cystic fibrosis transmembrane conductance regulator expression in mouse lung. Am J Physiol Lung Cell Mol Physiol 2011; 301:L557-67. [PMID: 21743028 DOI: 10.1152/ajplung.00094.2011] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We sought to establish whether the cystic fibrosis transmembrane conductance regulator (CFTR) regulates the activity of amiloride-sensitive sodium channels (ENaC) in alveolar epithelial cells of wild-type, heterozygous (Cftr(+/-)), knockout (Cftr(-/-)), and ΔF508-expressing mice in situ. RT-PCR studies confirmed the presence of CFTR message in freshly isolated alveolar type II (ATII) cells from wild-type mice. We patched alveolar type I (ATI) and ATII cells in freshly prepared lung slices from these mice and demonstrated the presence of 4-pS ENaC channels with the following basal open probabilities (P(o)): wild-type=0.21 ± 0.015: Cftr(+/-)=0.4 ± 0.03; ΔF508=0.55 ± 0.01; and Cftr(-/-)=and 0.81 ± 0.016 (means ± SE; n ≥ 9). Forskolin (5 μM) or trypsin (2 μM), applied in the pipette solution, increased the P(o) and number of channels in ATII cells of wild-type, Cftr(+/-), and ΔF508, but not in Cftr(-/-) mice, suggesting that the latter were maximally activated. Western blot analysis showed that lungs of all groups of mice had similar levels of α-ENaC; however, lungs of Cftr(+/-) and Cftr(-/-) mice had significantly higher levels of an α-ENaC proteolytic fragment (65 kDa) that is associated with active ENaC channels. Our results indicate that ENaC activity is inversely correlated to predicted CFTR levels and that CFTR heterozygous and homozygous mice have higher levels of proteolytically processed ENaC fragments in their lungs. This is the first demonstration of functional ENaC-CFTR interactions in alveolar epithelial cells in situ.
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Affiliation(s)
- Ahmed Lazrak
- Department of Anesthesiology, School of Medicine, University of Alabama at Birmingham, 35205-3703, USA
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30
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Cleavage of endogenous γENaC and elevated abundance of αENaC are associated with increased Na⁺ transport in response to apical fluid volume expansion in human H441 airway epithelial cells. Pflugers Arch 2011; 462:431-41. [PMID: 21667229 PMCID: PMC3155050 DOI: 10.1007/s00424-011-0982-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2011] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 10/31/2022]
Abstract
Using human H441 airway epithelial cells cultured at air-liquid interface (ALI), we have uniquely correlated the functional response to apical fluid volume expansion with the abundance and cleavage of endogenous α- and γENaC proteins in the apical membrane. Monolayers cultured at ALI rapidly elevated I (sc) when inserted into fluid-filled Ussing chambers. The increase in I (sc) was not significantly augmented by the apical addition of trypsin, and elevation was abolished by the protease inhibitor aprotinin and an inhibitor of the proprotein convertase, furin. These treatments also increased the IC₅₀ amiloride indicating that the effect was via inhibition of highly Na⁺-selective ENaC channels. Apical fluid, 5-500 μl for 1 h in culture, increased the spontaneous starting I (sc) in a dose-dependent manner, whilst maximal fluid-induced I (sc) in the Ussing chamber was unchanged. Apical fluid expansion increased the abundance of 63-65-kDa αENaC proteins in the apical membrane. However, this could not be attributed to increased cleavage as protease inhibitors had no effect on the ratio of cleaved to non-cleaved (90 kDa) αENaC proteins. Instead, fluid expansion increased αENaC abundance in the membrane. In contrast, function correlated well with γENaC cleavage at known sites by furin and extracellular proteases. Interestingly, cleavage of γENaC was associated with increased retrieval from the membrane via the proteosomal pathway. Thus, the response to apical fluid volume expansion in H441 airway epithelial cells involves cleavage of γENaC, and changes in α- and γENaC protein abundance at the apical membrane.
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Zheng H, Liu X, Rao US, Patel KP. Increased renal ENaC subunits and sodium retention in rats with chronic heart failure. Am J Physiol Renal Physiol 2010; 300:F641-9. [PMID: 21159737 DOI: 10.1152/ajprenal.00254.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Renal tubular dysfunction could be involved in the increased sodium and water reabsorption in chronic heart failure (CHF). The goal of the present study was to examine the molecular basis for the increased renal sodium and water retention in CHF. We hypothesized that dysregulation of renal epithelial sodium channels (ENaC) could be involved in the pathogenesis of CHF. The left coronary ligation-induced model of heart failure in the rat was used. Real-time PCR and Western blot analysis indicated that the mRNA and protein abundance of α-, β-, and γ-subunits of ENaC were significantly increased by in the cortex (mRNA: α-ENaC Δ104 ± 24%, β-ENaC Δ47 ± 16%, γ-ENaC Δ55 ± 18%; protein: α-ENaC Δ114 ± 28%, β-ENaC Δ150 ± 31%, γ-ENaC Δ39 ± 5% compared with sham rats) and outer medulla (mRNA: α-ENaC Δ52 ± 18%, β-ENaC Δ38 ± 8%, γ-ENaC Δ39 ± 13%; protein: α-ENaC Δ88 ± 16%, β-ENaC Δ94 ± 28%, γ-ENaC Δ45 ± 9% compared with sham rats) of CHF compared with sham-operated rats. Immunohistochemistry microscopy confirmed the increased labeling of α-, β-, and γ-ENaC subunits in the collecting duct segments in rats with CHF. Furthermore, there was a significant increase in diuretic (7-fold compared with sham) and natriuretic responses (3-fold compared with sham) to ENaC inhibitor benzamil in the rats with CHF. Absence of renal nerves produced a greater contribution of ENaC in sodium retention in rats with CHF. These results suggest that the increased expression of renal ENaC subunits may contribute to the renal sodium and water retention observed during CHF.
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Affiliation(s)
- Hong Zheng
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
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32
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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: 72] [Impact Index Per Article: 5.1] [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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33
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Decreased renal corin expression contributes to sodium retention in proteinuric kidney diseases. Kidney Int 2010; 78:650-9. [PMID: 20613715 DOI: 10.1038/ki.2010.197] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Patients with proteinuric kidney diseases often have symptoms of salt and water retention. It has been hypothesized that dysregulated sodium absorption is due to increased proteolytic cleavage of epithelial sodium channels (ENaCs) and increased Na,K-ATPase expression. Microarray analysis identified a reduction in kidney corin mRNA expression in rat models of puromycin aminonucleoside-induced nephrotic syndrome and acute anti-Thy1 glomerulonephritis (GN). As atrial natriuretic peptide (ANP) resistance is a mechanism accounting for volume retention, we analyzed the renal expression and function of corin; a type II transmembrane serine protease that converts pro-ANP to active ANP. Immunohistochemical analysis found that corin colocalized with ANP. The nephrotic and glomerulonephritic models exhibited concomitant increased pro-ANP and decreased ANP protein levels in the kidney consistent with low amounts of corin. Importantly, kidneys from corin knockout mice had increased amounts of renal β-ENaC and its activators, phosphodiesterase (PDE) 5 and protein kinase G II, when compared to wild-type mice. A similar expression profile was also found in cell culture suggesting the increase in PDE5 and kinase G II could account for the increase in β-ENaC seen in nephrotic syndrome and GN. Thus, we suggest that corin might be involved in the salt retention seen in glomerular diseases.
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Rollins BM, Garcia-Caballero A, Stutts MJ, Tarran R. SPLUNC1 expression reduces surface levels of the epithelial sodium channel (ENaC) in Xenopus laevis oocytes. Channels (Austin) 2010; 4:255-9. [PMID: 20519934 DOI: 10.4161/chan.4.4.12255] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Throughout the body, the epithelial Na(+) channel (ENaC) plays a critical role in salt and liquid homeostasis. In cystic fibrosis airways, for instance, improper regulation of ENaC results in hyperabsorption of sodium that causes dehydration of airway surface liquid. This dysregulation then contributes to mucus stasis and chronic lung infections. ENaC is known to undergo proteolytic cleavage, which is required for its ability to conduct Na(+) ions. We have previously shown that the short, palate lung and nasal epithelial clone (SPLUNC1) binds to and inhibits ENaC in both airway epithelia and in Xenopus laevis oocytes. In this study, we found that SPLUNC1 was more potent at inhibiting ENaC than either SPLUNC2 or long PLUNC1 (LPLUNC1), two other PLUNC family proteins that are also expressed in airway epithelia. Furthermore, we were able to shed light on the potential mechanism of SPLUNC1's inhibition of ENaC. While SPLUNC1 did not inhibit proteolytic activity of trypsin, it significantly reduced ENaC currents by reducing the number of ENaCs in the plasma membrane. A better understanding of ENaC's regulation by endogenous inhibitors may aid in the development of novel therapies designed to inhibit hyperactive ENaC in cystic fibrosis epithelia.
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Affiliation(s)
- Brett M Rollins
- Cystic Fibrosis/Pulmonary Research and Treatment Center, The University of North Carolina, Chapel Hill, NC, USA
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35
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Clark EB, Jovov B, Rooj AK, Fuller CM, Benos DJ. Proteolytic cleavage of human acid-sensing ion channel 1 by the serine protease matriptase. J Biol Chem 2010; 285:27130-27143. [PMID: 20601429 DOI: 10.1074/jbc.m110.153213] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Acid-sensing ion channel 1 (ASIC1) is a H(+)-gated channel of the amiloride-sensitive epithelial Na(+) channel (ENaC)/degenerin family. ASIC1 is expressed mostly in the central and peripheral nervous system neurons. ENaC and ASIC function is regulated by several serine proteases. The type II transmembrane serine protease matriptase activates the prototypical alphabetagammaENaC channel, but we found that matriptase is expressed in glioma cells and its expression is higher in glioma compared with normal astrocytes. Therefore, the goal of this study was to test the hypothesis that matriptase regulates ASIC1 function. Matriptase decreased the acid-activated ASIC1 current as measured by two-electrode voltage clamp in Xenopus oocytes and cleaved ASIC1 expressed in oocytes or CHO K1 cells. Inactive S805A matriptase had no effect on either the current or the cleavage of ASIC1. The effect of matriptase on ASIC1 was specific, because it did not affect the function of ASIC2 and no matriptase-specific ASIC2 fragments were detected in oocytes or in CHO cells. Three matriptase recognition sites were identified in ASIC1 (Arg-145, Lys-185, and Lys-384). Site-directed mutagenesis of these sites prevented matriptase cleavage of ASIC1. Our results show that matriptase is expressed in glioma cells and that matriptase specifically cleaves ASIC1 in heterologous expression systems.
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Affiliation(s)
- Edlira B Clark
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Biljana Jovov
- Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Arun K Rooj
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Catherine M Fuller
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Dale J Benos
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294.
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Li K, Guo D, Zhu H, Hering-Smith KS, Hamm LL, Ouyang J, Dong Y. Interleukin-6 stimulates epithelial sodium channels in mouse cortical collecting duct cells. Am J Physiol Regul Integr Comp Physiol 2010; 299:R590-5. [PMID: 20504903 DOI: 10.1152/ajpregu.00207.2009] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The aim of this study is to elucidate the effects of interleukin-6 (IL-6) on the expression and activity of the epithelial sodium channel (ENaC), which is one of the key mechanisms underlying tubular sodium reabsorption. M-1 cortical collecting duct cells were treated with IL-6 (100 ng/ml) for 12 h. Real-time polymerase chain reaction and immunoblotting were employed to examine the mRNA and protein abundance. Transepithelial voltage (V(te)) and resistance (R(te)) were measured with an ohm/voltmeter (EVOM, WPI). The equivalent current was calculated as the ratio of V(te) to R(te.) Treatment with IL-6 (n = 5) increased the mRNA abundance of alpha-ENaC by 11 +/- 7% (P = not significant), beta-ENaC by 78 +/- 14% (P = 0.01), gamma-ENaC by 185 +/- 38% (P = 0.02), and prostasin by 29 +/- 5% (P = 0.01), all normalized by beta-actin. Treatment with IL-6 increased the protein expression of alpha-ENaC by 19 +/- 3% (P = 0.001), beta-ENaC by 89 +/- 21% (P = 0.01), gamma-ENaC by 36 +/- 12% (P = 0.02), and prostasin by 33 +/- 6% (P = 0.02). The amiloride-sensitive sodium current increased by 37 +/- 5%, from 6.0 +/- 0.4 to 8.2 +/- 0.3 muA/cm(2) (P < 0.01), in the cells treated with IL-6 compared with controls (P = 0.01). Aprotinin (28 microg/ml), a prostasin inhibitor, reduced the amiloride-sensitive sodium current by 61 +/- 5%, from 6.1 +/- 0.3 to 3.7 +/- 0.2 muA/cm(2) (P = 0.01). The magnitude of the IL-6-induced amiloride-sensitive sodium current in the presence of aprotinin dropped by 57 +/- 2%, from 8.6 +/- 0.2 to 4.9 +/- 0.2 muA/cm(2) (P < 0.01). This study has identified a novel function of IL-6, namely, IL-6 may activate ENaC. Therefore, renal inflammation mediated by IL-6 likely contributes to impaired pressure natriuresis.
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Affiliation(s)
- Ke Li
- Georgia Prevention Institute, Dept. of Pediatrics, Medical College of Georgia, Augusta, GA 30912-3715, USA
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37
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Regulation of the epithelial Na+ channel and airway surface liquid volume by serine proteases. Pflugers Arch 2010; 460:1-17. [PMID: 20401730 DOI: 10.1007/s00424-010-0827-z] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/10/2010] [Accepted: 03/12/2010] [Indexed: 01/11/2023]
Abstract
Mammalian airways are protected from infection by a thin film of airway surface liquid (ASL) which covers airway epithelial surfaces and acts as a lubricant to keep mucus from adhering to the epithelial surface. Precise regulation of ASL volume is essential for efficient mucus clearance and too great a reduction in ASL volume causes mucus dehydration and mucus stasis which contributes to chronic airway infection. The epithelial Na(+) channel (ENaC) is the rate-limiting step that governs Na(+) absorption in the airways. Recent in vitro and in vivo data have demonstrated that ENaC is a critical determinant of ASL volume and hence mucus clearance. ENaC must be cleaved by either intracellular furin-type proteases or extracellular serine proteases to be active and conduct Na(+), and this process can be inhibited by protease inhibitors. ENaC can be regulated by multiple pathways, and once proteolytically cleaved ENaC may then be inhibited by intracellular second messengers such as cAMP and PIP(2). In the airways, however, regulation of ENaC by proteases seems to be the predominant mode of regulation since knockdown of either endogenous serine proteases such as prostasin, or inhibitors of ENaC proteolysis such as SPLUNC1, has large effects on ENaC activity in airway epithelia. In this review, we shall discuss how ENaC is proteolytically cleaved, how this process can regulate ASL volume, and how its failure to operate correctly may contribute to chronic airway disease.
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Butterworth MB. Regulation of the epithelial sodium channel (ENaC) by membrane trafficking. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1166-77. [PMID: 20347969 DOI: 10.1016/j.bbadis.2010.03.010] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 03/15/2010] [Accepted: 03/20/2010] [Indexed: 02/07/2023]
Abstract
The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in salt-sensitive hypertension. ENaC activity in epithelial cells is regulated both by open probability and channel number. This review focuses on the regulation of ENaC in the cells of the kidney cortical collecting duct by trafficking and recycling. The trafficking of ENaC is discussed in the broader context of epithelial cell vesicle trafficking. Well-characterized pathways and protein interactions elucidated using epithelial model cells are discussed, and the known overlap with ENaC regulation is highlighted. In following the life of ENaC in CCD epithelial cells the apical delivery, internalization, recycling, and destruction of the channel will be discussed. While a number of pathways presented still need to be linked to ENaC regulation and many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.
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Affiliation(s)
- Michael B Butterworth
- Department Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
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Planès C, Randrianarison NH, Charles RP, Frateschi S, Cluzeaud F, Vuagniaux G, Soler P, Clerici C, Rossier BC, Hummler E. ENaC-mediated alveolar fluid clearance and lung fluid balance depend on the channel-activating protease 1. EMBO Mol Med 2010; 2:26-37. [PMID: 20043279 PMCID: PMC3377187 DOI: 10.1002/emmm.200900050] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Sodium transport via epithelial sodium channels (ENaC) expressed in alveolar epithelial cells (AEC) provides the driving force for removal of fluid from the alveolar space. The membrane-bound channel-activating protease 1 (CAP1/Prss8) activates ENaC in vitro in various expression systems. To study the role of CAP1/Prss8 in alveolar sodium transport and lung fluid balance in vivo, we generated mice lacking CAP1/Prss8 in the alveolar epithelium using conditional Cre-loxP-mediated recombination. Deficiency of CAP1/Prss8 in AEC induced in vitro a 40% decrease in ENaC-mediated sodium currents. Sodium-driven alveolar fluid clearance (AFC) was reduced in CAP1/Prss8-deficient mice, due to a 48% decrease in amiloride-sensitive clearance, and was less sensitive to β2-agonist treatment. Intra-alveolar treatment with neutrophil elastase, a soluble serine protease activating ENaC at the cell surface, fully restored basal AFC and the stimulation by β2-agonists. Finally, acute volume-overload increased alveolar lining fluid volume in CAP1/Prss8-deficient mice. This study reveals that CAP1 plays a crucial role in the regulation of ENaC-mediated alveolar sodium and water transport and in mouse lung fluid balance.
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Affiliation(s)
- Carole Planès
- Département de Pharmacologie et de Toxicologie, Université de Lausanne, Lausanne, Switzerland
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40
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Rauh R, Diakov A, Tzschoppe A, Korbmacher J, Azad AK, Cuppens H, Cassiman JJ, Dötsch J, Sticht H, Korbmacher C. A mutation of the epithelial sodium channel associated with atypical cystic fibrosis increases channel open probability and reduces Na+ self inhibition. J Physiol 2010; 588:1211-25. [PMID: 20194130 DOI: 10.1113/jphysiol.2009.180224] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Increased activity of the epithelial sodium channel (ENaC) in the respiratory airways contributes to the pathophysiology of cystic fibrosis (CF), a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In some patients suffering from atypical CF a mutation can be identified in only one CFTR allele. We recently identified in this group of CF patients a heterozygous mutation (W493R) in the alpha-subunit of ENaC. Here, we investigate the functional effects of this mutation by expressing wild-type alpha beta gamma ENaC or mutant alpha(W493R)beta gamma ENaC in Xenopus oocytes. The alpha W493R mutation stimulated amiloride-sensitive whole-cell currents (Delta I(ami)) by approximately 4-fold without altering the single-channel conductance or surface expression of ENaC. As these data suggest that the open probability (P(o)) of the mutant channel is increased, we investigated the proteolytic activation of ENaC by chymotrypsin. Single-channel recordings revealed that chymotrypsin activated near-silent channels in outside-out membrane patches from oocytes expressing wild-type ENaC, but not in membrane patches from oocytes expressing the mutant channel. In addition, the alpha W493R mutation abolished Na(+) self inhibition of ENaC, which might also contribute to its gain-of-function effects. We conclude that the alpha W493R mutation promotes constitutive activation of ENaC by reducing the inhibitory effect of extracellular Na(+) and decreasing the pool of near-silent channels. The resulting gain-of-function phenotype of the mutant channel might contribute to the pathophysiology of CF in patients carrying this mutation.
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Affiliation(s)
- Robert Rauh
- Department of Cellular and Molecular Physiology, Friedrich-Alexander University of Erlangen-Nürnberg, Germany
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41
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Song W, Wei S, Zhou Y, Lazrak A, Liu G, Londino JD, Squadrito GL, Matalon S. Inhibition of lung fluid clearance and epithelial Na+ channels by chlorine, hypochlorous acid, and chloramines. J Biol Chem 2010; 285:9716-9728. [PMID: 20106988 DOI: 10.1074/jbc.m109.073981] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We investigated the mechanisms by which chlorine (Cl(2)) and its reactive byproducts inhibit Na(+)-dependent alveolar fluid clearance (AFC) in vivo and the activity of amiloride-sensitive epithelial Na(+) channels (ENaC) by measuring AFC in mice exposed to Cl(2) (0-500 ppm for 30 min) and Na(+) and amiloride-sensitive currents (I(Na) and I(amil), respectively) across Xenopus oocytes expressing human alpha-, beta-, and gamma-ENaC incubated with HOCl (1-2000 microm). Both Cl(2) and HOCl-derived products decreased AFC in mice and whole cell and single channel I(Na) in a dose-dependent manner; these effects were counteracted by serine proteases. Mass spectrometry analysis of the oocyte recording medium identified organic chloramines formed by the interaction of HOCl with HEPES (used as an extracellular buffer). In addition, chloramines formed by the interaction of HOCl with taurine or glycine decreased I(Na) in a similar fashion. Preincubation of oocytes with serine proteases prevented the decrease of I(Na) by HOCl, whereas perfusion of oocytes with a synthetic 51-mer peptide corresponding to the putative furin and plasmin cleaving segment in the gamma-ENaC subunit restored the ability of HOCl to inhibit I(Na). Finally, I(Na) of oocytes expressing wild type alpha- and gamma-ENaC and a mutant form of beta ENaC (S520K), known to result in ENaC channels locked in the open position, were not altered by HOCl. We concluded that HOCl and its reactive intermediates (such as organic chloramines) inhibit ENaC by affecting channel gating, which could be relieved by proteases cleavage.
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Affiliation(s)
- Weifeng Song
- Departments of Anesthesiology, Birmingham, Alabama 35205; Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205
| | - Shipeng Wei
- Departments of Anesthesiology, Birmingham, Alabama 35205; Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205
| | - Yongjian Zhou
- Departments of Anesthesiology, Birmingham, Alabama 35205
| | - Ahmed Lazrak
- Departments of Anesthesiology, Birmingham, Alabama 35205; Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205
| | - Gang Liu
- Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205; Medicine, Birmingham, Alabama 35205
| | - James D Londino
- Departments of Anesthesiology, Birmingham, Alabama 35205; Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205
| | - Giuseppe L Squadrito
- Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205; Environmental Health Sciences, Schools of Medicine and Public Health, Birmingham, Alabama 35205; Free Radical Biology, University of Alabama at Birmingham, Birmingham, Alabama 35205
| | - Sadis Matalon
- Departments of Anesthesiology, Birmingham, Alabama 35205; Centers for Pulmonary Injury and Repair, Birmingham, Alabama 35205; Medicine, Birmingham, Alabama 35205; Free Radical Biology, University of Alabama at Birmingham, Birmingham, Alabama 35205.
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42
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Evidence for a protein tether involved in somatic touch. EMBO J 2010; 29:855-67. [PMID: 20075867 PMCID: PMC2810375 DOI: 10.1038/emboj.2009.398] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Accepted: 12/02/2009] [Indexed: 11/09/2022] Open
Abstract
The gating of ion channels by mechanical force underlies the sense of touch and pain. The mode of gating of mechanosensitive ion channels in vertebrate touch receptors is unknown. Here we show that the presence of a protein link is necessary for the gating of mechanosensitive currents in all low-threshold mechanoreceptors and some nociceptors of the dorsal root ganglia (DRG). Using TEM, we demonstrate that a protein filament with of length approximately 100 nm is synthesized by sensory neurons and may link mechanosensitive ion channels in sensory neurons to the extracellular matrix. Brief treatment of sensory neurons with non-specific and site-specific endopeptidases destroys the protein tether and abolishes mechanosensitive currents in sensory neurons without affecting electrical excitability. Protease-sensitive tethers are also required for touch-receptor function in vivo. Thus, unlike the majority of nociceptors, cutaneous mechanoreceptors require a distinct protein tether to transduce mechanical stimuli.
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Svenningsen P, Uhrenholt TR, Palarasah Y, Skjødt K, Jensen BL, Skøtt O. Prostasin-dependent activation of epithelial Na+ channels by low plasmin concentrations. Am J Physiol Regul Integr Comp Physiol 2009; 297:R1733-41. [PMID: 19793956 DOI: 10.1152/ajpregu.00321.2009] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Several pathophysiological conditions, including nephrotic syndrome, are characterized by increased renal activity of the epithelial Na(+) channel (ENaC). We recently identified plasmin in nephrotic urine as a stimulator of ENaC activity and undertook this study to investigate the mechanism by which plasmin stimulates ENaC activity. Cy3-labeled plasmin was found to bind to the surface of the mouse cortical collecting duct cell line, M-1. Binding depended on a glycosylphosphatidylinositol (GPI)-anchored protein. Biotin-label transfer showed that plasmin interacted with the GPI-anchored protein prostasin on M-1 cells and that plasmin cleaved prostasin. Prostasin activates ENaC by cleavage of the gamma-subunit, which releases an inhibitory peptide from the extracellular domain. Removal of GPI-anchored proteins from the M-1 cells with phosphatidylinositol-specific phospholipase C (PI-PLC) inhibited plasmin-stimulated ENaC current in monolayers of M-1 cells at low plasmin concentration (1-4 microg/ml). At a high plasmin concentration of 30 microg/ml, there was no difference between cell layers treated with or without PI-PLC. Knockdown of prostasin attenuated binding of plasmin to M1 cells and blocked plasmin-stimulated ENaC current in single M-1 cells, as measured by whole-cell patch clamp. In M-1 cells expressing heterologous FLAG-tagged prostasin, gammaENaC and prostasin were colocalized. A monoclonal antibody directed against the inhibitory peptide of gammaENaC produced specific immunofluorescence labeling of M-1 cells. Pretreatment with plasmin abolished labeling of M-1 cells in a prostasin-dependent way. We conclude that, at low concentrations, plasmin interacts with GPI-anchored prostasin, which leads to cleavage of the gamma-subunit and activation of ENaC, while at higher concentrations, plasmin directly activates ENaC.
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Affiliation(s)
- Per Svenningsen
- Department of Physiology and Pharmacology, Institute of Medical Biology, Univeristy of Southern Denmark, DK-5000 Odense C., Denmark
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44
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Abstract
The study of human monogenic diseases [pseudohypoaldosteronism type 1 (PHA-1) and Liddle's syndrome] as well as mouse models mimicking the salt-losing syndrome (PHA-1) or salt-sensitive hypertension (Liddle's syndrome) have established the epithelial sodium channel ENaC as a limiting factor in vivo in the control of ionic composition of the extracellular fluid, regulation of blood volume and blood pressure, lung alveolar clearance, and airway mucociliary clearance. In this review, we discuss more specifically the activation of ENaC by serine proteases. Recent in vitro and in vivo experiments indicate that membrane-bound serine proteases are of critical importance in the activation of ENaC in different organs, such as the kidney, the lung, or the cochlea. Progress in understanding the basic mechanism of proteolytic activation of ENaC is accelerating, but uncertainty about the most fundamental aspects persists, leaving numerous still-unanswered questions.
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Affiliation(s)
- Bernard C Rossier
- Department of Pharmacology and Toxicology, University of Lausanne, CH-1005 Lausanne, Switzerland.
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45
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Haerteis S, Krueger B, Korbmacher C, Rauh R. The delta-subunit of the epithelial sodium channel (ENaC) enhances channel activity and alters proteolytic ENaC activation. J Biol Chem 2009; 284:29024-40. [PMID: 19717556 DOI: 10.1074/jbc.m109.018945] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is probably a heterotrimer with three well characterized subunits (alphabetagamma). In humans an additional delta-subunit (delta-hENaC) exists but little is known about its function. Using the Xenopus laevis oocyte expression system, we compared the functional properties of alphabetagamma- and deltabetagamma-hENaC and investigated whether deltabetagamma-hENaC can be proteolytically activated. The amiloride-sensitive ENaC whole-cell current (DeltaI(ami)) was about 11-fold larger in oocytes expressing deltabetagamma-hENaC than in oocytes expressing alphabetagamma-hENaC. The 2-fold larger single-channel Na(+) conductance of deltabetagamma-hENaC cannot explain this difference. Using a chemiluminescence assay, we demonstrated that an increased channel surface expression is also not the cause. Thus, overall channel activity of deltabetagamma-hENaC must be higher than that of alphabetagamma-hENaC. Experiments exploiting the properties of the known betaS520C mutant ENaC confirmed this conclusion. Moreover, chymotrypsin had a reduced stimulatory effect on deltabetagamma-hENaC whole-cell currents compared with its effect on alphabetagamma-hENaC whole-cell currents (2-fold versus 5-fold). This suggests that the cell surface pool of so-called near-silent channels that can be proteolytically activated is smaller for deltabetagamma-hENaC than for alphabetagamma-hENaC. Proteolytic activation of deltabetagamma-hENaC was associated with the appearance of a delta-hENaC cleavage product at the cell surface. Finally, we demonstrated that a short inhibitory 13-mer peptide corresponding to a region of the extracellular loop of human alpha-ENaC inhibited DeltaI(ami) in oocytes expressing alphabetagamma-hENaC but not in those expressing deltabetagamma-hENaC. We conclude that the delta-subunit of ENaC alters proteolytic channel activation and enhances base-line channel activity.
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Affiliation(s)
- Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
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46
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Role of the C-Terminal Part of the Extracellular Domain of the α-ENaC in Activation by Sulfonylurea Glibenclamide. J Membr Biol 2009; 230:133-41. [DOI: 10.1007/s00232-009-9193-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 07/28/2009] [Indexed: 10/20/2022]
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47
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Netzel-Arnett S, Bugge TH, Hess RA, Carnes K, Stringer BW, Scarman AL, Hooper JD, Tonks ID, Kay GF, Antalis TM. The glycosylphosphatidylinositol-anchored serine protease PRSS21 (testisin) imparts murine epididymal sperm cell maturation and fertilizing ability. Biol Reprod 2009; 81:921-32. [PMID: 19571264 DOI: 10.1095/biolreprod.109.076273] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
An estimated 25%-40% of infertile men have idiopathic infertility associated with deficient sperm numbers and quality. Here, we identify the membrane-anchored serine protease PRSS21, also known as testisin, to be a novel proteolytic factor that directs epididymal sperm cell maturation and sperm-fertilizing ability. PRSS21-deficient spermatozoa show decreased motility, angulated and curled tails, fragile necks, and dramatically increased susceptibility to decapitation. These defects reflect aberrant maturation during passage through the epididymis, because histological and electron microscopic structural analyses showed an increased tendency for curled and detached tails as spermatozoa transit from the corpus to the cauda epididymis. Cauda epididymal spermatozoa deficient in PRSS21 fail to mount a swelling response when exposed to hypotonic conditions, suggesting an impaired ability to respond to osmotic challenges facing maturing spermatozoa in the female reproductive tract. These data suggest that aberrant regulation of PRSS21 may underlie certain secondary male infertility syndromes, such as "easily decapitated" spermatozoa in humans.
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Affiliation(s)
- Sarah Netzel-Arnett
- Center for Vascular and Inflammatory Diseases, Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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48
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Kapoor N, Bartoszewski R, Qadri YJ, Bebok Z, Bubien JK, Fuller CM, Benos DJ. Knockdown of ASIC1 and epithelial sodium channel subunits inhibits glioblastoma whole cell current and cell migration. J Biol Chem 2009; 284:24526-41. [PMID: 19561078 DOI: 10.1074/jbc.m109.037390] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
High grade gliomas such as glioblastoma multiforme express multiple members of the epithelial sodium channel (ENaC)/Degenerin family, characteristically displaying a basally active amiloride-sensitive cation current not seen in normal human astrocytes or lower grade gliomas. Using quantitative real time PCR, we have shown higher expression of ASIC1, alphaENaC, and gammaENaC in D54-MG human glioblastoma multiforme cells compared with primary human astrocytes. We hypothesize that this glioma current is mediated by a hybrid channel composed of a mixture of ENaC and acid-sensing ion channel (ASIC) subunits. To test this hypothesis we made dominant negative cDNAs for ASIC1, alphaENaC, gammaENaC, and deltaENaC. D54-MG cells transfected with the dominant negative constructs for ASIC1, alphaENaC, or gammaENaC showed reduced protein expression and a significant reduction in the amiloride-sensitive whole cell current as compared with untransfected D54-MG cells. Knocking down alphaENaC or gammaENaC also abolished the high P(K)(+)/P(Na)(+) of D54-MG cells. Knocking down deltaENaC in D54-MG cells reduced deltaENaC protein expression but had no effect on either the whole cell current or K(+) permeability. Using co-immunoprecipitation we show interactions between ASIC1, alphaENaC, and gammaENaC, consistent with these subunits interacting with each other to form an ion channel in glioma cells. We also found a significant inhibition of D54-MG cell migration after ASIC1, alphaENaC, or gammaENaC knockdown, consistent with the hypothesis that ENaC/Degenerin subunits play an important role in glioma cell biology.
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Affiliation(s)
- Niren Kapoor
- Department of Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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49
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Kleyman TR, Carattino MD, Hughey RP. ENaC at the cutting edge: regulation of epithelial sodium channels by proteases. J Biol Chem 2009; 284:20447-51. [PMID: 19401469 DOI: 10.1074/jbc.r800083200] [Citation(s) in RCA: 223] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Epithelial Na+ channels facilitate the transport of Na+ across high resistance epithelia. Proteolytic cleavage has an important role in regulating the activity of these channels by increasing their open probability. Specific proteases have been shown to activate epithelial Na+ channels by cleaving channel subunits at defined sites within their extracellular domains. This minireview addresses the mechanisms by which proteases activate this channel and the question of why proteolysis has evolved as a mechanism of channel activation.
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Affiliation(s)
- Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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50
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Zhu H, Chao J, Guo D, Li K, Huang Y, Hawkins K, Wright N, Stallmann-Jorgenson I, Yan W, Harshfield GA, Dong Y. Urinary prostasin: a possible biomarker for renal pressure natriuresis in black adolescents. Pediatr Res 2009; 65:443-6. [PMID: 19127211 PMCID: PMC3826778 DOI: 10.1203/pdr.0b013e3181994b85] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Prostasin is a membrane-bound/secretive serine protease interacting with aldosterone and the epithelial sodium channel in the kidney. We and others have previously proposed the concept of stress-induced pressure natriuresis (SIPN) where increased urinary sodium excretion (UNaV) is coupled with elevated blood pressure (BP) in response to behavioral stress in normotensive adolescents. This study thus aimed to test the relationship between prostasin and pressure natriuresis using the SIPN model. A cohort of 102 normotensive black adolescents (mean age: 17.0 +/- 1.2 y; 56% females) were placed on a controlled sodium (4000 +/- 200 mg/d) and potassium (2600 +/- 200 mg/d) diet for three days before testing. The SIPN protocol consisted of a 1-h baseline period, a 1-h stress period (competitive video game), and a 1-h recovery period. During the stress period, BP elevation was coupled with an increase in UNaV. Urinary prostasin concentration had more than a 2-fold reduction from baseline (38.4 +/- 32.7 ng/mL) to stress (17.2 +/- 16.0 ng/mL), and further declined during recovery (12.1 +/- 16.2 ng/mL) (p < 0.001). Urinary prostasin was inversely correlated with UNaV during stress (r = -0.43, p = 0.0001), even after being normalized by urinary creatinine. Our data suggest that urinary prostasin could be a novel biomarker and/or mechanism for renal pressure natriuresis in normotensive black adolescents.
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Affiliation(s)
- Haidong Zhu
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Julie Chao
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, USA 29425
| | - Dehuang Guo
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Ke Li
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Ying Huang
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Kimberly Hawkins
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Nikki Wright
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Inger Stallmann-Jorgenson
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Weili Yan
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Gregory A. Harshfield
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
| | - Yanbin Dong
- Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, Georgia, USA 30907
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