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Gao Z, Sun J, Cai C, Gong X, Ma L. Pseudohypoaldosteronism type 1b in fraternal twins of a Chinese family: report of two cases and literature review. ARCHIVES OF ENDOCRINOLOGY AND METABOLISM 2023; 67:e000620. [PMID: 37252702 PMCID: PMC10665068 DOI: 10.20945/2359-3997000000620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 08/21/2022] [Indexed: 05/31/2023]
Abstract
Here, we report the clinical observations of two Chinese fraternal twins who presented with severe dehydration, poor feeding, and absence of stimuli responses within a few days of birth. Trio clinical exome sequencing of the family identified compound heterozygous intronic variants (c.1439+1G>C and c.875+1G>A ) in SCNN1A gene in these two patients. Sanger sequencing results showed that the c.1439+1G>C variant was inherited from the mother, and c.875+1G>A from the father, rarely reported in pseudohypoaldosteronism type 1 with sodium epithelial channel destruction (PHA1b) patients. Case 2 received timely symptomatic treatment and management after obtaining these results, which improved the clinical crisis. Our results suggest that the compound heterozygous splicing variants in SCNN1A were responsible for PHA1b in these Chinese fraternal twins. This finding extends the knowledge of the variant spectrum in PHA1b patients and highlights the application of exome sequencing in critically ill newborns. Finally, we discuss supportive case management, particularly in maintaining blood potassium concentration.
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Affiliation(s)
- Zhen Gao
- Department of Neonatology, Shanghai Children's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Jingjing Sun
- Department of Neonatology, Shanghai Children's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- NHC Key Laboratory of Medical Embryogenesis and Developmental Molecular Biology & Shanghai Key Laboratory of Embryo and Reproduction Engineering, Shanghai, China
| | - Cheng Cai
- Department of Neonatology, Shanghai Children's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- NHC Key Laboratory of Medical Embryogenesis and Developmental Molecular Biology & Shanghai Key Laboratory of Embryo and Reproduction Engineering, Shanghai, China
| | - Xiaohui Gong
- Department of Neonatology, Shanghai Children's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- NHC Key Laboratory of Medical Embryogenesis and Developmental Molecular Biology & Shanghai Key Laboratory of Embryo and Reproduction Engineering, Shanghai, China
| | - Li Ma
- Department of Neonatology, Shanghai Children's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- NHC Key Laboratory of Medical Embryogenesis and Developmental Molecular Biology & Shanghai Key Laboratory of Embryo and Reproduction Engineering, Shanghai, China,
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Lemmens-Gruber R, Tzotzos S. The Epithelial Sodium Channel-An Underestimated Drug Target. Int J Mol Sci 2023; 24:ijms24097775. [PMID: 37175488 PMCID: PMC10178586 DOI: 10.3390/ijms24097775] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 04/14/2023] [Accepted: 04/15/2023] [Indexed: 05/15/2023] Open
Abstract
Epithelial sodium channels (ENaC) are part of a complex network of interacting biochemical pathways and as such are involved in several disease states. Dependent on site and type of mutation, gain- or loss-of-function generated symptoms occur which span from asymptomatic to life-threatening disorders such as Liddle syndrome, cystic fibrosis or generalized pseudohypoaldosteronism type 1. Variants of ENaC which are implicated in disease assist further understanding of their molecular mechanisms in order to create models for specific pharmacological targeting. Identification and characterization of ENaC modifiers not only furthers our basic understanding of how these regulatory processes interact, but also enables discovery of new therapeutic targets for the disease conditions caused by ENaC dysfunction. Numerous test compounds have revealed encouraging results in vitro and in animal models but less in clinical settings. The EMA- and FDA-designated orphan drug solnatide is currently being tested in phase 2 clinical trials in the setting of acute respiratory distress syndrome, and the NOX1/ NOX4 inhibitor setanaxib is undergoing clinical phase 2 and 3 trials for therapy of primary biliary cholangitis, liver stiffness, and carcinoma. The established ENaC blocker amiloride is mainly used as an add-on drug in the therapy of resistant hypertension and is being studied in ongoing clinical phase 3 and 4 trials for special applications. This review focuses on discussing some recent developments in the search for novel therapeutic agents.
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Affiliation(s)
- Rosa Lemmens-Gruber
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, A-1090 Vienna, Austria
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Coelho Almeida A, Bastos Gomes M, Martins SA, Marques OP, Gomes MM, Antunes AM. A case of severe systemic type 1 pseudohypoaldosteronism with 10 years of evolution. J Pediatr Endocrinol Metab 2022; 35:1448-1452. [PMID: 35918792 DOI: 10.1515/jpem-2022-0201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 06/27/2022] [Indexed: 11/15/2022]
Abstract
Type 1 pseudohypoaldosteronism (PHA-1) is a rare genetic syndrome of unresponsiveness to aldosterone and presents in the neonatal period with hyperkalemia, hyponatremia and metabolic acidosis. The mortality rate can be high and multidisciplinary team is needed for optimal management and adequate growth and development of these patients. Many genotype-phenotype correlations remain uncertain, and the description of the evolution of cases can increase scientific knowledge about the psychomotor development and severity of the different mutations. We report the follow-up for the last 10 years of a patient, with previously unrecognized genetic findings identified. In addition, we reviewed the literature and compared it with other pediatric cases.
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Affiliation(s)
- André Coelho Almeida
- Department of Pediatrics and Neonatology, Centro Hospitalar de Trás-Os-Montes e Alto Douro, Vila Real, Portugal
| | - Mariana Bastos Gomes
- Department of Pediatrics, Unidade Local de Saúde do Alto Minho, Viana do Castelo, Portugal
| | - Sofia A Martins
- Pediatric Endocrinology and Diabetology Unit, Hospital de Braga, Braga, Portugal
| | | | - Maria Miguel Gomes
- Pediatric Endocrinology and Diabetology Unit, Hospital de Braga, Braga, Portugal.,School of Medicine, University of Minho, Braga, Portugal
| | - Ana M Antunes
- Pediatric Endocrinology and Diabetology Unit, Hospital de Braga, Braga, Portugal
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Serra G, Antona V, D'Alessandro MM, Maggio MC, Verde V, Corsello G. Novel SCNN1A gene splicing-site mutation causing autosomal recessive pseudohypoaldosteronism type 1 (PHA1) in two Italian patients belonging to the same small town. Ital J Pediatr 2021; 47:138. [PMID: 34134742 PMCID: PMC8207710 DOI: 10.1186/s13052-021-01080-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 05/20/2021] [Indexed: 12/29/2022] Open
Abstract
INTRODUCTION Pseudohypoaldosteronism type 1 (PHA1) is a rare genetic disease due to the peripheral resistance to aldosterone. Its clinical spectrum includes neonatal salt loss syndrome with hyponatremia and hypochloraemia, hyperkalemia, metabolic acidosis and increased plasmatic levels of aldosterone. Two genetically distinct forms of disease, renal and systemic, have been described, showing a wide clinical expressivity. Mutations in the genes encoding for the subunits of the epithelial sodium channels (ENaC) are responsible for generalized PHA1. PATIENTS' PRESENTATION We hereby report on two Italian patients with generalized PHA1, coming from the same small town in the center of Sicily. The first patient is a male child, born from the first pregnancy of healthy consanguineous Sicilian parents. A novel SCNN1A (sodium channel epithelial subunit alpha) gene mutation, inherited from both heterozygous parents, was identified by next generation sequencing (NGS) in the homozygous child (and later, also in the heterozygous maternal aunt). A more detailed family history disclosed a possible related twenty-year-old girl, belonging to the same Sicilian small town, with referred neonatal salt loss syndrome associated to hyperkalemia, and subsequent normal growth and neurodevelopment. This second patient had a PHA1 clinical diagnosis when she was about 1 year old. The genetic investigation was, then, extended to her and to her family, revealing the same mutation in the homozygous girl and in the heterozygous parents. CONCLUSIONS The neonatologist should consider PHA1 diagnosis in newborns showing hyponatremia, hyperkalemia and metabolic acidosis, after the exclusion of a salting-loss form of adrenogenital syndrome. The increased plasmatic levels of aldosterone and aldosterone/renin ratio, associated to a poor response to steroid administration, confirmed the diagnosis in the first present patient. An accurate family history may be decisive to identify the clinical picture. A multidisciplinary approach and close follow-up evaluations are requested, in view of optimal management, adequate growth and development of patients. Next generation sequencing (NGS) techniques allowed the identification of the SCNN1A gene mutation either in both patients or in other heterozygous family members, enabling also primary prevention of disease. Our report may broaden the knowledge of the genetic and molecular bases of PHA1, improving its clinical characterization and providing useful indications for the treatment of patients. Clinical approach must be personalized, also in relation to long-term survival and potential multiorgan complications.
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Affiliation(s)
- Gregorio Serra
- Department of Health Promotion, Mother and Child Care, Internal Medicine and Medical Specialties "G. D'Alessandro", University of Palermo, Palermo, Italy.
| | - Vincenzo Antona
- Department of Health Promotion, Mother and Child Care, Internal Medicine and Medical Specialties "G. D'Alessandro", University of Palermo, Palermo, Italy
| | | | - Maria Cristina Maggio
- Department of Health Promotion, Mother and Child Care, Internal Medicine and Medical Specialties "G. D'Alessandro", University of Palermo, Palermo, Italy
| | - Vincenzo Verde
- Department of Health Promotion, Mother and Child Care, Internal Medicine and Medical Specialties "G. D'Alessandro", University of Palermo, Palermo, Italy
| | - Giovanni Corsello
- Department of Health Promotion, Mother and Child Care, Internal Medicine and Medical Specialties "G. D'Alessandro", University of Palermo, Palermo, Italy
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Abdalla A, Alhassan MA, Tawfeeg R, Sanad A, Tawamie H, Abdullah M. Systemic pseudohypoaldosteronism-1 with episodic dyslipidemia in a Sudanese child. Endocrinol Diabetes Metab Case Rep 2021; 2021:EDM210010. [PMID: 34165441 PMCID: PMC8240716 DOI: 10.1530/edm-21-0010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 05/25/2021] [Indexed: 11/08/2022] Open
Abstract
SUMMARY Systemic pseudohypoaldosteronism type 1 (PHA1) is a rare genetic syndrome of tissue unresponsiveness to aldosterone caused by mutations affecting the epithelial Na channel (ENaC). The classical presentation is life-threatening neonatal/infantile salt-losing crises that mimic congenital adrenal hyperplasia (CAH). Consistently, extra-renal manifestations, including respiratory symptoms that resemble cystic fibrosis, are well reported. Clinical diagnosis is made by the presence of hyponatremia, hyperkalemia, metabolic acidosis, respiratory symptoms, evidence of high renal and extra-renal salt loss in addition to high plasma renin and aldosterone levels. We herein report a novel manifestation of PHA1: episodic dyslipidemia in a 7-month-old Sudanese boy that occurred during the salt-losing crises. Whole exome sequencing of the patient revealed one homozygous missense variant c.1636G>A p.(Asp546Asn) in the SCNN1B gene, confirming our clinical and laboratory findings that were compatible with PHA1. This report aims to highlight the possible explanation of dyslipidemia in PHA1 and its expected consequences in the long term. LEARNING POINTS A child presenting with features that mimic salt-losing congenital adrenal hyperplasia (CAH) crises that do not respond to glucocorticoid and mineralocorticoid therapy should alert the pediatricians to the possibility of end-organ resistance to aldosterone. Pseudohypoaldosteronism type 1 (PHA1) can be diagnosed even in the absence of advanced laboratory investigations. To our knowledge, this is the first case of systemic PHA1 to have a documented episodic dyslipidemia (primarily as marked hypertriglyceridemia).
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Affiliation(s)
- Asmahan Abdalla
- Department of Pediatric Endocrinologist, Gaafar Ibn Auf Children’s Tertiary Hospital, Khartoum, Sudan
| | | | - Reem Tawfeeg
- Department of Pediatric Respirologist, Elswaidi Charity Hospital, Khartoum, Sudan
| | - Ayman Sanad
- Department of Pediatrics, University of Shendi, Shendi, Sudan
| | - Hasan Tawamie
- Clinical Lab Operations at Centogene Laboratory, Rostock, Mecklenburg-Vorpommern, Germany
| | - Mohamed Abdullah
- Departmentof Pediatric Endocrinology, Faculty of Medicine, University of Khartoum, Khartoum, Sudan
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Shabbir W, Topcagic N, Aufy M. Activation of autosomal recessive Pseudohypoaldosteronism1 ENaC with aldosterone. Eur J Pharmacol 2021; 901:174090. [PMID: 33831414 DOI: 10.1016/j.ejphar.2021.174090] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 03/26/2021] [Accepted: 03/31/2021] [Indexed: 11/28/2022]
Abstract
The mineralocorticoid hormone aldosterone stimulates sodium reabsorption in the collecting ducts by increasing the activity of the epithelial sodium channel (ENaC). Being a rate-liming channel the loss of function mutations caused Pseudohypoaldosteronism 1 (PHA1). Despite elevated plasma aldosterone in PHA 1 patients the modulation of PHA 1 causing ENaC mutants with hormone has never been studied. After recording control ENaC current in PHA1 causing ENaC stop codon mutants we demonstrated the activation of aldosterone in the whole cell as well as single channel patch clamp assays. Single channel recoding experiments demonstrated that aldosterone can increase the open probability of all analyzed PHA 1 stop codon mutants and WT. Additionally, we demonstrated by western blot experiments that aldosterone can increase the expression of WT and PHA 1 stop codon mutants. Extensive whole cell patch clamp experiments demonstrated that C-terminal γ ENaC domain is necessary for aldosterone to activate whole cell current in HEK-293 cells. This novel finding of γ ENaC C-terminus dependent activation of whole cell current by aldosterone could alter our understanding of ENaC-mediated sodium reabsorption in the aldosterone-sensitive distal nephron (ASDN).
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Affiliation(s)
- Waheed Shabbir
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria.
| | - Nermina Topcagic
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
| | - Mohammed Aufy
- Institute for Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
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7
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Haq IJ, Althaus M, Gardner AI, Yeoh HY, Joshi U, Saint-Criq V, Verdon B, Townshend J, O'Brien C, Ben-Hamida M, Thomas M, Bourke S, van der Sluijs P, Braakman I, Ward C, Gray MA, Brodlie M. Clinical and molecular characterization of the R751L-CFTR mutation. Am J Physiol Lung Cell Mol Physiol 2020; 320:L288-L300. [PMID: 33296276 PMCID: PMC8476205 DOI: 10.1152/ajplung.00137.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Cystic fibrosis (CF) arises from mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in progressive and life-limiting respiratory disease. R751L is a rare CFTR mutation that is poorly characterized. Our aims were to describe the clinical and molecular phenotypes associated with R751L. Relevant clinical data were collected from three heterozygote individuals harboring R751L (2 patients with G551D/R751L and 1 with F508del/R751L). Assessment of R751L-CFTR function was made in primary human bronchial epithelial cultures (HBEs) and Xenopus oocytes. Molecular properties of R751L-CFTR were investigated in the presence of known CFTR modulators. Although sweat chloride was elevated in all three patients, the clinical phenotype associated with R751L was mild. Chloride secretion in F508del/R751L HBEs was reduced compared with non-CF HBEs and associated with a reduction in sodium absorption by the epithelial sodium channel (ENaC). However, R751L-CFTR function in Xenopus oocytes, together with folding and cell surface transport of R751L-CFTR, was not different from wild-type CFTR. Overall, R751L-CFTR was associated with reduced sodium chloride absorption but had functional properties similar to wild-type CFTR. This is the first report of R751L-CFTR that combines clinical phenotype with characterization of functional and biological properties of the mutant channel. Our work will build upon existing knowledge of mutations within this region of CFTR and, importantly, inform approaches for clinical management. Elevated sweat chloride and reduced chloride secretion in HBEs may be due to alternative non-CFTR factors, which require further investigation.
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Affiliation(s)
- Iram J Haq
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.,Paediatric Respiratory Medicine, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
| | - Mike Althaus
- Institute for Functional Gene Analytics, Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, Rheinbach, Germany
| | - Aaron Ions Gardner
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Hui Ying Yeoh
- Cellular Protein Chemistry, Science4Life, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Urjita Joshi
- Cellular Protein Chemistry, Science4Life, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Vinciane Saint-Criq
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Bernard Verdon
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Jennifer Townshend
- Paediatric Respiratory Medicine, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
| | - Christopher O'Brien
- Paediatric Respiratory Medicine, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
| | - Mahfud Ben-Hamida
- Department of Paediatrics, West Cumberland Hospital, Whitehaven, United Kingdom
| | - Matthew Thomas
- Paediatric Respiratory Medicine, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
| | - Stephen Bourke
- Respiratory Medicine, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom
| | - Peter van der Sluijs
- Cellular Protein Chemistry, Science4Life, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Science4Life, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Chris Ward
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Michael A Gray
- Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Malcolm Brodlie
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.,Paediatric Respiratory Medicine, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
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Anand P, Puranik A, Aravamudan M, Venkatakrishnan AJ, Soundararajan V. SARS-CoV-2 strategically mimics proteolytic activation of human ENaC. eLife 2020; 9:58603. [PMID: 32452762 PMCID: PMC7343387 DOI: 10.7554/elife.58603] [Citation(s) in RCA: 86] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 05/25/2020] [Indexed: 12/11/2022] Open
Abstract
Molecular mimicry is an evolutionary strategy adopted by viruses to exploit the host cellular machinery. We report that SARS-CoV-2 has evolved a unique S1/S2 cleavage site, absent in any previous coronavirus sequenced, resulting in the striking mimicry of an identical FURIN-cleavable peptide on the human epithelial sodium channel α-subunit (ENaC-α). Genetic alteration of ENaC-α causes aldosterone dysregulation in patients, highlighting that the FURIN site is critical for activation of ENaC. Single cell RNA-seq from 66 studies shows significant overlap between expression of ENaC-α and the viral receptor ACE2 in cell types linked to the cardiovascular-renal-pulmonary pathophysiology of COVID-19. Triangulating this cellular characterization with cleavage signatures of 178 proteases highlights proteolytic degeneracy wired into the SARS-CoV-2 lifecycle. Evolution of SARS-CoV-2 into a global pandemic may be driven in part by its targeted mimicry of ENaC-α, a protein critical for the homeostasis of airway surface liquid, whose misregulation is associated with respiratory conditions. Viruses hijack the cellular machinery of humans to infect their cells and multiply. The virus causing the global COVID-19 pandemic, SARS-CoV-2, is no exception. Identifying which proteins in human cells the virus co-opts is crucial for developing new ways to diagnose, prevent and treat COVID-19 infections. SARS-CoV-2 is covered in spike-shaped proteins, which the virus uses to gain entry into cells. First, the spikes bind to a protein called ACE2, which is found on the cells that line the respiratory tract and lungs. SARS-CoV-2 then exploits enzymes called proteases to cut, or cleave, its spikes at a specific site which allows the virus to infiltrate the host cell. Proteases identify which proteins to target based on the sequence of amino acids – the building blocks of proteins – at the cleavage site. However, it remained unclear which human proteases SARS-CoV-2 co-opts and whether its cut site is similar to human proteins. Now, Anand et al. show that the spike proteins on SARS-CoV-2 may have the same sequence of amino acids at its cut site as a human epithelial channel protein called ENaC-α. This channel is important for maintaining the balance of salt and water in many organs including the lungs. Further analyses showed that ENaC-α is often found in the same types of human lung and respiratory tract cells as ACE2. This suggests that SARS-CoV-2 may use the same proteases that cut ENaC-α to get inside human respiratory cells. It is possible that by hijacking the cutting mechanism for ENaC-α, SARS-CoV-2 interferes with the balance of salt and water in the lungs of COVID-19 patients. This may help explain why the virus causes severe respiratory symptoms. However, more studies are needed to confirm that the proteases that cut ENaC-α also cut the spike proteins on SARS-CoV-2, and how this affects the respiratory health of COVID-19 patients.
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Gopal-Kothandapani JS, Doshi AB, Smith K, Christian M, Mushtaq T, Banerjee I, Padidela R, Ramakrishnan R, Owen C, Cheetham T, Dimitri P. Phenotypic diversity and correlation with the genotypes of pseudohypoaldosteronism type 1. J Pediatr Endocrinol Metab 2019; 32:959-967. [PMID: 31301676 DOI: 10.1515/jpem-2018-0538] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Accepted: 05/27/2019] [Indexed: 12/27/2022]
Abstract
Background Type I pseudohypoaldosteronism (PHA1) is a rare condition characterised by profound salt wasting, hyperkalaemia and metabolic acidosis due to renal tubular resistance to aldosterone (PHA1a) or defective sodium epithelial channels (PHA1b or systemic PHA). Our aim was to review the clinical presentation related to the genotype in patients with PHA1. Methods A questionnaire-based cross-sectional survey was undertaken through the British Society of Paediatric Endocrinology and Diabetes (BSPED) examining the clinical presentation and management of patients with genetically confirmed PHA1. We also reviewed previously reported patients where genotypic and phenotypic information were reported. Results Genetic confirmation was made in 12 patients with PHA1; four had PHA1a, including one novel mutation in NR3C2; eight had PHA1b, including three with novel mutations in SCNN1A and one novel mutation in SCNN1B. It was impossible to differentiate between types of PHA1 from early clinical presentation or the biochemical and hormonal profile. Patients presenting with missense mutations of SCNN1A and SCNN1B had a less marked rise in serum aldosterone suggesting preservation in sodium epithelial channel function. Conclusions We advocate early genetic testing in patients with presumed PHA1, given the challenges in differentiating between patients with PHA1a and PHA1b. Clinical course differs between patients with NR3C2 and SCNN1A mutations with a poorer prognosis in those with multisystem PHA. There were no obvious genotype-phenotype correlations between mutations on the same gene in our cohort and others, although a lower serum aldosterone may suggest a missense mutation in SCNN1 in patients with PHA1b.
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Affiliation(s)
| | - Arpan B Doshi
- Sheffield Medical School, University of Sheffield, Sheffield, UK
| | - Kath Smith
- Department of Genetics, Sheffield Children's Hospital, Sheffield, UK
| | - Martin Christian
- Department of Paediatric Nephrology, Nottingham University Hospitals NHS Trust, Nottingham, UK
| | - Talat Mushtaq
- Department of Paediatric Endocrinology, Leeds General Infirmary, Leeds, UK
| | - I Banerjee
- Department of Paediatric Endocrinology, Royal Manchester Children's Hospital, Manchester, UK
| | - Raja Padidela
- Department of Paediatric Endocrinology, Royal Manchester Children's Hospital, Manchester, UK
| | - Renuka Ramakrishnan
- Department of Paediatric Endocrinology, Alder Hey Children's Hospital, Liverpool, UK
| | - Catherine Owen
- Department of Paediatric Endocrinology, The Newcastle Upon Tyne Hospitals and NHS Trust, Newcastle upon Tyne, UK
| | - Timothy Cheetham
- Department of Paediatric Endocrinology, The Newcastle Upon Tyne Hospitals and NHS Trust, Newcastle upon Tyne, UK
| | - Paul Dimitri
- Department of Paediatric Endocrinology, Sheffield Children's Hospital, Sheffield, UK.,Professor of Child Health and Consultant in Paediatric Endocrinology, The Department of Paediatric Endocrinology, The Academic Unit of Child Health, Damer St. Building, Sheffield Children's NHS Trust, Western Bank, Sheffield S10 2TH, UK
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10
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Turan I, Kotan LD, Tastan M, Gurbuz F, Topaloglu AK, Yuksel B. Molecular genetic studies in a case series of isolated hypoaldosteronism due to biosynthesis defects or aldosterone resistance. Clin Endocrinol (Oxf) 2018; 88:799-805. [PMID: 29582446 DOI: 10.1111/cen.13603] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 03/21/2018] [Accepted: 03/21/2018] [Indexed: 01/22/2023]
Abstract
BACKGROUND AND AIM Hypoaldosteronism is associated with either insufficient aldosterone production or aldosterone resistance (pseudohypoaldosteronism). Patients with aldosterone defects typically present with similar symptoms and findings, which include failure to thrive, vomiting, hyponatremia, hyperkalemia and metabolic acidosis. Accurate diagnosis of these clinical conditions therefore can be challenging. Molecular genetic analyses can help to greatly clarify this complexity. The aim of this study was to obtain an overview of the clinical and genetic characteristics of patients with aldosterone defects due to biosynthesis defects or aldosterone resistance. DESIGN AND PATIENTS We investigated the clinical and molecular genetic features of 8 consecutive patients with a clinical picture of aldosterone defects seen in our clinics during the period of May 2015 through October 2017. We screened CYP11B2 for aldosterone synthesis defects and NR3C2 and the three EnaC subunits (SCNN1A, SCNN1B and SCNN1G) for aldosterone resistance. RESULTS We found 4 novel and 2 previously reported mutations in the genes CYP11B2, NR3C2, SCNN1A and SCNN1G in 9 affected individuals from 7 unrelated families. CONCLUSION Molecular genetic investigations can help confidently diagnose these conditions and clarify the pathogenicity of aldosterone defects. This study may expand the clinical and genetic correlations of defects in aldosterone synthesis or resistance.
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Affiliation(s)
- Ihsan Turan
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
| | - Leman Damla Kotan
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
| | - Mehmet Tastan
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
| | - Fatih Gurbuz
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
| | - Ali Kemal Topaloglu
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
| | - Bilgin Yuksel
- Faculty of Medicine, Division of Pediatric Endocrinology, Cukurova University, Adana, Turkey
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11
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Berman JM, Mironova E, Stockand JD. Physiological regulation of the epithelial Na + channel by casein kinase II. Am J Physiol Renal Physiol 2017; 314:F367-F372. [PMID: 29021227 DOI: 10.1152/ajprenal.00469.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
epithelial Na+ channel, ENaC, is the final arbiter of sodium excretion in the kidneys. As such, discretionary control of ENaC by hormones is critical to the fine-tuning of electrolyte and water excretion and, consequently, blood pressure. Casein kinase 2 (CK2) phosphorylates ENaC. Phosphorylation by CK2 is necessary for normal ENaC activity. We tested the physiological importance of CK2 regulation of ENaC as the degree to which ENaC activity is dependent on CK2 phosphorylation in the living organism is unknown. This was addressed using patch-clamp analysis of ENaC in completely split-open collecting ducts and whole animal physiological studies of sodium excretion in mice. We also used ENaC-harboring CK2 phosphorylation site mutations to elaborate the mechanism. We found that ENaC activity in ex vivo preparations of murine collecting duct had a significant decrease in activity in response to selective antagonism of CK2. In whole animal experiments selective antagonism of CK2 caused a natriuresis similar to benzamil, but not additive to benzamil, suggesting an ENaC-dependent mechanism. Regulation of ENaC by CK2 was abolished by mutation of the canonical CK2 phosphorylation sites in beta and gamma ENaC. Together, these results demonstrate that the appropriate regulation of ENaC by CK2 is necessary for the normal physiological role played by this key renal ion channel in the fine-tuning of sodium excretion.
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Affiliation(s)
- Jonathan M Berman
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - Elena Mironova
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - James D Stockand
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
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12
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Willam A, Aufy M, Tzotzos S, El-Malazi D, Poser F, Wagner A, Unterköfler B, Gurmani D, Martan D, Iqbal SM, Fischer B, Fischer H, Pietschmann H, Czikora I, Lucas R, Lemmens-Gruber R, Shabbir W. TNF Lectin-Like Domain Restores Epithelial Sodium Channel Function in Frameshift Mutants Associated with Pseudohypoaldosteronism Type 1B. Front Immunol 2017; 8:601. [PMID: 28611771 PMCID: PMC5447021 DOI: 10.3389/fimmu.2017.00601] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 05/08/2017] [Indexed: 11/28/2022] Open
Abstract
Previous in vitro studies have indicated that tumor necrosis factor (TNF) activates amiloride-sensitive epithelial sodium channel (ENaC) current through its lectin-like (TIP) domain, since cyclic peptides mimicking the TIP domain (e.g., solnatide), showed ENaC-activating properties. In the current study, the effects of TNF and solnatide on individual ENaC subunits or ENaC carrying mutated glycosylation sites in the α-ENaC subunit were compared, revealing a similar mode of action for TNF and solnatide and corroborating the previous assumption that the lectin-like domain of TNF is the relevant molecular structure for ENaC activation. Accordingly, TNF enhanced ENaC current by increasing open probability of the glycosylated channel, position N511 in the α-ENaC subunit being identified as the most important glycosylation site. TNF significantly increased Na+ current through ENaC comprising only the pore forming subunits α or δ, was less active in ENaC comprising only β-subunits, and showed no effect on ENaC comprising γ-subunits. TNF did not increase the membrane abundance of ENaC subunits to the extent observed with solnatide. Since the α-subunit is believed to play a prominent role in the ENaC current activating effect of TNF and TIP, we investigated whether TNF and solnatide can enhance αβγ-ENaC current in α-ENaC loss-of-function frameshift mutants. The efficacy of solnatide has been already proven in pathological conditions involving ENaC in phase II clinical trials. The frameshift mutations αI68fs, αT169fs, αP197fs, αE272fs, αF435fs, αR438fs, αY447fs, αR448fs, αS452fs, and αT482fs have been reported to cause pseudohypoaldosteronism type 1B (PHA1B), a rare, life-threatening, salt-wasting disease, which hitherto has been treated only symptomatically. In a heterologous expression system, all frameshift mutants showed significantly reduced amiloride-sensitive whole-cell current compared to wild type αβγ-ENaC, whereas membrane abundance varied between mutants. Solnatide restored function in α-ENaC frameshift mutants to current density levels of wild type ENaC or higher despite their lacking a binding site for solnatide, previously located to the region between TM2 and the C-terminus of the α-subunit. TNF similarly restored current density to wild type levels in the mutant αR448fs. Activation of βγ-ENaC may contribute to this moderate current enhancement, but whatever the mechanism, experimental data indicate that solnatide could be a new strategy to treat PHA1B.
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Affiliation(s)
- Anita Willam
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria.,APEPTICO GmbH, Vienna, Austria
| | - Mohammed Aufy
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | | | - Dina El-Malazi
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Franziska Poser
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Alina Wagner
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Birgit Unterköfler
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Didja Gurmani
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - David Martan
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | | | | | | | | | - Istvan Czikora
- Vascular Biology Center, Medical College of Georgia, Augusta University, Augusta, GA, United States
| | - Rudolf Lucas
- Vascular Biology Center, Medical College of Georgia, Augusta University, Augusta, GA, United States
| | - Rosa Lemmens-Gruber
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Waheed Shabbir
- Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria.,APEPTICO GmbH, Vienna, Austria
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13
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Systemic Pseudohypoaldosteronism Type I: A Case Report and Review of the Literature. Case Rep Pediatr 2017; 2017:7939854. [PMID: 28484659 PMCID: PMC5412170 DOI: 10.1155/2017/7939854] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 02/15/2017] [Accepted: 03/19/2017] [Indexed: 12/12/2022] Open
Abstract
Systemic pseudohypoaldosteronism (PHA) type I is a rare genetic disorder resulting from mutations in the subunits of the epithelial sodium channel that manifests as severe salt wasting, hyperkalemia, and metabolic acidosis in infancy. In this article we report a patient with systemic PHA type I presenting with severe dehydration due to salt wasting at 6 days of life. She was found to have a known mutation in the SCNN1A gene and subsequently required treatment with sodium supplementation. We also review the clinical presentation, differential diagnosis, and treatment of systemic PHA type I and summarize data from 27 cases with follow-up data.
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14
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MacManes MD. Severe acute dehydration in a desert rodent elicits a transcriptional response that effectively prevents kidney injury. Am J Physiol Renal Physiol 2017; 313:F262-F272. [PMID: 28381460 DOI: 10.1152/ajprenal.00067.2017] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 03/28/2017] [Accepted: 03/28/2017] [Indexed: 12/14/2022] Open
Abstract
Animals living in desert environments are forced to survive despite severe heat, intense solar radiation, and both acute and chronic dehydration. These animals have evolved phenotypes that effectively address these environmental stressors. To begin to understand the ways in which the desert-adapted rodent Peromyscus eremicus survives, reproductively mature adults were subjected to 72 h of water deprivation, during which they lost, on average, 23% of their body weight. The animals reacted via a series of changes in the kidney, which included modulating expression of genes responsible for reducing the rate of transcription and maintaining water and salt balance. Extracellular matrix turnover appeared to be decreased, and apoptosis was limited. In contrast to the canonical human response, serum creatinine and other biomarkers of kidney injury were not elevated, suggesting that changes in gene expression related to acute dehydration may effectively prohibit widespread kidney damage in the cactus mouse.
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Affiliation(s)
- Matthew David MacManes
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, Durham, New Hampshire
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15
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Liu CC, Lin SH, Sung CC, Lin CM. A neonate with poor weight gain and hyperkalemia: Answers. Pediatr Nephrol 2017; 32:73-75. [PMID: 26628278 DOI: 10.1007/s00467-015-3281-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Revised: 11/08/2015] [Accepted: 11/10/2015] [Indexed: 10/22/2022]
Affiliation(s)
- Chiung-Chen Liu
- Department of Pediatrics, National Defense Medical Center, Tri-Service General Hospital, No. 325, Cheng-Kung Road, Section 2, Neihu 114, Taipei, Taiwan, Republic of China
| | - Shih-Hua Lin
- Division of Nephrology, Department of Medicine, National Defense Medical Center, Tri-Service General Hospital, Taipei, Taiwan
| | - Chih-Chien Sung
- Division of Nephrology, Department of Medicine, National Defense Medical Center, Tri-Service General Hospital, Taipei, Taiwan.,Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan
| | - Chien-Ming Lin
- Department of Pediatrics, National Defense Medical Center, Tri-Service General Hospital, No. 325, Cheng-Kung Road, Section 2, Neihu 114, Taipei, Taiwan, Republic of China. .,Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan.
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16
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Hanukoglu I, Hanukoglu A. Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases. Gene 2016; 579:95-132. [PMID: 26772908 PMCID: PMC4756657 DOI: 10.1016/j.gene.2015.12.061] [Citation(s) in RCA: 249] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Revised: 12/20/2015] [Accepted: 12/22/2015] [Indexed: 01/24/2023]
Abstract
The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.
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Affiliation(s)
- Israel Hanukoglu
- Laboratory of Cell Biology, Faculty of Natural Sciences, Ariel University, Ariel, Israel.
| | - Aaron Hanukoglu
- Division of Pediatric Endocrinology, E. Wolfson Medical Center, Holon, Israel; Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel
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17
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Perrier R, Boscardin E, Malsure S, Sergi C, Maillard MP, Loffing J, Loffing-Cueni D, Sørensen MV, Koesters R, Rossier BC, Frateschi S, Hummler E. Severe Salt-Losing Syndrome and Hyperkalemia Induced by Adult Nephron-Specific Knockout of the Epithelial Sodium Channel α-Subunit. J Am Soc Nephrol 2015; 27:2309-18. [PMID: 26701978 DOI: 10.1681/asn.2015020154] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 10/28/2015] [Indexed: 11/03/2022] Open
Abstract
Systemic pseudohypoaldosteronism type 1 (PHA-1) is a severe salt-losing syndrome caused by loss-of-function mutations of the amiloride-sensitive epithelial sodium channel (ENaC) and characterized by neonatal life-threatening hypovolemia and hyperkalemia. The very high plasma aldosterone levels detected under hypovolemic or hyperkalemic challenge can lead to increased or decreased sodium reabsorption, respectively, through the Na(+)/Cl(-) cotransporter (NCC). However, the role of ENaC deficiency remains incompletely defined, because constitutive inactivation of individual ENaC subunits is neonatally lethal in mice. We generated adult inducible nephron-specific αENaC-knockout mice (Scnn1a(Pax8/LC1)) that exhibit hyperkalemia and body weight loss when kept on a regular-salt diet, thus mimicking PHA-1. Compared with control mice fed a regular-salt diet, knockout mice fed a regular-salt diet exhibited downregulated expression and phosphorylation of NCC protein, despite high plasma aldosterone levels. In knockout mice fed a high-sodium and reduced-potassium diet (rescue diet), although plasma aldosterone levels remained significantly increased, NCC expression returned to control levels, and body weight, plasma and urinary electrolyte concentrations, and excretion normalized. Finally, shift to a regular diet after the rescue diet reinstated the symptoms of severe PHA-1 syndrome and significantly reduced NCC phosphorylation. In conclusion, lack of ENaC-mediated sodium transport along the nephron cannot be compensated for by other sodium channels and/or transporters, only by a high-sodium and reduced-potassium diet. We further conclude that hyperkalemia becomes the determining factor in regulating NCC activity, regardless of sodium loss, in the ENaC-mediated salt-losing PHA-1 phenotype.
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Affiliation(s)
- Romain Perrier
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Emilie Boscardin
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland; Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland
| | - Sumedha Malsure
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Chloé Sergi
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Marc P Maillard
- Service of Nephrology Department, University Hospital of Lausanne, Lausanne, Switzerland
| | - Johannes Loffing
- Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland; Institute of Anatomy, University of Zurich, Zurich, Switzerland; and
| | - Dominique Loffing-Cueni
- Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland; Institute of Anatomy, University of Zurich, Zurich, Switzerland; and
| | - Mads Vaarby Sørensen
- Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland; Institute of Anatomy, University of Zurich, Zurich, Switzerland; and
| | - Robert Koesters
- Department of Nephrology, Hôpital Tenon, Université Pierre et Marie Curie, Paris, France
| | - Bernard C Rossier
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland;
| | - Simona Frateschi
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland; Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland; Swiss National Center of Competence in Research "Kidney.CH", Zurich, Switzerland;
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18
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Chen J, Kleyman TR, Sheng S. Deletion of α-subunit exon 11 of the epithelial Na+ channel reveals a regulatory module. Am J Physiol Renal Physiol 2014; 306:F561-7. [PMID: 24402098 DOI: 10.1152/ajprenal.00587.2013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Epithelial Na(+) channel (ENaC) subunits (α, β, and γ) found in functional complexes are translated from mature mRNAs that are similarly processed by the inclusion of 13 canonical exons. We examined whether individual exons 3-12, encoding the large extracellular domain, are required for functional channel expression. Human ENaCs with an in-frame deletion of a single α-subunit exon were expressed in Xenopus oocytes, and their functional properties were examined by two-electrode voltage clamp. With the exception of exon 11, deletion of an individual exon eliminated channel activity. Channels lacking α-subunit exon 11 were hyperactive. Oocytes expressing this mutant exhibited fourfold greater amiloride-sensitive whole cell currents than cells expressing wild-type channels. A parallel fivefold increase in channel open probability was observed with channels lacking α-subunit exon 11. These mutant channels also exhibited a lost of Na(+) self-inhibition, whereas we found similar levels of surface expression of mutant and wild-type channels. In contrast, in-frame deletions of exon 11 from either the β- or γ-subunit led to a significant loss of channel activity, in association with a marked decrease in surface expression. Our results suggest that exon 11 within the three human ENaC genes encodes structurally homologous yet functionally diverse domains and that exon 11 in the α-subunit encodes a module that regulates channel gating.
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Affiliation(s)
- Jingxin Chen
- Renal-Electrolyte Div., Univ. of Pittsburgh, 3550 Terrace St., Pittsburgh, PA 15261.
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