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Wagner CA, Unwin R, Lopez-Garcia SC, Kleta R, Bockenhauer D, Walsh S. The pathophysiology of distal renal tubular acidosis. Nat Rev Nephrol 2023; 19:384-400. [PMID: 37016093 DOI: 10.1038/s41581-023-00699-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/27/2023] [Indexed: 04/06/2023]
Abstract
The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK.
| | - Robert Unwin
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
| | - Sergio C Lopez-Garcia
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
- Department of Paediatric Nephrology, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK
| | - Robert Kleta
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
| | - Detlef Bockenhauer
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
- Department of Paediatric Nephrology, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK
| | - Stephen Walsh
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
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2
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Yang M, Sheng Q, Ge S, Song X, Dong J, Guo C, Liao L. Mutations and clinical characteristics of dRTA caused by SLC4A1 mutations: Analysis based on published patients. Front Pediatr 2023; 11:1077120. [PMID: 36776909 PMCID: PMC9910804 DOI: 10.3389/fped.2023.1077120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2022] [Accepted: 01/06/2023] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND AND AIMS The genetic and clinical characteristics of patients with distal renal tubular acidosis (dRTA) caused by SLC4A1 mutations have not been systematically recorded before. Here, we summarized the SLC4A1 mutations and clinical characteristics associated with dRTA. METHODS Database was searched, and the mutations and clinical manifestations of patients were summarized from the relevant articles. RESULTS Fifty-three eligible articles involving 169 patients were included and 41 mutations were identified totally. Fifteen mutations involving 100 patients were autosomal dominant inheritance, 21 mutations involving 61 patients were autosomal recessive inheritance. Nephrocalcinosis or kidney stones were found in 72.27%, impairment in renal function in 14.29%, developmental disorders in 61.16%, hematological abnormalities in 33.88%, and muscle weakness in 13.45% of patients. The age of onset was younger (P < 0.01), urine pH was higher (P < 0.01), and serum potassium was lower (P < 0.001) in recessive patients than patients with dominant SLC4A1 mutations. Autosomal recessive inheritance was more often found in Asian patients (P < 0.05). CONCLUSIONS The children present with metabolic acidosis with high urinary pH, accompanying hypokalemia, hyperchloremia, nephrocalcinosis, growth retardation and hematological abnormalities should be suspected as dRTA and suggested a genetic testing. The patients with recessive dRTA are generally more severely affected than that with dominant SLC4A1 mutations. Autosomal recessive inheritance was more often found in Asian patients, and more attentions should be paid to the Asian patients.
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Affiliation(s)
- Mengge Yang
- Department of Endocrinology and Metabology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Ji-nan, China.,Cheeloo College of Medicine, Shandong University, Department of Endocrinology and Metabology, Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Institute of Nephrology, Ji-nan, China
| | - Qiqi Sheng
- Division of Endocrinology, Department of Internal Medicine, Qilu Hospital of Shandong University, Ji-nan, China
| | - Shenghui Ge
- Department of Endocrinology and Metabology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Ji-nan, China
| | - Xinxin Song
- College of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Ji-nan, China
| | - Jianjun Dong
- Division of Endocrinology, Department of Internal Medicine, Qilu Hospital of Shandong University, Ji-nan, China
| | - Congcong Guo
- Department of Endocrinology and Metabology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Ji-nan, China.,College of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Ji-nan, China
| | - Lin Liao
- Department of Endocrinology and Metabology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Ji-nan, China.,Cheeloo College of Medicine, Shandong University, Department of Endocrinology and Metabology, Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Institute of Nephrology, Ji-nan, China.,College of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Ji-nan, China
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Tabibzadeh N, Crambert G. Mechanistic insights into the primary and secondary alterations of renal ion and water transport in the distal nephron. J Intern Med 2023; 293:4-22. [PMID: 35909256 PMCID: PMC10087581 DOI: 10.1111/joim.13552] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The kidneys, by equilibrating the outputs to the inputs, are essential for maintaining the constant volume, pH, and electrolyte composition of the internal milieu. Inability to do so, either because of internal kidney dysfunction (primary alteration) or because of some external factors (secondary alteration), leads to pathologies of varying severity, leading to modification of these parameters and affecting the functions of other organs. Alterations of the functions of the collecting duct (CD), the most distal part of the nephron, have been extensively studied and have led to a better diagnosis, better management of the related diseases, and the development of therapeutic tools. Thus, dysfunctions of principal cell-specific transporters such as ENaC or AQP2 or its receptors (mineralocorticoid or vasopressin receptors) caused by mutations or by compounds present in the environment (lithium, antibiotics, etc.) have been demonstrated in a variety of syndromes (Liddle, pseudohypoaldosteronism type-1, diabetes insipidus, etc.) affecting salt, potassium, and water balance. In parallel, studies on specific transporters (H+ -ATPase, anion exchanger 1) in intercalated cells have revealed the mechanisms of related tubulopathies like distal renal distal tubular acidosis or Sjögren syndrome. In this review, we will recapitulate the mechanisms of most of the primary and secondary alteration of the ion transport system of the CD to provide a better understanding of these diseases and highlight how a targeted perturbation may affect many different pathways due to the strong crosstalk and entanglements between the different actors (transporters, cell types).
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Affiliation(s)
- Nahid Tabibzadeh
- Laboratoire de Physiologie Rénale et Tubulopathies, Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France.,EMR 8228 Unité Métabolisme et Physiologie Rénale, CNRS, Paris, France.,Assistance Publique Hôpitaux de Paris, Hôpital Bichât, Paris, France
| | - Gilles Crambert
- Laboratoire de Physiologie Rénale et Tubulopathies, Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France.,EMR 8228 Unité Métabolisme et Physiologie Rénale, CNRS, Paris, France
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4
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Deejai N, Sawasdee N, Nettuwakul C, Wanachiwanawin W, Sritippayawan S, Yenchitsomanus PT, Rungroj N. Impaired trafficking and instability of mutant kidney anion exchanger 1 proteins associated with autosomal recessive distal renal tubular acidosis. BMC Med Genomics 2022; 15:228. [PMID: 36320073 PMCID: PMC9623938 DOI: 10.1186/s12920-022-01381-y] [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: 05/26/2022] [Accepted: 10/21/2022] [Indexed: 11/06/2022] Open
Abstract
Background Mutations in solute carrier family 4 member 1 (SLC4A1) encoding anion exchanger 1 (AE1) are the most common cause of autosomal recessive distal renal tubular acidosis (AR dRTA) in Southeast Asians. To explain the molecular mechanism of this disease with hematological abnormalities in an affected family, we conducted a genetic analysis of SLC4A1 and studied wild-type and mutant AE1 proteins expressed in human embryonic kidney 293T (HEK293T) cells. Methods SLC4A1 mutations in the patient and family members were analyzed by molecular genetic techniques. Protein structure modeling was initially conducted to evaluate the effects of mutations on the three-dimensional structure of the AE1 protein. The mutant kidney anion exchanger 1 (kAE1) plasmid construct was created to study protein expression, localization, and stability in HEK293T cells. Results We discovered that the patient who had AR dRTA coexisting with mild hemolytic anemia carried a novel compound heterozygous SLC4A1 mutations containing c.1199_1225del (p.Ala400_Ala408del), resulting in Southeast Asian ovalocytosis (SAO), and c.1331C > A (p.Thr444Asn). Homologous modeling and in silico mutagenesis indicated that these two mutations affected the protein structure in the transmembrane regions of kAE1. We found the wild-type and mutant kAE1 T444N to be localized at the cell surface, whereas the mutants kAE1 SAO and SAO/T444N were intracellularly retained. The half-life of the kAE1 SAO, T444N, and SAO/T444N mutants was shorter than that of the wild-type protein. Conclusion These results suggest impaired trafficking and instability of kAE1 SAO/T444N as the likely underlying molecular mechanism explaining the pathogenesis of the novel SLC4A1 compound heterozygous mutation identified in this patient. Supplementary Information The online version contains supplementary material available at 10.1186/s12920-022-01381-y.
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Affiliation(s)
- Nipaporn Deejai
- grid.10223.320000 0004 1937 0490Division of Molecular Medicine, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Nunghathai Sawasdee
- grid.10223.320000 0004 1937 0490Division of Molecular Medicine, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Choochai Nettuwakul
- grid.10223.320000 0004 1937 0490Division of Molecular Medicine, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Wanchai Wanachiwanawin
- grid.10223.320000 0004 1937 0490Division of Hematology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Suchai Sritippayawan
- grid.10223.320000 0004 1937 0490Division of Nephrology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Pa-thai Yenchitsomanus
- grid.10223.320000 0004 1937 0490Division of Molecular Medicine, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Nanyawan Rungroj
- grid.10223.320000 0004 1937 0490Siriraj Genomics, Office of the Dean, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
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Fairweather SJ, Shah N, Brӧer S. Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 21:13-127. [PMID: 33052588 DOI: 10.1007/5584_2020_584] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H+ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b0,+AT-rBAT and the SLC6 family heteromer B0AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.
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Affiliation(s)
- Stephen J Fairweather
- Research School of Biology, Australian National University, Canberra, ACT, Australia. .,Resarch School of Chemistry, Australian National University, Canberra, ACT, Australia.
| | - Nishank Shah
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Stefan Brӧer
- Research School of Biology, Australian National University, Canberra, ACT, Australia.
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Sakuraya K, Nozu K, Oka I, Fujinaga S, Nagano C, Ohtomo Y, Iijima K. A different clinical manifestation in a Japanese family with autosomal dominant distal renal tubular acidosis caused by SLC4A1 mutation. CEN Case Rep 2020; 9:442-445. [DOI: 10.1007/s13730-020-00500-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Accepted: 06/22/2020] [Indexed: 10/23/2022] Open
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More TA, Kedar PS. Genotypic analysis of SLC4A1 A858D mutation in Indian population associated with distal renal tubular Acidosis (dRTA) coupled with hemolytic anemia. Gene 2020; 769:145241. [PMID: 33068675 DOI: 10.1016/j.gene.2020.145241] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 09/27/2020] [Accepted: 10/11/2020] [Indexed: 10/23/2022]
Abstract
INTRODUCTION Although distinctive, distal renal tubular acidosis (dRTA) and Hereditary Spherocytosis (HS) shares a common protein, the anion exchanger1 (AE1) encoded by SLC4A1gene. In spite of this, the co-existence of dRTA and HS has rarely been observed. To date, 23 mutations have been identified in SLC4A1 gene causing both autosomal recessive (AR) and autosomal dominant (AD) forms of dRTA. METHODS We have assessed the applicability of the High Resolution Melting curve (HRM) method for the detection of SLC4A1 (A858D) mutation in 12 Indian families having AR dRTA coupled with HS. The reliability of the HRM analysis was verified by comparing the results of the HRM method with those of conventional methods such as Polymerase Chain Reaction-Restriction Fragment-Length Polymorphism (PCR-RFLP) and Sanger sequencing thereby confirming the diagnosis. RESULTS We here described the clinical, hematological and genetic data of 16 individuals from 12 families having AR dRTA coupled with HS. All patients carried homozygous SLC4A1 (A858D) mutation, whereas their family members had heterozygous A858D obtained by HRM analysis and confirmed by RFLP and Sanger sequencing. CONCLUSION Our data indicates that a missense mutation of A858D in SLC4A1 gene is the most common cause of dRTA coupled with HS in the Indian population. HRM analysis can be used as a rapid screening method for common SLC4A1 mutations that cause AR dRTA in the Indian population.
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Affiliation(s)
- Tejashree Anil More
- Department of Hematogenetics, ICMR-National Institute of Immunohematology, KEM Hospital Campus, Parel, Mumbai 40012, India
| | - Prabhakar S Kedar
- Department of Hematogenetics, ICMR-National Institute of Immunohematology, KEM Hospital Campus, Parel, Mumbai 40012, India.
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8
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Bertocchio JP, Genetet S, Da Costa L, Walsh SB, Knebelmann B, Galimand J, Bessenay L, Guitton C, De Lafaille R, Vargas-Poussou R, Eladari D, Mouro-Chanteloup I. Red Blood Cell AE1/Band 3 Transports in Dominant Distal Renal Tubular Acidosis Patients. Kidney Int Rep 2020; 5:348-357. [PMID: 32154456 PMCID: PMC7056926 DOI: 10.1016/j.ekir.2019.12.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2019] [Revised: 11/26/2019] [Accepted: 12/31/2019] [Indexed: 11/30/2022] Open
Abstract
Introduction Anion exchanger 1 (AE1) (SLC4A1 gene product) is a membrane protein expressed in both kidney and red blood cells (RBCs): it exchanges extracellular bicarbonate (HCO3–) for intracellular chloride (Cl–) and participates in acid−base homeostasis. AE1 mutations in kidney α-intercalated cells can lead to distal renal tubular acidosis (dRTA). In RBC, AE1 (known as band 3) is also implicated in membrane stability: deletions can cause South Asian ovalocytosis (SAO). Methods We retrospectively collected clinical and biological data from patients harboring dRTA due to a SLC4A1 mutation and analyzed HCO3– and Cl– transports (by stopped-flow spectrophotometry) and expression (by flow cytometry, fluorescence activated cell sorting, and Coomassie blue staining) in RBCs, as well as RBC membrane stability (ektacytometry). Results Fifteen patients were included. All experience nephrolithiasis and/or nephrocalcinosis, 2 had SAO and dRTA (dRTA SAO+), 13 dominant dRTA (dRTA SAO−). The latter did not exert specific RBC membrane anomalies. Both HCO3– and Cl– transports were lower in patients with dRTA SAO+ than in those with dRTA SAO− or controls. Using 3 different extracellular probes, we report a decreased expression (by 52%, P < 0.05) in dRTA SAO+ patients by fluorescence activated cell sorting, whereas total amount of protein was not affected. Conclusion Band 3 transport function and expression in RBCs from dRTA SAO− patients is normal. However, in SAO RBCs, impaired conformation of AE1/band 3 corresponds to an impaired function. Thus, the driver of acid−base defect during dominant dRTA is probably an impaired membrane expression.
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Affiliation(s)
- Jean-Philippe Bertocchio
- Renal and Metabolic Diseases Unit, Assistance Publique-Hôpitaux de Paris, European Georges Pompidou Hospital, Paris, France.,Faculty of Medicine, Paris Descartes University, Paris, France.,Reference Center for Maladies Rénales Héréditaires de l'Enfant et de l'Adulte (MARHEA), Paris, France.,Genito-urinary Medical Oncology and Research Department, MD Anderson Cancer Center, Houston, Texas, USA
| | - Sandrine Genetet
- UMR_S1134, Integrated Red Globule Biology (IRGB), Inserm, University of Paris, Paris, France.,Team 1, Physiology of Normal and Pathologic Red Blood Cell, Institut National de la Transfusion Sanguine (INTS), Paris, France
| | - Lydie Da Costa
- UMR_S1134, Integrated Red Globule Biology (IRGB), Inserm, University of Paris, Paris, France.,UMR_S1134, Inserm, Paris, France.,Service d'Hématologie Biologique, Assistance Publique-Hôpitaux de Paris, Hôpital Robert Debré, Paris, France
| | - Stephen B Walsh
- Department of Renal Medicine, University College of London, London, UK
| | - Bertrand Knebelmann
- Nephrology Department, Assistance Publique-Hôpitaux de Paris, Necker-Enfants Malades Hospital, Paris, France
| | - Julie Galimand
- Service d'Hématologie Biologique, Assistance Publique-Hôpitaux de Paris, Hôpital Robert Debré, Paris, France
| | - Lucie Bessenay
- Pediatrics Department, University Hospital of Clermont-Ferrand, Clermont-Ferrand, France
| | - Corinne Guitton
- Pediatrics Department, Assistance Publique-Hôpitaux de Paris, Hôpital Bicêtre, Le Kremlin Bicêtre, France
| | - Renaud De Lafaille
- Nephrology Department, University Hospital of Bordeaux, Bordeaux, Aquitaine, France
| | - Rosa Vargas-Poussou
- Reference Center for Maladies Rénales Héréditaires de l'Enfant et de l'Adulte (MARHEA), Paris, France.,Institut National pour la Santé et la Recherche Médicale (INSERM), Unité Mixte de Recherche UMRS1138, Cordeliers Research Center, Paris, France.,Genetics Department, Assistance Publique-Hôpitaux de Paris, European Georges Pompidou Hospital, Paris, France
| | - Dominique Eladari
- Renal and Metabolic Diseases Department, CHU de la Réunion, Felix Guyon Hospital, Saint Denis, France.,INSERM, UMRS 1283-European Genomic Institute for Diabetes, Lille, France
| | - Isabelle Mouro-Chanteloup
- UMR_S1134, Integrated Red Globule Biology (IRGB), Inserm, University of Paris, Paris, France.,Team 1, Physiology of Normal and Pathologic Red Blood Cell, Institut National de la Transfusion Sanguine (INTS), Paris, France
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Wang C, Sun B, Zhang X, Huang X, Zhang M, Guo H, Chen X, Huang F, Chen T, Mi H, Yu F, Liu LN, Zhang P. Structural mechanism of the active bicarbonate transporter from cyanobacteria. NATURE PLANTS 2019; 5:1184-1193. [PMID: 31712753 DOI: 10.1038/s41477-019-0538-1] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Accepted: 09/27/2019] [Indexed: 05/11/2023]
Abstract
Bicarbonate transporters play essential roles in pH homeostasis in mammals and photosynthesis in aquatic photoautotrophs. A number of bicarbonate transporters have been characterized, among which is BicA-a low-affinity, high-flux SLC26-family bicarbonate transporter involved in cyanobacterial CO2-concentrating mechanisms (CCMs) that accumulate CO2 and improve photosynthetic carbon fixation. Here, we report the three-dimensional structure of BicA from Synechocystis sp. PCC6803. Crystal structures of the transmembrane domain (BicATM) and the cytoplasmic STAS domain (BicASTAS) of BicA were solved. BicATM was captured in an inward-facing HCO3--bound conformation and adopts a '7+7' fold monomer. HCO3- binds to a cytoplasm-facing hydrophilic pocket within the membrane. BicASTAS is assembled as a compact homodimer structure and is required for the dimerization of BicA. The dimeric structure of BicA was further analysed using cryo-electron microscopy and physiological analysis of the full-length BicA, and may represent the physiological unit of SLC26-family transporters. Comparing the BicATM structure with the outward-facing transmembrane domain structures of other bicarbonate transporters suggests an elevator transport mechanism that is applicable to the SLC26/4 family of sodium-dependent bicarbonate transporters. This study advances our knowledge of the structures and functions of cyanobacterial bicarbonate transporters, and will inform strategies for bioengineering functional BicA in heterologous organisms to increase assimilation of CO2.
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Affiliation(s)
- Chengcheng Wang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Bo Sun
- Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China
| | - Xue Zhang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Xiaowei Huang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Minhua Zhang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Hui Guo
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Xin Chen
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Fang Huang
- Institute of Integrative Biology, University of Liverpool, Liverpool, UK
| | - Taiyu Chen
- Institute of Integrative Biology, University of Liverpool, Liverpool, UK
| | - Hualing Mi
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Fang Yu
- Shanghai Key Laboratory of Plant Molecualr Sciences, College of Life Sciences, Shanghai Normal University, Shanghai, China
| | - Lu-Ning Liu
- Institute of Integrative Biology, University of Liverpool, Liverpool, UK
| | - Peng Zhang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
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De Vecchis D, Reithmeier RAF, Kalli AC. Molecular Simulations of Intact Anion Exchanger 1 Reveal Specific Domain and Lipid Interactions. Biophys J 2019; 117:1364-1379. [PMID: 31540709 PMCID: PMC6818359 DOI: 10.1016/j.bpj.2019.08.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 07/30/2019] [Accepted: 08/22/2019] [Indexed: 12/23/2022] Open
Abstract
Anion exchanger 1 (AE1) is responsible for the exchange of bicarbonate and chloride across the erythrocyte plasma membrane. Human AE1 consists of a cytoplasmic and a membrane domain joined by a 33-residue flexible linker. Crystal structures of the individual domains have been determined, but the intact AE1 structure remains elusive. In this study, we use molecular dynamics simulations and modeling to build intact AE1 structures in a complex lipid bilayer that resembles the native erythrocyte plasma membrane. AE1 models were evaluated using available experimental data to provide an atomistic view of the interaction and dynamics of the cytoplasmic domain, the membrane domain, and the connecting linker in a complete model of AE1 in a lipid bilayer. Anionic lipids were found to interact strongly with AE1 at specific amino acid residues that are linked to diseases and blood group antigens. Cholesterol was found in the dimeric interface of AE1, suggesting that it may regulate subunit interactions and anion transport.
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Affiliation(s)
- Dario De Vecchis
- Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, Leeds, United Kingdom
| | | | - Antreas C Kalli
- Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, Leeds, United Kingdom; Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.
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11
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The kidney anion exchanger 1 affects tight junction properties via claudin-4. Sci Rep 2019; 9:3099. [PMID: 30816203 PMCID: PMC6395713 DOI: 10.1038/s41598-019-39430-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Accepted: 01/24/2019] [Indexed: 12/14/2022] Open
Abstract
In the renal collecting duct, intercalated cells regulate acid-base balance by effluxing protons through the v-H+-ATPase, and bicarbonate via apical pendrin or the basolateral kidney anion exchanger 1 (kAE1). Additionally, collecting duct cells play an essential role in transepithelial absorption of sodium and chloride. Expression of kAE1 in polarized MDCK I cells was previously shown to decrease trans-epithelial electrical resistance (TEER), suggesting a novel role for kAE1 in paracellular permeability. In our study, we not only confirmed that inducible expression of kAE1 in mIMCD3 cells decreased TEER but we also observed (i) increased epithelial absolute permeability to both sodium and chloride, and (ii) that this effect was dependent on kAE1 activity. Further, kAE1 regulated tight junction properties through the tight junction protein claudin-4, a protein with which it physically interacts and colocalizes. These findings unveil a novel interaction between the junctional protein claudin-4 and the kidney anion exchanger, which may be relevant to ion and/or pH homeostasis.
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12
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Watanabe T. Improving outcomes for patients with distal renal tubular acidosis: recent advances and challenges ahead. PEDIATRIC HEALTH MEDICINE AND THERAPEUTICS 2018; 9:181-190. [PMID: 30588151 PMCID: PMC6296208 DOI: 10.2147/phmt.s174459] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Primary distal renal tubular acidosis (dRTA) is a rare genetic disorder caused by impaired distal acidification due to a failure of type A intercalated cells (A-ICs) in the collecting tubule. dRTA is characterized by persistent hyperchloremia, a normal plasma anion gap, and the inability to maximally lower urinary pH in the presence of systemic metabolic acidosis. Common clinical features of dRTA include vomiting, failure to thrive, polyuria, hypercalciuria, hypocitraturia, nephrocalcinosis, nephrolithiasis, growth delay, and rickets. Mutations in genes encoding three distinct transport proteins in A-ICs have been identified as causes of dRTA, including the B1/ATP6V1B1 and a4/ATP6V0A4 subunits of the vacuolar-type H+-ATPase (H+-ATPase) and the chloride–bicarbonate exchanger AE1/SLC4A1. Homozygous or compound heterozygous mutations in ATP6V1B1 and ATP6V0A4 lead to autosomal recessive (AR) dRTA. dRTA caused by SLC4A1 mutations can occur with either autosomal dominant or AR transmission. Red blood cell abnormalities have been associated with AR dRTA due to SLC4A1 mutations, including hereditary spherocytosis, Southeast Asia ovalocytosis, and others. Some patients with dRTA exhibit atypical clinical features, including transient and reversible proximal tubular dysfunction and hyperammonemia. Incomplete dRTA presents with inadequate urinary acidification, but without spontaneous metabolic acidosis and recurrent urinary stones. Heterozygous mutations in the AE1 or H+-ATPase genes have recently been reported in patients with incomplete dRTA. Early and sufficient doses of alkali treatment are needed for patients with dRTA. Normalized serum bicarbonate, urinary calcium excretion, urinary low-molecular-weight protein levels, and growth rate are good markers of adherence to and/or efficacy of treatment. The prognosis of dRTA is generally good in patients with appropriate treatment. However, recent studies showed an increased frequency of chronic kidney disease (CKD) in patients with dRTA during long-term follow-up. The precise pathogenic mechanisms of CKD in patients with dRTA are unknown.
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Affiliation(s)
- Toru Watanabe
- Department of Pediatrics, Niigata City General Hospital, Niigata City 950-1197, Japan,
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13
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Alonso-Varela M, Gil-Peña H, Coto E, Gómez J, Rodríguez J, Rodríguez-Rubio E, Santos F. Distal renal tubular acidosis. Clinical manifestations in patients with different underlying gene mutations. Pediatr Nephrol 2018; 33:1523-1529. [PMID: 29725771 DOI: 10.1007/s00467-018-3965-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 03/28/2018] [Accepted: 04/06/2018] [Indexed: 01/09/2023]
Abstract
BACKGROUND To evaluate whether there are differences in the phenotype of primary distal renal tubular acidosis (dRTA) patients according to the causal defective gene. METHODS Twenty-seven non-oriental patients with genetically confirmed dRTA were grouped according to the identified underlying mutations in either ATP6V1B1 (n = 10), ATP6V0A4 (n = 12), or SLC4A1 (n = 5) gene. Demographic features, growth impairment, biochemical variables and presence of deafness, nephrocalcinosis, and urolithiasis at diagnosis were compared among the three groups. RESULTS Patients with SLC4A1 mutations presented later than those with ATP6V1B1 or ATP6V0A4 defects (120 vs. 7 and 3 months, respectively). Hearing loss at diagnosis was present in the majority of patients with ATP6V1B1 mutations, in two patients with ATP6V0A4 mutations, and in none of cases harboring SLC4A1 mutations. Serum potassium concentration (X ± SD) was higher in SLC4A1 group (3.66 ± 0.44 mEq/L) than in ATP6V0A4 group (2.96 ± 0.63 mEq/L) (p = 0.046). There were no differences in the other clinical or biochemical variables analyzed in the three groups. CONCLUSIONS This study indicates that non-oriental patients with dRTA caused by mutations in the SLC4A1 gene present later and have normokalemia or milder hypokalemia. Hypoacusia at diagnosis is characteristically associated with ATP6V1B1 gene mutations although it may also be present in infants with ATP6V0A4 defects. Other phenotypical manifestations do not allow predicting the involved gene.
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Affiliation(s)
| | - Helena Gil-Peña
- University of Oviedo, Oviedo, Spain. .,AGC de Pediatría, Hospital Universitario Central de Asturias, 33011, Oviedo, Spain. .,Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Oviedo, Spain.
| | - Eliecer Coto
- University of Oviedo, Oviedo, Spain.,Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Oviedo, Spain.,AGC Laboratorio - Genética, Hospital Universitario Central de Asturias, Oviedo, Spain
| | - Juan Gómez
- Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Oviedo, Spain.,AGC Laboratorio - Genética, Hospital Universitario Central de Asturias, Oviedo, Spain
| | - Julián Rodríguez
- University of Oviedo, Oviedo, Spain.,AGC de Pediatría, Hospital Universitario Central de Asturias, 33011, Oviedo, Spain.,Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Oviedo, Spain
| | | | - Fernando Santos
- University of Oviedo, Oviedo, Spain.,AGC de Pediatría, Hospital Universitario Central de Asturias, 33011, Oviedo, Spain.,Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Oviedo, Spain
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14
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Rungroj N, Nettuwakul C, Sawasdee N, Sangnual S, Deejai N, Misgar RA, Pasena A, Khositseth S, Kirdpon S, Sritippayawan S, Vasuvattakul S, Yenchitsomanus PT. Distal renal tubular acidosis caused by tryptophan-aspartate repeat domain 72 (WDR72) mutations. Clin Genet 2018; 94:409-418. [PMID: 30028003 DOI: 10.1111/cge.13418] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Revised: 06/21/2018] [Accepted: 07/17/2018] [Indexed: 12/18/2022]
Abstract
Hereditary distal renal tubular acidosis (dRTA) is a rare genetic disease that is caused by mutations in SLC4A1, ATP6V1B1, or ATP6V0A4. However, there are many families with hereditary dRTA in whom the disease-causing genes are unknown. Accordingly, we performed whole exome sequencing and genetic studies of the members of a family with autosomal recessive dRTA of an unknown genetic etiology. Here, we report compound heterozygous pathogenic variations in tryptophan-aspartate repeat domain 72 (WDR72) (c.1777A>G [p.R593G] and c.2522T>A [p.L841Q]) in three affected siblings of a family with dRTA. Both variants segregated with dRTA in the family and were not observed in normal control subjects. Homologous modeling and in silico mutagenesis indicated that R593G and L841Q alter the H-bond formations in the nearby residues, affecting the WDR72 protein structure. All these evidences indicate that the identified WDR72 variations were probably to have caused hereditary dRTA in the reported family. In addition, homozygous nonsense mutation (c.2686C>T [p.R896X]) was identified in another family, strongly supporting the causal role of WDR72 in dRTA. Based on our literature review, WDR72 mutations associated with dRTA have not been previously described. This is the first identification of pathogenic variations in WDR72 as a cause of hereditary dRTA.
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Affiliation(s)
- N Rungroj
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.,Division of Molecular Genetics, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - C Nettuwakul
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - N Sawasdee
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - S Sangnual
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - N Deejai
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - R A Misgar
- Department of Endocrinology, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, India
| | - A Pasena
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.,Department of Immunology and Immunology Graduate Program, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - S Khositseth
- Department of Pediatrics, Faculty of Medicine, Thammasat University, Pathumthani, Thailand
| | - S Kirdpon
- Department of Pediatrics, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - S Sritippayawan
- Division of Nephrology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - S Vasuvattakul
- Division of Nephrology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - P T Yenchitsomanus
- Division of Molecular Medicine, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
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15
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Abstract
Distal renal tubular acidosis (DRTA) is defined as hyperchloremic, non-anion gap metabolic acidosis with impaired urinary acid excretion in the presence of a normal or moderately reduced glomerular filtration rate. Failure in urinary acid excretion results from reduced H+ secretion by intercalated cells in the distal nephron. This results in decreased excretion of NH4+ and other acids collectively referred as titratable acids while urine pH is typically above 5.5 in the face of systemic acidosis. The clinical phenotype in patients with DRTA is characterized by stunted growth with bone abnormalities in children as well as nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria, hypocitraturia, and relatively alkaline urine. Hypokalemia is a striking finding that accounts for muscle weakness and requires continued treatment together with alkali-based therapies. This review will focus on the mechanisms responsible for impaired acid excretion and urinary potassium wastage, the clinical features, and diagnostic approaches of hypokalemic DRTA, both inherited and acquired.
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16
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Zhang Z, Aung ZT, Simmons DG, Dawson PA. Molecular analysis of sequence and splice variants of the human SLC13A4 sulfate transporter. Mol Genet Metab 2017; 121:35-42. [PMID: 28385533 DOI: 10.1016/j.ymgme.2017.03.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 03/31/2017] [Accepted: 03/31/2017] [Indexed: 11/22/2022]
Abstract
The solute linked carrier 13A4 gene (SLC13A4) is abundantly expressed in the human and mouse placenta where it is proposed to transport nutrient sulfate to the fetus. In mice, targeted disruption of placental Slc13a4 leads to severe and lethal fetal phenotypes, however the involvement of SLC13A4 in human development is unknown. A search of the NCBI and Ensembl gene databases identified two alternatively spliced SLC13A4 mRNA transcripts and 98 SLC13A4 gene variants, including 85 missense, 4 splice site, 5 frameshift and 2 nonsense variants, as well as 2 in-frame deletions. We examined the relative abundance of the two SLC13A4 mRNA transcripts and then compared the sulfate transport function and plasma membrane expression of both isoforms as well as 6 sequence variants that predict disrupted SLC13A4 protein structure and function. SLC13A4 mRNA variant 1 has three additional nucleotides CAG compared to SLC13A4 mRNA variant 2 as a result of alternative splicing at the 5'-end of exon 6. Using qRT-PCR, we show a 4-fold higher abundance of SLC13A4 mRNA variant 1 compared to variant 2 in term human placentas and cultured BeWo and JEG-3 cell lines. The corresponding SLC13A4 protein isoforms 1 and 2 were found to have similar sulfate uptake activity and apical membrane expression in cultured MDCK cells. In addition, sulfate uptake into MDCK cells was similar between SLC13A4 isoform 1 and four missense variants N300S, F310C, E360Q and I570V, whereas V513M and frameshift variant L72Sfs led to partial (≈75% decrease) and complete loss-of-function, respectively. Localisation of these variants in MDCK cells showed N300S, E360Q, V513M and I570V expression on the apical plasma membrane, L72Sfs intracellularly and F310C on both apical and basolateral membranes. Our finding of partial and complete loss-of-function variants warrants further studies of the potential involvement of SLC13A4 in fetal pathophysiology.
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Affiliation(s)
- Zhe Zhang
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Zin Thu Aung
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - David G Simmons
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Paul A Dawson
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia.
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17
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The genetic and clinical spectrum of a large cohort of patients with distal renal tubular acidosis. Kidney Int 2017; 91:1243-1255. [PMID: 28233610 DOI: 10.1016/j.kint.2016.12.017] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 12/20/2016] [Accepted: 12/22/2016] [Indexed: 11/24/2022]
Abstract
Primary distal renal tubular acidosis is a rare genetic disease. Mutations in SLC4A1, ATP6V0A4, and ATP6V1B1 genes have been described as the cause of the disease, transmitted as either an autosomal dominant or recessive trait. Particular clinical features, such as sensorineural hearing loss, have been mainly described in association with mutations in one gene instead of the others. Nevertheless, the diagnosis of distal renal tubular acidosis is essentially based on clinical and laboratory findings, and the series of patients described so far are usually represented by small cohorts. Therefore, a strict genotype-phenotype correlation is still lacking, and questions about whether clinical and laboratory data should direct the genetic analysis remain open. Here, we applied next-generation sequencing in 89 patients with a clinical diagnosis of distal renal tubular acidosis, analyzing the prevalence of genetic defects in SLC4A1, ATP6V0A4, and ATP6V1B1 genes and the clinical phenotype. A genetic cause was determined in 71.9% of cases. In our group of sporadic cases, clinical features, including sensorineural hearing loss, are not specific indicators of the causal underlying gene. Mutations in the ATP6V0A4 gene are quite as frequent as mutations in ATP6V1B1 in patients with recessive disease. Chronic kidney disease was frequent in patients with a long history of the disease. Thus, our results suggest that when distal renal tubular acidosis is suspected, complete genetic testing could be considered, irrespective of the clinical phenotype of the patient.
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18
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Genetic defects underlying renal stone disease. Int J Surg 2016; 36:590-595. [PMID: 27838384 DOI: 10.1016/j.ijsu.2016.11.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 11/06/2016] [Accepted: 11/07/2016] [Indexed: 12/19/2022]
Abstract
Renal stones are common and are usually secondary to risk factors affecting the solubility of substances in the urinary tract. Primary, that is genetic, causes are rare but nevertheless are important to recognise so that appropriate treatments can be instigated and the risks to other family members acknowledged. A brief overview of the investigation of renal stones from a biochemical point of view is presented with emphasis on the problems that can arise. The genetic basis of renal stone disease caused by (i) derangement of a metabolic pathway, (ii) diversion to an insoluble product, (iii) failure of transport and (iv) renal tubular acidosis is described by reference to the disorders of adenine phosphoribosyl transferase (APRT) deficiency, primary hyperoxaluria, cystinuria and autosomal dominant distal renal tubular acidosis.
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19
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Vichot AA, Zsengellér ZK, Shmukler BE, Adams ND, Dahl NK, Alper SL. Loss of kAE1 expression in collecting ducts of end-stage kidneys from a family with SLC4A1 G609R-associated distal renal tubular acidosis. Clin Kidney J 2016. [PMID: 28638614 PMCID: PMC5469557 DOI: 10.1093/ckj/sfw074] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Distal renal tubular acidosis caused by missense mutations in kidney isoform of anion exchanger 1 (kAE1/SLC4A1), the basolateral membrane Cl−/HCO3− exchanger of renal alpha-intercalated cells, has been extensively investigated in heterologous expression systems but rarely in human kidneys. The preferential apical localization of distal renal tubular acidosis (dRTA)-associated kAE1 mutants R901X, G609R and M909T in cultured epithelial monolayers has not been examined in human kidney. Here, we present kidney tissues from dRTA-affected siblings heterozygous for kAE1 G609R, characterized by predominant absence rather than mistargeting of kAE1 in intercalated cells. Thus, studies of heterologous recombinant expression of mutant proteins should be, whenever possible, interpreted in comparison to affected patient tissues.
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Affiliation(s)
- Alfred A Vichot
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Zsuzsanna K Zsengellér
- Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Boris E Shmukler
- Division of Nephrology and Vascular Biology Research Center, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
| | - Nancy D Adams
- Division of Nephrology, University of Connecticut School of Medicine, Farmington, CT, USA
| | - Neera K Dahl
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Seth L Alper
- Division of Nephrology and Vascular Biology Research Center, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
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20
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Alexander RT, Cordat E, Chambrey R, Dimke H, Eladari D. Acidosis and Urinary Calcium Excretion: Insights from Genetic Disorders. J Am Soc Nephrol 2016; 27:3511-3520. [PMID: 27468975 DOI: 10.1681/asn.2016030305] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabolic acidosis is associated with increased urinary calcium excretion and related sequelae, including nephrocalcinosis and nephrolithiasis. The increased urinary calcium excretion induced by metabolic acidosis predominantly results from increased mobilization of calcium out of bone and inhibition of calcium transport processes within the renal tubule. The mechanisms whereby acid alters the integrity and stability of bone have been examined extensively in the published literature. Here, after briefly reviewing this literature, we consider the effects of acid on calcium transport in the renal tubule and then discuss why not all gene defects that cause renal tubular acidosis are associated with hypercalciuria and nephrocalcinosis.
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Affiliation(s)
- R Todd Alexander
- Departments of Pediatrics and .,Physiology, University of Alberta, Edmonton, Canada
| | | | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark; and
| | - Dominique Eladari
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.,Department of Physiologie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
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21
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Reithmeier RAF, Casey JR, Kalli AC, Sansom MSP, Alguel Y, Iwata S. Band 3, the human red cell chloride/bicarbonate anion exchanger (AE1, SLC4A1), in a structural context. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1507-32. [PMID: 27058983 DOI: 10.1016/j.bbamem.2016.03.030] [Citation(s) in RCA: 127] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 03/21/2016] [Accepted: 03/29/2016] [Indexed: 02/03/2023]
Abstract
The crystal structure of the dimeric membrane domain of human Band 3(1), the red cell chloride/bicarbonate anion exchanger 1 (AE1, SLC4A1), provides a structural context for over four decades of studies into this historic and important membrane glycoprotein. In this review, we highlight the key structural features responsible for anion binding and translocation and have integrated the following topological markers within the Band 3 structure: blood group antigens, N-glycosylation site, protease cleavage sites, inhibitor and chemical labeling sites, and the results of scanning cysteine and N-glycosylation mutagenesis. Locations of mutations linked to human disease, including those responsible for Southeast Asian ovalocytosis, hereditary stomatocytosis, hereditary spherocytosis, and distal renal tubular acidosis, provide molecular insights into their effect on Band 3 folding. Finally, molecular dynamics simulations of phosphatidylcholine self-assembled around Band 3 provide a view of this membrane protein within a lipid bilayer.
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Affiliation(s)
- Reinhart A F Reithmeier
- Department of Biochemistry, 1 King's College Circle, University of Toronto, Toronto M5S 1A8, Canada.
| | - Joseph R Casey
- Department of Biochemistry, Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Antreas C Kalli
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Yilmaz Alguel
- Division of Molecular Biosciences, Imperial College London, London, SW7 2AZ, UK
| | - So Iwata
- Division of Molecular Biosciences, Imperial College London, London, SW7 2AZ, UK
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22
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Gómez J, Gil-Peña H, Santos F, Coto E, Arango A, Hernandez O, Rodríguez J, Nadal I, Cantos V, Chocrón S, Vergara I, Madrid Á, Vazquez C, González LE, Blanco F. Primary distal renal tubular acidosis: novel findings in patients studied by next-generation sequencing. Pediatr Res 2016; 79:496-501. [PMID: 26571219 DOI: 10.1038/pr.2015.243] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 08/22/2015] [Indexed: 12/16/2022]
Abstract
BACKGROUND Primary distal renal tubular acidosis (DRTA) is a rare disease caused by loss-of-function mutations in at least three genes (ATP6V0A4, ATP6V1B1, and SLC4A1) involved in urinary distal acidification. The next-generation sequencing (NGS) technique facilitates the search for mutations in DRTA patients and helps to characterize the genetic and clinical spectrum of the disease. METHODS Ten DRTA patients were studied. They had normal serum anion gap (AG), metabolic acidosis with simultaneous positive urinary AG, and inability to maximally acidify the urine. The exons of the three genes were sequenced in two pools by ultrasequencing. Putative mutations were confirmed by corresponding Sanger sequencing of each exon. RESULTS We found 13 mutations in nine patients. ATP6V0A4: Intron16+2insA; p.R807Q; p.Q276fs; p.P395fs; Intron7-2T>C. ATP6V1B1: p.I386fs; p.R394Q. SLC4A1: p.V245M; p.R589C; p.R589H; p.G609A. One case was a compound heterozygous with a known mutation in ATP6V1B1 (p.G609R) and a pathogenic variation at SLC4A1 (p.E508K). One patient was negative for mutations. CONCLUSION This study evidences that NGS is labor and cost effective for the analysis of DRTA genes. Our results show for the first time SLC4A1 gene mutations in Spanish patients and disclose that compound heterozygosity at two different genes can be responsible for DRTA.
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Affiliation(s)
- Juan Gómez
- Department of Molecular Genetics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain
| | - Helena Gil-Peña
- Department of Pediatrics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain
| | - Fernando Santos
- Department of Pediatrics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain.,Department of Pediatrics, Universidad de Oviedo, Oviedo, Asturias, Spain
| | - Eliecer Coto
- Department of Molecular Genetics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain.,Red de Investigación Renal - REDINREN, Madrid, Madrid, Spain
| | - Ana Arango
- Department of Molecular Genetics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain
| | - Olaya Hernandez
- Department of Pediatrics, Universidad de Oviedo, Oviedo, Asturias, Spain
| | - Julián Rodríguez
- Department of Pediatrics, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain
| | - Inmaculada Nadal
- Department of Pediatrics, Complejo Hospitalario de Navarra, Pamplona, Navarra, Spain
| | - Virginia Cantos
- Department of Pediatrics, Hospital Infanta Elena, Huelva, Andalucía, Spain
| | - Sara Chocrón
- Department of Pediatrics, Hospital Vall d`Hebron, Barcelona, Barcelona, Spain
| | - Inés Vergara
- Department of Pediatrics, Hospital Materno-Infantil Teresa Herrera, A Coruña, Galicia, Spain
| | - Álvaro Madrid
- Department of Pediatrics, Hospital Vall d`Hebron, Barcelona, Barcelona, Spain
| | - Carlos Vazquez
- Department of Molecular Genetics, Complejo Hospitalario Universitario Insular Materno Infantil, Las Palmas de Gran Canaria, Canarias, Spain
| | - Luz E González
- Department of Pediatrics, Fundación Cardio Infantil, Bogotá, Colombia
| | - Fiona Blanco
- Department of Pediatrics, IIS-Fundación Jiménez Díaz, Madrid, Madrid, Spain
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Ito N, Ihara K, Kamoda T, Akamine S, Kamezaki K, Tsuru N, Sumazaki R, Hara T. Autosomal dominant distal renal tubular acidosis caused by a mutation in the anion exchanger 1 gene in a Japanese family. CEN Case Rep 2015; 4:218-222. [PMID: 28509104 DOI: 10.1007/s13730-015-0172-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Accepted: 02/24/2015] [Indexed: 11/28/2022] Open
Abstract
Autosomal dominant distal renal tubular acidosis (dRTA) is a rare disorder caused by a mutation in the AE1 gene encoding the chloride-bicarbonate (Cl-/HCO3-) anion exchanger 1 (AE1). Most patients with this disorder present with clinical symptoms in adulthood and their phenotype is milder than that of those with autosomal recessive dRTA. In this report, we describe a Japanese family with autosomal dominant dRTA in which the mother and her daughter presented with severe symptoms caused by hypokalemia at 2 years of age. The heterozygous AE1 mutation G609R, which is a known causative mutation of dRTA, was identified in both patients. To our knowledge, this is the first report of a Japanese family with autosomal dominant type dRTA caused by an AE1 mutation. We, therefore, propose that alterations of AE1 should be considered causative of autosomal dominant dRTA even if typical symptoms appear during early childhood and the clinical features are severe.
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Affiliation(s)
- Naoko Ito
- Department of Pediatrics, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8583, Japan.
| | - Kenji Ihara
- Department of Pediatrics, Faculty of Medicine, Oita University, 1-1 Idaigaoka, Hasama, Yufu, Oita, 879-5593, Japan
| | - Tomohiro Kamoda
- Department of Pediatrics, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8575, Japan
| | - Satoshi Akamine
- Department of Pediatrics, National Hospital Organization Kokura Medical Center, 10-1 Harugaoka, Kokuraminami-ku, Kitakyushu, Fukuoka, 802-8533, Japan
| | - Kentaro Kamezaki
- Department of Pediatrics, National Hospital Organization Kokura Medical Center, 10-1 Harugaoka, Kokuraminami-ku, Kitakyushu, Fukuoka, 802-8533, Japan
| | - Noboru Tsuru
- Tsuru Noboru Clinic, 2-5-8 Hirao, Chuo-ku, Fukuoka, 810-0014, Japan
| | - Ryo Sumazaki
- Department of Pediatrics, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8575, Japan
| | - Toshiro Hara
- Department of Pediatrics, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8583, Japan
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24
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Alka K, Casey JR. Bicarbonate transport in health and disease. IUBMB Life 2014; 66:596-615. [PMID: 25270914 DOI: 10.1002/iub.1315] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/10/2014] [Indexed: 12/28/2022]
Abstract
Bicarbonate (HCO3(-)) has a central place in human physiology as the waste product of mitochondrial energy production and for its role in pH buffering throughout the body. Because bicarbonate is impermeable to membranes, bicarbonate transport proteins are necessary to enable control of bicarbonate levels across membranes. In humans, 14 bicarbonate transport proteins, members of the SLC4 and SLC26 families, function by differing transport mechanisms. In addition, some anion channels and ZIP metal transporters contribute to bicarbonate movement across membranes. Defective bicarbonate transport leads to diseases, including systemic acidosis, brain dysfunction, kidney stones, and hypertension. Altered expression levels of bicarbonate transporters in patients with breast, colon, and lung cancer suggest an important role of these transporters in cancer.
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Affiliation(s)
- Kumari Alka
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
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Cordat E, Reithmeier RA. Structure, Function, and Trafficking of SLC4 and SLC26 Anion Transporters. CURRENT TOPICS IN MEMBRANES 2014; 73:1-67. [DOI: 10.1016/b978-0-12-800223-0.00001-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Batlle D, Haque SK. Genetic causes and mechanisms of distal renal tubular acidosis. Nephrol Dial Transplant 2013; 27:3691-704. [PMID: 23114896 DOI: 10.1093/ndt/gfs442] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The primary or hereditary forms of distal renal tubular acidosis (dRTA) have received increased attention because of advances in the understanding of the molecular mechanism, whereby mutations in the main proteins involved in acid-base transport result in impaired acid excretion. Dysfunction of intercalated cells in the collecting tubules accounts for all the known genetic causes of dRTA. These cells secrete protons into the tubular lumen through H(+)-ATPases functionally coupled to the basolateral anion exchanger 1 (AE1). The substrate for both transporters is provided by the catalytic activity of the cytosolic carbonic anhydrase II (CA II), an enzyme which is also present in the proximal tubular cells and osteoclasts. Mutations in ATP6V1B1, encoding the B-subtype unit of the apical H(+) ATPase, and ATP6V0A4, encoding the a-subtype unit, lead to the loss of function of the apical H(+) ATPase and are usually responsible for patients with autosomal recessive dRTA often associated with early or late sensorineural deafness. Mutations in the gene encoding the cytosolic CA II are associated with the autosomal recessive syndrome of osteopetrosis, mixed distal and proximal RTA and cerebral calcification. Mutations in the AE1, the gene that encodes the Cl(-)/HCO(3)(-) exchanger, usually present as dominant dRTA, but a recessive pattern has been recently described. Several studies have shown trafficking defects in the mutant protein rather than the lack of function as the major mechanism underlying the pathogenesis of dRTA from AE1 mutations.
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27
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Lopez-Rodriguez A, Holmgren M. Restoration of proper trafficking to the cell surface for membrane proteins harboring cysteine mutations. PLoS One 2012; 7:e47693. [PMID: 23082193 PMCID: PMC3474720 DOI: 10.1371/journal.pone.0047693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Accepted: 09/17/2012] [Indexed: 11/18/2022] Open
Abstract
A common phenotype for many genetic diseases is that the cell is unable to deliver full-length membrane proteins to the cell surface. For some forms of autism, hereditary spherocytosis and color blindness, the culprits are single point mutations to cysteine. We have studied two inheritable cysteine mutants of cyclic nucleotide-gated channels that produce achromatopsia, a common form of severe color blindness. By taking advantage of the reactivity of cysteine’s sulfhydryl group, we modified these mutants with chemical reagents that attach moieties with similar chemistries to the wild-type amino acids’ side chains. We show that these modifications restored proper delivery to the cell membrane. Once there, the channels exhibited normal functional properties. This strategy might provide a unique opportunity to assess the chemical nature of membrane protein traffic problems.
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Affiliation(s)
- Angelica Lopez-Rodriguez
- Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
| | - Miguel Holmgren
- Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
- * E-mail: .
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Zhang Z, Liu KX, He JW, Fu WZ, Yue H, Zhang H, Zhang CQ, Zhang ZL. Identification of Two Novel Mutations in the SLC4A1 Gene in Two Unrelated Chinese Families with Distal Renal Tubular Acidosis. Arch Med Res 2012; 43:298-304. [DOI: 10.1016/j.arcmed.2012.05.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 04/25/2012] [Indexed: 10/28/2022]
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Fry AC, Su Y, Yiu V, Cuthbert AW, Trachtman H, Karet Frankl FE. Mutation conferring apical-targeting motif on AE1 exchanger causes autosomal dominant distal RTA. J Am Soc Nephrol 2012; 23:1238-49. [PMID: 22518001 DOI: 10.1681/asn.2012020112] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Mutations in SLC4A1 that mislocalize its product, the chloride/bicarbonate exchanger AE1, away from its normal position on the basolateral membrane of the α-intercalated cell cause autosomal dominant distal renal tubular acidosis (dRTA). We studied a family exhibiting dominant inheritance and defined a mutation (AE1-M909T) that affects the C terminus of AE1, a region rich in potential targeting motifs that are incompletely characterized. Expression of AE1-M909T in Xenopus oocytes confirmed preservation of its anion exchange function. Wild-type GFP-tagged AE1 localized to the basolateral membrane of polarized MDCK cells, but AE1-M909T localized to both the apical and basolateral membranes. Wild-type AE1 trafficked directly to the basolateral membrane without apical passage, whereas AE1-M909T trafficked to both cell surfaces, implying the gain of an apical-targeting signal. We found that AE1-M909T acquired class 1 PDZ ligand activity that the wild type did not possess. In summary, the AE1-M909T mutation illustrates the role of abnormal targeting in dRTA and provides insight into C-terminal motifs that govern normal trafficking of AE1.
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Affiliation(s)
- Andrew C Fry
- Department of Medical Genetics, University of Cambridge, United Kingdom
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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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31
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Berend K, van Hulsteijn LH, Gans ROB. Chloride: the queen of electrolytes? Eur J Intern Med 2012; 23:203-11. [PMID: 22385875 DOI: 10.1016/j.ejim.2011.11.013] [Citation(s) in RCA: 160] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Revised: 10/20/2011] [Accepted: 11/22/2011] [Indexed: 12/26/2022]
Abstract
BACKGROUND Channelopathies, defined as diseases that are caused by mutations in genes encoding ion channels, are associated with a wide variety of symptoms and have been documented extensively over the past decade. In contrast, despite the important role of chloride in serum, textbooks in general do not allocate chapters exclusively on hypochloremia or hyperchloremia and information on chloride other than channelopathies is scattered in the literature. STUDY DESIGN To systematically review the function of chloride in man, data for this review include searches of MEDLINE, PubMed, and references from relevant articles including the search terms "chloride," "HCl," "chloride channel" "acid-base," "acidosis," "alkalosis," "anion gap" "strong anion gap" "Stewart," "base excess" and "lactate." In addition, internal medicine, critical care, nephrology and gastroenterology textbooks were evaluated on topics pertaining the assessment and management of acid-base disorders, including reference lists from journals or textbooks. CONCLUSION Chloride is, after sodium, the most abundant electrolyte in serum, with a key role in the regulation of body fluids, electrolyte balance, the preservation of electrical neutrality, acid-base status and it is an essential component for the assessment of many pathological conditions. When assessing serum electrolytes, abnormal chloride levels alone usually signify a more serious underlying metabolic disorder, such as metabolic acidosis or alkalosis. Chloride is an important component of diagnostic tests in a wide array of clinical situations. In these cases, chloride can be tested in sweat, serum, urine and feces. Abnormalities in chloride channel expression and function in many organs can cause a range of disorders.
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Affiliation(s)
- Kenrick Berend
- Nephrology department, St. Elisabeth Hospital, Willemstad, Curaçao, The Netherlands.
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32
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Glover M, Mercier Zuber A, Figg N, O'Shaughnessy KM. The activity of the thiazide-sensitive Na(+)-Cl(-) cotransporter is regulated by protein phosphatase PP4. Can J Physiol Pharmacol 2011; 88:986-95. [PMID: 20962898 DOI: 10.1139/y10-080] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cation transport in the distal mammalian nephron relies on the SLC12 family of membrane cotransporters that include the thiazide-sensitive Na(+)-Cl⁻ cotransporter (NCC). NCC is regulated through a scaffold of interacting proteins, including the WNK kinases, WNK 1 and WNK 4, which are mutated in the hypertensive Gordon's syndrome. Dynamic regulation of NCC function by kinases must involve dephosphorylation by phosphatases, as illustrated by the role of PP1 and PP2B in the regulation of KCC members of the SLC12 family. There are 2 phosphorylation-controlled regulatory pathways for NCC: type 1, mediated by WNK4 and affecting trafficking to the surface membrane, and type 2, affecting intrinsic transporter kinetics by phosphorylation of conserved N-terminal S/T amino acids. Using the Xenopus oocyte expression system, we show that PP4 inhibits NCC activity - but not trafficking to the surface membrane - by a mechanism that requires phosphatase activity and a conserved N-terminal amino acid of NCC, threonine 58. This action is distinct from WNK4 regulation of membrane trafficking. In the mouse kidney, PP4 is selectively expressed in the distal nephron, including cells of the distal convoluted tubule cells, suggesting that PP4 may have a physiological role in regulating NCC and hence NaCl reabsorption in vivo.
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Affiliation(s)
- Mark Glover
- Department of Medicine, University of Cambridge, UK
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33
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Human kidney anion exchanger 1 interacts with adaptor-related protein complex 1 μ1A (AP-1 mu1A). Biochem Biophys Res Commun 2010; 401:85-91. [DOI: 10.1016/j.bbrc.2010.09.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Accepted: 09/05/2010] [Indexed: 01/04/2023]
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Patterson ST, Reithmeier RAF. Cell surface rescue of kidney anion exchanger 1 mutants by disruption of chaperone interactions. J Biol Chem 2010; 285:33423-33434. [PMID: 20628050 DOI: 10.1074/jbc.m110.144261] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the human kidney anion exchanger 1 (kAE1) membrane glycoprotein cause impaired urine acidification resulting in distal renal tubular acidosis (dRTA). Dominant and recessive dRTA kAE1 mutants exhibit distinct trafficking defects with retention in the endoplasmic reticulum (ER), Golgi, or mislocalization to the apical membrane in polarized epithelial cells. We examined the interaction of kAE1 with the quality control system responsible for the folding of membrane glycoproteins and the retention and degradation of misfolded mutants. Using small molecule inhibitors to disrupt chaperone interactions, two functional, dominant kAE1 mutants (R589H and R901stop), retained in the ER and targeted to the proteasome for degradation by ubiquitination, were rescued to the basolateral membrane of Madin-Darby canine kidney cells. In contrast, the Golgi-localized, recessive G701D and the severely misfolded, ER-retained dominant Southeast Asian ovalocytosis (SAO) mutants were not rescued. These results show that functional dRTA mutants are retained in the ER due to their interaction with molecular chaperones, particularly calnexin, and that disruption of these interactions can promote their escape from the ER and cell surface rescue.
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Affiliation(s)
- Sian T Patterson
- From the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Reinhart A F Reithmeier
- From the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
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35
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Vasuvattakul S. Molecular Approach for Distal Renal Tubular Acidosis Associated AE1 Mutations. Electrolyte Blood Press 2010; 8:25-31. [PMID: 21468194 PMCID: PMC3041492 DOI: 10.5049/ebp.2010.8.1.25] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Accepted: 05/19/2010] [Indexed: 11/05/2022] Open
Abstract
The molecular approaches to distal renal tubular acidosis (dRTA) associated AE1 mutations lead us to understand the genetic and pathophysiological aspects of the acidification defects. An unanticipated high value of the urine-blood (U-B) PCO(2) after NaHCO(3) loading observed in a case of dRTA and southeast Asian ovalocytosis (SAO) might be from a mistarget of the AE1 to the luminal membrane of type A intercalated cells. The mutations of the AE1 gene resulted in SAO and also affected renal acidification function. Notwithstanding, after the NH4Cl loading in 20 individuals with SAO, the acidification in the distal nephron was normal. The presence of both SAO and G701D mutations of AE1 gene would explain the abnormal urinary acidification in the patients with the compound heterozogosity. In terms of the effect of the mutations on trafficking of AE1, truncated kidney isoform (kAE1) of wild-type showed a 'dominant-positive effect' in rescuing the recessive mutant kAE1 (S773P or G701D) trafficking to the plasma membrane, in contrast with the dominant mutant kAE1 (R589H) resulting in a 'dominant-negative effect' when heterodimerized with the wild-type kAE1. It is notable that the dominant mutants kAE1 (R901X or G609R) expression in MDCK cells clearly results in aberrant surface expression with some mutant protein appearing at the apical membrane. These might result in net bicarbonate secretion and increasing U-B PCO(2) in the distal nephron. The molecular physiological and genetic approaches have permitted identification of the molecular defects, predominantly in transporter proteins, and should in turn prompt development of novel therapeutic strategies.
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Affiliation(s)
- Somkiat Vasuvattakul
- Renal Division, Department of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
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36
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Shao L, Xu Y, Dong Q, Lang Y, Yue S, Miao Z. A novel SLC4A1 variant in an autosomal dominant distal renal tubular acidosis family with a severe phenotype. Endocrine 2010; 37:473-8. [PMID: 20960171 DOI: 10.1007/s12020-010-9340-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Accepted: 03/26/2010] [Indexed: 10/19/2022]
Abstract
Mutations in SLC4A1, encoding the chloride-bicarbonate exchanger AE1, cause distal renal tubular acidosis (dRTA), a disease of defective urinary acidification by the distal nephron. We searched for SLC4A1 gene mutations in six patients from a Chinese family with a severe phenotype of dRTA (growth impairment, severe metabolic acidosis, with/or without gross nephrocalcinosis and renal impairment). All coding regions of kidney isoform of AE1, including intron-exon boundaries, were analyzed using PCR followed by direct sequence analysis. A novel 1-bp duplication at nucleotide 2713 (c.2713dupG, band 3 Qingdao) in exon 20 of SLC4A1 in this family was identified by direct sequencing analysis. This duplication alters the encoded protein through codon 905, and results in a reading frame for 15 extra condons (instead of 8) before the new stop condon at position 919 (p.Asp905Glyfs15). We suggest that RTA should be considered as a diagnostic possibility in adult subjects with nephrocalcinosis and chronic renal insufficiency, and family survey should be carefully performed.
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Affiliation(s)
- Leping Shao
- Department of Nephrology, Affilated Hospital of Qingdao University School of Medicine, #16, Jiangsu Road, Qingdao 266003, People's Republic of China.
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Chang YH, Shaw CF, Jian SH, Hsieh KH, Chiou YH, Lu PJ. Compound mutations in human anion exchanger 1 are associated with complete distal renal tubular acidosis and hereditary spherocytosis. Kidney Int 2009; 76:774-83. [DOI: 10.1038/ki.2009.258] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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38
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Hereditary stomatocytosis and cation leaky red cells — Recent developments. Blood Cells Mol Dis 2009; 42:216-22. [DOI: 10.1016/j.bcmd.2009.01.014] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Accepted: 01/20/2009] [Indexed: 12/22/2022]
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39
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Wagner CA, Devuyst O, Bourgeois S, Mohebbi N. Regulated acid–base transport in the collecting duct. Pflugers Arch 2009; 458:137-56. [DOI: 10.1007/s00424-009-0657-z] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Revised: 02/22/2009] [Accepted: 02/24/2009] [Indexed: 02/07/2023]
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40
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Williamson RC, Brown ACN, Mawby WJ, Toye AM. Human kidney anion exchanger 1 localisation in MDCK cells is controlled by the phosphorylation status of two critical tyrosines. J Cell Sci 2008; 121:3422-32. [PMID: 18827007 DOI: 10.1242/jcs.035584] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
An important question in renal physiology is how the alpha-intercalated cells of the kidney regulate the distribution of the basolateral kidney anion exchanger 1 (kAE1) according to systemic acid-base status. Previous work using a MDCKI model system demonstrated that kAE1 basolateral targeting requires an N-terminal determinant and a critical C-terminal tyrosine (Y904). Here, we show that the N-terminal determinant is residue Y359, because a Y359A substitution mutant was mistargeted to the apical membrane. Further determinants might exist because a range of N-terminal kAE1 truncations that contained Y359 were incorrectly targeted to the TGN. Y359 and Y904 in kAE1 are phosphorylated upon pervanadate treatment and this phosphorylation is sensitive to specific Src kinase family inhibitors. We tested a range of stimuli on this model system and only the application of high nonphysiological concentrations of extracellular bicarbonate, and to a lesser extent hypertonicity or hyperosmolarity, induced tyrosine phosphorylation of kAE1. Treatment with pervanadate caused internalisation of kAE1 from the plasma membrane, but treatment with high concentrations of bicarbonate did not, because of the hypertonicity of the solution. We propose that alpha-intercalated cells control the distribution of kAE1 by reversible phosphorylation of tyrosine residues Y359 and Y904.
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Affiliation(s)
- Rosalind C Williamson
- University of Bristol, Department of Biochemistry, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK
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41
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Walsh S, Borgese F, Gabillat N, Unwin R, Guizouarn H. Cation transport activity of anion exchanger 1 mutations found in inherited distal renal tubular acidosis. Am J Physiol Renal Physiol 2008; 295:F343-50. [PMID: 18524859 DOI: 10.1152/ajprenal.00587.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Anion exchanger 1 (AE1) is encoded by SLC4A1 and mediates electroneutral anion exchange across cell membranes. It is the most abundant protein in the red cell membrane, but it is also found in the basolateral membrane of renal alpha-intercalated cells, where it is required for normal urinary acidification. Recently, four point mutations in red cell AE1 have been described that convert the anion exchanger to a cation conductance. SLC4A1 mutations can also cause type 1 hypokalemic distal renal tubular acidosis (dRTA). We investigated the properties of four dRTA-associated AE1 mutations (R589H, G609R, S613F, and G701D) by heterologous expression in Xenopus laevis oocytes. Although these AE1 mutants are functional anion exchangers, unlike the red cell disease mutants, we found that they also demonstrated a cation leak. We found a large cation leak in the G701D mutant. This mutant normally requires coexpression with glycophorin A for surface membrane expression in red blood cells and oocytes. However, we found that coexpressing wild-type kidney AE1 with G701D in oocytes still caused a cation leak, consistent with heterodimerized G701D reaching the cell membrane and retaining its cation conductance property. These findings have potential structural and functional implications for AE1, and they indicate that while anion exchange and cation conductance properties are distinct, they can coexist.
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Affiliation(s)
- Stephen Walsh
- Laboratoire de Physiologie des Membranes Cellulaires, UMR6548, Centre National de la Recherche Scientifique-Université de Nice, Bâtiment de Sciences Naturelles, Nice, France.
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Dominant-negative effect of Southeast Asian ovalocytosis anion exchanger 1 in compound heterozygous distal renal tubular acidosis. Biochem J 2008; 410:271-81. [PMID: 17941824 DOI: 10.1042/bj20070615] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2007] [Revised: 10/15/2007] [Accepted: 10/17/2007] [Indexed: 11/17/2022]
Abstract
The human chloride/bicarbonate AE1 (anion exchanger) is a dimeric glycoprotein expressed in the red blood cell membrane,and expressed as an N-terminal (Delta1-65) truncated form, kAE1(kidney AE1), in the basolateral membrane of alpha-intercalated cells in the distal nephron. Mutations in AE1 can cause SAO (Southeast Asian ovalocytosis) or dRTA (distal renal tubular acidosis), an inherited kidney disease resulting in impaired acid secretion. The dominant SAO mutation (Delta400-408) that results in an inactive transporter and altered erythrocyte shape occurs in manydRTA families, but does not itself result in dRTA. Compound heterozygotes of four dRTA mutations (R602H, G701D, DeltaV850 and A858D) with SAO exhibit dRTA and abnormal red blood cell properties. Co-expression of kAE1 and kAE1 SAO with the dRTAmutantswas studied in polarized epithelial MDCK(Madin-Darbycanine kidney) cells. Like SAO, the G701D and DeltaV850 mutants were predominantly retained intracellularly, whereas the R602H and A858D mutants could traffic to the basolateral membrane. When co-expressed in transfected cells, kAE1 WT (wild-type)and kAE1 SAO could interact with the dRTA mutants. MDCK cells co-expressing kAE1 SAO with kAE1 WT, kAE1 R602Hor kAE1 A858D showed a decrease in cell-surface expression of the co-expressed proteins. When co-expressed, kAE1 WT colocalized with the kAE1 R602H, kAE1 G701D, kAE1 DeltaV850 and kAE1 A858D mutants at the basolateral membrane, whereaskAE1 SAO co-localized with kAE1 WT, kAE1 R602H, kAE1 G701D, kAE1 DeltaV850 and kAE1 A858D in MDCK cells. The decrease in cell-surface expression of the dRTAmutants as a result of the interaction with kAE1 SAO would account for the impaired expression of functional kAE1 at the basolateral membrane of alpha-intercalated cells, resulting in dRTA in compound heterozygous patients.
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Williamson RC, Toye AM. Glycophorin A: Band 3 aid. Blood Cells Mol Dis 2008; 41:35-43. [PMID: 18304844 DOI: 10.1016/j.bcmd.2008.01.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2008] [Accepted: 01/04/2008] [Indexed: 11/24/2022]
Abstract
Band 3 (B3) is a major site of cytoskeletal attachment to the erythrocyte membrane and is important for gas exchange. A truncated isoform of B3 (kB3) is expressed in the alpha-intercalated cells of the kidney and its functional activity and basolateral localization are essential for acid secretion. B3 mutations generally lead to red blood cell (RBC) specific disease (hereditary spherocytosis (HS), Southeast Asian Ovalocytosis or hereditary stomatocytosis) or kidney disease (distal Renal Tubular Acidosis--dRTA). It is rare for both the RBC and kidney disease phenotypes to co-exist, but this does occur in knockout mice, and also in humans (B3 Coimbra and B3 Courcouronne) or cattle with homozygous HS mutations. This is because RBCs express a B3 chaperone-like molecule in the form of Glycophorin A that can rescue the majority of B3 mutations that cause dRTA but probably not the majority of HS mutations. The study of naturally occurring B3 variant blood and expression of B3 or kB3 mutants in heterologous expression systems has provided valuable information concerning B3 trafficking and interactions in the RBC and kidney. This article will review these studies and comment on our current understanding of the interaction between GPA with B3 and also on the proposed B3 centred macrocomplex.
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Affiliation(s)
- Rosalind C Williamson
- University of Bristol, Department of Biochemistry, School of Medical Sciences, University Walk, Bristol, BS8 1TD, UK
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Suzuki M, Vaisbich MH, Yamada H, Horita S, Li Y, Sekine T, Moriyama N, Igarashi T, Endo Y, Cardoso TP, de Sá LCF, Koch VH, Seki G, Fujita T. Functional analysis of a novel missense NBC1 mutation and of other mutations causing proximal renal tubular acidosis. Pflugers Arch 2007; 455:583-93. [PMID: 17661077 DOI: 10.1007/s00424-007-0319-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 07/03/2007] [Accepted: 07/03/2007] [Indexed: 10/23/2022]
Abstract
Mutations in the Na(+)-HCO(3)(-) cotransporter NBC1 cause severe proximal tubular acidosis (pRTA) associated with ocular abnormalities. Recent studies have suggested that at least some NBC1 mutants show abnormal trafficking in the polarized cells. This study identified a new homozygous NBC1 mutation (G486R) in a patient with severe pRTA. Functional analysis in Xenopus oocytes failed to detect the G486R activity due to poor surface expression. In ECV304 cells, however, G486R showed the efficient membrane expression, and its transport activity corresponded to approximately 50% of wild-type (WT) activity. In Madin-Darby canine kidney (MDCK) cells, G486R was predominantly expressed in the basolateral membrane domain as observed for WT. Among the previously identified NBC1 mutants that showed poor surface expression in oocytes, T485S showed the predominant basolateral expression in MDCK cells. On the other hand, L522P was exclusively retained in the cytoplasm in ECV304 and MDCK cells, and functional analysis in ECV304 cells failed to detect its transport activity. These results indicate that G486R, like T485S, is a partial loss of function mutation without major trafficking abnormalities, while L522P causes the clinical phenotypes mainly through its inability to reach the plasma membranes. Multiple experimental approaches would be required to elucidate potential disease mechanism by NBC1 mutations.
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Affiliation(s)
- Masashi Suzuki
- Department of Internal Medicine, Faculty of Medicine, Tokyo University, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
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Abstract
Inherited acidosis may result from a primary renal defect in acid-base handling, emphasizing the central role of the kidney in control of body pH; as a secondary phenomenon resulting from abnormal renal electrolyte handling; or from excess production of acid elsewhere in the body. Here, we review our current understanding of the inherited renal acidoses at a genetic and molecular level.
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Affiliation(s)
- Andrew C Fry
- Department of Medical Genetics and Division of Renal Medicine, University of Cambridge, Cambridge Institute for Medical Research, UK
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46
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Stehberger PA, Shmukler BE, Stuart-Tilley AK, Peters LL, Alper SL, Wagner CA. Distal renal tubular acidosis in mice lacking the AE1 (band3) Cl-/HCO3- exchanger (slc4a1). J Am Soc Nephrol 2007; 18:1408-18. [PMID: 17409310 DOI: 10.1681/asn.2006101072] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Mutations in the human gene that encodes the AE1 Cl(-)/HCO(3)(-) exchanger (SLC4A1) cause autosomal recessive and dominant forms of distal renal tubular acidosis (dRTA). A mouse model that lacks AE1/slc4a1 (slc4a1-/-) exhibited dRTA characterized by spontaneous hyperchloremic metabolic acidosis with low net acid excretion and, inappropriately, alkaline urine without bicarbonaturia. Basolateral Cl(-)/HCO(3)(-) exchange activity in acid-secretory intercalated cells of isolated superfused slc4a1-/- medullary collecting duct was reduced, but alternate bicarbonate transport pathways were upregulated. Homozygous mice had nephrocalcinosis associated with hypercalciuria, hyperphosphaturia, and hypocitraturia. A severe urinary concentration defect in slc4a1-/- mice was accompanied by dysregulated expression and localization of the aquaporin-2 water channel. Mice that were heterozygous for the AE1-deficient allele had no apparent defect. Thus, the slc4a1-/- mouse is the first genetic model of complete dRTA and demonstrates that the AE1/slc4a1 Cl(-)/HCO(3)(-) exchanger is required for maintenance of normal acid-base homeostasis by distal renal regeneration of bicarbonate in the mouse as well as in humans.
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Affiliation(s)
- Paul A Stehberger
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
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47
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Cordat E. Unraveling trafficking of the kidney anion exchanger 1 in polarized MDCK epithelial cells. Biochem Cell Biol 2007; 84:949-59. [PMID: 17215882 DOI: 10.1139/o06-200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Kidney anion exchanger 1 (kAE1) is a membrane glycoprotein expressed at the basolateral membrane of type A intercalated cells in the kidney collecting tubule. Mutations occurring in the gene encoding this protein can give rise to distal renal tubular acidosis (dRTA), a disease characterized by an impaired urine acidification, nephrocalcinosis, and renal failure. Here we review how the study of dRTA mutants in polarized epithelial cells has shed light on the cellular mechanisms resulting in this renal disease.
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Affiliation(s)
- Emmanuelle Cordat
- Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, ON M5S 1A8, Canada.
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48
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Cordat E, Reithmeier RAF. Expression and interaction of two compound heterozygous distal renal tubular acidosis mutants of kidney anion exchanger 1 in epithelial cells. Am J Physiol Renal Physiol 2006; 291:F1354-61. [PMID: 16849697 DOI: 10.1152/ajprenal.00015.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Kidney AE1 (kAE1) is a glycoprotein responsible for the electroneutral exchange of chloride for bicarbonate, promoting the reabsorption of bicarbonate into the blood by α-intercalated cells of the collecting tubule. Mutations occurring in the gene encoding kAE1 can induce defects in urinary acidification resulting in distal renal tubular acidosis (dRTA). We expressed two kAE1 dRTA mutants, A858D, a mild dominant mutation, and ΔV850, a recessive mutation, in epithelial Madin-Darby canine kidney (MDCK) cells. Individuals heterozygous with wild-type (WT) kAE1 either did not display any symptoms of dRTA (ΔV850/WT) or displayed a mild incomplete form of dRTA (A858D/WT), while compound heterozygotes (ΔV850/A858D) had dRTA. We found that the A858D mutant was slightly impaired in the endoplasmic reticulum (ER) exit but could target to the basolateral membrane of polarized MDCK cells. Despite an altered binding to an inhibitor affinity resin, anion transport assays showed that the A858D mutant was functional at the cell surface. The ΔV850 mutant showed altered binding to the affinity resin but was predominantly retained in the ER, resulting in undetectable AE1 expression at the basolateral membrane. When coexpressed in MDCK cells, the WT protein, and to a lesser extent the A858D mutant, enhanced the cell surface expression of the ΔV850 mutant. The ΔV850 mutant also affected the cell surface expression of the A858D mutant. Compound heterozygous (A858D/ΔV850) patients likely possess a decreased amount of functional anion exchangers at the basolateral membrane of their α-intercalated cells, resulting in impaired bicarbonate transport into the blood and defective acid transport into the urine.
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Affiliation(s)
- Emmanuelle Cordat
- Department of Biochemistry, Rm. 5216, Medical Sciences Bldg., Univ. of Toronto, Toronto, Ontario M5S 1A8, Canada.
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Sawasdee N, Udomchaiprasertkul W, Noisakran S, Rungroj N, Akkarapatumwong V, Yenchitsomanus PT. Trafficking defect of mutant kidney anion exchanger 1 (kAE1) proteins associated with distal renal tubular acidosis and Southeast Asian ovalocytosis. Biochem Biophys Res Commun 2006; 350:723-30. [PMID: 17027918 DOI: 10.1016/j.bbrc.2006.09.113] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 09/21/2006] [Indexed: 01/01/2023]
Abstract
Compound heterozygous anion exchanger 1 (AE1) SAO/G701D mutations result in distal renal tubular acidosis with Southeast Asian ovalocytosis. Interaction, trafficking and localization of wild-type and mutant (SAO and G701D) kAE1 proteins fused with hemagglutinin, six-histidine, Myc, or green fluorescence protein (GFP) were examined in human embryonic kidney (HEK) 293 cells. When individually expressed, wild-type kAE1 was localized at cell surface while mutant kAE1 SAO and G701D were intracellularly retained. When co-expressed, wild-type kAE1 could form heterodimer with kAE1 SAO or kAE1 G701D and could rescue mutant kAE1 proteins to express on the cell surface. Co-expression of kAE1 SAO and kAE1 G701D also resulted in heterodimer formation but intracellular retention without cell surface expression, suggesting their trafficking defect and failure to rescue each other to the plasma membrane, most likely the molecular mechanism of the disease in the compound heterozygous condition.
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Affiliation(s)
- Nunghathai Sawasdee
- Division of Medical Molecular Biology and BIOTEC-Medical Biotechnology Unit, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
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Toye AM, Parker MD, Daly CM, Lu J, Virkki LV, Pelletier MF, Boron WF. The human NBCe1-A mutant R881C, associated with proximal renal tubular acidosis, retains function but is mistargeted in polarized renal epithelia. Am J Physiol Cell Physiol 2006; 291:C788-801. [PMID: 16707554 DOI: 10.1152/ajpcell.00094.2006] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human electrogenic renal Na-HCO(3) cotransporter (NBCe1-A; SLC4A4) is localized to the basolateral membrane of proximal tubule cells. Mutations in the SLC4A4 gene cause an autosomal recessive proximal renal tubular acidosis (pRTA), a disease characterized by impaired ability of the proximal tubule to reabsorb HCO(3)(-) from the glomerular filtrate. Other symptoms can include mental retardation and ocular abnormalities. Recently, a novel homozygous missense mutant (R881C) of NBCe1-A was reported from a patient with a severe pRTA phenotype. The mutant protein was described as having a lower than normal activity when expressed in Xenopus oocytes, despite having normal Na(+) affinity. However, without trafficking data, it is impossible to determine the molecular basis for the phenotype. In the present study, we expressed wild-type NBCe1-A (WT) and mutant NBCe1-A (R881C), tagged at the COOH terminus with enhanced green fluorescent protein (EGFP). This approach permitted semiquantification of surface expression in individual Xenopus oocytes before assay by two-electrode voltage clamp or measurements of intracellular pH. These data show that the mutation reduces the surface expression rather than the activity of the individual protein molecules. Confocal microscopy on polarized mammalian epithelial kidney cells [Madin-Darby canine kidney (MDCK)I] expressing nontagged WT or R881C demonstrates that WT is expressed at the basolateral membrane of these cells, whereas R881C is retained in the endoplasmic reticulum. In summary, the pathophysiology of pRTA caused by the R881C mutation is likely due to a deficit of NBCe1-A at the proximal tubule basolateral membrane, rather than a defect in the transport activity of individual molecules.
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Affiliation(s)
- Ashley M Toye
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, United Kingdom
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