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Liu Y, Sheng W, Hou S, Hou M, Zhang Y, Wang X, Zhang S, Zhou F, Cai C, Wang W. Functional Characterization of a Novel SLC4A4 Variant and Uniparental Isodisomy in Proximal Renal Tubular Acidosis Patient. Biochem Genet 2024; 62:2469-2481. [PMID: 37952039 DOI: 10.1007/s10528-023-10554-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 10/20/2023] [Indexed: 11/14/2023]
Abstract
SLC4A4 variants are the etiologies of inherited proximal renal tubular acidosis (pRTA), which results in metabolic acidosis, hypokalemia, glaucoma, band keratopathy, and cataract. This study aims to characterize SLC4A4 variant and uniparental isodisomy of chromosome 4 in a patient, and analyse the functional characterization of SLC4A4 variants. This study analyzed renal tubular acidosis disease genes by whole exome sequencing (WES). H3M2 algorithm was used to analyze the run of homozygosity region in chromosomal regions in trio-WES data. The pathogenicity analysis of variants was performed using bioinformatics tools. Additionally, protein stability was analyzed by cycloheximide chase assay. Whole-cell patch clamping was used to examine the electrophysiological properties of NBCe1-A. A novel homozygous SLC4A4 variant was identified in the patient: a missense variant c.496C > T, p. Arg166Trp (NM_003759.4). But the father was heterozygous variant carrier, and the mother did not detect the variant. The H3M2 and UPDio algorithm revealed paternal uniparental isodisomy on chromosome 4 in the patient. SIFT, Poly Phen-2, FATHMM and Mutant Taster showed that the variant might be pathogenic. The tertiary structure analysis showed that the variant could cause structural damage to NBCe1 protein. Foldx results showed that the protein stability of the variant was slightly reduced. Cycloheximide chase assay demonstrated that the variant affects protein stability. The result of electrophysiological studies showed that the variant altered Na+/HCO3- cotransport activity of protein. In conclusion, the study is the first to report a pRTA patient with Arg166Trp variant with UPiD (4) pat and analyze the function of Arg166Trp variant.
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Affiliation(s)
- Yan Liu
- Clinical Pediatric College of Tianjin Medical University, Tianjin Medical University, Tianjin, 300134, China
- Department of Nephrology, Tianjin Children's Hospital (Tianjin University Children's Hospital), No.238 Longyan Road, Beichen District, Tianjin, 300134, China
| | - Wenchao Sheng
- Clinical Pediatric College of Tianjin Medical University, Tianjin Medical University, Tianjin, 300134, China
| | - Shaowei Hou
- School of Biomedical Engineering and Technology, Tianjin Medical University, Tianjin, 300070, China
| | - Mengzhu Hou
- Tianjin Pediatric Research Institute, Tianjin Children's Hospital (Tianjin University Children's Hospital), No.238 Longyan Road, Beichen District, Tianjin, 300134, China
- Tianjin Key Laboratory of Birth Defects for Prevention and Treatment, Tianjin, 300134, China
| | - Ying Zhang
- Clinical Pediatric College of Tianjin Medical University, Tianjin Medical University, Tianjin, 300134, China
| | - Xuetao Wang
- Tianjin Pediatric Research Institute, Tianjin Children's Hospital (Tianjin University Children's Hospital), No.238 Longyan Road, Beichen District, Tianjin, 300134, China
- Tianjin Key Laboratory of Birth Defects for Prevention and Treatment, Tianjin, 300134, China
| | - Shuyue Zhang
- Clinical Pediatric College of Tianjin Medical University, Tianjin Medical University, Tianjin, 300134, China
| | - Feiyu Zhou
- Clinical Pediatric College of Tianjin Medical University, Tianjin Medical University, Tianjin, 300134, China
| | - Chunquan Cai
- Tianjin Pediatric Research Institute, Tianjin Children's Hospital (Tianjin University Children's Hospital), No.238 Longyan Road, Beichen District, Tianjin, 300134, China.
- Tianjin Key Laboratory of Birth Defects for Prevention and Treatment, Tianjin, 300134, China.
| | - Wenhong Wang
- Department of Nephrology, Tianjin Children's Hospital (Tianjin University Children's Hospital), No.238 Longyan Road, Beichen District, Tianjin, 300134, China.
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2
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Kunchur MG, Mauch TJ, Parkanzky M, Rahilly LJ. A review of renal tubular acidosis. J Vet Emerg Crit Care (San Antonio) 2024; 34:325-355. [PMID: 39023331 DOI: 10.1111/vec.13407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 10/14/2022] [Accepted: 11/11/2022] [Indexed: 07/20/2024]
Abstract
OBJECTIVE To review the current scientific literature on renal tubular acidosis (RTA) in people and small animals, focusing on diseases in veterinary medicine that result in secondary RTA. DATA SOURCES Scientific reviews and original research publications on people and small animals focusing on RTA. SUMMARY RTA is characterized by defective renal acid-base regulation that results in normal anion gap hyperchloremic metabolic acidosis. Renal acid-base regulation includes the reabsorption and regeneration of bicarbonate in the renal proximal tubule and collecting ducts and the process of ammoniagenesis. RTA occurs as a primary genetic disorder or secondary to disease conditions. Based on pathophysiology, RTA is classified as distal or type 1 RTA, proximal or type 2 RTA, type 3 RTA or carbonic anhydrase II mutation, and type 4 or hyperkalemic RTA. Fanconi syndrome comprises proximal RTA with additional defects in proximal tubular function. Extensive research elucidating the genetic basis of RTA in people exists. RTA is a genetic disorder in the Basenji breed of dogs, where the mutation is known. Secondary RTA in human and veterinary medicine is the sequela of diseases that include immune-mediated, toxic, and infectious causes. Diagnosis and characterization of RTA include the measurement of urine pH and the evaluation of renal handling of substances that should affect acid or bicarbonate excretion. CONCLUSIONS Commonality exists between human and veterinary medicine among the types of RTA. Many genetic defects causing primary RTA are identified in people, but those in companion animals other than in the Basenji are unknown. Critically ill veterinary patients are often admitted to the ICU for diseases associated with secondary RTA, or they may develop RTA while hospitalized. Recognition and treatment of RTA may reverse tubular dysfunction and promote recovery by correcting metabolic acidosis.
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Affiliation(s)
| | - Teri Jo Mauch
- University of Nebraska Medical Center and Children's Hospital, Omaha, Nebraska, USA
- University of Utah Health Sciences Center, Salt Lake City, Utah, USA
| | | | - Louisa J Rahilly
- Cape Cod Veterinary Specialists, Buzzards Bay, Massachusetts, USA
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Bhandari R, Ekladious A, Javaid MM. Demystifying normal-anion-gap metabolic acidosis: pathophysiology, aetiology, evaluation and diagnosis. Intern Med J 2024; 54:1056-1065. [PMID: 38837536 DOI: 10.1111/imj.16418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Accepted: 05/08/2024] [Indexed: 06/07/2024]
Abstract
Normal-anion-gap metabolic acidosis (NAGMA) is a common but often under-recognised and poorly understood condition, especially by less-experienced clinicians. In adults, NAGMA might be an initial clue to a more significant underlying pathology, such as autoimmune diseases, hypergammaglobulinemia or drug toxicities. However, identifying the aetiology can be challenging due to the diverse processes involved in the development of acidosis. A better understanding of the pathophysiology of NAGMA can help treating physicians suspect and evaluate the condition early and reach the correct diagnosis. This article provides an overview of renal acid-base regulation, discusses the pathophysiological processes involved in developing NAGMA and provides a framework for evaluation to reach an accurate diagnosis.
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Affiliation(s)
- Ritesh Bhandari
- Department of General Medicine, North West Regional Hospital, Burnie, Tasmania, Australia
- Department of General Medicine, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Adel Ekladious
- Department of General Medicine and Acute Assessment Unit, Canberra Hospital, Canberra, Australian Capital Territory, Australia
- Faculty of Health and Medical Sciences, University of Western Australia, Perth, Western Australia, Australia
| | - Muhammad M Javaid
- Monash Rural Health Mildura, Monash University, Melbourne, Victoria, Australia
- Department of Renal Medicine, Woodlands Health, Singapore
- School of Medicine, Deakin University, Melbourne, Victoria, Australia
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Verma A, Mishra DK, Edward DP, Ramappa M. Band-shaped keratopathy in HNF4A-related Fanconi syndrome: a case report and review of the literature. Ophthalmic Genet 2024; 45:246-251. [PMID: 37997707 DOI: 10.1080/13816810.2023.2285310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/07/2023] [Accepted: 11/11/2023] [Indexed: 11/25/2023]
Abstract
BACKGROUND Fanconi's syndrome (FS) is characterized by type-2 renal tubular acidosis, short stature, and renal rickets, along with glycosuria, aminoaciduria, hypophosphaturia, and urinary bicarbonate wasting. The genetic form of FS has been linked to HNF4A variants. Although additional clinical features such as hearing impairment have recently been associated with HNF4A-linked FS, its ocular manifestation has not been described. MATERIAL AND METHODS Presenting a case of a 5-year-old male child with bilateral progressive corneal opacification and the presence of bilateral greyish-white deposits in the interpalpebral region since infancy. A next-generation sequencing (NGS)-based genetic testing was performed for the child followed by parental genetic testing for the identified variant. Furthermore, relevant works of literature were reviewed related to this condition. RESULTS Detailed corneal findings showed a bilateral band-shaped keratopathy (BSK) in the patient. Physical and systemic findings showed signs consistent with FS. Sequencing analysis revealed a novel heterozygous c.635C>T, (p.Pro212Leu) variant in the HNF4A gene in the proband and mother, while the father had a normal genotype. CONCLUSIONS Our case highlights the occurrence of BSK in an exceptionally rare manifestation of hereditary FS linked to HNF4A gene variant. The variant exists both in proband and asymptomatic mother. Therefore, the variable penetrance which is known to exist in HNF4A is acknowledged in this context. This report suggests the first documented instance establishing a plausible connection between BSK and HNF4A-associated FS, characterized by the variable penetrance attributed to the HNF4A gene.
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Affiliation(s)
- Anshuman Verma
- Kallam Anji Reddy Molecular Genetics Laboratory, Brien Holden Eye Research Centre, L V Prasad Eye Institute, Hyderabad, India
- Institute for Rare Eye Diseases and Ocular Genetics, L V Prasad Eye Institute, Hyderabad, India
| | - Dilip Kumar Mishra
- Ophthalmic Pathology Laboratory, L V Prasad Eye Institute, Hyderabad, India
| | - Deepak P Edward
- Department of Ophthalmology and Visual Sciences, University of Illinois Eye and Ear Infirmary, Chicago, Illinois, USA
| | - Muralidhar Ramappa
- Institute for Rare Eye Diseases and Ocular Genetics, L V Prasad Eye Institute, Hyderabad, India
- The Cornea Institute, L V Prasad Eye Institute, Hyderabad, India
- Jasti V Ramanamma Children's Eye Care Center, L V Prasad Eye Institute, Hyderabad, India
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Lee BR. Renal Tubular Acidosis in the Neonate. Neoreviews 2024; 25:e99-e106. [PMID: 38296789 DOI: 10.1542/neo.25-2-e99] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2024]
Abstract
See Bonus NeoBriefs videos and downloadable teaching slides Metabolic acidosis can manifest in the neonatal period and cause significant morbidity and mortality in neonates. Preterm infants are at an even higher risk of developing metabolic acidosis. If the acidosis results from a dysfunction of acid-base homeostasis by the renal system, the disorder is known as renal tubular acidosis (RTA). In this review, we will describe renal development and normal acid-base homeostasis by the renal system. We will also discuss the pathophysiology of the different types of RTA, laboratory findings to aid in diagnosis, and treatment considerations. Understanding RTA will help neonatal clinicians recognize and diagnose an infant affected by RTA and initiate treatment in a timely manner.
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Affiliation(s)
- Brian R Lee
- Department of Neonatology, Southern California Permanente Medical Group, Pasadena, CA
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Yang G, Mack H, Harraka P, Colville D, Savige J. Ocular manifestations of the genetic renal tubulopathies. Ophthalmic Genet 2023; 44:515-529. [PMID: 37702059 DOI: 10.1080/13816810.2023.2253901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Accepted: 08/26/2023] [Indexed: 09/14/2023]
Abstract
BACKGROUND The genetic tubulopathies are rare and heterogenous disorders that are often difficult to identify. This study examined the tubulopathy-causing genes for ocular associations that suggested their genetic basis and, in some cases, the affected gene. METHODS Sixty-seven genes from the Genomics England renal tubulopathy panel were reviewed for ocular features, and for retinal expression in the Human Protein Atlas and an ocular phenotype in mouse models in the Mouse Genome Informatics database. The genes resulted in disease affecting the proximal tubules (n = 24); the thick ascending limb of the loop of Henle (n = 10); the distal convoluted tubule (n = 15); or the collecting duct (n = 18). RESULTS Twenty-five of the tubulopathy-associated genes (37%) had ocular features reported in human disease, 49 (73%) were expressed in the retina, although often at low levels, and 16 (24%) of the corresponding mouse models had an ocular phenotype. Ocular abnormalities were more common in genes affected in the proximal tubulopathies (17/24, 71%) than elsewhere (7/43, 16%). They included structural features (coloboma, microphthalmia); refractive errors (myopia, astigmatism); crystal deposition (in oxalosis, cystinosis) and sclerochoroidal calcification (in Bartter, Gitelman syndromes). Retinal atrophy was common in the mitochondrial-associated tubulopathies. Structural abnormalities and crystal deposition were present from childhood, but sclerochoroidal calcification typically occurred after middle age. CONCLUSIONS Ocular abnormalities are uncommon in the genetic tubulopathies but may be helpful in recognizing the underlying genetic disease. The retinal expression and mouse phenotype data suggest that further ocular associations may become apparent with additional reports. Early identification may be necessary to monitor and treat visual complications.
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Affiliation(s)
- GeFei Yang
- Department of Medicine (Melbourne Health and Northern Health), The University of Melbourne, Royal Melbourne Hospital, Parkville, Australia
| | - Heather Mack
- Department of Surgery (Ophthalmology), The University of Melbourne, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia
| | - Philip Harraka
- Department of Medicine (Melbourne Health and Northern Health), The University of Melbourne, Royal Melbourne Hospital, Parkville, Australia
| | - Deb Colville
- Department of Surgery (Ophthalmology), The University of Melbourne, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia
| | - Judy Savige
- Department of Medicine (Melbourne Health and Northern Health), The University of Melbourne, Royal Melbourne Hospital, Parkville, Australia
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Guo W, Ji P, Xie Y. Genetic Diagnosis and Treatment of Inherited Renal Tubular Acidosis. KIDNEY DISEASES (BASEL, SWITZERLAND) 2023; 9:371-383. [PMID: 37901710 PMCID: PMC10601937 DOI: 10.1159/000531556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Accepted: 06/12/2023] [Indexed: 10/31/2023]
Abstract
Background Renal tubular acidosis (RTA) is caused by various disruptions to the secretion of H+ by distal renal tubules and/or dysfunctional reabsorption of HCO3- by proximal renal tubules, which causes renal acidification dysfunction, ultimately leading to a clinical syndrome characterized by hyperchloremic metabolic acidosis with a normal anion gap. With the development of molecular genetics and gene sequencing technology, inherited RTA has also attracted attention, and an increasing number of RTA-related pathogenic genes have been discovered and reported. Summary This paper focuses on the latest progress in the research of inherited RTA and systematically reviews the pathogenic genes, protein functions, clinical manifestations, internal relationship between genotypes and clinical phenotypes, diagnostic clues, differential diagnosis, and treatment strategies associated with inherited RTA. This paper aims to deepen the understanding of inherited RTA and reduce the missed diagnosis and misdiagnosis of RTA. Key Messages This review systematically summarizes the pathogenic genes, pathophysiological mechanisms, differential diagnosis, and treatment of different types of inherited RTA, which has good clinical value for guiding the diagnosis and treatment of inherited RTA.
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Affiliation(s)
- Wenkai Guo
- Department of Nephrology, First Medical Center of Chinese PLA General Hospital, Chinese PLA Institute of Nephrology, State Key Laboratory of Kidney Diseases, National Clinical Research Center for Kidney Diseases, Beijing, China
- School of Medicine, Nankai University, Tianjin, China
| | - Pengcheng Ji
- Department of Nephrology, First Medical Center of Chinese PLA General Hospital, Chinese PLA Institute of Nephrology, State Key Laboratory of Kidney Diseases, National Clinical Research Center for Kidney Diseases, Beijing, China
| | - Yuansheng Xie
- Department of Nephrology, First Medical Center of Chinese PLA General Hospital, Chinese PLA Institute of Nephrology, State Key Laboratory of Kidney Diseases, National Clinical Research Center for Kidney Diseases, Beijing, China
- School of Medicine, Nankai University, Tianjin, China
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8
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Verlander JW, Lee HW, Wall SM, Harris AN, Weiner ID. The proximal tubule through an NBCe1-dependent mechanism regulates collecting duct phenotypic and remodeling responses to acidosis. Am J Physiol Renal Physiol 2023; 324:F12-F29. [PMID: 36264886 PMCID: PMC9762982 DOI: 10.1152/ajprenal.00175.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 10/12/2022] [Accepted: 10/13/2022] [Indexed: 02/04/2023] Open
Abstract
The renal response to acid-base disturbances involves phenotypic and remodeling changes in the collecting duct. This study examines whether the proximal tubule controls these responses. We examined mice with genetic deletion of proteins present only in the proximal tubule, either the A variant or both A and B variants of isoform 1 of the electrogenic Na+-bicarbonate cotransporter (NBCe1). Both knockout (KO) mice have spontaneous metabolic acidosis. We then determined the collecting duct phenotypic responses to this acidosis and the remodeling responses to exogenous acid loading. Despite the spontaneous acidosis in NBCe1-A KO mice, type A intercalated cells in the inner stripe of the outer medullary collecting duct (OMCDis) exhibited decreased height and reduced expression of H+-ATPase, anion exchanger 1, Rhesus B glycoprotein, and Rhesus C glycoprotein. Combined kidney-specific NBCe1-A/B deletion induced similar changes. Ultrastructural imaging showed decreased apical plasma membrane and increased vesicular H+-ATPase in OMCDis type A intercalated cell in NBCe1-A KO mice. Next, we examined the collecting duct remodeling response to acidosis. In wild-type mice, acid loading increased the proportion of type A intercalated cells in the connecting tubule (CNT) and OMCDis, and it decreased the proportion of non-A, non-B intercalated cells in the connecting tubule, and type B intercalated cells in the cortical collecting duct (CCD). These changes were absent in NBCe1-A KO mice. We conclude that the collecting duct phenotypic and remodeling responses depend on proximal tubule-dependent signaling mechanisms blocked by constitutive deletion of proximal tubule NBCe1 proteins.NEW & NOTEWORTHY This study shows that the proximal tubule regulates collecting duct phenotypic and remodeling responses to acidosis.
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Affiliation(s)
- Jill W Verlander
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Susan M Wall
- Renal Division, Emory University, Atlanta, Georgia
| | - Autumn N Harris
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
- Deparment of Small Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension, and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
- Nephrology and Hypertension Section, Gainesville Veterans Administration Medical Center, Gainesville, Florida
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Muacevic A, Adler JR, Kaur K, Noorani R. An Intraoperative Episode of Severe Type II Renal Tubular Acidosis in an 83-Year-Old Woman. Cureus 2022; 14:e31786. [PMID: 36569703 PMCID: PMC9777354 DOI: 10.7759/cureus.31786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/22/2022] [Indexed: 11/24/2022] Open
Abstract
Type II renal tubular acidosis (RTA) is a rare defect in bicarbonate transport that can cause serious metabolic derangements. We report the case of a spontaneous, isolated intraoperative episode of severe type II RTA in an elderly woman who presented for radical neck dissection, mandible excision, and flap creation. Intraoperatively, she developed a stark metabolic acidosis with hypokalemia, progressively worsening base excess, and prolific urine output. Aggressive resuscitation with bicarbonate corrected all metabolic abnormalities. There was no identifiable trigger and the patient was successfully discharged with no further recurrences during hospitalization. The inability to identify the clinical presentation of RTA perioperatively can lead to poor outcomes.
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Alhasan K, D'Alessandri-Silva C, Mongia A, Topaloglu R, Tasic V, Filler G. Young Adults With Hereditary Tubular Diseases: Practical Aspects for Adult-Focused Colleagues. Adv Chronic Kidney Dis 2022; 29:292-307. [PMID: 36084976 DOI: 10.1053/j.ackd.2021.11.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 11/07/2021] [Accepted: 11/15/2021] [Indexed: 11/11/2022]
Abstract
Recent advances in the management of kidney tubular diseases have resulted in a significant cohort of adolescents and young adults transitioning from pediatric- to adult-focused care. Most of the patients under adult-focused care have glomerular diseases, whereas rarer tubular diseases form a considerable proportion of pediatric patients. The purpose of this review is to highlight the clinical signs and symptoms of tubular disorders, as well as their diagnostic workup, including laboratory findings and imaging, during young adulthood. We will then discuss more common disorders such as cystinosis, cystinuria, distal kidney tubular acidosis, congenital nephrogenic diabetes insipidus, Dent disease, rickets, hypercalciuria, and syndromes such as Bartter, Fanconi, Gitelman, Liddle, and Lowe. This review is a practical guide on the diagnostic and therapeutic approach of tubular conditions affecting young adults who are transitioning to adult-focused care.
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Affiliation(s)
- Khalid Alhasan
- Department of Pediatrics, College of Medicine, King Saud University, Riyadh, Saudi Arabia
| | - Cynthia D'Alessandri-Silva
- Department of Pediatrics, University of Connecticut School of Medicine, Farmington, and Nephrology, Connecticut Children's Medical Center, Hartford, CT
| | - Anil Mongia
- Department of Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY
| | - Rezan Topaloglu
- Department of Paediatrics, Division of Pediatric Nephrology, Hacettepe University School of Medicine, Ankara, Turkey
| | - Velibor Tasic
- University Children's Hospital, Medical School, Skopje, North Macedonia
| | - Guido Filler
- Department of Paediatrics, Division of Pediatric Nephrology, Western University, London, ON, Canada; Department of Medicine, Western University, London, ON, Canada; Department of Pathology and Laboratory Medicine, Western University, London, ON, Canada.
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Yamazaki O, Yamashita M, Li J, Ochiai-Homma F, Yoshida T, Hirahashi J, Furukawa T, Kozuma K, Fujigaki Y, Seki G, Hayashi M, Shibata S. A novel I551F variant of the Na +/HCO 3- cotransporter NBCe1-A shows reduced cell surface expression, resulting in diminished transport activity. Am J Physiol Renal Physiol 2021; 321:F771-F784. [PMID: 34719949 DOI: 10.1152/ajprenal.00584.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Homozygous mutations in SLC4A4, which encodes the electrogenic Na+/[Formula: see text] cotransporter (NBCe1), cause proximal renal tubular acidosis associated with extrarenal symptoms. Although 17` mutated sites in SLC4A4 have thus far been identified among patients with proximal renal tubular acidosis, the physiological significance of other nonsynonymous single-nucleotide variants (SNVs) remains largely undetermined. Here, we investigated the functional properties of SNVs in NBCe1. From the National Center for Biotechnology Information dbSNP database, we identified 13 SNVs that have not previously been characterized in the highly conserved, transmembrane domains of NBCe1-A. Immunocytochemical analysis revealed that the I551F variant was present predominantly in the cytoplasm in human embryonic kidney (HEK)-293 cells, whereas all other SNVs did not show as dramatic a change in subcellular distribution. Western blot analysis in HEK-293 cells demonstrated that the I551F variant showed impaired glycosylation and a 69% reduction in cell surface levels. To determine the role of I551 in more detail, we examined the significance of various artificial mutants in both nonpolarized HEK-293 cells and polarized Madin-Darby canine kidney cells, which indicated that only I551F substitution resulted in cytoplasmic retention. Moreover, functional analysis using Xenopus oocytes demonstrated that the I551F variant had a significantly reduced activity corresponding to 39% of that of the wild-type, whereas any other SNVs and artificial I551 mutants did not show significant changes in activity. Finally, immunofluorescence experiments in HEK-293 cells indicated that the I551F variant retained wild-type NBCe1-A in the cytoplasm. These data demonstrate that the I551F variant of NBCe1-A shows impaired transport activity predominantly through cytoplasmic retention and suggest that the variant can have a dominant negative effect by forming complexes with wild-type NBCe1-A.NEW & NOTEWORTHY Electrogenic Na+/[Formula: see text] cotransporter 1-A (NBCe1-A) in the proximal tubule regulates the acid/base balance and fluid volume homeostasis. From the National Center for Biotechnology Information dbSNP database, we identified the I551F variant of NBCe1-A, which showed reduced glycosylation, cell surface expression, and transport activity. We also found that the I551F variant can exert a dominant negative effect on wild-type NBCe1-A, suggesting its physiological significance.
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Affiliation(s)
- Osamu Yamazaki
- Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan.,Department of General Medicine, Keio University School of Medicine, Tokyo, Japan.,Apheresis and Dialysis Center, Keio University School of Medicine, Tokyo, Japan
| | - Maho Yamashita
- Apheresis and Dialysis Center, Keio University School of Medicine, Tokyo, Japan
| | - Jinping Li
- Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan
| | - Fumika Ochiai-Homma
- Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan
| | - Tadashi Yoshida
- Department of General Medicine, Keio University School of Medicine, Tokyo, Japan.,Apheresis and Dialysis Center, Keio University School of Medicine, Tokyo, Japan
| | - Junichi Hirahashi
- Department of General Medicine, Keio University School of Medicine, Tokyo, Japan.,Apheresis and Dialysis Center, Keio University School of Medicine, Tokyo, Japan
| | - Taiji Furukawa
- Department of Laboratory Medicine, Teikyo University School of Medicine, Tokyo, Japan
| | - Ken Kozuma
- Division of Cardiology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan
| | - Yoshihide Fujigaki
- Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan
| | | | - Matsuhiko Hayashi
- Department of General Medicine, Keio University School of Medicine, Tokyo, Japan.,Apheresis and Dialysis Center, Keio University School of Medicine, Tokyo, Japan.,Kawakita General Hospital, Center for Clinical Education, Tokyo, Japan
| | - Shigeru Shibata
- Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan
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12
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Downie ML, Lopez Garcia SC, Kleta R, Bockenhauer D. Inherited Tubulopathies of the Kidney: Insights from Genetics. Clin J Am Soc Nephrol 2021; 16:620-630. [PMID: 32238367 PMCID: PMC8092065 DOI: 10.2215/cjn.14481119] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The kidney tubules provide homeostasis by maintaining the external milieu that is critical for proper cellular function. Without homeostasis, there would be no heartbeat, no muscle movement, no thought, sensation, or emotion. The task is achieved by an orchestra of proteins, directly or indirectly involved in the tubular transport of water and solutes. Inherited tubulopathies are characterized by impaired function of one or more of these specific transport molecules. The clinical consequences can range from isolated alterations in the concentration of specific solutes in blood or urine to serious and life-threatening disorders of homeostasis. In this review, we focus on genetic aspects of the tubulopathies and how genetic investigations and kidney physiology have crossfertilized each other and facilitated the identification of these disorders and their molecular basis. In turn, clinical investigations of genetically defined patients have shaped our understanding of kidney physiology.
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Affiliation(s)
- Mallory L. Downie
- Department of Renal Medicine, University College London, London, United Kingdom,Department of Nephrology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Sergio C. Lopez Garcia
- Department of Renal Medicine, University College London, London, United Kingdom,Department of Nephrology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Robert Kleta
- Department of Renal Medicine, University College London, London, United Kingdom,Department of Nephrology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Detlef Bockenhauer
- Department of Renal Medicine, University College London, London, United Kingdom,Department of Nephrology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
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13
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Palmer BF, Kelepouris E, Clegg DJ. Renal Tubular Acidosis and Management Strategies: A Narrative Review. Adv Ther 2021; 38:949-968. [PMID: 33367987 PMCID: PMC7889554 DOI: 10.1007/s12325-020-01587-5] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 11/26/2020] [Indexed: 12/29/2022]
Abstract
Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid−base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.
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14
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Gil-Perotín S, Jaijo T, Verdú AG, Rubio P, Mazón M, Gasqué-Rubio R, Díaz S. Epilepsy, status epilepticus, and hemiplegic migraine coexisting with a novel SLC4A4 mutation. Neurol Sci 2021; 42:3647-3654. [PMID: 33439394 DOI: 10.1007/s10072-020-04961-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Accepted: 12/03/2020] [Indexed: 10/22/2022]
Abstract
BACKGROUND Recessive mutations in the SLC4A4 gene cause a syndrome characterised by proximal renal tubular acidosis (pRTA), mental retardation, dental and ocular abnormalities, and hemiplegic migraine. Rare cases involving the development of epilepsy or its severe complication-status epilepticus-have been described. METHODS The clinical and genetic status of four affected members in a Spanish family was studied. The SLC4A4 gene mutation was detected with a next-generation sequencing (NGS) panel in the proband, and Sanger confirmed the putative mutations in affected relatives. In silico analysis was performed to elucidate the putative effect of mutation on the splicing process. RESULTS A novel mutation, c.2562+2T>G, was identified in the homozygous state in all diseased members of the family. This mutation affected a canonical splice site and is predicted to abolish the wild-type donor site, which predicts a premature truncated NBCe1 protein with cotransport activity. The resulting protein lacks the 190 amino acids of the carboxyl-terminus, and the effect is likely to be a loss of function. All patients suffered from severe pRTA and ocular abnormalities, and the adults also suffered from neurological complications, such as hemiplegic migraine and/or epilepsy. Two developed life-threatening status epilepticus, although they fully recovered and remained free of seizures with valproate. CONCLUSION These results expand the clinical and mutational spectra of SLC4A4-related disease and have implications for understanding the potential role of NBCe1 in the pathophysiologic processes of hemiplegic migraine and epilepsy/status epilepticus associated with the mutation.
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Affiliation(s)
- Sara Gil-Perotín
- Neurology Department, University and Polytechnic Hospital La Fe, Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain.
- Neuroimmunology Unit, Health Research Institute La Fe (IISLAFE), Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain.
| | - Teresa Jaijo
- Genetic Unit, University and Polytechnic Hospital La Fe, Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain
- Molecular, Cellular and Genomics Biomedicine Research Group, Health Research Institute La Fe (IISLAFE), Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain
- CIBER de Enfermedades Raras (CIBERER), Madrid, Spain
| | - Andrés G Verdú
- Neurophysiology Department, University and Polytechnic Hospital La Fe, Avda. Fernando Abril Martorell 106, 46026, Valencia, Spain
| | - Pilar Rubio
- Neurophysiology Department, University and Polytechnic Hospital La Fe, Avda. Fernando Abril Martorell 106, 46026, Valencia, Spain
| | - Miguel Mazón
- Radiology Department, Hospital Arnau de Vilanova, C/San Clemente, 12, 46025, Valencia, Spain
| | - Raquel Gasqué-Rubio
- Neuroimmunology Unit, Health Research Institute La Fe (IISLAFE), Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain
| | - Samuel Díaz
- Neurology Department, University and Polytechnic Hospital La Fe, Avda. Fernando Abril Martorell, 106, 46026, Valencia, Spain
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15
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Moss FJ, Boron WF. Carbonic anhydrases enhance activity of endogenous Na-H exchangers and not the electrogenic Na/HCO 3 cotransporter NBCe1-A, expressed in Xenopus oocytes. J Physiol 2020; 598:5821-5856. [PMID: 32969493 PMCID: PMC7747792 DOI: 10.1113/jp280143] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 09/07/2020] [Indexed: 12/16/2022] Open
Abstract
KEY POINTS According to the HCO 3 - metabolon hypothesis, direct association of cytosolic carbonic anhydrases (CAs) with the electrogenic Na/HCO3 cotransporter NBCe1-A speeds transport by regenerating/consuming HCO 3 - . The present work addresses published discrepancies as to whether cytosolic CAs stimulate NBCe1-A, heterologously expressed in Xenopus oocytes. We confirm the essential elements of the previous experimental observations, taken as support for the HCO 3 - metabolon hypothesis. However, using our own experimental protocols or those of others, we find that NBCe1-A function is unaffected by cytosolic CAs. Previous conclusions that cytosolic CAs do stimulate NBCe1-A can be explained by an unanticipated stimulatory effect of the CAs on an endogenous Na-H exchanger. Theoretical analyses show that, although CAs could stimulate non- HCO 3 - transporters (e.g. Na-H exchangers) by accelerating CO2 / HCO 3 - -mediated buffering of acid-base equivalents, they could not appreciably affect transport rates of NBCe1 or other transporters carrying HCO 3 - , CO 3 = , or NaCO 3 - ion pairs. ABSTRACT The HCO 3 - metabolon hypothesis predicts that cytosolic carbonic anhydrase (CA) binds to NBCe1-A, promotes HCO 3 - replenishment/consumption, and enhances transport. Using a short step-duration current-voltage (I-V) protocol with Xenopus oocytes expressing eGFP-tagged NBCe1-A, our group reported that neither injecting human CA II (hCA II) nor fusing hCA II to the NBCe1-A carboxy terminus affects background-subtracted NBCe1 slope conductance (GNBC ), which is a direct measure of NBCe1-A activity. Others - using bovine CA (bCA), untagged NBCe1-A, and protocols keeping holding potential (Vh ) far from NBCe1-A's reversal potential (Erev ) for prolonged periods - found that bCA increases total membrane current (ΔIm ), which apparently supports the metabolon hypothesis. We systematically investigated differences in the two protocols. In oocytes expressing untagged NBCe1-A, injected with bCA and clamped to -40 mV, CO2 / HCO 3 - exposures markedly decrease Erev , producing large transient outward currents persisting for >10 min and rapid increases in [Na+ ]i . Although the CA inhibitor ethoxzolamide (EZA) reduces both ΔIm and d[Na+ ]i /dt, it does not reduce GNBC . In oocytes not expressing NBCe1-A, CO2 / HCO 3 - triggers rapid increases in [Na+ ]i that both hCA II and bCA enhance in concentration-dependent manners. These d[Na+ ]i /dt increases are inhibited by EZA and blocked by EIPA, a Na-H exchanger (NHE) inhibitor. In oocytes expressing untagged NBCe1-A and injected with bCA, EIPA abolishes the EZA-dependent decreases in ΔIm and d[Na+ ]i /dt. Thus, CAs/EZA produce their ΔIm and d[Na+ ]i /dt effects not through NBCe1-A, but endogenous NHEs. Theoretical considerations argue against a CA stimulation of HCO 3 - transport, supporting the conclusion that an NBCe1-A- HCO 3 - metabolon does not exist in oocytes.
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Affiliation(s)
- Fraser J. Moss
- Department of Physiology and Biophysics, Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Walter F. Boron
- Department of Physiology and Biophysics, Western Reserve University School of Medicine, Cleveland, OH 44106, USA
- Department of Medicine and Department of Biochemistry Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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16
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Defective bicarbonate reabsorption in Kir4.2 potassium channel deficient mice impairs acid-base balance and ammonia excretion. Kidney Int 2019; 97:304-315. [PMID: 31870500 DOI: 10.1016/j.kint.2019.09.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 09/16/2019] [Accepted: 09/23/2019] [Indexed: 11/21/2022]
Abstract
The kidneys excrete the daily acid load mainly by generating and excreting ammonia but the underlying molecular mechanisms are not fully understood. Here we evaluated the role of the inwardly rectifying potassium channel subunit Kir4.2 (Kcnj15 gene product) in this process. In mice, Kir4.2 was present exclusively at the basolateral membrane of proximal tubular cells and disruption of Kcnj15 caused a hyperchloremic metabolic acidosis associated with a reduced threshold for bicarbonate in the absence of a generalized proximal tubule dysfunction. Urinary ammonium excretion rates in Kcnj15- deleted mice were inappropriate to acidosis under basal and acid-loading conditions, and not related to a failure to acidify urine or a reduced expression of ammonia transporters in the collecting duct. In contrast, the expression of key proteins involved in ammonia metabolism and secretion by proximal cells, namely the glutamine transporter SNAT3, the phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase enzymes, and the sodium-proton exchanger NHE-3 was inappropriate in Kcnj15-deleted mice. Additionally, Kcnj15 deletion depolarized the proximal cell membrane by decreasing the barium-sensitive component of the potassium conductance and caused an intracellular alkalinization. Thus, the Kir4.2 potassium channel subunit is a newly recognized regulator of proximal ammonia metabolism. The kidney consequences of its loss of function in mice support the proposal for KCNJ15 as a molecular basis for human isolated proximal renal tubular acidosis.
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17
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Kashoor I, Batlle D. Proximal renal tubular acidosis with and without Fanconi syndrome. Kidney Res Clin Pract 2019; 38:267-281. [PMID: 31474092 PMCID: PMC6727890 DOI: 10.23876/j.krcp.19.056] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 06/13/2019] [Accepted: 06/19/2019] [Indexed: 01/02/2023] Open
Abstract
Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO3−) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO3− wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO3− not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO3− reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO3−, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaPi-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.
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Affiliation(s)
- Ibrahim Kashoor
- Division of Nephrology and Hypertension, Department of Medicine, The Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Daniel Batlle
- Division of Nephrology and Hypertension, Department of Medicine, The Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
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18
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Salerno EE, Patel SP, Marshall A, Marshall J, Alsufayan T, Mballo CSA, Quade BN, Parker MD. Extrarenal Signs of Proximal Renal Tubular Acidosis Persist in Nonacidemic Nbce1b/c-Null Mice. J Am Soc Nephrol 2019; 30:979-989. [PMID: 31040187 DOI: 10.1681/asn.2018050545] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 03/05/2019] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND The SLC4A4 gene encodes electrogenic sodium bicarbonate cotransporter 1 (NBCe1). Inheritance of recessive mutations in SLC4A4 causes proximal renal tubular acidosis (pRTA), a disease characterized by metabolic acidosis, growth retardation, ocular abnormalities, and often dental abnormalities. Mouse models of pRTA exhibit acidemia, corneal edema, weak dental enamel, impacted colons, nutritional defects, and a general failure to thrive, rarely surviving beyond weaning. Alkali therapy remains the preferred treatment for pRTA, but it is unclear which nonrenal signs are secondary to acidemia and which are a direct consequence of NBCe1 loss from nonrenal sites (such as the eye and enamel organ) and therefore require separate therapy. SLC4A4 encodes three major NBCe1 variants: NBCe1-A, NBCe1-B, and NBCe1-C. NBCe1-A is expressed in proximal tubule epithelia; its dysfunction causes the plasma bicarbonate insufficiency that underlies acidemia. NBCe1-B and NBCe1-C exhibit a broad extra-proximal-tubular distribution. METHODS To explore the consequences of Nbce1b/c loss in the absence of acidemia, we engineered a novel strain of Nbce1b/c-null mice and assessed them for signs of pRTA. RESULTS Nbce1b/c-null mice have normal blood pH, but exhibit increased mortality, growth retardation, corneal edema, and tooth enamel defects. CONCLUSIONS The correction of pRTA-related acidemia should not be considered a panacea for all signs of pRTA. The phenotype of Nbce1b/c-null mice highlights the physiologic importance of NBCe1 variants expressed beyond the proximal tubular epithelia and potential limitations of pH correction by alkali therapy in pRTA. It also suggests a novel genetic locus for corneal dystrophy and enamel hypomineralization without acidemia.
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Affiliation(s)
| | - Sangita P Patel
- Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and.,Research and Ophthalmology Services, VA Western New York Healthcare System, Buffalo, New York
| | | | | | | | | | | | - Mark D Parker
- Departments of Physiology and Biophysics and .,Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and
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19
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Finer G, Landau D. Clinical Approach to Proximal Renal Tubular Acidosis in Children. Adv Chronic Kidney Dis 2018; 25:351-357. [PMID: 30139461 DOI: 10.1053/j.ackd.2018.05.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Proximal renal tubular acidosis (pRTA) is an inherited or acquired clinical syndrome in which there is a decreased bicarbonate reclamation in the proximal tubule resulting in normal anion gap hyperchloremic metabolic acidosis. In children, pRTA may be isolated but is often associated with a general proximal tubular dysfunction known as Fanconi syndrome which frequently heralds an underlying systemic disorder from which it arises. When accompanied by Fanconi syndrome, pRTA is characterized by additional renal wasting of phosphate, glucose, uric acid, and amino acids. The most common cause of inherited Fanconi syndrome in the pediatric age group is cystinosis, a disease with therapeutic implications. In this article, we summarize the clinical presentation and differential diagnosis of pRTA and Fanconi syndrome and provide a practical approach to their evaluation in children.
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20
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Horita S, Simsek E, Simsek T, Yildirim N, Ishiura H, Nakamura M, Satoh N, Suzuki A, Tsukada H, Mizuno T, Seki G, Tsuji S, Nangaku M. SLC4A4 compound heterozygous mutations in exon-intron boundary regions presenting with severe proximal renal tubular acidosis and extrarenal symptoms coexisting with Turner's syndrome: a case report. BMC MEDICAL GENETICS 2018; 19:103. [PMID: 29914390 PMCID: PMC6006740 DOI: 10.1186/s12881-018-0612-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 05/21/2018] [Indexed: 12/14/2022]
Abstract
Background Congenital NBCe1A deficiency with the SLC4A4 mutation causes severe proximal renal tubular acidosis, which often comprises extrarenal symptoms, such as intellectual disability and developmental delay, glaucoma, cataract and band keratopathy. To date, almost all mutations have been found to be homozygous mutations located in exons. Case presentation We performed direct nucleotide sequencing analysis of exons and exon–intron boundary regions of the SLC4A4 in a patient presenting with severe renal proximal tubule acidosis, glaucoma and intellectual disability and her parents without these signs. The examination revealed compound heterozygous mutations in exon–intron boundary regions, c.1076 + 3A > C and c.1772 − 2A > T, neither of which have been reported previously. While the former mutation was found in the mother, the latter was found in the father. The transcript of the SLC4A4 gene was almost undetectable, and the patient was also diagnosed with Turner’s syndrome. Conclusions We identified two novel SLC4A4 mutations, c.1076 + 3A > C and c.1772 − 2A > T. When presented in a compound heterozygous state, these mutations caused a phenotype of severe renal proximal tubular acidosis along with glaucoma and mental retardation. This is the first report of congenital proximal renal tubular acidosis carrying compound heterozygous SLC4A4 mutations in exon–intron boundary regions. We suggest that an mRNA surveillance mechanism, nonsense-mediated RNA decay, following aberrant splicing was the reason that the SLC4A4 transcript was almost undetectable in the proband.
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Affiliation(s)
- Shoko Horita
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan.
| | - Enver Simsek
- Department of Paediatric Endocrinology, Eskisehir Osmangazi University School of Medicine, Esogu Meşelik Yerleşkesi, 26480, Eskisehir, Turkey
| | - Tulay Simsek
- Department of Ophthalmology, Eskisehir Osmangazi University School of Medicine, Esogu Meşelik Yerleşkesi, 26480, Eskisehir, Turkey
| | - Nilgun Yildirim
- Department of Ophthalmology, Eskisehir Osmangazi University School of Medicine, Esogu Meşelik Yerleşkesi, 26480, Eskisehir, Turkey
| | - Hiroyuki Ishiura
- Department of Neurology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - Motonobu Nakamura
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - Nobuhiko Satoh
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - Atsushi Suzuki
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - Hiroyuki Tsukada
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - Tomohito Mizuno
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
| | - George Seki
- Yaizu City Hospital, 1000, Dobara, Yaizu, 425 0055, Japan
| | - Shoji Tsuji
- Department of Molecular Neurology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan.,Institute of Medical Genomics, International University of Health and Welfare, 4-3, Kozunomori, Narita-shi, Chiba-ken, 286 8686, Japan
| | - Masaomi Nangaku
- Division of Nephrology and Endocrinology, The University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo, Tokyo, 113 0033, Japan
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21
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Lee HW, Osis G, Harris AN, Fang L, Romero MF, Handlogten ME, Verlander JW, Weiner ID. NBCe1-A Regulates Proximal Tubule Ammonia Metabolism under Basal Conditions and in Response to Metabolic Acidosis. J Am Soc Nephrol 2018; 29:1182-1197. [PMID: 29483156 DOI: 10.1681/asn.2017080935] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Accepted: 01/10/2018] [Indexed: 12/16/2022] Open
Abstract
Renal ammonia metabolism is the primary mechanism through which the kidneys maintain acid-base homeostasis, but the molecular mechanisms regulating renal ammonia generation are unclear. In these studies, we evaluated the role of the proximal tubule basolateral plasma membrane electrogenic sodium bicarbonate cotransporter 1 variant A (NBCe1-A) in this process. Deletion of the NBCe1-A gene caused severe spontaneous metabolic acidosis in mice. Despite this metabolic acidosis, which normally causes a dramatic increase in ammonia excretion, absolute urinary ammonia concentration was unaltered. Additionally, NBCe1-A deletion almost completely blocked the ability to increase ammonia excretion after exogenous acid loading. Under basal conditions and during acid loading, urine pH was more acidic in mice with NBCe1-A deletion than in wild-type controls, indicating that the abnormal ammonia excretion was not caused by a primary failure of urine acidification. Instead, NBCe1-A deletion altered the expression levels of multiple enzymes involved in proximal tubule ammonia generation, including phosphate-dependent glutaminase, phosphoenolpyruvate carboxykinase, and glutamine synthetase, under basal conditions and after exogenous acid loading. Deletion of NBCe1-A did not impair expression of key proteins involved in collecting duct ammonia secretion. These studies demonstrate that the integral membrane protein NBCe1-A has a critical role in basal and acidosis-stimulated ammonia metabolism through the regulation of proximal tubule ammonia-metabolizing enzymes.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Autumn N Harris
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Lijuan Fang
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Michael F Romero
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida; .,Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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22
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Myers EJ, Marshall A, Parker MD. The role of disease-linked residue glutamine-913 in support of the structure and function of the human electrogenic sodium/bicarbonate cotransporter NBCe1-A. Sci Rep 2018; 8:3066. [PMID: 29449648 PMCID: PMC5814396 DOI: 10.1038/s41598-018-20488-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 01/18/2018] [Indexed: 11/09/2022] Open
Abstract
Mutations in the sodium bicarbonate cotransporter NBCe1 (SLC4A4) cause proximal renal tubular acidosis (pRTA). We recently described a novel pRTA mutation p.Gln913Arg (Q913R), inherited in compound heterozygous form with p.Arg510His (R510H). Q913R causes intracellular retention of NBCe1 and a 'gain of function' Cl- leak. To learn more about the importance of glutamine at position 913, we substituted a variety of alternative amino-acid residues (Cys, Glu, Lys, Leu, Ser) at position 913. Studying cRNA-injected Xenopus oocytes by voltage clamp, we find that most de novo mutants exhibit close-to-normal NBCe1 activity; only Q913K expresses a Cl- leak. Studying transiently-transfected, polarised kidney cells by fluorescence microscopy we find that most de novo mutants (except Q913E) are intracellularly retained. A 3D homology model predicts that Gln913 is located in the gating domain of NBCe1 and neighbours the 3D space occupied by another pRTA-associated residue (Arg881), highlighting an important and conformationally-sensitive region of NBCe1. We conclude that the intracellular retention of Q913R is caused by the loss of Gln at position 913, but that the manifestation of the Cl- leak is related to the introduction of Arg at position 913. Our findings will inform future studies to elucidate the nature and the consequences of the leak.
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Affiliation(s)
- Evan J Myers
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, USA
- University of Rochester Medical Center, School of Medicine and Dentistry, Rochester, New York, USA
| | - Aniko Marshall
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, USA
| | - Mark D Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, USA.
- Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, USA.
- State University of New York Eye Institute, University at Buffalo: The State University of New York, Buffalo, New York, USA.
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23
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Parker MD. Mouse models of SLC4-linked disorders of HCO 3--transporter dysfunction. Am J Physiol Cell Physiol 2018; 314:C569-C588. [PMID: 29384695 DOI: 10.1152/ajpcell.00301.2017] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The SLC4 family Cl-/[Formula: see text] cotransporters (NBCe1, NBCe2, NBCn1, and NBCn2) contribute to a variety of vital physiological processes including pH regulation and epithelial fluid secretion. Accordingly, their dysfunction can have devastating effects. Disorders such as epilepsy, hemolytic anemia, glaucoma, hearing loss, osteopetrosis, and renal tubular acidosis are all genetically linked to SLC4-family gene loci. This review summarizes how studies of Slc4-modified mice have enhanced our understanding of the etiology of SLC4-linked pathologies and the interpretation of genetic linkage studies. The review also surveys the novel disease signs exhibited by Slc4-modified mice which could either be considered to presage their description in humans, or to highlight interspecific differences. Finally, novel Slc4-modified mouse models are proposed, the study of which may further our understanding of the basis and treatment of SLC4-linked disorders of [Formula: see text]-transporter dysfunction.
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Affiliation(s)
- Mark D Parker
- Department of Physiology and Biophysics, The State University of New York: The University at Buffalo , Buffalo, New York.,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York , Buffalo, New York.,State University of New York Eye Institutes, University at Buffalo: The State University of New York , Buffalo, New York
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Berend K. Review of the Diagnostic Evaluation of Normal Anion Gap Metabolic Acidosis. KIDNEY DISEASES 2017; 3:149-159. [PMID: 29344509 DOI: 10.1159/000479279] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2017] [Revised: 05/29/2017] [Indexed: 12/29/2022]
Abstract
Background Normal anion gap metabolic acidosis is a common but often misdiagnosed clinical condition associated with diarrhea and renal tubular acidosis (RTA). Early identification of RTA remains challenging for inexperienced physicians, and diagnosis and treatment are often delayed. Summary The presence of RTA should be considered in any patient with a high chloride level when the CL-/Na+ ratio is above 0.79, if the patient does not have diarrhea. In patients with significant hyperkalemia one should evaluate for RTA type 4, especially in diabetic patients, with a relatively conserved renal function. A still growing list of medications can produce RTA. Key Messages This review highlights practical aspects concerning normal anion gap metabolic acidosis.
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Abstract
Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH3 and NH4+, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.
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Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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26
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Lee HW, Handlogten ME, Osis G, Clapp WL, Wakefield DN, Verlander JW, Weiner ID. Expression of sodium-dependent dicarboxylate transporter 1 (NaDC1/SLC13A2) in normal and neoplastic human kidney. Am J Physiol Renal Physiol 2016; 312:F427-F435. [PMID: 27927654 PMCID: PMC5374311 DOI: 10.1152/ajprenal.00559.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 11/15/2016] [Accepted: 12/05/2016] [Indexed: 12/21/2022] Open
Abstract
Regulated dicarboxylate transport is critical for acid-base homeostasis, prevention of calcium nephrolithiasis, regulation of collecting duct sodium chloride transport, and the regulation of blood pressure. Although luminal dicarboxylate reabsorption via NaDC1 (SLC13A2) is believed to be the primary mechanism regulating renal dicarboxylate transport, the specific localization of NaDC1 in the human kidney is currently unknown. This study's purpose was to determine NaDC1's expression in normal and neoplastic human kidneys. Immunoblot analysis demonstrated NaDC1 expression with an apparent molecular weight of ~61 kDa. Immunohistochemistry showed apical NaDC1 immunolabel in the proximal tubule of normal human kidney tissue; well-preserved proximal tubule brush border was clearly labeled. Apical NaDC1 expression was evident throughout the entire proximal tubule, including the initial proximal convoluted tubule, as identified by origination from the glomerular tuft, and extending through the terminal of the proximal tubule, the proximal straight tubule in the outer medulla. We confirmed proximal tubule localization by colocalization with the proximal tubule specific protein, NBCe1. NaDC1 immunolabel was not detected other than in the proximal tubule. In addition, NaDC1 immunolabel was not detected in tumors of presumed proximal tubule origin, clear cell and papillary renal cell carcinoma, or in tumors of nonproximal tubule origin, oncocytoma and chromophobe carcinoma. In summary, 1) in the human kidney, apical NaDC1 immunolabel is present throughout the entire proximal tubule, and is not detectable in other renal cells; and 2) NaDC1 immunolabel is not present in renal tumors. These studies provide important information regarding NaDC1's role in human dicarboxylate metabolism.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - William L Clapp
- Department of Pathology, University of Florida College of Medicine, Gainesville, Florida; and
| | - Dara N Wakefield
- Department of Pathology, University of Florida College of Medicine, Gainesville, Florida; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; .,Nephrology and Hypertension Section, Gainesville Veterans Affairs Medical Center, Gainesville, Florida
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Klootwijk E, Dufek S, Issler N, Bockenhauer D, Kleta R. Pathophysiology, current treatments and future targets in hereditary forms of renal Fanconi syndrome. Expert Opin Orphan Drugs 2016. [DOI: 10.1080/21678707.2017.1259560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
| | - Stephanie Dufek
- Centre for Nephrology, University College London, London, UK
| | - Naomi Issler
- Centre for Nephrology, University College London, London, UK
| | | | - Robert Kleta
- Centre for Nephrology, University College London, London, UK
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Myers EJ, Yuan L, Felmlee MA, Lin YY, Jiang Y, Pei Y, Wang O, Li M, Xing XP, Marshall A, Xia WB, Parker MD. A novel mutant Na + /HCO3 - cotransporter NBCe1 in a case of compound-heterozygous inheritance of proximal renal tubular acidosis. J Physiol 2016; 594:6267-6286. [PMID: 27338124 DOI: 10.1113/jp272252] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/08/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The inheritance of two defective alleles of SLC4A4, the gene that encodes the widely-expressed electrogenic sodium bicarbonate cotransporter NBCe1, results in the bicarbonate-wasting disease proximal renal tubular acidosis (pRTA). In the present study, we report the first case of compound-heterozygous inheritance of pRTA (p.Arg510His/p.Gln913Arg) in an individual with low blood pH, blindness and neurological signs that resemble transient ischaemic attacks. We employ fluorescence microscopy on non-polarized (human embryonic kidney) and polarized (Madin-Darby canine kidney) renal cell lines and electrophysiology on Xenopus oocytes to characterize the mutant transporters (R510H and Q913R). Both mutant transporters exhibit enhanced intracellular retention in renal cells, an observation that probably explains the HCO3- transport deficit in the individual. Both mutants retain a close-to-normal per molecule Na+ /HCO3- cotransport activity in Xenopus oocytes, suggesting that they are suitable candidates for folding-correction therapy. However, Q913R expression is uniquely associated with a depolarizing, HCO3- independent, Cl- -conductance in oocytes that could have pathological consequences if expressed in the cells of patients. ABSTRACT Proximal renal tubular acidosis (pRTA) is a rare, recessively-inherited disease characterized by abnormally acidic blood, blindness, as well as below average height and weight. pRTA is typically associated with homozygous mutation of the solute carrier 4 family gene SLC4A4. SLC4A4 encodes the electrogenic sodium bicarbonate cotransporter NBCe1, a membrane protein that acts to maintain intracellular and plasma pH. We present the first description of a case of compound-heterozygous inheritance of pRTA. The individual has inherited two mutations in NBCe1: p.Arg510His (R510H) and p.Gln913Arg (Q913R), one from each parent. In addition to the usual features of pRTA, the patient exhibits unusual signs, such as muscle spasms and fever. We have recreated these mutant transporters for expression in model systems. We find that both of the mutant proteins exhibit substantial intracellular retention when expressed in mammalian renal cell lines. When expressed in Xenopus oocytes, we find that the R510H and Q913R-mutant NBCe1 molecules exhibit apparently normal Na+ /HCO3- cotransport activity but that Q913R is associated with an unusual HCO3- independent anion-leak. We conclude that a reduced accumulation of NBCe1 protein in the basolateral membrane of proximal-tubule epithelia is the most probable cause of pRTA in this case. We further note that the Q913R-associated anion-leak could itself be pathogenic if expressed in the plasma membrane of mammalian cells, compromising the benefit of strategies aiming to enhance mutant NBCe1 accumulation in the plasma membrane.
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Affiliation(s)
- Evan J Myers
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Lu Yuan
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Melanie A Felmlee
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.,Department of Pharmaceutics and Medicinal Chemistry, Thomas J. Long School of Pharmacy and Health Sciences, University of the Pacific, Stockton, California, USA
| | - Yuan-Yuan Lin
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yan Jiang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yu Pei
- Department of Endocrinology, Chinese People's Army General Hospital, Beijing, China
| | - Ou Wang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Mei Li
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Xiao-Ping Xing
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Aniko Marshall
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Wei-Bo Xia
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
| | - Mark D Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,State University of New York Eye Institutes, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.
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29
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Chronic Metabolic Acidosis Activates Renal Tubular Sodium Chloride Cotransporter through Angiotension II-dependent WNK4-SPAK Phosphorylation Pathway. Sci Rep 2016; 6:18360. [PMID: 26728390 PMCID: PMC4700450 DOI: 10.1038/srep18360] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 11/16/2015] [Indexed: 12/30/2022] Open
Abstract
The mechanism by which chronic metabolic acidosis (CMA) regulates sodium (Na(+))-chloride (Cl(-)) cotransporter (NCC) in the renal distal convoluted tubules remains unexplored. We examined the role of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and with-no-lysine kinase 4 (WNK4) on expression of NCC in mouse models of CMA. CMA was induced by NH4Cl in wild type mice (WTA mice), SPAK, and WNK4 knockout mice. The quantities of Ncc mRNA, expression of total NCC, phosphorylated (p)-NCC, SPAK and WNK4 in the kidneys as well as NCC inhibition with hydrochlorothiazide and Na(+) balance were evaluated. Relative to WT mice, WTA mice had similar levels of Ncc mRNA, but increased expression of total and p-NCC, SPAK, and WNK4 and an exaggerated response to hydrochlorothiazide which could not be observed in SPAK or WNK4 knockout mice with CMA. In WTA mice, increased plasma renin activity, aldosterone and angiotensin II concentrations accompanied by a significantly negative Na(+) balance. High Na(+) diet abolished the enhanced NCC expression in WTA mice. Furthermore, an angiotensin II type 1 receptor blocker rather than a mineralocorticoid receptor antagonist exerted a marked inhibition on Na(+) reabsorption and NCC phosphorylation in WTA mice. CMA increases WNK4-SPAK-dependent NCC phosphorylation and appears to be secondary to previous natriuresis with volume-dependent angiotensin II activation.
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30
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Handlogten ME, Osis G, Lee HW, Romero MF, Verlander JW, Weiner ID. NBCe1 expression is required for normal renal ammonia metabolism. Am J Physiol Renal Physiol 2015; 309:F658-66. [PMID: 26224717 PMCID: PMC4593816 DOI: 10.1152/ajprenal.00219.2015] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 07/26/2015] [Indexed: 11/22/2022] Open
Abstract
The mechanisms regulating proximal tubule ammonia metabolism are incompletely understood. The present study addressed the role of the proximal tubule basolateral electrogenic Na(+)-coupled bicarbonate cotransporter (NBCe1; Slc4a4) in renal ammonia metabolism. We used mice with heterozygous and homozygous NBCe1 gene deletion and compared these mice with their wild-type littermates. Because homozygous NBCe1 gene deletion causes 100% mortality before day 25, we studied mice at day 8 (±1 day). Both heterozygous and homozygous gene deletion caused a gene dose-related decrease in serum bicarbonate. The ability to lower urinary pH was intact, and even accentuated, with NBCe1 deletion. However, in contrast to the well-known effect of metabolic acidosis to increase urinary ammonia excretion, NBCe1 deletion caused a gene dose-related decrease in ammonia excretion. There was no identifiable change in proximal tubule structure by light microscopy. Examination of proteins involved in renal ammonia metabolism showed decreased expression of phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase, key enzymes in proximal tubule ammonia generation, and increased expression of glutamine synthetase, which recycles intrarenal ammonia and regenerates glutamine. Expression of key proteins involved in ammonia transport outside of the proximal tubule (rhesus B glycoprotein and rhesus C glycoprotein) was not significantly changed by NBCe1 deletion. We conclude from these findings that NBCe1 expression is necessary for normal proximal tubule ammonia metabolism.
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Affiliation(s)
- Mary E Handlogten
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hyun-Wook Lee
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Michael F Romero
- Department of Physiology and Biomedical Engineering and Nephrology and Hypertension, Mayo Clinic College Of Medicine, Rochester, Minnesota; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; Nephrology and Hypertension Section, Gainesville Veterans Administration Medical Center, Gainesville, Florida
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31
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Abstract
Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family.
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Affiliation(s)
- Christian Aalkjaer
- Department of Biomedicine, and the Water and Salt Research Center, Aarhus University, Aarhus, Denmark; Department of Physiology, Emory University School of Medicine, Atlanta, USA
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Gill HS, Choi KY, Kammili L, Popratiloff A. Rescue of the temperature-sensitive, autosomal-recessive mutation R298S in the sodium-bicarbonate cotransporter NBCe1-A characterized by a weakened dimer and abnormal aggregation. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1850:1286-96. [PMID: 25743102 PMCID: PMC4424423 DOI: 10.1016/j.bbagen.2015.02.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 02/15/2015] [Accepted: 02/23/2015] [Indexed: 01/17/2023]
Abstract
BACKGROUND Band keratopathy, an ocular disease that is characterized by hypercalcemia and opaque bands across the cornea, has been associated with kidney disease. Type-II renal tubular acidosis (RTA), a condition in which the kidneys fail to recover bicarbonate (HCO3-) in the proximal tubule of the nephron, results in HCO3- wastage in the urine and low blood pH. The development of these diseases is associated with autosomal-recessive mutations in the Na+-coupled HCO3- cotransporter NBCe1-A located at the basolateral membranes of either cell type. METHODS We provide insight into the devastating R298S mutation found in type-II RTA-afflicted individuals using confocal-microscopy imaging of fluorescently-tagged NBCe1-A and NBCe1-A-R298S molecules expressed in human corneal endothelial and proximal tubule cells and from in-depth biophysical studies of their cytoplasmic N-terminal domains (Nt and Nt-R298S), including Nt crystal structure, melting-temperature, and homodimer dissociation constant (KD) analyses. RESULTS We illuminate and rescue trafficking defects of the R298S mutation of NBCe1-A. The KD for Nt monomer-dimer equilibrium is established. The KD for Nt-R298S is significantly higher, but immeasurable due to environmental factors (pH, temperature, concentration) that result in dimer instability leading to precipitation. The crystal structure of Nt-dimer shows that R298 is part of a putative substrate conduit and resides near the dimer interface held together by hydrogen-bond networks. CONCLUSIONS The R298S is a temperature-sensitive mutation in Nt that results in instability of the colloidal system leading to abnormal aggregation. GENERAL SIGNIFICANCE Our findings provide new perspectives to the aberrant mechanism of certain ocular pathologies and type-II RTA associated with the R298S mutation.
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Affiliation(s)
- Harindarpal S Gill
- Department of Medicine, The George Washington University; Division of Renal & Hypertension, The GW Medical Faculty Associates, 2300 I (eye) Street NW, Ross Hall Room 436B, Washington D.C. 20052, United States.
| | - Kun-Young Choi
- Department of Medicine, The George Washington University; Division of Renal & Hypertension, The GW Medical Faculty Associates, 2300 I (eye) Street NW, Ross Hall Room 436B, Washington D.C. 20052, United States
| | - Lakshmi Kammili
- Department of Medicine, The George Washington University; Division of Renal & Hypertension, The GW Medical Faculty Associates, 2300 I (eye) Street NW, Ross Hall Room 436B, Washington D.C. 20052, United States
| | - Anastas Popratiloff
- Department of Medicine, The George Washington University; Division of Renal & Hypertension, The GW Medical Faculty Associates, 2300 I (eye) Street NW, Ross Hall Room 436B, Washington D.C. 20052, United States
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Ruffin VA, Salameh AI, Boron WF, Parker MD. Intracellular pH regulation by acid-base transporters in mammalian neurons. Front Physiol 2014; 5:43. [PMID: 24592239 PMCID: PMC3923155 DOI: 10.3389/fphys.2014.00043] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 01/23/2014] [Indexed: 12/22/2022] Open
Abstract
Intracellular pH (pHi) regulation in the brain is important in both physiological and physiopathological conditions because changes in pHi generally result in altered neuronal excitability. In this review, we will cover 4 major areas: (1) The effect of pHi on cellular processes in the brain, including channel activity and neuronal excitability. (2) pHi homeostasis and how it is determined by the balance between rates of acid loading (JL) and extrusion (JE). The balance between JE and JL determine steady-state pHi, as well as the ability of the cell to defend pHi in the face of extracellular acid-base disturbances (e.g., metabolic acidosis). (3) The properties and importance of members of the SLC4 and SLC9 families of acid-base transporters expressed in the brain that contribute to JL (namely the Cl-HCO3 exchanger AE3) and JE (the Na-H exchangers NHE1, NHE3, and NHE5 as well as the Na+- coupled HCO3− transporters NBCe1, NBCn1, NDCBE, and NBCn2). (4) The effect of acid-base disturbances on neuronal function and the roles of acid-base transporters in defending neuronal pHi under physiopathologic conditions.
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Affiliation(s)
- Vernon A Ruffin
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Ahlam I Salameh
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Mark D Parker
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
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Seidowsky A, Moulonguet-Doleris L, Hanslik T, Yattara H, Ayari H, Rouveix E, Massy ZA, Prinseau J. [Tubular renal acidosis]. Rev Med Interne 2013; 35:45-55. [PMID: 24070792 DOI: 10.1016/j.revmed.2013.08.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 07/25/2013] [Accepted: 08/17/2013] [Indexed: 11/30/2022]
Abstract
Renal tubular acidosis (RTAs) are a group of metabolic disorders characterized by metabolic acidosis with normal plasma anion gap. There are three main forms of RTA: a proximal RTA called type II and a distal RTA (type I and IV). The RTA type II is a consequence of the inability of the proximal tubule to reabsorb bicarbonate. The distal RTA is associated with the inability to excrete the daily acid load and may be associated with hyperkalaemia (type IV) or hypokalemia (type I). The most common etiology of RTA type IV is the hypoaldosteronism. The RTAs can be complicated by nephrocalcinosis and obstructive nephrolithiasis. Alkalinization is the cornerstone of treatment.
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Affiliation(s)
- A Seidowsky
- Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France; Service de médecine interne, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France; Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France.
| | - L Moulonguet-Doleris
- Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - T Hanslik
- Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France; Service de médecine interne, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - H Yattara
- Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - H Ayari
- Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - E Rouveix
- Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France; Service de médecine interne, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - Z A Massy
- Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France; Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
| | - J Prinseau
- Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France; Service de néphrologie, hôpital Ambroise-Paré, AP-HP, 92104 Boulogne-Billancourt cedex, France
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35
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Romero MF, Chen AP, Parker MD, Boron WF. The SLC4 family of bicarbonate (HCO₃⁻) transporters. Mol Aspects Med 2013; 34:159-82. [PMID: 23506864 DOI: 10.1016/j.mam.2012.10.008] [Citation(s) in RCA: 236] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Accepted: 08/28/2012] [Indexed: 01/13/2023]
Abstract
The SLC4 family consists of 10 genes (SLC4A1-5; SLC4A7-11). All encode integral membrane proteins with very similar hydropathy plots-consistent with 10-14 transmembrane segments. Nine SLC4 members encode proteins that transport HCO3(-) (or a related species, such as CO3(2-)) across the plasma membrane. Functionally, eight of these proteins fall into two major groups: three Cl-HCO3 exchangers (AE1-3) and five Na(+)-coupled HCO3(-) transporters (NBCe1, NBCe2, NBCn1, NBCn2, NDCBE). Two of the Na(+)-coupled transporters (NBCe1, NBCe2) are electrogenic; the other three Na(+)-coupled HCO3(-) transporters and all three AEs are electroneutral. In addition, two other SLC4 members (AE4, SLC4A9 and BTR1, SLC4A11) do not yet have a firmly established function. Most, though not all, SLC4 members are functionally inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS). SLC4 proteins play important roles many modes of acid-base homeostasis: the carriage of CO2 by erythrocytes, the transport of H(+) or HCO3(-) by several epithelia, as well as the regulation of cell volume and intracellular pH.
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Affiliation(s)
- Michael F Romero
- Physiology & Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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Haque SK, Ariceta G, Batlle D. Proximal renal tubular acidosis: a not so rare disorder of multiple etiologies. Nephrol Dial Transplant 2013; 27:4273-87. [PMID: 23235953 PMCID: PMC3616759 DOI: 10.1093/ndt/gfs493] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Proximal renal tubular acidosis (RTA) (Type II RTA) is characterized by a defect in the ability to reabsorb HCO3 in the proximal tubule. This is usually manifested as bicarbonate wastage in the urine reflecting that the defect in proximal tubular transport is severe enough that the capacity for bicarbonate reabsorption in the thick ascending limb of Henle's loop and more distal nephron segments is overwhelmed. More subtle defects in proximal bicarbonate transport likely go clinically unrecognized owing to compensatory reabsorption of bicarbonate distally. Inherited proximal RTA is more commonly autosomal recessive and has been associated with mutations in the basolateral sodium-bicarbonate cotransporter (NBCe1). Mutations in this transporter lead to reduced activity and/or trafficking, thus disrupting the normal bicarbonate reabsorption process of the proximal tubules. As an isolated defect for bicarbonate transport, proximal RTA is rare and is more often associated with the Fanconi syndrome characterized by urinary wastage of solutes like phosphate, uric acid, glucose, amino acids, low-molecular-weight proteins as well as bicarbonate. A vast array of rare tubular disorders may cause proximal RTA but most commonly it is induced by drugs. With the exception of carbonic anhydrase inhibitors which cause isolated proximal RTA, drug-induced proximal RTA is associated with Fanconi syndrome. Drugs that have been recently recognized to cause severe proximal RTA with Fanconi syndrome include ifosfamide, valproic acid and various antiretrovirals such as Tenofovir particularly when given to human immunodeficiency virus patients receiving concomitantly protease inhibitors such as ritonavir or reverse transcriptase inhibitors such as didanosine.
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Affiliation(s)
- Syed K Haque
- Division of Nephrology/Hypertension, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
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Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
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Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
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Wrong OM, Unwin RJ. Renal tubular acidosis: ‘RTA is no accident’. Clin Med (Lond) 2012. [DOI: 10.7861/clinmedicine.12-6-s22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Al-Haggar M. Fanconi-Bickel syndrome as an example of marked allelic heterogeneity. World J Nephrol 2012; 1:63-8. [PMID: 24175243 PMCID: PMC3782201 DOI: 10.5527/wjn.v1.i3.63] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/26/2011] [Revised: 05/25/2012] [Accepted: 06/01/2012] [Indexed: 02/06/2023] Open
Abstract
Renal tubular acidosis (RTA) encompasses many renal tubular disorders characterized by hyperchloremic metabolic acidosis with a normal anion gap. Untreated patients usually complain of growth failure, osteoporosis, rickets, nephrolithiasis and eventually renal insufficiency. Fanconi-Bickel syndrome (FBS) is an example of proximal RTA due to a single gene disorder; it is caused by defects in the facilitative glucose transporter 2 gene that codes for the glucose transporter protein 2 expressed in hepatocytes, pancreatic β-cells, enterocytes and renal tubular cells. It is a rare inherited disorder of carbohydrate metabolism manifested by huge hepatomegaly [hence it is classified as glycogen storage disease (GSD) type XI; GSD XI], severe hypophosphatemic rickets and failure to thrive due to proximal renal tubular dysfunction leading to glucosuria, phosphaturia, generalized aminoaciduria, bicarbonate wasting and hypophosphatemia. The disorder has been reported from all parts of Europe, Turkey, Israel, Arabian countries, Japan and North America. Many mutant alleles have been described, its exact frequency is unknown and there is no single mutation found more frequently than the others. The presence of consanguinity in affected families suggests an autosomal recessive pattern of inheritance. New cases of FBS have been recently reported in the Middle and Far East in collaboration with specialized centers. Two novel mutations have been discovered in two unrelated Egyptian families. The first was two bases deletion, guanine and adenine, (c.253_254delGA) causing a frameshift mutation (p. Glu85fs) and the second is mutation in exon6 in splicing acceptor site with intron5 (c.776-1G>C or IVS5-1G>A). Moreover, a new different mutation was described in a 3 year old Indian boy.
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Affiliation(s)
- Mohammad Al-Haggar
- Mohammad Al-Haggar, Pediatrics and Genetics, Mansoura University Children's Hospital, 35516 Mansoura, Egypt
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Kraut JA, Madias NE. Differential diagnosis of nongap metabolic acidosis: value of a systematic approach. Clin J Am Soc Nephrol 2012; 7:671-9. [PMID: 22403272 DOI: 10.2215/cjn.09450911] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Nongap metabolic acidosis is a common form of both acute and chronic metabolic acidosis. Because derangements in renal acid-base regulation are a common cause of nongap metabolic acidosis, studies to evaluate renal acidification often serve as the mainstay of differential diagnosis. However, in many cases, information obtained from the history and physical examination, evaluation of the electrolyte pattern (to determine if a nongap acidosis alone or a combined nongap and high anion gap metabolic acidosis is present), and examination of the serum potassium concentration (to characterize the disorder as hyperkalemic or hypokalemic in nature) is sufficient to make a presumptive diagnosis without more sophisticated studies. If this information proves insufficient, indirect estimates or direct measurement of urinary NH(4)(+) concentration, measurement of urine pH, and assessment of urinary HCO(3)(-) excretion can help in establishing the diagnosis. This review summarizes current information concerning the pathophysiology of this electrolyte pattern and the value and limitations of all of the diagnostic studies available. It also provides a systematic and cost-effective approach to the differential diagnosis of nongap metabolic acidosis.
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Affiliation(s)
- Jeffrey A Kraut
- Medical and Research Services, Veterans Administration Greater Los Angeles Healthcare System, California 90073, USA.
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Pereira PCB, Miranda DM, Oliveira EA, Silva ACSE. Molecular pathophysiology of renal tubular acidosis. Curr Genomics 2011; 10:51-9. [PMID: 19721811 PMCID: PMC2699831 DOI: 10.2174/138920209787581262] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2008] [Revised: 11/08/2008] [Accepted: 11/12/2008] [Indexed: 01/09/2023] Open
Abstract
Renal tubular acidosis (RTA) is characterized by metabolic acidosis due to renal impaired acid excretion. Hyperchloremic acidosis with normal anion gap and normal or minimally affected glomerular filtration rate defines this disorder. RTA can also present with hypokalemia, medullary nephrocalcinosis and nephrolitiasis, as well as growth retardation and rickets in children, or short stature and osteomalacia in adults. In the past decade, remarkable progress has been made in our understanding of the molecular pathogenesis of RTA and the fundamental molecular physiology of renal tubular transport processes. This review summarizes hereditary diseases caused by mutations in genes encoding transporter or channel proteins operating along the renal tubule. Review of the molecular basis of hereditary tubulopathies reveals various loss-of-function or gain-of-function mutations in genes encoding cotransporter, exchanger, or channel proteins, which are located in the luminal, basolateral, or endosomal membranes of the tubular cell or in paracellular tight junctions. These gene mutations result in a variety of functional defects in transporter/channel proteins, including decreased activity, impaired gating, defective trafficking, impaired endocytosis and degradation, or defective assembly of channel subunits. Further molecular studies of inherited tubular transport disorders may shed more light on the molecular pathophysiology of these diseases and may significantly improve our understanding of the mechanisms underlying renal salt homeostasis, urinary mineral excretion, and blood pressure regulation in health and disease. The identification of the molecular defects in inherited tubulopathies may provide a basis for future design of targeted therapeutic interventions and, possibly, strategies for gene therapy of these complex disorders.
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Affiliation(s)
- P C B Pereira
- Pediatric Nephrology Unit, Department of Pediatrics, School of Medicine - Federal University of Minas Gerais (UFMG), Belo Horizonte, MG, Brazil
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Abstract
Renal tubular acidosis (RTA) is a group of disorders observed in patients with normal anion gap metabolic acidosis. There are three major forms of RTA: A proximal (type II) RTA and two types of distal RTAs (type I and type IV). Proximal (type II) RTA originates from the inability to reabsorb bicarbonate normally in the proximal tubule. Type I RTA is associated with inability to excrete the daily acid load and may present with hyperkalaemia or hypokalaemia. The most prominent abnormality in type IV RTA is hyperkalaemia caused by hypoaldosteronism. This article extensively reviews the mechanism of hydrogen ion generation from metabolism of normal diet and various forms of RTA leading to disruptions of normal acid-base handling by the kidneys.
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Affiliation(s)
- P Reddy
- Department of Medicine, University of Florida College of Medicine, Jacksonville, FL 32209, USA.
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Severe metabolic acidosis causes early lethality in NBC1 W516X knock-in mice as a model of human isolated proximal renal tubular acidosis. Kidney Int 2011; 79:730-41. [PMID: 21228764 DOI: 10.1038/ki.2010.523] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We have identified a novel homozygous nonsense mutation (W516X) in the kidney-type electrogenic sodium bicarbonate cotransporter 1 (NBC1) in a patient with isolated proximal renal tubular acidosis (pRTA). To specifically address the pathogenesis of this mutation, we created NBC1 W516X knock-in mice to match the patient's abnormalities. The expression of NBC1 mRNA and protein in the kidneys of NBC1(W516X/W516X) mice were virtually absent, indicating that nonsense-mediated mRNA decay (NMD) is involved in the defective transcription and translation of this mutation. These mice not only recapitulated the phenotypes of this patient with growth retardation, pRTA, and ocular abnormalities, but also showed anemia, volume depletion, prerenal azotemia, and several organ abnormalities, culminating in dehydration and renal failure with early lethality before weaning. In isolated renal proximal tubules, both NBC1 activity and the rate of bicarbonate absorption were markedly reduced. Unexpectedly, there was no compensatory increase in mRNA of distal acid/base transporters. Sodium bicarbonate but not saline administration to these mutant mice markedly prolonged their survival, decreased their protein catabolism and attenuated organ abnormalities. The prolonged survival time uncovered the development of corneal opacities due to corneal edema. Thus, NBC1(W516X/W516X) mice with pRTA represent an animal model for metabolic acidosis and may be useful for testing therapeutic inhibition of NMD in vivo.
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Sieprath U, Lampen M, Firschke C. [45-year-old woman with muscle weakness and hypopotassemia]. Internist (Berl) 2010; 52:441-4. [PMID: 20941474 DOI: 10.1007/s00108-010-2666-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report a 45-year-old female patient with muscle weakness. We diagnosed renal tubular acidosis type I by laboratory findings of hypopotassemia, hypopotassuria, metabolic acidosis and basic urine. The muscle weakness improved rapidly by substitution of potassium and an alcalescent substance. Searching for associated autoimmune diseases we diagnosed primary biliary cirrhosis and initiated a therapy with ursodeoxycholic acid.
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Affiliation(s)
- U Sieprath
- Innere Abteilung, Ilmtalklinik GmbH, Pfaffenhofen a. d. Ilm.
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Sussman CR, Zhao J, Plata C, Lu J, Daly C, Angle N, DiPiero J, Drummond IA, Liang JO, Boron WF, Romero MF, Chang MH. Cloning, localization, and functional expression of the electrogenic Na+ bicarbonate cotransporter (NBCe1) from zebrafish. Am J Physiol Cell Physiol 2009; 297:C865-75. [PMID: 19625604 DOI: 10.1152/ajpcell.00679.2008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutations in the electrogenic Na+/nHCO3- cotransporter (NBCe1, SLC4A4) cause severe proximal renal tubular acidosis, glaucoma, and cataracts in humans, indicating NBCe1 has a critical role in acid-base homeostasis and ocular fluid transport. To better understand the homeostatic roles and protein ontogeny of NBCe1, we have cloned, localized, and downregulated NBCe1 expression in zebrafish, and examined its transport characteristics when expressed in Xenopus oocytes. Zebrafish NBCe1 (zNBCe1) is 80% identical to published mammalian NBCe1 cDNAs. Like other fish NBCe1 clones, zebrafish NBCe1 is most similar to the pancreatic form of mammalian NBC (Slc4a4-B) but appears to be the dominant isoform found in zebrafish. In situ hybridization of embryos demonstrated mRNA expression in kidney pronephros and eye by 24 h postfertilization (hpf) and gill and brain by 120 hpf. Immunohistochemical labeling demonstrated expression in adult zebrafish eye and gill. Morpholino knockdown studies demonstrated roles in eye and brain development and caused edema, indicating altered fluid and electrolyte balance. With the use of microelectrodes to measure membrane potential (Vm), voltage clamp (VC), intracellular pH (pH(i)), or intracellular Na+ activity (aNa(i)), we examined the function of zNBCe1 expressed in Xenopus oocytes. Zebrafish NBCe1 shared transport properties with mammalian NBCe1s, demonstrating electrogenic Na+ and HCO3- transport as well as similar drug sensitivity, including inhibition by 4,4'-diiso-thiocyano-2,2'-disulfonic acid stilbene and tenidap. These data indicate that NBCe1 in zebrafish shares many characteristics with mammalian NBCe1, including tissue distribution, importance in systemic water and electrolyte balance, and electrogenic transport of Na+ and HCO3-. Thus zebrafish promise to be useful model system for studies of NBCe1 physiology.
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Affiliation(s)
- Caroline R Sussman
- Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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Zietse R, Zoutendijk R, Hoorn EJ. Fluid, electrolyte and acid–base disorders associated with antibiotic therapy. Nat Rev Nephrol 2009; 5:193-202. [DOI: 10.1038/nrneph.2009.17] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Function and dysfunction of the PI system in membrane trafficking. EMBO J 2008; 27:2457-70. [PMID: 18784754 PMCID: PMC2536629 DOI: 10.1038/emboj.2008.169] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Accepted: 08/05/2008] [Indexed: 02/01/2023] Open
Abstract
The phosphoinositides (PIs) function as efficient and finely tuned switches that control the assembly–disassembly cycles of complex molecular machineries with key roles in membrane trafficking. This important role of the PIs is mainly due to their versatile nature, which is in turn determined by their fast metabolic interconversions. PIs can be tightly regulated both spatially and temporally through the many PI kinases (PIKs) and phosphatases that are distributed throughout the different intracellular compartments. In spite of the enormous progress made in the past 20 years towards the definition of the molecular details of PI–protein interactions and of the regulatory mechanisms of the individual PIKs and phosphatases, important issues concerning the general principles of the organisation of the PI system and the coordination of the different PI-metabolising enzymes remain to be addressed. The answers should come from applying a systems biology approach to the study of the PI system, through the integration of analyses of the protein interaction data of the PI enzymes and the PI targets with those of the ‘phenomes' of the genetic diseases that involve these PI-metabolising enzymes.
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Abstract
PURPOSE OF REVIEW Metabolic acidosis is a severe disturbance of extracellular pH homeostasis that can be caused both by inborn or acquired defects in renal acid excretion or metabolic acid production. Chronic metabolic acidosis causes osteomalacia with nephrocalcinosis and urolithiasis. In the setting of end-stage renal disease, metabolic acidosis is often associated with increased peripheral insulin resistance, and represents an additional independent morbidity risk factor. This review summarizes recent insight, gained primarily from mouse models, into the mechanisms whereby the kidney regulates and adapts acid excretion. RECENT FINDINGS Human genetics and various mouse models have shed new light on mechanisms that contribute to the kidney's ability to excrete acid and adapt appropriately to metabolism. Progress in four specific areas will be highlighted: mechanisms contributing to the synthesis and excretion of ammonia; insights into adaptive processes during acidosis; mechanisms by which the kidney may sense acidosis; and the pathophysiology of acquired and inborn errors of renal acid handling. SUMMARY Genetic mouse models and various messenger RNA and proteome profiling and screening technologies demonstrate the importance of various acid-base transporting proteins and a metabolic and regulatory network that contributes to the kidney's ability to maintain the systemic acid-base balance.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology and Zurich Center for Human Integrative Physiology (ZIHP), University of Zurich, Zurich, Switzerland.
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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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