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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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2
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Lacruz RS, Habelitz S, Wright JT, Paine ML. DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE. Physiol Rev 2017; 97:939-993. [PMID: 28468833 DOI: 10.1152/physrev.00030.2016] [Citation(s) in RCA: 223] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 01/10/2017] [Accepted: 01/10/2017] [Indexed: 12/16/2022] Open
Abstract
Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.
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Affiliation(s)
- Rodrigo S Lacruz
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - Stefan Habelitz
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - J Timothy Wright
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - Michael L Paine
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
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3
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Alexander RT, Cordat E, Chambrey R, Dimke H, Eladari D. Acidosis and Urinary Calcium Excretion: Insights from Genetic Disorders. J Am Soc Nephrol 2016; 27:3511-3520. [PMID: 27468975 DOI: 10.1681/asn.2016030305] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabolic acidosis is associated with increased urinary calcium excretion and related sequelae, including nephrocalcinosis and nephrolithiasis. The increased urinary calcium excretion induced by metabolic acidosis predominantly results from increased mobilization of calcium out of bone and inhibition of calcium transport processes within the renal tubule. The mechanisms whereby acid alters the integrity and stability of bone have been examined extensively in the published literature. Here, after briefly reviewing this literature, we consider the effects of acid on calcium transport in the renal tubule and then discuss why not all gene defects that cause renal tubular acidosis are associated with hypercalciuria and nephrocalcinosis.
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Affiliation(s)
- R Todd Alexander
- Departments of Pediatrics and .,Physiology, University of Alberta, Edmonton, Canada
| | | | - Régine Chambrey
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark; and
| | - Dominique Eladari
- Institut National de la Santé et de la Recherche Médicale U970, Paris Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.,Department of Physiologie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France
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4
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Drug-induced acid-base disorders. Pediatr Nephrol 2015; 30:1407-23. [PMID: 25370778 DOI: 10.1007/s00467-014-2958-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2014] [Revised: 08/28/2014] [Accepted: 09/03/2014] [Indexed: 10/24/2022]
Abstract
The incidence of acid-base disorders (ABDs) is high, especially in hospitalized patients. ABDs are often indicators for severe systemic disorders. In everyday clinical practice, analysis of ABDs must be performed in a standardized manner. Highly sensitive diagnostic tools to distinguish the various ABDs include the anion gap and the serum osmolar gap. Drug-induced ABDs can be classified into five different categories in terms of their pathophysiology: (1) metabolic acidosis caused by acid overload, which may occur through accumulation of acids by endogenous (e.g., lactic acidosis by biguanides, propofol-related syndrome) or exogenous (e.g., glycol-dependant drugs, such as diazepam or salicylates) mechanisms or by decreased renal acid excretion (e.g., distal renal tubular acidosis by amphotericin B, nonsteroidal anti-inflammatory drugs, vitamin D); (2) base loss: proximal renal tubular acidosis by drugs (e.g., ifosfamide, aminoglycosides, carbonic anhydrase inhibitors, antiretrovirals, oxaliplatin or cisplatin) in the context of Fanconi syndrome; (3) alkalosis resulting from acid and/or chloride loss by renal (e.g., diuretics, penicillins, aminoglycosides) or extrarenal (e.g., laxative drugs) mechanisms; (4) exogenous bicarbonate loads: milk-alkali syndrome, overshoot alkalosis after bicarbonate therapy or citrate administration; and (5) respiratory acidosis or alkalosis resulting from drug-induced depression of the respiratory center or neuromuscular impairment (e.g., anesthetics, sedatives) or hyperventilation (e.g., salicylates, epinephrine, nicotine).
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5
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Kurtz I. NBCe1 as a model carrier for understanding the structure-function properties of Na⁺ -coupled SLC4 transporters in health and disease. Pflugers Arch 2014; 466:1501-16. [PMID: 24515290 DOI: 10.1007/s00424-014-1448-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 01/07/2014] [Accepted: 01/08/2014] [Indexed: 01/17/2023]
Abstract
SLC4 transporters are membrane proteins that in general mediate the coupled transport of bicarbonate (carbonate) and share amino acid sequence homology. These proteins differ as to whether they also transport Na(+) and/or Cl(-), in addition to their charge transport stoichiometry, membrane targeting, substrate affinities, developmental expression, regulatory motifs, and protein-protein interactions. These differences account in part for the fact that functionally, SLC4 transporters have various physiological roles in mammals including transepithelial bicarbonate transport, intracellular pH regulation, transport of Na(+) and/or Cl(-), and possibly water. Bicarbonate transport is not unique to the SLC4 family since the structurally unrelated SLC26 family has at least three proteins that mediate anion exchange. The present review focuses on the first of the sodium-dependent SLC4 transporters that was identified whose structure has been most extensively studied: the electrogenic Na(+)-base cotransporter NBCe1. Mutations in NBCe1 cause proximal renal tubular acidosis (pRTA) with neurologic and ophthalmologic extrarenal manifestations. Recent studies have characterized the important structure-function properties of the transporter and how they are perturbed as a result of mutations that cause pRTA. It has become increasingly apparent that the structure of NBCe1 differs in several key features from the SLC4 Cl(-)-HCO3 (-) exchanger AE1 whose structural properties have been well-studied. In this review, the structure-function properties and regulation of NBCe1 will be highlighted, and its role in health and disease will be reviewed in detail.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, and Brain Research Institute, UCLA, Los Angeles, CA, USA,
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6
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Seki G, Horita S, Suzuki M, Yamazaki O, Usui T, Nakamura M, Yamada H. Molecular mechanisms of renal and extrarenal manifestations caused by inactivation of the electrogenic Na(+)-HCO3 (-) cotransporter NBCe1. Front Physiol 2013; 4:270. [PMID: 24101904 PMCID: PMC3787273 DOI: 10.3389/fphys.2013.00270] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Accepted: 09/10/2013] [Indexed: 11/13/2022] Open
Abstract
The electrogenic Na(+)-HCO3 (-) cotransporter NBCe1 plays an essential role in bicarbonate absorption from renal proximal tubules, but also mediates the other biological processes in extrarenal tissues such as bicarbonate secretion from pancreatic ducts, maintenance of tissue homeostasis in eye, enamel maturation in teeth, or local pH regulation in synapses. Homozygous mutation in NBCe1 cause proximal renal tubular acidosis (pRTA) associated with extrarenal manifestations such as short stature, ocular abnormalities, enamel abnormalities, and migraine. Functional analyses of NBCe1 mutants using different expression systems suggest that at least a 50% reduction of the transport activity may be required to induce severe pRTA. In addition to functional impairments, some NBCe1 mutants show trafficking defects. Some of the pRTA-related NBCe1 mutants showing the cytoplasmic retention have been shown to exert a dominant negative effect through hetero-oligomer complexes with wild-type NBCe1 that may explain the occurrence of extrarenal manifestations in the heterozygous carries of NBCe1 mutations. Both NBCe1 knockout (KO) and W516X knockin (KI) mice showed very severe pRTA and reproduced most of the clinical manifestations observed in human pRTA patients. Functional analysis on isolated renal proximal tubules from W516X KI mice directly confirmed the indispensable role of NBCe1 in bicarbonate absorption from this nephron segment. In this review, we will focus on the molecular mechanisms underling the renal and extrarenal manifestations caused by NBCe1 inactivation.
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Affiliation(s)
- George Seki
- Department of Internal Medicine, School of Medicine, The University of Tokyo Tokyo, Japan
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7
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Abstract
Renal tubular acidosis (RTA) is a group of transport defects in the reabsorption of bicarbonate, the excretion of hydrogen ion (H+), or both, resulting in systemic acidosis and hypokalemia with a normal glomerular filtration rate. Although isolated proximal (type 2) or distal (type 1) tubular pathologies are well characterized, a combined pathology leading to type 3 RTA is very rare. Here, we report a case of type 3 RTA, using an algorithmic approach to classify a scenario of hypokalemic metabolic acidosis in the setting of episodic flaccid paralysis.
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Affiliation(s)
- R P Goswami
- Department of Medicine, Institute of Post Graduate Medical Education and Research and Seth Sukhlal Karnani Hospital, Kolkata, India
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8
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Kao L, Sassani P, Azimov R, Pushkin A, Abuladze N, Peti-Peterdi J, Liu W, Newman D, Kurtz I. Oligomeric structure and minimal functional unit of the electrogenic sodium bicarbonate cotransporter NBCe1-A. J Biol Chem 2008; 283:26782-94. [PMID: 18658147 DOI: 10.1074/jbc.m804006200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The electrogenic sodium bicarbonate cotransporter NBCe1-A mediates the basolateral absorption of sodium and bicarbonate in the proximal tubule. In this study the oligomeric state and minimal functional unit of NBCe1-A were investigated. Wild-type (wt) NBCe1-A isolated from mouse kidney or heterologously expressed in HEK293 cells was predominantly in a dimeric state as was shown using fluorescence energy transfer, pulldown, immunoprecipitation, cross-linking experiments, and nondenaturing perfluorooctanoate-PAGE. NBCe1-A monomers were found to be covalently linked by S-S bonds. When each of the 15 native cysteine residues were individually removed on a wt-NBCe1-A backbone, dimerization of the cotransporter was not affected. In experiments involving multiple native cysteine residue removal, both Cys(630) and Cys(642) in extracellular loop 3 were shown to mediate S-S bond formation between NBCe1-A monomers. When native NBCe1-A cysteine residues were individually reintroduced into a cysteineless NBCe1-A mutant backbone, the finding that a Cys(992) construct that lacked S-S bonds functioned normally indicated that stable covalent linkage of NBCe1-A monomers was not a necessary requirement for functional activity of the cotransporter. Studies using concatameric constructs of wt-NBCe1-A, whose activity is resistant to methanesulfonate reagents, and an NBCe1-A(T442C) mutant, whose activity is completely inhibited by methanesulfonate reagents, confirmed that NBCe1-A monomers are functional. Our results demonstrate that wt-NBCe1-A is predominantly a homodimer, dependent on S-S bond formation that is composed of functionally active monomers.
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Affiliation(s)
- Liyo Kao
- Division of Nephrology, David Geffen School Medicine, UCLA, Los Angeles, California 90095-1689, USA
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9
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Inatomi J, Horita S, Braverman N, Sekine T, Yamada H, Suzuki Y, Kawahara K, Moriyama N, Kudo A, Kawakami H, Shimadzu M, Endou H, Fujita T, Seki G, Igarashi T. Mutational and functional analysis of SLC4A4 in a patient with proximal renal tubular acidosis. Pflugers Arch 2004; 448:438-44. [PMID: 15085340 DOI: 10.1007/s00424-004-1278-1] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2003] [Accepted: 03/11/2004] [Indexed: 11/25/2022]
Abstract
Permanent isolated proximal renal tubular acidosis (pRTA) with ocular abnormalities is a systemic disease with isolated pRTA, short stature and ocular abnormalities. We identified a novel homozygous deletion of nucleotide 2,311 adenine in the kidney type Na+/HCO3- cotransporter (kNBC1) cDNA in a patient with permanent isolated pRTA. This mutation is predicted to result in a frame shift at codon 721 forming a stop codon after 29 amino acids anomalously transcribed from the SLC4A4 gene. Cosegregation of this mutation with the disease was supported by heterozygosity in the parents of the affected patient. The absence of this mutation in 156 alleles of 78 normal individuals indicates that this mutation is related to the disease and is not a common DNA sequence polymorphism. When injected into Xenopus oocytes, the mutant cRNA failed to induce electrogenic transport activity. In addition, immunofluorescence and Western blot analysis failed to detect the expression of the full-length protein in mutant-injected oocytes. Our results expand the spectrum of kNBC1 mutations in permanent isolated pRTA with ocular abnormalities and increase our understanding of the renal tubular mechanism that is essential for acid-base homeostasis.
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Affiliation(s)
- Jun Inatomi
- Department of Pediatrics, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 112-8688, Tokyo, Japan
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10
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Roussa E, Nastainczyk W, Thévenod F. Differential expression of electrogenic NBC1 (SLC4A4) variants in rat kidney and pancreas. Biochem Biophys Res Commun 2004; 314:382-9. [PMID: 14733916 DOI: 10.1016/j.bbrc.2003.12.099] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The purpose of this study was to determine expression and localization of NH(2)-terminal variants of the electrogenic Na(+)-HCO(3)(-) co-transporter NBC1 (SLC4A4) in the rat kidney and pancreas. We generated two anti-peptide antibodies: alpha333 against the "mste" start (kidney; kNBC1) and alpha332 against the "mede" start (pancreas; pNBC1). Transcripts for both NBC1 variants were detected in kidney and pancreas by RT-PCR, though kNBC1 was more prominent in the kidney and pNBC1 was more prominent in the pancreas. Similar protein expression levels were detected by immunoblotting of plasma membranes (PM) from kidney cortex and pancreas. Immunohistochemistry with alpha333 recognized the "mste"-epitope in the basolateral plasma membrane (BLM) of renal proximal tubule. The "mede"-protein (alpha332) was similarly localized although staining was much less and more diffuse. In the pancreas, alpha332 stained BLM of acinar and duct cells. Some isolated duct cells were also stained at the apical PM. The "mste"-protein (alpha333) was absent in acinar cells but was located at the apical PM of duct cells. The data indicate that the two NH(2)-terminal NBC1 variants are co-expressed in kidney and pancreas, where they may contribute to HCO(3)(-) transport and pH regulation.
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Affiliation(s)
- Eleni Roussa
- Department of Neuroanatomy, Center for Anatomy, Georg-August-University Göttingen, D-37075 Göttingen, Germany.
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Satoh H, Moriyama N, Hara C, Yamada H, Horita S, Kunimi M, Tsukamoto K, Iso-O N, Inatomi J, Kawakami H, Kudo A, Endou H, Igarashi T, Goto A, Fujita T, Seki G. Localization of Na+-HCO-3 cotransporter (NBC-1) variants in rat and human pancreas. Am J Physiol Cell Physiol 2003; 284:C729-37. [PMID: 12444017 DOI: 10.1152/ajpcell.00166.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Mutations in Na(+)-HCO(3)(-) cotransporter (NBC-1) cause proximal renal tubular acidosis (pRTA) associated with ocular abnormalities. One pRTA patient had increased serum amylase, suggesting possible evidence of pancreatitis. To further delineate a link between NBC-1 inactivation and pancreatic dysfunction, immunohistochemical analysis was performed on rat and human pancreas using antibodies against kidney-type (kNBC-1) and pancreatic-type (pNBC-1) transporters. In rat pancreas, the anti-pNBC-1 antibody labeled acinar cells and both apical and basolateral membranes of medium and large duct cells. In human pancreas, on the other hand, the anti-pNBC-1 antibody did not label acinar cells, although it did label the basolateral membranes of the entire duct system. The labeling by anti-kNBC-1 antibody was detected in only a limited number of rat pancreatic duct cells. To examine the effects of pRTA-related mutations, R342S and R554H, on pNBC-1 function, we performed functional analysis and found that both mutants had reduced transport activities compared with the wild-type pNBC-1. These results indicate that pNBC-1 is the predominant variant that mediates basolateral HCO(3)(-) uptake into duct cells in both rat and human pancreas. The loss of pNBC-1 function is predicted to have significant impact on overall ductal HCO(3)(-) secretion, which could potentially lead to pancreatic dysfunction.
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Affiliation(s)
- Hiroaki Satoh
- Department of Internal Medicine, Faculty of Medicine, Tokyo University, Japan
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13
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Igarashi T, Sekine T, Inatomi J, Seki G. Unraveling the molecular pathogenesis of isolated proximal renal tubular acidosis. J Am Soc Nephrol 2002; 13:2171-7. [PMID: 12138151 DOI: 10.1097/01.asn.0000025281.70901.30] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Proximal renal tubular acidosis (pRTA) results from an impairment of bicarbonate (HCO(3)(-)) reabsorption in the renal proximal tubules and is characterized by a decreased renal HCO(3)(-) threshold. Proximal RTA most commonly occurs in association with multiple defects of proximal tubular transport (renal Fanconi syndrome). Although much more rare, pRTA may occur without other functional defects in proximal tubules (isolated pRTA). The presenting clinical symptom of isolated pRTA is usually growth retardation in infancy or early childhood. Three categories of isolated pRTA have been identified: (1) autosomal dominant pRTA; (2) autosomal recessive pRTA with ocular abnormalities; and (3) sporadic isolated pRTA. Autosomal dominant and autosomal recessive pRTA are usually permanent; life-long alkali therapy is needed. In contrast, sporadic isolated pRTA is transient; alkali therapy can be discontinued after several years without reappearance of symptoms. Recent genetic studies have begun to elucidate the molecular pathogenesis of inherited isolated pRTA. Studies in knockout mice have identified a candidate gene for autosomal dominant pRTA, SLC9A3, a gene encoding one of the five plasma membrane Na(+)/H(+) exchangers (NHE3). Patients with autosomal recessive pRTA and ocular abnormalities have recently been found to have mutations in the kidney type Na(+)/HCO(3)(-) cotransporter gene (SLC4A4). Identification of these gene mutations provides new insights into the molecular pathogenesis of pRTA.
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Affiliation(s)
- Takashi Igarashi
- Department of Pediatrics and Department of Internal Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
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14
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Deda G, Ekim M, Güven A, Karagöl U, Tümer N. Hypopotassemic paralysis: a rare presentation of proximal renal tubular acidosis. J Child Neurol 2001; 16:770-1. [PMID: 11669354 DOI: 10.1177/088307380101601013] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Neurologic manifestations can accompany systemic diseases, and primary disease can be identified with a careful history, physical examination, and laboratory investigations. A 14-year-old girl with paraplegia and absence of deep tendon reflexes in the lower extremities after 2 days of vomiting and diarrhea was referred to our pediatric neurology department with a diagnosis of Guillain-Barré syndrome. Short stature, dehydration, motor and mental retardation, bilateral cataracts, glaucoma, and band keratopathy were detected on physical examination. Hypopotassemia and severe metabolic acidosis were found on biochemical examination. Her paraplegia improved after appropriate fluid and electrolyte replacement, but metabolic acidosis persisted after cessation of intravenous therapy, and isolated proximal renal tubular acidosis was detected. Because she had isolated proximal renal tubular acidosis and other abnormalities, she was diagnosed with Donckerwolcke-Winsnes syndrome.
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Affiliation(s)
- G Deda
- Department of Pediatric Neurology, Ankara University Faculty of Medicine, Turkey.
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15
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Igarashi T, Inatomi J, Sekine T, Seki G, Shimadzu M, Tozawa F, Takeshima Y, Takumi T, Takahashi T, Yoshikawa N, Nakamura H, Endou H. Novel nonsense mutation in the Na+/HCO3- cotransporter gene (SLC4A4) in a patient with permanent isolated proximal renal tubular acidosis and bilateral glaucoma. J Am Soc Nephrol 2001; 12:713-718. [PMID: 11274232 DOI: 10.1681/asn.v124713] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Permanent isolated proximal renal tubular acidosis (pRTA) with ocular abnormalities is a systemic disease involving short stature, isolated pRTA, mental retardation, and ocular abnormalities. Kidney Na+/HCO3- cotransporter (kNBC1) cDNA from peripheral lymphocytes from a patient with permanent isolated pRTA and bilateral glaucoma was screened, and a novel homozygous mutation, namely a cytosine-to-thymine transition at nucleotide 234, which resulted in the formation of a stop codon at codon 29, was identified. This homozygous mutation, Q29X, was identified in the unique 5'-end of the kNBC1 gene (SLC4A4) of the patient. Cosegregation of this Q29X mutation with the disease and heterozygosity in the parents of the affected patient were observed. The absence of this mutation in 156 alleles from 78 Japanese individuals indicates that this mutation is directly related to the disease and is not a common DNA sequence polymorphism. This nonsense mutation predicts a truncated kNBC1 protein that lacks the 1007 amino acids of the carboxyl-terminus, and the effect on kNBC1 cotransport activity is likely to be a loss of function. In contrast, the pancreatic Na+/HCO3- cotransporter of the patient is not likely to be affected by this nonsense mutation. These results have implications for understanding the role of kNBC1 in the pathophysiologic processes of pRTA associated with ocular abnormalities and mental retardation.
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Affiliation(s)
- Takashi Igarashi
- Department of Pediatrics, Faculty of Medicine, University of Tokyo, Tokyo
| | - Jun Inatomi
- Department of Pharmacology and Toxicology, Kyourin University School of Medicine, Tokyo
| | - Takashi Sekine
- Department of Pediatrics, Faculty of Medicine, University of Tokyo, Tokyo
| | - George Seki
- Department of Nephrology and Endocrinology, Faculty of Medicine, University of Tokyo, Tokyo
| | - Mitsunobu Shimadzu
- Department of Genetics, Mitsubishi Yuka Bio-clinical Laboratories, Inc., Tokyo
| | - Fumiko Tozawa
- Department of Genetics, Mitsubishi Yuka Bio-clinical Laboratories, Inc., Tokyo
| | - Yasuhiro Takeshima
- Department of Pediatrics, Faculty of Medicine, Kobe University, Kobe, Japan
| | - Toru Takumi
- Department of Pediatrics, Faculty of Medicine, Kobe University, Kobe, Japan
| | | | | | - Hajime Nakamura
- Department of Pediatrics, Faculty of Medicine, Kobe University, Kobe, Japan
| | - Hitoshi Endou
- Department of Pharmacology and Toxicology, Kyourin University School of Medicine, Tokyo
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Abuladze N, Song M, Pushkin A, Newman D, Lee I, Nicholas S, Kurtz I. Structural organization of the human NBC1 gene: kNBC1 is transcribed from an alternative promoter in intron 3. Gene 2000; 251:109-22. [PMID: 10876088 DOI: 10.1016/s0378-1119(00)00204-3] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Several electrogenic sodium bicarbonate cotransporters have been cloned from different human organs. In the renal proximal tubule, the electrogenic sodium bicarbonate cotransporter kNBC1 (1035aa) mediates the majority of basolateral sodium bicarbonate absorption. In pancreatic ducts, the electrogenic sodium bicarbonate cotransporter pNBC1 (1079aa) mediates basolateral sodium bicarbonate influx. hNBC1 (hhNBC), cloned from human heart, is identical to pNBC1 at the amino acid level. We have demonstrated that kNBC1 and pNBC1 are highly homologous proteins that have different N-termini. In kNBC1, 41 amino acids replace the initial 85 amino acids of pNBC1. Whether these proteins are coded by one or more genes is unknown. In order to determine the genetic basis for these transcripts, we first characterized the genomic organization of the NBC1 gene (SLC4A4). NBC1 spans approximately 450 kilobases containing 26 exons that are flanked by typical splice donor and acceptor sequences at the intron-exon boundaries. Exon 1 is specific for the pNBC1 transcript. The first alternative exon of the hNBC1 transcript, containing the 5'-untranslated region, is derived from the last 43 nucleotides of intron 1 in the NBC1 gene coupled to exon 2. kNBC1 is transcribed from an alternative promoter in intron 3. In the first alternative exon of kNBC1, the last 313 nucleotides of intron 3 are coupled to exon 4, which is common to pNBC1 and hNBC1. The major transcription initiation site in kNBC1 is located 192 nucleotides upstream from the translation initiation codon. A minor start site is located 182 nucleotides upstream from the translation initiation codon. Structural analysis of the proximal kNBC1 promoter revealed an atypical TATA sequence (-33) and several potentially important transcription factor binding sites. Functional studies showed that the 5'-flanking region of the alternative kNBC1 promoter (-159 to+43) is sufficient for promoter activity. This work is the first demonstration that the three N-terminal transcripts of the human electrogenic sodium bicarbonate cotransporter NBC1 are encoded by the SLC4A4 gene. Furthermore, knowledge of the genomic organization and alternative promoter usage in the NBC1 gene provides a molecular basis for understanding disorders involving electrogenic sodium bicarbonate cotransporters and facilitates the elucidation of transcriptional control of NBC1 expression.
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Affiliation(s)
- N Abuladze
- Division of Nephrology, UCLA School of Medicine, 10833 Le Conte Avenue, Rm 7-155 Factor Building, Los Angeles, CA 90095-1689, USA
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Igarashi T, Inatomi J, Sekine T, Cha SH, Kanai Y, Kunimi M, Tsukamoto K, Satoh H, Shimadzu M, Tozawa F, Mori T, Shiobara M, Seki G, Endou H. Mutations in SLC4A4 cause permanent isolated proximal renal tubular acidosis with ocular abnormalities. Nat Genet 1999; 23:264-6. [PMID: 10545938 DOI: 10.1038/15440] [Citation(s) in RCA: 229] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Yoshimura M, Hara T, Maegaki Y, Koeda T, Okubo K, Hamasaki N, Sly WS, Takeshita K. A novel neurological disorder with progressive CNS calcification, deafness, renal tubular acidosis, and microcytic anemia. Dev Med Child Neurol 1997; 39:198-201. [PMID: 9112970 DOI: 10.1111/j.1469-8749.1997.tb07410.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Progressive calcification of the brain and the spinal cord at early infantile onset was observed in two siblings. They showed growth failure, psychomotor deterioration, deafness, vestibular dysfunction, microcytic hypochromic anemia, abnormal ratios of lymphocyte subpopulations, and slightly decreased bicarbonate on blood gas analysis. Distal renal tubular acidosis was demonstrated in one of them. Carbonic anhydrase II activity was normal. This new hereditary disease might have a defect in a molecule that is present in brain, spinal cord, kidney and hematocytes and is involved in H+/HCO3- production or transport.
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Affiliation(s)
- M Yoshimura
- Division of Child Neurology, Tottori University School of Medicine, Yonago, Japan
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