151
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Carboni I, Andreucci E, Caruso MR, Ciccone R, Zuffardi O, Genuardi M, Pela I, Giglio S. Medullary sponge kidney associated with primary distal renal tubular acidosis and mutations of the H+-ATPase genes. Nephrol Dial Transplant 2009; 24:2734-8. [DOI: 10.1093/ndt/gfp160] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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152
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Wagner CA, Devuyst O, Bourgeois S, Mohebbi N. Regulated acid–base transport in the collecting duct. Pflugers Arch 2009; 458:137-56. [DOI: 10.1007/s00424-009-0657-z] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Revised: 02/22/2009] [Accepted: 02/24/2009] [Indexed: 02/07/2023]
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153
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Brown D, Breton S, Ausiello DA, Marshansky V. Sensing, signaling and sorting events in kidney epithelial cell physiology. Traffic 2009; 10:275-84. [PMID: 19170982 PMCID: PMC2896909 DOI: 10.1111/j.1600-0854.2008.00867.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The kidney regulates body fluid, ion and acid/base homeostasis through the interaction of a host of channels, transporters and pumps within specific tubule segments, specific cell types and specific plasma membrane domains. Furthermore, renal epithelial cells have adapted to function in an often unique and challenging environment that includes high medullary osmolality, acidic pHs, variable blood flow and constantly changing apical and basolateral 'bathing' solutions. In this review, we focus on selected protein trafficking events by which kidney epithelial cells regulate body fluid, ion and acid-base homeostasis in response to changes in physiological conditions. We discuss aquaporin 2 and G-protein-coupled receptors in fluid and ion balance, the vacuolar H(+)-adenosine triphosphatase (V-ATPase) and intercalated cells in acid/base regulation and acidification events in the proximal tubule degradation pathway. Finally, in view of its direct role in vesicle trafficking that we outline in this study, we propose that the V-ATPase itself should, under some circumstances, be considered a fourth category of vesicle 'coat' protein (COP), alongside clathrin, caveolin and COPs.
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Affiliation(s)
- Dennis Brown
- Center for Systems Biology, Program in Membrane Biology and Nephrology Division, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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154
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Vidarsson H, Westergren R, Heglind M, Blomqvist SR, Breton S, Enerbäck S. The forkhead transcription factor Foxi1 is a master regulator of vacuolar H-ATPase proton pump subunits in the inner ear, kidney and epididymis. PLoS One 2009; 4:e4471. [PMID: 19214237 PMCID: PMC2637605 DOI: 10.1371/journal.pone.0004471] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Accepted: 12/22/2008] [Indexed: 12/21/2022] Open
Abstract
The vacuolar H(+)-ATPase dependent transport of protons across cytoplasmic membranes in FORE (forkhead related) cells of endolymphatic epithelium in the inner ear, intercalated cells of collecting ducts in the kidney and in narrow and clear cells of epididymis require expression of several subunits that assemble into a functional multimeric proton pump. We demonstrate that expression of four such subunits A1, B1, E2 and a4 all co-localize with the forkhead transcription factor Foxi1 in a subset of epithelial cells at these three locations. In cells, of such epithelia, that lack Foxi1 we fail to identify any expression of A1, B1, E2 and a4 demonstrating an important role for the transcription factor Foxi1 in regulating subunit availability. Promoter reporter experiments, electrophoretic mobility shift assays (EMSA) and site directed mutagenesis demonstrate that a Foxi1 expression vector can trans-activate an a4-promoter reporter construct in a dose dependent manner. Furthermore, we demonstrate using chromatin immunoprecipitation (ChIP) assays that Foxi1-dependent activation to a large extent depends on cis-elements at position -561/-547 in the a4 promoter. Thus, we provide evidence that Foxi1 is necessary for expression of at least four subunits in three different epithelia and most likely is a major determinant for proper assembly of a functional vacuolar H(+)-ATPase complex at these locations.
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Affiliation(s)
- Hilmar Vidarsson
- Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden
| | - Rickard Westergren
- Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden
| | - Mikael Heglind
- Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden
| | - Sandra Rodrigo Blomqvist
- Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden
| | - Sylvie Breton
- Center for Systems Biology, Program in Membrane Biology/Nephrology Division, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Sven Enerbäck
- Center of Medical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, Göteborg University, Göteborg, Sweden
- * E-mail:
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155
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Guillard M, Dimopoulou A, Fischer B, Morava E, Lefeber DJ, Kornak U, Wevers RA. Vacuolar H+-ATPase meets glycosylation in patients with cutis laxa. Biochim Biophys Acta Mol Basis Dis 2009; 1792:903-14. [PMID: 19171192 DOI: 10.1016/j.bbadis.2008.12.009] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Revised: 12/22/2008] [Accepted: 12/29/2008] [Indexed: 02/08/2023]
Abstract
Glycosylation of proteins is one of the most important post-translational modifications. Defects in the glycan biosynthesis result in congenital malformation syndromes, also known as congenital disorders of glycosylation (CDG). Based on the iso-electric focusing patterns of plasma transferrin and apolipoprotein C-III a combined defect in N- and O-glycosylation was identified in patients with autosomal recessive cutis laxa type II (ARCL II). Disease-causing mutations were identified in the ATP6V0A2 gene, encoding the a2 subunit of the vacuolar H(+)-ATPase (V-ATPase). The V-ATPases are multi-subunit, ATP-dependent proton pumps located in membranes of cells and organels. In this article, we describe the structure, function and regulation of the V-ATPase and the phenotypes currently known to result from V-ATPase mutations. A clinical overview of cutis laxa syndromes is presented with a focus on ARCL II. Finally, the relationship between ATP6V0A2 mutations, the glycosylation defect and the ARCLII phenotype is discussed.
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Affiliation(s)
- Mailys Guillard
- Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB, Nijmegen, The Netherlands
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156
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Stechman MJ, Loh NY, Thakker RV. Genetic causes of hypercalciuric nephrolithiasis. Pediatr Nephrol 2009; 24:2321-32. [PMID: 18446382 PMCID: PMC2770137 DOI: 10.1007/s00467-008-0807-0] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 02/15/2008] [Accepted: 02/25/2008] [Indexed: 12/19/2022]
Abstract
Renal stone disease (nephrolithiasis) affects 3-5% of the population and is often associated with hypercalciuria. Hypercalciuric nephrolithiasis is a familial disorder in over 35% of patients and may occur as a monogenic disorder that is more likely to manifest itself in childhood. Studies of these monogenic forms of hypercalciuric nephrolithiasis in humans, e.g. Bartter syndrome, Dent's disease, autosomal dominant hypocalcemic hypercalciuria (ADHH), hypercalciuric nephrolithiasis with hypophosphatemia, and familial hypomagnesemia with hypercalciuria have helped to identify a number of transporters, channels and receptors that are involved in regulating the renal tubular reabsorption of calcium. Thus, Bartter syndrome, an autosomal disease, is caused by mutations of the bumetanide-sensitive Na-K-Cl (NKCC2) co-transporter, the renal outer-medullary potassium (ROMK) channel, the voltage-gated chloride channel, CLC-Kb, the CLC-Kb beta subunit, barttin, or the calcium-sensing receptor (CaSR). Dent's disease, an X-linked disorder characterized by low molecular weight proteinuria, hypercalciuria and nephrolithiasis, is due to mutations of the chloride/proton antiporter 5, CLC-5; ADHH is associated with activating mutations of the CaSR, which is a G-protein-coupled receptor; hypophosphatemic hypercalciuric nephrolithiasis associated with rickets is due to mutations in the type 2c sodium-phosphate co-transporter (NPT2c); and familial hypomagnesemia with hypercalciuria is due to mutations of paracellin-1, which is a member of the claudin family of membrane proteins that form the intercellular tight junction barrier in a variety of epithelia. These studies have provided valuable insights into the renal tubular pathways that regulate calcium reabsorption and predispose to hypercalciuria and nephrolithiasis.
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Affiliation(s)
- Michael J. Stechman
- Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Oxford, OX3 7LJ UK
| | - Nellie Y. Loh
- Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Oxford, OX3 7LJ UK
| | - Rajesh V. Thakker
- Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Oxford, OX3 7LJ UK
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157
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Nikali K, Vanegas JJ, Burley MW, Martinez J, Lopez LM, Bedoya G, Wrong OM, Povey S, Unwin RJ, Ruiz-Linares A. Extensive founder effect for distal renal tubular acidosis (dRTA) with sensorineural deafness in an isolated South American population. Am J Med Genet A 2008; 146A:2709-12. [PMID: 18798332 DOI: 10.1002/ajmg.a.32495] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Kaisu Nikali
- Department of Genetics, Evolution and Environment, University College London, London, UK
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158
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Lee YS, Latham KE, Vandevoort CA. Effects of in vitro maturation on gene expression in rhesus monkey oocytes. Physiol Genomics 2008; 35:145-58. [PMID: 18697858 DOI: 10.1152/physiolgenomics.90281.2008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
In vitro oocyte maturation (IVM) holds great promise as a tool for enhancing clinical treatment of infertility, enhancing availability of nonhuman primates for development of disease models, and facilitating endangered species preservation. However, IVM outcomes have remained significantly below the success rates obtained with in vivo matured (VVM) oocytes from humans and nonhuman primates. A cDNA array-based analysis is presented, comparing the transcriptomes of VVM oocytes with IVM oocytes. We observe a small set of just 59 mRNAs that are differentially expressed between the two cell types. These mRNAs are related to cellular homeostasis, cell-cell interactions including growth factor and hormone stimulation and cell adhesion, and other functions such as mRNA stability and translation. Additionally, we observe in IVM oocytes overexpression of PLAGL1 and MEST, two maternally imprinted genes, indicating a possible interruption or loss of correct epigenetic programming. These results indicate that, under certain IVM conditions, oocytes that are molecularly highly similar to VVM oocytes can be obtained; however, the interruption of normal oocyte-somatic cell interactions during the final hours of oocyte maturation may preclude the establishment of full developmental competence.
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Affiliation(s)
- Young S Lee
- Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
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159
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Su Y, Blake-Palmer KG, Sorrell S, Javid B, Bowers K, Zhou A, Chang SH, Qamar S, Karet FE. Human H+ATPase a4 subunit mutations causing renal tubular acidosis reveal a role for interaction with phosphofructokinase-1. Am J Physiol Renal Physiol 2008; 295:F950-8. [PMID: 18632794 PMCID: PMC2576143 DOI: 10.1152/ajprenal.90258.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The vacuolar-type ATPase (H+ATPase) is a ubiquitously expressed multisubunit pump whose regulation is poorly understood. Its membrane-integral a-subunit is involved in proton translocation and in humans has four forms, a1-a4. This study investigated two naturally occurring point mutations in a4's COOH terminus that cause recessive distal renal tubular acidosis (dRTA), R807Q and G820R. Both lie within a domain that binds the glycolytic enzyme phosphofructokinase-1 (PFK-1). We recreated these disease mutations in yeast to investigate effects on protein expression, H+ATPase assembly, targeting and activity, and performed in vitro PFK-1 binding and activity studies of mammalian proteins. Mammalian studies revealed complete loss of binding between the COOH terminus of a4 containing the G-to-R mutant and PFK-1, without affecting PFK-1's catalytic activity. In yeast expression studies, protein levels, H+ATPase assembly, and targeting of this mutant were all preserved. However, severe (78%) loss of proton transport but less decrease in ATPase activity (36%) were observed in mutant vacuoles, suggesting a requirement for the a-subunit/PFK-1 binding to couple these two functions. This role for PFK in H+ATPase function was supported by similar functional losses and uncoupling ratio between the two proton pump domains observed in vacuoles from a PFK-null strain, which was also unable to grow at alkaline pH. In contrast, the R-to-Q mutation dramatically reduced a-subunit production, abolishing H+ATPase function completely. Thus in the context of dRTA, stability and function of the metabolon composed of H+ATPase and glycolytic components can be compromised by either loss of required PFK-1 binding (G820R) or loss of pump protein (R807Q).
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Affiliation(s)
- Ya Su
- Department of Medical Genetics, Cambridge University, Cambridge Institute for Medical Research, Addenbrooke's Hospital Box 139, Cambridge, CB2 0XY, UK
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160
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Tasic V, Korneti P, Gucev Z, Hoppe B, Blau N, Cheong HI. Atypical presentation of distal renal tubular acidosis in two siblings. Pediatr Nephrol 2008; 23:1177-81. [PMID: 18386070 DOI: 10.1007/s00467-008-0796-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/27/2007] [Revised: 02/15/2008] [Accepted: 02/15/2008] [Indexed: 12/29/2022]
Abstract
Primary distal renal tubular acidosis (dRTA) is an inherited disease characterized by the inability of the distal tubule to lower urine pH <5.50 during systemic acidosis. We report two male siblings who presented with severe hyperchloremic metabolic acidosis, high urinary pH, nephrocalcinosis, growth retardation, sensorineural hearing loss, and hypokalemic paralysis. Laboratory investigations revealed proximal tubular dysfunction (low molecular weight proteinuria, generalized hyperaminoaciduria, hypophosphatemia with hyperphosphaturia, and hypouricemia with hyperuricosuria). There was significant hyperoxaluria and laboratory evidence for mild rhabdomyolysis. Under potassium and alkali therapy, proximal tubular abnormalities, muscular enzymes, and oxaluria normalized. A homozygous mutation in the ATP6V1B1 gene, which is responsible for dRTA with early hearing loss, was detected in both siblings. In conclusion, proximal tubular dysfunction and hyperoxaluria may be found in children with dRTA and are reversible under appropriate therapy.
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Affiliation(s)
- Velibor Tasic
- Department of Pediatric Nephrology, Children's Hospital, 17 Vodnjanska, Skopje, Macedonia.
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161
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Stria vascularis and vestibular dark cells: characterisation of main structures responsible for inner-ear homeostasis, and their pathophysiological relations. The Journal of Laryngology & Otology 2008; 123:151-62. [DOI: 10.1017/s0022215108002624] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThe regulation of inner-ear fluid homeostasis, with its parameters volume, concentration, osmolarity and pressure, is the basis for adequate response to stimulation. Many structures are involved in the complex process of inner-ear homeostasis. The stria vascularis and vestibular dark cells are the two main structures responsible for endolymph secretion, and possess many similarities. The characteristics of these structures are the basis for regulation of inner-ear homeostasis, while impaired function is related to various diseases. Their distinct morphology and function are described, and related to current knowledge of associated inner-ear diseases. Further research on the distinct function and regulation of these structures is necessary in order to develop future clinical interventions.
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162
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Khositseth S, Sirikanaerat A, Khoprasert S, Opastirakul S, Kingwatanakul P, Thongnoppakhun W, Yenchitsomanus PT. Hematological abnormalities in patients with distal renal tubular acidosis and hemoglobinopathies. Am J Hematol 2008; 83:465-71. [PMID: 18266205 DOI: 10.1002/ajh.21151] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mutations of the human SLC4A1 gene encoding erythroid and kidney isoforms of anion exchanger 1 (AE1, band 3) result in erythrocyte abnormalities or distal renal tubular acidosis (dRTA) and such mutations are observed in Southeast Asia, where hemoglobinopathies are prevalent. Genetic and hematological studies in 18 Thai patients with dRTA have shown that 12 of them (67%) carried SLC4A1 mutations (7 G701D/G701D, 3 SAO/G701D, and 2 G701D/A858D). Of these 12 patients, three had homozygous G701D/G701D and heterozygous Hb E; one compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia; and one compound heterozygous G701D/A858D and heterozygous Hb E. Of 6 patients without SLC4A1 mutation, two each carried heterozygous or homozygous Hb E and one of the latter also had Hb H disease (--(SEA)/-alpha(4.2)). The blood smears of patients with homozygous G701D/G701D showed approximately 25% ovalocytes. Strikingly, the patients with coexistence of homozygous G701D/G701D and heterozygous Hb E had 58% ovalocytes. Similarly, the patients who had compound heterozygous SAO/G701D showed 49% ovalocytes, but the patient with coexistence of compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia had 70% ovalocytes. Our previous study has shown that under metabolic acidosis, the patients with homozygous G701D/G701D or compound heterozygous SAO/G701D had reticulocytosis, indicating compensated hemolysis. A patient with compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia presented with hemolytic anemia and hepatosplenomegaly which was alleviated by alkaline therapy. Taken together, the coexistence of both homozygous or compound heterozygous SLC4A1 mutations and hemoglobinopathy has a combined effect on red cell morphology and degree of hemolytic anemia, which is aggravated by acidosis.
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163
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Fuster D, Zhang J, Xie XS, Moe O. The vacuolar-ATPase B1 subunit in distal tubular acidosis: novel mutations and mechanisms for dysfunction. Kidney Int 2008; 73:1151-8. [DOI: 10.1038/ki.2008.96] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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164
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Lang F, Vallon V, Knipper M, Wangemann P. Functional significance of channels and transporters expressed in the inner ear and kidney. Am J Physiol Cell Physiol 2007; 293:C1187-208. [PMID: 17670895 DOI: 10.1152/ajpcell.00024.2007] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A number of ion channels and transporters are expressed in both the inner ear and kidney. In the inner ear, K+cycling and endolymphatic K+, Na+, Ca2+, and pH homeostasis are critical for normal organ function. Ion channels and transporters involved in K+cycling include K+channels, Na+-2Cl−-K+cotransporter, Na+/K+-ATPase, Cl−channels, connexins, and K+/Cl−cotransporters. Furthermore, endolymphatic Na+and Ca2+homeostasis depends on Ca2+-ATPase, Ca2+channels, Na+channels, and a purinergic receptor channel. Endolymphatic pH homeostasis involves H+-ATPase and Cl−/HCO3−exchangers including pendrin. Defective connexins (GJB2 and GJB6), pendrin (SLC26A4), K+channels (KCNJ10, KCNQ1, KCNE1, and KCNMA1), Na+-2Cl−-K+cotransporter (SLC12A2), K+/Cl−cotransporters (KCC3 and KCC4), Cl−channels (BSND and CLCNKA + CLCNKB), and H+-ATPase (ATP6V1B1 and ATPV0A4) cause hearing loss. All these channels and transporters are also expressed in the kidney and support renal tubular transport or signaling. The hearing loss may thus be paralleled by various renal phenotypes including a subtle decrease of proximal Na+-coupled transport (KCNE1/KCNQ1), impaired K+secretion (KCNMA1), limited HCO3−elimination (SLC26A4), NaCl wasting (BSND and CLCNKB), renal tubular acidosis (ATP6V1B1, ATPV0A4, and KCC4), or impaired urinary concentration (CLCNKA). Thus, defects of channels and transporters expressed in the kidney and inner ear result in simultaneous dysfunctions of these seemingly unrelated organs.
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Affiliation(s)
- Florian Lang
- Department of Physiology, Eberhard-Karls-University of Tübingen, Gmelinstrasse 5, Tübingen, Germany.
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165
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Paunescu TG, Russo LM, Da Silva N, Kovacikova J, Mohebbi N, Van Hoek AN, McKee M, Wagner CA, Breton S, Brown D. Compensatory membrane expression of the V-ATPase B2 subunit isoform in renal medullary intercalated cells of B1-deficient mice. Am J Physiol Renal Physiol 2007; 293:F1915-26. [PMID: 17898041 DOI: 10.1152/ajprenal.00160.2007] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mice deficient in the ATP6V1B1 ("B1") subunit of the vacuolar proton-pumping ATPase (V-ATPase) maintain body acid-base homeostasis under normal conditions, but not when exposed to an acid load. Here, compensatory mechanisms involving the alternate ATP6V1B2 ("B2") isoform were examined to explain the persistence of baseline pH regulation in these animals. By immunocytochemistry, the mean pixel intensity of apical B2 immunostaining in medullary A intercalated cells (A-ICs) was twofold greater in B1-/- mice than in B1+/+ animals, and B2 was colocalized with other V-ATPase subunits. No significant upregulation of B2 mRNA or protein expression was detected in B1-/- mice compared with wild-type controls. We conclude that increased apical B2 staining is due to relocalization of B2-containing V-ATPase complexes from the cytosol to the plasma membrane. Recycling of B2-containing holoenzymes between these domains was confirmed by the intracellular accumulation of B1-deficient V-ATPases in response to the microtubule-disrupting drug colchicine. V-ATPase membrane expression is further supported by the presence of "rod-shaped" intramembranous particles seen by freeze fracture microscopy in apical membranes of normal and B1-deficient A-ICs. Intracellular pH recovery assays show that significant (28-40% of normal) V-ATPase function is preserved in medullary ICs from B1-/- mice. We conclude that the activity of apical B2-containing V-ATPase holoenzymes in A-ICs is sufficient to maintain baseline acid-base homeostasis in B1-deficient mice. However, our results show no increase in cell surface V-ATPase activity in response to metabolic acidosis in ICs from these animals, consistent with their inability to appropriately acidify their urine under these conditions.
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Affiliation(s)
- Teodor G Paunescu
- Div. of Nephrology, Massachusetts General Hospital, 185 Cambridge St., CPZN 8150, Boston, MA 02114, USA.
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166
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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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167
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Joshua B, Kaplan DM, Raveh E, Lotan D, Anikster Y. Audiometric and imaging characteristics of distal renal tubular acidosis and deafness. The Journal of Laryngology & Otology 2007; 122:193-8. [PMID: 17669226 DOI: 10.1017/s0022215107009747] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractObjective:Primary distal renal tubular acidosis with sensorineural hearing loss is a rare autosomal recessive disease, usually caused by mutations in the ATP6V1B1 gene. The aim of this study was to characterise the phenotype of this disease, with emphasis on the auditory findings, in a cohort of Israeli children.Study design:Prospective study of five children, from three unrelated families, with distal renal tubular acidosis and bilateral sensorineural hearing loss, with mutations in the ATP6V1B1 gene.Methods:The following were collected from patients' medical records: biochemical and renal data, age at distal renal tubular acidosis diagnosis, and age at hearing loss. Hearing loss progression as well as current hearing status were assessed, and high resolution computed tomography of the temporal bone was performed. All patients underwent genetic testing.Results:Four patients were diagnosed with distal renal tubular acidosis before the age of six months and one at 24 months. All had the classical findings of low blood pH and inappropriately high urine pH. Hearing loss was diagnosed between the ages of three months and two years. The hearing loss was bilateral, asymmetrical and progressive, occasionally with a conductive component. Two children underwent cochlear implantation, at ages 10 and 15 years. High resolution computed tomography, performed in four patients between the ages of 2.5 and 15 years, showed bilaterally enlarged vestibular aqueducts. This was the only radiological abnormality in the inner ear in all cases. A different mutation in the ATP6V1B1 gene was found in each family.Conclusion:Several types of mutations in the ATP6V1B1 gene may cause distal renal tubular acidosis and sensorineural hearing loss. Patients display a typical progressive type of hearing loss and have enlarged vestibular aqueducts, with no other abnormalities being observed on imaging.
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Affiliation(s)
- B Joshua
- Department of Otorhinolaryngology & Head and Neck Surgery, Rabin Medical Center, Petah Tiqwa, Israel
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168
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Abstract
Inherited acidosis may result from a primary renal defect in acid-base handling, emphasizing the central role of the kidney in control of body pH; as a secondary phenomenon resulting from abnormal renal electrolyte handling; or from excess production of acid elsewhere in the body. Here, we review our current understanding of the inherited renal acidoses at a genetic and molecular level.
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Affiliation(s)
- Andrew C Fry
- Department of Medical Genetics and Division of Renal Medicine, University of Cambridge, Cambridge Institute for Medical Research, UK
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169
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Da Silva N, Shum WWC, El-Annan J, Păunescu TG, McKee M, Smith PJS, Brown D, Breton S. Relocalization of the V-ATPase B2 subunit to the apical membrane of epididymal clear cells of mice deficient in the B1 subunit. Am J Physiol Cell Physiol 2007; 293:C199-210. [PMID: 17392376 DOI: 10.1152/ajpcell.00596.2006] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
An acidic luminal pH in the epididymis contributes to maintaining sperm quiescent during their maturation and storage. The vacuolar H+ATPase (V-ATPase), located in narrow and clear cells, is a major contributor to luminal acidification. Mutations in one of the V-ATPase subunits, ATP6v1B1 (B1), cause distal renal tubular acidosis in humans but surprisingly, B1−/− mice do not develop metabolic acidosis and are fertile. While B1 is located in the apical membrane of narrow and clear cells, the B2 subunit localizes to subapical vesicles in wild-type mouse, rat and human epididymis. However, a marked increase (84%) in the mean pixel intensity of B2 staining was observed in the apical pole of clear cells by conventional immunofluorescence, and relocalization into their apical membrane was detected by confocal microscopy in B1−/− mice compared with B1+/+. Immunogold electron microscopy showed abundant B2 in the apical microvilli of clear cells in B1−/− mice. B2 mRNA expression, determined by real time RT-PCR using laser-microdissected epithelial cells, was identical in both groups. Semiquantitative Western blots from whole epididymis and cauda epididymidis showed no variation of B2 expression. Finally, the luminal pH of the cauda epididymidis was the same in B1−/− mice as in B1+/+ (pH 6.7). These data indicate that whereas overall expression of B2 is not affected in B1−/− mice, significant redistribution of B2-containing complexes occurs from intracellular compartments into the apical membrane of clear cells in B1−/− mice. This relocation compensates for the absence of functional B1 and maintains the luminal pH in an acidic range that is compatible with fertility.
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Affiliation(s)
- Nicolas Da Silva
- Massachusetts General Hospital, Harvard Medical School, Program in Membrane Biology, Nephrology Div., 185 Cambridge St., CPZN 8150, Boston, MA 02114-2790, USA.
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170
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Khositseth S, Sirikanerat A, Wongbenjarat K, Opastirakul S, Khoprasert S, Peuksungnern R, Wattanasirichaigoon D, Thongnoppakhun W, Viprakasit V, Yenchitsomanus PT. Distal renal tubular acidosis associated with anion exchanger 1 mutations in children in Thailand. Am J Kidney Dis 2007; 49:841-850.e1. [PMID: 17533027 DOI: 10.1053/j.ajkd.2007.03.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2006] [Accepted: 03/05/2007] [Indexed: 11/11/2022]
Abstract
BACKGROUND Mutations in the anion exchanger 1 (AE1) gene encoding the erythroid and kidney anion (chloride-bicarbonate) exchanger 1 may result in hereditary distal renal tubular acidosis (dRTA). Hemoglobinopathies are common in Thailand. We analyzed AE1 and hemoglobin mutations in children in Thailand with dRTA to evaluate their association with clinical manifestations. STUDY DESIGN Case series. SETTING & PARTICIPANTS 17 patients were recruited from 6 referral hospitals in 4 regions of Thailand. PREDICTORS AE1 mutations were detected by means of nucleotide sequence alterations. Hemoglobin E (HbE) was detected by means of hemoglobin typing, and thalassemia, by means of analysis of globin genes. Hemolytic anemia was indicated by decreased hemoglobin and hematocrit values in the presence of reticulocytosis. OUTCOMES & MEASUREMENTS Leading clinical manifestations in patients were failure to thrive and muscle weakness. Compensated or overt anemia was identified in some cases. Coexistence of AE1 mutations with HbE or alpha(+)-thalassemia was present in a number of patients. RESULTS 12 of 17 patients (70%) carried AE1 mutations, 7 patients (41%) had HbE, and 1 patient (6%) had alpha(+)-thalassemia. Patients with AE1 mutations presented with compensated hemolysis when they had metabolic acidosis. A patient with compound heterozygous Southeast Asian ovalocytosis/G701D and heterozygous alpha(+)-thalassemia showed severe hemolytic anemia. LIMITATIONS 5 patients (30%) without detectable AE1 mutation also were unknown for other genetic abnormalities. CONCLUSIONS Most of the patients with dRTA studied carried autosomal recessive AE1 mutations. Metabolic acidosis, which could be alleviated by adequate alkaline therapy, induced variable degrees of hemolysis in patients with dRTA associated with autosomal recessive AE1 mutations, especially in the presence of thalassemia.
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Affiliation(s)
- Sookkasem Khositseth
- Department of Pediatrics, Faculty of Medicine, Thammasat University, Bangkok, Thailand
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171
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Gil H, Santos F, García E, Alvarez MV, Ordóñez FA, Málaga S, Coto E. Distal RTA with nerve deafness: clinical spectrum and mutational analysis in five children. Pediatr Nephrol 2007; 22:825-8. [PMID: 17216496 DOI: 10.1007/s00467-006-0417-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Revised: 11/22/2006] [Accepted: 12/08/2006] [Indexed: 10/23/2022]
Abstract
Distal renal tubular acidosis (RTA) with nerve deafness is caused by mutations in the ATP6V1B1 gene causing defective function of the H+ -ATPase proton pump. We report five acidotic children (four males) from four unrelated families: blood pH 7.21-7.33, serum bicarbonate 10.8-14.7 mEq/l, minimum urinary pH 6.5-7.1 and fractional excretion of bicarbonate in the presence of normal bicarbonatemia 1.1-5.7%. Growth retardation and nephrocalcinosis, but not hypercalciuria, were common presenting manifestations. Hearing was normally preserved in one of the patients whose sister was severely deaf. One child was homozygous for a known mutation in exon 1: C>T (R31X). Three children were homozygous for a splicing mutation, intron 6 + 1G>A. The other patient was a compound heterozygote, having this mutation and a previously unreported mutation in exon 10: G>A (E330K). Our report shows that hearing loss is not always present in the syndrome of distal renal tubular acidosis with nerve deafness and the absence of hypercalciuria at diagnosis and describes a new mutation responsible for the disease in the ATP6V1B1 gene.
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Affiliation(s)
- Helena Gil
- Hospital Universitario Central de Asturias, Asturias, Spain
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172
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Blake-Palmer KG, Su Y, Smith AN, Karet FE. Molecular cloning and characterization of a novel form of the human vacuolar H+-ATPase e-subunit: An essential proton pump component. Gene 2007; 393:94-100. [PMID: 17350184 DOI: 10.1016/j.gene.2007.01.020] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 01/25/2007] [Accepted: 01/26/2007] [Indexed: 11/17/2022]
Abstract
Several of the 13 subunits comprising mammalian H(+)-ATPases have multiple alternative forms, encoded by separate genes and with differing tissue expression patterns. These may play an important role in the intracellular localization and activity of H(+)-ATPases. Here we report the cloning of a previously uncharacterized human gene, ATP6V0E2, encoding a novel H(+)-ATPase e-subunit designated e2. We demonstrate that in contrast to the ubiquitously expressed gene encoding the e1 subunit (previously called e), this novel gene is expressed in a more restricted tissue distribution, particularly kidney and brain. We show by complementation studies in a yeast strain deficient for the ortholog of this subunit, that either form of the e-subunit is essential for proper proton pump function. The identification of this novel form of the e-subunit lends further support to the hypothesis that subunit differences may play a key role in the structure, site and function of H(+)-ATPases within the cell.
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Affiliation(s)
- Katherine G Blake-Palmer
- Department of Medical Genetics, University of Cambridge, Cambridge Institute for Medical Research, Cambridge, UK
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173
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Kernan MJ. Mechanotransduction and auditory transduction in Drosophila. Pflugers Arch 2007; 454:703-20. [PMID: 17436012 DOI: 10.1007/s00424-007-0263-x] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Accepted: 03/22/2007] [Indexed: 11/28/2022]
Abstract
Insects are utterly reliant on sensory mechanotransduction, the process of converting physical stimuli into neuronal receptor potentials. The senses of proprioception, touch, and hearing are involved in almost every aspect of an adult insect's complex behavioral repertoire and are mediated by a diverse array of specialized sensilla and sensory neurons. The physiology and morphology of several of these have been described in detail; genetic approaches in Drosophila, combining behavioral screens and sensory electrophysiology with forward and reverse genetic techniques, have now revealed specific proteins involved in their differentiation and operation. These include three different TRP superfamily ion channels that are required for transduction in tactile bristles, chordotonal stretch receptors, and polymodal nociceptors. Transduction also depends on the normal differentiation and mechanical integrity of the modified cilia that form the neuronal sensory endings, the accessory structures that transmit stimuli to them and, in bristles, a specialized receptor lymph and transepithelial potential. Flies hear near-field sounds with a vibration-sensitive, antennal chordotonal organ. Biomechanical analyses of wild-type antennae reveal non-linear, active mechanical properties that increase their sensitivity to weak stimuli. The effects of mechanosensory and ciliary mutations on antennal mechanics show that the sensory cilia are the active motor elements and indicate distinct roles for TRPN and TRPV channels in auditory transduction and amplification.
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Affiliation(s)
- Maurice J Kernan
- Department of Neurobiology and Behavior and Center for Developmental Genetics, Stony Brook University, Stony Brook, NY 11794-5230, USA.
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174
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Batlle D, Moorthi KMLST, Schlueter W, Kurtzman N. Distal renal tubular acidosis and the potassium enigma. Semin Nephrol 2007; 26:471-8. [PMID: 17275585 DOI: 10.1016/j.semnephrol.2006.12.001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Severe hypokalemia is a central feature of the classic type of distal renal tubular acidosis (RTA), both in hereditary and acquired forms. In the past decade, many of the genetic defects associated with the hereditary types of distal RTA have been identified and have been the subject of a number of reviews. These genetic advances have expanded our understanding of the molecular mechanisms that lead to distal RTA. In this article, we review data published in the literature on plasma potassium from patients with inherited forms of distal RTA. The degree of hypokalemia varies depending on whether the disease is autosomal autosomal-recessive or dominant, but, interestingly, it occurs in defects caused by mutations in genes encoding the AE-1 exchanger, the carbonic anhydrase II gene, and genes encoding different subunits of the H+ adenosine triphosphatase. This shows that a unique defect involving the H+/K+-adenosine triphosphatase leading to renal potassium wastage cannot explain the hypokalemia seen in virtually all types of classic distal RTA.
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Affiliation(s)
- Daniel Batlle
- Division of Nephrology/Hypertension, Northwestern University Feinberg School of Medicine, Chicago, IL 60611-3008, USA.
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175
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Norgett EE, Borthwick KJ, Al-Lamki RS, Su Y, Smith AN, Karet FE. V1 and V0 domains of the human H+-ATPase are linked by an interaction between the G and a subunits. J Biol Chem 2007; 282:14421-7. [PMID: 17360703 DOI: 10.1074/jbc.m701226200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The specialized H(+)-ATPases found in the inner ear and acid-handling cells in the renal collecting duct differ from those at other sites, as they contain tissue-specific subunits, such as a4 and B1, and in the kidney, C2, d2, and G3 as well. These subunits replace the ubiquitously expressed forms. Previously, we have shown that, in major organs of both mouse and man, G3 subunit expression is limited to the kidney. Here we have shown wide-spread transcription of murine G3 in specific segments of microdissected nephron, and demonstrated additional G3 expression in epithelial fragments from human inner ear. We raised a polyclonal G3-specific antibody, which specifically detects G3 from human, mouse, and rat kidney lysates, and displays no cross-reactivity with G1 or G2. However, immunolocalization using this antibody on human and mouse kidney sections was unachievable, suggesting epitope masking. Phage display analysis and subsequent enzyme-linked immunosorbent assay, using the G3 antibody epitope peptide as bait, identified a possible interaction between the G3 subunit and the a4 subunit of the H(+)-ATPase. This interaction was verified by successfully using purified, immobilized full-length G3 to pull down the a4 subunit from human kidney membrane preparations. This confirms that a4 and G3 are component subunits of the same proton pump and explains the observed epitope masking. This interaction was also found to be a more general feature of human H(+)-ATPases, as similar G1/a1, G3/a1, and G1/a4 interactions were also demonstrated. These interactions represent a novel link between the V(1) and V(0) domains in man, which is known to be required for H(+)-ATPase assembly and regulation.
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Affiliation(s)
- Elizabeth E Norgett
- Department of Medical Genetics, Department of Medicine and Division of Renal Medicine, University of Cambridge, Cambridge, UK
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176
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Freimoser FM, Hürlimann HC, Jakob CA, Werner TP, Amrhein N. Systematic screening of polyphosphate (poly P) levels in yeast mutant cells reveals strong interdependence with primary metabolism. Genome Biol 2007; 7:R109. [PMID: 17107617 PMCID: PMC1794592 DOI: 10.1186/gb-2006-7-11-r109] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Revised: 10/04/2006] [Accepted: 11/15/2006] [Indexed: 11/30/2022] Open
Abstract
A systematic analysis of polyphosphate levels in yeast knockout strains for almost every non-essential gene identified 255 genes involved in the maintenance of normal polyphosphate content and provides insights into phosphate homeostasis. Background Inorganic polyphosphate (poly P) occurs universally in all organisms from bacteria to man. It functions, for example, as a phosphate and energy store, and is involved in the activation and regulation of proteins. Despite its ubiquitous occurrence and important functions, it is unclear how poly P is synthesized or how poly P metabolism is regulated in higher eukaryotes. This work describes a systematic analysis of poly P levels in yeast knockout strains mutated in almost every non-essential gene. Results After three consecutive screens, 255 genes (almost 4% of the yeast genome) were found to be involved in the maintenance of normal poly P content. Many of these genes encoded proteins functioning in the cytoplasm, the vacuole or in transport and transcription. Besides reduced poly P content, many strains also exhibited reduced total phosphate content, showed altered ATP and glycogen levels and were disturbed in the secretion of acid phosphatase. Conclusion Cellular energy and phosphate homeostasis is suggested to result from the equilibrium between poly P, ATP and free phosphate within the cell. Poly P serves as a buffer for both ATP and free phosphate levels and is, therefore, the least essential and consequently most variable component in this network. However, strains with reduced poly P levels are not only affected in their ATP and phosphate content, but also in other components that depend on ATP or free phosphate content, such as glycogen or secreted phosphatase activity.
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Affiliation(s)
| | | | - Claude A Jakob
- Institute of Microbiology, ETH Zurich, Zurich, Switzerland
| | - Thomas P Werner
- Institute of Plant Sciences, ETH Zurich, 8092 Zurich, Switzerland
| | - Nikolaus Amrhein
- Institute of Plant Sciences, ETH Zurich, 8092 Zurich, Switzerland
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177
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Breton S, Brown D. New insights into the regulation of V-ATPase-dependent proton secretion. Am J Physiol Renal Physiol 2006; 292:F1-10. [PMID: 17032935 DOI: 10.1152/ajprenal.00340.2006] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The vacuolar H(+)-ATPase (V-ATPase) is a key player in several aspects of cellular function, including acidification of intracellular organelles and regulation of extracellular pH. In specialized cells of the kidney, male reproductive tract and osteoclasts, proton secretion via the V-ATPase represents a major process for the regulation of systemic acid/base status, sperm maturation and bone resorption, respectively. These processes are regulated via modulation of the plasma membrane expression and activity of the V-ATPase. The present review describes selected aspects of V-ATPase regulation, including recycling of V-ATPase-containing vesicles to and from the plasma membrane, assembly/disassembly of the two domains (V(0) and V(1)) of the holoenzyme, and the coupling ratio between ATP hydrolysis and proton pumping. Modulation of the V-ATPase-rich cell phenotype and the pathophysiology of the V-ATPase in humans and experimental animals are also discussed.
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Affiliation(s)
- Sylvie Breton
- Program in Membrane Biology, Nephrology Division, Massachusetts General Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02114-2790, USA.
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178
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Wangemann P. Supporting sensory transduction: cochlear fluid homeostasis and the endocochlear potential. J Physiol 2006; 576:11-21. [PMID: 16857713 PMCID: PMC1995626 DOI: 10.1113/jphysiol.2006.112888] [Citation(s) in RCA: 330] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 07/14/2006] [Indexed: 12/13/2022] Open
Abstract
The exquisite sensitivity of the cochlea, which mediates the transduction of sound waves into nerve impulses, depends on the endocochlear potential and requires a highly specialized environment that enables and sustains sensory function. Disturbance of cochlear homeostasis is the cause of many forms of hearing loss including the most frequently occurring syndromic and non-syndromic forms of hereditary hearing loss, Pendred syndrome and Cx26-related deafness. The occurrence of these and other monogenetic disorders illustrates that cochlear fluid homeostasis and the generation of the endocochlear potential are poorly secured by functional redundancy. This review summarizes the most prominent aspects of cochlear fluid homeostasis. It covers cochlear fluid composition, the generation of the endocochlear potential, K(+) secretion and cycling and its regulation, the role of gap junctions, mechanisms of acid-base homeostasis, and Ca(2+) transport.
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Affiliation(s)
- Philine Wangemann
- Anatomy & Physiology Department, 205 Coles Hall, Kansas State University, Manhattan, 66506, USA.
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179
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Abstract
The vacuolar H(+)-ATPase is a multisubunit protein consisting of a peripheral catalytic domain (V(1)) that binds and hydrolyzes adenosine triphosphate (ATP) and provides energy to pump H(+) through the transmembrane domain (V(0)) against a large gradient. This proton-translocating vacuolar H(+)-ATPase is present in both intracellular compartments and the plasma membrane of eukaryotic cells. Mutations in genes encoding kidney intercalated cell-specific V(0) a4 and V(1) B1 subunits of the vacuolar H(+)-ATPase cause the syndrome of distal tubular renal acidosis. This review focuses on the function, regulation, and the role of vacuolar H(+)-ATPases in renal physiology. The localization of vacuolar H(+)-ATPases in the kidney, and their role in intracellular pH (pHi) regulation, transepithelial proton transport, and acid-base homeostasis are discussed.
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Affiliation(s)
- Patricia Valles
- Area de Fisiopatología, Departamento de Patología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina
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180
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Abstract
Not all vacuolar-type H(+)-ATPases (V-ATPases) are alike; those responsible for H(+) movement across plasma membranes contain some different, tissue-specific subunit isoforms. This brief review outlines those that have special relevance to the kidney, and illustrates their importance by describing various human diseases where loss of local proton pump function not only confers a severe phenotype, but has revealed related tissues where these same isoforms are expressed, signifying their physiological importance.
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Affiliation(s)
- Fiona E Karet
- Division of Renal Medicine and Department of Medical Genetics, Cambridge Institute for Medical Research, University of Cambridge, Box 139, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2XY, UK.
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181
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Ochotny N, Van Vliet A, Chan N, Yao Y, Morel M, Kartner N, von Schroeder HP, Heersche JNM, Manolson MF. Effects of human a3 and a4 mutations that result in osteopetrosis and distal renal tubular acidosis on yeast V-ATPase expression and activity. J Biol Chem 2006; 281:26102-11. [PMID: 16840787 DOI: 10.1074/jbc.m601118200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
V-ATPases are multimeric proton pumps. The 100-kDa "a" subunit is encoded by four isoforms (a1-a4) in mammals and two (Vph1p and Stv1p) in yeast. a3 is enriched in osteoclasts and is essential for bone resorption, whereas a4 is expressed in the distal nephron and acidifies urine. Mutations in human a3 and a4 result in osteopetrosis and distal renal tubular acidosis, respectively. Human a3 (G405R and R444L) and a4 (P524L and G820R) mutations were recreated in the yeast ortholog Vph1p, a3 (G424R and R462L), and a4 (W520L and G812R). Mutations in a3 resulted in wild type vacuolar acidification and growth on media containing 4 mM ZnCl2, 200 mM CaCl2, or buffered to pH 7.5 with V-ATPase hydrolytic and pumping activity decreased by 30-35%. Immunoblots confirmed wild type levels for V-ATPase a, A, and B subunits on vacuolar membranes. a4 G812R resulted in defective growth on selective media with V-ATPase hydrolytic and pumping activity decreased by 83-85% yet with wild type levels of a, A, and B subunits on vacuolar membranes. The a4 W520L mutation had defective growth on selective media with no detectable V-ATPase activity and reduced expression of a, A, and B subunits. The a4 W520L mutation phenotypes were dominant negative, as overexpression of wild type yeast a isoforms, Vph1p, or Stv1p, did not restore growth. However, deletion of endoplasmic reticulum assembly factors (Vma12p, Vma21p, and Vma22p) partially restored a and B expression. That a4 W520L affects both Vo and V1 subunits is a unique phenotype for any V-ATPase subunit mutation and supports the concerted pathway for V-ATPase assembly in vivo.
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Affiliation(s)
- Noelle Ochotny
- Department of Pharmacology, University of Toronto, Toronto, Ontario M5G 1G6, Canada
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182
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Yang Q, Li G, Singh SK, Alexander EA, Schwartz JH. Vacuolar H+-ATPase B1 Subunit Mutations that Cause Inherited Distal Renal Tubular Acidosis Affect Proton Pump Assembly and Trafficking in Inner Medullary Collecting Duct Cells. J Am Soc Nephrol 2006; 17:1858-66. [PMID: 16769747 DOI: 10.1681/asn.2005121277] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Point mutations in the B1 subunit of vacuolar H+ -ATPase are associated with impaired ability of the distal nephron to secrete acid (distal renal tubular acidosis). For testing of the hypothesis that these mutations interfere with assembly and trafficking of the H+ -ATPase, constructs that mimic seven known point mutations in inherited distal renal tubular acidosis (M) or wild-type (WT) B1 were transfected into a rat inner medullary collecting duct cell line to express green fluorescence protein (GFP)-B1WT or GFP-B1M fusion proteins. In co-immunoprecipitation studies, GFP-B1WT formed complexes with other H+ -ATPase subunits (c, H, and E), whereas GFP-B1M did not. Proteins that were immunoprecipitated with anti-GFP antibody from GFP-B1WT cells had ATPase activity, whereas proteins from GFP-B1M cells did not. Proton pump-mediated intracellular pH transport was inhibited in GFP-B1M-transfected cells but not in GFP-B1WT cells. GFP-B1WT and GFP-B1M are present in the apical membrane and increased with cellular acidification. In GFP-B1WT cells, the apical membrane fraction of GFP-B1, endogenous B1, and the 31-kD subunits of the H+ -ATPase increased with cell acidification. In GFP-B1M cells, the endogenous B1 and 31-kD subunits did not increase with acidification. B1 point mutations prevent normal assembly of the H+ -ATPase and also may act as an inhibitor of H+ -ATPase function by competing with endogenous intact H+ -ATPase for trafficking in inner medullary collecting duct cells.
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Affiliation(s)
- Qiongqiong Yang
- Renal Section, 1st Affiliated Hospital of Zhongshan University, Guangzhou, China
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183
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Beyenbach KW, Wieczorek H. The V-type H+ ATPase: molecular structure and function, physiological roles and regulation. ACTA ACUST UNITED AC 2006; 209:577-89. [PMID: 16449553 DOI: 10.1242/jeb.02014] [Citation(s) in RCA: 432] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
It was nearly 30 years before the V-type H+ ATPase was admitted to the small circle of bona fide transport ATPases alongside F-type and P-type ATPases. The V-type H+ ATPase is an ATP-driven enzyme that transforms the energy of ATP hydrolysis to electrochemical potential differences of protons across diverse biological membranes via the primary active transport of H+. In turn, the transmembrane electrochemical potential of H+ is used to drive a variety of (i) secondary active transport systems via H+-dependent symporters and antiporters and (ii) channel-mediated transport systems. For example, expression of Cl- channels or transporters next to the V-type H+ ATPase in vacuoles of plants and fungi and in lysosomes of animals brings about the acidification of the endosomal compartment, and the expression of the H+/neurotransmitter antiporter next to the V-type H+ ATPase concentrates neurotransmitters in synaptic vesicles. First found in association with endosomal membranes, the V-type H+ ATPase is now also found in increasing examples of plasma membranes where the proton pump energizes transport across cell membranes and entire epithelia. The molecular details reveal up to 14 protein subunits arranged in (i) a cytoplasmic V1 complex, which mediates the hydrolysis of ATP, and (ii) a membrane-embedded V0 complex, which translocates H+ across the membrane. Clever experiments have revealed the V-type H+ ATPase as a molecular motor akin to F-type ATPases. The hydrolysis of ATP turns a rotor consisting largely of one copy of subunits D and F of the V1 complex and a ring of six or more copies of subunit c of the V0 complex. The rotation of the ring is thought to deliver H+ from the cytoplasmic to the endosomal or extracellular side of the membrane, probably via channels formed by subunit a. The reversible dissociation of V1 and V0 complexes is one mechanism of physiological regulation that appears to be widely conserved from yeast to animal cells. Other mechanisms, such as subunit-subunit interactions or interactions of the V-type H+ ATPase with other proteins that serve physiological regulation, remain to be explored. Some diseases can now be attributed to genetic alterations of specific subunits of the V-type H+ ATPase.
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Affiliation(s)
- Klaus W Beyenbach
- Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA.
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184
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Vargas-Poussou R, Houillier P, Le Pottier N, Strompf L, Loirat C, Baudouin V, Macher MA, Déchaux M, Ulinski T, Nobili F, Eckart P, Novo R, Cailliez M, Salomon R, Nivet H, Cochat P, Tack I, Fargeot A, Bouissou F, Kesler GR, Lorotte S, Godefroid N, Layet V, Morin G, Jeunemaître X, Blanchard A. Genetic Investigation of Autosomal Recessive Distal Renal Tubular Acidosis: Evidence for Early Sensorineural Hearing Loss Associated with Mutations in theATP6V0A4Gene. J Am Soc Nephrol 2006; 17:1437-43. [PMID: 16611712 DOI: 10.1681/asn.2005121305] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Mutations in the ATP6V1B1 and ATP6V0A4 genes, encoding subunits B1 and 4 of apical H(+) ATPase, cause recessive forms of distal renal tubular acidosis (dRTA). ATP6V1B mutations have been associated with early sensorineural hearing loss (SNHL), whereas ATP6V0A4 mutations are classically associated with either late-onset SNHL or normal hearing. The phenotype and genotype of 39 new kindreds with recessive dRTA, 18 of whom were consanguineous, were assessed. Novel and known loss-of-function mutations were identified in 31 kindreds. Fourteen new and five recurrent mutations of the ATP6V0A4 gene were identified in 21 families. For the ATP6V1B1 gene, two new and two previously described mutations were identified in 10 families. Surprisingly, seven probands with ATP6V0A4 gene mutations developed severe early SNHL between the ages of 2 mo and 10 yr. No mutation was detected in eight families. These data extend the spectrum of disease-causing mutations and provide evidence for genetic heterogeneity in SNHL. The data also demonstrate that mutations in either of these genes may cause early deafness, and they highlight the importance of genetic screening for recessive forms of dRTA independent of hearing status.
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Affiliation(s)
- Rosa Vargas-Poussou
- Centre Hospitalier Universitaire de Rouen, Département de Pédiatrie Médicale, and Faculté de Médecine et de Pharmacie, Rouen, France.
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185
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Corey HE, Vallo A, Rodríguez-Soriano J. An analysis of renal tubular acidosis by the Stewart method. Pediatr Nephrol 2006; 21:206-11. [PMID: 16362393 DOI: 10.1007/s00467-005-2081-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Revised: 07/26/2005] [Accepted: 07/26/2005] [Indexed: 10/25/2022]
Abstract
Renal tubular acidosis (RTA) comprises a group of disorders characterized by a low capacity for net acid excretion and persistent hyperchloremic, metabolic acidosis. To investigate the role of chloride, we performed hypotonic (0.45%) saline-loading experiments in 12 children with alkali-treated distal RTA (dRTA) and compared the results with data obtained from 17 healthy control subjects. In patients, but not in controls, saline loading induced both hyperchloremia and metabolic acidosis. Hyperchloremia was associated with high total and high distal fractional reabsorption of chloride [C(H20)/(C(H20)+C(Cl))]. The increase in plasma chloride varied inversely with the fractional excretion of chloride (C(Cl)) and correlated with the decrease in blood pH. However, the urinary excretion of bicarbonate did not correlate with either changes in blood pH or plasma bicarbonate concentration. Our findings suggest that the mechanism of hyperchloremia was enhanced Cl(-)/HCO(3) (-) exchange by the distal tubule. The resulting metabolic acidosis is better explained by changes in the strong ion difference (the Stewart theory) than by changes in the urine bicarbonate excretion (the traditional theory).
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Affiliation(s)
- Howard E Corey
- The Children's Kidney Center of New Jersey, Goryeb Children's Hospital, Morristown Memorial Hospital, Morristown, New Jersey 07962, USA.
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186
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Feldman M, Prikis M, Athanasiou Y, Elia A, Pierides A, Deltas CC. Molecular investigation and long-term clinical progress in Greek Cypriot families with recessive distal renal tubular acidosis and sensorineural deafness due to mutations in the ATP6V1B1 gene. Clin Genet 2006; 69:135-44. [PMID: 16433694 DOI: 10.1111/j.1399-0004.2006.00559.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spectrum of distal renal tubular acidosis (dRTA) includes a genetically heterogeneous group of inherited conditions of both autosomal-dominant and recessive mode of inheritance. The basic defect is linked to the renal part of acid-base homeostasis, which is partly achieved by the regulated luminal secretion of H+ at the apical surface of the alpha-intercalated cells of renal collecting ducts. This is coupled to bicarbonate reabsorption with chloride counter transport across the basolateral membranes. Here, we describe the molecular findings of the first two Greek Cypriot families with recessive dRTA and the long-term clinical findings in four of five affected members. DNA linkage analysis with four polymorphic markers flanking the ATP6V1B1 gene on chromosome 2 gave evidence for positive linkage; direct DNA analysis by automated DNA sequencing revealed that patients in one family were homozygous for mutation 229+1G>T (IVS7+1G>T) and that patients in the second family were compound heterozygous for 229+1G>T and R157C. The mutations were found on four different haplotypes. Both the mutations were previously reported in patients of Turkish origin. Three known polymorphic variants were also identified. The five patients demonstrated the whole clinical spectrum of the disease including death in infancy, failure to thrive, rickets, nephrocalcinosis, nephrolithiasis, and episodes of hypokalemic paralysis. Some of the family members are now in their mid 30s and late 20s, and nephrolithiasis with recurrent renal colics is their main problem. Renal function has remained normal. In conclusion, early diagnosis in infancy and prompt treatment with alkali and potassium supplements is of great benefit to the patient with dRTA and ensures normal growth. The identification of responsible mutations facilitates antenatal or postnatal diagnosis in concerned families and improves the prognosis.
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Affiliation(s)
- M Feldman
- The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
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187
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Yenchitsomanus PT, Kittanakom S, Rungroj N, Cordat E, Reithmeier RAF. Molecular mechanisms of autosomal dominant and recessive distal renal tubular acidosis caused by SLC4A1 (AE1) mutations. J Mol Genet Med 2005; 1:49-62. [PMID: 19565014 PMCID: PMC2702069 DOI: 10.4172/1747-0862.1000013] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2005] [Revised: 09/06/2005] [Accepted: 09/13/2005] [Indexed: 12/22/2022] Open
Abstract
Mutations of SLC4A1 (AE1) encoding the kidney anion (Cl−/HCO3−) exchanger 1 (kAE1 or band 3) can result in either autosomal dominant (AD) or autosomal recessive (AR) distal renal tubular acidosis (dRTA). The molecular mechanisms associated with SLC4A1 mutations resulting in these different modes of inheritance are now being unveiled using transfected cell systems. The dominant mutants kAE1 R589H, R901X and S613F, which have normal or insignificant changes in anion transport function, exhibit intracellular retention with endoplasmic reticulum (ER) localization in cultured non-polarized and polarized cells, while the dominant mutants kAE1 R901X and G609R are mis-targeted to apical membrane in addition to the basolateral membrane in cultured polarized cells. A dominant-negative effect is likely responsible for the dominant disease because heterodimers of kAE1 mutants and the wild-type protein are intracellularly retained. The recessive mutants kAE1 G701D and S773P however exhibit distinct trafficking defects. The kAE1 G701D mutant is retained in the Golgi apparatus, while the misfolded kAE1 S773P, which is impaired in ER exit and is degraded by proteosome, can only partially be delivered to the basolateral membrane of the polarized cells. In contrast to the dominant mutant kAE1, heterodimers of the recessive mutant kAE1 and wild-type kAE1 are able to traffic to the plasma membrane. The wild-type kAE1 thus exhibits a ‘dominant-positive effect’ relative to the recessive mutant kAE1 because it can rescue the mutant proteins from intracellular retention to be expressed at the cell surface. Consequently, homozygous or compound heterozygous recessive mutations are required for presentation of the disease phenotype. Future work using animal models of dRTA will provide additional insight into the pathophysiology of this disease.
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Affiliation(s)
- Pa-Thai Yenchitsomanus
- Division of Medical Molecular Biology and BIOTEC-Medical Biotechnology Unit, Division of Molecular Genetics, Department of Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
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188
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Pietrement C, Sun-Wada GH, Silva ND, McKee M, Marshansky V, Brown D, Futai M, Breton S. Distinct expression patterns of different subunit isoforms of the V-ATPase in the rat epididymis. Biol Reprod 2005; 74:185-94. [PMID: 16192400 DOI: 10.1095/biolreprod.105.043752] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
In the epididymis and vas deferens, the vacuolar H(+)ATPase (V-ATPase), located in the apical pole of narrow and clear cells, is required to establish an acidic luminal pH. Low pH is important for the maturation of sperm and their storage in a quiescent state. The V-ATPase also participates in the acidification of intracellular organelles. The V-ATPase contains many subunits, and several of these subunits have multiple isoforms. So far, only subunits ATP6V1B1, ATP6V1B2, and ATP6V1E2, previously identified as B1, B2, and E subunits, have been described in the rat epididymis. Here, we report the localization of V-ATPase subunit isoforms ATP6V1A, ATP6V1C1, ATP6V1C2, ATP6V1G1, ATP6V1G3, ATP6V0A1, ATP6V0A2, ATP6V0A4, ATP6V0D1, and ATP6V0D2, previously labeled A, C1, C2, G1, G3, a1, a2, a4, d1, and d2, in epithelial cells of the rat epididymis and vas deferens. Narrow and clear cells showed a strong apical staining for all subunits, except the ATP6V0A2 isoform. Subunits ATP6V0A2 and ATP6V1A were detected in intracellular structures closely associated but not identical to the TGN of principal cells and narrow/clear cells, and subunit ATP6V0D1 was strongly expressed in the apical membrane of principal cells in the apparent absence of other V-ATPase subunits. In conclusion, more than one isoform of subunits ATP6V1C, ATP6V1G, ATP6V0A, and ATP6V0D of the V-ATPase are present in the epididymal and vas deferens epithelium. Our results confirm that narrow and clear cells are well fit for active proton secretion. In addition, the diverse functions of the V-ATPase may be established through the utilization of specific subunit isoforms. In principal cells, the ATP6V0D1 isoform may have a physiological function that is distinct from its role in proton transport via the V-ATPase complex.
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Affiliation(s)
- C Pietrement
- Program in Membrane Biology, Massachusetts General Hospital, Boston, MA 02114, USA
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189
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Jouret F, Auzanneau C, Debaix H, Wada GHS, Pretto C, Marbaix E, Karet FE, Courtoy PJ, Devuyst O. Ubiquitous and kidney-specific subunits of vacuolar H+-ATPase are differentially expressed during nephrogenesis. J Am Soc Nephrol 2005; 16:3235-46. [PMID: 16177003 DOI: 10.1681/asn.2004110935] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The vacuolar H(+)-ATPase (V-ATPase) is a ubiquitous multisubunit pump that is responsible for acidification of intracellular organelles. In the kidney, a particular form of V-ATPase, made of specific subunits isoforms, has been located at the plasma membrane of intercalated cells (IC). Mutations in genes encoding IC-specific subunits cause infant distal renal tubular acidosis (dRTA), suggesting that the segmental distribution of these subunits is acquired at birth or during early infancy. However, the comparative ontogeny of the IC-specific versus the ubiquitous subunits of V-ATPase and the mechanisms involved in their segmental expression remain unknown. Real-time reverse transcription-PCR, in situ hybridization, immunoblotting, immunostaining, and subcellular fractionation analyses characterized the expression and distribution of V-ATPase subunits, transcription factors, and differentiation markers during mouse nephrogenesis. Ubiquitous A, E1, B2, G1, and C1 subunits showed an early (embryonic day 13.5 [E13.5]) and stable expression throughout nephrogenesis, followed by a slight increase around birth. The developmental pattern of a1 was bimodal, with early induction, gradual decrease during organogenesis, and neonatal increase. These patterns contrasted with the later (from E15.5) and progressive expression of IC-specific a4, B1, G3, and C2 subunits, after the induction of the forkhead transcription factor Foxi1. From E15.5, Foxi1 mRNA was detected in IC, where it co-distributed with B1 in late nephrogenesis. Immunostaining showed that the distribution of ubiquitous E1 and B2 was acquired from E15.5, whereas a4 was located in IC during late nephrogenesis. Subcellular fractionation showed that in both fetal and mature (cortex and medulla) kidneys, E1 and a4 were located in endosomes. These data demonstrate a differential expression and a coordinate regulation of IC-specific versus ubiquitous V-ATPase subunits during nephrogenesis. They provide new insights into the complex regulation of V-ATPase subunits, the maturation of IC along the nephron, and the pathophysiology of hereditary dRTA.
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Affiliation(s)
- François Jouret
- Division of Nephrology, Université catholique de Louvain, 10 Avenue Hippocrate, Brussels, Belgium B-1200
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190
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Laing CM, Toye AM, Capasso G, Unwin RJ. Renal tubular acidosis: developments in our understanding of the molecular basis. Int J Biochem Cell Biol 2005; 37:1151-61. [PMID: 15778079 DOI: 10.1016/j.biocel.2005.01.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2004] [Revised: 12/31/2004] [Accepted: 01/07/2005] [Indexed: 11/17/2022]
Abstract
Renal tubular acidosis is a metabolic acidosis due to impaired acid excretion by the kidney. Hyperchloraemic acidosis with a normal anion gap and normal (or near normal) glomerular filtration rate, and in the absence of diarrhoea, defines this disorder. However, systemic acidosis is not always evident and renal tubular acidosis can present with hypokalaemia, medullary nephrocalcinosis and recurrent calcium phosphate stone disease, as well as growth retardation and rickets in children, or short stature and osteomalacia in adults. Renal dysfunction in renal tubular acidosis is not always confined to acid excretion and can be part of a more generalised renal tubule defect, as in the renal Fanconi syndrome. Isolated renal tubular acidosis is more usually acquired, due to drugs, autoimmune disease, post-obstructive uropathy or any cause of medullary nephrocalcinosis. Less commonly, it is inherited and may be associated with deafness, osteopetrosis or ocular abnormalities. The clinical classification of renal tubular acidosis has been correlated with our current physiological model of how the nephron excretes acid, and this has facilitated genetic studies that have identified mutations in several genes encoding acid and base ion transporters. In vitro functional studies of these mutant proteins in cell expression systems have helped to elucidate the molecular mechanisms underlying renal tubular acidosis, which ultimately may lead to new therapeutic options in what is still treatment only by giving an oral alkali.
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Affiliation(s)
- Christopher M Laing
- Centre for Nephrology, Royal Free and University College Medical School, London NW3, UK
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191
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Smith AN, Jouret F, Bord S, Borthwick KJ, Al-Lamki RS, Wagner CA, Ireland DC, Cormier-Daire V, Frattini A, Villa A, Kornak U, Devuyst O, Karet FE. Vacuolar H+-ATPase d2 subunit: molecular characterization, developmental regulation, and localization to specialized proton pumps in kidney and bone. J Am Soc Nephrol 2005; 16:1245-56. [PMID: 15800125 DOI: 10.1681/asn.2004090761] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The ubiquitous multisubunit vacuolar-type proton pump (H+- or V-ATPase) is essential for acidification of diverse intracellular compartments. It is also present in specialized forms at the plasma membrane of intercalated cells in the distal nephron, where it is required for urine acidification, and in osteoclasts, playing an important role in bone resorption by acid secretion across the ruffled border membrane. It was reported previously that, in human, several of the renal pump's constituent subunits are encoded by genes that are different from those that are ubiquitously expressed. These paralogous proteins may be important in differential functions, targeting or regulation of H+-ATPases. They include the d subunit, where d1 is ubiquitous whereas d2 has a limited tissue expression. This article reports on an investigation of d2. It was first confirmed that in mouse, as in human, kidney and bone are two of the main sites of d2 mRNA expression. d2 mRNA and protein appear later during nephrogenesis than does the ubiquitously expressed E1 subunit. Mouse nephron-segment reverse transcription-PCR revealed detectable mRNA in all segments except thin limb of Henle's loop and distal convoluted tubule. However, with the use of a novel d2-specific antibody, high-intensity d2 staining was observed only in intercalated cells of the collecting duct in fresh-frozen human kidney, where it co-localized with the a4 subunit in the characteristic plasma membrane-enhanced pattern. In human bone, d2 co-localized with the a3 subunit in osteoclasts. This different subunit association in different tissues emphasizes the possibility of the H+-ATPase as a future therapeutic target.
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Affiliation(s)
- Annabel N Smith
- Department of Medical Genetics, University of Cambridge, United Kingdom
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192
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Watanabe T. Proximal renal tubular dysfunction in primary distal renal tubular acidosis. Pediatr Nephrol 2005; 20:86-8. [PMID: 15549407 DOI: 10.1007/s00467-004-1693-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Revised: 08/12/2004] [Accepted: 08/13/2004] [Indexed: 11/26/2022]
Abstract
Low-molecular-weight (LMW) proteinuria has been described in patients with primary distal renal tubular acidosis (dRTA). However, other proximal renal tubular dysfunctions have rarely been reported. In this report we describe reversible and multiple proximal renal tubular cell dysfunctions in a patient with dRTA. A 4-year-old girl was admitted to our hospital for investigation of short stature and proteinuria. Laboratory studies revealed a hyperchloremic metabolic acidosis without aciduria, hypokalemia, hypouricemia with uricosuria, hypercalciuria, LMW proteinuria, phosphaturia, and generalized aminoaciduria. The patient was diagnosed as having dRTA with multiple proximal renal tubular dysfunctions. All proximal renal tubular dysfunction subsided 1.5 years after starting alkali therapy. The precise pathogenic mechanisms underlying the development of multiple proximal renal tubular dysfunctions in dRTA remained unclear. However, proximal renal tubular endosomal dysfunction resulting from a profound intracellular acidosis caused by vacuolar H+-ATPase dysfunction or hypokalemic nephropathy might contribute to the development of proximal renal tubular dysfunctions in patients with dRTA.
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Affiliation(s)
- Toru Watanabe
- Department of Pediatrics, Niigata City General Hospital, 2-6-1 Shichikuyama, Niigata 950-8739, Japan.
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193
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Ariceta G, Vallo A, Rodriguez-Soriano J. Acidosis increases magnesiuria in children with distal renal tubular acidosis. Pediatr Nephrol 2004; 19:1367-70. [PMID: 15503178 DOI: 10.1007/s00467-004-1609-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
In experimental animals, metabolic acidosis increases renal magnesium (Mg) excretion, whereas metabolic alkalosis reduces it. The objective of this study was to examine renal magnesium handling (U(Mg)) in children with primary distal renal tubular acidosis (DRTA). We measured U(Mg) in 11 children (3 females, 8 males, aged 6.9+/-4.9 years) with primary DRTA. They were studied either during spontaneous acidosis post treatment removal (3 patients) or after ammonium chloride (100 mmol/m2) induced acidosis (8 patients), and then following oral sodium bicarbonate load (4 g/1.73 m2). During acidosis (plasma pH 7.28+/-0.09, bicarbonate 13.2+/-4.3 mEq/l), U(Mg) was elevated (U(Mg/Cr) 0.18+/-0.06 mg/mg, normal values 0.1+/-0.06, P=0.003) although plasma Mg (P(Mg)) was in the normal range (1.93+/-0.31 mg/dl, controls 1.77+/-0.19, P=NS). After acute correction of metabolic acidosis (plasma pH 7.44+/-0.05, bicarbonate 25.6+/-1.6 mEq/l, P<0.001; urine pH 7.52+/-0.28, bicarbonate 86.9+/-39.1 mEq/l), U(Mg) decreased significantly (P=0.003), returning to control values after about 2 h (U(Mg/Cr) 0.09+/-0.06 mg/mg). Bicarbonate load resulted not only in reduction in U(Mg) but also in a decrease in urinary calcium excretion (U(Ca/Cr)) from 0.46+/-0.17 mg/mg to 0.14+/-0.12 mg/mg (P<0.001). We conclude that in children with primary DRTA, urinary Mg excretion is markedly increased and that this defect, like the hypercalciuric defect, is correctable by sodium bicarbonate administration.
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Affiliation(s)
- Gema Ariceta
- Division of Pediatric Nephrology, Department of Pediatrics, Hospital Clinico Universitario de Santiago de Compostela, Spain.
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194
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Peters TA, Monnens LAH, Cremers CWRJ, Curfs JHAJ. Genetic disorders of transporters/channels in the inner ear and their relation to the kidney. Pediatr Nephrol 2004; 19:1194-201. [PMID: 15365806 DOI: 10.1007/s00467-004-1626-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2004] [Revised: 07/15/2004] [Accepted: 07/19/2004] [Indexed: 10/26/2022]
Abstract
Inner ear physiology is reviewed with emphasis on features common to renal physiology. Genetic disorders in transporters/channels for chloride (ClC-K), bicarbonate (Cl(-)/HCO(3)(-) exchanger), protons (H(+)-ATPase), sodium (ENaC, NKKC1, NBC3, NHE3), potassium (KCNQ1/KCNE1, Kcc4), and water (AQP4) in the inner ear and their relation to the kidney are discussed. Based on data from human disorders (with or without mouse counterparts) and mouse models (without human counterparts) this article focuses on the involvement of these transporters/channels in hearing loss.
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Affiliation(s)
- Theo A Peters
- Department of Otorhinolaryngology, University Medical Center Nijmegen, Philips van Leydenlaan 15, 6525 EX Nijmegen, The Netherlands.
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195
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Abstract
Vacuolar H(+)-ATPases are ubiquitous multisubunit complexes mediating the ATP-dependent transport of protons. In addition to their role in acidifying the lumen of various intracellular organelles, vacuolar H(+)-ATPases fulfill special tasks in the kidney. Vacuolar H(+)-ATPases are expressed in the plasma membrane in the kidney almost along the entire length of the nephron with apical and/or basolateral localization patterns. In the proximal tubule, a high number of vacuolar H(+)-ATPases are also found in endosomes, which are acidified by the pump. In addition, vacuolar H(+)-ATPases contribute to proximal tubular bicarbonate reabsorption. The importance in final urinary acidification along the collecting system is highlighted by monogenic defects in two subunits (ATP6V0A4, ATP6V1B1) of the vacuolar H(+)-ATPase in patients with distal renal tubular acidosis. The activity of vacuolar H(+)-ATPases is tightly regulated by a variety of factors such as the acid-base or electrolyte status. This regulation is at least in part mediated by various hormones and protein-protein interactions between regulatory proteins and multiple subunits of the pump.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, Univ. of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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196
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Dinour D, Chang MH, Satoh JI, Smith BL, Angle N, Knecht A, Serban I, Holtzman EJ, Romero MF. A novel missense mutation in the sodium bicarbonate cotransporter (NBCe1/SLC4A4) causes proximal tubular acidosis and glaucoma through ion transport defects. J Biol Chem 2004; 279:52238-46. [PMID: 15471865 DOI: 10.1074/jbc.m406591200] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In humans and terrestrial vertebrates, the kidney controls systemic pH in part by absorbing filtered bicarbonate in the proximal tubule via an electrogenic Na+/HCO3- cotransporter (NBCe1/SLC4A4). Recently, human genetics revealed that NBCe1 is the major renal contributor to this process. Homozygous point mutations in NBCe1 cause proximal renal tubular acidosis (pRTA), glaucoma, and cataracts (Igarashi, T., Inatomi, J., Sekine, T., Cha, S. H., Kanai, Y., Kunimi, M., Tsukamoto, K., Satoh, H., Shimadzu, M., Tozawa, F., Mori, T., Shiobara, M., Seki, G., and Endou, H. (1999) Nat. Genet. 23, 264-266). We have identified and functionally characterized a novel, homozygous, missense mutation (S427L) in NBCe1, also resulting in pRTA and similar eye defects without mental retardation. To understand the pathophysiology of the syndrome, we expressed wild-type (WT) NBCe1 and S427L-NBCe1 in Xenopus oocytes. Function was evaluated by measuring intracellular pH (HCO3- transport) and membrane currents using microelectrodes. HCO3- -elicited currents for S427L were approximately 10% of WT NBCe1, and CO2-induced acidification was approximately 4-fold faster. Na+ -dependent HCO3- transport (currents and acidification) was also approximately 10% of WT. Current-voltage (I-V) analysis reveals that S427L has no reversal potential in HCO3-, indicating that under physiological ion gradient conditions, NaHCO3 could not move out of cells as is needed for renal HCO3- absorption and ocular pressure homeostasis. I-V analysis without Na+ further shows that the S427L-mediated NaHCO3 efflux mode is depressed or absent. These experiments reveal that voltage- and Na+ -dependent transport by S427L-hkNBCe1 is unfavorably altered, thereby causing both insufficient HCO3- absorption by the kidney (proximal RTA) and inappropriate anterior chamber fluid transport (glaucoma).
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Affiliation(s)
- Dganit Dinour
- Department of Nephrology and Hypertension, Chaim Sheba Medical Center, Tel-Hashomer, and Tel-Aviv University, 52621 Israel
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197
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Abstract
PURPOSE OF REVIEW Research in the past several years has led to the understanding of numerous genetic mutations that lead to inheritable forms of distal renal tubular acidosis (dRTA). Most of these mutations affect the physiology of the A-intercalated cells of the renal cortical collecting duct. These include mutations of genes encoding carbonic anhydrase II, kidney anion exchanger 1, and different subunits of the H+-ATPase proton pump. Genetic defects in any one of these components may impair renal acidification and thereby result in persistent acidosis, failure to thrive, and nephrocalcinosis. RECENT FINDINGS The present review provides a summary of the most recently identified genetic mutations resulting in a dRTA phenotype and, when possible, describes a mechanism. Most causes of dRTA are due to loss of function or inappropriate targeting of transporters. SUMMARY The collaboration of clinicians, geneticists, and renal physiologists has enabled us to better understand at the cellular level the different mechanisms leading to dRTA. Such information should lead to earlier diagnosis and treatment, thereby minimizing the irreversible complications affecting patients with this or similar diseases.
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Affiliation(s)
- Julie A Nicoletta
- Department of Pediatrics, University of Rochester School of Medicine, Box 777, 601 Elmwood Avenue, Rochester, New York 14642, USA
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Stehberger PA, Schulz N, Finberg KE, Karet FE, Giebisch G, Lifton RP, Geibel JP, Wagner CA. Localization and Regulation of the ATP6V0A4 (a4) Vacuolar H+-ATPase Subunit Defective in an Inherited Form of Distal Renal Tubular Acidosis. J Am Soc Nephrol 2003; 14:3027-38. [PMID: 14638902 DOI: 10.1097/01.asn.0000099375.74789.ab] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
ABSTRACT. Vacuolar-type H+-ATPases (V-H+-ATPases) are the major H+-secreting protein in the distal portion of the nephron and are involved in net H+secretion (bicarbonate generation) or H+reabsorption (net bicarbonate secretion). In addition, V-H+-ATPases are involved in HCO3−reabsorption in the proximal tubule and distal tubule. V-H+-ATPases consist of at least 13 subunits, the functions of which have not all been elucidated. Mutations in the accessory ATP6V0A4 (a4 isoform) subunit have recently been shown to cause an inherited form of distal renal tubular acidosis in humans. Here, the localization of this subunit in human and mouse kidney was studied and the regulation of expression and localization of this subunit in mouse kidney in response to acid-base and electrolyte intake was investigated. Reverse transcription-PCR on dissected mouse nephron segments amplified a4-specific transcripts in proximal tubule, loop of Henle, distal convoluted tubule, and cortical and medullary collecting duct. a4 protein was localized by immunohistochemistry to the apical compartment of the proximal tubule (S1/S2 segment), the loop of Henle, the intercalated cells of the distal convoluted tubule, the connecting segment, and all intercalated cells of the entire collecting duct in human and mouse kidney. All types of intercalated cells expressed a4. NH4Cl or NaHCO3loading for 24 h, 48 h, or 7 d as well as K+depletion for 7 and 14 d had no influence on a4 protein expression levels in either cortex or medulla as determined by Western blotting. Immunohistochemistry, however, demonstrated a subcellular redistribution of a4 in response to the different stimuli. NH4Cl and K+depletion led to a pronounced apical staining in the connecting segment, cortical collecting duct, and outer medullary collecting duct, whereas NaHCO3loading caused a stronger bipolar staining in the cortical collecting duct. Taken together, these results demonstrate a4 expression in the proximal tubule, loop of Henle, distal tubule, and collecting duct and suggest that under conditions in which increased V-H+-ATPase activity is required, a4 is regulated by trafficking but not protein expression. This may allow for the rapid adaptation of V-H+-ATPase activity to altered acid-base intake to achieve systemic pH homeostasis. The significance of a4 expression in the proximal tubule in the context of distal renal tubular acidosis will require further clarification.
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Affiliation(s)
- Paul A Stehberger
- Departments of Cellular and Molecular Physiology, Genetics, and Surgery, Yale University School of Medicine, New Haven, Connecticut, USA
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Manolson MF, Yu H, Chen W, Yao Y, Li K, Lees RL, Heersche JNM. The a3 isoform of the 100-kDa V-ATPase subunit is highly but differentially expressed in large (>or=10 nuclei) and small (<or= nuclei) osteoclasts. J Biol Chem 2003; 278:49271-8. [PMID: 14504271 DOI: 10.1074/jbc.m309914200] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Osteoclasts dissolve bone through acidification of an extracellular compartment by means of a multimeric vacuolar type H+-ATPase (V-ATPase). In mammals, there are four isoforms of the 100-kDa V-ATPase "a" subunit. Mutations in the a3 isoform result in deficient bone resorption and osteopetrosis, suggesting that a3 has a unique function in osteoclasts. It is thus surprising that several studies show a basal level of a3 expression in most tissues. To address this issue, we have compared a3 expression in bone with expression in other tissues. RNA blots revealed that the a3 isoform was expressed highest in bone and confirmed its expression (in decreasing order) in liver, kidney, brain, lung, spleen, and muscle. In situ hybridization on bone tissue sections revealed that the a3 isoform was highly expressed in multinucleated osteoclasts but not in mononuclear stromal cells, whereas the a1 isoform was expressed in both cell types at about the same level. We also found that a3 expression was greater in osteoclasts with 10 or more nuclei as compared with osteoclasts with five or fewer nuclei. We hypothesize that these differences in a3 expression may be associated with previously demonstrated differences between large and small osteoclasts with reference to their resorptive activity.
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Affiliation(s)
- Morris F Manolson
- Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada.
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Abstract
Given the unique biological requirements of sound transduction and the selective advantage conferred upon a species capable of sensitive sound detection, it is not surprising that up to 1% of the approximately 30,000 or more human genes are necessary for hearing. There are hundreds of monogenic disorders for which hearing loss is one manifestation of a syndrome or the only disorder and therefore is nonsyndromic. Herein we review the supporting evidence for identifying over 30 genes for dominantly and recessively inherited, nonsyndromic, sensorineural deafness. The state of knowledge concerning their biological roles is discussed in the context of the controversies within an evolving understanding of the intricate molecular machinery of the inner ear.
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Affiliation(s)
- Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland 20850, USA.
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