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Suhlrie A, Hennies I, Gellermann J, Büscher A, Hoyer P, Waldegger S, Wygoda S, Beetz R, Lange-Sperandio B, Klaus G, Konrad M, Holder M, Staude H, Rascher W, Oh J, Pape L, Tönshoff B, Haffner D. Twelve-month outcome in juvenile proliferative lupus nephritis: results of the German registry study. Pediatr Nephrol 2020; 35:1235-1246. [PMID: 32193650 DOI: 10.1007/s00467-020-04501-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 01/27/2020] [Accepted: 02/06/2020] [Indexed: 12/14/2022]
Abstract
BACKGROUND Children presenting with proliferative lupus nephritis (LN) are treated with intensified immunosuppressive protocols. Data on renal outcome and treatment toxicity is scare. METHODS Twelve-month renal outcome and comorbidity were assessed in 79 predominantly Caucasian children with proliferative LN reported to the Lupus Nephritis Registry of the German Society of Paediatric Nephrology diagnosed between 1997 and 2015. RESULTS At the time of diagnosis, median age was 13.7 (interquartile range 11.8-15.8) years; 86% showed WHO histology class IV, nephrotic range proteinuria was noted in 55%, and median estimated glomerular filtration rate amounted to 75 ml/min/1.73 m2. At 12 months, the percentage of patients with complete and partial remission was 38% and 41%, respectively. Six percent of patients were non-responders and 15% presented with renal flare. Nephrotic range proteinuria at the time of diagnosis was associated with inferior renal outcome (odds ratio 5.34, 95% confidence interval 1.26-22.62, p = 0.02), whereas all other variables including mode of immune-suppressive treatment (e.g., induction treatment with cyclophosphamide (IVCYC) versus mycophenolate mofetil (MMF)) were not significant correlates. Complications were reported in 80% of patients including glucocorticoid toxicity in 42% (Cushingoid appearance, striae distensae, cataract, or osteonecrosis), leukopenia in 37%, infection in 23%, and menstrual disorder in 20%. Growth impairment, more pronounced in boys than girls, was noted in 78% of patients. CONCLUSIONS In this cohort of juvenile proliferative LN, renal outcome at 12 months was good irrespectively if patients received induction treatment with MMF or IVCYC, but glucocorticoid toxicity was very high underscoring the need for corticoid sparing protocols. Graphical abstract.
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Affiliation(s)
- Adriana Suhlrie
- Department of Paediatric Kidney, Liver and Metabolic Diseases, Paediatric Research Center, Hannover Medical School Children's Hospital, Carl-Neuberg-Str. 1, 30625, Hannover, Germany.,Center for Rare Diseases, Hannover Medical School Children's Hospital, Hannover, Germany
| | - Imke Hennies
- Department of Paediatric Kidney, Liver and Metabolic Diseases, Paediatric Research Center, Hannover Medical School Children's Hospital, Carl-Neuberg-Str. 1, 30625, Hannover, Germany.,Center for Rare Diseases, Hannover Medical School Children's Hospital, Hannover, Germany
| | - Jutta Gellermann
- Department of Paediatrics, University Children's Hospital Berlin, University Hospital, Berlin Charité, Berlin, Germany
| | - Anja Büscher
- Department of Paediatrics II, University Hospital Essen, Essen, Germany
| | - Peter Hoyer
- Department of Paediatrics II, University Hospital Essen, Essen, Germany
| | - Siegfried Waldegger
- Department of Peadiatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | | | - Rolf Beetz
- University Children's Hospital Mainz, Mainz, Germany
| | - Bärbel Lange-Sperandio
- Dr. v. Hauner Children's Hospital, Division of Paediatric Nephrology, Ludwig-Maximilians, University of Munich, Munich, Germany
| | - Günter Klaus
- University Children's Hospital Marburg, Marburg, Germany
| | - Martin Konrad
- Department of General Paediatrics, University Children's Hospital, Münster, Germany
| | - Martin Holder
- Department of Pediatrics, Klinikum Stuttgart, Olgahospital, Stuttgart, Germany
| | - Hagen Staude
- University Children's Hospital Rostock, Rostock, Germany
| | - Wolfgang Rascher
- Department of Paediatrics and Adolescent Medicine, University Hospital Erlangen, Erlangen, Germany
| | - Jun Oh
- Department of Paediatrics, University Hamburg-Eppendorf, 20246, Hamburg, Germany
| | - Lars Pape
- Department of Paediatric Kidney, Liver and Metabolic Diseases, Paediatric Research Center, Hannover Medical School Children's Hospital, Carl-Neuberg-Str. 1, 30625, Hannover, Germany.,Center for Rare Diseases, Hannover Medical School Children's Hospital, Hannover, Germany
| | - Burkhard Tönshoff
- Department of Paediatrics I, University Children's Hospital Heidelberg, University of Heidelberg, Heidelberg, Germany
| | - Dieter Haffner
- Department of Paediatric Kidney, Liver and Metabolic Diseases, Paediatric Research Center, Hannover Medical School Children's Hospital, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. .,Center for Rare Diseases, Hannover Medical School Children's Hospital, Hannover, Germany.
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Kienzl-Wagner K, Waldegger S, Schneeberger S. Disease Recurrence-The Sword of Damocles in Kidney Transplantation for Primary Focal Segmental Glomerulosclerosis. Front Immunol 2019; 10:1669. [PMID: 31379860 PMCID: PMC6652209 DOI: 10.3389/fimmu.2019.01669] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 07/04/2019] [Indexed: 12/21/2022] Open
Abstract
A major obstacle in kidney transplantation for primary focal segmental glomerulosclerosis (FSGS) is the risk of disease recurrence. Recurrent FSGS affects up to 60% of first kidney grafts and exceeds 80% in patients who have lost their first graft due to recurrent FSGS. Clinical and experimental evidence support the hypothesis that a circulating permeability factor is the mediator in the pathogenesis of primary and recurrent disease. Despite all efforts, the causing agent has not yet been identified. Several treatment options for the management of recurrent FSGS have been proposed. In addition to plasma exchange, B-cell depleting antibodies are effective in recurrent FSGS. This indicates, that the secretion and/or activity of the postulated circulating permeability factor(s) may be B-cell related. This review summarizes the current knowledge on permeability factor(s) possibly related to the disease and discusses strategies for the management of recurrent FSGS. These include profound B-cell depletion prior to transplantation, as well as the salvage of an allograft affected by recurrent FSGS by transfer into a second recipient.
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Affiliation(s)
- Katrin Kienzl-Wagner
- Department of Visceral, Transplant and Thoracic Surgery, Medical University of Innsbruck, Innsbruck, Austria
| | - Siegfried Waldegger
- Department of Pediatrics, Medical University of Innsbruck, Innsbruck, Austria
| | - Stefan Schneeberger
- Department of Visceral, Transplant and Thoracic Surgery, Medical University of Innsbruck, Innsbruck, Austria
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3
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Jeck N, Waldegger S, Wissinger B, Schwab M, Lang F. Response: ClC-Kb Mutation Revisited. Hypertension 2019. [DOI: 10.1161/01.hyp.0000203774.46024.e7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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4
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Kienzl‐Wagner K, Rosales A, Scheidl S, Giner T, Bösmüller C, Rudnicki M, Oberhuber R, Margreiter C, Soleiman A, Öfner D, Waldegger S, Schneeberger S. Successful management of recurrent focal segmental glomerulosclerosis. Am J Transplant 2018; 18:2818-2822. [PMID: 29962080 PMCID: PMC6220932 DOI: 10.1111/ajt.14998] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 06/20/2018] [Accepted: 06/22/2018] [Indexed: 01/25/2023]
Abstract
Primary focal segmental glomerulosclerosis (FSGS) recurs in up to 55% of patients after kidney transplantation. Herein we report the successful management of recurrent FSGS. A 5-year-old boy with primary FSGS received a deceased donor renal transplant. Immediate and fulminant recurrence of FSGS caused anuric graft failure that was resistant to plasmapheresis and rituximab. After exclusion of structural or immunologic damage to the kidney by repeated biopsies, the allograft was retrieved from the first recipient on day 27 and transplanted into a 52-year-old second recipient who had vascular nephropathy. Immediately after retransplantation, the allograft regained function with excellent graft function persistent now at 3 years after transplant. After 2 years on hemodialysis, the boy was listed for kidney retransplantation. To prevent FSGS recurrence, pretreatment with ofatumumab was performed. Nephrotic range proteinuria still occurred after the second transplantation, which responded, however, to daily plasma exchange in combination with ofatumumab. At 8 months after kidney retransplantation graft function is good. The clinical course supports the hypothesis of a circulating permeability factor in the pathogenesis of FSGS. Successful ofatumumab pretreatment implicates a key role of B cells. Herein we provide a description of successful management of kidney failure by FSGS, carefully avoiding waste of organs.
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Affiliation(s)
- Katrin Kienzl‐Wagner
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | - Alejandra Rosales
- Department of PediatricsMedical University of InnsbruckInnsbruckAustria
| | - Stefan Scheidl
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | - Thomas Giner
- Department of PediatricsMedical University of InnsbruckInnsbruckAustria
| | - Claudia Bösmüller
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | - Michael Rudnicki
- Department of Internal MedicineMedical University of InnsbruckInnsbruckAustria
| | - Rupert Oberhuber
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | - Christian Margreiter
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | | | - Dietmar Öfner
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
| | | | - Stefan Schneeberger
- Department of Visceral, Transplant and Thoracic SurgeryMedical University of InnsbruckInnsbruckAustria
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5
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Cortina G, Ojinaga V, Giner T, Riedl M, Waldegger S, Rosales A, Trojer R, Hofer J. Therapeutic plasma exchange in children: One center's experience. J Clin Apher 2017; 32:494-500. [DOI: 10.1002/jca.21547] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2016] [Revised: 02/17/2017] [Accepted: 04/04/2017] [Indexed: 12/17/2022]
Affiliation(s)
- Gerard Cortina
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Violeta Ojinaga
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Thomas Giner
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Magdalena Riedl
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Siegfried Waldegger
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Alejandra Rosales
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Raphaela Trojer
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
| | - Johannes Hofer
- Department of Pediatrics; Medical University of Innsbruck; Innsbruck Austria
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Janecke AR, Xu R, Steichen-Gersdorf E, Waldegger S, Entenmann A, Giner T, Krainer I, Huber LA, Hess MW, Frishberg Y, Barash H, Tzur S, Schreyer-Shafir N, Sukenik-Halevy R, Zehavi T, Raas-Rothschild A, Mao C, Müller T. Deficiency of the sphingosine-1-phosphate lyase SGPL1 is associated with congenital nephrotic syndrome and congenital adrenal calcifications. Hum Mutat 2017; 38:365-372. [PMID: 28181337 DOI: 10.1002/humu.23192] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 02/01/2017] [Accepted: 02/03/2017] [Indexed: 01/21/2023]
Abstract
We identified two unrelated consanguineous families with three children affected by the rare association of congenital nephrotic syndrome (CNS) diagnosed in the first days of life, of hypogonadism, and of prenatally detected adrenal calcifications, associated with congenital adrenal insufficiency in one case. Using exome sequencing and targeted Sanger sequencing, two homozygous truncating mutations, c.1513C>T (p.Arg505*) and c.934delC (p.Leu312Phefs*30), were identified in SGPL1-encoding sphingosine-1-phosphate (S1P) lyase 1. SGPL1 catalyzes the irreversible degradation of endogenous and dietary S1P, the final step of sphingolipid catabolism, and of other phosphorylated long-chain bases. S1P is an intracellular and extracellular signaling molecule involved in angiogenesis, vascular maturation, and immunity. The levels of SGPL1 substrates, S1P, and sphingosine were markedly increased in the patients' blood and fibroblasts, as determined by liquid chromatography-tandem mass spectrometry. Vascular alterations were present in a patient's renal biopsy, in line with changes seen in Sgpl1 knockout mice that are compatible with a developmental defect in vascular maturation. In conclusion, loss of SGPL1 function is associated with CNS, adrenal calcifications, and hypogonadism.
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Affiliation(s)
- Andreas R Janecke
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria.,Division of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria
| | - Ruijuan Xu
- Department of Medicine, State University of New York (SUNY) at Stony Brook, Stony Brook, New York.,Stony Brook Cancer Center at State University of New York (SUNY) at Stony Brook, Stony Brook, New York
| | | | - Siegfried Waldegger
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Andreas Entenmann
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Thomas Giner
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Iris Krainer
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Lukas A Huber
- Division of Cell Biology, Medical University of Innsbruck, Innsbruck, Austria
| | - Michael W Hess
- Division of Histology and Embryology, Medical University of Innsbruck, Innsbruck, Austria
| | - Yaacov Frishberg
- Division of Pediatric Nephrology, Shaare Zedek Medical Center, Jerusalem, Israel
| | - Hila Barash
- Institute of Rare Diseases, Institute of Genetics, Sheba Medical center, Tel Hashomer, Israel
| | - Shay Tzur
- Laboratory of Molecular Medicine, Rambam Health Care Campus, Haifa, Israel.,Genomic Research Department, Emedgene Technologies, Tel Aviv, Israel
| | | | - Rivka Sukenik-Halevy
- Genetics Institute, Meir Medical Center, Kfar Saba, Israel.,Sackler school of medicine, Tel Aviv University, Ramat Aviv, Israel
| | - Tania Zehavi
- Department of Pathology, Meir Medical center, Kfar Saba, Israel
| | - Annick Raas-Rothschild
- Institute of Rare Diseases, Institute of Genetics, Sheba Medical center, Tel Hashomer, Israel.,Sackler school of medicine, Tel Aviv University, Ramat Aviv, Israel
| | - Cungui Mao
- Department of Medicine, State University of New York (SUNY) at Stony Brook, Stony Brook, New York.,Stony Brook Cancer Center at State University of New York (SUNY) at Stony Brook, Stony Brook, New York
| | - Thomas Müller
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
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7
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Heinz-Erian P, Akdar Z, Haerter B, Waldegger S, Giner T, Scholl-Bürgi S, Mueller T. Decreased Urinary Sodium-to-urinary Creatinine Ratio Identifies Sodium Depletion in Pediatric Acute Gastroenteritis. Klin Padiatr 2015; 228:24-8. [PMID: 26356318 DOI: 10.1055/s-0035-1559689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
UNLABELLED In acute gastroenteritis (AG) fecal losses may cause depletion of sodium (NaD) which may not be recognized because of normal plasma Na (pNa) concentrations. We studied the incidence of this state of normonatremic sodium depletion (NNaD) and the suitability of the urinary Na/urinary creatinine ratio (uNa/uCr) for diagnosing NNaD. PATIENTS 16 AG- and 16 healthy control children aged 0.8-15.0 years. METHODS Prospective cross sectional pilot study. Measurements of Na, K and creatinine in plasma (p) and urine (u). Calculation of uNa/uCr Ratio, fractional excretion of Na (FENa) and uNa/uK ratio as the hitherto best known parameters of prerenal Na depletion, respectively. RESULTS pNa concentrations were normal in 15/16 AG patients (93.8%) with only one subnormal value of 133 mmol/L, and a mean value of 137.9±2.3 mmol/L not different from the normal control group (139.4±2.2 mmol/L). Also, mean uNa concentrations and uNa/uK ratios did not differ between both groups. However, uNa/uCr ratios were below normal in 13/16 AG children (81.3%) but normal in all healthy controls with a significantly lower mean value in the AG group (12.6±8.8 vs. 31.2±8.3 mmol/mmol; p<0.0001). Similarly, 14/16 AG patients (87.5%) had a decreased FENa<0.5% with a mean FENa value significantly lower than in controls (0.36±0.28% vs. 0.95±0.26%, p<0.0001). The good agreement between FENa and uNa/uCr results was also reflected by a high correlation coefficient of r=0.9333. CONCLUSIONS The majority of AG patients was found to have NNaD as determined by uNa/uCr and FENa. Calculation of uNa/uCr may be useful for diagnosing NNaD in AG.
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Affiliation(s)
- P Heinz-Erian
- Department Pediatrics I, Medical University, Innsbruck, Austria
| | - Z Akdar
- Department Pediatrics I, Medical University, Innsbruck, Austria
| | - B Haerter
- Pediatric Surgery, Medical University, Innsbruck, Austria
| | - S Waldegger
- Department Pediatrics I, Medical University, Innsbruck, Austria
| | - T Giner
- Department Pediatrics I, Medical University, Innsbruck, Austria
| | - S Scholl-Bürgi
- Department Pediatrics I, Medical University, Innsbruck, Austria
| | - T Mueller
- Department Pediatrics I, Medical University, Innsbruck, Austria
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Cortina G, Trojer R, Waldegger S, Schneeberger S, Gut N, Hofer J. De novo tacrolimus-induced thrombotic microangiopathy in the early stage after renal transplantation successfully treated with conversion to everolimus. Pediatr Nephrol 2015; 30:693-7. [PMID: 25577332 DOI: 10.1007/s00467-014-3036-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 12/11/2014] [Accepted: 12/12/2014] [Indexed: 01/13/2023]
Abstract
BACKGROUND Calcineurin inhibitor (CNI)-induced thrombotic microangiopathy (TMA) is a rare complication after renal transplantation. It may be difficult to distinguish from CNI toxicity and acute antibody-mediated rejection (AMR). Its clinical presentation may vary from isolated localised forms up to catastrophic systemic presentations. CASE We report a case of tacrolimus-induced TMA soon after renal transplantation in an 11-year-old boy who received his second renal transplantation. His first graft was lost because of AMR. On day 12 after his second renal transplantation, his renal function started worsening and a kidney biopsy was performed, which showed histopathological signs of TMA. The diagnosis of tacrolimus-induced TMA was established after excluding AMR and other causes of de novo TMA. Genetic complement investigation disclosed two complement factor H risk polymorphisms as possible modifiers of TMA emergence. Treatment was based on replacing tacrolimus with everolimus, with a subsequent normalisation of renal function. CONCLUSION A prompt diagnosis of de novo TMA by early allograft biopsy is essential for the allograft outcome and genetic investigations for possible complement abnormalities are reasonable, not only for patients with a systemic aspect of their post-transplant TMA. Replacing tacrolimus with everolimus effectively controlled the TMA and stabilised renal function in our patient.
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Affiliation(s)
- Gerard Cortina
- Department of Paediatrics I, Innsbruck Medical University, Anichstrasse 35, 6020, Innsbruck, Austria
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9
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Musial K, Zwolinska D, Vivarelli M, Gerken C, Pelle T, Pedicelli S, Diomedi F, Klaus G, Waldegger S, Emma F, Ronco P, Debiec H, Camilla R, Coppo R, Bellur S, Cattran D, Cook T, Feehally J, Troyanov S, Emma F, Giannakakis C, Amore A, Mazzucco G, Berg U, Soderberg M, Mizerska-Wasiak M. Paediatric nephrology - B. Nephrol Dial Transplant 2013. [DOI: 10.1093/ndt/gft162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Renigunta A, Mutig K, Rottermann K, Schlichthörl G, Preisig-Müller R, Daut J, Waldegger S, Renigunta V. The glycolytic enzymes glyceraldehyde 3-phosphate dehydrogenase and enolase interact with the renal epithelial K+ channel ROMK2 and regulate its function. Cell Physiol Biochem 2011; 28:663-72. [PMID: 22178878 DOI: 10.1159/000335761] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/02/2011] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND/AIMS ROMK channels mediate potassium secretion and regulate NaCl reabsorption in the kidney. The aim was to study the functional implications of the interaction between ROMK2 (Kir1.1b) and two glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and enolase-α, which were identified as potential regulatory subunits of the channel complex. METHODS We performed a membrane yeast-two-hybrid screen of a human kidney cDNA library with ROMK2 as a bait. Interaction of ROMK2 with GAPDH and enolase was verified using GST pull-down, co-immunoprecipitation, immunohistochemistry and co-expression in Xenopus oocytes. RESULTS Confocal imaging showed co-localisation of enolase and GAPDH with ROMK2 in the apical membrane of the renal epithelial cells of the thick ascending limb. Over-expression of GAPDH or enolase-α in Xenopus oocytes markedly reduced the amplitude of ROMK2 currents but did not affect the surface expression of the channels. Co-expression of the glycolytically inactive GAPDH mutant C149G did not have any effect on ROMK2 current amplitude. CONCLUSION Our results suggest that the glycolytic enzymes GAPDH and enolase are part of the ROMK2 channel supramolecular complex and may serve to couple salt reabsorption in the thick ascending limb of the loop of Henle to the metabolic status of the renal epithelial cells.
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Affiliation(s)
- Aparna Renigunta
- Department of Paediatric Nephrology, Children's Hospital, University of Marburg, Baldingerstrasse, Marburg, Germany
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11
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Knop C, Heinzinger J, Maier RF, Waldegger S. Funktionelle Untersuchung neuer Mutationen des NaCl-Cotransporters der Niere beim Gitelman Syndrom. Klin Padiatr 2011. [DOI: 10.1055/s-0031-1273870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Renigunta A, Renigunta V, Saritas T, Decher N, Mutig K, Waldegger S. Tamm-Horsfall glycoprotein interacts with renal outer medullary potassium channel ROMK2 and regulates its function. J Biol Chem 2011; 286:2224-2235. [PMID: 21081491 PMCID: PMC3023518 DOI: 10.1074/jbc.m110.149880] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Revised: 10/27/2010] [Indexed: 09/12/2023] Open
Abstract
Tamm-Horsfall glycoprotein (THGP) or Uromodulin is a membrane protein exclusively expressed along the thick ascending limb (TAL) and early distal convoluted tubule (DCT) of the nephron. Mutations in the THGP encoding gene result in Familial Juvenile Hyperuricemic Nephropathy (FJHN), Medullary Cystic Kidney Disease type 2 (MCKD-2), and Glomerulocystic Kidney Disease (GCKD). The physicochemical and biological properties of THGP have been studied extensively, but its physiological function in the TAL remains obscure. We performed yeast two-hybrid screening employing a human kidney cDNA library and identified THGP as a potential interaction partner of the renal outer medullary potassium channel (ROMK2), a key player in the process of salt reabsorption along the TAL. Functional analysis by electrophysiological techniques in Xenopus oocytes showed a strong increase in ROMK current amplitudes when co-expressed with THGP. The effect of THGP was specific for ROMK2 and did not influence current amplitudes upon co-expression with Kir2.x, inward rectifier potassium channels related to ROMK. Single channel conductance and open probability of ROMK2 were not altered by co-expression of THGP, which instead increased surface expression of ROMK2 as determined by patch clamp analysis and luminometric surface quantification, respectively. Despite preserved interaction with ROMK2, disease-causing THGP mutants failed to increase its current amplitude and surface expression. THGP(-/-) mice exhibited increased ROMK accumulation in intracellular vesicular compartments when compared with WT animals. Therefore, THGP modulation of ROMK function confers a new role of THGP on renal ion transport and may contribute to salt wasting observed in FJHN/MCKD-2/GCKD patients.
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Affiliation(s)
- Aparna Renigunta
- From the Department of Pediatric Nephrology, Children's Hospital, Philipps University of Marburg, Baldingerstr., 35043 Marburg, Germany
| | - Vijay Renigunta
- the Institute of Physiology, Philipps University of Marburg, Deutschhausstr. 2, 35037 Marburg, Germany, and
| | - Turgay Saritas
- the Institute of Anatomy, Charité-University Medicine, Philippstr. 12, Berlin, Germany
| | - Niels Decher
- the Institute of Physiology, Philipps University of Marburg, Deutschhausstr. 2, 35037 Marburg, Germany, and
| | - Kerim Mutig
- the Institute of Anatomy, Charité-University Medicine, Philippstr. 12, Berlin, Germany
| | - Siegfried Waldegger
- From the Department of Pediatric Nephrology, Children's Hospital, Philipps University of Marburg, Baldingerstr., 35043 Marburg, Germany
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13
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Hou J, Renigunta A, Yang J, Waldegger S. Claudin-4 forms paracellular chloride channel in the kidney and requires claudin-8 for tight junction localization. Proc Natl Acad Sci U S A 2010; 107:18010-5. [PMID: 20921420 PMCID: PMC2964195 DOI: 10.1073/pnas.1009399107] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. The paracellular pathway in the collecting duct of the kidney is a predominant route for transepithelial chloride reabsorption that determines the extracellular NaCl content and the blood pressure. However, the molecular mechanisms underlying the paracellular chloride reabsorption in the collecting duct are not understood. Here we showed that in mouse kidney collecting duct cells, claudin-4 functioned as a Cl(-) channel. A positively charged lysine residue at position 65 of claudin-4 was critical for its anion selectivity. Claudin-4 was observed to interact with claudin-8 using several criteria. In the collecting duct cells, the assembly of claudin-4 into TJ strands required its interaction with claudin-8. Depletion of claudin-8 resulted in the loss of paracellular chloride conductance, through a mechanism involving its recruitment of claudin-4 during TJ assembly. Together, our data show that claudin-4 interacts with claudin-8 and that their association is required for the anion-selective paracellular pathway in the collecting duct, suggesting a mechanism for coupling chloride reabsorption with sodium reabsorption in the collecting duct.
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Affiliation(s)
- Jianghui Hou
- Renal Division, Washington University Medical School, St. Louis, MO 63110, USA.
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14
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Jeck N, Schlingmann P, Waldegger S, Maier RF, Klaus G. Bilaterale Nephrektomie bei ESRD und schwerer Therapie-refraktärer arterieller Hypertonie. Klin Padiatr 2010. [DOI: 10.1055/s-0030-1251050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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15
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Jeck N, Schlingmann P, Klaus G, Gröne HJ, Maier RF, Waldegger S. Purpura Schönlein Henoch (PSH) Nephritis: 2 Fälle mit nephritisch-nephrotischem Verlauf und postivem ANCA. Klin Padiatr 2010. [DOI: 10.1055/s-0030-1251048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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16
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Jeck N, Schlingmann P, Waldegger S, Maier RF, Konrad M. Kalium-Kanal Kir4.1– ein neuer Kandidat in der Pathogenese der hypokaliämischen Salzverlust-Tubulopathien. Klin Padiatr 2010. [DOI: 10.1055/s-0030-1251069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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17
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Wilke A, Borta A, Waldegger S, Klingmüller V, Maier RF. Grippale Symptome, Kreatinin-Anstieg und Thrombozytopenie: auch an Hantavirus-Infektion denken! Klin Padiatr 2009. [DOI: 10.1055/s-0029-1214343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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18
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Neubauer BA, Waldegger S, Heinzinger J, Hahn A, Kurlemann G, Fiedler B, Eberhard F, Muhle H, Stephani U, Garkisch S, Eeg-Olofsson O, Müller U, Sander T. KCNQ2 and KCNQ3 mutations contribute to different idiopathic epilepsy syndromes. Neurology 2008; 71:177-83. [PMID: 18625963 DOI: 10.1212/01.wnl.0000317090.92185.ec] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To explore the involvement of M-type potassium channels KCNQ2, Q3, and Q5 in the pathogenesis of common idiopathic epilepsies. METHODS Sequence analysis of the KCNQ2, Q3, and Q5 coding regions was performed in a screening sample consisting of 58 nuclear families with rolandic epilepsy. Subsequently, an association study was conducted for all discovered variants in a case-control sample comprising 459 German patients with idiopathic generalized epilepsy (IGE) and 462 population controls. RESULTS An in-frame deletion of codon 116 in KCNQ2 (p.Lys116del) and a missense mutation in KCNQ3 (p.Glu299Lys) were detected in two index cases exhibiting rolandic epilepsy and benign neonatal convulsions. Both mutations resulted in reduced potassium current amplitude in Xenopus oocytes. Mutation analysis of families with rolandic epilepsy without neonatal seizures discovered three novel missense variations (KCNQ2 p.Ile592Met, KCNQ3 p.Ala381Val, KCNQ3 p.Pro574Ser). The KCNQ2 p.Ile592Met variant displayed a significant reduction of potassium current amplitude in Xenopus oocytes and was present only once in 552 controls. Both missense variants identified in KCNQ3 (p.Ala381Val and p.Pro574Ser) were present in all affected family members and did not occur in controls, but did not show obvious functional abnormalities. The KCNQ3 missense variant p.Pro574Ser was also detected in 8 of 455 IGE patients but not in 454 controls (p = 0.008). In KCNQ2, a silent single nucleotide polymorphism (rs1801545) was found overrepresented in both epilepsy samples (IGE, p = 0.004). CONCLUSION Sequence variations of the KCNQ2 and KCNQ3 genes may contribute to the etiology of common idiopathic epilepsy syndromes.
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Affiliation(s)
- B A Neubauer
- Department of Pediatric Neurology, University of Giessen-Marburg, Feulgenstrasse 12, D-35385 Giessen, Germany.
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19
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Hou J, Renigunta A, Konrad M, Gomes AS, Schneeberger EE, Paul DL, Waldegger S, Goodenough DA. Claudin-16 and claudin-19 interact and form a cation-selective tight junction complex. J Clin Invest 2008; 118:619-28. [PMID: 18188451 DOI: 10.1172/jci33970] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Accepted: 11/07/2007] [Indexed: 12/12/2022] Open
Abstract
Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is an inherited disorder caused by mutations in the genes encoding the TJ proteins claudin-16 (CLDN16) and CLDN19; however, the mechanisms underlying the roles of these claudins in mediating paracellular ion reabsorption in the kidney are not understood. Here we showed that in pig kidney epithelial cells, CLDN19 functioned as a Cl(-) blocker, whereas CLDN16 functioned as a Na(+) channel. Mutant forms of CLDN19 that are associated with FHHNC were unable to block Cl(-) permeation. Coexpression of CLDN16 and CLDN19 generated cation selectivity of the TJ in a synergistic manner, and CLDN16 and CLDN19 were observed to interact using several criteria. In addition, disruption of this interaction by introduction of FHHNC-causing mutant forms of either CLDN16 or CLDN19 abolished their synergistic effect. Our data show that CLDN16 interacts with CLDN19 and that their association confers a TJ with cation selectivity, suggesting a mechanism for the role of mutant forms of CLDN16 and CLDN19 in the development of FHHNC.
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Affiliation(s)
- Jianghui Hou
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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20
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Krämer BK, Bergler T, Stoelcker B, Waldegger S. Mechanisms of Disease: the kidney-specific chloride channels ClCKA and ClCKB, the Barttin subunit, and their clinical relevance. ACTA ACUST UNITED AC 2008; 4:38-46. [DOI: 10.1038/ncpneph0689] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Accepted: 08/17/2007] [Indexed: 01/13/2023]
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21
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Schlingmann KP, Waldegger S, Konrad M, Chubanov V, Gudermann T. TRPM6 and TRPM7--Gatekeepers of human magnesium metabolism. Biochim Biophys Acta Mol Basis Dis 2007; 1772:813-21. [PMID: 17481860 DOI: 10.1016/j.bbadis.2007.03.009] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2007] [Revised: 03/28/2007] [Accepted: 03/28/2007] [Indexed: 11/27/2022]
Abstract
Human magnesium homeostasis primarily depends on the balance between intestinal absorption and renal excretion. Magnesium transport processes in both organ systems - next to passive paracellular magnesium flux - involve active transcellular magnesium transport consisting of an apical uptake into the epithelial cell and a basolateral extrusion into the interstitium. Whereas the mechanism of basolateral magnesium extrusion remains unknown, recent molecular genetic studies in patients with hereditary hypomagnesemia helped gain insight into the molecular nature of apical magnesium entry into intestinal brush border and renal tubular epithelial cells. Patients with Hypomagnesemia with Secondary Hypocalcemia (HSH), a primary defect in intestinal magnesium absorption, were found to carry mutations in TRPM6, a member of the melastatin-related subfamily of transient receptor potential (TRP) ion channels. Before, a close homologue of TRPM6, TRPM7, had been characterized as a magnesium and calcium permeable ion channel vital for cellular magnesium homeostasis. Both proteins share the unique feature of an ion channel fused to a kinase domain with homology to the family of atypical alpha kinases. The aim of this review is to summarize the data emerging from clinical and molecular genetic studies as well as from electrophysiologic and biochemical studies on these fascinating two new proteins and their role in human magnesium metabolism.
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Affiliation(s)
- Karl P Schlingmann
- University Children's Hospital, Philipps-University, Deutschhausstr. 12, 35037 Marburg, Germany.
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22
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Chubanov V, Schlingmann KP, Wäring J, Heinzinger J, Kaske S, Waldegger S, Mederos y Schnitzler M, Gudermann T. Hypomagnesemia with secondary hypocalcemia due to a missense mutation in the putative pore-forming region of TRPM6. J Biol Chem 2006; 282:7656-67. [PMID: 17197439 DOI: 10.1074/jbc.m611117200] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Hypomagnesemia with secondary hypocalcemia is an autosomal recessive disorder caused by mutations in the TRPM6 gene. Current experimental evidence suggests that TRPM6 may function in a specific association with TRPM7 by means of heterooligomeric channel complex formation. Here, we report the identification and functional characterization of a new hypomagnesemia with secondary hypocalcemia missense mutation in TRPM6. The affected subject presented with profound hypomagnesemia and hypocalcemia caused by compound heterozygous mutation in the TRPM6 gene: 1208(-1)G > A affecting the acceptor splice site preceding exon 11, and 3050C > G resulting in the amino acid change (P1017R) in the putative pore-forming region of TRPM6. To assess the functional consequences of the P1017R mutation, TRPM6(P1017R) and wild-type TRPM6 were co-expressed with TRPM7 in Xenopus oocytes and HEK 293 cells, and currents were assessed by two-electrode voltage clamp and whole cell patch clamp measurements, respectively. Co-expression of wild-type TRPM6 and TRPM7 resulted in a significant increase in the amplitude of TRPM7-like currents. In contrast, TRPM6(P1017R) suppressed TRPM7 channel activity. In line with these observations, TRPM7, containing the corresponding mutation P1040R, displayed a dominant-negative effect upon co-expression with wild-type TRPM7. Confocal microscopy and fluorescence resonance energy transfer recordings demonstrated that the P1017R mutation neither affects assembly of TRPM6 with TRPM7, nor co-trafficking of heteromultimeric channel complexes to the cell surface. We conclude that a functional defect in the putative pore of TRPM6/7 channel complexes is sufficient to impair body magnesium homeostasis.
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Affiliation(s)
- Vladimir Chubanov
- Institute for Pharmacology and Toxicology, Philipps-University Marburg, Karl-von-Frisch-Strasse 1, 35033 Marburg, Germany
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23
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Konrad M, Schaller A, Seelow D, Pandey AV, Waldegger S, Lesslauer A, Vitzthum H, Suzuki Y, Luk JM, Becker C, Schlingmann KP, Schmid M, Rodriguez-Soriano J, Ariceta G, Cano F, Enriquez R, Juppner H, Bakkaloglu SA, Hediger MA, Gallati S, Neuhauss SCF, Nurnberg P, Weber S. Mutations in the tight-junction gene claudin 19 (CLDN19) are associated with renal magnesium wasting, renal failure, and severe ocular involvement. Am J Hum Genet 2006; 79:949-57. [PMID: 17033971 PMCID: PMC1698561 DOI: 10.1086/508617] [Citation(s) in RCA: 331] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Accepted: 08/21/2006] [Indexed: 02/06/2023] Open
Abstract
Claudins are major components of tight junctions and contribute to the epithelial-barrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudin-19 for normal renal tubular function and undisturbed organization and development of the retina.
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Affiliation(s)
- Martin Konrad
- University Children's Hospital, Inselspital, Bern, Switzerland.
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24
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Pressler CA, Heinzinger J, Jeck N, Waldegger P, Pechmann U, Reinalter S, Konrad M, Beetz R, Seyberth HW, Waldegger S. Late-onset manifestation of antenatal Bartter syndrome as a result of residual function of the mutated renal Na+-K+-2Cl- co-transporter. J Am Soc Nephrol 2006; 17:2136-42. [PMID: 16807401 DOI: 10.1681/asn.2005101071] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Genetic defects of the Na+-K+-2Cl- (NKCC2) sodium potassium chloride co-transporter result in severe, prenatal-onset renal salt wasting accompanied by polyhydramnios, prematurity, and life-threatening hypovolemia of the neonate (antenatal Bartter syndrome or hyperprostaglandin E syndrome). Herein are described two brothers who presented with hyperuricemia, mild metabolic alkalosis, low serum potassium levels, and bilateral medullary nephrocalcinosis at the ages of 13 and 15 yr. Impaired function of sodium chloride reabsorption along the thick ascending limb of Henle's loop was deduced from a reduced increase in diuresis and urinary chloride excretion upon application of furosemide. Molecular genetic analysis revealed that the brothers were compound heterozygotes for mutations in the SLC12A1 gene coding for the NKCC2 co-transporter. Functional analysis of the mutated rat NKCC2 protein by tracer-flux assays after heterologous expression in Xenopus oocytes revealed significant residual transport activity of the NKCC2 p.F177Y mutant construct in contrast to no activity of the NKCC2-D918fs frameshift mutant construct. However, coexpression of the two mutants was not significantly different from that of NKCC2-F177Y alone or wild type. Membrane expression of NKCC2-F177Y as determined by luminometric surface quantification was not significantly different from wild-type protein, pointing to an intrinsic partial transport defect caused by the p.F177Y mutation. The partial function of NKCC2-F177Y, which is not negatively affected by NKCC2-D918fs, therefore explains a mild and late-onset phenotype and for the first time establishes a mild phenotype-associated SLC12A1 gene mutation.
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Affiliation(s)
- Carsten A Pressler
- Department of Pediatrics, Philipps University of Marburg, Marburg, Germany
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25
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Frey A, Lampert A, Waldegger S, Jeck N, Waldegger P, Artunc F, Seebohm G, Lang UE, Kupka S, Pfister M, Hoppe J, Gerloff C, Schaeffeler E, Schwab M, Lang F. Influence of gain of function epithelial chloride channel ClC-Kb mutation on hearing thresholds. Hear Res 2006; 214:68-75. [PMID: 16549283 DOI: 10.1016/j.heares.2006.02.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2005] [Revised: 01/05/2006] [Accepted: 02/01/2006] [Indexed: 10/24/2022]
Abstract
Hearing depends on functional ClC-K-type chloride channels composed of barttin with ClC-Ka or ClC-Kb. Loss-of-function mutations of the barttin gene BSND or of both, the ClC-Ka gene CLNKA and the ClC-Kb gene CLNKB lead to congenital deafness and renal salt wasting. Recently, we identified the gain-of-function mutation ClC-Kb(T481S) which is associated with increased blood pressure. To explore the impact of ClC-Kb(T481S) on hearing, healthy volunteers (n=329) and individuals suffering from tinnitus (n=246) volunteered for hearing tests (n=348) and genetic analysis (n=575). 19.1% of the individuals were heterozygote (ClC-Kb(T481S)/ClC-Kb) and 1.7% homozygote carriers. Pure tone average hearing threshold (PTAt) for air conduction was significantly (p<0.033) lower in ClC-Kb(T481S) carriers (13.2+/-1.2dB) than in wild-type individuals (17.1+/-0.9dB). The prevalence of ClC-Kb(T481S) carriers was significantly increased (29.7%) in individuals with PTAt<15dB (p<0.05) and significantly decreased (13.2%) in individuals with PTAt>30 dB (p<0.017). The difference was largely due to the female population. Bone conduction was less affected pointing to an effect of the mutation on middle ear function. Tinnitus tended to be more frequent in ClC-Kb(T481S) carriers, a difference, however, not statistically significant. In conclusion, hearing thresholds are slightly lower in carriers of ClC-Kb(T481S), i.e., the gain-of-function polymorphism ClC-Kb(T481S) exerts a subtle but significant protective effect against hearing loss.
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Affiliation(s)
- Andreas Frey
- Department of Physiology, University of Tübingen, Gmelinstrasse 5, D-72076 Tübingen, Germany
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26
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Schlingmann KP, Sassen MC, Weber S, Pechmann U, Kusch K, Pelken L, Lotan D, Syrrou M, Prebble JJ, Cole DEC, Metzger DL, Rahman S, Tajima T, Shu SG, Waldegger S, Seyberth HW, Konrad M. Novel TRPM6 mutations in 21 families with primary hypomagnesemia and secondary hypocalcemia. J Am Soc Nephrol 2005; 16:3061-9. [PMID: 16107578 DOI: 10.1681/asn.2004110989] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Primary hypomagnesemia with secondary hypocalcemia is a rare autosomal recessive disorder characterized by profound hypomagnesemia associated with hypocalcemia. Pathophysiology is related to impaired intestinal absorption of magnesium accompanied by renal magnesium wasting as a result of a reabsorption defect in the distal convoluted tubule. Recently, mutations in the TRPM6 gene coding for TRPM6, a member of the transient receptor potential (TRP) family of cation channels, were identified as the underlying genetic defect. Here, the results of a TRPM6 mutational analysis of 21 families with 28 affected individuals are presented. In this large patient cohort, a retrospective clinical evaluation based on a standardized questionnaire was also performed. Genotype analysis revealed TRPM6 mutations in 37 of 42 expected mutant alleles. Sixteen new TRPM6 mutations were identified, including stop mutations, frame-shift mutations, splice-site mutations, and deletions of exons. Electrophysiologic analysis of mutated ion channels after heterologous expression in Xenopus oocytes proved complete loss of function of TRPM6. Clinical evaluation revealed a homogeneous clinical picture at manifestation with onset in early infancy with generalized cerebral convulsions. Initial laboratory evaluation yielded extremely low serum magnesium levels, low serum calcium levels, and inadequately low parathyroid hormone levels. Treatment usually consisted of acute intravenous magnesium supplementation leading to relief of clinical symptoms and normocalcemia, followed by lifelong oral magnesium supplementation. Serum magnesium levels remained in the subnormal range despite adequate therapy. This is best explained by a disturbed magnesium conservation in the distal convoluted tubule, which emerged in all patients upon magnesium supplementation. Delay of diagnosis resulted in permanent neurologic damage in three patients.
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Affiliation(s)
- Karl P Schlingmann
- University Children's Hospital Marburg, Deutschhausstrasse 12, 35037 Marburg, Germany.
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27
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Lang F, Capasso G, Schwab M, Waldegger S. Renal tubular transport and the genetic basis of hypertensive disease. Clin Exp Nephrol 2005; 9:91-9. [PMID: 15980941 DOI: 10.1007/s10157-005-0355-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2004] [Accepted: 03/11/2005] [Indexed: 10/25/2022]
Abstract
Several monogenic hypertensive disorders are caused by genetic mutations leading to the deranged function and/or regulation of renal tubular NaCl transport, such as mutations of the renal epithelial Na+ channel (ENaC) in Liddle syndrome, of the kinase WNK1 (with no K) in Gordon syndrome, and of the mineralocorticoid receptor, or of 11beta-hydroxysteroid dehydrogenase. Moreover, excessive formation of aldosterone in glucocorticoid-remediable hypertension leads to severe hypertension. Conversely, impaired function of the Na+,K+,2Cl- cotransporter (NKCC2), the renal outer medullary K+ channel (ROMK1), and the renal epithelial Cl- channel ClCKb/Barttin causes Bartter syndrome and defective Na+,Cl+ cotransporter (NCCT) Gitelman syndrome, salt-wasting disorders with hypotension. These monogenic disorders are rare, but illustrate the significance of renal tubular transport in blood pressure regulation. There is little doubt, however, that deranged renal salt reabsorption significantly contributes to essential hypertension polymorphisms of several genes participating in the regulation of renal Na+ transport have been shown to be associated with blood pressure and prevalence of hypertension. Two common genes will be discussed in more detail. The first encodes the renal Cl- channel ClCKb. A gain-of-function mutation of ClCKb, increasing channel activity by 7- to 20-fold is found in approximately 20% of unselected Caucasians and 40% of an unselected African population. The second common gene variant (prevalence, 3%-5% in unselected Caucasians), to be discussed in more detail, affects the serum and glucocorticoid inducible kinase SGK1, a kinase upregulated by mineralocorticoids and enhancing the activity of ENaC, ROMK, and Na+/K+ATPase. Both gene variants are associated with slightly increased blood pressure. SGK1 further stimulates the glucose transporter SGLT1, and the SGK1 gene variant correlates, in addition, with increased body mass index.
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Affiliation(s)
- Florian Lang
- Department of Physiology, University of Tübingen, Gmelinstr. 5, D-72076 Tübingen, Germany.
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28
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Ludwig M, Doroszewicz J, Seyberth HW, Bökenkamp A, Balluch B, Nuutinen M, Utsch B, Waldegger S. Functional evaluation of Dent's disease-causing mutations: implications for ClC-5 channel trafficking and internalization. Hum Genet 2005; 117:228-37. [PMID: 15895257 DOI: 10.1007/s00439-005-1303-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2004] [Accepted: 03/07/2005] [Indexed: 10/25/2022]
Abstract
ClC-5 is a member of the ClC family of voltage-gated chloride channels. Loss-of-function mutations of its corresponding gene (CLCN5) cause Dent's disease, an X-linked kidney disorder, characterized by low-molecular weight proteinuria, hypercalciuria, nephrocalcinosis/nephrolithiasis, and progressive renal failure. Here, we examined the effect of different mutations on function and cellular trafficking of the recombinant protein. Mutant CLCN5 cDNAs were generated by site directed mutagenesis for two premature stop codon variants (R347X and M517IfsX528), and several missense mutations (C221R, L324R, G462 V, and R516 W). We also tested L521R (instead of L521RfsX526 observed) and mutants G506E and R648X (previously reported by others). After heterologous expression in Xenopus oocytes, ClC-5 channel activity and surface expression were determined by two-electrode voltage-clamp analysis and ClC-5 surface ELISA, respectively. Except for the R516 W and R648X variants, none of the mutated proteins induced functional chloride currents or reached the plasma membrane. This is readily understandable for the truncation mutations. Yet, the tested missense mutations are distributed over different transmembrane regions, implying that correct channel structure and orientation in the membrane is not only a prerequisite for proper ClC-5 function but also for Golgi exit. Interestingly, the R648X mutant although functionally compromised, displayed a significant increase in surface expression. This finding might be explained by the deletion of a ClC-5 carboxy-terminal PY-like internalization signal, which in turn impairs channel removal from the membrane. Our observations further imply that recruitment of ClC-5 to alternative routes (plasma membrane or early endosomes) in the trans-Golgi network is mediated via different signal sequences.
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Affiliation(s)
- Michael Ludwig
- Institut für Klinische Biochemie, Universität Bonn, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany.
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Embark HM, Böhmer C, Palmada M, Rajamanickam J, Wyatt AW, Wallisch S, Capasso G, Waldegger P, Seyberth HW, Waldegger S, Lang F. Regulation of CLC-Ka/barttin by the ubiquitin ligase Nedd4-2 and the serum- and glucocorticoid-dependent kinases. Kidney Int 2005; 66:1918-25. [PMID: 15496163 DOI: 10.1111/j.1523-1755.2004.00966.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND ClC-Ka and ClC-Kb, chloride channels participating in renal tubular Cl- transport, require the coexpression of barttin to become functional. Mutations of the barttin gene lead to the Bartter's syndrome variant BSND, characterized by congenital deafness and severe renal salt wasting. Barttin bears a proline-tyrosine motif, a target structure for the ubiquitin ligase Nedd4-2, which mediates the clearance of channel proteins from the cell membrane. Nedd4-2 is, in turn, a target of the serum- and glucocorticoid-inducible kinase SGK1, which phosphorylates and, thus, inactivates the ubiquitin ligase. ClC-Ka also possesses a SGK1 consensus site in its sequence. We hypothesized that ClC-Ka/barttin is stimulated by SGK1, and down-regulated by Nedd4-2, an effect that may be reversed by SGK1 and its isoforms, SGK2 or SGK3. METHODS To test this hypothesis, ClC-Ka/barttin was heterologously expressed in Xenopus oocytes with or without the additional expression of Nedd4-2, SGK1, SGK2, SGK3, constitutively active S422DSGK1, or inactive K127NSGK1. RESULTS Expression of ClC-Ka/barttin induced a slightly inwardly rectifying current that was significantly decreased upon coexpression of Nedd4-2, but not the catalytically inactive mutant C938SNedd4-2. The coexpression of S422DSGK1, SGK1, or SGK3, but not SGK2 or K127NSGK1 significantly stimulated the current. Moreover, S422DSGK1, SGK1, and SGK3 also phosphorylated Nedd4-2 and thereby inhibited Nedd4-2 binding to its target. The down-regulation of ClC-Ka/barttin by Nedd4-2 was abolished by elimination of the PY motif in barttin. CONCLUSION ClC-Ka/barttin channels are regulated by SGK1 and SGK3, which may thus participate in the regulation of transport in kidney and inner ear.
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Affiliation(s)
- Hamdy M Embark
- Department of Physiology I, University of Tübingen, Germany
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30
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Jeck N, Schlingmann KP, Reinalter SC, Kömhoff M, Peters M, Waldegger S, Seyberth HW. Salt handling in the distal nephron: lessons learned from inherited human disorders. Am J Physiol Regul Integr Comp Physiol 2005; 288:R782-95. [PMID: 15793031 DOI: 10.1152/ajpregu.00600.2004] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The molecular basis of inherited salt-losing tubular disorders with secondary hypokalemia has become much clearer in the past two decades. Two distinct segments along the nephron turned out to be affected, the thick ascending limb of Henle's loop and the distal convoluted tubule, accounting for two major clinical phenotypes, hyperprostaglandin E syndrome and Bartter-Gitelman syndrome. To date, inactivating mutations have been detected in six different genes encoding for proteins involved in renal transepithelial salt transport. Careful examination of genetically defined patients (“human knockouts”) allowed us to determine the individual role of a specific protein and its contribution to the overall process of renal salt reabsorption. The recent generation of several genetically engineered mouse models that are deficient in orthologous genes further enabled us to compare the human phenotype with the animal models, revealing some unexpected interspecies differences. As the first line treatment in hyperprostaglandin E syndrome includes cyclooxygenase inhibitors, we propose some hypotheses about the mysterious role of PGE2in the etiology of renal salt-losing disorders.
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Affiliation(s)
- Nikola Jeck
- MD, Univ. Children's Hospital, Philipps-Univ., Deutschhausstrasse 12, D-35037 Marburg, Germany. )
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31
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Friedrich B, Alexander D, Aicher WK, Duszenko M, Schaub TP, Passlick-Deetjen J, Waldegger S, Wolf S, Risler T, Lang F. Influence of standard haemodialysis treatment on transcription of human serum- and glucocorticoid-inducible kinase SGK1 and taurine transporter TAUT in blood leukocytes. Nephrol Dial Transplant 2005; 20:768-74. [PMID: 15701671 DOI: 10.1093/ndt/gfh697] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Standard haemodialysis (HD) rapidly alters osmolality and composition of extracellular fluid and, thus, challenges cell volume constancy. Cell volume-sensitive genes upregulated by osmotic cell shrinkage include those encoding for taurine transporter TAUT as well as for serum- and glucocorticoid-inducible kinase SGK1. METHODS Six HD patients were haemodialysed for 4 h with high-flux dialysers. Blood was drawn from the arterial section of the fistula immediately prior to start of HD and subsequently after 60, 120 and 240 min of HD treatment and, in addition, 120 min after HD treatment. Taurine plasma concentrations ([taurine]p) and erythrocytic taurine content ([taurine]e) were determined by high-performance liquid chromatography. SGK1 and TAUT transcript levels in leukocytes were quantified by real-time polymerase chain reaction. RESULTS The [taurine]p was significantly higher in HD patients before HD treatment when compared with healthy controls and it decreased significantly during 4 h of HD. The ratio of SGK1/GAPDH and of TAUT/GAPDH transcript levels increased significantly by 50% or 27%, respectively, during HD. CONCLUSIONS Standard HD treatment decreases plasma taurine concentration and upregulates leukocyte SGK1 and TAUT transcription. As SGK1 is a potent regulator of ion channels and transporters in nervous system, heart muscle and epithelial cells, the deranged regulation of SGK1 may contribute to acute side effects of HD treatment.
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Affiliation(s)
- Björn Friedrich
- Department of Internal Medicine, University of Tübingen, Germany
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32
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Doroszewicz J, Waldegger P, Jeck N, Seyberth H, Waldegger S. pH dependence of extracellular calcium sensing receptor activity determined by a novel technique. Kidney Int 2005; 67:187-92. [PMID: 15610242 DOI: 10.1111/j.1523-1755.2005.00069.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND Increasing evidence points to the role of the extracellular Calcium Sensing Receptor (CaSR) as a multimodal receptor responding to diverse physiologic stimuli, such as extracellular divalent and polyvalent cations, amino acids, and ionic strength. Within the kidney, these stimuli converge on the CaSR to coordinate systemic calcium and water homeostasis. In this process, the impact of urinary pH changes on the activity of the CaSR has not yet been defined. We therefore performed the present study to analyze the pH sensitivity of the CaSR. METHODS To assess the activation state of the CaSR, we developed a new method based on the functional coupling between CaSR activity and gating of calcium sensitive potassium currents mediated by SK4 potassium channels. Two-electrode voltage clamping was used to determine whole cell currents in Xenopus oocytes heterologously expressing rat CaSR and rat SK4 potassium channels. RESULTS Coexpression of CaSR and SK4 gave rise to potassium currents that were dependent on CaSR-mediated intracellular calcium release, and thereby corresponded to the activation state of the CaSR. In presence of extracellular calcium, ambient alkalinization above pH 7.5 increased CaSR activity. Evaluation of the CaSR calcium sensitivity at various ambient proton concentrations revealed that this effect was due to a sensitization of the CaSR towards extracellular calcium. CONCLUSION Coexpression with SK4 potassium channels provides a fast and sensitive approach to evaluate CaSR activity in Xenopus oocytes. As disclosed by this novel technique, CaSR activity is regulated by extracellular pH.
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33
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Palmada M, Dieter M, Boehmer C, Waldegger S, Lang F. Serum and glucocorticoid inducible kinases functionally regulate ClC-2 channels. Biochem Biophys Res Commun 2004; 321:1001-6. [PMID: 15358127 DOI: 10.1016/j.bbrc.2004.07.064] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2004] [Indexed: 12/22/2022]
Abstract
ClC-2 participates in the regulation of neuronal excitability, chloride secretion, and cell volume. The ClC-2 sequence contains a consensus site (Ser82) for phosphorylation by the serum and glucocorticoid inducible kinase isoforms SGK1-3. Thus, the present study explored whether ClC-2 is regulated by those kinases. ClC-2 expression in Xenopus oocytes induced inwardly rectifying currents that increased upon coexpression of SGK1-3 and the related kinase PKB. The stimulatory effect was still present upon disruption of the SGK phosphorylation site. SGKs can phosphorylate the ubiquitin ligase Nedd4-2 and prevent Nedd4-2 from binding to its target. Therefore, the role of Nedd4-2 in ClC-2 modulation was investigated. ClC-2 activity decreased upon Nedd4-2 coexpression, an effect reversed by the kinases. According to chemiluminescence ClC-2 membrane abundance was enhanced by SGKs and diminished by Nedd4-2. These observations suggest that SGK1-3 and Nedd4-2 regulate ClC-2 at least in part by modulating ClC-2 abundance at the plasma membrane.
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Affiliation(s)
- Monica Palmada
- Physiologisches Institut, Universität Tübingen, Gmelinstr. 5, D-72076 Tübingen, Germany
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34
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Jeck N, Waldegger P, Doroszewicz J, Seyberth H, Waldegger S. A common sequence variation of the CLCNKB gene strongly activates ClC-Kb chloride channel activity. Kidney Int 2004; 65:190-7. [PMID: 14675050 DOI: 10.1111/j.1523-1755.2004.00363.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
BACKGROUND Tubular transepithelial reabsorption of chloride along the nephron is a major determinant of body salt and water homeostasis and blood pressure regulation. About 40% of the glomerulary filtered sodium chloride are reabsorbed in the distal nephrons. Vectorial transepithelial sodium chloride transport is critically dependent on the function of basolateral ClC-K type chloride channels there. Modulation of ClC-Kb chloride channel activity by polymorphic variations of the CLCNKB gene, thus, could form a molecular basis for salt sensitivity of blood pressure regulation. In this study we tested the effect of several polymorphic variants on ClC-Kb chloride channel activity. METHODS After heterologous expression in Xenopus oocytes, ClC-Kb channel activity and surface expression in presence of the ClC-K beta subunit barttin were determined by two-electrode voltage-clamp analysis, immunofluorescence, and ClC-Kb surface enzyme-linked immunosorbent assay (ELISA). RESULTS Chloride currents induced by the ClC-Kb variants L27R, G214A, I419V, T562M, and E578K were not significantly different from wild-type currents. The ClC-KbT481S variation, however, which showed a frequency of 20% in our control population, dramatically activated chloride conductance by a factor of 20. Activation of chloride currents was also observed after introducing homologous mutations in ClC-Ka and ClC-K1, but not in ClC-2 and ClC-5 chloride channels. ClC-Kb activation by the T481S mutation did not change intrinsic ion channel pore properties and did not require increased surface expression of ClC-KbT481S. CONCLUSION Genetic heterogeneity of ClC-Kb chloride channels correlates with functional heterogeneity, which assigns ClC-Kb to a set of genes potentially relevant for polygenic salt-sensitivity of blood pressure regulation.
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Affiliation(s)
- Nikola Jeck
- Department of Pediatrics, Philipps University of Marburg, Germany
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35
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Jeck N, Waldegger S, Lampert A, Boehmer C, Waldegger P, Lang PA, Wissinger B, Friedrich B, Risler T, Moehle R, Lang UE, Zill P, Bondy B, Schaeffeler E, Asante-Poku S, Seyberth H, Schwab M, Lang F. Activating Mutation of the Renal Epithelial Chloride Channel ClC-Kb Predisposing to Hypertension. Hypertension 2004; 43:1175-81. [PMID: 15148291 DOI: 10.1161/01.hyp.0000129824.12959.f0] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The chloride channel ClC-Kb is expressed in the basolateral cell membrane of the distal nephron and participates in renal NaCl reabsorption. Loss-of-function mutations of ClC-Kb lead to classic Bartter syndrome, a rare salt-wasting disorder. Recently, we identified the ClC-Kb
T481S
polymorphism, which confers a strong gain-of-function effect on the ClC-Kb chloride channel. The present study has been performed to explore the prevalence of the mutation and its functional significance in renal salt handling and blood pressure regulation. As evident from electrophysiological analysis with the 2-electrode voltage-clamp technique, heterologous expression of ClC-Kb
T481S
in Xenopus oocytes gave rise to a current that was 7-fold larger than the current produced by wild-type ClC-Kb. The prevalence of the mutant allele was significantly higher in an African population from Ghana (22%) than in whites (12%). As tested in 1 white population, carriers of ClC-Kb
T481S
were associated with significantly higher systolic (by ≈6.0 mm Hg) and diastolic (by ≈4.2 mm Hg) blood pressures and significantly higher prevalence (45% versus 25%) of hypertensive (≥140/90 mm Hg) blood pressure levels. Individuals carrying ClC-Kb
T481S
had significantly higher plasma Na
+
concentrations and significantly decreased glomerular filtration rate. In conclusion, the mutation ClC-Kb
T481S
of the renal epithelial Cl
−
channel ClC-Kb strongly activates ClC-Kb chloride channel function in vitro and may predispose to the development of essential hypertension in vivo.
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Affiliation(s)
- Nikola Jeck
- Department of Pediatrics, University of Marburg, Germany
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36
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Schlingmann KP, Konrad M, Jeck N, Waldegger P, Reinalter SC, Holder M, Seyberth HW, Waldegger S. Salt wasting and deafness resulting from mutations in two chloride channels. N Engl J Med 2004; 350:1314-9. [PMID: 15044642 DOI: 10.1056/nejmoa032843] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Karl P Schlingmann
- Department of Pediatrics, Philipps University of Marburg, Marburg, Germany
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37
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Ludwig M, Waldegger S, Nuutinen M, Bökenkamp A, Reissinger A, Steckelbroeck S, Utsch B. Four additional CLCN5 exons encode a widely expressed novel long CLC-5 isoform but fail to explain Dent's phenotype in patients without mutations in the short variant. Kidney Blood Press Res 2004; 26:176-84. [PMID: 12886045 DOI: 10.1159/000071883] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/14/2003] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Dent's disease is caused by mutations in the CLCN5 gene coding for the chloride channel CLC-5. However, sequencing of CLCN5 exonic regions in some patients presenting with low-molecular-weight proteinuria and hypercalciuria - the hallmarks of Dent's disease - failed to identify causative mutations. AIM Given the observation that some species harbour a CLCN5 mRNA encoding an extended CLC-5 aminoterminus compared with the so far known human form, we worked on the presumption that an orthologous (longer) CLCN5 transcript is also present in humans and that our patients may have mutations herein. METHODS Extensive databank mining, reverse transcription polymerase chain reaction (RT-PCR) and automated sequencing were used in the search for novel CLCN5 transcripts. The human CLCN5 gene was investigated in 7 patients out of five families by direct automated sequencing of PCR-amplified DNA products. RESULTS Two new human CLCN5 transcripts expressed in kidney and various other tissues could be identified. These arise from a novel site of transcription initiation, alternative splicing and the use of four additional CLCN5 exons. If being translated, both these mRNAs would lead to an enlarged CLC-5 protein consisting of 816 amino acids by adding 70 aminoterminal residues to the so far known 746-amino-acid-long isoform. Sequence analysis of the henceforward 17 CLCN5 exons revealed no mutation in the patients with a phenotype resembling Dent's disease. CONCLUSIONS Despite the identification of further targets to explain Dent's disease, the molecular defect in our patients remains to be elucidated. Hence, their phenotype may be explained by mutations that affect so far unknown regulating elements of the CLCN5 gene or another gene(s), probably encoding CLC-5 accessory protein(s).
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Affiliation(s)
- Michael Ludwig
- Department of Clinical Biochemistry, University of Bonn, Bonn, Germany.
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38
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Chubanov V, Waldegger S, Mederos y Schnitzler M, Vitzthum H, Sassen MC, Seyberth HW, Konrad M, Gudermann T. Disruption of TRPM6/TRPM7 complex formation by a mutation in the TRPM6 gene causes hypomagnesemia with secondary hypocalcemia. Proc Natl Acad Sci U S A 2004; 101:2894-9. [PMID: 14976260 PMCID: PMC365716 DOI: 10.1073/pnas.0305252101] [Citation(s) in RCA: 260] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Impaired magnesium reabsorption in patients with TRPM6 gene mutations stresses an important role of TRPM6 (melastatin-related TRP cation channel) in epithelial magnesium transport. While attempting to isolate full-length TRPM6, we found that the human TRPM6 gene encodes multiple mRNA isoforms. Full-length TRPM6 variants failed to form functional channel complexes because they were retained intracellularly on heterologous expression in HEK 293 cells and Xenopus oocytes. However, TRPM6 specifically interacted with its closest homolog, the Mg(2+)-permeable cation channel TRPM7, resulting in the assembly of functional TRPM6/TRPM7 complexes at the cell surface. The naturally occurring S141L TRPM6 missense mutation abrogated the oligomeric assembly of TRPM6, thus providing a cell biological explanation for the human disease. Together, our data suggest an important contribution of TRPM6/TRPM7 heterooligomerization for the biological role of TRPM6 in epithelial magnesium absorption.
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Affiliation(s)
- Vladimir Chubanov
- Institute for Pharmacology and Toxicology, Philipps University Marburg, 35033 Marburg, Germany
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39
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Lang F, Henke G, Embark HM, Waldegger S, Palmada M, Böhmer C, Vallon V. Regulation of channels by the serum and glucocorticoid-inducible kinase - implications for transport, excitability and cell proliferation. Cell Physiol Biochem 2003; 13:41-50. [PMID: 12649601 DOI: 10.1159/000070248] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2002] [Indexed: 11/19/2022] Open
Abstract
The serum and glucocorticoid-inducible kinase SGK1 stimulates the Na+ channels ENaC and SCN5A, the K+ channels ROMK1, Kv1.3, and KCNE1/KCNQ1, the cation conductance induced by 4F2/LAT1 and the chloride conductance induced by CFTR. The isoforms SGK2 and SGK3 have similarly been shown to regulate ENaC, SCN5A, Kv1.3 and KCNE1/KCNQ1. The kinases regulate channel abundance in the plasma membrane in part by inhibition of the ubiquitin ligase Nedd4-2 and in part by interaction with trafficking molecules such as the Na+/H+ exchanger regulating factor NHERF2. An in vivo role of SGK1 mediated ENaC channel regulation in renal salt excretion and blood pressure control is documented by the impaired ability of SGK1 knockout mice to adequately reduce renal Na+ output and maintain blood pressure during dietary salt restriction and by enhanced blood pressure in individuals carrying certain polymorphisms in the SGK1 gene. The in vivo physiological significance of SGK dependent regulation of the other channels remains to be shown even though circumstantial evidence points to involvement in the regulation of epithelial transport, cell volume, cell proliferation, cardiac action potential and neuroexcitability. There is little doubt that further channels will be identified which are modulated by the SGKs and that further in vivo physiological functions will be defined where channel regulation by the SGKs plays a critical role.
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Affiliation(s)
- Florian Lang
- Department of Physiology, University of Tuebingen, Germany.
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40
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Peters M, Ermert S, Jeck N, Derst C, Pechmann U, Weber S, Schlingmann KP, Seyberth HW, Waldegger S, Konrad M. Classification and rescue of ROMK mutations underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome. Kidney Int 2003; 64:923-32. [PMID: 12911542 DOI: 10.1046/j.1523-1755.2003.00153.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Mutations in the renal K+ channel ROMK (Kir 1.1) cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a severe tubular disorder leading to renal salt and water wasting. Several studies confirmed the predominance of alterations of current properties in ROMK mutants. However, in most of these studies, analysis was restricted to nonmammalian cells and electrophysiologic methods. Therefore, for the majority of ROMK mutations, disturbances in protein trafficking remained unclear. The aim of the present study was the evaluation of different pathogenic mechanisms of 20 naturally occurring ROMK mutations with consecutive classification into mutational classes and identification of distinct rescue mechanisms according to the underlying defect. METHODS Mutated ROMK potassium channels were expressed in Xenopus oocytes and a human kidney cell line and analyzed by two electrode voltage clamp analysis, immunofluorescence, and Western blot analysis. RESULTS We identified 14 out of 20 ROMK mutations that did not reach the cell surface, indicating defective membrane trafficking. High expression levels rescued six out of 14 ROMK mutants, leading to significant K+ currents. In addition, two early inframe stop mutations could be rescued by aminoglycosides, resulting in full-length ROMK and correct trafficking to the plasma membrane in a subset of transfected cells. CONCLUSION In contrast to previous reports, most of the investigated ROMK mutations displayed a trafficking defect that might be rescued by pharmacologic agents acting as molecular chaperones. The evaluation of different disease-causing mechanisms will be essential for establishing new and more specific therapeutic strategies for HPS/aBS patients.
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Affiliation(s)
- Melanie Peters
- Department of Pediatrics, Philipps University Marburg, Marburg, Germany
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41
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Abstract
Hydrochloric acid is produced in parietal cells of the gastric glands by an H(+)/K(+)-ATPase. This proton pump couples the outwards movement of H(+) to the inwards movement of K(+) thus requiring the presence of luminal K(+) to operate. To maintain the activity of the pump, K(+) recirculates over the apical membrane via conductive pathways, the molecular nature of which has been identified in the past few years. This review gives a short overview about the recent advances in the understanding of the role of K(+) channels in the process of parietal cell H(+) secretion and focuses on the identification of KCNQ1/KCNE2 K(+) channel as the molecular correlate of the parietal cell apical potassium conductance.
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Affiliation(s)
- Siegfried Waldegger
- Department of Paediatrics, University Hospital Marburg, Deutschhausstrasse 12, 35037, Marburg, Germany.
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42
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Fillon S, Klingel K, Wärntges S, Sauter M, Gabrysch S, Pestel S, Tanneur V, Waldegger S, Zipfel A, Viebahn R, Häussinger D, Bröer S, Kandolf R, Lang F. Expression of the serine/threonine kinase hSGK1 in chronic viral hepatitis. Cell Physiol Biochem 2002; 12:47-54. [PMID: 11914548 DOI: 10.1159/000047826] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The human serine/threonine kinase hSGK1 is expressed ubiquitously with highest transcript levels in pancreas and liver. This study has been performed to determine the hSGK1 distribution in normal liver and its putative role in fibrosing liver disease. HSGK1-localization was determined by in situ hybridization, regulation of hSGK1-transcription by Northern blotting, fibronectin synthesis and hSGK1 phosphorylation by Western blotting. In normal liver hSGK1 was mainly transcribed by Kupffer cells. In liver tissue from patients with chronic viral hepatitis, hSGK1 transcript levels were excessively high in numerous activated Kupffer cells and inflammatory cells localized within fibrous septum formations. HSGK1 transcripts were also detected in activated hepatic stellate cells. Accordingly, Western blotting revealed that tissue from fibrotic liver expresses excessive hSGK1 protein as compared to normal liver. TGF-beta1 (2 ng/ml) increases hSGK1 transcription in both human U937 macro-phages and HepG2 hepatoma cells. H(2)O(2) (0.3 mM) activated hSGK1 and increased fibronectin formation in HepG2 cells overexpressing hSGK1 but not in HepG2 cells expressing the inactive mutant hSGK1(K127R). In conclusion hSGK1 is upregulated by TGF-beta1 during hepatitis and may contribute to enhanced matrix formation during fibrosing liver disease.
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MESH Headings
- Blotting, Western
- Carcinoma, Hepatocellular/metabolism
- Carcinoma, Hepatocellular/pathology
- Chronic Disease
- Fibronectins/biosynthesis
- Gene Expression Regulation/drug effects
- Hepatitis B/metabolism
- Hepatitis B/pathology
- Hepatitis C/metabolism
- Hepatitis C/pathology
- Hepatitis, Viral, Human/metabolism
- Hepatitis, Viral, Human/pathology
- Humans
- Hydrogen Peroxide/pharmacology
- Immediate-Early Proteins
- In Situ Hybridization
- Kupffer Cells/metabolism
- Kupffer Cells/pathology
- Liver/metabolism
- Liver/pathology
- Liver Cirrhosis/metabolism
- Liver Cirrhosis/pathology
- Macrophages/cytology
- Macrophages/drug effects
- Macrophages/metabolism
- Nuclear Proteins
- Oxidants/pharmacology
- Phosphorylation/drug effects
- Protein Serine-Threonine Kinases/biosynthesis
- Protein Serine-Threonine Kinases/genetics
- RNA, Messenger/analysis
- RNA, Messenger/biosynthesis
- Transforming Growth Factor beta/pharmacology
- Tumor Cells, Cultured
- U937 Cells
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Affiliation(s)
- Sophie Fillon
- Department for Physiology, University of Tübingen, Gmelinstrasse 5, D-72076 Tübingen, Germany
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43
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Waldegger S, Jeck N, Barth P, Peters M, Vitzthum H, Wolf K, Kurtz A, Konrad M, Seyberth HW. Barttin increases surface expression and changes current properties of ClC-K channels. Pflugers Arch 2002; 444:411-8. [PMID: 12111250 DOI: 10.1007/s00424-002-0819-8] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2002] [Revised: 02/01/2002] [Accepted: 02/06/2002] [Indexed: 11/28/2022]
Abstract
The term Bartter syndrome encompasses a heterogeneous group of autosomal recessive salt-losing nephropathies that are caused by disturbed transepithelial sodium chloride reabsorption in the distal nephron. Mutations have been identified in the NKCC2 (Na(+)-K(+)-2Cl(-)) cotransporter and ROMK potassium channel, which cooperate in the process of apical sodium chloride uptake, and ClC-Kb chloride channels, which mediate basolateral chloride release. Recently, mutations in barttin, a protein not related to any known ion transporter or channel, were described in BSND, a variant of Bartter syndrome associated with sensorineural deafness. Here we show that barttin functions as an activator of ClC-K chloride channels. Expression of barttin together with ClC-K in Xenopus oocytes increased ClC-K current amplitude, changed ClC-K biophysical properties, and enhanced ClC-K abundance in the cell membrane. Co-immunoprecipitation revealed a direct interaction of barttin with ClC-K. We performed in situ hybridization on rat kidney slices and RT-PCR analysis on microdissected nephron segments to prove co-expression of barttin, ClC-K1 and ClC-K2 along the distal nephron. Functional analysis of BSND-associated point mutations revealed impaired ClC-K activation by barttin. The results demonstrate regulation of a CLC chloride channel by an accessory protein and indicate that ClC-K activation by barttin is required for adequate tubular salt reabsorption.
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Affiliation(s)
- Siegfried Waldegger
- Department of Pediatrics, Philipps University of Marburg, Deutschhausstr. 12, 35033 Marburg, Germany.
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44
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Schlingmann KP, Weber S, Peters M, Niemann Nejsum L, Vitzthum H, Klingel K, Kratz M, Haddad E, Ristoff E, Dinour D, Syrrou M, Nielsen S, Sassen M, Waldegger S, Seyberth HW, Konrad M. Hypomagnesemia with secondary hypocalcemia is caused by mutations in TRPM6, a new member of the TRPM gene family. Nat Genet 2002; 31:166-70. [PMID: 12032568 DOI: 10.1038/ng889] [Citation(s) in RCA: 594] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Magnesium is an essential ion involved in many biochemical and physiological processes. Homeostasis of magnesium levels is tightly regulated and depends on the balance between intestinal absorption and renal excretion. However, little is known about specific proteins mediating transepithelial magnesium transport. Using a positional candidate gene approach, we identified mutations in TRPM6 (also known as CHAK2), encoding TRPM6, in autosomal-recessive hypomagnesemia with secondary hypocalcemia (HSH, OMIM 602014), previously mapped to chromosome 9q22 (ref. 3). The TRPM6 protein is a new member of the long transient receptor potential channel (TRPM) family and is highly similar to TRPM7 (also known as TRP-PLIK), a bifunctional protein that combines calcium- and magnesium-permeable cation channel properties with protein kinase activity. TRPM6 is expressed in intestinal epithelia and kidney tubules. These findings indicate that TRPM6 is crucial for magnesium homeostasis and implicate a TRPM family member in human disease.
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Affiliation(s)
- Karl P Schlingmann
- Department of Pediatrics, Philipps University of Marburg, Deutschhausstrasse 12, D-35037 Marburg, Germany
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45
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Wärntges S, Friedrich B, Henke G, Duranton C, Lang PA, Waldegger S, Meyermann R, Kuhl D, Speckmann EJ, Obermüller N, Witzgall R, Mack AF, Wagner HJ, Wagner A, Bröer S, Lang F. Cerebral localization and regulation of the cell volume-sensitive serum- and glucocorticoid-dependent kinase SGK1. Pflugers Arch 2002; 443:617-24. [PMID: 11907829 DOI: 10.1007/s00424-001-0737-1] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2001] [Revised: 08/21/2001] [Accepted: 09/13/2001] [Indexed: 10/27/2022]
Abstract
The serum- and glucocorticoid-dependent kinase SGK1 is regulated by alterations of cell volume, whereby cell shrinkage increases and cell swelling decreases the transcription, expression and activity of SGK1. The kinase is expressed in all human tissues studied including the brain. The present study was performed to localize the sites of SGK1 transcription in the brain, to elucidate the influence of the hydration status on SGK1 transcription and to explore the functional significance of altered SGK1 expression. Northern blot analysis of human brain showed SGK1 to be expressed in all cerebral structures examined: amygdala, caudate nucleus, corpus callosum, hippocampus, substantia nigra, subthalamic nucleus and thalamus. In situ hybridization and immunohistochemistry in the rat revealed increased expression of SGK1 in neurons of the hippocampal area CA3 after dehydration, compared with similar slices from brains of euvolaemic rats. Additionally, several oligodendrocytes, a few microglial cells, but no astrocytes, were positive for SGK1. The abundance of SGK1 mRNA in the temporal lobe, including hippocampus, was increased by dehydration and SGK1 transcription in neuroblastoma cells was stimulated by an increase of extracellular osmolarity. Co-expression studies in Xenopus laevis oocytes revealed that SGK1 markedly increased the activity of the neuronal K+ channel Kv1.3. As activation of K+ channels modifies excitation of neuronal cells, SGK1 may participate in the regulation of neuronal excitability.
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Affiliation(s)
- S Wärntges
- Physiologisches Institut der Universität Tübingen, Gmelinstrassse 5, 72076 Tübingen, Germany
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46
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Wagner CA, Ott M, Klingel K, Beck S, Melzig J, Friedrich B, Wild KN, Bröer S, Moschen I, Albers A, Waldegger S, Tümmler B, Egan ME, Geibel JP, Kandolf R, Lang F. Effects of the serine/threonine kinase SGK1 on the epithelial Na(+) channel (ENaC) and CFTR: implications for cystic fibrosis. Cell Physiol Biochem 2001; 11:209-18. [PMID: 11509829 DOI: 10.1159/000051935] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Cystic fibrosis (CF) is characterized by impaired Cl(-) secretion and increased Na(+) reabsorption in several tissues including respiratory epithelium. Many CFTR mutations have been identified over the past years. However, only a poor correlation between the genotype and lung phenotype was found suggesting additional factors influencing the phenotype and course of the disease. The serine/threonine kinase SGK1 has recently been shown to stimulate the activity of the epithelial Na(+) channel ENaC. A variety of stimuli such as aldosterone, cell shrinkage, insulin or TGF-beta1 stimulate transcription and activate the SGK1 kinase. Here we further examined the effects of SGK1 on ENaC and CFTR which have mutual interactions and we analyzed sgk1 mRNA abundance in lung tissue from CF patients. Coexpression of CFTR and h-SGK1 in Xenopus oocytes increased ENaC currents as previously described. In addition CFTR mediated currents were also stimulated. h-SGK1 accelerated the expression of the amiloride sensitive Na(+)- current in Xenopus oocytes paralleled by increased ENaC-protein abundance in the oocyte membrane, an effect which was reversed by a h-SGK1(K127R) mutation lacking the ATP-binding site. The cation selectivity or Na(+) affinity were not affected. However, coexpression of h-SGK1 with ENaC altered the sensitivity of the Na(+)-channel to the inhibitors amiloride and triamterene. The inhibitory effect of CFTR expression on ENaC current was not affected by coexpression of h-SGK1 in Xenopus oocytes. Lung tissue from CF patients strongly expressed the serine/threonine kinase h-sgk1 which was not the case for non-CF lung tissue. Loss of CFTR function itself in a CF lung epithelial cell line did not increase SGK1 expression. In summary, enhanced expression of h-SGK1 in epithelial cells of CF-lung tissue may be a novel pathophysiological factor contributing to increased Na(+) channel activity and thus to increased Na(+) transport in CF.
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Affiliation(s)
- C A Wagner
- Dept. of Physiology I, University of Tübingen.
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47
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Fillon S, Wärntges S, Matskevitch J, Moschen I, Setiawan I, Gamper N, Feng YX, Stegen C, Friedrich B, Waldegger S, Bröer S, Wagner CA, Huber SM, Klingel K, Vereninov A, Lang F. Serum- and glucocorticoid-dependent kinase, cell volume, and the regulation of epithelial transport. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:367-76. [PMID: 11913450 DOI: 10.1016/s1095-6433(01)00422-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Ample pharmacological evidence points to a role of kinases in the regulation of cell volume. Given the limited selectivity of most inhibitors, however, the specific molecules involved have remained largely elusive. The search for cell volume regulated genes in liver HepG2 cells led to the discovery of the human serum- and glucocorticoid-dependent serine/threonine kinase hsgk1. Transcription and expression of hsgk1 is markedly and rapidly upregulated by osmotic and isotonic cell shrinkage. The effect of osmotic cell shrinkage on hsgk1 is mediated by p38 kinase. Further stimuli of hsgk1 transcription include glucocorticoids, aldosterone, TGF-beta1, serum, increase of intracellular Ca2+ and phorbolesters, whereas cAMP downregulates hsgk1 transcription. The hsgk1 protein is expressed in several epithelial tissues including human pancreas, intestine, kidney, and shark rectal gland. Co-expression of hsgk1 with the renal epithelial Na+-channel ENaC or the Na+/K+/2Cl(-)-cotransporter NKCC2 (BSC1) in Xenopus oocytes, accelerates insertion of the transport proteins into the cell membrane and thus, stimulates channel or transport activity. Thus, hsgk1 participates in the regulation of transport by steroids and secretagogues increasing intracellular Ca2+-activity. The stimulation of hsgk1 transcription by TGF-beta1 may further bear pathophysiological relevance.
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Affiliation(s)
- S Fillon
- Department of Physiology, University of Tübingen, Germany
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48
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Abstract
The KCNQI potassium channel alpha-subunit can associate with various KCNE beta-subunits that drastically influence channel gating. Here we show that in the mouse gastrointestinal tract KCNQ1 is prominently expressed in stomach, small intestine and colon, while KCNE3 is expressed in the colon and to a lesser extent in small intestine. Immunostaining revealed that KCNQ1 colocalizes with KCNE3 in the basolateral membranes of crypt cells of the colon and small intestine. Together with the previously shown electrophysiological properties of KCNQ1/KCNE3 channels, this strongly suggests that they form the basolateral potassium conductance that is required for transepithelial cAMP-stimulated chloride secretion. In the stomach, KCNQ1 is expressed together with the H+/K+-ATPase in the luminal membrane of acid-secreting parietal cells of gastric glands. KCNE2, but neither KCNE1 nor KCNE3 was detected in the stomach by Northern analysis. Similar to KCNQ1, KCNE2 was present in gastric glands in only a subset of cells that probably represent parietal cells. The coexpression of KCNQ1 and KCNE2 in HEK293 cells yielded potassium currents that were open at resting voltages, suggesting that these heteromeric channels may underlie the apical potassium conductance in acid-secreting parietal cells that is necessary for the recycling of potassium ions during acid secretion via the H+/K+-ATPase.
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Affiliation(s)
- K Dedek
- Zentrum für Molekulare Neurobiologie Hamburg (ZMNH), Hamburg University, Germany
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Oliver D, He DZ, Klöcker N, Ludwig J, Schulte U, Waldegger S, Ruppersberg JP, Dallos P, Fakler B. Intracellular anions as the voltage sensor of prestin, the outer hair cell motor protein. Science 2001; 292:2340-3. [PMID: 11423665 DOI: 10.1126/science.1060939] [Citation(s) in RCA: 319] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Outer hair cells (OHCs) of the mammalian cochlea actively change their cell length in response to changes in membrane potential. This electromotility, thought to be the basis of cochlear amplification, is mediated by a voltage-sensitive motor molecule recently identified as the membrane protein prestin. Here, we show that voltage sensitivity is conferred to prestin by the intracellular anions chloride and bicarbonate. Removal of these anions abolished fast voltage-dependent motility, as well as the characteristic nonlinear charge movement ("gating currents") driving the underlying structural rearrangements of the protein. The results support a model in which anions act as extrinsic voltage sensors, which bind to the prestin molecule and thus trigger the conformational changes required for motility of OHCs.
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Affiliation(s)
- D Oliver
- Department of Physiology II, University of Tübingen, 72074 Tübingen, Germany
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50
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Waldegger S, Gabrysch S, Barth P, Fillon S, Lang F. h-sgk serine-threonine protein kinase as transcriptional target of p38/MAP kinase pathway in HepG2 human hepatoma cells. Cell Physiol Biochem 2001; 10:203-8. [PMID: 11093030 DOI: 10.1159/000016351] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The human serum and glucocorticoid dependent serine/threonine kinase h-sgk has previously been discovered as cell volume regulated gene. The present study has been performed to elucidate the involvement of p38-kinase in the transcriptional control of h-sgk by osmotic cell shrinkage. The p38-kinase has previously been cloned as the mammalian homologue of HOG1 kinase, which constitutes a part of the osmosensor in the yeast Saccharomyces cerevisiae. Phosphorylated (active) p38-kinase has been estimated with Western blotting, transcription of hsgk using Northern blotting. Both, increase of extracellular NaCl concentration by 50 mmol/l and addition of 10 micromol/l anisomycin increase phosphorylation of the p38-kinase within 5 to 10 minutes. h-sgk transcription is upregulated by addition of 50 mmol/l NaCl and by anisomycin (10 micromol/l), effects completely inhibited by the specific p38-kinase inhibitor, SB 203580 (10 micromol/l). In conclusion, the stimulation of h-sgk transcription by osmotic cell shrinkage is mediated by p38-kinase.
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Affiliation(s)
- S Waldegger
- Institut für Physiologie I, Gmelinstr. 5, D-72076 Tübingen, Germany
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