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Kok M, Brodsky JL. The biogenesis of potassium transporters: implications of disease-associated mutations. Crit Rev Biochem Mol Biol 2024; 59:154-198. [PMID: 38946646 PMCID: PMC11444911 DOI: 10.1080/10409238.2024.2369986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Revised: 06/02/2024] [Accepted: 06/16/2024] [Indexed: 07/02/2024]
Abstract
The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.
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Affiliation(s)
- Morgan Kok
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
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2
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Laghmani K. Protein Quality Control of NKCC2 in Bartter Syndrome and Blood Pressure Regulation. Cells 2024; 13:818. [PMID: 38786040 PMCID: PMC11120568 DOI: 10.3390/cells13100818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Revised: 05/03/2024] [Accepted: 05/09/2024] [Indexed: 05/25/2024] Open
Abstract
Mutations in NKCC2 generate antenatal Bartter syndrome type 1 (type 1 BS), a life-threatening salt-losing nephropathy characterized by arterial hypotension, as well as electrolyte abnormalities. In contrast to the genetic inactivation of NKCC2, inappropriate increased NKCC2 activity has been associated with salt-sensitive hypertension. Given the importance of NKCC2 in salt-sensitive hypertension and the pathophysiology of prenatal BS, studying the molecular regulation of this Na-K-2Cl cotransporter has attracted great interest. Therefore, several studies have addressed various aspects of NKCC2 regulation, such as phosphorylation and post-Golgi trafficking. However, the regulation of this cotransporter at the pre-Golgi level remained unknown for years. Similar to several transmembrane proteins, export from the ER appears to be the rate-limiting step in the cotransporter's maturation and trafficking to the plasma membrane. The most compelling evidence comes from patients with type 5 BS, the most severe form of prenatal BS, in whom NKCC2 is not detectable in the apical membrane of thick ascending limb (TAL) cells due to ER retention and ER-associated degradation (ERAD) mechanisms. In addition, type 1 BS is one of the diseases linked to ERAD pathways. In recent years, several molecular determinants of NKCC2 export from the ER and protein quality control have been identified. The aim of this review is therefore to summarize recent data regarding the protein quality control of NKCC2 and to discuss their potential implications in BS and blood pressure regulation.
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Affiliation(s)
- Kamel Laghmani
- Centre de Recherche des Cordeliers, INSERM, Sorbonne Université, Université de Paris, F-75006 Paris, France;
- CNRS, ERL8228, F-75006 Paris, France
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Münch J, Goodyer PR, Wagner CA. Tubular Diseases and Stones Seen From Pediatric and Adult Nephrology Perspectives. Semin Nephrol 2023; 43:151437. [PMID: 37968178 DOI: 10.1016/j.semnephrol.2023.151437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2023]
Abstract
The tubular system of the kidneys is a complex series of morphologic and functional units orchestrating the content of tubular fluid as it flows along the nephron and collecting ducts. Renal tubules maintain body water, regulate electrolytes and acid-base balance, reabsorb precious organic solutes, and eliminate specific metabolites, toxins, and drugs. In addition, decisive mechanisms to adjust blood pressure are governed by the renal tubules. Genetic as well as acquired disorders of these tubular functions may cause serious diseases that manifest both in childhood and adulthood. This article addresses a selection of tubulopathies and the underlying pathomechanisms, while highlighting the important differences in pediatric and adult nephrology care. These range from rare monogenic conditions such as nephrogenic diabetes insipidus, cystinosis, and Bartter syndrome that present in childhood, to the genetic and acquired tubular pathologies causing hypertension or nephrolithiasis that are more prevalent in adults. Both pediatric and adult nephrologists must be aware of these conditions and the age-dependent manifestations that warrant close interaction between the two subspecialties.
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Affiliation(s)
- Johannes Münch
- Institute of Physiology, University of Zurich, Zurich, Switzerland; Institute of Human Genetics, University of Zurich, Zurich, Switzerland; National Center of Competence in Research, NCCR Kidney.CH, Switzerland
| | - Paul R Goodyer
- McGill University Health Centre, Montreal, Quebec, Canada
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland; National Center of Competence in Research, NCCR Kidney.CH, Switzerland.
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4
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Choi N, Kim SH, Bae EH, Yang EM, Lee GH, Lee SH, Lee JH, Ahn YH, Cheong HI, Kang HG, Hyun HS, Kim JH. Long-term outcome of Bartter syndrome in 54 patients: A multicenter study in Korea. Front Med (Lausanne) 2023; 10:1099840. [PMID: 36993809 PMCID: PMC10040751 DOI: 10.3389/fmed.2023.1099840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Accepted: 02/16/2023] [Indexed: 03/14/2023] Open
Abstract
IntroductionBartter syndrome (BS) is a rare salt-wasting tubulopathy caused by mutations in genes encoding sodium, potassium, or chloride transporters of the thick ascending limb of the loop of Henle and/or the distal convoluted tubule of the kidney. BS is characterized by polyuria, failure to thrive, hypokalemia, metabolic alkalosis, hyperreninemia, and hyperaldosteronism. Potassium and/or sodium supplements, potassium-sparing diuretics, and nonsteroidal anti-inflammatory drugs can be used to treat BS. While its symptoms and initial management are relatively well known, long-term outcomes and treatments are scarce.MethodsWe retrospectively reviewed 54 Korean patients who were clinically or genetically diagnosed with BS from seven centers in Korea.ResultsAll patients included in this study were clinically or genetically diagnosed with BS at a median age of 5 (range, 0–271) months, and their median follow-up was 8 (range, 0.5–27) years. Genetic diagnosis of BS was confirmed in 39 patients: 4 had SLC12A1 gene mutations, 1 had KCNJ1 gene mutations, 33 had CLCNKB gene mutations, and 1 had BSND mutation. Potassium chloride supplements and potassium-sparing diuretics were administered in 94% and 68% of patients, respectively. The mean dosage of potassium chloride supplements was 5.0 and 2.1 mEq/day/kg for patients younger and older than 18 years, respectively. Nephrocalcinosis was a common finding of BS, and it also improved with age in some patients. At the last follow-up of 8 years after the initial diagnosis, 41% had short stature (height less than 3rd percentile) and impaired kidney function was observed in six patients [chronic kidney disease (CKD) G3, n = 4; CKD G5, n = 2].ConclusionBS patients require a large amount of potassium supplementation along with potassium-sparing agents throughout their lives, but tend to improve with age. Despite management, a significant portion of this population exhibited growth impairment, while 11% developed CKD G3–G5.
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Affiliation(s)
- Naye Choi
- Department of Pediatrics, Seoul National University College of Medicine, Seoul, Republic of Korea
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - Seong Heon Kim
- Department of Pediatrics, Seoul National University College of Medicine, Seoul, Republic of Korea
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - Eun Hui Bae
- Department of Internal Medicine, Medical School, Chonnam National University, Gwangju, Republic of Korea
| | - Eun Mi Yang
- Department of Pediatrics, Chonnam National University Hospital, Gwangju, Republic of Korea
| | - Geum Hwa Lee
- Department of Pediatrics, Yonsei University Severance Children's Hospital, Seoul, Republic of Korea
| | - Sang-Ho Lee
- Department of Internal Medicine, Kyung Hee University Hospital at Gangdong, Seoul, Republic of Korea
| | - Joo Hoon Lee
- Department of Pediatrics, Ulsan University Asan Medical Center, Seoul, Republic of Korea
| | - Yo Han Ahn
- Department of Pediatrics, Seoul National University College of Medicine, Seoul, Republic of Korea
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Republic of Korea
- Kidney Research Institute, Seoul National University Medical Research Center, Seoul, Republic of Korea
| | - Hae Il Cheong
- Department of Pediatrics, Hallym University Sacred Heart Hospital, Anyang, Republic of Korea
| | - Hee Gyung Kang
- Department of Pediatrics, Seoul National University College of Medicine, Seoul, Republic of Korea
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Republic of Korea
- Kidney Research Institute, Seoul National University Medical Research Center, Seoul, Republic of Korea
- Wide River Institute of Immunology, Seoul National University, Hongcheon, Republic of Korea
| | - Hye Sun Hyun
- Department of Pediatrics, Collage of Medicine, St. Vincent's Hospital, The Catholic University of Korea, Seoul, Republic of Korea
- *Correspondence: Hye Sun Hyun,
| | - Ji Hyun Kim
- Department of Pediatrics, Seoul National University College of Medicine, Seoul, Republic of Korea
- Department of Pediatrics, Seoul National University Bundang Hospital, Seongnam, Republic of Korea
- Ji Hyun Kim,
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Tian M, Peng H, Bi X, Wang YQ, Zhang YZ, Wu Y, Zhang BR. Late-Onset Bartter Syndrome Type II Due to a Novel Compound Heterozygous Mutation in KCNJ1 Gene: A Case Report and Literature Review. Front Med (Lausanne) 2022; 9:862514. [PMID: 35463019 PMCID: PMC9021870 DOI: 10.3389/fmed.2022.862514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 03/14/2022] [Indexed: 11/16/2022] Open
Abstract
Background Bartter syndrome (BS) type II is a rare autosomal recessive renal tubular disorder caused by mutations in the KCNJ1 gene, which encodes the apical renal outer medullary potassium (ROMK) channel in the thick ascending limb (TAL) of Henle’s loop. BS type II is typically considered as a disorder of infancy and seldom seen in adults. Case Presentation A 34-year-old woman was admitted with generalized body numbness and hand convulsions, without growth retardation. Laboratory tests revealed hypokalemic metabolic alkalosis, hyperreninemic hyperaldosteronism, and nephrocalcinosis. She was misdiagnosed during the initial diagnosis process and was finally diagnosed with late-onset BS type II via genetic testing through next-generation sequencing combined with Sanger sequencing. A novel compound heterozygous p.Leu207Ile/p. Cys308Arg variant in exon 5 of the KCNJ1 gene from her parents was identified and speculated to be a potential pathogenic gene variation. Conclusion We report a case of late-onset BS type II with a novel compound heterozygous mutation in KCNJ1. Both variants are novel and have never been reported. Our report will have a significant impact on the diagnosis of BS in other patients without typical clinical presentations and emphasizes the importance of genetic investigation.
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Affiliation(s)
- Mi Tian
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
| | - Hui Peng
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
| | - Xin Bi
- Guangzhou KingMed Center for Clinical Laboratory Co, Ltd., Guangzhou, China
| | - Yan-Qiu Wang
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
| | - Yong-Zhe Zhang
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
| | - Yan Wu
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
| | - Bei-Ru Zhang
- Department of Nephrology, Shengjing Hospital of China Medical University, Shenyang, China
- *Correspondence: Bei-Ru Zhang,
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Yi S, Li M, Yang Q, Zhang X, Chen F, Qin Z, Yi S, Huang L, Wei H, Zhang Q, Luo J. Novel SLC12A1 Mutations cause Bartter Syndrome in Two Patients with Different Prognoses. Clin Chim Acta 2022; 531:120-125. [DOI: 10.1016/j.cca.2022.03.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 03/27/2022] [Indexed: 11/17/2022]
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Portioli C, Ruiz Munevar MJ, De Vivo M, Cancedda L. Cation-coupled chloride cotransporters: chemical insights and disease implications. TRENDS IN CHEMISTRY 2021; 3:832-849. [PMID: 34604727 PMCID: PMC8461084 DOI: 10.1016/j.trechm.2021.05.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cation-coupled chloride cotransporters (CCCs) modulate the transport of sodium and/or potassium cations coupled with chloride anions across the cell membrane. CCCs thus help regulate intracellular ionic concentration and consequent cell volume homeostasis. This has been largely exploited in the past to develop diuretic drugs that act on CCCs expressed in the kidney. However, a growing wealth of evidence has demonstrated that CCCs are also critically involved in a great variety of other pathologies, motivating most recent drug discovery programs targeting CCCs. Here, we examine the structure–function relationship of CCCs. By linking recent high-resolution cryogenic electron microscopy (cryo-EM) data with older biochemical/functional studies on CCCs, we discuss the mechanistic insights and opportunities to design selective CCC modulators to treat diverse pathologies. The structural topology and function of all cation-coupled chloride cotransporters (CCCs) have been continuously investigated over the past 40 years, with great progress also thanks to the recent cryogenic electron microscopy (cryo-EM) resolution of the structures of five CCCs. In particular, such studies have clarified the structure–function relationship for the Na-K-Cl cotransporter NKCC1 and K-Cl cotransporters KCC1–4. The constantly growing evidence of the crucial involvement of CCCs in physiological and various pathological conditions, as well as the evidence of their wide expression in diverse body tissues, has promoted CCCs as targets for the discovery and development of new, safer, and more selective/effective drugs for a plethora of pathologies. Post-translational modification anchor points on the structure of CCCs may offer alternative strategies for small molecule drug discovery.
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Affiliation(s)
- Corinne Portioli
- Brain Development and Disease Laboratory, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genoa, Italy.,Laboratory of Molecular Modeling and Drug Discovery, IIT, Via Morego, 30 16163 Genoa, Italy
| | | | - Marco De Vivo
- Laboratory of Molecular Modeling and Drug Discovery, IIT, Via Morego, 30 16163 Genoa, Italy
| | - Laura Cancedda
- Brain Development and Disease Laboratory, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genoa, Italy.,Dulbecco Telethon Institute, Via Varese 16b, 00185 Rome, Italy
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8
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Kuroda J, Harada R, Hamada R, Okuda Y, Yoshida Y, Hataya H, Nozu K, Iijima K, Honda M, Ishikura K. Contradiction between genetic analysis and diuretic loading test in type I Bartter syndrome: a case report. BMC Nephrol 2021; 22:295. [PMID: 34461850 PMCID: PMC8404274 DOI: 10.1186/s12882-021-02497-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 08/12/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In typical cases of Bartter syndrome (BS), assessing response to diuretics (furosemide and thiazide), hereinafter referred to as diuretic loading test, may be used to diagnose the type by detecting which part of the kidney tubule is not functioning correctly. However, the diuretic loading test may not always agree with the results of genetic analyses. CASE PRESENTATION A 5-year-old boy was admitted due to lower extremity weakness and abnormal gait. He had a recurrent episode of muscle weakness and laboratory results showed severe hypokalemia. The direct genomic sequencing of the case revealed a new mutation in the SLC12A1 gene, which is associated with type I Bartter syndrome. Because there was the difference between the phenotype and genotype, we conducted a diuretic loading test to confirm the diagnosis. However, the results showed a clear increase in urine excretion of Na and Cl. These results were not consistent with typical type I BS, but consistent with the patient's phenotype. CONCLUSION The diuretic loading test has limited utility for diagnosis especially in atypical cases. On the other hand, this test, which allows assessment of channel function, is useful for better understanding of the genotype-phenotype correlation.
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Affiliation(s)
- Jumpei Kuroda
- Department of Nephrology and Neonatology, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan
| | - Ryoko Harada
- Department of Nephrology, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan
| | - Riku Hamada
- Department of Nephrology, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan.
| | - Yusuke Okuda
- Department of Pediatrics, Kitasato University School of Medicine, 1-15-1 Kitazato, Minami Ward, Sagamihara, Kanagawa, 252-0374, Japan
| | - Yasuhiro Yoshida
- Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Hiroshi Hataya
- Department of Nephrology and General Pediatrics, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan
| | - Kandai Nozu
- Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, Hyogo, 650-0017, Japan
| | - Kazumoto Iijima
- Department of Pediatrics, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, Hyogo, 650-0017, Japan
| | - Masataka Honda
- Department of Nephrology, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan
| | - Kenji Ishikura
- Department of Nephrology, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan.,Department of Pediatrics, Kitasato University School of Medicine, 1-15-1 Kitazato, Minami Ward, Sagamihara, Kanagawa, 252-0374, Japan
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9
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Shaukat I, Bakhos-Douaihy D, Zhu Y, Seaayfan E, Demaretz S, Frachon N, Weber S, Kömhoff M, Vargas-Poussou R, Laghmani K. New insights into the role of endoplasmic reticulum-associated degradation in Bartter Syndrome Type 1. Hum Mutat 2021; 42:947-968. [PMID: 33973684 DOI: 10.1002/humu.24217] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 04/12/2021] [Accepted: 04/30/2021] [Indexed: 12/13/2022]
Abstract
Mutations in Na-K-2Cl co-transporter, NKCC2, lead to type I Bartter syndrome (BS1), a life-threatening kidney disease. Yet, our knowledge of the molecular regulation of NKCC2 mutants remains poor. Here, we aimed to identify the molecular pathogenic mechanisms of one novel and three previously reported missense NKCC2 mutations. Co-immunolocalization studies revealed that all NKCC2 variants are not functional because they are not expressed at the cell surface due to retention in the endoplasmic reticulum (ER). Cycloheximide chase assays together with treatment by protein degradation and mannose trimming inhibitors demonstrated that the defect in NKCC2 maturation arises from ER retention and associated degradation (ERAD). Small interfering RNA (siRNA) knock-down experiments revealed that the ER lectin OS9 is involved in the ERAD of NKCC2 mutants. 4-phenyl butyric acid (4-PBA) treatment mimicked OS9 knock-down effect on NKCC2 mutants by stabilizing their immature forms. Importantly, out of the four studied mutants, only one showed an increased protein maturation upon treatment with glycerol. In summary, our study reveals that BS1 is among diseases linked to the ERAD pathway. Moreover, our data open the possibility that maturation of some ER retained NKCC2 variants is correctable by chemical chaperones offering, therefore, promising avenues in elucidating the molecular pathways governing the ERAD of NKCC2 folding mutants.
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Affiliation(s)
- Irfan Shaukat
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Dalal Bakhos-Douaihy
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Yingying Zhu
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Elie Seaayfan
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Sylvie Demaretz
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Nadia Frachon
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
| | - Stefanie Weber
- Division of Pediatric Nephrology and Transplantation, University Children's Hospital, Philipps-University, Marburg, Germany
| | - Martin Kömhoff
- Division of Pediatric Nephrology and Transplantation, University Children's Hospital, Philipps-University, Marburg, Germany
| | | | - Kamel Laghmani
- Centre de Recherche des Cordeliers, Sorbonne Université, Inserm, Université de Paris, Paris, France.,CNRS, ERL8228, Paris, France
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10
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Syndromes de Bartter–Gitelman. Nephrol Ther 2020; 16:233-243. [DOI: 10.1016/j.nephro.2020.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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11
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Nozu K, Yamamura T, Horinouchi T, Nagano C, Sakakibara N, Ishikura K, Hamada R, Morisada N, Iijima K. Inherited salt-losing tubulopathy: An old condition but a new category of tubulopathy. Pediatr Int 2020; 62:428-437. [PMID: 31830341 DOI: 10.1111/ped.14089] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 08/11/2019] [Accepted: 10/21/2019] [Indexed: 12/16/2022]
Abstract
Bartter syndrome (BS) and Gitelman syndrome (GS) are syndromes associated with congenital tubular dysfunction, characterized by hypokalemia and metabolic alkalosis. Clinically, BS is classified into two types: the severe antenatal/neonatal type, which develops during the fetal period with polyhydramnios and preterm delivery; and the relatively mild classic type, which is usually found during infancy with failure to thrive. GS can be clinically differentiated from BS by its age at onset, usually after school age, or laboratory findings of hypomagnesemia and hypocalciuria. Recent advances in molecular biology have shown that these diseases can be genetically classified into type 1 to 5 BS and GS. As a result, it has become clear that the clinical classification of antenatal/neonatal BS, classic BS, and GS does not always correspond to the clinical symptoms associated with the genotypes in a one-to-one manner; and there is clinically no clear differential border between type 3 BS and GS. This has caused confusion among clinicians in the diagnosis of these diseases. It has been proposed that the disease name "inherited salt-losing tubulopathy" can be used for cases of tubulopathies accompanied by hypokalemia and metabolic alkalosis. It is reasonable to use this term prior to genetic typing into type 1-5 BS or GS, to avoid confusion in a clinical setting. In this article, we review causative genes and phenotypic correlations, diagnosis, and treatment strategies for salt-losing tubulopathy as well as the clinical characteristics of pseudo-BS/GS, which can also be called a "salt-losing disorder".
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Affiliation(s)
- Kandai Nozu
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Tomohiko Yamamura
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Tomoko Horinouchi
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - China Nagano
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Nana Sakakibara
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Kenji Ishikura
- Kitasato University School of Medicine, Sagamihara, Japan
| | - Riku Hamada
- Department of Nephrology, Tokyo Metropolitan Children's Medical Center, Fuchu, Japan
| | - Naoya Morisada
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Kazumoto Iijima
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan
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12
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van der Wijst J, Belge H, Bindels RJM, Devuyst O. Learning Physiology From Inherited Kidney Disorders. Physiol Rev 2019; 99:1575-1653. [PMID: 31215303 DOI: 10.1152/physrev.00008.2018] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.
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Affiliation(s)
- Jenny van der Wijst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Hendrica Belge
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - René J M Bindels
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
| | - Olivier Devuyst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; Institute of Physiology, University of Zurich , Zurich , Switzerland ; and Division of Nephrology, Institute of Experimental and Clinical Research (IREC), Medical School, Université catholique de Louvain, Brussels, Belgium
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13
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Hureaux M, Ashton E, Dahan K, Houillier P, Blanchard A, Cormier C, Koumakis E, Iancu D, Belge H, Hilbert P, Rotthier A, Del Favero J, Schaefer F, Kleta R, Bockenhauer D, Jeunemaitre X, Devuyst O, Walsh SB, Vargas-Poussou R. High-throughput sequencing contributes to the diagnosis of tubulopathies and familial hypercalcemia hypocalciuria in adults. Kidney Int 2019; 96:1408-1416. [PMID: 31672324 DOI: 10.1016/j.kint.2019.08.027] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 08/07/2019] [Accepted: 08/22/2019] [Indexed: 12/15/2022]
Abstract
Hereditary tubulopathies are rare diseases with unknown prevalence in adults. Often diagnosed in childhood, hereditary tubulopathies can nevertheless be evoked in adults. Precise diagnosis can be difficult or delayed due to insidious development of symptoms, comorbidities and polypharmacy. Here we evaluated the diagnostic value of a specific panel of known genes implicated in tubulopathies in adult patients and compared to our data obtained in children. To do this we analyzed 1033 non-related adult patients of which 744 had a clinical diagnosis of tubulopathy and 289 had a diagnosis of familial hypercalcemia with hypocalciuria recruited by three European reference centers. Three-quarters of our tubulopathies cohort included individuals with clinical suspicion of Gitelman syndrome, kidney hypophosphatemia and kidney tubular acidosis. We detected pathogenic variants in 26 different genes confirming a genetic diagnosis of tubulopathy in 29% of cases. In 16 cases (2.1%) the genetic testing changed the clinical diagnosis. The diagnosis of familial hypercalcemia with hypocalciuria was confirmed in 12% of cases. Thus, our work demonstrates the genetic origin of tubulopathies in one out of three adult patients, half of the rate observed in children. Hence, establishing a precise diagnosis is crucial for patients, in order to guide care, to survey and prevent chronic complications, and for genetic counselling. At the same time, this work enhances our understanding of complex phenotypes and enriches the database with the causal variants described.
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Affiliation(s)
- Marguerite Hureaux
- Department of Genetics, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Paris, France; Paris Descartes Université, Sorbonne Paris Cité, Paris, France
| | - Emma Ashton
- North East Thames Regional Genetics Service Laboratories, Great Ormond Street Hospital for Children National Health Service Foundation Trust, London, UK
| | - Karin Dahan
- Center of Human Genetics, Institut de Pathologie et Génétique, Gosselies, Belgium; Division of Nephrology, Université Catholique de Louvain Medical School, Brussels, Belgium
| | - Pascal Houillier
- Paris Descartes Université, Sorbonne Paris Cité, Paris, France; Department of Physiological Functional Investigations, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Paris, France
| | - Anne Blanchard
- Paris Descartes Université, Sorbonne Paris Cité, Paris, France; Assistance Publique Hôpitaux des Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Centre d'Investigation Clinique 1418, Paris, France
| | - Catherine Cormier
- Rheumatology Department, Assistance Publique Hôpitaux de Paris, Hôpital Cochin, Reference Center for Rare Calcium and Phosphate Diseases, Paris, France
| | - Eugenie Koumakis
- Rheumatology Department, Assistance Publique Hôpitaux de Paris, Hôpital Cochin, Reference Center for Rare Calcium and Phosphate Diseases, Paris, France
| | - Daniela Iancu
- Department of Renal Medicine, University College London, London, UK
| | - Hendrica Belge
- Center of Human Genetics, Institut de Pathologie et Génétique, Gosselies, Belgium
| | - Pascale Hilbert
- Center of Human Genetics, Institut de Pathologie et Génétique, Gosselies, Belgium
| | | | | | - Franz Schaefer
- Paediatric Nephrology, Heidelberg University Center for Pediatrics and Adolescent Medicine, Heidelberg, Germany
| | - Robert Kleta
- Department of Renal Medicine, University College London, London, UK; Department of Pediatric Nephrology, Great Ormond Street Hospital for Children National Health Service Foundation Trust, London, UK
| | - Detlef Bockenhauer
- Department of Renal Medicine, University College London, London, UK; Department of Pediatric Nephrology, Great Ormond Street Hospital for Children National Health Service Foundation Trust, London, UK
| | - Xavier Jeunemaitre
- Department of Genetics, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Paris, France; Paris Descartes Université, Sorbonne Paris Cité, Paris, France
| | - Olivier Devuyst
- Division of Nephrology, Université Catholique de Louvain Medical School, Brussels, Belgium; Institute of Physiology, Zurich Center for Integrative Human Physiology (ZIHP), Mechanisms of Inherited Kidney Disorders Group, University of Zurich, Zurich, Switzerland.
| | - Stephen B Walsh
- Department of Renal Medicine, University College London, London, UK.
| | - Rosa Vargas-Poussou
- Department of Genetics, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Paris, France.
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Li J, Hu S, Nie Y, Wang R, Tan M, Li H, Zhu S. A novel compound heterozygous KCNJ1 gene mutation presenting as late-onset Bartter syndrome: Case report. Medicine (Baltimore) 2019; 98:e16738. [PMID: 31441846 PMCID: PMC6716717 DOI: 10.1097/md.0000000000016738] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
RATIONALE Bartter syndrome is an autosomal-recessive inherited disease in which patients present with hypokalemia and metabolic alkalosis. We present 1 case with Bartter syndrome, due to a novel compound heterozygous mutation in the KCNJ1 gene encoding the ATP-sensitive inward rectifier potassium channel in the thick ascending limb of the loop of Henle. PATIENT CONCERNS A patient was admitted to our hospital because of weakness, polyuria, and polydipsia. At presentation to our hospital, the female Chinese patient was 34 years old and her physical examination was normal. Laboratory studies revealed hypokalemia, metabolic alkalosis, hypercalciuria, hyperparathyroidemia, and hyper-reninemia. In addition, urinary potassium was obviously higher. Computer tomography scan confirmed the patient had the bilateral medullary nephrocalcinosis. DIAGNOSIS Blood samples were received from the patient and her parents, and deoxyribonucleic acid was extracted. The genetic analysis of SLC12A1, SLC12A3, KCNJ1, CLCNKB, BSND, and CASR was performed. The compound heterozygous KCNJ1 gene mutation was validated using conventional Sanger sequencing methods. INTERVENTIONS The patient was treated with potassium supplementation. Her blood and urine chemistries improved over the next week. Serum potassium normalized with improvement in polyuria and polydipsia over the next month. OUTCOMES Our patient was compound heterozygous for Thr234Ile and Thr71Met in the KCNJ1 gene. The c.701C>T variant predicted a change from a threonine codon to an isoleucine codon (p.Thr234Ile). The c.212C>T variant predicted a change from a threonine codon to a methionine codon (p.Thr71Met). The unaffected mother was heterozygous for the Thr234Ile mutation, whereas unaffected father was heterozygous for the Thr71Met mutation. LESSONS The phenotypes of the patient were similar to other patients with Bartter syndrome. The phenotypes of the patient could eventually be explained by the presence of the novel compound heterozygous p.Thr234Ile/p.Thr71Met variants in the KCNJ1 gene.
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Affiliation(s)
- Jingyi Li
- Department of Endocrinology, The First Affiliated Hospital, Tsinghua University
| | - Shoulong Hu
- Department of Ophthalmology, Beijing Children's Hospital, Capital Medical University
| | - Yi Nie
- Department of Endocrinology, The First Affiliated Hospital, Tsinghua University
| | - Rongfeng Wang
- Department of Radiology, The First Affiliated Hospital, Tsinghua University, Beijing, P.R. China
| | - Ming Tan
- Department of Endocrinology, The First Affiliated Hospital, Tsinghua University
| | - Hongmei Li
- Department of Endocrinology, The First Affiliated Hospital, Tsinghua University
| | - Shuanli Zhu
- Department of Endocrinology, The First Affiliated Hospital, Tsinghua University
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Han Y, Zhao X, Wang S, Wang C, Tian D, Lang Y, Bottillo I, Wang X, Shao L. Eleven novel SLC12A1 variants and an exonic mutation cause exon skipping in Bartter syndrome type I. Endocrine 2019; 64:708-718. [PMID: 30790175 DOI: 10.1007/s12020-019-01856-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 01/28/2019] [Indexed: 02/06/2023]
Abstract
INTRODUCTION Bartter syndrome type I (BS1) has been rarely reported in large groups. On the other hand, the phenomenon of exon skipping, in which exonic mutations result in abnormal splicing, has been reported to be associated with various diseases. Specifically, mutations that result in the disruption of exonic splicing enhancers (ESEs) and/or the creation of exonic splicing silencers (ESSs) can promote exon skipping. However, the aberrant exon skipping caused by an exonic variant in such splicing regulatory elements (SREs) sequences has never been reported in the causal gene of SLC12A1 in BS1. METHODS We analyze the variants in nine Chinese families with BS1, including eight with antenatal BS (aBS) and one presenting as classical BS (cBS), by next-generation sequencing. Then we used bioinformatics programs to analyze all these variants found in this study and identify candidate mutations that may induce exon skipping. Furthermore, the effects of identified variants were classified according to the 2015 American College of Medical Genetics and Genomics (ACMG) standards and guidelines. RESULTS Fifteen different variants of SLC12A1 gene were identified, including 11 novel ones. Two of the nine probands were homozygotes, the rest seven ones were compound heterozygotes. One candidate variant (c.1435C>G), not only significantly reduced ESEs scores but also markedly increased ESSs scores, were further investigated by mini-gene splicing assay, and found this single-nucleotide substitution causes abnormal splicing in vitro (exclusion of exon 11). Finally, among 15 variants, 9, 3, and 3 were classified as "pathogenic variants", "likely pathogenic variants", "variants with uncertain significance", respectively. CONCLUSION These data would enrich the human gene mutation database (HGMD) and would provide valuable references to the genetic counseling and diagnosis of BS1 for Chinese population. Additionally, our results suggest that aberrant exon skipping is one previously unrecognized mechanism by which an exonic variant in SLC12A1 can lead to BS1.
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Affiliation(s)
- Yue Han
- Department of Nephrology, The Affiliated Qingdao Municipal Hospital of Qingdao University, No.5 Donghai Middle Road, 266071, Qingdao, People's Republic of China
- Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Xiangzhong Zhao
- Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Sai Wang
- Department of Nephrology, The Affiliated Qingdao Municipal Hospital of Qingdao University, No.5 Donghai Middle Road, 266071, Qingdao, People's Republic of China
- Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Cui Wang
- Department of Nephrology, The Affiliated Qingdao Municipal Hospital of Qingdao University, No.5 Donghai Middle Road, 266071, Qingdao, People's Republic of China
- Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Dongxu Tian
- Department of Urology, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Yanhua Lang
- Department of Nursing, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China
| | - Irene Bottillo
- Division of Medical Genetics, Department of Molecular Medicine, Sapienza University, San Camillo-Forlanini Hospital, Rome, 00185, Italy
| | - Xinsheng Wang
- Department of Urology, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China.
| | - Leping Shao
- Department of Nephrology, The Affiliated Qingdao Municipal Hospital of Qingdao University, No.5 Donghai Middle Road, 266071, Qingdao, People's Republic of China.
- Central Laboratory, The Affiliated Hospital of Qingdao University, 266003, Qingdao, People's Republic of China.
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16
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Acar F, Işik G, Mutlu M, Kader Ş, Aslan Y, Kalyoncu M. Antenatal bartter syndrome caused by a novel homozygous mutation in SLC12A1 Gene. Indian J Nephrol 2019; 29:360-363. [PMID: 31571745 PMCID: PMC6755923 DOI: 10.4103/ijn.ijn_175_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Antenatal Bartter syndrome (BS) is an autosomal recessive hereditary renal tubular disorder caused by mutation in the solute carrier family 12 member 1 (SLC12A1) gene on chromosome 15q21.1. This syndrome is characterized by polyuria, hyponatremia, hypokalemic hypochloremic metabolic alkalosis, and hypercalciuria associated with increased urinary loss of electrolytes. Herein, we report a very low-birth-weight premature newborn with antenatal BS caused by a novel homozygous mutation in the SLC12A1 gene, c.596G>A (p.R199H).
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17
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Ares GR, Kassem KM, Ortiz PA. Fructose acutely stimulates NKCC2 activity in rat thick ascending limbs by increasing surface NKCC2 expression. Am J Physiol Renal Physiol 2018; 316:F550-F557. [PMID: 30516424 DOI: 10.1152/ajprenal.00136.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The thick ascending limb (TAL) reabsorbs 25% of the filtered NaCl through the Na+-K+-2Cl- cotransporter (NKCC2). NKCC2 activity is directly related to surface NKCC2 expression and phosphorylation. Higher NaCl reabsorption by TALs is linked to salt-sensitive hypertension, which is linked to consumption of fructose in the diet. However, little is known about the effects of fructose on renal NaCl reabsorption. We hypothesized that fructose, but not glucose, acutely enhances TAL-dependent NaCl reabsorption by increasing NKCC2 activity via stimulation of surface NKCC2 levels and phosphorylation at Thr96/101. We found that fructose (5 mM) increased transport-related O2 consumption in TALs by 11.1 ± 3.2% ( P < 0.05). The effect of fructose on O2 consumption was blocked by furosemide. To study the effect of fructose on NKCC2 activity, we measured the initial rate of NKCC2-dependent thallium influx. We found that 20 min of treatment with fructose (5 mM) increased NKCC2 activity by 58.5 ± 16.9% ( P < 0.05). We then used surface biotinylation to measure surface NKCC2 levels in rat TALs. Fructose increased surface NKCC2 expression in a concentration-dependent manner (22 ± 5, 49 ± 10, and 101 ± 59% of baseline with 1, 5, and 10 mM fructose, respectively, P < 0.05), whereas glucose or a glucose metabolite did not. Fructose did not change NKCC2 phosphorylation at Thre96/101 or total NKCC2 expression. We concluded that acute fructose treatment increases NKCC2 activity by enhancing surface NKCC2 expression, rather than NKCC2 phosphorylation. Our data suggest that fructose consumption could contribute to salt-sensitive hypertension by stimulating NKCC2-dependent NaCl reabsorption in TALs.
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Affiliation(s)
- Gustavo R Ares
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital , Detroit, Michigan
| | - Kamal M Kassem
- Department of Internal Medicine, University of Cincinnati Medical Center , Cincinnati, Ohio
| | - Pablo A Ortiz
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital , Detroit, Michigan.,Department of Physiology, Wayne State University , Detroit, Michigan
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18
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Graham LA, Aman A, Campbell DD, Augley J, Graham D, McBride MW, Fraser NJ, Ferreri NR, Dominiczak AF, Padmanabhan S. Salt stress in the renal tubules is linked to TAL-specific expression of uromodulin and an upregulation of heat shock genes. Physiol Genomics 2018; 50:964-972. [PMID: 30216136 PMCID: PMC6293113 DOI: 10.1152/physiolgenomics.00057.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Revised: 08/20/2018] [Accepted: 09/12/2018] [Indexed: 12/15/2022] Open
Abstract
Previously, our comprehensive cardiovascular characterization study validated Uromodulin as a blood pressure gene. Uromodulin is a glycoprotein exclusively synthesized at the thick ascending limb of the loop of Henle and is encoded by the Umod gene. Umod-/- mice have significantly lower blood pressure than Umod+/+ mice, are resistant to salt-induced changes in blood pressure, and show a leftward shift in pressure-natriuresis curves reflecting changes of sodium reabsorption. Salt stress triggers transcription factors and genes that alter renal sodium reabsorption. To date there are no studies on renal transcriptome responses to salt stress. Here we aimed use RNA-Seq to delineate salt stress pathways in tubules isolated from Umod+/+ mice (a model of sodium retention) and Umod-/- mice (a model of sodium depletion) ± 300 mosmol sodium chloride ( n = 3 per group). In response to salt stress, the tubules of Umod+/+ mice displayed an upregulation of heat shock transcripts. The greatest changes occurred in the expression of: Hspa1a (Log2 fold change 4.35, P = 2.48 e-12) and Hspa1b (Log2 fold change 4.05, P = 2.48 e-12). This response was absent in tubules of Umod-/- mice. Interestingly, seven of the genes discordantly expressed in the Umod-/- tubules were electrolyte transporters. Our results are the first to show that salt stress in renal tubules alters the transcriptome, increasing the expression of heat shock genes. This direction of effect in Umod+/+ tubules suggest the difference is due to the presence of Umod facilitating greater sodium entry into the tubule cell reflecting a specific response to salt stress.
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Affiliation(s)
- Lesley A Graham
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Alisha Aman
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Desmond D Campbell
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Julian Augley
- Wolfson Wohl Cancer Research Centre, Glasgow Polyomics, University of Glasgow, Bearsden, United Kingdom
| | - Delyth Graham
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Martin W McBride
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Niall J Fraser
- University of Dundee, Ninewells Hospital , Dundee , United Kingdom
| | - Nicholas R Ferreri
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Anna F Dominiczak
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
| | - Sandosh Padmanabhan
- The British Heart Foundation Centre of Excellence, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow , Glasgow , United Kingdom
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19
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Abstract
Bartter syndrome (BS) type 1 (OMIM #601678) is a hereditary salt-losing renal tubular disorder characterized by hypokalemic metabolic alkalosis, hypercalciuria, nephrocalcinosis, polyuria, recurrent vomiting, and growth retardation. It is caused by loss-of-function mutations of the SLC12A1 gene, encoding the furosemide-sensitive Na-K-Cl cotransporter. Recently, a phenotypic variability has been observed in patients with genetically determined BS, including absence of nephrocalcinosis, hypokalemia, and/or metabolic alkalosis in the first year of life as well as persistent metabolic acidosis mimicking distal renal tubular acidosis. We report the case of a child with a genetically determined diagnosis of Bartter syndrome type 1 who presented with a phenotype of nephrogenic diabetes insipidus, with severe hypernatremia and urinary concentrating defect. In these atypical cases, molecular analysis is mandatory to define the diagnosis, in order to establish the correct clinical and therapeutic management.
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20
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Zacchia M, Capolongo G, Rinaldi L, Capasso G. The importance of the thick ascending limb of Henle's loop in renal physiology and pathophysiology. Int J Nephrol Renovasc Dis 2018; 11:81-92. [PMID: 29497325 PMCID: PMC5818843 DOI: 10.2147/ijnrd.s154000] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The thick ascending limb (TAL) of Henle’s loop is a crucial segment for many tasks of the nephron. Indeed, the TAL is not only a mainstay for reabsorption of sodium (Na+), potassium (K+), and divalent cations such as calcium (Ca2+) and magnesium (Mg2+) from the luminal fluid, but also has an important role in urine concentration, overall acid–base homeostasis, and ammonia cycle. Transcellular Na+ transport along the TAL is a prerequisite for Na+, K+, Ca2+, Mg2+ homeostasis, and water reabsorption, the latter through its contribution in the generation of the cortico-medullar osmotic gradient. The role of this nephron site in acid–base balance, via bicarbonate reabsorption and acid secretion, is sometimes misunderstood by clinicians. This review describes in detail these functions, reporting in addition to the well-known molecular mechanisms, some novel findings from the current literature; moreover, the pathophysiology and the clinical relevance of primary or acquired conditions caused by TAL dysfunction are discussed. Knowing the physiology of the TAL is fundamental for clinicians, for a better understanding and management of rare and common conditions, such as tubulopathies, hypertension, and loop diuretics abuse.
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Affiliation(s)
- Miriam Zacchia
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, Università della Campania "Luigi Vanvitelli", Naples, Italy
| | - Giovanna Capolongo
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, Università della Campania "Luigi Vanvitelli", Naples, Italy
| | - Luca Rinaldi
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, Università della Campania "Luigi Vanvitelli", Naples, Italy
| | - Giovambattista Capasso
- Division of Nephrology, Department of Cardio-Thoracic and Respiratory Sciences, Università della Campania "Luigi Vanvitelli", Naples, Italy
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21
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Graham LA, Dominiczak AF, Ferreri NR. Role of renal transporters and novel regulatory interactions in the TAL that control blood pressure. Physiol Genomics 2017; 49:261-276. [PMID: 28389525 PMCID: PMC5451551 DOI: 10.1152/physiolgenomics.00017.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 03/27/2017] [Accepted: 04/05/2017] [Indexed: 12/31/2022] Open
Abstract
Hypertension (HTN), a major public health issue is currently the leading factor in the global burden of disease, where associated complications account for 9.4 million deaths worldwide every year. Excessive dietary salt intake is among the environmental factors that contribute to HTN, known as salt sensitivity. The heterogeneity of salt sensitivity and the multiple mechanisms that link high salt intake to increases in blood pressure are of upmost importance for therapeutic application. A continual increase in the kidney's reabsorption of sodium (Na+) relies on sequential actions at various segments along the nephron. When the distal segments of the nephron fail to regulate Na+, the effects on Na+ homeostasis are unfavorable. We propose that the specific nephron region where increased active uptake occurs as a result of variations in Na+ reabsorption is at the thick ascending limb of the loop of Henle (TAL). The purpose of this review is to urge the consideration of the TAL as contributing to the pathophysiology of salt-sensitive HTN. Further research in this area will enable development of a therapeutic application for targeted treatment.
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Affiliation(s)
- Lesley A Graham
- BHF Glasgow Cardiovascular Research Centre, University of Glasgow Cardiovascular and Medical Sciences, Glasgow, United Kingdom; and
| | - Anna F Dominiczak
- BHF Glasgow Cardiovascular Research Centre, University of Glasgow Cardiovascular and Medical Sciences, Glasgow, United Kingdom; and
| | - Nicholas R Ferreri
- Department of Pharmacology, New York Medical College, Valhalla, New York
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22
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Wongsaengsak S, Vidmar AP, Addala A, Kamil ES, Sequeira P, Fass B, Pitukcheewanont P. A novel SLC12A1 gene mutation associated with hyperparathyroidism, hypercalcemia, nephrogenic diabetes insipidus, and nephrocalcinosis in four patients. Bone 2017; 97:121-125. [PMID: 28095294 DOI: 10.1016/j.bone.2017.01.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/10/2017] [Accepted: 01/13/2017] [Indexed: 12/25/2022]
Abstract
Solute Carrier Family 12 member 1 (SLC12A1) gene encodes the sodium-potassium-chloride co-transporter (NKCC2) at the apical membrane of the thick ascending loop of Henle (TAL). Bartter's syndrome (BS) type I is a rare, autosomal recessive, renal tubular disorder associated with mutation of the SLC12A1 gene. Presenting features include: hypokalemic metabolic alkalosis, hypercalciuria and nephrocalcinosis. The many allelic variants reported present with a spectrum of phenotypes, biochemical abnormalities and clinical severities. However, to date, only two reports have described hyperparathyroidism and hypercalcemia in patients with SLC12A1 gene mutations. We describe 4 patients with 4 novel mutation variants in the SLC12A1 gene (c.735C>G, c.1137del, c.2498-2499del, and c.1833delT) presenting with variable degrees of hyperparathyroidism, hypercalcemia, hypokalemic metabolic alkalosis, nephrocalcinosis, and nephrogenic diabetes insipidus. The link between calcium and parathyroid hormone abnormalities in patients with SLC12A1 mutations is unclear; the cases described suggest an association between primary hyperparathyroidism and loss of function mutation of SLC12A1, which may result in an aberrant threshold of the calcium sensing receptor at the level of the kidney.
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Affiliation(s)
- Sariya Wongsaengsak
- Center for Endocrinology, Diabetes and Metabolism, Division of Endocrinology, Children's Hospital Los Angeles, Los Angeles, CA, United States
| | - Alaina P Vidmar
- Center for Endocrinology, Diabetes and Metabolism, Division of Endocrinology, Children's Hospital Los Angeles, Los Angeles, CA, United States
| | - Ananta Addala
- Pediatric Endocrinology, Los Angeles County and University Medical Center University of Southern California, Los Angeles, California, United States
| | - Elaine S Kamil
- Department of Pediatric Nephrology, Cedars-Sinai Medical Center, Los Angeles, CA, United States
| | - Paola Sequeira
- Pediatric Endocrinology, Los Angeles County and University Medical Center University of Southern California, Los Angeles, California, United States; Keck School of Medicine of University of Southern California, Los Angeles, CA, United States
| | - Benjamin Fass
- Pediatric Endocrinology, Kaiser Permanente Medical Center Los Angeles, Los Angeles, CA, United States
| | - Pisit Pitukcheewanont
- Center for Endocrinology, Diabetes and Metabolism, Division of Endocrinology, Children's Hospital Los Angeles, Los Angeles, CA, United States; Keck School of Medicine of University of Southern California, Los Angeles, CA, United States.
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23
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Breinbjerg A, Siggaard Rittig C, Gregersen N, Rittig S, Hvarregaard Christensen J. A novel variant in the SLC12A1 gene in two families with antenatal Bartter syndrome. Acta Paediatr 2017; 106:161-167. [PMID: 27748541 DOI: 10.1111/apa.13635] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 09/20/2016] [Accepted: 10/13/2016] [Indexed: 12/27/2022]
Abstract
AIM Bartter syndrome is an autosomal-recessive inherited disease in which patients present with hypokalaemia and metabolic alkalosis. We present two apparently nonrelated cases with antenatal Bartter syndrome type I, due to a novel variant in the SLC12A1 gene encoding the bumetanide-sensitive sodium-(potassium)-chloride cotransporter 2 in the thick ascending limb of the loop of Henle. METHODS Blood samples were received from the two cases and 19 of their relatives, and deoxyribonucleic acid was extracted. The coding regions of the SLC12A1 gene were amplified using polymerase chain reaction, followed by bidirectional direct deoxyribonucleic acid sequencing. RESULTS Each affected child in the two families was homozygous for a novel inherited variant in the SLC12A1gene, c.1614T>A. The variant predicts a change from a tyrosine codon to a stop codon (p.Tyr538Ter). The two cases presented antenatally and at six months of age, respectively. CONCLUSION The two cases were homozygous for the same variant in the SLC12A1 gene, but presented clinically at different ages. This could eventually be explained by the presence of other gene variants or environmental factors modifying the phenotypes. The phenotypes of the patients were similar to other patients with antenatal Bartter syndrome.
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Affiliation(s)
- Anders Breinbjerg
- Department of Pediatrics; Aarhus University Hospital; Aarhus Denmark
| | | | - Niels Gregersen
- Research Unit for Molecular Medicine; Aarhus University Hospital; Aarhus Denmark
| | - Søren Rittig
- Department of Pediatrics; Aarhus University Hospital; Aarhus Denmark
| | - Jane Hvarregaard Christensen
- Department of Pediatrics; Aarhus University Hospital; Aarhus Denmark
- Department of Biomedicine; Aarhus University; Aarhus Denmark
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Sun M, Ning J, Xu W, Zhang H, Zhao K, Li W, Li G, Li S. Genetic heterogeneity in patients with Bartter syndrome type 1. Mol Med Rep 2016; 15:581-590. [PMID: 28000888 PMCID: PMC5364841 DOI: 10.3892/mmr.2016.6063] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 11/01/2016] [Indexed: 12/28/2022] Open
Abstract
Bartter syndrome (BS) type 1 is an autosomal recessive kidney disorder caused by loss-of-function mutations in the solute carrier family 12 member 1 (SLC12A1) gene. To date, 72 BS type 1 patients harboring SLC12A1 mutations have been documented. Of these 144 alleles studied, 68 different disease-causing mutations have been detected in 129 alleles, and no mutation was detected in the remaining 15 alleles. The mutation types included missense/nonsense mutations, splicing mutations and small insertions and deletions ranging from 1 to 4 nucleotides. A large deletion encompassing a whole exon in the SLC12A1 gene has not yet been reported. The current study initially identified an undocumented homozygous frameshift mutation (c.1833delT) by Sanger sequencing analysis of a single infant with BS type 1. However, in a subsequent analysis, the mutation was detected only in the father's DNA. Upon further investigation using a next-generation sequencing approach, a deletion in exons 14 and 15 in both the patient and patient's mother was detected. The deletion was subsequently confirmed by use of a long-range polymerase chain reaction and was determined to be 3.16 kb in size based on sequencing of the junction fragment. The results of the present study demonstrated that pathogenic variants of SLC12A1 are heterogeneous. Large deletions appear to serve an etiological role in BS type 1, and may be more prevalent than previously thought.
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Affiliation(s)
- Mingran Sun
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Jing Ning
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Weihong Xu
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Han Zhang
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Kaishu Zhao
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Wenfu Li
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
| | - Guiying Li
- Key Laboratory for Molecular Enzymology and Engineering, The Ministry of Education, School of Life Sciences, Jilin University, Changchun, Jilin 130012, P.R. China
| | - Shibo Li
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma, OK 73117, USA
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Chuang GT, Lin SH, Tsau YK, Tsai IJ. Antenatal Bartter syndrome resembling nephrogenic diabetes insipidus in a 5-year-old boy. J Formos Med Assoc 2016; 115:382-383. [PMID: 25935500 DOI: 10.1016/j.jfma.2015.03.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2014] [Revised: 03/03/2015] [Accepted: 03/25/2015] [Indexed: 06/04/2023] Open
Affiliation(s)
- Gwo-Tsann Chuang
- Department of Pediatrics, National Taiwan University Children Hospital, Taipei, Taiwan
| | - Shih-Hua Lin
- Division of Nephrology, Department of Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Yong-Kwei Tsau
- Department of Pediatrics, National Taiwan University Children Hospital, Taipei, Taiwan
| | - I-Jung Tsai
- Department of Pediatrics, National Taiwan University Children Hospital, Taipei, Taiwan.
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26
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Kemter E, Rathkolb B, Becker L, Bolle I, Busch DH, Dalke C, Elvert R, Favor J, Graw J, Hans W, Ivandic B, Kalaydjiev S, Klopstock T, Rácz I, Rozman J, Schrewe A, Schulz H, Zimmer A, Fuchs H, Gailus-Durner V, Hrabe de Angelis M, Wolf E, Aigner B. Standardized, systemic phenotypic analysis of Slc12a1I299F mutant mice. J Biomed Sci 2014; 21:68. [PMID: 25084970 PMCID: PMC4237776 DOI: 10.1186/s12929-014-0068-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 07/17/2014] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND Type I Bartter syndrome is a recessive human nephropathy caused by loss-of-function mutations in the SLC12A1 gene coding for the Na+-K+-2Cl- cotransporter NKCC2. We recently established the mutant mouse line Slc12a1I299F exhibiting kidney defects highly similar to the late-onset manifestation of this hereditary human disease. Besides the kidney defects, low blood pressure and osteopenia were revealed in the homozygous mutant mice which were also described in humans. Beside its strong expression in the kidney, NKCC2 has been also shown to be expressed in other tissues in rodents i.e. the gastrointestinal tract, pancreatic beta cells, and specific compartments of the ear, nasal tissue and eye. RESULTS To examine if, besides kidney defects, further organ systems and/or metabolic pathways are affected by the Slc12a1I299F mutation as primary or secondary effects, we describe a standardized, systemic phenotypic analysis of the mutant mouse line Slc12a1I299F in the German Mouse Clinic. Slc12a1I299F homozygous mutant mice and Slc12a1I299F heterozygous mutant littermates as controls were tested at the age of 4-6 months. Beside the already published changes in blood pressure and bone metabolism, a significantly lower body weight and fat content were found as new phenotypes for Slc12a1I299F homozygous mutant mice. Small additional effects included a mild erythropenic anemia in homozygous mutant males as well as a slight hyperalgesia in homozygous mutant females. For other functions, such as immunology, lung function and neurology, no distinct alterations were observed. CONCLUSIONS In this systemic analysis no clear primary effects of the Slc12a1I299F mutation appeared for the organs other than the kidneys where Slc12a1 expression has been described. On the other hand, long-term effects additional and/or secondary to the kidney lesions might also appear in humans harboring SLC12A1 mutations.
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Ares GR, Ortiz PA. Dynamin2, clathrin, and lipid rafts mediate endocytosis of the apical Na/K/2Cl cotransporter NKCC2 in thick ascending limbs. J Biol Chem 2012; 287:37824-34. [PMID: 22977238 DOI: 10.1074/jbc.m112.386425] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Steady-state surface levels of the apical Na/K/2Cl cotransporter NKCC2 regulate NaCl reabsorption by epithelial cells of the renal thick ascending limb (THAL). We reported that constitutive endocytosis of NKCC2 controls NaCl absorption in native THALs; however, the pathways involved in NKCC2 endocytosis are unknown. We hypothesized that NKCC2 endocytosis at the apical surface depends on dynamin-2 and clathrin. Measurements of steady-state surface NKCC2 and the rate of NKCC2 endocytosis in freshly isolated rat THALs showed that inhibition of endogenous dynamin-2 with dynasore blunted NKCC2 endocytosis by 56 ± 11% and increased steady-state surface NKCC2 by 67 ± 27% (p < 0.05). Expression of the dominant negative Dyn2K44A in THALs slowed the rate of NKCC2 endocytosis by 38 ± 8% and increased steady-state surface NKCC2 by 37 ± 8%, without changing total NKCC2 expression. Inhibition of clathrin-mediated endocytosis with chlorpromazine blunted NKCC2 endocytosis by 54 ± 6%, while preventing clathrin from interacting with synaptojanin also blunted NKCC2 endocytosis by 52 ± 5%. Disruption of lipid rafts blunted NKCC2 endocytosis by 39 ± 4% and silencing caveolin-1 by 29 ± 4%. Simultaneous inhibition of clathrin- and lipid raft-mediated endocytosis completely blocked NKCC2 internalization. We concluded that dynamin-2, clathrin, and lipid rafts mediate NKCC2 endocytosis and maintain steady-state apical surface NKCC2 in native THALs. These are the first data identifying the endocytic pathway for apical NKCC2 endocytosis.
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Affiliation(s)
- Gustavo R Ares
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Wayne State University, Detroit, Michigan 48202, USA
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Seyberth HW, Schlingmann KP. Bartter- and Gitelman-like syndromes: salt-losing tubulopathies with loop or DCT defects. Pediatr Nephrol 2011; 26:1789-802. [PMID: 21503667 PMCID: PMC3163795 DOI: 10.1007/s00467-011-1871-4] [Citation(s) in RCA: 111] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Revised: 03/09/2011] [Accepted: 03/09/2011] [Indexed: 12/11/2022]
Abstract
Salt-losing tubulopathies with secondary hyperaldosteronism (SLT) comprise a set of well-defined inherited tubular disorders. Two segments along the distal nephron are primarily involved in the pathogenesis of SLTs: the thick ascending limb of Henle's loop, and the distal convoluted tubule (DCT). The functions of these pre- and postmacula densa segments are quite distinct, and this has a major impact on the clinical presentation of loop and DCT disorders - the Bartter- and Gitelman-like syndromes. Defects in the water-impermeable thick ascending limb, with its greater salt reabsorption capacity, lead to major salt and water losses similar to the effect of loop diuretics. In contrast, defects in the DCT, with its minor capacity of salt reabsorption and its crucial role in fine-tuning of urinary calcium and magnesium excretion, provoke more chronic solute imbalances similar to the effects of chronic treatment with thiazides. The most severe disorder is a combination of a loop and DCT disorder similar to the enhanced diuretic effect of a co-medication of loop diuretics with thiazides. Besides salt and water supplementation, prostaglandin E2-synthase inhibition is the most effective therapeutic option in polyuric loop disorders (e.g., pure furosemide and mixed furosemide-amiloride type), especially in preterm infants with severe volume depletion. In DCT disorders (e.g., pure thiazide and mixed thiazide-furosemide type), renin-angiotensin-aldosterone system (RAAS) blockers might be indicated after salt, potassium, and magnesium supplementation are deemed insufficient. It appears that in most patients with SLT, a combination of solute supplementation with some drug treatment (e.g., indomethacin) is needed for a lifetime.
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Affiliation(s)
- Hannsjörg W. Seyberth
- Department of Pediatrics and Adolescent Medicine, Philipps University, Marburg, Germany ,Lazarettgarten 23, 76829 Landau, Germany
| | - Karl P. Schlingmann
- Department of General Pediatrics, University Children’s Hospital, Münster, Germany
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Deschênes G, Fila M. Primary molecular disorders and secondary biological adaptations in bartter syndrome. Int J Nephrol 2011; 2011:396209. [PMID: 21941653 PMCID: PMC3177086 DOI: 10.4061/2011/396209] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Accepted: 06/01/2011] [Indexed: 12/17/2022] Open
Abstract
Bartter syndrome is a hereditary disorder that has been characterized by the association of hypokalemia, alkalosis, and the hypertrophy of the juxtaglomerular complex with secondary hyperaldosteronism and normal blood pressure. By contrast, the genetic causes of Bartter syndrome primarily affect molecular structures directly involved in the sodium reabsorption at the level of the Henle loop. The ensuing urinary sodium wasting and chronic sodium depletion are responsible for the contraction of the extracellular volume, the activation of the renin-aldosterone axis, the secretion of prostaglandins, and the biological adaptations of downstream tubular segments, meaning the distal convoluted tubule and the collecting duct. These secondary biological adaptations lead to hypokalemia and alkalosis, illustrating a close integration of the solutes regulation in the tubular structures.
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Affiliation(s)
- Georges Deschênes
- Pediatric Nephrology Unit, Hôpital Robert-Debré, 48 Bd Sérurier, 75019 Paris, France
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30
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Ares GR, Caceres PS, Ortiz PA. Molecular regulation of NKCC2 in the thick ascending limb. Am J Physiol Renal Physiol 2011; 301:F1143-59. [PMID: 21900458 DOI: 10.1152/ajprenal.00396.2011] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The kidney plays an essential role in blood pressure regulation by controlling short-term and long-term NaCl and water balance. The thick ascending limb of the loop of Henle (TAL) reabsorbs 25-30% of the NaCl filtered by the glomeruli in a process mediated by the apical Na(+)-K(+)-2Cl(-) cotransporter NKCC2, which allows Na(+) and Cl(-) entry from the tubule lumen into TAL cells. In humans, mutations in the gene coding for NKCC2 result in decreased or absent activity characterized by severe salt and volume loss and decreased blood pressure (Bartter syndrome type 1). Opposite to Bartter's syndrome, enhanced NaCl absorption by the TAL is associated with human hypertension and animal models of salt-sensitive hypertension. TAL NaCl reabsorption is subject to exquisite control by hormones like vasopressin, parathyroid, glucagon, and adrenergic agonists (epinephrine and norepinephrine) that stimulate NaCl reabsorption. Atrial natriuretic peptides or autacoids like nitric oxide and prostaglandins inhibit NaCl reabsorption, promoting salt excretion. In general, the mechanism by which hormones control NaCl reabsorption is mediated directly or indirectly by altering the activity of NKCC2 in the TAL. Despite the importance of NKCC2 in renal physiology, the molecular mechanisms by which hormones, autacoids, physical factors, and intracellular ions regulate NKCC2 activity are largely unknown. During the last 5 years, it has become apparent that at least three molecular mechanisms determine NKCC2 activity. As such, membrane trafficking, phosphorylation, and protein-protein interactions have recently been described in TALs and heterologous expression systems as mechanisms that modulate NKCC2 activity. The focus of this review is to summarize recent data regarding NKCC2 regulation and discuss their potential implications in physiological control of TAL function, renal physiology, and blood pressure regulation.
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Affiliation(s)
- Gustavo R Ares
- Hypertension and Vascular Research Division, Dept. of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202, USA
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31
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Rare mutations in SLC12A1 and SLC12A3 protect against hypertension by reducing the activity of renal salt cotransporters. J Hypertens 2011; 29:475-83. [PMID: 21157372 DOI: 10.1097/hjh.0b013e328341d0fd] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVES Screening for variants in SLC12A1 and SLC12A3 genes, encoding the renal Na:Cl (NCC) and Na:K:2Cl (NKCC2) cotransporters, respectively, in 3125 members of the Framingham Heart Study (FHS) revealed that carrying a rare mutation in one of these genes was associated with a significant reduction in blood pressure, in the risk of arterial hypertension, and of death due to cardiovascular disease. Because near 60% of the rare mutations identified have not been related to Bartter's or Gitelman's disease, the consequence of such mutations on cotransporter activity is unknown. METHODS We used the heterologous expression system of Xenopus laevis oocytes, microinjected with wild-type or mutant NCC or NKCC2 cRNAs, to examine the effect of these inferred NCC and NKCC2 mutations on the cotransporters' functional properties. Cotransporter activity was defined as the diuretic-sensitive radioactive tracer uptake and response to known modulators was assessed. RESULTS Basal NCC activity was significantly reduced in all NCC mutants and, excluding NCC-S186F, response to WNK3, WNK4, or intracellular chloride depletion was conserved. Similarly, basal activity was reduced in six out of nine NKCC2 mutants and response to WNK3 was maintained. No effect on protein expression was seen, except for NCC-S186F, which was significantly reduced. CONCLUSIONS The rare NCC or NKCC2 mutations found in the FHS significantly reduced the basal activity of the cotransporters. This observation supports that even a small, but chronic reduction of NCC or NKCC2 function results in a lower blood pressure and decreased risk of hypertension in otherwise healthy individuals in the general population.
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A novel compound heterozygous ROMK mutation presenting as late onset Bartter syndrome associated with nephrocalcinosis and elevated 1,25(OH)(2) vitamin D levels. Clin Exp Nephrol 2011; 15:572-6. [PMID: 21431899 DOI: 10.1007/s10157-011-0431-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 02/24/2011] [Indexed: 10/18/2022]
Abstract
Bartter syndrome (BS) is a rare renal tubular disorder presenting with hypokalemic metabolic alkalosis, which is classified into five types. KCNJ1 mutations usually cause the neonatal form of BS, type II BS (OMIM 241200). However, this report concerns a female patient with a novel, compound heterozygous KCNJ1 mutation that causes late-onset BS. The unique clinical findings of this case include persistently elevated 1,25(OH)(2) vitamin D levels, possibly due to increase prostaglandin E(2) levels, and medullary nephrocalcinosis. Treatment with COX-2 inhibitors resolved her hypercalciuria and improved her height and weight; renal function remains stable and there is no progression of nephrocalcinosis.
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Carmosino M, Rizzo F, Procino G, Basco D, Valenti G, Forbush B, Schaeren-Wiemers N, Caplan MJ, Svelto M. MAL/VIP17, a new player in the regulation of NKCC2 in the kidney. Mol Biol Cell 2010; 21:3985-97. [PMID: 20861303 PMCID: PMC2982131 DOI: 10.1091/mbc.e10-05-0456] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The renal-specific Na+-K+-2Cl- cotransporter (NKCC2) is the major salt transport pathway of the apical membrane of the mammalian thick ascending limb of Henle's loop. Here, we analyze the role of the tetraspan protein myelin and lymphocytes-associated protein (MAL)/VIP17 in the regulation of NKCC2. We demonstrated that 1) NKCC2 and MAL/VIP17 colocalize and coimmunoprecipitate in Lilly Laboratories cell porcine kidney cells (LLC-PK1) as well as in rat kidney medullae, 2) a 150-amino acid stretch of NKCC2 C-terminal tail is involved in the interaction with MAL/VIP17, 3) MAL/VIP17 increases the cell surface retention of NKCC2 by attenuating its internalization, and 4) this coincides with an increase in cotransporter phosphorylation. Interestingly, overexpression of MAL/VIP17 in the kidney of transgenic mice results in cysts formation in distal nephron structures consistent with the hypothesis that MAL/VIP17 plays an important role in apical sorting or in maintaining the stability of the apical membrane. The NKCC2 expressed in these mice was highly glycosylated and phosphorylated, suggesting that MAL/VIP17 also is involved in the stabilization of NKCC2 at the apical membrane in vivo. Thus, the involvement of MAL/VIP17 in the activation and surface expression of NKCC2 could play an important role in the regulated absorption of Na+ and Cl- in the kidney.
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Affiliation(s)
- Monica Carmosino
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06511, USA.
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Lee EH, Heo JS, Lee HK, Han KH, Kang HG, Ha IS, Choi Y, Cheong HI. A case of Bartter syndrome type I with atypical presentations. KOREAN JOURNAL OF PEDIATRICS 2010; 53:809-13. [PMID: 21189980 PMCID: PMC3004498 DOI: 10.3345/kjp.2010.53.8.809] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Revised: 06/23/2010] [Accepted: 07/14/2010] [Indexed: 11/27/2022]
Abstract
Bartter syndrome (BS) is an autosomal recessively inherited rare renal tubular disorder characterized by hypokalemic metabolic alkalosis and hyperreninemic hyperaldosteronism with normal to low blood pressure due to a renal loss of sodium. Genetically, BS is classified into 5 subtypes according to the underlying genetic defects, and BS is clinically categorized into antenatal BS and classical BS according to onset age. BS type I is caused by loss-of-function mutations in the SLC12A1 gene and usually manifests as antenatal BS. This report concerns a male patient with compound heterozygous missense mutations on SLC12A1 (p.C436Y and p.L560P) and atypical clinical and laboratory features. The patient had low urinary sodium and chloride levels without definite metabolic alkalosis until the age of 32 months, which led to confusion between BS and nephrogenic diabetes insipidus (NDI). In addition, the clinical onset of the patient was far beyond the neonatal period. Genetic study eventually led to the diagnosis of BS type I. The low urinary sodium and chloride concentrations may be caused by secondary NDI, and the later onset may suggest the existence of a genotype-phenotype correlation. In summary, BS type I may have phenotype variability including low urine sodium and chloride levels and later onset. A definitive diagnosis can be confirmed by genetic testing.
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Affiliation(s)
- Eun Hye Lee
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Korea
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Kemter E, Rathkolb B, Bankir L, Schrewe A, Hans W, Landbrecht C, Klaften M, Ivandic B, Fuchs H, Gailus-Durner V, Hrabé de Angelis M, Wolf E, Wanke R, Aigner B. Mutation of the Na+-K+-2Cl−cotransporter NKCC2 in mice is associated with severe polyuria and a urea-selective concentrating defect without hyperreninemia. Am J Physiol Renal Physiol 2010; 298:F1405-15. [DOI: 10.1152/ajprenal.00522.2009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The bumetanide-sensitive Na+-K+-2Cl−cotransporter NKCC2, located in the thick ascending limb of Henle's loop, plays a critical role in the kidney's ability to concentrate urine. In humans, loss-of-function mutations of the solute carrier family 12 member 1 gene ( SLC12A1), coding for NKCC2, cause type I Bartter syndrome, which is characterized by prenatal onset of a severe polyuria, salt-wasting tubulopathy, and hyperreninemia. In this study, we describe a novel chemically induced, recessive mutant mouse line termed Slc12a1I299Fexhibiting late-onset manifestation of type I Bartter syndrome. Homozygous mutant mice are viable and exhibit severe polyuria, metabolic alkalosis, marked increase in plasma urea but close to normal creatininemia, hypermagnesemia, hyperprostaglandinuria, hypotension,, and osteopenia. Fractional excretion of urea is markedly decreased. In addition, calcium and magnesium excretions are more than doubled compared with wild-type mice, while uric acid excretion is twofold lower. In contrast to hyperreninemia present in human disease, plasma renin concentration in homozygotes is not increased. The polyuria observed in homozygotes may be due to the combination of two additive factors, a decrease in activity of mutant NKCC2 and an increase in medullary blood flow, due to prostaglandin-induced vasodilation, that impairs countercurrent exchange of urea in the medulla. In conclusion, this novel viable mouse line with a missense Slc12a1 mutation exhibits most of the features of type I Bartter syndrome and may represent a new model for the study of this human disease.
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Affiliation(s)
- Elisabeth Kemter
- Chair for Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, and
- Institute of Veterinary Pathology, Center for Clinical Veterinary Medicine, LMU Munich, Munich
| | - Birgit Rathkolb
- Chair for Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, and
| | - Lise Bankir
- INSERM Unité 872, Centre de Recherche des Cordeliers, Paris, France
| | - Anja Schrewe
- Department of Medicine III, Division of Cardiology, University of Heidelberg, Heidelberg; and
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Wolfgang Hans
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Christina Landbrecht
- Chair for Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, and
| | - Matthias Klaften
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Boris Ivandic
- Department of Medicine III, Division of Cardiology, University of Heidelberg, Heidelberg; and
| | - Helmut Fuchs
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Valérie Gailus-Durner
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Martin Hrabé de Angelis
- Institute of Experimental Genetics, Helmholtz Zentrum München, Neuherberg, and Chair for Experimental Genetics, Technische Universität München, Munich, Germany
| | - Eckhard Wolf
- Chair for Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, and
| | - Ruediger Wanke
- Institute of Veterinary Pathology, Center for Clinical Veterinary Medicine, LMU Munich, Munich
| | - Bernhard Aigner
- Chair for Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, and
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Zaarour N, Demaretz S, Defontaine N, Mordasini D, Laghmani K. A highly conserved motif at the COOH terminus dictates endoplasmic reticulum exit and cell surface expression of NKCC2. J Biol Chem 2009; 284:21752-64. [PMID: 19535327 DOI: 10.1074/jbc.m109.000679] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Mutations in the apically located Na(+)-K(+)-2Cl(-) co-transporter, NKCC2, lead to type I Bartter syndrome, a life-threatening kidney disorder, yet the mechanisms underlying the regulation of mutated NKCC2 proteins in renal cells have not been investigated. Here, we identified a trihydrophobic motif in the distal COOH terminus of NKCC2 that was required for endoplasmic reticulum (ER) exit and surface expression of the co-transporter. Indeed, microscopic confocal imaging showed that a naturally occurring mutation depriving NKCC2 of its distal COOH-terminal region results in the absence of cell surface expression. Biotinylation assays revealed that lack of cell surface expression was associated with abolition of mature complex-glycosylated NKCC2. Pulse-chase analysis demonstrated that the absence of mature protein was not caused by reduced synthesis or increased rates of degradation of mutant co-transporters. Co-immunolocalization experiments revealed that these mutants co-localized with the ER marker protein-disulfide isomerase, demonstrating that they are retained in the ER. Cell treatment with proteasome or lysosome inhibitors failed to restore the loss of complex-glycosylated NKCC2, further eliminating the possibility that mutant co-transporters were processed by the Golgi apparatus. Serial truncation of the NKCC2 COOH terminus, followed by site-directed mutagenesis, identified hydrophobic residues (1081)LLV(1083) as an ER exit signal necessary for maturation of NKCC2. Mutation of (1081)LLV(1083) to AAA within the context of the full-length protein prevented NKCC2 ER exit independently of the expression system. This trihydrophobic motif is highly conserved in the COOH-terminal tails of all members of the cation-chloride co-transporter family, and thus may function as a common motif mediating their transport from the ER to the cell surface. Taken together, these data are consistent with a model whereby naturally occurring premature terminations that interfere with the LLV motif compromise co-transporter surface delivery through defective trafficking.
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Affiliation(s)
- Nancy Zaarour
- INSERM, UMRS 872-Equipe 3-ERL7226, 75006 Paris, France
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Gamba G, Friedman PA. Thick ascending limb: the Na(+):K (+):2Cl (-) co-transporter, NKCC2, and the calcium-sensing receptor, CaSR. Pflugers Arch 2009; 458:61-76. [PMID: 18982348 PMCID: PMC3584568 DOI: 10.1007/s00424-008-0607-1] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Accepted: 10/21/2008] [Indexed: 01/12/2023]
Abstract
The thick ascending limb of Henle's loop is a nephron segment that is vital to the formation of dilute and concentrated urine. This ability is accomplished by a consortium of functionally coupled proteins consisting of the apical Na(+):K(+):2Cl(-) co-transporter, the K(+) channel, and basolateral Cl(-) channel that mediate electroneutral salt absorption. In thick ascending limbs, salt absorption is importantly regulated by the calcium-sensing receptor. Genetic or pharmacological disruption impairing the function of any of these proteins results in Bartter syndrome. The thick ascending limb is also an important site of Ca(2+) and Mg(2+) absorption. Calcium-sensing receptor activation inhibits cellular Ca(2+) absorption induced by parathyroid hormone, as well as passive paracellular Ca(2+) transport. The present review discusses these functions and their genetic and molecular regulation.
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Affiliation(s)
- Gerardo Gamba
- Molecular Physiology Unit, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico
- Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Tlalpan, 14000 Mexico City, Mexico
| | - Peter A. Friedman
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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Atypical phenotype of type I Bartter syndrome accompanied by focal segmental glomerulosclerosis. Pediatr Nephrol 2009; 24:415-8. [PMID: 18830715 DOI: 10.1007/s00467-008-0999-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2008] [Revised: 07/31/2008] [Accepted: 08/12/2008] [Indexed: 10/21/2022]
Abstract
Type I Bartter syndrome (BS) is caused by mutations of the Na-K-2Cl cotransporter (NKCC2)-encoding SLC12A1 gene. The clinical phenotype of this severe form of BS is characterized by polyhydramnios, premature delivery, failure to thrive, and nephrocalcinosis, and the diagnosis is usually made during the antenatal-neonatal period. This report concerns a 29-year-old Japanese man with atypical type I BS due to a compound heterozygous mutation of the SLC12A1 gene. He was born after full-term pregnancy complicated by polyhydramnios. He first presented with asymptomatic proteinuria at the age of 20 years and was diagnosed with BS based on laboratory data. There were signs of moderate proteinuria, mild renal dysfunction and nephrocalcinosis. Renal biopsy showed focal segmental glomerulosclerosis (FSGS), and genetic testing revealed novel mutations of A555V and G809V in the SLC12A1 gene. The patient's sister showed the same clinical course, laboratory test abnormalities and gene mutations. Our patient had a type I BS with an atypical clinical course, which was diagnosed when he was 20 years old. Laboratory findings indicated phenotypic variability in this disease, and the presence of nephropathy suggested that FSGS might be one of the lesions causing end-stage renal failure in this disease.
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Seyberth HW. An improved terminology and classification of Bartter-like syndromes. ACTA ACUST UNITED AC 2008; 4:560-7. [PMID: 18695706 DOI: 10.1038/ncpneph0912] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2008] [Accepted: 07/04/2008] [Indexed: 12/15/2022]
Abstract
This Review outlines a terminology and classification of Bartter-like syndromes that is based on the underlying causes of these inherited salt-losing tubulopathies and is, therefore, more clinically relevant than the classical definition. Three major types of salt-losing tubulopathy can be defined: distal convoluted tubule dysfunction leading to hypokalemia (currently known as Gitelman or Bartter syndrome), the more-severe condition of polyuric loop dysfunction (often referred to as antenatal Bartter or hyperprostaglandin E syndrome), and the most-severe condition of combined loop and distal convoluted tubule dysfunction (antenatal Bartter or hyperprostaglandin E syndrome with sensorineural deafness). These three subtypes can each be further subdivided according to the identity of the defective ion transporter or channel: the sodium-chloride cotransporter NCCT or the chloride channel ClC-Kb in distal convoluted tubule dysfunction; the sodium-potassium-chloride cotransporter NKCC2 or the renal outer medullary potassium channel in loop dysfunction; and the chloride channels ClC-Ka and ClC-Kb or their beta-subunit Barttin in combined distal convoluted tubule and loop dysfunction. This new classification should help clinicians to better understand the pathophysiology of these syndromes and choose the most appropriate treatment for affected patients, while avoiding potentially harmful diagnostic and therapeutic approaches.
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Affiliation(s)
- Hannsjörg W Seyberth
- Center for Pediatric and Adolescent Medicine, Philipps University, Marburg, Germany.
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Abstract
PURPOSE OF REVIEW Studies of inherited conditions characterized by high or low blood pressure reveal the importance of a new signalling cascade, With no Lysine kinases (WNK) --> ste20/SPS1-related proline/alanine-rich kinase (SPAK)/oxidative stress-responsive kinase-1 (OSR1) --> Cation-Chloride Cotransporters (CCC), in regulating blood pressure and in the pathogenesis of essential hypertension. This review explores how these molecules interact to co-ordinate sodium homeostasis and how errors in these interactions may result in hypertension. RECENT FINDINGS Studies using transgenic animals and gene knockins have clarified the role of mutant WNK4 in hypertension, by revealing its main action to be increasing the expression and activity of sodium-chloride cotransporter (NCC) in the kidney. Functional studies show how phosphorylation of WNK1 regulates both its activity and ability to interact with SPAK/OSR1, and clearly place it upstream of SPAK/OSR1 in the cascade. The structural basis for the interactions between SPAK/OSR1 and targets has been identified. SUMMARY WNKs, activated by upstream kinases or autophosphorylation, bind and phosphorylate SPAK/OSR1, which in turn phosphorylate and activate NCCs and Na-K-Cl cotransporters (NKCCs). This increases sodium retention in the kidney (NKCC2, NCC) and vascular resistance (NKCC1), but decreases renin release (NKCC1). Hypertension-associated mutant WNKs increase surface expression and activation of renal tubular NKCC2 and NCC. Whether this adequately explains the hypertension awaits studies of these mutants in other tissues.
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Abstract
Hematuria may have a number of causes, of which the more common are urinary tract calculi, urinary tract infection, urinary tract neoplasms (including renal cell carcinoma and urothelial tumors), trauma to the urinary tract, and renal parenchymal disease. This article discusses the current status of imaging of patients suspected of having urologic causes of hematuria. The role of all modalities, including plain radiography, intravenous urography or excretory urography, retrograde pyelography, ultrasonography, and multidetector computed tomography (MDCT) in evaluation of these patients is discussed. The article highlights the current status of MDCT urography in imaging of patients with hematuria, and discusses various-often controversial-issues, such as optimal protocol design, accuracy of the technique in imaging of the urothelium, and the significant issue of radiation dose associated with MDCT urography.
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Affiliation(s)
- Owen J O'Connor
- Department of Radiology, Cork University Hospital, Wilton, Cork, Ireland
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Heffernan A, Steffensen TS, Gilbert-Barness E, Perlman S. Bartter syndrome presenting as poor weight gain and abdominal mass in an infant. Fetal Pediatr Pathol 2008; 27:232-43. [PMID: 18800266 DOI: 10.1080/15513810802216010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Bartter syndrome, a group of disorders that encompasses multiple genetic defects with similar clinical presentation, has been divided into six different genotypes, according to different genetic defects, and into three main clinical variants (or phenotypes). Classic laboratory findings in all variants include hypochloremia, hypokalemia, and metabolic alkalosis with excessive excretion of chloride and potassium. Classic Bartter syndrome, neonatal Bartter syndrome, and Gitelman syndrome are the three main clinical variants. Classic Bartter syndrome and neonatal Bartter syndrome have defects in genes that affect transport channels in the ascending loop of Henle, where as in Gitleman syndrome the defect occurs in the transport channels of the distal convoluted tubule. Classic Bartter syndrome and neonatal Bartter syndrome have similar presenting symptoms, potential outcomes, and treatment, but different ages at presentation. Gitelman syndrome, a more benign condition than the other clinical variants, has the classic hallmark finding of hypomagnesemia and low to normal excretion of calcium. This differentiates it from the classic and neonatal variants of the disease. With early diagnosis and proper treatment, Bartter syndrome has a good prognosis. But failure to identify it can lead to tubulointerstitial nephritis and renal failure. We present a case of a 6-month-old boy with Bartter syndrome who presented with poor weight gain and an abdominal mass.
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Affiliation(s)
- Annie Heffernan
- Department of Pediatrics, University of South Florida, Tampa General Hospital, Tampa, Florida 33611, USA.
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Adachi M, Asakura Y, Sato Y, Tajima T, Nakajima T, Yamamoto T, Fujieda K. Novel SLC12A1 (NKCC2) mutations in two families with Bartter syndrome type 1. Endocr J 2007; 54:1003-7. [PMID: 17998760 DOI: 10.1507/endocrj.k06-204] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Bartter syndrome (BS) type 1, also referred to antenatal BS, is a genetic tubulopathy with hypokalemic metabolic alkalosis and prenatal onset of polyuria leading to polyhydramnios. It has been shown that BS type 1 is caused by mutations in the SLC12A1 gene encoding bumetanide-sensitive Na-K-2Cl (-) cotransporter (NKCC2). We had the opportunity to care for two unrelated Japanese patients of BS type 1 with typical manifestations including polyhydramnios, prematurity, hypokalemia, alkalosis, and infantile-onset nephrocalcinosis. Analysis of the SLC12A1 gene demonstrated four novel mutations: N117X, G257S, D792fs and N984fs. N117X mutation is expected to abolish most of the NKCC2 protein, whereas G257, which is evolutionary conserved, resides in the third transmembrane domain. The latter two frameshift mutations reside in the intra-cytoplasmic C-terminal domain, which illustrates the importance of this domain for the NKCC2 function. In conclusion, we found four novel SLC12A1 mutations in two BS type 1 patients. Development of effective therapy for hypercalciuria is mandatory to prevent nephrocalcinosis and resultant renal failure.
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Affiliation(s)
- Masanori Adachi
- Department of Endocrinology & Metabolism, Clinical Research Institute, Kanagawa Children's Medical Center, Yokohama, Japan
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Lang F, Vallon V, Knipper M, Wangemann P. Functional significance of channels and transporters expressed in the inner ear and kidney. Am J Physiol Cell Physiol 2007; 293:C1187-208. [PMID: 17670895 DOI: 10.1152/ajpcell.00024.2007] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A number of ion channels and transporters are expressed in both the inner ear and kidney. In the inner ear, K+cycling and endolymphatic K+, Na+, Ca2+, and pH homeostasis are critical for normal organ function. Ion channels and transporters involved in K+cycling include K+channels, Na+-2Cl−-K+cotransporter, Na+/K+-ATPase, Cl−channels, connexins, and K+/Cl−cotransporters. Furthermore, endolymphatic Na+and Ca2+homeostasis depends on Ca2+-ATPase, Ca2+channels, Na+channels, and a purinergic receptor channel. Endolymphatic pH homeostasis involves H+-ATPase and Cl−/HCO3−exchangers including pendrin. Defective connexins (GJB2 and GJB6), pendrin (SLC26A4), K+channels (KCNJ10, KCNQ1, KCNE1, and KCNMA1), Na+-2Cl−-K+cotransporter (SLC12A2), K+/Cl−cotransporters (KCC3 and KCC4), Cl−channels (BSND and CLCNKA + CLCNKB), and H+-ATPase (ATP6V1B1 and ATPV0A4) cause hearing loss. All these channels and transporters are also expressed in the kidney and support renal tubular transport or signaling. The hearing loss may thus be paralleled by various renal phenotypes including a subtle decrease of proximal Na+-coupled transport (KCNE1/KCNQ1), impaired K+secretion (KCNMA1), limited HCO3−elimination (SLC26A4), NaCl wasting (BSND and CLCNKB), renal tubular acidosis (ATP6V1B1, ATPV0A4, and KCC4), or impaired urinary concentration (CLCNKA). Thus, defects of channels and transporters expressed in the kidney and inner ear result in simultaneous dysfunctions of these seemingly unrelated organs.
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Affiliation(s)
- Florian Lang
- Department of Physiology, Eberhard-Karls-University of Tübingen, Gmelinstrasse 5, Tübingen, Germany.
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