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Abstract
Mg2+ is essential for many cellular and physiological processes, including muscle contraction, neuronal activity, and metabolism. Consequently, the blood Mg2+ concentration is tightly regulated by balanced intestinal Mg2+ absorption, renal Mg2+ excretion, and Mg2+ storage in bone and soft tissues. In recent years, the development of novel transgenic animal models and identification of Mendelian disorders has advanced our current insight in the molecular mechanisms of Mg2+ reabsorption in the kidney. In the proximal tubule, Mg2+ reabsorption is dependent on paracellular permeability by claudin-2/12. In the thick ascending limb of Henle's loop, the claudin-16/19 complex provides a cation-selective pore for paracellular Mg2+ reabsorption. The paracellular Mg2+ reabsorption in this segment is regulated by the Ca2+-sensing receptor, parathyroid hormone, and mechanistic target of rapamycin (mTOR) signaling. In the distal convoluted tubule, the fine tuning of Mg2+ reabsorption takes place by transcellular Mg2+ reabsorption via transient receptor potential melastatin-like types 6 and 7 (TRPM6/TRPM7) divalent cation channels. Activity of TRPM6/TRPM7 is dependent on hormonal regulation, metabolic activity, and interacting proteins. Basolateral Mg2+ extrusion is still poorly understood but is probably dependent on the Na+ gradient. Cyclin M2 and SLC41A3 are the main candidates to act as Na+/Mg2+ exchangers. Consequently, disturbances of basolateral Na+/K+ transport indirectly result in impaired renal Mg2+ reabsorption in the distal convoluted tubule. Altogether, this review aims to provide an overview of the molecular mechanisms of Mg2+ reabsorption in the kidney, specifically focusing on transgenic mouse models and human hereditary diseases.
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Affiliation(s)
- Jeroen H F de Baaij
- Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands
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2
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Chernova I, Song W, Steach H, Hafez O, Al Souz J, Chen PM, Chandra N, Cantley L, Veselits M, Clark MR, Craft J. The ion transporter Na +-K +-ATPase enables pathological B cell survival in the kidney microenvironment of lupus nephritis. SCIENCE ADVANCES 2023; 9:eadf8156. [PMID: 36724234 PMCID: PMC9891690 DOI: 10.1126/sciadv.adf8156] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The kidney is a comparatively hostile microenvironment characterized by highsodium concentrations; however, lymphocytes infiltrate and survive therein in autoimmune diseases such as lupus. The effects of sodium-lymphocyte interactions on tissue injury in autoimmune diseases and the mechanisms used by infiltrating lymphocytes to survive the highsodium environment of the kidney are not known. Here, we show that kidney-infiltrating B cells in lupus adapt to elevated sodium concentrations and that expression of sodium potassium adenosine triphosphatase (Na+-K+-ATPase) correlates with the ability of infiltrating cells to survive. Pharmacological inhibition of Na+-K+-ATPase and genetic knockout of Na+-K+-ATPase γ subunit resulted in reduced B cell infiltration into kidneys and amelioration of proteinuria. B cells in human lupus nephritis biopsies also had high expression of Na+-K+-ATPase. Our study reveals that kidney-infiltrating B cells in lupus initiate a tissue adaption program in response to sodium stress and identifies Na+-K+-ATPase as an organ-specific therapeutic target.
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Affiliation(s)
- Irene Chernova
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
- Corresponding author. (I.C.); (J.C.)
| | - Wenzhi Song
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Holly Steach
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Omeed Hafez
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | - Jafar Al Souz
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Ping-Min Chen
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Nisha Chandra
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Lloyd Cantley
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Margaret Veselits
- Section of Rheumatology and Gwen Knapp Center for Lupus and Immunology Research, Departments of Medicine and Pathology, University of Chicago, Chicago, IL, USA
| | - Marcus R. Clark
- Section of Rheumatology and Gwen Knapp Center for Lupus and Immunology Research, Departments of Medicine and Pathology, University of Chicago, Chicago, IL, USA
| | - Joe Craft
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
- Corresponding author. (I.C.); (J.C.)
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3
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Ilenwabor BP, Schigt H, Kompatscher A, Bos C, Zuidscherwoude M, van der Eerden BCJ, Hoenderop JGJ, de Baaij JHF. FAM111A is dispensable for electrolyte homeostasis in mice. Sci Rep 2022; 12:10211. [PMID: 35715480 PMCID: PMC9205974 DOI: 10.1038/s41598-022-14054-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 05/31/2022] [Indexed: 11/24/2022] Open
Abstract
Autosomal dominant mutations in FAM111A are causative for Kenny-Caffey syndrome type 2. Patients with Kenny-Caffey syndrome suffer from severe growth retardation, skeletal dysplasia, hypoparathyroidism, hypocalcaemia, hyperphosphataemia and hypomagnesaemia. While recent studies have reported FAM111A to function in antiviral response and DNA replication, its role in regulating electrolyte homeostasis remains unknown. In this study, we assessed the role of FAM111A in the regulation of serum electrolyte balance using a Fam111a knockout (Fam111a-/-) C57BL/6 N mouse model. Fam111a-/- mice displayed normal weight and serum parathyroid hormone (PTH) concentration and exhibited unaltered magnesium, calcium and phosphate levels in serum and 24-hour urine. Expression of calciotropic (including Cabp28k, Trpv5, Klotho and Cyp24a1), magnesiotropic (including Trpm6, Trpm7, Cnnm2 and Cnnm4) and phosphotropic (Slc20a1, Slc20a2, Slc34a1 and Slc34a3) genes in the kidneys, duodenum and colon were not affected by Fam111a depletion. Only Slc34a2 expression was significantly upregulated in the duodenum, but not in the colon. Analysis of femurs showed unaffected bone morphology and density in Fam111a-/- mice. Kidney and parathyroid histology were also normal in Fam111a-/- mice. In conclusion, our study is the first to characterise the function of FAM111A in vivo and we report that mice lacking FAM111A exhibit normal electrolyte homeostasis on a standard diet.
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Affiliation(s)
- Barnabas P Ilenwabor
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Heidi Schigt
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Andreas Kompatscher
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Caro Bos
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Malou Zuidscherwoude
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Bram C J van der Eerden
- Department of Internal Medicine, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Joost G J Hoenderop
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Jeroen H F de Baaij
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands.
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Fedosova NU, Habeck M, Nissen P. Structure and Function of Na,K-ATPase-The Sodium-Potassium Pump. Compr Physiol 2021; 12:2659-2679. [PMID: 34964112 DOI: 10.1002/cphy.c200018] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
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Affiliation(s)
| | - Michael Habeck
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
| | - Poul Nissen
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
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5
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Marcoux AA, Tremblay LE, Slimani S, Fiola MJ, Mac-Way F, Haydock L, Garneau AP, Isenring P. Anatomophysiology of the Henle's Loop: Emphasis on the Thick Ascending Limb. Compr Physiol 2021; 12:3119-3139. [PMID: 34964111 DOI: 10.1002/cphy.c210021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The loop of Henle plays a variety of important physiological roles through the concerted actions of ion transport systems in both its apical and basolateral membranes. It is involved most notably in extracellular fluid volume and blood pressure regulation as well as Ca2+ , Mg2+ , and acid-base homeostasis because of its ability to reclaim a large fraction of the ultrafiltered solute load. This nephron segment is also involved in urinary concentration by energizing several of the steps that are required to generate a gradient of increasing osmolality from cortex to medulla. Another important role of the loop of Henle is to sustain a process known as tubuloglomerular feedback through the presence of specialized renal tubular cells that lie next to the juxtaglomerular arterioles. This article aims at describing these physiological roles and at discussing a number of the molecular mechanisms involved. It will also report on novel findings and uncertainties regarding the realization of certain processes and on the pathophysiological consequences of perturbed salt handling by the thick ascending limb of the loop of Henle. Since its discovery 150 years ago, the loop of Henle has remained in the spotlight and is now generating further interest because of its role in the renal-sparing effect of SGLT2 inhibitors. © 2022 American Physiological Society. Compr Physiol 12:1-21, 2022.
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Affiliation(s)
- Andrée-Anne Marcoux
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Laurence E Tremblay
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Samira Slimani
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Marie-Jeanne Fiola
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Fabrice Mac-Way
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Ludwig Haydock
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
| | - Alexandre P Garneau
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada.,Cardiometabolic Axis, School of Kinesiology and Physical Activity Sciences, University of Montréal, Montréal, QC, Canada
| | - Paul Isenring
- Nephrology Research Group, Department of Medicine, Laval University, Québec, QC, Canada
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6
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Ng HWY, Ogbeta JA, Clapcote SJ. Genetically altered animal models for ATP1A3-related disorders. Dis Model Mech 2021; 14:272403. [PMID: 34612482 PMCID: PMC8503543 DOI: 10.1242/dmm.048938] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Within the past 20 years, particularly with the advent of exome sequencing technologies, autosomal dominant and de novo mutations in the gene encoding the neurone-specific α3 subunit of the Na+,K+-ATPase (NKA α3) pump, ATP1A3, have been identified as the cause of a phenotypic continuum of rare neurological disorders. These allelic disorders of ATP1A3 include (in approximate order of severity/disability and onset in childhood development): polymicrogyria; alternating hemiplegia of childhood; cerebellar ataxia, areflexia, pes cavus, optic atrophy and sensorineural hearing loss syndrome; relapsing encephalopathy with cerebellar ataxia; and rapid-onset dystonia-parkinsonism. Some patients present intermediate, atypical or combined phenotypes. As these disorders are currently difficult to treat, there is an unmet need for more effective therapies. The molecular mechanisms through which mutations in ATP1A3 result in a broad range of neurological symptoms are poorly understood. However, in vivo comparative studies using genetically altered model organisms can provide insight into the biological consequences of the disease-causing mutations in NKA α3. Herein, we review the existing mouse, zebrafish, Drosophila and Caenorhabditis elegans models used to study ATP1A3-related disorders, and discuss their potential contribution towards the understanding of disease mechanisms and development of novel therapeutics.
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Affiliation(s)
- Hannah W Y Ng
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Jennifer A Ogbeta
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Steven J Clapcote
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK.,European Network for Research on Alternating Hemiplegia (ENRAH), 1120 Vienna, Austria
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7
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Themistocleous SC, Yiallouris A, Tsioutis C, Zaravinos A, Johnson EO, Patrikios I. Clinical significance of P-class pumps in cancer. Oncol Lett 2021; 22:658. [PMID: 34386080 PMCID: PMC8298992 DOI: 10.3892/ol.2021.12919] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 04/12/2021] [Indexed: 12/16/2022] Open
Abstract
P-class pumps are specific ion transporters involved in maintaining intracellular/extracellular ion homeostasis, gene transcription, and cell proliferation and migration in all eukaryotic cells. The present review aimed to evaluate the role of P-type pumps [Na+/K+ ATPase (NKA), H+/K+ ATPase (HKA) and Ca2+-ATPase] in cancer cells across three fronts, namely structure, function and genetic expression. It has been shown that administration of specific P-class pumps inhibitors can have different effects by: i) Altering pump function; ii) inhibiting cell proliferation; iii) inducing apoptosis; iv) modifying metabolic pathways; and v) induce sensitivity to chemotherapy and lead to antitumor effects. For example, the NKA β2 subunit can be downregulated by gemcitabine, resulting in increased apoptosis of cancer cells. The sarcoendoplasmic reticulum calcium ATPase can be inhibited by thapsigargin resulting in decreased prostate tumor volume, whereas the HKA α subunit can be affected by proton pump inhibitors in gastric cancer cell lines, inducing apoptosis. In conclusion, the present review highlighted the central role of P-class pumps and their possible use and role as anticancer cellular targets for novel therapeutic chemical agents.
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Affiliation(s)
- Sophia C Themistocleous
- Department of Medicine, School of Medicine, European University Cyprus, 2404 Nicosia, Cyprus
| | - Andreas Yiallouris
- Department of Medicine, School of Medicine, European University Cyprus, 2404 Nicosia, Cyprus
| | - Constantinos Tsioutis
- Department of Medicine, School of Medicine, European University Cyprus, 2404 Nicosia, Cyprus
| | - Apostolos Zaravinos
- Department of Life Sciences, School of Sciences, European University Cyprus, 2404 Nicosia, Cyprus.,College of Medicine, Member of Qatar University Health, Qatar University, 2713 Doha, Qatar
| | - Elizabeth O Johnson
- Department of Medicine, School of Medicine, European University Cyprus, 2404 Nicosia, Cyprus
| | - Ioannis Patrikios
- Department of Medicine, School of Medicine, European University Cyprus, 2404 Nicosia, Cyprus
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8
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Habeck M, Poulsen H. What FXYDs fix. J Gen Physiol 2021; 153:212005. [PMID: 33871566 PMCID: PMC8059070 DOI: 10.1085/jgp.202012845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Michael Habeck
- Danish Research Institute of Translational Neuroscience and the Center for Proteins in Memory, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Hanne Poulsen
- Danish Research Institute of Translational Neuroscience and the Center for Proteins in Memory, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
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9
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Bazard P, Frisina RD, Acosta AA, Dasgupta S, Bauer MA, Zhu X, Ding B. Roles of Key Ion Channels and Transport Proteins in Age-Related Hearing Loss. Int J Mol Sci 2021; 22:6158. [PMID: 34200434 PMCID: PMC8201059 DOI: 10.3390/ijms22116158] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 05/30/2021] [Accepted: 05/31/2021] [Indexed: 12/25/2022] Open
Abstract
The auditory system is a fascinating sensory organ that overall, converts sound signals to electrical signals of the nervous system. Initially, sound energy is converted to mechanical energy via amplification processes in the middle ear, followed by transduction of mechanical movements of the oval window into electrochemical signals in the cochlear hair cells, and finally, neural signals travel to the central auditory system, via the auditory division of the 8th cranial nerve. The majority of people above 60 years have some form of age-related hearing loss, also known as presbycusis. However, the biological mechanisms of presbycusis are complex and not yet fully delineated. In the present article, we highlight ion channels and transport proteins, which are integral for the proper functioning of the auditory system, facilitating the diffusion of various ions across auditory structures for signal transduction and processing. Like most other physiological systems, hearing abilities decline with age, hence, it is imperative to fully understand inner ear aging changes, so ion channel functions should be further investigated in the aging cochlea. In this review article, we discuss key various ion channels in the auditory system and how their functions change with age. Understanding the roles of ion channels in auditory processing could enhance the development of potential biotherapies for age-related hearing loss.
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Affiliation(s)
- Parveen Bazard
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
| | - Robert D. Frisina
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
- Department Communication Sciences and Disorders, College of Behavioral & Communication Sciences, Tampa, FL 33620, USA
| | - Alejandro A. Acosta
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
| | - Sneha Dasgupta
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
| | - Mark A. Bauer
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
| | - Xiaoxia Zhu
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
| | - Bo Ding
- Department of Medical Engineering, College of Engineering, University of South Florida, Tampa, FL 33620, USA; (P.B.); (A.A.A.); (S.D.); (M.A.B.); (X.Z.); (B.D.)
- Global Center for Hearing and Speech Research, University of South Florida, Tampa, FL 33612, USA
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10
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Cyclin M2 (CNNM2) knockout mice show mild hypomagnesaemia and developmental defects. Sci Rep 2021; 11:8217. [PMID: 33859252 PMCID: PMC8050252 DOI: 10.1038/s41598-021-87548-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Accepted: 03/26/2021] [Indexed: 02/02/2023] Open
Abstract
Patients with mutations in Cyclin M2 (CNNM2) suffer from hypomagnesaemia, seizures, and intellectual disability. Although the molecular function of CNNM2 is under debate, the protein is considered essential for renal Mg2+ reabsorption. Here, we used a Cnnm2 knock out mouse model, generated by CRISPR/Cas9 technology, to assess the role of CNNM2 in Mg2+ homeostasis. Breeding Cnnm2+/- mice resulted in a Mendelian distribution at embryonic day 18. Nevertheless, only four Cnnm2-/- pups were born alive. The Cnnm2-/- pups had a significantly lower serum Mg2+ concentration compared to wildtype littermates. Subsequently, adult Cnnm2+/- mice were fed with low, control, or high Mg2+ diets for two weeks. Adult Cnnm2+/- mice showed mild hypomagnesaemia compared to Cnnm2+/+ mice and increased serum Ca2+ levels, independent of dietary Mg2+ intake. Faecal analysis displayed increased Mg2+ and Ca2+ excretion in the Cnnm2+/- mice. Transcriptional profiling of Trpm6, Trpm7, and Slc41a1 in kidneys and colon did not reveal effects based on genotype. Microcomputed tomography analysis of the femurs demonstrated equal bone morphology and density. In conclusion, CNNM2 is vital for embryonic development and Mg2+ homeostasis. Our data suggest a previously undescribed role of CNNM2 in the intestine, which may contribute to the Mg2+ deficiency in mice and patients.
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11
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Yap JQ, Seflova J, Sweazey R, Artigas P, Robia SL. FXYD proteins and sodium pump regulatory mechanisms. J Gen Physiol 2021; 153:211866. [PMID: 33688925 PMCID: PMC7953255 DOI: 10.1085/jgp.202012633] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 02/03/2021] [Indexed: 12/12/2022] Open
Abstract
The sodium/potassium-ATPase (NKA) is the enzyme that establishes gradients of sodium and potassium across the plasma membrane. NKA activity is tightly regulated for different physiological contexts through interactions with single-span transmembrane peptides, the FXYD proteins. This diverse family of regulators has in common a domain containing a Phe-X-Tyr-Asp (FXYD) motif, two conserved glycines, and one serine residue. In humans, there are seven tissue-specific FXYD proteins that differentially modulate NKA kinetics as appropriate for each system, providing dynamic responsiveness to changing physiological conditions. Our understanding of how FXYD proteins contribute to homeostasis has benefitted from recent advances described in this review: biochemical and biophysical studies have provided insight into regulatory mechanisms, genetic models have uncovered remarkable complexity of FXYD function in integrated physiological systems, new posttranslational modifications have been identified, high-resolution structural studies have revealed new details of the regulatory interaction with NKA, and new clinical correlations have been uncovered. In this review, we address the structural determinants of diverse FXYD functions and the special roles of FXYDs in various physiological systems. We also discuss the possible roles of FXYDs in protein trafficking and regulation of non-NKA targets.
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Affiliation(s)
- John Q Yap
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Ryan Sweazey
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
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12
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Phospholamban and sarcolipin prevent thermal inactivation of sarco(endo)plasmic reticulum Ca2+-ATPases. Biochem J 2020; 477:4281-4294. [PMID: 33111944 DOI: 10.1042/bcj20200346] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 10/15/2020] [Accepted: 10/28/2020] [Indexed: 12/31/2022]
Abstract
Na+-K+-ATPase from mice lacking the γ subunit exhibits decreased thermal stability. Phospholamban (PLN) and sarcolipin (SLN) are small homologous proteins that regulate sarco(endo)plasmic reticulum Ca2+-ATPases (SERCAs) with properties similar to the γ subunit, through physical interactions with SERCAs. Here, we tested the hypothesis that PLN and SLN may protect against thermal inactivation of SERCAs. HEK-293 cells were co-transfected with different combinations of cDNAs encoding SERCA2a, PLN, a PLN mutant (N34A) that cannot bind to SERCA2a, and SLN. One-half of the cells were heat stressed at 40°C for 1 h (HS), and one-half were maintained at 37°C (CTL) before harvesting the cells and isolating microsomes. Compared with CTL, maximal SERCA activity was reduced by 25-35% following HS in cells that expressed either SERCA2a alone or SERCA2a and mutant PLN (N34A) whereas no change in maximal SERCA2a activity was observed in cells that co-expressed SERCA2a and either PLN or SLN following HS. Increases in SERCA2a carbonyl group content and nitrotyrosine levels that were detected following HS in cells that expressed SERCA2a alone were prevented in cells co-expressing SERCA2a with PLN or SLN, whereas co-expression of SERCA2a with mutant PLN (N34A) only prevented carbonyl group formation. In other experiments using knock-out mice, we found that thermal inactivation of SERCA was increased in cardiac left ventricle samples from Pln-null mice and in diaphragm samples from Sln-null mice, compared with WT littermates. Our results show that both PLN and SLN form a protective interaction with SERCA pumps during HS, preventing nitrosylation and oxidation of SERCA and thus preserving its maximal activity.
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13
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Maeoka Y, McCormick JA. NaCl cotransporter activity and Mg 2+ handling by the distal convoluted tubule. Am J Physiol Renal Physiol 2020; 319:F1043-F1053. [PMID: 33135481 DOI: 10.1152/ajprenal.00463.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The genetic disease Gitelman syndrome, knockout mice, and pharmacological blockade with thiazide diuretics have revealed that reduced activity of the NaCl cotransporter (NCC) promotes renal Mg2+ wasting. NCC is expressed along the distal convoluted tubule (DCT), and its activity determines Mg2+ entry into DCT cells through transient receptor potential channel subfamily M member 6 (TRPM6). Several other genetic forms of hypomagnesemia lower the drive for Mg2+ entry by inhibiting activity of basolateral Na+-K+-ATPase, and reduced NCC activity may do the same. Lower intracellular Mg2+ may promote further Mg2+ loss by directly decreasing activity of Na+-K+-ATPase. Lower intracellular Mg2+ may also lower Na+-K+-ATPase indirectly by downregulating NCC. Lower NCC activity also induces atrophy of DCT cells, decreasing the available number of TRPM6 channels. Conversely, a mouse model with increased NCC activity was recently shown to display normal Mg2+ handling. Moreover, recent studies have identified calcineurin and uromodulin (UMOD) as regulators of both NCC and Mg2+ handling by the DCT. Calcineurin inhibitors paradoxically cause hypomagnesemia in a state of NCC activation, but this may be related to direct effects on TRPM6 gene expression. In Umod-/- mice, the cause of hypomagnesemia may be partly due to both decreased NCC expression and lower TRPM6 expression on the cell surface. This mini-review discusses these new findings and the possible role of altered Na+ flux through NCC and ultimately Na+-K+-ATPase in Mg2+ reabsorption by the DCT.
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Affiliation(s)
- Yujiro Maeoka
- Division of Nephrology and Hypertension, Department of Medicine, Oregon Health and Science University, Portland, Oregon
| | - James A McCormick
- Division of Nephrology and Hypertension, Department of Medicine, Oregon Health and Science University, Portland, Oregon
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14
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Demine S, Schulte ML, Territo PR, Eizirik DL. Beta Cell Imaging-From Pre-Clinical Validation to First in Man Testing. Int J Mol Sci 2020; 21:E7274. [PMID: 33019671 PMCID: PMC7582644 DOI: 10.3390/ijms21197274] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 09/21/2020] [Accepted: 09/28/2020] [Indexed: 12/14/2022] Open
Abstract
There are presently no reliable ways to quantify human pancreatic beta cell mass (BCM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. Furthermore, the lack of beta cell imaging hampers the evaluation of the impact of new drugs aiming to prevent beta cell loss or to restore BCM in diabetes. We presently discuss the potential value of BCM determination as a cornerstone for individualized therapies in diabetes, describe the presently available probes for human BCM evaluation, and discuss our approach for the discovery of novel beta cell biomarkers, based on the determination of specific splice variants present in human beta cells. This has already led to the identification of DPP6 and FXYD2ga as two promising targets for human BCM imaging, and is followed by a discussion of potential safety issues, the role for radiochemistry in the improvement of BCM imaging, and concludes with an overview of the different steps from pre-clinical validation to a first-in-man trial for novel tracers.
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Affiliation(s)
- Stephane Demine
- Indiana Biosciences Research Institute, Indianapolis, IN 46202, USA;
| | - Michael L. Schulte
- Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (M.L.S.); (P.R.T.)
| | - Paul R. Territo
- Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (M.L.S.); (P.R.T.)
- Division of Clinical Pharmacology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Decio L. Eizirik
- Indiana Biosciences Research Institute, Indianapolis, IN 46202, USA;
- ULB Center for Diabetes Research, Medical Faculty, Université Libre de Bruxelles (ULB), 1070 Brussels, Belgium
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15
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Schmid V, Plössl K, Schmid C, Bernklau S, Weber BHF, Friedrich U. Retinoschisin and Cardiac Glycoside Crosstalk at the Retinal Na/K-ATPase. Invest Ophthalmol Vis Sci 2020; 61:1. [PMID: 32392309 PMCID: PMC7405613 DOI: 10.1167/iovs.61.5.1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Purpose Mutations in the RS1 gene, which encodes retinoschisin, cause X-linked juvenile retinoschisis, a retinal dystrophy in males. Retinoschisin specifically interacts with the retinal sodium–potassium adenosine triphosphatase (Na/K-ATPase), a transmembrane ion pump. Na/K-ATPases also bind cardiac glycosides, which control the activity of the pump and have been linked to disturbances in retinal homeostasis. In this study, we investigated the crosstalk between retinoschisin and cardiac glycosides at the retinal Na/K-ATPase and the consequences of this interplay on retinal integrity. Methods The effect of cardiac glycosides (ouabain and digoxin) on the binding of retinoschisin to the retinal Na/K-ATPase was investigated via western blot and immunocytochemistry. Also, the influence of retinoschisin on the binding of cardiac glycosides was analyzed via enzymatic assays, which quantified cardiac glycoside-sensitive Na/K-ATPase pump activity. Moreover, retinoschisin-dependent binding of tritium-labeled ouabain to the Na/K-ATPase was determined. Finally, a reciprocal effect of retinoschisin and cardiac glycosides on Na/K-ATPase localization and photoreceptor degeneration was addressed using immunohistochemistry in retinoschisin-deficient murine retinal explants. Results Cardiac glycosides displaced retinoschisin from the retinal Na/K-ATPase; however, retinoschisin did not affect cardiac glycoside binding. Notably, cardiac glycosides reduced the capacity of retinoschisin to regulate Na/K-ATPase localization and to protect against photoreceptor degeneration. Conclusions Our findings reveal opposing effects of retinoschisin and cardiac glycosides on retinal Na/K-ATPase binding and on retinal integrity, suggesting that a fine-tuned interplay between both components is required to maintain retinal homeostasis. This observation provides new insight into the mechanisms underlying the pathological effects of cardiac glycoside treatment on retinal integrity.
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16
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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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17
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The single-cell transcriptomic landscape of early human diabetic nephropathy. Proc Natl Acad Sci U S A 2019; 116:19619-19625. [PMID: 31506348 PMCID: PMC6765272 DOI: 10.1073/pnas.1908706116] [Citation(s) in RCA: 300] [Impact Index Per Article: 60.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Single-nucleus RNA sequencing revealed gene expression changes in early diabetic nephropathy that promote urinary potassium secretion and decreased calcium and magnesium reabsorption. Multiple cell types exhibited angiogenic signatures, which may represent early signs of aberrant angiogenesis. These alterations may help to identify biomarkers for disease progression or signaling pathways amenable to early intervention. Diabetic nephropathy is characterized by damage to both the glomerulus and tubulointerstitium, but relatively little is known about accompanying cell-specific changes in gene expression. We performed unbiased single-nucleus RNA sequencing (snRNA-seq) on cryopreserved human diabetic kidney samples to generate 23,980 single-nucleus transcriptomes from 3 control and 3 early diabetic nephropathy samples. All major cell types of the kidney were represented in the final dataset. Side-by-side comparison demonstrated cell-type–specific changes in gene expression that are important for ion transport, angiogenesis, and immune cell activation. In particular, we show that the diabetic thick ascending limb, late distal convoluted tubule, and principal cells all adopt a gene expression signature consistent with increased potassium secretion, including alterations in Na+/K+-ATPase, WNK1, mineralocorticoid receptor, and NEDD4L expression, as well as decreased paracellular calcium and magnesium reabsorption. We also identify strong angiogenic signatures in glomerular cell types, proximal convoluted tubule, distal convoluted tubule, and principal cells. Taken together, these results suggest that increased potassium secretion and angiogenic signaling represent early kidney responses in human diabetic nephropathy.
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18
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Mayan H, Farfel Z, Karlish SJD. Renal Mg handling, FXYD2 and the central role of the Na,K-ATPase. Physiol Rep 2018; 6:e13843. [PMID: 30175537 PMCID: PMC6119663 DOI: 10.14814/phy2.13843] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 07/30/2018] [Accepted: 08/01/2018] [Indexed: 12/15/2022] Open
Abstract
This article examines the central role of Na,K-ATPase (α1β1FXYD2) in renal Mg handling, especially in distal convoluted tubule (DCT), the segment responsible for final regulation of Mg balance. By considering effects of Na,K-ATPase on intracellular Na and K concentrations, and driving forces for Mg transport, we propose a consistent rationale explaining basal Mg reabsorption in DCT and altered Mg reabsorption in some human diseases. FXYD2 (γ subunit) is a regulatory subunit that adapts functional properties of Na,K-ATPase to cellular requirements. Mutations in FXYD2 (G41R), and transcription factors (HNF-1B and PCBD1) that affect FXYD2 expression are associated with hypomagnesemia with hypermagnesuria. These mutations result in impaired interactions of FXYD2 with Na,K-ATPase. Renal Mg wasting implies that Na,K-ATPase is inhibited, but in vitro studies show that FXYD2 itself inhibits Na,K-ATPase activity, raising K0.5 Na. However, FXYD2 also stabilizes the protein by amplifying specific interactions with phosphatidylserine and cholesterol within the membrane. Renal Mg wasting associated with impaired Na,K-ATPase/FXYD2 interactions is explained simply by destabilization and inactivation of Na,K-ATPase. We consider also the role of the Na,K-ATPase in Mg (and Ca) handling in Gitelman syndrome and Familial hyperkalemia and hypertension (FHHt). Renal Mg handling serves as a convenient marker for Na,K-ATPase activity in DCT.
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Affiliation(s)
- Haim Mayan
- Department of Medicine ESheba Medical CenterRamat GanIsrael
- Laboratory of Biochemical PharmacologySheba Medical CenterRamat GanIsrael
- Sackler School of MedicineTel Aviv UniversityTel AvivIsrael
| | - Zvi Farfel
- Department of Medicine ESheba Medical CenterRamat GanIsrael
- Laboratory of Biochemical PharmacologySheba Medical CenterRamat GanIsrael
- Sackler School of MedicineTel Aviv UniversityTel AvivIsrael
- Department of Biomolecular SciencesWeizmann Institute of ScienceRehovothIsrael
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19
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Abu-Amer N, Priel E, Karlish S, Farfel Z, Mayan H. Hypermagnesuria in Humans Following Acute Intravenous Administration of Digoxin. Nephron Clin Pract 2017; 138:113-118. [DOI: 10.1159/000481468] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 09/12/2017] [Indexed: 12/19/2022] Open
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20
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Plössl K, Royer M, Bernklau S, Tavraz NN, Friedrich T, Wild J, Weber BHF, Friedrich U. Retinoschisin is linked to retinal Na/K-ATPase signaling and localization. Mol Biol Cell 2017; 28:2178-2189. [PMID: 28615319 PMCID: PMC5531734 DOI: 10.1091/mbc.e17-01-0064] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 06/02/2017] [Accepted: 06/06/2017] [Indexed: 01/30/2023] Open
Abstract
Retinoschisin binds to the extracellular domain of Na/K-ATPase subunit β2. Retinoschisin inhibits Na/K-ATPase–associated signaling cascades and affects Na/K-ATPase localization. The retinoschisin-Na/K-ATPase complex overlaps with signaling mediators. Defective Na/K-ATPase signaling by retinoschisin deficiency may promote retinal dystrophy. Mutations in the RS1 gene cause X-linked juvenile retinoschisis (XLRS), a hereditary retinal dystrophy. We recently showed that retinoschisin, the protein encoded by RS1, regulates ERK signaling and apoptosis in retinal cells. In this study, we explored an influence of retinoschisin on the functionality of the Na/K-ATPase, its interaction partner at retinal plasma membranes. We show that retinoschisin binding requires the β2-subunit of the Na/K-ATPase, whereas the α-subunit is exchangeable. Our investigations revealed no effect of retinoschisin on Na/K-ATPase–mediated ATP hydrolysis and ion transport. However, we identified an influence of retinoschisin on Na/K-ATPase–regulated signaling cascades and Na/K-ATPase localization. In addition to the known ERK deactivation, retinoschisin treatment of retinoschisin-deficient (Rs1h-/Y) murine retinal explants decreased activation of Src, an initial transmitter in Na/K-ATPase signal transduction, and of Ca2+ signaling marker Camk2. Immunohistochemistry on murine retinae revealed an overlap of the retinoschisin–Na/K-ATPase complex with proteins involved in Na/K-ATPase signaling, such as caveolin, phospholipase C, Src, and the IP3 receptor. Finally, retinoschisin treatment altered Na/K-ATPase localization in photoreceptors of Rs1h-/Y retinae. Taken together, our results suggest a regulatory effect of retinoschisin on Na/K-ATPase signaling and localization, whereas Na/K-ATPase-dysregulation caused by retinoschisin deficiency could represent an initial step in XLRS pathogenesis.
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Affiliation(s)
- Karolina Plössl
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Melanie Royer
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Sarah Bernklau
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Neslihan N Tavraz
- Institute of Chemistry, Technical University of Berlin, 10623 Berlin, Germany
| | - Thomas Friedrich
- Institute of Chemistry, Technical University of Berlin, 10623 Berlin, Germany
| | - Jens Wild
- Institute of Clinical Microbiology and Hygiene, University Hospital of Regensburg, University of Regensburg, 93053 Regensburg, Germany
| | - Bernhard H F Weber
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Ulrike Friedrich
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
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21
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Abstract
The sodium and potassium gradients across the plasma membrane are used by animal cells for numerous processes, and the range of demands requires that the responsible ion pump, the Na,K-ATPase, can be fine-tuned to the different cellular needs. Therefore, several isoforms are expressed of each of the three subunits that make a Na,K-ATPase, the alpha, beta and FXYD subunits. This review summarizes the various roles and expression patterns of the Na,K-ATPase subunit isoforms and maps the sequence variations to compare the differences structurally. Mutations in the Na,K-ATPase genes encoding alpha subunit isoforms have severe physiological consequences, causing very distinct, often neurological diseases. The differences in the pathophysiological effects of mutations further underline how the kinetic parameters, regulation and proteomic interactions of the Na,K-ATPase isoforms are optimized for the individual cellular needs.
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Affiliation(s)
- Michael V Clausen
- Department of Molecular Biology and Genetics, Aarhus UniversityAarhus, Denmark
| | - Florian Hilbers
- Department of Molecular Biology and Genetics, Aarhus UniversityAarhus, Denmark
| | - Hanne Poulsen
- Department of Molecular Biology and Genetics, Aarhus UniversityAarhus, Denmark
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22
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Abstract
PURPOSE OF REVIEW Magnesium (Mg) imbalances are frequently overlooked. Hypermagnesemia usually occurs in preeclamptic women after Mg therapy or in end-stage renal disease patients, whereas hypomagnesemia is more common with a prevalence of up to 15% in the general population. Increasing evidence points toward a role for mild-to-moderate chronic hypomagnesemia in the pathogenesis of hypertension, type 2 diabetes mellitus, and metabolic syndrome. RECENT FINDINGS The kidneys are the major regulator of total body Mg homeostasis. Over the last decade, the identification of the responsible genes in rare genetic disorders has enhanced our understanding of how the kidney handles Mg. The different genetic disorders and medications contributing to abnormal Mg homeostasis are reviewed. SUMMARY As dysfunctional Mg homeostasis contributes to the development of many common human disorders, serum Mg deserves closer monitoring. Hypomagnesemic patients may be asymptomatic or may have mild symptoms. In severe hypomagnesemia, patients may present with neurological symptoms such as seizures, spasms, or cramps. Renal symptoms include nephrocalcinosis and impaired renal function. Most conditions affect tubular Mg reabsorption by disturbing the lumen-positive potential in the thick ascending limb or the negative membrane potential in the distal convoluted tubule.
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Kersten S, Arjona FJ. Ion transport in the zebrafish kidney from a human disease angle: possibilities, considerations, and future perspectives. Am J Physiol Renal Physiol 2017; 312:F172-F189. [DOI: 10.1152/ajprenal.00425.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 11/11/2016] [Accepted: 11/14/2016] [Indexed: 12/31/2022] Open
Abstract
Unique experimental advantages, such as its embryonic/larval transparency, high-throughput nature, and ease of genetic modification, underpin the rapid emergence of the zebrafish ( Danio rerio) as a preeminent model in biomedical research. Particularly in the field of nephrology, the zebrafish provides a promising model for studying the physiological implications of human solute transport processes along consecutive nephron segments. However, although the zebrafish might be considered a valuable model for numerous renal ion transport diseases and functional studies of many channels and transporters, not all human renal electrolyte transport mechanisms and human diseases can be modeled in the zebrafish. With this review, we explore the ontogeny of zebrafish renal ion transport, its nephron structure and function, and thereby demonstrate the clinical translational value of this model. By critical assessment of genomic and amino acid conservation of human proteins involved in renal ion handling (channels, transporters, and claudins), kidney and nephron segment conservation, and renal electrolyte transport physiology in the zebrafish, we provide researchers and nephrologists with an indication of the possibilities and considerations of the zebrafish as a model for human renal ion transport. Combined with advanced techniques envisioned for the future, implementation of the zebrafish might expand beyond unraveling pathophysiological mechanisms that underlie distinct genetic or environmentally, i.e., pharmacological and lifestyle, induced renal transport deficits. Specifically, the ease of drug administration and the exploitation of improved genetic approaches might argue for the adoption of the zebrafish as a model for preclinical personalized medicine for distinct renal diseases and renal electrolyte transport proteins.
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Affiliation(s)
- Simone Kersten
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands; and
- Nephrology Division, Department of Medicine, Massachusetts General Hospital, Charlestown, Massachusetts
| | - Francisco J. Arjona
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands; and
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Plössl K, Weber BHF, Friedrich U. The X-linked juvenile retinoschisis protein retinoschisin is a novel regulator of mitogen-activated protein kinase signalling and apoptosis in the retina. J Cell Mol Med 2016; 21:768-780. [PMID: 27995734 PMCID: PMC5345684 DOI: 10.1111/jcmm.13019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 09/26/2016] [Indexed: 02/01/2023] Open
Abstract
X-linked juvenile retinoschisis (XLRS) is a hereditary retinal dystrophy in young males, caused by mutations in the RS1 gene. The function of the encoded protein, termed retinoschisin, and the molecular mechanisms underlying XLRS pathogenesis are still unresolved, although a direct interaction partner of the secreted retinoschisin, the retinal Na/K-ATPase, was recently identified. Earlier gene expression studies in retinoschisin-deficient (Rs1h-/Y ) mice provided a first indication of pathological up-regulation of mitogen-activated protein (MAP) kinase signalling in disease pathogenesis. To further investigate the role for retinoschisin in MAP kinase regulation, we exposed Y-79 cells and murine Rs1h-/Y retinae to recombinant retinoschisin and the XLRS-associated mutant RS1-C59S. Although normal retinoschisin stably bound to retinal cells, RS1-C59S exhibited a strongly reduced binding affinity. Simultaneously, exposure to normal retinoschisin significantly reduced phosphorylation of C-RAF and MAP kinases ERK1/2 in Y-79 cells and murine Rs1h-/Y retinae. Expression of MAP kinase target genes C-FOS and EGR1 was also down-regulated in both model systems. Finally, retinoschisin treatment decreased pro-apoptotic BAX-2 transcript levels in Y-79 cells and Rs1h-/Y retinae. Upon retinoschisin treatment, these cells showed increased resistance against apoptosis, reflected by decreased caspase-3 activity (in Y-79 cells) and increased photoreceptor survival (in Rs1h-/Y retinal explants). RS1-C59S did not influence C-RAF or ERK1/2 activation, C-FOS or EGR1 expression, or apoptosis. Our data imply that retinoschisin is a novel regulator of MAP kinase signalling and exerts an anti-apoptotic effect on retinal cells. We therefore discuss that disturbances of MAP kinase signalling by retinoschisin deficiency could be an initial step in XLRS pathogenesis.
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Affiliation(s)
- Karolina Plössl
- Institute of Human Genetics, University of Regensburg, Regensburg, Germany
| | - Bernhard H F Weber
- Institute of Human Genetics, University of Regensburg, Regensburg, Germany
| | - Ulrike Friedrich
- Institute of Human Genetics, University of Regensburg, Regensburg, Germany
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25
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Ventéo S, Laffray S, Wetzel C, Rivat C, Scamps F, Méchaly I, Bauchet L, Raoul C, Bourinet E, Lewin GR, Carroll P, Pattyn A. Fxyd2 regulates Aδ- and C-fiber mechanosensitivity and is required for the maintenance of neuropathic pain. Sci Rep 2016; 6:36407. [PMID: 27805035 PMCID: PMC5090990 DOI: 10.1038/srep36407] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 10/12/2016] [Indexed: 01/24/2023] Open
Abstract
Identification of the molecular mechanisms governing sensory neuron subtype excitability is a key requisite for the development of treatments for somatic sensory disorders. Here, we show that the Na,K-ATPase modulator Fxyd2 is specifically required for setting the mechanosensitivity of Aδ-fiber low-threshold mechanoreceptors and sub-populations of C-fiber nociceptors, a role consistent with its restricted expression profile in the spinal somatosensory system. We also establish using the spared nerve injury model of neuropathic pain, that loss of Fxyd2 function, either constitutively in Fxyd2−/− mice or acutely in neuropathic rats, efficiently alleviates mechanical hypersensitivity induced by peripheral nerve lesions. The role of Fxyd2 in modulating Aδ- and C-fibers mechanosensitivity likely accounts for the anti-allodynic effect of Fxyd2 knockdown. Finally, we uncover the evolutionarily conserved restricted expression pattern of FXYD2 in human dorsal root ganglia, thus identifying this molecule as a potentially promising therapeutic target for peripheral neuropathic pain management.
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Affiliation(s)
- Stéphanie Ventéo
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France
| | - Sophie Laffray
- UMR5203, INSERM U1191, Institut de Génomique Fonctionnelle, 141 rue de la Cardonille, 34094 Montpellier, France.,Université de Montpellier, Place Eugène Bataillon, 34090 Montpellier, France
| | - Christiane Wetzel
- Department of Neuroscience, Max-Delbrück Center for Molecular Medicine, Robert-Rössle Str. 10, D-13125 Berlin, Germany
| | - Cyril Rivat
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France.,Université de Montpellier, Place Eugène Bataillon, 34090 Montpellier, France
| | - Frédérique Scamps
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France
| | - Ilana Méchaly
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France.,Université de Montpellier, Place Eugène Bataillon, 34090 Montpellier, France
| | - Luc Bauchet
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France.,Département de Neurochirurgie, Hôpital Gui de Chauliac, CHU, 80 avenue Augustin Fliche, 34295 Montpellier, France
| | - Cédric Raoul
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France
| | - Emmanuel Bourinet
- UMR5203, INSERM U1191, Institut de Génomique Fonctionnelle, 141 rue de la Cardonille, 34094 Montpellier, France
| | - Gary R Lewin
- Department of Neuroscience, Max-Delbrück Center for Molecular Medicine, Robert-Rössle Str. 10, D-13125 Berlin, Germany
| | - Patrick Carroll
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France
| | - Alexandre Pattyn
- INSERM U1051, Institut des Neurosciences de Montpellier, Hôpital St Eloi, 80 rue Augustin Fliche, 34091 Montpellier, France
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Holm R, Toustrup-Jensen MS, Einholm AP, Schack VR, Andersen JP, Vilsen B. Neurological disease mutations of α3 Na +,K +-ATPase: Structural and functional perspectives and rescue of compromised function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1807-1828. [PMID: 27577505 DOI: 10.1016/j.bbabio.2016.08.009] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Revised: 08/19/2016] [Accepted: 08/25/2016] [Indexed: 11/26/2022]
Abstract
Na+,K+-ATPase creates transmembrane ion gradients crucial to the function of the central nervous system. The α-subunit of Na+,K+-ATPase exists as four isoforms (α1-α4). Several neurological phenotypes derive from α3 mutations. The effects of some of these mutations on Na+,K+-ATPase function have been studied in vitro. Here we discuss the α3 disease mutations as well as information derived from studies of corresponding mutations of α1 in the light of the high-resolution crystal structures of the Na+,K+-ATPase. A high proportion of the α3 disease mutations occur in the transmembrane sector and nearby regions essential to Na+ and K+ binding. In several cases the compromised function can be traced to disturbance of the Na+ specific binding site III. Recently, a secondary mutation was found to rescue the defective Na+ binding caused by a disease mutation. A perspective is that it may be possible to develop an efficient pharmaceutical mimicking the rescuing effect.
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Affiliation(s)
- Rikke Holm
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | | | - Anja P Einholm
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Vivien R Schack
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Jens P Andersen
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
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Arystarkhova E. Beneficial Renal and Pancreatic Phenotypes in a Mouse Deficient in FXYD2 Regulatory Subunit of Na,K-ATPase. Front Physiol 2016; 7:88. [PMID: 27014088 PMCID: PMC4779850 DOI: 10.3389/fphys.2016.00088] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 02/22/2016] [Indexed: 11/25/2022] Open
Abstract
The fundamental role of Na,K-ATPase in eukaryotic cells calls for complex and efficient regulation of its activity. Besides alterations in gene expression and trafficking, kinetic properties of the pump are modulated by reversible association with single span membrane proteins, the FXYDs. Seven members of the family are expressed in a tissue-specific manner, affecting pump kinetics in all possible permutations. This mini-review focuses on functional properties of FXYD2 studied in transfected cells, and on noteworthy and unexpected phenotypes discovered in a Fxyd2−∕− mouse. FXYD2, the gamma subunit, reduces activity of Na,K-ATPase either by decreasing affinity for Na+, or reducing Vmax. FXYD2 mRNA splicing and editing provide another layer for regulation of Na,K-ATPase. In kidney of knockouts, there was elevated activity for Na,K-ATPase and for NCC and NKCC2 apical sodium transporters. That should lead to sodium retention and hypertension, however, the mice were in sodium balance and normotensive. Adult Fxyd2−∕− mice also exhibited a mild pancreatic phenotype with enhanced glucose tolerance, elevation of circulating insulin, but no insulin resistance. There was an increase in beta cell proliferation and beta cell mass that correlated with activation of the PI3K-Akt pathway. The Fxyd2−∕− mice are thus in a highly desirable state: the animals are resistant to Na+ retention, and showed improved glucose control, i.e., they display favorable metabolic adaptations to protect against development of salt-sensitive hypertension and diabetes. Investigation of the mechanisms of these adaptations in the mouse has the potential to unveil a novel therapeutic FXYD2-dependent strategy.
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Affiliation(s)
- Elena Arystarkhova
- Laboratory of Membrane Biology, Neurosurgery, Massachusetts General Hospital Boston, MA, USA
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Bech AP, Wetzels JF, Bongers EMHF, Nijenhuis T. Thiazide Responsiveness Testing in Patients With Renal Magnesium Wasting and Correlation With Genetic Analysis: A Diagnostic Test Study. Am J Kidney Dis 2016; 68:168-70. [PMID: 26830254 DOI: 10.1053/j.ajkd.2015.12.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 12/18/2015] [Indexed: 11/11/2022]
Affiliation(s)
- Anneke P Bech
- Radboud University Medical Center, Nijmegen, the Netherlands.
| | - Jack F Wetzels
- Radboud University Medical Center, Nijmegen, the Netherlands
| | | | - Tom Nijenhuis
- Radboud University Medical Center, Nijmegen, the Netherlands
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29
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Liu YB, Tewari A, Salameh J, Arystarkhova E, Hampton TG, Brashear A, Ozelius LJ, Khodakhah K, Sweadner KJ. A dystonia-like movement disorder with brain and spinal neuronal defects is caused by mutation of the mouse laminin β1 subunit, Lamb1. eLife 2015; 4. [PMID: 26705335 PMCID: PMC4749547 DOI: 10.7554/elife.11102] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 12/15/2015] [Indexed: 12/30/2022] Open
Abstract
A new mutant mouse (lamb1t) exhibits intermittent dystonic hindlimb movements and postures when awake, and hyperextension when asleep. Experiments showed co-contraction of opposing muscle groups, and indicated that symptoms depended on the interaction of brain and spinal cord. SNP mapping and exome sequencing identified the dominant causative mutation in the Lamb1 gene. Laminins are extracellular matrix proteins, widely expressed but also known to be important in synapse structure and plasticity. In accordance, awake recording in the cerebellum detected abnormal output from a circuit of two Lamb1-expressing neurons, Purkinje cells and their deep cerebellar nucleus targets, during abnormal postures. We propose that dystonia-like symptoms result from lapses in descending inhibition, exposing excess activity in intrinsic spinal circuits that coordinate muscles. The mouse is a new model for testing how dysfunction in the CNS causes specific abnormal movements and postures.
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Affiliation(s)
- Yi Bessie Liu
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - Ambika Tewari
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
| | - Johnny Salameh
- Department of Neurology, University of Massachusetts Medical School, Worcester, United States
| | - Elena Arystarkhova
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - Thomas G Hampton
- Neuroscience Discovery Core, Mouse Specifics Inc., Framingham, United States
| | - Allison Brashear
- Department of Neurology, Wake Forest University School of Medicine, Winston-Salem, United States
| | - Laurie J Ozelius
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - Kamran Khodakhah
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, United States
| | - Kathleen J Sweadner
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, United States
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30
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General and specific lipid-protein interactions in Na,K-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1729-43. [PMID: 25791351 DOI: 10.1016/j.bbamem.2015.03.012] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Revised: 02/20/2015] [Accepted: 03/09/2015] [Indexed: 11/20/2022]
Abstract
The molecular activity of Na,K-ATPase and other P2 ATPases like Ca(2+)-ATPase is influenced by the lipid environment via both general (physical) and specific (chemical) interactions. Whereas the general effects of bilayer structure on membrane protein function are fairly well described and understood, the importance of the specific interactions has only been realized within the last decade due particularly to the growing field of membrane protein crystallization, which has shed new light on the molecular details of specific lipid-protein interactions. It is a remarkable observation that specific lipid-protein interactions seem to be evolutionarily conserved, and conformations of specifically bound lipids at the lipid-protein surface within the membrane are similar in crystal structures determined with different techniques and sources of the protein, despite the rather weak lipid-protein interaction energy. Studies of purified detergent-soluble recombinant αβ or αβFXYD Na,K-ATPase complexes reveal three separate functional effects of phospholipids and cholesterol with characteristic structural selectivity. The observations suggest that these three effects are exerted at separate binding sites for phophatidylserine/cholesterol (stabilizing), polyunsaturated phosphatidylethanolamine (stimulatory), and saturated PC or sphingomyelin/cholesterol (inhibitory), which may be located within three lipid-binding pockets identified in recent crystal structures of Na,K-ATPase. The findings point to a central role of direct and specific interactions of different phospholipids and cholesterol in determining both stability and molecular activity of Na,K-ATPase and possible implications for physiological regulation by membrane lipid composition. This article is part of a special issue titled "Lipid-Protein Interactions."
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31
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Wang F, Cai B, Li KC, Hu XY, Lu YJ, Wang Q, Bao L, Zhang X. FXYD2, a γ subunit of Na⁺, K⁺-ATPase, maintains persistent mechanical allodynia induced by inflammation. Cell Res 2015; 25:318-34. [PMID: 25633594 DOI: 10.1038/cr.2015.12] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Revised: 10/09/2014] [Accepted: 12/15/2014] [Indexed: 01/08/2023] Open
Abstract
Na⁺, K⁺-ATPase (NKA) is required to generate the resting membrane potential in neurons. Nociceptive afferent neurons express not only the α and β subunits of NKA but also the γ subunit FXYD2. However, the neural function of FXYD2 is unknown. The present study shows that FXYD2 in nociceptive neurons is necessary for maintaining the mechanical allodynia induced by peripheral inflammation. FXYD2 interacted with α1NKA and negatively regulated the NKA activity, depolarizing the membrane potential of nociceptive neurons. Mechanical allodynia initiated in FXYD2-deficient mice was abolished 4 days after inflammation, whereas it persisted for at least 3 weeks in wild-type mice. Importantly, the FXYD2/α1NKA interaction gradually increased after inflammation and peaked on day 4 post inflammation, resulting in reduction of NKA activity, depolarization of neuron membrane and facilitation of excitatory afferent neurotransmission. Thus, the increased FXYD2 activity may be a fundamental mechanism underlying the persistent hypersensitivity to pain induced by inflammation.
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Affiliation(s)
- Feng Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Bing Cai
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Kai-Cheng Li
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xu-Ye Hu
- Shanghai Clinical Center, Chinese Academy of Sciences/XuHui Central Hospital, Shanghai, China
| | - Ying-Jin Lu
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Qiong Wang
- State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Lan Bao
- 1] State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China [2] School of Life Science and Technology, ShanghaiTech University, Shanghai 200031, China
| | - Xu Zhang
- 1] Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China [2] School of Life Science and Technology, ShanghaiTech University, Shanghai 200031, China
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32
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Arystarkhova E, Ralph DL, Liu YB, Bouley R, McDonough AA, Sweadner KJ. Paradoxical activation of the sodium chloride cotransporter (NCC) without hypertension in kidney deficient in a regulatory subunit of Na,K-ATPase, FXYD2. Physiol Rep 2014; 2:2/12/e12226. [PMID: 25472608 PMCID: PMC4332208 DOI: 10.14814/phy2.12226] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Na,K‐ATPase generates the driving force for sodium reabsorption in the kidney.
Na,K‐ATPase functional properties are regulated by small proteins belonging to the FXYD
family. In kidney FXYD2 is the most abundant: it is an inhibitory subunit expressed in almost every
nephron segment. Its absence should increase sodium pump activity and promote Na+
retention, however, no obvious renal phenotype was detected in mice with global deletion of FXYD2
(Arystarkhova et al. 2013). Here, increased total cortical Na,K‐ATPase activity was
documented in the Fxyd2−/− mouse, without increased
α1β1 subunit expression. We tested the hypothesis
that adaptations occur in distal convoluted tubule (DCT), a major site of sodium adjustments.
Na,K‐ATPase immunoreactivity in DCT was unchanged, and there was no DCT hypoplasia. There was
a marked activation of thiazide‐sensitive sodium chloride cotransporter (NCC; Slc12a3) in
DCT, predicted to increase Na+ reabsorption in this segment. Specifically, NCC
total increased 30% and NCC phosphorylated at T53 and S71, associated with activation,
increased 4‐6 fold. The phosphorylation of the closely related thick ascending limb (TAL)
apical NKCC2 (Slc12a1) increased at least twofold. Abundance of the total and cleaved (activated)
forms of ENaC α‐subunit was not different between genotypes.
Nonetheless, no elevation of blood pressure was evident despite the fact that NCC and NKCC2 are in
states permissive for Na+ retention. Activation of NCC and NKCC2 may reflect an
intracellular linkage to elevated Na,K‐ATPase activity or a compensatory response to
Na+ loss proximal to the TAL and DCT. We discovered a substantial activation of renal NCC cotransporter in mice genetically depleted
for the regulatory inhibitory subunit of Na,K‐ATPase, FXYD2. Surprisingly, no significant
changes in urine output as well as elevation of blood pressure were detected suggesting compensatory
adaptation elsewhere in nephron
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Affiliation(s)
- Elena Arystarkhova
- Laboratory of Membrane Biology, Massachusetts General Hospital, Boston, Massachusetts
| | - Donna L Ralph
- Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Yi Bessie Liu
- Laboratory of Membrane Biology, Massachusetts General Hospital, Boston, Massachusetts
| | - Richard Bouley
- MGH Center for Systems Biology, Program in Membrane Biology, Massachusetts General Hospital, Boston, Massachusetts
| | - Alicia A McDonough
- Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Kathleen J Sweadner
- Laboratory of Membrane Biology, Massachusetts General Hospital, Boston, Massachusetts
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33
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Konrad M, Schlingmann KP. Inherited disorders of renal hypomagnesaemia. Nephrol Dial Transplant 2014; 29 Suppl 4:iv63-71. [PMID: 25165187 DOI: 10.1093/ndt/gfu198] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The kidney plays a key role in the maintenance of normal magnesium balance. The distal tubule of the kidney, namely the thick ascending limb of the loop of Henle and the distal convoluted tubule, is crucial for the regulation of serum magnesium levels and body magnesium content. The identification of molecular defects related to rare inherited magnesium losing disorders has contributed greatly to a better understanding of the process of renal magnesium handling. Since the number of genetic defects related to magnesium metabolism is still increasing, it might be expected that our knowledge on magnesium physiology will further improve. This knowledge will hopefully lead to therapeutic strategies that enable specific therapies for patients suffering from the symptoms and possible sequelae of chronic magnesium depletion.
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Affiliation(s)
- Martin Konrad
- Department of General Pediatrics, University Children's Hospital, Münster, Germany
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34
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Gong XM, Ding Y, Yu J, Yao Y, Marassi FM. Structure of the Na,K-ATPase regulatory protein FXYD2b in micelles: implications for membrane-water interfacial arginines. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:299-306. [PMID: 24794573 DOI: 10.1016/j.bbamem.2014.04.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/19/2014] [Accepted: 04/23/2014] [Indexed: 01/06/2023]
Abstract
FXYD2 is a membrane protein responsible for regulating the function of the Na,K-ATPase in mammalian kidney epithelial cells. Here we report the structure of FXYD2b, one of two splice variants of the protein, determined by NMR spectroscopy in detergent micelles. Solid-state NMR characterization of the protein embedded in phospholipid bilayers indicates that several arginine side chains may be involved in hydrogen bond interactions with the phospholipid polar head groups. The structure and the NMR data suggest that FXYD2b could regulate the Na,K-ATPase by modulating the effective membrane surface electrostatics near the ion binding sites of the pump.
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Affiliation(s)
- Xiao-Min Gong
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yi Ding
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Jinghua Yu
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yong Yao
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Francesca M Marassi
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
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35
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Whole brain and brain regional coexpression network interactions associated with predisposition to alcohol consumption. PLoS One 2013; 8:e68878. [PMID: 23894363 PMCID: PMC3720886 DOI: 10.1371/journal.pone.0068878] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 06/01/2013] [Indexed: 01/02/2023] Open
Abstract
To identify brain transcriptional networks that may predispose an animal to consume alcohol, we used weighted gene coexpression network analysis (WGCNA). Candidate coexpression modules are those with an eigengene expression level that correlates significantly with the level of alcohol consumption across a panel of BXD recombinant inbred mouse strains, and that share a genomic region that regulates the module transcript expression levels (mQTL) with a genomic region that regulates alcohol consumption (bQTL). To address a controversy regarding utility of gene expression profiles from whole brain, vs specific brain regions, as indicators of the relationship of gene expression to phenotype, we compared candidate coexpression modules from whole brain gene expression data (gathered with Affymetrix 430 v2 arrays in the Colorado laboratories) and from gene expression data from 6 brain regions (nucleus accumbens (NA); prefrontal cortex (PFC); ventral tegmental area (VTA); striatum (ST); hippocampus (HP); cerebellum (CB)) available from GeneNetwork. The candidate modules were used to construct candidate eigengene networks across brain regions, resulting in three "meta-modules", composed of candidate modules from two or more brain regions (NA, PFC, ST, VTA) and whole brain. To mitigate the potential influence of chromosomal location of transcripts and cis-eQTLs in linkage disequilibrium, we calculated a semi-partial correlation of the transcripts in the meta-modules with alcohol consumption conditional on the transcripts' cis-eQTLs. The function of transcripts that retained the correlation with the phenotype after correction for the strong genetic influence, implicates processes of protein metabolism in the ER and Golgi as influencing susceptibility to variation in alcohol consumption. Integration of these data with human GWAS provides further information on the function of polymorphisms associated with alcohol-related traits.
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36
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Addition of subunit γ, K+ ions, and lipid restores the thermal stability of solubilized Na,K-ATPase. Arch Biochem Biophys 2013; 530:93-100. [DOI: 10.1016/j.abb.2012.12.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 12/21/2012] [Accepted: 12/23/2012] [Indexed: 11/19/2022]
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37
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Arystarkhova E, Liu YB, Salazar C, Stanojevic V, Clifford RJ, Kaplan JH, Kidder GM, Sweadner KJ. Hyperplasia of pancreatic beta cells and improved glucose tolerance in mice deficient in the FXYD2 subunit of Na,K-ATPase. J Biol Chem 2013; 288:7077-85. [PMID: 23344951 DOI: 10.1074/jbc.m112.401190] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Restoration of the functional potency of pancreatic islets either through enhanced proliferation (hyperplasia) or increase in size (hypertrophy) of beta cells is a major objective for intervention in diabetes. We have obtained experimental evidence that global knock-out of a small, single-span regulatory subunit of Na,K-ATPase, FXYD2, alters glucose control. Adult Fxyd2(-/-) mice showed significantly lower blood glucose levels, no signs of peripheral insulin resistance, and improved glucose tolerance compared with their littermate controls. Strikingly, there was a substantial hyperplasia in pancreatic beta cells from the Fxyd2(-/-) mice compared with the wild type littermates, compatible with an observed increase in the level of circulating insulin. No changes were seen in the exocrine compartment of the pancreas, and the mice had only a mild, well-adapted renal phenotype. Morphometric analysis revealed an increase in beta cell mass in KO compared with WT mice. This appears to explain a phenotype of hyperinsulinemia. By RT-PCR, Western blot, and immunocytochemistry we showed the FXYD2b splice variant in pancreatic beta cells from wild type mice. Phosphorylation of Akt kinase was significantly higher under basal conditions in freshly isolated islets from Fxyd2(-/-) mice compared with their WT littermates. Inducible expression of FXYD2 in INS 832/13 cells produced a reduction in the phosphorylation level of Akt, and phosphorylation was restored in parallel with degradation of FXYD2. Thus we suggest that in pancreatic beta cells FXYD2 plays a role in Akt signaling pathways associated with cell growth and proliferation.
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Affiliation(s)
- Elena Arystarkhova
- Laboratory Membrane Biology, Massachusetts General Hospital, Boston, Massachusetts 2114, USA.
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38
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Identification of a crab gill FXYD2 protein and regulation of crab microsomal Na,K-ATPase activity by mammalian FXYD2 peptide. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2588-97. [DOI: 10.1016/j.bbamem.2012.05.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 05/07/2012] [Accepted: 05/08/2012] [Indexed: 01/20/2023]
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39
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Li X, McClellan ME, Tanito M, Garteiser P, Towner R, Bissig D, Berkowitz BA, Fliesler SJ, Woodruff ML, Fain GL, Birch DG, Khan MS, Ash JD, Elliott MH. Loss of caveolin-1 impairs retinal function due to disturbance of subretinal microenvironment. J Biol Chem 2012; 287:16424-34. [PMID: 22451674 DOI: 10.1074/jbc.m112.353763] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Caveolin-1 (Cav-1), an integral component of caveolar membrane domains, is expressed in several retinal cell types, including photoreceptors, retinal vascular endothelial cells, Müller glia, and retinal pigment epithelium (RPE) cells. Recent evidence links Cav-1 to ocular diseases, including autoimmune uveitis, diabetic retinopathy, and primary open angle glaucoma, but its role in normal vision is largely undetermined. In this report, we show that ablation of Cav-1 results in reduced inner and outer retinal function as measured, in vivo, by electroretinography and manganese-enhanced MRI. Somewhat surprisingly, dark current and light sensitivity were normal in individual rods (recorded with suction electrode methods) from Cav-1 knock-out (KO) mice. Although photoreceptor function was largely normal, in vitro, the apparent K(+) affinity of the RPE-expressed α1-Na(+)/K(+)-ATPase was decreased in Cav-1 KO mice. Cav-1 KO retinas also displayed unusually tight adhesion with the RPE, which could be resolved by brief treatment with hyperosmotic medium, suggesting alterations in outer retinal fluid homeostasis. Collectively, these findings demonstrate that reduced retinal function resulting from Cav-1 ablation is not photoreceptor-intrinsic but rather involves impaired subretinal and/or RPE ion/fluid homeostasis.
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Affiliation(s)
- Xiaoman Li
- Department of Ophthalmology and Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
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40
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Regulation of the Na,K-ATPase gamma-subunit FXYD2 by Runx1 and Ret signaling in normal and injured non-peptidergic nociceptive sensory neurons. PLoS One 2012; 7:e29852. [PMID: 22253804 PMCID: PMC3258241 DOI: 10.1371/journal.pone.0029852] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Accepted: 12/05/2011] [Indexed: 01/03/2023] Open
Abstract
Dorsal root ganglia (DRGs) contain the cell bodies of sensory neurons which relay nociceptive, thermoceptive, mechanoceptive and proprioceptive information from peripheral tissues toward the central nervous system. These neurons establish constant communication with their targets which insures correct maturation and functioning of the somato-sensory nervous system. Interfering with this two-way communication leads to cellular, electrophysiological and molecular modifications that can eventually cause neuropathic conditions. In this study we reveal that FXYD2, which encodes the gamma-subunit of the Na,K-ATPase reported so far to be mainly expressed in the kidney, is induced in the mouse DRGs at postnatal stages where it is restricted specifically to the TrkB-expressing mechanoceptive and Ret-positive/IB4-binding non-peptidergic nociceptive neurons. In non-peptidergic nociceptors, we show that the transcription factor Runx1 controls FXYD2 expression during the maturation of the somato-sensory system, partly through regulation of the tyrosine kinase receptor Ret. Moreover, Ret signaling maintains FXYD2 expression in adults as demonstrated by the axotomy-induced down-regulation of the gene that can be reverted by in vivo delivery of GDNF family ligands. Altogether, these results establish FXYD2 as a specific marker of defined sensory neuron subtypes and a new target of the Ret signaling pathway during normal maturation of the non-peptidergic nociceptive neurons and after sciatic nerve injury.
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41
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Miles AJ, Wallace BA, Esmann M. Correlation of structural and functional thermal stability of the integral membrane protein Na,K-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2573-80. [PMID: 21712026 DOI: 10.1016/j.bbamem.2011.06.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2011] [Revised: 06/03/2011] [Accepted: 06/14/2011] [Indexed: 10/18/2022]
Abstract
The membrane-bound cation-transporting P-type Na,K-ATPase isolated from pig kidney membranes is much more resistant towards thermal inactivation than the almost identical membrane-bound Na,K-ATPase isolated from shark rectal gland membranes. The loss of enzymatic activity is correlated well with changes in protein structure as determined using synchrotron radiation circular dichroism (SRCD) spectroscopy. The enzymatic activity is lost at a 12°C higher temperature for pig enzyme than for shark enzyme, and the major changes in protein secondary structure also occur at T(m)'s that are ~10-15°C higher for the pig than for the shark enzyme. The temperature optimum for the rate of hydrolysis of ATP is about 42°C for shark and about 57°C for pig, both of which are close to the temperatures for onset of thermal unfolding. These results suggest that the active site region may be amongst the earliest parts of the structure to unfold. Detergent-solubilized Na,K-ATPases from the two sources show the similar differences in thermal stability as the membrane-bound species, but inactivation occurs at a lower temperature for both, and may reflect the stabilizing effect of a bilayer versus a micellar environment.
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Affiliation(s)
- Andrew J Miles
- Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, UK
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Sweadner KJ, Pascoa JL, Salazar CA, Arystarkhova E. Post-transcriptional control of Na,K-ATPase activity and cell growth by a splice variant of FXYD2 protein with modified mRNA. J Biol Chem 2011; 286:18290-300. [PMID: 21460224 DOI: 10.1074/jbc.m111.241901] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
In kidney, FXYD proteins regulate Na,K-ATPase in a nephron segment-specific way. FXYD2 is the most abundant renal FXYD but is not expressed in most renal cell lines unless induced by hypertonicity. Expression by transfection of FXYD2a or FXYD2b splice variants in NRK-52E cells reduces the apparent Na(+) affinity of the Na,K-ATPase and slows the cell proliferation rate. Based on RT-PCR, mRNAs for both splice variants were expressed in wild type NRK-52E cells as low abundance species. DNA sequencing of the PCR products revealed a base alteration from C to T in FXYD2b but not FXYD2a from both untreated and hypertonicity-treated NRK-52E cells. The 172C→T sequence change exposed a cryptic KKXX endoplasmic reticulum retrieval signal via a premature stop codon. The truncation affected trafficking of FXYD2b and its association with Na,K-ATPase and blocked its effect on enzyme kinetics and cell growth. The data may be explained by altered splicing or selective RNA editing of FXYD2b, a supplementary process that would ensure that it was inactive even if transcribed and translated, in these cells that normally express only FXYD2a. 172C→T mutation was also identified after mutagenesis of FXYD2b by error-prone PCR coupled with a selection for cell proliferation. Furthermore, the error-prone PCR alone introduced the mutation with high frequency, implying a structural peculiarity. The data confirm truncation of FXYD2b as a potential mechanism to regulate the amount of FXYD2 at the cell surface to control activity of Na,K-ATPase and cell growth.
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Affiliation(s)
- Kathleen J Sweadner
- Laboratory of Membrane Biology, Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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Bibert S, Liu CC, Figtree GA, Garcia A, Hamilton EJ, Marassi FM, Sweadner KJ, Cornelius F, Geering K, Rasmussen HH. FXYD proteins reverse inhibition of the Na+-K+ pump mediated by glutathionylation of its beta1 subunit. J Biol Chem 2011; 286:18562-72. [PMID: 21454534 DOI: 10.1074/jbc.m110.184101] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The seven members of the FXYD protein family associate with the Na(+)-K(+) pump and modulate its activity. We investigated whether conserved cysteines in FXYD proteins are susceptible to glutathionylation and whether such reactivity affects Na(+)-K(+) pump function in cardiac myocytes and Xenopus oocytes. Glutathionylation was detected by immunoblotting streptavidin precipitate from biotin-GSH loaded cells or by a GSH antibody. Incubation of myocytes with recombinant FXYD proteins resulted in competitive displacement of native FXYD1. Myocyte and Xenopus oocyte pump currents were measured with whole-cell and two-electrode voltage clamp techniques, respectively. Native FXYD1 in myocytes and FXYD1 expressed in oocytes were susceptible to glutathionylation. Mutagenesis identified the specific cysteine in the cytoplasmic terminal that was reactive. Its reactivity was dependent on flanking basic amino acids. We have reported that Na(+)-K(+) pump β(1) subunit glutathionylation induced by oxidative signals causes pump inhibition in a previous study. In the present study, we found that β(1) subunit glutathionylation and pump inhibition could be reversed by exposing myocytes to exogenous wild-type FXYD3. A cysteine-free FXYD3 derivative had no effect. Similar results were obtained with wild-type and mutant FXYD proteins expressed in oocytes. Glutathionylation of the β(1) subunit was increased in myocardium from FXYD1(-/-) mice. In conclusion, there is a dependence of Na(+)-K(+) pump regulation on reactivity of two specifically identified cysteines on separate components of the multimeric Na(+)-K(+) pump complex. By facilitating deglutathionylation of the β(1) subunit, FXYD proteins reverse oxidative inhibition of the Na(+)-K(+) pump and play a dynamic role in its regulation.
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Affiliation(s)
- Stéphanie Bibert
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne 1005, Switzerland
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Mishra NK, Peleg Y, Cirri E, Belogus T, Lifshitz Y, Voelker DR, Apell HJ, Garty H, Karlish SJD. FXYD proteins stabilize Na,K-ATPase: amplification of specific phosphatidylserine-protein interactions. J Biol Chem 2011; 286:9699-712. [PMID: 21228272 DOI: 10.1074/jbc.m110.184234] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FXYD proteins are a family of seven small regulatory proteins, expressed in a tissue-specific manner, that associate with Na,K-ATPase as subsidiary subunits and modulate kinetic properties. This study describes an additional property of FXYD proteins as stabilizers of Na,K-ATPase. FXYD1 (phospholemman), FXYD2 (γ subunit), and FXYD4 (CHIF) have been expressed in Escherichia coli and purified. These FXYD proteins associate spontaneously in vitro with detergent-soluble purified recombinant human Na,K-ATPase (α1β1) to form α1β1FXYD complexes. Compared with the control (α1β1), all three FXYD proteins strongly protect Na,K-ATPase activity against inactivation by heating or excess detergent (C(12)E(8)), with effectiveness FXYD1 > FXYD2 ≥ FXYD4. Heating also inactivates E(1) ↔ E(2) conformational changes and cation occlusion, and FXYD1 protects strongly. Incubation of α1β1 or α1β1FXYD complexes with guanidinium chloride (up to 6 m) causes protein unfolding, detected by changes in protein fluorescence, but FXYD proteins do not protect. Thus, general protein denaturation is not the cause of thermally mediated or detergent-mediated inactivation. By contrast, the experiments show that displacement of specifically bound phosphatidylserine is the primary cause of thermally mediated or detergent-mediated inactivation, and FXYD proteins stabilize phosphatidylserine-Na,K-ATPase interactions. Phosphatidylserine probably binds near trans-membrane segments M9 of the α subunit and the FXYD protein, which are in proximity. FXYD1, FXYD2, and FXYD4 co-expressed in HeLa cells with rat α1 protect strongly against thermal inactivation. Stabilization of Na,K-ATPase by three FXYD proteins in a mammalian cell membrane, as well the purified recombinant Na,K-ATPase, suggests that stabilization is a general property of FXYD proteins, consistent with a significant biological function.
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Affiliation(s)
- Neeraj Kumar Mishra
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovoth 76100, Israel
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Saito K, Nakamura N, Ito Y, Hoshijima K, Esaki M, Zhao B, Hirose S. Identification of zebrafish Fxyd11a protein that is highly expressed in ion-transporting epithelium of the gill and skin and its possible role in ion homeostasis. Front Physiol 2010; 1:129. [PMID: 21423371 PMCID: PMC3059942 DOI: 10.3389/fphys.2010.00129] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Accepted: 08/07/2010] [Indexed: 11/30/2022] Open
Abstract
FXYD proteins, small single-transmembrane proteins, have been proposed to be auxiliary regulatory subunits of Na+–K+-ATPase and have recently been implied in ion osmoregulation of teleost fish. In freshwater (FW) fish, numerous ions are actively taken up through mitochondrion-rich cells (MRCs) of the gill and skin epithelia, using the Na+ electrochemical gradient generated by Na+–K+-ATPase. In the present study, to understand the molecular mechanism for the regulation of Na+–K+-ATPase in MRCs of FW fish, we sought to identify FXYD proteins expressed in MRCs of zebrafish. Reverse-transcriptase PCR studies of adult zebrafish tissues revealed that, out of eight fxyd genes found in zebrafish database, only zebrafish fxyd11 (zfxyd11) mRNA exhibited a gill-specific expression. Double immunofluorescence staining showed that zFxyd11 is abundantly expressed in MRCs rich in Na+–K+-ATPase (NaK-MRCs) but not in those rich in vacuolar-type H+-transporting ATPase. An in situ proximity ligation assay demonstrated its close association with Na+–K+-ATPase in NaK-MRCs. The zfxyd11 mRNA expression was detectable at 1 day postfertilization, and its expression levels in the whole larvae and adult gills were regulated in response to changes in environmental ionic concentrations. Furthermore, knockdown of zFxyd11 resulted in a significant increase in the number of Na+–K+-ATPase–positive cells in the larval skin. These results suggest that zFxyd11 may regulate the transport ability of NaK-MRCs by modulating Na+–K+-ATPase activity, and may be involved in the regulation of body fluid and electrolyte homeostasis.
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Affiliation(s)
- Kaori Saito
- Department of Biological Sciences, Tokyo Institute of Technology Yokohama, Japan
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Harrington MG, Fonteh AN, Arakaki X, Cowan RP, Ecke LE, Foster H, Hühmer AF, Biringer RG. Capillary endothelial Na(+), K(+), ATPase transporter homeostasis and a new theory for migraine pathophysiology. Headache 2010; 50:459-78. [PMID: 19845787 PMCID: PMC8020446 DOI: 10.1111/j.1526-4610.2009.01551.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Cerebrospinal fluid sodium concentration ([Na(+)](csf)) increases during migraine, but the cause of the increase is not known. OBJECTIVE Analyze biochemical pathways that influence [Na(+)](csf) to identify mechanisms that are consistent with migraine. METHOD We reviewed sodium physiology and biochemistry publications for links to migraine and pain. RESULTS Increased capillary endothelial cell (CEC) Na(+), K(+), -ATPase transporter (NKAT) activity is probably the primary cause of increased [Na(+)](csf). Physiological fluctuations of all NKAT regulators in blood, many known to be involved in migraine, are monitored by receptors on the luminal wall of brain CECs; signals are then transduced to their abluminal NKATs that alter brain extracellular sodium ([Na(+)](e)) and potassium ([K(+)](e)). CONCLUSIONS We propose a theoretical mechanism for aura and migraine when NKAT activity shifts outside normal limits: (1) CEC NKAT activity below a lower limit increases [K(+)](e), facilitates cortical spreading depression, and causes aura; (2) CEC NKAT activity above an upper limit elevates [Na(+)](e), increases neuronal excitability, and causes migraine; (3) migraine-without-aura may arise from CEC NKAT over-activity without requiring a prior decrease in activity and its consequent spreading depression; (4) migraine triggers disturb, and treatments improve, CEC NKAT homeostasis; (5) CEC NKAT-induced regulation of neural and vasomotor excitability coordinates vascular and neuronal activities, and includes occasional pathology from CEC NKAT-induced apoptosis or cerebral infarction.
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Affiliation(s)
- Michael G Harrington
- Huntington Medical Research Institutes - Molecular Neurology, Pasadena, CA 91101, USA
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Hereditary tubular transport disorders: implications for renal handling of Ca2+ and Mg2+. Clin Sci (Lond) 2009; 118:1-18. [PMID: 19780717 DOI: 10.1042/cs20090086] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The kidney plays an important role in maintaining the systemic Ca2+ and Mg2+ balance. Thus the renal reabsorptive capacity of these cations can be amended to adapt to disturbances in plasma Ca2+ and Mg2+ concentrations. The reabsorption of Ca2+ and Mg2+ is driven by transport of other electrolytes, sometimes through selective channels and often supported by hormonal stimuli. It is, therefore, not surprising that monogenic disorders affecting such renal processes may impose a shift in, or even completely blunt, the reabsorptive capacity of these divalent cations within the kidney. Accordingly, in Dent's disease, a disorder with defective proximal tubular transport, hypercalciuria is frequently observed. Dysfunctional thick ascending limb transport in Bartter's syndrome, familial hypomagnesaemia with hypercalciuria and nephrocalcinosis, and diseases associated with Ca2+-sensing receptor defects, markedly change tubular transport of Ca2+ and Mg2+. In the distal convolutions, several proteins involved in Mg2+ transport have been identified [TRPM6 (transient receptor potential melastatin 6), proEGF (pro-epidermal growth factor) and FXYD2 (Na+/K+-ATPase gamma-subunit)]. In addition, conditions such as Gitelman's syndrome, distal renal tubular acidosis and pseudohypoaldosteronism type II, as well as a mitochondrial defect associated with hypomagnesaemia, all change the renal handling of divalent cations. These hereditary disorders have, in many cases, substantially increased our understanding of the complex transport processes in the kidney and their contribution to the regulation of overall Ca2+ and Mg2+ balance.
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Abstract
PURPOSE OF REVIEW Na,K-ATPase is an oligomeric protein composed of alpha subunits, beta subunits and FXYD proteins. The catalytic alpha subunit hydrolyzes ATP and transports the cations. Increasing experimental evidence suggest that beta subunits and FXYD proteins essentially contribute to the variable physiological needs of Na,K-ATPase function in different tissues. RECENT FINDINGS Beta subunits have a crucial role in the structural and functional maturation of Na,K-ATPase and modulate its transport properties. The chaperone function of the beta subunit is essential, for example, in the formation of tight junctions and cell polarity. Recent studies suggest that beta subunits also have inherent functions, which are independent of Na,K-ATPase activity and which may be involved in cell-cell adhesiveness and in suppression of cell motility. As for FXYD proteins, they modulate Na,K-ATPase activity in a tissue-specific way, in some cases in close cooperation with posttranslational modifications such as phosphorylation. SUMMARY A better understanding of the multiple functional roles of the accessory subunits of Na,K-ATPase is crucial to appraise their influence on physiological processes and their implication in pathophysiological states.
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Knoers NVAM. Inherited forms of renal hypomagnesemia: an update. Pediatr Nephrol 2009; 24:697-705. [PMID: 18818955 PMCID: PMC7811505 DOI: 10.1007/s00467-008-0968-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Revised: 07/22/2008] [Accepted: 07/23/2008] [Indexed: 12/19/2022]
Abstract
The kidney plays an important role in ion homeostasis in the human body. Several hereditary disorders characterized by perturbations in renal magnesium reabsorption leading to hypomagnesemia have been described over the past 50 years, with the most important of these being Gitelman syndrome, familial hypomagnesemia with hypercalciuria and nephrocalcinosis, familial hypomagnesemia with secondary hypocalcemia, autosomal dominant hypomagnesemia with hypocalciuria, and autosomal recessive hypomagnesemia. Only recently, following positional cloning strategies in affected families, have mutations in renal ion channels and transporters been identified in these diseases. In this short review, I give an update on these hypomagnesemic disorders. Elucidation of the genetic etiology and, for most of these disorders, also the underlying pathophysiology of the disease, has greatly increased our understanding of the normal physiology of renal magnesium handling. This is yet another example of the importance of studying rare disorders in order to unravel physiological and pathophysiological processes in the human body.
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Affiliation(s)
- Nine V. A. M. Knoers
- grid.10417.330000000404449382Department of Human Genetics 849, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
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