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Duan HY, Barajas-Martinez H, Antzelevitch C, Hu D. The potential anti-arrhythmic effect of SGLT2 inhibitors. Cardiovasc Diabetol 2024; 23:252. [PMID: 39010053 PMCID: PMC11251349 DOI: 10.1186/s12933-024-02312-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Accepted: 06/16/2024] [Indexed: 07/17/2024] Open
Abstract
Sodium-glucose cotransporter type 2 inhibitors (SGLT2i) were initially recommended as oral anti-diabetic drugs to treat type 2 diabetes (T2D), by inhibiting SGLT2 in proximal tubule and reduce renal reabsorption of sodium and glucose. While many clinical trials demonstrated the tremendous potential of SGLT2i for cardiovascular diseases. 2022 AHA/ACC/HFSA guideline first emphasized that SGLT2i were the only drug class that can cover the entire management of heart failure (HF) from prevention to treatment. Subsequently, the antiarrhythmic properties of SGLT2i have also attracted attention. Although there are currently no prospective studies specifically on the anti-arrhythmic effects of SGLT2i. We provide clues from clinical and fundamental researches to identify its antiarrhythmic effects, reviewing the evidences and mechanism for the SGLT2i antiarrhythmic effects and establishing a novel paradigm involving intracellular sodium, metabolism and autophagy to investigate the potential mechanisms of SGLT2i in mitigating arrhythmias.
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Affiliation(s)
- Hong-Yi Duan
- Department of Cardiology and Cardiovascular Research Institute, Renmin Hospital of Wuhan University, 238 Jiefang Road, Wuhan, 430060, Hubei, China
- Hubei Key Laboratory of Cardiology, Wuhan, 430060, Hubei, China
| | - Hector Barajas-Martinez
- Lankenau Institute for Medical Research, Lankenau Heart Institute, Wynnewood, PA, 19096, USA
- Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, 19107, USA
| | - Charles Antzelevitch
- Lankenau Institute for Medical Research, Lankenau Heart Institute, Wynnewood, PA, 19096, USA
- Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, 19107, USA
| | - Dan Hu
- Department of Cardiology and Cardiovascular Research Institute, Renmin Hospital of Wuhan University, 238 Jiefang Road, Wuhan, 430060, Hubei, China.
- Hubei Key Laboratory of Cardiology, Wuhan, 430060, Hubei, China.
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2
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Leyland B, Novichkova E, Dolui AK, Jallet D, Daboussi F, Legeret B, Li Z, Li-Beisson Y, Boussiba S, Khozin-Goldberg I. Acyl-CoA binding protein is required for lipid droplet degradation in the diatom Phaeodactylum tricornutum. PLANT PHYSIOLOGY 2024; 194:958-981. [PMID: 37801606 DOI: 10.1093/plphys/kiad525] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/28/2023] [Accepted: 07/15/2023] [Indexed: 10/08/2023]
Abstract
Diatoms (Bacillariophyceae) accumulate neutral storage lipids in lipid droplets during stress conditions, which can be rapidly degraded and recycled when optimal conditions resume. Since nutrient and light availability fluctuate in marine environments, storage lipid turnover is essential for diatom dominance of marine ecosystems. Diatoms have garnered attention for their potential to provide a sustainable source of omega-3 fatty acids. Several independent proteomic studies of lipid droplets isolated from the model oleaginous pennate diatom Phaeodactylum tricornutum have identified a previously uncharacterized protein with an acyl-CoA binding (ACB) domain, Phatrdraft_48778, here referred to as Phaeodactylum tricornutum acyl-CoA binding protein (PtACBP). We report the phenotypic effects of CRISPR-Cas9 targeted genome editing of PtACBP. ptacbp mutants were defective in lipid droplet and triacylglycerol degradation, as well as lipid and eicosapentaenoic acid synthesis, during recovery from nitrogen starvation. Transcription of genes responsible for peroxisomal β-oxidation, triacylglycerol lipolysis, and eicosapentaenoic acid synthesis was inhibited. A lipid-binding assay using a synthetic ACB domain from PtACBP indicated preferential binding specificity toward certain polar lipids. PtACBP fused to eGFP displayed an endomembrane-like pattern, which surrounded the periphery of lipid droplets. PtACBP is likely responsible for intracellular acyl transport, affecting cell division, development, photosynthesis, and stress response. A deeper understanding of the molecular mechanisms governing storage lipid turnover will be crucial for developing diatoms and other microalgae as biotechnological cell factories.
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Affiliation(s)
- Ben Leyland
- The Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel
| | - Ekaterina Novichkova
- The Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel
| | - Achintya Kumar Dolui
- The Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel
| | - Denis Jallet
- Toulouse Biotechnology Institute Bio & Chemical Engineering, Institut National de la Recherche Agronomique, Institute National Des Sciences Appliquees, Le Centre national de la recherche scientifique, Toulouse 31077, France
| | - Fayza Daboussi
- Toulouse Biotechnology Institute Bio & Chemical Engineering, Institut National de la Recherche Agronomique, Institute National Des Sciences Appliquees, Le Centre national de la recherche scientifique, Toulouse 31077, France
| | - Bertrand Legeret
- Aix-Marseille University, CEA, CNRS, BIAM, Institut de Biosciences et Biotechnologies Aix-Marseille, CEA Cadarache, Saint Paul-Lez-Durance 13108, France
| | - Zhongze Li
- Aix-Marseille University, CEA, CNRS, BIAM, Institut de Biosciences et Biotechnologies Aix-Marseille, CEA Cadarache, Saint Paul-Lez-Durance 13108, France
| | - Yonghua Li-Beisson
- Aix-Marseille University, CEA, CNRS, BIAM, Institut de Biosciences et Biotechnologies Aix-Marseille, CEA Cadarache, Saint Paul-Lez-Durance 13108, France
| | - Sammy Boussiba
- The Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel
| | - Inna Khozin-Goldberg
- The Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus 84990, Israel
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3
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Kumar M, Gaivin RJ, Khan S, Fedorov Y, Adams DJ, Zhao W, Lee HY, Dai X, Dealwis CG, Schelling JR. Definition of fatty acid transport protein-2 (FATP2) structure facilitates identification of small molecule inhibitors for the treatment of diabetic complications. Int J Biol Macromol 2023; 244:125328. [PMID: 37307967 PMCID: PMC10527240 DOI: 10.1016/j.ijbiomac.2023.125328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 06/06/2023] [Accepted: 06/08/2023] [Indexed: 06/14/2023]
Abstract
Diabetes is a major public health problem due to morbidity and mortality associated with end organ complications. Uptake of fatty acids by Fatty Acid Transport Protein-2 (FATP2) contributes to hyperglycemia, diabetic kidney and liver disease pathogenesis. Because FATP2 structure is unknown, a homology model was constructed, validated by AlphaFold2 prediction and site-directed mutagenesis, and then used to conduct a virtual drug discovery screen. In silico similarity searches to two low-micromolar IC50 FATP2 inhibitors, followed by docking and pharmacokinetics predictions, narrowed a diverse 800,000 compound library to 23 hits. These candidates were further evaluated for inhibition of FATP2-dependent fatty acid uptake and apoptosis in cells. Two compounds demonstrated nanomolar IC50, and were further characterized by molecular dynamic simulations. The results highlight the feasibility of combining a homology model with in silico and in vitro screening, to economically identify high affinity inhibitors of FATP2, as potential treatment for diabetes and its complications.
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Affiliation(s)
- Mukesh Kumar
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Robert J Gaivin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Shenaz Khan
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Yuriy Fedorov
- Department of Genetics, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Drew J Adams
- Department of Genetics, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Weiyang Zhao
- Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Hsueh-Yun Lee
- School of Pharmacy, College of Pharmacy, Taipei Medical University, Taipei 110, Taiwan
| | - Xinghong Dai
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Chris G Dealwis
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, United States of America; Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States of America
| | - Jeffrey R Schelling
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, United States of America; Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, United States of America.
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4
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The Contribution of Lipotoxicity to Diabetic Kidney Disease. Cells 2022; 11:cells11203236. [PMID: 36291104 PMCID: PMC9601125 DOI: 10.3390/cells11203236] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/02/2022] [Accepted: 10/12/2022] [Indexed: 11/17/2022] Open
Abstract
Lipotoxicity is a fundamental pathophysiologic mechanism in diabetes and non-alcoholic fatty liver disease and is now increasingly recognized in diabetic kidney disease (DKD) pathogenesis. This review highlights lipotoxicity pathways in the podocyte and proximal tubule cell, which are arguably the two most critical sites in the nephron for DKD. The discussion focuses on membrane transporters and lipid droplets, which represent potential therapeutic targets, as well as current and developing pharmacologic approaches to reduce renal lipotoxicity.
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5
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Dong Y, Li H, Ilie A, Gao Y, Boucher A, Zhang XC, Orlowski J, Zhao Y. Structural basis of autoinhibition of the human NHE3-CHP1 complex. SCIENCE ADVANCES 2022; 8:eabn3925. [PMID: 35613257 PMCID: PMC9132474 DOI: 10.1126/sciadv.abn3925] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 04/11/2022] [Indexed: 06/15/2023]
Abstract
Sodium-proton exchanger 3 (NHE3/SLC9A3) located in the apical membrane of renal and gastrointestinal epithelia mediates salt and fluid absorption and regulates pH homeostasis. As an auxiliary regulatory factor of NHE proteins, calcineurin B homologous protein 1 (CHP1) facilitates NHE3 maturation, plasmalemmal expression, and pH sensitivity. Dysfunctions of NHE3 are associated with renal and digestive system disorders. Here, we report the cryo-electron microscopy structure of the human NHE3-CHP1 complex in its inward-facing conformation. We found that a cytosolic helix-loop-helix motif in NHE3 blocks the intracellular cavity formed between the core and dimerization domains, functioning as an autoinhibitory element and hindering substrate transport. Furthermore, two phosphatidylinositol molecules are found to bind to the peripheric juxtamembrane sides of the complex, function as anchors to stabilize the complex, and may thus enhance its transport activity.
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Affiliation(s)
- Yanli Dong
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hang Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Alina Ilie
- Department of Physiology, McGill University, Montreal, Canada
| | - Yiwei Gao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Annie Boucher
- Department of Physiology, McGill University, Montreal, Canada
| | - Xuejun Cai Zhang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - John Orlowski
- Department of Physiology, McGill University, Montreal, Canada
| | - Yan Zhao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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6
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Ritter M, Bresgen N, Kerschbaum HH. From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death. Front Cell Dev Biol 2021; 9:651982. [PMID: 34249909 PMCID: PMC8261248 DOI: 10.3389/fcell.2021.651982] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 04/29/2021] [Indexed: 12/11/2022] Open
Abstract
The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.
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Affiliation(s)
- Markus Ritter
- Center for Physiology, Pathophysiology and Biophysics, Institute for Physiology and Pathophysiology, Paracelsus Medical University, Salzburg, Austria
- Institute for Physiology and Pathophysiology, Paracelsus Medical University, Nuremberg, Germany
- Gastein Research Institute, Paracelsus Medical University, Salzburg, Austria
- Ludwig Boltzmann Institute for Arthritis und Rehabilitation, Salzburg, Austria
- Kathmandu University School of Medical Sciences, Dhulikhel, Nepal
| | - Nikolaus Bresgen
- Department of Biosciences, University of Salzburg, Salzburg, Austria
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7
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Kundu R, Chandra A, Datta A. Fluorescent Chemical Tools for Tracking Anionic Phospholipids. Isr J Chem 2021. [DOI: 10.1002/ijch.202100003] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Rajasree Kundu
- Department of Chemical Sciences Tata Institute of Fundamental Research 1 Homi Bhabha Road, Colaba Mumbai 400005 India
| | - Amitava Chandra
- Department of Chemical Sciences Tata Institute of Fundamental Research 1 Homi Bhabha Road, Colaba Mumbai 400005 India
| | - Ankona Datta
- Department of Chemical Sciences Tata Institute of Fundamental Research 1 Homi Bhabha Road, Colaba Mumbai 400005 India
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8
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Khundmiri SJ, Chen L, Lederer ED, Yang CR, Knepper MA. Transcriptomes of Major Proximal Tubule Cell Culture Models. J Am Soc Nephrol 2021; 32:86-97. [PMID: 33122286 PMCID: PMC7894662 DOI: 10.1681/asn.2020010009] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Accepted: 09/16/2020] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Cultured cell lines are widely used for research in the physiology, pathophysiology, toxicology, and pharmacology of the renal proximal tubule. The lines that are most appropriate for a given use depend upon the genes expressed. New tools for transcriptomic profiling using RNA sequencing (RNA-Seq) make it possible to catalog expressed genes in each cell line. METHODS Fourteen different proximal tubule cell lines, representing six species, were grown on permeable supports under conditions specific for the respective lines. RNA-Seq followed standard procedures. RESULTS Transcripts expressed in cell lines variably matched transcripts selectively expressed in native proximal tubule. Opossum kidney (OK) cells displayed the highest percentage match (45% of proximal marker genes [TPM threshold =15]), with pig kidney cells (LLC-PK1) close behind (39%). Lower-percentage matches were seen for various human lines, including HK-2 (26%), and lines from rodent kidneys, such as NRK-52E (23%). Nominally, identical OK cells from different sources differed substantially in expression of proximal tubule markers. Mapping cell line transcriptomes to gene sets for various proximal tubule functions (sodium and water transport, protein transport, metabolic functions, endocrine functions) showed that different lines may be optimal for experimentally modeling each function. An online resource (https://esbl.nhlbi.nih.gov/JBrowse/KCT/) has been created to interrogate cell line transcriptome data. Proteomic analysis of NRK-52E cells confirmed low expression of many proximal tubule marker proteins. CONCLUSIONS No cell line fully matched the transcriptome of native proximal tubule cells. However, some of the lines tested are suitable for the study of particular metabolic and transport processes seen in the proximal tubule.
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Affiliation(s)
- Syed J. Khundmiri
- Department of Physiology and Biophysics, Howard University College of Medicine, Washington, DC
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Lihe Chen
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Eleanor D. Lederer
- Division of Nephrology and Hypertension, School of Medicine, University of Louisville and Robley Rex Veterans Affairs Medical Center, Louisville, Kentucky
| | - Chin-Rang Yang
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Mark A. Knepper
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
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9
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Winklemann I, Matsuoka R, Meier PF, Shutin D, Zhang C, Orellana L, Sexton R, Landreh M, Robinson CV, Beckstein O, Drew D. Structure and elevator mechanism of the mammalian sodium/proton exchanger NHE9. EMBO J 2020; 39:e105908. [PMID: 33118634 PMCID: PMC7737618 DOI: 10.15252/embj.2020105908] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 09/09/2020] [Accepted: 09/10/2020] [Indexed: 12/21/2022] Open
Abstract
Na+ /H+ exchangers (NHEs) are ancient membrane-bound nanomachines that work to regulate intracellular pH, sodium levels and cell volume. NHE activities contribute to the control of the cell cycle, cell proliferation, cell migration and vesicle trafficking. NHE dysfunction has been linked to many diseases, and they are targets of pharmaceutical drugs. Despite their fundamental importance to cell homeostasis and human physiology, structural information for the mammalian NHE was lacking. Here, we report the cryogenic electron microscopy structure of NHE isoform 9 (SLC9A9) from Equus caballus at 3.2 Å resolution, an endosomal isoform highly expressed in the brain and associated with autism spectrum (ASD) and attention deficit hyperactivity (ADHD) disorders. Despite low sequence identity, the NHE9 architecture and ion-binding site are remarkably similar to distantly related bacterial Na+ /H+ antiporters with 13 transmembrane segments. Collectively, we reveal the conserved architecture of the NHE ion-binding site, their elevator-like structural transitions, the functional implications of autism disease mutations and the role of phosphoinositide lipids to promote homodimerization that, together, have important physiological ramifications.
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Affiliation(s)
- Iven Winklemann
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Rei Matsuoka
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Pascal F Meier
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Denis Shutin
- Department of ChemistryUniversity of OxfordOxfordUK
| | - Chenou Zhang
- Department of PhysicsCenter for Biological PhysicsArizona State UniversityTempeAZUSA
| | - Laura Orellana
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Ricky Sexton
- Department of PhysicsCenter for Biological PhysicsArizona State UniversityTempeAZUSA
| | - Michael Landreh
- Department of Microbiology, Tumor and Cell BiologyKarolinska InstituteStockholmSweden
| | | | - Oliver Beckstein
- Department of PhysicsCenter for Biological PhysicsArizona State UniversityTempeAZUSA
| | - David Drew
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
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10
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Hendus-Altenburger R, Vogensen J, Pedersen ES, Luchini A, Araya-Secchi R, Bendsoe AH, Prasad NS, Prestel A, Cardenas M, Pedraz-Cuesta E, Arleth L, Pedersen SF, Kragelund BB. The intracellular lipid-binding domain of human Na +/H + exchanger 1 forms a lipid-protein co-structure essential for activity. Commun Biol 2020; 3:731. [PMID: 33273619 PMCID: PMC7713384 DOI: 10.1038/s42003-020-01455-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 11/03/2020] [Indexed: 12/03/2022] Open
Abstract
Dynamic interactions of proteins with lipid membranes are essential regulatory events in biology, but remain rudimentarily understood and particularly overlooked in membrane proteins. The ubiquitously expressed membrane protein Na+/H+-exchanger 1 (NHE1) regulates intracellular pH (pHi) with dysregulation linked to e.g. cancer and cardiovascular diseases. NHE1 has a long, regulatory cytosolic domain carrying a membrane-proximal region described as a lipid-interacting domain (LID), yet, the LID structure and underlying molecular mechanisms are unknown. Here we decompose these, combining structural and biophysical methods, molecular dynamics simulations, cellular biotinylation- and immunofluorescence analysis and exchanger activity assays. We find that the NHE1-LID is intrinsically disordered and, in presence of membrane mimetics, forms a helical αα-hairpin co-structure with the membrane, anchoring the regulatory domain vis-a-vis the transport domain. This co-structure is fundamental for NHE1 activity, as its disintegration reduced steady-state pHi and the rate of pHi recovery after acid loading. We propose that regulatory lipid-protein co-structures may play equally important roles in other membrane proteins.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Jens Vogensen
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Emilie Skotte Pedersen
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
| | - Alessandra Luchini
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark
| | - Raul Araya-Secchi
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark
| | - Anne H Bendsoe
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Nanditha Shyam Prasad
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Andreas Prestel
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
| | - Marité Cardenas
- Biofilms Research Center for Biointerfaces, Malmö University, Per Albin Hanssons Väg 35, 214 32, Malmö, Sweden
| | - Elena Pedraz-Cuesta
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Lise Arleth
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
| | - Stine F Pedersen
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark.
| | - Birthe B Kragelund
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark.
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11
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Pedersen SF, Counillon L. The SLC9A-C Mammalian Na +/H + Exchanger Family: Molecules, Mechanisms, and Physiology. Physiol Rev 2019; 99:2015-2113. [PMID: 31507243 DOI: 10.1152/physrev.00028.2018] [Citation(s) in RCA: 110] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Na+/H+ exchangers play pivotal roles in the control of cell and tissue pH by mediating the electroneutral exchange of Na+ and H+ across cellular membranes. They belong to an ancient family of highly evolutionarily conserved proteins, and they play essential physiological roles in all phyla. In this review, we focus on the mammalian Na+/H+ exchangers (NHEs), the solute carrier (SLC) 9 family. This family of electroneutral transporters constitutes three branches: SLC9A, -B, and -C. Within these, each isoform exhibits distinct tissue expression profiles, regulation, and physiological roles. Some of these transporters are highly studied, with hundreds of original articles, and some are still only rudimentarily understood. In this review, we present and discuss the pioneering original work as well as the current state-of-the-art research on mammalian NHEs. We aim to provide the reader with a comprehensive view of core knowledge and recent insights into each family member, from gene organization over protein structure and regulation to physiological and pathophysiological roles. Particular attention is given to the integrated physiology of NHEs in the main organ systems. We provide several novel analyses and useful overviews, and we pinpoint main remaining enigmas, which we hope will inspire novel research on these highly versatile proteins.
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Affiliation(s)
- S F Pedersen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
| | - L Counillon
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
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12
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Abstract
Fast opening and closing of voltage-gated sodium channels are crucial for proper propagation of the action potential through excitable tissues. Unlike potassium channels, sodium channel α-subunits are believed to form functional monomers. Yet, an increasing body of literature shows inconsistency with the traditional idea of a single α-subunit functioning as a monomer. Here we demonstrate that sodium channel α-subunits not only physically interact with each other but they actually assemble, function and gate as a dimer. We identify the region involved in the dimerization and demonstrate that 14-3-3 protein mediates the coupled gating. Importantly we show conservation of this mechanism among mammalian sodium channels. Our study not only shifts conventional paradigms in regard to sodium channel assembly, structure, and function but importantly this discovery of the mechanism involved in channel dimerization and biophysical coupling could open the door to new approaches and targets to treat and/or prevent sodium channelopathies. Voltage-gated sodium channels are expressed in excitable tissues and mutations have been linked to cardiac arrhythmias and channelopathies. Here the authors show that the sodium channel α-subunits interact to form a dimer and gate as dimer and that this functional dimerisation is conserved.
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13
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Kjaergaard M, Kragelund BB. Functions of intrinsic disorder in transmembrane proteins. Cell Mol Life Sci 2017; 74:3205-3224. [PMID: 28601983 PMCID: PMC11107515 DOI: 10.1007/s00018-017-2562-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 06/01/2017] [Indexed: 12/19/2022]
Abstract
Intrinsic disorder is common in integral membrane proteins, particularly in the intracellular domains. Despite this observation, these domains are not always recognized as being disordered. In this review, we will discuss the biological functions of intrinsically disordered regions of membrane proteins, and address why the flexibility afforded by disorder is mechanistically important. Intrinsically disordered regions are present in many common classes of membrane proteins including ion channels and transporters; G-protein coupled receptors (GPCRs), receptor tyrosine kinases and cytokine receptors. The functions of the disordered regions are many and varied. We will discuss selected examples including: (1) Organization of receptors, kinases, phosphatases and second messenger sources into signaling complexes. (2) Modulation of the membrane-embedded domain function by ball-and-chain like mechanisms. (3) Trafficking of membrane proteins. (4) Transient membrane associations. (5) Post-translational modifications most notably phosphorylation and (6) disorder-linked isoform dependent function. We finish the review by discussing the future challenges facing the membrane protein community regarding protein disorder.
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Affiliation(s)
- Magnus Kjaergaard
- Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Aarhus, Denmark.
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
- Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark.
- The Danish Research Institute of Translational Neuroscience (DANDRITE), Aarhus, Denmark.
| | - Birthe B Kragelund
- Structural Biology and NMR Laboratory and The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark
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14
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Zhou Y, Shi X, Chen H, Zhang S, Salker MS, Mack AF, Föller M, Mak TW, Singh Y, Lang F. DJ-1/Park7 Sensitive Na + /H + Exchanger 1 (NHE1) in CD4 + T Cells. J Cell Physiol 2017; 232:3050-3059. [PMID: 27509531 DOI: 10.1002/jcp.25516] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Accepted: 08/09/2016] [Indexed: 01/03/2023]
Abstract
DJ-1/Park7 is a redox-sensitive chaperone protein counteracting oxidation and presumably contributing to the control of oxidative stress responses and thus inflammation. DJ-1 gene deletion exacerbates the progression of Parkinson's disease presumably by augmenting oxidative stress. Formation of reactive oxygen species (ROS) is paralleled by activation of the Na+ /H+ exchanger 1 (NHE1). ROS formation in CD4+ T cells plays a decisive role in regulating inflammatory responses. In the present study, we explored whether DJ-1 is expressed in CD4+ T cells, and affects ROS production as well as NHE1 in those cells. To this end, DJ-1 and NHE1 transcript, and protein levels were quantified by qRT-PCR and Western blotting, respectively, intracellular pH (pHi ) utilizing bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence, NHE activity from realkalinization after an ammonium pulse, and ROS production utilizing 2',7' -dichlorofluorescin diacetate (DCFDA) fluorescence. As a result DJ-1 was expressed in CD4+ T cells. ROS formation, NHE1 transcript levels, NHE1 protein, and NHE activity were higher in CD4+ T cells from DJ-1 deficient mice than in CD4+ T cells from wild type mice. Antioxidant N-acetyl-cysteine (NAC) and protein tyrosine kinase (PTK) inhibitor staurosporine decreased the NHE activity in DJ-1 deficient CD4+ T cells, and blunted the difference between DJ-1-/- and DJ-1+/+ CD4+ T cells, an observation pointing to a role of ROS in the up-regulation of NHE1 in DJ-1-/- CD4+ T cells. In conclusion, DJ-1 is a powerful regulator of ROS production as well as NHE1 expression and activity in CD4+ T cells. J. Cell. Physiol. 232: 3050-3059, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Yuetao Zhou
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
| | - Xiaolong Shi
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
| | - Hong Chen
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
| | - Shaqiu Zhang
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany.,Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan, China
| | - Madhuri S Salker
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
| | - Andreas F Mack
- Institute of Clinical Anatomy and Cell Analysis, Eberhard-Karls-University, Tübingen, Germany
| | - Michael Föller
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany.,Campbell Family Institute for Breast Cancer Research, Ontario Cancer Institute, UHN, Toronto, Canada.,Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Tak W Mak
- Campbell Family Institute for Breast Cancer Research, Ontario Cancer Institute, UHN, Toronto, Canada
| | - Yogesh Singh
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
| | - Florian Lang
- Department of Cardiology, Vascular Medicine and Physiology, Eberhard-Karls-University, Tübingen, Germany
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15
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Webb BA, White KA, Grillo-Hill BK, Schönichen A, Choi C, Barber DL. A Histidine Cluster in the Cytoplasmic Domain of the Na-H Exchanger NHE1 Confers pH-sensitive Phospholipid Binding and Regulates Transporter Activity. J Biol Chem 2016; 291:24096-24104. [PMID: 27650500 DOI: 10.1074/jbc.m116.736215] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 09/18/2016] [Indexed: 01/26/2023] Open
Abstract
The Na-H exchanger NHE1 contributes to intracellular pH (pHi) homeostasis in normal cells and the constitutively increased pHi in cancer. NHE1 activity is allosterically regulated by intracellular protons, with greater activity at lower pHi However, the molecular mechanism for pH-dependent NHE1 activity remains incompletely resolved. We report that an evolutionarily conserved cluster of histidine residues located in the C-terminal cytoplasmic domain between two phosphatidylinositol 4,5-bisphosphate binding sites (PI(4,5)P2) of NHE1 confers pH-dependent PI(4,5)P2 binding and regulates NHE1 activity. A GST fusion of the wild type C-terminal cytoplasmic domain of NHE1 showed increased maximum PI(4,5)P2 binding at pH 7.0 compared with pH 7.5. However, pH-sensitive binding is abolished by substitutions of the His-rich cluster to arginine (RXXR3) or alanine (AXXA3), mimicking protonated and neutral histidine residues, respectively, and the RXXR3 mutant had significantly greater PI(4,5)P2 binding than AXXA3. When expressed in cells, NHE1 activity and pHi were significantly increased with NHE1-RXXR3 and decreased with NHE1-AXXA3 compared with wild type NHE1. Additionally, fibroblasts expressing NHE1-RXXR3 had significantly more contractile actin filaments and focal adhesions compared with fibroblasts expressing wild type NHE1, consistent with increased pHi enabling cytoskeletal remodeling. These data identify a molecular mechanism for pH-sensitive PI(4,5)P2 binding regulating NHE1 activity and suggest that the evolutionarily conserved cluster of four histidines in the proximal cytoplasmic domain of NHE1 may constitute a proton modifier site. Moreover, a constitutively activated NHE1-RXXR3 mutant is a new tool that will be useful for studying how increased pHi contributes to cell behaviors, most notably the biology of cancer cells.
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Affiliation(s)
- Bradley A Webb
- From the Department of Cell and Tissue Biology, University of California, San Francisco, California 94143 and
| | - Katharine A White
- From the Department of Cell and Tissue Biology, University of California, San Francisco, California 94143 and
| | - Bree K Grillo-Hill
- From the Department of Cell and Tissue Biology, University of California, San Francisco, California 94143 and
| | - André Schönichen
- From the Department of Cell and Tissue Biology, University of California, San Francisco, California 94143 and
| | - Changhoon Choi
- the Department of Radiation Oncology, Samsung Medical Center, Seoul, South Korea 06351
| | - Diane L Barber
- From the Department of Cell and Tissue Biology, University of California, San Francisco, California 94143 and
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16
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Singh Y, Zhou Y, Shi X, Zhang S, Umbach AT, Salker MS, Lang KS, Lang F. Alkaline Cytosolic pH and High Sodium Hydrogen Exchanger 1 (NHE1) Activity in Th9 Cells. J Biol Chem 2016; 291:23662-23671. [PMID: 27629415 DOI: 10.1074/jbc.m116.730259] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Indexed: 01/05/2023] Open
Abstract
CD4+ T helper 9 (Th9) cells are a newly discovered Th cell subset that produce the pleiotropic cytokine IL-9. Th9 cells can protect against tumors and provide resistance against helminth infections. Given their pivotal role in the adaptive immune system, understanding Th9 cell development and the regulation of IL-9 production could open novel immunotherapeutic opportunities. The Na+/H+ exchanger 1 (NHE1; gene name Slc9α1)) is critically important for regulating intracellular pH (pHi), cell volume, migration, and cell survival. The pHi influences cytokine secretion, activities of membrane-associated enzymes, ion transport, and other effector signaling molecules such as ATP and Ca2+ levels. However, whether NHE1 regulates Th9 cell development or IL-9 secretion has not yet been defined. The present study explored the role of NHE1 in Th9 cell development and function. Th cell subsets were characterized by flow cytometry and pHi was measured using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-acetoxymethyl ester (BCECF-AM) dye. NHE1 functional activity was estimated from the rate of realkalinization following an ammonium pulse. Surprisingly, in Th9 cells pHi and NHE1 activity were significantly higher than in all other Th cell subsets (Th1/Th2/Th17 and induced regulatory T cells (iTregs)). NHE1 transcript levels and protein abundance were significantly higher in Th9 cells than in other Th cell subsets. Inhibition of NHE1 by siRNA-NHE1 or with cariporide in Th9 cells down-regulated IL-9 and ATP production. NHE1 activity, Th9 cell development, and IL-9 production were further blunted by pharmacological inhibition of protein kinase Akt1/Akt2. Our findings reveal that Akt1/Akt2 control of NHE1 could be an important physiological regulator of Th9 cell differentiation, IL-9 secretion, and ATP production.
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Affiliation(s)
- Yogesh Singh
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany,
| | - Yuetao Zhou
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany
| | - Xiaolong Shi
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany
| | - Shaqiu Zhang
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany.,the Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China, and
| | - Anja T Umbach
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany
| | - Madhuri S Salker
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany
| | - Karl S Lang
- the Institute of Immunology, Medical Faculty, University of Duisburg-Essen, Hufelandstraße 55, 45147 Essen, Germany
| | - Florian Lang
- From the Departments of Cardiology, Cardiovascular Medicine and Physiology, Eberhard-Karls-Tübingen University, Tübingen, Gmelinstraße5, D-72076 Tübingen, Germany,
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17
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Wu Y, Zhang M, Liu R, Zhao C. Oxidative Stress-Activated NHE1 Is Involved in High Glucose-Induced Apoptosis in Renal Tubular Epithelial Cells. Yonsei Med J 2016; 57:1252-9. [PMID: 27401659 PMCID: PMC4960394 DOI: 10.3349/ymj.2016.57.5.1252] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 01/14/2016] [Accepted: 02/17/2016] [Indexed: 11/27/2022] Open
Abstract
PURPOSE Diabetic nephropathy (DN) is a prevalent chronic microvascular complication of diabetes mellitus involving disturbances in electrolytes and the acid-base balance caused by a disorder of glucose metabolism. NHE1 is a Na⁺/H⁺ exchanger responsible for keeping intracellular pH (pHi) balance and cell growth. Our study aimed to investigate roles of NHE1 in high glucose (HG)-induced apoptosis in renal tubular epithelial cells. MATERIALS AND METHODS Renal epithelial tubular cell line HK-2 was cultured in medium containing 5 mM or 30 mM glucose. Then, cell apoptosis, oxidative stress, NHE1 expression, and pHi were evaluated. NHE1 siRNA and inhibitor were used to evaluate its role in cell apoptosis. RESULTS HG significantly increased cell apoptosis and the production of reactive oxygen species (ROS) and 8-OHdG (p<0.05). Meanwhile, we found that HG induced the expression of NHE1 and increased the pHi from 7.0 to 7.6 after 48 h of incubation. However, inhibiting NHE1 using its specific siRNA or antagonist DMA markedly reduced cell apoptosis stimulated by HG. In addition, suppressing cellular oxidative stress using antioxidants, such as glutathione and N-acetyl cysteine, significantly reduced the production of ROS, accompanied by a decrease in NHE1. We also found that activated cyclic GMP-Dependent Protein Kinase Type I (PKG) signaling promoted the production of ROS, which contributed to the regulation of NHE1 functions. CONCLUSION Our study indicated that HG activates PKG signaling and elevates the production of ROS, which was responsible for the induction of NHE1 expression and dysfunction, as well as subsequent cell apoptosis, in renal tubular epithelial cells.
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Affiliation(s)
- Yiqing Wu
- Department of Nephrology, Tianjin Union Medicine Center, Tianjin, China
| | - Min Zhang
- Department of Nephrology, Tianjin Union Medicine Center, Tianjin, China
| | - Rui Liu
- Department of Rehabilitation, Tangdu Hospital, Fourth Military Medical University, Xi'an, China
| | - Chunjie Zhao
- Department of Cardiology, Tianjin Union Medicine Center, Tianjin, China.
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18
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Abstract
The longstanding focus in chronic kidney disease (CKD) research has been on the glomerulus, which is sensible because this is where glomerular filtration occurs, and a large proportion of progressive CKD is associated with significant glomerular pathology. However, it has been known for decades that tubular atrophy is also a hallmark of CKD and that it is superior to glomerular pathology as a predictor of glomerular filtration rate decline in CKD. Nevertheless, there are vastly fewer studies that investigate the causes of tubular atrophy, and fewer still that identify potential therapeutic targets. The purpose of this review is to discuss plausible mechanisms of tubular atrophy, including tubular epithelial cell apoptosis, cell senescence, peritubular capillary rarefaction and downstream tubule ischemia, oxidative stress, atubular glomeruli, epithelial-to-mesenchymal transition, interstitial inflammation, lipotoxicity and Na(+)/H(+) exchanger-1 inactivation. Once a a better understanding of tubular atrophy (and interstitial fibrosis) pathophysiology has been obtained, it might then be possible to consider tandem glomerular and tubular therapeutic strategies, in a manner similar to cancer chemotherapy regimens, which employ multiple drugs to simultaneously target different mechanistic pathways.
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19
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Mohamed IA, Mraiche F. Targeting osteopontin, the silent partner of Na+/H+ exchanger isoform 1 in cardiac remodeling. J Cell Physiol 2015; 230:2006-18. [PMID: 25677682 DOI: 10.1002/jcp.24958] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 02/06/2015] [Indexed: 12/11/2022]
Abstract
Cardiac hypertrophy (CH), characterized by the enlargement of cardiomyocytes, fibrosis and apoptosis, contributes to cardiac remodeling, which if left unresolved results in heart failure. Understanding the signaling pathways underlying CH is necessary to identify potential therapeutic targets. The Na(+) /H(+) -exchanger isoform I (NHE1), a ubiquitously expressed glycoprotein and cardiac specific isoform, regulates intracellular pH. Recent studies have demonstrated that enhanced expression/activity of NHE1 contributes to cardiac remodeling and CH. Inhibition of NHE1 in both in vitro and in vivo models have suggested that inhibition of NHE1 protects against hypertrophy. However, clinical trials using NHE1 inhibitors have proven to be unsuccessful, suggesting that additional factors maybe contributing to cardiac remodeling. Recent studies have indicated that the upregulation of NHE1 is associated with enhanced levels of osteopontin (OPN) in the setting of CH. OPN has been demonstrated to be upregulated in left ventricular hypertrophy, dilated cardiomyopathy and in diabetic cardiomyopathy. The cellular interplay between OPN and NHE1 in the setting of CH remains unknown. This review focuses on the role of NHE1 and OPN in cardiac remodeling and emphasizes the signaling pathways implicating OPN in the NHE1-induced hypertrophic response.
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20
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Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule. Cell Mol Life Sci 2015; 72:2061-74. [PMID: 25680790 DOI: 10.1007/s00018-015-1848-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 01/28/2015] [Accepted: 01/29/2015] [Indexed: 01/17/2023]
Abstract
The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.
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21
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Lakhe-Reddy S, Li V, Arnold TD, Khan S, Schelling JR. Mesangial cell αvβ8-integrin regulates glomerular capillary integrity and repair. Am J Physiol Renal Physiol 2014; 306:F1400-9. [PMID: 24740792 DOI: 10.1152/ajprenal.00624.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
αvβ8-Integrin is most abundantly expressed in the kidney, brain, and female reproductive organs, and its cognate ligand is latent transforming growth factor (LTGF)-β. Kidney αvβ8-integrin localizes to mesangial cells, and global β8-integrin gene (Itgb8) deletion results in embryonic lethality due to impaired placentation and cerebral hemorrhage. To circumvent the lethality and better define kidney αvβ8-integrin function, Cre-lox technology was used to generate mesangial-specific Itgb8-null mice. Platelet-derived growth factor-β receptor (PDGFBR)-Cre mice crossed with a reporter strain revealed functional Cre recombinase activity in a predicted mesangial pattern. However, mating between two different PDGFBR-Cre or Ren1(d)-Cre strains with Itgb8 (flox/-) mice consistently resulted in incomplete recombination, with no renal phenotype in mosaic offspring. Induction of a renal phenotype with Habu snake venom, a reversible mesangiolytic agent, caused exaggerated glomerular capillary microaneurysms and delayed recovery in Cre(+/-) PDGFRB (flox/-) mice compared with Cre(+/-) PDGFRB (flox/+) control mice. To establish the mechanism, in vitro experiments were conducted in Itgb8-null versus Itgb8-expressing mesangial cells and fibroblasts, which revealed β8-integrin-regulated adhesion to Arg-Gly-Asp (RGD) peptides within a mesangial-conditioned matrix as well as β8-integrin-dependent migration on RGD-containing LTGF-β or vitronectin matrices. We speculate that kidney αvβ8-integrin indirectly controls glomerular capillary integrity through mechanical tension generated by binding RGD peptides in the mesangial matrix, and healing after glomerular injury may be facilitated by mesangial cell migration, which is guided by transient β8-integrin interactions with RGD ligands.
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Affiliation(s)
- Sujata Lakhe-Reddy
- Department of Medicine, Case Western Reserve University, Rammelkamp Center for Research, MetroHealth Medical Center, Cleveland, Ohio; and
| | - Vincent Li
- Department of Medicine, Case Western Reserve University, Rammelkamp Center for Research, MetroHealth Medical Center, Cleveland, Ohio; and
| | - Thomas D Arnold
- Department of Pediatrics, University of California, San Francisco, California
| | - Shenaz Khan
- Department of Medicine, Case Western Reserve University, Rammelkamp Center for Research, MetroHealth Medical Center, Cleveland, Ohio; and
| | - Jeffrey R Schelling
- Department of Medicine, Case Western Reserve University, Rammelkamp Center for Research, MetroHealth Medical Center, Cleveland, Ohio; and
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22
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Khundmiri SJ, Salyer SA, Farmer B, Qipshidze-Kelm N, Murray RD, Clark BJ, Xie Z, Pressley TA, Lederer ED. Structural determinants for the ouabain-stimulated increase in Na-K ATPase activity. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1089-102. [PMID: 24566089 DOI: 10.1016/j.bbamcr.2014.02.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 02/06/2014] [Accepted: 02/12/2014] [Indexed: 01/11/2023]
Abstract
Recent studies suggest that at low concentrations, ouabain increases Na-K ATPase and NHE1 activity and activates the Src signaling cascade in proximal tubule cells. Our laboratory demonstrated that low concentrations of ouabain increase blood pressure in rats. We hypothesize that ouabain-induced increase in blood pressure and Na-K ATPase activity requires NHE1 activity and association. To test this hypothesis we treated rats with ouabain (1μgkg body wt(-1)day(-1)) for 9days in the presence or absence of the NHE1 inhibitor, zoniporide. Ouabain stimulated a significant increase in blood pressure which was prevented by zoniporide. Using NHE1-expressing Human Kidney cells 2 (HK2), 8 (HK8) and 11 (HK11) and Mouse Kidney cells from Wild type (WT) and NHE1 knock-out mice (SWE) cell lines, we show that ouabain stimulated Na-K ATPase activity and surface expression in a Src-dependent manner in NHE1-expressing cells but not in NHE1-deplete cells. Zoniporide prevented ouabain-induced stimulation of (86)Rb uptake in the NHE1-expressing cells. FRET and TIRF microscopy showed that ouabain increased association between GFP-NHE1 and mCherry-Na-K ATPase transfected into NHE1-deficient SWE cells. Mutational analysis demonstrated that the caveolin binding motif (CBM) of Na-K ATPase α1 is required for translocation of both Na-K ATPase α1 and NHE1 to the basolateral membrane. Mutations in activity or scaffold domains of NHE1 resulted in loss of ouabain-mediated regulation of Na-K ATPase. These results support that NHE1 is required for the ouabain-induced increase in blood pressure, and that the caveolin binding motif of Na-K ATPase α1 as well as the activity and scaffolding domains of NHE1 are required for their functional association.
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Affiliation(s)
- Syed J Khundmiri
- Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA; Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, KY, USA; Department of Physiology, University of Louisville, Louisville, KY, USA.
| | - Sarah A Salyer
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, KY, USA; Department of Physiology, University of Louisville, Louisville, KY, USA
| | - Brandon Farmer
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, KY, USA
| | | | - Rebecca D Murray
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, KY, USA; Department of Physiology, University of Louisville, Louisville, KY, USA
| | - Barbara J Clark
- Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY, USA
| | - Zijian Xie
- Department of Physiology, University of Toledo College of Medicine, Toledo, OH, USA
| | - Thomas A Pressley
- Department of Cell Physiology and Molecular Biophysics, Texas Tech Univ. Health Sciences Center, Lubbock, TX, USA
| | - Eleanor D Lederer
- Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA; Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, KY, USA; Department of Physiology, University of Louisville, Louisville, KY, USA
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23
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Khan S, Abu Jawdeh BG, Goel M, Schilling WP, Parker MD, Puchowicz MA, Yadav SP, Harris RC, El-Meanawy A, Hoshi M, Shinlapawittayatorn K, Deschênes I, Ficker E, Schelling JR. Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis. J Clin Invest 2014; 124:1057-68. [PMID: 24531551 DOI: 10.1172/jci71863] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 12/11/2013] [Indexed: 12/12/2022] Open
Abstract
Chronic kidney disease progression can be predicted based on the degree of tubular atrophy, which is the result of proximal tubule apoptosis. The Na+/H+ exchanger NHE1 regulates proximal tubule cell survival through interaction with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], but pathophysiologic triggers for NHE1 inactivation are unknown. Because glomerular injury permits proximal tubule luminal exposure and reabsorption of fatty acid/albumin complexes, we hypothesized that accumulation of amphipathic, long-chain acyl-CoA (LC-CoA) metabolites stimulates lipoapoptosis by competing with the structurally similar PI(4,5)P2 for NHE1 binding. Kidneys from mouse models of progressive, albuminuric kidney disease exhibited increased fatty acids, LC-CoAs, and caspase-2-dependent proximal tubule lipoapoptosis. LC-CoAs and the cytosolic domain of NHE1 directly interacted, with an affinity comparable to that of the PI(4,5)P2-NHE1 interaction, and competing LC-CoAs disrupted binding of the NHE1 cytosolic tail to PI(4,5)P2. Inhibition of LC-CoA catabolism reduced NHE1 activity and enhanced apoptosis, whereas inhibition of proximal tubule LC-CoA generation preserved NHE1 activity and protected against apoptosis. Our data indicate that albuminuria/lipiduria enhances lipotoxin delivery to the proximal tubule and accumulation of LC-CoAs contributes to tubular atrophy by severing the NHE1-PI(4,5)P2 interaction, thereby lowering the apoptotic threshold. Furthermore, these data suggest that NHE1 functions as a metabolic sensor for lipotoxicity.
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Hendus-Altenburger R, Kragelund BB, Pedersen SF. Structural dynamics and regulation of the mammalian SLC9A family of Na⁺/H⁺ exchangers. CURRENT TOPICS IN MEMBRANES 2014; 73:69-148. [PMID: 24745981 DOI: 10.1016/b978-0-12-800223-0.00002-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mammalian Na⁺/H⁺ exchangers of the SLC9A family are widely expressed and involved in numerous essential physiological processes. Their primary function is to mediate the 1:1 exchange of Na⁺ for H⁺ across the membrane in which they reside, and they play central roles in regulation of body, cellular, and organellar pH. Their function is tightly regulated through mechanisms involving interactions with multiple protein and lipid-binding partners, phosphorylations, and other posttranslational modifications. Biochemical and mutational analyses indicate that the SLC9As have a short intracellular N-terminus, 12 transmembrane (TM) helices necessary and sufficient for ion transport, and a C-terminal cytoplasmic tail region with essential regulatory roles. No high-resolution structures of the SLC9As exist; however, models based on crystal structures of the bacterial NhaAs support the 12 TM organization and suggest that TMIV and XI may form a central part of the ion-translocation pathway, whereas pH sensing may involve TMII, TMIX, and several intracellular loops. Similar to most ion transporters studied, SLC9As likely exist as coupled dimers in the membrane, and this appears to be important for the well-studied cooperativity of H⁺ binding. The aim of this work is to summarize and critically discuss the currently available evidence on the structural dynamics, regulation, and binding partner interactions of SLC9As, focusing in particular on the most widely studied isoform, SLC9A1/NHE1. Further, novel bioinformatic and structural analyses are provided that to some extent challenge the existing paradigm on how ions are transported by mammalian SLC9As.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark; Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Birthe B Kragelund
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Stine Falsig Pedersen
- Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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Shimada-Shimizu N, Hisamitsu T, Nakamura TY, Hirayama N, Wakabayashi S. Na+/H+ exchanger 1 is regulated via its lipid-interacting domain, which functions as a molecular switch: a pharmacological approach using indolocarbazole compounds. Mol Pharmacol 2013; 85:18-28. [PMID: 24136992 DOI: 10.1124/mol.113.089268] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The plasma membrane Na(+)/H(+) exchanger 1 (NHE1) is rapidly activated in response to various stimuli. The membrane-proximal cytoplasmic region (∼60 residues), termed the lipid-interacting domain (LID), is an important regulatory domain of NHE1. Here, we used a pharmacological approach to further characterize the role of LID in the regulation of NHE1. Pharmacological analysis using staurosporine-like indolocarbazole and bisindolylmaleimide compounds suggested that the phorbol ester- and receptor agonist-induced activation of NHE1 occurs through a protein kinase C-independent mechanism. In particular, only indolocarbazole compounds that inhibited NHE1 activation were able to interact with the LID, suggesting that the inhibition of NHE1 activation is achieved through the direct action of these compounds on the LID. Furthermore, in addition to phorbol esters and a receptor agonist, okadaic acid and hyperosmotic stress, which are known to activate NHE1 through unknown mechanisms, were found to promote membrane association of the LID concomitant with NHE1 activation; these effects were inhibited by staurosporine, as well as by a mutation in the LID. Binding experiments using the fluorescent ATP analog trinitrophenyl ATP revealed that ATP and the NHE1 activator phosphatidylinositol 4,5-bisphosphate bind competitively to the LID. These findings suggest that modulation of NHE1 activity by various activators and inhibitors occurs through the direct binding of these molecules to the LID, which alters the association of the LID with the plasma membrane.
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Affiliation(s)
- Naoko Shimada-Shimizu
- Department of Molecular Physiology, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan (N.S.-S., T.H., T.Y.N., S.W.); and Basic Medical Science & Molecular Medicine, Tokai University School of Medicine, Kanagawa, Japan (N.H.)
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Jalimarada SS, Ogando DG, Vithana EN, Bonanno JA. Ion transport function of SLC4A11 in corneal endothelium. Invest Ophthalmol Vis Sci 2013; 54:4330-40. [PMID: 23745003 DOI: 10.1167/iovs.13-11929] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE Mutations in SLC4A11, a member of the SLC4 superfamily of bicarbonate transporters, give rise to corneal endothelial cell dystrophies. SLC4A11 is a putative Na⁺ borate and Na⁺:OH⁻ transporter. Therefore we ask whether SLC4A11 in corneal endothelium transports borate (B[OH]₄⁻), bicarbonate (HCO3⁻), or hydroxyl (OH⁻) anions coupled to Na⁺. METHODS SLC4A11 expression in cultured primary bovine corneal endothelial cells (BCECs) was determined by semiquantitative PCR, SDS-PAGE/Western blotting, and immunofluorescence staining. Ion transport function was examined by measuring intracellular pH (pHi) or Na⁺ ([Na⁺](i)) in response to Ringer solutions with/without B(OH)₄⁻ or HCO₃⁻ after overexpressing or small interfering RNA (siRNA) silencing of SLC4A11. RESULTS SLC4A11 is localized to the basolateral membrane in BCEC. B(OH)₄⁻ (2.5-10 mM) in bicarbonate-free Ringer induced a rapid small acidification (0.01 pH unit) followed by alkalinization (0.05-0.1 pH unit), consistent with diffusion of boric acid into the cell followed by B(OH)₄⁻. However, the rate of B(OH)₄⁻-induced pHi change was unaffected by overexpression of SLC4A11. B(OH)₄⁻ did not induce significant changes in resting [Na⁺(i)] or the amplitude and rate of acidification caused by Na⁺ removal. siRNA-mediated knockdown of SLC4A11 (∼70%) did not alter pHi responses to CO₂/HCO₃⁻-rich Ringer, Na⁺-free induced acidification, or the rate of Na⁺ influx in the presence of bicarbonate. However, in the absence of bicarbonate, siSLC4A11 knockdown significantly decreased the rate (43%) and amplitude (48%) of acidification due to Na⁺ removal and recovery (53%) upon add-back. Additionally, the rate of acid recovery following NH₄⁺ prepulse was decreased significantly (27%) by SLC4A11 silencing. CONCLUSIONS In corneal endothelium, SLC4A11 displays robust Na⁺-coupled OH⁻ transport, but does not transport B(OH)₄⁻ or HCO₃⁻.
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Provost JJ, Wallert MA. Inside out: targeting NHE1 as an intracellular and extracellular regulator of cancer progression. Chem Biol Drug Des 2013; 81:85-101. [PMID: 23253131 DOI: 10.1111/cbdd.12035] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The sodium hydrogen exchanger isoform one is a critical regulator of intracellular pH, serves as an anchor for the formation of cytoplasmic signaling complexes, and modulates cytoskeletal organization. There is a growing interest in the potential for sodium hydrogen exchanger isoform one as a therapeutic target against cancer. Sodium hydrogen exchanger isoform one transport drives formation of membrane protrusions essential for cell migration and contributes to the establishment of a tumor microenvironment that leads to the rearrangement of the extracellular matrix further supporting tumor progression. Here, we focus on the potential impact that an inexpensive, $100 genome would have in identifying prospective therapeutic targets to treat tumors based upon changes in gene expression and variation of sodium hydrogen exchanger isoform one regulators. In particular, we will focus on the ezrin, radixin, moesin family proteins, calcineurin B homologous proteins, Ras/Raf/MEK/ERK signaling, and phosphoinositide signaling as they relate to the regulation of sodium hydrogen exchanger isoform one in cancer progression.
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Affiliation(s)
- Joseph J Provost
- Center for Biopharmaceutical Research and Production, North Dakota State University, Fargo, ND 58102, USA.
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Watts BA, George T, Good DW. Lumen LPS inhibits HCO3(-) absorption in the medullary thick ascending limb through TLR4-PI3K-Akt-mTOR-dependent inhibition of basolateral Na+/H+ exchange. Am J Physiol Renal Physiol 2013; 305:F451-62. [PMID: 23698118 DOI: 10.1152/ajprenal.00102.2013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Sepsis and endotoxemia induce defects in renal tubule function, but the mechanisms are poorly understood. Recently, we demonstrated that lipopolysaccharide (LPS) inhibits HCO3(-) absorption in the medullary thick ascending limb (MTAL) through activation of different Toll-like receptor 4 (TLR4) signaling pathways in the basolateral and apical membranes. Basolateral LPS inhibits HCO3(-) absorption through ERK-dependent inhibition of the apical Na(+)/H(+) exchanger NHE3. Here, we examined the mechanisms of inhibition by lumen LPS. Adding LPS to the lumen decreased HCO3(-) absorption by 29% in rat and mouse MTALs perfused in vitro. Inhibitors of phosphoinositide 3-kinase (PI3K) or its effectors Akt and mammalian target of rapamycin (mTOR) eliminated inhibition of HCO3(-) absorption by lumen LPS but had no effect on inhibition by bath LPS. Exposure to LPS for 15 min induced increases in phosphorylation of Akt and mTOR in microdissected MTALs that were blocked by wortmannin, consistent with activation of Akt and mTOR downstream of PI3K. The effects of lumen LPS to activate Akt and inhibit HCO3(-) absorption were eliminated in MTALs from TLR4(-/-) and MyD88(-/-) mice but preserved in tubules lacking Trif or CD14. Inhibition of HCO3(-) absorption by lumen LPS was eliminated under conditions that inhibit basolateral Na(+)/H(+) exchange and prevent inhibition of HCO3(-) absorption mediated through NHE1. Lumen LPS decreased basolateral Na(+)/H(+) exchange activity through PI3K. We conclude that lumen LPS inhibits HCO3(-) absorption in the MTAL through TLR4/MyD88-dependent activation of a PI3K-Akt-mTOR pathway coupled to inhibition of NHE1. Molecular components of the TLR4-PI3K-mTOR pathway represent potential therapeutic targets for sepsis-induced renal tubule dysfunction.
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Affiliation(s)
- Bruns A Watts
- Div. of Nephrology, 4.200 John Sealy Annex, The Univ. of Texas Medical Branch, 301 Univ. Blvd., Galveston, TX 77555-0562.
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Regulation of the cardiac Na⁺/H⁺ exchanger in health and disease. J Mol Cell Cardiol 2013; 61:68-76. [PMID: 23429007 DOI: 10.1016/j.yjmcc.2013.02.007] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 02/07/2013] [Accepted: 02/11/2013] [Indexed: 11/21/2022]
Abstract
The Na(+) gradient produced across the cardiac sarcolemma by the ATP-dependent Na(+)-pump is a constant source of energy for Na(+)-dependent transporters. The plasma membrane Na(+)/H(+) exchanger (NHE) is one such secondary active transporter, regulating intracellular pH, Na(+) concentration, and cell volume. NHE1, the major isoform found in the heart, is activated in response to a variety of stimuli such as hormones and mechanical stress. This important characteristic of NHE1 is intimately linked to heart diseases, including maladaptive cardiac hypertrophy and subsequent heart failure, as well as acute ischemic-reperfusion injury. NHE1 activation results in elevation of pH and intracellular Na(+) concentration, which potentially enhance downstream signaling cascades in the myocardium. Therefore, in addition to determining the mechanism underlying regulation of NHE1 activity, it is important to understand how the ionic signal produced by NHE1 is transmitted to the downstream targets. Extensive studies have identified many accessory factors that interact with NHE1. Here, we have summarized the recent progress on understanding the molecular mechanism underlying NHE1 regulation and have shown a possible signaling pathway leading to cardiac remodeling, which is initiated from NHE1. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".
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