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Zhong J, Dong J, Ruan W, Duan X. Potential Theranostic Roles of SLC4 Molecules in Human Diseases. Int J Mol Sci 2023; 24:15166. [PMID: 37894847 PMCID: PMC10606849 DOI: 10.3390/ijms242015166] [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: 08/29/2023] [Revised: 09/28/2023] [Accepted: 10/03/2023] [Indexed: 10/29/2023] Open
Abstract
The solute carrier family 4 (SLC4) is an important protein responsible for the transport of various ions across the cell membrane and mediating diverse physiological functions, such as the ion transporting function, protein-to-protein interactions, and molecular transduction. The deficiencies in SLC4 molecules may cause multisystem disease involving, particularly, the respiratory system, digestive, urinary, endocrine, hematopoietic, and central nervous systems. Currently, there are no effective strategies to treat these diseases. SLC4 proteins are also found to contribute to tumorigenesis and development, and some of them are regarded as therapeutic targets in quite a few clinical trials. This indicates that SLC4 proteins have potential clinical prospects. In view of their functional characteristics, there is a critical need to review the specific functions of bicarbonate transporters, their related diseases, and the involved pathological mechanisms. We summarize the diseases caused by the mutations in SLC4 family genes and briefly introduce the clinical manifestations of these diseases as well as the current treatment strategies. Additionally, we illustrate their roles in terms of the physiology and pathogenesis that has been currently researched, which might be the future therapeutic and diagnostic targets of diseases and a new direction for drug research and development.
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Affiliation(s)
| | | | | | - Xiaohong Duan
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Disease, Shaanxi Key Laboratory of Stomatology, Department of Oral Biology & Clinic of Oral Rare Diseases and Genetic Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an 710032, China; (J.Z.); (J.D.); (W.R.)
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Imenez Silva PH, Unwin R, Hoorn EJ, Ortiz A, Trepiccione F, Nielsen R, Pesic V, Hafez G, Fouque D, Massy ZA, De Zeeuw CI, Capasso G, Wagner CA. Acidosis, cognitive dysfunction and motor impairments in patients with kidney disease. Nephrol Dial Transplant 2021; 37:ii4-ii12. [PMID: 34718761 PMCID: PMC8713149 DOI: 10.1093/ndt/gfab216] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Indexed: 12/20/2022] Open
Abstract
Metabolic acidosis, defined as a plasma or serum bicarbonate concentration <22 mmol/L, is a frequent consequence of chronic kidney disease (CKD) and occurs in ~10–30% of patients with advanced stages of CKD. Likewise, in patients with a kidney transplant, prevalence rates of metabolic acidosis range from 20% to 50%. CKD has recently been associated with cognitive dysfunction, including mild cognitive impairment with memory and attention deficits, reduced executive functions and morphological damage detectable with imaging. Also, impaired motor functions and loss of muscle strength are often found in patients with advanced CKD, which in part may be attributed to altered central nervous system (CNS) functions. While the exact mechanisms of how CKD may cause cognitive dysfunction and reduced motor functions are still debated, recent data point towards the possibility that acidosis is one modifiable contributor to cognitive dysfunction. This review summarizes recent evidence for an association between acidosis and cognitive dysfunction in patients with CKD and discusses potential mechanisms by which acidosis may impact CNS functions. The review also identifies important open questions to be answered to improve prevention and therapy of cognitive dysfunction in the setting of metabolic acidosis in patients with CKD.
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Affiliation(s)
- Pedro H Imenez Silva
- Institute of Physiology, University of Zurich, Zürich, Switzerland.,National Center of Competence in Research NCCR Kidney.CH, Zürich, Switzerland
| | - Robert Unwin
- Department of Renal Medicine, Royal Free Hospital, University College London, London, UK
| | - Ewout J Hoorn
- Department of Internal Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Alberto Ortiz
- Department of Nephrology and Hypertension, IIS-Fundacion Jimenez Diaz, Universidad Autonoma de Madrid, Madrid, Spain
| | - Francesco Trepiccione
- Biogem Institute of Molecular Biology and Genetics, Ariano Irpino, Italy.,Department of Translational Medical Sciences, University of Campania "Luigi Vanvitelli," Naples, Italy
| | - Rikke Nielsen
- Department of Biomedicine-Anatomy, University of Aarhus, Aarhus, Denmark
| | - Vesna Pesic
- Department of Physiology, Faculty of Pharmacy, University of Belgrade, Belgrade, Serbia
| | - Gaye Hafez
- Department of Pharmacology, Faculty of Pharmacy, Altinbas University, Istanbul, Turkey
| | - Denis Fouque
- CarMeN, INSERM 1060, Université Claude Bernard Lyon 1, Lyon, France.,Service de Néphrologie, Lyon-Sud Hospital, Pierre-Bénite, France
| | - Ziad A Massy
- Department of Nephrology, Ambroise Paré University Hospital, Assistance Publique Hôpitaux de Paris, Boulogne-Billancourt, France.,Centre de Recherche en Epidémiologie et Santé des Populations, Institut National de la Santé et de la Recherche Médicale U1018-Team 5, Université de Versailles Saint-Quentin-en-Yvelines, University Paris Saclay, Villejuif, France
| | - Chris I De Zeeuw
- Department of Neuroscience, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands.,Netherlands Institute for Neuroscience, Royal Dutch Academy of Art and Science, Amsterdam, The Netherlands
| | - Giovambattista Capasso
- Biogem Institute of Molecular Biology and Genetics, Ariano Irpino, Italy.,Department of Translational Medical Sciences, University of Campania "Luigi Vanvitelli," Naples, Italy
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zürich, Switzerland.,National Center of Competence in Research NCCR Kidney.CH, Zürich, Switzerland
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3
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Du L, Zahra A, Jia M, Wang Q, Wu J. Understanding the Functional Expression of Na+-Coupled SLC4 Transporters in the Renal and Nervous Systems: A Review. Brain Sci 2021; 11:1276. [PMID: 34679341 PMCID: PMC8534249 DOI: 10.3390/brainsci11101276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 09/16/2021] [Accepted: 09/23/2021] [Indexed: 11/25/2022] Open
Abstract
Acid-base homeostasis is crucial for numerous physiological processes. Na+/HCO3- cotransporters (NBCs) belong to the solute carrier 4 (SLC4) family, which regulates intracellular pH as well as HCO3- absorption and secretion. However, knowledge of the structural functions of these proteins remains limited. Electrogenic NBC (NBCe-1) is thought to be the primary factor promoting the precise acid-base equilibrium in distinct cell types for filtration and reabsorption, as well as the function of neurons and glia. NBC dysregulation is strongly linked to several diseases. As such, the need for special drugs that interfere with the transmission function of NBC is becoming increasingly urgent. In this review, we focus on the structural and functional characteristics of NBCe1, and discuss the roles of NBCe1 in the kidney, central nervous system (CNS), and related disorders, we also summarize the research on NBC inhibitors. NBCe1 and the related pathways should be further investigated, so that new medications may be developed to address the related conditions.
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Affiliation(s)
- Le Du
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
| | - Aqeela Zahra
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
| | - Meng Jia
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
| | - Qun Wang
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
| | - Jianping Wu
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
- Health Science Center, Yangtze University, Jingzhou 434023, China
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4
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Elingaard-Larsen LO, Rolver MG, Sørensen EE, Pedersen SF. How Reciprocal Interactions Between the Tumor Microenvironment and Ion Transport Proteins Drive Cancer Progression. Rev Physiol Biochem Pharmacol 2020; 182:1-38. [PMID: 32737753 DOI: 10.1007/112_2020_23] [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: 12/18/2022]
Abstract
Solid tumors comprise two major components: the cancer cells and the tumor stroma. The stroma is a mixture of cellular and acellular components including fibroblasts, mesenchymal and cancer stem cells, endothelial cells, immune cells, extracellular matrix, and tumor interstitial fluid. The insufficient tumor perfusion and the highly proliferative state and dysregulated metabolism of the cancer cells collectively create a physicochemical microenvironment characterized by altered nutrient concentrations and varying degrees of hypoxia and acidosis. Furthermore, both cancer and stromal cells secrete numerous growth factors, cytokines, and extracellular matrix proteins which further shape the tumor microenvironment (TME), favoring cancer progression.Transport proteins expressed by cancer and stromal cells localize at the interface between the cells and the TME and are in a reciprocal relationship with it, as both sensors and modulators of TME properties. It has been amply demonstrated how acid-base and nutrient transporters of cancer cells enable their growth, presumably by contributing both to the extracellular acidosis and the exchange of metabolic substrates and waste products between cells and TME. However, the TME also impacts other transport proteins important for cancer progression, such as multidrug resistance proteins. In this review, we summarize current knowledge of the cellular and acellular components of solid tumors and their interrelationship with key ion transport proteins. We focus in particular on acid-base transport proteins with known or proposed roles in cancer development, and we discuss their relevance for novel therapeutic strategies.
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Affiliation(s)
- Line O Elingaard-Larsen
- Translational Type 2 Diabetes Research, Department of Clinical Research, Steno Diabetes Center Copenhagen, Gentofte, Denmark
| | - Michala G Rolver
- Section for Cell Biology and Physiology, Department of Biology, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Ester E Sørensen
- Section for Cell Biology and Physiology, Department of Biology, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Stine F Pedersen
- Section for Cell Biology and Physiology, Department of Biology, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
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Xie ZD, Guo YM, Ren MJ, Yang J, Wang SF, Xu TH, Chen LM, Liu Y. The Balance of [Formula: see text] Secretion vs. Reabsorption in the Endometrial Epithelium Regulates Uterine Fluid pH. Front Physiol 2018; 9:12. [PMID: 29422866 PMCID: PMC5788990 DOI: 10.3389/fphys.2018.00012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 01/05/2018] [Indexed: 12/26/2022] Open
Abstract
Uterine fluid contains a high concentration of HCO3- which plays an essential role in sperm capacitation and fertilization. In addition, the HCO3- concentration in uterine fluid changes periodically during the estrous cycle. It is well-known that the endometrial epithelium contains machineries involving the apical SLC26 family anion exchangers for secreting HCO3- into the uterine fluid. In the present study, we find for the first time that the electroneutral Na+/HCO3- cotransporter NBCn1 is expressed at the apical membrane of the endometrial epithelium. The protein abundance of the apical NBCn1 and that of the apical SLC26A4 and SLC26A6 are reciprocally regulated during the estrous cycle in the uterus. NBCn1 is most abundant at diestrus, whereas SLC26A4/A6 are most abundant at proestrus/estrus. In the ovariectomized mice, the expression of uterine NBCn1 is inhibited by β-estradiol, but stimulated by progesterone, whereas that of uterine SLC26A4/A6 is stimulated by β-estradiol. In vivo perfusion studies show that the endometrial epithelium is capable of both secreting and reabsorbing HCO3-. Moreover, the activity for HCO3- secretion by the endometrial epithelium is significantly higher at estrus than it is at diestrus. The opposite is true for HCO3- reabsorption. We conclude that the endometrial epithelium simultaneously contains the activity for HCO3- secretion involving the apical SLC26A4/A6 and the activity for HCO3- reabsorption involving the apical NBCn1, and that the acid-base homeostasis in the uterine fluid is regulated by the finely-tuned balance of the two activities.
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Affiliation(s)
- Zhang-Dong Xie
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Yi-Min Guo
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Mei-Juan Ren
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Jichun Yang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Shao-Fang Wang
- Wuhan National Laboratory for Optoelectronics, Britton Chance Center for Biomedical Photonics, Huazhong University of Science and Technology, Wuhan, China
| | - Tong-Hui Xu
- Wuhan National Laboratory for Optoelectronics, Britton Chance Center for Biomedical Photonics, Huazhong University of Science and Technology, Wuhan, China
| | - Li-Ming Chen
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Ying Liu
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
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Liu Y, Yang J, Chen LM. Structure and Function of SLC4 Family [Formula: see text] Transporters. Front Physiol 2015; 6:355. [PMID: 26648873 PMCID: PMC4664831 DOI: 10.3389/fphys.2015.00355] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 11/10/2015] [Indexed: 12/12/2022] Open
Abstract
The solute carrier SLC4 family consists of 10 members, nine of which are [Formula: see text] transporters, including three Na(+)-independent Cl(-)/[Formula: see text] exchangers AE1, AE2, and AE3, five Na(+)-coupled [Formula: see text] transporters NBCe1, NBCe2, NBCn1, NBCn2, and NDCBE, as well as "AE4" whose Na(+)-dependence remains controversial. The SLC4 [Formula: see text] transporters play critical roles in pH regulation and transepithelial movement of electrolytes with a broad range of demonstrated physiological relevances. Dysfunctions of these transporters are associated with a series of human diseases. During the past decades, tremendous amount of effort has been undertaken to investigate the topological organization of the SLC4 transporters in the plasma membrane. Based upon the proposed topology models, mutational and functional studies have identified important structural elements likely involved in the ion translocation by the SLC4 transporters. In the present article, we review the advances during the past decades in understanding the structure and function of the SLC4 transporters.
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Affiliation(s)
- Ying Liu
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Jichun Yang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science CenterBeijing, China
| | - Li-Ming Chen
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
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Abstract
Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family.
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Affiliation(s)
- Christian Aalkjaer
- Department of Biomedicine, and the Water and Salt Research Center, Aarhus University, Aarhus, Denmark; Department of Physiology, Emory University School of Medicine, Atlanta, USA
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Blood-brain barrier Na transporters in ischemic stroke. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2014; 71:113-46. [PMID: 25307215 DOI: 10.1016/bs.apha.2014.06.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Blood-brain barrier (BBB) endothelial cells form a barrier that is highly restrictive to passage of solutes between blood and brain. Many BBB transport mechanisms have been described that mediate transcellular movement of solutes across the barrier either into or out of the brain. One class of BBB transporters that is all too often overlooked is that of the ion transporters. The BBB has a rich array of ion transporters and channels that carry Na, K, Cl, HCO3, Ca, and other ions. Many of these are asymmetrically distributed between the luminal and abluminal membranes, giving BBB endothelial cells the ability to perform vectorial transport of ions across the barrier between blood and brain. In this manner, the BBB performs the important function of regulating the volume and composition of brain interstitial fluid. Through functional coupling of luminal and abluminal transporters and channels, the BBB carries Na, Cl, and other ions from blood into brain, producing up to 30% of brain interstitial fluid in healthy brain. During ischemic stroke cerebral edema forms by processes involving increased activity of BBB luminal Na transporters, resulting in "hypersecretion" of Na, Cl, and water into the brain interstitium. This review discusses the roles of luminal BBB Na transporters in edema formation in stroke, with an emphasis on Na-K-Cl cotransport and Na/H exchange. Evidence that these transporters provide effective therapeutic targets for reduction of edema in stroke is also discussed, as are recent findings regarding signaling pathways responsible for ischemia stimulation of the BBB Na transporters.
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Christensen HL, Nguyen AT, Pedersen FD, Damkier HH. Na(+) dependent acid-base transporters in the choroid plexus; insights from slc4 and slc9 gene deletion studies. Front Physiol 2013; 4:304. [PMID: 24155723 PMCID: PMC3804831 DOI: 10.3389/fphys.2013.00304] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Accepted: 10/02/2013] [Indexed: 02/02/2023] Open
Abstract
The choroid plexus epithelium (CPE) is located in the ventricular system of the brain, where it secretes the majority of the cerebrospinal fluid (CSF) that fills the ventricular system and surrounds the central nervous system. The CPE is a highly vascularized single layer of cuboidal cells with an unsurpassed transepithelial water and solute transport rate. Several members of the slc4a family of bicarbonate transporters are expressed in the CPE. In the basolateral membrane the electroneutral Na+ dependent Cl−/HCO3− exchanger, NCBE (slc4a10) is expressed. In the luminal membrane, the electrogenic Na+:HCO3− cotransporter, NBCe2 (slc4a5) is expressed. The electroneutral Na+:HCO3− cotransporter, NBCn1 (slc4a7), has been located in both membranes. In addition to the bicarbonate transporters, the Na+/H+ exchanger, NHE1 (slc9a1), is located in the luminal membrane of the CPE. Genetically modified mice targeting slc4a2, slc4a5, slc4a7, slc4a10, and slc9a1 have been generated. Deletion of slc4a5, 7 or 10, or slc9a1 has numerous impacts on CP function and structure in these mice. Removal of the transporters affects brain ventricle size (slc4a5 and slc4a10) and intracellular pH regulation (slc4a7 and slc4a10). In some instances, removal of the proteins from the CPE (slc4a5, 7, and 10) causes changes in abundance and localization of non-target transporters known to be involved in pH regulation and CSF secretion. The focus of this review is to combine the insights gathered from these knockout mice to highlight the impact of slc4 gene deletion on the CSF production and intracellular pH regulation resulting from the deletion of slc4a5, 7 and 10, and slc9a1. Furthermore, the review contains a comparison of the described human mutations of these genes to the findings in the knockout studies. Finally, the future perspective of utilizing these proteins as potential targets for the treatment of CSF disorders will be discussed.
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Liu Y, Qin X, Wang DK, Guo YM, Gill HS, Morris N, Parker MD, Chen LM, Boron WF. Effects of optional structural elements, including two alternative amino termini and a new splicing cassette IV, on the function of the sodium-bicarbonate cotransporter NBCn1 (SLC4A7). J Physiol 2013; 591:4983-5004. [PMID: 23959679 DOI: 10.1113/jphysiol.2013.258673] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The SLC4A7 gene encodes the electroneutral sodium/HCO3 cotransporter NBCn1, which plays important physiological and pathophysiological roles in many cell types. Previous work identified six NBCn1 variants differing in the sequence of the extreme N terminus--MEAD in rat only, MERF in human only--as well as in the optional inclusion of cassettes I, II, and III. Earlier work also left open the question of whether optional structural elements (OSEs) affect surface abundance or intrinsic (per-molecule) transport activity. Here, we demonstrate for the first time that SLC4A7 from one species can express both MEAD- and MERF-NBCn1. We also identify a novel cassette IV of 20 aa, and extend by 10 the number of full-length NBCn1 variants. The alternative N termini and four cassettes could theoretically produce 32 major variants. Moreover, we identify a group of cDNAs predicted to encode just the cytosolic N-terminal domain (Nt) of NBCn1. A combination of electrophysiology and biotinylation shows that the OSEs can affect surface abundance and intrinsic HCO3(-) transport activity of NBCn1, as expressed in Xenopus oocytes. Specifically, MEAD tends to increase whereas novel cassette IV reduces surface abundance. Cassettes II, III and novel cassette IV all appear to increase the intrinsic activity of NBCn1.
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Affiliation(s)
- Ying Liu
- L.-M. Chen: Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science and Technology, 1037 Luoyu Rd, Wuhan, Hubei, China 430074.
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Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
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Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
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12
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Coley AA, Ruffin VA, Moss FJ, Hopfer U, Boron WF. Immunocytochemical identification of electroneutral Na⁺-coupled HCO₃⁻ transporters in freshly dissociated mouse medullary raphé neurons. Neuroscience 2013; 246:451-67. [PMID: 23500099 DOI: 10.1016/j.neuroscience.2013.02.064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2012] [Revised: 02/27/2013] [Accepted: 02/28/2013] [Indexed: 01/09/2023]
Abstract
The medullary raphé (MR) of the medulla oblongata contains chemosensitive neurons that respond to increases in arterial [CO₂], by altering firing rate, with increases being associated with serotonergic (5-hydroxytryptamine [5HT]) neurons and decreases, with GABAergic neurons. Both types of neurons contribute to increased alveolar ventilation. Decreases in intracellular pH are thought to link the rise in [CO₂] to increased ventilation. Because electroneutral Na(+)-coupled HCO₃(-) transporters (nNCBTs), which help protect cells from intracellular acidosis, are expressed robustly in the neurons of the central nervous system, a key question is whether these transporters are present in chemosensitive neurons. Therefore, we used an immunocytochemistry approach to identify neurons (using a microtubule associated protein-2 monoclonal antibody) and specifically 5HT neurons (TPH monoclonal antibody) or GABAergic neurons (GAD2 monoclonal antibody) in freshly dissociated cells from the mouse MR. We also co-labeled with polyclonal antibodies against the three nNCBTs: NBCn1, NDCBE, and NBCn2. We exploited ePet-EYFP (enhanced yellow fluorescent protein) mice (with EYFP-labeled 5HT neurons) as well as mice genetically deficient in each of the three nNCBTs. Quantitative image analysis distinguished positively stained cells from background signals. We found that >80% of GAD2(+) cells also were positive for NDCBE, and >90% of the TPH(+) and GAD2(+) cells were positive for the other nNCBTs. Assuming that the transporters are independently distributed among neurons, we can conclude that virtually all chemosensitive MR neurons contain at least one nNCBT.
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Affiliation(s)
- A A Coley
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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Liu Y, Wang DK, Jiang DZ, Qin X, Xie ZD, Wang QK, Liu M, Chen LM. Cloning and functional characterization of novel variants and tissue-specific expression of alternative amino and carboxyl termini of products of slc4a10. PLoS One 2013; 8:e55974. [PMID: 23409100 PMCID: PMC3567025 DOI: 10.1371/journal.pone.0055974] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Accepted: 01/04/2013] [Indexed: 11/18/2022] Open
Abstract
Previous studies have shown that the electroneutral Na+/HCO3− cotransporter NBCn2 (SLC4A10) is predominantly expressed in the central nervous system (CNS). The physiological and pathological significances of NBCn2 have been well recognized. However, little is known about the tissue specificity of expression of different NBCn2 variants. Moreover, little is known about the expression of NBCn2 proteins in systems other than CNS. Here, we identified a set of novel Slc4a10 variants differing from the originally described ones by containing a distinct 5′ untranslated region encoding a new extreme amino-terminus (Nt). Electrophysiology measurements showed that both NBCn2 variants with alternative Nt contain typical electroneutral Na+-coupled HCO3− transport activity in Xenopus oocytes. Luciferase reporter assay showed that Slc4a10 contains two alternative promoters responsible for expression of the two types of NBCn2 with distinct extreme Nt. Western blotting showed that NBCn2 proteins with the original Nt are primarily expressed in CNS, whereas those with the novel Nt are predominantly expressed in the kidney and to a lesser extent in the small intestine. Due to alternative splicing, the known NBCn2 variants contain two types of carboxyl-termini (CT) differing in the optional inclusion of a PDZ-binding motif. cDNA cloning showed that virtually all NBCn2 variants expressed in epithelial tissues contain, but the vast majority of those from the neural tissues lack the PDZ-binding motif. We conclude that alternative transcription and splicing of Slc4a10 products are regulated in a tissue-specific manner. Our findings provide critical insights that will greatly influence the study of the physiology of NBCn2.
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Affiliation(s)
- Ying Liu
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - Deng-Ke Wang
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - De-Zhi Jiang
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - Xue Qin
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America
| | - Zhang-Dong Xie
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - Qing K. Wang
- Department of Genetics and Developmental Biology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - Mugen Liu
- Department of Genetics and Developmental Biology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
| | - Li-Ming Chen
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology, Wuhan, Hubei, China
- * E-mail:
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14
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Chen LM, Liu Y, Boron WF. Role of an extracellular loop in determining the stoichiometry of Na+-HCO₃⁻ cotransporters. J Physiol 2011; 589:877-90. [PMID: 21224233 DOI: 10.1113/jphysiol.2010.198713] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Na+–HCO₃⁻ cotransporters (NBCs) of the solute carrier 4 family (SLC4) are critical for regulating pH in cells as well as in fluids such as blood and cerebrospinal fluid. Moreover, mutations and gene disruptions in NBC are linked to a wide range of pathologies. NBCe1 (SLC4A4) is electrogenic because it has an apparent Na+:HCO₃⁻ stoichiometry of 1:2 or 1:3, whereas NBCn1 (SLC4A7) is electroneutral because it has an apparent stoichiometry of 1:1. Because stoichiometry influences the effect of transport on membrane potential and vice versa, a central question is what structural features underlie electrogenicity versus electroneutrality. A previous study on rat NBCe1/n1 chimeras demonstrated that the structural elements determining the electrogenicity of NBCe1-A are located within the transmembrane domain, excluding the large third extracellular loop. In the present study we generated a series of chimeras of human NBCe1-A and human NBCn1-A. We found that replacing merely the predicted fourth extracellular loop (EL4) – containing 32 amino acid residues that include 7 prolines – of human NBCe1-A with EL4 of NBCn1-A creates an electroneutral NBC. The opposite switch converts an electroneutral construct to one with electrogenic properties. The introduction of an N-glycosylation site into EL4 confirms that at least a part of it is exposed to the extracellular fluid. We hypothesize that putative EL4 either contributes to the substrate-binding vestibule or indirectly influences substrate binding by interacting with one or more transmembrane segments, thereby controlling the nature of transport.
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Affiliation(s)
- Li-Ming Chen
- Department of Biological Science, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science and Technology School of Life Science and Technology, 1037 Luoyu Road, Wuhan, Hubei Province 430074, P.R. China.
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15
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Majumdar D, Bevensee MO. Na-coupled bicarbonate transporters of the solute carrier 4 family in the nervous system: function, localization, and relevance to neurologic function. Neuroscience 2010; 171:951-72. [PMID: 20884330 DOI: 10.1016/j.neuroscience.2010.09.037] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 09/03/2010] [Accepted: 09/14/2010] [Indexed: 12/26/2022]
Abstract
Many cellular processes including neuronal activity are sensitive to changes in intracellular and/or extracellular pH-both of which are regulated by acid-base transporter activity. HCO(3)(-)-dependent transporters are particularly potent regulators of intracellular pH in neurons and astrocytes, and also contribute to the composition of the cerebrospinal fluid (CSF). The molecular physiology of HCO(3)(-) transporters has advanced considerably over the past ∼14 years as investigators have cloned and characterized the function and localization of many Na-Coupled Bicarbonate Transporters of the solute carrier 4 (Slc4) family (NCBTs). In this review, we provide an updated overview of the function and localization of NCBTs in the nervous system. Multiple NCBTs are expressed in neurons and astrocytes in various brain regions, as well as in epithelial cells of the choroid plexus. Characteristics of human patients with SLC4 gene mutations/deletions and results from recent studies on mice with Slc4 gene disruptions highlight the functional importance of NCBTs in neuronal activity, somatosensory function, and CSF production. Furthermore, energy-deficient states (e.g., hypoxia and ischemia) lead to altered expression and activity of NCBTs. Thus, recent studies expand our understanding of the role of NCBTs in regulating the pH and ionic composition of the nervous system that can modulate neuronal activity.
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Affiliation(s)
- D Majumdar
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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16
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Park HJ, Rajbhandari I, Yang HS, Lee S, Cucoranu D, Cooper DS, Klein JD, Sands JM, Choi I. Neuronal expression of sodium/bicarbonate cotransporter NBCn1 (SLC4A7) and its response to chronic metabolic acidosis. Am J Physiol Cell Physiol 2010; 298:C1018-28. [PMID: 20147654 DOI: 10.1152/ajpcell.00492.2009] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The sodium-bicarbonate cotransporter NBCn1 (SLC4A7) is an acid-base transporter that normally moves Na(+) and HCO(3)(-) into the cell. This membrane protein is sensitive to cellular and systemic pH changes. We examined NBCn1 expression and localization in the brain and its response to chronic metabolic acidosis. Two new NBCn1 antibodies were generated by immunizing a rabbit and a guinea pig. The antibodies stained neurons in a variety of rat brain regions, including hippocampal pyramidal neurons, dentate gyrus granular neurons, posterior cortical neurons, and cerebellar Purkinje neurons. Choroid plexus epithelia were also stained. Double immunofluorescence labeling showed that NBCn1 and the postsynaptic density protein PSD-95 were found in the same hippocampal CA3 neurons and partially colocalized in dendrites. PSD-95 was pulled down from rat brain lysates with the GST/NBCn1 fusion protein and was also coimmunoprecipitated with NBCn1. Chronic metabolic acidosis was induced by feeding rats with normal chow or 0.4 M HCl-containing chow for 7 days. Real-time PCR and immunoblot showed upregulation of NBCn1 mRNA and protein in the hippocampus of acidotic rats. NBCn1 immunostaining was enhanced in CA3 neurons, posterior cortical neurons, and cerebellar granular cells. Intraperitoneal administration of N-methyl-d-aspartate caused neuronal death determined by caspase-3 activity, and this effect was more severe in acidotic rats. Administering N-methyl-d-aspartate also inhibited NBCn1 upregulation in acidotic rats. We conclude that NBCn1 in neurons is upregulated by chronic acid loads, and this upregulation is associated with glutamate excitotoxicity.
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Affiliation(s)
- Hae Jeong Park
- Dept. of Physiology, Emory Univ., Atlanta, GA 30322, USA
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17
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Riihonen R, Nielsen S, Väänänen HK, Laitala-Leinonen T, Kwon TH. Degradation of hydroxyapatite in vivo and in vitro requires osteoclastic sodium-bicarbonate co-transporter NBCn1. Matrix Biol 2010; 29:287-94. [PMID: 20079835 DOI: 10.1016/j.matbio.2010.01.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 12/01/2009] [Accepted: 01/06/2010] [Indexed: 01/19/2023]
Abstract
Dissolution of the inorganic bone matrix releases not only calcium and phosphate ions, but also bicarbonate. Electroneutral sodium-bicarbonate co-transporter (NBCn1) is expressed in inactive osteoclasts, but its physiological role in bone resorption has remained unknown. We show here that NBCn1, encoded by the SLC4A7 gene, is directly involved in bone resorption. NBCn1 protein was specifically found at the bone-facing ruffled border areas, and metabolic acidosis increased NBCn1 expression in rats in vivo. In human hematopoietic stem cell cultures, NBCn1 mRNA expression was observed only after formation of resorbing osteoclasts. To further confirm the critical role of NBCn1 during bone resorption, human hematopoietic stem cells were transduced with SLC4A7 shRNA lentiviral particles. Downregulation of NBCn1 both on mRNA and protein level by lentiviral shRNAs significantly inhibited bone resorption and increased intracellular acidification in osteoclasts. The lentiviral particles did not impair osteoclast survival, or differentiation of the hematopoietic or mesenchymal precursor cells into osteoclasts or osteoblasts in vitro. Inhibition of NBCn1 activity may thus provide a new way to regulate osteoclast activity during pathological bone resorption.
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Affiliation(s)
- Riikka Riihonen
- Bone Biology Research Consortium, Department of Cell Biology and Anatomy, Institute of Biomedicine, University of Turku, FIN-20520 Turku, Finland
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18
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Boron WF, Chen L, Parker MD. Modular structure of sodium-coupled bicarbonate transporters. ACTA ACUST UNITED AC 2009; 212:1697-706. [PMID: 19448079 DOI: 10.1242/jeb.028563] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Mammalian genomes contain 10 SLC4 genes that, between them, encode three Cl-HCO(3) exchangers, five Na(+)-coupled HCO(3) transporters (NCBTs), one reported borate transporter, and what is reported to be a fourth Cl-HCO(3) exchanger. The NCBTs are expressed throughout the body and play important roles in maintaining intracellular and whole-body pH, as well as contributing to transepithelial transport processes. The importance of NCBTs is underscored by the genetic association of dysfunctional NCBT genes with blindness, deafness, epilepsy, hypertension and metal retardation. Key to understanding the action and regulation of NCBTs is an appreciation of the diversity of NCBT gene products. The transmembrane domains of human NCBT paralogs are 50-84% identical to each other at the amino acid level, and are capable of a diverse range of actions, including electrogenic Na/HCO(3) cotransport (i.e. NBCe1 and NBCe2) and electroneutral Na/HCO(3) cotransport (i.e. NBCn1 and NBCn2), as well as Na(+)-dependent Cl-HCO(3) exchange (i.e. NDCBE). Furthermore, by the use of alternative promoters and alternative-splicing events, individual SLC4 genes have the potential to generate multiple splice variants (as many as 16 in the case of NBCn1), each of which could have unique temporal and spatial patterns of distribution, unitary transporter activity (i.e. flux mediated by one molecule), array of protein-binding partners, and complement of regulatory stimuli. In the first section of this review, we summarize our present knowledge of the function and distribution of mammalian NCBTs and their multiple variants. In the second section of this review we consider the molecular consequences of NCBT variation.
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Affiliation(s)
- Walter F Boron
- Department of Physiology, Case Western Reserve University Medical School, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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Cooper DS, Yang HS, He P, Kim E, Rajbhandari I, Yun CC, Choi I. Sodium/bicarbonate cotransporter NBCn1/slc4a7 increases cytotoxicity in magnesium depletion in primary cultures of hippocampal neurons. Eur J Neurosci 2008; 29:437-46. [PMID: 19170751 DOI: 10.1111/j.1460-9568.2008.06611.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Growing evidence suggests that pharmacological inhibition of Na/H exchange and Na/HCO(3) transport provides protection against damage or injury in cardiac ischemia. In this study, we examined the contribution of the sodium/bicarbonate cotransporter NBCn1 (slc4a7) to cytotoxicity in cultured hippocampal neurons of rats. In neurons exposed to extracellular pH (pH(o)) ranging from 6.2 to 8.3, NBCn1 protein expression increased by fivefold at pH < 6.5 compared to the expression at pH(o) 7.4. At pH(o) 6.5, the intracellular pH of neurons was approximately 1 unit lower than that at pH 7.4. Immunochemistry showed a marked increase in NBCn1 immunofluorescence in plasma membranes and cytosol of the soma as well as in dendrites, at pH(o) 6.5. NBCn1 expression also increased by 40% in a prolonged Mg(2+)-free incubation at normal pH(o). Knockdown of NBCn1 in neurons had negligible effect on cell viability. The effect of NBCn1 knockdown on cytotoxicity was then determined by exposing neurons to 0.5 mm glutamate for 10 min and measuring lactate dehydrogenase (LDH) release from neurons. Compared to normal incubation (pH(o) 7.2 for 6 h) after glutamate exposure, acidic incubation (pH(o) 6.3 for 6 h) reduced cytotoxicity by 75% for control neurons and 78% for NBCn1-knockdown neurons. Thus, both controls and knockdown neurons showed acidic protection from cytotoxicity. However, in Mg(2+)-free incubation after glutamate exposure, NBCn1 knockdown progressively attenuated cytotoxicity. This attenuation was unaffected by acidic preincubation before glutamate exposure. We conclude that NBCn1 has a dynamic upregulation in low pH(o) and Mg(2+) depletion. NBCn1 is not required for acidic protection, but increases cytotoxicity in Mg(2+)-free conditions.
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Affiliation(s)
- Deborah S Cooper
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA
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Chen LM, Haddad GG, Boron WF. Effects of chronic continuous hypoxia on the expression of SLC4A8 (NDCBE) in neonatal versus adult mouse brain. Brain Res 2008; 1238:85-92. [PMID: 18775686 DOI: 10.1016/j.brainres.2008.08.033] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Revised: 08/06/2008] [Accepted: 08/14/2008] [Indexed: 01/20/2023]
Abstract
Na-coupled HCO(3) transporters (NCBTs) play important roles in brain pH regulation. One NCBT, the Na-driven Cl-HCO(3) exchanger (SLC4A8 or NDCBE), appears to be the major regulator of intracellular pH (pH(i)), at least in some hippocampal pyramidal neurons. NDCBE is widely expressed throughout the central nervous system in rodent brain. In a previous study, it has been demonstrated that CCH decreases the abundance of NBCn1 and NBCn2 proteins in four regions of the mouse brain: cerebral cortex (CX), subcortex (SCX), cerebellum (CB), and hippocampus (HC). Here we report the effect of CCH (11% O(2)) on the expression of NDCBE protein in mouse brain. Neonates (beginning at age P2) or adult mice (beginning at P90) were subjected to either normoxia or CCH for durations of 14 or 28 days. Membrane-protein levels were assessed by western blotting using our polyclonal antibody directed against NDCBE. In neonates, CCH significantly decreased NDCBE expression in HC after 14 days and SCX after 28 days, but had no significant effect for other combinations of region/duration. In adults, however, CCH significantly decreased (by 20-50%) the expression of NDCBE in all four brain regions, both with 14 and 28 day duration. Thus, the mouse brain exhibits marked developmental differences in the response of NDCBE protein expression to CCH. We hypothesize that decreases in adult NDCBE protein levels, which are probably out of proportion to the decreases in other proteins, may be part of an adaptive response that reduces energy consumption and/or stabilizes brain pH(i). The smaller or absent responses in the young animals could be related to neonatal hypoxia tolerance.
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Affiliation(s)
- Li-Ming Chen
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4970, USA.
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Prentice HM. Key contributions of the Na+/H+ exchanger subunit 1 and HCO3- transporters in regulating neuronal cell fate in prolonged hypoxia. Am J Physiol Regul Integr Comp Physiol 2007; 294:R448-50. [PMID: 18056979 DOI: 10.1152/ajpregu.00846.2007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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