1
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Competitive inhibition of the high-affinity choline transporter by tetrahydropyrimidine anthelmintics. Eur J Pharmacol 2021; 898:173986. [PMID: 33640406 DOI: 10.1016/j.ejphar.2021.173986] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 02/19/2021] [Accepted: 02/23/2021] [Indexed: 11/24/2022]
Abstract
The high-affinity choline transporter CHT1 mediates choline uptake, the rate-limiting and regulatory step in acetylcholine synthesis at cholinergic presynaptic terminals. CHT1-medated choline uptake is specifically inhibited by hemicholinium-3, which is a type of choline analog that acts as a competitive inhibitor. Although the substrate choline and the inhibitor hemicholinium-3 are well-established ligands of CHT1, few potent ligands other than choline analogs have been reported. Here we show that tetrahydropyrimidine anthelmintics, known as nicotinic acetylcholine receptor agonists, act as competitive inhibitors of CHT1. A ligand-dependent trafficking assay in cell lines expressing human CHT1 was designed to search for CHT1 ligands from a collection of biologically active compounds. We found that morantel as well as other tetrahydropyrimidines, pyrantel and oxantel, potently inhibits the high-affinity choline uptake activity of CHT1 in a competitive manner similar to the inhibitor hemicholinium-3. They also inhibit the high-affinity choline transporter from the nematode Caenorhabditis elegans. Finally, tetrahydropyrimidines potently inhibit the high-affinity choline uptake in rat brain synaptosomes at a low micromolar level, resulting in the inhibition of acetylcholine synthesis. The rank order of potency in synaptosomes is as follows: morantel > pyarantel > oxantel (Ki = 1.3, 5.7, and 8.3 μM, respectively). Our results reveal that tetrahydropyrimidine anthelmintics are novel CHT1 ligands that inhibit the high-affinity choline uptake for acetylcholine synthesis in cholinergic neurons.
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2
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Ojiakor O, Rylett R. Modulation of sodium-coupled choline transporter CHT function in health and disease. Neurochem Int 2020; 140:104810. [DOI: 10.1016/j.neuint.2020.104810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 06/16/2020] [Accepted: 07/09/2020] [Indexed: 12/27/2022]
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3
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Lindner M, Bell T, Iqbal S, Mullins PG, Christakou A. In vivo functional neurochemistry of human cortical cholinergic function during visuospatial attention. PLoS One 2017; 12:e0171338. [PMID: 28192451 PMCID: PMC5305251 DOI: 10.1371/journal.pone.0171338] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 01/19/2017] [Indexed: 11/24/2022] Open
Abstract
Cortical acetylcholine is involved in key cognitive processes such as visuospatial attention. Dysfunction in the cholinergic system has been described in a number of neuropsychiatric disorders. Levels of brain acetylcholine can be pharmacologically manipulated, but it is not possible to directly measure it in vivo in humans. However, key parts of its biochemical cascade in neural tissue, such as choline, can be measured using magnetic resonance spectroscopy (MRS). There is evidence that levels of choline may be an indirect but proportional measure of acetylcholine availability in brain tissue. In this study, we measured relative choline levels in the parietal cortex using functional (event-related) MRS (fMRS) during performance of a visuospatial attention task, with a modelling approach verified using simulated data. We describe a task-driven interaction effect on choline concentration, specifically driven by contralateral attention shifts. Our results suggest that choline MRS has the potential to serve as a proxy of brain acetylcholine function in humans.
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Affiliation(s)
- Michael Lindner
- Centre for Integrative Neuroscience and Neurodynamics, and School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom
| | - Tiffany Bell
- Centre for Integrative Neuroscience and Neurodynamics, and School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom
| | - Somya Iqbal
- Centre for Integrative Neuroscience and Neurodynamics, and School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom
| | | | - Anastasia Christakou
- Centre for Integrative Neuroscience and Neurodynamics, and School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom
- * E-mail:
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4
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Ennis EA, Blakely RD. Choline on the Move: Perspectives on the Molecular Physiology and Pharmacology of the Presynaptic Choline Transporter. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2016; 76:175-213. [PMID: 27288078 DOI: 10.1016/bs.apha.2016.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Genetic, biochemical, physiological, and pharmacological approaches have advanced our understanding of cholinergic biology for over 100 years. High-affinity choline uptake (HACU) was one of the last features of cholinergic signaling to be defined at a molecular level, achieved through the cloning of the choline transporter (CHT, SLC5A7). In retrospect, the molecular era of CHT studies initiated with the identification of hemicholinium-3 (HC-3), a potent, competitive CHT antagonist, though it would take another 30 years before HC-3, in radiolabeled form, was used by Joseph Coyle's laboratory to identify and monitor the dynamics of CHT proteins. Though HC-3 studies provided important insights into CHT distribution and regulation, another 15 years would pass before the structure of CHT genes and proteins were identified, a full decade after the cloning of most other neurotransmitter-associated transporters. The availability of CHT gene and protein probes propelled the development of cell and animal models as well as efforts to gain insights into how human CHT gene variation affects the risk for brain and neuromuscular disorders. Most recently, our group has pursued a broadening of CHT pharmacology, elucidating novel chemical structures that may serve to advance cholinergic diagnostics and medication development. Here we provide a short review of the transformation that has occurred in HACU research and how such advances may promote the development of novel therapeutics.
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Affiliation(s)
- E A Ennis
- Vanderbilt University School of Medicine, Nashville, TN, United States
| | - R D Blakely
- Vanderbilt University School of Medicine, Nashville, TN, United States.
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5
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Ennis EA, Wright J, Retzlaff CL, McManus OB, Lin Z, Huang X, Wu M, Li M, Daniels JS, Lindsley CW, Hopkins CR, Blakely RD. Identification and characterization of ML352: a novel, noncompetitive inhibitor of the presynaptic choline transporter. ACS Chem Neurosci 2015; 6:417-27. [PMID: 25560927 PMCID: PMC4367188 DOI: 10.1021/cn5001809] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
![]()
The high-affinity choline transporter
(CHT) is the rate-limiting
determinant of acetylcholine (ACh) synthesis, yet the transporter
remains a largely undeveloped target for the detection and manipulation
of synaptic cholinergic signaling. To expand CHT pharmacology, we
pursued a high-throughput screen for novel CHT-targeted small molecules
based on the electrogenic properties of transporter-mediated choline
transport. In this effort, we identified five novel, structural classes
of CHT-specific inhibitors. Chemical diversification and functional
analysis of one of these classes identified ML352 as a high-affinity
(Ki = 92 nM) and selective CHT inhibitor.
At concentrations that fully antagonized CHT in transfected cells
and nerve terminal preparations, ML352 exhibited no inhibition of
acetylcholinesterase (AChE) or cholineacetyltransferase (ChAT) and
also lacked activity at dopamine, serotonin, and norepinephrine transporters,
as well as many receptors and ion channels. ML352 exhibited noncompetitive
choline uptake inhibition in intact cells and synaptosomes and reduced
the apparent density of hemicholinium-3 (HC-3) binding sites in membrane
assays, suggesting allosteric transporter interactions. Pharmacokinetic
studies revealed limited in vitro metabolism and
significant CNS penetration, with features predicting rapid clearance.
ML352 represents a novel, potent, and specific tool for the manipulation
of CHT, providing a possible platform for the development of cholinergic
imaging and therapeutic agents.
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Affiliation(s)
| | | | | | - Owen B. McManus
- Johns Hopkins University Ion Channel Center, Baltimore, Maryland 21205, United States
| | - Zhinong Lin
- Johns Hopkins University Ion Channel Center, Baltimore, Maryland 21205, United States
| | - Xiaofang Huang
- Johns Hopkins University Ion Channel Center, Baltimore, Maryland 21205, United States
| | - Meng Wu
- Johns Hopkins University Ion Channel Center, Baltimore, Maryland 21205, United States
| | - Min Li
- Johns Hopkins University Ion Channel Center, Baltimore, Maryland 21205, United States
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6
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Granja MG, Braga LEG, Carpi-Santos R, de Araujo-Martins L, Nunes-Tavares N, Calaza KC, dos Santos AA, Giestal-de-Araujo E. IL-4 Induces Cholinergic Differentiation of Retinal Cells In Vitro. Cell Mol Neurobiol 2015; 35:689-701. [DOI: 10.1007/s10571-015-0164-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 02/03/2015] [Indexed: 12/01/2022]
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7
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Santoro ML, Santos CM, Ota VK, Gadelha A, Stilhano RS, Diana MC, Silva PN, Spíndola LMN, Melaragno MI, Bressan RA, Han SW, Abílio VC, Belangero SI. Expression profile of neurotransmitter receptor and regulatory genes in the prefrontal cortex of spontaneously hypertensive rats: relevance to neuropsychiatric disorders. Psychiatry Res 2014; 219:674-9. [PMID: 25041985 DOI: 10.1016/j.psychres.2014.05.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 04/22/2014] [Accepted: 05/18/2014] [Indexed: 12/12/2022]
Abstract
The spontaneously hypertensive rat (SHR) strain was shown to be a useful animal model to study several behavioral, pathophysiological and pharmacological aspects of schizophrenia and attention-deficit/hyperactivity disorder. To further understand the genetic underpinnings of this model, our primary goal in this study was to compare the gene expression profile of neurotransmitter receptors and regulators in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of SHR and Wistar rats (control group). In addition, we investigated DNA methylation pattern of promoter region of the genes differentially expressed. We performed gene expression analysis using a PCRarray technology, which simultaneously measures the expression of 84 genes related to neurotransmission. Four genes were significantly downregulated in the PFC of SHR compared to Wistar rats (Gad2, Chrnb4, Slc5a7, and Qrfpr) and none in nucleus accumbens. Gad2 and Qrfpr have CpG islands in their promoter region. For both, the promoter region was hypomethylated in SHR group, and probably this mechanism is not related with the downregulation of these genes. In summary, we identified genes that are downregulated in the PFC of SHR, and might be related to the behavioral abnormalities exhibited by this strain.
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Affiliation(s)
- Marcos Leite Santoro
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil; Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil
| | - Camila Maurício Santos
- Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Psychiatry, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Vanessa Kiyomi Ota
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil; Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil
| | - Ary Gadelha
- Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Psychiatry, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Roberta Sessa Stilhano
- Department of Biophysics and Investigation Center for Gene Therapy, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Mariana Cepollaro Diana
- Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Pharmacology, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Patrícia Natália Silva
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil; Department of Psychiatry, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Letícia Maria Nery Spíndola
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Maria Isabel Melaragno
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Rodrigo Affonseca Bressan
- Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Psychiatry, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Sang Won Han
- Department of Biophysics and Investigation Center for Gene Therapy, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Vanessa Costhek Abílio
- Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Pharmacology, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil
| | - Sintia Iole Belangero
- Genetics Division, Department of Morphology and Genetics, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil; Interdisciplinary Laboratory of Clinical Neurosciences (LiNC), Sao Paulo, Brazil; Department of Psychiatry, Federal University of Sao Paulo (UNIFESP), Sao Paulo, Brazil.
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8
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Diallinas G. Understanding transporter specificity and the discrete appearance of channel-like gating domains in transporters. Front Pharmacol 2014; 5:207. [PMID: 25309439 PMCID: PMC4162363 DOI: 10.3389/fphar.2014.00207] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 08/22/2014] [Indexed: 12/12/2022] Open
Abstract
Transporters are ubiquitous proteins mediating the translocation of solutes across cell membranes, a biological process involved in nutrition, signaling, neurotransmission, cell communication and drug uptake or efflux. Similarly to enzymes, most transporters have a single substrate binding-site and thus their activity follows Michaelis-Menten kinetics. Substrate binding elicits a series of structural changes, which produce a transporter conformer open toward the side opposite to the one from where the substrate was originally bound. This mechanism, involving alternate outward- and inward-facing transporter conformers, has gained significant support from structural, genetic, biochemical and biophysical approaches. Most transporters are specific for a given substrate or a group of substrates with similar chemical structure, but substrate specificity and/or affinity can vary dramatically, even among members of a transporter family that show high overall amino acid sequence and structural similarity. The current view is that transporter substrate affinity or specificity is determined by a small number of interactions a given solute can make within a specific binding site. However, genetic, biochemical and in silico modeling studies with the purine transporter UapA of the filamentous ascomycete Aspergillus nidulans have challenged this dogma. This review highlights results leading to a novel concept, stating that substrate specificity, but also transport kinetics and transporter turnover, are determined by subtle intramolecular interactions between a major substrate binding site and independent outward- or cytoplasmically-facing gating domains, analogous to those present in channels. This concept is supported by recent structural evidence from several, phylogenetically and functionally distinct transporter families. The significance of this concept is discussed in relationship to the role and potential exploitation of transporters in drug action.
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9
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Abstract
This article summarizes molecular properties of the high-affinity choline transporter (CHT1) with reference to the historical background focusing studies performed in laboratories of the author. CHT1 is present on the presynaptic terminal of cholinergic neurons, and takes up choline which is the precursor of acetylcholine. The Na(+)-dependent uptake of choline by CHT1 is the rate-limiting step for synthesis of acetylcholine. CHT1 is the integral membrane protein with 13 transmembrane segments, belongs to the Na(+)/glucose co-transporter family (SLC5), and has 20-25% homology with members of this family. A single nucleotide polymorphism (SNP) for human CHT1 has been identified, which has a replacement from isoleucine to valine in the third transmembrane segment and shows the choline uptake activity of 50-60% as much as that of wild-type CHT1. The proportion of this SNP is high among Asians. Possible importance of choline diet for those with this SNP was discussed.
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Affiliation(s)
- Tatsuya Haga
- Tokyo University, 7-3-1 Hongo, Tokyo 113-8654, Japan
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10
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Jørgensen TN, Christensen PM, Gether U. Serotonin-induced down-regulation of cell surface serotonin transporter. Neurochem Int 2014; 73:107-12. [PMID: 24462583 DOI: 10.1016/j.neuint.2014.01.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 01/06/2014] [Accepted: 01/09/2014] [Indexed: 01/15/2023]
Abstract
The serotonin transporter (SERT) terminates serotonergic signaling and enables refilling of synaptic vesicles by mediating reuptake of serotonin (5-HT) released into the synaptic cleft. The molecular and cellular mechanisms controlling SERT activity and surface expression are not fully understood. Here we demonstrate that the substrate 5-HT itself causes acute down-regulation of SERT cell surface expression. To assess surface SERT expression by ELISA, we used a SERT variant (TacSERT) where the N-terminus of SERT was fused to the intracellular tail of the extracellularly FLAG-tagged single-membrane spanning protein Tac. In stably transfected HEK293 cells, 5-HT caused a dose-dependent reduction in TacSERT surface signal with an EC50 value equivalent to the Km value observed for 5-HT uptake. The 5-HT-induced reduction in surface signal reached maximum within 40-60min and was blocked by the selective SERT inhibitor S-citalopram. 5-HT-induced reduction in SERT expression was further supported by surface biotinylation experiments showing 5-HT-induced reduction in wild type SERT plasma membrane levels. Moreover, preincubation with 5-HT lowered the Vmax for 5-HT uptake in cultured raphe serotonergic neurons, indicting that endogenous cell-surface resident SERT likewise is down-regulated in the presence of substrate.
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Affiliation(s)
- Trine Nygaard Jørgensen
- Molecular Neuropharmacology Laboratory, Department of Neuroscience and Pharmacology, The Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Peter Møller Christensen
- Molecular Neuropharmacology Laboratory, Department of Neuroscience and Pharmacology, The Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Ulrik Gether
- Molecular Neuropharmacology Laboratory, Department of Neuroscience and Pharmacology, The Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark.
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11
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Cuddy LK, Winick-Ng W, Rylett RJ. Regulation of the high-affinity choline transporter activity and trafficking by its association with cholesterol-rich lipid rafts. J Neurochem 2013; 128:725-40. [PMID: 24127780 DOI: 10.1111/jnc.12490] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 10/10/2013] [Accepted: 10/14/2013] [Indexed: 01/07/2023]
Abstract
The sodium-coupled, hemicholinium-3-sensitive, high-affinity choline transporter (CHT) is responsible for transport of choline into cholinergic nerve terminals from the synaptic cleft following acetylcholine release and hydrolysis. In this study, we address regulation of CHT function by plasma membrane cholesterol. We show for the first time that CHT is concentrated in cholesterol-rich lipid rafts in both SH-SY5Y cells and nerve terminals from mouse forebrain. Treatment of SH-SY5Y cells expressing rat CHT with filipin, methyl-β-cyclodextrin (MβC) or cholesterol oxidase significantly decreased choline uptake. In contrast, CHT activity was increased by addition of cholesterol to membranes using cholesterol-saturated MβC. Kinetic analysis of binding of [(3)H]hemicholinium-3 to CHT revealed that reducing membrane cholesterol with MβC decreased both the apparent binding affinity (KD) and maximum number of binding sites (Bmax ); this was confirmed by decreased plasma membrane CHT protein in lipid rafts in cell surface protein biotinylation assays. Finally, the loss of cell surface CHT associated with lipid raft disruption was not because of changes in CHT internalization. In summary, we provide evidence that CHT association with cholesterol-rich rafts is critical for transporter function and localization. Alterations in plasma membrane cholesterol cholinergic nerve terminals could diminish cholinergic transmission by reducing choline availability for acetylcholine synthesis. The sodium-coupled choline transporter CHT moves choline into cholinergic nerve terminals to serve as substrate for acetylcholine synthesis. We show for the first time that CHT is concentrated in cholesterol-rich lipid rafts, and decreasing membrane cholesterol significantly reduces both choline uptake activity and cell surface CHT protein levels. CHT association with cholesterol-rich rafts is critical for its function, and alterations in plasma membrane cholesterol could diminish cholinergic transmission by reducing choline availability for acetylcholine synthesis.
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Affiliation(s)
- Leah K Cuddy
- Molecular Brain Research Group, Robarts Research Institute, Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada
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12
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Lima CS, Dutra-Tavares AC, Nunes F, Nunes-Freitas AL, Ribeiro-Carvalho A, Filgueiras CC, Manhães AC, Meyer A, Abreu-Villaça Y. Methamidophos exposure during the early postnatal period of mice: immediate and late-emergent effects on the cholinergic and serotonergic systems and behavior. Toxicol Sci 2013; 134:125-39. [PMID: 23596261 DOI: 10.1093/toxsci/kft095] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Organophosphates (OPs) are among the most used pesticides. Although some OPs have had their use progressively more restricted, other OPs are being used without sufficient investigation of their effects. Here, we investigated the immediate neurochemical and delayed neurochemical and behavioral actions of the OP methamidophos to verify whether there are concerns regarding exposure during early postnatal development. From the third to the nineth postnatal day (PN), Swiss mice were sc injected with methamidophos (1mg/kg). At PN10, we assessed cholinergic and serotonergic biomarkers in the cerebral cortex and brainstem. From PN60 to PN63, mice were submitted to a battery of behavioral tests and subsequently to biochemical analyses. At PN10, the effects were restricted to females and to the cholinergic system: Methamidophos promoted increased choline transporter binding in the brainstem. At PN63, in the brainstem, there was a decrease in choline transporter, a female-only decrease in 5HT1A and a male-only increase in 5HT2 receptor binding. In the cortex, choline acetyltransferase activity was decreased and 5HT2 receptor binding was increased both in males and females. Methamidophos elicited behavioral alterations, suggestive of increased depressive-like behavior and impaired decision making. There were no significant alterations on anxiety-related measures and on memory/learning. Methamidophos elicited cholinergic and serotonergic alterations that depended on brain region, sex, and age of the animals. These outcomes, together with the behavioral effects, indicate that this OP is deleterious to the developing brain and that alterations are indeed identified long after the end of exposure.
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Affiliation(s)
- Carla S Lima
- Departamento de Ciências Fisiológicas, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
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13
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Okuda T, Osawa C, Yamada H, Hayashi K, Nishikawa S, Ushio T, Kubo Y, Satou M, Ogawa H, Haga T. Transmembrane topology and oligomeric structure of the high-affinity choline transporter. J Biol Chem 2012; 287:42826-34. [PMID: 23132865 DOI: 10.1074/jbc.m112.405027] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The high-affinity choline transporter CHT1 mediates choline uptake essential for acetylcholine synthesis in cholinergic nerve terminals. CHT1 belongs to the Na(+)/glucose cotransporter family (SLC5), which is postulated to have a common 13-transmembrane domain core; however, no direct experimental evidence for CHT1 transmembrane topology has yet been reported. We examined the transmembrane topology of human CHT1 using cysteine-scanning analysis. Single cysteine residues were introduced into the putative extra- and intracellular loops and probed for external accessibility for labeling with a membrane-impermeable, sulfhydryl-specific biotinylating reagent in intact cells expressing these mutants. The results provide experimental evidence for a topological model of a 13-transmembrane domain protein with an extracellular amino terminus and an intracellular carboxyl terminus. We also constructed a three-dimensional homology model of CHT1 based on the crystal structure of the bacterial Na(+)/galactose cotransporter, which supports our conclusion of CHT1 transmembrane topology. Furthermore, we examined whether CHT1 exists as a monomer or oligomer. Chemical cross-linking induces the formation of a higher molecular weight form of CHT1 on the cell surface in HEK293 cells. Two different epitope-tagged CHT1 proteins expressed in the same cells can be co-immunoprecipitated. Moreover, co-expression of an inactive mutant I89A with the wild type induces a dominant-negative effect on the overall choline uptake activity. These results indicate that CHT1 forms a homo-oligomer on the cell surface in cultured cells.
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Affiliation(s)
- Takashi Okuda
- Department of Pharmacology, Faculty of Pharmacy, Keio University, 1-5-30 Shibakoen, Minato-ku, Tokyo, Japan.
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14
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Ruggiero A, Wright J, Ferguson SM, Lewis M, Emerson K, Iwamoto H, Ivy MT, Holmstrand EC, Ennis EA, Weaver CD, Blakely RD. Nonoisotopic assay for the presynaptic choline transporter reveals capacity for allosteric modulation of choline uptake. ACS Chem Neurosci 2012; 3:767-81. [PMID: 23077721 PMCID: PMC3474274 DOI: 10.1021/cn3000718] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2012] [Accepted: 07/09/2012] [Indexed: 11/29/2022] Open
Abstract
Current therapies to enhance CNS cholinergic function rely primarily on extracellular acetylcholinesterase (AChE) inhibition, a pharmacotherapeutic strategy that produces dose-limiting side effects. The Na(+)-dependent, high-affinity choline transporter (CHT) is an unexplored target for cholinergic medication development. Although functional at the plasma membrane, CHT at steady-state is localized to synaptic vesicles such that vesicular fusion can support a biosynthetic response to neuronal excitation. To identify allosteric potentiators of CHT activity, we mapped endocytic sequences in the C-terminus of human CHT, identifying transporter mutants that exhibit significantly increased transport function. A stable HEK-293 cell line was generated from one of these mutants (CHT LV-AA) and used to establish a high-throughput screen (HTS) compatible assay based on the electrogenic nature of the transporter. We established that the addition of choline to these cells, at concentrations appropriate for high-affinity choline transport at presynaptic terminals, generates a hemicholinium-3 (HC-3)-sensitive, membrane depolarization that can be used for the screening of CHT inhibitors and activators. Using this assay, we discovered that staurosporine increased CHT LV-AA choline uptake activity, an effect mediated by a decrease in choline K(M) with no change in V(max). As staurosporine did not change surface levels of CHT, nor inhibit HC-3 binding, we propose that its action is directly or indirectly allosteric in nature. Surprisingly, staurosporine reduced choline-induced membrane depolarization, suggesting that increased substrate coupling to ion gradients, arising at the expense of nonstoichiometric ion flow, accompanies a shift of CHT to a higher-affinity state. Our findings provide a new approach for the identification of CHT modulators that is compatible with high-throughput screening approaches and presents a novel model by which small molecules can enhance substrate flux through enhanced gradient coupling.
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Affiliation(s)
- Alicia
M. Ruggiero
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Jane Wright
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Shawn M. Ferguson
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Michelle Lewis
- Vanderbilt Institute
of Chemical
Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6304, United States
| | - Katie
S. Emerson
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Hideki Iwamoto
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Michael T. Ivy
- Department of Biological Sciences, Tennessee State University, Nashville, Tennessee 37209-1561,
United States
| | - Ericka C. Holmstrand
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - Elizabeth. A. Ennis
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
| | - C. David Weaver
- Vanderbilt Institute
of Chemical
Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6304, United States
- Department
of Pharmacology, Vanderbilt University School of Medicine, Nashville,
Tennessee 37232-6600, United States
| | - Randy D. Blakely
- Center for Molecular
Neuroscience,
Department of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232-8548, United
States
- Department of Psychiatry, Vanderbilt
University School of Medicine, Nashville,
Tennessee 37232-8548, United States
| |
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