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Qian C, Wu Z, Sun R, Yu H, Zeng J, Rao Y, Li Y. Localization, proteomics, and metabolite profiling reveal a putative vesicular transporter for UDP-glucose. eLife 2021; 10:65417. [PMID: 34269178 PMCID: PMC8373376 DOI: 10.7554/elife.65417] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 07/15/2021] [Indexed: 11/27/2022] Open
Abstract
Vesicular neurotransmitter transporters (VNTs) mediate the selective uptake and enrichment of small-molecule neurotransmitters into synaptic vesicles (SVs) and are therefore a major determinant of the synaptic output of specific neurons. To identify novel VNTs expressed on SVs (thus identifying new neurotransmitters and/or neuromodulators), we conducted localization profiling of 361 solute carrier (SLC) transporters tagging with a fluorescent protein in neurons, which revealed 40 possible candidates through comparison with a known SV marker. We parallelly performed proteomics analysis of immunoisolated SVs and identified seven transporters in overlap. Ultrastructural analysis further supported that one of the transporters, SLC35D3, localized to SVs. Finally, by combining metabolite profiling with a radiolabeled substrate transport assay, we identified UDP-glucose as the principal substrate for SLC35D3. These results provide new insights into the functional role of SLC transporters in neurotransmission and improve our understanding of the molecular diversity of chemical transmitters.
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Affiliation(s)
- Cheng Qian
- School of Life Sciences, Tsinghua University, Beijing, China
| | - Zhaofa Wu
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China
| | - Rongbo Sun
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China
| | - Huasheng Yu
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Beijing, China
| | - Jianzhi Zeng
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Beijing, China
| | - Yi Rao
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Beijing, China.,Chinese Institute for Brain Research, Beijing, China
| | - Yulong Li
- State Key Laboratory of Membrane Biology, Peking University School of Life Sciences, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Beijing, China.,Chinese Institute for Brain Research, Beijing, China
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2
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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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3
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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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4
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DiCello JJ, Rajasekhar P, Eriksson EM, Saito A, Gondin AB, Veldhuis NA, Canals M, Carbone SE, Poole DP. Clathrin and GRK2/3 inhibitors block δ-opioid receptor internalization in myenteric neurons and inhibit neuromuscular transmission in the mouse colon. Am J Physiol Gastrointest Liver Physiol 2019; 317:G79-G89. [PMID: 31091149 DOI: 10.1152/ajpgi.00085.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Endocytosis is a major mechanism through which cellular signaling by G protein-coupled receptors (GPCRs) is terminated. However, recent studies demonstrate that GPCRs are internalized in an active state and continue to signal from within endosomes, resulting in effects on cellular function that are distinct to those arising at the cell surface. Endocytosis inhibitors are commonly used to define the importance of GPCR internalization for physiological and pathophysiological processes. Here, we provide the first detailed examination of the effects of these inhibitors on neurogenic contractions of gastrointestinal smooth muscle, a key preliminary step to evaluate the importance of GPCR endocytosis for gut function. Inhibitors of clathrin-mediated endocytosis (Pitstop2, PS2) or G protein-coupled receptor kinase-2/3-dependent phosphorylation (Takeda compound 101, Cmpd101), significantly reduced GPCR internalization. However, they also attenuated cholinergic contractions through different mechanisms. PS2 abolished contractile responses by colonic muscle to SNC80 and morphine, which strongly and weakly internalize δ-opioid and μ-opioid receptors, respectively. PS2 did not affect the increased myogenic contractile activity following removal of an inhibitory neural influence (tetrodotoxin) but suppressed electrically evoked neurogenic contractions. Ca2+ signaling by myenteric neurons in response to exogenous ATP was unaffected by PS2, suggesting inhibitory actions on neurotransmitter release rather than neurotransmission. In contrast, Cmpd101 attenuated contractions to the cholinergic agonist carbachol, indicating direct effects on smooth muscle. We conclude that, although PS2 and Cmpd101 are effective blockers of GPCR endocytosis in enteric neurons, these inhibitors are unsuitable for the study of neurally mediated gut function due to their inhibitory effects on neuromuscular transmission and smooth muscle contractility.NEW & NOTEWORTHY Internalization of activated G protein-coupled receptors is a major determinant of the type and duration of subsequent downstream signaling events. Inhibitors of endocytosis effectively block opioid receptor internalization in enteric neurons. The clathrin-dependent endocytosis inhibitor Pitstop2 blocks effects of opioids on neurogenic contractions of the colon in an internalization-independent manner. These inhibitors also significantly impact cholinergic neuromuscular transmission. We conclude that these tools are unsuitable for examination of the contribution of neuronal G protein-coupled receptor endocytosis to gastrointestinal motility.
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Affiliation(s)
- Jesse J DiCello
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia
| | - Pradeep Rajasekhar
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Emily M Eriksson
- Divisions of Population Health & Immunity and Infection and Immunity, The Walter and Eliza Hall Institute, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Ayame Saito
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia
| | - Arisbel B Gondin
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia
| | - Nicholas A Veldhuis
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia
| | - Meritxell Canals
- Centre for Membrane Proteins and Receptors, School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Simona E Carbone
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia
| | - Daniel P Poole
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Parkville, Victoria, Australia.,Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, Victoria, Australia
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5
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Blockage of High-Affinity Choline Transporter Increases Visceral Hypersensitivity in Rats with Chronic Stress. Gastroenterol Res Pract 2018; 2018:9252984. [PMID: 29849603 PMCID: PMC5904806 DOI: 10.1155/2018/9252984] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 03/14/2018] [Indexed: 12/19/2022] Open
Abstract
Background Visceral hypersensitivity is a common feature of irritable bowel syndrome. Cholinergic system involves in the development of visceral hypersensitivity, and high-affinity choline transporter (CHT1) is of crucial importance in choline uptake system. However, involvement of CHT1 in visceral hypersensitivity remains unknown. The research aimed to study the CHT1 expression in dorsal root ganglions (DRGs) and the role of CHT1 in visceral hypersensitivity. Methods Repetitive water avoidance stress (WAS) was used to induce visceral hypersensitivity in rats. Colorectal distension (CRD) was determined, and the abdominal withdrawal reflex (AWR) and threshold intensity data were recorded to measure the visceral sensitivity. After intraperitoneal injection of hemicholinium-3 (HC-3), the specific inhibitor of CHT1, CRD data were also recorded. The CHT1 expression of DRGs was investigated by Western blotting, immunohistochemistry, and quantitative RT-PCR. Acetylcholine levels in the DRGs were detected by the assay kit. Results Repetitive WAS increased the AWR score of CRD at high distension pressure and decreased the mean threshold of rats. The CHT1 expression and acetylcholine concentration of DRG were significantly increased in WAS rats. After the administration of HC-3, the AWR score in WAS group was significantly increased at higher distension pressure while the threshold intensity was significantly reduced compared to the normal saline group. Acetylcholine concentration was significantly lower than the normal saline rats. Conclusion Our research firstly reports that CHT1 is overexpressed in noninflammatory visceral hypersensitivity, and blockage of CHT1 can enhance the visceral hypersensitivity. CHT1 may play an inhibitory role in visceral hypersensitivity.
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6
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Sarter M, Phillips KB. The neuroscience of cognitive-motivational styles: Sign- and goal-trackers as animal models. Behav Neurosci 2018; 132:1-12. [PMID: 29355335 DOI: 10.1037/bne0000226] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Cognitive-motivational styles describe predominant patterns of processing or biases that broadly influence human cognition and performance. Here we focus on the impact of cognitive-motivational styles on the response to cues predicting the availability of food or addictive drugs. An individual may preferably conduct an analysis of the motivational significance of reward cues, with the result that such cues per se are perceived as rewarding and worth approaching and working for. Alternatively, a propensity for a "cold" analysis of the behavioral utility of a reward cue may yield search behavior for food or drugs but not involve cue approach. Animal models for studying the neuronal mechanisms mediating such styles have originated from research concerning behavioral indices that predict differential vulnerability to addiction-like behaviors. Rats classified as sign- or goal-trackers (STs, GTs) were found to have opposed attentional biases (bottom-up or cue-driven attention vs. top-down or goal-driven attentional control) that are mediated primarily via relatively unresponsive versus elevated levels of cholinergic neuromodulation in the cortex. The capacity for cholinergic neuromodulation in STs is limited by a neuronal choline transporter (CHT) that fails to support increases in cholinergic activity. Moreover, in contrast to STs, the frontal dopamine system in GTs does not respond to the presence of drug cues and, thus, biases against cue-oriented behavior. The opponent cognitive-motivational styles that are indexed by sign- and goal-tracking bestow different cognitive-behavioral vulnerabilities that may contribute to the manifestation of a wide range of neuropsychiatric disorders. (PsycINFO Database Record
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Affiliation(s)
- Martin Sarter
- Department of Psychology and Neuroscience Program, University of Michigan
| | - Kyra B Phillips
- Department of Psychology and Neuroscience Program, University of Michigan
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7
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Wang H, Salter CG, Refai O, Hardy H, Barwick KES, Akpulat U, Kvarnung M, Chioza BA, Harlalka G, Taylan F, Sejersen T, Wright J, Zimmerman HH, Karakaya M, Stüve B, Weis J, Schara U, Russell MA, Abdul-Rahman OA, Chilton J, Blakely RD, Baple EL, Cirak S, Crosby AH. Choline transporter mutations in severe congenital myasthenic syndrome disrupt transporter localization. Brain 2017; 140:2838-2850. [PMID: 29088354 DOI: 10.1093/brain/awx249] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 08/05/2017] [Indexed: 11/12/2022] Open
Abstract
The presynaptic, high-affinity choline transporter is a critical determinant of signalling by the neurotransmitter acetylcholine at both central and peripheral cholinergic synapses, including the neuromuscular junction. Here we describe an autosomal recessive presynaptic congenital myasthenic syndrome presenting with a broad clinical phenotype due to homozygous choline transporter missense mutations. The clinical phenotype ranges from the classical presentation of a congenital myasthenic syndrome in one patient (p.Pro210Leu), to severe neurodevelopmental delay with brain atrophy (p.Ser94Arg) and extend the clinical outcomes to a more severe spectrum with infantile lethality (p.Val112Glu). Cells transfected with mutant transporter construct revealed a virtually complete loss of transport activity that was paralleled by a reduction in transporter cell surface expression. Consistent with these findings, studies to determine the impact of gene mutations on the trafficking of the Caenorhabditis elegans choline transporter orthologue revealed deficits in transporter export to axons and nerve terminals. These findings contrast with our previous findings in autosomal dominant distal hereditary motor neuropathy of a dominant-negative frameshift mutation at the C-terminus of choline transporter that was associated with significantly reduced, but not completely abrogated choline transporter function. Together our findings define divergent neuropathological outcomes arising from different classes of choline transporter mutation with distinct disease processes and modes of inheritance. These findings underscore the essential role played by the choline transporter in sustaining acetylcholine neurotransmission at both central and neuromuscular synapses, with important implications for treatment and drug selection.
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Affiliation(s)
- Haicui Wang
- University Hospital Cologne, Department of Pediatrics, Kerpener Str. 62, 50937 Cologne, Germany.,Center for Molecular Medicine Cologne (CMMC), University of Cologne, Robert-Koch-Str. 21, 50931 Cologne, Germany
| | - Claire G Salter
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK.,Human Genetics and Genomic Medicine, Faculty of Medicine, University of Southampton, Southampton, SO16 6YD, UK
| | - Osama Refai
- Department of Biomedical Science, Charles E. Schmidt College of Medicine and Brain Institute, Florida Atlantic University, Jupiter, FL, USA
| | - Holly Hardy
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Katy E S Barwick
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Ugur Akpulat
- University Hospital Cologne, Department of Pediatrics, Kerpener Str. 62, 50937 Cologne, Germany.,Center for Molecular Medicine Cologne (CMMC), University of Cologne, Robert-Koch-Str. 21, 50931 Cologne, Germany.,Kastamonu University, 37150 Kastamonu, Turkey
| | - Malin Kvarnung
- Department of Molecular Medicine and Surgery, Center for Molecular Medicine, Karolinska Institutet, 17176 Stockholm, Sweden.,Department of Clinical Genetics, Karolinska University Hospital, 17176 Stockholm, Sweden
| | - Barry A Chioza
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Gaurav Harlalka
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Fulya Taylan
- Department of Molecular Medicine and Surgery, Center for Molecular Medicine, Karolinska Institutet, 17176 Stockholm, Sweden.,Science for Life Laboratory, Karolinska Institutet Science Park, 17121 Stockholm, Sweden
| | - Thomas Sejersen
- Science for Life Laboratory, Karolinska Institutet Science Park, 17121 Stockholm, Sweden.,Department of Women's and Children's Health, Division of Pediatric Neurology, Karolinska Institutet, 17176 Stockholm, Sweden
| | - Jane Wright
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
| | - Holly H Zimmerman
- Division of Medical Genetics, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA
| | - Mert Karakaya
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, Robert-Koch-Str. 21, 50931 Cologne, Germany
| | - Burkhardt Stüve
- Children's Hospital Social Pediatric Center, 50735 Cologne, Germany
| | - Joachim Weis
- Institute of Neuropathology and Jülich Aachen Research Alliance (JARA) Brain Translational Medicine, RWTH Aachen University, 52074 Aachen, Germany
| | - Ulrike Schara
- University Children's Hospital Essen, Essen, Germany
| | - Mark A Russell
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Omar A Abdul-Rahman
- Department of Pediatrics, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA
| | - John Chilton
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Randy D Blakely
- Department of Biomedical Science, Charles E. Schmidt College of Medicine and Brain Institute, Florida Atlantic University, Jupiter, FL, USA
| | - Emma L Baple
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
| | - Sebahattin Cirak
- University Hospital Cologne, Department of Pediatrics, Kerpener Str. 62, 50937 Cologne, Germany.,Center for Molecular Medicine Cologne (CMMC), University of Cologne, Robert-Koch-Str. 21, 50931 Cologne, Germany
| | - Andrew H Crosby
- RILD Wellcome Wolfson Centre, Royal Devon and Exeter NHS Foundation Trust, Barrack Road, Exeter, EX2 5DW, UK
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Janickova H, Prado VF, Prado MAM, El Mestikawy S, Bernard V. Vesicular acetylcholine transporter (VAChT) over-expression induces major modifications of striatal cholinergic interneuron morphology and function. J Neurochem 2017. [DOI: 10.1111/jnc.14105] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Helena Janickova
- Department of Physiology and Pharmacology and Department of Anatomy & Cell Biology; Robarts Research Institute; Molecular Medicine Laboratories; The University of Western Ontario; London Ontario Canada
| | - Vania F. Prado
- Department of Physiology and Pharmacology and Department of Anatomy & Cell Biology; Robarts Research Institute; Molecular Medicine Laboratories; The University of Western Ontario; London Ontario Canada
| | - Marco A. M. Prado
- Department of Physiology and Pharmacology and Department of Anatomy & Cell Biology; Robarts Research Institute; Molecular Medicine Laboratories; The University of Western Ontario; London Ontario Canada
| | - Salah El Mestikawy
- Sorbonne Universités; Université Pierre et Marie Curie UM 119 - CNRS UMR 8246 - INSERM U1130; Neurosciences Paris Seine - Institut de Biologie Paris Seine (NPS - IBPS); Paris France
- Department of Psychiatry; Douglas Mental Health University Institute; McGill University; Montreal Canada
| | - Véronique Bernard
- Sorbonne Universités; Université Pierre et Marie Curie UM 119 - CNRS UMR 8246 - INSERM U1130; Neurosciences Paris Seine - Institut de Biologie Paris Seine (NPS - IBPS); Paris France
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9
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Choudhary P, Armstrong EJ, Jorgensen CC, Piotrowski M, Barthmes M, Torella R, Johnston SE, Maruyama Y, Janiszewski JS, Storer RI, Skerratt SE, Benn CL. Discovery of Compounds that Positively Modulate the High Affinity Choline Transporter. Front Mol Neurosci 2017; 10:40. [PMID: 28289374 PMCID: PMC5326799 DOI: 10.3389/fnmol.2017.00040] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 02/03/2017] [Indexed: 01/09/2023] Open
Abstract
Cholinergic hypofunction is associated with decreased attention and cognitive deficits in the central nervous system in addition to compromised motor function. Consequently, stimulation of cholinergic neurotransmission is a rational therapeutic approach for the potential treatment of a variety of neurological conditions. High affinity choline uptake (HACU) into acetylcholine (ACh)-synthesizing neurons is critically mediated by the sodium- and pH-dependent high-affinity choline transporter (CHT, encoded by the SLC5A7 gene). This transporter is comparatively well-characterized but otherwise unexplored as a potential drug target. We therefore sought to identify small molecules that would enable testing of the hypothesis that positive modulation of CHT mediated transport would enhance activity-dependent cholinergic signaling. We utilized existing and novel screening techniques for their ability to reveal both positive and negative modulation of CHT using literature tools. A screening campaign was initiated with a bespoke compound library comprising both the Pfizer Chemogenomic Library (CGL) of 2,753 molecules designed specifically to help enable the elucidation of new mechanisms in phenotypic screens and 887 compounds from a virtual screening campaign to select molecules with field-based similarities to reported negative and positive allosteric modulators. We identified a number of previously unknown active and structurally distinct molecules that could be used as tools to further explore CHT biology or as a starting point for further medicinal chemistry.
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Affiliation(s)
| | | | | | | | | | | | | | - Yuya Maruyama
- Central Research Laboratory, Kissei Pharmaceutical Co., Ltd. Nagano, Japan
| | | | - R Ian Storer
- Pfizer, Worldwide Medicinal Chemistry Cambridge, UK
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10
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Ferreira-Vieira TH, Guimaraes IM, Silva FR, Ribeiro FM. Alzheimer's disease: Targeting the Cholinergic System. Curr Neuropharmacol 2016; 14:101-15. [PMID: 26813123 PMCID: PMC4787279 DOI: 10.2174/1570159x13666150716165726] [Citation(s) in RCA: 831] [Impact Index Per Article: 103.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 07/01/2015] [Accepted: 07/14/2015] [Indexed: 12/16/2022] Open
Abstract
Acetylcholine (ACh) has a crucial role in the peripheral and central nervous
systems. The enzyme choline acetyltransferase (ChAT) is responsible for
synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular
acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic
vesicles. Following depolarization, ACh undergoes exocytosis reaching the
synaptic cleft, where it can bind its receptors, including muscarinic and
nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by
the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is
recycled into the presynaptic nerve terminal by the high-affinity choline
transporter (CHT1). Cholinergic neurons located in the basal forebrain,
including the neurons that form the nucleus basalis of Meynert, are severely
lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia
affecting 25 million people worldwide. The hallmarks of the disease are the
accumulation of neurofibrillary tangles and amyloid plaques. However, there is
no real correlation between levels of cortical plaques and AD-related cognitive
impairment. Nevertheless, synaptic loss is the principal correlate of disease
progression and loss of cholinergic neurons contributes to memory and attention
deficits. Thus, drugs that act on the cholinergic system represent a promising
option to treat AD patients.
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Affiliation(s)
| | | | | | - Fabiola M Ribeiro
- Departamento de Bioquimica e Imunologia, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
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11
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Cholinergic genetics of visual attention: Human and mouse choline transporter capacity variants influence distractibility. ACTA ACUST UNITED AC 2016; 110:10-18. [PMID: 27404793 DOI: 10.1016/j.jphysparis.2016.07.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 07/07/2016] [Accepted: 07/08/2016] [Indexed: 11/20/2022]
Abstract
The basal forebrain cholinergic projection system to the cortex mediates essential aspects of visual attention performance, including the detection of cues and the response to performance challenges (top-down control of attention). Higher levels of top-down control are mediated via elevated levels of cholinergic neuromodulation. The neuronal choline transporter (CHT) strongly influences the synthesis and release of acetylcholine (ACh). As the capacity of the CHT to import choline into the neuron is a major, presynaptic determinant of cholinergic neuromodulation, we hypothesize that genetically-imposed CHT capacity variation impacts the balance of bottom-up versus top-down control of visual attention. Following a brief review of the cognitive concepts relevant for this hypothesis, we describe the key results from our research in mice and humans that possess genetically-imposed changes in choline uptake capacity. CHT subcapacity is associated with poor top-down attentional control and attenuated (cholinergic) activation of right frontal regions. Conversely, mice overexpressing the CHT, and humans expressing a CHT variant hypothesized to enhance choline transporter function, are relatively resistant to challenges of visual attention performance. Genetic or environmental modulation of CHT expression and function may be associated with vulnerabilities for cognitive disorders.
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12
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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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Iwamoto H, Calcutt MW, Blakely RD. Differential impact of genetically modulated choline transporter expression on the release of endogenous versus newly synthesized acetylcholine. Neurochem Int 2016; 98:138-45. [PMID: 27013347 DOI: 10.1016/j.neuint.2016.03.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Revised: 03/12/2016] [Accepted: 03/16/2016] [Indexed: 11/15/2022]
Abstract
The efficient import of choline into cholinergic nerve terminals by the presynaptic, high-affinity choline transporter (CHT, SLC5A7) dictates the capacity for acetylcholine (ACh) synthesis and release. Tissue levels of ACh are significantly reduced in mice heterozygous for a loss of function mutation in Slc5a7 (HET, CHT(+/-)), but significantly elevated in overexpressing, Slc5a7 BAC-transgenic mice (BAC). Since the readily-releasable pool of ACh is thought to constitute a small fraction of the total ACh pool, these genotype-dependent changes raised the question as to whether CHT expression or activity might preferentially influence the size of reserve pool ACh vesicles. In the current study, we approached this question by evaluating CHT genotype effects on the release of ACh from suprafused mouse forebrain slices. We treated slices from HET, BAC or wildtype (WT) controls with elevated K(+) and monitored release of both newly synthesized and storage pools of ACh. Newly synthesized ACh produced following uptake of [(3)H]choline was quantified by scintillation spectrometry whereas release of endogenous ACh storage pools was quantified by an HPLC-MS approach, from the same samples. Whereas endogenous ACh release scaled with CHT gene dosage, preloaded [(3)H]ACh release displayed no significant genotype dependence. Our findings suggest that CHT protein levels preferentially impact the capacity for ACh release afforded by mobilization of reserve pool vesicles.
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Affiliation(s)
- Hideki Iwamoto
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - M Wade Calcutt
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN, USA; Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Randy D Blakely
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA; Department of Psychiatry, Vanderbilt University School of Medicine, Nashville, TN, USA.
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14
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Bedore J, Martyn AC, Li AKC, Dolinar EA, McDonald IS, Coupland SG, Prado VF, Prado MA, Hill KA. Whole-Retina Reduced Electrophysiological Activity in Mice Bearing Retina-Specific Deletion of Vesicular Acetylcholine Transporter. PLoS One 2015; 10:e0133989. [PMID: 26226617 PMCID: PMC4520552 DOI: 10.1371/journal.pone.0133989] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 07/03/2015] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Despite rigorous characterization of the role of acetylcholine in retinal development, long-term effects of its absence as a neurotransmitter are unknown. One of the unanswered questions is how acetylcholine contributes to the functional capacity of mature retinal circuits. The current study investigates the effects of disrupting cholinergic signalling in mice, through deletion of vesicular acetylcholine transporter (VAChT) in the developing retina, pigmented epithelium, optic nerve and optic stalk, on electrophysiology and structure of the mature retina. METHODS & RESULTS A combination of electroretinography, optical coherence tomography imaging and histological evaluation assessed retinal integrity in mice bearing retina- targeted (embryonic day 12.5) deletion of VAChT (VAChTSix3-Cre-flox/flox) and littermate controls at 5 and 12 months of age. VAChTSix3-Cre-flox/flox mice did not show any gross changes in nuclear layer cellularity or synaptic layer thickness. However, VAChTSix3-Cre-flox/flox mice showed reduced electrophysiological response of the retina to light stimulus under scotopic conditions at 5 and 12 months of age, including reduced a-wave, b-wave, and oscillatory potential (OP) amplitudes and decreased OP peak power and total energy. Reduced a-wave amplitude was proportional to the reduction in b-wave amplitude and not associated with altered a-wave 10%-90% rise time or inner and outer segment thicknesses. SIGNIFICANCE This study used a novel genetic model in the first examination of function and structure of the mature mouse retina with disruption of cholinergic signalling. Reduced amplitude across the electroretinogram wave form does not suggest dysfunction in specific retinal cell types and could reflect underlying changes in the retinal and/or extraretinal microenvironment. Our findings suggest that release of acetylcholine by VAChT is essential for the normal electrophysiological response of the mature mouse retina.
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Affiliation(s)
- Jake Bedore
- Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Amanda C Martyn
- Molecular Medicine, Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Anson K C Li
- Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Eric A Dolinar
- Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Ian S McDonald
- Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Stuart G Coupland
- Ophthalmology, Cellular and Molecular Medicine, University of Ottawa, Ottawa Eye Institute, Ottawa, Ontario, Canada K1H 8L6
| | - Vania F Prado
- Molecular Medicine, Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Marco A Prado
- Molecular Medicine, Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Kathleen A Hill
- Department of Biology, The University of Western Ontario, London, Ontario, Canada N6A 5B7
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15
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Cuddy LK, Seah C, Pasternak SH, Rylett RJ. Differential regulation of the high-affinity choline transporter by wild-type and Swedish mutant amyloid precursor protein. J Neurochem 2015; 134:769-82. [DOI: 10.1111/jnc.13167] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 04/30/2015] [Accepted: 05/06/2015] [Indexed: 01/18/2023]
Affiliation(s)
- Leah K. Cuddy
- Molecular Medicine Research Group; Robarts Research Institute; London Ontario Canada
- Department of Physiology and Pharmacology; University of Western Ontario; London Ontario Canada
| | - Claudia Seah
- Molecular Medicine Research Group; Robarts Research Institute; London Ontario Canada
| | - Stephen H. Pasternak
- Molecular Medicine Research Group; Robarts Research Institute; London Ontario Canada
- Department of Physiology and Pharmacology; University of Western Ontario; London Ontario Canada
- Department of Clinical Neurological Sciences; Schulich School of Medicine & Dentistry; University of Western Ontario; London Ontario Canada
| | - Rebecca Jane Rylett
- Molecular Medicine Research Group; Robarts Research Institute; London Ontario Canada
- Department of Physiology and Pharmacology; University of Western Ontario; London Ontario Canada
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16
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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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17
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Dettmer J, Ursache R, Campilho A, Miyashima S, Belevich I, O'Regan S, Mullendore DL, Yadav SR, Lanz C, Beverina L, Papagni A, Schneeberger K, Weigel D, Stierhof YD, Moritz T, Knoblauch M, Jokitalo E, Helariutta Y. CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication. Nat Commun 2014; 5:4276. [PMID: 25008948 DOI: 10.1038/ncomms5276] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2013] [Accepted: 06/02/2014] [Indexed: 11/09/2022] Open
Abstract
Phloem, a plant tissue responsible for long-distance molecular transport, harbours specific junctions, sieve areas, between the conducting cells. To date, little is known about the molecular framework related to the biogenesis of these sieve areas. Here we identify mutations at the CHER1/AtCTL1 locus of Arabidopsis thaliana. The mutations cause several phenotypic abnormalities, including reduced pore density and altered pore structure in the sieve areas associated with impaired phloem function. CHER1 encodes a member of a poorly characterized choline transporter-like protein family in plants and animals. We show that CHER1 facilitates choline transport, localizes to the trans-Golgi network, and during cytokinesis is associated with the phragmoplast. Consistent with its function in the elaboration of the sieve areas, CHER1 has a sustained, polar localization in the forming sieve plates. Our results indicate that the regulation of choline levels is crucial for phloem development and conductivity in plants.
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Affiliation(s)
- Jan Dettmer
- 1] Cell Biology Division, Department of Biology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany [2]
| | - Robertas Ursache
- 1] Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland [2]
| | - Ana Campilho
- 1] Institute for Molecular and Cell Biology (IBMC), University of Porto, Porto 4150-180, Portugal [2]
| | - Shunsuke Miyashima
- Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland
| | - Ilya Belevich
- Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland
| | - Seana O'Regan
- Neurophotonics Laboratory, CNRS/Université Paris Descartes, 45, rue des Saints-Pères, 75270 Paris, France
| | - Daniel Leroy Mullendore
- School of Biological Sciences, Washington State University, Pullman, Washington 99164-4236, USA
| | - Shri Ram Yadav
- Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland
| | - Christa Lanz
- Department of Molecular Biology, Max Planck Institute for Developmental Biology, 72076 Tuebingen, Germany
| | - Luca Beverina
- Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Antonio Papagni
- Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Korbinian Schneeberger
- Max Planck Institute for Plant Breeding Research, Department for Plant Developmental Biology, 50829 Cologne, Germany
| | - Detlef Weigel
- Department of Molecular Biology, Max Planck Institute for Developmental Biology, 72076 Tuebingen, Germany
| | - York-Dieter Stierhof
- ZMBP, Mikroskopie, Universität Tübingen, Auf der Morgenstelle 5, 72076 Tübingen, Germany
| | - Thomas Moritz
- Department of Forest Genetics and Plant Physiology, Umeå Plant Science Center, Swedish University of Agricultural Sciences, SE-90183 Umeå, Sweden
| | - Michael Knoblauch
- School of Biological Sciences, Washington State University, Pullman, Washington 99164-4236, USA
| | - Eija Jokitalo
- Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland
| | - Ykä Helariutta
- Institute of Biotechnology, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki FIN-00014, Finland
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18
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Hartnett S, Zhang F, Abitz A, Li Y. Ubiquitin C-terminal hydrolase L1 interacts with choline transporter in cholinergic cells. Neurosci Lett 2014; 564:115-9. [PMID: 24525247 DOI: 10.1016/j.neulet.2014.02.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Revised: 01/27/2014] [Accepted: 02/02/2014] [Indexed: 02/02/2023]
Abstract
Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme, which is highly expressed in neuronal cells. Previous studies have indicated that UCHL1 is involved in cognitive function, neurodegenerative diseases, and neuromuscular junction development. Acetylcholine (Ach) is a critical neurotransmitter in these functions. Yet, the effect of UCHL1 on the cholinergic system has not been reported. In this study, using a cholinergic neuronal cell line, SN56, as an invitro model, we detected the physical interaction of UCHL1 and high affinity choline transporter (CHT), which is a key protein regulating Ach re-synthesis. Reduction of UCHL1 by siRNA gene knockdown significantly increased poly-ubiquitinated CHT and decreased native CHT protein level, but did not affect CHT mRNA expression. Biotinylation assay showed that UCHL1 is localized only in the cytosol of the cells and that the gene knockdown of UCHL1 significantly reduced cytosolic CHT but had no significant effect on membrane CHT level. These data provide novel and potentially important evidence that UCHL1 may play a role in the regulation of cholinergic function by affecting CHT ubiquitination and degradation.
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Affiliation(s)
- Sigurd Hartnett
- Division of Basic Biomedical Sciences, Sanford School of Medicine, The University of South Dakota, Vermillion, SD, 57069, USA
| | - Fan Zhang
- Division of Basic Biomedical Sciences, Sanford School of Medicine, The University of South Dakota, Vermillion, SD, 57069, USA
| | - Allison Abitz
- Division of Basic Biomedical Sciences, Sanford School of Medicine, The University of South Dakota, Vermillion, SD, 57069, USA
| | - Yifan Li
- Division of Basic Biomedical Sciences, Sanford School of Medicine, The University of South Dakota, Vermillion, SD, 57069, USA.
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19
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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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20
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Roy A, Fields WC, Rocha-Resende C, Resende RR, Guatimosim S, Prado VF, Gros R, Prado MAM. Cardiomyocyte-secreted acetylcholine is required for maintenance of homeostasis in the heart. FASEB J 2013; 27:5072-82. [PMID: 24018063 DOI: 10.1096/fj.13-238279] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Heart activity and long-term function are regulated by the sympathetic and parasympathetic branches of the nervous system. Parasympathetic neurons have received increased attention recently because acetylcholine (ACh) has been shown to play protective roles in heart disease. However, parasympathetic innervation is sparse in the heart, raising the question of how cholinergic signaling regulates cardiomyocytes. We hypothesized that non-neuronal secretion of ACh from cardiomyocytes plays a role in cholinergic regulation of cardiac activity. To test this possibility, we eliminated secretion of ACh exclusively from cardiomyocytes by targeting the vesicular acetylcholine transporter (VAChT). We find that lack of cardiomyocyte-secreted ACh disturbs the regulation of cardiac activity and causes cardiomyocyte remodeling. Mutant mice present normal hemodynamic parameters under nonstressful conditions; however, following exercise, their heart rate response is increased. Moreover, hearts from mutant mice present increased oxidative stress, altered calcium signaling, remodeling, and hypertrophy. Hence, without cardiomyocyte-derived ACh secretion, hearts from mutant mice show signs of imbalanced autonomic activity consistent with decreased cholinergic drive. These unexpected results suggest that cardiomyocyte-derived ACh is required for maintenance of cardiac homeostasis and regulates critical signaling pathways necessary to maintain normal heart activity. We propose that this non-neuronal source of ACh boosts parasympathetic cholinergic signaling to counterbalance sympathetic activity regulating multiple aspects of heart physiology.
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Affiliation(s)
- Ashbeel Roy
- 1Robarts Research Institute, 100 Perth Dr., London, Ontario, N6A 5K8, Canada. M.A.M.P.,
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21
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Abstract
Acetylcholine, the first chemical to be identified as a neurotransmitter, is packed in synaptic vesicles by the activity of VAChT (vesicular acetylcholine transporter). A decrease in VAChT expression has been reported in a number of diseases, and this has consequences for the amount of acetylcholine loaded in synaptic vesicles as well as for neurotransmitter release. Several genetically modified mice targeting the VAChT gene have been generated, providing novel models to understand how changes in VAChT affect transmitter release. A surprising finding is that most cholinergic neurons in the brain also can express a second type of vesicular neurotransmitter transporter that allows these neurons to secrete two distinct neurotransmitters. Thus a given neuron can use two neurotransmitters to regulate different physiological functions. In addition, recent data indicate that non-neuronal cells can also express the machinery used to synthesize and release acetylcholine. Some of these cells rely on VAChT to secrete acetylcholine with potential physiological consequences in the periphery. Hence novel functions for the oldest neurotransmitter known are emerging with the potential to provide new targets for the treatment of several pathological conditions.
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22
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The presynaptic choline transporter imposes limits on sustained cortical acetylcholine release and attention. J Neurosci 2013; 33:2326-37. [PMID: 23392663 DOI: 10.1523/jneurosci.4993-12.2013] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Functional variation in the gene encoding the presynaptic choline transporter (CHT) has been linked to attention-deficit/hyperactivity disorder. Here, we report that a heterozygous deletion in the CHT gene in mice (CHT(+/-)) limits the capacity of cholinergic neurons to sustain acetylcholine (ACh) release and attentional performance. Cortical microdialysis and amperometric methods revealed that, whereas wild-type and CHT(+/-) animals support equivalent basal ACh release and choline clearance, CHT(+/-) animals exhibit a significant inability to elevate extracellular ACh following basal forebrain stimulation, in parallel with a diminished choline clearance capacity following cessation of stimulation. Consistent with these findings, the density of CHTs in cortical synaptosomal plasma membrane-enriched fractions from unstimulated CHT(+/-) animals matched those observed in wild-type animals despite reductions in CHT levels in total extracts, achieved via a redistribution of CHT from vesicle pools. As a consequence, in CHT(+/-) animals, basal forebrain stimulation was unable to mobilize wild-type quantities of CHT to the plasma membrane. In behavioral studies, CHT(+/-) mice were impaired in performing a sustained attention task known to depend on cortical cholinergic activity. In wild-type mice, but not CHT(+/-) mice, attentional performance increased the density of CHTs in the synaptosomal membrane in the right frontal cortex. Basal CHT levels in vesicle-enriched membranes predicted the degree of CHT mobilization as well as individual variations in performance on the sustained attention task. Our findings demonstrate biochemical and physiological alterations that underlie cognitive impairments associated with genetically imposed reductions in choline uptake capacity.
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23
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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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Peroxynitrite donor SIN-1 alters high-affinity choline transporter activity by modifying its intracellular trafficking. J Neurosci 2012; 32:5573-84. [PMID: 22514319 DOI: 10.1523/jneurosci.5235-11.2012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Sodium-coupled, high-affinity choline transporters (CHTs) are inhibited by 3-morpholinosydnonimine (SIN-1) [peroxynitrite (ONOO⁻) donor]; ONOO⁻ can be produced from nitric oxide and reactive oxygen species during neurodegeneration. SIN-1 rapidly increases CHT internalization from the cell surface, and this correlates with decreased choline uptake. This study addresses mechanisms by which SIN-1 inhibits CHT function in human neuronal SH-SY5Y cells. Thus, mutant L531A-CHT, which does not constitutively internalize into cells by a clathrin-mediated process, is resistant to SIN-1 effects. This suggests that CHT inhibition is not due to oxidative-nitrosative inactivation of the protein and that decreased levels of cell surface CHT in SIN-1-treated cells is related to alterations in its trafficking and subcellular disposition. Dominant-negative proteins AP180C and dynamin-K44A, which interfere with clathrin-mediated and dynamin-dependent endocytosis, respectively, attenuate CHT inhibition by SIN-1. CHT in both vehicle- and SIN-1-treated cells colocalizes with Rab7, Rab9, and Lamp-1 in late endosomes and lysosomes to a similar extent. Lysosome inhibitors increase choline uptake, suggesting that CHT proteins are normally degraded by lysosomes, and this is not altered by oxidative stress. Unexpectedly, inhibitors of proteasomes, but not lysosomes, attenuate SIN-1-mediated inhibition of choline uptake, indicating that proteasomal degradation plays a role in regulating CHT disposition in SIN-1-treated cells. SIN-1 treatment also enhances CHT ubiquitination. Thus, CHT inhibition in SIN-1-treated cells is mediated by proteasomal degradation, which differs from inhibitory mechanisms for some neurotransmitter transporters under similar conditions. Increased oxidative-nitrosative stress in the microenvironment of cholinergic nerve terminals would diminish cholinergic transmission by reducing choline availability for ACh synthesis.
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25
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Rocha-Resende C, Roy A, Resende R, Ladeira MS, Lara A, de Morais Gomes ER, Prado VF, Gros R, Guatimosim C, Prado MAM, Guatimosim S. Non-neuronal cholinergic machinery present in cardiomyocytes offsets hypertrophic signals. J Mol Cell Cardiol 2012; 53:206-16. [PMID: 22587993 DOI: 10.1016/j.yjmcc.2012.05.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Revised: 04/17/2012] [Accepted: 05/03/2012] [Indexed: 12/19/2022]
Abstract
Recent work has provided compelling evidence that increased levels of acetylcholine (ACh) can be protective in heart failure, whereas reduced levels of ACh secretion can cause heart malfunction. Previous data show that cardiomyocytes themselves can actively secrete ACh, raising the question of whether this cardiomyocyte derived ACh may contribute to the protective effects of ACh in the heart. To address the functionality of this non-neuronal ACh machinery, we used cholinesterase inhibitors and a siRNA targeted to AChE (acetylcholinesterase) as a way to increase the availability of ACh secreted by cardiac cells. By using nitric oxide (NO) formation as a biological sensor for released ACh, we showed that cholinesterase inhibition increased NO levels in freshly isolated ventricular myocytes and that this effect was prevented by atropine, a muscarinic receptor antagonist, and by inhibition of ACh synthesis or vesicular storage. Functionally, cholinesterase inhibition prevented the hypertrophic effect as well as molecular changes and calcium transient alterations induced by adrenergic overstimulation in cardiomyocytes. Moreover, inhibition of ACh storage or atropine blunted the anti-hypertrophic action of cholinesterase inhibition. Altogether, our results show that cardiomyocytes possess functional cholinergic machinery that offsets deleterious effects of hyperadrenergic stimulation. In addition, we show that adrenergic stimulation upregulates expression levels of cholinergic components. We propose that this cardiomyocyte cholinergic signaling could amplify the protective effects of the parasympathetic nervous system in the heart and may counteract or partially neutralize hypertrophic adrenergic effects.
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Affiliation(s)
- Cibele Rocha-Resende
- Department of Physiology and Biophysics, Institute of Biological Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, MG, CEP 31270-901, Brazil.
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26
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Abreu BJ, Leite LF, Oliveira DL, Amaral E. Synaptic vesicle cycling is not impaired in a glutamatergic and a cholinergic synapse that exhibit deficits in acidification and filling. BRAZ J PHARM SCI 2012. [DOI: 10.1590/s1984-82502012000100017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of the present work was to investigate synaptic vesicle trafficking when vesicles exhibit alterations in filling and acidification in two different synapses: a cholinergic frog neuromuscular junction and a glutamatergic ribbon-type nerve terminal in the retina. These synapses display remarkable structural and functional differences, and the mechanisms regulating synaptic vesicle cycling might also differ between them. The lipophilic styryl dye FM1-43 was used to monitor vesicle trafficking. Both preparations were exposed to pharmacological agents that collapse ΔpH (NH4Cl and methylamine) or the whole ΔµH+ (bafilomycin), a necessary situation to provide the driving force for neurotransmitter accumulation into synaptic vesicles. The results showed that FM1-43 loading and unloading in neuromuscular junctions did not differ statistically between control and experimental conditions (P > 0.05). Also, FM1-43 labeling in bipolar cell terminals proved highly similar under all conditions tested. Despite remarkable differences in both experimental models, the present findings show that acidification and filling are not required for normal vesicle trafficking in either synapse.
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27
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Abstract
Cholinergic neurons are endowed with a high-affinity choline uptake system for efficient synthesis of acetylcholine at the presynaptic terminals. The high-affinity choline transporter CHT1 is responsible for choline uptake, the rate-limiting step in acetylcholine synthesis. However, endogenous physiological factors that affect CHT1 expression or function and consequently regulate the acetylcholine synthesis rate are essentially unknown. Here we demonstrate that extracellular substrate decreases the cell-surface expression of CHT1 in rat brain synaptosomes, primary cultures from the basal forebrain, and mammalian cell lines transfected with CHT1. Extracellular choline rapidly decreases cell-surface CHT1 expression by accelerating its internalization, a process that is mediated by a dynamin-dependent endocytosis pathway in HEK293 cells. Specific inhibitor hemicholinium-3 decreases the constitutive internalization rate and thereby increases cell-surface CHT1 expression. We also demonstrate that the constitutive internalization of CHT1 depends on extracellular pH in cultured cells. Our results collectively suggest that the internalization of CHT1 is induced by extracellular substrate, providing a novel feedback mechanism for the regulation of acetylcholine synthesis at the cholinergic presynaptic terminals.
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Elimination of the vesicular acetylcholine transporter in the striatum reveals regulation of behaviour by cholinergic-glutamatergic co-transmission. PLoS Biol 2011; 9:e1001194. [PMID: 22087075 PMCID: PMC3210783 DOI: 10.1371/journal.pbio.1001194] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 09/29/2011] [Indexed: 11/30/2022] Open
Abstract
A novel mouse model that eliminates cholinergic neurotransmission in the striatum while leaving glutamate release intact reveals differential effects on cocaine-induced behavior and dopaminergic responses. Cholinergic neurons in the striatum are thought to play major regulatory functions in motor behaviour and reward. These neurons express two vesicular transporters that can load either acetylcholine or glutamate into synaptic vesicles. Consequently cholinergic neurons can release both neurotransmitters, making it difficult to discern their individual contributions for the regulation of striatal functions. Here we have dissected the specific roles of acetylcholine release for striatal-dependent behaviour in mice by selective elimination of the vesicular acetylcholine transporter (VAChT) from striatal cholinergic neurons. Analysis of several behavioural parameters indicates that elimination of VAChT had only marginal consequences in striatum-related tasks and did not affect spontaneous locomotion, cocaine-induced hyperactivity, or its reward properties. However, dopaminergic sensitivity of medium spiny neurons (MSN) and the behavioural outputs in response to direct dopaminergic agonists were enhanced, likely due to increased expression/function of dopamine receptors in the striatum. These observations indicate that previous functions attributed to striatal cholinergic neurons in spontaneous locomotor activity and in the rewarding responses to cocaine are mediated by glutamate and not by acetylcholine release. Our experiments demonstrate how one population of neurons can use two distinct neurotransmitters to differentially regulate a given circuitry. The data also raise the possibility of using VAChT as a target to boost dopaminergic function and decrease high striatal cholinergic activity, common neurochemical alterations in individuals affected with Parkinson's disease. The neurotransmitters dopamine and acetylcholine play opposite roles in the striatum (a brain region involved in motor control and reward-related behaviour), and their balance is thought to be critical for striatal function. Acetylcholine in the striatum has been linked to a number of functions, including control of locomotor activity and response to drugs of abuse. However, striatal cholinergic interneurons can also release glutamate (in addition to acetylcholine) and it is presently unclear how these two neurotransmitters regulate striatal-dependent behaviour. Previous work has attempted to resolve this issue by ablating cholinergic neurons in the striatum, but this causes loss of both cholinergic and glutamatergic neurotransmission. In this study, we created a novel genetic mouse model which allowed us to selectively interfere with secretion of acetylcholine in the striatum, while leaving total striatal glutamate release intact. In these mice, we observed minimally altered behavioural responses to cocaine, suggesting that striatal glutamate, rather than acetylcholine, is critical for cocaine-induced behavioural manifestations. Furthermore, elimination of striatal acetylcholine release affects how striatal output neurons respond to dopamine, by up-regulating dopaminergic receptors and changing behavioural responses to dopaminergic agonists. Our experiments highlight a previously unappreciated physiological role of cholinergic-glutamatergic co-transmission and demonstrate how a population of neurons can use two distinct neurotransmitters to differentially regulate behaviour.
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Matsuo A, Bellier JP, Nishimura M, Yasuhara O, Saito N, Kimura H. Nuclear choline acetyltransferase activates transcription of a high-affinity choline transporter. J Biol Chem 2010; 286:5836-45. [PMID: 21163949 DOI: 10.1074/jbc.m110.147611] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Choline acetyltransferase (ChAT) synthesizes the neurotransmitter, acetylcholine, at cholinergic nerve terminals. ChAT contains nuclear localization signals and is also localized in the nuclei of neural and non-neuronal cells. Nuclear ChAT might have an as yet unidentified function, such as transcriptional regulation. In this study, we investigated the alteration of candidate gene transcription by ChAT. We chose high affinity choline transporter (CHT1) and vesicular acetylcholine transporter (VACHT) as candidate genes, which function together with ChAT in acetylcholine production. Using SH-SY5Y human neuroblastoma cells stably expressing wild-type human ChAT, we found that overexpressed ChAT enhanced transcription of the CHT1 gene but not the VACHT gene. In contrast, nuclear localization signal disrupted, and catalytically inactive mutant ChATs could not induce, CHT1 expression. Additionally, ChAT did not alter CHT1 expression in non-neuronal HEK293 cells. Our results suggest that ChAT activates the transcription of selected target genes in neuronal cells. Both enzymatic activity and nuclear translocation of ChAT are required for its transcriptional enhancement.
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Affiliation(s)
- Akinori Matsuo
- Molecular Neuroscience Research Center, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
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30
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Lee B, Sur BJ, Han JJ, Shim I, Her S, Lee HJ, Hahm DH. Krill phosphatidylserine improves learning and memory in Morris water maze in aged rats. Prog Neuropsychopharmacol Biol Psychiatry 2010; 34:1085-93. [PMID: 20677367 DOI: 10.1016/j.pnpbp.2010.05.031] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The ameliorating effect of phosphatidylserine (PS) isolated from krill (KR-PS) on the learning and memory deficits associated with normal aging in rats was investigated, as compared with soybean PS (SOY-PS). Rats were orally administered with KR-PS (20, 50 mg kg-1) and SOY-PS (50 mg kg-1) daily, for 7 days, 30 min before behavioral assessment using the Morris water maze (MWM). Changes in the cholinergic system were examined by measuring choline acetyltransferase (ChAT) and acetylcholinesterase (AchE) immunoreactivity in the hippocampus. The daily administration of KR-PS produced a significant improvement in the escape latency for finding the platform in the MWM, as compared with SOY-PS. Consistent with the behavioral results, KR-PS treatments significantly alleviated age-associated losses of cholinergic immunoreactivity, and muscarinic acetylcholine receptor type 1 (mAChR-M1) and choline transporter (CHT) mRNA expression in the hippocampus. These findings demonstrate that KR-PS showed significant neuroprotective activity against the neuronal and cognitive impairments that occur with normal aging in rats; comparable results were obtained with SOY-PS. These data indicate that oral administration of PS derived from marine life could substitute for bovine cerebral cortex PS (BC-PS) as therapy for the improvement of diminished memory function in elderly people.
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Affiliation(s)
- Bombi Lee
- Department of Oriental Medicine, Kyung Hee University, Acupuncture and Meridian Science Research Center, Seoul 130-701, Republic of Korea
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31
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Holmstrand EC, Asafu-Adjei J, Sampson AR, Blakely RD, Sesack SR. Ultrastructural localization of high-affinity choline transporter in the rat anteroventral thalamus and ventral tegmental area: differences in axon morphology and transporter distribution. J Comp Neurol 2010; 518:1908-24. [PMID: 20394050 DOI: 10.1002/cne.22310] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The high-affinity choline transporter (CHT) is a protein integral to the function of cholinergic neurons in the central nervous system (CNS). We examined the ultrastructural distribution of CHT in axonal arborizations of the mesopontine tegmental cholinergic neurons, a cell group in which CHT expression has yet to be characterized at the electron microscopic level. By using silver-enhanced immunogold detection, we compared the morphological characteristics of CHT-immunoreactive axon varicosities specifically within the anteroventral thalamus (AVN) and the ventral tegmental area (VTA). We found that CHT-immunoreactive axon varicosities in the AVN displayed a smaller cross-sectional area and a lower frequency of synapse formation and dense-cored vesicle content than CHT-labeled profiles in the VTA. We further examined the subcellular distribution of CHT and observed that immunoreactivity for this protein was predominantly localized to synaptic vesicles and minimally to the plasma membrane of axons in both regions. This pattern is consistent with the subcellular distribution of CHT displayed in other cholinergic systems. Axons in the AVN showed significantly higher levels of CHT immunoreactivity than those in the VTA and correspondingly displayed a higher level of membrane CHT labeling. These novel findings have important implications for elucidating regional differences in cholinergic signaling within the thalamic and brainstem targets of the mesopontine cholinergic system.
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Affiliation(s)
- Ericka C Holmstrand
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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32
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Gahring LC, Vasquez-Opazo GA, Rogers SW. Choline promotes nicotinic receptor alpha4 + beta2 up-regulation. J Biol Chem 2010; 285:19793-801. [PMID: 20392695 PMCID: PMC2888390 DOI: 10.1074/jbc.m110.108803] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Revised: 03/23/2010] [Indexed: 11/30/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChR) composed of alpha4 + beta2 subunits, the high affinity nicotine-binding site in the mammalian brain, up-regulate in response to chronic nicotine exposure. The identities of endogenous mediators of this process are unknown. We find that choline also up-regulates alpha4 + beta2 nAChRs stably expressed by HEK293 cells as measured by increased [(3)H]epibatidine density. Choline-mediated up-regulation is dose-dependent and corresponds with an increase in beta2 subunit protein expression. The choline kinase inhibitor hemicholinium-3 inhibits approximately 60% of choline-mediated up-regulation revealing both an HC3-dependent and -independent pathway. Furthermore, choline-mediated up-regulation is not additive with up-regulation agents such as nicotine, but it is additive with weaker promoters of the up-regulation process. When co-applied with the pro-inflammatory cytokine tumor necrosis factor alpha, choline-mediated up-regulation is increased further through a mechanism that includes an increase in both alpha4 and beta2 protein expression, and this is inhibited by the p38 MAPK inhibitor SB202190. These findings extend the view that up-regulation of alpha4 + beta2 nAChRs is a normal physiological response to altered metabolic and inflammatory conditions.
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Affiliation(s)
- Lorise C. Gahring
- From the Salt Lake City Veterans Affairs-Geriatrics Research, Education, and Clinical Center and
- the Departments of Internal Medicine and
| | | | - Scott W. Rogers
- From the Salt Lake City Veterans Affairs-Geriatrics Research, Education, and Clinical Center and
- Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84132
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Harrington AM, Lee M, Ong SY, Yong E, Farmer P, Peck CJ, Chow CW, Hutson JM, Southwell BR. Immunoreactivity for high-affinity choline transporter colocalises with VAChT in human enteric nervous system. Cell Tissue Res 2010; 341:33-48. [PMID: 20490865 DOI: 10.1007/s00441-010-0981-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 04/08/2010] [Indexed: 01/08/2023]
Abstract
Cholinergic nerves are identified by labelling molecules in the ACh synthesis, release and destruction pathway. Recently, antibodies against another molecule in this pathway have been developed. Choline reuptake at the synapse occurs via the high-affinity choline transporter (CHT1). CHT1 immunoreactivity is present in cholinergic nerve fibres containing vesicular acetylcholine transporter (VAChT) in the human and rat central nervous system and rat enteric nervous system. We have examined whether CHT1 immunoreactivity is present in nerve fibres in human intestine and whether it is colocalised with markers of cholinergic, tachykinergic or nitrergic circuitry. Human ileum and colon were fixed, sectioned and processed for fluorescence immunohistochemistry with antibodies against CHT1, class III beta-tubulin (TUJ1), synaptophysin, common choline acetyl-transferase (cChAT), VAChT, nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP). CHT1 immunoreactivity was present in many nerve fibres in the circular and longitudinal muscle, myenteric and submucosal ganglia, submucosa and mucosa in human colon and ileum and colocalised with immunoreactivity for TUJ1 and synaptophysin confirming its presence in nerve fibres. In nerve fibres in myenteric ganglia and muscle, CHT1 immunoreactivity colocalised with immunoreactivity for VAChT and cChAT. Some colocalisation occurred with SP immunoreactivity, but little with immunoreactivity for VIP or NOS. In the mucosa, CHT1 immunoreactivity colocalised with that for VIP and SP in nerve fibres and was also present in vascular nerve fibres in the submucosa and on epithelial cells on the luminal border of crypts. The colocalisation of CHT1 immunoreactivity with VAChT immunoreactivity in cholinergic enteric nerves in the human bowel thus suggests that CHT1 represents another marker of cholinergic nerves.
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Affiliation(s)
- Andrea M Harrington
- F Douglas Stephens Surgical Research Laboratory, Murdoch Childrens Research Institute, Parkville, Victoria, Australia
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34
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Black SAG, Ribeiro FM, Ferguson SSG, Rylett RJ. Rapid, transient effects of the protein kinase C activator phorbol 12-myristate 13-acetate on activity and trafficking of the rat high-affinity choline transporter. Neuroscience 2010; 167:765-73. [PMID: 20167259 DOI: 10.1016/j.neuroscience.2010.02.026] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Revised: 02/05/2010] [Accepted: 02/11/2010] [Indexed: 11/24/2022]
Abstract
Cholinergic neurons rely on the sodium-dependent choline transporter CHT to provide choline for synthesis of acetylcholine. CHT cycles between cell surface and subcellular organelles, but little is known about regulation of this trafficking. We hypothesized that activation of protein kinase C with phorbol ester modulates choline uptake by altering the rate of CHT internalization from or delivery to the plasma membrane. Using SH-SY5Y cells that stably express rat CHT, we found that exposure of cells to phorbol ester for 2 or 5 min significantly increased choline uptake, whereas longer treatment had no effect. Kinetic analysis revealed that 5 min phorbol ester treatment significantly enhanced V(max) of choline uptake, but had no effect on K(m) for solute binding. Cell-surface biotinylation assays showed that plasma membrane levels of CHT protein were enhanced following 5 min phorbol ester treatment; this was blocked by protein kinase C inhibitor bisindolylmaleimide-I. Moreover, CHT internalization was decreased and delivery of CHT to plasma membrane was increased by phorbol ester. Our results suggest that treatment of neural cells with the protein kinase C activator phorbol ester rapidly and transiently increases cell surface CHT levels and this corresponds with enhanced choline uptake activity which may play an important role in replenishing acetylcholine stores following its release by depolarization.
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Affiliation(s)
- S A G Black
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
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35
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Ivy MT, Newkirk RF, Wang Y, Townsel JG. A novel choline cotransporter sequestration compartment in cholinergic neurons revealed by selective endosomal ablation. J Neurochem 2009; 112:1295-304. [PMID: 20015153 DOI: 10.1111/j.1471-4159.2009.06543.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The sodium-dependent, high affinity choline transporter - choline cotransporter - (ChCoT, aka: cho-1, CHT1, CHT) undergoes constitutive and regulated trafficking between the plasma membrane and cytoplasmic compartments. The pathways and regulatory mechanisms of this trafficking are not well understood. We report herein studies involving selective endosomal ablation to further our understanding of the trafficking of the ChCoT. Selective ablation of early sorting and recycling endosomes resulted in a decrease of approximately 75% of [3H]choline uptake and approximately 70% of [3H]hemicholinium-3 binding. Western blot analysis showed that ablation produced a similar decrease in ChCoTs in the plasma membrane subcellular fraction. The time frame for this loss was approximately 2 h which has been shown to be the constitutive cycling time for ChCoTs in this tissue. Ablation appears to be dependent on the intracellular cycling of transferrin-conjugated horseradish peroxidase and the selective deposition of transferrin-conjugated horseradish peroxidase in early endosomes, both sorting and recycling. Ablated brain slices retained their capacity to recruit via regulated trafficking ChCoTs to the plasma membrane. This recruitment of ChCoTs suggests that the recruitable compartment is distinct from the early endosomes. It will be necessary to do further studies to identify the novel sequestration compartment supportive of the ChCoT regulated trafficking.
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Affiliation(s)
- Michael T Ivy
- Department of Biological Sciences, Tennessee State University, Nashville, TN, USA
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36
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The vesicular acetylcholine transporter is required for neuromuscular development and function. Mol Cell Biol 2009; 29:5238-50. [PMID: 19635813 DOI: 10.1128/mcb.00245-09] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The vesicular acetylcholine (ACh) transporter (VAChT) mediates ACh storage by synaptic vesicles. However, the VAChT-independent release of ACh is believed to be important during development. Here we generated VAChT knockout mice and tested the physiological relevance of the VAChT-independent release of ACh. Homozygous VAChT knockout mice died shortly after birth, indicating that VAChT-mediated storage of ACh is essential for life. Indeed, synaptosomes obtained from brains of homozygous knockouts were incapable of releasing ACh in response to depolarization. Surprisingly, electrophysiological recordings at the skeletal-neuromuscular junction show that VAChT knockout mice present spontaneous miniature end-plate potentials with reduced amplitude and frequency, which are likely the result of a passive transport of ACh into synaptic vesicles. Interestingly, VAChT knockouts exhibit substantial increases in amounts of choline acetyltransferase, high-affinity choline transporter, and ACh. However, the development of the neuromuscular junction in these mice is severely affected. Mutant VAChT mice show increases in motoneuron and nerve terminal numbers. End plates are large, nerves exhibit abnormal sprouting, and muscle is necrotic. The abnormalities are similar to those of mice that cannot synthesize ACh due to a lack of choline acetyltransferase. Our results indicate that VAChT is essential to the normal development of motor neurons and the release of ACh.
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37
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Krishnaswamy A, Cooper E. An activity-dependent retrograde signal induces the expression of the high-affinity choline transporter in cholinergic neurons. Neuron 2009; 61:272-86. [PMID: 19186169 DOI: 10.1016/j.neuron.2008.11.025] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 10/15/2008] [Accepted: 11/24/2008] [Indexed: 10/21/2022]
Abstract
A well-accepted view of developing circuits is that synapses must be active to mature and persist, whereas inactive synapses remain immature and are eventually eliminated. We question this long-standing view by investigating nonfunctional cholinergic nicotinic synapses in the superior cervical ganglia (SCG) of mice with a disruption in the alpha3 nicotinic receptor (nAChR) subunit gene, a gene essential for fast synaptic transmission in sympathetic ganglia. Using imaging and electrophysiology, we show that synapses persist for at least 2-3 months without postsynaptic activity; however, the presynaptic terminals lack high-affinity choline transporters (CHTs), and as a result, they are quickly depleted of transmitter. Moreover, we demonstrate with rescue experiments that CHT is induced by signals downstream of postsynaptic activity, converting immature terminals to mature terminals capable of sustaining transmitter release in response to high-frequency or continuous firing. Importantly, postsynaptic neurons must be continually active to maintain CHT in presynaptic terminals.
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Affiliation(s)
- Arjun Krishnaswamy
- Department of Physiology, McGill University, Montreal, H3G 1Y6 Quebec, Canada
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38
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MKC-231, a choline uptake enhancer: (3) mode of action of MKC-231 in the enhancement of high-affinity choline uptake. J Neural Transm (Vienna) 2008; 115:1037-46. [DOI: 10.1007/s00702-008-0049-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Accepted: 03/28/2008] [Indexed: 10/22/2022]
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39
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Cloning and molecular characterization of the orphan carrier protein Slc10a4: Expression in cholinergic neurons of the rat central nervous system. Neuroscience 2008; 152:990-1005. [DOI: 10.1016/j.neuroscience.2008.01.049] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2007] [Revised: 12/17/2007] [Accepted: 02/04/2008] [Indexed: 11/15/2022]
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40
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Ribeiro FM, Pinthong M, Black SAG, Gordon AC, Prado VF, Prado MAM, Rylett RJ, Ferguson SSG. Regulated recycling and plasma membrane recruitment of the high-affinity choline transporter. Eur J Neurosci 2008; 26:3437-48. [PMID: 18088276 DOI: 10.1111/j.1460-9568.2007.05967.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The high-affinity choline transporter (CHT1) is responsible for uptake of choline from the synaptic cleft and supplying choline for acetylcholine synthesis. CHT1 internalization by clathrin-coated vesicles is proposed to represent a mechanism by which high-affinity choline uptake can be modulated. We show here that internalized CHT1 is rapidly recycled back to the cell surface in both human embryonic kidney cells (HEK 293 cells) and SH-SY5Y neuroblastoma cells. This rapidly recycling pool of CHT1 comprises about 10% of total CHT1 protein. In the SH-SY5Y neuroblastoma cell line K(+)-depolarization promotes Ca(2+)-dependent increase in the rate of CHT1 recycling to the plasma membrane without affecting the rate of CHT1 internalization. K(+)-depolarization also increases the size of the pool of CHT1 protein that can be mobilized to the plasma membrane. Thus, the activity-dependent increase in plasma membrane CHT1 localization appears to be regulated by two mechanisms: (i) an increase in the rate of externalization of the intracellular CHT1 pool; and (ii) the recruitment of additional intracellular transporters to the recycling pool.
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Affiliation(s)
- Fabiola M Ribeiro
- Cell Biology Research Group, Robarts Research Institute London, Ontario, Canada
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41
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Pinthong M, Black SAG, Ribeiro FM, Pholpramool C, Ferguson SSG, Rylett RJ. Activity and Subcellular Trafficking of the Sodium-Coupled Choline Transporter CHT Is Regulated Acutely by Peroxynitrite. Mol Pharmacol 2007; 73:801-12. [DOI: 10.1124/mol.107.040881] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
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42
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Kristofiková Z, Kopecký V, Hofbauerová K, Hovorková P, Rípová D. Complex of Amyloid β Peptides with 24-Hydroxycholesterol and Its Effect on Hemicholinium-3 Sensitive Carriers. Neurochem Res 2007; 33:412-21. [PMID: 17717740 DOI: 10.1007/s11064-007-9443-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Accepted: 07/12/2007] [Indexed: 01/07/2023]
Abstract
Brains of Alzheimer disease patients in early stages of dementia contain an increased 24(S)-hydroxycholesterol (cerebrosterol)/cholesterol ratio when compared to controls. In this study, effects of amyloid beta peptides and of racemic 24-hydroxycholesterol were evaluated in vitro on undepleted or cholesterol-depleted hippocampal synaptosomes of young and old rats via a high-affinity choline transport and membrane anisotropy measurements. Depletion of membrane cholesterol decreased the transport of [3H]choline, increased the specific binding of [3H]hemicholinium-3 and decreased membrane anisotropy. However, less alterations were found in old when compared to young brains. 500 nM nonaggregated peptides were ineffective but aggregated fragment 1-42 evoked marked drops in the transport and anisotropy values on depleted synaptosomes. 50 microM 24-hydroxycholesterol inhibited choline transport on depleted synaptosomes but it did not influence membrane anisotropy. Peptides eliminated the actions of oxysterol on choline carriers in young but not in old rats. On the other hand, oxysterol eliminated the effects of peptides on membrane anisotropy. Our study suggests a possible role of membrane cholesterol in the regulation of choline carriers and supports data reporting a protective role of membrane cholesterol against toxic effects of amyloid beta peptides. Moreover, via Raman spectroscopy we demonstrate for the first time that peptides form a complex with 24-hydroxycholesterol.
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Affiliation(s)
- Zdena Kristofiková
- Alzheimer Disease Centre, Prague Psychiatric Centre, Ustavní 91, Prague 8 - Bohnice 181 03, Czech Republic.
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43
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Wang B, Yang L, Wang Z, Zheng H. Amyolid precursor protein mediates presynaptic localization and activity of the high-affinity choline transporter. Proc Natl Acad Sci U S A 2007; 104:14140-5. [PMID: 17709753 PMCID: PMC1955810 DOI: 10.1073/pnas.0704070104] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The key pathological features of Alzheimer's disease include synaptic dysfunction, profound changes in the cholinergic system, and deposition of beta-amyloid peptides generated by proteolytic processing of the amyloid-beta precursor protein (APP). However, the pathways linking APP with synaptic activity and cholinergic neuronal function are poorly understood. We report here that APP is essential in regulating the presynaptic expression and activity of the high-affinity choline transporter (CHT), a molecule that mediates the rate-limiting step of cholinergic synaptic transmission in both the neuromuscular junction and central cholinergic neurons. Loss of APP leads to aberrant localization of CHT at the neuromuscular synapses and reduced CHT activity at cholinergic projections. At the cellular level, we show that APP and CHT can be found in Rab5-positive endosomal compartments and that APP affects CHT endocytosis. Furthermore, we demonstrate that APP interacts with CHT through the C-terminal domain, providing support for a specific and direct regulation of CHT by APP through protein-protein interactions. These results identify a physiological activity of APP in cholinergic neurons, and our data indicate that deregulation of APP function may contribute to cholinergic impairment and AD pathogenesis.
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Affiliation(s)
| | - Li Yang
- *Huffington Center on Aging and
| | - Zilai Wang
- *Huffington Center on Aging and
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030
| | - Hui Zheng
- *Huffington Center on Aging and
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030
- To whom correspondence should be addressed. E-mail:
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Payette DJ, Xie J, Guo Q. Reduction in CHT1-mediated choline uptake in primary neurons from presenilin-1 M146V mutant knock-in mice. Brain Res 2006; 1135:12-21. [PMID: 17196556 PMCID: PMC1805819 DOI: 10.1016/j.brainres.2006.12.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Revised: 11/20/2006] [Accepted: 12/02/2006] [Indexed: 12/31/2022]
Abstract
The memory loss in Alzheimer's disease (AD) has been linked to cholinergic hypoactivity. Mutations in presenilin-1 (PS-1) may regulate cholinergic signaling, although their precise roles in cholinergic neurotransmission in AD are unsettled. Neuronal uptake of choline via the high affinity choline transporter (CHT1) is essential for cholinergic neurotransmission. CHT1 is a Na+-dependent, hemicholinium-3 (HC-3)-sensitive choline transporter. Although cholinergic neurons in the nucleus basalis of Meynert are a major source of cholinergic projections for the cerebral cortex, it is unclear whether cortical neurons exhibit intrinsic CHT1 activity that is altered in AD. We now report that primary cortical neurons express intrinsic and biologically active CHT1, and that, in these neurons, CHT1-mediated choline uptake activity is significantly reduced in PS-1 M146V mutant knock-in mice. Further kinetic studies using HC-3 binding and cell surface biotinylation assays showed that the PS-1 mutation inhibits CHT1 mediated choline uptake by reducing the ligand binding affinity of CHT1 without significantly altering levels of CHT1 expression in the plasma membrane. Since human neocortex has recently been shown to possess intrinsic cholinergic innervation, our results indicate that alterations in CHT1-mediated high affinity choline uptake in cortical neurons may contribute to Alzheimer's dementia.
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Affiliation(s)
| | | | - Qing Guo
- Correspondence: Qing Guo, Ph.D., Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, Phone: (405) 271-2226 ext. 56268., FAX: (405) 271-3181., E-mail:
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Bazalakova MH, Blakely RD. The high-affinity choline transporter: a critical protein for sustaining cholinergic signaling as revealed in studies of genetically altered mice. Handb Exp Pharmacol 2006:525-44. [PMID: 16722248 DOI: 10.1007/3-540-29784-7_21] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
In cholinergic neurons, the presynaptic choline transporter (CHT) mediates high-affinity choline uptake (HACU) as the rate-limiting step in acetylcholine (ACh) synthesis. It has previously been shown that HACU is increased by behaviorally and pharmacologically-induced activity of cholinergic neurons in vivo, but the molecular mechanisms of this change in CHT function and regulation have only recently begun to be elucidated. The recent cloning of CHT has led to the generation of new valuable tools, including specific anti-CHT antibodies and a CHT knockout mouse. These new reagents have allowed researchers to investigate the possibility of a presynaptic, CHT-mediated, molecular plasticity mechanism, regulated by and necessary for sustained in vivo cholinergic activity. Studies in various mouse models of cholinergic dysfunction, including acetylcholinesterase (AChE) transgenic and knockout mice, choline acetyltransferase (ChAT) heterozygote mice, muscarinic (mAChR) and nicotinic (mAChR) receptor knockout mice, as well as CHT knockout and heterozygote mice, have revealed new information about the role of CHT expression and regulation in response to long-term alterations in cholinergic neurotransmission. These mouse models highlight the capacity of CHT to provide for functional compensation in states of cholinergic dysfunction. A better understanding of modes of CHT regulation should allow for experimental manipulation of cholinergic signaling in vivo with potential utility in human disorders of known cholinergic dysfunction such as Alzheimer's disease, Parkinson's disease, schizophrenia, Huntington's disease, and dysautonomia.
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Affiliation(s)
- M H Bazalakova
- Vanderbilt School of Medicine, Suite 7140, MRB III, Nashville, TN 37232-8548, USA
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46
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Ribeiro FM, Black SAG, Prado VF, Rylett RJ, Ferguson SSG, Prado MAM. The "ins" and "outs" of the high-affinity choline transporter CHT1. J Neurochem 2006; 97:1-12. [PMID: 16524384 DOI: 10.1111/j.1471-4159.2006.03695.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Maintenance of acetylcholine (ACh) synthesis depends on the activity of the high-affinity choline transporter (CHT1), which is responsible for the reuptake of choline from the synaptic cleft into presynaptic neurons. In this review, we discuss the current understanding of mechanisms involved in the cellular trafficking of CHT1. CHT1 protein is mainly found in intracellular organelles, such as endosomal compartments and synaptic vesicles. The presence of CHT1 at the plasma membrane is limited by rapid endocytosis of the transporter in clathrin-coated pits in a mechanism dependent on a dileucine-like motif present in the carboxyl-terminal region of the transporter. The intracellular pool of CHT1 appears to constitute a reserve pool of transporters, important for maintenance of cholinergic neurotransmission. However, the physiological basis of the presence of CHT1 in intracellular organelles is not fully understood. Current knowledge about CHT1 indicates that stimulated and constitutive exocytosis, in addition to endocytosis, will have major consequences for regulating choline uptake. Future investigations of CHT1 trafficking should elucidate such regulatory mechanisms, which may aid in understanding the pathophysiology of diseases that affect cholinergic neurons, such as Alzheimer's disease.
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Affiliation(s)
- Fabiola M Ribeiro
- Departamento de Bioquímica-Imunologia, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
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47
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Ribeiro FM, Black SAG, Cregan SP, Prado VF, Prado MAM, Rylett RJ, Ferguson SSG. Constitutive high-affinity choline transporter endocytosis is determined by a carboxyl-terminal tail dileucine motif. J Neurochem 2005; 94:86-96. [PMID: 15953352 DOI: 10.1111/j.1471-4159.2005.03171.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Maintenance of acetylcholine synthesis depends on the effective functioning of a high-affinity sodium-dependent choline transporter (CHT1). Recent studies have shown that this transporter is predominantly localized inside the cell, unlike other neurotransmitter transporters, suggesting that the trafficking of CHT1 to and from the plasma membrane may play a crucial role in regulating choline uptake. Here we found that CHT1 is rapidly and constitutively internalized in clathrin-coated vesicles to Rab5-positive early endosomes. CHT1 internalization is controlled by an atypical carboxyl-terminal dileucine-like motif (L531, V532) which, upon replacement by alanine residues, blocks CHT1 internalization in both human embryonic kidney 293 cells and primary cortical neurons and results in both increased CHT1 cell surface expression and choline transport activity. Perturbation of clathrin-mediated endocytosis with dynamin-I K44A increases cell surface expression and transport activity to a similar extent as mutating the dileucine motif, suggesting that we have identified the motif responsible for constitutive CHT1 internalization. Based on the observation that the localization of CHT1 to the plasma membrane is transient, we propose that acetylcholine synthesis may be influenced by processes that lead to the attenuation of constitutive CHT1 endocytosis.
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Affiliation(s)
- Fabiola M Ribeiro
- Cell Biology Research Group, Robarts Research Institute, University of Western Ontario, London, Canada
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48
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Berse B, Szczecinska W, Lopez-Coviella I, Madziar B, Zemelko V, Kaminski R, Kozar K, Lips KS, Pfeil U, Blusztajn JK. Expression of high affinity choline transporter during mouse development in vivo and its upregulation by NGF and BMP-4 in vitro. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2005; 157:132-40. [PMID: 15885806 DOI: 10.1016/j.devbrainres.2005.03.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Revised: 03/22/2005] [Accepted: 03/23/2005] [Indexed: 11/29/2022]
Abstract
An important feature of cholinergic neurons is high-affinity choline transport, which allows them to reuse choline for the synthesis of ACh needed to support cholinergic neurotransmission. The choline transporter, designated CHT, was recently cloned. We applied RT/PCR to monitor the expression of CHT in the developing mouse CNS from embryonic day 14 (E14) to postnatal day 30 (P30). We found that CHT was expressed early in development, predominantly in the regions containing cholinergic neurons. In the spinal cord, CHT mRNA was present at close to adult levels at the earliest time point examined (E14) and showed almost no changes after birth. In the striatum and the septum, CHT mRNA increased steadily during embryonic stages and leveled off after birth. Surprisingly, CHT mRNA expression was also detected in other brain regions, notably in the cerebellum, where it peaked on E19, and then rapidly declined during postnatal development. CHT protein was detected by Western blotting as a band of apparent molecular weight of 70 kDa. The accumulation of this protein during development lagged behind mRNA accumulation in all tissues. We also examined the effects of NGF and BMP-4, the potent inducers of choline acetyltransferase and vesicular acetylcholine transporter genes, on CHT expression. Both factors increased CHT mRNA accumulation in primary septal cultures. The effect of NGF was dependent on the PI3K signaling, as it was abolished by the PI3K inhibitor LY294002. This result indicates that some of the signals regulating other cholinergic-specific genes also control CHT expression.
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Affiliation(s)
- Brygida Berse
- Department of Pathology and Laboratory Medicine, Boston University School of Medicine, 715 Albany Street, Room L-808C, Boston, MA 02118, USA.
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Ferreira LT, Santos MS, Kolmakova NG, Koenen J, Barbosa J, Gomez MV, Guatimosim C, Zhang X, Parsons SM, Prado VF, Prado MAM. Structural requirements for steady-state localization of the vesicular acetylcholine transporter. J Neurochem 2005; 94:957-69. [PMID: 16092939 DOI: 10.1111/j.1471-4159.2005.03244.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The vesicular acetylcholine transporter (VAChT) regulates the amount of acetylcholine stored in synaptic vesicles. However, the mechanisms that control the targeting of VAChT and other synaptic vesicle proteins are still poorly comprehended. These processes are likely to depend, at least partially, on structural determinants present in the primary sequence of the protein. Here, we use site-directed mutagenesis to evaluate the contribution of the C-terminal tail of VAChT to the targeting of this transporter to synaptic-like microvesicles in cholinergic SN56 cells. We found that residues 481-490 contain the trafficking information necessary for VAChT localization and that within this region L485 and L486 are strictly necessary. Deletion and alanine-scanning mutants lacking most of the carboxyl tail of VAChT, but containing residues 481-490, were still targeted to microvesicles. Moreover, we found that clathrin-mediated endocytosis of VAChT is required for targeting to microvesicles in SN56 and PC12 cells. The data provide novel information on the mechanisms and structural determinants necessary for VAChT localization to synaptic vesicles.
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Affiliation(s)
- Lucimar T Ferreira
- Program in Molecular Pharmacology, Departamento de Farmacologia, Belo Horizonte, Brazil
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50
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Nixon RA. Endosome function and dysfunction in Alzheimer's disease and other neurodegenerative diseases. Neurobiol Aging 2005; 26:373-82. [PMID: 15639316 DOI: 10.1016/j.neurobiolaging.2004.09.018] [Citation(s) in RCA: 285] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2004] [Revised: 09/07/2004] [Accepted: 09/15/2004] [Indexed: 11/20/2022]
Abstract
Endocytosis is universally important in cell function. In the brain, the roles of endosomes are relatively more complex due to the unique polar morphology of neurons and specialized needs for inter-cellular communication. New evidence shows that endosome function is altered in a surprising range of neurodegenerative disorders, including in several inherited neurologic disorders where the causative mutations occur in genes that regulate endosome function. In Alzheimer's disease (AD), endosome abnormalities are among the earliest neuropathologic features to develop and have now been closely linked to genetic risk factors for AD, including APP triplication in Trisomy 21 (Down syndrome, DS) and ApoE4 genotype in sporadic AD. Recent findings on endosome regulation and developmental and late-onset neurodegenerative disease disorders are beginning to reveal how endocytic pathway impairment may lead to neuronal dysfunction and cell death in these disorders and may also promote amyloidogenesis in AD.
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Affiliation(s)
- Ralph A Nixon
- Department of Psychiatry, NYU School of Medicine, New York, NY 10016, USA.
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