1
|
Davis SE, Cirincione AB, Jimenez-Torres AC, Zhu J. The Impact of Neurotransmitters on the Neurobiology of Neurodegenerative Diseases. Int J Mol Sci 2023; 24:15340. [PMID: 37895020 PMCID: PMC10607327 DOI: 10.3390/ijms242015340] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 10/16/2023] [Accepted: 10/17/2023] [Indexed: 10/29/2023] Open
Abstract
Neurodegenerative diseases affect millions of people worldwide. Neurodegenerative diseases result from progressive damage to nerve cells in the brain or peripheral nervous system connections that are essential for cognition, coordination, strength, sensation, and mobility. Dysfunction of these brain and nerve functions is associated with Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis, and motor neuron disease. In addition to these, 50% of people living with HIV develop a spectrum of cognitive, motor, and/or mood problems collectively referred to as HIV-Associated Neurocognitive Disorders (HAND) despite the widespread use of a combination of antiretroviral therapies. Neuroinflammation and neurotransmitter systems have a pathological correlation and play a critical role in developing neurodegenerative diseases. Each of these diseases has a unique pattern of dysregulation of the neurotransmitter system, which has been attributed to different forms of cell-specific neuronal loss. In this review, we will focus on a discussion of the regulation of dopaminergic and cholinergic systems, which are more commonly disturbed in neurodegenerative disorders. Additionally, we will provide evidence for the hypothesis that disturbances in neurotransmission contribute to the neuronal loss observed in neurodegenerative disorders. Further, we will highlight the critical role of dopamine as a mediator of neuronal injury and loss in the context of NeuroHIV. This review will highlight the need to further investigate neurotransmission systems for their role in the etiology of neurodegenerative disorders.
Collapse
Affiliation(s)
| | | | | | - Jun Zhu
- Department of Drug Discovery and Biomedical Sciences, College of Pharmacy, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA; (S.E.D.); (A.B.C.); (A.C.J.-T.)
| |
Collapse
|
2
|
Wang S, Neel AI, Adams KL, Sun H, Jones SR, Howlett AC, Chen R. Atorvastatin differentially regulates the interactions of cocaine and amphetamine with dopamine transporters. Neuropharmacology 2023; 225:109387. [PMID: 36567004 PMCID: PMC9872521 DOI: 10.1016/j.neuropharm.2022.109387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 12/12/2022] [Accepted: 12/18/2022] [Indexed: 12/24/2022]
Abstract
The function of the dopamine transporter (DAT) is regulated by membrane cholesterol content. A direct, acute removal of membrane cholesterol by methyl-β-cyclodextrin (MβCD) has been shown to reduce dopamine (DA) uptake and release mediated by the DAT. This is of particular interest because a few widely prescribed statins that lower peripheral cholesterol levels are blood-brain barrier (BBB) penetrants, and therefore could alter DAT function through brain cholesterol modulation. The goal of this study was to investigate the effects of prolonged atorvastatin treatment (24 h) on DAT function in neuroblastoma 2A cells stably expressing DAT. We found that atorvastatin treatment effectively lowered membrane cholesterol content in a concentration-dependent manner. Moreover, atorvastatin treatment markedly reduced DA uptake and abolished cocaine inhibition of DA uptake, independent of surface DAT levels. These deficits induced by atorvastatin treatment were reversed by cholesterol replenishment. However, atorvastatin treatment did not change amphetamine (AMPH)-induced DA efflux. This is in contrast to a small but significant reduction in DA efflux induced by acute depletion of membrane cholesterol using MβCD. This discrepancy may involve differential changes in membrane lipid composition resulting from chronic and acute cholesterol depletion. Our data suggest that the outward-facing conformation of DAT, which favors the binding of DAT blockers such as cocaine, is more sensitive to atorvastatin-induced cholesterol depletion than the inward-facing conformation, which favors the binding of DAT substrates such as AMPH. Our study on statin-DAT interactions may have clinical implications in our understanding of neurological side effects associated with chronic use of BBB penetrant statins.
Collapse
Affiliation(s)
- Shiyu Wang
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Anna I Neel
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Kristen L Adams
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Haiguo Sun
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Sara R Jones
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Allyn C Howlett
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States
| | - Rong Chen
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC, 27157, United States.
| |
Collapse
|
3
|
Amphetamine Stimulates Endocytosis of the Norepinephrine and Neuronal Glutamate Transporters in Cultured Locus Coeruleus Neurons. Neurochem Res 2020; 45:1410-1419. [PMID: 31912366 PMCID: PMC7260265 DOI: 10.1007/s11064-019-02939-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 12/16/2019] [Accepted: 12/18/2019] [Indexed: 12/12/2022]
Abstract
Amphetamines and amphetamine-derivatives elevate neurotransmitter concentrations by competing with endogenous biogenic amines for reuptake. In addition, AMPHs have been shown to activate endocytosis of the dopamine transporter (DAT) which further elevates extracellular dopamine (DA). We previously found that the biochemical cascade leading to this cellular process involves entry of AMPH into the cell through the DAT, stimulation of an intracellular trace amine-associated receptor, TAAR1, and activation of the small GTPase, RhoA. We also showed that the neuronal glutamate transporter, EAAT3, undergoes endocytosis via the same cascade in DA neurons, leading to potentiation of glutamatergic inputs. Since AMPH is a transported inhibitor of both DAT and the norepinephrine transporter (NET), and EAAT3 is also expressed in norepinephrine (NE) neurons, we explored the possibility that this signaling cascade occurs in NE neurons. We found that AMPH can cause endocytosis of NET as well as EAAT3 in NE neurons. NET endocytosis is dependent on TAAR1, RhoA, intracellular calcium and CaMKII activation, similar to DAT. However, EAAT3 endocytosis is similar in all regards except its dependence upon CaMKII activation. RhoA activation is dependent on calcium, but not CaMKII, explaining a divergence in AMPH-mediated endocytosis of DAT and NET from that of EAAT3. These data indicate that AMPHs and other TAAR1 agonists can affect glutamate signaling through internalization of EAAT3 in NE as well as DA neurons.
Collapse
|
4
|
Guilherme JPLF, Bigliassi M, Lancha Junior AH. Association study of SLC6A2 gene Thr99Ile variant (rs1805065) with athletic status in the Brazilian population. Gene 2019; 707:53-57. [PMID: 31075414 DOI: 10.1016/j.gene.2019.05.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 04/24/2019] [Accepted: 05/06/2019] [Indexed: 10/26/2022]
Abstract
Genetic variants in monoamine neurotransmitter genes have been recurrently associated with panic disorder, addiction and mood disorders. Recent evidence also indicates that norepinephrine neurotransmission can influence a series of psychophysical and psychobiological parameters related to athletic performance, and the presence of variants in the SLC6A2 (solute carrier family 6 member 2) gene, which encodes the norepinephrine transporter, can be detrimental to an adequate noradrenergic signaling. Accordingly, the objective of the present study was to explore the SLC6A2 Thr99Ile variant (rs1805065) in a cohort composed of highly-trained individuals and non-trained individuals. A total of 1556 Brazilians: 926 non-athletes and 630 athletes (322 endurance athletes and 308 power athletes) were compared in this case-control association study. The Thr99Ile variant showed only two genotypes (C/C or C/T), and a low minor allele frequency of ≈1%. However, none of the power athletes had the mutant T-allele (i.e., the C/T genotype), which may be related to decreased norepinephrine transporter activity. The genotype distribution and allele frequency observed in power athletes were significantly different when compared to non-athletes or endurance athletes. Therefore, the presence of the T-allele may decrease the chance of belonging to the group of athletes involved in explosive physical tasks. These results still need to be replicated in independent cohorts. However, it appears reasonable to assume that there is an association between the SLC6A2 gene variant and power athletic status.
Collapse
Affiliation(s)
- João Paulo L F Guilherme
- Laboratory of Applied Nutrition and Metabolism, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil; Endurance Performance Research Group, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil.
| | - Marcelo Bigliassi
- Endurance Performance Research Group, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil
| | - Antonio H Lancha Junior
- Laboratory of Applied Nutrition and Metabolism, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil
| |
Collapse
|
5
|
Navratna V, Gouaux E. Insights into the mechanism and pharmacology of neurotransmitter sodium symporters. Curr Opin Struct Biol 2019; 54:161-170. [PMID: 30921707 DOI: 10.1016/j.sbi.2019.03.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 03/07/2019] [Accepted: 03/08/2019] [Indexed: 12/17/2022]
Abstract
Neurotransmitter sodium symporters (NSS) belong to the SLC6 family of solute carriers and play an essential role in neurotransmitter homeostasis throughout the body. In the past decade, structural studies employing bacterial orthologs of NSSs have provided insight into the mechanism of neurotransmitter transport. While the overall architecture of SLC6 transporters is conserved among species, in comparison to the bacterial homologs, the eukaryotic SLC6 family members harbor differences in amino acid sequence and molecular structure, which underpins their functional and pharmacological diversity, as well as their ligand specificity. Here, we review the structures and mechanisms of eukaryotic NSSs, focusing on the molecular basis for ligand recognition and on transport mechanism.
Collapse
Affiliation(s)
- Vikas Navratna
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Eric Gouaux
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States; Howard Hughes Medical Institute, Oregon Health & Science University, Portland, OR, United States.
| |
Collapse
|
6
|
Hovde MJ, Larson GH, Vaughan RA, Foster JD. Model systems for analysis of dopamine transporter function and regulation. Neurochem Int 2018; 123:13-21. [PMID: 30179648 DOI: 10.1016/j.neuint.2018.08.015] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 08/23/2018] [Accepted: 08/31/2018] [Indexed: 02/07/2023]
Abstract
The dopamine transporter (DAT) plays a critical role in dopamine (DA) homeostasis by clearing transmitter from the extraneuronal space after vesicular release. DAT serves as a site of action for a variety of addictive and therapeutic reuptake inhibitors, and transport dysfunction is associated with transmitter imbalances in disorders such as schizophrenia, attention deficit hyperactive disorder, bipolar disorder, and Parkinson disease. In this review, we describe some of the model systems that have been used for in vitro analyses of DAT structure, function and regulation, and discuss a potential relationship between transporter kinetic values and membrane cholesterol.
Collapse
Affiliation(s)
- Moriah J Hovde
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND, 58202, USA
| | - Garret H Larson
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND, 58202, USA
| | - Roxanne A Vaughan
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND, 58202, USA
| | - James D Foster
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND, 58202, USA.
| |
Collapse
|
7
|
Mackie P, Lebowitz J, Saadatpour L, Nickoloff E, Gaskill P, Khoshbouei H. The dopamine transporter: An unrecognized nexus for dysfunctional peripheral immunity and signaling in Parkinson's Disease. Brain Behav Immun 2018; 70:21-35. [PMID: 29551693 PMCID: PMC5953824 DOI: 10.1016/j.bbi.2018.03.020] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 03/13/2018] [Accepted: 03/14/2018] [Indexed: 02/06/2023] Open
Abstract
The second-most common neurodegenerative disease, Parkinson's Disease (PD) has three hallmarks: dysfunctional dopamine transmission due, at least in part, to dopamine neuron degeneration; intracellular inclusions of α-synuclein aggregates; and neuroinflammation. The origin and interplay of these features remains a puzzle, as does the underlying mechanism of PD pathogenesis and progression. When viewed in the context of neuroimmunology, dopamine also plays a role in regulating peripheral immune cells. Intriguingly, plasma dopamine levels are altered in PD, suggesting collateral dysregulation of peripheral dopamine transmission. The dopamine transporter (DAT), the main regulator of dopaminergic tone in the CNS, is known to exist in lymphocytes and monocytes/macrophages, but little is known about peripheral DAT biology or how DAT regulates the dopaminergic tone, much less how peripheral DAT alters immune function. Our review is guided by the hypothesis that dysfunctional peripheral dopamine signaling might be linked to the dysfunctional immune responses in PD and thereby suggests a potential bidirectional communication between central and peripheral dopamine systems. This review seeks to foster new perspectives concerning PD pathogenesis and progression.
Collapse
Affiliation(s)
- Phillip Mackie
- University of Florida College of Medicine, Department of Neuroscience, Gainesville, FL 32611, United States
| | - Joe Lebowitz
- University of Florida College of Medicine, Department of Neuroscience, Gainesville, FL 32611, United States
| | - Leila Saadatpour
- University of Florida College of Medicine, Department of Neuroscience, Gainesville, FL 32611, United States
| | - Emily Nickoloff
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, United States
| | - Peter Gaskill
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, United States
| | - Habibeh Khoshbouei
- University of Florida College of Medicine, Department of Neuroscience, Gainesville, FL 32611, United States.
| |
Collapse
|
8
|
Targeting of dopamine transporter to filopodia requires an outward-facing conformation of the transporter. Sci Rep 2017; 7:5399. [PMID: 28710426 PMCID: PMC5511133 DOI: 10.1038/s41598-017-05637-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Accepted: 06/01/2017] [Indexed: 12/01/2022] Open
Abstract
Dopamine transporter (DAT) has been shown to accumulate in filopodia in neurons and non-neuronal cells. To examine the mechanisms of DAT filopodial targeting, we used quantitative live-cell fluorescence microscopy, and compared the effects of the DAT inhibitor cocaine and its fluorescent analog JHC1-64 on the plasma membrane distribution of wild-type DAT and two non-functional DAT mutants, R60A and W63A, that do not accumulate in filopodia. W63A did not bind JHC1-64, whereas R60A did, although less efficiently compared to the wild-type DAT. Molecular dynamics simulations predicted that R60A preferentially assumes an outward-facing (OF) conformation through compensatory intracellular salt bridge formation, which in turn favors binding of cocaine. Imaging analysis showed that JHC1-64-bound R60A mutant predominantly localized in filopodia, whereas free R60A molecules were evenly distributed within the plasma membrane. Cocaine binding significantly increased the density of R60A, but not that of W63A, in filopodia. Further, zinc binding, known to stabilize the OF state, also increased R60A concentration in filopodia. Finally, amphetamine, that is thought to disrupt DAT OF conformation, reduced the concentration of wild-type DAT in filopodia. Altogether, these data indicate that OF conformation is required for the efficient targeting of DAT to, and accumulation in, filopodia.
Collapse
|
9
|
Sweeney CG, Tremblay BP, Stockner T, Sitte HH, Melikian HE. Dopamine Transporter Amino and Carboxyl Termini Synergistically Contribute to Substrate and Inhibitor Affinities. J Biol Chem 2016; 292:1302-1309. [PMID: 27986813 DOI: 10.1074/jbc.m116.762872] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 12/09/2016] [Indexed: 11/06/2022] Open
Abstract
Extracellular dopamine and serotonin concentrations are determined by the presynaptic dopamine (DAT) and serotonin (SERT) transporters, respectively. Numerous studies have investigated the DAT and SERT structural elements contributing to inhibitor and substrate binding. To date, crystallographic studies have focused on conserved transmembrane domains, where multiple substrate binding and translocation features are conserved. However, it is unknown what, if any, role the highly divergent intracellular N and C termini contribute to these processes. Here, we used chimeric proteins to test whether DAT and SERT N and C termini contribute to transporter substrate and inhibitor affinities. Replacing the DAT N terminus with that of SERT had no effect on DA transport Vmax but significantly decreased DAT substrate affinities for DA and amphetamine. Similar losses in uptake inhibition were observed for small DAT inhibitors, whereas substituting the DAT C terminus with that of SERT affected neither substrate nor inhibitor affinities. In contrast, the N-terminal substitution was completely tolerated by the larger DAT inhibitors, which exhibited no loss in apparent affinity. Remarkably, all affinity losses were rescued in DAT chimeras encoding both SERT N and C termini. The sensitivity to amino-terminal substitution was specific for DAT, because replacing the SERT N and/or C termini affected neither substrate nor inhibitor affinities. Taken together, these findings provide compelling experimental evidence that DAT N and C termini synergistically contribute to substrate and inhibitor affinities.
Collapse
Affiliation(s)
- Carolyn G Sweeney
- From the Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, Worcester, Massachusetts 01604 and
| | - Bradford P Tremblay
- From the Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, Worcester, Massachusetts 01604 and
| | - Thomas Stockner
- the Institute for Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria
| | - Harald H Sitte
- the Institute for Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria
| | - Haley E Melikian
- From the Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, Worcester, Massachusetts 01604 and
| |
Collapse
|
10
|
Fairweather SJ, Bröer A, Subramanian N, Tumer E, Cheng Q, Schmoll D, O'Mara ML, Bröer S. Molecular basis for the interaction of the mammalian amino acid transporters B0AT1 and B0AT3 with their ancillary protein collectrin. J Biol Chem 2015; 290:24308-25. [PMID: 26240152 PMCID: PMC4591816 DOI: 10.1074/jbc.m115.648519] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 07/19/2015] [Indexed: 12/19/2022] Open
Abstract
Many solute carrier 6 (SLC6) family transporters require ancillary subunits to modify their expression and activity. The main apical membrane neutral amino acid transporters in mouse intestine and kidney, B(0)AT1 and B(0)AT3, require the ancillary protein collectrin or ACE2 for plasma membrane expression. Expression and activity of SLC6 neurotransmitter transporters are modulated by interaction with syntaxin 1A. Utilizing monocarboxylate-B(0)AT1/3 fusion constructs, we discovered that collectrin is also necessary for B(0)AT1 and B(0)AT3 catalytic function. Syntaxin 1A and syntaxin 3 inhibit the membrane expression of B(0)AT1 by competing with collectrin for access. A mutagenesis screening approach identified residues on trans-membrane domains 1α, 5, and 7 on one face of B(0)AT3 as a key region involved in interaction with collectrin. Mutant analysis established residues that were involved in collectrin-dependent functions as follows: plasma membrane expression of B(0)AT3, catalytic activation, or both. These results identify a potential binding site for collectrin and other SLC6 ancillary proteins.
Collapse
Affiliation(s)
| | | | - Nandhitha Subramanian
- Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia and
| | | | - Qi Cheng
- From the Research School of Biology and
| | - Dieter Schmoll
- the Sanofi-Aventis Deutschland GmbH, Industriepark Hoechst, Frankfurt am Main 65926, Germany
| | - Megan L O'Mara
- Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia and
| | | |
Collapse
|
11
|
Moritz AE, Rastedt DE, Stanislowski DJ, Shetty M, Smith MA, Vaughan RA, Foster JD. Reciprocal Phosphorylation and Palmitoylation Control Dopamine Transporter Kinetics. J Biol Chem 2015; 290:29095-105. [PMID: 26424792 DOI: 10.1074/jbc.m115.667055] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Indexed: 11/06/2022] Open
Abstract
The dopamine transporter is a neuronal protein that drives the presynaptic reuptake of dopamine (DA) and is the major determinant of transmitter availability in the brain. Dopamine transporter function is regulated by protein kinase C (PKC) and other signaling pathways through mechanisms that are complex and poorly understood. Here we investigate the role of Ser-7 phosphorylation and Cys-580 palmitoylation in mediating steady-state transport kinetics and PKC-stimulated transport down-regulation. Using both mutational and pharmacological approaches, we demonstrate that these post-translational modifications are reciprocally regulated, leading to transporter populations that display high phosphorylation-low palmitoylation or low phosphorylation-high palmitoylation. The balance between the modifications dictates transport capacity, as conditions that promote high phosphorylation or low palmitoylation reduce transport Vmax and enhance PKC-stimulated down-regulation, whereas conditions that promote low phosphorylation or high palmitoylation increase transport Vmax and suppress PKC-stimulated down-regulation. Transitions between these functional states occur when endocytosis is blocked or undetectable, indicating that the modifications kinetically regulate the velocity of surface transporters. These findings reveal a novel mechanism for control of DA reuptake that may represent a point of dysregulation in DA imbalance disorders.
Collapse
Affiliation(s)
- Amy E Moritz
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - Danielle E Rastedt
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - Daniel J Stanislowski
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - Madhur Shetty
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - Margaret A Smith
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - Roxanne A Vaughan
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| | - James D Foster
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9061
| |
Collapse
|
12
|
Fraser R, Chen Y, Guptaroy B, Luderman KD, Stokes SL, Beg A, DeFelice LJ, Gnegy ME. An N-terminal threonine mutation produces an efflux-favorable, sodium-primed conformation of the human dopamine transporter. Mol Pharmacol 2014; 86:76-85. [PMID: 24753048 DOI: 10.1124/mol.114.091926] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The dopamine transporter (DAT) reversibly transports dopamine (DA) through a series of conformational transitions. Alanine (T62A) or aspartate (T62D) mutagenesis of Thr62 revealed T62D-human (h)DAT partitions in a predominately efflux-preferring conformation. Compared with wild-type (WT), T62D-hDAT exhibits reduced [(3)H]DA uptake and enhanced baseline DA efflux, whereas T62A-hDAT and WT-hDAT function in an influx-preferring conformation. We now interrogate the basis of the mutants' altered function with respect to membrane conductance and Na(+) sensitivity. The hDAT constructs were expressed in Xenopus oocytes to investigate if heightened membrane potential would explain the efflux characteristics of T62D-hDAT. In the absence of substrate, all constructs displayed identical resting membrane potentials. Substrate-induced inward currents were present in oocytes expressing WT- and T62A-hDAT but not T62D-hDAT, suggesting equal bidirectional ion flow through T62D-hDAT. Utilization of the fluorescent DAT substrate ASP(+) [4-(4-(dimethylamino)styryl)-N-methylpyridinium] revealed that T62D-hDAT accumulates substrate in human embryonic kidney (HEK)-293 cells when the substrate is not subject to efflux. Extracellular sodium (Na(+) e) replacement was used to evaluate sodium gradient requirements for DAT transport functions. The EC50 for Na(+) e stimulation of [(3)H]DA uptake was identical in all constructs expressed in HEK-293 cells. As expected, decreasing [Na(+)]e stimulated [(3)H]DA efflux in WT- and T62A-hDAT cells. Conversely, the elevated [(3)H]DA efflux in T62D-hDAT cells was independent of Na(+) e and commensurate with [(3)H]DA efflux attained in WT-hDAT cells, either by removal of Na(+) e or by application of amphetamine. We conclude that T62D-hDAT represents an efflux-willing, Na(+)-primed orientation-possibly representing an experimental model of the conformational impact of amphetamine exposure to hDAT.
Collapse
Affiliation(s)
- Rheaclare Fraser
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Yongyue Chen
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Bipasha Guptaroy
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Kathryn D Luderman
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Stephanie L Stokes
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Asim Beg
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Louis J DeFelice
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Margaret E Gnegy
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| |
Collapse
|
13
|
Cameron KN, Kolanos R, Solis E, Glennon RA, De Felice LJ. Bath salts components mephedrone and methylenedioxypyrovalerone (MDPV) act synergistically at the human dopamine transporter. Br J Pharmacol 2013; 168:1750-7. [PMID: 23170765 DOI: 10.1111/bph.12061] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 10/20/2012] [Accepted: 11/09/2012] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND AND PURPOSE Bath salts is the street name for drug combinations that contain synthetic cathinone analogues, among them possibly mephedrone (MEPH) and certainly methylenedioxypyrovalerone (MDPV). In animal studies, cathinone and certain cathinone analogues release dopamine (DA), similar to the action of amphetamine (AMPH) and methamphetamine (METH). AMPH and METH act on the human DA transporter (hDAT); thus, we investigated MEPH and MDPV acting at hDAT. EXPERIMENTAL APPROACH We recorded electrical currents mediated by hDAT expressed in Xenopus laevis oocytes and exposed to: DA, METH, a known hDAT stimulant and DA releaser, MEPH, MDPV, MEPH + MDPV, or cocaine, a known hDAT inhibitor. KEY RESULTS DA, METH and MEPH induce an inward current (depolarizing) when the oocyte is held near the resting potential (-60 mV), therefore acting as excitatory hDAT substrates. Structurally analogous MDPV induces an outward (hyperpolarizing) current similar to cocaine, therefore acting as an inhibitory non-substrate blocker. CONCLUSIONS AND IMPLICATIONS Two components of bath salts, MEPH and MDPV, produce opposite effects at hDAT that are comparable with METH and cocaine, respectively. In our assay, MEPH is nearly as potent as METH; however, MDPV is much more potent than cocaine and its effect is longer lasting. When applied in combination, MEPH exhibits faster kinetics than MDPV, viz., the MEPH depolarizing current occurs seconds before the slower MDPV hyperpolarizing current. Bath salts containing MEPH (or a similar drug) and MDPV might then be expected initially to release DA and subsequently prevent its reuptake via hDAT. Such combined action possibly underlies some of the reported effects of bath salts abuse.
Collapse
Affiliation(s)
- Krasnodara N Cameron
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA 23298, USA
| | | | | | | | | |
Collapse
|
14
|
Pramod AB, Foster J, Carvelli L, Henry LK. SLC6 transporters: structure, function, regulation, disease association and therapeutics. Mol Aspects Med 2013; 34:197-219. [PMID: 23506866 DOI: 10.1016/j.mam.2012.07.002] [Citation(s) in RCA: 194] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 07/03/2012] [Indexed: 02/08/2023]
Abstract
The SLC6 family of secondary active transporters are integral membrane solute carrier proteins characterized by the Na(+)-dependent translocation of small amino acid or amino acid-like substrates. SLC6 transporters, which include the serotonin, dopamine, norepinephrine, GABA, taurine, creatine, as well as amino acid transporters, are associated with a number of human diseases and disorders making this family a critical target for therapeutic development. In addition, several members of this family are directly involved in the action of drugs of abuse such as cocaine, amphetamines, and ecstasy. Recent advances providing structural insight into this family have vastly accelerated our ability to study these proteins and their involvement in complex biological processes.
Collapse
Affiliation(s)
- Akula Bala Pramod
- Department of Pharmacology, Physiology and Therapeutics, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58203, United States
| | | | | | | |
Collapse
|
15
|
Midde NM, Huang X, Gomez AM, Booze RM, Zhan CG, Zhu J. Mutation of tyrosine 470 of human dopamine transporter is critical for HIV-1 Tat-induced inhibition of dopamine transport and transporter conformational transitions. J Neuroimmune Pharmacol 2013; 8:975-87. [PMID: 23645138 PMCID: PMC3740080 DOI: 10.1007/s11481-013-9464-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 04/18/2013] [Indexed: 01/08/2023]
Abstract
HIV-1 Tat protein plays a crucial role in perturbations of the dopamine (DA) system. Our previous studies have demonstrated that Tat decreases DA uptake, and allosterically modulates DA transporter (DAT) function. In the present study, we have found that Tat interacts directly with DAT, leading to inhibition of DAT function. Through computational modeling and simulations, a potential recognition binding site of human DAT (hDAT) for Tat was predicted. Mutation of tyrosine470 (Y470H) attenuated Tat-induced inhibition of DA transport, implicating the functional relevance of this residue for Tat binding to hDAT. Y470H reduced the maximal velocity of [³H]DA uptake without changes in the K(m) and IC₅₀ values for DA inhibition of DA uptake but increased DA uptake potency for cocaine and GBR12909, suggesting that this residue does not overlap with the binding sites in hDAT for substrate but is critical for these inhibitors. Furthermore, Y470H also led to transporter conformational transitions by affecting zinc modulation of DA uptake and WIN35,428 binding as well as enhancing basal DA efflux. Collectively, these findings demonstrate Tyr470 as a functional recognition residue in hDAT for Tat-induced inhibition of DA transport and transporter conformational transitions. The consequence of mutation at this residue is to block the functional binding of Tat to hDAT without affecting physiological DA transport.
Collapse
Affiliation(s)
- Narasimha M. Midde
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208 USA
| | - Xiaoqin Huang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536 USA
| | - Adrian M. Gomez
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208 USA
| | - Rosemarie M. Booze
- Department of Psychology, University of South Carolina, Columbia, SC 29208 USA
| | - Chang-Guo Zhan
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536 USA
| | - Jun Zhu
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208 USA
- Department of Psychology, University of South Carolina, Columbia, SC 29208 USA
| |
Collapse
|
16
|
Vaughan RA, Foster JD. Mechanisms of dopamine transporter regulation in normal and disease states. Trends Pharmacol Sci 2013; 34:489-96. [PMID: 23968642 DOI: 10.1016/j.tips.2013.07.005] [Citation(s) in RCA: 283] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 07/23/2013] [Accepted: 07/24/2013] [Indexed: 11/17/2022]
Abstract
The dopamine (DA) transporter (DAT) controls the spatial and temporal dynamics of DA neurotransmission by driving reuptake of extracellular transmitter into presynaptic neurons. Many diseases such as depression, bipolar disorder, Parkinson's disease (PD), and attention deficit hyperactivity disorder (ADHD) are associated with abnormal DA levels, implicating DAT as a factor in their etiology. Medications used to treat these disorders and many addictive drugs target DAT and enhance dopaminergic signaling by suppressing transmitter reuptake. We now understand that the transport and binding properties of DAT are regulated by complex and overlapping mechanisms that provide neurons with the ability to modulate DA clearance in response to physiological demands. These processes are controlled by endogenous signaling pathways and affected by exogenous transporter ligands, demonstrating their importance for normal neurotransmission, drug abuse, and disease treatments. Increasing evidence supports the disruption of these mechanisms in DA disorders, implicating dysregulation of transport in disease etiologies and suggesting these processes as potential points for therapeutic manipulation of DA availability.
Collapse
Affiliation(s)
- Roxanne A Vaughan
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202, USA.
| | | |
Collapse
|
17
|
Moritz AE, Foster JD, Gorentla BK, Mazei-Robison MS, Yang JW, Sitte HH, Blakely RD, Vaughan RA. Phosphorylation of dopamine transporter serine 7 modulates cocaine analog binding. J Biol Chem 2012; 288:20-32. [PMID: 23161550 DOI: 10.1074/jbc.m112.407874] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
As an approach to elucidating dopamine transporter (DAT) phosphorylation characteristics, we examined in vitro phosphorylation of a recombinant rat DAT N-terminal peptide (NDAT) using purified protein kinases. We found that NDAT becomes phosphorylated at single distinct sites by protein kinase A (Ser-7) and calcium-calmodulin-dependent protein kinase II (Ser-13) and at multiple sites (Ser-4, Ser-7, and Ser-13) by protein kinase C (PKC), implicating these residues as potential sites of DAT phosphorylation by these kinases. Mapping of rat striatal DAT phosphopeptides by two-dimensional thin layer chromatography revealed basal and PKC-stimulated phosphorylation of the same peptide fragments and comigration of PKC-stimulated phosphopeptide fragments with NDAT Ser-7 phosphopeptide markers. We further confirmed by site-directed mutagenesis and mass spectrometry that Ser-7 is a site for PKC-stimulated phosphorylation in heterologously expressed rat and human DATs. Mutation of Ser-7 and nearby residues strongly reduced the affinity of rat DAT for the cocaine analog (-)-2β-carbomethoxy-3β-(4-fluorophenyl) tropane (CFT), whereas in rat striatal tissue, conditions that promote DAT phosphorylation caused increased CFT affinity. Ser-7 mutation also affected zinc modulation of CFT binding, with Ala and Asp substitutions inducing opposing effects. These results identify Ser-7 as a major site for basal and PKC-stimulated phosphorylation of native and expressed DAT and suggest that Ser-7 phosphorylation modulates transporter conformational equilibria, shifting the transporter between high and low affinity cocaine binding states.
Collapse
Affiliation(s)
- Amy E Moritz
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203-9037, USA
| | | | | | | | | | | | | | | |
Collapse
|
18
|
Foster JD, Yang JW, Moritz AE, Challasivakanaka S, Smith MA, Holy M, Wilebski K, Sitte HH, Vaughan RA. Dopamine transporter phosphorylation site threonine 53 regulates substrate reuptake and amphetamine-stimulated efflux. J Biol Chem 2012; 287:29702-12. [PMID: 22722938 PMCID: PMC3436161 DOI: 10.1074/jbc.m112.367706] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
In the central nervous system, levels of extraneuronal dopamine are controlled primarily by the action of the dopamine transporter (DAT). Multiple signaling pathways regulate transport activity, substrate efflux, and other DAT functions through currently unknown mechanisms. DAT is phosphorylated by protein kinase C within a serine cluster at the distal end of the cytoplasmic N terminus, whereas recent work in model cells revealed proline-directed phosphorylation of rat DAT at membrane-proximal residue Thr(53). In this report, we use mass spectrometry and a newly developed phospho-specific antibody to positively identify DAT phosphorylation at Thr(53) in rodent striatal tissue and heterologous expression systems. Basal phosphorylation of Thr(53) occurred with a stoichiometry of ~50% and was strongly increased by phorbol esters and protein phosphatase inhibitors, demonstrating modulation of the site by signaling pathways that impact DAT activity. Mutations of Thr(53) to prevent phosphorylation led to reduced dopamine transport V(max) and total apparent loss of amphetamine-stimulated substrate efflux, supporting a major role for this residue in the transport kinetic mechanism.
Collapse
Affiliation(s)
- James D Foster
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202-9037, USA
| | | | | | | | | | | | | | | | | |
Collapse
|