Vesicular Monoamine Transporter

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Falk W Lohoff - One of the best experts on this subject based on the ideXlab platform.

  • deletion of the Vesicular Monoamine Transporter 1 vmat1 slc18a1 gene affects dopamine signaling
    Brain Research, 2019
    Co-Authors: Falk W Lohoff, Thomas N Ferraro, Gregory V Carr, Bethany R Brookshire, Irwin Lucki
    Abstract:

    The Vesicular Monoamine Transporter is involved in presynaptic catecholamine storage and neurotransmission. Two isoforms of the Transporter exist, VMAT1 and VMAT2, and both are expressed in the brain, though VMAT2 expression is more robust and has been more widely studied. In this study we investigated the role of VMAT1 KO on markers of dopaminergic function and neurotransmission, and dopamine-related behaviors. Null-mutant VMAT1 mice were studied behaviorally using the tail suspension test, elevated zero maze and locomotor activity assessments. Tissue Monoamines were measured both ex vivo and by using in vivo microdialysis. Protein expression of tyrosine hydroxylase and D2 dopamine receptors was measured using western blot analysis. Results show that VMAT1 KO mice have decreased dopamine levels in the frontal cortex, increased postsynaptic D2 expression, and lower frontal cortex tyrosine hydroxylase expression compared to WT mice. VMAT1 KO mice also show an exaggerated behavioral locomotor response to acute amphetamine treatment. We conclude that dopaminergic signaling is robustly altered in the frontal cortex of VMAT1 null-mutant mice and suggest that VMAT1 may be relevant to the pathogenesis and/or treatment of psychiatric illnesses including schizophrenia and bipolar disease.

  • genetic variation in the Vesicular Monoamine Transporter 1 vmat1 slc18a1 gene and alcohol withdrawal severity
    Alcoholism: Clinical and Experimental Research, 2016
    Co-Authors: Nisha Dutta, Sarah G Helton, Melanie L Schwandt, Xi Zhu, Reza Momenan, Falk W Lohoff
    Abstract:

    Background Alcohol withdrawal (AW) can be a serious consequence of alcohol dependence and consists of various neurochemical adaptations in the brain. One such neuroadaptation occurs in the Monoamine neurotransmitter system. Recently, a functional variant in the presynaptic Vesicular Monoamine Transporter gene (VMAT1/SLC18A1—Thr136Ile—rs1390938) was found to significantly increase transport of Monoamines into synaptic vesicles in vitro. We hypothesize that the alteration of magnitude of Monoamine release contributes to severity of AW symptoms. Methods Alcohol-dependent individuals (n = 609; European American n = 340; African American n = 216; other n = 53) were administered the Clinical Institute Withdrawal Assessment of Alcohol Scale, Revised (CIWA-Ar) questionnaire at the time of inpatient admission. Patients were subsequently genotyped for 12 single nucleotide polymorphism (SNP) markers in VMAT1. Association analyses were conducted on the combined sample and separated by ethnicity. Results Single marker association tests revealed a significant association between 3 VMAT1 markers and CIWA-Ar scores in the EA sample. The minor alleles of rs1390938 (A) and rs952859 (C) were significantly associated with lower CIWA-Ar scores (p = 0.0006; p = 0.0007), whereas the minor allele of rs3779672 (G) was significantly associated with higher scores (p = 0.006). Additionally, these 3 SNPs were found in a haplotype block that was significantly associated with lower CIWA-Ar scores after haplotype analyses were run (p = 0.009). Conclusions This study shows that genetic variants in VMAT1, including the functional SNP rs1390938, contribute to the severity of AW in patients of European descent. Our data show for the first time a role of presynaptic neurotransmitter release in AW severity. This finding could contribute to identifying patients at risk for severe AW and shed light into the pathophysiology of AW and its treatment.

  • functional genetic variants in the Vesicular Monoamine Transporter 1 modulate emotion processing
    Molecular Psychiatry, 2014
    Co-Authors: Falk W Lohoff, Jon Kar Zubieta, Thomas N Ferraro, Rachel Hodge, Sneha Narasimhan, Aleksandra H Nall, Brian J Mickey, Mary M Heitzeg, Scott A Langenecker, Ryan Bogdan
    Abstract:

    Emotional behavior is in part heritable and often disrupted in psychopathology. Identification of specific genetic variants that drive this heritability may provide important new insight into molecular and neurobiological mechanisms involved in emotionality. Our results demonstrate that the presynaptic Vesicular Monoamine Transporter 1 (VMAT1) Thr136Ile (rs1390938) polymorphism is functional in vitro, with the Ile allele leading to increased Monoamine transport into presynaptic vesicles. Moreover, we show that the Thr136Ile variant predicts differential responses in emotional brain circuits consistent with its effects in vitro. Lastly, deep sequencing of bipolar disorder (BPD) patients and controls identified several rare novel VMAT1 variants. The variant Phe84Ser was only present in individuals with BPD and leads to marked increase Monoamine transport in vitro. Taken together, our data show that VMAT1 polymorphisms influence Monoamine signaling, the functional response of emotional brain circuits and risk for psychopathology.

  • association study of the Vesicular Monoamine Transporter gene slc18a2 with tardive dyskinesia
    Journal of Psychiatric Research, 2013
    Co-Authors: Clement C Zai, Falk W Lohoff, Arun K Tiwari, Marina Mazzoco, Vincenzo De Luca, Daniel J Muller, Sajid A Shaikh, Natalie Freeman
    Abstract:

    Tardive dyskinesia (TD) is an involuntary movement disorder that can occur in up to 25% of patients receiving long-term first-generation antipsychotic treatment. Its etiology is unclear, but family studies suggest that genetic factors play an important role in contributing to risk for TD. The Vesicular Monoamine Transporter 2 (VMAT2) is an interesting candidate for genetic studies of TD because it regulates the release of neurotransmitters implicated in TD, including dopamine, serotonin, and GABA. VMAT2 is also a target of tetrabenazine, a drug used in the treatment of hyperkinetic movement disorders, including TD. We examined nine single-nucleotide polymorphisms (SNPs) in the SLC18A2 gene that encodes VMAT2 for association with TD in our sample of chronic schizophrenia patients (n = 217). We found a number of SNPs to be nominally associated with TD occurrence and the Abnormal Involuntary Movement Scale (AIMS), including the rs2015586 marker which was previously found associated with TD in the CATIE sample (Tsai et al., 2010), as well as the rs363224 marker, with the low-expression AA genotype appearing to be protective against TD (p = 0.005). We further found the rs363224 marker to interact with the putative functional D2 receptor rs6277 (C957T) polymorphism (p = 0.001), supporting the dopamine hypothesis of TD. Pending further replication, VMAT2 may be considered a therapeutic target for the treatment and/or prevention of TD.

  • association between polymorphisms in the Vesicular Monoamine Transporter 1 gene vmat1 slc18a1 on chromosome 8p and schizophrenia
    Neuropsychobiology, 2008
    Co-Authors: Falk W Lohoff, Andrew E Weller, Paul J Bloch, Russell J Buono, Glenn A Doyle, Thomas N Ferraro, Wade H Berrettini
    Abstract:

    Linkage studies have suggested a susceptibility locus for schizophrenia (SZ) exists on chromosome 8p21–22. The Vesicular Monoamine Transporter 1 gene (VMAT1), also known as SLC18A1, maps to this SZ su

Thomas N Ferraro - One of the best experts on this subject based on the ideXlab platform.

  • deletion of the Vesicular Monoamine Transporter 1 vmat1 slc18a1 gene affects dopamine signaling
    Brain Research, 2019
    Co-Authors: Falk W Lohoff, Thomas N Ferraro, Gregory V Carr, Bethany R Brookshire, Irwin Lucki
    Abstract:

    The Vesicular Monoamine Transporter is involved in presynaptic catecholamine storage and neurotransmission. Two isoforms of the Transporter exist, VMAT1 and VMAT2, and both are expressed in the brain, though VMAT2 expression is more robust and has been more widely studied. In this study we investigated the role of VMAT1 KO on markers of dopaminergic function and neurotransmission, and dopamine-related behaviors. Null-mutant VMAT1 mice were studied behaviorally using the tail suspension test, elevated zero maze and locomotor activity assessments. Tissue Monoamines were measured both ex vivo and by using in vivo microdialysis. Protein expression of tyrosine hydroxylase and D2 dopamine receptors was measured using western blot analysis. Results show that VMAT1 KO mice have decreased dopamine levels in the frontal cortex, increased postsynaptic D2 expression, and lower frontal cortex tyrosine hydroxylase expression compared to WT mice. VMAT1 KO mice also show an exaggerated behavioral locomotor response to acute amphetamine treatment. We conclude that dopaminergic signaling is robustly altered in the frontal cortex of VMAT1 null-mutant mice and suggest that VMAT1 may be relevant to the pathogenesis and/or treatment of psychiatric illnesses including schizophrenia and bipolar disease.

  • functional genetic variants in the Vesicular Monoamine Transporter 1 modulate emotion processing
    Molecular Psychiatry, 2014
    Co-Authors: Falk W Lohoff, Jon Kar Zubieta, Thomas N Ferraro, Rachel Hodge, Sneha Narasimhan, Aleksandra H Nall, Brian J Mickey, Mary M Heitzeg, Scott A Langenecker, Ryan Bogdan
    Abstract:

    Emotional behavior is in part heritable and often disrupted in psychopathology. Identification of specific genetic variants that drive this heritability may provide important new insight into molecular and neurobiological mechanisms involved in emotionality. Our results demonstrate that the presynaptic Vesicular Monoamine Transporter 1 (VMAT1) Thr136Ile (rs1390938) polymorphism is functional in vitro, with the Ile allele leading to increased Monoamine transport into presynaptic vesicles. Moreover, we show that the Thr136Ile variant predicts differential responses in emotional brain circuits consistent with its effects in vitro. Lastly, deep sequencing of bipolar disorder (BPD) patients and controls identified several rare novel VMAT1 variants. The variant Phe84Ser was only present in individuals with BPD and leads to marked increase Monoamine transport in vitro. Taken together, our data show that VMAT1 polymorphisms influence Monoamine signaling, the functional response of emotional brain circuits and risk for psychopathology.

  • association between polymorphisms in the Vesicular Monoamine Transporter 1 gene vmat1 slc18a1 on chromosome 8p and schizophrenia
    Neuropsychobiology, 2008
    Co-Authors: Falk W Lohoff, Andrew E Weller, Paul J Bloch, Russell J Buono, Glenn A Doyle, Thomas N Ferraro, Wade H Berrettini
    Abstract:

    Linkage studies have suggested a susceptibility locus for schizophrenia (SZ) exists on chromosome 8p21–22. The Vesicular Monoamine Transporter 1 gene (VMAT1), also known as SLC18A1, maps to this SZ su

  • variations in the Vesicular Monoamine Transporter 1 gene vmat1 slc18a1 are associated with bipolar i disorder
    Neuropsychopharmacology, 2006
    Co-Authors: Falk W Lohoff, Thomas N Ferraro, John P Dahl, Steven E Arnold, Jurgen Gallinat, Thomas Sander, Wade H Berrettini
    Abstract:

    The Vesicular Monoamine Transporter 1 gene (VMAT1/SLC18A1) maps to the shared bipolar disorder (BPD)/schizophrenia (SZ) susceptibility locus on chromosome 8p21. Vesicular Monoamine Transporters are involved in transport of Monoamine neurotransmitters which have been postulated to play a relevant role in the etiology of BPD and/or SZ. Variations in the VMAT1 gene might affect Transporter function and/or expression and might be involved in the etiology of BPD and/or SZ. Genotypes of 585 patients with BPD type I and 563 control subjects were obtained for three missense single nucleotide polymorphisms (SNPs) (Thr4Pro, Thr98Ser, Thr136Ile) and four non-coding SNPs (rs988713, rs2279709, rs3735835, rs1497020). All cases and controls were of European descent. Allele frequencies differed significantly for the potential functional polymorphism Thr136Ser between BPD patients and controls (p=0.003; df=1; OR=1.34; 95% CI: 1.11-1.62). Polymorphisms in the promoter region (rs988713: p=0.005, df=1; OR=1.31; 95% CI: 1.09-1.59) and intron 8 (rs2279709: p=0.039, df=1; OR=0.84; 95% CI: 0.71-0.99) were also associated with disease. Expression analysis confirmed that VMAT1 is expressed in human brain at the mRNA and protein level. Results suggest that variations in the VMAT1 gene may confer susceptibility to BPD in patients of European descent. Additional studies are necessary to confirm this effect and to elucidate the role of VMAT1 in central nervous system physiology.

Peter A Crooks - One of the best experts on this subject based on the ideXlab platform.

  • novel n 1 2 dihydroxypropyl analogs of lobelane inhibit Vesicular Monoamine Transporter 2 function and methamphetamine evoked dopamine release
    Journal of Pharmacology and Experimental Therapeutics, 2011
    Co-Authors: David B. Horton, Peter A Crooks, Guangrong Zheng, Kiran B. Siripurapu, Linda P Dwoskin
    Abstract:

    Lobelane, a chemically defunctionalized saturated analog of lobeline, has increased selectivity for the Vesicular Monoamine Transporter 2 (VMAT2) compared with the parent compound. Lobelane inhibits methamphetamine-evoked dopamine (DA) release and decreases methamphetamine self-administration. Unfortunately, tolerance develops to the ability of lobelane to decrease these behavioral effects of methamphetamine. Lobelane has low water solubility, which is problematic for drug development. The aim of the current study was to determine the pharmacological effect of replacement of the N-methyl moiety with a chiral N-1,2-dihydroxypropyl (N-1,2-diol) moiety, which enhances water solubility, altering the configuration of the N-1,2-diol moiety and incorporating phenyl ring substituents into the analogs. To determine VMAT2 selectivity, structure-activity relationships also were generated for inhibition of DA and serotonin Transporters. Analogs with the highest potency for inhibiting DA uptake at VMAT2 and at least 10-fold selectivity were evaluated further for ability to inhibit methamphetamine-evoked DA release from superfused striatal slices. (R)-3-[2,6-cis-di(4-methoxyphenethyl)piperidin-1-yl]propane-1,2-diol (GZ-793A), the (R)-4-methoxyphenyl-N-1,2-diol analog, and (R)-3-[2,6-cis-di(1-naphthylethyl)piperidin-1-yl]propane-1,2-diol (GZ-794A), the (R)-1-naphthyl-N-1,2-diol analog, exhibited the highest potency (Ki ∼30 nM) inhibiting VMAT2, and both analogs inhibited methamphetamine-evoked endogenous DA release (IC50 = 10.6 and 0.4 μM, respectively). Thus, the pharmacophore for VMAT2 inhibition accommodates the N-1,2-diol moiety, which improves drug-likeness and enhances the potential for the development of these clinical candidates as treatments for methamphetamine abuse.

  • design synthesis and interaction at the Vesicular Monoamine Transporter 2 of lobeline analogs potential pharmacotherapies for the treatment of psychostimulant abuse
    Current Topics in Medicinal Chemistry, 2011
    Co-Authors: Peter A Crooks, Guangrong Zheng, David B. Horton, Ashish P Vartak, John P Culver, Fang Zheng, Linda P Dwoskin
    Abstract:

    The Vesicular Monoamine Transporter-2 (VMAT2) is considered as a new target for the development of novel therapeutics to treat psychostimulant abuse. Current information on the structure, function and role of VMAT2 in psychostimulant abuse are presented. Lobeline, the major alkaloidal constituent of Lobelia inflata, interacts with nicotinic receptors and with VMAT2. Numerous studies have shown that lobeline inhibits both the neurochemical and behavioral effects of amphetamine in rodents, and behavioral studies demonstrate that lobeline has potential as a pharmacotherapy for psychostimulant abuse. Systematic structural modification of the lobeline molecule is described with the aim of improving selectivity and affinity for VMAT2 over neuronal nicotinic acetylcholine receptors and other neurotransmitter Transporters. This has led to the discovery of more potent and selective ligands for VMAT2. In addition, a computational neural network analysis of the affinity of these lobeline analogs for VMAT2 has been carried out, which provides computational models that have predictive value in the rational design of VMAT2 ligands and is also useful in identifying drug candidates from virtual libraries for subsequent synthesis and evaluation.

  • meso transdiene analogs inhibit Vesicular Monoamine Transporter 2 function and methamphetamine evoked dopamine release
    Journal of Pharmacology and Experimental Therapeutics, 2011
    Co-Authors: David B. Horton, Seth D Norrholm, Agripina G Deaciuc, John P Culver, Kiran B. Siripurapu, Marhaba Hojahmat, Joshua S. Beckmann, Steven B. Harrod, Michael T. Bardo, Peter A Crooks
    Abstract:

    Lobeline, a nicotinic receptor antagonist and neurotransmitter Transporter inhibitor, is a candidate pharmacotherapy for methamphetamine abuse. meso-Transdiene (MTD), a lobeline analog, lacks nicotinic receptor affinity, retains affinity for Vesicular Monoamine Transporter 2 (VMAT2), and, surprisingly, has enhanced affinity for dopamine (DA) and serotonin Transporters [DA Transporter (DAT) and serotonin Transporter (SERT), respectively]. In the current study, MTD was evaluated for its ability to decrease methamphetamine self-administration in rats relative to food-maintained responding. MTD specifically decreased methamphetamine self-administration, extending our previous work. Classical structure-activity relationships revealed that more conformationally restricted MTD analogs enhanced VMAT2 selectivity and drug likeness, whereas affinity at the dihydrotetrabenazine binding and DA uptake sites on VMAT2 was not altered. Generally, MTD analogs exhibited 50- to 1000-fold lower affinity for DAT and were equipotent or had 10-fold higher affinity for SERT, compared with MTD. Representative analogs from the series potently and competitively inhibited [3H]DA uptake at VMAT2. (3Z,5Z)-3,5-bis(2,4-dichlorobenzylidene)-1-methylpiperidine (UKMH-106), the 3Z,5Z-2,4-dichlorophenyl MTD analog, had improved selectivity for VMAT2 over DAT and importantly inhibited methamphetamine-evoked DA release from striatal slices. In contrast, (3Z,5E)-3,5-bis(2,4-dichlorobenzylidene)-1-methylpiperidine (UKMH-105), the 3Z,5E-geometrical isomer, inhibited DA uptake at VMAT2, but did not inhibit methamphetamine-evoked DA release. Taken together, these results suggest that these geometrical isomers interact at alternate sites on VMAT2, which are associated with distinct pharmacophores. Thus, structural modification of the MTD molecule resulted in analogs exhibiting improved drug likeness and improved selectivity for VMAT2, as well as the ability to decrease methamphetamine-evoked DA release, supporting the further evaluation of these analogs as treatments for methamphetamine abuse.

  • Phenyl Ring-Substituted Lobelane Analogs: Inhibition of [3H]Dopamine Uptake at the Vesicular Monoamine Transporter-2
    2010
    Co-Authors: Justin R Nickell, Peter A Crooks, Guangrong Zheng, Agripina G Deaciuc, Linda P Dwoskin
    Abstract:

    Lobeline attenuates the behavioral effects of methamphet-amine via inhibition of the Vesicular Monoamine Transporter (VMAT2). To increase selectivity for VMAT2, chemically defunc-tionalized lobeline analogs, including lobelane, were designed to eliminate nicotinic acetylcholine receptor affinity. The current study evaluated the ability of lobelane analogs to inhibit [3H]di-hydrotetrabenazine (DTBZ) binding to VMAT2 and [3H]dop-amine (DA) uptake into isolated synaptic vesicles and deter-mined the mechanism of inhibition. Introduction of aromatic substituents in lobelane maintained analog affinity for the [3H]DTBZ binding site on VMAT2 and inhibitory potency in the [3H]DA uptake assay assessing VMAT2 function. The most potent (Ki 13–16 nM) analogs in the series included para

  • meso-Transdiene Analogs Inhibit Vesicular Monoamine Transporter-2 Function and Methamphetamine-Evoked
    2010
    Co-Authors: David B. Horton, Seth D Norrholm, Agripina G Deaciuc, John P Culver, Kiran B. Siripurapu, Marhaba Hojahmat, Joshua S. Beckmann, Steven B. Harrod, Michael T. Bardo, Peter A Crooks
    Abstract:

    Lobeline, a nicotinic receptor antagonist and neurotransmitter Transporter inhibitor, is a candidate pharmacotherapy for meth-amphetamine abuse. meso-Transdiene (MTD), a lobeline ana-log, lacks nicotinic receptor affinity, retains affinity for Vesicular Monoamine Transporter 2 (VMAT2), and, surprisingly, has en-hanced affinity for dopamine (DA) and serotonin Transporters [DA Transporter (DAT) and serotonin Transporter (SERT), re-spectively]. In the current study, MTD was evaluated for its ability to decrease methamphetamine self-administration in rats relative to food-maintained responding. MTD specifically decreased methamphetamine self-administration, extending our previous work. Classical structure-activity relationships re-vealed that more conformationally restricted MTD analogs en-hanced VMAT2 selectivity and drug likeness, whereas affinity a

Wade H Berrettini - One of the best experts on this subject based on the ideXlab platform.

  • association between polymorphisms in the Vesicular Monoamine Transporter 1 gene vmat1 slc18a1 on chromosome 8p and schizophrenia
    Neuropsychobiology, 2008
    Co-Authors: Falk W Lohoff, Andrew E Weller, Paul J Bloch, Russell J Buono, Glenn A Doyle, Thomas N Ferraro, Wade H Berrettini
    Abstract:

    Linkage studies have suggested a susceptibility locus for schizophrenia (SZ) exists on chromosome 8p21–22. The Vesicular Monoamine Transporter 1 gene (VMAT1), also known as SLC18A1, maps to this SZ su

  • variations in the Vesicular Monoamine Transporter 1 gene vmat1 slc18a1 are associated with bipolar i disorder
    Neuropsychopharmacology, 2006
    Co-Authors: Falk W Lohoff, Thomas N Ferraro, John P Dahl, Steven E Arnold, Jurgen Gallinat, Thomas Sander, Wade H Berrettini
    Abstract:

    The Vesicular Monoamine Transporter 1 gene (VMAT1/SLC18A1) maps to the shared bipolar disorder (BPD)/schizophrenia (SZ) susceptibility locus on chromosome 8p21. Vesicular Monoamine Transporters are involved in transport of Monoamine neurotransmitters which have been postulated to play a relevant role in the etiology of BPD and/or SZ. Variations in the VMAT1 gene might affect Transporter function and/or expression and might be involved in the etiology of BPD and/or SZ. Genotypes of 585 patients with BPD type I and 563 control subjects were obtained for three missense single nucleotide polymorphisms (SNPs) (Thr4Pro, Thr98Ser, Thr136Ile) and four non-coding SNPs (rs988713, rs2279709, rs3735835, rs1497020). All cases and controls were of European descent. Allele frequencies differed significantly for the potential functional polymorphism Thr136Ser between BPD patients and controls (p=0.003; df=1; OR=1.34; 95% CI: 1.11-1.62). Polymorphisms in the promoter region (rs988713: p=0.005, df=1; OR=1.31; 95% CI: 1.09-1.59) and intron 8 (rs2279709: p=0.039, df=1; OR=0.84; 95% CI: 0.71-0.99) were also associated with disease. Expression analysis confirmed that VMAT1 is expressed in human brain at the mRNA and protein level. Results suggest that variations in the VMAT1 gene may confer susceptibility to BPD in patients of European descent. Additional studies are necessary to confirm this effect and to elucidate the role of VMAT1 in central nervous system physiology.

Gary W Miller - One of the best experts on this subject based on the ideXlab platform.

  • Vesicular Monoamine Transporter 2 vmat2 level regulates mptp vulnerability and clearance of excess dopamine in mouse striatal terminals
    Toxicological Sciences, 2016
    Co-Authors: Kelly M Lohr, Amy R Dunn, Kristen A Stout, Carlie A Hoffman, Alison I Bernstein, Minzheng Wang, Merry Chen, Miranda J Mcdaniel, Gary W Miller
    Abstract:

    The Vesicular Monoamine Transporter 2 (VMAT2) packages neurotransmitters for release during neurotransmission and sequesters toxicants into vesicles to prevent neuronal damage. In mice, low VMAT2 levels causes catecholaminergic cell loss and behaviors resembling Parkinson's disease, while high levels of VMAT2 increase dopamine release and protect against dopaminergic toxicants. However, comparisons across these VMAT2 mouse genotypes were impossible due to the differing genetic background strains of the animals. Following back-crossing to a C57BL/6 line, we confirmed that mice with approximately 95% lower VMAT2 levels compared with wild-type (VMAT2-LO) display significantly reduced Vesicular uptake, progressive dopaminergic terminal loss with aging, and exacerbated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity. Conversely, VMAT2-overexpressing mice (VMAT2-HI) are protected from the loss of striatal terminals following MPTP treatment. We also provide evidence that enhanced Vesicular filling in the VMAT2-HI mice modifies the handling of newly synthesized dopamine, indicated by changes in indirect measures of extracellular dopamine clearance. These results confirm the role of VMAT2 in the protection of vulnerable nigrostriatal dopamine neurons and may also provide new insight into the side effects of L-DOPA treatments in Parkinson's disease.

  • increased Vesicular Monoamine Transporter 2 vmat2 slc18a2 protects against methamphetamine toxicity
    ACS Chemical Neuroscience, 2015
    Co-Authors: Kelly M Lohr, Amy R Dunn, Kristen A Stout, Minzheng Wang, Thomas S Guillot, Ali Salahpour, Gary W Miller
    Abstract:

    The psychostimulant methamphetamine (METH) is highly addictive and neurotoxic to dopamine terminals. METH toxicity has been suggested to be due to the release and accumulation of dopamine in the cytosol of these terminals. The Vesicular Monoamine Transporter 2 (VMAT2; SLC18A2) is a critical mediator of dopamine handling. Mice overexpressing VMAT2 (VMAT2-HI) have an increased Vesicular capacity to store dopamine, thus augmenting striatal dopamine levels and dopamine release in the striatum. Based on the altered compartmentalization of intracellular dopamine in the VMAT2-HI mice, we assessed whether enhanced Vesicular function was capable of reducing METH-induced damage to the striatal dopamine system. While wildtype mice show significant losses in striatal levels of the dopamine Transporter (65% loss) and tyrosine hydroxylase (46% loss) following a 4 × 10 mg/kg METH dosing regimen, VMAT2-HI mice were protected from this damage. VMAT2-HI mice were also spared from the inflammatory response that follows METH treatment, showing an increase in astroglial markers that was approximately one-third of that of wildtype animals (117% vs 36% increase in GFAP, wildtype vs VMAT2-HI). Further analysis also showed that elevated VMAT2 level does not alter the ability of METH to increase core body temperature, a mechanism integral to the toxicity of the drug. Finally, the VMAT2-HI mice showed no difference from wildtype littermates on both METH-induced conditioned place preference and in METH-induced locomotor activity (1 mg/kg METH). These results demonstrate that elevated VMAT2 protects against METH toxicity without enhancing the rewarding effects of the drug. Since the VMAT2-HI mice are protected from METH despite higher basal dopamine levels, this study suggests that METH toxicity depends more on the proper compartmentalization of synaptic dopamine than on the absolute amount of dopamine in the brain.

  • a fluorescent based assay for live cell spatially resolved assessment of Vesicular Monoamine Transporter 2 mediated neurotransmitter transport
    Journal of Neuroscience Methods, 2012
    Co-Authors: Alison I Bernstein, Kristen A Stout, Gary W Miller
    Abstract:

    The Vesicular Monoamine Transporter 2 (VMAT2; Slc18a2) packages Monoamines into synaptic vesicles. Monoamine homeostasis is highly regulated and dysfunction may play a role in Parkinson's disease, Huntington's disease, drug addiction, and neuropsychiatric disorders. The primary function of VMAT2 is to sequester Monoamine neurotransmitters into vesicles for subsequent release; it also sequesters toxicants away from cytosolic sites of action. Identification of compounds that modify the action of VMAT2 may be useful as therapeutic agents for preventing or reversing Monoamine-related toxicity. Current methods for measuring VMAT2 function are unable to assess uptake in intact cells. Here, we adapted the Neurotransmitter Uptake Assay (Molecular Devices) to develop a measure of VMAT2 function in live whole cells. This assay contains a fluorescent compound, which is transported into cells by the plasma membrane Monoamine Transporters and has been marketed as a rapid, high-throughput, plate reader based assay for function of these plasma membrane Transporters. We demonstrate a modified version of this assay that can be used to visualize and measure transport into vesicles by VMAT2. HEK293 cell lines stably expressing the dopamine Transporter and a mCherry-VMAT2 fusion protein were generated. Confocal microscopy confirmed that the fluorescent compound is transported into mCherry-positive compartments. Furthermore, the VMAT2-specific inhibitor tetrabenazine (TBZ) blocks uptake into the mCherry-positive compartment. Confocal images can be analyzed to generate a measure of VMAT2 activity. In summary, we demonstrate a method for spatially resolved analysis of VMAT2-mediated uptake in live intact cells.

  • pacap38 increases Vesicular Monoamine Transporter 2 vmat2 expression and attenuates methamphetamine toxicity
    Neuropeptides, 2008
    Co-Authors: Thomas S Guillot, Jason R Richardson, Minzheng Wang, Tonya N Taylor, Brian J Ciliax, O Zachrisson, A Mercer, Gary W Miller
    Abstract:

    Pituitary adenylyl cyclase activating polypeptide, 38 amino acids (PACAP38) is a brain-gut peptide with diverse physiological functions and is neuroprotective in several models of neurological disease. In this study, we show that systemic administration of PACAP38, which is transported across the blood-brain barrier, greatly reduces the neurotoxicity of methamphetamine (METH). Mice treated with PACAP38 exhibited an attenuation of striatal dopamine loss after METH exposure as well as greatly reduced markers of oxidative stress. PACAP38 treatment also prevented striatal neuroinflammation after METH administration as measured by overexpression of glial fibrillary acidic protein (GFAP), an indicator of astrogliosis, and glucose Transporter 5 (GLUT5), a marker of microgliosis. In PACAP38 treated mice, the observed protective effects were not due to an altered thermal response to METH. Since the mice were not challenged with METH until 28 days after PACAP38 treatment, this suggests the neuroprotective effects are mediated by regulation of gene expression. At the time of METH administration, PACAP38 treated animals exhibited a preferential increase in the expression and function of the Vesicular Monoamine Transporter (VMAT2). Genetic reduction of VMAT2 has been shown to increase the neurotoxicity of METH, thus we propose that the increased expression of VMAT2 may underlie the protective actions of PACAP38 against METH. The ability of PACAP38 to increase VMAT2 expression suggests that PACAP38 signaling pathways may constitute a novel therapeutic approach to treat and prevent disorders of dopamine storage.

  • acute exposure to aroclor 1016 or 1260 differentially affects dopamine Transporter and Vesicular Monoamine Transporter 2 levels
    Toxicology Letters, 2004
    Co-Authors: Jason R Richardson, Gary W Miller
    Abstract:

    Polychlorinated biphenyls (PCBs) have been shown to specifically target the dopaminergic nervous system, resulting in long-term reduction of striatal dopamine (DA) levels. However, the mechanism(s) by which PCBs exert this effect is not known. Here we report that decreased striatal dopamine levels are observed 1, 7, and 14 days after acute exposure to the common PCB mixtures Aroclor 1016 or 1260. Dopamine Transporter (DAT) levels were decreased at all time points in Aroclor 1016 treated animals, and on Days 1 and 7 in Aroclor 1260 treated animals. Vesicular Monoamine Transporter 2 (VMAT2) levels were not affected by Aroclor 1016, but were significantly decreased 14 days after exposure to Aroclor 1260. Tyrosine hydroxylase expression, a marker of dopamine neuron integrity, was not significantly affected by PCB exposure at any time. These data suggest that PCB-induced reductions in striatal dopamine may be mediated by alterations in DAT and VMAT2 expression.