title: Increased expression of the dopamine transporter leads to loss of dopamine neurons, oxidative stress and l-DOPA reversible motor deficits.
abstract: The dopamine transporter is a key protein responsible for regulating dopamine homeostasis. Its function is to transport dopamine from the extracellular space into the presynaptic neuron. Studies have suggested that accumulation of dopamine in the cytosol can trigger oxidative stress and neurotoxicity. Previously, ectopic expression of the dopamine transporter was shown to cause damage in non-dopaminergic neurons due to their inability to handle cytosolic dopamine. However, it is unknown whether increasing dopamine transporter activity will be detrimental to dopamine neurons that are inherently capable of storing and degrading dopamine. To address this issue, we characterized transgenic mice that over-express the dopamine transporter selectively in dopamine neurons. We report that dopamine transporter over-expressing (DAT-tg) mice display spontaneous loss of midbrain dopamine neurons that is accompanied by increases in oxidative stress markers, 5-S-cysteinyl-dopamine and 5-S-cysteinyl-DOPAC. In addition, metabolite-to-dopamine ratios are increased and VMAT2 protein expression is decreased in the striatum of these animals. Furthermore, DAT-tg mice also show fine motor deficits on challenging beam traversal that are reversed with l-DOPA treatment. Collectively, our findings demonstrate that even in neurons that routinely handle dopamine, increased uptake of this neurotransmitter through the dopamine transporter results in oxidative damage, neuronal loss and l-DOPA reversible motor deficits. In addition, DAT over-expressing animals are highly sensitive to MPTP-induced neurotoxicity. The effects of increased dopamine uptake in these transgenic mice could shed light on the unique vulnerability of dopamine neurons in Parkinson's disease.
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: shababa.masoud@mail.utoronto.ca.
authors.forename: S T
authors.initials: ST
authors.lastname: Masoud
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: laura.vecchio@mail.utoronto.ca.
authors.forename: L M
authors.initials: LM
authors.lastname: Vecchio
authors.affiliation: Department of Medical Biology, Université du Québec à Trois-Rivières, QC G9A 5H7 Canada. Electronic address: yan.bergeron@uqtr.ca.
authors.forename: Y
authors.initials: Y
authors.lastname: Bergeron
authors.affiliation: Environmental and Occupational Health Sciences Institute, Rutgers, 170 Frelinghuysen Road, EOHSI 340, Piscataway, NJ 08854, USA. Electronic address: mhossain@eohsi.rutgers.edu.
authors.forename: M M
authors.initials: MM
authors.lastname: Hossain
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: Lien.nguyen@mail.utoronto.ca.
authors.forename: L T
authors.initials: LT
authors.lastname: Nguyen
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: kristel.bermejo@mail.utoronto.ca.
authors.forename: M K
authors.initials: MK
authors.lastname: Bermejo
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, NC 27599, USA. Electronic address: bkile04@gmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Kile
authors.affiliation: Neuroscience and Brain Technologies, Italian Institute of Technology, Via Morego 30, Genova 16163, Italy; Faculty of Biology and Soil Science, St. Petersburg State University, St. Petersburg 199034, Russia. Electronic address: tatiana.sotnikova@iit.it.
authors.forename: T D
authors.initials: TD
authors.lastname: Sotnikova
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: billsiesser@gmail.com.
authors.forename: W B
authors.initials: WB
authors.lastname: Siesser
authors.affiliation: Neuroscience and Brain Technologies, Italian Institute of Technology, Via Morego 30, Genova 16163, Italy; Faculty of Biology and Soil Science, St. Petersburg State University, St. Petersburg 199034, Russia; Skolkovo Institute of Science and Technology, Skolkovo, 143025 Moscow Region, Russia. Electronic address: Raul.Gainetdinov@iit.it.
authors.forename: R R
authors.initials: RR
authors.lastname: Gainetdinov
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, NC 27599, USA. Electronic address: rmw@unc.edu.
authors.forename: R M
authors.initials: RM
authors.lastname: Wightman
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: marc.caron@duke.edu.
authors.forename: M G
authors.initials: MG
authors.lastname: Caron
authors.affiliation: Environmental and Occupational Health Sciences Institute, Rutgers, 170 Frelinghuysen Road, EOHSI 340, Piscataway, NJ 08854, USA. Electronic address: jricha3@eohsi.rutgers.edu.
authors.forename: J R
authors.initials: JR
authors.lastname: Richardson
authors.affiliation: Department of Environmental Health, Emory University, Atlanta, GA 30322, USA; Department of Pharmacology, Emory University, Atlanta, GA 30322, USA; Department of Neurology, Emory University, Atlanta, GA 30322, USA. Electronic address: gwmille@emory.edu.
authors.forename: G W
authors.initials: GW
authors.lastname: Miller
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: a.ramsey@utoronto.ca.
authors.forename: A J
authors.initials: AJ
authors.lastname: Ramsey
authors.affiliation: Department of Medical Biology, Université du Québec à Trois-Rivières, QC G9A 5H7 Canada. Electronic address: Michel.Cyr@uqtr.ca.
authors.forename: M
authors.initials: M
authors.lastname: Cyr
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle - Rm 4302, Toronto, ON M5S 1A8, Canada. Electronic address: ali.salahpour@utoronto.ca.
authors.forename: A
authors.initials: A
authors.lastname: Salahpour
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D018726:Anti-Dyskinesia Agents / Q000494:pharmacology; D016923:Cell Death / Q000502:physiology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D059290:Dopaminergic Neurons / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D007980:Levodopa / Q000494:pharmacology; D008636:Mesencephalon / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009048:Motor Skills / Q000187:drug effects / Q000502:physiology; D009069:Movement Disorders / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D018384:Oxidative Stress / Q000502:physiology*; D020734:Parkinsonian Disorders / Q000503:physiopathology; D050493:Vesicular Monoamine Transport Proteins / Q000378:metabolism
chemical_list: D018726:Anti-Dyskinesia Agents; D050483:Dopamine Plasma Membrane Transport Proteins; C493453:Slc18a2 protein, mouse; D050493:Vesicular Monoamine Transport Proteins; D015102:3,4-Dihydroxyphenylacetic Acid; D007980:Levodopa; D004298:Dopamine
keywords: Cytosolic dopamine; Dopamine neuron loss; Dopamine transporter; MPTP; Motor deficits; Oxidative stress; Parkinson's disease; Transgenic mice; l-DOPA