Increased expression of the dopamine transporter leads to loss of dopamine neurons, oxidative stress and l-DOPA reversible motor deficits

Neurobiol Dis. 2015 Feb;74:66-75. doi: 10.1016/j.nbd.2014.10.016. Epub 2014 Oct 30.

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.

Keywords: Cytosolic dopamine; Dopamine neuron loss; Dopamine transporter; MPTP; Motor deficits; Oxidative stress; Parkinson's disease; Transgenic mice; l-DOPA.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3,4-Dihydroxyphenylacetic Acid / metabolism
  • Animals
  • Anti-Dyskinesia Agents / pharmacology
  • Cell Death / physiology
  • Cytosol / drug effects
  • Cytosol / metabolism
  • Dopamine / metabolism
  • Dopamine Plasma Membrane Transport Proteins / genetics
  • Dopamine Plasma Membrane Transport Proteins / metabolism*
  • Dopaminergic Neurons / drug effects
  • Dopaminergic Neurons / pathology
  • Dopaminergic Neurons / physiology*
  • Levodopa / pharmacology
  • Mesencephalon / drug effects
  • Mesencephalon / pathology
  • Mesencephalon / physiopathology*
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Motor Skills / drug effects
  • Motor Skills / physiology
  • Movement Disorders / drug therapy
  • Movement Disorders / pathology
  • Movement Disorders / physiopathology*
  • Oxidative Stress / physiology*
  • Parkinsonian Disorders / physiopathology
  • Vesicular Monoamine Transport Proteins / metabolism

Substances

  • Anti-Dyskinesia Agents
  • Dopamine Plasma Membrane Transport Proteins
  • Slc18a2 protein, mouse
  • Vesicular Monoamine Transport Proteins
  • 3,4-Dihydroxyphenylacetic Acid
  • Levodopa
  • Dopamine