The Vesicular Glutamate Transporter Modulates Sex and Region-Specific Differences in Dopaminergic Neuron α-Synuclein Toxicity by Modifying Cytosolic Dopamine Levels

Parkinson's disease disproportionately affects males; however, the cause of this sex difference is unknown. We found that expressing mutant -synuclein A53T in Drosophila dopamine neurons recapitulates the sex differences observed in human Parkinson's disease patients. Male flies exhibited greater age-related motor impairment and more severe dopamine neuron degeneration than females. Selective masculinization of female dopamine neurons via knockdown of the sex determination gene Transformer eliminated the observed sex differences in locomotor ability and neurodegeneration by increasing the severity of motor defects and degeneration in females. Transformer knockdown in dopamine neurons also reduced total vesicular glutamate transporter staining in the brain. Direct knockdown of the vesicular glutamate transporter in female dopamine neurons expressing -synuclein A53T exacerbated motor dysfunction, altered mitochondrial dynamics, and accelerated dopamine neuron degeneration. Increasing cytosolic dopamine via knockdown of the vesicular monoamine transporter or increasing total dopamine levels via levodopa treatment phenocopied vesicular glutamate transporter knockdown; furthermore, reducing total dopamine via alpha-methyl-p-tyrosine treatment protected against vesicular glutamate transporter knockdown. These results support a model in which lower VGLUT levels in dopamine neurons result in higher levels of cytosolic dopamine, which leads to dopamine mediated mitochondrial dysfunction and increased susceptibility to -synuclein A53T toxicity.