Dopamine Neuron VGLUT2 Expression in Parkinson's Disease

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PROJECT SUMMARY In Parkinson’s Disease (PD), dopamine (DA) neurons degenerate in the substantia nigra pars compacta (SNc). In contrast, the DA neurons of the ventral tegmental area (VTA) are relatively protected from PD-induced degeneration, but the cause of this neuroprotection is unknown. One possible answer may derive from the unique properties of VTA DA neurons: a subset of these cells co-release glutamate and express the vesicular glutamate transporter 2 (VGLUT2). DA neurons that express VGLUT2 are more likely to survive neurotoxic insult in animal models of PD, and DA neuron VGLUT2 upregulation is observed in neurons resilient to DA neurotoxins. Significantly, VGLUT2 expression is upregulated in DA neurons across Drosophila, rodents, non-human and human primates in response to cell stressors, suggesting that this an evolutionarily-conserved mechanism that confers protection against DA neuron degeneration. Moreover, in Drosophila, I discovered females express more Drosophila VGLUT (dVGLUT) compared to males. I also found males flies are markedly more vulnerable to DA neuron degeneration and exhibit more motor deficits compared to females in DA neurotoxin models of PD [e.g., paraquat and 6-hydroxydopamine (6OHDA)] analogous to the sex-specific sequelae of human PD. These findings indicate that VGLUT2 expression is likely part of a regulatory mechanism that may protect these cells and that likely impacts sex differences in PD. These data also show the genetically tractable fly model can be utilized as a powerful experimental system to investigate mechanisms of DA neuron resilience and vulnerability in PD. Given VGLUT’s roles in DA neuron resilience, the central goals of this proposal are to identify: 1) how DA neuron VGLUT expression impacts DA neuron vulnerability, 2) whether the sex differences in DA neuron resilience depend on differences in DA neuron VGLUT expression, and 3) how DA neuron VGLUT2 expression changes in human PD. I will test the hypothesis that DA neuron VGLUT expression confers increased protection in DA neurons, especially in females since they express more VGLUT compared to males. The long-term goals of this proposal are to i) determine the role of VGLUT in mediating vulnerability and sex differences in response to 6OHDA and paraquat in the fly model (Aim 1), and ii), measure DA neuron VGLUT2 expression in human PD (Aim 2). To test these goals, I will use RNA-interference to knock down dVGLUT expression in Drosophila DA neurons, and measure DA neuron vulnerability in male versus female flies in 6OHDA and paraquat PD models. In parallel, I will measure DA neuron VGLUT2 expression in human PD using postmortem human midbrain of both male and female PD patients and matched controls. These experiments will establish DA neuron VGLUT expression as a novel mechanism of neuroprotection in PD, leading to new, more effective therapies to prevent or mitigate the DA neurodegenerative effects of PD.