Genetic deletion of vesicular glutamate transporter in dopamine neurons increases vulnerability to MPTP-induced neurotoxicity in mice

Significance

Parkinson’s disease (PD) is a chronic dopamine (DA) neuron degenerative disorder. Little is known about factors that impact vulnerability of DA neurons to pathological insults. In this study, we found that vesicular glutamate transporter 2 (VgluT2) expression may play an important role in protecting DA neurons. Selective deletion of VgluT2 in DA neurons led to a significant reduction in expression of brain-derived neurotrophic factor and its receptor tyrosine receptor kinase B and a significant increase in DA neuron death caused by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Restoration of VgluT2 expression in DA neurons reversed these alterations. These findings suggest that reduced VgluT2 expression in DA neurons may constitute a risk factor in the development of PD and suggest potential therapeutic strategies for boosting resilience of DA neurons.

Abstract

A subset of midbrain dopamine (DA) neurons express vesicular glutamate transporter 2 (VgluT2), which facilitates synaptic vesicle loading of glutamate. Recent studies indicate that such expression can modulate DA-dependent reward behaviors, but little is known about functional consequences of DA neuron VgluT2 expression in neurodegenerative diseases like Parkinson’s disease (PD). Here, we report that selective deletion of VgluT2 in DA neurons in conditional VgluT2-KO (VgluT2-cKO) mice abolished glutamate release from DA neurons, reduced their expression of brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB), and exacerbated the pathological effects of exposure to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Furthermore, viral rescue of VgluT2 expression in DA neurons of VglutT2-cKO mice restored BDNF/TrkB expression and attenuated MPTP-induced DA neuron loss and locomotor impairment. Together, these findings indicate that VgluT2 expression in DA neurons is neuroprotective. Genetic or environmental factors causing reduced expression or function of VgluT2 in DA neurons may place some individuals at increased risk for DA neuron degeneration. Therefore, maintaining physiological expression and function of VgluT2 in DA neurons may represent a valid molecular target for the development of preventive therapeutic interventions for PD.