Overexpression of Vesicular Monoamine Transporter-2 may Block Neurotoxic Metabolites from Cytosolic Dopamine: a Potential Neuroprotective Therapy for Parkinson's Disease

The loss of nigrostriatal dopaminergic neurons containing neuromelanin underlies the motor symptoms of Parkinson's disease. Neuromelanin accumulation into autophagic lysosomes is evidence of ongoing cytosolic dopamine stress in these neurons during normal aging. The formation of neuromelanin is likely neuroprotective, as oxidation of cytosolic dopamine to quinones and aldehydes, as reviewed here, can produce a host of neurotoxic sequela. In addition to sequestration of dopamine and its metabolites in autophagic lysosomes, the uptake of dopamine into monoaminergic neurons mediated by vesicular monoamine transporter-2 (VMAT- 2), prevents dopamine oxidation. Dopamine is stable in monoaminergic vesicles due to their low pH, and thus overexpression of VMAT-2 may provide a target for potential neuroprotective therapy in Parkinson's disease.