Overexpression of Parkinson's disease-associated α-synuclein^A53T by recombinant adeno-associated virus in mice does not increase the vulnerability of dopaminergic neurons to MPTP

Mutations in the α-synuclein gene are linked to a rare dominant form of familial Parkinson's disease, and α-synuclein is aggregated in Lewy bodies of both sporadic and dominant Parkinson's disease. It has been proposed that mutated α-synuclein causes dopaminergic neuron loss by enhancing the vulnerability of these neurons to a variety of insults, including oxidative stress, apoptotic stimuli, and selective dopaminergic neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To test this hypothesis in vivo, we overexpressed human α-synuclein^A53T in the substantia nigra of normal and MPTP-treated mice by rAAV-mediated gene transfer. Determination of dopaminergic neuron survival, striatal tyrosine hydroxylase fiber density, and striatal content of dopamine and its metabolites in rAAV-injected and uninjected hemispheres demonstrated that α-synuclein^A53T does not increase the susceptibility of dopaminergic neurons to MPTP. Our findings argue against a direct detrimental role for (mutant) α-synuclein in oxidative stress and/or apoptotic pathways triggered by MPTP, but do not rule out the possibility that α-synuclein aggregation in neurons exposed to oxidative stress for long periods of time may be neurotoxic.