59. rAAV-Mediated Nigral Parkin Over-Expression Is Neuroprotective in the 6-OHDA Rat Model of Parkinson's Disease

Abstract

Parkinson's disease (PD) is a neuro-degenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although the underlying cause of the idiopathic form of the disease has yet to be found, several genes have been found that cause familial forms of PD. One such gene is parkin which has been identified as an ubiquitin E3 ligase which is involved in the ubiquitination and subsequent degradation of certain proteins. Mutations in this gene leads to an early onset form of PD called Autosomal Recessive Juvenile Parkinsonism (ARJP). Given the role of parkin in protein clearance, and the presence of Lewy Bodies in the disease, it is possible that protein aggregation is a neurotoxic event in idiopathic PD, and as such, over-expression of parkin may be neuroprotective in animal models of PD by enhancing the degradation of damaged or misfolded proteins. This was tested by doing intranigral injections of a recombinant adeno-associated virus (rAAV) expressing either a human form of parkin or green fluorescent protein (GFP) as control for viral transduction. 4 weeks following the viral injections all animals received a 4 site intrastriatal injection of the neurotoxin 6-hydroxydopamine (6-OHDA) resulting in a near complete depletion of striatal and nigral dopamine. Behavioral evaluation following the lesion indicates that parkin confers partial protection of the nigrostriatal tract. Amphetaine-induced rotational behavior was significantly reduced in the treatment group (|[minus]|67% as compared to controls). Testing for spontaneous limb-use in the cylinder testing paradigm also showed a slight, but significant improvement, where parkin treated animals used their affected limb approximately 20% of the time versus 10% for the control group. These data indicate that specific nigral over-expression of human parkin is partially neuroprotective at the functional level against a strong toxic stimulus, intrastriatal 6-OHDA. Additionally, the data suggest that enhanced ubiquitin-mediated clearance of damaged proteins is protective against a non-specific insult in nigrostriatal dopamine neurons.