A growing body of evidence has implicated oxidative stress as an important factor in the neuropathology associated with Parkinson's disease (PD). Dopaminergic nigrostriatal neurons, the predominant cell type lost in PD, are believed to be highly prone to free radical damage due to the propensity for dopamine to auto-oxidize and thereby produce elevated levels of hydrogen peroxide and catecholamine quinones. In vitro analysis suggests this reaction may be catalyzed by transition metals such as iron. Hydrogen peroxide formed during this process can either be converted by iron to form highly reactive and toxic hydroxyl radicals or removed through reduction by glutathione (GSH). GSH can also conjugate with quinones formed during dopamine oxidation preventing them from facilitating the release of iron from the iron-storage molecule ferritin. Alterations in both iron storage and glutathione (GSH) levels in the SN have been correlated with the neuronal degeneration accompanying PD but a direct causative role for either has yet to be definitively proved in vivo. We propose to use genetically engineered mouse lines generated in our laboratory as in vivo models to examine the role that alterations in GSH and free iron levels may play in the differential neurodegeneration of dopaminergic neurons of the substantia nigra in PD and how these two parameters may interact with one another to bring this about. This include the use of transgenic mice with altered SN expression levels of either ferrritin or glutamul cysteine synthetase (GCS), the rate limiting enzyme in GSH synthesis. We will use these in conjunction with the well-established MPTP toxicity model of PD to test whether chronic alterations in these molecules in vivo results in changes in neuronal loss associated with toxin treatment and/or aging and to delineate the specific biochemical processes responsible. Such in vivo systems should allow us not only to explore the mechanisms by which in vivo changes in these components may contribute to the neuropathology associated with PD but may also provide useful information for the design of future drug and genetic therapies for this disease.
