Parkinson?s disease (PD) is a neurodegenerative disorder resulting in loss of motor function stemming primarily from the loss of dopaminergic (DAergic) neurons within the substantia nigra (SN). Several studies have demonstrated elevated levels of intracellular iron in the Parkinsonian SN but whether this is causatively involved in dopaminergic SN cell death has been controversial. We previously reported that iron chelation via expression of the body?s major iron sequestering protein, ferritin, protects against DAergic SN neurodegeneration associated with the PD-inducing neurotoxin MPTP in young mice1. The aim of our current research is towards exploring whether iron elevation in young animals contributes to PD pathology via its activation of the enzyme prolyl hydroxylase (PH). When activated, PH can act as an inhibitor of hypoxiainducing factor 1 alpha (HIF-1?), a transcription factor which activates various genes involved in both protection against oxidative stress and in regulation of cellular iron metabolism. In our studies, inhibition of PHD by the specific inhibitor 3,4-dihydroxybenzoate (DHB) in vivo resulted in the stabilization of cytosolic HIF- 1? and significantly protected against MPTP-induced nigral dopaminergic cell loss. MPTP alone results in a significant increase in striatal iron levels that was found to be attenuated by co-treatment with DHB. In addition to HIF activation, we observed up-regulation of several downstream HIF-dependent genes including the mitochondrial antioxidant MnSOD and the iron regulatory protein HO-1 which has recently been demonstrated to contribute to cellular iron efflux. Additionally, MPTP-induced decreases in the iron export protein ferroportin were found to revert back to normal in the presence of DHB. In vitro, the HIF pathway was found to be activated in dopaminergic midbrain-derived rat N27 cells grown at 3% oxygen treated with two PHD inhibitors, DHB and DOMG, and an iron chelator, SIH. Concordant with in vivo data, MPP+ elicited an increase in total intracellular iron that was attenuated in the presence of DHB. In addition, MPP+ administration resulted in a concentration-dependent increase in levels of the iron import protein TfR that was significantly reduced in the presence of DHB. Taken together, data from this study suggest that the protection against MPTP neurotoxicity as a consequence of iron chelation may be mediated by inhibition of PH and subsequent increases in cellular HIF-1? levels that in turn activates genes involved in both protection against increased oxidative stress and dysregulation of cellular iron homeostasis. This study provides novel data extending the therapeutic aspects of HIF protein to a PD model of neurodegeneration and may prove beneficial in other diseases associated with metal-induced oxidative stress such as Alzheimer?s disease and multiple sclerosis.

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