| Parkinson's disease (PD) is the second most common neurodegenerative disease in the United States, affecting 1 to 2% of the population over the age of 65. PD is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), which leads to a variety of symptoms including resting tremor, rigidity, bradykinesia and postural abnormalities. The neurotoxins 6-hydroxydopamine (6-OHDA) and 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP), and its active metabolite, 1-methyl-4-phebylpyridinium (MPP +), cause dopaminergic cell loss in a variety of animal species and produce symptoms similar to those seen in PD. Evidence suggests that these toxins induce cells death through the production of reactive oxygen species (ROS) and oxidative stress; this causes oxidative modification of proteins, lipids and DNA. These damaged cellular components lead to activation of cell stress pathways, including the unfolded protein response (UPR), and subsequent release of cytochrome-c from the mitochondria and caspase activation. The BH3-only protein, PUMA/bbc3 (p&barbelow;53 u&barbelow;pregulated modulator of a&barbelow;poptosis/B&barbelow;c1-2 b&barbelow;inding c&barbelow;omponent 3), has been shown to be activated in response to many cellular stresses including endoplasmic reticulum (ER) stress, UPR and DNA damage. PUMA can also trigger cytochrome c release and downstream apoptotic events, such as caspase-3 activation. Together, this suggests that PUMA may serve as a link between cell stress pathways and the mitochondrial activation of apoptosis. Therefore, we hypothesized that PUMA may provide the link between the cell stress pathways activated by 6-OHDA and MPP+, such as UPR, and downstream mitochondrial events. To test this hypothesis, we compared the response of primary mesencephalic cultures from wild-type and PUMA -/- mice to 6-OHDA and MPP+. We also utilized cultures from p53 -/- and ATF3 -/- mice to further elucidate the pathways involved. We also tested this hypothesis in vivo. These studies demonstrate that PUMA is required for both 6-OHDA- and MPP +-induced cell death in vitro and for 6-OHDA-induced cell loss in vivo. The results also suggest that activation of UPR is a protective mechanism, while activation of DNA damage pathways mediated by p53 lead to the induction of apoptosis. |
