Mitochondrial localization of cellular prion protein (PrP ^C) invokes neuronal apoptosis in aged transgenic mice overexpressing PrP ^C

Recent studies suggest that the disease isoform of prion protein (PrP ^Sc) is non-neurotoxic in the absence of cellular isoform of prion protein (PrP ^C), indicating that PrP ^C may participate directly in the neurodegenerative damage by itself. Meanwhile, transgenic mice harboring a high-copy-number of wild-type mouse (Mo) PrP ^C develop a spontaneous neurological dysfunction in an age-dependent manner, even without inoculation of PrP ^Sc and thus, investigations of these aged transgenic mice may lead to the understanding how PrP ^C participate in the neurotoxic property of PrP. Here we demonstrate mitochondria-mediated neuronal apoptosis in aged transgenic mice overexpressing wild-type MoPrP ^C (Tg(MoPrP)4053/FVB). The aged mice exhibited an aberrant mitochondrial localization of PrP ^C concomitant with decreased proteasomal activity, while younger littermates did not. Such aberrant mitochondrial localization was accompanied by decreased mitochondrial manganese superoxide dismutase (Mn-SOD) activity, cytochrome c release into the cytosol, caspase-3 activation, and DNA fragmentation, most predominantly in hippocampal neuronal cells. Following cell culture studies confirmed that decrease in the proteasomal activity is fundamental for the PrP ^C-related, mitochondria-mediated apoptosis. Hence, the neurotoxic property of PrP ^C could be explained by the mitochondria-mediated neuronal apoptosis, at least in part.