Normal cellular prion protein protects against manganese-induced oxidative stress and apoptotic cell death

The normal prion protein is abundantly expressed in the central nervous system, but its biological function remains unclear. The prion protein has octapeptide repeat regions that bind to several divalent metals, suggesting that the prion proteins may alter the toxic effect of environmental neurotoxic metals. In the present study, we systematically examined whether prion protein modifies the neurotoxicity of manganese (Mn) by comparing the effect of Mn on mouse neural cells expressing prion protein (PrPC -cells) and prion-knockout (PrPKO-cells). Exposure to Mn (10 mu M-10mM) for 24 h produced a dose-dependent cytotoxic response in both PrPC -cells and Prp(KO)-cells. Interestingly, PrPC -cells (EC50 117.6 mu M) were more resistant to Mn-induced cytotoxicity, as compared to PrPKo -cells (EC50 59.9 mu M), suggesting a protective role for PrPC against Mn neurotoxicity. Analysis of intracellular Mn levels showed less Mn accumulation in PrPC -cells as compared to PrPKO-cells, but no significant changes in the expression of the metal transporter proteins transferrin and DMT-1. Furthermore, Mn-induced mitochondrial depolarization and reactive oxygen species (ROS) generation were significantly attenuated in PrPC -cells as compared to PrPKO -cells. Measurement of antioxidant status revealed similar basal levels of glutathione (GSH) in PrPC -cells and PrPKO -cells; however, Mn treatment caused greater depletion of GSH in PrPKO -cells. Mn-induced mitochondrial depolarization and ROS production were followed by time- and dose-dependent activation of the apoptotic cell death cascade involving caspase-9 and -3. Notably, DNA fragmentation induced by both Mn treatment and the oxidative stress inducer hydrogen peroxide (100 mu M) was significantly suppressed in PrPC -cells as compared to PrPKo -cells. Together, these results demonstrate that prion protein interferes with divalent metal Mn uptake and protects against Mn-induced oxidative stress and apoptotic cell death.