Normal Cellular Prion Protein Protects against Manganese-induced Oxidative Stress and Apoptotic Cell Death

摘要

The normal prion protein is abundantly expressed in the CNS, 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 (PrP^C -cells) and prion-knockout (PrP^KO -cells). Exposure to Mn (10 μM-1 mM) for 24 hr produced a dose-dependent cytotoxic response in both PrP^C -cells and PrP^KO -cells. Interestingly, PrP^C -cells (EC50 117.6μM) were more resistant to Mn-induced cytotoxicity, as compared to PrP^KO -cells (EC50 59.9μM), suggesting a protective role for PrP^C against Mn neurotoxicity. Analysis of intracellular Mn levels showed less Mn accumulation in PrP^C -cells as compared to PrP^KO -cells. Furthermore, Mn-induced mitochondrial depolarization and ROS generation were significantly attenuated in PrP^C -cells as compared to PrP^KO -cells. Measurement of antioxidant status revealed similar basal levels of glutathione (GSH) in PrP^C -cells and PrP^KO -cells; however, Mn treatment caused greater depletion of GSH in PrP^KO -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 oxidative stress-inducer hydrogen peroxide (100μM) was significantly suppressed in PrP^C -cells as compared to PrP^KO -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.