PrP mutants with different numbers of octarepeat sequences are more susceptible to the oxidative stress

One of the physiological functions of cellular prion protein (PrPC) is believed to work as a cellular resistance to oxidative stress, in which the octarepeats region within PrP plays an important role. However, the detailed mechanism is less clear. In this study, the expressing plasmids of wild-type PrP (PrP-PG5) and various PrP mutants containing 0 (PrP-PG0), 9 (PrP-PG9) and 12 (PrP-PG12) octarepeats were generated and PrP proteins were expressed both in E. coli and in mammalian cells. Protein aggregation and formation of carbonyl groups were clearly seen in the recombinant PrPs expressed from E. coli after treatment of H2O2. MTT and trypan blue staining assays revealed that the cells expressing the mutated PrPs within octarepeats are less viable than the cells expressing wild-type PrP. Statistically significant high levels of intracellular free radicals and low levels of glutathione peroxidase were observed in the cells transfected with plasmids containing deleted or inserted octarepeats. Remarkably more productions of carbonyl groups were detected in the cells expressing PrPs with deleted and inserted octarepeats after exposing to H2O2. Furthermore, cells expressing wild-type PrP showed stronger resistant activity to the challenge of H2O2 at certain extent than the mutated PrPs and mock. These data provided the evidences that the octarepeats number within PrP is critical for maintaining its activity of antioxidation. Loss of its protective function against oxidative stress may be one of the possible pathways for the mutated PrPs to involve in the pathogenesis of familial Creutzfeldt-Jacob diseases.