The octarepeat region of prion protein, but not the TM1 domain, is important for the antioxidant effect of prion protein

The cellular prion protein (PrPc) plays a crucial role in the pathogenesis of prion diseases, but its physiological function is far from understood. Several candidate functions have been proposed including binding and internalization of metal ions, a superoxide dismutase-like activity, regulation of cellular antioxidant activities, and signal transduction. The transmembrane (TM1) region of PrPc (residues 110–135) is particularly interesting because of its very high evolutionary conservation. We investigated a possible role of TM1 in the antioxidant defense, by assessing the impact of overexpressing wt-PrP or deletion mutants in N2A mouse neuroblastoma cells on intracellular reactive oxygen species (ROS) levels. Under conditions of oxidative stress, intracellular ROS levels were significantly lowered in cells overexpressing either wild-type PrPc (wt-PrP) or a deletion mutant affecting TM1 (Δ8TM1-PrP), but, as expected, not in cultures overexpressing a deletion mutant lacking the octapeptide region (Δocta-PrP). Overexpression of wt-PrP, Δ8TM1-PrP, or Δocta-PrP did not affect basal ROS levels. Interestingly, the mitochondrial membrane potential was significantly lowered in Δocta-PrP-transfected cultures in the absence of oxidative stress. We conclude that the protective effect of PrPc against oxidative stress involves the octarepeat region but not the TM1 domain nor the high-affinity copper binding site described for human residues His96/His111.