Prion protein and copper cooperatively protect neurons by modulating NMDA receptor through S-nitrosylation

Several neurodegenerative disorders show alterations in glutamatergic synapses and increased susceptibility to excitotoxicity. Mounting evidence suggests a central role for the cellular prion protein (PrP(C)) in neuroprotection. Therefore, the loss of PrP(C) function occurring in prion disorders may contribute to the disease progression and neurodegeneration. Indeed, PrP(C) modulates N-methyl-d-aspartate receptors (NMDAR), thus preventing cell death. In this study, we show that PrP(C) and copper cooperatively inhibit NMDAR through S-nitrosylation, a post-translational modification resulting from the chemical reaction of nitric oxide (NO) with cysteines.

Comparing wild-type Prnp (Prnp(+/+)) and PrP(C) knockout (Prnp(0/0)) mouse hippocampi, we found that GluN1 and GluN2A S-nitrosylation decrease in Prnp(0/0). Using organotypic hippocampal cultures, we found that copper chelation decreases NMDAR S-nitrosylation in Prnp(+/+) but not in Prnp(0/0). This suggests that PrP(C) requires copper to support the chemical reaction between NO and thiols. We explored PrP(C)-Cu neuroprotective role by evaluating neuron susceptibility to excitotoxicity in Prnp(+/+) and Prnp(0/0) cultures. We found that (i) PrP(C)-Cu modulates GluN2A-containing NMDAR, those inhibited by S-nitrosylation; (ii) PrP(C) and copper are interdependent to protect neurons from insults; (iii) neuronal NO synthase inhibition affects susceptibility in wild-type but not in Prnp(0/0), while (iv) the addition of a NO donor enhances Prnp(0/0) neurons survival.

Our results show that PrP(C) and copper support NMDAR S-nitrosylation and cooperatively exert neuroprotection. In addition to NMDAR, PrP(C) may also favor the S-nitrosylation of other proteins. Therefore, this mechanism may be investigated in the context of the different cellular processes in which PrP(C) is involved.