The toxicity of antiprion antibodies is mediated by the flexible tail of the prion protein

Biochemical and structural investigation of a model for prion-induced neurodegeneration—antibody binding to PrP C —reveals the role of the PrP flexible tail and reactive oxygen species in mediating toxicity. Prion tail linked to neurotoxicity The cellular prion protein contains a globular domain and a flexible tail. Here it is shown that antibodies against the globular domain cause neurotoxicity in mice and cerebellar cultured slices. This neurodegeneration is accompanied by a burst of reactive oxygen species production, and is suppressed by antioxidants, and toxicity is dependent on the presence of the superoxide-producing enzyme NOX2. Octapeptide repeats within the flexible-tail domain seem also to be required for toxicity, and antibodies against these repeats are able to prolong life in in mice expressing a toxic deletion mutant PrP C protein. These novel neurotoxicity mechanisms may be relevant to the pathogenesis of neurodegenerative disease due to prions and other agencies. Prion infections cause lethal neurodegeneration. This process requires the cellular prion protein (PrP C ; ref. 1 ), which contains a globular domain hinged to a long amino-proximal flexible tail 2 . Here we describe rapid neurotoxicity in mice and cerebellar organotypic cultured slices exposed to ligands targeting the α1 and α3 helices of the PrP C globular domain. Ligands included seven distinct monoclonal antibodies 3 , monovalent Fab 1 fragments and recombinant single-chain variable fragment miniantibodies. Similar to prion infections 4 , 5 , 6 , the toxicity of globular domain ligands required neuronal PrP C , was exacerbated by PrP C overexpression, was associated with calpain activation and was antagonized by calpain inhibitors. Neurodegeneration was accompanied by a burst of reactive oxygen species, and was suppressed by antioxidants. Furthermore, genetic ablation of the superoxide-producing enzyme NOX2 (also known as CYBB) protected mice from globular domain ligand toxicity. We also found that neurotoxicity was prevented by deletions of the octapeptide repeats within the flexible tail. These deletions did not appreciably compromise globular domain antibody binding, suggesting that the flexible tail is required to transmit toxic signals that originate from the globular domain and trigger oxidative stress and calpain activation. Supporting this view, various octapeptide ligands were not only innocuous to both cerebellar organotypic cultured slices and mice, but also prevent