Stabilization of microtubular cytoskeleton protects neurons from toxicity of N-terminal fragment of cytosolic prion protein.

Prion protein (PrP) mislocalized in the cytosol has been presumed to be the toxic entity responsible for the neurodegenerative process in transmissible spongiform encephalopathies (TSE), also called prion diseases. The mechanism underlying the neurotoxicity of cytosolic PrP (cytoPrP) remains, however, unresolved. In this study we analyze toxic effects of the cell-penetrating PrP fragment, PrP1-30--encompassing residues responsible for binding and aggregation of tubulin. We have found that intracellularly localized PrP1-30 disassembles microtubular cytoskeleton of primary neurons, which leads to the loss of neurites and, eventually, necrotic cell death. Accordingly, stabilization of microtubules by taxol reduced deleterious effects of cytosolic PrP1-30. Furthermore, we have demonstrated that decreased phosphorylation level of microtubule-associated proteins (MAPs), which also increases stability of microtubular cytoskeleton, protects neurons from the toxic effects of PrP1-30. CHIR98014 and LiCl--inhibitors of glycogen synthase kinase 3 (GSK-3), a major kinase responsible for phosphorylation of MAPs, inhibited PrP1-30-induced disruption of microtubular cytoskeleton and increased viability of peptide-treated neurons. We have also shown that the N-terminal fragment of cytoPrP may cause the loss of dendritic spines. PrP1-30-induced changes at the level of spines have also been prevented by stabilization of microtubules by taxol as well as LiCl. These observations indicate that the neurotoxicity of cytoPrP is tightly linked to the disruption of microtubular cytoskeleton. Importantly, this study implies that lithium, the commonly used mood stabilizer, may be a promising therapeutic agent in TSE, particularly in case of the disease forms associated with accumulation of cytoPrP.

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