Structural and cellular properties of human prion protein oligomers

The misfolding of the human prion protein (hPrP) and the consequent self-assembly into insoluble amyloid fibrils are associated with neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs). In this study, we investigated the stability and aggregation behaviour of the folded C-terminal domain of hPrP (hPrP^C_125-230) and observed that, under specific experimental conditions, this region of the protein rapidly aggregates into round-shaped oligomers. The isolated oligomers exhibited hallmarks properties of amyloid aggregates, including a β-sheet-rich structure, enhanced hydrophobic exposure, and Thioflavin T (ThT)-induced fluorescence. When incubated with neural precursor cells these hPrP oligomers, unlike monomeric species, induced mitochondrial fragmentation and network alterations, disrupted mitochondrial membrane potential, and reduced the cellular viability. Overall, these findings indicate that the C-terminal domain of hPrP can form toxic oligomers independently of the aggregation-prone 106-126 region, providing new insights on the hPrP-associated toxicity and highlighting the critical role of the C-terminal domain in PrP misfolding.