Novel method for classification of prion diseases by detecting PrP^res signal patterns from formalin-fixed paraffin-embedded samples

Prion disease is an infectious and fatal neurodegenerative disease. Western blotting (WB)-based identification of proteinase K (PK)-resistant prion protein (PrP^res) is considered a definitive diagnosis of prion diseases. In this study, we aimed to detect PrP^res using formalin-fixed paraffin-embedded (FFPE) specimens from cases of sporadic Creutzfeldt–Jakob disease (sCJD), Gerstmann–Sträussler–Scheinker disease (GSS), glycosylphosphatidylinositol-anchorless prion disease (GPIALP), and V180I CJD. FFPE samples were prepared after formic acid treatment to inactivate infectivity. After deparaffinization, PK digestion was performed, and the protein was extracted. In sCJD, a pronounced PrP^res signal was observed, with antibodies specific for type 1 and type 2 PrP^res exhibited a strong or weak signals depending on the case. Histological examination of serial sections revealed that the histological changes were compatible with the biochemical characteristics. In GSS and GPIALP, prion protein core-specific antibodies presented as PrP^res bands at 8–9 kDa and smear bands, respectively. However, an antibody specific for the C-terminus presented as smears in GSS, with no PrP^res detected in GPIALP. It was difficult to detect PrP^res in V180I CJD. Collectively, our findings demonstrate the possibility of detecting PrP^res in FFPE and classifying the prion disease types. This approach facilitates histopathological and biochemical evaluation in the same sample and is safe owing to the inactivation of infectivity. Therefore, it may be valuable for the diagnosis and research of prion diseases.