Prion diseases are diagnosed by the detection of accumulation of abnormal prion protein (PrP) using immunohistochemistry or the detection of protease-resistant abnormal PrP (PrPres). Although the abnormal PrP is neurotoxic by forming aggregates, recent studies suggest that the most infectious units are smaller than the amyloid fibrils. In the present study, we developed a simplified method by applying size-exclusion gel-filtration chromatography to examine PrP oligomers without proteinase K digestion in Creutzfeldt-Jakob disease (CJD) samples, and evaluated the correlation between disease severity and the polymerization degree of PrP. Brain homogenates of human CJD and non-CJD cases were applied to the gel-filtration spin columns, and fractionated PrP molecules in each fraction were detected by western blot. We observed that PrP oligomers could be detected by the simple gel-filtration method and distinctly separated from monomeric cellular PrP (PrPc). PrP oligomers were increased according to the disease severity, accompanied by the depletion of PrPc. The separated PrP oligomers were already protease-resistant in the case with short disease duration. In the cases with quite severe pathology the oligomeric PrP reached a plateau, which may indicate that PrP molecules could mostly develop into amyloid fibrils in the advanced stages. The increase of PrP oligomers correlated with the degree of histopathological changes such as spongiosis and gliosis. The decrease of monomeric PrPc was unexpectedly obvious in the diseased cases. Dynamic changes of both oligomerization of the human PrP and depletion of normal PrPc require further elucidation to develop a greater understanding of the pathogenesis of human prion diseases.
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