Colocalization of prion protein and β protein in the same amyloid plaques in patients with Gerstmann-Sträussler Syndrome

We examined paraffin-embedded brain sections from three patients with Creutzfeldt-Jakob disease (CJD) and four patients with Gerstmann-Sträussler syndrome (GSS) who also had β protein deposits in the brains. Immunostaining using anti-prion protein (PrP) and anti-β protein coupled with formic acid pretreatment, revealed PrP deposits and β protein deposits, respectively. In all four GSS patients examined, sequential double immunostaining and single immunostaining in serial sections or simultaneous double immunofluorescence revealed the colocalization of PrP and β protein in the same amyloid plaques. The plaques labeled with both antibodies were designated as β-PrP plaques. Small kuru plaques of less than 15 μm in diameter were rarely found to coexist with β deposits. The percentages of β-PrP plaques in larger kuru plaques were not constant among the four GSS patients. The colocalization patterns of both deposits were observed as being roughly of two types as follows: (1) diffuse β protein deposits located around the PrP core; and (2) a β protein core and PrP core simultaneously existing in one amyloid plaque. Under an electron microscope, we were able to confirm the presence of both β protein and PrP in a single plaque in four GSS patients older than 60 years old. In contrast, no colocalization of either deposits was seen in the amyloid plaque core fractions of a young GSS patient who had no β protein deposits, even at the electron microscopic level. Therefore, the colocalization of both proteins in a single plaque is believed to be age-related and incidental in GSS patients but suggests a similar morphogenesis of both amyloid deposits.