Colocalization of prion protein and beta 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 beta protein deposits in the brains. Immunostaining using anti-prion protein (PrP) and anti-beta protein coupled with formic acid pretreatment, revealed PrP deposits and beta 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 beta protein in the same amyloid plaques. The plaques labeled with both antibodies were designated as beta-PrP plaques. Small kuru plaques of less than 15 microns in diameter were rarely found to coexist with beta deposits. The percentages of beta-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 beta protein deposits located around the PrP core; and (2) a beta protein core and PrP core simultaneously existing in one amyloid plaque. Under an electron microscope, we were able to confirm the presence of both beta 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 beta 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.