A Molecular Analysis Of Prion Protein Expression In Alzheimer's Disease

In Prion Diseases, misfolding of neuronal prion protein (PrPC) to a pathogenic isomer (PrPSC) is associated with neuronal death. Previous pathological studies have demonstrated increased immunoreactivity of PrPC at Aβ plaques in Alzheimer's Disease, and it has been suggested that this either reflects a role for PrPC in the neuronal response to stress or is a feature of the neuropathogenesis of atypical subtypes of Alzheimer's disease. In this paper we utilised western blotting to examine the molecular characteristics of PrP in frozen Hippocampal tissue from 7 cases of Alzheimer's Disease in which prion protein expression was demonstrated by immunohistochemistry, before using Restriction Fragment Length Polymorphism (RFLP) methodology to define the genotype of the codon 129 polymorphism of PRNP in each case. We observed PrP accumulating as globular structures at A plaques, and within ependymal cells lining the lateral ventricle. Immunohistochemistry also showed that PrPC and Superoxide dismutase-1 where deposited in a similar pattern at Aβ plaques. Western blotting revealed that PrP in Alzheimer's disease is composed of the same 208-residue peptide expressed in non-diseased brain. Quantitative western blot analysis demonstrated increased levels of PrPC in a short duration case of Alzheimer's Disease, while, in the remaining cases, levels of PrPC decreased in parallel with increasing disease duration and decreasing brain mass. RFLP genotyping revealed that all codon 129 genotypes (M/M, M/V, V/V) were represented in our study cohort. Our data suggest that increased levels of PrPC may account for PrP immunoreactivity at plaques in Alzheimer's disease, and that PrP deposition is not restricted to certain atypical subtypes of Alzheimer's disease.