Developmental expression of the prion protein gene in glial cells.

Replication of prions is dependent on the presence of the host protein PrPc. During the course of disease, PrPc is converted into an abnormal isoform, PrPSc, which accumulates in the brain. Attempts to identify the cell type(s) in which prion replication and PrP conversion occur have reached conflicting results. Although PrP mRNA is present in high amounts in neurons throughout the life of the animal, PrPSc initially accumulates in astrocytes and possibly other glial cells and, later in the course of the disease, spreads diffusely in the tissue, often in white matter. We report here that PrP mRNA is expressed not only in neurons but also in astrocytes and oligodendrocytes throughout the brain of postnatal hamsters and rats. The level of glial Prp mRNA expression in neonatal animals was comparable to that of neurons and increased two-fold during postnatal development. A substantial portion of brain PrP mRNA is therefore contributed by glial cells. Our results provide an explanation for the accumulation of PrPSc in white matter tissue and in the cytoplasm of glial cells and argue for a direct involvement of glia in prion propagation.