Abnormal activation of glial cells in the brains of prion protein-deficient mice ectopically expressing prion protein-like protein, PrPLP/Dpl

BACKGROUND: Some lines of mice homozygous for a disrupted prion protein gene (Prnp), including Ngsk Prnp(0/0) mice, exhibit Purkinje cell degeneration as a consequence of the ectopic overexpression of the downstream gene for prion protein-like protein (PrPLP/Dpl) in the brain, but others, such as Zrch I Prnp(0/0) mice, show neither the neurodegeneration nor the expression of PrPLP/Dpl. In the present study, we found that Ngsk Prnp(0/0), but not Zrch I Prnp(0/0) mice, developed gliosis involving both astrocytes and microglia in the brain. MATERIALS AND METHODS: The brains from wild-type (Prnp(+/+)), Ngsk Prnp(0/0), Zrch I Prnp(0/0), and reconstituted Ngsk Prnp(0/0) mice carrying a mouse PrP transgene, designated Tg(P) Ngsk Prnp(0/0) mice, were subjected into Northern blotting and in situ hybridization using probes of glial fibrillary acidic protein (GFAP) and lysozyme M (LM) specific for astrocytes and microglia, respectively. Immunohistochemistry was also performed on the brain sections using anti-GFAP and anti-F4/80 antibodies. RESULTS: Northern blotting demonstrated upregulated expression of the genes for GFAP and LM in the brains of Ngsk Prnp(0/0), but not in Zrch I Prnp(0/0) mice. A transgene for normal mouse PrP(C) successfully rescued Ngsk Prnp(0/0) mice from the glial activation. In situ hybridization and immunohistochemistry revealed activated astrocytes and microglia mainly in the white matter of both the forebrains and cerebella. In contrast, there was no evidence of neuronal injury except for the Purkinje cell degeneration. Moreover, the glial cell activation was notable well before the onset of the Purkinje cell degeneration. CONCLUSIONS: These findings strongly suggest that ectopic PrPLP/Dpl in the absence of PrP(C) is actively involved in the glial-cell activation in the brain.