Prion protein on astrocytes or in extracellular fluid impedes neurodegeneration induced by truncated prion protein.

Prion protein (PrP) is a host-encoded membrane-anchored glycoprotein which is required for susceptibility to prion disease. PrP may also be important for normal brain functions such as hippocampal spatial memory. Previously transgenic mice expressing amino terminally truncated mouse PrP (Delta32-134) spontaneously developed a fatal disease associated with degeneration of cerebellar granular neurons as well as vacuolar degeneration of deep cerebellar and brain stem white matter. This disease could be prevented by co-expression of wild-type (WT) mouse PrP on neurons or oligodendroglia. In the present experiments we studied Delta32-134 PrP transgenic mice with WT PrP expression restricted to astroglia, an abundant CNS cell-type important for neuronal viability. Expression of WT PrP in astroglia was sufficient to rescue 50% of mice from disease and prolonged survival by 200 days in the other 50%. We also found that transgenic mice expressing full-length soluble anchorless PrP had increased survival by 100 days. Together these two results indicated that rescue from neurodegeneration induced by Delta32-134 PrP might involve interactions between neurons expressing truncated PrP and nearby astrocytes expressing WT PrP or extracellular fluid containing soluble WT PrP.