Neurodegenerative illness in transgenic mice expressing a transmembrane form of the prion protein

Although PrP(Sc) is thought to be the infectious form of the prion protein, it may not be the form that is responsible for neuronal cell death in prion diseases. (Ctm)PrP is a transmembrane version of the prion protein that has been proposed to be a neurotoxic intermediate underlying prion-induced pathogenesis. To investigate this hypothesis, we have constructed transgenic mice that express L9R-3AV PrP, a mutant prion protein that is synthesized exclusively in the (Ctm)PrP form in transfected cells. These mice develop a fatal neurological illness characterized by ataxia and marked neuronal loss in the cerebellum and hippocampus. (Ctm)PrP in neurons cultured from transgenic mice is localized to the Golgi apparatus, rather than to the endoplasmic reticulum as in transfected cell lines. Surprisingly, development of the neurodegenerative phenotype is strongly dependent on coexpression of endogenous, wild-type PrP. Our results provide new insights into the cell biology of (Ctm)PrP, the mechanism by which it induces neurodegeneration, and possible cellular activities of PrP(C).