Genesis of Mammalian Prions: From Non-infectious Amyloid Fibrils to a Transmissible Prion Disease

The transmissible agent of prion disease consists of a prion protein in its abnormal, b-sheet rich state (PrPSc), which is capable of replicating itself according to the template-assisted mechanism. This mechanism postulates that the folding pattern of a newly recruited polypeptide chain accurately reproduces that of a PrPSc template. Here we report that authentic PrPSc and transmissible prion disease can be generated de novo in wild type animals by recombinant PrP (rPrP) amyloid fibrils, which are structurally different from PrPSc and lack any detectable PrPSc particles. When induced by rPrP fibrils, a long silent stage that involved two serial passages preceded development of the clinical disease. Once emerged, the prion disease was characterized by unique clinical, neuropathological, and biochemical features. The long silent stage to the disease was accompanied by significant transformation in neuropathological properties and biochemical features of the proteinase K-resistant PrP material (PrPres) before authentic PrPSc evolved. The current work illustrates that transmissible prion diseases can be induced by PrP structures different from that of authentic PrPSc and suggests that a new mechanism different from the classical templating exists. This new mechanism designated as ‘‘deformed templating’ ’ postulates that a change in the PrP folding pattern from the one present in rPrP fibrils to an alternative specific for PrPSc can occur. The current work provides important new insight into the mechanisms underlying genesis of the transmissible protein state