Protease-sensitive synthetic prions

Prions arise when the cellular prion protein (PrPC) undergoes a self-propagating conformational change; the resulting infectious conformer is designated PrPSc. Frequently, PrPSc is protease-resistant but protease-sensitive (s) prions have been isolated in humans and other animals. We report here that protease-sensitive, synthetic prions were generated in vitro during polymerization of recombinant (rec) PrP into amyloid fibers. In 22 independent experiments, recPrP amyloid preparations, but not recPrP monomers or oligomers, transmitted disease to transgenic mice (n = 164), denoted Tg9949 mice, that overexpress N-terminally truncated PrP. Tg9949 control mice (n = 174) did not spontaneously generate prions although they were prone to late-onset spontaneous neurological dysfunction. When synthetic prion isolates from infected Tg9949 mice were serially transmitted in the same line of mice, they exhibited sPrPSc and caused neurodegeneration. Interestingly, these protease-sensitive prions did not shorten the life span of Tg9949 mice despite causing extensive neurodegeneration. We inoculated three synthetic prion isolates into Tg4053 mice that overexpress full-length PrP; Tg4053 mice are not prone to developing spontaneous neurological dysfunction. The synthetic prion isolates caused disease in 600–750 days in Tg4053 mice, which exhibited sPrPSc. These novel synthetic prions demonstrate that conformational changes in wild-type PrP can produce mouse prions composed exclusively of sPrPSc.
Author Summary Prions are infectious proteins that cause heritable, sporadic, and transmissible diseases in humans and other mammals. These infectious proteins arise when the normal form of the prion protein (PrP) adopts a self-perpetuating conformation. This disease-causing PrP form is frequently distinguished from normal PrP by its resistance to digestion by proteases although considerable evidence shows that protease-sensitive prions occur naturally in humans and sheep. Here we describe the generation of novel protease-sensitive synthetic prions. After producing recombinant PrP of the wild-type mouse sequence in Escherichia coli, we polymerized the protein into an amyloid fiber conformation. Mice inoculated with these amyloid fibers developed extensive neurodegeneration characteristic of prion disease, but did not generate protease-resistant PrP. Prions from sick animals were transmitted to healthy animals, which likewise developed neurodegeneration but not protease-resistant prions. These novel synthetic prions demonstrate that truncated wild-type PrP can undergo a conformational change that becomes infectious yet the protein remains protease sensitive.