Synthetic Scrapie Infectivity: Interaction between Recombinant PrP and Scrapie Brain-Derived RNA

Abstract

The key molecular event in human cerebral proteinopathies, which include Alzheimer's, Parkinson's and Huntington's diseases, is the structural conversion of a specific host protein into a β-sheet-rich conformer. With regards to this common mechanism, it appears difficult to explain the outstanding infectious properties attributed to PrP(Sc), the hallmark of another intriguing family of cerebral proteinopathies known as transmissible spongiform encephalopathies (TSE) or prion diseases. The infectious PrP(Sc) or "prion" is thought to be composed solely of a misfolded form of the otherwise harmless cellular prion protein (PrP(c)). To gain insight into this unique situation, we used the 263K scrapie hamster model to search for a putative PrP(Sc)-associated factor that contributes to the infectivity of PrP(Sc) amyloid. In a rigorously controlled set of experiments that included several bioassays, we showed that originally innocuous recombinant prion protein (recPrP) equivalent to PrP(c) is capable of initiating prion disease in hamsters when it is converted to a prion-like conformation (β-sheet-rich) in the presence of RNA purified from scrapie-associated fibril (SAF) preparations. Analysis of the recPrP-RNA infectious mixture reveals the presence of 2 populations of small RNAs of approximately 27 and 55 nucleotides. These unprecedented findings are discussed in light of the distinct relationship that may exist between this RNA material and the 2 biological properties, infectivity and strain features, attributed to prion amyloid.

The “Jekyll and Hyde” Actions of Nucleic Acids on the Prion-like Aggregation of Proteins

“…The minimal size of the nucleic acid molecule that can convert PrP into PrP Sc -like species is also arguable (18,36,45). The particular structure of the nucleic acid also seems to be important for the binding affinity and specificity.…”

“…Although no single RNA or DNA molecule has been found to be associated with PrP infectivity in vivo, recent work provides strong evidence that small RNA sequences (27-and 55-mers) associated with brain scrapie material can trigger the conversion of the recombinant protein to a disease-causing form when incubated with recombinant PrP C (45). Although not all preparations induced prion-like disease in recipient mice, these results indicate that a sustained RNA population is present in scrapie-associated fibrils, in partial disagreement with the protein-only hypothesis (27).…”

Rapid chemical decontamination of infectious CJD and scrapie particles parallels treatments known to disrupt microbes and biofilms

“…While restoration of TSE agent infectivity has been tried for many years in various preparations, 39,55 a small amount of infectivity was recently restored by combining phenol purified 263K brain nucleic acids with recombinant PrP. 13 Non-PrP proteins that are particle-associated 20,46 may also be needed to effectively transmit an agent genome from among the many nucleic acids present in all highly infectious preparations. 41,45 Thiourea (ThU) alone, or combined with urea, is very effective for destroying >4 logs of TSE infectivity within 1 hr at 22 C, and ThU has not been used previously for TSE agent disruption.…”

“…Misfolded recombinant PrP is not reproducibly infectious in animal or culture assays, even though massive amounts of PrPres amyloid are readily generated in a test tube. 4,[10][11][12][13] Huge increases in PrP-res can also coincide with a >5 log loss of FU-CJD agent from chronically infected living cell cultures. 12 This PrP-res is indistinguishable from the "infectious" PrP-res form, yet it is unable to produce any detectable agent in sensitive infectivity culture assays.…”

Interrelation of Prions With Non-Coding Rnas

“…While particular mechanisms of these conformational and biological changes have been unknown, it has been demonstrated that they require additional chaperone molecules such as lipids, proteoglycans and RNAs (Mabbott, 2017). TSE progressing is related to the exponential growth of PrP C transformation into its abnormal isoform PrP Sc (Saba et al, 2012), which is characterized by the changed tertiary structure of the molecule, where the α-spirals have transformed to make a new conformation with the β-layers (Simoneau et al, 2015). The characteristic histopathologic CNS changes in TSE include brain vacuolation, neurodegeneration, microgliosis, astrocytosis and pathological accumulation of PrP Sc (Mabbott, 2017).…”