Intra-host mathematical model of chronic wasting disease dynamics in deer (Odocoileus)

Bioassays of native cervid hosts have established the presence of infectious chronic wasting disease (CWD) prions in saliva, blood, urine, and feces of clinically diseased and pre-clinical infected deer. The intra-host trafficking of prions from the time of initial infection to shedding has been less well defined. We created a discrete-time compartmentalized model to simulate the misfolding catalysis, trafficking, and shedding of infectious prions throughout the organ systems of CWD-infected cervids. Using parameter values derived from experimental infections of North American deer (Odocoileus spp.), the exponential-based model predicts prion deposition over time with: 1) nervous tissues containing the highest deposition of prions at 20 months post-infection and 2) excreted fluids containing low levels of prions throughout infection with the highest numbers of prions predicted to be shed in saliva and feces (as high as 10 lethal doses (1.34 × 10²⁹ prions) in 11–15 months). These findings are comparable to prion deposition described in literature as assayed by conventional and ultrasensitive amplification assays. The comparison of our model to published data suggests that highly sensitive assays (sPMCA, RT-QuIC, and bioassay) are appropriate for early prion detection in bodily fluids and secretions. The model provides a view of intra-host prion catalysis leading to pre-clinical shedding and provides a framework for continued development of antemortem diagnostic methods.     

Protein Misfolding Cyclic Amplification of Prions

Prions are infectious agents that cause the inevitably fatal transmissible spongiform encephalopathy (TSE) in animals and humans^9,18. The prion protein has two distinct isoforms, the non-infectious host-encoded protein (PrP^C) and the infectious protein (PrP^Sc), an abnormally-folded isoform of PrP^{C 8}.One of the challenges of working with prion agents is the long incubation period prior to the development of clinical signs following host inoculation¹³. This traditionally mandated long and expensive animal bioassay studies. Furthermore, the biochemical and biophysical properties of PrP^Sc are poorly characterized due to their unusual conformation and aggregation states.PrP^Sc can seed the conversion of PrP^C to PrP^Scin vitro¹⁴. PMCA is an in vitro technique that takes advantage of this ability using sonication and incubation cycles to produce large amounts of PrP^Sc, at an accelerated rate, from a system containing excess amounts of PrP^C and minute amounts of the PrP^Sc seed¹⁹. This technique has proven to effectively recapitulate the species and strain specificity of PrP^Sc conversion from PrP^C, to emulate prion strain interference, and to amplify very low levels of PrP^Sc from infected tissues, fluids, and environmental samples^6,7,16,23 .This paper details the PMCA protocol, including recommendations for minimizing contamination, generating consistent results, and quantifying those results. We also discuss several PMCA applications, including generation and characterization of infectious prion strains, prion strain interference, and the detection of prions in the environment.     

Comparison of 2 synthetically generated recombinant prions

Prion is a protein-conformation-based infectious agent causing fatal neurodegenerative diseases in humans and animals. Our previous studies revealed that in the presence of cofactors, infectious prions can be synthetically generated in vitro with bacterially expressed recombinant prion protein (PrP). Once initiated, the recombinant prion is able to propagate indefinitely via serial protein misfolding cyclic amplification (sPMCA). In this study, we compared 2 separately initiated recombinant prions. Our results showed that these 2 recombinant prions had distinct biochemical properties and caused different patterns of spongiosis and PrP deposition in inoculated mice. Our findings indicate that various recombinant prions can be initiated in vitro and potential reasons for this variability are discussed.