Understanding Intra-Species and Inter-Species Prion Conversion and Zoonotic Potential Using Protein Misfolding Cyclic Amplification

Abstract

Prion diseases are fatal neurodegenerative disorders that affect humans and animals, and can also be transmitted from animals to humans. A fundamental event in prion disease pathogenesis is the conversion of normal host prion protein (PrPC) to a disease-associated misfolded form (PrPSc). Whether or not an animal prion disease can infect humans cannot be determined a priori. There is a consensus that classical bovine spongiform encephalopathy (C-type BSE) in cattle transmits to humans, and that classical sheep scrapie is of little or no risk to human health. However, the zoonotic potential of more recently identified animal prion diseases, such as atypical scrapie, H-type and L-type BSE and chronic wasting disease (CWD) in cervids, remains an open question. Important components of the zoonotic barrier are (i) physiological differences between humans and the animal in question, (ii) amino acid sequence differences of the animal and human PrPC, and (iii) the animal prion strain, enciphered in the conformation of PrPSc. Historically, the direct inoculation of experimental animals has provided essential information on the transmissibility and compatibility of prion strains. More recently, cell-free molecular conversion assays have been used to examine the molecular compatibility on prion replication and zoonotic potential. One such assay is Protein Misfolding Cyclic Amplification (PMCA), in which a small amount of infected tissue homogenate, containing PrPSc, is added as a seed to an excess of normal tissue homogenate containing PrPC, and prion conversion is accelerated by cycles of incubation and ultrasonication. PMCA has been used to measure the molecular feasibility of prion transmission in a range of scenarios using genotypically homologous and heterologous combinations of PrPSc seed and PrPC substrate. Furthermore, this method can be used to speculate on the molecular profile of PrPSc that might arise from a zoonotic transmission. We discuss the experimental approaches that have been used to model both the intra- and inter-species molecular compatibility of prions, and the factors affecting PrPc to PrPSc conversion and zoonotic potential. We conclude that cell-free prion protein conversion assays, especially PMCA, are useful, rapid and low-cost approaches for elucidating the mechanisms of prion propagation and assessing the risk of animal prions to humans.

Maternal COVID-19 Vaccination and Its Potential Impact on Fetal and Neonatal Development

“…Pregnant sheep have been used to study connections between maternal allergies and offspring lung development and risk of allergies [133,134]. Sheep are also considered ideal models for studying neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases [135], and due to their susceptibility to scrapie, are widely used to study prion diseases [136,137]. Sheep are also a well-recognized biomedical model for studying immunology [138], vaccine development and safety [139,140], and have been extensively used by our group and others to study the impact of maternal inflammation during pregnancy on offspring development [141].…”

PRNP Sequences of Tibetan Antelope, Blue Sheep, and Plateau Pika from the Qinghai-Tibet Plateau and Reactivity of PrP Proteins to Rodent-Adapted Scrapie Strains in RT-QuIC and PMCA

“…In contrast, the homologous PMCA products (139A-mouse PMCA-PrP res and 263K-hamster PMCA-PrP res ) showed no infectivity against the other animal [23]. Overcoming species barriers of prion infections by PMCA has been repeatedly documented to better understand the transmission between different species of animals and from animal-to-human [24]. Based on PMCA, PrP res can be generated in the reactions of different species of PrP Sc with PrP C from rabbits and dogs that are considered as poorly susceptible and tolerant to prion infection [25,26].…”

“…A further increase in PMCA rounds is warranted. In contrast, high efficiency of PMCA in circumventing species barriers lead to doubt that the species barriers in the real world are potentially underestimated; therefore, careful interpretation of the results of PMCA experiments are required [24]. Nevertheless, numerous species of ruminants have been verified to be susceptible to scrapie infection and bovine spongioform encephalopathy (BSE) [3,[27][28][29].…”

Conventional and State-of-the-Art Detection Methods of Bovine Spongiform Encephalopathy (BSE)

“…PMCA was used to assess the possibility of atypical BSE crossing the species barrier into humans. Neither H- nor L-type BSE induced significant conversion in PMCA in contrast to C-type BSE, indicating that atypical forms of BSE pose a poor zoonotic threat [ 153 , 154 ]. These findings contradict previous results that showed that L-type BSE was able to produce infectivity in a humanized transgenic mouse model overexpressing the human prion protein [ 155 ].…”