A Prion Protein Gene Polymorphism at Codon 138 Modulates Chronic Wasting Disease Pathogenesis
Date
2021-08
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Abstract
Prion diseases are fatal and infectious neurodegenerative diseases caused by prions. Chronic wasting disease (CWD) is a prion disease of cervids found in North America (NA), Scandinavia and South Korea. Although there are no reports of CWD in caribou (Rangifer tarandus spp.) in NA so far, previous findings show that reindeer (R. t. tarandus) are susceptible to CWD. Single amino acid substitutions (SAAS) within the cervid prion protein (PrP) sequence have been shown to prolong survival times and produce incomplete attack rates upon CWD infection. Prion protein SAAS have been found in caribou populations in NA, including a serine to asparagine substitution at codon 138 (S138N). Previous studies reported that animals harboring the N variant at this codon were either resistant or less susceptible to natural CWD prion exposure. Based on these reports, we hypothesized that the S138N PrP amino acid substitution modulates CWD pathogenesis. We report that the 138N allele frequency is rare among caribou in areas with high risk of contact with CWD-infected species, particularly in woodland caribou (R. t. caribou) herds in Saskatchewan and Alberta. We also report that the barren-ground caribou (R. t. groenlandicus) herds have higher frequencies of the 138N allele. We found that the S138N SAAS did not alter endogenous PrP properties, but rather impairs the prion conversion process. Transgenic knock-in (KI) mice expressing the 138NN PrP genotype did not develop clinical disease up to 700 days post-inoculation (dpi), whilst their wild-type deer (138SS) counter parts succumbed to CWD between ~450-580 dpi. The 138NN KI mice did, however, harbor prions capable of inducing conversion in an in vitro prion conversion assay. Remarkably, even upon intracerebral prion inoculation, seeding activity was first detected in the spleens of these KI mice. Our findings provide new insights into the role of PrP genotype in tissue tropism of prion replication. Caribou in NA are a Threatened species and an essential resource for Indigenous people. Thus, determining the mechanisms by which the 138N allele modulates CWD pathogenesis is important for future CWD management strategies, especially in areas where caribou are at a high risk of contracting the disease.
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Keywords
prion, chronic wasting disease, caribou, polymorphism, pathogenesis
Citation
Arifin, M. I. (2021). A prion protein gene polymorphism at Codon 138 modulates Chronic Wasting Disease pathogenesis (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.