Location: Virus and Prion Research
2019 Annual Report
Accomplishments
1. A method for long-term storage of prion protein was developed. Recent advances in prion disease diagnostic methods include the amplification of the amount of the infectious agent (abnormal prion protein) in a sample. One such technique, known as RT-QuIC, requires a steady supply of freshly purified prion protein which necessitates constant production that is not sustainable in a diagnostic laboratory setting. ARS researchers at Ames, Iowa, developed a method to dry and preserve the prion protein for long-term storage (months or years). This allows for production of the protein in larger quantities, and it can be shipped to diagnostic laboratories facilitating widespread use of RT-QuIC as a diagnostic method.
2. The impact of source genotype on scrapie transmission to elk was evaluated. Scrapie is a fatal disease of sheep that causes damaging changes in the brain. The infectious agent is an abnormal form of the prion protein, a protein normally found in animals. The abnormal or misfolded prion protein can cause disease in sheep of a specific genetics. However, some genetic lines of sheep are resistant to scrapie disease, and some are partially resistant. The RT-QuIC test is an assay that can detect and amplify the presence of abnormal prion protein in a tissue sample. This test can detect the difference between resistant, partially resistant, and susceptible sheep. It can be used in mouse models to evaluate if scrapie can be transmitted to other species, and how efficiently it may be transmitted. ARS researchers at Ames, Iowa, evaluated how different prion protein gene sequences in prion disease affected sheep can transmit in mouse models demonstrating genotypic background of both source and recipient can strongly influence susceptibility. Thus, not only the genotype of the recipient animal but also the genotype of the animal used as a source of the abnormal prion inoculum should be considered in the study of prion transmission.
3. Demonstrated that sheep homozygous for lysine-171 in the prion protein are resistant to classical sheep scrapie. Scrapie is a fatal disease of sheep and goats that causes damaging changes in the brain. The infectious agent is an abnormal protein called a prion that has misfolded from its normal state. Whether or not a sheep will get scrapie is determined by its genetics. A change in the deoxyribonucleic acid (DNA) that codes for the amino acid sequence of the host prion protein can cause the animal to be either resistant or susceptible to the disease. A specific location on this gene, codon 171, seems to play the biggest role in determining disease susceptibility. Sheep with the amino acid arginine (R) at 171 are resistant to scrapie while those with glutamine (Q) at that position are not. It has been suggested that lysine (K) at 171 may behave similarly to R because the two amino acids have a similar structure. ARS researchers at Ames, Iowa, tested whether sheep with one K allele at codon 171 (QK171) or two K alleles at codon 171 (KK171) had a different response to the disease than sheep that were QQ171. The study determined that while QK171 were not resistant to the disease after oronasal exposure, they took longer to develop scrapie than QQ171 sheep. While KK171 sheep were susceptible to the scrapie agent after intracranial inoculation, they were resistant to infection by the oronasal route. This work suggests that selective breeding for the K171 allele in sheep breeds where this allele is represented may help prevent the development of scrapie after natural exposure. This information is useful to sheep farmers and breeders that are selectively breeding animals with genotypes resistant to scrapie. Further, this result is important to regulators with roles in designing programs to enhance genetic resistance to scrapie.
4. Demonstrated that raccoons do not accumulate scrapie isoform of the prion protein (PrPSc) following inoculation with atypical scrapie. The prion diseases are fatal diseases of animals and humans that cause damaging changes in the brain. Animal prion diseases include scrapie in sheep, chronic wasting disease (CWD) in cervids, and transmissible mink encephalopathy (TME) in ranch-raised mink. The infectious agent is an abnormal protein called a prion that has misfolded from its normal state. This study tested whether raccoons develop clinical disease and/or accumulate abnormal prion protein after inoculation with prion agents from different species: TME from cattle, raccoons, or hamsters that occurs in two forms with distinct clinical signs and molecular properties called hyper and drowsy; CWD from white-tailed deer or elk; and atypical (Nor-98) scrapie from sheep. All raccoons inoculated with TME from raccoons or cattle developed clinical disease with short survival times. Raccoons inoculated with CWD from white-tailed deer, CWD from elk, or ‘hyper’ TME from hamsters did not develop clinical disease, but abnormal prion protein was detected in the brains of 25 percent of the raccoons in each study. The amount of abnormal prion protein in the brains of these raccoons was much less than in the brains of raccoons inoculated with TME from raccoons or cattle. None of the raccoons inoculated with ‘drowsy’ TME from hamsters or atypical scrapie from sheep developed clinical disease or detectable abnormal prion protein. ARS researchers at Ames, Iowa, work suggests that raccoons are susceptible to prion disease isolates from raccoons, cattle, white-tailed deer, and elk. Raccoons are omnivores that have a widespread geographical distribution and are known to scavenge animal carcasses. Therefore, they could provide a route of transmission of prions disease between farmed and wild animal species. This information is useful to farmers and people involved in control of prion disease in free-ranging animals.
Review Publications
Mammadova, N., Summers, C.M., Kokemuller, R.D., He, Q., Ding, S., Baron, T., Yu, C., Valentine, R.J., Sakaguchi, D.S., Kanthasamy, A.G., Greenlee, J.J., West Greenlee, M.H. 2019. Accelerated accumulation of retinal alpha-synuclein (pSer129) and tau, neuroinflammation, and autophagic dysregulation in a seeded mouse model of Parkinson's disease. Neurobiology of Disease. 121:1-16. https://doi.org/10.1016/j.nbd.2018.09.013.
Hwang, S., Greenlee, J.J., Vance, N.M., Nicholson, E.M. 2018. Source genotype influence on cross species transmission of transmissible spongiform encephalopathies evaluated by RT-QuIC. PLoS One. 13(12):e0209106. https://doi.org/10.1371/journal.pone.0209106.
Hwang, S., Tatum, T., Lebepe-Mazur, S., Nicholson, E.M. 2018. Preparation of lyophilized recombinant prion protein for TSE diagnosis by RT-QuIC. BMC Research Notes. 11:895. https://doi.org/10.1186/s13104-018-3982-5.
