Cell Tropism: The Role of Autophagy in Prion Susceptibility

• Author / Creator

  Norman, Albert G

• Prion disease, or transmissible spongiform encephalopathy (TSE), is a type of neurodegenerative disease for which there is no treatment and which is invariably fatal. Prion diseases are distinct in the field of biology and medicine, not only because they can be sporadic, infectious, or inherited, but also because they can transmit disease without the need for nucleic acids. Prion diseases, or prionopathies, arise when PrPC (the “C” denotes cellular, in relation to the normal version of the protein) which is α-helical rich, misfolds into a pathogenic form (PrPSc – the “Sc” denotes scrapie, named for the first known prion disease), which is comprised largely of β-sheets, and triggers a cascade of PrPC misfolding and aggregation, followed by neuronal loss. Prion strains are much different than viral or bacterial strains. Prion strains are defined by their abilities to induce distinct neuropathological deposition patterns of PrPSc, including distinct areas of involvement within the brain, incubation period, and clinical presentation. While it has been previously established that the disease specific isoform of the prion protein, PrPSc, is essential for establishing infection, it is not clear how PrPSc of different strains is able to induce distinct neuropathological profiles. Different cell features may preferentially facilitate strain propagation in certain brain regions; some of these cell features include levels of surface polyanion molecules, levels of PrPC expression, and membrane lipid content. Another aspect that can vary between cells is the level of basal autophagy, which plays a role in PrPSc clearance. We hypothesized that basal autophagy can influence cell susceptibility to prions. To investigate the relationship between autophagy and cell susceptibility, we examined the infection efficiency of RML-strain mouse-adapted scrapie prions in three cell lines (N2a, CAD5, and L929) in relation to the cells’ basal levels of autophagy. Contrary to our hypothesis, we found that basal autophagy level did not correlate with cell susceptibility in the three cell lines tested. We then modulated autophagy to determine if we could alter susceptibility to prion infection. Augmentation of autophagy was able to protect L929 cells from de novo prion infection, in addition to clearing chronically infected CAD5-RML cells of PrPSc material. We also found that early fluctuations in autophagy could predict the re-emergence of PrPSc material in subsequent passages for N2a and CAD5 cells, but not L929 cells and that an increase in the relative amount of PrPSc material in early passages could predict the return of PrPSc signal in later passages for all three cell lines. Unfortunately, due to technical issues we were unable to determine if autophagic inhibition increased cell susceptibility to prion infection. In conclusion, basal autophagy levels did not correlate with cell susceptibility to prion infection, even though increasing autophagy did reduce cell susceptibility to prion infection and clear cells of chronic prion infection. Interestingly, early autophagic flux and levels of PrPSc predicted whether PrPSc re-emerged in late passages.

• Subjects / Keywords

  • L929
  • PrP
  • Prion susceptibility
  • LC3
  • Cell tropism
  • N2a
  • Autophagy
  • Scrapie
  • Prion strain
  • Prions
  • CAD5

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ST7F99P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.