|WEST GREENLEE, M - Iowa State University|
|LIND, M - Iowa State University|
|MAMMADOVA, N - Iowa State University|
|KONDRU, N - Iowa State University|
|MANNE, S - Iowa State University|
|SMITH, J - Iowa State University|
|KANTHASAMY, A - Iowa State University|
Submitted to: American Journal of Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2016
Publication Date: 8/9/2016
Citation: West Greenlee, M.H., Lind, M., Kokemuller, R., Mammadova, N., Kondru, N., Manne, S., Smith, J., Kanthasamy, A., Greenlee, J. 2016. Temporal resolution of misfolded prion protein transport, accumulation, glial activation, and neuronal death in the retinas of mice inoculated with scrapie. American Journal of Pathology. 186(9):2302–2309.
Interpretive Summary: Prion diseases are invariably fatal neurologic diseases for which there is no known prevention or cure. Because of long incubation times and knowledge gaps in how the disease progresses, there is not a well-defined model for testing potential cures or preventative measures. The retina in the back of the eye contains central nervous tissue that is connected to, but spatially separated from the brain. We used assessment of the retina over a time course of scrapie progression in infected mice to carefully describe the relationship between the transport of misfolded prion protein (PrPSc) from the brain to the retina, the accumulation of PrPSc in the retina, the response of the surrounding retinal tissue to PrPSc accumulation, and resulting neuronal (photoreceptor) death. This work identifies a critical window between the onset of accumulation of abnormal prion and the response of retinal tissues, which occurs before neurodegeneration and cell death. This model provides concrete criteria that could be used to assess the effectiveness of anti-prion compounds. Our group and others will use this model to develop potential preventative measures for prion diseases, assess compounds that slow neurodegeneration, and define mechanisms of prion associated tissue damage. Because mechanisms of neurodegeneration in prion disease are similar to other protein misfolding diseases such as Alzheimer’s disease and Parkinson’s disease, use of this model could have a major impact on improving treatments for neurodegenerative diseases.
Technical Abstract: Currently, there is a lack of pathologic landmarks to describe the progression of prion disease in vivo. The goal of this work was to determine the temporal relationship between the transport of misfolded prion protein from the brain to the retina, the accumulation of PrPSc in the retina, the response of the surrounding retinal tissue to PrPSc accumulation, and resulting neuronal death in a mouse model of scrapie. C57Bl/6 mice were inoculated intracranially with RML scrapie. Animals were euthanized and retinal samples collected at 30, 60, 90, 105, 120 days post inoculation (dpi) or at the onset of clinical signs of disease (153 dpi average). Retinal homogenates were prepared for real-time quaking-induced conversion (RT-QuIC) analysis and whole globes were fixed for standard immunohistochemical analysis. Antibodies against the prion protein (6H4), glial fibrillary acidic protein (GFAP), and activated microglia (CD68) were used to assess accumulation of PrPSc and the resulting response of retinal tissue. Loss of photoreceptors was used as a measure of neuronal death, and was quantified using nuclear counts on hematoxylin-counterstained slides. PrPSc seeding activity was first detected using RT-QuIC in all samples at 60 dpi, which was approximately 40% of the total incubation of 153 days. Accumulation of PrPSc along with coincident activation of retinal glia, was first detected at 90 dpi, which was approximately 60% of the total incubation period. Activation of microglia was first detected at 105 dpi (70% of the total incubation period), but significant neuronal death measured by loss of photoreceptor cells was not detectable until 120 dpi, which was approximately 80% of the total incubation period. Our results demonstrate that by using the retina, we can resolve the temporal separation between several key events in the pathogenesis of prion disease. We have described a model with the temporal resolution sufficient to study the relationships between PrPSc transport, PrPSc accumulation, resultant tissue activation, and neuronal death. This model can be used to study the mechanisms that underlie these events and to evaluate the anti-prion activity of a variety of compounds in vivo.