Files
Abstract
Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases occurring in humans, cattle, and sheep. Conversion of the normal, host-encoded cellular prion protein (PrPC) to a misfolded, disease-associated isoform (PrPD) is the causative agent. Classical scrapie is the oldest described TSE, whereas atypical scrapie is more recent, but there are reported cases of both in Europe, US, and Canada. Globally, extensive eradication programs use passive and active surveillance in an effort to control and eliminate these diseases, as they are devastating economically and financially. Although surveillance has been effective in identification of affected animals, and the total number of scrapie cases has diminished, factors that contribute to prion permissibility and rate of prion accumulation remain unknown. Additionally, these factors could be extrapolated to human TSEs, providing the basis for development of a human cell culture system. Using immortalized ovine microglia clones, 6 genes with functions in apoptosis (survivin; follistatin-like 1), cell proliferation (osteonectin), efferocytosis (AXL tyrosine kinase inhibitor), cell-to-cell and cell-extracellular matrix adhesions (syndecan 4), and extracellular remodeling and repair (fibronectin 1) were studied for potential correlations with prion permissibility. Furthermore, expression of these genes relative to PRNP expression was evaluated. Transcript levels for matrix metalloproteinase 2 (MMP2) were also assessed to determine if expression was influenced by permissibility phenotype, or rate of prion accumulation. To study an animal prion disease that mirrors the human condition in length of incubation period and slow rate of prion accumulation, PrPSc pattern and localization was characterized in 4 sheep experimentally infected with a natural North American atypical scrapie isolate. Fibronectin 1 and survivin were strongly and negatively correlated with prion permissibility when evaluated relative to PRNP, and significant differential expression of survivin, osteonectin and follistatin-like 1 was between intermediately and poorly-permissive clones. Matrix metalloproteinase II transcript levels were significantly decreased in intermediately-permissive clones, and in cells with a fast rate of prion accumulation. In the atypical scrapie cases, PrPSc pattern and localization was similar to previously reported European pathotypes. These findings suggest potential determinants of prion permissibility exist, but further studies are needed to solidify these results.