The role of astrocytes in prion strain susceptibility

PROJECT SUMMARY AND ABSTRACT: Prion diseases are fatal neurodegenerative diseases in which the conversion of the cell-surface protein (PrPC) to its infectious conformer (PrPSc) leads to neuronal death. Distinct conformational variations in PrPSc result in prion strains, which can display widely different symptoms, cell type localization, and PrPSc deposition patterns in the brain. Single cell RNAseq analysis over the course of disease has revealed neuronal transcriptomic changes occur only in the final stages of the disease process, after symptoms have appeared, shortly before death. However, most preclinical transcriptomic alterations were found astrocytes, suggesting a key role for non- neuronal cells in prion pathogenesis. Astrocytes have comparable levels of PrPC to neurons and are infectible with prions. They can also phagocytose PrPSc and secrete inflammatory factors in response. The recent discovery of transcriptomic heterogeneity of astrocytes between brain regions suggests that astrocytes may contribute to the distinct regional deposition of PrPSc associated with different strains. My goal is to identify what astrocytic cellular processes impact prion disease and how astrocyte regional identity affects prion strain susceptibility. There has been limited previous research investigating the cellular mechanisms underlying astrocyte infection and its impact of astrocyte reactivity and processing of PrPSc. To address these gaps, this proposal uses an in vitro infection model of primary astrocytes, enabling the characterization of initial infection stages and offering the ability to understand the process at a mechanistic level. I hypothesize regionally distinct astrocytes differ in their susceptibility to prion strains because of variations in their uptake, localization, and propagation. In AIM 1, I will characterize the localization and processing of PrPSc by astrocytes and determine whether prion exposure is sufficient for activation. In AIM 2, I will characterize the prion strain susceptibility of astrocytes isolated from different brain regions and infected in culture, and by infection of organotypic brain slices. Accomplishing these goals will offer a more detailed mechanistic understanding of the impact of infected astrocytes in prion diseases, and beyond its contribution to the prion field, this research will shed light on the role of astrocytes in other neurodegenerative conditions.