Cellular Aspects of Prion Replication In Vitro

Abstract

Prion diseases or transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative disorders in mammals that are caused by unconventional agents predominantly composed of aggregated misfolded prion protein (PrP). Prions self-propagate by recruitment of host-encoded PrP into highly ordered β-sheet rich aggregates. Prion strains differ in their clinical, pathological and biochemical characteristics and are likely to be the consequence of distinct abnormal prion protein conformers that stably replicate their alternate states in the host cell. Understanding prion cell biology is fundamental for identifying potential drug targets for disease intervention. The development of permissive cell culture models has greatly enhanced our knowledge on entry, propagation and dissemination of TSE agents. However, despite extensive research, the precise mechanism of prion infection and potential strain effects remain enigmatic. This review summarizes our current knowledge of the cell biology and propagation of prions derived from cell culture experiments. We discuss recent findings on the trafficking of cellular and pathologic PrP, the potential sites of abnormal prion protein synthesis and potential co-factors involved in prion entry and propagation.

Cell-to-cell propagation of infectious cytosolic protein aggregates

“…Prion replication crucially depends on the autocatalytic formation of infectious entities, resulting in faithful inheritance of aggregates by daughter cells upon cell division (11). Exposure of cells to mammalian prions can induce a transient PrP Sc formation that does not result in persistent infection (20).…”

“…2 B-D; Movies S1, S2, S3, and S4). Thus, reminiscent of mammalian TSE agents in vitro, naturally transmitted NM-HA aggregates induce self-perpetuating heritable aggregates in recipient cells (11).…”

“…The exact mechanism of prion replication is not well-understood. Mammalian prions have been extensively studied in vitro (11). In cell lines, PrP Sc is faithfully propagated by progeny cells and spreads to neighboring cells, thereby inducing ongoing PrP Sc formation.…”

Caprine PrP variants harboring Asp-146, His-154 and Gln-211 alleles display reduced convertibility upon interaction with pathogenic murine prion protein in scrapie infected cells

“…cellular trafficking is also critical for proper folding 37 and conversion occurrence. Indeed, physiological PrP C trafficking results in its localization on the plasma membrane, in subcellular compartments and vehicles, 38 and enables its co-localization with PrP SC on the plasma membrane as well as in endo-cellular compartments with low pH, 39 where conversion takes place.…”

“…Indeed, physiological PrP C trafficking results in its localization on the plasma membrane, in subcellular compartments and vehicles, 38 and enables its co-localization with PrP SC on the plasma membrane as well as in endo-cellular compartments with low pH, 39 where conversion takes place. 37,40 We ensured physiological cell trafficking of the studied protein variants and their subsequent binding to the plasma membrane, by expressing murine-caprine chimeras consisting of the mature caprine PrP sequence, flanked by murine PrP regulatory elements, to enable Endoplasmatic Reticulum lumen targeting and GPI-anchor addition. Efficient conversion depends on the compatibility of the interacting PrP isoforms and is associated with both their primary sequence and structural similarity.…”