SCRAPIE STRAIN INFECTION IN-VITRO INDUCES CHANGES IN NEURONAL CELLS

PC12 cells, in the presence of nerve growth factor (NGF), support repl ication of the mouse-derived scrapie strains 139A and ME7, with the fo rmer yielding 100-1000-fold higher levels of infectivity. Infectivity remained cell-associated and cells did not show any gross morphologica l alterations, although changes were observed by electron microscopy i n the form of an increased number of lipid droplets in 139A-infected c ultures. Analysis of phospholipid metabolism in 139A infected cells in dicated that scrapie replication did not change the inositol phosphate levels, but did not stimulate phosphoinositide synthesis. Replication was not detected in PC12 cells infected with either the hamster-deriv ed 263K or rat-derived 139R scrapie strains.' Since scrapie-infected c ultures did not exhibit cell death or any gross changes, any scrapie-i nduced effects would probably be manifested in nonvital cellular funct ions. When compared to controls, infect with the 139A scrapie strain r esulted in decreased activity of the cholinergic pathway-related enzym es, as well as the GABA synthetic pathway; however, the adrenergic pat hway was unaffected by scrapie infection. The effects of the 139A scra pie strain on the cholinergic system appeared to be dose-dependent and were first detected prior to the detection of scrapie strain on the c holinergic system appeared to be dose-dependent and were first detecte d prior to the detection of scrapie agent replication in these cells. No neurotransmitter-related enzymatic changes were detected in 263K-or 139R-infected PC12 cells. The enzymatic changes observed in ME7-infec ted PC12 cells and in Chandler agent-infected mouse neuroblastoma cell s suggest that the significant changes in neurotransmitter levels in c ultures exhibiting low infectivity titers must involve factors other t han, but not excluding, replication of the agent. The role of addition al factors is also suggested in studies of protein kinase C activity i n 139A- and 139R-infected PC12 cells. These studies emphasize the valu e of the PC12 cell model system in examining the scrapie strain-host c ell interaction and, in addition, supported the concept of variation a mong scrapie strains.