title: Docosahexaenoic and eicosapentaenoic acids increase prion formation in neuronal cells.
abstract: BACKGROUND
  The transmissible spongiform encephalopathies, otherwise known as prion diseases, occur following the conversion of the cellular prion protein (PrPC) to an alternatively folded, disease-associated isoform (PrPSc). Recent studies suggest that this conversion occurs via a cholesterol-sensitive process, as cholesterol synthesis inhibitors reduced the formation of PrPSc and delayed the clinical phase of scrapie infection. Since polyunsaturated fatty acids also reduced cellular cholesterol levels we tested their effects on PrPSc formation in three prion-infected neuronal cell lines (ScGT1, ScN2a and SMB cells).
  
  
  RESULTS
  We report that treatment with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) or the cholesterol synthesis inhibitor simvastatin reduced the amounts of free cholesterol in membrane extracts from prion-infected neuronal cells. Simvastatin reduced cholesterol production while DHA and EPA promoted the conversion of free cholesterol to cholesterol esters. Crucially, while simvastatin reduced PrPSc formation, both DHA and EPA significantly increased the amounts of PrPSc in these cells. Unlike simvastatin, the effects of DHA and EPA on PrPSc content were not reversed by stimulation of cholesterol synthesis with mevalonate. Treatment of ScGT1 cells with DHA and EPA also increased activation of cytoplasmic phospholipase A2 and prostaglandin E2 production. Finally, treatment of neuronal cells with DHA and EPA increased the amounts of PrPC expressed at the cell surface and significantly increased the half-life of biotinylated PrPC.
  
  
  CONCLUSIONS
  We report that although treatment with DHA or EPA significantly reduced the free cholesterol content of prion-infected cells they significantly increased PrPSc formation in three neuronal cell lines. DHA or EPA treatment of infected cells increased activation of phospholipase A2, a key enzyme in PrPSc formation, and altered the trafficking of PrPC. PrPC expression at the cell surface, a putative site for the PrPSc formation, was significantly increased, and the rate at which PrPC was degraded was reduced. Cholesterol depletion is seen as a potential therapeutic strategy for prion diseases. However, these results indicate that a greater understanding of the precise relationship between membrane cholesterol distribution, PrPC trafficking, cell activation and PrPSc formation is required before cholesterol manipulation can be considered as a prion therapeutic.
authors.affiliation: Department of Pathology and Infectious Diseases, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts, UK, AL9 7TA. cbate@rvc.ac.uk
authors.forename: Clive
authors.initials: C
authors.lastname: Bate
authors.forename: Mourad
authors.initials: M
authors.lastname: Tayebi
authors.forename: Luisa
authors.initials: L
authors.lastname: Diomede
authors.forename: Mario
authors.initials: M
authors.lastname: Salmona
authors.forename: Alun
authors.initials: A
authors.lastname: Williams
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D004281:Docosahexaenoic Acids / Q000378:metabolism / Q000494:pharmacology*; D015118:Eicosapentaenoic Acid / Q000378:metabolism / Q000494:pharmacology*; D008798:Mevalonic Acid / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D064801:Phospholipase A2 Inhibitors; D054467:Phospholipases A2 / Q000378:metabolism; D018621:PrPC Proteins / Q000378:metabolism; D018620:PrPSc Proteins / Q000378:metabolism; D011328:Prions / Q000378:metabolism*; D019821:Simvastatin / Q000378:metabolism / Q000494:pharmacology
chemical_list: D064801:Phospholipase A2 Inhibitors; D018621:PrPC Proteins; D018620:PrPSc Proteins; D011328:Prions; D004281:Docosahexaenoic Acids; D002784:Cholesterol; D015118:Eicosapentaenoic Acid; D019821:Simvastatin; D054467:Phospholipases A2; D008798:Mevalonic Acid
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