Role of glycosylphosphatidylinositols in the activation of phospholipase A2 and the neurotoxicity of prions.
Prion-induced neuronal injury in vivo is associated with prostaglandin E(2) production, a process that can be reproduced in tissue-culture models of prion disease. In the present study, neuronal phospholipase A(2) was activated by glycosylphosphatidylinositols (GPIs) isolated from the cellular prion protein (PrP(c)) or from disease-associated isoforms (PrP(Sc)), resulting in prostaglandin E(2) production, but not by GPIs isolated from Thy-1. The ability of GPIs to activate neuronal phospholipase A(2) was lost following the removal of acyl chains or cleavage of the phosphatidylinositol-glycan linkage, and was inhibited by a mAb that recognized phosphatidylinositol. In competition assays, pretreatment of neurons with partial GPIs, inositol monophosphate or sialic acid reduced the production of prostaglandin E(2) in response to a synthetic miniprion (sPrP106), a synthetic correlate of a PrP(Sc) species found in Gerstmann-Straussler-Scheinker disease (HuPrP82-146), prion preparations or high concentrations of PrP-GPIs. In addition, neurons treated with inositol monophosphate or sialic acid were resistant to the otherwise toxic effects of sPrP106, HuPrP82-146 or prion preparations. This protective effect was selective, as inositol monophosphate- or sialic acid-treated neurons remained susceptible to the toxicity of arachidonic acid or platelet-activating factor. Addition of PrP-GPIs to cortical neuronal cultures increased caspase-3 activity, a marker of apoptosis that is elevated in prion diseases. In contrast, treatment of such cultures with inositol monophosphate or sialic acid greatly reduced sPrP106-induced caspase-3 activity and, in co-cultures, reduced the killing of sPrP106-treated neurons by microglia. These results implicate phospholipase A(2) activation by PrP-GPIs as an early event in prion-induced neurodegeneration.
Bate
Clive
C
Department of Veterinary Pathology, Glasgow University Veterinary School, Bearsden Road, Glasgow G61 1QH, UK.
Williams
Alun
A
Department of Pathology and Infectious Diseases, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA, UK.
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D015232:Dinoprostone / Q000096:biosynthesis; D004789:Enzyme Activation; D017261:Glycosylphosphatidylinositols / Q000502:physiology*; D051379:Mice; D017628:Microglia / Q000502:physiology; D009410:Nerve Degeneration; D009474:Neurons / Q000473:pathology*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011328:Prions / Q000633:toxicity*
D061945:Caspase Inhibitors; D017261:Glycosylphosphatidylinositols; D011328:Prions; D010741:Phospholipases A; D054467:Phospholipases A2; C505409:Casp3 protein, mouse; D053148:Caspase 3; D015232:Dinoprostone