Cytosolic phospholipase A2α inhibition prevents neuronal NMDA receptor-stimulated arachidonic acid mobilization and prostaglandin production but not subsequent cell death.

Phospholipase A2 (PLA2) enzymes encompass a superfamily of at least 13 extracellular and intracellular esterases that hydrolyze the sn-2 fatty acyl bonds of phospholipids to yield fatty acids and lysophospholipids. The purpose of this study was to characterize which phospholipase paralog regulates NMDA receptor-mediated arachidonic acid (AA) release. Using mixed cortical cell cultures containing both neurons and astrocytes, we found that [3H]-AA released into the extracellular medium following NMDA receptor stimulation (100 μM) increased with time and was completely prevented by the addition of the NMDA receptor antagonist MK-801 (10 μM) or by removal of extracellular Ca2+. Neither diacylglycerol lipase inhibition (RHC-80267; 10 μM) nor selective inhibition of Ca2+-independent PLA2 [bromoenol lactone (BEL); 10 μM] alone had an effect on NMDA receptor-stimulated release of [3H]-AA. Release was prevented by methyl arachidonyl fluorophosphonate (MAFP) (5 μM) and AACOCF3 (1 μM), inhibitors of both cytosolic PLA2 (cPLA2) and Ca2+-independent PLA2 isozymes. This inhibition effectively translated to block of NMDA-induced prostaglandin (PG) production. An inhibitor of p38MAPK, SB 203580 (7.5 μM), also significantly reduced NMDA-induced PG production providing suggestive evidence for the role of cPLA2α. Its involvement in release was confirmed using cultures derived from mice deficient in cPLA2α, which failed to produce PGs in response to NMDA receptor stimulation. Interestingly, neither MAFP, AACOCF3 nor cultures derived from cPLA2α null mutant animals showed any protection against NMDA-mediated neurotoxicity, indicating that inhibition of this enzyme may not be a viable protective strategy in disorders of the cortex involving over-activation of the NMDA receptor. [ABSTRACT FROM AUTHOR]