Cytosolic phospholipase A₂α upregulation mediates apoptotic neuronal death induced by aggregated amyloid-β peptide _1-42

Increased cytosolic phospholipase A₂α (cPLA ₂α) immunoreactivity and transcript were observed in Alzheimer's disease (AD) brain associated with amyloid deposits. Thus, the present study examined whether cPLA₂α upregulation participate in cortical neuron damage induced by aggregated Aβ_1-42 and determined its role in the signaling events leading to damage, using an antisense technology. Exposure of primary cortical neurons to 1 μM aggregated Aβ_1-42 for 24 h induced up-regulation and activation of cPLA₂α and apoptotic cell death of about 30% as detected by: cell count, MTT reduction, caspases-3 and -8 activation, DAPI and TUNEL staining, that were prevented by inhibition of cPLA₂α up-regulation and activity in the presence of antisense against cPLA ₂α (AS). cPLA₂α was rapidly activated upon addition of aggregated Aβ_1-42, as determined by its phosphorylated form on serine 505, and this activity was dependent on NADPH oxidase activity. NOX2- and NOX4-NADPH oxidase upregulation at 24 h of aggregated Aβ_1-42 exposure was not affected by the presence of AS, but superoxide production was reduced, probably due to NOX2 inhibition. cPLA₂α upregulation led to activation of neutral sphingomyelinase (N-SMase) as its activity was inhibited in the presence of AS, and could be restored by addition of arachidonic acid. Addition of ceramide analog induced caspase-8 activation leading to caspase-3 activation and apoptotic neuronal death. In conclusion, our results suggest that cPLA ₂α activity plays a crucial role in the signaling cascade leading to apoptotic neuronal death by aggregated Aβ_1-42 probably via activation of N-SMase, ceramide production and caspases-3 and -8.