Phospholipase A2 is involved in muscarinic receptor-mediated sAPPα release independently of cyclooxygenase or lypoxygenase activity in SH-SY5Y cells

The release of soluble amyloid precursor protein α (sAPPα), produced during α-secretase processing by cleavage within the β amyloid peptide domain of APP, is highly regulated by several external and internal signals. Because evidence suggests the involvement of inflammatory processes in the pathology of Alzheimer's disease and APP formation, we examined the involvement of the phospholipase A2 (PLA2) pathway and of its downstream cyclooxygenase (COX) and lipoxygenase (LOX) pathways in the regulation of sAPPα, release induced by muscarinic receptor activation in SH-SY5Y cells. The amount of sAPP released into the culture medium was analyzed using a monoclonal 6E10 antibody detecting sAPPα. Treatment with the PLA2 inhibitor, manoalide, blocked the release of oxoM (muscarinic receptor agonist)-stimulated sAPPα, and the muscarinic receptor-mediated sAPPα release was increased by the non-selective PLA2 activator mellitin. COX and LOX inhibitors inhibited exogenous AA-induced sAPPα release, but upregulated basal constitutive sAPPα release. However, treatment with COX or LOX inhibitors failed to significantly change oxoM-stimulated sAPPα release, and furthermore, muscarinic receptor activation inhibited AA-stimulated COX activity. Our results suggest that sAPPα release induced by muscarinic receptor activation is regulated by AA generation via PLA2 activation independently of COX and LOX activities, but that the COX and LOX pathways are possibly involved in the constitutive release of sAPPα.