Involvement of phospholipase A2 in the supply of fatty acids required for cholesterol esterification associated with uptake of oxidized low-density lipoprotein in macrophages

The formation of foam cells, a critical event in the early stages of atherosclerosis, is associated with the uptake of oxidized low-density lipoprotein (oxLDL) by macrophages and the subsequent accumulation of cholesterol ester formed by the catalytic action of acyl-CoA: cholesterol acyltransferase (ACAT). Although free cholesterol, a substrate for ACAT, is supplied from the intracellular cholesterol pool, little is known about the pathways involved in the supply of fatty acids, precursors for fatty acyl-CoA as another substrate for ACAT. Our recent studies were undertaken to examine the possible involvement of phospholipase A(2) (PLA(2)) in the supply of fatty acids required for the cholesterol esterification. In mouse peritoneal macrophages and RAW264.7 macrophages, oxLDL induced the liberation of fatty acids from membrane phospholipids to increase cholesterol ester having the fatty acids as an acyl chain. The changes in these lipids were suppressed by the inhibition of cytosolic PLA(2) (cPLA(2)). Although oxLDL did not affect the activity or amounts of cPLA(2), preincubation with oxLDL enhanced the release of fatty acids induced by Ca2+ ionophore, which accelerates the hydrolytic action of cPLA(2). We further observed that oxLDL induced the generation of ceramide through the de novo synthesis. Exogenous ceramide and 13-hydroxyoctadecadienoic acid, an oxidized lipid in oxLDL particles, also stimulated fatty acid release. Based on these findings, we propose that oxLDL activates cPLA(2) to supply fatty acids required for the cholesterol esterification, through the acceleration of the hydrolytic action of cPLA(2) by endogenous ceramide and by oxidized lipids in oxLDL particles in macrophages.