The oxidation of plasma LDLs (
low-density lipoproteins) is a key event in the pathogenesis of
atherosclerosis. LPC (
lysophosphatidylcholine) and
oxysterols are major
lipid constitutents of oxidized LDLs. In particular,
7-oxocholesterol has been found in plasma from cardiac patients and
atherosclerotic plaque. In the present study, we investigated the ability of
7-oxocholesterol and LPC to regulate the activation of eNOS (
endothelial nitric oxide synthase) and cPLA2 (cytosolic
phospholipase A2) that synthesize two essential factors for vascular wall integrity, NO (
nitric oxide) and
arachidonic acid. In endothelial cells from human umbilical vein cords, both
7-oxocholesterol (150 microM) and LPC (20 microM) decreased
histamine-induced NO release, but not the release activated by
thapsigargin. The two
lipids decreased NO release through a PI3K (phosphoinositide 3-kinase)-dependent pathway, and decreased eNOS phosphorylation. Their mechanisms of action were, however, different. The NO release reduction was dependent on
superoxide anions in LPC-treated cells and not in 7-oxocholesterol-treated ones. The Ca2+ signals induced by
histamine were abolished by LPC, but not by
7-oxocholesterol. The
oxysterol also inhibited (i) the
histamine- and
thapsigargin-induced
arachidonic acid release, and (ii) the phosphorylation of both cPLA2 and ERK1/2 (
extracellular-signal-regulated kinases 1/2). The results show that
7-oxocholesterol inhibits eNOS and cPLA2 activation by altering a Ca2+-independent upstream step of PI3K and ERK1/2 cascades, whereas LPC desensitizes eNOS by interfering with receptor-activated signalling pathways. This suggests that
7-oxocholesterol and LPC generate signals which cross-talk with heterologous receptors, effects which could appear at early stage of
atherosclerosis.