Lysophosphatidylcholine Stimulates the Release of Arachidonic Acid in Human Endothelial Cells

Abstract

Lysophosphatidylcholine (lyso-PC) is a product of phosphatidylcholine hydrolysis by phospholipase A 2 (PLA 2 ) and is present in cell membranes, oxidized lipoproteins, and atherosclerotic tissues. It has the ability to alter endothelial functions and is regarded as a causal agent in atherogenesis. In this study, the modulation of arachidonate release by lyso-PC in human umbilical vein endothelial cells was examined. Incubation of endothelial cells with lyso-PC resulted in an enhanced release of arachidonate in a time-and concentration-dependent manner. Maximum arachidonate release was observed at 10 min of incubation with 50 M lyso-PC. Lyso-PC species containing palmitoyl (C 16:0 ) or stearoyl (C 18:0 ) groups elicited the enhancement of arachidonate release, while other lysolipids such as lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol, or lysophosphatidate were relatively ineffective. Lyso-PC-induced arachidonate release was decreased by treatment of cells with PLA 2 inhibitors such as para-bromophenacyl bromide and arachidonoyl trifluoromethyl ketone. Furthermore, arachidonate release was attenuated in cells grown in the presence of antisense oligodeoxynucleotides that specifically bind cytosolic PLA 2 mRNA. Treatment of cells with lyso-PC resulted in a translocation of PLA 2 activity from the cytosolic to the membrane fractions of cells. Lyso-PC induced a rapid influx of Ca 2؉ from the medium into the cells, with a simultaneous enhancement of protein kinase C (PKC) activity in the membrane fractions. The lyso-PC-induced arachidonate release was attenuated when cells were preincubated with specific inhibitors of PKC (staurosporine and Ro31-8220) or a specific inhibitor of mitogen-activated protein kinase/extracellular regulated kinase kinase (PD098059). Taken together, the results of this study show that lyso-PC caused the elevation of cellular Ca 2؉ and the activation of PKC, which stimulated cytosolic PLA 2 in an indirect manner and resulted in an enhanced release of arachidonate.

Mechanisms by Which Elevated Intracellular Calcium Induces S49 Cell Membranes to Become Susceptible to the Action of Secretory Phospholipase A2

“…4). A stimulatory effect of lyso-PPC on cPLA 2 has also been reported previously (41), and the coupling of this event to hydrolysis by sPLA 2 was consistent with the proposal of Balsinde and Dennis (29). The second mechanism, also requiring calcium, was independent of the action of cPLA 2 and appeared to involve membrane perturbations such as transbilayer migration of phospholipids and production of microvesicles (see below).…”

“…As shown in Fig. 6, panel A, the release of fatty acid from the membrane normally observed upon the addition of lyso-PPC alone (5 M; curve a) was blocked by MAFP (curve b) consistent with a previous observation that lysolecithin can activate cPLA 2 (41). Also, the rate of hydrolysis upon addition of human sPLA 2 was reduced in cells treated with MAFP (Fig.…”

Membrane translocation of TRPC6 channels and endothelial migration are regulated by calmodulin and PI3 kinase activation

“…S9C), suggesting that G i -proteins are not involved. LysoPC can induce arachadonic acid release (25), causing Ca 2+ entry through arachidonate-regulated Ca 2+ channels (26). This could contribute to the Ca 2+ needed for Src kinase activation and subsequent events.…”

Mycobacterial Lysocardiolipin Is Exported from Phagosomes upon Cleavage of Cardiolipin by a Macrophage-Derived Lysosomal Phospholipase A2

“…Therefore, lysocardiolipin may be a candidate lipid involved in preventing phagolysosome fusion or suppression of CD4 T cell functions (26,31). Furthermore, lysophospholipids can influence signal transduction pathways, e.g., by stimulating arachidonic acid release and activating protein kinase C (32,33).…”