Hydrolysis of lipoproteins by sPLA2's enhances mitogenesis and eicosanoid release from vascular smooth muscle cells: Diverse activity of sPLA2's IIA, V and X.

Mitogenesis of Vascular Smooth Muscle Cells (VSMC) plays an important role in atherogenesis. Until recently, the effect of lipid subfractions has not been clarified. Secretory phospholipases A2 (sPLA2's) hydrolyse glycerophospholipids and release pro-inflammatory lyso-lipids, oxidized and non-oxidized fatty acids and isoprostanes. They localize in the vascular wall. We hypothesized that structurally similar sPLA2's may exert different impact on VSMC. The influence of sPLA2's, IIA, V, X, HDL, LDL, and hydrolysis products was tested on mitogenesis of VSMC, i.e., the early effect on the cell membrane phospholipids, and on PGE2 and LTB4 release, i.e., late effect of Cyclooxygenase and 5-lipooxygenase activity in VSMC. Mitogenesis was significantly enhanced by HDL and LDL, and by products of sPLA2 hydrolysis. Hydrolysis of HDL or LDL enhanced mitogenic activity in order V>X>IIA. The release of PGE2 was enhanced by group X sPLA2 and by HDL hydrolyzed by groups V and X. LDL and its hydrolysis products enhanced the release of PGE2 in order X>V>IIA. The release of LTB4 was markedly increased by LDL and HDL, and by hydrolytic products of group V and X, but not group IIA sPLA2. Our study demonstrates a diverse interaction of pro-inflammatory sPLA2's with HDL and LDL affecting both mitogenesis and eicosanoid release from VSMC, therefore potentially enhancing their pro-atherogenic activity.