Human lymphocytes stimulate prostacyclin synthesis in human umbilical vein endothelial cells. Involvement of endothelial cPLA2

Abstract

Prostacyclin (PGI2) contributes to the maintenance of a nonadhesive luminal surface in blood vessels due to its anti-platelet and vasodilatory properties. Here, we sought to determine whether peripheral blood lymphocytes (PBL) may regulate the PGI2 production of human umbilical vein endothelial cells (HUVEC). Cell-cell contact between HUVEC and lymphocytes markedly enhanced PGI2 synthesis as a function of the number of lymphocytes added. This stimulated synthesis was totally suppressed when lymphocytes and HUVEC were separated by a microporous insert. It was not due to prostaglandin H synthase up-regulation. The pretreatment of lymphocytes with the PGI2 synthase inhibitor tranylcypromine partially inhibited PGI2 synthesis (47%), suggesting a transcellular metabolism of the endothelial prostaglandin endoperoxide PGH2 by the lymphocyte PGI2 synthase. Experiments using [14C]arachidonate-labeled lymphocytes coincubated with unlabeled HUVEC, and [14C]arachidonate-labeled HUVEC coincubated with unlabeled lymphocytes showed that the arachidonic acid used for PGI2 synthesis was totally of endothelial origin. Furthermore, the PGI2 synthesis was strongly inhibited by the cytosolic phospholipase A2 inhibitor, MAFP and totally suppressed by the combination of the calcium chelators, BAPTA and EGTA. Collectively, these results suggest that lymphocytes trigger an outside-in signaling in endothelial cells involving cPLA2 activation. Overall, the switch-on for PGI2 synthesis induced by lymphocytes might serve as a protection against atherothrombogenesis.