Abstract
Changes in endothelium functions during ischemia are thought to be of importance in numerous pathological conditions, with, for instance, an increase in the release of inflammatory mediators like prostaglandins. Here, we showed that hypoxia increases phospholipase A2 (PLA2) activity in human umbilical vein endothelial cells. Both basal PLA2 activity and PG synthesis are sensitive to BEL and AACOCF3, respectively, inhibitors of calcium-independent PLA2 (iPLA2) and cytosolic PLA2 (cPLA2), while OPC, an inhibitor of soluble PLA2 (sPLA2) only inhibited the hypoxia-induced AA release and PGF2α synthesis. Hypoxia does not alter expression of iPLA2, sPLA2 and cPLA2 and cycloheximide did not inhibit PLA2 activation, indicating that hypoxia-induced increase in PLA2 activity is due to activation rather than induction. However, mRNA levels for sPLA2 displayed a 2-fold increase after 2 hr incubation under hypoxia. BAPTA, an intracellular calcium chelator, partially inhibited the AA release in normoxia and in hypoxia. Direct assays of specific PLA2 activity showed an increase in sPLA2 activity but not in cPLA2 activity after 2 hr hypoxia. Taken together, these results indicate that the hypoxia-induced increase in PLA2 activity is mostly due to the activation of sPLA2.
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