Regulation of Phospholipase A2 in Human Amnion

University Of Texas Hlth Science Center, San Antonio TX

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Abstract

DESCRIPTION (provided by applicant): The amnion is a major site of PGE2 production during labor and is a rich source of arachidonic acid, the precursor of PG production. In the fetal membranes, the amnion fibroblast cells produce approx 50-fold greater PGE2 per cell and overall account for a 5-fold greater production than the amnion epithelium. In the amnion fibroblasts, we have shown glucocorticoids increase PGE2 synthesis by up-regulation of cPLA2 and PGHS-2 enzymes. We described the presence of both the cytosolic and microsomal PGE synthase isoforms (cPGES and mPGES) in fetal membranes but that their expression did not change with gestational age or labor, nor were they induced by glucocorticoid treatment in isolated epithelial or fibroblast cells. The enzymes in the arachidonic acid cascade are now know to be functionally coupled at discrete cellular locations to produce specific PG's. We do not know if cPLA2 and PGHS-2 are coupled to either cPGES or mPGES in amnion cells at labor to produce PGE2. In fetal membranes obtained from patients at term, we observed a punctuate pattern of immunostaining for cPGES and mPGES, identical to that with Sudan Black B, a stain for lipid. Thus these enzymes may localize to lipid bodies (lipid droplets) which are foci for production of eicosanoids in inflammatory cells where cPLA2, PGHS-2, p38 MAP kinase and ERK1, 2 signal transduction molecules are associated with them. Lipid bodies can be lost during tissue or cell fixation possibly accounting for the previous absence of recognition in fetal membranes. Adipophilin and perilipin are found in association with lipid droplets perhaps serving structural and functional roles in various cell types. Both adipophilin and perilipin expression are upregulated by ligands to the transcription factor PPAR-gamma. We have demonstrated increasing adipophilin expression in the human fetal membranes throughout gestation, apparently in association with lipid bodies. Adipophilin was recently shown to be inducible by hypoxia and it is possible that in the avascular fetal membranes hypoxia may regulate adipophilin expression. The hypotheses to be tested are that either cPGES or mPGES are functionally coupled to cPLA2, and PGHS-2 to produce PGE2 at labor, that this may occur in lipid droplets, which are sites of accumulation of enzymes involved in eicosanoid synthesis including, cPLA2, PGHS-2, cPGES, mPGES, p38MAP Kinase and ERK1, 2, and that the PPAR-gamma and hypoxia-regulated proteins adipophilin and peripin play key roles in assembly and function of lipid droplets.