Differential expression of type II, IV and cytosolic PLA(2) messenger RNA in human intrauterine tissues at term

The involvement of phospholipase A(2) (PLA(2)) enzymes in the formation of biologically-active phospholipid metabolites by human gestational tissues has principally been characterized by the use of enzyme activity assays. While such assays have established the presence of functional PLA(2) activity, there is a paucity of information concerning the tissue distribution and relative contribution to net activity made by specific PLA(2) isozymes. In particular, both secretory and cytosolic isozymes may be involved in gestational tissue phospholipid metabolism. Thus, the aim of this study was to test the hypothesis that phospholipase A(2) mRNA transcripts encoding Type II, Type IV and cytosolic PLA(2), are tissue-specifically expressed in human amnion, choriodecidua and placenta obtained at term. The relative expression of polyA(+) mRNA encoding these PLA(2) isozymes was determined by Northern blot analysis and laser densitometry. The data obtained confirm the tissue-specific expression of PLA(2) mRNA in human intrauterine tissues. Cytosolic PLA(2) mRNA was most abundantly expressed in amnion when compared to either choriodecidua (which was 5-fold less than amnion; P < 0.001) or placenta (72-fold less than amnion; P < 0.001). In contrast, the secretory PLA(2) mRNA transcripts (i.e. Type II and Type IV) were most abundantly expressed in placenta. Type II PLA(2) mRNA expression in choriodecidua and amnion was 30-fold less than that observed in placenta (both P < 0.001). Type IV PLA(2) mRNA expression was 37-fold (P < 0.001) and 73-fold (P < 0.001) less in choriodecidua and amnion respectively. These data support the conclusion that cytosolic PLA(2) is the principal PLA(2) isozyme mediating phospholipid metabolism and the liberation of fatty acid substrate (i.e. arachidonic acid) in term amnion, while secretory PLA(2) isozymes, and in particular, Type II PLA(2), play a major role in phospholipid metabolism in term placenta.