Developmental maturation of baboon placental trophoblast: expression of messenger ribonucleic acid and protein levels of cytosolic and secretory phospholipases A2.

Although the human placenta at term exhibits high levels of phospholipase A2 (PLA2) enzyme activity, our understanding of the ontogenesis, regulation, and specific roles of placental phospholipases A2 remains relatively incomplete. Using the baboon as the experimental model, the present study determined whether the levels of the messenger ribonucleic acid (mRNA) for the cytosolic (cPLA2) and/or type IIa, nonpancreatic secretory (sPLA2) enzymes are developmentally regulated and modulated by glucocorticoid treatment. Total RNA was extracted from whole villous placenta obtained on days 60 (early; n = 3), 100 (mid; n = 3), and 165 (late; n = 4) of gestation (term = day 184) from untreated baboons and on day 100 (n = 4) after maternal administration on days 60-99 of betamethasone (3 mg/day). The complementary DNA to cPLA2 recognized a single 2.9-kb mRNA transcript in both baboon and human placenta. Mean (+/-SE) levels of cPLA2 mRNA, expressed, in arbitrary units as a ratio to that of beta-actin, were similar at early (0.19 +/- 0.05) and midgestation (0.34 +/- 0.17) and increased (P < 0.005) 10-fold (2.53 +/- 0.53) by late gestation. Levels of cPLA2 protein were also greater (P < 0.05) on day 165 (2.6 +/- 0.3 arbitrary units) than on day 60 (0.6 +/- 0.2). Like that in the human, the baboon placenta contained very high levels of a single 0.9-kb mRNA transcript for sPLA2. In contrast to that of cPLA2, normalized levels of sPLA2 mRNA were similar at all three time points and were associated with high levels of sPLA2 protein throughout gestation. Treatment with betamethasone increased (P < 0.02) cPLA2 mRNA levels on day 100 by over 4-fold, but had no effect on sPLA2 mRNA levels. Additional studies indicated that the mRNAs for sPLA2 and cPLA2 were detected in an enriched fraction of nontrophoblast cells isolated by collagenase dispersion and Percoll density centrifugation. The mRNA for cPLA2 was also expressed in cytotrophoblast and syncytiotrophoblast cell fractions. Collectively, these findings indicate that the baboon placenta expresses mRNA and protein for both the cytosolic and secretory PLA2 enzymes, and that expression of cPLA2 is developmentally regulated and modulated by glucocorticoids. We previously demonstrated an estrogen-dependent developmental increase in placental expression of specific components of the progesterone steroidogenic pathway during the second half of baboon pregnancy. The current findings indicate that the developmental increase in placental function also includes expression of at least one specific PLA2 enzyme controlling arachidonic acid mobilization and eicosanoid synthesis.