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Developmental Maturation of Baboon Placental Trophoblast: Expression of Messenger Ribonucleic Acid and Protein Levels of Cytosolic and Secretory Phospholipases A₂¹

Departments of Biochemistry (M.D.R.) and Physiology (G.J.P.), Eastern Virginia Medical School, Norfolk, Virginia 23501; and the Departments of Obstetrics/Gynecology/Reproductive Sciences and Physiology, Center for Studies in Reproduction (E.D.A.), University of Maryland School of Medicine, Baltimore, Maryland 21201

Address all correspondence and requests for reprints to: Gerald J. Pepe, Ph.D., Department of Physiology, Eastern Virginia Medical School, P.O. Box 1980, Norfolk, Virginia 23501-1980. E-mail: GJP{at}borg.evms.edu

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 ß-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.