Co-localization of microsomal prostaglandin E synthase-1 with cyclooxygenase-1 in layer II of murine placental syncytiotrophoblasts

Abstract The placenta is an organ that secretes prostaglandin (PG) E 2 into the fetal-placental circulation to regulate both vascular tone and remodeling of the fetal ductus arteriosus. Placental PGE 2 synthesis might be mediated by microsomal PGE synthase-1 (mPGES-1), in addition to cyclooxygenase (COX) isoforms. Thus, the purpose of this study is to clarify the temporal and spatial expression patterns of mPGES-1, together with COX-1 and COX-2, in murine placenta. We found that mPGES-1 and COX-1 protein levels continuously increased in the placental labyrinth from gestational day (GD) 13.5 to GD19.5, becoming higher than in the decidua or the junctional zone by GD17.5. The PGE 2 level at GD17.5 was also highest in the labyrinth. Immunofluorescence stainings for mPGES-1 and COX-1 in the labyrinth at GD17.5 overlapped and were located on the fetal side of the signals for connexin 26, which forms gap junctions between maternal-facing (SynT-I) and fetal-facing (SynT-II) syncytiotrophoblast layers, and on the maternal side of the signals for glucose transporter 1 on the basal plasma membrane of SynT-II. On the other hand, the signals for COX-2 did not overlap with those for mPGES-1. These results indicate that COX-1 and mPGES-1 are co-localized in murine placental SynT-II, facing the fetal-placental circulation. Therefore, SynT-II could contribute to placental synthesis of PGE 2 for release into the fetal-placental circulation.