Human placenta makes extracellular glutathione peroxidase and secretes it into maternal circulation

Extracellular glutathione peroxidase (eGPX) is a selenoglycoprotein distinct from cellular glutathione peroxidase (cGPX). The cDNA for eGPX has recently been cloned from human placenta. To determine whether human placenta makes both cGPX and eGPX and secretes eGPX, we used specific immunoprecipitations of 75Se metabolically labeled proteins from full-term placental explants in culture and perfused placental lobules. Placental explants and metabolically active, dually perfused placental lobules synthesized and contained both cGPX and eGPX and secreted eGPX. Perfused tissue secreted eGPX into the maternal but not into the fetal perfusate. In situ hybridizations using antisense and sense eGPX riboprobes were performed on sections of first-, second-, and third-trimester placentas. In the first-trimester placenta, transcripts were localized predominantly to cytotrophoblast cells, whereas in the full-term placenta syncytiotrophoblast cells and stromal cells but not fetal endothelial cells expressed eGPX mRNA. It is concluded that human placenta synthesizes both cGPX and eGPX and secretes eGPX into the maternal circulation, consistent with the location of the eGPX mRNA.