Expression of erythropoietin by the human placenta

Circulating levels of maternal erythropoietin (EPO) rise during gestation due to increased biosynthesis of the hormone. Our objective was to investigate the human placenta as a potential extrarenal site of EPO production. Using two monoclonal antibodies recognizing different antigenic determinants, we identified immunoreactive EPO associated with villous cytotrophoblast, endovascular and intravascular cytotrophoblast, cytotrophoblast cell columns, and syncytiotrophoblast of first and second-trimester placenta as well as syncytiotrophoblast and extravillous cytotrophoblast of normal third-trimester and preeclamptic placenta. In addition, cultured JAR (trophoblast-derived) choriocarcinoma cells, cytotrophoblasts isolated from term placenta, villous core cells, and possibly other nontrophoblast cells within the decidual basal plate expressed immunoreactive EPO. Using reverse transcription-polymerase chain reaction and EPO-specific primers, a 378 bp DNA product was amplified from placental tissues of various gestational ages, cytotrophoblasts isolated from term placenta, and JAR choriocarcinoma cells. The amplified product yielded restriction enzyme fragments of predicted sizes. On Southern analysis, hybridization was observed for two of these fragments in which the radiolabeled EPO cDNA probe did not overlap with the primer sequences. Finally, the JAR choriocarcinoma cells elaborated EPO into the culture medium as determined by enzyme-linked immunosorbant assay and expressed EPO mRNA as determined by Northern analysis, both of which were stimulated by hypoxia (15-20 torr). Taken together, these results suggest a new site of EPO expression: the trophoblast cell of the human placenta.