Polarized secretion of extracellular vesicles from the placenta to maternal and fetal bloodstreams in rats

The placenta is a maternal organ that secretes various proteins that support maternal pregnancy and fetal growth. Placenta-derived extracellular vesicles (EVs) encapsulate these proteins and are secreted into the maternal or fetal bloodstream in a polarized manner. In this study, we aimed to elucidate the distinct protein expression profiles of EV-enriched fractions obtained from the uterine veins, umbilical veins, and umbilical arteries of pregnant rats. EV-rich fractions were prepared from the plasma of pregnant rats using the Mag-NET method. In total, 2839 protein groups in the EV fractions were identified using global proteomics. The protein expression profiles of the EVs derived from the uterine veins mostly differed from those derived from the umbilical veins/arteries. However, a very limited difference in protein abundance was observed between the umbilical veins and arteries. The abundances of fetuin-B and alpha-fetoprotein were considerably greater in EVs from the uterine veins and umbilical veins/arteries, respectively, which is consistent with previous results. Prolactin-like hormones were predominantly expressed in EV-rich fractions collected from the uterine vein. These results suggest that the placenta undergoes polarized secretion of EVs into the maternal and fetal bloodstreams.