Single extracellular vesicle analysis in human amniotic fluid shows evidence of phenotype alterations in preeclampsia

Amniotic fluid surrounding the developing fetus is a complex biological fluid rich in metabolically active bio‐factors. The presence of extracellular vesicles (EVs) in amniotic fluid has been mainly related to foetal urine. We here characterized EVs from term amniotic fluid in terms of surface marker expression using different orthogonal techniques. EVs appeared to be a heterogeneous population expressing markers of renal, placental, epithelial and stem cells. Moreover, we compared amniotic fluid EVs from normal pregnancies with those of preeclampsia, a hypertensive disorder affecting up to 8% of pregnancies worldwide. An increase of CD105 (endoglin) expressing EVs was observed in preeclamptic amniotic fluid by bead‐based cytofluorimetric analysis, and further confirmed using a chip‐based analysis. HLA‐G, a typical placental marker, was not co‐expressed by the majority of CD105(+) EVs, in analogy with amniotic fluid stromal cell derived‐EVs. At a functional level, preeclampsia‐derived EVs, but not normal pregnancy EVs, showed an antiangiogenic effect, possibly due to the decoy effect of endoglin. Our results provide a characterization of term amniotic fluid‐EVs, supporting their origin from foetal and placental cells. In preeclampsia, the observed antiangiogenic characteristics of amniotic fluid‐EVs may reflect the hypoxic and antiangiogenic microenvironment and could possibly impact on the developing fetus or on the surrounding foetal membranes.