Endothelial Dysfunction in Severe Preeclampsia is Mediated by Soluble Factors, Rather than Extracellular Vesicles

In severe early-onset preeclampsia (sPE) the placenta releases soluble angiogenesis-regulating proteins, trophoblast-derived fragments, and extracellular vesicles (EVs). Their relative importance in disease pathogenesis is not presently understood. We explanted placental villi from healthy and sPE women then separated the media into: total-conditioned, EV-depleted and EV-enriched media. Three fractions were compared for; angiogenic protein secretion by ELISA, angiogenic and inflammation gene mRNA expression and leukocyte adhesion assay. sPE placental villi secreted significantly less PlGF (70 ± 18 pg/mL) than preterm controls (338 ± 203; p = 0.03). sFlt-1:PlGF ratios in total-conditioned (115 ± 29) and EV-depleted media (136 ± 40) from sPE placental villi were significantly higher than in EV-enriched media (42 ± 12; p < 0.01) or any preterm or term media. Fluorescent-labeled EVs derived across normal gestation, but not from sPE, actively entered HUVECs. From sPE placental villi, the soluble fraction, but not EV-enriched fraction, significantly repressed angiogenesis (0.83 ± 0.05 fold, p = 0.02), induced HO-1 mRNA (15.3 ± 5.1 fold, p < 0.05) and induced leukocyte adhesion (2.2 ± 0.4 fold, p = 0.04). Soluble media (total-conditioned and EV-depleted media) from sPE placental villi induced endothelial dysfunction in HUVEC, while the corresponding EV-enriched fraction showed no such effects. Our data suggest that soluble factors including angiogenesis-regulating proteins, dominate the vascular pathology of this disease.