Placental syncytiotrophoblast extracellular vesicles enter primary endothelial cells through clathrin-mediated endocytosis.

Introduction: The aim was to investigate syncytiotrophoblast extracellular vesicle (STBEV) uptake mechanisms by primary endothelial cells, the effects on gene expression, cell activation as well as the effect of aspirin.

Methods: The STBEVs were derived using the placental perfusion system, from normal or preeclamptic placentas. Endothelial uptake was analysed with flow cytometry. To elucidate uptake, different inhibitors were tested; Cytochalasin D, Chlorpromazine hydrochloride, Methyl-B-cyclodextrin, Dynasore and Wortmannin. Endothelial gene expression was evaluated using an endothelial cell biology qPCR array. Cell activation was studied by ICAM-1 surface expression after STBEV exposure, with and without aspirin treatment.

Results: Normal and preeclamptic STBEV uptake was blocked in similar ways. Chlorpromazine, Dynasore and Wortmannin almost completely blocked STBEV uptake. Methyl-B-cyclodextrin blocked 45-60% of the uptake while Cytochalasin D did not block uptake at all. Neither normal nor preeclamptic STBEVs had any significant effects on endothelial gene expression. Normal STBEVs down-regulated cell surface protein ICAM-1 expression, with and without aspirin treatment. Aspirin had no effect on STBEV uptake or cellular gene expression on its own, however it down regulated ICAM-1 protein expression in combination with preeclamptic STBEV exposure.

Discussion: STBEV uptake primarily occurred through clathrin-mediated endocytosis. The STBEVs had no significant effect on gene expression but did have effects on ICAM-1 surface expression. The prophylactic mechanisms of aspirin may be by preventing the endothelium from being activated by the preeclamptic STBEVs.