Characterisation of Syncytiotrophoblast Vesicles in Normal Pregnancy and Pre-Eclampsia: Expression of Flt-1 and Endoglin

Abstract

BackgroundThe placental syncytiotrophoblast releases micro and nanovesicles (STBM), into the maternal circulation in normal pregnancy and in increased amounts in pre-eclampsia (PE), which have proinflammatory and antiangiogenic activity and are implicated in PE pathophysiology. Better characterisation of STBM is essential to understand their role in PE.Methods and ResultsSTBM prepared by placental lobe dual perfusion (pSTBM) and mechanical disruption (mSTBM) were analysed by four colour flow cytometry (4CFC), nanoparticle tracking analysis (NTA) and Western blotting to determine vesicle size, purity and Flt-1 and endoglin (Eng) expression. Biological activity of STBM associated Flt-1 and endoglin was assessed by the ability of VEGF, PlGF and TGFβ to bind to mSTBM and inhibit mSTBM induced endothelial monolayer disruption. STBM content was consistently high (∼87–95%) across the different preparations. However, surface antigen intensities differed, with significantly lower placental alkaline phosphatase (P<0.05) and Eng (P<0.05) expression on mSTBM, and Flt-1 (P<0.05) expression on pSTBM. For PE placenta derived preparations, pSTBM contained lower Eng positive STBM (P<0.05) and mSTBM Eng expression was increased (P<0.05). Western blotting revealed increased Flt-1/sFlt-1 (P<0.02) and decreased placental alkaline phosphatase (P = 0.0002) content of PE placenta pSTBM. Using NTA, perfused PE placentas released significantly larger MV (P<0.001). Finally, VEGF, PlGF and TGFβ bound to mSTBM at physiologically relevant concentrations and inhibited mSTBM induced endothelial disruption (P<0.05-P<0.001).ConclusionsThis study has found differences in physical and antigenic characteristics of normal and PE placenta STBM preparations produced by placental perfusion or mechanical disruption. We have also demonstrated that large quantities of biologically active STBM associated endoglin and Flt-1/sFlt-1 could contribute to the increased circulating levels measured in PE patients and add to the perturbation of the maternal vascular endothelium, normally attributed to non-membrane bound sFlt-1 and sEndoglin.

Placenta-derived exosomes: potential biomarkers of preeclampsia

“…12,19,88 These studies have demonstrated an increase in STBEVs in ex vivo placental perfusates in PE in comparison to normal pregnancies. Furthermore, it has been established that STBEVs have a key role in immunomodulation during normal and complicated pregnancies, 12,83,89 and not as purified populations of constituent vesicles, such as exosomes.…”

Angiogenic Factors in Preeclampsia

“…40,41 These syncytial knots easily detach from the syncytiotrophoblast, resulting in free, multinucleated aggregates (50-to 150-μm diameter) that are loaded with sFlt1 protein and mRNA, and are capable of de novo gene transcription and translation. 40,42 Other studies using autopsy material have suggested that shed syncytial knots may contribute to circulating sFlt1 in preeclampsia. 43 Because these synytial microparticles are of fetal origin, this process of syncytial microparticle shedding may lead to chimerism, as fetal cells can be retained in the maternal blood and organs for decades after delivery.…”

Preeclampsia: a link between trophoblast dysregulation and an antiangiogenic state

“…Central to the pathophysiology of preeclampsia is ischemia of the placenta (15,16), which leads to the release of soluble factors and micro/nanovesicles (17,18) into the maternal circulation responsible for the clinical signs of preeclampsia: hypertension and proteinuria. These factors have been referred to as "toxins," hence the name "toxemia of pregnancy" (19).…”