Effect of Circulating Angiogenic Factors on Trophoblast Cell Proliferation

Preeclampsia is a potentially life threatening disorder of pregnancy which presents with raised blood pressure and proteinuria after twentieth week of gestation. It is one of the leading and mystical causes of maternal and fetal mortality worldwide. Abnormal placentation is suggested to be possibly the key feature of this disorder. Preeclampsia has been attributed to the presence of a circulating 'toxin' soluble fms-like tyrosine kinase-1 (sFlt-1) in maternal blood. sFlt-1 is normally produced and secreted by the placenta, however the presence, nature and effects of this toxin on trophoblast cells are not clearly understood. The binding of sFlt-1 with free Vascular Endothelial Growth Factor (VEGF) in maternal circulation and the subsequent effects of this on trophoblast cell proliferation are not fully known. OBJECTIVES: The present study was designed to estimate the levels of both VEGF and sFlt-1 in preeclamptic sera and also to investigate if the impaired or altered VEGF/sFlt-1 interaction of the two could affect trophoblast cell proliferation/viability. STUDY DESIGN: Methods: The serum levels of VEGF and sFlt-1in forty preeclamptic pregnant women and forty normotensive, nonproteinuric pregnant women (control) were analyzed by ELISA. The effect of preeclamptic sera on trophoblast cell proliferation was studied by treating trophoblast cell lines (JAR cells) with (i) preeclamptic sera, (ii) control sera, (iii) preeclamptic sera with recombinant VEGF and (iv) control sera with recombinant sFlt-1. Cell proliferation was determined by the Cell Titer 96 Aqueous One Solution Cell Proliferation assay. RESULTS: The levels of free VEGF were significantly lower (mean 170.53+36.56 pg/ml Vs 254.61+47.39 pg/ml, p<0.0001) and the levels of sFlt-1 were significantly higher (median 11295.25 pg/ml Vs 2936.2 pg/ml, p<0.0001) in the sera of preeclamptic women compared to the sera of control women respectively. A significant reduction in trophoblast cell proliferation was found in JAR cells treated with preeclamptic sera whereas the cell proliferation was enhanced when cells were treated with preeclamptic sera and recombinant VEGF. In contrast, the cell proliferation was enhanced in control sera treated JAR cells and this effect was reversed by the treatment with control sera and recombinant sFlt-1. CONCLUSIONS: Preeclampsia is associated with low serum levels of pro-angiogenic factor such as VEGF and high levels of anti-angiogenic factor i.e sFlt-1 and the imbalance of the two factors in the preeclamptic sera resulted in increased cytotoxicity of trophoblast cells (JAR cells) whereas cell proliferation was more in control sera treated JAR cells. This effect appears to be related to the changes in trophoblast sensitivity to sFlt-1 suggesting that circulating sFlt1 may have a role in the pathogenesis of the disease.