The role of VEGF-A165b in trophoblast survival

Background: Pre-eclampsia remains a dominant cause of maternal and fetal mortality in developed countries. In a previous prospective study we identified a fall in the VEGF-A isoform VEGF-A(165)b in the plasma of patients in the first trimester to be a predictor of later pre-eclampsia. VEGF-A(165)b has been shown to have potent cytoprotective properties in many cell types. We therefore tested the hypothesis that VEGF-A(165)b may be cytoprotective for placental trophoblasts. Methods: We used an immortalised first trimester trophoblast cell line exposed to chemical toxicity, and physiological (<2% O-2) and atmospheric oxygen (21% O-2) in the presence or absence of VEGF-A(165)b, angiogenic VEGF-A(165)a, a non-specific anti-VEGF-A blocking antibody (bevacizumab), or a specific anti-VEGF-A(165)b antibody. Cell viability and cytotoxicity were measured by trypan blue and LDH assay respectively. Results: Under high (21%) levels of oxygen, trophoblast viability was increased, and cytotoxicity reduced by exogenous recombinant VEGF-A(165)b (p < 0.05, n = 10) or VEGF-A(165)a. The cytoprotective effect was not seen under lower (<2%) oxygen conditions, where VEGF-A(165)b was upregulated. However inhibition of VEGF-A with blocking antibodies (bevacizumab or anti-VEGF-A(165)b) had marked cytotoxic effects under low oxygen conditions presumably through the blockade of autocrine survival pathways. Conclusions: These results show that when trophoblasts are exposed to lower oxygen tensions (as they are early in the 1st trimester) endogenous VEGF-A(165)b contributes to their survival through an autocrine pathway. In contrast in high oxygen conditions exogenous VEGF-A isoforms have a greater effect on trophoblast survival.