Background: The placental syncytiotrophoblast regulates nutrient and waste exchange between the fetus and the mother. Syncytialisation involves placental cytotrophoblast cells continuously fusing to the outer syncytial layer. Insufficient syncytialisation has been associated with preeclampsia and intrauterine growth restriction. The placental renin angiotensin system (RAS) is important for appropriate placental development. Reliant on the renin precursor, prorenin, binding to the prorenin receptor ((P)RR) to initiate the classical RAS cascade, prorenin/(P)RR binding can also induce intracellular signalling pathways important in placental development. A novel form of the (P)RR, the soluble (P)RR (s(P)RR) has been discovered, which in human glomerular epithelial cells, is cleaved by the pro-protein convertase furin.
Aims/Hypothesis: We hypothesised that the (P)RR is essential for syncytialisation and that syncytialisation will increase the expression and/or secretion of (P)RR, s(P)RR and furin in BeWo choriocarcinoma cells. Furthermore, we postulated that furin cleaves the s(P)RR in the BeWo.
Methods: BeWo choriocarcinoma cells were treated with forskolin (100μm) or vehicle (DMSO) control to induce syncytialisation. Additionally, BeWo cells were transfected overnight with either a (P)RR siRNA or furin siRNA, prior to treatment with forskolin. Cells and supernatant were collected after 48 hours incubation and underwent PCR, ELISA, western blot and immunocytochemistry analyses. Syncytialisation was quantified by measuring hCG secretion and E-cadherin expression.
Results: Syncytialisation increased active furin protein expression and s(P)RR secretion (P=0.02, P<0.001). While there was no change in E-cadherin protein expression, hCG secretion decreased upon treatment with (P)RR siRNA and forskolin (P=0.004) suggesting that the (P)RR is important for syncytialisation. Furin knockdown decreased s(P)RR secretion (P≤0.001).
Conclusions: The (P)RR and s(P)RR have roles in syncytialisation, as does active furin protein. Furthermore, furin could be responsible, in part, for the cleavage of the s(P)RR in BeWo cells. Corroboration of these results in human primary trophoblast cells is currently underway.