Background: Placenta from women with preeclampsia display insufficient syncytialisation and syncytial release of anti-angiogenic factors into the maternal circulation. Previous studies in our lab show that the prorenin receptor ((P)RR), a key component of tissue renin-angiotensin systems (RAS), is localised to the syncytiotrophoblast. Additionally, a soluble form of (P)RR (s(P)RR) exists and is detected in plasma and urine. Both placental (P)RR and plasma s(P)RR levels are elevated in preeclamptic women (Narita et. al 2016. Placenta). We hypothesise that (P)RR promotes syncytialisation and that s(P)RR is released from the syncytium.
Methods: Primary human trophoblasts and BeWo cells were incubated overnight then transfected with (P)RR siRNA, negative control siRNA or vehicle (lipofectamine/opti-MEM) for 48h. BeWo cells were also treated with 100mM forskolin (to induce syncytialisation) or vehicle (DMSO). Primary trophoblasts spontaneously syncytialise. hCG secretion and E-cadherin visualisation were used to assess syncytialisation.
Results: We are the first to show that s(P)RR is released from both BeWo and primary trophoblasts. Forskolin-induced syncytialisation of BeWo cells significantly increased s(P)RR secretion (P<0.001). There was no change in (P)RR mRNA expression with syncytialisation in either cell type.
Treatment with (P)RR siRNA significantly decreased (P)RR mRNA abundance and protein levels in BeWos (both P<0.0001), and (P)RR expression in primary trophoblasts (P<0.0001, N=5). (P)RR knockdown was associated with a significant decrease in forskolin-induced hCG secretion (P<0.01) and the percent of nuclei in the syncytium (P=0.05) in BeWos. Preliminary results in primary trophoblasts show no change in E-cadherin mRNA abundance upon (P)RR knock-down, although E-cadherin expression was significantly decreased with syncytialisation (P<0.0001).
Conclusion: In BeWo cells, (P)RR promotes syncytialisation however, preliminary studies in primary trophoblasts are yet to determine a role for (P)RR in syncytialisation. Both BeWo and primary trophoblasts secrete s(P)RR, highlighting that elevated levels of plasma s(P)RR in women with preeclampsia, could originate from the placenta.