Background: The soluble prorenin receptor (s(P)RR) is a newly discovered protein in the renin-angiotensin system pathway that is elevated in the plasma of women with preeclampsia (Narita et. al. 2016. Placenta). The pro-protein convertase, furin, is known to cleave the (P)RR to produce s(P)RR in human glomerular epithelial cells. We hypothesise that this also occurs in the placenta. Furin has previously been shown to promote BeWo choriocarcinoma and primary human trophoblast syncytialisation (Wang et. al. 2013. Cell Death and Disease). However, we have evidence to suggest the contrary.
Methods:BeWo cells were incubated overnight before transfection with furin siRNA, negative control siRNA or vehicle (lipofectamine/opti-MEM) or treatment withDEC-RVKR-CMK (furin inhibitor) or vehicle (DMSO). BeWo cells were also treated with 100mM forskolin (to induce syncytialisation) or vehicle (DMSO) for 48h. Spontaneously syncytialising primary human trophoblasts were transfected as above and incubated for 72h. hCG secretion and E-cadherin visualisation were used to assess syncytialisation.
Results: FURINmRNA expression and ‘active’ furin protein levels were significantly increased with forskolin treatment (both P<0.01) in BeWos. In primary trophoblasts, syncytialisation significantly decreased FURINmRNA expression (P<0.0001, N=5). Furin siRNA significantly decreased FURINmRNA expression, soluble and pro-furin protein levels (all P<0.0001) but had no effect on active furin protein levels. Neither furin knockdown or inhibition had any effect on the percent of nuclei in a syncytium or on the secretion of hCG from BeWo cells. Additionally, furin siRNA had no effect on E-cadherin mRNA expression in primary trophoblasts and DEC-RVKR-CMK had no effect on E-cadherin expression in BeWos. Both furin siRNA and DEC-RVKR-CMK significantly decreased s(P)RR secretion from BeWo cells (both P<0.0001).
Conclusion:Contrary to previous reports, furin knockdown/inhibition had no effect on syncytialisation of BeWo cells and preliminary results in primary trophoblasts suggest similar results. Furin cleaves the s(P)RR in BeWo cells.