PLAC4 is upregulated in severe early onset preeclampsia and upregulated with syncytialisation but not hypoxia

INTRODUCTION

Severe early onset preeclampsia is one of the most serious complications of pregnancy. Placental specific 4 (PLAC4) is very highly expressed in placenta relative to all other tissues. Recently in a biomarker screening study, we found PLAC4 mRNA was significantly upregulated in maternal whole blood and placenta obtained from cases of severe preeclampsia. Intriguingly however, very little is known about its expression or functional role in either normal pregnancy or pregnancies complicated by preeclampsia.

METHODS

The objective of this study was to characterize the protein expression and localization of PLAC4 in severe early onset preeclamptic placenta. Given so little of the biology of PLAC4 is known, we also examined whether the expression of PLAC4 alters with syncytialisation or placental hypoxia.

RESULTS

We found PLAC4 protein expression was significantly (p < 0.05) upregulated in severe early onset preeclamptic placentas (n = 24) compared to gestationally matched preterm controls (n = 12). PLAC4 protein was specifically localized to the syncytiotrophoblast of preterm, preeclamptic and term placentas. Functional analysis of PLAC4 mRNA and protein expression revealed a significant (p < 0.05) increase with syncytialisation of BeWo cells. However, exposure of either syncytialised BeWo cells or primary term placental explants to hypoxia (1% oxygen) did not alter the expression of either PLAC4 mRNA or protein.

CONCLUSION

In conclusion, we have found PLAC4 is significantly upregulated in association with severe preterm preeclampsia. Furthermore, it is upregulated with syncytialisation, but not hypoxia. It is possible PLAC4 may have a role in the pathogenesis of preeclampsia, and its biology merits further investigation.

MT-MMPs in pre-eclamptic placenta: relationship to soluble endoglin production

INTRODUCTION

Pre-eclampsia is a serious complication of pregnancy, characterized by severe endothelial dysfunction resulting in hypertension, proteinuria and maternal end-organ damage. Soluble endoglin is an anti-angiogenic factor released from placenta that has been linked to severe pre-eclampsia. We recently reported MMP-14 is capable of cleaving endoglin to release soluble endoglin from placenta, however inhibition studies only partially repressed production. To this end we have sought to identify other proteases that mediate endoglin shedding from placenta. MMP-14 is one of six-membrane-type (MT-) MMPs, a sub-family of the MMP superfamily, so named because they are membrane bound. MMP-15 is phylogenetically the closest MMP relative to MMP-14, however its inhibition has no effect on soluble endoglin production from placenta.

METHODS

Here we aimed to characterize the remaining four MT-MMPs (MMP-16, -17, -24 and -25) in severe early-onset pre-eclamptic placenta and assess their relative contribution to soluble endoglin production.

RESULTS

Immunolocalisation studies revealed MMP-16, -24 and -25 were localized to the syncytiotrophoblast, the same site as endoglin, whilst MMP-17 was predominantly localized to fetal vessels and underlying stroma. MMP-17 protein was significantly (p < 0.05) up-regulated in pre-eclamptic placentas compared to gestationally matched pre-term controls, whilst MMP-25 mRNA was significantly (p < 0.05) down regulated. siRNA knockdown of MMP-16, -17, -24 and -25 in syncytialised BeWo cells did not alter soluble endoglin production in vitro.

CONCLUSION

This is the first study to characterize MT-MMP protein localization in human placenta and indicates that MMP-14 is the only MT-MMP that contributes to soluble endoglin production in pre-eclampsia.