Identification of a MicroRNA Therapy Targeting sFlt-1 in Preeclampsia

Abstract

Preeclampsia is a multifactorial disease of the pregnancy contributing to maternal and neonatal morbidity and mortality worldwide. Typically, preeclampsia is characterised by the onset of new hypertension at or after 20 weeks’ gestation and can be accompanied by proteinuria and/or multiple organ failure. Despite decades of research, the only effective method to relieve preeclamptic symptoms is the removal of the placenta and the baby, which if not addressed in time, will progress to a potentially fatal end-stage disease - eclampsia with convulsion and eventual death. Anti-angiogenic soluble vascular endothelial growth factor (VEGF) receptor-1 (sFlt-1)-dependent loss of VEGF activity has been linked with the pathogenesis of preeclampsia. Abnormally high levels of sFlt-1 detected in maternal circulation and the placenta in women with preeclampsia falls dramatically postpartum, highlighting placenta as the main source of maternal sFlt-1. The protective heme oxygenase-1 (HO-1) enzyme acts as an inhibitor of sFlt-1 with low expression found in preeclamptic placenta. The exact mechanism behind this negative regulation is unknown, however it has been suggested that restoration of HO-1 expression and/or activity in preeclampsia may offer a therapeutic approach to regulate sFlt-1. MicroRNAs (miRNAs) are increasingly recognised as major gene regulators involved in pregnancy. We hypothesised that HO-1 regulates sFlt-1 via miRNA-dependent gene silencing. This could be employed as a strategy to treat abnormally high sFlt-1 levels associated with preeclampsia. We identified miR-122 to act downstream of HO-1 and inhibit sFlt-1 release in human endothelial cells. Adenovirus-mediated miR-122 overexpression in HO-1 compromised pregnant mice reduced maternal sFlt-1, improved fetal weight and inhibited the resorption rate without having any negative observational effects on the pregnancy. Viral-based delivery is known to induce immune response. To minimise health risks associated with off-target miR-122 overexpression, we also employed targeted liposomes to deliver the miR-122. Liposomes have been shown to successfully encapsulate nucleic acids, provide stable protection against degradation and facilitate cellular uptake. To minimise off-target effects and deliver miR-122 specifically to placenta, we designed the CGKRK surface-modified neutral PC liposomes and loaded it with miR-122. Intravenous administration of the decorated liposomes provided efficient miR-122 delivery to the placenta and resulted in effective down-regulation of placental ischaemia-induced sFlt-1 and reduction in fetal death rate. Based on these findings, exogenous miR-122 overexpression limits sFlt-1 release and improves poor fetal outcome in HO-1 compromised pregnancy. Surface functionalised liposomes present a novel therapeutic strategy to deliver miR-122 specifically to the placenta and limit sFlt-1 release observed in preeclampsia.