The angiomiR miR-155 has been implicated in the development of both healthy and abnormal placentae, yet the precise role is unknown. A known mRNA target of miR-155 is angiotensin II receptor 1 (AT1R). Increasing placental AT1R is pro-proliferative and promotes placentation, therefore we investigated the hypothesis that AT1R regulation by miR-155 controls placental growth.
To determine the effects of miR-155 on proliferation of trophoblasts, HTR-8/SVneo cells were cultured with a miR-155 mimic at varying concentrations. Increasing doses of the miR-155 mimic significantly reduced both AT1R mRNA abundance (by 60%) and trophoblast cell proliferation (by up to 90%) as assessed by qPCR and the xCELLigence RTCA system, respectively.
To support these in vitro experiments, we utilised a miR-155-/- mouse model to measure effects of miR-155 in the placenta. Pregnant miR-155+/+ and miR-155-/- mice were sacrificed at post-coital day 17.5 and tissues were collected. Placentae and fetuses were weighed, prior to immunohistochemistry and harvesting for RNA and protein. miR-155 was undetectable by qPCR in placentae from miR-155-/- dams, with AT1R mRNA and protein shown to be significantly increased (n=4-9 placentae/dam, 10 dams total).
Placentae from miR-155-/- dams showed significantly larger labyrinth zones and labyrinth:placental area ratios compared with controls, however placental weight was unchanged. Moreover, miR-155-/- dams produced pups that were significantly heavier, with unchanged fetal:placental weight ratios compared with control mice.
This study showed that placental miR-155 reduces AT1R mRNA and protein abundance, and decreases trophoblast proliferation. Knockout of miR-155 amplified labyrinth zone growth, increasing substrate transfer to the fetus, and subsequently increasing fetal weight. This shows that miR-155 controls placental growth by suppressing AT1R.
miR-155 regulation is clearly essential for normal placental, and hence fetal, growth. Since miR-155 is dysregulated and secreted in preeclampsia, it may be a useful biomarker or therapeutic target for early detection and resolution.