MicroRNA Regulation of Mitogenic Signaling Networks in the Human Placenta.

Placental cell growth depends on an adaptable combination of an endogenous developmental programme and the exogenous influence of maternal growth factors, both of which may be influenced by microRNA (miR)-dependent effects on gene expression. We have previously shown that global miR suppression in placenta accelerates proliferation and enhances levels of growth factor signalling mediators in cytotrophoblast. This study aimed to identify miRs involved in regulating placental growth. An initial array revealed 58 miR species whose expression differs between first trimester, when cytotrophoblast proliferation is rapid, and term, by which time proliferation has slowed. In silico analysis defined potential growth regulatory miRs; amongst these, hsa-miR-145, hsa-miR-377 and hsa-let-7a were predicted to target known placental growth genes, and were higher at term than in first trimester, so were selected for further analysis. Over-expression of miR-377 and Let-7a, but not miR-145, in first trimester placental explants significantly reduced basal cytotrophoblast proliferation and expression of ERK and c-myc. PCR arrays, in-silico analysis, western blotting and 3-UTR luciferase reporter assays revealed targets of miR-145 within the IGF-axis. Analysis of proliferation in placental explants overexpressing miR-145 demonstrated its role as a mediator of IGF-induced trophoblast proliferation. These findings identify miRs 377 and let-7a in regulation of endogenous cell growth and miR-145 in the placental response to maternal stimulation, and will aid the development of therapeutic strategies for problem pregnancies.