Fetal growth restriction and overgrowth (macrosomia) are both associated with altered placental development and problems at birth. Both conditions have lifelong impacts on health including an increased risk of developing cardiovascular disease and diabetes. Placental development depends on co-ordinated cellular growth and is enhanced by maternally-derived growth factors. MicroRNAs (miRs) are known to regulate gene expression and we have shown that global miR suppression in placenta enhances the stimulatory effect of insulin-like growth factors (IGFs) on placental cell (cytotrophoblast) proliferation. This study aimed to identify miRs involved in regulating placental growth. Rates of cytotrophoblast proliferation are higher in first trimester than at term. To identify regulators of proliferation, miR expression in first trimester (n=5) and term placental tissue (n=5) was compared in an array. 58 miRs were differentially expressed. Target prediction databases (miRecords) and Ingenuity Pathway Analysis software were used to classify these miRs. 10 miRs were predicted to target signalling cascades known to regulate proliferation. Three miRs, miR-145, miR-377 and Let-7a were predicted to regulate expression of placental growth genes and were selected for further analysis. The three were overexpressed in first trimester placental explants (n=6) by nucleofection of pre-miR precursors. Immunohistochemical analysis showed a significant reduction in proliferating cytotrophoblast cells (P<0.05) following overexpression of miR-377 and Let-7a but not miR-145. Predicted miR target gene products for these miRs, such as IGF1R, EGFR, ERK, AKT and SHP-2 were localised to cytotrophoblast cells, suggesting that they might mediate the growth regulatory response. Interestingly, cytotrophoblast expression of these signalling molecules, but not the receptors, was enhanced following global miR suppression induced by dicer knockdown. Our study has identified miRs potentially involved in regulating growth factor signalling in placental development. These findings will aid the development of miR-based therapeutic strategies for problem pregnancies.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.