Let-7b-5p differentially regulates human first trimester trophoblast migration and sFlt-1 through TLR7 and TLR8

Introduction: Preeclampsia is characterized by a pro-inflammatory, anti-migratory and anti-angiogenic placental phenotype. Impaired spiral artery remodeling stemming from trophoblast dysfunction is a key pathogenic mechanism. Little is known about the processes that govern trophoblast function normally and in preeclampsia. In preeclampsia, placental Let-7b-5p is reduced. The objectives of this study were to determine the normal function of Let-7b-5p in human trophoblast cells, to examine whether the ssRNA sensors, Toll-like receptor (TLR) 7 and/or TLR8 are mediators of trophoblast Let-7b-5p function, and whether disruption of this pathway promotes a preeclampsia-like phenotype in the trophoblast. Methods: The human first trimester trophoblast cell line, Sw.71, was transfected with a Let-7b-5p mimic, a Let-7b-5p inhibitor, or scramble control. Cells were treated with or without the TLR7 inhibitor IRS661 or the TLR8 inhibitor CUCPT9a. Trophoblast migration was measured using a two-chamber assay and interactions with human endometrial endothelial cells (HEECs) was measured using a 3D matrigel model. Trophoblast anti-angiogenic sFlt-1 release was measured by ELISA and sFLT1 mRNA measured by RT-qPCR. Results: Transfection of trophoblast cells with a Let-7b-5p mimic elevated migration through activation of TLR7 and TLR8, while in a TLR7-dependent manner, the Let-7b-5p mimic negatively regulated sFlt-1 production. Furthermore, inhibition of trophoblast Let-7b-5p reduced migration, elevated FLT1 mRNA expression and sFlt-1 release, and reduced trophoblast-endometrial endothelial cell interactions. Conclusions: This study highlights a role for TLR7/TLR8-activating Let-7b-5p in promoting normal trophoblast function and endothelial interactions and that disruption in this miR-driven signaling pathway may be relevant to processes driving a pre-eclamptic placental phenotype.