The association between microRNAs and progesterone elevation on the endometrial receptivity in in-vitro fertilization treatment cycles

Abstract

Elevated serum progesterone (P4) on the day of human chorionic gonadotrophin (HCG) administration was proven to adversely affect the pregnancy rate in in-vitro fertilization (IVF) treatment cycles. Recent evidence indicates that this progesterone elevation (PE) does not affect embryo quality but reducing endometrial receptivity. MicroRNAs (miRNAs) are small non-coding RNA that binds to the complementary 3’-untranslated region of the target gene and inhibits the expression of protein through translation/transcriptional silencing. MiRNAs play significant roles in many physiological and pathological roles in the human body. Previously, it was demonstrated that miR-30b and miR-30d are positively while miR-494 is negatively associated with endometrial receptivity. In this study, endometrial biopsies at window of implantation (HCG+ 6-8) were collected from IVF patients undergoing ovarian stimulation cycle with PE or normal serum P4 level at day of HCG administration. Epithelial and stromal cells were isolated from the biopsy samples and the expressions of miR-30b, -30d and -494 were compared between the two groups.

It was found that miR-30b and miR-30d were significantly decreased in the isolated epithelial cells of the PE group while there were no significant differences between stromal cells isolated from the two groups. MiR-494 was not differentially expressed between the two groups in neither epithelial nor stromal cells. In silicon analysis using computer algorithm and in vitro analysis using 3’untranslated region luciferase assay showed that miR-30b regulates tissue inhibitor of metalloproteinases 2 (TIMP2). Force-expression of miR-30b in Ishikawa cells suppressed both TIMP2 mRNA and protein expression. Real-time quantitative polymerase chain reaction showed that TIMP2 was higher expressed in PE epithelial cells when compared to the epithelial cells from the normal P4 group. Finally, the role of miR-30b in embryo attachment was assessed by trophoblast spheroid attachment assay. MiR-30b was force-expressed in endometrial Ishikawa cells to mimic endometrial epithelium from normal P4 responders while Ishikawa cells transfected with scramble to mimic the endometrial epithelial of PE responders. The transfected cells were cocultured with JEG3 trophoblast cell spheroids. It was found that the spheroid attachment rate was significantly higher in the miR-30b transfected group. Taken together, it was found that the adverse effect of PE in pregnancy rate is associated with a decrease expression of miR-30b in endometrial epithelium and miR-30b possibly exerts its effect on TIMP2 expression.