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

Abstract

Nearly all cells secrete and release extracellular vesicles (EVs) into the microenvironment for cell-cell communication. EVs contain lipids, mRNAs, microRNAs, and proteins. According to the origin and size, EVs were mainly divided into exosome (30-150nm) which was covered with endosomal membrane, and microvesicles (100-1000nm) which was wrapped with plasma membrane. As vehicles, EVs selectively pack contents from original cells and participate in various physiology and pathology process. Upon fusion to recipient cells, EVs release its contents and exert changes to recipient cells. MicroRNAs (miRNAs) are small non-coding RNA, which bind to 3’-untranslated region of messenger RNA (mRNA) to inhibit gene expression. Progesterone elevation (PE) on the day human chorionic gonadotrophin (HCG) administration has been identified to be associated with adverse effect on pregnancy in in-vitro fertilization (IVF) treatment cycles. Previously, it has been proved that the expression of miR-30b in endometrial epithelial cells was significantly decreased in PE while expression of miR-31 in endometrial epithelial cells was significantly increased during window of implantation. This study hypothesized that the effect of PE on implantation is partially associated with the EVs secreted by the endometrium on embryos. More specifically, upon PE, specific miRNAs were packed in endometrial EVs and these EVs fused with embryos and releasing their miRNA contents to reduce implantation capacity. In this study, Ishikawa cells and JEG3 cells which served as model for endometrium epithelial cells and trophoblast cells were cultured with different combinations of estrogen and progesterone(P4) aimed to mimic patients with normal or elevated progesterone.

Expression level of miR-30b and miR-31 were examined in the treated cells and derived EVs. The expression of miR-30b in Ishikawa cells and their EVs was significantly decreased in the PE group, when compared with the normal P4 group. However, miR-31 was not being affected. In JEG3 cells, neither miR-30b nor miR-31 were being affected. Electron microscopy revealed that the size of the EVs were not affected by P4 treatments. miR-30b over-expressed or suppressed EVs were used to mimic EVs from endometrium of normal or PE. The effect of EVs on implantation was assessed by spheroid attachment assay. The miR-30b suppressed EVs has marginal effect on spheroid attachment. Since the effect of miR-30b suppression may be limited by the experimental time length and concentration of EVs, miR-30b inhibitor was transfected into JEG3 cells directly before spheroid production. It was found that miR-30b inhibitor in spheroids significantly reduced spheroid attachment. In a word, miR-30b was suppressed in endometrium epithelial cells and their EVs, but similar responses were not observed in trophoblast cells and their EVs. PE reduced implantation may be caused by a reduction of miR-30b in endometrial EVs.