Embryo implantation: the molecular mechanism remains elusive

Uterine Expression of NDRG4 Is Induced by Estrogen and Up-Regulated during Embryo Implantation Process in Mice

Embryo implantation is an essential step for the establishment of pregnancy and dynamically regulated by estrogen and progesterone. NDRG4 (N-myc down-regulated gene 4) is a tumor suppressor that participates in cell survival, tumor invasion and angiogenesis. The objective of this study was to preliminarily explore the role of NDRG4 in embryo implantation. By immunohistochemistry (IHC) and quantitive RT-PCR (qRT-PCR), we found that uterine expression of NDRG4 was increased along with puberal development, and its expression in adult females reached the peak at the estrus stage during the estrus cycle. Furthermore, uterine NDRG4 expression was significantly induced by the treatment of estradiol (E₂) both in pre-puberty females and ovariectomized adult females. Uterine expression pattern of NDRG4 during the peri-implantation period in mice was determined by IHC, qRT-PCR and Western blot. It was observed that NDRG4 expression was up-regulated during the implantation process, and its expression level at the implantation sites was significantly higher than that at the inter-implantation sites. Meanwhile, an increased expression in NDRG4 was associated with artificial decidualization as well as the activation of delayed implantation. By qRT-PCR and Western blot, we found that the in vitro decidualization of endometrial stromal cells (ESCs) was accompanied by up-regulation of NDRG4 expression, whereas knockdown of its expression in these cells by siRNA inhibited the decidualization process. In addition, Western blot analysis showed that NDRG4 protein expression was decreased in human villus tissues of recurrent miscarriage (RM) patients compared to normal pregnant women. Collectively, these data suggested that uterine NDRG4 expression could be induced by estrogen, and NDRG4 might play an important role during early pregnancy.

Adrenomedullin 2 (ADM2) Regulates Mucin 1 at the Maternal-Fetal Interface in Human Pregnancy

Association of an altered expression of placental mucin 1 (MUC1) with first-trimester spontaneous abortion and its regulation in placenta by an invasion-promoting peptide, adrenomedullin 2 (ADM2), is not known. The objective of this study was to assess 1) the association of MUC1 mRNA expression in the placental villi and decidua with first-trimester spontaneous abortion, 2) the effects of ADM2 on the expression of MUC1 in trophoblast cells in the presence or absence of hypoxia, 3) the effects of ADM2 on expression of MUC1 in decidual stromal cells (DSCs), and 4) if ADM2 regulates the expression of MUC1 and MMP2 protein in trophoblastic spheroids. Data demonstrate that 1) expression of MUC1 mRNA in villous tissue is higher in spontaneous abortion compared to age-matched electively terminated pregnancies (P > 0.05), 2) ADM2 decreases the expression of MUC1 mRNA and protein in trophoblast cells and spheroids with concomitant increases in MMP2 immunoreactivity in the spheroids, 3) ADM2 decreases hypoxia-induced increases in MUC1 immunoreactivity in trophoblast cells, 4) decidual MUC1 mRNA expression is lower in spontaneous compared to elective abortions (P < 0.05), and 5) DSCs express MUC1 mRNA and protein and ADM2 decreases the expression of MUC1 mRNA and protein in DSCs. Taken together, this study demonstrates that first-trimester spontaneous abortion is associated with increases in MUC1 expression in villi and decreases in the decidual tissues, and suggests that ADM2 may contribute to the physiology of embryo implantation and placental growth via increasing MMP2 and decreasing MUC1 expression to facilitate trophoblast invasion.

Subcellular localization of L-selectin ligand in the endometrium implies a novel function for pinopodes in endometrial receptivity

BACKGROUND

Apical surfaces of human endometrial epithelium and endothelium are key elements for the initiation of molecular interactions to capture the blastocyst or leukocyte, respectively. The L-selectin adhesion system has been strongly proposed to play an important role in the initial steps of trophoblast adhesion and promotion of integrin-dependent processes, ultimately culminating in the establishment of the embryo-maternal interface. On the basis of these facts, we hypothesized a novel role for pinopodes as the first embryo-fetal contact sites to contain the highest subcellular expression of L-selectin ligand suggesting its role in early adhesion as predicted. Thus, the objective of this study was therefore to determine the subcellular pattern of distribution of the L-selectin ligand (MECA-79) in human endometrial apical membrane region during the window of implantation.

METHODS

Endometrial biopsies of secretory phases from fertile females ranging in age between 25 and 42 years were studied using several approaches, including scanning electron microscopy (SEM), immunostaining for light microscopy and transmission electron microscopy (TEM), and immunoblotting as well as statistical analysis of the area-related numerical densities of immunoreactive MECA-79-bound nanogolds to detect the expression pattern and the subcellular distribution pattern of L-selectin ligand (MECA-79) in human endometrium during the window of implantation.

RESULTS

The endometrial biopsies were scored according the dating criteria of Noyes et al. by an experienced histologist. The SEM images of the midluteal phase specimens revealed that fully developed pinopodes were abundant in our samples. HRP-immunostaining and immunofluorescent staining as well as immunoblotting revealed that MECA-79 was expressed in the midluteal phase specimens. The results of immunogold TEM illustrated the expression of MECA-79 in human pinopodes in the midluteal phase and a higher area-relate numerical density in pinopodes compared to that of the uterodome-free areas.

CONCLUSIONS

This is the first demonstration of the subcellular localization of MECA-79 in the human pinopodes which may indicate a novel role for pinopodes to be capable of shear-stress-dependent tethering-type adhesion in the initial phases of human embryo implantation.