Hormonal and Paracrine Regulation of Embryonic Implantation: A Workshop Report

Adverse effect of assisted reproductive technology-related hyperoestrogensim on the secretion and absorption of uterine fluid in superovulating mice during the peri-implantation period

OBJECTIVES

This study aimed to investigate the potential mechanism of hyperoestrogensim elicited by ovulation induction affects endometrial receptivity and leads to embryo implantation abnormality or failure.

STUDY DESIGN

Establishment of ovulation induction mouse model. Changes in mouse body weight, ovarian weight, serum E2 level and oestrous cycle were observed. During the peri-implantation period, morphological changes in the mouse uterus and implantation sites and the localization and protein levels of oestrogen receptors ERα and ERβ, the tight junction factors CLDN3 and OCLN, the aquaporins AQP3, AQP4 and AQP8, and the sodium channel proteins SCNN1α, SCNN1β and SCNN1γ were observed. The expression and cellular localization of ERα, CLDN3, AQP8 and SCNN1 β in RL95-2 cell line were also detected by western blotting and immunofluorescence.

RESULTS

Ovarian and body weights were significantly higher in the 5 IU and 10 IU groups than in the CON group. The E2 level was significantly higher in the 10 IU group than in the CON group. The mice in the 10 IU group had a disordered oestrous cycle and were in oestrus for a long time. At 5.5 dpc, significantly fewer implantation sites were observed in the 10 IU group than in the CON (p<0.001) and 5 IU (p<0.05) groups. The probability of abnormal implantation and abortion was higher in the 10 IU group than in the CON and 5 IU groups. CLDN3, OCLN, AQP8 and SCNN1β in the mouse endometrium were localized on the luminal epithelium and glandular epithelium and expression levels were lower in the 10 IU group than in the CON group. The protein expression level of ERα was increased by 50% in the 10 IU group compared to the CON group. The expressions of CLDN3, AQP8, SCNN1β in RL95-2 cell line were significantly depressed by the superphysiological E2, ERα agonist or ERβ agonist, which could be reversed by the oestrogen receptor antagonist.

CONCLUSION

ART-induced hyperoestrogenism reduces CLDN3, AQP8 and SCNN1β expression through ERα, thereby destroying tight junctions and water and sodium channels in the endometrial cavity epithelium, which may cause abnormal implantation due to abnormal uterine fluid secretion and absorption.

Effect of beta-cypermethrin exposure on embryo implantation in mice

The aim of this study was to investigate the effect of β-CP on embryo implantation in mice. Forty female mice were randomly assigned to four groups of 10 mice each: one control group and three β-CP treated groups. The control group was administered corn oil only, while the three β-CP-treated groups were given corn oil containing 5, 10, and 20 mg/kg bw d β-CP for 3 months through intragastric administration. The results indicated that the administration of β-CP decreased the rate of embryo implantation (all p < 0.05), E₂ level in the serum, and the expression of Homeobox A10 (HoxA10) protein. In addition, β-CP significantly increased ERa and PRA protein expression levels. These results suggest that β-CP can disrupt the balance of E₂ and P, influence ERa and PRA expression and their downstream-related molecule Hoxa10, and decrease embryo implantation.

Exposure of mice to benzo(a)pyrene impairs endometrial receptivity and reduces the number of implantation sites during early pregnancy

Benzo(a)pyrene (BaP) is a ubiquitous environmental pollutant. Studies have demonstrated it to be an endocrine-disrupting chemical that can cause adverse effects on the female reproductive system. However, the effect of BaP on early pregnancy has not been reported. We investigated the effect of BaP on endometrial receptivity and embryo implantation. Pregnant mice were dosed with BaP at 0.2, 2 and 20 mg/kg/day from day 1 (D1) to day 5 (D5) of gestation. Exposure to BaP impaired the morphology of the endometrium and decreased the number of implantation sites (p0.2=0.006, p2=0.167, p20=0.003). Levels of estrodiol (p<0.001, for three treatment group compare with control group) and progesterone-4 in plasma were elevated in BaP-treatment groups (p0.2<0.001, p2<0.001, p20=0.032). Expression of estrogen receptor-α was up-regulated (p0.2=0.002, p2=0.131, p20=0.024) whereas expression of the progesterone receptor was down-regulated (p0.2<0.001, p2=0.064, p20=0.021). Levels of receptivity-related genes HoxA10 (p0.2<0.001, p2=0.135, p20<0.001) and E-cadherin (p0.2=0.002, p2=0.624, p20=0.137) were changed by BaP. These results revealed that BaP can disrupt the balance of estrogen and progesterone, influence expression of their receptors and downstream related genes, lead to changes in endometrium receptivity, and reduce of the number of implantation sites.

Effects of DEHP on endometrial receptivity and embryo implantation in pregnant mice

Di-(2-ethylhexyl)-phthalate (DEHP) is a ubiquitous environmental pollutant and endocrine disruptor (ED) that causes serious adverse effects on animal and human health. The harmful effects of DEHP on human reproduction are increasingly recognized, especially in women. However, it is not known how endometrial receptivity and embryo implantation, which play important roles in the establishment of pregnancy, are affected by DEHP. This study was aimed towards investigating the effects of DEHP on endometrial receptivity and embryo implantation in pregnant mice. The pregnant mice received DEHP at 0, 250, 500 and 1000 mg/kg/day from day 1 (D1) of gestation until sacrifice. Administration of DEHP led to compromised endometrial receptivity and decreased number of implantation sites. The mRNA and protein expression levels of ERα, PR and E-cadherin, but not those of HoxA10 and MMP-2, were up-regulated by DEHP in the mouse endometrium. The results further suggested that DEHP disrupts the MAPK and NF-κB signaling pathways. This was maybe one of paths which influenced the E-cadherin expression. In conclusion, DEHP reduced endometrial receptivity and impaired embryo implantation by influencing the expression of hormone receptors and E-cadherin. Therefore, determining the full extent of the hazards of DEHP to human reproduction will be vital to developing and implementing effective protective measures.