Molecular and functional studies on human embryo implantation : targets for infertility and fertility regulation

Abstract

Background: An estimated one in four couples globally suffers from infertility or fertility related issues and rate of global infertility is about 10-15%. Despite the best optimization of assisted reproductive technique the pregnancy rate is not more than 30%. Poor understanding of the complex molecular interactions between the blastocyst and the receptive endometrium is one of the major reasons for unexplained infertility. Understanding the molecular mechanisms of human embryo implantation helps in improving pregnancy rates, management of infertility issues and helps in regulation of fertility by novel methods.

Aim: The overall aim of this thesis is to expand the understanding of various factors that affects endometrial receptivity and human embryo implantation process. The specific aims of the thesis are to explore the role of leukemia inhibitory factor (LIF) in implantation and viability of the human embryo and, to study the actions of ulipristal acetate (UPA) and two low doses of mifepristone on endometrial receptivity and human embryo implantation using an in vitro three-dimensional (3D) endometrial co-culture model, in addition to study progesterone regulated transcriptomic signature in epithelial and stromal compartments.

Materials, methods and results: Study 1 is an in vitro exploratory study of the role of LIF in human embryo implantation and its viability by using potent LIF inhibitor, polyethylene glycated leukemia inhibitory factor antagonist (PEGLA) in a 3D endometrial cell co-culture model. Inhibition of LIF by PEGLA significantly reduced blastocyst attachment to endometrial constructs and triggered apoptosis of blastocysts by down regulating embryonic AKT and up regulating caspase 3 as analyzed by immunofluorescence and RTPCR. Studies 2 and 3 were exploratory studies on endometrial receptivity and human embryo implantation process after treatment with 200 ng/ml UPA, a dose used for emergency contraception (study 2) and two low doses of mifepristone (0.5μM and 0.05μM, study 3) using an in vitro 3D endometrial cell co-culture model. Selected endometrial receptivity markers were analyzed by RTPCR from the endometrial constructs. The main findings of study 2 were that there was no significant difference in the blastocyst attachment rate to endometrial constructs when compared between UPA treated group (5/10 blastocysts attached) and control group (7/10 blastocysts attached). Of the studied 17 endometrial receptivity markers, HBEGF and IL6 were significantly upregulated and HAND2, OPN, CALCR and FGF2 were down-regulated with UPA treatment. The main findings of study 3 were that none of the embryos in 0.5μM of mifepristone attached to the endometrial constructs, whereas 4 out of 10 in 0.05 μM group and 7 out of 10 embryos in the control group attached to the cultures. Most of the studied receptivity markers were significantly altered with mifepristone exposure in a similar direction in both the treatment groups. Study 4 explored large-scale progesterone regulated transcriptomic signature in epithelial and stromal compartments by laser capture microdissection and microarray analysis in receptive and non-receptive (treatment with 200 mg mifepristone on LH+2) endometrium. Expression of Metallothioneins (MT1G and MT2A) and Ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3) was significantly downregulated in both stromal cells and glands, whereas SFRP4 was upregulated. ENPP3 protein and mRNA expression was significantly down regulated in epithelial compartment of non-receptive endometrium, but no stromal immunostaining was detected in either receptive or non-receptive endometrium. ENPP3 protein was observed in glycosylated form in both the endometrial tissue lysates and uterine fluid. The expression pattern of ENPP3 was similar to progesterone secretion - high in mid-secretory and low in proliferative phase. In vitro functional assay using 3D cell cultures confirmed the receptivity of the endometrial construct falling in line with the expression of ENPP3.

Conclusion: LIF plays a critical role in the process of human embryo implantation and viability of the blastocyst. UPA at a dose used as emergency contraception (30 mg single dose) does not affect endometrial receptivity and embryo implantation. Mifepristone at a concentration of 0.5μM affected endometrial receptivity and inhibited embryo implantation whereas 0.05μM mifepristone affected the studied genes known to be involved in endometrial receptivity, but had no effect on embryo implantation. ENPP3 is proposed as a novel molecular marker of progesterone regulated endometrial receptivity.