Endometrial, embryonic and ovarian aspects of human implantation

Abstract

The general aim of the studies was to add more understanding to the mechanism of human embryo implantation, which will allow us to improve pregnancy rates in assisted reproduction.

The simultaneous positive spatial and temporal expression of pinopodes with LIF, LIFR and HBEGF proteins in endometrial samples from healthy women was found. LIF and LIFR had different expression patterns. HB-EGF was present both inside the luminal epithelial cells and on the surface of pinopodes. The findings suggest that the simultaneous molecular and structural cell changes are important in the initiation of human blastocyst implantation. Human embryonic stem cells (hESC), derived from the inner cell mass (ICM) of human blastocyst, provide an excellent model for studying the events occurring in the embryonic side of the implantation.

Gene expression in the hESC line HS237 was analyzed using microarrays. Real-time RT-PCR was used to validate the microarray results in four cell lines (HS181, HS235, HS237, HS293). The expression of LIF, LIFR and gpl30 mRNA and protein was increased in differentiated HS237 cells when compared with those in undifferentiated cells. An inhibitor of LIF-mediated signaling, SOCS-1, was up-regulated in undifferentiated hESCs compared with differentiated ones. Increased levels of SOCS-1 might prevent LIF-induced STAT3 signal transduction in undifferentiated hESC and explain the LIF resistance in those cells.

Genes, expressed specifically and those shared in undifferentiated hESCs, differentiated hESCs and in fibroblasts were identified. Differentiation of hESC into other cell types began before the changes could be observed in light microscopy, as revealed by scanning electron microscopy. Both hypothyroidism and hyperthyroidism affect menstrual cycle. The mechanisms behind these reproductive abnormalities are not well known.

We described the presence and cellular distribution of TSH and thyroid hormone receptors (TR) protein and mRNA in normal human endometrium throughout the menstrual cycle and in human ovary. After stimulation with TSH and thyroid hormone, endometrial epithelial and stromal cells showed increased cAMP (activation of TSHR) and ERK1/2 (activation of TR receptors) expression. Significant down-regulation of LIF gene under thyroid hormone treatment in endometrial cells suggested involvement of thyroid hormone in human implantation. Granulosa cells (M) stimulated with TSH showed a significant increase in cAMP production, indicating activation of the TSHR. Stimulation with T4 resulted in increased concentration of ERK1/2 (activation of TR receptors). Real-time PCR did not show significant changes in the expression of glucose transporter1 and estrogen receptors (ER) alpha in endometrial cells or ERbeta genes in ovarian tissue or GCs after stimulation with TSH or T4.

The expression of TSHR, TRalpha1 and TRbeta1 receptors in the human ovary and endometrium suggests that reproductive disorders during thyroid dysfunction might result from direct effects of thyroid hormones on the ovaries and endometrium. Their strong expression in ovarian surface epithelium suggests a particular role in those cells, but the exact role remains to be solved.