Search

Background: Embryo implantation and decidualization are essential to the establishment and maintenance of successful pregnancy in both rodents and primates. Receptive endometrium synergism with well-developed blastocyst is prerequisite for successful embryo implantation. Melatonin, which is mainly synthesized by the pineal gland in vertebrates, promotes human blastocyst development and increases pregnancy rate. However, the role and underlying mechanism of melatonin on human endometrial receptivity and decidualization still remains poorly defined. Methods: Trophoblast JEG-3 spheroids were cocultured with endometrial epithelial cells. Real-time PCR, Western blot, siRNA transfection, epithelial-stromal cell coculture system, and assay of Ishikawa cell-conditioned medium were used to explore the effects of melatonin on human endometrial decidualization and the underlying molecular pathways. Findings: In this study, we showed that melatonin induces the expression of the endometrial receptive markers, integrin β3 and HOXA10 in the less-receptive endometrial epithelial cell line AN3 CA and increased the attachment rate of trophoblast JEG-3 spheroids on endometrial epithelial AN3 CA cells. In an epithelial-stromal coculture system, we further proved that melatonin-stimulated IFN-γ secretion from Ishikawa cells promotes in vitro decidualization of stromal cells through regulating progesterone receptor B (PRB). Under in vitro decidualization, IFN-γ significantly increases the levels IGFBP1 and PRL, which is abrogated by suppressing PRB. Under in vitro decidualization of endometrial stromal cells, the expression of the decidualization markers, IGFBP1 and PRL, is significantly stimulated by melatonin treatment. Melatonin obviously increases phosphorylated STAT3 level and decreases p-Akt level. Interpretation: Melatonin may play crucial roles in human endometrial receptivity and decidualization. The dialogue between endometrial epithelial and stromal cell mediated by melatonin should be beneficial for decidual process. Funding: National Key R&D Program of China (2018YFC1004403) and National Natural Science Foundation of China (31671563, 31871511). Declaration of Interests: The authors declare that there is no conflict of interest. Ethics Approval Statement: All human procedures were approved by the Institutional Committee on the Use of Human Subjects in Medical Research of Southern Medical University with written consent.

Embryo implantation and decidualization are key steps for successful reproduction. Although numerous factors have been identified to be involved in embryo implantation and decidualization, the mechanisms underlying these processes are still unclear. Based on our preliminary data, Prss56, a trypsin-like serine protease, is strongly expressed at implantation site in mouse uterus. However, the expression, regulation and function of Prss56 during early pregnancy are still unknown. In mouse uterus,Prss56is strongly expressed in the subluminal stromal cells at implantation site on day 5 of pregnancy compared to inter-implantation site. Under delayed implantation,Prss56expression is undetected. After delayed implantation is activated by estrogen, Prss56 is obviously induced at implantation site. Under artificial decidualization, Prss56 signal is seen at the primary decidual zone at the initial stage of artificial decidualization. When stromal cells are induced forin vitrodecidualization,Prss56expression is significantly elevated.Dtprpexpression underin vitrodecidualization is suppressed byPrss56siRNA. In cultured stromal cells, HB-EGF markedly stimulatesPrss56expression through EGFR/ERK pathway. Based on promoter analysis, we also showed that Egr2 is involved in Prss56 regulation by HB-EGF. Collectively,Prss56expression at implantation site is modulated by HB-EGF/EGFR/ERK signaling pathway and involved in mouse decidualization.

The establishment of decidualization is a prerequisite of successful pregnancy. Lysyl oxidase (Lox) is a copper-containing amine oxidase which catalyzes cross-linking of collagen and elastin in the ECM. Lox is expressed in the subluminal stroma surrounding the implanting blastocyst on day 5 of pregnancy. From days 6 to 8, the signals for Lox mRNA and protein are strongly detected in the decidual cells. The expression of Lox is under the control of estrogen via the GSK-3β/β-catenin/c-myc pathway. Dtprp is decreased by the inhibition of Lox activity. Furthermore, the inhibition of Lox activity decreases stromal cell migration and embryo adhesion. Our findings highlight the crucial role of Lox in endometrial stromal cells and deepen our understanding of decidualization.

Unfolded or misfolded protein accumulation in the endoplasmic reticulum lumen leads to endoplasmic reticulum stress (ER stress). Although it is known that ER stress is crucial for mammalian reproduction, little is known about its physiological significance and underlying mechanism during decidualization. Here we show that Ire-Xbp1 signal transduction pathway of unfolded protein response (UPR) is activated in decidual cells. The process of decidualization is compromised by ER stress inhibitor tauroursodeoxycholic acid sodium (TUDCA) and Ire specific inhibitor STF-083010 both in vivo and in vitro. A high concentration of ER stress inducer tunicamycin (TM) suppresses stromal cells proliferation and decidualization, while a lower concentration is beneficial. We further show that ER stress induces DNA damage and polyploidization in stromal cells. In conclusion, our data suggest that the GRP78/Ire1/Xbp1 signaling pathway of ER stress-UPR is activated and involved in mouse decidualization.