Decidualization is an essential step in the establishment of pregnancy. However, the functional contributions of long intergenic noncoding RNAs (LincRNAs) to decidualization have not been explored. To explore the regulation and role of LincRNAs during human decidualization, human endometrial stromal cells (HESCs) are induced to undergo in vitro decidualization by treating with estradiol-17β, db-cAMP and medroxyprogesterone acetate. LINC00473 (LINC473) expression is highly induced in HESCs after decidual stimulus. We found that cAMP-PKA pathway regulates the expression of LINC473 through IL-11-mediated STAT3 phosphorylation. RNA interference-mediated down-regulation of LINC473 inhibits in vitro decidualization. These results suggested that LINC473 might be functionally required for human decidualization. This is the first report demonstrating the presence of LincRNA during human decidualization.
Embryo implantation involves a sterile inflammatory reaction that is required for the invasion of the blastocyst into the decidua. Adenosine triphosphate (ATP) released from stressed or injured cells acts as an important signaling molecule to regulate many key physiological events, including sterile inflammation. We found that the amount of ATP in the uterine luminal fluid of mice increased during the peri-implantation period, and this depended on the presence of an embryo. We further showed that the release of ATP from receptive epithelial cells was likely stimulated by lactate released from the blastocyst through connexin hemichannels. The ATP receptor P2y2 was present on uterine epithelial cells during the preimplantation period and increased in the stromal cells during the time at which decidualization began. Pharmacological inhibition of P2y2 compromised decidualization and implantation. ATP-P2y2 signaling stimulated the phosphorylation of Stat3 in uterine luminal epithelial cells and the expression of early growth response 1 (Egr1) and prostaglandin-endoperoxide synthase 2 (Ptgs2, also known as Cox-2), all of which are required for decidualization and/or implantation, in stromal cells. Short exposure to high concentrations of ATP promoted decidualization of primary stromal cells, but longer exposures or lower ATP concentrations did not. The expression of genes encoding ATP-degrading ectonucleotidases increased in the decidua during the peri-implantation period, suggesting that they may limit the duration of the ATP signal. Together, our results indicate that the blastocyst-induced release of ATP from uterine epithelial cells during the peri-implantation period may be important for the initiation of stromal cell 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.
Local renin-angiotensin system (RAS) in female reproductive system is involved in many physiological and pathological processes, such as follicular development, ovarian angiogenesis, ovarian, and endometrial cancer progress. However, studies on the functional relevance of RAS in human endometrium are limited, especially for reninangiotensin-aldosterone system (RAAS). In this study, we defined the location of RAS components in human endometrium. We found that angiotensin II type-1 receptor (AT 1 R) and aldosterone synthase (CYP11B2), major components of RAAS, are specifically expressed in endometrial gland during mid-secretory phase. Aldosterone receptor, mineralocorticoid receptor (MR), is elevated in stroma in mid-secretory endometrium. In vitro, MR is also activated by aldosterone during decidualization. Activated MR initiates LKB1 expression, followed by phosphorylating of AMPK that stimulates PDK4 expression. The impact of PDK4 on decidualization is independent on PDHE1α inactivation. Based on co-immunoprecipitation, PDK4 interacts with p-CREB to prevent its ubiquitination for facilitating decidualization via FOXO1. Restrain of MR activation interrupts LKB1/p-AMPK/PDK4/p-CREB/FOXO1 pathway induced by aldosterone, indicating that aldosterone action on decidualization is mainly dependent on MR stimulation. Aldosterone biosynthesized in endometrial gland during mid-secretory phase promotes decidualization via activating MR/LKB1/p-AMPK/PDK4/p-CREB/FOXO1 signaling pathway. This study provides the valuable information for understanding the underlying mechanism during decidualization.
Maintenance of a suitable uterine milieu is important for embryo development and subsequent implantation during early pregnancy. High estrogen level in proestrous and estrous stages is essential for uterine anti-bacterial activity during preimplantation period. Lipocalin-2 is an essential molecule which prevents bacterial infection by sequestering iron. In this study, the highest expression of lipocalin-2 is observed in the endometrial epithelium on day 1 of normal pregnancy and pseudopregnancy, which exhibit a similar hormone scenario. By injecting the agonists for estrogen receptor α and estrogen receptor β in ovariectomized mice, we found estrogen receptor α is the dominant member for estrogen regulation on lipocalin-2 expression. Estrogen treatment in estrogen receptor α-knockout mice further confirmed the role of estrogen receptor α. Using published data from whole-genome estrogen receptor α binding site assay, significant estrogen receptor α recruitment peaks are found at the downstream of lipocalin-2 gene after estrogen treatment. Furthermore, to study the anti-bacterial activity of lipocalin-2 in uterus, Escherichia coli is injected to mimic bacterial infection. Our results showed an obvious induction of lipocalin-2 in Escherichia coli-treated group. Taken together, this study indicates estrogen regulation of lipocalin-2 in uterine epithelium is mediated by estrogen receptor α, and lipocalin-2 may have anti-bacterial activity during early pregnancy.
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, is strongly expressed in the subluminal stromal cells at implantation site on day 5 of pregnancy compared to inter-implantation site. Under delayed implantation, expression 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 for decidualization, expression is significantly elevated. expression under decidualization is suppressed by siRNA. In cultured stromal cells, HB-EGF markedly stimulates expression through EGFR/ERK pathway. Based on promoter analysis, we also showed that Egr2 is involved in Prss56 regulation by HB-EGF. Collectively, expression at implantation site is modulated by HB-EGF/EGFR/ERK signaling pathway and involved in mouse decidualization.
Lipocalin-2 (Lcn2) is a small glycoprotein involved in a number of biological processes such as inflammation and antibacterial response. In our study, Lcn2 is expressed in the subluminal stromal cells at implantation site on day 5 of pregnancy. The expression of Lcn2 in stromal cells is under the control of progesterone through Akt-c-Myc signaling pathway. Data from Lcn2 knockdown and recombinant protein treatments indicate that Lcn2 promotes mPGES-1 expression in stromal cells. The expression of Lcn2 and mPGES-1 is strongly stimulated by lipopolysaccharide (LPS), indicating that Lcn2 mediates LPS-induced inflammation. These findings shed light on the role of Lcn2 during decidualization.
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