The establishment of a receptive uterus is the prime requirement for embryo implantation. In mice, the E-2-induced cytokine leukemia inhibitory factor (LIF) is essential in switching the uterine luminal epithelium (LE) from a nonreceptive to a receptive state. Here we define the LIF-mediated switch using array analysis and informatics to identify LIF-induced changes in gene expression and annotated signaling pathways specific to the LE. We compare gene expression profiles at 0, 1, 3, and 6 h, following LIF treatment. During the first hour, the JAK-STAT signaling pathway is activated and the expression of 54 genes declines, primarily affecting LE cytoskeletal and chromatin organization as well as a transient reduction in the progesterone, TGFbetaR1, and ACVR1 receptors. Simultaneously 256 genes increase expression, of which 42 are transcription factors, including Sox, Kfl, Hes, Hey, and Hox families. Within 3 h, the expression of 3987 genes belonging to more than 25 biological process pathways was altered. We confirmed the mRNA and protein distribution of key genes from 10 pathways, including the Igf-1, Vegf, Toll-like receptors, actin cytoskeleton, ephrin, integrins, TGFbeta, Wnt, and Notch pathways. These data identify novel LIF-activated pathways in the LE and define the molecular basis between the refractory and receptive uterine phases. More broadly, these findings highlight the staggering capacity of a single cytokine to induce a dynamic and complex network of changes in a simple epithelium essential to mammalian reproduction and provide a basis for identifying new routes to regulating female reproduction.
Abstract Research on the effect of adenomyosis on the rate of success of IVF is controversial. Differences in study design, study power, criteria and instrument used to diagnose adenomyosis and choice of controls may explain these discrepancies. To establish whether embryo implantation is impaired in women with adenomyosis, women scheduled for IVF were prospectively evaluated for the presence of adenomyosis and whether this condition affected embryo implantation. Forty-nine women with adenomyosis diagnosed at transvaginal ultrasound with no abnormal uterine bleeding were recruited. They were matched for study period, age, day of embryo transfer and number of transferred embryos to 49 controls without the disease. In women with adenomyosis, 24 out of 76 embryos transferred implanted (32%); this occurred in 16 out of 76 (21%) in unaffected controls. The crude odds ratio of implantation in affected women was 1.73 (95% CI 0.83 to 3.60). The odds ratio adjusted for body mass index (the unique variable found to differ at univariate analysis) was 1.78 (95% CI 0.85 to 3.77). In conclusion, implantation rate is not impaired in asymptomatic women who are diagnosed with adenomyosis at transvaginal sonography. Affected women can be reassured about the effect of this condition on their chances of success.
Although embryo implantation is a prerequisite for human reproduction, it remains a poorly understood process. The molecular mechanisms regulating endometrial receptivity and/or embryo implantation are still largely unclear. Pubmed and Medline literature databases were searched for articles in English published up to December 2013 with relevant keywords including 'endometrium', 'Na+, Cl-, K+, or Ca2+ channels', 'ion channels', 'endometrial receptivity', 'blastocyst implantation' and 'embryo implantation'. At the time of writing, more than 14 types of ion channels, including the cystic fibrosis transmembrane conductance regulator, epithelial sodium channel and various Ca2+ and K+ channels, had been reported to be expressed in the endometrium or cells of endometrial origin. In vitro and/or in vivo studies conducted on different species, including rodents, pigs and humans, demonstrated the involvement of various ion channels in the process of embryo implantation by regulating: (i) uterine luminal fluid volume; (ii) decidualization; and (iii) the expression of the genes associated with implantation. Importantly, abnormal ion channel expression was found to be associated with implantation failure in IVF patients. Ion channels in the endometrium are emerging as important players in regulating endometrial receptivity and embryo implantation. Abnormal expression or function of ion channels in the endometrium may lead to impaired endometrial receptivity and/or implantation failure. Further investigation into the roles of endometrial ion channels may provide a better understanding of the complex process of embryo implantation and thus reveal novel targets for diagnosis and treatment of implantation failure.
Abstract Computer-automated time-lapse analysis has been shown to improve embryo selection by providing quantitative and objective information to supplement traditional morphology. In this multi-centre study, the relationship between such computer-derived outputs (High, Medium, Low scores), embryo implantation and clinical pregnancy were examined. Data were collected from six clinics, including 205 patients whose embryos were imaged by the EevaTM System. The Eeva scores were blinded and not considered during embryo selection. Embryos with High and Medium scores had significantly higher implantation rates than those with Low scores (37% and 35% versus 15%; P < 0.0001; P = 0.0004). Similar trends in implantation rates were observed in different IVF centres each using their own protocols. Further analysis revealed that patients with at least one High embryo transferred had significantly higher clinical pregnancy rates than those with only Low embryos transferred (51% versus 34%; P = 0.02), although patients' clinical characteristics across groups were comparable. These data, together with previous research and clinical studies, confirm that computer-automated Eeva scores provide valuable information, which may improve the clinical outcome of IVF procedures and ultimately facilitate the trend of single embryo selection.
Embryo implantation is a complex initial step in establishment of a successful pregnancy. Many mRNAs have been shown to be differentially expressed in the rat uterus during embryo implantation. However, the expression profiles of microRNAs (miRNAs), a key post‐transcriptional regulator of gene expression, in the rat uterus between the pre‐receptive and receptive phases are still unknown. Here, an miRNA microarray was used to examine differential expression of miRNAs in the rat uterus between the pre‐receptive and receptive phases. Twenty‐eight miRNAs were up‐regulated and 29 miRNAs were down‐regulated at least twofold during the receptive phase in rat uterus; these results were confirmed by Northern blotting. miR‐29a was only highly expressed in rat uterus during the implantation period, and activation of delayed implantation and artificial decidualization enhanced the miR‐29a level. Further investigation revealed that both the pro‐apoptotic factor genes Bak1 and Bmf and the anti‐apoptotic factor gene Bcl‐w are targets of miR‐29a. There was weak binding between miR‐29a and the 3′ UTR of the anti‐apoptotic factor gene Mcl1. Over‐expression of miR‐29a inhibited the late apoptosis of endometrial stromal cells, which may be due to the stronger binding capacity between miR‐29a and the 3′ UTR of pro‐apoptotic factors than that between miR‐29a and the 3′ UTR of anti‐apoptotic factors. Collectively, miR‐29a plays an important role during embryo implantation by regulating both pro‐apoptotic and anti‐apoptotic factors. miR‐29a may predominantly bind pro‐apoptotic factors, leading to inhibition of cell apoptosis. MiR-29a was highly expressed in rat uterus during the implantation period. Both pro‐apoptotic (Bak1 and Bmf) and anti‐apoptotic factors (Bcl-w) were the target genes of miR-29a. There was weak binding capacity between miR-29a and 3′‐UTR of anti‐apoptotic factor Mcl1. Over‐expression of miR-29a inhibited the late apoptosis of endometrial stromal cells, which may be caused by predominately combining pro‐apoptotic factors.
Implantation and placentation are critical steps for successful pregnancy. The pig has a non-invasive placenta and the uterine luminal epithelium is intact throughout pregnancy. To better understand the regulation mechanisms in functions of endometrium at three certain gestational stages that are critical for embryo/fetal loss in pigs, we characterized microRNA (miRNA) expression profiles in the endometrium on days 15 (implantation period), 26 (placentation period) and 50 (mid-gestation period) of gestation. The differentially expressed miRNAs across gestational days were detected and of which, 65 miRNAs were grouped into 4 distinct categories according to the similarities in their temporal expression patterns: (1) categories A and B contain majority of miRNAs (51 miRNAs, such as the miR-181 family) that were down-or up-regulated between gestational days 15 and 26, respectively; (2) categories C and D (14 miRNAs) consist miRNAs that were down-or up-regulated between gestational days 26 and 50, respectively. The expression patterns represented by eleven miRNAs were validated by qPCR. The majority of miRNAs were in categories A and B, suggesting that these miRNAs were involved in regulation of embryo implantation and placentation. The pathway analysis revealed that the predicted targets were involved in several pathways, such as focal adhesion, cell proliferation and tissue remolding. Furthermore, we identified that genes well-known to affect embryo implantation in pigs, namely SPP1, ITGB3 and ESR1, contain the miR-181a or miR-181c binding sites using the luciferase reporter system. The present study revealed distinctive miRNA expression patterns in the porcine endometrium during the implantation, placentation or mid-gestation periods. Additionally, our results suggested that miR-181a and miR-181c likely play important roles in the regulation of genes and pathways that are known to be involved in embryo implantation and placentation in pigs.
The establishment of a successful pregnancy requires the implantation of a competent blastocyst into a 'receptive' endometrium, facilitating the formation of a functional placenta. Inadequate or inappropriate implantation and placentation is a major reason for infertility and is thought to lead to first-trimester miscarriage, placental insufficiency and other obstetric complications. Blastocystendometrial interactions are critical for implantation and placental formation. The Notch signalling family is a receptor-ligand family that regulates cellular processes as diverse as proliferation, apoptosis, differentiation, invasion and adhesion. Notch signalling is achieved via cell-cell interaction; thus, via Notch, cells can have direct effects on the fate of their neighbours. Recently, a number of studies have identified Notch receptors and ligands in the endometrium, blastocyst and placenta. This review collates current knowledge of this large receptor-ligand family and explores the role of Notch signalling during implantation and placentation, drawing on information from both human and animal studies. Overall, the evidence suggests that Notch signalling is a critical component of fetal-maternal communication during implantation and placentation and that abnormal Notch expression is associated with impaired placentation and pre-eclampsia.