At implantation, the embryo expresses paternally derived alloantigens and evokes inflammation that can threaten reproductive success. To ensure a robust placenta and sustainable pregnancy, an active state of maternal immune tolerance mediated by CD4(+) regulatory T cells (Tregs) is essential. Tregs operate to inhibit effector immunity, contain inflammation, and support maternal vascular adaptations, thereby facilitating trophoblast invasion and placental access to the maternal blood supply. Insufficient Treg numbers or inadequate functional competence are implicated in idiopathic infertility and recurrent miscarriage as well as later-onset pregnancy complications stemming from placental insufficiency, including preeclampsia and fetal growth restriction. In this Review, we summarize the mechanisms acting in the conception environment to drive the Treg response and discuss prospects for targeting the T cell compartment to alleviate immune-based reproductive disorders.
The aim of this study was to investigate the effect of β-CP on embryo implantation in mice. Forty female mice were randomly assigned to four groups of 10 mice each: one control group and three β-CP treated groups. The control group was administered corn oil only, while the three β-CP-treated groups were given corn oil containing 5, 10, and 20 mg/kg bw d β-CP for 3 months through intragastric administration. The results indicated that the administration of β-CP decreased the rate of embryo implantation (all 0.05), E level in the serum, and the expression of Homeobox A10 (HoxA10) protein. In addition, β-CP significantly increased ERa and PRA protein expression levels. These results suggest that β-CP can disrupt the balance of E and P, influence ERa and PRA expression and their downstream-related molecule Hoxa10, and decrease embryo implantation.
Recent studies revealed that TMEM16A is involved in several reproductive processes, including ovarian estrogen secretion and ovulation, sperm motility and acrosome reaction, fertilization and myometrium contraction. However, little is known about the expression and function of TMEM16A in embryo implantation and decidualization. In this study, we focused on the expression and regulation of TMEM16A in mouse uterus during early pregnancy. We found that TMEM16A is upregulated in uterine endometrium in response to embryo implantation and decidualization. Progesterone treatment could induce TMEM16A expression in endometrial stromal cells through progesterone receptor/c-Myc pathway, which is blocked by progesterone receptor antagonist or the inhibitor of c-Myc signaling pathway. Inhibition of TMEM16A by small molecule inhibitor (T16Ainh-A01) resulted in impaired embryo implantation and decidualization in mice. Treatment with either specific siRNA of Tmem16a or T16Ainh-A01 inhibited the decidualization and proliferation of mouse endometrial stromal cells. In conclusion, our results revealed that TMEM16A is involved in embryo implantation and decidualization in mice, compromised function of TMEM16A may lead to impaired embryo implantation and decidualization.
Background/Aims: Hmgn2 is involved in regulating embryonic development, but its physiological function during embryo implantation and decidualization remains unknown. Methods: In situ hybridization, real-time PCR, RNA interference, gene overexpression and MTS assay were used to examine the expression of Hmgn2 in mouse uterus during the pre-implantation period and explore its function and regulatory mechanisms in epithelial adhesion junction and stromal cell proliferation and differentiation. Results: Hmgn2 was primarily accumulated in uterine luminal epithelia on day 4 of pregnancy and subluminal stromal cells around the implanting blastocyst at implantation sites on day 5. Similar results were observed during delayed implantation and activation. Meanwhile, Hmgn2 expression was visualized in the decidua. In uterine epithelial cells, silencing of Hmgn2 by specific siRNA reduced the expression of adhesion molecules Cdh1, Cdh2 and Ctnnb1 and enhanced the expression of Muc1, whereas constitutive activation of Hmgn2 exhibited the opposite effects, suggesting a role for Hmgn2 in attachment reaction during embryo implantation. Estrogen stimulated the expression of Hmgn2 in uterine epithelia, but the stimulation was abrogated by ER antagonist ICI 182,780. Further analysis evidenced that attenuation of Hmgn2 might eliminate the regulation of estrogen on the expression of Cdh1, Cdh2 and Ctnnb1. In uterine stromal cells, progesterone induced the accumulation of Hmgn2 which advanced the expression of Prl8a2 and Prl3c1, two well-known differentiation markers for decidualization, but did not affect the proliferation of stromal cells. Knockdown of Hmgn2 blocked the progesterone-induced differentiation of uterine stromal cells. Moreover, Hmgn2 might serve as an intermediate to mediate the regulation of progesterone on Hand2. Conclusion: Hmgn2 may play an important role during embryo implantation and decidualization.
Uterine glands are essential for pregnancy establishment. By employing forkhead box A2 (FOXA2)-deficient mouse models coupled with leukemia inhibitory factor (LIF) repletion, we reveal definitive roles of uterine glands in embryo implantation and stromal cell decidualization. Here we report that LIF from the uterine glands initiates embryo-uterine communication, leading to embryo attachment and stromal cell decidualization. Detailed histological and molecular analyses discovered that implantation crypt formation does not involve uterine glands, but removal of the luminal epithelium is delayed and subsequent decidualization fails in LIF-replaced glandless but not gland-containing FOXA2-deficient mice. Adverse ripple effects of those dysregulated events in the glandless uterus result in embryo resorption and pregnancy failure. These studies provide evidence that uterine glands synchronize embryo-endometrial interactions, coordinate on-time embryo implantation, and impact stromal cell decidualization, thereby ensuring embryo viability, placental growth, and pregnancy success.
Background/Aims: Embryo implantation is an essential process for eutherian pregnancy, but this process varies across eutherians. The genomic mechanisms that led to the emergence and diversification of embryo implantation are largely unknown. Methods: In this study, we analyzed transcriptomic changes during embryo implantation in mice and rats by using RNA-seq. Bioinformatics and evolutionary analyses were performed to characterize implantation-associated genes in these two species. Results: We identified a total of 518 differentially expressed genes in mouse uterus during implantation, of which 253 genes were up-regulated and 265 genes were down-regulated at the implantation sites compared with the inter-implantation sites. In rat uterus, there were 374 differentially expressed genes, of which 284 genes were up-regulated and 90 genes were down-regulated. A cross-species comparison revealed that 92 up-regulated genes and 20 down-regulated genes were shared. The differences and similarities between mice and rats were investigated further at the gene ontology, pathway, network, and causal transcription factor levels. Additionally, we found that embryo implantation might have evolved through the recruitment of ancient genes into uterine expression. The evolutionary rates of the differentially expressed genes in mouse and rat uterus were significantly lower than those of the non-changed genes, indicating that implantation-related genes are evolutionary conserved due to high selection pressure. Conclusion: Our study provides insights into the molecular mechanisms involved in the evolution of embryo implantation.
Abstract Tubulin polymerization promoting protein 3 (TPPP3) is known to be expressed in the endometrium in a cyclic manner, and its functional role in the physiology of implantation remains unknown. Here we demonstrate a novel function of TPPP3 during the window of implantation and in the establishment of pregnancy using a mouse model. The increased protein expression of TPPP3 and β-catenin during peri-implantation period, i.e. D5 (receptive phase, 0800 h), was observed as compared to that on D1 (nonreceptive phase, 0800 h). SiRNATPPP3-mediated knockdown of uterine TPPP3 resulted in implantation failure and inhibited the expression of receptivity markers: LIF, Integrin-β3, IHH, and Wnt4. TPPP3 silencing in mouse endometrial epithelial cells also prevented blastocyst attachment and the adhesion reaction. In delayed implantation experiment, expression of TPPP3 was increased in active implantation group (E2 + P4) compared to delayed implantation group (P4). The increased expression of TPPP3 in E2 + P4-treated Ishikawa cells compared to vehicle or P4 or E2 alone-treated Ishikawa cells also revealed its upregulation by E2. The suppression of β-catenin in uterus under the condition of transient knockdown of TPPP3 and the co-immunoprecipitation experiment revealed that regulation of β-catenin was mediated via TPPP3 during implantation. Additionally, in order to gain insight into TPPP3 collaborators, we identified TPPP3 interacting proteins by nanoLC-MS analysis in mouse uterus which might be involved during implantation. In conclusion, our study suggests that TPPP3 is important for embryo implantation and for the establishment of early pregnancy through modulation of β-catenin.
Successful embryo implantation requires a receptive endometrium. Poor uterine receptivity can account for implantation failure in women who experience recurrent pregnancy loss or multiple rounds of unsuccessful in vitro fertilization cycles. Here, we demonstrate that the transcription factor Forkhead Box O1 (FOXO1) is a critical regulator of endometrial receptivity in vivo. Uterine ablation of Foxo1 using the progesterone receptor Cre (Pgr(cre)) mouse model resulted in infertility due to altered epithelial cell polarity and apoptosis, preventing the embryo from penetrating the luminal epithelium. Analysis of the uterine transcriptome after Foxo1 ablation identified alterations in gene expression for transcripts involved in the activation of cell invasion, molecular transport, apoptosis, beta-catenin (CTNNB1) signaling pathway, and an increase in PGR signaling. The increase of PGR signaling was due to PGR expression being retained in the uterine epithelium during the window of receptivity. Constitutive expression of epithelial PGR during this receptive period inhibited expression of FOXO1 in the nucleus of the uterine epithelium. The reciprocal expression of PGR and FOXO1 was conserved in human endometrial samples during the proliferative and secretory phase. This demonstrates that expression of FOXO1 and the loss of PGR during the window of receptivity are interrelated and critical for embryo implantation.
Natural and synthetic progestogens have been commonly used to prevent recurrent pregnancy loss in women with inadequate progesterone secretion or reduced progesterone sensitivity. However, the clinical efficacy of progesterone and its analogs for maintaining pregnancy is variable. Additionally, the underlying cause of impaired endometrial progesterone responsiveness during early pregnancy remains unknown. Here, we demonstrated that uterine-selective depletion of BMI1, a key component of the polycomb repressive complex-1 (PRC1), hampers uterine progesterone responsiveness and derails normal uterine receptivity, resulting in implantation failure in mice. We further uncovered genetic and biochemical evidence that BMI1 interacts with the progesterone receptor (PR) and the E3 ligase E6AP in a polycomb complex-independent manner and regulates the PR ubiquitination that is essential for normal progesterone responsiveness. A close association of aberrantly low endometrial BMI1 expression with restrained PR responsiveness in women who had previously had a miscarriage indicated that the role of BMI1 in endometrial PR function is conserved in mice and in humans. In addition to uncovering a potential regulatory mechanism of BMI1 that ensures normal endometrial progesterone responsiveness during early pregnancy, our findings have the potential to help clarify the underlying causes of spontaneous pregnancy loss in women.