Dual source and target of heparin-binding EGF-like growth factor during the onset of implantation in the hamster

The Multiple Functions of HB-EGF in Female Reproduction and Related Cancer: Molecular Mechanisms and Targeting Strategies

Heparin-binding growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) ligand family which has a crucial role in women's health. However, there is a lack of comprehensive review to summarize the significance of HB-EGF. Therefore, this work first described the expression patterns of HB-EGF in the endometrium and ovary of different species and gestational time. Then, the focus was on exploring how it promotes the successful implantation and regulates the process of decidualization and the function of ovarian granulosa cells as an intermediate molecule. Otherwise, we also focused on the clinical and prognostic significance of HB-EGF in female-related cancers (including ovarian cancer, cervical cancer, and endometrial cancer) and breast cancer. Lastly, the article also summarizes the current drugs targeting HB-EGF in the treatment of ovarian cancer and breast cancer. Overall, these studies found that the expression of HB-EGF in the endometrium is spatiotemporal and species-specific. And it mediates the dialogue between the blastocyst and endometrium, promoting synchronous development of the blastocyst and endometrium as an intermediate molecule. HB-EGF may serve as a potentially valuable prognostic clinical indicator in tumors. And the specific inhibitor of HB-EGF (CRM197) has a certain anti-tumor ability, which can exert synergistic anti-tumor effects with conventional chemotherapy drugs. However, it also suggests that more research is needed in the future to elucidate its specific mechanisms and to accommodate clinical studies with a larger sample size to clarify its clinical value.

Effect of culture conditions and method of conception on mouse live birth rate

OBJECTIVE

To understand in a mouse model whether there are differences in the decidua and live birth rate after transfer of blastocysts generated by in vitro fertilization (IVF) or by superovulation with spontaneous mating into unstimulated recipients.

DESIGN

Animal experiment.

SETTING

University-affiliated tertiary hospital.

ANIMAL(S)

Mice.

INTERVENTION(S)

IVF embryos were generated and cultured in either Whitten medium (WM, suboptimal conditions) and 20% O₂ or KSOM medium with amino acids (KAA, optimal conditions) and 5% O₂. The control blastocysts from superovulated mice were flushed out of the uterus 3.5 days (E3.5) after mating (FB group). The resulting blastocysts were transferred to nonsuperovulated CF1 recipients mated to vasectomized males. To understand whether anomalies of decidua were present, the expression of genes involved in decidual development and inflammation was analyzed at E7.5 and E18.5. Similarly, immunostaining was used to evaluate whether the pathways involved in activation of mTORC1 (p-S6) and Cox2 signaling (Cox 2 staining) were altered.

MAIN OUTCOME MEASURE(S)

Live birth rate, gene expression, and immunostaining of decidua.

RESULT(S)

Implantation rates at E7.5 were similar, but in vivo embryos (FB groups) were predicted to result in live births 3.3 times higher (2.2-5.1) and 6.6 times higher (4.7-9.3) compared with optimal and suboptimal cultures, respectively. Expression of genes involved in decidual development and inflammation or localization and intensity of staining for p-S6 (mTOR pathway), or inflammation (Cox 2 pathway) were not different among the groups.

CONCLUSION(S)

The predicted live birth rate was decreased in mouse embryos generated by IVF compared with embryos generated by mating, whereas the implantation rate was not different. Suboptimal culture conditions resulted in lower birth rate. We did not find evidence of abnormalities in decidualization that could explain these findings. These data indicate that blastocysts cultured in stressful conditions are less competent, suggesting that decreasing the number of embryonic manipulations may result in higher live birth rates.

Expression of ER-α and ER-β during peri-implantation period in uterus is essential for implantation and decidualization in golden hamster

AIMS

The role of estrogen in embryo implantation in golden hamster (Mesocricetus auratus) is still ambiguous. In order to clarify it, we investigated the spatial distribution and expression of estrogen receptors, ER-α and ER-β in the uterus of pregnant hamster during peri-implantation period and identified the effect of estrogen receptor antagonist ICI-182,780 on the embryo implantation.

MAIN METHODS

We performed in vivo experiments on early pregnant hamsters involving treatment with ICI-182,780, an estrogen receptor antagonist. Immunohistochemistry, western blot analysis and quantitative PCR were employed to evaluate the spatio-temporal distribution and expression of ER-α and ER-β in the uterus of normal early pregnant and treated hamsters.

KEY FINDINGS

Results showed that embryo implantation was completely absent in ICI-182,780 treated uterine horn while, normal implantation occurred in control and vehicle treated horns. Both the receptors were differentially expressed in the uterus of hamster from day 1 (D1) to day7 (D7). In contrast, treated horns without any implantation site showed no trace of any receptors. Protein and mRNA expression of both the receptors were high around the day of implantation while, ER-β expression was up-regulated on D7 of embryo implantation. P value˂0.05 is considered significant.

SIGNIFICANCE

Spatio-temporal expression of ERs in the uterus during peri-implantation period have crucial role for endometrium receptivity and implantation in hamster. Recurrent implantation failure is the devastating problem among the desirable couple and is mainly due to defect in endometrium receptivity. This study may provide a new insight to manage the problem of idiopathic infertility.

Alkaline phosphatase protects lipopolysaccharide-induced early pregnancy defects in mice

Excessive cytokine inflammatory response due to chronic or superphysiological level of microbial infection during pregnancy leads to pregnancy complications such as early pregnancy defects/loss and preterm birth. Bacterial toxin lipopolysaccharide (LPS), long recognized as a potent proinflammatory mediator, has been identified as a risk factor for pregnancy complications. Alkaline phosphatase (AP) isozymes have been shown to detoxify LPS by dephosphorylation. In this study, we examined the role of alkaline phosphatase (AP) in mitigating LPS-induced early pregnancy complications in mice. We found that 1) the uterus prior to implantation and implantation sites following embryo implantation produce LPS recognition and dephosphorylation molecules TLR4 and tissue non-specific AP (TNAP) isozyme, respectively; 2) uterine TNAP isozyme dephosphorylates LPS at its sites of production; 3) while LPS administration following embryo implantation elicits proinflammatory cytokine mRNA levels at the embryo implantation sites (EISs) and causes early pregnancy loss, dephosphorylated LPS neither triggers proinflammatory cytokine mRNA levels at the EISs nor induces pregnancy complications; 4) AP isozyme supplementation to accelerate LPS detoxification attenuates LPS-induced pregnancy complications following embryo implantation. These findings suggest that a LPS dephosphorylation strategy using AP isozyme may have a unique therapeutic potential to mitigate LPS- or Gram-negative bacteria-induced pregnancy complications in at-risk women.

Leukemia inhibitory factor: roles in embryo implantation and in nonhormonal contraception

Leukaemia inhibitory factor (LIF) plays an indispensible role in embryo implantation. Aberrant LIF production is linked to implantation failure. LIF regulates multiple processes prior to and during implantation such as uterine transformation into a receptive state, decidualization, blastocyst growth and development, embryo-endometrial interaction, trophoblast invasion, and immune modulation. Due to its critical role, LIF has been a target for a nonhormonal contraception. In this review, we summarize up-to-date information on the role of LIF in implantation and its role in contraception.

Alkaline phosphatases contribute to uterine receptivity, implantation, decidualization, and defense against bacterial endotoxin in hamsters

Alkaline phosphatase (AP) activity has been demonstrated in the uterus of several species, but its importance in the uterus, in general and during pregnancy, is yet to be revealed. In this study, we focused on identifying AP isozyme types and their hormonal regulation, cell type, and event-specific expression and possible functions in the hamster uterus during the cycle and early pregnancy. Our RT-PCR and in situ hybridization studies demonstrated that among the known Akp2, Akp3, Akp5, and Akp6 murine AP isozyme genes, hamster uteri express only Akp2 and Akp6; both genes are co-expressed in luminal epithelial cells. Studies in cyclic and ovariectomized hamsters established that while progesterone (P₄) is the major uterine Akp2 inducer, both P₄ and estrogen are strong Akp6 regulators. Studies in preimplantation uteri showed induction of both genes and the activity of their encoded isozymes in luminal epithelial cells during uterine receptivity. However, at the beginning of implantation, Akp2 showed reduced expression in luminal epithelial cells surrounding the implanted embryo. By contrast, expression of Akp6 and its isozyme was maintained in luminal epithelial cells adjacent to, but not away from, the implanted embryo. Following implantation, stromal transformation to decidua was associated with induced expressions of only Akp2 and its isozyme. We next demonstrated that uterine APs dephosphorylate and detoxify endotoxin lipopolysaccharide at their sites of production and activity. Taken together, our findings suggest that uterine APs contribute to uterine receptivity, implantation, and decidualization in addition to their role in protection of the uterus and pregnancy against bacterial infection.

Adherens junction proteins in the hamster uterus: their contributions to the success of implantation

The adherens junction (AJ) is important for maintaining uterine structural integrity, composition of the luminal environment, and initiation of implantation by virtue of its properties of cell-cell recognition, adhesion, and establishment of cell polarity and permeability barriers. In this study, we investigated the uterine changes of AJ components E-cadherin, beta-catenin, and alpha-catenin at their mRNA and protein levels, together with the cellular distribution of meprinbeta, phospho-beta-catenin, and active beta-catenin proteins, in hamsters that show only ovarian progesterone-dependent uterine receptivity and implantation. By in situ hybridization and immunofluorescence, we have demonstrated that uterine epithelial cells expressed three of these AJ proteins and their mRNAs prior to and during the initial phase of implantation. Immunofluorescence study showed no change in epithelial expression patterns of uterine AJ proteins from Days 1 to 5 of pregnancy. With advancement of the implantation process, AJ components were primarily expressed in cells of the secondary decidual zone (SDZ), but not in the primary decidual zone (PDZ). In contrast, we noted strong expression of beta-catenin and alpha-catenin proteins in the PDZ, but not in the SDZ, of mice. Taken together, these results suggest that AJ proteins contribute to uterine barrier functions by cell-cell adhesion to ensure protection of the embryo. In addition, cleavage of E-cadherin by meprinbeta might contribute to weakening uterine epithelial cell-cell contact for blastocyst implantation. We also report that the nuclear localization of active beta-catenin from Day 4 onward in hamsters implies that beta-catenin/Wnt-signal transduction is activated in the uterus during implantation and decidualization.

Dynamics of zonula occludens-2 expression during preimplantation embryonic development in the hamster

The objective was to study the expression of zonula occludens-2, a tight junction protein, during preimplantation hamster embryonic development, to predict its possible localization, source, and roles in trophectoderm differentiation and blastocyst formation in this species. Comparison of zonula occludens-2 expression pattern between the hamster and mouse preimplantation embryos from the zygote up to the blastocyst stage was also an objective of this study. Zonula occludens-2 localization was noted in nuclei of blastomeres in all stages of hamster and mouse embryonic development. Compared to mice, where zonula occludens-2 was first localized in the interblastomere membrane at the morula stage, hamster embryos had membranous zonula occludens-2 localization from the 2-cell stage onwards. Based on combined results of immunolocalization study in parthenogenic embryos and ovarian and epididymal sections, and quantitative PCR done in oocytes and all developmental stages of preimplantation embryos, perhaps there was a carry-over of zonula occludens-2 proteins or mRNA from the dam to the embryo. Based on these findings, we inferred that maternally derived zonula occludens-2 was involved in nuclear functions, as well as differentiation of blastomeres and blastocoel formation during preimplantation embryonic development in the hamster.

Diverse functions of HBEGF during pregnancy

The establishment of pregnancy requires an intimate physical interaction and a molecular dialogue between the conceptus and the maternal reproductive tract that commences at implantation and continues until the placenta is formed and fully functional. Failure of the regulatory processes that ensure the fidelity of this relationship can precipitate a catastrophic pregnancy loss. One of the earliest identified molecular mediators of blastocyst implantation is heparin-binding epidermal growth factor (EGF)-like growth factor (HBEGF), which signals between the endometrium and implanting trophoblast cells to synchronize their corresponding developmental programs. HBEGF expression by trophoblast cells of the developing placenta appears to regulate extravillous differentiation and provide cytoprotection in a sometimes-hostile environment. This versatile member of the EGF signaling system will be examined in light of its associations with key events during early pregnancy.

Cell cycle regulatory control for uterine stromal cell decidualization in implantation

Uterine stromal cell decidualization is integral to successful embryo implantation, which is a gateway to pregnancy establishment. This process is characterized by stromal cell proliferation and differentiation into decidual cells with polyploidy. The molecular mechanisms that are involved in these events remain poorly understood. The current concept is that locally induced factors with the onset of implantation influence uterine stromal cell proliferation and/or differentiation through modulation of core cell cycle regulators. This review will aim to address the currently available knowledge on interaction between growth factor/homeobox and cell cycle regulatory signaling in the progression of various aspects of decidualization.

Lysophosphatidic acid signaling during embryo development in sheep: involvement in prostaglandin synthesis

We investigated the lysophosphatidic acid (LPA) pathway during early pregnancy in sheep. LPA was detected in the uteri of early-stage pregnant ewes. Using quantitative RT-PCR, the expression of autotaxin, the LPA-generating enzyme, was found in the endometrium and conceptus. In the latter autotaxin, transcript levels were low on d 12-14 and increased on d 15-16, in parallel with the level of LPA. Autotaxin was localized in the luminal epithelium and superficial glands of the endometrium and in trophectoderm cells of the conceptus. The expression of G protein-coupled receptors for LPA was also examined in the ovine conceptus. LPA receptor LPAR1 and LPAR3 transcripts were expressed during early pregnancy and displayed a peak on d 14, whereas the highest level of protein for both receptors was observed at d 17. LPAR1 was localized in cellular membranes and nuclear compartments of the trophectoderm cells, whereas LPAR3 was revealed only in membranes. LPA activated phosphorylation of the MAPK ERK1/2 in ovine trophectoderm-derived cells. Moreover, the bioactive lipid increased the proliferation of trophectoderm cells in culture, as shown by thymidine and bromodeoxyuridine incorporation. Furthermore, LPA induced changes to the organization of beta-actin and alpha-tubulin, suggesting a role for it in rearrangement of trophectoderm cells cytoskeleton. Because a link had previously been established between prostaglandin and LPA pathways, we analyzed the effect of LPA on prostaglandin synthesis. LPA induced an increase in the release of prostaglandin F2alpha and prostaglandin E2, with no significant modifications to cytosolic phospholipase A2alpha and prostaglandin synthase-2 expression. Taken together, our results suggest a new role for LPA-mediated signaling in the ovine conceptus at the time of implantation.

HB-EGF: a unique mediator of embryo-uterine interactions during implantation

An implantation-competent blastocyst, several hours prior to its attachment on the uterine wall, transmits signals to surrounding uterine cells and vice-versa to initiate a two-way interaction. The language of this precocious dialogue is versatile, taking advantage of secreted molecules for long-range interactions and membrane-bound molecules for more immediate interactions. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) was identified as an early messenger of implantation which uses both modes of communication. In this review, we discuss the footprint of HB-EGF as to how it was initially identified as a mediator of implantation and how it initiates embryo-uterine interactions during this process.

Leukemia inhibitory factor ligand-receptor signaling is important for uterine receptivity and implantation in golden hamsters (Mesocricetus auratus)

Blastocyst implantation occurs in the progesterone-primed uterus of hamsters, but not in mice where the progesterone-primed uterus requires estrogen influence. Leukemia inhibitory factor (Lif), an estrogen-regulated gene in mice, is an absolutely needed cytokine for uterine receptivity and implantation in this species. This study aimed to evaluate the importance of Lif ligand-receptor signaling during uterine receptivity and implantation in hamsters. We investigated whether or not the uterine expression patterns of Lif and its receptors, Lif-r and gp130, during the periimplantation period of pregnancy and its hormonal regulation in the ovariectomized hamster correlate with some of the vital phases of uterine changes during early pregnancy. Uterine Lif, Lif-r, and gp130 mRNA expressions were examined by Northern and in situ hybridization. During the uterine preparatory phase for implantation, Lif, Lif-r, and gp130 were expressed either in the gland, luminal epithelium or both. As the implantation process began, Lif expression was minimal, but Lif-r and gp130 extended to the decidual areas. This decidual expression of Lif-r and gp130 was not dependent on the presence of the embryo since these genes were expressed in the suture-induced deciduomata. We also observed that, while the uterine Lif was induced by estrogen, Lif-r and gp130 were induced by progesterone in ovariectomized hamsters. Additionally, we show that a Lif antibody when instilled intraluminally on day 3 of pregnancy reduced the number of implantation sites. Taken together, these data suggest that Lif signaling is important for uterine receptivity and implantation in hamsters.

The hamster as a model for embryo implantation: insights into a multifaceted process

Defects in preimplantation embryonic development, uterine receptivity, and implantation are the leading cause of infertility, pregnancy problems and birth defects. Significant progress has been made in our basic understanding of these processes using the mouse model, where implantation is ovarian estrogen-dependent in the presence of progesterone. However, an animal model where implantation is progesterone-dependent must also be studied to gain a full understanding of the embryo and uterine events that are required for implantation. In this regard, the hamster is a useful model and this review summarizes the information currently available regarding mechanisms involved in synchronous preimplantation embryo and uterine development for implantation in this species.

Stage-specific integration of maternal and embryonic peroxisome proliferator-activated receptor delta signaling is critical to pregnancy success

Successful pregnancy depends on well coordinated developmental events involving both maternal and embryonic components. Although a host of signaling pathways participate in implantation, decidualization, and placentation, whether there is a common molecular link that coordinates these processes remains unknown. By exploiting genetic, molecular, pharmacological, and physiological approaches, we show here that the nuclear transcription factor peroxisome proliferator-activated receptor (PPAR) delta plays a central role at various stages of pregnancy, whereas maternal PPARdelta is critical to implantation and decidualization, and embryonic PPARdelta is vital for placentation. Using trophoblast stem cells, we further elucidate that a reciprocal relationship between PPARdelta-AKT and leukemia inhibitory factor-STAT3 signaling pathways serves as a cell lineage sensor to direct trophoblast cell fates during placentation. This novel finding of stage-specific integration of maternal and embryonic PPARdelta signaling provides evidence that PPARdelta is a molecular link that coordinates implantation, decidualization, and placentation crucial to pregnancy success. This study is clinically relevant because deferral of on time implantation leads to spontaneous pregnancy loss, and defective trophoblast invasion is one cause of preeclampsia in humans.

Indian hedgehog, but not histidine decarboxylase or amphiregulin, is a progesterone-regulated uterine gene in hamsters

Implantation occurs only in the progesterone (P4)-primed uterus in the majority of species, but little effort has been given to identify P4-mediated molecules in these species. Using hamsters as a model for P4-dependent implantation and three well-known uterine receptivity-associated P4-regulated genes, Indian hedgehog (Ihh), histidine decarboxylase (Hdc), and amphiregulin (Areg), in mice that require ovarian estrogen for uterine receptivity and implantation, our strategy aimed to determine whether P4 regulates uterine expression of these genes in hamsters and whether the event- and cell-specific uterine expression patterns of these genes during the periimplantation period in hamsters follow similarly with their patterns in mice. We report here that P4-mediated Ihh signaling is important for uterine receptivity and implantation in hamsters because uterine epithelial Ihh expression was regulated by P4 and its expression patterns during the periimplantation period of hamsters closely follow its pattern in mice. In contrast, we noted no hormonal regulation of Hdc and Areg in the hamster uterus. However, this did not diminish their importance in hamsters because their expression patterns and functions are event and cell specific during the periimplantation period: whereas Hdc was expressed exclusively in d 4 uterine glands and regulated by the blastocyst, Areg was expressed on the decidual area adjacent to the embryo from d 5 onward and involved in stromal cell proliferation. We conclude that similarities and dissimilarities exist in uterine expression pattern of implantation-related genes, including hormonal regulation and their event-specific importance.

Importance of uterine cell death, renewal, and their hormonal regulation in hamsters that show progesterone-dependent implantation

This study was initiated to investigate the significance of uterine cell death and proliferation during the estrous cycle and early pregnancy and their correlation with sex steroids in hamsters where blastocyst implantation occurs in only progesterone-primed uteri. The results obtained in hamsters were also compared with mice where blastocyst implantation occurs in progesterone-primed uteri if estrogen is provided. Apoptotic cells in the uterus were detected by using terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) technique. Uterine cell proliferation was determined by 5-bromo-2'-deoxyuridine labeling followed by immunohistochemistry and methyl-tritiated [(3)H]thymidine labeling. Active caspase-3, an executor protein of cell death, expression was assayed by immunohistochemistry/immunofluorescence. Our results demonstrate that epithelial proliferation on the second day after mating marks the initiation of pregnancy-related uterine changes in both species despite their differences in hormonal requirements. Hamsters and mice showed subtle differences in uterine proliferative and apoptotic patterns during early pregnancy and in response to steroids. There existed almost a direct correlation between apoptosis and caspase-3 expression, suggesting uterine cell death mostly involves the caspase pathway. Consistent with these findings, we showed, for the first time, that execution of uterine epithelial cell apoptosis by caspase-3 is important for blastocyst implantation because a caspsase-3 inhibitor N-acetyl-DEVD-CHO when instilled inside the uterine lumen on d 3 of pregnancy inhibits implantation in hamsters and mice. The overall results indicate that uterine cell apoptosis and proliferation patterns are highly ordered cell-specific phenomena that play an important role in maintaining the sexual cycle and pregnancy-associated uterine changes.

17beta-estradiol enhances heparin-binding epidermal growth factor-like growth factor production in human keratinocytes

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) enhances reepithelialization in wounds. Estrogen is known to promote cutaneous wound repair. We examined the in vitro effects of 17beta-estradiol (E2) on HB-EGF production by human keratinocytes. E2 or membrane-impermeable BSA-conjugated E2 (E2-BSA) increased HB-EGF secretion, mRNA level, and promoter activity in keratinocytes. E2 or E2-BSA enhanced in vitro wound closure in keratinocytes, and the closure was suppressed by anti-HB-EGF antibody. Activator protein-1 (AP-1) and specificity protein 1 (Sp1) sites on HB-EGF promoter were responsible for the E2- or E2-BSA-induced transactivation. Antisense oligonucleotides against c-Fos, c-Jun, and Sp1 blocked E2- or E2-BSA-induced HB-EGF transactivation. E2 or E2-BSA enhanced DNA binding and transcriptional activity of AP-1 and generated c-Fos/c-Jun heterodimers by inducing c-Fos expression. E2 or E2-BSA enhanced DNA binding and transcriptional activity of Sp1 in parallel with the enhancement of Sp1 phosphorylation. These effects of E2 or E2-BSA were not blocked by the nuclear estrogen receptor antagonist ICI-182,780 or anti-estrogen receptor-alpha or -beta antibodies but were blocked by inhibitors of G protein, phosphatidylinositol-specific PLC, PKC-alpha, and MEK1. These results suggest that E2 or E2-BSA may enhance HB-EGF production via activation of AP-1 and Sp1. These effects of E2 or E2-BSA may be dependent on membrane G protein-coupled receptors different from nuclear estrogen receptors and on the receptor-mediated activities of phosphatidylinositol-specific PLC, PKC-alpha, and MEK1. E2 may enhance wound reepithelialization by promoting HB-EGF production in keratinocytes.

Embryo-uterine interactions via the neuregulin family of growth factors during implantation in the mouse

Neuregulins (NRGs) are cell-signaling molecules with recognized roles in cancer and development, but little is known about their role in embryo implantation. Among representative NRG-1 isoforms, neu differentiation factor (NDF, type I) is expressed in the female reproductive tract and is localized to the implantation site. Here, we show that sensory and motor neuron-derived factor (SMDF, type III) is expressed in the uterine subepithelial stroma around the blastocyst and is only upregulated at the time of implantation. The cellular distribution of SMDF is similar to that of NDF and requires an implantation-competent blastocyst. The glial growth factor (GGF, type II) isoform of NRG-1 and the NRG-2 and NRG-3 genes were not expressed in the peri-implantation uterus, as determined by reverse transcription-polymerase chain reaction or in situ hybridization. In contrast to the cellular expression pattern of NDF and SMDF, NRG-4 was present in the luminal and glandular epithelium throughout the uterus during the preimplantation period. Expression of NRG-4 declined in the uterine luminal epithelium during implantation but persisted in the glandular epithelium through Day 8 of pregnancy. Studies in ovariectomized mice showed that NRG-4 is a progesterone-regulated gene, with partial augmentation by estrogen. We also observed upregulation of the erbB2 and erbB3 receptors at the blastocyst stage of embryo development. Together, these findings suggest that a distinct subset of NRGs participates in the signaling network that directs embryo implantation. Upregulation of embryonic erbB2/ erbB3 in the blastocyst trophectoderm and induction of certain NRG-1 isoforms with blastocyst activation help to define additional aspects of the embryo-uterine cross-talk that underlies the implantation process.

Lysophosphatidic acid regulates murine blastocyst development by transactivation of receptors for heparin-binding EGF-like growth factor

Transient elevation of intracellular calcium (Ca2+(i)) by various means accelerates murine preimplantation development and trophoblast differentiation. Several G-protein-coupled receptors (GPCRs), including the lysophosphatidic acid (LPA) receptor (LPAR), induce Ca2+(i) transients and transactivate the EGF receptor (ErbB1) through mobilization of EGF family members, including heparin-binding EGF-like growth factor (HB-EGF). Because HB-EGF accelerates blastocyst differentiation in vitro, we examined whether crosstalk between LPA and HB-EGF regulates peri-implantation development. During mouse blastocyst differentiation, embryos expressed LPAR1 mRNA constitutively, LPAR2 only in late stage blastocysts and no LPAR3. Consistent with a mechanism based on Ca2+(i) signaling, LPA rapidly accelerated the rate of trophoblast outgrowth, an index of blastocyst differentiation, and chelation of Ca2+(i) with BAPTA-AM blocked LPA stimulation. Interfering with HB-EGF signaling through ErbB1 or ErbB4 also attenuated LPA stimulation. We established that mouse blastocysts indeed express HB-EGF and that LPA induces the transient accumulation of HB-EGF on the embryo surface, which was blocked by treatment with either BAPTA-AM or the protein trafficking inhibitor, brefeldin A. We conclude that LPA accelerates blastocyst differentiation through its ability to induce Ca2+(i) transients and HB-EGF autocrine signaling. Transactivation of ErbB1 or ErbB4 by HB-EGF could represent a convergent signaling pathway accessed in the trophoblast by stimuli that mobilize Ca2+(i).

Prostaglandin E2 Is a Product of Induced Prostaglandin-endoperoxide Synthase 2 and Microsomal-type Prostaglandin E Synthase at the Implantation Site of the Hamster

Certain uterine prostaglandins (PGs) are elevated at implantation sites and are needed to trigger the events of blastocyst implantation that include blastocyst-uterine attachment and stromal decidualization with vascular permeability changes. Several decades of investigations showed that treatment with PG synthesis inhibitors, prior to or during the time of implantation, resulted in either complete inhibition or a delay in implantation or reduction in the number of implantation sites with diminished decidual tissue. Consistent with these findings, we observed that whereas a selective PG endoperoxide synthase (Ptgs) 1 inhibitor SC-560 failed to inhibit implantation, a selective Ptgs2 inhibitor SC-236 showed significantly reduced number and size of implantation sites in progesterone-treated ovariectomized pregnant hamsters. It is known that Ptgs2 expression and Ptgs2-derived prostacyclin (PGI2) synthesis at implantation sites are needed for implantation in the mouse (a rodent that needs ovarian estrogen for implantation). However, it is unknown which Ptgs and PG synthases produce which PGs at implantation sites of the hamster (a rodent that does not need ovarian estrogen for implantation). Here we demonstrate that as blastocyst implantation proceeds, a reduction in Ptgs1 expression from uterine luminal epithelial cells and a gradual induction in Ptgs2 expression exclusively in luminal epithelial and adjacent decidual cells occurred at implantation sites of hamsters. Results also reveal that PGE2, but not PGI2, is the major PG at implantation sites where Ptgs2 and microsomal type PGE synthases but not PGI synthases are co-expressed. This elevated uterine PGE2 at implantation sites may serve to initiate or amplify physiological signals required for specific aspects of the implantation process in hamsters.

Heparin-binding EGF-like growth factor regulates human extravillous cytotrophoblast development during conversion to the invasive phenotype

Cytotrophoblasts of the anchoring villi convert during human placentation from a transporting epithelium to an invasive, extravillous phenotype that expresses a distinct repertoire of adhesion molecules. Developing extravillous trophoblasts accumulate heparin-binding EGF-like growth factor (HB-EGF), a multifunctional cytokine, which binds HER1 and HER4 of the human EGF receptor (HER/ErbB) family. HB-EGF is downregulated in placentae of women with preeclampsia, a disorder associated with deficient trophoblast invasion, raising important questions about its physiological impact on cytotrophoblasts. Addition of HB-EGF during explant culture of first-trimester chorionic villi enhanced extravillous trophoblast differentiation and invasive activity. Using a first-trimester human cytotrophoblast line, the potential for autocrine and paracrine regulation of the developing trophoblast was established based on the expression of all four HER isoforms, as well as HB-EGF and related growth factors. HB-EGF did not alter proliferation, but initiated extravillous differentiation, with decreased alpha6 integrin expression, increased alpha1, and elevated cell migration. Function-blocking antibodies against EGF family members reduced basal cell motility and antibody inhibition of either HER1 or HER4 ligation prevented HB-EGF-induced integrin switching. We conclude that HER-mediated autocrine and paracrine signaling by HB-EGF or other EGF family members induces cytotrophoblast differentiation to an invasive phenotype.

Differential Expression of Ezrin/Radixin/Moesin (ERM) and ERM-Associated Adhesion Molecules in the Blastocyst and Uterus Suggests Their Functions During Implantation1

Development of the blastocyst to implantation competency, differentiation of the uterus to the receptive state, and a cross talk between the implantation-competent blastocyst and the uterine luminal epithelium are all essential to the process of implantation. In the present investigation, we examined the possibility for a potential cross talk between the blastocyst and uterus involving the ezrin/radixin/moesin (ERM) proteins and ERM-associated cytoskeletal cross-linker proteins CD43, CD44, ICAM-1, and ICAM-2. In normal Day 4 blastocysts and after rendering dormant blastocysts to implantation-competent by estrogen in vivo (activated), the outer surface of mural trophectoderm cells showed much higher levels of radixin as compared to those in the polar trophectoderm cells, inner cell mass (ICM), and primitive endoderm. In contrast, ezrin was present on both the mural and the polar trophectoderm cell surfaces of normal Day 4 and activated blastocysts at higher intensity than dormant blastocysts. A distinct localization was noted in the primitive endoderm of dormant blastocysts that was not apparent in activated or normal Day 4 blastocysts. The expression of moesin was modestly higher at the mural trophectoderm of implantation-competent blastocysts, while the localization appeared to be present primarily on the polar trophectoderm cell surface of Day 4 blastocysts. The localization of ERM-associated adhesion molecules CD43, CD44, and ICAM-2 was more intense in the implantation-competent blastocysts compared with the dormant blastocysts. However, while CD44 was present both in the trophectoderm and in ICM, CD43 and ICAM-2 were localized primarily to the trophectoderm. The signal for ICAM-1 was very intense in the ICM but was modest in the trophectoderm. No significant changes in fluorescence intensity were noted between activated and dormant blastocysts. In the receptive uterus on Day 4 of pregnancy, ERM proteins were localized to the uterine epithelium, while on Day 5 the localization, especially of radixin and moesin, extended to the stroma surrounding the implantation chamber. With respect to ERM-associated adhesion molecules, while CD44 and ICAM-1 were exclusively localized in the stroma on Day 4, CD43 and ICAM-2 were localized to the epithelium. On Day 5, the localization of CD44 and ICAM-1 became highly concentrated in the antimesometrial stroma of the implantation chamber. The localization of CD43 and ICAM-2 remained mostly epithelial, although some stromal localization of CD43 was noted on Day 5. These results suggest that differential expression and distribution of ERM proteins and ERM-associated adhesion molecules are involved in the construction of the cellular architecture necessary for blastocyst activation and uterine receptivity leading to successful implantation.

HB-EGF directs stromal cell polyploidy and decidualization via cyclin D3 during implantation

Stromal cell polyploidy is a unique phenomenon that occurs during uterine decidualization following embryo implantation, although the developmental mechanism still remains elusive. The general consensus is that the aberrant expression and altered functional activity of cell cycle regulatory molecules at two particular checkpoints G1 to S and G2 to M in the cell cycle play an important role in the development of cellular polyploidy. Despite the compelling evidence of intrinsic cell cycle alteration, it has been implicated that the development of cellular polyploidy may be controlled by specific actions of extracellular growth regulators. Here we show a novel role for heparin-binding EGF-like growth factor (HB-EGF) in the developmental process of stromal cell polyploidy in mice. HB-EGF, which is one of the earliest known molecular mediators of implantation in mice and humans, promotes stromal cell polyploidy via upregulation of cyclin D3. Adenoviral delivery of antisense cyclin D3 attenuates cyclin D3 expression and abrogates HB-EGF-induced stromal cell polyploidy in vitro and in vivo. Collectively, the results demonstrate that the regulation of stromal cell polyploidy and decidualization induced by HB-EGF depend on cyclin D3 induction.