Expression of inhibin/activin subunits and their receptors and binding proteins in human preimplantation embryos

Zygotic activin A is dispensable for the mouse preimplantation embryo development and for the derivation and pluripotency of embryonic stem cells†

In this work, we aimed to determine the role of activin A during crucial events of mouse embryogenesis and distinguish the function of the protein of zygotic origin and the one secreted by the maternal reproductive tract. To this end, we recorded the progression of development and phenotype of Inhba knockout embryos and compared them with the heterozygotes and wild-type embryos using time-lapse imaging and detection of lineage-specific markers. We revealed that the zygotic activin A deficiency does not impair the course and rate of development of embryos to the blastocyst stage. Inhba knockout embryos form functional epiblast, as evidenced by their ability to give rise to embryonic stem cells. Our study is the first to show that derivation, maintenance in culture, and pluripotency of embryo-derived embryonic stem cells are exogenous and endogenous activin A independent. However, the implantation competence of activin A-deficient embryos may be compromised as indicated in the outgrowth assay.

A pilot study on the relationship between thrombospondin-1 (THBS1) and transforming growth factor beta1 (TGFβ1) in the bovine placenta during early mid-pregnancy as well as parturition with normally released and retained placenta

During pregnancy, it is necessary to create appropriate conditions for the development of the placenta and the fetus. However, during parturition, the placenta must be separated and subsequently removed as soon as possible to not expose the female to the possibility of infection. In this study, the relationship between thrombospondin-1 (THBS1) and transforming growth factor beta1 (TGFβ1) concentrations was described during bovine pregnancy (second, fourth, and sixth months; n = 3/each month), at normal parturition (NR) and parturition with fetal membrane retention (R). The presence of THBS1 and TGFβ1 was confirmed in bovine placental tissues of both maternal and fetal parts. Enzyme-linked immunosorbent assay showed statistically significant differences (p < 0.05) in THBS1 concentrations (pg/mg protein) between examined parturient samples (maternal part: 5.76 ± 1.61 in R vs. 2.26 ± 1.58 in NR; fetal part: 2.62 ± 1.94 in R vs. 1.70 ± 0.23 in NR). TGFβ1 concentrations (pg/mg protein) were significantly lower (p < 0.05) in the retained fetal membranes compared to the released fetal membranes in the maternal part of the placenta (26.22 ± 7.53 in NR vs. 17.80 ± 5.01 in R). The participation of THBS1 in the activation of TGFβ1 in parturient bovine placental tissues leading to the normal release of fetal membranes may be suggested.

Embryo-derive TNF promotes decidualization via fibroblast activation

Decidualization is a process in which endometrial stromal fibroblasts differentiate into specialized secretory decidual cells and essential for the successful establishment of pregnancy. The underlying mechanism during decidualization still remains poorly defined. Because decidualization and fibroblast activation share similar characteristics, this study was to examine whether fibroblast activation is involved in decidualization. In our study, fibroblast activation-related markers are obviously detected in pregnant decidua and under in vitro decidualization. ACTIVIN A secreted under fibroblast activation promotes in vitro decidualization. We showed that arachidonic acid released from uterine luminal epithelium can induce fibroblast activation and decidualization through PGI₂ and its nuclear receptor PPARδ. Based on the significant difference of fibroblast activation-related markers between pregnant and pseudopregnant mice, we found that embryo-derived TNF promotes CPLA_2α phosphorylation and arachidonic acid release from luminal epithelium. Fibroblast activation is also detected under human in vitro decidualization. Similar arachidonic acid-PGI₂-PPARδ-ACTIVIN A pathway is conserved in human endometrium. Collectively, our data indicate that embryo-derived TNF promotes CPLA_2α phosphorylation and arachidonic acid release from luminal epithelium to induce fibroblast activation and decidualization.

Activin A increases human trophoblast invasion by upregulating integrin β1 through ALK4

Activin A promotes human trophoblast invasion during the first trimester of pregnancy and is associated with preeclampsia and pregnancy-induced hypertension (PE/PIH) in naturally conceived pregnancies. However, whether integrin β1 mediates activin A-increased trophoblast invasion remains unknown and the evidence is limited regarding the predictive value of activin A for PE/PIH in women receiving in vitro fertilization (IVF) treatment. Here, we studied the role and underlying molecular mechanisms of integrin β1 in activin A-promoted invasion in immortalized (HTR8/SVneo) and primary human extravillous trophoblast (EVT) cells. A nest case-control study was designed to investigate the predictive/diagnostic value of activin A in IVF pregnancies. Results showed that integrin β1 expression increased after activin A treatment and knockdown of integrin β1 significantly decreased both basal and activin A-increased HTR8/SVneo cell invasion. SB431542 (TGF-β type I receptors inhibitor) abolished activin A-induced SMAD2/SMAD3 phosphorylation and integrin β1 overexpression. Activin A-upregulated integrin β1 expression was attenuated after the depletion of ALK4 or SMAD4 in both HTR8/SVneo and primary EVT cells. Furthermore, we found similar first-trimester activin A levels in IVF patients with or without subsequent PE/PIH. These results reveal that integrin β1 mediates activin A-promoted trophoblast invasion through ALK4-activated SMAD2/3-SMAD4 pathway, and the predictive/diagnostic value of first-trimester maternal serum activin A for hypertensive disorders of pregnancy might be different in IVF population.

Roles of insulin-like growth factor II in regulating female reproductive physiology

The number of growth factors involved in female fertility has been extensively studied, but reluctance to add essential growth factors in culture media has limited progress in optimizing embryonic growth and implantation outcomes, a situation that has ultimately led to reduced pregnancy outcomes. Insulin-like growth factor II (IGF-II) is the most intricately regulated of all known reproduction-related growth factors characterized to date, and is perhaps the predominant growth factor in human ovarian follicles. This review aims to concisely summarize what is known about the role of IGF-II in follicular development, oocyte maturation, embryonic development, implantation success, placentation, fetal growth, and in reducing placental cell apoptosis, as well as present strategies that use growth factors in culture systems to improve the developmental potential of oocytes and embryos in different species. Synthesizing the present knowledge about the physiological roles of IGF-II in follicular development, oocyte maturation, and early embryonic development should, on the one hand, deepen our overall understanding of the potential beneficial effects of growth factors in female reproduction and on the other hand support development (optimization) of improved outcomes for assisted reproductive technologies.

Activin A in Mammalian Physiology

Activins are dimeric glycoproteins belonging to the transforming growth factor beta superfamily and resulting from the assembly of two beta subunits, which may also be combined with alpha subunits to form inhibins. Activins were discovered in 1986 following the isolation of inhibins from porcine follicular fluid, and were characterized as ovarian hormones that stimulate follicle stimulating hormone (FSH) release by the pituitary gland. In particular, activin A was shown to be the isoform of greater physiological importance in humans. The current understanding of activin A surpasses the reproductive system and allows its classification as a hormone, a growth factor, and a cytokine. In more than 30 yr of intense research, activin A was localized in female and male reproductive organs but also in other organs and systems as diverse as the brain, liver, lung, bone, and gut. Moreover, its roles include embryonic differentiation, trophoblast invasion of the uterine wall in early pregnancy, and fetal/neonate brain protection in hypoxic conditions. It is now recognized that activin A overexpression may be either cytostatic or mitogenic, depending on the cell type, with important implications for tumor biology. Activin A also regulates bone formation and regeneration, enhances joint inflammation in rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory system. In this 30-yr review, we analyze the evidence for physiological roles of activin A and the potential use of activin agonists and antagonists as therapeutic agents.

Bone Morphogenetic Protein 2 Promotes Human Trophoblast Cell Invasion by Inducing Activin A Production

Bone morphogenetic protein (BMP) 2 and activin A belong to the TGF-β superfamily and are highly expressed in human endometrium and placenta. Studies have demonstrated that activin A and BMP2 play essential roles in the process of early embryo implantation by promoting human trophoblast cell invasion. However, whether activin A production can be regulated by BMP2 in human trophoblast cells remains unknown. The aim of our study was to determine the effects of BMP2 on activin A production and its role in human trophoblast invasion. Primary human extravillous trophoblast (EVT) cells were used as study models. BMP2 treatment significantly increased inhibin βA (INHBA) mRNA levels and activin A production without altering inhibin α and inhibin βB levels. BMP2-induced EVT cell invasion was attenuated by knockdown of INHBA. The increased INHBA transcription and activin A production by BMP2 were blocked by the type I receptor activin receptor (ACVR)-like kinase 2 (ALK2) and activin receptor-like kinase 3 (ALK3) inhibitor dorsomorphin homolog 1 (DMH-1). BMP2-induced INHBA upregulation was also inhibited by knockdown of type I receptor ALK3 or combined knockdown of type II receptors for BMP2 (BMPR2) and ACVR2A. Whereas BMP2 initiated both canonical SMAD1/5/8 and noncanonical SMAD2/3 signaling, only knockdown of SMAD4, but not SMAD2 and SMAD3, abolished the effects of BMP2 on INHBA. Our results show that BMP2 increases human trophoblast invasion by upregulating INHBA and activin A production via ALK3-BMPR2/ACVR2A-SMAD1/5/8-SMAD4 signaling.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Activin A Increases Human Trophoblast Invasion by Inducing SNAIL-Mediated MMP2 Up-Regulation Through ALK4

CONTEXT

Activin A increases matrix metalloproteinase (MMP) 2 expression and cell invasion in human trophoblasts, but whether the expression of MMP2 is essential for the proinvasive effect of activin A has yet to be determined. Moreover, the identity of the activin receptor-like kinase (ALK; TGF-β type I receptors) and downstream transcription factors (eg, SNAIL and SLUG) mediating the effects of activin on MMP2 expression and trophoblast cell invasion remains unknown.

OBJECTIVE

To elucidate the role of MMP2 in activin A-induced human trophoblast cell invasion as well as the involvement of ALK4 and SNAIL.

DESIGN

HTR8/SVneo immortalized human extravillous cytotrophoblast (EVT) cells and primary cultures of human first-trimester EVT cells were used as study models. Small interfering RNA (siRNA)-mediated knockdown approaches were used to investigate the molecular determinants of activin A-mediated functions.

MAIN OUTCOME MEASURES

Levels of mRNA and protein were examined by reverse transcription-quantitative real-time PCR and Western blot, respectively. Cell invasiveness was measured by Matrigel-coated transwell assays.

RESULTS

Treatment of HTR8/SVneo cells with activin A increased the production of SNAIL, SLUG, and MMP2 without altering that of MMP9, TIMP1, TIMP2, TWIST, RUNX2, ZEB1, or ZEB2. Similarly, activin A up-regulated the mRNA and protein levels of SNAIL and MMP2 in primary EVT cells. Knockdown of SNAIL attenuated activin A-induced MMP2 up-regulation in HTR8/SVneo and primary EVT cells. In HTR8/SVneo cells, activin A-induced production of SNAIL and MMP2 was abolished by pretreatment with the TGF-β type I receptor (ALK4/5/7) inhibitor SB431542 or siRNA targeting ALK4, SMAD2/3, or common SMAD4. Likewise, knockdown of ALK4 or SMAD4 abolished the stimulatory effects of activin A on SNAIL and MMP2 expression in primary EVT cells. Importantly, activin A-induced HTR8/SVneo and primary EVT cell invasion were attenuated by siRNA-mediated depletion of ALK4 or MMP2.

CONCLUSION

Activin A induces human trophoblast cell invasion by inducing SNAIL-mediated MMP2 expression through ALK4 in a SMAD2/3-SMAD4-dependent manner.

Vascular Endothelial Growth Factor-A (VEGF-A) Mediates Activin A-Induced Human Trophoblast Endothelial-Like Tube Formation

Remodeling of maternal spiral arteries during pregnancy requires a subpopulation of extravillous cytotrophoblasts (EVTs) to differentiate into endovascular EVTs. Activin A, which is abundantly expressed at the maternal-fetal interface, has been shown to promote trophoblast invasion, but its role in endovascular differentiation remains unknown. Vascular endothelial growth factor-A (VEGF-A) is well recognized as a key regulator in trophoblast endovascular differentiation. Whether and how activin A might regulate VEGF-A production in human trophoblasts and its relationship to endovascular differentiation have yet to be determined. In the present study, we found that activin A increased VEGF-A production in primary and immortalized (HTR8/SVneo) human EVT cells. In addition, activin A enhanced HTR8/SVneo endothelial-like tube formation, and these effects were attenuated by pretreatment with small interfering RNA targeting VEGF-A or the VEGF receptor 1/2 inhibitor SU4312. Pretreatment with the activin/TGF-β type 1 receptor (ALK4/5/7) inhibitor SB431542 abolished the stimulatory effects of activin A on phosphorylated mothers against decapentaplegic (SMAD)-2/3 phosphorylation, VEGF-A production, and endothelial-like tube formation. Moreover, small interfering RNA-mediated down-regulation of SMAD2, SMAD3, or common SMAD4 abolished the effects of activin A on VEGF-A production and endothelial-like tube formation. In conclusion, activin A may promote human trophoblast cell endothelial-like tube formation by up-regulating VEGF-A production in an SMAD2/3-SMAD4-dependent manner. These findings provide insight into the cellular and molecular events regulated by activin A during human implantation.

Soluble ligands and their receptors in human embryo development and implantation

Extensive evidence suggests that soluble ligands and their receptors mediate human preimplantation embryo development and implantation. Progress in this complex area has been ongoing since the 1980s, with an ever-increasing list of candidates. This article specifically reviews evidence of soluble ligands and their receptors in the human preimplantation stage embryo and female reproductive tract. The focus will be on candidates produced by the human preimplantation embryo and those eliciting developmental responses in vitro, as well as endometrial factors related to implantation and receptivity. Pathways to clinical translation, including innovative diagnostics and other technologies, are also highlighted, drawing from this collective evidence toward facilitating joint improvements in embryo quality and endometrial receptivity. This strategy could not only benefit clinical outcomes in reproductive medicine but also provide broader insights into the peri-implantation period of human development to improve fetal and neonatal health.

Role of activins in embryo implantation and diagnosis of ectopic pregnancy: a review

Embryo implantation is a major prerequisite for the successful establishment of pregnancy. Ectopic implantation outside the intrauterine cavity and the development of ectopic pregnancy (EP) is a major cause of maternal morbidity and occasionally mortality during the first trimester. EP may be induced by failure of tubal transport and/or increased tubal receptivity. Activins, their type II receptors and follistatin have been localised in the human endometrial and tubal epithelium and they are major regulators of endometrial and tubal physiology during the menstrual cycle. Pathological expression of activins and their binding protein, follistatin, was observed in tissue and serum samples collected from EP. Several studies with different designs investigated the diagnostic value of a single measurement of serum activin-A in the differentiation between normal intrauterine and failing early pregnancy and the results are controversial. Nevertheless, the diagnostic value of activins in EP, including the other activin isoforms (activin-B and -AB) and follistatin, merits further research. This review appraises the data to date researching the role of activins in the establishment of normal pregnancy and, pathogenesis and diagnosis of tubal EP.

Media composition: growth factors

Despite the fact that the fundamental principle underlying the most common method of culture media constitution is that of mimicking the natural environment of the preimplantation embryo, one major difference that remains between current embryo culture media and in vivo conditions is the absence of growth factors in vitro. Numerous growth factors are known to be present in the in vivo environment of human and nonhuman preimplantation embryos, often with peak concentrations corresponding to when fertilization and preimplantation embryo growth would occur. Although these growth factors are found in very small concentrations, they have a profound effect on tissue growth and differentiation through attachment to factor-specific receptors on cell surfaces. Receptors for many different growth factors have also been detected in human preimplantation embryos. Preimplantation embryos themselves express many growth factors. The growth factors and receptors are metabolically costly to produce, and thus their presence in the environment of the preimplantation embryo and in the embryo respectively strongly implies that embryos are designed to encounter and respond to the corresponding factors. Studies of embryo coculture also indirectly suggest that growth factors can improve in vitro development. Several animal and human studies attest to a probable beneficial effect of addition of growth factors to culture media. However, there is still ambiguity regarding the exact role of growth factors in embryonic development, the optimal dose of growth factors to be added to culture media, the combinatorial effect and endocrine of growth factors in embryonic development.

The expression of activins, their type II receptors and follistatin in human Fallopian tube during the menstrual cycle and in pseudo-pregnancy

BACKGROUND

The Fallopian tube (FT) is the site of fertilization and early embryonic development. We have previously reported the expression of activins, their receptors and follistatin by the FT. Here, our aim was to study the expression of tubal activins, their type II receptors and follistatin during the menstrual cycle and following exposure to hCG in vivo.

METHOD

A set of 30 FTs were collected from cycling women (n = 12) at different stages of the cycle (n = 4 in each stage) and pseudo-pregnant women (n = 3) at the time of hysterectomy for benign disease. The pseudo-pregnant women were injected with hCG in the days leading up to hysterectomy, and pseudo-pregnancy was confirmed by the persistence of amenorrhea, the presence of corpus luteum and decidualization of the endometrium. FT specimens were examined using immunohistochemistry and quantitative RT-PCR.

RESULTS

The expression of activin βA- and βB-subunits, activin type IIA and IIB receptors, and follistatin varied throughout the menstrual cycle, being lowest in the follicular phase and highest in the luteal phase. These results were demonstrated at the mRNA and protein level by quantitative RT-PCR and immunohistochemistry (P< 0.05). HCG injection rescued the expression of the candidate molecules from falling to the follicular stage levels but the expression remained lower than in the luteal phase.

CONCLUSIONS

We suggest that activins play a role in tubal physiology and early embryonic development. Additionally, exposure of the tubal epithelium to hCG modulates the expression of tubal activins.

Cytokines and Growth Factors in Implantation

Implantation failure is the most important rate limiting factor in the success of assisted reproductive techniques like In vitro fertilization–embryo transfer (IVF-ET). Cytokines are multifunctional signaling molecules having an implicit role in the human implantation process. This review focuses on the redundant roles of cytokines during the various stages of implantation. It also indicates that levels of cytokines in biological fluids like serum and follicular fluid obtained during oocyte retrieval might act as determinants of implantation potential of the blastocyst. Thus a holistic, metabolomic approach of analyzing biological fluids may provide a simpler approach to study the hitherto enigmatic process rather than the proteomic and genomic approach.

Transforming growth factor beta family expression at the bovine feto-maternal interface

BACKGROUND

Endometrial remodelling is necessary for implantation in all mammalian species. The TGF beta super-family plays a crucial role in this event in humans and mice. However, the role of TGF beta super-family members during implantation is still unclear in ruminants. In the present study, the spacio-temporal expression of TGF beta super-family members including activin was explored in bovine trophoblasts and endometrial tissue during the peri-implantation period in order to elucidate whether it is essential for promoting cell proliferation at the implantation site.

METHODS

Gene expression in the fetal membrane and endometrium of the gravid and non-gravid horn around Day 35 of gestation were analyzed with a custom-made oligo-microarray in cattle. The expression of activin and its related genes was also analyzed with quantitative RT-PCR. Activin-like activity in trophoblastic tissue and BT-1 cells was examined using a fibroblast cell proliferation test and Western blotting.

RESULTS

The expression of various TGF beta super-family related genes including activin was detected in trophoblasts and the endometrium in cattle. The most intensive activin expression was found in the gravid horn endometrium, and rather intense expression was detected in the non-gravid trophoblastic tissue. Extracts from the fetal membrane including trophoblasts and purified activin both stimulated fibroblast proliferation effectively, and activin was immunologically detected in BT-1 cells, which have trophoblastic features.

CONCLUSIONS

Specific expression of the activin gene (gene name: inhibin beta A) was found in the gravid horn endometrium during peri-implantation. An activin-like molecule, which was derived from the endometrium and trophoblasts, stimulated the proliferation of fibroblast cells. These results suggested that as in other species, the activity of TGF beta super-family members including activin-like molecules plays a pivotal role in endometrial remodelling, which is an essential process in implantation and placentogenesis during the peri-implantation period in cattle.

Expression of nodal signalling components in cycling human endometrium and in endometrial cancer

BACKGROUND

The human endometrium is unique in its capacity to remodel constantly throughout adult reproductive life. Although the processes of tissue damage and breakdown in the endometrium have been well studied, little is known of how endometrial regeneration is achieved after menstruation. Nodal, a member of the transforming growth factor-beta superfamily, regulates the processes of pattern formation and differentiation that occur during early embryo development.

METHODS

In this study, the expression of Nodal, Cripto (co-receptor) and Lefty A (antagonist) was examined by RT-PCR and immunohistochemistry across the menstrual cycle and in endometrial carcinomas.

RESULTS

Nodal and Cripto were found to be expressed at high levels in both stromal and epithelial cells during the proliferative phase of the menstrual cycle. Although immunoreactivity for both proteins in surface and glandular epithelium was maintained at relatively steady-state levels across the cycle, their expression was significantly decreased within the stromal compartment by the mid-secretory phase. Lefty expression, as has previously been reported, was primarily restricted to glandular epithelium and surrounding stroma during the late secretory and menstrual phases. In line with recent studies that have shown that Nodal pathway activity is upregulated in many human cancers, we found that Nodal and Cripto immunoreactivity increased dramatically in the transition from histologic Grade 1 to histologic Grades 2 and 3 endometrial carcinomas. Strikingly, Lefty expression was low or absent in all cancer tissues.

CONCLUSION

The expression of Nodal in normal and malignant endometrial cells that lack Lefty strongly supports an important role for this embryonic morphogen in the tissue remodelling events that occur across the menstrual cycle and in tumourogenesis.

Developmental exposure to Bisphenol a impairs the uterine response to ovarian steroids in the adult

Morphoregulator genes like members of the Hox gene family regulate uterine development and are associated with endocrine-related processes such as endometrial proliferation and differentiation in the adult uterus. Exposure to neonatal endocrine disruptors could affect signaling events governed by Hox genes, altering the developmental trajectory of the uterus with lasting consequences. We investigated whether neonatal exposure to bisphenol A (BPA) alters Hoxa10 and Hoxa11 mRNA uterine expression shortly after treatment as well as in the adult. Moreover, we studied whether xenoestrogen exposure may affect the adult uterine response to hormonal stimuli. Newborn females received vehicle, 0.05 mg/kg.d BPA, 20 mg/kg*d BPA, or diethylstilbestrol (0.2 microg/kg*d) on postnatal d 1, 3, 5, and 7). At postnatal d 8, real time RT-PCR assays showed a decrease in Hoxa10 and Hoxa11 expression in all xenoestrogen-treated groups. To evaluate the long-term effects, we used adult ovariectomized rats with hormonal replacement. The subepithelial stroma in BPA- and diethylstilbestrol-treated animals showed an impaired proliferative response to steroid treatment associated with a silencing of Hoxa10 but not associated with changes in the methylation pattern of the Hoxa10 promoter. BPA animals showed that the Hoxa10 reduction was accompanied by an increased stromal expression of the silencing mediator for retinoic acid and thyroid hormone receptor. The spatial coexpression of steroid receptors Hoxa10 and silencing mediator for retinoic acid and thyroid hormone receptor was established using immunofluorescence. Our data indicate that postnatal BPA exposure affects the steroid hormone-responsiveness of uterine stroma in adulthood. Whether this impaired hormonal response is associated with effects on uterine receptivity and decidualization is currently under investigation.

The importance of growth factors for preimplantation embryo development and in-vitro culture

PURPOSE OF REVIEW

The present paper reviews evidence that preimplantation embryos are naturally exposed and designed to respond to growth factors during preimplantation development.

RECENT FINDINGS

Recent studies have demonstrated that in-vivo human preimplantation embryos are exposed to a mixture of many different growth factors, expressed by the follicles, oviducts and endometrium. Receptors for many of these growth factors have also been shown to be expressed by preimplantation embryos, suggesting a functional role during preimplantation development. Studies of in-vitro fertilization in both animals and humans indicate that in-vitro culture of embryos in conventional media lacking growth factors can result in suboptimal growth and a variety of short-term and long-term developmental abnormalities. Studies of embryo coculture indirectly suggest that growth factors can improve in-vitro development. Many studies of defined growth factor supplements demonstrate that their inclusion in culture media can substantially improve preimplantation development and efficacy of in-vitro fertilization, and may reduce long-term developmental abnormalities as well.

SUMMARY

Embryos are naturally exposed to a complex mixture of growth factors that play an important role in preimplantation embryo development and that are likely to be of substantial benefit if added to in-vitro culture media.

Activin-A in myometrium: characterization of the actions on myometrial cells

Activin is a pleiotropic growth factor with a broad pattern of tissue distribution that includes reproductive tissues. Although direct actions of activin have been described in gonadal and uterine tissues, actions in the myometrium have not been defined. In this study we have characterized the responsiveness of uterine tissue and myometrial cell lines to activin-A. Uterine tissue and two myometrial cell lines, PHM1 (pregnant human myometrial 1) and hTERT HM (telomerase reverse transcriptase-infected human myometrial) respond to activin-A as measured by phosphorylation of Smad-2. Those cell lines express a full complement of activin receptors, as well as activin beta(A) subunit and follistatin. Activin inhibited proliferation of PHM1 and human telomerase reverse transcriptase-infected human myometrial cell line cells, with more extensive growth inhibition observed in PHM1s. In PHM1s, activin-A decreased oxytocin receptor and HoxA-10 mRNA expression but did not alter total progesterone receptor, cyclooxygenase-2 (Cox-2), and connexin 43 mRNA expression levels. Furthermore, treatment of PHM1 myometrial cells with activin-A attenuated oxytocin and thromboxaneA2 induced intracellular Ca(2+) accumulation. In conclusion, myometrial cells are activin sensitive, and activin-A can regulate myometrial cell functions.

Complex expression patterns support potential roles for maternally derived activins in the establishment of pregnancy in mouse

Maternal-fetal communications are critical for the establishment of pregnancy. Embryonic growth and differentiation factors produced by the oviduct and uterus play essential roles during the pre- and early post-implantation phases. Although several studies indicate roles for activin in embryonic development, gene-knockout studies have failed to identify a critical role in mammalian embryogenesis. We hypothesized that activin is produced by maternal tissues during the establishment of pregnancy, and thus maternally derived activin could compensate for the absence of embryonic activin in null homozygotes during critical developmental stages. We investigated the expression of inhibin alpha, activin betaA, and betaB subunits in the mouse oviduct and uterus during the estrous cycle and early pregnancy, and in the early conceptus. Inhibin alpha subunit was weakly expressed, while activin betaA and betaB subunits were strongly expressed in oviduct and uterus at estrous, and dramatically upregulated in the uterus on each day of pregnancy between days 3.5 and 8.5 post coitum. Prior to implantation, activin betaA and betaB subunits were immunolocalized to oviductal and uterine epithelial cells; following implantation they were expressed in the stroma, in a wave preceding decidualization. Later in pregnancy, activin betaA and betaB subunits were present in decidua basalis, trophoblast giant cells, and labyrinth zone of the developing placenta. Expression of activin betaA subunit was also detected in blastocysts and early post-implantation embryos. These data are consistent with a role for maternally derived activins in the support of the pre-implantation embryo, and during gastrulation and embryogenesis.

Expression of activin and inhibin subunits, receptors and binding proteins in human adrenocortical neoplasms

OBJECTIVE

The growth and differentiation factors activin and inhibin can affect tumour formation and steroid production in the adrenal cortex. These factors bind to type I (Alk-4), type II (ActRIIA, ActRIIB) and type III (betaglycan) receptors or to the activin-binding protein follistatin. Expression of these activin-related mRNAs was measured in different types of adrenocortical tissues and tumours to study the relationship with tumorigenesis.

DESIGN

Quantitative expression of activin-related mRNAs was investigated in patient adrenocortical samples.

PATIENTS

Twenty-eight human adrenocortical samples from normal and hyperplastic adrenals and from adrenocortical adenomas and carcinomas were collected after surgery for study purposes.

MEASUREMENTS

Using quantitative reverse transcription polymerase chain reaction (RT-PCR), we investigated the expression of inhibin alpha-, betaA- and betaB-subunits, follistatin, betaglycan, ActRIIA, ActRIIB and Alk-4 in the adrenocortical tissues. The expression of cytochrome P450c17 (CYP17) mRNA was also measured to investigate its association with inhibin and activin subunit expression.

RESULTS

All genes studied were expressed in all tissues, with the exception of the inhibin alpha-subunit in one hyperplastic adrenal and three adrenocortical carcinomas. Expression of inhibin betaA-subunit, follistatin, betaglycan, ActRIIA, ActRIIB and CYP17 differed between nontumorous adrenals and carcinomas.

CONCLUSIONS

These differences, together with correlation analysis, indicate parallel regulation of the expression of CYP17, the inhibin alpha-subunit, ActRIIA, ActRIIB, betaglycan and follistatin. We conclude that the expression of activin and inhibin subunits, receptors and binding proteins is affected by tumour formation in the adrenal gland and may play a role in tumorigenesis.

TGF-β superfamily expression and actions in the endometrium and placenta

Transforming growth factor β (TGFβ) superfamily members are closely associated with tissue remodelling events and reproductive processes. This review summarises the current state of knowledge regarding the expression and actions of TGFβ superfamily members in the uterus, during the menstrual cycle and establishment of pregnancy. TGFβs and activin β subunits are abundantly expressed in the endometrium, where roles in preparation events for implantation have been delineated, particularly in promoting decidualisation of endometrial stroma. These growth factors are also expressed by epithelial glands and secreted into uterine fluid, where interactions with preimplantation embryos are anticipated. Knockout models and embryo culture experiments implicate activins, TGFβs, nodal and bone morphogenetic proteins (BMPs) in promoting pre- and post-implantation embryo development. TGFβ superfamily members may therefore be important in the maternal support of embryo development. Following implantation, invasion of the decidua by fetal trophoblasts is tightly modulated. Activin promotes, whilst TGFβ and macrophage inhibitory cytokine-1 (MIC-1) inhibit, trophoblast migration in vitro, suggesting the relative balance of TGFβ superfamily members participate in modulating the extent of decidual invasion. Activins and TGFβs have similar opposing actions in regulating placental hormone production. Inhibins and activins are produced by the placenta throughout pregnancy, and have explored as a potential markers in maternal serum for pregnancy and placental pathologies, including miscarriage, Down’s syndrome and pre-eclampsia. Finally, additional roles in immunomodulation at the materno-fetal interface, and in endometrial inflammatory events associated with menstruation and repair, are discussed.

Cytokines, chemokines and growth factors in endometrium related to implantation

The complexity of the events of embryo implantation and placentation is exemplified by the number and range of cytokines with demonstrated roles in these processes. Disturbance of the normal expression or action of these cytokines results in complete or partial failure of implantation and abnormal placental formation in mice or humans. Of known importance are members of the gp130 family such as interleukin-11 (IL-11) and leukaemia inhibitory factor (LIF), the transforming growth factor beta (TGFbeta) superfamily including the activins, the colony-stimulating factors (CSF), the IL-1 system and IL-15 system. New data are also emerging for roles for a number of chemokines (chemoattractive cytokines) both in recruiting specific cohorts of leukocytes to implantation sites and in trophoblast differentiation and trafficking. This review focuses on those cytokines and chemokines whose expression pattern in the human endometrium is consistent with a potential role in implantation and placentation and for which some relevant actions are known. It examines what is known of their regulation and action along with alterations in clinically relevant situations.

Production and localization of activins and activin type IIA and IIB receptors by the human endosalpinx

Fallopian tubes from ten premenopausal women were collected and examined for the presence of inhibin, activin and its type IIA and IIB receptors (ActRIIA and ActRIIB) in the endosalpinx. Immunocytochemistry demonstrated clear staining for the betaA, betaB subunits and ActRIIA and ActRIIB that increased in intensity from the isthmus to the ampulla. No staining for the alpha subunit was observed. Whilst the staining of the betaA subunit and ActRIIA was seen in almost every epithelial cell, staining for the betaB subunit and ActRIIB was more variable. In situ hybridization and RT-PCR confirmed the presence of mRNA for the betaA, betaB subunits and ActRIIA and ActRIIB. These results indicated that the epithelium of the uterine tube is able to synthesize activin but not inhibin and has receptors for activin. Activins may thus act as paracrine regulators of tubal epithelial cell function, and embryonic activity may also bind to epithelial receptor and initiate intracellular processes that alter epithelial cell secretions.

Activin and follistatin in female reproduction

Activin and follistatin were initially identified in the follicular fluid based on their effects on pituitary FSH secretion in the mid-1980s. It is now evident that activin, follistatin and activin receptors are widely expressed in many tissues where they function as autocrine/paracrine regulators of a variety of physiological processes including reproduction. The major function of follistatin is to bind to activin with high affinity and block activin binding to its receptors. Total activin A and follistatin are also found in the maternal circulation throughout pregnancy. Activin A levels are increased in abnormal pregnancies such as pre-eclampsia, fetal growth restriction and gestational hypertension. The placenta, vascular endothelial cells and activated peripheral mononuclear cells (PBMC) may all contribute to the raised levels of activin A in pre-eclampsia with unaltered follistatin in pre-eclamptic placenta, PBMCs or vascular endothelial cells suggesting the availability of 'free' activin A that could be biologically active in these cells.

Human endometrium and decidua express follistatin-related gene (FLRG) mRNA and peptide

Activin-A is expressed by human endometrium, and the actions are counteracted by follistatin, its binding protein. We evaluated the endometrial mRNA and peptide expression of follistatin-related gene (FLRG), a protein that binds activin-A, preventing its interaction. By reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, FLRG expression was evaluated in tissues collected at early proliferative (EP; n = 8) and late proliferative (LP; n = 8); early secretory (ES; n = 9) and late secretory (LS; n = 10); and in pregnancy, maternal decidua (MD; n = 12). FLRG mRNA was expressed by all samples, and semi-quantitative analysis showed that FLRG expression was significantly ( P < 0.001) higher in MD. FLRG was strongly immunolocalized in epithelial cells of glands and vessel walls (cytoplasma and nucleus), but only in the stromal cells nucleus. In MD, FLRG immunostaining was found in the nucleus and cytoplasm of vessel endothelium, gland epithelial, and decidualized stromal cells. In conclusion, FLRG is expressed by the human endometrium, and the different cellular localization suggests novel putative functions.

In-vivo concentrations of inhibins, activin A and follistatin in human early pregnancy

The aims of this study were to investigate the relationship between inhibins, activin A and follistatin in first trimester fetal fluids, maternal serum, placenta and decidua, and to investigate if these hormones are present in the circulation of the early second trimester human fetus. Amniotic and coelomic fluid, maternal serum, placental villi and decidual tissue were obtained from normal pregnancies at 8-12 weeks. Fetal blood by cardiocentesis and maternal blood were collected at 14-16 weeks gestation. Placental extracts had higher concentrations of inhibins, activin A and follistatin compared with decidual extracts. In the second trimester, inhibins and follistatin were detectable in fetal blood at 14-16 weeks gestation. Maternal serum concentrations of inhibin A (P < 0.001) and follistatin (P < 0.05) were significantly higher than fetal serum whereas inhibin B (P < 0.01) and pro-alpha C concentrations (P < 0.001) were higher in fetal serum. Inhibin B concentrations were also higher in male fetal serum samples that had higher concentrations of testosterone. The presence of all molecular forms of inhibins, activin A and follistatin in the first trimester fetal fluids, placental and decidual extracts in the first trimester confirms other reports. In the second trimester, high concentrations of inhibin B with testosterone in the fetal circulation indicate that these hormones may interact in the development of the male fetal gonads.

Paracrine regulation of endometrial function: interaction between progesterone and corticotropin-releasing factor (CRF) and activin A

Under the influence of ovarian steroid hormones, endometrial cells aer able to produce a wide variety of growth factors and peptide hormones that area believed to promote: (1) physiological growth and differentiation during the endometrial cycle; (2) decidualization, an essential preparative event for establishment of pregnancy; and (3) pathological growth and differentiation in endometriosis and cancer. Among the local factors produced by the human endometrium, corticotropin-releasing factor (CRF) and activin A have been evaluated in terms of localization and effects. CRF is a neuropeptide expressed by the epithelial and stromal cells of the human endometrium in increasing amounts from the endometrial proliferative to the secretory phase. CRF expression also increases in the pregnant endometrium, from early in the pregnancy until term. CRF-type 1 receptor mRNA is only expressed by stromal cells. Progesterone induces CRF gene expression and release from decidualized cells and CRF decidualizes cultured stromal endometrial cells. Urocortin, a CRF-related peptide, has been identified in endometrial epithelial and stromal cells, and its function is still under investigation. Activin A is a growth factor expressed in increasing amounts throughout endometrial phases by both epithelial and stromal cells. This growth factor is secreted into the uterine cavity with higher levels in the secretory phase. Maternal decidua expresses activin A mRNA in increasing amounts from early pregnancy until term. Human endometrium also expresses activin-A receptors and follistatin, its binding protein. Activin A decidualizes cultured human endometrial stromal cells (an effect reversed by follistatin) and modulates embryonic trophoblast differentiation and adhesion. Activin A is expressed in endometriosis and endometrial adenocarcinoma.

Potential roles for endometrial inhibins, activins and follistatin during human embryo implantation and early pregnancy

The human endometrium is a remarkably dynamic tissue, undergoing cycles of proliferation, differentiation and breakdown every 28 days. In preparation for embryo implantation, the endometrium differentiates or decidualizes, involving widespread morphological and functional differentiation of endometrial stromal cells. If pregnancy occurs, the decidua regulates trophoblast invasion and forms the maternal component of the placenta. Uterine remodeling has long been known to be regulated by the ovarian steroid hormones 17beta-estradiol and progesterone; however, only recently has the importance of paracrine factors in mediating the cellular and biochemical changes been recognized. Many growth factors and cytokines, such as inhibins and activins, whose expression is generally limited to developmental and pathological states, are produced by actively remodeling endometrial cells, and play crucial roles in regulating endometrial cell function. Here, we present evidence for integral roles for the inhibin and activin family in the paracrine regulation of endometrial receptivity, decidualization and implantation.

Endocrinology of the peri-implantation period

Current research suggests that the appearance of endometrial integrins and pinopode appearance signal the opening of the receptive phase of the endometrium. These integrins may be activated by the interleukin-1 system (IL-1). IL-1beta, expressed by the blastocyst, induces vascular endothelial growth factor (VEGF) which, in turn, promotes angiogenesis and integrin expression in endometrial cells. The IL-1 system also triggers the expression of gamma interferon (IFN-gamma) from T lymphocytes. Decidual natural killer (NK) lymphocytes interact with invading trophoblast to generate leukaemia inhibitory factor (LIF). LIF induces uPA and gelatinase, enzymes which play a crucial role in trophoblastic invasion. Progesterone is a potent inhibitor of LIF, while oestrogen is a potent inducer. Oestrogen in serum reflects follicular IL-1beta level and correlates with the outcome of embryo transfer after in vitro fertilization (IVF). Progesterone induces nitric oxide (NO) synthesis in the decidua, and NO promotes local vasodilatation and uterine quiescenceMeasurement of placental protein 14 (PP14, glycodelin-A) in serum may be of value as a screening test for implantation potential. However, human chorionic gonadotrophin (hCG) remains the most reliable predictor of successful implantation and pregnancy viability. An ovulation + 14 hCG level < 50 IU/l is often predictive of a non-viable outcome, while an ovulation + 21 hCG of < 200 IU/l always indicates a non-viable pregnancy. hCG secretion by invading trophoblast appears to be negatively modulated by endothelin-1 (ET-1) and prostaglandin F(2alpha)(PGF2alpha), while tissue growth factors and collagenases are positive modulators of hCG expression.ProalphaC, an inhibin pro-monomer, may have some value in monitoring corpus luteum function. Inhibin A, activin A and follistatin all rises throughout pregnancy and peak at 36 weeks of gestation. Relaxin is another ovarian hormone that may have a role in predicting implantation. Relaxin induces placental protein 14 (PP14, glycodelin-A) expression in a receptive endometrium, and measurement of serum PP14 may be of value as a screening test for implantation potential.

Human endometrial stromal cells improve embryo quality by enhancing the expression of insulin-like growth factors and their receptors in cocultured human preimplantation embryos

OBJECTIVE

To demonstrate the mechanism by which human endometrial stromal cells improve embryo quality in coculture.

DESIGN

Randomized study.

SETTING

Academic research center.

PATIENT(S)

Patients undergoing IVF-ET.

INTERVENTION(S)

Donated human embryos were cultured randomly either alone (group A) or with human endometrial stromal cells (group B), and the embryonic expression of insulin-like growth factors (IGFs) and their receptors was detected by reverse transcriptase polymerase chain reaction after culture.

MAIN OUTCOME MEASURE(S)

The embryo frequency distribution of groups A and B before and after culture and the embryonic transcripts of the IGF family genes of the two study groups after culture were compared.

RESULT(S)

The embryo frequency distribution of the day 3 embryonic stages in groups A and B was not different. However, after culture, a statistically significant difference in blastocyst formation was observed between groups A and B. A significant increase in the expression of IGF-1, IGF-2, the IGF-1 receptor, and the insulin-receptor also was noted. Among the embryos that reached the blastocyst stage, the expression of IGF-1 and the IGF-1 receptor also was significantly different in the two study groups.

CONCLUSION(S)

Human endometrial stromal cells enhanced the expression of IGFs and their receptors in cocultured human embryos, which may be essential for improving embryo quality.