An Assessment of the Mechanophysical and Hormonal Impact on Human Endometrial Epithelium Mechanics and Receptivity

The endometrial epithelium and underlying stroma undergo profound changes to support and limit embryo adhesion and invasion, which occur in the secretory phase of the menstrual cycle during the window of implantation. This coincides with a peak in progesterone and estradiol production. We hypothesized that the interplay between hormone-induced changes in the mechanical properties of the endometrial epithelium and stroma supports this process. To study it, we used hormone-responsive endometrial adenocarcinoma-derived Ishikawa cells growing on substrates of different stiffness. We showed that Ishikawa monolayers on soft substrates are more tightly clustered and uniform than on stiff substrates. Probing for mechanical alterations, we found accelerated stress-relaxation after apical nanoindentation in hormone-stimulated monolayers on stiff substrates. Traction force microscopy furthermore revealed an increased number of foci with high traction in the presence of estradiol and progesterone on soft substrates. The detection of single cells and small cell clusters positive for the intermediate filament protein vimentin and the progesterone receptor further underscored monolayer heterogeneity. Finally, adhesion assays with trophoblast-derived AC-1M-88 spheroids were used to examine the effects of substrate stiffness and steroid hormones on endometrial receptivity. We conclude that the extracellular matrix and hormones act together to determine mechanical properties and, ultimately, embryo implantation.

Integrins and their potential roles in mammalian pregnancy

Integrins are a highly complex family of receptors that, when expressed on the surface of cells, can mediate reciprocal cell-to-cell and cell-to-extracellular matrix (ECM) interactions leading to assembly of integrin adhesion complexes (IACs) that initiate many signaling functions both at the membrane and deeper within the cytoplasm to coordinate processes including cell adhesion, migration, proliferation, survival, differentiation, and metabolism. All metazoan organisms possess integrins, and it is generally agreed that integrins were associated with the evolution of multicellularity, being essential for the association of cells with their neighbors and surroundings, during embryonic development and many aspects of cellular and molecular biology. Integrins have important roles in many aspects of embryonic development, normal physiology, and disease processes with a multitude of functions discovered and elucidated for integrins that directly influence many areas of biology and medicine, including mammalian pregnancy, in particular implantation of the blastocyst to the uterine wall, subsequent placentation and conceptus (embryo/fetus and associated placental membranes) development. This review provides a succinct overview of integrin structure, ligand binding, and signaling followed with a concise overview of embryonic development, implantation, and early placentation in pigs, sheep, humans, and mice as an example for rodents. A brief timeline of the initial localization of integrin subunits to the uterine luminal epithelium (LE) and conceptus trophoblast is then presented, followed by sequential summaries of integrin expression and function during gestation in pigs, sheep, humans, and rodents. As appropriate for this journal, summaries of integrin expression and function during gestation in pigs and sheep are in depth, whereas summaries for humans and rodents are brief. Because similar models to those illustrated in Fig. 1, 2, 3, 4, 5 and 6 are present throughout the scientific literature, the illustrations in this manuscript are drafted as Viking imagery for entertainment purposes.

Generating human blastoids modeling blastocyst-stage embryos and implantation

Human early development sets the stage for embryonic and adult life but remains difficult to investigate. A solution came from the ability of stem cells to organize into structures resembling preimplantation embryos-blastocysts-that we termed blastoids. This embryo model is available in unlimited numbers and could thus support scientific and medical advances. However, its predictive power depends on how faithfully it recapitulates the blastocyst. Here, we describe how we formed human blastoids that (1) efficiently achieve the morphology of the blastocyst and (2) form lineages according to the pace and sequence of blastocyst development, (3) ultimately forming cells that transcriptionally reflect the blastocyst (preimplantation stage). We employ three different commercially available 96- and 24-well microwell plates with results similar to our custom-made ones, and show that blastoids form in clinical in vitro fertilization medium and can be cryopreserved for shipping. Finally, we explain how blastoids replicate the directional process of implantation into endometrial organoids, specifically when these are hormonally stimulated. It takes 4 d for human blastoids to form and 10 d to prepare the endometrial implantation assay, and we have cultured blastoids up to 6 d (time-equivalent of day 13). On the basis of our experience, we anticipate that a person with ~1 year of human pluripotent stem cell culture experience and of organoid culture should be able to perform the protocol. Altogether, blastoids offer an opportunity to establish scientific and biomedical discovery programs for early pregnancy, and an ethical alternative to the use of embryos.

Chemical modification of hyaluronic acid improves its supportive action on embryo implantation

Hyaluronic acid (HA) is a supplement of the embryo transfer medium that improves embryo implantation. We have suggested that the supportive action of HA can be promoted by introducing additional artificial binding sites on the HA structure. HA was modified at carboxyl sites separately with thiol (SH) and N-hydroxysuccinimide (NHS), as mucoadhesive and amine-reactive groups, respectively. The mouse blastocysts were incubated with HA derivatives for 15 min. The HA coatings maintained their potential for enzymatic degradation and showed no detrimental effect on embryonic viability and developmental potential. After in vivo transfer, a significantly higher implantation rate was attained by HA-NHS treatment (80 %) compared with the HA-SH (53 %) and the commercial transfer medium, EmbryoGlue® (56 %). The HA-NHS was produced by a slight modification on the native structure of HA using a simple, fast, non-expensive and scalable chemistry which all promise applicability of this new HA derivative in assisted reproductive technologies.

Early human trophoblast development: from morphology to function

Human pregnancy depends on the proper development of the embryo prior to implantation and the implantation of the embryo into the uterine wall. During the pre-implantation phase, formation of the morula is followed by internalization of blastomeres that differentiate into the pluripotent inner cell mass lineage, while the cells on the surface undergo polarization and differentiate into the trophectoderm of the blastocyst. The trophectoderm mediates apposition and adhesion of the blastocyst to the uterine epithelium. These processes lead to a stable contact between embryonic and maternal tissues, resulting in the formation of a new organ, the placenta. During implantation, the trophectoderm cells start to differentiate and form the basis for multiple specialized trophoblast subpopulations, all of which fulfilling specific key functions in placentation. They either differentiate into polar cells serving typical epithelial functions, or into apolar invasive cells that adapt the uterine wall to progressing pregnancy. The composition of these trophoblast subpopulations is crucial for human placenta development and alterations are suggested to result in placenta-associated pregnancy pathologies. This review article focuses on what is known about very early processes in human reproduction and emphasizes on morphological and functional aspects of early trophoblast differentiation and subpopulations.

Embedding similarities between embryos and circulating tumor cells: fundamentals of abortifacients used for cancer metastasis chemoprevention

Background

The global epidemiological studies reported lower cancer risk after long-term use of contraceptives. Our systematic studies demonstrated that abortifacients are effective in preventing cancer metastases induced by circulating tumor cells (CTCs). However, the molecular and cellular mechanisms by which abortifacients prevent CTC-based cancer metastases are almost unknown. The present studies were designed to interdisciplinarily explore similarities and differences between embryo implantation and cancer cell adhesion/invasion.

Methods

Biomarker expressions on the seeding embryo JEG-3 and cancer MCF-7 cells, as well as embedding uterine endometrial RL95-2 and vascular endothelial HUVECs cells were examined and compared before and after treatments with 17β-estradiol plus progesterone and abortifacients. Effects of oral metapristone and mifepristone on embryo implantation in normal female mice and adhesion/invasion of circulating tumor cells (CTCs) in BALB/C female mice were examined.

Results

Both embryo JEG-3 and cancer MCF-7 cells expressed high sLex, CD47, CAMs, while both endometrial RL95-2 and endothelial HUVECs exhibited high integrins and ICAM-1. Near physiological concentrations of 17β-estradiol plus progesterone promoted migration and invasion of JEG-3 and MCF-7 cells via upregulating integrins and MMPs. Whereas, mifepristone and metapristone significantly inhibited migration and invasion of JEG-3 and MCF-7 cells, and inhibited JEG-3 and MCF-7 adhesion to matrigel, RL95-2 cells and HUVECs, respectively. The inhibitions were realized by downregulating sLex, MMPs in JEG-3 and MCF-7 cells, and downregulating integrins in RL95-2 cells and HUVECs, respectively. Mifepristone and metapristone significantly inhibited both embryo implantation and cancer cell metastasis in mice.

Conclusions

The similarities between the two systems provide fundamentals for abortifacients to intervene CTC adhesion/invasion to the distant metastatic organs. The present studies offer the rationale to repurpose abortifacients for safe and effective cancer metastasis chemoprevention.

Human Embryogenesis: A Comparative Perspective

Understanding human embryology has historically relied on comparative approaches using mammalian model organisms. With the advent of low-input methods to investigate genetic and epigenetic mechanisms and efficient techniques to assess gene function, we can now study the human embryo directly. These advances have transformed the investigation of early embryogenesis in nonrodent species, thereby providing a broader understanding of conserved and divergent mechanisms. Here, we present an overview of the major events in human preimplantation development and place them in the context of mammalian evolution by comparing these events in other eutherian and metatherian species. We describe the advances of studies on postimplantation development and discuss stem cell models that mimic postimplantation embryos. A comparative perspective highlights the importance of analyzing different organisms with molecular characterization and functional studies to reveal the principles of early development. This growing field has a fundamental impact in regenerative medicine and raises important ethical considerations.

The Possibility of Analyzing Endometrial Receptivity Using Cells from Embryo Transfer Catheters

It is very important to investigate the expression of endometrial receptive markers in the endometrium during implantation. Therefore, we examined whether it would be possible to analyze endometrial receptivity using cells from embryo transfer catheters. A total of 81 cycles from 81 consenting patients were enrolled in this study. The tip of the embryo transfer (ET) catheter was cut and immersed in a dedicated reagent. Confirmation of cell distribution was carried out using a Papanicolaou stain and immunocytochemistry. Protein expression was carried out by immunocytochemistry. The expressions of estrogen receptor α, progesterone receptor, and homeobox A10 mRNA were analyzed using quantitative reverse transcription-polymerase chain reaction. We analyzed the relationship between the gene expression profiles associated with pregnancy from endometrial cells. Samples collected from the ET catheter showed clear staining for endometrial cells. Most of the cells were endometrial epithelial cells. Cervical cells were not observed. The protein expression was also confirmed. Three genes were analyzed that are associated with endometrial receptivity. Progesterone receptor expression was 1.4-fold (p<0.05) and homeobox A10 was 2.8-fold (p<0.01) higher in patients who became non-pregnant group, compared to the pregnant group. Estrogen receptor α expression tended to be higher in the non-pregnant group (p=0.18). Our results suggest that endometrial receptivity can be evaluated using cells obtained from the ET catheter. This method may be useful for elucidating the cause of implantation failure by comparing a receptive and non-receptive endometrium at the time of ET.

Podocalyxin is a key negative regulator of human endometrial epithelial receptivity for embryo implantation

STUDY QUESTION

How is endometrial epithelial receptivity, particularly adhesiveness, regulated at the luminal epithelial surface for embryo implantation in the human?

SUMMARY ANSWER

Podocalyxin (PCX), a transmembrane protein, was identified as a key negative regulator of endometrial epithelial receptivity; specific downregulation of PCX in the luminal epithelium in the mid-secretory phase, likely mediated by progesterone, may act as a critical step in converting endometrial surface from a non-receptive to an implantation-permitting state.

WHAT IS KNOWN ALREADY

The human endometrium must undergo major molecular and cellular changes to transform from a non-receptive to a receptive state to accommodate embryo implantation. However, the fundamental mechanisms governing receptivity, particularly at the luminal surface where the embryo first interacts with, are not well understood. A widely held view is that upregulation of adhesion-promoting molecules is important, but the details are not well characterized.

STUDY DESIGN, SIZE, DURATION

This study first aimed to identify novel adhesion-related membrane proteins with potential roles in receptivity in primary human endometrial epithelial cells (HEECs). Further experiments were then conducted to determine candidates' in vivo expression pattern in the human endometrium across the menstrual cycle, regulation by progesterone using cell culture, and functional importance in receptivity using in vitro human embryo attachment and invasion models.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary HEECs (n = 9) were isolated from the proliferative phase endometrial tissue, combined into three pools, subjected to plasma membrane protein enrichment by ultracentrifugation followed by proteomics analysis, which led to the discovery of PCX as a novel candidate of interest. Immunohistochemical analysis determined the in vivo expression pattern and cellular localization of PCX in the human endometrium across the menstrual cycle (n = 23). To investigate whether PCX is regulated by progesterone, the master driver of endometrial differentiation, primary HEECs were treated in culture with estradiol and progesterone and analyzed by RT-PCR (n = 5) and western blot (n = 4). To demonstrate that PCX acts as a negative regulator of receptivity, PCX was overexpressed in Ishikawa cells (a receptive line) and the impact on receptivity was determined using in vitro attachment (n = 3-5) and invasion models (n = 4-6), in which an Ishikawa monolayer mimicked the endometrial surface and primary human trophoblast spheroids mimicked embryos. Mann-Whitney U-test and ANOVA analyses established statistical significance at *P ≤ 0.05 and **P ≤ 0.01.

MAIN RESULTS AND THE ROLE OF CHANCE

PCX was expressed on the apical surface of all epithelial and endothelial cells in the non-receptive endometrium, but selectively downregulated in the luminal epithelium from the mid-secretory phase coinciding with the establishment of receptivity. Progesterone was confirmed to be able to suppress PCX in primary HEECs, suggesting this hormone likely mediates the downregulation of luminal PCX in vivo for receptivity. Overexpression of PCX in Ishikawa monolayer inhibited not only the attachment but also the penetration of human embryo surrogates, demonstrating that PCX acts as an important negative regulator of epithelial receptivity for implantation.

LIMITATIONS, REASONS FOR CAUTION

Primary HEECs isolated from the human endometrial tissue contained a mixture of luminal and glandular epithelial cells, as further purification into subtypes was not possible due to the lack of specific markers. Future study would need to investigate how progesterone differentially regulates PCX in endometrial epithelial subtypes. In addition, this study used primary human trophoblast spheroids as human embryo mimics and Ishikawa as endometrial epithelial cells in functional models, future studies with human blastocysts and primary epithelial cells would further validate the findings.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study add important new knowledge to the understanding of human endometrial remodeling for receptivity. The identification of PCX as a negative regulator of epithelial receptivity and the knowledge that its specific downregulation in the luminal epithelium coincides with receptivity development may provide new avenues to assess endometrial receptivity and individualize endometrial preparation protocols in assisted reproductive technology (ART). The study also discovered PCX as progesterone target in HEECs, identifying a potentially useful functional biomarker to monitor progesterone action, such as in the optimization of progesterone type/dose/route of administration for luteal support.

STUDY FUNDING/COMPETING INTEREST(S)

Study funding was obtained from ESHRE, Monash IVF and NHMRC. LR reports potential conflict of interests (received grants from Ferring Australia; personal fees from Monash IVF Group and Ferring Australia; and non-financial support from Merck Serono, MSD, and Guerbet outside the submitted work. LR is also a minority shareholder and the Group Medical Director for Monash IVF Group, a provider of fertility preservation services). The remaining authors have no potential conflict of interest to declare.

TRIAL REGISTRATION NUMBER

NA.

In Vitro Implantation Model Using Human Endometrial SUSD2+ Mesenchymal Stem Cells and Myometrial Smooth Muscle Cells

Objective

This study evaluated a novel in vitro implantation model using human endometrial mesenchymal stem cells (EMSCs), SUSD2⁺, and myometrial smooth muscle cells (SMCs) that were co-cultured with mouse blastocysts as the surrogate embryo.

Materials and Methods

In this experimental study, SUSD2⁺ MSCs were isolated from human endometrial cell suspensions (ECS) at the fourth passage by magnetic-activated cell sorting. The ECS and SUSD2⁺ cells were separately co-cultured with human myometrial muscle cells for five days. After collection of mouse blastocysts, the embryos were placed on top of the co-cultured cells for 48 hours. The interaction between the embryo and the cultured cells was assessed morphologically at the histological and ultrastructural levels, and by expression profiles of genes related to implantation.

Results

Photomicrographs showed that trophoblastic cells grew around the embryonic cells and attached to theECS and SUSD2⁺ cells. Ultrastructural observations revealed pinopode and microvilli-like structures on the surfaces of both the ECS and SUSD2⁺ cells. Morphologically, the embryos developed to the egg-cylinder stage in both groups. Gene expression analysis showed no significant differences between the two groups in the presence of an embryo, but an increased expression of αV was detected in SUSD2⁺ cells compared to ECS cells in the absence of an embryo.

Conclusion

This study showed that SUSD2⁺ cells co-cultured with SMCs could interact with mouse embryos. The co-cultured cells could potentially be used as an implantation model.

Embryo implantation in the laboratory: an update on current techniques

BACKGROUND

The embryo implantation process is crucial for the correct establishment and progress of pregnancy. During implantation, the blastocyst trophectoderm cells attach to the epithelium of the endometrium, triggering intense cell-to-cell crosstalk that leads to trophoblast outgrowth, invasion of the endometrial tissue, and formation of the placenta. However, this process, which is vital for embryo and foetal development in utero, is still elusive to experimentation because of its inaccessibility. Experimental implantation is cumbersome and impractical in adult animal models and is inconceivable in humans.

OBJECTIVE AND RATIONALE

A number of custom experimental solutions have been proposed to recreate different stages of the implantation process in vitro, by combining a human embryo (or a human embryo surrogate) and endometrial cells (or a surrogate for the endometrial tissue). In vitro models allow rapid high-throughput interrogation of embryos and cells, and efficient screening of molecules, such as cytokines, drugs, or transcription factors, that control embryo implantation and the receptivity of the endometrium. However, the broad selection of available in vitro systems makes it complicated to decide which system best fits the needs of a specific experiment or scientific question. To orient the reader, this review will explore the experimental options proposed in the literature, and classify them into amenable categories based on the embryo/cell pairs employed.The goal is to give an overview of the tools available to study the complex process of human embryo implantation, and explain the differences between them, including the advantages and disadvantages of each system.

SEARCH METHODS

We performed a comprehensive review of the literature to come up with different categories that mimic the different stages of embryo implantation in vitro, ranging from initial blastocyst apposition to later stages of trophoblast invasion or gastrulation. We will also review recent breakthrough advances on stem cells and organoids, assembling embryo-like structures and endometrial tissues.

OUTCOMES

We highlight the most relevant systems and describe the most significant experiments. We focus on in vitro systems that have contributed to the study of human reproduction by discovering molecules that control implantation, including hormones, signalling molecules, transcription factors and cytokines.

WIDER IMPLICATIONS

The momentum of this field is growing thanks to the use of stem cells to build embryo-like structures and endometrial tissues, and the use of bioengineering to extend the life of embryos in culture. We propose to merge bioengineering methods derived from the fields of stem cells and reproduction to develop new systems covering a wider window of the implantation process.

Evaluation of Muc1 Gene Expression at The Time of Implantation in Diabetic Rat Models Treated with Insulin, Metformin and Pioglitazone in The Normal Cycle and Ovulation Induction Cycle

Background

Mucin-1(Muc1) is one of the first molecules in the endometrium that confronts implanting embryos. There is insufficient knowledge about the impacts of diabetes and drugs developed for diabetes treatment on expression of this molecule at the time of implantation. Therefore, this study aimed to investigate the impacts of diabetes and insulin, metformin and pioglitazone on Muc1 expression at the time of implantation.

Materials and Methods

This experimental study was conducted on a total of 63 female Wistar rats divided into 9 groups. To induce type 1diabetes, streptozotocin (STZ) and for induction of type 2 diabetes, nicotinamide (NA) and STZ were injected intraperitoneally. For superovulation, human menopausal gonadotropin (HMG) and human chorionic gonadotropin (HCG) were used. Insulin, metformin and pioglitazone were administered for two weeks. Finally, the endometrial expression of Muc1 was evaluated by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR).

Results

Muc1 expression was non-significantly increased in type 1 and type 2 diabetic groups compared to the control group (P=0.61 and 0.13, respectively); also, it increased in insulin-treated type 1 diabetic group compared to the control group (P=0.0001). Its expression was increased in insulin-treated type 1 diabetic group compared to untreated diabetic group (P=0.001). The expression level of Muc1 was significantly reduced in superovulated and insulintreated type 1 diabetic group compared to the insulin-treated type 1 diabetic group (P=0.001).

Conclusion

One of the causes of fertility problems in diabetes, is changes in Muc1 expression during implantation. On the other hand, the use of insulin in these patients can even lead to overexpression of this gene and worsen the condition. However, these changes can be partially mitigated by assisted reproductive technology (ART) such as superovulation. Also, treatment with metformin and pioglitazone can restore Muc1 expression to near normal levels and has beneficial effects on implantation.

Trophoblast attachment to the endometrial epithelium elicits compartment-specific transcriptional waves in an in-vitro model

RESEARCH QUESTION

Which are the early compartment-specific transcriptional responses of the trophoblast and the endometrial epithelium throughout early attachment during implantation?

DESIGN

An endometrial epithelium proxy (cell line Ishikawa) was co-cultured with spheroids of a green fluorescent protein (GFP) expressing trophoblast cell line (JEG-3). After 0, 8 and 24 h of co-culture, the compartments were sorted by fluorescence-activated cell sorting; GFP+ (trophoblast), GFP- (epithelium) and non-co-cultured control populations were analysed (in triplicate) by RNA-seq and gene set enrichment analysis (GSEA).

RESULTS

Trophoblast challenge induced a wave of transcriptional changes in the epithelium that resulted in 295 differentially regulated genes involving epithelial to mesenchymal transition (EMT), cell movement, apoptosis, hypoxia, inflammation, allograft rejection, myogenesis and cell signalling at 8 h. Interestingly, many of the enriched pathways were subsequently de-enriched by 24 h (i.e. EMT, cell movement, allograft rejection, myogenesis and cell signalling). In the trophoblast, the co-culture induced more transcriptional changes and regulation of a variety of pathways. A total of 1247 and 481 genes were differentially expressed after 8 h and from 8 to 24 h, respectively. Angiogenesis and hypoxia were over-represented at both stages, while EMT and cell signalling only were at 8 h; from 8 to 24 h, inflammation and oestrogen response were enriched, while proliferation was under-represented.

CONCLUSIONS

Successful attachment produced a series of dynamic changes in gene expression, characterized by an overall early and transient transcriptional up-regulation in the receptive epithelium, in contrast to a more dynamic transcriptional response in the trophoblast.

Novel 3D embryo implantation model within macroporous alginate scaffolds

Background

Implantation failure remains an unsolved obstacle in reproductive medicine. Previous studies have indicated that estrogen responsiveness, specifically by estrogen receptor alpha (ERα), is crucial for proper implantation. There is an utmost need for a reliable in vitro model that mimics the events in the uterine wall during the implantation process for studying the regulatory mechanisms governing the process. The current two-dimensional and hydrogel-based in vitro models provide only short-term endometrial cell culture with partial functionality.

Results

Endometrial biopsies showed an increase in E-cadherin expression on the typical window of implantation of fertile women, compared to negligible expression in recurrent implantation failure (RIF) patients. These clinical results indicated E-cadherin as a marker for receptivity. Three-dimensional (3D) macroporous alginate scaffolds were the base for epithelial endometrial cell-seeding and long-term culture under hormone treatment that mimicked a typical menstrual cycle. The RL95–2 epithelial cell culture in macroporous scaffolds was viable for 3 weeks and showed increased E-cadherin levels in response to estrogen. Human choriocarcinoma (JAR) spheroids were used as embryo models, seeded onto cell constructs and successfully adhered to the RL95–2 cell culture. Moreover, a second model of HEC-1A with low ERα levels, showed lower E-cadherin expression and no JAR attachment. E-cadherin expression and JAR attachment were recovered in HEC-1A cells that were transfected with ERα plasmid.

Conclusions

We present a novel model that enables culturing endometrial cells on a 3D matrix for 3 weeks under hormonal treatment. It confirmed the importance of ERα function and E-cadherin for proper implantation. This platform may serve to elucidate the regulatory mechanisms controlling the implantation process, and for screening and evaluating potential novel therapeutic strategies for RIF.

Investigating the role of CD44 and hyaluronate in embryo-epithelial interaction using an in vitro model

Implantation failure is an important impediment to increasing success rates in assisted reproductive technologies. Knowledge of the cascade of morphological and molecular events at implantation remains limited. Cell surface CD44 and hyaluronate (HA) have been reported in the uterus, but a role in intercellular interaction at implantation remains to be evaluated. Mouse embryos were co-cultured with human Ishikawa endometrial epithelial monolayers over 2 days. Attachment was tenuous during the first 24 h, after which it became stable, leading to breaching of the monolayer. The effects of enzymatically reducing the density of HA, or introducing a function-blocking antibody to CD44, were monitored during progression from weak to stable embryonic attachment. Hyaluronidase-mediated removal of surface HA from the epithelial cells enhanced the speed of attachment, while a similar treatment of embryos had no effect. The antibody to CD44 caused retardation of initial attachment. These results suggest that CD44-HA binding could be employed by embryos during initial docking, but the persistence of HA in epithelial cells might be detrimental to later stages of implantation by retarding attainment of stable attachment.

The effects of hyaluronate-containing medium on human embryo attachment to endometrial epithelial cells in vitro

STUDY QUESTION

Does embryo transfer medium containing hyaluronate (HA) promote the attachment phase of human embryo implantation?

SUMMARY ANSWER

HA-containing medium does not promote human blastocyst attachment to endometrial epithelial cells in vitro.

WHAT IS KNOWN ALREADY

Embryo transfer media containing high concentrations of HA are being used to increase implantation and live birth rates in IVF treatment, although the mechanism of action is unknown.

STUDY DESIGN, SIZE, DURATION

Expression of HA-interacting genes in frozen-thawed oocytes/embryos was assessed by microarray analysis (n = 21). Fresh and frozen human blastocysts (n = 98) were co-cultured with human endometrial epithelial Ishikawa cell layers. Blastocyst attachment and the effects of a widely used HA-containing medium were measured.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human embryos surplus to treatment requirements were donated with informed consent from several ART centres. Blastocyst-stage embryos were transferred at day 6 to confluent Ishikawa cell layers; some blastocysts were artificially hatched. Blastocyst attachment was monitored from 1 to 48 h, and the effects of blastocyst pre-treatment for 10 min with HA-containing medium were determined.

MAIN RESULTS AND THE ROLE OF CHANCE

Human embryos expressed the HA receptor genes CD44 and HMMR, hyaluronan synthase genes HAS1–3, and hyaluronidase genes HYAL1–3, at all stages of preimplantation development. Attachment of partially hatched blastocysts to Ishikawa cells at 24 and 48 h was related to trophectoderm grade (P = 0.0004 and 0.007, respectively, n = 34). Blastocysts of varying clinical grades that had been artificially hatched were all attached within 48 h (n = 21). Treatment of artificially hatched blastocysts with HA-containing medium did not significantly affect attachment at early (1–6 h) or late (24 and 48 h) time points, compared with control blastocysts (n = 43).

LIMITATIONS, REASONS FOR CAUTION

Using an adenocarcinoma-derived cell line to model embryo-endometrium attachment may not fully recapitulate in vivo interactions. The high levels of blastocyst attachment seen with this in vitro model may limit the sensitivity with which the effects of HA can be observed.

WIDER IMPLICATIONS OF THE FINDINGS

Morphological trophectoderm grade can be correlated with blastocyst attachment in vitro. HA-containing medium may increase pregnancy rates by mechanisms other than promoting blastocyst attachment to endometrium.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a grant from the Wellbeing of Women, the NIHR Local Comprehensive Research Network and NIHR Manchester Clinical Research Facility, the Department of Health Scientist Practitioner Training Scheme, and the Ministry of Higher Education, The State of Libya. None of the authors has any conflict of interest to declare.

Specific trophoblast transcripts transferred by extracellular vesicles affect gene expression in endometrial epithelial cells and may have a role in embryo-maternal crosstalk

Background

Successful establishment of pregnancy hinges on appropriate communication between the embryo and the uterus prior to implantation, but the nature of this communication remains poorly understood. Here, we tested the hypothesis that the endometrium is receptive to embryo-derived signals in the form of RNA.

Methods

We have utilized a non-contact co culture system to simulate the conditions of pre implantation environment of the uterus. We bioorthogonally tagged embryonic RNA and tracked the transferred transcripts to endometrium. Transferred transcripts were separated from endometrial transcripts and sequenced. Changes in endometrial transcripts were quantified using quantitative PCR.

Results

We show that three specific transcripts are transferred to endometrial cells. We subsequently demonstrate a role of extracellular vesicles (EVs) in this process, as EVs obtained from cultured trophoblast spheroids incubated with endometrial cells induced down-regulation of all the three identified transcripts in endometrial cells.

Finally, we show that EVs/nanoparticles captured from conditioned culture media of viable embryos as opposed to degenerating embryos induce ZNF81 down-regulation in endometrial cells, hinting at the functional importance of this intercellular communication.

Conclusion

Ultimately, our findings demonstrate the existence of an RNA-based communication which may be of critical importance for the establishment of pregnancy.

Expression of adhesion and extracellular matrix genes in human blastocysts upon attachment in a 2D co-culture system

STUDY QUESTION

What are the changes in human embryos, in terms of morphology and gene expression, upon attachment to endometrial epithelial cells?

SUMMARY ANSWER

Apposition and adhesion of human blastocysts to endometrial epithelial cells are predominantly initiated at the embryonic pole and these steps are associated with changes in expression of adhesion and extracellular matrix (ECM) genes in the embryo.

WHAT IS KNOWN ALREADY

Both human and murine embryos have been co-cultured with Ishikawa cells, although embryonic gene expression associated with attachment has not yet been investigated in an in vitro implantation model.

STUDY DESIGN, SIZE, DURATION

Vitrified human blastocysts were warmed and co-cultured for up to 48 h with Ishikawa cells, a model cell line for receptive endometrial epithelium.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Six days post-fertilization (6dpf) human embryos were co-cultured with Ishikawa cells for 12, 24 (7dpf) or 48 h (8dpf) and attachment rate and morphological development investigated. Expression of 84 adhesion and ECM genes was analysed by quantitative PCR. Immunofluorescence microscopy was used to assess the expression of three informative genes at the protein level. Data are reported on 145 human embryos. Mann-Whitney U was used for statistical analysis between two groups, with P < 0.05 considered significant.

MAIN RESULTS AND THE ROLE OF CHANCE

The majority of embryos attached to Ishikawa cells at the level of the polar trophectoderm; 41% of co-cultured embryos were loosely attached after 12 h and 86% firmly attached after 24 h. Outgrowth of hCG-positive embryonic cells at 8dpf indicated differentiation of trophectoderm into invasive syncytiotrophoblast. Gene expression analysis was performed on loosely attached and unattached embryos co-cultured with Ishikawa cells for 12 h. In contrast to unattached embryos, loosely attached embryos expressed THBS1, TNC, COL12A1, CTNND2, ITGA3, ITGAV and LAMA3 and had significantly higher CD44 and TIMP1 transcript levels (P = 0.014 and P = 0.029, respectively). LAMA3, THBS1 and TNC expressions were validated at the protein level in firmly attached 7dpf embryos. Thrombospondin 1 (THBS1) resided in the cytoplasm of embryonic cells whereas laminin subunit alpha 3 (LAMA3) and tenascin C (TNC) were expressed on the cell surface of trophectoderm cells. Incubation with a neutralizing TNC antibody did not affect the rate of embryo attachment or hCG secretion.

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

This in vitro study made use of an endometrial adenocarcinoma cell line to mimic receptive luminal epithelium. Also, the number of embryos was limited. Contamination of recovered embryos with Ishikawa cells was unlikely based on their differential gene expression profiles.

WIDER IMPLICATIONS OF THE FINDINGS

Taken together, we provide a 'proof of concept' that initiation of the implantation process coincides with the induction of specific embryonic genes. Genome-wide expression profiling of a larger sample set may provide insights into the molecular embryonic pathways underlying successful or failed implantation.

STUDY FUNDING AND COMPETING INTEREST(S)

A.A. was supported by a grant from the 'Instituut voor Innovatie door Wetenschap en Technologie' (IWT, 121716, Flanders, Belgium). This work was supported by the 'Wetenschappelijk Fonds Willy Gepts' (WFWG G142 and G170, Universitair Ziekenhuis Brussel). The authors declare no conflict of interest.

Transcriptomic analysis of the interaction of choriocarcinoma spheroids with receptive vs. non-receptive endometrial epithelium cell lines: an in vitro model for human implantation

PURPOSE

Several in vitro systems have been reported to model human implantation; however, the molecular dynamics of the trophoblast vs. the epithelial substrate during attachment have not been described. We have established an in vitro model which allowed us to dissect the transcriptional responses of the trophoblast and the receptive vs. non-receptive epithelium after co-culture.

METHODS

We established an in vitro system based on co-culture of (a) immortalized cells representing receptive (Ishikawa) or non-receptive (HEC-1-A) endometrial epithelium with (b) spheroids of a trophoblastic cell line (JEG-3) modified to express green fluorescent protein (GFP). After 48 h of co-culture, GFP+ (trophoblast cells) and GFP- cell fractions (receptive or non-receptive epithelial cells) were isolated by fluorescence-activated flow cytometry (FACS) and subjected to RNA-seq profiling and gene set enrichment analysis (GSEA).

RESULTS

Compared to HEC-1-A, the trophoblast challenge to Ishikawa cells differentially regulated the expression of 495 genes, which mainly involved cell adhesion and extracellular matrix (ECM) molecules. GSEA revealed enrichment of pathways related to cell division, cell cycle regulation, and metabolism in the Ishikawa substrate. Comparing the gene expression profile of trophoblast spheroids revealed that 1877 and 323 genes were upregulated or downregulated when co-cultured on Ishikawa substrates (compared to HEC-1-A), respectively. Pathways favorable to development, including tissue remodeling, organogenesis, and angiogenesis, were enhanced in the trophoblast compartment after co-culture of spheroids with receptive epithelium. By contrast, the co-culture with less receptive epithelium enriched pathways mainly related to trophoblast cell proliferation and cell cycle regulation.

CONCLUSIONS

Endometrial receptivity requires a transcriptional signature that determines the trophoblast response and drives attachment.

Sorcin is involved during embryo implantation via activating VEGF/PI3K/Akt pathway in mice

Our earlier studies have demonstrated the cyclic variation and also the altered expression of sorcin in endometrium during early-to-mid-secretory phase transition in women with unexplained infertility. The current study was undertaken to establish the functional role of sorcin in endometrial receptivity in mice. Results indicated that sorcin was highly expressed during the window of implantation in mice and functional blockage of sorcin caused significant reduction in number of implanted blastocyst. The receptivity markers (i.e.Integrin β3, HBEGF, IGFBP1, WNT4 and Cyclin E)) were found to be downregulated in sorcin knocked down uterine horn on day 5 as compared to untreated horn. The reduced attachment and expansion of BeWo spheroids on RL95-2 endometrial cells with sorcin knock down, in in vitro model of endometrium-trophoblast interaction further supported these findings. Uterine sorcin expression pattern during estrous cycle and in delayed implantation mice model suggested the upregulation of sorcin by estrogen. The functional blockade of sorcin induced the intracellular Ca⁺² levels in endometrial epithelial cells (EECs), which indicated that altered Ca⁺² homeostasis might be responsible for implantation failure. Sorcin silencing led to significant reduction in the expression of angiogenic factor VEGF and its downstream effector molecules i.e. PI3K, Akt and NOS. The migratory and invasive properties of HUVECs were abrogated by anti-VEGF or by adding culture media from sorcin blocked EECs, which indicated that sorcin might mediate angiogenesis during implantation. Taken together, sorcin is involved in the regulation of Ca⁺²-mediated angiogenesis via VEGF/PI3K/Akt pathway in endometrial cells and plays a crucial role in preparing the endometrium for implantation.

Organ-on-a-Chip Systems for Women's Health Applications

Biomedical research, for a long time, has paid little attention to the influence of sex in many areas of study, ranging from molecular and cellular biology to animal models and clinical studies on human subjects. Many studies solely rely on male cells/tissues/animals/humans, although there are profound differences in male and female physiology, which can significantly impact disease mechanisms, toxicity of compounds, and efficacy of pharmaceuticals. In vitro systems have been traditionally very limited in their capacity to recapitulate female-specific physiology and anatomy such as dynamic sex-hormone levels and the complex interdependencies of female reproductive tract organs. However, the advent of microphysiological organ-on-a-chip systems, which attempt to recreate the 3D structure and function of human organs, now gives researchers the opportunity to integrate cells and tissues from a variety of individuals. Moreover, adding a dynamic flow environment allows mimicking endocrine signaling during the menstrual cycle and pregnancy, as well as providing a controlled microfluidic environment for pharmacokinetic modeling. This review gives an introduction into preclinical and clinical research on women's health and discusses where organ-on-a-chip systems are already utilized or have the potential to deliver new insights and enable entirely new types of studies.

LEFTY2 inhibits endometrial receptivity by downregulating Orai1 expression and store-operated Ca2+ entry

Abstract

Early embryo development and endometrial differentiation are initially independent processes, and synchronization, imposed by a limited window of implantation, is critical for reproductive success. A putative negative regulator of endometrial receptivity is LEFTY2, a member of the transforming growth factor (TGF)-β family. LEFTY2 is highly expressed in decidualizing human endometrial stromal cells (HESCs) during the late luteal phase of the menstrual cycle, coinciding with the closure of the window of implantation. Here, we show that flushing of the uterine lumen in mice with recombinant LEFTY2 inhibits the expression of key receptivity genes, including Cox2, Bmp2, and Wnt4, and blocks embryo implantation. In Ishikawa cells, a human endometrial epithelial cell line, LEFTY2 downregulated the expression of calcium release-activated calcium channel protein 1, encoded by ORAI1, and inhibited store-operated Ca²⁺ entry (SOCE). Furthermore, LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, as well as YM-58483, inhibited, whereas the Ca²⁺ ionophore, ionomycin, strongly upregulated COX2, BMP2 and WNT4 expression in decidualizing HESCs. These findings suggest that LEFTY2 closes the implantation window, at least in part, by downregulating Orai1, which in turn limits SOCE and antagonizes expression of Ca²⁺-sensitive receptivity genes.

Key messages

•Endometrial receptivity is negatively regulated by LEFTY2.

•LEFTY2 inhibits the expression of key murine receptivity genes, including Cox2, Bmp2and Wnt4, and blocks embryo implantation.

•LEFTY2 downregulates the expression of Orai1 and inhibits SOCE.

•LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, and YM-58483 inhibit COX2, BMP2, and WNT4 expression in endometrial cells.

•Targeting LEFTY2 and Orai1 may represent a novel approach for treating unexplained infertility.

Electronic supplementary material

The online version of this article (10.1007/s00109-017-1610-9) contains supplementary material, which is available to authorized users.

Apposition to endometrial epithelial cells activates mouse blastocysts for implantation

STUDY QUESTION

How do interactions between blastocyst-stage embryos and endometrial epithelial cells regulate the early stages of implantation in an in vitro model?

SUMMARY ANSWER

Mouse blastocyst apposition with human endometrial epithelial cells initiates trophectoderm differentiation to trophoblast, which goes on to breach the endometrial epithelium.

WHAT IS KNOWN ALREADY

In vitro models using mouse blastocysts and human endometrial cell lines have proven invaluable in the molecular characterisation of embryo attachment to endometrial epithelium at the onset of implantation. Genes involved in embryonic breaching of the endometrial epithelium have not been investigated in such in vitro models.

STUDY DESIGN, SIZE, DURATION

This study used an established in vitro model of implantation to examine cellular and molecular interactions during blastocyst attachment to endometrial epithelial cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Mouse blastocysts developed from embryonic day (E) 1.5 in vitro were hatched and co-cultured with confluent human endometrial adenocarcinoma-derived Ishikawa cells in serum-free medium. A scale of attachment stability based on blastocyst oscillation upon agitation was devised. Blastocysts were monitored for 48 h to establish the kinetics of implantation, and optical sectioning using fluorescence microscopy revealed attachment and invasion interfaces. Quantitative PCR was used to determine blastocyst gene expression. Data from a total of 680 mouse blastocysts are reported, with 3-6 experimental replicates. T-test and ANOVA analyses established statistical significance at P < 0.05, P < 0.01 and P < 0.001.

MAIN RESULTS AND THE ROLE OF CHANCE

Hatched E4.5 mouse blastocysts exhibited weak attachment to confluent Ishikawa cells over the first 24 h of co-culture, with intermediate and stable attachment occurring from 28 h (E5.5 + 4 h) in a hormone-independent manner. Attached embryos fixed after 48 h (E6.5) frequently exhibited outgrowths, characterised morphologically and with antibody markers as trophoblast giant cells (TGCs), which had breached the Ishikawa cell layer. Beginning co-culture at E5.5 also resulted in intermediate and stable attachment from E5.5 + 4 h; however, these embryos did not go on to breach the Ishikawa cell layer, even when co-culture was extended to E7.5 (P < 0.01). Blastocysts cultured from E4.5 in permeable transwell inserts above Ishikawa cells before transfer to direct co-culture at E5.5 went on to attach but failed to breach the Ishikawa cell layer by E6.5 (P < 0.01). Gene expression analysis at E5.5 demonstrated that direct co-culture with Ishikawa cells from E4.5 resulted in downregulation of trophectoderm transcription factors Cdx2 (P < 0.05) and Gata3 (P < 0.05) and upregulation of the TGC transcription factor Hand1 (P < 0.05). Co-culture with non-endometrial human fibroblasts did not alter the expression of these genes.

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

The in vitro model used here combines human carcinoma-derived endometrial cells with mouse embryos, in which the cellular interactions observed may not fully recapitulate those in vivo. The data gleaned from such models can be regarded as hypothesis-generating, and research is now needed to develop more sophisticated models of human implantation combining multiple primary endometrial cell types with surrogate and real human embryos.

WIDER IMPLICATIONS OF THE FINDINGS

This study implicates blastocyst apposition to endometrial epithelial cells as a critical step in trophoblast differentiation required for implantation. Understanding this maternal regulation of the embryonic developmental programme may lead to novel treatments for infertility.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by funds from the charities Wellbeing of Women (RG1442) and Diabetes UK (15/0005207), and studentship support for SCB from the Anatomical Society. No conflict of interest is declared.

Embryo-epithelium interactions during implantation at a glance

At implantation, with the acquisition of a receptive phenotype in the uterine epithelium, an initial tenuous attachment of embryonic trophectoderm initiates reorganisation of epithelial polarity to enable stable embryo attachment and the differentiation of invasive trophoblasts. In this Cell Science at a Glance article, we describe cellular and molecular events during the epithelial phase of implantation in rodent, drawing on morphological studies both in vivo and in vitro, and genetic models. Evidence is emerging for a repertoire of transcription factors downstream of the master steroidal regulators estrogen and progesterone that coordinate alterations in epithelial polarity, delivery of signals to the stroma and epithelial cell death or displacement. We discuss what is known of the cell interactions that occur during implantation, before considering specific adhesion molecules. We compare the rodent data with our much more limited knowledge of the human system, where direct mechanistic evidence is hard to obtain. In the accompanying poster, we represent the embryo-epithelium interactions in humans and laboratory rodents, highlighting similarities and differences, as well as depict some of the key cell biological events that enable interstitial implantation to occur.

Impaired function of trophoblast cells derived from translocated hESCs may explain pregnancy loss in women with balanced translocation (11;22)

PURPOSE

The aim of the study was to study whether the trophoblasts carrying unbalanced translocation 11,22 [t(11;12)] display abnormal expression of trophoblastic genes and impaired functional properties that may explain implantation failure.

METHODS

t(11;22) hESCs and control hESCs were differentiated in vitro into trophoblast cells in the presence of BMP4, and trophoblast vesicles (TBVs) were created in suspension. The expression pattern of extravillous trophoblast (EVT) genes was compared between translocated and control TBVs. The functional properties of the TBVs were evaluated by their attachment to endometrium cells (ECC1) and invasion through trans-well inserts.

RESULTS

TBVs derived from control hESCs expressed EVT genes from functioning trophoblast cells. In contrast, TBVs differentiated from the translocated hESC line displayed impaired expression of EVT genes. Moreover, the number of TBVs that were attached to endometrium cells was significantly lower compared to the controls. Correspondingly, invasiveness of trophoblast-differentiated translocated cells was also significantly lower than that of the control cells.

CONCLUSIONS

These results may explain the reason for implantation failure in couple carriers of t(11;22). They also demonstrate that translocated hESCs comprise a valuable in vitro human model for studying the mechanisms underlying implantation failure.

Role of Mucin 1 and Glycodelin A in recurrent implantation failure

OBJECTIVE

To evaluate and compare the levels of Mucin 1 (MUC-1) and Glycodelin A (GdA) in precisely timed endometrial biopsies and blood samples taken from women with recurrent implantation failure, and women with proven fertility, in a control group.

DESIGN

Molecular studies in human blood and tissue.

SETTING

University hospital.

PATIENT(S)

Women with recurrent implantation failure and women with proven fertility.

INTERVENTION(S)

Primary endometrial cells and blood samples during the implantation "window" (between day 7 and day 9 after the surge in luteinizing hormone).

MAIN OUTCOME MEASURE(S)

Expression of MUC-1 and GdA in the human endometrium and in blood during the implantation window were analyzed by enzyme-linked immunosorbent assay. Additionally, MUC-1 and GdA levels in tissue were analyzed by western blot during the same period.

RESULT(S)

Both blood and tissue measurements of MUC-1 and GdA were significantly lower in women with recurrent implantation failure than in fertile women during the implantation window. In addition, we found a highly significant correlation between blood vs. tissue measurements of both MUC-1 and GdA.

CONCLUSION(S)

The present study reveals that blood and tissue levels of MUC-1 and GdA are much lower in women with RIF, compared with those in fertile women. Receptivity can be evaluated with noninvasive blood sampling, rather than more-invasive endometrium sampling, as the blood and tissue measurements of MUC-1 and GdA are correlated.

MicroRNA-199a mediates mucin 1 expression in mouse uterus during implantation

Embryo implantation is a complicated process involving interactions between the blastocyst and the luminal epithelium of the receptive uterus. Mucin 1 (MUC1) is an integral membrane glycoprotein expressed apically by secretory epithelial cells and the glandular epithelium in different organs, including the uterus. It is believed that loss of MUC1 on the surface of uterine epithelial cells is necessary for embryo implantation. The endogenous non-protein coding microRNAs (miRNAs) of 21-24 nucleotides are found in diverse organisms. It has been shown that miRNAs participate in a range of cellular processes by regulating gene expression at the post-transcriptional level. In the present study, the regulatory role of miRNA-199a on the expression of MUC1 in mouse uterus during implantation was investigated for its effect on embryo implantation. Western blotting and immunohistochemistry results showed high MUC1 expression on Day 0.5 and low expression by Day 4.5 of pregnancy. In contrast with MUC1 expression, increased miRNA-199a expression was evident at Day 4.5 of pregnancy, as measured by real-time reverse transcription-polymerase chain reaction. In addition, we demonstrated direct binding of miRNA-199a to the 3'-untranslated region of MUC1. Transfection of miRNA-199a into mouse uterine epithelial cells isolated from Day 0.5 of pregnancy also downregulated expression of MUC1. Therefore, the present study provides evidence that MUC1 is a direct target of miRNA-199a and suggests that development of novel strategies to facilitate a successful pregnancy and repair implantation failure humans may include miRNA.

MiR-145 suppresses embryo-epithelial juxtacrine communication at implantation by modulating maternal IGF1R

Successful implantation requires the synchronization of viable embryonic development with endometrial receptivity. The mechanisms allowing for the initiation of crosstalk between the embryo and the endometrium remain elusive; however, recent studies have revealed that there are alterations in endometrial microRNAs (miRs) in women suffering repeated implantation failure and that one of the altered miRs is miR-145. We assessed the role of miR-145 and its target IGF1R, in early implantation. miR-145 overexpression and IGF1R knockdown were achieved in Ishikawa endometrial cells. Quantitative PCR, western blotting and 3'UTR luciferase reporter assays confirmed that IGF1R is a direct target of miR-145 in the endometrium. Attachment of mouse embryos or IGF1-coated beads to endometrial epithelial cells was used to study the effects of altered miR-145 and/or IGF1R expression on early implantation events. miR-145 overexpression or specific reduction of IGF1R impaired attachment in both cases. An IGF1R target protector prevented the miR-145-mediated reduction in IGF1R and reversed the effect of miR-145 overexpression on attachment. The data demonstrate that miR-145 influences embryo attachment by reducing the level of IGF1R in endometrium.

Insulin-like growth factor 1 increases apical fibronectin in blastocysts to increase blastocyst attachment to endometrial epithelial cells in vitro

STUDY QUESTION

Does insulin-like growth factor 1 (IGF1) increase adhesion competency of blastocysts to increase attachment to uterine epithelial cells in vitro?

SUMMARY ANSWER

IGF1 increases apical fibronectin on blastocysts to increase attachment and invasion in an in vitro model of implantation.

WHAT IS KNOWN ALREADY

Fibronectin integrin interactions are important in attachment of blastocysts to uterine epithelial cells at implantation.

STUDY DESIGN, SIZE, DURATION

Mouse blastocysts (hatched or near completion of hatching) were cultured in serum starved (SS) medium with varying treatments for 24, 48 or 72 h. Treatments included 10 ng/ml IGF1 in the presence or absence of the PI3 kinase inhibitor LY294002, an IGF1 receptor (IGF1R) neutralizing antibody or fibronectin. Effects of treatments on blastocysts were measured by attachment of blastocysts to Ishikawa cells, blastocyst outgrowth and fibronectin and focal adhesion kinase (FAK) localization and expression. Blastocysts were randomly allocated into control and treatment groups and experiments were repeated a minimum of three times with varying numbers of blastocysts used in each experiment. FAK and integrin protein expression on Ishikawa cells was quantified in the presence or absence of IGF1.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Fibronectin expression and localization in blastocysts was studied using immunofluorescence and confocal microscopy. Global surface expression of integrin αvβ3, β3 and β1 was measured in Ishikawa cells using flow cytometry. Expression levels of phosphorylated FAK and total FAK were measured in Ishikawa cells and blastocysts by western blot and image J analysis. Blastocyst outgrowth was quantified using image J analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

The presence of IGF1 significantly increased mouse blastocyst attachment to Ishikawa cells compared with SS conditions (P < 0.01). IGF1 treatment resulted in distinct apical fibronectin staining on blastocysts, which was reduced by the PI3 kinase inhibitor LY294002. This coincided with a significant increase in blastocyst outgrowth in the presence of IGF1 (P < 0.01) or fibronectin (P < 0.001), which was abolished by LY294002 (P < 0.001). Apical expression of integrin αvβ3, β3 and β1 in Ishikawa cells was unaltered by IGF1. However, IGF1 increased phosphorylated FAK (P < 0.05) and total FAK expression in Ishikawa cells. FAK signalling is linked to integrin activation and can affect the integrins' ability to bind and recognize extracellular matrix proteins such as fibronectin. Treatment of blastocysts with IGF1 before co-culture with Ishikawa cells increased their attachment (P < 0.05). This effect was abolished in the presence of LY294002 (P < 0.001) or an IGF1R neutralizing antibody (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study uses an in vitro model of attachment that uses mouse blastocysts and human endometrial cells. This involves a species crossover and although this use has been well documented as a model for attachment (as human embryo numbers are limited) the results should be interpreted carefully.

WIDER IMPLICATIONS OF THE FINDINGS

This study presents mechanisms by which IGF1 improves attachment of blastocysts to Ishikawa cells and documents for the first time how IGF1 can increase adhesion competency in blastocysts. Failure of the blastocyst to implant is the major cause of human assisted reproductive technology (ART) failure. As growth factors are absent during embryo culture, their addition to embryo culture medium is a potential avenue to improve IVF success. In particular, IGF1 could prove to be a potential treatment for blastocysts before transfer to the uterus in an ART setting.

The human endometrium as a sensor of embryo quality

Human reproduction is characterized by a high degree of embryo wastage, which is largely ascribed to a high prevalence of embryo aneuploidy. It is proposed that maternal strategies have evolved that prevent inappropriate investment in invasive, but poorly viable embryos. Key to this is the emerging concept of the endometrium as biosensor, first identified in human in vitro embryo/decidualized stromal cell coculture systems and recently confirmed in an in vivo mouse model. In this review, the growing supporting experimental evidence for the biosensor component of decidualized endometrium is outlined, and recent insights into the nature of the embryo-derived signal detected by the endometrium and the biological processes by which this signal is thought to be converted into a go or no-go endometrial response are described. Finally, the clinical implications of this new paradigm of the choosy uterus are addressed.

The role of inflammation for a successful implantation

Approximately half of all human embryo implantations result in failed pregnancy. Multiple factors may contribute to this failure, including genetic or metabolic abnormalities of the embryo. However, many of these spontaneous early abortion cases are attributed to poor uterine receptivity. Furthermore, although many fertility disorders have been overcome by a variety of assisted reproductive techniques, implantation remains the rate-limiting step for the success of the in vitro fertilization (IVF) treatments. We, as well as others, have demonstrated that endometrial biopsies performed either during the spontaneous, preceding cycle, or during the IVF cycle itself, significantly improve the rate of implantation, clinical pregnancies, and live births. These observations suggest that mechanical injury of the endometrium may enhance uterine receptivity by provoking the immune system to generate an inflammatory reaction. In strong support of this idea, we recently found that dendritic cells (DCs), an important cellular component of the innate immune system, play a critical role in successful implantation in a mouse model. In this review, we discuss the hypothesis that the injury-derived inflammation in the biopsy-treated patients generates a focus for uterine DCs and Mac accumulation that, in turn, enhance the endometrial expression of essential molecules that facilitate the interaction between the embryo and the uterine epithelium.

In-vitro model systems for the study of human embryo-endometrium interactions

Implantation requires highly orchestrated interactions between the developing embryo and maternal endometrium. The association between abnormal implantation and reproductive failure is evident, both in normal pregnancy and in assisted reproduction patients. Failure of implantation is the pregnancy rate-limiting step in assisted reproduction, but, as yet, empirical interventions have largely failed to address this problem. Better understanding of the mechanisms underlying human embryo-endometrium signalling is a prerequisite for the further improvement of assisted reproduction outcomes and the development of effective interventions to prevent early pregnancy loss. Studying human embryo implantation is challenging since in-vivo experiments are impractical and unethical, and studies in animal models do not always translate well to humans. However, in recent years in-vitro models have been shown to provide a promising way forward. This review discusses the principal models used to study early human embryo development and initial stages of implantation in vitro. While each model has limitations, exploiting these models will improve understanding of the molecular mechanisms and embryo-endometrium cross-talk at the early implantation site. They provide valuable tools to study early embryo development and pathophysiology of reproductive disorders and have revealed novel disease mechanisms such as the role of epigenetic modifications in recurrent miscarriage.

Regulation of the hyaluronan system in ovine endometrium by ovarian steroids

In this study, we investigated steroid regulation of the hyaluronan (HA) system in ovine endometrium including HA synthases (HAS), hyaluronidases, and HA receptor-CD44 using 30 adult Welsh Mountain ewes. Eight ewes were kept intact and synchronized to estrous (day 0). Intact ewes were killed on day 9 (luteal phase; LUT; n=5) and day 16 (follicular phase; FOL; n=3). The remaining ewes (n=22) were ovariectomized and then treated (i.m.) with vehicle (n=6) or progesterone (n=8) for 10 days, or estrogen and progesterone for 3 days followed by 7 days of progesterone alone (n=8). Estradiol and progesterone concentrations in plasma correlated with the stage of estrous or steroid treatment. Our results showed trends (P<0.1) and statistically significant effects (P<0.05, by t-test) indicating that LUT had lower HAS1 and HAS2 and higher HAS3 and CD44 mRNA expression compared with FOL. This was reflected in immunostaining of the corresponding HAS proteins. Similarly, in ovariectomized ewes, progesterone decreased HAS1 and HAS2 and increased HAS3 and CD44, whereas estradiol tended to increase HAS2 and decrease CD44. Sometimes, HAS mRNA expression did not follow the same trend observed in the intact animals or the protein expression. HA and its associated genes and receptors were regulated by the steroids. In conclusion, these results show that the level of HA production and the molecular weight of HA in the endometrium are regulated by ovarian steroids through differential expression of different HAS both at the gene and at the protein levels.

Administration of calcitonin promotes blastocyst implantation in mice by up-regulating integrin β3 expression in endometrial epithelial cells

STUDY QUESTION

Does exogenous calcitonin improve the efficiency of implantation in mice by increasing uterine receptivity?

SUMMARY ANSWER

The administration of calcitonin could improve the efficiency of implantation by increasing the expression of several receptivity-related genes in endometrial epithelial cells (EECs).

WHAT IS KNOWN ALREADY

Calcitonin is one of the biomarkers of uterine receptivity, which is transiently produced in the uterine epithelia during the period of implantation both in humans and mouse.

STUDY DESIGN, SIZE, DURATION

Hormone-replaced mice were used for in vivo experiments. To evaluate the effect of calcitonin on uterine receptivity, the expression of endometrial genes was analyzed 36 h after i.p. injection of 0.5 IU calcitonin in a treatment group versus saline in the control. To evaluate the effect of calcitonin on implantation efficiency in vivo, two groups received 0.5 IU or 2 IU calcitonin (i.p.) 24 h before embryo transfer, and a control group received saline (i.p.) (n = 18 mice per group). Implantation sites were counted 7 days after embryo transfer. The RL95-2 human endometrial carcinoma cell line was used to study the mechanisms underlying the effect of calcitonin on gene expression in the endometria. Using an in vitro model of endometrium-trophoblast interaction, established with RL95-2 cells and JAR (human choriocarcinoma cell line) trophoblast, endometrial receptivity was evaluated by comparing attachment and outgrowth of JAR spheroids in control and treatment groups.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Uterine receptivity in ovariectomized mice was induced by injection of estradiol and progesterone. Expression of eight genes in murine endometrium and RL95-2 cells was analyzed by real-time RT-PCR, western blot, immunohistochemical analysis, flow cytometry and enzyme-linked immunosorbent assay. We tested the effects of a protein kinase C inhibitor, matrigel and an antibody against integrin αvβ3 using RL95-2 cells and performed attachment and outgrowth assays using the in vitro model of endometrium-trophoblast interaction. Implantation efficiency was evaluated by counting the implantation sites after embryo transfer.

MAIN RESULTS AND THE ROLE OF CHANCE

Calcitonin up-regulated αvβ3 in RL95 cells, which in turn resulted in increased levels of the leukemia inhibitory factor (LIF) and heparin binding-epidermal growth factor (HB-EGF) mRNA (both P < 0.01 versus control) and protein (both P < 0.05 versus control). The attachment and expansion of JAR spheroids was promoted by pretreatment of EECs with calcitonin (P < 0.05 versus control) together with significantly increased expression of αvβ3, LIF and HB-EGF. Moreover, the injection of calcitonin in the preimplantation phase increased the total number of implantation sites in treatment groups (55 in control versus 78 and 85 in 0.5 and 2 IU groups, respectively). Compared with the control group (3.11 ± 2.14), the average number of implantation sites in the 2 IU calcitonin treatment group increased (4.72 ± 1.87, P = 0.022).

LIMITATIONS, REASONS FOR CAUTION

Experiments were performed in mice and human cell lines but not in primary cultures of human endometrial cells.

WIDER IMPLICATIONS OF THE FINDINGS

The findings presented here have important implications, in that calcitonin administration (currently used for treatment of hypercalcemia or osteoporosis) may have clinical benefits in assisted reproduction programs, by facilitating endometrial receptivity and embryo implantation. However, further studies are required to confirm these findings.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by National Science Foundation of China (No. 81170619). There are no financial or commercial conflicts in this study.

Endometrial receptivity defects and impaired implantation in diabetic NOD mice

Implantation failure is a major hurdle to a successful pregnancy. The high rate of postimplantation fetal loss in nonobese diabetic (NOD) mice is believed to be related to an abnormal decidual production of interferon (IFN)gamma. To address whether diabetes alters the natural events associated with successful implantation, certain morphological and molecular features of uterine receptivity in diabetic NOD (dNOD) mice were examined in normally mated pregnancy and in concanavalin A (ConA)-induced pseudopregnancy. As opposed to normoglycemic NOD (cNOD) mice, dNOD mice expressed retarded maturation of their uterine pinopodes and overexpressed MUC1 mucin at implantation sites (P < 0.001). Uterine production of leukemia inhibitory factor (LIF) and phosphorylation of uterine NFkappaBp65 and STAT3-Ty705 were found to be low (P < 0.01) during Day 4.5 postcoitum, whereas IFNgamma was aberrantly overexpressed. Loss of temporal regulation of progesterone receptor A (PR A) and PR B, together with aberrantly increased expression of the protein inhibitor of activated STAT-y (PIASy) (P < 0.01) and reduced recruitment (P < 0.01) of the latter to nuclear progesterone receptor sites were prominent features of decidualization failure occurring at peri-implantation in dNOD mice. In conclusion, the aberrant expression of endometrial IFNgamma in dNOD mice is associated with a nonreceptive endometrial milieu contributing to peri-implantation embryo loss in type 1 diabetes.

Localization of B4GALNT2 and its role in mouse embryo attachment

OBJECTIVE

To investigate the location of β-1,4-N-acetylgalactosaminyltransferase II (B4GALNT2) and the involvement of this protein and Sd(a) antigen in embryonic implantation.

DESIGN

Cell and animal study.

SETTING

University.

ANIMAL(S)

Adult outbred Institute for Cancer Research mice.

INTERVENTION(S)

B4GALNT2 antibody injected into the uteri of mice in early pregnancy; E3.5 blastocysts and pregnant uterine tissues were collected.

MAIN OUTCOME MEASURE(S)

Protein expression was detected by immunofluorescence staining and Western blotting. Embryo attachment was assayed via in vitro and in vivo embryo implantation models.

RESULT(S)

The b4galnt2 gene expression in the 293T cell line showed the protein localized in the plasma membrane. We confirmed that B4GALNT2 was localized on the surface of E3.5 blastocysts but was an intracellular component in uterine epithelia. Finally, anti-B4GALNT2 and lectins inhibition assays demonstrated the involvement of B4GALNT2 and Sd(a) antigen in embryonic attachment in vitro and in vivo via the mouse system and human endometrial cell line (Ishikawa).

CONCLUSION(S)

B4GALNT2 expressed in the blastocyst may interact with a ligand on the endometrial surface, perhaps via Sd(a) also, to permit embryo implantation. Our data suggest that B4GALNT2 and Sd(a) antigen are essential for embryo implantation.

Human placentation from nidation to 5 weeks of gestation. Part II: Tools to model the crucial first days

Human pregnancy is unusual with respect to monthly spontaneous decidualisation as well as the degree of placental invasion and interaction with the decidualised endometrial stroma. This review covers in vivo animal models and in vitro cell culture models that have been used to study the earliest stages of human implantation and placentation from nidation to 5 weeks of gestation. The field has expanded rapidly in recent years due to the generation of human embryonic stem cell lines and the ability of some scientists to culture human blastocysts. These models have enabled researchers to begin to elucidate the interactions involved in human blastocyst apposition, adhesion and implantation. However, we still understand very little about the differentiation processes involved in the formation of the placenta. Continued improvements to current models, including the potential isolation of a human trophoblast stem cell, will significantly enhance our ability to define the molecular and structural events occurring during human implantation and early placental development.