Adhesiveness of the free surface of a human endometrial monolayer for trophoblast as related to actin cytoskeleton

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.

The Extracellular Vesicles Proteome of Endometrial Cells Simulating the Receptive Menstrual Phase Differs from That of Endometrial Cells Simulating the Non-Receptive Menstrual Phase

Successful embryo implantation into a receptive endometrium requires mutual endometrial-embryo communication. Recently, the function of extracellular vehicles (EVs) in cell-to-cell interaction in embryo-maternal interactions has been investigated. We explored isolated endometrial-derived EVs, using RL95-2 cells as a model of a receptive endometrium, influenced by the menstrual cycle hormones estrogen (E2; proliferative phase), progesterone (P4; secretory phase), and estrogen plus progesterone (E2P4; the receptive phase). EV sized particles were isolated by differential centrifugation and size exclusion chromatography. Nanoparticle tracking analysis was used to examine the different concentrations and sizes of particles and EV proteomic analysis was performed using shotgun label-free mass spectrometry. Our results showed that although endometrial derived EVs were secreted in numbers independent of hormonal stimulation, EV sizes were statistically modified by it. Proteomics analysis showed that hormone treatment changes affect the endometrial EV's proteome, with proteins enhanced within the EV E2P4 group shown to be involved in different processes, such as embryo implantation, endometrial receptivity, and embryo development, supporting the concept of a communication system between the embryo and the maternal endometrium via EVs.

How Mechanical Forces Change the Human Endometrium during the Menstrual Cycle in Preparation for Embryo Implantation

The human endometrium is characterized by exceptional plasticity, as evidenced by rapid growth and differentiation during the menstrual cycle and fast tissue remodeling during early pregnancy. Past work has rarely addressed the role of cellular mechanics in these processes. It is becoming increasingly clear that sensing and responding to mechanical forces are as significant for cell behavior as biochemical signaling. Here, we provide an overview of experimental evidence and concepts that illustrate how mechanical forces influence endometrial cell behavior during the hormone-driven menstrual cycle and prepare the endometrium for embryo implantation. Given the fundamental species differences during implantation, we restrict the review to the human situation. Novel technologies and devices such as 3D multifrequency magnetic resonance elastography, atomic force microscopy, organ-on-a-chip microfluidic systems, stem-cell-derived organoid formation, and complex 3D co-culture systems have propelled the understanding how endometrial receptivity and blastocyst implantation are regulated in the human uterus. Accumulating evidence has shown that junctional adhesion, cytoskeletal rearrangement, and extracellular matrix stiffness affect the local force balance that regulates endometrial differentiation and blastocyst invasion. A focus of this review is on the hormonal regulation of endometrial epithelial cell mechanics. We discuss potential implications for embryo implantation.

Loss of CD73 shifts transforming growth factor-β1 (TGF-β1) from tumor suppressor to promoter in endometrial cancer

In many tumors, CD73 (NT5E), a rate-limiting enzyme in adenosine biosynthesis, is upregulated by TGF-β and drives tumor progression. Conversely, CD73 is downregulated in endometrial carcinomas (EC) despite a TGF-β-rich environment. Through gene expression analyses of normal endometrium samples of the uterine cancer TCGA data set and genetic and pharmacological studies, we discovered CD73 loss shifts TGF-β1 from tumor suppressor to promoter in EC. TGF-β1 upregulated CD73 and epithelial integrity in vivo in the normal endometrium and in vitro in early stage EC cells. With loss of CD73, TGF-β1-mediated epithelial integrity was abrogated. EC cells developed TGF-β1-mediated stress fibers and macromolecule permeability, migration, and invasion increased. In human tumors, CD73 is downregulated in deeply invasive stage I EC. Consistent with shifting TGF-β1 activity, CD73 loss increased TGF-β1-mediated canonical signaling and upregulated cyclin D1 (CCND1) and downregulated p21 expression. This shift was clinically relevant, as CD73^Low/CCND1^High expression associated with poor tumor differentiation, increased myometrial and lymphatic/vascular space invasion, and patient death. Further loss of CD73 in CD73^Low expressing advanced stage EC cells increased TGF-β-mediated stress fibers, signaling, and invasiveness, whereby adenosine A1 receptor agonist, CPA, dampened TGF-β-mediated invasion. These data identify CD73 loss as essential for shifting TGF-β activity in EC.

Regulation of ARHGAP19 in the endometrial epithelium: a possible role in the establishment of uterine receptivity

BACKGROUND

The establishment of uterine receptivity is essential for embryo implantation initiation and involves a significant morphological transformation in the endometrial epithelial cells (EECs). The remodeling of junctional complexes and membrane-associated cytoskeleton is crucial for epithelial transformation. However, little is known about how this process is regulated in EECs during the receptive phase. ARHGAP19 is a Rho GTPase-activating protein that participates in various cytoskeletal-related events, including epithelial morphogenesis. Here, we investigated the role of ARHGAP19 in endometrial epithelial transformation during the establishment of uterine receptivity. The upstream regulator of ARHGAP19 was also investigated.

METHODS

ARHGAP19 expression was examined in mouse uteri during early pregnancy and in human EEC lines. The role of ARHGAP19 was investigated by manipulating its expression in EECs. The effect of ARHGAP19 on junctional proteins in EECs was examined by western blotting and immunofluorescence. The effect of ARHGAP19 on microvilli was examined by scanning electron microscopy. The upstream microRNA (miRNA) was predicted using online databases and validated by the dual-luciferase assay. The in vivo and in vitro effect of miRNA on endogenous ARHGAP19 was examined by uterine injection of miRNA agomirs and transfection of miRNA mimics or inhibitors.

RESULTS

ARHGAP19 was upregulated in the receptive mouse uteri and human EECs. Overexpression of ARHGAP19 in non-receptive EECs downregulated the expression of junctional proteins and resulted in their redistribution. Meanwhile, upregulating ARHGAP19 reorganized the cytoskeletal structure of EECs, leading to a decline of microvilli and changes in cell configuration. These changes weakened epithelial cell polarity and promoted the transition of non-receptive EECs to a receptive phenotype. Besides, miR-192-5p, a miRNA that plays a key role in maintaining epithelial properties, was validated as an upstream regulator of ARHGAP19.

CONCLUSION

These results suggested that ARHGAP19 may contribute to the transition of EECs from a non-receptive to a receptive state by regulating the remodeling of junctional proteins and membrane-associated cytoskeleton.

Changes in the expression and distribution of junction and polarity proteins in the porcine endometrium during early pregnancy period

The maternal endometrium undergoes transformations during early pregnancy period to regulate the paracellular permeability across the epithelium and to enable adhesion between the trophoblast and endometrial epithelial cells. These transformations, under the influence of ovarian hormones, are associated with a partial loss in polarity of epithelial cell that is regulated by tight junctions (TJ), adherens junctions (AJ) and associated polarity protein complexes. This study examined the change in expression and distribution of proteins associated with TJs, AJs and apical partition defective (PAR) complex in porcine endometrium on Days 10, 13 and 16 of estrous cycle and pregnancy. Moreover, effect of hormones, progesterone (P4) and 17-β estradiol (E2) on polar phenotype of endometrial epithelial cells was also investigated in vitro. There was pregnancy induced increase in gene and protein expression of TJ associated claudin-1 (CLDN1) on Day 13 of pregnancy as compared to corresponding day of estrous cycle and a decrease in TJ protein, zona occludens-1 (ZO-1) and PAR complex associated PAR6 expression levels on Day 16 of pregnancy (P < 0.05). Immunofluorescence studies revealed that on Days 10 and 13, TJ proteins occludin (OCLN) and ZO-1were primarily present in the apical region of lateral epithelial membrane. On Day 16 of pregnancy, whereas, OCLN redistributed into cytoplasm, ZO-1 decreased apically but was found to localize in the basal epithelium. The AJ proteins cadherin and β-catenin were located at the apical epithelium on Day 10 of estrous cycle and pregnancy and Day 13 of estrous cycle. On Days 13 and 16 of pregnancy both proteins were expressed in the lateral membrane and co-localization between these proteins was observed on Day 16. On Day 10, PAR complex proteins PAR3, cell division control protein 42 (CDC42) and atypical protein kinase C (aPKC) ζ were observed in apical epithelium and in lateral membrane and CDC42 was also present in the cytoplasm of epithelium. Pregnancy induced redistribution of aPKCζ to cytoplasm and CDC42 to apical surface of luminal epithelium was observed on Days 13 and 16. The in vitro P4 and E2 treatment of epithelial cells mimicked in vivo results. These results indicate that P4 and E2 regulate alterations in epithelium that may facilitate embryo implantation and given the role of cadherin, catenin and CDC42 in embryo invasion, change in distribution of these proteins may limit the invasiveness of porcine conceptuses into the stroma.

Transgelin 2 is required for embryo implantation by promoting actin polymerization

Infertility has been a great challenge in reproductive medicine. At least 40% of human pregnancy losses are clinically unrecognized and occur because of embryo implantation failure. Identification of the proteins and biochemical factors involved in embryo implantation and that are essential for crosstalk between the embryo and uterus can further increase female fertility rates. The actin cytoskeleton and actin-binding proteins (ABPs) are of great importance for cell morphology and rearrangement, which is crucial for trophoblast adhesion and invasion. However, the research on ABPs in embryo implantation is insufficient. In this report, we found that transgelin (TAGLN)2 is highly expressed in mouse blastocyst trophoblasts. Notably, inhibition of mouse blastocyst trophoblast TAGLN2 by lentivirus-mediated RNA interference significantly impaired embryo adhesion and implantation ability. Further in vitro experiments demonstrated that TAGLN2 knockdown with small interfering RNA observably decreased the invasion and migration abilities of human trophoblast cells. Immunofluorescence colocalization and microscale thermophoresis analysis showed that TAGLN2 directly binds to actin. In addition, knockdown of TAGLN2 in trophoblast cells resulted in a remarkable reduction in F-actin rather than G-actin. Our findings reveal an unidentified role of TAGLN2 in regulation of trophoblast invasion and adhesion by promoting actin polymerization.-Liang, X., Jin, Y., Wang, H., Meng, X., Tan, Z., Huang, T., Fan, S. Transgelin 2 is required for embryo implantation by promoting actin polymerization.

Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs

The establishment of pregnancy is a complex process that requires a well-coordinated interaction between the implanting conceptus and the maternal uterus. In pigs, the conceptus undergoes dramatic morphological and functional changes at the time of implantation and introduces various factors, including estrogens and cytokines, interleukin-1β2 (IL1B2), interferon-γ (IFNG), and IFN-δ (IFND), into the uterine lumen. In response to ovarian steroid hormones and conceptus-derived factors, the uterine endometrium becomes receptive to the implanting conceptus by changing its expression of cell adhesion molecules, secretory activity, and immune response. Conceptus-derived estrogens act as a signal for maternal recognition of pregnancy by changing the direction of prostaglandin (PG) F_2α from the uterine vasculature to the uterine lumen. Estrogens also induce the expression of many endometrial genes, including genes related to growth factors, the synthesis and transport of PGs, and immunity. IL1B2, a pro-inflammatory cytokine, is produced by the elongating conceptus. The direct effect of IL1B2 on endometrial function is not fully understood. IL1B activates the expression of endometrial genes, including the genes involved in IL1B signaling and PG synthesis and transport. In addition, estrogen or IL1B stimulates endometrial expression of IFN signaling molecules, suggesting that estrogen and IL1B act cooperatively in priming the endometrial function of conceptus-produced IFNG and IFND that, in turn, modulate endometrial immune response during early pregnancy. This review addresses information about maternal-conceptus interactions with respect to endometrial gene expression in response to conceptus-derived factors, focusing on the roles of estrogen and IL1B during early pregnancy in pigs.

An animal model of effects of nicotine exposure on endometrial receptivity and embryo implantation in pregnancy

OBJECTIVE

This study aims at evaluating the endometrial receptivity in uterus of pregnant rats exposed to nicotine via examination of integrin expression by immunohistochemical effect.

METHODS

In this study, 16 healthy pregnant rats were divided into two groups of control and study groups each comprising eight rats. The rats randomised to study group were given a certain amount of nicotine before and during the pregnancy. Integrin expression was detected in uterus of all rats by immunohistochemical staining. The effect of nicotine exposure on embryo implantation and the endometrial receptivity were immunohistochemically and pathologically evaluated.

RESULTS

Comparison of both groups revealed no difference in living, viable foetuses. Intensity and universality of immunohistochemical staining of Integrin β3 for endometrial epithelium and endometrial stroma were detected to be identical between the groups.

CONCLUSION

No immunochemical effect was observed on integrin expression, which is a very important part of receptivity in an animal model created with pregnant rats that were transdermally exposed to nicotine. Our study demonstrated that the harmful effect of nicotine use before and pregnancy on implantation is limited at the level of integrin expression, in a dose-dependent manner and also by considering the method of administration.

Uterine RAC1 via Pak1-ERM signaling directs normal luminal epithelial integrity conducive to on-time embryo implantation in mice

Successful embryo implantation requires functional luminal epithelia to establish uterine receptivity and blastocyst-uterine adhesion. During the configuration of uterine receptivity from prereceptive phase, the luminal epithelium undergoes dynamic membrane reorganization and depolarization. This timely regulated epithelial membrane maturation and precisely maintained epithelial integrity are critical for embryo implantation in both humans and mice. However, it remained largely unexplored with respect to potential signaling cascades governing this functional epithelial transformation prior to implantation. Using multiple genetic and cellular approaches combined with uterine conditional Rac1 deletion mouse model, we demonstrated herein that Rac1, a small GTPase, is spatiotemporally expressed in the periimplantation uterus, and uterine depletion of Rac1 induces premature decrease of epithelial apical-basal polarity and defective junction remodeling, leading to disrupted uterine receptivity and implantation failure. Further investigations identified Pak1-ERM as a downstream signaling cascade upon Rac1 activation in the luminal epithelium necessary for uterine receptivity. In addition, we also demonstrated that Rac1 via P38 MAPK signaling ensures timely epithelial apoptotic death at postimplantation. Besides uncovering a potentially important molecule machinery governing uterine luminal integrity for embryo implantation, our finding has high clinical relevance, because Rac1 is essential for normal endometrial functions in women.

Activation of Toll-like receptor 3 reduces actin polymerization and adhesion molecule expression in endometrial cells, a potential mechanism for viral-induced implantation failure

STUDY QUESTION

Does activation of endometrial Toll-like receptor 3 (TLR 3) affect cell receptivity to trophoblast adhesion?

SUMMARY ANSWER

TLR 3 activation in vitro reduces the attachment of trophoblast cells to endometrial cells by altering the cell cytoskeleton and reducing the expression of adhesion molecules in human endometrial cells.

WHAT IS KNOWN ALREADY

It is well documented that the presence of an infection at the time of implantation can lead to implantation failure. The female reproductive tract recognizes invading micro-organisms through the innate pathogen recognition receptors such as the TLRs.

STUDY DESIGN, SIZE, DURATION

Poly I:C was used as a TLR 3-specific ligand and endometrial cells were either treated or not with Poly I:C (treated versus control) in vitro. The experiments were performed in three replicates on three separate days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

An in vitro assay was developed using RL95-2 (a human endometrial cell line) and JAr (a human trophoblast cell line) cells. Initially, the percentage of attached JAr spheroids to RL95-2 was measured in response to TLR 3 activation. Next, actin polymerization in RL95-2 cells was assessed in response to TLR 2/6, 3 and 5 activation. Phalloidin was used to assess the mean fluorescence intensity of F-actin by flow cytometry or confocal microscopy. Secondly, the influence of TLR 2/6, 3 and 5 activation on the expression of cluster of differentiation 98 (CD98) and β3 integrin was determined. To further understand through which pathways the TLR 3-induced alterations occur, inhibitors were applied for Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), myeloid differentiation primary response 88 (MYD88), mitogen-activated protein kinases (MAPK) and nuclear factor pathways.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed that stimulation of TLR 3 in endometrial cells with different concentrations of Poly I:C led to a reduction in the percentage of trophoblasts attached to the endometrial cells in a dose-dependent manner (P < 0.05). This decrease was consistent in the Poly I:C treated group regardless of the co-incubation time (P < 0.05). In addition, our results demonstrated that actin polymerization and CD98 expression significantly decreased only in response to TLR 3 activation (P < 0.05). Activation of endometrial cells with TLR 2/6, 3 and 5 significantly reduced β3 integrin expression (P < 0.05). These alterations were shown to work via MYD88-MAPK pathways (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study has been performed in vitro. Future in vivo studies will be required in order to confirm our data.

WIDER IMPLICATIONS OF THE FINDINGS

This is a novel discovery which extends our current knowledge concerning diagnosis and treatment of viral-induced infertility cases.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the COST Action FA1201 (GEMINI) by granting a Short Term Scientific Mission and the Instituto de Salud Carlos III by granting Grant PI11/01645. The authors have no conflict of interest to declare.

Effects of galectin-3 inhibition on endometrial cell cycle and adhesion

Galectin-3 (gal-3) and its ligands have been implicated in cell transformation and cancer metastasis. Gal-3 protein has been found in uterine epithelial cells adjacent to implanting blastocysts in different cell types. In order to investigate the role of gal-3 in the establishment of human endometrial receptivity, the expression of gal-3 in human endometrial cell line RL95-2 was silenced by RNA interference technology using gal-3 specific small RNA. The expression of gal-3 was detected by the reverse transcriptase-polymerase chain reaction and Western blot analysis. After the suppression of gal-3, cell cycle changes and the expression of integrin β1 were detected by flow cytometry. The adhesive ability of RL95-2 cells was analyzed by the adhesion test. Gal-3 siRNA transfection efficiency reached 70%-90%. The expression of gal-3 mRNA and protein in RL95-2 cells was strongly inhibited by 70%-90% after RNA interference. Inhibition of gal-3 expression decreased S-phase but increased G1 phase cells. Integrin β1 expression was down-regulated, and the adhesive ability of RL95-2 cells to fibronectin (FN) was significantly reduced. Gal-3 may be involved in the establishment of endometrial receptivity by regulating the proliferation and adhesion of endometrial cells. The influence on adhesion may be related with the integrin modulation.

Annexin A2 is critical for embryo adhesiveness to the human endometrium by RhoA activation through F-actin regulation

Annexin A2 (ANXA2) is present in vivo in the mid- and late-secretory endometria and is mainly localized in the luminal epithelium. Our aim was to evaluate its function in regulating the human implantation process. With an in vitro adhesion model, constructed to evaluate how the mouse embryo and JEG-3 spheroids attach to human endometrial epithelial cells, we demonstrated that ANXA2 inhibition significantly diminishes embryo adhesiveness. ANXA2 is also implicated in endometrial epithelial cell migration and trophoblast outgrowth. ANXA2 was seen to be linked to the RhoA/ROCK pathway and to regulate cell adhesion. We noted that ANXA2 inhibition significantly reduces active RhoA, although RhoA inactivation does not alter the ANXA2 levels. RhoA inactivation and ROCK inhibition also moderate embryo adhesiveness to endometrial epithelial cells. We corroborated that the induction of constitutively active RhoA partially reverses the effects of ANXA2 inhibition on endometrial adhesiveness. These molecules colocalize on the plasma membrane of endometrial epithelial cells, and a large proportion of ANXA2 and RhoA are colocalized in the F-actin networks. The functional effects of ANXA2 inhibition and RhoA/ROCK inactivation are associated with significant alterations in F-actin organization and its depolymerization. ANXA2 may act upstream of the RhoA/ROCK pathway by regulating F-actin remodeling and is a key factor in human endometrial adhesiveness.

Measuring cell adhesion forces: theory and principles

Cell adhesion is an essential prerequisite for survival, communication, and navigation of cells in organisms. It is maintained by the organized binding of molecules from the cell membrane to the extracellular space. This chapter focuses on direct measurements of cellular binding strength at the level of single adhesion molecules. Using atomic force microscopy-based force measurements, adhesion strength can be monitored as a function of adhesion time and environmental conditions. In this way, cellular adhesion strategies like changes in affinity and avidity of adhesion molecules (e.g., integrins) are characterized as well as the molecular arrangement of adhesion molecules in the cell membrane (e.g., molecular clusters, focal adhesion spots, and linkage to the cytoskeleton or tether). Some prominent values for the data evaluation are presented as well as constraints and preparative techniques for successful cell adhesion force experiments.

Effect of primary human endometrial stromal cells on epithelial cell receptivity and protein expression is dependent on menstrual cycle stage

BACKGROUND

Successful implantation requires a receptive endometrium. We hypothesized that effects of endometrial stromal cells (ESC) on epithelial cell receptivity and trophoblast-endometrium interaction are menstrual cycle dependent.

METHODS

An endometrial in vitro 3D co-culture model of primary human ESC with the endometrial epithelial cell line (RL95-2) was constructed. Co-cultures were prepared using primary ESC from biopsies taken before the window of implantation (ESCbw) and during the window of implantation (ESCw), on cycle days 10-17 and 19-23, respectively. RL95-2 served as a constant parameter upon which the influence of ESC from different phases of the cycle was investigated. proMMP-2 (MMP, matrix metalloproteinase) and proMMP-9 secretion was tested in response to progesterone. Progesterone receptor B (PR-B) and plexin B1 protein expression and mRNA levels were investigated using immunofluorescence and RT-PCR, respectively.

RESULTS

Progesterone increased proMMP-2 secretion in primary ESCbw (P = 0.0046) but decreased proMMP-2 and proMMP-9 secretion in ESCw (P < 0.0005). In the presence of ESCbw, JAR spheroid attachment rate to overlying RL95-2 cells was decreased (P < 0.0001), whereas in the presence of ESCw, attachment rate was unchanged. Progesterone treatment restored epithelial cell receptivity in co-culture with ESCbw (P = 0.00004). A correlation between spheroid attachment rate and plexin B1 mRNA level was observed (P = 0.01). PR-B protein and mRNA level were influenced by the interplay between RL95-2 and stromal cells.

CONCLUSION

The effects of human primary ESC on epithelial cell receptivity and trophoblast-endometrium interaction depended upon whether the ESC were taken before or during the window of implantation.

Difucosylated oligosaccharide Lewis Y is contained within integrin αvβ3 on RL95-2 cells and required for endometrial receptivity

OBJECTIVE

To investigate whether Lewis Y (LeY) carried by integrin αvβ3 influences integrin αvβ3-mediated adhesion in an in vitro implantation model.

DESIGN

Laboratory research.

SETTING

Reproduction and glycobiology research laboratory.

INTERVENTION(S)

Specific antibody blockage of LeY or integrin αvβ3 and knockdown of FUT4 expression in RL95-2 cells by transient transfection of FUT4 siRNA.

MAIN OUTCOME MEASURE(S)

The expression of integrin αvβ3 and LeY in both endometrial tissues and RL95-2 cells was measured. LeY carried by integrin αvβ3 was identified by examining the immunoprecipitated integrin αvβ3. The effect of knocking down FUT4 on the expression of integrin αvβ3 and LeY and their impact on the adhesion of JAR cells to the RL95-2 cells were assessed.

RESULT(S)

Integrin αvβ3 and LeY are expressed in both secretory-stage human endometrial tissue and in RL95-2 cells. Although integrin αvβ3 carries LeY, knocking down FUT4 expression only reduces the expression of LeY but not of integrin αvβ3. Knocking down FUT4, antibody blockade of LeY or integrin αvβ3 consistently decreases the adhesion of JAR cells to the RL95-2 cells and prevents focal adhesion kinase (FAK) phosphorylation.

CONCLUSION(S)

LeY carried by integrin αvβ3 plays a critical role on the attachment of JAR cells to the RL95-2 cells and activates integrin αvβ3/FAK signaling.

Epigenetic regulation of E-cadherin controls endometrial receptivity

Key to the success of human reproduction is the capacity of an embryo to attach and implant into the endometrial wall after which a nutrient supply is established through placentation. Herein, we have examined the potential epigenetic regulation of uterine receptivity by use of the receptive RL95-2 and nonreceptive AN3-CA endometrial epithelial carcinoma cell lines. Using an in vitro model of embryo implantation, we demonstrate that inhibition of DNA methylation by 5'-aza-2'-deoxycytidine (AZA), resulted in the nonreceptive AN3-CA cell line becoming receptive to BeWo cell spheroid attachment. Examination of components of the adherens junction complex revealed that AZA specifically increased the expression of E-cadherin and plakoglobin at the mRNA and protein levels in AN3-CA cells, and E-cadherin protein expression was found to localize to sites of intercellular contact. Forced expression of E-cadherin in AN3-CA cells significantly enhanced receptivity. Small interfering RNA (siRNA)-mediated depletion of the individual DNA methyltransferase (DNMT) molecules did not induce E-cadherin expression in AN3-CA cells; however, concomitant siRNA-mediated depletion of both DNMT3A and DNMT3B induced the expression of E-cadherin. Furthermore, E-cadherin expression was significantly increased after the concomitant siRNA-mediated depletion of DNMT-1, -3A, and -3B in AN3-CA cells. Therefore, we have provided evidence that E-cadherin plays an important role in uterine receptivity and that E-cadherin expression is epigenetically regulated in AN3-CA cells, suppressed by the combined actions of DNMT-1, -3A, and -3B.

Progesterone receptor A and c-Met mediates spheroids-endometrium attachment

BACKGROUND

Implantation in humans involves cross talk between an active blastocyst and receptive endometrium. The role of the endometrial receptors in this complex embryo-maternal interaction is still unclear. We tested gene and protein expression of endometrial receptors (Progesterone receptor (PR) and c-Met) and the effect of theses receptors in endometrial receptivity.

METHODS

Two endometrial cell lines were used: HEC-1A and RL95-2 considered as being of low and high receptivity, respectively. Western blot and RT-PCR analysis were utilized to study the receptor expression profile.The role of endometrial receptors in endometrial receptivity was studied by attachment and invasion assays of JAR spheroids (made of a trophoblast cell line) on endometrial cells. Different manipulations of inhibition and stimulation of the endometrial receptors were used including: inhibition by specific antibodies against the receptors, or antagonist of the receptors, as well as transfection with antisense for the endometrial receptors, stimulation by specific ligands for the receptors and transfection with the gene for endometrial receptors.

RESULTS

Different protein expression patterns of endometrial receptors were observed between the tested endometrial cell lines. The expression levels of PRA ratio to PRB, and the 50 kDa c-MET isoform were significantly lower in HEC-1A as compared with RL95-2. Attachment rates and growth of JAR spheroids into HEC-1A were significantly lower as compared with RL95-2. Stimulation of PR with progesterone altered attachment rates to HEC-1A. Inhibition of PR with RU-486 mildly increased attachment rate to HEC-1A whereas it slightly decreased attachment rate to RL95-2. c-Met inhibition decreased attachment rates only to HEC-1A cells that expressing high levels of Plexin-B1 (PB1). Immunoprecipitation studies revealed that c-Met and PB1 associate in complexes in the endometrial cell lines.

CONCLUSION

Differential endometrial receptor profiles are expressed during the receptivity period. The attachment and invasion processes are separately regulated. We suggest a biologically functional role for PRA in endometrial receptivity and in the attachment process. c-Met contribution is minor and related with creation of a complex with PB1.

Membrane ERalpha-dependent activation of PKCalpha in endometrial cancer cells by estradiol

The purpose of this study was to investigate the role of the oestrogen receptor subtypes ERalpha and ERbeta in mediating the non-genomic effects of 17-beta-estradiol (E(2)) in two human endometrial cancer cell lines (RL95-2 and HEC-1A) expressing different levels of these receptor subtypes. Western blotting analysis using phosphorylation site-specific antibodies showed that physiological concentrations of E(2) rapidly (<20 min) activated PKCalpha, but not PKCdelta in the RL95-2 cell line. E(2) had no effect on PKCalpha or PKCdelta activity in the HEC-1A cell line and suppressed basal levels of PKA activity in both cell lines. PKCalpha activation coincided with its membrane translocation. ERalpha was detected in the RL95-2 cell line by Western blotting and RT-PCR but not in the HEC-1A cells, which did express ERbeta. A selective ERalpha agonist PPT had the same effect as E(2) on PKCalpha activation in the RL95-2 cells, but the selective ERbeta agonist DPN had no such effect. A 46kDa variant of ERalpha increased in abundance in the cell membrane within 20 min of E(2) treatment suggesting that ERalpha mediated the E(2) non-genomic effects on PKCalpha through the formation of a membrane associated signalling complex.

Endometrial modifications during early pregnancy in bonnet monkeys (Macaca radiata)

The present study was undertaken to investigate endometrial modifications that occur before embryo invasion in bonnet monkeys (Macaca radiata). These changes were analysed in luminal epithelium, glandular epithelium and stroma of endometrial functionalis on Day 6 post ovulation from pregnant and non-pregnant animals (n = 4 each) by transmission electron microscopy. Distinct features (i.e. loss of columnar shape by epithelial cells, changes in mitochondrial size and diffused apicolateral gap junctions) were observed in the luminal and glandular epithelium in pregnant animals. Stromal compaction was also observed in pregnant animals. Further, immunogold localisation studies demonstrated significantly higher expression (P < 0.05) of oestrogen receptor alpha, an oestrogen-regulated gene, in the glandular epithelium and stroma of the endometrium in pregnant animals compared with non-pregnant animals. Expression of two other genes known to be regulated by oestradiol, namely beta-actin and cyclo-oxygenase-1, were also significantly higher (P < 0.05) in the endometria of pregnant animals. These studies demonstrate marked changes in the endometrium before embryo invasion in bonnet monkeys. These studies also indicate altered oestrogenic activity in the uterine milieu before embryo invasion.

Development of an in vitro model for bovine placentation: a comparison of the in vivo and in vitro expression of integrins and components of extracellular matrix in bovine placental cells

BACKGROUND/AIMS

Interaction of trophoblastic integrins with the extracellular matrix plays a role in embryo implantation and trophoblast invasion. The phenomenon of restricted trophoblast invasion, observed in the bovine epitheliochorial placenta offers intriguing conditions to study invasive processes. The migration of bovine trophoblast giant cells is accompanied by the expression of specific integrins and corresponding extracellular matrix ligands.

METHODS

Primary cultures of different cell populations from cow placentomes were established and characterized, and in vitro phenotypes were compared with in vivo conditions by immunofluorescence.

RESULTS

Propagated epithelial cells were positive for cytokeratin and vimentin, while fibroblasts contained alpha-smooth muscle actin, desmin and vimentin. Epithelial cells coexpressed integrin subunits alpha(6) and beta(1) with laminin, and fibroblast cells were positive for alpha(v), beta(3), fibronectin and laminin. In contrast to cells in vivo, cultured epithelial cells secreted fibronectin, while collagen IV was not detected. The occurrence of integrin subunits was confirmed at mRNA level by RT-PCR.

CONCLUSION

We have established cell cultures isolated from maternal and fetal components of bovine placentomes expressing typical cytoskeletal filaments and integrin receptors also present in their in vivo counterparts. These bovine placentomal cells provide a suitable in vitro model for the study of cell-cell interactions.

Human uterine epithelial RL95-2 and HEC-1A cell-line adhesiveness: the role of plexin B1

OBJECTIVE

To study the expression of plexin-B1 in high- and low-receptive epithelial-endometrial cell lines, and its possible role in endometrial adhesiveness.

DESIGN

Controlled, laboratory study.

SETTING

Laboratory for Research in Reproductive Sciences, Department of Obstetrics and Gynecology, Ha'Emek Medical Center, Afula, Israel.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

This study was designed to explore and compare the expression and role of plexin-B1 in endometrial cell lines RL95-2 and HEC-1A, used as models of receptive and nonreceptive cells, respectively. The expression of plexin-B1 was analyzed by Western blotting and reverse-transcriptase polymerase chain reaction. The possible role of plexin-B1 in endometrial-trophoblast adhesiveness was studied with attachment and invasion assays. For further validation, we transfected HEC-1A cells with an expressing vector encoded for plexin-B1.

RESULT(S)

Significant differences in spheroid attachment was observed between RL95-2 and HEC-1A cells. Western blotting and reverse-transcriptase polymerase chain reaction revealed that in RL95-2 cells, the expression of plexin-B1 was significantly higher. An attachment assay that used RL95-2 cells in the presence of inhibiting antibodies against plexin-B1 significantly decreased the attachment rates of spheroids. A comparison between HEC-1A and transfected HEC-1A (HEC-1A-2) cells showed significant differences in spheroid attachment. No significant difference was found between HEC-1A-2 and RL95-2. An attachment assay using inhibitory antibodies against plexin-B1 significantly decreased the spheroid-attachment rate.

CONCLUSION(S)

Based on our results, we think that plexin-B1 contributes to trophoblast-endometrium interactions, most likely by enhancing adhesion properties.

Progesterone treatment and the progress of early pregnancy reduce desmoglein 1&2 staining along the lateral plasma membrane in rat uterine epithelial cells

Uterine epithelium undergoes dramatic changes during early pregnancy in preparation for implantation. We have studied distribution patterns of the desmosomal marker, desmoglein 1&2, in rat uterine epithelial cells during early pregnancy as well as in hormonally stimulated ovariectomised animals. On day 1 of pregnancy as well as in oestradiol treated rats, desmoglein 1&2 staining was localized along the entire length of the lateral plasma membrane. By day 3 and on subsequent days of pregnancy as well as in ovariectomised animals treated with progesterone alone or in combination with oestradiol, desmoglein 1&2 staining was concentrated at the apical portion of the lateral plasma membrane. We suggest that the reorganisation of these desmosomal cadherins is an important component of uterine epithelial receptivity and this relocation is under the control of the ovarian hormone progesterone.

Molecular mechanisms in uterine epithelium during trophoblast binding: the role of small GTPase RhoA in human uterine Ishikawa cells

Background

Embryo implantation requires that uterine epithelium develops competence to bind trophoblast to its apical (free) poles. This essential element of uterine receptivity seems to depend on a destabilisation of the apico-basal polarity of endometrial epithelium. Accordingly, a reorganisation of the actin cytoskeleton regulated by the small GTPase RhoA plays an important role in human uterine epithelial RL95-2 cells for binding of human trophoblastoid JAR cells. We now obtained new insight into trophoblast binding using human uterine epithelial Ishikawa cells.

Methods

Polarity of Ishikawa cells was investigated by electron microscopy, apical adhesiveness was tested by adhesion assay. Analyses of subcellular distribution of filamentous actin (F-actin) and RhoA in apical and basal cell poles were performed by confocal laser scanning microscopy (CLSM) with and without binding of JAR spheroids as well as with and without inhibition of small Rho GTPases by Clostridium difficile toxin A (toxin A). In the latter case, subcellular distribution of RhoA was additionally investigated by Western blotting.

Results

Ishikawa cells express apical adhesiveness for JAR spheroids and moderate apico-basal polarity. Without contact to JAR spheroids, significantly higher signalling intensities of F-actin and RhoA were found at the basal as compared to the apical poles in Ishikawa cells. RhoA was equally distributed between the membrane fraction and the cytosol fraction. Levels of F-actin and RhoA signals became equalised in the apical and basal regions upon contact to JAR spheroids. After inhibition of Rho GTPases, Ishikawa cells remained adhesive for JAR spheroids, the gradient of fluorescence signals of F-actin and RhoA was maintained while the amount of RhoA was reduced in the cytosolic fraction with a comparable increase in the membrane fraction.

Conclusion

Ishikawa cells respond to JAR contact as well as to treatment with toxin A with rearrangement of F-actin and small GTPase RhoA but seem to be able to modify signalling pathways in a way not elucidated so far in endometrial cells. This ability may be linked to the degree of polar organisation observed in Ishikawa cells indicating an essential role of cell phenotype modification in apical adhesiveness of uterine epithelium for trophoblast in vivo.

Induction of p38 mitogen-activated protein kinase-mediated apoptosis is involved in outgrowth of trophoblast cells on endometrial epithelial cells in a model of human trophoblast-endometrial interactions

During embryo implantation in species with hemochorial placentation, such as the mouse and human, trophoblast cells of the attached blastocyst penetrate the luminal epithelium of the endometrium before invasion into the endometrial stroma. Signs of apoptosis were demonstrated in luminal endometrial epithelial cells (EEC) adjacent to the trophoblast cells; however, the signaling mechanisms leading to apoptosis in EEC remain unclear. Because mitogen-activated protein kinases (MAPK) were shown to mediate apoptosis in several model systems and found to be activated in the uterus during decidualization, the possible involvement of MAPK during trophoblast-EEC interactions was studied. By coculturing BeWo human trophoblast spheroids with RL95-2 human EEC monolayers to mimic the blastocyst-endometrial interaction, we found that most spheroids rapidly attached to EEC monolayers and then progressively expanded, with marked dislodgment of EEC adjacent to the spreading trophoblast cells. Immunoblotting analysis showed that both p38 MAPK and extracellular signal-regulated kinase (ERK) were activated in EEC after coculture. However, only SB203580 (a p38 MAPK inhibitor), but not PD98059 (an ERK inhibitor), inhibited trophoblast outgrowth on EEC monolayers through the suppression of p38 MAPK activation in EEC. Furthermore, trophoblast expansion caused prominent EEC apoptosis at the spheroid-EEC interface, as detected by annexin V labeling and valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (which binds activated caspases) staining, and SB203580 significantly decreased the percentage of apoptotic cells. Our results, based on a model of human trophoblast-EEC interactions, establish that trophoblast cells cause activation of p38 MAPK in EEC and, consequently, induce apoptosis and displacement of EEC, a process that may facilitate implantation.

Cytoskeletal proteins in uterine epithelial cells only partially return to the pre-receptive state after the period of receptivity

Immunohistochemical staining of 5 cytoskeletal proteins (actin, alpha-actinin, gelsolin, plectin and plakoglobin) was used to investigate changes in distribution patterns of these proteins after the period of uterine receptivity for blastocyst implantation in the rat. Actin was found throughout the cytoplasm but it was concentrated along the apical plasma membrane on day 1 of pregnancy, decreased by day 6 and then increased again at day 9. Alpha-actinin and gelsolin were localized in distinctive bands along the apical plasma membrane at day 6 of pregnancy but became diffusely distributed at day 9. Plectin was localized along the apical and basal plasma membranes at day 6 but in higher amounts apically and at day 9, it was concentrated in apical and basal zones in the cells. Plakoglobin was found along the lateral and basal membranes with increased intensity along the apical third of the lateral plasma membrane from day 6 to day 9 of pregnancy. These results show that all 5 cytoskeletal proteins redistributed after the period of uterine receptivity: some exhibited a similar pattern of labelling to that found during the prereceptive state, whereas others only partially returned to the pre-receptive state. This change in distribution patterns may reflect differences in the epithelial barrier function before and after the period of receptivity.

Human peripheral blood mononuclear cells enhance cell-cell interaction between human endometrial epithelial cells and BeWo-cell spheroids

BACKGROUND

Previously, it was reported that T-lymphocytes derived from non-pregnant mice promote murine embryo implantation. In order to examine the immunological regulation of endometrial receptivity in humans, the effects of peripheral blood mononuclear cells (PBMCs) on endometrial epithelial cell (EEC) function were monitored by a newly developed attachment assay using primary human EEC culture and BeWo cell-derived spheroids.

METHODS AND RESULTS

EECs isolated from 25 women in the mid- and late proliferative and early, mid- and late secretory phases were subjected to monolayer culturing. Spheroids were constructed from BeWo cells, a human choriocarcinoma cell line, by incubation with continuous rolling, after which their interaction with cultured EECs was studied. The mean (+/- SEM) number of attached spheroids was significantly higher (P < 0.01) in the EEC culture derived from women in the mid-secretory phase (90 +/- 2.9%) than the other groups (ranging from 0 to 5.8 +/- 3.7%), which is in agreement with the existence of a so-called 'implantation window'. After 72 h co-culture of EECs with PBMCs, the number of attached spheroids significantly increased in the EEC cultures derived from the late proliferative and early secretory phases [65.0 +/- 21.7 versus 5.0 +/- 2.0% (P < 0.05) and 83.1 +/- 4.1 versus 4.4 +/- 1.9% (P < 0.01)].

CONCLUSIONS

This attachment assay appears to be a useful method with which to assess endometrial receptivity. Functional change of EECs induced by PBMCs suggests possible regulation of endometrial receptivity by immune cells.

Establishment of an efficient method to quantify embryo attachment to endometrial epithelial cell monolayers

During implantation, complex embryo-endometrium interactions result in blastocyst adhesion. To study the mechanisms of implantation, an effective assay for monitoring adhesiveness between embryos and endometrial epithelium is essential. In this study, we describe a simple and reliable method to quantify embryo-endometrium adhesion in vitro. Murine blastocysts or BeWo trophoblast spheroids were cocultured with monolayers of RL95-2 endometrial epithelial cells (EEC) grown in 96-well plates. At the end of coculture, the wells were filled with medium, and the plate was sealed with an adhesive film, inverted, and centrifuged at 25 x g for 5 min. After centrifugation, the plate was kept inverted and directly examined microscopically to determine whether the blastocysts or spheroids were attached to EEC monolayers. Our assay demonstrated that blastocysts recovered at 1200-1400 h on d 4 were more adherent to EEC than those recovered earlier, consistent with the timing of intrauterine embryo activation. Serum also enhanced blastocyst-EEC adhesion. Spheroid-EEC adhesion was inhibited by blocking Ca(2+) influx with extracellular Ca(2+) chelators (ethylenediaminetetraacetic acid or ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid) or a Ca(2+) channel blocker (verapamil) but not by interfering with Ca(2+) release from intracellular stores using chelating (1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) or depleting (thapsigargin) agents. Using 96-well plates for coculture, centrifugation, and examination to minimize transfer procedures, our assay system is readily applicable to investigate implantation mechanisms.

Benzo(a)pyrene, but not 2,3,7,8-tetrachlorodibenzo-p-dioxin, alters cell adhesion proteins in human uterine RL95-2 cells

This study compared the effects of benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), two aryl hydrocarbon receptor agonists, on cell attachment and adherens junction proteins in RL95-2 human uterine endometrial cells. Exposure to 10 microM BaP significantly decreased cell attachment to Matrigel, whereas 10 nM TCDD had no effect. Immunocytochemistry and Western immunoblot analysis showed that BaP, but not TCDD, produced a marked loss of plasma membrane epidermal growth factor receptor (EGF-R) localized along intercellular boundaries. BaP-treated cells exhibited significant decreases in beta-catenin and cadherin protein levels, while vinculin levels remained unchanged relative to control. In contrast, TCDD treatment had no effect on the levels of beta-catenin, cadherin, or vinculin. Further studies using the fluorescein labeled peptide phalloidin showed the presence of continuous subcortical actin filaments in control cells, whereas BaP-treated cells had subcortical actin aggregates. Thus, in contrast to TCDD, BaP produces a loss of cell attachment involving decreased localization of molecules important for cell-cell interactions in RL95-2 cells.

17beta-oestradiol stimulates capacitative Ca2+ entry in human endometrial cells

Oestrogen plays an essential role in regulating growth and differentiation in the human endometrium which undergoes dynamic morphological and functional changes during the menstrual cycle in preparation for implantation. In this tissue, it has been suggested that intracellular calcium could be a key signal in transducing early responses to steroid hormones. Here, we have investigated the rapid effects of 17beta-oestradiol on [Ca2+]i in a human endometrial cell line (RL95-2). Using confocal imaging microscopy, we show that physiological concentrations of 17beta-oestradiol trigger rapid and transient increases in [Ca2+]i. Our results demonstrate that 17beta-oestradiol-induced [Ca2+]i variations are critically dependent on calcium influx via lanthanum-sensitive calcium channels. Moreover, the 17beta-oestradiol-induced Ca2+ influx is significantly increased by the depletion of intracellular stores by thapsigargin and decreased by chelerythrine chloride, an inhibitor of protein kinase C. These data indicate a non-genomic action of 17beta-oestradiol to stimulate capacitative Ca2+ entry through store-operated calcium channels via a PKC-sensitive pathway.

Increased adhesiveness in cultured endometrial-derived cells is related to the absence of moesin expression

Human endometrial epithelial cells (EECs) are nonadhesive for embryos throughout most of the menstrual cycle. During the so-called implantation window, the apical plasma membrane of EECs acquire adhesive properties by undergoing a series of morphological and biochemical changes. The human endometrial-derived epithelial cell line, RL95-2, serves as an in vitro model for receptive uterine epithelium because of its high adhesiveness for trophoblast-derived cells. In contrast, the HEC-1-A cell line, which displays poor adhesive properties for trophoblast cells, is considered to be less receptive. The ezrin, radixin, and moesin protein family members, which are present underneath the apical plasma membrane, potentially act to link the cytoskeleton and membrane proteins. In the present study, we have further investigated the adhesive features in these two unrelated endometrial-derived cell lines using an established in vitro model for embryonic adhesion. We have also analyzed the protein pattern and mRNA expression of ezrin and moesin in RL95-2 cells versus HEC-1-A cells. The results demonstrate that RL95-2 cells were indeed more receptive (81% blastocyst adhesion) compared with HEC-1-A cells (46% blastocyst adhesion). An intermediate adhesion rate was found in primary EECs cultured on extracellular matrix gel, thus allowing a partial polarization of these cells (67% blastocyst adhesion). Furthermore, we found that moesin was absent from RL95-2 cells. In contrast, ezrin is expressed in both cell lines, yet it is reduced in adherent RL95-2 cells. Data are in agreement with the hypothesis that uterine receptivity requires down-regulation or absence of moesin, which is a less-polarized actin cytoskeleton.

Adhesion of trophoblast to uterine epithelium as related to the state of trophoblast differentiation: in vitro studies using cell lines

At the initial phase of embryo implantation, the trophoblast must have acquired competence for adhesion to the uterine epithelium, a condition whose cell biological basis is far from understood. In the present study, trophoblast-type cells (BeWo, JAr, and Jeg-3 choriocarcinoma cell lines) were treated with retinoic acid, methotrexate, dibutyryl-cAMP, or phorbol-12-myristate-13-acetate in order to modulate their ability to adhere to uterine epithelial cells (RL95-2). In an established model, multicellular spheroids of choriocarcinoma cells were transferred onto the surface of monolayer cultures of RL95-2 cells followed by a centrifugal force-based adhesion assay. In controls, about 45% of BeWo and JAr cell spheroids and 75% of Jeg-3 spheroids adhered to uterine monolayers within 30 min. Pretreatment of spheroids with either of the agents stimulated differentiation as indicated by the rate of chorionic gonadotropin secretion, but consistently reduced the adhesion to the endometrial monolayer in all three choriocarcinoma cell lines. While previous investigations had shown that invasiveness of trophoblast cells (into extracellular matrix) does not seem to be linked to the differentiation program in a simple manner, the present data suggest that such an (inverse) link may indeed exist with respect to the ability to initiate an adhesive interaction with the uterine epithelium. These observations support the view that epithelial cell interactions as typical for the initial phase of embryo implantation are regulated in a way that is clearly different from cell-matrix interactions governing later phases of trophoblast invasion into the endometrial stroma.

Blastocyst implantation: the adhesion cascade

This review covers the sequence of cell adhesion events occurring during implantation of the mammalian embryo, concentrating on data from mouse and human. The analogy is explored between initial attachment of trophoblast to the uterine lining epithelium and that of neutrophils to the endothelial lining of blood vessels at sites of inflammation. The possible role of various carbohydrate ligands in initial attachment of the blastocyst is reviewed. The evidence for subsequent stabilization of cell adhesion via integrins or the trophinin-tastin complex is discussed.

Morphological evidence for the 'implantation window' in human luminal endometrium

Endometrial tissue was taken from 21 normal fertile women (aged 18-40 years) between 4 and 13 days after the luteinizing hormone (LH) surge. Systematic random samples of luminal epithelium were taken for both light and electron microscopy and examined morphometrically. Throughout the luteal phase there were remarkably few changes in the volume fraction of nucleus, mitochondria, rough endoplasmic reticulum and 'vesicular system' to cell. Nuclear profile dimensions and cell height also did not change over time. Cell and organelle volume (estimated as volume weighted mean volume) did not change significantly, but showed numerically smallest values on day LH + 13. However the ratio of desmosomes to whole cell and both arithmetic mean thickness and harmonic mean thickness of basement membrane were minimal at the time when implantation would be most likely to occur, i.e. approximately 6 days after the LH peak. Therefore it appears that while some morphometric parameters in human luminal epithelial cells change little during the luteal phase, specific cellular changes occur to the basement membrane and desmosomes which may facilitate embryo implantation. These changes occurred around day LH+ 6 and may be a morphological representation of the 'implantation window'.

Immunohistochemical localization of receptors for progesterone and oestradiol-17 beta in the implantation site of the rhesus monkey

The aim of the present study was to examine the cellular basis of the involvement of oestradiol and progesterone in blastocyst implantation in the primate. To this end, the cellular distribution of receptors for oestradiol (ER) and progesterone (PR) in fetal trophoblast cells and in endometrial compartments of timed lacunar (pre-villous) and villous stages of placentation in primary implantation sites collected on days 13-22 of gestation were investigated in rhesus monkeys. Both in pre-villous stage tissue and in villous stage tissue, cytotrophoblast cells and syncytiotrophoblast cells and other trophoblast derived cells were PR positive, while they were generally ER negative. Maternal endometrial cells were ER negative, while epithelial cells, stromal cells and vascular endothelial cells in maternal endometrium showed heterogeneous staining patterns for PR depending on their relative location; these patterns, however, correlated well with glandular hyperplasia and differentiation, stromal-decidual transformation and vascular response seen during blastocyst implantation.

Presence of uterine pinopodes at the embryo-endometrial interface during human implantation in vitro

In order to study changes occurring on the surfaces of human endometrial epithelial cells in the presence of an implanted blastocyst, we used scanning electron microscopy for investigation of five endometrial biopsies and three human implantation sites obtained in vitro. All specimens showed areas with endometrial pinopodes, separated by cells displaying microvilli or cilia at the apical surface. Pinopode formation was more pronounced in endometrial biopsies than in cell cultures. All blastocysts adhered to pinopode presenting cells. Endometrial surface changes were not seen around the blastocysts. The results of this study demonstrate that cultured endometrial epithelial cells are capable of pinopode formation. Furthermore, endometrial epithelial pinopodes, generally considered as a marker of endometrial receptivity, seem to be directly involved in the adhesion of the blastocyst to the endometrial surface.