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

The role of nitric oxide in the outgrowth of trophoblast cells on human umbilical vein endothelial cells

OBJECTIVE

Embryo implantation is a complex process that requires coordinated trophoblast-endometrial interactions. Previous studies demonstrated that the identification of nitric oxide synthase (NOS) in trophoblast cells and the remodeling of the implantation process by nitric oxide (NO) support the important role of NO during implantation. However, the role of NO in trophoblast-endometrial interactions is unclear and is therefore examined in this study.

MATERIALS AND METHODS

We cocultured BeWo trophoblast spheroids with human umbilical vein endothelial cell (HUVEC) monolayers to mimic the trophoblast-endometrial interaction. N(ω)-Nitro-l-arginine methyl ester hydrochloride (l-NAME), a competitive inhibitor of NOS, and sodium nitroprusside (SNP), an NO donor, were used to test the role of NO in the trophoblast-endometrial interaction.

RESULTS

l-NAME diminished spheroid expansion on HUVEC monolayers in a concentration-dependent manner (p < 0.05). However, trophoblast spreading on HUVEC-free culture surfaces was unaffected by l-NAME treatment (p > 0.05). Significant suppression of spheroid expansion was found at the higher dose (1mM) of SNP (p < 0.05).

CONCLUSION

NO may be needed in the process of implantation, and an adequate but not overly NO-containing environment might be an important factor for successful implantation. This finding is worthy of further investigation.

Divergent endometrial inflammatory cytokine expression at peri-implantation period and after the stimulation by copper intrauterine device

Endometrial inflammation has contradictory effects. The one occurring at peri-implantation period is favourable for embryo implantation, whereas the other occurring after the stimulation by copper intrauterine device (Cu-IUD) prevents from embryo implantation. In this study, 8 week female ICR mice were used to investigate the endometrial inflammation, in which they were at proestrus stage (Group 1), at peri-implantation period (Group 2), and had a copper wire implanted into right uterine horn (Group 3). Cytokine array revealed that two cytokines were highly expressed in Group 2 and Group 3 as compared with Group 1, and seven cytokines, including tumour necrosis factor α (TNF-α), had selectively strong expression in Group 3. Immunohistochemistry demonstrated prominent TNF-α staining on the endometrium after Cu-IUD stimulation, and in vitro culture of human endometrial glandular cells with Cu induced TNF-α secretion. The increased TNF-α concentration enhanced in vitro THP-1 cells chemotaxis, and reduced embryo implantation rates. These results suggest that inflammatory cytokine profiles of endometrium are different between those at peri-implantation period and after Cu-IUD stimulation, and TNF-α is the one with selectively strong expression in the latter. It might account for the contradictory biological effects of endometrial inflammation.

Apoptotic effects of high estradiol concentrations on endometrial glandular cells

CONTEXT

High serum estradiol (E2) concentrations result in adverse reproductive outcome in in vitro fertilization cycles, and the detrimental effects are probably due to impaired endometrial receptivity.

OBJECTIVE

Endometrial glandular cells (EGCs) are the cells that embryos first interact with during implantation. Our objective is to examine the in vitro EGC alterations after high E2 treatment.

DESIGN

This was a prospective study.

SETTING

The study was conducted at a tertiary university hospital.

PATIENTS

Six women in the follicular phase participated in the study.

INTERVENTIONS

EGCs were purified from human endometrium and cultured with different concentrations (0, 10(-9), 10(-8), 10(-7), 10(-5), 10(-4) M) of E2.

MAIN OUTCOME MEASURE(S)

EGC apoptosis and its underlying mechanism were measured.

RESULTS

In vitro BeWo spheroid-EGC implantation assay demonstrated that the stimulation with 10(-5) and 10(-4) M E2 for 2 days decreased embryo implantation potentials. Presence of apoptotic bodies and DNA fragmentation and an increased percentage of sub-G1 phase were found in EGCs treated with high E2 concentrations. The high E2-treated EGCs could be rescued from apoptosis after the addition of estrogen receptor antagonist ICI 182 780. Western blot revealed increased inhibitory-κB (IκB)-α expression and decreased nuclear factor-κB (NF-κB) expression in high E2-treated EGCs, and NF-κB binding site-driven luciferase activity was decreased as well. When EGCs were pretreated with IκB-α small interfering RNA, high E2-induced B cell lymphoma 2 (Bcl-2) down-regulation did not occur and EGCs apoptosis was reduced. Bcl-2 overexpression also rescued high E2-induced EGCs from apoptosis.

CONCLUSIONS

High E2 concentrations induced EGCs apoptosis through enhancing IκB-α expression, which in turn suppressed NF-κB expression. The decreased nuclear NF-κB subsequently inhibited Bcl-2 expression and accordingly enhanced EGC apoptosis.

Quantifying the biomechanics of conception: L-selectin-mediated blastocyst implantation mechanics with engineered "trophospheres"

An estimated 12% of women in the United States suffer from some form of infertility. In vitro fertilization (IVF) is the most common treatment for infertility encompassing over 99% of all assisted reproductive technologies. However, IVF has a low success rate. Live birth rates using IVF can range from 40% in women younger than 35 years to 4% in women older than 42 years. Costs for a successful IVF outcome can be upward of $61,000. The low success rate of IVF has been attributed to the inability of the blastocyst to implant to the uterus. Blastocyst implantation is initiated by L-selectin expressing cells, trophoblasts, binding to L-selectin ligands, primarily sialyl Lewis X (sLeX), on the uterine surface endometrium. Legal and ethical considerations have limited the research on human subjects and tissues, whereas animal models are costly or do not properly mimic human implantation biochemistry. In this work, we describe a cellular model system for quantifying L-selectin adhesion mechanics. L-selectin expression was confirmed in Jeg-3, JAR, and BeWo cell lines, with only Jeg-3 cells exhibiting surface expression. Jeg-3 cells were cultured into three-dimensional spheres, termed "trophospheres," as a mimic to human blastocysts. Detachment assays using a custom-built parallel plate flow chamber show that trophospheres detach from sLeX functionalized slides with 2.75 × 10(-3) dyn of force and 7.5 × 10(-5) dyn-cm of torque. This work marks the first time a three-dimensional cell model has been utilized for quantifying L-selectin binding mechanics related to blastocyst implantation.

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

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

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.

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.

Calcitonin promotes outgrowth of trophoblast cells on endometrial epithelial cells: involvement of calcium mobilization and protein kinase C activation

Embryo implantation is a complex process that requires coordinated trophoblast-endometrial interactions. During implantation, trophoblast cells of the attached blastocyst penetrate the luminal epithelium of the endometrium before invasion into the endometrial stroma. Previous studies demonstrated that calcitonin was actively secreted by rat and human endometrial epithelial cells (EEC) during the implantation window and targeted disruption of endometrial calcitonin expression dramatically decreased embryo implantation rates; however, the role and signal transduction of calcitonin in trophoblast-endometrial interactions remained unclear and are therefore examined in this study. BeWo trophoblast and RL95-2 EEC lines were used because they preserve many properties of their respective normal tissues. We co-cultured BeWo trophoblast spheroids with RL95-2 EEC monolayers to mimic the blastocyst-endometrial interaction, and found that most spheroids quickly attached to EEC monolayers and then progressively expanded, with marked displacement of EEC adjacent to the outgrowing trophoblast cells. Interestingly, pretreatment of EEC monolayers with calcitonin before the addition of spheroids significantly enhanced trophoblast expansion on EEC monolayers. Cytosolic calcium (Ca(2+)) levels in EEC increased rapidly upon exposure to calcitonin, and blockade of Ca(2+) release by BAPTA-AM effectively prevented the promoting effect of calcitonin on trophoblast expansion on EEC. The Ca(2+)-dependent protein kinase C (PKC) was also activated in EEC after calcitonin treatment, and the PKC inhibitors staurosporine and calphostin C could completely abolish calcitonin-induced augmentation of trophoblast expansion on EEC. Our results suggest that calcitonin promotes trophoblastic displacement of EEC through calcium mobilization and PKC activation, thereby facilitating embryo implantation.

Interleukin-8 can stimulate progesterone secretion from a human trophoblast cell line, BeWo

Precise paracrine cross-talk between the embryo and the endometrium is essential for the establishment of a successful pregnancy. Previous studies have demonstrated that the expression of interleukin-8 (IL-8) in the endometrium is enhanced during the late-secretory phase and early pregnancy. Furthermore, IL-8 receptor (IL-8R) expression has been detected in trophoblast cells of the developing embryo. To clarify the roles of IL-8 in the endometrium-embryo interactions, the effects of IL-8 on hormone secretion by trophoblast cells were studied using the BeWo trophoblast cell line that retains hormone-secreting properties of normal trophoblast cells. Using reverse transcription-polymerase chain reaction, we found that IL-8R messenger ribonucleic acid (mRNA) was expressed in BeWo cells. The levels of IL-8R mRNA and protein expression in BeWo cells were similar to those in primary first-trimester trophoblast cells. Progesterone (P4) secretion of BeWo cells was comparable with that of first-trimester trophoblast cells but higher than that of third-trimester trophoblast cells. Treatment of BeWo cells with recombinant human IL-8 (rhIL-8) had no effect on cell proliferation, as determined by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. Interestingly, secretion of P4, but not human chorionic gonadotropin, from cultured BeWo cells was significantly enhanced when the cells were incubated with rhIL-8. Our results demonstrate that IL-8 may play an important role in the endometrium-embryo interactions by stimulating trophoblast secretion of P4 for maintenance of a successful pregnancy.

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.