Uterine cell death during implantation and early placentation

Early Syncytialization of the Ovine Placenta Revisited

Placentation is the development of a temporary arrangement between the maternal uterus and blastocyst-derived placental tissues designed to transport nutrients, gases, and other products from the mother to the embryo and fetus. Placentation differs histologically among species, but all types of placentation share the common trait of utilizing highly complex cell-to-cell and tissue-to-tissue morphological and biochemical interactions to remodel the uterine-placental interface. An elegant series of electron microscopy (EM) images supports the classification of ovine placentation as synepitheliochorial, because uterine luminal epithelial (LE) cells are maintained at the uterine-placental interface through incorporation into trophoblast syncytial plaques. In this review, we utilize immunofluorescence microscopy to provide further insights into early syncytialization of the ovine placenta. These observations, based on results using immunofluorescence microscopy, complement and expand, not replace, our understanding of syncytialization in sheep.

Genetic variants in the p53 pathway influence implantation and pregnancy maintenance in IVF treatments using donor oocytes

PURPOSE

Single-nucleotide polymorphisms (SNPs) in the p53 pathways have shown to play a role in endometrial receptivity and implantation in infertile women undergoing in vitro fertilization (IVF). The present study aimed to assess the influence of these gene variants over pregnancy success through a receptivity model in recipients of egg donation treatments, when factors such as age and quality of the oocytes are standardized.

METHODS

A nested case-control study was performed on 234 female patients undergoing their first fresh IVF treatment as recipients of donor oocytes. Genotyping of TP53 Arg72Pro (rs1042522), LIF (rs929271), MDM4 (rs1563828), and USP7 (rs1529916) SNPs in the recipients allowed comparison of allele and genotype frequencies and their association with the IVF treatment outcome.

RESULTS

Grouped by genotypes, patients showed differences in IVF outcomes after the embryo transfer. Arg72Pro (rs1042522) gene variant was associated to changes in implantation and clinical pregnancy rates. The polymorphisms USP7 (rs1529916) and MDM4 (rs1563828) were associated to differential ongoing pregnancy rates and variable miscarriage events, respectively.

CONCLUSIONS

This study highlights the association between gene polymorphisms related to P53 function and their influence over IVF reproductive outcomes. Arg72Pro variant may influence early events, as lower implantation rates were found in homozygous for Pro72 allele. By contrast, MDM4 (rs1563828) and USP7 (rs1529916) gene variants were associated with the later maintenance of pregnancy.

Dual role of TGF-β in early pregnancy: clues from tumor progression

TGF-β signaling in the endometrium is active during the implantation period and has a pivotal role in regulating endometrial receptivity and embryo implantation. During embryo implantation, both apoptosis and proliferation of endometrial cells happen at the same time and it seems TGF-β is the factor that controls both of these processes. As shown in cancer cells, in special conditions this cytokine can have a dual effect and switch the action from apoptosis to proliferation. Owing to the similarity between embryo implantation and cancer development and also unusual pattern of proliferation and remodeling in the uterus, in this review we suggest the existence of such a switching in endometrium during the early pregnancy. Moreover, we address some potential mechanisms that could regulate the switching. A better understanding of the molecular mechanisms regulating TGF-β action and signaling during the implantation period could pave the way for introducing novel therapeutic strategies in order to solve implantation-associated issues such as repeated implantation failure.

Endometrial injury increases expression of hypoxia-inducible factor and angiogenesis in the endometrium of women with recurrent implantation failure

RESEARCH QUESTION

The aim of this study was to compare expression of hypoxia-inducible factor 1-alpha (HIF-1α), angiogenesis and apoptosis in endometrial tissue near the implantation window of women with recurrent implantation failure (RIF) and in fertile control women, and to describe possible mechanisms of endometrial injury.

DESIGN

A controlled clinical study was conducted. Endometrial tissue specimens were obtained from 20 women undergoing IVF who had had at least three previous failed treatment cycles; normal endometrial specimens were obtained from 10 fertile control women.

RESULTS

HIF-1α expression was down-regulated in the endometrium of women with RIF compared with that of control women. In addition, micro-vessel density (MVD) was much lower in the endometrium of women with RIF than in that of the control women. Apoptosis was significantly reduced in the endometrium of the RIF group compared with the control group. Endometrial injury increased HIF-1α expression and MVD in endometrial samples of the RIF group, but apoptosis was not significantly altered.

CONCLUSIONS

HIF-1α expression, MVD and endometrial apoptosis were reduced in the peri-implantation endometrium of women with RIF. This suggests that altered endometrial HIF-1α expression and angiogenesis may contribute to implantation failure.

Association of Tumor Growth Factor-β and Interferon-γ Serum Levels With Insulin Resistance in Normal Pregnancy

Pregnancy is related to change in glucose metabolism and insulin production. The aim of our study was to determine the association of serum IFN-γ and TGF-β levels with insulin resistance during normal pregnancy. This cross sectional study was carried out on 97 healthy pregnant (in different trimesters) and 28 healthy non-pregnant women. Serum TGF-β and IFN-γ level were measured by ELISA method. Pregnant women had high level TGF-β and low level IFN-γ as compared non-pregnant women. Maternal serum TGF-β concentration significantly increased in third trimester as compared first and second trimester of pregnancy. Maternal serum IFN-γ concentration significantly decreased in third trimester as compared first and second trimester of pregnancy. Pregnant women exhibited higher score of HOMA IR as compared non-pregnant women. There were association between gestational age with body mass index (r=0.28, P=0.005), TGF-β (r=0.45, P<0.001) and IFN-γ (r=-0.50, P<0.001). There was significant association between Insulin resistance and TGF-β (r=0.17, p=0.05). Our findings suggest that changes in maternal cytokine level in healthy pregnant women were anti-inflammatory. Furthermore, Tumor Growth Factor-β appears has a role in induction insulin resistance in healthy pregnant women. However, further studies needed to evaluate role of different cytokines on insulin resistance in normal pregnancy.

Multiple-embryo transfer for studying very early maternal-embryo interactions in cattle

In the present paper, we highlight the need to study very early maternal-embryo interactions and discuss how these interactions can be addressed. Bovine species normally carry one or, less frequently, two embryos to term; there are very rare cases of triplets or higher-order multiple pregnancies in which all the offspring are born alive. Multiple-embryo transfer (MET) in cattle allows for the detection of endometrial responses in scenarios where single-embryo transfer would not. Although MET is non-physiological, the present study shows that at the very early embryonic stages, a uterus carrying zona-enclosed embryos does not exhibit non-physiological reactions. On the contrary, MET should be considered the sum of multiple individual effects triggered by developing embryos. We provide arguments to support our hypothesis that describe a rationale for current work with MET, and we discuss alternative hypotheses. Using cattle as a model, we describe how technical approaches to analyzing zona-enclosed early embryo-maternal interactions (i.e., transcriptomics, proteomics, and endometrial cell culture) can help identify molecular changes that may be difficult to observe when only a single embryo is present. We conclude that MET can be used for studying very early maternal-embryo interactions in vivo in monotocous species. Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/150/2/R35/suppl/DC1.

Calpain 2 activity increases at the time of implantation in rat uterine luminal epithelial cells and administration of calpain inhibitor significantly reduces implantation sites

The present study investigated the role of calpain 2 in rat uterine luminal epithelial cells during early pregnancy. Calpain 2 is an intracellular calcium-dependent proteolytic enzyme which cleaves numerous focal adhesion proteins. Calpain 2 was concentrated along the basal cell surface of uterine luminal epithelial cells at the predicted site of focal adhesions on day 1 of pregnancy and remained unchanged at the time of implantation as observed by immunofluorescence microscopy. However, Western blotting analysis showed a marked increase in the active form and a significant decrease in the latent form of calpain 2 at the time of implantation. The increase in calpain 2 activity coincides with the disassembly of focal adhesion proteins, talin, paxillin, integrin β1 and β3 from the site of focal adhesions. Intraperitoneal injection of calpain inhibitor, calpain inhibitor l (ALLN), significantly reduced the number of implantation sites, implying that calpain 2 plays an important role in implantation. The present study suggests a role for calpain 2 in the disassembly of focal adhesions, which has been previously shown to play a key role in uterine receptivity for implantation.

BMPR2 is required for postimplantation uterine function and pregnancy maintenance

Abnormalities in cell-cell communication and growth factor signaling pathways can lead to defects in maternal-fetal interactions during pregnancy, including immunologic rejection of the fetal/placental unit. In this study, we discovered that bone morphogenetic protein receptor type 2 (BMPR2) is essential for postimplantation physiology and fertility. Despite normal implantation and early placental/fetal development, deletion of Bmpr2 in the uterine deciduae of mice triggered midgestation abnormalities in decidualization that resulted in abnormal vascular development, trophoblast defects, and a deficiency of uterine natural killer cells. Absence of BMPR2 signaling in the uterine decidua consequently suppressed IL-15, VEGF, angiopoietin, and corin signaling. Disruption of these pathways collectively lead to placental abruption, fetal demise, and female sterility, thereby placing BMPR2 at a central point in the regulation of several physiologic signaling pathways and events at the maternal-fetal interface. Since trophoblast invasion and uterine vascular modification are implicated in normal placentation and fetal growth in humans, our findings suggest that abnormalities in uterine BMPR2-mediated signaling pathways can have catastrophic consequences in women for the maintenance of pregnancy.

Evaluation of FAS and caspase-3 in the endometrial tissue of patients with idiopathic infertility and recurrent pregnancy loss

OBJECTIVE

To investigate expression of BcL-2, FAS, FAS ligand (FASL) and cleaved caspase-3 in the endometrial tissue of women with idiopathic infertility (with two consecutive failed cycles of in vitro fertilization) and women with idiopathic recurrent pregnancy loss. The control group consisted of fertile women.

STUDY DESIGN

Endometrial tissue samples from fertile women (n=25), women with idiopathic infertility (n=25) and women with idiopathic recurrent pregnancy loss (n=25) were collected on the seventh or eighth postovulatory day of their menstrual cycles for evaluation. Expression of BcL-2, FAS, FASL and cleaved caspase-3 was assessed using immunohistochemical methods.

RESULTS

Expression of BcL-2 and FAS was significantly higher and lower, respectively, in the women with idiopathic infertility than in the other groups (p<0.01). Expression of cleaved caspase-3 was significantly lower in the women with idiopathic infertility than in the other groups (p<0.01). Expression of FASL was similar in all three groups.

CONCLUSION

Disturbances in endometrial apoptosis may be a contributing factor in patients with idiopathic infertility and recurrent pregnancy loss.

Association of FAS -1377 G>A and FAS -670 A>G functional polymorphisms of FAS gene of cell death pathway with recurrent early pregnancy loss risk

Apoptosis during the early stages of pregnancy enables the remodeling of the uterus for proper placentation. Apoptosis in the maternal activated cytotoxic T lymphocytes allows maternal immune tolerance to pregnancy and in glandular and stromal cells it helps with trophoblastic endometrial invasion. FAS gene is expressed at the maternal-fetal interface and is involved in the regulation of immune response and implantation. Altered FAS expression may result in altered apoptosis and ultimately affects both immune response and implantation. FAS -1377 G>A and FAS -670 A>G functional polymorphisms in the promoter region of FAS gene modulate its expression at transcriptional level. In a case-control study the contribution of FAS -1377 G>A and FAS -670 A>G polymorphisms to the risk of recurrent early pregnancy loss (REPL) was evaluated. DNA from 134 cases with a history of three or more REPL and 124 healthy controls with successful pregnancy outcomes were genotyped through PCR-RFLP. DNA sequencing was used to ascertain PCR-RFLP results. The genotype and allele frequencies for FAS -1377 G>A and FAS -670 A>G polymorphisms were compared in REPL and controls. FAS -1377 AA and AG genotypes were associated with an increased risk of REPL (OR, 3.25; 95%CI, 1.52-6.98 and OR, 2.62; 95%CI, 1.48-4.64, respectively), whereas FAS -670 genotypes conferred no risk. The -1377 AA/-670 GG genotypes combination of FAS polymorphisms showed highest risk (OR, 8.15; 95%CI, 2.75-25.81). Genotype combinations -1377 GA/-670 AA and -1377 GA/-670 AG were also statistically significant, suggestive of their role in REPL risk.

β(1) and β(3) integrins disassemble from basal focal adhesions and β(3) integrin is later localised to the apical plasma membrane of rat uterine luminal epithelial cells at the time of implantation

The present study investigated the expression of integrin subunits that are known to be associated with focal adhesions, namely β(1) and β(3) integrins in rat uterine luminal epithelial cells during early pregnancy. The β(1) and β(3) integrins were concentrated along the basal cell surface and were colocalised and structurally interacted with talin, a principal focal adhesion protein, on Day 1 of pregnancy. At the time of implantation, β(1) and β(3) integrins disassembled from the site of focal adhesions, facilitating the removal of uterine luminal epithelial cells for embryo invasion. Also at this time, β(3) integrin markedly increased along the apical membrane, suggesting a role in embryo attachment. This distributional change in β(1) and β(3) integrins seen at the time of implantation was predominantly under the influence of progesterone. Taken together, β(1) and β(3) integrin disassembly from focal adhesions and the increase in β(3) integrin apically are key components of hormonally regulated endometrial receptivity.

Trophinin-mediated cell adhesion induces apoptosis of human endometrial epithelial cells through PKC-δ

Trophinin is an intrinsic membrane protein expressed in trophectoderm cells of embryos and in uterine epithelial cells. Trophinin potentially mediates apical cell adhesion at human embryo implantation sites through trophinin-trophinin binding in these two cell types. Trophinin-mediated cell adhesion activates trophectoderm cells for invasion, whereas the effect of adhesion on maternal side is not known. We show that addition of GWRQ peptide, a previously established peptide that mimics trophinin-mediated cell adhesion, to human endometrial epithelial cells expressing trophinin induces their apoptosis. FAS involvement was excluded, as GWRQ did not bind to FAS, and FAS knockdown did not alter GWRQ-induced apoptosis. Immunoblotting analyses of protein kinases revealed an elevation of PKC-d protein in GWRQ-bound endometrial epithelial cells. In the absence of GWRQ, PKC-d associated with trophinin and remained cytoplasmic, but after GWRQ binding to the trophinin extracellular domain, PKC-d became tyrosine phosphorylated, dissociated from trophinin, and entered the nucleus. In PKC-d knockdown endometrial cells, GWRQ did not induce apoptosis.

Ovarian hormones regulate expression of the focal adhesion proteins, talin and paxillin, in rat uterine luminal but not glandular epithelial cells

During early pregnancy in the rat, focal adhesions disassemble in uterine luminal epithelial cells at the time of implantation to facilitate their removal so that the implanting blastocyst can invade into the underlying endometrial decidual cells. This study investigated the effect of ovarian hormones on the distribution and protein expression of two focal adhesion proteins, talin and paxillin, in rat uterine luminal and glandular epithelial cells under various hormone regimes. Talin and paxillin showed a major distributional change between different hormone regimes. Talin and paxillin were highly concentrated along the basal cell surface of uterine luminal epithelial cells in response to oestrogen treatment. However, this prominent staining of talin and paxillin was absent and also a corresponding reduction of paxillin expression was demonstrated in response to progesterone alone or progesterone in combination with oestrogen, which is also observed at the time of implantation. In contrast, the distribution of talin and paxillin in uterine glandular epithelial cells was localised on the basal cell surface and remained unchanged in all hormone regimes. Thus, not all focal adhesions are hormonally dependent in the rat uterus; however, the dynamics of focal adhesion in uterine luminal epithelial cells is tightly regulated by ovarian hormones. In particular, focal adhesion disassembly in uterine luminal epithelial cells, a key component to establish successful implantation, is predominantly under the influence of progesterone.

Transforming growth factor beta isoforms regulation of Akt activity and XIAP levels in rat endometrium during estrous cycle, in a model of pseudopregnancy and in cultured decidual cells

BACKGROUND

During the estrous cycle, the rat uterine endometrium undergoes many changes such as cell proliferation and apoptosis. If implantation occurs, stromal cells differentiate into decidual cells and near the end of pregnancy, a second wave of apoptosis occurs. This process called decidual regression, is tightly regulated as is it crucial for successful pregnancy. We have previously shown that TGF-beta1, TGF-beta2 and TGF-beta3 are expressed in the endometrium during decidual basalis regression, but although we had demonstrated that TGF- beta1 was involved in the regulation of apoptosis in decidual cells, the ability of TGF- beta2 and TGF-beta3 isoforms to trigger apoptotic mechanisms in these cells remains unknown. Moreover, we hypothesized that the TGF-betas were also present and regulated in the non-pregnant endometrium during the estrous cycle. The aim of the present study was to determine and compare the specific effect of each TGF-beta isoform in the regulation of apoptosis in sensitized endometrial stromal cells in vitro, and to investigate the regulation of TGF-beta isoforms in the endometrium during the estrous cycle in vivo.

METHODS

Rats with regular estrous cycle (4 days) were killed at different days of estrous cycle (diestrus, proestrus, estrus and metestrus). Pseudopregnancy was induced with sex steroids in ovariectomized rats and rats were killed at different days (days 1-9). Uteri were collected and either fixed for immunohistochemical staining (IHC) or processed for RT-PCR and Western analyses. For the in vitro part of the study, rats were ovariectomized and decidualization was induced using sex steroids. Endometrial stromal decidual cells were purified, cultured and treated with different concentrations of TGF-beta isoforms.

RESULTS

Our results showed that all three TGF-beta isoforms are present, but are localized differently in the endometrium during the estrous cycle and their expression is regulated differently during pseudopregnancy. In cultured stromal cells, we found that TGF-beta3 isoform induced Smad2 phosphorylation, indicating that the Smad pathway is activated by TGF-beta3 in these cells. Furthermore, TGF-beta2 and TGF-beta3 induced a dose-dependant increase of apoptosis in cultured stromal cells, as demonstrated by Hoechst nuclear staining. Noteworthy, TGF-beta2 and TGF-beta3 reduced the level of the anti-apoptotic XIAP protein, as well as the level of phosphorylated/active Akt, a well known survival protein, in a dose-dependent manner.

CONCLUSION

Those results suggest that TGF-beta might play an important role in the remodelling endometrium during the estrous cycle and in the regulation of apoptosis in rat decidual cells, in which inhibition of Akt survival pathway might be an important mechanism involved in the regulation of apoptosis.

Focal adhesions disassemble during early pregnancy in rat uterine epithelial cells

During early pregnancy in rodents, invasion of the blastocyst into the endometrial decidual cells is accompanied by the removal of uterine epithelial cells around the implantation sites. The present study investigated the distribution and expression of two focal adhesion proteins, namely talin and paxillin, in rat uterine epithelial cells during early pregnancy and their role in the loss of these cells at the time of implantation. A major distributional change of talin and paxillin was demonstrated in uterine epithelial cells during early pregnancy. From a highly concentrated expression along the basal cell surface on Day 1 of pregnancy, talin and paxillin were lost from the basal cell surface at the time of implantation. There was also a corresponding statistically significant decrease in paxillin seen through western blotting analysis. Together, these observations suggest that uterine epithelial cells are less adherent to the underlying basal lamina due to the disassembly of talin and paxillin from focal adhesions, facilitating removal of these cells at the time of implantation. This phenomenon was restricted to the period of receptivity because talin and paxillin reappeared along the basal cell surface soon after implantation.

Apoptosis is not altered by clomiphene citrate in pseudopregnant rat uteri

Clomiphene citrate (CC) remains one of the most often prescribed synthetic oestrogens used in the treatment of infertility even though the ensuing pregnancy rates are low. CC alters the uterine environment on most levels. Ovariectomised rats were treated with 5 mg progesterone (P) for 3 days and a 0.5 microg injection of oestrogen (E) on the third day (PP(PE)) thus inducing pseudopregnancy and rendering the uterus receptive to implantation 24 h later. Using this model, we investigated apoptosis in the rat uterus treated with 0.25 mg CC given prior to the PP(PE) treatment. Apoptotic cells in the uterus were localised using TUNEL and visualised with a FITC marker. There was a similar increase in apoptosis in the uterine luminal epithelium in the PP(PE) and CCPP(PE) treated animals; no changes were observed in apoptosis in the other uterine compartments when compared to the control. The CCPP(PE)-treated tissue showed tall epithelial cells with long microvilli while the PP(PE) tissue had short microvilli and low cuboidal epithelium. These results suggest that CC does not disrupt the normal apoptotic activity seen at implantation, but does change the morphology of the luminal epithelium, suggesting that these cellular changes could influence successful implantation.

Effects of beta-mercaptoethanol and cycloheximide on survival and DNA damage of bovine embryos stored at 4 degrees C for 72 h

The objectives of this study were to determine the effects of cycloheximide (CHX) and beta-mercaptoethanol (beta-ME) during storage of in vitro-produced (IVP) bovine blastocysts for 72 h at 4 degrees C on their survival, hatching capacity and DNA damage. In Experiment 1, when blastocysts were stored in a medium supplemented with 25, 50 or 100 microg/mL of CHX, or 25, 50 or 100 microM of beta-ME, the blastocysts stored with 25 microg/mL of CHX had a significantly higher survival rate than that of the blastocysts stored without CHX (79.5% versus 54.2%). In contrast, beta-ME had no apparent effects on the survival and hatching capacity of stored embryos. In Experiment 2, to investigate synergistic effects of CHX and beta-ME during storage of blastocysts on their developmental parameters and DNA damage, they were stored in the medium with CHX (25 microg/mL) and beta-ME (50 microM). The combination of CHX and beta-ME had no significant effects on the survival of blastocysts. The proportion (6.8%) of DNA-fragmented cells in the blastocysts stored with CHX was similar to that (5.4%) in the non-stored blastocysts (positive control) and significantly lower than that (9.7%) in the blastocysts stored without CHX and beta-ME (negative control). However, there were no significant differences among the proportions of dead cells of blastocysts in the storage groups. Therefore, the supplementation of CHX in the storage medium had a beneficial effect on the proportions of survival and DNA-fragmented cells in the stored embryos, whereas the beta-ME alone or in combination with CHX had no positive effects on either of these proportions.

TGF-beta expression during rat pregnancy and activity on decidual cell survival

BACKGROUND

During early rat pregnancy, trophoblast of the tiny embryo joins with the endometrium and epithelial cells undergo apoptosis. Near the end of pregnancy, regression of the decidua basalis (DB) is also observed (from day 14 to 20). However, little is known about the intra-cellular and molecular mechanisms involved in apoptosis regulation in the uterus during pregnancy. The objective of the present study was to investigate the presence and the developmental expression of transforming growth factor-beta isoforms (TGF-beta well known differentiation factor) in the rat endometrium throughout pregnancy and its action in vitro using cultured endometrial stromal cells.

METHODS

In vivo: Rats were killed at different days of pregnancy (days 2-20) and uteri removed to collect endometrial protein extracts or the uteri were fixed, embedded and sectioned for immunohistochemistry (IHC) and in situ cell death analyses using TdT-mediated dUTP nick end labeling (TUNEL). In vitro: Rats were ovariectomized and decidualization was induced using sex steroids. Endometrial stromal decidual cells were then collected and cultured.

RESULTS

An increase of apoptosis in the DB on days 14, 16 and 18 was observed. Cleaved caspase-3 was clearly detected during regression of the DB by Western analysis and immunofluorescence. Western analyses using endometrial protein extracts demonstrated that TGF-beta1, TGF-beta2 and TGF-beta3 were highly expressed at the time of DB regression (day 14). During early pregnancy, TGF-beta1 and -beta2 expressions raised at days 5.5 to 6.5. TGF-beta3 protein was not detected during early pregnancy. IHC analyses revealed that TGF-beta1 and -2 were found surrounding both epithelium (luminal and glandular) in the stroma compartment at the implantation site, and TGF-beta3 was mainly located surrounding endometrial epithelium in the stroma compartment. Smad2 phosphorylation was increased at the time of DB regression. In vitro studies using decidual endometrial stromal cells revealed that TGF-beta1 induced apoptosis and Smad2 phosphorylation. Moreover, TGF-beta1 reduced both Akt (a well known survival factor) phosphorylation and XIAP (X-linked inhibitor of apoptosis protein) expression in decidual endometrial stromal cells in vitro.

CONCLUSION

Taken together, these results suggest that TGF-beta isoforms are regulated differently during pregnancy and may have an important role in the control of apoptosis and cell survival at specific stages during pregnancy.

Human chorionic gonadotropin contributes to maternal immunotolerance and endometrial apoptosis by regulating Fas-Fas ligand system

The first known hormonal signal of the conceptus during implantation is human chorionic gonadotropin (hCG). Interestingly, increased apoptosis in human endometrium coincides with the implantation window. Factors from the fetal or placental origin as well as maternal hormonal factors are likely to have a potential role in the regulation of apoptotic signaling molecules. We hypothesized that hCG may be a placental link for the development of local maternal immunotolerance. Fas-Fas ligand (FasL) system is one of the apoptotic signaling pathways, shown to be important in the development of local immune tolerance during and after implantation. We report that hCG treatment decreases cell proliferation and increases apoptosis in endometrial cells. Moreover, hCG stimulates FasL mRNA and protein expression without affecting Fas mRNA in these cells. Interestingly, in coculture experiments, hCG-treated endometrial cells induce an increase in T cell apoptosis. Our in vivo results reveal that cells of early pregnancy decidua express strong FasL immunoreactivity, and decidual areas containing interstitial cytotrophoblasts have numerous TUNEL-positive cells. Compared with decidual areas devoid of interstitial cytotrophoblasts, we observed in decidual areas containing interstitial cytotrophoblasts clearly less amount of TUNEL-positive cells. These results suggest that hCG may be a link in the development of peritrophoblastic immune tolerance and may facilitate the trophoblast invasion by regulating proapoptotic molecules such as FasL in endometrial cells.

Tenascin, E-cadherin and P2X calcium channel receptor expression is increased during rat blastocyst implantation

The calcium-activated cell-adhesion proteins tenascin, E-cadherin and the purinergic (P2X) calcium channel receptors are expressed in an identical spatial and temporal pattern in uterine epithelium in the rat during implantation. On Day 1 of pregnancy (estrous), a diffuse cytoplasmic and specific basement membrane label for each of the proteins was observed throughout the uterine epithelium. On Day 3 of pregnancy, a specific and prominent lateral plasma membrane label for each protein was seen. At the time of implantation on Day 6, an additional and significant increase in the label for each was observed on the apical epithelium. At this time, the label for tenascin in the apical epithelium was increased 2.1-fold (p < 0.0004), that of E-cadherin was increased 2.5-fold (p < 0.0001) and the P2X receptor label was increased 2.0-fold (p < 0.0001). These observations suggest a major role for the calcium-activated adhesion proteins tenascin and E-cadherin in attachment and implantation, with ionic calcium for protein activation possibly provided by the P2X calcium channels. These events occur along the entire length of the uterine epithelium in preparation for blastocyst adhesion.

Regulation of Fas ligand expression by estradiol and progesterone in human endometrium

Implantation involves a complex set of events, including apoptosis in endometrial cells. Apoptosis in human endometrium coincides with the implantation window, suggesting a potential role for steroid hormones in its regulation. Fas ligand (FasL) is one of the mediators of apoptosis in differentiated cells and in embryonic development. Interaction of FasL with its receptor, Fas, induces apoptosis through autocrine and paracrine signaling. We hypothesized that FasL expression in human endometrium is cycle-dependent and that sex steroid hormones regulate FasL expression. We first studied menstrual cycle-dependent expression of FasL in human endometrium by immunohistochemistry in 24 samples. We then investigated the in vitro regulation of FasL expression by ovarian steroid hormones. Throughout the menstrual cycle immunohistochemical staining intensity was stronger in the functional layer of endometrium than it was in the basal layer. FasL immunoreactivity increased gradually through the mid- and late-proliferative phases in both endometrial stromal and glandular cells. Strong FasL expression was observed throughout the late-proliferative and secretory phases. Semiquantitative reverse transcription-polymerase chain reaction analysis in cultured endometrial glandular cells demonstrated that estradiol and progesterone stimulate FasL mRNA expression. Western blot analysis in endometrial glandular and stromal cells in culture revealed that estradiol alone and in combination with progesterone up-regulated FasL protein expression. These results suggest that estradiol and progesterone may have a role in the regulation of maternal immunotolerance for the implantation of a semiallograft embryo by inducing FasL expression. We speculate that increased FasL expression may mediate the apoptosis of endometrial cells and thus may play a role in trophoblast invasion.

Requirement of CDC45 for postimplantation mouse development

CDC45 is required for the initiation of DNA replication in Saccharomyces cerevisiae and functions as a DNA polymerase alpha loading factor in Xenopus, but its role in mammalian DNA replication is unknown. To investigate the genetic and physiological functions of CDC45, we used a gene targeting strategy to generate mice lacking a functional CDC45 gene. Homozygous mutant mice lacking a functional CDC45 gene underwent uterine implantation and induced uterine decidualization but did not develop substantially thereafter. Detailed analysis of CDC45 null embryos cultured in vitro revealed impaired proliferation of the inner cell mass. These findings make CDC45 the only putative replication factor experimentally proven to be essential for mammalian development. The CDC45 gene localizes to human chromosome 22q11.2 in the DiGeorge syndrome critical region (DGCR). Almost 90% of individuals with congenital cardiac and craniofacial defects have a monoallelic deletion in the DGCR that includes CDC45. We report here that heterozygous mutant mice develop into adulthood without any apparent abnormalities, so that it is unlikely that hemizygosity of CDC45 alone is responsible for the cardiac and craniofacial defects in the congenital syndromes.

Expression of apoptosis-related genes in human oocytes and embryos

PURPOSE

The objective was to study whether apoptosis occurs in human embryogenesis.

METHODS

Human viable, arrested, and nonviable embryos and immature, and nonfertilized oocytes donated by our patients were used to detect apoptosis by Tunel labeling, annexin staining, and single-cell reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

DNA fragmentation and phosphotidylserine translocation, the two markers for apoptosis, were detected frequently in fragmented human embryos derived from in vitro fertilization-embryo transfer (IVF-ET). Using RT-PCR, apoptotic genes also were detected in these embryos. The frequencies of gene expression in viable embryos, arrested embryos, nonviable embryos, immature oocytes, and non-fertilized oocytes were: 7/8, 5/5, 5/6, 0/6, 0/3, for Bax; 8/8, 5/5, 7/7, 0/4, 0/5 for Fas; 2/8, 0/2, 0/3, 0/5, 0/3 for BCL-2; 0/8, 1/3, 0/2, 0/3, 0/2 for Fas-ligand; and 8/8, 17/17, 21/21, 24/24, 15/15 for actin, respectively.

CONCLUSIONS

Our preliminary data did not show a significant difference in the expression frequency of all studied genes between viable embryos and nonviable or arrested embryos. However, the expression of Bax and Fas was noticeably higher in nonviable embryos than in viable embryos as judged by the intensities of amplicons visualized after ethidium bromide staining. In addition, BCL-2 was only detected in viable embryos. Whether embryos quality is related to the regulation of BCL-2, Bax, and Fas expressions requires further study.

Molecular genetics of implantation in the mouse

Embryo implantation is a complex developmental process requiring precise coordination between mother and offspring to ensure success. Implantation failure is clinically relevant to in vitro fertilization programs and to an understanding of diseases of pregnancy like preeclampsia. Basic and clinical research have identified a number of proteins involved in peri-implantation development, but an understanding of the implantation process and its cellular and molecular components is just beginning. This review will focus on the implantation and development of the murine embryo and placenta. The significance of ectopic expression and targeted mutagenesis models to these processes will be discussed.

Endometrial cell death during early pregnancy in the rat

In a study of early pregnancy in the rat, a high proportion of morphologically apoptotic, TUNEL and P2X7 positive cells were found to be present in the luminal epithelium and stroma prior to implantation. At the time of implantation on Day 6, apoptosis as measured by these indicators was reduced up to 4-fold in the non-implantation uterine epithelium but was markedly increased adjacent to the implanting blastocyst. It is proposed that apoptotic cell death is an important regulatory factor involved in uterine remodelling prior to and during implantation.

Mcl-1 deficiency results in peri-implantation embryonic lethality

We disrupted the Mcl-1 locus in murine ES cells to determine the developmental roles of this Bcl-2 family member. Deletion of Mcl-1 resulted in peri-implantation embryonic lethality. Mcl-1−/− embryos do not implant in utero, but could be recovered at E3.5–4.0. Null blastocysts failed to hatch or attach in vitro, indicating a trophectoderm defect, although the inner cell mass could grow in culture. Of note, Mcl-1−/−blastocysts showed no evidence of increased apoptosis, but exhibited a delay in maturation beyond the precompaction stage. This model indicates that Mcl-1 is essential for preimplantation development and implantation, and suggests that it has a function beyond regulating apoptosis.

Relationship between dead cells and DNA fragmentation in bovine embryos produced in vitro and stored at 4 degrees C

DNA fragmentation and its relationship with dead cells were examined in bovine blastocysts produced in vitro and stored at 4 degrees C for 1-5 days. Survival and development to the hatching and hatched blastocyst stage decreased with increasing storage time. Both were significantly lower at 72 hr than at 48 hr. None of the embryos stored for 120 hr developed to the hatching or hatched blastocyst stage. The proportion of dead cells per embryo increased progressively as the time of storage increased, until 69% of embryonic cells were dead after 120 hr of storage. There was no significant difference between the proportions of DNA fragmentation per embryo stored for 0 and 24 hr (12% vs 16%). However, the proportion of DNA fragmentation in embryos stored for longer than 48 hr was significantly greater than that in embryos stored for less than 24 hr. There were no significant differences among those stored for longer than 48 hr (28-33%). These results suggest that the reduced developmental competence of bovine embryos stored at 4 degrees C is characterized by necrotic change rather than apoptotic change.

Apoptotic cell death in artificially induced deciduoma of pseudopregnant mice

Deciduoma induced by mechanical stimulation in pseudopregnant mice is similar to the decidua in normal pregnancy and it undergoes regression after a certain period. Therefore, we examined cell death in deciduomas which were induced by artificial stimulation. To analyze the regression mechanism of artificially induced deciduoma, DNA fragmentation, in situ 3'-DNA nick end labeling, and RT-PCR were performed on day 6 to 14 of pseudopregnancy. DNA fragmentation appeared on day 8 and it increased to day 10 of pseudopregnancy in the traumatized uterine horn. A large number of apoptotic cells were found on day 10 in the periphery of deciduoma at the antimesometrial side. Deciduoma underwent degeneration on day 11 of pseudopregnancy. Expression of tumor necrosis factor-alpha (TNF-alpha) mRNA was high on days 8 and 10, then decreased, whereas the expression increased again on day 14. TNF-alpha protein was expressed from day 8 to day 12, showing a peak expression on day 10 when deciduoma reached maximum weight. Serum progesterone level was high in the traumatized pseudopregnant mice on day 6, then it gradually decreased. Life span of deciduoma was prolonged 4 days more by daily injection of progesterone. A reduction in serum progesterone coincides with TNF-alpha increase, resulting in an increase of apoptotic deciduomal cells at the regression period, and that the life span of deciduoma is prolonged by additive supply of progesterone.

Growth, development and differentiation: a functional food science approach

Few other aspects of food supply and metabolism are of greater biological importance than the feeding of mothers during pregnancy and lactation, and of their infants and young children. Nutritional factors during early development not only have short-term effects on growth, body composition and body functions but also exert long-term effects on health, disease and mortality risks in adulthood, as well as development of neural functions and behaviour, a phenomenon called 'metabolic programming'. The interaction of nutrients and gene expression may form the basis of many of these programming effects and needs to be investigated in more detail. The relation between availability of food ingredients and cell and tissue differentiation and its possible uses for promoting health and development requires further exploration. The course of pregnancy, childbirth and lactation as well as human milk composition and the short- and long-term outcome of the child are influenced by the intake of foods and particularly micronutrients, e.g. polyunsaturated fatty acids, Fe, Zn and I. Folic acid supplementation from before conception through the first weeks of pregnancy can markedly reduce the occurrence of severe embryonic malformations; other potential benefits of modulating nutrient supply on maternal and child health should be further evaluated. The evaluation of dietary effects on child growth requires epidemiological and field studies as well as evaluation of specific cell and tissue growth. Novel substrates, growth factors and conditionally essential nutrients (e.g. growth factors, amino acids, polyunsaturated fatty acids) may be potentially useful as ingredients in functional foods and need to be assessed carefully. Intestinal growth, maturation, and adaptation as well as long-term function may be influenced by food ingredients such as oligosaccharides, gangliosides, high-molecular-mass glycoproteins, bile salt-activated lipase, pre- and probiotics. There are indications for some beneficial effects of functional foods on the developing immune response, for example induced by antioxidant vitamins, trace elements, fatty acids, arginine, nucleotides, and altered antigen contents in infant foods. Peak bone mass at the end of adolescence can be increased by dietary means, which is expected to be of long-term importance for the prevention of osteoporosis at older ages. Future studies should be directed to the combined effects of Ca and other constituents of growing bone, such as P, Mg and Zn, as well as vitamins D and K, and the trace elements F and B. Pregnancy and the first postnatal months are critical time periods for the growth and development of the human nervous system, processes for which adequate substrate supplies are essential. Early diet seems to have long-term effects on sensory and cognitive abilities as well as behaviour. The potential beneficial effects of a balanced supply of nutrients such as I, Fe, Zn and polyunsaturated fatty acids should be further evaluated. Possible long-term effects of early exposure to tastes and flavours on later food choice preferences may have a major impact on public health and need to be further elucidated. The use of biotechnology and recombinant techniques may offer the opportunity to include various bioactive substances in special dietary products, such as human milk proteins, peptides, growth factors, which may have beneficial physiological effects, particularly in infancy and early childhood.

Death and replacement of uterine epithelial cells during oil-induced deciduoma development in the mouse

BACKGROUND

A decidual cell reaction can be induced in rodent endometrium by an intrauterine injection of oil. The epithelial lining is thought to be instrumental to transduce intralumenal stimuli for decidualization. One of the consequences of oil injection is the death of uterine epithelial cells. No information is available on the effect that sustained contact with oil has on the epithelium.

METHODS

A decidual cell reaction was induced in 4-day pseudopregnant mice by injection of 30 microliters of arachis oil into the uterine lumen. Samples from the uteri were collected 24, 48, and 72 h after the injection and prepared for transmission electron microscopy.

RESULTS

Twenty-four hours after the oil injection, some of the initial modifications of epithelial cell surfaces were very similar to those induced by the contact with the blastocyst during normal pregnancy. Uterine epithelial cells internalized injected oil and many cells were seen in various stages of degeneration. At 48 h, many epithelial cells were detached from the basal lamina. At 72 h, the uterine lining was re-established by flattened cells.

CONCLUSIONS

The contact of oil with the uterine epithelium of pseudo pregnant mice induces epithelial cell death in the antimesometrial region of the uterine crypt. There is, however, replacement of epithelial lining by epithelial cells, which probably migrate from the mesometrial region of the crypt. The prolonged presence of oil within the uterine lumen seems to induce cycles of epithelial cell death and replacement.

Granulated metrial gland cells: hypotheses concerning possible functions during murine gestation

Granulated metrial gland (GMG) cells are morphologically distinctive lymphoid cells found in the murine uterus only during gestation. The life history of GMG cells suggests that they have important roles during mammalian gestation but these roles have been difficult to define. Genetic and immunologic data suggest that GMG cells may be a specialized subset of natural killer (NK) lymphocytes. This has directed research on GMG cell functions towards questions of effector cell-target cell interactions. A broader range of potential functions is discussed and shifts in functional roles played by GMG cells are proposed over the course of gestation.

Trophoblastic invasion of the uterine epithelium in Calomys callosus (Rodentia, Cricetidae)

Implantation sites in the uterus of the cricetid rodent Calomys callosus were examined by light and electron microscopy at several points during day 4 of pregnancy to determine the changes occurring in the trophoblast and epithelial cells during the early blastocyst-endometrial relationship, particularly the epithelial removal phase. By morning, the blastocysts had already lodged in the antimesometrial region of the uterine crypts and the embryo-maternal interaction was limited to sparse contacts between the epithelial microvilli and the trophoblast surface. A few dense and altered epithelial cells were present. Three zones could be distinguished in the stromal region. In the subepithelial area, the stromal cells showed features similar to those found in other rodents during the early decidualization process. Effective epithelial invasion by the trophoblast occurred only in the evening, although at noon, apposition and attachment phases were identifiable. During invasion, the trophoblast processes were first seen insinuating between the epithelial cells, projecting towards the basal lamina, and finally replacing these cells. The epithelial cells in contact with the invading trophoblast exhibited severe disorganization similar to that found during the process of cell death by apoptosis. The removal of such cells occurred by trophoblast phagocytosis. Once in contact with the basal lamina, the trophoblast rapidly spread out both mesometrially and antimesometrially, phagocytosing the remaining epithelial cells. Trophoblast processes were also seen penetrating the basal lamina. Given that the epithelium breached and phagocytosed by the trophoblast habitually displays degenerative characteristics, we consider the mechanisms that might be involved in epithelial cell death and in the removal of the uterine epithelium, and the participation of the trophoblast in both these events.