Immunolocalization of extracellular matrix proteins and collagen synthesis in first-trimester human decidua

Regulation and Function of Laminin A5 during Mouse and Human Decidualization

Decidualization is essential to the establishment of pregnancy in rodents and primates. Laminin A5 (encoding by Laminin α5) is a member of the laminin family, which is mainly expressed in the basement membranes. Although laminins regulate cellular phenotype maintenance, adhesion, migration, growth, and differentiation, the expression, function, and regulation of laminin A5 during early pregnancy are still unknown. Therefore, we investigated the expression and role of laminin A5 during mouse and human decidualization. Laminin A5 is highly expressed in mouse decidua and artificially induced deciduoma. Laminin A5 is significantly increased under in vitro decidualization. Laminin A5 knockdown significantly inhibits the expression of Prl8a2, a marker for mouse decidualization. Progesterone stimulates the expression of laminin A5 in ovariectomized mouse uterus and cultured mouse stromal cells. We also show that progesterone regulates laminin A5 through the PKA-CREB-C/EBPβ pathway. Laminin A5 is also highly expressed in human pregnant decidua and cultured human endometrial stromal cells during in vitro decidualization. Laminin A5 knockdown by siRNA inhibits human in vitro decidualization. Collectively, our study reveals that laminin A5 may play a pivotal role during mouse and human decidualization via the PKA-CREB-C/EBPβ pathway.

Placental trophoblast cell-derived exosomal microRNA-1290 promotes the interaction between endometrium and embryo by targeting LHX6

Communication between the maternal uterus and the embryo is vital for a successful pregnancy. Exosomes, subtypes of extracellular vesicles comprising many bioactive factors, regulate the early stages of pregnancy, specifically during embryo implantation. Nevertheless, the mechanism by which exosomal microRNAs (miRNAs) derived from placental trophoblasts regulate embryo implantation remains elusive. We isolated and identified exosomes derived from placental trophoblast cells (HTR8/SVneo). Subsequently, we evaluated the loading miRNA in exosomes by small RNA sequencing. Consequently, we showed that trophoblast cell-derived exosomes could transfer to endometrial epithelial cells. Besides, these exosomes promoted the epithelial-mesenchymal transition (EMT) as well as migration of endometrial cells and were implicated in the regulation of inflammation. Further, the specific miRNAs were screened in exosomes, and as a result, miRNA (miR)-1290 was enriched specifically in exosomes. miR-1290 promoted the expression of inflammatory factors (interleukin [IL]-6 and IL-8) and migration of endometrial epithelial cells. In addition, exosomal miR-1290 promoted angiogenesis in vitro. More importantly, by targeting LHX6, trophoblast HTR8/SVneo cell-derived exosomal miR-1290 promoted the EMT process of endometrial epithelial cell HEC-1-A. Altogether, our findings provide novel insights into the mechanism of trophoblast cell-derived exosomes during embryo implantation.

The role of mesenchymal-epithelial transition in endometrial function

BACKGROUND

The human uterine endometrium undergoes significant remodeling and regeneration on a rapid and repeated basis, after parturition, menstruation, and in some cases, injury. The ability of the adult endometrium to undergo cyclic regeneration and differentiation/decidualization is essential for successful human reproduction. Multiple key physiologic functions of the endometrium require the cells of this tissue to transition between mesenchymal and epithelial phenotypes, processes known as mesenchymal-epithelial transition (MET) and epithelial-mesenchymal transition (EMT). Although MET/EMT processes have been widely characterized in embryonic development and in the context of malignancy, mounting evidence demonstrates the importance of MET/EMT in allowing the endometrium the phenotypic and functional flexibility necessary for successful decidualization, regeneration/re-epithelialization and embryo implantation.

OBJECTIVE AND RATIONALE

The objective of this review is to provide a comprehensive summary of the observations concerning MET and EMT and their regulation in physiologic uterine functions, specifically in the context of endometrial regeneration, decidualization and embryo implantation.

SEARCH METHODS

Using variations of the search terms 'mesenchymal-epithelial transition', 'mesenchymal-epithelial transformation', 'epithelial-mesenchymal transition', 'epithelial-mesenchymal transformation', 'uterus', 'endometrial regeneration', 'endometrial decidualization', 'embryo implantation', a search of the published literature between 1970 and 2018 was conducted using the PubMed database. In addition, we searched the reference lists of all publications included in this review for additional relevant original studies.

OUTCOMES

Multiple studies demonstrate that endometrial stromal cells contribute to the regeneration of both the stromal and epithelial cell compartments of the uterus, implicating a role for MET in mechanisms responsible for endometrial regeneration and re-epithelialization. During decidualization, endometrial stromal cells undergo morphologic and functional changes consistent with MET in order to accommodate embryo implantation. Under the influence of estradiol, progesterone and multiple other factors, endometrial stromal fibroblasts acquire epithelioid characteristics, such as expanded cytoplasm and rough endoplasmic reticulum required for greater secretory capacity, rounded nuclei, increased expression of junctional proteins which allow for increased cell-cell communication, and a reorganized actin cytoskeleton. During embryo implantation, in response to both maternal and embryonic-derived signals, the maternal luminal epithelium as well as the decidualized stromal cells acquire the mesenchymal characteristics of increased migration/motility, thus undergoing EMT in order to accommodate the invading trophoblast.

WIDER IMPLICATIONS

Overall, the findings support important roles for MET/EMT in multiple endometrial functions required for successful reproduction. The endometrium may be considered a unique wound healing model, given its ability to repeatedly undergo repair without scarring or loss of function. Future studies to elucidate how MET/EMT mechanisms may contribute to scar-free endometrial repair will have considerable potential to advance studies of wound healing mechanisms in other tissues.

Potential of Membranes Surrounding the Fetus as Immunoprotective Cell-Carriers for Allogeneic Transplantations

Background

Membranes surrounding the fetus play a crucial role in providing a physical and immunological barrier between a semiallogeneic fetus and mother during pregnancy. In this study, we tested whether cotransplantation of fetal membranes (FMs) and allogeneic donor cells would improve the retention and function of allografts in mice.

Methods

Intact and enzyme-digested membranes obtained from E18-E19 pregnant mice were subcutaneously cotransplanted with 10F7MN hybridoma cells that are of BALB/cByJ (Balb) origin and secrete anti-human CD235a antibody. Cells were transplanted into C57BL/6J (B6, allogeneic), Balb (syngeneic), and FVB/NJ (third-party) mice. Serum was collected after 1 and 3 weeks of cell transplantation and tested using flow cytometry for the presence of anti-human CD235a antibody. Immunosuppressive functions of membranes were further investigated by analyzing the cytokine profile of supernatants collected from allo-reactive mixed lymphocyte reactions (MLRs) using a multiplex cytokine assay.

Results

B6 mice transplanted with 10F7MN cells along with membranes syngeneic to the host had significantly higher levels of CD235a antibody when compared to B6 mice that received cells without membranes, allogenic membranes, or third-party membranes. Syngeneic membranes significantly inhibited T-cell proliferation in the presence of allogeneic stimuli and suppressed the release of Th1-cytokines such as IFNγ, TNFα, and IL-2 in MLRs. Additionally, increases in the levels of Th2-cytokines were found in MLRs containing membrane-derived cells.

Conclusions

Our study highlights the potential use of syngeneic FMs to act as potent cell-carriers that could improve graft retention as well as graft-specific immunoprotection during allograft transplantation.

Uterine and placental distribution of selected extracellular matrix (ECM) components in the dog

For many years, modifications of the uterine extracellular matrix (ECM) during gestation have not been considered as critical for successful canine (Canis lupus familiaris) pregnancy. However, previous reports indicated an effect of free-floating blastocysts on the composition of the uterine ECM. Here, the expression of selected genes involved in structural functions, cell-to-cell communication and inhibition of matrix metalloproteinases were targeted utilizing qPCR and immunohistochemistry. We found that canine free-floating embryos affect gene expression of FN1, ECM1 and TIMP4 This seems to be associated with modulation of trophoblast invasion, and proliferative and adhesive functions of the uterus. Although not modulated at the beginning of pregnancy, the decrease of structural ECM components (i.e. COL1, -3, -4 and LAMA2) from pre-implantation toward post-implantation at placentation sites appears to be associated with softening of the tissue in preparation for trophoblast invasion. The further decrease of these components at placentation sites at the time of prepartum luteolysis seems to be associated with preparation for the release of fetal membranes. Reflecting a high degree of communication, intercellular cell adhesion molecules are induced following placentation (Cx26) or increase gradually toward prepartum luteolysis (Cx43). The spatio-temporal expression of TIMPs suggests their active involvement in modulating fetal invasiveness, and together with ECM1, they appear to protect deeper endometrial structures from trophoblast invasion. With this, the dog appears to be an interesting model for investigating placental functions in other species, e.g. in humans in which Placenta accreta appears to share several similarities with canine subinvolution of placental sites (SIPS). In summary, the canine uterine ECM is only moderately modified in early pregnancy, but undergoes vigorous reorganization processes in the uterus and placenta following implantation.

GnRH regulates trophoblast invasion via RUNX2-mediated MMP2/9 expression

STUDY HYPOTHESIS

We hypothesized that Runt-related transcription factor 2 (RUNX2), matrix metalloproteinase (MMP)2 and MMP9 are involved in basal and gonadotrophin-releasing hormone (GnRH)-induced human extravillous trophoblast (EVT) cell invasion.

STUDY FINDING

Our finding indicates that GnRH-induced RUNX2 expression enhances the invasive capacity of EVT cells by modulating the expression of MMP2 and MMP9.

WHAT IS KNOWN ALREADY

GnRH is expressed in first-trimester placenta and exerts pro-invasive effects on EVT cells in vitro. RUNX2 regulates MMP2 and MMP9 expression and is often associated with invasive phenotypes.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

First-trimester human placenta (n = 9) was obtained from women undergoing elective termination of pregnancy. The localization of RUNX2, MMP2 and MMP9 in first-trimester human placenta was examined by immunohistochemistry. Primary or immortalized (HTR-8/SVneo) EVT cells were treated alone or in combination with GnRH, GnRH antagonist Antide, MAPK kinase inhibitor PD98095, phosphatidylinositol 3-kinase inhibitor LY294002, MMP2/9 inhibitor or small interfering RNAs (siRNAs) targeting RUNX2, MMP2 and/or MMP9. Protein and mRNA levels were measured by western blot and RT-PCR, respectively. Cell invasiveness was evaluated by transwell Matrigel or collagen I invasion assays.

MAIN RESULTS AND THE ROLE OF CHANCE

RUNX2, MMP2 and MMP9 were detected in the cell column regions of human first-trimester placental villi. GnRH treatment increased RUNX2 mRNA and protein levels in HTR-8/SVneo cells and primary EVTs, and these effects were attenuated by co-treatment with Antide, PD98095 or LY294002. Down-regulation of RUNX2 by siRNA reduced basal and GnRH-induced MMP2/9 expression and cell invasion. Moreover, pharmacological inhibition or siRNA-mediated knockdown of MMP2/9 reduced basal and GnRH-induced cell invasion.

LIMITATIONS, REASONS FOR CAUTION

The lack of an in vivo model is the major limitation of our in vitro study.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide important insight into the functions of the GnRH - GnRH receptor system in early implantation and placentation.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This research was supported by Canadian Institutes of Health Research (Grant #143317) to P.C.K.L. The authors have nothing to disclose.

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

CONTEXT

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

OBJECTIVE

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

DESIGN

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSION

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

Differences in collagen ultrastructure of human first trimester decidua basalis and parietalis: implications for trophoblastic invasion of the placental bed

AIM

The human embryo-maternal interface in the first trimester of pregnancy is an area of extensive tissue remodeling. Because collagen is the most abundant constituent of the extracellular matrix of the placental bed, successful invasion must involve its rapid turnover. We compared the nature and distribution of collagen fibrils in decidua basalis and parietalis.

METHODS

We used a direct-vision hysteroscopic technique to obtain biopsies of the decidua basalis and parietalis from 11 women undergoing pregnancy termination in the first trimester. The biopsies were subjected to light, transmission and scanning electron microscopy, and immunohistochemical studies using mouse monoclonal antibodies against cytokeratin 7 and collagen types I, III and V.

RESULTS

Collagen fibrils in the stroma of decidua basalis were significantly thicker when compared to those in decidua parietalis (56.48 ± 1.37 nm vs 45.64 ± 0.85 nm; P < 0.0001 [mean ± standard error]) between 9 and 12 weeks gestation, but this difference in thickness was not observed at gestations below 9 weeks. In basalis, the fibrils appeared disrupted at most places surrounding the decidual/trophoblast cells while a uniform regular arrangement was preserved throughout most of parietalis.

CONCLUSION

There are differences in the ultrastructure of collagen fibrils between basalis and parietalis, with thicker and disrupted fibrils within abundant amorphous tissue in basalis, and thinner uniform fibrils in parietalis. These differences may reflect an adaptive response by decidua or a direct consequence of the invading trophoblast cells.

Functional SNP -1562C/T in the promoter region of MMP9 and recurrent early pregnancy loss

Angiogenesis, invasion and decidualization play an important role in uterine preparation and embryo development. Matrix metalloproteinases (MMP) are crucial for the degradation/remodelling of the extracellular matrix and are involved in spiral artery formation and invasion of endometrium during implantation. A functional single-nucleotide polymorphism (SNP) in the MMP9 promoter, 1562C/T, is known to influence expression in an allele-specific manner. The present study evaluated the association between maternal genotype of SNP 1562C/T of MMP9 and recurrent early pregnancy loss (REPL) risk. This case–control study was comprised of REPL patients (n = 106) and women having one healthy child as controls (n = 111). Genotyping for SNP 1562C/T of MMP9 was performed by PCR/restriction fragment length polymorphism followed by DNA sequencing. Allele and genotype distribution did not differ significantly between patients and controls (by allele, chi-squared 0.228, odds ratio 1.12, 95% confidence interval 0.695–1.816; by genotype, chi-squared 0.893). Thus SNP 1562C/T of MMP9 was not associated with REPL risk in this population and further study in other populations will verify whether it is associated with REPL risk or not. REPL is a multifactorial pathology and other genetic or environmental factors may be contributing to the complex aetiology of REPL.

Extracellular matrix remodelling in rat endometrium during early pregnancy: the role of fibronectin and laminin

The endometrial extracellular matrix (ECM) remodelling has a crucial role in the establishment of a successful pregnancy. In addition to its basic function such as regulation of cell function, differentiation, migration, proliferation, the substantial alterations in the endometrial ECM may play a specific role in the trophoblast invasion, placentation, cell death and formation of the proper and functional implantation chamber around the embryo. In the present study, immunolocalizations of fibronectin and laminin were determined using avidin-biotin complex-peroxidase in rat implantation sites during 7-10 days of pregnancy. Both proteins were present in the basal membrane of blood vessels and in decidual matrix whereas they were absent or had very weak reactivity in the primary decidual zone on day 7. When placentation has begun, the immunoreactivity of both proteins was increased in the placental bed and in the basal membrane of blood vessels of the mesometrial region. The immunolocalization of both proteins seemed to be decreased in the antimesometrial decidua, however, it was increased in the mesometrial decidual matrix on days 9 and 10. Therefore, it could be suggested laminin and fibronectin demonstrating dynamic expressions in relation with the morphological differentiation of endometrial stroma may play crucial roles in the control of trophoblast adhesion and invasion, in placentation and angiogenesis, in the determination of cell shape and fate thus contributing the endometrial receptivity and a successful pregnancy.

Distribution of laminin, vimentin and desmin in the rat uterus during initial stages of implantation

The aim of this study was to investigate the immunohistochemical distribution of laminin, vimentin and desmin during the implantation period in the rat since ECM remodelling and the expression of intermediate filaments (Ifs) is essential for successful decidualization and implantation. On day 4 of pregnancy, laminin was found in a few endometrial stromal cells (ESC), the basement membrane of the numerous endometrial blood vessels, in endometrial glands and as well as in the uterine epithelium. The localization of vimentin on day 4 of pregnancy was widespread in the ESC. However, desmin immunoreactivity was low in ESC on this day of pregnancy. On day 6 of pregnancy, laminin and vimentin were localized in the decidual area underlying luminal epithelium and around the implanting embryo. Additionally, desmin was found to be present densely in decidual cells of the anti-mesometrial region where implantation takes place. Finally, on day 8 of pregnancy, laminin was present in decidual and parietal endodermal cells, whereas vimentin was immunolocalized in primary and secondary decidual regions in the endometrium. In contrast, desmin was detected in some parts of the secondary decidual zone. In conclusion, these proteins could have crucial roles in decidualization and implantation.

Distribution of collagen types I, III, and V in pregnant mouse endometrium

Decidualization in mice comprises a deep remodeling of extracellular matrix (ECM) components of the endometrium. In a previous biochemical study we showed that collagen types I and III are present in both pregnant and nonpregnant mouse endometrium, whereas collagen type V is expressed exclusively after the onset of decidualization. The distribution of collagen types in the pregnant mouse endometrium and possible changes of these molecular types in the different regions of the decidua is, however, not known. Using immunofluorescence and confocal microscopy we showed the presence of collagen types I, III, and V in the endometrial stroma of implantation and interimplantation sites from days 5 to 8 of pregnancy in the mouse. Collagen type III was chiefly expressed in the implantation sites and was the only collagen type to be present in the materno-fetal interface on the day of the embryo implantation. However, collagen type I was the predominant collagen in the interimplantation sites. Collagen type V was weakly expressed in the nondecidualized stroma during all periods but was expressed in larger amounts in the decidualized areas on day 7 of pregnancy, simultaneously with the accumulation of thick collagen fibrils in the same region. The highest immunofluorescence labeling for the three types of collagen was observed on day 7 when the antimesometrial decidual tissue achieved its greatest development. These data support previous studies that showed an intense ECM remodeling of the mouse endometrial stroma during the beginning of pregnancy. This outstanding remodeling may be important to stabilize placental anchorage.

Blastocysts don't go it alone. Extrinsic signals fine-tune the intrinsic developmental program of trophoblast cells

The preimplantation embryo floats freely within the oviduct and is capable of developing into a blastocyst independently of the maternal reproductive tract. While establishment of the trophoblast lineage is dependent on expression of developmental regulatory genes, further differentiation leading to blastocyst implantation in the uterus requires external cues emanating from the microenvironment. Recent studies suggest that trophoblast differentiation requires intracellular signaling initiated by uterine-derived growth factors and integrin-binding components of the extracellular matrix. The progression of trophoblast development from the early blastocyst stage through the onset of implantation appears to be largely independent of new gene expression. Instead, extrinsic signals direct the sequential trafficking of cell surface receptors to orchestrate the developmental program that initiates blastocyst implantation. The dependence on external cues could coordinate embryonic activities with the developing uterine endometrium. Biochemical events that regulate trophoblast adhesion to fibronectin are presented to illustrate a developmental strategy employed by the peri-implantation blastocyst.

Uterine extracellular matrix components are altered during defective decidualization in interleukin-11 receptor alpha deficient mice

BACKGROUND

Implantation of the embryo and successful pregnancy are dependent on the differentiation of endometrial stromal cells into decidual cells. Female interleukin-11 receptor alpha (IL-11Ralpha) deficient mice are infertile due to disrupted decidualization, suggesting a critical role for IL-11 and its target genes in implantation. The molecular targets of IL-11 in the uterus are unknown, but it is likely that IL-11 signaling modifies the expression of other genes important in decidualization. This study aimed to identify genes regulated by IL-11 during decidualization in mouse uterus, and to examine their expression and localization as an indication of functional significance during early pregnancy.

METHODS

Decidualization was artificially induced in pseudopregnant wild type (IL11Ra+/+) and IL-11Ralpha deficient (IL11Ra-/-) littermates by oil injection into the uterine lumen, and gene expression analyzed by NIA 15K cDNA microarray analysis at subsequent time points. Quantitative real-time RT-PCR was used as an alternative mRNA quantitation method and the expression and cellular localization of the protein products was examined by immunohistochemistry.

RESULTS

Among 15,247 DNA probes, 13 showed increased and 4 decreased expression in IL11Ra-/- uterus at 48 h of decidualization. These included 4 genes encoding extracellular matrix proteins; collagen III alpha1, secreted acidic cysteine-rich glycoprotein (SPARC), biglycan and nidogen-1 (entactin). Immunohistochemistry confirmed increased collagen III and biglycan protein expression in IL11Ra-/- uterus at this time. In both IL11Ra-/- and wild type uterus, collagen III and biglycan were primarily localized to the outer connective tissue and smooth muscle cells of the myometrium, with diffuse staining in the cytoplasm of decidualized stromal cells.

CONCLUSION

These data suggest that IL-11 regulates changes in the uterine extracellular matrix that are necessary for decidualization.

Physiologic role of decidual beta1 integrin and focal adhesion kinase in embryonic implantation

Implantation refers to a series of interactions between embryo and endometrium including hatching, attachment, and outgrowth. We investigated the expression and function of beta1 integrin and focal adhesion kinase (FAK) in human decidual cells during implantation. Immunofluorescent staining localized beta1 integrin to surfaces of cultured decidual cells. Double staining for beta1 integrin and mediators of intracellular signaling involving beta1 integrin, such as FAK and vinculin, colocalized beta1 integrin with these substances, suggesting that human decidual cells express beta1 integrin in the focal adhesion region. We next investigated the actions of beta1 integrin and FAK in implantation by co-culturing mouse embryos and human decidual cells. Mouse blastocysts attached to cultured decidual cells after embryo hatching, usually within 24 h of culture initiation. Blastocysts attached to decidual cells exhibited extensive outgrowth at 48 h. Treatment of decidual cells with an antibody against beta1 integrin or with an antisense FAK oligonucleotide did not affect hatching or attachment of blastocysts, but either one could inhibit outgrowth. Thus, it was concluded that human decidual beta1 integrin and FAK participate in this final step of implantation.

Decidualization induces the expression and activation of an extracellular protease neuropsin in mouse uterus

Uterine decidualization is accompanied by the remodeling of the cell-matrix and cell-cell interactions around the endometrial stromal cells to allow an appropriate invasion of trophoblasts. This remodeling is thought to require the proteolysis of extracellular matrix proteins or cell adhesion molecules; however, the molecular mechanism remains poorly understood. In this study, decidualization induced the expression and activation of an extracellular serine protease neuropsin in the mouse uterus. Although nonpregnant uteri contained little neuropsin, the protein content and enzymatic activity increased markedly and peaked at the midgestational period in pregnant uteri. Neuropsin expression and activity was also upregulated in artificially induced deciduomata but not in nondecidualized pseudopregnant uteri. Neuropsin is the first extracellular protease to show the evident induction of expression and activity by decidualization and might contribute to the remodeling of extracellular components after decidualization.

Extracellular matrix-dependent regulation of Fas ligand expression in human endometrial stromal cells

Interaction between endometrial stromal cells and extracellular matrix (ECM) components has a crucial role in the development of endometriosis. Endometrial stromal cells attach to the mesothelial surface of peritoneum by means of integrins during their initial implantation and growth in endometriosis. Similarly, interaction between integrin and the extracellular matrix is also crucial for the remodeling of the endometrium during early pregnancy. We hypothesized that adhesion of endometrial stromal cells to the extracellular matrix could suppress the immunologic reaction to implanting endometrial cells by inducing the expression of Fas ligand (FasL), a mediator of the apoptotic pathway. Western blot analysis of human endometrial stromal cells plated onto fibronectin, laminin, and collagen IV revealed higher levels of FasL protein expression compared with endometrial stromal cells that plated to BSA-coated plates (control). Immunocytochemistry results from endometrial stromal cells plated to extracellular matrix proteins demonstrated a similar up-regulation of FasL expression. Eutopic endometrial stromal cells from women with endometriosis demonstrated higher FasL expression on control plates and those coated with extracellular matrix proteins compared with those from women without endometriosis. Disruption of actin cytoskeleton in endometrial stromal cells by treatment with cytochalasin D blocked the increase of FasL protein expression that occurred in response to adhesion to the extracellular matrix. These results suggest that attachment of endometrial stromal cells during retrograde menstruation to a new environment such as peritoneum with increased expression of laminin, fibronectin, and collagen IV could lead to an increase in FasL expression. Induction of FasL expression by adhesion of endometrial stromal cells to the extracellular matrix may take part in the development of a relative immunotolerance by inducing apoptosis of cytotoxic T lymphocytes, which will allow further development of ectopic implants.

Effects of matrix proteins on the expression of matrix metalloproteinase-2, -9, and -14 and tissue inhibitors of metalloproteinases in human cytotrophoblast cells during the first trimester

The activity of matrix metalloproteinases (MMPs) specifies the ability of the trophoblast cell to degrade extracellular matrix (ECM) substrates. Usually the process of normal human placentation involves a coordinated interaction between the fetal-derived trophoblast cells and their microenvironment in the uterus. In this study, the effects of ECM proteins on the expression of MMP-2, -9, and -14 (membrane-type MMP-1); and the production of tissue inhibitors of metalloproteinase (TIMP) types -1, -2, and -3 have been investigated. Cytotrophoblast cells at 9 or 10 wk of gestation were cultured on various ECM coated dishes under serum-free conditions. Gelatin zymography analysis showed that cells grown on fibronectin (FN), laminin (LN), and vitronectin (VN) secreted more MMP-9 (about 1.5- to 3-fold more) than cells cultured on collagen I (Col I), whereas the secretion of MMP-9 by cells cultured on collagen IV (Col IV) was only half that by the cells on Col I. Northern Blot analysis gave the same results as zymography, indicating that expression of the MMP-9 gene in cytotrophoblast cells can be affected by matrix proteins. There was no significant difference in the expression of MMP-2 either at protein or mRNA levels among the cells cultured on the different matrix substrates. The expression of MMP-14 was regulated in a manner similar to that of MMP-2. Using ELISA, we detected higher levels of TIMP-1 in the culture medium of cells grown on VN, LN, and FN compared with that grown on Col I. But the expression of TIMP-3 mRNA was remarkably inhibited by VN, and ECM proteins had no effect on TIMP-1 and TIMP-2 mRNA expression. It was also observed that cultured cytotrophoblast cells expressed the corresponding receptors for the tested matrix proteins, such as integrins alpha(1), alpha(5), alpha(6), beta(1), and beta(4). Furthermore, the adhesiveness of cytotrophoblast cells on Col I, Col IV, FN, and LN was increased by 62%, 45%, 21%, and 22%, respectively, when compared with adhesiveness on VN. Isolated cytotrophoblast cells remained stationary when cultured on dishes coated with Col I and Col IV, but they assumed a more motile morphology and aggregated into a network when cultured on LN and VN. These data indicate that human trophoblast cells interact with their microenvironment to control their behavior and function.

Early Implantation Events in the Baboon (Papio anubis) with Special Reference to the Establishment of Anchoring Villi

The development of the baboon anchoring villus has been studied from day 14 to day 48 of gestation, using light and electron microscopy. At day 14, cords of trophoblast could be seen streaming into the endometrium, invading maternal vessels and forming blood-filled lacunae; by 20 days gestation some of these had differentiated into distinctive anchoring villi, with an outer covering of syncytiotrophoblast and inner cytotrophoblast cells which differed from those of floating villi in that a subpopulation detached from the syncytium to form an interconnecting network of cells within the centre of the villus. Subsequent migration of cytotrophoblast into the endometrium formed the cytotrophoblastic shell while fibrillin-like extracellular matrix biosynthesis within the body of the villus provided a firm mechanical support. At the trophoblast-decidual interface, a zone of necrosis and phagocytosis initially developed, which became less extensive with time, so that by 40 days a stable interface was evident with only residual pockets of necrosis. During this period, there was differentiation of decidual cells which by 28 days developed characteristic pedunculated cell processes, and later became surrounded by a basal lamina. The factors that control detachment of cytotrophoblast from the syncytium and the biosynthesis of the specialized, fibrillar extracellular matrix, features that are not apparent in other placental villi, require further investigation, possibly by carefully controlled in vitro experimentation.

Unusual patterns of intermediate filament protein expression by the trophoblast and decidual cells of the short-tailed fruit bat, Carollia perspicillata

In the short-tailed fruit bat (Carollia perspicillata) pregnancy can be prolonged by the occurrence of lengthy delays after implantation. This is associated with the development of highly invasive trophoblast that can penetrate the myometrium, mesenteries of the reproductive tract and the oviducts via perivascular (interstitial) routes. In order to confirm the identity and distribution of this trophoblast, intermediate filament protein immunocytochemistry was utilized. In some respects the expression of these proteins differed from what has been reported for more commonly-studied species. Cytotrophoblast in the placenta, its cytotrophoblastic shell and the highly invasive trophoblast strongly expressed cytokeratins. As pregnancy progressed, however, cytokeratin expression by syncytiotrophoblast lining much of the placental labyrinth became very weak. The cytotrophoblastic shell and highly invasive trophoblast also expressed vimentin. The highly invasive trophoblast was unusual in that it developed dendritic processes that sometimes extended out into adjacent tissues in great profusion. Decidual cells generally expressed desmin and vimentin; however, some also coexpressed cytokeratins. These observations indicate that some of the trophoblast in Carollia undergoes a significant epithelial-mesenchymal transformation. They also suggest that caution should be exercised in relying upon intermediate filament proteins as markers for cell identification purposes in exotic species, or when the patterns of protein expression by fetal and maternal cells might be altered in pathological or experimental situations.

Integrin trafficking regulates adhesion to fibronectin during differentiation of mouse peri-implantation blastocysts

Trophoblast cells of the peri-implantation blastocyst differentiate from a polarized epithelium, the trophectoderm, into invasive cells having an apical surface occupied by integrins that mediate adhesion to the extracellular matrix. Blastocyst differentiation was assessed during serum-free culture using a fibronectin binding assay with intact mouse blastocysts. Fibronectin binding activity became elevated during a 24-h "window" after approximately 72 h of culture. Blastocyst differentiation was unaffected by transcriptional inhibition with alpha-amanitin, however, exposure of cavitating morulae to the drug significantly delayed the onset of maximal fibronectin-binding activity. Inhibition of de novo protein synthesis with cycloheximide delayed development only when added during the first 24 h of blastocyst culture, indicating that proteins required for adhesion to fibronectin were synthesized at least 24 h before blastocyst differentiation was completed. Since blastocyst differentiation did not appear to be regulated temporally by gene expression, the possible role of protein trafficking was investigated using the inhibitor, brefeldin A. Brefeldin A caused a reversible, dose-dependent decrease in fibronectin-binding activity when added to the culture medium between 48 and 72 h of culture. During the period of brefeldin A sensitivity, alpha 5 beta 1 integrin, a major fibronectin receptor, translocated to the apical surface of trophoblast cells, as determined by immunohistochemistry and confocal microscopy. Mouse blastocysts expressed other integrins that recognize the central cell-binding domain of fibronectin, including the alpha v integrins and alpha llb beta 3, but not alpha4 which recognizes the lllCS site. Trafficking of alpha 5 beta 1, and possibly other integrins, to the apical surface of trophoblast cells appears to be a critical step in the differentiation of the mouse blastocyst to an invasive phenotype.

Tyrosine phosphorylation and subcellular localization of focal adhesion proteins during in vitro decidualization of human endometrial stromal cells

Human endometrial stromal cells undergo in vitro decidualization when treated with progesterone and estrogen. Using this model, we previously reported specific changes in the c-Src kinase activity and tyrosine phosphorylation of several proteins during in vitro decidualization. Focal adhesion kinase (FAK) and paxillin are known to form a complex with c-Src at the focal contacts and to participate in the integrin-mediated signal transduction as c-Src substrates. We here examined the tyrosine phosphorylation and subcellular localization of the focal adhesion proteins in stromal cells isolated from human endometrium. We found, however, that the total levels of FAK and paxillin tyrosine phosphorylation were not markedly changed during decidualization or after steroid withdrawal. In our culture system numerous multicellular nodules were developed in cultures of decidualized stromal cells, within whose nodules the focal contacts were found to disappear. Moreover, disruption of the focal contacts was accompanied by disorganization of the actin-based cytoskeleton. These findings suggest that tyrosine phosphorylation of the endometrial paxillin and FAK is not tightly regulated by the kinase activity of c-Src during in vitro decidualization. The escape from regulation by c-Src may be in part due to the dissociation of the focal adhesion proteins/c-Src complex caused by the breakdown of the focal adhesion plaques as well as the loss of the actin-based cytoskeletal architecture.

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'.

Matrix metalloproteinase and matrix metalloproteinase inhibitor expression in endometrial stromal cells during progestin-initiated decidualization and menstruation-related progestin withdrawal

Estradiol (E) primes human endometrial stromal cells (HESCs) for the decidualizing effects of progesterone in vivo and in vitro. Matrix metalloproteinase (MMP) expression was evaluated in confluent HESCs incubated in control medium, and in medium supplemented with either E, or the synthetic progestin medroxyprogesterone acetate (P), or E + P. Measurements with a specific ELISA indicated that basal pro-MMP-1 output was unaffected by E, whereas E + P, which induces the expression of several decidualization-related markers, produced a time-dependent inhibition in HESC-secreted levels of pro-MMP-1. Consistent with progestin inhibition of MMP-1 protein expression in the HESCs, P but not E, reduced steady state levels of MMP-1 messenger RNA (mRNA) as determined by Northern analysis. By contrast, mRNA levels for MMP-2 and the MMP inhibitor TIMP-1 were not altered by either P or E. Steroid withdrawal studies indicated that after MMP-1 expression was suppressed by incubation of the HESCs with E + P, 4 days of exposure to the antiprogestin RU 486 (mifepristone) significantly up-regulated MMP-1 levels in the conditioned medium by severalfold compared with cultures maintained in E + P. The change to steroid-free control medium required a more prolonged period of withdrawal to attain up regulatory effects that were comparable with those evoked by RU 486. The ELISA measurements were validated by immunoblot analysis with a specific MMP-1 antibody, which showed corresponding changes in a band at the expected mobility of about 50 kDa. Moreover, Northern analysis revealed parallel changes in MMP-1 mRNA levels, whereas neither MMP-2 nor TIMP-1 mRNA levels were modulated by adding or withdrawing steroids. The contrast between regulated MMP-1 expression and constitutive MMP-2 expression observed in the cultured HESCs is consistent with the demonstrated presence on the MMP-1 promoter of regulatory elements such as AP-1 and PEA-3 that are absent from the MMP-2 promoter. Extrapolation of these in vitro changes in HESCs to in vivo endometrial events suggests that: 1) inhibition of MMP-1 expression by E and progesterone would stabilize the perivascular endometrial ECM to prevent local hemorrhage during endovascular invasion by the implanting trophoblast; 2) enhanced expression of MMP-1 evoked by steroid withdrawal would mediate endometrial ECM degradation leading to sloughing of the functional layer during menstruation.

Characterisation of non-maternal serum proteins in amniotic fluid at weeks 16 to 18 of gestation

Proteins found in amniotic fluid are mainly serum proteins, probably of maternal origin. About 5% of the total protein concentration has the potential of being fetal or decidual in origin. Only a few of these proteins have been isolated and characterised. In order to describe the foetal and decidual components in amniotic fluid more extensively, a polyspecific antiserum to amniotic fluid at weeks 16-18 of gestation was raised. Specificities in the antiserum to serum proteins were removed by adsorption. Several proteins of non-serum protein origin reacted with the antiserum. Three of these proteins were chosen for isolation and further characterisation. With the use of immunological methods, SDS-PAGE and N-terminal sequencing we identified two of the proteins as C-terminal propeptides of procollagen Type I and Type III, which have not hitherto been described in amniotic fluid. The third protein, called here protein-4, showed up as homologous to fetal antigen-1 (FA-1) and human dlk, containing EGF-like domains and associated with growth in neuroendocrine tissues and tumours.

Autoradiography reveals regional metabolic differences in the endometrium of pregnant and nonpregnant mice

The rodent endometrium undergoes remarkable modifications during pregnancy, resulting from a redifferentiation of its fibroblasts. During this modification (decidualization), the fibroblasts transform into large, polyhedral cells that establish intercellular junctions. Decidualization proceeds from the subepithelial stroma towards the deep stroma situated next to the myometrium and creates regions composed of cells in different stages of differentiation. We studied by autoradiography whether cells of these different regions have different levels of macromolecular synthesis. Radioactive amino acids or radioactive sulfate were administered to mice during estrus or on different days of pregnancy. The animals were killed 30 min after injection of the precursors and the uteri were processed for light microscope autoradiography. Silver grains were counted over cells of different regions of the endometrium and are reported as the number of silver grains per area. Higher levels of incorporation of amino acids were found in pregnant animals as compared to animals in estrus. In pregnant animals, the region of decidual cells or the region of fibroblasts transforming into decidual cells showed the highest levels of synthesis. Radioactive sulfate incorporation, on the other hand, was generally higher in nonpregnant animals. Animals without decidual cell transformation (nonpregnant and 4th day of pregnancy) showed a differential incorporation by subepithelial and deep stroma fibroblasts. This study shows that regional differences in synthetic activity exist in cells that are in different stages of transformation into decidual cells as well as in different regions of the endometrium of nonpregnant mice.

Immunohistochemical localization of fibrillin in developing macaque and term human placentas and fetal membranes

The objective of this study was to examine the developmental appearance of the extracellular matrix glycoprotein fibrillin in macaque placentas and fetal membranes and to compare this distribution to that seen in term human placentas and fetal membranes. Standard immunoperoxidase methods were used on paraformaldehyde-fixed, paraffin-embedded tissues. At early gestational ages (26-30 days), fibrillin was found in cell columns and cytotrophoblastic shell, with weak staining in the villous stroma. Staining was abundant in the shell and columns at 53 days as well, and stronger staining was seen in the stroma of the chorionic plate and stem villi. Staining in the shell and remnants of the cell columns in later gestation continued to be positive, though variable. Generally, the strongest staining was present in the distal cytotrophoblastic shell. Stroma in the tips of anchoring villi was also strongly positive. Later in gestation, fibrillin was observed around the multilayered cytotrophoblast of the chorionic plate. Fibrillin was abundant in the stromal cores of human term placental villi. In early macaque amnion, fibrillin staining was abundant in a layer beneath the amniotic epithelium. Later in gestation, macaque chorioamnion staining was generally similar to human term chorioamnion staining, with the heaviest staining in portions of the compact and reticular layers. Fibrillin was sometimes localized in regions known to be rich in connective tissue microfibrils, but, in other regions known to have abundant microfibrils, fibrillin staining was weak. This suggests that some microfibrils in placenta may be composed predominantly of some other protein(s). The function of fibrillin in the various placental compartments is unknown at present. It may provide attachment points for cells while at the same time providing a strong, yet flexible, matrix to accommodate growth particularly in areas subject to shear stress.

Stromal differentiation and architecture of the human umbilical cord

In order to assess the characteristics of its stromal cells and the distribution of extracellular matrix proteins, we investigated, immunohistochemically and ultrastructurally, term, first and second trimester human umbilical cords. A differential distribution pattern of the various cytoskeletal proteins of stromal cells and extracellular matrix proteins was observed in different zones of the stroma, the subamniotic stroma, Wharton's jelly, and the vessels' adventitia. All three zones showed immunoreactivities for collagen types I, III and VI and for basement membrane molecules such as collagen type IV, laminin and heparan sulphate proteoglycan. Immunoreactivities for these extracellular matrix molecules were observed around cleft-like territories (stromal clefts) in the Wharton's jelly which were occupied by homogeneous ground substance but void of collagen fibrils and basal lamina molecules. Moreover, between the stromal clefts, slender cells were found which immunohistochemically and ultrastructurally corresponded to various stages of myofibroblastic differentiation. In earlier stages of gestation, stromal cells with a less complex expression pattern prevailed. The stromal clefts and the contractile cells together might serve as a system regulating the turgor of the cord.

Human trophoblast cell adhesion to extracellular matrix protein, entactin

PROBLEM

Trophoblast interaction with endometrial extracellular matrix (ECM) is crucial during human embryo implantation and placentation. Entactin, a ubiquitous basement membrane glycoprotein, plays a central role in ECM assembly, cell attachment, and chemotaxis. The present study was conducted to examine the possible role of entactin in promoting human trophoblast adhesion.

METHODS

Using an extended life span first trimester trophoblast cell line HTR-8/SVneo (HTR) and a cell adhesion assay, we measured the adherence of human first trimester trophoblasts to recombinant entactin and its domains. Also, we used flow cytometry and indirect immunofluorescence to detect the presence of integrins that may be involved in human trophoblast-entactin interaction; these methods were used to analyze HTR cells, as well as tissue sections and freshly isolated human trophoblasts from first trimester and term placenta.

RESULTS

We found that first trimester trophoblast cells were highly adherent to entactin and its E and G2 domains but not to G1 or G3 domains. Using indirect immunofluorescence and flow cytometry, we found that both beta 1 and beta 3 integrin subunits were expressed on the surface of HTR trophoblast cells adhering to entactin; in contrast, beta 2 and beta 4 integrin subunits were not detected. In addition, we found that alpha v beta 3 was expressed on freshly isolated villous cytotrophoblasts and cytotrophoblast and syncytiotrophoblasts in tissue sections from term placenta. The beta 3 integrin subunit was expressed in cytotrophoblasts and syncytiotrophoblasts in villi of first trimester placental tissue sections.

CONCLUSION

Recombinant entactin promotes human trophoblast cell adhesion through both its E and G2 domains and these specific adhesive interactions may be mediated by beta 1 and/or beta 3 class integrins.

Cell surface expression of HIP, a novel heparin/heparan sulfate binding protein, of human uterine epithelial cells and cell lines

Previous studies established that uterine epithelial cells and cell lines express cell surface heparin/heparan sulfate (HP/HS)-binding proteins (Wilson, O., Jacobs, A. L., Stewart, S., and Carson, D. D. (1990) J. Cell. Physiol. 143, 60-67; Raboudi, N., Julian, J., Rohde, L. H., and Carson, D. D. (1992) J. Biol. Chem. 267, 11930-11939). The accompanying paper (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823) describes the cloning of a full-length cDNA corresponding to a candidate cell surface HP/HS interacting protein, HIP, expressed by a variety of human epithelia. A synthetic peptide was synthesized corresponding to an amino acid sequence predicted from the cDNA sequence and used to prepare a rabbit polyclonal antibody. This antibody reacted with a protein with an apparent Mr of 24,000 by SDS-polyacrylamide gel electrophoresis that was highly enriched in the 100,000 x g particulate fraction of RL95 cells. This molecular weight is similar to that of the protein expressed by 3T3 cells transfected with HIP cDNA. HIP was solubilized from this particulate fraction with NaCl concentrations > or = 0.8 M demonstrating a peripheral association consistent with the lack of a membrane spanning domain in the predicted cDNA sequence. HIP was not released by heparinase digestion suggesting that the association is not via membrane-bound HS proteoglycans. NaCl-solubilized HIP bound to heparin-agarose in physiological saline and eluted with NaCl concentrations of 0.75 M and above. Furthermore, incubation of 125I-HP with transblots of the NaCl-solubilized HIP preparations separated by two-dimensional gel electrophoresis demonstrated direct binding of HP to HIP. Indirect immunofluorescence studies demonstrated that HIP is expressed on the surfaces of intact RL95 cells. Binding of HIP antibodies to RL95 cell surfaces at 4 degrees C was saturable and blocked by preincubation with the peptide antigen. Single cell suspensions of RL95 cells formed large aggregates when incubated with antibodies directed against HIP but not irrelevant antibodies. Finally, indirect immunofluorescence studies demonstrate that HIP is expressed in both lumenal and glandular epithelium of normal human endometrium throughout the menstrual cycle. In addition, HIP expression increases in the predecidual cells of post-ovulatory day 13-15 stroma. Collectively, these data indicate that HIP is a membrane-associated HP-binding protein expressed on the surface of normal human uterine epithelia and uterine epithelial cell lines.

Human endometrial matrix metalloproteinase-2, a putative menstrual proteinase. Hormonal regulation in cultured stromal cells and messenger RNA expression during the menstrual cycle

Proteinases are likely effectors of endometrial menstrual breakdown. We have investigated proteinase production by human endometrial stromal cells subjected in vitro to progesterone (P) withdrawal, the physiologic stimulus for menstruation. Culture media of cells exposed to estradiol, P, or estradiol plus P had low levels of proteolytic activity similar to cultures maintained in the absence of steroids. P withdrawal, or addition of RU486 to P-treated cultures, stimulated proteinase secretion. The stromal cell proteinase was characterized by gelatin zymography, inhibitor profile, and organomercurial activation, as a metalloproteinase present mostly as a 66-kD proenzyme with lower levels of a 62-kD active form. The P withdrawal-induced metalloproteinase was identified as matrix metalloproteinase-2 (MMP-2) by Western blotting. The increase of MMP-2 induced by P withdrawal was associated with the metalloproteinase-dependent breakdown of stromal cultures, involving dissolution of extracellular matrix and dissociation of stromal cells. Northern analysis showed the differential expression of MMP-2 mRNA in late secretory phase endometrium. These findings are consistent with the involvement of stromal cell-derived MMP-2 in the proteolysis of extracellular matrix promoting cyclic endometrial breakdown and the onset of menstrual bleeding.

Loss of laminin and type IV collagen in uterine luminal epithelial basement membranes during blastocyst implantation in the mouse

BACKGROUND

Removal of the uterine luminal epithelium and its basement membrane is necessary for successful implantation of invasive blastocysts. Few reports, however, have specifically addressed the penetration and loss of the uterine luminal epithelial basement membrane (UEBM). We investigated the loss of UEBM by examining the distribution of laminin and type IV collagen.

METHODS

Blastocyst implantation sites were collected from mice on days 5, 6, and 7 of pregnancy. Paraffin sections were prepared from these tissues and processed with standard immunoperoxidase techniques to reveal the distribution of laminin and type IV collagen.

RESULTS

On day 5 of pregnancy blastocysts were adherent to the uterine epithelium. The epithelium and UEBM were complete and uninterrupted. On day 6 the juxtaembryonic uterine epithelium was lost and focal discontinuities were seen along the UEBM. By 1200 hr the UEBM had receded to the region near the ectoplacental cone, but staining was reduced for both antigens over the entire region surrounded by decidual cells. This decreased staining of the UEBM occurred in areas not yet occupied by trophoblast cells. On day 7 the UEBM was lost over the entire embryonic half of the uterine lining, corresponding to the distribution of decidual cells.

CONCLUSIONS

Progressive loss of the UEBM occurred in a consistent spatiotemporal pattern following the onset of blastocyst implantation. Diminished immunoreactivity of laminin and type IV collagen in the UEBM was closely correlated with the area occupied by decidualized endometrial stroma and occurred in areas not yet in contact with trophoblast cells. We conclude that decidual cells are instrumental in the removal of UEBM during early pregnancy.

Expression of desmin and vimentin intermediate filaments in human decidual cells during first trimester pregnancy

Human endometrial stromal cells (decidual cells) display dramatic alterations in cell shape and size during decidualization. The present study was designed to demonstrate the expression of two major cytoskeletal elements, desmin and vimentin, in human pregnant endometrial decidual cells. Additionally, stage-dependent variations of those intermediate filaments (IFs) among gestational weeks were also evaluated with regard to the support and maintenance of decidualization. Materials were obtained from legal suction terminations of pregnancies of 3-10 weeks gestation. Tissue specimens were either blocked in paraffin or enzymatically dissociated for isolation of decidual cells which subsequently were cultured as monolayers. Immunoperoxidase and immunofluorescence staining methods were applied by using anti-desmin and anti-vimentin monoclonal antibodies. Both desmin and vimentin expression were observed during the early weeks of pregnancy (3-6 weeks). These two types of IFs were also detected in short-term cultures in a filamentous fashion either within the cell body or at cellular attachment plaques. When decidual cells were cultured for longer periods (40-60 days), the expression of desmin dramatically declined while vimentin expression was maintained in a rather diffuse and more abundant fashion. The in situ expression of desmin and vimentin in later weeks of gestation (7-10 weeks) correlated with immunofluorescence staining of long-term cultured cells in that desmin staining was very weak and mostly undetectable where vimentin expression persisted and was evenly distributed throughout the entire stroma. The results demonstrate the differential expression of two major IFs, desmin and vimentin, in human endometrial stromal cells during decidualization and subsequent placentation. The persistence of vimentin in all stages examined suggests that this IF is probably involved in cell morphology and nucleocytoplasmic integrity. The temporal pattern of desmin expression suggests a role for this IF during the rapid onset of the decidualization process.

Mouse trophoblast cell invasion of extracellular matrix purified from endometrial tissue: a model for peri-implantation development

We have investigated the invasive activity of mouse trophoblast cells during embryo implantation in vitro by culturing blastocysts with extracellular matrix (ECM) purified from mouse endometrium obtained on day 4 of pregnancy. Endometrium was dissected from lyophilized mouse uteri, and intact ECM was isolated by sequential precipitation in nonionic detergent and high salt. Electron microscopic examination of the ECM revealed typical collagen fibers plus an amorphous material resembling basement membrane. Electrophoretic analysis of the ECM revealed an enrichment of high molecular weight proteins, and immunoblotting indicated the presence of fibronectin, laminin, entactin, and type IV collagen, but not the intracellular proteins 2',3'-cyclic nucleotide-3'-phosphodiesterase or vimentin. Mouse blastocysts cultured with this ECM attached to it within 3 days, and the trophoblast cells began to migrate through the matrix in a manner resembling trophoblast invasion in utero. Unlike blastocysts cultured on plastic surfaces, the trophoblast did not flatten and become disorganized, but retained a polarized, spherical structure. Fluorescent microscopy with fluorescein isothiocyanate-labeled phalloidin revealed a high degree of microfilament organization and established that actin was absent from the ECM preparation. In the presence of a serum substitute, differentiation continued through yolk sac formation. Without serum components, yolk sac did not form; however, light and electron microscopic examination indicated that the invasive behavior of trophoblast cells persisted and was comparable to that of trophoblasts cultured in the presence of the serum substitute. A three-dimensional model for investigating trophoblast behavior in ECM from the endometrium should be of great value in elucidating the cellular and molecular events surrounding the process of blastocyst implantation.

Developmental changes in the cell columns and trophoblastic shell of the macaque placenta: an immunohistochemical study localizing type IV collagen, laminin, fibronectin and cytokeratins

Developmental changes in the organization of cells and extracellular matrix in the cell columns and trophoblastic shell of macaque placentas have been examined between 37 days of gestation and term. Between 37 and 53 days a thickened basement membrane developed between the trophoblast cells of the proximal cell columns and the mesenchymal cores of contiguous anchoring villi. This layer stained strongly for type IV collagen and laminin, but weakly for fibronectin. Large "lakes" of extracellular matrix immunoreactive for all 3 of these antigens were present in the distal columns, while smaller amounts were distributed between cells of the proximal columns. During this period the trophoblast cells in the proximal shell reorganized, forming strands of cells that were separated by bands of matrix immunoreactive for type IV collagen, laminin, and fibronectin. Staining for these antigens decreased abruptly at the junction between fetal and maternal tissues. Between 66 and 104 days the thick basement membrane of the proximal columns persisted, but stained only weakly for each of the 3 extracellular matrix antigens. The large lakes of matrix in the distal columns characteristic of earlier stages gradually disappeared. The cell columns became progressively shorter and the tips of the anchoring villi became embedded in the trophoblastic shell. The matrix of the shell decreased in immunostaining intensity except for narrow rims around the trophoblast cells. Gestational ages later than 104 days showed few additional changes in the distribution of the matrix antigens or cell organization of the columns and shell. The thick basement membrane-like layer persisted to term although it continued to stain weakly for the 3 matrix antigens. The distal ends of most anchoring villi were embedded in the trophoblastic shell. The developmental changes in the organization of the columns and shell may be related to changes in placental growth rate.

Differential expression of laminin, nidogen and collagen IV genes in the midgestation mouse placenta

The distribution of laminin A, B1, B2, nidogen and collagen alpha 1(IV) mRNA was studied in the 12.5-day mouse placenta and uterus. This was compared to the pattern of laminin, nidogen and collagen IV immunoreactivity in the placenta at this time. High levels of B2 mRNA were distributed throughout the decidual layer, compared to lower levels of laminin B1, nidogen and collagen IV. In contrast, laminin B1 and nidogen mRNA were found at very high levels in the trophoblast giant cells and cytotrophoblast. Laminin B2 was much lower in trophoblast cells than in the decidua. Nidogen mRNA levels were low in the decidual cells, but high in endothelial cells lining the placental blood spaces in the decidual layer. Immunofluorescence staining of the placenta showed colocalization of laminin, nidogen and collagen IV in fetal and maternal layers of the placenta. In the antimesometrial area where the uterine epithelium was reforming laminin B1 and B2 mRNA were uniformly distributed between the epithelium and stroma, whereas nidogen and collagen alpha 1(IV) mRNA were only produced by the stromal cells. In all cell types, apart from parietal endoderm cells forming Reichert's membrane, laminin A chain mRNA was very low or absent. These results demonstrate that laminin and nidogen genes are not coordinately expressed in the midgestation mouse placenta. Comparison of the distribution of these mRNAs with collagen alpha 1(IV) mRNA suggests that different regions of the placenta produce specialized extracellular matrices which may contain different ratios of these polypeptides.

Implantation and decidualization in rodents

This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.

Confocal immunofluorescence localization of collagen types I, III, IV, V and VI and their ultrastructural organization in term human fetal membranes

The distribution of collagen types I, III, IV, V and VI in term human fetal membranes was examined using conventional and confocal indirect immunofluorescence techniques. Collagens I and III were present in most of the layers of fetal membranes except in the trophoblast layer contrary to what has been previously reported. Although collagen IV is considered to be a basement membrane component our study, using monoclonal and polyclonal antibodies, showed its consistent presence in the spongy and reticular layers in high intensity. This was first report on the distribution of type V collagen in the chorion where it was found in the reticular and in the trophoblast layers. Type VI collagen was present mainly in the amnion and the reticular layer. The ultrastructural examination of the extracellular matrix showed that the main fibrous skeleton of the fetal membranes was formed of large banded fibres (Ultrastructurally identical to collagens types I and III) connected together and to the epithelial basement membranes by networks of unbanded filaments (collagen types V, VI and other components). The extensive and continuous networks formed by these collagens may be a major factor responsible for the mechanical integrity of the fetal membranes.

Recombinant entactin promotes mouse primary trophoblast cell adhesion and migration through the Arg-Gly-Asp (RGD) recognition sequence

In vitro culture of mouse blastocysts during the period coinciding with implantation has revealed that primary trophoblast cells can adhere and migrate in serum-free medium when provided with certain extracellular matrix components, including fibronectin and laminin. Tightly associated with laminin is the glycoprotein, entactin, that may play an important role in basement membrane assembly and cell attachment. Mouse blastocysts were studied using this in vitro model to determine whether entactin was capable of mediating trophoblast invasive activity. Although entactin has never been shown to promote cell migration, we report here that recombinant entactin supported blastocyst outgrowth in a dose-dependent manner, with a maximal effect at 20-50 micrograms/ml. The ability of trophoblast cells to adhere and migrate on entactin was specifically inhibited by anti-entactin antibody, but not by antibodies raised against laminin. The synthetic peptide, Gly-Arg-Gly-Asp-Ser-Pro, that contains the Arg-Gly-Asp (RGD) integrin recognition site, reversibly inhibited entactin-mediated blastocyst outgrowth in a dose-dependent manner, but had no effect on laminin-mediated outgrowth. The synthetic peptide, Gly-Phe-Arg-Gly-Asp-Gly-Gln, that comprises the actual RGD-containing sequence within entactin, promoted trophoblast outgrowth when immobilized on the substratum. Furthermore, a mutated recombinant entactin, altered to contain a Glu in place of Asp at the RGD site, provided no trophoblast cell adhesive activity. We conclude that entactin promotes trophoblast outgrowth through a mechanism mediated by the RGD recognition site, and that it may play an important role during invasion of the endometrial basement membrane at implantation.

Changes of the Golgi apparatus and lysosomes during decidualization in mice

The Golgi apparatus of the endometrial stromal cells of pregnant mice increases in size simultaneously with the differentiation of stromal cells into decidual cells. The activity of acid phosphatase in this organelle increases during this stage. On the other hand, the involuting decidual cells show morphological and cytochemical signs of Golgi regression (dilated cisternae, lack of enzymatic activity) together with the finding of numerous, pleomorphic lysosomes that have intense cytochemical label. These results confirm morphological data suggesting that decidual cell death occurs by autophagic degeneration.

Chorioallantoic placenta formation in the rat: I. Luminal epithelial cell death and extracellular matrix modifications in the mesometrial region of implantation chambers

On days 7 and 8 of pregnancy, mesometrial regions of rat gestation sites were examined by light microscopy and transmission electron microscopy to determine what changes occur before the chorioallantoic placenta forms in that region. By day 7, gestation sites contained a uterine lumen mesometrially and an antimesometrial extension of the uterine lumen, the implantation chamber. The implantation chamber consisted of a mesometrial chamber between the uterine lumen and the conceptus, an antimesometrial chamber that contained the conceptus, and a decidual crypt antimesometrial to the conceptus. Stromal cells that formed the walls of the implantation chamber were closely packed decidual cells, while those that surrounded the uterine lumen were loosely arranged. Late on day 7, a portion of the epithelium lining the mesometrial chamber was degenerating, but this area of initial degeneration was never adjacent to the antimesometrial chamber. By early day 8, most of the epithelial cells lining the mesometrial chamber were degenerating and were being sloughed into the chamber lumen. Although degeneration of these epithelial cells morphologically resembled necrosis, it was precisely controlled, since adjacent epithelial cells lining the uterine lumen remained healthy. The space that separated the denuded luminal surface of the mesometrial chamber from underlying decidual cells became wider and was occupied by an extracellular matrix rich in cross-banded collagen fibrils. Decidual cell processes, that earlier had penetrated the basal lamina beneath healthy epithelial cells, protruded into this matrix and penetrated the basal lamina at the luminal surface. By late day 8, large areas of denuded chamber wall were covered with decidual cell processes, little remained of the basal lamina, and cross-banded collagen fibrils were scarce in the area occupied by decidual cell processes. During the times studied, uterine tissues that formed the walls of the mesometrial chamber were not in direct contact with the conceptus. This study indicates that trophoblast does not play a direct role in epithelial degeneration, basal lamina penetration, or extracellular matrix modifications in the mesometrial region of implantation chambers where part of the chorioallantoic placenta forms, although trophoblast may be required to trigger or modulate some of the changes.

Current topic: structural responses of the primate endometrium to implantation

Morphological responses to implantation and pregnancy in the human and nonhuman primates include decidualization of the endometrial fibroblasts and accumulation of large numbers of large granular lymphocytes, formerly called endometrial granular cells, and may also include an epithelial plaque response and endothelial cell hypertrophy. Although stromal decidualization occurs in all species, it develops slower in macaques than in the human, and slower in the baboon than in the macaques. Cytologically, however, in all of these species there is extensive modification of the decidual cells by midgestation. Hypertrophy of luminal and gland neck epithelial cells is common in most monkeys and is also seen in the baboon, but has not been reported in humans. Large granular lymphocytes undergo changes in morphology during the first week after implantation in the rhesus monkey, the only species in which they have been studied in the immediate postimplantation period. Later in pregnancy many of the large granular lymphocytes are surrounded by decidual cells in this species. All of the responses can be elicited by trauma and appropriate hormonal conditions, but the epithelial plaque response forms first in the rhesus monkey and baboon. It is suggested that more complete fine structural and immunocytochemical studies of the different decidual regions at different gestational ages, combined with studies of the synthetic and antigenic nature of the different cell types, would allow determination of whether or not there are subpopulations of decidual cells in primates as well as suggesting possible functions of the cells in pregnancy.

Development of the discoidal hemochorial placenta in the black mastiff bat, Molossus ater: evidence for a role of maternal endothelial cells in the control of trophoblastic growth

In an effort to define further the factors that can influence trophoblastic growth, development of the discoidal chorioallantoic placenta was examined histologically in laboratory-bred black mastiff bats, Molossus ater. This placenta normally forms only at the cranial end of the right uterine horn. Its positioning was found to be related to the development of an unusual vascular tuft in the endometrium at this site following ovulation. When a decidual reaction occurred, the endothelial cells of the tuft vessels hypertrophied and their basal laminae became more prominent in sections stained for glycoproteins. Cytotrophoblast then proliferated preferentially around the tuft in the right horn and its vessels became surrounded by trophoblastic cuffs. A functional placenta was formed when trophoblastic tubules grew out from these cuffs, became interconnected, developed lumina, and began to carry maternal blood. Maternal endothelial cells generally persisted only in portions of the larger vascular tubules. These observations suggest that the endothelial cells of the tuft vessels may be secreting factors that influence early trophoblastic growth and are at least partially incorporated into the basal laminae of the endothelial cells. Evidence is reviewed which raises the possibility that endometrial endothelial cells might have a similar morphogenetic role in many other mammals with invasive trophoblast. Mitotic activity in the trophoblastic tubules of M. ater ceased when the tubules became patent and began to carry blood. Further growth was then accomplished by hypertrophy of the existing cytotrophoblast cells. Electron microscopic examination of near-term placentas confirmed that the interhemal barrier was hemomonochorial and lacked a continuous layer of syncytiotrophoblast.

Spontaneous decidual reactions and menstruation in the black mastiff bat, Molossus ater

Uterine function was assessed histologically in nonpregnant Molossus ater removed from a laboratory breeding colony. During the luteal phase of the cycle, bilateral decidual reactions were found to develop spontaneously in the absence of either embryos or experimental manipulation of the uterus. These included the formation of early decidual giant cells, closure of the uterine lumina, and morphological changes in the endometrial blood vessels. Some endothelial cell hypertrophy was noted in much of the decidua, but this was most pronounced in vessels associated with an unusual vascular tuft that formed in the endometrium surrounding the cranial end of the uterine lumen. These latter vessels also developed very prominent basal laminae. In pregnant bats, this tuft played a central role in the morphogenesis of the definitive discoidal chorioallantoic placenta. At the end of nonpregnant cycles, the decidua became necrotic and was sloughed off with associated bleeding. As in menstruating catarrhine primates, the endometrium of M. ater is vascularized by spiral arterioles and populated by distinctive granulocytes containing large, acidophilic granules. Increased coiling of these arterioles did not appear to be an essential element in the mechanism of mensturation in this species. M. ater is a monotocous, seasonal breeder, with a relatively long gestation period. Although it has a bicornuate uterus, ovulation and implantation appear to occur only on the right side of the tract. The ability to menstruate probably affords this bat an efficient mechanism for eliminating a highly differentiated endometrium from the usual implantation site in the event of a reproductive failure. In the wild, this may provide M. ater with another chance to establish a pregnancy at a still opportune time during the same breeding season.