Implantation and decidualization in rodents

Hormone-regulated expression and distribution of versican in mouse uterine tissues

BACKGROUND

Remodeling of the extracellular matrix is one of the most striking features observed in the uterus during the estrous cycle and after hormone replacement. Versican (VER) is a hyaluronan-binding proteoglycan that undergoes RNA alternative splicing, generating four distinct isoforms. This study analyzed the synthesis and distribution of VER in mouse uterine tissues during the estrous cycle, in ovariectomized (OVX) animals and after 17beta-estradiol (E2) and medroxyprogesterone (MPA) treatments, either alone or in combination.

METHODS

Uteri from mice in all phases of the estrous cycle, and animals subjected to ovariectomy and hormone replacement were collected for immunoperoxidase staining for versican, as well as PCR and quantitative Real Time PCR.

RESULTS

In diestrus and proestrus, VER was exclusively expressed in the endometrial stroma. In estrus and metaestrus, VER was present in both endometrial stroma and myometrium. In OVX mice, VER immunoreaction was abolished in all uterine tissues. VER expression was restored by E2, MPA and E2+MPA treatments. Real Time PCR analysis showed that VER expression increases considerably in the MPA-treated group. Analysis of mRNA identified isoforms V0, V1 and V3 in the mouse uterus.

CONCLUSION

These results show that the expression of versican in uterine tissues is modulated by ovarian steroid hormones, in a tissue-specific manner. VER is induced in the myometrium exclusively by E2, whereas MPA induces VER deposition only in the endometrial stroma.

The effect of hyperstimulation on transforming growth factor beta(1) and beta(2) in the rat uterus: possible consequences for embryo implantation

OBJECTIVE

To investigate the effect of exogenous gonadotropins on the expression of transforming growth factor (TGF) beta(1) and beta(2) in the rat uterus and its consequences for successful embryo implantation.

DESIGN

Controlled experimental research study.

SETTING

School of Anatomical Sciences, University of the Witwatersrand.

PATIENT(S)

Thirty-six adult, virgin, female Sprague-Dawley rats and two fertile males.

INTERVENTION(S)

Follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) were superimposed upon the normal hormonal milieu of normal, cycling female rats before mating. Uterine tissue was collected at peri-implantation stages (i.e., at 4.5, 5.5, and 6.5 days) after mating. Enzyme-linked immunosorbent assay (ELISA) was performed to estimate the blood estrogen and progesterone levels, and immunohistochemistry was performed to localize the TGF-beta(1) and TGF-beta(2) in the uterus.

MAIN OUTCOME MEASURE(S)

Hyperstimulation affecting the expression of both TGF-beta(1) and TGF-beta(2) during the peri-implantation period.

RESULT(S)

The release of ovarian steroids was altered, causing a change in the endogenous hormonal environment. A marked increase in the expression of TGF-beta(2) was distinct in the glandular epithelium. Expression of both TGF-beta(1) and TGF-beta(2) was weaker in the subluminal stroma when compared with the deeper stromal region.

CONCLUSION(S)

Hyperstimulation with exogenous hormones affects the expression of both TGF-beta(1) and TGF-beta(2), which may contribute to the disruption of the endometrial environment required for successful embryo implantation.

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.

Basigin-mediated gene expression changes in mouse uterine stromal cells during implantation

Implantation of mouse embryos is dependent on the proliferation and differentiation of uterine stromal cells in a process called decidualization. Decidualization both supports and limits the invasion of the implanting embryo and is regulated in part by the expression of matrix metalloproteinases (MMPs) and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Molecules that alter the balance between MMP and TIMP expression could prevent implantation of the embryo. The membrane glycoprotein basigin (CD147/EMMPRIN), a known inducer of MMPs, is necessary for normal implantation in the mouse. The purpose of this study was to investigate the potential roles of basigin during implantation in the mouse. Using an in vitro stromal cell culture system, we found that recombinant human basigin protein (rBSG) increases MMP-3 and MMP-9 expression without altering TIMP-3 expression. Our results also showed rBSG induces expression of cytokines IL-1alpha/beta and leukocyte chemoattractants, CCL3, CCL20, CXCL2, and CXCL5. More importantly, rBSG significantly suppressed stromal cell decidualization as shown by the inhibition of alkaline phosphatase-2 expression and activity by rBSG. However, rBSG did not affect stromal cell proliferation. Taken together, our data indicate that basigin mediates gene expression changes in mouse uterine stromal cells and suggests that temporal and spatial regulation of basigin expression may be involved in the recruitment of leukocytes to the mouse uterus during early pregnancy.

IL11 antagonist inhibits uterine stromal differentiation, causing pregnancy failure in mice

Hormonal contraceptives are unsuitable for many women; thus, the development of new, nonhormonal contraceptives is of great interest. In women, uterine epithelial expression of interleukin 11 (IL11) and its receptor (IL11RA) suggests IL11 is critical for blastocyst attachment during implantation. Il11ra-deficient mice are infertile due to a defective decidualization response to the blastocyst, leading to total pregnancy loss. We examined the effect of administering a PEGylated IL11 antagonist, PEGIL11A (where PEG is polyethylene glycol), on pregnancy outcomes in mice and IL11 signaling in human endometrial epithelial cells (HES). PEGIL11A was detected in sera up to 72 h after intraperitoneal (IP) injection versus up to 2 h for the non-PEGylated antagonist. Following IP injection, PEGIL11A localized to uterine decidual cells and reduced immunoreactive cyclin D3 (IL11 decidual target). To inhibit IL11 action during early decidualization, PEGIL11A or control were administered IP on Days 3-6 (beginning just prior to maximal decidual Il11 expression). On Day 6, mesometrial decidualization was disturbed in PEGIL11A-treated animals with regions of hemorrhage visible in the mesometrial decidua. On Day 10, severe decidual destruction was visible: implantation sites contained significant hemorrhage, and the uterine luminal epithelium had reformed, suggesting a return to estrous cycling. These results demonstrate that PEGIL11A blocked IL11 action in the decidua during early decidualization, which totally abolished pregnancy and which is equivalent to the Il11ra(-/-) mouse. PEGIL11A significantly diminished STAT3 phosphorylation in HES cells in vitro (P < or = 0.05). This study provides valuable information for PEGIL11A that could lead to the development of this protein as a nonhormonal contraceptive.

Moesin is involved in the cytoskeletal remodelling of rat decidual cells

The extensive actin cytoskeletal remodelling of the uterine stroma during early pregnancy involves changes in actin-binding proteins. This study provides the first detailed localisation of the actin-binding protein, moesin, in rat uterine endometrium during this period. Western blot analysis and immunofluorescence microscopy showed that the amount of moesin in the uterus peaked at the time of implantation, corresponding to the presence of intensely immunolabelling decidual cells. Furthermore, moesin increased in active membrane/cytoskeleton bound protein at the time of implantation, concomitantly decreasing in cytosolic protein. The increase of moesin at decidualisation corresponds with the appearance of alpha smooth muscle actin (alphaSMA) suggesting that decidual cells have contractile abilities that may aid in containing an invasive trophoblast. The results of this study suggest that moesin is important in developing a specialised cytoskeleton and increased adhesiveness of decidual cells, possibly functioning to bridge adhesion molecules to the underlying cytoskeleton.

Effects of tumor necrosis factor-alpha on cell proliferation, prostaglandins and matrix-metalloproteinases production in rat endometrial stromal cells cultured in vitro

Tumor necrosis factor-alpha (TNF-alpha) is known as a pluripotent cell mediator, and it is implicated in the control of uterine cell growth, differentiation and function during estrous cycle and pregnancy. In this study, we investigated the effect of TNF-alpha on endometrial stromal cells derived from rat uterus (rat endometrial stromal cells, RES). RES were isolated from rat endometrium at day 5 of pregnancy. Proliferation activities of RES were measured by using bromodeoxyuridine (BrdU) labeling kit, the productions of prostaglandin E2 (PGE2) and prostaglandin F2alpha (PGF2alpha) were measured by enzyme immunoassay kits and the production of matrix metalloproteinases (MMPs) was analyzed by gelatin-zymography. TNF-alpha, as well as epidermal growth factor and fibroblast growth factor-2, significantly increased the proliferation activity of RES (P<0.05). TNF-alpha selectively stimulated the production of PGE2 in RES (P<0.05), but not the production of PGF2alpha. Additionally, TNF-alpha did not stimulate the production of MMPs in RES at the concentration of 5 ng/mL, compared with the control groups (P>0.05). In conclusion, this study demonstrates several regulational functions of TNF-alpha on RES using in vitro culture system. The effects of TNF-alpha on proliferation and MMP production of RES have been shown for the first time. We believe that these results demonstrate part of the functions of TNF-alpha in endometrium and contribute to the better understanding of endometrial functions.

Implantation-related expression of epidermal growth factor family molecules and their regulation by progesterone in the pregnant rat

The uterine expressions of epidermal growth factor(EGF) family are examined to elucidate their exact role(s) in rat pregnancy. EGF and its receptors' (EGF-R) mRNA levels increased significantly at implantation after which their expression gradually decreased. Heparin-binding EGF (HB-EGF) and transforming growth factor-alpha (TGF-alpha) showed a modest expression at gestation day (GD), GD4 and GD3, respectively, but were much strongly expressed at mid-pregnancy.Amphiregulin (Areg) was strongly expressed around implantation (GD4) and at mid-pregnancy (GD12).Treatment of pregnant rats with RU486 at GD5 or GD8 blocked the expression of all the genes, and administration of immature rats with progesterone (P4) induced the uterine expression of all the genes except HB-EGF. In addition, HB-EGF,TGF-alpha, and Areg proteins in the uterine and glandular epitheliums may participate in mid-pregnancy. Taken together, all of these activities are likely to be controlled by P4 in the uterus of pregnant rats.

The antifertility effects of DNA vaccine-induced immune responses against uroguanylin

Previously we found that uroguanylin displayed a specific expression pattern in the uteri during pregnancy. In this study, the effect of uroguanylin in early pregnancy was studied by DNA vaccine, RT-PCR, Western blot, immunofluorescence and immunohistochemistry. The results showed that (1) the anti-rUfl antibodies could be elicited in the mice after immunization by recombinant plasmid pCR3.1-rUfl; (2) the birth rate of the female mice immunized by pCR3.1-rUfl was significantly reduced (p<0.01); (3) anti-rUfl antibodies could bind with uroguanylin in the uteri of the non-pregnant mice immunized by pCR3.1-rUfl; (4) in the non-mated experiments, in the uteri of normal, pCR3.1- and pCR3.1-rUfl-immunized mice, expression of p53 and vascular endothelial growth factor (VEGF) was not detected, Bax was expressed, and transforming growth factor beta 1 (TGFbeta1) expression was very little; (5) in the mated experiments, p53, Bax, VEGF and TGFbeta1 were expressed in the uteri of saline- and pCR3.1-immunized mice that were pregnant. However, their expression was significantly decreased in the uteri of the non-pregnant mice immunized by pCR3.1-rUfl on the 9th day of pregnancy (p<0.01). The results indicate that the immunization by pCR3.1-rUfl has antifertility effect.

Dickkopf-1 secreted by decidual cells promotes trophoblast cell invasion during murine placentation

Dickkopf-1 (Dkk1) is one of the secreted antagonists in the canonical Wnt signaling pathway. It plays important roles in diverse developmental processes. However, the role of Dkk1 in trophoblast cell invasion during placentation remains unclear. In this study, we found that Dkk1 was mainly expressed in maternal decidual tissue but trivially in ectoplacental cones (EPCs) in day 8 post coitum (p.c.) pregnant mouse uterus and that the efficiency of EPC attachment and outgrowth was increased when co-cultured with decidual cells, which secreted Dkk1, and this enhancement was abolished by pretreating decidual cells with Dkk1 blocking antibody before co-culture experiment. This indicates that Dkk1 secreted by decidual cells plays an important role in trophoblast cell invasion. Indeed, when recombinant mouse Dkk1 was added to EPCs in vitro, the efficiency of attachment and outgrowth was increased. Migration of EPCs toward the decidua was retarded when antisense Dkk1 oligonucleotide (ODN) was administered via intrauterine injection in vivo. Furthermore, the active beta-catenin nuclear location was lost when we treated cultured EPCs with recombinant mouse Dkk1, and the efficiency of EPCs attachment and outgrowth was obviously increased when we treated cultured EPCs with antisense beta-catenin ODN. Taken together, Dkk1 secreted by decidual cells may induce trophoblast cell invasion in the mouse and beta-catenin may be involved in such functions of Dkk1.

Identification of genes regulated by an interaction between alphavbeta3 integrin and vitronectin in murine decidua

The delicate balance between embryo invasion and suppression of maternal immune rejection requires a fully functional decidua in species with haemochorial placenta. Our understanding of the decidual function is very limited due to the molecular and cellular complexity involved in decidualisation. The cell adhesion molecule alpha(v)beta(3) integrin and its ligand vitronectin are upregulated in the mouse decidua during mid-pregnancy. The implications of interactions between alpha(v)beta(3) and vitronectin in regulating decidual function are not known. In the present study, interactions between alpha(v)beta(3) and vitronectin in the decidual cells of the mouse were blocked in vitro and effects on cell fate were evaluated by studying the differentially regulated genes by cDNA array and real-time polymerase chain reaction (PCR). The results indicate that expression of various genes involved in apoptotic and cell cycle pathways, as well as cytokine receptors, was deranged. Signalling through alpha(v)beta(3) seems to be important to maintain a balance between cell proliferation and apoptosis, along with the modulation of inflammatory responses of decidual cells.

Maternal and Embryonic Control of Uterine Sphingolipid-Metabolizing Enzymes During Murine Embryo Implantation1

During early gestation in invasively implanting species, the uterine stromal compartment undergoes dramatic remodeling, defined by the differentiation of stromal fibroblast cells into decidual cells. Lipid signaling molecules from a number of pathways are well-established functional components of this decidualization reaction. Because of a correlation in the events that transpire in the uterus during early implantation with known functions of bioactive sphingolipid metabolites established from studies in other organ systems, we hypothesized that uterine sphingolipid metabolism would change during implantation. By a combination of Northern blot, Western blot, and immunohistochemical analyses, we establish that enzymes at each of the major catalytic steps in the sphingolipid cascade become transcriptionally up-regulated in the uterus during decidualization. Each of the enzymes analyzed was up-regulated from Days of Pregnancy (DOP) 4.5-7.5. When comparing embryo-induced decidualization (decidual) with mechanically induced decidualization (deciduomal), sphingomyelin phosphodiesterase 1 (Smpd1) mRNA and sphingosine kinase 1 (SPHK1) protein were shown to be dually regulated in the endometrium by both maternal and embryonic factors. As measured by the diacyl glycerol kinase assay, ceramide levels rose in parallel with Smpd1 gene expression, suggesting that elevated transcription of sphingolipid enzymes results in heightened catalytic activity of the pathway. Altogether, these findings place sphingolipids on a growing list of lipid signaling molecules that become increasingly present at the maternal-embryonic interface.

The postimplantation embryo differentially regulates endometrial gene expression and decidualization

Transcriptomal changes in the uterine endometrium induced in response to the implanting embryo remain largely unknown. In this study, using Affymetrix mRNA expression microarray analysis, we identified genes differentially expressed in the murine endometrium in the presence or absence of the embryo. Compared with the pseudopregnant deciduoma induced by a mechanical stimulus in the absence of an embryo, approximately 1500 genes (753 up-regulated, 686 down-regulated; P < 0.05) were differentially expressed by at least 1.2-fold in the uterine decidua of pregnancy. Most of these genes fall into five major biological categories that include binding (45%), catalysis (24%), signal transduction (10%), transcriptional regulators (5%), and transporters (5%). This strong, embryo-induced transcriptomal impact represented approximately 10% of the total number of genes expressed in the decidualizing endometrium. Validation studies with mRNA and protein confirmed existence of the phylogenetically conserved, embryo-regulated genes involved in the following: 1) hemostasis and inflammation; 2) interferon signaling; 3) tissue growth and remodeling; and 4) natural killer cell function. Interestingly, whereas expression of many growth factors and their cognate receptors were not different between the decidual and deciduomal endometria, a number of proteases that degrade growth factors were selectively up-regulated in the decidual tissue. Increased expression of IGF and activin A neutralizing factors (i.e. HtrA1 and Fstl3) correlated with reduced stromal cell mitosis, tissue growth, and mitogenic signaling in the decidual endometrium. These results support the hypothesis that the implanting murine embryo takes a proactive role in modulating endometrial gene expression and development during early gestation.

The p160 steroid receptor coactivator 2, SRC-2, regulates murine endometrial function and regulates progesterone-independent and -dependent gene expression

The role of the p160 steroid receptor coactivator 2 (SRC-2) in the regulation of uterine function and progesterone (P4) signaling was investigated by determining the expression pattern of SRC-2 in the murine uterus during pregnancy and the impact of SRC-2 ablation on uterine function and global uterine gene expression in response to progesterone. SRC-2 is expressed in the endometrial luminal and glandular epithelium from pregnancy d 0.5. SRC-2 is then expressed in the endometrial stroma on pregnancy d 2.5-3.5. Once the embryo is implanted, SRC-2 is expressed in the endometrial stromal cells in the secondary decidual zone. This compartmental expression of SRC-2 can be mimicked by treatment of ovariectomized mice with estrogen and P4. Ablation of SRC-2 in the uterus resulted in a significant reduction in the ability of the uterus to undergo a hormonally induced decidual reaction. Microarray analysis of RNA from uteri of wild-type and SRC-2(-/-) mice treated with vehicle or P4 showed that SRC-2 was involved in the ability of progesterone to repress specific genes. This microarray analysis also revealed that the uteri of SRC-2(-/-) mice showed alterations in genes involved in estrogen receptor, Wnt, and bone morphogenetic protein signaling. This analysis indicates that SRC-2 regulates uterine function by modulating the regulation of developmentally important signaling molecules and the ability of P4 to repress specific genes.

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.

β-Catenin (CTNNB1) in the Mouse Uterus During Decidualization and the Potential Role of Two Pathways in Regulating Its Degradation

β-catenin plays a role in cell adhesion and as a transcriptional coactivator. Its levels are regulated in cells by controlling its degradation through ubiquitination by two different E3 ligase complexes. One complex contains β-transducing repeat containing (BTRC) protein, which binds to β-catenin when phosphorylated on specific (S33 and S37) residues, whereas the other involves calcyclin-binding protein (CACYBP). The aim of this study was to determine the localization and levels of total and active (S33/S37-dephosphorylated) β-catenin in the pregnant mouse uteri and those undergoing artificially stimulated decidualization. These two forms of β-catenin were localized almost exclusively to the endometrial epithelia just prior to the onset of implantation. Although this localization continued after the onset of implantation, there were less epithelial cells present in areas of the uterus undergoing decidualization. Rather, there was a progressive increase in β-catenin localization in endometrial stromal cells undergoing decidualization in the anti-mesometrial and, to a lesser extent, in the mesometrial regions. The presence of a conceptus was not required for the changes in localization seen in the pregnant uterus because similar findings were also seen in uteri undergoing artificially stimulated decidualization. Finally, overall levels of total, active (S33 and S37 dephosphorylated), and phosphorylated (S33/S37/T42) β-catenin protein and the steady-state levels of calcyclin-binding protein mRNA changed in the uterus during decidualization. The result of this study shows the changing localization and levels of β-catenin in the mouse uterus during decidualization. Further, the results suggest potential roles for both the BTRC and CACYBP E3 ligase mechanisms of β-catenin ubiquitination in the uterus during decidualization.

Granulated and non-granulated decidual prolactin-related protein-positive decidual cells in the pregnant mouse endometrium

PROBLEM

Identification of the cell types responsible for the synthesis of decidual prolactin-related protein (dPRP) in the pregnant mouse endometrium.

METHOD OF STUDY

Histochemistry and immunocytochemistry were used to determine peri-implantation dPRP and perlecan distribution in the mouse uterus.

RESULTS

We identified dPRP in pre-decidual and mature decidual cells from days 5 to 12 of pregnancy. On day 8, dPRP immunoreactivity was detected within cytoplasmic granules of a specific population of granulated decidual cells (GDCs). In mesometrial decidual cells, weak immunoreactivity was seen from days 7 to 14. Between days 11 and 14, dPRP was found in cytoplasm and in the extracellular matrix surrounding islands of spongiotrophoblast. Perlecan, a heparan sulfate proteoglycan, was co-localized with dPRP.

CONCLUSION

GDCs are a putative source of dPRP in pregnant mice. Co-localization of perlecan with dPRP suggests that the former acts as a dPRP reservoir and facilitates its paracrine effect in developing placental tissues.

Expression of uterine sensitization-associated gene-1 (USAG-1) in the mouse uterus during the peri-implantation period

Rat uterine sensitization-associated gene-1 (USAG-1) mRNA is expressed in the uterus during the peri-implantation period, and its mRNA expression in uterine epithelial cells is highest on day 5 of pregnancy. On the other hand, since changes in USAG-1 mRNA expression in the mouse uterus are not seen during the estrous cycle, USAG-1 expression might be specifically regulated by embryonic factors rather than by the maternal environment. However, the expression pattern and function of USAG-1 in the mouse uterus have not been determined. Thus, we examined the tissue-specific USAG-1 mRNA expression in the uteri of ICR mice during peri-implantation using real-time quantitative PCR. Uterine tissues, such as the myometrium, luminal epithelium, and stroma, were collected by laser capture microdissection at 3.5-6.5 dpc. USAG-1 mRNA was expressed in the uteri of pregnant mice from 3.5 dpc to 6.5 dpc, and the highest level of expression was seen at 4.5 dpc (P<0.01). Significantly high USAG-1 mRNA expression was detected in the luminal epithelium at 4.5 dpc (P<0.05). The stroma and myometrium exhibited unchanged expression levels of USAG-1 mRNA at 3.5-5.5 dpc. USAG-1 mRNA was undetectable in blastocysts and implanting embryos. Expression of USAG-1 mRNA appears to be associated with blastocyst implantation to the luminal epithelium, suggesting that physiological or biochemical contact of the blastocyst to the uterus is required for USAG-1 expression.

Changes in Fibrillin-1 in the Endometrium during the Early Stages of Pregnancy in Mice

Blastocyst reception and implantation require various adaptations of the uterine microenvironment. We have previously shown that in mice, remodeling of the extracellular matrix begins early in pregnancy, characterized by synthesis, degradation and alteration of collagen fibrillogenesis, accompanied by pregnancy stage-dependent expression of glycosaminoglycans and proteoglycans. Fibrillin-1 is a matrix glycoprotein that participates in the formation of elastic fibers and promotes cell adhesion through its integrin-binding domain. In the present study, we used light microscope immunohistochemistry to analyze the distribution of fibrillin-1 in the endometrial stroma of mice during estrous and diestrous, as well as in the pre- and postimplantation periods. Fibrillin-1 was found among endometrial fibroblasts and decidual cells, respectively, in the pre- and postimplantation periods. However, fibrillin-1 organization and distribution in the various regions of the endometrial stroma were found to be pregnancy stage dependent. Fibrillin-1 was also abundant in the basement membrane regions of blood vessels, as well as in the luminal and glandular epithelia. Fibrillin-1 at the maternal-fetal interface and in Reichert's membrane of embryos at up to 6 days of development might facilitate embryo expansion and fixation. Changes in the fibrillin-1 expression during the peri-implantation period suggest that fibrillin-1 plays a role in preparing the endometrium for embryo implantation.

Expression pattern of integrins and their ligands in mouse feto-maternal tissues during pregnancy

The role of integrins, the cell-surface glycoproteins involved in various cellular functions, is well documented. However, information about their role and expression profile during pregnancy is still scant. In the present study, the expression of the integrin subunits β3, α6 and α5, along with their ligands vitronectin, osteopontin, laminin and fibronectin, was investigated in mouse uterus during different stages of pregnancy, namely 6.5, 8.5 and 13.5 days post coitus (d.p.c.) by immunohistochemical localisation. Integrins β3, α6 and α5 and the extracellular matrix molecules vitronectin and osteopontin exhibited dynamic spatiotemporal changes in their expression pattern in gestational endometrium, whereas fibronectin and laminin demonstrated more-or-less ubiquitous expression. The inter-implantation sites showed localisation of most of these molecules predominantly in the luminal epithelium, whereas their expression was negligible in the stroma. The present study explores the possible role and relevance of the spatiotemporal expression of integrins and their ligands in endometrial/decidual function and the maintenance of pregnancy.

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.

Distinct expression and localization of serine protease HtrA1 in human endometrium and first-trimester placenta

Mammalian embryos cannot survive without the placenta. Development of the human placenta requires trophoblast proliferation, differentiation, and invasion as well as highly coordinated modulation of the maternal uterus. HtrA1 is a member of the recently identified mammalian HtrA (high temperature requirement factor A) serine protease family with a high level of expression in the placenta. In this study, we examined whether HtrA1 expression (mRNA and protein) is associated with placental development in the human. HtrA1 is up-regulated in both endometrial glands and decidual cells during endometrial preparation for embryo implantation and during first-trimester pregnancy at placentation. HtrA1 expression was also detected in certain trophoblast subtypes during early pregnancy. The villous syncytiotrophoblast and cytotrophoblast showed the strongest expression while the interstitial extravillous trophoblast showed the lowest or no expression of HtrA1. The distinct distribution of HtrA1 at the maternal-trophoblast interface suggests that HtrA1 may play a role in placental development.

Temporal expression profiling of the uterine luminal epithelium of the pseudo-pregnant mouse suggests receptivity to the fertilized egg is associated with complex transcriptional changes

BACKGROUND

The molecular basis of changes underlying the altered sensitivity of the uterine luminal epithelium (LE) to the embryo over the peri-implantation period is not fully understood.

METHODS

Microarray analysis was performed on purified LE isolated from the pseudo-pregnant mouse uterus at 12-h intervals from pre-receptivity through the implantation window to refractoriness. The aim was to identify genes whose expression changes in the LE during this period.

RESULTS

A total of 447 transcripts were identified whose abundance changed more than 2-fold in the LE but which did not change in the underlying stroma (S) and glands. Six major patterns of changing expression were noted. Of the 447 genes, 140 were expressed in LE at least 15-fold higher than in S and glandular epithelium (GE) (101 of these more than 20-fold). Detailed spatiotemporal expression profiles were derived for several genes previously implicated in implantation (including Edg7, Ptgs1, Pla2g4a and Alox15).

CONCLUSIONS

Functional changes in LE receptivity are characterized by changing constellations of gene expression. Pre-receptivity has a different molecular footprint to refractoriness. Because we have used the pseudo-pregnant mouse model, these changes are driven solely by endocrine signals rather than events downstream of embryo attachment. Some of these genes have been described in previous microarray studies on endometrium, but for the majority, this is the first time they have been implicated in implantation. The 140 genes enriched in the LE greatly expand the list of epithelial markers and provide many novel candidates for further studies to identify genes playing important roles in receptivity and embryo attachment.

Post-implantation mouse conceptuses produce paracrine signals that regulate the uterine endometrium undergoing decidualization

The uterus undergoes a series of dramatic changes in response to an implanting conceptus that, in some mammalian species, includes differentiation of the endometrial stroma into decidual tissue. This process, called decidualization, can be induced artificially in rodents indicating that the conceptus may not be essential for a proper maternal response in early pregnancy. In order to test this hypothesis, we determined if and how the conceptus affects uterine gene expression. We identified 5 genes (Angpt1, Angpt2, Dtprp, G1p2 and Prlpa) whose steady-state levels in the uterus undergoing decidualization depends on the presence of a conceptus. In situ hybridization revealed region-specific effects which suggested that various components of the conceptus and more than one signal from the conceptus are likely responsible for altering decidual cell function. Using cell culture models we found that trophoblast giant cells secrete a type I interferon-like molecule which can induce G1p2 expression in endometrial stromal cells. Finally, decidual Prlpa expression was reduced in the uterus adjacent to Hand1- and Ets2-deficient embryos, suggesting that normal trophoblast giant cells in the placenta are required for the conceptus-dependent effects on Prlpa expression in the mesometrial decidua. Overall, these results provide support for the hypothesis that molecular signals from the mouse conceptus have local effects on uterine gene expression during decidualization.

Sphingosine-1-Phosphate Receptor Expression and Signaling Correlate with Uterine Prostaglandin-Endoperoxide Synthase 2 Expression and Angiogenesis During Early Pregnancy1

Signaling mechanisms coordinating uterine angiogenesis and tissue remodeling during decidualization are not completely understood. Prostanoid signaling is thought to play a functionally important role in each of these events. In the present study, we demonstrate that the subfamily of G-protein-coupled receptors that binds and becomes activated by the terminal signaling lipid in the sphingolipid pathway, sphingosine-1-phosphate (S1P), were expressed during uterine decidualization. Three of the five known S1P receptors, termed endothelial differentiation genes (Edg; Edg1, Edg3, and Edg5) were upregulated in the uterine deciduum from Day of Pregnancy (DOP) 4.5 to 7.5, while Edg6 and Edg8 expression remained unchanged. Consistent with angiogenesis in general during decidualization, we believe EDG1 and EDG5 to be regulated by the embryo because no microvascular expression for these receptors was observed in oil-induced deciduomas. Observed expression of EDG1 and EDG5 showed a similar expression pattern to that previously reported for prostaglandin-endoperoxide synthase 2 (PTGS2), transitioning from the sublumenal stromal compartment in the antimesometrial pole (DOP 5) to the microvasculature of the mesometrial pole (DOP 7). Furthermore, these two receptors colocalized with PTGS2 at three additional sites at the maternal:fetal interface throughout pregnancy. Treatment of cultured predecidualized stromal cells with S1P resulted in upregulation of Ptgs2 mRNA and PTGS2 protein, but not the downstream enzyme prostacyclin synthase. These combined results suggest the existence of a link between the sphingolipid and prostanoid signaling pathways in uterine physiology, and that, based on their expression pattern, S1P receptors function to coordinate uterine mesometrial angiogenesis during the implantation phase of early gestation.

Collagen types I, III, and V constitute the thick collagen fibrils of the mouse decidua

A mammal's endometrium is deeply remodeled while receiving and implanting an embryo. In addition to cell proliferation and growth, endometrial remodeling also comprises synthesis and degradation of several molecular components of the extracellular matrix. All of these events are orchestrated by a precise sequence of ovarian hormones and influenced by several types of cytokines. As we have previously reported, an intriguing and rapid increase in collagen fibril diameter occurs in the decidualized areas of the endometrium, surrounding the implantation crypt, whereas collagen fibrils situated far from the embryo remain unchanged. Collagen fibrilogenesis is a complex molecular process coordinated by a number of factors, such as the types and amounts of glycosaminoglycans and proteoglycans associated with collagen molecules. Collagen genetic type, mechanical stress, aging, and other factors not yet identified also contribute to this development. A recent study suggests that thick fibrils from mouse decidua are formed, at least in part, by aggregation of thin fibrils existing in the stroma before the onset of decidualization. In the present ultrastructural study using single and double immunogold localization, we showed that both thin and thick collagen fibrils present in the mouse pregnant endometrium endometrium are heterotypic structures formed at least by type I, type III, and type V collagens. However, type V collagen predominates in the thick collagen fibrils, whereas it is almost absent of the thin collagen fibrils. The putative role of type V homotrimer in the rapid increase of the diameter of collagen fibrils of the mouse decidua is discussed.

Arrangement and fine structure of collagen fibrils in the decidualized mouse endometrium

The adaptations of the mouse uterus to pregnancy include extensive modifications of the cells and extracellular matrix of the endometrial connective tissue that surround the embryos. Around each implanted embryo this tissue redifferentiates into a transient structure called decidua, which is formed by polygonal cells joined by intercellular junctions. In the mouse, thick collagen fibrils with irregular profile appear in decidualized areas of the endometrium but not in the nondecidualized stroma and interimplantation sites. The fine organization of these thick fibrils has not yet been established. This work was addressed to understand the arrangement and fine structure of collagen fibrils of the decidua of pregnant mice during the periimplantation stage. Major modifications occurred in collagen fibrils that surrounded decidual cells: (1) the fibrils, which were arranged in parallel bundles in nonpregnant animals, became organized as baskets around decidual cells; (2) very thick collagen fibrils with very irregular profiles appeared around decidual cells. Analysis of replicas and serial sections suggests that the thick collagen fibrils form by the lateral aggregation of thinner fibrils to a central fibril resulting in very irregular profile observed in cross sections of thick fibrils. The sum of modifications of the collagen fibrils seem to represent an adaptation of the endometrium to better support the decidual cells while they hold the embryos during the beginning of their development. The deposition of thick collagen fibrils in the decidua may contribute to form a barrier that impedes leukocyte migration within the decidua, preventing immunological rejection of genetically dissimilar embryonic tissues.

Expression of nidogens in rat uterus and embryo during decidualization and implantation

The purpose of this study was to demonstrate the expression of nidogen-1 and nidogen-2 and their possible role in decidualization and implantation events during early pregnancy in rats. The tissue samples were examined from pregnant animals between gestational days 1-8 using immunocytochemistry. The uterine luminal epithelium, the glandular epithelium, and the myometrial smooth muscle cells stained strongly from gestational days 1-8 with both nidogen antibodies. At day 4 the decidual reaction areas began to appear in the stromal matrix and immunostaining of both nidogens revealed that the basement membrane of the surface epithelium was discontinuous. The differentiation of stromal cells into decidual cells was seen at gestational day 5 and both nidogens were weakly expressed in the decidualizing cells. At day 6, nidogen-2 immunoreactivity was higher in the primary decidual cells close to the embryo than nidogen-1, and during development of the decidual tissue both nidogens appeared in the endometrial stromal cells. At day 7, while expression of both nidogens declined in the primary decidual cells, their expression was markedly observed in the secondary decidual cells close to the myometrium. At day 8, expression of both nidogens was also observed to increase in the primary decidual cells. While nidogen-2 expression was seen in the parietal endoderm and primary ectoderm of the rat embryos at this developmental stage, nidogen-1 expression was only detected in the parietal endoderm. These results indicate that nidogen-1 and nidogen-2 could play important roles during embryogenesis, decidualization, and implantation in the endometrium of rat uterus.

Leukaemia inhibitory factor in implantation and uterine biology

Leukaemia inhibitory factor (LIF) is one of the most important cytokines in the reproductive tract. Without expression of LIF in the uterus, implantation of a blastocyst cannot begin. Yet, 13 years after publication of the phenotype of the LIF knockout mouse we are only just beginning to understand how LIF functions in the uterus. This review addresses our knowledge of the role of LIF in regulating implantation through its influence on the luminal epithelium and stromal decidualization, but also its influence on reproductive tract cells such as leukocytes and glandular epithelium, during the pre-implantation phase of pregnancy.

Expression and hormonal regulation of calcyclin-binding protein (CacyBP) in the mouse uterus during early pregnancy

Calcyclin-binding protein (Siah-1-Interacting Protein, CacyBP/SIP), is a calcium signaling protein involved in the degradation of beta-catenin, however, little is known about its role in reproductive biology. The present study was to character its temporospatial expression pattern and regulation in mouse uterus and to investigate whether it plays a role in the regulation of normal endometrial events. While prominently expressed in both luminal and glandular epithelia, CacyBP underwent dynamic changes during early pregnancy. CacyBP expression was observed weakly from days 1-4. An intense accumulation in luminal and glandular epithelia as well as decidua surrounding the embryo at later stages (days 5-7) was observed. Most notably, CacyBP accumulation in trophoblast was pronounced at day 7. Using ovariectomized and pseudopregnant mice, we found that progesterone (P(4)) and 17beta-estradiol (E(2)) led to increased expression of CacyBP gene and this could be abolished by Ru486 and tamoxifen, respectively. Antisense oligonucleotides (ODNs) against CacyBP significantly inhibited cultured endometrial stromal cells' (ESCs) apoptosis induced by UV irradiation. Injection of antisense ODNs into mouse uterine horn severely impaired the number of implanted blastocysts. Taken together, our results suggested that CacyBP expression was positively regulated by P(4) and E(2). CacyBP may be involved in the regulation of endometrial cell apoptosis during early pregnancy and play an important role in mouse endometrial events such as pregrancy establishment.

Interleukin-11 inhibits expression of insulin-like growth factor binding protein-5 mRNA in decidualizing human endometrial stromal cells

Differentiation of endometrial stromal cells into decidual cells is essential for successful embryo implantation. Interleukin (IL)-11 signalling is critical for normal decidualization in the mouse. The expression of IL-11 and its receptors during the menstrual cycle, and the effect of exogenous IL-11 on the decidualization of human endometrial stromal cells in vitro, suggests a role for this cytokine in human decidualization. As the downstream target genes of IL-11 are also likely to be critical mediators of this process, this study aimed to identify genes regulated by IL-11 in decidualizing human endometrial stromal cells in vitro. Stromal cells isolated from endometrial biopsies were decidualized with 17beta estradiol (E) and medroxyprogesterone acetate (EP) in the presence or absence of exogenous IL-11, and total RNA used for cDNA microarray analysis and real-time RT-PCR. Microarray analysis revealed 16 up-regulated and 11 down-regulated cDNAs in EP + IL-11-treated compared with EP-treated cells. The most down-regulated gene was insulin-like growth factor binding protein-5 (IGFBP-5) (3.6-fold). Using real-time RT-PCR, IL-11 was confirmed to decrease IGFBP-5 transcript abundance 102-fold (P = 0.016; n = 6). No difference in IGFBP-5 immunostaining intensity was detected in stromal cells decidualized in the presence or absence of IL-11, and there was no effect of exogenous IGFBP-5 on the progression of steroid-induced in vitro decidualization. Interactions between IL-11 and its target genes, including IGFBP-5, may contribute to the regulation of decidualization and/or mediate communication between the decidua and invading trophoblast at implantation.

Null Mutation of Krüppel-Like Factor9/Basic Transcription Element Binding Protein-1 Alters Peri-Implantation Uterine Development in Mice1

Female mice null for the basic transcription element binding protein-1 (Bteb1) gene have reduced numbers of implanting embryos. We hypothesized that the implantation defect, resulting in subfertility, is a consequence of developmental asynchrony between the embryo and uterine endometrium at peri-implantation. To address this, endometrium from wild-type (WT) and Bteb1(-/-) females at 0.5 to 5.5 days postcoitum (dpc) were evaluated for proliferation (BrdU labeling), apoptosis (TUNEL), and steroid hormone receptor expression (immunohistochemistry). Loss of BTEB1 did not affect serum estrogen (E) and progesterone (P) levels. In stroma (ST), the numbers of progesterone receptor (PGR) and HomeoboxA10 (HOXA10)-expressing cells were lower (3.5 and 4.5 dpc), while those of estrogen receptor-alpha (ESR1) were higher (3.5 dpc), with Bteb1 ablation. The peak of proliferation in luminal epithelium (LE), glandular epithelium (GE), and ST was delayed, while the apoptotic index in all cell types was increased (2.5 dpc) in Bteb1(-/-) relative to WT mice. The numbers of PGR-positive ST cells was negatively correlated with LE proliferation in WT mice; this correlation was lost in Bteb1(-/-) mice and was not observed before 2.5 dpc for both genotypes. Proliferation and apoptosis in all endometrial compartments, as well as the numbers of PGR-, HOXA10-, and ESR1-expressing ST cells, were lower in Bteb1(-/-) relative to WT mice after ovariectomy and E + P treatment. Results suggest that BTEB1, by regulating ST PGR expression and transactivation, participates in the paracrine control of LE proliferation by PGR and thus is important for establishment of a receptive uterus critical for successful implantation.

The effects of BIS-GMA and TEG-DMA on female mouse fertility

OBJECTIVES

The current study evaluated the effect of bisphenol A glycerolate dimethacrylate (BIS-GMA) and triethyleneglycol dimethacrylate (TEG-DMA) on female mouse fertility.

METHODS

Adult female mice were exposed to BIS-GMA or TEG-DMA (0, 25 and 100 microg/kg) intragastrically daily for 28 d and then mated with sexually mature untreated male mice and after mating their fertility was assessed.

RESULTS

In females exposed to BIS-GMA at both doses significant increases in the total number of resorptions out of the total number of implantations were observed, with a significant increase in the number of animals with resorptions at the higher dose. Significant reductions in body weights and significant increases in ovary weights were also observed. Exposure to TEG-DMA at a dose of 100 microg/kg resulted in significant reductions in pregnancy rates and a significant increase in the total number of embryonal resorptions. Significant reductions in body and uterine weights were also observed in females exposed to TEG-DMA.

SIGNIFICANCE

The results suggest that both BIS-GMA and TEG-DMA have reproductive toxic effects in female mice.

Synthesis and Structure−Activity Relationship of Novel 6-Aryl-1,4- dihydrobenzo[d][1,3]oxazine-2-thiones as Progesterone Receptor Modulators Leading to the Potent and Selective Nonsteroidal Progesterone Receptor Agonist Tanaproget

Tanaproget represents a potential first-in-class nonsteroidal PR agonist for contraception with improved safety and side effect profiles versus currently available steroidal oral contraceptives. Additional SAR, biological activity, and structural information from a tanaproget/hPR-LBD (hPR-LBD = human progesterone receptor ligand binding domain) cocrystal structure will also be presented.

Inhibition of Stat3 activation in the endometrium prevents implantation: a nonsteroidal approach to contraception

Activation of the receptors for leukemia inhibitory factor (LIF) and IL-11 is essential for embryo attachment and decidualization in mice. Both receptors induce activation of the Stat family of signal transducers via the Jak/Stat pathway. Here, we aimed to establish whether activation of Stat3 in maternal endometrium is essential for successful implantation. Functional blockade of Stat3 before implantation, by injection into the uterine lumen of a cell-permeable Stat3 peptide inhibitor, reduced embryo implantation specifically by 70% (P < 0.001). Stat3 is phosphorylated in the luminal epithelium (LE) in response to LIF, and this phosphorylation was significantly reduced both in vitro and in vivo by the Stat3 inhibitor. The inhibitor also blocked induction by LIF of several LIF-regulated genes in the LE including Irg1, which has been shown previously to be essential for implantation. Successful implantation is therefore dependent on phosphorylation and activation of Stat3 in the endometrium before implantation. This finding provides a target for contraceptive development, based on selective blockade of signal transduction pathways essential for implantation. This study demonstrates that cell-permeable peptide inhibitors can be used effectively to target intracellular signaling pathways in the uterine LE.

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.

Characterization of the uterine phenotype during the peri-implantation period for LIF-null, MF1 strain mice

Leukemia inhibitory factor plays a major role in the uterus and in its absence embryos fail to implant. Our knowledge of the targets for LIF and the consequences of its absence is still very incomplete. In this study, we have examined the ultrastructure of the potential implantation site in LIF-null MF1 female mice compared to that of wild type animals. We also compared expression of proteins associated with implantation in luminal epithelium and stroma. Luminal epithelial cells (LE) of null animals failed to develop apical pinopods, had increased glycocalyx, and retained a columnar shape during the peri-implantation period. Stromal cells of LIF-null animals showed no evidence of decidual giant cell formation even by day 6 of pregnancy. A number of proteins normally expressed in decidualizing stroma did not increase in abundance in the LIF-null animals including desmin, tenascin, Cox-2, bone morphogenetic protein (BMP)-2 and -7, and Hoxa-10. In wild type animals, the IL-6 family member Oncostatin M (OSM) was found to be transiently expressed in the luminal epithelium on late day 4 and then in the stroma at the attachment site on days 5-6 of pregnancy, with a similar but not identical pattern to that of Cox-2. In the LIF-null animals, no OSM protein was detected in either LE or stroma adjacent to the embryo, indicating that expression requires uterine LIF in addition to a blastocyst signal. Fucosylated epitopes: the H-type-1 antigen and those recognized by lectins from Ulex europaeus-1 and Tetragonolobus purpureus were enhanced on apical LE on day 4 of pregnancy. H-type-1 antigen remained higher on day 5, and was not reduced even by day 6 in contrast to wild type uterus. These data point to a profound disturbance of normal luminal epithelial and stromal differentiation during early pregnancy in LIF-nulls. On this background, we also obtained less than a Mendelian ratio of null offspring suggesting developmental failure.

Inhibiting Uterine PC6 Blocks Embryo Implantation: An Obligatory Role for a Proprotein Convertase in Fertility1

Successful embryo implantation involves complex interactions between the embryo and the uterus and is critical in establishing pregnancy. Proprotein convertase (PC) 6 (PC6) is one of the PC endoproteases regulating protein function through posttranslational activation of precursor proteins, including growth and differentiation factors. Here we show that PC6 protein is induced in the uterine stromal cells specifically at the site of embryo attachment during early pregnancy in mice. In vivo blocking of uterine production of PC6 protein using morpholino antisense oligonucleotides in mice resulted in total inhibition of implantation, revealing a vital role for PC6 in modulating the uterus for embryo implantation. Studies in primates (rhesus monkey and human) showed a dramatic upregulation of endometrial PC6 during the phase of uterine receptivity and at implantation, particularly during a critical uterine cell differentiation process termed decidualization. Thus, the current studies have demonstrated that PC6 is an essential molecule in modulating uterine function to support the establishment of embryo implantation. Interestingly, PC6 is one of the PCs identified to be important in processing the coat protein of HIV; inhibition of PCs has been suggested to be an effective approach to reduce HIV transmission. We therefore propose the novel concept that PC6 could be a potential nonhormonal target in the female reproductive tract for dual protection for women, both in preventing pregnancy and reducing HIV infection.

Serine protease HtrA1 is developmentally regulated in trophoblast and uterine decidual cells during placental formation in the mouse

Development of a hemochorial placenta involves trophoblast proliferation, differentiation, and invasion into the uterus to promote blood flow to the embryo. Trophoblast invasion is tightly controlled by expression of specific proteases in the trophoblast and highly coordinated activities in the uterus. One uterine event essential for placentation is the developmentally regulated formation and regression of the decidua. In mice, decidual regression takes place in a temporal- and spatial-specific manner that is coordinated with placental development. In this study, we identified that the serine protease HtrA1 (high temperature requirement factor A1) was specifically expressed in differentiated trophoblast cells, especially the giant cells, during the early stages of placental development. A high level of HtrA1 expression was also detected in decidua capsularis specifically at the decidual-trophoblast interface where active involution occurs. Thus, we have identified a previously unknown role for HtrA1 as a protease potentially important for trophoblast differentiation/invasion and uterine decidual regression during placental development.

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.

Expression and the biological activities of insulin-like growth factor-binding protein related protein 1 in rat uterus during the periimplantation period

IGF binding protein-related protein 1 (IGFBP-rP1) is highly expressed in the rat uterus around the time of implantation. In the present study, we determined the periimplantation localization of IGFBP-rP1 mRNA and assessed the effects of recombinant IGFBP-rP1 on the proliferative and prostacyclin (PGI(2))-producing abilities of cultured endometrial cells early in pregnancy. IGFBP-rP1 mRNA was detected at high levels in endometrial stromal cells close to the smooth muscle of interimplantation sites around the time of implantation but absent from decidual zones surrounding the embryo. Differential uterine IGFBP-rP1 expression was also recognized in the delayed implanting pregnant model, but the level of mRNA decreased as decidual tissues formed in the decidualization model. Recombinant IGFBP-rP1 inhibited the proliferation of endometrial stromal cells in vitro and arrested them in the G(1) phase of the cell cycle. Furthermore, IGFBP-rP1 significantly stimulated PGI(2) synthesis and cyclooxygenase II mRNA expression in myometrial cells, both of which are essential molecules for successful implantation. These data suggest that IGFBP-rP1 is an implantation-associated protein and that it modulates the proliferation of rat uterine cells and their production of PGI(2) during the periimplantation period.

Perlecan and Syndecan-4 in Uterine Tissues during the Early Pregnancy in Mice

PROBLEM

During early pregnancy in mice, there is recruitment of specific immune cells, remodeling of the endometrium, cell differentiation and synthesis of new molecules.

METHOD OF STUDY

Immunohistochemistry was used to determine the distribution of perlecan and syndecan-4 in the uteri before and after embryo implantation.

RESULTS

During pre-implantation, perlecan was identified in basement membranes and extracellular spaces of the endometrial stroma. In contrast, expression of syndecan-4 was quite weak. In the peri-implantation period, perlecan remained in the basement membranes, and it was no longer observed in the stroma and it was identified in the embryonic cells. On day 4 of pregnancy, syndecan-4 increased in the fibroblasts of the subepithelial stroma. After implantation, syndecan-4 was pronounced in pre-decidual and mature decidual cells.

CONCLUSIONS

The coordinate balance between the pre- and post-implantation periods suggests a role of these two molecules in the adaptive modification of the uterine microenvironment to receive and implant the embryo.

Expression analysis of the entire MMP and TIMP gene families during mouse tissue development

Matrix metalloproteinases (MMPs) and adamalysins (ADAMs) cleave many extracellular proteins, including matrix, growth factors, and receptors. We profiled the RNA levels of every MMP, several ADAMs, and inhibitors of metalloproteinases (TIMPs and RECK) in numerous mouse tissues during development and in the uterus during pregnancy. Observations include: most secreted MMPs are expressed at low to undetectable levels in tissues, whereas membrane-bound MMPs, ADAMs and inhibitors are abundant; almost every proteinase and inhibitor is present in the uterus or placenta at some time during gestation; the mouse collagenases mColA and mColB are found exclusively in the uterus and testis; and each tissue has its unique signature of proteinase and inhibitor expression.

Expression of Smad2 and Smad4, transforming growth factor-beta signal transducers in rat endometrium during the estrous cycle, pre-, and peri-implantation

SMADs are intracellular signaling molecules that transmit signals elicited by members of transforming growth factor-beta (TGF-beta) superfamily. To decipher the mechanism of TGF-beta signaling during the estrous cycle and implantation, we performed in situ hybridization to investigate the expression patterns of mRNAs for Smad2 and Smad4 in rat endometrium during the estrous cycle and on Days 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 of pregnancy. Intense epithelial expression of Smad2 mRNA at diestrus and proestrus was reduced at estrus and metaestrus, while Smad4 maintained its constitutive expression during the estrous cycle. During pre-implantation, both Smads were accumulated in the luminal epithelium and the glandular epithelium. Contrary to the dramatic Smad4 expression, Smad2 was highly down-regulated on Day 2.5 and was increased on Day 3.5. During peri-implantation, both Smads were expressed in the luminal epithelium, subepithelial stroma, and the primary decidual zone. Smad4 was down-modulated on Day 5.5. These results suggest that (a) both Smads are involved in the tissue remodeling of cycling and pregnant rat uteri; (b) TGF-beta signaling functions mainly in the epithelium during pre-implantation and Smad2 is involved in the endometrial switch from the neutral phase to the receptive phase; (c) TGF-beta signaling is down-regulated at the time when trophoblast invasion begins and both Smads are involved in the formation of the primary decidual zone.

Osteopontin: roles in implantation and placentation

Osteopontin (OPN) is an acidic member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of extracellular matrix proteins/cytokines that undergoes extensive posttranslational modification, including phosphorylation, glycosylation, and cleavage, yielding molecular mass variants ranging in size from 25 to 75 kDa. The result is a versatile protein(s) with multiple functions arising from its role as a mediator of cell-cell and cell-extracellular matrix (ECM) communication that encompass both normal and tumorigenic developmental processes, immunological responses during inflammation and wound healing, and biomineralization. Studies in primates, pigs, sheep, and rodents have revealed that OPN is a major constituent of the uterine-placental microenvironment with influence as 1) a component of histotroph required for adhesion and signal transduction at the uterine-placental interface throughout pregnancy, 2) a gene product expressed by uterine stroma contributing to a decidualization-like transformation that correlates with the degree of conceptus invasiveness, and 3) a product of resident uterine and placental immune cells that may regulate their behavior and cytokine production. This minireview summarizes information regarding uterine and placental expression of OPN that has accumulated over the past 15 yr, and we briefly describe structural/functional properties of this protein that are likely relevant to its role(s) during pregnancy. Comparative studies have offered insights into the potential hormonal/cytokine, cellular, and molecular mechanisms underlying OPN-mediated adhesion, remodeling, and cell-cell/cell-ECM communication within the uterus and placenta. OPN has the potential to profoundly impact pregnancy, and investigators are now challenged to focus on the mechanistic nature of the functions of this multifaceted and major component of the uterine-placental microenvironment.

A functional overlap of plasminogen and MMPs regulates vascularization during placental development

Both plasminogen activators and matrix metalloproteinases (MMPs) have been implicated in a variety of developmental processes in the mouse during embryo implantation and placentation. We show here that pharmacological treatment of plasminogen-deficient mice with the broad spectrum MMP inhibitor galardin leads to a high rate of embryonic lethality. Implantation sites from plasminogen-deficient galardin-treated mice at 7.5 days post coitus (dpc) showed delay in both decidualization and invasion of maternal vessels into the decidua. At 8.5 dpc, half of the embryos were runted and still at the developmental stage of a 7.5 dpc embryo. Most embryos that escaped these initial defects eventually died, probably from defective vascularization and development of the labyrinth layer of the placenta, although a direct role on embryo development cannot be ruled out. These results demonstrate that the combination of MMPs and plasminogen is essential for the proper development of the placenta. Plasminogen deficiency alone and galardin treatment alone had much less effect and there was a pronounced synergism on both placental vascularization and embryonic lethality, indicating a functional overlap between plasminogen and MMPs.

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.

Distribution of versican and hyaluronan in the mouse uterus during decidualization

Preparation for embryo implantation requires extensive adaptation of the uterine microenvironment. This process consists of cell proliferation and cell differentiation resulting in the transformation of endometrial fibroblasts into a new type of cell called decidual cell. In the present study, we followed the space-time distribution of versican and hyaluronan (HA) in different tissues of the uterus before and after embryo implantation. Fragments of mouse uteri obtained on the fourth, fifth, sixth and seventh days of pregnancy were fixed in Methacarn, embedded in Paraplast and cut into 5-microm thick sections. HA was detected using a biotinylated fragment of the proteoglycan aggrecan, which binds to this glycosaminoglycan with high affinity and specificity. Versican was detected by a polyclonal antibody. Both reactions were developed by peroxidase methods. Before embryo implantation, both HA and versican were present in the endometrial stroma. However, after embryo implantation, HA disappeared from the decidual region immediately surrounding the implantation chamber, whereas versican accumulated in the same region. The differences observed in the expression of HA and versican suggest that both molecules may participate in the process of endometrial decidualization and/or embryo implantation.

Estradiol receptor binding to the epithelium of uterine lumen and glands: region- and time-related changes during preimplantation and periimplantation periods studied by autoradiography

The presence and changes of estradiol nuclear binding and related functions in uterine luminal and glandular epithelium were studied before and after blastocyst implantation using receptor autoradiography with (3)H-estradiol-17beta in association with (3)H-thymidine incorporation and immunocytochemical binding of antibody to estrogen receptor ER-alpha. (3)H-estradiol nuclear binding is present but variable during days 1.5-7.5 of pregnancy. Sites of strong nuclear binding of (3)H-estradiol exhibit strong immunocytochemical staining with ER-alpha antibody. Qualitative and quantitative evaluation of autoradiograms reveal that there is a general increase of nuclear (3)H-estradiol binding during the first 3 days after fertilization in both luminal and glandular epithelium. The binding of estradiol is stronger in glandular epithelium from day 2.5 to day 7.5, paralleled by a rise in (3)H-thymidine incorporation on day 2.5. By comparison, in the epithelium of the uterine lumen (3)H-estradiol nuclear binding is low, but relatively high in epithelial cells at lateral branching of the lumen where the increase in (3)H-estradiol binding corresponds to an increased labeling index with (3)H-thymidine. A highly differentiated binding of (3)H-estradiol to luminal and glandular epithelium was demonstrated with region- and time-specific changes of related effects on cell proliferation, differentiation, and secretion, probably involving involution and remodeling. The strong (3)H-estradiol binding to glandular epithelium suggests that estradiol exerts pronounced effects on glandular activities in the periimplantation period.

Enhanced expression of uterine stathmin during the process of implantation and decidualization in rats

We used the library subtraction technique to identify genes specifically expressed in the rat uterus during early pregnancy. One such gene was that for stathmin, a factor that is associated with tubulin binding and the destabilization of microtubules. Stathmin was expressed at higher levels in implantation sites than in interimplantation sites on d 6 and 7 of pregnancy; the levels on d 6 and 7 were higher in implantation sites than in the entire uterus on d 3-5 of pregnancy or in nonpregnant uteri. Intense expression of stathmin mRNA was primarily limited to the subluminal stromal cells at the implantation site. Expression was also detected in the decidual zones and was accentuated during the period of decidualization (d 7-12). In the delayed implantation pregnant rat model, uterine stathmin expression was low, but increased after implantation induced by administration of 17beta-estradiol to the progesterone-primed animal. Further, decidualization in the pseudopregnant rat, induced by intrauterine infusion of oil, enhanced stathmin expression. Stathmin expression clearly increases in the uterus when stimulated by embryo implantation and decidualization and may play a role in the early stages of pregnancy.