Differential uterine expression of estrogen and progesterone receptors correlates with uterine preparation for implantation and decidualization in the mouse

Identification of Genes Regulated by Leukemia-Inhibitory Factor in the Mouse Uterus at the Time of Implantation

The endometrium is prepared for implantation by the actions of estradiol (E2) and progesterone (P4). In mice the luminal epithelium (LE) only becomes fully receptive to the attaching blastocyst in response to the nidatory estrogen surge on d 4 of pregnancy. The cytokine leukemia-inhibitory factor (LIF) is rapidly induced by nidatory estrogen and has been shown to be the primary mediator of its action. Implantation fails in the absence of LIF, and injection of LIF on d 4 of pregnancy can substitute for the nidatory estrogen. In this study, we sought to identify genes regulated by LIF in the uterine epithelium. We used oligonucleotide microarrays to compare the transcript profiles of paired uterine horns from LIF-deficient MF1 mice after intraluminal injection of LIF or PBS on d 4 of pseudopregnancy. IGF-binding protein 3 was identified as a gene up-regulated by LIF; this was confirmed by RT-PCR. In situ hybridization showed that the primary site of IGF-binding protein 3 expression is the luminal epithelium (LE), the known site of LIF action in the uterus. We identified two other genes: amphiregulin and immune response gene-1, the expression of which were also up-regulated by LIF. Immune response gene 1 has recently been shown to be essential for implantation. Expression of all three of these genes in the LE is known to be regulated by P4. The expression of osteoblast-specific factor 2 and leukocyte 12/15 lipoxygenase, which are also expressed in LE under the control of P4, were not increased by LIF. This suggests that one of the actions of LIF on LE may be to enhance the expression of a subset of P4-regulated genes.

Conceptus signals for establishment and maintenance of pregnancy

Establishment and maintenance of pregnancy results from signaling by the conceptus (embryo/fetus and associated extraembryonic membranes) and requires progesterone produced by the corpus luteum (CL). In most mammals, hormones produced by the trophoblast maintain progesterone production by acting directly or indirectly to maintain the CL. In domestic animals (ruminants and pigs), hormones from the trophoblast are antiluteolytic in that they act on the endometrium to prevent uterine release of luteolytic prostaglandin F2 alpha (PGF). In cyclic and pregnant sheep, progesterone negatively autoregulates expression of the progesterone receptor (PR) gene in the endometrial luminal (LE) and superficial glandular epithelium (GE). Available evidence in cyclic sheep indicates that loss of the PR is closely followed by increases in epithelial estrogen receptors (ER) and then oxytocin receptors (OTR), allowing oxytocin to induce uterine release of luteolytic PGF pulses. In pregnant sheep, the conceptus trophoblast produces interferon tau (IFN tau) that acts on the endometrium to inhibit transcription of the ER alpha gene directly and the OTR gene indirectly to abrogate development of the endometrial luteolytic mechanism. Subsequently, sequential, overlapping actions of progesterone, IFN tau, placental lactogen (PL) and growth hormone (GH) comprise a hormonal servomechanism that regulates endometrial gland morphogenesis and terminal differentiated function to maintain pregnancy in sheep. In pigs, the conceptus trophoblast produces estrogen that alters the direction of PGF secretion from an endocrine to exocrine direction, thereby sequestering luteolytic PGF within the uterine lumen. Conceptus estrogen also increases expression of fibroblast growth factor 7 (FGF-7) in the endometrial LE that, in turn, stimulates proliferation and differentiated functions of the trophectoderm, which expresses the FGF-7 receptor. Strategic manipulation of these physiological mechanisms can offer therapeutic schemes to improve uterine capacity, conceptus survival and reproductive health.

Subfertility, Uterine Hypoplasia, and Partial Progesterone Resistance in Mice Lacking the Krüppel-like Factor 9/Basic Transcription Element-binding Protein-1 (Bteb1) Gene

Progesterone receptor (PR), a ligand-activated transcription factor, is a key regulator of cellular proliferation and differentiation in reproductive tissues. The transcriptional activity of PR is influenced by co-regulatory proteins typically expressed in a tissue- and cell-specific fashion. We previously demonstrated that basic transcription element-binding protein-1 (BTEB1), a member of the Sp/Krüppel-like family of transcription factors, functionally interacts with the two PR isoforms, PR-A and PR-B, to mediate progestin sensitivity of target genes in endometrial epithelial cells in vitro. Here we report that ablation of the Bteb1 gene in female mice results in uterine hypoplasia, reduced litter size, and increased incidence of neonatal deaths in offspring. The reduced litter size is solely a maternal genotype effect and results from fewer numbers of implantation sites, rather than defects in ovulation. In the early pregnant uterus, Bteb1 expression in stromal cells temporally coincides with PR-A isoform-dependent decidual formation at the time of implantation. Expression of two implantation-specific genes, Hoxa10 and cyclin D3, was decreased in uteri of early pregnant Bteb1-null mutants, whereas that of Bteb3, a related family member, was increased, the latter possibly compensating for the loss of Bteb1. Progesterone responsiveness of several uterine genes was altered with Bteb1-null mutation. These results identify Bteb1 as a functionally relevant PR-interacting protein and suggest its selective modulation of cellular processes that are regulated by PR-A in the uterine stroma.

Progesterone and Placental Hormone Actions on the Uterus: Insights from Domestic Animals1

Progesterone is unequivocally required for maternal support of conceptus (embryo/fetus and associated extraembryonic membranes) survival and development. In cyclic sheep, progesterone is paradoxically involved in suppressing and then initiating development of the endometrial luteolytic mechanism. In cyclic and pregnant sheep, progesterone negatively autoregulates progesterone receptor (PR) gene expression in the endometrial luminal (LE) and superficial glandular epithelium (GE). In cyclic sheep, PR loss is closely followed by increases in epithelial estrogen receptor (ERalpha) and then oxytocin receptor (OTR), allowing oxytocin to induce uterine release of luteolytic prostaglandin F2alpha pulses. In pregnant sheep, the conceptus produces interferon tau (IFNtau) that acts on the endometrium to inhibit transcription of the ERalpha gene and thus development of the endometrial luteolytic mechanism. After Day 13 of pregnancy, the endometrial epithelia do not express the PR, whereas the stroma and myometrium remain PR positive. The absence of PR in the endometrial GE is required for onset of differentiated function of the glands during pregnancy. The sequential, overlapping actions of progesterone, IFNtau, placental lactogen (PL), and growth hormone (GH) comprise a hormonal servomechanism that regulates endometrial gland morphogenesis and terminal differentiated function during gestation. In pigs, estrogen, the pregnancy-recognition signal, increases fibroblast growth factor 7 (FGF-7) expression in the endometrial LE that, in turn, stimulates proliferation and differentiated functions of the trophectoderm, which expresses the receptor for FGF-7. Strategic manipulation of these physiological mechanisms may offer therapeutic schemes to improve uterine capacity, conceptus survival, and reproductive health of domestic animals and humans.

Molecular cues to implantation

Successful implantation is the result of reciprocal interactions between the implantation-competent blastocyst and receptive uterus. Although various cellular aspects and molecular pathways of this dialogue have been identified, a comprehensive understanding of the implantation process is still missing. The receptive state of the uterus, which lasts for a limited period, is defined as the time when the uterine environment is conducive to blastocyst acceptance and implantation. A better understanding of the molecular signals that regulate uterine receptivity and implantation competency of the blastocyst is of clinical relevance because unraveling the nature of these signals may lead to strategies to correct implantation failure and improve pregnancy rates. Gene expression studies and genetically engineered mouse models have provided valuable clues to the implantation process with respect to specific growth factors, cytokines, lipid mediators, adhesion molecules, and transcription factors. However, a staggering amount of information from microarray experiments is also being generated at a rapid pace. If properly annotated and explored, this information will expand our knowledge regarding yet-to-be-identified unique, complementary, and/or redundant molecular pathways in implantation. It is hoped that the forthcoming information will generate new ideas and concepts for a process that is essential for maintaining procreation and solving major reproductive health issues in women.

Fluctuations of fatty acid amide hydrolase and anandamide levels during the human ovulatory cycle

Implantation is possible within a defined period of the menstrual cycle, referred to as the 'implantation window'. It is during this critical period that proper dialog can be established between the blastocyst and a receptive endometrium. If for any reason this dialog is not established or is altered, the embryo is aborted. The factors responsible for the interaction between the embryo and the mother at the moment of implantation remain poorly understood. Recent studies indicate that endocannabinoids may contribute to the development of an adequate milieu at the implantation site. Here we show that the levels of anandamide and of its degrading enzyme, the fatty acid amide hydrolase, in peripheral lymphocytes undergo specific variations during the various phases of the human ovulatory cycle. In particular, we found the highest levels of fatty acid amide hydrolase activity and protein content, paralleled by the lowest anandamide concentrations, in the period that temporally coincides with the putative window of implantation in humans. On the other hand, the anandamide-synthesizing phospholipase D, the anandamide membrane transporter and the anandamide-binding cannabinoid receptors of lymphocytes did not change during the menstrual cycle. This study indicates that high fatty acid amide hydrolase activity and low anandamide levels may be among the factors that co-operate in the success of implantation. This would add to our understanding of the pathophysiological and therapeutic implications of the endocannabinoid system in human fertility.

HB-EGF directs stromal cell polyploidy and decidualization via cyclin D3 during implantation

Stromal cell polyploidy is a unique phenomenon that occurs during uterine decidualization following embryo implantation, although the developmental mechanism still remains elusive. The general consensus is that the aberrant expression and altered functional activity of cell cycle regulatory molecules at two particular checkpoints G1 to S and G2 to M in the cell cycle play an important role in the development of cellular polyploidy. Despite the compelling evidence of intrinsic cell cycle alteration, it has been implicated that the development of cellular polyploidy may be controlled by specific actions of extracellular growth regulators. Here we show a novel role for heparin-binding EGF-like growth factor (HB-EGF) in the developmental process of stromal cell polyploidy in mice. HB-EGF, which is one of the earliest known molecular mediators of implantation in mice and humans, promotes stromal cell polyploidy via upregulation of cyclin D3. Adenoviral delivery of antisense cyclin D3 attenuates cyclin D3 expression and abrogates HB-EGF-induced stromal cell polyploidy in vitro and in vivo. Collectively, the results demonstrate that the regulation of stromal cell polyploidy and decidualization induced by HB-EGF depend on cyclin D3 induction.

Differential Expression of Genes in the Endometrium at Implantation: Upregulation of a Novel Member of the E2 Class of Ubiquitin-Conjugating Enzymes1

The process of embryo attachment and implantation is accompanied by dramatic cellular and functional changes in the endometrium, the control and mechanisms of which are not clearly understood. The cDNA cloning of differentially expressed genes, specifically at implantation sites in the rabbit endometrium, was used to identify genes controlling functional and remodeling changes. Tissue from the endometrium of Day 6(3/4) (preimplantation) and Day 8 (implantation initiation) pregnant rabbits was used to screen for differentially expressed genes by combined cDNA subtraction/suppressive hybridization. Twenty-nine differentially expressed genes were identified encoding protein modification enzymes, signaling proteins, structural proteins, and enzymes. One of these is a novel member of the E2 ubiquitin-conjugating enzyme family we have designated UBCi (i for implantation), which displayed dramatic nucleotide and deduced amino acid sequence conservation between rabbits, humans, and mice. In situ hybridization indicated UBCi expression exclusively in the luminal epithelium of the endometrium while glandular epithelium, trophoblast, and myometrium were negative. Expression was specific for epithelial cells at implantation sites and was not detected in non-implant-site endometrium. UBCi mRNA was detected in both the mesometrial and antimesometrial epithelial cells of the implantation sites, sites undergoing both differentiation and/or apoptosis. These results identify a group of differentially expressed genes in the endometrium including UBCi and provide new focal targets for studying processes controlling cellular remodeling during implantation. The important roles of ubiquitination in controlling the activities and turnover of key signaling proteins suggest potential roles in controlling critical aspects of implantation.

Expression of neuropeptide Y is increased in murine endometrial epithelium during the peri-implantation period under regulation by sex steroids

Oligopeptide hormones are involved in cell–cell interaction during embryonal implantation and neuropeptide Y (NPY) is expressed in the human placenta and decidual cells in the third trimester of pregnancy. However, there is no report regarding the intrauterine localisation and the functions of NPY during the peri-implantation period. In the present study, the spatiotemporal changes in NPY expression in the murine uterus during the peri-implantation period were investigated using reverse transcription–polymerase chain reaction (RT-PCR), quantitative RT-PCR and immunohistochemical techniques, as were the effects of sex steroids on NPY mRNA expression in primary cultured murine uterine epithelial cells. Neuropeptide Y mRNA was increased in the pregnant murine uterus, as well as in the pseudopregnant murine uterus, during the peri-implantation period. Immunohistochemical analysis revealed increases in NPY expression in luminal and glandular epithelial cells and decidualised stromal cells. Neuropeptide Y mRNA expression was strongly induced in cultured epithelial cells in response to sex steroids. The data suggest that NPY is involved in cell–cell interactions during embryonic implantation.

Estrogen induces a systemic growth factor through an estrogen receptor-alpha-dependent mechanism

Estrogen induces proliferation of uterine epithelium through a paracrine action of estrogen receptor (ERalpha) in the underlying stroma. In ovariectomized mice primed with progesterone, estrogen stimulates proliferation in both the epithelium and the stroma. We set out to test whether a paracrine mode of action is involved in estrogen-induced proliferation of the uterine stroma. Epithelial and mesenchymal tissues derived from uteri of neonatal ERalpha null mice (ERalphaKO) or wild-type mice were separated and recombined in all four possible configurations (ERalpha+ or ERalpha- epithelium with ERalpha+ or ERalpha- mesenchyme) and grafted into female athymic mice. After 5 wk, hosts were ovariectomized and challenged with hormone treatment, and cellular proliferation was monitored by thymidine autoradiography. Results showed that, although the full response of the epithelium was dependent on an ERalpha-positive mesenchyme, stromal cell proliferation was independent of tissue ERalpha. This latter observation suggests that the response of the stroma was due to a systemic factor induced in the ERalpha-positive hosts. To test this possibility, pieces of whole uterus from neonatal wild-type or ERalphaKO mice were grafted into syngeneic wild-type or ERalphaKO hosts. In these whole-uterus grafts, estradiol stimulated ERalphaKO uterine stroma when they were grown in wild-type hosts but not when grown in ERalphaKO hosts. The epithelium of whole-uterus ERalphaKO grafts did not respond to estrogen, regardless of the host phenotype. These observations suggest that treatment of progesterone-primed mice with estradiol stimulates production of a systemic factor that is capable of inducing uterine stromal cell proliferation and that this systemic factor is produced by an ERalpha-dependent mechanism.

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.

Emerging roles for hedgehog-patched-Gli signal transduction in reproduction

Hedgehog (Hh) proteins are expressed during vertebrate development in some tissues with inductive properties and at epithelial-mesenchymal boundaries in several developing organs, including the lung, gut, hair follicle, and tooth. The Hh signaling pathway is highly conserved, and important clues to understanding the mechanism of Hh signal transduction in vertebrates have come from studies in Drosophila. In recent years, Hh signaling has been recognized during embryonic development and in some cases during postnatal life in several mammalian tissues whose functions are essential for reproduction, including the gonads, uterus, and hormonally responsive accessory sex glands such as the prostate and mammary gland. The role of the pathway in these tissues is highly reminiscent of its role at epithelial-mesenchymal-stromal boundaries in other organ systems, which has provided a framework within which to explore Hh signaling in tissues that function in reproduction. Some features unique to these tissues are emerging, including a role in proliferation and differentiation of male germline cells in mammals and apparent influences of sex steroids on Hh signaling. However, many questions remain about the function of Hh signaling in the gonads, uterus, prostate, and mammary gland, including factors regulating the signal transduction pathway, identification of downstream target genes, and roles for Hh signaling in diseases involving these tissues.

Selective interactions of Kruppel-like factor 9/basic transcription element-binding protein with progesterone receptor isoforms A and B determine transcriptional activity of progesterone-responsive genes in endometrial epithelial cells

The Sp/KLF transcription factor basic transcription element-binding protein (BTEB1) regulates gene transcription by binding to GC-rich sequence motifs present in the promoters of numerous tissue-specific as well as housekeeping genes. Similar to other members of this family, BTEB1 can act as a transactivator or transrepressor depending on cell and promoter context, although the molecular mechanism underlying these distinct activities remains unclear. Here we report that BTEB1 can mediate signaling pathways involving the nuclear receptor for the steroid hormone progesterone in endometrial epithelial cells by its selective interaction with the progesterone receptor (PR) isoforms, PR-A and PR-B. Functional interaction with ligand-activated PR-B resulted in superactivation of PR-B transactivity, facilitated the recruitment of the transcriptional integrator CREB-binding protein within the PR-dimer, and was dependent on the structure of the ligand bound by PR-B. By contrast, BTEB1 did not influence agonist-bound PR-A transactivity, although it augmented PR-A inhibition of PR-B-mediated transactivation as well as potentiated ligand-independent PR-A transcriptional activity in the presence of CREB-binding protein. We also demonstrate similar positive modulatory actions of BTEB1-related family members Krüppel-like family (KLF) 13/FKLF2/BTEB3 and Sp1 on PR-B transactivity. Further, we provide support for the potential significance of the selective functional interactions of PR isoforms with BTEB1 in the peri-implantation uterus using mouse and pig models and in the breast cancer cell lines MCF-7 and T47D. Our results suggest a novel mechanism for the divergent physiological consequences of PR-A and PR-B on progesterone-dependent gene transcription in the uterus involving select KLF members.

Decysin, a new member of the metalloproteinase family, is regulated by prolactin and steroids during mouse pregnancy

More than 300 separated actions have been attributed to prolactin (PRL), which could be correlated to the quasi-ubiquitous distribution of its receptor. Null mutation of the PRL receptor (PRLR) gene leads to female sterility caused by a failure of embryo implantation. Using the PRLR knockout mouse model and the mRNA differential display method, among 45 isolated genes, we identified UA+4 as a PRL and steroids-target gene during the peri-implantation period that encodes the decysin. Hormonally regulated in the uterus during pregnancy, this new member of disintegrin metalloproteinase is present in the uterus at the site of blastocyst apposition in nondifferentiated stromal cells at the antimesometrial pole and, interestingly, is colocalized with the PRLR. At midpregnancy, decysin expression persists specifically at the foeto-maternal junction around vessels. Although it has been previously suggested that decysin expression is related to immune function, its function during pregnancy remains to be clearly established.

Regulated expression of osteopontin in the peri-implantation rabbit uterus

Blastocyst attachment to the lining of the mammalian uterus during early implantation involves the initial apposition of the trophoblast to the uterine epithelial surface. Osteopontin (OPN) is a glycoprotein component of the extracellular matrix that is secreted by the glandular epithelium of mammalian uteri at the time of implantation. This protein is recognized by several members of the integrin family and promotes cell-cell attachment and adhesion. In the present study, rabbit uteri were examined using Northern and in situ hybridization to evaluate the temporal and spatial distribution of OPN mRNA during early pregnancy. Northern blot analysis demonstrated a dramatic increase in OPN expression on Days 4-7 of pregnancy, corresponding to the rise in circulating progesterone and the time of initial embryo attachment in this species. In situ hybridization analysis revealed OPN mRNA expression on Day 6.75 of pregnancy, which was most prominent on endometrial epithelium. Using immunofluorescence, OPN protein was present on the glandular epithelium on Day 6.75 of pregnancy, but was absent on blastocysts. Further, no expression of OPN mRNA or protein was found in the nonpregnant endometrium. Induction of endometrial OPN expression was observed in unmated rabbits treated with progesterone alone and was prevented by cotreatment with the antiprogestin ZK137.316. Estradiol-17beta had no effect on OPN expression by itself, and estrogen priming was not necessary to demonstrate the stimulatory effect of progesterone. In The rabbit uterus, as in other mammalian species studied, OPN is expressed in a stage-specific manner by the endometrial glands during the peri-implantation period and is regulated by progesterone.

Expression of hypoxia-inducible factors in the peri-implantation mouse uterus is regulated in a cell-specific and ovarian steroid hormone-dependent manner. Evidence for differential function of HIFs during early pregnancy

Increased uterine vascular permeability and angiogenesis are hallmarks of implantation and placentation. These events are profoundly influenced by vascular endothelial growth factor (VEGF). We previously showed that VEGF isoforms and VEGF receptors are expressed in the uterus, suggesting the role of VEGF in uterine vascular permeability and angiogenesis required for implantation and decidualization. We have recently shown that estrogen promotes uterine vascular permeability but inhibits angiogenesis, whereas progesterone stimulates angiogenesis with little effect on vascular permeability. However, the mechanism of differential steroid hormonal regulation of uterine angiogenesis remains unresolved. Oxygen homeostasis is essential for cell survival and is primarily mediated by hypoxia-inducible factors (HIFs). These factors are intimately associated with vascular events and induce VEGF expression by binding to the hypoxia response element in the VEGF promoter. HIFalpha isoforms function by forming heterodimers with the aryl hydrocarbon nuclear translocator (ARNT) (HIF-beta) family members. There is very limited information on the relationship among HIFs, ARNTs, and VEGF in the uterus during early pregnancy, although the role of HIFs in regulating VEGF and angiogenesis in cancers is well documented. Using molecular and physiological approaches, we here show that uterine expression of HIFs and ARNTs does not correlate with VEGF expression during the preimplantation period (days 1-4) in mice. In contrast, their expression follows the localization of uterine VEGF expression with increasing angiogenesis during the postimplantation period (days 5-8). This disparate pattern of uterine HIFs, ARNTs, and VEGF expression on days 1-4 of pregnancy suggests HIFs have multiple roles in addition to the regulation of angiogenesis during the peri-implantation period. Using pharmacological, molecular, and genetic approaches, we also observed that although progesterone primarily up-regulates uterine HIF-1alpha expression, estrogen transiently stimulates that of HIF-2alpha.

A genomic approach to identify novel progesterone receptor regulated pathways in the uterus during implantation

The cellular actions of steroid hormone progesterone (P) are mediated via its nuclear receptors, which regulate the expression of specific target genes. The identity of gene networks that are regulated by the P receptors (PRs) in the uterus at various stages of the reproductive cycle and pregnancy, however, remain largely unknown. In this study, we have used oligonucleotide microarrays to identify mRNAs whose expression in the pregnant mouse uterus is modulated by RU486, a well-characterized PR antagonist, which is also an effective inhibitor of implantation. We found that, in response to RU486, expression of mRNAs corresponding to 78 known genes was down-regulated at least 2-fold in the preimplantation mouse uterus. The PR regulation of several of these genes was ascertained by administering P to ovariectomized wild-type and PR knockout (PRKO) mice. Detailed spatio-temporal analysis of these genes in the pregnant uterus indicated that their expression in the epithelium and stroma could be correlated with the expression of PR in those cell types. Furthermore, time-course studies suggested that many of these genes are likely primary targets of PR regulation. We also identified 70 known genes that were up-regulated at least 2-fold in the pregnant uterus in response to RU486. Interestingly, initial examination of a number of RU486-inducible genes reveals that their uterine expression is also regulated by estrogen. The identification of several novel PR-regulated gene pathways in the reproductive tract is an important step toward understanding how P regulates the physiological events leading to implantation.

Identification of Indian hedgehog as a progesterone-responsive gene in the murine uterus

Progesterone (P4) plays a central role in normal uterine function, from embryo implantation in endometrium to establishment and maintenance of uterine quiescence during pregnancy in the myometrium. Considering its diverse physiological effects on female reproductive function, rather little is known about downstream events of P4 action. Recent progress in differential screening technologies facilitated identification of such inducible genes. We used uteri of wild-type and progesterone receptor null mutant mice as a starting material and screened for differentially expressed genes by medium-density cDNA expression array. Here, we report that the expression of the morphogen, Indian hedgehog (Ihh), is rapidly stimulated by P4 in the mouse uterus. The level of Ihh mRNA is induced within 3 h, after a single administration of P4 to ovariectomized mice. The induced Ihh mRNA and protein were localized to the luminal and glandular epithelial compartment of the endometrium. During pseudopregnancy, the Ihh mRNA level was transiently increased in the preimplantation period and d 3 and d 4 post coitum and then decreased rapidly at d 5 post coitum. Furthermore, the expression profile of patched-1, hedgehog interacting protein-1, and chicken ovalbumin upstream promoter-transcription factor II, genes known to be in the hedgehog signaling pathway in other tissues, followed the expression pattern of Ihh during the periimplantation period. Our results suggested that Ihh is regulated by P4, and the Ihh signaling axis may play a role in the preparation of the uterus for implantation during the periimplantation period.

Steroid receptor coactivator expression throughout the menstrual cycle in normal and abnormal endometrium

The endometrium of reproductive aged women undergoes cyclic developmental changes in preparation for implantation in response to estrogen and progesterone. These steroids and their receptors are tightly regulated throughout the menstrual cycle, and their actions are facilitated by the presence of steroid receptor coactivators of the p160 family. In this study using immunohistochemistry and Western blot analysis, we characterize the expression patterns of three coactivators, steroid receptor coactivator-1, amplified in breast cancer-1 (AIB1), and transcriptional intermediary factor-2 in human endometrium obtained prospectively from normal fertile women throughout the menstrual cycle. With the exception of glandular AIB1, which increased in the late secretory phase, none of the coactivators changed significantly during the menstrual cycle. We compared coactivator expression patterns in fertile endometrium to the endometrium of anovulatory (proliferative; n = 3) and clomiphene-induced ovulatory (secretory; n = 13) women with polycystic ovarian syndrome (PCOS), a group that have a higher likelihood of developing estrogen-induced endometrial hyperplasia and cancer. To control for the effect of clomiphene citrate, an additional group was included consisting of ovulatory women treated with clomiphene citrate for "male factor" infertility. Compared with both fertile and infertile controls, PCOS women exhibited elevated levels of AIB1 and transcriptional intermediary factor-2 expression in both epithelial and stromal cells. We postulate that increased coactivator expression may render the endometrium more sensitive to estrogen. In support of this, we describe an increased expression of ERalpha (an estrogen-induced gene product) during the menstrual cycle in PCOS endometrium compared with fertile controls. In summary, we demonstrate that the expression of p160 coactivators are regulated in endometrium during the menstrual cycle in normal fertile women but are overexpressed in the endometrium of women with PCOS. Based on these findings, we suggest a possible mechanism to explain the poor reproductive performance observed in PCOS and the increased incidence of endometrial hyperplasia and cancer noted in this group of women.

Indian hedgehog as a progesterone-responsive factor mediating epithelial-mesenchymal interactions in the mouse uterus

Genes encoding components of the hedgehog signaling pathway are dynamically expressed in the mouse uterus preparing for implantation. Indian hedgehog (Ihh), patched (Ptc), and Gli3 are expressed at low levels in the endometrial epithelium on day 1 of pregnancy. Transcription of Ihh increases dramatically in the luminal epithelium and glands from day 3, reaching very high levels on day 4. Over the same period, Ptc, Gli1, Gli2, and noggin are strongly upregulated in the underlying mesenchymal stroma. Transcription of Ihh in ovariectomized mice is induced by progesterone but not by estrogen. Lower induction of Ihh, Ptc, and Hoxa10 is seen in response to progesterone in the uteri of Pgr(-/-) mutant mice lacking progesterone nuclear steroid receptor. This finding suggests that the hormone may regulate Ihh through both nuclear receptor-dependent and -independent pathways. We describe a method for culturing uterine explants in the absence of epithelium. Under these conditions, recombinant N-SHH protein promotes the proliferation of mesenchyme cells and the expression of noggin. We propose that IHH made by the epithelium normally functions as a paracrine growth factor for stromal cells during the early stages of pregnancy.

Characterization of a prolactin-regulated gene in reproductive tissues using the prolactin receptor knockout mouse model

Prolactin (PRL) exerts pleiotropic physiological effects in various cells and tissues, although it is mainly considered as a regulator of reproduction and cell growth. Null mutation of the prolactin receptor (PRLR) gene leads to female sterility due to a failure of embryo implantation. Using this mouse model and the method of mRNA differential display, we identified PRL target genes that are regulated during the peri-implantation period. We characterized 1 among the 45 isolated genes, UA-3, which is regulated in the uterus as well as in the ovary during early pregnancy. This gene corresponds to a P311 mouse cDNA that was originally identified for its high expression in late-stage embryonic brain and adult cerebellum. We report here that UA-3 is present in numerous tissues as well as in ovary and uterus at the site of blastocyst apposition, and that its expression is hormonally regulated. Moreover, in situ hybridization reveals high expression in ovarian granulosa cells and in uterine epithelium. Recently, it has been suggested that P311 expression is tightly regulated at several levels by mechanisms that control cellular growth, transformation, motility, or a combination of these. Taken together, these results suggest that P311 could be involved in these processes during pregnancy, although its function remains to be clearly established.

Mechanisms of action of estrogen and progesterone

Estrogen and progesterone are steroid hormones that play a pivotal role in the regulation of mammalian reproduction. One primary action of these hormones is to regulate the development and function of the uterus. These hormones act by regulating the transcription of specific genes in the uterus. The actions of these hormones are mediated by their specific hormone receptors. These receptors are nuclear transcription factors, whose transcriptional regulatory activity is mediated by the binding of the specific steroid to these molecules. Once these receptors bind hormone, they can bind to specific cis-acting sequences in the promoter region of responsive genes and regulate transcription of these genes. In the regulation of transcription, these receptors interact with specific cofactors to activate the transcriptional machinery. A second gene family, the Steroid Receptor Coactivator (SRC) family, has been identified that serves to modulate the transcriptional activity of the hormone receptors. To date, three members of the SRC family have been identified. During the last decade, gene targeting technology has been used to identify the role of these receptors in the regulation of reproduction and uterine biology.

Endocannabinoids, hormone-cytokine networks and human fertility

Anandamide (N -arachidonoylethanolamine, AEA) is a major endocannabinoid, shown to impair mouse pregnancy and embryo development and to induce apoptosis in blastocysts. Here, we review the roles of AEA, of the AEA-binding cannabinoid (CB) receptors, of the selective AEA membrane transporter (AMT), and of the AEA-hydrolyzing enzyme fatty acid amide hydrolase (FAAH), in human gestation. In particular, we discuss the interplay between the endocannabinoid system and the hormone-cytokine array involved in the control of human pregnancy, showing that the endocannabinoids take part in the immunological adaptation occurring during early pregnancy. In this line, we discuss the critical role of FAAH in human peripheral lymphocytes, showing that the expression of this enzyme is regulated by progesterone, Th1 and Th2 cytokines, which also regulate fertility. Moreover, we show that AEA and the other endocannabinoid, 2-arachidonoylglycerol, inhibit the release of the fertility-promoting cytokine leukemia inhibitory factor from human lymphocytes. Taken together, low FAAH and consistently high blood levels of AEA, but not CB receptors or AMT, can be early (<8 weeks of gestation) markers of spontaneous abortion, potentially useful as diagnostic tools for large-scale, routine monitoring of gestation in humans.

Evidence for coordinated interaction of cyclin D3 with p21 and cdk6 in directing the development of uterine stromal cell decidualization and polyploidy during implantation

Uterine decidualization, characterized by stromal cell proliferation, and differentiation into specialized type of cells (decidual cells) with polyploidy, during implantation is critical to the pregnancy establishment in mice. The mechanisms by which the cell cycle events govern these processes are poorly understood. The cell cycle is tightly regulated at two particular checkpoints, G1-S and G2-M phases. Normal operation of these phases involves a complex interplay of cyclins, cyclin-dependent kinases (cdks) and cdk inhibitors (CKIs). We previously observed that upregulation of uterine cyclin D3 at the implantation site is tightly associated with decidualization in mice. To better understand the role of cyclin D3 in this process, we examined cell-specific expression and associated interactions of several cell cycle regulators (cyclins, cdks and CKIs) specific to different phases of the cell cycle during decidualization in mice. Among the various cell cycle molecules examined, coordinate expression and functional association of cyclin D3 with cdk4 suggest a role for proliferation and, that of cyclin D3 with p21 and cdk6 is consistent with the development of polyploidy during stromal cell decidualization.

Dual control of LIF expression and LIF receptor function regulate Stat3 activation at the onset of uterine receptivity and embryo implantation

Leukemia inhibitory factor (LIF) expression in the uterus is essential for embryo implantation in mice. Here we describe the spatial and temporal regulation of LIF signaling in vivo by using tissues isolated from uteri on different days over the implantation period. During this time, LIF receptors are expressed predominantly in the luminal epithelium (LE) of the uterus. Isolated epithelium responds to LIF by phosphorylation and nuclear translocation of signal transducer and activator of transcription (Stat) 3, but not by an increase in mitogen-activated protein kinase levels. The related cytokines Il-6, ciliary neurotrophic factor, as well as epidermal growth factor, do not activate Stat3, although epidermal growth factor stimulates mitogen-activated protein kinase. In vivo Stat3 activation is induced by LIF alone, resulting in the localization of Stat3 specifically to the nuclei of the LE coinciding with the onset of uterine receptivity. The responsiveness of the LE to LIF is regulated temporally, with Stat activation being restricted to day 4 of pregnancy despite the presence of constant levels of LIF receptor throughout the preimplantation period. Uterine receptivity is therefore under dual control and is regulated by both the onset of LIF expression in the endometrial glands and the release from inhibition of receptor function in the LE.

Estrogen receptor- and aromatase-deficient mice provide insight into the roles of estrogen within the ovary and uterus

Estrogen receptor (ER)- (alpha, beta, and both alpha and beta) and aromatase (Ar) knockout (KO) mice have been created to assess the biological effects of estrogens. This review article discusses the ovarian and uterine phenotypes of these mice. The data obtained have confirmed some older inferences about how the steroid acts, but have also revealed some unexpected aspects of estrogen action. Mol. Reprod. Dev. 59:336-346, 2001.

Increased expression of a novel heat shock protein transcript in the mouse uterus during decidualization and in response to progesterone

The objective of the present study was to identify and characterize transcripts whose levels are increased in the mouse uterus during decidualization. Using the method of suppression subtractive hybridization, we identified a novel transcript. This transcript contained a potential open reading frame that coded for a 196-amino-acid protein that shows homologies to the heat shock protein 20 family of genes. This transcript was expressed in several adult tissues and in the embryo. Its steady-state level was significantly greater in implantation segments of the uterus compared to nonimplantation segments. Furthermore, the steady-state levels of this novel transcript were significantly greater in uterine horns undergoing artificially induced decidualization compared to control contralateral horns. Using in situ hybridization methods, signals for the transcript were localized to the endometrial stromal cells that were undergoing decidualization. Finally, we found that progesterone caused a significant increase in the steady-state level of this novel transcript in the uterus when administered to ovariectomized mice. In the presence of estradiol-17 beta, this effect was significantly reduced. In conclusion, we have identified a novel transcript of a potential heat shock protein whose level is significantly increased in the uterus during decidualization and in response to progesterone.

Endometrial receptivity and the window of implantation

Implantation is a highly co-ordinated event that involves both embryonic and endometrial participation. The endometrium expresses a sophisticated repertoire of proteins during the menstrual cycle many of which help to define a period of receptivity collectively known as the 'window of implantation'. Many of these factors, which are temporally aligned with this window, are now seen as chemical messengers that are recognized by the embryo and facilitate embryonic growth and differentiation. The use of such proteins as biomarkers has also advanced our understanding of the implantation process and may identify women with implantation failure and infertility. While the study of endometrial receptivity is still evolving, the field is growing rapidly and will probably enhance our ability to diagnose and treat couples with infertility, especially in the arena of assisted reproductive technologies (ART).

Increased appearance of inducible nitric oxide synthase in the uterus and embryo at implantation

The aim of this study was to investigate the presence of iNOS in the murine uterus and embryo at implantation. Western blot analysis showed the presence of a 130-kDa band with strong reactivity to anti-iNOS antibody in the pre- and peri-implantation stage uteri. This band was faint in the postimplantation uteri. Immunocytochemical studies showed a heavy localization of iNOS specifically on the apical cells of the uterine endometrium in the pre- and peri-implantation stages. But the postimplantation uteri showed resorbed endometrium showing weaker expression of iNOS. The iNOS was induced by estrogen and the induction was intensified when progesterone was given along with estrogen. This truly mimics the in vivo situation since implantation in mice occurs when an estrogen surge occurs on a background of progesterone. The embryos too express iNOS at the peri-implantation stage. We suggest that iNOS expressed at peri-implantation would lead to enhanced NO production, which could act as a vasodilator and an angiogenic mediator. These effects could promote the attachment of the blastocyst to the uterus.

Dysregulation of EGF family of growth factors and COX-2 in the uterus during the preattachment and attachment reactions of the blastocyst with the luminal epithelium correlates with implantation failure in LIF-deficient mice

Various mediators, including cytokines, growth factors, homeotic gene products, and prostaglandins (PGs), participate in the implantation process in an autocrine, paracrine, or juxtacrine manner. However, interactions among these factors that result in successful implantation are not clearly understood. Leukemia inhibitory factor (LIF), a pleiotropic cytokine, was shown to be expressed in uterine glands on day 4 morning before implantation and is critical to this process in mice. However, the mechanism by which LIF executes its effects in implantation remains unknown. Moreover, interactions of LIF with other implantation-specific molecules have not yet been defined. Using normal and delayed implantation models, we herein show that LIF is not only expressed in progesterone (P4)-primed uterine glands before implantation in response to nidatory estrogen, it is also induced in stromal cells surrounding the active blastocyst at the time of the attachment reaction. This suggests that LIF has biphasic effects: first in the preparation of the receptive uterus and subsequently in the attachment reaction. The mechanism by which LIF participates in these events was addressed using LIF-deficient mice. We observed that while uterine cell-specific proliferation, steroid hormone responsiveness, and expression patterns of several genes are normal, specific members of the EGF family of growth factors, such as amphiregulin (Ar), heparin-binding EGF-like growth factor (HB-EGF), and epiregulin, are not expressed in LIF(-/-) uteri before and during the anticipated time of implantation, although EGF receptor family members (erbBs) are expressed correctly. Furthermore, cyclooxygenase-2 (COX-2), an inducible rate-limiting enzyme for PG synthesis and essential for implantation, is aberrantly expressed in the uterus surrounding the blastocyst in LIF(-/-) mice. These results suggest that dysregulation of specific EGF-like growth factors and COX-2 in the uterus contributes, at least partially, to implantation failure in LIF(-/-) mice. Since estrogen is essential for uterine receptivity, LIF induction, and blastocyst activation, it is possible that the nidatory estrogen effects in the P4-primed uterus for implantation are mediated via LIF signaling. However, we observed that LIF can only partially resume implantation in P4-primed, delayed implanting mice in the absence of estrogen, suggesting LIF induction is one of many functions that are executed by estrogen for implantation.

Essential function of Wnt-4 in mammary gland development downstream of progesterone signaling

Female reproductive hormones control mammary gland morphogenesis. In the absence of the progesterone receptor (PR) from the mammary epithelium, ductal side-branching fails to occur. We can overcome this defect by ectopic expression of the protooncogene Wnt-1. Transplantation of mammary epithelia from Wnt-4(-)/(-) mice shows that Wnt-4 has an essential role in side-branching early in pregnancy. PR and Wnt-4 mRNAs colocalize to the luminal compartment of the ductal epithelium. Progesterone induces Wnt-4 in mammary epithelial cells and is required for increased Wnt-4 expression during pregnancy. Thus, Wnt signaling is essential in mediating progesterone function during mammary gland morphogenesis.