Progesterone blocks estrogen-induced DNA synthesis through the inhibition of replication licensing

MCM6 Inhibits Decidualization via Cross-Talking with ERK Pathway in Human Endometrial Stromal Cells

Decidualization plays an important role in the implantation of the embryo, but the molecular action implicated in this process is not completely known. Herein, we found that, compared with the proliferative endometrial tissues, the expression of minichromosome maintenance complex component 6 (MCM6) was markedly decreased in the secretory endometrial tissues. To verify the function of MCM6 in decidualization, in vitro decidualization model was constructed by treating human endometrial stromal cells (HESCs) with estrogen (E2) and progesterone (P4). Consistently, MCM6 level was downregulated in E2P4-treated HESCs. Administration of E2P4 accumulated HESCs in G1 cell cycle phase, leading to cell growth suppression. Ectopic expression of MCM6 promoted the transition of G1/S and restored the proliferation of HESCs that were inhibited by E2P4. MCM6 overexpression led to aberrant activation of extracellular signal-regulated kinase (ERK) and treatment with ERK agonist Ro 67-7476 restored MCM6 expression and cell proliferation inhibited by E2P4. Our data suggested that MCM6/ERK feedback loop plays a negative role in E2P4-induced decidualization and implies that MCM6 may be a promising target for meliorating uterine receptivity.

Enhancing endometrial receptivity: the roles of human chorionic gonadotropin in autophagy and apoptosis regulation in endometrial stromal cells

Inadequate endometrial receptivity often results in embryo implantation failure and miscarriage. Human chorionic gonadotropin (hCG) is a key signaling molecule secreted during early embryonic development, which regulates embryonic maternal interface signaling and promotes embryo implantation. This study aimed to examine the impact of hCG on endometrial receptivity and its underlying mechanisms. An exploratory study was designed, and endometrial samples were obtained from women diagnosed with simple tubal infertility or male factor infertile (n = 12) and recurrent implantation failure (RIF, n = 10). Using reverse transcription-quantitative PCR and western blotting, luteinizing hormone (LH)/hCG receptor (LHCGR) levels and autophagy were detected in the endometrial tissues. Subsequently, primary endometrial stromal cells (ESCs) were isolated from these control groups and treated with hCG to examine the presence of LHCGR and markers of endometrial receptivity (HOXA10, ITGB3, FOXO1, LIF, and L-selectin ligand) and autophagy-related factors (Beclin1, LC3, and P62). The findings revealed that the expressions of receptivity factors, LHCGR, and LC3 were reduced in the endometrial tissues of women with RIF compared with the control group, whereas the expression of P62 was elevated. The administration of hCG to ESCs specifically activated LHCGR, stimulating an increase in the endometrial production of HOXA10, ITGB3, FOXO1, LIF and L-selectin ligands. Furthermore, when ESCs were exposed to 0.1 IU/mL hCG for 72 h, the autophagy factors Beclin1 and LC3 increased within the cells and P62 decreased. Moreover, the apoptotic factor Bax increased and Bcl-2 declined. However, when small interfering RNA was used to knock down LHCGR, hCG was less capable of controlling endometrial receptivity and autophagy molecules in ESCs. In addition, hCG stimulation enhanced the phosphorylation of ERK1/2 and mTOR proteins. These results suggest that women with RIF exhibit lower levels of LHCGR and compromised autophagy function in their endometrial tissues. Thus, hCG/LHCGR could potentially improve endometrial receptivity by modulating autophagy and apoptosis.

Progesterone Resistance in Endometriosis: Current Evidence and Putative Mechanisms

Endometriosis is an estrogen-dependent disease characterized by the growth of endometrial-like tissue outside the uterus. Progestins are currently the most commonly used treatment for endometriosis because of their excellent therapeutic effects and limited side effects. However, progestins have been unsuccessful in some symptomatic patients. The inability of the endometrium to respond properly to progesterone is known as progesterone resistance. An increasing body of evidence suggests the loss of progesterone signaling and the existence of progesterone resistance in endometriosis. The mechanisms of progesterone resistance have received considerable scholarly attention in recent years. Abnormal PGR signaling, chronic inflammation, aberrant gene expression, epigenetic alterations, and environmental toxins are considered potential molecular causes of progesterone resistance in endometriosis. The general objective of this review was to summarize the evidence and mechanisms of progesterone resistance. A deeper understanding of how these mechanisms contribute to progesterone resistance may help develop a novel therapeutic regimen for women with endometriosis by reversing progesterone resistance.

Loss of MIG-6 results in endometrial progesterone resistance via ERBB2

Female subfertility is highly associated with endometriosis. Endometrial progesterone resistance is suggested as a crucial element in the development of endometrial diseases. We report that MIG-6 is downregulated in the endometrium of infertile women with endometriosis and in a non-human primate model of endometriosis. We find ERBB2 overexpression in the endometrium of uterine-specific Mig-6 knockout mice (Pgr^cre/+Mig-6^f/f; Mig-6^d/d). To investigate the effect of ERBB2 targeting on endometrial progesterone resistance, fertility, and endometriosis, we introduce Erbb2 ablation in Mig-6^d/d mice (Mig-6^d/dErbb2^d/d mice). The additional knockout of Erbb2 rescues all phenotypes seen in Mig-6^d/d mice. Transcriptomic analysis shows that genes differentially expressed in Mig-6^d/d mice revert to their normal expression in Mig-6^d/dErbb2^d/d mice. Together, our results demonstrate that ERBB2 overexpression in endometrium with MIG-6 deficiency causes endometrial progesterone resistance and a nonreceptive endometrium in endometriosis-related infertility, and ERBB2 targeting reverses these effects.

Female subfertility is highly associated with endometriosis. Here the authors show that progesterone-induced MIG-6 is reduced in endometrium of infertile women and non-human primates with endometriosis, and in a mouse model find that Erbb2 is the key mediator of Mig-6 loss induced endometriosis-related infertility.

The Flavonoid Baicalein Negatively Regulates Progesterone Target Genes in the Uterus in Vivo

Baicalein is a flavonoid extracted from the root of Scutellaria baicalensis (Chinese skullcap) and is consumed as part of this botanical dietary supplement to reduce oxidative stress, pain, and inflammation. We previously reported that baicalein can also modify receptor signaling through the progesterone receptor (PR) and glucocorticoid receptor (GR) in vitro, which is interesting due to the well-established roles of both PR and GR in reducing inflammation. To understand the effects of baicalein on PR and GR signaling in vivo in the uterus, ovariectomized CD-1 mice were treated with DMSO, progesterone (P4), baicalein, P4 with baicalein, and P4 with RU486, a PR antagonist, for a week. The uteri were collected for histology and RNA sequencing. Our results showed that baicalein attenuated the antiproliferative effect of P4 on luminal epithelium as well as on the PR target genes HAND2 and ZBTB16. Baicalein did not change levels of PR or GR RNA or protein in the uterus. RNA sequencing data indicated that many transcripts significantly altered by baicalein were regulated in the opposite direction by P4. Similarly, a large portion of GO/KEGG terms and GSEA gene sets were altered in the opposite direction by baicalein as compared to P4 treatment. Treatment of baicalein did not change body weight, organ weight, or blood glucose level. In summary, baicalein functioned as a PR antagonist in vivo and therefore may oppose P4 action under certain conditions such as uterine hyperplasia, fibroids, and uterine cancers.

Progesterone triggers Rho kinase-cofilin axis during in vitro and in vivo endometrial decidualization

STUDY QUESTION

Can a combination of the focussed protein kinase assays and a wide-scale proteomic screen pinpoint novel, clinically relevant players in decidualization in vitro and in vivo?

SUMMARY ANSWER

Rho-dependent protein kinase (ROCK) activity is elevated in response to the combined treatment with progesterone and 8-Br-cAMP during in vitro decidualization, mirrored by increase of ROCK2 mRNA and protein levels and the phosphorylation levels of its downstream target Cofilin-1 (CFL1) in secretory versus proliferative endometrium.

WHAT IS KNOWN ALREADY

Decidualization is associated with extensive changes in gene expression profile, proliferation, metabolism and morphology of endometrium, yet only a few underlying molecular pathways have been systematically explored. In vitro decidualization of endometrial stromal cells (ESCs) can be reportedly induced using multiple protocols with variable physiological relevance. In our previous studies, cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA)/prolactin axis that is classically upregulated during decidualization showed dampened activation in ESCs isolated from polycystic ovary syndrome (PCOS) patients as compared to controls.

STUDY DESIGN, SIZE, DURATION

In vitro decidualization studies were carried out in passage 2 ESCs isolated from controls (N = 15) and PCOS patients (N = 9). In parallel, lysates of non-cultured ESCs isolated from proliferative (N = 4) or secretory (N = 4) endometrial tissue were explored. The observed trends were confirmed using cryo-cut samples of proliferative (N = 3) or secretory endometrium (N = 3), and in proliferative or secretory full tissue samples from controls (N = 8 and N = 9, respectively) or PCOS patients (N = 10 for both phases).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The activities of four target kinases were explored using kinase-responsive probes and selective inhibitors in lysates of in vitro decidualized ESCs and non-cultured ESCs isolated from tissue at different phases of the menstrual cycle. In the latter lysates, wide-scale proteomic and phosphoproteomic studies were further carried out. ROCK2 mRNA expression was explored in full tissue samples from controls or PCOS patients. The immunofluorescent staining of phosphorylated CFL1 was performed in full endometrial tissue samples, and in the in vitro decidualized fixed ESCs from controls or PCOS patients. Finally, the cellular migration properties were explored in live in vitro decidualized ESCs.

MAIN RESULTS AND THE ROLE OF CHANCE

During in vitro decidualization, the activities of PKA, protein kinase B (Akt/PKB), and ROCK are increased while the activity of casein kinase 2 (CK2) is decreased; these initial trends are observable after 4-day treatment (P < 0.05) and are further augmented following the 9-day treatment (P < 0.001) with mixtures containing progesterone and 8-Br-cAMP or forskolin. The presence of progesterone is necessary for activation of ROCK, yet it is dispensable in the case of PKA and Akt/PKB; in comparison to controls, PCOS patient-derived ESCs feature dampened response to progesterone. In non-cultured ESCs isolated from secretory vs proliferative phase tissue, only activity of ROCK is increased (P < 0.01). ROCK2 protein levels are slightly elevated in secretory versus proliferative ESCs (relative mean standard deviation < 50%), and ROCK2 mRNA is elevated in mid-secretory versus proliferative full tissue samples (P < 0.05) obtained from controls but not PCOS patients. Activation of ROCK2 downstream signalling results in increase of phospho-S3 CFL1 in secretory endometrium (P < 0.001) as well as in vitro decidualized ESCs (P < 0.01) from controls but not PCOS patients. ROCK2-triggered alterations in the cytoskeleton are reflected by the significantly decreased motility of in vitro decidualized ESCs (P < 0.05).

LARGE SCALE DATA

Proteomic and phosphoproteomic data are available via ProteomeXchange with identifier PXD026243.

LIMITATIONS, REASONS FOR CAUTION

The number of biological samples was limited. The duration of protocol for isolation of non-cultured ESCs from tissue can potentially affect phosphorylation pathways in cells, yet the possible artefacts were minimized by the identical treatment of proliferative and secretory samples.

WIDER IMPLICATIONS OF THE FINDINGS

The study demonstrated the benefits of combining the focussed kinase activity assay with wide-scale phosphoproteomics and showed the need for detailed elaboration of the in vitro decidualization protocols. ROCK was identified as the novel target of interest in decidualization, which requires closer attention in further studies-including the context of decidualization-related subfertility and infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Estonian Ministry of Education and Research, and the Estonian Research Council (PRG1076, PRG454, PSG230 and PSG608), Enterprise Estonia (EU48695), Horizon 2020 innovation grant (ERIN, Grant no. EU952516) of the European Commission, the COMBIVET ERA Chair, H2020-WIDESPREAD-2018-04 (Grant agreement no. 857418), the Academy of Finland (Project grants 315921 and 321763), the Finnish Medical Foundation and The Sigrid Juselius Foundation. The authors confirm that they have no conflict of interest with respect to the content of this article.

The Immunohistochemical Expression of MCM-3, -5, and -7 Proteins in the Uterine Fibroids

Uterine fibroids are the most common mesenchymal uterine neoplasms; their prevalence is estimated in 40%–60% of women under 35 and in 70%–80% of women over 50 years of age. The current research aims to focus on the etiopathogenesis of uterine fibroids, the factors that affect their growth, and markers with diagnostic and prognostic properties. The MCM (minichromosome maintenance) protein family consists of peptides whose primary function is participation in the molecular mechanism of creating replication forks while regulating DNA synthesis. The aim of this work was to determine the proliferative potential of uterine fibroid cells based on the expression of the Ki-67 antigen and the MCMs—i.e., MCM-3, MCM-5, and MCM-7. In addition, the expression of estrogen (ER) and progesterone (PgR) receptors was evaluated and correlated with the expression of the abovementioned observations. Ultimately, received results were analyzed in terms of clinical and pathological data. Materials and methods: In forty-four cases of uterine fibroids, immunohistochemical reactions were performed. A tissue microarray (TMA) technique was utilized and analyzed cases were assessed in triplicate. Immunohistochemistry was performed using antibodies against Ki-67 antigen, ER, PgR, MCM-3, MCM-5, and MCM-8 on an automated staining platform. Reactions were digitalized by a histologic scanner and quantified utilizing dedicated software for nuclear analysis. Assessment was based on quantification expression of the three histiospots, each representing one case in TMA. Results: In the study group (uterine fibroids), statistically significant stronger expression of all the investigated MCMs was observed, as compared to the control group. In addition, moderate and strong positive correlations were found between all tested proliferative markers. The expression of the MCM-7 protein also correlated positively with ER and PgR. With regard to clinical and pathological data, there was a negative correlation between the expression of MCMs and the number of both pregnancies and births. Significant reductions in MCM-5 and MCM-7 expression were observed in the group of women receiving oral hormonal contraceptives, while smoking women showed an increase in MCM-7, ER, and PgR. Conclusions: Uterine fibroid cells have greater proliferative potential, as evaluated by expression of the Ki-67 antigen and MCMs, than unaltered myometrial cells of the uterine corpus. The expression of MCM-7 was found to have strong or moderate correlations in all assessed relations. In the context of the clinical data, as well evident proliferative potential of MCMs, further studies are strongly recommended.

Identification and Analyzation of Differentially Expressed Transcription Factors in Endometriosis

Background: Endometriosis is interpreted as the existence of endometrium outside the uterine cavity, such as ovaries, fallopian tubes and pelvic cavity. Dysmenorrhea, abnormal menstruation, infertility, and chronic pelvic pain are the primary symptoms of endometriosis. Although there are many theories about the origin of endometriosis, the exact factor of the disease has not been confirmed. Therefore, many other mechanisms are still worth exploring. Materials and Methods: The gene lists of the transcription factors (TFs) were selected from the intersections of three databases. The limma R package was used to analyze the differentially expressed genes (DEGs) of GSE6364 and GSE7305 and the DEGs intersected with the TFs to obtain the differentially expressed TFs (DETFs). Subsequently, one-way ANOVA and Student's t-test were used to analyze the expression of DETFs in different phases of the endometrium and the endometrium of the infertile and fertile females with endometriosis, respectively. Enrichment analysis and PPI network were performed to reveal the molecular mechanisms of endometriosis. Finally, the plotROC R package was used to evaluate the sensitivity and specificity of hub TFs for the diagnosis of endometriosis. Results: A total of 54 DETFs were screened out in endometriosis. The expression of up-regulated DETFs was gradually increased from the early secretory to the proliferative phase of the endometrium. Most up-regulated DETFs increased expression in the endometrium of infertile females. The pathways of DETFs were mainly enriched in stem cell differentiation, transcription activity, steroid hormone receptor activity and herpes simplex virus. Two hub TFs (RUNX2 and BATF) and two sub-networks were finally acquired from the PPI network. RUNX2 and BATF also had high diagnostic value in endometriosis. Conclusion: We discovered and analyzed 54 DETFs that were closely related to endometriosis, which would contribute to explore new mechanisms of endometriosis and search for new diagnostic markers and effective therapeutic targets.

Molecular characterization of Wdr13 knockout female mice uteri: a model for human endometrial hyperplasia

Endometrial hyperplasia (EH) is a condition where uterine endometrial glands show excessive proliferation of epithelial cells that may subsequently progress into endometrial cancer (EC). Modern lifestyle disorders such as obesity, hormonal changes and hyperinsulinemia are known risk factors for EH. A mouse strain that mimics most of these risk factors would be an ideal model to study the stage-wise progression of EH disease and develop suitable treatment strategies. Wdr13, an X-linked gene, is evolutionarily conserved and expressed in several tissues including uteri. In the present study, Wdr13 knockout female mice developed benign proliferative epithelium that progressed into EH at around one year of age accompanied by an increase in body weight and elevated estradiol levels. Molecular characterization studies revealed increase in ERα, PI3K and a decrease in PAX2 and ERβ proteins in Wdr13 mutant mice uteri. Further, a decrease in the mRNA levels of cell cycle inhibitors, namely; p21 and cyclin G2 was seen. Leukocyte infiltration was observed in the uterine tissue of knockout mice at around 12 months of age. These physiological, molecular and pathological patterns were similar to those routinely seen in human EH disease and demonstrated the importance of WDR13 in mice uterine tissue. Thus, the genetic loss of Wdr13 in these mice led to mimicking of the human EH associated metabolic disorders making Wdr13 knockout female mice a potential animal model to study human endometrial hyperplasia.

BRCA1 Attenuates Progesterone Effects on Proliferation and NFκB Activation in Normal Human Mammary Epithelial Cells

Germline mutations in the breast cancer susceptibility gene BRCA1, encoding a tumor suppressor protein, greatly enhance the risk of breast and ovarian cancer. This tissue-specificity implicates the role of ovarian hormones. Indeed, BRCA1 has been demonstrated to regulate the signalling axis of the hormone, progesterone, and its receptor, the progesterone receptor (PR), and progesterone action has been implicated in BRCA1-related tumorigenesis. BRCA1 also plays important roles in oxidative stress and activating nuclear factor kappaB (NFκB) signalling pathways. Like wildtype BRCA1 function, PR signalling has also been shown to inhibit NFκB activation. Although PR and BRCA1 networks are known to interact, their interaction at the level of NFκB activation in the human breast is not understood. This study investigates the effect of reduced BRCA1 expression on proliferation and NFκB activation in human breast cells, and the impact of progesterone on these effects. The major findings are that: 1) Reduced BRCA1 levels inhibit cell growth in normal human mammary cells and breast cancer cells; 2) Reduced BRCA1 levels stimulated inflammatory targets and NFκB activity in normal human mammary cells; 3) Wildtype BRCA1 inhibited the pro-proliferative effects of progesterone in normal mammary epithelial cells, and; 4) Progesterone attenuated BRCA1-mediated NFκB activation in normal human mammary cells. These data have important implications for our understanding of progesterone action in BRCA1 mutation carriers, and how inhibition of this action may potentially delay tumorigenesis or impart a more favourable prognosis.

Chronic Exposure of Mice to Bisphenol-A Alters Uterine Fibroblast Growth Factor Signaling and Leads to Aberrant Epithelial Proliferation

Uterine epithelial proliferation is regulated in a paracrine manner by a complex interplay between estrogen (E) and progesterone (P) signaling, in which E stimulates proliferation and P inhibits it. Perturbation of steroid hormone signaling within the uterine milieu could contribute to the development of endometrial hyperplasia and cancer. It is well established that bisphenol-A (BPA) is an endocrine-disrupting chemical with weak estrogenic effects, although little is known about how it affects steroid hormone signaling in the adult uterus. Because BPA acts as a weak E, we hypothesized that chronic exposure to BPA would create an imbalance between E and P signaling and cause changes in the uterus, such as aberrant epithelial proliferation. Indeed, exposure to an environmentally relevant dose of BPA had a uterotrophic affect. BPA-treated mice showed increased proliferation, notably in the glandular epithelium, which are sites of origin for endometrial hyperplasia and cancer. Increased proliferation appeared to be mediated through a similar mechanism as E-induced proliferation, via activation of the fibroblast growth factor receptor pathway and phosphorylation of the ERK1/2 mitogen-activated protein kinases in the epithelium. Interestingly, BPA reduced expression of heart and neural crest derivatives expressed 2 (HAND2), a known mediator of the antiproliferative effects of P. BPA also increased methylation of a CpG island in the Hand2 gene promoter, suggesting that BPA may promote epithelial proliferation through epigenetic silencing of antiproliferative factors like HAND2. Collectively, these findings establish that chronic exposure to BPA impairs steroid hormone signaling in the mouse uterus, and may contribute to the pathogenesis of uterine hyperplasia and cancer.

SOX17 regulates uterine epithelial-stromal cross-talk acting via a distal enhancer upstream of Ihh

Mammalian pregnancy depends on the ability of the uterus to support embryo implantation. Previous studies reveal the Sox17 gene as a downstream target of the Pgr-Gata2-dependent transcription network that directs genomic actions in the uterine endometrium receptive for embryo implantation. Here, we report that ablating Sox17 in the uterine epithelium impairs leukemia inhibitory factor (LIF) and Indian hedgehog homolog (IHH) signaling, leading to failure of embryo implantation. In vivo deletion of the SOX17-binding region 19 kb upstream of the Ihh locus by CRISPR-Cas technology reduces Ihh expression specifically in the uterus and alters proper endometrial epithelial-stromal interactions, thereby impairing pregnancy. This SOX17-binding interval is also bound by GATA2, FOXA2, and PGR. This cluster of transcription factor binding is common in 737 uterine genes and may represent a key regulatory element essential for uterine epithelial gene expression.

Heparan Sulfate Proteoglycan Sulfation Regulates Uterine Differentiation and Signaling During Embryo Implantation

To prepare for embryo implantation, the uterus must undergo a series of reciprocal interactions between the uterine epithelium and the underlying stroma, which are orchestrated by ovarian hormones. During this process, multiple signaling pathways are activated to direct cell proliferation and differentiation, which render the uterus receptive to the implanting blastocysts. One important modulator of these signaling pathways is the cell surface and extracellular matrix macromolecules, heparan sulfate proteoglycans (HSPGs). HSPGs play crucial roles in signal transduction by regulating morphogen transport and ligand binding. In this study, we examine the role of HSPG sulfation in regulating uterine receptivity by conditionally deleting the N-deacetylase/N-sulfotransferase (NDST) 1 gene (Ndst1) in the mouse uterus using the Pgr-Cre driver, on an Ndst2- and Ndst3-null genetic background. Although development of the female reproductive tract and subsequent ovarian function appear normal in Ndst triple-knockout females, they are infertile due to implantation defects. Embryo attachment appears to occur but the uterine epithelium at the site of implantation persists rather than disintegrates in the mutant. Uterine epithelial cells continued to proliferate past day 4 of pregnancy, accompanied by elevated Fgf2 and Fgf9 expression, whereas uterine stroma failed to undergo decidualization, as evidenced by lack of Bmp2 induction. Despite normal Indian hedgehog expression, transcripts of Ptch1 and Gli1, both components as well as targets of the hedgehog (Hh) pathway, were detected only in the subepithelial stroma, indicating altered Hh signaling in the mutant uterus. Taken together, these data implicate an essential role for HSPGs in modulating signal transduction during mouse implantation.

Effect of daidzein and equol on DNA replication in MCF-7 cells

It has been reported that daidzein and equol stimulate DNA replication and proliferation of MCF-7 cells. However, their molecular mechanisms of action are still unclear. We examined the effects of daidzein and equol on DNA replication of MCF-7 cells, focusing on MCM2-7 proteins, which function as the replicative helicase. In the presence of either 1 μM of daidzein or equol, the number of cells in S-phase, which was determined by detecting bromodeoxyuridine incorporated into replicated DNA, almost doubled. The total amounts of MCM7 protein and chromatin-bound MCM7 protein increased in the presence of daidzein. The data suggest that phytoestrogens facilitate cell cycle progression in G1-phase by increasing the level of MCM proteins. In the presence of phytoestrogens, phosphorylation of Rb and levels of MCM2, 3 and 7 mRNA increased, suggesting that stimulation of MCM2-7 transcription is involved in the cell cycle progression. Under the same conditions, double-stranded DNA breakage in logarithmically growing MCF-7 cells, which was detected using anti-γ-H2AX antibodies, did not increase in the presence of equol.

Estrogen and progesterone signalling in the normal breast and its implications for cancer development

The ovarian hormones estrogen and progesterone are master regulators of the development and function of a broad spectrum of human tissues, including the breast, reproductive and cardiovascular systems, brain and bone. Acting through the nuclear estrogen (ER) and progesterone receptors (PR), both play complex and essential coordinated roles in the extensive development of the lobular alveolar epithelial structures of the normal breast during puberty, the normal menstrual cycle and pregnancy. The past decade has seen major advances in understanding the mechanisms of action of estrogen and progesterone in the normal breast and in the delineation of the complex hierarchy of cell types regulated by ovarian hormones in this tissue. There is evidence for a role for both ER and PR in driving breast cancer, and both are favourable prognostic markers with respect to outcome. In this review, we summarize current knowledge of the mechanisms of action of ER and PR in the normal breast, and implications for the development and management of breast cancer.

Dormant origins as a built-in safeguard in eukaryotic DNA replication against genome instability and disease development

DNA replication is a prerequisite for cell proliferation, yet it can be increasingly challenging for a eukaryotic cell to faithfully duplicate its genome as its size and complexity expands. Dormant origins now emerge as a key component for cells to successfully accomplish such a demanding but essential task. In this perspective, we will first provide an overview of the fundamental processes eukaryotic cells have developed to regulate origin licensing and firing. With a special focus on mammalian systems, we will then highlight the role of dormant origins in preventing replication-associated genome instability and their functional interplay with proteins involved in the DNA damage repair response for tumor suppression. Lastly, deficiencies in the origin licensing machinery will be discussed in relation to their influence on stem cell maintenance and human diseases.

Progesterone-induced miR-133a inhibits the proliferation of endometrial epithelial cells

AIM

This study aimed to understand the role of miR-133a in progesterone actions, explore the regulative mechanism of the progesterone receptor, and investigate the effects of miR-133a on the progesterone-inhibited proliferation of mouse endometrial epithelial cells.

METHODS

The expression of miR-133a induced by progesterone was detected by quantitative real-time PCR both in vivo and in vitro. Ishikawa subcell lines stably transfected with progesterone receptor subtypes were used to determine the receptor mechanism of progesterone inducing miR-133a. Specific miR-133a mimics or inhibitors were transfected into mouse uteri and primary cultured endometrial epithelial cells to overexpress or downregulate the miR-133a. The roles of miR-133a in the cell cycle and proliferation of endometrial epithelial cells were analysed by flow cytometry and Edu incorporation analysis. The protein levels of cyclinD2 in uterine tissue sections and primary cultured endometrial epithelial cells were determined by immunohistochemistry and Western blot analysis.

RESULTS

Progesterone could induce miR-133a expression in a PRB-dependent manner in endometrial epithelial cells. miR-133a inhibited endometrial epithelial cell proliferation by arresting cell cycle at the G₁ -S transition. Moreover, miR-133a acted as an inhibitor in downregulating cyclinD2 in endometrial epithelial cells.

CONCLUSION

We showed for the first time that progesterone-induced miR-133a inhibited the proliferation of endometrial epithelial cells by downregulating cyclinD2. Our research indicated an important mechanism for progesterone inhibiting the proliferation of endometrial epithelial cells by inducing special miRNAs to inhibit positive regulatory proteins in the cell cycle.

Conditional Ablation of Progesterone Receptor Membrane Component 1 Results in Subfertility in the Female and Development of Endometrial Cysts

Progesterone (P4) is essential for female fertility. The objective of this study was to evaluate the functional requirement of the nonclassical P4 receptor (PGR), PGR membrane component 1, in regulating female fertility. To achieve this goal, the Pgrmc1 gene was floxed by insertion of loxP sites on each side of exon 2. Pgrmc1 floxed (Pgrmc1(fl/fl)) mice were crossed with Pgr(cre) or Amhr2(cre) mice to delete Pgrmc1 (Pgrmc1(d/d)) from the female reproductive tract. A 6-month breeding trial revealed that conditional ablation of Pgrmc1 with Pgr(cre/+) mice resulted in a 40% reduction (P = .0002) in the number of pups/litter. Neither the capacity to ovulate in response to gonadotropin treatment nor the expression of PGR and the estrogen receptor was altered in the uteri of Pgrmc1(d/d) mice compared with Pgrmc1(fl/fl) control mice. Although conditional ablation of Pgrmc1 from mesenchymal tissue using Amhr2(cre/+) mice did not reduce the number of pups/litter, the total number of litters born in the 6-month breeding trial was significantly decreased (P = .041). In addition to subfertility, conditional ablation of Pgrmc1 using either Amhr2(cre/+) or Pgr(cre/+) mice resulted in the development of endometrial cysts starting around 4 months of age. Interestingly, pregnancy attenuated the formation of these uterine cysts. These new findings demonstrate that PGR membrane component 1 plays an important role in female fertility and uterine tissue homeostasis.

MCM2 mediates progesterone-induced endometrial stromal cell proliferation and differentiation in mice

Uterine decidualization characterized by stromal cell proliferation and differentiation is critical to the establishment of pregnancy in many species. Progesterone is a key factor in regulating endometrial cell decidualization, however, the molecular basis involved in mediating the effects of progesterone during decidualization remains largely unknown. We report here that the DNA replication licensing factor MCM2, one of the conserved set of six-related proteins (MCM complex: MCM2-7) essential for eukaryotic DNA replication, is dynamically expressed in both proliferative and differentiated stromal cells during mouse periimplantation uterus. Applying PR-knockout mouse model and pharmacological strategy, we further found that the expression of Mcm2 is induced by progesterone action in the mouse uterine stroma. Employing a primary cell culture system, we further demonstrated that siRNA-mediated silencing of MCM2 arrests the cell cycle at G1-S transition during stromal cell proliferation. Moreover, the downregulation of Mcm2 could also compromise stromal cell differentiation. Collectively, our studies uncovered the role of a unique DNA replication licensing molecule MCM2 in mediating Progesterone-induced stromal cell decidualization in mouse uterus.

Mechanisms of uterine estrogen signaling during early pregnancy in mice: an update

Adherence of an embryo to the uterus represents the most critical step of the reproductive process. Implantation is a synchronized event between the blastocyst and the uterine luminal epithelium, leading to structural and functional changes for further embryonic growth and development. The milieu comprising the complex process of implantation is mediated by estrogen through diverse but interdependent signaling pathways. Mouse models have demonstrated the relevance of the expression of estrogen-modulated paracrine factors to uterine receptivity and implantation window. More importantly, some factors seem to serve as molecular links between different estrogen pathways, promoting cell growth, acting as molecular chaperones, or amplifying estrogenic effects. Abnormal expression of these factors can lead to implantation failure and infertility. This review provides an overview of several well-characterized signaling pathways that elucidates the molecular cross talk involved in the uterus during early pregnancy.

What's new in estrogen receptor action in the female reproductive tract

Estrogen receptor alpha (ERα) is a critical player in development and function of the female reproductive system. Perturbations in ERα response can affect wide-ranging aspects of health in humans as well as in livestock and wildlife. Because of its long-known and broad impact, ERα mechanisms of action continue to be the focus on cutting-edge research efforts. Consequently, novel insights have greatly advanced understanding of every aspect of estrogen signaling. In this review, we attempt to briefly outline the current understanding of ERα mediated mechanisms in the context of the female reproductive system.

ARID1A Is Essential for Endometrial Function during Early Pregnancy

AT-rich interactive domain 1A gene (ARID1A) loss is a frequent event in endometriosis-associated ovarian carcinomas. Endometriosis is a disease in which tissue that normally grows inside the uterus grows outside the uterus, and 50% of women with endometriosis are infertile. ARID1A protein levels were significantly lower in the eutopic endometrium of women with endometriosis compared to women without endometriosis. However, an understanding of the physiological effects of ARID1A loss remains quite poor, and the function of Arid1a in the female reproductive tract has remained elusive. In order to understand the role of Arid1a in the uterus, we have generated mice with conditional ablation of Arid1a in the PGR positive cells (Pgrcre/+Arid1af/f; Arid1ad/d). Ovarian function and uterine development of Arid1ad/d mice were normal. However, Arid1ad/d mice were sterile due to defective embryo implantation and decidualization. The epithelial proliferation was significantly increased in Arid1ad/d mice compared to control mice. Enhanced epithelial estrogen activity and reduced epithelial PGR expression, which impedes maturation of the receptive uterus, was observed in Arid1ad/d mice at the peri-implantation period. The microarray analysis revealed that ARID1A represses the genes related to cell cycle and DNA replication. We showed that ARID1A positively regulates Klf15 expression with PGR to inhibit epithelial proliferation at peri-implantation. Our results suggest that Arid1a has a critical role in modulating epithelial proliferation which is a critical requisite for fertility. This finding provides a new signaling pathway for steroid hormone regulation in female reproductive biology and furthers our understanding of the molecular mechanisms that underlie dysregulation of hormonal signaling in human reproductive disorders such as endometriosis.

Minireview: Progesterone Regulation of Proliferation in the Normal Human Breast and in Breast Cancer: A Tale of Two Scenarios?

Progesterone (P), which signals through the P receptor (PR), is critical in normal development of the breast, but its signaling axis is also a major driver of breast cancer risk. Here we review recent advances in the understanding of P signaling in the normal human breast, with a focus on the importance of the balance between autocrine and paracrine signaling. To date, most data (which derive largely from mouse models or human breast cancer cell line studies) have demonstrated that the vast majority of PR+ cells appear to act as "sensor" cells, which respond to P stimulation by translating these hormonal cues into paracrine signals. However, growing evidence suggests that, dependent on the cellular context, P may also signal in an autocrine manner in a subset of cells in the normal mouse mammary gland and human breast. It has been suggested that it may be dysregulation of this autocrine signaling, resulting in a "switch" from a predominance of paracrine signaling to autocrine signaling in PR+ cells, which is an early event during breast tumorigenesis. This review summarizes current evidence in the literature that demonstrates the mechanisms through which P acts in the normal human breast, as well as highlighting the important questions that remain unanswered.

RNA-Seq-Based Transcriptome Analysis of Changes in Gene Expression Linked to Human Pregnancy Outcome After In Vitro Fertilization-Embryo Transfer

To promote the pregnancy rate of in vitro fertilization-embryo transfer (IVF-ET), we proposed to examine the differentially expressed gene during pregnancy success and failure. We used high-sequencing technology to characterize and compare the gene expression profiles of pregnancy success and pregnancy failure patients during 3 different stages: before IVF-ET (stage I), after ovarian stimulation (stage II), and day 15 after embryo transfer (stage III). Selected data from RNA-sequencing experiments were validated by quantitative real-time polymerase chain reaction (qRT-PCR). A total of 282, 208, and 372 genes in stages I, II, and III, respectively, were differentially expressed between pregnancy success and pregnancy failure, respectively. Through confirmation with qRT-PCR, compared to pregnancy failure, we demonstrated much lower level of major histocompatibility complex, human leukocyte antigen class I A, and an much higher level of human leukocyte antigen, class II DQ α1 (HLA-DQA1) in pregnancy success, although the HLA-DQA1 decreased with development duration of pregnancy. Interleukin 1β increased with the development duration of pregnancy in pregnancy failure group and was much higher than that in pregnancy success group. Hemoglobin δ decreased with the development duration of pregnancy in pregnancy failure women and maintained in a lower level in stage I and II but dramatically increased to a much higher level in stage III in pregnancy success women. Minichromosome maintenance complex component 4 significantly increased in stage III in pregnancy failure but not in pregnancy success women. The altered expression of genes implicated in immune response and inflammation, oocyte meiosis, rhythmic process, and so on. Therefore, the current results provide a strong basis for future research to expound the molecular mechanism coping with pregnancy outcome.

Impact of progesterone on stem/progenitor cells in the human breast

The epithelium of the human breast is made up of a branching ductal-lobular system, which is lined by a single layer of luminal cells surrounded by a contractile basal cell layer. The co-ordinated development of stem/progenitor cells into these luminal and basal cells is fundamentally important for breast morphogenesis. The ovarian steroid hormone, progesterone, is critical in driving proliferation and normal breast development, yet progesterone analogues have also been shown to be a major driver of breast cancer risk. Studies in recent years have revealed an important role for progesterone in stimulating the mammary stem cell compartment in the mouse mammary gland, and growing evidence supports the notion that progesterone also stimulates progenitor cells in both the normal human breast and in breast cancer cells. As changes in cell type composition are one of the hallmark features of breast cancer progression, these observations have critical implications in discerning the mechanisms of how progesterone increases breast cancer risk. This review summarises recent work regarding the impact of progesterone action on the stem/progenitor cell compartment of the human breast.

Activation of protein synthesis in mouse uterine epithelial cells by estradiol-17β is mediated by a PKC-ERK1/2-mTOR signaling pathway

The uterine epithelium of mice and humans undergoes cyclical waves of cell proliferation and differentiation under the regulation of estradiol-17β (E2) and progesterone (P4). These epithelial cells respond to E2 with increased protein and DNA synthesis, whereas P4 inhibits only the E2-induced DNA synthetic response. Here we show that E2 regulates protein synthesis in these epithelial cells through activating PKC that in turn stimulates ERK1/2 to phosphorylate and thereby activate the central regulator of protein synthesis mechanistic target of rapamycin (mTOR). This mTOR pathway is not inhibited by P4. Inhibitor studies with an estrogen receptor (ESR1) antagonist showed the dependence of this mTOR pathway on ESR1 but that once activated, a phosphorylation cascade independent of ESR1 propagates the pathway. E2 also stimulates an IGF1 receptor (IGF1R) to PI3 kinase to AKT to GSK-3β pathway required for activation of the canonical cell cycle machinery that is inhibited by P4. PKC activation did not stimulate this pathway nor does inhibition of PKC or ERK1/2 affect it. These studies therefore indicate a mechanism whereby DNA and protein synthesis are regulated by two ESR1-activated pathways that run in parallel with only the one responsible for the initiation of DNA synthesis blocked by P4. Inhibition of mTOR by rapamycin in vivo resulted in inhibition of E2-induced protein and DNA synthesis. Proliferative diseases of the endometrium such as endometriosis and cancer are common and E2 dependent. Thus, defining this mTOR pathway suggests that local (intrauterine or peritoneal) rapamycin administration might be a therapeutic option for these diseases.

Minireview: Steroid-regulated paracrine mechanisms controlling implantation

Implantation is an essential process during establishment of pregnancy in mammals. It is initiated with the attachment of the blastocyst to a receptive uterine epithelium followed by its invasion into the stromal tissue. These events are profoundly regulated by the steroid hormones 17β-estradiol and progesterone. During the past several years, mouse models harboring conditional gene knockout mutations have become powerful tools for determining the functional roles of cellular factors involved in various aspects of implantation biology. Studies using these genetic models as well as primary cultures of human endometrial cells have established that the estrogen receptor α, the progesterone receptor, and their downstream target genes critically regulate uterine growth and differentiation, which in turn control embryo-endometrial interactions during early pregnancy. These studies have uncovered a diverse array of molecular cues, which are produced under the influence of estrogen receptor α and progesterone receptor and exchanged between the epithelial and stromal compartments of the uterus during the progressive phases of implantation. These paracrine signals are critical for acquisition of uterine receptivity and functional interactions with the embryo. This review highlights recent work describing paracrine mechanisms that govern steroid-regulated uterine epithelial-stromal dialogue during implantation and their roles in fertility and disease.

The LIF-mediated molecular signature regulating murine embryo implantation

The establishment of a receptive uterus is the prime requirement for embryo implantation. In mice, the E2-induced cytokine leukemia inhibitory factor (LIF) is essential in switching the uterine luminal epithelium (LE) from a nonreceptive to a receptive state. Here we define the LIF-mediated switch using array analysis and informatics to identify LIF-induced changes in gene expression and annotated signaling pathways specific to the LE. We compare gene expression profiles at 0, 1, 3, and 6 h, following LIF treatment. During the first hour, the JAK-STAT signaling pathway is activated and the expression of 54 genes declines, primarily affecting LE cytoskeletal and chromatin organization as well as a transient reduction in the progesterone, TGFbetaR1, and ACVR1 receptors. Simultaneously 256 genes increase expression, of which 42 are transcription factors, including Sox, Kfl, Hes, Hey, and Hox families. Within 3 h, the expression of 3987 genes belonging to more than 25 biological process pathways was altered. We confirmed the mRNA and protein distribution of key genes from 10 pathways, including the Igf-1, Vegf, Toll-like receptors, actin cytoskeleton, ephrin, integrins, TGFbeta, Wnt, and Notch pathways. These data identify novel LIF-activated pathways in the LE and define the molecular basis between the refractory and receptive uterine phases. More broadly, these findings highlight the staggering capacity of a single cytokine to induce a dynamic and complex network of changes in a simple epithelium essential to mammalian reproduction and provide a basis for identifying new routes to regulating female reproduction.

Krüppel-like factors are effectors of nuclear receptor signaling

Binding of steroid and thyroid hormones to their cognate nuclear receptors (NRs) impacts virtually every aspect of postembryonic development, physiology and behavior, and inappropriate signaling by NRs may contribute to disease. While NRs regulate genes by direct binding to hormone response elements in the genome, their actions may depend on the activity of other transcription factors (TFs) that may or may not bind DNA. The Krüppel-like family of transcription factors (KLF) is an evolutionarily conserved class of DNA-binding proteins that influence many aspects of development and physiology. Several members of this family have been shown to play diverse roles in NR signaling. For example, KLFs (1) act as accessory transcription factors for NR actions, (2) regulate expression of NR genes, and (3) as gene products of primary NR response genes function as key players in NR-dependent transcriptional networks. In mouse models, deletion of different KLFs leads to aberrant transcriptional and physiological responses to hormones, underscoring the importance of these proteins in the regulation of hormonal signaling. Understanding the functional relationships between NRs and KLFs will yield important insights into mechanisms of NR signaling. In this review we present a conceptual framework for understanding how KLFs participate in NR signaling, and we provide examples of how these proteins function to effect hormone action.

Role of nuclear receptors in blastocyst implantation

The regulation of blastocyst implantation in the uterus is orchestrated by the ovarian hormones estrogen and progesterone. These hormones act via their nuclear receptors to direct the transcriptional activity of the endometrial compartments and create a defined period in which the uterus is permissive to embryo implantation termed the "window of receptivity". Additional members of the nuclear receptor family have also been described to have a potential role in endometrial function. Much of what we know about the function of these nuclear receptors during implantation we have learned from the use of mouse models. Transgenic murine models with targeted gene ablation have allowed us to identify a complex network of paracrine signaling between the endometrial epithelium and stroma. While some of the critical molecules have been identified, the mechanism underlying the intricate communication between endometrial compartments during the implantation window has not been fully elucidated. Defining this mechanism will help identify markers of a receptive uterine environment, ultimately providing a useful tool to help improve the fertility outlook for reproductively challenged couples. The aim of this review is to outline our current understanding of how nuclear receptors and their effector molecules regulate blastocyst implantation in the endometrium.

17β-Estradiol enhances response of mice spleen B cells elicited by TLR9 agonist

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies against nucleic acid-associated antigens. B cells play cardinal roles in SLE. Many evidences have proved estrogen contribute to the gender bias in SLE and 17β-estradiol (E2) could accelerate the disease by regulating B cells. On the other hand, B cells express TLR9 which recognized dsDNA and played a critical role in SLE. However, the crosstalk between estrogen and TLR9 in B cells remains unknown. So we investigated the E2 effect in the presence of the TLR9 ligand CpG on mice spleen B cells. We found that the up-regulation of cell viability, life-span, co-stimulation molecules (CD40, CD86) expression, IgM secretion, TLR9 and MCM6 expression were more significant than CpG ODN or E2 stimulated alone. It may provide a new way to investigate the mechanism of how E2 modulate the B cells function in lupus.

Genetic markers of ovarian follicle number and menopause in women of multiple ethnicities

Oocyte loss has a significant impact on fertility and somatic health. Yet, we know little about factors that impact this process. We sought to identify genetic variants associated with ovarian reserve (oocyte number as measured by antral follicle count, AFC). Based on recently published genome-wide scans that identified loci associated with age of menopause, we also sought to test our hypothesis that follicle number and menopausal age share underlying genetic associations. We analyzed menopause-related variants for association with follicle number in an independent population of approximately 450 reproductive-aged women of European and African ancestry; these women were assessed for AFC, anthropometric, clinical, and lifestyle factors. One SNP strongly associated with later menopausal age in Caucasian women (+1.07 ± 0.11 years) in previous work was also associated with higher follicle counts in Caucasians (+2.79 ± 1.67 follicles) in our study. This variant is within the Minichromosome Maintenance Complex Component 8 (MCM8) gene, which we found was expressed within oocytes in follicles of the human ovary. In genome-wide scans of AFC, we also identified one marginally genome-wide and several nominally significant SNPs within several other genes associated with follicle number in both ethnic groups. Further, there were overlapping variants associated with multiple ovarian reserve markers (AFC, serum hormone levels, menopausal age). This study provides the first evidence for direct genetic associations underlying both follicle number and menopause and identifies novel candidate genes. Genetic variants associated with ovarian reserve may facilitate discovery of genetic markers to predict reproductive health and lifespan in women.

KLF15 negatively regulates estrogen-induced epithelial cell proliferation by inhibition of DNA replication licensing

In the epithelial compartment of the uterus, estradiol-17β (E(2)) induces cell proliferation while progesterone (P(4)) inhibits this response and causes differentiation of the cells. In this study, we identified the mechanism whereby E(2) and P(4) reciprocally regulate the expression of minichromosome maintenance (MCM)-2, a protein that is an essential component of the hexameric MCM-2 to 7 complex required for DNA synthesis initiation. We show in the uterine epithelium that Kruppel-like transcription (KLF) factors, KLF 4 and 15, are inversely expressed; most importantly, they bind to the Mcm2 promoter under the regulation of E(2) and P(4)E(2), respectively. After P(4)E(2) exposure and in contrast to E(2) treated mice, the Mcm2 promoter displays increased histone 3 (H3) methylation and the recruitment of histone deacetylase 1 and 3 with the concomitant deacetylation of H3. This increased methylation and decreased acetylation is associated with an inhibition of RNA polymerase II binding, indicating an inactive Mcm2 promoter following P(4)E(2) treatment. Using transient transfection assays in the Ishikawa endometrial cell line, we demonstrate that Mcm2 promoter activity is hormonally stimulated by E(2) and that KLF15 inhibits this E(2) enhanced transcription. KLF15 expression also blocks Ishikawa cell proliferation through inhibition of MCM2 protein level. Importantly, in vivo expression of KLF15 in an estrogenized uterus mimics P(4)'s action by inhibiting E(2)-induced uterine epithelial MCM-2 expression and DNA synthesis. KLF15 is therefore a downstream physiological mediator of progesterone's cell cycle inhibitory action in the uterine epithelium.

Msx homeobox genes critically regulate embryo implantation by controlling paracrine signaling between uterine stroma and epithelium

The mammalian Msx homeobox genes, Msx1 and Msx2, encode transcription factors that control organogenesis and tissue interactions during embryonic development. We observed overlapping expression of these factors in uterine epithelial and stromal compartments of pregnant mice prior to embryo implantation. Conditional ablation of both Msx1 and Msx2 in the uterus resulted in female infertility due to a failure in implantation. In these mutant mice (Msx1/2^d/d), the uterine epithelium exhibited persistent proliferative activity and failed to attach to the embryos. Gene expression profiling of uterine epithelium and stroma of Msx1/2^d/d mice revealed an elevated expression of several members of the Wnt gene family in the preimplantation uterus. Increased canonical Wnt signaling in the stromal cells activated β-catenin, stimulating the production of a subset of fibroblast growth factors (FGFs) in these cells. The secreted FGFs acted in a paracrine manner via the FGF receptors in the epithelium to promote epithelial proliferation, thereby preventing differentiation of this tissue and creating a non-receptive uterus refractory to implantation. Collectively, these findings delineate a unique signaling network, involving Msx1/2, Wnts, and FGFs, which operate in the uterus at the time of implantation to control the mesenchymal-epithelial dialogue critical for successful establishment of pregnancy.

During implantation, various tissue compartments within the uterus, including epithelium and stroma, undergo sequential proliferation and differentiation as the embryo attaches to the uterus and invades into the maternal tissue. There is only limited understanding of the molecular signaling pathways that interconnect these tissue compartments to achieve a functional state of the uterus conducive to implantation. This study reveals that a unique signaling network regulated by the homeobox transcription factors MSX1 and MSX2 in the mouse uterus critically controls female fertility. Targeted mutation of Msx1 and Msx2 genes in female mice, which results in infertility, established that these factors suppress signaling by the morphogenic ligands, WNTS, in the uterus. In the absence of Msx1 and Msx2, the WNT signaling is elevated, leading to the production of a subset of fibroblast growth factors (FGFs) in uterine stroma. These FGFs act in a paracrine manner on the uterine epithelium to promote epithelial proliferation, which results in lack of uterine receptivity and implantation failure. This work, therefore, uncovers an important mechanism in mammalian reproduction and development by identifying key paracrine signals that arise from the uterine stroma to control epithelial function during implantation.

Optimization of immunolocalization of cell cycle proteins in human corneal endothelial cells

PURPOSE

En face observation of corneal endothelial cells (ECs) using flat-mounted whole corneas is theoretically much more informative than observation of cross-sections that show only a few cells. Nevertheless, it is not widespread for immunolocalization (IL) of proteins, probably because the endothelium, a superficial monolayer, behaves neither like a tissue in immunohistochemistry (IHC) nor like a cell culture in immunocytochemistry (ICC). In our study we optimized IL for ECs of flat-mounted human corneas to study the expression of cell cycle-related proteins.

METHODS

We systematically screened 15 fixation and five antigen retrieval (AR) methods on 118 human fresh or stored corneas (organ culture at 31 °C), followed by conventional immunofluorescence labeling. First, in an attempt to define a universal protocol, we selected combinations able to correctly localize four proteins that are perfectly defined in ECs (zonula occludens-1 [ZO-1] and actin) or ubiquitous (heterogeneous nuclear ribonucleoprotein L [hnRNP L] and histone H3). Second, we screened protocols adapted to the revelation of 9 cell cycle proteins: Ki67, proliferating cell nuclear antigen (PCNA), minichromosome maintenance protein 2 (MCM2), cyclin D1, cyclin E, cyclin A, p16(Ink4a), p21(Cip1) and p27(Kip1). Primary antibody controls (positive controls) were performed on both epithelial cells of the same, simultaneously-stained whole corneas, and by ICC on human ECs in in vitro non-confluent cultures. Both controls are known to contain proliferating cells. IL efficiency was evaluated by two observers in a masked fashion. Correct localization at optical microscopy level in ECs was define as clear labeling with no background, homogeneous staining, agreement with previous works on ECs and/or protein functions, as well as a meaningful IL in proliferating cells of both controls.

RESULTS

The common fixation with 4% formaldehyde (gold standard for IHC) failed to reveal 12 of the 13 proteins. In contrast, they were all revealed using either 0.5% formaldehyde at room temperature (RT) during 30 min alone or followed by AR with sodium dodecyl sulfate or trypsin, or pure methanol for 30 min at RT. Individual optimization was nevertheless often required to optimize the labeling. Ki67 was absent in both fresh and stored corneas, whereas PCNA was found in the nucleus, and MCM2 in the cytoplasm, of all ECs. Cyclin D1 was found in the cytoplasm in a paranuclear pattern much more visible after corneal storage. Cyclin E and cyclin A were respectively nuclear and cytoplasmic, unmodified by storage. P21 was not found in ECs with three different antibodies. P16 and p27 were exclusively nuclear, unmodified by storage.

CONCLUSIONS

IL in ECs of flat-mounted whole human corneas requires a specific sample preparation, especially to avoid overfixation with aldehydes that probably easily masks epitopes. En face observation allows easy analysis of labeling pattern within the endothelial layer and clear subcellular localization, neither of which had previously been described for PCNA, MCM2, or cyclin D1.

Epithelial progesterone receptor exhibits pleiotropic roles in uterine development and function

The ovarian steroid progesterone, acting through the progesterone receptor (PR), coordinates endometrial epithelial-stromal cell communication, which is critical for its development and function. PR expression in these cellular compartments is under tight temporal and endocrine control. Although ex vivo studies demonstrated the importance of stromal PR expression, they failed to show a role for epithelial PR in uterine function. Here, the in vivo role of PR in the uterine epithelium is defined using floxed PR (PR(f/f)) mice crossed to Wnt7a-Cre mice. Progesterone was unable to stimulate the expression of its epithelial target genes, including Ihh, in the Wnt7a-Cre(+)PR(f/-) mice. Analysis was conducted on Ihh to determine whether PR directly regulates epithelial gene transcription. ChIP-on-chip analysis identified PR binding sites in the 5'-flanking region of Ihh. Cotransfection of the proximal Ihh promoter with PR demonstrated that PR directly regulates Ihh transcription. Female Wnt7a-Cre(+)PR(f/-) mice are infertile due to defects in embryo attachment, stromal cell decidualization, and the inability to cease estrogen-induced epithelial cell proliferation. Finally, progesterone was unable to inhibit neonatal endometrial glandular development in Wnt7a-Cre(+)PR(f/-) mice. Thus, epithelial PR is necessary for the regulation of progesterone epithelial target gene expression, as well as uterine function and development.

The antiproliferative action of progesterone in uterine epithelium is mediated by Hand2

During pregnancy, progesterone inhibits the growth-promoting actions of estrogen in the uterus. However, the mechanism for this is not clear. The attenuation of estrogen-mediated proliferation of the uterine epithelium by progesterone is a prerequisite for successful implantation. Our study reveals that progesterone-induced expression of the basic helix-loop-helix transcription factor Hand2 in the uterine stroma suppresses the production of several fibroblast growth factors (FGFs) that act as paracrine mediators of mitogenic effects of estrogen on the epithelium. In mouse uteri lacking Hand2, continued induction of these FGFs in the stroma maintains epithelial proliferation and stimulates estrogen-induced pathways, resulting in impaired implantation. Thus, Hand2 is a critical regulator of the uterine stromal-epithelial communication that directs proper steroid regulation conducive for the establishment of pregnancy.

Targeting RANKL to a specific subset of murine mammary epithelial cells induces ordered branching morphogenesis and alveologenesis in the absence of progesterone receptor expression

Despite support for receptor of activated NF-κB ligand (RANKL) as a mediator of mammary progesterone action, the extent to which this cytokine can functionally contribute to established progesterone-induced mammary morphogenetic responses in the absence of other presumptive effectors is still unclear. To address this uncertainty, we developed an innovative bigenic system for the doxycycline-inducible expression of RANKL in the mammary epithelium of the progesterone receptor knockout (PRKO) mouse. In response to acute doxycycline exposure, RANKL is specifically expressed in the estrogen receptor α (ER) positive/progesterone receptor negative (ER(+)/PR(-)) cell type in the PRKO mammary epithelium, a cell type that is equivalent to the ER(+)/PR(+) cell type in the wild-type (WT) mammary epithelium. Notably, the ER(+)/PR(+) mammary cell normally expresses RANKL in the WT mammary epithelium during pregnancy. In this PRKO bigenic system, acute doxycycline-induced expression of RANKL results in ordered mammary ductal side branching and alveologenesis, morphological changes that normally occur in the parous WT mouse. This mammary epithelial expansion is accompanied by significant RANKL-induced luminal epithelial proliferation, which is driven, in part, by indirect induction of cyclin D1. Collectively, our findings support the conclusion that RANKL represents a critical mediator of mammary PR action and that restricted expression of this effector to the ER(+)/PR(+) mammary cell-type is necessary for a spatially ordered morphogenetic response to progesterone.

Incremental genetic perturbations to MCM2-7 expression and subcellular distribution reveal exquisite sensitivity of mice to DNA replication stress

Mutations causing replication stress can lead to genomic instability (GIN). In vitro studies have shown that drastic depletion of the MCM2-7 DNA replication licensing factors, which form the replicative helicase, can cause GIN and cell proliferation defects that are exacerbated under conditions of replication stress. To explore the effects of incrementally attenuated replication licensing in whole animals, we generated and analyzed the phenotypes of mice that were hemizygous for Mcm2, 3, 4, 6, and 7 null alleles, combinations thereof, and also in conjunction with the hypomorphic Mcm4(Chaos3) cancer susceptibility allele. Mcm4(Chaos3/Chaos3) embryonic fibroblasts have ∼40% reduction in all MCM proteins, coincident with reduced Mcm2-7 mRNA. Further genetic reductions of Mcm2, 6, or 7 in this background caused various phenotypes including synthetic lethality, growth retardation, decreased cellular proliferation, GIN, and early onset cancer. Remarkably, heterozygosity for Mcm3 rescued many of these defects. Consistent with a role in MCM nuclear export possessed by the yeast Mcm3 ortholog, the phenotypic rescues correlated with increased chromatin-bound MCMs, and also higher levels of nuclear MCM2 during S phase. The genetic, molecular and phenotypic data demonstrate that relatively minor quantitative alterations of MCM expression, homeostasis or subcellular distribution can have diverse and serious consequences upon development and confer cancer susceptibility. The results support the notion that the normally high levels of MCMs in cells are needed not only for activating the basal set of replication origins, but also "backup" origins that are recruited in times of replication stress to ensure complete replication of the genome.

A mouse model to dissect progesterone signaling in the female reproductive tract and mammary gland

Considering the regulatory complexities of progesterone receptor (PR) action throughout the female reproductive axis and mammary gland, we generated a mouse model that enables conditional ablation of PR function in a spatiotemporal specific manner. Exon 2 of the murine PR gene was floxed to generate a conditional PR allele (PR(flox)) in mice. Crossing the PR(flox/flox) mouse with the ZP3-cre transgenic demonstrated that the PR(flox) allele recombines to a PR null allele (PR(d)). Mice homozygous for the recombined null PR allele (PR(d/d)) exhibit uterine, ovarian, and mammary gland defects that phenocopy those of our previously described PR knockout (PRKO) model. Therefore, this conditional mouse model for PR ablation represents an invaluable resource with which to further define in a developmental and/or reproductive stage-specific manner the individual and integrative roles of distinct PR populations resident in multiple progesterone-responsive target sites.

Ablation of Indian hedgehog in the murine uterus results in decreased cell cycle progression, aberrant epidermal growth factor signaling, and increased estrogen signaling

Conditional ablation of Indian hedgehog (Ihh) in the murine uterus results in mice that are sterile because of defects in embryo implantation. We performed microarray analysis on these mice at the time point at which the Ihh target genes are induced by the administration of exogenous hormone to mimic Day 3.5 of pregnancy. This analysis identified 863 genes altered by the conditional ablation of Ihh. Of these, genes that regulated the cell cycle were overrepresented. In addition, genes involved in epidermal growth factor (EGF) and estrogen (E2) signaling were found to be deregulated upon Ihh ablation. Furthermore, upon conditional ablation of Ihh, 15-mo-old mice exhibited hallmarks of estrogenized uteri, such as cystically dilated glands and hyalinized stroma. Thus, Ihh regulates embryo implantation by having an impact on the cell cycle, EGF signaling, and E2 signaling.

Lack of CCAAT enhancer binding protein beta (C/EBPbeta) in uterine epithelial cells impairs estrogen-induced DNA replication, induces DNA damage response pathways, and promotes apoptosis

Female mice lacking the transcription factor C/EBPbeta are infertile and display markedly reduced estrogen (E)-induced proliferation of the uterine epithelial lining during the reproductive cycle. The present study showed that E-stimulated luminal epithelial cells of a C/EBPbeta-null uterus are able to proceed through the G1 phase of the cell cycle before getting arrested in the S phase. This cell cycle arrest was accompanied by markedly reduced levels of expression of E2F3, an E2F family member, and a lack of nuclear localization of cyclin E, a critical regulator of cdk2. An increased nuclear accumulation of p27, an inhibitor of the cyclin E-cdk2 complex, was also observed for the mutant epithelium. Gene expression profiling of C/EBPbeta-null uterine epithelial cells revealed that the blockade of E-induced DNA replication triggers the activation of several well-known components of the DNA damage response pathway, such as ATM, ATR, histone H2AX, checkpoint kinase 1, and tumor suppressor p53. The activation of p53 by ATM/ATR kinase led to increased levels of expression of p21, an inhibitor of G1-S-phase progression, which helps maintain cell cycle arrest. Additionally, p53-dependent mechanisms contributed to an increased apoptosis of replication-defective cells in the C/EBPbeta-null epithelium. C/EBPbeta, therefore, is an essential mediator of E-induced growth and survival of uterine epithelial cells of cycling mice.

Genomic profiling of microRNAs and messenger RNAs reveals hormonal regulation in microRNA expression in human endometrium

MicroRNAs (miRNAs), a class of small noncoding RNAs that regulate gene expression, have fundamental roles in biological processes, including cell differentiation and proliferation. These small molecules mainly direct either target messenger RNA (mRNA) degradation or translational repression, thereby functioning as gene silencers. Epithelial cells of the uterine lumen and glands undergo cyclic changes under the influence of the sex steroid hormones estradiol-17beta and progesterone. Because the expression of miRNAs in human endometrium has been established, it is important to understand whether miRNAs have a physiological role in modulating the expression of hormonally induced genes. The studies herein establish concomitant differential miRNA and mRNA expression profiles of uterine epithelial cells purified from endometrial biopsy specimens in the late proliferative and midsecretory phases. Bioinformatics analysis of differentially expressed mRNAs revealed cell cycle regulation as the most significantly enriched pathway in the late proliferative-phase endometrial epithelium (P = 5.7 x 10(-15)). In addition, the WNT signaling pathway was enriched in the proliferative phase. The 12 miRNAs (MIR29B, MIR29C, MIR30B, MIR30D, MIR31, MIR193A-3P, MIR203, MIR204, MIR200C, MIR210, MIR582-5P, and MIR345) whose expression was significantly up-regulated in the midsecretory-phase samples were predicted to target many cell cycle genes. Consistent with the role of miRNAs in suppressing their target mRNA expression, the transcript abundance of predicted targets, including cyclins and cyclin-dependent kinases, as well as E2F3 (a known target of MIR210), was decreased. Thus, our findings suggest a role for miRNAs in down-regulating the expression of some cell cycle genes in the secretory-phase endometrial epithelium, thereby suppressing cell proliferation.

DNA replication licensing and progenitor numbers are increased by progesterone in normal human breast

Proliferation in the nonpregnant human breast is highest in the luteal phase of the menstrual cycle when serum progesterone levels are high, and exposure to progesterone analogues in hormone replacement therapy is known to elevate breast cancer risk, yet the proliferative effects of progesterone in the human breast are poorly understood. In a model of normal human breast, we have shown that progesterone increased incorporation of 5-bromo-2'-deoxyuridine and increased cell numbers by activation of pathways involved in DNA replication licensing, including E2F transcription factors, chromatin licensing and DNA replication factor 1 (Cdt1), and the minichromosome maintenance proteins and by increased expression of proteins involved in kinetochore formation including Ras-related nuclear protein (Ran) and regulation of chromosome condensation 1 (RCC1). Progenitor cells competent to give rise to both myoepithelial and luminal epithelial cells were increased by progesterone, showing that progesterone influences epithelial cell lineage differentiation. Therefore, we have demonstrated that progesterone augments proliferation of normal human breast cells by both activating DNA replication licensing and kinetochore formation and increasing bipotent progenitor numbers.

Non-genomic progesterone actions in female reproduction

BACKGROUND

The steroid hormone progesterone is indispensable for mammalian procreation by controlling key female reproductive events that range from ovulation to implantation, maintenance of pregnancy and breast development. In addition to activating the progesterone receptors (PRs)-B and -A, members of the superfamily of ligand-dependent transcription factors, progesterone also elicits a variety of rapid signalling events independently of transcriptional or genomic regulation. This review covers our current knowledge on the mechanisms and relevance of non-genomic progesterone signalling in female reproduction.

METHODS

PubMed was searched up to August 2008 for papers on progesterone actions in ovary/breast/endometrium/myometrium/brain, focusing primarily on non-genomic signalling mechanisms.

RESULTS

Convergence and intertwining of rapid non-genomic events and the slower transcriptional actions critically determine the functional response to progesterone in the female reproductive system in a cell-type- and environment-specific manner. Several putative progesterone-binding moieties have been implicated in rapid signalling events, including the 'classical' PR and its variants, progesterone receptor membrane component 1, and the novel family of membrane progestin receptors. Progesterone and its metabolites have also been implicated in the allosteric regulation of several unrelated receptors, such as gamma-aminobutyric acid type A, oxytocin and sigma(1) receptors.

CONCLUSIONS

Identification of the mechanisms and receptors that relay rapid progesterone signalling is an area of research fraught with difficulties and controversy. More in-depth characterization of the putative receptors is required before the non-genomic progesterone pathway in normal and pathological reproductive function can be targeted for pharmacological intervention.

Modulation of 17beta-estradiol on the number and cytotoxicity of NK cells in vivo related to MCM and activating receptors

Natural killer (NK) cells are key components of immune systems and their activities could be regulated by sex hormones. In the present study we investigate the effects of estrogen on the number and cytotoxic activity of NK cells in vivo. The number and cytotoxicity of NK cells in four groups (control, sham+vehicle, Ovx+vehicle and Ovx+E2) were determined. The results showed that 17beta-estradiol (E2) increased the number of NK cells, but reduced their cytotoxicity. The increase of NK cells proportions by E2 may be mediated by up-regulating the expression of MCM7 and MCM10 proteins, which are required for DNA replication licensing in cell proliferation. The suppressed cytotoxicity of splenic NK cells by E2 may be attributable to the down-regulation of NK cells activating receptors-CD69, NKp46, NKG2DL and 2B4 (CD244), which directly inhibited NK cell activation, resulting in the reduced secretion of the soluble factors-granzyme B and FasL. INF-gamma might also act as a negative regulator in the low cytotoxicity of NK cells. In addition, the number of the NK cells is not parallel to their cytotoxicity with a long-term exposure to E2 in vivo. These results suggest that E2-mediated low cytotoxicity of NK cells may regulate host immune response in pregnancy and some female predominant diseases.

Gene expression analysis of endometrium reveals progesterone resistance and candidate susceptibility genes in women with endometriosis

The identification of molecular differences in the endometrium of women with endometriosis is an important step toward understanding the pathogenesis of this condition and toward developing novel strategies for the treatment of associated infertility and pain. In this study, we conducted global gene expression analysis of endometrium from women with and without moderate/severe stage endometriosis and compared the gene expression signatures across various phases of the menstrual cycle. The transcriptome analysis revealed molecular dysregulation of the proliferative-to-secretory transition in endometrium of women with endometriosis. Paralleled gene expression analysis of endometrial specimens obtained during the early secretory phase demonstrated a signature of enhanced cellular survival and persistent expression of genes involved in DNA synthesis and cellular mitosis in the setting of endometriosis. Comparative gene expression analysis of progesterone-regulated genes in secretory phase endometrium confirmed the observation of attenuated progesterone response. Additionally, interesting candidate susceptibility genes were identified that may be associated with this disorder, including FOXO1A, MIG6, and CYP26A1. Collectively these findings provide a framework for further investigations on causality and mechanisms underlying attenuated progesterone response in endometrium of women with endometriosis.

Assessment of the proliferative status of epithelial cell types in the endometrium of young and menopausal transition women

BACKGROUND

We determined protein and mRNA expressions of markers of normal human endometrial proliferation and hypothesized that dysregulation of the endometrial response to estradiol (E(2)) and progesterone would be observed in the older menopausal transition (MT) women compared with mid-reproductive age (MRA) controls.

METHODS

Endometrial biopsies were prospectively obtained from MRA and MT non-randomized healthy volunteers during proliferative (+/- exogenous E(2)) and secretory (MRA only) menstrual cycle phases. mRNA and/or nuclear protein expressions of proliferative markers (MKI67, PCNA and MCM2), cell-cycle regulators (cyclins A1, E1 and D1 and cyclin dependent kinase Inhibitor B; CCNA1, CCNE1, CCND1 and CDKN1B) and sex-steroid receptors [estrogen receptor (ER) and progesterone receptor (PR)] were assessed in endometrial lumen, gland and stroma.

RESULTS

MRA women had significantly higher proliferative than secretory expression of MKI67, PCNA, MCM2, CCNA1, CCNE1, ESR1 and PGR in lumen and gland (minimal stromal changes), whereas CDKN1B protein expression was higher during the secretory phase. E(2)-treatment of MT women led to relatively less MKI67 glandular protein expression compared with MRA women; no other age-related differences were observed.

CONCLUSION

Although the MT does not appear to alter the proliferative cell phenotype of endometrial epithelium and stroma, the data suggest that prior to the MT, age is associated with a decrease in some proliferative markers and steroid receptor expression status within different endometrial cell types.