Progesterone-dependent decidualization of the human endometrium is mediated by cAMP

The characteristics of integrins expression in decidualized human endometrial stromal cell induced by 8-Br-cAMP in in vitro

Integrins are heterodimeric glycoproteins that have been found to undergo dynamic temporal and spatial changes in the endometrium during the menstrual cycle and in early pregnancy. Specificity of integrins is known to be different in human endometrial stromal cells and decidual cells. These shifts of integrins suggested to play an important role in embryo implantation and can be modulated by progesterone, cAMP derivatives, and cytokines. The mechanisms of decidualization and its precise physiological role are still not clearly understood and in vitro systems could provide an alternative that overcomes limitations of studying such complex biological phenomena in vivo at the time of implantation. This study was undertaken to establish an in vitro model system for human decidualization using 8-bromo-cAMP and to investigate the characteristics of stromal integrin expression in vitro by 8-Br-cAMP. Endometrial stromal cells were isolated and cultured, and then were induced to decidualize by 0.5 mM 8-Br-cAMP for 15 days. Immunofluorescence staining and flow cytometric analyses of the integrin subunits (alpha1, alpha4, alpha5, alpha6, beta1 and alphavbeta3) were performed at day 9. In the presence of 8-Br-cAMP, the staining intensity of alphavbeta3 was significantly higher than control and measurements for alpha1, alpha4, alpha5, alpha6, and beta1 were similar. Immunofluorescent localization of the integrins reflected the differences obtained from the flow cytometric analyses described above. In summary, the expression of alphavbeta3 integrin increased in stromal cells in vitro decidualized by 8-Br-cAMP and this up-regulation of alphavbeta3 integrin expression during decidualization might influence on human implantation.

Different mechanisms for the induction of copper-zinc superoxide dismutase and manganese superoxide dismutase by progesterone in human endometrial stromal cells

BACKGROUND

The present study was undertaken to investigate the cAMP-dependent regulation of copper-zinc superoxide dismutase (Cu,Zn-SOD) and manganese SOD (Mn-SOD) by ovarian steroids in human endometrial stromal cells (ESC).

METHODS AND RESULTS

To examine the effect of cAMP on SOD expression, ESC were incubated with dibutyryl-cAMP (db-cAMP, 0.5 mmol/l), forskolin (25 micromol/l), or estradiol (E(2), 10(-8) mol/l) + medroxyprogesterone acetate (MPA, 10(-6) mol/l), for 18 days. E(2) + MPA significantly increased Cu,Zn-SOD activity and mRNA concentrations, whereas db-cAMP and forskolin had no effect. On the other hand, Mn-SOD activity and mRNA concentration were significantly increased by all of these treatments. Insulin-like growth factor-binding protein-1, a marker of decidualization, was clearly induced by db-cAMP, forskolin or E(2) + MPA, accompanied by morphological changes characteristic of decidualization. To study whether the increase in Mn-SOD by db-cAMP or E(2) + MPA was mediated by cAMP-dependent protein kinase A (PKA), ESC were incubated with protein kinase inhibitor (PKI) (10 microg/ml), an inhibitor of PKA, in the presence of db-cAMP or E(2) + MPA. The increase in Mn-SOD activity following db-cAMP or E(2) + MPA was completely inhibited by PKI.

CONCLUSIONS

In the process of decidualization, E(2) + MPA increases Mn-SOD expression via a cAMP-dependent pathway. Cu,Zn-SOD is also up-regulated by E(2) + MPA, but via a different pathway from that involving cAMP.

Cyclic AMP-induced forkhead transcription factor, FKHR, cooperates with CCAAT/enhancer-binding protein beta in differentiating human endometrial stromal cells

Decidual transformation of human endometrial stromal (ES) cells requires sustained activation of the protein kinase A (PKA) pathway. In a search for novel transcriptional mediators of this process, we used differential display PCR analysis of undifferentiated primary ES cells and cells stimulated with 8-bromo-cAMP (8-Br-cAMP). We now report on the role of forkhead homologue in rhabdomyosarcoma (FKHR), a recently described member of the forkhead/winged-helix transcription factor family, as a mediator of endometrial differentiation. Sustained 8-Br-cAMP stimulation resulted in the induction and nuclear accumulation of FKHR in differentiating ES cells. Immunohistochemical studies revealed that endometrial stromal expression of FKHR in vivo is confined to decidualizing cells during the late secretory phase of the cycle and coincides with the expression of CCAAT/enhancer-binding protein beta (C/EBPbeta). Reporter gene studies showed that FKHR potently enhances PKA-dependent activation of the tissue-specific decidual prolactin (dPRL) promoter, a major differentiation marker in human ES cells. Transcriptional augmentation by FKHR was effected through functional cooperation with C/EBPbeta and binding to a composite FKHR-C/EBPbeta response unit in the proximal promoter region. Furthermore, FKHR and C/EBPbeta were shown to interact directly in a glutathione S-transferase pull-down assay. These results provide the first evidence of regulated expression of FKHR and demonstrate that FKHR has an integral role in PKA-dependent endometrial differentiation through its ability to bind and functionally cooperate with C/EBPbeta.

Characteristics of the fetal/maternal interface with potential usefulness in the development of future immunological and pharmacological strategies

A study of the fundamental biology of the maternal-fetal interface reveals the complex interactions among multiple cell types and regulatory factors necessary to support a successful pregnancy. Cells of decidua and trophoblast lineages play central roles in creating the maternal-fetal interface and are sources of regulatory factors that can determine the quality and success of pregnancy. The regulatory factors considered here are major placental histocompatibility complex proteins, pregnancy-specific regulatory factors for uterine inflammatory cells, and hormone-controlled placental multidrug-resistant transport systems. Potential targets are discussed and presented as areas where researchers may identify novel pharmacological and immunological strategies that eventually will extend to the clinic to improve the quality and success of pregnancy.

IL-15 regulation in human endometrial stromal cells

A greater knowledge of IL-5 regulation within human endometrium is important in understanding key reproductive events and uterine Natural Killer cell function. In the present study, expression of IL-15 mRNA was shown to be up-regulated by both PGE(2) and IFN-gamma in cultures of human endometrial stromal cells (ESC). Release of IL-15 protein was also shown to be under the control of PGE(2) and IFN-gamma using an enzyme-linked immunosorbent assay for IL-15. In addition, 8-Bromo cAMP was able to increase IL-15 release from ESCs (P < 0.005) implying the actions of PGE(2) may be via this second messenger. Addition of a progestin appeared to enhance these effects. Real-time quantitative PCR has demonstrated an up-regulation in IL-15 mRNA expression in the late secretory phase of the menstrual cycle (P < 0.005) and a progressive rise in IFN-gamma expression throughout the secretory phase and into first trimester decidua. These results suggest that IL-15 regulation in the human endometrium is complex and that hormonal control may be indirect.

Differential effects of IL-11 on rat blastocysts and decidua during the peri-implantation period

PROBLEM

To study effects of interleukin-11 (IL-11) on blastocyst development and decidualization.

METHOD OF STUDY

Rats, injected with buffer (C) or IL-11 [1 mg/kg/day = high dose (HD), 60 microg/kg/week = low dose (LD)-1, 30 microg/kg twice a week = low dose (LD)-2] were made pregnant or pseudopregnant to obtain blastocysts or deciduomata.

RESULTS

As compared with C, more LD-2 blastocysts hatched in culture, while hatching and attachment of HD blastocysts was decreased. Blastocysts from untreated rats in IL-11 supplemented medium (4 ng/mL) demonstrated increased hatching and attachment. The weight of the decidualized uterus in HD and LD-2 pseudopregnant rats was reduced as compared with C and LD- 1. On deciduomata sections from IL-11 treated rats, the area inside the uterine muscle layer was reduced, and mitotic over pycnotic indices were increased in the anti-mesometrial area and decreased in the mesometrial area.

CONCLUSIONS

Low doses of IL-11 improve hatching and attachment of blastocysts, but both high and low doses impair decidualization.

Secretion of keratinocyte growth factor by cultured human endometrial stromal cells is induced through a cyclic adenosine monophosphate-dependent pathway

OBJECTIVE

To evaluate the effects of known modulators of endometrial function on the production of keratinocyte growth factor by endometrial stromal cells.

DESIGN

The effects of dibutyryl-cyclic adenosine monophosphate (db-cAMP), 12-O-tetradecanoylphorbol 13-acetate (TPA), ethinyl estradiol-17alpha (EE), and medroxyprogesterone acetate (MPA) on the secretion of keratinocyte growth factor by endometrial stromal cells were investigated.

SETTING

Research laboratory at a university medical school.

PATIENT(S)

Eleven endometrial specimens in the late proliferative phase.

INTERVENTION(S)

Endometrial stromal cells were incubated for 24 hours with db-cAMP, TPA, EE, or MPA.

MAIN OUTCOME MEASURE(S)

The concentration of keratinocyte growth factor in the culture media was measured using an ELISA.

RESULT(S)

Small amounts of keratinocyte growth factor were detected in the culture media of unstimulated endometrial stromal cells. The production of keratinocyte growth factor by endometrial stromal cells was stimulated with db-cAMP in a dose-dependent manner. The stimulatory effect of db-cAMP was inhibited by Rp-adenosine 3',5'-cyclic monophosphothioate. None of TPA, EE, nor MPA affected the keratinocyte growth factor production by these cells.

CONCLUSION(S)

These results suggest that a cAMP-dependent pathway may play an important role in the regulation of keratinocyte growth factor production by endometrial stromal cells. Keratinocyte growth factor secreted by endometrial stromal cells may be involved in the regeneration of the endometrium during the normal menstrual cycle and early pregnancy.

Functional association of PR and CCAAT/enhancer-binding protein beta isoforms: promoter-dependent cooperation between PR-B and liver-enriched inhibitory protein, or liver-enriched activatory protein and PR-A in human endometrial stromal cells

Activation of the decidual PRL (dPRL) promoter, a major differentiation marker in human endometrial stromal (ES) cells, by cAMP is effected through the induction and binding of CCAAT/enhancer-binding protein-beta (C/EBPbeta) to two overlapping cognate response elements in the promoter region dPRL-332/-270. Progesterone is essential for decidualization and potently enhances cAMP-dependent dPRL promoter activity. We now demonstrate that both liganded PR isoforms, PR-A and PR-B, are capable of trans-activating the dPRL-332/-270 region. The absence of a palindromic progesterone response element (PRE) within this promoter region suggested cross-coupling between C/EBPbeta and PR in human ES cells. Physical interaction between these distinct transcription factors was confirmed by glutathione-S-transferase pull-down assays, demonstrating that both C/EBPbeta isoforms, the full-length activator liver-enriched activatory protein (LAP) and the truncated inhibitor liver-enriched inhibitory protein (LIP), can bind PR-B as well as PR-A in vitro. Transient transfection studies in primary ES cells were used to examine the consequences of PR and C/EBPbeta interaction on activation of their respective response elements. Activation of mouse mammary tumor virus promoter or a reporter construct containing two isolated palindromic PREs by liganded PR-B was synergistically enhanced by coexpression of LIP, but not LAP. In contrast, PR-A failed to trans-activate these constructs significantly regardless of the presence of either C/EBPbeta isoform. Conversely, LAP-dependent activation of the dPRL-332/-270 region or a reporter construct driven by a single C/EBPbeta response element was greatly enhanced by PR-A, but not PR-B, in a ligand-dependent manner. These observations reveal that PR and C/EBPbeta isoform ratios are important determinants of the cellular response to ovarian progesterone in the reproductive tract; the predominance of PR-A and LAP favors expression of C/EBPbeta-dependent genes, whereas PR-B and LIP cooperate in activating PRE-driven promoters.

Gene induction and categorical reprogramming during in vitro human endometrial fibroblast decidualization

Gene induction and categorical reprogramming during in vitro human endometrial fibroblast decidualization. Physiol Genomics 7: 135-148, 2001. First published September 21, 2001; 10.1152/physiolgenomics.00061.2001.-Human decidual fibroblasts undergo a differentiative commitment to the acquisition of endocrine, metabolic, and structural cell functions in a process known as decidualization. Decidualization is critical for embryo implantation and placental function. We characterized gene expression pattern kinetics during decidual fibroblast differentiation by microarray analysis. Of 6,918 genes analyzed, 121 genes were induced by more than twofold, 110 were downregulated, and 50 showed biphasic behavior. Dynamically regulated genes were could be fit into nine K-means algorithm-based kinetic pattern groups, and by biologic classification, into five categories: cell and tissue function, cell and tissue structure, regulation of gene expression, expressed sequence tag (EST), and "function unknown." Reprogramming of genes within specific functional groups and gene families was a prominent feature that consisted of simultaneous induction and downregulation of a set of genes with related function. We previously observed a conceptually similar process during fetal trophoblast differentiation, in which the same phenomena applied to different genes. Of the 569 dynamically regulated genes regulated by either model, only 81 of these were in common. These results suggest that reprogramming of gene expression within focused functional categories represents a fundamental aspect of cellular differentiation.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Mutational analysis of the PRL receptor gene in human breast tumors with differential PRL receptor protein expression

PRL is a major growth and differentiating hormone in the human breast, with activation of the PRL-PRL receptor complex increasingly recognized as an important mechanism in the induction and progression of mammary tumors. Although constitutive activation of various hormone and growth factor receptors is newly recognized as a common cause of tumor development, the PRL receptor gene has not been analyzed for similar aberrations in breast and other tumors. Therefore, using bacterial artificial chromosomes containing the PRL receptor gene and intron-spanning PCR, we determined the exon-surrounding intron sequences providing primers for the first analysis of the entire coding region of the human PRL receptor gene. We examined the presence of PRL receptor in 41 breast tumors by immunohistochemistry and attempted a correlation of its expression to pathological grading of the disease. Then tumor cells were isolated by laser capture microdissection to examine DNA from 30 patients for PRL receptor mutations. The PRL receptor immunoreactive score did not correlate to the tumor size, histopathological grading, age, or family history of patients. PRL receptor immunoreactivity was predominantly found in steroid hormone receptor-positive tumors, but without overall correlation of immunoreactive score. In both PRL receptor-positive and PRL receptor- negative breast cancer cells, direct sequencing of the coding sequence of the PRL receptor gene did not detect any somatic or hereditary gene aberrations. In conclusion, PRL receptor mutations do not appear to be common in human breast cancer, suggesting that constitutive activation of the PRL receptor can be excluded as a major cause of mammary tumor genesis. The molecular structure of the PRL receptor seems to remain intact in tumor tissue, and systemic and local production of PRL may participate in tumor cell growth and proliferation through functional receptors.

Endometrial and myometrial corticotropin-releasing hormone (CRH): its regulation and possible roles

In human endometrium, both epithelial and stroma cells produce corticotropin-releasing hormone (CRH). Both types of cells also possess specific CRH-binding sites indicating a local effect of endometrial CRH. The transcription of the CRH gene in human endometrium is under the control of steroid hormones and locally produced prostanoids and interleukins. Endometrial CRH interacts with locally produced prostaglandins and interleukins. Based on these observations it can be hypothesized that CRH, prostaglandins and interleukins form a network responsible for the communication between epithelial and stromal cells, at the level of the endometrium, and between endometrial and myometrial cells at the level of uterus. The net product of these interaction is the micro-regulation of the decidualizing process and the preparation of endometrium for the implantation/nidation of the conceptus. Indeed, this network may represent the core of the intrauterine neuroendocrine-immune interactions involved in the decidualization of stroma and implantation of blastocyst. In addition, this network appears to be essential for the fine-tuning of myometrial tone.

The role of human chorionic gonadotropin on decidualization of endometrial stromal cells in vitro

Although decidualization of endometrial stromal cells (ESC) is crucial for blastocyst implantation and maintenance of pregnancy, its complex mechanism still remains largely unknown. It has long been believed that hCG can directly induce in vitro decidualization of ESC via cAMP signaling. Recently, however, it has been reported that the LH/CG receptor is not present in human endometrium, and the direct effect of hCG on decidualization has become controversial. To reevaluate the exact effect of hCG on decidualization, human ESC were isolated and cultured with hCG and/or ovarian steroids. ESC treated with 17beta-estradiol plus progesterone (E(2)/P) transformed morphologically and produced significant PRL, whereas ESC treated with hCG alone showed no significant increase in PRL in culture medium and exhibited no morphological changes. Moreover, hCG did not promote E(2)/P-induced PRL production or intracellular cAMP accumulation, and protein kinase A inhibitor failed to block E(2)/P-induced PRL production. These results suggest that hCG does not directly affect in vitro decidualization of human ESC and that the process of E(2)/P-induced in vitro decidualization might consist of several pathways, including the intracellular cAMP signaling cascade.

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

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

Progesterone receptor regulates decidual prolactin expression in differentiating human endometrial stromal cells

Human endometrial stromal (ES) cells in culture express PRL, a marker of decidualization, in response to sustained activation of protein kinase A (PKA). Cotreatment with the progestin medroxyprogesterone acetate (MPA) enhanced decidual PRL gene activation in the presence of elevated intracellular cAMP levels. This synergy became apparent, at protein and promoter level, after a lag period of 2 days and increased in a time-dependent manner thereafter. Pretreatment with cAMP advanced the time at which synergy between cAMP and MPA was apparent, suggesting that PKA activation sensitized ES cells to the effects of progestins. Analysis of the progesterone receptor (PR) indicated that PR-A was the predominant form in differentiating ES cells, but its abundance decreased markedly during the course of the decidualization response. The decline in PR levels was of functional relevance, as expression of PR-B or PR-A, by transient transfection, dramatically inhibited the activity of a decidual PRL promoter-reporter construct in response to cAMP. Furthermore, the expression of endogenous PRL protein in response to cAMP or cAMP plus MPA was substantially decreased by constitutive expression of green fluorescence protein-tagged PR, which was localized in the nucleus even in the absence of added ligand. Ligand-independent PR inhibition of the decidual PRL promoter was receptor specific, independent of known PR phosphorylation sites, and required minimally a functional DNA-binding domain. Transient expression of steroid receptor coactivator-1e (SRC-1e), but not SRC-1a, allowed synergy between cAMP and MPA without the requirement of sensitization by pretreatment with cAMP. This raised the possibility that SRC-1e was a component of cAMP-dependent sensitization of ES cells, but there was no evidence of altered messenger RNA expression of either SRC-1 isoform during decidualization. In conclusion, cellular PR levels determine the onset of the decidualization response. Initiation of this process requires elevated intracellular cAMP levels that sensitize ES cells to the actions of progestins through down-regulation of cellular PR levels and possibly via modulation of function of an intermediate factor(s) such as SRC-1e.

The decidualizing effect of progesterone may involve direct transcriptional activation of corticotrophin-releasing hormone from human endometrial stromal cells

The hypothalamic neuropeptide corticotrophin-releasing hormone (CRH) is also produced by human endometrial cells and is directly involved in the decidualization process as a paracrine inducer. The aim of the present work was to examine the effect of progesterone, the main decidualizing factor, on endometrial CRH, in primary cultures of human endometrial stromal cells. The effect of progesterone was examined by measuring the effects of medroxyprogesterone acetate (MPA) on (i) the concentration of immunoreactive CRH in isolated human endometrial stromal cells and (ii) the activity of the CRH promoter in human endometrial stromal cells transfected with a 0.9 kb fragment of the 5'-flanking region of the human CRH gene coupled to luciferase reporter. The data show that MPA increased the production and secretion of immunoreactive CRH from stromal cells and induced the activity of the CRH promoter, both in a dose-dependent manner. These effects were partially reversed by a molar excess of the antiprogestin RU 486 and were completely abolished in the presence of 100 nmol/l of the cAMP inhibitor, Rp-cAMP. The effect of progesterone on the CRH promoter requires the existence of an intact CRH sequence since experiments carried out with a deleted palindromic cAMP response element (CRE: 5'-TGACGTCA) at -224 bp of the CRH promoter resulted in a complete loss of MPA effect. In conclusion, these data provide evidence that progesterone induces the transcription of CRH gene in human endometrial stroma. This effect coupled with the decidualizing properties of progesterone and CRH may indicate that progesterone and CRH form a decidualizing local pathway within the human endometrium.