Roles of estrogen receptor α and β in the regulation of proliferation in endometrial carcinoma

Endometrial carcinoma (EC), an estrogen-dependent gynecological malignancy, is prevalent worldwide. Estrogen receptor α (ERα) and estrogen receptor β (ERβ) are two main estrogen receptor isoforms, which mediate estrogen-induced proliferation in EC. However, the dynamic changes of ERα and ERβ subtype expression and their functions on proliferation in EC remain elusive. In this study, we aimed to investigate the expression of ERα and ERβ in para-tumor eutopic endometrium, endometrial atypical hyperplasia and EC by immunohistochemistry and then analyse their clinical significance. Subsequently, Ishikawa cells with ERα or ERβ knockdown by lentivirus transfection were used to explore the relationship between ERα/ERβ and cell proliferation, and preliminarily evaluate whether metformin’s inhibitory effect on estrogen-induced cell proliferation was mediated by ERα and ERβ. We found that the expression of ERα and ERβ were markedly changed in endometrial hyperplasia and EC compared with that in para-tumor eutopic endometrium and exhibited different expression trends. Through further analysis, we discovered that ERα presented higher expression in endometrial atypical hyperplasia and early stage of EC than that in para-tumor eutopic endometrium, while the expression of ERβ gradually decreased from para-tumor eutopic endometrium to EC. Additionally, the cell cycle-related protein, CyclinD1 was gradually increased but p21 decreased. Furthermore, knockdown of ERα and ERβ severally in Ishikawa cells either inhibited or promoted estrogen-induced cell proliferation through regulating CyclinD1 and p21 expression. Meanwhile, the inhibitory effect of metformin on estrogen-induced cell proliferation was respectively blunted or partly reversed by knockdown of ERα or ERβ. Altogether, ERα and ERβ have different expression patterns in the progression of EC either facilitating or suppressing cell proliferation through regulating the expression of CyclinD1 and p21 in EC cells, and may also mediate the inhibitory effect of metformin on estrogen-induced EC cells proliferation.     

Endometrial microvascular growth in normal and dysfunctional states

As a tissue that exhibits rapid cyclical growth and shedding throughout the reproductive life of the female, human endometrium provides a good model for the study of normal physiological angiogenesis. The objective of this paper is to summarize recent data on endometrial vascular growth, present new data on regional variability in endothelial cell proliferation within the endometrium, and interpret this information in light of current knowledge of the mechanisms by which angiogenesis occurs. Conventional angiogenesis normally involves a series of steps which include endothelial cell activation, breakdown of the basement membrane, migration and proliferation of the endothelial cell, fusion of sprouts, and tube formation. Other mechanisms by which angiogenesis occurs include intussusception and vessel elongation. Using immunohistochemical techniques we have shown repeatedly that levels of endothelial cell proliferation within human endometrium do not show any consistent pattern across the different stages of the menstrual cycle, which is unexpected since significant vascular growth must occur during the proliferative phase, when the endometrium increases in thickness by up to 4-fold. There are two possible explanations for this; either there is no obligatory link between endometrial endothelial cell proliferation and new vessel formation, or there is significant variation in endothelial cell proliferation within different regions of the same uterus. Multiple samples from hysterectomy specimens subsequently demonstrated that the variability is due to real differences between individuals, as well as showing that the endothelial cell proliferation index is significantly elevated in functionalis compared with basalis. During these studies we observed that endothelial cell proliferation nearly always appeared inside existing endometrial vessels, rather than be associated with structures that could be identified as vascular sprouts. To explore further whether sprout formation occurs during endometrial angiogenesis, we investigated the immunohistochemical distribution of integrin alphavbeta3 on endometrial endothelial cells. As for endothelial cell proliferation, integrin alphavbeta3 immunostaining was seen only on endothelial cells that appeared within existing blood vessels. The results from these studies have major implications for our understanding of the mechanisms that control endometrial angiogenesis. The lack of correlation between menstrual cycle stage and endothelial cell proliferation index, or endothelial cell expression of integrin alphavbeta3, suggests that vascular growth is not under the overall control of oestrogen and progesterone.     

Endometrial endothelial cell proliferation during the menstrual cycle

Adult endometrium is a tissue in which physiological angiogenesisoccurs regularly and provides an accessible source of materialfor study. Endometrial biopsies and immunohistochemistry wereused to test two hypotheses: firstly, that there are peaks ofendothelial cell proliferation in human endometrium during themenstrual cycle, and secondly that in-vitro endothelial cellmigratory signal production by human endometrium (measured ina previous study) accompanies endothelial cell proliferativeactivity in vivo. Proliferating cells were identified usinganti-proliferating cell nuclear antigen, and endothelial cellswere identified using anti-CD34. The method was validated bya smaller, separate study using bromodeoxyuridine incorporationand detection with formalin-fixed biopsies, and comparison withproliferating cell nuclear antigen staining. The main study(n=50) showed that significant peaks of endometrial endothelialcell proliferation could not be identified, due to the largevariability in endothelial cell proliferative activity betweenindividuals at the same stage of the menstrual cycle. Endometrialendothelial cell migratory signal production did not correlatewith endothelial cell proliferation (n = 27). Results suggestthat blood vessel growth in the endometrium may occur by a processthat differs from the traditional concept of angiogenesis, whichhas been derived mainly from in-vitro or in-vivo experimentalstudies     

Endometrial leukocytes and menstruation

This review examines evidence supporting the concept that menstruation occurs as a result of an inflammatory process. In the endometrium, leukocyte numbers rise in the late secretory phase following the fall in serum progesterone concentrations. It is postulated that products released following activation of these leukocytes are critically important for menstruation. Mast cells, eosinophils, neutrophils and macrophages in particular are involved. Endometrial granular lymphocytes may also play a role, although their increase in numbers is somewhat earlier during the menstrual cycle than that of the others, suggesting perhaps a primary role in embryo implantation. Leukocyte products include a range of proteases, chemokines and cytokines which in concert result in focal production and activation of matrix metalloproteinases by endometrial cells and the subsequent breakdown of tissue that characterizes menstruation. Regulation of leukocyte entry, proliferation, differentiation and activation within the endometrium is not yet well understood, although both chemokines and cytokines produced locally by endometrial cells are clearly implicated. The role of progesterone in regulating these events is still not understood although the lack of progesterone receptors on endometrial leukocytes suggests indirect actions.     

CD9 is expressed on human endometrial epithelial cells in association with integrins alpha(6), alpha(3) and beta(1)

Recently we reported that CD9 is involved in the invasion of a trophoblast-like choriocarcinoma cell line, BeWo, probably through the regulation of integrin functions. Integrins have also been reported to be expressed in the human endometrium and it has been suggested that they play important roles in blastocyst implantation. This study used immunohistochemistry to investigate the expression of CD9 in the endometrium during the menstrual cycle. CD9 was found to be intensely expressed on the cell surface of the glandular epithelium throughout the menstrual cycle without any apparent differences in staining intensity. In addition, Western blotting analysis of the affinity-purified proteins confirmed that CD9 was associated with integrins beta(1), alpha(3) and alpha(6) in the human endometrium. Therefore it can be concluded that CD9, in association with integrins alpha(6), alpha(3) and beta(1), is a constitutive molecule of the endometrial glandular epithelium. These results also suggest that CD9 may be an important regulator of these integrins in the human endometrium.     

Secretory endometrium highly expresses urocortin messenger RNA and peptide: possible role in the decidualization process

BACKGROUND: Urocortin (UCN) gene expression and synthesis have been reported in epithelial and stromal cells of the human endometrium. In this study we evaluated (i) UCN messenger RNA (mRNA) expression and peptide production in uterine specimens collected throughout the endometrial cycle, (ii) UCN secretion after decidualization of cultured human endometrial stromal cells (HESCs) and (iii) the effect of UCN on endometrial decidualization. METHODS: HESCs were isolated from samples of human endometrium collected from healthy patients with normal menstrual cycle and cultured in presence of cAMP, 17-beta-estradiol (E(2)) + medroxyprogesterone acetate (MPA) and UCN. UCN levels were measured in endometrial extracts by an enzyme immunoassay, and changes of endometrial UCN mRNA expression were measured by RT-PCR analysis. RESULTS: UCN peptide concentrations and mRNA expression were highest in the secretory phase of the menstrual cycle (P < 0.001, late secretory versus early and late proliferative phase) and higher in the late than the early secretory phase (P < 0.01). After decidualization of HESC with cAMP or E(2) + MPA, UCN levels rose in parallel with prolactin concentrations by days 6 (P < 0.01, for all). Finally, the addition of UCN to HESCs, with or without E(2) + MPA, induced the release of prolactin. CONCLUSIONS: The evidence that (i) UCN is highly expressed in the secretory phase of the endometrial cycle; (ii) cAMP and E(2) + MPA modulate secretion of UCN and (iii) UCN induces HESCs decidualization together suggest a possible role for UCN in endometrial physiology.     

Endometrial effects of three doses of trimegestone,a new orally active progestogen,on the postmenopausal endometrium

Objective: To study the effects of oral trimegestone on endometrial histology and vaginal bleeding when given in combination with oral 17-β-oestradiol. Methods: This was a prospective, randomised, double-blind, parallel groups, pilot comparative study. Thirty-eight healthy postmenopausal women with normal endometrial histology were given oral 17-β-oestradiol, 2 mg/day for three continuous cycles of 28 days, plus oral trimegestone, 0.10, 0.25 or 0.50 mg/day from day 15 to day 28 of each cycle. A Vabra biopsy was performed late in the oestradiol/trimegestone phase of cycle 3 and examined for histological evidence of secretory transformation of the endometrium. Characteristics of vaginal bleeding were recorded on a daily basis. Results: Thirty-seven women completed the study, of whom 31 yielded adequate tissue for histological assessment. All showed secretory transformation of the endometrium. Bleeding was of earlier onset and longer duration with the lowest dose of trimegestone. Conclusions: Trimegestone is a highly effective oral progestogen for endometrial protection, all doses inducing secretory endometrial transformation. Although bleeding patterns suggest a weaker effect of the lowest dose used, the minimum effective dose for endometrial protection has still to be determined and may be lower than those used in this study.     

Expression of macrophage inflammatory protein-3alpha in an endometrial epithelial cell line,HHUA, and cultured human endometrial stromal cells

It has been demonstrated that human endometrial epithelial cells (EEC) and stromal cells (ESC) produce a variety of chemokines in vivo and in vitro. To evaluate the expression of macrophage inflammatory protein (MIP)-3alpha in endometrial cells, the production of MIP-3alpha by an EEC line, HHUA, and cultured ESC stimulated with various inflammatory mediators was evaluated by ELISA. Unstimulated HHUA and ESC constitutively secreted MIP-3alpha. Tumour necrosis factor-alpha and interleukin-1beta significantly stimulated the secretion of MIP-3alpha by HHUA and ESC. Lipopolysaccharide also stimulated the secretion of MIP-3alpha by ESC, but not by HHUA. These results show that the concentration of MIP-3alpha in the endometrium is modulated by these inflammatory mediators. MIP-3alpha may contribute to the normal and pathological processes of human reproduction by regulating the trafficking of immature dendritic cells and memory T lymphocytes into the endometrium.     

Kinetics of tumour necrosis factor-alpha,soluble tumour necrosis factor receptors,interleukin 1-beta and its receptor antagonist during serious infections

Tumour necrosis factor-α (TNF) and interleukin-1β (IL-1β) are the central mediators in the genesis of sepsis. The proinflammatory effects of these cytokines are counteracted in vivo by natural inhibitors. Soluble TNF receptors (sTNFR) are shed upon inflammatory stimuli such as IL-1β and TNF itself. Circulating TNF can be complexed by these receptors, thus preventing TNF from binding to effector cells. The binding of IL-1β to its receptor can be blocked by high concentrations of interleukin-1 receptor antagonist (IL-1Ra), which is produced and released upon nearly the same stimuli as IL-1β. This review presents some aspects of the kinetic behaviour of native sTNFR and of the production of native IL-1Ra during severe infections. It appears that in fulminant septicaemia, the plasma concentration of TNF is increased only transiently, during the very early stage of the infection. The concentration of sTNFR, in contrast, remains elevated much longer, probably due to a slower clearance. During the acute stage of severe infectious diseases, peripheral blood cells cannot be stimulated to produce IL-1β. The production of IL-1Ra, in contrast, is not affected. Thus, the kinetic behaviour and regulation of TNF and IL-1β, is different from that of their antiinflammatory counterparts.     

Variation in the expression of cellular retinoid binding proteins in human endometrium throughout the menstrual cycle

Human endometrium is a glandular epithelial tissue with a substantialunderlying stroma. Under the influence of ovarian steroids,endometrium undergoes a cyclical pattern of proliferation followedby secretory differentiation. Since retinoids promote the differentiationof many epithelia to secretory phenotypes they may be involvedin controlling the secretory differentiation of human endometrialepithelium. Cytosolic binding proteins for retinol (cellularretinol binding protein) and retinoic acid (cellular retinoicacid binding protein) may play an important part in regulatingthe availability of retinoic acid to its nuclear receptors andwe have therefore asked whether expression of mRNA for theseproteins varies in relation to endometrial differentiation.In a series of 54 endometrial biopsies, both endometrial epithelialand stromal cells expressed mRNA for cellular retinol bindingprotein type I at a constant level throughout the menstrualcycle. Cellular retinoic acid binding protein type II was alsoexpressed but the level of expression varied dramatically, beingelevated in the proltferative phase and depressed during thesecretory phase of the menstrual cycle in both epithelial andstromal cells. These data suggest that cytosolic binding proteinsmodulate the supply of retinoic acid to the nuclei of endometrialcells during the menstrual cycle and that retinoic acid is involvedin the cyclical control of endometrial differentiation. cellular retinoic acid binding protein/cellular retinol binding protein/endometrium     

Progressive rise in the expression of interleukin-6 in human endometrium during menstrual cycle is initiated during the implantation window

In order to be prepared for implantation, human endometriumundergoes a predictable series of proliferative and secretorychanges. Cytokines play an important role in regulation of thesechanges. Therefore, in this study, we immunolocalized the cytokine,interleukin-6 (IL-6), its receptor and the signal transducergp130 in human endometrium throughout the menstrual cycle. Duringthe entire menstrual cycle, the IL-6 receptor and gp130 werefound primarily in the endometrial glands and to a lesser extentin the stroma. The immunoreactivity of these proteins did notchange in endometrial cells during the entire menstrual cyclewith an exception of reduced immunoreactivity of gp130 in endometrialglands during menstrual phase. Immunostaining showed that immunoreactiveIL-6 was weakly expressed in human endometrium during the proliferativephase. Strong immunoreactivity for IL-6 appeared in endometriumduring the putative 'implantation window'. Expression was byfar most pronounced both in the glandular and surface epithelialcells. The amount of immunoreactive IL-6 in the epithelium progressivelyincreased during the secretory/menstrual phases. During thelate secretory phase, only stromal cells in the upper functionalisexhibited immunoreactivity for IL-6. Western blot analysis corroboratedthe immunohistochemical data. Human endometrial IL-6 consistedof a protein with an apparent mobility of 26 kDa. The immunoreactiveband of IL-6 was weak in the proliferative phase. The expressionof this protein increased progressively during the secretory/menstrualphases. The findings show a cell-specific pattern of distributionfor immunoreactive IL-6 in human endometrium. The menstrualcycle-dependent expression of IL-6 suggests that this cytokinemay play a role in changes in endometrium that prepare thistissue for implantation and menstrual shedding. cytokine/endometrium/implantation/interleukin/interleukin-6