Estrogen receptors in rat uterine cell cultures: effects of medium on receptor concentration

Procyanidin B2 alleviates uterine toxicity induced by cadmium exposure in rats: The effect of oxidative stress, inflammation, and gut microbiota

Environmental exposure to hazardous materials causes enormous socioeconomic problems due to its deleterious impacts on human beings, agriculture and animal husbandry. As an important hazardous material, cadmium can promote uterine oxidative stress and inflammation, leading to reproductive toxicity. Antioxidants have been reported to attenuate the reproductive toxicity associated with cadmium exposure. In this study, we investigated the potential protective effect of procyanidin oligosaccharide B2 (PC-B2) and gut microbiota on uterine toxicity induced by cadmium exposure in rats. The results showed that the expression levels of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were reduced in utero. Proinflammatory cytokines (including tumor necrosis factor-α, interleukin-1β and interleukin-6), the NLRP3 inflammasome, Caspase-1 and pro-IL-1β were all involved in inflammatory-mediated uterine injury. PC-B2 prevented CdCl2-induced oxidative stress and inflammation in uterine tissue by increasing antioxidant enzymes and reducing proinflammatory cytokines. Additionally, PC-B2 significantly reduced cadmium deposition in the uterus, possibly through its significant increase in MT1, MT2, and MT3 mRNA expression. Interestingly, PC-B2 protected the uterus from CdCl2 damage by increasing the abundance of intestinal microbiota, promoting beneficial microbiota, and inhibiting harmful microbiota. This study provides novel mechanistic insights into the toxicity of environmental cadmium exposure and indicates that PC-B2 could be used in the prevention of cadmium exposure-induced uterine toxicity.

Stromal-epithelial interactions modulate estrogen responsiveness in normal human endometrium

The coculture of endometrial epithelial cells (EEC) with stromal cells (ESC) allows achievement of an improved in vitro system for studying interactions between cells via soluble signals. The purpose of this study was to investigate whether 17beta-estradiol and insulin can induce proliferation of EEC through ESC-secreted factors. No evidence of estrogen-induced EEC proliferation has been reported so far in the conventional culture methods. To this end, we used an in vitro bicameral coculture model where human EEC were grown on extracellular matrix-coated inserts applied in dishes containing ESC. Proliferation was assessed by tritiated thymidine incorporation. Homogeneity of endometrial cell populations was ascertained immunocytochemically. 17beta-estradiol did not induce any proliferative effect on EEC cultured alone. Endometrial epithelial cell proliferation was significantly enhanced in EEC/ESC cocultures; moreover, it was further increased by 17beta-estradiol addition. Insulin increased proliferation in EEC cultured alone, but again the effect was more pronounced in EEC/ESC cocultures. Coincubation of 17beta-estradiol and an antibody against insulin-like growth factor I (IGF I) led to neutralization of ESC-mediated EEC proliferation. This work provides evidence that the effect of 17beta-estradiol on human EEC proliferation may be mediated at least in part through ESC-secreted IGF I. We also showed that insulin effect is also partially due to ESC activation.

Methoxychlor mimics the action of 17 beta-estradiol on induction of uterine epidermal growth factor receptors in immature female rats

Epidermal growth factor (EGF) and its receptor (EGF-R) have been implicated as mediators for estrogen induced cellular growth. This study examines whether the action of the estrogenic pesticide methoxychlor (MXC) parallels the action of 17 beta-estradiol (E2) on uterine EGF-R. Administration of 20 micrograms E2/sexually immature female rat increased 125I-EGF binding to membranes extracted from whole uteri 175% over endogenous levels, while 500 mg MXC/kg led to a 156% increase. E2 in both 20 and 40 micrograms/rat doses and 500 mg MXC/kg led to maximal stimulation over endogenous levels, 12-h posttreatment. Rats were treated with E2, MXC, or vehicle plus 100 micrograms actinomycin-D (ACT-D) or 100 micrograms cycloheximide (CYCLO) per rat to determine if mRNA transcription and translation are involved in the increased EGF-R binding following estrogenic treatment. Only ACT-D inhibited the estrogenic stimulation of EGF-R binding, resulting in a 44% decrease when given concurrently with E2 or MXC, suggesting transcription is required. Additionally, ACT-D decreased endogenous receptor levels by 55%. No other differences were detected. When EGF-R binding data were analyzed by the method of Scatchard, both E2 and MXC, at maximal dosages, elevated uterine EGF-R binding sites by over 200% after 12 h as measured by maximal binding (Bmax) with no significant difference in dissociation constant (Kd) values. These results demonstrate that both E2 and MXC can stimulate the number of EGF-R binding sites without significantly altering the receptor binding affinity (Kd). Further, this stimulation is time dependent and is affected by dose.

Changes in population density elicit quantitative and qualitative changes in the estrogen receptor in intact GH4C1 pituitary tumor cells

We have previously demonstrated that population density alters the responsiveness of GH4C1 pituitary tumor cells to 17 beta-estradiol (E2). At a low population density E2 was observed to increase prolactin mRNA and stimulate cell proliferation, whereas this estrogen was unable to elicit these responses when the cells were maintained at a 4-fold higher population density. In an attempt to determine the mechanism through which population density alters responsiveness to E2, the steady-state level of estrogen receptor (ER), the affinity of ER for E2, and ER down-regulation have been examined in both intact and fractionated cells using ligand binding and ligand exchange assays. Data presented herein demonstrate that (1) GH4C1 cells maintained at low density expressed fewer ER than cells cultured at high density; (2) ER in cells cultured at high density displayed a reduced affinity for E2; (3) ER down-regulation occurring within 1 h of E2 addition appeared to be more pronounced in high density cultures; and (4) steady-state levels of ER were similar in low and high density cells treated with E2 for 1 through 5 days. Although none of these observations appear to correlate with the previously observed effects of population density on the responsiveness of GH4C1 cells to E2, they further illustrate the potential of the culture environment to alter the responsiveness to estrogenic stimuli by altering the properties of the ER.

The concentration of estrogen receptors in rabbit uterine myocytes decreases in culture

OBJECTIVE

The purpose of this study was to determine whether the concentration of estrogen receptors in cultured myocytes is preserved after dispersion.

STUDY DESIGN

Primary myocytes were prepared from rabbit myometrium by collagenase dispersion after removing the endometrium and were isolated with Percoll density gradients. The cells were assayed for estrogen receptor concentration at intervals after dispersion by means of a whole-cell binding assay. Unpaired t test was used for comparisons.

RESULTS

The concentration of estrogen receptors on the first day after dispersion was 12,058 +/- 1096 sites per cell (mean +/- SEM) and decreased to 4389 +/- 1223 site per cell within 9 to 14 days after dispersion (63% decline, p < 0.001). A similar decrease was observed when 2 nmol/L estradiol was present in the medium.

CONCLUSION

The concentration of estrogen receptors in isolated rabbit uterine myocytes decreases after dispersion. This may partly explain the difficulty of demonstrating in vitro estrogen effects on myocytes, which are well established in vivo.

Stimulation of DNA synthesis in rat uterine cells by growth factors and uterine extracts

Replicative DNA synthesis, as measured by thymidine incorporation, has been measured in rat uterine cells in primary culture in response to growth factors. Insulin, insulin-like growth factor-I (IGF-I), multiplication-stimulating activity (MSA) and platelet-derived growth factor (PDGF) stimulated DNA synthesis, while estradiol, epidermal growth factor (EGF), transforming growth factor-beta (TGF-beta), basic fibroblast growth factor (bFGF) and relaxin did not stimulate or did so weakly and only at very high concentrations. Uterine acid extracts also stimulated DNA synthesis. IGF-I stimulated at concentrations consistent with its acting through the IGF-I receptor; however, insulin stimulated at concentrations higher than expected for its acting through its receptor and this its action may be mediated through the IGF-I receptor. IGF-I was found in uterine tissue by radioimmunoassay (RIA). There was a 5- to 10-fold increase in IGF-I in the uteri from ovariectomized rats that had been treated with estradiol 24 h earlier. This is analogous to the increase in growth factor activity found previously in rat uterus after 24-h estradiol treatment (Beck, C.A. and Garner, C.W. (1989) Mol. Cell. Endocrinol. 63, 93-101). These data are consistent with the hypothesis that estradiol effects in the uterus are in part mediated through IGF-I.

Rat myometrial smooth muscle cells show high levels of gap junctional communication under a variety of culture conditions

Gap junctional communication was examined in rat myometrial smooth muscle cells cultured under a variety of conditions. As a functional measure of gap junctional communication, donor cells were microinjected with the fluorescent dye, Lucifer yellow, and the transfer of dye from donor cells to primary neighbor cells was monitored by fluorescence microscopy. In a myometrial smooth muscle cell line established from midgestation (Day 10) rats, high levels of dye transfer, in excess of 90%, were observed in primary cultures and at Passages 1 and 10. A slight decrease in dye transfer to 75% was observed at Passage 5. Similarly, high levels of dye transfer were observed in a smooth muscle cell line established from the myometrium of a late-gestation (Day 19) rat under subconfluent as well as confluent culture conditions. Myometrial smooth muscle cell cultures established from sexually immature 19-day-old rats also exhibited high levels of dye transfer in primary cultures and at Passage 10. Treatment of primary myometrial smooth muscle cell cultures derived from immature 19-day-old rats with 17 beta-estradiol (50 ng/ml) and 4-pregnen-3,20-dione (150 ng/ml) for 48 h in vitro had no significant effect on the high levels of dye transfer. Thus, extensive dye transfer was observed in the rat myometrial smooth muscle cells under all culture conditions examined, regardless of sexual maturity or gestational stage of the animal, in vitro hormone treatment, or cell density.

Growth and cell cycle regulation of mRNA levels in GH3 cells

In the rat anterior pituitary gland, estrogen increases both prolactin (PRL) mRNA levels and stimulates the proliferation of PRL-producing cells. The temporal sequence of these events suggests that PRL gene expression may be coordinated with cell proliferation. We investigated the relationship between cell cycle progression and the accumulation of the PRL mRNA, as well as several other mRNAs, in the rat pituitary tumor GH3 cell line. Serum-deprived cells progressed from G0 to S phase in 20-24 h following serum stimulation. During this time, beta-actin mRNA levels increased 7-fold in 5 h, then returned to basal levels prior to the beginning of S phase. Histone H1 mRNA levels increased approximately 3-fold as cells entered S phase. These data are consistent with the cell cycle-dependent regulation of beta-actin and histone H1 gene expression reported for other cell types. Glucocorticoid receptor mRNA levels were barely detectable in serum-deprived cells but rapidly increased 3- to 5-fold following serum stimulation. This increase resulted in glucocorticoid receptor mRNA levels that were equivalent to those seen in cells maintained in serum-containing medium, suggesting that serum factors regulate glucocorticoid receptor gene expression. In contrast to these changes in gene expression, the levels of PRL and growth hormone (GH) mRNAs gradually increased 2-fold while the cells progressed through G1 phase. Similarly, in cells synchronized to progress through S and G2 phases following aphidicolin treatment, histone H1 gene expression showed a specific increase in S phase cells, whereas PRL and GH mRNA levels changed little with cell cycle progression. These results indicate that the levels of PRL and GH mRNAs are not regulated in a cell cycle-dependent manner. When changes in estrogen responsiveness were determined during the cell cycle, we found that estradiol treatment was capable of increasing PRL mRNA accumulation independent of cell cycle progression and cell cycle distribution in synchronized GH3 cells. These results support the hypothesis that the hormonal regulation of PRL gene expression is not significantly affected by cell growth.

Prolonged cultivation of rat uterine cells with preserved estrogen responsiveness

A rat uterine cell culture was prepared as an experimental system for investigation of mechanisms of steroid hormone actions. Cells frequently supplemented with fresh medium were successfully cultured for 4 weeks through 2 successive passages. Studies of estrogen responsiveness in the primary culture as well as in it's first subculture were performed by a small scale uptake assay for determination of specific steroid binding. Scatchard analysis of specific ovarian hormone binding confirmed that cultured uterine cells preserve both estradiol and progesterone receptors. Characteristics of specific [3H]estradiol binding detected in cells of the first subculture were comparable to those obtained in the initial primary culture. The number of specific estradiol binding sites was diminished to one third of the initial values only in cells of the second subculture, 22 days after isolation of cells from tissue. In the primary culture and in it's first subculture the cells responded to estradiol with a 2-3-fold increase in progesterone receptor level. The subcellular distribution of steroid receptors was also studied; estradiol receptor complexes were detected predominantly in the nuclei whereas progesterone receptors were nearly equally distributed between nuclei and cytosol.

Growth of mouse vaginal epithelial cells in culture: functional integrity of the estrogen receptor system and failure of estrogen to induce proliferation

Normal mouse vaginal epithelial cells isolated from ovariectomized ca. 40-day-old BALB/cCrg1 mice were purified by Percoll density gradient centrifugation and grown in primary culture using a collagen gel matrix and a serum-free complete medium. During the 9-day culture period, a 6-fold increase in cell number was observed. Addition of estrogen to the medium did not enhance epithelial cell proliferation. In fact, all doses of estrogen (180 fM to 18 nM) were inhibitory, resulting in only a 3- to 4-fold increase in cell number by day 9 of culture. Continuous exposure to estradiol (1.8 nM) for 9 days in the serum-free complete medium resulted in a decrease in cytosolic estrogen receptors with associated nuclear accumulation of estrogen receptors. A corresponding increase of cytosolic progestin receptors was also observed, indicating that no qualitative modification of the estrogen receptor system had occurred. Thus, despite its effectiveness in specific product synthesis (progestin receptors), estrogen does not stimulate proliferation of vaginal cells in this culture system, but rather inhibits epithelial cell proliferation.

Evidence for age-dependent changes in Sertoli cell androgen receptor concentration

Cytosol and nuclear receptor concentrations in Sertoli cells isolated from the testes of 15-, 25-, and 35-day-old rats were measured using hydroxylapatite separation procedures. In these cells the mean Kd of the cytosol receptor for methyltrienolone (3H-R1881) ranged between 2.3 and 2.9 nM, and the concentration of cytosol androgen receptor per mg Sertoli cell DNA increased over the 15-to 35-day age interval. However, when the data were expressed per mg cytosol protein, no increase was observed. The increase in receptor concentration per mg DNA paralleled the increase in cytosol protein/DNA ratio. The concentration of androgen receptor per mg DNA in nuclear extracts also increased with age. Consequently, total Sertoli cell androgen receptor increases over the time interval in which meiosis is first completed in the testis.

Estrogen responsiveness of fetal guinea pig uterine cells in culture

Cells from the uterus of the guinea pig fetus have been grown as a monolayer culture in serum-containing medium. Cells from the first subculture showed high concentrations of progesterone receptor (PR; 9.3-13.8 pmol/mg DNA) even after 9 days in medium containing charcoal-treated serum and estradiol did not induce any further increase. The antiestrogens, tamoxifen and monohydroxytamoxifen, both had an inhibitory effect which could be overcome by estradiol. The progestins, progesterone and R5020, as well as the antiprogestin, RU38486, also decreased the PR concentration. Estrogen receptor (ER) levels did not vary with the compounds tested but were found to be low compared to concentrations found in the fetal guinea pig uterus at 55-65 days of gestation. None of the compounds tested had any effect on the growth of the fetal uterine cells so that the modulation of PR concentrations was dissociated from the regulation of cell growth. It is concluded that estrogens are necessary but not sufficient factors in the control of PR levels in fetal uterine cells. The establishment of a culture system for separate types of fetal uterine cells will permit us to study in vitro the factors involved in the growth effects of estrogens and the control of PR synthesis.

Remodeling the estrogen receptor model

The estrogen receptor model has revised to make it compatible with new data on subcellular localization of the receptor and physical characteristics of solubilized versus immobilized receptors. Our current model suggests that receptors, with or without bound estrogen, are present in the nuclear fraction. Furthermore, the receptor behaves as if it were immobilized or bound to some nuclear constituent at all times. Thus, the association of the estrogen-free receptor (unbound receptor) to a target site in the nucleus is considered to be the critical event in defining the nature of the response to estrogenic hormones.