Local paracrine effects of estradiol are central to parturition in the rhesus monkey

The central biochemical mechanisms involved in primate parturition are still unclear. Studies in both humans and nonhuman primates such as the baboon and rhesus monkey indicate that many factors play a part in the cascade of interactive positive feedforward loops that progressively promote parturition: changes in maternal endocrinology, a nocturnal switch in myometrial activity from low amplitude, infrequent contractures to high amplitude, high frequency contractions (see Fig. 1), dilation of the cervix and biochemical changes in the fetal membranes that lead to rupture. Here we demonstrate that infusion of the aromatase inhibitor 4-hydroxyandrostenedione (4OHA) inhibits conversion of androgen to estrogen and prevents premature delivery caused by administration of androgen to pregnant rhesus monkeys at 0.8 of pregnancy term. 4OHA also inhibited the androstenedione induced maternal endocrine and fetal membrane biochemical changes, and alteration of myometrial activity patterns. Secondly, peripheral estrogen infusions increased myometrial activity but did not produce preterm delivery or fetal membrane changes. We conclude that paracrine functions of estrogen at its site of production play critical and central roles in delivery in the non-human primate.

Transcriptional regulation of the tissue factor gene by progestins in human endometrial stromal cells

Decidualization of estradiol (E2)-primed human endometrial cells (HESCs) by progesterone is associated with elevated levels of tissue factor (TF), the primary initiator of hemostasis. Similarly, in cultured human HESCs, the synthetic progestin, medroxyprogesterone acetate (MPA), enhances TF protein and messenger ribonucleic acid (mRNA) levels. Although ineffective alone, E2 potentiates this progestin enhancement of TF expression by HESCs. The current study examines mechanisms underlying MPA enhancement of TF mRNA expression in HESCs. In the presence of the transcription-blocking agent dichlororibofuranosylbenzimidazole, no significant differences were noted in the half-lives of TF mRNA isolated from HESCs treated with E2 alone or with E2 plus MPA. This indicates that MPA-enhanced TF mRNA levels do not reflect changes in the stability of the TF message. To test the effect of progestin on TF promoter activity and to ascertain the mechanism of promoter regulation, primary or first passaged HESCs were transfected with TF promoter constructs spanning the regions -2106 to +121 (TFp(-2106)), -278 to +121 (TFp(-278)), and -111 to +14 (TFp(-111)) bp upstream of the transcription start site. MPA was found to enhance TF transcription by 20-fold in HESCs transfected with TFp(-2106) after correcting for transfection efficiencies with a beta-galactosidase reporter plasmid. Interestingly, levels of E2- plus MPA-stimulated transcription were significantly increased using TFp(-278) compared to TFp(-2106), suggesting that the region between -2106 and -278 bp may contain an inhibitory element. In addition, rates of MPA-stimulated transcription using TFp(-111) were significantly reduced compared to values obtained using TFp(-2106) and were even further reduced compared to values obtained using TFp(-278). This suggests that regulatory elements in the -111 bp region of the TF promoter are necessary for progestin-mediated regulation of the TF gene in HESCs, but are not sufficient to account for maximal rates of TF gene transcription. Our results also demonstrated that induction of steady state TF mRNA by MPA was abolished by treating cells with E2 plus MPA in conjunction with the protein synthesis inhibitor cycloheximide. In light of the absence of a complete progesterone or estrogen response element in the published 5'-sequence of the TF promoter, our results suggest that progestin-enhanced transcription of TF mRNA in stromal cells may be mediated by an uncharacterized protein intermediate(s).

Glucocorticoid effects in the human placenta: evidence that dexamethasone-mediated inhibition of fibronectin expression in cytotrophoblasts involves a protein intermediate

Oncofetal fibronectin is an extracellular matrix protein that is suggested to play an important role in regulating adherence at uterine-placental interfaces. The purpose of the present study was to elucidate a mechanism through which glucocorticoids (GCs) inhibit the synthesis of FN in human placenta as part of their matrix-suppressive action near parturition. We observed that treatment of cytotrophoblasts isolated from human term placentas for 48 h with 10(-7) mol/L dexamethasone (DEX) down-regulated levels of FN expression to 13-19% of control levels in immunoprecipitation, Northern blotting, and enzyme-linked immunosorbent assay experiments. Conversely, GC treatment increased FN expression in placental fibroblasts to 164-310% of control levels in Northern blotting and enzyme-linked immunosorbent assay procedures, suggesting that GC-mediated suppression of FN expression is specific to cytotrophoblasts. Results indicated that the DEX-mediated suppression of FN expression in cytotrophoblasts was not mediated through changes in the stability of FN messenger ribonucleic acid (mRNA). Run-on transcription assays using isolated nuclei suggested that GC treatment did not markedly affect transcription of the FN gene in cytotrophoblasts. To test whether the GC-mediated suppression of FN expression was mediated through a protein intermediate, levels of FN mRNA were examined by Northern blotting in cells treated for 48 h with and without 10(-7) mol/L DEX and cycloheximide (CHX; 125 ng/mL). We observed that CHX treatment increased FN expression in DEX-treated cells to 91% of control values. We noted that whereas the presence of 100-300 ng/mL CHX reversed the DEX-mediated inhibition of FN mRNA expression in cytotrophoblasts, it did not alter the overall rates of protein synthesis in DEX-treated and control cells. These data suggest that suppression of FN mRNA expression by GC in cytotrophoblasts requires de novo protein synthesis and is mediated through a short lived intermediate, the synthesis of which is inhibited at low concentrations of CHX. Thus, GC-induced protein intermediates may influence uterine-placental adherence by modulating levels of oncofetal FN at sites of uterine-placental contact.

Apoptosis and Fas expression in human fetal membranes

Apoptosis (i.e. programmed cell death) plays a key role in maintaining reproductive function in the ovary, mammary and prostate glands, uterus, and testis. The purpose of the present report was to determine, based on biochemical and morphological parameters, whether cells in human fetal membranes undergo apoptosis and express Fas (CD95), a cell surface receptor that mediates apoptosis. Using the terminal deoxynucleotidyl transferase deoxy-UTP-nick end labeling immunohistochemical technique, apoptotic nuclei were identified in amnion epithelial, chorionic trophoblast, and decidua parietalis cell layers of human fetal membranes at term. Electron microscopy of fetal membranes revealed ultrastructural characteristics in amnion epithelium and chorion trophoblast cell layers consistent with apoptosis, including condensation of chromatin along the periphery of the nucleus and nuclear shrinkage. The apoptotic index (percentage of terminal deoxynucleotidyl transferase deoxy-UTP-nick end labeling-positive nuclei of the total nuclei) ranged from 8-29% in amnion epithelial, chorionic trophoblast, and decidual cell layers from women at 23-30, 31-36, and 37-42 weeks gestation. The apoptotic index was statistically greater in the 37-42 week group than in the 23-30 week group in chorionic trophoblast (P < 0.05) and decidual cell (P < 0.01) layers. In contrast, the apoptotic index in the amnion epithelial cell layer was statistically greater (P < 0.05) in the 23-30 week group than in the 31-36 week group, suggesting that apoptosis may be independently regulated in amnion epithelial, chorionic trophoblast, and decidual cell types. Based on the importance of Fas in mediating apoptosis, we investigated whether Fas was expressed by human fetal membrane cells. Immunohistochemical staining of fetal membranes with anti-Fas antibody localized Fas in amnion epithelial, chorionic trophoblast, and decidua parietalis cell layers. A 266-bp band corresponding to the cytoplasmic domain of Fas was detected in samples of amnion, chorion, decidua, and placenta by RT-PCR. Northern blotting revealed a molecular weight of approximately 1.9 kilobases for Fas messenger ribonucleic acid in amniotic tissue. These data suggest that apoptosis and Fas signaling may play a role in remodeling of fetal membrane architecture across gestation.

Antiphospholipid immunoglobulin G antibodies reduce annexin-V levels on syncytiotrophoblast apical membranes and in culture media of placental villi

OBJECTIVES

The mechanism by which antiphospholipid antibodies are associated with pregnancy loss and thromboembolism has not been established. We previously showed that annexin-V, a phospholipid-binding protein with potent anticoagulant activity, is present on the apical membranes of the syncytiotrophoblasts that line placental villi and that this protein is reduced, by immunohistochemistry, on placentas of patients with antiphospholipid antibodies. We therefore investigated whether annexin-V in apical membranes of placental villi is quantitatively reduced by antiphospholipid antibody immunoglobulin G.

STUDY DESIGN

Placentas were obtained from an index patient with antiphospholipid syndrome with intrauterine growth restriction and from a patient with an uncomplicated pregnancy who were both delivered by cesarean section. Apical villous membranes were isolated and annexin-V levels were measured by enzyme-linked immunosorbent assay. We then studied the effects of antiphospholipid immunoglobulin G on placental villous apical annexin-V in vitro. Antiphospholipid immunoglobulin G was isolated from the sera of five different patients with antiphospholipid antibody syndrome along with five paired control immunoglobulin Gs. Short-term cultures were established from normal placental villi and were exposed to the antibodies, after which isolated apical membranes and culture media were immunoassayed for annexin-V levels.

RESULTS

Measurements of apical membrane-associated annexin-V from the antiphospholipid placenta showed significantly less apical membrane-associated annexin-V than did the normal placenta (mean +/- SEM: 4.9 +/- 0.4 micrograms/gm villi for antiphospholipid placenta vs 10.2 +/- 0.6 micrograms/gm villi for control, p < 0.001, n = 4). Exposure of placental villous cultures to five different antiphospholipid immunoglobulin Gs for 24 hours resulted in significant reduction of the levels of apical membrane annexin-V (mean +/- SEM: 3.9 +/- 0.3 micrograms/gm villi) compared with paired controls (5.1 +/- 0.3 micrograms/gm villi, p = 0.02). Villi incubated with the different antiphospholipid immunoglobulin Gs had significantly less annexin-V in conditioned media (mean +/- SEM: 45.1 +/- 4.9 ng/gm villi) compared with the paired normal immunoglobulin G control levels (72.6 +/- 11.4 ng/gm villi, p = 0.03).

CONCLUSIONS

Antiphospholipid immunoglobulin G reduces the levels of syncytiotrophoblast apical membrane-associated annexin-V in placental villi and the release of annexin-V into surrounding media. Reduction of this anticoagulant protein at the maternal-fetal interface may account for the pregnancy loss observed in patients with antiphospholipid syndrome. Short-term culture of placental villi may offer an in vitro model to further study the mechanism of this effect of antiphospholipid antibodies.

Pregnancy loss in the antiphospholipid-antibody syndrome--a possible thrombogenic mechanism

BACKGROUND

The mechanisms of vascular thrombosis and pregnancy loss in the antiphospholipid-antibody syndrome are unknown. Levels of annexin V, a phospholipid-binding protein with potent anticoagulant activity, are markedly reduced on placental villi from women with this syndrome. Hypercoagulability in such women may therefore be due to the reduction of surface-bound annexin V by antiphospholipid antibodies. To test this idea, we studied how antiphospholipid antibodies affect levels of annexin V on cultured trophoblasts and human umbilical-vein endothelial cells and how they affect the procoagulant activity of these cells.

METHODS

We isolated IgG fractions from three patients with the antiphospholipid-antibody syndrome and from normal controls. These antibodies were incubated with cultured BeWo cells (a placental-trophoblast cell line), primary cultured trophoblasts, and human umbilical-vein endothelial cells. Annexin V on the cell surfaces was measured by an enzyme-linked immunosorbent assay. The coagulation times of plasma overlaid on the cells were also determined.

RESULTS

Trophoblasts and endothelial cells exposed to antiphospholipid-antibody IgG as compared with control IgG had reduced levels of annexin V (trophoblasts, 0.37 +/- 0.02 vs. 0.85 +/- 0.12 ng per well, P=0.02; endothelial cells, 1.6 +/- 0.04 vs. 2.1 +/- 0.05 ng per well, P=0.001). Also, trophoblasts and endothelial cells exposed to antiphospholipid-antibody IgG had faster mean (+/- SE) plasma coagulation times than cells exposed to control IgG (trophoblasts, 8.7 +/- 2.0 vs. 21.3 +/- 2.9 minutes, P=0.02; endothelial cells, 9.8 +/- 0.8 vs. 14.2 +/- 1.2 minutes, P=0.04).

CONCLUSIONS

Antiphospholipid antibodies reduce the levels of annexin V and accelerate the coagulation of plasma on cultured trophoblasts and endothelial cells. The reduction of annexin V levels on vascular cells may be an important mechanism of thrombosis and pregnancy loss in the antiphospholipid-antibody syndrome.

Expression of Fas ligand by human cytotrophoblasts: implications in placentation and fetal survival

Recent data indicated that local production of Fas ligand (FasL) by cells of the eye and testis may confer immune tolerance at these sites. In the present study, we examined the in vivo and in vitro patterns of expression of FasL in the human placenta to provide a potential mechanism through which the fetus is afforded protection against the cytolytic actions of lymphocytes present within maternal decidua across gestation. Immunohistochemical staining of first trimester human placental tissue sections revealed the presence of FasL in cytotrophoblasts in free floating villi, anchoring villi, and cytotrophoblastic islands. FasL staining was also pronounced in syncytiotrophoblasts of term placenta indicating that FasL expression is maintained across gestation. Multiple molecular forms of FasL, suggestive of altered patterns of glycosylation, were detected in extracts of term placenta, amnion and chorion by Western blotting. In addition, in vitro expression of FasL was demonstrated to increase 2 to 3-fold during differentiation of primary cultures of cytotrophoblasts isolated from human term placentas. Local production of FasL by human cytotrophoblasts provides a mechanism through which cytotrophoblasts may induce immune tolerance and self-regulate survival during invasion and subsequent placentation.

Production of premature delivery in pregnant rhesus monkeys by androstenedione infusion

The endocrine mechanism involved in term and preterm delivery in primates, including pregnant women, are poorly understood. In the term monkey, fetal plasma androgen concentration rises to two hundred times the maternal concentration which remains unchanged. Placental conversion of androgen to estrogen results in increased maternal plasma estrogen concentration at term in both pregnant nonhuman primates and women. In the present study, continuous infusion of androstenedione to 0.8 gestation monkeys resulted in the premature occurrence of labor-type myometrial activity and increases in maternal plasma estrogen, oxytocin and amnion fibronectin concentrations similar to those measured at normal-term labor. Androstenedione induction of these normal-term biochemical and endocrine changes accompanied by fetal membrane rupture, cervical dilatation and live delivery provides a rich opportunity to study the molecular and physiological mechanisms of both term and preterm labor in primates.

Opposing actions of transforming growth factor-beta and glucocorticoids in the regulation of fibronectin expression in the human placenta

Alterations in the expression of extracellular matrix (ECM) proteins in the placenta and fetal membranes have been linked to parturition whether occurring before or at term. In the present study, we examined the individual and combined effects of transforming growth factor (TGF)-beta and dexamethasone (DEX) on the expression of oncofetal fibronectin (onfFN), i.e. a major ECM protein synthesized by placenta, in cytotrophoblasts isolated from human term placentas to establish a model system from which to evaluate the actions of positive and negative regulators of ECM protein expression in the human placenta. Cytotrophoblasts were maintained for 21=62 h in medium supplemented with 4% charcoal-stripped calf serum in the presence or absence of TGF-beta (2 ng/mL) and DEX (10(-7) mol/L). Levels of onfFN in culture media were determined by immunoassay. TGF-beta treatment alone induced approximately a 150% increase in media levels of onfFN after 21 and 45 h of culture when compared with control, whereas DEX treatment alone reduced levels of onfFN to 15% of control levels. Media levels of onfFN in cells treated with both TGF-beta and DEX were 40-90% of control levels. Similarly, treatment of cells with TGF-beta alone promoted a 100-250% increase in rates of FN synthesis and levels of FN messenger ribonucleic acid, whereas DEX treatment alone reduced these indices of FN expression to approximately 10% of control levels. In cells treated with TGF-beta and DEX, levels of ECM protein synthesis and FN messenger ribonucleic acid were between 30 and 100% of control values. Similar patterns of regulation of FN expression by TGF-beta and DEX were observed when experiments were carried out in serum-free medium. Our results suggest that during pregnancy, TGF-beta and glucocorticoids may be important opposing physiological regulators of placental ECM protein expression.

Reduction of extracellular matrix protein expression in human amnion epithelial cells by glucocorticoids: a potential role in preterm rupture of the fetal membranes

Low levels of expression of extracellular matrix (ECM) proteins in chorioamniotic membranes is a characteristic of prematurely ruptured membranes, a condition associated with 40% of preterm deliveries. In light of the rise in levels of glucocorticoids (GC) in amniotic fluid associated with preterm labor, in the present study we examined the effects of GC on the expression of major ECM proteins in cultures of amnion epithelial cells recovered after digestion of human term amnions. Amnion cells were maintained with and without 10(-7) mol/L dexamethasone (DEX), and levels of the ECM protein fibronectin (FN) were determined by enzyme-linked immunosorbent assay. DEX treatment reduced FN expression in amnion epithelial cells to 15-30% of control levels and reduced FN expression in placental cells to 30-50% of control levels. Conversely, DEX treatment weakly stimulated FN expression in chorion cell cultures. DEX treatment did not affect the total level of amnion cell protein, indicating that the effects of DEX in amnion cells did not result from a general reduction in protein synthesis. Cortisol and DEX reduced FN expression in amnion cells, with half-maximal effective concentrations of approximately 60 and 8 nmol/L, respectively. In immunoprecipitation studies, DEX treatment reduced FN and collagen III synthesis to 20% of control levels, suggesting that GC may coordinately reduce the synthesis of major ECM proteins in amnion cells. Similarly, DEX treatment reduced the levels of FN messenger ribonucleic acids in amnion cells to approximately 15% of control levels. DEX treatment also promoted a marked reduction in FN expression in amnion cells cultured in serum-free medium to 10-50% of control levels. Our results indicate that GC negatively regulate ECM protein expression in amnion epithelial cells, suggesting a potential role in the genesis of altered fetal membrane ECM protein expression associated with prematurely ruptured membranes.

Reduction of annexin-V (placental anticoagulant protein-I) on placental villi of women with antiphospholipid antibodies and recurrent spontaneous abortion

OBJECTIVE

The mechanism by which antiphospholipid antibodies are associated with pregnancy loss and thromboembolic conditions has yet to be elucidated. Annexin-V, an anticoagulant phospholipid-binding protein, is normally present in syncytiotrophoblasts lining the placental villi, where it may play a role in the maintenance of intervillous blood fluidity. We therefore investigated the distribution of annexin-V in placentas of patients with antiphospholipid antibodies in situ and then used short-term villous cultures to study the direct effect of antiphospholipid antibodies on the immunolocation of annexin-V.

STUDY DESIGN

We performed a blinded study by means of computerized morphometric analysis of placental tissues that were stained for annexin-V with affinity-purified polyclonal antibody in an avidin-biotin peroxidase system. The distribution of villous surface annexin-V on cross sections of placentas of patients with antiphospholipid antibodies was compared with that of placentas from patients with uncomplicated pregnancies, elective abortions, and pregnancy losses not associated with antiphospholipid antibodies (n = 8 for each group). We quantitated villous surface annexin-V in cultured placental villi that were incubated with antiphospholipid antibodies immunoglobulin G compared with normal immunoglobulin G and measured annexin-V levels by enzyme-linked immunosorbent assay in conditioned media and in the villi.

RESULTS

The mean villous surface annexin-V of the group with antiphospholipid antibodies was 26.2% +/- 17% (SD) versus 93.9% +/- 5.7% in the normal control group (p < 0.0001). Villi from patients undergoing elective abortions and with pregnancy losses that were not attributed to antiphospholipid antibodies also showed higher mean villous surface annexin-V levels (86.9% +/- 10.6% and 83.5% +/- 11.3%, respectively, p < 0.0001). Organ culture of normal placental villi with affinity-purified immunoglobulin G from patients with antiphospholipid antibodies showed a dose-dependent decrease of villous surface annexin-V over a concentration range of 1.5 micrograms/ml to 1.5 mg/ml. Annexin-V concentrations in conditioned media were significantly lower in the presence of antiphospholipid antibodies immunoglobulin G compared with normal immunoglobulin G (49.4 +/- 8.9 ng/gm wet weight vs 57.2 +/- 11.5 ng/gm, respectively, p < 0.05). In contrast, the mean level of annexin-V in placental villi incubated with antiphospholipid antibodies immunoglobulin G was greater than in villi incubated with normal immunoglobulin G, 1328 +/- 130 ng/gm wet weight versus 1183 +/- 165 ng/gm (p < 0.02).

CONCLUSIONS

Patients with antiphospholipid antibodies and a history of previous pregnancy losses have a significant reduction in annexin-V immunostaining on placental villous surfaces, and antiphospholipid antibodies immunoglobulin G can directly decrease levels of villous surface annexin-V on cultured placental villi. Assays of annexin-V in the conditioned media and cell pellets of cultured placental villi suggest that the mechanism for antiphospholipid antibodies-mediated reduced annexin-V surface staining is an inhibition of annexin-V transport to the villous surface rather than displacement by antiphospholipid antibodies from the surface. This antiphospholipid antibodies-induced deficiency of placental surface annexin-V may contribute to the placental thrombosis observed in these patients.

Negative regulation of placental fibronectin expression by glucocorticoids and cyclic adenosine 3',5'-monophosphate

Fibronectin is a ubiquitous extracellular matrix (ECM) protein known to play a critical role in cell adhesion. In the present study we dissected the effects of glucocorticoids and cyclic adenosine 3',5'-monophosphate (cAMP) on FN expression in cultures of cytotrophoblasts isolated from human term placentas to identify compounds which may influence uterine-placental adherence. Based on immunoassay data, relative to controls, glucocorticoid treatment (1-1000 nM) of cytotrophoblasts specifically inhibited media levels of oncofetal FN (i.e., FNs bearing an oncofetal epitope) 65-92%. Treatment of cytotrophoblasts with androgens, estrogens, and progestins (1-1000 nM) did not markedly affect onfFN expression. Corticotropin-releasing hormone (CRH) treatment (200 nM) alone had no effect on levels on onfFN. In combination experiments using 100 nM dexamethasone (DEX), 1000 nM medroxyprogesterone acetate (MPA), 10 nM estradiol (E2) and 200 nM corticotropin-releasing hormone CRH, we observed that DEX treatment also promoted approximately an 85% reduction in media levels of onfFN. This indicated that glucocorticoids profoundly suppress FN expression in the presence of high concentrations of other steroids and pregnancy-associated paracrine effectors. To examine the influence of ECM protein composition on glucocorticoid-mediated suppression of onfFN expression, cells were inoculated on untreated culture wells or on wells coated with FN, laminin, or collagen I. We observed that DEX treatment downregulated onfFN levels 70-85% under each of these conditions, suggesting that glucocorticoid effects on FN expression were not dependent on the presence of an exogenous ECM. Treatment of cytotrophoblasts with 8-bromo-cAMP resulted in a dose-dependent reduction in onfFN expression to 3% of control levels with an EC50 of 150 nM. Based on Northern blotting, treatment of cytotrophoblasts with 100 nM DEX, 1 mM 8-bromo-cAMP, or 2 nM relaxin inhibited steady state levels of FN mRNA approximately 90% relative to controls. Our results suggest that during pregnancy glucocorticoids and compounds that alter intracellular concentrations of cAMP may profoundly suppress FN expression and therefore may have dramatic effects on uterine-placental adherence.

The expression of the placental anticoagulant protein, annexin V, by villous trophoblasts: immunolocalization and in vitro regulation

We evaluated the histological and ultrastructural localization of the potent anticoagulant protein, annexin V, at the light and electron microscopic levels, using immunohistochemistry and an immunogold method. Annexin V was found to localize to the microvillar surface of the villous syncytiotrophoblasts. Isolated villous-derived trophoblasts were then utilized to evaluate the expression of annexin 1 protein mRNA in response to syncytialization in vitro, as well as to exposure to adenylate cyclase and protein kinase C agonists. Levels of immunoreactive annexin V released into the conditioned media and associated with cell protein were assessed by ELISA while levels of annexin V mRNA were evaluated by Northern analysis. No significant change in either media or cell-associated annexin V concentrations were detected over time in culture or in response to 1.5 mM 8-bromo-cyclic-adenosine-monophosphate (8-b-cAMP) or 0.15 nM phorbol ester myristic acid (PMA). These results indicate that annexin V is ideally positioned to inhibit intervillous thrombosis and maintain the fluidity of the intervillous circulation. Moreover, the absence of trophoblast annexin V regulation by intracellular second messenger regulators suggests that this crucial placental anticoagulant factor is constitutively produced.

Developmental regulation of glucocorticoid-mediated effects on extracellular matrix protein expression in the human placenta

The extracellular matrix (ECM) protein fibronectin (FN) is a critical regulator of uterine-placental adherence. In the present report we compared the effects of glucocorticoids on FN expression in cytotrophoblast cultures isolated from human first trimester and term placentas to elucidate potential steroid-dependent cellular mechanisms associated with human parturition. Based on immunoassays, treatment of first trimester cytotrophoblasts with 10(-7) M dexamethasone (DEX) for 2 cr 4 days reduced medium levels of oncofetal FN (onfFN; i.e. FNs bearing an oncofetal epitope) to approximately 80% of control levels. Conversely, treatment of cytotrophoblasts isolated from term placentas with DEX dramatically reduced medium levels of onfFN to approximately 12% of control values. Treatment of both first trimester and term cells with 10(-6) M progestin, mineralocorticoid, or estrogen had no significant effect on onfFN expression in either cell type. Glucocorticoids specifically down-regulated medium levels of onfFN in term cells, but not in first trimester cells. In contrast, DEX treatment promoted an approximately 3- to 7-fold increase in levels of hCG in both first trimester and term cytotrophoblasts, suggesting that the effects of glucocorticoid on FN and hCG expression are elicited through independent cell-signaling pathways. In first trimester cells, DEX promoted a reduction in rates of FN and laminin synthesis to 60-70% of control levels. In term cells, DEX treatment reduced levels of FN and laminin synthesis to approximately 10% of control levels. Similarly, DEX treatment down-regulated levels of FN mRNA to approximately 60% and 10% of control values in first trimester and term cells, respectively. The first trimester of human pregnancy is associated with low levels of glucocorticoids and reduced glucocorticoid responsiveness. These conditions would favor high levels of placental ECM protein synthesis, thus stabilizing uterine-placental adherence. Conversely, elevated levels of glucocorticoids near parturition and increased glucocorticoid responsiveness would inhibit placental ECM protein synthesis, reducing uterine-placental adherence and promoting the separation of placenta from uterus.

Activity of growth hormone peptides bGH 96-133 and hGH 95-133 in 3T3-F442A cells

Chemically synthesized bovine growth hormone (bGH) bGH 96-133 and its human homologue, hGH 95-133, have similar in vitro biological activities. Unlike native GH, bGH 96-133 and hGH 95-133 were completely without adipogenic or anti-insulin activity at doses up to 10 microM. bGH 96-133 had insulin-like activity, with a 100% increase in glucose uptake at 10 microM. bGH was anti-mitogenic and bGH 96-133 and hGH 95-133 were mitogenic (EC50 approximately 180 nM and maximal response at 1-2 microM). Only bGH 96-133 and hGH 95-133 displaced [125I]hGH 95-133 binding from 3T3-F442A fibroblasts with a Kd between 60-120 nM. bGH, hGH, insulin and IGF-I were without effect on [125I]hGH 95-133 binding. bGH 96-133 and hGH 95-133 did not significantly inhibit [125I]hGH or [125I]IGF-I binding. These experiments indicate that GH containing peptides bGH 96-133 and hGH 95-133 have mitogenic and insulin-like activity without the adipogenic, anti-insulin or anti-mitogenic activity of bGH. These peptides have a specific binding site which appears to be distinct from the GH, insulin and IGF-I receptors.

Cyclic adenosine 3',5'-monophosphate induces prolactin expression in stromal cells isolated from human proliferative endometrium

In vitro decidualization of stromal cells isolated from human proliferative endometrium and cultured in RPMI-1640 containing 2% charcoal-treated fetal bovine serum and 0.1 U/ml insulin was achieved by adding to the medium cAMP derivatives [(Bu)2cAMP (db-cAMP) and 8-bromo-cAMP] or forskolin. PRL production under these conditions was demonstrated by documenting the synthesis of PRL mRNA (approximately 1.1 kilobase), the output of immunoprecipitable [35S]methionine-labeled PRL migrating as a single 23-kilodalton band during gel electrophoresis, and the time- and concentration-dependent secretion of PRL into the medium, measured by RIA (maximal on days 4-5 using 0.5 mM db-cAMP). Medroxyprogesterone acetate (1 microM) enhanced (1.7- to 2.5-fold) the effect of db-cAMP, 8-bromo-cAMP, or forskolin on PRL production, as evaluated by Western blotting analysis. Further evidence for a participation of db-cAMP in the decidualization process was provided by its ability to induce immunocytochemically detectable heat shock protein-27, insulin-like growth factor-binding protein-1, desmin, and laminin, all compounds produced by human decidual cells, but not expressed by stromal cells. The induction of PRL by cAMP may be a key step in the process of differentiation of fibroblast-like stromal cells to the decidual phenotype, as it has been previously reported by this laboratory that, under similar culture conditions, PRL itself is capable of inducing the production of heat shock protein-27, insulin-like growth factor-binding protein-1, desmin, and laminin in stromal cells isolated from proliferative endometrium.

Mitogenic and receptor activities of human growth hormone 108-129

We have selectively synthesized a number of peptides encompassing the region of helix 3 of growth hormone (GH). These peptides and native human (h) GH have been evaluated for mitogenic and receptor activities in 3T3-F442A preadipocytes. In this system, wild type hGH is anti-mitogenic. In contrast, hGH 108-129 stimulated DNA synthesis while other GH-derived peptides were ineffective. hGH (L) 108-129 had an EC50 of about 0.2 nM and was maximally effective at about 0.5 nM in stimulating [3H]thymidine incorporation in 3T3-F442A cells. hGH (L) 108-129 was mitogenically as active as insulin-like growth factor-I and more active than insulin. It was less effective than transforming growth factor-beta. By cell cycle analysis, hGH (L) 108-129 increased the proportion of cells in S/G2/M phases to 28%. hGH, when coincubated with hGH (L) 108-129, blocked the mitogenic response of the peptide. A monoclonal antibody to the GH receptor significantly reduced binding of 125I-hGH to its receptor but had no effect on binding of 125I-hGH (L) 108-129. Affinity cross-linking of 125I-hGH to its receptor was not duplicated with 125I-hGH (L) 108-129. No other GH peptides or insulin competed for binding of 125I-hGH 108-129. Scatchard analysis indicated a Kd of 5.2 nM with 5.6 x 10(5) binding sites/cell for hGH (L) 108-129. These studies indicate that hGH (L) 108-129, a sequence encompassing helix 3 of hGH, acts by binding to a site other than the GH receptor and evokes high mitogenic responses.

Steroid-modulated stromal cell tissue factor expression: a model for the regulation of endometrial hemostasis and menstruation

This study examined steroidal regulation of tissue factor expression by cultured endometrial stromal cells. Confluent stromal cell cultures derived from cycling human endometria were exposed to vehicle control, 10(-8) mol/L estradiol (E2), 10(-8)-10(-6) mol/L medroxyprogesterone acetate (MPA), or both E2 and MPA for 2-24 days in serum-containing medium. The progestin enhanced immunoreactive and functionally active stromal cell tissue factor content, achieving peak effects by 8-12 days of culture. Although E2 alone was ineffective, it augmented MPA-enhanced tissue factor content by 8 days of culture, with continued increases beyond 20 days. Dose-dependent effects on tissue factor protein content were observed between 10(-8)-10(-6) mol/L MPA added alone or together with E2. The content of tissue factor mRNA was also increased by MPA and synergistically increased by E2 plus MPA. Similar steroidal effects on stromal cell tissue factor protein and mRNA content were observed using a defined medium. After optimal induction of tissue factor expression by E2 plus MPA, removal of these steroids reduced levels of stromal cell tissue factor mRNA and protein, with virtually complete reversal by day 7 of withdrawal. These time-course and dose-response relationships establish in vitro conditions with which to dissect factors controlling endometrial hemostasis, whereas the observed effects of steroid withdrawal establish a novel model for the study of mechanisms regulating normal and abnormal uterine bleeding.

Glucocorticoid suppression of human placental fibronectin expression: implications in uterine-placental adherence

Increased levels of glucocorticoids are associated with human parturition whether occurring before or at term. In the present study we examined the effects of glucocorticoids on placental fibronectin (FN) expression in cytotrophoblasts, isolated from human term placentas, to provide a potential mechanism through which glucocorticoids may influence uterine-placental adherence near parturition. Based on immunoassays, relative to controls, media levels of placental FNs bearing an oncofetal epitope (onfFN) were inhibited 65-80% by treatment with 10(-7) M dexamethasone (DEX) during experiments in which cumulative levels and daily release of onfFN were measured. DEX treatment increased human CG production by cytotrophoblasts approximately 3-fold without affecting the levels of total protein, suggesting that DEX treatment did not reduce placental function. DEX and cortisol inhibited onfFN expression with an EC50 of 2 and 16 nM, respectively. Other steroids were not effective in down-regulating onfFN expression, indicating that this was a glucocorticoid-specific response. In immunoprecipitation studies, treatment of cytotrophoblasts with 10(-7) M DEX for 3 days inhibited both release of labeled FN to the media and its incorporation into cell-associated material by approximately 80%. Results from Northern blotting indicated that DEX treatment suppressed levels of FN messenger RNA approximately 90% relative to controls. Levels of labeled laminin in media were inhibited approximately 80% by a 3-day treatment with 10(-7) M DEX, suggesting that glucocorticoids may coordinately suppress the synthesis of multiple extracellular matrix proteins in cytotrophoblasts. In our model, we propose that glucocorticoids may suppress placental extracellular matrix protein synthesis, which could lead to decreased uterine-placental adherence and be associated with parturition.

Mechanisms involved in the decidualization of human endometrial stromal cells

Nearly homogeneous preparations of stromal cells derived from human proliferative endometrium can be obtained by treating endometrial fragments with collagenase in order to disperse stromal elements, filtering the mixture a 25 microns opening sieve to separate them from gland, and incubating the dispersed cells to culture dishes. Exposure of stromal cell cultures to db-cAMP, 8-Br-cAMP or forskolin in RPMI 1640 medium containing 2% ct-FCS and 0.1 U/ml insulin induces the expression of prolactin (PRL), evident from 1) its secretion to the culture medium, measured by radioimmunoassay and by Western blot analysis, 2) the incorporation of 35S-methionine in a protein precipitated with a PRL antibody and co-migrating with authentic PRL during electrophoresis, and 3) the synthesis of PRL mRNA determined by Northern blot analysis. The cAMP effect on PRL production is enhanced by progestins, which by themselves are weak PRL inducers under similar experimental conditions. As expected from previous findings in our laboratory, showing that addition of PRL to the culture medium induces decidualization of endometrial stromal cells, cAMP derivatives not only induce PRL but also provoke differentiation of the fibroblast-like stromal cells to the decidual phenotype, as evident from morphologic changes and by the expression of products characteristic of decidual cells, e.g. IGFBP-1, desmin, hsp 27 and laminin. These findings suggest a PRL-mediated, progesterone-enhanced decidualization mechanism initiated by physiologic agents increasing cAMP levels in stromal cells.

Steroid regulation of oncofetal fibronectin expression in human cytotrophoblasts

Oncofetal fibronectin (onfFN) is a uniquely glycosylated form of FN suggested to play a critical role in uterine/placental adherence during pregnancy. In the present study we have examined steroid regulation of onfFN in highly purified preparations (> or = 95%) of cytotrophoblasts isolated from human term placentas. Based on immunoassays, relative to controls, treatment of cytotrophoblasts with 10(-6) M medroxyprogesterone acetate (MPA) down-regulated media levels of onfFN 25, 53, 59, and 62% on days 1, 2, 3 and 4, respectively. The pattern of steroid regulation and levels of total FN were nearly identical to that of onfFN suggesting that chronic steroid treatment regulates synthesis of FN and not its oncofetal glycosylation. MPA treatment induced a 2-fold stimulation in media levels of hCG indicating that increased placental function was associated with steroid-mediated changes in FN expression. Steroid specificity experiments demonstrated that MPA, cortisol, and dexamethasone were potent inhibitors of onfFN expression whereas estradiol (E2), deoxycorticosterone, testosterone, progesterone, and the synthetic progestin OD-14, were not. This suggested that glucocorticoids and not progestins may be the physiologic regulators of placental FN expression and that MPA may mediate its matrix-modifying activity through a glucocorticoid-like mechanism. Treatment of cells with dexamethasone (10(-7) M) did not affect the levels of total protein synthesis or the release of human placental lactogen to the culture medium. This indicated that steroid-mediated down-regulation of onfFN expression in cytotrophoblasts did not result from a general reduction of protein synthesis. Based on densitometric scanning of Western blots, MPA and dexamethasone treatments down-regulated media levels of onfFN 70% relative to control levels. Northern blotting revealed that MPA and dexamethasone mediated a 60-90% reduction in steady state levels of FN mRNA in the presence or absence of E2. Our in vitro model may provide a unique system to evaluate steroidal effects on extracellular matrix (ECM) protein expression. In addition, we suggest that steroids may critically regulate placental ECM protein synthesis, and thus affect trophoblast/uterine adherence throughout pregnancy and expulsion of the placenta and membranes following delivery of the fetus.

Progestational regulation of human endometrial stromal cell tissue factor expression during decidualization

Decidualized endometrial stromal cells from mid- to late secretory phase and decidual cells from gestational human endometrium displayed prominent immunohistochemical staining for tissue factor, a primary initiator of hemostasis. Consistent with the regulation by progesterone of the decidualization process in vivo, medroxy-progesterone acetate elevated the tissue factor content of primary stromal cell cultures 8-fold over basal values. This increase paralleled the release of immunoreactive PRL, a marker of decidualization. The induced, as well as basal, tissue factor displayed full functional activity and the expected electrophoretic mobility (46 kilodaltons). Moreover, Northern analysis of RNA from cultured stromal cells indicated that medroxyprogesterone acetate increased tissue factor mRNA levels approximately 10-fold relative to control levels. In contrast, cultured stromal cell tissue factor protein content and mRNA levels were unaffected by exogenous estradiol. These findings indicate that enhancement of endometrial stromal cell tissue factor content is associated with progesterone induction of the decidualization process. In humans, trophoblastic invasion of the endometrial vasculature during blastocyst implantation risks hemorrhage. Therefore, increases in perivascular decidual cell tissue factor expression could serve to promote periimplantational endometrial hemostasis.