Localization and characterization of urocortin during human pregnancy

Corticotropin-Releasing Factor Family: A Stress Hormone-Receptor System's Emerging Role in Mediating Sex-Specific Signaling

No organ in the body is impervious to the effects of stress, and a coordinated response from all organs is essential to deal with stressors. A dysregulated stress response that fails to bring systems back to homeostasis leads to compromised function and ultimately a diseased state. The components of the corticotropin-releasing factor (CRF) family, an ancient and evolutionarily conserved stress hormone-receptor system, helps both initiate stress responses and bring systems back to homeostasis once the stressors are removed. The mammalian CRF family comprises of four known agonists, CRF and urocortins (UCN1–3), and two known G protein-coupled receptors (GPCRs), CRF₁ and CRF₂. Evolutionarily, precursors of CRF- and urocortin-like peptides and their receptors were involved in osmoregulation/diuretic functions, in addition to nutrient sensing. Both CRF and UCN1 peptide hormones as well as their receptors appeared after a duplication event nearly 400 million years ago. All four agonists and both CRF receptors show sex-specific changes in expression and/or function, and single nucleotide polymorphisms are associated with a plethora of human diseases. CRF receptors harbor N-terminal cleavable peptide sequences, conferring biased ligand properties. CRF receptors have the ability to heteromerize with each other as well as with other GPCRs. Taken together, CRF receptors and their agonists due to their versatile functional adaptability mediate nuanced responses and are uniquely positioned to orchestrate sex-specific signaling and function in several tissues.

Neuroendocrinology of pregnancy and parturition

During pregnancy, the maternal brain drives a series of adaptive mechanisms that are fundamental for allowing fetal growth and development, protecting both mother and fetus from adverse programming and timing of parturition. This neuroendocrine concept is even more complex as fetal brain and placenta also participate as regulators of maternal-placental-fetal physiology. The placenta is now seen as a neuroendocrine organ, acting as a source of several neuroactive factors that may exert their biologic effects either locally or by entering maternal and fetal circulation, thus acting in an autocrine, paracrine, and endocrine manner. A variety of hypothalamic neurohormones (GnRH, GHRH, somatostatin, CRH, oxytocin) are expressed in the placenta. When stress occurs during pregnancy, the maternal, fetal, and placental hypothalamic-pituitary-adrenal (HPA) axes are activated to stimulate a series of responses contributing to maintain physiologic conditions while at the same time avoiding the adverse effects of stress on the mother and offspring. However, when stress is excessive, a number of obstetric complications may occur, such as preterm birth, pre-eclampsia and intrauterine growth restriction, related to an impairment of the placental adaptive response.

Variation in the maternal corticotrophin releasing hormone-binding protein (CRH-BP) gene and birth weight in Blacks, Hispanics and Whites

BACKGROUND

Given the unique role of the corticotrophin-releasing hormone (CRH) system in human fetal development, the aim of our study was to estimate the association of birth weight with DNA sequence variation in three maternal genes involved in regulating CRH production, bioavailability and action: CRH, CRH-Binding Protein (CRH-BP), and CRH type 1 receptor (CRH-R1), respectively, in three racial groups (African-Americans, Hispanics, and non-Hispanic Whites).

METHODS

Our study was carried out on a population-based sample of 575 mother-child dyads. We resequenced the three genes in mouse-human hybrid somatic cell lines and selected SNPs for genotyping.

RESULTS

A significant association was observed in each race between birth weight and maternal CRH-BP SNP genotypes. Estimates of linkage disequilibrium and haplotypes established three common haplotypes marked by the rs1053989 SNP in all three races. This SNP predicted significant birth weight variation after adjustment for gestational age, maternal BMI, parity, and smoking. African American and Hispanic mothers carrying the A allele had infants whose birth weight was on average 254 and 302 grams, respectively, less than infants having C/C mothers. Non-Hispanic White mothers homozygous for the A allele had infants who were on average 148 grams less than those infants having A/C and C/C mothers.

CONCLUSIONS

The magnitudes of the estimates of the birth weight effects are comparable to the combined effects of multiple SNPs reported in a recent meta-analysis of 6 GWAS studies and is quantitatively larger than that associated with maternal cigarette smoking. This effect was persistent across subpopulations that vary with respect to ancestry and environment.

Distribution of urocortins and corticotropin-releasing factor receptors in the cardiovascular system

Urocortins are human homologues of urotensin I, a fish corticotropin-releasing-factor- (CRF-) like peptide secreted from the urophysis. There are three urocortins: urocortin 1, urocortin 2, and urocortin 3 in mammals. We have shown that urocortin 1 and urocortin 3 are endogenously synthesized in the myocardial cells of human heart and may act on CRF type 2 receptor (CRFR2) expressed in the heart. Expression levels of urocortin 1 in the heart and plasma urocortin 1 levels are elevated in patients with heart failure. Recent studies have shown that urocortins have various biological actions in the cardiovascular system, such as a vasodilator action, a positive inotropic action, a cardioprotective action against ischemia/reperfusion injury, and suppressive actions against the renin angiotensin system and the sympathetic nervous system. Urocortins and CRFR2 may therefore be a potential therapeutic target for cardiovascular diseases, such as congestive heart failure, hypertension, and myocardial infarction.

Neuroendocrine mechanisms in pregnancy and parturition

The complex mechanisms controlling human parturition involves mother, fetus, and placenta, and stress is a key element activating a series of physiological adaptive responses. Preterm birth is a clinical syndrome that shares several characteristics with term birth. A major role for the neuroendocrine mechanisms has been proposed, and placenta/membranes are sources for neurohormones and peptides. Oxytocin (OT) is the neurohormone whose major target is uterine contractility and placenta represents a novel source that contributes to the mechanisms of parturition. The CRH/urocortin (Ucn) family is another important neuroendocrine pathway involved in term and preterm birth. The CRH/Ucn family consists of four ligands: CRH, Ucn, Ucn2, and Ucn3. These peptides have a pleyotropic function and are expressed by human placenta and fetal membranes. Uterine contractility, blood vessel tone, and immune function are influenced by CRH/Ucns during pregnancy and undergo major changes at parturition. Among the others, neurohormones, relaxin, parathyroid hormone-related protein, opioids, neurosteroids, and monoamines are expressed and secreted from placental tissues at parturition. Preterm birth is the consequence of a premature and sustained activation of endocrine and immune responses. A preterm birth evidence for a premature activation of OT secretion as well as increased maternal plasma CRH levels suggests a pathogenic role of these neurohormones. A decrease of maternal serum CRH-binding protein is a concurrent event. At midgestation, placental hypersecretion of CRH or Ucn has been proposed as a predictive marker of subsequent preterm delivery. While placenta represents the major source for CRH, fetus abundantly secretes Ucn and adrenal dehydroepiandrosterone in women with preterm birth. The relevant role of neuroendocrine mechanisms in preterm birth is sustained by basic and clinic implications.

Urocortin in second trimester amniotic fluid: its role as predictor of preterm labor

Backgound. The existence of a “placental clock” which determines the duration of gestation has been previously proposed. It is related to placental CRH secretion and is active from an early phase in human pregnancy. Urocortin is a specific ligand for the corticotropin-releasing factor (CRF) receptor expressed by human trophoblast and fetal membranes. The purpose of this study was to evaluate whether urocortin concentrations in the early second trimester amniotic fluid might serve to predict preterm delivery. Method. The urocortin concentrations in early second trimester amniotic fluid were measured in 41 pregnancies with term delivery and in 41 pregnancies with preterm delivery by using an immunoradiometric assay. Conditional logistic regression analysis was used for statistical analysis. Results. Mean amniotic fluid urocortin concentrations in women with preterm labor were 1.55 ± 0.63 ng/mL while those in women with term labor were 1.6 ± 0.49 ng/mL (p: NS). No statistical significant results were found when comparing amniotic fluid urocortin concentrations in women with preterm premature rupture of membranes leading to preterm labor (n = 19) to women with term delivery without premature rupture of membranes. Conclusion. These results suggest that urocortin concentrations in the amniotic fluid of genetic amniocentesis are not predictive of preterm labor and birth.

Differential regulation of prostaglandin production mediated by corticotropin-releasing hormone receptor type 1 and type 2 in cultured human placental trophoblasts

Prostaglandin (PG) production by intrauterine tissues plays a key part in the control of pregnancy and parturition. The present study was to investigate the role of placenta-derived CRH and CRH-related peptides in the regulation of PG synthesis and metabolism. We found that placental trophoblasts expressed both CRH-R1 and CRH-R2. Treatment of cultured placental cells with either a CRH or urocortin I (UCNI) antibody resulted in a significant decrease in PGE2 release. Both CRH and UCNI antibodies significantly decreased mRNA and protein expression of synthetic enzymes cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX)-2 and increased mRNA and protein expression of 15-hydroxyprostaglandin dehydrogenase (PGDH), the key enzyme of PG metabolism. CRH-R1/-R2 antagonist astressin and CRH-R1 antagonist antalarmin significantly inhibited PGE2 release, whereas CRH-R2 antagonist astressin-2b had no effect on PGE(2) release. Administration of astressin decreased expression of cPLA2 but had no effect on COX-2 expression. Antalarmin reduced cPLA2 and COX-2 expression, whereas astressin-2b did not alter cPLA2 expression but increased COX-2 expression. PGDH expression was enhanced by these three antagonists. Cells treated with exogenous CRH and UCNI showed an increase in PGE(2) release and expression of cPLA2 and COX-2 but a decrease in PGDH expression. UCNII and UCNIII had no effect on PGE2 release but decreased COX-2 and PGDH expression. Our results suggested CRH and CRH-related peptides act on CRH-R1 and CRH-R2 to exert different effects on PG biosynthetic enzymes cPLA2 and COX-2 and thereby modulate output of PGs from placenta, which would be important for controlling pregnancy and parturition.

Corticotropin-releasing hormone receptor type 1 and type 2 mediate differential effects on 15-hydroxy prostaglandin dehydrogenase expression in cultured human chorion trophoblasts

Throughout gestation, the chorion laeve controls the levels of biologically active prostaglandins (PGs) by its high level of nicotinamide adenine dinucleotide-dependent 15-hydroxy PG dehydrogenase (PGDH). In this study, we investigate the effects mediated by CRH receptors on the expression of PGDH in the chorion. We found that both CRHR1 and CRHR2 were localized in cultured chorion trophoblast cells, with CRH-R1alpha, R1beta, R1c, R1e, and R1f and CRHR2beta isoforms identified in these cells. To block the actions of endogenous CRH and its related peptides, cultured chorion trophoblasts were treated with an increasing concentration of alpha-helical CRH 9-41, the nonselective CRH receptor antagonist, which resulted in decreased mRNA and protein expression as well as the activity of PGDH. To investigate the individual role of CRHR1 and CRHR2, cell cultures were treated with the specific CRHR1 antagonist antalarmin and CRHR2 antagonist astressin2B, respectively. The results showed that antalarmin increased whereas astressin2B decreased mRNA and protein expression as well as the activity of PGDH in chorion cells. When the cells were treated with an exclusive CRHR2 agonist, urocortin II, elevated expression and activity of PGDH was exhibited. However, cells treated with either exogenous CRH or urocortin I showed significantly increased PGDH expression, and these effects could be blocked by astressin2B but not by antalarmin. We suggest that, in chorion trophoblast cells, CRHR1 and CRHR2 mediate divergent effects on PGDH expression, and this may provide a precise regulation of PGs levels from chorion to myometrium during pregnancy.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Urocortin 2 and urocortin 3 are expressed by the human placenta, deciduas, and fetal membranes

OBJECTIVE

Urocortin 2 (UCN2) and urocortin 3 (UCN 3) are recently identified neuropeptides showing homology to corticotropin-releasing factor (CRF). In the present study, we evaluated their expression and localization in gestational tissues (placenta, decidua, fetal membranes), and their effect on placental adrenocorticotropic hormone secretion.

STUDY DESIGN

The study was performed in a tertiary clinical care center. Tissues were obtained at first (n = 8; 8-11 weeks of pregnancy) and third (n = 8; 38-40 gestational weeks) trimester. The mRNA expression was evaluated by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR); the cellular localization by immunohistochemistry; ACTH levels were measured in media collected from cultured placental villi.

RESULTS

All tissues analyzed expressed UCN2 and UCN3 mRNA. UCN2 and UCN3 were localized in cytotrophoblast and syncytiotrophoblast cells; UCN2 was present in maternal and fetal vessels and in amniotic cells, while UCN3 was absent. Finally, UCN2 and UCN3 did not stimulate ACTH secretion.

CONCLUSION

Gestational tissues differentially express UCN2 and UCN3 and, despite their homology to CRF, they did not stimulate placental ACTH secretion.

Secretion of adiponectin by human placenta: differential modulation of adiponectin and its receptors by cytokines

AIMS/HYPOTHESIS

Pregnancy, a state of insulin resistance, is associated with elevated levels of cytokines and profound alterations in metabolism. Serum adiponectin, an adipokine with anti-inflammatory and insulin-sensitising properties, has been shown to be lower in patients with gestational diabetes mellitus, a state of greater insulin resistance than normal pregnancies. Hypothesising that the human placenta is a source of adiponectin, we investigated its expression and secretion, and the regulation by cytokines of adiponectin and its receptors.

METHODS

Real-time RT-PCR, radioimmunoassay, Western blotting, radioligand binding and immunofluorescent analyses were applied to demonstrate the expression, secretion and functionality of placental adiponectin.

RESULTS

Adiponectin gene expression and protein were found in the human term placenta, with expression primarily in the syncytiotrophoblast. RIA of conditioned media from explant experiments revealed that the placenta can secrete adiponectin in vitro. Addition of conditioned media to HEK-293 cells transfected with the gene for adiponectin receptor-1 (ADIPOR1) altered the phosphorylation status of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase, an effect abolished after preabsorption with adiponectin antibody. Cytokines, including TNF-alpha, IFN-gamma, IL-6 and leptin, differentially modulated placental adiponectin receptors as well as adiponectin gene expression and secretion. Interestingly, in placentae from women with gestational diabetes mellitus, we observed significant downregulation of adiponectin mRNA, significant upregulation of ADIPOR1 expression, and a non-significant increase in ADIPOR2 expression.

CONCLUSIONS/INTERPRETATION

Our results indicate that the human placenta produces and secretes adiponectin, and that adiponectin and its receptors are differentially regulated by cytokines and their expression altered in women with gestational diabetes mellitus. Collectively, our novel data suggest that adiponectin may play a role in adapting energy metabolism at the materno-fetal interface.

Expression of urocortin in the extravillous human trophoblast at the implantation site

Urocortin (UCN) is a 40 amino acid peptide which is closely related to corticotropin-releasing hormone and binds with high affinity to both CRH type 1 and type 2 receptors. UCN is expressed in human reproductive tissues including endometrium, ovary, and placenta. This study was designed to investigate the cellular localization of UCN at the implantation site of the human blastocyst, as well as the regulation of the UCN promoter by two major intracellular signaling pathways, the cAMP/PKA and diacylglycerol/PKC pathways, in cells of placental origin. For this reason, immunohistochemistry was performed on tissue sections from paraffin-embedded human first trimester placentas and freshly isolated human invasive extravillous trophoblast cells (EVT) were analyzed for UCN expression using RT-PCR and immunofluorescence. Finally, UCN promoter activity was analyzed in the JEG3 human choriocarcinoma cell line. Immunohistochemistry revealed expression of UCN in the cytotrophoblast, the EVT and decidual cells. Both UCN mRNA and peptide were detectable in freshly isolated EVT. Finally, a human UCN promoter luciferase reporter construct transfected into JEG3 cells was significantly inducible by phorbol ester plus ionomycin, but not by phorbol ester alone or by forskolin. Collectively, the present study reports the expression of UCN in EVT and the activation of the UCN gene promoter by the diacylglycerol/PKC pathway. The functional significance of urocortin for the physiology of EVT requires further investigation.

The hypothalamic-pituitary-adrenal axis in pregnancy: challenges in disease detection and treatment

Pregnancy dramatically affects the hypothalamic-pituitary-adrenal axis leading to increased circulating cortisol and ACTH levels during gestation, reaching values in the range seen in Cushing's syndrome (CS). The cause(s) of increased ACTH may include placental synthesis and release of biologically active CRH and ACTH, pituitary desensitization to cortisol feedback, or enhanced pituitary responses to corticotropin-releasing factors. In this context, challenges in diagnosis and management of disorders of the hypothalamic-pituitary-adrenal axis in pregnancy are discussed. CS in pregnancy is uncommon and is associated with fetal morbidity and mortality. The diagnosis may be missed because of overlapping clinical and biochemical features in pregnancy. The proportion of patients with primary adrenal causes of CS is increased in pregnancy. CRH stimulation testing and inferior petrosal sinus sampling can identify patients with Cushing's disease. Surgery is a safe option for treatment in the second trimester; otherwise medical therapy may be used. Women with known adrenal insufficiency that is appropriately treated can expect to have uneventful pregnancies. Whereas a fetal/placental source of cortisol may mitigate crisis during gestation, unrecognized adrenal insufficiency may lead to maternal or fetal demise either during gestation or in the puerperium. Appropriate treatment and management of labor are reviewed.

Corticotropin-releasing hormone (CRH) and urocortin act through type 1 CRH receptors to stimulate dehydroepiandrosterone sulfate production in human fetal adrenal cells

CONTEXT

Near term, the human fetal adrenal increases the production of cortisol and dehydroepiandrosterone sulfate (DHEAS). DHEAS, which acts as substrate for placental estrogen production, induces key changes involved in parturition.

OBJECTIVE

The objective of this study was to determine quantitatively the effect of CRH on mRNA levels of enzymes needed for DHEAS production (steroidogenic acute regulatory protein, CYP11A, CYP17, and SULT2A1), to determine the CRH receptor (CRH-R) subtype(s) responsible for CRH action, and to determine the effect of CRH on CRH-R mRNA expression in human adrenal fetal zone (FZ) cells.

DESIGN

Human adrenal FZ cells were treated with CRH, ACTH, urocortin (Unc), and CRH antagonists, and RNA was analyzed by microarray and real-time RT-PCR.

SETTING

This study was performed at an academic research laboratory.

MAIN OUTCOME MEASURE

The main outcome measure was the expression of steroidogenic enzymes and CRH-R.

RESULTS

Microarray analysis of human FZ cells treated for 24 h with CRH or ACTH showed increased mRNA expression levels of the genes needed for DHEAS production. Real-time RT-PCR analysis confirmed these data. Induction was lost in the presence of CRH-R1 antagonists, but not CRH-R2 antagonists. Stimulation was reproduced by Unc. The CRH-R1alpha mRNA splice variant was the only type 1 receptor isoform expressed in the fetal adrenal, and treatment with CRH up-regulates its mRNA levels.

CONCLUSIONS

CRH, Unc, and ACTH stimulate all elements of the DHEAS synthetic pathway and activate CRH-R1 as well. The resulting increased DHEAS levels can be used for placental estrogen synthesis and contribute to the process leading to parturition in humans.

Reduced maternal plasma urocortin concentrations and impaired uterine artery blood flow at human mid pregnancy

OBJECTIVE

Urocortin is a placental neuropeptide belonging to the family of corticotropin-releasing factors (CRFs), playing a role in the uteroplacental blood flow regulation through the binding to specific CRF receptors. Since CRF receptors are expressed in the uterine vascular bed of pregnant rats, and because urocortin has a relaxant effect on uterine vasculature, we evaluated mid-gestation plasma urocortin levels in women with impaired blood flow through uterine arteries.

METHODS

Maternal plasma urocortin was assayed by specific radioimmunoassay and uterine artery resistance index (RI) by Doppler evaluation at 22-24 weeks' gestation in 57 healthy pregnant women, of which 29 showed a monolateral or bilateral uterine artery notch. Statistical analysis was performed by one-way analysis of variance (ANOVA), followed by post-hoc Tukey test for multiple comparison and Pearson correlation coefficient test.

RESULTS

The mean uterine artery RI was significantly (P <.001) higher in women with a notch than healthy controls. Mean +/- SEM maternal plasma urocortin levels were significantly (P <.001) lower in women with unilateral (52.03 +/- 3.25 pg/mL) or bilateral (47.01 +/- 4.16 pg/mL) uterine artery notch than in healthy control pregnant women (84.01 +/- 3.5 pg/mL). While no difference was found in urocortin levels between patients with unilateral or bilateral uterine artery notch, urocortin concentrations inversely correlated with the mean RI (Pearson r = -0.7318; 95% confidence interval -0.8334 to -0.5822; P <.0001).

CONCLUSIONS

The present findings suggest that reduced levels of circulating urocortin are associated with increased uterine artery resistances and support the hypothesis that urocortin may regulate uterine artery tone at mid gestation.

Effect of hypoxia on urocortin production in human gestational trophoblasts in vitro

PROBLEM

Urocortin is produced by the placenta throughout pregnancy but its regulation remains unknown. The effect of hypoxia on placental urocortin production is not known. The aim of this study was to determine the effect of in vitro hypoxia on human trophoblastic urocortin production.

METHOD OF STUDY

Placental explants and primary cultures were incubated in anaerobe hypoxic bags for 24 h in a humidified incubator. Urocortin peptide secretion and mRNA (messenger RNA) production was determined by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Morphological and functional integrity was verified by immunohistochemical analysis of urocortin expression. Vascular endothelial growth factor expression was used to verify the generation of cellular hypoxia in our in vitro system.

RESULTS

Hypoxia did not affect urocortin secretion or mRNA expression in explant and single-cell cultures. Production was greater from first trimester than term explants and from single-cell primary cultures more than from explant cultures.

CONCLUSIONS

Hypoxia does not influence human placental urocortin secretion or mRNA expression in vitro.

Localization and physiological roles of urocortin

Urocortin, a 40 amino acid peptide, is a corticotropin-releasing factor (CRF) related peptide, and can bind to all three types of CRF receptors (CRF type 1, type 2a and type 2b receptors) with higher affinities for these receptors than CRF. Immunoreactivity of urocortin is widely distributed in central nervous, digestive, cardiovascular, reproductive, immune and endocrine systems. Urocortin plays important roles in appetite-suppression, immunomodulation, steroidogenesis in the ovary, maintenance of the placental function, labor, and cardioprotection via CRF receptors. Although urocortin has potent adrenocorticotropin (ACTH) releasing activity in vitro, endogenous urocortin does not act on pituitary ACTH secretion in vivo.

Urocortins in human reproduction

Data on biological effects and localization of corticotropin-releasing factor (CRF), a neuropeptide structurally and biologically related to urocortins, have triggered the study on expression of urocortins and their function in human reproductive tissues. Ovary, endometrium, placenta and fetal membranes (amnion and chorion), myometrium, and prostate are sources of urocortin 1 and, they also express urocortin binding sites (receptors and CRF-binding protein), thus suggesting that these tissues are also targets of urocortin 1. The current concept thus is that urocortin 1 may affect the physiology of human reproduction through paracrine/autocrine actions. In particular, in vitro data have shown that urocortin 1 plays a major role in human placenta: it stimulates the secretion of ACTH, prostaglandins and activin A from cultured human placental cells, and regulates placental vessel resistance to blood flow. Furthermore, when incubated in myometrial strips, urocortins stimulate uterine contractility, by activating specific intracellular pathways. Taken together, these findings do suggest an important role of urocortins in the physiology of pregnancy and parturition.

Urocortin II is expressed in human pregnant myometrial cells and regulates myosin light chain phosphorylation: potential role of the type-2 corticotropin-releasing hormone receptor in the control of myometrial contractility

The family of CRH-related peptides are suggested to play important roles in the control of myometrial contractility during pregnancy and labor. In this study we investigated the expression of urocortin II (UCN II) in human myometrium and its ability to phosphorylate intracellular components that can be involved in modulating myometrial contractility. Using RT-PCR and fluorescent in situ hybridization, we demonstrated that UCN II and type-2 CRH receptor (CRH-R2) mRNAs were expressed in human nonpregnant and pregnant myometrium. Immunofluorescent studies confirmed protein expression of UCN II in human pregnant myometrial cells, whereas chemical cross-linking studies with radiolabeled UCN II confirmed the presence of CRH-R2 sites with an apparent molecular mass of 50 kDa. Treatment of primary human myometrial cells with UCN II to specifically activate CRH-R2 resulted in a dose-dependent increase of myosin light chain (MLC(20)) phosphorylation. Activation of protein kinase C (PKC) and ERK1/2 was required for the UCN II-induced activation of MLC(20), because treatment of myometrial cells with inhibitors of MAPK kinase 1 (U0126) and PKC (bisindolylmaleimide) inhibited the UCN II-induced phosphorylation of MLC(20). Furthermore, the UCN II effect on MLC(20) was dependent on RhoA translocation to the membrane and subsequent activation of RhoA-associated kinase, as shown by the use of the specific inhibitors exoenzyme C3 and Y27632. Collectively, our data suggest a distinctive role for CRH-R2- specific agonists like UCN II in the control of myometrial contractility during human pregnancy involving sequential activation of PKC, MAPK kinase 1, ERK1/2, RhoA, and RhoA-associated kinase, leading to the MLC(20) phosphorylation.

Paracrine regulation of endometrial function: interaction between progesterone and corticotropin-releasing factor (CRF) and activin A

Under the influence of ovarian steroid hormones, endometrial cells aer able to produce a wide variety of growth factors and peptide hormones that area believed to promote: (1) physiological growth and differentiation during the endometrial cycle; (2) decidualization, an essential preparative event for establishment of pregnancy; and (3) pathological growth and differentiation in endometriosis and cancer. Among the local factors produced by the human endometrium, corticotropin-releasing factor (CRF) and activin A have been evaluated in terms of localization and effects. CRF is a neuropeptide expressed by the epithelial and stromal cells of the human endometrium in increasing amounts from the endometrial proliferative to the secretory phase. CRF expression also increases in the pregnant endometrium, from early in the pregnancy until term. CRF-type 1 receptor mRNA is only expressed by stromal cells. Progesterone induces CRF gene expression and release from decidualized cells and CRF decidualizes cultured stromal endometrial cells. Urocortin, a CRF-related peptide, has been identified in endometrial epithelial and stromal cells, and its function is still under investigation. Activin A is a growth factor expressed in increasing amounts throughout endometrial phases by both epithelial and stromal cells. This growth factor is secreted into the uterine cavity with higher levels in the secretory phase. Maternal decidua expresses activin A mRNA in increasing amounts from early pregnancy until term. Human endometrium also expresses activin-A receptors and follistatin, its binding protein. Activin A decidualizes cultured human endometrial stromal cells (an effect reversed by follistatin) and modulates embryonic trophoblast differentiation and adhesion. Activin A is expressed in endometriosis and endometrial adenocarcinoma.

High levels of intrauterine corticotropin-releasing hormone, urocortin, tryptase, and interleukin-8 in spontaneous abortions

Stress induces CRH secretion that activates hypothalamic-pituitary-adrenal axis and is also abortogenic. In addition to hypothalamus, CRH and its analog urocortin (Ucn) are also secreted locally outside the brain where they activate mast cells leading to inflammation; however, the level of CRH and Ucn or mast cell mediators has not been examined in products of conception (POC). CRH and Ucn were measured by enzyme immunoassay, tryptase by fluoroenzyme immunoassay, and IL-8 by ELISA in POC of 7-9 wk gestation from Caucasian women; they were divided into group I with elective abortions (n = 4), group II with one spontaneous abortion (n = 12), and group III with at least two spontaneous abortions (n = 7). CRH, Ucn, tryptase, and IL-8 levels were higher (P < 0.05) in group III (8683 +/- 1201 pg/g, 7961 +/- 1499 pg/g, 1553 +/- 572 ng/g, and 8317 +/- 1874 pg/g, respectively) than group II (2561 +/- 314 pg/g, 2349 +/- 394 pg/g, 403 +/- 97 ng/g, and 3199 +/- 449 pg/g, respectively) and group I (163 +/- 162 pg/g, 328 +/- 327 pg/g, 72 +/- 31 ng/g, and 3681 +/- 931 pg/g, respectively). Immunostaining of POC showed significantly more tryptase in group III women. High POC levels of CRH and Ucn under stress in habitual spontaneous abortions may activate uterine mast cells to secrete abortogenic tryptase and IL-8.

Role of placenta in preeclampsia

Preeclampsia, which manifests itself as hypertension, proteinuria, and edema in pregnancy, requires the presence of trophoblast tissue but not a fetus. It is characterized by abnormal trophoblast invasion of the spiral arteries of the decidua and myometrium leading to a failure to establish an adequate uteroplacental blood flow and, therefore, is thought to give rise to relatively hypoxic trophoblast tissue. This, in turn, may promote an exaggerated state of oxidative stress in the placenta. This hypoxia/oxidative stress may then further attenuate trophoblast invasion but also alters placental villous angiogenesis leading to a poorly developed fetoplacental vasculature with abnormal reactivity. Oxidative stress per se may also affect vascular reactivity, blood flow, and oxygen and nutrient delivery to the fetus, which ultimately may be compromised. The synthetic and transport functions of the syncytiotrophoblast may also be altered, and there is an increased rate of trophoblast apoptosis. The linkage among abnormal trophoblast invasion, trophoblast dysfunction, and the maternal disease remains unidentified. The presumptive humoral factor that is released by the preeclamptic placenta to cause maternal disease remains elusive. Current therapies to prevent preeclampsia aim toward preventing the maternal syndrome, not preventing the primary pathophysiology.

Urocortin: a mechanism for the sustained activation of the HPA axis in the late-gestation ovine fetus?

We hypothesized that urocortin might be produced in the pituitary of the late-gestation ovine fetus in a manner that could contribute to the regulation of ACTH output. We used in situ hybridization and immunohistochemistry to identify urocortin mRNA and protein in late-gestation fetal pituitary tissue. Levels of urocortin mRNA rose during late gestation and were associated temporally with rising concentrations of pituitary proopiomelanocortin (POMC) mRNA. Urocortin was localized both to cells expressing ACTH and to non-ACTH cells by use of dual immunofluorescence histochemistry. Transfection of pituitary cultures with urocortin antisense probe reduced ACTH output, whereas added urocortin stimulated ACTH output from cultured pituitary cells. Cortisol infusion for 96 h in chronically catheterized late-gestation fetal sheep significantly stimulated levels of pituitary urocortin mRNA. We conclude that urocortin is expressed in the ovine fetal pituitary and localizes with, and can stimulate output of, ACTH. Regulation of urocortin by cortisol suggests a mechanism to override negative feedback and sustain feedforward of fetal hypothalamic-pituitary-adrenal function, leading to birth.

Corticotropin-releasing factor, urocortin and endothelin-1 stimulate activin A release from cultured human placental cells

Human placenta produces activin A, a glycoprotein belonging to the transforming growth factor beta superfamily, which modulates several placental immune and endocrine functions. However, substances involved in controlling placental activin A production are not yet completely elucidated. The aim of the present study was to investigate the effects of placental products, corticotropin-releasing factor (CRF), urocortin, prostaglandin E(2) (PGE(2)) and endothelin-1 (ET-1) on activin A release from cultured human placental cells. Placental tissue was collected at term from normal pregnancies and a trophoblast-enriched cell preparation was cultured for 48 h. The test substances were applied (concentration from 10(-9)-10(-7)M) and the medium was harvested after 3 h incubation; vehicle-treated cells (controls) were present in each experiment. Activin A concentrations in culture medium were measured by using a specific two-site enzyme immunoassay. The addition of CRF resulted in a dose-related increase of activin A concentrations (P < 0.01). The stimulatory effect of CRF was significantly reversed by alpha-helical CRF(9-41), the CRF receptor antagonist. Urocortin showed a stimulating effect on activin A release from placental cells (P < 0.05) but not dose-related; the effect of urocortin was reversed by an equimolar dose of CRF antagonist, astressin. ET-1 significantly increased activin A concentrations in the culture medium only at the highest concentration, 10(-7)M (P < 0.05). No difference in activin A release was observed after incubating the cells with PGE(2). The evidence that CRF, urocortin and ET-1 stimulate activin A secretion from cultured placental cells suggests that these vasoactive factors may affect the changes of placental activin A secretion in pre-eclamptic woman.

Characterising the corticotropin-releasing hormone (CRH) receptors mediating CRH and urocortin actions during human pregnancy and labour

The mechanism of human labour remains unresolved. One of the most important regulatory signals, however, appears to be corticotropin-releasing hormone (CRH), a hypothalamic peptide that controls the body's response to stress, which is also produced by the placenta and intrauterine tissues during pregnancy. CRH belongs to a family of peptides that includes urocortin, which shares sequence homology with CRH and is also expressed by the placenta and intrauterine tissues. During human pregnancy circulating CRH appears to have five main target tissues: the myometrium, the placenta, the fetal membranes, the fetal adrenal cortex and the vasculature. In these tissues CRH plays a role in the control of myometrial contractility,placenta vasodilation, peptide and prostaglandin production and adrenal steroidogenesis and probably many more, yet unidentified processes. The actions of CRH in these tissues are mediated via specific G-protein coupled membrane-bound receptors. These receptors have different functional characteristics, depending on where they are expressed and on the stage of pregnancy. In addition, their function depends upon other intracellular signals via communication between signalling cascades. These findings led us to propose a hypothesis for a dual role of CRH and other CRH-like peptides during pregnancy and labour.

Human placental corticotropin-releasing factor (CRF) in the adaptive response to pregnancy

Several findings suggest a role of placental hormones in the regulation of maternal and fetal physiology during pregnancy. The placenta and its accessory membranes, amnion and chorion, although of fetal origin, actually undertake the role of intermediary barriers and active messengers in the maternal-fetal dialogue. They synthesize, metabolize and serve as targets for numerous hormones and cytokines which control all aspects of pregnancy and parturition. Among these, corticotropin-releasing factor (CRF) has been one of the most investigated in the last decade. The secretion of placental CRF is autonomous, but increasing evidence indicates that maternal or fetal physiological and pathological conditions may influence such secretion. In the event of acute or chronic metabolic, physical or infection stress, the placenta takes part in a stress syndrome by releasing CRF, which may contribute to restore local blood flow, and to influence the timing of delivery. Placental CRF and cytokines produced in case of intrauterine infection may activate labour, thereby helping the fetus to escape from a hostile environment.On the background of maternal and/or fetal stress elicited by a number of pathological conditions, CRF appears to play a role in coordinating adaptive changes in uterine perfusion,maternal metabolism, fluid balance and possibly uterine contractility.

Urocortin relaxes rat tail arteries by a PKA-mediated reduction of the sensitivity of the contractile apparatus for calcium

1. Urocortin is an endogenous vasodilator although the mechanism of vasorelaxation is not completely understood. The hypothesis that an alteration of smooth muscle calcium concentration is involved was tested using isometric tension recording and calcium fluorimetry. The relationship between contraction and intracellular calcium was also estimated. 2. Urocortin produced a concentration dependent relaxation (pD(2) 8.59+/-0.06, n=6) of vessels pre-contracted with a physiological salt solution containing 42 mM KCl (42 mM K-PSS). 3. Removal of the endothelium did not alter the effect of urocortin, pD(2) was 8.49+/-0.11, n=5. 4. Corticotropin-releasing factor relaxed 42 mM K-PSS pre-contracted vessels with less potency compared to urocortin (pD(2) 6.99+/-0.28, n=5). 5. Urocortin at 100 nM relaxed vessels pre-contracted with 42 mM K-PSS by 59.6+/-4.6% (n=8) and vessels pre-contracted with 500 nM noradrenaline by 25.2+/-6.8% (n=6). Both effects were not accompanied by a change in the intracellular calcium concentration. 6. Urocortin at 100 nM produced a significant rightward shift of 0.33+/-0.07 units of normalized intracellular calcium (n=5) of the relationship between tension and intracellular calcium. 7. The urocortin-induced relaxation was considerably reduced in the presence of 0.3 mM Rp-8-CPT-cAMPS, a cyclic AMP-dependent protein kinase (PKA) inhibitor. 8. The PKA-activator Sp-5,6-DCl-cBIMPS relaxed 42 mM K-PSS pre-contracted vessels (pD(2) 4.98+/-0.07, n=6). Sp-5,6-DCl-cBIMPS at 0.1 mM relaxed vessels by 85.3+/-2.5% (n=5), but did not change the intracellular calcium concentration. 9. In conclusion, the data show that urocortin is a potent, endothelium-independent dilator of rat tail arteries and suggest that this effect is mediated by PKA causing a reduction of the sensitivity of the contractile apparatus for calcium.