Corticotropin-releasing hormone effects on human pregnant vs. nonpregnant myometrium explants estimated from a mathematical model of uterine contraction

Effects of corticotropin-releasing hormone on the expression of adenosine triphosphate-sensitive potassium channels (Kir6.1/SUR2B) in human term pregnant myometrium

Objective

Corticotropin-releasing hormone (CRH) is a crucial regulator of human pregnancy and parturition. Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels are important for regulating myometrial quiescence during pregnancy. We investigated regulatory effects of different concentrations of CRH on KATP channel expression in human myometrial smooth muscle cells (HSMCs) in in vitro conditions.

Methods

After treating HSMCs with different concentrations of CRH (1, 10, 10², 10³, 10⁴ pmol/L), mRNA and protein expression of K_ATP channel subunits (Kir6.1 and SUR2B) was analyzed by reverse transcription-polymerase chain reaction and western blot. We investigated which CRH receptor was involved in the reaction and measured the effects of CRH on intracellular Ca²⁺ concentration when oxytocin was administered in HSMCs using Fluo-8 AM ester.

Results

When HSMCs were treated with low (1 pmol/L) and high (10³, 10⁴ pmol/L) CRH concentrations, K_ATP channel expression significantly increased and decreased, respectively. SUR2B mRNA expression at low and high CRH concentrations was significantly antagonized by antalarmin (CRH receptor-1 antagonist) and astressin 2b (CRH receptor-2 antagonist), respectively; however, Kir6.1 mRNA expression was not affected. After oxytocin treatment, the intracellular Ca²⁺ concentration in CRH-treated HSMCs was significantly lowered in low concentration of CRH (1 pmol/L), but not in high concentration of CRH (10³ pmol/L), compared to control.

Conclusion

Our data demonstrated the regulatory effect was different when HSMCs were treated with low (early pregnancy-like) and high (labor-like) CRH concentrations and the KATP channel expression showed significant increase and decrease. This could cause inhibition and activation, respectively, of uterine muscle contraction, demonstrating opposite dual actions of CRH.

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.

Corticotropin-releasing hormone interacts with interleukin-1β to regulate prostaglandin H synthase-2 expression in human myometrium during pregnancy and labor

CONTEXT

The onset of labor appears to involve the activation of myometrial inflammatory pathways, and transcription factors such as nuclear factor-κB (NF-κB) control expression of the contraction-associated proteins required to induce a procontractile phenotype. These responses might involve CRH, which integrates immune and neuroendocrine systems.

OBJECTIVES

In human myometrium we investigated cyclooxygenase 2 (PGHS2) expression and regulation by CRH and the proinflammatory cytokine IL-1β before and after labor.

DESIGN

Myometrial tissues obtained from pregnant women at term before (n = 12) or during labor (n = 10) and pathological cases of choriamnionitis-associated term labor (n = 5) were used to isolate primary myocytes and investigate in vitro, CRH effects on basal and IL-1β regulated p65 activation and PGHS2 expression.

RESULTS

In nonlaboring myometrial cells, CRH was unable to induce NF-κB nuclear translocation; however, it altered the temporal dynamics of IL-1β-driven NF-κB nuclear entry by initially delaying entry and subsequently prolonging retention. These CRH-R1-driven effects were associated with a modest inhibitory action in the early phase (within 2 hours) of IL-1β stimulated PGHS2 mRNA expression, whereas prolonged stimulation for 6-18 hours augmented the IL-1β effects. The early-phase effect required intact protein kinase A activity and was diminished after the onset of labor. The presence of chorioamnionitis led to exaggerated PGHS2 mRNA responses to IL-1β but diminished effects of CRH.

CONCLUSIONS

CRH is involved in the inflammatory regulation of PGHS2 expression before and during labor; these actions might be important in priming and preparing the myometrium for labor and cellular adaptive responses to inflammatory mediators.

Mechanics and energetics of myosin molecular motors from nonpregnant human myometrium

Mechanical properties of spontaneously contracting isolated nonpregnant human myometrium (NPHM) were investigated throughout the whole continuum of load from zero load up to isometry. This made it possible to assess the three-dimensional tension-velocity-length (T-V-L) relationship characterizing the level of contractility and to determine crossbridge (CB) kinetics of myosin molecular motors. Seventy-seven muscle strips were obtained from hysterectomy in 42 nonpregnant patients. Contraction and relaxation parameters were measured during spontaneous mechanical activity. The isotonic tension-peak velocity (T-V) relationship was hyperbolic in 30 cases and nonhyperbolic in 47 cases. When the T-V relationship was hyperbolic, the Huxley formalism could be used to calculate CB kinetics and CB unitary force. At the whole muscle level and for a given isotonic load level, part of the V-L phase plane showed a common pathway, so that a given instantaneous length corresponded to only one possible instantaneous velocity, independent of time and initial length. At the molecular level, rate constants for CB attachment and detachment were dramatically low, ∼100 times lower than those of striated muscles, and ∼5 to 10 times lower than those of other smooth muscles. The CB unitary force was ∼1.4 ± 0.1 pN. NPHM shared similar basic contractile properties with striated muscles, reflected in the three-dimensional T-V-L relationship characterizing the contractile level. Low CB attachment and detachment rate constants made it possible to generate normal CB unitary force and normal muscle tension in NPHM, even though it contracted extremely slowly compared with other muscles.

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.

Evidence that corticotropin-releasing hormone modulates myometrial contractility during human pregnancy

As human pregnancy advances, CRH increases exponentially and is hypothesized to trigger the transition from myometrial quiescence to active contractions at labor. Paradoxically, CRH stimulates cAMP production, suggesting it should cause relaxation. To evaluate CRH as a mediator of quiescence, the effect of CRH on contractions in preterm and term myometria with concurrent progesterone (P4) was determined. In late gestation, we hypothesized that high concentrations of CRH down-regulate agonist-activated-cAMP relaxatory pathways and that increased phosphodiesterase (PDE) activity induces heterologous down-regulation of agonist-activated-cAMP pathways. CRH caused dose-dependent relaxation of spontaneously contracting myometrial strips of 31 +/- 8% (mean +/- sem; n = 12) and 35 +/- 20% (n = 3) in term and preterm samples, respectively. CRH with P4 pretreatment caused a 40 +/- 13% (n = 4) reduction in contractility, whereas in matched samples, CRH alone exerted a 26 +/- 6% (n = 4) reduction, with a shift of CRH dose-response curves (P < 0.01, ANOVA). Pretreatment of strips with 10(-7) m CRH did not attenuate relaxation induced by subsequent CRH (n = 3) or salbutamol (beta(2)-agonist) treatment (n = 9). PDE inhibition by rolipram showed a 2.2- and 1.5-fold increase in maximal relaxation induced by CRH and salbutamol, respectively, with a shift of both dose-response curves (P < 0.05 and P < 0.01, ANOVA). In conclusion, CRH at physiological concentrations acts synergistically with P4 contributing to myometrial quiescence. P4 withdrawal may reduce CRH-mediated relaxation. Our functional model does not support homologous or heterologous down-regulation of agonist-stimulated-cAMP pathways by high CRH concentrations. PDE inhibition potentiates CRH and salbutamol-induced relaxation. Up-regulation of PDEs, through chronic cAMP elevation by CRH, could provide a mechanism for down-regulation of agonist-stimulated-cAMP pathways at term.

Placental corticotrophin-releasing hormone and its receptors in human pregnancy and labour: still a scientific enigma

It is now accepted that, in humans, placental corticotrophin-releasing hormone (CRH) is involved in the mechanisms controlling the onset of labour; however, the precise biological role in foeto-maternal tissues remain enigmatic. Maternal plasma levels of CRH rise exponentially as pregnancy progresses towards term and peak during labour; however, evidence to link this with an active role in the onset and progression of labour, is still inconclusive. Certainly, one of the tissues targeted by CRH is the myometrial smooth muscle, which expresses a plethora of specific CRH receptors. This finding implicates CRH in the mechanisms preparing the myometrial microenvironment for the onset of labour and possibly in the regulation of active contractility during labour. Other gestational tissues also targeted by CRH include the placenta, foetal membranes and foetal adrenals, where CRH might regulate distinct physiological functions, ranging from control of vascular tone to adrenal steroidogenesis and prostaglandin synthesis and activity. Given the unique, among mammals, pattern of human placental CRH secretion and CRH receptor expression and signalling during pregnancy and labour, there are only limited biological tools available to delineate the actions of CRH in foeto-maternal tissues, primarily based on in vitro characterisation of the signalling and molecular events driven by CRH. This review will set in context the current concepts about the role of CRH and its receptors during pregnancy and labour, focusing on the unresolved questions and paradoxes that currently exist.

The onset of labor alters corticotropin-releasing hormone type 1 receptor variant expression in human myometrium: putative role of interleukin-1beta

CRH targets the human myometrium during pregnancy. The efficiency of CRH actions is determined by expression of functional receptors (CRH-R), which are dynamically regulated. Studies in myometrial tissue biopsies using quantitative RT-PCR demonstrated that the onset of labor, term or preterm, is associated with a significant 2- to 3-fold increase in CRH-R1 mRNA levels. Detailed analysis of myometrial CRH-R1 mRNA variants showed a decline of the pro-CRH-R1 mRNA encoding the CRH-R1beta variant during labor and increased mRNA levels of CRH-R1d mRNA. Studies in myometrial cells identified IL-1beta as an important regulator of myometrial CRH-R1 gene expression because prolonged treatment of myometrial cells with IL-1beta (1 ng/ml) for 18 h induced expression of CRH-R1 mRNA levels by 1.5- to 2-fold but significantly attenuated CRH-R1beta mRNA expression by 70%. In contrast, IL-1beta had no effect on CRH-R1d mRNA expression. Studies using specific inhibitors suggest that ERK1/2, p38 MAPK, and downstream nuclear translocation of nuclear factor-kappaB mediate IL-1beta effects on myometrial CRH-R1 gene. However, the increased CRH-R1 mRNA expression was associated with a dampening of the receptor efficacy to activate the adenylyl cyclase/cAMP signaling cascade. Thus, our findings suggest that IL-1beta is an important regulator of CRH-R1 expression and functional activity, and this interaction might play a role in the transition of the uterus from quiescence to active contractions necessary for the onset of parturition.