Corticotropin-releasing Hormone Gene Research Articles

Primary social relationships influence the development of the hypothalamic–pituitary–adrenal axis in the rat

In the developing rodent, there is a period from about days 4 to 14 when the adrenal response to stress is either minimal or non-existent. This has been designated as the stress hyporesponsive period (SHRP). Numerous experiments have demonstrated that maternal factors are critical for the regulation of the pup's hypothalamic–pituitary–adrenal (HPA) axis and the maintenance of the SHRP. Following 24 h of maternal deprivation, the neonatal rat shows elevated basal levels of corticosterone (CORT) and exhibits a robust CORT and ACTH response to mild stress. Further, c- fos mRNA in the paraventricular nucleus (PVN) is enhanced following stress in deprived pups. At least three aspects of maternal behavior play a role in the regulation of the HPA axis during development. Tactile stimulation appears capable of inhibiting most of the brain-related changes that occur following maternal deprivation. Feeding is essential for maintaining the adrenal-unresponsive and reduces the sensitivity of the adrenal to ACTH. Passive contact suppresses the response to stress. In the adult, corticotropin-releasing hormone (CRH) is the major neuropeptide that controls pituitary ACTH secretion. In the maternally deprived pup, CRH gene transcription is downregulated and arginine vasopressin (AVP) appears to assume the major regulatory hormone that modulates ACTH. These data all indicate that maternal factors are responsible for actively inhibiting the endocrine responses to stress postnatally. Thus, during development, most of the peripheral and central stress-responsive systems are capable of being activated. However, under conditions of normal dam–pup interactions, these responses are mostly suppressed by the dam's behavioral interaction with the pups.

Regulation of corticotropin-releasing hormone in vitro

Studies examining regulation of corticotropin-releasing hormone (CRH) in vitro have been used to validate findings obtained in vivo and more importantly have been used as model systems to better understand signalling mechanisms responsible for the expression of the CRH gene and peptide. Most in vitro studies examining CRH have utilized hypothalamic tissue while a few have focused on the amygdala. Furthermore, clonal cell lines have also been utilized as models of central nervous system CRH neurons. Stimuli that have been implicated in regulating hypothalamic CRH in vitro include protein kinase A (PKA) and protein kinase C (PKC) activators, glucocorticoids, biogenic amines, cytokines and the gaseous neurotransmitters. CRH levels in the amygdala in vitro are affected by some of the same stimuli that regulate hypothalamic CRH; however there is evidence supporting differential regulation of CRH in these two brain regions by some of the same stimuli. Only a few studies in aggregate have investigated the signal transduction mechanisms responsible for CRH expression. These mechanistic studies have focused on PKA- and glucocorticoid-mediated changes in CRH expression. Clearly much more investigative work in better understanding CRH regulation in vitro is needed.

Endometrial and myometrial corticotropin-releasing hormone (CRH): its regulation and possible roles

In human endometrium, both epithelial and stroma cells produce corticotropin-releasing hormone (CRH). Both types of cells also possess specific CRH-binding sites indicating a local effect of endometrial CRH. The transcription of the CRH gene in human endometrium is under the control of steroid hormones and locally produced prostanoids and interleukins. Endometrial CRH interacts with locally produced prostaglandins and interleukins. Based on these observations it can be hypothesized that CRH, prostaglandins and interleukins form a network responsible for the communication between epithelial and stromal cells, at the level of the endometrium, and between endometrial and myometrial cells at the level of uterus. The net product of these interaction is the micro-regulation of the decidualizing process and the preparation of endometrium for the implantation/nidation of the conceptus. Indeed, this network may represent the core of the intrauterine neuroendocrine—immune interactions involved in the decidualization of stroma and implantation of blastocyst. In addition, this network appears to be essential for the fine-tuning of myometrial tone.

The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it’s activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.

Repressor Element Silencing Transcription Factor/Neuron-restrictive Silencing Factor (REST/NRSF) Can Act as an Enhancer as Well as a Repressor of Corticotropin-releasing Hormone Gene Transcription

The repressor element-1/neuron-restrictive silencing element (RE-1/NRSE) mediates transcriptional repression by the repressor element silencing transcription factor/neuron-restrictive silencing factor (REST/NRSF) in many neuron-specific genes. REST/NRSF is expressed most highly in non-neural tissues, where it is thought to repress gene transcription, but is also found in developing neurons and at low levels in the brain. Its null mutation in vivo results in embryonic lethality in mice. While the RE-1/NRSE-mediated repressive influence of REST/NRSF is well established, results in transgenic studies have suggested that the action of the system is more complex. Here, we report that transcription of the corticotropin releasing hormone (CRH) gene is regulated by REST/NRSF, in part through the RE-1/NRSE. Expression of transfected Crh-luciferase constructs was down-regulated by REST/NRSF in a RE-1/NRSE-dependent fashion in both muscle-derived L6 and REST/NRSF co-transfected neuronal PC12 cells. Treatment of L6 cells with trichostatin A revealed that REST/NRSF repression depends, in part, on histone deacetylase activity in these cells. In another neuronal cell line, NG108, REST/NRSF also repressed expression from constructs containing an intact RE-1/NRSE. However, unexpectedly, REST/NRSF up-regulated expression levels of constructs lacking an intact RE-1/NRSE. These results suggest that REST/NRSF can act as both a repressor of Crh transcription, via the Crh RE-1/NRSE, and an enhancer of Crh transcription, via a mechanism independent of the Crh RE-1/NRSE.

Appetite-Suppressing Effects of Urotensin I and Corticotropin-Releasing Hormone in Goldfish (Carassius auratus)

Fish urotensin I (UI), a member of the corticotropin-releasing hormone (CRH) family of peptides, is a potent inhibitor of food intake in mammals, yet the role of UI in the control of food intake in fish is not known. Therefore, to determine the acute effects of UI on appetite relative to those of CRH, goldfish were given intracerebroventricular (i.c.v.) injections of carp/goldfish UI and rat/human CRH (0.2–200 ng/g) and food intake was assessed for a 2-hour period after the injection. UI and CRH both suppressed food intake in a dose-related manner and UI (ED₅₀ = 3.8 ng/g) was significantly more potent than CRH (ED₅₀ = 43.1 ng/g). Pretreatment with the CRH receptor antagonist, α-helical CRH_(9–41), reversed the reduction in food intake induced by i.c.v. UI and CRH. To assess whether endogenous UI and CRH modulate fish appetite, goldfish were given intraperitoneal implants of the glucocorticoid receptor antagonist, RU-486 (50 and 100 µg/g), or the cortisol synthesis inhibitor, metyrapone (100 and 200 µg/g), and food intake was monitored over the following 72 h. Fish treated with either RU-486 or metyrapone were characterized by a sustained and dose-dependent reduction in food intake. Pretreatment with i.c.v. implants of α-helical CRH_(9–41) partially reversed the appetite-suppressing effects of RU-486 and metyrapone. In a parallel experiment, the effects of RU-486 (100 µg/g) and metyrapone (200 µg/g) intraperitoneal implants on brain UI and CRH gene expression were assessed. Relative to sham-implanted controls, fish treated with RU-486 or metyrapone had elevated UI mRNA levels in the hypothalamus and CRH mRNA levels in the telencephalon-preoptic brain region. Together, these results suggest that UI is a potent anorectic peptide in the brain of goldfish and that endogenous CRH-related peptides can play a physiological role in the control of fish appetite.

Mechanism of Anticonvulsant Action of ACTH

The hypothesis that systemic or intraventricular administration of corticotropin (ACTH) acts directly on limbic neurons to modulate corticotropin-releasing hormone (CRH) gene expression, independently of adrenal stimulation, was tested and confirmed in experiments on developing rats (9-11 days postnatal) at the University of California, Irvine.

Corticotropin (ACTH) acts directly on amygdala neurons to down‐regulate corticotropin‐releasing hormone gene expression

The hormone corticotropin (ACTH) is employed as therapy for diverse neurological disorders, but the mechanisms for its efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system (CNS) have been attributed to activation of glucocorticoid receptors. However, in several human disorders, ACTH has therapeutic actions that differ qualitatively or quantitatively from those of steroids. This study tested the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors and focused on the effects of ACTH on the expression of corticotropin-releasing hormone (CRH), a neuropeptide involved in neuroimmune functions and in certain developmental seizures. The results demonstrated that ACTH potently reduced CRH expression in amygdala neurons. This down-regulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced down-regulation of CRH expression. Taken together, these data indicate that ACTH activates central melanocortin receptors to modulate CRH gene expression in amygdala, supporting the notion that direct, steroid-independent actions of ACTH may account for some of its established clinical effects on the CNS.

Decreased CRH mRNA expression in the fetal guinea pig hypothalamus following maternal nutrient restriction

The regulation of corticotropin-releasing hormone (CRH) mRNA expression following maternal nutrient restriction was examined in the fetal hypothalamus. Pregnant guinea pigs were food restricted for 48 h or fed normally during late gestation. After nutrient restriction, CRH mRNA levels in the hypothalamic paraventricular nucleus of the fetus were determined using in situ hybridization and were found to be significantly decreased ( P<0.0001) compared to controls. In conclusion, we have successfully sequenced the coding sequence of the guinea pig CRH gene, and have shown that a short period (48 h) of maternal nutrient restriction inhibits CRH mRNA expression in the fetal hypothalamus.

Adrenalectomy dramatically modifies the dynamics of neuropeptide and c-fos gene responses to stress in the hypothalamic paraventricular nucleus.

We have used in situ hybridization and radio-immunoassay to compare temporal dynamics of components in the hypothalamo-pituitary limb of the hypothalamo-pituitary-adrenal axis during sustained hypovolemic stress in adrenalectomized (ADX) rats to those previously reported in intact animals. We asked three questions: first, does corticotropin-releasing hormone (CRH) gene transcription occur in neuroendocrine neurones of the hypothalamic paraventricular nucleus (PVH) of ADX rats, and if so, how is it temporally organized; second, what is the expression pattern of the vasopressin and other genes known to be colocalized in these neuroendocrine neurones; third, if adrenocorticotropin hormone (ACTH) secretion occurs, what is its temporal profile? We found that sustained hypovolemia evoked a brief episode of CRH gene transcription in ADX rats that occurred earlier than in intact rats. However, in contrast to saline-injected controls, this activation was not maintained because declines in CRH hnRNA and mRNA were seen as the stress continued. Although increased vasopressin gene transcription was not seen in intact hypovolemic rats, robust increases were measured throughout in ADX rats, suggesting that in the absence of corticosterone the vasopressin gene is transcribed preferentially to the CRH gene during sustained hypovolemia. c-fos and preproenkephalin mRNA profiles also exhibited earlier onsets compared to intact rats. Finally, the onset and duration of ACTH secretion was the same in ADX rats as previously reported in intact rats. Collectively, these data support two hypotheses regarding the actions of corticosterone. First, that it provides some form of facilitatory signal allowing neuroendocrine CRH transcriptional mechanisms to remain active during sustained hypovolemia. Second, that it strongly inhibits the response of the vasopressin gene to hypovolemic stress.

α-Melanocyte stimulating hormone prevents fasting-induced suppression of corticotropin-releasing hormone gene expression in the rat hypothalamic paraventricular nucleus

During fasting, corticotropin-releasing hormone (CRH) mRNA decreases in the hypothalamic paraventricular nucleus (PVN), but the mechanism by which this takes place is not well understood. To test the hypothesis that the melanocortin system may be involved in the regulation of CRH mRNA in the PVN during fasting, the effect of intracerebroventricularly administered α-melanocyte stimulating hormone (MSH) on CRH mRNA in the PVN was studied in fasted animals by in situ hybridization histochemistry. Whereas fasting suppressed CRH mRNA levels in the PVN, α-MSH at doses of 150 and 300 ng every 6 h for 64 h prevented the fasting-induced suppression of CRH gene expression in the PVN. These data indicate that the suppression of α-MSH synthesis may be responsible for the decreased CRH gene expression in the PVN during fasting.

Stress-Induced Alterations in Corticotropin-Releasing Hormone and Vasopressin Gene Expression in the Paraventricular Nucleus during Ontogeny

From postnatal day (PND) 4 to 14, neonates display a minimal pituitary-adrenal response to mild stress, the so-called ‘stress hyporesponsive period’ (SHRP). During the SHRP, maternal deprivation (MD) alters the pituitary-adrenal system, enabling neonates to become endocrine responsive to specific stimuli. We have previously reported that during the SHRP, mild stress enhances corticotropin-releasing hormone (CRH) messenger RNA (mRNA) expression in the paraventricular nucleus (PVN). Insofar as elevated CRH mRNA was observed both in the presence and absence of adrenocorticotropin (ACTH) release, we hypothesized that other ACTH secretagogues may participate in the pituitary stress response. During the SHRP, does arginine vasopressin (AVP) complement the actions of CRH which might be reflected centrally by the enhanced biosynthesis of both neuropeptides? To test this hypothesis we examined the time course of stress-induced CRH and AVP mRNA in the PVN at PND 6, 12, and 18. As an index of neural activity, c-fos mRNA in the PVN was also examined. Restraint was used as the stressor and MD was employed to enable an endocrine response during the SHRP. Despite the absence of stress-induced ACTH, in nondeprived pups during the SHRP, CRH mRNA was rapidly enhanced. In their maternally deprived (DEP) counterparts, ACTH levels were increased, and a significant induction of CRH mRNA was only observed at day 12. AVP mRNA levels were elevated in DEP 12-day-old pups at 15, 30 and 60 min. In rats beyond the SHRP, plasma ACTH levels, CRH and AVP mRNA were all enhanced following restraint. At PND 18, elevated CRH mRNA was not observed until 4 h after stimulus. Following restraint, c-fos mRNA was increased at all three ages, although the magnitude of c-fos response was less during the SHRP. These results demonstrate that when restraint elicits prototypical ACTH release, the neonatal central response is to enhance the biosynthesis of both AVP and CRH. If nucleic acid changes correlate with release, the increased synthesis of both neuropeptides may indicate the potential for AVP to synergize with CRH during the neonatal stress response.

Centrally Administered Murine-Leptin Stimulates the Hypothalamus-Pituitary- Adrenal Axis through Arginine-Vasopressin

Starvation induces a decrease in circulating leptin levels and activation of the hypothalamus-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis in unfed rodents or genetically leptin-deficient ob/ob mice, whereas it stimulates corticotropin-releasing hormone (CRH) gene expression in the paraventricular nucleus (PVN). However, the interactions between leptin, CRH and the HPA axis are poorly understood and are likely to be complex. We recently demonstrated that central leptin administration caused increases in plasma arginine-vasopressin (AVP) and AVP gene expression of the PVN in nonstressful rats. AVP stimulates the release of adrenocorticotropic hormone (ACTH), but it also potentiates the action of CRH on ACTH release. In this study, we investigated the effects of leptin on plasma ACTH and corticosterone levels, CRH mRNA of the PVN and proopiomelanocortin (POMC) mRNA of the pituitary in nonstrained rats. Intracerebroventricularly administered leptin caused increases in plasma ACTH and corticosterone levels in dose-dependent manners. In Northern blot analyses, the leptin injection induced significant increases in the expression of CRH mRNA in the PVN and POMC mRNA in the pituitary. The increased plasma ACTH and corticosterone levels by leptin were attenuated with intracerebroventricular pretreatment of a V_1a receptor antagonist (OPC-21268) or a V_1a/V_1b receptor antagonist (dP[Tyr(Me)²]AVP), but not with that of a V₂ receptor antagonist (OPC-31260). The leptin-induced CRH mRNA expression in the PVN and POMC mRNA expression in the pituitary were also reduced by the pretreatment with OPC-21268 and dP[Tyr(Me)²]AVP. These results suggest that intracerebroventricular leptin administration activates the HPA axis by AVP receptor activation through V_1a receptors in the PVN which in turn activates CRH neurons to drive ACTH and corticosterone secretion in concert with AVP in nonstrained rats.

Rapid induction of corticotropin-releasing hormone gene transcription in the paraventricular nucleus of the developing rat.

Neonates from postnatal days (pnd) 4-14 display a minimal pituitary-adrenal response to mild stress, the so-called stress hyporesponsive period (SHRP). However, during the SHRP, maternal deprivation (deprived) alters the pituitary-adrenal system, enabling neonates to become endocrine responsive to specific stimuli. Although neonates do display stress-induced ACTH, there is limited evidence for enhanced CRH gene expression early in development. The present experiment examined whether a mild stimulus (isotonic saline injection) administered to deprived and nondeprived neonates would enhance CRH biosynthesis in the paraventricular nucleus. Using in situ hybridization we measured the time course of CRH heteronuclear RNA (hnRNA) and messenger RNA at 15, 30, and 240 min poststimulus. Pnd 6, 12, and 18 were included to examine the CRH gene response during and outside of the SHRP. Despite the minimal endocrine response of nondeprived pups during the SHRP, CRH hnRNA and messenger RNA were elevated at 15 min (all ages). Both transcripts were enhanced at 15-30 min in deprived (pnd 12 and 18) pups; however, the magnitude of the response was less than that in nondeprived pups. These data indicate that during ontogeny there is a rapid stimulus-induced CRH biosynthesis. Thus, during development, the central components of the hypothalamic-pituitary-adrenal axis may be stress hyperresponsive rather than hyporesponsive.

Glucocorticoid stimulation of corticotropin-releasing hormone gene expression requires a cyclic adenosine 3',5'-monophosphate regulatory element in human primary placental cytotrophoblast cells.

Production of placental CRH, which is identical to the peptide synthesized and secreted in the hypothalamus, has been linked to human parturition. Glucocorticoids stimulate placental CRH secretion and messenger ribonucleic acid expression, in contrast to their inhibition of CRH synthesis in the hypothalamus. A positive feedforward loop involving glucocorticoid-CRH-ACTH-glucocorticoid is thought to drive the exponential increase in placental CRH leading to delivery. Tissue-specific effects of glucocorticoids on CRH expression are therefore of interest. Using human primary placental cells, we investigated the mechanism by which glucocorticoids stimulate placental CRH gene expression. Nuclear run-on transcription shows that in human placental cells glucocorticoids up-regulate transcription of human CRH (hCRH). Using transient transfection assays we demonstrate that dexamethasone up-regulates both basal and cAMP-stimulated hCRH promoter activity, correlating well with the increase in endogenous CRH peptide levels. Through mutagenesis and deletion analyses we show that dexamethasone stimulation of hCRH gene transcription requires a functional cAMP regulatory element (CRE); this CRE is adequate to confer dexamethasone stimulation upon a heterologous promoter, and electrophoretic mobility shift assay studies show that a placental nuclear protein specifically binds to the hCRH CRE.

Rapid Induction of Corticotropin-Releasing Hormone Gene Transcription in the Paraventricular Nucleus of the Developing Rat

Rapid Induction of Corticotropin-Releasing Hormone Gene Transcription in the Paraventricular Nucleus of the Developing Rat

Association and linkage studies of CRH and PENK genes in bipolar disorder: a collaborative IGSLI study.

Corticotropin-releasing hormone (CRH) and proenkephalin (PENK) are hypothalamic peptides involved in the stress response and hypothalamic-pituitary axis regulation. Previous research has implicated these peptides in the pathogenesis of affective disorders. In this study we investigated two polymorphisms located in the genes that code for CRH and PENK by means of association and linkage analyses. A total of 138 bipolar patients and 108 controls were included in the association study. In addition, 24 families were available for linkage analysis, including six families of probands with documented periodic positivity of dexamethasone suppression tests (DST) during remission. We found no association of bipolar disorder with either gene. Similarly, we did not find any evidence of linkage (P = 0.56 for CRH and 0.52 for PENK) in the entire sample or in the subsample of families of DST positive probands. In conclusion, our study does not support the hypothesis that genes coding for CRH or PENK contribute to the genetic susceptibility to bipolar disorder. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:178-181, 2000.

Corticotropin-releasing hormone gene expression in primary placental cells is modulated by cyclic adenosine 3',5'-monophosphate.

CRH, the principal neuropeptide regulator of pituitary ACTH secretion, is also expressed in placenta. Placental CRH has been linked to the process of human parturition. However, the mechanisms regulating transcription of the CRH gene in placenta remain unclear. cAMP signaling pathways play important roles in regulating the expression of a diverse range of endocrine genes in the placenta. Therefore, we have explored the effect of cAMP on CRH promoter activity in primary cultures of human placental cells. Both forskolin and 8-bromo-cAMP, activators of protein kinase A, can increase CRH promoter activity 5-fold in transiently transfected human primary placental cells, in a manner that parallels the increase in endogenous CRH peptide. Maximal stimulation of CRH promoter activity occurs at 500 micromol/L 8-bromo-cAMP and 10 micromol/L forskolin. Electrophoretic mobility shift assay and mutation analysis combined with transient transfection demonstrate that in placental cells cAMP stimulates CRH gene expression through a cAMP regulatory element in the proximal CRH promoter region and involves a placental nuclear protein interacting specifically with the cAMP regulatory element.

Corticotropin-Releasing Hormone Gene Expression in Primary Placental Cells Is Modulated by Cyclic Adenosine 3',5'-Monophosphate

Corticotropin-Releasing Hormone Gene Expression in Primary Placental Cells Is Modulated by Cyclic Adenosine 3',5'-Monophosphate

Childhood sexual abuse and preterm labor in adulthood: an endocrinological hypothesis

Anecdotal reports link adverse pregnancy outcomes, such as preterm delivery, to women with histories of childhood sexual abuse. Although little research has been conducted on this subject, we provide an overview of known health effects of violence against women and posit a biological explanation for adverse pregnancy outcomes among this population. Specifically, we hypothesize that early traumatic experiences of childhood sexual abuse may activate corticotropin releasing hormone (CRH) gene expression in the brain, and a vulnerability to elevated CRH gene expression in the placenta. Those traumatized by early abuse may be more susceptible to stress vı́s a vı́s CRH dysregulation during a major psychosocial stressor, such as pregnancy. Elevated CRH has been associated with preterm labor.