C/EBP activates the human corticotropin-releasing hormone gene promoter

Age Dependent Hypothalamic and Pituitary Responses to Novel Environment Stress or Lipopolysaccharide in Rats

Previously, we have shown that the transcription factor nuclear factor interleukin (NF-IL)6 can be used as an activation marker for inflammatory lipopolysaccharide (LPS)-induced and psychological novel environment stress (NES) in the rat brain. Here, we aimed to investigate age dependent changes of hypothalamic and pituitary responses to NES (cage switch) or LPS (100 μg/kg) in 2 and 24 months old rats. Animals were sacrificed at specific time points, blood and brains withdrawn and analyzed using immunohistochemistry, RT-PCR and bioassays. In the old rats, telemetric recording revealed that NES-induced hyperthermia was enhanced and prolonged compared to the young group. Plasma IL-6 levels remained unchanged and hypothalamic IL-6 mRNA expression was increased in the old rats. Interestingly, this response was accompanied by a significant upregulation of corticotropin-releasing hormone mRNA expression only in young rats after NES and overall higher plasma corticosterone levels in all aged animals. Immunohistochemical analysis revealed a significant upregulation of NF-IL6-positive cells in the pituitary after NES or LPS-injection. In another important brain structure implicated in immune-to-brain communication, namely, in the median eminence (ME), NF-IL6-immunoreactivity was increased in aged animals, while the young group showed just minor activation after LPS-stimulation. Interestingly, we found a higher amount of NF-IL6-CD68-positive cells in the posterior pituitary of old rats compared to the young counterparts. Moreover, aging affected the regulation of cytokine interaction in the anterior pituitary lobe. LPS-treatment significantly enhanced the secretion of the cytokines IL-6 and TNFα into supernatants of primary cell cultures of the anterior pituitary. Furthermore, in the young rats, incubation with IL-6 and IL-10 antibodies before LPS-stimulation led to a robust decrease of IL-6 production and an increase of TNFα production by the pituitary cells. In the old rats, this specific cytokine interaction could not be detected. Overall, the present results revealed strong differences in the activation patterns and pathways between old and young rats after both stressors. The prolonged hyperthermic and inflammatory response seen in aged animals seems to be linked to dysregulated pituitary cytokine interactions and brain cell activation (NF-IL6) in the hypothalamus-pituitary-adrenal axis.

The flame retardant 2,2',4,4'-Tetrabromodiphenyl ether enhances the expression of corticotropin-releasing hormone in the placental cell model JEG-3

Polybrominated diphenyl ethers (PBDEs) are chemicals used as flame retardants in household products. After disposing of these items, PBDEs leach from the products by surface water. BDE-47 is a PBDE congener commonly isolated from contaminated food and is the most studied isomer. The placenta is the major source of hormones during pregnancy, and an elevated level of corticotrophin-releasing hormone (CRH) is associated with premature delivery. In the present study, we examined changes in the placental CRH expression under BDE-47 exposure in the JEG-3 cell model system. These placental cells are derived from human choriocarcinoma. Our result showed that this pollutant induced the CRH mRNA expression at 0.5 nM or above in the cells. A similar trend was observed when CRH peptide was determined by Western analysis in the cell lysates. As previous studies have shown the importance of signal transduction pathways in the gene regulation, the status of some protein kinases in the present study was investigated. The phosphorylated PKCα, JNK, and P38 were increased by the toxicant treatment, and administering the specific inhibitors could counteract the induced CRH expression. It appeared that the signaling transduction pathway of PKC was a significant contributor in the transcriptional regulation. Further study by using Electrophoretic Mobility Shift Assay suggested that AP-2 was the ultimate DNA-binding element for the initiation of gene transcription. Because an untimely increased CRH may compromise fetal development and induce preterm birth, the present study suggested that endocrine changes in pregnancy should be taken into consideration in the next assessment.

Inflammatory transcription factors as activation markers and functional readouts in immune-to-brain communication

Immune-to-brain communication pathways involve humoral mediators, including cytokines, central modulation by neuronal afferents and immune cell trafficking to the brain. During systemic inflammation these pathways contribute to mediating brain-controlled sickness symptoms including fever. Experimentally, activation of these signaling pathways can be mimicked and studied when injecting animals with pathogen associated molecular patterns (PAMPS). One central component of the brain inflammatory response, which leads, for example, to fever induction, is transcriptional activation of brain cells via cytokines and PAMPS. We and others have studied the spatiotemporal activation and the physiological significance of transcription factors for the induction of inflammation within the brain and the manifestation of fever. Evidence has revealed a role of nuclear factor (NF)κB in the initiation, signal transducer and activator of transcription (STAT)3 in the maintenance and NF-interleukin (IL)6 in the maintenance or even termination of brain-inflammation and fever. Moreover, psychological stressors, such as exposure to a novel environment, leads to increased body core temperature and genomic NF-IL6-activation, suggesting a potential use of NF-IL6-immunohistochemistry as a multimodal brain cell activation marker and a role for NF-IL6 for differential brain activity. In addition, the nutritional status, as reflected by circulating levels of the cytokine-like hormone leptin, influence immune-to-brain communication and age-dependent changes in LPS-induced fever. Overall, transcription factors remain therapeutically important targets for the treatment of brain-inflammation and fever induction during infectious/non-infectious inflammatory and psychological stress. However, the exact physiological role and significance of these transcription factors requires to be further investigated.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Aflatoxin B1 augments the synthesis of corticotropin releasing hormone in JEG-3 placental cells

Aflatoxins pose a major threat to food safety. These toxins are classified as hepatocarcinogens; however, their effect on the other tissues is unclear. During pregnancy, the fetus and placental tissues are especially sensitive to toxin exposure. In the present study aflatoxin B1 was found to induce the mRNA expression of corticotrophin-releasing hormone (CRH) in placental cells. A corresponding increase in CRH peptide in the culture medium was also observed. Since signal transduction pathways have been described previously in the control of CRH transcription, the status of protein kinase Cs (PKCs) and mitogen-activated protein kinases (MAPKs) were determined by Western analysis. In the aflatoxin B1-treated cultures, PKC α/βII/δ and ERK-1/2 were activated. As the PKC inhibitor bisindolylmaleimide I and the ERK inhibitor PD98059 could revert the induced CRH expression, the pathways dictated by PKC and ERK were likely involved in the transcriptional regulation. Electrophoretic mobility shift assay showed that C/EBP could be the ultimate activated transcription factor. Taken together, this study demonstrated that aflatoxin B1 could increase the parturition-related placental hormone in vitro. These findings might have significant implications for public health.

Activation of the inflammatory transcription factor nuclear factor interleukin-6 during inflammatory and psychological stress in the brain

BACKGROUND

The transcription factor nuclear factor interleukin 6 (NF-IL6) is known to be activated by various inflammatory stimuli in the brain. Interestingly, we recently detected NF-IL6-activation within the hypothalamus-pituitary-adrenal (HPA)-axis of rats after systemic lipopolysaccharide (LPS)-injection. Thus, the aim of the present study was to investigate whether NF-IL6 is activated during either, inflammatory, or psychological stress in the rat brain.

METHODS

Rats were challenged with either the inflammatory stimulus LPS (100 μg/kg, i.p.) or exposed to a novel environment. Core body temperature (Tb) and motor activity were monitored using telemetry, animals were killed at different time points, brains and blood removed, and primary cell cultures of the anterior pituitary lobe (AL) were investigated. Analyses were performed using immunohistochemistry, RT-PCR, and cytokine-specific bioassays.

RESULTS

Stress stimulation by a novel environment increased NF-IL6-immunoreactivity (IR) in the pituitary's perivascular macrophages and hypothalamic paraventricular cells and a rise in Tb lasting approximately 2 h. LPS stimulation lead to NF-IL6-IR in several additional cell types including ACTH-IR-positive corticotrope cells in vivo and in vitro. Two other proinflammatory transcription factors, namely signal transducer and activator of transcription (STAT)3 and NFκB, were significantly activated and partially colocalized with NF-IL6-IR in cells of the AL only after LPS-stimulation, but not following psychological stress. In vitro NF-IL6-activation was associated with induction and secretion of TNFα in folliculostellate cells, which could be antagonized by the JAK-STAT-inhibitor AG490.

CONCLUSIONS

We revealed, for the first time, that NF-IL6 activation occurs not only during inflammatory LPS stimulation, but also during psychological stress, that is, a novel environment. Both stressors were associated with time-dependent activation of NF-IL6 in different cell types of the brain and the pituitary. Moreover, while NF-IL6-IR was partially linked to STAT3 and NFκB activation, TNFα production, and ACTH-IR after LPS stimulation; this was not the case after exposure to a novel environment, suggesting distinct underlying signaling pathways. Overall, NF-IL6 can be used as a broad activation marker in the brain and might be of interest for therapeutic approaches not only during inflammatory but also psychological stress.

Spatiotemporal nuclear factor interleukin-6 expression in the rat brain during lipopolysaccharide-induced fever is linked to sustained hypothalamic inflammatory target gene induction

Rats injected with lipopolysaccharide (LPS) show brain-controlled sickness symptoms, including fever. In these animals, early genomic activation of brain cells was previously monitored by immunohistochemical detection of transcription factors such as nuclear factor (NF)-κB or signal transducer and activator of transcription (STAT)3 and was linked to the initiation or maintenance of the febrile response. To investigate whether NF-IL6 might be another important transcription factor implicated in this kind of immune-to-brain signaling, rats were injected with LPS (100 μg/kg, intraperitoneally) or phosphate-buffered saline, and brains were analyzed by immunohistochemistry, real-time PCR, or Western blot 4, 6, 8, and 10 hours later. Moderate to strong LPS-induced nuclear NF-IL6 immunoreactivity (IR) occurred in a time-dependent manner within circumventricular organs, namely, the vascular organ of the lamina terminalis, the subfornical organ, the area postrema, and the median eminence, brain structures with a leaky blood-brain barrier. Furthermore, nuclear NF-IL6-IR was observed in the pituitary gland, the choroid plexus, and the meninges as well as blood vessels throughout the entire brain. Endothelial, microglial, and ependymal cells, astrocytes, perivascular macrophages, and neurons exhibited LPS-induced nuclear NF-IL6-IR; mRNA levels of NF-IL6, responsive inflammatory genes, and NF-IL6 protein levels were significantly elevated. As opposed to observations on STAT3 or NFκB, the percentage of NF-IL6-reactive cells increased in parallel to late phases of the febrile response. In conclusion, these results suggest a potential role for NF-IL6 in the maintenance or possibly the termination of LPS-induced fever. Moreover, we propose NF-IL6 to be a delayed brain cell activation marker.

Transcription factor expression in the hypothalamo-neurohypophyseal system of the dehydrated rat: upregulation of gonadotrophin inducible transcription factor 1 mRNA is mediated by cAMP-dependent protein kinase A

The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamo-neurohypophyseal system (HNS) undergo a dramatic function-related plasticity during dehydration. We hypothesize that alterations in steady-state transcript levels might be partially responsible for this remodeling. In turn, regulation of transcript abundance might be mediated by transcription factors. We used microarrays to identify changes in the expression of mRNAs encoding transcription factors in response to water deprivation in the SON. We observed downregulation of 10 and upregulation of 28 transcription factor transcripts. For five of the upregulated mRNAs, namely gonadotropin inducible ovarian transcription factor 1 (Giot1), Giot2, cAMP-responsive element binding protein 3-like 1, CCAAT/enhancer binding protein beta, and activating transcription factor 4, in situ hybridization was used to confirm the array results, demonstrating a significant increase in expression in SON and PVN magnocellular neurons (MCNs) after 3 d of water deprivation and, in some cases, upregulation in parvocellular PVN neurons. Using a viral vector expressing a potent inhibitor of cAMP-dependent protein kinase A (PKA), we show that the osmotically induced increase in the abundance of transcripts encoding Giot1 is mediated in vivo by the PKA pathway. We thus suggest that signaling pathways activated by dehydration in MCNs mediate transcription factor gene activation, which, in turn, regulate target genes that mediate HNS remodeling.

Frontal lobe epilepsy and mutations of the corticotropin-releasing hormone gene

Nocturnal frontal lobe epilepsy up to now has been considered a channelopathy caused by mutations in the alpha(4) and beta(2) subunits of the neuronal nicotinic acetylcholine receptor. However, these mutations account for only a minority of patients, and the existence of at least a new locus for the disease has been demonstrated. In one Italian nocturnal frontal lobe epilepsy family, we identified two new putative loci on chromosomes 3 and 8, where several candidate genes are mapped. In particular, on chromosome 8, corticotropin-releasing hormone gene (CRH) appears to be a good candidate. We therefore searched for CRH mutations in the proband. The study allowed the identification of a nucleotide variation in the promoter that was subsequently detected in all affected and obligate carrier members of the same family, in two sporadic cases, in all affected members of an additional compliant family, and in the proband of a noncompliant family. Moreover, a different mutation in the promoter was detected in a familial case. In vitro experiments showed altered levels of gene expression. CRH alterations could explain several autosomal dominant nocturnal frontal lobe epilepsy clinical features.

Expression and distribution of transcription factor CCAAT/enhancer-binding protein in the central nervous system of Lymnaea stagnalis

The transcription factor, CCAAT/enhancer-binding protein (C/EBP), is involved in important physiological processes, such as cellular proliferation and differentiation, homeostasis, and higher-order functions of the brain. In the present study, we investigated the distribution of mRNA and protein of C/EBP in the central nervous system of the pond snail, Lymnaea stagnalis, by in situ hybridization and immunohistochemistry. Specificity of the anti-mammalian C/EBP antibody against Lymnaea C/EBP (LymC/EBP) was confirmed by combination of sodium dodecyl sulfate polyacrylamide gel electrophoresis or isoelectric focusing and immunoblotting. Cells positive for in situ hybridization were immunoreactive for LymC/EBP in all 11 ganglia. The motoneurons (B1, B2, B4, and B4 clusters) in the buccal ganglia and interneurons (cerebral giant cell, CGC) in the cerebral ganglia were positive for in situ hybridization and were immunopositive. In the pedal ganglion, the right pedal dorsal 1 (RPeD1), pedal A, and pedal C clusters exhibited positive signals of in situ hybridization and immunohistochemistry for LymC/EBP. CGC and RPeD1 are key neurons for associative learning. In addition, the neuropeptidergic cells in the cerebral, pleural, parietal, and visceral ganglia were positive for in situ hybridization and immunoreactive. Interestingly, although the cytoplasm of almost all immunopositive cells was stained, some neuropeptidergic cells located in the light parietal and visceral ganglia exhibited immunoreactivity in nuclei. Our results suggest that LymC/EBP is involved in learning and memory and in the expression and/or secretion of neuropeptides in Lymnaea.

IL-1β-mediated neuropeptide and immediate early gene mRNA induction is defective in Lewis hypothalamic cell cultures

We previously found that Lewis (LEW/N) hypothalamic cells respond to interleukin-1beta (IL-1beta) with reduced corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) peptide synthesis and secretion compared to Fischer (F344/N) cells. To investigate whether this peptide hyporesponsiveness in LEW/N cells is secondary to their deficient mRNA expression, temporal mRNA expression patterns of CRH, AVP, and several hypothalamic neuropeptides induced by IL-1beta in LEW/N and F344/N hypothalamic dissociated cell cultures were delineated by quantitative real-time polymerase chain reaction (RT-PCR). To investigate the molecular mechanisms underlying neuropeptide mRNA induction in cells of both strains, temporal mRNA expression patterns of immediate early genes (IEGs) and several signal transduction-associated molecules were also examined. We found that LEW/N hypothalamic cells were hyporesponsive to IL-1beta induction of neuropeptide and IEG mRNA, while LEW/N cells transcribed more IL-1 receptor and inducible nitric oxide synthase (iNOS) compared to F344N/N cells, suggesting that LEW/N and F344/N hypothalamic cells are differentially activated by IL-1beta.

Modulation of corticotropin-releasing hormone receptor type 2 mRNA expression by CRH deficiency or stress in the mouse heart

The actions of corticotropin-releasing hormone (CRH) and the related peptides are coordinated by two receptors, CRH receptor type 1 (CRH-R1) and CRH receptor type 2 (CRH-R2). In this study, we examined the effects of CRH deficiency and/or stress due to physically restraint or lipopolysaccharide (LPS) administration on expression of transcripts for CRH-R2 (CRH-R2 mRNA) as well as urocortin (UCN) mRNA in the atria and ventricle using female and male CRH-deficient (knockout, KO) mice. We show that restraint stress caused a significant increase in plasma corticosterone levels in female CRH KO mice, but LPS administration induced a significant increase in plasma corticosterone levels in both female and male CRH KO mice. CRH deficiency caused a robust decrease in basal levels of CRH-R2 mRNA and a significant increase of UCN mRNA expression in the atria and ventricle of female as well as male mice. Restraint stress markedly reduced CRH-R2 mRNA and increased UCN mRNA expression on atria as well as ventricle in both female and male wild-type (WT) mice. Following LPS injection to both female and male mice, CRH-R2 mRNA expression was decreased and UCN mRNA expression was increased in the atria and ventricle of both WT and CRH KO mice in each sex. We speculate that stress or lack of CRH may increase urocortin, which in turn down-regulates CRH-R2 mRNA expression in the heart. These data indicate: (1) that lack of CRH may decreases cardiac CRH-R2 mRNA expression in basal state, (2) that inhibitory effect of CRH deficiency on cardiac CRH-R2 mRNA expression in stress condition seems to be more closely linked to type of stressor than rise in plasma corticosterone level.

AP-2alpha modulates human corticotropin-releasing hormone gene expression in the placenta by direct protein-protein interaction

Since AP-2alpha induces the expression of hPL, hCG and other syncytiotrophoblast-specific marker genes in cytotrophoblast cells during in vitro differentiation, we have examined whether AP-2alpha also induces hCRH gene expression during differentiation of cytotrophoblast cells. Infection of human cytotrophoblast cells in vitro with an adenovirus expressing AP-2alpha resulted in a twofold increase in hCRH mRNA levels, while infection with an adenovirus expressing a dominant/negative mutant of AP-2alpha inhibited basal hCRH mRNA levels by 40% and completely blocked the induction of hCRH mRNA by AP-2alpha. Transient transfection studies in AtT-20 and HepG2 cells indicated that the induction of hCRH mRNA levels was due, at least in part, to transcriptional activation of the hCRH gene. Gel mobility shift and immunoprecipitation assays strongly suggest that AP-2alpha induces hCRH gene expression by interacting with CREB and not by binding directly to the hCRH promoter.

Cutaneous expression of corticotropin-releasing hormone (CRH), urocortin, and CRH receptors

Studies in mammalian skin have shown expression of the genes for corticotropin-releasing hormone (CRH) and the related urocortin peptide, with subsequent production of the respective peptides. Recent molecular and biochemical analyses have further revealed the presence of CRH receptors (CRH-Rs). These CRH-Rs are functional, responding to CRH and urocortin peptides (exogenous or produced locally) through activation of receptor(s)-mediated pathways to modify skin cell phenotype. Thus, when taken together with the previous findings of cutaneous expression of POMC and its receptors, these observations extend the range of regulatory elements of the hypothalamic-pituitary-adrenal axis expressed in mammalian skin. Overall, the cutaneous CRH/POMC expression is highly reactive to common stressors such as immune cytokines, ultraviolet radiation, cutaneous pathology, or even the physiological changes associated with the hair cycle phase. Therefore, similar to its central analog, the local expression and action of CRH/POMC elements appear to be highly organized and entrained, representing general mechanism of cutaneous response to stressful stimuli. In such a CRH/POMC system, the CRH-Rs may be a central element.

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.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.

CRH-like peptides protect cardiac myocytes from lethal ischaemic injury

Simulated ischaemia causes both necrotic and apoptotic death of primary cultures of neonatal rat cardiac myocytes. Simulated ischaemia is associated with increased expression of urocortin mRNA and with the release of urocortin peptide into the medium. Exogenous urocortin is more potent than corticotropin releasing hormone (CRH) in protecting cardiac myocytes from necrotic and apoptotic death induced by ischaemia, and the cardioprotective effects of ischaemia-preconditioned media are abrogated by antagonists to the CRH family of peptides. Simulated ischaemia increases cardiac myocyte expression of CCAAT enhancer binding (C/EBP) transcription factors, and of the p65 subunit of NFkappaB, and reporter activity of a construct incorporating a fragment of the urocortin promoter containing a C/EBP consensus site is also enhanced by simulated ischaemia. The data suggest that ischaemia, acting partly through increased expression of C/EBP transactivators, increases expression of urocortin mRNA, which is rapidly translated to the mature form. The mature peptide is rapidly released, and exerts autocrine/paracrine protective effects through the cardiac CRH-R2 receptor which preferentially binds urocortin.

Urocortin messenger ribonucleic acid: tissue distribution in the rat and regulation in thymus by lipopolysaccharide and glucocorticoids

Urocortin (Ucn), a new mammalian member of the CRF family, is a candidate endogenous ligand for type 2 CRF receptors. In a survey of peripheral tissues from adult male rats, we found that Ucn messenger RNA (mRNA) was abundant in the gastrointestinal tract and immune tissues such as thymus and spleen. We next tested the hypothesis that levels of Ucn mRNA levels in thymus and spleen would be altered after immune activation. As measured by ribonculease protection assay, lipopolysaccharide (LPS) induced a 2-fold time-dependent increase in thymic Ucn mRNA levels within 6 h. By contrast, splenic Ucn mRNA levels decreased after LPS. Because LPS activates the hypothalamus-pituitary-adrenal (HPA) axis, we examined whether the effects of LPS on Ucn mRNA might be mediated through changes in HPA axis hormones. Ucn mRNA in thymus, but not spleen, was significantly increased after ACTH injection; however, LPS did not increase Ucn expression in the thymus of adrenalectomized rats with corticosterone replacement, despite substantial increases in ACTH. Finally, sc injection of corticosterone stimulated Ucn mRNA comparably to that of LPS. Together, these results suggest that Ucn mRNA expression can increase after immune activation in a corticosterone-dependent manner, and that such changes in Ucn mRNA may be an additional consequence of HPA axis activation.

The decidualizing effect of progesterone may involve direct transcriptional activation of corticotrophin-releasing hormone from human endometrial stromal cells

The hypothalamic neuropeptide corticotrophin-releasing hormone (CRH) is also produced by human endometrial cells and is directly involved in the decidualization process as a paracrine inducer. The aim of the present work was to examine the effect of progesterone, the main decidualizing factor, on endometrial CRH, in primary cultures of human endometrial stromal cells. The effect of progesterone was examined by measuring the effects of medroxyprogesterone acetate (MPA) on (i) the concentration of immunoreactive CRH in isolated human endometrial stromal cells and (ii) the activity of the CRH promoter in human endometrial stromal cells transfected with a 0.9 kb fragment of the 5'-flanking region of the human CRH gene coupled to luciferase reporter. The data show that MPA increased the production and secretion of immunoreactive CRH from stromal cells and induced the activity of the CRH promoter, both in a dose-dependent manner. These effects were partially reversed by a molar excess of the antiprogestin RU 486 and were completely abolished in the presence of 100 nmol/l of the cAMP inhibitor, Rp-cAMP. The effect of progesterone on the CRH promoter requires the existence of an intact CRH sequence since experiments carried out with a deleted palindromic cAMP response element (CRE: 5'-TGACGTCA) at -224 bp of the CRH promoter resulted in a complete loss of MPA effect. In conclusion, these data provide evidence that progesterone induces the transcription of CRH gene in human endometrial stroma. This effect coupled with the decidualizing properties of progesterone and CRH may indicate that progesterone and CRH form a decidualizing local pathway within the human endometrium.