Leukemia inhibitory factor regulates glucocorticoid receptor expression in the hypothalamic-pituitary-adrenal axis

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine belonging to the gp130 family. LIF is induced peripherally and within the brain during inflammatory or chronic autoimmune diseases and is a potent stimulator of the hypothalamic-pituitary-adrenal (HPA) axis. Here we investigated the role of LIF in mediating glucocorticoid receptor (GR) expression in the HPA axis. LIF treatment (3 microg/mouse, i.p.) markedly decreased GR mRNA levels in murine hypothalamus (5-fold, P < 0.01) and pituitary (1.7-fold, P < 0.01) and downregulated GR protein levels. LIF decreased GR expression in murine corticotroph cell line AtT20 within 2 h, and this effect was sustained for 8 h after treatment. LIF-induced GR mRNA reduction was abrogated in AtT20 cells overexpressing dominant-negative mutants of STAT3, indicating that intact JAK-STAT signaling is required to mediate LIF effects on GR expression. Conversely, mice with LIF deficiency exhibited increased GR mRNA levels in the hypothalamus and pituitary (3.5- and 3.5-fold, respectively; P < 0.01 for both) and increased GR protein expression when compared with wild-type littermates. The suppressive effects of dexamethasone on GR were more pronounced in LIF-null animals. These data suggest that LIF maintains the HPA axis activation by decreasing GR expression and raise the possibility that LIF might contribute to the development of central glucocorticoid resistance during inflammation.     

Evidence that endogenous SST inhibits ACTH and ghrelin expression by independent pathways

Corticosterone and total ghrelin levels are increased in somatostatin (SST) knockout mice (Sst-/-) compared with SST-intact controls (Sst+/+). Because exogenous ghrelin can increase glucocorticoids, the question arises whether elevated levels of ghrelin contribute to elevated corticosterone levels in Sst-/- mice. We report that Sst-/- mice had elevated mRNA levels for pituitary proopiomelanocortin (POMC), the precursor of adrenocorticotropic hormone (ACTH), whereas mRNA levels for hypothalamic corticotropin-releasing hormone (CRH) did not differ from Sst+/+ mice. Furthermore, SST suppressed pituitary POMC mRNA levels and ACTH release in vitro independently of CRH actions. In contrast, it has been reported that ghrelin increases glucocorticoids via a central effect on CRH secretion and that n-octanoyl ghrelin is the form of ghrelin that activates the GHS-R1a and modulates CRH neuronal activity. Consistent with elevations in total ghrelin levels, Sst-/- mice displayed an increase in stomach ghrelin mRNA levels, whereas hypothalamic and pituitary expression of ghrelin was not altered. Despite the increase in total ghrelin levels, circulating levels of n-octanoyl ghrelin were not altered in Sst-/- mice. Because glucocorticoids and ghrelin increase in response to fasting, we examined the impact of fasting on the adrenal axis and ghrelin in Sst+/+ and Sst-/- mice and found that endogenous SST does not significantly contribute to this adaptive response. We conclude that endogenous SST inhibits basal ghrelin gene expression in a tissue specific manner and independently and directly inhibits pituitary ACTH synthesis and release. Thus endogenous SST exerts an inhibitory effect on ghrelin synthesis and on the adrenal axis through independent pathways.     

Vasopressinergic regulation of the hypothalamic-pituitary-adrenal axis: implications for stress adaptation

In addition to its role on water conservation, vasopressin (VP) regulates pituitary ACTH secretion by potentiating the stimulatory effects of corticotropin releasing hormone (CRH). The pituitary actions of VP are mediated by plasma membrane receptors of the V1b subtype, coupled to calcium-phospholipid signaling systems. VP is critical for adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress as indicated by preferential expression of VP over CRH in parvocellular neurons of the hypothalamic paraventricular nucleus, and the upregulation of pituitary VP receptors during stress paradigms associated with corticotroph hyperresponsiveness. V1b receptor mRNA levels and coupling of the receptor to phospolipase C are stimulated by glucocorticoids, effects which may contribute to the refractoriness of VP-stimulated ACTH secretion to glucocorticoid feedback. The data suggest that vasopressinergic regulation of the HPA axis is critical for sustaining corticotroph responsiveness in the presence of high circulating glucocorticoid levels during chronic stress.     

BuShenYiQi Granule Inhibits Atopic Dermatitis via Improving Central and Skin Hypothalamic -Pituitary -Adrenal Axis Function

BackgroundDysfunction of central and skin Hypothalamic-Pituitary-Adrenal (HPA) axis play important roles in pathogenesis of atopic dermatitis (AD). Our previous studies showed that several Chinese herbs could improve HPA axis function. In this study, we evaluated the anti-inflammatory effects of BuShenYiQi granule (BSYQ), a Chinese herbs formula, in AD mice and explored the effective mechanism from regulation of HPA axis.MethodsThe ovalbumin (OVA) induced AD mice model were established and treated with BSYQ. We evaluated dermatitis score and histology analysis of dorsal skin lesions, meanwhile, serum corticosterone (CORT), adrenocorticotropic hormone (ACTH), corticotropin-releasing hormone (CRH) and inflammatory cytokines were determined by ELISA. The changes of CRH/proopiomelanocortin(POMC) axis elements, corresponding functional receptors and crucial genes of glucocorticosteroidogenesis in the skin were measured by quantitative real-time PCR and western blot, respectively.ResultsThe symptoms and pathological changes in skin of AD mice were significantly improved and several markers of inflammation and allergy descended obviously after BSYQ treatment. We found that AD mice had insufficient central HPA tone, but these conditions were markedly improved after BSYQ treatment. The AD mice also showed a disturbed expression of skin HPA. In lesion skin of AD mice, the mRNA and protein expressions of CRH decreased significantly, on the contrary, POMC and cytochrome P450 side-chain cleavage enzyme (CYP11A1) increased markedly, meanwhile, NR3C1 (mouse GR), CRHR2 and 11-hydroxylase type 1(CYP11B1) were reduced locally. Most of these tested indexes were improved after BSYQ treatment.ConclusionsAD mice displayed the differential expression pattern of central and skin HPA axis and BSYQ treatment significantly alleviated the symptoms of AD mice and presented anti-inflammatory and anti-allergic effects via regulating the expression of central and skin HPA axis.     

Repeated citalopram treatment but not stress exposure attenuates hypothalamic-pituitary-adrenocortical axis response to acute citalopram injection

Many experimental, clinical and epidemiological studies have shown a direct connection between exposure to stress or adverse life events and disease, but little is known about the effect of stress on the action of drugs. The aim of this study was to test the hypothesis that previous exposure to stress changes the action of the antidepressant drug citalopram (10 mg/kg, i.p.) on hypothalamic-pituitary-adrenocortical (HPA) axis function, gene expression of selected neuropeptides and serotonin reuptake. Three different stress models were used, which included immobilization, restraint and unpredictable stress stimuli. Samples of plasma for hormone measurement were taken from conscious cannulated animals. Changes in corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) gene expression in the paraventricular nucleus of the hypothalamus and the anterior pituitary, respectively, and the ability of citalopram to inhibit serotonin reuptake were investigated. The exposure to three different stress models did not influence citalopram action on individual parameters of HPA axis and on serotonin reuptake. On the other hand, repeated administration of the drug led to significant attenuation of ACTH and CRH mRNA responses. The present results allow to suggest that the stressors used did not influence serotonergic neurotransmission to the extent that would modify HPA axis response to citalopram challenge. Activation of HPA axis by acute citalopram treatment was found to be accompanied by increased CRH gene expression in the hypothalamus. Repeated administration of the drug led to the development of tolerance to activation of central and peripheral components of HPA axis, but not to serotonin reuptake inhibition.     

CRH stimulation of corticosteroids production in melanocytes is mediated by ACTH

The response to systemic stress is organized along the hypothalamic-pituitary-adrenal axis (HPA), whereas the response to a peripheral stress (solar radiation) is mediated by epidermal melanocytes (cells of neural crest origin) responsible for the pigmentary reaction. Melanocytes express proopiomelanocortin (POMC), corticotropin-releasing hormone (CRH), and CRH receptor-1 (CRH-R1) and can produce corticosterone. In the present study, incubation of normal epidermal melanocytes with CRH was found to trigger a functional cascade structured hierarchically and arranged along the same algorithm as in the HPA axis: CRH activation of CRH-R1 stimulated cAMP accumulation and increased POMC gene expression and production of ACTH. CRH and ACTH also enhanced production of cortisol and corticosterone, and cortisol production was also stimulated by progesterone. The chemical identity of the cortisol was confirmed by liquid chromatography-mass spectrometry (LC/MS2) with [corrected] mass spectrometry-mass spectrometry analyses. POMC gene silencing abolished the stimulatory effect of CRH on corticosteroid synthesis, indicating that this is indirect and mediated via production of ACTH. Thus the melanocyte response to CRH is highly organized along the same functional hierarchy as the HPA axis. This pattern demonstrates the fractal nature of the response to stress with similar activation sequence at the single-cell and whole body levels.     

Mice overexpressing CRH show reduced responsiveness in plasma corticosterone after a5-HT1A receptor challenge

Corticotropin-releasing hormone (CRH) overproduction and serotonergic dysfunction have both been implicated in a range of psychiatric disorders, such as anxiety and depression, and several studies have shown interactions between these two neurotransmitter systems. In this study, we investigated the effects of CRH challenge on hypothalamo-pituitary-adrenal (HPA) axis activity in female transgenic mice overproducing CRH. Furthermore, the effects of mild stress on HPA axis activity and body temperature were investigated in these mice. Pre- and post-synaptic 5-HT_1A receptor function were studied by monitoring body temperature and plasma corticosterone levels after challenge with the 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propyl-amino)-tetralin (8-OH-DPAT). Hypothermia in response to 8-OH-DPAT treatment did not differ between transgenic and wild type mice, indicating unaltered somatodendritic 5-HT_1A autoreceptor function in mice overproducing CRH. In wild type mice 8-OH-DPAT increased plasma corticosterone levels, but not in transgenic animals. CRH injection, however, increased corticosterone levels in both groups. These data suggest desensitization of post-synaptic, but not pre-synaptic, 5-HT_1A receptors in mice overproducing CRH. These findings resemble those seen in depressed patients following 5-HT_1A challenge, which is in accord with the hypothesized role of CRH in the pathogenesis of depression.     

Evidence suggesting that ghrelin O-acyl transferase inhibitor acts at the hypothalamus to inhibit hypothalamo-pituitary-adrenocortical axis function in the rat

Production of n-octanoyl-modified ghrelin (GHREL), an active form of the peptide requires prohormone processing protease and GHREL O-acyltransferase (GOAT), as well as n-octanoic acid. Recently a selective GOAT antagonist (GO-CoA-Tat) was invented and this tool was used to study the possible role of endogenous GHREL in regulating HPA axis function in the rat. Administration of GOAT inhibitor (GOATi) resulted in a notable decrease in plasma ACTH, aldosterone and corticosterone concentrations at min 60 of experiment. Octanoic acid (OA) administration had no effect on levels of studied hormones. Plasma levels of unacylated and acylated GHREL remained unchanged for 60min after either GOATi or OA administration. Under experimental conditions applied, no significant changes were observed in the levels of GOAT mRNA in hypothalamus, pituitary, adrenal and stomach fundus. After GOATi injection hypothalamic CRH mRNA levels were elevated at 30 min and pituitary POMC mRNA levels at 60 min. Both GOATi and OA lowered basal, but not K(+)-stimulated CRH release by hypothalamic explants and had no effect on basal or CRH-stimulated ACTH release by pituitary slices. Neither GOATi nor OA affected corticosterone secretion by freshly isolated or cultured rat adrenocortical cells. Thus, results of our study suggest that in the rat endogenous GHREL exerts tonic stimulating effect on hypothalamic CRH release. This effect could be demonstrated by administering rats with selected inhibitor of ghrelin O-acyltransferase, the enzyme responsible for GHREL acylation, a process which is absolutely required for both GHSR-1a binding and its central endocrine activities.     

Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by ultraviolet radiation

The hypothalamic-pituitary-adrenal (HPA) axis maintains basal and stress-related homeostasis in vertebrates. Skin expresses all elements of the HPA axis including corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), ACTH, β-endorphin (β-END) with corresponding receptors, the glucocorticoidogenic pathway, and the glucocorticoid receptor (GR). To test the hypothesis that cutaneous responses to environmental stressors follow the organizational structure of the central response to stress, the activity of the "cutaneous HPA" axis homolog was investigated after exposure to ultraviolet radiation (UVR) wavelengths of UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm) in human skin organ culture and in co-cultured keratinocytes/melanocytes. The level of stimulation of CRH, POMC, MC1R, MC2R, CYP11A1, and CYP11B1 genes was dependent on UV wavelengths and doses, with the highest effects observed for highly energetic UVC and UVB. ELISA and Western assays showed significant production of CRH, POMC, ACTH, and CYP11A1 proteins and of cortisol, with a decrease in GR expression only after UVB and UVC. However, β-END expression was also stimulated by UVA. Immunocytochemistry localized the deposition of the aforesaid antigens predominantly to the epidermis with additional accumulation of CRH, β-END, and ACTH in the dermis. UVR-stimulated CYP11A1 expression was seen in the basal layer of the epidermis and cells of adjacent dermis. Thus, the capacity to activate or change the spatial distribution of the cutaneous HPA axis elements is dependent on highly energetic wavelengths (UVC and UVB), implying a dependence of a local stress response on their noxious activity with overlapping or alternative mechanisms activated by UVA.     

CRH inhibits NF-kappa B signaling in human melanocytes

Corticotropin releasing hormone (CRH), a messenger of stress at the central level, is expressed in the epidermis where it operates within local equivalent of hypothalamo-pituitary axis. CRH inhibits NF-κB activity in human immortalized epidermal (PIG1) melanocytes. In melanocytes CRH stimulates pro-opiomelanocortin (POMC) mRNA and adrenocorticotropin (ACTH) peptide production. Knockdown of POMC levels by transfecting cells with antisense oligonucleotides blocks the effect of CRH on NF-κB signaling indicating that the above inhibition is indirect, e.g. through activation of POMC. We suggest that induction of POMC by CRH serves as a feedback mechanism to self-restrict inflammatory response in the skin.     

Feedback control of glucocorticoid production is established during fetal development.

BACKGROUND: Glucocorticoids are involved in the regulation of metabolic, immunological, and developmental processes. Their synthesis is tightly controlled by feedback regulation through the hypothalamus-pituitary-adrenal (HPA) axis, allowing the organism to respond to stress in an adequate manner and to adapt to new situations. Disturbance of these regulatory mechanisms leads to major human diseases. By generating mice with a targeted mutation in the glucocorticoid receptor (GR) locus, it was possible to analyze the mechanism by which glucocorticoids control the HPA axis, under conditions where at least part of the feedback control was absent early in development. MATERIALS AND METHODS: RNase-protection and in situ hybridization assays were used to compare messenger RNA (mRNA) levels of genes involved in the control of the HPA axis in both GR-mutant and wild-type animals. RESULTS: Negative feedback regulation of the HPA axis by glucocorticoids, which is established around Day E16.5 of embryonic development in wild-type mice, does not occur in GR-mutants, resulting in an increased expression of proopiomelanocortin mRNA in the anterior lobe of the pituitary and of corticotropin-releasing hormone mRNA in the paraventricular nucleus of the hypothalamus. However, the expression of both arginine vasopressin and mineralocorticoid receptor in the brain is not affected. In the neurointermediate lobe of the pituitary, expression of the proopiomelanocortin gene was inversely regulated, compared with its expression in the anterior lobe. CONCLUSIONS: GR-dependent regulation of the HPA axis is established during fetal development, suggesting that maternal factors have an important role in influencing the HPA axis of the adult offspring.     

Pleiotropic effects of corticotropin releasing hormone on normal human skin keratinocytes

The hypothalamic-pituitary-adrenal (HPA) axis is the major stress response system. Several components of the HPA axis, such as corticotropin-releasing hormone (CRH) and POMC peptides and their receptors are also present in the skin. In earlier studies, we showed that CRH inhibits cellular proliferation of immortalized human keratinocytes. We now examine further the functional activity of the HPA axis in the skin, by characterizing the actions of CRH on normal foreskin keratinocytes. The CRH receptor was detected as CRH-R1 antigen at 47 kDa in the cultured keratinocytes by Western blotting, and immunohistochemistry demonstrated its presence in the epidermal and follicular keratinocytes. CRH is also biologically active in cultured keratinocytes, where it inhibits proliferation and enhances the interferon-gamma-stimulated expression of the hCAM and ICAM-1 adhesion molecules and of the HLA-DR antigen. These effects were concentration-dependent, with maximal activity at CRH 10(-7) M. Thus, in the keratinocyte, the most important cellular component of the epidermis, CRH appears to induce a shift in energy metabolism away from proliferation activity, and toward the enhancement of immunoactivity. Therefore, similar to its central actions, cutaneous CRH may also he involved in the stress response, but at a highly localized level.     

Deducing corticotropin-releasing hormone receptor type 1 signaling networks from gene expression data by usage of genetic algorithms and graphical Gaussian models

Background  

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is a hallmark of complex and multifactorial psychiatric diseases such as anxiety and mood disorders. About 50-60% of patients with major depression show HPA axis dysfunction, i.e. hyperactivity and impaired negative feedback regulation. The neuropeptide corticotropin-releasing hormone (CRH) and its receptor type 1 (CRHR1) are key regulators of this neuroendocrine stress axis. Therefore, we analyzed CRH/CRHR1-dependent gene expression data obtained from the pituitary corticotrope cell line AtT-20, a well-established in vitro model for CRHR1-mediated signal transduction. To extract significantly regulated genes from a genome-wide microarray data set and to deduce underlying CRHR1-dependent signaling networks, we combined supervised and unsupervised algorithms.