Corticotropin-releasing hormone deficiency results in impaired splenocyte response to lipopolysaccharide

Corticotropin-releasing hormone deficiency results in impaired analgesic response during CFA-induced inflammation

PURPOSE

Corticotropin-releasing hormone (CRH) plays an important role in relief of pain by releasing analgesia-associated molecules in several inflammatory states. During inflammation, peripheral CRH acts on cells of the immune system to stimulate the local expression of proopiomelanocortin (POMC) and the production of β-endorphin, which in turn binds to opioid receptors on sensory neurons to produce antinociception. In the present study, we further investigated the role of endogenous CRH in inflammatory pain by determining the effects of Crh-deficiency on this process.

METHODS

For this purpose, we used Crh-deficient (Crh-/-) mice and their wildtype (Crh + / +) littermates in the CFA (Complete Freund's Adjuvant)-induced inflammatory pain model. Pain thresholds were evaluated with the Hargreaves apparatus.

RESULTS

Our experiments showed that Crh deficiency led to increased pain response, which was associated with decreased POMC mRNA levels in locally inflamed paws of these mice. Furthermore, Crh-/- mice had higher paw edema than Crh + / + mice. Histological evaluation of inflamed paw tissues revealed increased inflammatory response in Crh-/- mice. Protein levels of proinflammatory cytokines, such as IL-6, TNF-α, and IL-1β, were higher in inflamed tissue of Crh-/- mice compared to wildtype mice. Corticosterone replacement increased the pain threshold of Crh-/- mice, restored their paw volume to the levels of wildtype mice, and significantly reduced their proinflammatory cytokine levels. Furthermore, glucocorticoid administration significantly increased POMC mRNA expression in the inflamed paw.

CONCLUSION

Our data suggest that genetic deficiency of CRH is associated with increased pain. This effect is likely attributable to the accompanying glucocorticoid insufficiency and is in part mediated by opioids expressed locally.

DOCK8: regulator of Treg in response to corticotropin-releasing hormone

BACKGROUND

Atopic dermatitis (AD) is exacerbated by psychological factors, such as stress. We previously reported that corticotrophin-releasing hormone (CRH) treatment in AD patients decreased the proportion of IL-10(+) Tr1 cells, a subset of inducible regulatory T cells (Tregs). However, changes in the function of Tregs in response to CRH have yet to be studied.

METHODS

We analyzed the total proteins taken from CRH-treated and untreated Tregs from AD mice model (NC/Nga mice) using a quantitative proteomic analysis for the different protein expressions.

RESULTS

We found a statistically decreased protein level of DOCK8 in CRH-treated Tregs from AD mice. In human, DOCK8 protein levels were also significantly decreased in CRH-treated Tregs from AD patients. Moreover, the expression of DOCK8 in Tregs was inversely correlated with the anxiety levels in the AD patients. In addition to the clinical correlation of DOCK8 with the stress level of AD patients, the knockdown of DOCK8 in Tregs reduced the inhibitory cytokines, IL-10 and TGF-β, and inhibited the regulatory function of Tregs to suppress the proliferation and TNF-α release of CD4(+) T cells in vitro.

CONCLUSION

This study provides new insights on the mechanisms of stress-induced AD aggravation by showing that CRH downregulated DOCK8 expression in Tregs that not only clinically correlates with anxiety levels of AD patients but also regulates suppressive function of Tregs on CD4(+) T cells.

Identification of a novel interaction between corticotropin releasing hormone (Crh) and macroautophagy

In inflammatory bowel disease (IBD), compromised restitution of the epithelial barrier contributes to disease severity. Owing to the complexity in the pathogenesis of IBD, a variety of factors have been implicated in its progress. In this study, we report a functional interaction between macroautophagy and Corticotropin Releasing Hormone (Crh) in the gut. For this purpose we used DSS colitis model on Crh -/- or wild-type (wt) with pharmacological inhibition of autophagy. We uncovered sustained basal autophagy in the gut of Crh -/- mice, which persisted over the course of DSS administration. Autophagy inhibition resulted in partial rescue of Crh -/- mice, while it increased the expression of Crh in the wt gut. Similarly, Crh deficiency was associated with sustained activation of base line autophagy. In vitro models of amino acid deprivation- and LPS-induced autophagy confirmed the in vivo findings. Our results indicate a novel role for Crh in the intestinal epithelium that involves regulation of autophagy, while suggesting the complementary action of the two pathways. These data suggest the intriguing possibility that targeting Crh stimulation in the intestine may provide a novel therapeutic approach to support the integrity of the epithelial barrier and to protect from chronic colitis.

Key role of CRF in the skin stress response system

The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.

A novel role of peripheral corticotropin-releasing hormone (CRH) on dermal fibroblasts

Corticotropin-releasing hormone, or factor, (CRH or CRF) exerts important biological effects in multiple peripheral tissues via paracrine/autocrine actions. The aim of our study was to assess the effects of endogenous CRH in the biology of mouse and human skin fibroblasts, the primary cell type involved in wound healing. We show expression of CRH and its receptors in primary fibroblasts, and we demonstrate the functionality of fibroblast CRH receptors by induction of cAMP. Fibroblasts genetically deficient in Crh (Crh-/-) had higher proliferation and migration rates and compromised production of IL-6 and TGF-β1 compared to the wildtype (Crh+/+) cells. Human primary cultures of foreskin fibroblasts exposed to the CRF(1) antagonist antalarmin recapitulated the findings in the Crh-/- cells, exhibiting altered proliferative and migratory behavior and suppressed production of IL-6. In conclusion, our findings show an important role of fibroblast-expressed CRH in the proliferation, migration, and cytokine production of these cells, processes associated with the skin response to injury. Our data suggest that the immunomodulatory effects of CRH may include an important, albeit not explored yet, role in epidermal tissue remodeling and regeneration and maintenance of tissue homeostasis.

Activation of phosphatidylinositol 3-kinase/protein kinase B by corticotropin-releasing factor in human monocytes

Corticotropin-releasing factor (CRF) exerts proinflammatory effects in peripheral tissues, whereas the intracellular pathways mediating these effects have not been completely characterized yet. We have previously shown that CRF induces nuclear factor-kappaB DNA-binding activity in mouse and human leukocytes. Here we demonstrate that in the human monocytic THP-1 cells, CRF activates the phosphatidylinositol 3-kinase (PI3K)/Akt and ERK1/2 pathways. These effects of CRF are mediated by corticotropin-releasing factor receptor 2 (CRF2), as suggested by their abolishment after treatment with the specific CRF2 antagonist, astressin 2B. The CRF-mediated PI3K/Akt activation induces cell survival as suggested by the stimulation of the antiapoptotic factor Bcl-2. ERK1/2 activation results in up-regulation of IL-8 expression, an effect inhibited by the CRF-induced activation of PI3K/Akt. These studies demonstrate novel effects of CRF in human monocytes mediated by the activation of PI3K/Akt. Moreover, they reveal pathway-specific effects of the CRF/CRF2 system in chemokine activation and cell survival that may be of importance for the development of novel therapeutics for inflammatory diseases.

Alpha-melanocyte-stimulating hormone attenuates behavioral effects of corticotropin-releasing factor in isolated guinea pig pups

During a 3-hr period of social isolation in a novel environment, guinea pig pups exhibit an initial active phase of behavioral responsiveness, characterized primarily by vocalizing, which is then followed by a stage of passive responsiveness in which pups display a distinctive crouch, eye-closing, and extensive piloerection. Prior treatment of pups with alpha-melanocyte-stimulating hormone (alpha-MSH) reduces each of the passive behaviors. The onset of passive responding during separation can be accelerated with peripheral injection of corticotropin-releasing factor (CRF). To examine whether CRF produces its effects through a mechanism similar to that of prolonged separation, we examined the effect of administering alpha-MSH to pups injected with CRF. As expected, CRF markedly enhanced passive responding during a 60-min period of separation. alpha-MSH delivered by either intracerebroventricular infusion or intraperitoneal injection significantly reduced each of the passive behavioral responses without significantly affecting active behavior. These findings, together with previous results indicating that it is the anti-inflammatory property of alpha-MSH that is responsible for its behavioral effects during prolonged separation, suggest that peripheral CRF speeds the induction of passive responding through a mechanism involving enhanced proinflammatory activity.

Corticotropin releasing factor receptor 1 (CRF1) and CRF2 agonists exert an anti-inflammatory effect during the early phase of inflammation suppressing LPS-induced TNF-alpha release from macrophages via induction of COX-2 and PGE2

Corticotropin-releasing factor (CRF), the principal regulator of the hypothalamus-pituitary-adrenal (HPA) axis, also modulates the inflammatory response directly, via its effect on mast cells and macrophages. On macrophages, it augments production of lipopolysaccharide (LPS)-induced pro-inflammatory cytokines. CRF and its related peptides may also act as anti-inflammatory agents. Aim of the present work was to examine the role of macrophages on the anti-inflammatory effects of CRF-peptides and the mechanism involved. Thus, we examined if CRF receptor 1 (CRF1) and CRF2 agonists exert any anti-inflammatory effect on primary mouse macrophages. We have found that: (a) CRF, Urocortin (UCN)1 and UCN2 transiently suppressed the release of Tumor Necrosis Factor-alpha (TNF-alpha) in LPS-activated macrophages, an effect peaking at 4 h. This effect did not involve changes on TNF-alpha transcription. (b) CRF peptide-induced suppression of TNF-alpha release depended on induction of COX-2 and PGE2 synthesis. (c) Use of specific CRF1 and CRF2 antagonists suggested that this effect involved both CRF receptor types. (d) The effect of CRF-peptides on COX-2 was mediated via PI3K and p38MAPK. (e) Longer exposure of macrophages to CRF-peptides resulted in induction of TNF-alpha production via enhancement of its transcription. In conclusion, this is the first report suggesting that CRF1 and CRF2 agonists exert a biphasic effect on macrophages. During the early stages of the inflammatory response, they suppress TNF-alpha release via induction of COX-2/PGE2 while later on they induce TNF-alpha transcription. Hence, the reported anti-inflammatory effect of CRF-peptides appears to involve macrophages and is confined at the early stage of inflammation.

Corticotropin-Releasing Hormone Receptor 2-Deficient Mice Have Reduced Intestinal Inflammatory Responses

Corticotropin-releasing hormone (CRH) and urocortins (Ucn) bind with various affinities to two G-protein-coupled receptors, CRHR1 and CRHR2, which are expressed in brain and in peripheral tissues, including immune cells. CRHR2-deficient mice display anxiety-like behavior, hypersensitivity to stress, altered feeding behavior and metabolism, and cardiovascular abnormalities. However, the phenotype of these mice in inflammatory responses has not been determined. In the present study we found that compared with wild-type CRHR2-null mice developed substantially reduced intestinal inflammation and had lower intestinal mRNA expression of the potent chemoattractants keratinocyte chemokine and monocyte chemoattractant protein 1 following intraluminal exposure to Clostridium difficile toxin A, a potent enterotoxin that mediates antibiotic-associated diarrhea and colitis in humans. This effect was recapitulated by administration of astressin 2B, a selective CRHR2 antagonist, before toxin A exposure. Moreover, Ab array analysis revealed reduced expression of several inflammatory chemokines, including keratinocyte chemokine and monocyte chemoattractant protein 1 in toxin A-exposed mice pretreated with astressin 2B. Real-time RT-PCR of wild-type mouse intestine showed that only UcnII, but not other Ucn, was significantly up-regulated by ileal administration of toxin A at 4 h compared with buffer exposure. We also found that human colonic epithelial HT-29 cells express CRHR2alpha mRNA, whereas expression of beta and gamma spliced variants was minimal. Moreover, treatment of HT-29 cells with UcnII, which binds exclusively to CRHR2, stimulated expression of IL-8 and monocyte chemoattractant protein 1. Taken together, these results provide direct evidence that CRHR2 mediates intestinal inflammatory responses via release of proinflammatory mediators at the colonocyte level.

Corticotropin Releasing Factor (CRF) activation of NF-kappaB-directed transcription in leukocytes

1. The aim of this study was to test whether CRF enhanced nuclear factor kappa B (NF-kappaB)-directed gene transcription in leukocytes and the receptor specificity of the effect. Initially, we examined the ability of CRF to modulate an antigen-specific, in vitro antibody response. Since that could be mediated by NF-kappaB transcription factor activity, we tested CRF in a NF-kappaB driven luciferase gene expression reporter assay. 2. CRF enhanced the antigen-specific antibody production in a dose- and time-dependent manner. RAW 264.7 macrophage cells and splenocytes stained by immunohistochemistry were positive for CRF receptors and CRF. Expression of both was up-regulated by mitogen treatment of the splenocytes. CRF also enhanced the NF-kappaB-regulated reporter assay and this could be blocked by a CRF-R1 receptor antagonist. 3. In light of these findings, it seems likely that CRF enhanced the antigen-specific antibody response through the CRF-R1 receptor by elevation of NF-kappaB activity. This study provides further support for the concept that CRF can act as an immunomodulator mediating neuro-immune interactions.

Corticotropin-releasing hormone contributes to the peripheral inflammatory response in experimental autoimmune encephalomyelitis

Peripheral corticotropin-releasing hormone (CRH) is thought to have proinflammatory effects. We used the model of experimental autoimmune encephalomyelitis (EAE) to study the role of CRH in an immune-mediated disease. We showed that CRH-deficient mice are resistant to EAE, with a decrease in clinical score as well as decreased cellular infiltration in the CNS. Furthermore, Ag-specific responses of primed T cells as well as anti-CD3/anti-CD28 TCR costimulation were decreased in crh(-/-) mice with decreased production of Th1 cytokines and increased production of Th2 cytokines. Wild-type mice treated in vivo with a CRH antagonist showed a decrease in IFN-gamma production by primed T cells in vitro. This effect of CRH is independent of its ability to increase corticosterone production, because adrenalectomized wild-type mice had similar disease course and severity as control mice. We found that IkappaBalpha phosphorylation induced by TCR cross-linking was decreased in crh(-/-) T cells. We conclude that peripheral CRH exerts a proinflammatory effect in EAE with a selective increase in Th1-type responses. These findings have implications for the treatment of Th1-mediated diseases such as multiple sclerosis.

Altered cytokine expression in tissues of mice subjected to simulated microgravity

Space flight is known to induce microgravity-associated immune dysfunction in humans, non-human primates and rodents. To understand the mechanism underlying these defects, several studies in rodents have been conducted in a ground-based antiorthostatic suspension (AOS) model that would mimic the effects of microgravity. In all these in vivo studies that showed the effects on cytokine profiles actually investigated the ex vivo production from culturing the cells isolated from whole organism that was exposed to space flight and/or microgravity. So, the purpose of the study was to examine the in vivo expression of cytokines in mice in immunologically important tissue environments of mice that were subjected to AOS. Cytokines such as Interleukin-1beta, (IL-1beta), IL-2, IL-3, IL-6, Interferon-gamma (IFN-gamma) and Tumor Necrosis Factor-alpha (TNF-alpha) were measured by Enzyme Linked Immunosorbent Assay (ELISA) in the homogenates of spleen tissue, lymph nodes and also in serum of AOS mice and compared with that of control mice. AOS induced no change in the IL-3 levels, but IL-1beta was increased significantly whereas IL-2 levels decreased in spleen, lymph nodes and serum. IL-6 levels did not differ in spleen but were significantly increased in lymph nodes and serum of AOS mice. IFN-gamma levels in spleen did not change but showed nonsignificant reduction in lymph nodes and significant reduction in serum in response to AOS. TNF-alpha levels in spleen and serum were unchanged and increased in lymph nodes. This in vivo cytokine study confirms the earlier findings that microgravity-simulated conditions induce tissue-specific immune response.

Effects of space flight conditions on the function of the immune system and catecholamine production simulated in a rodent model of hindlimb unloading

The rodent model of hindlimb unloading has been successfully used to simulate some of the effects of space flight conditions. Previous studies have indicated that mice exposed to hindlimb-unloading conditions have decreased resistance to infections compared to restrained and normally housed control mice.

OBJECTIVE

The purpose of this study was to clarify the mechanisms involved in resistance to infection in this model by examining the effects of hindlimb unloading on the function of the immune system and its impact on the production of catecholamines.

METHODS

Female Swiss Webster mice were hindlimb-unloaded during 48 h and the function of the immune system was assessed in spleen and peritoneal cells immediately after this period. In addition, the kinetics of catecholamine production was measured throughout the hindlimb-unloading period.

RESULTS

The function of the immune system was significantly suppressed in the hindlimb-unloaded group compared to restrained and normally housed control mice. Levels of catecholamines were increased in the hindlimb-unloaded group and peaked at 12 h following the commencement of unloading.

CONCLUSION

These results suggest that physiological responses of mice are altered early after hindlimb unloading and that catecholamines may play a critical role in the modulation of the immune system. These changes may affect the ability of mice to resist infections.