Specific up-regulation of CRH or AVP secretion by acetylcholine or lipopolysaccharide in inflammatory susceptible Lewis rat fetal hypothalamic cells

LUMAN/CREB3 Plays a Dual Role in Stress Responses as a Cofactor of the Glucocorticoid Receptor and a Regulator of Secretion

LUMAN/CREB3, originally identified through its interaction with a cell cycle regulator HCFC1, is a transcription factor involved in the unfolded protein response during endoplasmic reticulum stress. Previously using gene knockout mouse models, we have shown that LUMAN modulates the glucocorticoid (GC) response leading to enhanced glucocorticoid receptor (GR) activity and lower circulating GC levels. Consequently, the stress response is dysregulated, leading to a blunted stress response in the Luman-deficient mice. One question that remained was how LUMAN deficiency affected the stress response at the cellular level leading to the changes in the physiological stress response. Here, we found that LUMAN interacts with GR through a putative nuclear receptor box site and can activate GR in the absence of a ligand. Further investigation showed that, when activated, LUMAN binds to the glucocorticoid response element (GRE), increasing the activity of GR exponentially compared to GR-ligand binding alone. On the other hand, we also found that in the absence of LUMAN, cells were more sensitive to cellular stress, exhibiting decreased secretory capacity. Hence our current data suggest that LUMAN may function both as a transcriptional cofactor of GR and a hormone secretion regulator, and through this, plays a role in stress sensitivity and reactivity to stress.

Nuclear receptors in inflammation control: repression by GR and beyond

Inflammation is a protective response of organisms to pathogens, irritation or injury. Primary inflammatory sensors activate an array of signaling pathways that ultimately converge upon a few transcription factors such as AP1, NFκB and STATs that in turn stimulate expression of inflammatory genes to ultimately eradicate infection and repair the damage. A disturbed balance between activation and inhibition of inflammatory pathways can set the stage for chronic inflammation which is increasingly recognized as a key pathogenic component of autoimmune, metabolic, cardiovascular and neurodegenerative disorders. Nuclear receptors (NRs) are a large family of transcription factors many of which are known for their potent anti-inflammatory actions. Activated by small lipophilic ligands, NRs interact with a wide range of transcription factors, cofactors and chromatin-modifying enzymes, assembling numerous cell- and tissue-specific DNA-protein transcriptional regulatory complexes with diverse activities. Here we discuss established and emerging roles and mechanisms by which NRs and, in particular, the glucocorticoid receptor (GR) repress genes encoding cytokines, chemokines and other pro-inflammatory mediators.

Psychological Stress and the Cutaneous Immune Response: Roles of the HPA Axis and the Sympathetic Nervous System in Atopic Dermatitis and Psoriasis

Psychological stress, an evolutionary adaptation to the fight-or-flight response, triggers a number of physiological responses that can be deleterious under some circumstances. Stress signals activate the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Elements derived from those systems (e.g., cortisol, catecholamines and neuropeptides) can impact the immune system and possible disease states. Skin provides a first line of defense against many environmental insults. A number of investigations have indicated that the skin is especially sensitive to psychological stress, and experimental evidence shows that the cutaneous innate and adaptive immune systems are affected by stressors. For example, psychological stress has been shown to reduce recovery time of the stratum corneum barrier after its removal (innate immunity) and alters antigen presentation by epidermal Langerhans cells (adaptive immunity). Moreover, psychological stress may trigger or exacerbate immune mediated dermatological disorders. Understanding how the activity of the psyche-nervous -immune system axis impinges on skin diseases may facilitate coordinated treatment strategies between dermatologists and psychiatrists. Herein, we will review the roles of the HPA axis and the sympathetic nervous system on the cutaneous immune response. We will selectively highlight how the interplay between psychological stress and the immune system affects atopic dermatitis and psoriasis.

CCR2 antagonism improves insulin resistance, lipid metabolism, and diabetic nephropathy in type 2 diabetic mice

Chemokine ligand 2 (CCL2) binds to its receptor C-C chemokine receptor 2 (CCR2), initiating tissue inflammation, and recent studies have suggested a beneficial effect of a blockade of this pathway in diabetic nephropathy. To investigate the mechanism of protection, we studied the effect of RS504393, a CCR2 antagonist, on insulin resistance and diabetic nephropathy in db/db mice. Administering this antagonist improved insulin resistance as confirmed by various biomarkers, including homeostasis model assessment index levels, plasma insulin levels, and lipid abnormalities. Mice treated with the antagonist had a significant decrease in epididymal fat mass as well as phenotypic changes of adipocytes into small differentiated forms with decreased CCL2 expression and lipid hydroperoxide levels. In addition, treatment with the CCR2 antagonist markedly decreased urinary albumin excretion, mesangial expansion, and suppressed profibrotic and proinflammatory cytokine synthesis. Furthermore, the CCR2 antagonist improved lipid metabolism, lipid hydroperoxide, cholesterol, and triglyceride contents of the kidney, and decreased urinary 8-isoprostane levels. Hence, our findings suggest that CCR2 antagonists can improve insulin resistance by modulation of the adipose tissue and restore renal function through both metabolic and anti-fibrotic effects in type 2 diabetic mice.

Strain-specific BDNF expression of rat primary astrocytes

By producing brain-derived neurotrophic factor (BDNF), astrocytes play a role in disease resistance. This study was undertaken to investigate whether primary astrocytes derived from LEW/N and F344/N rats differentially express BDNF. LEW/N astrocytes expressed more BDNF mRNA and protein than F344/N astrocytes in basal and valproic acid (VPA)-stimulated conditions. VPA suppresses HDAC enzyme activity without affecting HDAC gene and protein expression in astrocytes of both strains. Blockade of TrkB receptors resulted in similar fold decreases in basal BDNF mRNA levels between two strains. The results suggest that inhibition of HDAC activity and BDNF-TrkB autocrine loop are involved in regulation of astrocytic BDNF transcription, whereas the mechanisms for elevated constitutive gene BDNF expression of LEW/N astrocytes remain to be investigated.

Interleukin-6 and the hypothalamic-pituitary-adrenal activation in a tumor bearing mouse

Tumor derived cytokines have been suggested to activate the hypothalamic-pituitary-adrenal (HPA) axis; that is, increase the hypothalamic releases of corticotropin-releasing hormone (CRH) and adrenocorticotrophic hormone. The authors previously reported that tumor mice bearing a human oral squamous cell carcinoma exhibit an anorectic phenotype with increased expression of CRH mRNA in their hypothalamic paraventricular nuclei. This study examined the plasma levels of tumor-derived cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), in order to determine potential mediator(s) implicated in CRH expression in this tumor mouse model. Plasma corticosterone levels were assayed as well to confirm the HPA activation. In the results, plasma levels of IL-6, but not TNF-alpha, were increased significantly in the tumor mice compared with age-matching non-tumor controls. Plasma corticosterone levels were also increased in the tumor mice. These results together with the previous findings suggest IL-6 as a potential mediator in the control of hypothalamic CRH expression in the authors' tumor mouse model.

Gene regulation system of vasopressin and corticotropin-releasing hormone

The neurohypophyseal hormones, arginine vasopressin and corticotropin-releasing hormone (CRH), play a crucial role in the physiological and behavioral response to various kinds of stresses. Both neuropeptides activate the hypophysial-pituitary-adrenal (HPA) axis, which is a central mediator of the stress response in the body. Conversely, they receive the negative regulation by glucocorticoid, which is an end product of the HPA axis. Vasopressin and CRH are closely linked to immune response; they also interact with pro-inflammatory cytokines. Moreover, as for vasopressin, it has another important role, which is the regulation of water balance through its potent antidiuretic effect. Hence, it is conceivable that vasopressin and CRH mediate the homeostatic responses for survival and protect organisms from the external world.

A tight and elaborate regulation system of the vasopressin and CRH gene is required for the rapid and flexible response to the alteration of the surrounding environments. Several important regulatory elements have been identified in the proximal promoter region in the vasopressin and CRH gene. Many transcription factors and intracellular signaling cascades are involved in the complicated gene regulation system. This review focuses on the current status of the basic research of vasopressin and CRH. In addition to the numerous known facts about their divergent physiological roles, the recent topics of promoter analyses will be discussed.

Stress and hypothalamic-pituitary-adrenal axis function in experimental autoimmune encephalomyelitis and multiple sclerosis - a review

Multiple sclerosis (MS) is an inflammatory and degenerative disease of the CNS with an assumed autoimmune-mediated pathogenesis. Stressful life events have been hypothesized as potential triggers of disease exacerbation. Animal studies using experimental autoimmune encephalomyelitis (EAE), as a model for MS, suggest that decreased hypothalamic-pituitary-adrenal (HPA) function may play a role in the increased susceptibility and severity of the disease. Histopathological studies of the hypothalamus point to disturbances in corticotropin-releasing hormone (CRH) regulation as a result of MS lesions in this area. Functional endocrine tests (e.g., the combined Dexamethasone-CRH test) showed a disturbed negative feedback after steroid application in MS patients. Hyper- and hypoactivity of the HPA axis, have been described to be associated with more severe courses. This paper presents an overview of the evidence for a role of HPA dysfunction in EAE and MS based on stress-experimental studies.

Effects of carrageenan and morphine on acute inflammation and pain in Lewis and Fischer rats

The present study used inbred, histocompatible Fischer 344 (FIS) and Lewis (LEW) rats to begin to explore the role of the hypothalamic-pituitary-adrenal (HPA) axis in the immune processes and pain behavior associated with the carrageenan model of acute hindpaw inflammation. Because the HPA axis contributes in part to morphine's analgesic and immunomodulatory properties, the present study also assessed the effects of morphine in carrageenan-inflamed LEW and FIS rats. The results showed that carrageenan-induced hindpaw swelling and pain behavior were greater in FIS than in LEW rats. The enhanced hindpaw swelling in FIS rats correlated with an increase in myeloperoxidase (MPO; a measure of neutrophils) in the inflamed hindpaw. FIS rats showed lower circulating levels of TNFalpha, higher IL-6 levels, and similar IL-1beta and nitric oxide levels, when compared to LEW rats. Morphine produced a significant decrease in carrageenan-induced hindpaw swelling and MPO in both strains, but morphine did not significantly alter circulating cytokine/mediator levels. Morphine's analgesic effects were greater in the inflamed than the noninflamed hindpaw, and they did not correlate with morphine's anti-inflammatory effects. In fact, low doses of morphine produced a mechanical allodynia and hyperalgesia in the noninflamed hindpaw of FIS, but not LEW, rats. These results suggest a positive relationship between HPA axis activity and acute inflammation and inflammatory pain. In contrast, little evidence is provided for HPA axis involvement in morphine's anti-inflammatory or analgesic effects.

Sequence of pituitary–adrenal cortical hormone responses to low-dose physostigmine administration in young adult women and men

We previously demonstrated greater HPA axis activation in adult men compared to adult women following low-dose administration of the anticholinesterase inhibitor, physostigmine (PHYSO). Because blood sampling was done infrequently following PHYSO, the rise times of AVP, ACTH1-39, and cortisol could not be determined. In the present study, we determined the sequence of hormone increases by frequent blood sampling following PHYSO. Twelve adult women and 12 adult men underwent three test sessions 5-7 days apart: PHYSO, saline control, and repeat PHYSO. As in the earlier study, PHYSO produced no side effects in half the subjects and mild side effects in the other half, with no significant female-male differences. None of the hormone responses was significantly correlated with the presence or absence of side effects. In both women and men, the AVP increase preceded the ACTH1-39 increase, which in turn preceded the cortisol increase. The AVP and ACTH AUCs were significantly positively correlated in both women and men, supporting AVP as an acute stimulus to ACTH secretion. Also as in the earlier study, the AVP response to PHYSO was more than twice as great in men as in women, but the difference was not statistically significant. We therefore analyzed the results of both studies combined (N=26 women and 26 men). The men had a significantly greater AVP response and a trend toward a greater ACTH1-39 response compared to the women. These findings further support the concept of sexual diergism (functional sex difference) in the influence of CNS cholinergic systems on HPA hormone secretion.

Acute inflammatory and neuropathic pain in Lewis and Fischer rats

Inbred, histocompatible Lewis and Fischer 344 rats (LEW and FIS) have been used to identify an inverse relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and susceptibility to autoimmune and chronic inflammatory disorders, with LEW showing blunted HPA axis activity and increased susceptibility toward the development of autoimmunity and chronic inflammation, and FIS showing the opposite relationship. In the present study, LEW and FIS were used to determine the relationship between HPA axis function and acute inflammatory pain (carrageenan-induced hindpaw inflammation) and neuropathic pain (partial sciatic nerve ligation; PSNL). The results showed that carrageenan-induced thermal and mechanical allodynia and hyperalgesia were greater in FIS than in LEW. Similarly, FIS showed more carrageenan-induced hindpaw swelling and higher levels of myeloperoxidase (a measure of neutrophils) in the carrageenan-inflamed hindpaw. After PSNL, LEW showed a profound mechanical allodynia and hyperalgesia, whereas mechanical sensitivity in FIS was unaltered. However, FIS, but not LEW, developed thermal allodynia and hyperalgesia after PSNL. These results provide strong evidence for a positive relationship between HPA axis activity and acute inflammatory pain. The results also support a relationship between HPA axis activity and neuropathic pain, but the relationship is complex and may depend on the pain assay.

The role of cytokines in mediating effects of prenatal infection on the fetus: implications for schizophrenia

Maternal infections with bacterial or viral agents during pregnancy are associated with an increased incidence of schizophrenia in the offspring at adulthood although little is known about the mechanism by which maternal infection might affect fetal neurodevelopment. Exposure of pregnant rodents to the bacterial endotoxin, lipopolysaccharide (LPS), results in behavioral deficits in the adult offspring that are relevant to schizophrenia. It is however unknown whether these effects are due to the direct action of the inflammatory stimulus on the developing fetus, or due to secondary immune mediators (cytokines) activated at maternal/fetal sites. In this study we sought to elucidate the site of action of LPS, following a single intraperitoneal (i.p.) injection, in pregnant rats at gestation day 18. Animals received 5 muCi of iodinated LPS ((125)I-LPS) and its distribution was assessed in maternal/fetal tissues (1-8 h). In addition, induction of the inflammatory cytokines, TNF-alpha, IL-1beta and IL-6, was measured in maternal/fetal tissues following maternal LPS challenge (0.05 mg/kg, i.p.) (2-8 h). (125)I-LPS was detected in maternal tissues and placenta, but not the fetus. This distribution was accompanied by significant increases in TNF-alpha, IL-1beta and IL-6 in maternal plasma and placenta, but not in fetal liver or brain. A significant increase in IL-1beta was however detected in fetal plasma, possibly due to transfer from the maternal circulation or placenta. Collectively, these data suggest that effects of maternal LPS exposure on the developing fetal brain are not mediated by the direct action of LPS, but via indirect actions at the level of the maternal circulation or placenta.

Regulatory role of the pituitary-adrenal axis in experimental colitis: effect of adrenalectomy on the clinical course and the TH1/TH2 immune profile

BACKGROUND

The hypothalamic-pituitary-adrenal (HPA) axis plays an important role in modulating immune reactions in inflammatory bowel disease. Our aim was to assess the role of the HPA axis in the pathogenesis of immunomediated colitis in mice.

METHODS

Trinitrobenzene sulfonic acid (TNBS) colitis was induced in Balb/c mice. Sham operation (sham+TNBS) or bilateral adrenalectomy (Adex+TNBS) was performed 3 days later. Control groups underwent adrenalectomy without colitis induction (Adex) or were untreated [naïve mice (Naïve)]. Mice were monitored for survival, weight loss, and macroscopic and microscopic scores of colitis. FACS analysis of CD4, CD8, natural killer T lymphocytes, and serum levels of adrenocorticotropic hormone (ACTH), corticosterone (CS), interferon-gamma (IFN-gamma), interleukin-10 (IL-10), and IL-1beta were measured. Production of prostaglandin E2 (PGE2) and binding capacity to glucocorticoid receptor (GR) in colonic mucosa were also assessed.

RESULTS

By day 7 following induction of colitis there was a marked increase in ACTH and CS levels in the colitis as compared with the control group (86 +/- 6.5 pg/mL and 16 +/- 1.9 pg/mL, and 23.3 +/- 2 pg/mL and 2.8 +/- 0.8 pg/mL, respectively). There was a decrease in ACTH and CS levels by day 28 in the colitis group, but the levels were still significantly higher than the levels in controls. Adrenalectomy markedly exacerbated colitis. The macroscopic and microscopic scores increased from 2.79 +/- 0.03 and 2.0 +/- 0.1 in the sham+TNBS group to 3.3 +/- 0.3 and 3.2 +/- 0.3 in the Adex+TNBS group. Survival and weight loss correlated with these differences. A significant increase in IL-10, IFN-gamma, and PGE2 was noted in the Adex+TNBS group compared with the sham+TNBS group. Splenic CD4 lymphocytes decreased in the sham+TNBS and Adex+TNBS groups as compared with control groups (Adex and naïve). The CD8/CD4 ratio was significantly higher in the Adex+TNBS compared with the sham+TNBS group. Colitis also caused a significant decrease in the specific binding capacity of labeled dexamethasone to colonic mucosa.

CONCLUSIONS

TNBS induced colitis activated the HPA axis and reduced the sensitivity of the inflamed mucosa to circulating glucocorticoids. Adrenalectomy markedly exacerbated TNBS-induced colitis. The effect was associated with changes in the peripheral CD8/CD4 ratio and with a TH1 cytokine shift. Our results suggest that adrenocortical hormones play an important role in the regulation of the immune system in experimental colitis.

The febrile response to intraperitoneal lipopolysaccharide: strain and gender differences in rats

The acute-phase febrile responses of the inbred Lewis (LEW) and Fischer 344 (F344) rat strains and their parent Sprague-Dawley (S-D) strain to immune challenge with lipopolysaccharide (LPS) were compared. LEW and S-D males and females displayed a biphasic febrile response with a markedly attenuated second phase in F344 rats. At 2 h after LPS (50 microg/kg), corticosterone was significantly higher in F344 than in LEW rats, but serum interleukin-1beta was higher only in F344 than LEW males. These data suggest that the greater LPS-induced corticosterone response of F344 rats mediates differences between febrile responses of F344 and LEW males and females.

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.

Lewis hypothalamic cells constitutively and upon stimulation express higher levels of mRNA for pro-inflammatory cytokines and related molecules: comparison with inflammatory resistant Fischer rat hypothalamic cells

Endogenous hypothalamic pro-inflammatory cytokines modulate the hypothalamic-pituitary-adrenal (HPA) axis responses. To investigate whether hypothalamic IL-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) are associated with differential inflammatory susceptibilities between Lewis (LEW/N) and Fischer (F344/N) rats, mRNA levels of pro-inflammatory cytokines and related molecules in hypothalamic cell cultures of both strains were quantified by real-time polymerase chain reaction (PCR). In addition to IL-1beta, IL-6, TNF-alpha, and their receptors, LEW/N hypothalamic cells also transcribed more anti-inflammatory molecules, IL-1RII, IL-1RA, and transforming growth factor (TGFbeta1), than F334/N cells. Our findings suggest that a balance exists between transcripts for endogenous pro- and anti-inflammatory molecules in LEW/N rats that may allow them, under basal conditions, to maintain hypothalamic homeostasis and health. However, under stimulated conditions, this balance may be more easily perturbed toward chronic inflammation.