Redox regulation of the glucocorticoid receptor

Apelin/APJ system: a novel promising target for anti-oxidative stress in stroke

The apelin/APJ system has garnered increasing attention in recent years. In this review, we comprehensively discuss the physiological and pathological mechanisms of the apelin/APJ system in stroke. The apelin/APJ system is widely expressed in the central nervous system (CNS). However, the distribution of the apelin/APJ system varies across different regions and subcellular organelles of the brain. Additionally, the neuroprotective effects of the apelin/APJ system have been reported to inhibit oxidative and nitrative stresses via various signaling pathways. Despite this, the clinical application of the apelin/APJ system remains distant, as apelin has numerous active forms and signaling pathways. The development of a range of drugs targeting the apelin/APJ system holds promise for treating stroke.

Perinatal protein malnutrition alters maternal behavior and leads to maladaptive stress response, neurodevelopmental delay and disruption on DNA methylation machinery in female mice offspring

Deficiencies in maternal nutrition have long-term consequences affecting brain development of the progeny and its behavior. In the present work, female mice were exposed to a normal-protein or a low-protein diet during gestation and lactation. We analyzed behavioral and molecular consequences of malnutrition in dams and how it affects female offspring at weaning. We have observed that a low-protein diet during pregnancy and lactation leads to anxiety-like behavior and anhedonia in dams. Protein malnutrition during the perinatal period delays physical and neurological development of female pups. Glucocorticoid levels increased in the plasma of malnourished female offspring but not in dams when compared to the control group. Interestingly, the expression of glucocorticoid receptor (GR) was reduced in hippocampus and amygdala on both malnourished dams and female pups. In addition, malnourished pups exhibited a significant increase in the expression of Dnmt3b, Gadd45b, and Fkbp5 and a reduction in Bdnf VI variant mRNA in hippocampus. In contrast, a reduction on Dnmt3b has been observed on the amygdala of weaned mice. No changes have been observed on global methylation levels (5-methylcytosine) in hippocampal genomic DNA neither in dams nor female offspring. In conclusion, deregulated behaviors observed in malnourished dams might be mediated by a low expression of GR in brain regions associated with emotive behaviors. Additionally, low-protein diet differentially deregulates the expression of genes involved in DNA methylation/demethylation machinery in female offspring but not in dams, providing an insight into regional- and age-specific mechanisms due to protein malnutrition.

Prolonged maternal exposure to glucocorticoids alters selenoprotein expression in the developing brain

Aberrant activation of the stress-response system in early life can alter neurodevelopment and cause long-term neurological changes. Activation of the hypothalamic-pituitary-adrenal axis releases glucocorticoids into the bloodstream, to help the organism adapt to the stressful stimulus. Elevated glucocorticoid levels can promote the accumulation of reactive oxygen species, and the brain is highly susceptible to oxidative stress. The essential trace element selenium is obtained through diet, is used to synthesize antioxidant selenoproteins, and can mitigate glucocorticoid-mediated oxidative damage. Glucocorticoids can impair antioxidant enzymes in the brain, and could potentially influence selenoprotein expression. We hypothesized that exposure to high levels of glucocorticoids would disrupt selenoprotein expression in the developing brain. C57 wild-type dams of recently birthed litters were fed either a moderate (0.25 ppm) or high (1 ppm) selenium diet and administered corticosterone (75 μg/ml) via drinking water during postnatal days 1 to 15, after which the brains of the offspring were collected for western blot analysis. Glutathione peroxidase 1 and 4 levels were increased by maternal corticosterone exposure within the prefrontal cortex, hippocampus, and hypothalamus of offspring. Additionally, levels of the glucocorticoid receptor were decreased in the hippocampus and selenoprotein W was elevated in the hypothalamus by corticosterone. Maternal consumption of a high selenium diet independently decreased glucocorticoid receptor levels in the hippocampus of offspring of both sexes, as well as in the prefrontal cortex of female offspring. This study demonstrates that early life exposure to excess glucocorticoid levels can alter selenoprotein levels in the developing brain.

Selenium Protects Mouse Hypothalamic Cells from Glucocorticoid-Induced Endoplasmic Reticulum Stress Vulnerability and Insulin Signaling Impairment

The use of glucocorticoid medications is known to cause metabolic side effects such as overeating, excess weight gain, and insulin resistance. The hypothalamus, a central regulator of feeding behavior and energy expenditure, is highly responsive to glucocorticoids, and it has been proposed that it plays a role in glucocorticoid-induced metabolic defects. Glucocorticoids can alter the expression and activity of antioxidant enzymes and promote the accumulation of reactive oxygen species. Recent evidence indicates that selenium can counter the effects of glucocorticoids, and selenium is critical for proper hypothalamic function. This study sought to determine whether selenium is capable of protecting hypothalamic cells from dysfunction caused by glucocorticoid exposure. We treated mHypoE-44 mouse hypothalamic cells with corticosterone to study the effects on cellular physiology and the involvement of selenium. We found that corticosterone administration rendered cells more vulnerable to endoplasmic reticulum stress and the subsequent impairment of insulin signaling. Supplementing the cell culture media with additional selenium alleviated endoplasmic reticulum stress and promoted insulin signaling. These findings implicate a protective role of selenium against chronic glucocorticoid-induced hypothalamic dysfunction.

Psychologically Traumatic Oxidative Stress; A Comprehensive Review of Redox Mechanisms and Related Inflammatory Implications

The organism's energy requirements for homeostatic balance are covered by the redox mechanisms. Yet in case of psychologically traumatic stress, allostatic regulations activate both pro-oxidant and antioxidant molecules as well as respective components of the inflammatory system. Thus a new setpoint of dynamic interactions among redox elements is reached. Similarly, a multifaceted interplay between redox and inflammatory fields is activated with the mediation of major effector systems such as the immune system, Hypothalamic-Pituitary-Adrenal axis, kynurenine, and the glycaemic regulatory one. In case of sustained and/or intense traumatic stress the prophylactic antioxidant components are inadequate to provide the organism with neuroprotection finally culminating in Oxidative Stress and subsequently to cellular apoptosis. In parallel multiple inflammatory systems trigger and/or are triggered by the redox systems in tight fashion so that the causation sequence appears obscure. This exhaustive review aims at the comprehension of the interaction among components of the redox system as well as to the collection of disperse findings relative to the redox-inflammatory interplay in the context of traumatic stress so that new research strategies could be developed.

Oxidative Stress and the Central Nervous System

Biochemical integrity of the brain is vital for normal functioning of the central nervous system (CNS). One of the factors contributing to cerebral biochemical impairment is a chemical process called oxidative stress. Oxidative stress occurs upon excessive free radical production resulting from an insufficiency of the counteracting antioxidant response system. The brain, with its high oxygen consumption and lipid-rich content, is highly susceptible to oxidative stress. Therefore, oxidative stress-induced damage to the brain has a strong potential to negatively impact normal CNS functions. Although oxidative stress has historically been considered to be involved mainly in neurodegenerative disorders such as Alzheimer disease, Huntington disease, and Parkinson disease, its involvement in neuropsychiatric disorders, including anxiety disorders and depression, is beginning to be recognized. This review is a discussion of the relevance of cerebral oxidative stress to impairment of emotional and mental well-being.

Ligand-Bound GeneSwitch Causes Developmental Aberrations in Drosophila that Are Alleviated by the Alternative Oxidase

Culture of Drosophila expressing the steroid-dependent GeneSwitch transcriptional activator under the control of the ubiquitous α-tubulin promoter was found to produce extensive pupal lethality, as well as a range of dysmorphic adult phenotypes, in the presence of high concentrations of the inducing drug RU486. Prominent among these was cleft thorax, seen previously in flies bearing mutant alleles of the nuclear receptor Ultraspiracle and many other mutants, as well as notched wings, leg malformations, and bristle abnormalities. Neither the α-tubulin-GeneSwitch driver nor the inducing drug on their own produced any of these effects. A second GeneSwitch driver, under the control of the daughterless promoter, which gave much lower and more tissue-restricted transgene expression, exhibited only mild bristle abnormalities in the presence of high levels of RU486. Coexpression of the alternative oxidase (AOX) from Ciona intestinalis produced a substantial shift in the developmental outcome toward a wild-type phenotype, which was dependent on the AOX expression level. Neither an enzymatically inactivated variant of AOX, nor GFP, or the alternative NADH dehydrogenase Ndi1 from yeast gave any such rescue. Users of the GeneSwitch system should be aware of the potential confounding effects of its application in developmental studies.

Cysteine oxidation impairs systemic glucocorticoid responsiveness in children with difficult-to-treat asthma

BACKGROUND

The mechanisms underlying glucocorticoid responsiveness are largely unknown. Although redox regulation of the glucocorticoid receptor (GR) has been reported, it has not been studied in asthmatic patients.

OBJECTIVE

We characterized systemic cysteine oxidation and its association with inflammatory and clinical features in healthy children and children with difficult-to-treat asthma. We hypothesized that cysteine oxidation would be associated with increased markers of oxidative stress and inflammation, increased features of asthma severity, decreased clinically defined glucocorticoid responsiveness, and impaired GR function.

METHODS

PBMCs were collected from healthy children (n = 16) and children with asthma (n = 118) aged 6 to 17 years. Children with difficult-to-treat asthma underwent glucocorticoid responsiveness testing with intramuscular triamcinolone. Cysteine, cystine, and inflammatory chemokines and reactive oxygen species generation were quantified, and expression and activity of the GR were assessed.

RESULTS

Cysteine oxidation was present in children with difficult-to-treat asthma and accompanied by increased reactive oxygen species generation and increased CCL3 and CXCL1 mRNA expression. Children with the greatest extent of cysteine oxidation had more features of asthma severity, including poorer symptom control, greater medication use, and less glucocorticoid responsiveness despite inhaled glucocorticoid therapy. Cysteine oxidation also modified the GR protein by decreasing available sulfhydryl groups and decreasing nuclear GR expression and activity.

CONCLUSIONS

A highly oxidized cysteine redox state promotes a posttranslational modification of the GR that might inhibit its function. Given that cysteine oxidation is prevalent in children with difficult-to-treat asthma, the cysteine redox state might represent a potential therapeutic target for restoration of glucocorticoid responsiveness in this population.

Activation of the hypothalamic-pituitary-adrenal stress axis induces cellular oxidative stress

Glucocorticoids released from the adrenal gland in response to stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis induce activity in the cellular reduction-oxidation (redox) system. The redox system is a ubiquitous chemical mechanism allowing the transfer of electrons between donor/acceptors and target molecules during oxidative phosphorylation while simultaneously maintaining the overall cellular environment in a reduced state. The objective of this review is to present an overview of the current literature discussing the link between HPA axis-derived glucocorticoids and increased oxidative stress, particularly focussing on the redox changes observed in the hippocampus following glucocorticoid exposure.

Epigenetic alteration by DNA-demethylating treatment restores apoptotic response to glucocorticoids in dexamethasone-resistant human malignant lymphoid cells

Background

Glucocorticoids (GCs) are often included in the therapy of lymphoid malignancies because they kill several types of malignant lymphoid cells. GCs activate the glucocorticoid receptor (GR), to regulate a complex genetic network, culminating in apoptosis. Normal lymphoblasts and many lymphoid malignancies are sensitive to GC-driven apoptosis. Resistance to GCs can be a significant clinical problem, however, and correlates with resistance to several other major chemotherapeutic agents.

Methods

We analyzed the effect of treatment with the cytosine analogue 5 aza-2’ deoxycytidine (AZA) on GC resistance in two acute lymphoblastic leukemia (T or pre-T ALL) cell lines- CEM and Molt-4- and a (B-cell) myeloma cell line, RPMI 8226. Methods employed included tissue culture, flow cytometry, and assays for clonogenicity, cytosine extension, immunochemical identification of proteins, and gene transactivation. High throughput DNA sequencing was used to confirm DNA methylation status.

Conclusions

Treatment of these cells with AZA resulted in altered DNA methylation and restored GC-evoked apoptosis in all 3 cell lines. In CEM cells the altered epigenetic state resulted in site-specific phosphorylation of the GR, increased GR potency, and GC-driven induction of the GR from promoters that lie in CpG islands. In RPMI 8226 cells, expression of relevant coregulators of GR function was altered. Activation of p38 mitogen-activated protein kinase (MAPK), which is central to a feed-forward mechanism of site-specific GR phosphorylation and ultimately, apoptosis, occurred in all 3 cell lines. These data show that in certain malignant hematologic B- and T-cell types, epigenetically controlled GC resistance can be reversed by cell exposure to a compound that causes DNA demethylation. The results encourage studies of application to in vivo systems, looking towards eventual clinical applications.

Severe life stress and oxidative stress in the brain: from animal models to human pathology

SIGNIFICANCE

Severe life stress (SLS), as opposed to trivial everyday stress, is defined as a serious psychosocial event with the potential of causing an impacting psychological traumatism.

RECENT ADVANCES

Numerous studies have attempted to understand how the central nervous system (CNS) responds to SLS. This response includes a variety of morphological and neurochemical modifications; among them, oxidative stress is almost invariably observed. Oxidative stress is defined as disequilibrium between oxidant generation and the antioxidant response.

CRITICAL ISSUES

In this review, we discuss how SLS leads to oxidative stress in the CNS, and how the latter impacts pathophysiological outcomes. We also critically discuss experimental methods that measure oxidative stress in the CNS. The review covers animal models and human observations. Animal models of SLS include sleep deprivation, maternal separation, and social isolation in rodents, and the establishment of hierarchy in non-human primates. In humans, SLS, which is caused by traumatic events such as child abuse, war, and divorce, is also accompanied by oxidative stress in the CNS.

FUTURE DIRECTIONS

The outcome of SLS in humans ranges from resilience, over post-traumatic stress disorder, to development of chronic mental disorders. Defining the sources of oxidative stress in SLS might in the long run provide new therapeutic avenues.

Protection against glucocorticoid-induced damage in human tenocytes by modulation of ERK, Akt, and forkhead signaling

Antiinflammatory glucocorticoid (GC) injections are extensively used to treat painful tendons. However, GC cause severe tissue wasting in other collagen-producing tissues such as skin and bone. The objective of this study was to determine the effects of GC on tenocytes and to explore strategies to protect against unwanted side effects of GC treatment. Cell survival, collagen production, and the induction of signaling pathways in primary human tenocytes treated with dexamethasone (Dex) were assessed. Antioxidant and growth factor approaches to protection were tested. Dex treatment resulted in reduced viable cell number, cell proliferation, and collagen production. Dex induced reactive oxygen species generation in tenocytes and strongly up-regulated the stress-response transcription factors FOXO1 and FOXO3A. Phosphorylation of ERK and protein kinase B/Akt, which regulate cell proliferation and also inhibit forkhead activity, was decreased. Chemical inhibition of ERK or Akt activity significantly reduced tenocyte cell number. Ameliorating the Dex-induced reduction in ERK or Akt activity by cotreatment with vitamin C or insulin protected against the Dex-induced reduction in cell number. Silencing FOXO1 prevented the Dex-induced reduction in collagen 1α1 expression. Cotreatment with vitamin C or insulin protected against the Dex-induced increase in FOXO and the Dex-induced inhibition of collagen 1α1 expression. Reduced ERK and Akt activation and increased forkhead signaling contribute to the negative effects of GC on tenocytes. Cotreatment therapies that target these signaling pathways are protective. Vitamin C in particular may be a clinically useable co-therapy to reduce connective tissue side effects associated with GC therapy.

T cells from burn-injured mice demonstrate a loss of sensitivity to glucocorticoids

Glucocorticoids (GC) are steroid hormones that modulate T cell functions and restrain their hyperresponsiveness following stimulation. Naive T lymphocytes are sensitive to GC but become more resistant when they are activated. A balance between activation and inhibition signals is important for a targeted and effective T cell response. Thermal injury is characterized by an immune dysfunction and hyperactive T cells visible at day 10 postburn. In this study, our objective was to evaluate T cell sensitivity to GC following thermal injury and to identify mechanisms that could modulate their sensitivity. One mechanism that we hypothesized was increased p38 mitogen-activated protein kinase (MAPK) activity that could lead to GC resistance. Male C57BL/6 mice underwent a full-thickness 20% total body surface area. At 10 days postinjury, splenic T cells were isolated. Glucocorticoid receptor (GR) expression was higher in T cells from burn-injured mice. Interestingly, these cells were also less sensitive to GC-induced apoptosis prior to and poststimulation. Furthermore, anti-CD3-activated T cells from burn-injured mice showed increased proliferation and CD25 expression, which resisted corticosterone's (CORT) suppressive effect. Anti-CD3-activated CD4(+)CD44(+) memory cells from burn-injured mice expressed the highest level of CD25 and were resistant to CORT. Increased phosphorylation of p38 MAPK was also noted in activated T cells from burn-injured mice. Pharmacological inhibition of p38 MAPK decreased cell proliferation and normalized interferon-gamma (IFNgamma) production. In conclusion, we demonstrate that a unique event like burn injury induces a loss of sensitivity to GC in splenic T cells and have identified p38 MAPK as a key modulator for this resistance.

Crosstalk between TNF and glucocorticoid receptor signaling pathways

TNF is a Janus-faced protein. It possesses impressive anti-tumor activities, but it is also one of the strongest known pro-inflammatory cytokines, which hampers its use as a systemic anti-cancer agent. TNF has been shown to play a detrimental role in inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease. Glucocorticoids are strongly anti-inflammatory and exert their therapeutic effects through binding to their receptor, the glucocorticoid receptor. Therefore, glucocorticoids have been used for over half a century for the treatment of inflammatory diseases. However, many patients are or become resistant to the therapeutic effects of glucocorticoids. Inflammatory cytokines have been suggested to play an important role in this steroid insensitivity or glucocorticoid resistance. This review aims to highlight the mechanisms of mutual inhibition between TNF and GR signaling pathways.

Effect of methanol-induced oxidative stress on the neuroimmune system of experimental rats

It is well known that the nervous system has increased susceptibility to methanol intoxication. The present study reveals the effect of methanol intoxication on antioxidant status, lipid peroxidation and DNA integrity in hypothalamic-pituitary-adrenal (HPA) axis organs and spleen. Non-specific and specific immune functions were analyzed. In addition, open field behavior, plasma corticosterone level and blood methanol level were estimated. Male Wistar albino rats were intoxicated with methanol (2.37 g/kg b.wt., i.p.) for 1 day, 15 and 30 days. Administration of methanol showed significant increase in enzymatic (superoxide dismutase, catalase, glutathione peroxidase), non-enzymatic (reduced glutathione and Vitamin C) antioxidants and lipid peroxidation (LPO) in hypothalamus and adrenal gland of day 1 group. However, decrease in enzymatic and non-enzymatic antioxidants with concomitant increase in LPO level were observed in 15 and 30 days groups. Plasma corticosterone level was significantly increased in day 1 and 15 days groups whereas, 30 days methanol intoxication group showed considerable decrease in corticosterone level compared with control animals. Cell-mediated immune response of footpad thickness was significantly decreased with an increased leukocyte migration inhibition. Humoral immune response of antibody titers was elevated in methanol-intoxicated groups. Neutrophil functions, adherence and phagocytic index (PI) were found to be significantly decreases. Furthermore, significant increase in the avidity index and nitro blue tetrozolium reduction was observed in the methanol exposed animals. Day 1 methanol exposed group showed increased PI compared to the control ones. Methanol exposure for 30 days showed an increased DNA fragmentation in the hypothalamus, adrenal glands, and spleen. In conclusion, exposure to methanol-induced oxidative stress disturbs the HPA-axis function altering the level of corticosterone, which lead to varied non-specific and specific immune response in experimental rats.

Identification and characterization of novel variants of the thioredoxin reductase 3 new transcript 1 TXNRD3NT1

We have identified and characterized a new gene sequence, TXNRD3NT1, whose transcripts, corresponding to the EST AA430236, were found by Affymetrix DNA chip analysis to be significantly down regulated in affected psoriatic tissue. The full-length cDNA of TXNRD3NT1 was isolated and characterized by combining 5'- and 3'-RACE (rapid amplication of cDNA ends) with screening a keratinocyte cDNA library, designing appropriate PCR primers, cloning amplified products, sequencing, and sequence analysis. Because part of this gene overlaps the previously described thioredoxin reductase 3 (TXNRD3) gene, we have named it TXNRD3NT1 (TXNRD3 new transcript 1). The full-length TXNRD3NT1 cDNA has 1133 nucleotides with a 251-bp 3-UTRand 2 poly(A)signal variants and 2 poly (A) sites. The TXNRD3NT1 cDNA ORF encodes for 133 amino acids, with the first four residues coding for a tubulin-beta mRNA autoregulation signal. Mapping the cDNA nucleotide sequence to the human genome sequence revealed that the TXNRD3NT1 gene has 4 exons located on Chromosome 3, at position 3q21. Exons 1 and 2 of the TXNRD3NT1 gene overlap with exons 15 and 16 of the thioredoxin reductase 2 gene which has different ORFs to that of TXNRD3NT1. The translation initiation codon ATG was found in exon 3 of the TXNRD3NT1 gene. RT-PCR showed that the full-length variant of the TXNRD3NT1 gene was expressed in only four issues (pancreas, esophagus, bone marrow, and keratinocytes) of the 30 different tissues tested. In most other tissues, an aberrant and truncated form of the transcript (i.e., missing exon 3 and part of exon 4) was detected. The result of a preliminary association study between psoriasis and single microsatellite marker of the TXNRD3NT1 gene suggests that it may not be a significant genetic determinant of psoriasis. However, we cannot exclude the possibility that other sequence variants may still exist within the TXNRD3NT1 gene. Sequence analysis of the TXNRD3NT1 gene from 8 psoriasis patients and 8 healthy controls revealed a number of synonymous SNPs that may be useful markers for future disease association studies.

p38 Mitogen-activated protein kinase (MAPK) is a key mediator in glucocorticoid-induced apoptosis of lymphoid cells: correlation between p38 MAPK activation and site-specific phosphorylation of the human glucocorticoid receptor at serine 211

Glucocorticoids (GCs) induce apoptosis in lymphoid cells through activation of the GC receptor (GR). We have evaluated the role of p38, a MAPK, in lymphoid cell apoptosis upon treatment with the synthetic GCs dexamethasone (Dex) or deacylcortivazol (DAC). The highly conserved phosphoprotein p38 MAPK is activated by specific phosphorylation of its threonine180 and tyrosine182 residues. We show that Dex and DAC stimulate p38 MAPK phosphorylation and increase the mRNA of MAPK kinase 3, a specific immediate upstream activator of p38 MAPK. Enzymatic assays confirmed elevated activity of p38 MAPK. Pharmacological inhibition of p38 MAPK activity was protective against GC-driven apoptosis in human and mouse lymphoid cells. In contrast, inhibition of the MAPKs, ERK and cJun N-terminal kinase, enhanced apoptosis. Activated p38 MAPK phosphorylates specific downstream targets. Because phosphorylation of the GR is affected by MAPKs, we examined its phosphorylation state in our system. We found serine 211 of the human GR to be a substrate for p38 MAPK both in vitro and intracellularly. Mutation of this site to alanine greatly diminished GR-driven gene transcription and apoptosis. Our results clearly demonstrate a role for p38 MAPK signaling in the pathway of GC-induced apoptosis of lymphoid cells.

Property of thimerosal-induced decrease in cellular content of glutathione in rat thymocytes: a flow cytometric study with 5-chloromethylfluorescein diacetate

There is a concern on the part of public health community that adverse health consequences by thimerosal, a preservative in vaccines for infants, may occur among infants during immunization schedule. Therefore, the effect of thimerosal on cellular content of glutathione was examined on thymocytes obtained from 4-week-old rats using a flow cytometer and 5-chloromethylfluorescein diacetate. Thimerosal at concentrations ranging from 1 to 10 microM reduced the cellular content of glutathione in a concentration-dependent manner, and the complete depletion of cellular glutathione was observed when the cells were treated with 30 microM thimerosal. L-Cysteine significantly attenuated the actions of thimerosal to reduce the glutathione content and to increase the intracellular Ca2+ concentration. Prolonged incubation (24 h) with 1-3 microM thimerosal induced the apoptosis. The cytotoxic action of thimerosal was greatly augmented when the cells suffered oxidative stress induced by H2O2. It may be unlikely that thimerosal exerts potent cytotoxic action under the in vivo condition because the blood concentration of thimerosal after receiving vaccines does not seem to reach micromolar range and nonprotein thiols at micromolar concentrations are present in the blood.

Attenuation by reactive oxygen species of glucocorticoid suppression on proopiomelanocortin gene expression in pituitary corticotroph cells

Up-regulation of hypothalamo-pituitary-adrenal axis is maintained during acute inflammation and/or infection, in the face of sustained elevation of plasma glucocorticoid hormone. Inflammatory stress is usually associated with high plasma cytokine levels and increased generation of reactive oxygen species (ROS) as well. In this study, we examined the effect of ROS on the negative feedback regulation of glucocorticoid in hypothalamo-pituitary-adrenal axis using AtT20 corticotroph cells in vitro. When the cells were treated with H2O2, glucocorticoid suppression on the proopiomelanocortin gene promoter activity was attenuated in a dose-dependent manner. H2O2 also inhibited the ligand-stimulated nuclear translocation of glucocorticoid receptor. The released glucocorticoid suppression by H2O2 was not observed when the cells were cotreated with antioxidants. Together, these results suggest that increased ROS generation in the oxidative redox state attenuates the glucocorticoid negative feedback system, at least in part, by interfering with the nuclear translocation of glucocorticoid receptor and eliminating the repression on proopiomelanocortin gene expression.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.