Redox-dependent regulation of nuclear import of the glucocorticoid receptor

Lymphocyte glucocorticoid receptor expression level and hormone-binding properties differ between war trauma-exposed men with and without PTSD

OBJECTIVE

Posttraumatic stress disorder (PTSD) has been shown to be associated with altered glucocorticoid receptor (GR) activity. We studied the expression and functional properties of the receptor in peripheral blood mononuclear cells (PBMCs) from non-traumatized healthy individuals (healthy controls; n=85), and war trauma-exposed individuals with current PTSD (n=113), with life-time PTSD (n=61) and without PTSD (trauma controls; n=88). The aim of the study was to distinguish the receptor alterations related to PTSD from those related to trauma itself or to resilience to PTSD.

METHODS

Functional status of the receptor was assessed by radioligand binding and lysozyme synthesis inhibition assays. The level of GR gene expression was measured by quantitative PCR and immunoblotting.

RESULTS

Current PTSD patients had the lowest, while trauma controls had the highest number of glucocorticoid binding sites (Bmax) in PBMCs. Hormone-binding potential (Bmax/KD ratio) of the receptor was diminished in the current PTSD group in comparison to all other study groups. Correlation between Bmax and KD that normally exists in healthy individuals was decreased in the current PTSD group. Contrasting Bmax data, GR protein level was lower in trauma controls than in participants with current or life-time PTSD.

CONCLUSIONS

Current PTSD is characterized by reduced lymphocyte GR hormone-binding potential and by disturbed compensation between Bmax and hormone-binding affinity. Resilience to PTSD is associated with enlarged fraction of the receptor molecules capable of hormone binding, within the total receptor molecule population in PBMCs.

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.

The chemotherapeutic potential of Terminalia ferdinandiana: Phytochemistry and bioactivity

Plants contain a myriad of natural compounds which exhibit important bioactive properties. These compounds may provide alternatives to current medications and afford a significant avenue for new drug discovery. Despite this, little information is available in the literature regarding native Australian plants and their potential for medicinal and industrial uses. Recent studies have reported Terminalia ferdinandiana to be an extremely good source of antioxidants. Indeed, T. ferdinandiana has been reported to have ascorbic acid levels per gram of fruit more than 900 times higher than blueberries. T. ferdinandiana also has high levels of a variety of other antioxidants, including phenolic compounds and anthocyanins. Antioxidants have been associated with the prevention of cancer, cardiovascular diseases, and neurological degenerative disorders. They are also linked with antidiabetic bioactivities and have been associated with the reduction of obesity. Antioxidants can directly scavenge free radicals, protecting cells against oxidative stress-related damage to proteins, lipids, and nucleic acids. Therefore, T. ferdinandiana has potential in the treatment of a variety of diseases and disorders and its potential bioactivities warrant further investigation.

Steroid-resistant asthma

Steroid-resistant asthma (SRA) refers to patients with symptoms consistent with asthma who show very poor or no response at all to high doses of inhaled or even of systemic corticosteroids. The current article reviews the SRA related literature focusing on the problems associated with the definition of SRA (especially its association with difficult to control, or severe asthma), its various phenotypes, its molecular basis, and the potential treatment options. The article also discusses the limitations of some of the key criteria used for the determination of SRA and proposes a modified set of criteria that are more applicable to children.

Increased HDAC in association with decreased plasma cortisol in older adults with chronic fatigue syndrome

Hypocortisolism is a frequent finding in individuals with chronic fatigue syndrome (CFS) with other research findings implying potential dysregulation of glucocorticoid signaling. Glucocorticoid signaling is under the influence of several pathways, several of which are of interest in the study of CFS. Oxidative stress and decreased antioxidant capacity are known to disrupt the hypothalamic-pituitary-adrenal (HPA) axis (Epel et al., 2004) and the presence of histone deacetylases (HDAC) could also impact glucocorticoid signaling. The intent of this pilot study was to investigate the relationship among oxidative stress elements, select HDAC's (2/3) and glucocorticoid receptor signaling in an elderly sample with CFS. Findings suggest increased histone deacetylase activity, lower total antioxidant power, in the context of decreased plasma cortisol and increased plasma dehydroepiandrosterone concomitant with decreased expression of the encoding gene for the glucocorticoid receptor. These findings support the presence of HPA axis dysregulation in elderly individuals with CFS.

On the trail of the glucocorticoid receptor: into the nucleus and back

The glucocorticoid receptor (GR) belongs to the superfamily of steroid receptors and is an important regulator of physiological and metabolic processes. In its inactive state, GR is unbound by ligand and resides in the cytoplasm in a chaperone complex. When it binds glucocorticoids, it is activated and translocates to the nucleus, where it functions as a transcription factor. However, the subcellular localization of GR is determined by the balance between its rates of nuclear import and export. The mechanism of GR nuclear transport has been extensively studied. Originally, it was believed that nuclear import of GR is initiated by dissociation of the chaperone complex in the cytoplasm. However, several studies show that the chaperone machinery is required for nuclear transport of GR. In this review, we summarize the contribution of various chaperone components involved in the nuclear transport of GR and propose an updated model of its nuclear import and export. Moreover, we review the importance of ligand-independent nuclear transport and compare the nuclear transport of GR with that of other steroid receptors.

Molecular and cellular mechanism of lung injuries due to exposure to sulfur mustard: a review

Sulfur mustard (SM), a potent chemical weapon agent, was used by Iraqi forces against Iranian in the Iraq-Iran war (1981-1989). Chronic obstructive pulmonary disease (COPD) is a late toxic pulmonary consequence after SM exposure. The COPD observed in these patients is unique (described as Mustard Lung) and to some extent different from COPD resulted from other well-known causes. Several mechanisms have been hypothesized to contribute to the pathogenesis of COPD including oxidative stress, disruption of the balance between apoptosis and replenishment, proteinase-antiproteinase imbalance and inflammation. However, it is not obvious which of these pathways are relevant to the pathogenesis of mustard lung. In this paper, we reviewed studies addressing the pathogenicity of mustard lung, and reduced some recent ambiguities in this field. There is ample evidence in favor of crucial role of both oxidative stress and apoptosis as two known mechanisms that are more involved in pathogenesis of mustard lung comparing to COPD. However, according to available evidences there are no such considerable data supporting neither proteolytic activity nor inflammation mechanism as the main underlying pathogenesis in Mustard Lung.

Increased inflammatory signaling and lethality of influenza H1N1 by nuclear thioredoxin-1

Background

Cell culture studies show that the antioxidant thiol protein, thioredoxin-1 (Trx1), translocates to cell nuclei during stress, facilitates DNA binding of transcription factors NF-κB and glucocorticoid receptor (GR) and potentiates signaling in immune cells. Excessive proinflammatory signaling in vivo contributes to immune hyper-responsiveness and disease severity, but no studies have addressed whether nuclear Trx1 mediates such responses.

Methodology/Principal Findings

Transgenic mice (Tg) expressing human Trx1 (hTrx1) with added nuclear localization signal (NLS) showed broad tissue expression and nuclear localization. The role of nuclear Trx1 in inflammatory signaling was examined in Tg and wild-type (WT) mice following infection with influenza (H1N1) virus. Results showed that Tg mice had earlier and more extensive NF-κB activation, increased TNF-α and IL-6 expression, greater weight loss, slower recovery and increased mortality compared to WT. Decreased plasma glutathione (GSH) and oxidized plasma GSH/GSSG redox potential (E_hGSSG) following infection in Tg mice showed that the increased nuclear thiol antioxidant caused a paradoxical downstream oxidative stress. An independent test of this nuclear reductive stress showed that glucocorticoid-induced thymocyte apoptosis was increased by NLS-Trx1.

Conclusion/Significance

Increased Trx1 in cell nuclei can increase severity of disease responses by potentiation of redox-sensitive transcription factor activation.

Nortriptyline reverses corticosteroid insensitivity by inhibition of phosphoinositide-3-kinase-δ

Corticosteroid insensitivity represents a major barrier to the treatment of chronic obstructive pulmonary disease (COPD) and severe asthma. It is caused by oxidative stress, leading to reduced histone deacetylase-2 (HDAC2) function through activation of phosphoinositide-3-kinase-δ (PI3Kδ). The tricyclic antidepressant nortriptyline has been identified in high-throughput screens as an agent that increases corticosteroid responsiveness. The aim of this study was to identify the molecular mechanism whereby nortriptyline increases corticosteroid sensitivity. Phosphorylation of Akt, a footprint of PI3K activation, and HDAC activity were evaluated by Western blotting and fluorescent activity assay in U937 monocytic cells. Corticosteroid sensitivity was evaluated by the inhibition of tumor necrosis factor α (TNFα)-induced interleukin 8 (IL-8) production by budesonide. Hydrogen peroxide (H(2)O(2)) or cigarette smoke extract (CSE) increased the level of phosphorylated Akt (pAkt) and reduced HDAC activity. Pretreatment with nortriptyline inhibited pAkt induced by CSE and H(2)O(2) as well as restored HDAC activity that had been decreased by H(2)O(2) and CSE. In addition, nortriptyline inhibited PI3Kδ activity, but had no effect on the PI3Kα and PI3Kγ isoforms. Although CSE reduced the effects of budesonide on TNFα-induced IL-8 production in U937 cells, nortriptyline reversed CSE-induced corticosteroid insensitivity. Nortriptyline restores corticosteroid sensitivity induced by oxidative stress via direct inhibition of PI3Kδ and is a potential treatment for corticosteroid-insensitive diseases such as COPD and severe asthma.

Glucocorticoid insensitivity as a future target of therapy for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by an abnormal and chronic inflammatory response in the lung that underlies the chronic airflow obstruction of the small airways, the inexorable decline of lung function, and the severity of the disease. The control of this inflammation remains a key strategy for treating the disease; however, there are no current anti-inflammatory treatments that are effective. Although glucocorticoids (GCs) effectively control inflammation in many diseases such as asthma, they are less effective in COPD. The molecular mechanisms that contribute to the development of this relative GC-insensitive inflammation in the lung of patients with COPD remain unclear. However, recent studies have indicated novel mechanisms and possible therapeutic strategies. One of the major mechanisms proposed is an oxidant-mediated alteration in the signaling pathways in the inflammatory cells in the lung, which may result in the impairment of repressor proteins used by the GC receptor to inhibit the transcription of proinflammatory genes. Although these studies have described mechanisms and targets by which GC function can be restored in cells from patients with COPD, more work is needed to completely elucidate these and other pathways that may be involved in order to allow for more confident therapeutic targeting. Given the relative GC-insensitive nature of the inflammation in COPD, a combination of therapies in addition to a restoration of GC function, including effective alternative anti-inflammatory targets, antioxidants, and proresolving therapeutic strategies, is likely to provide better targeting and improvement in the management of the disease.

Redox control systems in the nucleus: mechanisms and functions

Proteins with oxidizable thiols are essential to many functions of cell nuclei, including transcription, chromatin stability, nuclear protein import and export, and DNA replication and repair. Control of the nuclear thiol-disulfide redox states involves both the elimination of oxidants to prevent oxidation and the reduction of oxidized thiols to restore function. These processes depend on the common thiol reductants, glutathione (GSH) and thioredoxin-1 (Trx1). Recent evidence shows that these systems are controlled independent of the cytoplasmic counterparts. In addition, the GSH and Trx1 couples are not in redox equilibrium, indicating that these reductants have nonredundant functions in their support of proteins involved in transcriptional regulation, nuclear protein trafficking, and DNA repair. Specific isoforms of glutathione peroxidases, glutathione S-transferases, and peroxiredoxins are enriched in nuclei, further supporting the interpretation that functions of the thiol-dependent systems in nuclei are at least quantitatively distinct, and probably also qualitatively distinct, from similar processes in the cytoplasm. Elucidation of the distinct nuclear functions and regulation of the thiol redox pathways in nuclei can be expected to improve understanding of nuclear processes and also to provide the basis for novel approaches to treat aging and disease processes associated with oxidative stress in the nuclei.

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.

Nuclear redox signaling

Reactive oxygen species have been described to modulate proteins within the cell, a process called redox regulation. However, the importance of compartment-specific redox regulation has been neglected for a long time. In the early 1980s and 1990s, many in vitro studies introduced the possibility that nuclear redox signaling exists. However, the functional relevance for that has been greatly disregarded. Recently, it has become evident that nuclear redox signaling is indeed one important signaling mechanism regulating a variety of cellular functions. Transcription factors, and even kinases and phosphatases, have been described to be redox regulated in the nucleus. This review describes several of these proteins in closer detail and explains their functions resulting from nuclear localization and redox regulation. Moreover, the redox state of the nucleus and several important nuclear redox regulators [Thioredoxin-1 (Trx-1), Glutaredoxins (Grxs), Peroxiredoxins (Prxs), and APEX nuclease (multifunctional DNA-repair enzyme) 1 (APEX1)] are introduced more precisely, and their necessity for regulation of transcription factors is emphasized.

Greater resistance to inflammation at adulthood could contribute to extended life span of p66(Shc-/-) mice

Evidence is mounting that reactive oxygen species (ROS) produced because of stressful challenges could interfere with the proper functioning of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in greater vulnerability to aging and neurodegeneration. Here we tested the hypothesis that p66(Shc-/-) mice, which have been described to have an extended life span and a high resistance to oxidative stress, might be less susceptible to the effects of inflammatory insults at adulthood. Although adrenocortical reactivity in response to bacterial endotoxin (lipopolysaccharide, LPS) did not differ as a function of the genotype, a hyperdrive of the HPA axis was revealed following treatment with a synthetic glucocorticoid agonist. When measuring changes in hippocampal oxidative status following LPS, only wild-type (WT) subjects showed increased levels of F(2)-isoprostanes, an index of lipid peroxidation and free radical formation. At the same time, the neurotrophin brain-derived neurotrophic factor was selectively increased in WT subjects, while levels of prostaglandin E(2) were decreased in the mutants. Overall, the greater resilience to inflammation-induced changes in the p66(Shc-/-) mutants might underlie the better health status and the longevity characterizing these mice.

Therapeutic targets for new therapy for corticosteroid refractory asthma

BACKGROUND

Corticosteroids are the most potent anti-inflammatory agents for the treatment of mild to moderate asthma. However, a small percentage of the asthma population (< 10%) do not respond well, or at all, to corticosteroid therapy, and this severe corticosteroid-refractory asthma contributes to more than 50% of health care expenditure for all asthma because these is no appropriate pharmacological therapy.

METHODS

If the molecular mechanism of corticosteroid insensitivity is uncovered, it may in turn provide insights into the key mechanism of corticosteroid action and rational implementation of treatment regimens that restore corticosteroid sensitivity or replace corticosteroid therapy. This review focuses on why severe asthma patients are corticosteroid-insensitive, and discusses present and future therapeutic and preventative strategies for corticosteroid-refractory asthma.

CONCLUSIONS

Corticosteroid-refractory asthma is a heterogeneous disease and can be controlled by add-on treatment of corticosteroid-sparing agents or effective new drugs based on individual abnormalities. The elucidation of the cause of the relative lack of corticosteroid response in this subgroup of asthmatic individuals may have important implications for other diseases.

Zinc coordination is required for and regulates transcription activation by Epstein-Barr nuclear antigen 1

Epstein-Barr Nuclear Antigen 1 (EBNA1) is essential for Epstein-Barr virus to immortalize naïve B-cells. Upon binding a cluster of 20 cognate binding-sites termed the family of repeats, EBNA1 transactivates promoters for EBV genes that are required for immortalization. A small domain, termed UR1, that is 25 amino-acids in length, has been identified previously as essential for EBNA1 to activate transcription. In this study, we have elucidated how UR1 contributes to EBNA1's ability to transactivate. We show that zinc is necessary for EBNA1 to activate transcription, and that UR1 coordinates zinc through a pair of essential cysteines contained within it. UR1 dimerizes upon coordinating zinc, indicating that EBNA1 contains a second dimerization interface in its amino-terminus. There is a strong correlation between UR1-mediated dimerization and EBNA1's ability to transactivate cooperatively. Point mutants of EBNA1 that disrupt zinc coordination also prevent self-association, and do not activate transcription cooperatively. Further, we demonstrate that UR1 acts as a molecular sensor that regulates the ability of EBNA1 to activate transcription in response to changes in redox and oxygen partial pressure (pO₂). Mild oxidative stress mimicking such environmental changes decreases EBNA1-dependent transcription in a lymphoblastoid cell-line. Coincident with a reduction in EBNA1-dependent transcription, reductions are observed in EBNA2 and LMP1 protein levels. Although these changes do not affect LCL survival, treated cells accumulate in G0/G1. These findings are discussed in the context of EBV latency in body compartments that differ strikingly in their pO₂ and redox potential.

Epstein-Barr virus (EBV) infects human B-cells and immortalizes them. Immortalization results in diseases that range from infectious mononucleosis to malignancies such as lymphomas. During immortalization, EBV expresses a small number of viral genes that modulate cellular proliferation and differentiation. One of the genes expressed by EBV, Epstein-Barr nuclear antigen 1 (EBNA1), activates the expression of the other viral genes required for immortalization. In this report, we have explored the mechanism by which EBNA1 activates gene expression. We have determined that EBNA1 uses the micronutrient zinc to self-associate, and that self-association is necessary for it to activate gene expression. Further, we have determined that environmental conditions such as oxygen tension and oxidative stress modulate EBNA1's capacity to self-associate, and therefore to activate gene expression. The gene expression profile and proliferative phenotype of EBV-infected cells is known to vary in differing environmental niches in the human body, such as lymph nodes and in peripheral circulation. We interpret our results to postulate that these differences arise as a consequence of varying oxygen tension in these microenvironments on EBNA1's capacity to activate viral gene expression. Our findings can be exploited to devise novel therapeutics against EBV-associated diseases that target EBNA1 through oxidative stress.

A review of candidate pathways underlying the association between asthma and major depressive disorder

OBJECTIVE

To consider the mechanisms that may link asthma and major depressive disorder (MDD). Asthma and MDD co-occur at higher rates than expected, but whether this reflects shared underlying pathophysiological mechanisms is not known.

METHODS

A review of the epidemiological data linking asthma and MDD was conducted and the possible biological mechanisms that could account for the high rate of this comorbidity were reviewed.

RESULTS

MDD occurs in almost half of patients with asthma assessed in tertiary care centers. Dysregulation of the hypothalamic pituitary adrenal axis may predispose people to both MDD and asthma, and similar alterations in the immune, autonomic nervous, and other key systems are apparent and may contribute to this increased risk of co-occurrence.

CONCLUSIONS

High rates of MDD in asthma may result from the stress of chronic illness, the medications used to treat it, or a combination of the two. The high level of co-occurrence may also reflect dysregulation of certain stress-sensitive biological processes that contribute to the pathophysiology of both conditions.

Radical-free biology of oxidative stress

Free radical-induced macromolecular damage has been studied extensively as a mechanism of oxidative stress, but large-scale intervention trials with free radical scavenging antioxidant supplements show little benefit in humans. The present review summarizes data supporting a complementary hypothesis for oxidative stress in disease that can occur without free radicals. This hypothesis, which is termed the "redox hypothesis," is that oxidative stress occurs as a consequence of disruption of thiol redox circuits, which normally function in cell signaling and physiological regulation. The redox states of thiol systems are sensitive to two-electron oxidants and controlled by the thioredoxins (Trx), glutathione (GSH), and cysteine (Cys). Trx and GSH systems are maintained under stable, but nonequilibrium conditions, due to a continuous oxidation of cell thiols at a rate of about 0.5% of the total thiol pool per minute. Redox-sensitive thiols are critical for signal transduction (e.g., H-Ras, PTP-1B), transcription factor binding to DNA (e.g., Nrf-2, nuclear factor-kappaB), receptor activation (e.g., alphaIIbbeta3 integrin in platelet activation), and other processes. Nonradical oxidants, including peroxides, aldehydes, quinones, and epoxides, are generated enzymatically from both endogenous and exogenous precursors and do not require free radicals as intermediates to oxidize or modify these thiols. Because of the nonequilibrium conditions in the thiol pathways, aberrant generation of nonradical oxidants at rates comparable to normal oxidation may be sufficient to disrupt function. Considerable opportunity exists to elucidate specific thiol control pathways and develop interventional strategies to restore normal redox control and protect against oxidative stress in aging and age-related disease.

Transcriptomic profiles of Drosophila melanogaster third instar larval midgut and responses to oxidative stress

Oligoarray analysis was used to determine the number and nature of genes expressed in third instar Drosophila melanogaster larval midguts. The majority of transcripts were associated with protein synthesis and metabolism. Serine proteases were the main proteolytic enzymes detected. Some 40% of the cytochrome P450 genes and 74% of the glutathione S transferases (GSTs) in the genome of D. melanogaster were observed to be expressed in the midgut by oligoarray analysis. We also identified potential transcription factor binding motifs (TFBMs) of P450s, GSTs and carboxylesterases. Many of the midgut-expressed GST genes contained candidate TFBMs homologous to TFBMs in mammals that have been associated with responses to oxidative stress. We also investigated the response of GSTs in the midgut to dietary H2O2, which showed a dosage-based differential response.

Psychological factors in asthma

Asthma has long been considered a condition in which psychological factors have a role. As in many illnesses, psychological variables may affect outcome in asthma via their effects on treatment adherence and symptom reporting. Emerging evidence suggests that the relation between asthma and psychological factors may be more complex than that, however. Central cognitive processes may influence not only the interpretation of asthma symptoms but also the manifestation of measurable changes in immune and physiologic markers of asthma. Furthermore, asthma and major depressive disorder share several risk factors and have similar patterns of dysregulation in key biologic systems, including the neuroendocrine stress response, cytokines, and neuropeptides. Despite the evidence that depression is common in people with asthma and exerts a negative impact on outcome, few treatment studies have examined whether improving symptoms of depression do, in fact, result in better control of asthma symptoms or improved quality of life in patients with asthma.

Chicken 11beta-hydroxysteroid dehydrogenase type 2: partial cloning and tissue distribution

NAD(+)-dependent 11beta-hydroxysteroid dehydrogenase (11HSD2) converts glucocorticoids to 11-oxo derivatives and thus decreases their local concentration and prevents them from activating corticosteroid receptors. In this paper we report the partial cloning, characterization and tissue distribution of chicken 11HSD2. A cDNA of 991bp was cloned from kidney mRNA by reverse transcription and polymerase chain reaction. At the amino acid level, the sequence of PCR product had 56-59% homology with mammalian and 46-48% with fish 11HSD2. The consensus sequences of the short-chain dehydrogenase/reductase superfamily such as the catalytic activity motif Tyr-X-X-X-Lys and cosubstrate-binding motif Gly-X-X-X-Gly-X-Gly, were found in the cloned cDNA. Analysis of the tissue expression of chicken 11HSD2 mRNA and NAD(+)-dependent 11beta-oxidase activity showed a similar tissue distribution pattern in the majority of tissues. High levels of expression and activity were found in kidney, small intestine, colon and oviduct; low in ovary and almost zero in brain, liver and testis.

High glucose activates pituitary proopiomelanocortin gene expression: possible role of free radical-sensitive transcription factors

BACKGROUND

Hyperglycemia is recognized as a metabolic stress, and indeed it is known to stimulate hypothalamo-pituitary-adrenal (HPA) axis, a representative anti-stress system, in patients with diabetes mellitus or in animal models of hyperglycemia. Thus, we tried to clarify the molecular mechanism of glucose-induced HPA axis activation.

METHODS

We studied the effect of high glucose on the transcriptional regulation of proopiomelanocortin (POMC) gene that encodes adrenocorticotropic hormone, a central mediator of HPA axis, using AtT20 corticotroph cell line in vitro.

RESULTS

We found that high glucose concentration (24 mM) significantly stimulated the 5'-promoter activity of POMC gene. The effect was promoter-specific, and was mimicked by nuclear factor-kappaB (NF-kappaB)- or AP1-responsive promoters but not by cAMP-responsive element or serum-response element-containing promoters. Furthermore, the stimulatory effect of high glucose on POMC gene was eliminated by NF-kappaB and AP1 inhibitors, suggesting the involvement of the transcriptional factors. The POMC 5'-promoter has the canonical NF-kappaB consensus sequence, and gel shift assay showed the binding of NF-kappaB to the element. Finally, the effect of high glucose was completely abolished by treatment with a radical quencher 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL).

CONCLUSIONS

Our data suggest that hyperglycemia activates POMC gene expression, at least partly, via NF-kappaB/AP1, and that high-glucose-induced free radical generation may mediate the activation of these transcription factors, which in turn stimulates the transcription of POMC gene.

Cooperative inhibitory effects of budesonide and formoterol on eosinophil superoxide production stimulated by bronchial epithelial cell conditioned medium

BACKGROUND

Improved asthma control by combinations of inhaled glucocorticosteroids (GCs) and long-acting beta(2)-agonists (LABAs) includes a reduced frequency and severity of exacerbations. In view of the association of exacerbations with increased airway inflammation, the question has arisen as to whether LABAs are able to complement the known anti-inflammatory activity of GCs. To address this, we studied the effects of a LABA, formoterol (FORM), and a GC, budesonide (BUD), alone and in combination, on bronchial epithelial cell-mediated eosinophil superoxide production in vitro.

METHODS

We employed 2 experimental approaches. First, superoxide production by human eosinophils incubated with conditioned medium (CM) from human bronchial epithelial cells cultured for 24 h with vehicle, BUD, FORM or BUD + FORM was measured (Epi/Eos assay). Second, eosinophils were stimulated with vehicle-CM to which the drugs were added (Eos assay). Superoxide production was determined as the superoxide dismutase-inhibitable reduction of ferricytochrome C.

RESULTS

CM increased eosinophil superoxide generation (p < 0.01) and epithelial-derived granulocyte macrophage colony-stimulating factor was the mediator responsible. In both assays, FORM dose-dependently inhibited eosinophil superoxide similarly and in the same concentration range as BUD. The BUD + FORM combination was more effective than BUD alone, and it completely inhibited CM-induced superoxide production in the Epi/Eos assay, suggesting complementary effects of both drugs on bronchial epithelial cells and eosinophils.

CONCLUSIONS

The cooperative, inhibitory effects of BUD and FORM on eosinophils and bronchial epithelial cells, in terms of their effects on eosinophil superoxide production, may represent a possible mechanism for the enhanced anti-inflammatory efficacy of BUD and FORM combination therapy of asthma.

Analysis of intranuclear binding process of glucocorticoid receptor using fluorescence correlation spectroscopy

The diffusion properties of EGFP-hGRalpha and mutants C421G, A458T and I566 in living cells were analyzed. The wild type and mutants C421G and A458T translocated from the cytoplasm to the nucleus after addition of Dex; however, the Brownian motions of the proteins were different. The diffusion constant of wild-type GRalpha after addition of Dex slowed to 15.6% of that in the absence of Dex, whereas those of A458T and C421G slowed to 34.8% and 61.7%, respectively. This is the first report that dimer formation is less important than the binding activity of GRalpha to GRE in the living cell.

Diffusion analysis of glucocorticoid receptor and antagonist effect in living cell nucleus

The diffusion properties of hGRalpha in living cells have been analyzed. The hGRalpha translocalized from the cytosol to the nucleus after addition of Dex just as RU486; however, the Brownian motions of the proteins in nucleus were different. In order to analysis microenvironment of the nucleus of living cell, four different tandem EGFPs were constructed. Diffusion of tandem EGFP was dependent on the length of the protein as a rod-like molecule in solution. We found two kinds of mobility, fast diffusional mobility as a major component and much slower diffusional mobility as a major component in living cells nucleoplasm. On the bases of this analysis, we compared the diffusion property of hGRalpha in the nucleus at the presence of Dex or RU486 by distribution of diffusion constants. Our result may suggest that EGFP-hGRalpha is activated by RU486 and kept the stage of binding cofactor, GRE and final complex. Finally this means that dimerization is not required for association with GRE, although it is required for stabilization of a complex of EGFP-hGRalpha.

Reduction of glucocorticoid receptor ligand binding by the 11-beta hydroxysteroid dehydrogenase type 2 inhibitor, Thiram

Endogenous and synthetic glucocorticoids (GCs), such as cortisol and dexamethasone (Dex), modulate airway inflammation, regulate the production of surfactant by lung epithelial cells, and influence fetal lung maturation. The 11-beta hydroxysteroid dehydrogenase type 2 (HSD2) enzyme catalyzes the oxidation of bioactive cortisol and Dex to their 11-keto metabolites. Thiram (tetramethylthiuram disulfide) specifically inhibits HSD2 activity by oxidizing cysteine residues located in the cofactor binding domain of the enzyme. During studies performed to define a potential role for HSD2 in modulating GC action in human lung epithelial cells, we observed that exposure of intact human lung epithelial cells (NCI-H441) to 50 microM Thiram significantly attenuated the down-stream effects of Dex (100 nM) on the expression of two GC-sensitive genes, pulmonary surfactant proteins A and B. This observation appeared to be inconsistent with simple inhibition of HSD2 activity. Although Thiram inhibited HSD2 oxidase activity in a dose-dependent manner without affecting HSD2 protein expression, Thiram also reduced specific binding of [3H]-Dex to the glucocorticoid receptor (GR). Pre-treatment of cells with 1 mM dithiothreitol (DTT), a thiol-reducing agent, completely blocked the inhibitory effect of Thiram on ligand binding. These results are suggestive that Thiram may alter the ligand-binding domain of the GR by oxidizing critical thiol-containing amino acid residues. Taken collectively, these data demonstrate that attenuated down-stream GC signaling, via decreased binding of ligand to the GR, is a novel cellular effect of Thiram exposure in human lung epithelial cells.

Importin 13 regulates nuclear import of the glucocorticoid receptor in airway epithelial cells

Antiinflammatory effects of glucocorticoids are critical to treatment of airway inflammation in such common disorders as asthma. There is considerable variation in responsiveness to glucocorticoid, and prolonged exposure can result in glucocorticoid resistance. We cloned LGL2, a glucocorticoid-inducible gene in fetal rat lung. We described the characterization of lgl2 as a nuclear transport protein, classified as importin 13 (IPO13), and demonstrated developmental regulation of IPO13 nucleocytoplasmic shuttling. We now report on the identification of the glucocorticoid receptor (GR) as a cargo substrate for IPO13. Binding of GR and IPO13 was demonstrated by GR-GST pulldown and coimmunoprecipitation. To investigate the role of IPO13 in modulating GR signaling in the lung, we studied IPO13-regulated GR transport in airway epithelial cells. Small interfering RNAs that inhibited IPO13 synthesis prevented nuclear translocation of GR. Silencing of IPO13 also abrogated the ability of cortisol to inhibit synthesis of the inflammatory cytokine IL-8 after stimulation with TNF-alpha. Our findings support a role for IPO13 in promoting nuclear occupancy of GR in a way that strongly potentiates the antiinflammatory effects of glucocorticoids. We speculate that variation in cellular levels of IPO13 and intracellular IPO13 shuttling rates may contribute to glucocorticoid resistance.

Update on glucocorticoid action and resistance

Extensive development of inhaled and oral glucocorticoids has resulted in highly potent molecules that have been optimized to target activity to the lung and minimize systemic exposure. These have proved highly effective for most asthmatic subjects, but despite these developments, there are a number of subjects with asthma who fail to respond to even high doses of inhaled or even oral glucocorticoids. Advances in delineating the fundamental mechanisms of glucocorticoid pharmacology, especially the concepts of transactivation and transrepression and cofactor recruitment, have resulted in better understanding of the molecular mechanisms whereby glucocorticoids suppress inflammation. The existence of multiple mechanisms underlying glucocorticoid insensitivity raises the possibility that this might indeed reflect different diseases with a common phenotype, and studies examining the efficacy of potential new agents should be targeted toward subgroups of patients with severe corticosteroid-resistant asthma who clearly require effective new drugs and other approaches to improved asthma control.

Epigenetics and airways disease

Epigenetics is the term used to describe heritable changes in gene expression that are not coded in the DNA sequence itself but by post-translational modifications in DNA and histone proteins. These modifications include histone acetylation, methylation, ubiquitination, sumoylation and phosphorylation. Epigenetic regulation is not only critical for generating diversity of cell types during mammalian development, but it is also important for maintaining the stability and integrity of the expression profiles of different cell types. Until recently, the study of human disease has focused on genetic mechanisms rather than on non-coding events. However, it is becoming increasingly clear that disruption of epigenetic processes can lead to several major pathologies, including cancer, syndromes involving chromosomal instabilities, and mental retardation. Furthermore, the expression and activity of enzymes that regulate these epigenetic modifications have been reported to be abnormal in the airways of patients with respiratory disease. The development of new diagnostic tools might reveal other diseases that are caused by epigenetic alterations. These changes, despite being heritable and stably maintained, are also potentially reversible and there is scope for the development of 'epigenetic therapies' for disease.

Oxidative stress in asthma and COPD: antioxidants as a therapeutic strategy

Asthma and chronic obstructive pulmonary disease (COPD) are inflammatory lung diseases that are characterized by systemic and chronic localized inflammation and oxidative stress. Sources of oxidative stress arise from the increased burden of inhaled oxidants, as well as elevated amounts of reactive oxygen species (ROS) released from inflammatory cells. Increased levels of ROS, either directly or via the formation of lipid peroxidation products, may play a role in enhancing the inflammatory response in both asthma and COPD. Moreover, in COPD it is now recognized as the main pathogenic factor for driving disease progression and increasing severity. ROS and lipid peroxidation products can influence the inflammatory response at many levels through its impact on signal transduction mechanisms, activation of redox-sensitive transcriptions factors, and chromatin regulation resulting in pro-inflammatory gene expression. It is this impact of ROS on chromatin regulation by reducing the activity of the transcriptional co-repressor, histone deacetylase-2 (HDAC-2), that leads to the poor efficacy of corticosteroids in COPD, severe asthma, and smoking asthmatics. Thus, the presence of oxidative stress has important consequences for the pathogenesis, severity, and treatment of asthma and COPD. However, for ROS to have such an impact, it must first overcome a variety of antioxidant defenses. It is likely, therefore, that a combination of antioxidants may be effective in the treatment of asthma and COPD. Various approaches to enhance the lung antioxidant screen and clinical trials of antioxidant compounds are discussed.

Nuclear and mitochondrial compartmentation of oxidative stress and redox signaling

New methods to measure thiol oxidation show that redox compartmentation functions as a mechanism for specificity in redox signaling and oxidative stress. Redox Western analysis and redox-sensitive green fluorescent proteins provide means to quantify thiol/disulfide redox changes in specific subcellular compartments. Analyses using these techniques show that the relative redox states from most reducing to most oxidizing are mitochondria > nuclei > cytoplasm > endoplasmic reticulum > extracellular space. Mitochondrial thiols are an important target of oxidant-induced apoptosis and necrosis and are especially vulnerable to oxidation because of the relatively alkaline pH. Maintenance of a relatively reduced nuclear redox state is critical for transcription factor binding in transcriptional activation in response to oxidative stress. The new methods are applicable to a broad range of experimental systems and their use will provide improved understanding of the pharmacologic and toxicologic actions of drugs and toxicants.

Enforced expression of superoxide dismutase 2/manganese superoxide dismutase disrupts autocrine interleukin-6 stimulation in human multiple myeloma cells and enhances dexamethasone-induced apoptosis

Autocrine pathways of proliferative and anti-apoptotic growth factors represent a serious impediment to the treatment of many types of tumors. In particular, interleukin-6 (IL-6), a pleiotropic cytokine known to play a critical role in the survival and growth of multiple myeloma cells, participates in an autocrine stimulation loop that serves to inhibit the induction of apoptosis during chemotherapy. Manganese superoxide dismutase (MnSOD) is an important antioxidant enzyme encoded by the SOD2 gene that attenuates oxidative free radicals in the mitochondria by catalyzing the formation of hydrogen peroxide from superoxide radicals. Transcription factor activity and binding is influenced by the oxidative state of cells, and dysregulation of MnSOD levels can result in abnormal patterns of gene expression. In the human multiple myeloma cell line IM-9, an autocrine IL-6 loop exists, which enables the cell to resist the effects of dexamethasone, a common treatment for multiple myeloma. Here, we show that SOD2 expression is epigenetically silenced in IM-9 cells, and replacement of MnSOD reduces cell proliferation and partially restores susceptibility to dexamethasone. The restoration of MnSOD also serves to decrease the expression levels of IL-6 by reducing the ability of activator protein-1, an important mediator of IL-6 expression in multiple myeloma cells, to bind to its enhancer site. These results show the importance of free radical-mediated dysregulation of autocrine growth factor loops in tumor cells and their effect on cell growth and response to chemotherapy.

A redox signature score identifies diffuse large B-cell lymphoma patients with a poor prognosis

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease in which approximately 40% of the patients respond well to current chemotherapy, but the prognosis for the other 60% is poor. The Leukemia/Lymphoma Molecular Profiling Project (LLMPP) used microarray technology to define a molecular profile for each of 240 patients with DLBCL and develop a molecular outcome predictor score that accurately predicted patient survival. Data from our laboratory and others suggest that alterations in antioxidant defense enzyme levels and redox environment can be oncogenic and affect the response to glucocorticoid treatment, one of the components of combination chemotherapy regimens for lymphoma. The goal of the current study was to reanalyze the LLMPP microarray data to determine whether the levels of antioxidant defense enzymes and redox proteins were correlated with prognosis in DLBCL. We found that patients with DLBCL with the worst prognosis, according to the outcome predictor score, had decreased expression of catalase, glutathione peroxidase, manganese superoxide dismutase, and VDUP1, a protein that inhibits thioredoxin activity. The data suggest that the patients with the worst prognosis combine a decrease in antioxidant defense enzyme expression with an increase in thioredoxin system function (the redox signature score).

Functional impairment of telomerase in sublines derived from human lung adenocarcinoma exposed to mild oxidative stress

We investigated the effects of a sublethal concentration of H(2)O(2) on cancer cells by using sublines derived from human lung adenocarcinoma cell line A549 cells exposed to 200 microM H(2)O(2). These sublines (AST cells) showed an elongated morphology distinct from the rounded morphology of A549 cells. Notably, AST cells demonstrated telomere shortening despite displaying telomerase activity and expressing human telomerase reverse transcriptase (hTERT). This functional impairment of telomerase occurred due to perturbed subcellular localization of hTERT in AST cells. Endogenous as well as ectopically expressed hTERT was localized in the nuclei of A549 cells; however, in AST cells, the localization was mainly in the cytoplasm. Furthermore, these AST cells demonstrated decreased tumorigenic features both in vitro and in vivo. These results suggest that depletion of hTERT from nuclei not only endows cancer cells with a finite replicative life span accompanied by telomere shortening, but also decreases the tumorigenicity of cancer cells.

Mediators of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem that is now a leading cause of death. COPD is associated with a chronic inflammatory response, predominantly in small airways and lung parenchyma, which is characterized by increased numbers of macrophages, neutrophils, and T lymphocytes. The inflammatory mediators involved in COPD have not been clearly defined, in contrast to asthma, but it is now apparent that many lipid mediators, inflammatory peptides, reactive oxygen and nitrogen species, chemokines, cytokines, and growth factors are involved in orchestrating the complex inflammatory process that results in small airway fibrosis and alveolar destruction. Many proteases are also involved in the inflammatory process and are responsible for the destruction of elastin fibers in the lung parenchyma, which is the hallmark of emphysema. The identification of inflammatory mediators and understanding their interactions is important for the development of anti-inflammatory treatments for this important disease.

The distinct agonistic properties of the phenylpyrazolosteroid cortivazol reveal interdomain communication within the glucocorticoid receptor

Recent structural analyses of the nuclear receptors establish a paradigm of receptor activation, in which agonist binding induces the ligand binding domain (LBD)/activation function-2 helix to form a charge clamp for coactivator recruitment. However, these analyses have not sufficiently addressed the mechanisms for differential actions of various synthetic steroids in terms of fine tuning of multiple functions of whole receptor molecules. In the present study, we used the glucocorticoid receptor (GR)-specific agonist cortivazol (CVZ) to probe the plasticity and functional modularity of the GR. Structural docking analysis revealed that although CVZ is more bulky than other agonists, it can be accommodated in the ligand binding pocket of the GR by reorientation of several amino acid side chains but without major alterations in the active conformation of the LBD. In this induced fit model, the phenylpyrazole A-ring of CVZ establishes additional contacts with helices 3 and 5 of the LBD that may contribute to a more stable LBD configuration. Structural and functional analysis revealed that CVZ is able to compensate for the deleterious effects of a C-terminal deletion of the LBD in a manner that mimics the stabilizing influence of the F602S point mutation. CVZ-mediated productive recruitment of transcriptional intermediary factor 2 to the C-terminally deleted LBD requires the receptor's own DNA binding domain and is positively influenced by the N-terminal regions of GR or progesterone receptor. These results support a model where ligand-dependent conformational changes in the LBD play a role in GR-mediated gene regulation via modular interaction with the DBD and activation function-1.

Increased anti-oxidant enzyme activity and biological oxidation in placentae of pregnancies complicated by maternal asthma

Our previous work has demonstrated that alterations in placental function are associated with changes in fetal development in pregnancies complicated by asthma. The pathophysiology of asthma in adults and children and intrauterine growth restriction during pregnancy are associated with oxidative stress. Based on this information, we examined whether placental anti-oxidant pathways and markers of biological oxidation were altered in pregnancies complicated by asthma. Anti-oxidant enzyme activities of superoxide dismutase, glutathione peroxidase and thioredoxin reductase, thioredoxin concentrations, lipid and protein oxidation levels were measured in placentae of pregnancies complicated by asthma and compared to uncomplicated, non-asthmatic pregnancies. Placental tissue homogenates of pregnancies complicated by asthma demonstrated significantly increased levels of lipid peroxidation (25.7+/-1.8 micromol/mg protein versus 12.1+/-1.6 micromol/mg protein, P=0.008) and protein carbonyl concentrations (414.6+/-51.4 units/mg protein versus 222.3+/-32.6 units/mg protein, P=0.0032) when compared to non-asthmatic controls. The activities of the anti-oxidant proteins superoxide dismutase (2.17+/-0.09 units/mg protein versus 1.67+/-0.09 units/mg protein, P=0.014) and thioredoxin reductase (54.0+/-6.9 units/mg protein versus 28.7+/-6.0 units/mg protein, P=0.009) were significantly increased in the presence of maternal asthma. Placental thioredoxin levels (102.9+/-5.3 ng/mg protein versus 92.9+/-8.6 ng/mg protein, P=0.37) and glutathione peroxidase activity (27.3+/-2.2 mmol/min/mg protein versus 28.3+/-2.2 mmol/min/mg, P=0.83) were not significantly different in pregnancies complicated by asthma and non-asthmatic pregnancies. There was no effect of fetal sex, asthma severity or treatment for asthma on these pathways. Maternal asthma during pregnancy is associated with increased placental enzymatic anti-oxidant capacity and also increased protein oxidation suggesting there is a compensatory increase in anti-oxidant activity in response to increased oxidative stress.

Redox regulation of histone deacetylases and glucocorticoid-mediated inhibition of the inflammatory response

Gene expression, at least in part, is regulated by changes in histone acetylation status induced by activation of the proinflammatory redox-sensitive transcription factors activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB). Hyperacetylated histone is associated with open actively transcribed DNA and enhanced inflammatory gene expression. In contrast, hypoacetylated histone is linked to a closed repressed DNA state and a lack of gene expression. The degree of inflammatory gene expression is a result of a balance between histone acetylation and histone deacetylation. One of the major mechanisms of glucocorticoid function is to recruit histone deacetylase enzymes to the site of active gene expression, thus reducing inflammation. Oxidative stress can enhance inflammatory gene expression by further stimulating AP-1- and NF-kappaB-mediated gene expression and elevating histone acetylation. In addition, oxidants can reduce glucocorticoid function by attenuating histone deacetylase activity and expression. Thus, oxidant stress, acting through changes in chromatin structure, can enhance inflammation and induce a state of relative glucocorticoid insensitivity. This may account for the lack of glucocorticoid sensitivity in patients with chronic obstructive pulmonary disease. Antioxidants should reduce the inflammation and restore glucocorticoid sensitivity in these subjects.

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits Glucocorticoid Binding and Signaling in Macrophages through a Peroxisome Proliferator-Activated Receptor γ-Independent Process

15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is involved in the control of inflammatory reaction. We tested the hypothesis that 15d-PGJ(2) would exert this control in part by modulating the sensitivity of inflammatory cells to glucocorticoids. Human U937cells and mouse RAW 264.7 cells were exposed to 15d-PGJ(2), and binding experiments were performed with [(3)H]dexamethasone as a glucocorticoid receptor (GR) ligand. 15d-PGJ(2) caused a transient and concentration-dependent decrease in [(3)H]dexamethasone-specific binding to either cells through a decrease in the number of GR per cell without significant modification of the K(d) value. These changes were related to functional alteration of the GR rather than to a decrease in GR protein. They did not require the engagement of peroxisome proliferator-activated receptor gamma (PPARgamma), because the response to 15d-PGJ(2) was neither mimicked by the PPARgamma agonist ciglitazone nor prevented by the PPARgamma antagonist bisphenol A diglycidyl ether. 15d-PGJ(2) altered GR possibly through the interaction of its cyclopentenone ring with GR cysteine residues because the cyclopentenone ring per se could mimic the effect of 15d-PGJ(2), and modification of GR cysteine residues with methyl methanethiosulfonate suppressed the response to 15d-PGJ(2). Finally, 15d-PGJ(2)-induced decreases in glucocorticoid binding to GR resulted in parallel decreases in the ability of GR to activate the transcription of a glucocorticoid-inducible reporter gene and to reduce the expression of monocyte chemoattractant protein-1. Together these data suggest that 15d-PGJ(2) limits glucocorticoid binding and signaling in monocytes/macrophages through a PPARgamma-independent and cyclopentenone-dependent mechanism. It provides a way in which 15d-PGJ(2) would exert proinflammatory activities in addition to its known anti-inflammatory activities.

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.

Pharmacology of airway inflammation in asthma and COPD

The current asthma therapies are not cures and symptoms return soon after treatment is stopped even after long term treatment. Although inhaled glucocorticoids are highly effective in controlling airway inflammation in asthma, they are ineffective in the small group of patients with glucocorticoid-dependent and -resistant asthma. With very few exceptions, COPD is caused by tobacco smoking, and smoking cessation is the only truly effective treatment of COPD available. Current pharmacological treatment of COPD is unsatisfactory, as it does not significantly influence the severity of the disease or its natural course. Glucocorticoids are scarcely effective in COPD patients without concomitant asthma. Bronchodilators improves symptoms and quality of life, in COPD patients, but, with the exception of tiotropium, they do not significantly influence the natural course of the disease. Theophylline is the only drug which has been demonstrated to have a significant effect on airway inflammation in patients with COPD. Here we review the pharmacology of currently used antiinflammatory therapies for asthma and COPD and their proposed mechanisms of action. Recent understanding of disease mechanisms in severe steroid-dependent and -resistant asthma and in COPD, has lead to the development of novel compounds, which are in various stages of clinical development. We review the current status of some of these new potential drugs.

Role of the glucocorticoid receptor for regulation of hypoxia-dependent gene expression

Glucocorticoids are secreted from the adrenal glands and act as a peripheral effector of the hypothalamic-pituitary-adrenal axis, playing an essential role in stress response and homeostatic regulation. In target cells, however, it remains unknown how glucocorticoids fine-tune the cellular pathways mediating tissue and systemic adaptation. Recently, considerable evidence indicates that adaptation to hypoxic environments is influenced by glucocorticoids and there is cross-talk between hypoxia-dependent signals and glucocorticoid-mediated regulation of gene expression. We therefore investigated the interaction between these important stress-responsive pathways, focusing on the glucocorticoid receptor (GR) and hypoxia-inducible transcription factor HIF-1. Here we show that, under hypoxic conditions, HIF-1-dependent gene expression is further up-regulated by glucocorticoids via the GR. This up-regulation cannot be substituted by the other steroid receptors and is suggested to result from the interaction between the GR and the transactivation domain of HIF-1 alpha. Moreover, our results also indicate that the ligand binding domain of the GR is essential for this interaction, and the critical requirement for GR agonists suggests the importance of the ligand-mediated conformational change of the GR. Because these proteins are shown to colocalize in the distinct compartments of the nucleus, we suggest that these stress-responsive transcription factors have intimate communication in close proximity to each other, thereby enabling the fine-tuning of cellular responses for adaptation.

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure

Aldosterone classically promotes unidirectional transepithelial sodium transport, thereby regulating blood volume and blood pressure. Recently, both clinical and experimental studies have suggested additional, direct roles for aldosterone in the cardiovascular system. To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, transgenic mice overexpressing 11beta-hydroxysteroid dehydrogenase type 2 in cardiomyocytes were generated using the mouse alpha-myosin heavy chain promoter. This enzyme converts glucocorticoids to receptor-inactive metabolites, allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. These studies confirm the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and reveal a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiological conditions. In addition, these data support the hypothesis that aldosterone blockade may provide additional therapeutic benefit in the treatment of heart failure.

Clinical research in chronic obstructive pulmonary disease: needs and opportunities

Chronic obstructive pulmonary disease (COPD) is a common condition, and one difficult to manage. Available treatments, other than smoking cessation, are only minimally effective, and the knowledge basis for clinical decision making is limited. To identify areas in which further clinical research may lead to significant improvements in the care of patients with COPD, the National Heart, Lung, and Blood Institute convened a Working Group, entitled "Clinical Research in COPD: Needs and Opportunities," on March 21-22, 2002. This group of experts identified important questions in the field and made the following recommendations: (1) establish a multicenter Clinical Research Network to perform multiple, short-term clinical trials of treatments in patients with moderate-to-severe COPD; (2) create a system for the standardized collection, processing, and distribution of lung tissue specimens and associated clinical and laboratory data; (3) develop standards for the classification and staging of COPD; (4) characterize the development and progression of COPD using measures and biomarkers that relate to current concepts of pathogenesis; and (5) evaluate indications for long-term oxygen therapy for patients with COPD.