Anti-inflammatory functions of glucocorticoid-induced genes

The five Rs of glucocorticoid action during inflammation: ready, reinforce, repress, resolve, and restore

Glucocorticoids are essential for maintaining homeostasis and regulate a wide variety of physiological processes. Therapeutically, synthetic glucocorticoids are widely prescribed for the treatment of inflammation, autoimmune disorders, and malignancies of lymphoid origin. In this review we examine emerging evidence highlighting both proinflammatory and anti-inflammatory actions of glucocorticoids on both the innate and adaptive immune systems. We incorporate these findings into the more traditional anti-inflammatory role attributed to glucocorticoids, and propose how the two seemingly disparate processes seamlessly work together to resolve cellular responses to inflammatory stimuli. These ideas provide a framework by which glucocorticoids ready and reinforce the innate immune system, and repress the adaptive immune system, to help to resolve inflammation and restore homeostasis.

Glucocorticoid repression of inflammatory gene expression shows differential responsiveness by transactivation- and transrepression-dependent mechanisms

Binding of glucocorticoid to the glucocorticoid receptor (GR/NR3C1) may repress inflammatory gene transcription via direct, protein synthesis-independent processes (transrepression), or by activating transcription (transactivation) of multiple anti-inflammatory/repressive factors. Using human pulmonary A549 cells, we showed that 34 out of 39 IL-1β-inducible mRNAs were repressed to varying degrees by the synthetic glucocorticoid, dexamethasone. Whilst these repressive effects were GR-dependent, they did not correlate with either the magnitude of IL-1β-inducibility or the NF-κB-dependence of the inflammatory genes. This suggests that induction by IL-1β and repression by dexamethasone are independent events. Roles for transactivation were investigated using the protein synthesis inhibitor, cycloheximide. However, cycloheximide reduced the IL-1β-dependent expression of 13 mRNAs, which, along with the 5 not showing repression by dexamethasone, were not analysed further. Of the remaining 21 inflammatory mRNAs, cycloheximide significantly attenuated the dexamethasone-dependent repression of 11 mRNAs that also showed a marked time-dependence to their repression. Such effects are consistent with repression occurring via the de novo synthesis of a new product, or products, which subsequently cause repression (i.e., repression via a transactivation mechanism). Conversely, 10 mRNAs showed completely cycloheximide-independent, and time-independent, repression by dexamethasone. This is consistent with direct GR transrepression. Importantly, the inflammatory mRNAs showing attenuated repression by dexamethasone in the presence of cycloheximide also showed a significantly greater extent of repression and a higher potency to dexamethasone compared to those mRNAs showing cycloheximide-independent repression. This suggests that the repression of inflammatory mRNAs by GR transactivation-dependent mechanisms accounts for the greatest levels of repression and the most potent repression by dexamethasone. In conclusion, our data indicate roles for both transrepression and transactivation in the glucocorticoid-dependent repression of inflammatory gene expression. However, transactivation appears to account for the more potent and efficacious mechanism of repression by glucocorticoids on these IL-1β-induced genes.

It takes two to tango: dimerisation of glucocorticoid receptor and its anti-inflammatory functions

For a number of years, there has been a widespread view that the adverse side-effects of prolonged glucocorticoid (GC) treatment are a result of glucocorticoid receptor (GR)-mediated gene activation, whilst the beneficial anti-inflammatory effects result from GR-mediated 'transrepression'. Since the introduction of the dimerisation-deficient GR mutant, GR(dim), was apparently unable to activate gene transcription, yet still able to repress pro-inflammatory gene transcription, the search for novel GR modulators has centred on the separation of gene activation from repression by prevention of GR dimerisation. However, recent work has questioned the conclusions drawn from these early GR(dim) studies, with evidence that GR(dim) mutants not only activate gene transcription, but that, in direct contradiction to the initial GR(dim) work, are also capable of forming dimers. This review of the current literature highlights the versatility of the GR in forming homodimer interactions, as well as the ability to bind to alternate nuclear receptors, and investigates the potential implications such varying GR dimer conformations may have for the design of GR ligands with a safer side effect profile.

Dexamethasone Induces FcγRIIb Expression in RBL-2H3 Cells

Mast cells are involved in allergic responses, protection against pathogens and autoimmune diseases. Dexamethasone (Dex) and other glucocorticoids suppress FcεRI-mediated release of inflammatory mediators from mast cells. The inhibition mechanisms were mainly investigated on the downstream signaling of Fc receptor activations. Here, we addressed the effects of Dex on Fc receptor expressions in rat mast cell line RBL-2H3. We measured mRNA levels of Fc receptors by real-time PCR. As expected, Dex decreased the mRNA levels of activating Fc receptor for IgE (FcεR) I and increased the mRNA levels of the inhibitory Fc receptor for IgG FcγRIIb. Interestingly, Dex stimulated transcriptions of other activating receptors such as Fc receptors for IgG (FcγR) I and FcγRIII. To investigate the mechanisms underlying transcriptional regulation, we employed a transcription inhibitor actinomycin D and a translation inhibitor cycloheximide. The inhibition of protein synthesis without Dex treatment enhanced FcγRI and FcγRIII mRNA levels potently, while FcεRI and FcγRIIb were minimally affected. Next, we examined expressions of the Fc receptors on cell surfaces by the flow cytometric method. Only FcγRIIb protein expression was significantly enhanced by Dex treatment, while FcγRI, FcγRIII and FcεRI expression levels were marginally changed. Our data showed, for the first time, that Dex regulates Fc receptor expressions resulting in augmentation of the inhibitory receptor FcγRIIb.

Corticosteroid resistance in sepsis is influenced by microRNA-124--induced downregulation of glucocorticoid receptor-α

OBJECTIVE

Acquired glucocorticoid resistance frequently complicates the therapy of sepsis. It leads to an exaggerated proinflammatory response and has been related to altered expression profiles of glucocorticoid receptor isoforms glucocorticoid receptor-α (mediating anti-inflammatory effects) and glucocorticoid receptor-β (acting as a dominant negative inhibitor). We investigated the impact of glucocorticoid receptor isoforms on glucocorticoid effects in human T-cells. We hypothesized that 1) changes of the ratio of glucocorticoid receptor isoforms impact glucocorticoid resistance and 2) glucocorticoid receptor-α expression is controlled by microRNA-mediated gene silencing.

DESIGN

Laboratory-based study.

SETTING

University research laboratory.

SUBJECTS AND PATIENTS

Healthy volunteers, sepsis patients.

METHODS

First, T-cells from healthy volunteers (native and CD3/CD28-stimulated cells with or without addition of hydrocortisone) were analyzed for the expression of glucocorticoid receptor-isoforms by quantitative polymerase chain reaction. Additionally, effects of gene silencing of glucocorticoid receptor-β by siRNA transfection were determined. Secondly, microRNA-mediated silencing was evaluated by cloning of a glucocorticoid receptor-α-specific 3'-untranslated-region reporter construct and subsequent transfection experiments in cell cultures. Effects of miRNA transfection on glucocorticoid receptor-α expression were analyzed in Jurkat T-cells and in T-cells from healthy volunteers (quantitative polymerase chain reaction and Western blotting). Finally, expression of glucocorticoid receptor-α, glucocorticoid receptor-β, and miR-124 was tested in T-cells of sepsis patients (n=24).

MEASUREMENTS AND MAIN RESULTS

Stimulation of T-cells induced a significant upregulation of glucocorticoid receptor-α (not glucocorticoid receptor-β) thereby possibly rendering T-cells more sensitive to glucocorticoids; this T-cell response was hindered by hydrocortisone. Silencing of glucocorticoid receptor-β doubled the inhibitory effects of glucocorticoids on interleukin-2 production. MicroRNA-124 was proved to specifically downregulate glucocorticoid receptor-α. Furthermore, a glucocorticoid-induced three-fold upregulation of microRNA-124 was found. T-cells of sepsis patients exhibited slightly decreased glucocorticoid receptor-α and slightly increased miR-124 expression levels, whereas glucocorticoid receptor-β expression was two-fold upregulated (p<.01) and exhibited a remarkable interindividual variability.

CONCLUSIONS

Glucocorticoid treatment induces expression of miR-124, which downregulates glucocorticoid receptor-α thereby limiting anti-inflammatory effects of glucocorticoids. Steroid treatment might aggravate glucocorticoid resistance in patients with high glucocorticoid receptor-β levels.

Org 214007-0: a novel non-steroidal selective glucocorticoid receptor modulator with full anti-inflammatory properties and improved therapeutic index

Glucocorticoids (GCs) such as prednisolone are potent immunosuppressive drugs but suffer from severe adverse effects, including the induction of insulin resistance. Therefore, development of so-called Selective Glucocorticoid Receptor Modulators (SGRM) is highly desirable. Here we describe a non-steroidal Glucocorticoid Receptor (GR)-selective compound (Org 214007-0) with a binding affinity to GR similar to that of prednisolone. Structural modelling of the GR-Org 214007-0 binding site shows disturbance of the loop between helix 11 and helix 12 of GR, confirmed by partial recruitment of the TIF2-3 peptide. Using various cell lines and primary human cells, we show here that Org 214007-0 acts as a partial GC agonist, since it repressed inflammatory genes and was less effective in induction of metabolic genes. More importantly, in vivo studies in mice indicated that Org 214007-0 retained full efficacy in acute inflammation models as well as in a chronic collagen-induced arthritis (CIA) model. Gene expression profiling of muscle tissue derived from arthritic mice showed a partial activity of Org 214007-0 at an equi-efficacious dosage of prednisolone, with an increased ratio in repression versus induction of genes. Finally, in mice Org 214007-0 did not induce elevated fasting glucose nor the shift in glucose/glycogen balance in the liver seen with an equi-efficacious dose of prednisolone. All together, our data demonstrate that Org 214007-0 is a novel SGRMs with an improved therapeutic index compared to prednisolone. This class of SGRMs can contribute to effective anti-inflammatory therapy with a lower risk for metabolic side effects.

Glucocorticoid sensitivity in Behçet's disease

OBJECTIVE

Glucocorticoid (GC) sensitivity is highly variable among individuals and has been associated with susceptibility to develop (auto-)inflammatory disorders. The purpose of the study was to assess GC sensitivity in Behçet's disease (BD) by studying the distribution of four GC receptor (GR) gene polymorphisms and by measuring in vitro cellular GC sensitivity.

METHODS

Healthy controls and patients with BD in three independent cohorts were genotyped for four functional GR gene polymorphisms. To gain insight into functional differences in in vitro GC sensitivity, 19 patients with BD were studied using two bioassays and a whole-cell dexamethasone-binding assay. Finally, mRNA expression levels of GR splice variants (GR-α and GR-β) were measured.

RESULTS

Healthy controls and BD patients in the three separate cohorts had similar distributions of the four GR polymorphisms. The Bcll and 9β minor alleles frequency differed significantly between Caucasians and Mideast and Turkish individuals. At the functional level, a decreased in vitro cellular GC sensitivity was observed. GR number in peripheral blood mononuclear cells was higher in BD compared with controls. The ratio of GR-α/GR-β mRNA expression levels was significantly lower in BD.

CONCLUSIONS

Polymorphisms in the GR gene are not associated with susceptibility to BD. However, in vitro cellular GC sensitivity is decreased in BD, possibly mediated by a relative higher expression of the dominant negative GR-β splice variant. This decreased in vitro GC sensitivity might play an as yet unidentified role in the pathophysiology of BD.

The p38 MAPK Pathway in Rheumatoid Arthritis: A Sideways Look

The p38 mitogen-activated protein kinase (MAPK) signaling pathway has been strongly implicated in many of the processes that underlie the pathology of rheumatoid arthritis (RA). For many years it has been considered a promising target for development of new anti-inflammatory drugs with which to treat RA and other chronic immune-mediated inflammatory diseases. However, several recent clinical trials have concluded in a disappointing manner. Why is this so, if p38 MAPK clearly contributes to the excessive production of inflammatory mediators, the destruction of bone and cartilage? We argue that, to explain the apparent failure of p38 inhibitors in the rheumatology clinic, we need to understand better the complexities of the p38 pathway and its many levels of communication with other cellular signaling pathways. In this review we look at the p38 MAPK pathway from a slightly different perspective, emphasising its role in post-transcriptional rather than transcriptional control of gene expression, and its contribution to the off-phase rather than the on-phase of the inflammatory response.

Epidermal inactivation of the glucocorticoid receptor triggers skin barrier defects and cutaneous inflammation

The glucocorticoid (GC) receptor (GR) mediates the effects of physiological and pharmacological GC ligands and has a major role in cutaneous pathophysiology. To dissect the epithelial versus mesenchymal contribution of GR in developing and adult skin, we generated mice with keratinocyte-restricted GR inactivation (GR epidermal knockout or GR(EKO) mice). Developing and early postnatal GR(EKO) mice exhibited impaired epidermal barrier formation, abnormal keratinocyte differentiation, hyperproliferation, and stratum corneum (SC) fragility. At birth, GR(EKO) epidermis showed altered levels of epidermal differentiation complex genes, proteases and protease inhibitors which participate in SC maintenance, and innate immunity genes. Many upregulated genes, including S100a8/a9 and Tslp, also have increased expression in inflammatory skin diseases. Infiltration of macrophages and degranulating mast cells were observed in newborn GR(EKO) skin, hallmarks of atopic dermatitis. In addition to increased extracellular signal-regulated kinase activation, GR(EKO) newborn and adult epidermis had increased levels of phosphorylated signal transducer and activator of transcription 3, a feature of psoriasis. Although adult GR(EKO) epidermis had a mild phenotype of increased proliferation, perturbation of skin homeostasis with detergent or phorbol ester triggered an exaggerated proliferative and hyperkeratotic response relative to wild type. Together, our results show that epidermal loss of GR provokes skin barrier defects and cutaneous inflammation.

Mechanisms of the anti-inflammatory effects of glucocorticoids: genomic and nongenomic interference with MAPK signaling pathways

Glucocorticoids (GCs) are steroid hormones produced by the adrenal gland and regulated by the hypothalamus-pituitary-adrenal axis. GCs mediate effects that mostly result in transcriptional regulation of glucocorticoid receptor target genes. Mitogen-activated protein kinases (MAPKs) comprise a family of signaling proteins that convert extracellular stimuli into the activation of intracellular transduction pathways via phosphorylation of a cascade of substrates. They modulate a variety of physiological cell processes, such as proliferation, apoptosis, and development. However, when MAPKs are improperly activated by proinflammatory and/or extracellular stress stimuli, they contribute to the regulation of proinflammatory transcription factors, thus perpetuating activation of the inflammatory cascade. One of the mechanisms by which GCs exert their anti-inflammatory effects is negative interference with MAPK signaling pathways. Several functional interactions between GCs and MAPK signaling have been discovered and studied. Some of these interactions involve the GC-mediated up-regulation of proteins that in turn interfere with the activation of MAPK, such as glucocorticoid-induced-leucine zipper, MAPK phosphatase-1, and annexin-1. Other mechanisms include activated GR directly interacting with components of the MAPK pathway and negatively regulating their activation. The multiple interactions between GCs and MAPK pathways and their potential biological relevance in mediating the anti-inflammatory effects of GCs are reviewed.

In vitro glucocorticoid sensitivity is associated with clinical glucocorticoid therapy outcome in rheumatoid arthritis

Introduction

Genetic and disease-related factors give rise to a wide spectrum of glucocorticoid (GC) sensitivity in rheumatoid arthritis (RA). In clinical practice, GC treatment is not adapted to these differences in GC sensitivity. In vitro assessment of GC sensitivity before the start of therapy could allow more individualized GC therapy. The aim of the study was to investigate the association between in vitro and in vivo GC sensitivity in RA.

Methods

Thirty-eight early and 37 established RA patients were prospectively studied. In vitro GC sensitivity was assessed with dexamethasone-induced effects on interleukin-2 (IL-2) and glucocorticoid-induced leucine zipper (GILZ) messenger RNA expression in peripheral blood mononuclear cells (PBMCs). A whole-cell dexamethasone-binding assay was used to measure number and affinity (1/K_D) of glucocorticoid receptors (GRs).

In vivo GC sensitivity was determined by measuring the disease activity score (DAS) and health assessment questionnaire disability index (HAQ-DI) score before and after 2 weeks of standardized GC treatment.

Results

GR number was positively correlated with improvement in DAS. IL-2-EC₅₀ and GILZ-EC₅₀ values both had weak near-significant correlations with clinical improvement in DAS in intramuscularly treated patients only. HAQ responders had lower GILZ-EC₅₀ values and higher GR number and K_D.

Conclusions

Baseline cellular in vitro glucocorticoid sensitivity is modestly associated with in vivo improvement in DAS and HAQ-DI score after GC bridging therapy in RA. Further studies are needed to evaluate whether in vitro GC sensitivity may support the development of tailor-made GC therapy in RA.

Corticosteroid-induced gene expression in allergen-challenged asthmatic subjects taking inhaled budesonide

BACKGROUND AND PURPOSE

Inhaled corticosteroids (ICS) are the cornerstone of asthma pharmacotherapy and, acting via the glucocorticoid receptor (GR), reduce inflammatory gene expression. While this is often attributed to a direct inhibitory effect of the GR on inflammatory gene transcription, corticosteroids also induce the expression of anti-inflammatory genes in vitro. As there are no data to support this effect in asthmatic subjects taking ICS, we have assessed whether ICS induce anti-inflammatory gene expression in subjects with atopic asthma.

EXPERIMENTAL APPROACH

Bronchial biopsies from allergen-challenged atopic asthmatic subjects taking inhaled budesonide or placebo were subjected to gene expression analysis using real-time reverse transcriptase-PCR for the corticosteroid-inducible genes (official gene symbols with aliases in parentheses): TSC22D3 [glucocorticoid-induced leucine zipper (GILZ)], dual-specificity phosphatase-1 (MAPK phosphatase-1), both anti-inflammatory effectors, and FKBP5 [FK506-binding protein 51 (FKBP51)], a regulator of GR function. Cultured pulmonary epithelial and smooth muscle cells were also treated with corticosteroids before gene expression analysis.

KEY RESULTS

Compared with placebo, GILZ and FKBP51 mRNA expression was significantly elevated in budesonide-treated subjects. Budesonide also increased GILZ expression in human epithelial and smooth muscle cells in culture. Immunostaining of bronchial biopsies revealed GILZ expression in the airways epithelium and smooth muscle of asthmatic subjects.

CONCLUSIONS AND IMPLICATIONS

Expression of the corticosteroid-induced genes, GILZ and FKBP51, is up-regulated in the airways of allergen-challenged asthmatic subjects taking inhaled budesonide. Consequently, the biological effects of corticosteroid-induced genes should be considered when assessing the actions of ICS. Treatment modalities that increase or decrease GR-dependent transcription may correspondingly affect corticosteroid efficacy.

Glucocorticoid regulation of inflammation and its functional correlates: from HPA axis to glucocorticoid receptor dysfunction

Enhanced susceptibility to inflammatory and autoimmune disease can be related to impairments in HPA axis activity and associated hypocortisolism, or to glucocorticoid resistance resulting from impairments in local factors affecting glucocorticoid availability and function, including the glucocorticoid receptor (GR). The enhanced inflammation and hypercortisolism that typically characterize stress-related illnesses, such as depression, metabolic syndrome, cardiovascular disease, or osteoporosis, may also be related to increased glucocorticoid resistance. This review focuses on impaired GR function as a molecular mechanism of glucocorticoid resistance. Both genetic and environmental factors can contribute to impaired GR function. The evidence that glucocorticoid resistance can be environmentally induced has important implications for management of stress-related inflammatory illnesses and underscores the importance of prevention and management of chronic stress. The simultaneous assessment of neural, endocrine, and immune biomarkers through various noninvasive methods will also be discussed.

Glucocorticoid receptor dimerization induces MKP1 to protect against TNF-induced inflammation

Glucocorticoids acting through the glucocorticoid receptor (GR) inhibit TNF-induced lethal inflammation. Here, we demonstrate that GR dimerization plays a role in reducing TNF sensitivity. In mutant mice unable to dimerize GR, we found that TNF failed to induce MAPK phosphatase 1 (MKP1). We assessed TNF sensitivity in Mkp1(-/-) mice and found increased inflammatory gene induction in livers, increased circulating cytokines, cell death in intestinal epithelium, severe intestinal inflammation, hypothermia, and death. Mkp1(-/-) mice had increased levels of phosphorylated JNK, which promotes apoptosis, in liver tissue. We further examined JNK-deficient mice for their response to TNF. Although Jnk1(-/-) mice showed no change in sensitivity to TNF, Jnk2(-/-) mice were significantly protected against TNF, identifying JNK2 as an essential player in inflammation induced by TNF. Furthermore, we found that loss of Jnk2 partially rescued the increased sensitivity of Mkp1(-/-) and mutant GR mice to TNF. Our data show that GR dimerization inhibits JNK2 through MKP1 and protects from TNF-induced apoptosis and lethal inflammation.

Anti-inflammatory effects of selective glucocorticoid receptor modulators are partially dependent on up-regulation of dual specificity phosphatase 1

BACKGROUND AND PURPOSE

It is thought that the anti-inflammatory effects of glucocorticoids (GCs) are largely due to GC receptor (GR)-mediated transrepression of NF-κB and other transcription factors, whereas side effects are caused by activation of gene expression (transactivation). Selective GR modulators (SGRMs) that preferentially promote transrepression should retain anti-inflammatory properties whilst causing fewer side effects. Contradicting this model, we found that anti-inflammatory effects of the classical GC dexamethasone were partly dependent on transactivation of the dual specificity phosphatase 1 (DUSP1) gene. We wished to determine whether anti-inflammatory effects of SGRMs are also mediated by DUSP1.

EXPERIMENTAL APPROACH

Dissociated properties of two SGRMs were confirmed using GR- and NF-κB-dependent reporters, and capacity to activate GC-responsive elements of the DUSP1 gene was tested. Effects of SGRMs on the expression of DUSP1 and pro-inflammatory gene products were assessed in various cell lines and in primary murine Dusp1(+/+) and Dusp1(-/-) macrophages.

KEY RESULTS

The SGRMs were able to up-regulate DUSP1 in several cell types, and this response correlated with the ability of the compounds to suppress COX-2 expression. Several anti-inflammatory effects of SGRMs were ablated or significantly impaired in Dusp1(-/-) macrophages.

CONCLUSIONS AND IMPLICATIONS

Like dexamethasone, SGRMs appear to exert anti-inflammatory effects partly via the up-regulation of DUSP1. This finding has implications for how potentially therapeutic novel GR ligands are identified and assessed.

The impact of endogenous annexin A1 on glucocorticoid control of inflammatory arthritis

Objectives

To establish the role and effect of glucocorticoids and the endogenous annexin A1 (AnxA1) pathway in inflammatory arthritis.

Methods

Ankle joint mRNA and protein expression of AnxA1 and its receptors were analysed in naive and arthritic mice by real-time PCR and immunohistochemistry. Inflammatory arthritis was induced with the K/BxN arthritogenic serum in AnxA1^+/+ and AnxA1^−/− mice; in some experiments, animals were treated with dexamethasone (Dex) or with human recombinant AnxA1 or a protease-resistant mutant (termed SuperAnxA1). Readouts were arthritic score, disease incidence, paw oedema and histopathology, together with pro-inflammatory gene expression.

Results

All elements of the AnxA1 pathway could be detected in naive joints, with augmentation during ongoing disease, due to the infiltration of immune cells. No difference in arthritis intensity of profile could be observed between AnxA1^+/+ and AnxA1^−/− mice. Treatment of mice with Dex (10 µg intraperitoneally daily from day 2) afforded potent antiarthritic effects highly attenuated in the knockouts: macroscopic changes were mirrored by histopathological findings and pro-inflammatory gene (eg, Nos2) expression. Presence of proteinase 3 mRNA in the arthritic joints led the authors to test AnxA1 and the mutant SuperAnxA1 (1 µg intraperitoneally daily in both cases from day 2), with the latter one being able to accelerate the resolving phase of the disease.

Conclusion

AnxA1 is an endogenous determinant for the therapeutic efficacy of Dex in inflammatory arthritis. Such an effect can be partially mimicked by application of SuperAnxA1 which may represent the starting point for novel antiarthritic therapeutic strategies.

Oxygenated compounds from the bioconversion of isostevic acid and their inhibition of TNF-α and COX-2 expressions in LPS-stimulated RAW 264.7 cells

Fourteen oxygenated compounds were isolated from the preparative-scale biotransformation of isostevic acid (ent-beyeran-19-oic acid). Incubation of it with Aspergillus niger BCRC 32720 produced eight metabolites, four with Bacillus megaterium ATCC 14581, and another four with Mortierella isabellina ATCC 38063. In addition to their structural elucidation by NMR spectroscopy and HRMS, structures of four of these were further confirmed by X-ray diffraction studies. Real-time reverse transcription PCR analysis found that 15 of these compounds displayed significant in vitro anti-inflammatory activity in lipopolysaccharide-stimulated RAW 264.7 macrophages by reducing the levels of both TNF-α and COX-2 mRNA relative to control cells stimulated by LPS alone. The activity of one metabolite was similar to that of dexamethasone in inhibiting the expression of TNF-α mRNA, while all test compounds except two of them were more potent than dexamethasone in inhibiting the expression of the COX-2 mRNA.

Keratinocyte-targeted overexpression of the glucocorticoid receptor delays cutaneous wound healing

Delayed wound healing is one of the most common secondary adverse effects associated to the therapeutic use of glucocorticoid (GC) analogs, which act through the ligand-dependent transcription factor GC-receptor (GR). GR function is exerted through DNA-binding-dependent and –independent mechanisms, classically referred to as transactivation (TA) and transrepression (TR). Currently both TA and TR are thought to contribute to the therapeutical effects mediated by GR; however their relative contribution to unwanted side effects such as delayed wound healing is unknown. We evaluated skin wound healing in transgenic mice with keratinocyte-restricted expression of either wild type GR or a mutant GR that is TA-defective but efficient in TR (K5-GR and K5-GR-TR mice, respectively). Our data show that at days (d) 4 and 8 following wounding, healing in K5-GR mice was delayed relative to WT, with reduced recruitment of granulocytes and macrophages and diminished TNF-α and IL-1β expression. TGF-β1 and Kgf expression was repressed in K5-GR skin whereas TGF-β3 was up-regulated. The re-epithelialization rate was reduced in K5-GR relative to WT, as was formation of granulation tissue. In contrast, K5-GR-TR mice showed delays in healing at d4 but re-established the skin breach at d8 concomitant with decreased repression of pro-inflammatory cytokines and growth factors relative to K5-GR mice. Keratinocytes from both transgenic mice closed in vitro wounds slower relative to WT, consistent with the in vivo defects in cell migration. Overall, the delay in the early stages of wound healing in both transgenic models is similar to that elicited by systemic treatment with dexamethasone. Wound responses in the transgenic keratinocytes correlated with reduced ERK activity both in vivo and in vitro. We conclude that the TR function of GR is sufficient for negatively regulating early stages of wound closure, while TA by GR is required for delaying later stages of healing.

Maps and legends: the quest for dissociated ligands of the glucocorticoid receptor

Glucocorticoids are steroid hormones that have pleiotropic effects on development, metabolism, cognitive function and other aspects of physiology. Since the demonstration more than sixty years ago of their capacity to suppress inflammation, synthetic glucocorticoids have been extremely widely used in the treatment of inflammatory diseases. However, their clinical use is limited by numerous, unpredictable and potentially serious side effects. Glucocorticoids regulate gene expression both positively and negatively. Both of these effects are mediated by the glucocorticoid receptor, a ligand-dependent transcription factor. It has become widely accepted that anti-inflammatory effects of glucocorticoids are mostly due to inhibition of transcription, whereas the activation of transcription by the glucocorticoid receptor accounts for the majority of side effects. This dogma (which we refer to as the "transrepression hypothesis") predicts the possibility of uncoupling therapeutic, anti-inflammatory effects from side effects by identifying novel, selective ligands of the glucocorticoid receptor, which preferentially mediate inhibition rather than activation of transcription. It is argued that such "dissociated" glucocorticoid receptor ligands should retain anti-inflammatory potency but cause fewer side effects. Here we critically re-examine the history and foundations of the transrepression hypothesis. We argue that it is incompatible with the complexity of gene regulation by glucocorticoids and poorly supported by experimental evidence; that it no longer aids clear thinking about the actions of the glucocorticoid receptor; and that it will not prove a fruitful basis for continued refinement and improvement of anti-inflammatory drugs that target the glucocorticoid receptor.

The anticancer plant triterpenoid, avicin D, regulates glucocorticoid receptor signaling: implications for cellular metabolism

Avicins, a family of apoptotic triterpene electrophiles, are known to regulate cellular metabolism and energy homeostasis, by targeting the mitochondria. Having evolved from “ancient hopanoids,” avicins bear a structural resemblance with glucocorticoids (GCs), which are the endogenous regulators of metabolism and energy balance. These structural and functional similarities prompted us to compare the mode of action of avicin D with dexamethasone (Dex), a prototypical GC. Using cold competition assay, we show that Avicin D competes with Dex for binding to the GC receptor (GR), leading to its nuclear translocation. In contrast to Dex, avicin-induced nuclear translocation of GR does not result in transcriptional activation of GC-dependent genes. Instead we observe a decrease in the expression of GC-dependent metabolic proteins such as PEPCK and FASN. However, like Dex, avicin D treatment does induce a transrepressive effect on the pro-inflammatory transcription factor NF-κB. While avicin's ability to inhibit NF-κB and its downstream targets appear to be GR-dependent, its pro-apoptotic effects were independent of GR expression. Using various deletion mutants of GR, we demonstrate the requirement of both the DNA and ligand binding domains of GR in mediating avicin D's transrepressive effects. Modeling of avicin-GR interaction revealed that avicin molecule binds only to the antagonist confirmation of GR. These findings suggest that avicin D has properties of being a selective GR modulator that separates transactivation from transrepression. Since the gene-activating properties of GR are mainly linked to its metabolic effects, and the negative interference with the activity of transcription factors to its anti-inflammatory and immune suppressive effects, the identification of such a dissociated GR ligand could have great potential for therapeutic use.

Glucocorticoid receptor dimerization is required for survival in septic shock via suppression of interleukin-1 in macrophages

Sepsis is controlled by endogenous glucocorticoids (GCs). Previous studies provided evidence that crosstalk of the monomeric GC receptor (GR) with proinflammatory transcription factors is the crucial mechanism underlying the suppressive GC effect. Here we demonstrate that mice with a dimerization-deficient GR (GR(dim)) are highly susceptible to sepsis in 2 different models, namely cecal ligation and puncture and lipopolysaccharide (LPS)-induced septic shock. TNF-α is normally regulated in these mice, but down-regulation of IL-6 and IL-1β is diminished. LPS-treated macrophages derived from GR(dim) mice are largely resistant to GC actions in vitro in terms of morphology, surface marker expression, and gene expression. Treatment with recombinant IL-1 receptor antagonist improved survival of GR(dim) mice and mice lacking the GR in macrophages (GR(LysMCre)) mice. This suggests that regulation of IL-1β in macrophages by GCs is pivotal to control sepsis.

Glucocorticoids sensitize the innate immune system through regulation of the NLRP3 inflammasome

Glucocorticoids have long been recognized as powerful anti-inflammatory compounds that are one of the most widely prescribed classes of drugs in the world. However, their role in the regulation of innate immunity is not well understood. We sought to examine the effects of glucocorticoids on the NOD-like receptors (NLRs), a central component of the inflammasome and innate immunity. Surprisingly, we show that glucocorticoids induce both NLRP3 messenger RNA and protein, which is a critical component of the inflammasome. The glucocorticoid-dependent induction of NLRP3 sensitizes the cells to extracellular ATP and significantly enhances the ATP-mediated release of proinflammatory molecules, including mature IL-1β, TNF-α, and IL-6. This effect was specific for glucocorticoids and dependent on the glucocorticoid receptor. These studies demonstrate a novel role for glucocorticoids in sensitizing the initial inflammatory response by the innate immune system.

High density micromass cultures of a human chondrocyte cell line: a reliable assay system to reveal the modulatory functions of pharmacological agents

Osteoarthritis is a highly prevalent and disabling disease for which we do not have a cure. The identification of suitable molecular targets is hindered by the lack of standardized, reproducible and convenient screening assays. Following extensive comparisons of a number of chondrocytic cell lines, culture conditions, and readouts, we have optimized an assay utilizing C-28/I2, a chondrocytic cell line cultured in high-density micromasses. Utilizing molecules with known effects on cartilage (e.g. IL-1β, TGFβ1, BMP-2), we have exploited this improved protocol to (i) evoke responses characteristic of primary chondrocytes; (ii) assess the pharmacodynamics of gene over-expression using non-viral expression vectors; (iii) establish the response profiles of known pharmacological treatments; and (iv) investigate their mechanisms of action. These data indicate that we have established a medium-throughput methodology for studying chondrocyte-specific cellular and molecular responses (from gene expression to rapid quantitative measurement of sulfated glycosaminoglycans by Alcian blue staining) that may enable the discovery of novel therapeutics for pharmacological modulation of chondrocyte activation in osteoarthritis.

Influenza virus infection induces the nuclear relocalization of the Hsp90 co-chaperone p23 and inhibits the glucocorticoid receptor response

The genomic RNAs of influenza A viruses are associated with the viral polymerase subunits (PB1, PB2, PA) and nucleoprotein (NP), forming ribonucleoprotein complexes (RNPs). Transcription/replication of the viral genome occurs in the nucleus of infected cells. A role for Hsp90 in nuclear import and assembly of newly synthetized RNA-polymerase subunits has been proposed. Here we report that the p23 cochaperone of Hsp90, which plays a major role in glucocorticoid receptor folding and function, associates with influenza virus polymerase. We show that p23 is not essential for viral multiplication in cultured cells but relocalizes to the nucleus in influenza virus-infected cells, which may alter some functions of p23 and Hsp90. Moreover, we show that influenza virus infection inhibits glucocorticoid receptor-mediated gene transactivation, and that this negative effect can occur through a p23-independent pathway. Viral-induced inhibition of the glucocorticoid receptor response might be of significant importance regarding the physiopathology of influenza infections in vivo.

Glucocorticoid receptors, epidermal homeostasis and hair follicle differentiation

Glucocorticoids (GCs) exert their biological and therapeutical actions through the GC receptor (GR), a ligand-dependent transcription factor. Synthetic GC derivatives are widely prescribed for treating numerous cutaneous inflammatory and immune diseases due to their great efficacy. However, chronic treatment with GCs produces adverse side-effects including skin atrophy, delayed wound healing, and in certain cases, GC resistance. The mechanisms underlying the therapeutic actions of the GR in skin have been extensively studied; in contrast, the role of GR as a modulator of epidermal development and homeostasis has received less attention. The ubiquitous functional inactivation of GR results in defective epidermal formation although the underlying mechanisms have not been fully characterized. The use of transcriptomic approaches both in vitro and in vivo allowed the identification of genes that are regulated by GR in developing and adult skin. A main goal to understand the role of GR in skin biology is to identify primary transcriptional targets as well as the signaling pathways mediating GR action. Furthermore, it will be important to decipher the contribution of GR in the different cellular compartments of the skin, including keratinocytes of the interfollicular epidermis and hair follicles, and their respective stem cell progenitors. Additionally, recent findings indicating that the skin acts as a true peripheral endocrine organ implies greater complexity than originally thought. The local production of GCs and other steroid hormones should be considered as a modulator of skin function under homeostatic and diseased conditions. Finally, studying GR function in skin should take into account that the mineralocorticoid receptor may also mediate GC actions and/or regulate transcription either by itself or in combination with GR. Addressing these issues should help to elucidate the mechanisms by which Gr contributes to establishment of a competent epidermal barrier and may also have implications in the context of dermatological treatments based on GC-analogs.

Tumor necrosis factor inhibits glucocorticoid receptor function in mice: a strong signal toward lethal shock

As glucocorticoid resistance (GCR) and the concomitant burden pose a worldwide problem, there is an urgent need for a more effective glucocorticoid therapy, for which insights into the molecular mechanisms of GCR are essential. In this study, we addressed the hypothesis that TNFα, a strong pro-inflammatory mediator in numerous inflammatory diseases, compromises the protective function of the glucocorticoid receptor (GR) against TNFα-induced lethal inflammation. Indeed, protection of mice by dexamethasone against TNFα lethality was completely abolished when it was administered after TNFα stimulation, indicating compromised GR function upon TNFα challenge. TNFα-induced GCR was further demonstrated by impaired GR-dependent gene expression in the liver. Furthermore, TNFα down-regulates the levels of both GR mRNA and protein. However, this down-regulation seems to occur independently of GC production, as TNFα also resulted in down-regulation of GR levels in adrenalectomized mice. These findings suggest that the decreased amount of GR determines the GR response and outcome of TNFα-induced shock, as supported by our studies with GR heterozygous mice. We propose that by inducing GCR, TNFα inhibits a major brake on inflammation and thereby amplifies the pro-inflammatory response. Our findings might prove helpful in understanding GCR in inflammatory diseases in which TNFα is intimately involved.

Role of GILZ in immune regulation, glucocorticoid actions and rheumatoid arthritis

Glucocorticoids have been exploited therapeutically for more than six decades through the use of synthetic glucocorticoids as anti-inflammatory agents, and are still used in as many as 50% of patients suffering from inflammatory diseases such as rheumatoid arthritis (RA). Better understanding of the mechanisms of action of glucocorticoids could enable the development of therapies that dissociate the broad-spectrum benefits of glucocorticoids from their adverse metabolic effects. The glucocorticoid-induced leucine zipper protein (GILZ; also known as TSC22 domain family protein 3) is a glucocorticoid-responsive molecule whose interactions with signal transduction pathways, many of which are operative in RA and other inflammatory diseases, suggest that it is a key endogenous regulator of the immune response. The overlap between the observed effects of GILZ on the immune system and those of glucocorticoids strongly suggest GILZ as a critical mediator of the therapeutic effects of glucocorticoids. Observations of the immunomodulatory effects of GILZ in human RA synovial cells, and in an in vivo model of RA, support the hypothesis that GILZ is a key glucocorticoid-induced regulator of inflammation in RA. Moreover, evidence that the effect of GILZ on bone loss might be in contrast to those of glucocorticoids suggests manipulation of GILZ as a potential means of dissociating the beneficial anti-inflammatory effects of glucocorticoids from their negative metabolic repercussions.

Microglial glucocorticoid receptors play a pivotal role in regulating dopaminergic neurodegeneration in parkinsonism

Among the pathogenic processes contributing to dopaminergic neuron (DN) death in Parkinson disease (PD), evidence points to non-cell-autonomous mechanisms, particularly chronic inflammation mounted by activated microglia. Yet little is known about endogenous regulatory processes that determine microglial actions in pathological states. We examined the role of glucocorticoid receptors (GRs), activated by glucocorticoids released in response to stress and known to regulate inflammation, in DN survival. Overall GR level was decreased in substantia nigra of PD patients and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. GR changes, specifically in the microglia after MPTP treatment, revealed a rapid augmentation in the number of microglia displaying nuclear localization of GR. Mice with selective inactivation of the GR gene in macrophages/microglia (GR(LysMCre)) but not in DNs (GR(DATCre)) showed increased loss of DNs after MPTP intoxication. This DN loss in GR(LysMCre) mice was not prevented by corticosterone treatment, in contrast to the protection observed in control littermates. Moreover, absence of microglial GRs augmented microglial reactivity and led to their persistent activation. Analysis of inflammatory genes revealed an up-regulation of Toll-like receptors (TLRs) by MPTP treatment, particularly TLR9, the level of which was high in postmortem parkinsonian brains. The regulatory control of GR was reflected by higher expression of proinflammatory genes (e.g., TNF-α) with a concomitant decrease in anti-inflammatory genes (e.g., IL-1R2) in GR(LysMCre) mice. Indeed, in GR(LysMCre) mice, alterations in phosphorylated NF-κB levels indicated its protracted activation. Together, our data indicate that GR is important in curtailing microglial reactivity, and its deregulation in PD could lead to sustained inflammation-mediated DN injury.

The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights

Since the discovery of glucocorticoids in the 1940s and the recognition of their anti-inflammatory effects, they have been amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. However, their clinical efficacy is compromised by the metabolic effects of long-term treatment, which include osteoporosis, hypertension, dyslipidaemia and insulin resistance/type 2 diabetes mellitus. In recent years, a great deal of effort has been invested in identifying compounds that separate the beneficial anti-inflammatory effects from the adverse metabolic effects of glucocorticoids, with limited effect. It is clear that for these efforts to be effective, a greater understanding is required of the mechanisms by which glucocorticoids exert their anti-inflammatory and immunosuppressive actions. Recent research is shedding new light on some of these mechanisms and has produced some surprising new findings. Some of these recent developments are reviewed here.

Monocyte response to LPS after exposure to corticosteroids and chloroquine with implications for systemic lupus erythematosus

Essential part of a response to infection is early pathogen recognition and adequate initiation of innate immunity. One of the hallmarks of systemic lupus erythematosus (SLE) is reduced resistance to infection despite overall hyperactivity of the immune system. Immunosuppressive drugs (high-dose corticosteroids and cytotoxic agents) are independent risk factors for infection in SLE, with bacteria as predominant cause. To investigate whether less aggressive immunomodulatory treatment may still affect recognition and response to Gram-negative bacteria, we measured TLR4 expression in monocytes of untreated SLE patients and patients on chloroquine and low-dose steroid therapy and examined the drugs' influence on monocyte TLR4 expression in peripheral blood mononuclear cell (PBMC) culture. Additionally, we determined whether induction of monocyte NF-κB signalling, TNF-α and IL-6 production with lipopolysaccharide (LPS), a TLR4 ligand, can be altered with dexamethasone, chloroquine or both. There was no statistically significant difference in TLR4 expression between patients with SLE and controls, even though treated SLE patients tended to have lower frequency of TLR4(+) monocytes and TLR4 mean fluorescence intensity than healthy controls. However, neither dexamethasone nor chloroquine had major influence on TLR4 expression in vitro or suppressed LPS-induced NF-κB activation in monocytes, although dexamethasone decreased TNF-α and IL-6 production. Therefore, even if low-dose steroids or chloroquine do not seem to affect TLR4 expression and signalling, steroids might decrease cytokine production in response to LPS.

Respiratory syncytial virus represses glucocorticoid receptor-mediated gene activation

Respiratory syncytial virus (RSV) is a common cause of bronchiolitis in infants. Although antiinflammatory in nature, glucocorticoids have been shown to be ineffective in the treatment of RSV-induced bronchiolitis and wheezing. In addition, the effectiveness of glucocorticoids at inhibiting RSV-induced proinflammatory cytokine production in cell culture has been questioned. In this study, we have investigated the effect of RSV infection on glucocorticoid-induced gene activation in lung epithelium-derived cells. We show that RSV infection inhibits dexamethasone induction of three glucocorticoid receptor (GR)-regulated genes (glucocorticoid-inducible leucine zipper, FK506 binding protein, and MAPK phosphatase 1) in A549, BEAS-2B cells, and primary small airway epithelial cells. UV irradiation of the virus prevents this repression, suggesting that viral replication is required. RSV is known to activate the nuclear factor κB (NFκB) pathway, which is mutually antagonistic towards the GR pathway. However, specific inhibition of NFκB had no effect on the repression of GR-induced genes by RSV infection, indicating that RSV repression of GR is independent of NFκB. RSV infection of A549 cells does not alter GR protein levels or GR nuclear translocation but does reduce GR binding to the promoters of the glucocorticoid responsive genes analyzed in this study. Repression of GR by RSV infection may account for the apparent clinical ineffectiveness of glucocorticoids in RSV bronchiolitis therapy. In addition, this data adds to our previously published data suggesting that GR may be a general target for infectious agents. Identifying the mechanisms through which this suppression occurs may lead to the development of novel therapeutics.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

The human glucocorticoid receptor as an RNA-binding protein: global analysis of glucocorticoid receptor-associated transcripts and identification of a target RNA motif

Posttranscriptional regulation is emerging as a key factor in glucocorticoid (GC)-mediated gene regulation. We investigated the role of the human GC receptor (GR) as an RNA-binding protein and its effect on mRNA turnover in human airway epithelial cells. Cell treatment with the potent GC budesonide accelerated the decay of CCL2 mRNA (t(1/2) = 8 ± 1 min versus 62 ± 17 min in DMSO-treated cells) and CCL7 mRNA (t(1/2) = 15 ± 4 min versus 114 ± 37 min), but not that of CCL5 mRNA (t(1/2)=231 ± 8 min versus 266 ± 5 min) in the BEAS-2B cell line. This effect was inhibited by preincubation with an anti-GR Ab, indicating that GR itself plays a role in the turnover of these transcripts. Coimmunoprecipitation and biotin pulldown experiments showed that GR associates with CCL2 and CCL7 mRNAs, but not CCL5 mRNA. These methods confirmed CCL2 mRNA targeting by GR in human primary airway epithelial cells. Association of the GR was localized to the 5' untranslated region of CCL2 mRNA and further mapped to nt 44-60. The collection of transcripts associated with GR, identified by immunoprecipitation of GR-mRNA complexes followed by microarray analysis, revealed 479 transcripts that associated with GR. Computational analysis of the primary sequence and secondary structures of these transcripts yielded a GC-rich motif, which was shown to bind to GR in vitro. This motif was used to predict binding of GR to an additional 7889 transcripts. These results indicate that cytoplasmic GR interacts with a subset of mRNA through specific sequences and can regulate turnover rates, suggesting a novel posttranscriptional role for GR as an RNA-binding protein.

The human periodontal ligament cell: a fibroblast-like cell acting as an immune cell

BACKGROUND

Periodontal ligament cells are fibroblast-like cells characterized by collagen production but also possessing some osteoblastic features. In the light of numerous studies presented during recent times, which show that human periodontal ligament cells also produce cytokines and chemokines in response to inflammation promoters, it is reasonable to suggest that periodontal ligament cells play a role as promoters of periodontal inflammation through these mechanisms.

MATERIAL AND METHODS

The periodontal ligament, which harbours the periodontal ligament cells, is a part of the attachment apparatus comprised of periodontal ligament cells, extracellular matrix and fibres, attaching the root cement to the alveolar bone. Periodontal ligament cells are in close proximity to bacteria within the plaque and the pocket, and thus these cells are readily accessible to bacterial endotoxins and other promoters of inflammation.

RESULTS

Cytokines and chemokines, released by periodontal ligament cells upon stimulation with inflammation promoters, reach the blood vessels easily thanks to rich vascularization of the periodontium stimulating recruitment of white blood cells to the site of inflammation. In addition to classical inflammatory cells, such as leucocytes, macrophages and mast cells, the periodontal ligament cells also contribute to periodontal inflammation via their production and release of cytokines and chemokines.

CONCLUSION

Therefore, pharmacological treatment of periodontitis should aim to reduce the release of proinflammatory agents not only from classical inflammatory cells but also from periodontal ligament cells.

Transcriptional regulation of human dual specificity protein phosphatase 1 (DUSP1) gene by glucocorticoids

BACKGROUND

Glucocorticoids are potent anti-inflammatory agents commonly used to treat inflammatory diseases. They convey signals through the intracellular glucocorticoid receptor (GR), which upon binding to ligands, associates with genomic glucocorticoid response elements (GREs) to regulate transcription of associated genes. One mechanism by which glucocorticoids inhibit inflammation is through induction of the dual specificity phosphatase-1 (DUSP1, a.k.a. mitogen-activated protein kinase phosphatase-1, MKP-1) gene.

METHODOLOGY/PRINCIPAL FINDINGS

We found that glucocorticoids rapidly increased transcription of DUSP1 within 10 minutes in A549 human lung adenocarcinoma cells. Using chromatin immunoprecipitation (ChIP) scanning, we located a GR binding region between -1421 and -1118 upstream of the DUSP1 transcription start site. This region is active in a reporter system, and mutagenesis analyses identified a functional GRE located between -1337 and -1323. We found that glucocorticoids increased DNase I hypersensitivity, reduced nucleosome density, and increased histone H3 and H4 acetylation within genomic regions surrounding the GRE. ChIP experiments showed that p300 was recruited to the DUSP1 GRE, and RNA interference experiments demonstrated that reduction of p300 decreased glucocorticoid-stimulated DUSP1 gene expression and histone H3 hyperacetylation. Furthermore, overexpression of p300 potentiated glucocorticoid-stimulated activity of a reporter gene containing the DUSP1 GRE, and this coactivation effect was compromised when the histone acetyltransferase domain was mutated. ChIP-reChIP experiments using GR followed by p300 antibodies showed significant enrichment of the DUSP1 GRE upon glucocorticoid treatment, suggesting that GR and p300 are in the same protein complex recruited to the DUSP1 GRE.

CONCLUSIONS/SIGNIFICANCE

Our studies identified a functional GRE for the DUSP1 gene. Moreover, the transcriptional activation of DUSP1 by glucocorticoids requires p300 and a rapid modification of the chromatin structure surrounding the GRE. Overall, understanding the mechanism of glucocorticoid-induced DUSP1 gene transcription could provide insights into therapeutic approaches against inflammatory diseases.

Insights on glucocorticoid receptor activity modulation through the binding of rigid steroids

BACKGROUND

The glucocorticoid receptor (GR) is a transcription factor that regulates gene expression in a ligand-dependent fashion. This modular protein is one of the major pharmacological targets due to its involvement in both cause and treatment of many human diseases. Intense efforts have been made to get information about the molecular basis of GR activity.

METHODOLOGY/PRINCIPAL FINDINGS

Here, the behavior of four GR-ligand complexes with different glucocorticoid and antiglucocorticoid properties were evaluated. The ability of GR-ligand complexes to oligomerize in vivo was analyzed by performing the novel Number and Brightness assay. Results showed that most of GR molecules form homodimers inside the nucleus upon ligand binding. Additionally, in vitro GR-DNA binding analyses suggest that ligand structure modulates GR-DNA interaction dynamics rather than the receptor's ability to bind DNA. On the other hand, by coimmunoprecipitation studies we evaluated the in vivo interaction between the transcriptional intermediary factor 2 (TIF2) coactivator and different GR-ligand complexes. No correlation was found between GR intranuclear distribution, cofactor recruitment and the homodimerization process. Finally, Molecular determinants that support the observed experimental GR LBD-ligand/TIF2 interaction were found by Molecular Dynamics simulation.

CONCLUSIONS/SIGNIFICANCE

The data presented here sustain the idea that in vivo GR homodimerization inside the nucleus can be achieved in a DNA-independent fashion, without ruling out a dependent pathway as well. Moreover, since at least one GR-ligand complex is able to induce homodimer formation while preventing TIF2 coactivator interaction, results suggest that these two events might be independent from each other. Finally, 21-hydroxy-6,19-epoxyprogesterone arises as a selective glucocorticoid with potential pharmacological interest. Taking into account that GR homodimerization and cofactor recruitment are considered essential steps in the receptor activation pathway, results presented here contribute to understand how specific ligands influence GR behavior.

Classic glucocorticoids versus non-steroidal glucocorticoid receptor modulators: survival of the fittest regulator of the immune system?

The search for novel glucocorticoid receptor (GR) modulators with similar anti-inflammatory properties as conventional steroids, but with a reduction in the number or severity of the side effects has been a long-standing goal, and still remains a challenge today. The quest for these so-called 'dissociated GR ligands' is mainly based on the hypothesis that the occurrence of undesirable side effects is mostly associated with GR-mediated transactivation, whereas transrepression of many pro-inflammatory genes (e.g. cytokines and enzymes involved in inflammatory processes) is more involved in GR-mediated anti-inflammatory effects. As glucocorticoids (GCs) can also enhance the transcription of anti-inflammatory genes, the GR-mediated activation-repression dissociation hypothesis has to be nuanced. However, an enhanced selectivity of GR-affected genes, while upholding the desired anti-inflammatory potential, is still believed to contribute to a more beneficial therapeutic profile with fewer side effects. The initial pharmacological focus on steroidal scaffolds as a basis to dissociate the functionalities of GR has, due to a lack of success, recently been shifted to a focus on non-steroidal ligands. The current work reviews recent advances on the characterization of a generation of novel non-steroidal GR ligands.

Pharmacokinetics and pharmacodynamics of dexamethasone after oral administration in apparently healthy horses

OBJECTIVE

To assess pharmacokinetic and pharmacodynamic properties of dexamethasone administered PO as a solution or powder, compared with properties of dexamethasone solution administered IV, in apparently healthy horses.

ANIMALS

6 adult horses.

PROCEDURES

Serum cortisol concentration for each horse was determined before each treatment (baseline values). Dexamethasone (0.05 mg/kg) was administered PO (in solution or powdered form) or IV (solution) to horses from which feed had or had not been withheld (unfed and fed horses, respectively). Each horse received all 6 treatments in random order at 2-week intervals; PO and IV administrations of dexamethasone were accompanied by IV or PO sham treatments, respectively. Plasma dexamethasone and serum cortisol concentrations were assessed at predetermined intervals.

RESULTS

Maximum plasma dexamethasone concentration after PO administration of powdered dexamethasone in unfed horses was significantly higher than the maximum plasma concentration after PO administration of dexamethasone solution in unfed or fed horses. Mean bioavailability of dexamethasone ranged from 28% to 66% but was not significantly different among horses receiving either formulation PO in the unfed or fed state. After dexamethasone treatment PO or IV, serum cortisol concentrations were significantly less than baseline at 1 to 72 hours in unfed horses and at 2 to 48 hours in fed horses.

CONCLUSIONS AND CLINICAL RELEVANCE

PO or IV administration of dexamethasone resulted in suppression of cortisol secretion in unfed and fed adult horses; the magnitude of suppression did not differ among treatment groups, and serum cortisol concentrations returned to baseline after 48 to 72 hours.

Lower sensitivity of nasal polyp fibroblasts to glucocorticoid anti-proliferative effects

BACKGROUND

Treatment with glucocorticoids (GCs) is the cornerstone of nasal polyp (NP) therapy, but some patients respond poorly to them. Fibroblasts are involved in both inflammation and remodelling of NP. We aimed to evaluate whether NP fibroblasts are less sensitive to GCs' anti-proliferative and anti-inflammatory effects, compared to nasal mucosa (NM) fibroblasts.

METHODS

Fibroblasts were obtained from NP (n = 8) from asthmatic patients undergoing endoscopic surgery and NM (n = 8) from patients undergoing nasal corrective surgery. Fibroblasts were stimulated with DMEM at 0.5% or 5% FBS, or TGF-β (5 ng/ml), with or without dexamethasone (10(-11) to 10(-5)M) for different times. Cell proliferation, collagen mRNA expression and IL-6 and IL-8 release were measured.

RESULTS

After 3-days, dexamethasone dose-dependently inhibited proliferation of NM (p < 0.001) but not that of NP fibroblasts. Dexamethasone (10(-6)M) reduced by 25% the proliferation of NM fibroblasts. Dexamethasone also inhibited proliferation of NM (p < 0.01) but not that of NP fibroblasts at 5-days. TGF-β induced collagen-1α1, -1α2, and -3α1 mRNA levels in both NM and NP fibroblasts (p < 0.05), and dexamethasone did not alter TGF-β-induced collagen mRNA levels in either fibroblast type at 24 h. Dexamethasone dose-dependently decreased (p < 0.05) FBS-induced IL-6 and IL-8 release in both NM and NP fibroblasts at 4 h, although at 10(-8)M, dexamethasone inhibited cytokine production in NM (p < 0.05) but not in NP fibroblasts.

CONCLUSIONS

This impaired sensitivity of nasal polyp fibroblasts to in vitro glucocorticoid effects concurs in part with the poor clinical response that these nasal polyp patients show to glucocorticoid treatment.

Apolipoprotein E negatively regulates house dust mite-induced asthma via a low-density lipoprotein receptor-mediated pathway

RATIONALE

Distinct sets of corticosteroid-unresponsive genes modulate disease severity in asthma.

OBJECTIVES

To identify corticosteroid-unresponsive genes that provide new insights into disease pathogenesis and asthma therapeutics.

METHODS

Experimental murine asthma was induced by nasal administration of house dust mite for 5 days per week. Dexamethasone and apolipoprotein E (apo E) mimetic peptides were administered via osmotic minipumps.

MEASUREMENTS AND MAIN RESULTS

Genome-wide expression profiling of the lung transcriptome in a house dust mite-induced model of murine asthma identified increases in apo E mRNA levels that persisted despite corticosteroid treatment. House dust mite-challenged apo E⁻(/)⁻ mice displayed enhanced airway hyperreactivity and goblet cell hyperplasia, which could be rescued by administration of an apo E(130-149) mimetic peptide. Administration of the apo E(130-149) mimetic peptide to house dust mite-challenged apo E⁻(/)⁻ mice also inhibited eosinophilic airway inflammation, IgE production, and the expression of Th2 and Th17 cytokines. House dust mite-challenged low-density lipoprotein receptor (LDLR) knockout mice displayed a similar phenotype as apo E⁻(/)⁻ mice with enhanced airway hyperreactivity, goblet cell hyperplasia, and mucin gene expression, but could not be rescued by the apo E(130-149) mimetic peptide, consistent with a LDLR-dependent mechanism.

CONCLUSIONS

These findings for the first time identify an apo E-LDLR pathway as an endogenous negative regulator of airway hyperreactivity and goblet cell hyperplasia in asthma. Furthermore, our results demonstrate that strategies that activate the apo E-LDLR pathway, such as apo E mimetic peptides, might be developed into a novel treatment approach for patients with asthma.

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.

Glucocorticoid efficacy in asthma: is improved tissue remodeling upstream of anti-inflammation

Synthetic glucocorticoids (GCs), such as prednisone, are among the most widely prescribed drugs worldwide and are used to treat many acute and chronic inflammatory conditions. The current paradigm of GC efficacy is that they are potent anti-inflammatory agents. Decreased inflammation in many disorders is thought to lead to decreased pathological tissue remodeling. However, this model has never been validated. In particular, improvements in inflammation have not been shown to improve the rate of lung function decline in asthma. Herein, we present an alternative paradigm, where GC efficacy is mediated through more successful tissue remodeling, with reduction in inflammation secondary to successful regeneration.

11beta-Hydroxysteroid dehydrogenase type 1 is an important regulator at the interface of obesity and inflammation

Systemic glucocorticoid excess, as exemplified by the Cushing syndrome, leads to obesity and all further symptoms of the metabolic syndrome. The current obesity epidemic, however, is not characterized by increased plasma cortisol concentrations, but instead comes along with chronic low-grade inflammation in adipose tissue and concomitant increased levels of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1, gene HSD11B1), a parameter known to cause obesity in a mouse model. 11beta-HSD1 represents an intracellular amplifier of active glucocorticoid, thus enhances the associated effects on the inflammatory response as well as on nutrient and energy metabolism, and may therefore cause and exacerbate obesity by local increase of glucocorticoid concentrations. Obtained by extensive literature and database searching, the present review includes comprehensive lists of primary glucocorticoid-sensitive genes and gene products as well as of the thus far known regulators of HSD11B1 expression with implication in inflammation and metabolic disease. Collectively, the data clearly show that, in addition to amplifying active glucocorticoid and thus profoundly modulating inflammation and nutrient metabolism, 11beta-HSD1 is subject to tight control of multiple additional immunomodulatory and metabolic regulators. Hence, 11beta-HSD1 acts at the interface of inflammation and obesity and represents an efficient integrator and effector of local inflammatory and metabolic state.