Repression of TNF-alpha-induced IL-8 expression by the glucocorticoid receptor-beta involves inhibition of histone H4 acetylation

Modeling the Progression of Placental Transport from Early- to Late-Stage Pregnancy by Tuning Trophoblast Differentiation and Vascularization

The early-stage placental barrier is characterized by a lack of fetal circulation and by a thick trophoblastic barrier, whereas the later-stage placenta consists of vascularized chorionic villi encased in a thin, differentiated trophoblast layer, ideal for nutrient transport. In this work, predictive models of early- and late-stage placental transport are created using blastocyst-derived placental stem cells (PSCs) by modulating PSC differentiation and model vascularization. PSC differentiation results in a thinner, fused trophoblast layer, as well as an increase in human chorionic gonadotropin secretion, barrier permeability, and secretion of certain inflammatory cytokines, which are consistent with in vivo findings. Further, gene expression confirms this shift toward a differentiated trophoblast subtype. Vascularization results in a molecule type- and size-dependent change in dextran and insulin permeability. These results demonstrate that trophoblast differentiation and vascularization have critical effects on placental barrier permeability and that this model can be used as a predictive measure to assess fetal toxicity of xenobiotic substances at different stages of pregnancy.

Research progress on the mechanism of astragaloside IV in the treatment of asthma

Asthma is a common chronic respiratory disease, and its treatment is a core problem and challenge in clinical practice. Glucocorticoids (GCs) are the first-line therapy for the treatment of asthma. Local and systemic adverse reactions caused by GCs create obstacles to the treatment of asthma. Therefore, the research target is to find a new, safe, and effective therapeutic medicine at present. Natural products are an important source for treating asthma with low cost and low toxicity. Astragaloside IV (AS-IV) is an active ingredient of traditional Chinese medicine Astragalus mongholicus Bunge. Previous studies have indicated that AS-IV plays a therapeutic role in the treatment of asthma by inhibiting airway inflammation and remodeling the airway, and by regulating immunity and neuroendocrine function (Fig. 1) . It has a variety of biological characteristics such as multi-target intervention, high safety, and good curative effect. This article reviews the specific mechanism of AS-IV for the treatment of asthma to provide references for subsequent research.

Re-analysis of Single Cell Transcriptome Reveals That the NR3C1-CXCL8-Neutrophil Axis Determines the Severity of COVID-19

SARS-CoV-2 infection has recently been declared a pandemic. Some patients showing severe symptoms exhibit drastic inflammation and airway damage. In this study, we re-analyzed published scRNA-seq data of COVID-19 patient bronchoalveolar lavage fluid to further classify and compare immunological features according to the patient’s disease severity. Patients with severe symptoms showed DNA damage and apoptotic features of epithelial cells. Our results suggested that epithelial damage was associated with neutrophil infiltration. Myeloid cells of severe patients showed higher expression of proinflammatory cytokines and chemokines such as CXCL8. As a result, neutrophils were abundant in lungs of patients from the severe group. Furthermore, recruited neutrophils highly expressed genes related to neutrophil extracellular traps. Neutrophil-mediated inflammation was regulated by glucocorticoid receptor expression and activity. Based on these results, we suggest that severe COVID-19 symptoms may be determined by differential expression of glucocorticoid receptors and neutrophils.

PI3K inhibitor treatment ameliorates the glucocorticoid insensitivity of PBMCs in severe asthma

BACKGROUND

Glucocorticoid (GC) insensitivity is an important feature of severe and fatal asthma. Oxidative stress can induce phosphoinositide-3-kinase (PI3K) activation, contributing to the development of GC insensitivity in chronic airway diseases. However, the underlying molecular mechanism of PI3K in the pathogenesis of severe asthma remains unknown.

METHODS

We isolated peripheral blood mononuclear cells (PBMCs) from 34 participants (12 patients with mild/moderate asthma, 10 patients with severe asthma, and 12 control subjects). H₂O₂ was used to stimulate the human macrophage line U937 to mimic the oxidative stress status in severe asthma. The ability of candidate compounds, namely, azithromycin, PI3K inhibitors (BEZ235 and LY294002) and a p38 MAPK inhibitor (BIRB796), to ameliorate GC insensitivity in severe asthma was evaluated.

RESULTS

PBMCs from patients with severe asthma exhibited dose-dependent and time-dependent GC insensitivity, which correlated with reduced activity of histone deacetylase 2 (HDAC2) (p < 0.05) and elevated expression of proinflammatory genes [nuclear factor-κB (NF-κB) and activator protein-1 (AP-1)] (p < 0.01) compared with these parameters in the control group. The PI3K inhibitors (BZE235 and LY294002) significantly restored the GC sensitivity of PBMCs from patients with severe asthma. In vitro, the PI3K inhibitors (BZE235 and LY294002) ameliorated GC insensitivity in H₂O₂/TNFα-induced IL-8 release from U937 cells by independently restoring the activity of HDAC2 or inhibiting the activation of transcription factors.

CONCLUSIONS

This study demonstrates that PI3K inhibitors ameliorate GC insensitivity in severe asthma by restoring HDAC2 activity and inhibiting the phosphorylation of nuclear signaling transcription factors.

Steroid-resistant nephrotic syndrome: pharmacogenetics and epigenetic points and views

Introduction: Glucocorticoids (GCs) are the first-line therapy for patients with nephrotic syndrome (NS), a common glomerular disease, that cause complete remission in most of the cases. In response to the treatment, NS patients are divided into glucocorticoid-sensitive and -resistant. This variation is due to the differences in pharmacokinetics and pharmacodynamics of GCs in each patient that affect the response to the treatment modality. Since the genetic variations in drug-metabolizing enzymes and transporter proteins significantly impact the pharmacokinetics, efficacy and safety of the applied medications, this review highlights the basic mechanisms of genetic variations involved in GCs metabolism in drug-resistant NS patients.Areas covered: This review explains the pharmacogenetic variations that influence the profile of GCs responses and their pharmacokinetics in NS patients. Moreover, the epigenetic variations including histone modifications and miRNA gene regulation that have an influence on GCs responses will review. A comprehensive literature search was performed using different keywords to the reviewed topics.Expert opinion: The accumulative data suggest the importance of pharmacogenetic studies to develop personalized therapies and increase the GCs responsiveness in these patients. It is imperative to know that genetic testing does not give absolute answers to all existing questions in steroid resistance.

The shift in the balance between osteoblastogenesis and adipogenesis of mesenchymal stem cells mediated by glucocorticoid receptor

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into several tissues, such as bone, cartilage, and fat. Glucocorticoids affect a variety of biological processes such as proliferation, differentiation, and apoptosis of various cell types, including osteoblasts, adipocytes, or chondrocytes. Glucocorticoids exert their function by binding to the glucocorticoid receptor (GR). Physiological concentrations of glucocorticoids stimulate osteoblast proliferation and promote osteogenic differentiation of MSCs. However, pharmacological concentrations of glucocorticoids can not only induce apoptosis of osteoblasts and osteocytes but can also reduce proliferation and inhibit the differentiation of osteoprogenitor cells. Several signaling pathways, including the Wnt, TGFβ/BMP superfamily and Notch signaling pathways, transcription factors, post-transcriptional regulators, and other regulators, regulate osteoblastogenesis and adipogenesis of MSCs mediated by GR. These signaling pathways target key transcription factors, such as Runx2 and TAZ for osteogenesis and PPARγ and C/EBPs for adipogenesis. Glucocorticoid-induced osteonecrosis and osteoporosis are caused by various factors including dysfunction of bone marrow MSCs. Transplantation of MSCs is valuable in regenerative medicine for the treatment of osteonecrosis of the femoral head, osteoporosis, osteogenesis imperfecta, and other skeletal disorders. However, the mechanism of inducing MSCs to differentiate toward the osteogenic lineage is the key to an efficient treatment. Thus, a better understanding of the molecular mechanisms behind the imbalance between GR-mediated osteoblastogenesis and adipogenesis of MSCs would not only help us to identify the pathogenic causes of glucocorticoid-induced osteonecrosis and osteoporosis but also promote future clinical applications for stem cell-based tissue engineering and regenerative medicine. Here, we primarily review the signaling mechanisms involved in adipogenesis and osteogenesis mediated by GR and discuss the factors that control the adipo-osteogenic balance.

Targeting HDAC Complexes in Asthma and COPD

Around three million patients die due to airway inflammatory diseases each year. The most notable of these diseases are asthma and chronic obstructive pulmonary disease (COPD). Therefore, new therapies are urgently needed. Promising targets are histone deacetylases (HDACs), since they regulate posttranslational protein acetylation. Over a thousand proteins are reversibly acetylated, and acetylation critically influences aberrant intracellular signaling pathways in asthma and COPD. The diverse set of selective and non-selective HDAC inhibitors used in pre-clinical models of airway inflammation show promising results, but several challenges still need to be overcome. One such challenge is the design of HDAC inhibitors with unique selectivity profiles, such as selectivity towards specific HDAC complexes. Novel strategies to disrupt HDAC complexes should be developed to validate HDACs further as targets for new anti-inflammatory pulmonary treatments.

Mucin 1 downregulation impairs the anti-necroptotic effects of glucocorticoids in human bronchial epithelial cells

AIMS

To investigate whether mucin 1 (MUC1) downregulation reduced the sensitivity of tumor necrosis factor-alpha (TNF-α)-induced bronchial epithelial cells to glucocorticoid-mediated necroptosis and explore the underlying mechanisms.

MAIN METHODS

The human lung bronchial epithelial cell line (16HBE) was transfected with small interfering RNA (siRNA) against MUC1 and then stimulated by TNF-α, where some cells were pretreated with dexamethasone. Flow cytometry was performed to analyze necroptosis in 16HBE cells, and western blot analysis was used to detect protein expression levels of MUC1, glucocorticoid receptor (GR)α, GRβ, NF-κB p65, phospho-p65 (p-p65), and histone deacetylase-2 (HDAC2). Additionally, nuclear translocation of MUC1 and GRα was assessed by immunofluorescence.

KEY FINDINGS

We observed that MUC1 downregulation by siRNA significantly augmented TNF-α-induced necroptosis in 16HBE cells, and that dexamethasone showed impaired anti-necroptotic effects of MUC1 downregulation. Furthermore, we found that GRα nuclear translocation was inhibited in 16HBE cells with MUC1 downregulation, and that dexamethasone-mediated inhibition of p65 phosphorylation was lower in cells transfected with MUC1-siRNA compared to those transfected with negative control siRNA.

SIGNIFICANCE

Impaired GRα nuclear translocation and inhibited p-p65 expression might contribute to glucocorticoid resistance caused by MUC1 deficiency in TNF-α-induced necroptosis in 16HBE cells, and should be considered as a potential target for the development of novel therapeutics for asthma.

E4BP4 facilitates glucocorticoid sensitivity of human bronchial epithelial cells via down-regulation of glucocorticoid receptor-beta

It has recently been recognized that a subset of asthma patients suffer from glucocorticoid (GC) insensitivity, and glucocorticoid receptor-β (GR-β) is associated with corticosteroid resistance, but the underlying mechanisms remain unknown. Here we demonstrated that Interleukin-17A induced glucocorticoid sensitivity in human bronchial epithelial cells (16HBE) is enhanced, which is depend on E4 promoter-binding protein 4 (E4BP4) mediated GR-β expression. Our data show that the expression of E4BP4 is significantly up-regulated in 16HBE cells, and the depletion of E4BP4 dramatically decreased glucocorticoid sensitivity in IL-17A induced 16HBE cells. Mechanistic studies revealed that E4BP4 plays a crucial role in Interleukin-17A induced glucocorticoid sensitivity in 16HBE cells via down-regulating GR-β, which is probably mediated by PI3K/Akt activation. Collectively, we can draw the conclusion that E4BP4 contribute to enhance the GCs sensitivity, which may offer a new strategy for therapeutic intervention for GC-insensitive asthma.

Functional analysis reveals no transcriptional role for the glucocorticoid receptor β-isoform in zebrafish

In humans, two splice variants of the glucocorticoid receptor (GR) exist: the canonical α-isoform, and the β-isoform, which has been shown to have a dominant-negative effect on hGRα. Previously, we have established the occurrence of a GR β-isoform in zebrafish, and in the present study we have investigated the functional role of the zebrafish GRβ (zGRβ). Reporter assays in COS-1 cells demonstrated a dominant-negative effect of zGRβ but no such effect was observed in zebrafish PAC2 cells using induction of the fk506 binding protein 5 (fkbp5) gene as readout. Subsequently, we generated a transgenic fish line with inducible expression of zGRβ. Transcriptome analysis suggested transcriptional regulation of genes by zGRβ in this line, but further validation failed to confirm this role. Based on these results, its low expression level and its poor evolutionary conservation, we suggest that the zebrafish GR β-isoform does not have a functional role in transcriptional regulation.

Corticosteroids: Mechanisms of Action in Health and Disease

Glucocorticoids are primary stress hormones that regulate a variety of physiologic processes and are essential for life. The actions of glucocorticoids are predominantly mediated through the classic glucocorticoid receptor (GR). GRs are expressed throughout the body, but there is considerable heterogeneity in glucocorticoid sensitivity and biologic responses across tissues. The conventional belief that glucocorticoids act through a single GR protein has changed dramatically with the discovery of a diverse collection of receptor isoforms. This article provides an overview of the molecular mechanisms that regulate glucocorticoid actions, highlights the dynamic nature of hormone signaling, and discusses the molecular properties of the GR isoforms.

Molecular Actions of Glucocorticoids in Cartilage and Bone During Health, Disease, and Steroid Therapy

Cartilage and bone are severely affected by glucocorticoids (GCs), steroid hormones that are frequently used to treat inflammatory diseases. Major complications associated with long-term steroid therapy include impairment of cartilaginous bone growth and GC-induced osteoporosis. Particularly in arthritis, GC application can increase joint and bone damage. Contrarily, endogenous GC release supports cartilage and bone integrity. In the last decade, substantial progress in the understanding of the molecular mechanisms of GC action has been gained through genome-wide binding studies of the GC receptor. These genomic approaches have revolutionized our understanding of gene regulation by ligand-induced transcription factors in general. Furthermore, specific inactivation of GC signaling and the GC receptor in bone and cartilage cells of rodent models has enabled the cell-specific effects of GCs in normal tissue homeostasis, inflammatory bone diseases, and GC-induced osteoporosis to be dissected. In this review, we summarize the current view of GC action in cartilage and bone. We further discuss future research directions in the context of new concepts for optimized steroid therapies with less detrimental effects on bone.

Glucocorticoids and the Lung

The lung is a major clinical target of glucocorticoid-based therapeutics, and GR signaling has broad effects on respiratory physiology and inflammation. During lung development, expression of GR in the mesenchyme is required for normal terminal alveolar epithelial differentiation. Prenatal administration of exogenous glucocorticoids (GCs) to prevent neonatal respiratory distress syndrome, however, promotes alveolar maturation and accelerates surfactant expression in a manner consistent with direct effects on the developing alveolar epithelium. Likewise, cell autonomous effects of GCs in regulating gene expression and phenotype of the airway epithelium and airway smooth muscle have been demonstrated to control important therapeutic effects of GCs in treating asthma and chronic obstructive pulmonary disease. Here, mechanisms and consequences of GR signaling in the developing lung and in treating obstructive lung disease are reviewed, with a focus on direct effects of GR signaling on alveolar differentiation, surfactant expression, and airway epithelial and smooth muscle pathophysiology.

The biology of the glucocorticoid receptor: new signaling mechanisms in health and disease

Glucocorticoids are primary stress hormones necessary for life that regulate numerous physiologic processes in an effort to maintain homeostasis. Synthetic derivatives of these hormones have been mainstays in the clinic for treating inflammatory diseases, autoimmune disorders, and hematologic cancers. The physiologic and pharmacologic actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily of ligand-dependent transcription factors. Ligand-occupied GR induces or represses the transcription of thousands of genes through direct binding to DNA response elements, physically associating with other transcription factors, or both. The traditional view that glucocorticoids act through a single GR protein has changed dramatically with the discovery of a large cohort of receptor isoforms with unique expression, gene-regulatory, and functional profiles. These GR subtypes are derived from a single gene by means of alternative splicing and alternative translation initiation mechanisms. Posttranslational modification of these GR isoforms further expands the diversity of glucocorticoid responses. Here we discuss the origin and molecular properties of the GR isoforms and their contribution to the specificity and sensitivity of glucocorticoid signaling in healthy and diseased tissues.

Evidence for a glucocorticoid receptor beta splice variant in the rat and its physiological regulation in liver

Glucocorticoids are important regulators of metabolism and immune function. Synthetic glucocorticoids are extensively used for immunosuppression/anti-inflammatory therapy. Since the glucocorticoid receptor (GR) is central to most hormone effects; its in vivo regulation will influence hormone/drug action. An alternative splice variant, GRβ, is present in humans and may function as a dominant negative regulator of GR transcriptional activity. Recently, a similar splice variant was reported in mouse, although the mechanism of alternative splicing differs from that in humans. We present evidence that a splice variant of GR with an alternative C-terminus also occurs in the rat by a mechanism of intron inclusion. A highly quantitative qRT-PCR assay for the simultaneous measurement of both splice variants in a single sample was developed in order to accurately measure their regulation. We used this assay to assess the tissue specific expression of both mRNAs, and demonstrate that GRα is predominant in all tissues. In addition, the regulation of both GRα and GRβ mRNA by various physiological factors in rat liver was assessed. GRα showed a robust circadian rhythm, which was entrained with the circadian oscillation of the endogenous hormone. Time series experiments showed that both corticosteroids and LPS but not insulin dosing resulted in the transient down-regulation of GRα mRNA. LPS treatment also resulted in down-regulation of GRβ expression. A modest up-regulation in GRβ expression was observed only in animals having chronically elevated plasma insulin concentrations. However the expression of GRβ was significantly lower than that of GRα in all cases.

Glucocorticoid receptor-beta up-regulation and steroid resistance induction by IL-17 and IL-23 cytokine stimulation in peripheral mononuclear cells

PURPOSE

Most asthmatic patients have well controlled symptoms with regular treatment, but some require much higher doses of inhaled and oral corticosteroids, or in rare cases fail to respond; these patients may present Th-17 cell infiltration and associated cytokines (IL-17A and -F) in the airways, sputum and peripheral blood. Because glucocorticoid receptor-beta (GR-beta) is associated with corticosteroid resistance, we investigated whether Th-17 associated cytokines induce steroid insensitivity in PBMCs via GR-beta up-regulation.

METHODS

GR-alpha, GR-beta, GILZ and IL-6 expression were analyzed in PBMCs stimulated with IL-2/IL-4, IL-17A/IL-17F and IL-23 cytokines by quantitative RT-PCR. Dexamethasone-inhibition of PHA-induced proliferation and Dexamethasone-induced apoptosis were determined by either (3)H-thymidine or CFSE-labelled cells and by Annexin-V staining and flow cytometry.

RESULTS

IL-17 and IL-23 cytokines significantly increased GR-beta expression. IL-2/IL-4 significantly decreased GR-alpha expression without affecting GR-beta. IL17, IL-23 and IL2 + 4 stimulations significantly hampered Dexamethasone-inhibition of proliferation (Dex EC(50) for: IL-17A + F = 251 nM; IL-23 = 435 nM; IL2 + 4 = 950 nM; Medium = 90 nM). IL2 + 4 and IL17A + F but not IL-23, significantly hampered Dexamethasone-induced apoptosis (1400 and 320 nM Dex, respectively). Dexamethasone's trans-activation of GILZ and trans-repression of NF-kB-driven IL-6 expression were both inhibited by IL2 + 4; IL17 + IL23 antagonized Dex trans-repression in PBMC from asthmatics.

CONCLUSIONS

GR-beta up-regulation by IL-17/IL-23 cytokines is associated with induced steroid insensitivity in PBMCs, observed as diminished Dexamethasone's effects on cell proliferation, apoptosis and gene regulation. Steroid resistance induced by IL-2/IL-4 was associated with decreased GR-alpha expression. This study supports the possibility that Th-17 lymphocytes and associated cytokines play a role in the mechanism of steroid hypo-responsiveness in severe asthmatics.

Downregulation of PCAF by miR-181a/b provides feedback regulation to TNF-α-induced transcription of proinflammatory genes in liver epithelial cells

Aberrant cellular responses to proinflammatory cytokines, such as TNF-α, are pathogenic features in most chronic inflammatory diseases. A variety of extracellular and intracellular feedback pathways has evolved to prevent an inappropriate cellular reaction to these proinflammatory cytokines. In this study, we report that TNF-α treatment of human and mouse cholangiocytes and hepatocytes downregulated expression of p300/CBP-associated factor (PCAF), a coactivator and an acetyltransferase that promotes histone acetylation and gene transcription. Of these upregulated microRNAs in TNF-α-treated cells, miR-181a/b (miR-181a and miR-181b) suppressed translation of PCAF mRNA. Functional manipulation of miR-181a/b caused reciprocal alterations in PCAF protein expression in cultured cholangiocytes and hepatocytes. Inhibition of miR-181a/b function with anti-miRs blocked TNF-α-induced suppression of PCAF expression. Promoter recruitment of PCAF was shown to be associated with TNF-α-induced transcription of inflammatory genes. Intriguingly, pretreatment of cells with TNF-α inhibited transcription of inflammatory genes in response to subsequent TNF-α stimulation. Overexpression of PCAF or inhibition of miR-181a/b function with anti-miRs attenuated the inhibitory effects of TNF-α pretreatment on epithelial inflammatory response to subsequent TNF-α stimulation. Downregulation of PCAF and the inhibitory effects of TNF-α pretreatment on liver epithelial inflammatory response were further confirmed in a mouse model of TNF-α i.p. injection. These data suggest that PCAF is a target for miR-181a/b, and downregulation of PCAF by TNF-α provides negative feedback regulation to inflammatory reactions in liver epithelial cells, a process that may be relevant to the epigenetic fine-tuning of epithelial inflammatory processes in general.

The dominant negative β isoform of the glucocorticoid receptor is uniquely expressed in erythroid cells expanded from polycythemia vera patients

Glucocorticoid receptor (GR) agonists increase erythropoiesis in vivo and in vitro. To clarify the effect of the dominant negative GRβ isoform (unable to bind STAT-5) on erythropoiesis, erythroblast (EB) expansion cultures of mononuclear cells from 18 healthy (nondiseased) donors (NDs) and 16 patients with polycythemia vera (PV) were studied. GRβ was expressed in all PV EBs but only in EBs from 1 ND. The A3669G polymorphism, which stabilizes GRβ mRNA, had greater frequency in PV (55%; n = 22; P = .0028) and myelofibrosis (35%; n = 20) patients than in NDs (9%; n = 22) or patients with essential thrombocythemia (6%; n = 15). Dexamethasone stimulation of ND cultures increased the number of immature EBs characterized by low GATA1 and β-globin expression, but PV cultures generated great numbers of immature EBs with low levels of GATA1 and β-globin irrespective of dexamethasone stimulation. In ND EBs, STAT-5 was not phosphorylated after dexamethasone and erythropoietin treatment and did not form transcriptionally active complexes with GRα, whereas in PV EBs, STAT-5 was constitutively phosphorylated, but the formation of GR/STAT-5 complexes was prevented by expression of GRβ. These data indicate that GRβ expression and the presence of A3669G likely contribute to development of erythrocytosis in PV and provide a potential target for identification of novel therapeutic agents.

Cellular processing of the glucocorticoid receptor gene and protein: new mechanisms for generating tissue-specific actions of glucocorticoids

Glucocorticoids regulate numerous physiological processes and are mainstays in the treatment of inflammation, autoimmune disease, and cancer. The traditional view that glucocorticoids act through a single glucocorticoid receptor (GR) protein has changed in recent years with the discovery of a large cohort of receptor subtypes arising from alternative processing of the GR gene. These isoforms differ in their expression, gene regulatory, and functional profiles. Post-translational modification of these proteins further expands GR diversity. Here, we discuss the origin and molecular properties of the GR isoforms and their contribution to the sensitivity and specificity of the glucocorticoid response.

Discovery of glucocorticoid receptor-beta in mice with a role in metabolism

Glucocorticoid hormones control diverse physiological processes, including metabolism and immunity, by activating the major glucocorticoid receptor (GR) isoform, GRalpha. However, humans express an alternative isoform, human (h)GRbeta, that acts as an inhibitor of hGRalpha to produce a state of glucocorticoid resistance. Indeed, evidence exists that hGRbeta contributes to many diseases and resistance to glucocorticoid hormone therapy. However, rigorous testing of the GRbeta contribution has not been possible, because rodents, especially mice, are not thought to express the beta-isoform. Here, we report expression of GRbeta mRNA and protein in the mouse. The mGRbeta isoform arises from a distinct alternative splicing mechanism utilizing intron 8, rather than exon 9 as in humans. The splicing event produces a form of beta that is similar in structure and functionality to hGRbeta. Mouse (m)GRbeta has a degenerate C-terminal region that is the same size as hGRbeta. Using a variety of newly developed tools, such as a mGRbeta-specific antibody and constructs for overexpression and short hairpin RNA knockdown, we demonstrate that mGRbeta cannot bind dexamethasone agonist, is inhibitory of mGRalpha, and is up-regulated by inflammatory signals. These properties are the same as reported for hGRbeta. Additionally, novel data is presented that mGRbeta is involved in metabolism. When murine tissue culture cells are treated with insulin, no effect on mGRalpha expression was observed, but GRbeta was elevated. In mice subjected to fasting-refeeding, a large increase of GRbeta was seen in the liver, whereas mGRalpha was unchanged. This work uncovers the much-needed rodent model of GRbeta for investigations of physiology and disease.

Induction of glucocorticoid receptor-beta expression in epithelial cells of asthmatic airways by T-helper type 17 cytokines

BACKGROUND

Corticosteroid insensitivity in asthmatics is associated with an increased expression of glucocorticoid receptor-beta (GR-beta) in many cell types. T-helper type 17 (Th17) cytokine (IL-17A and F) expressions increase in mild and in difficult-to-treat asthma. We hypothesize that IL-17A and F cytokines alone or in combination, induce the expression of GR-beta in bronchial epithelial cells.

OBJECTIVES

To confirm the expression of the GR-beta and IL-17 cytokines in the airways of normal subjects and mild asthmatics and to examine the effect of cytokines IL-17A and F on the expression of GR-beta in bronchial epithelial cells obtained from normal subjects and asthmatic patients.

METHODS

The expression of IL-17A and F, GR-alpha and GR-beta was analysed in bronchial biopsies from mild asthmatics and normal subjects by Q-RT-PCR. Immunohistochemistry for IL-17 and GR-beta was performed in bronchial biopsies from normal and asthmatic subjects. The expression of IL-6 in response to IL-17A and F and dexamethasone was determined by Q-RT-PCR using primary airway epithelial cells from normal and asthmatic subjects.

RESULTS

We detected significantly higher levels of IL-17A mRNA expression in the bronchial biopsies from mild asthmatics, compared with normal. GR-alpha expression was significantly lower in the biopsies from asthmatics compared with controls. The expression of IL-17F and GR-beta in biopsies from asthmatics was not significantly different from that of controls. Using primary epithelial cells isolated from normal subjects and asthmatics, we found an increased expression of GR-beta in response to IL-17A and F in the cells from asthmatics (P< or =0.05). This effect was only partially significant in the normal cells. Dexamethasone significantly decreased the IL-17-induced IL-6 expression in cells from normal individuals but not in those from asthmatics (P< or =0.05).

CONCLUSION

Evidence of an increased GR-beta expression in epithelial cells following IL-17 stimulation suggests a possible role for Th17-associated cytokines in the mechanism of steroid hypo-responsiveness in asthmatic subjects.

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.