Corticosteroid effects on cell signalling

Glucocorticoid receptor gene polymorphisms associated with progression of lung disease in young patients with cystic fibrosis

Background

The variability in the inflammatory burden of the lung in cystic fibrosis (CF) patients together with the variable effect of glucocorticoid treatment led us to hypothesize that glucocorticoid receptor (GR) gene polymorphisms may affect glucocorticoid sensitivity in CF and, consequently, may contribute to variations in the inflammatory response.

Methods

We evaluated the association between four GR gene polymorphisms, TthIII, ER22/23EK, N363S and BclI, and disease progression in a cohort of 255 young patients with CF. Genotypes were tested for association with changes in lung function tests, infection with Pseudomonas aeruginosa and nutritional status by multivariable analysis.

Results

A significant non-corrected for multiple tests association was found between BclI genotypes and decline in lung function measured as the forced expiratory volume in one second (FEV₁) and the forced vital capacity (FVC). Deterioration in FEV₁ and FVC was more pronounced in patients with the BclI GG genotype compared to the group of patients with BclI CG and CC genotypes (p = 0.02 and p = 0.04 respectively for the entire cohort and p = 0.01 and p = 0.02 respectively for F508del homozygous patients).

Conclusion

The BclI polymorphism may modulate the inflammatory burden in the CF lung and in this way influence progression of lung function.

Animal models of asthma

Animal models of asthma are a tool that allows studies to be conducted in the setting of an intact immune and respiratory system. These models have highlighted the importance of T-helper type 2 driven allergic responses in the progression of asthma and have been useful in the identification of potential drug targets for interventions involving allergic pathways. However, a number of drugs that have been shown to have some efficacy in animal models of asthma have shown little clinical benefit in human asthmatics. This may be due to a number of factors including the species of animal chosen and the methods used to induce an asthmatic phenotype in animals that do not normally develop a disease that could be characterized as asthma. The range of animal models available is vast, with the most popular models being rodents (inbred mice and rats) and guinea-pigs, which have the benefit of being easy to handle and being relatively cost effective compared with other models that are available. The recent advances in transgenic technology and the development of species-specific probes, particularly in mice, have allowed detailed mechanistic studies to be conducted. Despite these advances in technology, there are a number of issues with current animal models of asthma that must be recognized including the disparity in immunology and anatomy between these species and humans, the requirement for adjuvant during senitization in most models, the acute nature of the allergic response that is induced and the use of adult animals as the primary disease model. Some larger animal models using sheep and dogs have been developed that may address some of these issues but they also have different biology from humans in many ways and are extremely costly, with very few probes available for characterizing allergic responses in the airway in these species. As research in this area continues to expand, the relative merits and limitations of each model must be defined and understood in order to evaluate the information that is obtained from these models and to extrapolate these findings to humans so that effective drug therapies can be developed. Despite these issues, animal models have been, and will continue to be, vital in understanding the mechanisms that are involved in the development and progression of asthma.

Dexamethasone modulates ErbB tyrosine kinase expression and signaling through multiple and redundant mechanisms in cultured rat hepatocytes

Glucocorticoids paradoxically exert both stimulatory and inhibitory effects on the proliferation of cultured rat hepatocytes. We studied the effects of dexamethasone, a synthetic glucocorticoid, on the proliferation of cultured rat hepatocytes. The timing of growth factor addition modified the action of high-dose dexamethasone (10(-6) M) on DNA synthesis. When we added transforming growth factor-alpha at the time of plating, 10(-6) M dexamethasone weakly stimulated DNA synthesis by 26% relative to cells cultured in dexamethasone-free media. When we delayed growth factor addition until 24-48 h after plating, 10(-6) M dexamethasone inhibited DNA synthesis by 50%. Using immunological methods, we analyzed the expression and signaling patterns of the ErbB kinases in dexamethasone-treated cells. High-dose dexamethasone stabilized the expression of epidermal growth factor receptor (EGFr) and ErbB3, and it suppressed the de novo expression of ErbB2 that occurs during the third and fourth day of culture in 10(-8) M dexamethasone. High-dose dexamethasone by 72 h suppressed basal and EGF-associated phosphorylation of ERK and Akt. The reduction in ERK1/2 phosphorylation correlated with suppression of a culture-dependent increase in Son-of sevenless 1 (Sos1) and ERK1/2 expression. High-dose dexamethasone in hepatocytes stabilized or upregulated several inhibitory effectors of EGFr/ErbB2 and ERK, including receptor-associated late transducer (RALT) and MKP-1, respectively. Thus 10(-6) M dexamethasone exerts a time-dependent and redundant inhibitory effect on EGFr-mediated proliferative signaling in hepatocytes, targeting not only the ErbB proteins but also their various positive and negative effectors.

Asthma therapy and airway remodeling

Asthma is characterized by variable degrees of chronic inflammation and structural alterations in the airways. The most prominent abnormalities include epithelial denudation, goblet cell metaplasia, subepithelial thickening, increased airway smooth muscle mass, bronchial gland enlargement, angiogenesis, and alterations in extracellular matrix components, involving large and small airways. Chronic inflammation is thought to initiate and perpetuate cycles of tissue injury and repair in asthma, although remodeling may also occur in parallel with inflammation. In the absence of definite evidence on how different remodeling features affect lung function in asthma, the working hypothesis should be that structural alterations can lead to the development of persistent airway hyperresponsiveness and fixed airway obstruction. It is still unanswered whether and when to begin treating patients with asthma to prevent or reverse deleterious remodeling, which components of remodeling to target, and how to monitor remodeling. Consequently, efforts are being made to understand better the effects of conventional anti-inflammatory therapies, such as glucocorticosteroids, on airway structural changes. Animal models, in vitro studies, and some clinical studies have advanced present knowledge on the cellular and molecular pathways involved in airway remodeling. This has encouraged the development of biologicals aimed to target various components of airway remodeling. Progress in this area requires the explicit linking of modern structure-function analysis with innovative biopharmaceutical approaches.

Inhibition of T-cell activation in vitro in human peripheral blood mononuclear cells by pimecrolimus and glucocorticosteroids and combinations thereof

Pimecrolimus is an ascomycin macrolactam derivative that has been recently approved for the topical treatment of atopic dermatitis. In this study we report for the first time on a direct comparison of the inhibitory activity of pimecrolimus and the glucocorticosteroids betamethasone 17-valerate, dexamethasone and hydrocortisone at the level of T-cell proliferation and cytokine production. Stimulated human peripheral blood mononuclear cell (PBMC) systems were used that are either sensitive or resistant to calcineurin inhibitors or glucocorticosteroids. Pimecrolimus and the glucocorticosteroids inhibited dose-dependently T-cell proliferation and cytokine production in a sensitive system (anti-CD3 mAb-stimulated PBMC) with the following rank order of potency: pimecrolimus approximately betamethasone 17-valerate approximately dexamethasone > hydrocortisone. In resistant systems (anti-CD3 plus anti-CD28- or Staphylococcal enterotoxin B-stimulated PBMC), pimecrolimus or the glucocorticosteroids alone exerted either no effect, or only a partial inhibitory effect. However, combinations of pimecrolimus with a glucocorticosteroid synergistically and strongly inhibited T-cell proliferation. Taken together, the data indicate that medium potency glucocorticosteroids, such as betamethasone 17-valerate and dexamethasone, are as potent T-cell inhibitors as pimecrolimus. Furthermore, the experimental evidence suggests that combinations of glucocorticosteroids and pimecrolimus could be used clinically to achieve superior therapeutic efficacy, when monotherapy with the individual agents is unsatisfactory.

Expression profiling in vivo demonstrates rapid changes in lung microRNA levels following lipopolysaccharide-induced inflammation but not in the anti-inflammatory action of glucocorticoids

Background

At present, nothing is known of the role of miRNAs in the immune response in vivo despite the fact that inflammation is thought to underlie multiple acute and chronic diseases. In these circumstances, patients are commonly treated with corticosteroids such as dexamethasone.

Results

To address this question, we have examined the differential expression of 104 miRNAs using real-time PCR during the innate immune response in mouse lung following exposure to aerosilised lipopolysaccharide (LPS). Following challenge, we observed rapid and transient increase in both the mean (4.3-fold) and individual levels of miRNA expression (46 miRNAs) which peaked at 3 hrs. Crucially, this increase was correlated with a reduction in the expression of tumour necrosis factor (TNF)-α, keratinocyte-derived chemokine (KC) and macrophage inflammatory protein (MIP)-2, suggesting a potential role for miRNAs in the regulation of inflammatory cytokine production. Examination of the individual miRNA expression profiles showed time dependent increases in miR-21, -25, -27b, -100, 140, -142-3p, -181c, 187, -194, -214, -223 and -224. Corticosteroid studies showed that pre-treatment with dexamethasone at concentrations that inhibited TNF-α production, had no effect either alone or upon the LPS-induced miRNA expression profile.

Conclusion

We have shown that the LPS-induced innate immune response is associated with widespread, rapid and transient increases in miRNA expression in the mouse lung and we speculate that these changes might be involved in the regulation of the inflammatory response. In contrast, the lack of effect of dexamethasone in either control or challenged animals implies that the actions of glucocorticoids per se are not mediated through changes in miRNAs expression and that LPS-induced increases in miRNA expression are not mediated via classical inflammatory transcription factors.

Expression profiling of Dexamethasone-treated primary chondrocytes identifies targets of glucocorticoid signalling in endochondral bone development

Background

Glucocorticoids (GCs) are widely used anti-inflammatory drugs. While useful in clinical practice, patients taking GCs often suffer from skeletal side effects including growth retardation in children and adolescents, and decreased bone quality in adults. On a physiological level, GCs have been implicated in the regulation of chondrogenesis and osteoblast differentiation, as well as maintaining homeostasis in cartilage and bone. We identified the glucocorticoid receptor (GR) as a potential regulator of chondrocyte hypertrophy in a microarray screen of primary limb bud mesenchyme micromass cultures. Some targets of GC regulation in chondrogenesis are known, but the global effects of pharmacological GC doses on chondrocyte gene expression have not been comprehensively evaluated.

Results

This study systematically identifies a spectrum of GC target genes in embryonic growth plate chondrocytes treated with a synthetic GR agonist, dexamethasone (DEX), at 6 and 24 hrs. Conventional analysis of this data set and gene set enrichment analysis (GSEA) was performed. Transcripts associated with metabolism were enriched in the DEX condition along with extracellular matrix genes. In contrast, a subset of growth factors and cytokines were negatively correlated with DEX treatment. Comparing DEX-induced gene expression data to developmental changes in gene expression in micromass cultures revealed an additional layer of complexity in which DEX maintains the expression of certain chondrocyte marker genes while inhibiting factors that promote vascularization and ultimately ossification of the cartilaginous template.

Conclusion

Together, these results provide insight into the mechanisms and major molecular classes functioning downstream of DEX in primary chondrocytes. In addition, comparison of our data with microarray studies of DEX treatment in other cell types demonstrated that the majority of DEX effects are tissue-specific. This study provides novel insights into the effects of pharmacological GC on chondrocyte gene transcription and establishes the foundation for subsequent functional studies.

Expression of interleukin-17F in a mouse model of allergic asthma

BACKGROUND

Interleukin (IL)-17F is a recently discovered cytokine and is derived from a panel of limited cell types, such as activated CD4+ T cells, basophils, and mast cells. IL-17F is known to induce several cytokines and chemokines. However, its involvement in airway inflammation has not been well understood. To this end, the expression of IL-17F and the inhibitory effects of glucocorticoids on its expression in a mouse model of asthma were examined.

METHODS

Five-week-old BALB/c male mice were sensitized by intraperitoneal injection (i.p.) of ovalbumin (OVA) with alum, and challenged by daily inhalation of aerosolized 1% OVA. 24 h after last challenge (OVA/OVA), the expression of IL-17F was examined in lung tissues by immunohistochemistry and reverse-transcription polymerase chain reaction. Control mice were sensitized and challenged with saline (Sham/Sham). In addition, a group OF OVA-sensitized mice received i.p. injection of water-soluble dexamethasone (DEX) in saline 1 h before ova challenge (OVA/DEX).

RESULTS

In sham-challenged mice, IL-17F was not expressed in the lungs, while, in contrast, IL-17F was predominantly expressed in bronchial epithelial cells in addition to the infiltrating inflammatory cells in OVA/OVA mice. Further, the expression of IL-17 F was significantly attenuated by the treatment of mice with DEX.

CONCLUSION

These results suggest that bronchial epithelium-derived IL-17F may represent a new pharmacological target for glucocorticoids and may play a role in allergic asthma.

Histone deacetylase inhibitors suppress natural killer cell cytolytic activity

Treatment of transformed cells from leukemia or solid tumors with histone deacetylase inhibitors (HDACi) was shown to increase their sensitivity to NK cell lysis. In this study, treatment of IL-2-activated NK cells with HDACi including suberoylanilide hydroxamic acid and valproic acid was studied. Both drugs at therapeutic concentrations inhibited NK cell cytotoxicity on human leukemic cells. This inhibition was associated with decreased expression and function of NK cell activating receptors NKp46 and NKp30 as well as impaired granule exocytosis. NFkappaB activation in IL-2-activated NK cells was inhibited by both HDACi. Pharmacologic inhibition of NFkappaB activity resulted in similar effects on NK cell activity like those observed for HDACi. These results demonstrate for the first time that HDACi prevent NK cytotoxicity by downregulation of NK cell activating receptors probably through the inhibition of NFkappaB activation.

Receptor regulation in neuroendocrine-immune communication: current knowledge and future perspectives

Immune cells express receptors for every hormone or neurotransmitter we know so far. The neuroendocrine system signals to the immune system via the release of hormones and neurotransmitters that regulate cellular activity via these receptors. Much attention has been focused on the effect of glucocorticoids and catecholamines on the immune system. Glucocorticoids communicate with immune cells via glucocorticoid receptors of which the activity itself changes during immune activation. Many neuroendocrine mediators are ligands for G-protein coupled receptors on immune cells. Cytokines, oxygen-radicals, and catecholamines can influence the responsiveness of G-protein coupled receptors via decreasing the intracellular level of so-called G-protein coupled receptor kinases, of which the subtype GRK2 is highly expressed in immune cells. Therefore, changes in only one kinase can modulate the sensitivity of many receptors. We describe here that sensitivity of neuroendocrine receptors on immune cells is constantly regulated by inflammatory processes or chronic stress, which implies that not only the activity of the neuroendocrine system determines communication but that the sensitivity of receptors is a major factor in determining the final immune response. Finally, consequences of alterations in GRK2 during (neuro)-inflammatory diseases are discussed.

Therapeutic doses of glucocorticoids: implications for oral medicine

Glucocorticoids can cause adverse systemic side-effects ranging from iatrogenic Cushing's syndrome during treatment, to hypothalamic-pituitary-adrenal axis suppression and clinically significant adrenal insufficiency when the agents are discontinued. While the oral route of administration is most often implicated, it is now becoming more apparent that inhaled and topical administration also can cause these effects. Given the high therapeutic value of glucocorticoids, the ability to prescribe these agents while maintaining a low risk-to-benefit ratio for patients is critical. The aim of this review is to provide oral healthcare practitioners with a practical guide to commonly used glucocorticoids, their adverse effects, and perioperative use.

Regulation of inflammation and redox signaling by dietary polyphenols

Reactive oxygen species (ROS) play a key role in enhancing the inflammation through the activation of NF-kappaB and AP-1 transcription factors, and nuclear histone acetylation and deacetylation in various inflammatory diseases. Such undesired effects of oxidative stress have been found to be controlled by the antioxidant and/or anti-inflammatory effects of dietary polyphenols such as curcumin (diferuloylmethane, a principal component of turmeric) and resveratrol (a flavonoid found in red wine). The phenolic compounds in fruits, vegetables, tea and wine are mostly derivatives, and/or isomers of flavones, isoflavones, flavonols, catechins, tocopherols, and phenolic acids. Polyphenols modulate important cellular signaling processes such as cellular growth, differentiation and host of other cellular features. In addition, they modulate NF-kappaB activation, chromatin structure, glutathione biosynthesis, nuclear redox factor (Nrf2) activation, scavenge effect of ROS directly or via glutathione peroxidase activity and as a consequence regulate inflammatory genes in macrophages and lung epithelial cells. However, recent data suggest that dietary polyphenols can work as modifiers of signal transduction pathways to elicit their beneficial effects. The effects of polyphenols however, have been reported to be more pronounced in vitro using high concentrations which are not physiological in vivo. This commentary discusses the recent data on dietary polyphenols in the control of signaling and inflammation particularly during oxidative stress, their metabolism and bioavailability.

Effects of TGF-β and glucocorticoids on map kinase phosphorylation, IL-6/IL-11 secretion and cell proliferation in primary cultures of human lung fibroblasts

Transforming growth factor-beta1 (TGF-beta1) is crucially involved in the fibrotic events characterizing interstitial lung diseases (ILDs), as well as in the airway remodeling process typical of asthma. Within such a context, the aim of our study was to investigate, in primary cultures of normal and fibrotic human lung fibroblasts (HLFs), the effects of TGF-beta1 on mitogen-activated protein kinase (MAPK) phosphorylation, cell proliferation, and production of interleukins 6 (IL-6) and 11 (IL-11), in the presence or absence of a pretreatment with budesonide (BUD). MAPK phosphorylation was detected by Western blotting, cell viability and proliferation were evaluated using Trypan blue staining and [(3)H]-thymidine incorporation assay, respectively, and the release of IL-6 and IL-11 into cell culture supernatants was assessed by ELISA. TGF-beta1 (10 ng/ml) significantly stimulated MAPK phosphorylation (P < 0.01), and also enhanced cell proliferation as well as the secretion of both IL-6 and IL-11, which reached the highest increases at the 72nd h of cell exposure to this growth factor. All such effects were prevented by BUD (10(-8) M) and, with the exception of IL-6 release, also by a mixture of MAPK inhibitors. Therefore, our findings suggest that the fibrotic action exerted by TGF-beta1 in the lung is mediated at least in part by MAPK activation and by an increased synthesis of the profibrogenic cytokines IL-6 and IL-11; all these effects appear to be prevented by corticosteroids via inhibition of MAPK phosphorylation.

Novel signal transduction modulators for the treatment of airway diseases

Multiple signal transduction pathways are involved in the inflammatory process in the airways of patients with asthma and chronic obstructive pulmonary disease (COPD), hence modulators of these pathways may result in novel anti-inflammatory treatments. The advantage of this approach is that these pathways are activated in many inflammatory and structural cells of the airways, hence a broad spectrum of anti-inflammatory effects may be possible. However, this also makes it more likely that side effects may be limiting, but this may not be a problem if the signal transduction pathway is selectively activated in disease and the therapeutic index may be increased by inhaled delivery. Phosphodiesterase-4 (PDE4) inhibitors are the most advanced treatment in this category as anti-inflammatory treatment for asthma and COPD, although side effects are dose limiting. Other promising approaches are inhibitors of p38 mitogen-activated protein (MAP) kinase, inhibitor of nuclear factor-kappaB kinase-2 (IKK2), and Syk kinase, all of which are in clinical development. Several other kinases and transcription factors are also targets for novel drug development. It is likely that modulators of signal transduction pathways may lead to the development of several novel anti-inflammatory treatments for asthma and COPD in the future.