Effects of glucocorticoids on activation of c-jun N-terminal, extracellular signal-regulated, and p38 MAP kinases in human pulmonary endothelial cells

Role of Endothelial Glucocorticoid Receptor in the Pathogenesis of Kidney Diseases

Glucocorticoids, as multifunctional hormones, are widely used in the treatment of various diseases including nephrological disorders. They are known to affect immunological cells, effectively treating many autoimmune and inflammatory processes. Furthermore, there is a growing body of evidence demonstrating the potent role of glucocorticoids in non-immune cells such as podocytes. Moreover, novel data show additional pathways and processes affected by glucocorticoids, such as the Wnt pathway or autophagy. The endothelium is currently considered as a key organ in the regulation of numerous kidney functions such as glomerular filtration, vascular tone and the regulation of inflammation and coagulation. In this review, we analyse the literature concerning the effects of endothelial glucocorticoid receptor signalling on kidney function in health and disease, with special focus on hypertension, diabetic kidney disease, glomerulopathies and chronic kidney disease. Recent studies demonstrate the potential role of endothelial GR in the prevention of fibrosis of kidney tissue and cell metabolism through Wnt pathways, which could have a protective effect against disease progression. Another important aspect covered in this review is blood pressure regulation though GR and eNOS. We also briefly cover potential therapies that might affect the endothelial glucocorticoid receptor and its possible clinical implications, with special interest in selective or local GR stimulation and potential mitigation of GC treatment side effects.

Plasmodium berghei NK65 in Combination with IFN-γ Induces Endothelial Glucocorticoid Resistance via Sustained Activation of p38 and JNK

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is an often lethal complication of malaria. Currently, no adequate therapy for this syndrome exists. Although glucocorticoids (GCs) have been used to improve clinical outcome of ARDS, their therapeutic benefits remain unclear. We previously developed a mouse model of MA-ARDS, in which dexamethasone treatment revealed GC resistance. In the present study, we investigated GC sensitivity of mouse microvascular lung endothelial cells stimulated with interferon-γ (IFN-γ) and Plasmodium berghei NK65 (PbNK65). Upon challenge with IFN-γ alone, dexamethasone inhibited the expression of CCL5 (RANTES) by 90% and both CCL2 (MCP-1) and CXCL10 (IP-10) by 50%. Accordingly, whole transcriptome analysis revealed that dexamethasone differentially affected several gene clusters and in particular inhibited a large cluster of IFN-γ-induced genes, including chemokines. In contrast, combined stimulation with IFN-γ and PbNK65 extract impaired inhibitory actions of GCs on chemokine release, without affecting the capacity of the GC receptor to accumulate in the nucleus. Subsequently, we investigated the effects of GCs on two signaling pathways activated by IFN-γ. Dexamethasone left phosphorylation and protein levels of signal transducer and activator of transcription 1 (STAT1) unhampered. In contrast, dexamethasone inhibited the IFN-γ-induced activation of two mitogen-activated protein kinases (MAPK), JNK, and p38. However, PbNK65 extract abolished the inhibitory effects of GCs on MAPK signaling, inducing GC resistance. These data provide novel insights into the mechanisms of GC actions in endothelial cells and show how malaria may impair the beneficial effects of GCs.

Long-term treatment in pediatric asthma: an update on chemical pharmacotherapy

INTRODUCTION

Asthma is the most common chronic disease in childhood, affecting approximately 10% of all children, and is the leading cause of hospitalization in developed countries. In this paper we aimed to review the evidence on chemical pharmacotherapy for long-term treatment of pediatric asthma, according to the latest updates. Area covered: Long-term treatment, essential for controlling symptoms and reducing future risks including exacerbations and decline in lung function, includes control agents such as inhaled corticosteroids, long-acting beta2-adrenergic agonists, and leukotriene modifiers. More recent strategies based on the use of a biological drug such as omalizumab, which is a monoclonal antibody directed against immunoglobulin E (IgE), can be considered in selected patients with severe asthma. Expert opinion: In the near future, the challenge of childhood asthma treatment will be to improve the chemical drugs that already exist as well as to carefully characterize the several different asthma subtypes, with special regard to children with severe disease. A better definition of patient features, made possible by the current advanced knowledge of the pathobiology of severe asthma, can ultimately allow the identification of specific phenotypes and endotypes of severe asthma, aimed to personalize pharmacological treatment.

The MEK/ERK pathway is the primary conduit for Borrelia burgdorferi-induced inflammation and P53-mediated apoptosis in oligodendrocytes

Lyme neuroborreliosis (LNB) affects both the central and peripheral nervous systems. In a rhesus macaque model of LNB we had previously shown that brains of rhesus macaques inoculated with Borrelia burgdorferi release inflammatory mediators, and undergo oligodendrocyte and neuronal cell death. In vitro analysis of this phenomenon indicated that while B. burgdorferi can induce inflammation and apoptosis of oligodendrocytes per se, microglia are required for neuronal apoptosis. We hypothesized that the inflammatory milieu elicited by the bacterium in microglia or oligodendrocytes contributes to the apoptosis of neurons and glial cells, respectively, and that downstream signaling events in NFkB and/or MAPK pathways play a role in these phenotypes. To test these hypotheses in oligodendrocytes, several pathway inhibitors were used to determine their effect on inflammation and apoptosis, as induced by B. burgdorferi. In a human oligodendrocyte cell line (MO3.13), inhibition of the ERK pathway in the presence of B. burgdorferi markedly reduced inflammation, followed by the JNK, p38 and NFkB pathway inhibition. In addition to eliciting inflammation, B. burgdorferi also increased total p53 protein levels, and suppression of the ERK pathway mitigated this effect. While inhibition of p53 had a minimal effect in reducing inflammation, suppression of the ERK pathway or p53 reduced apoptosis as measured by active caspase-3 activity and the TUNEL assay. A similar result was seen in primary human oligodendrocytes wherein suppression of ERK or p53 reduced apoptosis. It is possible that inflammation and apoptosis in oligodendrocytes are divergent arms of MAPK pathways, particularly the MEK/ERK pathway.

Glucocorticoids inhibit GATA-3 phosphorylation and activity in T cells

Glucocorticoid (GC) immunosuppression and anti-inflammatory action involve the regulation of several transcription factors (TFs). GCs inhibit the acute production of T-helper (Th) 1 and Th2 cytokines but ultimately favor a shift toward Th2 phenotype. GCs inhibit the transcriptional activity of T-bet Th1 TF by a transrepression mechanism. Here we analyze GC regulation of GATA-3, the master driver of Th2 differentiation. We found that GCs inhibit GATA-3 transcriptional activity. We demonstrate that this mechanism does not involve physical interaction between the glucocorticoid receptor (GR) and GATA-3 or reduction of GATA-3 binding to DNA, as described previously for T-bet. Instead, GCs inhibit GATA-3 activity by inhibition of p38 mitogen-activated protein kinase induced GATA-3 phosphorylation. GCs also inhibit GATA-3 mRNA and protein expression. Finally, GATA-3 inhibition affects the interleukin-5 gene, a central Th2 cytokine. The IC(50) of dexamethasone is 10 nM with a maximum effect at 100 nM. All inhibitory actions were blocked by the GR antagonist RU38486 (1 uM), proving the specificity of GR action. In view of the crucial role of GATA-3 in T-cell differentiation and inflammation, we propose that the mechanism of GATA-3 inhibition compared with that in T-bet may have relevant implications in understanding and modulating the anti-inflammatory and Th-regulatory properties of GCs.

Host immune responses to rhinovirus: mechanisms in asthma

Viral respiratory infections can have a profound effect on many aspects of asthma including its inception, exacerbations, and, possibly, severity. Of the many viral respiratory infections that influence asthma, the common cold virus, rhinovirus, has emerged as the most frequent illness associated with exacerbations and other aspects of asthma. The mechanisms by which rhinovirus influences asthma are not fully established, but current evidence indicates that the immune response to this virus is critical in this process. Many airway cell types are involved in the immune response to rhinovirus, but most important are respiratory epithelial cells and possibly macrophages. Infection of epithelial cells generates a variety of proinflammatory mediators to attract inflammatory cells to the airway with a subsequent worsening of underlying disease. Furthermore, there is evidence that the epithelial airway antiviral response to rhinovirus may be defective in asthma. Therefore, understanding the immune response to rhinovirus is a key step in defining mechanisms of asthma, exacerbations, and, perhaps most importantly, improved treatment.

Dexamethasone-induced expression of endothelial mitogen-activated protein kinase phosphatase-1 involves activation of the transcription factors activator protein-1 and 3',5'-cyclic adenosine 5'-monophosphate response element-binding protein and the generation of reactive oxygen species

We have recently identified the MAPK phosphatase (MKP)-1 as a novel mediator of the antiinflammatory properties of glucocorticoids (dexamethasone) in the human endothelium. However, nothing is as yet known about the signaling pathways responsible for the up-regulation of MKP-1 by dexamethasone in endothelial cells. Knowledge of the molecular basis of this new alternative way of glucocorticoid action could facilitate the identification of new antiinflammatory drug targets. Thus, the aim of our study was to elucidate the underlying molecular mechanisms. Using Western blot analysis, we found that dexamethasone rapidly activates ERK, c-jun N-terminal kinase (JNK), and p38 MAPK in human umbilical vein endothelial cells. By applying the kinase inhibitors PD98059 (MAPK kinase-1) and SP600125 (JNK), ERK and JNK were shown to be crucial for the induction of MKP-1. Using EMSA and a decoy oligonucleotide approach, the transcription factors activator protein-1 (activated by ERK and JNK) and cAMP response element-binding protein (activated by ERK) were found to be involved in the up-regulation of MKP-1 by dexamethasone. Interestingly, dexamethasone induces the generation of reactive oxygen species (measured by dihydrofluorescein assay), which participate in the signaling process by triggering JNK activation. Our work elucidates a novel alternative mechanism for transducing antiinflammatory effects of glucocorticoids in the human endothelium. Thus, our study adds valuable information to the efforts made to find new antiinflammatory principles utilized by glucocorticoids. This might help to gain new therapeutic options to limit glucocorticoid side effects and to overcome resistance.

MAPK phosphatase-1 represents a novel anti-inflammatory target of glucocorticoids in the human endothelium

Glucocorticoids are well-established anti-inflammatory drugs thought to mainly act by inhibition of proinflammatory transcription factors like NF-kappaB. In recent years, however, transcription factor-independent mechanisms of glucocorticoid action have been proposed, namely the influence on MAPK pathways. Here we identify MAPK phosphatase-1 (MKP-1) as a pivotal mediator of the anti-inflammatory action of glucocorticoids in the human endothelium. We applied dexamethasone (Dex) to TNF-alpha-activated human endothelial cells and used the adhesion molecule E-selectin as inflammatory read-out parameter. Dex is known to reduce the expression of E-selectin, which is largely regulated by NF-kappaB. Here, we communicate that Dex at low concentrations (1-100 nM) markedly attenuates E-selectin expression without affecting NF-kappaB. Importantly, Dex is able to increase the expression of MKP-1, which causes an inactivation of TNF-alpha-induced p38 MAPK and mediates inhibition of E-selectin expression. In endothelial MKP-1(-/-) cells differentiated from MKP-1(-/-) embryonic stem cells and in MKP-1-silenced human endothelial cells, Dex did not inhibit TNF-alpha-evoked E-selectin expression. Thus, our findings introduce MKP-1 as a novel and crucial mediator of the anti-inflammatory action of glucocorticoids at low concentrations in the human endothelium and highlight MKP-1 as an important and promising anti-inflammatory drug target.

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.

Stimulus-dependent glucocorticoid-resistance of GM-CSF production in human cultured airway smooth muscle

For a subpopulation of asthmatics, symptoms persist even with high doses of glucocorticoids. Glucocorticoids reduce the levels of the proinflammatory and fibrogenic cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF) produced by human cultured airway smooth muscle (ASM). We have contrasted the effects of a synthetic glucocorticoid, dexamethasone, on thrombin- and IL-1alpha-stimulated GM-CSF production in human ASM cells. Although IL-1alpha stimulated three-fold higher levels of GM-CSF mRNA and protein compared to thrombin, dexamethasone concentration-dependently reduced IL-1alpha-stimulated GM-CSF more potently and to a greater extent than the response to thrombin. This pattern of glucocorticoid regulation was also observed at the GM-CSF mRNA level and was reproduced with other glucocorticoids such as fluticasone propionate. IL-1alpha and thrombin stimulated NF-kappa B-dependent luciferase expression equally. Dexamethasone treatment reduced luciferase expression stimulated by both IL-1alpha and thrombin. The GM-CSF mRNA half life was markedly prolonged by IL-1alpha compared to thrombin. This IL-1alpha-induced GM-CSF mRNA stability was prevented by either dexamethasone or the p38(MAPK) inhibitor, SB203580, neither of which influenced GM-CSF mRNA stability in thrombin-treated cells. Dexamethasone inhibited p38(MAPK) phosphorylation in IL-1alpha-stimulated ASM, whereas thrombin does not stimulate p38(MAPK) phosphorylation. These data suggest that the mechanism underlying the greater potency and efficacy of glucocorticoids in reducing GM-CSF synthesis stimulated by IL-1alpha depends on inhibition of the involvement of p38(MAPK)-induced increases in GM-CSF message stability.

Mitogen-activated protein kinases and asthma

Mitogen-activated protein kinases (MAPKs) are evolutionary conserved enzymes which play a key role in signal transduction mediated by cytokines, growth factors, neurotransmitters and various types of environmental stresses. In the airways, these extracellular stimuli elicit complex inflammatory and structural changes leading to the typical features of asthma including T cell activation, eosinophil and mast cell infiltration, as well as bronchial hyperresponsiveness and airway remodelling. Because MAPKs represent an important point of convergence for several different signalling pathways, they affect multiple aspects of normal airway function and also significantly contribute to asthma pathophysiology. Therefore, this review focuses on the crucial involvement of MAPKs in asthma pathogenesis, thus also discussing their emerging role as molecular targets for anti-asthma drugs.

IL-1beta induces IL-8 in bronchial cells via NF-kappaB and NF-IL6 transcription factors and can be suppressed by glucocorticoids

IL-1beta may contribute to airway inflammation by inducing pro-inflammatory cytokines and chemokines from bronchial epithelial cells. In the current study, we investigated the cis-acting sites within the IL-8 promoter, and signalling pathways important in IL-8 production from BEAS2B cells following IL-1beta stimulation. IL-1beta treatment (0.1-10 ng/mL) upregulated IL-8 protein production in a dose dependent manner and IL-8 mRNA in a time dependent manner. IL-1beta induced upregulation of IL-8 promoter-reporter constructs, indicating that the mechanism of upregulation was pre-transcriptional. Using IL-8 promoter constructs with mutated cis-acting sites, it was found that both the NF-kappaB and NF-IL6 sites together were required for IL-8 promoter induction following IL-1beta treatment. Using chemical inhibitors or dominant negative mutants, we found that IL-8 promoter activity required IkappaB kinase beta, IkappaB, but not the MAP kinases p38 or c-Jun N-terminal kinase 2. Fluticasone propionate was able to suppress IL-1beta induced IL-8 protein and promoter activation, using both a -1481 bp fragment and a -133 bp fragment, indicating that the glucocorticoid response element found at -330 bp was not required for fluticasone mediated suppression of IL-8 promoter activation.

Potential genetic influences on the response to asthma treatment

Genetic factors play a key role in determining the widely heterogeneous response to pharmacological treatment detectable among asthmatics. In particular, polymorphisms of the genes encoding relevant anti-asthma drug targets contribute significantly to such a variability. Therefore, it is very important to characterize asthmatic patient's genotypes and the related phenotypic patterns, in order to predict the individual therapeutic outcome. This pharmacogenetic approach will eventually help clinicians to optimize and personalize anti-asthma treatment, and will also provide useful information with regard to pre- and post-marketing evaluation of both effectiveness and side effects of newly introduced drugs.

Effects of cortisol on cardiac myocytes and on expression of cardiac genes in fetal sheep

In 17 fetal sheep aged 129 days, the effects of large-dose infusions of cortisol (72.1 mg/day for 2–3 days) on proliferation, binucleation, and hypertrophy of cardiac myocytes, cardiac expression of angiotensinogen, angiotensin receptor subtypes 1 and 2, Glut-1, glucocorticoid and mineralocorticoid receptors, proteins of the MAPK pathways and calcineurin were studied. Cortisol levels were 8.7 ± 2.3 nM (SE) in 8 control and 1,028 ± 189 nM in 9 treated fetuses ( P < 0.001). Cortisol had no effect on myocyte binucleation. Left ventricular free wall (LVFW) uni- and binucleated myocytes were larger in cortisol-treated fetuses ( P < 0.001, P < 0.05). Cortisol-treated fetuses had higher right ventricular free wall (RVFW) and LVFW angiotensinogen (Aogen) mRNA levels (treated: 2.30 ± 0.37, n = 8 and 2.05 ± 0.45, n = 7 vs. control: 0.94 ± 0.12, n = 8 and 0.67 ± 0.09, n = 7, P < 0.02). Levels of the glucose transporter Glut-1 mRNA were lower in the LVFW of treated fetuses (0.83 ± 0.23 vs. 1.47 ± 0.30 in control, P < 0.05, n = 7, 8). The higher the cortisol level, the greater the Aogen mRNA level (RVFW, r = 0.61, P < 0.01, n = 16; LVFW, r = 0.83, P < 0.0003, n = 14). There were no other changes in mRNA levels nor in levels of extracellular kinase, JNK, p38, their phosphorylated forms, and calcineurin. Thus high levels of cortisol such as occur after birth do not affect fetal cardiac myocyte binucleation or number but are associated with higher levels of ventricular Aogen mRNA, lower levels of Glut-1 mRNA, and hypertrophy of LVFW myocytes. These effects could impact on postnatal cardiac development.

Effects of hydrogen peroxide on MAPK activation, IL-8 production and cell viability in primary cultures of human bronchial epithelial cells

The airway epithelium is continuously exposed to inhaled oxidants, including airborne pollutants and cigarette smoke, which can exert harmful proinflammatory and cytotoxic effects. Therefore, the aim of our study was to investigate, in primary cultures of human bronchial epithelial cells (HBEC), the signal transduction pathways activated by increasing concentrations (0.25, 0.5, and 1 mM) of hydrogen peroxide (H(2)O(2)), as well as their effects on IL-8 production and cell viability. The reported results show that H(2)O(2) elicited, in a concentration-dependent fashion, a remarkable increase in phosphorylation-dependent activation of mitogen-activated protein kinases (MAPKs), associated with a significant induction of IL-8 synthesis and a dramatically enhanced cell death. Pre-treatment of HBEC with MAPK inhibitors was able to significantly inhibit the effects of H(2)O(2) on IL-8 secretion, and to effectively prevent cell death. Therefore, these findings suggest that MAPKs play a key role as molecular transducers of the airway epithelial injury triggered by oxidative stress, as well as potential pharmacologic targets for indirect antioxidant intervention.

Activation and cellular localization of the p38 and JNK MAPK pathways in rat crescentic glomerulonephritis

BACKGROUND

The p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) are intracellular signal transduction pathways involved in the production of inflammatory mediators. Little, however, is known about the contribution of these pathways to renal inflammation, nor the cell types in which these pathways are activated within normal and inflamed kidneys. The aim of this study was therefore to delineate the pattern and cellular localization of p38 and JNK activation in normal rat kidney and rat acute and chronic inflammatory renal disease.

METHODS

Normal male Sprague-Dawley rats and groups of rats given accelerated anti-glomerular basement membrane (GBM) disease were killed at 3 hours, day 1, day 7, or day 28 and examined for p38 and JNK pathway activation by Western blotting and immunolocalization of the phosphorylated p38 (p-p38) and JNK (p-JNK) kinases.

RESULTS

In terms of glomerular MAPK activation, Western blotting identified the presence of both p-p38 and p-JNK in normal glomeruli, localized by immunohistochemistry to podocytes and epithelial cells of Bowman's capsule. In anti-GBM disease, Western blotting showed that p38 activation peaked at 3 hours and remained elevated above normal throughout the disease time course. JNK activation (via the 54 kD isoform) likewise increased at 3 hours of anti-GBM disease and remained elevated throughout disease. At 3 hours, p-p38, but not p-JNK, was localized to neutrophils and glomerular endothelial cells. p-JNK was localized to glomerular endothelial cells at day 7. Macrophages, lymphocytes, activated podocytes, and myofibroblasts were positive for both p-p38 and p-JNK. In terms of tubular MAPK activation, Western blotting identified p38 and JNK activation in tubules of normal kidney. Immunostaining showed that most cortical tubules contained some p-p38 and p-JNK stained cells. There was a significant increase in tubular p38 activation at 3 hours of anti-GBM disease, followed by increased JNK activation of the 54 kD isoform from day 7 onward, and the 46 kD isoform at day 28. Immunostaining of diseased tissue localized p-p38 and p-JNK to virtually all cortical tubular cells.

CONCLUSION

The p38 and JNK MAPK pathways are activated in glomeruli and tubules of normal kidney. In acute anti-GBM disease, there was an increase in p38 activation within glomerular endothelial cells and within infiltrating neutrophils, suggesting an important role for p38 MAPK in acute inflammation. In progressive anti-GBM disease, p38 and JNK activation in podocytes, glomerular endothelial cells, infiltrating macrophages, T cells, and myofibroblasts suggests that both the p38 and JNK MAPK pathways are important in chronic inflammation and fibrosis. Blockade of these pathways may therefore be potentially therapeutic in the treatment of acute and chronic renal inflammation.

Transcription of stem cell factor (SCF) is potentiated by glucocorticoids and interleukin‐1β through concerted regulation of a GRE‐like and an NF‐κB response element

Expression of stem cell factor SCF, a major mast cell growth factor, is potentiated shortly after co-treatment with interleukin (IL)-1beta and glucocorticoids. SCF promoter contains a GRE-like sequence and a putative kappaB site. We assessed the mechanisms of the regulation of SCF transcription in human lung fibroblasts in culture. Chromatin immunoprecipitation showed that co-treatment with IL-1beta and the glucocorticoid budesonide increased the SCF promoter occupancy by NF-kappaB and GR, as compared with IL-1beta and budesonide alone. In reporter gene assays, IL-1beta time-dependently increased the promoter activity, which was abolished by either pre-treatment with the MAP kinase inhibitors PD98059 (MEK) and SB203580 (p38), pre-treatment with the NF-kappaB inhibitor PDTC, or deletion of the kappaB site. Budesonide time-dependently decreased the promoter activity, an effect requiring the GRE-like element. Co-treatment with IL-1beta and budesonide potentiated the promoter activity at 30 min, an effect blocked by PD98059 and SB203580, PDTC, or deletion of the kappaB or GRE-like element. In conclusion, the GRE-like sequence mediating the repression of SCF expression, thus acting as a negative-responsive element, is turned into a positive element in an NF-kappaB site-dependent manner, indicating a concerted action of these two regulatory elements in the potentiation of SCF gene expression.

Effects of transforming growth factor-[beta] and budesonide on mitogen-activated protein kinase activation and apoptosis in airway epithelial cells

Airway epithelial cells play a central role in the inflammatory, apoptotic, and remodeling processes associated with asthma. Within this context, a key function is exerted by transforming growth factor-beta (TGF-beta), whose biological effects are mediated at least in part by mitogen-activated protein kinases (MAPKs). The aim of our study was to investigate, in primary cultures of human bronchial epithelial cells (HBEC), the effects of TGF-beta (10 ng/ml) on both MAPK activation and apoptosis, in the presence or absence of a pretreatment with budesonide (10-8 M). MAPK activation was detected by Western blotting, using anti-phospho-MAPK monoclonal antibodies, which specifically recognize the phosphorylated, active forms of these enzymes. Apoptosis was assayed by caspase-3 activation and fluorescence microscopy, using annexin-V (An-V) and propidium iodide (PI) as markers of cell death. Our results show that TGF-beta induced a marked ( reverse similar 9-fold) increase in p38 MAPK phosphorylation, and also dramatically enhanced cell death, which was completely prevented by specific MAPK inhibitors. Both MAPK activation and apoptosis were effectively inhibited by budesonide (BUD), thereby suggesting that the powerful antiapoptotic action of inhaled glucocorticoids may be very important for their protective role against epithelial injury, which represents a key pathogenic event in asthma.

CX-659S, a diaminouracil derivative, indirectly inhibits the function of Langerhans cells by blocking the MEK1/2-Erk1/2 pathway in keratinocytes

Keratinocytes are an important component of the skin immune system, and keratinocyte-derived cytokines control the function of Langerhans cells. We previously showed that CX-659S, a novel diaminouracil derivative, had an inhibitory effect on hapten-induced contact hypersensitivity reaction in mice. In this study, we investigated the mechanism by which CX-659S elicits its inhibitory effect. CX-659S inhibited the expressions of CD80 and CD86, but not that of CD54, on Langerhans cells in epidermal cell suspensions. Exogenous granulocyte-macrophage colony-stimulating factor restored the CX-659S-induced inhibition of CD80 and CD86 expressions of Langerhans cells. The production of interleukin-2 from allogeneic T cells was also inhibited when the cells were stimulated with CX-659S-treated epidermal cells, and this inhibition was suppressed by the addition of granulocyte-macrophage colony-stimulating factor during CX-659S treatment. As CX-659S significantly inhibited production of granulocyte-macrophage colony-stimulating factor from keratinocytes, CX-659S was thought to indirectly affect Langerhans cells by inhibiting the function of keratinocytes. These effects of CX-659S were preceded by blockade of the phosphorylation of extracellular-signal-regulated kinase 1/2 and their direct activators, mitogen-activated protein kinase/extracellular-signal-regulated kinase 1/2 (MEK1/2), but not p38 mitogen-activated protein kinase or inhibitory nuclear factor kappaBalpha, in keratinocytes. Furthermore, a specific MEK1/2 inhibitor, U0126, mimicked the effect of CX-659S. CX-659S, a keratinocyte-response modifier, would be an effective therapeutic compound to inhibit contact hypersensitivity reaction, its action mechanism being different from those of other immunosuppressive agents such as glucocorticosteroids or cyclosporine A.

Molecular mechanisms of corticosteroid actions in chronic inflammatory airway diseases

Although corticosteroids have been used for a long time as a very effective therapy of airway inflammatory diseases such as asthma, only recently the molecular basis of their mechanism of action has begun to be elucidated. These hormones exert their biological and pharmacological actions by binding to cytoplasmic receptors that, upon activation, translocate to the nucleus where they interact with specific genomic sequences thus modulating gene expression. However, many glucocorticoid effects responsible for their anti-inflammatory and anti-asthmatic activity take place irrespectively of receptor binding to DNA. In particular, ligand-bound glucocorticoid receptors can repress several different pro-inflammatory genes by physically associating, via protein-protein interactions, with various transcription factors and with the macromolecular complexes implicated in regulation of chromatin structure and function. In this regard, an important role is played by the influences of corticosteroids on the intrinsic histone acetyltransferase and deacetylase functions of coactivators and corepressors, respectively. Furthermore, the signal transduction pathways mediated by mitogen-activated protein kinases are newly recognized, key targets of glucocorticoids. Indeed, these enzymatic cascades are crucially involved in the regulation of gene expression in that they are essential for the activity of a high number of transcription factors. Therefore, the recent advances made in such a rapidly growing research field are providing new insights into the mode of action of corticosteroids, thereby also unveiling novel promising therapeutic strategies directly targeted to the molecular events underlying the inflammatory, immune, and apoptotic processes implicated in the pathogenesis of asthma and other airway diseases.