Proteomic signatures of eosinophilic and neutrophilic asthma from serum and sputum

BACKGROUND

Eosinophilic and neutrophilic asthma defined by high levels of blood and sputum eosinophils and neutrophils exemplifies the inflammatory heterogeneity of asthma, particularly severe asthma. We analysed the serum and sputum proteome to identify biomarkers jointly associated with these different phenotypes.

METHODS

Proteomic profiles (N = 1129 proteins) were assayed in sputum (n = 182) and serum (n = 574) from two cohorts (U-BIOPRED and ADEPT) of mild-moderate and severe asthma by SOMAscan. Using least absolute shrinkage and selection operator (LASSO)-penalised logistic regression in a stability selection framework, we sought sparse sets of proteins associated with either eosinophilic or neutrophilic asthma with and without adjustment for established clinical factors including oral corticosteroid use and forced expiratory volume.

FINDINGS

We identified 13 serum proteins associated with eosinophilic asthma, including 7 (PAPP-A, TARC/CCL17, ALT/GPT, IgE, CCL28, CO8A1, and IL5-Rα) that were stably selected while adjusting for clinical factors yielding an AUC of 0.84 (95% CI: 0.83-0.84) compared to 0.62 (95% CI: 0.61-0.63) for clinical factors only. Sputum protein analysis selected only PAPP-A (AUC = 0.81 [95% CI: 0.80-0.81]). 12 serum proteins were associated with neutrophilic asthma, of which 5 (MMP-9, EDAR, GIIE/PLA2G2E, IL-1-R4/IL1RL1, and Elafin) complemented clinical factors increasing the AUC from 0.63 (95% CI: 0.58-0.67) for the model with clinical factors only to 0.89 (95% CI: 0.89-0.90). Our model did not select any sputum proteins associated with neutrophilic status.

INTERPRETATION

Targeted serum proteomic profiles are a non-invasive and scalable approach for subtyping of neutrophilic and eosinophilic asthma and for future functional understanding of these phenotypes.

FUNDING

U-BIOPRED has received funding from the Innovative Medicines Initiative (IMI) Joint Undertaking under grant agreement no. 115010, resources of which are composed of financial contributions from the European Union's Seventh Framework Programme (FP7/2007-2013), and European Federation of Pharmaceutical Industries and Associations (EFPIA) companies' in-kind contributions (www.imi.europa.eu). ADEPT was funded by Johnson & Johnson/Janssen pharmaceutical Company.

Role of DCLK1/Hippo pathway in type II alveolar epithelial cells differentiation in acute respiratory distress syndrome

BACKGROUND

Delay in type II alveolar epithelial cell (AECII) regeneration has been linked to higher mortality in patients with acute respiratory distress syndrome (ARDS). However, the interaction between Doublecortin-like kinase 1 (DCLK1) and the Hippo signaling pathway in ARDS-associated AECII differentiation remains unclear. Therefore, the objective of this study was to understand the role of the DCLK1/Hippo pathway in mediating AECII differentiation in ARDS.

MATERIALS AND METHODS

AECII MLE-12 cells were exposed to 0, 0.1, or 1 μg/mL of lipopolysaccharide (LPS) for 6 and 12 h. In the mouse model, C57BL/6JNarl mice were intratracheally (i.t.) injected with 0 (control) or 5 mg/kg LPS and were euthanized for lung collection on days 3 and 7.

RESULTS

We found that LPS induced AECII markers of differentiation by reducing surfactant protein C (SPC) and p53 while increasing T1α (podoplanin) and E-cadherin at 12 h. Concurrently, nuclear YAP dynamic regulation and increased TAZ levels were observed in LPS-exposed AECII within 12 h. Inhibition of YAP consistently decreased cell levels of SPC, claudin 4 (CLDN-4), galectin 3 (LGALS-3), and p53 while increasing transepithelial electrical resistance (TEER) at 6 h. Furthermore, DCLK1 expression was reduced in isolated human AECII of ARDS, consistent with the results in LPS-exposed AECII at 6 h and mouse SPC-positive (SPC+) cells after 3-day LPS exposure. We observed that downregulated DCLK1 increased p-YAP/YAP, while DCLK1 overexpression slightly reduced p-YAP/YAP, indicating an association between DCLK1 and Hippo-YAP pathway.

CONCLUSIONS

We conclude that DCLK1-mediated Hippo signaling components of YAP/TAZ regulated markers of AECII-to-AECI differentiation in an LPS-induced ARDS model.

SARS-CoV2 in public spaces in West London, UK during COVID-19 pandemic

BACKGROUND

Spread of SARS-CoV2 by aerosol is considered an important mode of transmission over distances >2 m, particularly indoors.

OBJECTIVES

We determined whether SARS-CoV2 could be detected in the air of enclosed/semi-enclosed public spaces.

METHODS AND ANALYSIS

Between March 2021 and December 2021 during the easing of COVID-19 pandemic restrictions after a period of lockdown, we used total suspended and size-segregated particulate matter (PM) samplers for the detection of SARS-CoV2 in hospitals wards and waiting areas, on public transport, in a university campus and in a primary school in West London.

RESULTS

We collected 207 samples, of which 20 (9.7%) were positive for SARS-CoV2 using quantitative PCR. Positive samples were collected from hospital patient waiting areas, from hospital wards treating patients with COVID-19 using stationary samplers and from train carriages in London underground using personal samplers. Mean virus concentrations varied between 429 500 copies/m³ in the hospital emergency waiting area and the more frequent 164 000 copies/m³ found in other areas. There were more frequent positive samples from PM samplers in the PM2.5 fractions compared with PM10 and PM1. Culture on Vero cells of all collected samples gave negative results.

CONCLUSION

During a period of partial opening during the COVID-19 pandemic in London, we detected SARS-CoV2 RNA in the air of hospital waiting areas and wards and of London Underground train carriage. More research is needed to determine the transmission potential of SARS-CoV2 detected in the air.

Favipiravir in patients hospitalised with COVID-19 (PIONEER trial): a multicentre, open-label, phase 3, randomised controlled trial of early intervention versus standard care

BACKGROUND

COVID-19 has overwhelmed health services globally. Oral antiviral therapies are licensed worldwide, but indications and efficacy rates vary. We aimed to evaluate the safety and efficacy of oral favipiravir in patients hospitalised with COVID-19.

METHODS

We conducted a multicentre, open-label, randomised controlled trial of oral favipiravir in adult patients who were newly admitted to hospital with proven or suspected COVID-19 across five sites in the UK (n=2), Brazil (n=2) and Mexico (n=1). Using a permuted block design, eligible and consenting participants were randomly assigned (1:1) to receive oral favipiravir (1800 mg twice daily for 1 day; 800 mg twice daily for 9 days) plus standard care, or standard care alone. All caregivers and patients were aware of allocation and those analysing data were aware of the treatment groups. The prespecified primary outcome was the time from randomisation to recovery, censored at 28 days, which was assessed using an intention-to-treat approach. Post-hoc analyses were used to assess the efficacy of favipiravir in patients aged younger than 60 years, and in patients aged 60 years and older. The trial was registered with clinicaltrials.gov, NCT04373733.

FINDINGS

Between May 5, 2020 and May 26, 2021, we assessed 503 patients for eligibility, of whom 499 were randomly assigned to favipiravir and standard care (n=251) or standard care alone (n=248). There was no significant difference between those who received favipiravir and standard care, relative to those who received standard care alone in time to recovery in the overall study population (hazard ratio [HR] 1·06 [95% CI 0·89-1·27]; n=499; p=0·52). Post-hoc analyses showed a faster rate of recovery in patients younger than 60 years who received favipiravir and standard care versus those who had standard care alone (HR 1·35 [1·06-1·72]; n=247; p=0·01). 36 serious adverse events were observed in 27 (11%) of 251 patients administered favipiravir and standard care, and 33 events were observed in 27 (11%) of 248 patients receiving standard care alone, with infectious, respiratory, and cardiovascular events being the most numerous. There was no significant between-group difference in serious adverse events per patient (p=0·87).

INTERPRETATION

Favipiravir does not improve clinical outcomes in all patients admitted to hospital with COVID-19, however, patients younger than 60 years might have a beneficial clinical response. The indiscriminate use of favipiravir globally should be cautioned, and further high-quality studies of antiviral agents, and their potential treatment combinations, are warranted in COVID-19.

FUNDING

LifeArc and CW+.

YAP-regulated type II alveolar epithelial cell differentiation mediated by human umbilical cord-derived mesenchymal stem cells in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) contributes to higher mortality worldwide. Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have immunomodulatory and regenerative potential. However, the effects of hUC-MSCs as an ARDS treatment remain unclear. We investigated the role of hUC-MSCs in the differentiation of type II alveolar epithelial cells (AECII) by regulating Yes-associated protein (YAP) in ARDS. Male C57BL/6JNarl mice were intratracheally (i.t.) administered lipopolysaccharide (LPS) to induce an ARDS model, followed by a single intravenous (i.v.) dose of hUC-MSCs. hUC-MSCs improved pulmonary function, decreased inflammation on day 3, and mitigated lung injury by reducing the lung injury score and increasing lung aeration (%) in mice on day 7 (p < 0.05). hUC-MSCs inactivated YAP on AECII and facilitated cell differentiation by decreasing Pro-surfactant protein C (Pro-SPC) and galectin 3 (LGALS3) while increasing podoplanin (T1α) in lungs of mice (p < 0.05). In AECII MLE-12 cells, both coculture with hUC-MSCs after LPS exposure and the YAP inhibitor, verteporfin, reduced Pro-SPC and LGALS3, whereas the YAP inhibitor increased T1α expression (p < 0.05). In conclusion, hUC-MSCs ameliorated lung injury of ARDS and regulated YAP to facilitate AECII differentiation.

Mitochondrial Transfer Regulates Bioenergetics in Healthy and Chronic Obstructive Pulmonary Disease Airway Smooth Muscle

Mitochondrial dysfunction has been reported in chronic obstructive pulmonary disease (COPD). Transfer of mitochondria from mesenchymal stem cells to airway smooth muscle cells (ASMCs) can attenuate oxidative stress-induced mitochondrial damage. It is not known whether mitochondrial transfer can occur between structural cells in the lungs or what role this may have in modulating bioenergetics and cellular function in healthy and COPD airways. Here, we show that ASMCs from both healthy ex-smokers and subjects with COPD can exchange mitochondria, a process that happens, at least partly, via extracellular vesicles. Exposure to cigarette smoke induces mitochondrial dysfunction and leads to an increase in the donation of mitochondria by ASMCs, suggesting that the latter may be a stress response mechanism. Healthy ex-smoker ASMCs that receive mitochondria show increases in mitochondrial biogenesis and respiration and a reduction in cell proliferation, irrespective of whether the mitochondria are transferred from healthy ex-smoker or COPD ASMCs. Our data indicate that mitochondrial transfer between structural cells is a homeostatic mechanism for the regulation of bioenergetics and cellular function within the airways and may represent an endogenous mechanism for reversing the functional consequences of mitochondrial dysfunction in diseases such as COPD.

ORMDL3 regulates cigarette smoke-induced endoplasmic reticulum stress in airway smooth muscle cells

BACKGROUND

Orosomucoid 1-like protein 3 (ORMDL3), a transmembrane protein localized in the endoplasmic reticulum (ER), has been genetically associated with chronic obstructive pulmonary disease (COPD), in addition to childhood-onset asthma. However, the functional role of ORMDL3 in the pathogenesis of COPD is still unknown.

OBJECTIVE

Because cigarette smoke is the major risk factor for COPD, we aimed to investigate the role of ORMDL3 in cigarette smoke-induced human airway smooth muscle cell (HASMC) injury.

METHODS

The mRNA and protein expression of ORMDL3 was examined in HASMCs from nonsmokers and smokers without or with COPD. Knockdown of ORMDL3 in primary healthy HASMCs was performed using small interfering RNA before exposure to cigarette smoke medium (CSM) for 24 hours. Inflammatory, proliferative/apoptotic, ER stress, and mitochondrial markers were evaluated.

RESULTS

Elevation of ORMDL3 mRNA and protein expression was observed in HASMCs of smokers without or with COPD. CSM caused significant upregulation of ORMDL3 expression in healthy nonsmokers. ORMDL3 knockdown regulated CSM-induced inflammation, cell proliferation, and apoptosis. Silencing ORMDL3 led to reduction of CSM-induced ER stress via inhibition of unfolded protein response pathways such as activating transcription factor 6 and protein kinase RNA-like ER kinase. ORMDL3 was also involved in CSM-induced mitochondrial dysfunction via the mitochondrial fission process.

CONCLUSIONS

We report the induction of ORMDL3 in HASMCs after cigarette smoke exposure. ORMDL3 may mediate cigarette smoke-induced activation of unfolded protein response pathways during airway smooth muscle cell injury.

Molecular mechanisms of oxidative stress in asthma

The lungs are exposed to reactive oxygen species oxygen (ROS) produced as a result of inhalation of oxygen, as well as smoke and other air pollutants. Cell metabolism and the NADPH oxidases (Nox) generate low levels of intracellular ROS that act as signal transduction mediators by inducing oxidative modifications of histones, enzymes and transcription factors. Redox signalling is also regulated by localised production and sensing of ROS in mitochondria, the endoplasmic reticulum (ER) and inside the nucleus. Intracellular ROS are maintained at low levels through the action of a battery of enzymatic and non-enzymatic antioxidants. Asthma is a heterogeneous airway inflammatory disease with different immune endotypes; these include atopic or non-atopic Th2 type immune response associated with eosinophilia, or a non-Th2 response associated with neutrophilia. Airway remodelling and hyperresponsiveness accompany the inflammatory response in asthma. Over-production of ROS resulting from infiltrating immune cells, particularly eosinophils and neutrophils, and a concomitant impairment of antioxidant responses lead to development of oxidative stress in asthma. Oxidative stress is augmented in severe asthma and during exacerbations, as well as by air pollution and obesity, and causes oxidative damage of tissues promoting airway inflammation and hyperresponsiveness. Furthermore, deregulated Nox activity, mitochondrial dysfunction, ER stress and/or oxidative DNA damage, resulting from exposure to irritants, inflammatory mediators or obesity, may lead to redox-dependent changes in cell signalling. ROS play a central role in airway epithelium-mediated sensing, development of innate and adaptive immune responses, and airway remodelling and hyperresponsiveness. Nonetheless, antioxidant compounds have proven clinically ineffective as therapeutic agents for asthma, partly due to issues with stability and in vivo metabolism of these compounds. The compartmentalised nature of ROS production and sensing, and the role of ROS in homeostatic responses and in the action of corticosteroids and β2-adrenergic receptor agonists, adds another layer of complexity to antioxidant therapy development. Nox inhibitors and mitochondrial-targeted antioxidants are in clinical development for a number of diseases but they have not yet been investigated in asthma. A better understanding of the complex role of ROS in the pathogenesis of asthma will highlight new opportunities for more targeted and effective redox therapies.

Study of Mesenchymal Stem Cell-Mediated Mitochondrial Transfer in In Vitro Models of Oxidant-Mediated Airway Epithelial and Smooth Muscle Cell Injury

Mesenchymal stem cells (MSCs) have emerged as an attractive candidate for cell-based therapy. In the past decade, many animal and pilot clinical studies have demonstrated that MSCs are therapeutically beneficial for the treatment of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). However, due to the scarcity of adult human MSCs, human-induced pluripotent stem cells mesenchymal stem cells (iPSCs) are now increasingly used as a source of MSCs. iPSCs are derived by reprogramming somatic cells from a wide variety of tissues such as skin biopsies and then differentiating them into iPSC-MSCs. One of the mechanisms through which MSCs exert their protective effects is mitochondrial transfer. Specifically, transfer of mitochondria from iPSC-MSCs to lung cells was shown to protect lung cells against oxidative stress-induced mitochondrial dysfunction and apoptosis and to reduce lung injury and inflammation in in vivo models of lung disease. In this chapter, we detail our methods to visualize and quantify iPSC-MSC-mediated mitochondrial transfer and to study its effects on oxidant-induced airway epithelial and smooth muscle cell models of acute airway cell injury.

Role of Metabolic Reprogramming in Pulmonary Innate Immunity and Its Impact on Lung Diseases

Lung innate immunity is the first line of defence against inhaled allergens, pathogens and environmental pollutants. Cellular metabolism plays a key role in innate immunity. Catabolic pathways, including glycolysis and fatty acid oxidation (FAO), are interconnected with biosynthetic and redox pathways. Innate immune cell activation and differentiation trigger extensive metabolic changes that are required to support their function. Pro-inflammatory polarisation of macrophages and activation of dendritic cells, mast cells and neutrophils are associated with increased glycolysis and a shift towards the pentose phosphate pathway and fatty acid synthesis. These changes provide the macromolecules required for proliferation and inflammatory mediator production and reactive oxygen species for anti-microbial effects. Conversely, anti-inflammatory macrophages use primarily FAO and oxidative phosphorylation to ensure efficient energy production and redox balance required for prolonged survival. Deregulation of metabolic reprogramming in lung diseases, such as asthma and chronic obstructive pulmonary disease, may contribute to impaired innate immune cell function. Understanding how innate immune cell metabolism is altered in lung disease may lead to identification of new therapeutic targets. This is important as drugs targeting a number of metabolic pathways are already in clinical development for the treatment of other diseases such as cancer.

Mesenchymal stem cells alleviate oxidative stress-induced mitochondrial dysfunction in the airways

BACKGROUND

Oxidative stress-induced mitochondrial dysfunction can contribute to inflammation and remodeling in patients with chronic obstructive pulmonary disease (COPD). Mesenchymal stem cells protect against lung damage in animal models of COPD. It is unknown whether these effects occur through attenuating mitochondrial dysfunction in airway cells.

OBJECTIVE

We sought to examine the effect of induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) on oxidative stress-induce mitochondrial dysfunction in human airway smooth muscle cells (ASMCs) in vitro and in mouse lungs in vivo.

METHODS

ASMCs were cocultured with iPSC-MSCs in the presence of cigarette smoke medium (CSM), and mitochondrial reactive oxygen species (ROS) levels, mitochondrial membrane potential (ΔΨm), and apoptosis were measured. Conditioned medium from iPSC-MSCs and transwell cocultures were used to detect any paracrine effects. The effect of systemic injection of iPSC-MSCs on airway inflammation and hyperresponsiveness in ozone-exposed mice was also investigated.

RESULTS

Coculture of iPSC-MSCs with ASMCs attenuated CSM-induced mitochondrial ROS, apoptosis, and ΔΨm loss in ASMCs. iPSC-MSC-conditioned medium or transwell cocultures with iPSC-MSCs reduced CSM-induced mitochondrial ROS but not ΔΨm or apoptosis in ASMCs. Mitochondrial transfer from iPSC-MSCs to ASMCs was observed after direct coculture and was enhanced by CSM. iPSC-MSCs attenuated ozone-induced mitochondrial dysfunction, airway hyperresponsiveness, and inflammation in mouse lungs.

CONCLUSION

iPSC-MSCs offered protection against oxidative stress-induced mitochondrial dysfunction in human ASMCs and in mouse lungs while reducing airway inflammation and hyperresponsiveness. These effects are, at least in part, dependent on cell-cell contact, which allows for mitochondrial transfer, and paracrine regulation. Therefore iPSC-MSCs show promise as a therapy for oxidative stress-dependent lung diseases, such as COPD.

Reduced suppressive effect of β2-adrenoceptor agonist on fibrocyte function in severe asthma

Background

Patients with severe asthma have increased airway remodelling and elevated numbers of circulating fibrocytes with enhanced myofibroblastic differentiation capacity, despite being treated with high doses of corticosteroids, and long acting β₂-adrenergic receptor (AR) agonists (LABAs). We determined the effect of β₂-AR agonists, alone or in combination with corticosteroids, on fibrocyte function.

Methods

Non-adherent non-T cells from peripheral blood mononuclear cells isolated from healthy subjects and patients with non-severe or severe asthma were treated with the β₂-AR agonist, salmeterol, in the presence or absence of the corticosteroid dexamethasone. The number of fibrocytes (collagen I⁺/CD45⁺ cells) and differentiating fibrocytes (α-smooth muscle actin⁺ cells), and the expression of CC chemokine receptor 7 and of β₂-AR were determined using flow cytometry. The role of cyclic adenosine monophosphate (cAMP) was elucidated using the cAMP analogue 8-bromoadenosine 3′,5′-cyclic monophosphate (8-Br-cAMP) and the phosphodiesterase type IV (PDE4) inhibitor, rolipram.

Results

Salmeterol reduced the proliferation, myofibroblastic differentiation and CCR7 expression of fibrocytes from healthy subjects and non-severe asthma patients. Fibrocytes from severe asthma patients had a lower baseline surface β₂-AR expression and were relatively insensitive to salmeterol but not to 8-Br-cAMP or rolipram. Dexamethasone increased β₂-AR expression and enhanced the inhibitory effect of salmeterol on severe asthma fibrocyte differentiation.

Conclusions

Fibrocytes from patients with severe asthma are relatively insensitive to the inhibitory effects of salmeterol, an effect which is reversed by combination with corticosteroids.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0678-7) contains supplementary material, which is available to authorized users.

Intracellular interactions of umeclidinium and vilanterol in human airway smooth muscle

Background

Intracellular mechanisms of action of umeclidinium (UMEC), a long-acting muscarinic receptor antagonist, and vilanterol (VI), a long-acting β₂-adrenoceptor (β₂R) agonist, were investigated in target cells: human airway smooth-muscle cells (ASMCs).

Materials and methods

ASMCs from tracheas of healthy lung-transplant donors were treated with VI, UMEC, UMEC and VI combined, or control compounds (salmeterol, propranolol, ICI 118.551, or methacholine [MCh]). Cyclic adenosine monophosphate (cAMP) was measured using an enzyme-linked immunosorbent assay, intracellular free calcium ([Ca²⁺]_i) using a fluorescence assay, and regulator of G-protein signaling 2 (RGS2) messenger RNA using real-time quantitative polymerase chain reaction.

Results

VI and salmeterol (10⁻¹²–10⁻⁶ M) induced cAMP production from ASMCs in a concentration-dependent manner, which was greater for VI at all concentrations. β₂R antagonism by propranolol or ICI 118.551 (10⁻¹²–10⁻⁴ M) resulted in concentration-dependent inhibition of VI-induced cAMP production, and ICI 118.551 was more potent. MCh (5×10⁻⁶ M, 30 minutes) attenuated VI-induced cAMP production (P<0.05), whereas pretreatment with UMEC (10⁻⁸ M, 1 hour) restored the magnitude of VI-induced cAMP production. ASMC stimulation with MCh (10⁻¹¹–5×10⁻⁶ M) resulted in a concentration-dependent increase in [Ca²⁺]_i, which was attenuated with UMEC pretreatment. Reduction of MCh-induced [Ca²⁺]_i release was greater with UMEC + VI versus UMEC. UMEC enhanced VI-induced RGS2 messenger RNA expression.

Conclusion

These data indicate that UMEC reverses cholinergic inhibition of VI-induced cAMP production, and is a more potent muscarinic receptor antagonist when in combination with VI versus either alone.

Reversal of corticosteroid insensitivity by p38 MAPK inhibition in peripheral blood mononuclear cells from COPD

BACKGROUND

Corticosteroids (CS) have limited efficacy in the treatment of chronic obstructive pulmonary disease (COPD). p38 mitogen-activated protein kinase (MAPK) activation is increased in lung macrophages of COPD. We investigated whether p38 MAPK inhibition can modulate CS insensitivity of peripheral blood mononuclear cells (PBMCs) from patients with COPD.

METHODS

PBMCs from patients with COPD (n=8) or healthy smokers (n=8) were exposed to lipopolysaccharide (LPS) with a selective p38 MAPK inhibitor (GW856553; 10(-10)-10(-6) M), with dexamethasone (10(-10)-10(-6) M), or with both. Phosphorylated glucocorticoid receptor (GR) was measured by Western blot.

RESULTS

Baseline (P<0.01) and LPS-induced (P<0.05) CXCL8 release was greater in PBMCs from COPD compared to healthy smokers. Inhibition of LPS-induced CXCL8 release by dexamethasone (10(-6) M) was reduced, and baseline and LPS-induced p38 MAPK activation increased in PBMCs of COPD. GW856553 (10(-9) and 10(-10) M) synergistically increased the inhibitory effect of dexamethasone (10(-8) and 10(-6) M) on LPS-induced CXCL8 release in COPD. Similar results were obtained for IL-6 release. GW856553 inhibited dexamethasone- and LPS-activated phosphorylation of serine 211 on GR. CS insensitivity in COPD PBMCs is reversed by inhibition of p38 MAPK activity, partly by preventing phosphorylation of GR at serine 211.

CONCLUSION

p38 MAPK inhibition may be beneficial in COPD by restoring CS sensitivity.

Impaired nuclear translocation of the glucocorticoid receptor in corticosteroid-insensitive airway smooth muscle in severe asthma

RATIONALE

Patients with severe asthma (SA) are less responsive to the beneficial effects of corticosteroid (CS) therapy, and relative CS insensitivity has been shown in airway smooth muscle cells (ASMC) from patients with SA.

OBJECTIVES

We investigated whether there was a defect in the actions of the glucocorticoid receptor (GR) underlying the ability of CS to suppress the inflammatory response in ASMC of patients with SA. ASMC from healthy subjects (n = 10) and subjects with severe (n = 8) and nonsevere asthma (N-SA; n = 8) were cultured from endobronchial biopsies.

MEASUREMENTS AND MAIN RESULTS

GR expression in ASMC from SA and N-SA was reduced compared with that from healthy subjects by 49% (P < 0.01). Although baseline levels of nuclear GR were similar, GR nuclear translocation induced by dexamethasone (10(-7) M) in SA was 60% of that measured in either healthy subjects or subjects with N-SA. Tumor necrosis factor (TNF)-α induced greater nuclear factor (NF)-κB (p65) mRNA expression in ASMC from subjects with SA (5.6- vs. 2.0-fold; P < 0.01), whereas baseline and TNF-α-induced nuclear translocation and dexamethasone-mediated suppression of p65 expression were similar between groups. Dexamethasone, although not modulating TNF-α-induced p65 nuclear translocation, attenuated p65 recruitment to the CCL11 promoter in the healthy and N-SA groups, but this suppressive effect was impaired in subjects with SA.

CONCLUSIONS

Decreased GR expression with impaired nuclear translocation in ASMC, associated with reduced dexamethasone-mediated attenuation of p65 recruitment to NF-κB-dependent gene promoters, may underlie CS insensitivity of severe asthma.

Increased phenotypic differentiation and reduced corticosteroid sensitivity of fibrocytes in severe asthma

BACKGROUND

Patients with severe asthma are less responsive to corticosteroid therapy and show increased airway remodeling. The mesenchymal progenitors, fibrocytes, may be involved in the remodeling of asthmatic airways. We propose that fibrocytes in severe asthma are different from those in nonsevere asthma.

OBJECTIVES

To examine the survival, myofibroblastic differentiation, and C-C chemokine receptor 7 (CCR7) expression in blood fibrocytes from patients with severe and nonsevere asthma and study the effect of corticosteroids on fibrocyte function.

METHODS

The nonadherent non-T-cell fraction of blood mononuclear cells was isolated from healthy subjects and patients with nonsevere and severe asthma. Total and differentiating fibrocytes were identified by their expression of CD45, collagen I, and α-smooth muscle actin using flow cytometry. The expression of CCR7 and of the glucocorticoid receptor was measured by using flow cytometry.

RESULTS

Increased numbers of circulating fibrocytes, with greater myofibroblastic differentiation potential, were observed in patients with severe asthma. Dexamethasone induced apoptosis, leading to reduction in the number of cultured fibrocytes and total nonadherent non-T cells from healthy subjects and patients with nonsevere asthma but not from patients with severe asthma. Dexamethasone reduced CCR7 expression in fibrocytes from patients with nonsevere asthma but not from patients with severe asthma. Glucocorticoid receptor expression was attenuated in fibrocytes from patients with severe asthma.

CONCLUSIONS

Patients with severe asthma have elevated numbers of circulating fibrocytes that show enhanced myofibroblastic differentiation and that are less responsive to the effects of corticosteroids.

Sputum-to-serum hydrogen sulfide ratio in COPD

OBJECTIVES

Hydrogen sulfide (H₂S) is a gas produced by respiratory cells including smooth muscle cells and may play a role as a cellular gasotransmitter. We evaluated whether H₂S levels in serum or sputum could represent a new biomarker of COPD in a cross-sectional study.

METHODS

H₂S levels in sputum and serum samples were measured using a sulfide-sensitive electrode in 64 patients with stable COPD (S-COPD), 29 COPD subjects during acute exacerbation (AE-COPD), 14 healthy smokers and 21 healthy non-smokers.

RESULTS

Sputum H₂S levels in AE-COPD subjects were higher than those in S-COPD, healthy smoking and non-smoking subjects (p<0.001), but serum H₂S levels in AE-COPD were lower than those in S-COPD (p<0.001). Thus, the sputum-to-serum ratio of H₂S (H₂S ratio) in AE-COPD subjects were higher than those in stable COPD, healthy smoking and non-smoking subjects (p<0.001). In 14 COPD subjects whose H₂S ratios were measured during and after an exacerbation, the mean ratio was increased during exacerbation (p<0.05). H₂S ratio was positively correlated with St. George's Respiratory Questionnaire score, sputum neutrophils and IL-6 and IL-8 levels in sputum and serum (p<0.01) but inversely correlated with sputum macrophages (%), FEV₁%predicted and FEV₁/FVC (p<0.01). The cut-off level of H₂S ratio to indicate an exacerbation was ≥0.44 (sensitivity of 93.1% and specificity of 84.5%).

CONCLUSIONS

The ratio of sputum-to-serum levels of H₂S may provide a useful marker of COPD indicative of obstructive neutrophilic inflammation and of potential ongoing exacerbation.

Impaired macrophage phagocytosis of bacteria in severe asthma

Background

Bacteria are frequently cultured from sputum samples of severe asthma patients suggesting a defect in bacterial clearance from the airway. We measured the capacity of macrophages from patients with asthma to phagocytose bacteria.

Methods

Phagocytosis of fluorescently-labelled polystyrene beads, Haemophilus influenzae or Staphylococcus aureus by broncholaveolar lavage alveolar macrophages (AM) and by monocyte-derived macrophages (MDM) from non-asthmatics, mild-moderate and severe asthmatic patients was assessed using fluorimetry.

Results

There were no differences in phagocytosis of polystyrene beads by AMs or MDMs from any of the subject groups. There was reduced phagocytosis of Haemophilus influenzae and Staphylococcus aureus in MDMs from patients with severe asthma compared to non-severe asthma (p < 0.05 and p < 0.01, respectively) and healthy subjects (p < 0.01and p < 0.001, respectively). Phagocytosis of Haemophilus influenzae and Staphylococcus aureus by AM was also reduced in severe asthma compared to normal subjects (p < 0.05). Dexamethasone and formoterol did not suppress phagocytosis of bacteria by MDMs from any of the groups.

Conclusions

Persistence of bacteria in the lower airways may result partly from a reduced phagocytic capacity of macrophages for bacteria. This may contribute to increased exacerbations, airway colonization and persistence of inflammation.

Bromodomain and extraterminal proteins suppress NF-E2-related factor 2-mediated antioxidant gene expression

Oxidative stress, a pathogenetic factor in many conditions, including chronic obstructive pulmonary disease, arises due to accumulation of reactive oxygen species and defective antioxidant defenses in the lungs. The latter is due, at least in part, to impaired activation of NF-E2-related factor 2 (Nrf2), a transcription factor involved in the activation of antioxidant and cytoprotective genes. The bromodomain and extraterminal (BET) proteins, Brd2, Brd3, Brd4, and BrdT, bind to acetylated lysine residues on histone or nonhistone proteins recruiting transcriptional regulators and thus activating or repressing gene transcription. We investigated whether BET proteins modulate the regulation of Nrf2-dependent gene expression in primary human airway smooth muscle cells and the human monocytic cell line, THP-1. Inhibition of BET protein bromodomains using the inhibitor JQ1+ or attenuation of Brd2 and Brd4 expression using small interfering RNA led to activation of Nrf2-dependent transcription and expression of the antioxidant proteins heme oxygenase-1, NADPH quinone oxidoreductase 1, and glutamate-cysteine ligase catalytic subunit. Also, JQ1+ prevented H2O2-induced intracellular reactive oxygen species production. By coimmunoprecipitation, BET proteins were found to be complexed with Nrf2, whereas chromatin-immunoprecipitation studies indicated recruitment of Brd2 and Brd4 to Nrf2-binding sites on the promoters of heme oxygenase-1 and NADPH quinone oxidoreductase 1. BET proteins, particularly Brd2 and Brd4, may play a key role in the regulation of Nrf2-dependent antioxidant gene transcription and are hence an important target for augmenting antioxidant responses in oxidative stress-mediated diseases.

Lipid-laden bronchoalveolar macrophages in asthma and chronic cough

BACKGROUND

The presence of lipids in alveolar macrophages (AMs) may impair their phagocytic response, and determine airway inflammation and obstruction.

OBJECTIVE

To determine the factors such as severity of asthma, chronic cough, airway inflammation and obesity that may influence the presence of lipids in lung macrophages.

METHODS

Bronchoalveolar lavage fluid (BALF) was obtained from 38 asthmatics (21 severe and 17 mild/moderate), 16 subjects with chronic cough and 11 healthy control subjects. The presence of lipids in macrophages was detected using an Oil-red-O stain and an index of lipid-laden macrophages (LLMI) was obtained.

RESULTS

LLMI scores were higher in healthy subjects (median 48 [IQR 10-61]) and the severe asthma group (37 [11.5-61]) compared to mild/moderate asthmatics (7 [0.5-37]; p < 0.05 each). Subjects reporting a history of gastro-oesophageal reflux disease (GORD) had higher LLMI values (41.5 [11.3-138] versus 13 [0-39.3], p = 0.02). There was no significant correlation between LLMI and chronic cough, BAL cell differential counts, FEV1, FEV1/FVC or body mass index (BMI).

CONCLUSIONS

The reduced LLMI in mild/moderate asthma may be related to lower incidence of GORD. However, this was not related to the degree of airflow obstruction, obesity or airway inflammation.

Domiciliary diurnal variation of exhaled nitric oxide fraction for asthma control

A major goal of asthma management is maintaining optimal control. Current assessment is based on symptoms and lung function. We evaluated whether domiciliary daily home exhaled nitric oxide fraction (FeNO) monitoring could be useful as an index of asthma control. 50 asthmatic subjects and 15 healthy volunteers with a range of asthma severity underwent asthma control questionnaire (ACQ), spirometry before and after salbutamol and sputum induction. FeNO and peak expiratory flow (PEF) were measured twice daily for 2 weeks. A record of exacerbations was obtained 3 months later. Diurnal FeNO variation in uncontrolled asthmatics was significantly greater than in controlled asthmatics (p<0.01). PEF variation was not different. The daily variation of FeNO levels was also greater in uncontrolled asthmatics compared with controlled asthmatic and healthy subjects (p<0.01). 80% of uncontrolled asthmatics experienced at least one or more exacerbations over the 3 months after the enrolment. The combination of diurnal FeNO variation ≥ 16.6% and ACQ scores ≥ 1.8 was best at predicting uncontrolled asthma (area under curve 0.91, 95% CI 0.86-0.97; p<0.001). Diurnal variation in FeNO can be used as a biomarker of asthma control and as a predictor of the risk of future exacerbation. Prospective studies are warranted.

A polymorphism affecting MYB binding within the promoter of the PDCD4 gene is associated with severe asthma in children

A previous genome-wide association study in asthma revealed putative associations that merit further investigation. In this study, the genome-wide significant associations of SNPs at the 5% false discovery rate were examined in independent groups of severe asthmatics. The panel consisted of 397 severe asthmatic adults, 116 severe asthmatic children, and a collection of 207 family-trios with an asthmatic proband. Three SNPs in the PDCD4 gene (rs6585018:G>A, rs1322997:C>A, and rs34104444:G>A) were significantly associated with severe childhood asthma (P values: 0.003, 0.002, 0.004) and total immunoglobulin E (IgE) levels (P values: 0.034, 0.041, 0.052). In an independent group of 234 asthmatic children and 652 controls, PDCD4 SNPs rs1407696:T>G and rs11195360:T>C were associated with total IgE levels (P values: 0.006, 0.014). In silico analysis of PDCD4 locus showed that rs6585018:G>A had the potential to affect MYB transcription factor binding, shown to act as a PDCD4-transcription inducer. Electromobility shift assays and reporter assays revealed that rs6585018:G>A alters MYB binding thereby influencing the expression of PDCD4. SNPs within MYB itself confer susceptibility to eosinophilia and asthma. Our association between a variant MYB binding site in PDCD4 and the severest form of childhood asthma therefore suggests that PDCD4 is a novel molecule of importance to asthmatic inflammatory responses.

Obesity-associated severe asthma represents a distinct clinical phenotype: analysis of the British Thoracic Society Difficult Asthma Registry Patient cohort according to BMI

BACKGROUND

Obesity has emerged as a risk factor for the development of asthma and it may also influence asthma control and airway inflammation. However, the role of obesity in severe asthma remains unclear. Thus, our objective was to explore the association between obesity (defied by BMI) and severe asthma.

METHODS

Data from the British Thoracic Society Difficult Asthma Registry were used to compare patient demographics, disease characteristics, and health-care utilization among three BMI categories (normal weight: 18.5-24.99; overweight: 25-29.99; obese: 30) in a well-characterized group of adults with severe asthma.

RESULTS

The study population consisted of 666 patients with severe asthma; the group had a median BMI of 29.8 (interquartile range, 22.5-34.0). The obese group exhibited greater asthma medication requirements in terms of maintenance corticosteroid therapy (48.9% vs 40.4% and 34.5% in the overweight and normal-weight groups, respectively), steroid burst therapy, and short-acting b 2 -agonist use per day. Significant differences were seen with gastroesophageal reflux disease (53.9% vs 48.1% and 39.7% in the overweight and normal weight groups, respectively) and proton pump inhibitor use. Bone density scores were higher in the obese group, while pulmonary function testing revealed a reduced FVC and elevated carbon monoxide transfer coefficient. Serum IgE levels decreased with increasing BMI and the obese group was more likely to report eczema, but less likely to have a history of nasal polyps.

CONCLUSIONS

Patients with severe asthma display particular characteristics according to BMI that support the view that obesity-associated severe asthma may represent a distinct clinical phenotype.

IL-22 suppresses IFN-γ-mediated lung inflammation in asthmatic patients

BACKGROUND

IL-22 controls tissue homeostasis by both proinflammatory and anti-inflammatory effects. However, the anti-inflammatory mechanisms of IL-22 remain poorly investigated.

OBJECTIVE

We sought to investigate the anti-inflammatory role for IL-22 in human asthma.

METHODS

T-cell lines derived from lung biopsy specimens of asthmatic patients were characterized by means of flow cytometry. Human bronchial epithelial cells from healthy and asthmatic subjects were stimulated with IL-22, IFN-γ, or the combination of both cytokines. Effects of cytokine stimulation were investigated by using whole-genome analysis, ELISA, and flow cytometry. The functional consequence of cytokine stimulation was evaluated in an in vitro wound repair model and T cell-mediated cytotoxicity experiments. In vivo cytokine expression was measured by using immunohistochemistry and Luminex assays in bronchoalveolar lavage fluid of healthy and asthmatic patients.

RESULTS

The current study identifies a tissue-restricted antagonistic interplay of IL-22 and the proinflammatory cytokine IFN-γ. On the one hand, IFN-γ antagonized IL-22-mediated induction of the antimicrobial peptide S100A7 and epithelial cell migration in bronchial epithelial cells. On the other hand, IL-22 decreased epithelial susceptibility to T cell-mediated cytotoxicity by inhibiting the IFN-γ-induced expression of MHC-I, MHC-II, and CD54/intercellular adhesion molecule 1 molecules. Likewise, IL-22 inhibited IFN-γ-induced secretion of the proinflammatory chemokines CCL5/RANTES and CXCL10/interferon-inducible protein 10 in vitro. Consistently, the IL-22 expression in bronchoalveolar lavage fluid of asthmatic patients inversely correlated with the expression of CCL5/RANTES and CXCL10/interferon-inducible protein 10 in vivo.

CONCLUSIONS

IL-22 might control the extent of IFN-γ-mediated lung inflammation and therefore play a tissue-restricted regulatory role.

Corticosteroid insensitivity of chemokine expression in airway smooth muscle of patients with severe asthma

BACKGROUND

Patients with severe asthma are less responsive to the beneficial effects of corticosteroid therapy.

OBJECTIVE

We investigated whether corticosteroid insensitivity was present in airway smooth muscle cells (ASMCs) of patients with severe asthma.

METHODS

ASMCs cultured from bronchial biopsy specimens of nonasthmatic control subjects (n = 12) and patients with nonsevere (n = 10) or severe (n = 10) asthma were compared for the effect of dexamethasone on suppression of TNF-α- and IFN-γ-induced CCL11 (eotaxin), CXCL8 (IL-8), and CX3CL1 (fractalkine) expression. The mechanisms of corticosteroid insensitivity are also determined.

RESULTS

CCL11 release was higher in ASMCs of patients with nonsevere but not severe asthma and nonasthmatic control subjects; CXCL8 and CX3CL1 release were similar in all groups. In patients with severe asthma, dexamethasone caused less suppression of CCL11 and CXCL8 release induced by TNF-α. Dexamethasone potentiated TNF-α- and IFN-γ-induced CX3CL1 release equally in all 3 groups. TNF-α-induced phosphorylated p38 mitogen-activated protein kinase levels were increased in ASMCs from patients with severe asthma compared with those from patients with nonsevere asthma and nonasthmatic subjects, whereas TNF-α-induced phosphorylated c-Jun N-terminal kinase and phosphorylated extracellular signal-related kinase levels were increased in all asthmatic groups. A p38 inhibitor increased the inhibitory effect of dexamethasone.

CONCLUSIONS

ASMCs of patients with severe asthma are corticosteroid insensitive; this might be secondary to heightened p38 mitogen-activated protein kinase levels.

TGF-β regulates Nox4, MnSOD and catalase expression, and IL-6 release in airway smooth muscle cells

Reactive oxygen species (ROS) are generated as a result of normal cellular metabolism, mainly through the mitochondria and peroxisomes, but their release is enhanced by the activation of oxidant enzymes such as NADPH oxidases or downregulation of endogenous antioxidant enzymes such as manganese-superoxide dismutase (MnSOD) and catalase. Transforming growth factor-β (TGF-β), found to be overexpressed in airway smooth muscle (ASM) from asthmatic and chronic obstructive pulmonary disease patients, may be a pivotal regulator of abnormal ASM cell (ASMC) function in these diseases. An important effect of TGF-β on ASMC inflammatory responses is the induction of IL-6 release. TGF-β also triggers intracellular ROS release in ASMCs by upregulation of NADPH oxidase 4 (Nox4). However, the effect of TGF-β on the expression of key antioxidant enzymes and subsequently on oxidant/antioxidant balance is unknown. Moreover, the role of redox-dependent pathways in the mediation of the proinflammatory effects of TGF-β in ASMCs is unclear. In this study, we show that TGF-β induced the expression of Nox4 while at the same time inhibiting the expression of MnSOD and catalase. This change in oxidant/antioxidant enzymes was accompanied by elevated ROS levels and IL-6 release. Further studies revealed a role for Smad3 and phosphatidyl-inositol kinase-mediated pathways in the induction of oxidant/antioxidant imbalance and IL-6 release. The changes in oxidant/antioxidant enzymes and IL-6 release were reversed by the antioxidants N-acetyl-cysteine (NAC) and ebselen through inhibition of Smad3 phosphorylation, indicating redox-dependent activation of Smad3 by TGF-β. Moreover, these findings suggest a potential role for NAC in preventing TGF-β-mediated pro-oxidant and proinflammatory responses in ASMCs. Knockdown of Nox4 using small interfering RNA partially prevented the inhibition of MnSOD but had no effect on catalase and IL-6 expression. These findings provide novel insights into redox regulation of ASM function by TGF-β.

Inhibition of p38 MAPK-dependent bronchial contraction after ozone by corticosteroids

We determined the role of p38 mitogen-activated protein kinase (MAPK) in the increased airway smooth muscle (ASM) contractile responses following ozone and modulation by corticosteroids. Mice were exposed to air or ozone (3 ppm for 3 h) and isometric contractile responses of bronchial rings to acetylcholine (ACh) were measured using a myograph in the presence of p38 MAPK inhibitor, SB239063 (10⁻⁶ M) or dexamethasone (10⁻⁶ M). Because MAPK phosphatase (MKP)-1 is a negative regulator of p38 MAPK, we also studied these effects in MKP-1(-/-) mice. Bronchial rings from ozone-exposed wild-type and MKP-1(-/-) mice showed increased contractile responses, with a leftward shift of the dose-response curve in MKP-1(-/-) mice. SB239063 inhibited bronchial contraction equally in air- and ozone-exposed C57/BL6 and MKP-1(-/-) mice. Dexamethasone inhibited ACh-induced bronchial contraction in both air- and ozone-exposed C57/BL6 mice, but not in air- or ozone-exposed MKP-1(-/-) mice. ACh-stimulated p38 MAPK and heat shock protein (HSP)27 phosphorylation, as measured by Western blotting, and this effect was suppressed by SB239063 in C57/BL6 and MKP-1(-/-) mice, but not by dexamethasone in either air- or ozone-exposed MKP-1(-/-) mice. p38 MAPK plays a role in maximal ACh-induced isometric contractile responses and increased contractility induced by ozone. Dexamethasone inhibits ACh-induced ASM contraction through phosphorylation of p38 MAPK and HSP27.

Glucocorticoid suppression of CX3CL1 (fractalkine) by reduced gene promoter recruitment of NF-kappaB

Glucocorticoids are an important anti-inflammatory treatment of many inflammatory diseases including asthma. However, the mechanisms by which they mediate their suppressive effects are not fully understood. Respiratory epithelial cells are a source of CX(3)CL1 (fractalkine), which mediates cell adhesion and acts as a chemoattractant for monocytes, T cells, and mast cells. We show, in lung A549 epithelial cells, that the tumor necrosis factor-alpha (TNF-alpha) and IFNgamma synergistically induced protein release and mRNA expression of CX(3)CL1 is inhibited by dexamethasone, without interfering with cytokine-induced nuclear translocation of NF-kappaB, and by an inhibitor of IkappaB kinase 2, AS602868. DNA binding assays confirmed the ability of NF-kappaB to bind to the proximal CX(3)CL1 promoter. Chromatin immunoprecipitation assays showed a 5-fold increase in the recruitment of NF-kappaB to the CX(3)CL1 gene promoter in response to IFNgamma/TNF-alpha; this too was reversed by dexamethasone. In contrast, dexamethasone did not displace NF-kappaB from the granulocyte-macrophage colony-stimulating factor gene promoter. We conclude that CX(3)CL1 expression is regulated through the NF-kappaB pathway and that dexamethasone inhibits CX(3)CL1 expression through a glucocorticoid receptor-dependent (RU486 sensitive) mechanism. This study also provides support for the action of glucocorticoids mediating their suppressive effects on expression by interfering with the binding of transcriptional activators at native gene promoters.

Induction and regulation of matrix metalloproteinase-12 in human airway smooth muscle cells

Background

The elastolytic enzyme matrix metalloproteinase (MMP)-12 has been implicated in the development of airway inflammation and remodeling. We investigated whether human airway smooth muscle cells could express and secrete MMP-12, thereby participating in the pathogenesis of airway inflammatory diseases.

Methods

Laser capture microdissection was used to collect smooth muscle cells from human bronchial biopsy sections. MMP-12 mRNA expression was analysed by quantitative real-time RT-PCR. MMP-12 protein expression and secretion from cultured primary airway smooth muscle cells was further analysed by Western blot. MMP-12 protein localization in bronchial tissue sections was detected by immunohistochemistry. MMP-12 activity was determined by zymography. The TransAM AP-1 family kit was used to measure c-Jun activation and nuclear binding. Analysis of variance was used to determine statistical significance.

Results

We provide evidence that MMP-12 mRNA and protein are expressed by in-situ human airway smooth muscle cells obtained from bronchial biopsies of normal volunteers, and of patients with asthma, COPD and chronic cough. The pro-inflammatory cytokine, interleukin (IL)-1β, induced a >100-fold increase in MMP-12 gene expression and a >10-fold enhancement in MMP-12 activity of primary airway smooth muscle cell cultures. Selective inhibitors of extracellular signal-regulated kinase, c-Jun N-terminal kinase and phosphatidylinositol 3-kinase reduced the activity of IL-1β on MMP-12, indicating a role for these kinases in IL-1β-induced induction and release of MMP-12. IL-1β-induced MMP-12 activity and gene expression was down-regulated by the corticosteroid dexamethasone but up-regulated by the inflammatory cytokine tumour necrosis factor (TNF)-α through enhancing activator protein-1 activation by IL-1β. Transforming growth factor-β had no significant effect on MMP-12 induction.

Conclusion

Our findings indicate that human airway smooth muscle cells express and secrete MMP-12 that is up-regulated by IL-1β and TNF-α. Bronchial smooth muscle cells may be an important source of elastolytic activity, thereby participating in remodeling in airway diseases such as COPD and chronic asthma.

Phenylephrine requires the TATA box to activate transcription of GLUT1 in neonatal rat cardiac myocytes

Cardiac hypertrophy and heart failure occur in association to alterations in glucose uptake and metabolism. Phenylephrine, among other hypertrophic agonists, has been reported to increase expression of GLUT1 in neonatal rat cardiac myocytes by activating transcription. However, the specific cis- or trans-acting factors in the GLUT1 gene that are targeted by this agonist remain elusive. Here we describe that the activity of the -99/+134 basal promoter of rat GLUT1 is increased by phenylephrine. Nevertheless, this is not mediated by previously described binding sites (GC-box, MG1E) in the promoter. Rather, the TATA box is required by the agonist to activate transcription from the promoter. Interestingly, The Ras-ERK mitogen-activated protein (MAP) kinase pathway is involved in the actions of phenylephrine on GLUT1 transcription, and the effects of Ras on the activity of the promoter depend on the integrity of the TATA box. Our data indicate that phenylephrine induces the expression of the TBP-associated factor TAF(II)250 mRNA, which increases in parallel to the expression of GLUT1, suggesting that altering the expression of basal transcription factors could be one mechanism by which phenylephrine may regulate the activity of the GLUT1 promoter.

Identification of novel, cardiac-restricted transcription factors binding to a CACC-box within the human cardiac troponin I promoter

OBJECTIVES

The expression of the human cardiac troponin I (hTnIc) gene is developmentally regulated and tissue-specific. In analysing the putative binding elements within the proximal promoter, a CACC-box sequence overlapping a consensus Sp1 element has been identified. The aim of this study was to characterise the factors binding to this element and to determine their importance in the transcriptional activity of the promoter.

METHODS

A combination of supershift and competition electrophoretic mobility shift assays (EMSA) were used to identify the binding of factors to the overlapping CACC-box/Sp1 consensus element. The functional importance of this element was tested by transient transfection into primary neonatal rat cardiac myocytes in culture.

RESULTS

At least four factors were able to interact with this region including the zinc finger proteins Sp1, Sp3 and two potentially novel factors. Whereas both Sp1 and Sp3 bound to the consensus Sp1 element, and to a lesser extent the CACC-box, two of the complexes required the intact CACC-box for binding. Site-directed mutagenesis of this region showed that the CACC-box is essential for hTnIc promoter-reporter activity. Further characterisation using EMSA indicated that the factors binding the hTnIc CACC-box are unlikely to be zinc finger proteins as they are insensitive to the addition of divalent cation chelating agents. They were also unable to bind to other known CACC-box elements. These factors are present in both human and rat cardiac muscle but absent from a number of cell lines including several derived from skeletal muscle.

CONCLUSION

The human cardiac troponin I gene promoter requires an upstream CACC-box element for full activity. This element binds at least two complexes which represent novel, tissue-restricted DNA-binding activity present in the heart which we have named HCB1 and HCB2 for heart CACC-box binding factors.

Identification of cis-acting DNA elements required for expression of the human cardiac troponin I gene promoter

The human cardiac troponin I (TnIc) gene exhibits both cardiac-specific and developmentally regulated expression. The structure and expression of this gene as well as the identification of putative regulatory elements have been described previously. This study shows that a minimal promoter containing 98 bp of sequence is sufficient to drive transcription in neonatal rat cardiac myocytes. This region contains several putative cis -regulatory elements including an Initiator element surrounding the start site of transcription, an A/T-rich (TATA/MEF-2) element, two GATA elements and a cytosine-rich region containing overlapping CACC box and Sp1 elements. Using electrophoretic mobility shift assays (EMSAs) this study demonstrates the binding of MEF-2, Oct-1, and recombinant TBP to the A/T-rich element and of GATA-4 to both GATA elements. The CACC/Sp element binds the zinc finger transcription factors Sp1 and Sp3 in addition to an unidentified complex present in neonatal rat cardiac myocytes. Mutation of each of these sites has a deleterious effect on promoter activity as assayed by transient transfection into cardiac myocytes. The data suggest that transcriptional activity of the human TnIc gene can be driven by a compact promoter region and that within this region GATA, MEF-2 Sp1 and CACC box-binding factors are required for optimal activity. Furthermore, a comparison with data obtained for identical elements in the promoters of rodent TnIc genes identifies differences between species which may be of consequence for species-specific promoter function.

Close physical linkage of human troponin genes: organization, sequence, and expression of the locus encoding cardiac troponin I and slow skeletal troponin T

Based on chromosomal mapping data, we recently revealed an unexpected linkage of troponin genes in the human genome: the six genes encoding striated muscle troponin I and troponin T isoforms are located at three chromosomal sites, each of which carries a troponin I-troponin T gene pair. Here we have investigated the organization of these genes at the DNA level in isolated P1 and PAC genomic clones and demonstrate close physical linkage in two cases through the isolation of individual clones containing a complete troponin I-troponin T gene pair. As an initial step toward fully characterizing this pattern of linkage, we have determined the organization and complete sequence of the locus encoding cardiac troponin I and slow skeletal troponin T and thereby also provide the first determination of the structure and sequence of a slow skeletal troponin T gene. Our data show that the genes are organized head to tail and are separated by only 2.6 kb of intervening sequence. In contrast to other troponin genes, and despite their close proximity, the cardiac troponin I and slow skeletal troponin T genes show independent tissue-specific expression. Such close physical linkage has implications for the evolution of the troponin gene families, for their regulation, and for the analysis of mutations implicated in cardiomyopathy.

Isolation and characterization of the human cardiac troponin I gene (TNNI3)

Troponin I (TnI) is a constituent protein of the troponin complex located on the thin filament of striated muscle that provides a calcium-sensitive switch for striated muscle contraction. Unlike other contractile proteins, the cardiac isoform of troponin I (TnIc) is expressed only in cardiac muscle and therefore offers a model for cardiac-specific expression. It is also subject to developmental regulation with increased expression occurring at the time of birth. Here we describe the isolation and characterization of the human TnIc gene (HGMW-approved symbol TNNI3) and its promoter. The gene comprises eight exons contained within 6.2 kb of genomic DNA. The proximal promoter and 1.1-kb 5'-flanking region were sequenced, and several putative cis-acting elements that are conserved between the human and the mouse TnIc genes were identified. In addition, multiple copies of a 37-bp chromosome 19-specific mini-satellite sequence were identified within this region. Following transfection, 2300 bp of 5' sequence is active in both cardiac myocytes and skeletal muscle cells but is inactive in fibroblasts, indicating that it can drive expression but is insufficient to confer cardiac specificity.

Gene expression during cardiac development

The vertebrate heart forms as two concentric epithelial cylinders of myocardium and endocardium separated by an extended basement membrane matrix commonly referred to as cardiac jelly. Subsequent maturation involves a complex series of events including asymmetric changes in cell shape and division which contribute to bending and the formation of the bulboventricular loop, the formation of specialised tissues including endocardial cushion tissue of the atrioventricular (AV) and outflow tract regions, the development of conductive tissue and myocyte maturation leading to the overall pattern of expression characteristic of mature heart muscle. These processes depend on a precise spatial and temporal control of gene expression both of genes encoding regulatory molecules and those encoding structural components of the heart. In this chapter we address three aspects of cardiac development, namely, the determination of cell fate during formation of endocardial cushion tissue in the embryonic heart, transitions in troponin gene expression during fetal myocyte maturation, and the use of cloning techniques based on the polymerase chain reaction for identifying transcription factors present in the heart.

Developmental expression of troponin I isoforms in fetal human heart

We have used antibodies specific for troponin I proteins to examine human cardiac development and have detected a transiently expressed developmental isoform. This isoform is distinct from adult cardiac troponin I (TnIc) but is indistinguishable, on the basis of electrophoretic mobility and antibody reactivity, from the isoform found in slow skeletal muscle (TnIs). Furthermore, we show that mRNA for TnIs is present in fetal, but not adult, heart. Analysis of a developmental series of fetal samples indicates that there is a transition in expression from TnIs to TnIc which occurs between 20 weeks fetal and 9 months postnatal development.