Targeting airway smooth muscle in airways diseases: an old concept with new twists

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Differential estrogen-receptor activation regulates extracellular matrix deposition in human airway smooth muscle remodeling via NF-κB pathway

Altered airway smooth muscle (ASM) mass and extracellular matrix (ECM) deposition in airways are characteristic features of remodeling in asthma. Increased ECM production modulates ASM cell proliferation and leads to airway remodeling. Our previous studies showed that ASM from patients with asthma exhibited increased expression of estrogen receptor (ER)-β, which upon activation down-regulated ASM proliferation, implicating an important role for estrogen signaling in airway physiology. There is no current information on the effect of differential ER activation on ECM production. In this study, we evaluated the effect of ER-α vs. ER-β activation on ECM production, deposition, and underlying pathways. Primary human ASM cells isolated from asthmatics and nonasthmatics were treated with E₂, an ER-α agonist [propylpyrazoletriol (PPT)], and an ER-β agonist [WAY-200070 (WAY)] with TNF-α or platelet-derived growth factor (PDGF) followed by evaluation of ECM production and deposition. Expression of proteins and genes corresponding to ECM were measured using Western blotting and quantitative RT-PCR with subsequent matrix metalloproteinase (MMP) activity. Molecular mechanisms of ER activation in regulating ECM were evaluated by luciferase reporter assays for activator protein 1 (AP-1) and NF-κB. TNF-α or PDGF significantly (P < 0.001) increased ECM deposition and MMP activity in human ASM cells, which was significantly reduced with WAY treatment but not with PPT. Furthermore, TNF-α- or PDGF-induced ECM gene expression in ASM cells was significantly reduced with WAY (P < 0.001). Moreover, WAY significantly down-regulated the activation of NF-κB (P < 0.001) and AP-1 (P < 0.01, P < 0.05) in ASM cells from asthmatics and nonasthmatics. Overall, we demonstrate differential ER signaling in controlling ECM production and deposition. Activation of ER-β diminishes ECM deposition via suppressing the NF-κB pathway activity and might serve as a novel target to blunt airway remodeling.-Ambhore, N. S., Kalidhindi, R. S. R., Pabelick, C. M., Hawse, J. R., Prakash, Y. S., Sathish, V. Differential estrogen-receptor activation regulates extracellular matrix deposition in human airway smooth muscle remodeling via NF-κB pathway.

Modulation of Bronchomotor Tone Pathways in Airway Smooth Muscle Function and Bronchomotor Tone in Asthma

Airway smooth muscle is the primary cell mediating bronchomotor tone. The milieu created in the asthmatic lung modulates airway smooth muscle contractility and relaxation. Experimental findings suggest intrinsic abnormalities in airway smooth muscle derived from patients with asthma in comparison with airway smooth muscle from those without asthma. These changes to excitation-contraction pathways may underlie airway hyperresponsiveness and increased airway resistance associated with asthma.

Estrogen receptor beta signaling inhibits PDGF induced human airway smooth muscle proliferation

Airway smooth muscle (ASM) cell hyperplasia driven by persistent inflammation is a hallmark feature of remodeling in asthma. Sex steroid signaling in the lungs is of considerable interest, given epidemiological data showing more asthma in pre-menopausal women and aging men. Our previous studies demonstrated that estrogen receptor (ER) expression increases in asthmatic human ASM; however, very limited data are available regarding differential roles of ERα vs. ERβ isoforms in human ASM cell proliferation. In this study, we evaluated the effect of selective ERα and ERβ modulators on platelet-derived growth factor (PDGF)-stimulated ASM proliferation and the mechanisms involved. Asthmatic and non-asthmatic primary human ASM cells were treated with PDGF, 17β-estradiol, ERα-agonist and/or ERβ-agonist and/or G-protein-coupled estrogen receptor 30 (GPR30/GPER) agonist and proliferation was measured using MTT and CyQuant assays followed by cell cycle analysis. Transfection of small interfering RNA (siRNA) ERα and ERβ significantly altered the human ASM proliferation. The specificity of siRNA transfection was confirmed by Western blot analysis. Gene and protein expression of cell cycle-related antigens (PCNA and Ki67) and C/EBP were measured by RT-PCR and Western analysis, along with cell signaling proteins. PDGF significantly increased ASM proliferation in non-asthmatic and asthmatic cells. Treatment with PPT showed no significant effect on PDGF-induced proliferation, whereas WAY interestingly suppressed proliferation via inhibition of ERK1/2, Akt, and p38 signaling. PDGF-induced gene expression of PCNA, Ki67 and C/EBP in human ASM was significantly lower in cells pre-treated with WAY. Furthermore, WAY also inhibited PDGF-activated PCNA, C/EBP, cyclin-D1, and cyclin-E. Overall, we demonstrate ER isoform-specific signaling in the context of ASM proliferation. Activation of ERβ can diminish remodeling in human ASM by inhibiting pro-proliferative signaling pathways, and may point to a novel perception for blunting airway remodeling.

Contraction-dependent TGF-β1 activation is required for thrombin-induced remodeling in human airway smooth muscle cells

AIMS

Thrombin is a serine proteinase that is not only involved in coagulation cascade, but also mediates a number of biological responses relevant to tissues repair, and induces bronchoconstriction. TGF-β plays a pivotal role in airway remodeling due to its effects on airway smooth muscle proliferation and extracellular matrix (ECM) deposition. Recently, bronchoconstriction itself is found to constitute a form of strain and is highly relevant to asthmatic airway remodeling. However, the underlying mechanisms remain unknown. Here, we investigated the role of contraction- dependent TGF-β activation in thrombin-induced remodeling in human airway smooth muscle (HASM) cells.

MATERIALS AND METHODS

Primary HASM cells were treated with or without thrombin in the absence or presence of anti-TGF-β antibody, cytochalasin D and formoterol. CFSE labeling index or CCK-8 assay were performed to test cell proliferation. RT-PCR and Western blotting were used to examined ECM mRNA level and collagen Iα1, α-actin protein expression, respectively. Immunofluorescence was also used to confirm contraction induced by thrombin in HASM cells.

KEY FINDING

Thrombin stimulation enhanced HASM cells proliferation and activated TGF-β signaling. Thrombin induced ECM mRNA and collagen Iα1 protein expression, and these effects are mediated by TGF-β. Abrogation of TGF-β activation by contraction inhibitors cytochalasin D and formoterol prevents the thrombin-induced effects.

SIGNIFICANCE

These findings suggest that contraction-dependent TGF-β activation could be a mechanism by which thrombin leads to the development of asthmatic airway remodeling. Blocking physical forces with bronchodilator would be an intriguing way in reducing airway remodeling in asthma.

A core viral protein binds host nucleosomes to sequester immune danger signals

Viral proteins mimic host protein structure and function to redirect cellular processes and subvert innate defenses. Small basic proteins compact and regulate both viral and cellular DNA genomes. Nucleosomes are the repeating units of cellular chromatin and play an important part in innate immune responses. Viral-encoded core basic proteins compact viral genomes, but their impact on host chromatin structure and function remains unexplored. Adenoviruses encode a highly basic protein called protein VII that resembles cellular histones. Although protein VII binds viral DNA and is incorporated with viral genomes into virus particles, it is unknown whether protein VII affects cellular chromatin. Here we show that protein VII alters cellular chromatin, leading us to hypothesize that this has an impact on antiviral responses during adenovirus infection in human cells. We find that protein VII forms complexes with nucleosomes and limits DNA accessibility. We identified post-translational modifications on protein VII that are responsible for chromatin localization. Furthermore, proteomic analysis demonstrated that protein VII is sufficient to alter the protein composition of host chromatin. We found that protein VII is necessary and sufficient for retention in the chromatin of members of the high-mobility-group protein B family (HMGB1, HMGB2 and HMGB3). HMGB1 is actively released in response to inflammatory stimuli and functions as a danger signal to activate immune responses. We showed that protein VII can directly bind HMGB1 in vitro and further demonstrated that protein VII expression in mouse lungs is sufficient to decrease inflammation-induced HMGB1 content and neutrophil recruitment in the bronchoalveolar lavage fluid. Together, our in vitro and in vivo results show that protein VII sequesters HMGB1 and can prevent its release. This study uncovers a viral strategy in which nucleosome binding is exploited to control extracellular immune signaling.

Nicotine exaggerates LPS-induced airway hyperreactivity via JNK-mediated up-regulation of Toll-like receptor 4

Tobacco smokers often display increased airway hyperreactivity (AHR) when faced with bacterial infections. The present study uses a murine organ-culture model to dissect the mechanisms involved in this exaggerated smooth muscle response. Nicotine simulates the effects of smoking, and LPS represents bacterial infection. Contractile responses of isolated murine tracheal segments were analyzed in myographs after organ culture with increasing concentrations of LPS and/or nicotine for 4 days with or without specific MAPK inhibitors. Nicotine's effect on the expression of cell surface Toll-like receptors (TLRs), MCP-1, COX-2, and TNF-α were examined by real-time PCR. Increased protein expression was verified by immunohistochemistry. LPS concentration-dependently increased contractile responses to bradykinin and des-Arg(9)-bradykinin. A combination of nicotine and low-dose LPS caused powerful synergistic contractions along with increased kinin receptor expression. Specific kinin B1 and B2 receptor inhibitors blocked this reaction. Nicotine increased mRNA and protein expression of TLR4 and -6 in the epithelium and smooth muscle layer, with MCP-1 and COX-2 mRNA increasing in parallel. Specific inhibition of JNK attenuated nicotine's effects. In conclusion, long-term exposure to nicotine up-regulated the expression of TLR4 and -6 via a JNK-related pathway, causing an exaggeration of the LPS-induced local airway inflammation and increased AHR. This might offer a mechanistic explanation to the increased AHR seen in tobacco smokers confronted with bacterial infections.

Genetic factors regulating lung vasculature and immune cell functions associate with resistance to pneumococcal infection

Streptococcus pneumoniae is an important human pathogen responsible for high mortality and morbidity worldwide. The susceptibility to pneumococcal infections is controlled by as yet unknown genetic factors. To elucidate these factors could help to develop new medical treatments and tools to identify those most at risk. In recent years genome wide association studies (GWAS) in mice and humans have proved successful in identification of causal genes involved in many complex diseases for example diabetes, systemic lupus or cholesterol metabolism. In this study a GWAS approach was used to map genetic loci associated with susceptibility to pneumococcal infection in 26 inbred mouse strains. As a result four candidate QTLs were identified on chromosomes 7, 13, 18 and 19. Interestingly, the QTL on chromosome 7 was located within S. pneumoniae resistance QTL (Spir1) identified previously in a linkage study of BALB/cOlaHsd and CBA/CaOlaHsd F2 intercrosses. We showed that only a limited number of genes encoded within the QTLs carried phenotype-associated polymorphisms (22 genes out of several hundred located within the QTLs). These candidate genes are known to regulate TGFβ signalling, smooth muscle and immune cells functions. Interestingly, our pulmonary histopathology and gene expression data demonstrated, lung vasculature plays an important role in resistance to pneumococcal infection. Therefore we concluded that the cumulative effect of these candidate genes on vasculature and immune cells functions as contributory factors in the observed differences in susceptibility to pneumococcal infection. We also propose that TGFβ-mediated regulation of fibroblast differentiation plays an important role in development of invasive pneumococcal disease. Gene expression data submitted to the NCBI Gene Expression Omnibus Accession No: GSE49533

SNP data submitted to NCBI dbSNP Short Genetic Variation http://www.ncbi.nlm.nih.gov/projects/SNP/snp_viewTable.cgi?handle=MUSPNEUMONIA.

The role of IgE-receptors in IgE-dependent airway smooth muscle cell remodelling

Background

In allergic asthma, IgE increases airway remodelling but the mechanism is incompletely understood. Airway remodelling consists of two independent events increased cell numbers and enhanced extracellular matrix deposition, and the mechanism by which IgE up-regulates cell proliferation and extracellular matrix deposition by human airway smooth muscle cells in asthma is unclear.

Objective

Characterise the role of the two IgE receptors and associated signalling cascades in airway smooth muscle cell remodelling.

Methods

Primary human airway smooth muscle cells (8 asthmatics, 8 non-asthmatics) were stimulated with human purified antibody-activated IgE. Proliferation was determined by direct cell counts. Total collagen deposition was determined by Sircol; collagen species deposition by ELISA. IgE receptors were silenced by siRNA and mitogen activated protein kinase (MAPK) signalling was blocked by chemical inhibitors.

Results

IgE dose-dependently increased extracellular matrix and collagen deposition by airway smooth muscle cells as well as their proliferation. Specifically in cells of asthma patients IgE increased the deposition of collagen-type-I, -III, –VII and fibronectin, but did not affect the deposition of collagens type-IV. IgE stimulated collagen type-I and type-VII deposition through IgE receptor-I and Erk1/2 MAPK. Proliferation and deposition of collagens type-III and fibronectin involved both IgE receptors as well as Erk1/2 and p38 MAPK. Pre-incubation (30 minutes) with Omalizumab prevented all remodelling effects completely. We observed no changes in gelatinase activity or their inhibitors.

Conclusion & Clincal Relevance

Our study provides the molecular biological mechanism by which IgE increases airway remodelling in asthma through increased airway smooth muscle cell proliferation and deposition of pro-inflammatory collagens and fibronectin. Blocking IgE action prevents several aspects of airway smooth muscle cell remodelling. Our findings may explain the recently described reduction of airway wall thickness in severe asthma patients treated with humanised anti-IgE antibodies.