Annalicia Vaughan

Biomarkers of progression of chronic obstructive pulmonary disease (COPD)

Disease progression of chronic obstructive pulmonary disease (COPD) is variable, with some patients having a relatively stable course, while others suffer relentless progression leading to severe breathlessness, frequent acute exacerbations of COPD (AECOPD), respiratory failure and death. Radiological markers such as CT emphysema index, bronchiectasis and coronary artery calcification (CAC) have been linked with increased mortality in COPD patients. Molecular changes in lung tissue reflect alterations in lung pathology that occur with disease progression; however, lung tissue is not routinely accessible. Cell counts (including neutrophils) and mediators in induced sputum have been associated with lung function and risk of exacerbations. Examples of peripheral blood biological markers (biomarkers) include those associated with lung function (reduced CC-16), emphysema severity (increased adiponectin, reduced sRAGE), exacerbations and mortality [increased CRP, fibrinogen, leukocyte count, IL-6, IL-8, and tumor necrosis factor α (TNF-α)] including increased YKL-40 with mortality. Emerging approaches to discovering markers of gene-environment interaction include exhaled breath analysis [volatile organic compounds (VOCs), exhaled breath condensate], cellular and systemic responses to exposure to air pollution, alterations in the lung microbiome, and biomarkers of lung ageing such as telomere length shortening and reduced levels of sirtuins. Overcoming methodological challenges in sampling and quality control will enable more robust yet easily accessible biomarkers to be developed and qualified, in order to optimise personalised medicine in patients with COPD.

Personalizing and targeting therapy for COPD: the role of molecular and clinical biomarkers.

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease characterized by persistent airflow limitation. It is the third leading cause of death worldwide, and there are currently no curative strategies for this disease. Many factors contribute to COPD susceptibility, progression and exacerbations. These include cigarette smoking, environmental and occupational pollutants, respiratory infections and comorbidities. As the clinical phenotypes of COPD are so variable, it has been difficult to devise an individualized treatment plan for patients with this complex chronic disease. This review will highlight how potential clinical, inflammatory, genomic and epigenomic biomarkers for COPD could be used to personalize treatment, leading to improved disease management and prevention for our patients.

How microRNAs orchestrate the lung's biological responses

Micro RNAs (miRNAs) have emerged as an important mechanism of epigenetic regulation of gene expression. MicroRNAs are non-coding, single-stranded RNA species of ∼22 nucleotides in length that are involved in gene silencing and other effects on gene expression. MicroRNAs mediate gene silencing through messenger RNA (mRNA) degradation (partial complementarity to mRNA molecules in the RNAinduced silencing complex) or translational repression (inhibition of translational machinery). Approximately 1100 human microRNAs have been discovered, with each potentially targeting up to hundreds of mRNAs, and regulating around 60% of human genes. These small, non-coding RNAs influence a myriad of gene pathways and cellular functions in health and disease. However, their exact role in the pathogenesis of lung diseases such as asthma, chronic obstructive pulmonary disease, lung cancer and other conditions remains to be determined. Recent studies have shown that microRNA expression is altered in different lung disease states. MicroRNA expression has been implicated in various pathogenic mechanisms linked to lung diseases, including oxidative stress, cell proliferation, protease-antiprotease imbalance, tumorigenesis and inflammation. There is also dysregulated expression of microRNAs in structural components of the lung, such as the bronchial epithelium. For instance, miR-19a is overexpressed in human bronchial epithelial cells (HBEC) of patients with severe asthma, and miR-17 has been shown to regulate interleukin-8 expression of HBEC from patients with cystic fibrosis. MicroRNA expression is altered in HBEC after exposure to environmental agents such as diesel exhaust particles and cigarette smoke extract. Extending these principles, in this issue of Respirology, Cristan Herbert, Rakesh Kumar and colleagues report on their systematic search for relevant microRNAs involved in the response of airway epithelial cells to viral-like stimuli. Through predictive online databases, a number of microRNAs were identified as potential regulators of mediators involved in the anti-viral response of airway epithelial cells. Three of these microRNAs (miR-139-5p, miR-423-5p and miR-542-3p) had significantly decreased expression in airway epithelial cells pretreated with Th2 cytokines (interleukin 4 and interleukin 13) and challenged with double-stranded RNA, which mimics viral nucleic acid. This was consistent with reduced gene silencing effects of these microRNAs, leading to enhanced Th2 mediator expression and anti-viral responses. miR-135a-5p showed a trend to reduced expression, and miR-223-3p showed increased expression. This key study demonstrates a number of novel approaches. Instead of commencing with global expression studies using microRNA arrays, the investigators defined a gene set of relevance to Th2 and anti-viral responses in asthma, and then interrogated multiple online databases to identify microRNAs which were predicted to regulate these genes. This ‘reverse search’ (from genes back to the regulating microRNAs) proved to be an efficient approach, even taking in account the many algorithms used in the predictive databases and the partial complementarity (imperfect binding) of microRNAs to mRNA sequences. After biological validation of microRNA expression in the in vitro model, a ‘forward search’ found additional gene targets relevant to inflammatory and anti-viral responses. Both positive and negative regulator microRNAs were identified in these experiments, and the microRNAs were relevant across human and mouse genes. Their study used a conceptually simple model— human airway epithelial cells, conditioned with Th2 cytokines and challenged with viral mimics—to discover microRNAs with complex function. The challenge now is to translate this model and its findings further; for example, by testing multiple types of human lung cells, additional cytokines and challenges, preclinical (animal) models examining whole lungs and ultimately clinical studies in patients. Nevertheless, this study provides initial support for the role of microRNAs in orchestrating some of the excessive anti-viral responses of the lung, which could either initiate or perpetuate the airway inflammation that is characteristic of asthma. Important studies such as this one by Herbert et al. improve our understanding of the role of microRNAs in regulating gene expression and their contribution to the pathogenesis of asthma and other chronic lung diseases. Altered microRNA expression could serve as useful biomarkers of the presence of lung disease, or a marker of disease severity. A promising avenue for therapeutics is the targeting of microRNAs, through use of mimics to enhance microRNA effects, or antagomirs to block microRNA effects. Targeting microRNAs could then enable the therapeutic coverage of networks of expressed genes, and have potentially greater treatment effect than just targeting one or a small number of molecular targets. However, before microRNA agonists or antagonists bs_bs_banner

Removal of Organic Content from Diesel Exhaust Particles Alters Cellular Responses of Primary Human Bronchial Epithelial Cells Cultured at an Air-Liquid Interface

Background Exposure to air pollutants, including diesel particulate matter, has been linked to adverse respiratory health effects. Inhaled diesel particulate matter contains adsorbed organic compounds. It is not clear whether the adsorbed organics or the residual components are more deleterious to airway cells. Using a physiologically relevant model, we investigated the role of diesel organic content on mediating cellular responses of primary human bronchial epithelial cells (HBECs) cultured at an air-liquid interface (ALI). Methods Primary HBECs were cultured and differentiated at ALI for at least 28 days. To determine which component is most harmful, we compared primary HBEC responses elicited by residual (with organics removed) diesel emissions (DE) to those elicited by neat (unmodified) DE for 30 and 60 minutes at ALI, with cigarette smoke condensate (CSC) as the positive control, and filtered air as negative control. Cell viability (WST-1 cell proliferation assay), inflammation (TNF-α, IL-6 and IL-8 ELISA) and changes in gene expression (qRT-PCR for HO-1, CYP1A1, TNF-α and IL-8 mRNA) were measured. Results Immunofluorescence and cytological staining confirmed the mucociliary phenotype of primary HBECs differentiated at ALI. Neat DE caused a comparable reduction in cell viability at 30 or 60 min exposures, whereas residual DE caused a greater reduction at 60 min. When corrected for cell viability, cytokine protein secretion for TNF-α, IL-6 and IL-8 were maximal with residual DE at 60 min. mRNA expression for HO-1, CYP1A1, TNF-α and IL-8 was not significantly different between exposures. Conclusion This study provides new insights into epithelial cell responses to diesel emissions using a physiologically relevant aerosol exposure model. Both the organic content and residual components of diesel emissions play an important role in determining bronchial epithelial cell response in vitro. Future studies should be directed at testing potentially useful interventions against the adverse health effects of air pollution exposure.