Molecular mechanisms underlying the development and propagation of preschool wheeze and asthma: the role of interleukin (IL)-33 and activin A

Context of the Research: Although approximately 40% of children under 5 years old wheeze, most grow out of their symptoms, and only some of the wheezers, (about one-third) develop asthma by school-age. We know that children who develop asthma have damage and scarring of the tubes (airways) in their lungs very early, between about 1 and 3 years of age, which remains at least until early adulthood. The factors that determine which preschool wheezers will develop asthma include a genetic susceptibility, development of early allergies and also getting early lung infections, especially with viruses. We are not able to predict which preschool wheezers will develop asthma, and importantly, there are no medicines which stop children from having reduced lung function and lessen airway scarring and damage. It is difficult to make measurements of lung scarring in very young children, since this needs samples taken from the lungs during a general anaesthetic. We have already developed a novel newborn mouse model to mimic how early preschool wheeze in infants caused by allergies leads to school-aged asthma. We have used house dust mites to cause mouse asthma. So far, we have shown that two chemicals seem very important in causing this type of allergic asthma. They are called interleukin (IL)-33 and activin. We think that these are new molecules whose action could be blocked as a treatment to stop the development of asthma from preschool wheeze. However, we have not yet explored the effect of virus infection in this model, and critically, as happens to young children, we have not looked at the interplay of viruses and allergies in our mouse model.
Aims and Objectives: The aim of this project is therefore to make a newborn mouse model of virus lung infection, using 2 viruses that cause wheezing in young children. We will then look at the production of the important molecules that we have already found in the allergic asthma model in the virus infection model alone, and when both virus infection and house dust mites are used together. We think that the molecules will have different importance in young mice which are still developing disease compared to older mice with the full blown disease. Once we have established the important molecules that are involved in virus induced disease, allergy induced disease, and a combination of both, we will confirm the findings from the animal experiments in samples from children with severe symptoms. At the Brompton Hospital, we have developed a programme of using a special camera (bronchoscope) to look into the lungs of children with really severe wheeze or asthma to help to work out why their symptoms are so bad. In addition, if the child's parents agree, we have permission from the ethics committee to use any excess samples that remain after the clinical report for research. We will look at blood samples, airway washings and tiny pieces of tissue (biopsies) from the airways, and compare preschool children who only wheeze with virus infections, to those who wheeze with and without viruses, to school-aged children who have asthma. The samples are so tiny that we need to make targeted measurements, hence the need for the animal model to guide us as to which molecules are most promising. We will ascertain the role of at least 2 new molecules (IL-33 and activin) in the development of asthma from preschool wheeze. By also comparing the molecules in preschool children with wheezing to those in older children with asthma, we will be able to decide whether blocking one or other of the molecules may be better for treating younger children, when they are developing asthma, compared to older children who already have asthma.
Potential Applications and Benefits: This project will allow us to work out whether targeting and blocking the action of these very new molecules might be the best way of stopping the very early damage and scarring that occurs in the lungs of young children that wheeze and develop asthma.

Wheezing disorders are common in infants and preschool children, but not all wheezers develop asthma, and little is known about the molecular mechanisms underlying the pathogenesis of preschool wheeze and the determinants of its progression to asthma. We hypothesise that interleukin (IL)-33 and activin A are produced early after allergen exposure, and that secondary signals such as exposure to virus contribute to their production and interaction in the development of asthma.
Research Objectives: To develop a neonatal mouse model of respiratory virus infection with and without concurrent allergen exposure to model childhood preschool wheeze, and explore the molecular mechanisms underlying the development of airway hyperresponsiveness (AHR), inflammation (AI) and remodelling (AR), and confirm these in airway samples from children with severe wheeze and asthma.
Methodology and experimental design: Neonatal mice will be exposed intra-nasally to human metapneumovirus or rhinovirus. Viral persistence and replication, and impact on AHR, AI and AR will be assessed. Subsequently, effects on all parameters after virus or allergen alone, or together, will be quantified. In addition, the underlying molecular pathways involving Th2 cytokines, innate cytokines and remodelling cytokines will be explored. Finally, molecular targets identified in the neonatal model will be confirmed in airway samples obtained bronchoscopically (broncho-alveolar lavage (BAL) and endobronchial biopsies) from children with severe wheeze and asthma.
Techniques: Measurement of murine neonatal lung function. Assessment of inflammation and cytokines using flow cytometry. Quantification of airway remodelling in histological sections using computer aided image analysis.
Application: This project will allow us to identify novel therapeutic targets that may prevent the development of asthma from preschool wheeze, and also to compare targets involved in disease inception to those in disease persistence.

International researchers worldwide will benefit from the findings since we will determine the role of at least two new potential therapeutic targets for early intervention in preschool wheeze. This project will allow us to confirm the roles novel molecules such as interleukin (IL)-33 and activin in the clinical phenotypes of early wheezing, and how they interact in the context of allergen and viral exposure to determine the development of asthma. We are not aware of any other groups concentrating on the mechanisms underlying the development of early preschool wheeze and the factors that determine its progression to asthma.
Currently we have no means of preventing the early and permanent loss of lung function, and the development of asthma, in susceptible children. They are thus committed to prolonged morbidity, medication usage, and even mortality. The medications that we have available are predominantly steroids, but in the younger preschoolers, these do not always work, and we have very few other treatment options. Current asthma therapies are only palliative, suppressing symptoms and airway inflammation as far as possible, but not changing the natural history of the disease. Furthermore, treatments are completely ineffective in preventing the development of airway remodelling (scarring). Thus there is an urgent need to find a way of intervening early to prevent the development of the disease. There are approximately 5.2 million asthmatics in the UK, and of these, 1.1 million are children. Children with severe asthma are at high risk of significant morbidity and mortality, and use a disproportionate amount of healthcare resources. The estimated annual cost to the NHS resulting from asthma is £889million. In the long term, if successful, the identification of novel therapeutic targets to prevent disease from this project, will allow a reduction in the burden of disease, both by impacting patient morbidity and healthcare costs.
Importantly, we know from longitudinal cohort studies that children with severe asthma remain severe in adulthood, and nearly half develop chronic obstructive pulmonary disease (COPD). Thus they continue to suffer significant morbidity, with a huge impact on quality of life, and continued use of healthcare resources. If successful, the identification of novel therapeutic targets from this project would ultimately result in an alteration in the natural history of the disease such that morbidity from childhood disease, which at present continues into adulthood, would be significantly lowered.
Time-scale for clinical benefit:
If molecular targets that prevent the development of asthma from preschool wheeze are identified, the time-scale to which benefits would reach patients is about 10 years.
Benefits to staff working on the project:
Dr Stephen Lui who will be working on the project will gain significant experience in managing budgets and in time management as he will be in charge of all animal work, and will also be responsible for ordering appropriate reagents and consumables for the experiments. Furthermore, he will be expected to contribute intellectually to the project by analysing data, presenting at scientific meetings, and writing up for publication. All of these will provide significant skills that can be used in other employment sectors.