Dissecting the inflammatory twitch in allergically inflamed mice

Pathophysiology to Phenotype in the Asthma of Obesity

Obesity affects numerous diseases, including asthma, for reasons that remain incompletely understood. Recent research suggests that the asthma of obesity is not a single disease, and that it breaks out into at least two distinct phenotypes. One phenotype is conventional allergic asthma modulated by obesity, whereas another arises solely due to the presence of obesity. The latter is postulated to be a consequence of the chronic lung compression caused by the obese chest wall in individuals with particularly collapsible lungs. Allergic obese asthma, on the other hand, appears to result from the way that obesity affects the immune system, which we hypothesize can be understood in terms of effects on the dynamic regulation of the inflammatory response.

A theoretical model of inflammation- and mechanotransduction-driven asthmatic airway remodelling

Inflammation, airway hyper-responsiveness and airway remodelling are well-established hallmarks of asthma, but their inter-relationships remain elusive. In order to obtain a better understanding of their inter-dependence, we develop a mechanochemical morphoelastic model of the airway wall accounting for local volume changes in airway smooth muscle (ASM) and extracellular matrix in response to transient inflammatory or contractile agonist challenges. We use constrained mixture theory, together with a multiplicative decomposition of growth from the elastic deformation, to model the airway wall as a nonlinear fibre-reinforced elastic cylinder. Local contractile agonist drives ASM cell contraction, generating mechanical stresses in the tissue that drive further release of mitogenic mediators and contractile agonists via underlying mechanotransductive signalling pathways. Our model predictions are consistent with previously described inflammation-induced remodelling within an axisymmetric airway geometry. Additionally, our simulations reveal novel mechanotransductive feedback by which hyper-responsive airways exhibit increased remodelling, for example, via stress-induced release of pro-mitogenic and pro-contractile cytokines. Simulation results also reveal emergence of a persistent contractile tone observed in asthmatics, via either a pathological mechanotransductive feedback loop, a failure to clear agonists from the tissue, or a combination of both. Furthermore, we identify various parameter combinations that may contribute to the existence of different asthma phenotypes, and we illustrate a combination of factors which may predispose severe asthmatics to fatal bronchospasms.