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 procontractile 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

Purification of mouse MEP-1, a nuclear protein which binds to the metal regulatory elements of genes encoding metallothionein.

Metal regulatory elements (MREs) shared by metallothionein (MT) gene promoters are essential for metal induction of MT genes. MEP-1, a nuclear protein which binds to these elements has been purified from heavy metal-resistant mouse L cells using footprinting, Southwestern and UV cross-linking techniques to assay its binding activity. The purification scheme, starting from crude nuclear extracts, involved a combination of heparin-Sepharose and MRE-DNA affinity chromatography. The purified protein preparation showed a single polypeptide band of 108 kDa on polyacrylamide gel electrophoresis, and 2D-gel analyses revealed the presence of a protein species migrating as a single population of approximately 110 kDa. MEP-1 does not appear to be glycosylated since it eluted with the flow-through on a Wheat Germ Sepharose column. It was retained by a zinc-Chelating Sepharose column suggesting that amino acid residues (i.e., cysteine, histidine) which have an affinity for zinc ions are exposed on the protein surface. Binding studies with the purified protein indicated that it binds specifically to MRE sequences and that the binding can be abolished by a point mutation in the MRE core consensus sequence or by the addition of the chelating agent 1,10-phenanthroline. Binding activity can be restored by the addition of zinc ions to the chelated protein. These results suggest that MEP-1 is one of the major proteins interacting with MRE sequences

Airway smooth muscle tone increases airway responsiveness in healthy young adults

© 2017 the American Physiological Society. Force adaptation, a process whereby sustained spasmogenic activation (viz., tone) of airway smooth muscle (ASM) increases its contractile capacity, has been reported in isolated ASM tissues in vitro, as well as in mice in vivo. The objective of the present study was to assess the effect of tone on airway responsiveness in humans. Ten healthy volunteers underwent methacholine challenge on two occasions. One challenge consisted of six serial doses of saline followed by a single high dose of methacholine. The other consisted of six low doses of methacholine 5 min apart followed by a higher dose. The cumulative dose was identical for both challenges. After both methacholine challenges, subjects took a deep inspiration (DI) to total lung capacity as another way to probe ASM mechanics. Responses to methacholine and the DI were measured using a multifrequency forced oscillation technique. Compared with a single high dose, the challenge preceded by tone led to an elevated response measured by respiratory system resistance (Rrs) and reactance at 5 Hz. However, there was no difference in the increase in Rrs at 19 Hz, suggesting a predominant effect on smaller airways. Increased tone also reduced the efficacy of DI, measured by an attenuated maximal dilation during the DI and an increased renarrowing post-DI. We conclude that ASM tone increases small airway responsiveness to inhaled methacholine and reduces the effectiveness of DI in healthy humans. This suggests that force adaptation may contribute to airway hyperresponsiveness and the reduced bronchodilatory effect of DI in asthma