Dissecting the roles of ADAM33 in allergic airways disease

Abstract

A disintegrin and metalloproteinase 33 (ADAM33) was identified in 2002 as an asthma susceptibility gene; it has also been shown to be associated with bronchial hyperresponsiveness (BHR), atopy and lung function decline. Studies in asthmatic patients have identified a soluble, enzymatically active form of the protein (sADAM33) which is increased in asthmatic bronchoalveolar lavage fluid, and correlates with disease severity. In support of a functional role for ADAM33 in asthma, transgenic mice expressing human sADAM33 exhibit increased airway remodelling and susceptibility to allergic airways disease, whereas mice lacking endogenous Adam33 are relatively protected against allergic airways disease.

The aim of this investigation was to use unbiased approaches, specifically, next generation RNA sequencing to investigate airway responses involving ADAM33. The first objective was to investigate the transcriptome of transgenic mice where sADAM33 expression had been induced under allergen naive conditions to identify mechanisms by which this may promote susceptibility to allergic airways disease. The second objective was to study how baseline and allergic airway responses were altered in response to Adam33 abrogation, investigating the transcriptome of Adam33 knockout and wildtype mice that had been challenged with saline or house dust mite to identify ADAM33 dependent allergic mechanisms.

The first investigation identified a novel association between expression of human sADAM33 in murine airways and the induction of an immune response-associated gene signature, including cytotoxic lymphocyte markers, and an interferon inducible gene signature. Further exploration of this signal identified a significant increase in granzyme B mRNA and protein in the lungs of sADAM33 mice, which was accompanied by an altered natural killer cell phenotype. Natural killer cells in sADAM33 mice retained their expression of the activation marker NKp46 and homeostatic marker KLRG1, identifying an increased NKp46+ KLRG1+ population, which preferentially expressed granzyme B. These results suggest that sADAM33 in the airway, may drive natural killer cells towards a more mature cytotoxic phenotype, which could be influential in subsequent allergic responses, identifying a role for sADAM33 in disease promotion.

RNA sequencing of Adam33 knockout and wildtype mice identified only 6 genes (inclusive of Adam33) differentially expressed between saline challenged mice, suggesting a requirement for an environmental stimulus to drive differential responses in these models. House dust mite challenge drove a clear separation in the based upon genotype at the whole transcriptome level, identifying a substantial differential response to allergic sensitisation between Adam33 knockout and wildtype mice. Pathway analysis identified an ADAM33-dependent metabolic response, with a particular emphasis on oxidative phosphorylation complexes, implicating mitochondrial mediated mechanisms of disease. Further work is required to dissect these mechanisms, identifying the cellular source and their involvement in allergic airways disease. The similarity between the allergen naive wildtype and Adam33 knockout mice, and the identified role for ADAM33 in disease predisposition and allergic responses, suggest that ADAM33 could be a suitable target for future asthma modifying therapies.

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Identifiers

ORCID for Hans Haitchi: orcid.org/0000-0001-8603-302X

ORCID for Donna Davies: orcid.org/0000-0002-5117-2991

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