MARCKS protein is a potential target in a naturally occurring equine model of neutrophilic asthma.

BACKGROUND: Asthma is a chronic inflammatory airway disease that affects millions of people worldwide. Horses develop asthma spontaneously and serve as a relevant model for multiple phenotypes and endotypes of human asthma. In horses with equine asthma (EA), environmental organic dust triggers increased inflammatory cytokines, excess airway mucus, reversible bronchoconstriction, and airway inflammation. In horses with severe EA (sEA), lower airway inflammation is invariably neutrophilic, making sEA a potential model for severe neutrophilic asthma in humans. Alveolar macrophages (AM) and airway neutrophils contribute to lower airway inflammation and tissue damage through the release of cytokines and toxic mediators including reactive oxygen species. Previous work shows that the Myristoylated Alanine Rich C Kinase Substrate (MARCKS) protein is increased in activated macrophages and neutrophils and is an essential regulator of inflammatory functions in these cell types. We hypothesized that MARCKS protein would be increased in bronchoalveolar lavage (BAL) cells from horses with EA, and that in vitro inhibition of MARCKS with a specific inhibitor peptide known as MyristoylAted N-terminal Sequence (MANS), would diminish cytokine production and respiratory burst. METHODS: BAL cells from two populations of healthy and asthmatic horses were evaluated for cytology and MARCKS protein analysis. Isolated alveolar macrophages and peripheral blood neutrophils were stimulated with zymosan to evaluate MARCKS inhibition in cytokine secretion and respiratory burst. RESULTS: We found increased levels of normalized MARCKS protein in total BAL cells from horses with asthma compared to normal horses. MARCKS inhibition with the MANS peptide had no effect on zymosan-stimulated release of tumor necrosis factor alpha (TNFα) or interleukin-8 (IL-8) from alveolar macrophages but did attenuate zymosan-stimulated respiratory burst in both alveolar macrophages and peripheral blood neutrophils. CONCLUSIONS: These findings point to a possible role for MARCKS in the pathophysiology of neutrophilic equine asthma and support further investigation of MARCKS as a novel anti-inflammatory target for severe neutrophilic asthma.