Airway smooth muscle remodelling in mild and moderate equine asthma.
Authors: Dupuis-Dowd Florence, Lavoie Jean-Pierre
Journal: Equine veterinary journal
Summary
# Airway smooth muscle remodelling in mild and moderate equine asthma Whilst severe equine asthma is known to involve structural thickening of airway smooth muscle coupled with altered contractility, little evidence exists regarding smooth muscle changes in milder disease presentations. Dupuis-Dowd and Lavoie examined endobronchial biopsies from 18 horses with mild-to-moderate asthma (MEA) and seven healthy controls, measuring smooth muscle cell proliferation via PCNA immunohistochemistry and assessing expression of the hypercontractile (+)insert smooth muscle myosin heavy chain (SMMHC) isoform using RT-qPCR. Asthmatic horses demonstrated approximately 1.5-fold greater (+)insert SMMHC expression compared to controls, though absolute smooth muscle cell proliferation and myocyte density did not differ significantly between groups; notably, however, proliferating myocyte percentages correlated strongly with pulmonary neutrophilia (r = 0.80) and (+)insert SMMHC expression (r = 0.66) in asthmatic horses. These findings extend our understanding of smooth muscle dysfunction beyond severe disease, suggesting that functional remodelling—characterised by shifts towards more contractile phenotypes—occurs early in asthma progression and may be linked to inflammatory status. For practitioners, this work supports the potential development of smooth muscle biomarkers as objective measures of disease severity and therapeutic response, which could ultimately inform earlier intervention strategies and more targeted management protocols.
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Practical Takeaways
- •Smooth muscle remodelling in equine asthma progresses from mild disease onwards, not just in severe cases, suggesting early intervention may be beneficial
- •Changes in smooth muscle contractile protein expression can be detected before significant proliferation occurs, potentially allowing earlier detection and monitoring of asthma progression
- •The correlation between inflammatory markers and smooth muscle changes provides potential biomarkers for assessing asthma severity and therapeutic response in clinical practice
Key Findings
- •(+)insert SMMHC isoform expression was 1.5 times greater in horses with mild and moderate asthma compared to controls (P = 0.02)
- •No significant differences in airway smooth muscle cell proliferation or myocyte density between asthmatic and control horses
- •Percentage of proliferating myocytes correlated with pulmonary neutrophilia (r = 0.80, P = 0.01) and with (+)insert SMMHC expression (r = 0.66, P = 0.03) in asthmatic horses
- •Bronchial smooth muscle remodelling occurs in mild forms of equine asthma, not just in severe disease