Airway smooth muscle (ASM) orientation and morphology determine the ability of the muscle to constrict the airway. In asthma, ASM mass is increased, but it is unknown whether ASM orientation and morphology are altered as well, or whether the remodelling at the source of the mass increase is ongoing. We dissected human airway trees from asthmatic and control lungs. Stained, intact airway sections were imaged in axial projection to show ASM bundle orientation, while cross-sectional histological slides were used to assess ASM area, bundle thickness and ASM bundle to basement membrane distance. We also used these slides to assess cell size, proliferation and apoptosis. We showed that ASM mass increase in cartilaginous airways is primarily the result of an increase of ASM bundle thickness (as measured radially in an airway cross-section) and coincides with an increased distance of the ASM bundles to the airway perimeter. ASM orientation was unchanged in all airways. Apoptosis markers and cell size did not show differences between asthmatics and controls. Our findings show that ASM mass increase likely contributes to the airway constricting capacity of the muscle. Both the increased bundle thickness and increased thickness of the airway wall inwards of the ASM bundles could further enhance this capacity. Turnover of ASM appears to be the same in airways and biopsies, but the lack of correlation between different markers of proliferation casts doubt on the specificity of markers generally used to assess proliferation.
- smooth muscle orientation
- airway morphology
- Copyright © 2016, American Journal of Physiology-Lung Cellular and Molecular Physiology