Mechanics of Airway Smooth Muscle Cells and the Response to Stretch

Airway smooth muscle (ASM) cells are continuously exposed to stretching as we breathe, and this stretching regulates the cell contractility that is ultimately responsible for making breathing difficult. The past dozen years have led to major advances in our understanding of the rheology of the ASM and of the mechanical response to imposed stretch. This review covers the highly adaptable ability of cell function to be maintained over large length changes and reviews characteristic softening and lengthening behaviors. It covers foundations of theoretical interpretations based on myosin dynamics to recent findings that have lead to redefining much of the acute mechanics of the ASM as a soft glassy material. ASM is far from equilibrium, crowded with jostling, interacting molecules with mechanics that are fragile and easily disrupted by large stretches, yet which easily and slowly recover from each stretch. Chronic stretching leads to further changes as contractile phenotype becomes altered. The response to stretch has become one of the most important characteristics of ASM mechanics and defines its function, and ultimately may underlie dysfunction in airway diseases such as asthma.