The impact of low-frequency, low-force cyclic stretching of human bronchi on airway responsiveness

Abstract

BackgroundIn vivo, the airways are constantly subjected to oscillatory strain (due to tidal breathing during spontaneous respiration) and (in the event of mechanical ventilation) positive pressure. This exposure is especially problematic for the cartilage-free bronchial tree. The effects of cyclic stretching (other than high-force stretching) have not been extensively characterized. Hence, the objective of the present study was to investigate the functional and transcriptional response of human bronchi to repetitive mechanical stress caused by low-frequency, low-force cyclic stretching.MethodsAfter preparation and equilibration in an organ bath, human bronchial rings from 66 thoracic surgery patients were stretched in 1-min cycles of elongation and relaxation over a 60-min period. For each segment, the maximal tension corresponded to 80% of the reference contraction (the response to 3 mM acetylcholine). The impact of cyclic stretching (relative to non-stretched controls) was examined by performing functional assessments (epithelium removal and incubation with sodium channel agonists/antagonists or inhibitors of intracellular pathways), biochemical assays of the organ bath fluid (for detecting the release of pro-inflammatory cytokines), and RT-PCR assays of RNA isolated from tissue samples.ResultsThe application of low-force cyclic stretching to human bronchial rings for 60 min resulted in an immediate, significant increase in bronchial basal tone, relative to non-cyclic stretching (4.24 ± 0.16 g vs. 3.28 ± 0.12 g, respectively; p < 0.001). This cyclic stimulus also increased the affinity for acetylcholine (−log EC50: 5.67 ± 0.07 vs. 5.32 ± 0.07, respectively; p p < 0.001). Removal of airway epithelium and pretreatment with the Rho-kinase inhibitor Y27632 and inward-rectifier K+ or L-type Ca2+ channel inhibitors significantly modified the basal tone response. Exposure to L-NAME had opposing effects in all cases. Pro-inflammatory pathways were not involved in the response; cyclic stretching up-regulated the early mRNA expression of MMP9 only, and was not associated with changes in organ bath levels of pro-inflammatory mediators.ConclusionLow-frequency, low-force cyclic stretching of whole human bronchi induced a myogenic response rather than activation of the pro-inflammatory signaling pathways mediated by mechanotransduction.

Stretch-induced actomyosin contraction in epithelial tubes: Mechanotransduction pathways for tubular homeostasis

“…This conformational change of ROCK results in its autophosphorylation and activation. ROCK activation is important for contractile response, as upon inhibition of ROCK activity with the ROCK inhibitor Y27632, the basal tone of cyclically stretched isolated human bronchi is significantly affected [81]. Once activated, ROCK phosphorylates MLC [82], enabling myosin binding to actin and contraction [83].…”

Breathing on Chip: Dynamic flow and stretch tune cellular composition and accelerate mucociliary maturation of airway epitheliumin vitro

“…These effects of moderate levels of mechanical cues are in contrast with the upregulation of inflammatory markers reported previously in the context of mechanical ventilation and excessive mechanical stretch and compression 9,18 . Contrary to studies using whole mount tissue 19 , undifferentiated primary cells 20 or cell lines 21,39,43 , our model may have captured phenotype-modulating, potentially even beneficial, effects of normal airflow and stretch by (i) using human primary cells from multiple human donors, (ii) allowing the basal cells to differentiate into a pseudostratified airway epithelium in the presence of mechanical stimulation, and (iii) applying mechanical stimulation over prolonged times, i.e. over 7 days compared to 24-48h 43,44 , in order to capture adaptive remodeling rather than an acute insult.…”

“…While these and other studies [14][15][16] demonstrate the complex, and still mostly unresolved, effects of breathing-related forces on alveolar epithelial biology, even less is known about their contribution to airway epithelial biology, mainly due to the lack of experimental platforms allowing studies on welldifferentiated airway epithelial cell cultures at the air-liquid interface (ALI). Previous work has focused on the detrimental effects of mechanical ventilation 17 or bronchoconstriction 18 , and employed whole airway tissue mounts 19 , undifferentiated bronchial epithelial basal cells 20 , or cell lines 21 . This leaves unresolved the fundamental question of whether healthy respiratory forces positively impact human airway epithelial biology.…”

Use of human airway smooth muscle in vitro and ex vivo to investigate drugs for the treatment of chronic obstructive respiratory disorders

“…Airway hyperinflation induces mechanical stress on the bronchial wall leading to the release of reactive oxygen species (ROS) and inflammatory factors such as leukotrienes (LT) via nitric oxide synthase activation leading to contractile ASM response dependent on Rho-kinase (Faisy et al, 2011). Airway stretch also increases the responsiveness to ACh and expression of matrix metallopeptidase 9 (MMP-9) (Le Guen et al, 2015Guen et al, , 2016. Mechanical stress can be reproduced in vitro via bronchial QS of 0.25 and 0.50 mm.…”