Mechanical forces induce an asthma gene signature in healthy airway epithelial cells

Abstract

Bronchospasm compresses the bronchial epithelium, and this compressive stress has been implicated in asthma pathogenesis. However, the molecular mechanisms by which this compressive stress alters pathways relevant to disease are not well understood. Using air-liquid interface cultures of primary human bronchial epithelial cells derived from non-asthmatic donors and asthmatic donors, we applied a compressive stress and then used a network approach to map resulting changes in the molecular interactome. In cells from non-asthmatic donors, compression by itself was sufficient to induce inflammatory, late repair, and fibrotic pathways. Remarkably, this molecular profile of non-asthmatic cells after compression recapitulated the profile of asthmatic cells before compression. Together, these results show that even in the absence of any inflammatory stimulus, mechanical compression alone is sufficient to induce an asthma-like molecular signature. Bronchial epithelial cells (BECs) form a physical barrier that protects pulmonary airways from inhaled irritants and invading pathogens 1,2. Moreover, environmental stimuli such as allergens, pollutants and viruses can induce constriction of the airways 3 and thereby expose the bronchial epithelium to compressive mechanical stress. In BECs, this compressive stress induces structural, biophysical, as well as molecular changes 4,5 , that interact with nearby mesenchyme 6 to cause epithelial layer unjamming 1 , shedding of soluble factors, production of matrix proteins, and activation matrix modifying enzymes, which then act to coordinate inflammatory and remodeling processes 4,7-10. Growing evidence supports the notion that mechanical stress in the airway induces not only developmental, homeostatic and reparative responses in the healthy lung but also pathophysiologic processes in the asthmatic lung 2,11-13. For example, mechanical stimuli induce early inflammatory and remodeling factors 6,7,14,15 , microRNAs (miRs) 16,17 , and cell proliferation 18. Using protein-protein interaction networks, here we compare responses to compressive stress in human BECs (HBECs) obtained from non-asthmatic versus asthmatic donors. Our hypothesis was, that using a systems biology approach to examine the effect of mechanical forces acting on structural cells in the airway, will elucidate the complex transcriptional programs that contribute to disease development and pathophysiology.

Genomic signatures of the unjamming transition in compressed human bronchial epithelial cells

“…HBECs, grew them to confluence under Air Liquid Interface (ALI), and then exposed them to an apico-to-basal pressure difference of 30 cm H2O 15,26,29,30,[36][37][38] (see Materials and Methods). Following the same experimental protocol described in Kılıç et al 30 , this pressure was maintained for 3 hours and then released ( Fig. 1a).…”

“…Compared with HBECs derived from non-asthmatic donors, HBECs derived from asthmatic donors exhibit phenotypic characteristics of unjammed tissues, with more elongated shapes and prominent collective migratory behavior 11 . At the transcriptional level, a recent study has shown that asthmatic HBECs and nonasthmatic HBECs at 24 hours post-compression exhibit similar transcriptional patterns as genes associated with airway remodeling and ECM reorganization 30 .…”

“…In well-differentiated primary human bronchial epithelial cells (HBECs), mechanical compression unjams the epithelial layer 11,15 and activates signaling pathways including EGFR [21][22][23] , TGF-β receptor [24][25][26][27] and ERK 15,23 . In the same model system, it also induces procoagulant factors 28,29 and induces an asthma-like transcriptional pattern that involves inflammatory, fibrotic and remodeling processes 30 .…”

Epithelial layer unjamming shifts energy metabolism toward glycolysis

“…UJT is known to occur during embryonic development 19 , 20 , injury repair 21 , tumor metastasis 22 , 23 , and in the asthmatic airways 19 , 24 . Both the UJT and the EMT potentiate epithelial plasticity and migration, but underlying mechanisms of UJT versus EMT are distinct 19 , 20 , 25 , 26 . Unlike the case of the EMT, for example, in the case of the UJT the cell–cell junction and barrier function remain fully intact 25 .…”

Epithelial layer unjamming shifts energy metabolism toward glycolysis

“…UJT is known to occur during embryonic development 19,20 , injury repair 21 , tumor metastasis 22,23 , and in the asthmatic airways 19,24 . Both the UJT and the EMT potentiate epithelial plasticity and migration, but underlying mechanisms of UJT versus EMT are distinct 19,20,25,26 . Unlike the case of the EMT, for example, in the case of the UJT the cell-cell junction and barrier function remain fully intact 25 .…”