Irradiation Induces Epithelial Cell Unjamming

Abstract

The healthy and mature epithelial layer is ordinarily quiescent, non-migratory, solid-like, and jammed. However, in a variety of circumstances the layer transitions to a phase that is dynamic, migratory, fluid-like and unjammed. This has been demonstrated in the developing embryo, the developing avian airway, the epithelial layer reconstituted in vitro from asthmatic donors, wounding, and exposure to mechanical stress. Here we examine the extent to which ionizing radiation might similarly provoke epithelial layer unjamming. We exposed primary human bronchial epithelial (HBE) cells maintained in air-liquid interface (ALI) to sub-therapeutic doses (1 Gy) of ionizing radiation (IR). We first assessed: (1) DNA damage by measuring p-H2AX, (2) the integrity of the epithelial layer by measuring transepithelial electrical resistance (TEER), and (3) the extent of epithelial cell differentiation by detecting markers of differentiated airway epithelial cells. As expected, IR exposure induced DNA damage but, surprisingly, disrupted neither normal differentiation nor the integrity of the epithelial cell layer. We then measured cell shape and cellular migration to determine the extent of the unjamming transition (UJT). IR caused cell shape elongation and increased cellular motility, both of which are hallmarks of the UJT as previously confirmed. To understand the mechanism of IR-induced UJT, we inhibited TGF-β receptor activity, and found that migratory responses were attenuated. Together, these observations show that IR can provoke epithelial layer unjamming in a TGF-β receptor-dependent manner.

Bronchoconstriction: a potential missing link in airway remodelling

“…While discovering the UJT marked by cellular motility in the experimental system (figure 1a), a novel metric-based on cell shape was proposed to predict UJT based on a theoretical computational model of epithelial cells (figure 1b). This cell shape elongation predicted by the theoretical model has been further validated in the experimental data [40,[58][59][60].…”

“…10: 200254 the epithelial-to-mesenchymal transition (EMT) through the activation of the TGF-β receptor. However, signs of EMT were not observed during the UJT in HBE cells [59,61].…”

“…(b) Phalloidin staining from the corresponding cells above show the differences in cell shape between jammed and unjammed layers. HBE cells maintain a cobblestone-like shape in the jammed layer, whereas become elongated shape in the unjammed layer.Figure from[59] with the permission from the publisher.…”

In primary airway epithelial cells, the unjamming transition is distinct from the epithelial-to-mesenchymal transition

“…But as the system progressively unjams and transitions to a fluid-like phase local rearrangements amongst neighboring cells become increasingly possible and tend to be cooperative, intermittent, and heterogeneous 46,[51][52][53][54] . While poorly understood, cellular jamming and unjamming have been identified in epithelial systems in vitro 37,39,43,46,48,49,[54][55][56] , in developmental systems in vivo 39,42,50,[57][58][59] , and have been linked to the pathobiology of asthma [37][38][39] and cancer 45,47,60,61 .…”

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

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] For example, experimental data from both in vitro [1][2][3]5,7,11,15 and in vivo 2,6 studies have shown that UJT occurs spontaneously during physiological events such as embryonic development 2,6,9 as well as during pathophysiological events including wound repair 1,16 and cancer metastasis 4,8,9,17,18 . In addition, stimuli such as radiation 19 , stretch 2 , and mechanical compression 2,11,15 , all of which are associated with lung diseases, also have the capacity to trigger UJT. In the jammed phase each cell becomes virtually frozen in place -trapped by its immediate neighbors-in a collective phase where intercellular rearrangements are rare.…”