Different modes of fluidization in Human Bronchial Epithelial Cells -- the Unjamming Transition vs. the Epithelial-Mesenchymal Transition

Epithelial tissues are non-migratory and behave as a jammed system under homeostatic conditions. Using a jammed layer of human lung epithelial cells we compare a new mode of tissue fluidization, induced by mechanical compression, namely the unjamming transition (UJT) with the epithelial-mesenchymal transition (EMT). Our analyses of experimental data reveal the following: Strong cellular elongation and large fast moving Nematic swirls during the UJT while retaining epithelial nature. All these features are lost during the EMT when the cells become mesenchymal. To further our understanding we developed a dynamic vertex model (DVM) which differs from previous vertex models in that the cell edges can now become curved and can thus reflect the competition of the forces acting on the edge locally. These forces include cortical tension, intracellular-pressure differences, and polarized motility forces. We explore different paths of solid-to-fluid transitions based on different parameters in the model, such as individual cell motility and preferred cell shapes, and compare our predictions with the experimental observations on UJT and EMT. Based on our comparisons, we propose that the UJT could be an alternative route to fluidization of jammed epithelial tissues, independent of the EMT.