Continuum interpretation of mechano-adaptation in micropatterned epithelia informed by in vitro experiments
Authors: Cook Bernard L , Alford Patrick W 
Published: August 2023

Abstract
Epithelial tissues adapt their form and function following mechanical perturbations, or mechano-adapt, and these changes often result in reactive forces that oppose the direction of the applied change. Tissues subjected to ectopic tensions, for example, employ behaviors that lower tension, such as increasing proliferation or actomyosin turnover. This oppositional behavior suggests that the tissue has a mechanical homeostasis. Whether attributed to maintenance of cellular area, cell density, or cell and tissue tensions, epithelial mechanical homeostasis has been implicated in coordinating embryonic morphogenesis, wound healing, and maintenance of adult tissues. Despite advances toward understanding the feedback between mechanical state and tissue response in epithelia, more work remains to be done to examine how tissues regulate mechanical homeostasis using epithelial sheets with defined micropatterned shapes. Here, we used cellular microbiaxial stretching (CμBS) to investigate mechano-adaptation in micropatterned tissues of different shape consisting of Madin–Darby canine kidney cells. Using the CμBS platform, tissues were subjected to a 30% stretch that was held for 24 h. We found that, following stretch, tissue stresses immediately increased then slowly evolved over time, approaching their pre-stretch values by 24 h. Organization of the actin cytoskeletal was found to play a role in this process: anisotropic ally structured tissues exhibited anisotropic stress patterns, and the cytoskeletal became more aligned following stretch and reorganized over time. Interestingly, in unstretched tissues, stresses also decreased, which was found to be driven by proliferation-induced cellular confinement and change in tissue thickness. We modeled these behaviors with a continuum-based model of epithelial growth that accounted for stress-induced actin remodeling and proliferation, and found this model to strongly capture experimental behavior. Ultimately, this combined experimental-modeling approach suggests that epithelial mechano-adaptation depends on cellular architecture and proliferation, which can be modeled with a field-averaged approach applicable to more specific contexts in which change is driven by epithelial mechanical homeostasis.
Insight box Epithelial tissues adapt their form and function following mechanical perturbation, and it is thought that this ‘mechano-adaptation’ plays an important role in driving processes like embryonic morphogenesis, wound healing, and adult tissue maintenance. Here, we use cellular microbiaxial stretching to probe this process in vitro in small epithelial tissues whose geometries were both controlled and varied. By using a highly precise stretching device and a continuum mechanics modeling framework, we revealed that tissue mechanical state changes following stretch and over time, and that this behavior can be explained by stress-dependent changes in actin fibers and proliferation. Integration of these approaches enabled a systematic approach to empirically and precisely measure these phenomena.