(665g) Invited Talk: Biomechanics of Epithelial Tissue Homeostasis, Collapse, and Eversion

Organization of cells into functional tissues is essential to development and wound healing. Irregular or uncontrolled growth and assembly of cells leads to pathologies such as tumor formation and cancer. In recent years, model tissues grown in culture into functional cell clusters called organoids have been widely used in drug development and regenerative medicine, as well as in vitro studies of morphogenesis, host-pathogen interactions, and tissue repair. When cultured within 3D extracellular matrices, epithelial cells spontaneously grow into a spherical organoid called an acinus, which consists of a contiguous monolayer of polarized cells surrounding a fluid-filled lumen. The morphology and stability of the acinar structure depends on the tensile forces between cells in the monolayer and lumen pressure created by the osmotic gradient across the monolayer. In this work, we describe our studies on the mechanical stability of MDCK epithelial acinar structures. Upregulation of Rho GTPase activity in already assembled acini with lumens results in a collapse of the luminal space, while inhibition of Rho kinase results in a luminal expansion. These changes can be induced directly by modulating Rho or indirectly by several different types of perturbations. Remarkably, after collapse, the acinus everts itself and achieves apical-out polarity, as opposed to the normal apical-in polarity. Myosin activity is high on the basal surface and low on the apical surface pre-eversion. Likewise, apical surfaces are more curved than basal surfaces. We interpret these findings with a vertex-based theoretical model of the acinus. Our experimental and theoretical results suggest that acinar eversion is mechanically driven by the surface tension difference between the apical and basal surfaces of the cells in the monolayer.