Construction of Cell-Cell Interaction Networks – CoCCINet

Mechanical integrity is a critical feature of tissue homeostasis. Cell transformation, tumour growth and metastasis dissemination are systematically associated with cell mechanical deregulation and tissue disorganisation. Mechanical equilibrium within multicellular arrangements depends on the regulation of cell adhesion, shape and contractility at the individual cell level. The epithelial-mesenchymal transition (EMT) is an interesting working model to study the mechanical laws of multicellular arrangements as it relies on modifications of individual cell mechanical properties that have consequences on global tissue architecture. Following specific intracellular modifications a coherent layer of epithelial cells turned into a group of individual and migrating mesenchymal cells. Experimentaly EMT is characterized in vitro by the modification of gene expression profiles and actin remodelling at the individual cell level. However, in physiological contexts, its main features are global mechanical changes and tissue reorganisation, but currently no quantitative method has been developed to quantify these mechanical events. A clear understanding of the mechanism and the consequences of EMT would require an accurate and quantitative description of the mechanical properties of cells arrangements subjected to EMT. Our aim is to analyse quantitatively the spatial organisations of epithelial and mesenchymal multicellular assemblies when constrained in microfabricated environments. Cells will be plated on micropatterns made of extra-cellular matrix. Micropattern geometries will be made of defined combinations of adhesive and non adhesive regions. We plan to describe the specific microenvironment geometries promoting stable and stationary multicellular arrangements and compare them to geometries in which cells move around each other. This should help us to identify the geometrical and mechanical parameters implicated in the establishment of multicellular equilibria. Finally, by comparing equilibria in epithelial and mesenchymal arrangements, we hope to bring to light the cellular parameters involved in EMT and their implication in tissue reorganisation. Our experimental approach will be coupled to the establishment of a physical model of multicellular organisation. Each spatial configuration of a multicellular assembly is associated with an energy characterising the mechanical constraints in the structure. This energy depends on cell-cell adhesion, cell-extracellular matrix (ECM) adhesion and on the internal tensions supporting cell shapes. We plan to use numerical simulations of the Cellular Plot Model (CPM) to characterize the energetic profile associated with each type of spatial organisation in response to a given geometry of the adhesive microenvironment. Thereby we will determine the stable configurations that cells will most probably adopt. Thus we expect to formalize and to test numerically and experimentally the physical laws that govern multicellular mechanical equilibria. Once validated our model will help us design in silico cell dispositions within large and stable multicellular arrangements. We will then fabricate the corresponding microenvironment to support it. Finally we will use the reproducible changes in the mechanical equilibria adopted by two or four epithelial cells during EMT, for example a switch between a stable to an unstable state or a change in the relative cell positions within the structure, to screen on a cell chip the kinases and the cytoskeleton proteins implicated in the transition. Contrary to classical approaches, cells would not be characterized by their genetic expression profile but by their morphological and mechanical response.