EAGER: Exploring Cell-Cell Gap as a Critical Parameter in Biological Phase Changes

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Biological systems sometimes rapidly change behavior when the number of cells becomes large enough. This EArly-concept Grant for Exploratory Research (EAGER) project is based on preliminary data showing that for one type of mammalian cell, that it is the distance between the cells that triggers the different behavior. This was observed for a particular type of muscle cell. When the cells are 100 micrometers apart, the form into muscle "fibers" automatically. When they are further than 100 micrometers apart, they do not. This observation will be further examined in fibroblasts. The compression of extracellular matrix by fibroblasts is fundamental to the healing of wounds and also to the original morphogenesis of organs. The project will determine whether this threshold of 100 micrometers is also true for fibroblasts from mice, monkeys and humans. As a test of the breadth of the observation, the 100 micrometer threshold will also be tested using the Protista Dictyostelium that has the property of aggregating into larger structures under some conditions. If the results of the experiments are comparable among the different cell types, the project will have developed significant support for the existence of a threshold distance for the activation of a tissue "phase change" in the aggregation of fibroblasts and of Dictyostelium. This could improve our understanding of a variety of conditions where tissues apparently show a phase change in behavior including embryogenesis, cancer tumorigenesis, in vitro tissue formation, bacterial biofilm formation and a variety of collective phenomena in the microbial world. Identification of critical distance conditions will help with predicting the path of morphogenesis of 3D printed tissues with cells and extracellular matrix. The research will be carried out by a graduate and two undergraduate students. One of the UG students will be from the Department of Biology, the others from Engineering. Thus, the students will be trained in multidisciplinary fields. Special effort will be made to recruit students from minorities and under-represented groups to conduct the research. The project is inspired by recent experimental findings suggesting that muscle cells within 100 micrometers of each other in 3D culture compact the ECM and form myotubes (PI's lab), endothelial cells within 100 micrometers of each other form vasculature, fibroblasts in collagen within 100 micrometers of each other compact the collagen. When the cell-cell gap exceeds 100 micrometers, none of these processes occur. The hypothesis of a critical distance will be tested using fibroblasts from multiple species (mouse, monkey and human) in a collagen matrix mixed with fluorescent beads for optically tracking compaction and cluster formation by slime mold cells (Dictyostelium). In order to gain insight on the experimental observations of the threshold cell-cell gap, a mathematical model will be created to simulate the experimental observations. Each cell remodels the matrix around them by adhering to the matrix and by pulling the fibers as the cell filopodia generate contractile forces. Each cell forms a zone of remodeled matrix with higher stiffness under tension. If cells are far apart, their zones remain independent of each other. In a system with many cells, such non-interacting zones maintain global symmetry. When the cells are close to each other, their zones overlap, and symmetry is broken. The stiffness between the cells becomes higher, and the cells form a stiffer fibrous bridge between them. More filopodia tend to extend along the bridge compared to other directions, the cells become polarized and elongated while remaining contractile. This results in an attractive interaction between the cells that will compact the matrix. Three types of fibroblasts from mouse (embryonic fibroblast, NIH/3T3), monkey (kidney fibroblasts) and human (lung) will be used to test hypothesis on matrix compaction, and slime mold cells (Dictyostelium discoideum) will be used to test for generality. All of these cell types have comparable size, ~ 10 micrometer in diameter. Hence, we predict similar critical distances for all cell types.