Lateral boundary mechanosensing by adherent cells in a collagen gel system

Cell adhesion responses to in-depth physical properties such as substrate roughness and topography are well described but little is known about the influence of lateral physical cues such as tissue boundaries on the function of adherent cells. Accordingly, we developed a model system to examine remote cell sensing of lateral boundaries. The model employs floating thin collagen gels supported by rigid grids of varying widths. The dynamics, lengths, and numbers of cell extensions were regulated by grid opening size, which in turn determined the distance of cells from rigid physical boundaries. In smaller grids (200 μm and 500 μm wide), cell-induced deformation fields extended to, and were resisted by, the grid boundaries. However, in larger grids (1700 μm wide), the deformation field did not extend to the grid boundaries, which strongly affected the mean length and number of cell extensions (∼60% reduction). The generation of cell extensions in collagen gels required expression of the β1 integrin, focal adhesion kinase and actomyosin activity. We conclude that the presence of physical boundaries interrupts the process of cell-mediated collagen compaction and fiber alignment in the collagen matrix and enhances the formation of cell extensions. This new cell culture platform provides a geometry that more closely approximates the native basement membrane and will help to elucidate the roles of cell extensions and lateral mechanosensing on extracellular matrix remodeling by invasion and degradation.