REAL TIME IMAGING OF CELL MECHANICAL COUPLING IN 3D FIBROUS GELS

Cells are able to apply active mechanical forces against their extracellular environment. While the force applied by a single cell is miniscule, collectively cells can reshape and remodel large-scale tissue during normal biological processes such as embryonic development and wound healing, as well as in pathological processes like fibrosis and tumorigenesis.

We embed fibroblast cells (3T3) in 3D fibrin gels and visualize both the cells and the matrix using real-time, 3D confocal microscopy (i.e. 4D imaging) . The matrix starts out as a uniform fiber network. Gradually, the cells deform the matrix around them while creating bands of increased fiber density and alignment between each other. Such bands mechanically couple cells over long distances and at a large scale. In this study we have examined the manner in which such bands are formed over time, their mechanical properties and the possible effect on cells behavior. Our results demonstrate that cell induced matrix deformation is dependent on active forces generated by the cells. The pulling forces exerted by the cells lead to matrix displacement that are quantified by traction force microscopy. During band formation, the displacement increases between the mechanically interacting cells, and the mean direction of the displacement is approximately 30 degrees relative to the formed band. In the matrix between mechanically isolated cells, where no bands are formed, the magnitude of displacement stays relatively constant and shows no clear directionality. The deformation between cells is largely plastic, irreversible, indicated that the matrix does not relax to its uniformed state when myosin II is inhibited. Cell protrusions and protrusion branching are found to play a role in band formation. Finally, we see a significant morphological differences between mechanically-coupled and mechanically-isolated cells indicating that such mechanical coupling impact biological activity.

Mechanical connections between cells via the matrix may facilitate large scale coordination of cells in fibrous matrix. Better understanding of these mechanisms could improve our understanding of various biological processes such as wound healing, and organogenesis.