Date of Award
Doctor of Philosophy (PhD)
Epithelial cell collectives utilize extra-cellular matrix (ECM) fibers to undergo collective migration critical in regeneration, repair and cancer metastasis. However, very little is known about the various factors which determine the ability of cellular collectives to utilize ECM fibers to undergo these critical processes in-vivo. First part of the dissertation focusses on understanding how cell collectives exploit specific properties, like stiffness and fiber length to undergo collective streaming. It is also unclear how cellular forces, cell-cell adhesion, and velocities are coordinated within streams. To independently tune stiffness and collagen fiber length, we developed new hydrogels and discovered invasion-like streaming of normal epithelial cells on soft substrates coated with long collagen fibers. Here, streams arise from a surge in cell velocities, forces, YAP activity, and mesenchymal markers in regions of high stress anisotropy. Coordinated velocities and symmetric distribution of tensile and compressive stresses support persistent stream growth. Stiff matrices diminish cell-cell adhesions, disrupt front-rear velocity coordination, and do not promote sustained fiber-dependent streaming. Rac inhibition reduces cell elongation and cell-cell cooperation, resulting in a complete loss of streaming in all matrix conditions. Our results reveal a stiffness-modulated effect of collagen fiber length on collective cell streaming and unveil a biophysical mechanism of streaming governed by a delicate balance of enhanced forces, monolayer cohesion, and Rac-based cell-cell cooperation.While in the first part collagen fibers were randomly oriented, second part of the dissertation focusses on how cell collectives exploit aligned extracellular matrix fibers for directed migration. Here, we show that fibers serve as active conduits for spatial propagation of cellular mechanotransduction through matrix exoskeleton, leading to directed collective cell migration. Epithelial (MCF10A) cell clusters adhered to soft substrates with aligned collagen fibers (AF) migrate faster with much lesser traction forces, compared to uniform fibers (UF). Fiber alignment causes motility and force transmission deeper into cell monolayer, leading to polarized cell flocking, compared to jamming-like migration on UF. Using a motor-clutch model, we explain that ‘force-effective’ fast migration phenotype occurs due to rapid stabilization of cellular contractile forces enabled by aligned ligand connectivity. As a result, cells migrate faster with lesser effort, thereby revealing that aligned matrix topographies may help conserve energy for cell migration.
Spencer Lake, Nathaniel Huebsch, Michael Greenberg, Mark Meacham,