Mechanisms of Leukocyte Migration: An Investigation of Motility in 3-Dimensional Environments

Cell migration is a crucial aspect of many biological processes ranging from development, to cancer cell metastasis. One very important process is the inflammatory response, where neutrophils must migrate through a diverse set of environments as they travel from the bloodstream, across cell monolayers and through the extravascular space which contains other cells and extracellular matrix before reaching locations of injury or infection. Although many studies have focused on the biochemical and molecular signaling events involved in the entire process, little is know about the role of mechanics in the last step, which is essentially migration through a 3-dimensional (3-D) confined environment. Extracellular matrix structure and stiffness have been shown to affect 3-D cell migration. However, it is unclear whether an optimal balance must exist between these factors for neutrophils to navigate and migrate complex 3-D environments in the presence of a chemoattractant. In the present thesis, we aim to investigate whether matrix porosity and stiffness play a determinant role in 3-D neutrophil chemotaxis. Using novel assays, imaging and computational analysis techniques, we found that although neutrophils are able to engage in directed migration in a range of matrix environments, optimal migration occurs at low densities and stiffnesses. Also, we see that these cells engage in periodic shape and motion changes that are independent of the nature of their matrix. However, unique forces are exerted on their surrounding environments in matrices with high porosities and low stiffnesses. These results demonstrate that although 3-D neutrophil migration is a robust process, the mechanical environment plays a very important role on the ability of these cells to move in 3-D spaces.