Mechanics Of Adhesion Dependent And Independent Neutrophil Migration In Three-Dimensional Extra-Cellular Matrices

While much research has been dedicated to the identification of the cascade of specific biochemical processes involved in the recruitment of neutrophils, much less is known about the mechanical events driving their migration; in particular, how they generate the necessary traction forces to migrate across three-dimensional (3-D) extravascular spaces and the importance of forming cell-substrate adhesions during this process is unclear. In this study, we investigate the importance of cell-substrate adhesions on the mechanics of 3-D neutrophil motility in collagen gels using Elastographic 3D Force Microscopy (E3DFM). We used wild type neutrophil-like differentiated human promyelocytic leukemia (dHL-60) cells and talin 1 knockout dHL60 cells, which were unable to engage their integrins, as our model systems. Both cell lines were were embedded in collagen matrices containing fluorescent micro-beads. Neutrophil motility was induced via the introduction of the neutrophil chemokine formyl-Methionyl-Leucyl-Phenylalanine (fMLP) in a custom build device. Both Confocal and Fluorescent microscopy techniques were used to image the movement of the embedded micro-beads as well as fluorescently labeled cells. Particle Image Velocimetry (PIV) and Finite Deformation Theory were used to compute displacement fields in the collagen matrices. Stress fields in the matrices were computed using a constitutive relationship with several material parameters. The over determined nature of the problem was used to estimate the aforementioned material parameters. We will present data showing that morphological changes and migratory patterns differed depending on the cellu0027s ability to form cell-substrate adhesions. We will also provide data showing a clear relationship between the aforementioned migratory characteristics and computed displacement and stress fields around migrating neutrophils in collagen matrices. The results from our study show that neutrophils migrating in 3-D environments employ distinct mechanical mechanisms that depend on their ability to form adhesions.