Alterations of physical interaction in a collective cell migration by an electric stimulus

Abstract

Cell migration plays an essential role in regulation of developmental and pathological conditions. In many of these processes, cells move cohesively either as clusters, chains, or sheets in a collective manner. This collectiveness in cell migration is particularly relevant in wound healing, morphogenesis, neovascularization, or cancer metastasis. The most marked characteristic of the collective migration is the cooperativity amongst neighboring cells due to physical connections through cell adhesions. The emergence of the collective behavior can be regulated by several external stimuli, either mechanical, geometrical, or chemical. While the collective behavior in the cell monolayer has gained much attention, the response of collective cells to an external stimulus in a cooperative view is not fully understood. Therefore, it is our goal to investigate how the collective behaviors arise in response to externally applied physical stimulation. We first choose a direct current electric field (dcEF) as a source for non-invasive cue for cell migration, and create the cellular strip by employing a micro-patterning technique with mammary gland epithelial cell, MCF-10A. Cellular motions are assessed by the particle imaging velocimetry (PIV) and the cell-substrate adhesion forces are quantified by the traction force microscopy (TFM), based on which the intercellular stresses can be calculated. The specific aims of this work are 1) to develop an integrated platform where a stable EF can be applied to the cell strip on a bead laden hydrogel, 2) to monitor the cellular motions and forces under the electric stimulation using PIV and TFM, 3) to quantify the changes in the cellular cooperativity of collective cell migration in both kinematic and dynamic perspectives, and finally 4) to identify the key biomolecular components responsible for these changes. The generated platform allows real time monitoring of the dynamic changes in cellular motions as well as the bead displacement from which traction force can be calculates. Upon EF stimulation of 0.5V/cm, the cells show enhanced migration with increased heterogeneity and complexity in their motions. The cellular tractions inside the strip also show spatial heterogeneity with dynamic temporal fluctuations with the electric stimuli. Both spatial and temporal fluctuations may be associated with a number of different factors such as changes in cellular proliferation rate, integrity of the cell-cell junctions, or any EF-induced intracellular signals that affect cellular migration. Our immunofluorescent images indicate that the integrity of E-cadherin is compromised with apparent internalization with the EF. Our protein assays using Western Blot identify EGFR, ERK, AKT, and Src as possible candidates for the EF-induced responses in enhanced migration of MCF-10A. In summary, the combinatorial effects of the reduced cell-cell junctional stability and the increased migratory capacity of individual cells by EF stimulation may contribute to the accumulation of fluctuations in cellular tractions and intercellular stresses, leading to the enhanced cooperative migration in the cellular monolayer.