Investigating the Dual Effects of Substrate Stiffness and Direct Current Electric Fields on the Collective Cell Migration Dynamics of MDCK-II Epithelial Cells

Abstract

Processes like wound healing, cancer metastasis, and embryogenesis, are reliant on the collective migration of cells. Understanding the mechanisms behind these processes is tied to an in-depth knowledge of mechanobiology and stimuli, such as electric fields, that are influential in guiding the directional migration of groups of cells. Electrotaxis is an effective method in manipulating the movement and directionality of multicellular structures. However, studies that have investigated both electrotaxis and collective cell migration have neglected to conduct more of their experiments on soft substrates that are similar in stiffness to in vivo tissues and extracellular matrix. This is relevant because cells are able to sense their micro-environments and presumably act and move differently depending on the stiffness of their microenvironment. Therefore, it is important to conduct experiments in conditions that are biologically similar or relevant, particularly when developing clinical applications. To rectify this widespread oversight, in this study I investigate the migration dynamics of MDCK-II epithelial cells when seeded on soft substrates and exposed to D.C. electric fields (dcEF). This project required fabricating polyacrylamide gels at multiple stiffnesses and conducting expansion and electrotaxis experiments using these gels. I observed that cell sheets that are exposed to electric fields experience a dramatic increase in average speed, when plated on hard substrates, but only a moderate increase when plated on soft substrates. In addition, cell sheets migrate randomly in the absence of dcEF, but quickly engage in directed motion, towards the cathode, in the presence of dcEF. Lastly, velocity distributions differ according to substrate stiffness whereby cell sheets experience the highest velocities at the center when seeded on hard substrates, while cell sheets experience the highest velocities at the edges when seeded on soft substrates. Although these experiments need to be repeated to increase the N of the assays, the present data suggests a correlation between substrate stiffness and directionality and presents an opportunity for more studies to conduct their experiments using a range of substrate stiffnesses.