Alterations in basal lamina stiffness and focal adhesion turnover affect epithelial dynamics during corneal wound healing
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Epithelial wound healing is essential for maintaining the function and clarity of the cornea. Successful repair after injury involves the coordinated movements of cell sheets over the wounded region. While collective migration has been the focus of many studies, the effects that environmental changes have on this form of movement are poorly understood. In certain pathologies where the cornea exists in a chronic hypoxic state, wound healing is delayed. The goal of this work is to examine the changes in corneal structure in hypoxic corneas that may affect migration and to determine the effects that changes in basement membrane stiffness and focal adhesion turnover have on epithelial cell migration. We analyzed migration after injury in organ cultures and determined that hypoxic corneas exhibited alterations in leading edge morphology. Under hypoxia, fibronectin localization to the apical epithelium and anterior stroma was reduced. Investigators have suggested that alterations in basal lamina composition may increase the stiffness of the membrane. To examine the effect that increased stiffness has on collective migration we performed traction force microscopy. Using multi-layered corneal epithelial sheets, we developed a novel method to analyze the generation of cellular traction forces and the directionality of sheet movement on polyacrylamide gels. We determined that the leading edges of corneal epithelial sheets undergo contraction prior to migration. Alterations in stiffness affected the amount of force exerted by cells at the leading edge. On stiffer surfaces, individual cells within sheets exhibited greater movement compared to cells on softer substrates. To further assess sheet dynamics, we examined the activation of focal adhesion proteins in hypoxic corneas and in human corneal limbal epithelial (HCLE) cells seeded onto soft and rigid substrates. Wounded hypoxic corneas displayed alterations in the localization of the focal adhesion proteins paxillin and vinculin. In HCLE cells cultured on stiff substrates, there was an elevation in vinculin pY1065 phosphorylation after injury, a reduction in vinculin-positive focal adhesions, and decreased actin bundle thickness. Our results demonstrate that changes in membrane stiffness may affect cellular tractions and vinculin dynamics, possibly contributing to the delayed healing response associated with certain corneal pathologies.