Corneal opacities, the third major cause of blindness in the world, may be a result of endothelial dystrophies, epithelial dystrophies, fibrosis or a haz in the stroma due to dysregulated wound healing. Corneal wound healing is largely influenced by the extracellular environment both through soluble signals and from biophysical cues such as substratum topography and extracellular matrix stiffness. Research from our lab and others have demonstrated intrinsic biophysical attributes of the extracellular matrix profoundly modulate a host of fundamental phenotypic characteristics of cells such as adhesion, migration, shape, size and proliferation accompanied by activation/inhibition specific signaling pathways. Despite the fundamental importance of biophysical cues, a significant knowledge gap remains in our understanding of how these biophysical cues influence basic cellular responses and wound healing in the cornea. In this proposal we will determine the expression and localization impact of signaling pathways that mediate corneal wound healing. YAP (Yes- associated protein) and TAZ (transcriptional co-activator with PDZ-binding motif) serve as a pair of transducers linking changes in the extracellular environment, such as a change in topography or of matrix stiffness. These two proteins are at the intersection of multiple signaling pathways that influence wound healing. Preliminary data demonstrate that the stiffness of the corneal stroma increases by 10-fold within 7 days after wounding by phototherapeutic keratectomy (PTK) in rabbits. This was associated with YAP/TAZ being markedly localized in the nucleus of epithelial cells resulting in their transcriptional activation of growth factors such as CTGF and TGF. A robust expression of YAP/TAZ was observed in the anterior stromal cells in vivo following corneal wounding. This leads to the central hypothesis that expression and localization of YAP/TAZ are essential mediators of signaling events in corneal cells influenced by external biophysical stimuli and are a fundamental part of corneal wound repair. This proposal would delineate the influence of YAP/TAZ in corneal cells (A) in vitro, (B) in the healing of corneal wounds in rabbits in vivo, and (C) the healing of corneal wounds in conditional knockout mice for YAP, TAZ and the double knockout in vivo. These studies will define the signaling pathways influenced by YAP/TAZ mediated by external biophysical cues in the epithelial cells and will also identify changes that occur in the stroma during wound healing.
The cornea can be wounded by accidents, improper contact lens usage and complications of common surgeries such as Lasik and if these wounds do not heal quickly and properly, scars or opacities can permanently impair vision in that eye. Recent research highlights the importance of tissue properties, such as stiffness and topography, in encouraging proper wound healing behavior of cells; however, this is largely understudied in corneal wounds. The goal of this project is to examine the mechanisms that corneal cells use to respond to the physical properties of the tissue, and identify and target novel molecules to improve wound healing outcomes in the cornea.
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