Cellular and molecular biology of Wnt signaling and versican expression in myofibroblast differentiation

Wound healing is a complex and dynamic process that restores tissue integrity after injury, but also contributes pathologically to the development of fibrosis. Growing evidence suggests a role for Wnt signaling during normal and aberrant wound healing. The proteoglycan versican is a target of Wnt signaling that is expressed following injury and accumulates pathologically in many chronic inflammatory conditions. In this dissertation, I hypothesized that Wnt signaling and its target versican are key regulators of mesenchymal cell phenotype. In Aim 1, I demonstrated that treatment of cultured fibroblasts with Wnt3a, a canonical Wnt ligand, stimulates the formation of a myofibroblast-like phenotype characterized by increased expression of smooth muscle α-actin. These changes appear to be mediated by Wnt3a upregulating the expression of TGF-β and its associated signaling through SMAD2 in a β-catenin-dependent mechanism. In Aim 2, I show that Wnt3a alters the phenotype of vascular smooth muscle cells and stimulates the formation of a contractile and secretory phenotype in these cells that is associated with increased gap junction communication. Again, these changes occurred through a mechanism that was dependent on canonical Wnt signaling. In Aim 3, I explored the functional roles of versican by examining its expression following injury to cultures of valve myofibroblasts. My data indicate that versican is secreted as extracellular matrix following injury to valve cells, and suggests a role for the membrane receptor CD44 in organizing this provisional versican matrix. In Aim 4, I delved further into the functional roles of versican by expressing this proteoglycan in murine fibroblasts. In this aim I showed that versican expression promotes myofibroblast differentiation, and these changes appear to be mediated by activation of TGF-β signaling. Lastly, in Aim 5, I explored potential intracellular functions for versican, and provide evidence to suggest versican localizes to the nucleus in mesenchymal cells where it regulates the organization of the mitotic spindle during cell division. Collectively, these data suggest Wnt signaling and versican are key regulators of mesenchymal cell phenotype, and as such, are important mediators of a wound healing response.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat