(49a) Tuning Capillary Network Formation with Bioactive Motifs in a 3D Matrix
A variety of angiogenic growth factors, including vascular endothelial growth factor (VEGF), play critical roles in postnatal neovascularization, and these molecules are extensively studied to treat ischemic tissues by rebuilding capillary networks. Like most growth factors, VEGF binds to specific receptors on the surface of endothelial progenitor or precursor cells, and activate cellular signaling pathways involved in capillary formation. Neovascularization depends on the extent to which VEGF binds to cellular receptors. Commonly, the extent of VEGF binding is related to the VEGF concentration in a tissue, and the subsequent ability to stimulate capillary formation in a preclinical setting. However, it would be more advantageous to develop a method to control the extent of VEGF binding at a given VEGF concentration and thus improve the efficacy of VEGF in a clinical setting. Therefore, this study presents our recent finding that the extent of VEGF binding and subsequent capillary formation is regulated with fibronectin derivatives and an extracellular matrix. Based on the findings that fibronectin in an extracellular matrix improves the angiogenic efficacy, we hypothesized that a cell adhesion domain and a VEGF domain of fibronectin play critical roles in enhance the extent of VEGF binding. We examined this hypothesis using several recombinant fibronectin fragments in a fibrin or collagen gel. According to a three dimensional sprouting assay, the fibronectin fragment, which included type I domains and a type III domain, was able to increase the length of sprouts 24% (69.6µm to 86.7µm) and the sprouting ratio by 22% (1.0 to 1.22 sprouts/bead) as compared with control conditions in a fibrin gel. Furthermore, the role of the fibronectin fragments in stimulating sprouting became insignificant in a collagen gel. These results indicate that defined domains of fibronectin improve the VEGF efficacy, but its effect is mediated by an extracellular matrix. The underlying mechanism was further examined by quantifying the number of VEGF bound to cells. Overall, this study demonstrates combined roles of fibronectin and matrix in regulating vascular development and also novel strategy of improving vascularization therapies.