Vascular Endothelial Growth Factor (VEGF) Presentation Modulates Endothelial Cell Signaling and Vascular Branching in engineered matrices in vitro and in vivo

The process of angiogenesis, defined by the development of new blood vessels from pre-existing vessels, is essential in tissue remodeling and regeneration. This complex process involves extensive interplay between cells, soluble factors and extra-cellular matrix (ECM) components. Insufficient angiogenesis, implicated in many disease processes such as heart failure and stroke, results in inadequate nutrient and oxygen delivery. Thus, therapeutic strategies to promote revascularization have been extensively investigated. Although several angiogenic growth factors have been identified and delivery investigated to induce revascularization, no clinical product exists to date to promote revascularization. This thesis investigates the delivery of Vascular Endothelial Growth Factor (VEGF) from bioengineered matrices to promote revascularization in the brain. Two approaches will be described, non-viral gene delivery and protein delivery, both from matrix metalloproteinase degradable hyaluronic acid based hydrogels. Non-viral gene delivery has the potential to overcome limitations with protein degradation and inactivation by delivering plasmid DNA (more chemically stable then proteins). Non-viral gene delivery to cells seeded within hyaluronic acid matrices was investigated to begin to understand the process of gene transfer within hydrogel matrices. However, due to the low protein expression achieved, protein delivery was investigated. To directly deliver VEGF from our hydrogel biomaterials we first investigated how the presentation of VEGF affected endothelial cell activation. We showed that through controlling the discrete distribution of VEGF and integrin co-ligands in engineered matrices, ECs phenotype can be modulated to favor the tip cell phenotype when VEGF is bound and clustered, leading to controlled vessel branching. In addition, we found that controlled vessel branching leads to enhanced blood vessels with pericyte coverage after stroke. Further studies should be done to further improve the efficiency of our delivery strategy and their effect on tissue regeneration through a controlled vessel formation.