Exploring and Harnessing the Role of Hypoxia Inducible Factors in Vascularizing Modular Tissue Constructs

In my doctoral work, I identified hypoxia-inducible factor (HIF) as a primary mechanism driving modular tissue-induced vascularization, and harnessed it to enhance blood vessel formation in this platform. HIF orchestrates a range of cellular responses, but its role in driving vascularization of engineered tissues has yet to be specified. In the first pillar of my work, HIF was inhibited using pharmacological and genetic methods to define its contribution to vessel formation in modular tissues. Both inhibitory methods, systemic digoxin delivery and shRNA-mediated inhibition of HIF-1 in graft endothelial cells (EC), reduced vascularization and oxygenation of tissue constructs. Moreover, these methods elucidated different mechanisms underlying HIF-mediated vascularization. Systemic digoxin treatment reduced early recruitment of endothelial progenitor cells and monocytes/macrophages to implants. Inhibition of HIF-1 in graft EC reduced their angiogenic function in normal and serum-reduced conditions in vitro, highlighting the importance of HIF in graft-derived vascularization. After defining the significance of its role, we harnessed HIF to enhance rapid and mature vessel formation in modular tissues. In the second pillar of my work, microparticles releasing HIF-stabilizing deferoxamine (DFO) were incorporated into EC-only modular constructs, on the premise that local HIF stabilization would drive vascularization even in the absence of mesenchymal stromal cells (MSC). Indeed, vessel densities were increased at day 7 and 21, corresponding with increased vessel maturation and perfusion at day 21. Furthermore, DFO-releasing microparticles increased the recruitment of neutrophils and alternatively activated macrophages to the implant. Although vessel formation was rescued to some degree, it was not comparable to that in MSC-containing modular constructs. Nonetheless, the mechanisms elucidated here could be harnessed to develop strategies that tune vascularization in modular tissues, and to improve engraftment of therapeutic cells.Ph.D