Date of Award
Doctor of Philosophy (PhD)
Although advances have been made in our understanding of the molecular regulation of adult neovascularization, therapies directed at neovascular growth in solid malignancies or tissue ischemia remain suboptimal. Hypoxia-inducible factor-1 (HIF-1) has emerged as an attractive therapeutic target because it is a key transcriptional activator of many genes controlling neovascularization. However, modeling HIF-1 induction of adult neovascularization from angiogenic signaling initiation to de-novo growth and maintenance of vascular networks remains unexplored. As a first step towards determining HIF-1-mediated adult neovascularization, we created a conditional mouse model of doxycyline (DOX)-regulated HIF-1 activation in a prototypic epithelium, mouse skin (TetON-HIF-1 mouse). TetON-HIF-1 mice evidenced three stages of neovascularization: development (DOX d0-14), maintenance (DOX d14-60), and transgene-dependent regression, which occurred despite extensive and tight pericyte coverage. Photoacoustic microscopy (PAM) mapped microvascular architecture and quantified volumetric changes in neocapillary morphogenesis, arteriovenous remodeling, and microvessel regression. Developmental stage endothelial proliferation downregulation was associated with a DNA damage checkpoint consisting of p53, p21, and endothelial gamma-H2AX induction. The developmental stage was sensitive, whereas the maintenance stage was resistant to DC101 (VEGFR2 inhibitor antibody) treatment. HIF-1 recruited myeloid cells did not mediate VEGFR2 inhibitor resistance. Thus HIF-1 neovascularization in the adult is self-regulated via cell autonomous endothelial checkpoints and resistant to angiogenesis inhibitors independent of perivascular or myeloid cells. Next, to more specifically test the necessity of VEGF in HIF-1 mediated adult neovascularization, we combined TetON-HIF-1, K14-Cre, and VEGFflox/flox genotypes to create TetON-HIF-1:VEGFÄ mice in which HIF-1 and its target genes could be activated in adult skin in the context of VEGF depletion. Doxycycline HIF-1 induction failed to produce neovascularization in TetON-HIF-1:VEGFÄ mice despite marked upregulation of many pro-angiogenic HIF targets, including PlGF, adrenomedullin, angiogenin, and PAI-1. Endothelial sprouting was persistent despite loss of VEGF, consistent with marked reduction in Dll4-Notch-1 signaling. Lack of TetON-HIF-1:VEGFÄ neovascularization could be partially rescued by phorbol ester TPA-induced stromal neutrophil infiltration. Taken together, our data highlights the necessity of VEGF during HIF-1-mediated adult neovascularization. As such, targeting both HIF-1 and VEGF in HIF-1 dysregulated diseases either for ablation (cancer) or induction (ischemia) may be a more effective treatment option.
Chair and Committee
Jeffrey M. Arbeit
Kyunghee Choi, Daniel C. Link, Robert P. Mecham, David M. Ornitz, Joshua B. Rubin
Oladipupo, Sunday Samson, "Mechanisms of Adult Neovascularization Nediated by Epithelial HIF-1 Activation" (2010). Arts & Sciences Electronic Theses and Dissertations. 617.
Available for download on Monday, December 15, 2110
Permanent URL: https://doi.org/10.7936/K71Z42PH