VEGF is essential for hypoxia-inducible factor-mediated neovascularization but dispensable for endothelial sprouting

Abstract

Although our understanding of the molecular regulation of adult neovascularization has advanced tremendously, vascular-targeted therapies for tissue ischemia remain suboptimal. The master regulatory transcription factors of the hypoxia-inducible factor (HIF) family are attractive therapeutic targets because they coordinately up-regulate multiple genes controlling neovascularization. Here, we used an inducible model of epithelial HIF-1 activation, the TetON-HIF-1 mouse, to test the requirement for VEGF in HIF-1 mediated neovascularization. TetON-HIF-1, K14-Cre, and VEGF flox/flox alleles were combined to create TetON-HIF-1:VEGF Δ mice to activate HIF-1 and its target genes in adult basal keratinocytes in the absence of concomitant VEGF. HIF-1 induction failed to produce neovascularization in TetON-HIF-1:VEGF Δ mice despite robust up-regulation of multiple proangiogenic HIF targets, including PlGF, adrenomedullin, angiogenin, and PAI-1. In contrast, endothelial sprouting was preserved, enhanced, and more persistent, consistent with marked reduction in Dll4-Notch-1 signaling. Optical-resolution photoacoustic microscopy, which provides noninvasive, label-free, high resolution, and wide-field vascular imaging, revealed the absence of both capillary expansion and arteriovenous remodeling in serially imaged individual TetON-HIF-1:VEGF Δ mice. Impaired TetON-HIF-1:VEGF Δ neovascularization could be partially rescued by 12- O -tetradecanoylphorbol-13-acetate skin treatment. These data suggest that therapeutic angiogenesis for ischemic cardiovascular disease may require treatment with both HIF-1 and VEGF.

Multi-parametric quantitative microvascular imaging with optical-resolution photoacoustic microscopy in vivo

“…Figure 8(a) is the original volumetric photoacoustic image with depth encoded in color; Figs. 8(b) and 8(c) are the images with vessels extracted using the simple thresholding algorithm in our previous work [8] and the algorithm developed in this study, respectively. Finally, to validate the consistency of the performance of our algorithm, the vasculature in three in vivo OR-PAM images acquired at different regions of an anesthetized mouse were segmented and quantified.…”

“…As a result, it is becoming a powerful tool for studying the microcirculation in many physiological and pathological conditions [6]. For example, recently, OR-PAM has been applied to the longitudinal study of angiogenesis (the imaging of angiogenesis at a series of time points over a period of timedays or weeks-to monitoring the evolution of angiogenesis) [7,8], which plays a critical role in tumor growth, invasion, and metastasis [9,10]. Such studies may open up new opportunities to better understand the dynamics of the tumor microenvironment, as well as to assess the efficacy of anti-angiogenic and/or combined tumor therapies in the early stages [11][12][13].…”

“…Quantitative imaging of these parameters in vivo at different time points can provide us insights into the dynamics of tumor angiogenesis [13][14][15][16][17][18]. In previous studies, we used a simple thresholding approach, together with cross-section vessel tracking, to segment the microvasculature in OR-PAM images [7,8]. However, to offer truly accurate quantification for the intricate microvascular images acquired by OR-PAM, a more rigorous vascular segmentation and quantification algorithm is needed.…”

Reflection-mode in vivo photoacoustic microscopy with subwavelength lateral resolution

“…Therefore, OR-PAM can label-freely image microvasculature at the capillary level based on the intrinsic optical absorption from hemoglobin; in addition, using spectroscopic photoacoustic measurement, it can spectrally identify a variety of endogenous and/or exogenous chromophores [7][8][9]. To date, OR-PAM has successfully demonstrated the capability of providing optical-absorption-based anatomic, functional, and molecular information, and found broad applications in vascular biology [10], neurology [11], and ophthalmology [12].…”

Redox Signaling Pathways Involved in Neuronal Ischemic Preconditioning

“…to hypoxia and enzymes involved in metabolism. HIF activation results in up-regulation of genes to protect a cell from hypoxia, such as vascular endothelial growth factor (angiogenesis) [132,133], erythropoietin (erythropoiesis) [132], and phosphofructokinase (glycolysis) [134].…”