Endothelial cell activation in a VEGF-A gradient: Relevance to cell fate decisions

Department of Pediatrics, University of Cincinnati, Cincinnati, Ohio, United States
Microvascular Research (Impact Factor: 2.13). 02/2010; 80(1):65-74. DOI: 10.1016/j.mvr.2010.02.001
Source: PubMed
Distribution of vascular endothelial cell growth factor A (VEGF-A) as a gradient determines microvascular endothelial cell (EC) fate during organogenesis. While much is understood about mechanisms of differential distribution, less is known about how EC perceive and interpret a graded VEGF-A signal to generate positional target gene activation. Using microvascular EC, we analyzed the effect of time and graded VEGF-A input on VEGFR2 autophosphorylation, signal kinase activation and induction of immediate-early genes. The threshold and time to peak activation of VEGFR2 were dependent on signal strength over a 50-fold range in concentration with 3-fold concentration differences readily distinguished. Longer duration of exposure did not compensate for low concentration of VEGF-A, suggesting intensity and duration of signal were not interpreted equivalently. With the same conditions, graded and time-sensitive information was transduced through the PLCgamma/p44/p42MAPK signal pathway but not the parallel AKT pathway. Analysis of MAPK-induced angiogenic immediate-early genes determined that EGR-1, EGR-3, and NR4A1 were dependent on graded input while NR4A2 and DSCR1 were independent with 'switch-like' induction. These data demonstrate rapid, linear integration of VEGF-A levels but independent interpretation of duration of signal and identify potential nodes for segregation of gradient-dependent and -independent responses. These results describe how microvascular EC fate decisions can be determined by comparatively moderate changes in VEGF signal strength, resulting in combinatorial changes in the repertoire of immediate-early genes for transcription effectors.

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    • "We hypothesize that in the iPSC-EC sprouting experiments, the N-VBP microspheres initially sequestered VEGF and served as a 'source' for local VEGF release (Fig. 5A). N-VBP microspheres encapsulated in three dimensional hydrogels could also have contributed to the formation of spatial VEGF gradients within the hydrogels [43], which would be expected to promote iPSC-EC chemotaxis and sprouting [49,50]. Future work will be needed to examine this hypothesis by pre-incubating VBP microspheres in VEGF-containing medium and subsequently encapsulating the VEGF-containing microspheres in the sprouting assay to generate a uniform spatial distribution of VEGF throughout the hydrogel. "
    [Show abstract] [Hide abstract] ABSTRACT: Vascular endothelial growth factor (VEGF) spatial and temporal activity must be tightly controlled during angiogenesis to form perfusable vasculature in a healing wound. The native extracellular matrix (ECM) regulates growth factor activity locally via sequestering, and researchers have used ECM-mimicking approaches to regulate the activity of VEGF in cell culture and in vivo. However, the impact of dynamic, affinity-mediated growth factor sequestering has not been explored in detail with biomaterials. Here, we sought to modulate VEGF activity dynamically over time using poly(ethylene glycol) microspheres containing VEGF-binding peptides (VBPs) and exhibiting varying degradation rates. The degradation rate of VBP microspheres conferred a differential ability to up- or down-regulate VEGF activity in culture with primary human endothelial cells. VBP microspheres with fast-degrading crosslinks reduced VEGF activity and signaling, while VBP microspheres with no inherent degradability sequestered and promoted VEGF activity in culture with endothelial cells. VBP microspheres with degradable crosslinks significantly reduced neovascularization in vivo, but neither non-degradable VBP microspheres nor bolus delivery of soluble VBP reduced neovascularization. The covalent incorporation of VBP to degradable microspheres was required to reduce neovascularization in a mouse model of choroidal neovascularization in vivo, which demonstrates a potential clinical application of degradable VBP microspheres to reduce pathological angiogenesis. The results herein highlight the ability to modulate the activity of a sequestered growth factor by changing the crosslinker identity within PEG hydrogel microspheres. The insights gained here may instruct the design and translation of affinity-based growth factor sequestering biomaterials for regenerative medicine applications.
    Full-text · Article · Mar 2016 · Biomaterials
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    • "For instance, the differential activation of jagged1 and DII4 in the Notch signaling pathway determines the distinct fate (tip vs. stalk) of two adjacent endothelial cells exposed to a VEGF gradient during the angiogenic process [85]. A recent study has further demonstrated that the mitogen-activated protein kinase pathway is triggered by VEGF in individual microvascular endothelial cells, whereas their adjoining cells are silent [86]. The dissimilar response of neighboring cells to VEGF might be linked to the wide variation in VEGFR-2 levels, as only about 60% of UCB-ECFCs express it (unpublished data from our group). "
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    Full-text · Article · May 2013 · Stem cells and development
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    • "VEGFA and EPO stimulate angiogenesis, and EPO additionally enhances the production of red blood cells. Endothelial cells are the predominant target of VEGFA, because of their ability to grow towards a hypoxic region following a VEGFA gradient and thereby forming new blood vessels [4,5]. The cellular signaling response to hypoxia needs to be tightly regulated, since already a small deviation of the balance between pro-and anti-angiogenic factors can cause several severe diseases such as ocular and inflammatory disorders. "
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    Full-text · Article · Aug 2012 · PLoS ONE
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