Exogenous pro-angiogenic stimuli cannot prevent physiologic vessel regression
ABSTRACT In healing wounds, rising levels of vascular endothelial growth factor (VEGF) induce a period of robust angiogenesis. The levels of pro-angiogenic factors in the wound begin to decline just before a period of vascular regression, suggesting that these mediators are necessary to sustain vessel density. The purpose of this study was to determine if the maintenance of pro-angiogenic stimuli in the wound would prevent physiological vessel regression.
A standard subcutaneous sponge wound model was modified by the addition of a mini-osmotic pump, allowing manipulation of the wound milieu by the addition of exogenous growth factors. After initial characterization of this model, exogenous VEGF (10 microg/mL), FGF (10 microg/mL), PDGF (10 microg/mL), or VEGF (10 microg/mL) plus FGF (10 microg/mL) were delivered to wounds and blood vessel density analyzed by immunohistochemistry.
VEGF administration resulted in a transient increase in wound vessel density (P < 0.05). None of the pro-angiogenic growth factors (VEGF, FGF, PDGF, VEGF/FGF) were able to prevent vascular regression (P = NS).
These findings suggest that the anti-angiogenic signals that mediate physiological vascular regression in wounds are strongly dominant over pro-angiogenic stimuli during the later phases of wound healing. Clinical manipulation of anti-angiogenic signals in addition to the currently used pro-angiogenic targets may be needed to achieve therapeutic modulation of blood vessel density.
Conference Paper: The role of Sprouty 2 in wound angiogenesis[Show abstract] [Hide abstract]
ABSTRACT: Objectives: Angiogenesis, a crucial component of wound healing, follows a branched tubular development and is regulated by signals received by receptor tyrosine kinases (RTKs). Mammalian Sprouty (Spry) proteins are known to function by specifically antagonizing the activation of the mitogen-activated protein kinase (MAPK) signaling pathway by RTKs, especially vascular endothelial growth factor (VEGF) receptors. The purpose of this research is to determine the role of Sprouty 2 in the regulation of wound angiogenesis. Methods: To examine Spry2 levels during wound healing in vivo, excisional dermal wounds were made on the dorsum of 6-to-8 week-old female FVB-strain mice using 3-mm punch-biopsy instruments; wound samples were harvested and analyzed for mRNA expression of Spry2 at 0, 1, 3, 5, 7, 10, 14, 21, 28 days post-injury using Real-Time PCR and GAPDH as endogenous control (n=5). In another study, gel containing Spry2, negative dominant Y55F mutant of Spry2, or green fluorescent protein (GFP) control was applied topically to healing wounds 5 days post-injury; wound samples were harvested 10 days post-injury and analyzed for vascularity using PECAM-1 staining (n=3). Results: mRNA expression quantification experiments showed that Spry2 mRNA levels increase after day 5 and peak at day 14 post-injury, a time when vascular regression occurs (p<0.05). Western blot protein analyses confirmed the general pattern of Spry2 expression. Quantification of positive PECAM-1 staining showed a decrease in blood vessel formation in Spry2 treated mice compared to the GFP control group, whereas mice treated with the Y55F mutant exhibited a relative increase in vascularity. Conclusion: Spry2 production follows a defined pattern that parallels the pattern of wound angiogenesis, with peak Spry2 levels occurring during active vascular regression. Application of exogenous Spry2 to wounds inhibits angiogenesis. Taken together, the results suggest that Spry2 down-regulates vascularity and/or vascular branching during wound angiogenesis. R01 GM50875 (LAD); T32 DE018381 (LAD,MW)IADR General Session 2009; 04/2009
[Show abstract] [Hide abstract]
ABSTRACT: Significance: Angiogenesis, the growth of new blood vessels from existing vessels, is an important aspect of the repair process. Restoration of blood flow to damaged tissues provides oxygen and nutrients required to support the growth and function of reparative cells. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic growth factors in the skin, and the amount of VEGF present in a wound can significantly impact healing. Recent Advances: The activity of VEGF was once considered to be specific for endothelial cells lining the inside of blood vessels, partly because VEGF receptor (VEGFR) expression was believed to be restricted to endothelial cells. It is now known, however, that VEGFRs can be expressed by a variety of other cell types involved in wound repair. For example, keratinocytes and macrophages, which both carry out important functions during wound healing, express VEGFRs and are capable of responding directly to VEGF. Critical Issues: The mechanisms by which VEGF promotes angiogenesis are well established. Recent studies, however, indicate that VEGF can directly affect the activity of several nonendothelial cell types present in the skin. The implications of these extra-angiogenic effects of VEGF on wound repair are not yet known, but they suggest that this growth factor may play a more complex role during wound healing than previously believed. Future Directions: Despite the large number of studies focusing on VEGF and wound healing, it is clear that the current knowledge of how VEGF contributes to the repair of skin wounds is incomplete. Further research is needed to obtain a more comprehensive understanding of VEGF activities during the wound healing process.10/2014; 3(10):647-661. DOI:10.1089/wound.2013.0517