Pigment Epithelium-Derived Factor (PEDF) as a Regulator of Wound Angiogenesis

Abstract

Although the inflammatory and proliferative phases of wound healing have been well described, much less is known about how healing resolves. During the resolution phase, pruning of the capillary bed and maturation of capillaries occurs and influences the final strength and fidelity of the wound. PEDF, an endogenous anti-angiogenic factor, is produced in wounds and may contribute to the removal of capillaries during wound resolution. This study utilized PEDF−/− mice to examine how PEDF influences wound angiogenesis, particularly capillary density and permeability. The absence of PEDF led to transient changes in dermal wound closure and collagen content, but caused substantial changes in wound angiogenesis. Compared to wild type (WT) mice, wounds from PEDF−/− mice exhibited a significant increase in capillaries during the proangiogenic phase of repair, and a delay in capillary pruning. Conversely, the addition of rPEDF caused a reduction in capillary density within skin wounds in WT mice. In vitro studies showed that PEDF inhibited migration and tube formation by dermal microvascular endothelial cells, and caused a decrease in the expression of VEGFR2, VCAM-1, and other surface receptors. The results demonstrate that loss of PEDF causes a distinctive wound healing phenotype that is characterized by increased angiogenesis and delayed resolution. The findings suggest that PEDF most likely acts through multiple mechanisms to regulate proper capillary refinement in wounds.

Compromised angiogenesis and vascular Integrity in impaired diabetic wound healing

“…Most striking was the difference in capillary content at day 10 post-wounding, with WT wounds showing nearly 4 times as much capillary content as diabetic wounds at this time point (p< 0.01) ( Fig 1A and 1B). This time point was of particular significance because previous studies in our lab showed that days 7-10 represent the peak of angiogenesis in normally healing wounds [9,10,21]. These results demonstrated a deficit in diabetic wound healing during the crucial switch from capillary growth to pruning and maturation.…”

“…Significantly lower levels of CXCR3 and its ligand, CXCL10, both of which are well known to be important to wound resolution [36], were observed in diabetic wounds. The expression of SPRY2 [37], TSP1 [38], and PEDF [9,10], all factors that are known to promote vascular pruning in wounds, was also significantly decreased in wounds from db/db mice. Interestingly TSP1 may play a dual role in wounds, as it can affect not only local capillary regression, but also has been described to have a positive effect on the activity of vascular precursor cells.…”

“…For vascular permeability analysis, at day 10 post-wounding, 200μl and 250μl of FITC/dextran (Sigma, 15mg/ml in PBS) were injected into the retro-orbital venous plexus of WT and db/db mice, respectively, 30 min before the animals were euthanized [9,10]. The dosages were different to accommodate for the variation in blood volume between the WT and db/db mice [19].…”

“…Once the healing wound bed is filled with immature granulation tissue and immature microvasculature, resolution factors including Sprouty2 (SPRY2) and pigment epithelium derived factor (PEDF) trigger vascular maturation and remodeling. Previously published data from our laboratory demonstrates that SPRY2 negatively regulates capillary growth while PEDF is responsible for much of the apoptosis driven vascular pruning that occurs during wound maturation [9,10]. Wound maturation is further characterized by the stabilization of microvascular capillaries and the vascular basement membrane by a special population of mural cells called pericytes.…”

Cutaneous Wound Healing in Diabetic Mice Is Improved by Topical Mineralocorticoid Receptor Blockade

“…The length of the newly formed epidermis was calculated by adding the lengths of the neoepithelial tongues on both sides of the wound from the tip of the epidermis to the site of the first hair follicle at the wound margin. The surface of CD31 þ blood vessels (with open and closed lumen) was measured in 5 different fields on CD31-labeled sections, and the data are presented as a percentage of the total surface of the wound (Cho et al, 2006;Khosrotehrani et al, 2011;Michalczyk et al, 2018). Double stained Ki67/CD31 cells were used as an index of neovascularization in wounds.…”