Diabetes and Wound Angiogenesis

Diabetes Mellitus Type II (DM2) is a growing international health concern with no end in sight. Complications of DM2 involve a myriad of comorbidities including the serious complications of poor wound healing, chronic ulceration, and resultant limb amputation. In skin wound healing, which has definite, orderly phases, diabetes leads to improper function at all stages. While the etiology of chronic, non-healing diabetic wounds is multi-faceted, the progression to a non-healing phenotype is closely linked to poor vascular networks. This review focuses on diabetic wound healing, paying special attention to the aberrations that have been described in the proliferative, remodeling, and maturation phases of wound angiogenesis. Additionally, this review considers therapeutics that may offer promise to better wound healing outcomes

Vascular Function in Diabetic Wound Healing

Vascular deficits are recognized as a fundamental contributing factor of diabetes-associated diseases. In diabetic wound healing, changes in capillary growth and function are thought to greatly affect wound healing outcomes. Although multiple previous studies have demonstrated that the proangiogenic phase of wound healing is greatly blunted in the context of diabetes, a comprehensive understanding of the mechanisms that regulate skin revascularization and capillary stabilization in diabetic wounds is lacking. The work presented here uses imaging modalities and molecular analysis to carefully examine how vascular maturation and functionality differs in diabetic wounds compared to normal wild type wounds. To begin to examine vascular deficits in the context of diabetes, we first sought data in human subjects to show that alterations exist in human diabetic ulcers. For these experiments, we analyzed existing genomic databases to determine if human diabetic foot ulcers show differential expression of vascular maturation markers. We found that in human diabetic foot skin there is significant downregulation in many maturation factors involved in capillary pruning and stability. Following these experiments, we employed an experimental model of diabetic wound healing, that of the genetically diabetic db/db mouse, to examine vascular repair in diabetic wounds in detail. In the db/db mouse experiments, we first we confirmed that genetically diabetic mice show a slower closure rate and delayed onset of angiogenesis during wound healing with closure achieved between days 17-19 compared to days 11-13 in wild type control. With this knowledge, we went on to examine the expression of a large group of known factors that influence capillary recruitment, maturation, and stability, and along with markers that are expressed in dermal pericytes. These studies demonstrated that diabetic wounds have significant perturbations in almost all aspects of vascular regrowth and maturation. Specifically, we saw significant down regulation in the following factors: VEGF-A, SPRY2, PEDF, LRP6, TSP1, IP10, CXCR3, PDGFR-β, HB-EGF, EGFR, TGFβ-1, Sema3a, Nrp1, Ang2, NG2, and RGS5. Next, we investigated angiogenesis by staining for CD31+ ECs. We found that at D10 post wounding that diabetic mice have significantly decreased levels of capillaries in the wound bed. Pericyte coverage, a marker of capillary maturation, was then quantified in both wild type and diabetic wounds. We found a trend of diabetic wound capillaries having an increased number of capillaries without pericyte association. Turning our attention to functional attributes of wound capillaries, the permeability of capillaries was compared in diabetic wounds and normal wild type wounds at D10 post wounding using FITC-conjugated, high molecular weight dextran. Here, we concluded that diabetic vessels exhibit significantly increased amounts of extravascular leakage of FITC-dextran reagent compared to normal wounds. Lastly, we used microCT to explore the dynamics of vessel growth and regression during wound healing. This approach allowed us to compare capillary architecture in detail in diabetic and normal wild type wounds. Our data suggests that vessels initially exhibit a significantly increased number of vessel volume, vessel surface area, vessel length, and vessel branches at D7 compared to D14 and 21. Together, these studies provide novel information about the complexity of the perturbation in angiogenesis that is seen in wounds of diabetic individuals

Compromised angiogenesis and vascular Integrity in impaired diabetic wound healing.

Vascular deficits are a fundamental contributing factor of diabetes-associated diseases. Although previous studies have demonstrated that the pro-angiogenic phase of wound healing is blunted in diabetes, a comprehensive understanding of the mechanisms that regulate skin revascularization and capillary stabilization in diabetic wounds is lacking. Using a mouse model of diabetic wound healing, we performed microCT analysis of the 3-dimensional architecture of the capillary bed. As compared to wild type, vessel surface area, branch junction number, total vessel length, and total branch number were significantly decreased in wounds of diabetic mice as compared to WT mice. Diabetic mouse wounds also had significantly increased capillary permeability and decreased pericyte coverage of capillaries. Diabetic wounds exhibited significant perturbations in the expression of factors that affect vascular regrowth, maturation and stability. Specifically, the expression of VEGF-A, Sprouty2, PEDF, LRP6, Thrombospondin 1, CXCL10, CXCR3, PDGFR-β, HB-EGF, EGFR, TGF-β1, Semaphorin3a, Neuropilin 1, angiopoietin 2, NG2, and RGS5 were down-regulated in diabetic wounds. Together, these studies provide novel information about the complexity of the perturbation of angiogenesis in diabetic wounds. Targeting factors responsible for wound resolution and vascular pruning, as well those that affect pericyte recruitment, maturation, and stability may have the potential to improve diabetic skin wound healing