Hyperbaric oxygen therapy activates hypoxia‐inducible factor 1 (HIF‐1), which contributes to improved wound healing in diabetic mice

Hyperbaric oxygen (HBO) therapy has been used as an adjunctive therapy for diabetic foot ulcers, although its mechanism of action is not completely understood. Recently, it has been shown that HBO mobilizes the endothelial progenitor cells (EPCs) from bone marrow that eventually will aggregate in the wound. However, the gathering of the EPCs in diabetic wounds is impaired because of the decreased levels of local stromal‐derived factor‐1α (SDF‐1α). Therefore, we investigated the influence of HBO on hypoxia‐inducible factor 1 (HIF‐1), which is a central regulator of SDF‐1α and is down‐regulated in diabetic wounds. The effects of HBO on HIF‐1α function were studied in human dermal fibroblasts, SKRC7 cells, and HIF‐1α knock‐out and wild‐type mouse embryonic fibroblasts using appropriate techniques (Western blot, quantitative polymerase chain reaction, and luciferase hypoxia‐responsive element reporter assay). Cellular proliferation was assessed using H3‐thymidine incorporation assay. The effect of HIF in combination with HBOT was tested by inoculating stable HIF‐1α‐expressing adenovirus (Adv‐HIF) into experimental wounds in db/db mice exposed to HBO. HBO activates HIF‐1α at several levels by increasing both HIF‐1α stability (by a non‐canonical mechanism) and activity (as shown both by induction of relevant target genes and by a specific reporter assay). HIF‐1α induction has important biological relevance because the induction of fibroblast proliferation in HBO disappears when HIF‐1α is knocked down. Moreover, the local transfer of stable HIF‐1α‐expressing adenovirus (Adv‐HIF) into experimental wounds in diabetic (db/db mice) animals has an additive effect on HBO‐mediated improvements in wound healing. In conclusion, HBO stabilizes and activates HIF‐1, which contributes to increased cellular proliferation. In diabetic animals, the local transfer of active HIF further improves the effects of HBO on wound healing

Triggering of a Dll4–Notch1 loop impairs wound healing in diabetes

Diabetic foot ulcerations (DFUs) represent a major medical, social, and economic problem. Therapeutic options are restricted due to a poor understanding of the pathogenic mechanisms. The Notch pathway plays a pivotal role in cell differentiation, proliferation, and angiogenesis, processes that are profoundly disturbed in diabetic wounds. Notch signaling is activated upon interactions between membrane-bound Notch receptors (Notch 1-4) and ligands (Jagged 1-2 and Delta-like 1, 3, 4), resulting in cell-context-dependent outputs. Here, we report that Notch1 signaling is activated by hyperglycemia in diabetic skin and specifically impairs wound healing in diabetes. Local inhibition of Notch1 signaling in experimental wounds markedly improves healing exclusively in diabetic, but not in nondiabetic, animals. Mechanistically, high glucose levels activate a specific positive Delta-like 4 (Dll4)-Notch1 feedback loop. Using loss-of-function genetic approaches, we demonstrate that Notch1 inactivation in keratinocytes is sufficient to cancel the repressive effects of the Dll4-Notch1 loop on wound healing in diabetes, thus making Notch1 signaling an attractive locally therapeutic target for the treatment of DFUs

The mRNA expression of IGF-I, IGF-II and IGF-IR in the skin of liver-specific IGF-I deficient mice versus WT control animals with or without diabetes.

<p>The mRNA expression of IGF-I, IGF-II and IGF-IR in the skin of liver-specific IGF-I deficient mice versus WT control animals with or without diabetes.</p

Histological analysis of the wounds in liver-specific IGF-I deficient mice versus controls.

<p>Granulation and collagen deposition level were evaluated by histological analysis after hematoxylin-eosin (HE) and Masson Goldner staining, respectively (scale bar: 25 μm). Angiogenesis was analyzed after anti-CD31 immunohistochemical staining (scale bar: 100 μm).</p