High glucose environment induces M1 macrophage polarization that impairs keratinocyte migration via TNF-α: An important mechanism to delay the diabetic wound healing.

Background: Macrophages play important roles during wound healing, and delayed healing in diabetics is associated with sustained inflammation. M1 type macrophage is recognized to secrete excessive amount of tumor necrosis factor-alpha (TNF-α) as compared to its M2 counterpart.

Objectives: We hypothesized that macrophage polarization is different between diabetic and normal rats during skin wounding and has direct impact on keratinocyte function in the context of re-epithelialization.

Methods: Skin wounds were created in diabetic and control rats. The phenotypes of infiltrating macrophages, the levels of TNF-α, and the rate of wound closure were determined. Using cell model, the effects of M1 type macrophage on keratinocyte migration were evaluated, and the potential regulatory pathways were determined.

Results: The percentage of M1 macrophages and the levels of TNF-α expression were significantly higher in the perilesional area of diabetic rats as compared to control. The condition media (CM) from M1 type macrophage upregulated tissue inhibitor metalloproteinases (TIMP)-1 expression in keratinocytes and significantly reduced keratinocyte migratory capacity. Addition of neutralizing TNF-α antibody to the CM or gene-silencing of TIMP1 in keratinocytes restored the keratinocyte migratory capacity. Treating wounds of diabetic rats with TNF-α antagonist improved the wound healing process.

Conclusions: In summary, high glucose wound environment harbored more M1 macrophages infiltration, an event that created excess TNF-α micro-environment. TNF-α upregulated TIMP1 expression in keratinocytes and resulted in impaired keratinocyte migration. Taken together, these events contributed to impaired wound healing during diabetic condition, and targeting TNF-α is a potential therapeutic option to improve diabetic wound healing.