Keap1-Mediated Nrf2 Dysfunction as a Source of Oxidative Damage in Human Diabetic Wounds

Purpose: Despite advancements in disease management and wound therapies, chronic diabetic ulcers represent the leading cause of non-traumatic lower extremity amputations in the United States. The Nrf2 master antioxidant transcription factor has emerged as a promising target for combatting the oxidative stress underlying these wounds. We have previously implicated Keap1-mediated Nrf2 dysfunction in delayed diabetic wound healing, and as a therapeutic target, in mice. However, whether these findings extend to human diabetic wounds remains unknown.

Methods: Intact skin (S) and wound tissue (W) was obtained from diabetic (D) and nondiabetic (ND) patients, and analyzed for reactive oxygen species (ROS) end products (8-OhDG DNA assay), and with immunohistochemistry (IHC), qPCR (gene expression), and western blot (protein expression). Student’s t-tests were used for statistical analysis.

Results: Both DS and DW contained more than 2-fold ROS end products, respectively, compared to NDS and NDW (2.344 vs. 1.117 ng/mL and 4.648 vs. 1.866 ng/mL, p<0.008). DS and DW exhibited 2-fold and 2.5-fold decreases in epidermal Nrf2 staining, respectively, compared to NS and NW (p<0.001). Keap1-the cytoplasmic Nrf2 repressor-was overexpressed in DW when compared to NDW (p<0.04). DW showed a 75% reduction in nuclear Nrf2 protein expression (p<0.02) as compared to NDW. DW also exhibited a 25% relative reduction in gene expression of MnSOD, a key Nrf2 downstream antioxidant enzyme, and 5-fold decrease in epidermal cytoplasmic MnSOD staining compared to NDW, p<0.03.

Conclusion: Here, we implicate Nrf2 dysfunction in impaired redox homeostasis and consequent oxidative damage in both human diabetic skin and diabetic wounds as compared to nondiabetics. We also identify Keap1 as a likely mediator of impaired healing in diabetic wounds. These results recapitulate our previous findings in mice, further validating this critical pathway as a promising target for understanding and treating diabetic wound healing.