Remote Continuous Microinjury-Triggered Cytokines Facilitate Severe Diabetic Foot Ulcer Healing via the Ras/Raf/MEK/ERK Pathway

Abstract

Purpose: Microinjury can trigger in situ tissue repair. Bone transport consists of continuous microinjuries/microfracture and induces bone formation and angiogenesis. Tibial cortex transverse transport (TTT) was found to promote angiogenesis at the foot and the healing of diabetic foot ulcers (DFUs). However, the underlying mechanism remains largely unknown. Methods: We divided 72 Sprague-Dawley rats with DFUs into the control, sham, and TTT groups. Wound measurement and histology were performed to evaluate the wound healing processes. Enzyme-linked immunosorbent assay, flow cytometry, immuno-histochemistry, and Western Blot were used to assess angiogenesis and the activity of endothelial progenitor cells (EPCs) and the Ras/ Raf/MEK/ERK signaling pathway. Results: We found accelerated wound healing, improved epidermal continuity, and increased dermal thickness in the TTT group than the control and the sham groups. Higher levels of serum TGF-β1, PDGF-BB, and VEGF were detected in the TTT group. These changes were in parallel with the expression of TGF-β1, PDGF-BB, and VEGF in the foot wounds and the frequency of EPCs in both bone marrow and peripheral circulation, which implied that the secreted TGF-β1, PDGF-BB, and VEGF promote proliferation and migration of EPCs to the foot wounds. The expression of CD31+ cells, SMA-α+ cells, and the Ras/Raf/MEK/ERK pathway was higher in the TTT group than in the control and sham groups. Conclusion: The findings showed that TTT enhanced the production of growth factors that in turn activated EPC proliferation and migration through the Ras/Raf/MEK/ERK pathway, ultimately contributing to angiogenesis and DFU healing. Based on these findings, we proposed a theory that remote continuous microinjuries can trigger the repair of target tissues (ie, microinjury-induced remote repair, MIRR). Future studies are needed to validate this theory.