Dynamic Histological Events and Molecular Changes in Excisional Wound Healing of Diabetic DB/DB Mice

Wound contraction and re-epithelialization over the entire healing process had never been histologically examined daily in diabetic mouse wounds. Correlating morphological characters with molecular changes may be essential to understand the potential mechanism of impeded diabetic wound healing.

In 99 db/db and 63 db/m mice, dorsal-paired 8 mm-diameter wounds were created. Wound contraction and re-epithelialization were histologically analyzed daily-six wounds per group each day. A novel three-dimensional collagen gel model was used to study diabetic dermal fibroblast contractility. Fibroblast-to-myofibroblasts differentiation and TGFβ-SMAD signaling pathway through the diabetic db/db wound healing process were studied by immunohistochemistry.

Db/db wounds presented delayed closure with impaired wound contraction. Re-epithelialization was not slow but showed thinner epithelial formation and irregular keratinocyte arrangement. Diabetic dermal fibroblasts had significantly lower contractile ability than nondiabetic fibroblasts. In db/db wounds, α-SMA, the marker of myofibroblasts, showed constantly low through the healing, which represented reduced fibroblast-to-myofibroblasts differentiation. Remarkably weak staining of TGFβRI and low accumulation of Smad3 in nuclei were observed.

We demonstrated and precisely located downregulated TGFβ signaling pathway in db/db wounds by showing low expression of TGFβRI and failure of Smad3 translocation from cytoplasm to nuclei, which was not reported previously. The downregulated TGFβ signaling pathway may contribute to the attenuated fibroblast-to-myofibroblast differentiation. Deficient re-epithelialization and defective wound contraction contribute principally to delayed healing of diabetic db/db wounds.