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Wound Edge Inversion Delays Healing And Contributes To Dystrophic Scar Formation In A Mouse Model
Shawn Jeffrey Loder, MD1, Phoebe Lee, BS1, David Guerrero, BS1, Wayne Vincent Nerone, BS1, J Peter Rubin, MD2, Lauren Kokai, PhD1.
1University of Pittsburgh, Pittsburgh, PA, USA, 2University of Pittsburgh, PITTSBURGH, PA, USA.

PURPOSE: Management of dystrophic scars often requires surgical excision in the delayed periods as there are few reliable options to prophylax against the formation off dystrophic scars during physiologic or pathologic wound healing. This is in part because of limitations in the availability of genetically tractable small-animal models which can reliably generate the desired dystrophic tissue architecture. While using small animal models of wound healing is desired, the nature of murine dermal healing through contracture makes it poorly suited to the study of later wound sequalae such as dystrophic scars. We have previously demonstrated that tissue-edge inward folding mimicking the architecture of epibole mitigates contracture, restricts epithelialization, and prolongs wound opening. Here we demonstrate that murine epibolous wounds generate an environment of sustained inflammatory infiltration and proliferative granulation and ultimately generate consistent and reliable dystrophic scars in mice.
METHODS: Male C57BL/6J control (wt/wt) and diabetic (db/db) mice received bilateral 6mm excisional wounds. Each wound was stratified as either untreated control or chronic model. Chronic wounds were generated by incising skin flaps, which were sutured to the dermis side to create a folded skin edge. A first (acute) cohort was s were maintained for 14-days until all control wounds had closed and/or epithelialized and were harvested for flow cytometry for neutrophils and/or macrophages and/or histology for pan-keratin (epithelium) and alpha-smooth-muscle actin (myofibroblasts). A second (delayed) cohort was maintained until closure up to 63 days. Photographs were taken at time of sacrifice and samples were collected for H&E and Massonís Trichrome Stain
RESULTS: The epibolous wound environment maintained prolonged neutrophil-dominant inflammatory infiltrate up to 2-weeks with simultaneous enrichment of macrophage/monocyte populations (p<0.05). Epibolous wounds demonstrated reduced frequency of epithelialization as defined by pan-keratin signaling. In epibolous wounds without epithelialization, strong alpha-smooth-muscle actin signal was noted. When allowed to proceed to maturation, scars from epibole injuries remained significantly larger (p<0.05). This was true in both control and diabetic models. All wound-edge inversion injuries demonstrated gross and histologic evidence of dystrophic healing and collagen deposition compared to controls
CONCLUSION: Previously we demonstrated that wound-edge inversion to mimic epibole prolongs wound opening. Here we demonstrate that this translates to prolongs inflammation and a transition of murine healing to a more human-relevant granulation pattern. Furthermore, the delay of closure results in a consistent dystrophic scar without need for thermal, radiological, chemical or biological interference. Consequently, this simple surgical maneuver enhances our ability to study and intervene in the process of acute and chronic wound development and dystrophic scar formation in a histologically humanized model while retaining access to the genetic tractability of murine stock.


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