A Novel Nude Mouse Model of Hypertrophic Scarring Using Scratched Full Thickness Human Skin Grafts

Abstract

Objective: Hypertrophic scar (HTS) is a dermal form of fibroproliferative disorder that develops following deep skin injury. HTS can cause deformities, functional disabilities, and aesthetic disfigurements. The pathophysiology of HTS is not understood due to, in part, the lack of an ideal animal model. We hypothesize that human skin with deep dermal wounds grafted onto athymic nude mice will develop a scar similar to HTS. Our aim is to develop a representative animal model of human HTS. Approach: Thirty-six nude mice were grafted with full thickness human skin with deep dermal scratch wound before or 2 weeks after grafting or without scratch. The scratch on the human skin grafts was made using a specially designed jig that creates a wound >0.6 mm in depth. The xenografts were morphologically analyzed by digital photography. Mice were euthanized at 1, 2, and 3 months postoperatively for histology and immunohistochemistry analysis. Results: The mice developed raised and firm scars in the scratched xenografts with more contraction, increased infiltration of macrophage, and myofibroblasts compared to the xenografts without deep dermal scratch wound. Scar thickness and collagen bundle orientation and morphology resembled HTS. The fibrotic scars in the wounded human skin were morphologically and histologically similar to HTS, and human skin epithelial cells persisted in the remodeling tissues for 1 year postengraftment. Innovation and Conclusions: Deep dermal injury in human skin retains its profibrotic nature after transplantation, affording a novel model for the assessment of therapies for the treatment of human fibroproliferative disorders of the skin. INTRODUCTIONSkin wound healing is an extremely complex process that involves the reactions and interactions of inflammatory cells, growth factors, and cytokines.1 This orchestrated process can be divided into four overlapped phases starting with hemostasis, followed by inflammation and proliferation, and ending by maturation, including collagen remodeling to restore the damaged skin integrity through formation of a mature scar.

Evolution of ischemia and neovascularization in a murine model of full thickness human wound healing

“…Several studies have shown that grafting human skin onto an immunocompromised mouse leads to hypertrophic scarring 14,15,20 . Hypertrophic scarring, most often thought of as a dermal process, also receives input from the neighboring epidermis 27,28 .…”

“…In this study we follow the gross and histologic changes in grafted human skin as it heals from an ischemic insult in a model of full thickness human skin wound healing, using the NBSGW mouse. While other investigators have described full thickness human skin healing on the athymic mouse, this model has been abandoned in favor of transplantation of partial thickness skin 6,14,20,30,31 . Partial thickness skin is often chosen over full thickness skin because it heals faster (generally within 7 weeks in our experience; unpublished data); the thinner dermal component revascularizes more rapidly, therefore, the model is ready for experimentation sooner than full thickness skin.…”

“…Human skin grafting onto the immunocompromised mouse has been previously described 10,16,17,20 . Briefly, animal use protocol approval was obtained from the University of Wisconsin Institutional Animal Care and Use Committee and the Research Animal Resource and Compliance office.…”

Cellular and Molecular Mechanism of Dermal Fibrosis Following Burn Injury, and Exploration of Therapeutic Approaches

“…In histology, we found reduced hair follicles and rete ridges, increased cells and blood vessels, thin collagen fiber accumulation parallel to the skin surface, elevated TGFβ and reduced decorin, and recruitment of macrophages, mast cells, fibrocytes and myofibroblasts. To confirm that human skin survives the wound healing process, black human skin was grafted onto mouse and black scar developed ( Figure 3D) [4][5][6]. Besides nude mice, scars also developed in RAG1, RAG2 and TCR knockout mice, in which mature T, B, NK cells and T cell receptors are deficient, suggesting that non-specific immune cells such as macrophages and mast cells may play a significant role in this dermal fibrotic model [7].…”

“…The roles of non-specific immune cells in wound healing and scarring have being studied now. Based on this model, we further modified the mouse model by grafting full-thickness human skin with a deep wound, in which the deep wound was created using a jig before or after grafting, which may create a more promising dermal fibrotic mouse model ( Figure 4) [6].…”