LETTER TO THE EDITOR Abnormal Responses of Keloid Tissue to Wounding Identified Using In Vitro Model System

Dear Sir, Keloids are thick, raised scars that represent an extreme form of abnormal scarring. Unlike normal scars, keloids extend beyond the original wound margin and rarely regress; instead, they tend to proliferate indefinitely.1-4 These bulky scars can significantly impair function due to itching, pain, and decreased range of motion5 and can negatively impact psychosocial well-being and overall quality of life.5-7 Although many different therapeutic modalities exist, keloids are extremely resistant to treatment and have a high rate of recurrence.1,2,8-10 Development of effective, targeted interventions has been limited due to an incomplete understanding of the pathophysiology of keloid scarring. Furthermore, because keloid scarring is only found in humans, there are no animal models of keloid scarring, which has hindered the evaluation of novel therapies. Ethical considerations preclude wound healing studies in patients susceptible to keloid scarring. Therefore, in the absence of suitable animal models, organotypic models represent a feasible alternative for investigation of wounding in keloid tissue. In the current study, we investigated engineered skin substitutes (ESS) composed of keratinocytes, fibroblasts, and collagen-glycosaminoglycan biopolymers, as an in vitro organotypic keloid model to analyze changes in gene expression in response to wounding. Primary human fibroblasts and keratinocytes were isolated and cultured11,12 from excised keloid scar or normal skin, collected with University of Cincinnati Institutional Review Board approval. ESS were prepared by sequential inoculation of fibroblasts and keratinocytes onto approximately 40 cm2 collagen-glycosaminoglycan biopolymer sponges.11,13,14 After 7 days of culture at the air-liquid interface, ESS were cut in half, and one piece of each was wounded using a skin graft mesher; approximation of the cut edges permitted healing of the wounded ESS to occur. Histological analysis of sections of normal and keloid ESS 14 days after keratinocyte inoculation demonstrated a well-stratified epidermal layer and a dermal component