M.S. Hu

Excess Dermal Tissue Remodeling In Vivo: Does It Settle?

Background: Surgical manipulation of skin may result in undesired puckering of excess tissue, which is generally assumed to settle over time. In this article, the authors address the novel question of how this excess tissue remodels. Methods: Purse-string sutures (6-0 nylon) were placed at the midline dorsum of 22 wild-type BALB/c mice in a circular pattern marked with tattoo ink. Sutures were cinched and tied under tension in the treatment group, creating an excess tissue deformity, whereas control group sutures were tied without tension. After 2 or 4 weeks, sutures were removed. The area of tattooed skin was measured up to 56 days after suture removal. Histologic analysis was performed on samples harvested 14 days after suture removal. Results: The majority of excess tissue deformities flattened within 2 days after suture removal. However, the sutured skin in the treatment group decreased in area by an average of 18 percent from baseline (n = 9), compared to a 1 percent increase in the control group (n = 10) at 14 days after suture removal (p < 0.05). This was similarly observed at 28 days (treatment, −11.7 percent; control, 4.5 percent; n = 5; p = 0.0243). Despite flattening, deformation with purse-string suture correlated with increased collagen content of skin, in addition to increased numbers of myofibroblasts. Change in area did not correlate with duration of suture placement. Conclusions: Excess dermal tissue deformities demonstrate the ability to remodel with gross flattening of the skin, increased collagen deposition, and incomplete reexpansion to baseline area. Further studies will reveal whether our findings in this mouse model translate to humans.

Discussion: Transplantation of an LGR6+ Epithelial Stem Cell-Enriched Scaffold for Repair of Full-Thickness Soft-Tissue Defects: The In Vitro Development of Polarized Hair-Bearing Skin.

www.PRSJournal.com 508 R complex soft-tissue injuries remains a challenge to plastic surgeons. Reduced regenerative capacity is attributed in part to the lack of mesenchymal stem cells and epithelial stem cells in full-thickness wounds. Without this stem cell niche, subsequent progeny, and inability to polarize surrounding cells, regeneration of the tissue layers is not possible. Consequently, Lough et al. isolated leucine-rich, repeat-containing, G-protein–coupled receptor 6 (LGR6+) epithelial stem cells, seeded them onto scaffolds in an in vivo burn wound model, and characterized the subsequent pro-angiogenic response, thereby demonstrating a clinically applicable stem cell–based scaffold that improves healing and hair growth in full-thickness wounds. Prior research has shown that LGR6+ epithelial stem cells in the follicular bulge are capable of differentiating into all cellular lineages of the skin and interfollicular epidermis.1 The authors aimed to exploit these cells by isolating via fluorescenceactivated cell sorting and seeding them onto simple collagen-based scaffolds for use in full-thickness wounds. Lough et al. utilized green fluorescent protein–expressing LGR6+ epithelial stem cells and confocal microscopy to demonstrate the ability to adhere to and proliferate on acellular matrices. Next, they placed LGR6+ epithelial stem cell scaffolds on 3-mm burn wounds on the dorsum of athymic nude mice. After 10 days, burn injuries treated with the scaffolds healed significantly more than untreated wound beds and matrix controls. In addition, wounds treated with the scaffolds produced nascent hair follicles by day 14, corroborating published literature describing the hair-producing capability of LGR6+ epithelial stem cells.2 Finally, the authors combined stromal vascular fraction—rich in myriad cell types such as adipose-derived stromal cells/mesenchymal stem cells, endothelial progenitor cells, preadipocytes, T cells, B cells, mast cells, and macrophages—and LGR6+ epithelial stem cells and showed a synergistic augmentation of pro-angiogenic transcripts with the combination of the two entities. These data are important, but not surprising given the previous reports regarding adipose-derived stromal cells promoting angiogenesis.3 However, what is rather remarkable is the polarization of cells, whereby green fluorescent protein–expressing LGR6+ epithelial stem cells aggregate at the surface of the scaffold while red fluorescent protein– expressing stromal vascular fraction favors an internal subepithelial position. Lough et al. postulate that the epithelial stem cells and adiposederived stromal cells/mesenchymal stem cells in stromal vascular fraction initiate a primitive dermal-epidermal interface within the three-dimensional environment of the matrix. In their article, the authors effectively present a novel methodology for a hybrid graft alternative that utilizes an epithelial stem cell subpopulation capable of producing all elements of functional skin. This promises to circumvent current limitations, such as requiring large donor sites of healthy skin. Moreover, this concept improves on cultured epithelial autografts by enriching for the essential multilineage stem cell population—LGR6+

LOP23: Impaired Regenerative Ability of Aged and Diabetic Adipose Derived Stem Cells is Caused by Depletion of Cell Subpopulations

INTRODUCTION: Neovascularization is essential for tissue repair. Both aged and diabetic patients suffer from a reduced neovascular response leading to complications in wound healing. While it has been shown that mesenchymal stem cells derived from adipose tissue (ASCs) promote tissue regeneration, it also becomes increasingly clear that their function is impaired in aged and diabetic populations. Here we investigate the impact of aging and diabetes on the regenerative potential of ASCs.