Fetal wound healing using a genetically modified murine model: the contribution of P-selectin

Actin cable formation and epidermis-dermis positional relationship during complete skin regeneration

Up to a certain developmental stage, a fetus can completely regenerate wounds in the skin. To clarify the mechanism of fetal skin regeneration, identifying when the skin switches from fetal-type wound regeneration to adult-type wound repair is necessary. We hypothesized that this switch occurs at several time points and that complete skin regeneration requires epidermal–dermal interactions and the formation of actin cables. We compared normal skin and wound morphology at each developmental stage. We examined two parameters: epidermal texture and dermal structure. We found that the three-dimensional structure of the skin was completely regenerated in full-thickness skin incisions made before embryonic day (E) 13. However, the skin texture did not regenerate in wounds made after E14. We also found that the dermal structure regenerates up to E16, but wounds created after E17 heal as scars with dermal fibrosis. By controlling the activity of AMP-activated protein kinase and altering actin cable formation, we could regulate scar formation in utero. These findings may contribute to therapies that allow complete skin regeneration without scarring.

A Murine Incisional Fetal Wound-Healing Model to Study Scarless and Fibrotic Skin Repair

The ideal response to skin injury is the complete regeneration of normal tissue without scar formation. This regenerative response is known to occur at early stages of embryonic development but is lost as the skin becomes more mature. In more developed skin, the wound-healing response is suboptimal and results in the formation of scar tissue. Scar tissue can be a significant clinical concern, causing skin dysfunction as well as psychosocial issues related to poor aesthetic outcomes. Mouse models of fetal wound healing can be useful for understanding what regulatory pathways lead to skin regeneration and scarless healing in less developed skin or scarring and fibrotic healing in more developed skin. Here, a reproducible incisional wound model in developing mice is described that our lab has used repeatedly to study scarless and fibrotic fetal wound healing.

Inflammation as an orchestrator of cutaneous scar formation: a review of the literature

Inflammation is a key phase in the cutaneous wound repair process. The activation of inflammatory cells is critical for preventing infection in contaminated wounds and results in the release of an array of mediators, some of which stimulate the activity of keratinocytes, endothelial cells, and fibroblasts to aid in the repair process. However, there is an abundance of data suggesting that the strength of the inflammatory response early in the healing process correlates directly with the amount of scar tissue that will eventually form. This review will summarize the literature related to inflammation and cutaneous scar formation, highlight recent discoveries, and discuss potential treatment modalities that target inflammation to minimize scarring.

Co‑culture with human fetal epidermal keratinocytes promotes proliferation and migration of human fetal and adult dermal fibroblasts

The repair strategy for the healing of skin wounds in fetuses differs from that in adults. Proliferation and migration of dermal fibroblasts are the main mechanisms associated with skin wound healing, as well as the complex interactions between epidermal keratinocytes (KCs) and dermal fibroblasts. In order to investigate the effects of fetal skin epidermal KCs on fetal and adult human dermal fibroblasts, KCs and fibroblasts were isolated from the skin tissue of mid‑gestational human fetuses and adults, and co‑cultured using a Transwell® system. When fetal mid‑gestational KCs were co‑cultured with either fetal or adult dermal fibroblasts, the proliferative and migratory potential of the fibroblasts was significantly enhanced. Furthermore, these phenotypic changes were concomitant with the upregulation of numerous proteins including mouse double minute 2 homolog, cyclin B1, phospho‑cyclin‑dependent kinase 1, phospho‑extracellular signal‑regulated kinase, and phospho‑AKT, along with C‑X‑C chemokine receptor 4, phospho‑p38 mitogen activated protein kinase, matrix metalloproteinase (MMP)‑2 and MMP‑9. Notably, no significant differences were observed between fetal and adult dermal fibroblasts in their responses to fetal mid‑gestational epidermal KCs, indicating that the cells from these two developmental stages respond in a similar manner to co‑culture with KCs.

Examining the role of mast cells in fetal wound healing using cultured cells in vitro

Mast cells play an important role during the inflammatory phase of wound healing, and studies suggest that they also influence scar formation and remodeling. Recently, our laboratory has characterized the mast cell response to injury in a fetal wound healing model. In this model, early gestation fetal skin regenerates and heals without a scar (scarless wounds) and late gestation skin heals with a scar (fibrotic wounds). Differences in mast cell number, maturity, and activity were identified between scarless and scar-forming fetal wounds. To study mast cell function in more detail, in vitro experiments are useful. This chapter outlines methods to expand, purify, and study the function of mast cells harvested from murine fetal skin. Using these methods, cultured mast cells retain many of the differences in maturity and activation seen during fetal skin development in vivo. Studying the function of mast cells in vitro could help define the mechanisms by which mast cells contribute to wound repair and ultimately lead to better therapies for improving wound repair and reducing scar formation.