Somatic epidermal stem cells at the basal layer of epidermis is responsible to maintain skin homeostasis. When cutaneous injuries occur, skin homeostasis and integrity is damaged, leading to fatal traumatizing under severe conditions. Skin wound healing is an intrinsic self-saving chain-reaction, which is crucial in facilitating the replacement of damaged or lost tissue. Immense amounts of research have uncovered the mechanisms underlying this complex and highly regulated process. It is commonly agreed that wound healing is separated into four overlapping stages: hemostasis, inflammation, re-epithelialization and remodeling. In this review, we will dissect the biological process of adult skin wound healing process and emphasize the importance of epidermal stem cells during the wound healing. Then we will comprehensively discuss the current clinical treatment techniques used on patients with cutaneous wounds. For both traditional skin grafting procedures and advanced keratinocytes grafting techniques, somatic epidermal stem cells and their essential functions during skin wound healing are fundamental components underlying these effective approaches. In this review, we will discuss in detail the advantages and disadvantages of each leading technique used in clinical wound treatment and highlight the importance of epidermal stem cells in skin wound healing. Introduction As part of the largest organ in the adult mammalian body, the skin epidermis has significant functions in protecting the host from external environment (e.g.
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irradiation, pathogen, dehydration and physical stress), and elaborating the body surface with appendages [1,2]. Under circumstance of cutaneous wounds, damaged epidermis requires appropriate healing process to repair or regenerate skin functions. The skin homeostasis is sustained by skin somatic stem cells, which are localized within the basal layer (Fig. 1) of the skin epithelium and underlie the remarkable resilience of skin. To replenish cells that are lost during tissue turnover or following injury, epidermal stem cells periodically exit from their niches at basement membrane and execute their program of terminal differentiation. Four layers of keratinocytes at different stages of differentiation compose the skin epidermis. …show more content…
Using mouse skin as an example (Fig. 1), from the innermost and least differentiated layer, the skin epidermis is consisted of stratum basale, stratum spinosum, stratum granulosum and stratum cornuem. Keratinocytes differentiation initiates when basal keratinocytes move towards outside layers, which is a process called stratification. Because of the residence of epidermal stem cells at the basal layer, only basal keratinocytes possess the ability of proliferation and giving rise to the other three differentiated epidermal layers throughout the life of an organism [3]. Therefore, epidermal stem cells are crucial in fueling the skin epidermal turnover (desquamation) and facilitating the replacement of damaged or lost tissue [1-4]. In this review, we will talk about the biological process of adult skin wound healing and the essential contributions of epidermal stem cells during these steps. We will also discuss the implementation of current clinical approaches in wound treatment that are closely based upon epidermal stem cells and their functions. Skin wound healing is a highly regulated process that involves essential functions of various cell types. Skin wound healing begins immediate after wounding and may last for months or years. In adult skin wound healing, fibrosis and scar formation are the main form of skin repair, in which many types of cells, growth factors and cytokines orchestrate and fulfil the closure of the skin wound. One thing worth to point out is that there are certain skin components that cannot fully recover after wound closure in adult skin wound healing. The appendages under the epidermis, such as hair follicles and sweat glands, have no ability to regenerate after severe injuries. Moreover, the scar tissue of the healed epidermis is different from intact skin, as the connections between epidermis and dermis, which anchors epidermis to the underlying connective matrix, are lost after wound healing [5]. In addition, pigmentation commonly vanishes during wound healing, especially for severe wounds. Later in this review, I will discuss recent studies with improvement in pigmentation of wound healing. Adult skin wound healing is commonly divided into four phases (reviewed in reference 6; Figure 2) which spatial-temporally overlaps: Hemostasis- If the injury reaches beyond the epidermal layer, the blood vessels are damaged and cause hemorrhage. Soon, blood clot forms a provisional wound matrix immediately after wound occurs and it takes a couple hours.
irradiation, pathogen, dehydration and physical stress), and elaborating the body surface with appendages [1,2]. Under circumstance of cutaneous wounds, damaged epidermis requires appropriate healing process to repair or regenerate skin functions. The skin homeostasis is sustained by skin somatic stem cells, which are localized within the basal layer (Fig. 1) of the skin epithelium and underlie the remarkable resilience of skin. To replenish cells that are lost during tissue turnover or following injury, epidermal stem cells periodically exit from their niches at basement membrane and execute their program of terminal differentiation. Four layers of keratinocytes at different stages of differentiation compose the skin epidermis. …show more content…
Using mouse skin as an example (Fig. 1), from the innermost and least differentiated layer, the skin epidermis is consisted of stratum basale, stratum spinosum, stratum granulosum and stratum cornuem. Keratinocytes differentiation initiates when basal keratinocytes move towards outside layers, which is a process called stratification. Because of the residence of epidermal stem cells at the basal layer, only basal keratinocytes possess the ability of proliferation and giving rise to the other three differentiated epidermal layers throughout the life of an organism [3]. Therefore, epidermal stem cells are crucial in fueling the skin epidermal turnover (desquamation) and facilitating the replacement of damaged or lost tissue [1-4]. In this review, we will talk about the biological process of adult skin wound healing and the essential contributions of epidermal stem cells during these steps. We will also discuss the implementation of current clinical approaches in wound treatment that are closely based upon epidermal stem cells and their functions. Skin wound healing is a highly regulated process that involves essential functions of various cell types. Skin wound healing begins immediate after wounding and may last for months or years. In adult skin wound healing, fibrosis and scar formation are the main form of skin repair, in which many types of cells, growth factors and cytokines orchestrate and fulfil the closure of the skin wound. One thing worth to point out is that there are certain skin components that cannot fully recover after wound closure in adult skin wound healing. The appendages under the epidermis, such as hair follicles and sweat glands, have no ability to regenerate after severe injuries. Moreover, the scar tissue of the healed epidermis is different from intact skin, as the connections between epidermis and dermis, which anchors epidermis to the underlying connective matrix, are lost after wound healing [5]. In addition, pigmentation commonly vanishes during wound healing, especially for severe wounds. Later in this review, I will discuss recent studies with improvement in pigmentation of wound healing. Adult skin wound healing is commonly divided into four phases (reviewed in reference 6; Figure 2) which spatial-temporally overlaps: Hemostasis- If the injury reaches beyond the epidermal layer, the blood vessels are damaged and cause hemorrhage. Soon, blood clot forms a provisional wound matrix immediately after wound occurs and it takes a couple hours.