Basal Cells in the Epidermis and Epidermal Differentiation

Epidermal stem cells: skin surveillance and clinical perspective

The skin epidermis is continually influenced by a myriad of internal and external elements. At its basal layer reside epidermal stem cells, which fuels epidermal renovation and hair regeneration with powerful self-renewal ability, as well as keeping diverse signals that direct their activity under surveillance with quick response. The importance of epidermal stem cells in wound healing and immune-related skin conditions has been increasingly recognized, and their potential for clinical applications is attracting attention. In this review, we delve into recent advancements and the various physiological and psychological factors that govern distinct epidermal stem cell populations, including psychological stress, mechanical forces, chronic aging, and circadian rhythm, as well as providing an overview of current methodological approaches. Furthermore, we discuss the pathogenic role of epidermal stem cells in immune-related skin disorders and their potential clinical applications.

Skin Development and Disease: A Molecular Perspective

Skin, the largest organ in the human body, is a crucial protective barrier that plays essential roles in thermoregulation, sensation, and immune defence. This complex organ undergoes intricate processes of development. Skin development initiates during the embryonic stage, orchestrated by molecular cues that control epidermal specification, commitment, stratification, terminal differentiation, and appendage growth. Key signalling pathways are integral in coordinating the development of the epidermis, hair follicles, and sweat glands. The complex interplay among these pathways is vital for the appropriate formation and functionality of the skin. Disruptions in multiple molecular pathways can give rise to a spectrum of skin diseases, from congenital skin disorders to cancers. By delving into the molecular mechanisms implicated in developmental processes, as well as in the pathogenesis of diseases, this narrative review aims to present a comprehensive understanding of these aspects. Such knowledge paves the way for developing innovative targeted therapies and personalised treatment approaches for various skin conditions.

Poly-l-lactic acid microspheres delay aging of epidermal stem cells in rat skin

Objective

Injectable skin fillers offer a wider range of options for cutaneous anti-aging and facial rejuvenation. PLLA microspheres are increasingly favored as degradable and long-lasting fillers. The present study focused solely on the effect of PLLA on dermal collagen, without investigating its impact on the epidermis. In this study, we investigated the effects of PLLA microspheres on epidermal stem cells (EpiSCs).

Methods

Different concentrations of PLLA microspheres on epidermal stem cells (EpiSCs) in vitro through culture, and identification of primary rat EpiSCs. CCK-8 detection, apoptosis staining, flow cytometry, Transwell assay, wound healing assay, q-PCR analysis, and immunofluorescence staining were used to detect the effects of PLLA on EpiSCs. Furthermore, we observed the effect on the epidermis by injecting PLLA into the dermis of the rat skin in vivo.

Results

PLLA microspheres promote cell proliferation and migration while delaying cell senescence and maintaining its stemness. In vitro, Intradermal injection of PLLA microspheres in the rat back skin resulted in delayed aging, as evidenced by histological and immunohistochemical staining of the skin at 2, 4, and 12 weeks of follow-up.

Conclusion

This study showed the positive effects of PLLA on rat epidermis and EpiSCs, while providing novel insights into the anti-aging mechanism of PLLA.

Regulation of epidermal stratification and development by basal keratinocytes

The epidermis is a stratified squamous epithelium distributed in the outermost layer of the skin and is intimately involved in the formation of a physical barrier to pathogens. Basal keratinocytes possess the properties of stem cells and play an essential role in epidermal development and skin damage recovery. Therefore, understanding the molecular mechanism of how basal keratinocytes participate in epidermal development and stratification is vital for preventing and treating skin lesions. During epidermal morphogenesis, the symmetric division of basal keratinocytes contributes to the extension of skin tissues, while their asymmetric division and migration facilitate epidermal stratification. In this review, we summarize the process of epidermal stratification and illustrate the molecular mechanisms underlying epidermal morphogenesis. Furthermore, we discuss the coordination of multiple signaling pathways and transcription factors in epidermal stratification, together with the roles of cell polarity and cell dynamics during the process.

ALDH3B1 protects interfollicular epidermal cells against lipid peroxidation via the NRF2 pathway

Reactive oxygen species (ROS) production is critical for the initiation of wound repair; however, persistently high levels of ROS can lead to lipid peroxidation in cells and thus affect wound healing. Iron is a transition metal that is an essential component of almost all living cells and organisms. When present in excess in cells and tissues, iron disrupts redox homeostasis and catalyzes the generation of ROS, leading to increased lipid peroxidation. In this study, we found that after treating interfollicular epidermal (IFE) cells with different concentrations of holotransferrin (0 µg/ml, 1 µg/ml, 10 µg/ml, 100 µg/ml, and 1 mg/ml), the intracellular iron content increased, and cell viability and function did not differ significantly among the treatment groups of cells. In addition, the level of lipid peroxidation in IFE cells did not increase following holotransferrin treatment. We speculated that there is a protective mechanism within IFE cells that reduces the occurrence of intracellular lipid peroxidation. We also found that the elevated intracellular iron content of IFE cells was accompanied by elevated ALDH3B1 expression. We investigated the effect of ALDH3B1 on the level of lipid peroxidation in IFE cells and found that elevated ALDH3B1 expression decreased the damage to IFE cells induced by lipid peroxidation. In addition, the NRF2 pathway was found to affect the expression of ALDH3B1, which in turn affected lipid peroxidation in IFE cells. These findings suggest that in IFE cells, activation of the NRF2 pathway can increase the expression of ALDH3B1 and thus reduce the production of intracellular ROS and the occurrence of intracellular lipid peroxidation. Therefore, ALDH3B1 may be a potential target for the treatment of chronic wounds.