Effects of keratinocyte-derived and fibroblast-derived exosomes on human epidermal melanocytes

Keratinocytes - Amplifiers of Immune Responses in Systemic Lupus Erythematosus

PURPOSE OF REVIEW

Epithelial cells have been acknowledged as important players in autoimmune diseases by directing and enhancing inflammatory responses. Here, we summarize recent publications that examine keratinocyte (KC) dysfunction and its contribution to cutaneous and systemic disease in systemic lupus erythematosus patients.

RECENT FINDINGS

Chronic upregulation of type I interferon (IFN) in KCs is a feature of both lesional and nonlesional lupus skin. This IFN rich environment modulates epidermal cell death responses and promotes inflammatory responses to UV light exposure. In addition, newer technologies such as single cell RNA-seq are informing our understanding of lupus-specific intercellular crosstalk and how this contributes to disease. Recent discoveries in KC dysfunction in lupus skin include aberrant IFN responses to environmental stress, enhanced cytokine and chemokine secretion and epigenetic changes leading to increased cell death. Further research will enable precision therapies for lupus treatment.

Physiological skin oxygen levels: An important criterion for skin cell functionality and therapeutic approaches

The skin is made up of different layers with various gradients, which maintain a complex microenvironment, particularly in terms of oxygen levels. However, all types of skin cells are cultured in conventional incubators that do not reproduce physiological oxygen levels. Instead, they are cultured at atmospheric oxygen levels, a condition that is far removed from physiology and may lead to the generation of free radicals known to induce skin ageing. This review aims to summarize the current literature on the effect of physiological oxygen levels on skin cells, highlight the shortcomings of current in vitro models, and demonstrate the importance of respecting skin oxygen levels. We begin by clarifying the terminology used about oxygen levels and describe the specific distribution of oxygen in the skin. We review and discuss how skin cells adapt their oxygen consumption and metabolism to oxygen levels environment, as well as the changes that are induced, particularly, their redox state, life cycle and functions. We examine the effects of oxygen on both simple culture models and more complex reconstructed skin models. Finally, we present the implications of oxygen modulation for a more therapeutic approach.

Exosome-derived microRNAs: emerging players in vitiligo

Exosome-derived microRNAs (miRNAs) are biomacromolecules and nanoscale extracellular vesicles originating from intracellular compartments that are secreted by most cells into the extracellular space. This review examines the formation and function of exosomal miRNAs in biological information transfer, explores the pathogenesis of vitiligo, and highlights the relationship between exosomal miRNAs and vitiligo. The aim is to deepen the understanding of how exosomal miRNAs influence immune imbalance, oxidative stress damage, melanocyte-keratinocyte interactions, and melanogenesis disorders in the development of vitiligo. This enhanced understanding may contribute to the development of potential diagnostic and therapeutic options for vitiligo.

Mitochondrial dynamics and metabolism across skin cells: implications for skin homeostasis and aging

Aging of human skin is a complex process leading to a decline in homeostasis and regenerative potential of this tissue. Mitochondria are important cell organelles that have a crucial role in several cellular mechanisms such as energy production and free radical maintenance. However, mitochondrial metabolism as well as processes of mitochondrial dynamics, biogenesis, and degradation varies considerably among the different types of cells that populate the skin. Disturbed mitochondrial function is known to promote aging and inflammation of the skin, leading to impairment of physiological skin function and the onset of skin pathologies. In this review, we discuss the essential role of mitochondria in different skin cell types and how impairment of mitochondrial morphology, physiology, and metabolism in each of these cellular compartments of the skin contributes to the process of skin aging.

Effects of MITF on marker protein expression of multivesicular bodies and miRNA omics of extracellular vesicles of mice melanocyte cell line

Extracellular vesicles (EVs) are heterogeneous membrane-bound complexes of cell-derived and nanosized structures originating from the endosomal system and subsequently released from the plasma membrane. EVs contribute significantly to intercellular communication and are involved in pigmentation processes that rely on tight communication between keratinocytes and melanocytes in the epidermis. Microphthalmia-associated transcription factor (MITF) induces melanogenesis and modulates the expression factors involved in melanosome biogenesis, maturation and dispersal in melanocytes. Here, we evaluated the effects of MITF on the fate of multivesicular bodies and the biogenesis of extracellular vesicles of melanocytes. It was found that MITF increased the expression of subunits of the endosomal sorting complex, required for transport (ESCRT), including VPS37, VPS36B, and tetraspanin CD81, which are key mediators of multivesicular body biogenesis. Over 110 miRNAs, including miR-211-5p, miR-335-5p, let-7g-5p and miR-28a-3p, were differentially expressed in melanocyte-derived EVs after overexpression of MITF in melanocytes. These miRNAs have been reported to be key regulators of plasma protein binding, changes in the cell membrane system and transferase activity. These results suggest that while enhancing melanogenesis, melanocytes may mediate intercellular communication with surrounding cells by serving as EV delivery vehicles.

Current Understanding of the Role of Senescent Melanocytes in Skin Ageing

Melanocytes reside within the basal epidermis of human skin, and function to protect the skin from ultraviolet light through the production of melanin. Prolonged exposure of the skin to UV light can induce irreparable DNA damage and drive cells into senescence, a sustained cell cycle arrest that prevents the propagation of this damage. Senescent cells can also be detrimental and contribute to skin ageing phenotypes through their senescence-associated secretory phenotype. Senescent cells can act in both an autocrine and paracrine manner to produce widespread tissue inflammation and skin ageing. Recently, melanocytes have been identified as the main senescent cell population within the epidermis and have been linked to a variety of skin ageing phenotypes, such as epidermal thinning and the presence of wrinkles. However, the literature surrounding melanocyte senescence is limited and tends to focus on the role of senescence in the prevention of melanoma. Therefore, this review aims to explore the current understanding of the contribution of senescent melanocytes to human skin ageing.