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Every cell in the human body has a unique set of somatic mutations, but it remains difficult to comprehensively genotype an individual cell 1 . Here we describe ways to overcome this obstacle in the context of normal human skin, thus offering a glimpse into the genomic landscapes of individual melanocytes from human skin. As expected, sun-shielded melanocytes had fewer mutations than sun-exposed melanocytes. However, melanocytes from chronically sun-exposed skin (for example, the face) had a lower mutation burden than melanocytes from intermittently sun-exposed skin (for example, the back). Melanocytes located adjacent to a skin cancer had higher mutation burdens than melanocytes from donors without skin cancer, implying that the mutation burden of normal skin can be used to measure cumulative sun damage and risk of skin cancer. Moreover, melanocytes from healthy skin commonly contained pathogenic mutations, although these mutations tended to be weakly oncogenic, probably explaining why they did not give rise to discernible lesions. Phylogenetic analyses identified groups of related melanocytes, suggesting that melanocytes spread throughout skin as fields of clonally related cells that are invisible to the naked eye. Overall, our results uncover the genomic landscapes of individual melanocytes, providing key insights into the causes and origins of melanoma. A combination of clonal expansion and DNA amplification is used to sequence genetic material from individual melanocytes, shedding light on the mutational landscape of these cells and the development of melanomas.

Melanin, the pigment produced by specialized cells, melanocytes, is responsible for skin and hair color. Skin pigmentation is an important protective mechanism against the DNA damaging and mutagenic effects of solar ultraviolet radiation (UV). It is acknowledged that exposure to UV is the main etiological environmental factor for all forms of skin cancer, including melanoma. DNA repair capacity is another major factor that determines the risk for skin cancer. Human melanocytes synthesize eumelanin, the dark brown form of melanin, as well as pheomelanin, which is reddish-yellow in color. The relative rates of eumelanin and pheomelanin synthesis by melanocytes determine skin color and the sensitivity of skin to the drastic effects of solar UV. Understanding the complex regulation of melanocyte function and how it responds to solar UV has a huge impact on developing novel photoprotective strategies to prevent skin cancer, particularly melanoma, the most fatal form, which originates from melanocytes. This review provides an overview of the known differences in the photoprotective effects of eumelanin versus pheomelanin, how these two forms of melanin are regulated genetically and biochemically, and their impact on the DNA damaging effects of UV exposure. Additionally, this review briefly discusses the role of paracrine factors, focusing on α-melanocortin (α-melanocyte stimulating hormone; α-MSH), in regulating melanogenesis and the response of melanocytes to UV, and describes a chemoprevention strategy based on targeting the melanocortin 1 receptor (MC1R) by analogs of its physiological agonist α-MSH.

Skin is a major target of oxidative stress. Increasing evidence suggests that oxidative stress is the cause of melanocyte disappearance in vitiligo, which is an acquired pigmentary skin disorder characterized by patches of skin that have lost pigmentation. New herbal extracts with antioxidant activity are therefore being studied. 6-Shogaol (6-SG), an active compound from ginger, is capable of attenuating oxidative stress-induced ageing and neurotoxicity. Subsequently, to investigate whether 6-SG could protect melanocytes from oxidative stress, cultured human primary epidermal melanocytes (HEMn-MPs) were treated with hydrogen peroxide (H2O2) in the presence or absence of 6-SG. The 6-SG exhibited protective effects against H2O2-induced cell death by reducing oxidative stress. In addition, the 6-SG treatment activated the Nrf2-antioxidant response element signaling pathway by upregulating the mRNA expression of the antioxidant enzyme heme oxygenase 1 (HO-1), and protein expression of Nrf2, NAD(P)H: quinine oxidoreductase 1 (Nqo1), and HO-1. Furthermore, the 6-SG also displayed protective effects on melanocytes against Rhododendrol-induced oxidative stress. We concluded that 6-SG protects melanocytes against oxidative stress in vitro, and its protective effect is associated with the activation of the Nrf2-antioxidant response element signaling pathway. 6-SG, therefore, has potential for use in the prevention of melanocyte loss in the early stages of vitiligo or other pigmentary disorders.

Vitiligo is an acquired depigmenting disorder characterized by progressive melanocyte loss, yet its cellular mechanisms remain incompletely understood. Here, we identify a melanocyte dedifferentiation-like shift as a potentially reversible pathogenic mechanism. In healthy skin, melanocytes reside within a basement membrane niche defined by dystroglycan-laminin-211 adhesion. In vitiligo, extracellular matrix remodeling with reduced laminin-211 and increased laminin-332 is associated with a shift toward integrin α3β1-laminin-332 interactions. This alteration correlates with melanocyte dedifferentiation-like changes, together with Rho-F-actin remodeling, and coordinated alterations in Hippo, MAPK, and c-Jun signaling. Affected melanocytes exhibit reduced pigmentation and features of neural crest-like states, including multilineage potential. Importantly, these changes are partially reversible. Pharmacological modulation restored melanocyte differentiation and pigmentation in mouse models and ex vivo human skin, with JAK inhibition also promoting redifferentiation. These findings identify a microenvironment-driven mechanism in vitiligo and suggest potential therapeutic strategies. This study shows that melanocytes in vitiligo undergo reversible dedifferentiation driven by changes in the skin microenvironment. Targeting these pathways restores pigmentation, suggesting new therapeutic strategies for repigmentation.

Adult stem cells (SCs) are essential for tissue maintenance and regeneration yet are susceptible to senescence during aging. We demonstrate the importance of the amount of the oxidized form of cellular nicotinamide adenine dinucleotide (NAD⁺) and its effect on mitochondrial activity as a pivotal switch to modulate muscle SC (MuSC) senescence. Treatment with the NAD⁺ precursor nicotinamide riboside (NR) induced the mitochondrial unfolded protein response and synthesis of prohibitin proteins, and this rejuvenated MuSCs in aged mice. NR also prevented MuSC senescence in the mdx (C57BL/10ScSn-Dmdmdx/J) mouse model of muscular dystrophy. We furthermore demonstrate that NR delays senescence of neural SCs and melanocyte SCs and increases mouse life span. Strategies that conserve cellular NAD⁺ may reprogram dysfunctional SCs and improve life span in mammals.

The skin serves as a physical barrier and an immunological interface that protects the body from the external environment 1 – 3 . Aberrant activation of immune cells can induce common skin autoimmune diseases such as vitiligo, which are often characterized by bilateral symmetric lesions in certain anatomic regions of the body 4 – 6 . Understanding what orchestrates the activities of cutaneous immune cells at an organ level is necessary for the treatment of autoimmune diseases. Here we identify subsets of dermal fibroblasts that are responsible for driving patterned autoimmune activity, by using a robust mouse model of vitiligo that is based on the activation of endogenous auto-reactive CD8 + T cells that target epidermal melanocytes. Using a combination of single-cell analysis of skin samples from patients with vitiligo, cell-type-specific genetic knockouts and engraftment experiments, we find that among multiple interferon-γ (IFNγ)-responsive cell types in vitiligo-affected skin, dermal fibroblasts are uniquely required to recruit and activate CD8 + cytotoxic T cells through secreted chemokines. Anatomically distinct human dermal fibroblasts exhibit intrinsic differences in the expression of chemokines in response to IFNγ. In mouse models of vitiligo, regional IFNγ-resistant fibroblasts determine the autoimmune pattern of depigmentation in the skin. Our study identifies anatomically distinct fibroblasts with permissive or repressive IFNγ responses as the key determinant of body-level patterns of lesions in vitiligo, and highlights mesenchymal subpopulations as therapeutic targets for treating autoimmune diseases. Single-cell analyses of skin samples from patients with vitiligo and functional genetic experiments in vitiligo mouse models show that distinct fibroblast subsets drive the organ level lesion patterns in this autoimmune disease.

Certain transcription factors have vital roles in lineage development, including specification of cell types and control of differentiation. Microphthalmia-associated transcription factor (MITF) is a key transcription factor for melanocyte development and differentiation. MITF regulates expression of numerous pigmentation genes to promote melanocyte differentiation, as well as fundamental genes for maintaining cell homeostasis, including genes encoding proteins involved in apoptosis (eg, BCL2) and the cell cycle (eg, CDK2). Loss-of-function mutations of MITF cause Waardenburg syndrome type IIA, whose phenotypes include depigmentation due to melanocyte loss, whereas amplification or specific mutation of MITF can be an oncogenic event that is seen in a subset of familial or sporadic melanomas. In this article, we review basic features of MITF biological function and highlight key unresolved questions regarding this remarkable transcription factor.

Extrinsic skin aging is driven by environmental factors, including ultraviolet (UV) radiation and air pollution. While melanocytes serve as key protectors against UV-induced damage, their role in aging, particularly through the process of senescence, remains underexplored. Here, we exposed human neonatal melanocytes and ex vivo skin explants to UV (UVA + UVB), urban particulate matter (UPM), and their combination (UV + UPM) to assess the effects on melanocyte function and skin aging. We demonstrate that combined UV + UPM exposure triggers oxidative stress, mitochondrial and DNA damage, senescence, apoptosis, and modulation of melanogenesis in human neonatal melanocytes. In addition, skin explants subjected to the same treatments showed hallmark features of aging, including epidermal thinning, barrier disruption, fibrosis, and altered pigmentation. These findings highlight that melanocytes respond to environmental stress through multiple interconnected mechanisms, potentially affecting both cell survival and pigmentary function. Our model offers a useful platform to study how environmental stressors affect melanocyte function and skin biology, potentially supporting the development of future strategies targeting pigmentation disorders and environmentally driven skin aging.

Cutaneous melanoma accounts for the majority of skin cancer-related deaths, and its incidence increases each year. The growing number of melanoma cases, especially in advanced stages, poses a significant socio-medical challenge throughout the world. Extensive research on melanoma pathogenesis identifies UV radiation as the most important factor in melanocytic transformation. Oxidative effects of UV irradiation exert their influence on melanoma pathogenesis primarily through modification of nucleic acids, proteins, and lipids, further disrupting cellular signaling and cell cycle regulation. Its effects extend beyond melanocytes, leading to immunosuppression in the exposed skin tissue, which consequently creates conditions for immune surveillance evasion and further progression. In this review, we focus on the specific molecular changes observed in the UV-dependent oxidative stress environment and their biological consequences in the course of the disease, which have not been considered in previous reviews on melanoma. Nonetheless, data show that the exact role of oxidative stress in melanoma initiation and progression remains unclear, as it affects cancerous cells differently depending on the specific context. A better understanding of the pathophysiological basis of melanoma development holds promise for identifying potential targets, which could lead to effective melanoma prevention strategies.

Empirical and anecdotal evidence has associated stress with accelerated hair greying (formation of unpigmented hairs) 1 , 2 , but so far there has been little scientific validation of this link. Here we report that, in mice, acute stress leads to hair greying through the fast depletion of melanocyte stem cells. Using a combination of adrenalectomy, denervation, chemogenetics 3 , 4 , cell ablation and knockout of the adrenergic receptor specifically in melanocyte stem cells, we find that the stress-induced loss of melanocyte stem cells is independent of immune attack or adrenal stress hormones. Instead, hair greying results from activation of the sympathetic nerves that innervate the melanocyte stem-cell niche. Under conditions of stress, the activation of these sympathetic nerves leads to burst release of the neurotransmitter noradrenaline (also known as norepinephrine). This causes quiescent melanocyte stem cells to proliferate rapidly, and is followed by their differentiation, migration and permanent depletion from the niche. Transient suppression of the proliferation of melanocyte stem cells prevents stress-induced hair greying. Our study demonstrates that neuronal activity that is induced by acute stress can drive a rapid and permanent loss of somatic stem cells, and illustrates an example in which the maintenance of somatic stem cells is directly influenced by the overall physiological state of the organism. Stress induces hair greying in mice through depletion of melanocyte stem cells, which is mediated by the activation of sympathetic nerves rather than through immune attack or adrenal stress hormones.