Interleukins 1 alpha and 6 and tumor necrosis factor-alpha are paracrine inhibitors of human melanocyte proliferation and melanogenesis

Regulatory gene network for coffee-like color morph of TYRP1 mutant of oujiang color common carp

BACKGROUND

Neither a TYRP1-mediated highly conserved genetic network underlying skin color towards optimum defense nor the pathological tendency of its mutation is well understood. The Oujiang Color Common Carp (Cyprinus carpio var. color) as a model organism, offering valuable insights into genetics, coloration, aquaculture practices, and environmental health. Here, we performed a comparative skin transcriptome analysis on TYRP1 mutant and wild fishes by applying a conservative categorical approach considering different color phenotypes.

RESULTS

Our results reveal that an unusual color phenotype may be sensitized with TYRP1 mutation as a result of upregulating several genes related to an anti-inflammatory autoimmune system in response to the COMT-mediated catecholamine neurotransmitters in the skin. Particularly, catecholamines-derived red/brown, red with blue colored membrane attack complex, and brown/grey colored reduced eumelanin are expected to be aggregated in the regenerated cells.

CONCLUSIONS

It is, thus, concluded that the regenerated cells with catecholamines, membrane attack complex, and eumelanin altogether may contribute to the formation of the unusual (coffee-like) color phenotype in TYRP1 mutant.

Immune dysregulation and inflammation causing hypopigmentation in post kala-azar dermal leishmaniasis: partners in crime?

Post kala-azar dermal leishmaniasis (PKDL), a heterogeneous dermal sequela of visceral leishmaniasis (VL), is challenging in terms of its etiopathogenesis. Hypopigmentation is a consistent clinical feature in PKDL, but mechanisms contributing to the loss of melanocytes remains poorly defined. Like other hypopigmentary dermatoses - for example, vitiligo, psoriasis, and leprosy - the destruction of melanocytes is likely a multifactorial phenomenon, key players being immune dysregulation and inflammation. This review focuses on immunological mechanisms responsible for the 'murder' of melanocytes, prime suspects at the lesional sites being CD8+ T cells and keratinocytes and their criminal tools being proinflammatory cytokines, for example, IFN-γ, IL-6, and TNF-α. Collectively, these may cause decreased secretion of melanocyte growth factors, loss/attenuation of cell adhesion molecules and inflammasome activation, culminating in melanocyte death.

Dark pigmentation and related low FMOD expression increase IL-3 and facilitate plasmacytoid dendritic cell maturation

According to epidemiological research, skin autoimmune diseases are more prevalent among black Americans. We postulated that pigment-producing melanocytes may contribute to local immune regulation in the microenvironment. We examined murine epidermal melanocytes in vitro to determine the role of pigment production in immune responses mediated by dendritic cell (DC) activation. Our study revealed that darkly pigmented melanocytes produce more IL-3 and the pro-inflammatory cytokines, IL-6 and TNF-α, and consequently induce plasmacytoid DC (pDC) maturation. Additionally, we demonstrate that low pigment-associated fibromodulin (FMOD) interferes with cytokine secretion and subsequent pDC maturation.

Chemical Constituents from Streblus taxoides Wood with Their Antibacterial and Antityrosinase Activities Plus in Silico Study

Hyperpigmentation frequently occurs after inflammation from bacterial infection. Thus, the inhibition activity of tyrosinase, the key enzyme to catalyze the melanogenesis and/or inhibition of bacterial infection, could decrease melanin production. Hence, the potential inhibitors could be discovered from natural products. ω-Hydroxymoracin C (1), a new compound with two other 2-arylbenzofurans, i.e., moracin M (2) and moracin C (3), and two stilbenes, i.e., 3, 4, 3', 5'-tetrahydroxybibenzyl (4) and piceatannol (5), were isolated from the wood of Streblus taxoides. Compound 4 showed a strong inhibitory activity against tyrosinase enzyme with an IC₅₀ value of 35.65 µg/mL, followed by compound 2 with an IC₅₀ value of 47.34 µg/mL. Conversely, compound 1, 3 and 5 showed moderate activity, with IC₅₀ values of 109.64, 128.67 and 149.73 µg/mL, respectively. Moreover, compound 1 and 3 showed an antibacterial effect against some Staphylococcus spp. Thus, the isolated compounds exhibited potential antityrosine and antibacterial effects. Additionally, an in silico study was performed in order to predict theoretical molecular interactions between the obtained metabolites from S. taxoides and tyrosinase as an extended in vitro enzyme binding assay experiment.

Biologic and targeted therapeutics in vitiligo

BACKGROUND

Vitiligo is a long-standing progressive autoimmune disease with depigmented macules/patches with significant psychological morbidity to the patients. From being one of the most poorly understood diseases in the past, there has been a rampant advance in determining the molecular and genetic factors influencing the disease process. More light has been shed on the complex intracellular environment and interplay between innate and adaptive immunity. Numerous cytokines and signaling pathways have been associated with disease pathogenesis in the recent past.

OBJECTIVE

The aim of this review the efficacy of biologic and targeted therapeutics in vitiligo.

METHODS

A detailed literature search was conducted on databases like PubMed, COCHRANE Central, EMBASE and Google Scholar using keywords-"biologics," "vitiligo," "treatment," "repigmentation," "JAK inhibitors,", "TNF-ꭤ inhibitors," and "IL17/23 inhibitors," Relevant studies and review articles in English were analyzed in detail and report was written. This article aimed at a comprehensive review of all the biologicals and newer targeted therapeutics tried in vitiligo and their efficacy with an insight into the potential complications arising as a result of the therapy.

RESULTS

Most conventional vitiligo treatment modalities are restricted to generalized nonspecific immunosuppressants like topical and oral corticosteroids, calcineurin inhibitors, phototherapy, and surgical modalities. There have been reports and studies on the usage of biologicals in treating vitiligo. JAK inhibitors have shown good efficacy in vitiligo; however, it lacks substantial evidence in the form of randomized control trials. Similarly, the use of targeted therapeutics in treating vitiligo is substantiated by limited evidence and requires more randomized trials for further evidence.

CONCLUSION

JAK inhibitors have shown promising results and good tolerability; Adjuvant phototherapy can achieve a superior response compared to monotherapy. Though TNF-ꭤ has been tried in a few cases, it is best used if vitiligo is present in association with other chronic autoimmune diseases for which it is indicated. More in vitro studies and clinical research are required to understand the pathogenesis clearly, and therapy has to be targeted at specific pathways for a better approach toward vitiligo. Treatment aimed at induction and differentiation of melanocytes may be added to achieve faster repigmentation.

The role of cytokines and vitamin D in vitiligo pathogenesis

Vitiligo is a pigment-related disease with a global prevalence of 0.2% to 1.8% associated with considerable burden on quality of life. The treatment is still a challenge because of relapses and/or incomplete re-pigmentation. Although the exact cause is still unclear, its pathogenesis seems to be justifiable with the autoimmune theory, supported by the results of clinical research. In this narrative review, we aimed to summarize the evidence related to cytokines and vitiligo development. This review is consisted of English articles published in PubMed and Google Scholar concerning levels of inflammatory mediators, especially interleukins, in vitiligo patients over the last 20 years. References of relevant articles were also considered for review. Crucial role of dysregulated levels of interleukins and their synergistic function to each other, in the onset or progression of the disease is evident. The theory of autoimmune vitiligo is reinforced by the results of the studies in the literature, due to the association of pathogenesis with increased secretion of pro-inflammatory mediators and reduction of anti-inflammatory mediators. Decreased vitamin D levels may have a considerable role in vitiligo development by affecting Th1- and Th17-related immune responses. Cytokines play an important role in the pathogenesis or progression of the disease. Moreover, we believe that decreased vitamin D level has a considerable role in vitiligo development by affecting Th1- and Th17-related immune responses.

Establishment and validation of evaluation models for post-inflammatory pigmentation abnormalities

Post-inflammatory skin hyper- or hypo-pigmentation is a common occurrence with unclear etiology. There is currently no reliable method to predict skin pigmentation outcomes after inflammation. In this study, we analyzed the 5 GEO datasets to screen for inflammatory-related genes involved in melanogenesis, and used candidate cytokines to establish different machine learning (LASSO regression, logistic regression and Random Forest) models to predict the pigmentation outcomes of post-inflammatory skin. Further, to further validate those models, we evaluated the role of these candidate cytokines in pigment cells. We found that IL-37, CXCL13, CXCL1, CXCL2 and IL-19 showed high predictive value in predictive models. All models accurately classified skin samples with different melanogenesis-related gene scores in the training and testing sets (AUC>0.7). Meanwhile, we mainly evaluated the effects of IL-37 in pigment cells, and found that it increased the melanin content and expression of melanogenesis-related genes (MITF, TYR, TYRP1 and DCT), also enhanced tyrosinase activity. In addition, CXCL13, CXCL1, CXCL2 and IL-19 could down-regulate the expression of several melanogenesis-related genes. In conclusion, evaluation models basing on machine learning may be valuable in predicting outcomes of post-inflammatory pigmentation abnormalities. IL-37, CXCL1, CXCL2, CXCL13 and IL-19 are involved in regulating post-inflammatory pigmentation abnormalities.

Solamargine Alleviated UVB-Induced Inflammation and Melanogenesis in Human Keratinocytes and Melanocytes via the p38 MAPK Signaling Pathway, a Promising Agent for Post-inflammatory Hyperpigmentation

Post-inflammatory hyperpigmentation (PIH) is a common acquired pigmentary disorder occurring after skin inflammation or injury. Ultraviolet B irradiation could exaggerate PIH clinically due to its effect on promoting cutaneous inflammation and melanogenesis in keratinocytes and melanocytes, respectively. Solamargine (SM), a steroidal alkaloid glycoside extracted from Solanum undatum, significantly inhibits Ultraviolet B (UVB)-induced pro-inflammatory cytokines IL-1α, IL-1β, IL-8, and IFN-γ, as well as paracrine melanogenic factors ET-1, α-MSH, and bFGF in human keratinocytes. Additionally, SM significantly attenuated UVB-induced melanin synthesis in human epidermal melanocytes through down-regulation of tyrosinase activity and expression of MITF, TRP-1, TRP-2, and tyrosinase. SM exerted an anti-inflammatory effect in UVB-irradiated keratinocytes through the p38 MAPK/Nrf2/HO-1 signaling pathway. With its anti-inflammatory and whitening effect, SM may improve PIH through paracrine regulations of keratinocytes and direct action on melanocytes, making it a promising agent for PIH.

Preferential stimulation of melanocytes by M2 macrophages to produce melanin through vascular endothelial growth factor

Post-inflammatory hyperpigmentation is a skin discoloration process that occurs following an inflammatory response or wound. As the skin begins to heal, macrophages first exhibit a proinflammatory phenotype (M1) during the early stages of tissue repair and then transition to a pro-healing, anti-inflammatory phenotype (M2) in later stages. During this process, M1 macrophages remove invading bacteria and M2 macrophages remodel surrounding tissue; however, the relationship between macrophages and pigmentation is unclear. In this study, we examined the effect of macrophages on melanin pigmentation using human induced pluripotent stem cells. Functional melanocytes were differentiated from human induced pluripotent stem cells and named as hiMels. The generated hiMels were then individually cocultured with M1 and M2 macrophages. Melanin synthesis decreased in hiMels cocultured with M1 macrophages but significantly increased in hiMels cocultured with M2 macrophages. Moreover, the expression of vascular endothelial growth factor was increased in M2 cocultured media. Our findings suggest that M2 macrophages, and not M1 macrophages, induce hyperpigmentation in scarred areas of the skin during tissue repair.

The Expression Pattern of Genes Related to Melanogenesis and Endogenous Opioids in Psoriasis

The melanocortin system is a major regulator of stress responses in the skin and is responsible for the induction of melanin synthesis through activation of melanogenesis enzymes. The expression of both melanocortin system genes and melanogenesis enzyme genes is altered in psoriasis, and the focus here was on twelve genes related to the signal transduction between them. Additionally, five endogenous opioid system genes that are involved in cutaneous inflammation were examined. Quantitative real-time-PCR was utilized to measure mRNA expression in punch biopsies from lesional and non-lesional skin of psoriasis patients and from the skin of healthy control subjects. Most of the genes related to melanogenesis were down-regulated in patients (CREB1, MITF, LEF1, USF1, MAPK14, ICAM1, PIK3CB, RPS6KB1, KIT, and ATRN). Conversely, an up-regulation occurred in the case of opioids (PENK, PDYN, and PNOC). The suppression of genes related to melanogenesis is in agreement with the reported reduction in pigmentation signaling in psoriatic skin and potentially results from the pro-inflammatory environment. The increase in endogenous opioids can be associated with their involvement in inflammatory dysregulation in psoriasis.

Imiquimod induced vitiligo-like lesions-A consequence of modified melanocyte function

INTRODUCTION

Imiquimod plays an important role in the management of condyloma and premalignant lesions. Successively, an increase of hypopigmented lesions following imiquimod application has been reported. However, the mechanisms of imiquimod on melanocytes remain unclear. This study was designed to assess the effect of Imiquimod on the functions of melanocytes in vitro.

METHODS

Primary cultured melanocytes were isolated from normal control skin tissue. After incubation with imiquimod for 48 h in vitro, cell viability was analyzed by cell counting kit-8 assay. Apoptosis was detected using the Annexin V-fluorescein-5-isothiocyanate flow cytometry assay. Melanin content and tyrosinase activity in melanocytes were measured by colorimetric method and the modified dopachrome method. The production of inflammatory cytokine interleukin 8 (IL-8), IL-6, and soluble ICAM-1 (soluble Intercellular Adhesion Molecule-1[sICAM-1]) in melanocytes were measured by enzyme-linked immunosorbent assay (ELISA). Toll-like receptor 7 (TLR7), toll-like receptor 9 (TLR9) protein, and autophagy-related proteins microtubule-associated protein 1A/1B-light chain 3 (LC3-II), p62, mechanistic target of rapamycin (mTOR), and Atg5 were assessed using western blot analysis.

RESULTS

Imiquimod significantly inhibited the activity of tyrosinase activity and decreased melanin content in melanocytes and significantly increased apoptosis and IL-6, IL-8, and sICAM-1 production in melanocytes. Moreover, the expression of TLR7 and TLR9 proteins were significantly increased, and the expression of mTOR, p62 protein were markedly decreased, but the expression of LC3II/I and Atg5 protein were significantly increased in melanocytes after incubating with imiquimod.

CONCLUSIONS

This study shows that imiquimod directly inhibits melanogenesis and increases melanocyte apoptosis rates. These effects combined with the upregulation of TLR7 and TLR9 together with increased autophagy activity and inflammatory cytokines production, might be the main reasons leading to hypopigmented lesions after imiquimod application.

A Lower Irradiation Dose of 308 nm Monochromatic Excimer Light Might Be Sufficient for Vitiligo Treatment: A Novel Insight Gained from In Vitro and In Vivo Analyses

A 308 nm monochromatic excimer light (MEL) is widely used to treat patients with vitiligo. However, dose optimization still needs to be clarified. This study aimed to obtain objective evidence regarding various doses of MEL irradiation, induced cell level changes in vitro, and skin level alterations in vivo. Cultured human keratinocytes were irradiated with MEL using various doses. After irradiation at low doses, stem cell factor, endothelin-1, and glycoprotein nonmetastatic melanoma protein B, factors that activate and protect melanocytes, were found to be significantly elevated in keratinocytes. After irradiation using medium and high doses, inflammatory cytokines were induced. The amount of ATP released and the level of inflammasome activation, which are known to be related to interleukin-1β activation, were also increased. The back skin of guinea pigs and mice were irradiated with MEL at varying doses. After irradiation, an increase of epidermal melanin and epidermal melanocytes was confirmed, using the minimal erythemal dose or less. In rhododendrol-induced leukoderma guinea pigs, a much lower dose of MEL irradiation was effective, when compared with the effective dose for control guinea pigs. Our results suggest that a lower irradiation dose of MEL might be sufficient and more suitable for repigmentation in vitiligo treatment.

The calcium-binding protein S100B reduces IL6 production in malignant melanoma via inhibition of RSK cellular signaling

S100B is frequently elevated in malignant melanoma. A regulatory mechanism was uncovered here in which elevated S100B lowers mRNA and secreted protein levels of interleukin-6 (IL6) and inhibits an autocrine loop whereby IL6 activates STAT3 signaling. Our results showed that S100B affects IL6 expression transcriptionally. S100B was shown to form a calcium-dependent protein complex with the p90 ribosomal S6 kinase (RSK), which in turn sequesters RSK into the cytoplasm. Consistently, S100B inhibition was found to restore phosphorylation of a nuclear located RSK substrate, CREB, which is a potent transcription factor for IL6 expression. Thus, elevated S100B reduces IL6-STAT3 signaling via RSK signaling pathway in malignant melanoma. Indeed, the elevated S100B levels in malignant melanoma cell lines correspond to low levels of IL6 and p-STAT3.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

Increased Circulatory Interleukin-17A Levels in Patients with Progressive and Leukotrichial Vitiligo

Background

Vitiligo is a chronic condition characterized by skin depigmentation. Although not life-threatening, it significantly impacts quality of life. The pathophysiology of vitiligo remains poorly understood, and treatment options are limited. Mounting evidence supports the importance of autoreactive T cells and, particularly interleukin-17A- (IL-17A-) secreting Th17 cells, in vitiligo. IL-17A targeting has been proven successful in various inflammatory dermatological conditions, including psoriasis and lupus erythematosus.

Objective

We evaluated the relationship between serum levels of IL-17A and the clinicopathological characteristics of Vietnamese vitiligo patients.

Methods

In this cross-sectional study, we analyzed data from 52 nonsegmental vitiligo patients and 50 age- and sex-matched healthy individuals. Serum levels of IL-17A were measured using an enzyme-linked immunosorbent assay. We evaluated the correlation between IL-17A levels and clinical characteristics including leukotrichia, disease duration, vitiligo activity, and body surface area involvement.

Results

Patients with progressive vitiligo had significantly higher IL-17A levels than patients with stable vitiligo (P = 0.014) or healthy individuals (P = 0.002). In addition, serum IL-17A levels were higher in vitiligo patients with leukotrichia than in patients without it (P = 0.04). Furthermore, serum IL-17A levels were negatively correlated with age (r = -0.39, P = 0.004) and age of onset (r = -0.33, P = 0.016) in vitiligo patients.

Conclusions

Higher serum levels of IL-17A in patients with progressive vitiligo and leukotrichia suggest a potential role of IL-17A in melanocyte destruction in the epidermis and the follicular matrix.

Diversified Stimuli-Induced Inflammatory Pathways Cause Skin Pigmentation

The production of melanin pigments by melanocytes and their quantity, quality, and distribution play a decisive role in determining human skin, eye, and hair color, and protect the skin from adverse effects of ultraviolet radiation (UVR) and oxidative stress from various environmental pollutants. Melanocytes reside in the basal layer of the interfollicular epidermis and are compensated by melanocyte stem cells in the follicular bulge area. Various stimuli such as eczema, microbial infection, ultraviolet light exposure, mechanical injury, and aging provoke skin inflammation. These acute or chronic inflammatory responses cause inflammatory cytokine production from epidermal keratinocytes as well as dermal fibroblasts and other cells, which in turn stimulate melanocytes, often resulting in skin pigmentation. It is confirmed by some recent studies that several interleukins (ILs) and other inflammatory mediators modulate the proliferation and differentiation of human epidermal melanocytes and also promote or inhibit expression of melanogenesis-related gene expression directly or indirectly, thereby participating in regulation of skin pigmentation. Understanding of mechanisms of skin pigmentation due to inflammation helps to elucidate the relationship between inflammation and skin pigmentation regulation and can guide development of new therapeutic pathways for treating pigmented dermatosis. This review covers the mechanistic aspects of skin pigmentation caused by inflammation.

Tumor Necrosis Factor-alpha affects melanocyte survival and melanin synthesis via multiple pathways in vitiligo

Tumor necrosis factor-α (TNF-α) is a major mediator of inflammation and its increased levels have been analyzed in vitiligo patients. Vitiligo is a depigmentary skin disarray caused due to disapperance of functional melanocytes. The aim of the study was to investigate the role of TNF-α in melanocyte biology, analyzing candidate molecules of melanocytes and immune homeostasis. Our results showed increased TNF-α transcripts in vitiligenous lesional and non-lesional skin. Melanocytes upon exogenous stimulation with TNF-α exhibited a significant reduction in cell viability with elevated cellular and mitochondrial ROS and compromised complex I activity. Moreover, we observed a reduction in melanin content via shedding of dendrites, down-regulation of MITF-M, TYR and up-regulation of TNFR1, IL6, ICAM1 expression, whereas TNFR2 levels remain unaltered. TNF-α exposure stimulated cell apoptosis at 48 h and autophagy at 12 h, elevating ATG12 and BECN1 transcripts. Our novel findings establish the functional link between autophagy and melanocyte destruction. Overall, our study suggests a key function of TNF-α in melanocyte homeostasis and autoimmune vitiligo pathogenesis.

The Role of the NKG2D in Vitiligo

Vitiligo is an acquired multifactorial disease that affects melanocytes and results in skin depigmentation. In this review, we examine the role of cells stress and self-reactive T cells responses. Given the canonical and non-canonical functions of NKG2D, such as authenticating stressed target and enhance TCR signaling, we examine how melanocyte stress leads to the expression of ligands that are recognized by the activating receptor NKG2D, and how its signaling results in the turning of T cells against self (melanocyte suicide by proxy). We also discuss how this initiation phase is followed by T cell perpetuation, as NKG2D signaling results in self-sustained long-lasting T cells, with improved cytolytic properties.

Immune-modulatory effects of lenalidomide inhibited the progression of lesions in a vitiligo mouse model

Vitiligo, an autoimmune disorder, is associated with altered cytokine levels and T lymphocytes. Lenalidomide modulates immune system components by altering cytokine production and regulating T-cell stimulation. In this study, effect of lenalidomide was checked on the development of vitiligo lesions, level of various cytokines, and T lymphocytes in the mouse model. The vitiligo mouse model was developed by immunizing C57BL/6 mouse with anti-mouse tyrosine-related protein 2. Lenalidomide was orally given to mice daily, and the effect was observed on the development of vitiligo lesions. The level of T lymphocytes in blood was checked by flow cytometry. Serum cytokine levels were checked by enzyme-linked immunosorbent assay. Vitiligo lesions were found significantly smaller in lenalidomide-treated mice models. It significantly decreased the serum levels of IFN-γ, TNF-α, IL-1β, and IL-6 but elevated the levels of IL-4 and IL-10. It non-significantly elevated CD4⁺ /CD8⁺ T-cell ratio. Lenalidomide had an inhibitory effect on the development of vitiligo lesions in mice models by suppressing the serum level of pro-inflammatory cytokines and increasing anti-inflammatory cytokine levels. It modulated the immune response in vitiligo mice models toward an anti-inflammatory profile suggesting its use in the management of vitiligo.

The Paracrine Effect of Adipose-Derived Stem Cells Orchestrates Competition between Different Damaged Dermal Fibroblasts to Repair UVB-Induced Skin Aging

Background

Human dermal fibroblasts (HDFs) are the primary cells in skin and are associated with UVB-induced skin photoaging. Adipose-derived stem cells (ASCs) have been proposed as a treatment for skin aging. The goal of this study was to investigate paracrine mechanisms by which ASCs repair HDFs damage from UVB exposure.

Methods

ASCs were cocultured with UVB-irradiated and nonirradiated HDFs. We compared HDF senescence, proliferation, migration, oxidative stress, and cytokine expression. In a nude mouse UVB-induced photoaging model, ASCs were injected subcutaneously, and skin samples were collected weekly between postoperative weeks 3 through 7. Histological analysis, PCR, ELISA, and immunohistochemistry were used to analyze the effect of ASCs.

Results

Compared with UVB-irradiated HDFs, nonirradiated HDFs showed higher proliferation and migration, reduced apoptosis, and fewer senescent cells when cocultured with ASCs. The expression of extracellular matrix-related cytokines was also regulated by ASCs. In addition, ASCs effectively reversed UVB-induced skin photoaging in vivo. We propose that ASCs more robustly coordinate healthy HDFs than UVB-damaged HDFs to repair aging skin.

Conclusions

ASCs improved the function of both UVB-damaged and healthy HDFs through paracrine effects. However, the impact of ASCs on healthy HDFs was greater than UVB-damaged HDFs. These findings help to elucidate the underlying mechanisms of the skin rejuvenation effect of ASCs.

An update on Vitiligo pathogenesis

Vitiligo, the most common depigmenting disorder of the skin, is undergoing a period of intense advances in both disease understanding and therapeutic possibilities leading the way to the beginning of a new era for the disorder. Its pathophysiology has gathered the attention of researchers for years, and many advances have been made in the clarification of the interaction between different factors that result in depigmented macule formation. The complex interplay between non-immunological and immunological factors in vitiligo is key for the development of the disease, and the participation of cells other than melanocytes, such as keratinocytes, fibroblasts, natural killer cells, and innate lymphoid cells, has been shown. Recent advances have also brought to the understanding of the complex part played by a specific subtype of T cells: T-resident memory cells. This review analyzes some of the most recent insights in vitiligo pathogenesis underlining the interactions between different cell types, which are the basis for the therapeutic approaches under development.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

Increased expression of Toll-like receptor 7 and 9 in vitiligo melanocytes: a pilot study

BACKGROUND

Toll-like receptors (TLRs) are expressed on human melanocytes, and play an important role in innate and acquired immunity. The role of TLRs in the pathogenesis of vitiligo has not been fully described.

AIM

To investigate the expression of TLRs in melanocytes from patients with vitiligo and healthy controls (HCs).

METHODS

Primary cultured vitiligo and control melanocytes were obtained from perilesional normal skin of patients with generalized vitiligo and HCs. TLRs mRNA expression in melanocytes were determined by real-time reverse transcription PCR and protein expression by western blotting. Apoptosis was analysed using an annexin V-fluorescein isothiocyanate apoptosis detection kit, and tyrosinase activity and melanin content were measured by a modified dopachrome and colorimetric method. Interleukin (IL)-6, IL-8 and soluble cell adhesion molecule (sICAM)-1 expression were measured by ELISA.

RESULTS

In vitiligo melanocytes, compared with control melanocytes, apoptosis rate, expression of TLR7 and TLR9 mRNA and protein, and production of IL-8, IL-6 and sICAM-1 were significantly increased, whereas tyrosinase activity and melanin content were significantly decreased.

CONCLUSIONS

Our results suggest that the increased expression of TLR7 and TLR9 might correlate with melanocyte dysfunction in vitiligo.

Investigation of the Role of Interleukin 6 in Vitiligo Pathogenesis

Interleukin-6 (IL6) is involved in pathogenesis of several autoimmune disorders including vitiligo. Hence, we aimed to investigate the association of IL6 -174 G/C and -572 G/C polymorphisms and its transcript levels with vitiligo; to evaluate the effect of IL-6 on normal human melanocyte (NHM) viability and expression of IL6R, MITF and TYR. IL6 -174 G/C and -572 G/C polymorphisms were genotyped by ARMS-PCR and PCR-RFLP respectively in 343 controls and 322 vitiligo patients. IL6 transcript levels were estimated from PBMCs (96 controls and 77 patients) and skin samples (15 controls and 15 patients) by qPCR. NHM viability was assessed by MTT; IL6R, MITF and TYR transcript and protein levels were monitored by qPCR and ICC respectively. Genetic analyses revealed no association of IL6 -174 G/C polymorphism (p> .05) with vitiligo. Analysis of IL6 -572 G/C revealed reduced risk of vitiligo in individuals with GC/CC genotypes compared to GG genotype (p = .010). IL6 expression was significantly increased (p = .0197) in PBMCs of patients. Further, IL6 expression was significantly higher in non-lesional skin compared to controls (p = .009). In-vitro NHM viability was decreased upon IL-6 exposure (10-50 ng/ml; p< .05), with significantly increased IL6R transcript (p = .042) and protein levels (p = .003) however, MITF transcript (p = .0003) and protein levels (p = .016), and TYR transcript levels (p = .001) were significantly decreased. The results suggest that IL6 -572 G/C polymorphism might be associated with vitiligo susceptibility in Gujarat population. Moreover, increased IL6 expression in vitiligo patients and its effect on NHM suggest a potential role in melanocyte biology.

CONCLUSION

The results suggest that IL6 - 572 G/C polymorphism might be associated with vitiligo susceptibility in Gujarat population. Moreover, increased IL6 expression in vitiligo patients and its effect on NHM suggest a potential role in melanocyte biology.

Type-1 cytokines regulate MMP-9 production and E-cadherin disruption to promote melanocyte loss in vitiligo

Loss of melanocytes is the pathological hallmark of vitiligo, a chronic inflammatory skin depigmenting disorder induced by exaggerated immune response, including autoreactive CD8 T cells producing high levels of type 1 cytokines. However, the interplay between this inflammatory response and melanocyte disappearance remains to be fully characterized. Here, we demonstrate that vitiligo skin contains a significant proportion of suprabasal melanocytes, associated with disruption of E-cadherin expression, a major protein involved in melanocyte adhesion. This phenomenon is also observed in lesional psoriatic skin. Importantly, apoptotic melanocytes were mainly observed once cells were detached from the basal layer of the epidermis, suggesting that additional mechanism(s) could be involved in melanocyte loss. The type 1 cytokines IFN-γ and TNF-α induce melanocyte detachment through E-cadherin disruption and the release of its soluble form, partly due to MMP-9. The levels of MMP-9 are increased in the skin and sera of patients with vitiligo, and MMP-9 is produced by keratinocytes in response to IFN-γ and TNF-α. Inhibition of MMP-9 or the JAK/STAT signaling pathway prevents melanocyte detachment in vitro and in vivo. Therefore, stabilization of melanocytes in the basal layer of the epidermis by preventing E-cadherin disruption appears promising for the prevention of depigmentation occurring in vitiligo and during chronic skin inflammation.

Up-Regulation of Activating Transcription Factor 3 in Human Fibroblasts Inhibits Melanoma Cell Growth and Migration Through a Paracrine Pathway

The treatment of melanoma has remained a difficult challenge. Targeting the tumor stroma has recently attracted attention for developing novel strategies for melanoma therapy. Activating transcription factor 3 (ATF3) plays a crucial role in regulating tumorigenesis and development, but whether the expression of ATF3 in human dermal fibroblasts (HDFs) can affect melanoma development hasn't been studied. Our results show that ATF3 expression is downregulated in stromal cells of human melanoma. HDFs expressing high levels of ATF3 suppressed the growth and migration of melanoma cells in association with downregulation of different cytokines including IL-6 in vitro. In vivo, HDFs with high ATF3 expression reduced tumor formation. Adding recombinant IL-6 to melanoma cells reversed those in vitro and in vivo effects, suggesting that ATF3 expression by HDFs regulates melanoma progression through the IL-6/STAT3 pathway. More importantly, HDFs pretreated with cyclosporine A or phenformin to induce ATF3 expression inhibited melanoma cell growth in vitro and in vivo. In summary, our study reveals that ATF3 suppresses human melanoma growth and that inducing the expression of ATF3 in HDFs can inhibit melanoma growth, a new potential melanoma therapeutic approach.

The enigma and challenges of vitiligo pathophysiology and treatment

Vitiligo is the most common acquired pigmentary disorder, which afflicts 0.5%-1% of the world population, and is characterized by depigmented skin patches resulting from melanocyte loss. Vitiligo has a complex etiology and varies in its manifestations, progression, and response to treatment. It presents as an autoimmune disease, evidenced by circulating melanocyte-specific antibodies, and association with other autoimmune diseases. However, autoimmunity may be secondary to the high oxidative stress in vitiligo skin and to intrinsic defects in melanocytes and their microenvironment, which contribute to aberrant stress response, neo-antigenicity, and susceptibility of melanocytes to immune attack and apoptosis. There is also a genetic predisposition to vitiligo, which sensitizes melanocytes to environmental agents, such as phenolic compounds. Currently, there are different treatment modalities for re-pigmenting vitiligo skin. However, when repigmentation is achieved, the major challenge is maintaining the pigmentation, which is lost in 40% of cases. In this review, we present an overview of the clinical aspects of vitiligo, its pathophysiology, the intrinsic defects in melanocytes and their microenvironment, and treatment strategies. Based on lessons from the biology of human melanocytes, we present our perspective of how repigmentation of vitiligo skin can be achieved and sustained.

Critical role of metabotropic glutamate receptor 4 in bone marrow-derived dendritic cells in the Th17 cell differentiation and the melanogenesis of B16 cells

Vitiligo is an acquired pigmentary disorder resulting from selective destruction of melanocytes. Emerging studies have suggested that T helper cell 17 (Th17) is potentially implicated in vitiligo development and progression. It was recently discovered that metabotropic glutamate receptor 4 (mGluR4) can modulate Th17-mediated adaptive immunity. However, the influence of mGluR4 on melanogenesis of melanocytes has yet to be elucidated. In the present study, we primarily cultured mouse bone marrow-derived dendritic cells (BMDC) and then knocked down and over-expressed mGluR4 using transfection. Transduced BMDC were co-cultured with CD4⁺ T cells and the expression of Th17-related cytokines were measured. The morphology and melanogenesis of B16 cells were observed after being treated with co-culture medium of CD4⁺ T cells and transduced BMDC. We found that mGluR4 knockdown did not affect the co-stimulatory CD80 and CD86 upregulation after lipopolysaccharide stimulation but did increase the expression of Th17-related cytokines, and further down-regulated the expression of microphthalmia-associated transcription factor (MITF) and the downstream genes, decreased melanin production, and destroyed the morphology of B16 cells. Conversely, over-expression of mGluR4 reduced the expression of CD80 and CD86, suppressed the production of Th17-related cytokines, increased the expression of MITF, and did not destroy the morphology of B16 cells. Our study confirmed that mGluR4 modulated the Th17 cell polarization and resulted in the alteration of melanogenesis and morphology of B16 cells. Collectively, these findings suggest mGluR4 might be a potent target involved in the immune pathogenesis of vitiligo.

Emerging drugs for the treatment of vitiligo

Introduction: Vitiligo is a relatively common autoimmune depigmenting disorder of the skin. There has been a great advance in understanding the pathological basis, which has led to the development and utilization of various new molecules in treating vitiligo. This review aims at a comprehensively describing the treatments available and the emerging treatment aspects and the scope for future developments.Areas covered: This study comprehensively summarizes the current concepts in the pathogenesis of vitiligo with special focus on the cytokine and signaling pathways, which are the targets for newer drugs. JAK kinase signaling pathways and the cytokines involved are the focus of vitiligo treatment in current research, followed by antioxidant mechanisms and repigmenting mechanisms. Topical immunosuppressants may be an alternative to steroids in localized vitiligo. Newer repigmenting agents like basic fibroblast growth factors, afamelanotide have been included and a special emphasis is laid on the upcoming targeted immunotherapy.Expert opinion: The treatment of vitiligo needs to be multimodal with emphasis on targeting different limbs of the pathogenesis. Topical and oral JAK inhibitors are the most promising new class of drugs currently available for treating vitiligo and acts best in conjunction with NB-UVB.

Roles of inflammation factors in melanogenesis (Review)

The occurrence of hyperpigmentation or hypopigmentation after inflammation is a common condition in dermatology and cosmetology. Since the exact mechanism of its occurrence is not yet known, prevention and treatment are troublesome. Previous studies have confirmed that α-melanocyte-stimulating hormone, stem cell factor and other factors can promote melanogenesis-related gene expression through the activation of signaling pathways. Recent studies have revealed that a variety of inflammatory mediators can also participate in the regulation of melanogenesis in melanocytes. In this review, we summarized that interleukin-18, interleukin-33, granulocyte-macrophage colony stimulating factor, interferon-γ, prostaglandin E2 have the effect of promoting melanogenesis, while interleukin-1, interleukin-4, interleukin-6, interleukin-17 and tumor necrosis factor can inhibit melanogenesis. Further studies have found that these inflammatory factors may activate or inhibit melanogenesis-related signaling pathways (such as protein kinase A and mitogen activated protein kinase) by binding to corresponding receptors, thereby promoting or inhibiting the expression of melanogenesis-related genes and regulating skin pigmentation processes. This suggests that the development of drugs or treatment methods from the perspective of regulating inflammation can provide new ideas and new targets for the treatment of pigmented dermatosis. This review outlines the current understanding of the inflammation factors' roles in melanogenesis.

Premature cell senescence in human skin: Dual face in chronic acquired pigmentary disorders

Although senescence was originally described as an in vitro acquired cellular characteristic, it was recently recognized that senescence is physiologically and pathologically involved in aging and age-related diseases in vivo. The definition of cellular senescence has expanded to include the growth arrest caused by various cellular stresses, including DNA damage, inadequate mitochondria function, activated oncogene or tumor suppressor genes and oxidative stress. While senescence in normal aging involves various tissues over time and contributes to a decline in tissue function even with healthy aging, disease-induced premature senescence may be restricted to one or a few organs triggering a prolonged and more intense rate of accumulation of senescent cells than in normal aging. Organ-specific high senescence rate could lead to chronic diseases, especially in post-mitotic rich tissue. Recently, two opposite acquired pathological conditions related to skin pigmentation were described to be associated with premature senescence: vitiligo and melasma. In both cases, it was demonstrated that pathological dysfunctions are not restricted to melanocytes, the cell type responsible for melanin production and transport to surrounding keratinocytes. Similar to physiological melanogenesis, dermal and epidermal cells contribute directly and indirectly to deregulate skin pigmentation as a result of complex intercellular communication. Thus, despite senescence usually being reported as a uniform phenotype sharing the expression of characteristic markers, skin senescence involving mainly the dermal compartment and its paracrine function could be associated with the disappearance of melanocytes in vitiligo lesions and with the exacerbated activity of melanocytes in the hyperpigmentation spots of melasma. This suggests that the difference may arise in melanocyte intrinsic differences and/or in highly defined microenvironment peculiarities poorly explored at the current state of the art. A similar dualistic phenotype has been attributed to intratumoral stromal cells as cancer-associated fibroblasts presenting a senescent-like phenotype which influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. Here, we present a framework dissecting senescent-related molecular alterations shared by vitiligo and melasma patients and we also discuss disease-specific differences representing new challenges for treatment.

Possible role of BMP-4 in the hyper-pigmentation of psoriatic plaques after anti-TNF-α treatment

Psoriasis over-expresses several inflammatory mediators, which impacts the activity of melanocytes. Tyrosinase (Tyr) and microphthalmia-associated transcription factor (MITF) are the primary regulators of melanogenesis. Furthermore, bone morphogenetic proteins (BMPs) modulate various pathobiologic processes including inflammation, melanogenesis and melanomagenesis. To determine the association between psoriasis and melanogenesis, psoriatic lesional skin was screened through gene expression, immunohistochemistry, immunogold staining and melanin content assays. The present study detected a decreased expression of Tyr, MITF and BMP-4 in psoriatic lesional skin compared with healthy skin. Tyr, BMP-4 and melanin content were also evaluated in the psoriatic lesional skin of patients receiving adalimumab therapy, before and after 16 weeks of treatment. TNF-α blockade modulated the Tyr, BMP-4 and melanin content of the patient skin lesions, which supported the hypothesis that hyper-pigmentation may occur in areas of psoriatic plaque after biological treatment. The present study confirmed the influence of the psoriatic pro-inflammatory network on melanogenesis, exerting an inhibitory effect mediated by TNF-α. Furthermore, the results regarding BMP-4 in the present study add another important element to the mechanism of psoriasis.

Keratinocyte-derived IL-36γ plays a role in hydroquinone-induced chemical leukoderma through inhibition of melanogenesis in human epidermal melanocytes

Chemical leukoderma is an acquired type of vitiligo that can be initiated by various exogenous chemicals such as hydroquinone (HQ), rhododendrol (RD), or 4-tertiary butyl phenol (4-TBP). Despite the importance of epidermal keratinocytes in diverse dermatological conditions, their toxicological role in chemical leukoderma is poorly understood. To elucidate their role in the pathogenesis of chemical leukoderma, genome-scale transcriptional analysis was performed in human epidermal keratinocytes (HEKs) treated with a sub-cytotoxic HQ concentration (10 µM). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway-based functional enrichment analysis of HQ-induced differentially expressed genes (DEGs) revealed that HQ significantly upregulated DEGs related to the IL-17 signaling pathway and significantly downregulated DEGs associated with melanogenesis in HEKs. The meta-analysis between the HQ-induced and cytokine-induced transcriptional data (GSE53751) showed that 58 DEGs were commonly upregulated between HQ- and IL-17A-treated HEKs. Notably, the expression of IL36G was significantly increased in HEKs in response to both HQ and IL-17A. IL-36γ (2 µg/ml) directly inhibits melanin biosynthesis in cultured human epidermal melanocytes (HEMs) and downregulates the gene transcription of key enzymes in the melanogenesis pathway including TYR, DCT, and TYRP1. Moreover, IL-36γ autocrinally regulated keratinocyte function to produce the proinflammatory cytokines IL-36γ, IL-6, and CXCL8/IL-8 in a concentration-dependent manner, suggesting that IL-36γ may stimulate the amplification cycle of cutaneous inflammation. In this regard, hydroquinone-induced IL-36γ from human keratinocytes plays a pivotal role in the development of chemical leukoderma by autocrinally or paracrinally modulating the crosstalk between keratinocytes and melanocytes.

The Therapeutic Effects of Baicalin on Vitiligo Mice

Vitiligo is a commom disease of skin. Its pathogenesis is complex, resulting in the incapacity to find a targeted cure. Baicalin, which is isolated from Scutellariae radix, has been known to exhibit a number of pharmacological effects on autoimmune diseases. In this study, we explored the effects of Baicalin on the recovery of vitiligo stimulated by monophenylketone in mice. We observed that Baicalin slowed down the progression of depigmentation, decreased the incidence of depigmentation, and reduced the area of depigmentation. Moreover, reflectance confocal microscopy (RCM) shown that Baicalin increased the epidermal melanocytes in depigmented skin. Baicalin decreased CD8 + T cell infiltration in mice skin, and decreased the expression of CXCL10 and CXCR3. Baicalin significantly decreased the levels of serum cytokine (interleukin [IL]-6, tumor necrosis factor [TNF]-α, interferon-γ [IFN-γ], and IL-13). Collectively, these data suggest that Baicalin play an important role in the occurrence and development of vitiligo.

Role of IL-17A receptor blocking in melanocyte survival: A strategic intervention against vitiligo

Cytokines regulate immune response and inflammation and play an important role in depigmentation process of an autoimmune disease, vitiligo. We sought to determine how inflammatory cytokines influence the progression of vitiligo, and based on that, we develop a logical therapeutic intervention using primary melanocyte culture. Melanocytes were cultured and exposed to IL-17A, IL-1β, IFN-γ and TGF-β for 4 days. Melanocytes proliferation, tyrosinase assay and melanin content were measured. Real-Time PCR was used to analyse mRNA expression of genes specific for melanocytes growth and pigmentation. Anti-IL-17A receptor antibody was used to block IL-17A receptors expressed on melanocytes. Protein expression of MITF and TYR was assessed by immunofluorescence and Western blotting. A gradual decline in the melanocyte population, melanin content and tyrosinase activity was observed after different cytokine treatment. The expression of MITF and its downstream genes after blocking with anti-IL-17RA, an increased melanin content, increased expression of TYR, MITF along with its downstream genes, and cell proliferation was observed.

BMP6-induced modulation of the tumor micro-milieu

Melanoma is the deadliest form of skin cancer with rising incidence, creating a significant health problem. We discovered increased expression of bone morphogenetic protein 6 (BMP6) in melanoma cells and tissues, and observed that BMP6 deficiency caused significantly delayed tumor onset and decelerated tumor progression in a melanoma mouse model. Moreover, we determined that BMP6 inhibits dermal mast cell recruitment and found that mast cell-derived mediators significantly reduced melanoma growth in vitro. In line with this, mast cell deficiency accelerated tumor onset and progression in a melanoma mouse model. Analysis of human melanoma tissues revealed a strong negative correlation between melanoma proliferation and mast cell infiltration. This study elucidates a novel role of BMP6-induced modulation of the tumor microenvironment.

Vitiligo: Focus on Clinical Aspects, Immunopathogenesis, and Therapy

Vitiligo is an acquired chronic depigmenting disorder of the skin, with an estimated prevalence of 0.5% of the general population, characterized by the development of white macules resulting from a loss of epidermal melanocytes. The nomenclature has been revised after an extensive international work within the vitiligo global issues consensus conference, and vitiligo (formerly non-segmental vitiligo) is now a consensus umbrella term for all forms of generalized vitiligo. Two other subsets of vitiligo are segmental vitiligo and unclassified/undetermined vitiligo, which corresponds to focal disease and rare variants. A series of hypopigmented disorders may masquerade as vitiligo, and some of them need to be ruled out by specific procedures including a skin biopsy. Multiple mechanisms are involved in melanocyte disappearance, namely genetic predisposition, environmental triggers, metabolic abnormalities, impaired renewal, and altered inflammatory and immune responses. The auto-immune/inflammatory theory is the leading hypothesis because (1) vitiligo is often associated with autoimmune diseases; (2) most vitiligo susceptibility loci identified through genome-wide association studies encode immunomodulatory proteins; and (3) prominent immune cell infiltrates are found in the perilesional margin of actively depigmenting skin. However, other studies support melanocyte intrinsic abnormalities with poor adaptation of melanocytes to stressors leading to melanocyte instability in the basal layer, and release of danger signals important for the activation of the immune system. Recent progress in the understanding of immune pathomechanisms opens interesting perspectives for innovative treatment strategies. The proof of concept in humans of targeting of the IFNγ /Th1 pathway is much awaited. The interplay between oxidative stress and altered immune responses suggests that additional strategies aiming at limiting type I interferon activation pathway as background stabilizing therapies could be an interesting approach in vitiligo. This review covers classification and clinical aspects, pathophysiology with emphasis on immunopathogenesis, and promising therapeutic approaches.

Re-appraisal of Keratinocytes' Role in Vitiligo Pathogenesis

Background

Vitiligo is a common pigmentary disorder. Studies on its pathogenesis extensively investigated melanocytes' abnormalities and few studies searched for keratinocytes' role in disease development. Liver X receptor-α (LXR-α) is a member of nuclear hormone receptors that acts as a transcription factor. Its target genes are the main regulators of melanocyte functions.

Aim

The aim of this study is to investigate keratinocytes' role in vitiligo pathogenesis through immunohistochemical expression of LXR-α in lesional, perilesional, and distant nonlesional vitiligo skin.

Materials and Methods

This case-control study was carried out on 44 participants. These included 24 patients with vitiligo and 20 age- and sex-matched normal individuals as a control group. Biopsies, from cases, were taken from lesional, perilesional, and distant nonlesional areas. Evaluation was done using immunohistochemical technique.

Results

Keratinocyte LXR-α expression was upregulated in the lesional and perilesional skin (follicular and interfollicular epidermis) compared with control skin (P <0.001 for all). There was significant association between higher histoscore (H-score) in lesional epidermis (P <0.001) and in hair follicle (P =0.001) and the presence of angiogenesis. There was significant association between higher H-score in lesional epidermis and suprabasal vacuolization (P =0.02). No significant association was found between H-score or expression percentage and clinical data of selected cases.

Conclusion

LXR-α upregulation is associated with keratinocyte damage in vitiligo lesional skin that leads to decreased keratinocyte-derived mediators and growth factors supporting the growth and/or melanization of surrounding melanocytes. Therefore, melanocyte function and survival are affected.

Paracrine regulation of melanogenesis

Melanocytes are generally characterized by the basic ability of melanin synthesis and transfer to adjacent keratinocytes. This constitutes an individual skin phenotype and provides epidermal protection from various stimuli, such as ultraviolet irradiation, through a complex process called melanogenesis, which can be regulated by autocrine or paracrine factors. Recent evidence has revealed the paracrine effects of keratinocytes on melanogenesis by secreting cytokines, including α-melanocyte stimulating hormone and endothelin-1. In addition to keratinocytes, there are other types of cells in the skin, such as fibroblasts and immune cells, which are also actively involved in the regulation of melanocyte behaviour through the production of paracrine factors. In addition, extracellular matrix proteins, which are secreted mainly by skin-resident cells, not only play direct roles in regulating melanocyte morphology and functions but also provide structural support between the epidermis and dermis to control the distribution of various secreted cytokines from keratinocytes and/or fibroblasts, which are potentially involved in the regulation of melanogenesis. Moreover, understanding the origin of melanocytes (neural crest cells) and the presence of nerve endings in the epidermis can reveal the intimate contact between melanocytes and cutaneous specific nervous system proteins. Melanocytes are associated with all these networks with corresponding receptors expressed on the cell surface. In this review, we provide an overview of recent advances in determining the intimate relationships between melanocytes and their surrounding elements, which provide insights into the complex nature of the regulation of melanogenesis.

Repeated ultraviolet irradiation induces the expression of Toll-like receptor 4, IL-6, and IL-10 in neonatal human melanocytes

BACKGROUND

Human melanocytes express Toll-like receptor 4 (TLR4), which regulates ultraviolet (UV)-induced cutaneous immunosuppression in Langerhans cells. Lipopolysaccharide (LPS) stimulation increases melanocyte pigmentation and TLR4 expression, while inducing local innate inflammatory responses.

AIMS

We investigated whether UV radiation induces TLR4 expression in neonatal human melanocytes (NHMs) and how this affects the immune system.

METHODS

We cultured NHMs with LPS treatment or with one-time or repeated UVA or UVB exposure, and investigated and compared the effects on TLR4 expression, melanin contents, and cytokine production.

RESULTS

NHMs in the resting state did not express TLR4. LPS stimulation induced TLR4 expression and increased pigmentation. TLR4 expression was not detected after single-dose UVA or UVB treatment, but pigmentation increased. Repeated UV treatment induced TLR4 expression and increased pigmentation. LPS stimulation and repeated UV treatment increased IL-6 secretion, and repeated UVB treatment increased IL-10 secretion.

CONCLUSION

These results suggest that human melanocytes may actively participate in UV-induced immune modulation.

The Relationship of Psoriasis and Melanocytic Nevi

Background:

There is limited data about the relationship between psoriasis and melanocytic lesions and melanoma. Immunologic pathways which were implicated in psoriasis induce a reduction in the number of melanocytic nevi.

Aims and Objectives:

To investigate the number of melanocytic nevi in psoriatic patients compared with controls and its relationship with disease severity and type of treatment.

Methods:

We performed a prospective study in 100 psoriatic patients and 100 controls. Clinical data were recorded for all participants.

Results:

As compared with controls, patients had overall fewer nevi congenital nevi. Among psoriatic patients, biologic agents and disease severity did not correlate with the number of nevi.

Conclusions:

Psoriatic patients have fewer nevi than controls. Frequency of nevi in psoriatic patients is not related to treatment and disease severity.

4-n-butylresorcinol enhances proteolytic degradation of tyrosinase in B16F10 melanoma cells

OBJECTIVE

4-n-butylresorcinol is a competitive inhibitor of tyrosinase and has been used as an antimelanogenic agent. However, its inhibition mechanism in intact cells is not fully understood. To elucidate the cellular mechanism, we compared in vitro and in vivo inhibitory effects of 4-n-butylresorcinol on tyrosinase activity.

METHODS

B16F10 melanoma cells were cultured in media containing α-MSH in the presence or absence of 4-n-butylresorcinol. Tyrosinase mRNA levels, protein levels and activity in B16F10 cells were compared by real-time PCR, immunostaining combined with western blot and colorimetric analysis, respectively. Melanin concentration was measured by colorimetry both in the cells and in the media. Tyrosinase glycosylation and proteolytic degradation were analysed by immunoblotting after cells were treated with Endo H/PNGase F and E64/proteasome inhibitors, respectively.

RESULTS

4-n-butylresorcinol inhibited tyrosinase activity and melanin synthesis more effectively in intact cells than in cell lysates. Western blotting and real-time RT-PCR showed that 4-n-butylresorcinol reduced protein levels, but not mRNA levels, of tyrosinase in B16F10 cells. 4-n-butylresorcinol showed no effect on the processing of tyrosinase glycosylation or on trafficking to melanosomes. However, treatment of B16F10 cells with E64 or proteasome inhibitor abrogated the 4-n-butylresorcinol-induced decrease of tyrosinase. Moreover, 4-n-butylresorcinol activated p38 MAPK, resulting in increased ubiquitination of tyrosinase.

CONCLUSION

4-n-butylresorcinol inhibits melanogenesis by enhancing proteolytic degradation of tyrosinase as well as competitive binding to tyrosinase. These findings will help to develop new, effective and safe chemicals for the treatment of hyperpigmentation disorders.

Toll-like receptors and cutaneous melanoma

Innate immune cells recognize highly conserved pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs). Previous studies have demonstrated that PRRs also recognize endogenous molecules, termed damage-associated molecular patterns (DAMPs) that are derived from damaged cells. PRRs include Toll-like receptors (TLRs), scavenger receptors, C-type lectin receptors and nucleotide oligomerization domain-like receptors. To date, 10 TLRs have been identified in humans and each receptor responds to a different ligand. The recognition of PAMPS or DAMPs by TLRs leads to the activation of signaling pathways and cellular responses with subsequent pro-inflammatory cytokine release, phagocytosis and antigen presentation. In the human skin, TLRs are expressed by keratinocytes and melanocytes: The main cells from which skin cancers arise. TLRs 1-6 and 9 are expressed in keratinocytes, while TLRs 2-5, 7, 9 and 10 have been identified in melanocytes. It is hypothesized that TLRs may present a target for melanoma therapies. In this review, the involvement of TLRs in the pathogenesis and treatment of melanoma was discussed.

Focus on Vitiligo: A Generalized Skin Disorder

Vitiligo is an acquired pigmentation disorder due to a disappearance of functioning melanocytes from the epidermis and clinically characterized by achromic patches, often spreading over time. It is still not fully understood how melanocytes disappear in vivo, inducing these peculiar lesions. There are three major hypotheses for the pathogenesis of the disease: the autoimmune hypothesis considers that the disappearance of melanocytes is due to an autoimmune effector mechanism, the neural hypothesis suggests that an accumulation of neurochemical substances is able to damage epidermal melanocytes, and the metabolic hypothesis indicates that an increased sensitivity of melanocytes to oxidative stress is the crucial factor of the disease. Besides these well accepted hypotheses there are also some new interpretations based on a defective adhesion of melanocytic cells, an imbalance in the epidermal production of cytokines and an altered expression of melanocyte receptors. All these theories seem to be based on convincing evidence, indicating that they may contribute in variable proportions to the disease. There is also reasonable evidence at present that vitiligo potentially involves the whole integument, suggesting that it is a generalized skin disorder probably including different cell types during the active phase of the disease. It appears that the different theories may integrate with each other, supporting the concept that in vitiligo there is a final common step, i.e. a loss of pigment in the epidermis as well as different, possibly interacting, pathways leading up to this conclusive result.