Physiological factors that regulate skin pigmentation

Mouse models of UV-induced melanoma: genetics, pathology, and clinical relevance

Melanocytes, a neural crest cell derivative, produce pigment to protect keratinocytes from ultraviolet radiation (UVR). Although melanocytic lesions such as nevi and cutaneous malignant melanomas are known to be associated with sun exposure, the role of UVR in oncogenesis is complex and has yet to be clearly elucidated. UVR appears to have a direct mutational role in inducing or promoting melanoma formation as well as an indirect role through microenvironmental changes. Recent advances in the modeling of human melanoma in animals have built platforms upon which prospective studies can begin to investigate these questions. This review will focus exclusively on genetically engineered mouse models of UVR-induced melanoma. The role that UVR has in mouse models depends on multiple factors, including the waveband, timing, and dose of UVR, as well as the nature of the oncogenic agent(s) driving melanomagenesis in the model. Work in the field has examined the role of neonatal and adult UVR, interactions between UVR and common melanoma oncogenes, the role of sunscreen in preventing melanoma, and the effect of UVR on immune function within the skin. Here we describe relevant mouse models and discuss how these models can best be translated to the study of human skin and cutaneous melanoma.

The importance of recognizing paraneoplastic symptoms: a case report of Neuroendocrine Small Cell Carcinoma of the Endometrium presenting as Paraneoplastic Cushing's Syndrome

This is the second well documented case of paraneoplastic Cushing's syndrome arising from a small cell carcinoma of the endometrium described in English literature. This tumour has an aggressive biological behaviour and early detection provides the only opportunity for long-term survival. In that regard recognition of associated paraneo- plastic features might be helpful.

Oleoylethanolamide inhibits α-melanocyte stimulating hormone-stimulated melanogenesis via ERK, Akt and CREB signaling pathways in B16 melanoma cells

The present study aimed to examine the potential inhibitory activity of oleoylethanolamide (OEA) on α-melanocyte stimulating hormone (α-MSH)-stimulated melanogenesis and the molecular mechanism(s) involved in the process in B16 mouse melanoma cells. Our data demonstrated that OEA markedly inhibited melanin synthesis and tyrosinase activity in α-MSH-stimulated B16 cells. In addition, the expression of melanogenesis-related proteins, such as melanocortin-1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase-related protein-1 (TRP-1) and tyrosinase, was suppressed in a concentration-dependent manner by OEA. In addition, OEA may suppress melanogenesis through a peroxisome proliferator-activated receptor α (PPARα)-independent pathway. Moreover, OEA activated ERK, Akt, p38 pathways and inhibits CREB pathway in α-MSH-stimulated B16 cells. The specific ERK inhibitor PD98059 partly blocked OEA-inhibited melanin synthesis and tyrosinase activity and partly abrogated the OEA-suppressed expression of melanogenic proteins. Furthermore, OEA presented remarkable inhibition on the body pigmentation in the zebrafish model system. Our findings demonstrated that OEA is an effective inhibitor of hyperpigmentation through activation of ERK, Akt and p38 pathways, inhibition of the CREB pathway, and subsequent down-regulation of MITF, TRP-1 and tyrosinase production.

Targeting GPNMB with glembatumumab vedotin: Current developments and future opportunities for the treatment of cancer

GPNMB has emerged as an immunomodulator and an important positive mediator of tumor progression and metastasis in numerous solid cancers. Tumor intrinsic GPNMB-mediated effects on cellular signaling, coupled with the ability of GPNMB to influence the primary tumor and metastatic microenvironments in a non-cell autonomous fashion, combine to augment malignant cancer phenotypes. In addition, GPNMB is often overexpressed in a variety of cancers, making it an attractive therapeutic target. In this regard, glembatumumab vedotin, an antibody-drug conjugate (ADC) that targets GPNMB, is currently in clinical trials as a single agent in multiple cancers. In this review, we will describe the physiological functions of GPNMB in normal tissues and summarize the processes through which GPNMB augments tumor growth and metastasis. We will review the pre-clinical and clinical development of glembatumumab vedotin, evaluate on-going clinical trials, explore emerging opportunities for this agent in new disease indications and discuss exciting possibilities for this ADC in the context of combination therapies.

Paracrine regulation of melanocyte genomic stability: a focus on nucleotide excision repair

UV radiation is a major environmental risk factor for the development of melanoma by causing DNA damage and mutations. Resistance to UV damage is largely determined by the capacity of melanocytes to respond to UV injury by repairing mutagenic photolesions. The nucleotide excision repair (NER) pathway is the major mechanism by which cells correct UV photodamage. This multistep process involves the basic steps of damage recognition, isolation, localized strand unwinding, assembly of a repair complex, excision of the damage-containing strand 3' and 5' to the photolesion, synthesis of a sequence-appropriate replacement strand, and finally ligation to restore continuity of genomic DNA. In melanocytes, the efficiency of NER is regulated by several hormonal pathways including the melanocortin and endothelin signaling pathways. Elucidating molecular mechanisms by which melanocyte DNA repair is regulated offers the possibility of developing novel melanoma-preventive strategies to reduce UV mutagenesis, especially in UV-sensitive melanoma-prone individuals.

p75 Neurotrophin Receptor in the Skin: Beyond Its Neurotrophic Function

p75 neurotrophin receptor (p75^NTR), also known as CD271, is the low-affinity receptor that, together with the tyrosine kinase receptor tropomyosin-receptor kinase (Trk), mediate neurotrophin (NT) functions. Beside their classic role in skin innervation, NT and their receptors constitute a complex cutaneous network associated with a number of autocrine and paracrine activities. In this context, the role of p75^NTR is becoming more and more important. This review will focus on the intriguing functions of p75^NTR in healthy and diseased skin. First, p75^NTR counterbalances the proliferative and survival activities of its cognate receptor Trk by inducing keratinocyte apoptosis. In addition, p75^NTR identifies an early transit-amplifying (TA) keratinocyte population and plays a critical role in keratinocyte stem cell transition to its progeny as well as in epidermal differentiation. p75^NTR is absent in psoriatic TA cells, thus rendering these cells resistant to apoptosis. On the other hand, p75^NTR infection restores NT-induced apoptosis in psoriatic keratinocytes. Taken together, these results provide evidence for a critical role of p75^NTR in epidermal homeostasis, while its lack may account for the TA defect in psoriasis. While the issue of p75^NTR as a marker of melanoma initiating cells is still to be solved, there is strong evidence that downregulation of this receptor is a precondition to melanoma invasion and metastasis in vitro and in vivo. All in all, this review points to p75^NTR as a major actor in both physiologic and pathologic conditions at the skin level.

N-(4-methoxyphenyl) caffeamide-induced melanogenesis inhibition mechanisms

Background

The derivative of caffeamide exhibits antioxidant and antityrosinase activity. The activity and mechanism of N-(4-methoxyphenyl) caffeamide (K36E) on melanogenesis was investigated.

Methods

B16F0 cells were treated with various concentrations of K36E; the melanin contents and related signal transduction were studied. Western blotting assay was applied to determine the protein expression, and spectrophotometry was performed to identify the tyrosinase activity and melanin content.

Results

Our results indicated that K36E reduced α-melanocyte-stimulating hormone (α-MSH)-induced melanin content and tyrosinase activity in B16F0 cells. In addition, K36E inhibited the expression of phospho-cyclic adenosine monophosphate (cAMP)-response element-binding protein, microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein-1 (TRP-1). K36E activated the phosphorylation of protein kinase B (AKT) and glycogen synthase kinase 3 beta (GSK3β), leading to the inhibition of MITF transcription activity. K36E attenuated α-MSH induced cAMP pathways, contributing to hypopigmentation.

Conclusions

K36E regulated melanin synthesis through reducing the expression of downstream proteins including p-CREB, p-AKT, p-GSK3β, tyrosinase, and TRP-1, and activated the transcription factor, MITF. K36E may have the potential to be developed as a skin whitening agent.

G protein-coupled estrogen receptor enhances melanogenesis via cAMP-protein kinase (PKA) by upregulating microphthalmia-related transcription factor-tyrosinase in melanoma

OBJECTIVE

This study investigated the role and mechanism of action of G protein-coupled estrogen receptor (GPER) in melanogenesis.

METHODS

GPER expression was detected in the A375 human melanoma cell line and B16 mouse melanoma cell line. Cell proliferation, melanin content, tyrosinase (TYR) activity, cyclic adenosine monophosphate (cAMP) level, and TYR and microphthalmia-related transcription factor (MITF) expression were measured. GPER activation was altered by agonist and antagonist treatment and its expression was downregulated by gene silencing. Estradiol-induced melanin synthesis and the activation of related signaling pathways were suppressed by inhibiting GPER via antagonist treatment. The relationship between GPER and TYR was evaluated in clinical chloasma samples by immunohistochemistry.

RESULTS

Upregulation of GPER in A375 cells promoted melanogenesis, favored as indicated by increases in TYR and MITF expression and TYR activity. GPER activated melanin production via the cAMP-protein kinase (PK) A pathway, suggesting that GPER plays an important role in estrogen-induced melanin synthesis. The effect of GPER activation on cAMP-MITF-TYR signaling was also demonstrated in B16 cells. A significant association was observed between GPER and TYR expression in chloasma skin lesions relative to normal skin.

CONCLUSION

GPER enhances melanin synthesis via cAMP-PKA-MITF-TYR signaling and modulates the effects of estrogen in melanogenesis. GPER is therefore a potential drug target for chloasma treatment.

The effect of simultaneous exposure of HEMn-DP and HEMn-LP melanocytes to nicotine and UV-radiation on the cell viability and melanogenesis

Nicotine is a main compound of tobacco plants and may affect more than a billion people all over the world that are permanently exposed to nicotine from cigarettes, various forms of smoking cessation therapies, electronic cigarettes or second-hand smoke. It is known that nicotine forms complexes with melanin what may lead to accumulation of this alkaloid in tissues of living organisms containing the pigment. This may affect the viability of cells and process of melanin biosynthesis that takes place in melanocytes. Although UV radiation is known to be a particular inductor of melanin biosynthesis, its simultaneous effect with nicotine on this process as well as the viability of human cells containing melanin have not been assessed so far. The aim of this study was to examine the simultaneous impact of nicotine and UV radiation on viability and melanogenesis in cultured normal human melanocytes dark (HEMn-DP) and light (HEMn-LP) pigmented. Nicotine together with UV radiation induced concentration-dependent loss in melanocytes viability. The higher cell loss was observed in dark pigmented melanocytes in comparison to light pigmented cells. Simultaneous exposure of cells to nicotine and UV radiation also caused changes in melanization process in both tested cell lines. The data suggest that simultaneous exposure of melanocytes to nicotine and UV radiation up-regulates melanogenesis and affects cell viability. Observed processes are more pronounced in dark pigmented cells.

Loss of strumpellin in the melanocytic lineage impairs the WASH Complex but does not affect coat colour

The five-subunit WASH complex generates actin networks that participate in endocytic trafficking, migration and invasion in various cell types. Loss of one of the two subunits WASH or strumpellin in mice is lethal, but little is known about their role in mammals in vivo. We explored the role of strumpellin, which has previously been linked to hereditary spastic paraplegia, in the mouse melanocytic lineage. Strumpellin knockout in melanocytes revealed abnormal endocytic vesicle morphology but no impairment of migration in vitro or in vivo and no change in coat colour. Unexpectedly, WASH and filamentous actin could still localize to vesicles in the absence of strumpellin, although the shape and size of vesicles was altered. Blue native PAGE revealed the presence of two distinct WASH complexes, even in strumpellin knockout cells, revealing that the WASH complex can assemble and localize to endocytic compartments in cells in the absence of strumpellin.

Ultra-structural effects of different low-level lasers on normal cultured human melanocytes: an in vitro comparative study

The aim of this study was to investigate the effects of the different types of low-level laser therapy (LLLT) on the ultra-structure and number of melanosomes in normal cultured human melanocytes. Specific effects of various types of LLLT on the ultra-structure of melanosomes have not yet been reported. Melanocytes were exposed to LLLT at an energy level of 2.0 J/cm², using a blue (457 nm), red (635 nm), or ultraviolet (UV) (355 nm) laser. After 72 h of irradiation, the melanocytes were fixed in 2.5 % glutaraldehyde (pH 7.2) phosphate buffer for 8 h and analyzed by transmission electron microscopy. Four developmental stages (I to IV) of melanosomes were observed, and their numbers were counted manually. The percentage of stages I, II, III, and IV melanosomes was 12.8, 14.2, 22.6, and 50.3 %, respectively, in the control (sham light). However, the melanosome percentages were 41.2, 5.4, 8.2, and 24.2 % in stages I, II, III, and IV, respectively, in the blue laser-treated group; 58.4, 6.1, 9.3, and 26.2 % for stages I, II, III, and IV, respectively, in the red laser-treated group; and 31.3, 11.1, 16.5, and 41.1 % for stages I, II, III, and IV, respectively, in the UV laser-treated group. The present data show that the amount of stage I is significantly higher (P < 0.0001) in the LLLT-treated cells compared to the control, which indicates significant stimulation of melanogenesis. The red laser was more effective than the other lasers. Moreover, the effects of LLLT on the ultra-structure of melanosomes need to be studied in a larger number of subject groups.

Cross-talk between interferon-gamma and interleukin-18 in melanogenesis

Skin is the largest organ in our body and strategically placed to provide a metabolically active biological barrier against a range of noxious stressors. A lot of inflammatory cytokines, which are increased after ultraviolet (UV) irradiation produced by keratinocytes or other immunocytes, are closely related to pigmentary changes, including interleukin-18 (IL-18) and interferon-γ (IFN-γ). In this study, the effect of cross-talk between IL-18 and IFN-γ on melanogenesis was investigated. Treatment with IL-18 resulted in a dose-dependent increase of melanogenesis, while IFN-γ made an opposite effect. This influence of IL-18 and IFN-γ was mediated by regulations of microphthalmia-associated transcription factor (MITF) and its downstream enzymatic cascade expressions. Furthermore, IFN-γ inhibited basal and IL-18-induced melanogenesis. IFN-γ increased signal transducer and activator of transcription-1 (STAT-1) phosphorylation to play its position in regulating melanin pigmentation, and its inhibitory effect could be prevented by Janus Kinase 1 (JAK 1) inhibitor. IFN-γ could inhibit melanogenesis by decreasing melanocyte dendrite formation. In addition, IFN-γ inhibited the expressions of Rab Pases to suppress the mature and transport of melanosomes. IL-18 could rapidly induce Akt and PTEN phosphorylation and p65 expression in B16F10 cells. When treatment with IL-18 and IFN-γ together, the phosphorylation level of Protein Kinase B (Akt) and phosphatase and tensin homolog deleted on chromosome ten (PTEN) and expression of p65 NF-κB were inhibited, compared with treated with IL-18 only. Our studies indicated that IFN-γ could directly induce B16F10 cells apoptosis in vitro. Furthermore, we demonstrated that IFN-γ markedly up-regulated IL-18 binding protein (BP) production in normal human foreskin-derived epidermal keratinocytes in dose-dependent manner. UVB irradiation induced protease-activated receptor-2 (PAR-2) expression in NHEK, IFN-γ could inhibit this enhancement in a dose-dependent manner. These data suggest that IFN-γ plays a role in regulating inflammation- or UV-induced pigmentary changes, in direct/indirect manner.

Inhibitory effect of 2-methyl-naphtho[1,2,3-de]quinolin-8-one on melanosome transport and skin pigmentation

Melanosomes are lysosome-related organelles with specialized capabilities of melanin synthesis and movement mediated by the Rab27a-Melanophilin-MyosinVa protein complex. In this study, we found that 2-methyl-naphtho[1,2,3-de]quinolin-8-one (MNQO) induced melanosome aggregation around the nucleus in melan-a melanocytes and in melan-a melanocytes/SP-1 keratinocyte co-cultures without inducing toxicity or changing the melanin content. Western blot and real-time PCR analyses showed that MNQO decreased expression of the Rab27a, Melanophilin and MyosinVa proteins and mRNAs, respectively, in melan-a melanocytes. In a reconstituted human epidermis model, treatment with 0.001% MNQO reduced skin pigmentation. Also, MNQO reduced skin pigmentation in brown guinea pigs induced by UVB irradiation. These results indicated that regulation of melanosome transport may serve as a good target for new skin depigmenting agents and MNQO itself could be a candidate.

1-Phenyl-3-(2-thiazolyl)-2-thiourea inhibits melanogenesis via a dual-action mechanism

1-Phenyl-3-(2-thiazolyl)-2-thiourea (PTTU) is a well-characterized dopamine β-hydroxylase inhibitor that prevents 6-hydroxydopamine-induced degenerative neuronal disease. However, the effect of PTTU on melanogenesis has not been reported. In this study, we examined the effect of PTTU on melanogenesis and studied its mechanism of action. We found that PTTU decreased melanin biosynthesis in a dose-dependent manner in normal human epidermal melanocytes (NHEMs). PTTU also inhibited tyrosinase catalytic activity in NHEMs. Moreover, PTTU treatment led to reduced protein levels of tyrosinase in NHEMs, while the protein levels of tyrosinase-related protein-1, tyrosinase-related protein-2, and microphthalmia-associated transcription factor were not affected. However, PTTU treatment did not affect the mRNA expression of tyrosinase. We found that PTTU-accelerated tyrosinase degradation via the ubiquitin-dependent proteasome pathway. In summary, we found that PTTU decreased melanin biosynthesis by decreasing the enzymatic activity and stability of tyrosinase. Our results indicate that PTTU could be used as a depigmentation agent for hyperpigmentation disorder.

Skin Pigmentation and Pigmentary Disorders: Focus on Epidermal/Dermal Cross-Talk

Variation in human skin and hair color is the most notable aspect of human variability and several studies in evolution, genetics and developmental biology contributed to explain the mechanisms underlying human skin pigmentation, which is responsible for differences in skin color across the world's populations. Despite skin pigmentation is primarily related to melanocytes functionality, the surrounding keratinocytes and extracellular matrix proteins and fibroblasts in the underlying dermal compartment actively contribute to cutaneous homeostasis. Many autocrine/paracrine secreted factors and cell adhesion mechanisms involving both epidermal and dermal constituents determine constitutive skin pigmentation and, whenever deregulated, the occurrence of pigmentary disorders. In particular, an increased expression of such mediators and their specific receptors frequently lead to hyperpigmentary conditions, such as in melasma and in solar lentigo, whereas a defect in their expression/release is related to hypopigmented disorders, as seen in vitiligo. All these interactions underline the relevant role of pigmentation on human evolution and biology.

Platelet-derived growth factor regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner

BACKGROUND

Although many kinds of keratinocyte-derived factors are known to regulate the proliferation and differentiation of human melanocytes, it is not well defined whether dermis-derived factors work in a similar way.

OBJECTIVE

The aim of this study is to clarify whether dermal factors are involved in regulating the proliferation and differentiation of human melanocytes.

METHODS

Human epidermal melanoblasts were cultured serially in a serum-free growth medium. Platelet-derived growth factor-BB (PDGF-BB) was supplemented to the medium, and the effects on the proliferation of melanoblasts/melanocytes and the differentiation of melanocytes were studied.

RESULTS

PDGF-BB stimulated the proliferation of melanoblasts cultured in melanoblast-proliferation medium, but inhibited the proliferation of melanocytes cultured in melanocyte-proliferation medium. By contrast, PDGF-BB stimulated the differentiation, dendritogenesis, and melanogenesis of melanocytes through the stimulation of tyrosinase activity and the expressions of tyrosinase and tyrosinase-related protein-1.

CONCLUSION

These results suggest that PDGF-BB regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner. PDGF-BB seems to be one of the dermal factors that regulate the proliferation and differentiation of human melanocytes.

Functional Characterization of the Odorant Receptor 51E2 in Human Melanocytes

Olfactory receptors, which belong to the family of G-protein-coupled receptors, are found to be ectopically expressed in non-sensory tissues mediating a variety of cellular functions. In this study we detected the olfactory receptor OR51E2 at the transcript and the protein level in human epidermal melanocytes. Stimulation of primary melanocytes with the OR51E2 ligand β-ionone significantly inhibited melanocyte proliferation. Our results further showed that β-ionone stimulates melanogenesis and dendritogenesis. Using RNA silencing and receptor antagonists, we demonstrated that OR51E2 activation elevated cytosolic Ca(2+) and cAMP, which could mediate the observed increase in melanin synthesis. Co-immunocytochemical stainings using a specific OR51E2 antibody revealed subcellular localization of the receptor in early endosomes associated with EEA-1 (early endosome antigen 1). Plasma membrane preparations showed that OR51E2 protein is present at the melanocyte cell surface. Our findings thus suggest that activation of olfactory receptor signaling by external compounds can influence melanocyte homeostasis.

The effects of IGF1 on the melanogenesis in alpaca melanocytes in vitro

In order to investigate the effects of the insulin-like growth factor 1(IGF-1) on alpaca melanocyte in vitro, different dosees of IGF1 (0, 10, 20, 40 ng/ml) were added in the medium of alpaca melanocyte. The RTCA machine was used to monitor the proliferation, quantitative real-time PCR, and western blot to test the relative gene expression, ELISA to test cAMP production, and spectrum method to test the melanin production. The results showed that compared to the normal melanocyte, the proliferation of melanocytes was increased within 60 h following adding IGF1. It also showed that cAMP content produced by melanocytes was increased, microphthalmia-associtated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein 2 (TYRP2) expression was increased, and melanin production with most obvious change in 10 ng/ml supplementary group, when compared with the control group. The results suggested that IGF1 with the dose of 10 ng/ml had the important effects on the melanogenesis in alpaca melanocyte by the cAMP pathway.

The Development of Sugar-Based Anti-Melanogenic Agents

The regulation of melanin production is important for managing skin darkness and hyperpigmentary disorders. Numerous anti-melanogenic agents that target tyrosinase activity/stability, melanosome maturation/transfer, or melanogenesis-related signaling pathways have been developed. As a rate-limiting enzyme in melanogenesis, tyrosinase has been the most attractive target, but tyrosinase-targeted treatments still pose serious potential risks, indicating the necessity of developing lower-risk anti-melanogenic agents. Sugars are ubiquitous natural compounds found in humans and other organisms. Here, we review the recent advances in research on the roles of sugars and sugar-related agents in melanogenesis and in the development of sugar-based anti-melanogenic agents. The proposed mechanisms of action of these agents include: (a) (natural sugars) disturbing proper melanosome maturation by inducing osmotic stress and inhibiting the PI3 kinase pathway and (b) (sugar derivatives) inhibiting tyrosinase maturation by blocking N-glycosylation. Finally, we propose an alternative strategy for developing anti-melanogenic sugars that theoretically reduce melanosomal pH by inhibiting a sucrose transporter and reduce tyrosinase activity by inhibiting copper incorporation into an active site. These studies provide evidence of the utility of sugar-based anti-melanogenic agents in managing skin darkness and curing pigmentary disorders and suggest a future direction for the development of physiologically favorable anti-melanogenic agents.

A Novel Role of Serotonin Receptor 2B Agonist as an Anti-Melanogenesis Agent

BW723C86, a serotonin receptor 2B agonist, has been investigated as a potential therapeutic for various conditions such as anxiety, hyperphagia and hypertension. However, the functional role of BW723C86 against melanogenesis remains unclear. In this study, we investigate the effect of serotonin receptor 2B (5-HTR2B) agonist on melanogenesis and elucidate the mechanism involved. BW723C86 reduced melanin synthesis and intracellular tyrosinase activity in melan-A cells and normal human melanocytes. The expression of melanogenesis-related proteins (tyrosinase, TRP-1 and TRP-2) and microphthalmia-associated transcription factor (MITF) in melan-A cells decreased after BW723C86 treatment. The promoter activity of MITF was also reduced by BW723C86 treatment. The reduced level of MITF was associated with inhibition of protein kinase A (PKA) and cAMP response element-binding protein (CREB) activation by BW723C86 treatment. These results suggest that the serotonin agonist BW723C86 could be a potential therapeutic agent for skin hyperpigmentation disorders.

Sex-specific genetic effects associated with pigmentation, sensitivity to sunlight, and melanoma in a population of Spanish origin

BACKGROUND

Human pigmentation is a polygenic quantitative trait with high heritability. In addition to genetic factors, it has been shown that pigmentation can be modulated by oestrogens and androgens via up- or down-regulation of melanin synthesis. Our aim was to identify possible sex differences in pigmentation phenotype as well as in melanoma association in a melanoma case-control population of Spanish origin.

METHODS

Five hundred and ninety-nine females (316 melanoma cases and 283 controls) and 458 males (234 melanoma cases and 224 controls) were analysed. We genotyped 363 polymorphisms (single nucleotide polymorphisms (SNPs)) from 65 pigmentation gene regions.

RESULTS

When samples were stratified by sex, we observed more SNPs associated with dark pigmentation and good sun tolerance in females than in males (107 versus 75; P = 2.32 × 10(-6)), who were instead associated with light pigmentation and poor sun tolerance. Furthermore, six SNPs in TYR, SILV/CDK2, GPR143, and F2RL1 showed strong differences in melanoma risk by sex (P < 0.01).

CONCLUSIONS

We demonstrate that these genetic variants are important for pigmentation as well as for melanoma risk, and also provide suggestive evidence for potential differences in genetic effects by sex.

The Evaluation of Endothelin-1 and Endothelin Receptor Type A Gene Polymorphisms in Patients with Vitiligo

Background:

Endothelin-1 (EDN1) and EDN receptor type A (EDNRA) are implicated in melanocyte functions.

Aim and Objectives:

This study examines the role of EDN1 (G5665T and T-1370G) and EDNRA (C + 70G and G-231A) polymorphisms as a risk factor for vitiligo, and evaluates the relationship between genotypes and clinical characteristics of vitiligo patients.

Materials and Methods:

We analyzed genotype/allele distributions of EDN1 and EDNRA polymorphisms in 100 patients with vitiligo and 185 healthy controls by real-time polymerase chain reaction.

Results:

There was no notable risk for vitiligo afflicted by studied polymorphisms. However, the presence of EDNRA +70 variant G allele was found to be related with decreased risk for development of generalized type of vitiligo (odds ratio [OR]: 0.42, 95% confidence interval [CI] = 0.21–0.86, p_corr = 0.03) and showed protective effect against associated diseases seen in vitiligo (OR: 0.49, 95% CI = 0.27–0.88, p_corr = 0.034). Haplotype analysis demonstrated a strong (disequilibrium coefficient = 0.73, r² = 0.405) linkage disequilibrium between EDN1 G5665T and T-1370G polymorphisms. The EDN1 5665/-1330 TT haplotype was over represented significantly in controls than in patients (P = 0.04).

Conclusion:

The studied polymorphisms do not seem to be a major risk for vitiligo. Haplotype analysis denoting protective effects against vitiligo may indicate an indirect interaction in the course of vitiligo. In addition, EDNRA + 70 polymorphism is protective against generalized type of vitiligo and associated diseases.

Inhibitory effect of Phalaenopsis orchid extract on WNT1-induced immature melanocyte precursor differentiation in a novel in vitro solar lentigo model

Recently, it has been reported that increased expression of WNT1 accelerates the differentiation of melanocyte stem cells (McSCs) in solar lentigines (SLs), hyperpigmented maculae commonly seen on sun-exposed areas of the skin. In this study, to establish an in vitro SL model, human epidermal squamous carcinoma cell line HSC-1, which expresses higher levels of WNT1 than normal human epidermal keratinocytes, was co-cultured with early passage normal human epidermal melanocytes (NHEMs) as an in vitro McSC model. As a result, mRNA expression levels of melanocyte differentiation-related genes MITF and TYR in NHEMs were significantly increased by co-culturing with HSC-1 cells. Furthermore, Phalaenopsis orchid extract (Phex) inhibited McSCs differentiation by suppressing WNT1 expression via down-regulation of DLX2, a transcriptional activator of WNT1, in HSC-1 cells. Therefore, our finding suggested that extracts such as Phex, which suppresses WNT1 expression, may be useful as a novel treatment of SLs.

Biological processes in solar lentigo: insights brought by experimental models

Common in ageing patient, the solar lentigo is a macular hyperpigmented skin lesion that results from chronic exposure to ultraviolet irradiations. Despite sharing numerous features with other pigmented spots, the diagnostic of this benign lesion is well characterized at the tissue level. Recent studies shed lights on several factors and their pathogenic mechanisms involved in the development of the solar lentigo. This review summarizes how diverse experimental approaches allowed the identification of several biomarkers, which contribute to a better understanding on the initiation and the maintenance of this pigmentary disorder.

A primer on pigmentation

There is at least a temporary loss of skin pigmentation with all but first-degree burns. Commonly, pigment changes persist for months, and sometimes, permanent changes in skin color add to the ultimate change in appearance that commonly affects burn patients. There are many different treatment modalities for the treatment of pigment changes, but most of them have little scientific basis and often lead to disappointing results. The purpose of this review is to discuss the molecular and cellular mechanisms of skin pigmentation, mechanisms of repigmentation after burns, treatment options for dealing with pigmentation changes, and advice for dealing with the sun after burn injury.

Characterization of pigmented dermo-epidermal skin substitutes in a long-term in vivo assay

In our laboratory, we have been using human pigmented dermo-epidermal skin substitutes for short-term experiments since several years. Little is known, however, about the long-term biology of such constructs after transplantation. We constructed human, melanocyte-containing dermo-epidermal skin substitutes of different (light and dark) pigmentation types and studied them in a long-term animal experiment. Developmental and maturational stages of the epidermal and dermal compartment as well as signs of homoeostasis were analysed 15 weeks after transplantation. Keratinocytes, melanocytes and fibroblasts from human skin biopsies were isolated and assembled into dermo-epidermal skin substitutes. These were transplanted onto immuno-incompetent rats and investigated 15 weeks after transplantation. Chromameter evaluation showed a consistent skin colour between 3 and 4 months after transplantation. Melanocytes resided in the epidermal basal layer in physiological numbers and melanin accumulated in keratinocytes in a supranuclear position. Skin substitutes showed a mature epidermis in a homoeostatic state and the presence of dermal components such as Fibrillin and Tropoelastin suggested advanced maturation. Overall, pigmented dermo-epidermal skin substitutes show a promising development towards achieving near-normal skin characteristics and epidermal and dermal tissue homoeostasis. In particular, melanocytes function correctly over several months whilst remaining in a physiological, epidermal position and yield a pigmentation resembling original donor skin colour.

Microphthalmia-associated transcription factor/T-box factor-2 axis acts through Cyclin D1 to regulate melanocyte proliferation

OBJECTIVES

Control of cell proliferation is critical for accurate cell differentiation and tissue formation, during development and regeneration. Here, we have analysed the role of microphthalmia-associated transcription factor MITF and its direct target, T-box factor TBX2, in regulating proliferation of mammalian neural crest-derived melanocytes.

MATERIALS AND METHODS

Immunohistochemistry was used to examine spatial and temporal expression of TBX2 in melanocytes in vivo. RNAi and cell proliferation analysis were used to investigate functional roles of TBX2. Furthermore, quantitative RT-PCR, western blot analysis and flow cytometry were used to further scrutinize molecular mechanisms underlying TBX2-dependent cell proliferation.

RESULTS

TBX2 was found to be co-expressed with MITF in melanocytes of mouse hair follicles. Specific Tbx2 knockdown in primary neural crest cells led to inhibition MITF-positive melanoblast proliferation. Tbx2 knockdown in melan-a cells led to reduction in Cyclin D1 expression and G1-phase cell cycle arrest. TBX2 directly activated Ccnd1 transcription by binding to a specific sequence in the Ccnd1 promoter, and the defect in cell proliferation could be rescued partially by overexpression of Cyclin D1 in Tbx2 knockdown melanocytes.

CONCLUSIONS

Results suggest that the Mitf-Tbx2-Cyclin D1 pathway played an important role in regulation of melanocyte proliferation, and provided novel insights into the complex physiology of melanocytes.

Extraction conditions of white rose petals for the inhibition of enzymes related to skin aging

In order to assess inhibitory potentials of white rose petal extracts (WRPE) on the activities of enzymes related to dermal aging according to the extraction conditions, three extraction methods were adopted. WRPE was prepared by extracting dried white rose (Rosa hybrida) petals with 50% ethanol (WRPE-EtOH), Pectinex® SMASH XXL enzyme (WRPE-enzyme) or high temperature-high pressure (WRPE-HTHP). In the inhibition of matrix metalloproteinase-1, although the enzyme activity was fully inhibited by all 3 extracts at 100 µg/mL in 60 min, partial inhibition (50-70%) was achieved only by WRPE-EtOH and WRPE-enzyme at 50 µg/mL. High concentrations (≥250 µg/mL) of all 3 extracts markedly inhibited the elastase activity. However, at low concentrations (15.6-125 µg/mL), only WRPE-EtOH inhibited the enzyme activity. Notably, WRPE-EtOH was superior to WRPE-enzyme and WRPE-HTHP in the inhibition of tyrosinase. WRPE-EtOH significantly inhibited the enzyme activity from 31.2 µM, reaching 80% inhibition at 125 µM. In addition to its strong antioxidative activity, the ethanol extract of white rose petals was confirmed to be effective in inhibiting skin aging-related enzymes. Therefore, it is suggested that WRPE-EtOH could be a good candidate for the improvement of skin aging such as wrinkle formation and pigmentation.

The first clinical experience on efficacy of topical flutamide on melasma compared with topical hydroquinone: a randomized clinical trial

Background

Treatment of melasma is unsatisfactory most of the times. Hormonal role is shown to exist in pathogenesis of the melasma, and sex-hormone related drugs may have an effect on melasma.

Aim

To investigate efficacy of 1% flutamide cream versus 4% hydroquinone cream on melasma.

Methods

In a parallel randomized clinical trial, 74 women with melasma were allocated to receive a sunscreen along with 4% hydroquinone cream or 1% flutamide cream. Melasma Area and Severity Index (MASI), mexameter melanin assay, and patient satisfaction were investigated.

Results

Mean age of the participants was 33.8 years. Mean length of time suffering from Melasma was 96.3 months. The subjects reported in average 1.1 hours per day of exposure to sunlight. Mean standardized total patient satisfaction score was 28.8 (standard deviation [SD] 17.2) in flutamide group patients versus 18 (SD 15.5) in control group (P<0.01). Regardless of treatment group, the skin darkness assessed upon MASI scales was reduced over the treatment course (P<0.001). Using mixed effects, longitudinal modeling showed better treatment efficacy based on MASI scale for flutamide group compared to the hydroquinone group (P<0.05). However, longitudinal analysis of mexameter scores did not reveal any significant difference in melanin measurements between flutamide and hydroquinone.

Conclusion

Topical flutamide appeared as effective as topical hydroquinone in treating melasma using mexameter assessment but with a better MASI improvement trend and higher patient satisfaction in flutamide treatment versus topical hydroquinone. As the present study is possibly the first clinical experience on efficacy of topical flutamide on melasma, it would be quite unreasonable to recommend clinical use of it before future studies replicate the results on its efficacy and safety.

Expression and tissue distribution of hepatocyte growth factor (HGF) and its receptor (c-Met) in alpacas (Vicugna pacos) skins associated with white and brown coat colors

Hepatocyte growth factor (HGF)/c-Met signaling has been considered as a key pathway in both melanocyte development and melanogenesis. To understand better the expression patterns and tissue distribution characterization of HGF and its receptor c-Met in skin of white versus brown alpaca (Vicugna pacos), we detected the tissue distribution of HGF and c-Met using immunohistochemistry and analyzed the expression patterns by using Western blot and quantitative real time PCR (qPCR). Immunohistochemistry analysis demonstrated that HGF staining robustly increased in the dermal papilla and mesenchymal cells of white alpaca skin compared with that of brown. However, c-Met staining showed strongly positive result, particularly inhair matrix and root sheath in brown alpaca skin. Western blot and qPCR results suggested that HGF and c-Met were expressed at significantly high levels in white and brown alpaca skins, respectively, and protein and transcripts possessed the same expression pattern in white and brown alpaca skins. The results suggested that HGF/c-Met signaling functions in alpaca coat color formation offer essential theoretical basis for further exploration of the role of HGF/c-Met signaling in pigment formation.

Chemical constituents derived from Artocarpus xanthocarpus as inhibitors of melanin biosynthesis

Twenty-four compounds, including the previously unknown artoxanthocarpuone A, artoxanthocarpuone B, hydroxylakoochin A, methoxylakoochin A, epoxylakoochin A, and artoxanthol, were isolated and characterized spectroscopically. Among them, artoxanthol is stilbene oligomer presumably constructed in a 5,11,12-triphenyl hexahydrochrysene scaffold by a Diels-Alder type of reaction, for which a biosynthetic pathway is proposed. Artoxanthol, alboctalol, steppogenin, norartocarpetin, resveratrol, oxyresveratrol, and chlorophorin potently inhibited mushroom tyrosinase activity with IC50 values from 0.9 to 5.7 μM that were all far stronger than the positive controls. Artoxanthocarpuone A, artoxanthocarpuone B, methoxylakoochin A, lakoochin A, cudraflavone C, artonin A, resveratrol, and chlorophorin reduced tyrosinase activity and inhibited α-melanocyte-stimulating hormone-induced melanin production in B16F10 melanoma cells without affecting cell proliferation. Collectively, the results suggest that the constituents of Artocarpus xanthocarpus have potential to be used as depigmentation agents.

Endothelial Cells Promote Pigmentation through Endothelin Receptor B Activation

Findings of increased vascularization in melasma lesions and hyperpigmentation in acquired bilateral telangiectatic macules suggested a link between pigmentation and vascularization. Using high-magnification digital epiluminescence dermatoscopy, laser confocal microscopy, and histological examination, we showed that benign vascular lesions of the skin have restricted but significant hyperpigmentation compared with the surrounding skin. We then studied the role of microvascular endothelial cells in regulating skin pigmentation using an in vitro co-culture model using endothelial cells and melanocytes. These experiments showed that endothelin 1 released by microvascular endothelial cells induces increased melanogenesis signaling, characterized by microphthalmia-associated transcription factor phosphorylation, and increased tyrosinase and dopachrome tautomerase levels. Immunostaining for endothelin 1 in vascular lesions confirmed the increased expression on the basal layer of the epidermis above small vessels compared with perilesional skin. Endothelin acts through the activation of endothelin receptor B and the mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK)1/2, and p38, to induce melanogenesis. Finally, culturing of reconstructed skin with microvascular endothelial cells led to increased skin pigmentation that could be prevented by inhibiting EDNRB. Taken together these results demonstrated the role of underlying microvascularization in skin pigmentation, a finding that could open new fields of research for regulating physiological pigmentation and for treating pigmentation disorders such as melasma.

Structural and reactivity models for copper oxygenases: cooperative effects and novel reactivities

Dioxygen is widely used in nature as oxidant. Nature itself has served as inspiration to use O2 in chemical synthesis. However, the use of dioxygen as an oxidant is not straightforward. Its triplet ground-state electronic structure makes it unreactive toward most organic substrates. In natural systems, metalloenzymes activate O2 by reducing it to more reactive peroxide (O2(2-)) or superoxide (O2(-)) forms. Over the years, the development of model systems containing transition metals has become a convenient tool for unravelling O2-activation mechanistic aspects and reproducing the oxidative activity of enzymes. Several copper-based systems have been developed within this area. Tyrosinase is a copper-based O2-activating enzyme, whose structure and reactivity have been widely studied, and that serves as a paradigm for O2 activation at a dimetal site. It contains a dicopper center in its active site, and it catalyzes the regioselective ortho-hydroxylation of phenols to catechols and further oxidation to quinones. This represents an important step in melanin biosynthesis and it is mediated by a dicopper(II) side-on peroxo intermediate species. In the present accounts, our research in the field of copper models for oxygen activation is collected. We have developed m-xylyl linked dicopper systems that mimick structural and reactivity aspects of tyrosinase. Synergistic cooperation of the two copper(I) centers results in O2 binding and formation of bis(μ-oxo)dicopper(III) cores. These in turn bind and ortho-hydroxylate phenolates via an electrophilic attack of the oxo ligand over the arene. Interestingly the bis(μ-oxo)dicopper(III) cores can also engage in ortho-hydroxylation-defluorination of deprotonated 2-fluorophenols, substrates that are well-known enzyme inhibitors. Analysis of Cu2O2 species with different binding modes show that only the bis(μ-oxo)dicopper(III) cores can mediate the reaction. Finally, the use of unsymmetric systems for oxygen activation is a field that still remains rather unexplored. We envision that the unsymmetry might infere interesting new reactivities. We contributed to this topic with the development of an unsymmetric ligand (m-XYL(N3N4)), whose dicuprous complex reacts with O2 and forms a trans-peroxo dicopper(II) species that showed a markedly different reactivity compared to a symmetric trans-peroxo dicopper(II) analog. Nucleophilic reactivity is observed for the unsymmetric trans-peroxo dicopper(II) species against electrophilies such as H(+), CO2 and aldehydes, and neither oxygen atom transfer nor hydrogen abstraction is observed when reacting with oxygen atom acceptors (triphenyl phosphine, sulfides) and substrates with weak C-H bonds. Instead, electrophilic monooxygenase-like ortho-hydroxylation reactivity is described for these unsymmetric species upon reaction with phenolates. Finally, by using a second dinucleating unsymmetric ligand (L(N3N4)), we have described copper(I) containing heterodimetallic systems and explored their O2 binding properties. Site specific metalation led to the generation of dimeric heterometallic M'CuO2CuM' species from intermolecular O2 binding at copper sites.

Modulation of Melanogenesis and Antioxidant Status of Melanocytes in Response to Phototoxic Action of Doxycycline

Doxycycline is a commonly used tetracycline antibiotic showing the broad spectrum of antibacterial action. However, the use of this antibiotic is often connected with the risk of phototoxic reactions that lead to various skin disorders. One of the factors influencing the photosensitivity reactions is the melanin content in melanocytes. In this study, the impact of doxycycline and UVA irradiation on cell viability, melanogenesis and antioxidant defense system in cultured normal human epidermal melanocytes (HEMn-DP) was examined. The exposure of cells to doxycycline and UVA radiation resulted in concentration-dependent loss in melanocytes viability and induced melanin biosynthesis. Significant changes were stated in cellular antioxidant enzymes activity: SOD, CAT and GPx, which indicates alterations of antioxidant defense system. The results obtained in vitro may explain the mechanisms of phototoxic reactions that occur in normal human epidermal melanocytes in vivo after exposure of skin to doxycycline and UVA radiation.

Hesperidin, A Popular Antioxidant Inhibits Melanogenesis via Erk1/2 Mediated MITF Degradation

Regulation of melanogenesis has been the focus of treatment for hyperpigmentary skin disorders. Although hesperidin is one of the most well-known, naturally occurring flavonoids with antioxidant and anti-inflammatory effect, its anti-melanogenic effect is not known. The present study aims to determine the anti-melanogenic effect of hespiridin as well as its underlying molecular mechanisms. Melanin contents were measured in normal human melanocytes and B16F10 melanoma cells. Protein and mRNA levels of tyrosinase, microphthalmia-associated transcription factor (MITF), tyrosinase related protein-1 (TRP-1) and TRP-2 were determined. Melanogenesis-regulating signals were examined. In results, hesperidin strongly inhibited melanin synthesis and tyrosinase activity. Hesperidin decreased tyrosinase, TRP-1, and TRP-2 protein expression but increased phospho-extracellular signal-regulated kinase 1/2 (p-Erk1/2) expression. Specific inhibitor of Erk1/2 or proteasome inhibitor reversed the inhibition of melanogenesis induced by hesperidin. Taken together, hesperidin, a popular antioxidant, stimulated Erk1/2 phosphorylation which subsequently degraded MITF which resulted in suppression of melanogenic enzymes and melanin synthesis.

Genetics of skin color variation in Europeans: genome-wide association studies with functional follow-up

In the International Visible Trait Genetics (VisiGen) Consortium, we investigated the genetics of human skin color by combining a series of genome-wide association studies (GWAS) in a total of 17,262 Europeans with functional follow-up of discovered loci. Our GWAS provide the first genome-wide significant evidence for chromosome 20q11.22 harboring the ASIP gene being explicitly associated with skin color in Europeans. In addition, genomic loci at 5p13.2 (SLC45A2), 6p25.3 (IRF4), 15q13.1 (HERC2/OCA2), and 16q24.3 (MC1R) were confirmed to be involved in skin coloration in Europeans. In follow-up gene expression and regulation studies of 22 genes in 20q11.22, we highlighted two novel genes EIF2S2 and GSS, serving as competing functional candidates in this region and providing future research lines. A genetically inferred skin color score obtained from the 9 top-associated SNPs from 9 genes in 940 worldwide samples (HGDP-CEPH) showed a clear gradual pattern in Western Eurasians similar to the distribution of physical skin color, suggesting the used 9 SNPs as suitable markers for DNA prediction of skin color in Europeans and neighboring populations, relevant in future forensic and anthropological investigations.

DCT protects human melanocytic cells from UVR and ROS damage and increases cell viability

Dopachrome tautomerase (DCT) is involved in the formation of the photoprotective skin pigment eumelanin and has also been shown to have a role in response to apoptotic stimuli and oxidative stress. The effect of DCT on UVR DNA damage responses and survival pathways in human melanocytic cells was examined by knockdown experiments using melanoma cells, neonatal foreskin melanoblasts (MB) in monoculture and in co-culture with human keratinocytes. MB cell strains genotyped as either MC1R WT or MC1R RHC homozygotes, which are known to be deficient in DCT, were transduced with lentivirus vectors for either DCT knockdown or overexpression. We found melanoma cell survival was reduced by DCT depletion and by UVR over time. UVR-induced p53 and pp53-Ser15 levels were reduced with DCT depletion. Knockdown of DCT in MC1R WT and MC1R RHC MB cells reduced their survival after UVR exposure, whereas increased DCT protein levels enhanced survival. DCT depletion reduced p53 and pp53-Ser15 levels in WM266-4 melanoma and MC1R WT MB cells, while MC1R RHC MB cells displayed variable levels. Both MC1R WT and RHC genotypes of MB cells were responsive to UVR at 3 h with increases in both p53 and pp53-Ser15 proteins. MC1R WT MB cell strains in coculture with keratinocytes have an increased cell survival after UVR exposure when compared to those in monoculture, a protective effect which appears to be conferred by the keratinocytes.