alpha-Melanocortin and endothelin-1 activate antiapoptotic pathways and reduce DNA damage in human melanocytes

An overview of benefits and risks of chronic melanocortin-1 receptor activation

The melanocortin-1 receptor (MC1R) is a G protein-coupled receptor that plays a pivotal role in human skin pigmentation, melanin synthesis, redox homeostasis and inflammation. Loss-of-function MC1R variants suppress G protein-coupled receptor coupling or cell surface expression leading to a decrease in adenyl cyclase activation and intracellular levels of cyclic adenosine monophosphate. Chronic activation of MC1R can occur in certain medical conditions such as Addison's disease and physiologic states such as pregnancy melasma. MC1R activation is more commonly caused by environmental exposure to ultraviolet (UV) radiation. Approved pharmacologic melanocortin agonists that activate MC1R signalling in a targeted manner or as a bystander effect have recently become available for erythropoietic protoporphyria, sexual desire disorders, monogenic obesity and syndromic obesity. Further, small peptide analogues of α-melanocortin-stimulating hormone, human MC1R selective agonists, are photoprotective, decreasing the adverse impact of UV radiation (a primary risk factor for skin cancer) and are being investigated as potential chemoprevention strategies. MC1R activation through induction of UV-protective skin pigmentation increased DNA repair, and control of aberrant cell growth may reduce the risk of melanoma but importantly does not prevent melanoma particularly in individuals with risk factors and regular skin examination remains critical in high-risk individuals.

Protective Effects of Keratinocyte-Derived GCSF and CCL20 on UVB-Induced Melanocyte Damage

The skin microenvironment created by keratinocytes (KC) influences the stress responses of melanocytes (MC) to UVB insults. This study employed RNA sequencing analysis as well as in vitro and in vivo models to elucidate the underlying mechanisms. Our RNA-Seq analysis revealed a statistically significant upregulation of GCSF and CCL20 genes in UVB-irradiated KC, correlating with the protective effects of KC on MC responses to UVB exposure. Recombinant GCSF and CCL20 exhibited the most pronounced modulation of UVB-induced MC responses. These effects included the attenuation of apoptosis and reduction of ROS formation, along with the upregulation of tyrosinase and tyrosinase-related protein-1, which are involved in the melanogenic pathway. ELISA was also used to confirm that UVB could induce the secretion of GCSF and CCL20 from KC. A similar correlation between GCSF and CCL20 expression in KC and tyrosinase levels in MC was observed in UVB-irradiated mouse skin. Our study provides novel insights into the protective role of GCSF and CCL20 in the paracrine effects of KC on UVB-induced MC damage through the modulation of stress response pathways, the MITF-tyrosinase axis, and the regulation of p53. These findings have implications for the development of pharmacological strategies targeting KC-derived paracrine factors for the prevention of skin photodamage.

Melanoma-associated melanocortin 1 receptor variants confer redox signaling-dependent protection against oxidative DNA damage

Cutaneous melanoma, a lethal skin cancer, arises from malignant transformation of melanocytes. Solar ultraviolet radiation (UVR) is a major environmental risk factor for melanoma since its interaction with the skin generates DNA damage, either directly or indirectly via oxidative stress. Pheomelanin pigments exacerbate oxidative stress in melanocytes by UVR-dependent and independent mechanisms. Thus, oxidative stress is considered to contribute to melanomagenesis, particularly in people with pheomelanic pigmentation. The melanocortin 1 receptor gene (MC1R) is a major melanoma susceptibility gene. Frequent MC1R variants (varMC1R) associated with fair skin and red or yellow hair color display hypomorphic signaling to the cAMP pathway and are associated with higher melanoma risk. This association is thought to be due to production of photosensitizing pheomelanins as well as deficient induction of DNA damage repair downstream of varMC1R. However, the data on modulation of oxidative DNA damage repair by MC1R remain scarce. We recently demonstrated that varMC1R accelerates clearance of reactive oxygen species (ROS)-induced DNA strand breaks in an AKT-dependent manner. Here we show that varMC1R also protects against ROS-dependent formation of 8-oxodG, the most frequent oxidative DNA lesion. Since the base excision repair (BER) pathway mediates clearance of these DNA lesions, we analyzed induction of BER enzymes in human melanoma cells of varMC1R genotype. Agonist-mediated activation of both wildtype (wtMC1R) and varMC1R significantly induced OGG and APE-1/Ref1, the rate-limiting BER enzymes responsible for repair of 8-oxodG. Moreover, we found that NADPH oxidase (NOX)-dependent generation of ROS was responsible for AKT activation and oxidative DNA damage repair downstream of varMC1R. These observations provide a better understanding of the functional properties of melanoma-associated MC1R alleles and may be useful for the rational development of strategies to correct defective varMC1R responses for efficient photoprotection and melanoma prevention in fair-skinned individuals.

MC1R and age heteroclassification of face phenotypes in the Rio Grande do Sul population

BACKGROUND

Forensic DNA phenotyping (FDP) consists of the use of methodologies for predicting externally visible characteristics (EVCs) from the genetic material of biological samples found in crime scenes and has proven to be a promising tool in aiding human identification in police activities. Currently, methods based on multiplex assays and statistical models of prediction of EVCs related to hair, skin, and iris pigmentation using panels of SNP and INDEL biomarkers have already been developed and validated by the forensic scientific community. As well as traces of pigmentation, an individual's perceived age (PA) can also be considered an EVC and its estimation in unknown individuals can be useful for the progress of investigations. Liu and colleagues (2016) were pioneers in evidencing that, in addition to lifestyle and environmental factors, the presence of SNP and INDEL variants in the MC1R gene - which encodes a transmembrane receptor responsible for regulating melanin production - seems to contribute to an individual's PA. The group highlighted the association between these MC1R gene polymorphisms and the PA in the European population, where carriers of risk haplotypes appeared to be up to 2 years older in comparison to their chronological age (CA).

PURPOSE

Understanding that genotype-phenotype relationships cannot be extrapolated between different population groups, this study aimed to test this hypothesis and verify the applicability of this variant panel in the Rio Grande do Sul admixed population.

METHODS

Based on genomic data from a sample of 261 volunteers representative of gaucho population and using a multiple linear regression (MLR) model, our group was able to verify a significant association among nine intronic variants in loci adjacent to MC1R (e.g., AFG3L1P, TUBB3, FANCA) and facial age appearance, whose PA was defined after age heteroclassification of standard frontal face images through 11 assessors.

RESULTS

Different from that observed in European populations, our results show that the presence of effect alleles (R) of the selected variants in our sample influenced both younger and older face phenotypes. The influence of each variant on PA is expressed as β values.

CONCLUSIONS

There are important molecular mechanisms behind the effects of MC1R locus on PA, and the genomic background of each population seems to be crucial to determine this influence.

Role of Dermal Factors Involved in Regulating the Melanin and Melanogenesis of Mammalian Melanocytes in Normal and Abnormal Skin

Mammalian melanin is produced in melanocytes and accumulated in melanosomes. Melanogenesis is supported by many factors derived from the surrounding tissue environment, such as the epidermis, dermis, and subcutaneous tissue, in addition to numerous melanogenesis-related genes. The roles of these genes have been fully investigated and the molecular analysis has been performed. Moreover, the role of paracrine factors derived from epidermis has also been studied. However, the role of dermis has not been fully studied. Thus, in this review, dermis-derived factors including soluble and insoluble components were overviewed and discussed in normal and abnormal circumstances. Dermal factors play an important role in the regulation of melanogenesis in the normal and abnormal mammalian skin.

Therapeutic Effects of Stimulating the Melanocortin Pathway in Regulating Ocular Inflammation and Cell Death

Alpha-melanocyte-stimulating hormone (α-MSH) and its binding receptors (the melanocortin receptors) play important roles in maintaining ocular tissue integrity and immune homeostasis. Particularly extensive studies have demonstrated the biological functions of α-MSH in both immunoregulation and cyto-protection. This review summarizes the current knowledge of both the physiological and pathological roles of α-MSH and its receptors in the eye. We focus on recent developments in the biology of α-MSH and the relevant clinical implications in treating ocular diseases.

A gel-forming α-MSH analog promotes lasting melanogenesis

The α-MSH peptide plays a significant role in the regulation of pigmentation via the melanocortin 1 receptor (MC1R). It increases the DNA repair capacity of melanocytes and reduces the incidence of skin cancers. As such, α-MSH analogs could have the utility for protecting against UV-induced skin DNA damage in susceptible patients. Recently, α-MSH analogs have been approved for the treatment of erythropoietic protoporphyria, hypoactive sexual desire, or pediatric obesity. However, the delivery of these drugs requires inconvenient implants or frequent injections. We recently found that select palmitoylated melanocortin analogs such as afamelanotide and adrenocorticotropin peptides self-assemble to form liquid gels in situ. To explore the utility of these novel analogs, we studied their pharmacological characteristics in vitro and in vivo. Acylated afamelanotide (DDE 313) and ACTH1-24 (DDE314) analogs form liquid gels at 6-20% and have a significantly increased viscosity at >2.5% compared to original analogs. Using the DDE313 analog as a prototype, we showed gel-formation reduces the passage of DDE313 through Centricon filters, and subcutaneous injection of analog gel in rats leads to the sustained presence of the peptide in circulation for >12 days. In addition, DDE313 darkened the skin of frogs for >4 weeks, whereas those injected with an equivalent dose of afamelanotide lost the tanning response within a few days. Because self-assembled gels allow sustained activation of melanocortin receptors, further studies of these analogs may allow the development of effective and convenient tanning therapies to prophylactically protect against UV-induced malignant transformation of skin cells in susceptible patients.

Enhanced Natural Strength: Lamiaceae Essential Oils and Nanotechnology in In Vitro and In Vivo Medical Research

The Lamiaceae is one of the most important families in the production of essential oils known to have a wide spectrum of biological activity. Recent research has highlighted the dermatological capabilities of various Lamiaceae essential oils, which appear to offer potential in free radical scavenging and anti-inflammatory activity. Some have also been extensively studied for their tissue remodeling and wound-healing, anti-aging, anti-melanogenic, and anti-cancer properties. Certain Lamiaceae essential oils are promising as novel therapeutic alternatives for skin disorders. This potential has seen substantial efforts dedicated to the development of modern formulations based on nanotechnology, enabling the topical application of various Lamiaceae essential oils. This review provides a comprehensive summary of the utilization of various essential oils from the Lamiaceae family over the past decade. It offers an overview of the current state of knowledge concerning the use of these oils as antioxidants, anti-inflammatory agents, wound-healers, anti-aging agents, anti-melanogenic agents, and anticancer agents, both alone and in combination with nanoparticles. Additionally, the review explores their potential applicability in patents regarding skin diseases.

Anhydrous Alum Inhibits α-MSH-Induced Melanogenesis by Down-Regulating MITF via Dual Modulation of CREB and ERK

Melanogenesis, the intricate process of melanin synthesis, is central to skin pigmentation and photoprotection and is regulated by various signaling pathways and transcription factors. To develop potential skin-whitening agents, we used B16F1 melanoma cells to investigate the inhibitory effects of anhydrous alum on melanogenesis and its underlying molecular mechanisms. Anhydrous alum (KAl(SO4)2) with high purity (>99%), which is generated through the heat-treatment of hydrated alum (KAl(SO4)2·12H2O) at 400 °C, potentiates a significant reduction in melanin content without cytotoxicity. Anhydrous alum downregulates the master regulator of melanogenesis, microphthalmia-associated transcription factor (MITF), which targets key genes involved in melanogenesis, thereby inhibiting α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis. Phosphorylation of the cAMP response element-binding protein, which acts as a co-activator of MITF gene expression, is attenuated by anhydrous alum, resulting in compromised MITF transcription. Notably, anhydrous alum promoted extracellular signal-regulated kinase phosphorylation, leading to the impaired nuclear localization of MITF. Overall, these results demonstrated the generation and mode of action of anhydrous alum in B16F1 cells, which constitutes a promising option for cosmetic or therapeutic use.

A Side-by-Side Comparison of Wildtype and Variant Melanocortin 1 Receptor Signaling with Emphasis on Protection against Oxidative Damage to DNA

Common variants of the MC1R gene coding the α-melanocyte stimulating hormone receptor are associated with light skin, poor tanning, blond or red hair, and increased melanoma risk, due to pigment-dependent and -independent effects. This complex phenotype is usually attributed to impaired activation of cAMP signaling. However, several MC1R variants show significant residual coupling to cAMP and efficiently activate mitogenic extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling. Yet, residual signaling and the key actions of wildtype and variant MC1R have never been assessed under strictly comparable conditions in melanocytic cells of identical genetic background. We devised a strategy based on CRISPR-Cas9 knockout of endogenous MC1R in a human melanoma cell line wildtype for BRAF, NRAS and NF1, followed by reconstitution with epitope-labeled MC1R constructs, and functional analysis of clones expressing comparable levels of wildtype, R151C or D294H MC1R. The proliferation rate, shape, adhesion, motility and sensitivity to oxidative DNA damage were compared. The R151C and D294H RHC variants displayed impaired cAMP signaling, intracellular stability similar to the wildtype, triggered ERK1/2 activation as effectively as the wildtype, and afforded partial protection against oxidative DNA damage, although less efficiently than the wildtype. Therefore, common melanoma-associated MC1R variants display biased signaling and significant genoprotective activity.

Cutaneous interaction with visible light: What do we know?

Visible light has been used therapeutically in dermatology for years for a variety of cosmetic and medical indications, including skin rejuvenation and the treatment of inflammatory and neoplastic conditions, among others. Until recently, visible light was thought to be relatively inert compared to its spectral neighbors, ultraviolet and infrared radiation. However, recent literature has described the ability of visible light to cause erythema in light skin and pigmentary changes in individuals with darker skin types. Concern surrounding its potentially damaging cutaneous effects has been raised in both the medical community and social media outlets. In this article, we provide an evidenced-based review describing what is currently known about visible light, focusing on its role in dermatologic diseases including disorders of hyperpigmentation such as melasma and postinflammatory hyperpigmentation.

EGCG, GCG, TFDG, or TSA Inhibiting Melanin Synthesis by Downregulating MC1R Expression

Without affecting cell viability, epigallocatechin gallate (EGCG), gallocatechin gallate (GCG), theaflavine-3,3'-digallate (TFDG), or theasinensin A (TSA) have been found to effectively reduce intracellular melanin content and tyrosinase (TYR) activity. However, studies on the anti-melanogenic mechanism of the above samples remain weak, and the activities of these samples in regulating melanogenesis at the molecular level lack comparison. Using B16F10 cells with the α-melanocyte-stimulating hormone (α-MSH) stimulation and without the α-MSH stimulation as models, the effects of EGCG, GCG, TFDG, or TSA on cell phenotypes and expression of key targets related to melanogenesis were studied. The results showed that α-MSH always promoted melanogenesis with or without adding the four samples. Meanwhile, the anti-melanogenic activities of the four samples were not affected by whether the α-MSH was added in the medium or not and the added time of the α-MSH. On this basis, the 100 µg/mL EGCG, GCG, TFDG, or TSA did not affect the TYR catalytic activity but inhibited melanin formation partly through downregulating the melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), and the TYR family. The downregulation abilities of catechins on the TYR family and MITF expression were stronger than those of dimers at both the transcription and translation levels, while the ability of dimers to downregulate the MC1R expression was stronger than that of catechins at both the transcription and translation levels to some extent. The results of molecular docking showed that these four samples could stably bind to MC1R protein. Taken together, this study offered molecular mechanisms for the anti-melanogenic activity of the EGCG, GCG, TFDG, and TSA, as potential effective components against the UV-induced tanning reactions, and a key target (MC1R) was identified.

Hydrolyzed Conchiolin Protein (HCP) Extracted from Pearls Antagonizes both ET-1 and α-MSH for Skin Whitening

Pearl powder is a famous traditional Chinese medicine that has a long history in treating palpitations, insomnia, convulsions, epilepsy, ulcers, and skin lightining. Recently, several studies have demonstrated the effects of pearl extracts on protection of ultraviolet A (UVA) induced irritation on human skin fibroblasts and inhibition of melanin genesis on B16F10 mouse melanoma cells. To further explore the effect we focused on the whitening efficacy of pearl hydrolyzed conchiolin protein (HCP) on human melanoma MNT-1 cells under the irritation of alpha-melanocyte-stimulating hormone (α-MSH) or endothelin 1 (ET-1) to evaluate the intracellular tyrosinase and melanin contents, as well as the expression levels of tyrosinase (TYR), tyrosinase related protein 1 (TRP-1), and dopachrome tautomerase (DCT) genes and related proteins. We found that HCP could decrease the intracellular melanin content by reducing the activity of intracellular tyrosinase and inhibiting the expression of TYR, TRP-1, DCT genes and proteins. At the same time, the effect of HCP on melanosome transfer effect was also investigated in the co-culture system of immortalized human keratinocyte HaCaT cells with MNT-1. The result indicated that HCP could promote the transfer of melanosomes in MNT-1 melanocytes to HaCaT cells, which might accelerate the skin whitening process by quickly transferring and metabolizing melanosomes during keratinocyte differentiation. Further study is needed to explore the mechanism of melanosome transfer with depigmentation.

The αMSH-Dependent PI3K Pathway Supports Energy Metabolism, via Glucose Uptake, in Melanoma Cells

Stimulation of melanocytes and murine melanoma cells with αMSH plus the PI3K inhibitor LY294002 resulted in ROS increase, oxidative DNA damage, and pigment retention. We performed cellular and molecular biology assays (Western blot, FACS, immunofluorescence analysis, scratch assay) on murine and human melanoma cells. Treatment with αMSH plus LY294002 altered cortical actin architecture. Given that cytoskeleton integrity requires energy, we next evaluated ATP levels and we observed a drop in ATP after exposure to αMSH plus LY294002. To evaluate if the αMSH-activated PI3K pathway could modulate energy metabolism, we focused on glucose uptake by analyzing the expression of the Glut-1 glucose translocator. Compared with cells treated with αMSH alone, those exposed to combined treatment showed a reduction of Glut-1 on the plasma membrane. This metabolic alteration was associated with changes in mitochondrial mass. A significant decrease of the cell migratory potential was also observed. We demonstrated that the αMSH-dependent PI3K pathway acts as a regulator of energy metabolism via glucose uptake, influencing the actin cytoskeleton, which is involved in melanosome release and cell motility. Hence, these results could constitute the basis for innovative therapeutical strategies.

Human cutaneous interfollicular melanocytes differentiate temporarily under genotoxic stress

DNA-damage response of cutaneous interfollicular melanocytes to fractionated radiotherapy was investigated by immunostaining of tissue sections from punch biopsies collected before, during, and after the treatment of patients for breast cancer. Our clinical assay with sterilized hair follicles, excluded the migration of immature melanocytes from the bulge, and highlighted interfollicular melanocytes as an autonomous self-renewing population. About thirty percent are immature. Surrounding keratinocytes induced and maintained melanocyte differentiation as long as treatment was ongoing. Concomitant with differentiation, melanocytes were protected from apoptosis by transient upregulation of Bcl-2 and CXCR2. CXCR2 upregulation also indicated the instigation of premature senescence, preventing proliferation. The stem cell factor BMI1 was constitutively expressed exclusively in interfollicular melanocytes and further upregulated upon irradiation. BMI1 prevents apoptosis, terminal differentiation, and premature senescence, allowing dedifferentiation post-treatment, by suppressing the p53/p21-and p16-mediated response and upregulating CXCR2 to genotoxic damage. The pre-treatment immature subset of interfollicular melanocytes was restored after the exposure ended.

Cytoglobin inhibits non-thermal plasma-induced apoptosis in melanoma cells through regulation of the NRF2-mediated antioxidant response

Melanoma arises from pigment-producing cells called melanocytes located in the basal layers of the epidermis of the skin. Cytoglobin (CYGB) is a ubiquitously expressed hexacoordinated globin that is highly enriched in melanocytes and frequently downregulated during melanomagenesis. Previously, we showed that non-thermal plasma (NTP)-produced reactive oxygen and nitrogen species (RONS) lead to the formation of an intramolecular disulfide bridge that would allow CYGB to function as a redox-sensitive protein. Here, we investigate the cytotoxic effect of indirect NTP treatment in two melanoma cell lines with divergent endogenous CYGB expression levels, and we explore the role of CYGB in determining treatment outcome. Our findings are consistent with previous studies supporting that NTP cytotoxicity is mediated through the production of RONS and leads to apoptotic cell death in melanoma cells. Furthermore, we show that NTP-treated solutions elicit an antioxidant response through the activation of nuclear factor erythroid 2-related factor 2 (NRF2). The knockdown and overexpression of CYGB respectively sensitizes and protects melanoma cells from RONS-induced apoptotic cell death. The presence of CYGB enhances heme-oxygenase 1 (HO-1) and NRF2 protein expression levels, whereas the absence impairs their expression. Moreover, analysis of the CYGB-dependent transcriptome demonstrates the tumor suppressor long non-coding RNA maternally expressed 3 (MEG3) as a hitherto undescribed link between CYGB and NRF2. Thus, the presence of CYGB, at least in melanoma cells, seems to play a central role in determining the therapeutic outcome of RONS-inducing anticancer therapies, like NTP-treated solutions, possessing both tumor-suppressive and oncogenic features. Hence, CYGB expression could be of interest either as a biomarker or as a candidate for future targeted therapies in melanoma.

Implications of Oxidative Stress in the Pathogenesis and Treatment of Hyperpigmentation Disorders

Oxidative stress represents an imbalance between the generation of reactive oxygen and nitrogen species and the ability of antioxidant systems to decompose those products. Oxidative stress is implicated in the pathogenesis of hyperpigmentation, hypopigmentation, melanoma, and other skin diseases. Regulatory networks involving oxidative stress and related pathways are widely represented in hypopigmentation diseases, particularly vitiligo. However, there is no complete review into the role of oxidative stress in the pathogenesis of hyperpigmentation disorders, especially regarding associations involving oxidative stress and cellular signaling pathways. Here, we review oxidative and antioxidant systems, oxidative stress-induced signal transduction mechanisms, and effects of antioxidant drugs used in preclinical and clinical settings in hyperpigmentation disorders.

Oxidative Stress-Related Mechanisms in Melanoma and in the Acquired Resistance to Targeted Therapies

Melanoma is a highly aggressive cancer with the poorest prognosis, representing the deadliest form of skin cancer. Activating mutations in BRAF are the most frequent genetic alterations, present in approximately 50% of all melanoma cases. The use of specific inhibitors towards mutant BRAF variants and MEK, a downstream signaling target of BRAF in the MAPK pathway, has significantly improved progression-free and overall survival in advanced melanoma patients carrying BRAF mutations. Nevertheless, despite these improvements, resistance still develops within the first year of therapy in around 50% of patients, which is a significant problem in managing BRAF-mutated advanced melanoma. Understanding these mechanisms is one of the mainstreams of the research on BRAFi/MEKi acquired resistance. Both genetic and epigenetic mechanisms have been described. Moreover, in recent years, oxidative stress has emerged as another major force involved in all the phases of melanoma development, from initiation to progression until the onsets of the metastatic phenotype and chemoresistance, and has thus become a target for therapy. In the present review, we discuss the current knowledge on oxidative stress and its signaling in melanoma, as well as the oxidative stress-related mechanisms in the acquired resistance to targeted therapies.

Theoretical Exploring of a Molecular Mechanism for Melanin Inhibitory Activity of Calycosin in Zebrafish

Tyrosinase is an oxidase that is the rate-limiting enzyme for controlling the production of melanin in the human body. Overproduction of melanin can lead to a variety of skin disorders. Calycosin is an isoflavone from Astragali Radix, which is a traditional Chinese medicine that exhibits several pharmacological activities including skin whitening. In our study, the inhibitory effect of calycosin on melanin production is confirmed in a zebrafish in vivo model by comparing with hydroquinone, kojic acid, and arbutin, known as tyrosinase inhibitors. Moreover, the inhibitory kinetics of calycosin on tyrosinase and their binding mechanisms are determined using molecular docking techniques, molecular dynamic simulations, and free energy analysis. The results indicate that calycosin has an obvious inhibitory effect on zebrafish pigmentation at the concentration of 7.5 μM, 15 μM, and 30 μM. The IC₅₀ of calycosin is 30.35 μM, which is lower than hydroquinone (37.35 μM), kojic acid (6.51 × 10³ μM), and arbutin (3.67 × 10⁴ μM). Furthermore, all the results of molecular docking, molecular dynamics simulations, and free energy analysis suggest that calycosin can directly bind to the active site of tyrosinase with very good binding affinity. The study indicates that the combination of computer molecular modeling and zebrafish in vivo assay would be feasible in confirming the result of the in vitro test and illustrating the target-binding information.

Behind the Scene: Exploiting MC1R in Skin Cancer Risk and Prevention

Melanoma and non-melanoma skin cancers (NMSCs) are the most frequent cancers of the skin in white populations. An increased risk in the development of skin cancers has been associated with the combination of several environmental factors (i.e., ultraviolet exposure) and genetic background, including melanocortin-1 receptor (MC1R) status. In the last few years, advances in the diagnosis of skin cancers provided a great impact on clinical practice. Despite these advances, NMSCs are still the most common malignancy in humans and melanoma still shows a rising incidence and a poor prognosis when diagnosed at an advanced stage. Efforts are required to underlie the genetic and clinical heterogeneity of melanoma and NMSCs, leading to an optimization of the management of affected patients. The clinical implications of the impact of germline MC1R variants in melanoma and NMSCs' risk, together with the additional risk conferred by somatic mutations in other peculiar genes, as well as the role of MC1R screening in skin cancers' prevention will be addressed in the current review.

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.

The protective role of MC1R in chromosome stability and centromeric integrity in melanocytes

Variants in the melanocortin-1 receptor (MC1R) gene, encoding a trimeric G-protein-coupled receptor and activated by α-melanocyte-stimulating hormone (α-MSH), are frequently associated with red or blonde hair, fair skin, freckling, and skin sensitivity to ultraviolet (UV) light. Several red hair color variants of MC1R are also associated with increased melanoma risk. MC1R variants affect melanoma risk independent of phenotype. Here, we demonstrated that MC1R is a critical factor in chromosome stability and centromere integrity in melanocytes. α-MSH/MC1R stimulation prevents melanocytes from UV radiation-induced damage of chromosome stability and centromere integrity. Mechanistic studies indicated that α-MSH/MC1R-controlled chromosome stability and centromeric integrity are mediated by microphthalmia-associated transcription factor (Mitf), a transcript factor needed for the α-MSH/MC1R signaling and a regulator in melanocyte development, viability, and pigment production. Mitf directly interacts with centromere proteins A in melanocytes. Given the connection among MC1R variants, red hair/fair skin phenotype, and melanoma development, these studies will help answer a question with clinical relevance “why red-haired individuals are so prone to developing melanoma”, and will lead to the identification of novel preventive and therapeutic strategies for melanomas, especially those with redheads.

Neuroendocrine Factors in Melanoma Pathogenesis

Simple Summary

Melanoma is a very aggressive and fatal malignant tumor. While curable if diagnosed in its early stages, advanced melanoma, despite the complex therapeutic approaches, is associated with one of the highest mortality rates. Hence, more and more studies have focused on mechanisms that may contribute to melanoma development and progression. Various studies suggest a role played by neuroendocrine factors which can act directly on tumor cells, modulating their proliferation and metastasis capability, or indirectly through immune or inflammatory processes that impact disease progression. However, there are still multiple areas to explore and numerous unknown features to uncover. A detailed exploration of the mechanisms by which neuroendocrine factors can influence the clinical course of the disease could open up new areas of biomedical research and may lead to the development of new therapeutic approaches in melanoma.

Abstract

Melanoma is one of the most aggressive skin cancers with a sharp rise in incidence in the last decades, especially in young people. Recognized as a significant public health issue, melanoma is studied with increasing interest as new discoveries in molecular signaling and receptor modulation unlock innovative treatment options. Stress exposure is recognized as an important component in the immune-inflammatory interplay that can alter the progression of melanoma by regulating the release of neuroendocrine factors. Various neurotransmitters, such as catecholamines, glutamate, serotonin, or cannabinoids have also been assessed in experimental studies for their involvement in the biology of melanoma. Alpha-MSH and other neurohormones, as well as neuropeptides including substance P, CGRP, enkephalin, beta-endorphin, and even cellular and molecular agents (mast cells and nitric oxide, respectively), have all been implicated as potential factors in the development, growth, invasion, and dissemination of melanoma in a variety of in vitro and in vivo studies. In this review, we provide an overview of current evidence regarding the intricate effects of neuroendocrine factors in melanoma, including data reported in recent clinical trials, exploring the mechanisms involved, signaling pathways, and the recorded range of effects.

The α-melanocyte-stimulating hormone/melanocortin-1 receptor interaction: A driver of pleiotropic effects beyond pigmentation

Melanocortin-1 Receptor (MC1R), when stimulated by alpha-melanocyte-stimulating hormone (α-MSH), is a driver of eumelanogenesis. Brown/black eumelanin is an effective filter against ultraviolet radiation (UVR) and is a scavenger of free radicals. Several polymorphic variants of MC1R are frequent in red-head people. These polymorphisms reduce the ability of MC1R to promote eumelanogenesis after its activation and spontaneous pheomelanogenesis take place. Since pheomelanin can act as an endogenous photosensitizer, people carrying MC1R polymorphisms are more susceptible to skin cancer. Here, we summarize current knowledge on the biology of MC1R beyond its ability to drive eumelanogenesis. We analyze its capacity to cope with oxidative insult and consequent DNA damage. We describe its ability to transduce through different pathways. We start from the canonical pathway, the cAMP/protein kinase A (PKA) pathway mainly involved in promoting eumelanogenesis, and protection from oxidative damage, and we then move on to describe more recent knowledge concerning ERK pathways, phosphoinositide 3-kinase (PI3K) pathway/AKT, and α-MSH/Peroxisome proliferators activated receptor-γ (PPAR-γ) connection. We describe MC1R polymorphic variants associated with melanoma risk which represent an open window of clinical relevance.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Seven traditional Chinese herbal extracts fermented by Lactobacillus rhamnosus provide anti-pigmentation effects by regulating the CREB/MITF/tyrosinase pathway

Skin pigmentation is resulted from several processes, such as melanin synthesis transportation and abnormal melanin accumulation in keratinocytes. Various studies have suggested that seven traditional Chinese herbal extracts from Atractylodes macrocephala, Paeonia lactiflora, Bletilla striata, Poria cocos, Dictamnus dasycarpus, Ampelopsis japonica and Tribulus terrestris (which we collectively named ChiBai), show several protective effects toward skin-related diseases. Lactobacillus rhamnosus, a lactic acid bacterium, has been reported to treat skin inflammation and atopic dermatitis. In this study, the broth produced by the cofermentation of ChiBai with Lactobacillus rhamnosus was studied for its effects on skin pigmentation through in vitro and in vitro experiments. In the in vitro experiments, we found that the fermented broth of ChiBai (FB-ChiBai) suppressed alpha-melanocyte stimulating hormone (α-MSH)-induced melanogenesis in B16F0 murine melanoma cells without any cytotoxicity at a concentration of 0.5%. FB-ChiBai significantly attenuated melanin production, tyrosinase activities and melanogenesis-related signaling pathways. Treatment with FB-ChiBai also reduced the nuclear translocation and promoter binding activities of MITF. In the in vivo experiments, FB-ChiBai was topically applied to the dorsal skin of C57BL/6J nude mice and concurrently irradiated with UVB, three times a week for 8 weeks. The results indicated that FB-ChiBai alleviated UVB-induced hyperpigmentation by reducing epidermal hyperplasia and inhibiting the CREB/MITF/tyrosinase pathway. In conclusion, our data indicated that the anti-melanogenic effects of FB-ChiBai are mediated by the inhibition of CREB/MITF/tyrosinase signaling pathway. The findings suggest that FB-ChiBai can protect against UV-B irradiation and that it might be used as an agent in cosmetic products to protect against UVB-induced hyperpigmentation.

Pharmacologic manipulation of skin pigmentation

Skin complexion is among the most recognizable phenotypes between individuals and is mainly determined by the amount and type of melanin pigment deposited in the epidermis. Persons with dark skin complexion have more of a brown/black pigment known as eumelanin in their epidermis whereas those with fair skin complexions have less. Epidermal eumelanin acts as a natural sunblock by preventing incoming UV photons from penetrating into the skin and therefore protects against UV mutagenesis. By understanding the signaling pathways and regulation of pigmentation, strategies can be developed to manipulate skin pigmentation to improve UV resistance and to diminish skin cancer risk.

Development of hMC1R Selective Small Agonists for Sunless Tanning and Prevention of Genotoxicity of UV in Melanocytes

Activation of the human melanocortin 1 receptor (hMC1R) expressed on melanocytes by α-melanocortin plays a central role in regulating human pigmentation and reducing the genotoxicity of UV by activating DNA repair and antioxidant defenses. For the development of a hMC1R-targeted photoprotection strategy, we designed tetra- and tripeptide agonists with modifications that provide the necessary lipophilicity and hMC1R selectivity to be effective drugs. These peptides proved to be superior to most of the existing analogs of the physiological tridecapeptide α-melanocortin because of their small size and high hMC1R selectivity. Testing on primary cultures of human melanocytes showed that these peptides are highly potent with prolonged stimulation of melanogenesis, enhanced repair of UV-induced DNA photoproducts, and reduced apoptosis. One of the tripeptides, designated as LK-514 (5), with a molecular weight of 660 Da, has unprecedented (>100,000) hMC1R selectivity when compared with the other melanocortin receptors hMC3R, hMC4R, and hMC5R, and increases pigmentation (sunless tanning) in a cultured, three-dimensional skin model. These new analogs should be efficacious in preventing skin cancer, including melanoma, and treatment of skin disorders, such as vitiligo and polymorphic light eruptions.

Zingiber mioga Extract Improves Moisturization and Depigmentation of Skin and Reduces Wrinkle Formation in UVB-Irradiated HRM-2 Hairless Mice

Here, we investigated the effects of Zingiber mioga extracts (FSH-ZM) on the moisturization and depigmentation of skin as well as wrinkle formation in UVB-irradiated HRM-2 hairless mice. The mice were divided into six groups as follows: normal control (NC), UVB-irradiated control (C), positive control 1 (PC1, L-ascorbic acid 200 mg/kg b.w.), positive control 2 (PC2, Arbutin 200 mg/kg b.w.), Z100 (FSH-ZM 100 mg/kg b.w.), and Z200 (FSH-ZM 200 mg/kg b.w.). The experiment spanned a period of 6 weeks. We found that FSH-ZM led to an increase in the expression of hyaluronan synthase 2, fibrillin-1, and elastin mRNAs, and showed improved skin hydration in HRM-2 hairless mice compared to that in the UVB-irradiated control group. Furthermore, FSH-ZM also inhibited the expression of inflammatory cytokines and wrinkle forming factors generated by UVB and reduced the formation of wrinkles in the test group relative to that in the control group by increasing collagen synthesis. Moreover, we found that FSH-ZM decreased the expression of melanogenesis factors, which improved depigmentation in UVB-irradiated hairless mice. These results suggest that Zingiber mioga can potentially be utilized to develop products aimed at improving skin moisturization and depigmentation and reducing wrinkle formation.

Stromal Cells Present in the Melanoma Niche Affect Tumor Invasiveness and Its Resistance to Therapy

Malignant melanoma is a highly metastatic type of cancer, which arises frequently from transformed pigment cells and melanocytes as a result of long-term UV radiation exposure. In recent years, the incidence of newly diagnosed melanoma patients reached 5% of all cancer cases. Despite the development of novel targeted therapies directed against melanoma-specific markers, patients' response to treatment is often weak or short-term due to a rapid acquisition of drug resistance. Among the factors affecting therapy effectiveness, elements of the tumor microenvironment play a major role. Melanoma niche encompasses adjacent cells, such as keratinocytes, cancer-associated fibroblasts (CAFs), adipocytes, and immune cells, as well as components of the extracellular matrix and tumor-specific physicochemical properties. In this review, we summarize the current knowledge concerning the influence of cancer-associated cells (keratinocytes, CAFs, adipocytes) on the process of melanomagenesis, tumor progression, invasiveness, and the emergence of drug resistance in melanoma. We also address how melanoma can alter the differentiation and activation status of cells present in the tumor microenvironment. Understanding these complex interactions between malignant and cancer-associated cells could improve the development of effective antitumor therapeutic strategies.

Cell-type-specific Modulation of Non-homologous End Joining of Gamma Ray-induced DNA Double-strand Breaks by cAMP Signaling in Human Cancer Cells

BACKGROUND

Cyclic AMP (cAMP) signaling is activated by various hormones and neurotransmitters and regulates numerous physiological phenomena, including energy metabolism, gene expression, and proliferation. cAMP signaling plays a role in the repair of DNA damage, but its specific function is inconsistent in the literature. The present study aimed to investigate the mechanism of the different roles of cAMP signaling in DNA repair by analyzing the cell-type differences in the modulation of DNA repair by cAMP signaling following γ-ray irradiation.

METHODS

cAMP signaling was activated in human malignant melanoma cells (SK-MEL-2 and SK-MEL-28), human uterine cervical cancer cells (HeLa and SiHa) and human non-small cell lung cancer cells (H1299 and A549) by expressing a constitutively active mutant of the long-form stimulatory α subunit of GTP-binding protein or by treating with isoproterenol and prostaglandin E2 before γ-ray irradiation. DNA damage was quantitated by western blot analysis of γ-H2AX, and non-homologous end joining (NHEJ) was assessed by fluorescent reporter plasmid repair assay and immunofluorescence of microscopic foci of XRCC4 and DNA-ligase IV.

RESULTS

cAMP signaling modulated DNA damage, apoptosis and the NHEJ repair following γ-ray irradiation differently depending upon the cell type. cAMP signaling regulated the phosphorylation of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) at Ser2056 and Thr2609 in cell-type-specific manners following γ-ray irradiation, an activity that was mediated by protein kinase A.

CONCLUSION

cAMP signaling modulates the NHEJ repair of γ-ray-induced DNA damage in melanoma cells, uterine cervical cancer cells and lung cancer cells in a cell-type-specific manner, and the modulation is likely mediated by protein kinase A-dependent phosphorylation of DNA-PKcs. This study suggests that cell- and tissue-specific modulation of DNA damage repair by cAMP signaling may contribute to improve the therapeutic efficiency of radiation therapy.

Activation of the Melanocortin-1 Receptor by NDP-MSH Attenuates Oxidative Stress and Neuronal Apoptosis through PI3K/Akt/Nrf2 Pathway after Intracerebral Hemorrhage in Mice

Oxidative stress and neuronal apoptosis play crucial roles in secondary brain injury (SBI) after intracerebral hemorrhage (ICH). Recently, Nle4-D-Phe7-α-melanocyte-stimulating hormone (NDP-MSH), a synthetic agonist of the melanocortin-1 receptor (Mc1r), has been proved to inhibit neuroinflammatory in several diseases. This study is aimed at exploring if NDP-MSH could reduce oxidative stress and neuronal apoptosis following ICH, as well as the potential mechanism. A mouse ICH model was induced by autologous blood injection. NDP-MSH was intraperitoneally injected at 1 h after ICH. Mc1r siRNA and PI3K inhibitor LY294002 were administrated to inhibit the expression of Mc1r and phosphorylation of PI3K, respectively. Neurological test, brain water content, enzyme-linked immunosorbent assay (ELISA), terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), immunofluorescence, and Western blot analysis were utilized in this study. The results exhibited that Mc1r was mainly expressed in neurons, and its level in the ipsilateral hemisphere was significantly elevated after ICH. NDP-MSH treatment significantly attenuated the neurological deficits and brain water content 24 hours after ICH, which was accompanied by the inhibition of oxidative stress and neuronal apoptosis. The administration of NDP-MSH after ICH significantly promoted the expression of Mc1r, p-PI3K, p-Akt, and p-Nrf2, followed by an increase of Bcl-2 and reduction of cleaved caspase-3. Conversely, downregulating the expression of Mc1r and phosphorylation of PI3K aggravated the neurological deficits and brain edema at 24 hours after ICH, meanwhile, the effect of NDP-MSH on the expression of Mc1r, p-PI3K, p-Akt, p-Nrf2, Bcl-2, and cleaved caspase 3 was also abolished. In conclusion, our data suggest that the activation of Mc1r by NDP-MSH ameliorates oxidative stress and neuronal apoptosis through the PI3K/Akt/Nrf2 signaling pathway after ICH in mice.

Inhibition of non-homologous end joining of gamma ray-induced DNA double-strand breaks by cAMP signaling in lung cancer cells

DNA double-strand breaks (DSB) are formed by various exogenous and endogenous factors and are repaired by homologous recombination and non-homologous end joining (NHEJ). DNA-dependent protein kinase (DNA-PK) is the principal enzyme for NHEJ. We explored the role and the underlying mechanism of cAMP signaling in the NHEJ repair of DSBs resulted from gamma ray irradiation to non-small cell lung cancer (NSLC) cells. Activated cAMP signaling by expression of an activated stimulatory GTP-binding protein or by pretreatment with isoproterenol and prostaglandin E2, delayed the repair of DSBs resulted from gamma ray irradiation, and the delaying effects depended on protein kinase A (PKA). Activated cAMP signaling suppressed XRCC4 and DNA ligase IV recruitment into DSB foci, and reduced phosphorylation at T2609 in DNA-PK catalytic subunit (DNA-PKcs) with a concomitant increase in phosphorylation at S2056 in PKA-dependent ways following gamma ray irradiation. cAMP signaling decreased phosphorylation of T2609 by protein phosphatase 2A-dependent inhibition of ATM. We conclude that cAMP signaling delays the repair of gamma ray-induced DNA DSBs in NSLC cells by inhibiting NHEJ via PKA-dependent pathways, and that cAMP signaling differentially modulates DNA-PKcs phosphorylation at S2056 and T2609, which might contribute to the inhibition of NHEJ in NSLC cells.

Solar ultraviolet-induced DNA damage response: Melanocytes story in transformation to environmental melanomagenesis

Exposure to sunlight is both beneficial, as it heats the planet to a comfortable temperature, and potentially harmful, since sunlight contains ultraviolet radiation (UVR), which is deemed detrimental for living organisms. Earth's ozone layer plays a vital role in blocking most of the extremely dangerous UVC; however, low frequency/energy UVR (i.e., UVB and UVA) seeps through in minute amount and reaches the Earth's surface. Both UVB and UVA are physiologically responsible for a plethora of skin ailments, including skin cancers. The UVR is readily absorbed by the genomic DNA of skin cells, causing DNA bond distortion and UV-induced DNA damage. As a defense mechanism, the DNA damage response (DDR) signaling in skin cells activates nucleotide excision repair (NER), which is responsible for the removal of UVR-induced DNA photolesions and helps maintain the genomic integrity of the cells. Failure of proper NER function leads to mutagenesis and development of skin cancers. One of the deadliest form of skin cancers is melanoma which originates upon the genetic transformation of melanocytes, melanin producing skin cells. NER is a well-studied DNA repair system in the whole skin, as a tissue, but not much is known about it in melanocytes. Therefore, this review encapsulates NER in melanocytes, with a specific focus on its functional regulators and their cross talks due to skin heterogeneity and divulging the potential knowledge gap in the field.

Metabolomics Reveals the Alteration of Metabolic Pathway by Alpha-Melanocyte-Stimulating Hormone in B16F10 Melanoma Cells

The purpose of this study was to understand the changes of metabolic pathway induced by alpha-melanocyte-stimulating hormone (α-MSH) in B16F10 melanoma cells in an untargeted metabolomics approach. Cells were treated with 100 nM of α-MSH and then incubated for 48 h. α-MSH increased tyrosinase activity and melanin content by 56.5 and 61.7%, respectively, compared to untreated cells after 48 h of cultivation. The clear separation between groups was observed in the principal component analysis score plot, indicating that the levels of metabolites of melanoma cells were altered by treatment with α-MSH. Metabolic pathways affected by α-MSH were involved in some amino acid metabolisms. The increased levels of fumaric acid, malic acid, oxaloacetic acid and citric acid related to the citric acid cycle pathway after α-MSH treatment suggested enhanced energy metabolism. Metabolic pathways altered by α-MSH treatment can provide useful information to develop new skin pigmentation inhibitors or anti-obesity drugs.

The PI3K pathway induced by αMSH exerts a negative feedback on melanogenesis and contributes to the release of pigment

The melanocortin-1 receptor (MC1R) belongs to the family of the G protein-coupled receptor (GPCR). Activated GPCRs can promote the phosphoinositide 3-kinase (PI3K) pathway. Few studies deal with the role of the PI3K pathway activation in response to αMSH. On B16-F10 cell line, we investigated the αMSH-dependent modulation of pAKT/AKT, as a key element of the PI3K pathway after rapid and prolonged stimulation. We demonstrated that αMSH triggers a rapid modulation of AKT which culminates in an increase in its phosphorylation. We highlighted a comparable upregulation of pAKT after exposure to αMSH on primary cultures of normal human melanocytes (NHMs) expressing a wild-type MC1R. On B16-F10 cells, NHMs, and an ex vivo model of human skin biopsies, we explored the influence of PI3K/AKT signaling triggered by αMSH, focusing on the control of melanogenesis and pigment release. We showed that the αMSH-dependent PI3K/AKT pathway exerts a negative feedback on melanogenesis and promotes the extracellular release of pigment. We strengthened the role of the PI3K/AKT pathway triggered by αMSH in preserving redox equilibrium and genome integrity, highlighting its role in affecting cell survival.

The hallmarks of severe pulmonary arterial hypertension: the cancer hypothesis-ten years later

Severe forms of pulmonary arterial hypertension (PAH) are most frequently the consequence of a lumen-obliterating angiopathy. One pathobiological model is that the initial pulmonary vascular endothelial cell injury and apoptosis is followed by the evolution of phenotypically altered, apoptosis-resistant, proliferating cells and an inflammatory vascular immune response. Although there may be a vasoconstrictive disease component, the increased pulmonary vascular shear stress in established PAH is caused largely by the vascular wall pathology. In this review, we revisit the "quasi-malignancy concept" of severe PAH and examine to what extent the hallmarks of PAH can be compared with the hallmarks of cancer. The cancer model of severe PAH, based on the growth of abnormal vascular and bone marrow-derived cells, may enable the emergence of novel cell-based PAH treatment strategies.

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.

RIPK1 regulates the survival of human melanocytes upon endoplasmic reticulum stress

Vitiligo is a common congenital or acquired disfiguring skin disorder. At present, endoplasmic reticulum (ER) stress has been identified to serve a critical role in the pathogenesis of vitiligo. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a protein serine/threonine kinase. The specific molecular mechanism of RIPK1 in human melanocytes upon ER stress remains to be determined. In the present study, RIPK1 was significantly downregulated in tunicamycin (TM)-induced ER stressed-human melanocytes. Subsequently, to explore the role of RIPK1 in ER stress-induced human melanocytes, human melanocytes were transfected with control or RIPK1 plasmids for 24 h and then treated with 3 µM TM for 48 h. Reverse transcription-quantitative PCR and western blot analysis indicated that the expression levels of protein kinase R-like endoplasmic reticulum kinase, eukaryotic translation initiation factor 2 subunit 1 and CCAAT-enhancer-binding protein homologous protein were significantly increased in the TM-treated group compared with the controls. In addition, the effect of high RIPK1 expression on ER stress-induced human melanocyte survival was studied. The present results indicated that TM inhibited cell viability and promoted apoptosis in human primary epidermal melanocytes. Western blot analysis demonstrated that the expression of Bax and caspase-3 was upregulated and the expression of Bcl-2 was downregulated in TM-treated human melanocytes. The effects of TM on human melanocytes were reversed by RIPK1 overexpression. Therefore, RIPK1 overexpression may have an effect on the PI3K/AKT/mTOR signaling pathway in human melanocytes under ER stress. The results of the current study demonstrated that RIPK1 could protect human melanocytes from cell damage induced by ER stress by regulating the PI3K/AKT/mTOR and ER stress signaling pathways, thereby serving a protective role in the occurrence and development of vitiligo.

Therapeutic targeting of protein S-acylation for the treatment of disease

The post-translational modification protein S-acylation (commonly known as palmitoylation) plays a critical role in regulating a wide range of biological processes including cell growth, cardiac contractility, synaptic plasticity, endocytosis, vesicle trafficking, membrane transport and biased-receptor signalling. As a consequence, zDHHC-protein acyl transferases (zDHHC-PATs), enzymes that catalyse the addition of fatty acid groups to specific cysteine residues on target proteins, and acyl proteins thioesterases, proteins that hydrolyse thioester linkages, are important pharmaceutical targets. At present, no therapeutic drugs have been developed that act by changing the palmitoylation status of specific target proteins. Here, we consider the role that palmitoylation plays in the development of diseases such as cancer and detail possible strategies for selectively manipulating the palmitoylation status of specific target proteins, a necessary first step towards developing clinically useful molecules for the treatment of disease.

ΜicroRNA‑421 participates in vitiligo development through regulating human melanocyte survival by targeting receptor‑interacting serine/threonine kinase 1

Vitiligo is a common localized or generalized skin pigmentation disorder. Endoplasmic reticulum (ER) stress may be implicated in the development of vitiligo. microRNA-421 (miR-421) has been reported to be dysregulated in various human tumors. However, there is no report to date on the role of miR-421 in vitiligo development. The present study demonstrated that 3 µM tunicamycin (TM) increased the expression of the ER stress-related proteins protein kinase RNA-like endoplasmic reticulum kinase (PERK), α subunit of eukaryotic translation initiation factor 2 (eIF2α) and C/EBP homologous protein (CHOP) in human primary epidermal melanocytes. Moreover, TM suppressed melanocyte viability and induced apoptosis. Reverse transcription-quantitative PCR analysis demonstrated that TM promoted miR-421 expression in human melanocytes. Next, TargetScan and dual luciferase reporter gene assay indicated that receptor-interacting serine/threonine kinase 1 (RIPK1) was a direct target of miR-421. RIPK1 expression was significantly downregulated in TM-induced human melanocytes. Subsequently, the effect of miR-421 downregulation on the damage of human melanocytes induced by ER stress was investigated. Human melanocytes were transfected with inhibitor control, miR-421 inhibitor, miR-421 inhibitor + control-short hairpin (sh)RNA, or miR-421 inhibitor + RIPK1-shRNA for 24 h and then treated with TM (3 µM) for 48 h. TM was found to upregulate PERK, eIF2α and CHOP protein expression in human melanocytes, which was reduced by an miR-421 inhibitor. In addition, the miR-421 inhibitor increased viability and reduced apoptosis in TM-treated melanocytes. Furthermore, all these effects of the miR-421 inhibitor on TM-induced human melanocytes were reversed by RIPK1-shRNA. Further analyses revealed that the miR-421 inhibitor activated the phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway in TM-induced human melanocytes. These data collectively suggest that miR-421 may serve as a new treatment target in vitiligo development.

Role of alpha-melanocyte stimulating hormone (α-MSH) in modulating the molecular mechanism adopted by melanocytes of Bos indicus under UVR stress

Ultraviolet radiations (UVR) are responsible for a wide variety of acute and chronic effects on the animal skin. However, the effect of UVR-induced oxidative stress and protection through paracrine factors on animal skin has received little attention. We previously demonstrated how heat stress-induced adaptation in Bos indicus melanocytes was dependent on the level of melanin and reduction of apoptosis. Therefore, in the present investigation, the survival mechanisms adopted by melanocytes under UV stress and the role of α-MSH in cell survival under in vitro conditions were studied. After the treatment of melanocyte cells with UVR (using Osram ultravitalux 300 W lamp), analysis of Gene expression using Real-Time PCR was done to study the adopted molecular pathways under stressful conditions. In addition, α-MSH was used to assess its modulating role in cell survival under stress. This study revealed the increase in the expression of genes related to melanogenesis, cell cycle, heat shock proteins, and apoptosis of the cells after UVR stress and demonstrated the role of paracrine factor (α-MSH) in elevating the protection response to stressful conditions like UVR stress by increasing the melanogenesis and decreasing the mitochondrial-mediated apoptosis. Based on the results of the present study, it can be stated that α-MSH can play a pivotal role in the protection of animal skin cells under stressful conditions in climate-changing scenario.

Discovery of a Highly Selective MC1R Agonists Pentapeptide to Be Used as a Skin Pigmentation Enhancer and with Potential Anti-Aging Properties

One of the first lines of cutaneous defense against photoaging is (a) the synthesis of melanin and (b) the initiation of an oxidative stress response to protect skin against the harmful effects of solar radiation. Safe and selective means to stimulate epidermal pigmentation associated with oxidative stress defense are; however, scarce. Activation of the melanocortin-1 receptor (MC1R) on epidermal melanocytes represents a key step in cutaneous pigmentation initiation and, additionally, it regulates cellular defense mechanisms like oxidative stress and DNA-repair. Thus, making the activation of MC1R an attractive strategy for modulating skin pigmentation and oxidative stress. In this context, we designed and synthesized pentapeptides that act as MC1R agonists. These peptides bound, with high potency, to MC1R and activated cAMP synthesis in CHO cells expressing human MC1R. Using one lead pentapeptide, we could show that this activation of MC1R was specific as testing the activation of other G-protein coupled receptors, including the MC-receptor family, was negative. In vitro efficacy on mouse melanoma cells showed similar potency as for the synthetic MC1R agonist alpha-melanocyte stimulating hormone (NDP-alpha-MSH). Moreover, we could reproduce this activity in human skin tissue culture. The lead pentapeptide was able to induce ex-vivo protein expression of key melanogenesis markers melanocyte inducing transcription factor (MITF), tyrosinase (TYR), and tyrosinase-related protein 1 (TYRP-1). Concerning oxidative stress response, we found that the pentapeptide enhanced the activation of Nrf2 after UVA-irradiation. Our results make this pentapeptide an ideal candidate as a skin pigmentation enhancer that mimics alpha-MSH and may also have anti-photoaging effects on the skin.

TNFα-signal and cAMP-mediated signals oppositely regulate melanoma- associated ganglioside GD3 synthase gene in human melanocytes

Analyses of expression and regulation of ganglioside synthases in melanocytes are important to understand roles of gangliosides in melanomagenesis. In this study, we analyzed the expression and regulatory mechanisms of glycosyltransferase genes responsible for ganglioside synthesis in normal melanocytes. We reported previously that culture supernatants of UVB-irradiated keratinocytes induced upregulation of ganglioside GD3 synthase gene in melanocytes, and mainly TNFα was responsible for it. Then, we found that elimination of dibutyryl cyclic AMP and IBMX from the medium also resulted in upregulation of the GD3 synthase gene. The addition of α-melanocyte-stimulating hormone which increases cAMP, to the medium led to a significant reduction in the GD3 synthase gene expression level, and a PKA inhibitor enhanced the GD3 synthase gene level. These results suggest that signals mediated via TNFα and cAMP oppositely regulate GD3 synthase gene expression in melanocytes. The results of an IKK inhibitor indicate the possibility that TNFα induces GD3 synthase gene expression via NF-κB signaling in melanocytes. When melanoma cells were treated by these factors, no fluctuation in the GD3 synthase gene expression level was observed, although an IKK inhibitor significantly suppressed it, suggesting that ganglioside synthase genes are regulated in distinct manners between melanocytes and melanomas.

Endothelin-1 and α-melanocortin have redundant effects on global genome repair in UV-irradiated human melanocytes despite distinct signaling pathways

Human melanocyte homeostasis is sustained by paracrine factors that reduce the genotoxic effects of ultraviolet radiation (UV), the major etiological factor for melanoma. The keratinocyte-derived endothelin-1 (End-1) and α-melanocyte-stimulating hormone (α-MSH) regulate human melanocyte function, proliferation and survival, and enhance repair of UV-induced DNA photoproducts by binding to the G_q - and G_i -protein-coupled endothelin B receptor (EDNRB), and the G_s -protein-coupled melanocortin 1 receptor (MC1R), respectively. We hereby report that End-1 and α-MSH regulate common effectors of the DNA damage response to UV, despite distinct signaling pathways. Both factors activate the two DNA damage sensors ataxia telangiectasia and Rad3-related and ataxia telangiectasia mutated, enhance DNA damage recognition by reducing soluble nuclear and chromatin-bound DNA damage binding protein 2, and increase total and chromatin-bound xeroderma pigmentosum (XP) C. Additionally, α-MSH and End-1 increase total levels and chromatin localization of the damage verification protein XPA, and the levels of γH2AX, which facilitates recruitment of DNA repair proteins to DNA lesions. Activation of EDNRB compensates for MC1R loss of function, thereby reducing the risk of malignant transformation of these vulnerable melanocytes. Therefore, MC1R and EDNRB signaling pathways represent redundant mechanisms that inhibit the genotoxic effects of UV and melanomagenesis.

Royal Jelly (Bee Product) Decreases Inflammatory Response in Wistar Rats Induced with Ultraviolet Radiation

BACKGROUND

Ultraviolet (UV) radiation damages human skin by triggering various types of cellular damage, several main factors involved are nuclear-related factor 2 (Nrf2), nuclear factor kappa-light-chain-enhancer of activated B cells (nF-kB) and pro-inflammatory cytokine, TNF alpha. Royal jelly (RJ) possesses the effect of protecting DNA and tissue against oxidative damage.

AIM

This study aimed to assess the efficacy of RJ as a protector of ultraviolet radiation, by assessing endogenous anti-oxidant expression (Nrf2), transcription factors (Nf-kB) and proinflammatory cytokines (TNF alpha).

METHODS

This study was an experimental study with post-test control group design. Thirty Wistar rats were induced by exposing 40 Watt UV-B lamps for 2 hours/day in 14 days. The rats were grouped into groups with RJ cream application with doses of 2.5%, 5%, and 10%, negative control with vaseline, and normal control. Examination of Nrf2 and NF-kB levels was carried out by ELISA. Quantitative analysis to obtain the percentage of TNF alpha expression on the tissue was entered into the ImageJ® program. Bivariate analysis was carried out by the T-test.

RESULTS

Nrf2 levels elevated following the increase of RJ dose, with the highest level was at RJ 10%. Nf-kB levels decreased following the increase of RJ dose, with the lowest level was at RJ 10%. TNF alpha expression was reduced in groups of RJ in various doses. Increased dose resulted in a more diminished level of TNF alpha.

CONCLUSION

Royal jelly cream application protected the skin from UV radiation by increasing cellular antioxidants and suppressing inflammatory cascade.

Targeting MC1R depalmitoylation to prevent melanomagenesis in redheads

Some genetic melanocortin-1 receptor (MC1R) variants responsible for human red hair color (RHC-variants) are consequently associated with increased melanoma risk. Although MC1R signaling is critically dependent on its palmitoylation primarily mediated by the ZDHHC13 protein-acyl transferase, whether increasing MC1R palmitoylation represents a viable therapeutic target to limit melanomagenesis in redheads is unknown. Here we identify a specific and efficient in vivo strategy to induce MC1R palmitoylation for therapeutic benefit. We validate the importance of ZDHHC13 to MC1R signaling in vivo by targeted expression of ZDHHC13 in C57BL/6J-MC1R^RHC mice and subsequently inhibit melanomagenesis. By identifying APT2 as the MC1R depalmitoylation enzyme, we are able to demonstrate that administration of the selective APT2 inhibitor ML349 treatment efficiently increases MC1R signaling and represses UVB-induced melanomagenesis in vitro and in vivo. Targeting APT2, therefore, represents a preventive/therapeutic strategy to reduce melanoma risk, especially in individuals with red hair.

Melanocortin-1 receptor is a palmitoylated protein and variants of the receptor are associated with red hair colour and susceptibility to melanoma. Here, the authors describe a method to enhance the palmitoylation of the receptor, which can inhibit melanomagenesis in mice.

The Melanocortin 1 receptor and its influence on naevi and melanoma in dark-skinned phenotypes

It is well appreciated that melanocortin 1 receptor variants can produce a fair skinned and red-haired phenotype that has a strong association with increased melanoma risk. These patients are easily recognised and given appropriate attention. What may not be appreciated is that darker-skinned individuals may also carry melanocortin 1 receptor variant alleles and that they can also be at increased risk of melanoma. Considering that melanocortin 1 receptor is crucial for melanocyte proliferation, regulation and differentiation do the naevi of these darker-skinned individuals have specific features that help identify them as carrying one of these melanocortin 1 receptor variants and do melanomas that develop in dark-skinned melanocortin 1 receptor variant carriers have particular characteristics?

cAMP-mediated regulation of melanocyte genomic instability: A melanoma-preventive strategy

Malignant melanoma of the skin is the leading cause of death from skin cancer and ranks fifth in cancer incidence among all cancers in the United States. While melanoma mortality has remained steady for the past several decades, melanoma incidence has been increasing, particularly among fair-skinned individuals. According to the American Cancer Society, nearly 10,000 people in the United States will die from melanoma this year. Individuals with dark skin complexion are protected damage generated by UV-light due to the high content of UV-blocking melanin pigment in their epidermis as well as better capacity for melanocytes to cope with UV damage. There is now ample evidence that suggests that the melanocortin 1 receptor (MC1R) is a major melanoma risk factor. Inherited loss-of-function mutations in MC1R are common in melanoma-prone persons, correlating with a less melanized skin complexion and poorer recovery from mutagenic photodamage. We and others are interested in the MC1R signaling pathway in melanocytes, its mechanisms of enhancing genomic stability and pharmacologic opportunities to reduce melanoma risk based on those insights. In this chapter, we review melanoma risk factors, the MC1R signaling pathway, and the relationship between MC1R signaling and DNA repair.