Melanocortin 1 receptor variants: functional role and pigmentary associations

Melanocortin 1 Receptor Regulates Pathological and Physiological Cardiac Remodeling

BACKGROUND

The melanocortin 1 receptor (MC1R) is abundantly expressed in the skin and leukocytes, where it regulates skin pigmentation and inflammatory responses. Recently, MC1R was also found in the heart, but its functional role has remained unknown. We aimed to investigate whether MC1R is involved in the regulation of pathological or physiological cardiac remodeling.

METHODS AND RESULTS

Recessive yellow mice, as a model of global MC1R deficiency, and cardiomyocyte-specific MC1R knockout mice were subjected to transverse aortic constriction or voluntary wheel running to induce pathological or physiological cardiac hypertrophy, respectively. Mice were phenotyped for cardiac structure and function by echocardiography, histology, and quantitative PCR analysis. H9c2 cells and neonatal mouse ventricular cardiac myocytes were used as in vitro models to investigate the effects of pharmacological MC1R activation on hypertrophy-related responses. We found that the expression of MC1R progressively declines in the failing mouse heart. MC1R recessive yellow mice showed blunted hypertrophic response to transverse aortic constriction-induced pressure overload and exercise training. This phenotype was recapitulated in MC1R knockout mice, demonstrating that MC1R deficiency specifically in cardiomyocytes is responsible for the antihypertrophic effect. However, MC1R knockout mice subjected to pressure overload showed left ventricular dilatation that was associated with reduced ejection fraction and changes in left ventricular diastolic function. At the molecular level, the mRNA expression of myosin heavy chain β was upregulated in the hearts of MC1R knockout mice. In contrast, selective activation of MC1R promoted hypertrophic responses in cultured cardiomyocytes.

CONCLUSIONS

Cardiomyocyte-specific MC1R deficiency attenuates physiological and pathological cardiac hypertrophy in mice, while pharmacological activation of MC1R promotes cardiomyocyte hypertrophy.

Melanoma in Northwestern Romania: An Analysis of Epidemiological and Histopathological Characteristics and Associated Risk Factors

Background: Cutaneous melanoma (CM) is a malignant tumor originating from melanocytes. Despite improvements in prevention, Central and Eastern European countries continue to report higher rates of advanced-stage melanoma and lower survival rates. This study aims to characterize CM and the associated risk factors in Northwestern Romania. Methods: This cross-sectional cohort study was conducted in Cluj and Bihor counties. Between January 2023 and May 2024, 172 patients with histopathologically confirmed melanoma completed a standardized questionnaire addressing demographics, sun exposure history, nevi count, and melanoma-specific characteristics. Results: The median age at diagnosis of participants was 44 years. The median Breslow index (BI) was 1.5 mm, and 39% of cases presented with a BI > 2 mm. Superficial spreading melanoma (SSM) was the most common subtype, predominantly affecting women, while nodular melanoma (NM) was more frequent in men. Higher BI was associated with NM and acral lentiginous melanoma (ALM). Limbs were women's most frequent tumor site, whereas the trunk was predominant in men. Significant associations were observed between younger age at diagnosis and factors such as high nevus count, indoor activity, and smoking status. Rural residents reported a higher history of sunburns compared to urban residents. Conclusions: Our findings underscore the importance of targeted public health interventions to promote early detection and primary prevention of melanoma. Establishing a national melanoma registry is crucial to improving epidemiological surveillance and reducing the burden of melanoma in Romania.

Giant Centella asiatica, a novel cultivar rich in madecassoside and asiaticoside, suppresses α‑melanocyte‑stimulating hormone‑induced melanogenesis through MC1R binding

The present study investigated the anti‑melanogenesis effects of Giant Centella asiatica (GCA), a new cultivator of Centella asiatica (CA) cataloged by the Korea Forest Service in 2022, and compared its efficacy with that of traditional CA. GCA has a high yield per unit area and enhanced antioxidant properties. The anti‑melanogenic effects of GCA were investigated using B16F10 melanoma cells and a 3D human skin‑equivalent model. Key molecular mechanisms were elucidated through western blotting, cAMP assays and molecular docking studies. Focus was addressed on the effect of GCA on skin whitening by comparing the ability of a GCA extract to inhibit melanin production in B16F10 melanoma cells and a 3D human skin‑equivalent model to that of CA. The results showed that the GCA extracts more effectively reduced melanin production, which was attributed to their higher content of two active components, madecassoside and asiaticoside. Further investigation revealed that GCA primarily inhibited melanogenesis through the PKA‑cAMP response element‑binding (CREB)‑microphthalmia‑associated transcription factor (MITF) axis, a key regulatory pathway in melanin synthesis. Notably, the present study, to the best of our knowledge, is the first to demonstrate that madecassoside and asiaticoside, the two principal compounds in GCA, directly bound to MC1R, which contributed to the significant skin‑whitening effects. Moreover, GCA reduced melanin production in a 3D human skin‑equivalent model, showing efficacy within a complex skin environment. These results demonstrated the superior effectiveness of GCA to that of CA for skin anti‑melanogenesis, indicating its potential as a promising natural material for targeting pigmentation disorders.

Hepatocyte-specific loss of melanocortin 1 receptor disturbs fatty acid metabolism and promotes adipocyte hypertrophy

BACKGROUND/OBJECTIVES

Melanocortins mediate their biological functions via five different melanocortin receptors (MC1R - MC5R). MC1R is expressed in the skin and leukocytes, where it regulates skin pigmentation and inflammatory responses. MC1R is also present in the liver and white adipose tissue, but its functional role in these tissues is unclear. This study aimed at determining the regulatory role of MC1R in fatty acid metabolism.

METHODS

Male recessive yellow (Mc1re/e) mice, a model of global MC1R deficiency, and male hepatocyte-specific MC1R deficient mice (Mc1r LKO) were fed a chow or Western diet for 12 weeks. The mouse models were characterized for body weight and composition, liver adiposity, adipose tissue mass and morphology, glucose metabolism and lipid metabolism. Furthermore, qPCR and RNA sequencing analyses were used to investigate gene expression profiles in the liver and adipose tissue. HepG2 cells and primary mouse hepatocytes were used to study the effects of pharmacological MC1R activation.

RESULTS

Chow- and Western diet-fed Mc1re/e showed increased liver weight, white adipose tissue mass and plasma triglyceride (TG) concentration compared to wild type mice. This phenotype occurred without significant changes in food intake, body weight, physical activity or glucose metabolism. Mc1r LKO mice displayed a similar phenotype characterized by larger fat depots, increased adipocyte hypertrophy and enhanced accumulation of TG in the liver and plasma. In terms of gene expression, markers of de novo lipogenesis, inflammation and apoptosis were upregulated in the liver of Mc1r LKO mice, while enzymes regulating lipolysis were downregulated in white adipose tissue of these mice. In cultured hepatocytes, selective activation of MC1R reduced ChREBP expression, which is a central transcription factor for lipogenesis.

CONCLUSIONS

Hepatocyte-specific loss of MC1R disturbs fatty acid metabolism in the liver and leads to an obesity phenotype characterized by enhanced adipocyte hypertrophy and TG accumulation in the liver and circulation.

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.

The impact of genetic variants related to vitamin D and autoimmunity: A systematic review

Over the past few years, there has been a notable increment in scientific literature aimed at unraveling the genetic foundations of vitamin D signaling and its implications for susceptibility to autoimmunity, however, most of them address isolated diseases. Here, we conducted a systematic review of genetic variants related to vitamin D and autoimmune diseases and we discussed the current landscape of susceptibility and outcomes. Of 65 studies analyzed, most variants cited are in vitamin D binding protein (VDBP; rs2282679 GC gene), 25-hydroxylase (rs10751657 CYP2R1), 1α-hydroxylase (rs10877012, CYP27B1) and the nuclear hormone receptor superfamily [FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232), and TaqI (rs731236) in VDR gene]. Therefore, our findings confirmed the associations of several genetic variants of vitamin D signaling with a broad spectrum of autoimmune diseases/traits. In addition, given the low number of papers found with functional analysis, further studies to elucidate the real effect that the variants exert on Vitamin D signaling are recommended.

Identification of Candidate Genes for Red-Eyed (Albinism) Domestic Guppies Using Genomic and Transcriptomic Analyses

Guppies are small tropical fish with brightly colored bodies and variable tail shapes. There are two phenotypes of domestic guppy eye color: red and black. The wild type is black-eyed. The main object of this study was to identify candidate genes for the red-eyed phenotype in domestic guppies. We hope to provide molecular genetic information for the development of new domestic guppy strains. Additionally, the results also contribute to basic research concerning guppies. In this study, 121 domestic guppies were used for genomic analysis (GWAS), and 44 genes were identified. Furthermore, 21 domestic guppies were used for transcriptomic analysis, and 874 differentially expressed genes (DEGs) were identified, including 357 upregulated and 517 downregulated genes. Through GO and KEGG enrichment, we identified some important terms or pathways mainly related to melanin biosynthesis and ion transport. qRT-PCR was also performed to verify the differential expression levels of four important candidate genes (TYR, OCA2, SLC45A2, and SLC24A5) between red-eyed and black-eyed guppies. Based on the results of genomic and transcriptomic analyses, we propose that OCA2 is the most important candidate gene for the red-eyed phenotype in guppies.

The multifunctional human ocular melanocortin system

Immune privilege in the eye involves physical barriers, immune regulation and secreted proteins that together limit the damaging effects of intraocular immune responses and inflammation. The neuropeptide alpha-melanocyte stimulating hormone (α-MSH) normally circulates in the aqueous humour of the anterior chamber and the vitreous fluid, secreted by iris and ciliary epithelium, and retinal pigment epithelium (RPE). α-MSH plays an important role in maintaining ocular immune privilege by helping the development of suppressor immune cells and by activating regulatory T-cells. α-MSH functions by binding to and activating melanocortin receptors (MC1R to MC5R) and receptor accessory proteins (MRAPs) that work in concert with antagonists, otherwise known as the melanocortin system. As well as controlling immune responses and inflammation, a broad range of biological functions is increasingly recognised to be orchestrated by the melanocortin system within ocular tissues. This includes maintaining corneal transparency and immune privilege by limiting corneal (lymph)angiogenesis, sustaining corneal epithelial integrity, protecting corneal endothelium and potentially enhancing corneal graft survival, regulating aqueous tear secretion with implications for dry eye disease, facilitating retinal homeostasis via maintaining blood-retinal barriers, providing neuroprotection in the retina, and controlling abnormal new vessel growth in the choroid and retina. The role of melanocortin signalling in uveal melanocyte melanogenesis however remains unclear compared to its established role in skin melanogenesis. The early application of a melanocortin agonist to downregulate systemic inflammation used adrenocorticotropic hormone (ACTH)-based repository cortisone injection (RCI), but adverse side effects including hypertension, edema, and weight gain, related to increased adrenal gland corticosteroid production, impacted clinical uptake. Compared to ACTH, melanocortin peptides that target MC1R, MC3R, MC4R and/or MC5R, but not adrenal gland MC2R, induce minimal corticosteroid production with fewer adverse systemic effects. Pharmacological advances in synthesising MCR-specific targeted peptides provide further opportunities for treating ocular (and systemic) inflammatory diseases. Following from these observations and a renewed clinical and pharmacological interest in the diverse biological roles of the melanocortin system, this review highlights the physiological and disease-related involvement of this system within human eye tissues. We also review the emerging benefits and versatility of melanocortin receptor targeted peptides as non-steroidal alternatives for inflammatory eye diseases such as non-infectious uveitis and dry eye disease, and translational applications in promoting ocular homeostasis, for example, in corneal transplantation and diabetic retinopathy.

Differences and Similarities in Epidemiology and Risk Factors for Cutaneous and Uveal Melanoma

Both cutaneous melanoma (CM) and uveal melanoma (UM) represent important causes of morbidity and mortality. In this review, we evaluate the available knowledge on the differences and similarities between cutaneous melanoma and uveal melanoma, focusing on the epidemiological aspects and risk factors. Uveal melanoma is a rare condition but is the most prevalent primary intra-ocular malignant tumor in adults. Cutaneous melanoma, on the other hand, is significantly more common. While the frequency of cutaneous melanoma has increased in the last decades worldwide, the incidence of uveal melanoma has remained stable. Although both tumors arise from melanocytes, they are very distinct entities biologically, with complex and varied etiologies. Both conditions are encountered more frequently by individuals with a fair phenotype. ultraviolet-radiation is an important, well-documented risk factor for the development of CM, but has shown not to be of specific risk in UM. Although cutaneous and ocular melanomas seem to be inherited independently, there are reported cases of concomitant primary tumors in the same patient.

An Epidemiological Update on Indoor Tanning and the Risk of Skin Cancers

Indoor tanning (sunbeds, solarium) uses artificial ultraviolet radiation (UVR) to stimulate cosmetic tanning of the skin. Indoor tanning has been officially classified as a human carcinogen in 2009 by the International Agency for Research on Cancer of the World Health Organization (WHO). The differences in the prevalence of sunbed use across countries and over the years highlight underlying legislative, climatic, and cultural differences. Indoor tanning-seeking behaviors may be driven by motivations for an appealing appearance, largely influenced by gender and age, and several misconceptions that a prevacation tan safeguards the skin, that sunbeds can be used to treat acne or to increase vitamin D, or that tanning is a healthy habit. This review provides an epidemiological update on the prevalence of sunbed use, who tends to use sunbeds and why, and details the current evidence on the association of sunbeds with skin cancers, including cutaneous melanoma, basal cell carcinoma (BCC), and cutaneous squamous cell carcinoma (cSCC). A statistically significant higher risk of cutaneous melanoma, BCC and cSCC with the use of sunbeds has been consistently demonstrated. This risk of skin cancer is even higher with the more frequent use of sunbeds, underscoring a dose-response relationship, and in those first exposed to sunbeds at a younger age. Preventive measures against sunbed use include legislation restricting sunbed use, educational campaigns to inform and discourage from indoor tanning, as well as using the internet, online advertising messages and the social media to reach larger audiences and to promote an untanned appearance.

Current Debates on Etiopathogenesis and Treatment Strategies for Vitiligo

Vitiligo is an acquired, chronic, and progressive depigmentation or hypopigmentation characterized by the destruction of melanocytes and the occurrence of white patches or macules in the skin, mucosal surface of eyes, and ears. Melanocytes are the melanin pigment-producing cells of the skin which are destroyed in pathological conditions called vitiligo. Approximately 0.5 - 2.0% of the population is suffering from vitiligo, and a higher prevalence rate of up to 8.8% has been reported in India. It is caused by various pathogenic factors like genetic predisposition, hyperimmune activation, increased oxidative stress, and alteration in neuropeptides level. Genetic research has revealed a multi- genetic inheritance that exhibits an overlap with other autoimmune disorders. However, melanocytes specific genes are also affected (such as DDR1, XBP1, NLRP1, PTPN22, COMT, FOXP3, ACE, APE, GSTP1, TLR, SOD, and CTLA-4). A number of therapeutic options are employed for the treatment of vitiligo. The topical corticosteroids and immunomodulators are currently in practice for the management of vitiligo. Phototherapies alone and in combinations with other approaches are used in those patients who do not respond to the topical treatment. The main focus of this review is on the etiopathological factors, pharmacological management (phototherapy, topical, systemic, and surgical therapy), and herbal drugs used to treat vitiligo.

Current Concepts of Vitiligo Immunopathogenesis

Vitiligo is an acquired immune-mediated disorder of pigmentation clinically characterized by well-defined depigmented or chalk-white macules and patches on the skin. The prevalence of vitiligo varies by geographical area, affecting 0.5% to 2% of the population. The disease imposes a significant psychological burden due to its major impact on patients’ social and emotional aspects of life. Given its autoimmune background, vitiligo is frequently associated with other autoimmune diseases or immune-mediated diseases. Vitiligo is a multifaceted disorder that involves both genetic predisposition and environmental triggers. In recent years, major predisposing genetic loci for the development of vitiligo have been discovered. The current findings emphasize the critical role of immune cells and their mediators in the immunopathogenesis of vitiligo. Oxidative-stress-mediated activation of innate immunity cells such as dendritic cells, natural killer, and ILC-1 cells is thought to be a key event in the early onset of vitiligo. Innate immunity cells serve as a bridge to adaptive immunity cells including T helper 1 cells, cytotoxic T cells and resident memory T cells. IFN-γ is the primary cytokine mediator that activates the JAK/STAT pathway, causing keratinocytes to produce the key chemokines CXCL9 and CXCL10. Complex interactions between immune and non-immune cells finally result in apoptosis of melanocytes. This paper summarizes current knowledge on the etiological and genetic factors that contribute to vitiligo, with a focus on immunopathogenesis and the key cellular and cytokine players in the disease’s inflammatory pathways.

Revealing the genetic basis of eyelid pigmentation in Hereford cattle

Ocular squamous cell carcinoma and infectious keratoconjunctivitis are common ocular pathologies in Hereford cattle with considerable economic impact. Both pathologies have been associated with low eyelid pigmentation, and thus, genetic selection for higher eyelid pigmentation could reduce their incidence. The objective of the present study was to reveal the genetic basis of eyelid pigmentation in Hereford cattle. The analysis included a single-step genome-wide association study (ssGWAS) and a subsequent gene-set analysis in order to identify individual genes, genetic mechanisms and biological pathways implicated in this trait. Data consisted of eyelid pigmentation records in 1,165 Hereford bulls and steers, visually assessed in five categories between 0% and 100%. Genotypic data for 774,660 single nucleotide polymorphism markers were available for 886 animals with pigmentation records. Pedigree information of three generations of ancestors of animals with phenotype was considered in this study, with a total of 4,929 animals. Our analyses revealed that eyelid pigmentation is a moderately heritable trait, with heritability estimates around 0.41. The ssGWAS identified at least eight regions, located on BTA1, BTA3, BTA5, BTA14, BTA16, BTA18, BTA19 and BTA24, associated with eyelid pigmentation. These regions harbor genes that are directly implicated in melanocyte biology and skin pigmentation, such as ADCY8, PLD1, KITLG, and PRKCA. The gene-set analysis revealed several functional terms closely related to melanogenesis, such as positive regulation of melanocyte differentiation and regulation of ERK1 and ERK2 cascade. Overall, our findings provide evidence that eyelid pigmentation is a heritable trait influenced by many loci. Indeed, the ssGWAS detected several candidate genes that are directly implicated in melanocyte biology, including melanogenesis. This study contributes to a better understanding of the genetic and biological basis of eyelid pigmentation and presents novel information that could aid to design breeding strategies for reducing the incidence of ocular pathologies in cattle. Additional research on the genetic link between eyelid pigmentation and ocular pathologies is needed.

Melanoma in children and adolescents: analysis of susceptibility genes in 123 Italian patients

BACKGROUND

A polygenic inheritance involving high, medium and low penetrance genes has been suggested for melanoma susceptibility in adults, but genetic information is scarce for paediatric patients.

OBJECTIVE

We aim to analyse the major high and intermediate melanoma risk genes, CDKN2A, CDK4, POT1, MITF and MC1R, in a large multicentre cohort of Italian children and adolescents in order to explore the genetic context of paediatric melanoma and to reveal potential differences in heritability between children and adolescents.

METHODS

One-hundred-twenty-three patients (<21 years) from nine Italian centres were analysed for the CDKN2A, CDK4, POT1, MITF, and MC1R melanoma predisposing genes. The rate of gene variants was compared between sporadic, familial and multiple melanoma patients and between children and adolescents, and their association with clinico-pathological characteristics was evaluated.

RESULTS

Most patients carried MC1R variants (67%), while CDKN2A pathogenic variants were found in 9% of the cases, the MITF E318K in 2% of patients and none carried CDK4 or the POT1 S270N pathogenic variant. Sporadic melanoma patients significantly differed from familial and multiple cases for the young age at diagnosis, infrequent red hair colour, low number of nevi, low frequency of CDKN2A pathogenic variants and of the MC1R R160W variant. Melanoma in children (≤12 years) had more frequently spitzoid histotype, were located on the head/neck and upper limbs and had higher Breslow thickness. The MC1R V92M variant was more common in children than in adolescents. CDKN2A common polymorphisms and MC1R variants were associated with a high number of nevi.

CONCLUSION

Our results confirm the scarce involvement of the major high-risk susceptibility genes in paediatric melanoma and suggest the implication of MC1R gene variants especially in the children population.

Melanoma therapeutics: a literature review

Melanoma is a relentless type of skin cancer which involves myriad signaling pathways which regulate many cellular processes. This makes melanoma difficult to treat, especially when identified late. At present, therapeutics include chemotherapy, surgical resection, biochemotherapy, immunotherapy, photodynamic and targeted approaches. These interventions are usually administered as either a single-drug or in combination, based on tumor location, stage, and patients' overall health condition. However, treatment efficacy generally decreases as patients develop treatment resistance. Genetic profiling of melanocytes and the discovery of novel molecular factors involved in the pathogenesis of melanoma have helped to identify new therapeutic targets. In this literature review, we examine several newly approved therapies, and briefly describe several therapies being assessed for melanoma. The goal is to provide a comprehensive overview of recent developments and to consider future directions in the field of melanoma.

Molecular Markers and Targets in Melanoma

Melanoma develops as a result of several genetic alterations, with UV radiation often acting as a mutagenic risk factor. Deep knowledge of the molecular signaling pathways of different types of melanoma allows better characterization and provides tools for the development of therapies based on the intervention of signals promoted by these cascades. The latest World Health Organization classification acknowledged the specific genetic drivers leading to melanoma and classifies melanocytic lesions into nine distinct categories according to the associate cumulative sun damage (CSD), which correlates with the molecular alterations of tumors. The largest groups are melanomas associated with low-CSD or superficial spreading melanomas, characterized by frequent presentation of the BRAFV600 mutation. High-CSD melanomas include lentigo maligna type and desmoplastic melanomas, which often have a high mutation burden and can harbor NRAS, BRAFnon-V600E, or NF1 mutations. Non-CSD-associated melanomas encompass acral and mucosal melanomas that usually do not show BRAF, NRAS, or NF1 mutations (triple wild-type), but in a subset may have KIT or SF3B1 mutations. To improve survival, these driver alterations can be treated with targeted therapy achieving significant antitumor activity. In recent years, relevant improvement in the prognosis and survival of patients with melanoma has been achieved, since the introduction of BRAF/MEK tyrosine kinase inhibitors and immune checkpoint inhibitors. In this review, we describe the current knowledge of molecular pathways and discuss current and potential therapeutic targets in melanoma, focusing on their clinical relevance of development.

Examining the molecular basis of coat color in a nocturnal primate family (Lorisidae)

Organisms use color for camouflage, sexual signaling, or as a warning sign of danger. Primates are one of the most vibrantly colored Orders of mammals. However, the genetics underlying their coat color are poorly known, limiting our ability to study molecular aspects of its evolution. The role of the melanocortin 1 receptor (MC1R) in color evolution has been implicated in studies on rocket pocket mice (Chaetodipus intermediusi), toucans (Ramphastidae), and many domesticated animals. From these studies, we know that changes in MC1R result in a yellow/red or a brown/black morphology. Here, we investigate the evolution of MC1R in Lorisidae, a monophyletic nocturnal primate family, with some genera displaying high contrast variation in color patterns and other genera being monochromatic. Even more unique, the Lorisidae family has the only venomous primate: the slow loris (Nycticebus). Research has suggested that the contrasting coat patterns of slow lorises are aposematic signals for their venom. If so, we predict the MC1R in slow lorises will be under positive selection. In our study, we found that Lorisidae MC1R is under purifying selection (ω = 0.0912). In Lorisidae MC1R, there were a total of 75 variable nucleotides, 18 of which were nonsynonymous. Six of these nonsynonymous substitutions were found on the Perodicticus branch, which our reconstructions found to be the only member of Lorisidae that has predominantly lighter coat color; no substitutions were associated with Nycticebus. Our findings generate new insight into the genetics of pelage color and evolution among a unique group of nocturnal mammals and suggest putative underpinnings of monochromatic color evolution in the Perodicticus lineage.

Melanocortin-1 receptor (MC1R) genotypes do not correlate with size in two cohorts of medium-to-giant congenital melanocytic nevi

Congenital melanocytic nevi (CMN) are cutaneous malformations whose prevalence is inversely correlated with projected adult size. CMN are caused by somatic mutations, but epidemiological studies suggest that germline genetic factors may influence CMN development. In CMN patients from the U.K., genetic variants in MC1R, such as p.V92M and loss-of-function variants, have been previously associated with larger CMN. We analyzed the association of MC1R variants with CMN characteristics in two distinct cohorts of medium-to-giant CMN patients from Spain (N = 113) and from France, Norway, Canada, and the United States (N = 53), similar at the clinical and phenotypical level except for the number of nevi per patient. We found that the p.V92M or loss-of-function MC1R variants either alone or in combination did not correlate with CMN size, in contrast to the U.K. CMN patients. An additional case-control analysis with 259 unaffected Spanish individuals showed a higher frequency of MC1R compound heterozygous or homozygous variant genotypes in Spanish CMN patients compared to the control population (15.9% vs. 9.3%; p = .075). Altogether, this study suggests that MC1R variants are not associated with CMN size in these non-UK cohorts. Additional studies are required to define the potential role of MC1R as a risk factor in CMN development.

The repertoire of family A-peptide GPCRs in archaic hominins

Given the importance of G-protein coupled receptors in the regulation of many physiological functions, deciphering the relationships between genotype and phenotype in past and present hominin GPCRs is of main interest to understand the evolutionary process that contributed to the present-day variability in human traits and health. Here, we carefully examined the publicly available genomic and protein sequence databases of the archaic hominins (Neanderthal and Denisova) to draw up the catalog of coding variations in GPCRs for peptide ligands, in comparison with living humans. We then searched in the literature the functional changes, phenotypes and risk of disease possibly associated with the detected variants. Our survey suggests that Neanderthal and Denisovan hominins were likely prone to lower risk of obesity, to enhanced platelet aggregation in response to thrombin, to better response to infection, to less anxiety and aggressiveness and to favorable sociability. While some archaic variants were likely advantageous in the past, they might be responsible for maladaptive disorders today in the context of modern life and/or specific regional distribution. For example, an archaic haplotype in the neuromedin receptor 2 is susceptible to confer risk of diabetic nephropathy in type 1 diabetes in present-day Europeans. Paying attention to the pharmacological properties of some of the archaic variants described in this study may be helpful to understand the variability of therapeutic efficacy between individuals or ethnic groups.

The influence of MC1R on dermal morphological features of photo-exposed skin in women revealed by reflectance confocal microscopy and optical coherence tomography

BACKGROUND

The melanocortin 1 receptor (MC1R) gene is one of the major determinants of skin pigmentation. It is a highly polymorphic gene and some of its polymorphisms have been related to specific skin phenotypes, increased risk of skin cancers and skin photoageing. Currently, its contribution to changes in dermal features in photo-exposed skin is unknown.

OBJECTIVE

The main objective of this study is to evaluate the potential correlation between MC1R status and specific healthy photo-exposed skin characteristics.

MATERIALS AND METHODS

Skin facial features were estimated by evaluation with standard digital photography with automated features count, reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) in 100 healthy women. Skin of the forearms was used as a control.

RESULTS

The study found an association between RHC MC1R polymorphisms and dermal features in photo-exposed areas being represented by increased vessel density and pixel density in OCT (P = .025 and P = .001, respectively) and increased coarse collagen in RCM (P = .034), as compared to non-RHC subjects. To our knowledge this is previously unreported. Additionally, previously reported correlations between light hair colour and pigmented spots with MC1R RHC polymorphisms have been confirmed.

CONCLUSIONS

Our results suggest the role of RHC MC1R variants in dermal variations of facial skin, as compared to non-RHC variants. To our knowledge this is previously unreported.

Immune therapy of melanoma: Overview of therapeutic vaccines

Melanoma is the most serious type of skin cancer which develops from the occurrence of genetic mutations in the melanocytes. Based on the features of melanoma tumors such as location, genetic profile and stage, there are several therapeutic strategies including surgery, chemotherapy, and radiotherapy. However, because of the appearance resistance mechanisms, the efficiency of these treatments strategies may be reduced. It has been demonstrated that therapeutic monoclonal antibodies can improve the efficiency of melanoma therapies. Recently, several mAbs, such as nivolumab, pembrolizumab, and ipilimumab, were approved for the immunotherapy of melanoma. The antibodies inhibit immune checkpoint receptors such as CTL4 and pd-1. Another therapeutic strategy for the treatment of melanoma is cancer vaccines, which improve clinical outcomes in patients. The combination therapy using antibodies and gene vaccine give us a new perspective in the treatment of melanoma patients. Herein, we present the recent progressions in the melanoma immunotherapy, especially dendritic cells mRNA vaccines by reviewing recent literature.

Association between heterozygote Val92Met MC1R gene polymorphisms with incidence of melasma: a study of Javanese women population in Yogyakarta

Introduction: Melasma is an acquired hypermelanosis of the face. The pathogenesis of melasma is multifactorial and may be caused by interactions between genetics and the environment. Research has shown that skin pigmentation is regulated by the Melanocortin-1 Receptor gene (MC1R). In Japanese populations, Val92Met and Arg163Gln genotypes of MC1R gene polymorphisms are associated with freckles and lentigo solaris, because they have skin types II–III, but for Indonesians who are skin type IV, hyperpigmentation disorders are often melasma.

Purpose: This study aimed to identify the association between Val92Met and Arg163Gln genotypes of MC1R gene polymorphisms with the incidence of melasma in a Javanese women population.

Patients and methods: This study used unmatched case-control design, conducted by clinical examination and questionnaire. Data were analyzed with Chi-squared test and Odds Ratio (OR).

Results: This study evaluated 158 Javanese women from 18–60 years old with 79 case and 79 control subjects. The genotype of Val92Met was found more common in melasma subjects than in non-melasma (p=0.005) with (OR2.53; 95% CI:1.21–5.29). By using a bivariate test we showed sun exposure and family history of melasma were risk factors for melasma (OR:1.99; 95% CI:1.04–3.78) and (OR:35.32; 95% CI:10.25–121.70). However, genotype of Arg163Gln was not a risk factor for the incidence of melasma (OR: 0.86; 95% CI:0.39–1.89).

Conclusion: The findings showed Val92Met genotypes, sun exposure and family history were risk factors for melasma incidence. This is the first study on incidence of melasma in an Indonesian population and contributes to ongoing efforts to understand the mechanisms of melasma.

Neuroendocrine Aspects of Skin Aging

Skin aging is accompanied by a gradual loss of function, physiological integrity and the ability to cope with internal and external stressors. This is secondary to a combination of complex biological processes influenced by constitutive and environmental factors or by local and systemic pathologies. Skin aging and its phenotypic presentation are dependent on constitutive (genetic) and systemic factors. It can be accelerated by environmental stressors, such as ultraviolet radiation, pollutants and microbial insults. The skin’s functions and its abilities to cope with external stressors are regulated by the cutaneous neuroendocrine systems encompassing the regulated and coordinated production of neuropeptides, neurohormones, neurotransmitters and hormones, including steroids and secosteroids. These will induce/stimulate downstream signaling through activation of corresponding receptors. These pathways and corresponding coordinated responses to the stressors decay with age or undergo pathological malfunctions. This affects the overall skin phenotype and epidermal, dermal, hypodermal and adnexal functions. We propose that skin aging can be attenuated or its phenotypic presentation reversed by the topical use of selected factors with local neurohormonal activities targeting specific receptors or enzymes. Some of our favorite factors include melatonin and its metabolites, noncalcemic secosteroids and lumisterol derivatives, because of their low toxicity and their desirable local phenotypic effects.

Inherited MC1R variants in patients with melanoma are associated with better survival in women

Background

Women have a better melanoma prognosis, and fairer skin/hair colour. The presence of inherited MC1R variants has been associated with a better melanoma prognosis, but its interaction with sex is unknown.

Objectives

To evaluate the relationship between germline MC1R status and survival, and determine any association with sex.

Methods

This was a cohort study including 1341 patients with melanoma from the Melanoma Unit of the Hospital Clinic of Barcelona, between January 1996 and April 2018. We examined known sex‐related prognosis factors as they relate to features of melanoma and evaluated the sex‐specific role of MC1R in overall and melanoma‐specific survival. Hazard ratios (HRs) were calculated using univariate and multivariate Cox logistic regression.

Results

Men showed lower overall survival than women (P < 0·001) and the presence of inherited MC1R variants was not associated with better survival in our cohort. However, in women the presence of MC1R variants was associated with better overall survival in the multivariate analysis [HR 0·57, 95% confidence interval (CI) 0·38–0·85; P = 0·006] but not in men [HR 1·26, 95% CI 0·89–1·79; P = 0·185 (P‐value for interaction 0·004)]. Analysis performed for melanoma‐specific survival showed the same level of significance.

Conclusions

Inherited MC1R variants are associated with improved overall survival in women with melanoma but not in men. Intrinsic sex‐dependent features can modify the role of specific genes in melanoma prognosis. We believe that survival studies of patients with melanoma should include analysis by sex and MC1R genotype.

What's already known about this topic?

Inherited MC1R variants have been associated with a better melanoma prognosis, but their interaction with sex is unknown.

What does this study add?

MC1R variants are related to better overall survival and melanoma‐specific survival in women but not in men.

What is the translational message?

These differences between the sexes could imply future changes in melanoma follow‐up and treatment strategies.

This provides a basis for understanding the interaction between sex‐related genes and germline variants in cancer.

https://www.bjdonline.com/article/

Linked Editorial:https://doi.org/10.1111/bjd.18555

MC1R variants in childhood and adolescent melanoma: a retrospective pooled analysis of a multicentre cohort

BACKGROUND

Germline variants in the melanocortin 1 receptor gene (MC1R) might increase the risk of childhood and adolescent melanoma, but a clear conclusion is challenging because of the low number of studies and cases. We assessed the association of MC1R variants with childhood and adolescent melanoma in a large study comparing the prevalence of MC1R variants in child or adolescent patients with melanoma to that in adult patients with melanoma and in healthy adult controls.

METHODS

In this retrospective pooled analysis, we used the M-SKIP Project, the Italian Melanoma Intergroup, and other European groups (with participants from Australia, Canada, France, Greece, Italy, the Netherlands, Serbia, Spain, Sweden, Turkey, and the USA) to assemble an international multicentre cohort. We gathered phenotypic and genetic data from children or adolescents diagnosed with sporadic single-primary cutaneous melanoma at age 20 years or younger, adult patients with sporadic single-primary cutaneous melanoma diagnosed at age 35 years or older, and healthy adult individuals as controls. We calculated odds ratios (ORs) for childhood and adolescent melanoma associated with MC1R variants by multivariable logistic regression. Subgroup analysis was done for children aged 18 or younger and 14 years or younger.

FINDINGS

We analysed data from 233 young patients, 932 adult patients, and 932 healthy adult controls. Children and adolescents had higher odds of carrying MC1R r variants than did adult patients (OR 1·54, 95% CI 1·02-2·33), including when analysis was restricted to patients aged 18 years or younger (1·80, 1·06-3·07). All investigated variants, except Arg160Trp, tended, to varying degrees, to have higher frequencies in young patients than in adult patients, with significantly higher frequencies found for Val60Leu (OR 1·60, 95% CI 1·05-2·44; p=0·04) and Asp294His (2·15, 1·05-4·40; p=0·04). Compared with those of healthy controls, young patients with melanoma had significantly higher frequencies of any MC1R variants.

INTERPRETATION

Our pooled analysis of MC1R genetic data of young patients with melanoma showed that MC1R r variants were more prevalent in childhood and adolescent melanoma than in adult melanoma, especially in patients aged 18 years or younger. Our findings support the role of MC1R in childhood and adolescent melanoma susceptibility, with a potential clinical relevance for developing early melanoma detection and preventive strategies.

FUNDING

SPD-Pilot/Project-Award-2015; AIRC-MFAG-11831.

MITF and UV responses in skin: From pigmentation to addiction

Ultraviolet radiation (UVR) has numerous effects on skin, including DNA damage, tanning, vitamin D synthesis, carcinogenesis, and immunomodulation. Keratinocytes containing damaged DNA secrete both α-melanocyte-stimulating hormone (α-MSH), which stimulates pigment production by melanocytes, and the opioid β-endorphin, which can trigger addiction-like responses to UVR. The pigmentation (tanning) response is an adaptation that provides some delayed protection against further DNA damage and carcinogenesis, while the opioid response may be an evolutionary adaptation for promoting sun-seeking behavior to prevent vitamin D deficiency. Here, we review the pigmentation response to UVR, driven by melanocytic microphthalmia-associated transcription factor (MITF), and evidence for UVR-induced melanomagenesis and addiction. We also discuss potential applications of a novel approach to generate protective pigmentation in the absence of UVR (sunless tanning) using a topical small-molecule inhibitor of the salt-inducible kinase (SIK) family.

Ultraviolet radiation-mediated development of cutaneous melanoma: An update

Ultraviolet (UV) light is absorbed by nucleic acids, proteins or other endogenous chromophores, such as porphyrins, flavins and melanin, triggering biological processes in skin cells. Both UV-induced mutations in melanocytes and changes in the immune microenvironment are understood to play a role in the development of cutaneous melanoma. The degree of UV-induced stress and the protection against this stress are influenced by both intracellular and intercellular molecular interactions. The present review summarizes the known major molecular biological changes induced by UV light in the skin that play a role in melanoma initiation and promotion. Nevertheless, cutaneous melanoma is not a homogenous disease, and the interaction of variable environmental exposure and different genetic susceptibility and other host factors lead to the formation of melanomas with different biological behavior and clinical characteristics. This review highlights the challenges in the understanding of how UV radiation contributes to the formation of cutaneous melanoma, and reviews the new results of photobiology and their link to tumor genetics and tumor immunology with potential implications on melanoma prevention and therapeutic strategies. The information presented here is expected to add clarity to ongoing research efforts in this field to aid the development of novel strategies to prevent and treat melanoma.

cAMP-independent non-pigmentary actions of variant melanocortin 1 receptor: AKT-mediated activation of protective responses to oxidative DNA damage

The melanocortin 1 receptor gene (MC1R), a well-established melanoma susceptibility gene, regulates the amount and type of melanin pigments formed within epidermal melanocytes. MC1R variants associated with increased melanoma risk promote the production of photosensitizing pheomelanins as opposed to photoprotective eumelanins. Wild-type (WT) MC1R activates DNA repair and antioxidant defenses in a cAMP-dependent fashion. Since melanoma-associated MC1R variants are hypomorphic in cAMP signaling, these non-pigmentary actions are thought to be defective in MC1R-variant human melanoma cells and epidermal melanocytes, consistent with a higher mutation load in MC1R-variant melanomas. We compared induction of antioxidant enzymes and DNA damage responses in melanocytic cells of defined MC1R genotype. Increased expression of catalase (CAT) and superoxide dismutase (SOD) genes following MC1R activation was cAMP-dependent and required a WT MC1R genotype. Conversely, pretreatment of melanocytic cells with an MC1R agonist before an oxidative challenge with Luperox decreased (i) accumulation of 8-oxo-7,8-dihydro-2'-deoxyguanine, a major product of oxidative DNA damage, (ii) phosphorylation of histone H2AX, a marker of DNA double-strand breaks, and (iii) formation of DNA breaks. These responses were comparable in cells WT for MC1R or harboring hypomorphic MC1R variants without detectable cAMP signaling. In MC1R-variant melanocytic cells, the DNA-protective responses were mediated by AKT. Conversely, in MC1R-WT melanocytic cells, high cAMP production downstream of MC1R blocked AKT activation and was responsible for inducing DNA repair. Accordingly, MC1R activation could promote repair of oxidative DNA damage by a cAMP-dependent pathway downstream of WT receptor, or via AKT in cells of variant MC1R genotype.

Cutaneous melanoma: From pathogenesis to therapy (Review)

In less than 10 years, melanoma treatment has been revolutionized with the approval of tyrosine kinase inhibitors and immune checkpoint inhibitors, which have been shown to have a significant impact on the prognosis of patients with melanoma. The early steps of this transformation have taken place in research laboratories. The mitogen‑activated protein kinase (MAPK) pathway, phosphoinositol‑3‑kinase (PI3K) pathway promote the development of melanoma through numerous genomic alterations on different components of these pathways. Moreover, melanoma cells deeply interact with the tumor microenvironment and the immune system. This knowledge has led to the identification of novel therapeutic targets and treatment strategies. In this review, the epidemiological features of cutaneous melanoma along with the biological mechanisms involved in its development and progression are summarized. The current state‑of‑the‑art of advanced stage melanoma treatment strategies and the currently available evidence of the use of predictive and prognostic biomarkers are also discussed.

A Common Variant in the MC1R Gene (p.V92M) is associated with Alzheimer's Disease Risk

Despite the recent identification of some novel risk genes for Alzheimer's disease (AD), the genetic etiology of late-onset Alzheimer's disease (LOAD) remains largely unknown. The inclusion of these novel risk genes to the risk attributable to the APOE gene accounts for roughly half of the total genetic variance in LOAD. The evidence indicates that undiscovered genetic factors may contribute to AD susceptibility. In the present study, we sequenced the MC1R gene in 525 Spanish LOAD patients and in 160 controls. We observed that a common MC1R variant p.V92M (rs2228479), not related to pigmentation traits, was present in 72 (14%) patients and 15 (9%) controls and confers increased risk of developing LOAD (OR: 1.99, 95% CI: 1.08-3.64, p = 0.026), especially in those patients whose genetic risk could not be explained by APOE genotype. This association remains and even increased in the subset of 69 patients with typical AD cerebrospinal fluid profile (OR: 3.40 95% CI: 1.40-8.27, p = 0.007). We did not find an association between p.V92M and age of onset of AD. Further studies are necessary to elucidate the role of MC1R in brain cells through the different MC1R pathways.

Finasteride inhibits melanogenesis through regulation of the adenylate cyclase in melanocytes and melanoma cells

Finasteride is a well-known 5α-reductase inhibitor used for treatment of alopecia and prostate cancer. But the effect of finasteride in regulating melanogenesis is still unclear. In the present study the role of finasteride on melanogenesis was investigated. Finasteride decrease melanin level in melanocyte melan-a cells and B16F10 melanoma cells without inducing cytotoxicity. MC1R (melanocortin 1 receptor) protein expression was also inhibited by finasteride thereby decreasing the expression of adenylate cyclase, MITF (Melanogenesis associated transcription factor), tyrosinases, TRP (tyrosinase-related protein) -1 and -2. Thus our study suggest that finasteride inhibits melanogenesis in melanocyte and melanoma cells by inhibiting MC1R.

Melanocortin 1 Receptor Deficiency Promotes Atherosclerosis in Apolipoprotein E-/- Mice

OBJECTIVE

The MC1-R (melanocortin 1 receptor) is expressed by monocytes and macrophages where it mediates anti-inflammatory actions. MC1-R also protects against macrophage foam cell formation primarily by promoting cholesterol efflux through the ABCA1 (ATP-binding cassette transporter subfamily A member 1) and ABCG1 (ATP-binding cassette transporter subfamily G member 1). In this study, we aimed to investigate whether global deficiency in MC1-R signaling affects the development of atherosclerosis.

APPROACH AND RESULTS

Apoe^-/- (apolipoprotein E deficient) mice were crossed with recessive yellow (Mc1r^e/e) mice carrying dysfunctional MC1-R and fed a high-fat diet to induce atherosclerosis. Apoe^-/- Mc1r^e/e mice developed significantly larger atherosclerotic lesions in the aortic sinus and in the whole aorta compared with Apoe^-/- controls. In terms of plaque composition, MC1-R deficiency was associated with less collagen and smooth muscle cells and increased necrotic core, indicative of more vulnerable lesions. These changes were accompanied by reduced Abca1 and Abcg1 expression in the aorta. Furthermore, Apoe^-/- Mc1r^e/e mice showed a defect in bile acid metabolism that aggravated high-fat diet-induced hypercholesterolemia and hepatic lipid accumulation. Flow cytometric analysis of leukocyte profile revealed that dysfunctional MC1-R enhanced arterial accumulation of classical Ly6C^high monocytes and macrophages, effects that were evident in mice fed a normal chow diet but not under high-fat diet conditions. In support of enhanced arterial recruitment of Ly6C^high monocytes, these cells had increased expression of L-selectin and P-selectin glycoprotein ligand 1.

CONCLUSIONS

The present study highlights the importance of MC1-R in the development of atherosclerosis. Deficiency in MC1-R signaling exacerbates atherosclerosis by disturbing cholesterol handling and by increasing arterial monocyte accumulation.

Selection on the Major Color Gene Melanocortin-1-Receptor Shaped the Evolution of the Melanocortin System Genes

Modular genetic systems and networks have complex evolutionary histories shaped by selection acting on single genes as well as on their integrated function within the network. However, uncovering molecular coevolution requires the detection of coevolving sites in sequences. Detailed knowledge of the functions of each gene in the system is also necessary to identify the selective agents driving coevolution. Using recently developed computational tools, we investigated the effect of positive selection on the coevolution of ten major genes in the melanocortin system, responsible for multiple physiological functions and human diseases. Substitutions driven by positive selection at the melanocortin-1-receptor (MC1R) induced more coevolutionary changes on the system than positive selection on other genes in the system. Contrarily, selection on the highly pleiotropic POMC gene, which orchestrates the activation of the different melanocortin receptors, had the lowest coevolutionary influence. MC1R and possibly its main function, melanin pigmentation, seems to have influenced the evolution of the melanocortin system more than functions regulated by MC2-5Rs such as energy homeostasis, glucocorticoid-dependent stress and anti-inflammatory responses. Although replication in other regulatory systems is needed, this suggests that single functional aspects of a genetic network or system can be of higher importance than others in shaping coevolution among the genes that integrate it.

The MeLiM Minipig: An Original Spontaneous Model to Explore Cutaneous Melanoma Genetic Basis

Melanoma is the deadliest skin cancer and is a major public health concern with a growing incidence worldwide. As for other complex diseases, animal models are needed in order to better understand the mechanisms leading to pathology, identify potential biomarkers to be used in the clinics, and eventually molecular targets for therapeutic solutions. Cutaneous melanoma, arising from skin melanocytes, is mainly caused by environmental factors such as UV radiation; however a significant genetic component participates in the etiology of the disease. The pig is a recognized model for spontaneous development of melanoma with features similar to the human ones, followed by a complete regression and a vitiligo-like depigmentation. Three different pig models (MeLiM, Sinclair, and MMS-Troll) have been maintained through the last decades, and different genetic studies have evidenced a complex inheritance of the disease. As in humans, pigmentation seems to play a prominent role, notably through MC1R and MITF signaling. Conversely, cell cycle genes as CDKN2A and CDK4 have been excluded as predisposing for melanoma in MeLiM. So far, only sparse studies have focused on somatic changes occurring during oncogenesis, and have revealed major cytological changes and a potential dysfunction of the telomere maintenance system. Finally, the spontaneous tumor progression and regression occurring in these models could shed light on the interplay between endogenous retroviruses, melanomagenesis, and adaptive immune response.

The p. R151C Polymorphism in MC1R Gene Modifies the Age of Onset in Spanish Huntington's Disease Patients

The expansion of CAG repeats (≥36 CAG) in the HTT gene is the only known genetic cause of Huntington's disease (HD) and the main determinant of the course of the disease. The length of the expanded CAG repeats correlates inversely with the age of onset (AOO) but does not completely determine it. We investigated the role of the melanocortin 1 receptor (MC1R) gene as a modifier factor of AOO in 600 HD patients from Spain. We sequenced the entire region of the MC1R gene and analyzed all the nonsynonymous MC1R genetic variants with a minor allele frequency of at least 0.01 in HD patients. The variability in AOO attributable to the CAG repeats and MC1R polymorphisms was evaluated using a multiple linear regression model. We found that the loss-of-function p. R151C MC1R polymorphism has a significant influence on the AOO (P = 0.004; Bonferroni-corrected P = 0.032) which explains 1.42% of the variance in AOO that cannot be accounted for by the expanded CAG repeat. Our results suggest that the MC1R gene could modify the AOO in Spanish HD patients and encourage the evaluation of loss-of-function MC1R polymorphisms in other HD populations with a higher frequency of these MC1R polymorphisms.

MC1R variants affect the expression of melanocortin and melanogenic genes and the association between melanocortin genes and coloration

The melanocortin-1 receptor (MC1R) gene influences coloration by altering the expression of genes acting downstream in the melanin synthesis. MC1R belongs to the melanocortin system, a genetic network coding for the ligands that regulate MC1R and other melanocortin receptors controlling different physiological and behavioural traits. The impact of MC1R variants on these regulatory melanocortin genes was never considered, even though MC1R mutations could alter the influence of these genes on coloration (e.g. by decreasing MC1R response to melanocortin ligands). Using barn owl growing feathers, we investigated the differences between MC1R genotypes in the (co)expression of six melanocortin and nine melanogenic-related genes and in the association between melanocortin gene expression and phenotype (feather pheomelanin content). Compared to the MC1R rufous allele, responsible for reddish coloration, the white allele was not only associated with an expected lower expression of melanogenic-related genes (TYR, TYRP1, OCA2, SLC45A2, KIT, DCT) but also with a lower MC1R expression and a higher expression of ASIP, the MC1R antagonist. More importantly, the expression of PCSK2, responsible for the maturation of the MC1R agonist, α-melanocyte-stimulating hormone, was positively related to pheomelanin content in MC1R white homozygotes but not in individuals carrying the MC1R rufous allele. These findings indicate that MC1R mutations not only alter the expression of melanogenic-related genes but also the association between coloration and the expression of melanocortin genes upstream of MC1R. This suggests that MC1R mutations can modulate the regulation of coloration by the pleiotropic melanocortin genes, potentially decoupling the often-observed associations between coloration and other phenotypes.

The impact of skin colour on human photobiological responses

Terrestrial solar ultraviolet radiation (UVR) exerts both beneficial and adverse effects on human skin. Epidemiological studies show a lower incidence of skin cancer in people with pigmented skins compared to fair skins. This is attributed to photoprotection by epidermal melanin, as is the poorer vitamin D status of those with darker skins. We summarize a wide range of photobiological responses across different skin colours including DNA damage and immunosuppression. Some studies show the generally modest photoprotective properties of melanin, but others show little or no effect. DNA photodamage initiates non‐melanoma skin cancer and is reduced by a factor of about 3 in pigmented skin compared with white skin. This suggests that if such a modest reduction in DNA damage can result in the significantly lower skin cancer incidence in black skin, the use of sunscreen protection might be extremely beneficial for susceptible population. Many contradictory results may be explained by protocol differences, including differences in UVR spectra and exposure protocols. We recommend that skin type comparisons be done with solar‐simulated radiation and standard erythema doses or physical doses (J/m²) rather than those based solely on clinical endpoints such as minimal erythema dose (MED).

Born blonde: a recessive loss-of-function mutation in the melanocortin 1 receptor is associated with cream coat coloration in Antarctic fur seals

Although the genetic basis of color variation has been extensively studied in humans and domestic animals, the genetic polymorphisms responsible for different color morphs remain to be elucidated in many wild vertebrate species. For example, hypopigmentation has been observed in numerous marine mammal species but the underlying mutations have not been identified. A particularly compelling candidate gene for explaining color polymorphism is the melanocortin 1 receptor (MC1R), which plays a key role in the regulation of pigment production. We therefore used Antarctic fur seals (Arctocephalus gazella) as a highly tractable marine mammal system with which to test for an association between nucleotide variation at the MC1R and melanin‐based coat color phenotypes. By sequencing 70 wild‐type individuals with dark‐colored coats and 26 hypopigmented individuals with cream‐colored coats, we identified a nonsynonymous mutation that results in the substitution of serine with phenylalanine at an evolutionarily highly conserved structural domain. All of the hypopigmented individuals were homozygous for the allele coding for phenylalanine, consistent with a recessive loss‐of‐function allele. In order to test for cryptic population structure, which can generate artefactual associations, and to evaluate whether homozygosity at the MC1R could be indicative of low genome‐wide heterozygosity, we also genotyped all of the individuals at 50 polymorphic microsatellite loci. We were unable to detect any population structure and also found that wild‐type and hypopigmented individuals did not differ significantly in their standardized multilocus heterozygosity. Such a lack of association implies that hypopigmented individuals are unlikely to suffer disproportionately from inbreeding depression, and hence, we have no reason to believe that they are at a selective disadvantage in the wider population.

A novel role for pigment genes in the stress response in rainbow trout (Oncorhynchus mykiss)

In many vertebrate species visible melanin-based pigmentation patterns correlate with high stress- and disease-resistance, but proximate mechanisms for this trait association remain enigmatic. Here we show that a missense mutation in a classical pigmentation gene, melanocyte stimulating hormone receptor (MC1R), is strongly associated with distinct differences in steroidogenic melanocortin 2 receptor (MC2R) mRNA expression between high- (HR) and low-responsive (LR) rainbow trout (Oncorhynchus mykiss). We also show experimentally that cortisol implants increase the expression of agouti signaling protein (ASIP) mRNA in skin, likely explaining the association between HR-traits and reduced skin melanin patterning. Molecular dynamics simulations predict that melanocortin 2 receptor accessory protein (MRAP), needed for MC2R function, binds differently to the two MC1R variants. Considering that mRNA for MC2R and the MC1R variants are present in head kidney cells, we hypothesized that MC2R activity is modulated in part by different binding affinities of the MC1R variants for MRAP. Experiments in mammalian cells confirmed that trout MRAP interacts with the two trout MC1R variants and MC2R, but failed to detect regulation of MC2R signaling, possibly due to high constitutive MC1R activity.

Single-nucleotide polymorphism of MC1R, ASIP, and TYRP2 genes in wild and farmed foxes (Vulpes vulpes)

DNA mutations within genes associated with melanogenesis can affect melanin production, leading to dyschromias. Genes that are involved in synthesis of melatonin and may affect the color of skin are melanocortin 1 receptor (MC1R), agouti locus (ASIP), and tyrosinase-related protein-2 (TYRP2). In this study, SNP identification within ASIP, MC1R, and TYRP2 gene fragments in wild and farmed foxes (Vulpes vulpes) was performed. Nine mutations in the ASIP gene which allowed us to distinguish seven SNP profiles, fourteen mutations and five SNP profiles in the MC1R gene, and seven SNP profiles based on four polymorphic nucleotides in the TYRP2 gene were detected. Analyses of obtained profiles indicate that ASIP did not undergo mutations in the wild, and significant variability of SNP profiles was found for TYRP2, with specific haplotypes noted for farm foxes and American and European wild foxes.

"Fifty Shades" of Black and Red or How Carboxyl Groups Fine Tune Eumelanin and Pheomelanin Properties

Recent advances in the chemistry of melanins have begun to disclose a number of important structure-property-function relationships of crucial relevance to the biological role of human pigments, including skin (photo) protection and UV-susceptibility. Even slight variations in the monomer composition of black eumelanins and red pheomelanins have been shown to determine significant differences in light absorption, antioxidant, paramagnetic and redox behavior, particle morphology, surface properties, metal chelation and resistance to photo-oxidative wear-and-tear. These variations are primarily governed by the extent of decarboxylation at critical branching points of the eumelanin and pheomelanin pathways, namely the rearrangement of dopachrome to 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and the rearrangement of 5-S-cysteinyldopa o-quinoneimine to 1,4-benzothiazine (BTZ) and its 3-carboxylic acid (BTZCA). In eumelanins, the DHICA-to-DHI ratio markedly affects the overall antioxidant and paramagnetic properties of the resulting pigments. In particular, a higher content in DHICA decreases visible light absorption and paramagnetic response relative to DHI-based melanins, but markedly enhances antioxidant properties. In pheomelanins, likewise, BTZCA-related units, prevalently formed in the presence of zinc ions, appear to confer pronounced visible and ultraviolet A (UVA) absorption features, accounting for light-dependent reactive oxygen species (ROS) production, whereas non-carboxylated benzothiazine intermediates seem to be more effective in inducing ROS production by redox cycling mechanisms in the dark. The possible biological and functional significance of carboxyl retention in the eumelanin and pheomelanin pathways is discussed.

The MC1R Gene and Youthful Looks

Looking young for one's age has been a desire since time immemorial. This desire is attributable to the belief that appearance reflects health and fecundity. Indeed, perceived age predicts survival [1] and associates with molecular markers of aging such as telomere length [2]. Understanding the underlying molecular biology of perceived age is vital for identifying new aging therapies among other purposes, but studies are lacking thus far. As a first attempt, we performed genome-wide association studies (GWASs) of perceived facial age and wrinkling estimated from digital facial images by analyzing over eight million SNPs in 2,693 elderly Dutch Europeans from the Rotterdam Study. The strongest genetic associations with perceived facial age were found for multiple SNPs in the MC1R gene (p < 1 × 10(-7)). This effect was enhanced for a compound heterozygosity marker constructed from four pre-selected functional MC1R SNPs (p = 2.69 × 10(-12)), which was replicated in 599 Dutch Europeans from the Leiden Longevity Study (p = 0.042) and in 1,173 Europeans of the TwinsUK Study (p = 3 × 10(-3)). Individuals carrying the homozygote MC1R risk haplotype looked on average up to 2 years older than non-carriers. This association was independent of age, sex, skin color, and sun damage (wrinkling, pigmented spots) and persisted through different sun-exposure levels. Hence, a role for MC1R in youthful looks independent of its known melanin synthesis function is suggested. Our study uncovers the first genetic evidence explaining why some people look older for their age and provides new leads for further investigating the biological basis of how old or young people look.

Pigmentary Markers in Danes--Associations with Quantitative Skin Colour, Nevi Count, Familial Atypical Multiple-Mole, and Melanoma Syndrome

To investigate whether pigmentation genes involved in the melanogenic pathway (melanogenesis) contributed to melanoma predisposition, we compared pigmentary genetics with quantitative skin pigmentation measurements, the number of atypical nevi, the total nevus count, and the familial atypical multiple mole and melanoma (FAMMM) syndrome. We typed 32 pigmentary SNP markers and sequenced MC1R in 246 healthy individuals and 116 individuals attending periodic control for malignant melanoma development, 50 of which were diagnosed with FAMMM. It was observed that individuals with any two grouped MC1R variants (missense, NM_002386:c. 456C > A (p.TYR152*), or NM_002386:c.83_84insA (p.Asn29Glnfs*14) had significantly (p<0.001) lighter skin pigmentation of the upper-inner arm than those with none or one MC1R variant. We did not observe any significant association of the MC1R variants with constitutive pigmentation measured on the buttock area. We hypothesize that the effect of MC1R variants on arm pigmentation is primarily reflecting the inability to tan when subjected to UVR. A gender specific effect on skin pigmentation was also observed, and it was found that the skin pigmentation of females on average were darker than that of males (p<0.01). We conclude that MC1R variants are associated with quantitative skin colour in a lightly pigmented Danish population. We did not observe any association between any pigmentary marker and the FAMMM syndrome. We suggest that the genetics of FAMMM is not related to the genetics of the pigmentary pathway.

Genetic Susceptibility to Vitiligo: GWAS Approaches for Identifying Vitiligo Susceptibility Genes and Loci

Vitiligo is an autoimmune disease with a strong genetic component, characterized by areas of depigmented skin resulting from loss of epidermal melanocytes. Genetic factors are known to play key roles in vitiligo through discoveries in association studies and family studies. Previously, vitiligo susceptibility genes were mainly revealed through linkage analysis and candidate gene studies. Recently, our understanding of the genetic basis of vitiligo has been rapidly advancing through genome-wide association study (GWAS). More than 40 robust susceptible loci have been identified and confirmed to be associated with vitiligo by using GWAS. Most of these associated genes participate in important pathways involved in the pathogenesis of vitiligo. Many susceptible loci with unknown functions in the pathogenesis of vitiligo have also been identified, indicating that additional molecular mechanisms may contribute to the risk of developing vitiligo. In this review, we summarize the key loci that are of genome-wide significance, which have been shown to influence vitiligo risk. These genetic loci may help build the foundation for genetic diagnosis and personalize treatment for patients with vitiligo in the future. However, substantial additional studies, including gene-targeted and functional studies, are required to confirm the causality of the genetic variants and their biological relevance in the development of vitiligo.

Update in genetic susceptibility in melanoma

Melanoma is the most deadly of the common skin cancers and its incidence is rapidly increasing. Approximately 10% of cases occur in a familial context. To date, cyclin-dependent kinase inhibitor 2A (CDKN2A), which was identified as the first melanoma susceptibility gene more than 20 years ago, is the main high-risk gene for melanoma. A few years later cyclin-dependent kinase 4 (CDK4) was also identified as a melanoma susceptibility gene. The technologic advances have allowed the identification of new genes involved in melanoma susceptibility: Breast cancer 1 (BRCA1) associated protein 1 (BAP1), CXC genes, telomerase reverse transcriptase (TERT), protection of telomeres 1 (POT1), ACD and TERF2IP, the latter four being involved in telomere maintenance. Furthermore variants in melanocortin 1 receptor (MC1R) and microphthalmia-associated transcription factor (MITF) give a moderately increased risk to develop melanoma. Melanoma genetic counseling is offered to families in order to better understand the disease and the genetic susceptibility of developing it. Genetic counseling often implies genetic testing, although patients can benefit from genetic counseling even when they do not fulfill the criteria for these tests. Genetic testing for melanoma predisposition mutations can be used in clinical practice under adequate selection criteria and giving a valid test interpretation and genetic counseling to the individual.

Identification and functional characterization of natural human melanocortin 1 receptor mutant alleles in Pakistani population

Melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor of the melanocyte's plasma membrane, is a major determinant of skin pigmentation and phototype. Upon activation by α-melanocyte stimulating hormone, MC1R triggers the cAMP cascade to stimulate eumelanogenesis. We used whole-exome sequencing to identify causative alleles in Pakistani families with skin and hair hypopigmentation. Six MC1R mutations segregated with the phenotype in seven families, including a p.Val174del in-frame deletion and a p.Tyr298* nonsense mutation, that were analyzed for function in heterologous HEK293 cells. p.Tyr298* MC1R showed no agonist-induced signaling to the cAMP or ERK pathways, nor detectable agonist binding. Conversely, signaling was comparable for p.Val174del and wild-type in HEK cells overexpressing the proteins, but binding analysis suggested impaired cell surface expression. Flow cytometry and confocal imaging studies revealed reduced plasma membrane expression of p.Val174del and p.Tyr298*. Therefore, p.Tyr298* was a total loss-of-function (LOF) allele, while p.Val174del displayed a partial LOF attribute.