Bleomycin-induced fibrosis in MC1 signalling-deficient C57BL/6J-Mc1r(e/e) mice further supports a modulating role for melanocortins in collagen synthesis of the skin

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.

Discovery of MT-7117 (Dersimelagon Phosphoric Acid): A Novel, Potent, Selective, and Nonpeptidic Orally Available Melanocortin 1 Receptor Agonist

Activation of the melanocortin 1 receptor (MC1R) mediates melanogenesis in melanocytes, anti-inflammatory effects in inflammatory cells, and antifibrotic effects in fibroblasts. Thus, MC1R agonists are expected to be beneficial for treating skin, autoimmune, inflammatory, and fibrotic diseases. Afamelanotide, an α-melanocyte-stimulating hormone (α-MSH) analogue MC1R agonist, is used clinically for treating erythropoietic protoporphyria (EPP) as a subcutaneous implant formulation. We explored nonpeptidic small-molecule MC1R agonists with the aim of identifying more convenient oral drugs. By exploring the structure of previously reported compound 5, we discovered compound 11 (MT-7117: dersimelagon phosphoric acid). This compound exhibited strong MC1R agonistic activity, good pharmacokinetic properties, and excellent safety profiles. Furthermore, compound 11 was effective in animal pigmentation evaluation and skin fibrosis model studies. Compound 11 is currently in clinical trials for the treatment of EPP, X-linked protoporphyria (XLP), and systemic sclerosis (SSc). Proof of concept was obtained in phase 2 clinical studies on EPP and XLP.

Melanocortin therapies to resolve fibroblast-mediated diseases

Stromal cells have emerged as central drivers in multiple and diverse diseases, and consequently, as potential new cellular targets for the development of novel therapeutic strategies. In this review we revise the main roles of fibroblasts, not only as structural cells but also as players and regulators of immune responses. Important aspects like fibroblast heterogeneity, functional specialization and cellular plasticity are also discussed as well as the implications that these aspects may have in disease and in the design of novel therapeutics. An extensive revision of the actions of fibroblasts on different conditions uncovers the existence of numerous diseases in which this cell type plays a pathogenic role, either due to an exacerbation of their 'structural' side, or a dysregulation of their 'immune side'. In both cases, opportunities for the development of innovative therapeutic approaches exist. In this regard, here we revise the existing evidence pointing at the melanocortin pathway as a potential new strategy for the treatment and management of diseases mediated by aberrantly activated fibroblasts, including scleroderma or rheumatoid arthritis. This evidence derives from studies involving models of in vitro primary fibroblasts, in vivo models of disease as well as ongoing human clinical trials. Melanocortin drugs, which are pro-resolving mediators, have shown ability to reduce collagen deposition, activation of myofibroblasts, reduction of pro-inflammatory mediators and reduced scar formation. Here we also discuss existing challenges, both in approaching fibroblasts as therapeutic targets, and in the development of novel melanocortin drug candidates, that may help advance the field and deliver new medicines for the management of diseases with high medical needs.

Dersimelagon, a novel oral melanocortin 1 receptor agonist, demonstrates disease-modifying effects in preclinical models of systemic sclerosis

Background

Activation of melanocortin 1 receptor (MC1R) is known to exert broad anti-inflammatory and anti-fibrotic effects. The purpose of this study is to investigate the potential of dersimelagon, a novel oral MC1R agonist, as a therapeutic agent for systemic sclerosis (SSc).

Methods

The effects of dersimelagon phosphoric acid (MT-7117) on skin fibrosis and lung inflammation were evaluated in bleomycin (BLM)-induced SSc murine models that were optimized for prophylactic and therapeutic evaluation. Microarray-based gene expression analysis and serum protein profiling were performed in the BLM-induced SSc models. The effect of MT-7117 on transforming growth factor-β (TGF-β)-induced activation of human dermal fibroblasts was evaluated in vitro. Immunohistochemical analyses of MC1R expression in the skin of SSc patients were performed.

Results

Prophylactic treatment with MT-7117 (≥ 0.3 mg/kg/day p.o.) significantly inhibited skin fibrosis and lung inflammation, and therapeutic treatment with MT-7117 (≥ 3 mg/kg/day p.o.) significantly suppressed the development of skin fibrosis in the BLM-induced SSc models. Gene array analysis demonstrated that MT-7117 exerts an anti-inflammatory effect via suppression of the activation of inflammatory cells and inflammation-related signals; additionally, vascular dysfunction was extracted as the pathology targeted by MT-7117. Serum protein profiling revealed that multiple SSc-related biomarkers including P-selectin, osteoprotegerin, cystatin C, growth and differentiation factor-15, and S100A9 were suppressed by MT-7117. MT-7117 inhibited the activation of human dermal fibroblasts by suppressing TGF-β-induced ACTA2 (encoding α-smooth muscle actin) mRNA elevation. MC1R was expressed by monocytes/macrophages, neutrophils, blood vessels (endothelial cells), fibroblasts, and epidermis (keratinocytes) in the skin of SSc patients, suggesting that these MC1R-positive cells could be targets for MT-7117.

Conclusions

MT-7117 demonstrates disease-modifying effects in preclinical models of SSc. Investigations of its mechanism of action and target expression analyses indicate that MT-7117 exerts its positive effect by affecting inflammation, vascular dysfunction, and fibrosis, which are all key pathologies of SSc. The results of the present study suggest that MT-7117 is a potential therapeutic agent for SSc. A phase 2 clinical trial investigating the efficacy and tolerability of MT-7117 in patients with early, progressive diffuse cutaneous SSc is currently in progress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02899-3.

Melanogenic effect of dersimelagon (MT-7117), a novel oral melanocortin 1 receptor agonist

Background

The activation of melanocortin 1 receptor (MC1R) on melanocytes stimulates the production of eumelanin. A tridecapeptide α melanocyte‐stimulating hormone (αMSH) is known to induce skin pigmentation.

Objectives

We characterised the properties of a novel oral MC1R agonist dersimelagon (MT‐7117) with respect to its specific binding to MC1R, downstream signalling and eumelanin production in experimental models.

Methods

The competitive binding and production of intracellular cyclic adenosine 3′, 5′‐monophosphate in cells expressing recombinant melanocortin receptors were examined. A mouse melanoma cell line B16F1 was used for the evaluation of in vitro melanin production. The in vitro activity of MT‐7117 was determined with αMSH and [Nle⁴, D‐Phe⁷]‐αMSH (NDP‐αMSH) as reference comparators. The change of coat colour and skin pigmentation were evaluated after repeat administration of MT‐7117 by oral gavage to C57BL/6J‐A^y/+ mice and cynomolgus monkeys, respectively.

Results

MT‐7117 showed the highest affinity for human MC1R compared to the other melanocortin receptors evaluated and agonistic activity for human, cynomolgus monkey and mouse MC1R, with EC₅₀ values in the nanomolar range. In B16F1 cells, MT‐7117 increased melanin production in a concentration‐dependent manner. In vivo, MT‐7117 (≥0.3 mg/kg/day p.o.) significantly induced coat colour darkening in mice. MT‐7117 (≥1 mg/kg/day p.o.) induced significant skin pigmentation in monkeys and complete reversibility was observed after cessation of its administration.

Conclusions

MT‐7117 is a novel oral MC1R agonist that induces melanogenesis in vitro and in vivo, suggesting its potential application for the prevention of phototoxic reactions in patients with photodermatoses, such as erythropoietic protoporphyria and X‐linked protoporphyria.

Neuropeptide Cortistatin Regulates Dermal and Pulmonary Fibrosis in an Experimental Model of Systemic Sclerosis

INTRODUCTION

Scleroderma, or systemic sclerosis, is a complex connective tissue disorder characterized by autoimmunity, vasculopathy, and progressive fibrosis of the skin and internal organs. Because its aetiology is unknown, the identification of genes/factors involved in disease severity, differential clinical forms, and associated complications is critical for understanding its pathogenesis and designing novel treatments. Neuroendocrine mediators in the skin emerge as potential candidates. We investigated the role played by the neuropeptide cortistatin in a preclinical model of scleroderma.

METHODS

Dermal fibrosis was induced by repetitive intradermal injections of bleomycin in wild-type and cortistatin-deficient mice. The histopathological signs and expression of fibrotic markers were evaluated in the skin and lungs.

RESULTS

An inverse correlation between cortistatin levels and fibrogenic activation exists in the damaged skin and dermal fibroblasts. Bleomycin-challenged skin lesions of mice that are partially and totally deficient in cortistatin showed exacerbated histopathological signs of scleroderma, characterized by thicker and more fibrotic dermal layer, enlarged epidermis, and increased inflammatory infiltration in comparison to those of wild-type mice. Cortistatin deficiency enhanced dermal collagen deposits, connective tissue growth factor expression, loss of microvessels, and predisposition to suffer severe complications that co-occur with dermal exposition to bleomycin, including pulmonary fibrotic disease and increased mortality. Treatment with cortistatin mitigated these pathological processes.

DISCUSSION/CONCLUSION

We identify cortistatin as an endogenous break of skin inflammation and fibrosis. Deficiency in cortistatin could be a marker of poor prognosis of scleroderma and associated complications. Cortistatin-based therapies emerge as attractive candidates to treat severe forms of systemic sclerosis and to manage fibrosis-related side effects of bleomycin chemotherapy in oncologic patients.

MC1R Functions, Expression, and Implications for Targeted Therapy

The G protein-coupled MC1R is expressed in melanocytes and has a pivotal role in human skin pigmentation, with reduced function in human genetic variants exhibiting a red hair phenotype and increased melanoma predisposition. Beyond its role in pigmentation, MC1R is increasingly recognized as promoting UV-induced DNA damage repair. Consequently, there is mounting interest in targeting MC1R for therapeutic benefit. However, whether MC1R expression is restricted to melanocytes or is more widely expressed remains a matter of debate. In this paper, we review MC1R function and highlight that unbiased analysis suggests that its expression is restricted to melanocytes, granulocytes, and the brain.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Digital immunohistological dissection of immune privilege collapse in syringotropic autoimmune diseases: Implication for the pathogenesis

BACKGROUND

Syringotropic cell infiltration is a histological hallmark of some autoimmune diseases. However, its underlying mechanism remains unclear.

OBJECTIVES

To assess the immune privilege (IP) of the human sweat gland (SwG) in homeostasis and in syringotropic autoimmune diseases.

METHODS

We combined quantitative digital image microdissection with immunohistochemisty to analyze IP molecule expression in SwG of normal and diseased skin. The human skin organ culture model was used to examine the influence of proinflammatory conditions on IP in SwG.

RESULTS

In the normal subjects (n = 10), major histocompatibility complex (MHC) class І expression was significantly reduced in SwGs compared to the epidermis. In contrast, IP-guardians, macrophage migration inhibitory factor (MIF) and alpha-melanocyte stimulating hormone (α-MSH) were upregulated in SwGs. MHC class І was upregulated in whole SwGs in lupus erythematosus (LE; n = 7) and scleroderma/morphea (Scl; n = 9), whereas differential expression was noted only in the secretory portion in Sjögren's syndrome (SjS) (n = 4). MIF expression level inversely correlated with that of MHC class I in all samples tested, and downregulation of α-MSH was detected in LE SwGs alone. The severity of inflammatory changes and MIF and ⍺-MSH expression were inversely correlated in LE. CD200 expression was decreased exclusively in atrophic stage of Scl. In a human skin organ culture model, intratissue injection of interferon-gamma up-regulated MHC class I and downregulated MIF and α-MSH.

CONCLUSIONS

These findings indicate that SwGs enjoy IP. Dysregulated IP molecule expression may lead to SwG IP collapse and contribute to distinct inflammatory cell distribution in syringotropic autoimmune disorders.

Are melanocortin peptides future therapeutics for cutaneous wound healing?

Cutaneous wound healing is a complex process divided into different phases, that is an inflammatory, proliferative and remodelling phase. During these phases, a variety of resident skin cell types but also cells of the immune system orchestrate the healing process. In the last year, it has been shown that the majority of cutaneous cell types express the melanocortin 1 receptor (MC1R) that binds α-melanocyte-stimulating hormone (α-MSH) with high affinity and elicits pleiotropic biological effects, for example modulation of inflammation and immune responses, cytoprotection, antioxidative defense and collagen turnover. Truncated α-MSH peptides such as Lys-Pro-Val (KPV) as well as derivatives like Lys-d-Pro-Thr (KdPT), the latter containing the amino acid sequence 193-195 of interleukin-1β, have been found to possess anti-inflammatory effects but to lack the pigment-inducing activity of α-MSH. We propose here that such peptides are promising future candidates for the treatment of cutaneous wounds and skin ulcers. Experimental approaches in silico, in vitro, ex vivo and in animal models are outlined. This is followed by an unbiased discussion of the pro and contra arguments of such peptides as future candidates for the therapeutic management of cutaneous wounds and a review of the so-far available data on melanocortin peptides and derivatives in wound healing.

Widespread dynamic and pleiotropic expression of the melanocortin-1-receptor (MC1R) system is conserved across chick, mouse and human embryonic development

Background

MC1R, a G‐protein coupled receptor with high affinity for alpha‐melanocyte stimulating hormone (αMSH), modulates pigment production in melanocytes from many species and is associated with human melanoma risk. MC1R mutations affecting human skin and hair color also have pleiotropic effects on the immune response and analgesia. Variants affecting human pigmentation in utero alter the congenital phenotype of both oculocutaneous albinism and congenital melanocytic naevi, and have a possible effect on birthweight.

Methods and Results

By in situ hybridization, RT‐PCR and immunohistochemistry, we show that MC1R is widely expressed during human, chick and mouse embryonic and fetal stages in many somatic tissues, particularly in the musculoskeletal and nervous systems, and conserved across evolution in these three amniotes. Its dynamic pattern differs from that of TUBB3, a gene overlapping the same locus in humans and encoding class III β‐tubulin. The αMSH peptide and the transcript for its precursor, pro‐opiomelanocortin (POMC), are similarly present in numerous extra‐cutaneous tissues. MC1R genotyping of variants p.(V60M) and p.(R151C) was undertaken for 867 healthy children from the Avon Longitudinal Study of Parent and Children (ALSPAC) cohort, and birthweight modeled using multiple logistic regression analysis. A significant positive association initially found between R151C and birth weight, independent of known birth weight modifiers, was not reproduced when combined with data from an independent genome‐wide association study of 6,459 additional members of the same cohort.

Conclusions

These data clearly show a new and hitherto unsuspected role for MC1R in noncutaneous solid tissues before birth.

Multiplex serum protein analysis reveals potential mechanisms and markers of response to hyperimmune caprine serum in systemic sclerosis

Background

Hyperimmune caprine serum (HICS) is a novel biological therapy with potential benefit for skin in established diffuse cutaneous systemic sclerosis. Here we report multiplex protein analysis of blood samples from a placebo-controlled phase II clinical trial and explore mechanisms of action and markers of response.

Methods

Patients were treated with HICS (n = 10) or placebo (n = 10) over 26 weeks, with follow-up open-label treatment to 52 weeks in 14 patients. Serum or plasma samples at baseline, 26 and 52 weeks were analysed using multiplex or individual immunoassays for 41 proteins. Patterns of change were analysed by clustering using Netwalker 1.0, Pearson coefficient and significance analysis of microarrays (SAM) correction.

Results

Cluster analysis, SAM multiplex testing and paired comparison of individual analytes identified proteins that were upregulated or downregulated during treatment with HICS. There was upregulation of the hypothalamo-pituitary-adrenal axis after HICS treatment evidenced by increases in α-MSH and ACTH in cases treated with HICS. Interestingly, significant increase in PIIINP was associated with HICS treatment and improved MRSS suggesting that this may be a marker of extracellular matrix turnover. Other relevant factors reduced in HICS-treated patients compared with controls, although not reaching statistical significance included COMP, CCL2, IL6, TIMP2, Fractalkine and TGFβ1 levels.

Conclusions

Our results suggest mechanisms of action for HICS, including upregulation of α-MSH, that has been shown to be anti-fibrotic in preclinical models, and possible markers to be included in future trials targeting skin in diffuse cutaneous systemic sclerosis.

Trial registration

Eudract, No. 2007-003122-24. ClinTrials.gov, No. NCT00769028. Registered 7 October 2008.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1252-x) contains supplementary material, which is available to authorized users.

Skin fibrosis: Models and mechanisms

Matrix synthesis, deposition and remodeling are complex biological processes that are critical in development, maintenance of tissue homeostasis and repair of injured tissues. Disturbances in the regulation of these processes can result in severe pathological conditions which are associated with tissue fibrosis as e.g. in Scleroderma, cutaneous Graft-versus-Host-Disease, excessive scarring after trauma or carcinogenesis. Therefore, finding efficient treatments to limit skin fibrosis is of major clinical importance. However the pathogenesis underlying the development of tissue fibrosis is still not entirely resolved. In recent years progress has been made unraveling the complex cellular and molecular mechanisms that determine fibrosis. Here we provide an overview of established and more recently developed mouse models that can be used to investigate the mechanisms of skin fibrosis and to test potential therapeutic approaches.

Is Nox4 a key regulator of the activated state of fibroblasts in systemic sclerosis?

The family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases consists of phagocytic gp91(phox) and six-related isoforms. Recent evidence indicates that the NADPH oxidase isoform Nox4 controls vascular, renal and pulmonary injury. We propose that Nox4 is an intrinsic regulator of the activated state of dermal fibroblasts in systemic sclerosis (SSc). Profibrotic cytokines on the one hand and antifibrogenic factors such as α-melanocyte-stimulating hormone on the other hand may target Nox4 as an intracellular nodal point. Via increased or decreased generation of reactive oxygen species and/or hydrogen peroxide, Nox4 could orchestrate collagen synthesis, differentiation of dermal fibroblasts into a profibrotic myofibroblast phenotype and thus dermal fibrosis. Confirmation of this hypothesis will have important consequences in our understanding of the activated state of dermal fibroblasts in SSc. Based on the availability of clinically useful Nox4 inhibitors, novel antifibrotic therapies of SSc can be envisioned.

Oligosaccharide modification by N-acetylglucosaminyltransferase-V in macrophages are involved in pathogenesis of bleomycin-induced scleroderma

Oligosaccharide modification by N-acetylglucosaminyltransferase-V (GnT-V), which catalyses the formation of β1,6 GlcNAc (N-acetylglucosamine) branches on N-glycans, is associated with various pathologies, such as cancer metastasis, multiple sclerosis and liver fibrosis. In this study, we demonstrated the involvement of GnT-V in the pathophysiology of scleroderma. High expression of GnT-V was observed in infiltrating cells in skin section samples from systemic and localized patients with scleroderma. Most of the infiltrating cells were T cells and macrophages, most of which were CD163(+) M2 macrophages. To determine the role of GnT-V in scleroderma, we next investigated skin sclerosis in GnT-V knockout (MGAT5(-/-) ) mice. Expression of GnT-V was also elevated in bleomycin (BLM)-injected sclerotic skin, and MGAT5(-/-) mice were resistant to BLM-induced skin sclerosis with reduced collagen type 1 α1 content, suggesting the biological significance of GnT-V in skin sclerosis. Furthermore, the number of CD163(+) M2 macrophages and CD3-positive T cells in BLM-induced skin sclerosis was significantly fewer in MGAT5(-/-) mice. In bone marrow-derived macrophages (BMDMs), IL-4-induced expressions of Fizz1 and Ym1 were significantly reduced in MGAT5(-/-) mice-derived BMDMs. Taken together, these results suggest the induction of GnT-V in skin sclerosis progression is possibly dependent on increased numbers of M2 macrophages in the skin, which are important for tissue fibrosis and remodelling.

Deficiency in Melanocortin 1 Receptor Signaling Predisposes to Vascular Endothelial Dysfunction and Increased Arterial Stiffness in Mice and Humans

Objective—

The melanocortin 1 receptor (MC1-R) is expressed by vascular endothelial cells and shown to enhance nitric oxide (NO) availability and vasodilator function on pharmacological stimulation. However, the physiological role of MC1-R in the endothelium and its contribution to vascular homeostasis remain unresolved. We investigated whether a lack of functional MC1-R signaling carries a phenotype with predisposition to vascular abnormalities.

Approach and Results—

Recessive yellow mice (MC1R e/e ), deficient in MC1-R signaling, and their wild-type littermates were studied for morphology and functional characteristics of the aorta. MC1R e/e mice showed increased collagen deposition and arterial stiffness accompanied by an elevation in pulse pressure. Contractile capacity and NO-dependent vasodilatation were impaired in the aorta of MC1R e/e mice supported by findings of decreased NO availability. These mice also displayed elevated levels of systemic and local cytokines. Exposing the mice to high-sodium diet or acute endotoxemia revealed increased susceptibility to inflammation-driven vascular dysfunction. Finally, we investigated whether a similar phenotype can be found in healthy human subjects carrying variant MC1-R alleles known to attenuate receptor function. In a longitudinal analysis of 2001 subjects with genotype and ultrasound data (The Cardiovascular Risk in Young Finns Study), weak MC1-R function was associated with lower flow-mediated dilatation response of the brachial artery and increased carotid artery stiffness.

Conclusions—

The present study demonstrates that deficiency in MC1-R signaling is associated with increased arterial stiffness and impairment in endothelium-dependent vasodilatation, suggesting a physiological role for MC1-R in the regulation of arterial tone.

Race and Melanocortin 1 Receptor Polymorphism R163Q Are Associated with Post-Burn Hypertrophic Scarring: A Prospective Cohort Study

The genetic determinants of post-burn hypertrophic scarring (HTS) are unknown, and melanocortin 1 receptor (MC1R) loss-of-function leads to fibrogenesis in experimental models. To examine the associations between self-identified race and MC1R single- nucleotide polymorphisms (SNPs) with severity of post-burn HTS, we conducted a prospective cohort study of burned adults admitted to our institution over 7 years. Subjects were evaluated using the Vancouver Scar Scale (VSS), asked to rate their itching, and genotyped for 8 MC1R SNPs. Testing for association with severe HTS (VSS>7) and itch severity (0-10) was based on multivariate regression with adjustment for known risk factors. Of 425 subjects analyzed, 77% identified as White. The prevalence of severe HTS (VSS>7) was 49%, and the mean itch score was 3.9. In multivariate analysis, Asian (prevalence ratio [PR] 1.54; 95% CI: 1.13-2.10), Black/African American (PR 1.86; 95% CI: 1.42-2.45), and Native American (PR 1.87; 95% CI: 1.48-2.35) race were independently associated with severe HTS. MC1R SNP R163Q was also significantly (P<0.001) associated with severe HTS. Asian race (linear regression coefficient 1.32; 95% CI: 0.23-2.40) but not MC1R SNP genotype was associated with increased itch score. We conclude that MC1R genotype may influence post-burn scarring.

Melanocortin 1 receptor and skin pathophysiology: beyond colour, much more than meets the eye

The melanocortin 1 receptor (MC1R), a G protein-coupled receptor preferentially expressed in melanocytes, mediates the pigmentary effects of α melanocyte-stimulating hormone (αMSH). MC1R is also expressed in other cutaneous cell types, particularly keratinocytes and dermal fibroblasts, suggesting non-pigmentary actions of the αMSH/MC1R system. Böhm and Stegemann now report a dramatic effect of mouse Mc1r functional status on susceptibility to skin fibrosis and collagen types I and III metabolism, in a study combining the powerful mouse model provided by the natural Mc1r(e/e) knockout and an established model of skin fibrosis. The study underscores the antifibrotic role for the skin αMSH/MC1R system.