Spatial and temporal localization of the melanocortin 1 receptor and its ligand α-melanocyte-stimulating hormone during cutaneous wound repair

The Effect of Fat Grafting on Scars Hyperpigmentation: A Systematic Review and Meta-Analysis

BACKGROUND

Hyperpigmented scars, particularly in exposed body areas, can be difficult to conceal and may evoke psychological distress. While the precise causes of scar dyschromia are not fully understood, alterations in melanogenic activity appear to hold more significance than changes in melanocyte quantity. Current treatments encompass laser interventions. However, it is essential to consider their costs and potential complications in relation to their limited proven effectiveness. Fat grafting has gained interest as a scar modulation technique due to its regenerative properties, and its efficacy in reducing scar hyperpigmentation is currently under investigation.

METHODS

A systematic review and meta-analysis was reported according to PRISMA guidelines. PubMed, Embase, and Cochrane Library databases were accessed. PROSPERO registration number is CRD42023457778. The primary outcome was a change in scar pigmentation after fat grafting. Pigmentation changes after fat grafting were calculated using the standardized mean difference (SMD) between baseline and postoperative scores according to POSAS and VSS scales. Bias assessment was conducted according to the National Institute for Health and Clinical Excellence quality assessment tool.

RESULTS

A total of 8 articles meeting inclusion and exclusion criteria were identified, involving 323 patients with hyperpigmented scars treated with fat grafting. A significant difference in scar pigmentation was noted after treatment with fat grafting according to observers' ratings, with a SMD of - 1.09 [95% CI: - 1.32; - 0.85], p<0.01. The SMD for patient-reported scar pigmentation after treatment with fat grafting was - 0.99 [96% CI: - 1.31; - 0.66], p<0.01. Four studies provided objective measurements of melanin changes after fat grafting and revealed inconsistent findings compared to subjective observations.

CONCLUSIONS

Fat grafting shows promise in ameliorating hyperpigmented scars based on subjective assessments, but further corroborating evidence from objective measures is required.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

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.

Pro-resolving and anti-arthritic properties of the MC1 selective agonist PL8177

Background

Melanocortins are peptides endowed with anti-inflammatory and pro-resolving activities. Many of these effects are mediated by the Melanocortin receptor 1 (MC₁) as reported in several experimental settings. As such, MC₁ can be a viable target for the development of new therapies that mimic endogenous pro-resolving mediators. The aim of this study was to assess the immunopharmacology of a selective MC₁ agonist (PL8177) in vitro and in a mouse model of inflammatory arthritis.

Methods

PL8177 and the natural agonist αMSH were tested for activation of mouse and human Melanocortin receptors (MC_1,3,4,5), monitoring cAMP accumulation and ERK1/2 phosphorylation, using transiently transfected HEK293A cells. The anti-inflammatory and pro-resolving effects of PL8177 and αMSH were evaluated using mouse peritoneal Macrophages. Finally, a model of K/BxN serum transfer induced arthritis was used to determine the in vivo potential of PL8177.

Results

PL8177 activates mouse and human MC₁ with apparent EC₅₀ values of 0.01 and 1.49 nM, respectively, using the cAMP accumulation assay. Similar profiles were observed for the induction of ERK phosphorylation (EC₅₀: 0.05 and 1.39 nM). PL8177 displays pro-resolving activity (enhanced Macrophage efferocytosis) and counteracts the inflammatory profile of zymosan-stimulated macrophages, reducing the release of IL-1β, IL-6, TNF-α and CCL-2. In the context of joint inflammation, PL8177 (3mg/kg i.p.) reduces clinical score, paw swelling and incidence of severe disease as well as the recruitment of immune cells into the arthritic joint.

Conclusion

These results demonstrate that the MC₁ agonism with PL8177 affords therapeutic effects in inflammatory conditions including arthritis.

Significance

Drugs targeting the Melanocortin system have emerged as promising therapeutics for several conditions including inflammation or obesity. Multiple candidates are under clinical development, and some have already reached approval. Here we present the characterization of a novel drug candidate, PL8177, selective for the Melanocortin 1 receptor (MC₁), demonstrating its selectivity profile on cAMP and ERK1/2 phosphorylation signaling pathways, of relevance as selective drugs will translate into lesser off-target effect. PL8177 also demonstrated, not only anti-inflammatory activity, but pro-resolving actions due to its ability to enhance efferocytosis (i.e. the phagocytosis of apoptotic cells), endowing this molecule with therapeutic advantages compared to classical anti-inflammatory drugs. Using a mouse model of inflammatory arthritis, the compound demonstrated in vivo efficacy by reducing clinical score, paw swelling and overall disease severity. Taken together, these results present Melanocortin-based therapies, and specifically targeting MC₁ receptor, as a promising strategy to manage chronic inflammatory diseases.

The Local Neuropeptide System of Keratinocytes

Neuropeptides have been known for over 50 years as chemical signals in the brain. However, it is now well established that the synthesis of this class of peptides is not restricted to neurons. For example, human skin not only expresses several functional receptors for neuropeptides but, also, can serve as a local source of neuroactive molecules such as corticotropin-releasing hormone, melanocortins, and β-endorphin. In contrast, an equivalent of the hypothalamic-pituitary axis in the oral mucosa has not been well characterized to date. In view of the differences in the morphology and function of oral mucosal and skin cells, in this review I surveyed the existing evidence for a local synthesis of hypothalamic-pituitary, opiate, neurohypophyseal, and neuroendocrine neuropeptides in both epidermal and oral keratinocytes.

Cutaneous innervation in impaired diabetic wound healing

Type 2 diabetes is associated with several potential comorbidities, among them impaired wound healing, chronic ulcerations, and the requirement for lower extremity amputation. Disease-associated abnormal cellular responses, infection, immunological and microvascular dysfunction, and peripheral neuropathy are implicated in the pathogenesis of the wound healing impairment and the diabetic foot ulcer. The skin houses a dense network of sensory nerve afferents and nerve-derived modulators, which communicate with epidermal keratinocytes and dermal fibroblasts bidirectionally to effect normal wound healing after trauma. However, the mechanisms through which cutaneous innervation modulates wound healing are poorly understood, especially in humans. Better understanding of these mechanisms may provide the basis for targeted treatments for chronic diabetic wounds. This review provides an overview of wound healing pathophysiology with a focus on neural involvement in normal and diabetic wound healing, as well as future therapeutic perspectives to address the unmet needs of diabetic patients with chronic wounds.

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.

Hypertrophic Scarring: Current Knowledge of Predisposing Factors, Cellular and Molecular Mechanisms

Hypertrophic scarring (HSc) is an age-old problem that still affects millions of people physically, psychologically, and economically. Despite advances in surgical techniques and wound care, prevention and treatment of HSc remains a challenge. Elucidation of factors involved in the development of this common fibroproliferative disorder is crucial for further progress in preventive and/or therapeutic measures. Our knowledge about pathophysiology of HSc at the cellular and molecular level has grown considerably in recent decades. In this article, current knowledge of predisposing factors and the cellular and molecular mechanisms of HSc has been reviewed.

Translational Neuroendocrinology of Human Skin: Concepts and Perspectives

Human skin responds to numerous neurohormones, neuropeptides, and neurotransmitters that reach it via the vasculature or skin nerves, and/or are generated intracutaneously, thus acting in a para- and autocrine manner. This review focuses on how neurohormones impact on human skin physiology and pathology. We highlight basic concepts, major open questions, and translational research perspectives in cutaneous neuroendocrinology and argue that greater emphasis on neuroendocrine human skin research will foster the development of novel dermatological therapies. Furthermore, human skin and its appendages can be used as highly accessible and clinically relevant model systems for probing nonclassical, ancestral neurohormone functions. This calls for close interdisciplinary collaboration between dermatologists, skin biologists, neuroendocrinologists, and neuropharmacologists.

Autonomic nerve dysfunction and impaired diabetic wound healing: The role of neuropeptides

Lower extremity ulcerations represent a major complication in diabetes mellitus and involve multiple physiological factors that lead to impairment of wound healing. Neuropeptides are neuromodulators implicated in various processes including diabetic wound healing. Diabetes causes autonomic and small sensory nerve fibers neuropathy as well as inflammatory dysregulation, which manifest with decreased neuropeptide expression and a disproportion in pro- and anti- inflammatory cytokine response. Therefore to fully understand the contribution of autonomic nerve dysfunction in diabetic wound healing it is crucial to explore the implication of neuropeptides. Here, we will discuss recent studies elucidating the role of specific neuropeptides in wound healing.

Activation of Resolution Pathways to Prevent and Fight Chronic Inflammation: Lessons From Asthma and Inflammatory Bowel Disease

Formerly considered as a passive process, the resolution of acute inflammation is now recognized as an active host response, with a cascade of coordinated cellular and molecular events that promotes termination of the inflammatory response and initiates tissue repair and healing. In a state of immune fitness, the resolution of inflammation is contained in time and space enabling the restoration of tissue homeostasis. There is increasing evidence that poor and/or inappropriate resolution of inflammation participates in the pathogenesis of chronic inflammatory diseases, extending in time the actions of pro-inflammatory mechanisms, and responsible in the long run for excessive tissue damage and pathology. In this review, we will focus on how resolution can be the target for therapy in "Th1/Th17 cell-driven" immune diseases and "Th2 cell-driven" immune diseases, with inflammatory bowel diseases (IBD) and asthma, as relevant examples. We describe the main cells and mediators stimulating the resolution of inflammation and discuss how pharmacological and dietary interventions but also life style factors, physical and psychological conditions, might influence the resolution phase. A better understanding of the impact of endogenous and exogenous factors on the resolution of inflammation might open a whole area in the development of personalized therapies in non-resolving chronic inflammatory diseases.

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.

The Role of Immature and Mature Adipocytes in Hair Cycling

Hair follicles (HFs) strongly interact with adipocytes within the dermal white adipose tissue (dWAT), suggesting a strong physiological dependence on the content of immature and mature adipocytes in this layer. This content is regulated by the proliferation and differentiation of adipocyte precursors, as well as by dedifferentiation of mature existing adipocytes. Spatially, long-range interactions between HFs and dWAT involve the exchange of extracellular vesicles which are differentially released by precursors, preadipocytes, and mature adipocytes. Different exogenous factors, including light irradiation, are likely to modify the release of adipocyte-derived exosomes in dWAT, which can lead to aberrations of the HF cycle. Consequently, dWAT should be considered as a potential target for the modulation of hair growth.

MC1R gene polymorphisms are associated with dysfunctional immune responses and wound infection after burn injury

BACKGROUND

Systemic inflammatory response syndrome (SIRS) is associated with organ failure and infectious complications after major burn injury. Recent evidence has linked melanocortin signaling to anti-inflammatory and wound-repair functions, with mutations in the melanocortin 1 receptor (MC1R) gene leading to increased inflammatory responses. Our group has previously demonstrated that MC1R gene polymorphisms are associated with postburn hypertrophic scarring. Thus, we hypothesized that MC1R single nucleotide polymorphisms (SNPs) would be associated with increased burn-induced SIRS and increased infectious complications.

METHODS

We performed a retrospective cohort study of adults (>18 y of age) admitted to our burn center with >20% total body surface area (TBSA) partial/full thickness burns between 2006 and 2013. We screened for five MC1R SNPs (V60L, V92M, R151C, R163Q, T314T) by polymerase chain reaction from genomic DNA isolated from blood samples. We performed a detailed review of each patient chart to identify age, sex, race, ethnicity, %TBSA burned, burn wound infections (BWIs), and 72-hr intravenous fluid volume, the latter a surrogate for a dysfunctional inflammatory response to injury. Association testing was based on multivariable regression.

RESULTS

Of 106 subjects enrolled, 82 had complete data for analysis. Of these, 64 (78%) were male, with a median age of 39 and median burn size of 30% TBSA. A total of 36 (44%) subjects developed BWIs. The median total administered IV crystalloid in first 72h was 24.6 L. In multivariate analysis, the R151C variant allele was a significant independent risk factor for BWI (adjusted prevalence ratio 2.03; 95% CI: 1.21-3.39; P = 0.007), and the V60L variant allele was independently associated with increased resuscitation fluid volume (P = 0.021).

CONCLUSIONS

This is the first study to demonstrate a significant association between genetic polymorphisms and a nonfatal burn-induced SIRS complication. Our findings suggest that MC1R polymorphisms contribute to dysfunctional responses to burn injury that may predict infectious and inflammatory complications.

Breast cancer recurrence after reconstruction: know thine enemy

Breast reconstruction proceeding cancer treatment carries risk, regardless of the type of surgery. From fat grafting, to flap placement, to implants, there is no guarantee that reconstruction will not stimulate breast cancer recurrence. Research in this field is clearly divided into two parts: scientific interventional studies and clinical retrospective evidence. The reconstructive procedure offers hypoxia, a wound microenvironment, bacterial load, adipose derived stem cells; agents shown experimentally to cause increased cancer cell activity. This is compelling scientific evidence which serves to bring uncertainty and fear to the reconstructive procedure. In the absence of clinical evidence, this laboratory literature landscape is now informing surgical choices. Curiously, clinical studies have not shown a clear link between breast cancer recurrence and reconstructive surgery. Where does that leave us? This review aims to analyze the science and the surgery, thereby understanding the oncological fear which accompanies breast cancer reconstruction.

The molecular pathogenesis of morphoea: from genetics to future treatment targets

A number of immunoinflammatory and profibrotic mechanisms are recognized in the pathogenesis of broad sclerotic skin processes and, more specifically, morphoea. However, the precise aetiopathogenesis is complex and remains unclear. Morphoea is clinically heterogeneous, with variable anatomical patterning, depth of tissue involvement and sclerotic, inflammatory, atrophic and dyspigmented morphology. Underlying mechanisms determining these reproducible clinical subsets are poorly understood but of great clinical and therapeutic relevance. Regional susceptibility mechanisms (e.g. environmental triggers, mosaicism and positional identity) together with distinct pathogenic determinants (including innate, adaptive and imbalanced pro- and antifibrotic signalling pathways) are likely implicated. In the age of genetic profiling and personalized medicine, improved characterization of the environmental, systemic, local, genetic and immunopathological factors underpinning morphoea pathogenesis may open the door to novel targeted therapeutic approaches.

Immune resolution mechanisms in inflammatory arthritis

The past two decades have witnessed major advancements in the clinical management of inflammatory arthritis, with new treatment strategies in some cases providing a marked improvement in patient outcomes. However, it is widely accepted that current strategies do not provide the 'total therapeutic solution', in view of the proportion of patients who do not respond to therapy, the important incidence of adverse effects and the development of an immune response against antibodies or fusion proteins used therapeutically. Moreover, although some therapeutic approaches can effectively bring about an end to inflammation, mechanisms to promote the recovery and/or repair of damage are required. Harnessing the concepts and mechanisms of the resolution of inflammation is a new approach to the treatment of inflammatory pathologies; this approach could help address the unmet need for new therapeutic approaches that not only control but also revert the course of inflammatory rheumatic diseases.

α-MSH modulates cell adhesion and inflammatory responses of synovial fibroblasts from osteoarthritis patients

INTRODUCTION

The synovium is a target for neuropeptides. Melanocortins have attained particular attention as they elicit antiinflammatory effects. Although synovial fluid from patients with rheumatic diseases contains α-melanocyte-stimulating hormone (α-MSH) it is unknown whether synovial fibroblasts generate α-MSH and respond to melanocortins.

METHODS

Synovial tissue was obtained from osteoarthritis (OA) patients. Cells were isolated and prepared either as primary mixed synoviocytes or propagated as synovial fibroblasts (OASFs). Melanocortin receptor (MC) and proopiomelanocortin (POMC) expression were investigated by endpoint RT-PCR, immunofluorescence and Western immunoblotting. Functional coupling of MC1 was assessed by cAMP and Ca(2+) assays. Cell adhesion was monitored by the xCELLigence system. Secretion of α-MSH, tumour necrosis factor (TNF), interleukin (IL)-6 and IL-8 was determined by ELISA.

RESULTS

OASFs in vitro expressed MC1. MC1 transcripts were present in synovial tissue and appropriate immunoreactivity was detected in synovial fibroblasts in situ. OASFs contained truncated POMC transcripts but neither full-length POMC mRNA, POMC protein nor α-MSH were detectable. In accordance with this only truncated POMC transcripts were present in synovial tissue. α-MSH increased cAMP dose-dependently but did not alter calcium in OASFs. α-MSH also enhanced adhesion of OASFs to fibronectin and reduced TNF, IL-6 and IL-8 secretion in primary mixed synoviocyte cultures. In OASFs, α-MSH modulated basal and TNF/IL-1β-mediated secretion of IL-6 and IL-8.

CONCLUSION

Synovial fibroblasts express MC1in vitro and in situ. α-MSH elicits biological effects in these cells suggesting an endogenous immunomodulatory role of melanocortins within the synovium. Our results encourage in vivo studies with melanocortins in OA models.

Targeted metabolic profiling of wounds in diabetic and nondiabetic mice

While cellular metabolism is known to regulate a number of key biological processes such as cell growth and proliferation, its role in wound healing is unknown. We hypothesized that cutaneous injury would induce significant metabolic changes and that the impaired wound healing seen in diabetes would be associated with a dysfunctional metabolic response to injury. We used a targeted metabolomics approach to characterize the metabolic profile of uninjured skin and full-thickness wounds at day 7 postinjury in nondiabetic (db/-) and diabetic (db/db) mice. By liquid chromatography mass spectrometry, we identified 129 metabolites among all tissue samples. Principal component analysis demonstrated that uninjured skin and wounds have distinct metabolic profiles and that diabetes alters the metabolic profile of both uninjured skin and wounds. Examining individual metabolites, we identified 62 with a significantly altered response to injury in the diabetic mice, with many of these, including glycine, kynurenate, and OH-phenylpyruvate, implicated in wound healing for the first time. Thus, we report the first comprehensive analysis of wound metabolic profiles, and our results highlight the potential for metabolomics to identify novel biomarkers and therapeutic targets for improved wound healing outcomes.

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.

Melanocortin peptides: potential targets in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease resulting in loss of self-tolerance with multiple organs, such as the kidney, skin, joints, and the central nervous system (CNS), being targeted. Numerous immunosuppressant therapies are currently being used for the treatment of SLE, but their clinical utility is somewhat variable because of the clinical heterogeneity. Melanocortins are a family of peptides derived from the common precursor protein pro-opiomelanocortin. These multifunctional peptides activate five subtypes of melanocortin receptors expressed on immune, skin, muscle, bone, and kidney cells and cells within the CNS. Melanocortin peptides have demonstrated a variety of biologic actions including immunomodulation, melanogenesis, and renoprotection. This review aims to introduce the melanocortin system and explore the mechanisms by which they may be beneficial in diseases such as SLE.

Active Nanofibrous Membrane Effects on Gingival Cell Inflammatory Response

Alpha-melanocyte stimulating hormone (α-MSH) is involved in normal skin wound healing and also has anti-inflammatory properties. The association of α-MSH to polyelectrolyte layers with various supports has been shown to improve these anti-inflammatory properties. This study aimed to evaluate the effects of nanofibrous membrane functionalized with α-MSH linked to polyelectrolyte layers on gingival cell inflammatory response. Human oral epithelial cells (EC) and fibroblasts (FB) were cultured on plastic or electrospun Poly-#-caprolactone (PCL) membranes with α-MSH covalently coupled to Poly-L-glutamic acid (PGA-α-MSH), for 6 to 24 h. Cells were incubated with or without Porphyromonas gingivalis lipopolysaccharide (Pg-LPS). Cell proliferation and migration were determined using AlamarBlue test and scratch assay. Expression of interleukin-6 (IL-6), tumor necrosis factor (TNF-α), and transforming growth factor-beta (TGF-β) was evaluated using RT-qPCR method. Cell cultures on plastic showed that PGA-α-MSH reduced EC and FB migration and decreased IL-6 and TGF-β expression in Pg-LPS stimulated EC. PGA-α-MSH functionalized PCL membranes reduced proliferation of Pg-LPS stimulated EC and FB. A significant decrease of IL-6, TNF-α, and TGF-β expression was also observed in Pg-LPS stimulated EC and FB. This study showed that the functionalization of nanofibrous PCL membranes efficiently amplified the anti-inflammatory effect of PGA-α-MSH on gingival cells.

A multimodal assessment of melanin and melanocyte activity in abnormally pigmented hypertrophic scar

Using a validated swine model of human scar formation, hyperpigmented and hypopigmented scar samples were examined for their histological and optical properties to help elucidate the mechanisms and characteristics of dyspigmentation. Full-thickness wounds were created on the flanks of red Duroc pigs and allowed to heal. Biopsies from areas of hyperpigmentation, hypopigmentation, and uninjured tissue were fixed and embedded for histological examination using Azure B and primary antibodies to S100B, HMB45, and α-melanocyte-stimulating hormone (α-MSH). Spatial frequency domain imaging (SFDI) was then used to examine the optical properties of scars. Hyperpigmentation was first noticeable in healing wounds around weeks 2 to 3, gradually becoming darker. There was no significant difference in S100B staining for the presence of melanocytes between hyperpigmented and hypopigmented scar samples. Azure B staining of melanin was significantly greater in histological sections from hyperpigmented areas than in sections from both uninjured skin and hypopigmented scar (P < .0001). There was significantly greater staining for α-MSH in hyperpigmented samples compared with hypopigmented samples (P = .0121), and HMB45 staining was positive for melanocytes in hyperpigmented scar. SFDI at a wavelength of 632 nm resulted in an absorption coefficient map correlating with visibly hyperpigmented areas of scars. In a red Duroc model of hypertrophic scar formation, melanocyte number is similar in hyperpigmented and hypopigmented tissues. Hyperpigmented tissues, however, show a greater amount of melanin and α-MSH, along with immunohistochemical evidence of stimulated melanocytes. These observations encourage further investigation of melanocyte stimulation and the inflammatory environment within a wound that may influence melanocyte activity. Additionally, SFDI can be used to identify areas of melanin content in mature, pigmented scars, which may lead to its usefulness in wounds at earlier time points before markedly apparent pigmentation abnormalities.

Race Does Not Predict Melanocyte Heterogeneous Responses to Dermal Fibroblast-Derived Mediators

Introduction

Abnormal pigmentation following cutaneous injury causes significant patient distress and represents a barrier to recovery. Wound depth and patient characteristics influence scar pigmentation. However, we know little about the pathophysiology leading to hyperpigmentation in healed shallow wounds and hypopigmentation in deep dermal wound scars. We sought to determine whether dermal fibroblast signaling influences melanocyte responses.

Methods and Materials

Epidermal melanocytes from three Caucasians and three African-Americans were genotyped for single nucleotide polymorphisms (SNPs) across the entire genome. Melanocyte genetic profiles were determined using principal component analysis. We assessed melanocyte phenotype and gene expression in response to dermal fibroblast-conditioned medium and determined potential mesenchymal mediators by proteome profiling the fibroblast-conditioned medium.

Results

Six melanocyte samples demonstrated significant variability in phenotype and gene expression at baseline and in response to fibroblast-conditioned medium. Genetic profiling for SNPs in receptors for 13 identified soluble fibroblast-secreted mediators demonstrated considerable heterogeneity, potentially explaining the variable melanocyte responses to fibroblast-conditioned medium.

Discussion

Our data suggest that melanocytes respond to dermal fibroblast-derived mediators independent of keratinocytes and raise the possibility that mesenchymal-epidermal interactions influence skin pigmentation during cutaneous scarring.

Gene Expression Variations of Red-White Skin Coloration in Common Carp (Cyprinus carpio)

Teleosts have more types of chromatophores than other vertebrates and the genetic basis for pigmentation is highly conserved among vertebrates. Therefore, teleosts are important models to study the mechanism of pigmentation. Although functional genes and genetic variations of pigmentation have been studied, the mechanisms of different skin coloration remains poorly understood. The koi strain of common carp has various colors and patterns, making it a good model for studying the genetic basis of pigmentation. We performed RNA-sequencing for red skin and white skin and identified 62 differentially expressed genes (DEGs). Most of them were validated with RT-qPCR. The up-regulated DEGs in red skin were enriched in Kupffer's vesicle development while the up-regulated DEGs in white skin were involved in cytoskeletal protein binding, sarcomere organization and glycogen phosphorylase activity. The distinct enriched activity might be associated with different structures and functions in erythrophores and iridophores. The DNA methylation levels of two selected DEGs inversely correlated with gene expression, indicating the participation of DNA methylation in the coloration. This expression characterization of red-white skin along with the accompanying transcriptome-wide expression data will be a useful resource for further studies of pigment cell biology.

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.

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

The melanocortin-1 receptor (MC1 ) binds α-melanocyte-stimulating hormone (α-MSH) with high affinity and has a physiological role in cutaneous melanin pigmentation. Previously, we reported that human dermal fibroblasts also express functional MC1 . α-MSH suppressed transforming growth factor-β1 - and bleomycin (BLM)-induced collagen synthesis in vitro and in vivo. Using MC1 signalling-deficient C57BL/6J-Mc1r(e/e) mice, we tested as to whether MC1 has a regulatory role on dermal collagen synthesis in the BLM model of scleroderma. Notably, mice with a C57BL/6J genetic background were previously shown to be BLM-non-susceptible. Interestingly, treatment of C57BL/6J-Mc1r(e/e) but not of C57BL/6J-wild-type mice with BLM increased cutaneous collagen type I content at RNA and protein level along with development of skin fibrosis. Cutaneous levels of connective tissue growth factor and monocyte chemotactic protein-1 were also increased in BLM-treated C57BL/6J-Mc1r(e/e) mice. Primary dermal fibroblasts from C57BL/6J-wt mice further expressed MC1 , suggesting that these cells are directly targeted by melanocortins to affect collagen production of the skin. Our findings support the concept that MC1 has an endogenous regulatory function in collagen synthesis and controls the extent of fibrotic stress responses of the skin.

ACTH: The forgotten therapy

Although anti-inflammatory drugs are among the most common class of marketed drugs, chronic inflammatory conditions such as rheumatoid arthritis, multiple sclerosis or inflammatory bowel disease still represent unmet needs. New first-in-class drugs might be discovered in the future but the repurpose and further development of old drugs also offers promise for these conditions. This is the case of the melanocortin adrenocorticotropin hormone, ACTH, used in patients since 1952 but regarded as the last therapeutic option when other medications, such as glucocorticoids, cannot be used. Better understanding on its physiological and pharmacological mechanisms of actions and new insights on melanocortin receptors biology have revived the interest on rescuing this old and effective drug. ACTH does not only induce cortisol production, as previously assumed, but it also exerts anti-inflammatory actions by targeting melanocortin receptors present on immune cells. The endogenous agonists for these receptors (ACTH, α-, β-, and γ-melanocyte stimulating hormones), are also produced locally by immune cells, indicating the existence of an endogenous anti-inflammatory tissue-protective circuit involving the melanocortin system. These findings suggested that new ACTH-like melanocortin drugs devoid of steroidogenic actions, and hence side effects, could be developed. This review summarizes the actions of ACTH and melanocortin drugs, their role as endogenous pro-resolving mediators, their current clinical use and provides an overview on how recent advances on GPCR functioning may lead to a novel class of drugs.

Improved cutaneous wound healing after intraperitoneal injection of alpha-melanocyte-stimulating hormone

Skin wound healing is a complex process involving many types of cells and molecules and often results in scar tissue formation in adult mammals. However, scarless healing occurs in foetal skin and minimal scars may occur after cutaneous healing in the adult with reduced inflammation. Alpha-melanocyte-stimulating hormone (α-MSH) is widely distributed within the central nervous system and in other body regions, such as the skin, and has strong anti-inflammatory activity. The aim in the present experiments was to learn whether intraperitoneal (i.p) injection of α-MSH just before skin wounds antagonize inflammation and improves skin wound healing in adult mice. C57BL/6 young adult mice received an i.p. injection of 1 mg/kg of α-MSH and, 30 min later, two circular through-and-through holes (6.5 mm diameter) were made in their dorsal skin under anaesthesia. Control mice were wounded after vehicle injection. The wound healing process was analysed macroscopically and microscopically at 3, 7, 40 and 60 days. Skin samples were fixed in formalin, embedded in paraffin, sectioned at 5 μm, stained with H&E or toluidine blue for cell analysis or Gomori's trichrome for extracellular matrix (ECM) analysis. Other samples were fixed in DMSO+methanol, embedded in paraplast and incubated with anti-CD45, antismooth muscle actin, anticollagen-I and anticollagen-III for immunofluorescence analysis. Alpha-MSH significantly reduced the number of leucocytes, mast cells and fibroblasts at 3 and 7 days after injury. On days 40 and 60, α-MSH reduced scar area and improved the organization of the collagen fibres indicating that it may direct the healing into a more-regenerative/less-scarring pathway.

Insufficient expression of the melanocortin-1 receptor by human dermal fibroblasts contributes to excess collagen synthesis in keloid scars

Activation of the α-melanocyte-stimulating hormone (αMSH)/melanocortin-1 receptor (MC1R) signalling pathway exerts antagonistic actions on cutaneous inflammatory and fibrogenic responses in addition to promoting pigment production. Herein, the expression of MC1R by keloid-derived fibroblasts and keloid scar tissue was investigated using a range of techniques. MC1R mRNA expression levels in five different keloid fibroblast cell lines were significantly reduced to less than half compared with five normal fibroblast cell lines (P < 0.05). Immunohistological analysis of tissue samples indicated that MCR1 immunoreactivity in both epidermal and dermal compartments of five keloid tissue samples was dramatically decreased compared with normal skin (P < 0.05). Insufficient expression of MC1R on human dermal fibroblasts might abolish the αMSH-mediated suppression of collagen production and myofibroblast transformation elicited by the profibrotic cytokine-transforming growth factor-β1. Restoration of reduced MC1R by dermal fibroblasts may lead to novel scar-reducing therapeutic approaches for treating this refractory fibrotic disease.

Resolution of inflammation: examples of peptidergic players and pathways

Appreciation for the resolution of inflammation has increased in recent years, with the detailing of specific mediators and pathways and the identification of (receptor) targets that could be exploited for innovative anti-inflammatory drug discovery programmes. Thus, acute inflammation resolves by the intervention of endogenous anti-inflammatory mediators that reduce white blood cell recruitment and promote removal of migrated leukocytes by apoptosis and phagocytosis by resident 'cleaners', such as the macrophages, resulting ultimately in the repair of the inflamed or injured tissue. Here, we explore a selection of pro-resolving proteinaceous mediators and targets, such as melanocortins and galectins.

MC1R, the cAMP pathway, and the response to solar UV: extending the horizon beyond pigmentation

The melanocortin 1 receptor (MC1R) is a G protein-coupled receptor crucial for the regulation of melanocyte proliferation and function. Upon binding melanocortins, MC1R activates several signaling cascades, notably the cAMP pathway leading to synthesis of photoprotective eumelanin. Polymorphisms in the MC1R gene are a major source of normal variation of human hair color and skin pigmentation, response to ultraviolet radiation (UVR), and skin cancer susceptibility. The identification of a surprisingly high number of MC1R natural variants strongly associated with pigmentary phenotypes and increased skin cancer risk has prompted research on the functional properties of the wild-type receptor and frequent mutant alleles. We summarize current knowledge on MC1R structural and functional properties, as well as on its intracellular trafficking and signaling. We also review the current knowledge about the function of MC1R as a skin cancer, particularly melanoma, susceptibility gene and how it modulates the response of melanocytes to UVR.

Malignant melanoma and melanocortin 1 receptor

The conventional chemotherapeutic treatment of malignant melanoma still remains poorly efficient in most cases. Thus the use of specific features of these tumors for development of new therapeutic modalities is highly needed. Melanocortin 1 receptor (MC1R) overexpression on the cell surface of the vast majority of human melanomas, making MC1R a valuable marker of these tumors, is one of these features. Naturally, MC1R plays a key role in skin protection against damaging ultraviolet radiation by regulating eumelanin production. MC1R activation is involved in regulation of melanocyte cell division. This article reviews the peculiarities of regulation and expression of MC1R, melanocytes, and melanoma cells, along with the possible connection of MC1R with signaling pathways regulating proliferation of tumor cells. MC1R is a cell surface endocytic receptor, thus considered perspective for diagnostics and targeted drug delivery. A number of new therapeutic approaches that utilize MC1R, including endoradiotherapy with Auger electron and α- and β-particle emitters, photodynamic therapy, and gene therapy are now being developed.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

Chondroprotective and anti-inflammatory role of melanocortin peptides in TNF-α activated human C-20/A4 chondrocytes

BACKGROUND AND PURPOSE

Melanocortin MC(1) and MC(3 ) receptors, mediate the anti-inflammatory effects of melanocortin peptides. Targeting these receptors could therefore lead to development of novel anti-inflammatory therapeutic agents. We investigated the expression of MC(1) and MC(3) receptors on chondrocytes and the role of α-melanocyte-stimulating hormone (α-MSH) and the selective MC(3) receptor agonist, [DTRP(8) ]-γ-MSH, in modulating production of inflammatory cytokines, tissue-destructive proteins and induction of apoptotic pathway(s) in the human chondrocytic C-20/A4 cells.

EXPERIMENTAL APPROACH

Effects of α-MSH, [DTRP(8) ]-γ-MSH alone or in the presence of the MC(3/4) receptor antagonist, SHU9119, on TNF-α induced release of pro-inflammatory cytokines, MMPs, apoptotic pathway(s) and cell death in C-20/A4 chondrocytes were investigated, along with their effect on the release of the anti-inflammatory cytokine IL-10.

KEY RESULTS

C-20/A4 chondrocytes expressed functionally active MC(1,3) receptors. α-MSH and [DTRP(8) ]-γ-MSH treatment, for 30 min before TNF-α stimulation, provided a time-and-bell-shaped concentration-dependent decrease in pro-inflammatory cytokines (IL-1β, IL-6 and IL-8) release and increased release of the chondroprotective and anti-inflammatory cytokine, IL-10, whilst decreasing expression of MMP1, MMP3, MMP13 genes.α-MSH and [DTRP(8) ]-γ-MSH treatment also inhibited TNF-α-induced caspase-3/7 activation and chondrocyte death. The effects of [DTRP(8) ]-γ-MSH, but not α-MSH, were abolished by the MC(3/4) receptor antagonist, SHU9119.

CONCLUSION AND IMPLICATIONS

Activation of MC(1) /MC(3) receptors in C-20/A4 chondrocytes down-regulated production of pro-inflammatory cytokines and cartilage-destroying proteinases, inhibited initiation of apoptotic pathways and promoted release of chondroprotective and anti-inflammatory cytokines. Developing small molecule agonists to MC(1) /MC(3) receptors could be a viable approach for developing chondroprotective and anti-inflammatory therapies in rheumatoid and osteoarthritis.

Bioactive oligopeptides in dermatology: Part I

Short sequence amino acids or oligopeptides represent a relatively new and promising area of dermatology. Oligopeptides are defined as peptide sequences ranging from 2 to 20 amino acids. This class of proteins includes potent biologically active compounds, which can modulate various cellular and molecular processes. The medical potential of short sequence peptides was initially characterized many decades ago with the identification of biological mediators such as angiotensin, vasopressin, oxytocin and bradykinin. However, the role of oligopeptides in affecting biological activity within the skin has only recently been explored. Currently, the dermatologic use of protein peptide fragments is a rapidly growing field of research. Recent studies suggest that treatment with various biologically active peptides can result in favourable clinical outcomes such as for the treatment of hyperpigmentation disorders with tyrosinase inhibitors and the use of collagen synthesis modulators to diminish skin laxity. In this review, we explore the roles of biologically active short sequence peptides as potential therapeutics through the modulation of collagen, elastin and melanin synthesis.

The impact of endogenous annexin A1 on glucocorticoid control of inflammatory arthritis

Objectives

To establish the role and effect of glucocorticoids and the endogenous annexin A1 (AnxA1) pathway in inflammatory arthritis.

Methods

Ankle joint mRNA and protein expression of AnxA1 and its receptors were analysed in naive and arthritic mice by real-time PCR and immunohistochemistry. Inflammatory arthritis was induced with the K/BxN arthritogenic serum in AnxA1^+/+ and AnxA1^−/− mice; in some experiments, animals were treated with dexamethasone (Dex) or with human recombinant AnxA1 or a protease-resistant mutant (termed SuperAnxA1). Readouts were arthritic score, disease incidence, paw oedema and histopathology, together with pro-inflammatory gene expression.

Results

All elements of the AnxA1 pathway could be detected in naive joints, with augmentation during ongoing disease, due to the infiltration of immune cells. No difference in arthritis intensity of profile could be observed between AnxA1^+/+ and AnxA1^−/− mice. Treatment of mice with Dex (10 µg intraperitoneally daily from day 2) afforded potent antiarthritic effects highly attenuated in the knockouts: macroscopic changes were mirrored by histopathological findings and pro-inflammatory gene (eg, Nos2) expression. Presence of proteinase 3 mRNA in the arthritic joints led the authors to test AnxA1 and the mutant SuperAnxA1 (1 µg intraperitoneally daily in both cases from day 2), with the latter one being able to accelerate the resolving phase of the disease.

Conclusion

AnxA1 is an endogenous determinant for the therapeutic efficacy of Dex in inflammatory arthritis. Such an effect can be partially mimicked by application of SuperAnxA1 which may represent the starting point for novel antiarthritic therapeutic strategies.