Propiomelanocortin (POMC) gene expression by normal skin and keloid fibroblasts in culture: modulation by cytokines

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.

Polycyclic aromatic hydrocarbons regulate the pigmentation pathway and induce DNA damage responses in keratinocytes, a process driven by systemic immunity

BACKGROUND

Urban pollution is correlated with an increased prevalence of skin pigmentation disorders, however the physiological processes underlying this association are unclear.

OBJECTIVES

To delineate the relationship between polycyclic aromatic hydrocarbons (PAHs), a key constituent of atmospheric pollution, and immunity/skin pigmentation pathways.

METHODS

We exposed peripheral blood mononuclear cells (PBMC) to PAHs and performed cytokines/chemokine profiling. We then examined the effect of immune activation on pigmentation by co-culturing PBMC and Benzo(a)pyrene (BaP) with reconstructed human pigmented epidermis (RHPE). To study the mechanism, we treated keratinocytes with conditioned medium from BaP-exposed PBMC and studied DNA damage responses, aryl hydrocarbon receptor (AhR) activation and pro-pigmentation factor, proopiomelanocortin (POMC) secretion.

RESULTS

PAHs induced up-regulation of inflammatory cytokines/chemokine in PBMC. Co-culturing of RHPE with PBMC+BaP resulted in increased melanin content and localization. BaP-conditioned medium significantly increased DNA damage, p53 stabilization, AhR activation and POMC secretion in keratinocytes. We found that IFNγ induced DNA damage, while TNFα and IL-8 potentiated POMC secretion in keratinocytes. Importantly, BaP-conditioned medium-induced DNA damage and POMC secretion is prevented by antioxidants vitamin E, vitamin C and sulforaphane, as well as the prototypical corticosteroid dexamethasone. Finally, vitamin C and sulforaphane enhanced the genome protective and depigmentation effects of dexamethasone, providing proof-of-concept for a combinatorial approach for the prevention and/or correction of PAH-induced pigment spots formation.

CONCLUSION

Our study reveals the importance of systemic immunity in regulating PAH-induced skin pigmentation, and provide a new keratinocyte DNA damage response mechanistic target for the prevention or reversal of pollution-associated skin pigmentation.

The Keloid Disorder: Heterogeneity, Histopathology, Mechanisms and Models

Keloids constitute an abnormal fibroproliferative wound healing response in which raised scar tissue grows excessively and invasively beyond the original wound borders. This review provides a comprehensive overview of several important themes in keloid research: namely keloid histopathology, heterogeneity, pathogenesis, and model systems. Although keloidal collagen versus nodules and α-SMA-immunoreactivity have been considered pathognomonic for keloids versus hypertrophic scars, conflicting results have been reported which will be discussed together with other histopathological keloid characteristics. Importantly, histopathological keloid abnormalities are also present in the keloid epidermis. Heterogeneity between and within keloids exists which is often not considered when interpreting results and may explain discrepancies between studies. At least two distinct keloid phenotypes exist, the superficial-spreading/flat keloids and the bulging/raised keloids. Within keloids, the periphery is often seen as the actively growing margin compared to the more quiescent center, although the opposite has also been reported. Interestingly, the normal skin directly surrounding keloids also shows partial keloid characteristics. Keloids are most likely to occur after an inciting stimulus such as (minor and disproportionate) dermal injury or an inflammatory process (environmental factors) at a keloid-prone anatomical site (topological factors) in a genetically predisposed individual (patient-related factors). The specific cellular abnormalities these various patient, topological and environmental factors generate to ultimately result in keloid scar formation are discussed. Existing keloid models can largely be divided into in vivo and in vitro systems including a number of subdivisions: human/animal, explant/culture, homotypic/heterotypic culture, direct/indirect co-culture, and 3D/monolayer culture. As skin physiology, immunology and wound healing is markedly different in animals and since keloids are exclusive to humans, there is a need for relevant human in vitro models. Of these, the direct co-culture systems that generate full thickness keloid equivalents appear the most promising and will be key to further advance keloid research on its pathogenesis and thereby ultimately advance keloid treatment. Finally, the recent change in keloid nomenclature will be discussed, which has moved away from identifying keloids solely as abnormal scars with a purely cosmetic association toward understanding keloids for the fibroproliferative disorder that they are.

New approach to the understanding of keloid: psychoneuroimmune-endocrine aspects

The skin is a dynamic and complex organ that relies on the interrelation among different cell types, macromolecules, and signaling pathways. Further, the skin has interactions with its own appendages and other organs such as the sebaceous glands and hair follicles, the kidney, and adrenal glands; systems such as the central nervous system; and axes such as the hypothalamic–pituitary–adrenal axis. These continuous connections give the skin its versatility, and when an injury is caused, some triggers start a cascade of events designed to restore its integrity. Nowadays, it is known that this psychoneuroimmune–endocrine intercommunication modulates both the homeostatic condition and the healing process. In this sense, the skin conditions before a trauma, whether of endogenous (acne) or exogenous origin (injury or surgical incision), could regulate the process of tissue repair. Most skin diseases such as psoriasis and atopic dermatitis, among others, have in their pathophysiology a psychogenic component that triggers integrated actions in the nervous, immune, and endocrine systems. However, fibroproliferative disorders of wound healing, such as hypertrophic scar and keloid, are not yet included in this listing, despite showing correlation with stress, especially with the psychosocial character. This review, by understanding the “brain–skin connection”, presents evidence that allows us to understand the keloid as a psychomediated disease.

Differential expression of proopiomelanocortin (POMC) transcriptional variants in human skin cells

The aims of this study were to examine content and expression level of proopiomelanocortin (POMC) mRNA variants in human dermal fibroblasts (HDF) as compared to primary keratinocytes and HaCaT cells of keratinocyte origin. Primary fibroblasts and keratinocytes were obtained from normal human foreskin. Full-length and total (i.e. the full-length, truncated and/or alternatively spliced) POMC mRNA in skin cells were determined by qRT-PCR using specific probes. The full-length POMC mRNA in HDF is neither constitutively expressed, nor could be induced by corticotropin releasing hormone (CRH) or cytokines interferon γ (IFN-γ) and transforming growth factor-β1 (TGF-β1). However, the truncated/alternatively spliced POMC mRNA variants are constitutively expressed in HDF and could be moderately increased with CRH and the cytokines. Primary keratinocytes, in addition to truncated/alternatively spliced POMC mRNA variants, also constitutively express full-length POMC mRNA, both being downregulated during in vitro culturing. Unlike primary keratinocytes, HaCaT cells, express only truncated/alternatively spliced POMC mRNA variants. The level of POMC mRNA expression in HaCaT cells was associated with differentiation stage, being higher in more differentiated cells. Thus, in this study we have shown for the first time that HDF do not express the full-length POMC mRNA, either constitutively or upon activation, opposing to primary keratinocytes which constitutively express the full-length POMC mRNA as a minor variant. Although expressing only truncated/alternatively spliced POMC mRNA variant, HDF express POMC peptide, showing that those transcriptional variants are translatable. Truncated/alternatively spliced POMC mRNA variants, expressed both in HDF and keratinocytes are subjected to regulation, implicating their functionality. Furthermore, the IFN-γ-induced up-regulation at transcriptional level was associated with increased level of POMC peptide detected in HDF lysates. Thus, data of this study have shown that HDF express only truncated/alternatively spliced POMC mRNA variants, which are probably biologically relevant as they could be translated to POMC peptide, both constitutively and upon activation.

Roles of Gr-1+ leukocytes in postincisional nociceptive sensitization and inflammation

BACKGROUND

Neutrophils are one of the predominant immune cells initially migrating to surgical wound edges. They produce mediators both associated with supporting (interleukin [IL]-1β, C5a) and reducing (opioid peptides) pain. Studies demonstrate neutrophil depletion/blockade reduces nociceptive sensitization after nerve injury and carrageenan administration, but enhance sensitization in complete Freund's adjuvant inflammation. This research identifies the contribution of infiltrating neutrophils to incisional pain and inflammation.

METHODS

Antibody-mediated Gr1 neutrophil depletion preceded hind paw incisions. Sensitization to mechanical and thermal stimuli, effects on edema and local levels of IL-1β and C5a were measured. Local effects of C5a or IL-1 receptor antagonists PMX-53 and anakinra on sensitization after neutrophil depletion were examined. Groups of 4-8 mice were used.

RESULTS

Anti-Gr1 antibody depleted more than 90% of circulating and infiltrating skin neutrophils after incision. Neutrophil depletion did not change magnitude or duration of mechanical hypersensitivity in incised mice. However, paw edema was significantly reduced and heat hypersensitivity was slightly increased in depleted animals. In depleted animals IL-1β levels were half of controls 24 h after incision, whereas C5a levels were increased in both. Prominent IL-1β immunohistochemical staining of epidermis was seen in both groups. PMX-53 and anakinra reduced incisional mechanical and heat nociceptive sensitization to the same extent, regardless of neutrophil depletion.

CONCLUSIONS

Neutrophil-derived IL-1β and C5a do not appear to contribute critically to peri-incisional nociceptive signaling. Other sources of mediators, such as epidermal cells, may need to be considered. Controlling inflammatory activation of resident cells in epidermis/deeper structures may show therapeutic efficacy in reducing pain from surgical incisions.

Feather follicles express two classes of pro-opiomelanocortin (POMC) mRNA using alternative promoters in chickens

Feather coloration in chickens mainly depends on melanin produced by melanocytes located in the feather follicles. The melanocortin 1 receptor (MC1R) on follicular melanocytes regulates melanin synthesis; however, the source of the melanocortins that interact with the receptors remains unclear. In this study, we examine the potential expression of melanocortins and characterize the mRNAs for the precursor pro-opiomelanocortin (POMC) in chicken feather follicles. Reverse transcription-polymerase chain reaction (RT-PCR) revealed the expression of mRNAs for POMC, prohormone convertase 1 (PC1) and PC2, and western blotting detected adrenocorticotropic hormone (ACTH)-related products of POMC processing in feather follicles, suggesting that melanocortins are produced locally in the tissues of chickens. A combination of 5'RACE (rapid amplification of cDNA 5' end), 3'RACE and RT-PCR analyzes identified two classes of POMC mRNA, class a and class b, which encode the same full-length POMC protein but have different non-coding leader exons. Class a mRNAs were expressed specifically in feather follicles, whereas class b mRNAs were expressed in the pituitary, hypothalamus, and various peripheral tissues that we examined. Within the feather follicles, the class a mRNAs were distributed in epidermal layers from middle to distal locations, whereas the class b mRNAs were mainly expressed in pulp at proximal locations. Our findings suggest that feather pigmentation is regulated by locally produced melanocortins, and indicate that the melanocortins encoded by the different classes of POMC mRNAs may play different intra-follicular roles in chickens. This is the first report that demonstrates alternative promoter usage generating different full-length POMC mRNAs in vertebrates.

Keloid scarring: bench and bedside

Wound healing is a fundamental complex-tissue reaction leading to skin reconstitution and thereby ensuring survival. While, fetal wounds heal without scarring, a normal "fine line" scar is the clinical outcome of an undisturbed wound healing in adults. Alterations in the orchestrated wound healing process result in hypertrophic or keloid scarring. Research in the past decades attempted to identify genetic, cellular, and molecular factors responsible for these alterations. These attempts lead to several new developments in treatments for keloids, such as, imiquimod, inhibition of transforming growth factor beta, and recombinant interleukin-10. The urgent need for better therapeutics is underlined by recent data substantiating an impaired quality of life in keloid and hypertrophic scar patients. Despite the increasing knowledge about the molecular regulation of scar formation no unifying theory explaining keloid development has been put forward until today. This review aims to give an overview about the genetic and molecular background of keloids and focus of the current research on keloid scarring with special emphasis on new forthcoming treatments. Clinical aspects and the spectrum of scarring are summarized.

Gene expression analysis of melanocortin system in vitiligo

BACKGROUND

The melanocortin system in the skin coordinates pigmentation and immune response and could be implicated in the pathogenesis of vitiligo.

OBJECTIVES

We aimed to analyze changes in expression of genes involved in skin pigmentation (melanocortin system and enzymes involved in melanin synthesis).

METHODS

With quantitative RT-PCR we measured the mRNA expression levels of eight genes from the melanocortin system and two enzymes involved in melanogenesis. RNA was extracted from both lesional and non-lesional skin of vitiligo patients and in non-sun-exposed skin of healthy subjects.

RESULTS

POMC (proopiomelanocortin) expression was lower in lesional skin compared to non-lesional skin. Expression of melanocortin receptors was increased in unaffected skin of vitiligo patients compared to healthy subjects and decreased in lesional skin compared to uninvolved skin of vitiligo patients, the differences were statistically significant in the cases of MC1R (melanocortin receptor 1) and MC4R (melanocortin receptor 4). TRP1 and DCT genes were down-regulated in lesional skin compared to non-lesional vitiligo skin or skin of healthy controls and up-regulated in uninvolved vitiligo skin compared to healthy control samples. In non-lesional skin, POMC expression was not elevated, possibly indicating that systemic influences are involved in up-regulation of MC receptor genes. Decreased expression of the analyzed genes in the lesional skin is not surprising, but statistically significant increased expression of studied genes in non-lesional skin from vitiligo patients is not described previously.

CONCLUSION

In our mind, up-regulation of melanocortin system in non-lesional skin could be systemic compensation to restore normal pigmentation in lesions.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Melanocyte stimulating hormone peptides inhibit TNF-alpha signaling in human dermal fibroblast cells

Alpha-melanocyte stimulating hormone (alpha-MSH) has been identified as a potent anti-inflammatory in various tissues including the skin. It has previously been shown in skin cell keratinocytes and melanocytes/melanoma cells that MSH peptides inhibit TNF-alpha stimulated NF-kappaB activity and intercellular adhesion molecule-1 (ICAM-1) upregulation. However, the precise anti-inflammatory role of MSH peptides in dermal fibroblasts is unclear. Some studies report on pro-inflammatory responses, while others on anti-inflammatory responses. The present study confirms MC1R expression in cultured human dermal fibroblasts and reports that the MSH peptides alpha-MSH and KP(-D-)V inhibit TNF-alpha stimulated NF-kappaB activity and ICAM-1 upregulation, consistent with an anti-inflammatory role. However, involvement of IkappaB-alpha regulation by either peptide was not confirmed, supporting a mechanism independent of the NF-kappaB inhibitor. In conclusion, alpha-MSH and KP(-D-)V peptides have an anti-inflammatory action on dermal fibroblast signaling by inhibiting the pro-inflammatory activity of TNF-alpha in vitro.

Epidemiology, aetiology and management of abnormal scarring: a review of the literature

Keloid and hypertrophic scars are the result of abnormal processes in scar formation. This paper reviews the literature and the many debates concerning the processes that cause abnormal scarring.

The keloid phenomenon: Progress toward a solution

For centuries, keloids have been an enigma and despite considerable research to unravel this phenomenon no universally accepted treatment protocol currently exists. Historically, the etiology of keloids has been hypothesized by multiple different theories; however, a more contemporary view postulates a multifactoral basis for this disorder involving nutritional, biochemical, immunological, and genetic factors that play a role in this abnormal wound healing. Critical to the process of preventing or managing keloids is the need to locally control fibroblasts and their activities at the wound site. In recent years, considerable evidence has accumulated demonstrating the importance of fatty acids and bioactive lipids in health and disease, especially those involving inflammatory disorders or immune dysfunction. If hypertrophic scarring and keloid formation can be argued to have significant inflammatory histories, then it is possible to postulate a role for lipids in their etiology and potentially in their treatment. This report briefly visits past views and theories on keloid formation and treatment, and offers a theoretical rationale for considering adjuvant fatty acid therapy for keloid management. Sufficient scientific evidence in support of fatty acid strategies for the prevention and treatment of keloids currently exists, which offer opportunities to bridge the gap between the laboratory and the clinic. The intent of this paper is to serve as a basic guideline for researchers, nutritionists, and clinicians interested in keloids and to propose new directions for keloid management.

Melanocortins in fibroblast biology--current update and future perspective for dermatology

The skin is a target organ and source for proopiomelanocortin (POMC)-derived peptides, such as alpha-melanocyte-stimulating hormone (alpha-MSH), which acts by binding to melanocortin receptors (MC-Rs). Recent progress in our understanding of the cutaneous POMC system has demonstrated that human dermal fibroblasts (HDFs) are a novel target for alpha-MSH. MC-1R is expressed by HDFs in vitro and in situ. MC-1R expression is also detectable in human connective tissue sheath fibroblasts (CTSFs) and in dermal papilla cells (DPCs) of the hair follicle, the latter concomitantly expressing MC-1R and MC-4R in vitro and in situ. Both HDFs and DPCs are capable of generating POMC-derived peptides, although cell-specific differences exist in the expression of prohormone convertases and the amounts of POMC-derived peptides generated. Functional studies have shown that alpha-MSH exerts anti-inflammatory actions in human fibroblastic skin cells by suppressing interleukin-1 (IL-1)-induced IL-8 production, activation of the transcription factor activator protein-1 (AP-1) and induction of intercellular adhesion molecule-1 by interferon-alpha. In addition, alpha-MSH antagonizes the effect of transforming growth factor-beta1 (TGF-beta1) on collagen synthesis in HDFs in vitro and exerts antifibrogenic activity in a mouse model of cutaneous fibrosis. These findings indicate that fibroblastic cells participate in the cutaneous POMC system in which alpha-MSH appears to act as a modulator of inflammatory and fibrogenic responses. The biological activities of alpha-MSH in fibroblastic cells of the skin point towards novel clues in our understanding of the pathophysiology of fibrotic skin disorders and inflammatory diseases of the hair follicle and, finally, suggest innovative therapeutic options for the treatment of these conditions.

The neuro-immuno-cutaneous-endocrine network: relationship between mind and skin

Brain-body(skin) influences are bi-directional and skin should be considered as an active neuro-immuno-endocrine interface, where effector molecules act as common words used in a dynamic dialogue between brain, immune-system and skin. It has been widely demonstrated that stimuli received in the skin can influence the immune, endocrine and nervous systems at both a local and central level. However, the brain can also modulate inflammatory conditions locally induced in the skin. It has been experimentally demonstrated that intracerebral administration of the tridecapeptide alpha-MSH or even its COOH-terminal tripeptide can in fact inhibit cutaneous inflammation induced by the application of topical irritants and intradermal injection of cytokines. The skin can therefore alter the pharmacology of the CNS by releasing large amounts of NPs which obviously do work locally in the skin and beyond the skin. Alpha-MSH may represent a key molecule for understanding this aspect of cutaneous-immune-neuro-endocrine-mental biological communication, being it is also generated in the skin. This molecule may in the future be used as a potent anti-inflammatory agent in clinical dermatology, and preclinical trials are presently in progress.

Neuromediators--a crucial component of the skin immune system

There is increasing evidence that the cutaneous nervous system modulates physiological and pathophysiological effects including cell growth and differentiation, immunity and inflammation as well as tissue repair. Both cutaneous nervous fibers and inflammatory cells are able to release neuromediators and thereby activate specific receptors on target cells in the skin or transient immunocompetent cells. Cutaneous neuromediators include classical neurotransmitters such as catecholamines and acetylcholine being released from the automatic nervous system or cutaneous cells. On the other hand neuropeptides including substance P, calcitonin gene related peptide (CRGP), vasointestinal peptide (VIP) or proopiomelanocortin (POMC) derived peptides such as alpha melanocyte stimulating hormone (alphaMSH) may be released from sensory or autonomic nerve fibers and several epidermal as well as dermal cells. Neuropeptides are known to activate a variety of cutaneous cells through high affinity neuropeptide receptors or by direct activation of intracellular G-protein signalling cascades. Via the modulation of transcription factor activation (NF-kappaB, AP-1, STAT-3) they regulate the expression of adhesion molecules and proinflammatory cytokines in different cells and thereby function as modulators of immune and inflammatory reactions. Accordingly, neuropeptides such as CGRP or alphaMSH in vitro were found to downregulate costimulatory molecule expression on dendritic cells and in vivo via the generation of suppressor T-lymphocytes to induce hapten specific tolerance. Proteinases such as tryptase or neural endopeptidase inactivate neuropeptides in the extracellular space or at the cell surface thereby terminating neuropeptide induced inflammatory or immune responses. Proteinase-activated receptors (PAR) are recently described receptors that may have high impact in regulating cutaneous neurogenic inflammation. In the skin PAR-2 being expressed on sensory neurons and endothelial cells is self activated by tethered peptide ligands that are exposed after extracellular amino-terminal cleavage by trypsin or mast cell tryptase. PAR-2 agonists were found to induce the release of CGRP and SP which mediate vasodilation, plasma extravasation as well as the expression of adhesion molecules on vascular endothelial cells and thus elicit neurogenic inflammation. These findings indicate that the neuromediator network including neuropeptide receptors as well as proteinases play an important role in the maintenance of tissue integrity and the regulation of inflammatory and immune responses in the skin.

Elevated stratum corneum hydrolytic activity in Netherton syndrome suggests an inhibitory regulation of desquamation by SPINK5-derived peptides

Netherton syndrome is a congenital ichthyosis associated with erythroderma, hair shaft defects, and atopic features. The mutations of the secretory serine protease inhibitor Kazal-type 5 gene have been identified in Netherton syndrome patients; however, the actual physiologic substrates of the serine protease inhibitor Kazal-type 5 proprotein are unknown, and how the genetic defects cause characteristic skin phenotype remains uncertain. Here, we describe the serine protease inhibitor Kazal-type 5 gene mutations, including two novel non-sense mutations, and genotype-phenotype correlation in three Netherton syndrome patients in two unrelated Japanese families. Furthermore, based on the reappraisal of the structure of the serine protease inhibitor Kazal-type 5 proprotein, demonstration of the presence of carboxypeptidase in normal keratinocytes, and the observation of mRNA localization of the serine protease inhibitor Kazal-type 5 transcripts in the uppermost epidermis as well as pilosebaceous units, we propose a hypothetical model of proteolytic processing of the serine protease inhibitor Kazal-type 5 proprotein in the epidermis and inhibitory regulation of corneocyte desquamation by a set of serine protease inhibitor Kazal-type 5-derived peptides. This hypothesis is supported by the marked increase of trypsin-like hydrolytic activity demonstrated in stratum corneum samples from our Netherton syndrome patients. The findings in this study suggest that the defective inhibitory regulation of desquamation due to the serine protease inhibitor Kazal-type 5 gene mutations may cause over-desquamation of corneocytes in Netherton syndrome, leading to severe skin permeability barrier dysfunction.

Human dermal fibroblasts express prohormone convertases 1 and 2 and produce proopiomelanocortin-derived peptides

In the last few years it has become apparent that the skin is a locoregional source for several proopiomelanocortin-derived peptides including alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. The enzymes that regulate expression of these neuropeptides are the prohormone convertases 1 and 2. In this study we demonstrate, by reverse transcriptase polymerase chain reaction and Western immunoblotting, that cultured human dermal fibroblasts express prohormone convertases 1 and 2 as well as 7B2, which is an essential cofactor for enzymatic activity of prohormone convertase 2. Immunofluorescence studies revealed prohormone convertase 1 to be mainly expressed in the perinuclear region in vesicular structures resembling the trans-Golgi network, whereas prohormone convertase 2 was found in the trans-Golgi network as well as in vesicular structures diffusely distributed in the peripheral cytoplasm. Expression of both enzymes was also confirmed in fibroblasts of normal adult human skin by immunohistochemistry using antibodies against prohormone convertases 1 and 2 and vimentin. To assess the relevance of prohormone convertase 1 and 2 expression in human dermal fibroblasts, we studied the expression of proopiomelanocortin and proopiomelanocortin-derived peptides. Proopiomelanocortin expression was detected by reverse transcriptase polymerase chain reaction and Western immunoblotting. Alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin were mainly located in vesicular structures as demonstrated by immunofluorescence. Production of these peptides was confirmed by radioimmunoassay, immunoradiometric assay, or enzyme immunoassay. Among several stimuli tested, interleukin-1 was found to upregulate production of alpha-melanocyte-stimulating hormone in human dermal fibroblasts. In summary, we have shown that human dermal fibroblasts express the enzymatic machinery for proopiomelanocortin processing and make proopiomelanocortin, alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. Production of proopiomelanocortin peptides by human dermal fibroblasts may be relevant for fibroblast functions such as collagen degradation and/or regulation of dermal immune responses.

Expression of proopiomelanocortin peptides in human dermal microvascular endothelial cells: evidence for a regulation by ultraviolet light and interleukin-1

Proopiomelanocortin peptides such as alpha-melanocyte-stimulating hormone and adrenocorticotropin are expressed in the epidermal and dermal compartment of the skin after noxious stimuli and are recognized as modulators of immune and inflammatory reactions. Human dermal microvascular endothelial cells mediate leukocyte-endothelial interactions during cutaneous inflammation by the expression of cellular adhesion molecules and cytokines such as interleukin-1. This study addresses the hypothesis that human dermal microvascular endothelial cells express both proopiomelanocortin and prohormone convertases, which are required to generate proopiomelanocortin peptides. Semiquantitative reverse transcriptase polymerase chain reaction and northern blot studies revealed a constitutive expression of proopiomelanocortin mRNA by human dermal microvascular endothelial cells in vitro that was time- and concentration-dependently upregulated by interleukin-1 beta. Furthermore, irradiation of human dermal microvascular endothelial cells with ultraviolet A1 (30J per cm(2)) or ultraviolet B (12.5 mJ per cm(2)) enhanced proopiomelanocortin expression as well as the production and release of the proopiomelanocortin peptides adrenocorticotropin and alpha-melanocyte-stimulating hormone. In addition to proopiomelanocortin, prohormone convertase 1 mRNA expression was detected by reverse transcriptase polymerase chain reaction in unstimulated human dermal microvascular endothelial cells and was augmented after exposure to alpha-melanocyte- stimulating hormone, interleukin-1 beta, or irradiation with ultraviolet. These findings demonstrate that human dermal microvascular endothelial cells express proopiomelanocortin and prohormone convertase 1 required for the generation of adrenocorticotropin. Additionally, human dermal microvascular endothelial cells express mRNA for the prohormone convertase 2 binding protein 7B2. Taken together these findings indicate that human dermal microvascular endothelial cells upon stimulation express both proopiomelanocortin and prohormone convertases required for the generation of alpha-melanocyte-stimulating hormone. As proopiomelanocortin peptides were found to regulate the production of human dermal microvascular endothelial cell cytokines and adhesion molecules and to have a variety of anti-inflammatory properties these peptides may significantly contribute to the modulation of skin inflammation. J Invest Dermatol 115:1021-1028 2000

Keloids in rural black South Africans. Part 3: a lipid model for the prevention and treatment of keloid formations

In the third part of this study a basic lipid model (regarding phospholipids, triglycerides, cholesterol esters and free fatty acids) for keloids (n=20), compared with normal skin of keloid prone and non-keloid prone patients (n=20 of each), was constructed according to standard methods, to serve as a sound foundation for essential fatty acid supplementation strategies in the prevention and treatment of keloid formations. Essential fatty acid deficiency (EFAD) of the omega-6 series (linoleic acid (LA), g-linolenic acid (GLA), and dihomo-g-linolenic acid (DGLA)) and the omega-3 series (a-linolenic acid (ALA) and eicosapentaenoic acid (EPA)), but enhanced arachidonic acid (AA) levels, were prevalent in keloid formations. Enhanced AA, but a deficiency of AA precursors (LA, GLA and DGLA) and inflammatory competitors (DGLA and EPA), are inevitably responsible for the overproduction of pro-inflammatory metabolites (prostaglandin E(2)(PGE(2))) participating in the pathogenesis of inflammation. Of particular interest was the extremely high free oleic acid (OA) levels present, apart from the high free AA levels, in the keloid formations. OA stimulates PKC activity which, in turn, activates PLA(2)activity for the release or further release of AA from membrane pools. Interactions between EFAs, eicosanoids, cytokines, growth factors and free radicals can modulate the immune response and the immune system in undoubtedly involved in keloid formation. The histopathology of keloids can be adequately explained by: persistence of inflammatory- and cytokine-mediated reactions in the keloid/dermal interface and peripheral areas, where fibroblast proliferation and continuous depletion of membrane linoleic acid occur; microvascular regeneration and circulation of sufficient EFAs in the interface and peripheral areas, where maintenance of metabolic active fibroblasts for collagen production occur; microvessel occlusion and hypoxia in the central areas, where deprivation of EFAs and oxygen with consequent fibroblast apoptosis occur, while excessive collagen remain. All these factors contribute to different fibroblast populations present in: the keloid / dermal interface and peripheral areas where increases in fibroblast proliferation and endogenous TGF-b occur, and these metabolic active fibroblast populations are responsible for enhanced collagen production: the central areas where fibroblast populations under hypoxic conditions occur, and these fibroblasts are responsible for excessive collagen production. It was concluded that: fibroblast membrane EFAD of AA precursors and inflammatory competitors, but prevailing enhanced AA levels, can contribute to a chain of reactions eventually responsible for keloid formations.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.

Detection of melanocortin-1 receptor antigenicity on human skin cells in culture and in situ

The proopiomelanocortin (POMC) products alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropin (ACTH) bind to specific receptors known as the melanocortin (MC) receptors. There is increasing evidence that the MC receptor subtype 1 (MC-1R) is expressed in vitro by several other cutaneous cell types besides melanocytes and keratinocytes. Our knowledge on the MC-1R expression in skin, however, remains fragmentary. In order to examine the expression of MC-1R in human skin cells in vitro and In situ, we made use of a recently described antibody directed against the amino acids 2-18 of the human MC-1R. Flow cytometry analysis revealed the highest MC-1R antigenicity in normal melanocytes and keratinocytes, followed by dermal fibroblasts, microvascular endothelial cells and WM35 melanoma cells. Little or no expression was detected in KB carcinoma cells and Fs4 fibroblasts. In normal human skin, immunoreactivity for the anti-MC-1R antibody was detected in hair follicle epithelia, sebocytes, secretory and ductal epithelia of sweat glands, and periadnexal mesenchymal cells. Interfollicular epidermis was largely unreactive in adult skin as opposed to undifferentiated keratinocytes of fetal skin. Our findings form a framework within which MC-1 receptor expression can be studied in various skin diseases.

POMC and fibroblast biology

We evidenced in vitro proopiomelanocortin (POMC) mRNA-transcription in human dermal fibroblasts using Northern blot hybridization. Modulation of POMC gene expression by cytokines (transforming growth factor-beta, TGF-beta, and tumor necrosis factor-alpha, TNF-alpha) was investigated by incubating human normal fibroblasts with 1 and 10 ng/ml cytokines, either alone or in combination, for 24 hours. Our results show that dermal fibroblasts express POMC at significant levels under unstimulated conditions. POMC steady-state levels were significantly reduced by addition of TGF-beta. On the other hand, TNF-alpha exerted a stimulatory effect on POMC mRNA transcription, partially counteracting the effect of TGF-beta. These data provide the first demonstration of POMC gene expression in cultured skin fibroblasts. The opposite regulatory effect of TGF-beta and TNF-alpha, two cytokines primarily involved in extracellular matrix regulation, suggests a possible role for POMC-derived peptides in fibroblast activity. We also investigated POMC mRNA expression in keloid-derived fibroblasts in culture, and its regulation by TGF-beta added at the highest concentration documented for inhibition. Keloid-derived fibroblasts showed clearly detectable levels of POMC mRNA in basal conditions, and no alteration of POMC gene expression was observed when TGF-beta was added in culture. The altered TGF-beta regulation of POMC mRNA levels suggest that POMC-derived peptides may play a role in the pathogenesis of keloid formation through an autocrine/paracrine network, resulting in modulation of extracellular matrix synthesis.

The role of proopiomelanocortin-derived peptides in skin fibroblast and mast cell functions

We have previously described proopiomelanocortin (POMC) gene-expression in human normal cultured dermal fibroblasts, and its dose- and time-dependent modulation by transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha). The aim of the work described here was to investigate POMC-derived peptide release in vitro by cultured fibroblasts following incubation with different concentrations of both TNF-alpha and TGF-beta for 24 hours (1, 5, and 10 ng/ml). The effect of simultaneous addition of both TNF-alpha and TGF-beta (10 ng/ml) was also evaluated. Culture supernatants of human skin fibroblasts were collected to detect adrenocorticotropin hormone (ACTH), alpha-melanotropin (alpha-MSH), and beta-endorphin (beta-EP) levels by specific immunoenzymatic assay. We investigated the in vitro histamine-releasing activity of the POMC-derived peptides, alpha-MSH and beta-EP, on human foreskin mast cells. Detection of cleavage products in supernatants from cultured normal human dermal fibroblasts indicated intracellular processing by POMC protein. We were able to measure detectable levels of all peptides in basal conditions. TNF-alpha addition resulted in an increase in beta-EP and ACTH levels. TGF-beta-stimulated fibroblasts showed no alteration in beta-EP and alpha-MSH levels, whereas ACTH release was significantly enhanced. Both alpha-MSH and beta-EP induced histamine release from human foreskin mast cells in vitro with beta-EP-induced histamine levels as high as those observed with the calcium ionophore, ionomycin. Our data document fibroblast POMC-derived peptide release and modulation by cytokines, suggesting that they have a possible role in extracellular matrix deposit regulation and skin inflammation.

POMC-derived peptides and their biological action

It has long been known that a large number of POMC-related peptides are found in skin. In this introduction I describe the formation of POMC-derived peptides in various tissues to indicate that processing is largely tissue-dependent. I focus on the peptides from the N-terminal fragment, such as gamma-MSH, ACTH and alpha-MSH, and beta-lipopropin as well as beta-endorphin. I touch on the factors that control the synthesis of the various peptides, which are now numerous and varied, and again are tissue specific. The biologic activity of the peptides generated from POMC are described in relation to their possible action in skin. In addition, I describe a new class of peptides induced in skin following injury and which are of great interest.

Alpha-melanocyte-stimulating hormone modulates activation of NF-kappa B and AP-1 and secretion of interleukin-8 in human dermal fibroblasts

Alpha-melanocyte-stimulating hormone (alpha-MSH) has evolved as a mediator of diverse biological activities in an ever-growing number of non-melanocytic cell types. One mechanism by which alpha-MSH exerts its effects is modulation of AP-1 and NF-kappa B. These two transcription factors also play an important role in fibroblasts, in extracellular matrix composition, and in cytokine expression. By use of electric mobility shift assays, we demonstrate that alpha-MSH (10(-6) to 10(-14) M) activates AP-1 in human dermal fibroblasts, whereas coincubation with interleukin-1 beta (IL-1 beta) results in suppression of its activation. alpha-MSH also induces activation of NF-kappa B but does not modulate DNA binding on costimulation with IL-1 beta. Since AP-1 and NF-kappa B are key elements in controlling interleukin-8 (IL-8) transcription, human fibroblasts were treated with alpha-MSH and IL-1 beta for 24 hours, and cytokine levels in the supernatants were measured by ELISA. alpha-MSH alone had little effect, whereas coincubation with IL-1 beta led to marked downregulation of IL-8 secretion (at most 288 +/- 152 ng/mL) when compared to treatment with IL-1 beta alone (919 +/- 157 ng/mL). Our results indicate that alpha-MSH exerts modulatory effects on the activation of NF-kappa B and AP-1, and that it can regulate chemokine secretion in human dermal fibroblasts. These effects of alpha-MSH may have important regulatory functions in extracellular matrix composition, wound healing, or angiogenesis.

Cutaneous immunomodulation and coordination of skin stress responses by alpha-melanocyte-stimulating hormone

The capacity of the skin immune system to mount various types of immune responses is largely dependent on their ability to release and respond to different signals provided by immunoregulatory mediators such as cytokines. There is recent evidence that neuropeptides such as alpha-melanocyte-stimulating hormone (alpha MSH), upon stimulation, are released by epidermal cells including keratinocytes, Langerhans cells, and melanocytes as well as immunocompetent cells. Moreover, alpha MSH recently has been recognized as a potent immunomodulating agent, which inhibits the production and activity of immunoregulatory and proinflammatory cytokines such as IL-1, IL-2, interferon-gamma, downregulates the expression of costimulatory molecules (B7) on antigen-presenting cells; and recently turned out to be a potent inducer of inhibitory mediators such as cytokine synthesis inhibitory factor interleukin-10. Recently, it also was discovered that monocytes among the five known melanocortin (MC) receptors only express MC-1, which is specific for alpha MSH. The expression of MC-1 on monocytes is upregulated by mitogens, endotoxins, and proinflammatory cytokines. There is also recent evidence for the in vivo relevance of the immunosuppressing capacity of alpha MSH. Accordingly, in animals alpha MSH has been shown to inhibit the induction of contact hypersensitivity reactions and to induce hapten-specific tolerance. These findings indicate that, in addition to the cytokine network, neurohormones within the cutaneous microenvironment are a crucial element for the induction, elicitation, and regulation of cutaneous immune and inflammatory responses.