Cutaneous Biology Research Articles

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.

54th Annual Montagna Symposium on the Biology of Skin

Approximately one hundred participants gathered for the 54th Annual Montagna Symposium on the Biology of Skin at Salishan Resort from 13 to 17 October 2005, to listen to and discuss the presentations of 20 invited speakers, six short talks chosen from submitted abstracts, and 22 posters. This meeting continues to follow the tradition established in 1950 by Dr William Montagna. It is a forum where basic cutaneous biologists and clinically trained scientists meet with clinicians to discuss a single major topic in cutaneous biology. The topic for the 54th Annual Montagna Symposium was ‘‘Tissue Remodeling and Repair: Molecular Mechanisms and Clinical Challenges’’. The flow of presentations was designed to lead the discussion from basic aspects of skin biology to clinical challenges and potential opportunities. These included plenary sessions with vibrant discussions and a breakout session, where we discussed topics necessary to advance wound healing research (see ‘‘Highlights of Clinician/Scientist Translational Discussion Session’’, this issue). As in the past, we took time for an excursion to the Oregon Coast Aquarium or, for those who preferred, a hike in the coastal hills or a walk on the beach. We ended with a salmon bake on the beach at the home of AAD president-elect Diane Baker, MD and her husband, allergy-specialist Jim Baker, MD. Paul Martin began the Symposium on Thursday night with a lively keynote talk that included movies of ‘‘dancing cells’’. These showed migration patterns of cells using the model organisms Drosophila and zebrafish. Inflammation: On Friday morning, we began with Karin Scharffetter-Kochanek discussing her work with CD18deficient mice. She showed that they had delayed wound closure primarily owing to a decrease in leukocytes in the wound bed. Brian Nickoloff followed with a comparison of how psoriatic lesions relate to wound healing. Walter Wahli showed us that peroxisome proliferator-activated receptorb/d regulate tissue repair, and Dennis Roop showed us that p63 is critical for tissue homeostasis. Cell–matrix interactions: On Friday afternoon, Lisa Coussens described the role of leukocytes in premalignant cell progression. George Davis followed with an engaging look at how tube morphogenesis and vessel formation requires a balance between matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). William Park continued this theme and demonstrated that skin wounds required matrix metalloproteinase1, whereas oral mucosal wounds required matrix metalloproteinase7. Richard Clark talked about making a ‘‘smart matrix’’ that utilized functional domains of proteins required to heal wounds. Leslie Gold ended this session with a discussion of calreticulin and how it accelerates wound healing. To cap the day, Andrew Blauvelt, dermatologist-specialist on Langerhans cell research, led the dermatology residents and fellows on a guided tour of the poster session. Scarring and fibrotic disease: Participants heard Thomas Krieg discuss how fibroblasts interact differently with the surrounding matrix during normal repair versus fibrosis. Paul Noble offered perspective with a discussion of how repair in lung tissue differed from that in skin. Susan Gilmour introduced polyamines and their necessity to cell survival during wound healing. Using zebrafish as a model, Jean Schwarzbauer demonstrated that tenascin is required for wound repair. In short talks, Sabine Eming, winner of a Eugene M. Farber Travel Award for Young Investigators, demonstrated the requirement of vascular endothelial growth factor-A for repair of chronic wounds, and Donna Kusewitt showed that the embryonic transcription factor Slug is required for cutaneous wound re-epithelialization. The afternoon was spent hiking on the beach, in the coastal hills, or touring the Oregon Coast Aquarium. The Banquet Dinner was held in the Cedar Room at Salishan Resort. After dinner, Walter Lobitz was recognized as a Founding Member of the Montagna Symposium. At 96 years old, he gave a rousing talk about the origins of the dermatology specialty and the symposium on cutaneous biology founded by William Montagna (edited text of his talk is in this issue).

Neuropeptide Control Mechanisms in Cutaneous Biology: Physiological and Clinical Significance

The skin as a barrier and immune organ is exposed to omnipresent environmental challenges such as irradiation or chemical and biologic hazards. Neuropeptides released from cutaneous nerves or skin and immune cells in response to noxious stimuli are mandatory for a fine-tuned regulation of cutaneous immune responses and tissue maintenance and repair. They initialize host immune responses, but are equally important for counter regulation of proinflammatory events. Interaction of the nervous and immune systems occurs both locally - at the level of neurogenic inflammation and immunocyte activation - and centrally - by controlling inflammatory pathways such as mononuclear activation or lymphocyte cytokine secretion. Consequently, a deregulated neurogenic immune control results in disease manifestation and frequently accompanies chronic development of cutaneous disorders. The current understanding, therapeutic options, and open questions of the role that neuropeptides such as substance P, calcitonin gene-related peptide, vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide, neuropeptide Y, or others play in these events are discussed. Progress in this field will likely result in novel therapies for the management of diseases characterized by deregulated inflammation, tissue remodeling, angiogenesis, and neoplasm.

Interstitial Mycosis Fungoides or Not: Is it a Diagnosable Entity?

Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, PA Abstracts Presented at the 9th ISDP Joint Meeting, San Francisco, California, March 1–2, 2006

Skin layer‐specific transcriptional profiles in normal and recessive yellow (Mc1re/Mc1re) mice

The melanocortin 1 receptor (Mc1r) plays a central role in cutaneous biology, but is expressed at very low levels by a small fraction of cells in the skin. In humans, loss-of-function MC1R mutations cause fair skin, freckling, red hair, and increased predisposition to melanoma; in mice, Mc1r loss-of-function is responsible for the recessive yellow mutation, associated with pheomelanic hair and a decreased number of epidermal melanocytes. To better understand how Mc1r signaling affects different cutaneous phenotypes, we examined large-scale patterns of gene expression in different skin components (whole epidermal sheets, basal epidermal cells and whole skins) of neonatal (P2.5) normal and recessive yellow mice, starting with a 26K mouse cDNA microarray. From c. 17 000 genes whose levels could be accurately measured in neonatal skin, we identified 883, 2097 and 552 genes that were uniquely expressed in the suprabasal epidermis, basal epidermis and dermis, respectively; specific biologic roles could be assigned for each class. Comparison of normal and recessive yellow mice revealed 69 differentially expressed genes, of which the majority had not been previously implicated in Mc1r signaling. Surprisingly, many of the Mc1r-dependent genes are expressed in cells other than melanocytes, even though Mc1r expression in the skin is confined almost exclusively to epidermal melanocytes. These results reveal new targets for Mc1r signaling, and point to a previously unappreciated role for a Mc1r-dependent paracrine effect of melanocytes on other components of the skin.

Syndecan‐4 is required for Toll‐like receptor‐dependent interleukin‐12 production and host resistance to microbial infection

Syndecans are a family of heparan sulfate proteoglycans that regulate the interaction between cell-surface receptors and extracellular ligands. We found that syndecan-4 expression is strongly induced in spleen after infection with Listeria monocytogenes and in macrophages stimulated with Toll-like receptor (TLR) agonists. To examine the function of syndecan-4 in immunity, wild-type and syndecan-4 knockout mice were infected with L. monocytogenes and their ability to resist the infection was determined. Syndecan-4 knockout mice exhibited greatly increased bacterial burdens in spleen and liver, indicating that syndecan-4 plays an important role in fighting listerial infection. Macrophages that recognized infected microbes produce a battery of proinflammatory cytokines and thereby alert other immune cells to the presence of an infectious agent. Syndecan-4-deficient macrophages were defective in inducing the transcription of the interleukin (IL)-12 subunit p40 in response to TLR agonists, suggesting that syndecan-4 is required for linking TLR signaling to IL-12 p40 transcription and promote the immune response to L. monocytogenes. This study was supported by a grant to the Cutaneous Biology Research Center from Shiseido, Ltd.

The Editors' Choice

The Editors' Choice

Perspectives of an Editor Emeritus of the JID

I was editor of the Journal of Investigative Dermatology (JID) from mid-1987 to mid-1992, a period that coincided with the transformation of biomedical research by molecular biology and molecular genetics. During these years, the JID grew in size and scope and enjoyed the broad and committed support of the membership of both the Society for Investigative Dermatology (SID) and the European Society for Dermatological Research (ESDR), for which it was the official journal. More importantly, it became recognized by a new generation of molecular biologists and geneticists as an attractive venue for the publication of research findings in basic cutaneous biology. Our editorial board solidified support for the journal among our traditional constituency in the ESDR and SID, making it an effort of true collaboration between the two societies.

The status quo and quo vadis of mast cells

Mast cells (MCs) have been intensely investigated over the past two decades, e.g. the numbers of PubMed-listed reports on MCs have steadily increased and doubled over the past twenty years. Surprisingly, many recent findings that have fundamentally changed our understanding of MC biology and functions have yet to be sufficiently recognized by scientists interested in cutaneous biology and clinical dermatologists. The aim of this study is to review recent hallmark contributions to the field of MC research, to outline the development of our current knowledge of MCs, and to predict the outcome of future MC research efforts. The development of straightforward rodent in vivo models has allowed for the identification and characterization of various novel MC functions. MC effects are not limited to the induction of pathology, but can serve important functions in maintaining health and preventing disease. Attempts to better define the role of MCs in the human system may lead to novel strategies for treating inflammatory disorders and could eventually allow us to utilize MCs for improving responses to environmental danger signals.

Hoxb13 Up-regulates Transglutaminase Activity and Drives Terminal Differentiation in an Epidermal Organotypic Model

Hox genes act to differentiate and pattern embryonic structures by promoting the proliferation of specific cell types. An exception is Hoxb13, which functions as a proapoptotic and antiproliferative protein during development of the caudal spinal cord and tail vertebrae and has also been implicated in adult cutaneous wound repair. The adult epidermis, which expresses several Hox genes including Hoxb13, is continually renewed in a program of growth arrest, differentiation, and a specialized form of apoptosis (cornification). Yet little is known about the function(s) of these genes in skin. Based on its role during embryogenesis, Hoxb13 is an attractive candidate to be involved in the regulation of epidermal differentiation. Here, we demonstrate that Hoxb13 overexpression in an adult organotypic epidermal model recapitulates actions of Hoxb13 reported in embryonic development. Epidermal cell proliferation is decreased, apoptosis increased, and excessive terminal differentiation observed, as characterized by enhanced transglutaminase activity and excessive cornified envelope formation. Overexpression of Hoxb13 also produces abnormal phenotypes in the epidermal tissue that resemble certain pathological features of dysplastic skin diseases. Our results suggest that Hoxb13 functions to promote epidermal differentiation, a critical process for skin regeneration and for the maintenance of normal barrier function.

Defensive Defensins: A Response to the Commentary “In Defense of Skin”

Defensive Defensins: A Response to the Commentary “In Defense of Skin”

Perspectives: A New Series of Articles Begins in this Issue of JID

In this issue of the JID we are proud to introduce a new series of articles entitled ‘Perspectives’. It is our goal to provide the investigative community with an up-to-date source of the latest research in a wide variety of fields of current interest and importance to cutaneous and epithelial biology. Perspectives are designed to be short focused updates, and they are aimed at bringing the typical JID reader up to speed on a topical area of interest. They are not intended to be all-inclusive reviews, but rather to provide a general background with a focus on the most up-to-date work. Figures for these articles have been created by a medical illustrator in collaboration with the authors, to ensure they are high-quality illustrations that will serve our readers well. The first articles in our Perspectives series appears in this month's JID and are focused on Innate Immunity. The innate immunity comprises the host's immediate response to a wide variety of infectious and other threats and also plays a key role in the adaptive immune response. In this issue are articles by Jenny Kim and Robert Modlin on Toll Like Receptors, Clemens Esche, Cristiana Stellato and Lisa Beck on the role of chemokines in innate and acquired immunity and Marissa H. Braff, Antoanella Bardan, Victor Nizet and Richard Gallo on anti-microbial peptides. In an upcoming issue the series will continue with an article by Richard Sonthimer on the role of C1q on innate and a discussion of the interface between innate and acquired immunity by Rachael Clark and Thomas Kupper. Upcoming topics in the Perspectives series will include: Immune T Cells (Tregs, cytotoxic T cells and γ/δ T cells), Techniques for Analysis of Microarrays, Vascular and Lymphatic Vessels in the Skin, Epidermal and Follicular Stem Cells, Human Thermal Plume, Apoptosis, Neuroendocrinology of the Skin, and Anti-oxidants in the Skin. Recognized specialists in each field have agreed to write a brief update for future publication in the JID. The Editors are grateful to the authors of these articles, who have contributed their work to us without compensation. We hope you find this new series to be intellectually stimulating, and that it serves its goal of bringing you up to date on important, developing issues in the field. We invite your input regarding future topics and potential authors; we would be especially interested in developing contributions from experts outside of dermatology and traditional investigative dermatology and cutaneous biology.

Alpha 9 acetylcholine receptors are essential for epidermal differentiation

Extraneuronally, acetylcholine (Ach) is synthesized, stored and secreted in the tegumental cells covering the inner and outer surfaces of the body. It acts via nicotinic (nAchR) and muscarinic (mAchR) receptors in a paracrine and autocrine fashion influencing various keratinocyte functions. Using in vitro studies, we present evidence that effects of cholinergic agonists and antagonists on cutaneous biology are dependent upon specific Ach‐R, localised in the different compartments of the skin. Using immunohistochemistry on frozen section of normal skin we could previously demonstrate a differential distribution of alpha 3*, alpha 7, alpha 9 and beta 1 nAchR and m1, m3–5 mAchR in human epidermis. Here we show the functional significance of AchR blockage using organotypical keratinocytes cultures. Cholinergic agonists and antagonists were added on the day of the lift to the air‐liquid interface. After 5 days, blockage of all AchR using mecamylamine and atropine resulted in complete inhibition of terminal differentiation. Mecamylamine and atropine alone had only a retarding effect suggesting an additive mechanism of nAchR and mAchR blockage. Specific inhibition of α9 homooligomers with strychnine produced the strongest effects leaving behind only a keratinocytes monolayer. Stimulation of AchR with either nicotine or muscarine in short term organotypic cultures did not produce dramatic changes of epidermal morphology. We conclude that alpha 9 AchR that are located in the basal and lower suprabasal layers of the epidermis, are crucially involved in terminal differentiation of keratinocytes. The functional significance of other nAchR expressed in the epidermis remains unclear, due to the lack of specific agonists and antagonists.

Peroxisome Proliferator-Activated Receptors and their Ligands

Glucocorticoids have remained one of the most frequently used classes of drugs for the treatment of skin diseases since their introduction more than 50 years ago. As a result of the discovery of new members of the nuclear hormone receptor (NR) superfamily, alternative therapeutic interventions that target retinoid and vitamin D receptors have been developed. Peroxisome proliferator-activated receptors (PPARs) comprise another important NR subfamily, consisting of three different isotypes: PPARalpha, PPARdelta (PPARbeta) and PPARgamma. These NRs are activated by a variety of natural and synthetic ligands such as fatty acids, eicosanoids, and antidiabetic and antihyperlipidaemic agents. While these receptors are established as regulators of gene expression in lipid and glucose homeostasis, evidence is now accumulating that PPARs also play a crucial role in cutaneous biology. Results from in vitro and in vivo studies have indicated the involvement of PPARs in epidermal maturation, proliferation and differentiation, as well as in immune and inflammatory responses, carcinogenesis, hyperpigmentation and skin wound healing. Furthermore, treatment of psoriatic patients with PPARgamma activators (thiazolidinediones) has been shown to induce beneficial effects. However, the effects of PPAR ligands should be carefully evaluated to determine whether they are in fact mediated via PPAR-dependent mechanisms. Nonetheless, PPARs seem to have significant potential as therapeutic targets in skin inflammatory disorders.

Novel aspects in cutaneous biology of acetylcholine synthesis and acetylcholine receptors

Extraneuronal acetylcholine (ACh) has been demonstrated to influence a plethora of cutaneous cell functions in an autocrine, paracrine and endocrine fashion. Through the differentiation-specific expression of its different nicotinic (nACh-R) and muscarinic (mACh-R) receptors, ACh acts upon keratinocyte proliferation and migration, terminal differentiation and barrier formation, sweat and sebum secretion as well as microcirculation and angiogenesis. Only very recently it has been recognized that acetylcholinesterase, but not cholineacetyltransferase, activity is regulated by hydrogen peroxide. Considering that the outer layer of the human skin can be a target for UV-generated H2O2 in the millimolar range, this mechanism needs to be taken into account for the regulation of ACh homeostasis in skin biology. Consequently, ACh can accumulate, as shown, for example, in the depigmentation process in vitiligo. There is a highly regulated distribution of ACh-R in human epidermis and adnexal structures, supporting previously observed effects of cholinergic compounds on keratinocyte biology. Most significantly, the regulated expression of ACh-R in sebaceous glands advocates a role for ACh in sebum production and as a promoter of sebocyte differentiation, thus offering an explanation for skin diseases associated with altered sebum production after chronic nicotine exposure. So far, ACh-induced sweat production has been thought to be under the exclusive control of mACh-R. However, recently, the presence of both different nACh-R and mACh-R in myoepithelial and acinar cells of eccrine sweat glands has been documented, indicating a more complex regulation of sweat production and expulsion.

Epidermolysis Bullosa: The Expanding Mutation Database

Epidermolysis bullosa (EB) is a group of heritable mechanobullous disorders characterized by fragility of the skin within the cutaneous basement membrane zone (BMZ) (Fine et al, 2000). The severity of skin manifestations can be highly variable, so that in one end of the spectrum the skin findings may be relatively minor blistering tendency primarily on the hands and feet, whereas at the other end of the spectrum the compromised integrity of skin can result in early postnatal demise of the affected individual. Prior to identification of the gene/protein systems harboring mutations in different variants of EB, this phenotypic variability was quite puzzling, compounded by the fact that there are a number of extracutaneous manifestations associated with the skin findings. This phenotypic complexity, coupled with classifications riddled with eponyms, has led to a suggestion that there are 30 different subtypes of EB (Anton-Lamprecht and Gedde-Dahl, 2002). Traditionally, EB has been divided into three broad categories: (a) the simplex forms demonstrate tissue separation within the basal keratinocytes; (b) the junctional forms depict tissue separation within the lamina lucida of the dermal–epidermal basement membrane; and (c) the dystrophic forms show tissue cleavage below the lamina densa within the upper papillary dermis (Fig 1). We have recently proposed a fourth subtype, the hemidesmosomal variants of EB, in which the tissue separation is at the basal cell/lamina lucida interface at the level of hemidesmosomes (Fig 1) (Pulkkinen and Uitto, 1998). In fact, the hemidesmosomal variants include the following clinical entities: (a) Generalized atrophic benign EB (GABEB) that has been previously included in the category of non-Herlitz junctional EB (JEB); (b) EB with pyloric atresia where tissue separation is either just outside of the plasma membrane of the basal cells or in the low intracellular compartment and has occasionally been referred as ‘‘pseudo-junctional’’ EB; (c) EB with muscular dystrophy which shows low intracellular cytolysis occasionally suggested to belong to the simplex category of EB (Pulkkinen and Uitto, 1998). With the advent of molecular genetics in general and essential completion of the human genome project, specific mutations have now been identified in ten distinct genes expressed within the cutaneous BMZ (Table I) (Uitto et al, 2002). The compartmentalized expression of these genes within the cutaneous BMZ, the types and combinations of the mutations, and their consequences at the mRNA and protein levels, when superimposed on the individuals’ genetic background and combined with environmental factors, explain the spectrum of severity in EB. Considerable clinical and molecular heterogeneity is recognized particularly in the JEB, which has been traditionally divided into Herlitz (lethal) and non-Herlitz variants depending on the severity and outcome of the disease. Specifically, most children with the Herlitz variant die within the first year of life, whereas non-Herlitz patients have life-long blistering but their lifespan is not significantly compromised. The Herlitz JEB is due to absence of laminin 5, and mutations have been identified in three genes (LAMA3, LAMB3, and LAMC2), which encode the subunit polypeptides a3, b3, and g2 of laminin 5, respectively. Most of these mutations result in premature termination codon for translation (PTC) (Nakano et al, 2000). In non-Herlitz variants, missense mutations have been identified also in the laminin 5 genes, but in addition, mutations can reside in the 180 kDa bullous pemphigoid antigen/type XVII collagen gene, BPAG2/ COL17A1 (Nakano et al, 2002). In this issue, Posteraro et al (2004) have analyzed an Italian cohort of 19 patients with JEB, 11 being affected with the severe Herlitz type and eight with milder non-Herlitz type. The authors concentrated their analysis on LAMA3, LAMB3, and LAMC2 and identified 18 mutations, seven of which were previously unpublished. In accordance with previous observations, PTC mutations in both alleles of the laminin 5 genes were predominant in Herlitz JEB patients, whereas splicing or missense mutations resulting in reduced synthesis of partially functional laminin 5 were predominantly found in non-Herlitz variants. The authors also disclosed a number of recurrent mutations, including R635X in the LAMB3 gene, a mutation frequent in Caucasian Herlitz JEB patients, particularly in Northern European

Acetylcholine receptors in cutaneous biology – receptorology and therapeutic implications

Free cytotransmitter acetylcholine (ACh) is present in physiologically relevant concentrations in human skin, and ACh and cholinergic drugs alter vital functions of keratinocytes (KCs). KCs respond to ACh via classical ACh receptor types that use Ca2+ as a second messenger. The repertoire of cholinergic receptors changes with cell maturation, so that at each stage of their development, KCs respond to ACh via different combinations of nicotinic (nAChR) and muscarinic (mAChR) receptors. Basal KCs respond to ACh predominantly via α3β2(β4) ± α5 nAChRs and the M3 mAChR; prickle KCs have more α5‐containing α3 nAChRs and also express α9 nAChR as well as M4 and M5 mAChRs; granular KCs posses mainly α7 nAChR and M1 mAChR. We used three independent approaches to elucidate role of each receptor in KC biology: 1) Subtype selective drugs, 2) Gene silencing with small interfering RNA or antisense oligonucleotides, and 3) Gene knockout in transgenic mice. Obtained results indicate that KC nAChRs and mAChR exhibit synergistic control of cell adhesion and crawling locomotion. KC cell‐cell adhesion is regulated through α3 and α9 nAChRs as well as M3 mAChR. KC chemokinesis is controlled by α3 and α7 nAChRs and M3 and M4 mAChRs. KC chemotaxis toward nicotinic agonists is mediated by α7 nAChR. These findings offer novel insights into the mechanisms of ACh‐mediated modulation of epidermalization and may aid the development of novel methods to promote wound healing and inhibit tumor metastasis.

Introduction to JID Symposium Proceedings 52nd Annual Montagna Symposium on the Biology of Skin “Stem Cells in Skin” Held at Snowmass, Colorado, USA, June 13–17, 2003

The 52nd Annual Montagna Symposium on the Biology of Skin was held at Snowmass, Colorado, June 13–17, 2003. It followed in the tradition established in 1950 by Dr William Montagna, who established a forum where basic cutaneous biologists and clinically trained scientists met to discuss a single major topic in cutaneous biology. The topic for the 52nd Annual Montagna Symposium on the Biology of Skin was Stem Cells in Skin. As in the past symposia, the flow of presentations was designed to lead the discussion from the basic aspects of stem cell biology to potential clinical applications. Each presentation is presented in written form in the JID Montagna Symposium Supplement (September 2004).

α‐MSH as a modulator of apoptosis in cutaneous biology

The molecular pathways regulating ultraviolet (UV) radiation‐induced apoptosis of melanocytes, a cell population crucially involved in the protection of epidermal keratinocytes against the harmful effects of UV light, are poorly characterized. We show that the α‐melanocyte‐stimulating hormone (α‐MSH) blocks UVB‐induced apoptosis of normal human melanocytes in vitro. The effect of α‐MSH is not restricted to melanocytes but is also operative in cells that do not produce melanin, for example in human epidermal keratinocytes and in dermal fibroblasts. α‐MSH not only delays but also protects melanocytes from UVB‐induced cell death. The anti‐apoptotic activity of α‐MSH is not mediated by a filtering effect or induction of melanin synthesis. α‐MSH also does not induce changes in the cell cycle distribution or expression of Bcl2, Bclx, CD95 (Fas/APO‐1) and FasL. In contrast, α‐MSH markedly reduces the formation of cyclobutane pyrimidine dimers induced by UVB radiation. Human dermal fibroblasts carrying a defective XPA gene are not protected from UVB‐induced apoptosis by α‐MSH. These results highlight a novel biological activity of α‐MSH as well as novel regulatory pathways within the UV response of skin cells targeted by this neuropeptide.

Gene expression profiles of three different models of reconstructed human epidermis and classical cultures of keratinocytes using cDNA arrays.

The gene expression profiles of three different models of reconstructed human epidermis were analyzed in a comparative study using cDNA array technology. The study also included normal human subconfluent keratinocytes cultured on plastic. Arrays were custom-made and comprised 504 known genes related to cutaneous biology. The gene expression profiles of the three reconstructed epidermis models shared 86% similarity; only 22 of the 504 examined genes showed a different expression level. A comparison of the 3D models with keratinocyte cultures on plastic dishes revealed a set of six genes with a considerably higher expression in the 3D models. These genes were keratin 1, corneodesmosin, filaggrin, loricrin, calmodulin-like skin protein and caspase 14, all related to keratinocyte terminal differentiation. The reported data may contribute to a better understanding and characterization of reconstructed epidermal models and may also serve as established references for investigations related to epidermal differentiation and proliferation.