Role of BMP-4 and Its Signaling Pathways in Cultured Human Melanocytes

Genome-wide characterization of the TGF-β gene family and their expression in different tissues during tail regeneration in the Schlegel's Japanese gecko Gekko japonicus

The transforming growth factor-β (TGF-β) gene family is unique to animals and is involved in various important processes including tissue regeneration. Here, we identified 52 TGF-β family genes based on genome sequences of the gecko (Gekko japonicus), compared TGF-β genes between G. japonicus and other four reptilian species, and evaluated the expression of 14 randomly selected genes in muscle, kidney, liver, heart, and brain during tail regeneration to investigate whether their expression was tissue-dependent. We detected 23 conserved domains, 13 in the TGF-β ligand subfamily, and 10 in the receptor subfamily. The pattern of higher genetic variation in the ligand subfamily than in the receptor subfamily in vertebrates might result from the precise localization of agonists and antagonists in the cell surface and intracellular compartment. TGF-β genes were unevenly distributed across 15 chromosomes in G. japonicus, presumably resulting from gene losses and gains during evolution. Genes in the TGF-β receptor subfamily (ACVR2A, ACVR2B, ACVR1, BMPR1A, ACVRL1, BMPR2 and TGFBR1) played a vital role in the TGF-β signal pathway. The expression of all 14 randomly selected TGF-β genes was tissue-specific. Our study supports the speculation that some TGF-β family genes are involved in the early stages of tail regeneration.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Evaluation of TILI-2 as an Anti-Tyrosinase, Anti-Oxidative Agent and Its Role in Preventing Melanogenesis Using a Proteomics Approach

There is a desire to develop new molecules that can combat hyperpigmentation. To this end, the N-terminal cysteine-containing heptapeptide TILI-2 has shown promising preliminary results. In this work, the mechanism by which it works was evaluated using a series of biochemical assays focusing on known biochemical pathways, followed by LC-MS/MS proteomics to discover pathways that have not been considered before. We demonstrate that TILI-2 is a competitive inhibitor of tyrosinase’s monophenolase activity and it could potentially scavenge ABTS and DPPH radicals. It has a very low cytotoxicity up to 1400 µM against human fibroblast NFDH cells and macrophage-like RAW 264.7 cells. Our proteomics study revealed that another putative mechanism by which TILI-2 may reduce melanin production involves the disruption of the TGF-β signaling pathway in mouse B16F1 cells. This result suggests that TILI-2 has potential scope to be used as a depigmenting agent.

Protective effects of Thai silk sericins and their related mechanisms on UVA-induced phototoxicity and melanogenesis: Investigation in primary melanocyte cells using a proteomic approach

UV radiation causes excess production of melanin as a result of hyperpigmentation and skin disorders. Silk sericin exhibited bioactivities to skin and inhibited UV-induced phototoxicity and melanogenesis in skin cells; however, the mechanism related to sericin against UV-induced melanogenesis has not been investigated. This study aimed to investigate the protective effects of Thai silk sericins against UVA-induced phototoxicity and melanogenesis and their related mechanisms. Thai silk sericins exhibited cytoprotective effects against UV-induced toxicity in human primary melanocytes by attenuation of cytotoxicity, intracellular ROS generation, and mitochondrial potential impairment. Pre- and post-treatment with sericin significantly inhibited melanin synthesis and tyrosinase activity against UVA exposure. In addition, sericin S2 could reduce the basal melanin content in zebrafish embryos. The proteomic analysis demonstrated that Thai silk sericins altered the protein expression in melanocytes especially proteins related to stress, inflammatory, cytokine stimulation, cell proliferation, and cell survival processes that contribute to cytoprotective effect and inhibitory effect on melanogenesis of sericin. Moreover, we demonstrated the novel mechanism of Thai silk sericins in inhibiting UVA-induced melanogenesis via increasing BMP4 expression in MAPK/ERK signaling pathway. These evidences support the potential use of Thai silk sericins in prevention of hyperpigmentation in skin disorders especially after UVA exposure.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

Bone Morphogenic Protein Signaling and Melanoma

OPINION STATEMENT

Malignant melanoma is a deadly form of skin cancer caused by neoplastic transformation of melanocytic cells. Despite recent progress in melanoma therapy, by inhibition of activated oncogenes or immunotherapy, survival rate for metastatic melanoma patients remains low. The remarkable phenotypic plasticity of melanoma cells allows for rapid development of invasive properties and metastatic tumors, the main cause of mortality in melanoma patients. Phenotypic and molecular analyses of developing tumors revealed that epithelial-mesenchymal transition (EMT), a cellular and molecular mechanism, controls transition from mature melanocyte to less differentiated melanocyte lineage progenitor cells forming melanoma tumors. This transition is facilitated by persistence of transcriptional regulatory circuit characteristic of embryonic stage in mature melanocytes. Switching of the developmental program of mature melanocyte to EMT is induced by accumulated mutations, especially targeting BRAF, N-RAS, or MEK1/2 signaling pathways, and further promoted by dynamic stimuli from local environment including hypoxia, interactions with extracellular matrix and growth factors or cytokines. Recent reports demonstrate that signaling mediated by transforming growth factor-β (TGF-β) and bone morphogenic proteins (BMPs) play critical roles in inducing EMT by controlling expression of critical transcription factors. BMPs are essential modulators of differentiation, proliferation, apoptosis, invasiveness, and metastases in developing melanoma tumors. They control transcription and epigenetic landscape of melanoma cells. Better understanding of the role of BMPs may lead to new strategies to control EMT processes in melanocyte cell lineage and to achieve clinical benefits for the patients.

BMP signaling: at the gate between activated melanocyte stem cells and differentiation

Through recurrent bouts synchronous with the hair cycle, quiescent melanocyte stem cells (McSCs) become activated to generate proliferative progeny that differentiate into pigment-producing melanocytes. The signaling factors orchestrating these events remain incompletely understood. Here, we use single-cell RNA sequencing with comparative gene expression analysis to elucidate the transcriptional dynamics of McSCs through quiescence, activation, and melanocyte maturation. Unearthing converging signs of increased WNT and BMP signaling along this progression, we endeavored to understand how these pathways are integrated. Employing conditional lineage-specific genetic ablation studies in mice, we found that loss of BMP signaling in the lineage leads to hair graying due to a block in melanocyte maturation. We show that interestingly, BMP signaling functions downstream from activated McSCs and maintains WNT effector, transcription factor LEF1. Employing pseudotime analysis, genetics, and chromatin landscaping, we show that following WNT-mediated activation of McSCs, BMP and WNT pathways collaborate to trigger the commitment of proliferative progeny by fueling LEF1- and MITF-dependent differentiation. Our findings shed light upon the signaling interplay and timing of cues that orchestrate melanocyte lineage progression in the hair follicle and underscore a key role for BMP signaling in driving complete differentiation.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

Additive Effect of a Combination of Artocarpus lakoocha and Glycyrrhiza glabra Extracts on Tyrosinase Inhibition in Melanoma B16 Cells

Artocarpus lakoocha (Al) and Glycyrrhiza glabra (Gg) extracts have been reported to show tyrosinase inhibitory activity and melanin pigment reduction. This is the first study to assess the combination of Al and Gg extracts in enhancing inhibition of tyrosinase and reduction of melanin pigments. Al and Gg extracted by maceration in 70% and 95% ethanol were analyzed for oxyresveratrol and glabridin using Ultra High Performance Liquid Chromatography. Extracts of Al and Gg singly and combinations of Al95 and Gg95 were tested for cytotoxicity, tyrosinase inhibitory activity, and reduction of melanin pigments in melanoma B16 cells. Al95 had higher antioxidant, tyrosinase inhibitory activity and reduced more melanin pigments in B16 cells compared to Al70, and exhibited higher levels of oxyresveratrol. Gg95 inhibited oxidative stress and mushroom tyrosinase better than Gg70, and exhibited higher levels of glabridin. Combinations of Al95 and Gg95 at various ratios (concentration of 0.1 mg/mL) were not cytotoxic to B16 cells. Interestingly, Al95 and Gg95 combined at a ratio 9:1 reduced melanin pigment up to 53% in B16 cells. This combination of Al95 and Gg95 extracts exhibited the additive effect of reducing melanin pigments by suppressing the expression of microphthalmia-associated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein-2 (TRP-2) in B16 cells. The combination of Al and Gg extracts could be developed as skin care products for hyperpigmentation treatment.

ID1-Mediated BMP Signaling Pathway Potentiates Glucagon-Like Peptide-1 Secretion in Response to Nutrient Replenishment

Glucagon-like peptide-1 (GLP-1) is a well-known incretin hormone secreted from enteroendocrinal L cells in response to nutrients, such as glucose and dietary fat, and controls glycemic homeostasis. However, the detailed intracellular mechanisms of how L cells control GLP-1 secretion in response to nutrients still remain unclear. Here, we report that bone morphogenetic protein (BMP) signaling pathway plays a pivotal role to control GLP-1 secretion in response to nutrient replenishment in well-established mouse enteroendocrinal L cells (GLUTag cells). Nutrient starvation dramatically reduced cellular respiration and GLP-1 secretion in GLUTag cells. Transcriptome analysis revealed that nutrient starvation remarkably reduced gene expressions involved in BMP signaling pathway, whereas nutrient replenishment rescued BMP signaling to potentiate GLP-1 secretion. Transient knockdown of inhibitor of DNA binding (ID)1, a well-known target gene of BMP signaling, remarkably reduced GLP-1 secretion. Consistently, LDN193189, an inhibitor of BMP signaling, markedly reduced GLP-1 secretion in L cells. In contrast, BMP4 treatment activated BMP signaling pathway and potentiated GLP-1 secretion in response to nutrient replenishment. Altogether, we demonstrated that BMP signaling pathway is a novel molecular mechanism to control GLP-1 secretion in response to cellular nutrient status. Selective activation of BMP signaling would be a potent therapeutic strategy to stimulate GLP-1 secretion in order to restore glycemic homeostasis.

Dyspigmented hypertrophic scars: Beyond skin color

Although pigment synthesis is well understood, relevant mechanisms of psychologically debilitating dyspigmentation in nascent tissue after cutaneous injuries are still unknown. Here, differences in genomic transcription of hyper- and hypopigmented tissue relative to uninjured skin were investigated using a red Duroc swine scar model. Transcription profiles differed based on pigmentation phenotypes with a trend of more upregulation or downregulation in hyper- or hypopigmented scars, respectively. Ingenuity Pathway Analysis of significantly modulated genes in both pigmentation phenotypes showed pathways related to redox, metabolic, and inflammatory responses were more present in hypopigmented samples, while those related to stem cell development differentiation were found mainly in hyperpigmented samples. Cell-cell and cell-extracellular matrix interactions and inflammation responses were predicted (z-score) active in hyperpigmented and inactive in hypopigmented. The proinflammatory high-mobility group box 1 pathway showed the opposite trend. Analysis of differentially regulated mutually exclusive genes showed an extensive presence of metabolic, proinflammatory, and oxidative stress pathways in hypopigmented scars, while melanin synthesis, glycosaminoglycans biosynthesis, and cell differentiation pathways were predominant in hyperpigmented scar. Several potential therapeutic gene targets have been identified.

In vitro modeling of hyperpigmentation associated to neurofibromatosis type 1 using melanocytes derived from human embryonic stem cells

"Café-au-lait" macules (CALMs) and overall skin hyperpigmentation are early hallmarks of neurofibromatosis type 1 (NF1). One of the most frequent monogenic diseases, NF1 has subsequently been characterized with numerous benign Schwann cell-derived tumors. It is well established that neurofibromin, the NF1 gene product, is an antioncogene that down-regulates the RAS oncogene. In contrast, the molecular mechanisms associated with alteration of skin pigmentation have remained elusive. We have reassessed this issue by differentiating human embryonic stem cells into melanocytes. In the present study, we demonstrate that NF1 melanocytes reproduce the hyperpigmentation phenotype in vitro, and further characterize the link between loss of heterozygosity and the typical CALMs that appear over the general hyperpigmentation. Molecular mechanisms associated with these pathological phenotypes correlate with an increased activity of cAMP-mediated PKA and ERK1/2 signaling pathways, leading to overexpression of the transcription factor MITF and of the melanogenic enzymes tyrosinase and dopachrome tautomerase, all major players in melanogenesis. Finally, the hyperpigmentation phenotype can be rescued using specific inhibitors of these signaling pathways. These results open avenues for deciphering the pathological mechanisms involved in pigmentation diseases, and provide a robust assay for the development of new strategies for treating these diseases.

Skin as a living coloring book: how epithelial cells create patterns of pigmentation

The pigmentation of mammalian skin and hair develops through the interaction of two basic cell types - pigment donors and recipients. The pigment donors are melanocytes, which produce and distribute melanin through specialized structures. The pigment recipients are epithelial cells, which acquire melanin and put it to use, collectively yielding the pigmentation visible to the eye. This review will focus on the pigment recipients, the historically less understood cell type. These end-users of pigment are now known to exert a specialized control over the patterning of pigmentation, as they identify themselves as melanocyte targets, recruit pigment donors, and stimulate the transfer of melanin. As such, this review will discuss the evidence that the skin is like a coloring book: the pigment recipients create a 'picture,' a blueprint for pigmentation, which is colorless initially but outlines where pigment should be placed. Melanocytes then melanize the recipients and 'color in' the picture.

Vitis amurensis Ruprecht root inhibited α-melanocyte stimulating hormone-induced melanogenesis in B16F10 cells

BACKGROUND/OBJECTIVES

The root of Vitis amurensis Ruprecht, a sort of wild-growing grape, has been used in oriental medicine for treatment of skin ailments; however, its dermatological activity is not sufficiently understood. The aim of this study was to investigate tyrosinase inhibitory and anti-melanogenic activities of V. amurensis Ruprecht root methanol extract (VARM) in B16F10 mouse melanoma cells and to attempt to isolate and identify the active compound issued from VARM.

MATERIALS/METHODS

Anti-melanogenic activity of VARM was analyzed in α-melanocyte stimulating hormone (MSH)-stimulated B16F10 cells through evaluation of antioxidative activity as well as inhibited tyrosinase activity and melanin contents compared with those of kojic acid and arbutin. After anti-melanogenic analysis of VARM, serial fractionation, nuclear magnetic resonance (NMR), and thin layer chromatorgraphy (TLC) were applied for identification of active compounds contained in VARM.

RESULTS

VARM significantly inhibited oxidative stress and tyrosinase activity and attenuated α-MSH-induced melanin production in B16F10 cells. For isolation of active compounds, VARM was fractionated using a series of organic solvents, including dichloromethane (CH₂Cl₂), ethyl acetate (EtOAc), and n-butanol (n-BuOH). Among fractions showing anti-melanogenic activity, the CH₂Cl₂ fraction induced the most potent attenuation of melanogenesis without cytotoxicity and the major compound in the CH₂Cl₂ fraction was identified as betulinic acid. Betulinic acid isolated from the CH₂Cl₂ fraction of VARM significantly attenuated α-MSH-induced melanogenesis in a dose dependent manner, which was stronger than that of arbutin used as a positive control.

CONCLUSIONS

These results indicate that VARM inhibits oxidative stress, tyrosinase activity, and α-MSH-induced melanogenesis in B16F10 cells, due primarily to the active compound, betulinic acid, in the CH₂Cl₂ fraction.

Necessity of Smad4 for the normal development of the mouse lacrimal gland

PURPOSE

Smad4, a key intracellular mediator in TGF-β signaling, plays a critical role in the normal development of many tissues/organs. However, its functional role in the development of the lacrimal gland (LG) has never been reported. The aim of this study was to investigate the role Smad4 may play in the development of LG by using Smad4 conditional knockout mice and comparing their LG changes with the LG in normal control mice.

METHODS

Smad4 in the LG, as well as in the lens, cornea, and ectoderm of the eyelids, was conditionally inactivated by using Pax6 promoter-driven Cre-transgenic mice. Lac Z reporter was used to visualize the developing LG by X-gal staining, and standard histologic approaches were used to reveal morphologic alterations.

RESULTS

Inactivation of Smad4 resulted in reduction in the size and number of acini in the embryonic LG and in pigment accumulation within the LG, although it did not affect the formation of the primary lacrimal bud. After birth, the LG from Smad4-mutant mice developed slowly, and pigment was observed starting from the P7 mutant LG. Thereafter, the mutant LG was considerably smaller than the normal LG and was eventually replaced by adipose tissue.

CONCLUSIONS

These results support the notion that Smad4 is essential for the normal development and maintenance of the mouse LG.

Bone morphogenetic protein signaling suppresses wound-induced skin repair by inhibiting keratinocyte proliferation and migration

Bone morphogenetic protein (BMP) signalling plays a key role in the control of skin development and postnatal remodelling by regulating keratinocyte proliferation, differentiation and apoptosis. To study the role of BMPs in wound-induced epidermal repair, we used transgenic mice overexpressing the BMP downstream component Smad1 under the control of a K14 promoter as an in vivo model, as well as ex vivo and in vitro assays. K14-caSmad1 mice exhibited retarded wound healing associated with significant inhibition of proliferation and increased apoptosis in healing wound epithelium. Furthermore, microarray and qRT-PCR analyses revealed decreased expression of a number of cytoskeletal/cell motility-associated genes including wound-associated keratins (Krt16, Krt17) and Myo5a, in the epidermis of K14-caSmad1 mice versus wild-type controls during wound healing. BMP treatment significantly inhibited keratinocyte migration ex vivo, and primary keratinocytes of K14-caSmad1 mice showed retarded migration compared to wild-type controls. Finally, siRNA-mediated silencing of Bmpr-1B in primary mouse keratinocytes accelerated cell migration and was associated with increased expression of Krt16, Krt17 and Myo5a compared to controls. Thus, this study demonstrates that BMPs inhibit keratinocyte proliferation, cytoskeletal organization and migration in regenerating skin epithelium during wound healing, and raises a possibility for using BMP antagonists for the management of chronic wounds.

Vitiligo road map

Vitiligo is a depigmenting disorder stemming from melanocyte loss or dysfunction. It has a complex, multifaceted etiology. We constructed a "vitiligo road map," consisting of basic science, clinical, and treatment components, in order to better portray our current understanding of vitiligo pathogenesis and reflect upon novel biomarkers and therapeutic targets for future research. The melanocyte map elaborates on the molecular processes and intracellular signaling pathways initiated by various external autocrine/paracrine factors in representing normal melanocyte homeostatic functions modulating its viability, proliferation, differentiation, dendricity, migration, and melanogenic processes. This vitiligo map identifies known inducers/triggers of vitiligo onset and progression that cultivate a microenvironment for melanocyte disappearance, real or functional. This map describes the molecular mechanisms of currently utilized clinical and experimental treatments of vitiligo that facilitate repigmentation.

Heterogeneity of neural crest-derived melanocytes

The majority of melanocytes originate from the neural crest cells (NCC) that migrate, spread on the whole embryo’s body to form elements of the nervous system and skeleton, endocrinal glands, muscles and melanocytes. Human melanocytes differentiate mainly from the cranial and trunk NCC. Although melanocyte development has traditionally been associated with the dorsally migrating trunk NCC, there is evidence that a part of melanocytes arise from cells migrating ventrally. The ventral NCC differentiate into neurons and glia of the ganglia or Schwann cells. It has been suggested that the precursors for Schwann cells differentiate into melanocytes. As melanoblasts travel through the dermis, they multiply, follow the process of differentiation and invade the forming human fetal epidermis up to third month. After birth, melanocytes lose the ability to proliferate, except the hair melanocytes that renew during the hair cycle. The localization of neural crest-derived melanocytes in non-cutaneous places e.g. eye (the choroid and stroma of the iris and the ciliary body), ear (cells of the vestibular organ, cochlear stria vascularis), meninges of the brain, heart seems to indicate that repertoire of melanocyte functions is much wider than we expected e.g. the protection of tissues from potentially harmful factors (e.g. free radicals, binding toxins), storage ions, and anti-inflammatory action.

Bone morphogenetic proteins differentially regulate pigmentation in human skin cells

Bone morphogenetic proteins (BMPs) are a large family of multi-functional secreted signalling molecules. Previously BMP2/4 were shown to inhibit skin pigmentation by downregulating tyrosinase expression and activity in epidermal melanocytes. However, a possible role for other BMP family members and their antagonists in melanogenesis has not yet been explored. In this study we show that BMP4 and BMP6, from two different BMP subclasses, and their antagonists noggin and sclerostin were variably expressed in melanocytes and keratinocytes in human skin. We further examined their involvement in melanogenesis and melanin transfer using fully matched primary cultures of adult human melanocytes and keratinocytes. BMP6 markedly stimulated melanogenesis by upregulating tyrosinase expression and activity, and also stimulated the formation of filopodia and Myosin-X expression in melanocytes, which was associated with increased melanosome transfer from melanocytes to keratinocytes. BMP4, by contrast, inhibited melanin synthesis and transfer to below baseline levels. These findings were confirmed using siRNA knockdown of BMP receptors BMPR1A/1B or of Myosin-X, as well as by incubating cells with the antagonists noggin and sclerostin. While BMP6 was found to use the p38MAPK pathway to regulate melanogenesis in human melanocytes independently of the Smad pathway, p38MAPK, PI3-K and Smad pathways were all involved in BMP6-mediated melanin transfer. This suggests that pigment formation may be regulated independently of pigment transfer. These data reveal a complex involvement of regulation of different members of the BMP family, their antagonists and inhibitory Smads, in melanocytes behaviour.

In vitro dedifferentiation of melanocytes from adult epidermis

In previous work we described a novel culture technique using a cholera toxin and PMA-free medium (Mel-mix) for obtaining pure melanocyte cultures from human adult epidermis. In Mel-mix medium the cultured melanocytes are bipolar, unpigmented and highly proliferative. Further characterization of the cultured melanocytes revealed the disappearance of c-Kit and TRP-1 and induction of nestin expression, indicating that melanocytes dedifferentiated in this in vitro culture. Cholera toxin and PMA were able to induce c-Kit and TRP-1 protein expressions in the cells, reversing dedifferentiation. TRP-1 mRNA expression was induced in dedifferentiated melanocytes by UV-B irradiated keratinocyte supernatants, however direct UV-B irradiation of the cells resulted in further decrease of TRP-1 mRNA expression. These dedifferentiated, easily accessible cultured melanocytes provide a good model for studying melanocyte differentiation and possibly transdifferentiation. Because melanocytes in Mel-mix medium can be cultured with human serum as the only supplement, this culture system is also suitable for autologous cell transplantation.