In vitro dedifferentiation of melanocytes from adult epidermis

Isolation of tdTomato Expressing Inter-follicular Epidermal Melanocytes or Keratinocytes from Mouse Tail Skin

The epidermis is the outermost layer of the skin. It is made up of mostly keratinocytes along with a small number of melanocytes and Langerhans cells. Melanocytes produce a pigment called melanin, which is transferred to the keratinocytes, and protects these cells from damage from UV radiation, as well as generating hair and skin colours. In this important relationship, keratinocytes exert control over melanocytes. Many questions regarding keratinocyte-melanocyte interactions have yet to be answered, and would benefit from study in model systems, to address diseases such as vitiligo and cutaneous melanoma. Most of the mouse is covered in fur and these areas lack the skin pigmenting inter-follicular epidermal (IFE) melanocytes. However, the mouse tail is pigmented analogously to human skin. Here, we present a method for isolating IFE melanocytes or keratinocytes expressing the tdTomato marker from the mouse tail, using fluorescence-activated cell sorting (FACS). The method involves firstly separating the tail skin epidermis from the dermis, and then digesting the epidermis to produce dissociated cells, which can then be sorted. These isolated cell populations can be studied using RNAseq or cultured in vitro. This protocol isolates IFE melanocytes or keratinocytes and immediately provides reasonable yields of cells, without the need to stain the cells for cell specific markers.

BRAFV600E induces reversible mitotic arrest in human melanocytes via microrna-mediated suppression of AURKB

Benign melanocytic nevi frequently emerge when an acquired BRAFV600E mutation triggers unchecked proliferation and subsequent arrest in melanocytes. Recent observations have challenged the role of oncogene-induced senescence in melanocytic nevus formation, necessitating investigations into alternative mechanisms for the establishment and maintenance of proliferation arrest in nevi. We compared the transcriptomes of melanocytes from healthy human skin, nevi, and melanomas arising from nevi and identified a set of microRNAs as highly expressed nevus-enriched transcripts. Two of these microRNAs-MIR211-5p and MIR328-3p-induced mitotic failure, genome duplication, and proliferation arrest in human melanocytes through convergent targeting of AURKB. We demonstrate that BRAFV600E induces a similar proliferation arrest in primary human melanocytes that is both reversible and conditional. Specifically, BRAFV600E expression stimulates either arrest or proliferation depending on the differentiation state of the melanocyte. We report genome duplication in human melanocytic nevi, reciprocal expression of AURKB and microRNAs in nevi and melanomas, and rescue of arrested human nevus cells with AURKB expression. Taken together, our data describe an alternative molecular mechanism for melanocytic nevus formation that is congruent with both experimental and clinical observations.

Phenotypic plasticity of melanocytes derived from human adult skin

We previously described a novel in vitro culture technique for dedifferentiated human adult skin melanocytes. Melanocytes cultured in a defined, cholera toxin and PMA free medium became bipolar, unpigmented, and highly proliferative. Furthermore, TRP-1 and c-Kit expression disappeared and EGFR receptor and nestin expression were induced in the cells. Here, we further characterized the phenotype of these dedifferentiated cells and by comparing them to mature pigmented melanocytes we detected crucial steps in their phenotype change. Our data suggest that normal adult melanocytes easily dedifferentiate into pluripotent stem cells given the right environment. This dedifferentiation process described here for normal melanocyte is very similar to what has been described for melanoma cells, indicating that phenotype switching driven by environmental factors is a general characteristic of melanocytes that can occur independent of malignant transformation.

Dedifferentiation of human epidermal melanocytes in vitro by long-term trypsinization

Human epidermal melanocytes can be induced to form melanocyte spheroids and revert to immature characteristics by long-term trypsinization (LTT). To further explore the biological characteristics of melanocytes after LTT and to study the underlying mechanism. Melanocytes were subjected to long-term (2 h) trypsinization in this study, after which their viability, proliferation and autophagy were characterized. The expression of melanocyte markers [human melanoma black45 (HMB45), tyrosinase (TYR) and Nestin] was detected and relative expression levels of mRNAs encoding TYR, Nestin, c-Kit and microphthalmia-associated transcription factor (MITF) were determined. After LTT, more short spindle-shaped melanocytes appeared and viability assays demonstrated that most melanocytes survived that treatment but had decreased proliferation rates compared to the untreated controls. There was a significant increase in autophagy of melanocytes after LTT and the expression of TYR was decreased compared with untreated control melanocytes. There were no significant differences in the expression of HMB45 or Nestin between the two groups. Compared with untreated melanocytes, levels of message ribonucleic acid (mRNAs) encoding TYR, c-Kit and MITF were decreased after LTT, while Nestin mRNA levels were increased. These results clarified that Long-term treatment with trypsin causes the dedifferentiation of mature epidermal melanocytes in vitro.

Melanocyte Precursors in the Hair Follicle Bulge of Repigmented Vitiligo Skin Are Controlled by RHO-GTPase, KCTD10, and CTNNB1 Signaling

In repigmentation of human vitiligo, the melanocyte (MC) precursors in the hair follicle bulge proliferate, migrate, and differentiate to repopulate the depigmented epidermis. Here, we present a comprehensive characterization of pathways and signals in the bulge that control the repigmentation process. Using biopsies from patients with vitiligo, we have selectively harvested, by laser capture microdissection, MC and keratinocyte precursors from the hair follicle bulge of untreated vitiligo skin and vitiligo skin treated with narrow-band UVB. The captured material was subjected to whole transcriptome RNA-sequencing. With this strategy, we found that repigmentation in the bulge MC precursors is driven by KCTD10, a signal with unknown roles in the skin, and CTNNB1 (encoding β-catenin) and RHO guanosine triphosphatase [RHO GTPase, RHO], two signaling pathways previously shown to be involved in pigmentation biology. Knockdown studies in cultured human MCs of RHOJ, the upmost differentially expressed RHO family component, corroborated with our findings in patients with vitiligo, identified RHOJ involvement in UV response and melanization, and confirmed previously identified roles in melanocytic cell migration and apoptosis. A better understanding of mechanisms that govern repigmentation in MC precursors will enable the discovery of molecules that induce robust repigmentation phenotypes in vitiligo.

The tolerance of human epidermal cells to trypsinization in vitro

To characterize the tolerance of different types of human epidermal cells to trypsinization in vitro and develop a new method to separate and purify melanocytes according to their tolerance to trypsinization. Epidermal cells were obtained by separating the epidermis from human foreskins. Some of those cells were used for routine culture, and then were subjected to differential trypsin digestion. The remaining epidermal cells were resuspended in a 0.25% trypsin solution and then were neutralized by the addition of bovine serum at different time points. Immunofluorescence staining of HMB45, K15 and vimentin was used to identify melanocytes, keratinocytes and fibroblasts, respectively. We found that Keratinocytes, melanocytes and fibroblasts are primary cells obtained from conventional cultures of human skin. Purified keratinocytes and melanocytes can be obtained by conventional differential trypsin digestion, but fibroblasts in the melanocyte population quickly gain a survival advantage after passage. With longer trypsin digestion times, the number of adherent cells decreased, the time required for cell attachment increased, and the proportion of melanocytes increased. There were no obvious keratinocytes in cell populations obtained after 12 h of trypsinization of epidermal cells, and more short spindle-shaped melanocytes appeared, all of which were HMB45-positive. In conclusion, the tolerance of human epidermal melanocytes to trypsinization in vitro was better than epidermal keratinocytes, and that property can be used to purify melanocytes and was better than traditional differential trypsin digestion. The morphology of cells that survived the long-term trypsin digestion changed and they had good proliferative activity, but seemed to be more immature.

Deciphering skin re-pigmentation patterns in vitiligo: an update on the cellular and molecular events involved

Current treatment of vitiligo is still a great challenge, since most cases of vitiligo have variable re-pigmentation outcomes due to their unpredictable responses to existing therapeutic regimens. There is an urgent need to identify this re-pigmentation process and to develop novel therapies. This review illustrates the most current research and latest understanding of vitiligo skin re-pigmentation and related regulatory mechanisms. Literature was collected from PubMed until January 2020, using the search terms including "vitiligo," "re-pigmentation," "phototherapy," "narrow-band ultraviolet B, " "excimer," "fractional carbon dioxide laser," and "melanocyte stem cells." Literature was mainly derived from English articles. Article type was not limited. Emerging evidence suggests that patients with vitiligo present various re-pigmentation patterns following ultraviolet B phototherapy, which relies on different cell reservoirs from the perilesional margins and/or from uninvolved hair follicles to replenish functional melanocytes that are lost in vitiliginous skin. The following events are likely to be involved in this re-pigmentation process, including: 1) changes in the paracrine secretion and distribution of transforming growth factor-β1 in the bulge area and in the epidermis; 2) the enhanced transfer of dermal pro-melanogenic growth factors to the epidermis; and 3) the induction of a C-X-C motif chemokine ligand (CXCL) 12-enriched micro-environment that efficiently recruits CXCR4- or CXCR7-positive melanocytes. Ongoing studies on the cellular and molecular events underlying vitiligo re-pigmentation will help design new therapeutic strategies to improve treatment outcomes.

pH-controlled histone acetylation amplifies melanocyte differentiation downstream of MITF

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. This involves the rapid and selective induction of melanocyte maturation genes, while concomitantly the expression of other effector genes is maintained. In this study, using cell-based and zebrafish model systems, we report on a pH-mediated feed-forward mechanism of epigenetic regulation that enables selective amplification of the melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of the enzyme carbonic anhydrase 14 (CA14). Nuclear localization of CA14 leads to an increase of the intracellular pH, resulting in the activation of the histone acetyl transferase p300/CBP. In turn, enhanced H3K27 histone acetylation at selected differentiation genes facilitates their amplified expression via MITF. CRISPR-mediated targeted missense mutation of CA14 in zebrafish results in the formation of immature acidic melanocytes with decreased pigmentation, establishing a central role for this mechanism during melanocyte differentiation in vivo. Thus, we describe an epigenetic control system via pH modulation that reinforces cell fate determination by altering chromatin dynamics.

Tracking keratinocytes and melanocytes using carboxyfluorescein hydroxysuccinimidyl ester staining

Introduction

The treatment of burn wounds and hypopigmentation conditions often require autologous transplantation of keratinocytes and melanocytes. Tracking transplanted cells to ascertain their contribution to tissue recapitulation presents a challenge. This study demonstrates a methodology based on passive staining with carboxyfluorescein hydroxysuccinimidyl ester (CFSE) that enables localization of cells in tissue sections to investigate the fate of transplanted cells in wound re-epithelialisation.

Methods

Viability and migration of CFSE-stained keratinocytes and melanocytes were investigated using viability staining and scratch assays, while proliferation of cells was measured using flow cytometry. In addition, CFSE-stained keratinocytes and melanocytes were transplanted to a human ex vivo wound model, either in suspension, or with the aid of macroporous gelatine microcarriers. Wounds were analysed seven, 14 and 21 days post transplantation using cryosectioning and fluorescence microscopy. Sections from wounds with transplanted co-cultured keratinocytes and melanocytes were stained for pancytokeratin to distinguish keratinocytes.

Results

CFSE-staining of keratinocytes and melanocytes did not affect the viability, migration or proliferation of the cells. Transplanted cells were tracked in ex vivo wounds for 21 days, illustrating that the staining had no effect on wound re-epithelialisation. In conclusion, this study presents a novel application of CFSE-staining for tacking transplanted primary human keratinocytes and melanocytes.

Exploring Differential Connexin Expression across Melanocytic Tumor Progression Involving the Tumor Microenvironment

The incidence of malignant melanoma, one of the deadliest cancers, continues to increase. Here we tested connexin (Cx) expression in primary melanocytes, melanoma cell lines and in a common nevus, dysplastic nevus, and thin, thick, and metastatic melanoma tumor progression series involving the tumor microenvironment by utilizing in silico analysis, qRT-PCR, immunocyto-/histochemistry and dye transfer tests. Primary melanocytes expressed GJA1/Cx43, GJA3/Cx46 and low levels of GJB2/Cx26 and GJC3/Cx30.2 transcripts. In silico data revealed downregulation of GJA1/Cx43 and GJB2/Cx26 mRNA, in addition to upregulated GJB1/Cx32, during melanoma progression. In three melanoma cell lines, we also showed the loss of GJA1/Cx43 and the differential expression of GJB1/Cx32, GJB2/Cx26, GJA3/Cx46 and GJC3/Cx30.2. The dominantly paranuclear localization of connexin proteins explained the ~10–90 times less melanoma cell coupling compared to melanocytes. In melanocytic tumor tissues, we confirmed the loss of Cx43 protein, fall of cell membrane and elevated paranuclear Cx32 with moderately increased cytoplasmic Cx26 and paranuclear Cx30.2 positivity during tumor progression. Furthermore, we found Cx43, Cx26 and Cx30 proteins upregulated in the melanoma adjacent epidermis, and Cx43 in the tumor flanking vessels. Therefore, differential connexin expression is involved in melanocytic tumor progression where varying connexin isotypes and levels reflect tumor heterogeneity-related bidirectional adaptive interactions with the microenvironment.

Quantitative analysis of melanin content in a three-dimensional melanoma cell culture

Reliable measurement of the amount of melanin produced by melanocytes is essential to study various skin disorders and to evaluate the efficacy of candidate reagents for such disorders or for whitening purposes. Conventional melanin quantification methods are based on absorption spectroscopy, which measures the melanin from lysed cells grown on two-dimensional (2D) surfaces. The 2D culture environment is intrinsically different from in vivo systems though, and therefore cells often lose their original phenotypes. Melanocytes in particular lose their ability to synthesize melanin, thereby requiring melanogenesis stimulators such as alpha-melanocyte stimulating hormone (α-MSH) to promote melanin synthesis. In this study, we compared melanin synthesis in B16 murine melanoma cells grown in 2D and three-dimensional culture environments. B16 cells instantly formed an aggregate in a hanging-drop culture, and synthesized melanin efficiently without treatment of α-MSH. We were able to measure the melanin secreted from a single melanocyte aggregate, indicating that our method enables non-invasive long-term monitoring of melanin synthesis and secretion in a high-throughput format. We successfully tested the developed platform by quantifying the depigmenting effects of arbutin and kojic acid.

Isolation and Culture of Epidermal Melanocytes

Melanocytes which represent around 5% of epidermal cells are located in the basal layer. To culture melanocytes we used trypsin digestion instead of dispase to obtain a cell suspension containing only basal keratinocytes and melanocytes. Melanocytes are cells which need a great attention. Indeed they dedifferentiate easily in culture as soon as they are in pure culture. Factors secreted by contaminating keratinocytes allow melanocytes to stay dendritic but by regulating their number avoid their growth. In order to age, phototype and other individual dependent factors regulate the behavior of melanocytes in vitro. Thus, microscopic examination of melanocytes has to be performed each day to adapt conditions of culture to each primary cell culture. This is the secret to have a nice melanocyte culture.

Skin cells for use in an alternate diagnostic method for Duchenne muscular dystrophy

The importance of molecular diagnosis and identification of disease-associated variants for Duchenne muscular dystrophy (DMD) is evident in the age of gene-based therapies and personalised medicine. Detection of the causative DMD variant and determination of its effects on dystrophin expression is best achieved by analysis of RNA extracted from muscle biopsy material. However, this is not done routinely, as the procedure can be traumatic, especially to young children, and carries risk of complications related to the use of anaesthetic. As skin biopsies are safer and straightforward to perform than muscle biopsies, we investigated the utility of cultured human epidermal melanocytes and dermal fibroblasts as alternative tools for RNA-based diagnosis of DMD. Shallow skin biopsies from 5 boys with genetically confirmed diagnoses of DMD were used to culture fibroblasts and melanocytes. Biopsies were sampled, and tolerated without complications, using local anaesthetic cream. Dystrophin expression in the cultured cells was assessed using immunocytochemical staining, quantitative real-time PCR and cDNA sequencing methodologies. We observed differential expression of the full-length dystrophin muscle transcript, with significantly more robust expression in melanocytes, compared to that in fibroblasts. Our results suggest that cultured skin melanocytes may present an alternative tool for RNA-based genetic diagnosis of DMD.

Development and validation of a simple method for the extraction of human skin melanocytes

Primary melanocytes in culture are useful models for studying epidermal pigmentation and efficacy of melanogenic compounds, or developing advanced therapy medicinal products. Cell extraction is an inevitable and critical step in the establishment of cell cultures. Many enzymatic methods for extracting and growing cells derived from human skin, such as melanocytes, are described in literature. They are usually based on two enzymatic steps, Trypsin in combination with Dispase, in order to separate dermis from epidermis and subsequently to provide a suspension of epidermal cells. The objective of this work was to develop and validate an extraction method of human skin melanocytes being simple, effective and applicable to smaller skin samples, and avoiding animal reagents. TrypLE™ product was tested on very limited size of human skin, equivalent of multiple 3-mm punch biopsies, and was compared to Trypsin/Dispase enzymes. Functionality of extracted cells was evaluated by analysis of viability, morphology and melanin production. In comparison with Trypsin/Dispase incubation method, the main advantages of TrypLE™ incubation method were the easier of separation between dermis and epidermis and the higher population of melanocytes after extraction. Both protocols preserved morphological and biological characteristics of melanocytes. The minimum size of skin sample that allowed the extraction of functional cells was 6 × 3-mm punch biopsies (e.g., 42 mm²) whatever the method used. In conclusion, this new procedure based on TrypLE™ incubation would be suitable for establishment of optimal primary melanocytes cultures for clinical applications and research.

Global Gene Expression Analysis in an in vitro Fibroblast Model of Idiopathic Pulmonary Fibrosis Reveals Potential Role for CXCL14/CXCR4

Idiopathic Pulmonary Fibrosis (IPF) is a progressive disorder that is marked by an over accumulation of activated fibroblast populations. Despite the improved understanding of many mechanisms within this disease, global gene expression analysis has few focused studies on the fibroblast, the central effector cell of progressive fibrosis. We present a unique analysis of IPF pulmonary fibroblasts as they transition through cell culture and identify in vitro altered cellular processes. Fibroblasts were isolated from diseased (n = 8) and non-diseased (n = 4) lungs. Global gene expression analysis was carried out at the initial point of isolation and after 3 weeks of culture. We identify several genes that are altered by removal of the fibroblast from the IPF environment. Comparison of this subset of genes to four previously published whole lung analyses refined our list to a small subset of key fibroblast specific genes important in IPF. Application of STRING database analysis and confirmation via in-vitro and histological assay highlights the CXCL14/CXCR4 chemokine axis with a possible role in the progression and/or activation of fibroblasts within the IPF lung. Our findings, present a possible therapeutic target for IPF and a model for the study and discovery of novel protein and processes in this terrible disease.

Differential miRNA expression profiles in human keratinocytes in response to protein kinase C inhibitor

Aberrant expression of microRNAs (miRNAs) is widely accepted to be involved in keratinocyte differentiation and to be dependent on activation of the protein kinase C (PKC) pathway. However, the miRNA profiles and biological characteristics of keratinocytes induced by specific inhibitors of PKC have yet to be elucidated. The present study aimed to explore the differential miRNA expression profiles in keratinocytes treated with the PKC inhibitor GF109203X, by conducting a bioinformatics analysis. Parts of the GF109203X‑induced keratinocytes formed distinct clones after 2 days of culture, and the expression of intergrin β1, cytokeratin (CK)19 and CK14 were positive, whereas CK10 expression was negative. A total of 79 miRNAs were differentially expressed in keratinocytes treated with GF109203X, among which 45 miRNAs were upregulated and 34 were downregulated. The significantly upregulated microRNAs includedhsa‑miR‑1‑3p and miR‑181c‑5p, whereas hsa‑miR‑31‑5p and hsa‑let‑7c‑3p were significantly downregulated. In addition, the results of reverse transcription‑quantitative polymerase chain reaction exhibited consistency with the microarray results. An enrichment analysis demonstrated that certain target genes of the differentially expressed miRNAs serve an important role in cell proliferation and differentiation, cell cycle progression and apoptosis, etc. These results revealed that GF109203X induced the differential expression of certain miRNAs when keratinocytes began showing the characteristics of epidermal‑like stem cells, which may provide a novel approach for wound healing and regeneration of skin tissues.

Cosmeceutical Effects of Galactomannan Fraction from Arenga pinnata Fruits In vitro

BACKGROUND

Cosmeceuticals refer to natural cosmetics with medical-like benefits due to their bioactive contents. Sugar palm fruit (Arenga pinnata) extract has been claimed for its anti-aging effect in vitro. However, its active compounds for cosmeceuticals is still unclear.

OBJECTIVE

This study was aimed to extract galactomannan from A. pinnata fruits and test its efficacy for tyrosinase inhibition, antioxidant, and anti-photoaging activities in vitro.

MATERIALS AND METHODS

Galactomannan from A. pinnata fruits was extracted by freeze drying and identified for its chemical compounds by using pyrolysis gas chromatography-mass spectrometry (py-GC/MS). Galactomannan was tested for its tyrosinase inhibition in both cell-based (melanocytes) and enzymatic assays, antioxidant activity using ferrous ion chelating assay (FCA) assay, and anti-photoaging activity for inhibiting the gene expression of matrix metalloproteinase-1 (MMP-1) and MMP-13 in macrophages using quantitative real-time polymerase chain reaction (qRT-PCR) analysis.

RESULTS

Identification of galactomannan fraction from A. pinnata fruits by py-GC/MS mainly consisted of oxonium ion and glucosides. For cellular assay, galactomannan at 5 μg/mL inhibited >50% of tyrosinase activity in melanocytes induced by phorbol myristate acetate. At the enzymatic level, galactomannan at similar concentration showed less tyrosinase activity inhibition (~20%). FCA results showed that galactomannan at 10 μg/mL exerted >50% of antioxidant activity. The qRT-PCR data indicated that galactomannan at 5 μg/mL inhibited >50% of MMP-1 and MMP-13 gene expressions in ultraviolet B-treated macrophages.

CONCLUSION

Galactomannan fraction from A. pinnata fruits has efficacy for enlightening effect, antioxidant, and anti-photoaging activity in the dose-independent pattern, indicating its cosmeceutical effects for skin healthcare.

SUMMARY

A. pinnata fruit containing galactomannan has cosmeceutical potentials through enlightening effect, antioxidant, and anti-photoaging activity in vitro.Galactomannan fraction has inhibitory effect on tyrosinase activity in both cellular melanocytes and enzymatic systems.Galactomannan fraction has strong protection against UVB-irradiation effect by inhibiting collagenase genes (MMP-1 and MMP-13) in macrophages. Abbreviations Used: Py-GC/MS: Pyrolysis-Gas Chromatography-Mass Spectrometry; FCA: Ferrous chelating activity; MMP: Matrix metalloproteinase; qRT-PCR: Quantitative Real-Time Polymerase Chain Reaction; PMA: Phorbol myristate acetate; UV: Ultraviolet; RPMI: Roswell Park Memorial Institute; DMEM: Dulbecco's modified eagle media; FBS: Fetal bovine serum; PBS: Phosphate buffered saline; MTT: 3-(4,5-diethylthiazol-2-yl)-2,5-dipheniltetrazolium bromide; L-DOPA: L-3,4-dihydroxyphenylalanine; EDTA: Ethylenediaminetetraacetic acid; GAPDH: Glyceraldehyde 3-phosphate dehydrogenase; DPPH: 1,1-diphenyl-2-picryl-hydrazyl; SPF: Sun protection factor.

NF1 and Neurofibromin: Emerging Players in the Genetic Landscape of Desmoplastic Melanoma

Neurofibromatosis type I (NF1), a monogenic disorder with an autosomal dominant mode of inheritance, is caused by alterations in the NF1 gene which codes for the protein neurofibromin. Functionally, NF1 is a tumor suppressor as it is GTPase-activating protein that negatively regulates the MAPK pathway. More recently, much attention has focused on the role of NF1 and neurofibromin in melanoma as mutations in NF1 have been found to constitute 1 of the 4 distinct genomic categories of melanoma, with the other 3 comprising BRAF, NRAS, and "triple-wild-type" subtypes. In this review, we parse the literature on NF1 and neurofibromin with a view to clarifying and gaining a better understanding of their precise role/s in melanomagenesis. We begin with a historic overview, followed by details regarding structure and function and characterization of neural crest development as a model for genetic reversion in neoplasia. Melanogenesis in NF1 sets the stage for the discussion on the roles of NF1 and neurofibromin in neural crest-derived neoplasms including melanoma with particular emphasis on NF1 and neurofibromin as markers of melanocyte dedifferentiation in desmoplastic melanoma.

Melanosome transfer to keratinocyte in the chicken embryonic skin is mediated by vesicle release associated with Rho-regulated membrane blebbing

During skin pigmentation in amniotes, melanin synthesized in the melanocyte is transferred to keratinocytes by a particle called the melanosome. Previous studies, mostly using dissociated cultured cells, have proposed several different models that explain how the melanosome transfer is achieved. Here, using a technique that labels the plasma membrane of melanocytes within a three-dimensional system that mimics natural tissues, we have visualized the plasma membrane of melanocytes with EGFP in chicken embryonic skin. Confocal time-lapse microscopy reveals that the melanosome transfer is mediated, at least in part, by vesicles produced by plasma membrane. Unexpectedly, the vesicle release is accompanied by the membrane blebbing of melanocytes. Blebs that have encapsulated a melanosome are pinched off to become vesicles, and these melanosome-containing vesicles are finally engulfed by neighboring keratinocytes. For both the membrane blebbing and vesicle release, Rho small GTPase is essential. We further show that the membrane vesicle-mediated melanosome transfer plays a significant role in the skin pigmentation. Given that the skin pigmentation in inter-feather spaces in chickens is similar to that in inter-hair spaces of humans, our findings should have important consequences in cosmetic medicine.

Self-Antigen Presentation by Keratinocytes in the Inflamed Adult Skin Modulates T-Cell Auto-Reactivity

Keratinocytes have a pivotal role in the regulation of immune responses, but the impact of antigen presentation by these cells is still poorly understood, particularly in a situation where the antigen will be presented only in adult life. Here, we generated a transgenic mouse model in which keratinocytes exclusively present a myelin basic protein (MBP) peptide covalently linked to the major histocompatibility complex class II β-chain, solely under inflammatory conditions. In these mice, inflammation caused by epicutaneous contact sensitizer treatment resulted in keratinocyte-mediated expansion of MBP-specific CD4(+) T cells in the skin. Moreover, repeated contact sensitizer application preceding a systemic MBP immunization reduced the reactivity of the respective CD4(+) T cells and lowered the symptoms of the resulting experimental autoimmune encephalomyelitis. This downregulation was CD4(+) T-cell-mediated and dependent on the presence of the immune modulator Dickkopf-3. Thus, presentation of a neo self-antigen by keratinocytes in the inflamed, adult skin can modulate CD4(+) T-cell auto-aggression at a distal organ.

In ovo gene manipulation of melanocytes and their adjacent keratinocytes during skin pigmentation of chicken embryos

During skin pigmentation in avians and mammalians, melanin is synthesized in the melanocytes, and subsequently transferred to adjacently located keratinocytes, leading to a wide coverage of the body surface by melanin-containing cells. The behavior of melanocytes is influenced by keratinocytes shown mostly by in vitro studies. However, it has poorly been investigated how such intercellular cross-talk is regulated in vivo because of a lack of suitable experimental models. Using chicken embryos, we developed a method that enables in vivo gene manipulations of melanocytes and keratinocytes, where these cells are separately labeled by different genes. Two types of gene transfer techniques were combined: one was a retrovirus-mediated gene infection into the skin/keratinocytes, and the other was the in ovo DNA electroporation into neural crest cells, the origin of melanocytes. Since the Replication-Competent Avian sarcoma-leukosis virus long terminal repeat with Splice acceptor (RCAS) infection was available only for the White leghorn strain showing little pigmentation, melanocytes prepared from the Hypeco nera (pigmented) were back-transplanted into embryos of White leghorn. Prior to the transplantation, enhanced green fluorescent protein (EGFP)(+) Neo(r+) -electroporated melanocytes from Hypeco nera were selectively grown in G418-supplemented medium. In the skin of recipient White leghorn embryos infected with RCAS-mOrange, mOrange(+) keratinocytes and transplanted EGFP(+) melanocytes were frequently juxtaposed each other. High-resolution confocal microscopy also revealed that transplanted melanocytes exhibited normal behaviors regarding distribution patterns of melanocytes, dendrite morphology, and melanosome transfer. The method described in this study will serve as a useful tool to understand the mechanisms underlying intercellular regulations during skin pigmentation in vivo.

Novel method for isolating human melanoblasts from keratinocyte culture

The characterization of melanoblasts is important for understanding their in vivo development, melanoma formation, and pigment-related disorders. However, no methods have been reported for the isolation of melanoblasts from human skin. Using a 'calcium-pulse' technique, involving the differentiation of human keratinocytes with high calcium and the subsequent spontaneous separation of the epidermal sheets, we effectively isolated human melanoblasts (keratinocyte-adapted melanoblasts, KaMBs) from keratinocyte culture. The KaMBs expressed early melanogenesis-related genes, including BRN2, which is a known melanoblast marker. Moreover, the KaMBs displayed much higher proliferative and growth capacities than the primary melanocytes. Considering that keratinocytes might provide an in vivo-like environment for KaMBs during isolation and in vitro culture, the 'calcium-pulse' technique offers an unprecedented, easy, and efficient method for the isolation of human melanoblasts, retaining the original characteristics of these cells.

New procedure for epidermal cell isolation using kiwi fruit actinidin, and improved culture of melanocytes in the presence of leukaemia inhibitory factor and forskolin

OBJECTIVES

Conventional isolation of epidermis from the dermis and disruption of epidermal sheets to liberate the cells, are performed using proteolytic enzymes such as thermolysin or collagenase. Selective population expansion of melanocytes is achieved by suppressing proliferation of keratinocytes and fibroblasts in epidermal cell suspensions, using phorbol esters and cholera toxin. Here, we introduce a new procedure for isolation of epidermal cells, using proteolytic activity of kiwi fruit actinidin, and also an improved growth medium for melanocytes in the presence of leukaemia inhibitory factor (LIF) and forskolin.

MATERIALS AND METHODS

Dermo-epidermal separation and epidermal sheet cell dispersion were performed using actinidin compared to conventional proteases including collagenase, thermolysin or trypsin. Thereafter, melanocyte culture was performed in two common media and one modified medium to discover optimization for these cells.

RESULTS

We found that dermo-epidermal separation and epidermal sheet cell dispersion using kiwi fruit actinidin were considerably better than previously used methods, both from the aspect of less fibroblast and keratinocyte contamination, and of more viable native cells. Also, melanocytes proliferated better in phorbol ester- and cholera toxin-free proliferation medium supplemented with LIF and forskolin.

CONCLUSION

Less contamination and higher numbers of viable cells were actinidin preferential for separation of epidermis and isolation of epidermal cells. Supplementation of LIF and forskolin to new medium increased proliferation potential of melanocytes in comparison to exogenous mitogens.

Transdifferentiation of mesenchymal stem cells-derived adipogenic-differentiated cells into osteogenic- or chondrogenic-differentiated cells proceeds via dedifferentiation and have a correlation with cell cycle arresting and driving genes

It is generally accepted that after differentiation bone marrow mesenchymal stem cells (MSC) become lineage restricted and unipotent in an irreversible manner. However, current results imply that even terminally differentiated cells transdifferentiate across lineage boundaries and therefore act as a progenitor cells for other lineages. This leads to the questions that whether transdifferentiation occurs via direct cell-to-cell conversion or dedifferentiation to a progenitor cells and subsequent differentiation, and whether MSC potency decreases or increases during differentiation. To address these questions, MSC were differentiated into adipogenic lineage cells, followed by dedifferentiation. The process of dedifferentiation was also confirmed by single cell clonal analysis. Finally the dedifferentiated cells were used for adipogenesis, osteogenesis and chondrogenesis. Histology, FACS, qPCR and GeneChip analyses of undifferentiated MSC, adipogenic-differentiated and dedifferentiated cells were performed. Interestingly, gene profiling and bioinformatics demonstrated that upregulation (DHCR24, G0S2, MAP2K6, SESN3) and downregulation (DST, KAT2, MLL5, RB1, SMAD3, ZAK) of distinct genes have an association with cell cycle arrest in adipogenic-differentiated cells and perhaps narrow down the lineage potency. However, the upregulation (CCND1, CHEK, HGF, HMGA2, SMAD3) and downregulation (CCPG1, RASSF4, RGS2) of these genes have an association with cell cycle progression and maybe motivate dedifferentiation of adipogenic-differentiated cells. We found that dedifferentiated cells have a multilineage potency comparable to MSC, and also observed the associative role of proliferation genes with cell cycle arrest and progression. Concluded, our results indicate that transdifferentiation of adipogenic-differentiated cells into osteogenic- or chondrogenic-differentiated cells proceeds via dedifferentiation and correlates with cell cycle arresting and deriving genes. Regarding clinical use, the knowledge of potency and underlying mechanisms are prerequisites.

Melanocytes--a novel tool to study mitochondrial dysfunction in Duchenne muscular dystrophy

Dystrophin is a subsarcolemmal protein that, by linking the actin cytoskeleton to the extracellular matrix via dystroglycans, is critical for the integrity of muscle fibers. Here, we report that epidermal melanocytes, obtained from conventional skin biopsy, express dystrophin with a restricted localization to the plasma membrane facing the dermal–epidermal junction. In addition the full-length muscle isoform mDp427 was clearly detectable in melanocyte cultures as assessed by immunohistochemistry, RNA, and Western blot analysis. Melanocytes of Duchenne muscular dystrophy (DMD) patients did not express dystrophin, and the ultrastructural analysis revealed typical mitochondrial alterations similar to those occurring in myoblasts from the same patients. Mitochondria of melanocytes from DMD patients readily accumulated tetramethylrhodamine methyl ester, indicating that they are energized irrespective of the presence of dystrophin but, at variance from mitochondria of control donors, depolarized upon the addition of oligomycin, suggesting that they are affected by a latent dysfunction unmasked by inhibition of the ATP synthase. Pure melanocyte cultures can be readily obtained by conventional skin biopsies and may be a feasible and reliable tool alternative to muscle biopsy for functional studies in dystrophinopathies. The mitochondrial dysfunction occurring in DMD melanocytes could represent a promising cellular biomarker for monitoring dystrophinopathies also in response to pharmacological treatments. J. Cell. Physiol. 228: 1323–1331, 2013. © 2012 Wiley Periodicals, Inc.