Regulation of pigment cell-specific gene expression by MITF

Extracellular vesicles released by keratinocytes regulate melanosome maturation, melanocyte dendricity, and pigment transfer

Extracellular vesicles (EVs) facilitate the transfer of proteins, lipids, and genetic material between cells and are recognized as an additional mechanism for sustaining intercellular communication. In the epidermis, the communication between melanocytes and keratinocytes is tightly regulated to warrant skin pigmentation. Melanocytes synthesize the melanin pigment in melanosomes that are transported along the dendrites prior to the transfer of melanin pigment to keratinocytes. EVs secreted by keratinocytes modulate pigmentation in melanocytes [(A. Lo Cicero et al., Nat. Commun. 6, 7506 (2015)]. However, whether EVs secreted by keratinocytes contribute to additional processes essential for melanocyte functions remains elusive. Here, we show that keratinocyte EVs enhance the ability of melanocytes to generate dendrites and mature melanosomes and promote their efficient transfer. Further, keratinocyte EVs carrying Rac1 induce important morphological changes, promote dendrite outgrowth, and potentiate melanin transfer to keratinocytes. Hence, in addition to modulating pigmentation, keratinocytes exploit EVs to control melanocyte plasticity and transfer capacity. These data demonstrate that keratinocyte-derived EVs, by regulating melanocyte functions, are major contributors to cutaneous pigmentation and expand our understanding of the mechanism underlying skin pigmentation via a paracrine EV-mediated communication.

Clinically compliant cryopreservation of differentiated retinal pigment epithelial cells

BACKGROUND AIMS

Age-related macular degeneration (AMD) is the most common cause of blindness in elderly patients within developed countries, affecting more than 190 million worldwide. In AMD, the retinal pigment epithelial (RPE) cell layer progressively degenerates, resulting in subsequent loss of photoreceptors and ultimately vision. There is currently no cure for AMD, but therapeutic strategies targeting the complement system are being developed to slow the progression of the disease.

METHODS

Replacement therapy with pluripotent stem cell-derived (hPSC) RPEs is an alternative treatment strategy. A cell therapy product must be produced in accordance with Good Manufacturing Practices at a sufficient scale to facilitate extensive pre-clinical and clinical testing. Cryopreservation of the final cell product is therefore highly beneficial, as the manufacturing, pre-clinical and clinical testing can be separated in time and location.

RESULTS

We found that mature hPSC-RPE cells do not survive conventional cryopreservation techniques. However, replating the cells 2-5 days before cryopreservation facilitates freezing. The replated and cryopreserved hPSC-RPE cells maintained their identity, purity and functionality as characteristic RPEs, shown by cobblestone morphology, pigmentation, transcriptional profile, RPE markers, transepithelial resistance and pigment epithelium-derived factor secretion. Finally, we showed that the optimal replating time window can be tracked noninvasively by following the change in cobblestone morphology.

CONCLUSIONS

The possibility of cryopreserving the hPSC-RPE product has been instrumental in our efforts in manufacturing and performing pre-clinical testing with the aim for clinical translation.

Naturally-Occurring Tyrosinase Inhibitors Classified by Enzyme Kinetics and Copper Chelation

Currently, there are three major assaying methods used to validate in vitro whitening activity from natural products: methods using mushroom tyrosinase, human tyrosinase, and dopachrome tautomerase (or tyrosinase-related protein-2, TRP-2). Whitening agent development consists of two ways, melanin synthesis inhibition in melanocytes and downregulation of melanocyte stimulation. For melanin levels, the melanocyte cell line has been used to examine melanin synthesis with the expression levels of TRP-1 and TRP-2. The proliferation of epidermal surfaced cells and melanocytes is stimulated by cellular signaling receptors, factors, or mediators including endothelin-1, α-melanocyte-stimulating hormone, nitric oxide, histamine, paired box 3, microphthalmia-associated transcription factor, pyrimidine dimer, ceramide, stem cell factors, melanocortin-1 receptor, and cAMP. In addition, the promoter region of melanin synthetic genes including tyrosinase is upregulated by melanocyte-specific transcription factors. Thus, the inhibition of growth and melanin synthesis in gene expression levels represents a whitening research method that serves as an alternative to tyrosinase inhibition. Many researchers have recently presented the bioactivity-guided fractionation, discovery, purification, and identification of whitening agents. Melanogenesis inhibition can be obtained using three different methods: tyrosinase inhibition, copper chelation, and melanin-related protein downregulation. There are currently four different types of inhibitors characterized based on their enzyme inhibition mechanisms: competitive, uncompetitive, competitive/uncompetitive mixed-type, and noncompetitive inhibitors. Reversible inhibitor types act as suicide substrates, where traditional inhibitors are classified as inactivators and reversible inhibitors based on the molecule-recognizing properties of the enzyme. In a minor role, transcription factors can also be downregulated by inhibitors. Currently, the active site copper iron-binding inhibitors such as kojic acid and chalcone exhibit tyrosinase inhibitory activity. Because the tyrosinase catalysis site structure is important for the mechanism determination of tyrosinase inhibitors, understanding the enzyme recognition and inhibitory mechanism of inhibitors is essential for the new development of tyrosinase inhibitors. The present review intends to classify current natural products identified by means of enzyme kinetics and copper chelation to exhibit tyrosinase enzyme inhibition.

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.

New Butyroside D from Argan Press Cake Possess Anti-Melanogenesis Effect via MITF Downregulation in B16F10 and HEM Cells

Hyperpigmentation is a skin condition where patches of skin become darker in color due to excess melanin production upon UV exposure leading to melasma, which are lentigines or post inflammatory hyperpigmentation that psychologically affecting a great number of people. The present study investigates the anti-melanogenic effect of Butyroside D and the underling mechanism. After the confirmation of the non-cytotoxic effect of Butyroside D on B16F10 cells, we proceeded with analyzing the impact of the treatment at low and high concentration (i.e., 0.2 μM and 2 μM) using gene profiling analysis and examined the differentiation in gene expression. Our results identify cyclic adenosine monophosphate (cAMP), Wnt/β-catenin and Mitogen-Activated Protein Kinase (MAPK) signaling pathways to be downregulated upon treatment with Butyroside D. These pathways were targeted to further validate the effect of Butyroside D on membrane receptors melanocortin 1 receptor (MC1R) and receptor tyrosine kinase (c-Kit), related microphthalmia-associated transcription factor (MITF) and consequently tyrosinase (TYR), and tyrosine-related protein-1 (TYRP-1) that were all shown to be downregulated and, therefore, leading to the repression of melanin biosynthesis. Finally, the anti-melanogenic effect of Butyroside D was confirmed on human epidermal melanocytes (HEM) cells by inhibiting the activation of cAMP pathway generally mediated through α-melanocyte-stimulating hormone (α-MSH) and MC1R. Overall, this study suggests the potential applicability of this purified compound for the prevention of hyperpigmentation conditions.

Potential anti-ageing effects of probiotic-derived conditioned media on human skin cells

In this study, the protective functions of bacteria-free conditioned media from Bifidobacterium and Lactobacillus species against ultraviolet radiation-induced skin ageing and associated cellular damage were investigated. The effects of ultraviolet radiation-induced reactive oxygen species production were suppressed by all conditioned media; particularly, the loss of cell viability and downregulation of collagen gene expression were significantly reversed by the conditioned media from B. longum and B. lactis. Further exa mination of potential anti-pigmentation effects revealed that the B. lactis-derived conditioned media significantly inhibited tyrosinase activity and alpha-melanocyte-stimulating hormone-induced melanin production in human epidermal melanocytes. Further, the conditioned media suppressed the phosphorylation of extracellular signal- related kinase, which functions as an upstream regulator of melanogenesis. Therefore, B. lactis-derived conditioned media can potentially protect against cellular damage involved in skin-ageing processes.

MicroRNA-183-5p regulates MITF expression in vitiligo skin depigmentation

Microphthalmia-associated transcription factor (MITF) is a master regulatory factor for melanocytes. MITF regulates multiple pigmentary genes for maintaining cellular homeostasis. MicroRNAs (miRNAs) play crucial roles in numerous biological processes however their molecular/cellular mechanisms to regulate pigmentation have not been fully explored. This study was undertaken to investigate the role of miRNAs in skin depigmentation via regulation of MITF gene. Depigmentation in C57BL/6 black mice was induced by an autoimmune response against tyrosinase. Bioinformatics approach was used to detect miRNAs conserved in 3'untraslated region (3'UTR) of MITF mRNA. The iMC23 mouse melanocytes were used for transfection experiments. The data demonstrated that the MITF mRNA/protein was markedly low in lesional skin of depigmented mice (p < 0.05). Targetscan genomic database determined that 3'UTR of mouse MITF constitutes 4819 nucleotide bases and has 23 conserved sites for different miRNAs To validate the pairing of these predicted miRNAs with MITF mRNA, five miRNAs were deregulated in lesional skin (p < 0.05). Among them, mmu-miR-181a-5p and mmu-miR-183-5p were up-regulated, whereas mmu-miR-26a-5p, mmu-miR-26b-5p and mmu-miR-32-5p were down-regulated (p < 0.05). To verify these results, the iMC23 mouse melanocytes were used. Transfection of iMC23 cells with specific miRNAs mimics or inhibitors or with 3'UTR reporter clone of MITF, showed only mmu-miR-183-5p binds to 3'UTR of MITF mRNA and regulates its expression in iMC23 melanocytes. In conclusions, this is the first study shows that miR-183-5p is a direct regulator of MITF in iMC23 melanocytes. Thus, miR-183-5p is an important regulator of melanocytes homeostasis and may be a novel target for autoimmune depigmentation therapy.

Deubiquitination of MITF-M Regulates Melanocytes Proliferation and Apoptosis

Microphthalmia-associated transcription factor-M (MITF-M) is the key gene in the proliferation and differentiation of melanocytes, which undergoes an array of post-translation modifications. As shown in our previous study, deubiquitinase USP13 is directly involved in melanogenesis. However, it is still ambiguous that the effect of USP13-mediated MITF-M expression on melanocytes proliferation and apoptosis. Herein, we found that MITF-M overexpressing melanocytes showed high cell proliferation, reduced apoptosis, and increased melanin levels. Besides, melanin-related genes, TYR, DCT, GPNMB, and PMEL, were significantly up-regulated in MITF-M overexpressing melanocytes. Furthermore, Exogenous USP13 significantly upregulated the endogenous MITF-M protein level, downregulated USP13 significantly inhibited MITF-M protein levels, without altering MITF-M mRNA expression. In addition, USP13 upregulation mitigated the MITF-M degradation and significantly increased the half-life of MITF-M. Also, USP13 stabilized the exogenous MITF protein levels. In conclusion, the MITF-M level was regulated by USP13 deubiquitinase in melanocytes, affecting melanocytes proliferation and apoptosis. This study provides the theoretical basis for coat color transformation that could be useful in the development of the new breed in fur animals.

A Basic Domain-Derived Tripeptide Inhibits MITF Activity by Reducing its Binding to the Promoter of Target Genes

The keratinocytes in UV-irradiated skin produce and secrete α-melanocyte-stimulating hormone. α-Melanocyte-stimulating hormone upregulates the expression of MITF in melanocytes through the cAMP‒protein kinase A‒CREB signaling pathway. Thereafter, MITF induces the expression of melanogenic genes, including the tyrosinase gene TYR and TYRP-1 and TYRP-2 genes, which leads to the synthesis and accumulation of melanin. In this study, we examined whether MITF basic region-derived tripeptides can bind to the DNA-binding domain of MITF and inhibit MITF-induced melanogenesis through the inhibition of MITF‒DNA binding. MITF-KGR, a representative MITF-derived tripeptide, suppressed the transcriptional activity of MITF by disrupting its binding to the promoter region of the target genes, which resulted in the inhibition of skin epidermis thickness and melanin synthesis in vivo and in vitro. Our results indicate that MITF-KGR exerts an inhibitory effect on melanogenesis by targeting MITF.

Essential Oils of Alpinia nantoensis Retard Forskolin-Induced Melanogenesis via ERK1/2-Mediated Proteasomal Degradation of MITF

The anti-melanogenic activity of essential oils of Alpinia nantoensis and their bioactive ingredients were investigated in vitro. Treatment with leaf (LEO) and rhizome (REO) essential oils of A. nantoensis, significantly reduced forskolin-induced melanin production followed by down-regulation of tyrosinase (TYR) and tyrosinase related protein-1 (TRP-1) expression at both transcriptional and translational levels. Further studies revealed that down-regulation TYR and TRP-1 were caused by LEO/REO-mediated suppression of Microphthalmia-associated transcription factor (MITF), as evidenced by reduced nuclear translocation of MITF. Also, we found that LEO/REO induce the sustained activation of ERK1/2, which facilitate subsequent proteasomal degradation of MITF, as confirmed by that LEO/REO failed to inhibits MITF activity in ERK1/2 inhibitor treated cells. In addition, a significant increase of ubiquitinated MITF was observed after treatment with LEO and REO. Furthermore, the chemical composition of LEO and REO were characterized by gas chromatography-mass spectrometry (GC-MS) resulted that camphor, camphene, α-pinene, β-pinene, isoborneol and _D-limonene were the major compounds in both LEO and REO. Further studies revealed that α-pinene and _D-limonene were the active components responsible for the anti-melanogenic properties of LEO and REO. Based on the results, this study provided a strong evidence that LEO and REO could be promising natural sources for the development of novel skin-whitening agents for the cosmetic purposes.

Isolindleyin exerts anti-melanogenic effects in human epidermal melanocytes via direct binding to tyrosinase

To overcome dermatological concerns causing abnormally excessive melanin synthesis, highly effective and safe skin depigmentation compounds have been identified in the cosmetic and pharmaceutical industries. Among several methods used to achieve skin depigmentation, inhibition of tyrosinase is one of the most effective, since tyrosinase is a crucial enzyme in melanogenesis. Herein, isolindleyin, a novel inhibitor of human tyrosinase, was introduced and evaluated for its anti-melanogenic effects in human epidermal melanocytes. The results revealed that isolindleyin was directly bound to tyrosinase and it suppressed melanin synthesis. The binding mode between isolindleyin and the active sites of human tyrosinase was investigated using computational molecular docking at the atomic level. Isolindleyin binding was found to be stabilized by hydrophobic interactions between His 367 and Val 377 and by hydrogen bonds between Ser 380 and Asn 364. The results of this study revealed the anti-melanogenic effects of isolindleyin that could contribute toward overcoming dermatological concerns that cause abnormally excessive melanin synthesis.

Transcriptome Reveals Multi Pigmentation Genes Affecting Dorsoventral Pattern in Avian Body

Certain animals exhibit a special dorsoventral pattern with a lighter ventral side compared to the dorsal one and this phenomenon was preserved in the long-term evolution process. Birds also retain this trait. Recently, Inaba et al. (2019) found that ASIP (agouti signal protein) regulated interconversion between different melanocyte types leads to dorsal stripe pattern, which may partly explain the birds' dorsoventral plumage color difference. In this study, we used the embryo samples of LBM (light brown mottling) ducks (Anas platyrhynchos) with white ventral and dark dorsal body parts to investigate the mechanism of dorsoventral color variation. Firstly, melanin deposition process of duck embryos was investigated. The result indicated that E13 and E16 were the active stages of melanin synthesis. Moreover, the melanin deposition on the dorsum of LBM ducks was higher than that on the ventral side throughout. Then, RNA-seq was conducted for the dorsal and ventral skin tissues from E7 (early), E13 (middle) and E19 (late) of LBM ducks. Expression pattern analysis showed that the mRNA expression of most melanin synthesis related genes were at the highest level at E13, which was consistent with the section analysis. A correlation was found between melanogenesis pathway and dorsoventral color difference by co-expression analysis. In the DEG (differentially expressed gene) analysis, we added the dorsal skin transcriptome of embryonic white and black duck of same subspecies (Anas platyrhynchos domestica) for horizontal comparison. The results showed that 8 melanogenesis related genes (TYR, TYRP1, MLANA, RAB38, OCA2, TSPAN10, MC1R, and MSLN) were the common DEGs (Differential expressed genes) in the comparisons of body parts and breeds suggesting that the underlying molecular regulatory mechanism of dorsoventral plumage color difference may be similar to that of albino and melanic duck, which were caused by the different expression of multiple genes in melanin synthesis pathway. In addition, the molecular regulation of melanin synthesis pathway in the dorsal and ventral side of LBM ducks was analyzed. In this pathway, ASIP, MC1R, TYR, and TYRP1 have differential mRNA expression. ASIP, as an upstream gene in this pathway, was likely to play a decisive role in determining the dorsoventral plumage pattern.

User guide to MiT-TFE isoforms and post-translational modifications

The microphthalmia-associated transcription factor (MITF) is at the core of melanocyte and melanoma fate specification. The related factors TFEB and TFE3 have been shown to be instrumental for transcriptional regulation of genes involved in lysosome biogenesis and autophagy, cellular processes important for mediating nutrition signals and recycling of cellular materials, in many cell types. The MITF, TFEB, TFE3, and TFEC proteins are highly related. They share many structural and functional features and are targeted by the same signaling pathways. However, the existence of several isoforms of each factor and the increasing number of residues shown to be post-translationally modified by various signaling pathways poses a difficulty in indexing amino acid residues in different isoforms across the different proteins. Here, we provide a resource manual to cross-reference amino acids and post-translational modifications in all isoforms of the MiT-TFE family in humans, mice, and zebrafish and summarize the protein accession numbers for each isoform of these factors in the different genomic databases. This will facilitate future studies on the signaling pathways that regulate different isoforms of the MiT-TFE transcription factor family.

Ultraviolet B irradiation enhances the secretion of exosomes by human primary melanocytes and changes their exosomal miRNA profile

Objective

Melanocytes play a central role in skin homeostasis. In this study, we focus on the function of melanocyte releasing exosomes as well as exosomal microRNAs (miRNAs) and investigate whether ultraviolet B (UVB) irradiation exerts an impact on it.

Materials and methods

Exosomes derived from human primary melanocytes were isolated through differential centrifugation and were identified in three ways, including transmission electron microscopy observation, nanoparticle tracking analysis, and Western blot analysis. Melanocytes were irradiated with UVB for the indicated time, and then melanin production and exosome secretion were measured. The exosomal miRNA expression profile of melanocytes were obtained by miRNA sequencing and confirmed by real-time PCR.

Results

Exosomes derived from human primary melanocytes were verified. UVB irradiation induced melanin production and increased the exosome release by the melanocytes. In total, 15 miRNAs showed higher levels in UVB-irradiated melanocyte-derived exosomes compared with non-irradiated ones, and the top three upregulated exosomal miRNAs were miR-4488, miR-320d, and miR-7704 (fold change > 4.0).

Conclusion

It is verified for the first time that UVB irradiation enhanced the secretion of exosomes by melanocytes and changed their exosomal miRNA profile. This findings open a new direction for investigating the communication between melanocytes and other skin cells, and the connection between UVB and skin malignant initiation.

Tyrosinase-Targeting Gallacetophenone Inhibits Melanogenesis in Melanocytes and Human Skin-Equivalents

Demands for safe depigmentation compounds are constantly increasing in the pharmaceutical and cosmetic industry, since the numerous relevant compounds reported to date have shown undesirable side effects or low anti-melanogenic effects. In this study, we reported three novel inhibitors of tyrosinase, which is the key enzyme in melanogenesis, identified using docking-based high throughput virtual screening of an in-house natural compound library followed by mushroom tyrosinase inhibition assay. Of the three compounds, gallacetophenone showed high anti-melanogenic effect in both human epidermal melanocytes and a 3D human skin model, MelanoDerm. The inhibitory effect of gallacetophenone on tyrosinase was elucidated by computational molecular modeling at the atomic level. Binding of gallacetophenone to the active site of tyrosinase was found to be stabilized by hydrophobic interactions with His367, Ile368, and Val377; hydrogen bonding with Ser380 and a water molecule bridging the copper ions. Thus, our results strongly suggested gallacetophenone as an anti-melanogenic ingredient that inhibits tyrosinase.

3,4,5-Tri-O-Caffeoylquinic Acid Promoted Hair Pigmentation Through β-Catenin and Its Target Genes

The hair follicle undergoes a regular cycle composed of three phases: anagen, catagen, and telogen. The life of follicular melanocytes is totally linked to the hair cycle; and during anagen or the growth phase, the melanocytes are active and produce the melanin responsible of hair shaft pigmentation. Various signaling pathways regulate the hair growth cycle and, therefore, the pigmentation; we distinguish the Wnt/β-catenin signaling pathway as it plays a major role in the development, growth, and proliferation of the melanocytes and the activation of melanogenesis enzymes and the related transcription factor. In this study, 3,4,5-tri-O-caffeoylquinic acid (TCQA), a caffeoylquinic acid derivative, stimulated the pigmentation in C3H mouse hair follicle, in human melanocytes, and B16F10 melanoma cells. An enhancement in pigmentation associated genes was observed upon TCQA treatment in vivo and in vitro. Interestingly, the expression of β-catenin was remarkably upregulated in mouse treated skin and in pigment cell lines. Moreover, TCQA upregulated CTNNB1 expression after inhibition in human melanocytes. Taken together, this study suggests that TCQA triggered β-catenin activation to enhance the pigmentation during the anagen phase of the hair cycle.

A New Tyrosinase Inhibitor from the Red Alga Symphyocladia latiuscula (Harvey) Yamada (Rhodomelaceae)

A marine red alga, Symphyocladia latiuscula (Harvey) Yamada (Rhodomelaceae), is a rich source of bromophenols with a wide array of biological activities. This study investigates the anti-tyrosinase activity of the alga. Moderate activity was demonstrated by the methanol extract of S. latiuscula, and subsequent column chromatography identified three bromophenols: 2,3,6-tribromo-4,5-dihydroxybenzyl methyl alcohol (1), 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether (2), and bis-(2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether) (3). Bromophenols 1 and 3 exhibited potent competitive tyrosinase inhibitory activity against l-tyrosine substrates, with IC₅₀ values of 10.78 ± 0.19 and 2.92 ± 0.04 μM, respectively. Against substrate l-3,4-dihydroxyphenylalanine (l-DOPA), compounds 1 and 3 demonstrated moderate activity, while 2 showed no observable effect. The experimental data were verified by a molecular docking study that found catalytic hydrogen and halogen interactions were responsible for the activity. In addition, compounds 1 and 3 exhibited dose-dependent inhibitory effects in melanin and intracellular tyrosinase levels in α-melanocyte-stimulating hormone (α-MSH)-induced B16F10 melanoma cells. Compounds 3 and 1 were the most effective tyrosinase inhibitors. In addition, increasing the bromine group number increased the mushroom tyrosinase inhibitory activity.

MiT/TFE Family of Transcription Factors, Lysosomes, and Cancer

Cancer cells have an increased demand for energy sources to support accelerated rates of growth. When nutrients become limiting, cancer cells may switch to nonconventional energy sources that are mobilized through nutrient scavenging pathways involving autophagy and the lysosome. Thus, several cancers are highly reliant on constitutive activation of these pathways to degrade and recycle cellular materials. Here, we focus on the MiT/TFE family of transcription factors, which control transcriptional programs for autophagy and lysosome biogenesis and have emerged as regulators of energy metabolism in cancer. These new findings complement earlier reports that chromosomal translocations and amplifications involving the MiT/TFE genes contribute to the etiology and pathophysiology of renal cell carcinoma, melanoma, and sarcoma, suggesting pleiotropic roles for these factors in a wider array of cancers. Understanding the interplay between the oncogenic and stress-adaptive roles of MiT/TFE factors could shed light on fundamental mechanisms of cellular homeostasis and point to new strategies for cancer treatment.

Improved antimelanogenesis and antioxidant effects of polysaccharide from Cuscuta chinensis Lam seeds after enzymatic hydrolysis

Cuscuta chinensis polysaccharide (CPS) was extracted using hot water and enzymatically hydrolyzed C. chinensis polysaccharide (ECPS) was produced by the mannase enzymatic hydrolysis process. The purpose of this research was to investigate the antimelanogenic activity of ECPS and CPS in B16F10 melanoma cells. The in vitro antioxidant activity was assessed by their ferric iron reducing power and DPPH free radical scavenging activities. The molecular mass distribution of polysaccharides was determined using SEC-MALLS-RI. CPS was successfully enzymatically degraded using mannase and the weighted average molecular weights of CPS and ECPS were 434.6 kDa and 211.7 kDa. The results of biological activity assays suggested that the enzymatically hydrolyzed polysaccharide had superior antimelanogenic activity and antioxidant effect than the original polysaccharide. ECPS exhibited antimelanogenic activity by down-regulating the expression of tyrosinase, MITF, and TRP-1 without cytotoxic effects in B16F10 melanoma cells. In conclusion, ECPS have the potential to become a skin whitening product.

Oleoylethanolamide inhibits α-melanocyte stimulating hormone-stimulated melanogenesis via ERK, Akt and CREB signaling pathways in B16 melanoma cells

The present study aimed to examine the potential inhibitory activity of oleoylethanolamide (OEA) on α-melanocyte stimulating hormone (α-MSH)-stimulated melanogenesis and the molecular mechanism(s) involved in the process in B16 mouse melanoma cells. Our data demonstrated that OEA markedly inhibited melanin synthesis and tyrosinase activity in α-MSH-stimulated B16 cells. In addition, the expression of melanogenesis-related proteins, such as melanocortin-1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase-related protein-1 (TRP-1) and tyrosinase, was suppressed in a concentration-dependent manner by OEA. In addition, OEA may suppress melanogenesis through a peroxisome proliferator-activated receptor α (PPARα)-independent pathway. Moreover, OEA activated ERK, Akt, p38 pathways and inhibits CREB pathway in α-MSH-stimulated B16 cells. The specific ERK inhibitor PD98059 partly blocked OEA-inhibited melanin synthesis and tyrosinase activity and partly abrogated the OEA-suppressed expression of melanogenic proteins. Furthermore, OEA presented remarkable inhibition on the body pigmentation in the zebrafish model system. Our findings demonstrated that OEA is an effective inhibitor of hyperpigmentation through activation of ERK, Akt and p38 pathways, inhibition of the CREB pathway, and subsequent down-regulation of MITF, TRP-1 and tyrosinase production.

Interleukin-like EMT inducer regulates partial phenotype switching in MITF-low melanoma cell lines

ILEI (FAM3C) is a secreted factor that contributes to the epithelial-to-mesenchymal transition (EMT), a cell biological process that confers metastatic properties to a tumor cell. Initially, we found that ILEI mRNA is highly expressed in melanoma metastases but not in primary tumors, suggesting that ILEI contributes to the malignant properties of melanoma. While melanoma is not an epithelial cell-derived tumor and does not undergo a traditional EMT, melanoma undergoes a similar process known as phenotype switching in which high (micropthalmia-related transcription factor) MITF expressing (MITF-high) proliferative cells switch to a low expressing (MITF-low) invasive state. We observed that MITF-high proliferative cells express low levels of ILEI (ILEI-low) and MITF-low invasive cells express high levels of ILEI (ILEI-high). We found that inducing phenotype switching towards the MITF-low invasive state increases ILEI mRNA expression, whereas phenotype switching towards the MITF-high proliferative state decreases ILEI mRNA expression. Next, we used in vitro assays to show that knockdown of ILEI attenuates invasive potential but not MITF expression or chemoresistance. Finally, we used gene expression analysis to show that ILEI regulates several genes involved in the MITF-low invasive phenotype including JARID1B, HIF-2α, and BDNF. Gene set enrichment analysis suggested that ILEI-regulated genes are enriched for JUN signaling, a known regulator of the MITF-low invasive phenotype. In conclusion, we demonstrate that phenotype switching regulates ILEI expression, and that ILEI regulates partial phenotype switching in MITF-low melanoma cell lines.

Melanogenesis inhibition activity of floralginsenoside A from Panax ginseng berry

Background

Panax ginseng is a traditional herb used for medicinal purposes in eastern Asia. P. ginseng contains various ginsenosides with pharmacological effects. In this study, floralginsenoside A (FGA), ginsenoside Rd (GRD), and ginsenoside Re (GRE) were purified from P. ginseng berry.

Methods

Chemical structures of FGA, GRD, and GRE were determined based on spectroscopic methods, including fast atom bombardment mass spectroscopy, ID-nuclear magnetic resonance, and infrared spectroscopy. Inhibitory activities of these compounds on melanogenesis were studied by measuring the expression of protein and melanin content in the melan-a cell line. This inhibitory activity was confirmed by observing pigmentation and tyrosinase activities of zebrafish.

Results

GRD, GRE, and FGA were not cytotoxic at concentrations less than 20μM, 80μM, and 160μM in melan-a cells, respectively. GRD, GRE, and FGA inhibited melanin biosynthesis in melan-a cells by 15.2%, 22.9%, and 23.9% at 20μM, 80μM, and 160μM, respectively. FGA was observed to display the most potent inhibitory effect. In addition, FGA decreased microphthalmia-associated transcription factor protein expression in a dose-dependent manner. Moreover, FGA induced extracellular signal-regulated kinase phosphorylation level in melan-a cells. In addition, melanin pigment content and tyrosinase activity in zebrafish treated with FGA at160μM were reduced.

Conclusion

FGA showed the most potent inhibition of melanogenesis in both in vitro and in vivo studies. This study suggests that FGA purified from P. ginseng may be an effective melanogenesis inhibitor.

Agmatine modulates melanogenesis via MITF signaling pathway

Agmatine contained in soybean is also found in Manaca, an anti-aging plant, inhabited in Amazon and induces vasodilation by the promotion of NO synthesis in blood vessel. However, the research of agmatine on melanin synthesis related to hair greying is lacking. The aim of this study was to investigate the melanogenic effect of agmatine via regulation of MITF signaling pathway in B16F1 cells. It was determined whether agmatine regulates melanin synthesis at cellular level in addition to the effect of agmatine on mushroom tyrosinase in vitro in the presence of different concentrations of agmatine. Furthermore, the effect of agmatine on the protein expressions of tyrosinase, TRP-1, TRP-2, BMP-4, BMP-6, C-KIT, p-p38, MITF and C-FOS were examined by western blot analysis. In addition, immunofluorescence staining was carried out to visualize the location of MITF expression in cell. Agmatine at 256μM or more increased melanin synthesis as well as tyrosinase activity. Moreover, whereas agmatine increased the expression levels of TRP-1, BMP-6, p-p38 and MITF, it reduced the expression level of BMP-4. It was also found that agmatine enhanced the expression level of MITF in nucleus. These results suggest that agmatine could induce melanin synthesis though the regulation of MITF transcription factor via BMP-6/p38 signaling pathway.

Effects of Ganodermanondiol, a New Melanogenesis Inhibitor from the Medicinal Mushroom Ganoderma lucidum

Ganoderma lucidum, a species of the Basidiomycetes class, has been attracting international attention owing to its wide variety of biological activities and great potential as an ingredient in skin care cosmetics including “skin-whitening” products. However, there is little information available on its inhibitory effect against tyrosinase activity. Therefore, the objectives of this study were to investigate the chemical composition of G. lucidum and its inhibitory effects on melanogenesis. We isolated the active compound from G. lucidum using ethanol extraction and ethyl acetate fractionation. In addition, we assayed its inhibitory effects on tyrosinase activity and melanin biosynthesis in B16F10 melanoma cells. In this study, we identified a bioactive compound, ganodermanondiol, which inhibits the activity and expression of cellular tyrosinase and the expression of tyrosinase-related protein-1 (TRP-1), TRP-2, and microphthalmia-associated transcription factor (MITF), thereby decreasing melanin production. Furthermore, ganodermanondiol also affected the mitogen-activated protein kinase (MAPK) cascade and cyclic adenosine monophosphate (cAMP)-dependent signaling pathway, which are involved in the melanogenesis of B16F10 melanoma cells. The finding that ganodermanondiol from G. lucidum exerts an inhibitory effect on tyrosinase will contribute to the use of this mushroom in the preparation of skin care products in the future.

Novel Anti-Melanogenesis Properties of Polydeoxyribonucleotide, a Popular Wound Healing Booster

Polydeoxyribonucleotide (PDRN), a deoxyribonucleotide polymer, is popularly used for faster healing of cutaneous wounds and boosting of neocollagenesis of photoaged skin among current dermatologic practitioners. Some patients receiving PDRN injection treatment also reported improvement of photoaging-associated mottled pigmentation (PMP). To investigate the effect of PDRN on cutaneous melanogenesis, we examined the effect of PDRN and an available product (Placentex^®) containing PDRN on melanogenesis using human melanocytes-keratinocytes cocultures and mouse melanocytes. Melanin content, tyrosinase activity, and levels of microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein (TRP-1) were determined. Intracellular signaling pathways were assessed by Western blotting. PDRN and Placentex^® led to decreases in melanin content, tyrosinase activity, and MITF and TRP-1 expression with concomitant increases in phosphorylated forms of extracellular signal-regulated protein kinase (ERK) and AKT in mouse melanocytes. More importantly, both PDRN and Placentex^® significantly suppressed the melanin content in human melanocyte–keratinocyte cocultures. Clinical evaluation of six female patients with facial hyperpigmentation after three sessions of intradermal PDRN injections using a 5-point scale revealed that PDRN led to more than noticeable improvements in hyperpigmented lesions. This is the first study to demonstrate that PDRN, which is known for its wound-healing properties, may have novel anti-melanogenesis and potential skin whitening properties.

Dioscin Derived from Solanum melongena L. "Usukawamarunasu" Attenuates α-MSH-Induced Melanogenesis in B16 Murine Melanoma Cells via Downregulation of Phospho-CREB and MITF

This study aimed to chemically isolate and explore an antimelanogenesis inducer in extracts of Solanum melongena L. "Usukawamarunasu" eggplant. We successfully identified dioscin ([25R]-Spirost-5-en-3β-yl) 2-O-(6-deoxy-α-L-mannopyranosyl) - 4-O-(6-deoxy-α-L-mannopyranosyl)-β-D-glucopyranoside] in the plant, and examined the effects of α-melanocyte-stimulating hormone (MSH)-induced melanogenesis in B16 murine melanoma cells by this plant-derived dioscin. Immunoblot analysis suggested that dioscin reduced the expression of tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2, resulting in inhibition of intracellular production of melanin. In addition, dioscin caused reduction of phosphorylated cAMP-responsive element binding protein 1 transcription factors (CREB), which led to a reduction of microphthalmia-related transcription factor (MITF) in α-MSH-stimulated cells, but did not affect phosphorylation of extracellular signal-regulated kinase. Furthermore, dioscin significantly downregulated the expression of tyrosinase, TRP-1, and TRP-2, which led to the reduction of α-MSH-induced melanogenesis in B16 cells. These results suggest that dioscin may decrease the level of MITF via inhibition of phosphorylation of CREB in α-MSH-induced melanogenesis in B16 cells.

Exosomes released by keratinocytes modulate melanocyte pigmentation

Cells secrete extracellular vesicles (EVs), exosomes and microvesicles, which transfer proteins, lipids and RNAs to regulate recipient cell functions. Skin pigmentation relies on a tight dialogue between keratinocytes and melanocytes in the epidermis. Here we report that exosomes secreted by keratinocytes enhance melanin synthesis by increasing both the expression and activity of melanosomal proteins. Furthermore, we show that the function of keratinocyte-derived exosomes is phototype-dependent and is modulated by ultraviolet B. In sum, this study uncovers an important physiological function for exosomes in human pigmentation and opens new avenues in our understanding of how pigmentation is regulated by intercellular communication in both healthy and diseased states.

The activity of melanocytes determines skin pigmentation, and is regulated by a tight dialogue with keratinocytes. Here, the authors show that exosomes released by keratinocytes have a direct effect on melanocyte function, and exosome content is dependent on skin phototype and is modulated by ultraviolet B radiation.

The newt (Cynops pyrrhogaster) RPE65 promoter: molecular cloning, characterization and functional analysis

The adult newt has the ability to regenerate the neural retina following injury, a process achieved primarily by the retinal pigment epithelium (RPE). To deliver exogenous genes to the RPE for genetic manipulation of regenerative events, we isolated the newt RPE65 promoter region by genome walking. First, we cloned the 2.8 kb RPE65 promoter from the newt, Cynops pyrrhogaster. Sequence analysis revealed several conserved regulatory elements described previously in mouse and human RPE65 promoters. Second, having previously established an I-SceI-mediated transgenic protocol for the newt, we used it here to examine the -657 bp proximal promoter of RPE65. The promoter assay used with F0 transgenic newts confirmed transgene expression of mCherry fluorescent protein in the RPE. Using bioinformatic tools and the TRANSFAC database, we identified a 340 bp CpG island located between -635 and -296 bp in the promoter; this region contains response elements for the microphthalmia-associated transcription factor known as MITF (CACGTG, CATGTG), and E-boxes (CANNTG). Sex-determining region box 9 (or SOX9) response element previously reported in the regulation of RPE genes (including RPE65) was also identified in the newt RPE65 promoter. Third, we identified DNA motif boxes in the newt RPE65 promoter that are conserved among other vertebrates. The newt RPE65 promoter is an invaluable tool for site-specific delivery of exogenous genes or genetic manipulation systems for the study of retinal regeneration in this animal.

Quercetin-3-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranoside suppresses melanin synthesis by augmenting p38 MAPK and CREB signaling pathways and subsequent cAMP down-regulation in murine melanoma cells

In this study, the effect of purified quercetin-3-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosid (QCGG) on melanogenesis was investigated. QCGG was isolated from the calyx of a traditional Korean medicinal herb, Persimmon (Diospyros kaki). The hypopigmentation effects of QCGG were determined by examination of cellular melanin contents, tyrosinase activity assay, cAMP assay, and Western blotting of α-MSH-stimulated B16F10 mouse melanoma cells. Our results showed that QCGG inhibited both melanin synthesis and tyrosinase activity in a concentration-dependent manner as well as significantly reduced the expression of melanogenic proteins such as microphthalmia-associated transcription factor (MITF), tyrosinase-related protein-1, tyrosinase-related protein-2, and tyrosinase. Moreover, QCGG inhibited intracellular cAMP levels, cAMP response element-binding protein (CREB), and p38 MAPK expression in α-MSH-stimulated B16F10 cells. Taken together, the suppressive effects of QCGG on melanogenesis may involve down-regulation of MITF and its downstream signaling pathway via phosphorylation of p38 MAPK and CREB along with reduced cAMP levels. These results indicate that QCGG reduced melanin synthesis by reducing expression of tyrosine and tyrosine-related proteins via extracellular signal-related protein kinase (ERK) activation, followed by down-regulation of CREB, p38, and MITF.

Effect of the tyrosinase inhibitor (S)-N-trans-feruloyloctopamine from garlic skin on tyrosinase gene expression and melanine accumulation in melanoma cells

In our searching for novel tyrosinase inhibitors from natural sources, (S)-N-trans-feruloyloctopamine isolated from garlic skin was found to be a potential mushroom tyrosinase inhibitor. Here, we examined the effects of the potential tyrosinase inhibitor in B16F10 cells on intracellular melanin contents, cytotoxicity, and the signaling mechanism involved in the expression of tyrosinase. The results showed the inhibitor displayed little or no cytotoxicity at all concentrations examined and decreased the relative melanin contents in a dose-dependent manner in the α-MSH-stimulated B16F10 cells. Real-time PCR and Western blot analysis showed that it inhibits melanogenesis signaling by down-regulates mRNA and protein expression levels of tyrosinase, which leads to a lower melanin contents. These results suggested that (S)-N-trans-feruloyloctopamine was an ideal tyrosinase inhibitor, and could be used in food and medical industry.

Generation of highly enriched populations of optic vesicle-like retinal cells from human pluripotent stem cells

The protocol outlined below is used to differentiate human pluripotent stem cells (hPSCs) into retinal cell types through a process that faithfully recapitulates the stepwise progression observed in vivo. From pluripotency, cells are differentiated to a primitive anterior neural fate, followed by progression into two distinct populations of retinal progenitors and forebrain progenitors, each of which can be manually separated and purified. The hPSC-derived retinal progenitors are found to self-organize into three-dimensional optic vesicle-like structures, with each aggregate possessing the ability to differentiate into all major retinal cell types. The ability to faithfully recapitulate the stepwise in vivo development in a three-dimensional cell culture system allows for the study of mechanisms underlying human retinogenesis. Furthermore, this methodology allows for the study of retinal dysfunction and disease modeling using patient-derived cells, as well as high-throughput pharmacological screening and eventually patient-specific therapies.

Genome-wide transcriptome analysis of human epidermal melanocytes

Because human epidermal melanocytes (HEMs) provide critical protection against skin cancer, sunburn, and photoaging, a genome-wide perspective of gene expression in these cells is vital to understanding human skin physiology. In this study we performed high throughput sequencing of HEMs to obtain a complete data set of transcript sizes, abundances, and splicing. As expected, we found that melanocyte specific genes that function in pigmentation were among the highest expressed genes. We analyzed receptor, ion channel and transcription factor gene families to get a better understanding of the cell signaling pathways used by melanocytes. We also performed a comparative transcriptomic analysis of lightly versus darkly pigmented HEMs and found 16 genes differentially expressed in the two pigmentation phenotypes; of those, only one putative melanosomal transporter (SLC45A2) has known function in pigmentation. In addition, we found 166 transcript isoforms expressed exclusively in one pigmentation phenotype, 17 of which are genes involved in signal transduction. Our melanocyte transcriptome study provides a comprehensive view and may help identify novel pigmentation genes and potential pharmacological targets.

Kaliziri extract upregulates tyrosinase, TRP-1, TRP-2 and MITF expression in murine B16 melanoma cells

Background

Kaliziri extract (KZE) is a traditional Uyghur medicine (TUM), used by traditional hospitals in China as an injection for treatment of vitiligo for more than 30 years. Clinical application has shown that this medicine has obvious therapeutic effects. However, its phytochemical analysis and mechanism have not been examined.

Methods

KZE was extracted from seeds of Kaliziri [Vernonia anthelmintica (L.) Willd.] in ethanol-water (80:20, v/v), its components were identified by LC-MS/MS, and the signaling pathway of melanin synthesis in KZE treated murine B16 melanoma cells was examined by western blotting.

Results

Liquid chromatography-mass spectrometry analysis confirmed that the main components of KZE are flavonoids. KZE increased the tyrosinase activity and melanin content in a dose-dependent manner at concentrations of 5-40 μg/ml, and treatment with 20 μg/ml of KZE enhanced the expression of tyrosinase in B16 cells in a time-dependent manner.

Conclusions

KZE induced melanogenesis by increasing the expression of TYR, TRP-1, TRP-2 and MITF in B16 cells.

Octaphlorethol A isolated from Ishige foliacea inhibits α-MSH-stimulated induced melanogenesis via ERK pathway in B16F10 melanoma cells

In this study, the potent skin-whitening effects of Octaphlorethol A (OPA) isolated from Ishige foliacea was investigated through inhibitory effect of melanin synthesis and tyrosinase activity in alpha-melanocyte stimulating hormone (α-MSH) induced B16F10 melanoma cells. OPA markedly inhibited melanin synthesis and tyrosinase activity in a concentration-dependent manner. We also found that OPA decreased microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 and -2 (TRP-1 and TRP-2) protein expressions. Moreover, OPA reduces p38 MAPK protein levels and activates extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinases (JNKs) protein expressions in B16F10 cells. A specific ERK inhibitor PD98059 significantly blocks OPA-inhibited melanin synthesis and tyrosinase activity, whereas a p38MAP and JNK inhibitor had no effect. These findings provide evidence demonstrating that the anti-melanogenic effect of OPA is mediated through the activation of ERK signal pathway in B16F10 cells. These results indicate that OPA has the potential to be used as a melanogenesis inhibitor in the food and cosmetics industry.

Microphthalmia transcription factor regulates pancreatic β-cell function

Precise regulation of β-cell function is crucial for maintaining blood glucose homeostasis. Pax6 is an essential regulator of β-cell-specific factors like insulin and Glut2. Studies in the developing eye suggest that Pax6 interacts with Mitf to regulate pigment cell differentiation. Here, we show that Mitf, like Pax6, is expressed in all pancreatic endocrine cells during mouse postnatal development and in the adult islet. A Mitf loss-of-function mutation results in improved glucose tolerance and enhanced insulin secretion but no increase in β-cell mass in adult mice. Mutant β-cells secrete more insulin in response to glucose than wild-type cells, suggesting that Mitf is involved in regulating β-cell function. In fact, the transcription of genes critical for maintaining glucose homeostasis (insulin and Glut2) and β-cell formation and function (Pax4 and Pax6) is significantly upregulated in Mitf mutant islets. The increased Pax6 expression may cause the improved β-cell function observed in Mitf mutant animals, as it activates insulin and Glut2 transcription. Chromatin immunoprecipitation analysis shows that Mitf binds to Pax4 and Pax6 regulatory regions, suggesting that Mitf represses their transcription in wild-type β-cells. We demonstrate that Mitf directly regulates Pax6 transcription and controls β-cell function.

Analysis of a gene regulatory cascade mediating circadian rhythm in zebrafish

In the study of circadian rhythms, it has been a puzzle how a limited number of circadian clock genes can control diverse aspects of physiology. Here we investigate circadian gene expression genome-wide using larval zebrafish as a model system. We made use of a spatial gene expression atlas to investigate the expression of circadian genes in various tissues and cell types. Comparison of genome-wide circadian gene expression data between zebrafish and mouse revealed a nearly anti-phase relationship and allowed us to detect novel evolutionarily conserved circadian genes in vertebrates. We identified three groups of zebrafish genes with distinct responses to light entrainment: fast light-induced genes, slow light-induced genes, and dark-induced genes. Our computational analysis of the circadian gene regulatory network revealed several transcription factors (TFs) involved in diverse aspects of circadian physiology through transcriptional cascade. Of these, microphthalmia-associated transcription factor a (mitfa), a dark-induced TF, mediates a circadian rhythm of melanin synthesis, which may be involved in zebrafish's adaptation to daily light cycling. Our study describes a systematic method to discover previously unidentified TFs involved in circadian physiology in complex organisms.

Wnt10b promotes differentiation of mouse hair follicle melanocytes

Previous research has revealed that Wnt10b activates canonical Wnt signaling, which is integral to melanocyte differentiation in hair follicles (HFs). However, the function of Wnt10b in HF melanocytes remains poorly understood. We determined using Dct-LacZ transgenic mice that Wnt10b is mainly expressed near and within melanocytes of the hair bulbs during the anagen stage of the hair cycle. We also found that Wnt10b promotes an increase in melanocyte maturation and pigmentation in the hair bulbs of the mouse HF. To further explore the potential functions of Wnt10b in mouse HF melanocytes, we infected iMC23 cells with Ad-Wnt10b to overexpress Wnt10b. We demonstrated that Wnt10b promotes the differentiation of melanocytes by activating canonical Wnt signaling in melanocytes.

Alcohol extract from Vernonia anthelmintica (L.) willd seed enhances melanin synthesis through activation of the p38 MAPK signaling pathway in B16F10 cells and primary melanocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Vernonia anthelmintica (L.) willd has been used in folk medicine to treat leukoderma in China for centuries. The promoting activities of its extract (AVE) in melanogenesis and possible signaling pathways were investigated in this article.

MATERIALS AND METHODS

The improving activities of AVE were examined by melanin synthesis, tyrosinase activity assay and Western blot in B16F10 mouse melanoma cells and normal human primary melanocytes (NHMC).

RESULTS

AVE increased the tyrosinase activity and melanin content in a dosage-dependent manner at concentrations of 1-40 μg/ml and treatment with 20 μg/ml AVE enhanced the expression of tyrosinase time-dependently in both B16F10 cells and NHMC. Whether AVE affects the expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression, was investigated. Our results showed that AVE induced MITF protein expression up-regulation. Besides, Western blot analysis revealed that AVE promoted the level of phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) markedly at 0-6 h, while the level of phosphorylation of CREB at 0-2 h. The special p38 MAPK inhibitor, SB203580, and protein kinase A (PKA) inhibitor, H89, both attenuated the AVE-induced up-regulation of MITF and tyrosinase expression in B16F10 cells and NHMC. However, SB203580 could significantly decrease the melanin biosynthesis induced by AVE, but not H89.

CONCLUSION

AVE exerts its improving effect on melanogenesis mainly by p38 MAPK activation and MITF induction of tyrosinase.

Wnt3a inhibits proliferation but promotes melanogenesis of melan-a cells

Melanocytes are pigment-producing cells responsible for coloration of skin and hair. Although the importance of Wnt3a in melanocyte development has been well recognized, the role of Wnt3a in mature melanocytes has not been elucidated. This study was conducted to further explore the effects of Wnt3a on melanocyte proliferation and melanogenesis, and to elucidate the possible mechanisms involved. We infected melan-a cells with AdWnt3a to serve as the production source of the Wnt3a protein. MTT assay, 5-bromodeoxyuridine incorporation assay and flow cytometric analysis showed that Wnt3a inhibited the proliferation of melan-a cells and this was associated with decrease of cells in the S phase and increase of cells in the G(1) phase. Melanin content and tyrosinase activity assay revealed that Wnt3a significantly promoted melanogenesis of melan-a cells. Furthermore, western blot analysis showed that Wnt3a upregulated the expression of microphthalmia-associated transcription factor and its downstream target genes, tyrosinase and tyrosinase-related protein 1 in melan-a cells. Collectively, our results suggest that Wnt3a plays an important role in melanocyte homeostasis.

Effect of saucerneol D on melanin production in cAMP-elevated melanocytes

Intracellular cAMP stimulates microphthalmia-associated transcription factor (MITF) induction in melanocytes through cAMP-responsive element binding protein (CREB), which plays a pivotal role in the gene expression of tyrosinase for melanin biosynthesis. In the present study, saucerneol D as a lignan constituent of Saururus chinensis (Saururaceae family) efficiently inhibited melanin production with IC(50) values of 188-297 nM in B16 melanoma cells stimulated with α-melanocyte stimulating hormone (α-MSH) or other cAMP elevators. Moreover, saucerneol D down-regulated α-MSH-induced gene expression of tyrosinase at the transcription level in B16 cells, but it did not directly inhibit the catalytic activity of cell-free tyrosinase. As to the molecular basis of hypopigmenting action, saucerneol D inhibited α-MSH-induced phosphorylation of CREB in the cells, and sequentially suppressed MITF induction. Taken together, this study provides saucerneol D down-regulated the gene expression of tyrosinase, resulting in the inhibition of cAMP-induced melanin biosynthesis, and suggests pharmacological potential of the lignan structure in skin hyperpigmentation.

Manassantin A inhibits cAMP-induced melanin production by down-regulating the gene expressions of MITF and tyrosinase in melanocytes

Microphthalmia-associated transcription factor (MITF) is inducible in response to cAMP through the cAMP-responsive element-binding protein (CREB) and plays a pivotal role in the melanocyte-specific expression of tyrosinase or tyrosinase-related proteins (TRPs) for melanin biosynthesis. Manassantin A from Saururus chinensis inhibits cAMP-induced melanin production in B16 melanoma cells. Here, we focused on molecular basis of the antimelanogenic activity. Manassantin A consistently inhibited the cAMP elevator 3-isobutyl-1-methylxanthine (IBMX)- or dibutyryl cAMP-induced melanin production in B16 cells or in melan-a melanocytes by down-regulating the expression of tyrosinase or TRP1 gene. Moreover, manassantin A suppressed MITF induction through IBMX-activated CREB pathway, directly inhibiting the Ser-133 phosphorylation of CREB. However, manassantin A did not affect IBMX-increased cAMP levels in these cells but also other cAMP-dependent melanogenic pathways through post-translational modifications of MITF. This putative molecular mechanism of manassantin A in the inhibition of melanin production suggests its pharmacological potential in skin hyperpigmentation.

Downregulation of NFAT2 promotes melanogenesis in B16 melanoma cells

Nuclear factor of activated T-cells (NFAT) proteins are, calcium-regulated transcription factors, key regulator of stimulation-dependent gene activation. In our microarray analysis for the genes expressed in human black and white hairs, NFAT2 was significantly upregulated in the white hair, compared to the black hair. The aim of this study was to investigate functional role of NFAT2 in melanogenesis. Western blot analysis was performed to investigate the expression of NFAT2 protein in B16 melanoma cells. Our data showed that NFAT2 expression was increased in the hypopigmented B16 cells, while tyrosinase and MITF expression was decreased. To investigate the potential role of NFAT2, the recombinant adenovirus expressing microRNA specific for NFAT2 was transduced into the cultured B16 melanoma cells. Consistently, inhibition of NFAT2 enhanced tyrosinase activity and melanin content. Moreover, cyclosporine A, which is known as a calcineurin inhibitor blocking NFAT activation, enhanced tyrosinase activity and melanin content. These data suggest that NFAT2 may play an important role in regulation of melanogenesis in melanocyte.

Differentiation of zebrafish melanophores depends on transcription factors AP2 alpha and AP2 epsilon

A model of the gene-regulatory-network (GRN), governing growth, survival, and differentiation of melanocytes, has emerged from studies of mouse coat color mutants and melanoma cell lines. In this model, Transcription Factor Activator Protein 2 alpha (TFAP2A) contributes to melanocyte development by activating expression of the gene encoding the receptor tyrosine kinase Kit. Next, ligand-bound Kit stimulates a pathway activating transcription factor Microphthalmia (Mitf), which promotes differentiation and survival of melanocytes by activating expression of Tyrosinase family members, Bcl2, and other genes. The model predicts that in both Tfap2a and Kit null mutants there will be a phenotype of reduced melanocytes and that, because Tfap2a acts upstream of Kit, this phenotype will be more severe, or at least as severe as, in Tfap2a null mutants in comparison to Kit null mutants. Unexpectedly, this is not the case in zebrafish or mouse. Because many Tfap2 family members have identical DNA–binding specificity, we reasoned that another Tfap2 family member may work redundantly with Tfap2a in promoting Kit expression. We report that tfap2e is expressed in melanoblasts and melanophores in zebrafish embryos and that its orthologue, TFAP2E, is expressed in human melanocytes. We provide evidence that Tfap2e functions redundantly with Tfap2a to maintain kita expression in zebrafish embryonic melanophores. Further, we show that, in contrast to in kita mutants where embryonic melanophores appear to differentiate normally, in tfap2a/e doubly-deficient embryonic melanophores are small and under-melanized, although they retain expression of mitfa. Interestingly, forcing expression of mitfa in tfap2a/e doubly-deficient embryos partially restores melanophore differentiation. These findings reveal that Tfap2 activity, mediated redundantly by Tfap2a and Tfap2e, promotes melanophore differentiation in parallel with Mitf by an effector other than Kit. This work illustrates how analysis of single-gene mutants may fail to identify steps in a GRN that are affected by the redundant activity of related proteins.

Neural crest-derived pigment cells, known as melanocytes, are important to an organism's survival because they protect skin cells from ultraviolet radiation, camouflage the organism from predators, and contribute to sexual selection. Networks of regulatory proteins control the steps of melanocyte development, including lineage specification, migration, survival, and differentiation. Gaps in our understanding of these networks hamper progress in effective prevention and treatment of diseases of melanocytes, including metastatic melanoma and vitiligo. Studies conducted in tissue-culture cells and mouse embryos implicate regulatory proteins including the transcription factor TFAP2A, the growth factor receptor KIT, and the transcription factor MITF as being important for multiple steps in melanocyte development. Abnormalities in TFAP2A, KIT, and MITF expression in melanoma highlight the importance of this pathway in human disease. Here we show that a gene closely related to TFAP2A, tfap2e, is expressed in zebrafish embryonic melanocytes and human melanocytes. We provide evidence that Tfap2e cooperates with Tfap2a to promote expression of zebrafish kita in embryonic melanocytes. Further we show that an effector of Tfap2a/e activity other than Kita is required for melanocyte differentiation and that this effector acts upstream or in parallel with Mitfa activity. These findings reveal unexpected complexity to the gene-regulatory network governing melanocyte differentiation.

Regulation of human skin pigmentation in situ by repetitive UV exposure: molecular characterization of responses to UVA and/or UVB

UV radiation is a major environmental factor that affects pigmentation in human skin and can eventually result in various types of UV-induced skin cancers. The effects of various wavelengths of UV on melanocytes and other types of skin cells in culture have been studied, but little is known about gene expression patterns in situ following in situ exposure of human skin to different types of UV (UVA and/or UVB). Paracrine factors expressed by keratinocytes and/or fibroblasts that affect skin pigmentation might be regulated differently by UV, as might their corresponding receptors expressed on melanocytes. To test the hypothesis that different mechanisms are involved in the pigmentary responses of the skin to different types of UV, we used immunohistochemical and whole human genome microarray analyses to characterize human skin in situ to examine how melanocyte-specific proteins and paracrine melanogenic factors are regulated by repetitive exposure to different types of UV compared with unexposed skin as a control. The results show that gene expression patterns induced by UVA or UVB are distinct-UVB eliciting dramatic increases in a large number of genes involved in pigmentation as well as in other cellular functions, whereas UVA had little or no effect on these. The expression patterns characterize the distinct responses of the skin to UVA or UVB, and identify several potential previously unidentified factors involved in UV-induced responses of human skin.

Mechanisms for reaching the differentiated state: Insights from neural crest-derived melanocytes

Black pigment cells, or melanocytes, are the major contributing cells to pigmentation in vertebrate organisms. Although the function of these cells is distinct depending on the organism, the events involved in their development are remarkably similar. Here, we review the mechanisms involved in the early development of melanocytes from neural crest, many of which are conserved in organisms as diverse as zebrafish, birds and humans. We also discuss recent studies that provide further insight into how melanocyte differentiation is achieved and maintained.

Epithelial phenotype and the RPE: is the answer blowing in the Wnt?

Cells of the human retinal pigment epithelium (RPE) have a regular epithelial cell shape within the tissue in situ, but for reasons that remain elusive the RPE shows an incomplete and variable ability to re-develop an epithelial phenotype after propagation in vitro. In other epithelial cell cultures, formation of an adherens junction (AJ) composed of E-cadherin plays an important early inductive role in epithelial morphogenesis, but E-cadherin is largely absent from the RPE. In this review, the contribution of cadherins, both minor (E-cadherin) and major (N-cadherin), to RPE phenotype development is discussed. Emphasis is placed on the importance for future studies of actin cytoskeletal remodeling during assembly of the AJ, which in epithelial cells results in an actin organization that is characteristically zonular. Other markers of RPE phenotype that are used to gauge the maturation state of RPE cultures including tissue-specific protein expression, protein polarity, and pigmentation are described. An argument is made that RPE epithelial phenotype, cadherin-based cell-cell adhesion and melanization are linked by a common signaling pathway: the Wnt/beta-catenin pathway. Analyzing this pathway and its intersecting signaling networks is suggested as a useful framework for dissecting the steps in RPE morphogenesis. Also discussed is the effect of aging on RPE phenotype. Preliminary evidence is provided to suggest that light-induced sub-lethal oxidative stress to cultured ARPE-19 cells impairs organelle motility. Organelle translocation, which is mediated by stress-susceptible cytoskeletal scaffolds, is an essential process in cell phenotype development and retention. The observation of impaired organelle motility therefore raises the possibility that low levels of stress, which are believed to accompany RPE aging, may produce subtle disruptions of cell phenotype. Over time these would be expected to diminish the support functions performed by the RPE on behalf of photoreceptors, theoretically contributing to aging retinal disease such as age-related macular degeneration (AMD). Analyzing sub-lethal stress that produces declines in RPE functional efficiency rather than overt cell death is suggested as a useful future direction for understanding the effects of age on RPE organization and physiology. As for phenotype and pigmentation, a role for the Wnt/beta-catenin pathway is also suggested in regulating the RPE response to oxidative stress. Exploration of this pathway in the RPE therefore may provide a unifying strategy for advancing our understanding of both RPE phenotype and the consequences of mild oxidative stress on RPE structure and function.

Immunohistochemistry and in situ hybridization in the study of human skin melanocytes

Although keratinocytes are the most numerous type of cell in the skin, melanocytes are also key players as they produce and distribute melanin that protects the skin from ultraviolet (UV) radiation. In vitro experiments on melanocytic cell lines are useful to study melanogenesis and their progression towards melanoma. However, interactions of melanocytes with keratinocytes and with other types of cells in the skin, such as fibroblasts and Langerhans cells, are also crucial. We describe two techniques, immunohistochemistry (IHC) and tissue in situ hybridization (TISH), that can be used to identify and study melanocytes in the skin and their responses to UV or other stimuli in situ. We describe a practical method to localize melanocytic antigens on formalin-fixed, paraffin-embedded tissue sections and in frozen sections using indirect immunofluorescence with conjugated secondary antibodies. In addition, we detail the use of TISH and its combination with IHC to study mRNA levels of genes expressed in the skin at cellular resolution. This methodology, along with relevant tips and troubleshooting items, are important tools to identify and study melanocytes in the skin.