Understanding Melanocyte Stem Cells for Disease Modeling and Regenerative Medicine Applications

Melanocytes in regenerative medicine applications and disease modeling

Melanocytes are dendritic cells localized in skin, eyes, hair follicles, ears, heart and central nervous system. They are characterized by the presence of melanosomes enriched in melanin which are responsible for skin, eye and hair pigmentation. They also have different functions in photoprotection, immunity and sound perception. Melanocyte dysfunction can cause pigmentary disorders, hearing and vision impairments or increased cancer susceptibility. This review focuses on the role of melanocytes in homeostasis and disease, before discussing their potential in regenerative medicine applications, such as for disease modeling, drug testing or therapy development using stem cell technologies, tissue engineering and extracellular vesicles.

Dynamic regulation of chromatin accessibility during melanocyte stem cell activation

Melanocyte stem cells (McSCs) of the hair follicle are necessary for hair pigmentation and can serve as melanoma cells of origin when harboring cancer-driving mutations. McSCs can be released from quiescence, activated, and undergo differentiation into pigment-producing melanocytes during the hair cycle or due to environmental stimuli, such as ultraviolet-B (UVB) exposure. However, our current understanding of the mechanisms regulating McSC stemness, activation, and differentiation remains limited. Here, to capture the differing possible states in which murine McSCs can exist, we sorted melanocyte nuclei from quiescent (telogen) skin, skin actively producing hair shafts (anagen), and skin exposed to UVB. With these sorted nuclei, we then utilized single-nucleus assay for transposase-accessible chromatin with high-throughput sequencing (snATAC-seq) and characterized three melanocyte lineages: quiescent McSCs (qMcSCs), activated McSCs (aMcSCs), and differentiated melanocytes (dMCs) that co-exist in all three skin conditions. Furthermore, we successfully identified differentially accessible genes and enriched transcription factor binding motifs for each melanocyte lineage. Our findings reveal potential gene regulators that determine these melanocyte cell states and provide new insights into how aMcSC chromatin states are regulated differently under divergent intrinsic and extrinsic cues. We also provide a publicly available online tool with a user-friendly interface to explore this comprehensive dataset, which will provide a resource for further studies on McSC regulation upon natural or UVB-mediated stem cell activation.

Lesional CD8+ T-Cell Number Predicts Surgical Outcomes of Melanocyte-Keratinocyte Transplantation Surgery for Vitiligo

The melanocyte-keratinocyte transplantation procedure (MKTP) treats stable and recalcitrant vitiligo. Despite careful selection of candidates based on clinical stability, the success of the procedure is unpredictable. The aim of our study was to define the immunological profile of stable vitiligo lesions undergoing MKTP and correlate them with clinical outcomes. We included 20 MKTP candidates with vitiligo and a patient with piebaldism as a control. Prior to MKTP, T-cell subsets and chemokines in the recipient skin were measured by flow cytometry and ELISA. During MKTP, melanocytes in the donor skin were quantified by flow cytometry. After MKTP, patients were followed for 12 months and repigmentation was assessed clinically and by ImageJ analysis of clinical photographs. Baseline immunologic biomarkers, duration of clinical stability, and transplanted melanocyte number were correlated to postsurgical repigmentation scores. CD8+ T cells were elevated in 43% of the clinically stable vitiligo lesions. CD8+ T-cell number negatively correlated with postsurgical repigmentation scores (r = -0.635, P = 0.002). Duration of clinical stability, skin chemokines, and transplanted melanocyte number did not influence postsurgical repigmentation. This study demonstrates that CD8+ T-cell number correlates negatively with success of postsurgical repigmentation and can be a biomarker to identify ideal surgical candidates.

Sox9 regulates melanocytic fate decision of adult hair follicle stem cells

The bulge of hair follicles harbors Nestin⁺ (neural crest like) stem cells, which exhibit the potential to generate various cell types including melanocytes. In this study, we aimed to determine the role of Sox9, an important regulator during neural crest development, in melanocytic differentiation of those adult Nestin⁺ cells. Immunohistochemical analysis after conditional Sox9 deletion in Nestin⁺ cells of adult mice revealed that Sox9 is crucial for melanocytic differentiation of these cells and that Sox9 acts as a fate determinant between melanocytic and glial fate. A deeper understanding of factors that regulate fate decision, proliferation and differentiation of these stem cells provides new aspects to melanoma research as melanoma cells share many similarities with neural crest cells. In summary, we here show the important role of Sox9 in melanocytic versus glial fate decision of Nestin⁺ stem cells in the skin of adult mice.

Melanocyte stem cells in skin diseases and their potential in cell-based therapy

Melanocytes have a complex function and play an important role in a variety of regulatory mechanisms in the human system. Melanocyte stem cells (MelSCs) serve as a reservoir to replenish the melanocytes by regenerating new ones, and they are capable of self-renewal and differentiation to maintain their homeostasis, repair, and regeneration in tissues. The numerical decrease and functional impairment of MelSCs may be closely related to the development and treatment response of many skin diseases. However, the current knowledge about MelSCs mainly comes from studies in mice, and little is known about human MelSC markers; especially, their markers are still unclear or lack consensus. This leads to uncertainty in clinical findings, which further limits our comprehensive understanding of pigmentary disorders and also hinders the progress of new treatments. Thus, in this review article, combined with our previous and current work, we summarize and update the recent advances in MelSC research, including the molecular markers of human MelSCs and their niche, as well as the association of MelSCs with skin diseases, including vitiligo, hair greying, and melanoma. Due to the limited tools available to explore the identified characteristics of human MelSCs, pluripotent stem cells can provide a new research model for further study, especially combined with CRISPR/Cas9 technology. The visualization of human MelSCs' development and differentiation can help to identify their molecular characteristics and understand their cellular fate dynamically, which will allow us not only to further explore their roles in associated diseases, but also to achieve MelSC-based cellular therapy.

A Beginner's Introduction to Skin Stem Cells and Wound Healing

The primary function of the skin is that of a physical barrier against the environment and diverse pathogens; therefore, its integrity is essential for survival. Skin regeneration depends on multiple stem cell compartments within the epidermis, which, despite their different transcriptional and proliferative capacity, as well as different anatomical location, fall under the general term of skin stem cells (SSCs). Skin wounds can normally heal without problem; however, some diseases or extensive damage may delay or prevent healing. Non-healing wounds represent a serious and life-threatening scenario that may require advanced therapeutic strategies. In this regard, increased focus has been directed at SSCs and their role in wound healing, although emerging therapeutical approaches are considering the use of other stem cells instead, such as mesenchymal stem cells (MSCs). Given its extensive and broad nature, this review supplies newcomers with an introduction to SSCs, wound healing, and therapeutic strategies for skin regeneration, thus familiarizing the reader with the subject in preparation for future in depth reading.

UV-induced reduction in Polycomb repression promotes epidermal pigmentation

Ultraviolet (UV) radiation is a prime environmental stressor that our epidermis is exposed to on a daily basis. To avert UV-induced damage, epidermal stem cells (EpSCs) become pigmented via a process of heterotypic interaction between melanocytes and EpSCs; however, the molecular mechanisms of this interaction are not well understood. In this study, we show that the function of a key chromatin regulator, the Polycomb complex, was reduced upon UV exposure in human and mouse epidermis. Genetic ablation of key Polycomb subunits in murine EpSCs, mimicking depletion upon UV exposure, results in an increased number of epidermal melanocytes and subsequent epidermal pigmentation. Genome-wide transcriptional and chromatin studies show that Polycomb regulates the expression of UV-responsive genes and identifies type II collagen (COL2A1) as a critical secreted regulator of melanogenesis and epidermal pigmentation. Together, our findings show how UV exposure induces Polycomb-mediated changes in EpSCs to affect melanocyte behavior and promote epidermal pigmentation.

4-Octylphenol induces developmental abnormalities and interferes the differentiation of neural crest cells in Xenopus laevis embryos

Developmental toxicity of 4-octylphenol (OP), an estrogenic endocrine disruptor was verified using frog embryo teratogenesis assay Xenopus. LC₅₀, EC_{50Malformtion} and EC_{50Melanocyte-dysgenesis} of OP were 9.9, 10.5, and 2.4 μM, respectively. In tadpoles, despite the low teratogenic index, 2 μM OP significantly inhibited head cartilage development and tail malformation. The total length of tadpole was significantly increased at 5 μM and decreased at 10 μM OP. In OP-treated tadpoles, head cartilages were frequently missed and col2a1 mRNA was decreased at 2 μM, indicating a chondrogenic defect in developing head. In the head skin of 1 μM OP-treated tadpoles, number of melanocytes and melanogenic pathway genes expression were significantly decreased. In the head-neck junction of stage 22 embryos, OP increased foxd3 and sox10 mRNA and SOX10(+) neural crest cells (NCCs) in somite mesoderm and endoderm, indicating the inhibition of chondrogenic differentiation, ectopic migration to endoderm, and undifferentiation of NCCs by OP. Together, OP-induced head dysplasia and inhibition of melanogenesis may be attributable to deregulation of neural crest cells in embryos. In tadpoles, OP at 1 μM significantly increased lipid hydroperoxide and induced spliced xbp1 mRNA, an IRE1 pathway endoplasmic reticulum stress (ERS) marker and p-eIF2α protein, a PERK pathway ERS marker. OP at 10 μM induced CHOP mRNA, pro-apoptotic genes expression, DNA fragmentation, and cleaved caspase-3, suggesting that OP differentially induced ERS and apoptosis according to the concentration in embryos. In 5-10 μM OP-treated stage 22 embryos and stage 45 tadpole heads, Ki67 was significantly increased, suggesting the apoptosis-induced proliferation of embryonic cells in the OP-treated embryos. Together, OP should be managed as a developmental toxicant altering the behavior of NCCs in vertebrates.

RAD6B Loss Disrupts Expression of Melanoma Phenotype in Part by Inhibiting WNT/β-Catenin Signaling

Canonical Wnt signaling is critical for melanocyte lineage commitment and melanoma development. RAD6B, a ubiquitin-conjugating enzyme critical for translesion DNA synthesis, potentiates β-catenin stability/activity by inducing proteasome-insensitive polyubiquitination. RAD6B expression is induced by β-catenin, triggering a positive feedback loop between the two proteins. RAD6B function in melanoma development/progression was investigated by targeting RAD6B using CrispR/Cas9 or an RAD6-selective small-molecule inhibitor #9 (SMI#9). SMI#9 treatment inhibited melanoma cell proliferation but not normal melanocytes. RAD6B knockout or inhibition in metastatic melanoma cells downregulated β-catenin, β-catenin-regulated microphthalmia-associated transcription factor (MITF), sex-determining region Y-box 10, vimentin proteins, and MITF-regulated melan A. RAD6B knockout or inhibition decreased migration/invasion, tumor growth, and lung metastasis. RNA-sequencing and stem cell pathway real-time RT-PCR analysis revealed profound reductions in WNT1 expressions in RAD6B knockout M14 cells compared with control. Expression levels of β-catenin-regulated genes VIM, MITF-M, melan A, and TYRP1 (a tyrosinase family member critical for melanin biosynthesis) were reduced in RAD6B knockout cells. Pathway analysis identified gene networks regulating stem cell pluripotency, Wnt signaling, melanocyte development, pigmentation signaling, and protein ubiquitination, besides DNA damage response signaling, as being impacted by RAD6B gene disruption. These data reveal an important and early role for RAD6B in melanoma development besides its bonafide translesion DNA synthesis function, and suggest that targeting RAD6B may provide a novel strategy to treat melanomas with dysregulated canonical Wnt signaling.

BMP4-Induced Differentiation of Human Hair Follicle Neural Crest Stem Cells into Precursor Melanocytes from Hair Follicle Bulge

Background

Vitiligo is a skin depigmentation disorder, for which, repigmentation treatment with combined follicular unit extraction (FUE) graft and narrowband ultraviolet B (NBUVB) is considered superior to micro-punch graft therapy. BMP4 can induce MITF expression in Neural crest stem cells (NCSCs), and α-MSH subsequently promotes the differentiation of MITF-expressing cells along the melanocyte lineage.

Objective

To investigate why FUE grafting is superior to epidermal mini grafting in promoting hair follicles (HF) melanocyte cell survival and longevity, we planned the in vitro experiments HF bulge NCSCs differentiate into melanocyte precursors under the co-treatment of BMP4 and α-MSH.

Methods

Cells that migrated from the HF bulge of scalp were cultured and assessed using immunofluorescence. Transcriptome analysis was performed on RNA sequencing results.

Results

Basic fibroblast growth factor promotes the proliferation and survival of NCSCs, with spontaneous differentiation into SOX10+/SOX2+ glial progenitors, but not into SOX10+/MITF+ precursor melanocytes. Both BMP4 and α-MSH promoted the differentiation into MITF-expressing cells. RNA sequencing revealed a downregulation in neuregulin-1 (NRG1) and sermaphorin 3C (SEMA3C), and upregulation in WNT10A. Furthermore, FUE grafting had a source of reservoir melanocytes superior to mini- grafting in treatment for vitiligo.

Conclusion

We obtained SOX10+/MITF+ precursor melanocytes through an induction of differentiation along the melanocyte lineage by BMP4 and α-MSH. According to the RNA sequencing results that NRG1 and SEMA3C were downregulated and WNT10A was upregulated, we postulated that HF NCSCs differentiated into melanocyte by co-treatment of BMP4 and α-MSH. Overall, FUE grafting is a more robust and substitutive treatment option for vitiligo.

Resistance of melanoma cells to anticancer treatment: a role of vascular endothelial growth factor

Melanoma is one of the most aggressive and resistant to treatment neoplasms. There are still many challenges despite many promising advances in anticancer treatment. Currently, the main problem for all types of treatment is associated with heterogeneity. Due to heterogeneity of cancer cells, "precise" targeting of a medicine against a single phenotype limits the efficacy of treatment and affects resistance to applied therapy. Therefore it is important to understand aetiology and reasons for heterogeneity in order to develop effective and long-lasting treatment. This review summarises roles of vascular endothelial growth factor (VEGF) that may stimulate growth of a melanoma tumour irrespective of its proangiogenic effects, contributing to cancer heterogeneity. VEGF triggers processes associated with extracellular matrix remodelling, cell migration, invasion, angiogenesis, inhibition of immune responses and favours phenotypic plasticity and epithelial-mesenchymal transition. Consequently, it participates in mechanisms of interactions between melanoma cancer cells and microenvironment and it can modify sensitivity to therapeutic factors.

Patterned cutaneous hypopigmentation phenotype characterization: A retrospective study in 106 children

BACKGROUND

Cutaneous patterned hypopigmentation's phenotype is highly variable and may be associated with extracutaneous anomalies.

OBJECTIVE

We evaluated the phenotypic and clinical characteristics of patients with cutaneous patterned hypopigmentation to determine whether certain patterns were more likely to be associated with underlying anomalies.

METHODS

The charts of 106 children with cutaneous patterned hypopigmentation were reviewed retrospectively (2007-2018) at Sainte-Justine University Hospital Centre, in Montreal, Canada. Retrieved information included sex, age at diagnosis, phototype, pattern, and distribution of the cutaneous lesions and the presence of extracutaneous findings. Data were recorded on a software tool which collects and analyzes phenotypic information.

RESULTS

The predominant types of cutaneous patterned hypopigmentation were along Blaschko's lines in narrow (38.7%) and broad bands (53.8%). Mixed patterns were observed in 22.5% of children. The anterior trunk and posterior trunk were most frequently affected (69% and 56%, respectively). Extracutaneous involvement, especially neurological and developmental, was present in 28.3% of patients and was significantly associated with ≥ 4 involved body sites.

CONCLUSION

Distribution and types of cutaneous patterned hypopigmentation were not predictive of extracutaneous findings, with the exception of multiple sites involvement and possibly centrofacial location and blocklike lesions. Follow-up until school entry should help identify subtler associated extracutaneous anomalies.

Contribution of Human Hair in Solar UV Transmission in Skin: Implications for Melanoma Development

Melanoma is the deadliest type of skin cancer with its prevalence on the rise. Recently, the melanocyte stem cells in hair follicles have been identified as the possible origin of melanoma upon exposure to ultraviolet radiation (UVR) through skin. It is hypothesized that colourless vellus hair (predominant in childhood) can serve as an alternative pathway in transmitting these ultraviolet (UV) photons to the stem cells. To investigate this, we have used the CRAIC microspectrophotometer to investigate the optical properties of 'vellus-like' hairs and terminal hairs of different colours using UV-VIS-NIR light sources. It was found that the average attenuation coefficient of 'vellus-like' hair is significantly lower than that of terminal hair in the UVA (p < 0.0001) and UVB (p < 0.001) wavelength ranges. Next, the optical properties of hairs are applied to simulations for examining their influence on UV transmission into the skin. The results show that the presence of vellus hair would increase the solar UV transmission to the melanocyte stem cell layer significantly. The findings explain why children are particularly vulnerable to sun exposure and the positive correlation found between the incidence of melanoma in adults' bodies and the number of vellus hairs in these areas.

Tyrosinase and nestin immunohistochemical expression in melanocytic nevi as a histopathologic pattern to trace melanocyte differentiation and nevogenesis

While histological analysis represents a powerful tool for the classification of melanocytic lesions as benign or malignant, a clear-cut distinction between a nevus and a melanoma is sometimes a challenging step of the diagnostic process. The immunohistochemical detection of tyrosinase, cardinal melanogenic enzyme during melanocytic maturation, has often been helpful in formulating a differential diagnosis due to the peculiar staining pattern in nevocytes compared with melanoma cells. Tyrosinase distribution in nevi appears to overlap with the cytoarchitectural changes observable within these lesions, that result in epidermal or superficial dermal nevocytes being larger and strongly expressing melanocytic differentiation antigens, such as tyrosinase, compared with deeper dermal nevus cells. Our study aimed to evaluate the immunohistochemical expression pattern of tyrosinase in different histological types of acquired dysplastic melanocytic nevi, including junctional, compound, and intradermal nevi. Moreover, to estimate whether in nevocytes the expression of tyrosinase was associated with their differentiation state, we investigated the expression of two recognized markers of pluripotency, CD34 and nestin. In all examined nevi, our analysis revealed a remarkable immunoreactivity for tyrosinase in junctional and superficial dermal nevocytes and a decreasing gradient of staining in dermal nevocytes, up to become negative in deeper dermis. Meanwhile, junctional and dermal nevocytes were lacking in CD34 protein. Furthermore, nestin immunostaining showed an opposite distribution compared with tyrosinase, leading us to look into the tyrosinase/nestin expression pattern in melanocytic nevus as a tool to better understand the final stages of differentiation of melanocyte precursors toward their ultimate anatomical site into the epidermis.

Spatiotemporal Labeling of Melanocytes in Mice

Melanocytes are pigment producing cells in the skin that give rise to cutaneous malignant melanoma, which is a highly aggressive and the deadliest form of skin cancer. Studying melanocytes in vivo is often difficult due to their small proportion in the skin and the lack of specific cell surface markers. Several genetically-engineered mouse models (GEMMs) have been created to specifically label the melanocyte compartment. These models give both spatial and temporal control over the expression of a cellular ‘beacon’ that has an added benefit of inducible expression that can be activated on demand. Two powerful models that are discussed in this review include the melanocyte-specific, tetracycline-inducible green fluorescent protein expression system (iDct-GFP), and the fluorescent ubiquitination-based cell cycle indicator (FUCCI) model that allows for the monitoring of the cell-cycle. These two systems are powerful tools in studying melanocyte and melanoma biology. We discuss their current uses and how they could be employed to help answer unresolved questions in the fields of melanocyte and melanoma biology.

Regulation of melanocyte stem cell behavior by the niche microenvironment

Somatic stem cells are regulated by their niches to maintain tissue homeostasis and repair throughout the lifetime of an organism. An excellent example to study stem cell/niche interactions is provided by the regeneration of melanocytes during the hair cycle and in response to various types of injury. These processes are regulated by neighboring stem cells and multiple signaling pathways, including WNT/β-catenin, KITL/KIT, EDNs/EDNRB, TGF-β/TGF-βR, α-MSH/MC1R, and Notch signaling. In this review, we highlight recent studies that have advanced our understanding of the molecular crosstalk between melanocyte stem cells and their neighboring cells, which collectively form the niche microenvironment, and we focus on the question of how McSCs/niche interactions shape the responses to genotoxic damages and mechanical injury.

Biochemical aspects of mammalian melanocytes and the emerging role of melanocyte stem cells in dermatological therapies

Skin color in animals is richer than human beings and is determined by different types of pigments. Melanin is the key pigment responsible for the diverse pigmentation found in animal and human skin, hair, and eyes. Melanin pigment is synthesized by melanocytes and is consecutively transferred to adjacent keratinocytes; here, it acts as an internal sunscreen to defend from ultraviolet (UV) damage. Any defect in the process of melanocytes development and/or melanin synthesis results in esthetic problem of abnormal pigmentation. Clinically, abnormal pigmentation displays distinct increased or reduced pigment levels, known as hyperpigmentation or hypopigmentation. These defects affect either the melanocyte number or its function. Herein, we discuss the fundamental aspects of melanocytes/melanin biology taken together the underlying cause of pigmentary disorders. The current chapter also gives an insight into the melanocyte stem cells biology, which in turn can facilitate the development of novel treatment regimens for dermatological disorders.

Current and Future Perspectives of Stem Cell Therapy in Dermatology

Stem cells are undifferentiated cells capable of generating, sustaining, and replacing terminally differentiated cells and tissues. They can be isolated from embryonic as well as almost all adult tissues including skin, but are also generated through genetic reprogramming of differentiated cells. Preclinical and clinical research has recently tremendously improved stem cell therapy, being a promising treatment option for various diseases in which current medical therapies fail to cure, prevent progression or relieve symptoms. With the main goal of regeneration or sustained genetic correction of damaged tissue, advanced tissue-engineering techniques are especially applicable for many dermatological diseases including wound healing, genodermatoses (like the severe blistering disorder epidermolysis bullosa) and chronic (auto-)inflammatory diseases. This review summarizes general aspects as well as current and future perspectives of stem cell therapy in dermatology.

Genomic Assessment of Blitz Nevi Suggests Classification as a Subset of Blue Nevus Rather Than Spitz Nevus: Clinical, Histopathologic, and Molecular Analysis of 18 Cases

Blitz nevi/tumors are a distinct subset of melanocytic neoplasia which show mixed morphologic features of Spitz and blue nevus. Genomically, most blue nevi have GNAQ or GNA11 mutations while most Spitzoid neoplasms have either an HRAS mutation or translocations involving MET, ROS, BRAF, ALK1, NTRK1, and RET. The criteria used for the assessment of malignancy in blue and Spitzoid lesions are different, and these lesions have different prognostic markers. In this study, we assess the clinical, morphological, and genomic changes in 18 cases of Blitz nevi/tumors to better characterize this subset of neoplasms and determine their optimal genomic classification. Most lesions occurred on the extremities followed by the head and neck region typical of blue nevi. Histology showed most cases having a prominent plexiform growth pattern with cells aggregating around the adnexal structures and neurovascular bundles also typical of blue nevi. Using next generation sequencing, we detected the presence of somatic mutations in GNAQ or GNA11 in 4 of 7 cases (57%) of Blitz nevi with sufficient DNA available for sequencing. Normal skin samples in these 4 cases were sequenced to confirm that the GNAQ or GNA11 mutations were somatic mutations. All 4 cases were negative for immunohistochemical assessment for wild-type BRAF, RET, ALK, and NTRK1 and mutational analysis of HRAS was also negative in all cases. Hence, our study suggests that Blitz nevi/tumors are a distinct subset which genomically are best classified as a subset of blue nevi.

Trends in Regenerative Medicine: Repigmentation in Vitiligo Through Melanocyte Stem Cell Mobilization

Vitiligo is the most frequent human pigmentary disorder, characterized by progressive autoimmune destruction of mature epidermal melanocytes. Of the current treatments offering partial and temporary relief, ultraviolet (UV) light is the most effective, coordinating an intricate network of keratinocyte and melanocyte factors that control numerous cellular and molecular signaling pathways. This UV-activated process is a classic example of regenerative medicine, inducing functional melanocyte stem cell populations in the hair follicle to divide, migrate, and differentiate into mature melanocytes that regenerate the epidermis through a complex process involving melanocytes and other cell lineages in the skin. Using an in-depth correlative analysis of multiple experimental and clinical data sets, we generated a modern molecular research platform that can be used as a working model for further research of vitiligo repigmentation. Our analysis emphasizes the active participation of defined molecular pathways that regulate the balance between stemness and differentiation states of melanocytes and keratinocytes: p53 and its downstream effectors controlling melanogenesis; Wnt/β-catenin with proliferative, migratory, and differentiation roles in different pigmentation systems; integrins, cadherins, tetraspanins, and metalloproteinases, with promigratory effects on melanocytes; TGF-β and its effector PAX3, which control differentiation. Our long-term goal is to design pharmacological compounds that can specifically activate melanocyte precursors in the hair follicle in order to obtain faster, better, and durable repigmentation.

Prospect of Human Pluripotent Stem Cell-Derived Neural Crest Stem Cells in Clinical Application

Neural crest stem cells (NCSCs) represent a transient and multipotent cell population that contributes to numerous anatomical structures such as peripheral nervous system, teeth, and cornea. NCSC maldevelopment is related to various human diseases including pigmentation abnormalities, disorders affecting autonomic nervous system, and malformations of teeth, eyes, and hearts. As human pluripotent stem cells including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) can serve as an unlimited cell source to generate NCSCs, hESC/hiPSC-derived NCSCs can be a valuable tool to study the underlying mechanisms of NCSC-associated diseases, which paves the way for future therapies for these abnormalities. In addition, hESC/hiPSC-derived NCSCs with the capability of differentiating to various cell types are highly promising for clinical organ repair and regeneration. In this review, we first discuss NCSC generation methods from human pluripotent stem cells and differentiation mechanism of NCSCs. Then we focus on the clinical application potential of hESC/hiPSC-derived NCSCs on peripheral nerve injuries, corneal blindness, tooth regeneration, pathological melanogenesis, Hirschsprung disease, and cardiac repair and regeneration.

Wnt/β-catenin signaling inhibitor ICG-001 enhances pigmentation of cultured melanoma cells

BACKGROUND

Wnt/β-catenin signaling is important in development and differentiation of melanocytes.

OBJECTIVE

The object of this study was to evaluate the effects of several Wnt/β-catenin signaling inhibitors on pigmentation using melanoma cells.

METHODS

Melanoma cells were treated with Wnt/β-catenin signaling inhibitors, and then melanin content and tyrosinase activity were checked.

RESULTS

Although some inhibitors showed slight inhibition of pigmentation, we failed to observe potential inhibitory effect of those chemicals on pigmentation of HM3KO melanoma cells. Rather, one of powerful Wnt/β-catenin signaling inhibitors, ICG-001, increased the pigmentation of HM3KO melanoma cells. Pigmentation-enhancing effect of ICG-001 was reproducible in other melanoma cell line MNT-1. Consistent with these results. ICG-001 increased the expression of pigmentation-related genes, such as MITF, tyrosinase and TRP1. When ICG-001 was treated, the phosphorylation of CREB was significantly increased. In addition, ICG-001 treatment led to quick increase of intracellular cAMP level, suggesting that ICG-001 activated PKA signaling. The blockage of PKA signaling with pharmaceutical inhibitor H89 inhibited the ICG-001-induced pigmentation significantly.

CONCLUSIONS

These results suggest that PKA signaling is pivotal in pigmentation process itself, while the importance of Wnt/β-catenin signaling should be emphasized in the context of development and differentiation.