Nrf2 negatively regulates melanogenesis by modulating PI3K/Akt signaling

ROS and calcium signaling are critical determinant of skin pigmentation

Pigmentation is a protective phenomenon that shields skin cells from UV-induced DNA damage. Perturbations in pigmentation pathways predispose to skin cancers and lead to pigmentary disorders. These ailments impart psychological trauma and severely affect the patients' quality of life. Emerging literature suggests that reactive oxygen species (ROS) and calcium (Ca2+) signaling modules regulate physiological pigmentation. Further, pigmentary disorders are associated with dysregulated ROS homeostasis and changes in Ca2+ dynamics. Here, we systemically review the literature that demonstrates key role of ROS and Ca2+ signaling in pigmentation and pigmentary disorders. Further, we discuss recent studies, which have revealed that organelle-specific Ca2+ transport mechanisms are critical determinant of pigmentation. Importantly, we deliberate upon the possibility of clinical management of pigmentary disorders by therapeutically targeting ROS generation and cellular Ca2+ handling toolkit. Finally, we highlight the key outstanding questions in the field that demand critical and timely attention. Although an important role of ROS and Ca2+ signaling in regulating skin pigmentation has emerged, the underlying molecular mechanisms remain poorly understood. In future, it would be vital to investigate in detail the signaling cascades that connect perturbed ROS homeostasis and Ca2+ signaling to human pigmentary disorders.

Joint Genomic and Transcriptomic Analysis Reveals Candidate Genes Associated with Plumage Color Traits in Matahu Ducks

Plumage color is a key trait for identifying waterfowl breeds with significant economic importance. A white-feathered group has recently emerged within the native Matahu duck population, presenting an opportunity for breeding new lines. However, the genetic basis for this plumage variation is still unknown, necessitating further research. This study aims to identify the genetic mechanisms underlying the emergence of white-feathered individuals in the Matahu duck population through combined genome and transcriptome analysis, providing insights for selective breeding and the development of new white-feathered lines. In this study, a total of 1344 selected genes and 1406 significantly differentially expressed genes were identified through selection signal analysis and transcriptomic analysis, respectively. The functional enrichment of these genes revealed several key signaling pathways, including those related to cGMP-PKG, cAMP, PI3K-Akt, and MAPK. Furthermore, important candidate genes involved in melanin biosynthesis, such as MITF, MC1R, TYR, TYRP1, and ABCB6, were identified. Notably, 107 genes were detected by both methods, and, among these, DGKI, GPRC5B, HMX1, STS, ADGRA1, PRKAR2B, and HOXB9 are suggested to play a role in melanin formation and potentially influence plumage traits. Through the integrative approach combining genomic selection signals and transcriptomic analyses, we identified several candidate genes directly associated with plumage color, including MITF, TYR, TYRP1, and MC1R, along with multiple signaling pathways linked to melanin formation. We hypothesize that the expression of DGKI, GPRC5B, HMX1, STS, ADGRA1, PRKAR2B, and HOXB9, detected by both methods, may be closely related to the regulation of plumage color traits. These findings provide a foundational basis for further research aimed at elucidating the genetic mechanisms governing plumage color variation in ducks.

A novel liquid plasma derivative inhibits melanogenesis through upregulation of Nrf2

Non-thermal plasma (NTP) is an emerging technology with extensive applications in biomedicine, including treatment of abnormal pigmentation. However, very few studies have investigated how plasma induces anti-melanogenesis. Here, liquid plasma was prepared by treating an NTP jet with helium and oxygen (as carrier gases) for 15 min in serum-free culture media. In the zebrafish model, pigmentation ratio was observed with or without liquid plasma. The anti-melanogenic effect of liquid plasma was evaluated in human melanocytes by assessing the expression of melanogenesis-related genes using western blotting, RT-PCR, and immunohistochemistry. Liquid plasma reduced pigmentation in the zebrafish model and inhibited melanin synthesis in primary human melanocytes. Intracellular reactive oxygen species levels decreased and Nrf2 expression increased in liquid plasma-treated melanocytes. Liquid plasma affected microphthalmia-associated transcription factor (MITF) and tyrosinase mRNA and protein levels, tyrosinase activity, and melanin content. Considering the role of Wnt/β-catenin and PI3K/Akt pathways in melanogenesis, the effect of liquid plasma on this pathway was determined; liquid plasma decreased active β-catenin, LEF1/TCF4, MITF, and tyrosinase levels in a time-dependent manner and inhibited the nuclear translocation of β-catenin. This inhibition subsequently suppressed melanogenesis by downregulating MITF and tyrosinase. These results suggest that liquid plasma may be used for treating pigmentary disorders.

Unlocking the Bioactive Potential and Exploring Novel Applications for Portuguese Endemic Santolina impressa

The infusion of Santolina impressa, an endemic Portuguese plant, is traditionally used to treat various infections and disorders. This study aimed to assess its chemical profile by HPLC-DAD-ESI-MSn and validate its anti-inflammatory potential. In addition, the antioxidant capacity and effects on wound healing, lipogenesis, melanogenesis, and cellular senescence, all processes in which a dysregulated inflammatory response plays a pivotal role, were unveiled. The anti-inflammatory potential was assessed in lipopolysaccharide (LPS)-stimulated macrophages, cell migration was determined using a scratch wound assay, lipogenesis was assessed on T0901317-stimulated keratinocytes and melanogenesis on 3-isobutyl-1-methylxanthine (IBMX)-activated melanocytes. Etoposide was used to induce senescence in fibroblasts. Our results point out a chemical composition predominantly characterized by dicaffeoylquinic acids and low amounts of flavonols. Regarding the infusion's bioactive potential, an anti-inflammatory effect was evident through a decrease in nitric oxide production and inducible nitric oxide synthase and pro-interleukin-1β protein levels. Moreover, a decrease in fibroblast migration was observed, as well as an inhibition in both intracellular lipid accumulation and melanogenesis. Furthermore, the infusion decreased senescence-associated β-galactosidase activity, γH2AX nuclear accumulation and both p53 and p21 protein levels. Overall, this study confirms the traditional uses of S. impressa and ascribes additional properties of interest in the pharmaceutical and dermocosmetics industries.

Exploring the Influence of Cold Plasma on Epidermal Melanogenesis In Situ and In Vitro

Epidermal melanin synthesis determines an individual's skin color. In humans, melanin is formed by melanocytes within the epidermis. The process of melanin synthesis strongly depends on a range of cellular factors, including the fine-tuned interplay with reactive oxygen species (ROS). In this context, a role of cold atmospheric plasma (CAP) on melanin synthesis was proposed due to its tunable ROS generation. Herein, the argon-driven plasma jet kINPen® MED was employed, and its impact on melanin synthesis was evaluated by comparison with known stimulants such as the phosphodiesterase inhibitor IBMX and UV radiation. Different available model systems were employed, and the melanin content of both cultured human melanocytes (in vitro) and full-thickness human skin biopsies (in situ) were analyzed. A histochemical method detected melanin in skin tissue. Cellular melanin was measured by NIR autofluorescence using flow cytometry, and a highly sensitive HPLC-MS method was applied, which enabled the differentiation of eu- and pheomelanin by their degradation products. The melanin content in full-thickness human skin biopsies increased after repeated CAP exposure, while there were only minor effects in cultured melanocytes compared to UV radiation and IBMX treatment. Based on these findings, CAP does not appear to be a useful option for treating skin pigmentation disorders. On the other hand, the risk of hyperpigmentation as an adverse effect of CAP application for wound healing or other dermatological diseases seems to be neglectable.

Thiol starvation triggers melanoma state switching in an ATF4 and NRF2-dependent manner

The cystine/glutamate antiporter xCT is an important source of cysteine for cancer cells. Once taken up, cystine is reduced to cysteine and serves as a building block for the synthesis of glutathione, which efficiently protects cells from oxidative damage and prevents ferroptosis. As melanomas are particularly exposed to several sources of oxidative stress, we investigated the biological role of cysteine and glutathione supply by xCT in melanoma. xCT activity was abolished by genetic depletion in the Tyr::CreER; BrafCA; Ptenlox/+ melanoma model and by acute cystine withdrawal in melanoma cell lines. Both interventions profoundly impacted melanoma glutathione levels, but they were surprisingly well tolerated by murine melanomas in vivo and by most human melanoma cell lines in vitro. RNA sequencing of human melanoma cells revealed a strong adaptive upregulation of NRF2 and ATF4 pathways, which orchestrated the compensatory upregulation of genes involved in antioxidant defence and de novo cysteine biosynthesis. In addition, the joint activation of ATF4 and NRF2 triggered a phenotypic switch characterized by a reduction of differentiation genes and induction of pro-invasive features, which was also observed after erastin treatment or the inhibition of glutathione synthesis. NRF2 alone was capable of inducing the phenotypic switch in a transient manner. Together, our data show that cystine or glutathione levels regulate the phenotypic plasticity of melanoma cells by elevating ATF4 and NRF2.

Genome-wide association study (GWAS) analysis of black color trait in the leopard coral grouper (Plectropomus leopardus) using whole genome resequencing

The leopard coral grouper (Plectropomus leopardus) is a coral reef fish species that exhibits rapid and diverse color variation. However, the presence of melanoma and the high proportion of individuals displaying black color in artificial breeding have led to reduced economic and ornamental value. To pinpoint single nucleotide polymorphisms (SNPs) and potential genes linked to the black pigmentation characteristic in this particular species, This study gathered a cohort of 360 specimens from diverse origins and conducted a comprehensive genome-wide association analysis (GWAS) employing whole-genome resequencing. As a result, 57 SNPs related to the black skin trait were identified, and a grand total of 158 genes were annotated within 50 kb of these SNPs. Subsequently, GWAS was applied to three populations (LED, QHH, and QHL), and the corresponding results were compared with the analysis results of the total population. The results of the four GWAS models showed significant enrichment in Rap1 signaling pathway, melanin biosynthesis, metabolic pathways, tyrosine metabolism, cAMP signaling pathway, AMPK signaling pathway, PI3K-Akt signaling pathway, EGFR tyrosine kinase inhibitor resistance, HIF-1 signaling pathway, Ras signaling pathway, MAPK signaling pathway, etc. (p < 0.05), which were mainly associated with eleven genes (POL4, MET, E2F2, COMT, ZBED1, TYRP2, FOXP2, THIKA, LORF2, MYH16 and SOX2). Significant differences (p < 0.05) were observed in the expression of all 11 genes in the dorsal skin tissue, in 10 genes except COMT in the ventral skin tissue, and in all 11 genes in the caudal fin tissue. These findings imply that the control of body color in the P. leopardus is the result of the joint action of multiple genes and signaling pathways. These findings will contribute to a more profound comprehension of the genetic attributes that underlie the development of black skin in the vibrant P. leopardus, thus furnishing a theoretical foundation for genetic enhancement.

Immunoregulation: the interplay between metabolism and redox homeostasis

Regulatory T cells are fundamental for the induction and maintenance of immune homeostasis, with their dysfunction resulting in uncontrolled immune responses and tissue destruction predisposing to autoimmunity, transplant rejection and several inflammatory and metabolic disorders. Recent discoveries have demonstrated that metabolic processes and mitochondrial function are critical for the appropriate functioning of these cells in health, with their metabolic adaptation, influenced by microenvironmental factors, seen in several pathological processes. Upon activation regulatory T cells rearrange their oxidation-reduction (redox) system, which in turn supports their metabolic reprogramming, adding a layer of complexity to our understanding of cellular metabolism. Here we review the literature surrounding redox homeostasis and metabolism of regulatory T cells to highlight new mechanistic insights of these interlinked pathways in immune regulation.

Roflumilast enhances the melanogenesis and attenuates oxidative stress-triggered damage in melanocytes

BACKGROUND

The management of vitiligo is challenging due to limited treatment options, and therapeutic strategy varies according to the active or stable stage of vitiligo. PDE4 inhibitor has been used to treat various skin diseases, but the efficacy in vitiligo treatment is mixed.

OBJECTIVE

In this study, we aimed to investigate whether roflumilast, a PDE4 inhibitor, induces melanogenesis and attenuates oxidative stress-triggered damage in melanocytes, and if so, what is the mechanism.

METHODS

Melanin content assay, qRT-PCR, western blotting, ELISA, immunofluorescence assays, immunohistochemistry, small interfering RNA, flow cytometry, and transmission electron microscopy were employed.

RESULTS

Our results demonstrated that roflumilast alone only slightly increased melanogenesis, however, the combination of roflumilast and forskolin could boost cAMP levels, hence promoting melanogenesis more significantly. Moreover, roflumilast attenuated H₂O₂-induced apoptosis and mitochondrial morphological changes in melanocytes by reducing ROS levels. Furthermore, roflumilast activated AhR/Nrf2 pathway via cAMP whereas AhR silencing blocked roflumilast-induced Nrf2 nuclear translocation and reversed the inhibitory effect of roflumilast on H₂O₂-induced ROS production. Finally, we observed that the lesional skin of active vitiligo patients exhibited higher PDE4 expression levels.

CONCLUSION

roflumilast enhances the melanogenesis effect of forskolin and protects melanocytes from H₂O₂-induced apoptosis by cAMP/AhR/Nrf2-activated ROS inhibition, highlighting its therapeutic potential in vitiligo treatment.

The Role of Oxidative Stress in Vitiligo: An Update on Its Pathogenesis and Therapeutic Implications

Vitiligo is an autoimmune skin disorder caused by dysfunctional pigment-producing melanocytes which are attacked by immune cells. Oxidative stress is considered to play a crucial role in activating consequent autoimmune responses related to vitiligo. Melanin synthesis by melanocytes is the main intracellular stressor, producing reactive oxygen species (ROS). Under normal physiological conditions, the antioxidative nuclear factor erythroid 2-related factor 2 (Nrf2) pathway functions as a crucial mediator for cells to resist oxidative stress. In pathological situations, such as with antioxidant defects or under inflammation, ROS accumulate and cause cell damage. Herein, we summarize events at the cellular level under excessive ROS in vitiligo and highlight exposure to melanocyte-specific antigens that trigger immune responses. Such responses lead to functional impairment and the death of melanocytes, which sequentially increase melanocyte cytotoxicity through both innate and adaptive immunity. This report provides new perspectives and advances our understanding of interrelationships between oxidative stress and autoimmunity in the pathogenesis of vitiligo. We describe progress with targeted antioxidant therapy, with the aim of providing potential therapeutic approaches.

Dimethyl Itaconate Inhibits Melanogenesis in B16F10 Cells

Itaconate is a metabolite produced to counteract and resolve pro-inflammatory responses when macrophages are challenged with intracellular or extracellular stimuli. In the present study, we have observed that dimethyl itaconate (DMI) inhibits melanogenesis in B16F10 cells. DMI inhibits microphthalmia-associated transcription factor (MITF) and downregulates the expression of MITF target genes, such as tyrosinase (TYR), tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2). DMI also decreases the level of melanocortin 1 receptor (MC1R) and the production of α-melanocyte stimulating hormone (α-MSH), resulting in the inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) and MITF activities. The structure–activity relationship (SAR) study illustrates that the α,β-unsaturated carbonyl moiety in DMI, a moiety required to target KELCH-like ECH-associated protein 1 (KEAP1) to activate NF-E2-related factor 2 (NRF2), is necessary to inhibit melanogenesis and knocking down Nrf2 attenuates the inhibition of melanogenesis by DMI. Together, our study reveals that the MC1R-ERK1/2-MITF axis regulated by the KEAP1-NRF2 pathway is the molecular target responsible for the inhibition of melanogenesis by DMI.

The NRF2 antagonist ML385 inhibits PI3K-mTOR signaling and growth of lung squamous cell carcinoma cells

BACKGROUND

Lung squamous cell carcinoma (LUSC) currently has limited therapeutic options because of the relatively few validated targets and the lack of clinical drugs for some of these targets. Although NRF2/NFE2L2 pathway activation commonly occurs in LUSC, NRF2 has predominantly been studied in other cancer models. Here, we investigated the function of NRF2 in LUSC, including in organoid models, and we explored the activity of a small molecule NRF2 inhibitor ML385, which has not previously been investigated in LUSC.

METHODS

We first explored the role of NRF2 signaling in LUSC cancer cell line and organoid proliferation through NRF2 knockdown or ML385 treatment, both in vivo and in vitro. Next, we performed Western blot and immunofluorescence assays to determine the effect of NRF2 inhibition on PI3K-mTOR signaling. Finally, we used cell viability and clonogenic assays to explore whether ML385 could sensitize LUSC cancer cells to PI3K inhibitors.

RESULTS

We find that downregulation of NRF2 signaling inhibited proliferation of LUSC cancer cell lines and organoids, both in vivo and in vitro. We also demonstrate that inhibition of NRF2 reduces PI3K-mTOR signaling, with two potential mechanisms being involved. Although NRF2 promotes AKT phosphorylation, it also acts downstream of AKT to increase RagD protein expression and recruitment of mTOR to lysosomes after amino acid stimulation. We also find that ML385 potentiates LUSC growth inhibition by a pan-PI3K inhibitor, which correlates with stronger inhibition of PI3K-mTOR signaling.

CONCLUSIONS

Our data provide additional support for NRF2 promoting LUSC growth through PI3K-mTOR activation and support development of NRF2 inhibitors for the treatment of LUSC.

NRF2 in dermo-cosmetic: From scientific knowledge to skin care products

The skin is the organ that is most susceptible to the impact of the exposome. Located at the interface with the external environment, it protects internal organs through the barrier function of the epidermis. It must adapt to the consequences of the harmful effects of solar radiation, the various chemical constituents of atmospheric pollution, and wounds associated with mechanical damage: oxidation, cytotoxicity, inflammation, and so forth. In this biological context, a capacity to adapt to the various stresses caused by the exposome is essential; otherwise, more or less serious conditions may develop accelerated aging, pigmentation disorders, atopy, psoriasis, and skin cancers. Nrf2-controlled pathways play a key role at this level. Nrf2 is a transcription factor that controls genes involved in oxidative stress protection and detoxification of chemicals. Its involvement in UV protection, reduction of inflammation in processes associated with healing, epidermal differentiation for barrier function, and hair regrowth, has been demonstrated. The modulation of Nrf2 in the skin may therefore constitute a skin protection or care strategy for certain dermatological stresses and disorders initiated or aggravated by the exposome. Nrf2 inducers can act through different modes of action. Keap1-dependent mechanisms include modification of the cysteine residues of Keap1 by (pro)electrophiles or prooxidants, and disruption of the Keap1-Nrf2 complex. Indirect mechanisms are suggested for numerous phytochemicals, acting on upstream pathways, or via hormesis. While developing novel and safe Nrf2 modulators for skin care may be challenging, new avenues can arise from natural compounds-based molecular modeling and emerging concepts such as epigenetic regulation.

NRF2 in the Epidermal Pigmentary System

Melanogenesis is a major part of the environmental responses and tissue development of the integumentary system. The balance between reduction and oxidation (redox) governs pigmentary responses, for which coordination among epidermal resident cells is indispensable. Here, we review the current understanding of melanocyte biology with a particular focus on the "master regulator" of oxidative stress responses (i.e., the Kelch-like erythroid cell-derived protein with cap'n'collar homology-associated protein 1-nuclear factor erythroid-2-related factor 2 system) and the autoimmune pigment disorder vitiligo. Our investigation revealed that the former is essential in pigmentogenesis, whereas the latter results from unbalanced redox homeostasis and/or defective intercellular communication in the interfollicular epidermis (IFE). Finally, we propose a model in which keratinocytes provide a "niche" for differentiated melanocytes and may "imprint" IFE pigmentation.

Connecting Metabolic Rewiring With Phenotype Switching in Melanoma

Melanoma is a complex and aggressive cancer type that contains different cell subpopulations displaying distinct phenotypes within the same tumor. Metabolic reprogramming, a hallmark of cell transformation, is essential for melanoma cells to adopt different phenotypic states necessary for adaptation to changes arising from a dynamic milieu and oncogenic mutations. Increasing evidence demonstrates how melanoma cells can exhibit distinct metabolic profiles depending on their specific phenotype, allowing adaptation to hostile microenvironmental conditions, such as hypoxia or nutrient depletion. For instance, increased glucose consumption and lipid anabolism are associated with proliferation, while a dependency on exogenous fatty acids and an oxidative state are linked to invasion and metastatic dissemination. How these different metabolic dependencies are integrated with specific cell phenotypes is poorly understood and little is known about metabolic changes underpinning melanoma metastasis. Recent evidence suggests that metabolic rewiring engaging transitions to invasion and metastatic progression may be dependent on several factors, such as specific oncogenic programs or lineage-restricted mechanisms controlling cell metabolism, intra-tumor microenvironmental cues and anatomical location of metastasis. In this review we highlight how the main molecular events supporting melanoma metabolic rewiring and phenotype-switching are parallel and interconnected events that dictate tumor progression and metastatic dissemination through interplay with the tumor microenvironment.

Dimethyl Itaconate Reduces α-MSH-Induced Pigmentation via Modulation of AKT and p38 MAPK Signaling Pathways in B16F10 Mouse Melanoma Cells

Dimethyl itaconate (DMI) exhibits an anti-inflammatory effect. Activation of nuclear factor erythroid 2-related factor 2 (NRF2) is implicated in the inhibition of melanogenesis. Therefore, DMI and itaconic acid (ITA), classified as NRF2 activators, have potential uses in hyperpigmentation reduction. The activity of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), an important transcription factor for MITF gene promoter, is regulated by glycogen synthase kinase 3β (GSK3β) and protein kinase A (PKA). Here, we investigated the inhibitory effect of ITA and DMI on alpha-melanocyte-stimulating hormone (α-MSH)-induced MITF expression and the modulatory role of protein kinase B (AKT) and GSK3β in melanogenesis in B16F10 mouse melanoma cells. These cells were incubated with α-MSH alone or in combination with ITA or DMI. Proteins were visualized and quantified using immunoblotting and densitometry. Compared to ITA, DMI treatment exhibited a better inhibitory effect on the α-MSH-induced expression of melanogenic proteins such as MITF. Our data indicate that DMI exerts its anti-melanogenic effect via modulation of the p38 mitogen-activated protein kinase (MAPK) and AKT signaling pathways. In conclusion, DMI may be an effective therapeutic agent for both inflammation and hyperpigmentation.

Role of Phytochemicals in Skin Photoprotection via Regulation of Nrf2

Ethnopharmacological studies have become increasingly valuable in the development of botanical products and their bioactive phytochemicals as novel and effective preventive and therapeutic strategies for various diseases including skin photoaging and photodamage-related skin problems including abnormal pigmentation and inflammation. Exploring the roles of phytochemicals in mitigating ultraviolet radiation (UVR)-induced skin damage is thus of importance to offer insights into medicinal and ethnopharmacological potential for development of novel and effective photoprotective agents. UVR plays a role in the skin premature aging (or photoaging) or impaired skin integrity and function through triggering various biological responses of skin cells including apoptosis, oxidative stress, DNA damage and inflammation. In addition, melanin produced by epidermal melanocytes play a protective role against UVR-induced skin damage and therefore hyperpigmentation mediated by UV irradiation could reflect a sign of defensive response of the skin to stress. However, alteration in melanin synthesis may be implicated in skin damage, particularly in individuals with fair skin. Oxidative stress induced by UVR contributes to the process of skin aging and inflammation through the activation of related signaling pathways such as the mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1), the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), the nuclear factor kappa B (NF-κB) and the signal transducer and activator of transcription (STAT) in epidermal keratinocytes and dermal fibroblasts. ROS formation induced by UVR also plays a role in regulation of melanogenesis in melanocytes via modulating MAPK, PI3K/Akt and the melanocortin 1 receptor (MC1R)-microphthalmia-associated transcription factor (MITF) signaling cascades. Additionally, nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated antioxidant defenses can affect the major signaling pathways involved in regulation of photoaging, inflammation associated with skin barrier dysfunction and melanogenesis. This review thus highlights the roles of phytochemicals potentially acting as Nrf2 inducers in improving photoaging, inflammation and hyperpigmentation via regulation of cellular homeostasis involved in skin integrity and function. Taken together, understanding the role of phytochemicals targeting Nrf2 in photoprotection could provide an insight into potential development of natural products as a promising strategy to delay skin photoaging and improve skin conditions.

Revisiting the role of melatonin in human melanocyte physiology: A skin context perspective

The evolutionarily ancient methoxyindoleamine, melatonin, has long perplexed investigators by its versatility of functions and mechanisms of action, which include the regulation of vertebrate pigmentation. Although first discovered through its potent skin-lightening effects in amphibians, melatonin's role in human skin and hair follicle pigmentation and its impact on melanocyte physiology remain unclear. Synthesizing our limited current understanding of this role, we specifically examine its impact on melanogenesis, oxidative biology, mitochondrial function, melanocyte senescence, and pigmentation-related clock gene activity, with emphasis on human skin, yet without ignoring instructive pointers from nonhuman species. Given the strict dependence of melanocyte functions on the epithelial microenvironment, we underscore that melanocyte responses to melatonin are best interrogated in a physiological tissue context. Current evidence suggests that melatonin and some of its metabolites inhibit both, melanogenesis (via reducing tyrosinase activity) and melanocyte proliferation by stimulating melatonin membrane receptors (MT1, MT2). We discuss whether putative melanogenesis-inhibitory effects of melatonin may occur via activation of Nrf2-mediated PI3K/AKT signaling, estrogen receptor-mediated and/or melanocortin-1 receptor- and cAMP-dependent signaling, and/or via melatonin-regulated changes in peripheral clock genes that regulate human melanogenesis, namely Bmal1 and Per1. Melatonin and its metabolites also accumulate in melanocytes where they exert net cyto- and senescence-protective as well as antioxidative effects by operating as free radical scavengers, stimulating the synthesis and activity of ROS scavenging enzymes and other antioxidants, promoting DNA repair, and enhancing mitochondrial function. We argue that it is clinically and biologically important to definitively clarify whether melanocyte cell culture-based observations translate into melatonin-induced pigmentary changes in a physiological tissue context, that is, in human epidermis and hair follicles ex vivo, and are confirmed by clinical trial results. After defining major open questions in this field, we close by suggesting how to begin answering them in clinically relevant, currently available preclinical in situ research models.

Development of targeted therapy of NRF2high esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a deadly disease and one of the most aggressive cancers of the gastrointestinal tract. As a master transcription factor regulating the stress response, NRF2 is often mutated and becomes hyperactive, and thus causes chemo-radioresistance and poor survival in human ESCC. There is a great need to develop NRF2 inhibitors for targeted therapy of NRF2high ESCC. In this review, we mainly focus on three aspects, NRF2 inhibitors and their mechanisms of action, screening novel drug targets, and evaluation of NRF2 activity in the esophagus. A research strategy has been proposed to develop NRF2 inhibitors using human ESCC cells and mouse models.

Diversity of Adenostemma lavenia, multi-potential herbs, and its kaurenoic acid composition between Japan and Taiwan

Adenostemma lavenia (L.) Kuntze (Asteraceae) is widely distributed in tropical regions of East Asia, and both A. lavenia and A. madurense (DC) are distributed in Japan. In China and Taiwan, A. lavenia is used as a folk medicine for treating lung congestion, pneumonia, and hepatitis. However, neither phylogenic nor biochemical analysis of this plants has been performed to date. We have reported that the aqueous extract of Japanese A. lavenia contained high levels of ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic acid (11αOH-KA; a kaurenoic acid), which is a potent anti-melanogenic compound. Comparison of chloroplast DNA sequences suggested that A. lavenia is originated from A. madurense. Analyses of kaurenoic acids revealed that Japanese A. lavenia and A. madurense contained high levels of 11αOH-KA and moderate levels of 11α,15OH-KA, while Taiwanese A. lavenia mainly contained 9,11αOH-KA. The diverse biological activities (downregulation of Tyr, tyrosinase, gene expression [anti-melanogenic] and iNOS, inducible nitric oxide synthase, gene expression [anti-inflammatory], and upregulation of HO-1, heme-oxygenase, gene expression [anti-oxidative]) were associated with 11αOH-KA and 9,11αOH-KA but not with 11α,15OH-KA. Additionally, 11αOH-KA and 9,11αOH-KA decreased Keap1 (Kelch-like ECH-associated protein 1) protein levels, which was accompanied by upregulation of protein level and transcriptional activity of Nrf2 (NF-E2-related factor-2) followed by HO-1 gene expression. 11αOH-KA and 9,11αOH-KA differ from 11α,15OH-KA in terms of the presence of a ketone (αβ-unsaturated carbonyl group, a thiol modulator) at the 15^th position; therefore, thiol moieties on the target proteins, including Keap1, may be important for the biological activities of 11αOH-KA and 9,11αOH-KA and A. lavenia extract.

Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells

PURPOSE

Excessive exposure of skin to solar radiation is associated with greatly increased production of reactive oxygen and nitrogen species (ROS, RNS) resulting in oxidative stress (OS), inflammation, immunosuppression, the production of matrix metalloproteinase, DNA damage and mutations. These events lead to increased incidence of various skin disorders including photoaing and both non-melanoma and melanoma skin cancers. The ultraviolet (UV) part of sunlight, in particular, is responsible for structural and cellular changes across the different layers of the skin. Among other effects, UV photons stimulate oxidative damage to biomolecules via the generation of unstable and highly reactive compounds. In response to oxidative damage, cytoprotective pathways are triggered. One of these is the pathway driven by the nuclear factor erythroid-2 related factor 2 (Nrf2). This transcription factor translocates to the nucleus and drives the expression of numerous genes, among them various detoxifying and antioxidant enzymes. Several studies concerning the effects of UV radiation on Nrf2 activation have been published, but different UV wavelengths, skin cells or tissues and incubation periods were used in the experiments that complicate the evaluation of UV radiation effects.

CONCLUSIONS

This review summarizes the effects of UVB (280-315 nm) and UVA (315-400 nm) radiation on the Nrf2 signaling pathway in dermal fibroblasts and epidermal keratinocytes and melanocytes. The effects of natural compounds (pure compounds or mixtures) on Nrf2 activation and level as well as on Nrf2-driven genes in UV irradiated human skin fibroblasts, keratinocytes and melanocytes are briefly mentioned as well.HighlightsUVB radiation is a rather poor activator of the Nrf2-driven pathway in fibroblastsUVA radiation stimulates Nrf2 activation in dermal fibroblastsEffects of UVA on the Nrf2 pathway in keratinocytes and melanocytes remain unclearLong-term Nrf2 activation in keratinocytes disturbs their normal differentiationPharmacological activation of Nrf2 in the skin needs to be performed carefully.

Oxidative stress in the skin: Impact and related protection

Skin, our first interface to the external environment, is subjected to oxidative stress caused by a variety of factors such as solar ultraviolet, infrared and visible light, environmental pollution, including ozone and particulate matters, and psychological stress. Excessive reactive species, including reactive oxygen species and reactive nitrogen species, exacerbate skin pigmentation and aging, which further lead to skin tone unevenness, pigmentary disorder, skin roughness and wrinkles. Besides these, skin microbiota are also a very important factor ensuring the proper functions of skin. While environmental factors such as UV and pollutants impact skin microbiota compositions, skin dysbiosis results in various skin conditions. In this review, we summarize the generation of oxidative stress from exogenous and endogenous sources. We further introduce current knowledge on the possible roles of oxidative stress in skin pigmentation and aging, specifically with emphasis on oxidative stress and skin pigmentation. Meanwhile, we summarize the science and rationale of using three well-known antioxidants, namely vitamin C, resveratrol and ferulic acid, in the treatment of hyperpigmentation. Finally, we discuss the strategy for preventing oxidative stress-induced skin pigmentation and aging.

Arbutin as a Skin Depigmenting Agent with Antimelanogenic and Antioxidant Properties

Arbutin is a compound of hydroquinone and D-glucose, and it has been over 30 years since there have been serious studies on the skin lightening action of this substance. In the meantime, there have been debates and validation studies about the mechanism of action of this substance as well as its skin lightening efficacy and safety. Several analogs or derivatives of arbutin have been developed and studied for their melanin synthesis inhibitory action. Formulations have been developed to improve the stability, transdermal delivery, and release of arbutin, and device usage to promote skin absorption has been developed. Substances that inhibit melanin synthesis synergistically with arbutin have been explored. The skin lightening efficacy of arbutin alone or in combination with other active ingredients has been clinically evaluated. Combined therapy with arbutin and laser could give enhanced depigmenting efficacy. The use of arbutin causes dermatitis rarely, and caution is recommended for the use of arbutin-containing products, especially from the viewpoint that hydroquinone may be generated during product use. Studies on the antioxidant properties of arbutin are emerging, and these antioxidant properties are proposed to contribute to the skin depigmenting action of arbutin. It is hoped that this review will help to understand the pros and cons of arbutin as a cosmetic ingredient, and will lead to future research directions for developing advanced skin lightening and protecting cosmetic products.

mGPDH Deficiency leads to melanoma metastasis via induced NRF2

Oxidative stress critically influences carcinogenesis and the progression of melanoma, and aggressive malignant melanoma activity is due to its high metastatic ability. Some findings in several cancer cell lines have indicated that mGPDH, a component of the mitochondrial respiratory chain, also modulates oxidative stress. However, the role of mGPDH in melanoma remains elusive. Here, we report that the mGPDH protein level is decreased in human skin melanoma compared to normal skin and decreased in metastatic melanoma compared to primary melanoma. Our in vivo and in vitro experiments indicated that mGPDH depletion accelerated melanoma migration and invasion without affecting proliferation or apoptosis. Mechanistically, we found elevated NRF2 protein levels in human skin melanoma and mGPDH‐knockout (ko) metastatic xenografts in the lungs of nude mice. Moreover, in A375 melanoma cells, the loss of mGPDH‐induced NRF2 expression but did not affect NRF2 protein degradation. Additionally, melanoma metastasis induced by the loss of mGPDH was rescued by the further down‐regulation of NRF2 in vivo and in vitro. Consistently, mGPDH overexpression (oe) depressed NRF2 expression and attenuated the malignant properties of melanoma cells. In conclusion, our findings suggest that mGPDH suppresses melanoma metastasis by inhibiting NRF2 and downstream oxidative signals, highlighting the therapeutic potential of mGPDH for melanoma treatment.

Marliolide Derivative Induces Melanosome Degradation via Nrf2/p62-Mediated Autophagy

Nuclear factor erythroid 2-related factor 2 (Nrf2), which is linked to autophagy regulation and melanogenesis regulation, is activated by marliolide. In this study, we investigated the effect of a marliolide derivative on melanosome degradation through the autophagy pathway. The effect of the marliolide derivative on melanosome degradation was investigated in α-melanocyte stimulating hormone (α-MSH)-treated melanocytes, melanosome-incorporated keratinocyte, and ultraviolet (UV)B-exposed HRM-2 mice (melanin-possessing hairless mice). The marliolide derivative, 5-methyl-3-tetradecylidene-dihydro-furan-2-one (DMF02), decreased melanin pigmentation by melanosome degradation in α-MSH-treated melanocytes and melanosome-incorporated keratinocytes, evidenced by premelanosome protein (PMEL) expression, but did not affect melanogenesis-associated proteins. The UVB-induced hyperpigmentation in HRM-2 mice was also reduced by a topical application of DMF02. DMF02 activated Nrf2 and induced autophagy in vivo, evidenced by decreased PMEL in microtubule-associated proteins 1A/1B light chain 3B (LC3)-II-expressed areas. DMF02 also induced melanosome degradation via autophagy in vitro, and DMF02-induced melanosome degradation was recovered by chloroquine (CQ), which is a lysosomal inhibitor. In addition, Nrf2 silencing by siRNA attenuated the DMF02-induced melanosome degradation via the suppression of p62. DMF02 induced melanosome degradation in melanocytes and keratinocytes by regulating autophagy via Nrf2-p62 activation. Therefore, Nrf2 activator could be a promising therapeutic agent for reducing hyperpigmentation.

Crm1-Dependent Nuclear Export of Bach1 is Involved in the Protective Effect of Hyperoside on Oxidative Damage in Hepatocytes and CCl4-induced Acute Liver Injury

Background

Nrf2-Bach1 antioxidant signaling pathway is considered as one of the most important mechanisms of cellular resistance to oxidative injury. The effect of hyperoside (Hyp) on the expression and distribution of Bach1, the relationship of Hyp's antioxidative effect and the influence of Bach1 remains unclear.

Purpose

The aim of this study was to investigate the role and mechanisms of Bach1 in the protective effect of Hyp on oxidative liver injury.

Methods

The protective effect of Hyp on oxidative stress injury was observed in vivo and in vitro. Next, the influence of Hyp on Bach1 expression and distribution, and competitive combination of Nrf2-Bach1 with ARE in H₂O₂-induced L02 cell was studied by Western blot, RT-PCR, immunofluorescence and CHIP assay. Finally, the expressions of Crm1, ERK and p38 and their roles on Hyp mediated nuclear export of Bach1 were investigated by Western blot.

Results

Hyp ameliorated the pathological damage, reduced the liver index, AST, ALT and MDA activities, and increased SOD and GSH levels in the CCl₄-induced acute liver injury mouse model. Hyp attenuated H₂O₂-induced oxidative stress injury in L02 cells. Hyp promoted the early rapid redistribution of Bach1 from nucleus to cytoplasm. CHIP analyses demonstrated that Hyp enhanced the levels of Nrf2-ARE complex, and weakened the levels of Bach1-ARE complex within three hours. In addition, Hyp enhanced transport protein Crm1 expression and ERK1/2 activity. And LMB, a Crm1 inhibitor, attenuated the effect of Hyp on Bach1 nuclear export and anti-oxidation. U0126, an ERK1/2 inhibitor, reduced the effect of Hyp on Crm1 expression and the Bach1 redistribution.

Conclusion

The hepatoprotective mechanism of Hyp was related to improve Bach1 nuclear export depending on ERK1/2-Crm1 to upregulate the level of Nrf2 binding to ARE.

NRF2-dependent stress defense in tumor antioxidant control and immune evasion

The transcription factor NRF2 is known as the master regulator of the oxidative stress response. Tumor entities presenting oncogenic activation of NRF2, such as lung adenocarcinoma, are associated with drug resistance, and accumulating evidence demonstrates its involvement in immune evasion. In other cancer types, the KEAP1/NRF2 pathway is not commonly mutated, but NRF2 is activated by other means such as radiation, oncogenic activity, cytokines, or other pro-oxidant triggers characteristic of the tumor niche. The obvious effect of stress-activated NRF2 is the protection from oxidative or electrophilic damage and the adaptation of the tumor metabolism to changing conditions. However, data from melanoma also reveal a role of NRF2 in modulating differentiation and suppressing anti-tumor immunity. This review summarizes the function of NRF2 in this tumor entity and discusses the implications for current tumor therapies.

Pathogenic and therapeutic role for NRF2 signaling in ultraviolet light-induced skin pigmentation

Mottled skin pigmentation and solar lentigines from chronic photodamage with aging involve complex interactions between keratinocytes and melanocytes. However, the precise signaling mechanisms that could serve as therapeutic targets are unclear. Herein, we report that expression of nuclear factor erythroid 2-related factor 2 (NRF2), which regulates reduction-oxidation reactions, is altered in solar lentigines and photodamaged skin. Moreover, mottled skin pigmentation in humans could be treated with topical application of the NRF2 inducer sulforaphane (SF). Similarly, UV light-induced pigmentation of WT mouse ear skin could be treated or prevented with SF treatment. Conversely, SF treatment was unable to reduce UV-induced ear skin pigmentation in mice deficient in NRF2 or in mice with keratinocyte-specific conditional deletion of IL-6Rα. Taken together, NRF2 and IL-6Rα signaling are involved in the pathogenesis of UV-induced skin pigmentation, and specific enhancement of NRF2 signaling could represent a potential therapeutic target.

5-Hydroxytryptamine (5-HT) Positively Regulates Pigmentation via Inducing Melanoblast Specification and Melanin Synthesis in Zebrafish Embryos

It has been reported that 5-hydroxytryptamine (5-HT) is related to melanogenesis in mice and melanoma cells. However, the underlying mechanisms of 5-HT in regulating pigmentation remains unknown. In this study, we aim to clarify the regulatory mechanism of 5-HT in the pigmentation of zebrafish embryos and B16F10 cells. Our results show that 5-HT induces the pigmentation of zebrafish embryos in a dosage-dependent manner at concentrations of 0.01-1 mM. Whole mount in situ hybridizations and qRT-PCR in zebrafish embryos indicate that the expression of neural crest cells marker gene sox10 is not changed in embryos treated with 5-HT compared to control group. The expression of mitfa, the marker gene of melanoblasts, is increased in the presence of 5-HT. Furthermore, 5-HT increased the expression of regeneration associated genes, namely kita, mitfa, and dct, after ablation of the melanogenic cells in zebrafish embryos. The experiments in B16F10 cells show that 5-HT promotes melanin synthesis by up-regulating the expression of key proteins MITF, TYR, TRP-1, and TRP-2. Especially, the small molecule inhibitor of PKA signaling, but not AKT and MAPK signaling, attenuates the up-regulation of MITF and TYR resulted from 5-HT induction in B16F10 cells. These results will help us to further understand the regulatory network of vertebrate pigmentation.

Melatonin Induces Melanogenesis in Human SK-MEL-1 Melanoma Cells Involving Glycogen Synthase Kinase-3 and Reactive Oxygen Species

Melatonin is present in all living organisms where it displays a diversity of physiological functions. Attenuation of melanogenesis by melatonin has been reported in some mammals and also in rodent melanoma cells. However, melatonin may also stimulate melanogenesis in human melanoma cells through mechanisms that have not yet been revealed. Using the human melanoma cells SK-MEL-1 as a model, an increase in both tyrosinase activity and melanin was already observed at 24 h after melatonin treatment with maximal levels of both being detected at 72 h. This effect was associated with the induction in the expression of the enzymes involved in the synthesis of melanin. In this scenario, glycogen synthase kinase-3β seems to play a significant function since melatonin decreased its phosphorylation and preincubation with specific inhibitors of this protein kinase (lithium or BIO) reduced the expression and activity of tyrosinase. Blocking of PI3K/AKT pathway stimulated melanogenesis and the effect was suppressed by the inhibitors of glycogen synthase kinase-3β. Although melatonin is a recognized antioxidant, we found that it stimulates reactive oxygen species generation in SK-MEL-1 cells. These chemical species seem to be an important signal in activating the melanogenic process since the antioxidants N-acetyl-l-cysteine and glutathione decreased both the level and activity of tyrosinase stimulated by melatonin. Our results support the view that regulation of melanogenesis involves a cross-talk between several signaling pathways.

Therapeutic Potential of Patient iPSC-Derived iMelanocytes in Autologous Transplantation

Induced pluripotent stem cells (iPSCs) are a promising melanocyte source as they propagate indefinitely and can be established from patients. However, the in vivo functions of human iPSC-derived melanocytes (hiMels) remain unknown. Here, we generated hiMels from vitiligo patients using a three-dimensional system with enhanced differentiation efficiency, which showed characteristics of human epidermal melanocytes with high sequence similarity and involved in multiple vitiligo-associated signaling pathways. A modified hair follicle reconstitution assay in vivo showed that MITF⁺PAX3⁺TYRP1⁺ hiMels were localized in the mouse hair bulb and epidermis and produced melanin up to 7 weeks after transplantation, whereas MITF⁺PAX3⁺TYRP1^- hiMelanocyte stem cells integrated into the bulge-subbulge regions. Overall, these data demonstrate the long-term functions of hiMels in vivo to reconstitute pigmented hair follicles and to integrate into normal regions for both mature melanocytes and melanocyte stem cells, providing an alternative source of personalized cellular therapy for depigmentation.

Fernblock® Upregulates NRF2 Antioxidant Pathway and Protects Keratinocytes from PM2.5-Induced Xenotoxic Stress

Humans in modern industrial and postindustrial societies face sustained challenges from environmental pollutants, which can trigger tissue damage from xenotoxic stress through different mechanisms. Thus, the identification and characterization of compounds capable of conferring antioxidant effects and protection against these xenotoxins are warranted. Here, we report that the natural extract of Polypodium leucotomos named Fernblock®, known to reduce aging and oxidative stress induced by solar radiations, upregulates the NRF2 transcription factor and its downstream antioxidant targets, and this correlates with its ability to reduce inflammation, melanogenesis, and general cell damage in cultured keratinocytes upon exposure to an experimental model of fine pollutant particles (PM_2.5). Our results provide evidence for a specific molecular mechanism underpinning the protective activity of Fernblock® against environmental pollutants and potentially other sources of oxidative stress and damage-induced aging.

ΜicroRNA‑421 participates in vitiligo development through regulating human melanocyte survival by targeting receptor‑interacting serine/threonine kinase 1

Vitiligo is a common localized or generalized skin pigmentation disorder. Endoplasmic reticulum (ER) stress may be implicated in the development of vitiligo. microRNA-421 (miR-421) has been reported to be dysregulated in various human tumors. However, there is no report to date on the role of miR-421 in vitiligo development. The present study demonstrated that 3 µM tunicamycin (TM) increased the expression of the ER stress-related proteins protein kinase RNA-like endoplasmic reticulum kinase (PERK), α subunit of eukaryotic translation initiation factor 2 (eIF2α) and C/EBP homologous protein (CHOP) in human primary epidermal melanocytes. Moreover, TM suppressed melanocyte viability and induced apoptosis. Reverse transcription-quantitative PCR analysis demonstrated that TM promoted miR-421 expression in human melanocytes. Next, TargetScan and dual luciferase reporter gene assay indicated that receptor-interacting serine/threonine kinase 1 (RIPK1) was a direct target of miR-421. RIPK1 expression was significantly downregulated in TM-induced human melanocytes. Subsequently, the effect of miR-421 downregulation on the damage of human melanocytes induced by ER stress was investigated. Human melanocytes were transfected with inhibitor control, miR-421 inhibitor, miR-421 inhibitor + control-short hairpin (sh)RNA, or miR-421 inhibitor + RIPK1-shRNA for 24 h and then treated with TM (3 µM) for 48 h. TM was found to upregulate PERK, eIF2α and CHOP protein expression in human melanocytes, which was reduced by an miR-421 inhibitor. In addition, the miR-421 inhibitor increased viability and reduced apoptosis in TM-treated melanocytes. Furthermore, all these effects of the miR-421 inhibitor on TM-induced human melanocytes were reversed by RIPK1-shRNA. Further analyses revealed that the miR-421 inhibitor activated the phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway in TM-induced human melanocytes. These data collectively suggest that miR-421 may serve as a new treatment target in vitiligo development.

The Regulation of NFE2L2 (NRF2) Signalling and Epithelial-to-Mesenchymal Transition in Age-Related Macular Degeneration Pathology

Age-related macular degeneration (AMD) is a mounting cause of loss of sight in the elderly in the developed countries, a trend enhanced by the continual ageing of the population. AMD is a multifactorial and only partly understood, malady. Unfortunately, there is no effective treatment for most AMD patients. It is known that oxidative stress (OS) damages the retinal pigment epithelium (RPE) and contributes to the progression of AMD. We review here the potential importance of two OS-related cellular systems in relation to AMD. First, the nuclear factor erythroid 2-related factor 2 (NFE2L2; NRF2)-mediated OS response signalling pathway is important in the prevention of oxidative damage and a failure of this system could be critical in the development of AMD. Second, epithelial-to-mesenchymal transition (EMT) represents a change in the cellular phenotype, which ultimately leads to the fibrosis encountered in RPE, a characteristic of AMD. Many of the pathways triggering EMT are promoted by OS. The possible interconnections between these two signalling routes are discussed here. From a broader perspective, the control of NFE2L2 and EMT as ways of preventing OS-derived cellular damage could be potentially valuable in the therapy of AMD.

Intrinsic and extrinsic regulation of human skin melanogenesis and pigmentation

In human skin, melanogenesis is a tightly regulated process. Indeed, several extracellular signals are transduced via dedicated signalling pathways and mostly converge to MITF, a transcription factor integrating upstream signalling and regulating downstream genes involved in the various inherent mechanisms modulating melanogenesis. The synthesis of melanin pigments occurs in melanocytes inside melanosomes where melanogenic enzymes (tyrosinase and related proteins) are addressed with the help of specific protein complexes. The melanosomes loaded with melanin are then transferred to keratinocytes. A more elaborate level of melanogenesis regulation comes into play via the action of non-coding RNAs (microRNAs, lncRNAs). Besides this canonical regulation, melanogenesis can also be modulated by other non-specific intrinsic pathways (hormonal environment, inflammation) and by extrinsic factors (solar irradiation such as ultraviolet irradiation, environmental pollution). We developed a bioinformatic interaction network gathering the multiple aspects of melanogenesis and skin pigmentation as a resource to better understand and study skin pigmentation biology.

Activation of AKT pathway by Nrf2/PDGFA feedback loop contributes to HCC progression

Nuclear factor erythroid-2-related factor 2 (Nrf2), a master transcription factor in the antioxidant response, has been found to be ubiquitously expressed in various cancer cells and in the regulation tumor proliferation, invasion, and chemoresistance activities. The regulatory roles of Nrf2 in controlling Hepatocellular carcinoma (HCC) progression remain unclear. In this study, we demonstrated that Nrf2 was significantly elevated in HCC cells and tissues and was correlated with poor prognosis of HCCs. Consistently, Nrf2 significantly promoted HCC cell growth both in vitro and in vivo. Further investigation suggested a novel association of Nrf2 with Platelet-Derived Growth Factor-A (PDGFA). Nrf2 promoted PDGFA transcription by recruiting specificity protein 1 (Sp1) to its promoter, resulting in increased activation of the AKT/p21 pathway and cell cycle progression of HCC cells. As a feedback loop, PDGFA enhanced Nrf2 expression and activation in an AKT dependent manner. In line with these findings, expression of Nrf2 and PDGFA were positively correlated in HCC tissues. Taken together, this study uncovers a novel mechanism of the Nrf2/PDGFA regulatory loop that is crucial for AKT-dependent HCC progression, and thereby provides potential targets for HCC therapy.

Reprogramming human A375 amelanotic melanoma cells by catalase overexpression: Reversion or promotion of malignancy by inducing melanogenesis or metastasis

Advanced melanoma is the most aggressive form of skin cancer. It is highly metastatic and dysfunctional in melanogenesis; two processes that are induced by H₂O₂. This work presents a melanoma cell model with low levels of H₂O₂ induced by catalase overexpression to study differentiation/dedifferentiation processes. Three clones (A7, C10 and G10) of human A375 amelanotic melanoma cells with quite distinct phenotypes were obtained. These clones faced H₂O₂ scavenging by two main strategies. One developed by clone G10 where ROS increased. This resulted in G10 migration and metastasis associated with the increased of cofilin-1 and CAP1. The other strategy was observed in clone A7 and C10, where ROS levels were maintained reversing malignant features. Particularly, C10 was not tumorigenic, while A7 reversed the amelanotic phenotype by increasing melanin content and melanocytic differentiation markers. These clones allowed the study of potential differentiation and migration markers and its association with ROS levels in vitro and in vivo, providing a new melanoma model with different degree of malignancy.

Keap1 knockdown in melanocytes induces cell proliferation and survival via HO-1-associated β-catenin signaling

BACKGROUND

Nrf2-Keap1 signaling pathway protects cells against photo-oxidative stress. Yet in recent works, its role in melanogenesis together with cell protection functions against oxidative stress has been gaining interest. However, its effect on melanogenesis still has contradictory results from different studies.

OBJECTIVE

The aims of our study were to investigate the effect of Keap1 silencing in melanocyte on melanogenesis and its associated mechanism.

METHODS

Primary human epidermal melanocytes and melan-a cell line were used for this experiment. RNA sequencing was done to identify genes involved in melanocyte biology using Keap1 knockdown through siRNA techniques. And melanogenesis and the expression of melanogenesis-associated molecules were evaluated in Keap1 silenced melanocyte to examine the effects of Keap1 on melanogenesis, melanocyte growth, and related pathways.

RESULTS

RNA-sequencing data revealed that Keap1 knockdown in primary human epidermal melanocytes (PHEMs) induced cell survival-related gene expression. Additionally, siRNA-mediated inhibition of Keap1 led to upregulation of MITF and melanogenesis-associated molecules along with Nrf2 activation in PHEMs. HO-1, a major gene that is upregulated in RNA-sequencing using Keap1-silenced PHEMs, protected melanocytes against H₂O₂-induced cell death and upregulated MITF and β-catenin expression. Further, increased expression of melanogenesis-associated molecules after Keap1 silencing was validated to occur through HO-1-associated β-catenin activation in a Keap1 and HO-1 double knockdown experiment.

CONCLUSION

This work suggests that Keap1 silencing in melanocytes induced melanogenesis and the expression of melanogenesis-associated molecules through HO-1-associated β-catenin activation. Keap1 downregulation in melanocytes is important for cell proliferation and survival.

Double-stranded RNA induces inflammation via the NF-κB pathway and inflammasome activation in the outer root sheath cells of hair follicles

Alopecia areata (AA), a chronic, relapsing, hair-loss disorder, is considered to be a T cell-mediated autoimmune disease. It affects approximately 1.7% of the population, but its precise pathogenesis remains to be elucidated. Despite the recent attention focused on the roles of inflammasomes in the pathogenesis of autoinflammatory diseases, little is known about inflammasome activation in AA. Thus, in this study, we investigated the pattern of NLRP3 inflammasome activation in the outer root sheath (ORS) cells of hair follicles. We found that interleukin (IL)-1β and caspase-1 expression was increased in hair follicle remnants and inflammatory cells of AA tissue specimens. After stimulation of ORS cells with the double-stranded (ds)RNA mimic polyinosinic:polycytidylic acid (poly[I:C]), the activation of caspase-1 and secretion of IL-1β were enhanced. Moreover, NLRP3 knockdown decreased this poly(I:C)-induced IL-1β production. Finally, we found that high-mobility group box 1 (HMGB1) translocated from the nucleus to the cytosol and was secreted into the extracellular space by inflammasome activation. Taken together, these findings suggest that ORS cells are important immunocompetent cells that induce NLRP3 inflammasomes. In addition, dsRNA-induced IL-1β and HMGB1 secretion from ORS cells may contribute to clarifying the pathogenesis and therapeutic targets of AA.

Phosphorylation of MITF by AKT affects its downstream targets and causes TP53-dependent cell senescence

Microphthalmia-associated transcription factor (MITF) plays a crucial role in the melanogenesis and proliferation of melanocytes that is dependent on its abundance and modification. Here, we report that epidermal growth factor (EGF) induces senescence and cyclin-dependent kinase inhibitor 1A (CDKN1A) expression that is related to MITF. We found that MITF could bind TP53 to regulate CDKN1A. Furthermore, the interaction between MITF and TP53 is dependent on AKT activity. We found that AKT phosphorylates MITF at S510. Phosphorylated MITF S510 enhances its affinity to TP53 and promotes CDKN1A expression. Meanwhile, the unphosphorylative MITF promotes TYR expression. The levels of p-MITF-S510 are low in 90% human melanoma samples. Thus the level of p-MITF-S510 could be a possible diagnostic marker for melanoma. Our findings reveal a mechanism for regulating MITF functions in response to EGF stimulation and suggest a possible implementation for preventing the over proliferation of melanoma cells.

Nrf2 Transcription Factor Can Directly Regulate mTOR: LINKING CYTOPROTECTIVE GENE EXPRESSION TO A MAJOR METABOLIC REGULATOR THAT GENERATES REDOX ACTIVITY

Nrf2 is a master transcription factor that regulates a wide variety of cellular proteins by recognizing and binding to antioxidant response elements (AREs) in their gene promoter regions. In this study we show that increasing cellular Nrf2 results in transcriptional activation of the gene for mTOR, which is central to the PI3K signaling pathway. This is the case in cells with normal physiological PI3K. However, in cells with abnormally active PI3K increased cellular Nrf2 levels have no effect on mTOR. ChIP assays results show that increased Nrf2 binding is associated with decreased p65 binding and H3-K27me3 signal (marker of gene repression) as well as increased H3-K4me3 signal (marker of gene activation). However, in cells with PI3K activation, no effect of cellular Nrf2 increase on mTOR transcription was observed. In these cells, increasing Nrf2 levels increases Nrf2 promoter binding marginally, whereas p65 binding and H3-K27me3 mark were significantly increased, and H3-K4me3 signal is reduced. Together, these data show for the first time that Nrf2 directly regulates mTOR transcription when the PI3K pathway is intact, whereas this function is lost when PI3K is activated. We have identified a link between the Nrf2 system of sensing environmental stress and mTOR, which is a key cellular protein in metabolism. Studies in cells with activating mutations in the PI3K pathway suggest that Nrf2 transcriptional regulation of mTOR is related to promoter binding of p65 and of methylation of histone residues permissive of transcription.

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.

Stress chaperone mortalin regulates human melanogenesis

In order to identify the cellular factors involved in human melanogenesis, we carried out shRNA-mediated loss-of-function screening in conjunction with induction of melanogenesis by 1-oleoyl-2-acetyl-glycerol (OAG) in human melanoma cells using biochemical and visual assays. Gene targets of the shRNAs (that caused loss of OAG-induced melanogenesis) and their pathways, as determined by bioinformatics, revealed involvement of proteins that regulate cell stress response, mitochondrial functions, proliferation, and apoptosis. We demonstrate, for the first time, that the mitochondrial stress chaperone mortalin is crucial for melanogenesis. Upregulation of mortalin was closely associated with melanogenesis in in vitro cell-based assays and clinical samples of keloids with hyperpigmentation. Furthermore, its knockdown resulted in compromised melanogenesis. The data proposed mortalin as an important protein that may be targeted to manipulate pigmentation for cosmetic and related disease therapeutics.

Photoprotection by dietary phenolics against melanogenesis induced by UVA through Nrf2-dependent antioxidant responses

Dietary phenolics may play a protective role in UV-mediated skin pigmentation through their antioxidant and UV-absorbing actions. In this study, we investigated whether genetic silencing of Nrf2, regulating the transcription of antioxidant genes, affected melanogenesis in primary human epidermal melanocytes (HEMn) and B16F10 melanoma cells subjected to UVA (8 J/cm²) exposure. Then, we explored the antimelanogenic actions of phenolics; caffeic acid (CA) and ferulic acid (FA) providing partial UVA protection; quercetin (QU) and rutin (RU) providing strong UVA protection and; avobenzone (AV), an efficient UVA filter, in association with modulation of Nrf2-mediated antioxidant defenses in response to UVA insults in B16F10 cells. Upon oxidative insults, Nrf2 silencing promoted melanogenesis in both HEMn and B16F10 cells irradiated with UVA. Stimulation of melanogenesis by UVA correlated with increased ROS and oxidative DNA damage (8-OHdG), GSH depletion as well as a transient downregulation of Nrf2 nuclear translocation and of Nrf2-ARE signaling in B16F10 cells. All test compounds exerted antimelanogenic effects with respect to their abilities to reverse UVA-mediated oxidative damage as well as downregulation of Nrf2 activity and its target antioxidants (GCLC, GST and NQO1) in B16F10 cells. In conclusion, defective Nrf2 may promote melanogenesis under UVA irradiation through oxidative stress mechanisms. Compounds with antioxidant and/or UVA absorption properties could protect against UVA-induced melanogenesis through indirect regulatory effect on Nrf2-ARE pathway.

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Depletion of Nrf2 could stimulate melanogenesis under UVA-mediated oxidative stress.

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UVA caused time-course changes of Nrf2 activity and its target antioxidants.

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Phenolics could inhibit UVA-induced melanogenesis through modulation of Nrf2 pathway.

Identification of a possible susceptibility locus for UVB-induced skin tanning phenotype in Korean females using genomewide association study

A two-stage genomewide association (GWA) analysis was conducted to investigate the genetic factors influencing ultraviolet (UV)-induced skin pigmentation in Korean females after UV exposure. Previously, a GWA study evaluating ~500 000 single nucleotide polymorphisms (SNPs) in 99 Korean females identified eight SNPs that were highly associated with tanning ability. To confirm these associations, we genotyped the SNPs in an independent replication study (112 Korean females). We found that a novel SNP in the intron of the WW domain-containing oxidoreductase (WWOX) gene yielded significant replicated associations with skin tanning ability (P-value = 1.16 × 10(-4) ). To understand the functional consequences of this locus located in the non-coding region, we investigated the role of WWOX in human melanocytes using a recombinant adenovirus expressing a microRNA specific for WWOX. Inhibition of WWOX expression significantly increased the expression and activity of tyrosinase in human melanocytes. Taken together, our results suggest that genetic variants in the intronic region of WWOX could be determinants in the UV-induced tanning ability of Korean females. WWOX represents a new candidate gene to evaluate the molecular basis of the UV-induced tanning ability in individuals.

The antimycotic agent clotrimazole inhibits melanogenesis by accelerating ERK and PI3K-/Akt-mediated tyrosinase degradation

Azole antimycotic agents are known to have anti-inflammatory and anti-cancer effects, which are mediated through their effects on the p38-cyclooxygenase-2 (COX-2)-prostaglandin E2 (PGE2) pathway, as well as anti-oxidant effects. Furthermore, pyridinyl imidazole compounds, such as SB203580 have recently been shown to inhibit melanogenesis. Accordingly, we hypothesized that azole antifungal agents might affect skin pigmentation. We herein investigated the effect of clotrimazole, the most commonly used azole antifungal agent, on melanogenesis. Intriguingly, clotrimazole reduced the melanin content in human melanocytes and mouse melanocytes, as well as in B16F10 mouse melanoma cells. Clotrimazole reduced levels of tyrosinase protein without altering mRNA expression. Simultaneous treatment with a proteasomal inhibitor restored both the suppression of melanin synthesis, and the downregulation of tyrosinase level, by clotrimazole. Clotrimazole also induced the phosphorylation of extracellular signal-regulated kinase (ERK) and PI3K/Akt, while each inhibitor of these two signals abolished the decrease of melanin synthesis by clotrimazole. Thus, our data suggest that clotrimazole inhibits melanin synthesis by promoting the proteasomal degradation of tyrosinase, which is mediated through activation of the ERK and Akt signaling pathways. These results may indicate a new role for clotrimazole as a molecular-mechanism-based, safe depigmenting agent for topical management of hyper-pigmentary sequelae related to fungal infection, or for other skin inflammatory disorders.

The role of transcription factor Nrf2 in skin cells metabolism

Skin, which is a protective layer of the body, is in constant contact with physical and chemical environmental factors. Exposure of the skin to highly adverse conditions often leads to oxidative stress. Moreover, it has been observed that skin cells are also exposed to reactive oxygen species generated during cell metabolism particularly in relation to the synthesis of melanin or the metabolism in immune system cells. However, skin cells have special features that protect them against oxidative modifications including transcription factor Nrf2, which is responsible for the transcription of the antioxidant protein genes such as antioxidant enzymes, small molecular antioxidant proteins or interleukins, and multidrug response protein. In the present study, the mechanisms of Nrf2 activation have been compared in the cells forming the various layers of the skin: keratinocytes, melanocytes, and fibroblasts. The primary mechanism of control of Nrf2 activity is its binding by cytoplasmic inhibitor Keap1, while cells have also other controlling mechanisms, such as phosphorylation of Nrf2 and modifications of its activators (e.g., Maf, IKKβ) or inhibitors (e.g., Bach1, caveolae, TGF-β). Moreover, there are a number of drugs (e.g., ketoconazole) used in the pharmacotherapy of skin diseases based on the activation of Nrf2, but they may also induce oxidative stress. Therefore, it is important to look for compounds that cause a selective activation of Nrf2 particularly natural substances such as curcumin, sulforaphane, or extracts from the broccoli leaves without side effects. These findings could be helpful in the searching for new drugs for people with vitiligo or even melanoma.