Melanogenesis-related Proteins Research Articles

Photobiomodulation Using 830 nm Lighting-Emitting Diode Inhibits Melanogenesis via FOXO3a in Human Melanocyte.

Photobiomodulation (PBM) using 830 nm light-emitting diode (LED) benefits tissue regeneration, wound healing and neural stimulation. However, there is not much exploration of its effect on melanocytes and exvivo skin model. This study aims to investigate the mechanism behind the anti-melanogenic activity of 830 nm LED and provides evidence for its activity in human exvivo skin model. Our results showed that 830 nm LED at fluences ranging from 5 to 20 J/cm2 inhibited melanosome maturation and reduced melanin content, tyrosinase activity and melanogenesis-related proteins. 830 nm LED inhibited the phosphorylation of AKT and its downstream FOXO3a, leading to nuclear translocation of FOXO3a. Furthermore, FOXO3a knockdown and AKT activator like SC79 could reverse the melanogenesis inhibition phenotype induced by 830 nm LED. In human exvivo skin model, Fontana-Masson staining revealed a decrease in epidermal basal pigmentation after 830 nm LED irradiation. Taken together, 830 nm LED demonstrated the anti-melanogenic activity via FOXO3a.

The biochemistry of melanogenesis: an insight into the function and mechanism of melanogenesis-related proteins.

Melanin is an amino acid derivative produced by melanocyte through a series of enzymatic reactions using tyrosinase as substrate. Human skin and hair color is also closely related to melanin, so understanding the mechanisms and proteins that produce melanin is very important. There are many proteins involved in the process of melanin expression, For example, proteins involved in melanin formation such as p53, HNF-1α (Hepatocyte nuclear factor 1α), SOX10 (Sry-related HMg-Box gene 10) and pax3 (paired box gene 3), MC1R(Melanocortin 1 Receptor), MITF (Microphthalmia-associated transcription factor), TYR (tyrosinase), TYRP1 (tyrosinase-related protein-1), TYRP2 (tyrosinase-related protein-2), and can be regulated by changing their content to control the production rate of melanin. Others, such as OA1 (ocular albinism type 1), Par-2 (protease-activated receptor 2) and Mlph (Melanophilin), have been found to control the transfer rate of melanosomes from melanocytes to keratinocytes, and regulate the amount of human epidermal melanin to control the depth of human skin color. In addition to the above proteins, there are other protein families also involved in the process of melanin expression, such as BLOC, Rab and Rho. This article reviews the origin of melanocytes, the related proteins affecting melanin and the basic causes of related gene mutations. In addition, we also summarized the active ingredients of 5 popular whitening cosmetics and their mechanisms of action.

Hydrolyzed conchiolin protein inhibits melanogenesis through PKA/CREB and MEK/ERK signalling pathways.

Hydrolyzed conchiolin protein (HCP) derived from pearl and nacre extracts exerts skin-lightening effects; however, the underlying molecular mechanisms are not fully understood. Herein, we investigated the effect of HCP on melanogenesis and the signalling pathways involved. B16F10 cells and PIG cells were treated with HCP to verify its ability to inhibit melanin. Western Blot, immunofluorescence, and flow cytometry methods were performed to investigate the effect of HCP on melanogenesis signalling pathway proteins. The inhibitors were used to further validate the effect of HCP on PKA/CREB and MEK/ERK signalling pathways. To further evaluate the whitening ability of HCP, changes in melanin were detected using 3D melanin skin model and zebrafish model. HCP was found to significantly inhibit melanin synthesis and decrease the expression of melanogenesis-related proteins, such as microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein-2, in a dose-dependent manner. Additionally, we revealed that HCP suppresses melanogenesis via the regulation of the PKA/cAMP response element-binding (CREB) and MEK/extracellular signalling-regulated kinase (ERK) signalling pathways. Using 3D melanin skin models, we demonstrated that HCP can achieve skin-lightening effects by improving apparent chroma, increasing apparent brightness, and inhibiting melanin synthesis. Furthermore, HCP exhibits skin-whitening effects in a zebrafish model. These results suggest that HCP suppresses the melanogenesis signalling cascade by inhibiting the PKA/CREB, MEK/ERK signalling pathway and downregulating MITF and its downstream signalling pathways, resulting in decreased melanin synthesis. In summary, HCP is a potential anti-pigmentation agent with promising applications in cosmetics and pharmaceutical products.

The amino acid transporter SLC16A10 promotes melanogenesis by facilitating the transportation of phenylalanine.

Phenylalanine is a crucial amino acid in the process of melanogenesis. However, the exact mechanism by which it is transported into melanocytes has not been disclosed. The aim of this study was to identify and examine the key transporters that are responsible for phenylalanine transportation and evaluate their significance in melanogenesis. The amino acid transporter SLC16A10 was found to be up-regulated in both melasma (GSE72140) and sun-exposed skin (GSE67098). The protein levels of SLC16A10 were proportional to the melanin content in melanocytic nevi, indicating that SLC16A10 was related to melanogenesis. After SLC16A10 overexpression, melanin increased significantly in MNT1 cells. Meanwhile, the expression of melanogenesis-related proteins such as TYR and TYRP1 increased, while their RNA levels did not change. Transcriptomics data indicated that SLC16A10 can enhance the function of ribosome. Furthermore, targeted metabolomics data and ELISA results demonstrated SLC16A10 mainly affected the transport of phenylalanine into the cells. Then, phenylalanine was added to the cell culture medium after SLC16A10 overexpression, melanin synthesis in cells furtherly increased, which verified that SLC16A10 enhances melanogenesis by promoting the uptake of phenylalanine. Finally, we found that SLC16A10 expression increased after UVB irradiation. Knockdown SLC16A10 reduced UVB-induced melanin production and phenylalanine uptake by cells. In summary, SLC16A10 enhances melanogenesis by promoting the uptake of phenylalanine, and upregulation SLC16A10 is likely responsible for the UVB-induced hyperpigmentation as well.

Whitening effects of fermented Trigonotis radicans var. sericea with Lactobacillus brevis in α-MSH-stimulated B16F10 melanoma cells

This study was designed to compare the whitening effects of 60% ethanol extracts of Trigonotis radicans var. sericea (TR) and Lactobacillus brevis-fermented T. radicans var. sericea (FTR). Measurement of cytotoxicity in B16-F10 melanoma cells to confirm the whitening effect, FTR showed higher cell viability than TR. FTR showed inhibitory activity on melanin contents similar to the normal group at concentrations of 50 and 100 μg/mL. MITF expression was used to confirm the effect on melanogenesis-related protein expression. TR and FTR showed significant concentration-dependent decrease, and FTR showed lower expressions than the normal group at concentrations of 25, 50, and 100 μg/mL. Additionally, the mRNA expression of melanogenesis-related genes (MC1R, Rab27a, TGF-β1 and Myo5a) were measured by RT-qPCR to confirm the whitening effect. In MC1R expression at a concentration of 100 μg/mL in FTR showed effective inhibitory activities, and in TGF-β1 expression, TR and FTR both showed effective activities compared to normal groups even at low concentrations. Results of myo5a and Rab27a, a similar pattern was shown, and FTR showed effective inhibitory activities at a concentration of 100 μg/mL. As a result, FTR had higher whitening effects through bioconversion and is expected to be a good material for whitening functional cosmetics.

Integrative pharmacology reveals the mechanisms of Erzhi pills, A traditional Chinese formulation, stimulating melanogenesis

Ethnopharmacological relevanceErzhi pills (EZP), a traditional Chinese medicine formula prescribed for the treatment of vitiligo, has shown promising efficacy. However, the oral bioactive components and mechanisms underlying the promotion of melanogenesis by EZP remain unclear. Aim of the studyThis study aimed to investigate the pharmacological basis and mechanism of EZP in promoting melanogenesis. Materials and methodsUHPLC-TOF-MS analysis was used to identify absorbed phytochemicals in serum after oral administration of EZP. Network pharmacology methods were used to predict potential targets and pathways involved in the melanogenic activity of EZP, resulting in the construction of a “compound-target-pathway” network. Zebrafish and B16F10 cells were used to evaluate the effects of EZP on tyrosinase activity and melanin content. Western blot and ELISA analyses were used to validate the effects of EZP on melanogenesis-related proteins, including MITF, TYR, CREB, p-CREB, and cAMP. ResultsUHPLC-TOF-MS analysis identified 36 compounds derived from EZP in serum samples. Network pharmacology predictions revealed 89 target proteins associated with the identified compounds and closely related to vitiligo. GO and KEGG analyses indicated the involvement of the cAMP/PKA signaling pathway in the promotion of melanogenesis by EZP. Experimental results showed that EZP increased tyrosinase activity and melanin content in zebrafish and B16F10 cells without inducing toxicity. Western blot and ELISA results suggested that the melanogenic effect of EZP may be related to the activation of the cAMP/PKA signaling pathway. These results confirm the feasibility of combining serum pharmacological and network pharmacological approaches. ConclusionsEZP have the potential to increase tyrosinase activity and melanin content in zebrafish and cells possibly through activation of the cAMP/PKA pathway.

Low-dose imiquimod induces melanogenesis in melanoma cells through an ROS-mediated pathway

BackgroundMelanogenesis is the process of melanin maturation which not only protects skin from UV radiation but also plays an important role in antigenicity of melanomas. Imiquimod (IMQ) is a toll-like receptor 7 (TLR7) agonist that exhibits antiviral and anticancer activity. ObjectiveTo explore whether IMQ could induce melanogenesis in melanoma cells. MethodsThe mouse melanoma cell line B16F10, the mouse immortalized melanocyte Melan-A, and human melanoma cell lines MNT-1, C32 and A375 were utilized in this study. The pigmented level was observed by the centrifuged cell pellet. The intracellular and extracellular melanin levels were examined in the absorbance in NaOH-extracted cell lysate and cell-cultured medium, respectively. The expression of melanogenesis related proteins was examined by immunoblotting. The intracellular cyclic AMP amount was evaluated by the cAMP Glo assay kit. The activity of phosphodiesterase 4B (PDE4B) was investigated by CREB reporter assay with overexpressed PDE4B or not. ResultsWe demonstrated that a low dose of IMQ could trigger melanogenesis in B16F10 cells. IMQ induced microphthalmia-associated transcription factor (MITF) nuclear translocation, upregulated the expression of melanogenesis-related proteins, increased tyrosinase (TYR) activity, and led to pigmentation in B16F10 cells. Next, we found that IMQ-induced melanogenesis was activated by excessive intracellular cAMP accumulation, which was regulated through IMQ-mediated PDE4B inhibition. Finally, IMQ-induced ROS production was found to be involved in melanogenesis by its control of PDE4B activity. ConclusionsLow dose of IMQ could activate melanogenesis through the ROS/PDE4B/PKA pathway in melanoma cells.

Fraxin inhibits melanogenesis by suppressing the ERK/MAPK pathway and antagonizes oxidative stress by activating the NRF2 pathway

Hyperpigmentation disorders, such as melasma and freckles, are highly prevalent and draw increasing attention. Patients thus tend to seek effective and safe cosmetic whitening agents. Fraxin, a bioactive substance extracted from Cortex Fraxini, possesses anti-inflammation and antioxidant properties. In this study, we further explored the anti-melanogenic activities of fraxin were explored in vitro and in vivo. We found that pretreatment with fraxin decreased the melanin content of MNT1 cells and zebrafishes. In MNT1 cells, melanogenesis-related proteins, such as MITF, TYR, TYRP1, and DCT were down-regulated and tyrosinase activity was reduced under fraxin treatment. Further exploration of the mechanism revealed that fraxin could inhibit the phosphorylation of ERK, which is closely related to melanogenesis. Besides, fraxin also protected MNT1 cells from H2O2-induced apoptosis via scavenging reactive oxygen species (ROS) in cells. Further experimentation revealed that fraxin could activate NRF2 and upregulate antioxidase CAT and HO-1. In conclusion, fraxin could be an effective agent with anti-melanogenesis and antioxidant properties for hyperpigmentation disorders.

6-Methylcoumarin Promotes Melanogenesis through the PKA/CREB, MAPK, AKT/PI3K, and GSK3β/β-Catenin Signaling Pathways.

We investigated the effects of four coumarin derivatives, namely, 6-methylcoumarin, 7-methylcoumarin, 4-hydroxy-6-methylcoumarin, and 4-hydroxy-7-methylcoumarin, which have similar structures on melanogenesis in a murine melanoma cell line from a C57BL/6J mouse called B16F10. Our results showed that only 6-methylcoumarin significantly increased the melanin synthesis in a concentration-dependent manner. In addition, the tyrosinase, TRP-1, TRP-2, and MITF protein levels were found to significantly increase in response to 6-methylcoumarin in a concentration-dependent manner. To elucidate the molecular mechanism whereby 6-methylcoumarin-induced melanogenesis influences the melanogenesis-related protein expression and melanogenesis-regulating protein activation, we further assessed the B16F10 cells. The inhibition of the ERK, Akt, and CREB phosphorylation, and conversely, the increased p38, JNK, and PKA phosphorylation activated the melanin synthesis via MITF upregulation, which ultimately led to increased melanin synthesis. Accordingly, 6-methylcoumarin increased the p38, JNK, and PKA phosphorylation in the B16F10 cells, whereas it decreased the phosphorylated ERK, Akt, and CREB expressions. In addition, the 6-methylcoumarin activated GSK3β and β-catenin phosphorylation and reduced the β-catenin protein level. These results suggest that 6-methylcoumarin stimulates melanogenesis through the GSK3β/β-catenin signal pathway, thereby affecting the pigmentation process. Finally, we tested the safety of 6-methylcoumarin for topical applications using a primary human skin irritation test on the normal skin of 31 healthy volunteers. We found that 6-methylcoumarin did not cause any adverse effects at concentrations of 125 and 250 μM. Our findings indicate that 6-methylcoumarin may be an effective pigmentation stimulator for use in cosmetics and the medical treatment of photoprotection and hypopigmentation disorders.

Stimulatory effects of Lycium shawii on human melanocyte proliferation, migration, and melanogenesis: In vitro and in silico studies.

There is no first-line treatment for vitiligo, a skin disease characterized by a lack of melanin produced by the melanocytes, resulting in an urgent demand for new therapeutic drugs capable of stimulating melanocyte functions, including melanogenesis. In this study, traditional medicinal plant extracts were tested for cultured human melanocyte proliferation, migration, and melanogenesis using MTT, scratch wound-healing assays, transmission electron microscopy, immunofluorescence staining, and Western blot technology. Of the methanolic extracts, Lycium shawii L. (L. shawii) extract increased melanocyte proliferation at low concentrations and modulated melanocyte migration. At the lowest tested concentration (i.e., 7.8μg/mL), the L. shawii methanolic extract promoted melanosome formation, maturation, and enhanced melanin production, which was associated with the upregulation of microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein (TRP)-1 and TRP-2 melanogenesis-related proteins, and melanogenesis-related proteins. After the chemical analysis and L. shawii extract-derived metabolite identification, the in silico studies revealed the molecular interactions between Metabolite 5, identified as apigenin (4,5,6-trihydroxyflavone), and the copper active site of tyrosinase, predicting enhanced tyrosinase activity and subsequent melanin formation. In conclusion, L. shawii methanolic extract stimulates melanocyte functions, including melanin production, and its derivative Metabolite 5 enhances tyrosinase activity, suggesting further investigation of the L. shawii extract-derived Metabolite 5 as a potential natural drug for vitiligo treatment.

Peripheral Blood of Vitiligo Patients-Derived Exosomal MiR-21-5p Inhibits Melanocytes Melanogenesis via Targeting SATB1.

Vitiligo is a common depigmentation disease characterized by progressive destruction and disappearance of epidermal melanocytes. Exosomes have been discovered to regulate the pigment status of melanocytes. We aimed to explore the role of exosomes from peripheral blood of vitiligo patients on melanogenesis. Human melanocytes cell line PIG1 was treated with exosomes from the healthy volunteers or exosomes from the vitiligo patients referred to the Department of Dermatology, Children's Hospital Affiliated to Zhengzhou University, China and transfected with miR-21-5p mimic or inhibitor. Exosome labeling assay was used to assess whether exosomes were absorbed by melanocytes. Melanin content and tyrosinase activity assays were performed to investigate melanogenesis in melanocytes. The levels of melanogenesis-related genes and proteins were detected by RT-qPCR and western blot assays. Dual-luciferase reporter assay was performed to confirm the relationship between miR-21-5p and special AT-rich sequence binding protein-1 (SATB1). Exosomes from peripheral blood of vitiligo patients were transferred into melanocytes and suppressed melanin content, tyrosinase activity and melanogenesis-related genes and proteins levels. Besides, miR-21-5p was highly expressed in exosomes from peripheral blood of vitiligo patients. The results of the gain- and loss-of-function experiments demonstrated that miR-21-5p inhibited the melanogenesis of melanocytes. Furthermore, miR-21-5p inhibitor abolished the inhibitory role of exosomes from peripheral blood of vitiligo patients. Subsequently, miR-21-5p directly targeted SATB1 in melanocytes. Furthermore, overexpression of SATB1 reversed the inhibitory roles of miR-21-5p mimic on melanin content, tyrosinase activity, and melanogenesis-related protein expression. Peripheral blood of vitiligo patients-derived exosomal miR-21-5p inhibited melanocytes melanogenesis via targeting SATB1.

Study on the Mechanism of miR-125b-5p Affecting Melanocyte Biological Behavior and Melanogenesis in Vitiligo through Regulation of MITF.

The goal was to confirm the mechanism by which miR-125b-5p influences melanocyte biological behavior and melanogenesis in vitiligo by regulating MITF. oe-MITF, sh-MITF, miR-125b-5p mimic, NC-mimic, NC-inhibitor, and miR-125b-5p inhibitor were transfected into cells by cell transfection. Western blotting was used to detect the related protein expression, qRT-PCR was used to detect miR-125b-5p and MITF expression, immunohistochemistry was used to detect the MITF-positive cells in vitiligo patients tissues, and a dual-luciferase reporter system was used to detect the target of miR-125b-5p and MITF. PIG1 and PIG3V cell proliferation by the CCK-8 method, cell cycle progression and apoptosis by flow cytometry, apoptosis was detected by TUNEL, Tyr activity and melanin content were measured using Tyr and melanin content assay kits. Compared with the healthy control group, the expression of miR-125b-5p in the tissues and serum of vitiligo patients was upregulated, and the expression of MITF was downregulated; compared with PIG1 cells, the expression of miR-125b-5p and MITF in the PIG3V group was consistent with the above. Compared with the NC-minic group, the cell proliferation activity of the miR-125b-5p mimic group decreased, apoptosis increased, and the expression levels of melanogenesis-related proteins Tyr, Tyrp1, Tyrp2, and DCT were downregulated. Compared with the NC-inhibitor group, the above indices in the miR-125b-5p inhibitor group were all opposite to those in the miR-125b-5p mimic group. Transfection of oe-MITF into the miR-125b-5p mimic group reversed the effect of the miR-125b-5p mimic, while transfection of sh-MITF enhanced the effect of the miR-125b-5p mimic. miR-125b-5p affects vitiligo melanocyte biological behavior and melanogenesis by downregulating MITF expression.

Antioxidant and Anti-Melanogenesis Effects of Colloidal Gold Camellia sinensis L. Extracts.

Green tea extract derived from the leaves of Camellia sinensis L. (CS), is a representative beverage with antioxidant, anti-cancer, and anti-viral properties. CS extract is also used in cosmetics. Colloidal gold is generally a sol or colloidal suspension of gold nanoparticles in water. Colloidal gold green tea (CGCS), cultivated as a fertilizer using this colloidal gold solution, contains gold minerals and possesses anti-inflammatory, analgesic, and anti-tumor properties. However, the skin bioactivity of CGCS has not yet been investigated. In this study, we investigated the effect of the CGCS extract on skin whitening. CGCS extract contained high levels of phenols and flavonoids and displayed 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity in a concentration-dependent manner. CGCS extract inhibited melanin synthesis and tyrosinase activity in B16F10 cells more effectively than the CS extract. Moreover, the CGCS extract decreased the expression levels of the melanogenesis-related proteins, tyrosinase, tyrosinase-related proteins (TRPs), and microphthalmia-associated transcription factor (MITF). In conclusion, our study showed that the CGCS extract inhibits the expression of tyrosinase, TRP-1, and TRP-2 via the downregulation of MITF, thereby inhibiting melanin synthesis. Therefore, CGCS can potentially be used as a skin-whitening ingredient in the cosmetic industry.

Peripheral benzodiazepine receptor TSPO needs to be reconsidered before using as a drug target for a pigmentary disorder.

The peripheral benzodiazepine receptor (TSPO/PBR) is highly conserved among different species but with perplexing biochemical functions. Multiple ligands of TSPO show commendable regulatory activities in lots of biological functions, such as neuro-protection, cholesterol transport, and so on. These researches support that TSPO may be a potential target for disease treatment and drug development. Previous studies have shown that its ligands benzodiazepines show a satisfactory effect on melanogenic promotion. However, the potential application of TSPO in drug development for pigmentary disorder needs further investigation. In this study, we confirmed the melanogenesis induction of TSPO ligand, Ro5-4864 in mouse melanoma cell lines, human skin tissue, and zebrafish embryos by inducing melanin synthesis and melanosome transport. Molecular genetics and pharmacological studies showed that TSPO deficiency did not affect melanin production in B16F10 cells and zebrafish embryos, nor did it affect the melanin promotion effect of Ro5-4864. Whether or not TSPO exists, the expression of lots of melanogenesis-related proteins, such as TYR, TRP-1, DCT, Mlph, and Rab27 was upregulated with the Ro5-4864 administration. These results indicated that Ro5-4864 induces melanogenesis in a TSPO-independent manner, which is inconsistent with previous research. This research is a reminder that we need to be very careful during target validation in drug development.

Silencing of Rab23 by siRNA inhibits ultraviolet B-induced melanogenesis via downregulation of PKA/CREB/MITF.

Recent investigations have shown that the Rab family of GTPases is associated with all aspects of melanogenesis. However, the effect of Rab23, which localizes to the plasma membrane and regulates the endocytic pathway within eukaryotic cells, in melanogenesis has not been reported. To understand the role of Rab23 in UVB-induced melanogenesis, we evaluated changes in the level of melanin, activity of tyrosinase and levels of melanogenesis-related proteins such as microphthalmia transcription factor and tyrosinase-related protein-1 (TRP-1) and the melanosome transport-related protein complex Rab27a-melanophilin-myosin Va after the downregulation of Rab23 in B16F10 and SK-MEL-2 cells with or without UVB irradiation. Our results showed that downregulating Rab23 reduced the melanin level and tyrosinase activity and inhibited the expression of proteins involved in UVB-induced melanogenesis. Rab23 colocalized with mature melanosomes marked with TRP-1. Furthermore, downregulating Rab23 induced the abnormal accumulation of melanosomes around the nucleus. We demonstrated that the downregulation of Rab23 inhibited melanin synthesis and melanosome transport by decreasing the PKA/CREB/MITF pathway, which is the key regulator of UVB-induced melanogenesis.

Identification of a Novel Class of Anti-Melanogenic Compounds, (Z)-5-(Substituted benzylidene)-3-phenyl-2-thioxothiazolidin-4-one Derivatives, and Their Reactive Oxygen Species Scavenging Activities.

The rate-determining role of tyrosinase makes it a critical component in the mechanism that is responsible for melanogenesis. Thirteen (Z)-5-(substituted benzylidene)-3-phenyl-2-thioxothiazolidin-4-one ((Z)-BPTT) analogs were designed based on the structural features of two potent tyrosinase inhibitors, viz. (Z)-5-(3-hydroxy-4-methoxybenzylidene)-2-thioxothiazolidin-4-one (5-HMT) and (Z)-2-(2,4-dihydroxybenzylidene)benzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one (compound I). The trisubstituted double bond geometry of the (Z)-BPTT analogs that were generated by Knoevenagel condensation was determined using vicinal 1H and 13C coupling constants in 13C NMR spectra. Four analogs, numbers 1–3 and 6, inhibited mushroom tyrosinase 9 to 29 times more potently than kojic acid did. Kinetic study results indicated that these four analogs inhibited mushroom tyrosinase competitively and this was supported by docking simulation. Also, docking results using human tyrosinase suggested that analogs 2 and 3 might be potent human tyrosinase inhibitors. In vitro studies using B16F10 cells (a melanoma cell line) showed that analogs 1, 2, 3, and 6 inhibited cellular tyrosinase and melanin production more than kojic acid did, without perceptible cytotoxicity. In particular, analog 2, which possesses a catechol group, exerted an extremely potent anti-melanogenic effect. In addition, analog 2 showed strong scavenging activity against DPPH and ABTS radicals. Furthermore, analog 2 not only reduced ROS levels, which induce melanogenesis, but it also suppressed tyrosinase and MITF (microphthalamia-associated transcription factor) protein levels and the expressions of melanogenesis-related genes. These results suggest that analog 2 is an efficient tyrosinase inhibitor that alleviates melanogenesis by dual mechanisms of (i) the inhibition of melanogenesis-related proteins and genes and (ii) the direct inhibition of tyrosinase activity.

Nicotinamide mononucleotide reduces melanin production in aged melanocytes by inhibiting cAMP/Wnt signaling

BackgroundNicotinamide mononucleotide (NMN) is a representative anti-aging drug that, after long-term administration in mice, causes an increase in energy and lipid metabolism, improves eye function, immune response, and increases insulin sensitivity. However, the effects of NMN on skin pigmentation are still unknown. ObjectiveIn this study, we aimed to demonstrate the effects of NMN on melanogenesis. MethodsNMN was applied to both young and aged melanocytes, and melanin production, protein expression, and mRNA levels were analyzed. A reconstituted human skin model was used to validate the effect of NMN on melanogenesis in vivo. ResultsNMN treatment showed no apparent effects on young melanocytes, however, in aged melanocytes, a marked reduction in melanin production was observed. NMN treatment also efficiently reduced melanin production in a reconstituted human skin with aged melanocytes. Genome-wide analysis showed the downregulation of melanogenesis-related cyclic adenosine monophosphate (cAMP)/Wnt signaling in aged melanocytes. Moreover, NMN treatment downregulated forskolin-induced expression of melanogenesis-related proteins, tyrosinase (TYR), tyrosinase-related protein (TRP)− 1, and TRP-2. Nicotinamide adenine dinucleotide (NAD+), an NMN product within the cells, also reduced cAMP/Wnt signaling in aged melanocytes. SLC12A6 was the most highly expressed gene among the SLC12A family members in melanocytes and was significantly influenced by NMN or NAD+ treatment, indicating that SLC12A6 protein is an NMN transporter in melanocytes. ConclusionNMN reduces melanogenesis in aged melanocytes by downregulating the signaling of melanogenesis-associated receptors. Therefore, NMN is a human-friendly anti-melanogenic agent with the potential to aid in aging-related hyperpigmentation therapy.

Interferon-gamma induces melanogenesis via post-translational regulation of tyrosinase.

Melanogenesis (melanin pigment production) in melanocytes is canonically stimulated by the alpha melanocyte stimulating hormone (αMSH), which activates the cyclic-AMP-mediated expression of the melanocyte inducing transcription factor (MITF) and its downstream melanogenic genes, including the principal rate-limiting melanogenic enzyme tyrosinase (TYR). Here, we report that interferon-gamma (IFNG; type II interferon), but not interferon-alpha (a type I interferon), induces a noncanonical melanogenic pathway in mouse and human melanocytic cells. Inhibition of IFNG pathway by the JAK1/2 inhibitor ruxolitinib or knocking out Stat1gene abrogated the IFNG-induced melanogenesis. Interestingly, IFNG-induced melanogenesis was independent of MITF. IFNG markedly increased the TYR protein expression but did not affect the mRNA expression, suggesting a post-translational regulatory mechanism. In contrast, IFNG had no effect on the expression of other melanogenesis-related proteins, for example, tyrosinase-related protein 1 (TYRP1) and dopachrome tautomerase (DCT). Glycosidase digestion assays revealed that IFNG treatment increased the mature glycosylated form of TYR, but not its de novo synthesis. Moreover, cycloheximide chase assay showed that degradation of TYR was decreased in IFNG-treated cells. These results suggest that the IFNG-STAT1 pathway regulates melanogenesis via regulation of the post-translational processing and protein stability of TYR.

Melanoma, Melanin, and Melanogenesis: The Yin and Yang Relationship.

Melanin pigment plays a critical role in the protection against the harmful effects of ultraviolet radiation and other environmental stressors. It is produced by the enzymatic transformation of L-tyrosine to dopaquinone and subsequent chemical and biochemical reactions resulting in the formation of various 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI) oligomers—main constituents of eumelanin, and benzothiazine and benzothiazole units of pheomelanin. The biosynthesis of melanin is regulated by sun exposure and by many hormonal factors at the tissue, cellular, and subcellular levels. While the presence of melanin protects against the development of skin cancers including cutaneous melanoma, its presence may be necessary for the malignant transformation of melanocytes. This shows a complex role of melanogenesis in melanoma development defined by chemical properties of melanin and the nature of generating pathways such as eu- and pheomelanogenesis. While eumelanin is believed to provide radioprotection and photoprotection by acting as an efficient antioxidant and sunscreen, pheomelanin, being less photostable, can generate mutagenic environment after exposure to the short-wavelength UVR. Melanogenesis by itself and its highly reactive intermediates show cytotoxic, genotoxic, and mutagenic activities, and it can stimulate glycolysis and hypoxia-inducible factor 1-alpha (HIF-1α) activation, which, combined with their immunosuppressive effects, can lead to melanoma progression and resistance to immunotherapy. On the other hand, melanogenesis-related proteins can be a target for immunotherapy. Interestingly, clinicopathological analyses on advanced melanomas have shown a negative correlation between tumor pigmentation and diseases outcome as defined by overall survival and disease-free time. This indicates a “Yin and Yang” role for melanin and active melanogenesis in melanoma development, progression, and therapy. Furthermore, based on the clinical, experimental data and diverse effects of melanogenesis, we propose that inhibition of melanogenesis in advanced melanotic melanoma represents a realistic adjuvant strategy to enhance immuno-, radio-, and chemotherapy.

Effects of tea polyphenols on UVA-induced melanogenesis via inhibition of α-MSH-MC1R signalling pathway.

IntroductionUltraviolet (UV) irradiation is a major environmental factor affecting photoaging, which is characterized by skin wrinkle formation and hyperpigmentation. Although many factors are involved in the melanogenesis progress, UV is thought to play a major role in tanning. The pathway of α-melanocyte-stimulating hormone (α-MSH)-melanocortin receptor 1 (MC1R) is associated with UV-induced melanogenesis. Thus, α-MSH antagonists may have applications in the prevention of melanogenesis.AimTo investigate the effects of tea polyphenols (TPS) on pigmentation, and further explore the underlying mechanism.Material and methodsHuman keratinocyte cell line (HaCaT) cells and Human epidermal melanocytes (HEM) were exposed to UVA and treated with different concentrations of TPS or Nonapeptide-1 acetate salt (N-1A). Then, cell viability, melanin content, and tyrosinase activity of both kinds of cells were detected. Quantification of α-MSH in HaCaT cells and HEM cells determined by ELISA assays. Immunohistochemistry of HEM cells was employed to further investigate the expression of melanogenesis-related proteins.ResultsThe different concentrations of TPS were found to decrease the melanin content, tyrosinase activity and melanogenesis-related proteins such as microphthalmia-associated transcription factor (MITF), tyrosinase-related protein (TRP)1, and TRP2. Besides, TPS inhibited α-MSH-MC1R signalling through directly suppressed α-MSH expression rather than the down-regulated expression level of MC1R.ConclusionsOur findings indicate that TPS may be a potential whitening agent for use in cosmetics and the medical treatment of hyperpigmentation disorders.