Oxidative Stress In Melanocytes Research Articles

Apigenin Ameliorates H2O2-Induced Oxidative Damage in Melanocytes through Nuclear Factor-E2-Related Factor 2 (Nrf2) and Phosphatidylinositol 3-Kinase (PI3K)/Protein Kinase B (Akt)/Mammalian Target of Rapamycin (mTOR) Pathways and Reducing the Generation of Reactive Oxygen Species (ROS) in Zebrafish

Background: Apigenin is one of the natural flavonoids found mainly in natural plants, as well as some fruits and vegetables, with celery in particular being the most abundant. Apigenin has antioxidant, anti-tumor, anti-inflammatory, and anticancer effects. In this research, we attempted to further investigate the effects of apigenin on the mechanism of repairing oxidative cell damage. The present study hopes to provide a potential candidate for abnormal skin pigmentation disorders. Methods: We used 0.4 mM H2O2 to treat B16F10 cells for 12 h to establish a model of oxidative stress in melanocytes, and then we gave apigenin (0.1~5 μM) to B16F10 cells for 48 h, and detected the expression levels of melanin synthesis-related proteins, dendritic regulation-related proteins, antioxidant signaling pathway- and Nrf2 signaling pathway-related proteins, autophagy, and autophagy-regulated pathways by immunoblotting using Western blotting. The expression levels of PI3K/Akt/mTOR proteins were measured by β-galactosidase staining and Western blotting for cellular decay, JC-1 staining for mitochondrial membrane potential, and Western blotting for mitochondrial fusion- and mitochondrial autophagy-related proteins. Results: Apigenin exerts antioxidant effects by activating the Nrf2 pathway, and apigenin up-regulates the expression of melanin synthesis-related proteins Tyr, TRP1, TRP2, and gp100, which are reduced in melanocytes under oxidative stress. By inhibiting the expression of senescence-related proteins p53 and p21, and delaying cellular senescence, we detected the mitochondrial membrane potential using JC-1, and found that apigenin improved the reduction in mitochondrial membrane potential in melanocytes under oxidative stress, and maintained the normal function of mitochondria. In addition, we further detected the key regulatory proteins of mitochondrial fusion and division, MFF, p-DRP1 (S637), and p-DRP1 (S616), and found that apigenin inhibited the down-regulation of fusion-associated protein, p-DRP1 (S637), and the up-regulation of division-associated proteins, MFF and p-DRP1 (S616), due to oxidative stress in melanocytes, and promoted the mitochondrial fusion and ameliorated the imbalance between mitochondrial division and fusion. We further detected the expression of fusion-related proteins OPA1 and Mitofusion-1, and found that apigenin restored the expression of the above fusion proteins under oxidative stress, which further indicated that apigenin promoted mitochondrial fusion, improved the imbalance between mitochondrial division and fusion, and delayed the loss of mitochondrial membrane potential. Apigenin promotes the expression of melanocyte autophagy-related proteins and the key mitochondrial autophagy proteins BNIP3L/Nix under oxidative stress, and activates the PINK1/Parkin signaling pathway by up-regulating the expression of autophagy-related proteins, as well as the expression of PINK1 and Parkin proteins, to promote melanocyte autophagy and mitochondrial autophagy. Conclusions: Apigenin exerts anti-melanocyte premature aging and detachment effects by promoting melanin synthesis, autophagy, and mitochondrial autophagy in melanocytes, and inhibiting oxidative cell damage and senescence.

Paeoniflorin regulates RhoA/ROCK1 and Nrf2 pathways in PDLIM1-dependent or independent manners in oxidative stressed melanocytes.

The adhesive properties of vitiligo melanocytes have decreased under oxidative stress., cytoskeleton proteins can control cell adhesion. Paeoniflorin (PF) was proved to resist hydrogen peroxide (H2O2)-induced oxidative stress in melanocytes via nuclear factorE2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway. This study was to investigate whether PF exerts anti-oxidative effect through influencing cytoskeleton markers or potential signaling pathway. Human Oxidative Stress Plus array was used to identify the differentially expressed genes between H2O2 + PF group and H2O2 only group, in PIG1 and PIG3V melanocyte cell lines respectively. Western blotting was used to verify the PCR array results and to test the protein expression levels of cytoskeleton markers including Ras homolog family member A (RhoA), Rho-associated kinase 1 (ROCK1) and antioxidative marker Nrf2. Small interfering RNA was used to knock down PDZ and LIM domain 1 (PDLIM1). PF increased the expressions of PDLIM1, RhoA and ROCK1 in H2O2-induced PIG1, in contrast, decreased the expressions of PDLIM1 and ROCK1 in H2O2-induced PIG3V. Knockdown of PDLIM1 increased the expressions of RhoA and Nrf2 in PF-pretreated H2O2-induced PIG1, and ROCK1 and Nrf2 in PF-pretreated H2O2-induced PIG3V. PF regulates RhoA/ROCK1 and Nrf2 pathways in PDLIM1-dependent or independent manners in H2O2-induced melanocytes. In PIG1, PF promotes PDLIM1 to inhibit RhoA/ROCK1 pathway or activates Nrf2/HO-1 pathway, separately. In PIG3V, PF directly downregulates ROCK1 in PDLIM1-independent manner or upregulates Nrf2 dependent of PDLIM1.

Melanoma-associated melanocortin 1 receptor variants confer redox signaling-dependent protection against oxidative DNA damage

Cutaneous melanoma, a lethal skin cancer, arises from malignant transformation of melanocytes. Solar ultraviolet radiation (UVR) is a major environmental risk factor for melanoma since its interaction with the skin generates DNA damage, either directly or indirectly via oxidative stress. Pheomelanin pigments exacerbate oxidative stress in melanocytes by UVR-dependent and independent mechanisms. Thus, oxidative stress is considered to contribute to melanomagenesis, particularly in people with pheomelanic pigmentation. The melanocortin 1 receptor gene (MC1R) is a major melanoma susceptibility gene. Frequent MC1R variants (varMC1R) associated with fair skin and red or yellow hair color display hypomorphic signaling to the cAMP pathway and are associated with higher melanoma risk. This association is thought to be due to production of photosensitizing pheomelanins as well as deficient induction of DNA damage repair downstream of varMC1R. However, the data on modulation of oxidative DNA damage repair by MC1R remain scarce. We recently demonstrated that varMC1R accelerates clearance of reactive oxygen species (ROS)-induced DNA strand breaks in an AKT-dependent manner. Here we show that varMC1R also protects against ROS-dependent formation of 8-oxodG, the most frequent oxidative DNA lesion. Since the base excision repair (BER) pathway mediates clearance of these DNA lesions, we analyzed induction of BER enzymes in human melanoma cells of varMC1R genotype. Agonist-mediated activation of both wildtype (wtMC1R) and varMC1R significantly induced OGG and APE-1/Ref1, the rate-limiting BER enzymes responsible for repair of 8-oxodG. Moreover, we found that NADPH oxidase (NOX)-dependent generation of ROS was responsible for AKT activation and oxidative DNA damage repair downstream of varMC1R. These observations provide a better understanding of the functional properties of melanoma-associated MC1R alleles and may be useful for the rational development of strategies to correct defective varMC1R responses for efficient photoprotection and melanoma prevention in fair-skinned individuals.

Phototoxic action of meloxicam contributes to dysregulation of redox homeostasis in normal human skin cells – Molecular and biochemical analysis of antioxidant enzymes in melanocytes and fibroblasts

The phototoxic effect of meloxicam (MLX) raises the question of the effect of the drug on the redox homeostasis of normal human skin cells. The main objective of the study was to analyze the effect of MLX and/or UVA radiation (UVAR) on the redox homeostasis of human normal skin cells – melanocytes and fibroblasts. MLX was found to affect the activity and expression of enzymes of the antioxidant system differently depending on the cell line used. The drug decreased the activity and expression of superoxide dismutase type 1 and 2 (SOD1 and SOD2), catalase (CAT) and glutathione peroxidase (GPx) in fibroblasts, while increasing the activity of these enzymes in melanocytes. UVA radiation enhanced the effects of the drug. In conclusion, MLX in combination with UVAR induces oxidative stress in melanocytes and fibroblasts, however, the analyses showed that the drug's effect the activity and expression of SOD, CAT and GPx differently, depending on the cell line. The observed dissimilarity between tested cell lines may result from the presence of melanin pigments.

Evaluation of oxidative stress levels as biomarkers in vitiligo patients

Abstract Objective: Vitiligo is a skin disease that causes the loss of melanocyte cells, which produce pigment in the skin. There is evidence that oxidative stress plays an important role in vitiligo disease of unknown pathogenesis. Evidence suggests that there is increased oxidative stress in melanocytes in patients with vitiligo. The aim of this study is to investigate oxidative stress markers in patients with vitiligo. Materials and Methods: Blood samples were taken from 23 vitiligo patients and 23 healthy control groups without any disease in Bezmialem Vakıf University Hospital Dermatology and Venereal Diseases Outpatient Clinic. Total antioxidant levels (TAS) and total oxidant levels (TOS) were measured photometrically method with blood samples. The oxidative stress index (OSI) was calculated as the TOS to TAS level ratio. Results: When the results of the vitiligo patient group were compared with the control group, TOS and OSI were found to be significantly higher than the control group (P < 0.05). No statistically significant result was found in TAS. Conclusions: Our results show that oxidative stress plays a role in the pathogenesis of vitiligo.

Autophagy in psoriasis and vitiligo

Autophagy is a primary catabolic process in eukaryotes which is responsible for degrading dysfunctional and redundant cellular organelles and proteins. The autophagy process plays several roles in maintaining cellular homeostasis, including an endogenous defence mechanism that might play an important role in the development and progression of skin diseases. Psoriasis and vitiligo are common chronic inflammatory skin disorders. Psoriasis is characterized by well-demarcated, erythematous, thickened plaques with an overlying scale. Exact aetiology is complex and influenced by genetic and environmental factors but is not entirely explained. Defects of autophagy in psoriatic skin are likely involved in increased inflammation and disturbed keratinocyte differentiation. Research indicates that autophagy disorders may be associated with various pathways and molecules such as PI3K/AKT/mTOR or toll-like receptors. Vitiligo is characterized by the loss of functional melanocytes. Many hypotheses have been proposed for the pathogenesis of this disease. Autoimmunity and oxidative stress in melanocytes remain the most frequently mentioned. Deregulated autophagy in vitiligo melanocytes might disrupt the antioxidant defence system, which causes melanocytes to have oxidative insults. Still, due to the complexity of this process, its precise role in immune-related inflammatory skin diseases such as psoriasis and vitiligo remains unclear. Objective results will enable the application of new therapeutic strategies.

Methylcobalamin Protects Melanocytes from H2O2-Induced Oxidative Stress by Activating the Nrf2/HO-1 Pathway.

PurposeOxidative stress is considered a major determinant in the pathogenesis of vitiligo. Methylcobalamin (MeCbl) is an activated form of vitamin B12 that regulates inflammatory factors, counters oxidative stress, and reduces apoptosis in many disease models. However, the specific mechanism of MeCbl repigmentation against vitiligo is unknown. In this study, we explored the effect of MeCbl on melanocytes following hydrogen peroxide (H2O2)-induced oxidative stress.MethodsWe established an oxidative stress model using the immortalized human normal melanocyte cell line PIG1. We used a Cell Counting Kit-8 (CCK-8) to detect drug cytotoxicity, and we measured the melanin content of cells using the NaOH method. Intracellular oxidative damage was assessed by flow cytometry and antioxidant enzyme detection kits. In addition, we assessed the presence of apoptosis by flow cytometry and Western blots. We explored the underlying mechanisms of MeCbl during oxidative stress in melanocytes by analyzing the results of experiments based on real-time quantitative polymerase chain reaction (RT-qPCR), Western blotting, and laser scanning confocal immunofluorescence microscopy. Finally, we repeated the experiments after applying an inhibitor to block the Nrf2 pathway.ResultsWe found that MeCbl treatment enhanced cell viability, increased melanin content, reduced intracellular reactive oxygen species (ROS) accumulation, increased the activities of antioxidant enzyme superoxide dismutase (SOD) and catalase (CAT), reduced melanocyte apoptosis, and up-regulated the expression of the Nrf2/HO-1 pathway. Moreover, the protective effects of MeCbl were significantly weakened after inhibiting the Nrf2/HO-1 pathway.ConclusionOur results indicate that MeCbl attenuated the H2O2-induced oxidative stress in melanocytes by activating the Nrf2/HO-1 pathway, this suggests that MeCbl may be an effective treatment against vitiligo.

Minocycline Impact on Redox Homeostasis of Normal Human Melanocytes HEMn-LP Exposed to UVA Radiation and Hydrogen Peroxide.

Minocycline is a semisynthetic tetracycline antibiotic. In addition to its antibacterial activity, minocycline shows many non-antibiotic, beneficial effects, including antioxidative action. The property is responsible, e.g., for anti-inflammatory, neuroprotective, and cardioprotective effects of the drug. However, long-term pharmacotherapy with minocycline may lead to hyperpigmentation of the skin. The reasons for the pigmentation disorders include the deposition of the drug and its metabolites in melanin-containing cells and the stimulation of melanogenesis. The adverse drug reaction raises a question about the influence of the drug on melanocyte homeostasis. The study aimed to assess the effect of minocycline on redox balance in human normal melanocytes HEMn-LP exposed to hydrogen peroxide and UVA radiation. The obtained results indicate that minocycline induced oxidative stress in epidermal human melanocytes. The drug inhibited cell proliferation, decreased the level of reduced thiols, and stimulated the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). The described changes were accompanied by an increase in the intracellular level of ROS. On the other hand, pretreatment with minocycline at the same concentrations increased cell viability and significantly attenuated the oxidative stress in melanocytes exposed to hydrogen peroxide and UVA radiation. Moreover, the molecular docking analysis revealed that the different influence of minocycline and other tetracyclines on CAT activity can be related to the location of the binding site.

Molecular and Biochemical Basis of Fluoroquinolones-Induced Phototoxicity-The Study of Antioxidant System in Human Melanocytes Exposed to UV-A Radiation.

Phototoxicity of fluoroquinolones is connected with oxidative stress induction. Lomefloxacin (8-halogenated derivative) is considered the most phototoxic fluoroquinolone and moxifloxacin (8-methoxy derivative) the least. Melanin pigment may protect cells from oxidative damage. On the other hand, fluoroquinolone–melanin binding may lead to accumulation of drugs and increase their toxicity to skin. The study aimed to examine the antioxidant defense system status in normal melanocytes treated with lomefloxacin and moxifloxacin and exposed to UV-A radiation. The obtained results demonstrated that UV-A radiation enhanced only the lomefloxacin-induced cytotoxic effect in tested cells. It was found that fluoroquinolones alone and with UV-A radiation decreased superoxide dismutase (SOD) activity and SOD1 expression. UV-A radiation enhanced the impact of moxifloxacin on hydrogen peroxide-scavenging enzymes. In turn, lomefloxacin alone increased the activity and the expression of catalase (CAT) and glutathione peroxidase (GPx), whereas UV-A radiation significantly modified the effects of drugs on these enzymes. Taken together, both analyzed fluoroquinolones induced oxidative stress in melanocytes, however, the molecular and biochemical studies indicated the miscellaneous mechanisms for the tested drugs. The variability in phototoxic potential between lomefloxacin and moxifloxacin may result from different effects on the antioxidant enzymes.

Paeoniflorin Resists H2O2-Induced Oxidative Stress in Melanocytes by JNK/Nrf2/HO-1 Pathway.

Paeoniflorin (PF) possesses multiple biological functions including anti-oxidization. PF is the major bioactive ingredient of total glycosides of paeony (TGP), which could promote re-pigmentation of vitiligo. The study was sought to investigate the effects and potential signaling pathways of PF on hydrogen peroxide (H2O2)-induced oxidative stress in melanocytes. The results showed that pretreatment with 50 µM PF significantly inhibited cell apoptosis, enhanced cell viability, and suppressed reactive oxygen species (ROS) accumulation by enhancing the productions of superoxide dismutase (SOD) and antioxidant enzymes catalase (CAT). Furthermore, PF activated c-Jun amino terminal kinase (JNK) and the nuclear factor E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway to counteract H2O2-induced oxidative damage in PIG1 and PIG3V. Taken together, our study firstly demonstrates that PF resists H2O2-induced oxidative stress in melanocytes probably by activating JNK/Nrf2/HO-1 signaling, suggesting a potential therapeutic application of PF on vitiligo.

Chlortetracycline and melanin biopolymer – The risk of accumulation and implications for phototoxicity: An in vitro study on normal human melanocytes

Tetracyclines belong to antimicrobial classes with the highest consumption in veterinary medicine and agriculture, which leads to the contamination of the environment and food products, as well as to antibiotic resistance and adverse drug reactions. Chloro-derivatives of tetracyclines are thought to be relatively more phototoxic than others and belong to the most frequently cited drugs as photosensitizers. Melanins are heterogenous biopolymers determining skin, hair and eye colour. They are biosynthesized in a multistep process in melanocytes. Melanins, besides photoprotective and antioxidant properties, may also contribute to adverse skin drug reactions, which involve e.g. hyperpigmentation disorders and phototoxic reactions. Furthermore, they have the ability to form a drug-melanin complex, which leads to deposition of the drug or its metabolites in pigmented tissues. The aim of the study was to examine the ability of chlortetracycline to form a complex with melanin, as well as the effect of the drug on viability, antioxidant defence system and melanogenesis in normal human epidermal melanocytes exposed to the UVA radiation. The obtained results show for the first time that chlortetracycline forms a complex with melanin polymers, which creates a possibility of the drug accumulation in pigmented tissues. A simultaneous exposition of normal melanocytes to chlortetracycline and to the UVA radiation decreases cell viability, proportionally to the drug concentration and the irradiation time. The phototoxic effect appears to be related to the induction of oxidative stress in melanocytes, mainly through an increase of SOD and a decrease of the CAT activity. Chlortetracycline itself does not influence the melanin content or the activity of tyrosinase. The UVA radiation appeared to be a conditioning factor stimulating melanogenesis, whereas the presence of the drug augmented this effect.

Kanamycin induces free radicals formation in melanocytes: An important factor for aminoglycosides ototoxicity.

Ototoxicity is well-documented but not fully understood undesirable side effect of aminoglycoside antibiotic, kanamycin. Kanamycin is capable of binding to melanin biopolymers-natural pigments of the skin, hair,and eyes. Melanin-producing cells, melanocytes, are also present in the inner ear and are known to be necessary for normal hearing. It was considered that melanin content in the inner ear may influence aminoglycoside-induced ototoxic effect. The impact of kanamycin on melanocytes homeostasis may thus play role in the antibiotic-induced ototoxic effect. Previously, we demonstrated that kanamycin disturbs homeostasis in light-pigmented melanocytes. To investigate if/how melanization contributes to this phenomenon, the study using in vitro model of dark-pigmented melanocytes is required. Spectrophotometric measurements and electron paramagnetic resonance (EPR) spectroscopy analysis were performed. Kanamycin induced aconcentration-dependent loss in HEMn-DP melanocytes viability. The value of IC 50 was estimated to be 5.0 mM. Modulation of the activity of analyzed antioxidant enzymes and increased production of free radicals as well as the decrease of the melanin content were observed. Our results confirmed that kanamycin generates oxidative stress in melanocytes. The increased level of free radicals caused by kanamycin may be responsible for the imbalance of antioxidant defense and the reduction of melanin content in melanocytes. The role of melanin in the mechanism of kanamycin-induced hearing impairment was discussed and the obtained results were compared with the previously demonstrated data concerning light-pigmented melanocytes.

Therapeutic management of vitiligo.

Affecting 0.5% of the world's population, vitiligo is an acquired skin disorder that poses major challenges in terms of dermatological care. Characterized by patchy depigmentation, the disease is frequently associated with cosmetic disfigurement and considerable psychological distress. The primary pathophysiological causes for the loss of functional melanocytes are thought to include genetic predisposition, autoimmune mechanisms, and oxidative stress. The present article highlights treatment recommendations contained in the European guidelines as well as those provided by recent reviews on vitiligo. Current therapeutic options are based on three approaches: (1) Regulation of the autoimmune response using topical and systemic immunomodulatory agents (corticosteroids and calcineurin inhibitors); (2) decrease in oxidative stress in melanocytes by means of topical and systemic antioxidants; and (3) activation of melanocyte regeneration using phototherapy (UVB in particular) and transplantation of pigment cells. In addition, patients should be educated in techniques for cosmetic camouflage. Following successful repigmentation, application of calcineurin inhibitors is recommended to prevent recurrences. Combination therapies of the aforementioned approaches are generally considered to be more successful than monotherapies. Early initiation of treatment is associated with a more favorable prognosis. Using the above treatment options, it may be possible to halt disease progression, stabilize depigmented lesions, and achieve repigmentation. Only in exceptional cases should permanent depigmentation be considered as a possible option. New insights into the pathogenesis of vitiligo will likely give rise to novel therapeutic approaches.

The nuclear factor (erythroid-derived 2)-like 2 (NRF2) antioxidant response promotes melanocyte viability and reduces toxicity of the vitiligo-inducing phenol monobenzone.

Vitiligo, characterised by progressive melanocyte death, can be initiated by exposure to vitiligo-inducing phenols (VIPs). VIPs generate oxidative stress in melanocytes and activate the master antioxidant regulator NRF2. While NRF2-regulated antioxidants are reported to protect melanocytes from oxidative stress, the role of NRF2 in the melanocyte response to monobenzone, a clinically relevant VIP, has not been characterised. We hypothesised that activation of NRF2 may protect melanocytes from monobenzone-induced toxicity. We observed that knockdown of NRF2 or NRF2-regulated antioxidants NQO1 and PRDX6 reduced melanocyte viability, but not viability of keratinocytes and fibroblasts, suggesting that melanocytes were preferentially dependent upon NRF2 activity for growth compared to other cutaneous cells. Furthermore, melanocytes activated the NRF2 response following monobenzone exposure and constitutive NRF2 activation reduced monobenzone toxicity, supporting NRF2's role in the melanocyte stress response. In contrast, melanocytes from individuals with vitiligo (vitiligo melanocytes) did not activate the NRF2 response as efficiently. Dimethyl fumarate-mediated NRF2 activation protected normal and vitiligo melanocytes against monobenzone-induced toxicity. Given the contribution of oxidant-antioxidant imbalance in vitiligo, modulation of this pathway may be of therapeutic interest.

Generation of hydroxyl radicals and singlet oxygen during oxidation of rhododendrol and rhododendrol-catechol.

The generation of hydroxyl radicals and singlet oxygen during the oxidation of 4-(4-hydroxyphenyl)-2-butanol (rhododendrol) and 4-(3,4-dihydroxyphenyl)-2-butanol (rhododendrol-catechol) with mushroom tyrosinase in a phosphate buffer (pH 7.4) was examined as the model for the reactive oxygen species generation via the two rhododendrol compounds in melanocytes. The reaction was performed in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin trap reagents for hydroxyl radical or 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP), an acceptor of singlet oxygen, and their electron spin resonances were measured. An increase in the electron spin resonances signal attributable to the adduct of DMPO reacting with the hydroxyl radical and that of 4-oxo-TEMP reacting with singlet oxygen was observed during the tyrosinase-catalyzed oxidation of rhododendrol and rhododendrol-catechol, indicating the generation of hydroxyl radical and singlet oxygen. Moreover, hydroxyl radical generation was also observed in the autoxidation of rhododendrol-catechol. We show that generation of intermediates during tyrosinase-catalyzed oxidation of rhododendrol enhances oxidative stress in melanocytes.

Distinct Role of Sesn2 in Response to UVB-Induced DNA Damage and UVA-Induced Oxidative Stress in Melanocytes.

Ultraviolet (UV) radiation, including both UVB and UVA irradiation, is the major risk factor for causing skin cancer including melanoma. Recently, we have shown that Sesn2, a member of the evolutionarily conserved stress-inducible protein family Sestrins (Sesn), is upregulated in human melanomas as compared to melanocytes in normal human skin, suggesting an oncogenic role of Sesn2. However, the role of Sesn2 in UVB and UVA response is unknown. Here, we demonstrated that both UVB and UVA induce Sesn2 upregulation in melanocytes and melanoma cells. UVB induces Sesn2 expression through the p53 and AKT3 pathways. Sesn2 negatively regulates UVB-induced DNA damage repair. In comparison, UVA induces Sesn2 upregulation through mitochondria but not Nrf2. Sesn2 ablation increased UVA-induced Nrf2 induction and inhibits UVA-induced ROS production, indicating that Sesn2 acts as an upstream regulator of Nrf2. These findings suggest previously unrecognized mechanisms in melanocyte response to UVB and UVA irradiation and potentially in melanoma formation.

Melanocyte Regeneration in Vitiligo Requires WNT beneath their Wings

Melanocytes in patients with vitiligo possess intrinsic abnormalities that contribute to its pathogenesis. In this issue, Regazzetti, et al. report that CXCL10 expression reflects subtle inflammation in normal-appearing skin but not in stable depigmented lesions, supporting the hypothesis that melanocytes themselves initiate autoimmune inflammation prior to clinically evident disease. In addition, they find that oxidative stress in melanocytes impairs WNT signaling and that targeting this pathway induces melanoblast differentiation. Thus, activating the WNT pathway may serve as an adjunctive strategy to support repigmentation in patients with vitiligo.

Selenium for the Prevention of Cutaneous Melanoma

The role of selenium (Se) supplementation in cancer prevention is controversial; effects often depend on the nutritional status of the subject and on the chemical form in which Se is provided. We used a combination of in vitro and in vivo models to study two unique therapeutic windows for intervention in the process of cutaneous melanomagenisis, and to examine the utility of two different chemical forms of Se for prevention and treatment of melanoma. We studied the effects of Se in vitro on UV-induced oxidative stress in melanocytes, and on apoptosis and cell cycle progression in melanoma cells. In vivo, we used the HGF transgenic mouse model of UV-induced melanoma to demonstrate that topical treatment with l-selenomethionine results in a significant delay in the time required for UV-induced melanoma development, but also increases the rate of growth of those tumors once they appear. In a second mouse model, we found that oral administration of high dose methylseleninic acid significantly decreases the size of human melanoma xenografts. Our findings suggest that modestly elevation of selenium levels in the skin might risk acceleration of growth of incipient tumors. Additionally, certain Se compounds administered at very high doses could have utility for the treatment of fully-malignant tumors or prevention of recurrence.

Vitiligo-Inducing Phenols Activate the Unfolded Protein Response in Melanocytes Resulting in Upregulation of IL6 and IL8

Vitiligo is characterized by depigmented skin patches due to loss of epidermal melanocytes. Oxidative stress may play a role in vitiligo onset, while autoimmunity contributes to disease progression. In this study we sought to identify mechanisms that link disease triggers and spreading of lesions. A hallmark of melanocytes at the periphery of vitiligo lesions is dilation of the endoplasmic reticulum (ER). We hypothesized that oxidative stress results in redox disruptions that extend to the ER, causing accumulation of misfolded peptides, which activates the unfolded protein response (UPR). We used 4-tertiary butyl phenol (4-TBP) and monobenzyl ether of hydroquinone (MBEH), known triggers of vitiligo. We show that expression of key UPR components, including the transcription factor X-box binding protein 1 (XBP1), are increased following exposure of melanocytes to phenols. XBP1 activation increases production of immune mediators interleukin-6 (IL6) and IL8. Co-treatment with XBP1 inhibitors reduced IL6 and IL8 production induced by phenols, while over-expression of XBP1 alone increased their expression. Thus, melanocytes themselves produce cytokines associated with activation of an immune response following exposure to chemical triggers of vitiligo. These results expand our understanding of the mechanisms underlying melanocyte loss in vitiligo and pathways linking environmental stressors and autoimmunity.

Redox-Dependent Translocation of p53 to Mitochondria or Nucleus in Human Melanocytes after UVA- and UVB-Induced Apoptosis

The p53 protein is an important transcription factor and tumor suppressor that is induced in response to many forms of cellular stress. UVA irradiation of human melanocytes caused generation of reactive oxygen species, which altered the intracellular redox balance and was accompanied by translocation of p53 to mitochondria. In contrast, UVB did not affect the redox status and p53 was translocated to the nucleus. Although different intracellular location of p53, UVA/B induced apoptosis through the intrinsic pathway detected as translocation of Bax to mitochondria, release of cytochrome c, and activation of caspases. These events were all prevented by inhibition of p53 with pifithrin-alpha. Furthermore, inhibition of p53 prevented lysosomal membrane permeabilization, detected as translocation of cathepsins to the cytosol, after UVB exposure, whereas UVA-induced lysosomal release was unaffected by inhibition of p53. In control cells, p53 coimmunoprecipitated with the antiapoptotic proteins Bcl-2 and Bcl-x(L) and upon UVA exposure the interaction was replaced by binding to the proapoptotic proteins Bax, Noxa, and Puma. Our findings suggest that UVA-induced apoptosis is caused by extensive oxidative damage leading to p53-regulated mitochondrial release, whereas UVB induces DNA damage and apoptosis signaling upstream of lysosomal membrane permeabilization.