Autophagy induced by resveratrol suppresses α-MSH-induced melanogenesis

Antioxidant Potential-Rich Betel Leaves (Piper betle L.) Exert Depigmenting Action by Triggering Autophagy and Downregulating MITF/Tyrosinase In Vitro and In Vivo

Each individual has a unique skin tone based on the types and quantities of melanin pigment, and oxidative stress is a key element in melanogenesis regulation. This research sought to understand the in vitro and in vivo antioxidant and depigmenting properties of betel leaves (Piper betle L.) extract (PBL) and the underlying mechanism. Ethyl acetate fractions of PBL (PBLA) demonstrated excellent phenolic content (342 ± 4.02 mgGAE/g) and strong DPPH, ABTS radicals, and nitric oxide (NO) scavenging activity with an IC₅₀ value of 41.52 ± 1.02 μg/mL, 45.60 ± 0.56 μg/mL, and 51.42 ± 1.25 μg/mL, respectively. Contrarily, ethanolic extract of PBL (PBLE) showed potent mushroom, mice, and human tyrosinase inhibition activity (IC₅₀ = 7.72 ± 0.98 μg/mL, 20.59 ± 0.83 μg/mL and 24.78 ± 0.56 μg/mL, respectively). According to gas chromatography-mass spectrometry, PBL is abundant in caryophyllene, eugenol, O-eugenol, 3-Allyl-6-methoxyphenyl acetate, and chavicol. An in vitro and in vivo investigation showed that PBLE suppressed tyrosinase (Tyr), tyrosinase-related protein-1 and -2 (Trp-1 and Trp-2), and microphthalmia-associated transcription factors (MITF), decreasing the formation of melanin in contrast to the untreated control. PBLE reduced the cyclic adenosine monophosphate (cAMP) response to an element-binding protein (CREB) phosphorylation by preventing the synthesis of cAMP. Additionally, it activates c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (p38), destroying Tyr and MITF and avoiding melanin production. Higher levels of microtubule-associated protein-light chain 3 (LC3-II), autophagy-related protein 5 (Atg5), Beclin 1, and lower levels of p62 demonstrate that PBLE exhibits significant anti-melanogenic effects via an autophagy-induction mechanism, both in vitro and in vivo. Additionally, PBLE significantly reduced the amount of lipid peroxidation while increasing the activity of several antioxidant enzymes in vivo, such as catalase, glutathione, superoxide dismutase, and thioredoxin. PBLE can therefore be employed in topical formulations as a potent skin-whitening agent.

The Function of Autophagy as a Regulator of Melanin Homeostasis

Melanosomes are melanocyte-specific organelles that protect cells from ultraviolet (UV)-induced deoxyribonucleic acid damage through the production and accumulation of melanin and are transferred from melanocytes to keratinocytes. The relatively well-known process by which melanin is synthesized from melanocytes is known as melanogenesis. The relationship between melanogenesis and autophagy is attracting the attention of researchers because proteins associated with autophagy, such as WD repeat domain phosphoinositide-interacting protein 1, microtubule-associated protein 1 light chain 3, autophagy-related (ATG)7, ATG4, beclin-1, and UV-radiation resistance-associated gene, contribute to the melanogenesis signaling pathway. Additionally, there are reports that some compounds used as whitening cosmetics materials induce skin depigmentation through autophagy. Thus, the possibility that autophagy is involved in the removal of melanin has been suggested. To date, however, there is a lack of data on melanosome autophagy and its underlying mechanism. This review highlights the importance of autophagy in melanin homeostasis by providing an overview of melanogenesis, autophagy, the autophagy machinery involved in melanogenesis, and natural compounds that induce autophagy-mediated depigmentation.

Lipopolysaccharide reduces melanin synthesis in vitiligo melanocytes by regulating autophagy

Vitiligo is an autoimmune-related disease with a complex aetiology that involves innate immunity. Toll-like receptors (TLRs) are important parts of innate immunity and are related to a variety of autoimmune diseases, including vitiligo, through an unknown mechanism. In this study, we found that the TLR4 gene expression was increased in blood samples of patients with advanced stage vitiligo, and then we evaluated the effect of TLR4 ligand lipopolysaccharide (LPS) on melanin synthesis in a vitiligo melanocyte cell line PIG3V and along with its mechanism. LPS suppressed melanin synthesis, downregulated the expression of melanin synthesis-related proteins, and activated autophagy in vitiligo melanocytes. Inhibiting autophagy with 3-methyladenine or chloroquine blocked these effects. This suggests that LPS inhibits skin pigmentation by modulating autophagy, thus providing novel insights into the pathogenesis of vitiligo.

Autophagy in skin barrier and immune-related skin diseases

Autophagy is a process which is highly conserved in eukaryotes to degrade or recycle cytoplasmic components through lysosomes to maintain cellular homeostasis. Recent studies have shown that autophagy also plays critical roles in cell apoptosis, inflammation, pathogen clearance, and so on under stressed conditions and thereby has been linked to a variety of human disorders. The skin is the largest organ of the body and serves as the first line of defense against environmental insult. Skin as a nutrient-poor environment requires recycling of limited resources via the autophagy machinery to maintain homeostasis. Therefore, dysregulation of autophagy has been linked to skin diseases. In this review, we describe the molecular machinery and regulation of autophagy, discuss its role in keratinocytes and skin barrier, skin immune cells, and immune-related skin diseases including autoimmune skin disorders, allergic skin diseases, infectious skin disorders, and antitumor immunity against skin tumor. Finally, we highlight the potential of autophagy as a therapeutic target for immune-related skin diseases, and delivery of autophagy-related molecules (such as inducers, inhibitors, or nucleic acid molecules) by virtue of physical materials (such as nanoparticles) or biological materials (such as peptides) to skin topically may obtain clinical benefits in immune-related skin diseases. Moreover, developing autophagy-related gene product-based biomarkers may be promising to diagnose immune-related skin diseases.

Imiquimod induced vitiligo-like lesions-A consequence of modified melanocyte function

INTRODUCTION

Imiquimod plays an important role in the management of condyloma and premalignant lesions. Successively, an increase of hypopigmented lesions following imiquimod application has been reported. However, the mechanisms of imiquimod on melanocytes remain unclear. This study was designed to assess the effect of Imiquimod on the functions of melanocytes in vitro.

METHODS

Primary cultured melanocytes were isolated from normal control skin tissue. After incubation with imiquimod for 48 h in vitro, cell viability was analyzed by cell counting kit-8 assay. Apoptosis was detected using the Annexin V-fluorescein-5-isothiocyanate flow cytometry assay. Melanin content and tyrosinase activity in melanocytes were measured by colorimetric method and the modified dopachrome method. The production of inflammatory cytokine interleukin 8 (IL-8), IL-6, and soluble ICAM-1 (soluble Intercellular Adhesion Molecule-1[sICAM-1]) in melanocytes were measured by enzyme-linked immunosorbent assay (ELISA). Toll-like receptor 7 (TLR7), toll-like receptor 9 (TLR9) protein, and autophagy-related proteins microtubule-associated protein 1A/1B-light chain 3 (LC3-II), p62, mechanistic target of rapamycin (mTOR), and Atg5 were assessed using western blot analysis.

RESULTS

Imiquimod significantly inhibited the activity of tyrosinase activity and decreased melanin content in melanocytes and significantly increased apoptosis and IL-6, IL-8, and sICAM-1 production in melanocytes. Moreover, the expression of TLR7 and TLR9 proteins were significantly increased, and the expression of mTOR, p62 protein were markedly decreased, but the expression of LC3II/I and Atg5 protein were significantly increased in melanocytes after incubating with imiquimod.

CONCLUSIONS

This study shows that imiquimod directly inhibits melanogenesis and increases melanocyte apoptosis rates. These effects combined with the upregulation of TLR7 and TLR9 together with increased autophagy activity and inflammatory cytokines production, might be the main reasons leading to hypopigmented lesions after imiquimod application.

The Role of Autophagy in Skin Fibroblasts, Keratinocytes, Melanocytes, and Epidermal Stem Cells

Human skin acts as a barrier to protect our bodies from UV rays and external pathogens and to prevent water loss. Phenotypes of aging, or natural aging due to chronic damage, include wrinkles and the reduction of skin thickness that occur because of a loss of skin cell function. The dysregulation of autophagy, a lysosome-related degradation pathway, can lead to cell senescence, cancer, and various human diseases due to abnormal cellular homeostasis. Here, we discuss the roles and molecular mechanisms of autophagy involved in the anti-aging effects of autophagy and the relationship between autophagy and aging in skin cells.

The anti-melanogenic effects of ellagic acid through induction of autophagy in melanocytes and suppression of UVA-activated α-MSH pathways via Nrf2 activation in keratinocytes

Ellagic acid (EA) is a natural phenol antioxidant in different fruits, vegetables, and nuts. As a copper iron chelator from the tyrosinase enzyme's active site, EA was reported to inhibit melanogenesis in melanocytes. Here, we demonstrated the anti-melanogenic mechanisms of EA through autophagy induction in melanoma B16F10 cells and the role of Nrf2 and UVA (3 J/cm²)-activated α-melanocyte stimulating hormone (α-MSH) pathways in keratinocyte HaCaT cells. In vitro data showed that EA suppressed the tyrosinase activity and melanogenesis by suppressing cAMP-mediated CREB and MITF signaling mechanisms in α-MSH-stimulated B16F10 cells. ERK, JNK, and AKT pathways were involved in this EA-regulated MITF downregulation. Notably, EA induced autophagy in B16F10 cells was evidenced from increased LC3-II accumulation, p62/SQSTM1 activation, ATG4B downregulation, acidic vesicular organelle (AVO) formation, PI3K/AKT/mTOR inhibition, and Beclin-1/Bcl-2 dysregulation. Interestingly, 3-MA (an autophagy inhibitor) pretreatment or LC3 silencing (siRNA transfection) of B16F10 cells significantly reduced EA-induced anti-melanogenic activity. Besides this, in UVA-irradiated keratinocyte HaCaT cells, EA suppressed ROS production and α-MSH generation. Moreover, EA mediated the activation and nuclear translocation of Nrf2, leading to antioxidant γ-GCLC, HO-1, and NQO-1 protein expression in HaCaT cells. However, Nrf2 knockdown has significantly impaired this effect, and there was an uncontrolled ROS generation following UVA irradiation. JNK, PKC, and ROS pathways were involved in the activation of Nrf2 in HaCaT cells. In vivo experiments using the zebrafish model confirmed that EA inhibited tyrosinase activity and endogenous pigmentation. In conclusion, ellagic acid is an effective skin-whitening agent and might be used as a topical applicant.

Anti-Melanogenic Effects of Ethanol Extracts of the Leaves and Roots of Patrinia villosa (Thunb.) Juss through Their Inhibition of CREB and Induction of ERK and Autophagy

Patrinia villosa (Thunb.) Juss is a traditional herb commonly used in East Asia including Korea, Japan, and China. It has been administered to reduce and treat inflammation in Donguibogam, Korea. The mechanism for its anti-inflammatory effects has already been reported. In this study, we confirmed the efficacy of Patrinia villosa (Thunb.) Juss ethanol extract (Pv-EE) for inducing autophagy and investigate its anti-melanogenic properties. Melanin secretion and content were investigated using cells from the melanoma cell line B16F10. Pv-EE inhibited melanin in melanogenesis induced by α-melanocyte-stimulating hormone (α-MSH). The mechanism of inhibition of Pv-EE was confirmed by suppressing the mRNA of microphthalmia-associated transcription factor (MITF), decreasing the phosphorylation level of CREB, and increasing the phosphorylation of ERK. Finally, it was confirmed that Pv-EE induces autophagy through the autophagy markers LC3B and p62, and that the anti-melanogenic effect of Pv-EE is inhibited by the autophagy inhibitor 3-methyl adenine (3-MA). These results suggest that Pv-EE may be used as a skin protectant due to its anti-melanin properties including autophagy.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

1-phenyl 2-thiourea (PTU) activates autophagy in zebrafish embryos

1-phenyl 2-thiourea (PTU) is a Tyr (tyrosinase) inhibitor that is extensively used to block pigmentation and improve optical transparency in zebrafish (Danio rerio) embryo. Here, we reported a previously undescribed effect of PTU on macroautophagy/autophagy in zebrafish embryos. Upon 0.003% PTU treatment, aberrant autophagosome and autolysosome formation, accumulation of lysosomes, and elevated autophagic flux were observed in various tissues and organs of zebrafish embryos, such as skin, brain, and muscle. Similar to PTU treatment, autophagic activation and lysosomal accumulation were also observed in the somatic tyr mutant zebrafish embryos, which suggest that Tyr inhibition may contribute to PTU-induced autophagic activation. Furthermore, we demonstrated that autophagy contributes to pigmentation inhibition, but is not essential to the PTU-induced pigmentation inhibition. With the involvement of autophagy in a wide range of physiological and pathological processes and the routine use of PTU in zebrafish research of autophagy-related processes, these observations raise a novel concern in autophagy-related studies using PTU-treated zebrafish embryos.Abbreviations: 3-MA: 3-methyladenine; Atg: autophagy-related; BSA: bovine serum albumin; CHT: caudal hematopoietic tissue; CQ: chloroquine; GFP: green fluorescent protein; hpf: hour-post-fertilization; Map1lc3/Lc3: microtubule-associated protein 1 light chain 3; NGS: normal goat serum; PtdIns3K: class III phosphatidylinositol 3-kinase; PTU: 1-phenyl 2-thiourea; RFP: red fluorescent protein; Sqstm1: sequestosome 1; tyr: tyrosinase.

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.

Role of Resveratrol in Regulating Cutaneous Functions

Protective role of the skin is against external insults and maintenance of electrolyte homeostasis of the body. Cutaneous dysfunction can account for the development of both cutaneous and systemic disorders. Thus, improvements in cutaneous functions can benefit a number of extracutaneous and cutaneous functions. Resveratrol, a natural ingredient, displays multiple benefits for various systems/organs, including the skin. The benefits of resveratrol for cutaneous functions include stimulation of keratinocyte differentiation and antimicrobial peptide expression, inhibition of keratinocyte proliferation and cutaneous inflammation, UV protection, anticancer, antiaging, and inhibition of melanogenesis. The mechanisms of action of resveratrol include activation of sirtuin 1 and nuclear factor erythroid 2-related factor 2, and inhibition of mitogen-activated protein kinase signaling. Evidence suggests that topical resveratrol could be a valuable alternative not only for daily skin care, but also for the prevention and treatment of various cutaneous disorders. This review summarizes the benefits of resveratrol for cutaneous functions.

Roles of inflammation factors in melanogenesis (Review)

The occurrence of hyperpigmentation or hypopigmentation after inflammation is a common condition in dermatology and cosmetology. Since the exact mechanism of its occurrence is not yet known, prevention and treatment are troublesome. Previous studies have confirmed that α-melanocyte-stimulating hormone, stem cell factor and other factors can promote melanogenesis-related gene expression through the activation of signaling pathways. Recent studies have revealed that a variety of inflammatory mediators can also participate in the regulation of melanogenesis in melanocytes. In this review, we summarized that interleukin-18, interleukin-33, granulocyte-macrophage colony stimulating factor, interferon-γ, prostaglandin E2 have the effect of promoting melanogenesis, while interleukin-1, interleukin-4, interleukin-6, interleukin-17 and tumor necrosis factor can inhibit melanogenesis. Further studies have found that these inflammatory factors may activate or inhibit melanogenesis-related signaling pathways (such as protein kinase A and mitogen activated protein kinase) by binding to corresponding receptors, thereby promoting or inhibiting the expression of melanogenesis-related genes and regulating skin pigmentation processes. This suggests that the development of drugs or treatment methods from the perspective of regulating inflammation can provide new ideas and new targets for the treatment of pigmented dermatosis. This review outlines the current understanding of the inflammation factors' roles in melanogenesis.

Human Skin Lightening Efficacy of Resveratrol and Its Analogs: From in Vitro Studies to Cosmetic Applications

Antioxidants are deemed useful in controlling oxidative stress associated with extrinsic skin aging and pigmentation disorders. Resveratrol is a polyphenol compound found in many edible plants such as Vitis vinifera, and its inhibitory effects on the catalytic activity, gene expression, and posttranslational modifications of tyrosinase, a key enzyme in the melanin biosynthetic pathway, provide a mechanistic basis for its antimelanogenic effects seen in melanocytic cells, three-dimensionally reconstituted skin models, and in vivo animal models. As a potent antioxidant and a modulator of nuclear factor erythroid 2-related factor 2 (Nrf2), and sirtuin 1, resveratrol can also regulate multiple signaling pathways associated with inflammation and premature aging. Recent clinical studies have supported the efficacy of resveratrol and its analogs, such as resveratryl triacetate (RTA) and resveratryl triglycolate (RTG), in human skin lightening and antiaging. These findings suggest that resveratrol and its analogs are potentially useful as skin lightening and antiaging agents in cosmetics.

Antiphotoaging and Antimelanogenic Effects of Penthorum chinense Pursh Ethanol Extract due to Antioxidant- and Autophagy-Inducing Properties

Ethnopharmacological Relevance. Penthorum chinense Pursh (Penthoraceae) is a traditional herbal plant that has been used in China for the treatment of jaundice, cholecystitis, edema, and infectious hepatitis. In addition, the Korea Medicinal Plant Dictionary states that Penthorum chinense Pursh can be used to treat contusions and skin bruises by improving blood flow. Recent studies have shown that Penthorum chinense Pursh ethanol extract (Pc-EE) exhibits strong antioxidant effects. In this study, we examined the effects of Pc-EE on UVB-induced or H₂O₂-induced oxidative stress, as well as its antimelanogenic properties. Cell viability, matrix metalloproteinase (MMP) expression, cyclooxygenease-2 (COX-2), and interleukin-6 (IL-6) expression and moisturizing factors were investigated in keratinocytes. Collagen synthesis induction was measured in HEK293T cells. For melanogenesis, the effects of Pc-EE on melanin content and tyrosinase activity were measured. Additionally, the antimelanogenic- and autophagy-inducing activities of Pc-EE were examined using immunoblotting and confocal microscopy. Pc-EE protected HaCaT cells against death from UVB irradiation- or H₂O₂-induced oxidative stress. Pc-EE increased the promoter activity of the type 1 procollagen gene Col1A1 and decreased the expression of MMPs, COX-2, IL-6, and hyaluronidase induced by UVB irradiation- or H₂O₂-induced oxidative stress. Pc-EE showed a strong antioxidant effect in the DPPH assay. In α-melanocyte-stimulating hormone- (α-MSH-) stimulated B16F10 cells, Pc-EE reduced melanin production, decreased tyrosinase expression and microphthalmia-associated transcription factor (MITF) protein levels, and decreased the phosphorylation levels of p38 and JNK. In HEK293T cells, Pc-EE promoted the expression of GFP-LC3B. In B16F10 cells, the LC3B and melanin contents were reduced by Pc-EE and were restored by the autophagy inhibitor 3-methyladenine (3-MA). These results suggest that Pc-EE can be used as a skin protection agent due to its antiapoptotic, antiaging, anti-inflammatory, and antimelanogenic properties.

Resveratrol as a Multifunctional Topical Hypopigmenting Agent

Melanin is produced in melanocytes and stored in melanosomes, after which it is transferred to keratinocytes and, thus, determines skin color. Despite its beneficial sun-protective effects, abnormal accumulation of melanin results in esthetic problems. A range of topical hypopigmenting agents have been evaluated for their use in the treatment of pigmentary disorders with varying degrees of success. Hydroquinone (HQ), which competes with tyrosine, is the main ingredient in topical pharmacological agents. However, frequent occurrence of adverse reactions is an important factor that limits its use. Thus, efforts to discover effective topical hypopigmenting agents with less adverse effects continue. Here, we describe the potential of resveratrol to function as an effective hypopigmenting agent based on its mechanism of action. Resveratrol is not only a direct tyrosinase inhibitor but an indirect inhibitor as well. Additionally, it can affect keratinocytes, which regulate the function of melanocytes. Resveratrol regulates the inflammatory process of keratinocytes and protects them from oxidative damage. In this way, it prevents keratinocyte-induced melanocyte stimulation. Furthermore, it has a rescuing effect on the stemness of interfollicular epidermal cells that can repair signs of photoaging in the melasma, a typical pigmentary skin disorder. Overall, resveratrol is a promising potent hypopigmenting agent.

Unraveling the human protein atlas of metastatic melanoma in the course of ultraviolet radiation-derived photo-therapy

To explore the photo-therapeutic capacity of UV radiation in solid tumors, we herein employed an nLC-MS/MS technology to profile the proteomic landscape of irradiated WM-266-4 human metastatic-melanoma cells. Obtained data resulted in proteomic catalogues of 5982 and 7280 proteins for UVB- and UVC-radiation conditions, respectively, and indicated the ability of UVB/C-radiation forms to eliminate metastatic-melanoma cells through induction of synergistically operating programs of apoptosis and necroptosis. However, it seems that one or more WM-266-4 cell sub-populations may escape from UV-radiation's photo-damaging activity, acquiring, besides apoptosis tolerance, an EMT phenotype that likely offers them the advantage of developing resistance to certain chemotherapeutic drugs. Low levels of autophagy may also critically contribute to the selective survival and growth of UV-irradiated melanoma-cell escapers. These are the cells that must be systemically targeted with novel therapeutic schemes, like the one of UV radiation and Irinotecan herein suggested to be holding strong promise for the effective treatment of metastatic-melanoma patients. Given the dual nature of UV radiation to serve as both anti-tumorigenic and tumorigenic agent, all individuals being subjected to risk factors for melanoma development have to be appropriately informed and educated, in order to integrate the innovative PPPM concept in their healthcare-sector management.

SIGNIFICANCE

This study reports the application of nLC-MS/MS technology to deeply map the proteomic landscape of UV-irradiated human metastatic-melanoma cells. Data bioinformatics processing led to molecular-network reconstructions that unearthed the dual nature of UV radiation to serve as both anti-tumorigenic and tumorigenic factor in metastatic-melanoma cellular environments. Our UV radiation-derived "photo-proteomic" atlas may prove valuable for the identification of new biomarkers and development of novel therapies for the disease. Given that UV radiation represents a major risk factor causing melanoma, a PPPM-based life style and clinical practice must be embraced by all individuals being prone to disease's appearance and expansion.

Dysregulation of autophagy in melanocytes contributes to hypopigmented macules in tuberous sclerosis complex

BACKGROUND

Tuberous sclerosis complex (TSC) gene mutations lead to constitutive activation of the mammalian target of rapamycin (mTOR) pathway, resulting in a broad range of symptoms. Hypopigmented macules are the earliest sign. Although we have already confirmed that topical rapamycin treatment (an mTOR inhibitor) protects patients with TSC against macular hypopigmentation, the pathogenesis of such lesions remains poorly understood.

OBJECTIVE

Recently emerging evidence supports a role for autophagy in skin pigmentation. Herein, we investigated the impact of autophagic dysregulation on TSC-associated hypopigmentation.

METHODS

Skin samples from 10 patients with TSC, each bearing characteristic hypopigmented macules, and 6 healthy donors were subjected to immunohistochemical and electron microscopic analyses. In addition, TSC2-knockdown (KD) was investigated in human epidermal melanocytes by melanin content examination, real-time PCR, western blotting analyses, and intracellular immunofluorescence staining.

RESULTS

Activation of the mTOR signaling pathway decreased melanocytic pigmentation in hypopigmented macules of patients with TSC and in TSC2-KD melanocytes. In addition, LC3 expression (a marker of autophagy) and autophagosome counts increased, whereas, intracellular accumulation of autophagic degradative substrates (p62 and ubiquitinated proteins) was evident in TSC2-KD melanocytes. Furthermore, depigmentation in TSC2-KD melanocytes was accelerated by inhibiting autophagy (ATG7-KD or bafilomycin A1-pretreatment) and was completely reversed by induction of autophagy via mTOR-dependent (rapamycin) or mTOR-independent (SMER28) exposure. Finally, dysregulation of autophagy, marked by increased LC3 expression and accumulation of ubiquitinated proteins, was also observed in melanocytes of TSC-related hypopigmented macules.

CONCLUSION

Our data demonstrate that melanocytes of patients with TSC display autophagic dysregulation, which thereby reduced pigmentation, serving as the basis for the hypomelanotic macules characteristic of TSC.

Light-emitting diode 585nm photomodulation inhibiting melanin synthesis and inducing autophagy in human melanocytes

BACKGROUND

Melasma is a common hyperpigmentation skin disease on face. Light-emitting diode (LED) photomodulation (585nm) is reported to be effective for the treatment of melasma. However, whether and how LED photomodulation would influence melanogenesis of human epidermal melanocytes (HEMs) is unknown.

OBJECTIVE

To evaluate the effects of LED photomodulation (585nm) on melanogenesis in HEMs.

METHODS

HEMs were irradiated with fluences of 0, 5, 10 and 20J/cm² 585nm LED light. After 5-day treatment, cell viability was analyzed by CCK-8 assay, and apoptosis was assessed by Annexin V APC assay. Melanin content and tyrosinase activity were measured by spectrophotometer. Melanosome stage and autophagosomes were determined under transmission electron microscope (TEM). The formation of autophagic punctate structures was observed under confocal microscope. RT-PCR and western blotting were used to assess the expression of relative mRNA and protein levels.

RESULTS

Yellow light LED 585nm had no effects on HEMs cell viability and apoptosis. Treatment with LED 585nm from 5J/cm² to 20J/cm² inhibited melanosome maturation, decreased melanin content and tyrosinase activity. Inhibition was accompanied by the decreased expression of tyrosinase (TYR), tyrosinase-related protein-1 (TRP-1) and microphthalmia-associated transcription factor (MITF) on both mRNA and protein levels. Autophagosomes were observed under TEM. Autophagic punctate structures of microtubule-associated protein light chain 3 (LC3) proteins were induced by LED 585nm light. The configuration change of LC3 from LC3-I to LC3-II, and the degradation of p62 protein were observed after LED 585nm. Furthermore, we also revealed that the anti-melanogenic effect of LED 585nm photomodulation was reversed by 3-Methyladenine (3-MA), which inhibits autophagy by blocking autophagosome formation via the inhibition of type III Phosphatidylinositol 3-kinases (PI-3K).

CONCLUSIONS

Our finding demonstrated that LED photomodulation with 585nm wavelength suppressed melanin content in HEMs, and the effect was caused by its dose-dependent inhibition on melanogenesis and the induction of HEMs autophagy. This may provide new insights into the efficacy of LED photomodulation in the treatment of hyperpigmentation disorders.

Recent development of signaling pathways inhibitors of melanogenesis

Human skin, eye and hair color rely on the production of melanin, depending on its quantity, quality, and distribution, Melanin plays a monumental role in protecting the skin against the harmful effect of ultraviolet radiation and oxidative stress from various environmental pollutants. However, an excessive production of melanin causes serious dermatological problems such as freckles, solar lentigo (age spots), melasma, as well as cancer. Hence, the regulation of melanin production is important for controlling the hyper-pigmentation. Melanogenesis, a biosynthetic pathway to produce melanin pigment in melanocyte, involves a series of intricate enzymatic and chemical catalyzed reactions. Several extrinsic factors include ultraviolet radiation and chemical drugs, and intrinsic factors include molecules secreted by surrounding keratinocytes or melanocytes, and fibroblasts, all of which regulate melanogenesis. This article reviews recent advances in the development of melanogenesis inhibitors that directly/indirectly target melanogenesis-related signaling pathways. Efforts have been made to provide a description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Arginase-2, a miR-1299 target, enhances pigmentation in melasma by reducing melanosome degradation via senescence-induced autophagy inhibition

Expression profiles revealed miR-1299 downregulation concomitant with arginase-2 (ARG2) upregulation in hyperpigmented skin of melasma patients. Opposite regulation of tyrosinase and PMEL17 by miR-1299 and inverse relationship between miR-1299 and ARG2 expression denoted a role of miR-1299 in pigmentation with ARG2 as a miR-1299 target. ARG2 overexpression or knock-down in keratinocytes, the main source of ARG2 in epidermis, positively regulated tyrosinase and PMEL17 protein levels, but not mRNA levels or melanosome transfer. ARG2 overexpression in keratinocytes reduced autophagy equivalent to 3-MA, an autophagy inhibitor which also increased tyrosinase and PMEL17 protein levels, whereas ARG2 knock-down induced opposite results. Autophagy inducer rapamycin reduced ARG2-increased tyrosinase and PMEL17 protein levels. Also, autophagy was reduced in late passage-induced senescent keratinocytes showing ARG2 upregulation. ARG2, but not 3-MA, stimulated keratinocyte senescence. These results suggest that ARG2 reduces autophagy in keratinocytes by stimulating cellular senescence, resulting in skin pigmentation by reducing degradation of transferred melanosomes.

Dysfunction of Autophagy: A Possible Mechanism Involved in the Pathogenesis of Vitiligo by Breaking the Redox Balance of Melanocytes

Vitiligo is a common chronic acquired pigmentation disorder characterized by loss of functional melanocytes from the epidermis and follicular reservoir. Among multiple hypotheses which have been proposed in the pathogenesis of vitiligo, autoimmunity and oxidative stress-mediated toxicity in melanocytes remain most widely accepted. Macroautophagy is a lysosome-dependent degradation pathway which widely exists in eukaryotic cells. Autophagy participates in the oxidative stress response in many cells, which plays a protective role in preventing damage caused by oxidative stress. Recent studies have enrolled autophagy as an important regulator in limiting damage caused by UV light and lipid oxidation, keeping oxidative stress in a steady state in epidermal keratinocytes and maintaining normal proliferation and aging of melanocytes. Impairment of autophagy might disrupt the antioxidant defense system which renders melanocytes to oxidative insults. These findings provide supportive evidence to explore new ideas of the pathogenesis of vitiligo and other pigmentation disorders.

Depigmentation of α-melanocyte-stimulating hormone-treated melanoma cells by β-mangostin is mediated by selective autophagy

Melanogenesis is a key pathway for the regulation of skin pigmentation and the development of skin-lightening/skin-whitening drugs or cosmetics. In this study, we found that β-mangostin from seedcases of Garcinia mangostana inhibited α-melanocyte-stimulating hormone (α-MSH)-mediated melanogenesis in B16F10 melanoma cells and a three-dimensional human skin model. β-Mangostin significantly inhibited the protein level of tyrosinase induced by α-MSH in UPS (ubiquitin proteasome system)-independent and lysosome-dependent manner. The inhibition of autophagy by 3-methyladenine treatment or ATG5 knockdown effectively recovered premelanosome protein as well as tyrosinase degraded by the β-mangostin treatment. However, rapamycin, a representative non-selective autophagy inducer, triggered autophagy in α-MSH-stimulated cells, which was characterized by a considerable decrease in p62, but it was unable to inhibit melanogenesis. Melanosome-engulfing autophagosomes were observed using transmission electron microscopy. Furthermore, previously formed melanin could be degraded effectively in an autophagy-dependent manner in β-mangostin-treated cells. Taken together, our results suggest that β-mangostin inhibits the melanogenesis induced by α-MSH via an autophagy-dependent mechanism, and thus, the depigmentation effect of β-mangostin may depend on autophagy targeted at the melanosome rather than non-selective autophagy.

Downregulation of melanogenesis: drug discovery and therapeutic options

Melanin, primarily responsible in humans for hair, eye and skin pigmentation, is produced by melanocytes through a process called melanogenesis. However, the abnormal accumulation of melanin causes dermatological problems such as café-au-lait macules ephelides (freckles), solar lentigo (age spots) and melasma, as well as cancer and vitiligo. Hence the regulation of melanogenesis is very important for treating hyperpigmentary disorders. Numerous antimelanogenic agents that target tyrosinase activity and/or stability, melanosome maturation, transfer and trafficking, or melanogenesis-related signaling pathways have been developed. This article reviews recent advances in research and development of human tyrosinase and melanogenesis-related signaling pathway inhibitors. Attempts have been made to provide a complete description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Autophagy regulates spermatid differentiation via degradation of PDLIM1

Spermiogenesis is a complex and highly ordered spermatid differentiation process that requires reorganization of cellular structures. We have previously found that Atg7 is required for acrosome biogenesis. Here, we show that autophagy regulates the round and elongating spermatids. Specifically, we found that Atg7 is required for spermatozoa flagella biogenesis and cytoplasm removal during spermiogenesis. Spermatozoa motility of atg7-null mice dropped significantly with some extra-cytoplasm retained on the mature sperm head. These defects are associated with an impairment of the cytoskeleton organization. Functional screening revealed that the negative cytoskeleton organization regulator, PDLIM1 (PDZ and LIM domain 1 [elfin]), needs to be degraded by the autophagy-lysosome-dependent pathway to facilitate the proper organization of the cytoskeleton. Our results thus provide a novel mechanism showing that autophagy regulates cytoskeleton organization mainly via degradation of PDLIM1 to facilitate the differentiation of spermatids.

Hinokitiol Inhibits Melanogenesis via AKT/mTOR Signaling in B16F10 Mouse Melanoma Cells

H inokitiol purified from the heartwood of cupressaceous plants has had various biological functions of cell differentiation and growth. Hinokitiol has been demonstrated as having an important role in anti-inflammation and anti-bacteria effect, suggesting that it is potentially useful in therapies for hyperpigmentation. Previously, hinokitiol inhibited the production of melanin by inhibiting tyrosinase activity. The autophagic signaling pathway can induce hypopigmentation. This study is warranted to investigate the mechanism of hinokitiol-induced hypopigmentation through autophagy in B16F10 melanoma cells. The melanin contents and expression of microthphalmia associated transcription factor (MITF) and tyrosinase were inhibited by treatment with hinokitiol. Moreover, the phosphorylation of the protein express levels of phospho-protein kinase B (P-AKT) and phospho-mammalian targets of rapamycin (P-mTOR) were reduced after hinokitiol treatment. In addition, the microtubule associated protein 1 light chain 3 (LC3) -II and beclin 1 (autophagic markers) were increased after the B16F10 cell was treated with hinokitiol. Meanwhile, hinokitiol decreased cellular melanin contents in a dose-dependent manner. These findings establish that hinokitiol inhibited melanogenesis through the AKT/mTOR signaling pathway.

Microtubule-associated protein light chain 3 is involved in melanogenesis via regulation of MITF expression in melanocytes

Although autophagy plays a role in melanogenesis by regulating melanosome degradation and biogenesis in melanocytes, a detailed understanding of the regulatory functions of autophagy factors is lacking. Here, we report a mechanistic link between microtubule-associated protein light chain 3 (LC3) activation and melanogenesis. We observed high expression of LC3 in melanosome-associated pigment-rich melanocytic nevi of sun-exposed skin, as indicated by patterns of melanosomal protein MART1 expression. Rapamycin-induced autophagy significantly increased the melanin index, tyrosinase activity and expression of several proteins linked to melanosome biogenesis, including microphthalmia transcription factor (MITF), pre-melanosome protein and tyrosinase, in Melan-a melanocytes. siRNA-mediated knockdown of LC3, but not beclin-1 or ATG5, decreased melanin content and tyrosinase activity. LC3 knockdown also markedly inhibited MITF expression and subsequent rapamycin-induced melanosome formation. More importantly, LC3 knockdown suppressed α-MSH-mediated melanogenesis by attenuating cAMP response element-binding protein (CREB) phosphorylation and MITF expression in Melan-a cells via decreased extracellular signal-regulated kinase (ERK) activity. Overexpression of constitutively active ERK reversed the effect of LC3 knockdown on CREB phosphorylation and MITF expression. These findings demonstrate that LC3 contributes to melanogenesis by increasing ERK-dependent MITF expression, thereby providing a mechanistic insight into the signaling network that links autophagy to melanogenesis.

Resveratrol ameliorates hepatic steatosis and inflammation in methionine/choline-deficient diet-induced steatohepatitis through regulating autophagy

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is one of the leading causes of chronic liver disease that can progress to liver fibrosis, cirrhosis and eventually hepatocellular carcinoma. Resveratrol, a naturally occurring phytoalexin, is believed to have therapeutic effects on hepatic steatosis. However, the effect of resveratrol on NASH and the underlying mechanism is not fully illustrated. In the present study, we aimed to exam the effect of resveratrol on methionine/choline-deficient (MCD) diet or medium-induced hepatic steatosis, oxidation and inflammation, and to explore the possible mechanism.

METHODS

C57BL/6 mice and AML12 cells were treated with MCD alone or in combination with different concentrations of resveratrol (100 mg/kg/day or 250 mg/kg/day for mice and 25 μmol/L, 50 μmol/L, or 100 μmol/L for cells). Levels of aminotransferases (ALT), interleukin 1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α) were measured, concentrations of triglyceride (TG) and thiobarbituric acid reactive substances (TBARs) were determined, and expressions of proteins involved in autophagy were analyzed.

RESULTS

The results indicate that MCD diet or medium induced NASH in mouse and AML12 cell, which was confirmed by the elevated levels of TG, TNF-α, IL-1β, IL-6, ALT and TBARS in mice serum or cell culture medium. Resveratrol administration slowed down NASH progression, decreased the levels of ALT, TG, TBARS, IL-1β, IL-6, downregulated mRNA expressions of TNF-α, IL-1β, IL-6, and regulated the expressions of proteins involved in autophagy, both in vitro and in vivo. However, an autophagical inhibitor significantly impaired the protective role of resveratrol on liver injury and inflammation.

CONCLUSIONS

Resveratrol can attenuate hepatic steatosis and inflammation in MCD-induced NASH by regulating autophagy. Thus, resveratrol may be a promising agent for inhibiting lipid accumulation and inflammatory processes associated with NASH.

Understanding the ultrastructural aspects of berberine-induced skin-darkening activity in the toad, Bufo melanostictus, melanophores

Berberine is an active compound of Berberis vulgaris (Daruhaldi) with known multiple pharmacological activities, including antimicrobial, antiviral, anti-inflammatory, cholesterol-lowering, and anticancer effects. The present work aimed to study the ultrastructural effects of berberine to determine its skin-darkening potential using Bufo melanostictus melanophores, which has not been done to date. Light and electron microscopic analysis of isolated dorsal skin melanophores of B. melanostictus has been done after treatment with various concentrations of berberine, along with specific antagonists and agonists of β-adrenoceptors in order to explore the mechanism of action of berberine-induced skin darkening. The results showed that the number of melanophores with melanin-loaded dendrites increased in the subepidermal layer significantly in berberine-treated skin pieces in a dose-dependent manner leading to skin darkening. Highly electron-dense melanosomes of Stage IV increased considerably due to the enhanced process of melanization. These effects were found to be antagonized by propranolol, and were also found to be highly potentiated by isoprenaline, which is a specific β-adrenoceptor agonist. The findings show that berberine possesses a skin-darkening potential and could be used as a safe melanogenic agent for the treatment of hypopigmentation disorders or vitiligo.

Interactions between Autophagy and Bacterial Toxins: Targets for Therapy?

Autophagy is a physiological process involved in defense mechanisms for clearing intracellular bacteria. The autophagic pathway is finely regulated and bacterial toxins interact with this process in a complex manner. Bacterial toxins also interact significantly with many biochemical processes. Evaluations of the effects of bacterial toxins, such as endotoxins, pore-forming toxins and adenylate cyclases, on autophagy could support the development of new strategies for counteracting bacterial pathogenicity. Treatment strategies could focus on drugs that enhance autophagic processes to improve the clearance of intracellular bacteria. However, further in vivo studies are required to decipher the upregulation of autophagy and potential side effects limiting such approaches. The capacity of autophagy activation strategies to improve the outcome of antibiotic treatment should be investigated in the future.

BIX-01294-induced autophagy regulates elongation of primary cilia

Previously, we showed that BIX-01294 treatment strongly activates autophagy. Although, the interplay between autophagy and ciliogenesis has been suggested, the role of autophagy in ciliogenesis is controversial and largely unknown. In this study, we investigated the effects of autophagy induced by BIX-01294 on the formation of primary cilia in human retinal pigmented epithelial (RPE) cells. Treatment of RPE cells with BIX-01294 caused strong elongation of the primary cilium and increased the number of ciliated cells, as well as autophagy activation. The elongated cilia in serum starved cultured cells were gradually decreased by re-feeding the cells with normal growth medium. However, the disassembly of cilia was blocked in the BIX-01294-treated cells. In addition, both genetic and chemical inhibition of autophagy suppressed BIX-01294-mediated ciliogenesis in RPE cells. Taken together, these results suggest that autophagy induced by BIX-01294 positively regulates the elongation of primary cilium.

Inhibition of autophagy suppresses sertraline-mediated primary ciliogenesis in retinal pigment epithelium cells

Primary cilia are conserved cellular organelles that regulate diverse signaling pathways. Autophagy is a complex process of cellular degradation and recycling of cytoplasmic proteins and organelles, and plays an important role in cellular homeostasis. Despite its potential importance, the role of autophagy in ciliogenesis is largely unknown. In this study, we identified sertraline as a regulator of autophagy and ciliogenesis. Sertraline, a known antidepressant, induced the growth of cilia and blocked the disassembly of cilia in htRPE cells. Following treatment of sertraline, there was an increase in the number of cells with autophagic puncta and LC3 protein conversion. In addition, both a decrease of ATG5 expression and the treatment of an autophagy inhibitor resulted in the suppression of the sertraline-induced activation of autophagy in htRPE cells. Interestingly, we found that genetic and chemical inhibition of autophagy attenuated the growth of primary cilia in htRPE cells. Taken together, our results suggest that the inhibition of autophagy suppresses sertraline-induced ciliogenesis.

Targeting autophagy in skin diseases

Autophagy is a major intracellular degradative process by which cytoplasmic materials are sequestered in double-membraned vesicles and degraded upon fusion with lysosomes. Under normal circumstances, basal autophagy is necessary to maintain cellular homeostasis by scavenging dysfunctional or damaged organelles or proteins. In addition to its vital homeostatic role, this degradation pathway has been implicated in many different cellular processes such as cell apoptosis, inflammation, pathogen clearance, and antigen presentation and thereby has been linked to a variety of human disorders, including metabolic conditions, neurodegenerative diseases, cancers, and infectious diseases. The skin, the largest organ of the body, serves as the first line of defense against many different environmental insults; however, only a few studies have examined the effect of autophagy on the pathogenesis of skin diseases. This review provides an overview of the mechanisms of autophagy and highlights recent findings relevant to the role of autophagy in skin diseases and strategies for therapeutic modulation.

Suppression of autophagy dysregulates the antioxidant response and causes premature senescence of melanocytes

Autophagy is the central cellular mechanism for delivering organelles and cytoplasm to lysosomes for degradation and recycling of their molecular components. To determine the contribution of autophagy to melanocyte (MC) biology, we inactivated the essential autophagy gene Atg7 specifically in MCs using the Cre-loxP system. This gene deletion efficiently suppressed a key step in autophagy, lipidation of microtubule-associated protein 1 light chain 3 beta (LC3), in MCs and induced slight hypopigmentation of the epidermis in mice. The melanin content of hair was decreased by 10-15% in mice with autophagy-deficient MC as compared with control animals. When cultured in vitro, MCs from mutant and control mice produced equal amounts of melanin per cell. However, Atg7-deficient MCs entered into premature growth arrest and accumulated reactive oxygen species (ROS) damage, ubiquitinated proteins, and the multi-functional adapter protein SQSTM1/p62. Moreover, nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent expression of NAD(P)H dehydrogenase, quinone 1, and glutathione S-transferase Mu 1 was increased, indicating a contribution of autophagy to redox homeostasis in MCs. In summary, the results of our study suggest that Atg7-dependent autophagy is dispensable for melanogenesis but necessary for achieving the full proliferative capacity of MCs.

Mitochondrial dynamics regulate melanogenesis through proteasomal degradation of MITF via ROS-ERK activation

Mitochondrial dynamics control mitochondrial functions as well as their morphology. However, the role of mitochondrial dynamics in melanogenesis is largely unknown. Here, we show that mitochondrial dynamics regulate melanogenesis by modulating the ROS-ERK signaling pathway. Genetic and chemical inhibition of Drp1, a mitochondrial fission protein, increased melanin production and mitochondrial elongation in melanocytes and melanoma cells. In contrast, down-regulation of OPA1, a mitochondria fusion regulator, suppressed melanogensis but induced massive mitochondrial fragmentation in hyperpigmented cells. Consistently, treatment with CCCP, a mitochondrial fission chemical inducer, also efficiently repressed melanogenesis. Furthermore, we found that ROS production and ERK phosphorylation were increased in cells with fragmented mitochondria. And inhibition of ROS or ERK suppressed the antimelanogenic effect of mitochondrial fission in α-MSH-treated cells. In addition, the activation of ROS-ERK pathway by mitochondrial fission induced phosphorylation of serine73 on MITF accelerating its proteasomal degradation. In conclusion, mitochondrial dynamics may regulate melanogenesis by modulating ROS-ERK signaling pathway.