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Seborrheic keratosis (SK) is a common benign tumour, often associated with hyperpigmentation. To investigate the mechanism of melanin accumulation in SK, we have conducted comprehensive gene expression and histological analyses. We obtained five pairs of skin samples, including non‐lesional and SK samples, from the backs of three male Japanese participants aged 40–59 years. To examine melanocytes and keratinocytes in SK, three pairs of skin samples were separated by laser capture microdissection into the basal layer and the other layer in the epidermis. We performed a comprehensive gene expression analysis to identify differentially expressed genes between non‐lesional and SK skin, followed by gene ontology and pathway analysis. We found abnormal morphogenesis and cell proliferation in the basal layer, along with increased immune response and impaired cell differentiation and metabolism in the other layer of SK. We focused on cell proliferation and differentiation, as these are directly associated with melanin accumulation. Immunohistochemical analyses of Ki67, keratin 10, and keratin 14 demonstrated the decreases in the proliferation and early differentiation of the epidermis. Contrarily, no significant changes were observed in terminal differentiation markers, filaggrin and loricrin. Although the number of melanocytes was higher in SK than in non‐lesional skin, melanogenic activity showed no difference. These results indicated that melanin accumulation in SK is caused by delayed melanin excretion due to reduced turnover around the basal and spinous layers of the epidermis and melanin production due to an increased number of melanocytes. Our findings provide new insights for therapeutic approaches in SK. [ABSTRACT FROM AUTHOR]

While the evidence for the implication of opioid receptors (OPr) in ageing is growing, there is, to our knowledge, no study focusing directly on changes in vivo cutaneous OPr expression with increasing age. We thus investigated OPr expression in 30 healthy female Asian volunteers in Southern China whose ages range from the early 20s to the early 60s. Excisional biopsies were taken from the sun‐exposed extensor area of the lower arm and the photo‐protected area of the upper inner arm. The thickness of the epidermal layers, melanin content, as well as expression of mu‐opioid receptors (MOPr) and delta‐opioid receptors (DOPr) were compared between different age ranges and photo‐exposure status. Significant increased epidermal hypertrophy on the extensor surface was observed. There was significant reduction of DOPr in the epidermis with increasing age, independent of photo‐ageing. The increase of melanin was significantly correlated with epidermal DOPr expression, not with MOPr expression. DOPr expression could thus serve as a marker for real biological ageing unaffected by chronic photo‐exposure. Additionally, DOPr expression was inversely correlated with the deposition of melanin. Based on these results, we hypothesise that regulation of DOPr expression could be used to improve aged skin, including hyperpigmentation. [ABSTRACT FROM AUTHOR]

Skin hyperpigmentation is mainly caused by excessive synthesis of melanin; however, there is still no safe and effective therapy for its removal. Here, we found that the dermal freezer was able to improve UVB‐induced hyperpigmentation of guinea pigs without causing obvious epidermal damage. We also mimic freezing stimulation at the cellular level by rapid freezing and observed that freezing treatments <2.5 min could not decrease cell viability or induce cell apoptosis in B16F10 and Melan‐A cells. Critically, melanin content and tyrosinase activity in two cells were greatly reduced after freezing treatments. The dramatic decrease in tyrosinase activity was associated with the downregulation of MITF, TYR, TRP‐1 and TRP‐2 protein expression in response to freezing treatments for two cells. Furthermore, our results first demonstrated that freezing treatments significantly reduced the levels of p‐GSK3β and β‐catenin and the nuclear accumulation of β‐catenin in B16F10 and Melan‐A cells. Together, these data suggest that fast freezing treatments can inhibit melanogenesis‐related gene expression in melanocytes by regulating the Wnt/β‐catenin signalling pathway. The inhibition of melanin production eventually contributed to the improvement in skin hyperpigmentation induced by UVB. Therefore, fast freezing treatments may be a new alternative of skin whitening in the clinic in the future. [ABSTRACT FROM AUTHOR]

Melasma is a common condition of hyperpigmented facial skin. Picosecond lasers are reported to be effective for the treatment of melasma. We aimed to identify the most effective therapeutic mode and elucidate the potential molecular mechanisms of picosecond lasers for the treatment of melasma. Female Kunming mice with melasma‐like conditions were treated using four different picosecond laser modes. Concurrently, in vitro experiments were conducted to assess changes in melanin and autophagy in mouse melanoma B16‐F10 cells treated with these laser modes. Changes in melanin in mouse skin were detected via Fontana–Masson staining, and melanin particles were evaluated in B16‐F10 cells. Real‐time polymerase chain reaction and western blotting were used to analyse the expression levels of melanosome and autophagy‐related messenger ribonucleic acid (mRNA) and proteins. A combination of large‐spot low‐fluence 1064‐nm and fractional 1064‐nm picosecond lasers resulted insignificant decreases in melanin as well as in mRNA and protein expression of melanin‐synthesizing enzymes (TYR, TRP‐1 and MITF). This combination also led to increased expression of the autophagy‐related proteins, Beclin1 and ATG5, with a marked decrease in p62 expression. Intervention with the PI3K activator, 740 Y‐P, increased TYR, TRP‐1, MITF, p‐PI3K, p‐AKT, p‐mTOR and p62 expression but decreased the expression of LC3, ATG5 and Beclin1. A combination of large‐spot low‐fluence 1064‐nm and fractional 1064‐nm picosecond lasers proved more effective and safer. It inhibits melanin production, downregulates the PI3K/AKT/mTOR pathway, enhances melanocyte autophagy and accelerates melanin metabolism, thereby reducing melanin content. [ABSTRACT FROM AUTHOR]

This article discusses the potential anti-aging effects of a topical BCL-2 inhibitor called ABT-737 on skin photoaging in mice. Photoaging is caused by long-term exposure to ultraviolet radiation (UVR) and is characterized by changes in the dermis and epidermis, as well as an increase in senescent cells. ABT-737 has been shown to eliminate senescent cells and delay aging when administered through intraperitoneal injection. This study aimed to investigate the effects of ABT-737 when applied topically. The results showed that ABT-737 gel improved skin smoothness, reduced wrinkles, increased collagen fiber density, and decreased epidermal thickness in the mice. It also inhibited the expression of BCL-2 and reduced the levels of p21 and Mmp2, which are associated with photoaging. The study suggests that ABT-737 has potential as a topical treatment for photoaging. [Extracted from the article]

Far‐UVC radiation sources of wavelengths 222 nm and 233 nm represent an interesting potential alternative for the antiseptic treatment of the skin due to their high skin compatibility. Nevertheless, no studies on far‐UVC‐induced DNA damage in different skin types have been published to date, which this study aims for. After irradiating the skin with far‐UVC of the wavelengths 222 and 233 nm as well as broadband UVB, the tissue was screened for cyclobutane pyrimidine dimer‐positive (CPD+) cells using immunohistochemistry. The epidermal DNA damage was lower in dark skin types than in fair skin types after irradiation at 233 nm. Contrary to this, irradiation at 222 nm caused no skin type‐dependent differences, which can be attributed to the decreased penetration depth of radiation. UVB showed the relatively strongest differences between light and dark skin types when using a suberythemal dose of 3 mJ/cm2. As melanin is known for its photoprotective effect, we evaluated the ratio of melanin content in the stratum basale and stratum granulosum in samples of different skin types using two‐photon excited fluorescence lifetime imaging (TPE‐FLIM) finding a higher ratio up to skin type IV–V. As far‐UVC is known to penetrate only into the upper layers of the viable skin, the aforementioned melanin ratio could explain the less pronounced differences between skin types after irradiation with far‐UVC compared to UVB. [ABSTRACT FROM AUTHOR]

Dyschromatosis universalis hereditaria (DUH) is characterized by diffuse symmetrically distributed hypopigmented macules mixed with hyperpigmentation. DUH is divided into three types by Online Mendelian inheritance in man (OMIM) that is, DUH1 (OMIM 127500), DUH2 (OMIM 612715) and DUH3 (OMIM 615402) according to the different linkage regions. Although each condition possesses corresponding phenotypic characteristics and the prognosis for each is somewhat different, these disorders are highly overlapped and difficult to differentiate in the clinical setting. Our latest study reveals a novel DUH subtype that presents a mild phenotype of pigmentation anomalies and is named PER3rs772027021 SNP related DUH or DUH4 by us, which make the DUH subtype can be further retyped. Heterozygous distribution or mosaic‐like distribution of melanin is a newly discovered pathological features that is uniquely demonstrated in the affected layers of DUH1 and DUH4 patients. In this review, DUH is further divided into four subtypes according the causative genes and their mutational sites, and the mutation regions described in the previous reports. To make an accurate diagnosis, we suggest that Sanger sequencing or the target region sequencing (TRS) to the candidate causative genes related melanogenesis may be the most effective and convenient method of clinical diagnosis or/and prenatal diagnosis for DUH and DUH‐like patients. More importantly, heterozygous distribution or mosaic‐like distribution of melanin can be utilized for differential diagnosis of DUH. We also investigate the underlying molecular mechanism to form mosaic‐like melanin in the affected layers of hyper‐ and/or hypo‐pigmented macules from DUH1 and DUH4 patients. This review provides a molecular and pathological delineation of four types of DUH and aims to establish a concise diagnostic strategy to allow clinical dermatologists to make an accurate diagnosis. [ABSTRACT FROM AUTHOR]

Dowling–Degos disease (DDD) is an autosomal dominant hereditary skin disease characterized by acquired reticular hyperpigmentation in flexural sites, and one of its causative genes is KRT5 gene. But the effect of KRT5, expressed only in keratinocytes, on melanocytes is unclear. Other pathogenic genes of DDD include POFUT1, POGLUT1 and PSENEN genes, which is involved in posttranslational modification of Notch receptor. In this study, we aim to determine the ablation of keratinocyte KRT5 affect melanogenesis in melanocyte through Notch signalling pathway. Here we found that KRT5 downregulation decreased the expression of the Notch ligand in keratinocytes and Notch1 intracellular domain in melanocytes, by establishing two cell models of ablation of KRT5 in keratinocytes based on CRISPR/Cas9 site‐directed mutation and lentivirus‐mediated shRNA. Treatment of melanocytes with Notch inhibitors had same effects with ablation of KRT5 on increase of TYR and decrease of Fascin1. Activation of Notch signalling reverses the effect of ablation of KRT5 on melanogenesis. Immunohistochemistry of DDD lesions with KRT5 gene mutation confirmed changes in the expression of relevant molecules in Notch signalling. Our research elucidates molecular mechanism of KRT5‐Notch signalling pathway in the regulation of melanocytes by keratinocytes, and preliminary reveal the mechanism of DDD pigment abnormality caused by KRT5 mutation. These findings identify potential therapeutic targets of the Notch signalling pathway for the treatment of skin pigment disorders. [ABSTRACT FROM AUTHOR]

It remains unclear how the multifunctional indoleamine neurohormone, melatonin, alters melanin production and melanocytes within intact human epidermis under physiologically relevant conditions. In the current pilot study, we aimed to clarify this in long‐term organ‐cultured, full‐thickness human eyelid skin, selected for its clinically recognized sensitivity to pigmentation‐modulatory hormones. Warthin‐Starry histochemistry showed that 100 μM melatonin significantly increased epidermal melanin content and melanocyte dendricity after 6 days of organ culture, even though tyrosinase activity in situ was inhibited, as assessed by quantitative immunohistomorphometry. While the higher melatonin dose tested here (200 μM) did not change epidermal melanization, but again inhibited tyrosinase activity, it increased the number and proliferation of both gp100+ epidermal melanocytes and keratinocytes as well as protein expression of the premelanosomal marker, gp100, ex vivo. Contrary to most previous studies, these eyelid skin organ culture results suggest that long‐term melatonin application exerts overall stimulatory, dose‐dependent effects on the epidermal pigmentary unit within intact human skin, which appear surprisingly tyrosinase‐independent. While these provocative preliminary findings require further work‐up and independent confirmation, they encourage one to systematically explore whether prolonged melatonin therapy can (re‐)stimulate melanogenesis and increase the pool/activity of epidermal melanocytes in hypopigmented skin lesions. [ABSTRACT FROM AUTHOR]

Melanocytes stimulated by ultraviolet radiation (UVR) produce melanin and melanosomes, which causes skin pigmentation and acts as an important physiological defence process for photoprotection. Neutral luminal pH of melanosomes is critical for providing optimal conditions for the rate‐limiting, pH‐sensitive melanin synthesizing enzyme tyrosinase (TYR). As a major component of extraocular phototransduction pathway, transient receptor potential ankyrin1 (TRPA1) can be activated by ultraviolet B (UVB) and reported to be expressed in melanocytes. However, whether TRPA1 is involved in the regulation of melanogenesis remains unclear. Melanogenic activity of TRPA1 was evaluated in primary normal human epidermal melanocytes (HEMs) and murine B16‐F10 cell cultures, and the effects of topical applications of TRPA1 specific agonist and antagonist on UVB‐induced skin pigmentation were confirmed on in vivo guinea pig models. Calcium (Ca2+) imaging and pH imaging were performed to analyse the effects of TRPA1 on intracellular Ca2+ concentration ([Ca2+]ic) and melanosome luminal pH. TRPA1 regulated melanin synthesis, UVB‐induced Ca2+ influx and melanosome luminal pH in HEMs and B16‐F10 cells. Topical treatment of TRPA1 specific agonist JT010 increased UVB‐induced skin pigmentation in guinea pigs, while topical using of TRPA1 selective antagonist HC‐030031 mitigated such pigmentation. Our results indicated that TRPA1 activated by UVB enhanced the skin pigmentation, most likely by regulating the [Ca2+]ic and the melanosomal pH, consequently influencing the enzymatic activity of TYR. Therefore, the results suggest TRPA1 as a potential therapeutic target in the treatment of skin pigmented disorders that are at high risk under UVB irradiation. [ABSTRACT FROM AUTHOR]

Solar lentigo (SL) is a hyperpigmented macule that occurs in sun‐exposed areas and is characterized by the accumulation of melanin pigment in the epidermis. On the contrary, melanin‐incorporated macrophages have also been identified in the dermis, which is thought to be caused by melanin transfer due to disruption of the basement membrane, but the detailed mechanism remains unclear. In this study, we analysed SL lesions by pathological methods and examined the mechanism of melanin accumulation in the dermis using cultured skin models in vitro. First, we observed a significant decrease in type IV collagen (COL4), a major component of the basement membrane, in SL lesions. The basement membrane is known to be formed by the interaction of keratinocytes and dermal cells. Therefore, we constructed skin models containing fibroblasts or dermal stem cells and examined their effects on basement membrane formation. The results showed a markedly enhanced production of COL4 mediated by dermal stem cell‐derived exosomes. The analysis of melanin localization in the SL dermis revealed that CD163‐positive macrophages and CD271‐positive dermal stem cells both took up melanin pigment. Exosomes of dermal stem cells incorporating melanosomes were less effective in promoting COL4 expression. These findings suggest that while the promotion of COL4 production in keratinocytes by dermal stem cell‐derived exosomes is important for maintaining basement membrane homeostasis, this mechanism is disrupted in SL lesions, leading to chronic melanin accumulation in the dermis. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is an emerging dermatological technique with the potential to discriminate biochemically between cell types in a label‐free and non‐invasive manner. Here, we use live single‐cell Raman spectroscopy and principal component analysis (PCA) to fingerprint mouse melanoblasts, melanocytes, keratinocytes and melanoma cells. We show the differences in their spectra are attributable to biomarkers in the melanin biosynthesis pathway and that melanoma cells are a heterogeneous population that sit on a trajectory between undifferentiated melanoblasts and differentiated melanocytes. We demonstrate the utility of Raman spectroscopy as a highly sensitive tool to probe the melanin biosynthesis pathway and its immediate response to ultraviolet (UV) irradiation revealing previously undescribed opposing responses to UVA and UVB irradiation in melanocytes. Finally, we identify melanocyte‐specific accumulation of β‐carotene correlated with a stabilisation of the UVR response in lipids and proteins consistent with a β‐carotene‐mediated photoprotective mechanism. In summary, our data show that Raman spectroscopy can be used to determine the differentiation status of cells of the melanocyte lineage and describe the immediate and temporal biochemical changes associated with UV exposure which differ depending on cell type, differentiation status and competence to synthesise melanin. Our work uniquely applies Raman spectroscopy to discriminate between cell types by biological function and differentiation status while they are growing in culture. In doing so, we demonstrate for the first time its utility as a tool with which to probe the melanin biosynthesis pathway. [ABSTRACT FROM AUTHOR]

Oral tranexamic acid (TA) has been an effective treatment for melasma with unclear mechanism. The present study aimed to demonstrate the effect of TA on melanogenesis via regulation of TGF‐β1 expression in keratinocytes. We firstly determined the expression level of TGF‐β1 in TA‐treated keratinocyte‐conditioned medium (KCM). Then, the mRNA and protein levels of microphthalmia‐associated transcription factor (MITF), tyrosinase (TYR) and tyrosinase‐related protein 1 (TRP‐1) of human epidermal melanocytes (NHEMs) in the presence of TA‐treated KCM were evaluated via RT‐PCR and western blot analysis. Moreover, melanin content and tyrosinase activity were quantified. TGF‐β1 gene was knocked down by small interfering RNA (siRNA) in keratinocytes. The mRNA and protein levels of TGF‐β1 in keratinocytes were significantly increased after TA treatment. Melanin contents, tyrosinase activity, protein and mRNA levels of TYR, MITF and TRP‐1 were downregulated in NHEMs in the presence of TA‐treated KCM. Knockdown of TGF‐β1 in keratinocytes could attenuate the inhibitory effect of TA‐treated KCM on melanogenesis. TA could stimulate TGF‐β1 expression in keratinocytes, which further inhibits melanogenesis through the paracrine signalling. [ABSTRACT FROM AUTHOR]

Kynurenine (KYN), the most abundant metabolite of tryptophan, is classically associated with immune tolerance and tumor immune escape. In the last years, KYN is in the spotlight in other biological processes. Here, we showed that KYN inhibited tyrosinase expression and melanin content in primary human melanocyte and keratinocyte co‐cultures. Furthermore, KYN decreased melanosome content in a 3D human skin reconstruction model. In these experiments, we used tyrosine + NH4Cl to induce pigmentation. We compared the inhibitory effect of KYN on melanogenesis with the already known inhibitory effect promoted by IFN‐γ. Since increased KYN production depends on the IFN‐γ‐inducible enzyme indoleamine‐2,3‐dioxygenase (IDO), we propose that part of the effect of IFN‐γ on melanogenesis involves KYN production. From that, we tested if, during melanogenesis, changes in tryptophan metabolism would occur. For this purpose, we measured tryptophan, KYN and downstream products along with pigmentation. There were no significant changes in Trp metabolism, except for the high consumption of kynurenic acid. Our data identify the skin as a potential target for the action of KYN relevant for skin physiology and pigmentation. The results are discussed concerning the high production of KYN in skin inflammatory disorders and cancer. [ABSTRACT FROM AUTHOR]

Melanin is synthesised within melanocytes and transferred to keratinocytes in human skin, thereby regulating skin colour and protecting skin cells against UVR‐induced damage. We commonly divide human skin into six phototypes (SPT)‐I to ‐VI (Fitzpatrick scale) according to the skin's tanning response to UVR. In this pilot study, we investigated the impact of UVR (maximum 311nm), blue (peak 450nm) and green visible light (peak 530nm) on melanin production and type in healthy human skin histocultures (SPT‐I, ‐II and ‐III). UVR, blue and green light stimulated a surface tanning response in SPT‐II and ‐III, but not SPT‐I. Using the Warthin‐Starry stain for sensitive melanin detection, all three light treatments induced melanogenesis in SPT‐II and ‐III skin. Surprisingly, blue and green light (but not UVR) stimulated melanin synthesis in SPT‐I skin. Moreover, melanin synthesis induced by blue and green visible light in SPT‐I, SPT‐II, and SPT‐III skin was not associated with a detectable increase in DNA damage or cell apoptosis. By contrast, both responses were detected after UVR. These data suggest that blue and green visible light can stimulate melanin production in fair‐skinned individuals without, at least some of, the harmful consequences of UVR‐induced pigmentation. We are currently examining the molecular basis of UVR‐independent melanogenesis in fair skin. [ABSTRACT FROM AUTHOR]

Melanoma has traditionally been viewed as an ultraviolet (UV) radiation-induced malignancy. While UV is a common inducing factor, other endogenous stresses such as metal ion accumulation or the melanin pigment itself may provide alternative pathways to melanoma progression. Eumelanosomes within melanoma often exhibit disrupted membranes and fragmented pigment which may be due to alterations in their amyloid-based striated matrix. The melanosomal amyloid can itself be toxic, especially in combination with reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by endogenous NADPH oxidase (NOX) and nitric oxide synthase (NOS) enzymes, a toxic mix that may initiate melanomagenesis. Further understanding of the loss of the melanosomal organization, the behaviour of the exposed melanin and the induction of ROS/RNS in melanomas may provide critical insights into this deadly disease.

If I had a euro for every manuscript that crosses my virtual desk, as a reviewer or editor, which purports to describe a new human skin pigmentation wonder modulator, I would now be a rich man. An important benefit of their high-throughput platform, in my view, is that it does not rely on non-human or transformed pigment cell lines, which often can have rather unstable melanogenesis trajectories (eg B16 melanoma models).8,26 Still, I await with interest to see how fully representative hiPSC-melanocytes are of the melanocytes that 'live" within the normal or pathological adult human epidermal melanin unit. After the authors confirmed that these cells were both pure and expressed the melanocyte-specific marker, PMEL-17.42 They found pigment cells from these two skin phototypes extreme exhibited striking differences in melanosome/ melanin granule content, and so could be assessed by flow cytometry based on intrinsic forward light scatter area (FSC-A) and light absorption characteristics. [Extracted from the article]

In this study, we describe a simple and straightforward assay using induced pluripotent stem cell‐derived melanocytes and high‐throughput flow cytometry, to identify the effect induced by pigment regulating agents on melanin content. The assay is based on the correlation between forward light‐scatter characteristics and melanin content, with pigmented cells displaying high light absorption/low forward light scatter, while the opposite is true for lowly pigmented melanocytes, as a result of genetic background or chemical treatments. Orthogonal validation is then performed by regular melanin quantification. Such approach was validated using a set of 80 small molecules and yielded a confirmed hit. The assay described in this study may prove a useful tool to identify modulators of melanogenesis in human melanocytes. [ABSTRACT FROM AUTHOR]

Topicals and chemical peels are the standard of care for management of facial hyperpigmentation. However, traditional therapies have come under recent scrutiny, such as topical hydroquinone (HQ) has some regulatory restrictions, and high concentration trichloroacetic acid (TCA) peel pose a risk in patients with skin of colour. The objective of our research was to identify, investigate and elucidate the mechanism of action of a novel TCA- and HQ-free professional-use chemical peel to manage common types of facial hyperpigmentation. Using computational modelling and in vitro assays on tyrosinase, we identified proprietary multi-acid synergistic technology (MAST). After a single application on human skin explants, MAST peel was found to be more effective than a commercial HQ peel in inhibiting melanin (histochemical imaging and gene expression). All participants completed the case study (N = 9) without any adverse events. After administration of the MAST peel by a dermatologist, the scoring and VISIA photography reported improvements in hyperpigmentation, texture and erythema, which could be linked to underlying pathophysiological changes in skin after peeling, visualized by non-invasive optical biopsy of face. Using reflectance confocal microscopy (VivaScope®) and multiphoton tomography (MPTflex™), we observed reduction in melanin, increase in metabolic activity of keratinocytes, and no signs of inflammatory cells after peeling. Subsequent swabbing of the cheek skin found no microbiota dysbiosis resulting from the chemical peel. The strong efficacy with minimum downtime and no adverse events could be linked to the synergistic action of the ingredients in the novel HQ- and TCA-free professional peel technology., (© 2024 Colgate‐Palmolive Company. Experimental Dermatology published by John Wiley & Sons Ltd.)

Besides their many other functions, hair shafts (HS) also are a repository for potentially noxious compounds. These are neutralized by their deposition within terminally differentiated, avital epithelial cells (trichocytes) that also facilitate the interaction of potential toxins with melanin, a toxin‐adsorbent biopolymer. Trichocytes are completely extruded via HS shedding during exogen, an actively controlled process. This underappreciated functional property of the human hair follicle (HF) makes it a bona fide excretory (mini‐) organ. Here, we ask whether the ca. 2 million HFs of the human integument operate in part as primitive, spatially dispersed kidney‐like excretory organs. Despite the many obvious differences between kidneys and HFs, this provocative hypothesis is also supported by other underappreciated renal‐follicular similarities such as anatomical parallels between Bowman's capsule and the anagen hair bulb, renal podocytes and HF winged cells ["Fuegelzellen"], and hypoxia‐dependent production of erythropoietin and extensive prostaglandin synthesis by human scalp HFs—just as in the kidney. The proposed kidney‐like excretory function of HFs may have constituted a major selection advantage of mammals during evolution and could be clinically relevant. We explain how the many open questions (eg, how are molecules destined to be excreted by hair shaft entrapment recognized, taken up and deposited into hair matrix cells?) can be tested experimentally. Finally, we explore how the therapeutic targeting of kidney‐like excretory HF functions may usefully complement classical nephrological therapy (dialysis) and ask whether stimulation of intrafollicular erythropoietin synthesis might become exploitable for the benefit of patients with renal anaemia. [ABSTRACT FROM AUTHOR]

Ageing is characterized by the accumulation of chronic and irreversible oxidative damage, chronic inflammation and organ dysfunction. To attenuate these ageing‐related changes, various natural phytochemicals are often applied. Trans‐communic acid (TCA), an active component of brown pine leaf extract, has antimicrobial and cancer chemopreventive activity and inhibits ultraviolet B (UVB)‐induced MMP‐1 expression. To determine whether the phytochemical TCA could affect the lifespan of an ageing model, Caenorhabditis elegans prevent ageing‐related phenotypes of the skin. Caenorhabditis elegans (C. elegans) wild‐type N2 and mutant strains were used in this study to explore the lifespan extension effect of TCA and its mechanism. We estimated lipofuscin accumulation and melanin levels, which are closely associated with skin senescence. Moreover, we explored the mechanism of action associated with ageing attenuation. We performed oxidative stress resistance and thermotolerance assays in C. elegans and surface plasmon resonance analysis of TCA binding with the forkhead box‐O3a (FoxO3a) protein. TCA, which is the active component in Korean red pine (Pinus densiflora), attenuated ageing‐related changes in skin cells. TCA lowered lipofuscin accumulation in fibroblasts and decreased melanin levels in melanocytes. These protective effects were mediated by activation of the representative longevity gene FoxO3a, which was induced by direct binding with TCA. Interestingly, TCA extended the lifespan of C. elegans, although it did not affect stress resistance, oxidative stress or thermotolerance. These results strongly suggest that TCA prevents the senescent phenotype of model organisms and exhibits beneficial effects on ageing‐related skin phenotypes through direct FoxO3a activation. [ABSTRACT FROM AUTHOR]

Cytokines regulate immune response and inflammation and play an important role in depigmentation process of an autoimmune disease, vitiligo. We sought to determine how inflammatory cytokines influence the progression of vitiligo, and based on that, we develop a logical therapeutic intervention using primary melanocyte culture. Melanocytes were cultured and exposed to IL‐17A, IL‐1β, IFN‐γ and TGF‐β for 4 days. Melanocytes proliferation, tyrosinase assay and melanin content were measured. Real‐Time PCR was used to analyse mRNA expression of genes specific for melanocytes growth and pigmentation. Anti‐IL‐17A receptor antibody was used to block IL‐17A receptors expressed on melanocytes. Protein expression of MITF and TYR was assessed by immunofluorescence and Western blotting. A gradual decline in the melanocyte population, melanin content and tyrosinase activity was observed after different cytokine treatment. The expression of MITF and its downstream genes after blocking with anti‐IL‐17RA, an increased melanin content, increased expression of TYR, MITF along with its downstream genes, and cell proliferation was observed. [ABSTRACT FROM AUTHOR]

Placental extracts have been widely used as skin lightening agents in the Japanese cosmetic market. Here, we show that placental extracts contain factors that can decrease or increase melanin synthesis by normal human melanocytes in vitro in possible association with mitochondrial respiration. When normal human melanocytes were treated with a whole porcine placental extract, melanin synthesis was decreased. In contrast, a porcine placental extract in which exudates and insoluble materials including lipids had been removed increased melanin synthesis. In addition, the amount of tyrosinase, the enzyme critical for melanin synthesis, changed in accordance with the alteration of melanin synthesis. Interestingly, the amount of manganese‐dependent superoxide dismutase (MnSOD), a mitochondrial‐resident antioxidant enzyme, was increased when melanin synthesis was decreased by the whole placental extract. Mitochondrial respiration and glycolysis also changed following treatment with the placental extracts. These results suggest that placental extracts contain factors that can increase or decrease melanin synthesis by normal human melanocytes and that mitochondrial function may be associated with the placental extract‐induced regulation of melanogenesis. [ABSTRACT FROM AUTHOR]

Sunburn causes inflammation, which increases melanin production in skin and causes hyperpigmentation. Angiopoietin‐like protein (ANGPTL) 2 is an inflammatory mediator induced in sun‐exposed skin areas. However, whether ANGPTL2 functions in melanin production remains unclear. To assess this possibility, we overexpressed Angptl2 in the melanoma line B16 and in the keratinocyte line HaCaT. Relative to controls, Angptl2‐expressing B16 cells produced higher melanin levels via tyrosinase induction. Accordingly, Angptl2‐expressing HaCaT cells secreted relatively high levels of both endothelin‐1 (ET‐1) and α‐melanocyte‐stimulating hormone (α‐MSH). Moreover, treatment with an extract from Chrysanthemum indicum × Erigeron annuus (CE) suppressed ANGPTL2 expression and repressed tyrosinase induction in melanocytes and of α‐MSH and ET‐1 in keratinocytes. Our data suggest that ANGPTL2 expression in keratinocytes and melanin‐producing cells accelerates pigment production and that treatment of skin with a CE extract could prevent melanin accumulation. [ABSTRACT FROM AUTHOR]

Skin pigmentation is directed by epidermal melanin units, characterized by long-lived and dendritic epidermal melanocytes ( MC) that interact with viable keratinocytes ( KC) to contribute melanin to the epidermis. Previously, we reported that MC: KC contact is required for melanosome transfer that can be enhanced by filopodi, and by UVR/ UVA irradiation, which can upregulate melanosome transfer via Myosin X-mediated control of MC filopodia. Both MC and KC express Ca2+-dependent E-cadherins. These homophilic adhesion contacts induce transient increases in intra- KC Ca2+, while ultraviolet radiation ( UVR) raises intra- MC Ca2+ via calcium-selective ORAI1 ion channels; both are associated with regulating melanogenesis. However, how Ca2+ triggers melanin transfer remains unclear. Here we evaluated the role of E-cadherin in UVR-mediated melanin transfer in human skin cells. MC and KC in human epidermis variably express filopodia-associated E-cadherin, Cdc42, VASP and β-catenin, all of which were upregulated by UVR in human MC in vitro. Knockdown of E-cadherin revealed that this cadherin is essential for UVR-induced MC filopodia formation and melanin transfer. Moreover, Ca2+ induced a dose-dependent increase in filopodia formation and melanin transfer, as well as increased β-catenin, Cdc42, Myosin X and E-cadherin expression in these skin cells. Together, these data suggest that filopodial proteins and E-cadherin, which are upregulated by intracellular ( UVR-stimulated) and extracellular Ca2+ availability, are required for filopodia formation and melanin transfer. This may open new avenues to explore how Ca2+ signalling influences human pigmentation. [ABSTRACT FROM AUTHOR]

Loss-of-function melanocortin 1 receptor (MC1R) polymorphisms are common in UV-sensitive fair-skinned individuals and are associated with blunted cAMP second messenger signalling and higher lifetime risk of melanoma because of diminished ability of melanocytes to cope with UV damage. cAMP signalling positions melanocytes to resist UV injury by upregulating synthesis of UV-blocking eumelanin pigment and by enhancing the repair of UV-induced DNA damage. cAMP enhances melanocyte nucleotide excision repair (NER), the genome maintenance pathway responsible for the removal of mutagenic UV photolesions, through cAMP-activated protein kinase (protein kinase A)-mediated phosphorylation of the ataxia telangiectasia-mutated and Rad3-related (ATR) protein on the S435 residue. We investigated the interdependence of cAMP-mediated melanin upregulation and cAMP-enhanced DNA repair in primary human melanocytes and a melanoma cell line. We observed that the ATR-dependent molecular pathway linking cAMP signalling to the NER pathway is independent of MITF activation. Similarly, cAMP-mediated upregulation of pigment synthesis is independent of ATR, suggesting that the key molecular events driving MC1R-mediated enhancement of genome maintenance (eg PKA-mediated phosphorylation of ATR) and MC1R-induced pigment induction (eg MITF activation) are distinct. [ABSTRACT FROM AUTHOR]

Artificial UV irradiation of murine skin is a frequently used method for testing photosensitivity, study carcinogenesis and photoprotective effects of different compounds. However, doses of UV radiation and mouse strains used in experiments vary greatly. The genetic background of mice may influence the photosensitivity as melanin content, pigmentation and hair cycle parameters are dissimilar. Doses of UV are often expressed in relation to the minimal erythema dose ( MED) that was not necessarily determined for the given strain. We set out to standardize the method of measuring photosensitivity in three commonly used mouse strains, C57 BL/6N, Balb/c and SKH-1. We found that MED may not be determined for some strains as erythema development in mice with diverse genotypes differs greatly. We measured the oedema response in vivo and ex vivo by using OCT. Given the strain-specific variability of erythema, we introduced Clinically Relevant Dose ( CRD) as a new term to replace MED in experiments, to describe the lowest dose that triggers a perceptible skin reaction in mice. Not only the CRD but the proportion of erythema and oedema were different in strains examined. C57 BL/6N mice display skin reactions at the lowest UVB dose, while SKH-1 hairless mice show changes, mostly oedema, after higher doses of UVB. The cellular composition and skin thickness were examined by histopathology. IL-1beta and IL-6 levels in skin correlated with the increasing doses of UVB. Despite the variations in the degree of erythema and oedema, no major differences in cytokine expressions were seen among various strains of mice. [ABSTRACT FROM AUTHOR]

Melanin is the predominant pigment responsible for skin colour and is synthesized by the melanocyte in the basal layer of the epidermis and then transferred to surrounding keratinocytes. Despite its optical properties, melanin is barely detectable in unstained sections of human epidermis. However, identification and localization of melanin is of importance for the study of skin pigmentation in health and disease. Current methods for the histologic quantification of melanin are suboptimal and are associated with significant risk of misinterpretation. The aim of this study was to reassess the existing literature and to develop a more effective histological method of melanin quantification in human skin. Moreover, we confirm that Warthin-Starry (WS) stain provides a much more sensitive and more specific melanin detection method than the commonplace Fontana-Masson (FM) stain. For example, WS staining sensitivity allowed the visualization of melanin even in very pale Caucasian skin that was missed by FM or Von Kossa (VK) stains. From our reassessment of the histology-related literature, we conclude that so-called melanin dust is most likely an artifact of discoloration due to non-specific silver deposition in the stratum corneum. Unlike FM and VK, WS was not associated with this non-specific stratum corneum darkening, misinterpreted previously as 'degraded' melanin. Finally, WS melanin particle counts were largely similar to previously reported manual counts by transmission electron microscopy, in contrast to both FM and VK. Together these findings allow us to propose a new histology/Image J-informed method for the accurate and precise quantification of epidermal melanin in skin. [ABSTRACT FROM AUTHOR]

The development of antimelanogenic agents is important for the prevention of serious aesthetic problems such as melasma, freckles, age spots and chloasma. The aim of this study was to investigate the antimelanogenic effect of sesamol, an active lignan isolated from Sesamum indicum, in melan-a cells. Sesamol strongly inhibited melanin biosynthesis and the activity of intracellular tyrosinase by decreasing cyclic adenosine monophosphate ( cAMP) accumulation. Sesamol significantly decreased the expression of melanogenesis-related genes, such as tyrosinase, tyrosinase-related protein-1,2 ( TRP-1,2), microphthalmia-associated transcription factor ( MITF) and melanocortin 1 receptor ( MC1R). In addition, sesamol also induces phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase ( JNK). Moreover, sesamol dose-dependently decreased zebrafish pigment formation, tyrosinase activity and expression of melanogenesis-related genes. These findings indicate that sesamol inhibited melanin biosynthesis by down-regulating tyrosinase activity and melanin production via regulation of gene expression of melanogenesis-related proteins through modulation of MITF activity, which promoted phosphorylation of p38 and JNK in melan-a cells. Together, these results suggest that sesamol strongly inhibits melanin biosynthesis, and therefore, sesamol represents a new skin-whitening agent for use in cosmetics. [ABSTRACT FROM AUTHOR]

TGF- β and the inhibitors of differentiation (Id) are linked. Smad7 and other TGF- β inhibitors can potently suppress melanomagenesis; however, little work examining Ids has been reported in melanoma, particularly for Id4. Here, we report that Id4, but not Id2 or Id3 expression, surprisingly, activated robust melanin production in xenografts of previously amelanotic (lacking pigment) 1205Lu/Smad7 (S7) cells. Fontana-Masson stain and de-novo expression of MART-1 and tyrosinase proteins confirmed melanin production. Additionally, pigment-laden CD163+ mouse histiocytes with areas of extensive necrosis were found throughout S7/Id4 tumors, but not in parental 1205Lu, S7/Id2 or S7Id3-derived tumors. Mechanistic investigation revealed increased nuclear M-microphthalmia-associated transcription factor ( MITF) and MART-1 promoter activation following Id4 expression in 1205Lu and WM852 melanoma cells, suggesting broader implications for Id4 in melanin synthesis. In human tumors, melanin colocalized with Id4 expression establishing a correlation. Current chemotherapeutics for melanoma are only marginally effective. Immunotherapy provides the most promise, yet the role of innate immunity is poorly understood. Here, TGF- β suppression followed by Id4 expression results in extensive melanin synthesis and robust histiocyte recruitment following tumorigenesis, a novel role for Id4. Our results suggest that TGF- β suppression coupled with pigment overproduction triggers an innate immune response resulting in tumor necrosis. [ABSTRACT FROM AUTHOR]

In living cells, melanin pigment is formed within melanosomes, which not only protect the cells from autodestruction, but also serve as second messenger organelles regulating important skin functions, with melanocytes acting as primary sensory and regulatory cells of the epidermis. Yet, one can argue that skin melanin, which may negatively affect cellular homeostasis in melanoma, really exerts protective functions. Consequently, the actual functions of melanin and the melanogenic pathway in skin biology remains enigmatic. Yet, the solution of this riddle seems simple - to check the actual influence of natural melanin on skin cells in the dark. Since many interesting hypotheses and theories put forward in this respect did not survive confrontation with the experiment, a leading pigment research group from Naples was brave to 'jump off the cliff' by confronting theory with experimental reality. They showed that, in the dark, human hair-derived melanin promotes inflammatory responses in keratinocytes, lowers their viability, promotes oxidative stress, and that pheomelanin does so more strongly than eumelanin. Thus, pheomelanin hardly protects red-haired individuals, even when avoiding the sun. Black hairs do not do much better either, unless they undergo graying. [ABSTRACT FROM AUTHOR]

The relationship between melanin pigmentation and metastatic phenotype of melanoma cells is an intricate issue, which needs to be unambiguously determined to fully understand the process of metastasis of malignant melanoma. Despite significant research efforts undertaken to solve this problem, the outcomes are far from being satisfying. Importantly, none of the proposed explanations takes into consideration biophysical aspects of the phenomenon such as cell elasticity. Recently, we have demonstrated that melanin granules dramatically modify elastic properties of pigmented melanoma cells. This prompted us to examine the mechanical effects of melanosomes on the transmigration abilities of melanoma cells. Here, we show for the first time that melanin granules inhibit transmigration abilities of melanoma cells in a number of granules dependent manner. Moreover, we demonstrate that the inhibitory effect of melanosomes is mechanical in nature. Results obtained in this study demonstrate that cell elasticity may play a key role in the efficiency of melanoma cells spread in vivo. Our findings may also contribute to better understanding of the process of metastasis of malignant melanoma. [ABSTRACT FROM AUTHOR]

Ultraviolet radiation ( UVR) is the most common mutagen that melanocytes are exposed to. UVR causes a diverse range of DNA photolesions contributing to genome instability and promotes melanoma and non-melanoma development. Melanocytes are pigment-producing cells that synthesise the photoprotective melanins when the melanocortin-1 receptor ( MC1R) is activated. MC1R is a G-protein-coupled receptor expressed predominantly in melanocytes. Its signalling pathway has been directly linked to melanogenesis, enhanced cytoprotection against UV damage and augmented DNA repair response. Interestingly, previous studies have revealed that MC1R signalling induces the transcription of the NR4A subfamily of orphan nuclear receptors in response to UV. In line with this, studies have also observed that NR4A receptors are recruited to distinct nuclear foci in response to cellular stress, independent of their transcriptional roles. Here, we review the regulated expression of NR4A2 and its potential roles upon cellular stress conditions. Current work in developing synthetic NR4A2 agonists further provides exciting avenues for exploring the potential role of NR4A2 as an antiskin cancer drug target. [ABSTRACT FROM AUTHOR]

The diversity of human skin phenotypes and the ubiquitous exposure to ultraviolet radiation ( UVR) underscore the need for a non-invasive tool to predict an individual's UVR sensitivity. We analysed correlations between UVR sensitivity, melanin content, diffuse reflectance spectroscopy ( DR) and UVR-induced DNA damage in the skin of subjects from three racial/ethnic groups: Asian, Black or African American and White. UVR sensitivity was determined by evaluating each subject's response to one minimal erythemal dose ( MED) of UVR one day after the exposure. Melanin content was measured using DR and by densitometric analysis of Fontana- Masson staining ( FM) in skin biopsies taken from unexposed areas. An individual's UVR sensitivity based on MED was highly correlated with melanin content measured by DR and by FM. Therefore, a predictive model for the non-invasive determination of UVR sensitivity using DR was developed. The MED precision was further improved when we took race/ethnicity into consideration. The use of DR serves as a tool for predicting UVR sensitivity in humans that should be invaluable for determining appropriate UVR doses for therapeutic, diagnostic and/or cosmetic devices. [ABSTRACT FROM AUTHOR]

Skin hyperpigmentation is commonly treated by topical drug application. Several naturally occurring compounds exhibit attractive biological effects including anti-melanogenic activity. Chemically modified derivatives of those compounds are expected to be more efficient. However, efficacy and safety testing processes are of significant consideration to identify the most effective compound among them. Herein, we demonstrated a tiered approach to investigate the antipigmentation activity of 17 trans-N-coumaroyltyramine derivatives. First, we evaluated the in chemico antityrosinase activity, then the cytotoxicity of the most potent derivatives using a mitochondrial activity-based assay, followed with the in vitro anti-melanogenic activity in two dimensional (2D) monolayer human melanocytes. The selected derivatives were topically applied on a three dimensional (3D) pigmented-reconstructed human epidermis (pRhE) containing melanocytes and keratinocytes to evaluate their depigmenting activity. Two of the 17 derivatives displayed a significant reduction in pigmentation in the 3D pRhE, comparable to kojic acid, a known tyrosinase inhibitor. In addition, a molecular docking experiment indicated an interaction of the three derivatives and tyrosinase, suggesting that these derivatives have potent anti-melanogenic activity through tyrosinase inhibition. Our findings provide an alternative approach for investigating skin-whitening agents, thereby facilitating the research and development of skin-whitening products that need not be tested on animals., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Pheomelanin is supposed to be the first type of melanin found in vertebrates, in contrast to the main type - eumelanin. Our study aimed at detecting pheomelanin in the skin of Hymenochirus boettgerii. We employed electron paramagnetic resonance ( EPR) spectroscopy, and transmission electron microscopy ( TEM), supplemented with standard histology and immunochemistry. We identified pheomelanin in the dorsal skin of adult frogs (not only in the dermis, but also in the epidermis) and in the dorsal tadpole. Our work identifies Hymenochirus boettgerii as a model in the basic study on the mechanism, evolution and role of melanogenesis in animals, including human. [ABSTRACT FROM AUTHOR]