Genetic disorders of pigmentation

Phoenix dactylifera L. Seed Extract Exhibits Antioxidant Effects and Attenuates Melanogenesis in B16F10 Murine Melanoma Cells by Downregulating PKA Signaling

Background: The mode of action of Phoenix dactylifera seed extract in skin care has never been explored. Methods: P. dactylifera L. seeds were extracted by ultrasonic extraction. The antioxidant characteristics of the extract were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS⁺) assays and scavenging methods. The total phenolic content, reducing capacity, iron (II) ion-chelation, and intracellular reactive oxygen species (ROS)-scavenging capacities were also investigated. The effects of P. dactylifera L. seed extract on melanogenesis were evaluated spectrophotometrically by a mushroom tyrosinase activity assay, determination of intracellular tyrosinase activity, and melanin content. The expression levels of melanogenesis-related proteins were analyzed by Western blotting. Results: The results revealed that the P. dactylifera L. seed extract exerted apparent antioxidant capacity and significantly decreased intracellular ROS content at concentrations of 0.245 and 0.49 (mg/mL). Furthermore, the extract decreased the expression of melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP1), and tyrosinase-related protein-2 (TRP2), and inhibited melanogenesis in B16F10 cells. Conclusions: Our results revealed that P. dactylifera L. seed extract attenuated melanogenesis in B16F10 cells by downregulating protein kinase A (PKA) signaling pathways. Hence, the extract could be used as a type of skin-whitening agent in skin care products.

Pigmentation and vision: Is GPR143 in control?

Albinism, typically characterized by decreased melanin synthesis, is associated with significant visual deficits owing to developmental changes during neurosensory retina development. All albinism is caused by genetic mutations in a group of diverse genes including enzymes, transporters, G-protein coupled receptor. Interestingly, these genes are not expressed in the neurosensory retina. Further, regardless of cause of albinism, all forms of albinism have the same retinal pathology, the extent of which is variable. In this review, we explore the possibility that this similarity in retinal phenotype is because all forms of albinism funnel through the same final common pathway. There are currently seven known genes linked to the seven forms of ocular cutaneous albinism. These types of albinism are the most common, and result in changes to all pigmented tissues (hair, skin, eyes). We will discuss the incidence and mechanism, where known, to develop a picture as to how the mutations cause albinism. Next, we will examine the one form of albinism which causes tissue-specific pathology, ocular albinism, where the eye exhibits the retinal albinism phenotype despite near normal melanin synthesis. We will discuss a potential way to treat the disease and restore normal retinal development. Finally, we will briefly discuss the possibility that this same pathway may intersect with the most common cause of permanent vision loss in the elderly.

Gomisin N Inhibits Melanogenesis through Regulating the PI3K/Akt and MAPK/ERK Signaling Pathways in Melanocytes

Gomisin N, one of the lignan compounds found in Schisandra chinensis has been shown to possess anti-oxidative, anti-tumorigenic, and anti-inflammatory activities in various studies. Here we report, for the first time, the anti-melenogenic efficacy of Gomisin N in mammalian cells as well as in zebrafish embryos. Gomisin N significantly reduced the melanin content without cellular toxicity. Although it was not capable of modulating the catalytic activity of mushroom tyrosinase in vitro, Gomisin N downregulated the expression levels of key proteins that function in melanogenesis. Gomisin N downregulated melanocortin 1 receptor (MC1R), adenylyl cyclase 2, microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). In addition, Gomisin N-treated Melan-A cells exhibited increased p-Akt and p-ERK levels, which implies that the activation of the PI3K/Akt and MAPK/ERK pathways may function to inhibit melanogenesis. We also validated that Gomisin N reduced melanin production by repressing the expression of MITF, tyrosinase, TRP-1, and TRP-2 in mouse and human cells as well as in developing zebrafish embryos. Collectively, we conclude that Gomisin N inhibits melanin synthesis by repressing the expression of MITF and melanogenic enzymes, probably through modulating the PI3K/Akt and MAPK/ERK pathways.

Supercritical Fluid Extract of Spent Coffee Grounds Attenuates Melanogenesis through Downregulation of the PKA, PI3K/Akt, and MAPK Signaling Pathways

The mode of action of spent coffee grounds supercritical fluid CO₂ extract (SFE) in melanogenesis has never been reported. In the study, the spent coffee grounds were extracted by the supercritical fluid CO₂ extraction method; the chemical constituents of the SFE were investigated by gas chromatography-mass spectrometry (GC-MS). The effects of the SFE and its major fatty acid components on melanogenesis were evaluated by mushroom tyrosinase activity assay and determination of intracellular tyrosinase activity and melanin content. The expression level of melanogenesis-related proteins was analyzed by western blotting assay. The results revealed that the SFE of spent coffee grounds (1–10 mg/mL) and its major fatty acids such as linoleic acid and oleic acid (6.25–50 μM) effectively suppressed melanogenesis in the B16F10 murine melanoma cells. Furthermore, the SFE decreased the expression of melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). The SFE also decreased the protein expression levels of p-JNK, p-p38, p-ERK, and p-CREB. Our results revealed that the SFE of spent coffee grounds attenuated melanogenesis in B16F10 cells by downregulation of protein kinase A (PKA), phosphatidylinositol-3-kinase (PI3K/Akt), and mitogen-activated protein kinases (MAPK) signaling pathways, which may be due to linoleic acid and oleic acid.

Vitiligo

Vitiligo, an acquired pigmentary disorder of unknown origin, is the most frequent cause of depigmentation worldwide, with an estimated prevalence of 1%. The disorder can be psychologically devastating and stigmatising, especially in dark skinned individuals. Vitiligo is clinically characterised by the development of white macules due to the loss of functioning melanocytes in the skin or hair, or both. Two forms of the disease are well recognised: segmental and non-segmental vitiligo (the commonest form). To distinguish between these two forms is of prime importance because therapeutic options and prognosis are quite different. The importance of early treatment and understanding of the profound psychosocial effect of vitiligo will be emphasised throughout this Seminar.

Discovery of highly potent tyrosinase inhibitor, T1, with significant anti-melanogenesis ability by zebrafish in vivo assay and computational molecular modeling

Tyrosinase is involved in melanin biosynthesis and the abnormal accumulation of melanin pigments leading to hyperpigmentation disorders that can be treated with depigmenting agents. A natural product T1, bis(4-hydroxybenzyl)sulfide, isolated from the Chinese herbal plant, Gastrodia elata, is a strong competitive inhibitor against mushroom tyrosinase (IC₅₀ = 0.53 μM, Ki = 58 ± 6 nM), outperforms than kojic acid. The cell viability and melanin quantification assay demonstrate that 50 μM of T1 apparently attenuates 20% melanin content of human normal melanocytes without significant cell toxicity. Moreover, the zebrafish in vivo assay reveals that T1 effectively reduces melanogenesis with no adverse side effects. The acute oral toxicity study evidently confirms that T1 molecule is free of discernable cytotoxicity in mice. Furthermore, the molecular modeling demonstrates that the sulfur atom of T1 coordinating with the copper ions in the active site of tyrosinase is essential for mushroom tyrosinase inhibition and the ability of diminishing the human melanin synthesis. These results evident that T1 isolated from Gastrodia elata is a promising candidate in developing pharmacological and cosmetic agents of great potency in skin-whitening.

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.

Supercritical fluid extract of Lycium chinense Miller root inhibition of melanin production and its potential mechanisms of action

Background

The mode of action of Lycium chinense Miller root extract in skin care has never been explored. In the present study, Lycium chinense Miller root was extracted by the supercritical fluid CO₂ extraction method.

Methods

In the present study, the components of the root extract were analyzed by HPLC. The effects of the extract on tyrosinase activity and melanin content were determined spectrophotometrically; the expression of melanogenesis-related proteins was determined by Western blotting; the possible signaling pathways involved in the root extract-mediated depigmentation were also investigated using specific inhibitors.

Results

The results revealed that the SFE of Lycium chinense Miller root (2.37-7.11 mg/mL) effectively suppressed intracellular tyrosinase activity and decreased the melanin content in B16F10 cells. The root extract also effectively decreased intracellular reactive oxygen species (ROS) levels. Furthermore, the root extract decreased the expression of melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase and tyrosinase-related protein-1 (TRP-1) and then inhibited melanogenesis in B16F10 cells. The root extract also showed antioxidant capacities and depleted cellular ROS.

Conclusions

Our results indicate that the SFE of Lycium chinense Miller root inhibited melanogenesis in B16F10 cells by down-regulation of both mitogen-activated protein kinases (MAPK) and protein kinase A (PKA) signaling pathways or through its antioxidant properties.

Hydroalcoholic extract of Rhodiola rosea L. (Crassulaceae) and its hydrolysate inhibit melanogenesis in B16F0 cells by regulating the CREB/MITF/tyrosinase pathway

We investigated the effects of an aqueous alcohol extract of Rhodiola rosea (R. rosea) and its hydrolysate on melanin synthesis and the mechanisms mediating the activity. The ratio of tyrosol to salidroside was 2.3 in hydroalcoholic extract, and 51.0 in hydrolysate. We found that R. rosea extract and its hydrolysate inhibited melanin synthesis and tyrosinase activity in mouse melanoma cells (B16F0 cells). R. rosea extract also inhibited gene and protein expression of melanocortin 1 receptor (MC1R) and inhibited c-AMP response element binding protein (CREB) phosphorylation, suppressed the activation of AKT and glycogen synthase kinase-3 beta (GSK3β), and inhibited the expression of microphthalmia-associated transcription factor (MITF) and tyrosinase-related protein 1 (TRP-1). R. rosea hydrolysate inhibited the phosphorylation of CREB, the activation of AKT and GSK3β, and the expression of MITF and tyrosinase. Our results suggest that R. rosea extract is a novel tyrosinase inhibitor and that it exerts its effects by regulating the CREB/MITF/tyrosinase pathway in B16F0. Further in vivo studies are needed to determine the effectiveness of R. rosea extract as a skin whitening agent.

Inhibitory effect of p-hydroxybenzyl alcohol on tyrosinase activity and melanogenesis

Tyrosinase is a key enzyme catalyzing the rate-limiting step for the biosynthesis pathway of melanin pigment, which is the most important determinant of the color of skin. Inhibiting tyrosinase and repressing melanocyte metabolism can reduce melanin production. Among the possible melanin reducing compounds, tyrosinase inhibitors are most promising for treating pigmentation and are used as skin-whitening agents in the cosmetic industry. In our investigation, some new tyrosinase inhibitors from plants have been identified to have high tyrosinase inhibitory activity. Specifically, p-hydroxybenzyl alcohol (4HBA) was found to inhibit the monophenolase activity of mushroom tyrosinase. When 4HBA binds with the enzyme, conformation of the enzyme is altered and its activity decreases. The inhibitory effect of 4HBA on melanogenesis has been studied using cultured mouse melanoma cells. Melanin synthesis in cell culture with 4HBA at 1.0 mM was decreased to 45% of control and below 1.0 mM there was no effect on cell growth. The inhibitory effects of 4HBA on melanogenesis are due to the direct inhibition of melanosomal tyrosinase activity, rather than to the suppression of tyrosinase gene. These results showed that 4HBA is a promising and safe agent for skin whitening.

Influence of N-glycan processing disruption on tyrosinase and melanin synthesis in HM3KO melanoma cells

Tyrosinase, a type I membrane glycoprotein, is synthesized and glycosylated in the endoplasmic reticulum (ER) and Golgi. The enzyme is subsequently transported to melanosomes where it participates in melanogenesis. Previous studies showed that the disruption of early ER N-glycan processing by deoxynojirimycin (DNJ), an inhibitor of alpha-glucosidase, suppresses tyrosinase enzymatic activity and melanogenesis. However, the disruption of late glycan processing, mainly performed by ER and Golgi alpha-1,2-mannosidases, on tyrosinase enzymatic activity and melanogenesis remains to be investigated. Following treatment of HM3KO human melanoma cells with deoxymannojirimycin (DMJ), an inhibitor of alpha-1,2-mannosidase, transport of tyrosinase to the melanosome, enzymatic activity, and melanogenesis were reduced in a dose-dependent manner. However, DMJ did not directly inhibit tyrosinase enzymatic activity and expression. Interestingly, an extract of Streptomyces subrutilus culture medium (ESSCM) containing DMJ and DNJ as the main components inhibited glycosylation and transport of tyrosinase to the melanosome as well as melanin synthesis, but with no negative effects on cell viability. These inhibitory effects of ESSCM were stronger than those of DMJ or DNJ alone. Tyrosinase glycosylation and melanogenesis in HM3KO melanoma cells were more effectively inhibited by DMJ and DNJ combined than DMJ or DNJ alone. Accordingly, we propose that ESSCM is a potential candidate for treating undesirable hyperpigmentation conditions, such as melasma, postinflammatory melanoderma, and solar lentigo.

Inhibitory effects of plant extracts on tyrosinase, L-DOPA oxidation, and melanin synthesis

For medical, pharmacological, and cosmetic reasons, the demand for effective and safe depigmentating agents has increased. In this study, 101 plant extracts (methanol or water extracts) were screened for their inhibitory activities against tyrosinase, (L-3, 4,-dihydroxyphenylalanine) L-DOPA oxidation, and melanin biosynthesis in B16 mouse melanoma cells. Of the extracts examined, 31 showed over 50% inhibition of mushroom tyrosinase at a concentration of 666 microg/Ml, and 11 inhibited L-DOPA auto-oxidation at this concentration. In particular, extracts of Broussonetia kazinoki var. humilis (leaves and stems), Broussonetia papyrifera (leaves and bark), Cornus officinalis (fruit), Rhus javanica (gallnut), and Pinus densiflora (leaves) inhibited both tyrosinase activity and L-DOPA oxidation in a concentration-dependent manner. Seventeen plant extracts that inhibited tyrosinase were further tested for their inhibitory effects on melanogenesis. In B16 mouse melanoma cells, extracts of Acorus gramineus, Capsella bursa-pastoris, Morus bombycis, Perilla frutescens var. crispa, Quercus dentate (bark), Rhus javanica (gallnut), Schizopepon bryoniaefolius, or Sophora flavescens markedly inhibited (>50%) melanin synthesis at 50 microg/Ml. These plants represent a potential source of novel whitening agents for ultraviolet (UV)-sensitive skin.

Inhibition of tyrosinase activity by N,N-unsubstituted selenourea derivatives

This study investigated inhibitory effects of N,N-unsubstituted selenourea derivatives on tyrosinase activity. Three types of N,N-unsubstituted selenoureas derivatives exhibited inhibitory effect on dopa (3,4-dihydroxyphenylalanine) oxidase activity of mushroom tyrosinase. Compound D at a concentration of 200 microM exhibited 55.5% of inhibition on dopa oxidase activity of mushroom tyrosinase. This inhibitory effect was higher than that of kojic acid (39.4%), a well known tyrosinase inhibitor. Moreover, the compound D identified as a noncompetitive inhibitor by Lineweaver-Burk plot analysis. In addition, compound D also inhibited the melanin production in melan-a cells.

4,4'-Dihydroxybiphenyl as a new potent tyrosinase inhibitor

The color of mammalian skin is determined by many factors, for which visible ones are the degree and distribution of melanin pigmentation. Because tyrosinase, (polyphenol oxidase) is the key enzyme for melanin biosynthesis, the use of various tyrosinase inhibitors is a common practice for whitening purpose in cosmetics. In the present study, the inhibition of tyrosinase by 4,4'-dihydroxybiphenyl (44'-BP) was investigated. In addition to tyrosinase inhibiting activity, melanin biosynthesis was assessed in B16F10 melanoma cells (B16 cells). The results showed that 44'-BP exhibits a strong anti-tyrosinase activity with IC50=1.91 microM. The kinetic analysis of tyrosinase inhibition revealed that 44'-BP acts a competitive inhibitor (Ki=4.0 x 10(-4) M at 2.5 microM and Ki =21 x 10(-5) M at 5 microM). Furthermore, data on melanin biosynthesis indicated that the amount of melanin was clearly suppressed by 44'-BP.

Tyrosinase processing and intracellular trafficking is disrupted in mouse primary melanocytes carrying the underwhite (uw) mutation. A model for oculocutaneous albinism (OCA) type 4

Oculocutaneous albinism (OCA) type 4 is a newly identified human autosomal recessive hypopigmentary disorder that disrupts pigmentation in the skin, hair and eyes. Three other forms of OCA have been previously characterized, each resulting from the aberrant processing and/or sorting of tyrosinase, the enzyme critical to pigment production in mammals. The disruption of tyrosinase trafficking occurs at the level of the endoplasmic reticulum (ER) in OCA1 and OCA3, but at the post-Golgi level in OCA2. The gene responsible for OCA4 is the human homologue of the mouse underwhite (uw) gene, which encodes the membrane-associated transporter protein (MATP). To characterize OCA4, we investigated the processing and sorting of melanogenic proteins in primary melanocytes derived from uw/uw mice and from wild-type mice. OCA4 melanocytes were found to be constantly secreted into the medium dark vesicles that contain tyrosinase and two other melanogenic enzymes, Tyrp1 (tyrosinase-related protein 1) and Dct (DOPAchrome tautomerase); this secretory process is not seen in wild-type melanocytes. Although tyrosinase was synthesized at comparable rates in wild-type and in uw-mutant melanocytes, tyrosinase activity in uw-mutant melanocytes was only about 20% of that found in wild-type melanocytes, and was enriched only about threefold in melanosomes compared with the ninefold enrichment in wild-type melanocytes. OCA4 melanocytes showed a marked difference from wild-type melanocytes in that tyrosinase was abnormally secreted from the cells, a process similar to that seen in OCA2 melanocytes, which results from a mutation of the pink-eyed dilution (P) gene. The P protein and MATP have 12 transmembrane regions and are predicted to function as transporters. Ultrastructural analysis shows that the vesicles secreted from OCA4 melanocytes are mostly early stage melanosomes. Taken together, our results show that in OCA4 melanocytes, tyrosinase processing and intracellular trafficking to the melanosome is disrupted and the enzyme is abnormally secreted from the cells in immature melanosomes, which disrupts the normal maturation process of those organelles. This mechanism explains the hypopigmentary phenotype of these cells and provides new insights into the involvement of transporters in the normal physiology of melanocytes.

Development of 5-[(3-aminopropyl)phosphinooxy]-2-(hydroxymethyl)-4H-pyran-4-one as a novel whitening agent

A stable derivative of kojic acid, 5-[(3-aminopropyl)phosphinooxy]-2-(hydroxymethyl)-4H-pyran-4-one (Kojyl-APPA), was synthesized in good yield. The effects of Kojyl-APPA on tyrosinase activity and melanin synthesis were investigated. Kojyl-APPA showed tyrosinase inhibition effect (30%) in situ, but not in vitro. Kojyl-APPA inhibited tyrosinase activity significantly at 24 h after treatment in normal human melanocytes. It means that Kojyl-APPA is not a direct inhibitor of tyrosinase itself, but it is converted to a potential inhibitor kojic acid enzymatically in cells. In addition, Kojyl-APPA decreased melanin content to 75% of control in melanoma cells and decreased neomelanin synthesis to 43% of control in normal human melanocytes. Its permeation through skin increased by about 8 times as compared with kojic acid.

Pink-eyed dilution protein modulates arsenic sensitivity and intracellular glutathione metabolism

Mutations in the mouse p (pink-eyed dilution) and human P genes lead to melanosomal defects and ocular developmental abnormalities. Despite the critical role played by the p gene product in controlling tyrosinase processing and melanosome biogenesis, its precise biological function is still not defined. We have expressed p heterologously in the yeast Saccharomyces cerevisiae to study its function in greater detail. Immunofluorescence studies revealed that p reaches the yeast vacuolar membrane via the prevacuolar compartment. Yeast cells expressing p exhibited increased sensitivity to a number of toxic compounds, including arsenicals. Similarly, cultured murine melanocytes expressing a functional p gene were also found to be more sensitive to arsenical compounds compared with p-null cell lines. Intracellular glutathione, known to play a role in detoxification of arsenicals, was diminished by 50% in p-expressing yeast. By using the glutathione-conjugating dye monochlorobimane, in combination with acivicin, an inhibitor of vacuolar gamma-glutamyl cysteine transpeptidase, involved in the breakdown of glutathione, we found that p facilitates the vacuolar accumulation of glutathione. Our data demonstrate that the pink-eyed dilution protein increases cellular sensitivity to arsenicals and other metalloids and can modulate intracellular glutathione metabolism.

Oculocutaneous albinism types 1 and 3 are ER retention diseases: mutation of tyrosinase or Tyrp1 can affect the processing of both mutant and wild-type proteins

Various types of oculocutaneous albinism (OCA) are associated with reduced pigmentation in the skin, hair, and eyes that results from mutations in genes involved in melanin synthesis. Immortal mouse melanocyte lines (melan-a, melan-b, and melan-c) provide opportune models with which to investigate the etiology of two different types of OCA (types I and III), which arise from mutations in Tyr and Tyrp1, respectively. We compared intracellular processing, sorting, and degradation of tyrosinase and Tyrp1, and the effects on their catalytic function and melanin synthesis, in these wild-type and mutant melanocytes. A mutation in either Tyr or Tyrp1 increased the time of association of tyrosinase and Tyrp1 with calnexin and Bip, which in turn resulted in the retention of these mutant products in the ER. A mutation in either gene selectively enhanced the duration and efficiency of chaperone interactions (even with the wild-type protein in the mutant melanocytes) and markedly slowed their transport to melanosomes. These results show that OCA1 and OCA3 are (in some cases, at least) ER retention diseases wherein a mutation in one melanogenic protein affects the maturation and stability of the other in the melanogenic pathway.

The molecular basis of oculocutaneous albinism type 1 (OCA1): sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation

Oculocutaneous albinism type 1 (OCA1) is an autosomal recessive disease resulting from mutations of the tyrosinase gene (TYR). To elucidate the molecular basis of OCA1 phenotypes, we analysed the early processing and maturation of several different types of mutant tyrosinase with various degrees of structural abnormalities (i.e. two large deletion mutants, two missense mutants that completely destroy catalytic function and three missense mutants that have a temperature-sensitive phenotype). When expressed in COS7 cells, all mutant tyrosinases were sensitive to endoglycosidase H digestion, and immunostaining showed their localization in the endoplasmic reticulum (ER) and their failure to be sorted further to their target organelles. Pulse-chase experiments showed that all mutant tyrosinases were retained by calnexin in the ER and that they were degraded at similarly rapid rates, which coincided with their dissociation from calnexin. Temperature-sensitive mutant enzymes were sorted more efficiently at 31 degrees C than at 37 degrees C, and their degradation was accelerated at 37 degrees C compared with 31 degrees C. Thus in contrast to the current concept that mutant tyrosinases are transported to melanosomes but are functionally inactive there, our results suggest that mutant tyrosinases may not be transported to melanosomes in the first place. We conclude that a significant component of mutant tyrosinase malfunction in OCA1 results from their retention and degradation in the ER compartment. This quality-control process is highly sensitive to minimal changes in protein folding, and so even relatively minor mutations in peripheral sequences of the enzyme not involved with catalytic activity may result in a significant reduction of functional enzyme in melanosomes.

Catecholamines are required for the acquisition of secretory responsiveness by sweat glands

The sympathetic innervation of sweat glands undergoes a developmental change in transmitter phenotype from catecholaminergic to cholinergic. Acetylcholine elicits sweating and is necessary for development and maintenance of secretory responsiveness, the ability of glands to produce sweat after nerve stimulation or agonist administration. To determine whether catecholamines play a role in the development or function of this system, we examined the onset of secretory responsiveness in two transgenic mouse lines, one albino and the other pigmented, that lack tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Although both lines lack TH, their catecholamine levels differ because tyrosinase in pigmented mice serves as an alternative source for catecholamine synthesis (Rios et al., 1999). At postnatal day 21 (P21), 28 glands on average are active in interdigital hind footpads of albino TH wild-type mice. In contrast, fewer than one gland is active in albino TH null mice, which lack catecholamines in gland innervation. Treatment of albino TH null mice with DOPA, a catecholamine precursor, from P11 to P21 increases the number of active glands to 14. Pigmented TH null mice, which have faint catecholamine fluorescence in the developing gland innervation, possess 12 active glands at P21, indicating that catecholamines made via tyrosinase, albeit reduced from wild-type levels, support development of responsiveness. Gland formation and the appearance of cholinergic markers occur normally in albino TH null mice, suggesting that catecholamines act directly on gland cells to trigger their final differentiation and to induce responsiveness. Thus, catecholamines, like acetylcholine, are essential for the development of secretory responsiveness.

One-allele system in the Korean for MboI-RFLP in exon 1 of the human tyrosinase (TYR) gene

Oculocutaneous albinism is an autosomal recessive genetic disorder. Several types of oculocutaneous albinism are caused by mutation in related genes. Oculocutaneous albinism 1 is associated with the tyrosinase gene. The human tyrosinase gene (TYR) encodes tyrosinase, a key enzyme in melanin biosynthesis. As exon 1 of the gene shows an MboI-RFLP within codon 192 in Caucasians, we studied allele frequencies of MboI 192 polymorphism in 200 chromosomes from 100 unrelated normal Korean individuals. As a result, only one allele system, the presence of the MboI 192 site, was detected in the Korean.

Effects of 4-tertiary butylphenol on the tyrosinase activity in human melanocytes

Vitiligo is a common dermatological disorder characterized by the development of complete pigment loss from focal lesions that tends to increase in size over time. The etiology of vitiligo, resulting in the disappearance of functional melanocytes from involved skin, is not clearly understood. As a consequence, no satisfactory therapy has been developed. A subtype of vitiligo, termed 'occupational' or 'contact' vitiligo, is increased in individuals who are exposed to materials containing phenolic derivatives, such as 4-tertiary butylphenol (4-TBP). Phenolic derivatives are structurally similar to tyrosine, the initial substrate of tyrosinase in the biochemical synthesis of melanin. Therefore, it has been proposed that phenolic derivatives compete with tyrosine for hydroxylation by tyrosinase and interfere with the completion of melanin synthesis and/or generate cytotoxic intermediates. Our results demonstrated that 4-TBP competitively inhibited both tyrosine hydroxylase and dihydroxyphenylalanine (DOPA) oxidase activities of tyrosinase, i.e., the first two catalytic steps in the biochemical conversion of tyrosine to melanin in cultured human melanocytes. This inhibition occurred at concentrations that did not influence the viability of melanocytes. The tyrosinase activity inhibited by 4-TBP was recovered after removing the treatment. 4-TBP did not affect the function of other enzymes, such as succinate-tetrazolium reductase, acid phosphatase and sulfatase. Since depigmentation occurred without a cytotoxic response after exposure of melanocytes to low concentration of 4-TBP, it is unclear whether the interaction between 4-TBP and tyrosinase leads to the destruction of the melanocytes in 'contact/occupational' vitiligo.

Cysteine transport in melanosomes from murine melanocytes

The synthesis of pheomelanin requires the incorporation of thiol-containing compound(s) during the process of mammalian melanogenesis. Since melanins are produced only in specialized, membrane-bound organelles, known as melanosomes, such thiol donor(s) must cross the membrane barrier from the cytosol to the melanosome interior. Cysteine and/or glutathione (GSH) were proposed as suitable thiol donors, although uptake of these compounds into melanosomes was not previously characterized. In this study, we show that cysteine is transported, in a temperature- and concentration-dependent manner, across membranes of melanosomes derived from murine melanocytes. Additional proof that cysteine uptake results from a carrier-mediated process and is not due to simple diffusion or to a membrane channel, was obtained in countertransport experiments, in which melanosomes preloaded with cysteine methyl ester took up significantly more [35S]cysteine than did unloaded controls. In contrast, we were unable to detect any significant uptake of [35S]GSH over a wide concentration range, in the presence or in the absence of reducing agent. This study is the first demonstration of melanosomal membrane transport of cysteine, and it strongly suggests that free cysteine is the thiol source utilized for pheomelanin synthesis in mammalian melanocytes.

Mouse models of Hermansky Pudlak syndrome: a review

Hermansky Pudlak Syndrome (HPS) is a recessively inherited disease affecting the contents and/or the secretion of several related subcellular organelles including melanosomes, lysosomes, and platelet dense granules. It presents with disorders of pigmentation, prolonged bleeding, and ceroid deposition, often accompanied by severe fibrotic lung disease and colitis. In the mouse, the disorder is clearly multigenic, caused by at least 14 distinct mutations. Studies on the mouse mutants have defined the granule abnormalities of HPS and have shown that the disease is associated with a surprising variety of phenotypes affecting many tissues. This is an exciting time in HPS research because of the recent molecular identification of the gene causing a major form of human HPS and the expected identifications of several mouse HPS genes. Identifications of mouse HPS genes are expected to increase our understanding of intracellular vesicle trafficking, lead to discovery of new human HPS genes, and suggest diagnostic and therapeutic approaches toward the more severe clinical consequences of the disease.

Mutations in microphthalmia, the mouse homolog of the human deafness gene MITF, affect neuroepithelial and neural crest-derived melanocytes differently

The mouse microphthalmia (Mitf) gene encodes a basic-helix-loop-helix-zipper transcription factor whose mutations are associated with abnormalities in neuroepithelial and neural crest-derived melanocytes. In wild type embryos, Mitf expression in neuropithelium and neural crest precedes that of the melanoblast marker Dct, is then co-expressed with Dct, and gradually fades away except in cells in hair follicles. In embryos with severe Mitf mutations, neural crest-derived Mitf-expressing cells are rare, lack Dct expression, and soon become undetectable. In contrast, the neuroepithelial-derived Mitf-expressing cells of the retinal pigment layer are retained, express Dct, but not the melanogenic enzyme genes tyrosinase and Tyrp1, and remain unpigmented. The results show that melanocyte development critically depends on functional Mitf and that Mitf mutations affect the neural crest and the neuroepithelium in different ways.

Linear hypopigmentation and hyperpigmentation, including mosaicism

Linear streaks of hypopigmentation or hyperpigmentation along Blaschko's lines are currently grouped under the names hypomelanosis of Ito (HI) and linear and whorled hypermelanosis (LWH). Recent studies have suggested that these linear pigmentary anomalies reflect underlying genetic mosaicism. Mosaic individuals are composed of two or more genetically distinct cell populations, a normal and an abnormal population. In HI and LWH, the types of genetic defects that are detectable in the abnormal population are highly variable, including tetraploidy, partial or complete trisomies, translocations, and point mutations. These results, together with recent studies indicating the incidence of extracutaneous anomalies is lower in HI but higher in LWH than previously estimated, have important clinical implications. The need for a revised nomenclature as well as possible modifications in current recommendations for patient management are discussed.

Spectrophotometric characterization of eumelanin and pheomelanin in hair

Mammalian melanins exist in two chemically distinct forms: the brown to black eumelanins and the yellow to reddish-brown pheomelanins. They can be quantified by HPLC analysis of pyrrole-2,3,5-tricarboxylic acid (PTCA) and aminohydroxyphenylalanine (AHP). We recently developed a spectrophotometric method for assaying the total amount of eu- and pheomelanins by dissolving melanins in Soluene-350 plus water. In this study, we examined whether absorbance at 500 nm (A500) of the Soluene-350 solution reflects the total amount of melanins obtained by the HPLC methods, and whether the ratio of absorbances between 650 and 500 nm reflects the eumelanin/total melanin ratio in mouse hair, sheep wool, and human hair. Our findings were as follows: (1) Total melanin levels calculated from A500 values correlate well with those obtained from PTCA and AHP values by multiplying with the following factors: for mice, PTCA x 45 + AHP x 2.5; for sheep, PTCA x 40 + AHP x 15; and for humans, PTCA x 160 + AHP x 10. (2) The A650/ A500 ratios were higher (0.25-0.33) in black to brown hair while they were significantly lower (0.10-0.14) in yellow to red hair. These results indicate that (1) the A500 value can be used to quantify the total combined amount of eu- and pheomelanins, and (2) the A650/A500 ratio can serve as a parameter to estimate the eumelanin/total melanin ratio. The present method provides a convenient way to qualitatively characterize eu- and pheomelanins in melanins produced in follicular melanocytes.

The interaction of agouti signal protein and melanocyte stimulating hormone to regulate melanin formation in mammals

Important regulatory controls of melanogenesis that operate at the subcellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are reviewed. Melanocyte stimulating hormone and agouti signal protein have antagonistic roles and possibly opposing mechanisms of action in the melanocyte. In the mouse, melanocyte stimulating hormone promotes melanogenic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin production and elicits the synthesis of pheomelanin rather than eumelanin. We are now beginning to understand the complex controls involved in regulating this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physiological consequences for melanocyte function and undoubtedly play important roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection.