Sphingosylphosphorylcholine is a Melanogenic Stimulator for Human Melanocytes

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Cutting Edge of the Pathogenesis of Atopic Dermatitis: Sphingomyelin Deacylase, the Enzyme Involved in Its Ceramide Deficiency, Plays a Pivotal Role

Atopic dermatitis (AD) is characterized clinically by severe dry skin and functionally by both a cutaneous barrier disruption and an impaired water-holding capacity in the stratum corneum (SC) even in the nonlesional skin. The combination of the disrupted barrier and water-holding functions in nonlesional skin is closely linked to the disease severity of AD, which suggests that the barrier abnormality as well as the water deficiency are elicited as a result of the induced dermatitis and subsequently trigger the recurrence of dermatitis. These functional abnormalities of the SC are mainly attributable to significantly decreased levels of total ceramides and the altered ceramide profile in the SC. Clinical studies using a synthetic pseudo-ceramide (pCer) that can function as a natural ceramide have indicated the superior clinical efficacy of pCer and, more importantly, have shown that the ceramide deficiency rather than changes in the ceramide profile in the SC of AD patients plays a central role in the pathogenesis of AD. Clinical studies of infants with AD have shown that the barrier disruption due to the ceramide deficiency is not inherent and is essentially dependent on postinflammatory events in those infants. Consistently, the recovery of trans-epidermal water loss after tape-stripping occurs at a significantly slower rate only at 1 day post-tape-stripping in AD skin compared with healthy control (HC) skin. This resembles the recovery pattern observed in Niemann-Pick disease, which is caused by an acid sphingomyelinase (aSMase) deficiency. Further, comparison of ceramide levels in the SC between before and after tape-stripping revealed that whereas ceramide levels in HC skin are significantly upregulated at 4 days post-tape-stripping, their ceramide levels remain substantially unchanged at 4 days post-tape-stripping. Taken together, the sum of these findings strongly suggests that an impaired homeostasis of a ceramide-generating process may be associated with these abnormalities. We have discovered a novel enzyme, sphingomyelin (SM) deacylase, which cleaves the N-acyl linkage of SM and glucosylceramide (GCer). The activity of SM deacylase is significantly increased in AD lesional epidermis as well as in the involved and uninvolved SC of AD skin, but not in the skin of patients with contact dermatitis or chronic eczema, compared with HC skin. SM deacylase competes with aSMase and β-glucocerebrosidase (BGCase) to hydrolyze their common substrates, SM and GCer, to yield their lysoforms sphingosylphosphorylcholine (SPC) and glucosylsphingosine (GSP), respectively, instead of ceramide. Consistently, those reaction products (SPC and GSP) accumulate to a greater extent in the involved and uninvolved SC of AD skin compared with chronic eczema or contact dermatitis skin as well as HC skin. Successive chromatographies were used to purify SM deacylase to homogeneity with a single band of ≈43 kDa and with an enrichment of >14,000-fold. Analysis of a protein spot with SM deacylase activity separated by 2D-SDS-PAGE using MALDI-TOF MS/MS allowed its amino acid sequence to be determined and to identify it as the β-subunit of acid ceramidase (aCDase), an enzyme consisting of α- and β-subunits linked by amino-bonds and a single S-S bond. Western blotting of samples treated with 2-mercaptoethanol revealed that whereas recombinant human aCDase was recognized by antibodies to the α-subunit at ≈56 and ≈13 kDa and the β-subunit at ≈43 kDa, the purified SM deacylase was detectable only by the antibody to the β-subunit at ≈43 kDa. Breaking the S-S bond of recombinant human aCDase with dithiothreitol elicited the activity of SM deacylase with an apparent size of ≈40 kDa upon gel chromatography in contrast to aCDase activity with an apparent size of ≈50 kDa in untreated recombinant human aCDase. These results provide new insights into the essential role of SM deacylase as the β-subunit aCDase that causes the ceramide deficiency in AD skin.

Sphingomyelin Deacylase, the Enzyme Involved in the Pathogenesis of Atopic Dermatitis, Is Identical to the β-Subunit of Acid Ceramidase

A ceramide deficiency in the stratum corneum (SC) is an essential etiologic factor for the dry and barrier-disrupted skin of patients with atopic dermatitis (AD). Previously, we reported that sphingomyelin (SM) deacylase, which hydrolyzes SM and glucosylceramide at the acyl site to yield their lysoforms sphingosylphosphorylcholine (SPC) and glucosylsphingosine, respectively, instead of ceramide and/or acylceramide, is over-expressed in AD skin and results in a ceramide deficiency. Although the enzymatic properties of SM deacylase have been clarified, the enzyme itself remains unidentified. In this study, we purified and characterized SM deacylase from rat skin. The activities of SM deacylase and acid ceramidase (aCDase) were measured using SM and ceramide as substrates by tandem mass spectrometry by monitoring the production of SPC and sphingosine, respectively. Levels of SM deacylase activity from various rat organs were higher in the order of skin > lung > heart. By successive chromatography using Phenyl-5PW, Rotofor, SP-Sepharose, Superdex 200 and Shodex RP18-415, SM deacylase was purified to homogeneity with a single band of an apparent molecular mass of 43 kDa with an enrichment of > 14,000-fold. Analysis by MALDI-TOF MS/MS using a protein spot with SM deacylase activity separated by 2D-SDS-PAGE allowed its amino acid sequence to be determined and identified as the β-subunit of aCDase, which consists of α- and β-subunits linked by amino bonds and a single S-S bond. Western blotting of samples treated with 2-mercaptoethanol revealed that, whereas recombinant human aCDase was recognized by antibodies to the α-subunit at ~56 kDa and ~13 kDa and the β-subunit at ~43 kDa, the purified SM deacylase was detectable only by the antibody to the β-subunit at ~43 kDa. Breaking the S-S bond of recombinant human aCDase with dithiothreitol elicited the activity of SM deacylase with ~40 kDa upon gel chromatography. These results provide new insights into the essential role of SM deacylase expressed as an aCDase-degrading β-subunit that evokes the ceramide deficiency in AD skin.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Glucerabacter canisensis gen. nov., sp. nov., isolated from dog feces and its effect on the hydrolysis of plant glucosylceramide in the intestine of dogs

A Gram-positive, obligately anaerobic, oval-rod shaped, non-spore-forming, and non-pigmented bacterium, designated strain NATH-2371^T (= JCM31739^T = DSM105698^T), was isolated from dog feces. Comparative 16S rRNA gene sequence analysis revealed that strain NATH-2371^T belongs to Clostridium cluster XIVa, and the closest strains were Coprococcus comes ATCC 27758^T (94.8% 16S rRNA gene sequence similarity) and Clostridium nexile DSM 1787^T (94.0%). Strain NATH-2371^T produced acetate, formate, and ethanol from glucose. Predominant cellular fatty acids are C_16:0 and C_16:0 DMA. On the basis of the phenotypic and genotypic differences, strain NATH-2371^T represents a novel species in a new genus of the family Lachnospiraceae, for which the name Glucerabacter canisensis gen. nov., sp. nov., is proposed. This strain was found to efficiently hydrolyze plant glucosylceramide (GluCer). The abundance of strain NATH-2371^T in dog feces was higher in young dogs than in old dogs. Incubation of dog fecal bacteria showed that GluCer-hydrolyzing activity decreased with the age of dogs. The cell number of strain NATH-2371^T in dog feces appeared to be correlated with GluCer hydrolysis. Thus, this bacterium is likely to play a major role in GluCer hydrolysis in the dog intestine.

Antioxidant and renoprotective effects of sphingosylphosphorylcholine on contrast-induced nephropathy in rats

Contrast induced nephropathy (CIN) is a major cause of morbidity, and increased costs as well as an increased risk of death. This study was evaluated effects of exogenous sphingosylphosphorylcholine (SPC) administration on CIN in rats. Eight animals were included in each of the following eight groups: control, control phosphate-buffered solution (PBS), control SPC 2, control SPC 10, CIN, CIN PBS, CIN SPC 2 and CIN SPC 10. The induced nephropathy was created by injected with 4 g iodine/kg body weight. SPC was administered 3 d at a daily two different doses of 2 μm/mL and 10 μm/mL intraperitoneally. The severity of renal injury score was determined by the histological and immunohistochemical changes in the kidney. Malondialdehyde (MDA), nitric oxide (NO) and superoxide dismutase (SOD) were determined to evaluate the oxidative status in the renal tissue. Treatment with 2 and 10 μM SPC inhibited the increase in renal MDA, NO levels significantly and also attenuated the depletion of SOD in the renal injuryCIN. These data were supported by histopathological findings. The inducible nitric oxide synthase positive cells and apoptotic cells in the renal tissue were observed to be reduced with the 2 and 10 μM SPC treatment. These findings suggested that 2 and 10 μM doses can attenuate renal damage in contrast nephropathy by prevention of oxidative stress and apoptosis. The low and high dose SPC may be a promising new therapeutic agent for CIN.

Effects of sphingosylphosphorylcholine against oxidative stress and acute lung ınjury ınduced by pulmonary contusion in rats

BACKGROUND/PURPOSE

The goal of this study was to evaluate effects of exogenous sphingosylphosphorylcholine (SPC) administration on acute lung injury induced by pulmonary contusion in rats.

METHODS

Eight animals were included in each of the following five groups: control, contusion, contusion phosphate-buffered solution (PBS), contusion SPC 2, contusion SPC 10. SPC was administered 3 days at a daily two different doses of 2 μm/ml and 10 μm/ml intraperitoneally. The severity of lung injury was determined by the neutrophil activation and histological and immunohistochemical changes in the lung. Malondialdehyde (MDA), nitric oxide (NO), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione (GSH) were determined to evaluate the oxidative status in the lung tissue.

RESULTS

Treatment with 2 μM SPC inhibited the increase in lung MDA and NO levels significantly and also attenuated the depletion of SOD, GPx, and GSH in the lung injury induced by pulmonary contusion. These data were supported by histopathological findings. The inducible nitric oxide synthase (iNOS) positive cells and apoptotic cells in the lung tissue were observed to be reduced with the 2 μM SPC treatment. But, the 10 μM SPC treatment did not provide similar effects.

CONCLUSIONS

In conclusion, these findings suggested that 2 μM SPC can attenuate lung damage in pulmonary contusion by prevention of oxidative stress, inflammatory process and apoptosis. All these findings suggest that low dose SPC may be a promising new therapeutic agent for acute lung injury.

The regulation of epidermal melanogenesis via cAMP and/or PKC signaling pathways: insights for the development of hypopigmenting agents

Abnormal pigmentation, particularly hyperpigmentation, is major issue of concern for people with colored skin. Several hypopigmenting agents, which exert their action by inhibiting tyrosinase activity and/or transcription, have been used for treatment. However, results have been discouraging. To manage abnormal pigmentation properly, the mechanisms of melanogenesis should be understood. Endogenous and exogenous factors affect melanogenesis via intracellular machineries. cAMP and PKC are critical factors of important transduction pathways and cross-talk between them could amplify the melanogenic effect. Here, factors involved in melanogenesis regulation via cAMP and/or PKC pathways are reviewed with their action mechanisms.

Involvement of mTOR signaling in sphingosylphosphorylcholine-induced hypopigmentation effects

BACKGROUND

Sphingosylphosphorylcholine (SPC) acts as a potent lipid mediator and signaling molecule in various cell types. In the present study, we investigated the effects of SPC on melanogenesis and SPC-modulated signaling pathways related to melanin synthesis.

METHODS

Melanin production was measured in Mel-Ab cells. A luciferase assay was used to detect transcriptional activity of the MITF promoter. Western blot analysis was performed to examine SPC-induced signaling pathways.

RESULTS

SPC produced significant hypopigmentation effects in a dose-dependent manner. It was found that SPC induced not only activation of Akt but also stimulation of mTOR, a downstream mediator of the Akt signaling pathway. Moreover, SPC decreased the levels of LC3 II, which is known to be regulated by mTOR. Treatment with the mTOR inhibitor rapamycin eliminated decreases in melanin and LC3 II levels by SPC. Furthermore, we found that the Akt inhibitor LY294002 restored SPC-mediated downregulation of LC3 II and inhibited the activation of mTOR by SPC.

CONCLUSIONS

Our data suggest that the mTOR signaling pathway is involved in SPC-modulated melanin synthesis.

Sphingosylphosphorylcholine inhibits melanin synthesis via pertussis toxin-sensitive MITF degradation

Objectives

Sphingolipids act as structural components in cell membranes, and form lipid intermediates that have functional roles as signalling molecules in various cellular processes. Our previous findings have suggested that sphingolipid metabolites are deeply involved in the regulation of melanogenic processes. In this study we aimed to examine sphingosylphosphorylcholine-mediated signalling pathways related to melanogenesis.

Methods

We determined the hypopigmenting effects and the related signalling pathways of sphingosylphosphorylcholine in Mel-Ab cells. In particular, we analysed the involvement of the G-protein-coupled receptor in sphingosylphosphorylcholine-induced MITF degradation.

Key findings

Western blotting revealed that sphingosylphosphorylcholine induced the activation of extracellular signal-regulated kinase (ERK), as well as Akt. Moreover, the specific Akt pathway inhibitor LY294002 blocked the hypopigmenting effect of sphingosylphosphorylcholine and abrogated the sphingosylphosphorylcholine-mediated down-regulation of microphthalmia-associated transcription factor (MITF), showing that the Akt pathway is involved in sphingosylphosphorylcholine-mediated melanin inhibition. Treatment with the proteasome inhibitor MG132 blocked the decrease in MITF by sphingosylphosphorylcholine, but sphingosylphosphorylcholine did not decrease the level of MITF mRNA, indicating that the reduction in the level of MITF results from MITF degradation. Furthermore, pre-incubation of Mel-Ab cells with pertussis toxin completely abolished the hypopigmenting effects and the activation of ERK and Akt by sphingosylphosphorylcholine, suggesting that the effects of sphingosylphosphorylcholine are mainly dependent on the G-protein-coupled receptor).

Conclusions

Together, these results suggest that sphingosylphosphorylcholine reduces melanin synthesis via pertussis toxin-sensitive ERK and Akt activation, and subsequent MITF degradation.

A single UVB exposure increases the expression of functional KIT in human melanocytes by up-regulating MITF expression through the phosphorylation of p38/CREB

KIT is an essential receptor that modulates melanocyte function and whose function is disrupted in several pigmentary disorders. However, little is known about the effects of a single UVB exposure on the expression of KIT and two important regulatory transcription factors, MITF and AP-2 alpha, in human melanocytes. We found that a single UVB exposure of human melanocytes induces an early decrease and a subsequent increase in functional KIT expression in concert with up-regulated MITF expression. The increased MITF expression was accompanied by a markedly stimulated and prolonged phosphorylation of p38/CREB. The UVB-stimulated expression of KIT could be completely abolished by a p38 inhibitor, concomitant with a reduced phosphorylation of CREB and a down-regulation of MITF expression. Interestingly, in non-UVB exposed human melanocytes, a MEK inhibitor stimulated the phosphorylation of p38/CREB which was associated with an increased production of MITF and KIT in a pattern similar to that induced by UVB. These findings indicate that UVB stimulates functional KIT expression in human melanocytes via the up-regulation of MITF which is, in turn, due to the activation of p38 and CREB.

Sphingolipid-mediated restoration of Mitf expression and repigmentation in vivo in a mouse model of hair graying

Recent advances in the identification and characterisation of stem cell populations has led to substantial interest in understanding the precise triggers that would operate to induce activation of quiescent stem cells. Melanocyte stem cells (MSCs) reside in the bulge region of the hair follicles and are characterised by reduced expression of the microphthalmia-associated transcription factor (Mitf) and its target genes implicated in differentiation. Vitiligo is characterised by progressive destruction of differentiated melanocytes. However, therapies using UV irradiation therapy can induce a degree of repigmentation, suggesting that MSCs may be activated. As Mitf is implicated in control of proliferation, we have explored the possibility that inducing Mitf expression via lipid-mediated activation of the p38 stress-signalling pathway may represent a re-pigmentation strategy. Here we have isolated from placental extract a C18:0 sphingolipid able to induce Mitf and tyrosinase expression via activation of the p38 stress-signalling pathway. Strikingly, in age-onset gray-haired C57BL/6J mice that exhibit decaying Mitf expression, topical application of placental sphingolipid leads to increased Mitf in follicular melanocytes and fresh dense black hair growth. The results raise the possibility that lipid-mediated activation of the p38 pathway may represent a novel approach to an effective vitiligo therapy.

Sophisticated Functions for a Simple Molecule: The Role of Glucosylceramides in Fungal Cells

It is well known that mammalian glycosphingolipids (GSL) play key roles in different physiological and pathophysiological processes. The simplest GSL, glucosylceramide (GlcCer), is formed through the enzymatic transfer of glucose to a ceramide moiety. In mammalian cells this molecule is the building block for the synthesis of lactosylceramides and many other complex GSLs. In fungal cells GlcCer is a major neutral GSL that has been considered during decades merely as a structural component of cell membranes. The recent literature, however, describes the participation of fungal GlcCer in vital processes such as secretion, cell wall assembly, recognition by the immune system and regulation of virulence. In this review we discuss the most recent information regarding fungal GlcCer, including (i) new aspects of GlcCer metabolism, (ii) the involvement of these molecules in virulence mechanisms, (iii) their role as targets of new antifungal drugs and immunotherapeutic agents and, finally, (v) their potential participation on cellular signaling in response to different stimuli.

The role of lysosphingolipids in the regulation of biological processes

This review summarizes data on the role of lysosphingolipids (glucosyl- and galactosylsphingosines, sphingosine-1-phosphate, sphingosine-1-phosphocholine) in the regulation of various biological processes in normal and pathological states.

Activation of the Mitf promoter by lipid-stimulated activation of p38-stress signalling to CREB

The microphthalmia-associated transcription factor Mitf plays a critical role in regulating many aspects of melanocyte biology. It is required for melanoblast and postnatal melanocyte survival, regulates proliferation, and activates genes associated with differentiation such as tyrosinase and related genes involved in melanogenesis. Identifying the signals that regulate Mitf expression is crucial if we are to understand how cells of the melanocyte lineage respond to environmental cues. Here we show that the Mitf promoter is induced by lipid signalling via the p38 stress-activated kinase pathway that is also activated by a wide range of receptors as well as UV irradiation. Signalling via p38 leads to increased phosphorylation and activation of cyclic adenosine monophosphate response element-binding (CREB) that binds and activates the Mitf promoter via the cyclic adenosine monophosphate (cAMP) response element. Moreover, we also show that activation of p38 mediated by lipids is potentiated by inhibition of the PI3kinase pathway but not by inhibition of protein kinase A (PKA). The results identify a mechanism in which stress signalling via p38 leads to activation of CREB, enhanced Mitf expression and consequently increased tyrosinase expression. The results are relevant for the regulation of melanocytes by Mitf, but also raise the possibility that lipid mediated activation of p38 signalling may represent a potential therapy for vitiligo.

Transcriptional activation of tyrosinase gene by human placental sphingolipid

The sphingolipids, a class of complex bioactive lipids, are involved in diverse cellular functions such as proliferation, differentiation, and apoptosis as well as growth inhibition. Recently sphingosylphosphorylcholine (SPC), sphingosine-1-phosphate (S1P), and C2-ceramide (C2-Cer), sphingolipid containing acetic acid are emerging as melanogenic regulators. A bioactive sphingolipid (PSL) was isolated from hydroalcoholic extract of fresh term human placenta and it induced melanogenesis in an in vitro culture of mouse melanoma B16F10 cells. Tyrosinase, the rate-limiting enzyme for melanogenesis, is required to be upregulated for the increased melanin production. The expression of tyrosinase, both at protein as well as mRNA level, was higher in the PSL treated B16F10 cells as evidenced by Western blot and RT-PCR analysis. Actinomycin D and cycloheximide, inhibitors of transcription and translation, respectively, inhibited PSL-induced tyrosinase activity and its protein expression showing decrease in melanogenesis, correspondingly. The activity of GFP coupled tyrosinase promoter was upregulated in transfected B16F10 cells after treating with PSL as determined by fluorescence microscopy, fluorometric analysis, and Western blot. These results, thus, suggested that PSL upregulated tyrosinase gene expression at transcription level through promoter activation to show increased melanogenesis. Therefore, PSL as an inducer of melanogenesis might account for the recovery of pigment in depigmentation disorder.

Sphingosylphosphorylcholine-induced ERK activation inhibits melanin synthesis in human melanocytes

Sphingosylphosphorylcholine (SPC) is emerging as a potent signaling-lipid mediator. In this study, we investigated the effects of SPC on melanogenesis using cultured human melanocytes. Our results show that SPC significantly inhibits melanin synthesis in a concentration-dependent manner, and further that it reduces the activity of tyrosinase, the rate-limiting melanogenic enzyme. SPC treatment was also found to induce short-thick dendrites in human melanocytes, but not to reduce tyrosinase activity in a cell-free system, whereas kojic acid directly inhibited tyrosinase. These results suggest that SPC reduces pigmentation by indirectly regulating tyrosinase. In further experiments, SPC was found to downregulate microphthalmia-associated transcription factor (MITF) and tyrosinase, and Western blotting showed that SPC induces the activations of extracellular signal-regulated kinase (ERK) and 90 kDa ribosomal S6 kinase (RSK-1). Moreover, the specific ERK pathway inhibitor, PD98059, blocked the hypopigmentation effect of SPC, and abrogated the SPC-mediated downregulation of MITF. These results suggest that the ERK pathway is involved in the melanogenic signaling cascade, and that ERK activation by SPC reduces melanin synthesis via MITF downregulation.

Human placental lipid induces melanogenesis through p38 MAPK in B16F10 mouse melanoma

Melanogenesis is one of the characteristic functional activities of melanocyte/melanoma and is regulated via mitogen-activated protein kinase (MAPK) and Akt/protein kinase B (PKB) pathways. Placental total lipid fraction (PTLF), prepared from a hydroalcoholic extract of fresh term human placenta contains sphingolipids and was recently shown to stimulate melanogenesis via up-regulation of the key enzyme tyrosinase in B16F10 mouse melanoma cells. How such lipids mediate their effects on pigmentation and tyrosinase expression is a particularly important aspect of melanogenesis. To study the signaling that leads to tyrosinase expression, we have investigated the roles of the MAPK and Akt/PKB pathways in B16F10 melanoma cells in melanogenesis in response to PTLF. Treatment of cells with PTLF led to the time dependent phosphorylation of p38 MAPK. SB203580, a p38 MAPK inhibitor, completely blocked the PTLF-induced melanogenesis by inhibiting promoter activity and subsequent expression of tyrosinase. Phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002 a blocker of the Akt signaling pathway, or an inhibitor of MEK (MAPK/ERK Kinase), PD98059 when included along with PTLF was found to potentiate PTLF-induced phosphorylation of p38 MAPK together with tyrosinase expression and melanogenesis. The results suggest that the activation of p38 MAPK plays a crucial role in PTLF-induced B16F10 melanogenesis by up-regulating tyrosinase expression.

Human placental lipid induces melanogenesis by increasing the expression of tyrosinase and its related proteins in vitro

Lipids, particularly sphingolipids, are emerging as novel regulators of cellular activity. A placental total lipid fraction (PTLF), the total lipid prepared from an hydroalcoholic extract of fresh term human placenta, was previously shown to have a pigment-inducing activity in an animal model. The PTLF contains sphingolipids which stimulate DNA synthesis and melanin formation with marked morphological changes in B16F10 melanoma cells. In order to identify the mechanism underlying the increased melanin synthesis, B16F10 cells were treated with PTLF to assess the catalytic activities of tyrosinase (i.e. tyrosine hydroxylase and DOPA oxidase), the key regulatory enzyme of melanin synthesis. Tyrosine hydroxylase (estimated by the release of (3)H(2)O) as well as DOPA oxidase (measured spectrophotometrically and also in non-denaturing gels), was stimulated significantly by PTLF. Western blot analysis demonstrated an increase in the expression of tyrosinase, tyrosinase related proteins 1 and 2 (TRP1 and TRP2) at the protein level and RT-PCR analysis revealed stimulated transcription of tyrosinase, TRP1 and TRP2 mRNAs in PTLF-treated B16F10 cells. Actinomycin D and cycloheximide, inhibitors of transcription and translation, respectively, inhibited PTLF-induction of tyrosinase activity with a corresponding decrease in melanogenesis. In all cases, the response to PTLF was similar to that induced by alpha-melanocyte stimulating hormone, a well-known stimulator of melanogenesis. Thus, these results provide the basis of action of PTLF stimulated melanogenesis in B16F10 cells showing that this placental extract is a strong inducer of pigmentation at the transcriptional and translational levels.

Autocrine and paracrine regulation of melanocytes in human skin and in pigmentary disorders

Recently melanogenic paracrine or autocrine cytokine networks have been discovered in vitro between melanocytes and other types of skin cells. These include endothelin (ET)-1, granulocyte macrophage colony stimulating factor, membrane-type stem cell factor (SCF) and growth-related oncogene-alpha for interactions between keratinocytes and melanocytes, and hepatocyte growth factor and soluble type SCF for interactions between fibroblasts and melanocytes. These networks are also associated with corresponding receptors expressed on melanocytes, including ET B receptor and the SCF receptor, c-KIT. Consistent with in vitro findings on the melanogenic paracrine or autocrine cytokine networks, we have found that the up- or down-regulation of such networks is intrinsically involved in vivo in the stimulation of melanocyte functions in several epidermal hyper- or hypo-pigmentary disorders. These are ET-1/ET B receptor as well as membrane type SCF/c-KIT for ultraviolet B-melanosis, granulocyte macrophage colony stimulating factor for ultraviolet A-melanosis, ET-1/ET B receptor as well as membrane type SCF for lentigo senilis, growth related oncogene-alpha for Riehl's melanosis, sphingosylphosphorylcholine for hyperpigmentation in atopic dermatitis, ET-1 for seborrhoeic keratosis, soluble type SCF as well as hepatocyte growth factor for dermatofibroma and café-au-lait macules, and c-KIT for vitiligo vulgaris. These unveiled regulatory mechanisms involved in the abnormal up- or down-regulated levels of lesional melanocyte function provide new insights into therapeutic tools utilizing blockage of responsible cytokine networks.