Vitiligo: a manifestation of apoptosis?

Vitiligo, reactive oxygen species and T-cells

The acquired depigmenting disorder of vitiligo affects an estimated 1% of the world population and constitutes one of the commonest dermatoses. Although essentially asymptomatic, the psychosocial impact of vitiligo can be severe. The cause of vitiligo remains enigmatic, hampering efforts at successful therapy. The underlying pathogenesis of the pigment loss has, however, been clarified to some extent in recent years, offering the prospect of effective treatment, accurate prognosis and rational preventative strategies. Vitiligo occurs when functioning melanocytes disappear from the epidermis. A single dominant pathway is unlikely to account for all cases of melanocyte loss in vitiligo; rather, it is the result of complex interactions of biochemical, environmental and immunological events, in a permissive genetic milieu. ROS (reactive oxygen species) and H2O2 in excess can damage biological processes, and this situation has been documented in active vitiligo skin. Tyrosinase activity is impaired by excess H2O2 through oxidation of methionine residues in this key melanogenic enzyme. Mechanisms for repairing this oxidant damage are also damaged by H2O2, compounding the effect. Numerous proteins and peptides, in addition to tyrosinase, are similarly affected. It is possible that oxidant stress is the principal cause of vitiligo. However, there is also ample evidence of immunological phenomena in vitiligo, particularly in established chronic and progressive disease. Both innate and adaptive arms of the immune system are involved, with a dominant role for T-cells. Sensitized CD8+ T-cells are targeted to melanocyte differentiation antigens and destroy melanocytes either as the primary event in vitiligo or as a secondary promotive consequence. There is speculation on the interplay, if any, between ROS and the immune system in the pathogenesis of vitiligo. The present review focuses on the scientific evidence linking alterations in ROS and/or T-cells to vitiligo.

Erythrocyte malondialdehyde and glutathione levels in vitiligo patients

BACKGROUND

Vitiligo is an acquired and progressive hypomelanotic disease that manifests as circumscribed depigmented patches on the skin. Although the precise mechanism remains to be elucidated, an imbalance of the oxidant/antioxidant system has been proposed as an important etiologic mechanism.

OBJECTIVE

The objective of this study was to evaluate the oxidant/antioxidant status of vitiligo patients at the erythrocyte level.

METHODS

Fifty-three vitiligo patients and 65 phototype-, age-, and sex-matched healthy controls were included in this study. Blood samples were collected from all subjects, and all patients were instructed to answer a questionnaire.

RESULTS

Erythrocyte levels of malondialdehyde (MDA) and glutathione (GSH) were measured. All patients were told to answer a questionnaire regarding their habitual behavior, including frequency of smoking and type of diet. We observed significantly lower levels of GSH in vitiligo patients, but the levels of MDA did not differ between patients and controls. Vitiligo patients who smoked showed significantly lower GSH levels compared to non-smoking patients, but the levels of MDA were unchanged between the 2 groups.

CONCLUSION

From our results, we conclude that reduced erythrocytic or systemic GSH levels constitute a distinctive feature in vitiligo patients regardless of disease activity.

Analysis of interleukin-10 levels in lesions of vitiligo following treatment with topical tacrolimus

BACKGROUND

Vitiligo is an acquired dermatological condition that is characterized by depigmentation of patches of skin. It is relatively common, occuring in about 0.38-0.50% of the general population, and can engender significant cosmetic disfigurement and psychological sequelae in the affected individual. Recent studies demonstrate that topical tacrolimus (Protopic; Astellas, Markham, ON, Canada) is efficacious in the treatment of vitiligo. We propose that the successful treatment of vitiligo with topical tacrolimus involves the unique immunosuppressive actions of the T lymphocyte T-helper (Th) 2 cytokine, interleukin (IL)-10.

OBJECTIVES

We aimed to monitor clinical changes in lesions of vitiligo treated with topical tacrolimus 0.1% ointment and quantify IL-10 cytokine levels in nonvitiliginous skin, as well as lesions of vitiligo before and following topical tacrolimus therapy.

METHODS

Clinical evaluation of lesions of vitiligo on the basis of surface area and follicular repigmentation under Wood's lamp was performed in 20 enrolled adult patients. Biopsy specimens were obtained from nonvitiliginous skin, as well as lesions of vitiligo before and following topical tacrolimus therapy. Specimens were processed and analysed for expression of IL-10 using the method of enzyme-linked immunosorbent assay.

RESULTS

A statistically significant mean +/- SEM decrease in vitiligo lesion size of 41.0 +/- 5.2% was observed following 3 months of treatment. A pattern of follicular repigmentation was noted by the third month of treatment for all patients completing the study. In addition, there was a statistically significant difference between IL-10 expression in vitiligo lesions following treatment for 3 months with topical tacrolimus compared with untreated vitiligo lesions (P = 0.017) and normal skin (P = 0.004).

CONCLUSIONS

These results confirm that topical tacrolimus is an effective treatment for vitiligo. We propose that topical tacrolimus increases IL-10 expression in vitiligo lesions, and thereby inhibits melanocyte destruction triggered by unchecked Th1 pathways in vitiligo.

Expressional changes in the intracellular melanogenesis pathways and their possible role in the pathogenesis of vitiligo

BACKGROUND

Main pathway in human melanocytes through which signal from the melanocortin system reaches the melanogenesis enzymes is cAMP/PKA pathway and it is modulated by Wnt and MAPK pathways. In our previous study we established significant increase of melanocortin receptor expression in unaffected skin of vitiligo patients compared to healthy subjects.

OBJECTIVE

The aim of this study was to assess the gene expression profile of the intracellular signalling pathways linking melanocortin system with enzymes involved in melanogenesis.

METHODS

Using QRT-PCR method, mRNA expression levels of eight genes related to signal transduction from the melanocortin system to melanogenesis enzymes was measured in lesional and non-lesional skin of vitiligo patients and in the skin of healthy control subjects. Following genes were analyzed in the study: MITF, CREB1, p38, USF1, PIK3CB (PI3K), RPS6KB1, LEF1 and BCL2.

RESULTS

The mRNA levels of MITF, LEF1, p38, PIK3CB and RPS6KB1 were decreased in lesional skin of vitiligo patients compared to skin of healthy control subjects. We also found increased expression of USF1 and BCL2 in non-lesional skin of vitiligo patients compared to skin of healthy control subjects. mRNA levels of MITF and BCL2 were decreased in lesional skin of vitiligo patients compared to non-lesional skin of vitiligo patients.

CONCLUSIONS

Present study indicates increased expression of the genes of the intracellular melanogenesis pathway in the non-lesional skin of vitiligo patients. This finding suggests activation of melanogenesis pathway in the non-lesional skin of vitiligo.

Impaired PI3K/Akt Activation-Mediated NF-κB Inactivation Under Elevated TNF-α Is More Vulnerable to Apoptosis in Vitiliginous Keratinocytes

Levels of the cytokines IL-6, IL-1alpha, and tumor necrosis factor-alpha (TNF-alpha) are significantly higher in lesional than in non-lesional skin of patients with vitiligo. However, how cytokines affect pigmentation is not fully understood. To examine the mechanism, Western blot analysis with TNF-alpha, Fas ligand (FasL), and downstream signaling molecules such as I-kappaB, NF-kappaB, TNF-R1-associated factor 2, Akt, and PTEN (phosphatase and tension homologue) were performed for the suction-blistered depigmented and normally pigmented epidermis from 10 patients. Levels of TNF-alpha and FasL were significantly higher in the depigmented epidermis. Interestingly, phosphorylation levels of I-kappaB, NF-kappaB, and Akt were lower in the depigmented epidermis. Moreover, PTEN, which could inhibit the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway, was significantly higher in depigmented epidermis, implying that vitiliginous keratinocytes may be more susceptible to TNF-alpha-mediated apoptosis through impaired Akt and NF-kappaB activation. To test this hypothesis, cultured normal human keratinocytes were treated with TNF-alpha in the presence of a PI3K inhibitor to suppress Akt activation. Keratinocytes showing impaired Akt activation demonstrated increased apoptosis with less activation of NF-kappaB. Thus, reduced activation of NF-kappaB via impaired PI3K/Akt activation under increased TNF-alpha levels could result in increased apoptosis of vitiliginous keratinocytes.

Neurogenic dysregulation, oxidative stress, autoimmunity, and melanocytorrhagy in vitiligo: can they be interconnected?

Several hypotheses have been proposed to explain vitiligo, including the neural theory, impaired redux status, autoimmunity, and more recently melanocytorrhagy arising from defective cell-cell adhesion. It is most likely that the loss of melanocytes in vitiligo arises through a combination of pathogenic mechanisms that act in concert. Here, we discuss the potential interconnection of several mechanisms that are likely to operate. These include the alteration of melanocyte-specific factors by reactive oxygen species to produce neo-antigens and the role of hypoxia and oxidative stress in antigen presentation and the auto-immune destruction of melanocytes.

Keratinocyte cultures from involved skin in vitiligo patients show an impaired in vitro behaviour

Vitiligo depigmentation is considered a consequence of either melanocyte disappearance or loss of functioning melanocytes in the involved areas. However, it has been reported that keratinocytes in involved vitiligo skin are damaged too. Based on this evidence, we evaluated the in vitro behaviour, in life span cultures, of involved and uninvolved vitiligo keratinocytes and their expression of proliferation, differentiation and senescence markers. An additional purpose was to investigate whether vitiligo keratinocytes from depigmented skin are able to sustain survival and growth of normal melanocytes (when added in co-culture experiments), as normal human keratinocytes manage to do. Our results demonstrate that almost all involved vitiligo keratinocytes have a shorter life span in vitro than the uninvolved cells and all of them do not maintain melanocytes in culture in a physiological ratio. Modification of proliferation and senescence marker expression also occurs. Indeed, we detected low initial expression levels of the senescence marker p16 in involved vitiligo keratinocytes, despite their shorter in vitro life span, and increased expression of proliferating cell nuclear antigen and p53. This preliminary analysis of a small number of in vitro cultured vitiligo keratinocytes suggests an impaired senescence process in lesional vitiligo keratinocytes and attempts to regulate it.

Glutathione prevented dopamine-induced apoptosis of melanocytes and its signaling

BACKGROUND

Dopamine (DA), a monoamine neurotransmitter, is a well-known neurotoxin and plays an etiologic role in neurodegenerative disorders such as Parkinson's disease. DA exerts its toxic effect by generation of reactive oxygen species and quinone product. Vitiligo, a depigmentary disorder of the skin and hair characterized by selective destruction of melanocytes, has been reported to show increased levels of DA with onset and progression of the disease.

OBJECTIVE

The aim of this study is to investigate the cytotoxic effect of DA on melanocytes and to search for protective antioxidants against DA-induced toxicity. In addition, molecular mechanism of cell death was also investigated.

METHODS

Cells were treated with DA and cell viabilities were measured by crystal violet staining method. To investigate the cytoprotective activity of various antioxidants, vitamin C, vitamin E, Trolox, quercetin, N-acetylcysteine (NAC) and l-glutathione (GSH) were used. To study cytoprotective effects of NAC and GSH, Mel-Ab cells and cultured normal human melanocytes were pretreated with NAC or GSH, then DA solution was added. DA-induced apoptosis and activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) were also observed by flow cytometric analysis and Western blotting.

RESULTS

The viability of DA-treated Mel-Ab cells significantly decreased in a dose-dependent manner while keratinocytes were much more resistant to DA-toxicity, which was a consistent finding with the selective melanocyte loss observed in vitiligo. Among various antioxidants used in this study, only thiol-containing antioxidants such as NAC or GSH inhibited both JNK and p38 MAPK activation and apoptosis, indicating the unique protective capacity of thiol compounds. Cultured normal human melanocytes were also susceptible to DA and thiol compounds were very efficiently protective against DA-induced cytotoxicity.

CONCLUSION

DA-induced apoptosis and cytoprotective effect of thiol compounds shown in this study could be a clue to understand pathogenesis of viltigo and provide a new therapeutic strategy.

Cell death of melanophores in zebrafish trpm7 mutant embryos depends on melanin synthesis

Transient receptor potential melastatin 7 (TRPM7) is a broadly expressed, non-selective cation channel. Studies in cultured cells implicate TRPM7 in regulation of cell growth, spreading, and survival. However, zebrafish trpm7 homozygous mutants display death of melanophores and temporary paralysis, but no gross morphological defects during embryonic stages. This phenotype implies that melanophores are unusually sensitive to decreases in Trpm7 levels, a hypothesis we investigate here. We find that pharmacological inhibition of caspases does not rescue melanophore viability in trpm7 mutants, implying that melanophores die by a mechanism other than apoptosis. Consistent with this possibility, ultrastructural analysis of dying melanophores in trpm7 mutants reveals abnormal melanosomes and evidence of a ruptured plasma membrane, indicating that cell death occurs by necrosis. Interestingly, inhibition of melanin synthesis largely prevents melanophore cell death in trpm7 mutants. These results suggest that melanophores require Trpm7 in order to detoxify intermediates of melanin synthesis. We find that unlike TRPM1, TRPM7 is expressed in human melanoma cell lines, indicating that these cells may also be sensitized to reduction of TRPM7 levels.

Dopamine-induced apoptosis in human melanocytes involves generation of reactive oxygen species

BACKGROUND

Previous studies have shown that significant increases in urinary and plasma levels of several monoamines and their metabolites characterize the onset of vitiligo and its progression. Recently, both epidermal keratinocytes and melanocytes were found to have the capacity for the biosynthesis of several catecholamines and serotonin. Some monoamines and their metabolites can induce apoptosis and cytotoxicity in neural cells. However, no previous report has investigated the potential role of these monoamines in inducing apoptosis or cytotoxicity in melanocytes.

OBJECTIVES

To study the effects of dopamine (DA), norepinephrine (NE), epinephrine (EP), and serotonin (5-HT) on melanocyte cytotoxicity and apoptosis.

METHODS

Primary cultures of normal human melanocytes established from the foreskins of normal individuals were treated with different concentrations of DA, NE, EP and 5-HT for 5 and 7 days. Cell viability was measured by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Melanocyte apoptosis was evaluated by morphological examination and flow cytometric analysis. We also measured the generation of reactive oxygen species (ROS) after DA treatment.

RESULTS

Among the four monoamines used in this study, only DA had an effect, dose-dependently decreasing the melanocyte viability at concentrations ranging from 0.01 to 100 micromol L(-1) (0.1 and 1 micromol L(-1), P < 0.05; 10 micromol L(-1), P < 0.01). In addition, DA-induced melanocyte apoptosis was evidenced by the increased percentage of sub-G1 cells from 7.71 +/- 0.28% (control) to 12.22 +/- 1.05% (0.1 micromol L(-1) DA) (P < 0.005), and treatment with the antioxidant N-acetylcysteine (NAC) reversed this apoptotic effect. DA treatment led to the generation of ROS, which could be prevented by pretreatment with NAC.

CONCLUSIONS

DA can induce melanocyte apoptosis, which might be related to the generation of ROS. This novel effect might play an important role in the development or progression of vitiligo, which is currently viewed as a disease process closely related to melanocyte apoptosis.

Skin diseases in consequence of endocrine alterations

The skin is a target organ of several hormones. Specific diseases appear in consequence of hypo- or hypersecretion of endocrine organs, particularly in the elderly patient. There, knowledge of skin alterations is important not only for dermatologists, but also for endocrinologists and other physicians, because a clinical diagnosis of the underlying disease is often possible. In this review, a number of representative skin diseases having an endocrinological basis are described. These include acanthosis nigricans, diseases due to alterations of androgen metabolism, carcinoid syndrome, diseases due to alterations of corticosteroid metabolism, diseases in association with diabetes mellitus, diseases due to alterations of estrogen metabolism, genetic syndromes including dermatological and endocrine symptoms, the glucagonoma syndrome, diseases due to dysfunctions of growth hormone secretion, diseases in association with Merkel cells of the skin, diseases due to dysfunctions of the thyroid gland, diseases to alteration of vitamin D metabolism, and vitiligo and disorders of pigmentation.

Activation of dual apoptotic pathways in human melanocytes and protection by survivin

Apoptosis resistance in melanoma is a primary cause of treatment failure. Apoptotic pathways in melanocytes, from which melanoma arises, are poorly characterized. Human melanocytes were susceptible to apoptosis following exposure to UV radiation (UVB, 24-48 hours), 4-tert-butylphenol (4-TBP, 1-4 hours), and cisplatin (24-48 hours). These responses were associated with Bid cleavage, caspase activation (caspases 3, 8, and 9), mitochondrial depolarization and release of cytochrome c, Smac/DIABLO, and apoptosis-inducing factor (AIF), but not endonuclease G. The apoptotic responses and AIF release were caspase-independent, as they were not blocked by zVal-Ala-Asp(OMe)-fluoromethyl ketone (zVAD-fmk). While RNA interference-mediated knockdown of AIF protected melanocytes against apoptosis induced by serum withdrawal, apoptotic responses to UVB, cisplatin, and 4-TBP were not compromised by AIF knockdown, even in the presence of zVAD-fmk. Finally, adenoviral-mediated expression of Survivin, an inhibitor of apoptosis expressed in melanoma but not melanocytes, protected melanocytes against UVB-induced apoptosis. Survivin expression in melanocytes partially blocked caspase activation and release of mitochondrial release of AIF, cytochrome c, and Smac induced by UVB. These data indicate that multiple stimuli can activate both caspase-dependent and caspase-independent apoptotic pathways in melanocytes, and that endogenous expression of Survivin in melanoma may contribute to apoptosis resistance by multiple mechanisms.

Lack of association with TNF-alpha-308 promoter polymorphism in patients with vitiligo

Vitiligo is an acquired depigmentary disorder of the skin, characterized by incomplete penetrance, multiple susceptibility loci and genetic heterogeneity. An immunologic hypothesis is currently advanced as a possible pathogenesis of vitiligo. The cytokines have an important role in pathogenesis of autoimmunity in which tumor necrosis factor-alpha (TNF-alpha), a paracrine inhibitor of melanocytes, is especially important. Several single-nucleotide polymorphisms (SNP) have been identified in the human TNF gene promoter. The polymorphism at position -308 (TNF-308), which involves substituting G for A and designing the AA genotype, leads to a higher rate of TNF gene transcription than the wild-type GG genotype in in vitro expression studies. It has also been linked to increased susceptibility to several chronic metabolic, degenerative, inflammatory and autoimmune diseases. Therefore, we investigated the TNF-alpha-308 SNP in patients with vitiligo. We examined 61 patients with vitiligo. Healthy age-, ethnically- and sex-matched individuals (n = 123) served as controls. Polymerase chain reaction amplification was used for analysis of the polymorphism at position -308 in promoter of TNF-alpha gene. We found that the distribution of TNF-alpha genotypes in vitiligo patients did not differ from that in control subjects (P > 0.05). Moreover, there was no association between TNF-alpha genotypes and types of vitiligo. In conclusion, we suggest that TNF-alpha-308 SNP is not a genetic risk factor for vitiligo susceptibility.

PI3K mediates protection against TRAIL-induced apoptosis in primary human melanocytes

Melanocytes are cells of the epidermis that synthesize melanin, which is responsible for skin pigmentation. Transformation of melanocytes leads to melanoma, a highly aggressive neoplasm, which displays resistance to apoptosis. In this report, we demonstrate that TNF-related apoptosis-inducing ligand (TRAIL), which was thought to kill only transformed cells, promotes very efficiently apoptosis of primary human melanocytes, leading to activation of caspases 8, 9 and 3, and the cleavage of vital proteins. Further, we show that stem cell factor (SCF), a physiologic melanocyte growth factor that activates both the phosphatidyl-inositol-3 kinase (PI3K) and the extracellular regulated kinase (ERK) pathways, strongly protects melanocytes from TRAIL and staurosporine killing. Interestingly, inhibition of PI3K or its downstream target AKT completely blocks the antiapoptotic effect of SCF, while inhibition of ERK has only a moderate effect. Our data indicate that protection evoked by SCF/PI3K/AKT cascade is not mediated by an increase in the intracellular level of FLIP. Further, only a sustained PI3K activity can protect melanocytes from apoptosis, thereby indicating that the PI3K/AKT pathway plays a pivotal role in melanocyte survival. The results gathered in this report bring new information on the molecular mechanisms involved in primary melanocyte apoptosis and survival that would help to better understand the process by which melanomas acquire their resistance to apoptosis.

Non-lesional vitiliginous melanocytes are not characterized by an increased proneness to nitric oxide-induced apoptosis

Nitric oxide (NO) is a reactive endogenous molecule with multiple functions including inflammation and immunity. NO stimulates melanogenesis by activating soluble guanylyl cyclase (sGC) resulting in increases in intracellular guanosine 3',5'-cyclic monophosphate (cGMP). In vitro experiments showed that NO could inhibit the de novo attachment of melanocytes to extracellular matrix (ECM) suggesting that NO-induced aberrant perturbation of melanocyte-ECM interaction could be a reason for melanocyte loss in vitiliginous lesions. Here, we examined whether there might be differences between normal melanocytes and vitiliginous melanocytes (VMs) with respect to NO-induced detachment from ECM and whether cGMP is involved. We used the direct NO donor (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate and the peroxynitrite donor 3-morpholino-sydnonimine for the present studies. These donors induced detachment of both normal melanocytes and non-lesional VMs in a time- and concentration-dependent manner with comparable susceptibility and similar expression profile of sGC. Treatment of melanocytes with caspase inhibitors reduced cell detachment, indicating that a major part of the detachment is due to apoptosis. The NO-induced detachment but not apoptosis was partly inhibited in the presence of sGC and cGMP-dependent protein kinase inhibitors. In addition, the membrane-permeable cGMP analog 8-(4-chlorophenyethio/guanosine-3',5'-cyclic monophosphate (PCPT) cGMP was not able to induce apoptosis in melanocytes, suggesting that NO-induced detachment of melanocytes via apoptosis is cGMP-independent. The present results also indicate that there are no apparent differences between NO-induced detachment of non-lesional vitiliginous and normal melanocytes from ECM.

Less keratinocyte-derived factors related to more keratinocyte apoptosis in depigmented than normally pigmented suction-blistered epidermis may cause passive melanocyte death in vitiligo

Stem cell factor (SCF) of keratinocyte origin regulates melanocyte growth and survival. Deprivation of survival factors causes the apoptosis of melanocytes. Vitiligo often develops following physical trauma, even if this is minor. The exact mechanism of the Koebner phenomenon in vitiligo is unclear. Apoptosis of keratinocytes, which occurs more in depigmented suction-blistered epidermis than in the normally pigmented counterpart, could reduce levels of keratinocyte-derived factors such as SCF and basic fibroblast growth factor (bFGF). Levels of SCF expression were examined in the depigmented and normally pigmented paired epidermis of 19 patients with vitiligo, and bFGF expression in six patients. The expression of SCF (p<0.001) and bFGF was usually reduced in the depigmented compared with the normally pigmented epidermis. Apoptosis of cultured normal human keratinocytes, which was induced by staurosporine, resulted in a concentration-dependent decrease in levels of SCF mRNA and protein. Normal human melanocytes proliferated more in medium containing SCF or keratinocyte (XB-2) feeder than in medium with neither. Deprivation of SCF or keratinocyte feeder in the culture medium induced a marked decrease in melanocytes as a result of apoptosis. Therefore, lower expression of keratinocyte-derived factors, including SCF, in vitiliginous keratinocytes, which could result from keratinocyte apoptosis, might be responsible for passive melanocyte death and may explain the Koebner phenomenon.

Mitochondria Give Cells a Tan

The discovery of melanogenin, a small molecule that induces pigmentation in melanocytes, has led to identification of a mitochondrial protein as target. The finding is relevant therapeutically, and argues for how chemical biology can be used to elucidate organelle-specific functions.

Physiopathology and genetics of vitiligo

Generalized vitiligo is an acquired disorder in which white patches of skin and overlying hair result from autoimmune loss of melanocytes from involved areas. The autoimmune pathogenesis of vitiligo has become a rapidly evolving field of research. A humoral immune reaction has been implicated through the detection of circulating antibodies. However, recent research focuses on a melanocyte-specific cytotoxic-T-cell immune reaction in the melanocyte destruction. Several candidate genes have been proposed for vitiligo susceptibility. They include genes important for melanin biosynthesis, response to oxidative stress and/or regulation of autoimmunity. A recent genome-wide scan performed on families with numerous members presenting vitiligo has clearly revealed linkage of susceptibility loci.

Keratinocytes in the depigmented epidermis of vitiligo are more vulnerable to trauma (suction) than keratinocytes in the normally pigmented epidermis, resulting in their apoptosis

BACKGROUND

Vitiligo may develop following minor physical trauma. However, in autologous epidermal grafting, depigmentation of the donor (normally pigmented) site from a suction blister is rare, even in cases displaying failure of repigmentation at the recipient (depigmented) site.

OBJECTIVES

To examine whether the suction procedure is more likely to damage keratinocytes in the depigmented than in the normally pigmented epidermis of vitiligo, and to determine what kind of damage occurs to the keratinocytes.

METHODS

Paired roofs of suction blisters from five patients with generalized vitiligo, five with localized and seven with segmental type, were used for the study. Multiple new lesions developed in two of the five patients with the generalized type. Apoptosis of keratinocytes in the epidermis was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick end labelling (TUNEL) staining, with immunohistochemistry for Bax and active caspase 3. Expression of Bcl-2, Bax, FLIP and p53, activation of caspases 3, 8 and 9, and cleavage of poly(adenosine diphosphate ribose) polymerase (PARP) in the epidermis were analysed by Western blotting in four patients with each type.

RESULTS

Apoptotic keratinocytes, which stained with TUNEL and anti-Bax and antiactive caspase 3 antibodies, were scattered in the blistered epidermis, mainly in the lower portions. The depigmented epidermis displayed significantly more apoptotic keratinocytes than the normally pigmented epidermis. The numerical difference between the paired epidermides was related to the disease activity and not to the type of lesions. The number of apoptotic keratinocytes in the normally pigmented epidermis was as high as that in the depigmented epidermis in the two patients with active generalized type vitiligo. Expression of Bax and p53 in the depigmented epidermis was higher than in the normally pigmented epidermis, whereas expression of FLIP was lower. In addition, the activation of caspases 3, 8 and 9, and cleavage of PARP, were increased in the depigmented compared with the normally pigmented epidermis. The degree of difference in expression and activation was parallel to the results of the TUNEL assay.

CONCLUSIONS

The keratinocytes in the depigmented compared with the normally pigmented epidermis of vitiligo may become apoptotic more easily after suction.

The effect of antisense tyrosinase-related protein 1 on melanocytes and malignant melanoma cells

BACKGROUND

Tyrosinase-related proteins (TRPs) include tyrosinase, TRP-1 and TRP-2. The functions of tyrosinase and TRP-2 have been determined, but the biological role of TRP-1 is still controversial and is not well known in humans.

OBJECTIVES

To study further the biological role of the human TRP-1 gene in melanocytes and melanoma cells.

METHODS

TRP-1 cDNA was subcloned into eukaryotic expression vector pcDNA3.1 in the reverse direction, and antisense recombinant vector was transfected into melanocytes and a melanoma cell line using Lipofectamine 2000. Positive cells were selected by geneticin. TRP-1 mRNA level was measured by reverse transcription-polymerase chain reaction (RT-PCR), and TRP-1 protein level by Western blot. Cell cycles were determined by flow cytometry, and the activity of tyrosinase was evaluated by L-DOPA reaction. Light microscopy, electron microscopy and flow cytometry were used to observe cell morphology and apoptosis. For in vivo assays, the antitumour activity of antisense TRP-1 against the malignant melanoma (MM) cell line, Libr, was evaluated in an animal-tumour model of subcutaneous tumours.

RESULTS

Positive transfected cells steadily expressed TRP-1 antisense RNA. RT-PCR and Western blot showed a low level of TRP-1 mRNA and TRP-1 protein, respectively. Cell cycles were blocked in the G1 stage, and the activity of tyrosinase decreased significantly (P < 0.01). Light and electron microscopy showed abnormal cell morphology, and apoptosis was detected. The neoplasia activity of antisense TRP-1-transfected MM cells was significantly lower than that of MM cells (P < 0.01).

CONCLUSIONS

TRP-1 plays an important role in the proliferation, morphology and tyrosinase activity of melanocytes and melanoma cells.

Hypopigmentary Skin Disorders

Alterations of skin and hair pigmentation are important features that have warranted treatment from ancient history on up to modern time. In some cultures, even today patients with vitiligo are regarded as social outcasts and are affected considerably both emotionally and physically. This article presents current options and future directions for the treatment of hypopigmentary disorders. Whereas with congenital disorders, such as albinism and phenylketonuria, no causal therapy has been established up to now, several treatment options for acquired hypopigmentary disorders have been investigated. In particular, in vitiligo, one of the most prevalent hypopigmentary disorders, a number of treatment modalities have been employed in the past 30 years. However, most of them are only able to palliate, not cure, the disease. Depending on the distribution of the hypopigmented lesions (localised or generalised) and the state of the disease (active or stable), several therapeutic options, for example phototherapy, surgical skin grafts, autologous melanocyte transplantation and immunomodulators, can be applied alone or in combination. For phototherapy, because of unfavourable results and adverse effects, ultraviolet (UV) A has been largely replaced by narrow-band UVB for repigmentation of generalised vitiligo. Although immunomodulators, such as corticosteroids, have been used both topically and systemically over the past 3 decades for the treatment of disseminated vitiligo, they are only suitable for the treatment of acrofacial and localised forms because of adverse effects. Hence, new immunomodulatory agents, such as calcineurin antagonists, have recently been introduced as new promising tools to treat acquired hypopigmentary disorders. However, all therapeutic approaches are hampered by the fact that the pathophysiology of hypopigmentary disorders is still poorly understood.

Sphingosine-1-phosphate promotes mouse melanocyte survival via ERK and Akt activation

In this study, we investigated the signalling pathways induced by ultraviolet B (UVB) and the effects of sphingosine-1-phosphate on UVB-induced apoptosis of mouse melanocytes, Mel-Ab, and observed the cytoprotective effects of sphingosine-1-phosphate on UVB-induced apoptosis. Since sphingosine-1-phosphate is a well-known mitogenic agent, we thought it possible that the mitogenic effect of sphingosine-1-phosphate might contribute to cell survival. However, we found that sphingosine-1-phosphate significantly inhibits DNA synthesis. We next examined the regulation of the three major subfamilies of mitogen-activated protein (MAP) kinases and of the Akt pathway by sphingosine-1-phosphate against UVB-induced apoptosis. UVB irradiation resulted in the remarkable and sustained activation of c-Jun N-terminal kinase (JNK), while p38 MAP kinase was only transiently activated. The basal level of extracellular signal-regulated protein kinase (ERK) phosphorylation decreased 30 min after UVB irradiation, whereas the basal level of Akt phosphorylation was unaffected by UVB. We also found that sphingosine-1-phosphate potently stimulates the phosphorylation of both ERK and Akt, which are involved in the cell survival-signalling cascade. Furthermore, the specific inhibition of the ERK and Akt pathways by PD98059 and LY294002, respectively, restored the cytoprotective effect induced by sphingosine-1-phosphate. On the other hand, the p38 inhibitor SB203580 additively enhanced the cytoprotective effect on sphingosine-1-phosphate. Based on these results, we conclude that the activation of p38 MAP kinase plays an important role in UVB-induced apoptosis, and that sphingosine-1-phosphate probably exert its cytoprotective effect in Mel-Ab cells through ERK and Akt activation.

Sphingosine-1-phosphate-induced ERK activation protects human melanocytes from UVB-induced apoptosis

Ultraviolet B (UVB) is known to induce apoptosis in human melanocytes. Here we show the cytoprotective effect of sphingosine-1-phosphate (S1P) against UVB-induced apoptosis. We also show that UVB-induced apoptosis of melanocytes is mediated by caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage, and that S1P prevents apoptosis by inhibiting this apoptotic pathway. We further investigated three major mitogen-activated protein (MAP) kinases after UVB irradiation. UVB gradually activated c-Jun N-terminal kinase (JNK) and p38 MAP kinase, while extracellular signal-regulated protein kinase (ERK) was inactivated transiently. Blocking of the p38 MAP kinase pathway using SB203580 promoted cell survival and inhibited the activation of caspase-3 and PARP cleavage. These results suggest that p38 MAP kinase activation may play an important role in the UVB-induced apoptosis of human melanocytes. To explain this cytoprotective effect, we next examined whether S1P could inhibit UVB-induced JNK and p38 MAP kinase activation. However, S1P was not found to have any influence on UVB-induced JNK or p38 MAP kinase activation. In contrast, S1P clearly stimulated the phosphorylation of ERK, and the specific inhibition of the ERK pathway using PD98059 abolished the cytoprotective effect of S1P. Based on these results, we conclude that the activation of p38 MAP kinase plays an important role in UVB-induced apoptosis, and that S1P may show its cytoprotective effect through ERK activation in human melanocytes.

Evidence for an autoimmune pathogenesis of vitiligo

Vitiligo is a depigmenting disorder characterized by the development of white patches in various distributions, which are due to the loss of melanocytes from the epidermis. A variety of arguments from clinical observations to research findings in human and animal models support the hypothesis of autoimmunity and are reviewed in this article. The association with autoimmune diseases and organ-specific autoantibodies is well known. Various effective treatment options have an immunosuppressive effect. Today the autoimmune pathogenesis of the disease has become a rapidly evolving field of research. Detection of circulating melanocyte antibodies in human and animal models implicates a possible role of humoral immunity. Histological and immunohistochemical studies in perilesional skin suggest the involvement of cellular immunity in vitiligo. Recently, T-cell analyses in peripheral blood further support this hypothesis. Interestingly, new insights in the association of vitiligo and melanoma may help to clarify the role of autoimmunity in the development of vitiligo.