Expression and modulation of apoptosis regulatory molecules in human melanocytes: significance in vitiligo

Analysis of granulysin expression in vitiligo and halo-nevus

Vitiligo and halo nevus are immune-mediated skin diseases that have a similar pathogenesis and involve cellular cytotoxicity mechanisms that are not yet fully understood. In this study, we investigated the expression patterns of the cytolytic molecule granulysin (GNLY) in different cytotoxic cells in skin samples of vitiligo and halo nevus. Skin biopsies were taken from perilesional and lesional skin of ten vitiligo patients, eight patients with halo nevus and ten healthy controls. We analysed the expression of GNLY by immunohistochemistry in CD8+ and CD56+ NK cells. A significantly higher accumulation of GNLY+, CD8+ GNLY+ and fewer CD56+ GNLY+ cells was found in the lesional skin of vitiligo and halo nevus than in the healthy skin. These cells were localised in the basal epidermis and papillary dermis, suggesting that GNLY may be involved in the immune response against melanocytes. Similarly, but to a lesser extent, upregulation of GNLY+ and CD8+ GNLY+ cells was observed in the perilesional skin of vitiligo and halo nevus compared to healthy controls. In this study, we demonstrated for the first time an increased expression of CD8+ GNLY+ T lymphocytes and CD56+ GNLY+ NK cells in lesions of vitiligo and halo nevus, indicating the role of GNLY in the pathogenesis of both diseases.

The Risk of Keratinocyte Cancer in Vitiligo and the Potential Mechanisms Involved

Although light skin types are associated with increased skin cancer risk, a lower incidence of both melanoma and nonmelanoma skin cancer (NMSC) has been reported in patients with vitiligo. We performed a systematic review and meta-analysis on the NMSC risk in patients with vitiligo, indicating a reduced relative risk ratio of NMSC in vitiligo. Furthermore, we propose a series of hypotheses on the underlying mechanisms, including both immune-mediated and nonimmune-mediated pathways. This study reveals insights into the relationship between vitiligo and keratinocyte cancer and can also be used to better inform patients with vitiligo.

The Role of Oxidative Stress in Vitiligo: An Update on Its Pathogenesis and Therapeutic Implications

Vitiligo is an autoimmune skin disorder caused by dysfunctional pigment-producing melanocytes which are attacked by immune cells. Oxidative stress is considered to play a crucial role in activating consequent autoimmune responses related to vitiligo. Melanin synthesis by melanocytes is the main intracellular stressor, producing reactive oxygen species (ROS). Under normal physiological conditions, the antioxidative nuclear factor erythroid 2-related factor 2 (Nrf2) pathway functions as a crucial mediator for cells to resist oxidative stress. In pathological situations, such as with antioxidant defects or under inflammation, ROS accumulate and cause cell damage. Herein, we summarize events at the cellular level under excessive ROS in vitiligo and highlight exposure to melanocyte-specific antigens that trigger immune responses. Such responses lead to functional impairment and the death of melanocytes, which sequentially increase melanocyte cytotoxicity through both innate and adaptive immunity. This report provides new perspectives and advances our understanding of interrelationships between oxidative stress and autoimmunity in the pathogenesis of vitiligo. We describe progress with targeted antioxidant therapy, with the aim of providing potential therapeutic approaches.

Melanocytes and keratinocytes morphological changes in vitiligo patients. A histological, immunohistochemical and ultrastructural analysis

Vitiligo is an idiopathic acquired chronic stigmatizing disease. It is a pigmentary disorder that affects the skin and the mucous membranes, and it is characterized by well-circumscribed, depigmented milky white macules and patches. It has an estimated prevalence of 0.5-2% of the population worldwide. In the previous studies, several mechanisms such as autoimmune, oxidative stress, genetic factors, melanocytorrhagy, and neural hypothesis have been suggested for vitiligo pathogenesis.We aimed to assess the morphological changes of epidermal melanocytes and keratinocytes in patients with vitiligo. This aim will be fulfilled by histological, ultrastructural, and immunohistochemical analysis of skin biopsies from lesioned and non-lesioned sites in vitiligo patients.The study was carried out on 15 selected patients with stable vitiligo vulgaris but not receiving treatment in the last year and they fulfilled our inclusion criteria.Biopsies were taken from lesioned and non-lesioned sites in the same vitiligo patients, and they are processed for examinations by LM (using Hx & E, and Masson Fontana stain), immunohistochemical analysis (using Melan-A, E-cadherin, and caspase-3), and TEM (to demonstrate the ultra-structures).By LM, staining with Hx & E, lesioned skin in vitiligo patients showed hyperkeratosis, basal vacuolization, acanthosis with an increase in the epidermal thickness, ballooning of keratinocytes, and spongiosis. Regarding melanocytes, we observed a few numbers of melanocytes, also we detected some basal epidermal cells contain brown melanin granules. Using Fontana-Masson stain, we found that the melanin pigment is present in both lesioned and non-lesioned skin of vitiligo patients. We confirmed the presence of melanocytes in the lesioned skin by the immunohistochemical staining with Melan-A. The epidermal cells in lesioned skin of vitiligo patients showed weak positive expression of E-cadherin between them and an increase in the number of apoptotic Caspase-3 positive cells. BY TEM, the lesioned skin in vitiligo patients showed that the keratinocytes and melanocytes had various degenerative changes, disturbance of desmosomes in between keratinocytes, and absence of melanosomes in the keratinocytes. The detected melanocytes were degenerated and contained some melanosomes, melanin granules, and autophagosomes.We concluded that vitiligo pathogenesis is a combination of several factors and cannot be explained by only one mechanism. The pathology in the lesioned vitiliginous skin is a combination of several degenerative changes in keratinocytes, and melanocytes.

A Concise Review on the Role of Endoplasmic Reticulum Stress in the Development of Autoimmunity in Vitiligo Pathogenesis

Vitiligo is characterized by circumscribed depigmented macules in the skin resulting due to the autoimmune destruction of melanocytes from the epidermis. Both humoral as well as cell-mediated autoimmune responses are involved in melanocyte destruction. Several studies including ours have established that oxidative stress is involved in vitiligo onset, while autoimmunity contributes to the disease progression. However, the underlying mechanism involved in programing the onset and progression of the disease remains a conundrum. Based on several direct and indirect evidences, we suggested that endoplasmic reticulum (ER) stress might act as a connecting link between oxidative stress and autoimmunity in vitiligo pathogenesis. Oxidative stress disrupts cellular redox potential that extends to the ER causing the accumulation of misfolded proteins, which activates the unfolded protein response (UPR). The primary aim of UPR is to resolve the stress and restore cellular homeostasis for cell survival. Growing evidences suggest a vital role of UPR in immune regulation. Moreover, defective UPR has been implicated in the development of autoimmunity in several autoimmune disorders. ER stress-activated UPR plays an essential role in the regulation and maintenance of innate as well as adaptive immunity, and a defective UPR may result in systemic/tissue level/organ-specific autoimmunity. This review emphasizes on understanding the role of ER stress-induced UPR in the development of systemic and tissue level autoimmunity in vitiligo pathogenesis and its therapeutics.

The fate of melanocyte: Mechanisms of cell death in vitiligo

Loss of melanocytes (MCs) is the most notable feature of vitiligo. Hence, it is critical to clarify the mechanisms of MC destruction in vitiligo. Apoptosis is most widely studied cell death pathways in vitiligo. In addition, the other two forms of cell death, conventional necrosis and autophagy seem to be involved in the death of vitiligo MCs under certain situations. Moreover, new types of regulated cell death including necroptosis, pyroptosis, and ferroptosis may also participate in the pathogenesis of vitiligo. Anoikis is likely to be connected with the death of detached MCs, which is provoked specifically by loss of anchorage. Primary phagocytosis, later called phagoptosis can execute death of viable cells, probably partly responsible for the loss of MCs in vitiligo. In this review, we aim to summarize the latest insights into various forms of MC death in vitiligo and discuss the corresponding mechanisms.

Efficacy of Cyclosporine After Autologous Noncultured Melanocyte Transplantation in Localized Stable Vitiligo-A Pilot, Open Label, Comparative Study

BACKGROUND

Understanding the pathogenesis of vitiligo has lead to innovation of new drugs and new uses of the existing drugs to enhance treatment outcome.

OBJECTIVE

The aim of this observational pilot study was to assess the role of cyclosporine (CsA) to tackle the commonest aesthetic problem "perilesional halo" after autologous noncultured melanocyte-keratinocyte cell transplant (NCMKT) for localized, stable vitiligo.

MATERIALS AND METHODS

Of the total 50 enrolled patients who underwent NCMKT for stable/resistant vitiligo, aged 12 to 68 years (mean 29.92 years), 18 were male and 32 were female. Group I (n = 25) patients did not receive any postoperative treatment. Group II (n = 25) patients received CsA postoperatively at 3 mg·kg·d for 3 weeks followed by 1.5 mg·kg·d for 6 weeks.

RESULTS

In Group I, results were as follows: 28% (n = 7) achieved >75% repigmentation, 16% (n = 4) achieved 50% to 75% repigmentation, 52% (n = 13) achieved 25% to 50% repigmentation, and 4% (n = 1) achieved <25% repigmentation. In Group II, 100% (n = 25) achieved >75% (median 90.7%) repigmentation post-NCMKT at the end of 6 months.

CONCLUSION

This new drug regimen using CsA resulted in rapid and uniform repigmentation without leaving any perilesional halo in Group II patients after NCMKT.

Impact of high-mobility group box 1 on melanocytic survival and its involvement in the pathogenesis of vitiligo

BACKGROUND

Vitiligo is attributable to loss of functional melanocytes and is the most common acquired depigmenting disorder. Oxidative stress and intense ultraviolet irradiation are known to aggravate this condition. The nonhistone high-mobility group box 1 (HMGB1) DNA-binding protein is a physiological activator of immune responses, cellular proliferation and cell death. Although it is implicated in the pathogenesis of autoimmune diseases and cutaneous disorders, the precise role of HMGB1 in melanocytes has yet to be studied.

OBJECTIVES

To elucidate the effect of HMGB1 on melanocytic survival and its involvement in the pathogenesis of vitiligo.

METHODS

Melanocytes were treated with recombinant HMGB1 (rHMGB1). Thereafter, apoptosis-, autophagy- and melanogenesis-related molecules were detected. Ex vivo skin organ culture was performed after rHMGB1 treatment. Also, levels of HMGB1 were examined in blood and skin specimens from patients with vitiligo.

RESULTS

In this study, rHMGB1 increased expression of cleaved caspase 3 and decreased melanin production and expression of melanogenesis-related molecules. rHMGB1-induced caspase 3 activation was confirmed through preincubation with a pan-caspase inhibitor. In ex vivo experiments for the confirmation of HMGB1-induced melanocyte apoptosis, melanocyte disappearance and increased caspase 3 activation were observed in rHMGB1-treated skin tissues. In Western blot analysis and enzyme-linked immunosorbent assay, patients with active vitiligo showed significantly higher blood levels of HMGB1 (vs. healthy controls). Also, greater expression of HMGB1 was observed in vitiliginous skin (vs. uninvolved skin).

CONCLUSIONS

External stimuli (e.g. oxidative stress and ultraviolet irradiation) may trigger HMGB1 release by keratinocytes, thereby perpetuating vitiligo through HMGB1-induced melanocytic apoptosis.

A similar local immune and oxidative stress phenotype in vitiligo and halo nevus

BACKGROUND

Vitiligo and halo nevus are two common T-cell-mediated skin disorders. Although autoimmunity has been suggested to be involved in both diseases, the relationship between vitiligo and halo nevus is not fully understood.

OBJECTIVE

The aim of the current study was to investigate whether vitiligo and halo nevus share the same immunological and oxidative stress response.

METHODS

Infiltrations of T cells, and expressions of chemokine receptors (CXCR3, CCR4, CCR5) and cytotoxic markers (Granzyme B, Perforin) in the lesions of vitiligo and halo nevus were examined by immunohistochemistry. Enzyme-linked immunosorbent assay was performed to analyze the expressions of chemokines in the serum samples and cytotoxic markers secreted by CD8⁺ T cells which were sorted from the peripheral blood mononuclear cells in healthy donors, vitiligo and halo nevus patients. Tissue levels of chemokine receptors and CXCR3 ligands in healthy controls, vitiligo patients and halo nevus patients were determined by qRT-PCR analysis. The percentages of CXCR3⁺ CD4⁺ T and CXCR3⁺ CD8⁺ T cells from the peripheral blood samples were examined by flow cytometry. Tissue and serum hydrogen peroxide (H₂O₂) concentrations were measured using H₂O₂ assay kit.

RESULTS

Immunohistochemistry revealed a significant T-cell response, with pronounced dermal infiltrates of CD8⁺ T cells in vitiligo and halo nevus. The inflammatory cytotoxic markers such as Granzyme B and Perforin were also elevated in vitiligo and halo nevus, suggesting inflammatory responses in situ. By qRT-PCR and ELISA assay, we found significantly increased expressions of the chemokine receptor CXCR3 and its ligands, especially the accumulated CXCL10 in the skin lesions of vitiligo and halo nevus. Moreover, the level of H₂O₂, a key player involved in regulation of the immune response was significantly upregulated in the skin lesions of vitiligo and halo nevus. In addition, the increased H₂O₂ concentration correlated positively with CXCL10 level in skin lesions of vitiligo and halo nevus.

CONCLUSIONS

These results demonstrate a H₂O₂-involved autoimmune phenotype in vitiligo and halo nevus, characterized by increased level of IFN-γ-inducible chemokine pair CXCL10-CXCR3, as well as a dense CD8⁺ T infiltration in the skin lesions, thus suggesting a similar pathogenesis of the two diseases.

IL-33 circulating serum levels are increased in patients with non-segmental generalized vitiligo

IL-33 is a recently identified cytokine, encoded by the IL-33 gene, which is a member of the IL-1 family that drives the production of T-helper-2 (Th-2)-associated cytokines. Serum levels of IL-33 have been reported to be up-regulated in various T-helper (Th)-1/Th-17-mediated diseases, such as psoriasis, rheumatoid arthritis, and inflammatory bowel. To investigate whether cytokine imbalance plays a role in the pathogenesis of vitiligo, we performed a case-control association study by enzyme-linked immunosorbent assay of IL-33 in our patients. IL-33 serum levels were measured by a quantitative enzyme immunoassay technique in patients with non-segmental generalized vitiligo and compared with those of healthy controls. IL-33 serum levels in patients with vitiligo were significantly increased than those in healthy controls. There was a positive correlation of IL-33 serum levels with extension of vitiligo and disease activity. This study suggests a possible systemic role of IL-33 in the pathogenesis of vitiligo. Inhibiting IL-33 activity might be a novel therapeutic strategy in the treatment of autoimmune inflammatory disease, like vitiligo.

Vitiligo: interplay between oxidative stress and immune system

Vitiligo is a multifactorial polygenic disorder with a complex pathogenesis, linked with both genetic and non-genetic factors. The precise modus operandi for vitiligo pathogenesis has remained elusive. Theories regarding loss of melanocytes are based on autoimmune, cytotoxic, oxidant-antioxidant and neural mechanisms. Reactive oxygen species (ROS) in excess have been documented in active vitiligo skin. Numerous proteins in addition to tyrosinase are affected. It is possible that oxidative stress is one among the main principal causes of vitiligo. However, there also exists ample evidence for altered immunological processes in vitiligo, particularly in chronic and progressive conditions. Both innate and adaptive arms of the immune system appear to be involved as a primary event 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 article focuses on the scientific evidences linking oxidative stress and immune system to vitiligo pathogenesis giving credence to a convergent terminal pathway of oxidative stress-autoimmunity-mediated melanocyte loss.

CD8+ T cells from vitiligo perilesional margins induce autologous melanocyte apoptosis

Cell-mediated autoimmunity has been suggested to be involved in the melanocyte apoptosis that occurs in vitiligo. We investigated the cytotoxicity to autologous melanocytes of CD8⁺ T cells from the perilesional margins and peripheral blood samples of vitiligo patients. CD8⁺ T cells isolated from skin biopsied from the edges of depigmented skin patches of vitiligo patients or from peripheral blood samples of the same donors were proliferated in culture medium. The primary cultures of CD8⁺ T cells and autologous melanocytes were mixed at ratios of 1:1, 1:2 or 1:5 and incubated for 3 days. The apoptosis of the melanocytes was analyzed by flow cytometry. Secreted cytokines in selected samples were measured by cytokine arrays. The results show that the CD8⁺ T cells were successfully isolated from the vitiligo perilesional margins. This cell population showed a significantly higher percentage of CD69 expression (56.13±3.55 versus 29.93±2.35%, p<0.01) and CD137 expression (41.74±1.06 versus 25.97±1.63%, p<0.01) compared with CD8⁺ T cells in peripheral blood from the same donors. The co-culturing of CD8⁺ T cells from lesional skin with autologous melanocytes induced apoptosis in the melanocytes (16.63±1.21, 16.71±0.63 and 18.32±1.60% for CD8⁺ T cells and autologous melanocytes at ratios of 1:1, 1:2 and 1:5, respectively). IL-6 levels were much higher in the co-culture (3.01-fold higher than in a melanocyte monoculture and 17.32-fold higher than in a CD8⁺ T-cell monoculture). The CD8⁺ T cells were also demonstrated to secrete more IL-13. Taken together, our data demonstrate that the infiltration of active CD8⁺ T cells takes place in the vitiligo perilesional margins. Those CD8⁺ T cells present significantly higher activation levels and higher cytotoxicity to autologous melanocytes than their counterparts from peripheral blood samples. These data suggest that CD8⁺ T cells are likely to be involved in the pathogenesis of vitiligo.

The concept of stability of vitiligo: a reappraisal

Stability is taken as the most important parameter before opting for any transplantation technique to treat vitiligo. But, simultaneous donor site repigmentation and depigmentation of grafts at the recipient site has been noted. Similarly donor site depigmentation with complete repigmentation of the recipient area with pigment growing out from each graft has been observed. Successful repigmentation after regrafting in previous punch failure cases has also been reported. Koebner's phenomenon from history (Kp-h) and test grafting were the only available indicators to assess stability. It is quite ironic to note that even after four decades of experience in vitiligo surgery, there seems to be little consensus among workers regarding the optimal required period of stability. Moreover, the exact concept of stability in vitiligo is itself still not transparent and defined beyond doubt Overdependence on KpH or TG may be sometimes misleading in vitiligo. These two reveal the apparent clinical stability only and that may not be the true reflection of stability status of the disease at the molecular level. Antimelanocyte cytotoxic reactivity was observed among CD8+ TCC isolated from perilesional biopsies of patients with vitiligo. An attempt should be made to clearly fathom and define stability, not merely only on clinical ground but along with electron microscopy and histoenzymological analysis of the perilesional and nonlesional skin of vitiligo patients. Probably some growth factors which are responsible for both mitogenic and melanogenic stimulation of melanocytes should also be taken into account. Some serological test(s) could guide us to measure these growth factors.

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.

A functional single-nucleotide polymorphism in the catechol-O-methyltransferase gene alter vitiligo risk in a Chinese population

Vitiligo is an acquired hypomelanotic skin disorder resulting from the loss of functional melanocytes. The COMT-158 polymorphism can reduce COMT enzyme activity and may thus lead to the overproduction of toxic radicals in the melanocyte microenvironment. To determine whether this polymorphism in the COMT gene is associated with an increased risk of vitiligo in Chinese populations, we used a polymerase chain reaction sequence-specific primer (PCR-SSP) technique to determine the frequency of the polymorphism COMT-158 G > A in 749 vitiligo patients and 763 healthy controls. We found that compared to the COMT-158 GG genotype, the COMT-158 GA genotype (adjusted odds ratio [OR], 1.39; 95% confidence interval [CI], 1.13-1.72) and the combined GA + AA genotype (adjusted OR, 1.41; 95% CI, 1.15-1.74) were associated with an increased risk of generalized vitiligo. The association was more pronounced in patients with early-onset vitiligo (adjusted OR, 1.95; 95% CI, 1.45-2.60), those with a family history of vitiligo (adjusted OR, 3.84; 95% CI, 2.47-5.96), and female patients (adjusted OR, 1.74; 95% CI, 1.29-2.36). When we further clinically stratified the vitiligo patients according to their disease types, we found that the combined GA + AA genotype was associated with vitiligo vulgaris (adjusted OR, 1.31; 95% CI, 1.02-1.68), focal vitiligo (adjusted OR, 1.62; 95% CI, 1.17-2.25), and universal vitiligo (adjusted OR, 1.50; 95% CI, 0.98-2.30), but not with acrofacial vitiligo (adjusted OR, 1.53; 95% CI, 0.86-2.73) or segmental vitiligo (adjusted OR, 1.35; 95% CI, 0.72-2.51). In conclusion, this COMT gene polymorphism may have contributed to the etiology of vitiligo in our Chinese population. Larger population-based studies are required to verify our findings.

Immortalization of human melanocytes does not alter the de novo properties of nitric oxide to induce cell detachment from extracellular matrix components via cGMP

Nitric oxide (NO) is an important mediator in many (patho)physiological processes including inflammation and skin cancer. A key transducer in NO signaling is the soluble guanylyl cyclase (sGC) that catalyzes the formation of guanosine 3',5'-cyclic monophosphate (cGMP). The basic mechanism of NO-cGMP signaling in melanocytic cells is, however, not well elucidated. A setback for such studies is the limited availability of patient-derived melanocytes. Here, we report that immortalized human normal and vitiliginous cell lines generated via cell transfection with human papilloma virus 16 genes E6 and E7 express NO synthase and guanylyl cyclase isoforms and the multidrug resistance-associated proteins 4 and 5 as selective cGMP exporters. Donors of NO (e.g., the NONOate (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate (PAPA-NO) and reactive nitrogen oxygen species (RNOS) like 3-morpholino-sydnonimine (SIN-1) as a donor of peroxynitrite as well as YC-1 as a NO-independent sGC stimulator increased intracellular cGMP levels in immortalized melanocytes (up to eightfold over controls), indicating the expression of functional sGC in these cells. PAPA-NO and SIN-1 also reduced the attachment of immortalized melanocytes to extracellular matrix (ECM) components like fibronectin which was dependent on cellular melanin content and cGMP. Such effects on melanoma cells were positively related to metastatic potential and were cGMP independent. Intriguingly, nonpigmented metastatic melanoma cells were more sensitive to exogenous sources of RNOS than of NO. Thus, immortalized melanocytes can be used as a tool for further research on differences in cell signaling between the different melanocytic lineages in particular towards impairment of cell-ECM adhesion by NO or RNOS, which may be important in metastasis and vitiligo pathogenesis.

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.

Vitiligo: new and emerging treatments

Vitiligo is a cosmetically disfiguring condition, and, although there is no therapeutic full solution yet, some treatment may induce good results in most patients. The disease can be successfully treated with various medical options. Both nonfocused or focused narrowband ultraviolet B phototherapy represents the current treatment of choice, to minimize side effects and reach optimal clinical results. Topical novel approaches are also considered. Surgical methods, consisting of autologous transplantation methods, is generally recommended for focal/stable vitiligo, after medical therapy has failed. Finally, for patients with extensive vitiligo, depigmentation of the residual melanin should be taken into account.

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.

Apoptosis of melanocytes in vitiligo results from antibody penetration

Vitiligo is a rather common disease characterized by depigmentation of skin and mucosae due to the loss of melanocytes, most likely as a result of autoimmune phenomena. In this study we demonstrated apoptotic markers in residual melanocytes in skin biopsies of patients with vitiligo, as well as the presence of serum antibodies to melanocyte-specific antigens in the vast majority of patients. Moreover, we were able to prove that serum IgG antibodies from vitiligo patients, but not from healthy controls, were capable to penetrate into cultured melanocytes in vitro, and trigger them to engage in apoptosis. Our results are consonant with the theory that melanocyte-specific antibodies are responsible for the deletion of melanocytes through antibody penetration and apoptosis.

Vitiligo puzzle: the pieces fall in place

Over the years, the role of biochemical, immunological, genetic, and other biological aspects in the pathogenesis of vitiligo has been studied. So far, no convincing model describing the interplay of these contributing factors has been formulated. Based on existing research, we propose that vitiligo has a multi-factorial etiology, characterized by multiple steps, but always involving an increase of external or internal phenol/catechol concentration, serving as a preferred surrogate substrate of tyrosinase, competing with its physiological substrate tyrosine. The conversion of these substrates into reactive quinones is reinforced by a disturbed redox balance (increasing hydrogen peroxide). Such reactive quinones can be covalently bound to the catalytic centre of tyrosinase (haptenation). This could give rise to a new antigen, carried by Langerhans cells to the regional lymph node, stimulating the proliferation of cytotoxic T cells. However, the activation of such cytotoxic cells is only a first step in skin melanocyte killing, which also depends on a shift in the balance between immune defence and tolerance, e.g. resulting from a decrease in properly functioning T-regulatory cells. With this new model, based on a synthesis of several of the existing theories, in mind, the external and internal factors involved in the etiopathogenesis of vitiligo are reviewed, against the background of reported clinical data, experimental studies and existing and potential new therapies. A similar complex mechanism may also lead to some other autoimmune diseases.

Repigmentation of vitiligo with punch grafting and narrow-band UV-B (311 nm)--a prospective study

BACKGROUND

Phototherapy is already established as an effective mode of therapy in vitiligo. An evidence-based study was carried out of the effect of narrow-band (311 nm) ultraviolet-B (NB-UV-B) radiation in 66 surgically treated patients with recalcitrant vitiligo in whom autologous mini-punch grafting was deployed.

METHODS

A total of 2613 grafts were placed over 108 lesions on 17 regions in 66 individuals (39 females and 27 males) with stable, refractory vitiligo. The age range was 21-48 years. Postsurgically, they were exposed to a suberythemal dose of NB-UV-B (311 nm). Different parameters of surgical repigmentation were documented.

RESULTS

Successful repigmentation was achieved in 57 (86.36%) cases. The appearance of repigmentation (AOR) time in different regions varied between 14 and 32 days, with an overall average of approximately 20.6 days. Maximum pigment spread (MPS) reached 12 mm with an average of 6.5 mm. The relationship between the donor graft area and area of surgical repigmentation was also calculated. Cobblestoning was the most common (31.8%) complication, but improved with time and/or interference.

CONCLUSIONS

Punch grafting in combination with phototherapy (NB-UV-B, 311 nm) was found to be an easy, safe, inexpensive, and effective method of repigmenting static and stubborn vitiligo. Different facets of punch grafting-induced and phototherapy-aided surgical repigmentation were taken into consideration. The area of repigmentation, MPS, and relationship between the donor graft area and area of surgical repigmentation were documented.

A review and a new hypothesis for non-immunological pathogenetic mechanisms in vitiligo

Vitiligo is an acquired depigmenting disorder characterized by the loss of functioning epidermal melanocytes because of multifactorial and overlapping pathogenetic mechanisms. Besides the immunological approach, the study of the metabolic deregulations leading to toxic damage of the melanocytes appears to be more and more relevant. It was only last year that the first in vitro evidence supporting the link and the temporal sequence between the immune response and the cellular oxidative stress was provided, suggesting that the intrinsic damage of the melanocytes is primitive. What can be the guide line of the multiple altered metabolisms? A compromised membrane could render the cell sensitive to the external and internal agents differently, usually ineffective on the cell activity and survival. The primitive altered arrangement of the lipids may affect the transmembrane housing of proteins with enzymatic or receptorial activities, also conferring on them antigenic properties.

Therapeutic implications of autoimmune vitiligo T cells

Vitiligo is an autoimmune disease presenting with progressive loss of skin pigmentation. The disease strikes 1% of the world population, generally during teenage years. The progressive loss of melanocytes from depigmenting vitiligo skin is accompanied by cellular infiltrates containing both CD4+ and CD8+ T lymphocytes. Infiltrating cytotoxic T cells with high affinity T cell receptors have likely escaped clonal deletion in the thymus, allowing such T cells to enter the circulation. Through the expression of CLA, these T cells home to the skin where they express type 1-cytokine profiles and mediate melanocyte apoptosis via the granzyme/perforin pathway. T cells found juxtapositionally apposed to remaining melanocytes can be isolated from the skin. Vitiligo T cells have demonstrated reactivity to antigens previously recognized as target antigens for T cells infiltrating melanoma tumors. In a comparison to existing melanoma-derived T cells, vitiligo T cells displayed superior reactivity towards melanoma cells. It is thought that genes encoding the TCRs expressed by vitiligo skin infiltrating T cells can be cloned and expressed in melanoma T cells, thereby generating a pool of circulating T cells with high affinity for their targets that can re-direct the immune response towards the tumor.

Changes in different melanocyte populations during hair follicle involution (catagen)

Melanin synthesis in the hair follicle (HF) is strictly coupled to the growth stage of the hair cycle and is interrupted during follicle regression (catagen) and resting. Using tyrosine-related protein 2 (Trp)2-LacZ transgenic mice as a model, we show that distinct melanocyte subpopulations of the HF display distinct patterns of apoptosis and survival during catagen. Melanocytes located in the outer root sheath express Bcl-2 and are TUNEL-negative. Part of the pigment-producing melanocytes located above the follicular papilla expresses Fas, TUNEL, and is likely to undergo apoptosis, whereas the other part of these melanocytes expresses c-kit, Bcl-2, and becomes visible in the follicular papilla. During late catagen, TUNEL and Ki-67 negative melanocytes expressing Bcl-2 are seen in the secondary germ of the HF. Lack of proliferation in the follicular melanocytes during catagen suggests that secondary hair germ of late catagen HF is most likely repopulated by melanocytes arising from the outer root sheath or follicular papilla of early/mid-catagen HF. Taken together, these data suggest a possible scenario and mechanisms of the remodeling of the follicular pigmentary unit during HF anagen-catagen-telogen transition and may be used for the establishing in vivo models for pharmacological modulation of melanocyte apoptosis and survival during the hair cycle.

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.

Bcl-2 Reduced and Fas Activated by the Inhibition of Stem Cell Factor/KIT Signaling in Murine Melanocyte Precursors

Stem cell factor (SCF) and its receptor, KIT, are essential to the migration and differentiation of melanocytes during embryogenesis. We previously demonstrated that apoptosis is induced by blocking survival function of the SCF/KIT interaction in a mouse neural crest cell (NCC) primary culture. Using the NCCmelb4 cell line, we investigated the occurrence of apoptosis in the cultured cells when KIT receptors were blocked by the monoclonal anti-KIT antibody (ACK2). Apoptosis following treatment with ACK2 was detected by DNA fragmentation assay, in situ apoptosis detection, and electron microscopy. We noted a decrease in extracellular signal-related kinase (ERK) and ribosomal S6 kinase (RSK) protein expression following ACK2 incubation. Western blot analysis and real-time quantitative RT-PCR revealed an apparent time-dependent reduction in Bcl-2 protein levels with respect to ACK2 within the NCCmelb4 cells. In terms of Bax expression, a difference was not found. Fas and caspase8 proteins increased time-dependently in proportion to ACK2 incubation. We noted apoptotic cell death upon addition of ACK2, with evidence of possible involvement of Bcl-2 and Fas in the induction of apoptosis. In contrast, no significant correlation between Fas ligand (Fas-L) expression and ACK2 was found. Fas activation appears to occur independent of Fas-L during ACK2-induced cell death. Therefore, we propose that Fas-L expression in NCCmelb4 cells does not play a major role in facilitating apoptosis. Furthermore, we hypothesize that these molecules combined with SCF/KIT play an important role in regulating the induction of vertebrate NCC apoptosis during embryogenesis.

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.

Autoimmune aspects of depigmentation in vitiligo

Autoimmune depigmentation of the skin, vitiligo, afflicts a considerable number of people, yet no effective therapeutic modalities have been developed to treat it. In part, this can be attributed to the obscure etiology of the disease, which has begun to reveal itself only recently. It is known that pigment is lost as a function of reduced melanocyte numbers in the epidermis, and that depigmentation is accompanied by T cell influx to the skin in the vast majority of patients. Characterizing such infiltrating T cells as type 1 proinflammatory cytokine-secreting cells reactive with melanocyte-specific antigen is a major step toward effective therapy. Melanoma research has shown that differentiation antigens, also expressed by normal melanocytes, can be immunogenic when expressed in the melanosomal compartment of the cell. Similar reactivity to melanosomal antigens is apparent for T cells infiltrating vitiligo skin. It may eventually be possible to treat patients with decoy antigens that anergize such Tcells, or to prevent recruitment of the T cells to the skin altogether. In this respect, it is important that T cells are recruited to the skin as a function of dendritic cell activation and that dendritic cells are likely activated at sites of epidermal trauma as a consequence of stress proteins that spill over into the microenvironment. Stress proteins chaperoning antigens representative of the cells from which they were derived are then processed by dendritic cells and contribute to their activation. Activated dendritic cells not only migrate to draining lymph nodes to recruit T cells but may execute cytotoxic effector functions as well. The contribution of the effector functions to actual depigmentation of the skin remains to be investigated.

Apoptosis in feathers of Smyth line chickens with autoimmune vitiligo

Vitiligo is an acquired dermatological disorder characterized by a loss of epidermal melanocytes resulting in depigmentation of the skin. Mechanisms underlying the destruction of melanocytes in vitiligo remain unclear. An animal model to study spontaneously occurring autoimmune vitiligo is the mutant Smyth line (SL) of chickens. This investigation was designed to determine whether the pathogenesis of depigmentation in Smyth line chicken vitiligo (SLV) involves an apoptotic mechanism. Terminal deoxynucleotide transferase-mediated fluorescein-dUTP nick end labeling (TUNEL) was used to detect in situ cell apoptosis in cryostat sections of 2-week-old regenerating feathers. Two-week-old regenerating feathers were obtained from SL chickens and their normally pigmented controls including the parental Brown line (BL) and Light Brown Leghorn (LBL) chickens at 6, 8, 10 and 12 weeks of age. In feathers from vitiliginous SL chickens, the number of TUNEL+ cells was significantly (P<or=0.05) higher than that in the feathers of non-vitiliginous SL, BL or LBL chickens. These TUNEL+ cells were primarily located in the epithelial barb ridge where melanocyte cell bodies are located. The extent of this apoptosis in the feathers of SLV chickens varied with the severity of depigmentation of the feathers (i.e., highest in active depigmentation), suggesting a close association between apoptosis and the disappearance of melanocytes. In addition to TUNEL staining, most sections were double-stained with monoclonal antibodies specific to either CD8 or MHC class II molecules to further explore the relationship between CD8+ feather-infiltrating lymphocytes and this increase in apoptotic cells. Compared to normally pigmented controls, the number of CD8+ and MHC class II+ cells in the feather pulp and the barb ridge increased 2-4 weeks before the visible onset of SLV, and was directly related to the changes in the number of TUNEL+ cells prior to, at onset and during depigmentation. Moreover, some of these infiltrating CD8+ cells were localized next to or near the TUNEL+ cells. These observations suggest that enhanced apoptosis in the feather of SLV chickens is a pathogenic mechanism involved in the death of melanocytes and appears to be induced by infiltrating cytotoxic T lymphocytes (CD8+).

Squamous cell carcinoma in vitiligo lesion after long-term PUVA therapy

Photochemotherapy using psoralen and ultraviolet (UV)A irradiation (PUVA) is a useful treatment method for vitiligo. However, long-term PUVA therapy may cause several adverse effects including skin cancer, especially squamous cell carcinoma (SCC). We describe a case of SCC in vitiligo lesion after long-term PUVA therapy.

A critical appraisal of vitiligo etiologic theories. Is melanocyte loss a melanocytorrhagy?

Common generalized vitiligo is an acquired depigmenting disorder characterized by a chronic and progressive loss of melanocytes from the epidermis and follicular reservoir. However, the mechanism of melanocyte disappearance has never been clearly understood, and the intervention of cellular and humoral autoimmune phenomena as primary events remains unproven. In this review, is discussed the data supporting the major theories of vitiligo, namely melanocyte destruction (autoimmune, neural and impaired redox status) and melanocyte inhibition or defective adhesion. Based on recent morphologic findings in vivo supporting a chronic detachment and transepidermal loss of melanocytes in common generalized vitiligo, a new theory is suggested proposing melanocytorrhagy as the primary defect underlying melanocyte loss, integrating most of the possible triggering/precipitating/enhancing effects of other known factors.

Increased epidermal functioning wild-type p53 expression in vitiligo

Despite the lack of protective melanin and increased oxidative stress due to mM concentrations of epidermal H2O2 in vitiligo, there is no significantly increased risk for chronic actinic damage and non-melanoma skin cancer. Therefore the question arises, which protective mechanisms could be involved in the skin of these patients preventing the initiation of these cancers. Recently an overexpression of p53 has been shown in vitiligo. Unfortunately there was no further characterization of this elevated p53. Employing a functional colour yeast assay, the study presented herein demonstrates for the first time the overexpression of a functioning wild-type p53 protein in both depigmented and 'normal' pigmented epidermis of patients with vitiligo compared with healthy controls. Surprisingly long-term narrowband UVB (311 nm) treatment does not alter this expression. Moreover, MDM-2, PCNA and p21 protein expression remain unchanged compared with healthy controls. This increased epidermal p53 in vitiligo coincides with decreased thioredoxin reductase (TR) protein levels in both depigmented and pigmented skin whereas mRNA expression is unaffected. Because TR is one transcriptional target of p53, these results support a wild-type functionality, which was further supported by the specific p53 FASAY yeast test. To our knowledge this is the first example of persistent elevated functioning wild-type p53 in humans. Based on our results we hypothesize that the low incidence for actinic damage, basal cell and squamous cell carcinoma as documented in vitiligo could well reside in a protective function of up-regulated wild-type p53.

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.

Melanocyte detachment after skin friction in non lesional skin of patients with generalized vitiligo

BACKGROUND

In vitiligo, melanocytes are gradually lost in depigmented macules of the skin. The disappearance of melanocytes has, however, not been clearly observed and consequently the aetiology of the disease (autoimmune, neural, cytotoxic) is still elusive. The starting point of vitiligo macules is frequently determined by local conditions such as wounds and excoriations, but may also follow minor traumas such as pressure or repeated friction. This prominent feature is often neglected.

OBJECTIVES

To clarify the biological consequences of repeated friction on the attachment and survival of melanocytes in non lesional vitiligo skin.

METHODS

Light reproducible skin friction was performed for 4 min on the volar forearm of 18 patients with extensive vitiligo and five controls with normal healthy skin. Biopsies from the test area and control skin were taken at 1, 4, 24 and 48 h following friction. Serial sections were examined with standard light microscopy, transmission electron microscopy, histochemistry and immunohistochemistry (dihydroxyphenylalanine, HMB-45, E-cadherin and an early apoptosis marker, M30 cytoDEATH antibody).

RESULTS

The observation of sections at 1 and 48 h after friction on vitiligo skin and at all time points in controls revealed no changes. In contrast, in vitiligo skin at 4 and 24 h after friction, several melanocytes had undergone detachment and were found in various suprabasal positions, including the stratum spinosum, granular layer, and within and outside the stratum corneum.

CONCLUSIONS

Detachment and transepidermal elimination of melanocytes following minor mechanical trauma in non lesional vitiligo skin is probably the cause of depigmentation occurring in the isomorphic response (Koebner phenomenon). We propose that transepidermal elimination of melanocytes in vitiligo should be regarded as a possible mechanism of chronic loss of pigment cells, perhaps previously damaged by another process.

Apoptosis regulators and responses in human melanocytic and keratinocytic cells

Apoptosis in keratinocytes is required for epidermal turnover, stratum corneum formation, and removal of ultraviolet-damaged premalignant cells. Its role in melanocyte homeostasis and transformation, on the other hand, has not been defined, although apoptosis resistance is a commonly recognized feature of melanoma. We examined the expression of apoptosis regulators in melanocytes, keratinocytes, melanoma, and HaCat cells. Melanocytic cells expressed relatively high levels of Bcl-2, Bcl-X(L), Mcl-1, C-IAP-1, C-IAP-2, XIAP, Livin, and Apaf-1. The only apoptotic regulator that was differentially expressed in melanoma cells and not melanocytes was Survivin, whereas Bax was expressed in melanocytes but not in most melanoma lines. Keratinocytic cells, on the other hand, expressed high levels of FLIP and were relatively deficient in Bcl-2 family proteins. Levels of p53 were highest in HaCat cells and some of the melanoma lines, and barely detectable in melanocytes and keratinocytes. Next, susceptibility of these cells types to apoptosis induced by ultraviolet B, the tyrosine analog 4-tert-butylphenol, and cytotoxic drugs was examined. Melanocytes were relatively resistant to ultraviolet B, whereas keratinocytes were unresponsive to 4-tert-butylphenol. Melanocytes and keratinocytes were generally less susceptible than melanoma lines and HaCat cells to etoposide, cisplatin, and staurosporine. Induction of apoptosis in these cell types was generally associated with decreased levels of Mcl-1, XIAP, and Livin, and increased levels of p53, whereas levels of other apoptotic regulators were unaltered. These results provide insights into the potential roles of apoptosis in the function and transformation of epidermal melanocytes and keratinocytes.

Vitiligo: a manifestation of apoptosis?

Vitiligo is a common cutaneous disorder that has significant biological and social consequences for those affected. It is characterized by a loss of melanocytes from the epidermis, which results in the absence of melanin, i.e. depigmentation. There are numerous hypotheses about the etiology of vitiligo, but no data to definitively prove one theory over another. It is likely that there are numerous causes for the loss of these melanocytes. One way to approach the identification of the etiology is to determine the mechanism by which the melanocytes are destroyed. The two known mechanisms for the destruction of cells are necrosis and apoptosis. One purpose of this paper is to review the extant data that might suggest which of the two mechanisms is operative against melanocytes in patients with vitiligo. The histological data, and some laboratory data, support apoptosis, rather than necrosis, as the mechanism for removal of melanocytes. Apoptosis can be induced by a variety of factors, including immune cytokines, some environmental chemicals (for example substituted hydroquinones such as monobenzone) or other molecular mechanisms. Current therapies, such as corticosteroids and ultraviolet light, do affect apoptosis in a variety of ways. Confirmation of apoptosis as a mechanism, and identification of how apoptosis is initiated to produce vitiligo, can serve as a basis for devising medications that might stop the progression of the disorder. The problem of vitiligo would be essentially solved if there was a medication that is well tolerated in children, adults and pregnant women, and that would halt the progression of the depigmentation. The study of apoptosis, mechanisms of its induction, and the ways to block apoptosis, is one possible way to find both the causes of depigmentation and medications to prevent its progression.