Dysfunction Of Melanocytes Research Articles

Tyrosine Kinase Inhibitor Imatinib Mesylate Induces Generalized Skin Hypopigmentation In Chinese Patients with Chronic Myelogenous Leukemia.

AbstractAbstract 4475Imatinib mesylate is a selective tyrosine kinase inhibitor targeting BCR-ABL fusion protein. In the therapy of either interferon refractory or newly diagnosed chronic myeloid leukemia (CML), imatinib significantly improved the prognosis of the disease, albeit with typically mild to moderate adverse effects. In recent years, increasing attention has been focused on the skin hypopigmentation developed after the initiation of imatinib therapy, especially in Asian countries such as India, with the incidence between 33% and 85%, though sparsely reported in western countries. The inhibition of c-kit by imatinib may be a possible explanation, but the exact mechanism for this hypopigmentation caused by imatinib and its potential risk in patients is poorly understood. Here we report our clinical observation of this side effect of imatinib therapy among Chinese CML patients in our institution, as well as a brief in vitro study aiming to investigate the mechanism of the hypopigmentory effect and evaluate its potential risk. Among 116 patients who took imatinib for CML therapy, 90 of them (77.6%) had reported to develop generalized hypopigmentation or whitening in the skin. This side effect usually developed within 3 months after initiation of imatinib, persistent during the therapy, and reversible upon imatinib discontinuation, according to our interviews and observation. More interestingly, in three of these CML patients who originally had vitiligo, the cosmetic appearance seemed to be improved during imatinib therapy due to the whitening effect on normal pigmented skin areas. To further confirm and understand this side effect, we examined the impact of imatinib on cultured normal human melanocytes derived from the foreskins of healthy Chinese adults. Melanocytes were treat with various concentrations of imatinib (1~16 μ M) for different periods of time (1~7 days). Cell proliferation and apoptosis were detected by cell counting kit-8 and flow cytometric assay, respectively. The melanogenic activity of the melanocytes was detected by melanin content assay and tyrosinase activity assay. Moreover, the role of stem cell factor (SCF) and its receptor c-kit in imatinib induced hypopigmentation were investigated. We found that imatinib not only concentration-dependently inhibited melanocyte proliferation in vitro (IC50=6.23 μ M), but also resulted in massive melanocyte apoptosis at concentrations higher than 8 μ M (P<0.01). Even at low concentrations (1-8 μ M), imatinib was able to cause decreases in total melanin content (P<0.05) and tyrosinase activity (P<0.05) which were responsible for skin pigmentation. In addition, imatinib (1-8 μ M) completely abrogated SCF (5 ng/ml) induced melanocyte proliferation (P<0.01) and melanogenesis (P<0.01), through the inhibition of the phosphorylation of c-kit receptor (Tyr 703 and Tyr 719) and the downstream signal transduction, which is pivotal for melanocyte proliferation and melanin synthesis after ultraviolet exposure. These results reveal that imatinib may cause destruction or dysfunction of melanocytes in patients through the inactivation of SCF/c-kit signaling, leading to inability of the skin to produce melanin and perform protection against ultraviolet radiation. Therefore, CML patients who take imatinib are necessarily to be warned for this side effect, and diminish the intensive exposure to sunlight. Although an ethnic or genetic basis for the prevalence difference can not be excluded yet, we tend to believe that the hypopigmentation effect of imatinib was probably underestimated in caucasian patients due to their light skin color. Since the melanocytes used in this study were all isolated from the skin samples of Chinese volunteers, further study may be done to determine whether the similar results can be achieved in primary melanocytes from other ethnic group. Disclosures:No relevant conflicts of interest to declare.

Keratinocyte dysfunction in vitiligo epidermis: cytokine microenvironment and correlation to keratinocyte apoptosis.

Vitiligo is a skin disorder characterized by loss of functional melanocytes. Keratinocytes contribute to melanocyte homeostasis, and keratinocyte alteration may play a role in melanocyte dysfunction in vitiligo. In particular, the release of melanogenic mediators and the level of functioning keratinocytes may affect melanocyte dysfunction in vitiligo epidermis. Keratinocyte-derived mediators involved in pigmentation, analysed by in situ hybridization, and epidermal apoptosis, detected by TUNEL assay and electron microscopy, were evaluated in lesional and perilesional skin biopsies from 15 patients with active vitiligo and in 5 control subjects. Among the melanogenic mediators, stem cell factor (SCF) and endothelin-1 (ET-1) mRNA were significantly reduced in lesional as compared to perilesional epidermis, whereas no difference was observed in mRNA of basic fibroblastic growth factor (bFGF) and granulocyte-monocyte colony stimulating factor (GM-CSF). The expression of mRNA for tumor necrosis factor (TNF)-alpha and interleukin-6 (IL-6), two pro-inflammatory cytokines with an inhibitory effect on pigmentation, was increased in the epidermis from vitiligo biopsies, whereas their expression was practically undetectable in the skin of control subjects. Apoptotic keratinocytes were more abundant in lesional vs. perilesional skin of vitiligo patients and were absent in the epidermis of control subjects. Changes in expression of keratinocyte-derived mediators observed in the present study are consistent with their differential functions in melanocyte regulation. In particular, increased TNF-alpha could contribute to keratinocyte apoptosis, which results in reduced release of melanogenic cytokines and ultimately in melanocyte disappearance.

Association of glutathione S-transferase gene polymorphisms ( GSTM1 and GSTT1) of vitiligo in Korean population

Vitiligo is an acquired pigmentary disorder of the skin involving melanocyte dysfunction. It has been reported that melanocyte impairment could be related to increased oxidative stress. The glutathione S-transferases ( GSTs) are group of polymorphic enzymes that are important in protection against oxidative stress. To find the relationship between GSTM1 and GSTT1 polymorphisms with vitiligo susceptibility, GSTM1 and GSTT1 (homozygous deletion vs. non-deleted) polymorphisms between vitiligo patients ( n = 310) and healthy controls ( n = 549) were analyzed. We observed significant association in null alleles of the GSTM1 ( P < 0.001, OR = 2.048, 95% CI = 1.529–2.743). GSTM1 null type was also statistically different between two vitiligo subtypes and controls (Focal P < 0.001, OR = 2.224, 95% CI = 1.499–3.298; Generalized P = 0.001, OR = 1.974, 95% CI = 1.342–2.904). However, no significant association in GSTT1 ( P = 0.869, OR = 1.024, 95% CI = 0.775–1.353) was observed with vitiligo. In combined analysis of GSTM1 and GSTT1, both null type and GSTM1/ GSTT1 (null/present) group showed significant differences between controls and vitiligo patients. These results suggest that GSTM1 null type might be associated with vitiligo susceptibility in Korean population.

Decreased CD117 expression in hypopigmented mycosis fungoides correlates with hypomelanosis: lessons learned from vitiligo

Hypopigmented mycosis fungoides is an uncommon clinical variant of cutaneous T-cell lymphoma. We hypothesized that hypomelanosis in hypopigmented mycosis fungoides may have a similar mechanism as in vitiligo, a condition in which it is believed that alterations in expression of CD117 (stem cell factor receptor/KIT protein) on epidermal melanocytes and abnormal interactions between melanocytes and surrounding keratinocytes may play a pathogenic role. To test the hypothesis that similar mechanisms might also explain hypopigmentation in hypopigmented mycosis fungoides, skin specimens from five cases each of hypopigmented mycosis fungoides and vitiligo were studied immunohistochemically for immunophenotype of the infiltrating cells, CD117 (expressed by epidermal melanocytes), and pan melanoma cocktail of antigens (gp100, tyrosinase, and MART-1) expression; cases of conventional mycosis fungoides and normal skin were studied in parallel as controls. Our findings confirm a predominance of CD8+ neoplastic T cells in hypopigmented mycosis fungoides. Similarly, the epidermal lymphocytic infiltrate in vitiligo was also composed of CD8+ cytotoxic T cells, in contrast to an epidermal infiltrate composed of CD4+ T cells in conventional mycosis fungoides. The average number of epidermal CD117 expressing cells followed the same pattern of decreased expression in hypopigmented mycosis fungoides as in vitiligo, whereas the levels in conventional mycosis fungoides were higher, and similar to that observed in normal skin. Furthermore, a decreased number of melanocytes per high-power field of the length of the biopsy was present in hypopigmented mycosis fungoides and vitiligo, as compared with either conventional mycosis fungoides or normal skin, suggesting a correlation between decreased expression of CD117 and decreased number of melanocytes. We propose that decreased expression of CD117 and its downstream events in melanocytes may be initiated by cytotoxic effects of melanosomal-antigen-specific CD8+ neoplastic T lymphocytes, resulting in destabilization of CD117 and leading to dysfunction and/or loss of melanocytes in the epidermis of hypopigmented mycosis fungoides.

Epidermal dermal junction and spots in human skin

Epidermal dermal junction and spots in human skin

Mechanisms underlying the dysfunction of melanocytes in vitiligo epidermis: role of SCF/KIT protein interactions and the downstream effector, MITF-M.

Little is known about the mechanisms involved in the dysfunction of melanocytes in vitiligo epidermis. It is hypothesized that some cytokine/receptor interactions may be affected, resulting in dysfunction and/or loss of melanocytes. This study has compared the expression of endothelin (ET)-1, the ET-1 receptor (ET(B)R), granulocyte macrophage colony stimulating factor (GM-CSF), stem cell factor (SCF), the SCF receptor (KIT protein), tyrosinase, and S100 alpha between lesional and non-lesional vitiligo epidermis. Analysis by reverse transcription-polymerase chain reaction (RT-PCR) and by western blotting for ET-1 and SCF unexpectedly demonstrated up-regulated expression of these cytokines in lesional vitiligo epidermis. Immunohistochemistry with antibodies to melanocyte markers revealed that at the edge of the lesional epidermis, melanocytes remain and express tyrosinase, S100 alpha and ET(B)R, but not KIT protein or melanocyte-specific microphthalmia-associated transcription factor (MITF-M). Quantitation of the staining revealed a slight or moderate decrease in the number of S100 alpha, tyrosinase, and ET(B)R-positive cells at the edge of the lesional epidermis. In contrast, the number of cells expressing KIT protein was markedly decreased at the edge of the lesional epidermis compared with the non-lesional epidermis. At the centre of the lesional epidermis, there was complete loss of melanocytes expressing KIT protein, S100 alpha, ET(B)R, and/or tyrosinase. Western blotting revealed down-regulated expression of c-kit and MITF-M proteins at the edge of the lesional epidermis in vitiligo. These findings suggest that reduction in the expression of KIT protein by melanocytes and its downstream effectors, including MITF-M, may be associated with the dysfunction and/or loss of melanocytes in vitiligo epidermis.

Delayed-Amelanotic (DAM or Smyth) Chicken: Melanocyte Dysfunction In Vivo and In Vitro

Chickens of the autoimmune delayed-amelanotic (DAM or Smyth) line develop postnatal feather amelanosis and severe visual defects, both of which are presumed to be due to a dysfunction of melanocytes and a subsequent autoimmune response that eliminates pigment cells. In this report we elucidate further the melanocytic defect. We present a morphologic analysis of the mildly affected erratic (eDAM) group of Smyth chicken whose partial depigmentation and lack of visual impairment resemble human vitiligo more so than do the complete amelanosis and blindness in the classical Smyth line. Histologically, the sequential events leading to amelanosis in the young Smyth chicken occur simultaneously in the feathers of adult eDAM Smyth chickens, and the infiltration of the feather pulp with mononuclear leukocytes correlates with the extent of local pigmentary abnormality. Cytochemical localizations of dopa-oxidase and acid-phosphatase activities in eDAM feather melanocytes suggest that melanogenesis and autophagocytosis of melanosomes occur in tandem and that the rates of both are higher in these cells than in melanocytes of normally pigmented control chickens. Assays for tyrosinase activity in feather follicles indicate a hypermelanization in eDAM feathers and in the pigmented feathers of young Smyth chicks prior to the onset of depigmentation. Finally, we report on the establishment of pure, proliferative cultures of neural crest-derived melanocytes from control and Smyth chicken embryos. The degenerative events in Smyth chicken melanocyte cultures mimic in part those of the cells in vivo and are therefore indicative of a genetic defect that is independent of the immune system.

Greying with age in mice: relation to expression of murine leukemia viruses

Some strains of C57BL/10 H-2-congenic mice were found to exhibit greying with age, whereas others did not. Two patterns of greying were observed, diffuse greying beginning at 4 to 6 months of age and patterned greying beginning at 4 to 6 weeks. Strains exhibiting either greying pattern expressed high levels of infectious ecotropic and mink cell focus-inducing murine leukemia viruses (MuLV) in tests of thymus and spleen and in cultures from skin or tail biopsies, whereas nongreying strains expressed little virus until late in life. Electron microscopy demonstrated large accumulations of MuLV in grey, but not in black areas, of skin from a mouse with patterned greying. Infectious MuLV was produced spontaneously by embryos of greying, but not of nongreying, mice and pups of nongreying strains fostered on greying mothers turned grey after 3 months. These results suggest that greying with age results from melanocyte dysfunction that occurs subsequent to pre- or early postnatal infection with MuLV.

Melanocyte-lymphocyte interaction in human graft-versus-host disease.

Pigmentary disorders in chronic human GvHD comprise reticular or diffuse hyper- and hypopigmentation and seem to result from an interaction between lymphocytes and melanocytes. This interaction could be visualized by standard microscopy with a specific staining for melanin. The main ultrastructural findings were, in hyperpigmented areas: broad contact between melanocytes and lymphocytes, numerous and packed melanosomes, presence of cytoplasmic lipid droplets; in hypopigmented areas: disintegrating melanocytes with large intercellular spaces, small melanosomes, numerous lipid droplets, vacuolated organelles, as well as condensed and convoluted nuclei. Different hypotheses to explain the dysfunction of melanocytes are presented.