Epidermal melanocytes in segmental vitiligo show altered expression of E-cadherin, but not P-cadherin

Emerging Role of Fibroblasts in Vitiligo: A Formerly Underestimated Rising Star

Vitiligo is a disfiguring depigmentation disorder characterized by loss of melanocytes. Although numerous studies have been conducted on the pathogenesis of vitiligo, the underlying mechanisms remain unclear. Although most studies have focused on melanocytes and keratinocytes, growing evidence suggests the involvement of dermal fibroblasts, residing deeper in the skin. This review aims to elucidate the role of fibroblasts in both the physiological regulation of skin pigmentation and their pathological contribution to depigmentation, with the goal of shedding light on the involvement of fibroblasts in vitiligo. The topics covered in this review include alterations in the secretome, premature senescence, autophagy dysfunction, abnormal extracellular matrix, autoimmunity, and metabolic changes.

Impact of house dust mite in vitiligo skin: environmental contribution to increased cutaneous immunity and melanocyte detachment

BACKGROUND

Vitiligo is an autoimmune skin disorder characterized by loss of melanocytes. Protease-mediated disruption of junctions between keratinocytes and/or keratinocyte intrinsic dysfunction may directly contribute to melanocyte loss. House dust mite (HDM), an environmental allergen with potent protease activity, contributes to respiratory and gut disease but also to atopic dermatitis and rosacea.

OBJECTIVES

To verify if HDM can contribute to melanocyte detachment in vitiligo and if so, by which mechanism(s).

METHODS

Using primary human keratinocytes, human skin biopsies from healthy donors and patients with vitiligo, and 3D reconstructed human epidermis, we studied the effect of HDM on cutaneous immunity, tight and adherent junction expression and melanocyte detachment.

RESULTS

HDM increased keratinocyte production of vitiligo-associated cytokines and chemokines and increased expression of toll-like receptor (TLR)-4. This was associated with increased in situ matrix-metalloproteinase (MMP)-9 activity, reduced cutaneous expression of adherent protein E-cadherin, increased soluble E-cadherin in culture supernatant and significantly increased number of suprabasal melanocytes in the skin. This effect was dose-dependent and driven by cysteine protease Der p1 and MMP-9. Selective MMP-9 inhibitor, Ab142180, restored E-cadherin expression and inhibited HDM-induced melanocyte detachment. Keratinocytes from patients with vitiligo were more sensitive to HDM-induced changes than healthy keratinocytes. All results were confirmed in a 3D model of healthy skin and in human skin biopsies.

CONCLUSIONS

Our results highlight that environmental mite may act as an external source of pathogen-associated molecular pattern molecules in vitiligo and topical MMP-9 inhibitors may be useful therapeutic targets. Whether HDM contributes to the onset of flares in vitiligo remains to be tested in carefully controlled trials.

Varicella-zoster virus in actively spreading segmental vitiligo skin: Pathological, immunochemical, and ultrastructural findings (a first and preliminary study)

Segmental vitiligo (SV) is a unilateral subtype of vitiligo which is clinically characterized by a cutaneous depigmentation and histologically by a melanocyte loss from the epidermis and hair follicle reservoirs. To date, its pathogenesis remains a mystery. In many cases, this skin depigmentation shares several clinical features and dysfunctions with herpes zoster (HZ). So, for the first time, we examined whether any nucleus and cell fusion associated with a positive immunolabelling of varicella-zoster virus (VZV) and VZV mature virions could be found in SV skin samples as in herpes zoster (HZ). A total of 40 SV samples were used for histological and immunochemical studies. Control samples were obtained from three HZ, and 10 generalized vitiligo lesions. For ultrastructural study, three recent SV and one HZ as controls were recruited. Here, we report that nuclear fusion in epidermal cells were statistically associated with recent SV (p < .001), whereas syncytia formation was associated with long-lasting SV (p = .001). A positive detection of VZV antigen was statistically associated in the epidermis with recent SV and in the dermis with long-lasting SV (p = .001). Finally, the discovery of mature virions in 3/3 recent SV samples provides additional arguments for our viral hypothesis.

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.

Surgical procedures and innovative approaches for vitiligo regenerative treatment and melanocytorrhagy

Surgical treatments for vitiligo are a safe and effective treatment modality for select patients with vitiligo. Many techniques of vitiligo surgery exist, each with unique advantages and disadvantages. We reviewed the various surgical therapies and innovative approaches for vitiligo regenerative treatment reported in the literature. Surgical therapies can be subdivided into tissue grafting methods and cellular grafting methods. Tissue grafting methods mainly include mini punch grafts, suction blister roof grafts, and hair follicle grafts. Cellular grafting methods include cultured and non-cultured treatments. The efficacy needs to be improved largely due to the poor proliferation and quality of the autologous melanocytes. Rho-associated protein kinase inhibitor enhances primary melanocyte culture proliferation from vitiligo patients to prevent apoptosis. Innovative approaches using stem cell methods could prove invaluable in developing a novel cell therapy for patients suffering from vitiligo. We succeeded in inducing melanin pigmentation in mice skin in vivo using our human induced pluripotent stem cell-derived melanocytes. In addition, we reviewed melanocytorrhagy, detachment and transepidermal loss of melanocytes, and melanocyte-related adhesion molecules. These adhesion molecules include epithelial cadherin, discoidin domain receptor tyrosine kinase 1, glycoprotein non-metastatic melanoma protein B, macrophage migration inhibiting factor, 17β-hydroxysteroid dehydrogenase 1, and E26 transformation-specific 1.

The Role of MicroRNAs in Vitiligo: Regulators and Therapeutic Targets

Vitiligo is an acquired skin disorder clinically characterized by the progressive appearance of white maculae due to a loss of functioning epidermal melanocytes. Studies have shown that microRNAs (miRNAs) modulate cellular differentiation, proliferation and apoptosis, including immune cell and melanocyte development and functions. The role of miRNAs in the pathogenesis of several immune-related diseases has been explored. Novel approaches to target miRNAs have recently emerged allowing modulation of miRNAs levels in diverse pathological processes, thus making them promising targets for molecular-based diagnostics and therapy. Here, we report the present status of research on miRNAs expression and functional alterations in vitiligo, in order to more fully understand the role of these molecules in vitiligo pathology.

Autoimmunity in Segmental Vitiligo

The autoimmune basis of segmental vitiligo (SV) has only recently been recognized. Systemic autoimmune diseases are less frequently associated compared to non-segmental vitiligo (NSV), but localized skin disorders - in particular linear morphea - have been repeatedly observed in patients with SV. The inflammatory response is documented on a clinical level with cases displaying erythematous borders or a hypochromic stage, on a histopathological level with predominantly CD8 lymphocytes migrating toward the basal layer and by flow cytometry demonstrating the antimelanocyte specificity of these cytotoxic T cells. The increased risk for halo naevi and NSV in these patients further underline the immune-mediated mechanisms of SV. Nonetheless, the localized and unique distribution pattern points to somatic mosaicism. This places SV in a category of similar diseases such as lichen striatus, blaschkitis, linear lupus erythematosus, and linear scleroderma where an immune reaction against genetically mutated skin cells is believed to be the underlying cause. All these disorders are characterized by a young age of onset, a temporary disease activity with spontaneous resolution, limited response to treatment, and often long-term sequelae. Although challenging, genetic research proving this genetic mosaicism could offer crucial insights into the pathogenesis of both segmental and non-segmental vitiligo.

miR-9 regulates melanocytes adhesion and migration during vitiligo repigmentation induced by UVB treatment

The decreased adhesion ability of melanocytes to the neighboring keratinocytes prompts melanocytes to lose from the epidermis, comprising the critical step in vitiligo pathogenesis. The repigmentation process involves the migration of melanocytes to the lesional area. This study aims to investigate the role and mechanism of microRNA (miR)-9 in the adhesion and migration of melanocytes during vitiligo repigmentation induced by UVB treatment. The HaCaT keratinocytes were used to mimic lesional condition and the PIG1 melanocytes as perilesional condition. Human lesional vitiligo specimens showed increased miR-9 and decreased adhesion molecules such as E-cadherin and β1 integrin. Furthermore, UVB exposure upregulated IL-10, E-cadherin, and β1 integrin, downregulated miR-9 in HaCaT cells. Moreover, the increased IL-10 by UVB exposure decreased miR-9 level by inducing miR-9 methylation via methyltransferase DNMT3A in HaCaT cells. Additionally, miR-9 targeted and inhibited E-cadherin and β1 integrin in HaCaT cells, and suppressed migration of PIG1 cells to UVB-exposed HaCaT cells. In conclusion, miR-9 was suppressed by IL-10 and inhibited migration of PIG1 cells to HaCaT cells during UVB-mediated vitiligo repigmentation.

CDH1 and DDR1 common variants confer risk to vitiligo and autoimmune comorbidities

The weaker expression of the two main proteins adhering melanocytes to the epidermis basal layer, Epithelial Cadherin (E-cadherin) and Discoidin Domain Receptor Tyrosine kinase 1 (DDR1), has been implicated as one of the aggravating factors in the loss of melanocytes in vitiligo. The present study was designed to assess the association between single nucleotide polymorphisms (SNP) in the genes encoding these proteins, CDH1 and DDR1, and the risk of developing vitiligo. The independent case-control study was conducted on the sample including152 patients with vitiligo and 152 matched controls. A questionnaire was completed for recording demographic and clinical characteristics of vitiligo patients. Venous blood samples were taken from all the subjects. Genotype frequencies were determined for CDHI C/T (rs 10431924) and DDRI A/C (rs 2267641) genes polymorphisms using polymerase chain reaction (PCR) amplification method and Restriction Fragment Length Polymorphism (RFLP) analysis. The CDH1 CC genotype was found to be significantly associated with the risk of developing vitiligo. The results of stratified analysis revealed a correlation between CDH1 CC genotype and late age of onset, clinical type of vitiligo, the absence of autoimmune comorbidities and family history of autoimmune disorders. However, the expression level of CDH1 TT genotype increased significantly in patients with autoimmune comorbidities. There was also a significant relationship between the DDR1 CC genotype and the risk of developing vitiligo. The results of stratified analysis revealed a correlation between DDR1 CC genotype and early age of onset, clinical type of vitiligo and absence of family history of autoimmune disorders. The findings of the study confirm the conjecture previously made in the literature regarding the melanocytes' adhesion deficit as an initial step for pigment loss in vitiligo and emphasize the substantial role of friction and koebner phenomenon in the pathogenesis of vitiligo. Moreover, a probable association can be proposed between the adhesion deficit involved in vitiligo and autoimmune disorders.

Molecular and cellular basis of depigmentation in vitiligo patients

Vitiligo is a chronic skin disease characterized by the appearance of zones of depigmentation. It is mostly described as an autoimmune disease in which the immune system destroys the melanocytes. Consistent with this origin, genetic studies have implicated genes encoding proteins mediating the immune response targeting melanocytes in the aetiology of this disease, together with proteins specific to these cells. However, the destruction of melanocytes by the immune system is neither global nor complete, because the patients do not display total depigmentation. The etiopathology of vitiligo is clearly complex and cannot be simply reduced to an autoimmune reaction directed against pigmented cells. Intrinsic changes have been observed in the melanocytes, keratinocytes and dermal cells of vitiligo patients. Identification of the molecular and cellular changes occurring in normally pigmented skin in vitiligo patients, and an understanding of these changes, is essential to improve the definition of trigger events for this disease, with a view to developing treatments with long-term efficacy. This review focuses on the early events identified to date in the non-lesional regions of the skin in vitiligo patients and discusses the process of repigmentation from melanocyte stem cells.