The melanocytorrhagic hypothesis of vitiligo tested on pigmented, stressed, reconstructed epidermis

Enhancing Transcutaneous Drug Delivery: Advanced Perspectives on Skin Models

Skin acts as a dynamic interface with the environment. Pathological alterations in the skin barrier are associated with skin diseases. These conditions are characterized by specific impairments in epidermal barrier functions. Despite its protective nature, the skin can be a relevant route of drug administration, both for topical and transdermal therapy, allowing for improved drug delivery and reducing the incidence of adverse reactions. This manuscript reviews transcutaneous drug delivery as a strategy for treating localized and systemic conditions, highlighting the importance of skin models in the evaluation of drug efficacy and barrier function. It explores advances in in vitro, ex vivo, in vivo, and in silico models for studying cellular uptake, wound healing, oxidative stress, anti-inflammatory, and immune modulation activities. Disease-specific skin models are also discussed.

Autologous Cultured Tissue Engineering Epidermal Sheet Transplantation to Treat Vitiligo of the Hands

BACKGROUND

Despite numerous therapeutic modalities for vitiligo, their efficacy varies. Managing vitiligo affecting the hands poses a particularly intricate challenge, with outcomes trailing those in other anatomical regions.

OBJECTIVE

Assess the determinants influencing the efficacy and safety of autocultured tissue engineering epidermal sheets transplantation in treating hand vitiligo, observed over a 6-month follow-up period.

METHODS

A retrospective analysis was conducted on 33 patients who underwent treatment for hand vitiligo using autocultured tissue engineering epidermal sheets transplantation. Repigmentation extent was evaluated by 2 dermatologists.

RESULTS

The cohort comprised 33 patients, including 24 males and 9 females, with an average age of 26.91 ± 9.24 years (range: 10-49 years). The mean duration of the disease was 11.61 ± 7.83 years (range: 1.5-34 years). Vitiligo lesion stability ranged from 6 months to 4 years, with an average duration of stability calculated at 1.715 ± 1 year. After 6 months, 75.8% (25/33) of patients exhibited a favorable response, with 39.4% (13/33) showing complete or near-complete repigmentation. No adverse events, such as infections or scar formation, were recorded.

CONCLUSION

The authors' investigation suggests that autocultured tissue engineering epidermal sheets transplantation is a highly effective and safe therapeutic approach for hand vitiligo, offering a promising treatment avenue.

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.

LncRNA-mRNA co-expression network revealing the regulatory roles of lncRNAs in melanogenesis in vitiligo

Vitiligo is characterized by the progressive disappearance of melanocytes, resulting in depigmentation. Long noncoding RNAs (lncRNAs) are a class of noncoding RNAs that play an essential role in the regulation of inflammation and immunity. Published reports on the expression profile of lncRNAs in vitiligo cases and the potential biological function of lncRNAs in vitiligo are lacking. We performed RNA-Seq to identify the functions of lncRNAs in vitiligo. In total, 32 upregulated lncRNAs and 78 downregulated lncRNAs were identified in skin lesions with vitiligo. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis demonstrated that mRNAs regulated by abnormally expressed lncRNAs are most relevant to melanocyte function and melanogenesis. We identified 14 aberrantly expressed lncRNAs through the co-expression pattern that regulate the melanogenesis-related genes DCT, TYR, and TYRP1. Therefore, we speculate that these hub genes may be involved in pathological mechanisms in melanocytes in vitiligo. These genes are closely related to melanogenesis in vitiligo. Abnormally expressed lncRNAs directly or indirectly act on these target genes to regulate melanogenesis. Identifying lncRNAs and clarifying the regulatory roles of the lncRNA-mRNA network may be helpful to develop novel diagnoses or treatment targets for vitiligo.

Mechanisms of melanocyte death in vitiligo

Vitiligo is an autoimmune depigment disease results from extensive melanocytes destruction. The destruction of melanocyte is thought to be of multifactorial causation. Genome-wide associated studies have identified single-nucleotide polymorphisms in a panel of susceptible loci as risk factors in melanocyte death. But vitiligo onset can't be solely attributed to a susceptive genetic background. Oxidative stress triggered by elevated levels of reactive oxygen species accounts for melanocytic molecular and organelle dysfunction, a minority of melanocyte demise, and melanocyte-specific antigens exposure. Of note, the self-responsive immune function directly contributes to the bulk of melanocyte deaths in vitiligo. The aberrantly heightened innate immunity, type-1-skewed T helper, and incompetent regulatory T cells tip the balance toward autoreaction and CD8+ cytotoxic T lymphocytes finally execute the killing of melanocytes, possibly alarmed by resident memory T cells. In addition to the well-established apoptosis and necrosis, we discuss several death modalities like oxeiptosis, ferroptosis, and necroptosis that are probably employed in melanocyte destruction. This review focuses on the various mechanisms of melanocytic death in vitiligo pathogenesis to demonstrate a panorama of that. We hope to provide new insights into vitiligo pathogenesis and treatment strategies by the review.

Melanoma Inhibitory Activity (MIA) Is Able to Induce Vitiligo-Like Depigmentation in an in vivo Mouse Model by Direct Injection in the Tail

In the complex pathogenesis of vitiligo, the exact mechanism of the dermatosis is still to be clarified. We previously demonstrated that a protein called melanoma inhibitory activity (MIA) is present in non-segmental vitiligo skin and seems to cause the detachment of melanocytes, consequently creating the depigmented macules. In this study, we present an animal model of vitiligo on the basis of the ability of the MIA protein to induce vitiligo-like lesions. Twenty pigmented mice were chosen for the experiments and received injections in the tail with saline (control group) or with saline + MIA protein (treated group). The control group did not show any sign of depigmentation. The treated group showed, instead, clear zones of complete depigmentation in the injected areas in each mouse, with the appearance of white patches with whitening of the hair and a clear-cut edge. Histological examination of the tail in the treated zone showed the absence of melanocytes, without the presence of any inflammatory cell or any sign of skin inflammation patterns, confirming the detachment of the melanocyte operated by the MIA protein. These data seem to confirm a possible role played by the MIA protein in the pathogenesis of vitiligo and may support the development of treatments able to inhibit its action as an alternative therapeutic strategy for this disorder.

Expression of discoidin domain receptor 1 and E-cadherin in epidermis affects melanocyte behavior in rhododendrol-induced leukoderma mouse model

Vitiligo is a depigmentation disease characterized by gradual loss of melanin and melanocytes from the epidermis. The mechanism of melanocyte loss is not yet known. In this report, we showed that the expression of discoidin domain receptor 1 and E-cadherin, known adhesion molecules, was variable or absent in the epidermis of rhododendrol-induced leukoderma (RDIL) mice during the depigmentation process. Our findings suggest that melanocyte damage by rhododendrol promotes reduction of adhesion molecules not only in melanocytes but also in keratinocytes, and this is associated with the detachment of melanocytes from the basal layer.

DDR1 and DDR2 in skin

DDR1 and DDR2 are expressed in skin but their expression differs according to the skin compartment, epidermis, dermis, hypodermis and to the embryonic origin of the cells. In skin, it seems that during physiological processes such as wound healing or pathological processes such as tumorigenesis or systemic sclerosis development only one of the DDR is dysregulated. Furthermore, the altered DDR in pathological process is not necessarily the DDR implicated in basal homeostasis. Indeed, in epidermis, while DDR1 is the main DDR involved in melanocyte homeostasis, DDR2 seems to be the main DDR implicated in melanoma. On the contrary, in dermis, while DDR2 is necessary for normal wound healing, dysregulation of DDR1 is associated with abnormal wound healing leading to keloid. In conclusion, targeting DDR could be a therapeutic solution, however side effects have to be managed carefully.

Clinical and Molecular Aspects of Vitiligo Treatments

Vitiligo is an asymptomatic but cosmetically disfiguring disorder that results in the formation of depigmented patches on skin and/or mucosae. Vitiligo can be segmental or non-segmental depending upon the morphology of the clinical involvement. It can also be classified as progressing or stable based on the activity of the disease. Further, the extent of involvement can be limited (localized disease) or extensive (generalized disease). The treatment of vitiligo therefore depends on the clinical classification/characteristics of the disease and usually comprises of 2 strategies. The first involves arresting the progression of active disease (to provide stability) in order to limit the area involved by depigmentation. The second strategy aims at repigmentation of the depigmented area. It is also important to maintain the disease in a stable phase and to prevent relapse. Accordingly, a holistic treatment approach for vitiligo should be individualistic and should take care of all these considerations. In this review, we shall discuss the vitiligo treatments and their important clinical and molecular aspects.

Aquaporin 3 and E-Cadherin Expression in Perilesional Vitiligo Skin

INTRODUCTION

Vitiligo is a common dermatologic disorder with debated aetiology. Most studies focused on role of melanocytes and few investigated the role of keratinocytes in pathogenesis of the disease.

AIM

To investigate the keratinocyte adhesion in perilesional vitiligo skin through the immunolocalization of Aquaporin-3 (AQP3) and E-cadherin.

SETTING AND DESIGN

Sixty five subjects were selected. These included 40 cases with vitiligo and 25 age and gender-matched healthy subjects as a control group.

MATERIALS AND METHODS

Skin biopsies were taken from perilesional skin of cases and from site-matched areas of control subjects. The expression of AQP3 and E-cadherin was evaluated by immunohistochemical techniques.

STATISTICAL ANALYSIS

Results were statistically analysed using IBM personal computer and the statistical package SPSS version 11. Fisher-exact and Chi-square tests were used to study the association between two qualitative variables. Mann-Whitney test was used for comparison between quantitative variables not normally distributed. Spearman's correlation coefficient was used to assess correlation between two quantitative variables. The p≤0.05 was considered significant.

RESULTS

Regarding AQP3 expression, strong intensity, diffuse distribution, higher percent of expression and higher H-score (p<0.001 for all) were significantly associated with control skin compared with perilesional skin in follicular and inter-follicular epidermis. Regarding E-cadherin expression, moderate intensity, higher percent of expression and higher H- score (p<0.001 for all) were significantly associated with control skin compared with perilesional skin in follicular and inter-follicular epidermis. No significant association was found between E-cadherin and AQP3 H-scores or percent of expression and clinical data of selected cases. No significant correlation was detected between E-cadherin and AQP3 H-scores or percent of expression and age of cases, disease duration or Vitiligo Disease Activity (VIDA) score.

CONCLUSION

The following sequence of events can be suggested for vitiligo pathogenesis, based on findings in perilesional skin: AQP3 is downregulated by a primary unknown factor and this will lead to down regulation of its downstream molecules, mainly phosphatidylinositol 3-kinase, E-cadherin and catenins, which is followed by defective keratinocyte adhesion and decreased release of keratinocyte-derived growth factors. Subsequently a secondary event, physical trauma, oxidative stress or autoantibodies, may lead to exfoliation of keratinocytes and pigmented cells.

A New View of Vitiligo: Looking at Normal-Appearing Skin

Debate over the pathogenesis of vitiligo is still ongoing among scientists, with several hypotheses currently under consideration. The study by Wagner et al. in this issue focuses on the role of E-cadherin-mediated cell adhesion in vitiliginous epidermis under oxidative and mechanical stress. Their work highlights how alterations in cell-cell adhesion across nonlesional melanocyte membranes in patients with vitiligo argue for primary intrinsic defects in the melanocytes.

Altered E-Cadherin Levels and Distribution in Melanocytes Precede Clinical Manifestations of Vitiligo

Vitiligo is the most common depigmenting disorder resulting from the loss of melanocytes from the basal epidermal layer. The pathogenesis of the disease is likely multifactorial and involves autoimmune causes, as well as oxidative and mechanical stress. It is important to identify early events in vitiligo to clarify pathogenesis, improve diagnosis, and inform therapy. Here, we show that E-cadherin (Ecad), which mediates the adhesion between melanocytes and keratinocytes in the epidermis, is absent from or discontinuously distributed across melanocyte membranes of vitiligo patients long before clinical lesions appear. This abnormality is associated with the detachment of the melanocytes from the basal to the suprabasal layers in the epidermis. Using human epidermal reconstructed skin and mouse models with normal or defective Ecad expression in melanocytes, we demonstrated that Ecad is required for melanocyte adhesiveness to the basal layer under oxidative and mechanical stress, establishing a link between silent/preclinical, cell-autonomous defects in vitiligo melanocytes and known environmental stressors accelerating disease expression. Our results implicate a primary predisposing skin defect affecting melanocyte adhesiveness that, under stress conditions, leads to disappearance of melanocytes and clinical vitiligo. Melanocyte adhesiveness is thus a potential target for therapy aiming at disease stabilization.

Revised classification/nomenclature of vitiligo and related issues: the Vitiligo Global Issues Consensus Conference

During the 2011 International Pigment Cell Conference (IPCC), the Vitiligo European Taskforce (VETF) convened a consensus conference on issues of global importance for vitiligo clinical research. As suggested by an international panel of experts, the conference focused on four topics: classification and nomenclature; definition of stable disease; definition of Koebner's phenomenon (KP); and 'autoimmune vitiligo'. These topics were discussed in seven working groups representing different geographical regions. A consensus emerged that segmental vitiligo be classified separately from all other forms of vitiligo and that the term 'vitiligo' be used as an umbrella term for all non-segmental forms of vitiligo, including 'mixed vitiligo' in which segmental and non-segmental vitiligo are combined and which is considered a subgroup of vitiligo. Further, the conference recommends that disease stability be best assessed based on the stability of individual lesions rather than the overall stability of the disease as the latter is difficult to define precisely and reliably. The conference also endorsed the classification of KP for vitiligo as proposed by the VETF (history based, clinical observation based, or experimentally induced). Lastly, the conference agreed that 'autoimmune vitiligo' should not be used as a separate classification as published evidence indicates that the pathophysiology of all forms of vitiligo likely involves autoimmune or inflammatory mechanisms.

Artificial skin in perspective: concepts and applications

Skin, the largest organ of the human body, is organized into an elaborate layered structure consisting mainly of the outermost epidermis and the underlying dermis. A subcutaneous adipose-storing hypodermis layer and various appendages such as hair follicles, sweat glands, sebaceous glands, nerves, lymphatics, and blood vessels are also present in the skin. These multiple components of the skin ensure survival by carrying out critical functions such as protection, thermoregulation, excretion, absorption, metabolic functions, sensation, evaporation management, and aesthetics. The study of how these biological functions are performed is critical to our understanding of basic skin biology such as regulation of pigmentation and wound repair. Impairment of any of these functions may lead to pathogenic alterations, including skin cancers. Therefore, the development of genetically controlled and well characterized skin models can have important implications, not only for scientists and physicians, but also for manufacturers, consumers, governing regulatory boards and animal welfare organizations. As cells making up human skin tissue grow within an organized three-dimensional (3D) matrix surrounded by neighboring cells, standard monolayer (2D) cell cultures do not recapitulate the physiological architecture of the skin. Several types of human skin recombinants, also called artificial skin, that provide this critical 3D structure have now been reconstructed in vitro. This review contemplates the use of these organotypic skin models in different applications, including substitutes to animal testing.