Possible patterns of epidermal melanocyte disappearance in nonsegmental vitiligo: a clinicopathological study

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.

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.

Clinical Features, Immunopathogenesis, and Therapeutic Strategies in Vitiligo

Vitiligo is an autoimmune disease of the skin characterized by epidermal melanocyte loss resulting in white patches, with an approximate prevalence of 0.5-2% worldwide. Several precipitating factors by chemical exposure and skin injury present commonly in patients with vitiligo. Although the diagnosis appears to be straightforward for the distinct clinical phenotype and specific histological features, vitiligo provides many challenges including chronicity, treatment resistance, frequent relapse, associated profound psychosocial effect, and negative impact on quality of life. Multiple mechanisms are involved in melanocyte disappearance, including genetics, environmental factors, and immune-mediated inflammation. Compelling evidence supports the melanocyte intrinsic abnormalities with poor adaptation to stressors leading to instability and release of danger signals, which will activate dendritic cells, natural killer cells, and innate lymphoid cells to initiate innate immunity, ultimately resulting in T-cell mediated adaptive immune response and melanocyte destruction. Importantly, the cross- talk between keratinocytes, melanocytes, and immune cells, such as interferon (IFN)-γ signaling pathway, builds inflammatory loops that give rise to the disease deterioration. Improved understanding of the immune pathogenesis of vitiligo has led to the development of new therapeutic options including Janus kinase (JAK) inhibitors targeting IFN-γ signaling pathways, which can effectively reverse depigmentation. Furthermore, definition of treatment goals and integration of comorbid diseases into vitiligo management have revolutionized the way vitiligo is treated. In this review, we highlight recent developments in vitiligo clinical aspects and immune pathogenesis. Our key objective is to raise awareness of the complexity of this disease, the potential of prospective therapy strategies, and the need for early and comprehensive management.

Pathogenesis of vitiligo

Vitiligo is an autoimmune disease in which CD8+ T-cells target and destroy melanocytes, leaving areas of skin without pigment production. Nonsegmental vitiligo, the classical form of the disease, results in symmetrical, bilateral white patches. Vitiligo is a chronic, unpredictable disease, characterized by flares, with depigmentation and periods of disease arrest alternating. This process can be stressful and negatively impact one’s quality of life. Various hypotheses have been offered, including cellular stress causing degeneration of melanocytes, chemical toxicity causing melanocyte death, and neural changes that influence melanocytes or their ability to produce melanin. Recently, the interaction between oxidative stress and autoimmune-mediated melanocyte loss has been proposed as the primary pathogenesis of vitiligo. It is now well accepted that interferon-γ and/or C-X-C motif chemokine ligand 10 axis is functionally required for both progression and maintenance of vitiligo, making this pathway a potential therapeutic target. Most therapeutic interventions in the management of vitiligo have been developed based on this immunopathogenesis. This article aims to review the current understanding of the vitiligo pathogenesis.

Semi-Automatic Tool for Vitiligo Detection and Analysis

Vitiligo vulgaris is an autoimmune disease which causes a strong reduction of the cells producing melanin, which is the main skin pigment. This results in the growth of white patches on patients’ skin, which are more or less visible, depending on the skin phototype. Precise, objective and fast detection of vitiligo patches would be crucial to produce statistically relevant data on huge populations, thus giving an insight on the disease. However, few methods are available in literature. In the present paper, a semi-automatic tool based on image processing to detect facial vitiligo patches is described. The tool requires pictures to be captured under black light illumination, which enhances patches contrast with respect to healthy skin. The user is only required to roughly define the regions of interest and set a global threshold, thus, no specific image-processing skills are required. An adaptive algorithm then automatically discerns between vitiligo and healthy skin pixels. The tools also allow for a statistical data interpretation by overlapping the detected patches of all patients on a face template through an occurrence map. Preliminary results obtained on a small population of 15 patients allowed us to assess the tool’s performance. Patch detection was checked by an experienced dermatologist, who confirmed the detection for all the studied patients, thus supporting the effectiveness of the proposed tool.

Clinical visible signs of disease activity in vitiligo: a systematic review and meta-analysis

Vitiligo is an unpredictable depigmenting disorder for which a static method to assess disease activity is lacking. Presence of certain skin manifestations may be indicative of disease activity. Here, we evaluated the current evidence for an association between clinical signs and reported disease activity in vitiligo. A systematic review and meta-analysis was performed based on a search in PubMed, Embase and Cochrane Library. Literature reporting skin manifestations and disease activity was analysed based on descriptive analyses and, if applicable, odd ratios. Forty-six observational studies were selected and analysed, including 28 case reports. Reported clinical signs in relation to active vitiligo were as follows: Koebner's phenomenon, confetti-like depigmentations, tri- and hypochromic lesions (including poorly defined borders), inflammatory borders/areas, itch and leukotrichia. Based on this search, strong evidence was found for Koebner's phenomenon. Poorly defined borders and confetti lesions are potential markers, although more data are needed to confirm this. Evidence for other skin manifestations was inconclusive, whereas case reports on inflammatory borders were indicative of active disease. Limitations included the lack of randomized controlled trials, large-scale prospective studies and heterogeneity due to inconsistent definitions. This systematic review urges the vitiligo community to come forward with consensus-based definitions as well as a reliable scoring system to assess these clinical signs and to design optimal trials to investigate their true predictive value.

Cross-Sectional Study of Dermatoscopic Findings in Relation to Activity in Vitiligo: BPLeFoSK Criteria for Stability

Background:

Stability in vitiligo is an important concept in guiding patient management and a vital prerequisite before vitiligo surgery. Disease activity of vitiligo based on patient’s history is imprecise. It is practically impossible to perform biopsy from all lesions of vitiligo to ascertain stability. Dermatoscopy can be used to examine all clinical lesions in a patient of vitiligo. There is a need to validate many reported dermatoscopic findings for universal use.

Aims:

To analyze the significance of dermatoscopic findings in the activity of vitiligo and to devise a cutoff score for stable vitiligo.

Materials and Methods:

Dermatoscopic examination was performed in 85 patients clinically diagnosed with vitiligo. Six dermatoscopic parameters, namely, border, pigment network, perilesional hyperpigmentation, perifollicular pigmentation, satellite lesions, and micro-Koebner phenomenon (acronym: BPLeFoSK) were evaluated against Wood’s lamp findings as standard. Chi-square test was used to test association between categorical variables. Cutoff values for stability for these six parameters were plotted in receiver operating curve.

Results:

A total of 131 vitiligo lesions were analyzed with dermatoscopy. Absence of satellite lesions and absence of micro-Koebner phenomenon were the most sensitive parameters (96.7% and 100%, respectively). Sharp border and absent or reticulate pigment network within the vitiligo patch were the most specific findings (100% and 91.5%, respectively).

Conclusion:

A cutoff score of more than or equal to 1.5 using the “BPLeFoSK criteria” indicates stability in the vitiligo lesion.

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.

Biomarkers of disease activity in vitiligo: A systematic review

The pathophysiology of vitiligo is complex although recent research has discovered several markers which are linked to vitiligo and associated with disease activity. Besides providing insights into the driving mechanisms of vitiligo, these findings could reveal potential biomarkers. Activity markers can be used to monitor disease activity in clinical trials and may also be useful in daily practice. The aim of this systematic review was to document which factors have been associated with vitiligo activity in skin and blood. A second goal was to determine how well these factors are validated in terms of sensitivity and specificity as biomarkers to determine vitiligo activity. Both in skin (n=43) as in blood (n=66) an adequate number of studies fulfilled the predefined inclusion criteria. These studies used diverse methods and investigated a broad range of plausible biomarkers. Unfortunately, sensitivity and specificity analyses were scarce. In skin, simple histopathology with or without supplemental CD4 and CD8 stainings can still be considered as the gold standard, although more recently chemokine (C-X-C motif) ligand (CXCL) 9 and NLRP1 have demonstrated a good and possibly even better association with progressive disease. Regarding circulating biomarkers, cytokines (IL-1β, IL-17, IFN-γ, TGF-β), autoantibodies, oxidative stress markers, immune cells (Tregs), soluble CDs (sCD25, sCD27) and chemokines (CXCL9, CXCL10) are still competing. However, the two latter may be preferable as both chemokines and soluble CDs are easy to measure and the available studies display promising results. A large multicenter study could make more definitive statements regarding their sensitivity and specificity.

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.