Oxidative Stress-Induced HMGB1 Release from Melanocytes: A Paracrine Mechanism Underlying the Cutaneous Inflammation in Vitiligo

Unveiling the Unseen: Exploring Cellular Dynamics in Nonlesional Vitiligo Skin

Vitiligo is a multifactorial disease involving genetic predispositions, intrinsic melanocyte abnormalities, and deregulated immune response. Recent studies show nonlesional skin involvement. Nonlesional melanocytes display mitochondrial dysfunction and increased oxidative stress affecting their adhesion and function and contribute to immune activation. Keratinocytes and fibroblasts display structural and functional abnormalities impairing melanocyte support and differentiation. They also contribute to the altered immune response by secreting proinflammatory chemokines. Despite immune cell infiltration, nonlesional skin remains clinically unaffected, suggesting that regulatory mechanisms maintain immune activation at a subclinical level. This review provides an overview of the cellular alterations in vitiligo nonlesional skin.

Oxidative stress-induced release of mitochondrial DNA (mtDNA) promotes the progression of vitiligo by activating the cGAS-STING signaling pathway in monocytes

Vitiligo, driven by cytotoxic CD8+ T cells destroying melanocytes, has recently been linked to mitochondrial DNA (mtDNA), a DAMP known to trigger innate immunity. However, the precise role of mtDNA in vitiligo pathogenesis remains poorly understood. In this study, we observed significantly elevated mtDNA levels in both the serum and depigmented lesions of vitiligo patients. Importantly, we found that oxidative stress induces mtDNA production in keratinocytes and vascular endothelial cells, providing a plausible source for its systemic and localized accumulation. Using the mouse odel, we demonstrated that exogenous mtDNA administration markedly accelerated progression of vitiligo, as evidenced by pronounced tail depigmentation. Mechanistically, mtDNA can activate the cGAS-STING-IFN-α/β pathway in monocytes, leading to an increased production of IFN-γ by CD8+ T cells while simultaneously reducing the frequency and functionality of regulatory CD4+ T cells (Tregs). Consistent with these findings, mtDNA treatment in vitiligo mice led to heightened infiltration of IFN-γ+ CD8+ T cells into affected tissues, accompanied by a significant decrease in Treg numbers and activity, thereby exacerbating the autoimmune response. Collectively, these findings underscore the pivotal role of mtDNA-STING signaling in vitiligo progression and highlight this pathway as a promising target for therapeutic intervention. Our findings suggest that mtDNA may serve as a crucial mediator in the pathogenesis of vitiligo and other autoimmune diseases, providing new insights into potential therapeutic targets.

HMGB1: new biomarker and therapeutic target of autoimmune and autoinflammatory skin diseases

High-mobility group box 1 (HMGB1) is expressed in almost all human cells. During cell activation and cell death, the nucleoprotein HMGB1 can translocate to the extracellular space, thus mediating the early inflammatory response as an alarmin or damage-associated molecular pattern (DAMP). Extracellular HMGB1 interacts with immune cells by binding to pattern recognition Toll-like receptors (TLRs), including TLR2 and TLR4, and the receptor for advanced glycation end products (RAGE), thus mediating the immune response to protect the host against pathogens and maintain immune balance. HMGB1 is reportedly upregulated and is a critical biomarker for monitoring disease activity in several chronic inflammatory or autoimmune disorders, including multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus and vitiligo. Additionally, the inhibition of HMGB1 expression or its activity has beneficial effects on disease activity in animal models of autoimmune diseases. Thus, HMGB1 is an indispensable biomarker and an important therapeutic target for autoimmune diseases. This review provides a detailed summary of the biological function of HMGB1 and provides a comprehensive outlook in terms of HMGB-focused diagnostic and therapeutic applications in autoimmune skin diseases.

Senescence as a molecular target in skin aging and disease

Skin aging represents a multifactorial process influenced by both intrinsic and extrinsic factors, collectively known as the skin exposome. Cellular senescence, characterized by stable cell cycle arrest and secretion of pro-inflammatory molecules, has been implicated as a key driver of physiological and pathological skin aging. Increasing evidence points towards the role of senescence in a variety of dermatological diseases, where the accumulation of senescent cells in the epidermis and dermis exacerbates disease progression. Emerging therapeutic strategies such as senolytics and senomorphics offer promising avenues to target senescent cells and mitigate their deleterious effects, providing potential treatments for both skin aging and senescence-associated skin diseases. This review explores the molecular mechanisms of cellular senescence and its role in promoting age-related skin changes and pathologies, while compiling the observed effects of senotherapeutics in the skin and discussing the translational relevance.

Cytosolic mtDNA-cGAS-STING axis mediates melanocytes pyroptosis to promote CD8+ T-cell activation in vitiligo

BACKGROUND

The cGAS-STING axis, a DNA sensor pathway, has recently emerged as a key hub in sensing stress signals and initiating the immune cascade in several diseases. However, its role in the pathogenesis of vitiligo remains unclear.

OBJECTIVE

To explore the pathogenic role of the cGAS-STING axis in linking oxidative stress and CD8+ T-cell-mediated anti-melanocytic immunity in vitiligo.

METHODS

The expression status of the cGAS-STING axis and cytosolic mtDNA were evaluated in the oxidatively stressed epidermal cells and vitiligo perilesional skin, respectively. Then, we investigated the activation of cGAS-STING axis in mtDNA-treated melanocytes, and the influence of cGAS or STING silencing on mtDNA-induced melanocytes pyroptosis. Finally, the paracrine effects of melanocytes pyroptosis on CD8+ T cell activation were explored.

RESULTS

We initially demonstrated that the cGAS-STING axis in melanocytes was highly susceptible to oxidative stress and activated in the vitiliginous melanocytes of perilesional skin, accompanied by enhanced cytosolic mtDNA accumulation. Our mechanistic in vitro experiments confirmed that oxidative stress-induced mitochondrial damage in epidermal cells led to cytosolic mtDNA accumulation, which served as a trigger in activating the cGAS-STING axis in melanocytes. Furthermore, the cytosolic mtDNA-cGAS-STING axis was verified to mediate melanocytes pyroptosis. More importantly, we found that IL-1β and IL-18 produced by pyroptotic melanocytes promoted the activation of CD8+ T cells from patients with vitiligo.

CONCLUSION

The present study confirmed that the cytosolic mtDNA-cGAS-STING axis of melanocytes played an important role in oxidative stress-triggered CD8+ T-cell response, providing novel insights into mechanisms underlying vitiligo onset.

Biomimetic polydopamine loaded with janus kinase inhibitor for synergistic vitiligo therapy via hydrogel microneedles

BACKGROUND

Both oxidative stress and autoimmune responses play crucial roles in the development of vitiligo. Under oxidative stress, the apoptotic melanocytes expose self-antigens and release high mobility group box 1 (HMGB1), triggering autoimmune activation and recruiting CD8+ T cells. This process further leads to the destruction of melanocytes, resulting in the lack of melanin granules. Additionally, the accumulated CD8+ T cells release interferon-γ (IFN-γ) to activate janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway in keratinocytes. Both oxidative stress and IFN-γ-JAK-STAT activation induce keratinocytes to express and release T cell chemotactic factors, exacerbating the process of vitiligo. Reducing the accumulation of CD8+ T cells by safeguarding melanocytes and keratinocytes from oxidative stress may be contemplated as a promising approach for vitiligo therapy.

RESULTS

In this study, we introduce a novel therapeutic agent called PDA-JAKi, which is capable of both eliminating oxidative stress and inhibiting T cell activation. Specifically, we have incorporated the janus kinase inhibitor (JAKi) tofacitinib into antioxidant polydopamine (PDA) nanoparticles, resulting in the formation of uniform PDA-JAKi nanodrug. PDA-JAKi effectively mitigates oxidative stress-induced apoptosis in melanocytes, reducing the antigen presentation and release of HMGB1. In addition, PDA-JAKi simultaneously attenuates oxidative stress and blocks the IFN-γ-JAK-STAT pathway to reduce the expression of C-X-C motif chemokine ligand 9/10/16 (CXCL9/10/16) in keratinocytes. We precisely deliver this therapeutic agent to the dermis using microneedle (MN) patches, aiming to enhance therapeutic efficacy compared to traditional drug administration methods. After PDA-JAKi MN treatment, the symptoms of vitiligo in mice are alleviated, and the affected areas regain pigmentation. Enhancements have been observed in the dermal thickness, the numbers of melanocytes and the content of melanin within the treated skin area. Moreover, there is a notable reduction in reactive oxygen species (ROS) level. Concurrently, substantial decreases were noted in CD8+ T cell infiltration, as well as the levels of IFN-γ and chemotactic factors CXCL9/10/16.

CONCLUSIONS

In summary, PDA-JAKi MN patches emerge as a promising therapeutic agent for vitiligo treatment.

LL37-DNA Complex Drives Vitiligo Progression Through TLR9-MyD88 Signaling Pathways

Vitiligo is an autoimmune disorder characterized by chronic depigmentation and milk-white patches on the skin. Skin infiltration by autoreactive CD8+ T cells causes melanocyte destruction in vitiligo. Multiple risk factors, particularly immune-related inflammatory factors, are involved in the disappearance of melanocytes. LL37 is a classic damage-associated molecular pattern molecule that is involved in the development of various autoimmune diseases. An enhanced expression of LL37 in vitiligo is known; however, the exact role of LL37 in melanocyte loss has not yet been elucidated. In the present study, we detected increased LL37 expression in vitiligo serum and lesions. Furthermore, we confirmed that cultured keratinocytes released LL37 after treatment with H2O2. Moreover, the LL37-DNA complex enhanced the secretion of CXCL9, CXCL10, and CXCL16 from keratinocytes via the TLR9-MyD88 signaling pathway and facilitated the migration of CD8+ T cells. Altogether, our study demonstrates that LL37 released from keratinocytes binds to DNA and contributes to melanocyte destruction under oxidative stress-induced autoimmunity in vitiligo.

Targeting Periplakin of Novel Benzenesulfonamides as Highly Selective Agonists for the Treatment of Vitiligo

Vitiligo is the most common cause of depigmentation worldwide, with immunosuppressive treatments often being inefficient and prone to recurrence, making it essential to identify new therapeutic targets. Periplakin (PPL) has been identified and confirmed as a key factor in vitiligo-related depigmentation. Based on this, a series of selective PPL agonists, specifically benzenesulfonamides, have been developed. Among these, compound I-3 exhibits superior efficacy compared to ruxolitinib, the only FDA-approved treatment for vitiligo. I-3 has been shown to increase cAMP levels by regulating PPL, which enhances MITF expression, a key transcription factor in melanin biosynthesis. Additionally, I-3 promotes melanin production by regulating tryptophan metabolism. In summary, PPL is a promising drug target, and I-3 has strong potential for future treatment of vitiligo due to its high selectivity and favorable druggability.

Prevalence of co-existing autoimmune and autoinflammatory diseases in vitiligo: a survey-based study from Egypt

BACKGROUND

The exact cause of vitiligo is still unknown. Genetic factors, self-destruction of melanocytes, the autoimmune process, and oxidative stress all can contribute to the pathogenesis of vitiligo.

OBJECTIVES

The aim of this study was to figure out the frequency of coexisting autoimmune and autoinflammatory diseases (AIIDs) in Egyptian patients with vitiligo and identify the associated risk factors.

MATERIALS AND METHODS

Egyptian children and adults with vitiligo and their parents were asked to answer a web-based survey. The survey consisted of multiple questions centered around demographic, clinical, and therapeutic data. The vitiligo disease activity (VIDA) score was evaluated for all the patients. Patients were also asked about the presence of co-existing AIIDs.

RESULTS

There was a total of 294 participants, mostly females (54.8%), with a median age of 35 years and a median disease duration of 9 years. Nearly 27% had at least one AIID. The most common associated AIIDs were autoimmune thyroid disease (47 patients, 16%), followed by alopecia areata (14 patients,4.8%), then psoriasis and rheumatoid arthritis (11 patients, 3.7%). Univariate regression analysis revealed that age (OR 1.02, P = 0.036), female gender (OR 2.2, P = 0.004), disease duration (OR 1.04, P < 0.001), affected body surface area (OR 1.7, P = 0.048), and family history of AIIDs (OR 2.7, P < 0.001) were predictors for the presence of AIIDs in patients with vitiligo.

CONCLUSION

AIIDs are prevalent among vitiligo patients. Age, female gender, and family history of AIIDs are the main predictors of the presence of AIIDs in vitiligo patients.

Vitiligo: From Pathogenesis to Treatment

Recent advances in vitiligo have provided promising treatment options, particularly through understanding the immune-mediated mechanisms leading to depigmentation. The inflammatory components in both vitiligo (non-segmental) and segmental vitiligo have similarities. Both are believed to result from an immune-based destruction of melanocytes by anti-melanocyte-specific cytotoxic T cells. The JAK-STAT pathway is activated with IFN-γ as the crucial cytokine and Th1-associated chemokines such as CXCL9 and CXCL10 recruit immune cells towards vitiligo skin. Nonetheless, clear differences are also present, such as the localized nature of segmental vitiligo, likely due to somatic mosaicism and increased presence of poliosis. The differing prevalence of poliosis suggests that the follicular immune privilege, which is known to involve immune checkpoints, may be more important in vitiligo (non-segmental). Immunomodulatory therapies, especially those targeting the JAK-IFNγ pathway, are currently at the forefront, offering effective inhibition of melanocyte destruction by cytotoxic T cells. Although Janus Kinase (JAK) inhibitors demonstrate high repigmentation rates, optimal results can take several months to years. The influence of environmental UV exposure on repigmentation in patients receiving immunomodulating drugs remains largely underexplored. Nonetheless, the combined effect of phototherapy with JAK inhibitors is impressive and suggests a targeted immune-based treatment may still require additional stimulation of melanocytes for repigmentation. Identifying alternative melanocyte stimulants beyond UV light remains crucial for the future management of vitiligo.

The amino acid transporter SLC16A10 promotes melanogenesis by facilitating the transportation of phenylalanine

Phenylalanine is a crucial amino acid in the process of melanogenesis. However, the exact mechanism by which it is transported into melanocytes has not been disclosed. The aim of this study was to identify and examine the key transporters that are responsible for phenylalanine transportation and evaluate their significance in melanogenesis. The amino acid transporter SLC16A10 was found to be up-regulated in both melasma (GSE72140) and sun-exposed skin (GSE67098). The protein levels of SLC16A10 were proportional to the melanin content in melanocytic nevi, indicating that SLC16A10 was related to melanogenesis. After SLC16A10 overexpression, melanin increased significantly in MNT1 cells. Meanwhile, the expression of melanogenesis-related proteins such as TYR and TYRP1 increased, while their RNA levels did not change. Transcriptomics data indicated that SLC16A10 can enhance the function of ribosome. Furthermore, targeted metabolomics data and ELISA results demonstrated SLC16A10 mainly affected the transport of phenylalanine into the cells. Then, phenylalanine was added to the cell culture medium after SLC16A10 overexpression, melanin synthesis in cells furtherly increased, which verified that SLC16A10 enhances melanogenesis by promoting the uptake of phenylalanine. Finally, we found that SLC16A10 expression increased after UVB irradiation. Knockdown SLC16A10 reduced UVB-induced melanin production and phenylalanine uptake by cells. In summary, SLC16A10 enhances melanogenesis by promoting the uptake of phenylalanine, and upregulation SLC16A10 is likely responsible for the UVB-induced hyperpigmentation as well.

Up-and-Coming Drugs for the Treatment of Vitiligo

Vitiligo is a chronic autoimmune disease that causes depigmented patches on the skin. It affects 0.5%-2.0% of the global population. It goes beyond physical appearance, often leading to stigmatization, low self-esteem, and depression, burdening patients with psychosocial challenges. The pathogenesis of vitiligo involves the loss of melanocytes due to autoreactive CD8+ T cells, triggered by environmental stressors and exacerbated by cellular vulnerabilities and immune responses. The release of danger signals and pro-inflammatory factors initiates an immune cascade perpetuating melanocyte destruction, mainly driven by interferon-γ and the C-X-C motif chemokine ligand 9/10-chemokine receptor 3 axis. Long-lasting tissue-resident memory T cells (Trms) and cytokines contribute to lesion persistence. Current treatments focus on topical steroids and tacrolimus, systemic steroids, and phototherapies, but their efficacy remains suboptimal, necessitating the development of new therapeutic options. Building on recent advancements in understanding the immunological mechanisms in vitiligo pathogenesis, with the initiation of Food and Drug Administration approval of topical ruxolitinib, various potential treatment options such as JAK inhibitors, cytokine blockers, and Trm or regulatory T cell targeting agents are being clinically researched and anticipated for vitiligo based on both preclinical and clinical data. This review aims to categorize and summarize the diverse investigational drugs currently undergoing clinical trials for vitiligo. By examining clinical outcomes, it is anticipated that this review will bring hope to dermatologists and patients regarding vitiligo, a condition that has historically posed challenges and transform it into a realm of potential possibilities.

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.

Membranal Expression of Calreticulin Induced by Unfolded Protein Response in Melanocytes: A Mechanism Underlying Oxidative Stress-Induced Autoimmunity in Vitiligo

Calreticulin (CRT), a damage-associated molecular pattern molecule, is reported to translocate from the endoplasmic reticulum to the membrane in melanocytes under oxidative stress. To investigate the potential role of CRT in the pathogenesis of vitiligo, we analyzed the correlation between CRT and ROS in serum and lesions of vitiligo, detected CRT and protein kinase RNA-like endoplasmic reticulum kinase (PERK) expression in vitiligo lesions, and studied the production of CRT and mediators of unfolded protein response (UPR) pathway and then tested the chemotactic migration of CD8+ T cells or CD11c+ CD86+ cells. Initially, we verified the overexpression of CRT in perilesional epidermis that was positively correlated with the disease severity of vitiligo. Furthermore, the PERK branch of UPR was confirmed to be responsible for the overexpression and membranal translocation of CRT in melanocytes under oxidative stress. We also found that oxidative stress-induced membranal translocation of CRT promoted the activation and migration of CD8+ T cells in vitiligo. In addition, dendritic cells from patients with vitiligo were also prone to maturation with the coincubation of melanocytes harboring membranal CRT. CRT could be induced on the membrane of melanocytes through UPR and might play a role in oxidative stress-triggered CD8+ T-cell response in vitiligo.

TRPM2-dependent autophagy inhibition exacerbates oxidative stress-induced CXCL16 secretion by keratinocytes in vitiligo

Vitiligo is a depigmented skin disease due to the destruction of melanocytes. Under oxidative stress, keratinocyte-derived chemokine C-X-C motif ligand 16 (CXCL16) plays a critical role in recruiting CD8+ T cells, which kill melanocytes. Autophagy serves as a protective cell survival mechanism and impairment of autophagy has been linked to increased secretion of the proinflammatory cytokines. However, the role of autophagy in the secretion of CXCL16 under oxidative stress has not been investigated. Herein, we initially found that autophagy was suppressed in both keratinocytes of vitiligo lesions and keratinocytes exposed to oxidative stress in vitro. Autophagy inhibition also promoted CXCL16 secretion. Furthermore, upregulated transient receptor potential cation channel subfamily M member 2 (TRPM2) functioned as an upstream oxidative stress sensor to inhibit autophagy. Moreover, TRPM2-mediated Ca2+ influx activated calpain to shear autophagy related 5 (Atg5) and Atg12-Atg5 conjugate formation was blocked to inhibit autophagy under oxidative stress. More importantly, Atg5 downregulation enhanced the binding of interferon regulatory factor 3 (IRF3) to the CXCL16 promoter region by activating Tank-binding kinase 1 (TBK1), thus promoting CXCL16 secretion. These findings suggested that TRPM2-restrained autophagy promotes CXCL16 secretion via the Atg5-TBK1-IRF3 signaling pathway under oxidative stress. Inhibition of TRPM2 may serve as a potential target for the treatment of vitiligo. © 2024 The Pathological Society of Great Britain and Ireland.

The effects of advanced glycation end-products on skin and potential anti-glycation strategies

The advanced glycation end-products (AGEs) are produced through non-enzymatic glycation between reducing sugars and free amino groups, such as proteins, lipids or nucleic acids. AGEs can enter the body through daily dietary intake and can also be generated internally via normal metabolism and external stimuli. AGEs bind to cell surface receptors for AGEs, triggering oxidative stress and inflammation responses that lead to skin ageing and various diseases. Evidence shows that AGEs contribute to skin dysfunction and ageing. This review introduces the basic information, the sources, the metabolism and absorption of AGEs. We also summarise the detrimental mechanisms of AGEs to skin ageing and other chronic diseases. For the potential strategies for counteracting AGEs to skin and other organs, we summarised the pathways that could be utilised to resist glycation. Chemical and natural-derived anti-glycation approaches are overviewed. This work offers an understanding of AGEs to skin ageing and other chronic diseases and may provide perspectives for the development of anti-glycation strategies.

JAK inhibitors for the treatment of vitiligo

Vitiligo is an autoimmune disease involving melanocyte-targeting T cells initiated by environmental and genetic factors. Steroids and tacrolimus have been used as topical treatments. Recently, novel topical agents targeting Janus kinase (JAK), a family of tyrosine kinases that regulates cytokine signaling, have emerged. Ruxolitinib is the first approved in vitiligo therapy. Furthermore, ritlecitinib is currently under clinical trials for oral treatment of active vitiligo. In this review, we discuss the possibility of topical JAK inhibitors as promising options for the treatment of vitiligo with regard to their mechanism of action, efficacy and safety.

ISG15-USP18 Dysregulation by Oxidative Stress Promotes IFN-γ Secretion from CD8+ T Cells in Vitiligo

Excessive oxidative stress is thought to play pathologic roles in cellular senescence and autoimmune disorders by inducing inflammation and breaking down immune tolerance. In this study, we sought to identify the factors linking oxidative stress to autoimmunity and cellular senescence in vitiligo, where elevated oxidative stress plays an important role. RNA sequencing analysis of hydrogen peroxide-treated melanocytes revealed upregulation of ISG15. The upregulation of ISG15 was observed in vitiligo skin tissues as well as in the blood of patients with vitiligo, whereas USP18 downregulation was observed in vitiligo melanocytes and vitiligo skin tissues. Oxidative stress induced hypermethylation of the USP18 promoter region in keratinocytes and melanocytes, and USP18 promoter hypermethylation was also confirmed in vitiligo skin tissues. Our results indicate that USP18 promoter hypermethylation caused by oxidative stress increases ISG15 expression in keratinocytes and melanocytes along with senescence changes, leading CD8+ T cells to produce IFN-γ, the main pathogenic cytokine in vitiligo. Therefore, the ISG15-USP18 network may be important in oxidative stress-induced autoimmunity and cellular senescence in vitiligo pathogenesis.

The Role of Regulatory Cell Death in Vitiligo

Vitiligo is one of the common chronic autoimmune skin diseases in clinic, which is characterized by localized or generalized depigmentation and seriously affects the physical and mental health of patients. At present, the pathogenesis of vitiligo is not clear; mainly, heredity, autoimmunity, oxidative stress, melanocyte (MC) self-destruction, and the destruction, death, or dysfunction of MCs caused by various reasons are always the core of vitiligo. Regulatory cell death (RCD) is an active and orderly death mode of cells regulated by genes, which widely exists in various life activities, plays a pivotal role in maintaining the homeostasis of the organism, and is closely related to the occurrence and development of many diseases. With the deepening of the research and understanding of RCD, people gradually found that there are many different forms of RCD in the lesions and perilesional skin of vitiligo patients, such as apoptosis, autophagy, pyroptosis, ferroptosis, and so on. Different cell death modes have different mechanisms in vitiligo, and different RCDs can interact and regulate each other. In this article, the mechanism related to RCD in the pathogenesis of vitiligo is reviewed, which provides new ideas for exploring the pathogenesis and targeted treatment of vitiligo.

HMGB1 in the interplay between autophagy and apoptosis in cancer

Lysosome-mediated autophagy and caspase-dependent apoptosis are dynamic processes that maintain cellular homeostasis, ensuring cell health and functionality. The intricate interplay and reciprocal regulation between autophagy and apoptosis are implicated in various human diseases, including cancer. High-mobility group box 1 (HMGB1), a nonhistone chromosomal protein, plays a pivotal role in coordinating autophagy and apoptosis levels during tumor initiation, progression, and therapy. The regulation of autophagy machinery and the apoptosis pathway by HMGB1 is influenced by various factors, including the protein's subcellular localization, oxidative state, and interactions with binding partners. In this narrative review, we provide a comprehensive overview of the structure and function of HMGB1, with a specific focus on the interplay between autophagic degradation and apoptotic death in tumorigenesis and cancer therapy. Gaining a comprehensive understanding of the significance of HMGB1 as a biomarker and its potential as a therapeutic target in tumor diseases is crucial for advancing our knowledge of cell survival and cell death.

CXCL16 exacerbates Pseudomonas aeruginosa keratitis by promoting neutrophil activation

Pseudomonas aeruginosa (PA) keratitis is a major cause of blindness characterized by corneal inflammation. In a murine model of PA keratitis, we assessed the detrimental effects of CXC chemokine ligand 16 (CXCL16). Quantitative PCR (qPCR), western blotting (WB) and immunofluorescence were used to measure the expression and localization of CXCL16 and its receptor, CXC chemokine receptor 6 (CXCR6). Clinical scores, plate counting, and hematoxylin-eosin staining were used to assess infection severity and its exacerbation by CXCL16. Immunofluorescence, myeloperoxidase assays, and flow cytometry were used to detect neutrophil activity and colocalization with CXCR6. WB and immunofluorescence were used to measure levels of reactive oxygen species (ROS) and matrix metalloproteinases (MMPs). These methods also were used to measure the activation of downstream NF-κB signaling and its positive feedback on CXCL16 expression. ELISA, flow cytometry, and qPCR were used to measure the expression of CXCL2 and T helper 17 (Th17) cell-related genes. CXCL16 and CXCR6 expression was increased in infected corneas. Topical application of CXCL16 exacerbated keratitis by increasing corneal bacterial load and promoting neutrophil infiltration, whereas neutralizing antibody against CXCL16 had the opposite effect. CXCL16 also increased ROS and MMP levels. This neutrophil activation may be caused by its positive feedback with the NF-κB pathway and the upregulation of CXCL2 and Th17 cell related-genes. These data suggest that CXCL16 is an attractive therapeutic target for PA keratitis.

A case of vitiligo after COVID-19 vaccination: a possible role of thymic dysfunction

During the coronavirus disease 2019 (COVID-19) pandemic, vaccines help control the spread of infection. To date, 47 vaccines have been approved, with another 227 candidates in various stages of development. In the short period of time since the beginning of their use, evidence has begun to emerge of complications following vaccination in the form of the development or exacerbation of a number of pathological conditions (Block et al., 2022; Haseeb et al., 2022). For example, a population-based study in France identified 1612 cases of myocarditis and 1613 cases of pericarditis requiring hospital treatment within five months of vaccination (le Vu et al., 2022).

Exploring the mechanism of Liuwei Dihuang formula for promoting melanin synthesis in juvenile zebrafish based on network pharmacology and molecular docking

Background

Vitiligo stands as a challenging skin disorder with limited treatment options available. LiuWei DiHuang formula (LDF), a renowned Traditional Chinese medicine, has exhibited promising results in treating vitiligo over an extended period. However, the precise underlying mechanism of its action remains elusive.

Methods

Employing a comprehensive network pharmacology approach, this study identified active compounds and their corresponding targets within LDF, while also pinpointing vitiligo-associated targets sourced from the TCMSP database, OMIM, DisGenNET, and Genecards. A network was established to illustrate the connections between active compounds and targets, alongside a protein-protein interaction network. Further analyses, encompassing Gene Ontology (GO) function and KEGG pathway enrichment, were conducted using the DAVID platform. Molecular docking simulations were performed utilizing AutoDockTools and AutoDockVina software. To validate the outcomes of the systematic pharmacological investigation, experiments were conducted using juvenile zebrafish.

Results

The collective effort of the network pharmacology approach yielded a compilation of 41 compounds and 192 targets. Molecular docking simulations notably revealed the lowest binding energies for CAT-quercetin and CAT-Kaempferol interactions. The utilization of juvenile zebrafish experiments highlighted a significant increase in melanocyte count following methoxsalen and LDF treatment. Notably, LDF prominently augmented the expression levels of proteins related to melanogenesis. Additionally, LDF showcased the capacity to enhance CAT and SOD levels while concurrently reducing ROS and MDA activity. In contrast to the model group, substantial increases in protein and mRNA levels of Nrf2 and HO-1 were observed in response to LDF treatment (P < 0.05).

Conclusion

Through a meticulous network pharmacology approach, this study successfully predicted active components and potential targets associated with LDF's application in vitiligo treatment. The therapeutic effectiveness of LDF against vitiligo is postulated to stem from its regulation of oxidative stress factors and the Nrf2/HO-1 pathway.

Neutrophil extracellular traps enhance S. aureus skin colonization by oxidative stress induction and downregulation of epidermal barrier genes

Staphylococcus aureus is the most common cause of bacterial skin infections in humans, including patients with atopic dermatitis (AD). Polymorphonuclear neutrophils (PMNs) are the first cells to infiltrate an infection site, where they usually provide an effective first line of defense, including neutrophil extracellular trap (NET) formation. Here, we show that infiltrating PMNs in inflamed human and mouse skin enhance S. aureus skin colonization and persistence. Mechanistically, we demonstrate that a crosstalk between keratinocytes and PMNs results in enhanced NET formation upon S. aureus infection, which in turn induces oxidative stress and expression of danger-associated molecular patterns such as high-mobility-group-protein B1 (HMGB1) in keratinocytes. In turn, HMGB1 enhances S. aureus skin colonization and persistence by promoting skin barrier dysfunctions by the downregulation of epidermal barrier genes. Using patient material, we show that patients with AD exhibit enhanced presence of PMNs, NETs, and HMGB1 in the skin, demonstrating the clinical relevance of our finding.

Oxidative stress and ROS-mediated cellular events in RSV infection: potential protective roles of antioxidants

Respiratory syncytial virus (RSV), a member of the Pneumoviridae family, can cause severe acute lower respiratory tract infection in infants, young children, immunocompromised individuals and elderly people. RSV is associated with an augmented innate immune response, enhanced secretion of inflammatory cytokines, and necrosis of infected cells. Oxidative stress, which is mainly characterized as an imbalance in the production of reactive oxygen species (ROS) and antioxidant responses, interacts with all the pathophysiologic processes above and is receiving increasing attention in RSV infection. A gradual accumulation of evidence indicates that ROS overproduction plays an important role in the pathogenesis of severe RSV infection and serves as a major factor in pulmonary inflammation and tissue damage. Thus, antioxidants seem to be an effective treatment for severe RSV infection. This article mainly reviews the information on oxidative stress and ROS-mediated cellular events during RSV infection for the first time.

Metagenomic sequencing reveals altered gut microbial compositions and gene functions in patients with non-segmental vitiligo

BACKGROUND

Vitiligo has been correlated with an abnormal gut microbiota. We aimed to systematically identify characteristics of the gut microbial compositions, genetic functions, and potential metabolic features in patients with non-segmental vitiligo.

METHODS

Twenty-five patients with non-segmental vitiligo and 25 matched healthy controls (HCs) were enrolled. Metagenomic sequencing and bioinformatic analysis were performed to determine the gut microbiota profiles. Differences in gut microbiota diversity and composition between patients with vitiligo and HCs were analyzed. Gene functions and gut metabolic modules were predicted with the Kyoto Encyclopedia of Gene and Genomes (KEGG) and MetaCyc databases.

RESULTS

Compared with HCs, alpha diversity of intestinal microbiome in vitiligo patients was significantly reduced. At the species level, the relative abundance of Staphylococcus thermophiles was decreased, and that of Bacteroides fragilis was increased in patients with vitiligo compared with those of the HCs. Linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed representative microbial markers of Lachnospiraceae_bacterium_BX3, Massilioclostridium_coli, TM7_phylum_sp_oral_taxon_348 and Bacteroides_fragilis for patients with vitiligo. KEGG gene function analysis showed that the NOD-like receptor signaling pathway was significantly enriched in patients with vitiligo. Gut metabolic modules (GMMs) analysis showed that cysteine degradation was significantly down-regulated, and galactose degradation was up-regulated in patients with vitiligo. A panel of 28 microbial features was constructed to distinguish patients with vitiligo from HCs.

CONCLUSIONS

The gut microbial profiles and genetic functions of patients with vitiligo were distinct from those of the HCs. The identified gut microbial markers may potentially be used for earlier diagnosis and treatment targets.

Circulatory levels of alarmins in patients with non-segmental vitiligo: Potential biomarkers for disease diagnosis and activity/severity assessment

Background

Non-segmental vitiligo (NSV) is an autoimmune skin disorder that is difficult to determine disease activity/severity and thus to treat. Alarmins have emerged as promising biomarkers in various diseases, so further confirmation of their potential roles in NSV would be of considerable value. With the present work, we aimed to determine the serum levels of alarmins in patients with NSV, correlate these alarmins with disease activity and severity, and analyze the predictive value of the combination of these markers.

Methods

104 NSV patients and 56 healthy controls were enrolled at the Xijing Hospital of Fourth Military Medical University between September 1, 2018, and June 30, 2019. The serum levels of alarmins (including IL-33, IL-1α, S100A9, S100A12, S100B, and HMGB1) were measured with enzyme-linked immunosorbent assays. The predictive performance of these biomarkers was evaluated with the area under the receiver operating characteristic curve (AUC), sensitivity, specificity, and other representative statistics.

Results

A total of 104 patients with NSV (mean [SD] age, 34.2 [13.0] years; 62 [59.6%] male) and 56 healthy controls (mean [SD] age, 34.8 [13.5] years; 34 [60.7%] male) were enrolled. For vitiligo diagnosis, S100B had the highest sensitivity (92.31%), whereas HMGB1 had the highest specificity (85.71%); the combination of IL-1α, S100B, S100A9, and HMGB1 increased the AUC value to 0.925, with a sensitivity of 87.50% and a specificity of 85.71%. Multivariate logistic regression analysis showed S100B (OR, 1.019; 95% CI, 1.002-1.038; P =0.03), S100A9 (OR, 1.002; 95% CI, 1.001-1.003; P<0.001), and HMGB1 (OR, 1.915; 95% CI, 1.186-3.091; P =0.008) were significantly associated with vitiligo activity. S100A9 had the highest accuracy in discriminating patients at the active stage from the stable stage, with an AUC value of 0.827. The combination of these alarmins had an AUC value of 0.860 to assess disease activity, with a sensitivity of 90.00% and a specificity of 72.97%. Furthermore, S100B (r=0.61, P <0.001), S100A9 (r=0.33, P <0.001), and HMGB1 (r = 0.51, P <0.001) levels were positively correlated with the affected body surface area (BSA) in NSV patients.

Conclusions

Serum S100B, S100A9, and HMGB1 might be biomarkers for diagnosing and assessing the activity/severity of NSV, either used alone or in combination.

Damage-associated molecular patterns in vitiligo: igniter fuse from oxidative stress to melanocyte loss

OBJECTIVES

The pathogenesis of vitiligo remains unclear. In this review, we comprehensively describe the role of damage associated molecular patterns (DAMPs) during vitiligo pathogenesis.

METHODS

Published papers on vitiligo, oxidative stress and DAMPs were collected and reviewed via database searching on PubMed, MEDLINE and Embase, etc.

RESULTS

Oxidative stress may be an important inducer of vitiligo. At high oxidative stress levels, damage-associated molecular patterns (DAMPs) are released from keratinocytes or melanocytes in the skin and induce downstream immune responses during vitiligo. Treatment regimens targeting DAMPs can effectively improve disease severity.

DISCUSSION

DAMPs play key roles in initiating host defenses against danger signals, deteriorating the condition of vitiligo. DAMP levels in serum and skin may be used as biomarkers to indicate vitiligo activity and prognosis. Targeted therapies, incorporating HMGB1, Hsp70, and IL-15 could significantly improve disease etiology. Thus, novel strategies could be identified for vitiligo treatment by targeting DAMPs.

GATA3 ameliorates melanocyte injuries in vitiligo through SIRT3‐mediated HMGB1 deacetylation

Vitiligo is a skin depigmentation disorder. GATA3 expression is downregulated in vitiligo patients, and its role and regulatory mechanism in vitiligo are unclear. GATA3 and HMGB1 levels were detected by qRT-PCR in peripheral blood cells of vitiligo patients and healthy controls, as well as H₂ O₂ -treated PIG1 cells. Their expression correlation was assessed by Pearson analysis. qRT-PCR, MTT assay, Ki67 immunostaining, flow cytometry, ELISA and Western blot were applied to determine GATA3 expression, cell survival, cell proliferation, cell apoptosis, melanin contents, and melanin-related protein expressions. The cellular distributions of HMGB1 and its deacetylation levels were detected by Western blot. The binding of GATA3 to SIRT3 promoter and effects on SIRT3 expression and HMGB1 deacetylation was determined by dual-luciferase assay, ChIP assay, and Western blot. GATA3 was decreased, and HMGB1 was increased in vitiligo. Pearson correlation assay showed that they were negatively correlated. H₂ O₂ significantly inhibited cell survival, proliferation, melanin secretion, and melanin-related protein expressions but remarkably increased cell apoptosis. GATA3 overexpression could distinctly reverse the effects of H₂ O₂ through decreasing HMGB1 expression and retained HMGB1 in nuclear due to the decreased HMGB1 acetylation. GATA3 bound to the SIRT3 and subsequently decreased H₂ O₂ -induced HMGB1 acetylation. Overexpressing HMGB1 or knockdown of SIRT3 could reverse the effects of GATA3 overexpression. GATA3 inhibited H₂ O₂ -induced injury in PIG1 cells and enhanced melanin secretion by SIRT3-regulated HMGB1 deacetylation, which might provide new evidence to treat vitiligo.

Identification of CKS2 and RRM2 as potential markers of vitiligo using bioinformatics analysis

Previous studies have attempted to elucidate the molecular mechanism of vitiligo; however, its pathogenesis remains unclear. This study aimed to explore biomarkers related to vitiligo through bioinformatic analysis. The microarray datasets GSE53146 and GSE65127 were downloaded from the Gene Expression Omnibus database. Firstly, differentially expressed genes (DEGs) in GSE53146 were screened, and then an enrichment analysis was performed. Secondly, the protein-protein interaction (PPI) network of DEGs was constructed using the STRING database, and the key genes were screened using the MCODE plugin in Cytoscape and verified using GSE65127. Finally, quantiseq was used to evaluate immune cell infiltration in vitiligo, then to observe the correlation between biomarkers and immune cells. In total, 544 DEGs were identified, including 342 upregulated and 202 downregulated genes. Gene Ontology (GO) enrichment showed that DEGs were related to inflammatory and immune responses, and Kyoto Encyclopedia of Genes and Genomes enrichment showed that DEGs were involved in many autoimmune diseases. In the PPI network, 7 key genes, CENPN, CKS2, PLK4, RRM2, TPX2, CCNA2, and CDC45 were identified by MCODE cluster and verified using the GSE65127 dataset. With an area under the curve (AUC) > 0.8 as the standard, 2 genes were screened, namely CKS2 and RRM2. Further immune infiltration analysis showed that M2 macrophages were involved in the pathogenesis of vitiligo, whereas CKS2 and RRM2 were both related to M2 macrophages. This study shows that CKS2 and RRM2 have potential as biomarkers of vitiligo and provides a theoretical basis for a better understanding of the pathogenesis of vitiligo.

Unraveling the relation between vitiligo, Interleukin 17, and serum amyloid A

BACKGROUND

There is debate concerning the precise etiopathogenesis of vitiligo. According to certain theories, a series of inflammatory responses that mediate the loss of melanocytes are caused by both cellular and humoral immune responses. It has also been demonstrated that Interleukin 17 (IL-17) promotes melanocyte death and inhibits melanogenesis through different mechanisms. Serum Amyloid A (SAA) levels are over-expressed in autoimmune diseases. Th17 cytokines are regulated by serum amyloid A proteins.

AIMS

To measure serum levels of IL-17 and SAA in vitiligo patients aiming to explain their possible role in disease pathogenesis and the other aim is to correlate their levels with disease activity and severity.

METHODS

This study included 60 vitiligo patients and 40 healthy age and sex controls. Enzyme-linked immunosorbent assay was used to measure serum levels of SAA and IL-17.

RESULTS

This study revealed significant increase in levels of serum IL-17 and SAA in patients than controls (p < 0.05). Both markers showed significant positive correlations with VASI score and duration of vitiligo; only IL-17 showed statistically significant positive correlation with VIDA scores. Patients with vitiligo showed a statistically significant positive connection between serum IL-17 levels and SAA (γ = 0.992, p-value <0.05).

CONCLUSION

Increased serum level of IL-17 and SAA in vitiligo patients together with their positive relation to vitiligo severity and the duration of the disease show that these two markers play a key role in the vitiligo development.

Role of HMGB1 in Vitiligo: Current Perceptions and Future Perspectives

Vitiligo is a chronic depigmenting disorder of the skin and mucosa caused by the destruction of epidermal melanocytes. Although the exact mechanism has not been elucidated, studies have shown that oxidative stress plays an important role in the pathogenesis of vitiligo. High mobility group box protein B1 (HMGB1) is a major nonhistone protein and an extracellular proinflammatory or chemotactic molecule that is actively secreted or passively released by necrotic cells. Recent data showed that HMGB1 is overexpressed in both blood and lesional specimens from vitiligo patients. Moreover, oxidative stress triggers the release of HMGB1 from keratinocytes and melanocytes, indicating that HMGB1 may participate in the pathological process of vitiligo. Overall, this review mainly focuses on the role of HMGB1 in the potential mechanisms underlying vitiligo depigmentation under oxidative stress. In this review, we hope to provide new insights into vitiligo pathogenesis and treatment strategies.

Alarmins in autoimmune diseases

Alarmins are endogenous, constitutively expressed, chemotacting and immune activating proteins or peptides released because of non-programmed cell death (i.e. infections, trauma, etc). They are considered endogenous damage-associated molecular patterns (DAMPs), able to induce a sterile inflammation. In the last years, several studies highlighted a possible role of different alarmins in the pathogenesis of various autoimmune and immune-mediated diseases. We reviewed the relevant literature about this topic, for about 160 articles. Particularly, we focused on systemic autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, idiopathic inflammatory myopathies, ANCA-associated vasculitides, Behçet's disease) and cutaneous organ-specific autoimmune diseases (vitiligo, psoriasis, alopecia, pemphigo). Finally, we discussed about future perspectives and potential therapeutic implications of alarmins in autoimmune diseases. In fact, identification of receptors and downstream signal transducers of alarmins may lead to the identification of antagonistic inhibitors and agonists, with the capacity to modulate alarmins-related pathways and potential therapeutic applicability.

Current Concepts of Vitiligo Immunopathogenesis

Vitiligo is an acquired immune-mediated disorder of pigmentation clinically characterized by well-defined depigmented or chalk-white macules and patches on the skin. The prevalence of vitiligo varies by geographical area, affecting 0.5% to 2% of the population. The disease imposes a significant psychological burden due to its major impact on patients’ social and emotional aspects of life. Given its autoimmune background, vitiligo is frequently associated with other autoimmune diseases or immune-mediated diseases. Vitiligo is a multifaceted disorder that involves both genetic predisposition and environmental triggers. In recent years, major predisposing genetic loci for the development of vitiligo have been discovered. The current findings emphasize the critical role of immune cells and their mediators in the immunopathogenesis of vitiligo. Oxidative-stress-mediated activation of innate immunity cells such as dendritic cells, natural killer, and ILC-1 cells is thought to be a key event in the early onset of vitiligo. Innate immunity cells serve as a bridge to adaptive immunity cells including T helper 1 cells, cytotoxic T cells and resident memory T cells. IFN-γ is the primary cytokine mediator that activates the JAK/STAT pathway, causing keratinocytes to produce the key chemokines CXCL9 and CXCL10. Complex interactions between immune and non-immune cells finally result in apoptosis of melanocytes. This paper summarizes current knowledge on the etiological and genetic factors that contribute to vitiligo, with a focus on immunopathogenesis and the key cellular and cytokine players in the disease’s inflammatory pathways.

The delicate relation between melanocytes and skin immunity: A game of hide and seek

Melanocytes exhibit a complex and intriguing relationship with the skin immune response, leading to several clinical conditions. In some disorders, inappropriate melanocyte destruction (e.g., vitiligo, halo naevi) is problematic, while in others, immune tolerance should be broken (melanoma). Important parts of the dysregulated pathways have been unraveled in pigment disorders, ranging from upregulated interferon (IFN)-γ signaling to memory T cells, regulatory T cells, and immune checkpoints. Although a network of many factors is involved, targeting key players such as IFN-γ or checkpoint inhibitors (e.g., programmed death-ligand 1 (PD-L1)] can shift the balance and lead to impressive outcomes. In this review, we focus on the immunological mechanisms of the most common inflammatory disorders where the interaction of the immune system with melanocytes plays a crucial role. This can provide new insights into the current state of melanocyte research.

Multimodal analyses of vitiligo skin identifies tissue characteristics of stable disease

Vitiligo is an autoimmune skin disease characterized by the destruction of melanocytes by autoreactive CD8⁺ T cells. Melanocyte destruction in active vitiligo is mediated by CD8⁺ T cells, but the persistence of white patches in stable disease is poorly understood. The interaction between immune cells, melanocytes, and keratinocytes in situ in human skin has been difficult to study due to the lack of proper tools. We combine noninvasive multiphoton microscopy (MPM) imaging and single-cell RNA-Seq (scRNA-Seq) to identify subpopulations of keratinocytes in stable vitiligo patients. We show that, compared with nonlesional skin, some keratinocyte subpopulations are enriched in lesional vitiligo skin and shift their energy utilization toward oxidative phosphorylation. Systematic investigation of cell-to-cell communication networks show that this small population of keratinocyte secrete CXCL9 and CXCL10 to potentially drive vitiligo persistence. Pseudotemporal dynamics analyses predict an alternative differentiation trajectory that generates this new population of keratinocytes in vitiligo skin. Further MPM imaging of patients undergoing punch grafting treatment showed that keratinocytes favoring oxidative phosphorylation persist in nonresponders but normalize in responders. In summary, we couple advanced imaging with transcriptomics and bioinformatics to discover cell-to-cell communication networks and keratinocyte cell states that can perpetuate inflammation and prevent repigmentation.

Thiol-Disulfide Homeostasis in Skin Diseases

Oxidative stress represents the imbalance between oxidants and antioxidants and has been associated with a wide range of diseases. Thiols are the most important compounds in antioxidant defense. There is an equilibrium between thiols and their oxidized forms, disulfides, known as dynamic thiol-disulfide homeostasis (TDH). In 2014, Erel and Neselioglu developed a novel automated assay to measure thiol and disulfide levels. Subsequently, many researchers have used this simple, inexpensive and fast method for evaluating TDH in various disorders. We have reviewed the literature on the role of TDH in skin diseases. We identified 26 studies that evaluated TDH in inflammatory diseases (psoriasis, seborrheic dermatitis, atopic dermatitis, vitiligo, acne vulgaris and rosacea), allergic diseases (acute and chronic urticaria) and infectious diseases (warts, pityriasis rosea and tinea versicolor). The results are heterogeneous, but in most cases indicate changes in TDH that shifted toward disulfides or toward thiols, depending on the extent of oxidative damage.

The Current Status of Antioxidants in the Treatment of Vitiligo in China

Little is known about the use of antioxidants in the clinical treatment of vitiligo. To investigate the specific use of antioxidants in the treatment of vitiligo and the possible reasons behind its use in China, we conducted a prospective questionnaire-based study using an online questionnaire comprising 26 questions in 5 areas. A total of 323 clinical frontline dermatologists participated in this study. Differences among groups were compared using Pearson’s chi-square test. Ordinal logistic regression was used to develop knowledge–use multiple regression models. Among the 323 dermatologists, 293 (90.7%) approved the oxidative stress theory of vitiligo, and 182 (56.3%) encouraged the use of antioxidants for treating vitiligo; nonetheless, only 11.8% frequently treated vitiligo with antioxidants. Insufficient knowledge of antioxidants was a significant predictor of lower frequency of antioxidant usage (adjusted odds ratio, 0.401 [95% confidence interval, 0.256-0.629]; $P<.001$ ). The predictors associated with higher antioxidant efficacy included advanced or rapid progression, moderate or moderate-to-severe vitiligo, age of 0–2 years or 13–18 years, segmental vitiligo, oral and topical combination therapy, and course duration of <1 month. The use of antioxidants for treating vitiligo is highly encouraged; however, the rates of their clinical use are considerably low. Insufficient knowledge of antioxidants is associated with a lower frequency of antioxidant usage. The synergistic curative efficacy of antioxidants could be affected by the stage, type, severity, age of patients with vitiligo, and method of using antioxidants.

MicroRNA-637 Relieves Oxidative Damage in Human Melanocytes Through Down-Regulating Transient Receptor Potential Melastatin 2 Expression

Background: Vitiligo, a chronic, autoimmune destruction of melanocytes, caused by the disappearance of epidermal melanocytes, but the mechanism is not fully understood. Although emerging evidence demonstrated that abnormal regulation of microRNAs (miRNAs) were associated with the pathogenesis of diseases, the functions of miR-637 in vitiligo remain unclear. Objective: This research was designed to explore the potential roles of miR-637 in hydrogen peroxide (H2O2)-induced human primary melanocytes in vitiligo. Methods: Human primary melanocytes were induced by 250 μmol/L H2O2 for 4 h to establish oxidative injury of melanocytes model. Cell viability and apoptosis analyzed by MTT and flow cytometry assay, respectively. The relevance between miR-637 and transient receptor potential melastatin 2 (TRPM2) was checked using TargetScan and dual luciferase reporter gene assay. The expression of miR-637 and TRPM2 was evaluated using qRT-PCR and/or Western blot analysis. Reactive oxygen species (ROS) accumulation, superoxide dismutase (SOD) and catalase (CAT) activities were measured using specific assay kits. In addition, the expression of Bcl-2 and Bax were evaluated using Western blot assay. Results: TRPM2 was up-regulated, while miR-637 was down-regulated in H2O2-stimulated human primary melanocytes. TRPM2 directly interacted with miR-637. Up-regulation of miR-637 memorably increased miR-637 level and inhibited TRPM2 expression. Furthermore, miR-637 mimic fortified cell viability, reduced apoptotic cells, enhanced Bcl-2 expression, reduced Bax level, as well as inhibited the ratio of Bax/Bcl-2 in H2O2-induced melanocytes. Meanwhile, miR-637 mimic obviously suppressed the accumulation of ROS and increased SOD and CAT activity. Nevertheless, all these findings were inverted by TRPM2-plasmid. Likewise, TRPM2-siRNA led to increased cell viability, reduced apoptotic cells, enhanced Bcl-2 expression, reduced Bax level, inhibited Bax/Bcl-2 ratio, inhibited ROS production, but increased SOD and CAT activity in H2O2-induced melanocytes. Conclusion: Our findings suggested that TRPM2 was up-regulated, while miR-637 was down-regulated in injurious melanocytes of vitiligo. Up-regulation of miR-637 relieved oxidative stress-stimulated melanocyte injury via down-regulating TRPM2 expression. Our results provide new insights into the functions of miR-637 in the development of vitiligo, indicating that miR-637 may be a latent target for vitiligo therapy.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Patho-immunological mechanisms of vitiligo: the role of the innate and adaptive immunities and environmental stress factors

Epidermal melanocyte loss in vitiligo, triggered by stresses ranging from trauma to emotional stress, chemical exposure or metabolite imbalance, to the unknown, can stimulate oxidative stress in pigment cells, which secrete damage-associated molecular patterns that then initiate innate immune responses. Antigen presentation to melanocytes leads to stimulation of autoreactive T-cell responses, with further targeting of pigment cells. Studies show a pathogenic basis for cellular stress, innate immune responses and adaptive immunity in vitiligo. Improved understanding of the aetiological mechanisms in vitiligo has already resulted in successful use of the Jak inhibitors in vitiligo. In this review, we outline the current understanding of the pathological mechanisms in vitiligo and locate loci to which therapeutic attack might be directed.

The Promising Role of Chemokines in Vitiligo: From Oxidative Stress to the Autoimmune Response

Vitiligo is a common chronic autoimmune skin disorder featured with depigmented patches and underlying destruction of melanocytes in the lesional skin. Multiple factors and mechanisms have been proposed for the etiopathogenesis of vitiligo, among which oxidative stress has been widely accepted as a key factor in initiating melanocyte loss. The altered redox status caused by oxidative stress, including the overproduction of reactive oxygen species (ROS) and the decreased activity of the antioxidant system in the skin, surrenders the resistance of melanocytes to exogenous or endogenous stimuli and eventually impairs the normal defense mechanism, leading to the absence of melanocytes. Considering the important role of innate and adaptive immunity in vitiligo, there is mounting evidence revealing an association between oxidative stress and autoimmunity. Since the significant changes of chemokines have been documented in vitiligo in many recent studies, it has been suggested that ROS-mediated chemotactic signals are not only the biomarkers of disease progression and prognosis but also are involved in the pathogenesis of vitiligo by facilitating the innate and adaptive immune cells, especially melanocyte-specific T cells, trafficking to the lesional areas of vitiligo. In this review, we discuss the interaction between oxidative stress and autoimmune response orchestrated by chemokines, including CXCL16-CXCR6 axis, CXCL9/CXCL10-CXCR3 axis, and other altered chemokines in vitiligo, and we also try to provide insight into potential therapeutic options through targeting these pathways.

Folic Acid Protects Melanocytes from Oxidative Stress via Activation of Nrf2 and Inhibition of HMGB1

Vitiligo is a cutaneous depigmentation disease due to loss of epidermal melanocytes. Accumulating evidence has indicated that oxidative stress plays a vital role in vitiligo via directly destructing melanocytes and triggering inflammatory response that ultimately undermines melanocytes. Folic acid (FA), an oxidized form of folate with high bioavailability, exhibits potent antioxidant properties and shows therapeutic potential in multiple oxidative stress-related diseases. However, whether FA safeguards melanocytes from oxidative damages remains unknown. In this study, we first found that FA relieved melanocytes from H₂O₂-induced abnormal growth and apoptosis. Furthermore, FA enhanced the activity of antioxidative enzymes and remarkably reduced intracellular ROS levels in melanocytes. Subsequently, FA effectively activated nuclear factor E2-related factor 2 (Nrf2) pathway, and Nrf2 knockdown blocked the protective effects of FA on H₂O₂-treated melanocytes. Additionally, FA inhibited the production of proinflammatory HMGB1 in melanocytes under oxidative stress. Taken together, our findings support the protective effects of FA on human melanocytes against oxidative injury via the activation of Nrf2 and the inhibition of HMGB1, thus indicating FA as a potential therapeutic agent for the treatment of vitiligo.

Clinical Significance of Serum Oxidative Stress Markers to Assess Disease Activity and Severity in Patients With Non-Segmental Vitiligo

Non-segmental vitiligo (NSV) is a chronic autoimmune disease characterized by progressive depigmentation of the skin. Oxidative stress (OS) has been proposed as one among the main principal causes in the development and establishment of a sustained autoimmune state in patients with NSV. However, the disease-associated OS biomarkers in clinical practice are not well studied. In this study, we found significantly reduced antioxidant enzymes [catalase (CAT) and superoxide dismutase (SOD)], total antioxidant capacity (TAC), and increased levels of lipid oxidation product malondialdehyde (MDA) and oxidative DNA damage byproduct [8-hydroxy-2-deoxyguanosine (8-OHdG)] in serum of NSV patients compared with healthy controls (HC). Serum TAC, MDA, and 8-OHdG levels were correlated with disease activity in all patients with NSV and much lower in patients receiving conventional treatment in the past 1 year compared to that without treatment. In addition, both serum MDA and 8-OHdG levels were significantly correlated with CXCL10 expression in patients with NSV. And the serum TAC, MDA, and 8-OHdG levels were also correlated with affected body surface area and Vitiligo Area Scoring Index score in patients with NSV. This study demonstrates dysregulated OS status in patients with NSV and provides the evidence that the serum TAC, MDA, and 8-OHdG have a capacity to indicate the activity and severity in patients with NSV.

HSF1-Dependent Autophagy Activation Contributes to the Survival of Melanocytes Under Oxidative Stress in Vitiligo

Autophagy plays a protective role in oxidative stress‒induced melanocyte death. Dysregulated autophagy increases the sensitivity of melanocytes in response to oxidative damage and promotes melanocyte degeneration in vitiligo. However, the molecular mechanism underlying this process is not fully understood. In this study, using RNA-sequencing technology, we compared the transcriptome change between normal and vitiligo melanocytes with or without treatment of oxidative stress. We found that ATG5 and ATG12, the critical components for autophagosome formation, were significantly reduced in vitiligo melanocytes under oxidative stress. Mechanistically, HSF1 is the prime transcription factor for both ATG5 and ATG12, accounting for the reduced level of ATG5 and ATG12 in vitiligo melanocytes. Deficiency of HSF1 led to accumulation of intracellular ROS, imbalance of mitochondrion membrane potential, and apoptosis in melanocytes exposure to oxidative stress. Furthermore, overexpression of HSF1 could ameliorate oxidative stress‒induced melanocytes death through the activation of autophagy by upregulating ATG5 and ATG12. These findings suggested that targeting HSF1-ATG5/12 axis could prevent oxidative stress‒induced melanocyte death and may be used as a therapeutic strategy for vitiligo treatment.

Development of a Multi-Target Strategy for the Treatment of Vitiligo via Machine Learning and Network Analysis Methods

Vitiligo is a complex disorder characterized by the loss of pigment in the skin. The current therapeutic strategies are limited. The identification of novel drug targets and candidates is highly challenging for vitiligo. Here we proposed a systematic framework to discover potential therapeutic targets, and further explore the underlying mechanism of kaempferide, one of major ingredients from Vernonia anthelmintica (L.) willd, for vitiligo. By collecting transcriptome and protein-protein interactome data, the combination of random forest (RF) and greedy articulation points removal (GAPR) methods was used to discover potential therapeutic targets for vitiligo. The results showed that the RF model performed well with AUC (area under the receiver operating characteristic curve) = 0.926, and led to prioritization of 722 important transcriptomic features. Then, network analysis revealed that 44 articulation proteins in vitiligo network were considered as potential therapeutic targets by the GAPR method. Finally, through integrating the above results and proteomic profiling of kaempferide, the multi-target strategy for vitiligo was dissected, including 1) the suppression of the p38 MAPK signaling pathway by inhibiting CDK1 and PBK, and 2) the modulation of cellular redox homeostasis, especially the TXN and GSH antioxidant systems, for the purpose of melanogenesis. Meanwhile, this strategy may offer a novel perspective to discover drug candidates for vitiligo. Thus, the framework would be a useful tool to discover potential therapeutic strategies and drug candidates for complex diseases.

Ginsenoside Rk1 protects human melanocytes from H2O2‑induced oxidative injury via regulation of the PI3K/AKT/Nrf2/HO‑1 pathway

Vitiligo is a cutaneous depigmentation disorder caused by melanocyte injury or aberrant functioning. Oxidative stress (OS) is considered to be a major cause of the onset and progression of vitiligo. Ginsenoside Rk1 (RK1), a major compound isolated from ginseng, has antioxidant activity. However, whether RK1 can protect melanocytes against oxidative injury remains unknown. The aim of the present study was to investigate the potential protective effect of RK1 against OS in the human PIG1 melanocyte cell line induced with hydrogen peroxide (H₂O₂), and to explore its underlying mechanism. PIG1 cells were pretreated with RK1 (0, 0.1, 0.2 and 0.4 mM) for 2 h followed by exposure to 1.0 mM H₂O₂ for 24 h. Cell viability and apoptosis were determined with Cell Counting Kit‑8 and flow cytometry assays, respectively. The activity levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH‑Px) were analyzed using ELISA kits. Protein expression levels, including Bax, caspase‑3, Bcl‑2, phosphorylated‑AKT, AKT, nuclear factor erythroid 2‑related factor 2 (Nrf2), heme oxygenase‑1 (HO‑1), cytosolic Nrf2 and nuclear Nrf2, were analyzed using western blot analysis. In addition, the expression and localization of Nrf2 were detected by immunofluorescence. RK1 treatment significantly improved cell viability, reduced the apoptotic rate and increased the activity levels of SOD, CAT and GSH‑Px in the PIG1 cell line exposed to H₂O₂. In addition, RK1 treatment notably induced Nrf2 nuclear translocation, increased the protein expression levels of Nrf2 and HO‑1, and the ratio of phosphorylated‑AKT to AKT in the PIG1 cells exposed to H₂O₂. Furthermore, LY294002 could reverse the protective effect of RK1 in melanocytes against oxidative injury. These data demonstrated that RK1 protected melanocytes from H₂O₂‑induced OS by regulating Nrf2/HO‑1 protein expression, which may provide evidence for the application of RK1 for the treatment of 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.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.