A Possible Modulator of Vitiligo Metabolic Impairment: Rethinking a PPARγ Agonist

Glucose transporter-1 (GLUT-1) upregulation in vitiligo: A possible link to skin depigmentation

BACKGROUND

Vitiligo is a prevalent autoimmune skin disorder characterized by progressive depigmented patches of the skin and/or mucosa. Lately, extensive research has been investigating molecular pathogenesis underlying vitiligo, epidermal-immune cell crosstalk, structural aberrations in cellular skin components and immune cell metabolism derangements. Glucose transporter-1 (GLUT-1) has recently proved to be increased in proinflammatory conditions and autoimmune diseases. GLUT-1 expression is upregulated in rheumatoid arthritis, systemic lupus erythematosus, psoriasis and chronic spongiotic dermatitis.

OBJECTIVE

To investigate GLUT-1 expression in vitiligo.

SUBJECTS AND METHODS

The study included 30 vitiligo patients "vitiligo vulgaris" and 30 healthy individuals. Biopsies of the patients' lesional vitiligo skin and the control group's normal skin were obtained. They were all tested for GLUT-1 mRNA expression using real-time polymerase chain reaction (RT-PCR) and GLUT-1 antibody expression using immunohistochemistry (IHC). Hematoxylin and eosin (H&E) staining for the specimens was additionally done for histopathological assessment.

RESULTS

GLUT-1 expression was upregulated in lesional skin of vitiligo patients compared to normal control skin (P-value < 0.001). Also, lesional specimens from stable disease showed more GLUT-1 expression than active disease but without a significant difference (P-value = 0.283). There was no significant correlation between the proposed vitiligo histological scoring system and vitiligo signs of the disease activity score.

CONCLUSION

GLUT-1 could play a crucial role in vitiligo disease onset, persistence and progression, through keratinocyte-melanocyte-fibroblast-immune cell crosstalk, being the initially deranged metabolic pathway for all these cells giving an insight into vitiligo metabolomics.

Defective Intracellular Insulin/IGF-1 Signaling Elucidates the Link Between Metabolic Defect and Autoimmunity in Vitiligo

Background: Vitiligo is featured by the manifestation of white maculae and primarily results from inflammatory/immune-selective aggression to melanocytes. The trigger mechanism leading to the activation of resident immune cells in the skin still lacks a molecular description. There is growing evidence linking altered mitochondrial metabolism to vitiligo, suggesting that an underlying metabolic defect may enable a direct activation of the immune system. Recent evidence demonstrated the association of vitiligo with disorders related to systemic metabolism, including insulin resistance (IR) and lipid disarrangements. However, IR, defined as a cellular defect in the insulin-mediated control of glucose metabolism, and its possible role in vitiligo pathogenesis has not been proven yet. Methods: In this study, we compared the Ins/IGF-1 intracellular signaling of dermal and epidermal cells isolated from non-lesional vitiligo skin to that belonging to cells obtained from healthy donors. Results: We demonstrated that due to the intensified glucose uptake, S6, and insulin receptor substrate 1 (IRS1) chronic phosphorylation, their inducibilities were downsized, a condition that coincides with the definition of insulin resistance at the cellular level. Correspondingly, the mitogenic and metabolic activities normally provoked by Ins/IGF-1 exposure resulted in significantly compromised vitiligo cells (p ≤ 0.05). Besides all the vitiligo-derived skin cells manifesting an energetic disequilibrium consisting of a low ATP, catabolic processes activation, and chronic oxidative stress, the functional consequences of this state appear amplified in the keratinocyte lineage. Conclusion: The presented data argue for insulin and IGF-1 resistance collocating dysfunctional glucose metabolism in the mechanisms of vitiligo pathogenesis. In vitiligo keratinocytes, the intrinsic impairment of intracellular metabolic activities, particularly when associated with stimulation with Ins/IGF-1, converges into an aberrant pro-inflammatory phenotype that may initiate immune cell recruitment.

Characterization of Gut Microbiota in Patients with Active Spreading Vitiligo Based on Whole-Genome Shotgun Sequencing

Vitiligo is an autoimmune skin disease with a significant psychological burden and complex pathogenesis. While genetic factors contribute approximately 30% to its development, recent evidence suggests a crucial role of the gut microbiome in autoimmune diseases. This study investigated differences in gut microbiome composition and metabolic pathways between active spreading vitiligo patients and healthy controls using shotgun whole-genome sequencing in a Korean cohort. Taxonomic profiling reveals distinct characteristics in microbial community structure, with vitiligo patients showing an imbalanced proportion dominated by Actinomycetota and Bacteroidota. The vitiligo group exhibited significantly reduced abundance of specific species including Faecalibacterium prausnitzii, Faecalibacteriumduncaniae, and Meamonas funiformis, and increased Bifidobacterium bifidum compared to healthy controls. Metabolic pathway analysis identified significant enrichment in O-glycan biosynthesis pathways in vitiligo patients, while healthy controls showed enrichment in riboflavin metabolism and bacterial chemotaxis pathways. These findings provide new insights into the gut-skin axis in vitiligo pathogenesis and suggest potential therapeutic targets through microbiota modulation.

Identification of Upregulating Genes, Transcription Factors, and miRNAs in Vitiligo. In silico Study

Background

Depigmentation of specific areas of the skin is a persistent and long-lasting dermatologic disorder known as vitiligo, stemming from the impairment and disruption of melanocytes both structurally and functionally, leading to the loss of pigmentation in those regions.

Aim

Our objective was to identify the pivotal genes and upstream regulators, transcription factors (TFs), microRNAs (miRNAs), and pathways implicated in the pathogenesis of vitiligo.

Methods

An integrated analysis was conducted using microarray datasets on vitiligo obtained from the Gene Expression Omnibus (GEO) database. The functional annotation and potential pathways of differentially expressed genes (DEGs) were additionally investigated through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. Various bioinformatics approaches were utilized, making use of publicly accessible databases to identify appropriate TFs and miRNAs.

Results

Our investigation identified TYR, MLANA, TYRP1, PMEL, OCA2, SLC45A2, GPR143, DCT, TRPM1, and EDNRB as the most appropriate genes associated with vitiligo. Our suggestion is that the identified biological processes include developmental pigmentation (GO:0048066) and pigment metabolic processes (GO:0042440) as the most suitable biological processes. In contrast, the KEGG pathways that showed significance in our analysis are Tyrosine metabolism (Path: hsa00350) and Melanogenesis (Path: hsa04916). We hypothesized the involvement of ten TFs and 73 miRNAs in the regulation of genes related to vitiligo.

Conclusion

TYR, MLANA, TYRP1, PMEL, OCA2, SLC45A2, GPR143, DCT, TRPM1, and EDNRB are the top ten genes that are pivotal in the progression and exhibition of vitiligo. The biological, cellular, molecular, and KEGG pathways of those genes has an imperative role in the pathogenesis of vitiligo. TFs and miRNAs that interact with this gene are listed, shedding light on the regulatory mechanisms governing the expression of these key genes in vitiligo.

Markers of Metabolic Abnormalities in Vitiligo Patients

While vitiligo is primarily caused by melanocyte deficiency or dysfunction, recent studies have revealed a notable prevalence of metabolic syndrome (MetS) among patients with vitiligo. This suggests shared pathogenic features between the two conditions. Individuals with vitiligo often exhibit variations in triglyceride levels, cholesterol, and blood pressure, which are also affected in MetS. Given the similarities in their underlying mechanisms, genetic factors, pro-inflammatory signalling pathways, and increased oxidative stress, this study aims to highlight the common traits between vitiligo and metabolic systemic disorders. Serum analyses confirmed increased low-density lipoprotein (LDL) levels in patients with vitiligo, compared to physiological values. In addition, we reported significant decreases in folate and vitamin D (Vit D) levels. Oxidative stress is one of the underlying causes of the development of metabolic syndromes and is related to the advancement of skin diseases. This study found high levels of inflammatory cytokines, such as interleukin-6 (IL-6) and chemokine 10 (CXCL10), which are markers of inflammation and disease progression. The accumulation of insulin growth factor binding proteins 5 (IGFBP5) and advanced glycation end products (AGEs) entailed in atherosclerosis and diabetes onset, respectively, were also disclosed in vitiligo. In addition, the blood-associated activity of the antioxidant enzymes catalase (Cat) and superoxide dismutase (SOD) was impaired. Moreover, the plasma fatty acid (FAs) profile analysis showed an alteration in composition and specific estimated activities of FAs biosynthetic enzymes resembling MetS development, resulting in an imbalance towards pro-inflammatory n6-series FAs. These results revealed a systemic metabolic alteration in vitiligo patients that could be considered a new target for developing a more effective therapeutic approach.

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

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

New Insights into the Role of PPARγ in Skin Physiopathology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor expressed in many tissues, including skin, where it is essential for maintaining skin barrier permeability, regulating cell proliferation/differentiation, and modulating antioxidant and inflammatory responses upon ligand binding. Therefore, PPARγ activation has important implications for skin homeostasis. Over the past 20 years, with increasing interest in the role of PPARs in skin physiopathology, considerable effort has been devoted to the development of PPARγ ligands as a therapeutic option for skin inflammatory disorders. In addition, PPARγ also regulates sebocyte differentiation and lipid production, making it a potential target for inflammatory sebaceous disorders such as acne. A large number of studies suggest that PPARγ also acts as a skin tumor suppressor in both melanoma and non-melanoma skin cancers, but its role in tumorigenesis remains controversial. In this review, we have summarized the current state of research into the role of PPARγ in skin health and disease and how this may provide a starting point for the development of more potent and selective PPARγ ligands with a low toxicity profile, thereby reducing unwanted side effects.

Capsaicin combined with stem cells improved mitochondrial dysfunction in PIG3V cells, an immortalized human vitiligo melanocyte cell line, by inhibiting the HSP70/TLR4/mTOR/FAK signaling axis

BACKGROUND

Vitiligo is a common autoimmune skin disease. Capsaicin has been found to exert a positive effect on vitiligo treatment, and mesenchymal stem cells (MSCs) are also confirmed to be an ideal cell type. This study aimed to explore the influence of capsaicin combined with stem cells on the treatment of vitiligo and to confirm the molecular mechanism of capsaicin combined with stem cells in treating vitiligo.

METHODS AND RESULTS

PIG3V cell proliferation and apoptosis were detected using CCK-8 and TUNEL assays, MitoSOX Red fluorescence staining was used to measure the mitochondrial ROS level, and JC-1 staining was used to detect the mitochondrial membrane potential. The expression of related genes and proteins was detected using RT‒qPCR and Western blotting. Coimmunoprecipitation was used to analyze the protein interactions between HSP70 and TLR4 or between TLR4 and mTOR. The results showed higher expression of HSP70 in PIG3V cells than in PIG1 cells. The overexpression of HSP70 reduced the proliferation of PIG3V cells, promoted apoptosis, and aggravated mitochondrial dysfunction and autophagy abnormalities. The expression of HSP70 could be inhibited by capsaicin combined with MSCs, which increased the levels of Tyr, Tyrp1 and DCT, promoted the proliferation of PIG3V cells, inhibited apoptosis, activated autophagy, and improved mitochondrial dysfunction. In addition, capsaicin combined with MSCs regulated the expression of TLR4 through HSP70 and subsequently affected the mTOR/FAK signaling pathway CONCLUSIONS: Capsaicin combined with MSCs inhibits TLR4 through HSP70, and the mTOR/FAK signaling pathway is inhibited to alleviate mitochondrial dysfunction and autophagy abnormalities in PIG3V cells.

Decreased ZMIZ1 suppresses melanogenesis in vitiligo by regulating mTOR/AKT/GSK-3β-mediated glucose uptake

The loss of epidermal melanocytes is a distinguishing feature of vitiligo (VIT), a prevalent and long-lasting skin ailment. While various hypotheses exist to explain the cause of VIT, the precise mechanisms leading to this disease remain unclear. Zinc finger MIZ-type containing 1 (ZMIZ1) has a strong link with the development and occurrence of VIT. However, the exact role of ZMIZ1 and its underlying mechanisms in VIT are not well understood. Our study aims to illustrate that targeting ZMIZ1 is an effective therapeutic and prophylactic strategy for treating VIT. We obtained the RNA expression profile of VIT samples using RNA-seq and determined the locations and expression of ZMIZ1 in these samples via immunochemistry. Glucose uptake was analyzed through immunofluorescence and glucose uptake assay. We evaluated mRNA levels using qPCR and used plasmids transfection to knock down ZMIZ1 in PIG1 and PIG3V cell lines. The activation of the mTOR/AKT/GSK-3β signalling pathway was assessed using Western blotting analysis. We found that ZMIZ1 expression was decreased in VIT samples. Decreased ZMIZ1 expression inhibits the proliferation, migration, and invasion of melanocytes in vitro. Moreover, we revealed that decreased ZMIZ1 could also inhibit the glucose uptake of melanocytes in vitro. Decreased ZMIZ1 expression inhibits the activation of the mTOR/AKT/GSK-3β pathway and the expression of melanin synthesis-related proteins in melanocytes. Finally, we demonstrated that decreased ZMIZ1 may inhibit the cell viability of melanocytes and the synthesis of melanin by mTOR/AKT/GSK-3β-mediated oxidative stress in vitro. In conclusion, our study suggests that decreased ZMIZ1 suppresses melanogenesis in vitiligo by regulating the mTOR/AKT/GSK-3β-mediated glucose uptake in vitro, making ZMIZ1 an attractive therapeutic target for the treatment of VIT.

The underestimated role of mitochondria in vitiligo: From oxidative stress to inflammation and cell death

Vitiligo is an acquired depigmentary disorder characterized by the depletion of melanocytes in the skin. Mitochondria shoulder multiple functions in cells, such as production of ATP, maintenance of redox balance, initiation of inflammation and regulation of cell death. Increasing evidence has implicated the involvement of mitochondria in the pathogenesis of vitiligo. Mitochondria alteration will cause the abnormalities of mitochondria functions mentioned above, ultimately leading to melanocyte loss through various cell death modes. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a critical role in mitochondrial homeostasis, and the downregulation of Nrf2 in vitiligo may correlate with mitochondria damage, making both mitochondria and Nrf2 promising targets in treatment of vitiligo. In this review, we aim to discuss the alterations of mitochondria and its role in the pathogenesis of vitiligo.

Trained immunity in the pathogenesis of vitiligo

Vitiligo is caused by an autoimmune reaction against melanocytes leading to melanocyte loss. The cause of vitiligo is an interaction between genetic susceptibility and environmental factors. Both the adaptive immune system-through cytotoxic CD8+ T cells and melanocyte specific antibodies-and the innate immune system are involved in these immune processes in vitiligo. While recent data stressed the importance of innate immunity in vitiligo, the question remains why vitiligo patients' immune response becomes overly activated. Could a long-term increase in innate memory function, described as trained immunity after vaccination and in other inflammatory diseases, play a role as an enhancer and continuous trigger in the pathogenesis of vitiligo? After exposure to certain stimuli, innate immune system is able to show an enhanced immunological response to a secondary trigger, indicating a memory function of the innate immune system, a concept termed trained immunity. Trained immunity is regulated by epigenetic reprogramming, including histone chemical modifications and changes in chromatin accessibility that cause sustained changes in the transcription of specific genes. In responses to an infection, trained immunity is beneficial. However, there are indications of a pathogenic role of trained immunity in inflammatory and autoimmune diseases, with monocytes presenting features of a trained phenotype, resulting in increased cytokine production, altered cell metabolism through mTOR signaling, and epigenetic modifications. This hypothesis paper focusses on vitiligo studies that have shown these indications, suggesting the involvement of trained immunity in vitiligo. Future studies focusing on metabolic and epigenetic changes in innate immune cell populations in vitiligo could help in elucidating the potential role of trained immunity in vitiligo pathogenesis.

Recent Insights into the Role of PPARs in Disease

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that play important roles in cell proliferation, differentiation, metabolism, and cancer [...].