Micro RNAs upregulated in Vitiligo skin play an important role in its aetiopathogenesis by altering TRP1 expression and keratinocyte-melanocytes cross-talk

Exosome-derived microRNAs: emerging players in vitiligo

Exosome-derived microRNAs (miRNAs) are biomacromolecules and nanoscale extracellular vesicles originating from intracellular compartments that are secreted by most cells into the extracellular space. This review examines the formation and function of exosomal miRNAs in biological information transfer, explores the pathogenesis of vitiligo, and highlights the relationship between exosomal miRNAs and vitiligo. The aim is to deepen the understanding of how exosomal miRNAs influence immune imbalance, oxidative stress damage, melanocyte-keratinocyte interactions, and melanogenesis disorders in the development of vitiligo. This enhanced understanding may contribute to the development of potential diagnostic and therapeutic options for vitiligo.

SIRT7 Inhibits Melanin Synthesis of PIG1 and PIG3V by Suppressing the Succinylation of EZR

Background

Vitiligo is an autoimmune disease characterized by loss of skin pigmentation and currently has no effective treatment. This study aimed to investigate the function of SIRT7, being an important desuccinylase mediating multiple disease progression, and its mechanism in vitiligo progression.

Methods

Normal human melanocytes (NHM) PIG1 and vitiligo human melanocytes (VHM) PIG3V were utilized in this research. The role of sirtuin 7 (SIRT7) and Ezrin (EZR) on melanin synthesis was investigated by detecting tyrosinase activity, melanin content, α-MSH levels, and the protein levels of melanin-related markers. The function of EZR was identified via rescue experiments, while the underlying mechanism was investigated via bioinformatic analysis, co-immunoprecipitation (co-IP), immunoprecipitation (IP), and Western blot techniques.

Results

Results showed that only SIRT7 was highly expressed in vitiligo human melanocytes, where knockingdown SIRT7 translated into increased melanin synthesis in melanocytes. Mechanistically, SIRT7 knockdown promoted the succinylation of EZR at the Lys (K)60 site. Moreover, overexpressing EZR induced higher melanin synthesis in melanocytes, while its knocking down exerted the opposite effect by inhibiting SIRT7 knockdown-induced melanin synthesis.

Conclusion

SIRT7 inhibited melanin synthesis in melanocytes by suppressing the succinylation of EZR. These findings are envisaged to provide a novel theoretical basis for vitiligo treatment.

Immune dysregulation and inflammation causing hypopigmentation in post kala-azar dermal leishmaniasis: partners in crime?

Post kala-azar dermal leishmaniasis (PKDL), a heterogeneous dermal sequela of visceral leishmaniasis (VL), is challenging in terms of its etiopathogenesis. Hypopigmentation is a consistent clinical feature in PKDL, but mechanisms contributing to the loss of melanocytes remains poorly defined. Like other hypopigmentary dermatoses - for example, vitiligo, psoriasis, and leprosy - the destruction of melanocytes is likely a multifactorial phenomenon, key players being immune dysregulation and inflammation. This review focuses on immunological mechanisms responsible for the 'murder' of melanocytes, prime suspects at the lesional sites being CD8+ T cells and keratinocytes and their criminal tools being proinflammatory cytokines, for example, IFN-γ, IL-6, and TNF-α. Collectively, these may cause decreased secretion of melanocyte growth factors, loss/attenuation of cell adhesion molecules and inflammasome activation, culminating in melanocyte death.

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.

The Essential Role of microRNAs in Inflammatory and Autoimmune Skin Diseases-A Review

The etiopathogenesis of autoimmune skin diseases is complex and still not fully understood. The role of epigenetic factors is emphasized in the development of such diseases. MicroRNAs (miRNAs), a group of non-coding RNAs (ncRNAs-non-coding RNAs), are one of the important post-transcriptional epigenetic factors. miRNAs have a significant role in the regulation of the immune response by participating in the process of the differentiation and activation of B and T lymphocytes, macrophages, and dendritic cells. Recent advances in research on epigenetic factors have provided new insights into the pathogenesis and potential diagnostic and therapeutic targets of many pathologies. Numerous studies revealed a change in the expression of some microRNAs in inflammatory skin disorders, and the regulation of miRNA expression is a promising therapeutic goal. This review presents the state of the art regarding changes in the expression and role of miRNAs in inflammatory and autoimmune skin diseases, including psoriasis, atopic dermatitis, vitiligo, lichen planus, hidradenitis suppurativa, and autoimmune blistering diseases.

Vitiligo: An immune disease and its emerging mesenchymal stem cell therapy paradigm

Melanocyte damage, innate immune response, adaptive immune response, and immune inflammatory microenvironment disorders are involved in the development of the immunological pathogenic mechanism of vitiligo. Mesenchymal stem cells are considered an ideal type of cells for the treatment of vitiligo owing to their low immunogenicity, lower rates of transplant rejection, and ability to secrete numerous growth factors, exosomes, and cytokines in vivo. The regulation of signaling pathways related to oxidative stress and immune imbalance in the immunological pathogenesis of vitiligo can improve the immune microenvironment of tissue injury sites. In addition, co-transplantation with melanocytes can reverse the progression of vitiligo. Therefore, continuous in-depth research on the immunopathogenic mechanism involved in this disease and mesenchymal stem cell-based therapy is warranted for the treatment of vitiligo in the future.

Melanogenesis and the Targeted Therapy of Melanoma

Pigment production is a unique character of melanocytes. Numerous factors are linked with melanin production, including genetics, ultraviolet radiation (UVR) and inflammation. Understanding the mechanism of melanogenesis is crucial to identify new preventive and therapeutic strategies in the treatment of melanoma. Here, we reviewed the current available literatures on the mechanisms of melanogenesis, including the signaling pathways of UVR-induced pigment production, MC1R's central determinant roles and MITF as a master transcriptional regulator in melanogenesis. Moreover, we further highlighted the role of targeting BRAF, NRAS and MC1R in melanoma prevention and treatment. The combination therapeutics of immunotherapy and targeted kinase inhibitors are becoming the newest therapeutic option in advanced melanoma.

MicroRNAs: Emerging players in the pathogenesis of vitiligo

Vitiligo is an autoimmune skin disease characterized by presence of pale patchy areas of depigmentation. MicroRNAs (miRNAs) are important regulators of gene expression and play significant roles in diverse biological and pathological processes. Accumulating evidence has shown that miRNAs were differentially expressed in skin lesions and peripheral blood mononuclear cells of patients with vitiligo. In particular, miRNAs are significantly correlated with the development and progression of vitiligo. The abundance of some miRNAs in serum was also correlated with the vitiligo lesion severity, indicating that miRNAs might serve as prognostic biomarkers. Importantly, the direct involvement of miRNAs in the pathogenesis of vitiligo has been demonstrated. For example, increased expression of miR-25 contributes to vitiligo through promoting the dysfunction and oxidative stress-induced destruction of melanocytes. However, there are limited studies on the function and mechanism of deregulated miRNAs in vitiligo. Further studies are required to establish clinical applications of miRNAs for vitiligo. More in-depth investigations of miRNAs are needed for the understanding of the pathogenesis of vitiligo and the development of novel therapeutic targets. This present review summarizes the current literature on the deregulation and pathogenic roles of miRNAs in vitiligo. We also highlight the potential clinical applications of miRNAs in patients with vitiligo.

Advances in vitiligo: Update on therapeutic targets

Vitiligo, whose treatment remains a serious concern and challenge, is an autoimmune skin disease characterized by patches of depigmentation. The increasing application of molecular-targeted therapy in skin diseases, such as psoriasis and systemic lupus erythematosus, has dramatically improved their condition. Besides, there is a favorable effect of repigmentation in the treatment of the above diseases combined with vitiligo, implying that molecular-targeted therapy may also have utility in vitiligo treatment. Recently, the role of cytokine and signaling pathways in vitiligo pathogenesis are increasingly recognized. Thus, investigations are underway targeting the molecules described above. In this paper, we present a synopsis of current practices in vitiligo treatment and introduce the improvement in identifying new molecular targets and applying molecular-targeted therapies, including those under development in vitiligo treatment, providing valuable insight into establishing further precision medicine for vitiligo patients.

Differential Expression of Serum Exosomal Hsa-miR-487b-3p in Progressive Vitiligo Before and After Systemic Corticosteroid Treatment

Background

Vitiligo is an acquired skin depigmentation disease. It can be misdiagnosed at an early stage and tend to relapse. Serum markers are essential to monitoring the progression of vitiligo. Exosomal miRNAs act as the communication mediator between melanocytes and immune cells. Our study aimed to use serum exosomal miRNAs as a reference for evaluating vitiligo progression.

Methods

The miRNAs were extracted from the serum exosomes of ten progressive vitiligo patients (before and after treatment) and ten healthy individuals. We profiled miRNAs expression by RNA sequencing and screened out potential miRNAs and plotted their receiver operating characteristic (ROC) curves to explore their sensitivity and specificity as prognostic biomarkers in vitiligo progression. We examined the correlation between miRNA expression and the lesion area. Different databases were used to predict gene targets of miRNAs, which were analyzed by gene ontology and Kyoto encyclopedia of genes and genomes (KEGG).

Results

Our results showed that 141 miRNAs were differentially expressed in serum exosomes of progressive vitiligo patients, and 365 miRNAs were differentially expressed in these patients after treatment compared to healthy individuals. The expression of hsa-miR-487b-3p was significantly lower in these patients compared to healthy individuals. Still, there was no difference in its levels in patients after corticosteroid treatment compared to healthy controls. ROC curve analysis (area under curve = 0.840) indicated that hsa-miR-487b-3p could serve as a biomarker for the prognosis of vitiligo progression. Its expression positively correlated with the lesion area. A total of 41 target genes of hsa-miR-487b-3p were predicted via different databases. KEGG pathways were enriched in phenylalanine metabolism, glycan degradation, and protein export.

Conclusion

Serum exosomal hsa-miR-487b-3p can be a biomarker to detect vitiligo progression. The predicted target genes of hsa-miR-487b-3p were enriched in catabolism. Thus, its in progressive vitiligo may accelerate catabolism in melanocytes and cause its impairment.

Update on the pathogenesis of vitiligo

Vitiligo is a complex disease whose pathogenesis results from the interaction of genetic components, metabolic factors linked to cellular oxidative stress, melanocyte adhesion to the epithelium, and immunity (innate and adaptive), which culminate in aggression against melanocytes. In vitiligo, melanocytes are more sensitive to oxidative damage, leading to the increased expression of proinflammatory proteins such as HSP70. The lower expression of epithelial adhesion molecules, such as DDR1 and E-cadherin, facilitates damage to melanocytes and exposure of antigens that favor autoimmunity. Activation of the type 1-IFN pathway perpetuates the direct action of CD8+ cells against melanocytes, facilitated by regulatory T-cell dysfunction. The identification of several genes involved in these processes sets the stage for disease development and maintenance. However, the relationship of vitiligo with environmental factors, psychological stress, comorbidities, and the elements that define individual susceptibility to the disease are a challenge to the integration of theories related to its pathogenesis.

MicroRNA-183-5p regulates MITF expression in vitiligo skin depigmentation

Microphthalmia-associated transcription factor (MITF) is a master regulatory factor for melanocytes. MITF regulates multiple pigmentary genes for maintaining cellular homeostasis. MicroRNAs (miRNAs) play crucial roles in numerous biological processes however their molecular/cellular mechanisms to regulate pigmentation have not been fully explored. This study was undertaken to investigate the role of miRNAs in skin depigmentation via regulation of MITF gene. Depigmentation in C57BL/6 black mice was induced by an autoimmune response against tyrosinase. Bioinformatics approach was used to detect miRNAs conserved in 3'untraslated region (3'UTR) of MITF mRNA. The iMC23 mouse melanocytes were used for transfection experiments. The data demonstrated that the MITF mRNA/protein was markedly low in lesional skin of depigmented mice (p < 0.05). Targetscan genomic database determined that 3'UTR of mouse MITF constitutes 4819 nucleotide bases and has 23 conserved sites for different miRNAs To validate the pairing of these predicted miRNAs with MITF mRNA, five miRNAs were deregulated in lesional skin (p < 0.05). Among them, mmu-miR-181a-5p and mmu-miR-183-5p were up-regulated, whereas mmu-miR-26a-5p, mmu-miR-26b-5p and mmu-miR-32-5p were down-regulated (p < 0.05). To verify these results, the iMC23 mouse melanocytes were used. Transfection of iMC23 cells with specific miRNAs mimics or inhibitors or with 3'UTR reporter clone of MITF, showed only mmu-miR-183-5p binds to 3'UTR of MITF mRNA and regulates its expression in iMC23 melanocytes. In conclusions, this is the first study shows that miR-183-5p is a direct regulator of MITF in iMC23 melanocytes. Thus, miR-183-5p is an important regulator of melanocytes homeostasis and may be a novel target for autoimmune depigmentation therapy.

Role of miRNAs in melanin metabolism: Implications in melanin-related diseases

BACKGROUND

MicroRNAs (miRNAs) are short single-stranded non-coding RNAs that regulate degradation and expression of messenger RNA (mRNA) and play a wide range of key roles in different biological processes. They mediate different stages of melanocyte differentiation, growth, and apoptosis through a variety of pathways and can mediate melanin production by targeting key enzymes.

AIMS

This article was aimed to review the role of miRNAs in melanin metabolism and to introduce the role and significance of miRNAs in melanin-related diseases.

MATERIALS & METHODS

Systematic search and retrospective review were performed on the published data.

RESULTS

This paper reviews the process of melanin synthesis and the regulatory mechanism, explores the miRNA expression profiles in different model organisms, and introduces the mechanisms of several key miRNAs participating in melanin metabolism through target genes. We also explore the potential role of miRNA as a new target for the treatment of melanin metabolism disease, including vitiligo, melanoma, and chloasma.

CONCLUSION

miRNAs play a key role in melanin-related diseases, and the miRNAs involved may be potential therapeutic targets.

MicroRNAs as biomarkers of atrophic scarring in acne: a cross-sectional analysis of 41 patients

BACKGROUND

Acne is the commonest inflammatory dermatosis seen worldwide. Atrophic acne scarring is a frequent complication, which can arise from acne of any severity. Micro (mi)RNAs are noncoding RNA molecules of 19-25 nucleotides that function as post-transcriptomic mediators of gene expression. They have demonstrated differential expression in various pathologies, such as eczema and psoriasis, allowing for a unique miRNA 'signature' profile to be established for different disease states.

AIM

To establish a miRNA signature for acne, and acne-associated atrophic scarring and to identify if a pattern of circulating miRNA is evident in patients who are prone to scarring.

METHODS

In total, 41 participants were consecutively recruited to this study. Circulating miRNA was quantified from plasma samples in all 41 patients, while in 8 patients, and in a further validation cohort of 9 patients, whole miRNAome was undertaken from tissue specimens, which included lesional, normal and where present, scarred skin.

RESULTS

Three miRNAs, miR-223, miR-21 and miR-150, were statistically significantly overexpressed in acne lesions, and notably, in clinically uninvolved skin in participants prone to scarring. In this subgroup, we also found statistically significantly elevated levels of circulating miRNA-21 and miRNA-150.

CONCLUSION

The presence of elevated levels of these specific miRNAs in the serum of patients with acne raises the potential of a blood test to identify those at risk of scarring, allowing for earlier intervention with effective therapy.

Association between long noncoding RNA taurine-upregulated gene 1 and microRNA-377 in vitiligo

BACKGROUND

Taurine-upregulated gene 1 (TUG1) is one of the long noncoding RNAs (lncRNAs) that plays a role in melanogenesis. MicroRNA-377 (miRNA-377) is a conserved noncoding RNA that regulates angiogenesis and promotes oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are components of the nuclear hormone receptor superfamily. PPAR-γ activators stimulate melanogenesis. Interleukin (IL)-17 has been implicated in the pathogenesis of several immunological diseases. This work aimed at detecting the expression levels of lncRNA TUG1, miRNA-377, PPAR-γ, and IL-17 among vitiligo subjects and to investigate their possible role in the pathogenesis of vitiligo.

METHODS

This study was conducted on 30 healthy controls and 30 vitiligo patients. LncRNA TUG1 and miRNA-377 were detected in serum by real-time polymerase chain reaction (PCR). Also, expressions of PPAR-γ and IL-17 were assessed in tissue by real-time PCR.

RESULTS

LncRNA TUG1 and PPAR-γ levels were significantly downregulated in the vitiligo group compared with the control group. On the other hand, miRNA-377 and IL-17 were significantly upregulated in the vitiligo group compared with the control group.

CONCLUSION

This study demonstrated the dysregulated expressions of lncRNA TUG1 and miRNA-377 in patients with vitiligo suggesting that both contributed to the pathogenesis of vitiligo that might be through PPAR-γ downregulation and IL-17 upregulation.

Extracellular Vesicles as Potential Theranostic Platforms for Skin Diseases and Aging

Extracellular vesicles (EVs), naturally secreted by cells, act as mediators for communication between cells. They are transported to the recipient cells along with cargoes such as nucleic acids, proteins, and lipids that reflect the changes occurring within the parent cells. Thus, EVs have been recognized as potential theranostic agents for diagnosis, treatment, and prognosis. In particular, the evidence accumulated to date suggests an important role of EVs in the initiation and progression of skin aging and various skin diseases, including psoriasis, systemic lupus erythematosus, vitiligo, and chronic wounds. This review highlights recent research that investigates the role of EVs and their potential as biomarkers and therapeutic agents for skin diseases and aging.

Identification of a Potentially Functional circRNA-miRNA-mRNA Regulatory Network in Melanocytes for Investigating Pathogenesis of Vitiligo

CircRNAs have been reported to play essential roles in regulating immunity and inflammation, which may be an important regulatory factor in the development of vitiligo. However, the expression profile of circRNAs and their potential biological functions in vitiligo have not been reported so far. In our study we found there are 64 dysregulated circRNAs and 14 dysregulated miRNAs in the patients with vitiligo. Through the correlation analysis, we obtained 12 dysregulated circRNAs and 5 dysregulated miRNAs, forming 48 relationships in the circRNA-miRNA-mRNA regulatory network. Gene Ontology analysis indicated dysregulated circRNAs in vitiligo is closely related to the disorder of the metabolic pathway. The KEGG pathway of dysregulation of circRNAs mainly enriched in the biological processes such as ubiquitin mediated proteolysis, endocytosis and RNA degradation, and in Jak-STAT signaling pathway. Therefore, we found the circRNA-miRNA-mRNA regulatory network are involved in the regulation of numerous melanocyte functions, and these dysregulated circRNAs may closely related to the melanocyte metabolism. Our study provides a theoretical basis for studying the vitiligo pathogenesis from the perspective of circRNA-miRNA-mRNA network.

The long noncoding RNA MALAT1 suppresses miR-211 to confer protection from ultraviolet-mediated DNA damage in vitiligo epidermis by upregulating sirtuin 1

BACKGROUND

The absence of melanocytes poses a challenge for long-term tissue homeostasis in vitiligo. Surprisingly, while individuals with Fitzpatrick phototypes I-II (low melanin content) have a higher incidence of melanoma and nonmelanoma skin cancer, people with vitiligo are at a decreased risk for the same.

OBJECTIVES

To understand the molecular mechanisms that protect vitiligo skin from ultraviolet (UV)-induced DNA damage by (i) characterizing differentially expressed microRNAs in lesional vs. nonlesional epidermis and (ii) identifying their upstream regulators and downstream gene targets.

METHODS

Genome-wide microRNA profiling of nonlesional and lesional epidermis was performed on five individuals with stable nonsegmental vitiligo using next-generation RNA sequencing. The relevance of the upstream regulator and downstream target gene of the most differentially expressed microRNA was studied.

RESULTS

Our study found sirtuin1 (SIRT1), an NAD-dependent deacetylase, to be a direct target of miR-211 - the most significantly downregulated microRNA in lesional epidermis. Inhibition of SIRT1 with EX-527 downregulated keratin 10 and involucrin, suggesting that SIRT1 promotes keratinocyte differentiation. Overexpression of miR-211 mimic led to a significant increase in γ-H2AX positivity and cyclobutane pyrimidine dimer (CPD) formation, hallmarks of UVB-mediated DNA damage. These effects could be ameliorated by the addition of resveratrol, a SIRT1 activator. Furthermore, a long noncoding RNA, MALAT1, was identified as a negative upstream regulator of miR-211. Overexpression of MALAT1 resulted in increased expression of SIRT1 and a concomitant removal of UVB-induced CPDs in primary keratinocytes.

CONCLUSIONS

These findings establish a novel MALAT1-miR-211-SIRT1 signalling axis that potentially confers protection to the 'amelanotic' keratinocytes in vitiligo.

Serum levels of miRNA-21-5p in vitiligo patients and effects of miRNA-21-5p on SOX5, beta-catenin, CDK2 and MITF protein expression in normal human melanocytes

BACKGROUND

Epigenetics of vitiligo was evaluated in few studies. In particular, the role of miR-21, a microRNA involved in various processes, including melanogenesis, was never investigated.

OBJECTIVE

Evaluation of serum levels of miR-21-5p in vitiligo patients and miR-21-5p effects on melanogenesis.

METHODS

We measured serum levels of miR-21-5p in 40 patients affected by nonsegmental vitiligo and 40 sex- and age-matched healthy controls. Next, normal human melanocytes were transfected with miR-21-5p to study the effects of this microRNA, which targeted some proteins involved in melanogenesis pathway like SOX5, beta-catenin, cyclin-dependent kinase 2 (CDK2), and MITF.

RESULTS

The expression of miR-21-5p in vitiligo patients was 3.6-4454.4 fold (mean 990.4 ± 1397.9) higher than in controls. The relative expression of miR-21-5p was directly and significantly correlated with disease severity, defined by VASI (Vitiligo Area and Severity Index) score (Rho = 0.89, p = 10^-7), but not other individual or clinical characteristics. In the second part of the study, a significant reduction of SOX5, beta-catenin and CDK2 protein expression and increase of MITF protein expression was observed in cultured melanocytes after 24 h trasfection with miR-21-5p.

CONCLUSION

According to literature, miR-21-5p upregulation and consequent SOX5 downregulation should upregulate melanogenesis, while vitiligo is characterized by skin depigmentation. Our results suggest that current knowledge of the pathogenesis of vitiligo is probably incomplete. Clinical manifestations could result from an altered balance between metabolic pathways with contrasting effects. In this view, miR-21-5p upregulation might be a tentative compensation mechanism. Further studies appear necessary to confirm and better understand our results and their importance.

SFRP5 inhibits melanin synthesis of melanocytes in vitiligo by suppressing the Wnt/β-catenin signaling

Secreted frizzled-related protein 5 (SFRP5) plays a pivotal role in regulating the development of many tissues and organs, however, as an inhibitor of Wnt signaling, the role of SFRP5 in vitiligo remains unknown. Hence, we speculated that SFRP5 might be associated with melanogenesis in melanocytes by regulating Wnt signaling in vitiligo. In this study, we found that SFRP5 was overexpressed in the skin lesions of patients with vitiligo. Compared with that in normal epidermal melanocytes (PIG1), the expression of SFRP5 was increased in vitiligo melanocytes (PIG3V). To investigate the effect of SFRP5 on melanin synthesis, PIG1 cells were infected with recombinant SFRP5 adenovirus (AdSFRP5), and PIG3V cells were infected with recombinant siSFRP5 adenovirus (AdsiSFRP5). The results showed that SFRP5 overexpression inhibited melanin synthesis in PIG1 cells through downregulation of microphthalmia-associated transcription factor (MITF) and its target proteins via suppression of the Wnt/β-catenin signaling pathway. Accordingly, SFRP5 silencing increased melanin synthesis and activated the Wnt signaling pathway in PIG3V cells. Moreover, SFRP5 overexpression also downregulated the transcriptional activity of T cell factor/lymphoid enhancer factor (TCF/LEF) in PIG1 cells. Furthermore, this inhibitory effect of SFRP5 on melanin synthesis was reversed by treatment with the β-catenin agonist, SKL2001. The inhibitory action of SFRP5 in pigmentation was further confirmed in vivo using a nude mouse model. Hence, our results indicate that SFRP5 can inhibit melanogenesis in melanocytes. Additionally, our findings showed that SFRP5 plays a vital role in the development of vitiligo, and thus may serve as a potential therapeutic target for vitiligo.

Current insight into the roles of microRNA in vitiligo

Vitiligo is a common chronic depigmented skin disease characterized by melanocyte loss or dysfunction in the lesion. The pathogenesis of vitiligo has not been fully clarified. Most studies have suggested that the occurrence and progression of vitiligo are due to multiple factors and gene interactions in which noncoding RNAs contribute to an individual's susceptibility to vitiligo. Noncoding RNAs, including microRNAs (miRNAs), are a hot topic in posttranscriptional regulatory mechanism research. miRNAs are noncoding RNAs with a length of approximately 22 nucleotides and play a negative regulatory role by binding to the 3'-UTR or 5'-UTR of the target mRNA to inhibit translation or initiate mRNA degradation. Previous studies have screened the differential expression profiles of miRNAs in the skin lesions, melanocytes, peripheral blood mononuclear cells (PBMCs) and sera of patients and mouse models with vitiligo. Moreover, several studies have focused on miRNA-25, miRNA-155 and other miRNAs involved in melanin metabolism, oxidative stress, and melanocyte proliferation and apoptosis. These miRNAs and regulatory processes further illuminate the pathogenesis of vitiligo and provide hope for the application of small molecules in the treatment of vitiligo. In this review, we summarize miRNA expression profiles in different tissues of vitiligo patients and the mechanisms by which key miRNAs mediate vitiligo development.

Melanoma and Vitiligo: In Good Company

Cutaneous melanoma represents the most aggressive form of skin cancer, whereas vitiligo is an autoimmune disorder that leads to progressive destruction of skin melanocytes. However, vitiligo has been associated with cutaneous melanoma since the 1970s. Most of the antigens recognized by the immune system are expressed by both melanoma cells and normal melanocytes, explaining why the autoimmune response against melanocytes that led to vitiligo could be also present in melanoma patients. Leukoderma has been also observed as a side effect of melanoma immunotherapy and has always been associated with a favorable prognosis. In this review, we discuss several characteristics of the immune system responses shared by melanoma and vitiligo patients, as well as the significance of occurrence of leukoderma during immunotherapy, with special attention to check-point inhibitors.