Pu Song

Impaired Activation of the Nrf2-ARE Signaling Pathway Undermines H2O2-Induced Oxidative Stress Response: A Possible Mechanism for Melanocyte Degeneration in Vitiligo

Vitiligo melanocytes possess higher susceptibility to oxidative insults. Consistent with this, impairment of the antioxidant defense system has been reported to be involved in the onset and progression of vitiligo. Our previous study showed that the nuclear factor E2-related factor 2-antioxidant response element (Nrf2-ARE) pathway and its downstream antioxidant enzyme heme oxygenase-1 (HO-1) are crucial for melanocytes to cope with H2O2-induced oxidative damage. Here, we sought to determine whether the diminished Nrf2-ARE activity that contributes to reduced downstream antioxidant enzymes and increased oxidative stress could be the reason why melanocytes are more vulnerable to vitiligo. We found that vitiligo melanocytes exhibited hypersensitivity to H2O2-induced oxidative injury because of reduced Nrf2 nuclear translocation and transcriptional activity, which led to decreased HO-1 expression and aberrant redox balance. Moreover, we also found that the level of serum HO-1 was significantly decreased and that of IL-2 was markedly increased in 113 vitiligo patients when compared with healthy controls. These data demonstrate that impaired activation of Nrf2 under oxidative stress could result in decreased expression of antioxidant enzymes and increased death of vitiligo melanocytes.

Association between FOXP3 polymorphisms and vitiligo in a Han Chinese population

Vitiligo is an autoimmune chronic depigmentation disorder caused by melanocyte loss. Previous studies found that CD4+CD25+ regulatory T‐cell (Treg) dysfunction was involved in the pathogenesis of vitiligo and that gene polymorphisms in forkhead box P3 (FOXP3) – a master regulator of Treg development and function – were associated with susceptibility to some autoimmune disorders. Therefore, we hypothesized that functional polymorphisms of the FOXP3 gene might be associated with vitiligo via dysregulation of Treg cells.

The association of functional polymorphisms in the aryl hydrocarbon receptor (AHR) gene with the risk of vitiligo in Han Chinese populations.

Background  Vitiligo is an acquired depigmentation disorder resulting from selective destruction of melanocytes. The aryl hydrocarbon receptor (AHR) is vital to the regulation of melanogenesis and melanocyte proliferation and differentiation through modulating the expressions of melanogenesis‐related genes. AHR mutations may negatively affect AHR proteins and its target genes. Therefore, we hypothesized that AHR polymorphisms might be involved in vitiligo by impacting the transcriptional activities of related genes as mentioned above.

Genetic polymorphisms in the methylenetetrahydrofolate reductase gene (MTHFR) and risk of vitiligo in Han Chinese populations: a genotype–phenotype correlation study

Recent evidence has revealed an elevation of total homocysteine (tHcy) in patients with vitiligo. Methylenetetrahydrofolate reductase (MTHFR) is one of the main enzymes regulating homocysteine (Hcy) metabolism. Thus, polymorphisms of MTHFR could potentially contribute to the development of vitiligo by affecting MTHFR activity and tHcy levels.

AHR promoter variant modulates its transcription and downstream effectors by allele-specific AHR-SP1 interaction functioning as a genetic marker for vitiligo

Vitiligo is an acquired depigmentation disorder largely caused by defective melanocyte- or autoimmunity-induced melanocyte destruction. The aryl hydrocarbon receptor (AHR) is essential for melanocyte homeostasis and immune process, and abnormal AHR was observed in vitiligo. We previously identified the T allele of AHR −129C > T variant as a protective factor against vitiligo. However, biological characterization underlying such effects is not fully certain, further validation by mechanistic research is warranted and was conducted in the present study. We showed that −129T allele promoted AHR transcriptional activity through facilitating its interaction with SP1 transcription factor (SP1) compared with −129C allele. We subsequently found reduced peripheral AHR and SP1 transcript expressions in vitiligo and a negative correlation of AHR level with disease duration. We also investigated AHR-related cytokines and observed increased serum TNF-α concentration and diminished serum levels of IL-10 and TGF-β1 in vitiligo. Further genetic analysis showed that -129T carriers possessed higher levels of AHR and IL-10 than −129C carriers. Therefore, our study indicates that the modulation of AHR transcription by a promoter variant has a profound influence on vitiligo, not only advancing our understanding on AHR function but also providing novel insight into the pathogenesis of degenerative or autoimmune diseases including vitiligo.

Simvastatin Protects Human Melanocytes from H2O2-Induced Oxidative Stress by Activating Nrf2

The prevention of hydrogen peroxide (H2O2)-induced oxidative stress has proved to be beneficial to vitiligo patients. Simvastatin possesses antioxidative capacity and has shown protective effect in various oxidative stress-related diseases. However, whether simvastatin can protect human melanocytes against oxidative stress has not been investigated. In this study, we initially found that pretreatment with 0.1 μmol/L to 1.0 μmol/L simvastatin led to increased cell viability and decreased cell apoptosis of melanocytes in response to H2O2. In addition, simvastatin was able to potentiate the activity of antioxidant enzymes and lessen intracellular reactive oxygen species accumulation. Furthermore, we found that simvastatin promoted the activation of nuclear erythroid 2-related factor (Nrf2) and that knockdown of Nrf2 abolished the protective effect of simvastatin against H2O2-induced oxidative damage. More importantly, the mutual enhancement between mitogen-activated protein kinase pathways and p62 contributed to simvastatin-induced Nrf2 activation in melanocytes. Finally, simvastatin showed more antioxidative capacity and better protective effect than aspirin in H2O2-treated melanocytes. Taken together, our results show that simvastatin protects human melanocytes from H2O2-induced oxidative stress by activating Nrf2, thus supporting simvastatin as a potential therapeutic agent for vitiligo.

Genetic polymorphism of the Nrf2 promoter region is associated with vitiligo risk in Han Chinese populations

The nuclear factor erythroid‐derived two‐like 2‐antioxidant response element (Nrf2‐ARE) pathway and its downstream antioxidant enzyme heme oxygenase‐1 (HMOX1 or HO‐1) play essential roles in H2O2‐induced oxidative damage in human melanocytes. However, the link between Nrf2 promoter polymorphisms and susceptibility to oxidative stress‐related diseases such as vitiligo is unknown. This study evaluated the association of the Nrf2 and HO‐1 genes polymorphisms with vitiligo susceptibility. In this case–control study of 1136 Han Chinese vitiligo patients and 1200 controls, Nrf2 (rs35652124 and rs6721961) and HO‐1 (rs2071746) genes were genotyped by PCR‐restriction fragment length polymorphism analysis. Overall, a significantly decreased risk of vitiligo was found to be associated with Nrf2 rs35652124 CC and combined (CT+CC) genotypes [odds ratio (OR) 0.64, 95% confidence interval (CI) 0.50–0.83 and OR, 0.84, 95% CI 0.71–0.99, respectively], as well as among subgroups: female, onset age ≤20 and never smoker. We subsequently found that Nrf2 rs35652124 C allele had higher transcriptional activity in the luciferase reporter assay compared with Nrf2 rs35652124 T allele. Furthermore, we investigated serum HO‐1 activity was associated with the rs35652124 CT+CC genotype and lower in patients than in controls (P = 0.024). Logistic regression analysis showed a dose–response relationship between lower vitiligo risk and increased HO‐1 activity in rs35652124 CT+CC genotype carriers (Ptrend < 0.05). These findings indicate that the C allele of rs35652124 located in the promoter region of Nrf2 gene is associated with protective effect on vitiligo in a Han Chinese population.

MicroRNA-17-92 cluster promotes the proliferation and the chemokine production of keratinocytes: implication for the pathogenesis of psoriasis

Keratinocytes are the main epidermal cell type that constitutes the skin barrier against environmental damages, which emphasizes the balance between the growth and the death of keratinocytes in maintaining skin homeostasis. Aberrant proliferation of keratinocytes and the secretion of inflammatory factors from keratinocytes are related to the formation of chronic inflammatory skin diseases like psoriasis. MicroRNA-17-92 (miRNA-17-92 or miR-17-92) is a miRNA cluster that regulates cell growth and immunity, but the role of miR-17-92 cluster in keratinocytes and its relation to skin diseases have not been well investigated. In the present study, we initially found that miR-17-92 cluster promoted the proliferation and the cell-cycle progression of keratinocytes via suppressing cyclin-dependent kinase inhibitor 2B (CDKN2B). Furthermore, miR-17-92 cluster facilitated the secretion of C-X-C motif chemokine ligand 9 (CXCL9) and C-X-C motif chemokine ligand 10 (CXCL10) from keratinocytes by inhibiting suppressor of cytokine signaling 1 (SOCS1), which enhanced the chemotaxis for T lymphocytes formed by keratinocytes. In addition, we detected increased expression of miR-17-92 cluster in psoriatic lesions and the level of lesional miR-17-92 cluster was positively correlated with the disease severity in psoriasis patients. At last, miR-17-92 cluster was increased in keratinocytes by cytokines through the activation of signal transducers and activators of transcription 1 (STAT1) signaling pathway. Our findings demonstrate that cytokine-induced overexpression of miR-17-92 cluster can promote the proliferation and the immune function of keratinocytes, and thus may contribute to the development of inflammatory skin diseases like psoriasis, which implicates miR-17-92 cluster as a potential therapeutic target for psoriasis and other skin diseases with similar inflammatory pathogenesis.

TRPM2 mediates mitochondria-dependent apoptosis of melanocytes under oxidative stress

Abstract Abnormal mitochondrial calcium accumulation plays a critical role in oxidative stress‐induced apoptosis of melanocytes. Transient receptor potential cation channel subfamily M member 2 (TRPM2) is a calcium channel sensitive to oxidative stress. However, whether TRPM2 participates in melanocyte apoptosis under oxidative stress was unknown before. In the present study, we initially found that hydrogen peroxide (H2O2) induced the demethylation of the promoter region in TRPM2 gene and increased the expression of TRPM2 in normal human melanocytes (NHMs). Meanwhile, TRPM2 was overexpressed in lesional melanocytes of vitiligo that is a skin disease caused by melanocyte loss under oxidative stress. Furthermore, either TRPM2 inhibitors or TRPM2 shRNA could ameliorate H2O2‐induced apoptosis, mitochondrial reactive oxygen species (ROS) accumulation and mitochondrial membrane potential (MMP) loss in NHMs, which was similar to the effects of an anti‐oxidant. More importantly, TRPM2 mediated the calcium influx into the cytoplasm and the mitochondria of NHMs exposed to H2O2, and a specific mitochondrial Ca2+ uptake inhibitor Ruthenium 360 (Ru360) could also protect NHMs from apoptosis and mitochondrial damages caused by H2O2. Taken together, our findings demonstrate that oxidative stress promotes the expression of TRPM2 and thus facilitates mitochondria‐dependent apoptosis of melanocytes by increasing calcium influx. Our study indicates that TRPM2 is a potential target for protecting melanocytes against oxidative damages in vitiligo. Graphical abstract Figure. No caption available. HighlightsOxidative stress increases TRPM2 expression in melanocytes probably by DNA demethylation.TRPM2 causes mitochondria‐dependent melanocyte apoptosis via calcium influx.TRPM2 is a promising target for protecting melanocytes under oxidative stress.