A functional single-nucleotide polymorphism in the catechol-O-methyltransferase gene alter vitiligo risk in a Chinese population

A frame-shift mutation in COMTD1 is associated with impaired pheomelanin pigmentation in chicken

The biochemical pathway regulating the synthesis of yellow/red pheomelanin is less well characterized than the synthesis of black/brown eumelanin. Inhibitor of gold (IG phenotype) is a plumage colour variant in chicken that provides an opportunity to further explore this pathway since the recessive allele (IG) at this locus is associated with a defect in the production of pheomelanin. IG/IG homozygotes display a marked dilution of red pheomelanin pigmentation, whilst black pigmentation (eumelanin) is only slightly affected. Here we show that a 2-base pair insertion (frame-shift mutation) in the 5th exon of the Catechol-O-methyltransferase containing domain 1 gene (COMTD1), expected to cause a complete or partial loss-of-function of the COMTD1 enzyme, shows complete concordance with the IG phenotype within and across breeds. We show that the COMTD1 protein is localized to mitochondria in pigment cells. Knockout of Comtd1 in a mouse melanocytic cell line results in a reduction in pheomelanin metabolites and significant alterations in metabolites of glutamate/glutathione, riboflavin, and the tricarboxylic acid cycle. Furthermore, COMTD1 overexpression enhanced cellular proliferation following chemical-induced transfection, a potential inducer of oxidative stress. These observations suggest that COMTD1 plays a protective role for melanocytes against oxidative stress and that this supports their ability to produce pheomelanin.

Catecholamines' accumulation and their disturbed metabolism at perilesional site: a possible cause of vitiligo progression

Catecholamines (epinephrine, norepinephrine and dopamine) are considered toxic to the melanocytes and may play an important role in the development of depigmented patches on the skin. This study was done to evaluate the levels of catecholamines in skin and plasma samples of active vitiligo patients' and gene expression changes in catecholamines' metabolism regulatory genes (COMT and GTPCH1), immunoregulatory genes (CTLA4 and PTPN22), and Catalase in active vitiligo patients. In this single-centre, prospective, case-control study, 30 patients with active vitiligo were recruited and skin biopsies from the perilesional site and plasma samples were collected. Skin biopsies from the normal site in vitiligo patients and healthy controls (n = 15) and plasma samples from controls were also obtained. Catecholamines' estimation was done via high-performance liquid chromatography. Gene expression variations were investigated via reverse transcription-polymerase chain reaction (PCR) and real-time PCR. Epinephrine, norepinephrine and dopamine levels were significantly higher in perilesional skin biopsies as compared to controls (P = 0.035, 0.024, and 0.006, respectively). However, epinephrine, norepinephrine and dopamine levels observed in patients' plasma samples were comparable to controls. The mRNA expression level of the Catalase gene was found to be upregulated at the perilesional site of patients as compared to the non-affected site of same patients (P < 0.001) and healthy controls (P = 0.037). Transcriptional expression of GTPCH1 and COMT were observed to be increased significantly at the perilesional site of patients in comparison to controls (P = 0.004 and P = 0.046, respectively). Our results support the presence of oxidative stress, inflammation and induced immune response in vitiligo patients at the perilesional sites. The increased inflammatory response may lead to catecholamines upregulation resulting in oxidative stress and melanocyte damage.

Identification of pathogenic genes and transcription factors in vitiligo

Our study aimed to identify the key genes and upstream regulators in vitiligo. To screen the pathogenic genes of vitiligo, an integrated analysis was performed by using the microarray datasets in vitiligo derived from the Gene Expression Omnibus (GEO) database. The functional annotation and potential pathways of differentially expressed genes (DEGs) were further explored by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. We constructed a vitiligo-specific transcriptional regulatory network to identify crucial transcriptional factors that target the DEGs in vitiligo. From two GEO datasets, we identified 1863 DEGs (744 downregulated DEGs and 1,119 upregulated DEGs [false discovery rate < 0.05, |Combined.ES| > 1]) between lesional tissues and nonlesional tissues. GO and KEGG analyses revealed that ubiquitin-mediated proteolysis and the endoplasmic reticulum were significantly enriched pathways for DEGs. The expressions of premelanosome (PMEL), melan-A (MLANA), dopachrome tautomerase (DCT), SRY-boxtranscription factor 10 (SOX10), tyrosinase-related protein 1 (TYRP1), and melanocortin 1 receptor (MC1R) were shown to be involved in the pathogenesis of vitiligo. We concluded that PMEL, MLANA), DCT, SOX10, TYRP1, and MC1R may play a role in vitiligo, among which TYRP1 and MC1R are regulated by forkhead box J2 (FOXJ2). Our finding may contribute to the development of new potential biomarkers, reveal the underlying pathogenesis of vitiligo, and identify novel therapeutic targets for vitiligo.

miR-196a-2 rs11614913 polymorphism is associated with vitiligo by affecting heterodimeric molecular complexes of Tyr and Tyrp1

Tyrosinase and tyrosinase-related protein 1 (Tyr-Tyrp1) complex plays a critical role in the synthesis of melanin intermediates, which involves the production of reactive oxygen species (ROS) and contributes to the development of vitiligo. Based on our previous observation that rs11614913 single nucleotide polymorphism (SNP) in miR-196a-2 could affect the risk of vitiligo by influencing Tyrp1, we hypothesized that the same SNP could also regulate the level of Tyr in vitiligo. The aim of this study was to evaluate the potential association between rs11614913 SNP in miR-196a-2 and serum Tyr level in vitiligo and the regulatory role of miR-196a-2 in the expression of Tyr in melanocytes. The serum Tyr level was detected in 116 patients with vitiligo and 116 controls by ELISA plate assay. The expression level of Tyrp1 and Tyr in PIG1(normal melanocyte cell lines) cells was analyzed by western blotting. The ROS level and apoptosis rate in PIG1 cells transfected with si-Tyr or control siRNA were tested by flow cytometry. The results show that the individuals with TT+TC genotypes in miR-196a-2 and higher Tyr level in serum had an increased risk of vitiligo compared with those who had the CC genotype and lower Tyr level (P < 0.001). Furthermore, the rs11614913 C allele in miR-196a-2 enhanced its inhibitory regulation on the expression of Tyr, the down-regulation of which in melanocytes successfully reduced the intracellular ROS levels and the apoptosis rate. In conclusion, our findings suggest that miR-196a-2 polymorphisms can regulate the Tyr levels, which influences the susceptibility of vitiligo.

Vitiligo--part 1

Vitiligo is a chronic stigmatizing disease, already known for millennia, which mainly affects melanocytes from epidermis basal layer, leading to the development of hypochromic and achromic patches. Its estimated prevalence is 0.5% worldwide. The involvement of genetic factors controlling susceptibility to vitiligo has been studied over the last decades, and results of previous studies present vitiligo as a complex, multifactorial and polygenic disease. In this context, a few genes, including DDR1, XBP1 and NLRP1 have been consistently and functionally associated with the disease. Notwithstanding, environmental factors that precipitate or maintain the disease are yet to be described. The pathogenesis of vitiligo has not been totally clarified until now and many theories have been proposed. Of these, the autoimmune hypothesis is now the most cited and studied among experts. Dysfunction in metabolic pathways, which could lead to production of toxic metabolites causing damage to melanocytes, has also been investigated. Melanocytes adhesion deficit in patients with vitiligo is mainly speculated by the appearance of Köebner phenomenon, recently, new genes and proteins involved in this deficit have been found.

Analysis of oxidative stress status, catalase and catechol-O-methyltransferase polymorphisms in Egyptian vitiligo patients

Vitiligo is the most common depigmentation disorder of the skin. Oxidative stress is implicated as one of the probable events involved in vitiligo pathogenesis possibly contributing to melanocyte destruction. Evidence indicates that certain genes including those involved in oxidative stress and melanin synthesis are crucial for development of vitiligo. This study evaluates the oxidative stress status, the role of catalase (CAT) and catechol-O-Methyltransferase (COMT) gene polymorphisms in the etiology of generalized vitiligo in Egyptians. Total antioxidant capacity (TAC) and malondialdehyde (MDA) levels as well as CAT exon 9 T/C and COMT 158 G/A polymorphisms were determined in 89 patients and 90 age and sex-matched controls. Our results showed significantly lower TAC along with higher MDA levels in vitiligo patients compared with controls. Meanwhile, genotype and allele distributions of CAT and COMT polymorphisms in cases were not significantly different from those of controls. Moreover, we found no association between both polymorphisms and vitiligo susceptibility. In conclusion, the enhanced oxidative stress with the lack of association between CAT and COMT polymorphisms and susceptibility to vitiligo in our patients suggest that mutations in other genes related to the oxidative pathway might contribute to the etiology of generalized vitiligo in Egyptian population.

The angiotensin-converting enzyme gene insertion/deletion polymorphism in Indian patients with vitiligo: a case-control study and meta-analysis

BACKGROUND

Vitiligo is a common, acquired, idiopathic depigmenting skin disorder. Although the exact pathogenesis remains unknown, genetic susceptibility and autoimmune responses play a role in vitiligo development. Previous studies have suggested that the D allele of the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is associated with vitiligo in Indians and Koreans. Furthermore, significantly higher serum ACE levels have been demonstrated in patients with some autoimmune and autoinflammatory disorders.

OBJECTIVES

The objectives were to investigate any association between the ACE I/D polymorphism and vitiligo susceptibility in an Indian population, and to compare serum ACE levels in patients with vitiligo and healthy subjects.

METHODS

The ACE I/D genotypes of 79 patients with vitiligo and 100 normal individuals were determined by polymerase chain reaction amplification. A meta-analysis was done to compare the distribution of the ACE I/D alleles and genotypes in the current and three previous studies. Serum ACE levels were evaluated by enzyme-linked immunosorbent assay.

RESULTS

A significant increase in the frequency of the ACE I/D D allele was evident in patients with vitiligo in both the case-control study [P=0·005; odds ratio (OR) 1·87; 95% confidence intervals (CI) 1·22-2·85] and the meta-analysis (P=0·044; OR 1·44; 95% CI 1·01-2·06). Serum ACE levels were significantly increased in patients with vitiligo compared with healthy subjects (P<0·0001).

CONCLUSIONS

In agreement with earlier reports, the ACE I/D D allele is associated with vitiligo susceptibility in the Indian population. The significantly elevated serum ACE levels in our cohort of patients with vitiligo concur with those previously found in patients with some other autoimmune diseases.

Genetic variants of the APE1 gene and the risk of vitiligo in a Chinese population: a genotype-phenotype correlation study

Vitiligo is an acquired depigmentation disorder, and reactive oxygen species play an important role in melanocyte damage. Base excision repair is the major pathway responsible for removing reactive oxygen species-induced DNA damage, in which APE1, ADPRT, and XRCC1 play key roles. To investigate the association between genetic variations of these genes and the risk of vitiligo in Chinese populations, we genotyped APE1-Asp148Glu, ADPRT-Val762Ala, and XRCC1-Arg399Gln polymorphisms and measured serum 8-OHdG levels in a hospital-based case-control study. We found that a significantly increased risk of vitiligo was associated with the APE1 Asp/Glu (adjusted odds ratio (OR) 1.24; 95% confidence interval (CI) 1.02-1.52) and Glu/Glu genotypes (adjusted OR 1.48; 95% CI 1.13-1.93), compared with the APE1 Asp/Asp genotype, whereas no vitiligo risk was associated with the genotypes ADPRT-Val762Ala and XRCC1-Arg399Gln. Furthermore, serum 8-OHdG levels were elevated in the APE1-148Glu allele carriers (Asp/Glu+Glu/Glu), in an allele dose-response manner, with the risk of vitiligo (Ptrend<0.05). In addition, we found that the APE1-148Glu variant increased the 8-OHdG levels of cultured human melanocytes treated with H2O2, without any impact on the endonuclease activity. These data suggest that the APE1-Asp148Glu polymorphism aggravates oxidative stress in human melanocytes and contributes to genetic predisposition to vitiligo in Chinese people.

Possible contribution of GSTP1 and other xenobiotic metabolizing genes to vitiligo susceptibility

Vitiligo is an acquired pigmentary disorder with several proposed pathogenesis mechanisms and complex multifactorial genetic predisposition. We analyzed 65 polymorphisms in genes potentially relevant to vitiligo pathogenesis mechanism to reveal novel and confirm reported genetic risk factors in general Russian population. We found that polymorphism rs1138272 (TC + CC) in GSTP1 gene encoding enzyme involved in xenobiotic metabolism is associated with vitiligo (Bonferroni adjusted P value 0.0015) with extraordinary high odds ratio 13.03, and haplotype analysis confirmed association of GSTP1 gene with vitiligo risk. Moreover, analysis of variations in several genes encoding enzymes of xenobiotic metabolism showed that higher risk of vitiligo is associated with higher number of risk alleles. This finding reveals possible contribution of genetic background to observed imbalance of oxidative stress control in vitiligo through cumulative effect of multiple genetic variations in xenobiotic metabolizing genes, supporting the concept of multigenic nature of vitiligo with multiple low-risk alleles cumulatively contributing to vitiligo risk.

Comprehensive association analysis of candidate genes for generalized vitiligo supports XBP1, FOXP3, and TSLP

We previously carried out a genome-wide association study of generalized vitiligo (GV) in non-Hispanic whites, identifying 13 confirmed susceptibility loci. In this study, we re-analyzed the genome-wide data set (comprising 1,392 cases and 2,629 controls) to specifically test association of all 33 GV candidate genes that have previously been suggested for GV, followed by meta-analysis incorporating both current and previously published data. We detected association of three of the candidate genes tested: TSLP (rs764916, P=3.0E-04, odds ratio (OR)=1.60; meta-P for rs3806933=3.1E-03), XBP1 (rs6005863, P=3.6E-04, OR=1.17; meta-P for rs2269577=9.5E-09), and FOXP3 (rs11798415, P=5.8E-04, OR=1.19). Association of GV with CTLA4 (rs12992492, P=5.9E-05, OR=1.20; meta-P for rs231775=1.0E-04) seems to be secondary to epidemiological association with other concomitant autoimmune diseases. Within the major histocompatibility complex (MHC), at 6p21.33, association with TAP1-PSMB8 (rs3819721, P=5.2E-06) seems to derive from linkage disequilibrium with major primary signals in the MHC class I and class II regions.