Genetic Variants Of DNA Repair Genes And Their Association With Vitiligo Susceptibility And Phototherapy Prognosis

Vitiligo is a common pigmentary disorder of the skin characterized by the loss offunctional epidermal melanocytes and the presence of white macules and patches. Theetiology of vitiligo has not yet been elucidated, although various theories have beensuggested, including autoimmunity, toxic metabolites, neurological factors, and geneticpredisposition. Recently, some studies have suggested that oxidative stress may be thetriggering event in the melanocyte impairment of vitiligo. Base excision repair (BER) isthe main pathway responsible for the removal of oxidative DNA damage. Geneticvariations in these genes can alter BER function and thus infuence the DNA damagerepair capacity of individual, which may increase oxidative DNA damage in melanocytesand lead to the risk of vitiligo. Narrow-band ultraviolet B (NB-UVB) is an effective wayin the treatment of vitiligo, its therapeutic mechanism is that DNA photoproductscyclobutane pyrimidine dimers (CPDs) is formed during the irradiation and thus inducesskin immunosuppression. The repair of DNA photoproducts is mainly performed bynucleotide excision repair (NER) pathway. Genetic polymorphisms in NER genes have animpact on the reapir capacity of DNA photoproducts and thus influence the condition of skin immunosuppression, which finally contribute to the variation of phototherapyprognosis.No previous research has investigated the association between geneticpolymorphisms of DNA repair genes and vitiligo susceptibility and phototherapyprognosis. Therefore, we tested this hypothesis in a hospital-based case-control studycombined with functional studies, which could provide new clues for the pathogenesis andclinical treatment of vitiligo.Methods:We screened and confirmed the functional SNPs that MAF>5%in BER and NERgenes through searching SNPs in online databases and literatures in Chinese population.We investigated the association of BER SNPs (hOGG1Ser326Cys、APE1Asp148Glu、ADPRT Val762Ala、XRCC1Arg399Gln) with the risk of vitiligo in a hospital-basedcase-control study of1000vitiligo patients and1000vitiligo-free control subjects. Then,we constructed eukaryotic expression vectors containing different genotypes of APE1Asp148Glu, transfected PIG1cells and observed the effect of APE1Asp148Glu SNP onmelanocytes against oxidative stress and APE1activity through ELISA and nucleotidefluorescence electrophoresis. Furthermore, we measured serum8-OHdG levels ofindividuals with different genotypes of APE1Asp148Glu.In the meantime, we investigated the association of NER SNPs (XPA A23G、XPCCi11A、XPC Lys939Gln、ERCC1C118T) with vitiligo phototherapy prognosis in86vitiligo patients who received NB-UVB treatment. Furthermore, we examined the impactof ERCC1C118T SNP on the apoptosis of T lymphocyte and CPDs accumulation throughflow cytometry and ELISA.Results:1. We found that a signifcantly increased risk of vitiligo was associated with theAPE1Asp/Glu (adjusted OR1.24;95%CI1.02-1.52) and Glu/Glu genotypes (adjustedOR1.48;95%CI1.13-1.93), compared with the APE1Asp/Asp genotype, whereas novitiligo risk was associated with the genotypes hOGG1Ser326Cys, ADPRT-Val762Ala andXRCC1-Arg399Gln. Moreover, the association was more pronounced in male patients and those with active vitiligo, nonsegmental vitiligo, and a vitiligo onset age of>20years.These data suggest that the APE1-Asp148Glu SNP may have a greater effect on the risk ofvitiligo in these subgroups.2. Our results showed that patients with the APE1-148Glu risk genotypes (Asp/Glu+Glu/Glu) had higher serum8-OHdG levels than those with the Asp/Asp genotype (P <0.001). In addition, compared with those having the Asp/Asp genotype, the patients withthe APE1-148Glu risk genotypes (Asp/Glu+Glu/Glu) had higher serum8-OHdG levelsamong smokers (P <0.001). Furthermore, when the8-OHdG levels were trichotomized bythe levels of the controls, a dose-response relationship between increased risk and elevatedlevels was evident (Ptrend<0.05). Consistent with the preceding results, the individualswith the1-2APE1-Asp148Glu risk alleles and the upper tertile8-OHdG level (>694.71pg/ml) had a larger increase in the risk of vitiligo (adjusted OR3.99;95%CI1.29-12.38)compared with those who had the0risk allele of APE1-Asp148Glu and the lower tertile8-OHdG level (≤533.84pg/ml).3. We successfully constructed eukaryotic expression vectors containingpCDNA3.1-APE1-148Asp and pCDNA3.1-APE1-148Glu. The8-OHdG levels inpCDNA3.1-APE1-148Glu-containing cells were significantly higher than those inpCDNA3.1-APE1-148Asp-containing cells (P <0.05). However, we did not observesignificantly decreased AP endonuclease activity of cellular proteins inpCDNA3.1-APE1-148Glu-containing cells compared with that inpCDNA3.1-APE1-148Asp-containing cells.4. We found that the vitiligo patients with the ERCC1118CC genotype had a betterprognosis of NB-UVB therapy, compared with those with the ERCC1118TT and CTgenotypes, whereas no such association was documented among the genotypes XPA A23G,XPC Ci11A and XPC Lys939Gln.5. The results of flow cytometry assay showed that the apoptosis rate of Tlymphocytes from the patients with ERCC1118CC genotype was significantly higherthan that of lymphocytes from the patients with ERCC1118TT and CT genotypes underNB-UVB irradiation (P <0.01). Furthermore, we found that the CPDs level of T lymphocytes from patients with CC genotype was significantly elevated than those withTT and CT genotypes.Conclusion:1. The APE1Asp148Glu SNP was significantly associated with the risk of vitiligo.We found a signifcantly increased risk of vitiligo was associated with the APE1Asp/Gluand Glu/Glu genotypes compared with the APE1Asp/Asp genotype, whereas no vitiligorisk was associated with the genotypes hOGG1Ser326Cys, ADPRT-Val762Ala andXRCC1-Arg399Gln.2. The APE1Asp148Glu SNP may weaken BER repair capacity, increase oxidativeDNA damage of human melanocytes and affect the risk of vitiligo in a Chinesepopulation.3. The ERCC1C118T SNP was significantly correlated with the prognosis ofNB-UVB therapy. A better prognosis of NB-UVB therapy associated with ERCC1118CCgenotype was found, while no vitiligo risk was associated with the genotypes XPA A23G,XPC Ci11A and XPC Lys939Gln.4. The ERCC1C118T CC genotype can lead to an increase of CPDs under NB-UVBirradiation, induce the apoptosis of T lymphocytes, and thus participate in the prognosis ofvitiligo phototherapy.