title: Altered DNA Methylation and Expression Profiles of 8-Oxoguanine DNA Glycosylase 1 in Lens Tissue from Age-related Cataract Patients.
abstract: OBJECTIVE
  Oxidative stress and DNA damage contribute to the pathogenesis of age-related cataract (ARC). Most oxidative DNA lesions are repaired via the base excision repair (BER) proteins including 8-oxoguanine DNA glycosylase 1 (OGG1). This study examined DNA methylation of CpG islands upstream of OGG1 and their relation to the gene expression in lens cortex from ARC patients.
  
  
  METHODS
  The clinical case-control study consisted of 15 cortical type of ARC patients and 15 age-matched non-ARC controls who received transparent lens extraction due to vitreoretinal diseases. OGG1 expression in lens cortex was analyzed by qRT-PCR and Western blot. The localization and the proportion of cells positive for OGG1 were determined by immunofluorescence. Bisulfite-sequencing PCR (BSP) was performed to evaluate the methylation status of CpG islands near OGG1 in DNA extracted from lens cortex. To test relationship between the methylation and the expression of the gene of interest, 5-Aza-2'-deoxycytidine (5-Aza-dC) was used to induce demethylation of cultured human lens epithelium B-3 (HLE B-3). To test the role of OGG1 in the repair of cellular damage, HLE B-3 was transfected with OGG1 vector, followed by ultraviolet radiation b (UVB) exposure to induce apoptosis.
  
  
  RESULTS
  The mRNA and protein levels of OGG1 were significantly reduced in the lens cortex of ARC. Immunofluorescence showed that the proportion of OGG1-positive cells decreased significantly in ARC cortex in comparison with the control. The CpG island in first exon of OGG1 displayed hypermethylation in the DNA extracted from the lens cortex of ARC. Treatment of HLEB-3 cells with 5-Aza-dC upregulated OGG1 expression. UVB-induced apoptosis was attenuated after transfection with OGG1.
  
  
  CONCLUSIONS
  A reduced OGG1 expression was correlated with hypermethylation of a CpG island of OGG1 in lens cortex of ARC. The role of epigenetic change in OGG1 gene in the susceptibility to oxidative stress induced cortical ARC is warranted to further study.
authors.affiliation: Eye Institute, Affiliated Hospital of Nantong University , Nantong, Jiangsu Province , China and.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Fei
authors.initials: F
authors.lastname: Li
authors.forename: Guowei
authors.initials: G
authors.lastname: Zhang
authors.forename: Lihua
authors.initials: L
authors.lastname: Kang
authors.forename: Bai
authors.initials: B
authors.lastname: Qin
authors.forename: Huaijin
authors.initials: H
authors.lastname: Guan
mesh_terms: D000375:Aging; D017209:Apoptosis / Q000528:radiation effects; D015153:Blotting, Western; D016022:Case-Control Studies; D002386:Cataract / Q000378:metabolism*; D002478:Cells, Cultured; D018899:CpG Islands / Q000235:genetics; D045647:DNA Glycosylases / Q000235:genetics* / Q000378:metabolism*; D019175:DNA Methylation; D004847:Epithelial Cells / Q000378:metabolism / Q000528:radiation effects; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation / Q000502:physiology*; D005822:Genetic Vectors; D006801:Humans; D007904:Lens Cortex, Crystalline / Q000378:metabolism* / Q000473:pathology; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D014162:Transfection; D014466:Ultraviolet Rays
chemical_list: D012333:RNA, Messenger; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human
keywords: 8-oxoguanine DNA glycosylase 1; Age-related cataract; DNA methylation; lens cortex; oxidative stress