Huaijin Guan

Altered DNA Methylation and Expression Profiles of 8-Oxoguanine DNA Glycosylase 1 in Lens Tissue from Age-related Cataract Patients

Abstract Purpose: 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. Conclusion: 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.

The Associations between Single Nucleotide Polymorphisms of DNA Repair Genes, DNA Damage, and Age-Related Cataract: Jiangsu Eye Study

PURPOSE Age-related cataract (ARC) is one of the most common causes of severe visual impairment among the elderly worldwide with four subtypes, such as cortical, nuclear, subcapsular, and mixed types. DNA damage and malfunction of DNA repair are believed to contribute to the pathogenesis of ARC. This study examined the associations of 18 single nucleotide polymorphisms (SNPs) in four DNA repair genes (BLM, WRN, ERCC6, and OGG1) with ARC in Han Chinese from the Jiangsu Eye Study, a population-based epidemiologic study. We also determined the possible functional consequence of the SNPs to DNA damage. METHODS Eighteen SNPs in four DNA repair genes were genotyped in 789 ARC patients and 531 normal controls from the Jiangsu Eye Study. The Comet assay was to assess the extent of DNA damage in peripheral lymphocytes of selected subjects. RESULTS The results show that WRN-rs11574311 was initially associated with ARC in general, cortical, and mixed cataracts (P = 0.003, odds ratio [OR] = 1.49; P = 0.001, OR = 1.68; and P < 0.0001, OR = 2.08), BLM-rs1063147 with nuclear cataract (P = 0.03, OR = 1.31), WRN-rs2725383 with cortical cataract (P = 0.01, OR = 1.49), and WRN-rs4733220 and WRN-rs2725338 with mixed cataract (P = 0.04, OR = 0.74; P = 0.003, OR = 0.60). However, the significances of some of the above-cited associations disappeared after multiple testing corrections. WRN-rs11574311 remains associated with cortical and mixed cataract and WRN-rs2725338 with mixed cataract after multiple testing correction. We did not find any correlation between DNA damage of peripheral lymphocytes and SNP types. CONCLUSIONS We concluded that WRN genes might be involved in ARC pathogenesis in the Han Chinese population. The associations were ARC subtype specific. These findings stress the importance of detailed phenotyping in ARC subtypes, which may be associated with different risk factors and disease mechanisms.

The association between copy number variations in glutathione S-transferase M1 and T1 and age-related cataract in a Han Chinese population.

PURPOSE To determine the contribution of copy number variation (CNV) in glutathione S-transferase M1 (GSTM1) and glutathione S-transferase T1 (GSTT1) to the susceptibility to age-related cataract (ARC) and its subtypes in a Han Chinese population. METHODS ARC cases (n = 279) and controls (n = 145) were included from a Han Chinese population-based prospective study. Quantitative RT-PCR and the DeltaCt method were used to determine the presence of no, one, or multiple alleles of GSTM1 and GSTT1. The RNaseP gene was used as the internal control. RESULTS The GSTT1 null genotype was associated with ARC with an odds ratio (OR) of 1.56 (P < 0.05). Deletion of at least one GSTT1 allele also influenced the onset of ARC (OR = 2.16, P < 0.01). Consistent associations were observed between GSTT1 CNV and cortical cataract. The deletion of at least one GSTT1 allele was associated with an OR of 4.81 for developing cortical ARC (P < 0.001), although individuals who had more than two copies of GSTT1 had a reduced risk of cortical ARC (OR = 0.19, P < 0.05). The frequency of the GSTT1 null genotype in the Han Chinese population differed dramatically from that in Caucasians. No association was detected between GSTM1 CNV and ARC. CONCLUSIONS An association was observed between GSTT1 CNV and ARC in a Han Chinese population. The GSTT1 CNV is most closely associated with cortical cataract risk. The loss of at least one GSTT1 allele increases the risk of cortical cataract, whereas gain in GSTT1 copy number reduces the risk.

Copy number variations of DNA repair genes and the age-related cataract: Jiangsu Eye Study.

PURPOSE DNA damage is critical in the pathogenesis of age-related cataract (ARC). This study examined the association of copy number variations (CNVs) of DNA repair genes with susceptibility to ARC in the Han Chinese. METHODS Study participants were from the population-based Jiangsu Eye Study, which includes 780 ARC patients and 525 controls. DNA was extracted from blood for copy number (CN) assays using RT-PCR. The Comet assay was to assess DNA damage in peripheral lymphocytes. RESULTS Novel CNV was detected in WRN. Initial analyses found that CN = 3+ for WRN had an increased risk of ARC (odds ratio [OR] = 1.88, P = 0.02); CN = 1 for HSF4 had an increased risk of ARC (OR = 4.09, P = 0.004). CN = 3+ for WRN was associated with nuclear and posterior subcapsular cataract (OR = 2.06, P = 0.02; OR = 3.72, P = 0.02). CN = 1 for HSF4 was associated with nuclear and posterior subcapsular cataract (OR = 5.73, P = 0.001; OR = 6.80, P = 0.01). The combination WRN and HSF4 CNVs markedly increased the risk of ARC; the OR was increased from 2.63 by HSF4 alone to 6.80 by combined WRN and HSF4 CNVs. However, after multiple testing correction, only HSF4 CNV was associated with ARC overall and with nuclear and posterior subcapsular cataract as well. The DNA damage in lymphocytes from ARC patients was significantly higher when compared to normal controls. CONCLUSIONS HSF4 and WRN CNVs might be involved in ARC pathogenesis in the Han Chinese. These findings suggest the importance of DNA repair in ARC susceptibility and distinct risk factors in ARC subtypes.

Polymorphisms of the WRN gene and DNA damage of peripheral lymphocytes in age-related cataract in a Han Chinese population

Werner syndrome is caused by mutations in the DNA repair Werner helicase (WRN) gene and characterized by accelerated aging including cataracts. Age-related cataract (ARC) cases (N = 504) and controls (N = 244) were recruited from a population-based study to evaluate the association of single-nucleotide polymorphisms (SNPs) of WRN and another DNA repair gene (human 8-oxoguanine DNA N-glycosylase 1) with ARC. Among the five SNPs tested, only WRN rs1346044 was found to be significantly associated between cases and controls before multiple-testing adjustment. The minor C allele of rs1346044 was associated with ARC with an odds ratio (OR) of 0.66, suggesting a protective role of the C allele for developing ARC. The stratification analysis on the subtypes of ARC showed that rs1346044 was significantly associated with cortical cataract, but not with nuclear, posterior subcapsular, and mixed types after multiple-testing adjustment (OR = 0.51, p < 0.01). The genetic model analysis showed that the results fit the dominant model (OR = 0.44, p < 0.001). The comet assay used to assess the extent of DNA damage in peripheral lymphocytes of ARC cases found that the DNA damage in lymphocytes from patients with CC genotype was significantly less than that in patients with TT genotype. We concluded that the C allele of rs1346044, a non-synonymous SNP resulting in the conversion of Cys to Arg at amino acid position 1367 of WRN, alters susceptibility to ARC, especially the cortical type of the disease, in the Han Chinese. The underlying mechanism of its protective role might be related to the improved DNA repair function.

Acetylated 8-oxoguanine DNA glycosylase 1 and its relationship with p300 and SIRT1 in lens epithelium cells from age-related cataract

The human 8-oxoguanine-DNA glycosylase 1 (OGG1) is the major DNA glycosylase responsible for repair of 7,8-dihydro-8-oxoguanine (8-oxoG) and ring-opened fapyguanine, critical mutagenic DNA lesions that are induced by reactive oxygen species. OGG1 acetylation has been demonstrated playing an important role in response to DNA damage. Here, we investigated the relationship between acetylated OGG1 (Ac-OGG1) and ARC, and clarified the effect of p300 and SIRT1 on the 8-oxoG excision ability of OGG1 in ARC development. Our results showed that anterior lens capsules from ARC group had higher proportion of 8-oxoG positive LECs than those from control group. OGG1 mRNA and protein levels significantly increased in ARC group compared with control group, while the protein levels of Ac-OGG1 were lower in ARC group. We investigated the factors involved in OGG1 acetylation and found that p300 and SIRT1 are the major acetyltransferases for OGG1 acetylation. We also identified acetylation of K338/K341 lysine residues in OGG1 has an important role on the repair activity of OGG1 to oxidative damage after H2O2 exposure in human lens epithelial cells (HLE-B3). Taken together, these data demonstrate that OGG1 acetylation regulates its function in response to DNA damage and could be one of the mechanisms of ARC.

Expression and methylation of DNA repair genes in lens epithelium cells of age-related cataract.

The development of age-related cataract (ARC) is associated with DNA damage of the lens epithelial cells (LECs). This study aimed to investigate the expression level of DNA repair genes in LECs of ARC and examine whether any altered expression observed could result from DNA methylation of the promoter region of the genes. The expression levels of DNA repair genes were evaluated by microarray analysis. The results were further confirmed by qRT-PCR. DNA methylation of genes with altered expression was determined by bisulfite-specific (BSP) PCR. The mRNA levels of 10 DNA repair genes were decreased and the level of 1 DNA repair gene was increased in LECs of ARC patients compared with controls. The promoter region of the MGMT gene was hypermethylated in ARC tissue compared to controls. The data provide evidence that altered expression of DNA repair genes is associated with pathogenesis of ARC. DNA methylation of MGMT may regulate the expression of the gene and be involved in the development of ARC.

Genetic dissection of the Gpnmb network in the eye

PURPOSE To use a systematic genetics approach to investigate the regulation of Gpnmb, a gene that contributes to pigmentary dispersion syndrome (PDS) and pigmentary glaucoma (PG) in the DBA/2J (D2) mouse. METHODS Global patterns of gene expression were studied in whole eyes of a large family of BXD mouse strains (n = 67) generated by crossing the PDS- and PG-prone parent (DBA/2J) with a resistant strain (C57BL/6J). Quantitative trait locus (eQTL) mapping methods and gene set analysis were used to evaluate Gpnmb coexpression networks in wild-type and mutant cohorts. RESULTS The level of Gpnmb expression was associated with a highly significant cis-eQTL at the location of the gene itself. This autocontrol of Gpnmb is likely to be a direct consequence of the known premature stop codon in exon 4. Both gene ontology and coexpression network analyses demonstrated that the mutation in Gpnmb radically modified the set of genes with which Gpnmb expression is correlated. The covariates of wild-type Gpnmb are involved in biological processes including melanin synthesis and cell migration, whereas the covariates of mutant Gpnmb are involved in the biological processes of posttranslational modification, stress activation, and sensory processing. CONCLUSIONS These results demonstrated that a systematic genetics approach provides a powerful tool for constructing coexpression networks that define the biological process categories within which similarly regulated genes function. The authors showed that the R150X mutation in Gpnmb dramatically modified its list of genetic covariates, which may explain the associated ocular pathology.

The changes of 8-OHdG, hOGG1, APE1 and Pol β in lenses of patients with age-related cataract.

Abstract Purpose: To evaluate the changes of oxidative DNA damage (in the form of 8-OHdG) and three key DNA base-excision repair (BER) proteins, human 8-oxoguanine DNA glycosylase 1 (hOGG1), apurinic/apyrimidinic endonuclease 1 (APE1) and DNA polymerase β (Pol β), in lens epithelium cells (LECs), cortex and nucleus of lenses with age-related cataract (ARC) and age-matched controls. Methods: A total of 90 patients with ARC and 21 control subjects were enrolled. The samples included the anterior lens capsules (mainly composed of LECs) and various portions of lens. An ELISA assay was used to assess the 8-OHdG levels of genomic DNA extracted. Immunofluorescence and Western blot were used to analyze the localization and quantification of three BER proteins, respectively. Results: The 8-OHdG levels in lenses with ARC were higher than those of controls, and were not different among ARC subtypes. The 8-OHdG levels were the highest in the nucleus, followed by the LECs and cortex. The repair proteins were predominantly detected in the cellular nuclei of the LECs and superficial cortical cells. In the LECs, the protein levels of the three BER enzymes were higher in ARC than in controls. In the cortex, a downward trend of the levels of three BER enzymes was found with the increasing opaque degrees. In the nucleus, no enzymes were detected. Conclusions: Our findings indicate that the oxidative DNA damage increases in lenses with ARC, and the three BER enzymes compensatively increase in the LECs, while decreasing in the opaque cortex. The results suggest that the oxidative DNA damage may be related ARC and the alteration of DNA repair enzyme levels in ARC is associated with the location and opaque degrees of lens.

DNA Damage in Lens Epithelial Cells and Peripheral Lymphocytes from Age-Related Cataract Patients

Background: Oxidative DNA damage may be one of the etiologies of age-related cataract (ARC). We quantified DNA damage in lens epithelial cells (LECs) and peripheral blood lymphocytes of ARC. Methods: A total of 64 patients with different types of ARC and 23 control subjects were enrolled. Fresh LECs and peripheral lymphocytes were collected and DNA damage was evaluated by alkaline comet assay. The percentage of DNA in the tail of comets (%Tail DNA) and the olive tail moment (OTM) were calculated by CASP software. Results: The results showed the %Tail DNA and OTM in LECs and lymphocytes in the overall cataract patient group were significantly higher than those in the control subjects. The %Tail DNA and OTM of LECs and lymphocytes showed no differences among cortical, nuclear and posterior subcapsular cataracts. The %Tail DNA and OTM in LECs were significantly lower than those in lymphocytes but a significant correlation of the DNA damage was found between them. Conclusion: We concluded that DNA damage in lens and peripheral blood lymphocytes increased in ARC. The results imply that local and systemic oxidative DNA damage might play certain roles in ARC pathogenesis.