Association Study Of Polymorphisms In Multisynthetase Complex Genes And DNA Damage Levels

In the past years, with the rapid increase of economics, environmental problems have become to be serious. Air pollution is a main environmental hazard for public health. The level of particulate matter, especially PM2.5 level is often used as indicator for air pollution. PM2.5 refers to the particulate matter, whose particle aerodynamic diameter≤2.5μm. In our country, the major sourse of PM2.5 is the coal combustion and traffic exhaust emission. Many epidemiology studies have shown that PM2.5 is associated with the morbility and mortality of respiratory and cardiovascular disease. A lot of in vitro experimental studies have demonstrated that organic chemical substances and transition metals absorbed in PM2.5 can oxygen generate free radicals and reactive oxygen species (ROS), hence resulting in genetic damage and cell malignancy. In the other hand, PM2.5 can stimulate bronchus and promote the release of inflammatory stimulation factor, resulting in immune inflammatory reaction. Recent studies have shown that organic chemical substances and transition metals can cause DNA damage, cardiopulmonary disease and malignant tumor. So far, most studies focused on the mechanisms of different constitute of PM2.5 on DNA damage. However, few studies studies focused on the different DNA damage levels of different subjects at population genetic level.In the other hand, once DNA damage occurs, cells elicit an elaborate signaling network, namely the DNA damage response (DDR). DNA damage response mainly include DNA damage repair and mediated apoptosis for heavier DNA damage to maintain genomic stability. Therefore, genes involved in DNA damage repair and cell apoptosis may be associated with DNA damage levels. Individual variation in DNA damage levels was observed among the subjects exposure to equal or similar concentrations of environmental agents for this reason.Aminoacyl-tRNA synthetases (ARSs) are functional proteins that play important role. ARSs function as catalytic enzymes in the process of protein synthesis. ARSs catalyze amino acids to their cognate tRNAs with a high fidelity and ensure the formation of aminoacyl-tRNA, hence involved in protein synthesis. ARS-interacting multifunctional proteins (AIMPs) including AIMP1, AIMP2 and AIMP3 can specifically bind to ARSs to maintain the stability of complex and ensure translation process with high fidelity and efficiency.In mammals, eight different ARSs, including aspartyl-tRNA synthetase (DARS), bifunctional glutamyl-prolyl-tRNA synthetase (EPRS), isoleucyl-tRNA synthetase (IARS), lysyl-tRNA synthetase (KARS), leucyl-tRNA synthetase (LARS), methionyl-tRNA synthetase (MARS), glutaminyl-tRNA synthetase (QARS) and arginyl-tRNA synthetase (RARS), form a complex with the three AIMPs. The complex is named multisynthetase complex (MSC). The complex is involved in many biological processes including angiogenesis, cell proliferation, splicing, cytokine activation, signal transduction and DNA damage repair. In order to investigate the association between genetic variants in MSC genes and DNA damage levels, we recruited 307 subjects in 3 different cities in China. We investigated the association with personal 24-hour PM2.5 exposure levels, personal DNA damage levels and genotyping data.In the current study,307 subjects were recruited from southern, central and northern China (110 from Zhuhai,118 from Wuhan and 79 from Tianjin). All subjects were disease-free genetically unrelated Han Chinese more than 40 years old, who had resided locally for more than 5 years. Each subject was interviewed to collect demographic data. Besides, we also monitor personal 24-hour PM2.5 exposure levels using PM2.5 samplers. DNA damage levels were evaluated using single cell gel electrophoresis (comet assay). The percentage of tail DNA (%Tail) was regarded as the indicator of DNA damage levels.In the current study, based on Hapmap, HaploView and SNPinfo database, we selected the potential fuctional SNPs in MSC genes for genotyping using Illumina genotype platform. Multiple linear regression was applied to evaluate the association between gengtic variants and DNA damage levels in each city with the adjustment of age, sex, PM2.5 exposure level, pack-years of smoking and BMI. A meta-analysis across the three cohorts was performed to estimate the overall effects of each SNP.The results showed that subjects in Zhuhai were exposed to the least level of PM2.5 (median value:68.35μg/m3). Median and highest levels were detected in subjects of Wuhan and Tianjin (median value:114.96μg/m3 and 146.60μg/m3 respectively). Consistently with the PM2.5 exposure levels, a similar pattern of DNA damage levels was observed with a median% Tail DNA of 1.36,1.85 and 2.97 for subjects from Zhuhai, Wuhan and Tianjin, respectively. The group is equally divided into four sub groups according to PM2.5 exposure levels, We found a significant allele-dosage effect between the PM2.5 exposure levels and DNA damage levels (Ptrend =3×10-6).The association results after mata-analysis showed that rs12199241 in AIMP3 (G>A), rs5030754 in EPRS (G>A) and rs3784929 in KARS (G>A) were significantly associated with personal DNA damage levels (P=0.001,0.016 and 0.033 respectively). After multiple testing, the association of rs12199241 was still significant, with a P value equal to 0.023 with the FDR test.To avoid the bias caused by potential confounding factors, we then performed stratification analysis in which the associations between the three identified SNPs and DNA damage levels were evaluated in subgroups based on age, sex and smoking. The results showed that there was a consistent direction of effects and similar association strengths were observed between subgroups for each SNP and no significant difference were observed between subgroups (P for heterogeneity>0.05).Based on the association results, rs12199241-A, rs5030754-A and rs3784929-A were defined as risk alleles for DNA damage. In the combined analysis, compared with individuals without risk alleles (median tail%:1.51), those carrying "2-4" alleles suffered heavier DNA damage significantly (median tail%:2.92). We found a significant allele-dosage effect between the number of risk alleles and DNA damage levels (Ptrend=3.59×10-5). There was no significant gene-environment interaction effect between genotypes and PM2.5 exposure levels.Based on the public data GTEX (Genotype-Tissue Expression), we performed functional annotation for the three SNPs. The results showed that the A allele of rs12199241 was significantly associated with decreased AIMP3 expression levels in lung tissue (P=7×10-5). It is biologically plausible for the association results.In summary, we detected personal PM2.5 levels, DNA damage levels and genotyped 23 potential functional SNPs for the 307 subjects from three different cohorts in China to evaluate the association between SNPs and DNA damage level. The results showed that 3 SNPs were associated with DNA damage levels, indicating these genetic variants may account for DNA damage levels. This study provided evidences for elucidating the mechanisms of PM2.5-modulated DNA damage from population genetic level. This study also brought enlightenment for studies of body damage caused by PM2.5.