SOD Mediates Mitochondrial Epigenetic Regulation in NIHL

Dianpeng Wang^1*Liuwei Shi²Caiping Li³Dafeng Lin¹Xiangli Yang¹Peimao Li¹Wen Zhang¹Yan Guo¹Liting Zhou²Naixing Zhang¹

• ¹Shenzhen Prevention and Treatment Center for Occupational Diseases,China, Shenzhen, China
• ²Jilin University School of Public Health, Changchun, China
• ³Southern Medical University School of Public Health, Guangzhou, China

Occupational noise-induced hearing loss (NIHL) is linked to the overproduction of mitochondrial reactive oxygen species after noise exposure. This cross-sectional study investigated the relationship between mitochondrial DNA (mtDNA) D-loop region methylation and oxidative stress in 150 participants divided into three age and sex matched groups: a control group (n=50, workers without noise exposure and with normal hearing), an exposed group (n=50, workers with significant noise exposure but normal hearing), and a case group (n=50, workers diagnosed with NIHL). The subjects among groups were matched for sex and age to control confounding factors. Methylation levels of the mtDNA D-loop region were determined by the quantitative PCR following bisulfite conversion, while mitochondrial DNA copy number (mtDNA-CN) was assessed using the real-time PCR. Oxidative stress markers—including superoxide dismutase (SOD), glutathione peroxidase (GPX), total antioxidant status (TAS), and malondialdehyde (MDA)—were quantified via substrate-specific assays, ultraviolet enzymatic methods, and colorimetric techniques. Results showed the case group (141.6±46.80 U/mL) showed lower SOD than the control (159.5±18.68 U/mL, P<0.05) and exposed groups (164.0±15.44 U/mL, P<0.01),MDA was higher in the case group (232.8±134.5 nmol/mL) than in the control (193.5±84.13 nmol/mL) and exposed groups (187.3±60.76 nmol/mL), with a significant overall difference (F=3.162, P<0.05). The case group showed lower methylation [1.205 (0.595, 2.748) %] than both the control [1.710 (0.912, 3.225) %] and exposed groups [1.850 (0.987, 4.093) %] (H=7.492, P<0.05).The case group exhibited higher mtDNA-CN levels [397.7 (205.9, 532.1)] compared to both the blank control group [317.4 (234.6, 549.6)] and the exposed group [225.1 (125.3, 445.0)] (H=9.213, P<0.05).Methylation levels of the D-loop region were positively correlated with SOD and negatively correlated with MDA. Mediation analysis indicated that SOD may mediate the relationship between D-loop methylation and bilateral high-frequency hearing thresholds, suggesting an indirect epigenetic regulatory mechanism. These findings imply that noise-induced oxidative imbalance, reflected by reduced SOD, may lead to D-loop hypomethylation, contributing to the development of NIHL. These methylation sites may serve as preliminary biomarkers for further research on preventive strategies.