Mitochondrial Damage Induced By Occupational Noise Exposure And Its Association With Cardiovascular System Abnormalities

ObjectiveAt present,epidemiological studies have shown that occupational noise exposure can lead to an increase in the incidence of cardiovascular diseases such as hypertension,coronary heart disease,stroke,etc.But most of the studies are cross-sectional,and the results are still controversial,as well as the molecular biological mechanism is still unclear.This dissertation intends to study the effects of noise exposure on workers' blood pressure,mtDNA copy number,mitochondrial fission and fusion protein expression and its influencing factors in occupational population,and the effects of noise on cardiovascular system and mitochondrial damage were furtherly verified in animal experiments.MethodsIn the population study,249 workers working in A textile factory in Zhejiang Province were selected as the research subjects in 2018.According to the working duration of noise working,the participated subjects were divided into three groups(<ly,1-4y and ? 4y),with 76,97 and 76 participants respectively.A self-designed questionnaire was used to collect general demographic information and occupation-related information of the subjects The blood pressure level and prevalence rate of hypertension of the study subjects were compared,and the effects of different influencing factors were furtherly analyzed in a regression model.After the collection of EDTA anticoagulant peripheral venous blood,peripheral blood genomic DNA were extracted,and the mtDNA copy number level was detected by real-time fluorescence quantitative PCR(RT-qPCR),and the mtDNA copy number level was compared among the subjects in group<1y,1-4y and?4y,and the regression model was established to analyze the influencing factors.In 2019,all subjects in 2018 were furtherly followed up,and the study procedures and methods used for studying the relationship between noise and blood pressure and hypertension prevalence as well as mtDNA copy number were the same as in 2018.The expression levels of mitochondrial fusion and fission protein in peripheral blood plasma of the exposed population in 2018 were detected by ELISA,and the differences of these proteins among group<1y,1-4y and?4y in 2018 were compared and the factors influencing the proteins expression were analyzed.In animal experiments,40 adult male SD rats aged 6-8 weeks were randomly divided into 4 groups:control group,55dB group,85dB group and 103dB group,with 10 rats in each group and 5 in each cage.All rats were given normal food,water and light.The control group was not treated,and the noise generator of Aihua company was used to send out sine wave signals of 4kHz with noise intensity of 55dB,85dB and 103dB,respectively.The experimental rats of the corresponding group were exposed to the noise environment for 2 hours a day.At 15 days and 30 days,5 rats in each group were sacrificed and peripheral blood and myocardial tissue were collected.Peripheral blood plasma was separated for detecting blood lipid level and the level of Angiotensin ?.Genomic DNA and total RNA were extracted from myocardial tissue and peripheral blood,and it was used for detecting mtDNA copy number and the mRNA expression of mitochondrial fission and fusion genes.The expression of fission and fusion protein was also detected.in myocardial tissue.ResultsIn population studies,the median age of<1y,1-4y and?4y group was 36.00(12.00),37.00(12.00),43.00(7.00)years old,respectively,with significant differences between the three groups(P<0.001).Among the three groups,workers receiving high school education or above accounted for 38.10%,47.62%and 14.29%,respectively,with significant differences between the three groups(P<0.05).There was no significant difference in the distribution of BMI,gender,smoking,alcohol consumption,working mode and earplug wearing among the three groups(P>0.05).The median blood pressure of the subjects in<1y,1-4y and?4y group were 122.00(19.00)/74.00(12.00),121.00(16.00)/75.00(13.00)and 131.00(19.00)/77.00(13.00)mmHg,respectively.The difference of SBP level between the three groups was statistically significant(P<0.05),SBP level of subjects in the? 4y group was significantly higher than that in the<1y group(P<0.05),while DBP changes were not significant(P>0.05).The results of regression analysis showed that the change of SBP level was significantly correlated with age,sex and BMI of the study subjects,while there was no significant correlation with noise exposure.In 2019,the median blood pressure levels of the subjects in the<ly,1-4y and?4y group were 122.50(15.00)/78.50(11.00),123.00(18.00)/78.00(12.00),and 127.50(18.00)/81.00(14.00)mmHg,respectively,and there was no statistical difference(P>0.05)in SBP/DBP between the three groups.The prevalence rates of hypertension in<1y,1-4y and?4y group were 13.16%,17.53%and 21.05%in 2018,respectively.However,there was no statistical significance between three groups(P>0.05).While the prevalence of hypertension of the three groups in 2019 was 14.47%,15.46%and 30.26%,respectively.The prevalence of hypertension increased significantly with the increase of working duration(P<0.01)mtDNA copy number test results shows that there were significant differences in COX1 and ND1 mtDNA copy number levels in peripheral blood genomes of subjects in groups<1y,1-4y and?4y in 2018,and mtDNA copy number levels of subjects in groups 1-4y and ?4y were significantly lower than those in group<1y(P<0.01).There was no significant difference in COX1 and ND1 mtDNA copy number among the subjects<1y,1-4y and?4y group in 2019(P>0.05).Regression analysis showed that the decrease of copy number in 2018 was related to the exposure grouping of noise,and mtDNA copy number in ?4y group was significantly lower than that in<1y group.Compared with 2018,mtDNA copy number decrease in COX1 and ND1 group<ly and 1-4y in 2019 was statistically significant(P<0.001),while mtDNA copy number level in?4y group of 2019 was not significantly different from that of 2018(P>0.05).For fission and fusion protein,the expression levels of FIS1 protein in plasma were 1.50(1.75),1.42(3.04),1.19(1.54)ng/mL in the group<1y,1-4y and?4y in 2018,and the MFN2 levels were 2.98(1.6),2.84(1.14),and 3.39(1.68)ng/mL,respectively.There was no significant difference in FIS1 expression among the three groups(P>0.05),while there was a significant difference in MFN2 expression,with MFN2 expression significantly higher in group?4y than in 1-4y group(P<0.05).In animal experiments,15 days after noise exposure,the difference of rat peripheral blood plasma angiotensin(Ang ?)level between the control group,55dB,85dB and 103dB group was not significant.After noise exposure for 30 days,the plasma Ang ? level between four groups of rate exists significant differences,the peripheral blood plasma of Ang ? levels in 85dB group and 103dB group were significantly higher than that of control group(P<0.01).Noise exposure for 15 days had no significant effect on peripheral blood lipid level of rats,but after 30 days of noise exposure,there were significant differences in low-density lipoprotein levels.Compared with the control group,low-density lipoprotein levels in the 85dB group were significantly increased(P<0.05).Histopathological examination revealed that the myocardial fibers in the 85dB and 103dB groups were swollen and distorted compared with those in the control group.The ultrastructure of mitochondria was observed under transmission electron,and it was found that the mitochondrial membrane was swollen and cristal fracture in the noise exposed group.After 15 days of noise exposure,there was no significant difference in mitochondrial membrane potential between the control group,55dB group,85dB group and 103dB group(P>0.05).After 30 days of noise exposure,there were significant differences in mitochondrial membrane potential among the four groups.Compared with the control group,mitochondrial membrane potential decreased in the 85dB group and the 103dB group,with statistically significant differences(P<0.05)After 15 days of noise exposure,the mtDNA copy Numbers of COX1 and ND1 were significantly different in the control group,55dB group,85dB group and 103dB group(P<0.05),and the mtDNA copy numbers of 85dB group and 103dB group were significantly decreased compared with the control group(P<0.05).However,after 30 days of noise exposure,there was no significant difference in copy number of COX1 and ND1 mtDNA between the control group,55dB group,85dB group and 103dB group(P>0.05).In myocardial tissue,15 days after noise exposure,the differences of mRNA expression levels of the fission and fusion gene(MFN2?OPA1?DRP1?FIS1)between the control group and the noise exposure group rats were significant(P<0.05),of which 85dB and 103dB group rats of MFN2,OPA1 and DRP1 genes relative mRNA level was significantly higher than that of control group,the FIS1 relative mRNA expression level in 103dB group rats was significantly higher than that of control group(P<0.05).Noise exposure after 30 days,the expression of mRNA expression of MFN2,OPA1 and DRP1 gene level between control group,55dB group,85 dB and 103dB group of rats in myocardial tissue were not significant(P>0.05),and relative mRNA expression level of DRP1 gene exists significant.Compared with the control group,the relative mRNA expression level of DRP1 genes in 55dB,85dB and 103dB group rats decreased significantly(P<0.05).In peripheral blood genomes,mRNA expression levels of MFN2,DRP1 and FIS1 were not significantly different among the control group,55dB,85dB and 103dB group after 15 days or 30days noise exposure(P>0.05).After 15 days noise exposure,ELISA quantitative results showed that significant differences of MFN2 and OPA1 protein expression were found among the control group,55dB and 85dB and 103dB group in the myocardial tissue of rats.The MFN2 level in myocardial tissue from 103dB group rats was significantly increased as compared with the control group.The OPA1 protein expression levels in 55dB and 85dB and 103dB group rats were significantly higher than that of control group(P<0.05),while the changes of DRP1 and FIS 1 protein expression levels have no statistical significance among four group(P>0.05).After 30 days of noise exposure,there was no significant difference in the expression levels of MFN2,OPA1,DRP1 and FIS1 proteins in the myocardial tissues of rats between groups(P>0.05).ConclusionsExposure to occupational noise will increase the risk of hypertension in workers and lead to decreased mtDNA copy number and increased MFN2 protein expression in peripheral blood of exposed people.Noise treatment can cause increase of rat angiotensin II levels and low density lipoprotein cholesterol,decrease in copy number of mtDNA,disorder of the expression in fission and fusion gene mRNA and increased the mitochondria fusion protein expression levels.Noise exposure induced mitochondria DNA damage maybe associated with the development of cardiovascular disease.