Study On The Association Between Occupational Aluminum Exposure And Histone Lysine Methylation

Objective:To explore the relationship between occupational Aluminum exposure and histone lysine methylation,and analyze the relation of Aluminum,trimethyl histone H3 lysine 4(H3K4me3),dimethyl histone H3 lysine 9(H3K9me2),trimethyl histone H3 lysine 27(H3K27me3)in lymphocytes and brain-derived neurotrophic factor(BDNF),early growth response protein 1(EGR1)in plasma,aming to provide evidence for the exploration of aluminum-induced neurotoxicity in the future.Methods:By cluster random sampling method,a total of 235 male workers from Shanxi Aluminum Factory who occupationally exposed to aluminum were recruited in the study.An occupational epidemiological investigation questionnaire and cognitive tests were used,in which includes Mini-Mental State Examination(MMSE),Clock Drawing Test(CDT),Digit Span Test(DST,including forward teat DSFT and backward test DSBT),Fuld Object Memory Evaluation(FOME)and Verbal Fluency Test(VFT),to collect subjects' basic information and assess their cognitive function.Intravenous blood samples were collected when subjects were not eating in the morning,the plasma and lymphocytes were gathered and stored at-80 ?.Concentration of Aluminum in plasma was tested by graphite furnace atomic absorption spectrometry.The subjects were divided into three groups by the 25,50 and 75 percentile of the blood aluminum concentration,as low,middle and high aluminum concentration group.The contents of H3K4me3,H3K9me2,H3K27me3 in lymphocyte and BDNF,EGR1 in plasma were determined by enzyme-linked immunosorbent assay(ELISA).Results:1.Relationship between cognition of workers occupationally exposed to aluminum and BDNF and EGR1 in plasma.(1)The aluminum concentration of workers in the control group was 142.94 ± 53.80 ?g/L(n=135),and the exposure group was 155.07 ± 71.17 ?g/L(n=100),but the difference was no found between them(F=1.488,P>0.05).The 25 percentile,median and 75 percentile of aluminum concentration in plasma respectively were 100.14 ?g/L,134.36 ?g/L,178.96 ?g/L.So all subjects were divided into three groups according to the 25,50 and 75 percentile of the aluminum concentration in plasma,as the low aluminum concentration group 82.88(72.69,92.40)mg/L,the middle aluminum concentration group 134.46(115.74,154.68)mg/L and the high aluminum concentration group 228.59(204.91,263.87)mg/L.(2)Comparison of the basic information of workers with different aluminum levels: There are no significant difference in age,working year,educated year,smoking rate and drinking rate,(all P>0.05).(3)Cognitive function of workers with different aluminum levels in plasma: The scores of MMSE,DSFT,DSBT,DST of high aluminum group were 27.98±1.53,9.19±2.00,6.08±1.63,15.27±3.11 respectively,lower than those of low and middle aluminum groups,all P<0.05.Scores of MMSE(28.20± 1.52),DSBT(6.21±2.33),DST(16.12 ±3.86)of middle aluminum group all decreased,compared with those of low aluminum group,all P<0.05.(4)Correlation of aluminum concentration and cognitive function: Multiple correlation analysis showed that aluminum concentration in plasma negatively correlated with,MMSE(rs=-0.252,P<0.01),DSFT(rs=-0.197,P<0.01),DST(rs=-0.181,P<0.01),respectively,which indicated that aluminum exposure down-regulated cognitive function,especially showed noticeable effect on abilities of learning and memory.(5)The multiple stepwise regression analysis of factors affecting cognitive function showed that aluminum concentration in plasma,age,working year and educated year may all affect the cognitive function.(6)Stratified analysis of the expression of BDNF and EGR1 in plasma: the expression of BDNF(F=5.385,P=0.005)in plasma was statistically different in different aluminum level groups(P<0.05).Compared with the low aluminum group,the level of BDNF of the high aluminum concentration group and the middle aluminum concentration group both decreased(all P<0.05).The concentration of EGR1 in different aluminum concentration groups was significantly different(F=6.853,P=0.001).Compared with the low aluminum group and the middle aluminum group,the level of EGR1 of the high aluminum group decreased(P<0.05).However,after stratification analysis according to age,working year and educated year,the results all showed: Expression of BDNF and EGR1 levels in plasma between different groups have no statistical significance.(7)Correlation of aluminum concentration,BDNF,EGR1 and cognitive function: Multiple correlation analysis showed that aluminum concentration in plasma negatively correlated with BDNF(r=-0.214,P<0.01),EGR1(r=-0.315,P<0.01),MMSE(rs=-0.252,P<0.01),DSFT(rs=-0.197,P<0.01),DST(rs=-0.181,P<0.01),respectively,which indicated that aluminum exposure down-regulated cognitive function,especially showed noticeable effect on abilities of learning and memory.Score of MMSE had positively correlation with BDNF(rs=0.140,P<0.05)and EGR1(rs=0.201,P<0.05).It suggested the cognitive function was changed along with the decreasing of BDNF and EGR1 concentration.2.Modification of histone lysine methylation and its influence in occupational aluminum exposure workers.(1)Effects of aluminum exposure on the expression of H3K4me3 in lymphocytes: The concentration of H3K4me3 in lymphocytes of different aluminum concentration groups was significantly different(F=3.572,P=0.031).Compared with the low aluminum concentration group,the level of H3K4me3 of the high aluminum concentration group decreased(P<0.05).But no differences were found between the high aluminum concentration group and the middle aluminum concentration group,between the middle aluminum concentration group and the low aluminum concentration group(P>0.05).(2)Effects of aluminum exposure on the expression of H3K9me2 in lymphocytes: The concentration of H3K9me2 in lymphocytes of different aluminum concentration groups was significantly different(F=9.551,P=0.001).Compared with the low aluminum concentration group and the middle aluminum concentration group,the concentration of H3K9me2 of the high aluminum concentration group increased(P<0.05).The level of middle aluminum concentration group was up-regulated than the low aluminum concentration group,but there was no significant difference between them(P>0.05).(3)Effects of aluminum exposure on the expression of H3K27me3 in lymphocytes: The concentration of H3K27me3 in lymphocytes of different aluminum concentration groups was significantly different(F=3.641,P=0.028).Compared with the low aluminum concentration group,the concentration of H3K27me3 of the high aluminum concentration group was up-regulated(P<0.05).The level of middle aluminum concentration group was up-regulated than the low aluminum concentration group,but there was no significant difference between them(P>0.05).(4)Correlation of aluminum concentration,H3K4me3,H3K9me2,H3K27me3: Multiple correlation analysis showed that aluminum concentration in plasma negatively correlated with H3K4me3 in lymphocytes(r=-0.307,P<0.01),positively correlated with H3K9me2 in lymphocytes(r=0.329,P<0.01),H3K27me3 in lymphocytes(r=0.387,P<0.01),respectively,which indicated that aluminum exposure down-regulated the expression of H3K4me3 and up-regulated the expression of H3K9me2 and H3K27me3.(5)Correlation of BDNF,EGR1,H3K4me3,H3K9me2,H3K27me3: Multiple correlation analysis showed that BDNF and EGR1 in plasma positively correlated with H3K4me3 in lymphocytes(r=0.202,P<0.05;r=0.361,P<0.01),which suggested H3K4me3 up-regualated BDNF and EGR1.BDNF in plasma negatively correlated with H3K9me2 in lymphocytes(r=-0.286,P<0.01),however,EGR1 negatively correlated with H3K27me3 in lymphocytes(r=-0.241,P<0.05),indicating H3K9me2 down-regualated BDNF and H3K27me3 down-regualated EGR1.(6)Multiple stepwise regression analysis between BDNF,EGR1 and H3K4me3,H3K9me2,H3K27me3: There was a linear regression relationship between BDNF and H3K4me3,H3K9me2;between EGR1 and H3K4me3,H3K27me3 simultaneously.Conclusions:1.Long-term occupational aluminum exposure may impair workers' cognitive function,along with deseasing levels of BDNF,EGR1 in plasma.There is a certain correlation between aluminum concentration,cognitive function and BDNF,EGR1,suggesting that aluminum may affect learning and memory through regulating the expression of BDNF,EGR1.2.The expression of BDNF,EGR1 has correlation with levels of H3K4me3,H3K9me2 and H3K27me3.H3K4me3,H3K9me2 and H3K27me3 may take part in the process of cognitive function change caused by occupational aluminum exposure,by commanding expression of BDNF and EGR1.