| [Objective]Exposed to particulate matter(PM),the main component of air pollutants,is related to the global burden of disease and non-accidental mortality.Polycyclic aromatic hydrocarbon(PAH)is the main carcinogenic organic component adsorbed on PM.7,8-dihydrodiol-9,10-epoxidebenzo[a]pyrene(BPDE)is the main active metabolite of benzo[a]pyrene(BaP).Every day,about 93%of children under the age of 15 years(1.8 billion)breathe polluted air with higher levels of PM than the guidelines of World Health Organization(WHO),which puts their health and development at risk.Due to the main physiologic characteristics,including the period of growth,more outdoor activities and higher respiratory frequency,children are sensitive to PM.PAH can not only cause DNA breakage,mutation and changes of methylation but also affect telomere homeostasis.As a protective molecule at the end of the linear chromosome arm in eukaryotes,telomeres keep the end of chromosomes stable by inhibiting DNA damage signals and preventing improper recruitment of DNA damage repair enzymes.The length of telomeres can be regarded as an early biomarker to characterize the biological function of telomeres and DNA damage.The maintenance of telomere length(TL)was mediated by telomerase,shelterin and CST(CTC1-STN1-TEN1)complex and epigenetics of subtelomere regions.As the catalytic subunit of telomerase,dyskerin pseudouridine synthase 1(DKC1]can stabilize the RNA component of telomerase.Protection of telomeres protein 1(POT1),located at the ends of chromosomes,can associate with TPP1 subunit to inhibit ATR-dependent DNA damage and recruit telomerase to the telomeres for DNA replication.As a component of the CST complex,telomere length regulation protein(TEN 1)can stabilize the interaction between CTC1,STN1 and telomere DNA,and plays an vital role in lagging strand filling synthesis.The deletion of TEN 1 can lead to telomere shortening.In addition,epidemiological studies have shown that lower DNA methylation levels among healthy adolescents are closely correlated with shorter TL.DNA methylation is dependent on the regulatory effect of DNA methyltransferases(DNMTs).At present,there are relatively few studies on the changes of TL among children caused by PAH components of particulate matter,and the telomere regulatory molecules.Therefore,in this study,we determined the serum BPDE-albumin adducts levels and the telomere length of peripheral blood leukocytes to illustrate the damage effect of PAH on children's telomere.The damage effect by analyzing the effect of serum BPDE-albumin adduct on the telomere regulatory molecules such as DKC1,POT1,TEN1,DNMT1 and DNMT3A in leukocytes,and the mediating regulatory role of telomere regulatory molecules in the correlation between PAH adducts and telomere length.[Method]In this cross-sectional molecular epidemiological study,two boarding schools in the high-PM exposed area and the low-PM exposed area in a city of East China were selected,respectively,and the eligible school-age children were recruited.A total of 273 children were enrolled,including 163 in the high-PM exposed group and 110 in the low-PM exposed group.The annual average concentrations of fine particulate matter(PM2.5)and inhalable particulate matter(PM10)from the environmental monitoring stations near the school were collected.The PM2.5 in the campus of the two schools were sampled at stationary points.The levels of PAH were detected by high performance liquid chromatography.The levels of urinary cotinine were measured by gas chromatography mass spectrometry.The serum BPDE-albumin adduct levels were detected by enzyme linked immunosorbent assay(ELISA).And peripheral blood leukocyte TL was detected by monochrome multiplex quantitative polymerase chain reaction(PCR).Real-time quantitative polymerase chain reaction(RT-qPCR)was used to detect the expression levels of telomere regulatory molecules(DKC1,POT1,TEN1,DNMT1 and DNMT3A)in leukocytes.Linear regression model was used to analyze the correlation or dose-response relationship between serum BPDE-albumin adducts and the telomere regulatory molecules.The simple mediating effect model and chain multiple mediating effect model were used to analyze the role of telomere regulatory molecules in the alterations of TL among children induced by PAH components.[Results]1.PAH components of PM caused the alterations of leukocytes relative telomere length among children.The average annual exposure levels of PM2.5 and PM10 in the high-PM exposed area were significantly higher than those in the low-PM exposed(P<0.01).The levels of environmental PM2.5 in the high-PM exposed group was higher than that in the low-PM exposed group(P<0,05).Correlations of PM2.5 with total PAHs(r=0.675,P<0.01)and BaP(r=0.691,P<0.01)were significant.The levels of serum BPDE-albumin adduct in high-PM exposed group was 26.85%higher than that in the low-PM exposed group(P<0.01).The TL of peripheral white blood cells in the high-PM exposed group was 4.48%shorter than that in the low-PM exposed group(P<0.01).The serum BPDE-albumin adduct was negatively correlated with TL(r=-0.145,P<0.05).The results of linear regression model analysis showed that 10%increment in the serum BPDE-albumin adduct with the 0.84%decrease of TL after adjusting age,gender,BMI z-score and urinary cotinine levels(P<0.05).2.The changes of telomere regulation molecules caused by PAH among children.The expression levels of DKC1,POT1 and TEN1 in leukocytes were not significantly different between the high-PM exposed group and the low-PM exposed group(P>0.05).In the high-PM exposed group,the expression levels of DNMT1 and DNMT3A were lower in children with detected urinary cotinine than those in children with undetected urinary cotinine(P<0.05).The expression levels of DNMT3A among girls and children with detected urinary cotinine in high-PM exposure group was lower than that in low-PM exposed group(P<0.05).In boys,the results of stratified analysis by BMI z-score and urinary cotinine level showed that DNMT1 expression level was 3.97%higher in the high-PM exposure group than that in the low-PM exposed group after adjusting for age,BMI z-score,urinary cotinine level and WBC count(P<0.05).The serum BPDE-albumin adduct was inversely correlated with the expression levels of leukocyte DNMT1 and DNMT3A(r=-0.139 and-0.254,P<0.05).After adjusting for age,sex,BMI z-score,urinary cotinine level,and WBC count,the DNMT1 expression levels were decreased by 3.26%,3.80%,and 3.67%respectively for every 10%increase in serum BPDE-albumin adducts in the general population,boys,and children with normal weight(P<0.05).The DNMT3A expression level was decreased by 4.13%,3.70%,4.35%,4,29%,4.31%,6.31%,3.41%respectively for every 10%increase in serum BPDE-albumin adducts in the general population,boys,girls,children with normal weight,children with overweight,children with detected urinary cotinine and children with undetected urinary cotinine(P<0.05).3.The role of DNMT3A in alterations of TL caused by PAH among children.No statistical correlation was found between leukocyte DNMT1 expression level and TL in the general population and in each subgroup analyzed by stratification(P>0.05).But DNMT3A expression level was positively correlated with TL in girls and the children with normal weight(r=0.214 and 0.149,P<0.05).There is a simple mediating effect of leukocyte DNMT3A in serum BPDE-albumin adduct and leukocyte TL shortening in girls and children with normal weight after controlling for age,gender,BMI z-score,urinary cotinine and WBC count.However,no chain multiple mediating effect was found between serum BPDE-albumin adduct and TL changes with leukocyte DNMT3A and PDT1.[Conclusion]1.PAH components of PM could cause the shortening of leukocyte telomere length among children.There is a dose-effect relationship between serum BPDE-albumin adduct and telomere length in boys.2.There are negatively correlation relationship and dose-effect relationship between serum BPDE-albumin adduct and leukocyte DNMT1 and DNMT3A expression levels among children with PM exposure.3.There is a mediating effect of leukocyte DNMT3A in serum BPDE-albumin adduct and leukocyte TL shortening in girls and children with normal weight. |
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