Effects Of Low-dose Mercury Exposure In Newborns On MRNA Expression Profiles

Objective:Newborns are vulnerable to low-dose mercury（Hg）exposure.The mechanism of Hg toxicity to newborns is complex and still unclear.This study was designed to evaluate Hg exposure in newborns of Wanshan Hg Mining Area（WHMA）,and screen the difference in m RNA expression profile by high-throughput sequencing technology,which finally explore the molecular mechanism of Hg toxicity in newborns.Methods:Pregnant women lived in WHMA for more than one year were selected as the study objects.A questionnaire survey was conducted on pregnant women to obtain the information on occupation,height,weight,dietary habits,etc.The data of routine blood test indexes were collected in the clinical laboratory of People’s Hospital,Wanshan County.A total of 114 UCB samples were collected.The THg concentrations in UCB were determined by cold vapor atomic fluorescence spectroscopy（CVAFS）.We divided the study population into the case and control groups according to the THg concentrations in the UCB samples.We selected three samples in each group for m RNA sequencing.Related differentially expressed genes were screened for Gene Ontology（GO）and Kyoto Encyclopedia of Genes and Genomes（KEGG）pathway analysis.The quantitative real time polymerase chain reaction（q RT-PCR）was used to verify the results obtained by high-throughput sequencing.Spearman rank correlation was used to analyze the relationship between THg in UCB and routine blood test indexes of pregnant women.We divided the study population into four groups according to the THg concentrations in the UCB samples:1^st≤P₂₅;P₂₅<2^nd≤P₅₀;P₅₀<3^rd<P₇₅;4^th≥P₇₅.Kruskal-Wallis H test was used to compare the routine blood test indexes of pregnant women between four groups.Results:（1）In Wanshan,the median(P₂₅,P₇₅)of THg concentrations in UCB of newborns was3.57（2.48,6.04）μg/L,with a range of 0.53～29.4μg/L,and 28.9%（33/114）exceeded5.8μg/L recommended by the United States Environmental Protection Agency（USEPA）.（2）Compared with the control group,504 m RNA differentially expressed genes were observed in the case group,including 456 upregulated and 48downregulated genes.Expressions of the hemoglobin subunit gamma2（HBG2）genes in UCB were significantly upregulated(P=1.28×10^-14),while the expressions of cluster of differentiation 177（CD177）genes were significantly downregulated(P=4.83×10^-4).（3）GO functional analysis showed that most of the differential genes were concentrated in autophagy of mitochondrion,heme biosynthetic process and erythrocyte development in biological process（BP）.In Cellular Component（CC）,most of the differential genes were concentrated in hemoglobin complex,spectrin-associated cytoskeleton and intrinsic component of membrane.In molecular function（MF）,most of the differential genes were concentrated in oxygen carrier activity,oxygen binding and 2 iron,2 sulfur cluster binding.（4）KEGG pathway analysis showed that Hg exposures were mainly associated with the pathways involved in Huntington’s disease,Parkinson’s disease,and Alzheimer’s disease.（5）The results obtained from q RT-PCR and high throughput sequencing were highly consistent（P<0.05）,indicating that the high throughput sequencing results were accurate.（6）The correlation coefficients（r_s）of THg concentrations in UCB with platelet（PLT）,neutrophil（NE#）,and white blood cell（WBC）were 0.240,0.228,and0.243,respectively.The THg concentrations in UCB showed significant positive correlations with PLT,NE#,and WBC（P<0.05）.The 4^thgroup showed significantly higher NE#and WBC than 1^stgroup（P<0.05）.Conclusion:The Hg exposure in newborns from Wanshan area indicated median/low level over the world,but long term low-dose Hg exposure still cause certain health risks in newborns.Differential gene expression profiles showed that Hg exposure mainly affected the functions of autophagy of mitochondrion and oxidative stress.The main related pathways were similar with those involved in neurodegenerative diseases such as Huntington disease,Parkinson disease and Alzheimer disease.In addition,low-dose Hg exposure can alter genes in immune-related signaling pathway,which may affect the immune function in pregnant women.