Application Of Plasma MicroRNA As Molecular Biomarker For Workers Occupationally Exposed To Mercury

Mercury is one of the earliest metal elements human found and used,and it is the only metal in the form of liquid in the normal temperature and pressure.The application of mercury in industry is very extensive,it is commonly used in thermometer,sphygmomanometer,barometer,fluorescent lamp manufacture.In mercury thermometer manufacturing industry,mercury is the main occupational hazard factors.MicroRNA(miRNA)is a kind of small RNA molecules which are about 20～24 nt long and have no ability of encoding protein.MicroRNA plays an important role in regulating gene expression through pairing with target messenger RNA and inhibiting messenger RNA translation.More and more environmental epigenetics evidence suggests that exposure to occupational and environmental heavy metal could alter epigenetic changes such as miRNA expression pattern,DNA methylation and histone modification.Recently,microRNAs in plasma or serum have been used as stable,noninvasive biomarkers to indicate diseases and drew the attention of many scholars.Numerous studies have revealed that microRNAs have been promising noninvasive biomarkers of tumor and cardiovascular disease.Herein,we expect to identify mercury related plasma microRNAs as potential molecular biomarkers for occupational mercury exposure using chip analysis and real-time fluorescence quantification PCR technology.Objectives:To identify occupational mercury exposure related plasma miRNA and evaluate its diagnostic value in occupational mercury poisoning.Methods:According to study objectives,we divided the subjects into(A)mercury poisoning group,(B)mercury absorbing group and(C)control group by Diagnostic Criteria of Occupational Mercury Poisoning(GBZ 89-2007)of China.Each group has 10 individuals.In the microRNA screening stage,microarray assays were conducted to detect the miRNA expression levels in pooled plasma samples between the three groups.Next,preliminary validations of the candidate miRNAs were conducted in the same workers by Taqman microRNA assay and quantitative Real-Time PCR.Subsequently,two miRNAs were selected for expanded validation in other 30 mercury poisoning individuals,30 mercury absorbing individuals and 30 control workers.Last,ROC(receiver operating characteristic)curve and Youden index were used to evaluate the diagnostic value of validated miRNAs for mercury poisoning and absorbing.Lastly,the biological functions of the possible target genes of miRNAs were predicted by using Gene Ontology(GO)function enrichment analysis and Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway analysis.Results:In the discovery stage,a total of eight miRNAs conformed to our selection criteria.In the preliminary validation,the relative expression levels of hsa-miR-92a-3p and hsa-miR-486-5p were upregulated in the mercury poisoning and absorbing group compared with the control group(P<0.05).In the expanded validation stage,the plasma levels of hsa-miR-92a-3p and hsa-miR-486-5p were dramatically upregulated in the mercury poisoning and absorbing group compared with the control group(P<0.001),which was consistent with the results of preliminary validation and microarray analysis.ROC curve proved that the AUC of miR-92a-3p and miR-486-5p for mercury poisoning were 0.912 and 0.908 and the AUC for mercury absorbing were 0.717 and 0.721.The cutoff point which Youden index was the largest was determined as the best diagnostic point.The sensitivity and specificity of miR-92a-3p for mercury poisoning were 0.60 and 0.77.The sensitivity and specificity of miR-92a-3p for mercury absorbing were 0.70 and 0.97.The sensitivity and specificity of miR-486-5p for mercury poisoning were 0.77 and 0.90.The sensitivity and specificity of miR-486-5p for mercury absorbing were 0.57 and 0.80.MiR-92a-3p and miR-486-5p have high specificity but low sensitivity for the diagnosis of occupational mercury poisoning and mercury absorbing.Conclusion:Herein,we found that the expression levels of plasma miR-92a-3p and miR-486-5p of mercury poisoning and absorbing workers were upregulated.Plasma miR-92a-3p and miR-486-5p might prove to be potential biomarkers of mercury exposed workers.However,future studies are necessary to prove the causation between miR-92a-3p and miR-486-5p level alterations and mercury exposure and the underlying mechanism of these two miRNAs in mercury poisoning.