Analysis of DNA methylation in peripheral blood of patients with coal-burning-borne endemic fluorosis / 中华地方病学杂志

ABSTRACT

Objective:To explore the DNA methylation patterns and methylation differential genes of patients with coal-burning-borne endemic fluorosis, and to provide a basis for study of the pathogenesis of fluoride-induced body injury.Methods:A case-control study was conducted in Shuicheng County, Liupanshui, Guizhou Province, ten patients with severe fluorosis were selected as the fluorosis group in Douqing Township, where people burning high fluorine coal in open range all year round; and ten people without fluorosis phenotype were selected as the control group in Huaga Township, where firewood was the main fuel. Peripheral blood samples were collected from the two groups of people. Reduced representation bisulfite sequencing (RRBS) technique was used to detect the whole genome DNA methylation pattern ( n = 4) and DNA differentially methylated region (DMR), the DMR differential degree (log 2Ratio) and KEGG pathway enrichment analysis were used to screen the methylation differential genes, and real-time PCR was used to verify the mRNA expression levels of the candidate methylation differential genes( n = 10). Results:The methylation pattern analysis results showed that the methylation levels of all C bases in the genome DNA of the fluorosis group and the control group were (61.53 ± 0.59)% and (62.48 ± 1.53)%, respectively; among them, the methylated levels at CG sites were (63.75 ± 0.65)%, (64.36 ± 1.01)%, at CHG sites were (13.79 ± 0.72)%, (16.69 ± 4.06)%, and at CHH sites were (25.12 ± 1.72)%, (29.77 ± 3.97)%. Compared with the control group, patients in the fluorosis group had 1 000 DMR distributed on different autosomes; and the chromosome 19 was the most with 104 segments. There were 978 DMR-related genes, including 265 hypermethylation genes and 713 hypomethylation genes; KEGG pathway enrichment analysis showed that methylation differential genes were mainly involved in cell metabolism, cancers, and phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) and other signaling pathways; combined with the differential degree of DMR, the hypermethylated succinate dehydrogenase complex flavoprotein subunit A pseudogene 3 (SDHAP3, log 2Ratio = 3.487) and hypomethylated nuclear factor κB inhibitor kinase regulatory subunit γ (IKBKG, log 2Ratio =-4.436) were selected as the candidate genes. There were statistically significant differences in the mRNA expression levels of SDHAP3 (0.54 ± 0.08, 1.00 ± 0.00) and IKBKG (1.32 ± 0.39, 1.00 ± 0.00) between fluorosis group and control group ( F = 22.94, 15.09, P < 0.01 or < 0.05). Conclusion:There are a large number of methylation differential genes in the genomes of patients with coal-burning-borne endemic fluorosis and controls, the hypermethylated SDHAP3 and hypomethylated IKBKG may be involved in fluoride induced body injury.