Genome-wide differential DNA methylation in hippocampus of rats after benzo(a)pyrene exposure

Abstract

Objective To study the differential DNA methylation in the hippocampus of rats exposed to benzo(a)pyrene and explore the mechanism of benzo(a)pyrene-induced functional impairment of the hippocampus. Methods Twenty male SD rats (3 weeks old) were randomly divided into control group and benzo(a)pyrene exposure group (n=10), and in the latter group, the rats were exposed to benzo(a)pyrene delivered via gavage on a daily basis for 7 consecutive weeks. After the exposure, Morris water maze test was performed to assess the changes in the spatial memory and learning ability of rats; the brain tissues were dissected for morphological examination of the hippocampal neurons with HE staining. Reduced representation bisulfite sequencing (RRBS) of the genomic DNA from the hippocampus was performed, followed by GO and KEGG analyses of the sequencing data; qRT-PCR was used to detect the expression levels of Tnr and Pla2g2a mRNAs. Results Morris water maze test and HE staining showed that exposure to benzo(a)pyrene resulted in obvious impairment of the spatial learning and memory abilities and caused hippocampal injuries in rats. DNA methylation sequencing identified 32 differentially methylated regions; GO analysis enriched 871 GO items and KEGG analysis obtained 52 pathways, of which 145 GO items and 11 pathways were significantly enriched (P < 0.05). Compared with the control rats, the benzo(a)pyrene-exposed rats showed significantly decreased Tnr mRNA expression and increased Pla2g2a mRNA expressions in the hippocampus(P < 0.05). Conclusion A number of differentially methylated sites occur in the genomic DNA in rat hippocampus following benzo(a)pyrene exposure, and these sites may provide important clues in exploring the mechanism of benzo(a)pyrene-induced hippocampal injury.

Keywords

• benzo(a)pyrene
• hippocampus
• dna methylation
• rats