3.6 Preferential Hypermethylation in DMCs and DMRs of F1
Generation
To identify a potential mechanism for epigenetic damage, we assessed
differentially methylated CpGs (DMCs) and differentially methylated
regions (DMRs) in the liver of 10 ppb and 245 ppb F1 mice (Table
1) since these dose levels are most relevant to human exposures. In the
F1 animals of both sexes, we found an excess of hypermethylated CpG
sites at both doses. Specifically, in F1 females, we found 259 (66%)
hypermethylated and 132 (34%) hypomethylated DMCs within the 10-ppb
group, and 157 (61%) hypermethylated and 99 (39%) hypomethylated DMCs
within the 245-ppb group. Only 4 (80%) DMRs were hypermethylated and 1
DMR hypomethylated in the 10-ppb group, whereas no DMRs were identified
in the 245-ppb group. In F1 males, we identified 299 (65%)
hypermethylated and 196 (42%) hypomethylated DMCs within the 10-ppb
group, and 265 (64%) hypermethylated and 151 (36%) hypomethylated DMCS
in the 245-ppb group. Only 3 (43%) hypermethylated and 4 (57%)
hypomethylated DMRs were identified in the 10 ppb iAs group, whereas 9
(82%) hypermethylated and 2 (18%) hypomethylated DMRs were identified
in the 245-ppb group. Our results show F1 males have more dysregulated
methylation in DMCs and DMRs compared to F1 females, regardless of the
exposure group.
The F2 mice sustained similar overall numbers of differentially
methylated CpG sites and recapitulated the hypermethylation bias seen in
F1 animals. Our F2 results indicate higher DMC and DMR content within F2
females compared to F2 males, a contrast to the F1 generation
(Table 1) . Females of the 10-ppb group had preferential DMC
hypermethylation in the liver, where 320 (60%) hypermethylated and 217
(40%) hypomethylated DMCs were identified in the 10-ppb group. We
identified 9 (56%) hypermethylated and 7 (44%) hypomethylated DMRs
within the 10-ppb group. Females of the 245-ppb group had a slight bias
towards hypomethylation, where 208 (57%) hypomethylated and 156 (43%)
hypermethylated DMCs were identified. We found 1 (20%) hypermethylated
and 4 (80%) hypomethylated DMRs in the 245 ppb F2 females. Within the
10-ppb F2 males, we identified 140 (54%) hypermethylated and 118 (46%)
hypomethylated DMCs, detecting 1 hypermethylated DMR. F2 males in the
245-ppb group had 144 (52%) hypermethylated and 133 (48%)
hypomethylated DMCs, and only 1 hypermethylated DMR. Our findings show
female DMCs and DMRs within the liver are more reactive to prenatal
exposure to iAs in both the 10 ppb and 245 ppb groups when compared to
males.