Transgenerational diabetogenic effects of preconception exposure to inorganic arsenic in C57BL/6 mice are associated with dysregulation of DNA methylation and gene expression in G1 and G2 offspring.

Chronic exposure to inorganic arsenic (iAs) has been linked to diabetes, but the role of iAs exposure prior to conception and its transgenerational effects are understudied. Our recent study using C57BL/6 J mice found that exposure of both parents to 2 ppm iAs in drinking water prior to mating resulted in diabetic phenotypes in two consecutive generations of offspring, suggesting epigenetic inheritance. The goal of the present study was to determine if iAs exposure prior to conception was associated with heritable dysregulation of DNA methylation in parental (G0) germ cells and/or differential expression of diabetes-associated genes in G1 and G2 offspring. The Infinium Mouse Methylation BeadChip was employed to assess CpG methylation in G0 sperm and in G1 and G2 sperm, liver, and adipose tissue. DNA methylation in oocytes was assessed by whole-genome bisulfite sequencing. RNA sequencing was used to identify differentially expressed genes (DEGs). We found that the preconception iAs exposure significantly altered expression of genes in tissues of G1 and G2 offspring. Notably, 55% of DEGs in G1 male liver, 64% in G1 female liver, 42% in G2 male liver, 42% in G2 male adipose tissue, and 27% in G2 female adipose tissue contained differentially methylated CpG sites, including CpG sites that were also differentially methylated in G0 sperm. Many of these sites displayed the same direction of change in methylation, suggesting epigenetic inheritance. Some of the DEGs with differentially methylated CpG sites were identified in diabetes-associated pathways, including insulin signaling pathway, glucose transmembrane transport, and miRNA targeting of PI3K-Akt signaling pathway. Thus, the iAs-induced transmissible changes in DNA methylation may underlie the diabetogenic phenotypes found in G1 and G2 offspring.