Prenatal exposure to cadmium alters the transciptome of regulatory T cells in C57BL/6 mice and may contribute to immunological health of the offspring

Cadmium (Cd) is a carcinogen present at superfund sites, in battery manufacturing facilities, in and around zinc smelters, and in cigarettes (the most common exposure pathway). In humans, prenatal Cd exposure (preCd) is associated with differential DNA methylation patterns in blood leukocytes of mother-baby pairs. C57BL/6 mice chronically exposed to low doses of Cd in utero develop abnormal immune phenotypes including reduced regulatory T cell (Treg) numbers in the spleen, but not thymus, of adult animals. These data suggest that the probable immune consequences of preCd exposure are cause for alarm. To further define the mechanisms behind these phenotypic differences, we isolated Treg and CD4+ T conventional (Tconv) cells from the spleens of preCd offspring at 8 woa. Target cells were enriched using magnetic isolation prior to purification by flow cytometry. RNA-seq and Ingenuity Pathway analyses were conducted to define the Treg and Tconv transcriptomes and identify mechanisms dysregulated with preCd exposure. Treg cells exhibited more changes in gene expression than Tconv cells. In the splenic Tregs, there were 289 significantly changed genes (166 upregulated and 135 downregulated) in females and 135 (82 upregulated and 53 downregulated) in males. Of note, only 23 upregulated genes and 3 downregulated genes were shared between females and males. However, common pathways, including CREB1 signaling, were disrupted in both sexes. As CREB signaling plays an important role in TGFβ-mediated generation and maintenance of FoxP3 Tregs, inhibition of this pathway may promote Treg instability and contribute to the decrease in Treg numbers observed in the periphery of preCd-exposed mice.