Continuous Developmental and Early Life Trichloroethylene Exposure Promoted DNA Methylation Alterations in Polycomb Protein Binding Sites in Effector/Memory CD4+ T Cells

Abstract

Trichloroethylene (TCE) is an industrial solvent and drinking water pollutant associated with CD4 + T cell-mediated autoimmunity. In our mouse model, discontinuation of TCE exposure during adulthood after developmental exposure did not prevent immunotoxicity. To determine whether persistent effects were linked to epigenetic changes we conducted whole genome reduced representation bisulfite sequencing (RRBS) to evaluate methylation of CpG sites in autosomal chromosomes in activated effector/memory CD4 + T cells. Female MRL+/+ mice were exposed to vehicle control or TCE in the drinking water from gestation until ~37 weeks of age [postnatal day (PND) 259]. In a subset of mice, TCE exposure was discontinued at ~22 weeks of age (PND 154). At PND 259, RRBS assessment revealed more global methylation changes in the continuous exposure group vs. the discontinuous exposure group. A majority of the differentially methylated CpG regions (DMRs) across promoters, islands, and regulatory elements were hypermethylated (~90%). However, continuous developmental TCE exposure altered the methylation of 274 CpG sites in promoters and CpG islands. In contrast, only 4 CpG island regions were differentially methylated (hypermethylated) in the discontinuous group. Interestingly, 2 of these 4 sites were also hypermethylated in the continuous exposure group, and both of these island regions are associated with lysine 27 on histone H3 (H3K27) involved in polycomb complex-dependent transcriptional repression via H3K27 tri-methylation. CpG sites were overlapped with the Open Regulatory Annotation database. Unlike the discontinuous group, continuous TCE treatment resulted in 129 DMRs including 12 unique transcription factors and regulatory elements; 80% of which were enriched for one or more polycomb group (PcG) protein binding regions (i.e., SUZ12, EZH2, JARID2, and MTF2). Pathway analysis of the DMRs indicated that TCE primarily altered the methylation of genes associated with regulation of cellular metabolism and cell signaling. The results demonstrated that continuous developmental exposure to TCE differentially methylated binding sites of PcG proteins in effector/memory CD4 + cells. There were minimal yet potentially biologically significant effects that occurred when exposure was discontinued. These results point toward a novel mechanism by which chronic developmental TCE exposure may alter terminally differentiated CD4 + T cell function in adulthood.

Epigenetic alterations induced by genotoxic occupational and environmental human chemical carcinogens: An update of a systematic literature review

“…Many of these studies focused on the trichloroethylene exposure-associated CD4+ T cell-mediated autoimmunity. For example, MRL mice were exposed to trichloroethylene via drinking water until adulthood; continuous exposure throughout development showed significant differentially methylated binding sites of PcG proteins, potentially representing a mechanism by which trichloroethylene alters the function of effector/memory CD4+ cells and induced immunotoxicity [225][226][227]. Further investigation into this mechanism demonstrated hypermethylation of CpG sites within the IFN- promoter of effector/memory CD4+ T cells, representing especially sensitive sites to chronic trichloroethylene exposure [228].…”

Glomerular Damage in Trichloroethylene-Sensitized Mice: Targeting Cathepsin L-Induced Hyperactive mTOR Signaling

“…Trichloroethylene (TCE) is a volatile and chlorinated organic solvent widely used in industrial settings such as metal degreasing, parts cleaning, and refrigerants manufacturing ( Byrum et al, 2019 ; Pan et al, 2019 ). Over the past decades, the extensive use of TCE has caused more than 50 million pounds annually released into the environment in the United States and even heavier in China ( Huang et al, 2014 ).…”