Chronic Exposure to Water Pollutant Trichloroethylene Increased Epigenetic Drift in CD4 ⁺ T cells

Abstract

Aim: Autoimmune disease and CD4+ T-cell alterations are induced in mice exposed to the water pollutant trichloroethylene (TCE). We examined here whether TCE altered gene-specific DNA methylation in CD4 + T cells as a possible mechanism of immunotoxicity. Materials & methods: Naive and effector/memory CD4 + T cells from mice exposed to TCE (0.5 mg/ml in drinking water) for 40 weeks were examined by bisulfite next-generation DNA sequencing. Results: A probabilistic model calculated from multiple genes showed that TCE decreased methylation control in CD4 + T cells. Data from individual genes fitted to a quadratic regression model showed that TCE increased gene-specific methylation variance in both CD4 subsets. Conclusion: TCE increased epigenetic drift of specific CpG sites in CD4 + T cells.

Chronic exposure to trichloroethylene increases DNA methylation of the Ifng promoter in CD4+ T cells

“…(27) We extended that finding to examine epigenetic drift specifically associated with Ifng . Interesting, variance in the CpG sites in the Ifng promoter increased when CD4 + T cells differentiated from naïve to effector/memory CD4 + T cells (Figure 4).…”

“…The analysis targeted the region of the Ifng promoter where methylation of individual CpGs has been shown to regulate gene expression (23) . The CpG sites we examined are in an 800 bp region approximately centered on the transcription start site (TSS) and included seven CpG sites in the upstream (promoter) region and eight CpG sites in the downstream (exon and intron) region (27) . CpG sites in the Ifng promoter displayed consistently low-to-medium (under 40%) levels of DNA methylation regardless of CD4 + T cell subset, mouse age, or TCE exposure.…”

“…This mathematical phenomenon has been described by others. (39) In comparison to the CpG sites for the other genes examined, the CpG sites in the Ifng promoter did not conform well to the model in which methylation variability was linked to mean methylation levels (27) . This suggested that compared to several other genes methylation of CpGs in the Ifng promoter was less tightly controlled, and more susceptibility to changes induced by external factors such as exposure to TCE.…”

“…(27) This pattern was very stable over time, and variation in the DNA methylation of a particular site was largely due to stochastic effects related to mean methylation of the site. Thus, variance for sites that averaged 0–20% or 80–100% methylation was uniformly low, while variance was highest for CpG sites where the average methylation was intermediate.…”

“…(27) The resulting CD62L hi CD4 + T cells (naïve CD4 + ) or CD62L lo CD4 + T cells (effector/memory CD4 + T cells) were stimulated with immobilized anti-CD3 antibody and anti-CD28 antibody for 20 hours. (28) The resulting culture supernatants were collected and evaluated for IFN-γ by ELISA, and the activated CD4 + T cells themselves were frozen in RLT (Qiagen) for subsequent examination of DNA methylation.…”