Lead exposure induces dysregulation of constitutive heterochromatin hallmarks in live cells

Lead (Pb) is a heavy metal contaminant commonly found in air, soil, and drinking water due to legacy uses. Excretion of ingested Pb can result in extensive kidney damages due to elevated oxidative stress. Epigenetic alterations induced by exposure to Pb have also been implied but remain poorly understood. In this work, we assessed changes in repressive epigenetic marks, namely DNA methylation ((me)CpG) and histone 3 lysine 9 tri-methylation (H3K9me3) after exposure to Pb. Live cell epigenetic probes coupled to bimolecular fluorescence complementation (BiFC) were used to monitor changes in the selected epigenetic marks. Exposure to Pb significantly lowered (me)CpG and H3K9me3 levels in HEK293T cells suggesting global changes in constitutive heterochromatin. A heterodimeric pair of probes that tags chromatin regions enriched in both (me)CpG and H3K9me3 further confirmed our findings. The observed epigenetic changes can be partially attributed to aberrant transcriptional changes induced by Pb, such as overexpression of TET1 after Pb exposure. Lastly, we monitored changes in selected heterochromatin marks after removal of Pb and found that changes in these markers do not immediately recover to their original level suggesting potential long-term damages to chromatin structure.