Lead Exposure Triggers DNA Damage in TK6 Cells Via Alteration of DNA Repair Gene Expression and Hypermethylation of Ku80 Promoter Region.

Lead (Pb) is a widespread environmental metal with recognized genotoxicity, yet whether it impairs DNA damage repair via epigenetic regulation remains unclear. Here, human lymphoblastoid TK6 cells were exposed to a series of concentrations of lead acetate solutions at 0, 120, 240, 480 µM for 24 h. We quantified cell viability, oxidative stress indicators (ROS, MDA, SOD, CAT), DNA damage markers (the Comet assay indicators Tail Length, Tail DNA % and Tail Moment and γ-H2AX levels), DNA damage repair capacity using 3-AB method based on the Comet assay, cell cycle and apoptosis, and the mRNA and protein expressions of DNA repair genes (RAD51, CHEK2, BRCA1, Ku80, MSH2, LIG4). We further measured expressions of DNA methyltransferase DNMT1 and demethylase TET2, and methylation of the Ku80 promoter region by Pyrosequencing. The results suggested that Pb exposure decreased cell viability, increased ROS levels and MDA content while reduced SOD and CAT activity. Pb exposure induced dose-dependent increases in DNA single-strand breaks (SSBs) and double-strand breaks (DSBs), as evidenced by elevated Tail Length, Tail DNA%, Tail Moment and fluorescence intensity of γ-H2AX levels. G0/G1-phase arrest and apoptosis also rose with dose. In addition, DNA damage repair capacity of TK6 cells were decreased in a dose-dependent manner after Pb exposure. DNA damage repair genes showed a biphasic response-elevated at lower doses and suppressed at higher doses-at both mRNA and protein levels. The methylation level in promoter region of Ku80 increased with dose and coincided with higher DNMT1 and lower TET2 expression. Collectively, Pb exposure induces oxidative stress and DNA damage in TK6 cells; higher lead concentration inhibited DNA repair capacity, potentially via DNMT1/TET2 mediated hypermethylation of the Ku80 promoter region.