BJ 5ta

Mitochondrial DNA Copy Number and Damage Following Exposure to X-rays in HeLa Cells and BJ1-hTERT Cells

This study investigated the radiation-induced impacts on mitochondrial DNA in vitro and in vivo, as well as the transgenerational inheritance.

Human cervical cancer HeLa cells and telomerase-immortalized normal fibroblast BJ1-hTERT cells were exposed to X-rays at 0.5-8 Gy. As shown in Fig. 1A, DNA was extracted from HeLa and BJ1-hTERT cells cultured for 6, 24, and 48 h after irradiation. The mitochondrial DNA copy numbers (mtDNAcns) and radiation-induced damage were then examined by real-time PCR analysis (Fig. 1B).

As shown in Fig. 2A for HeLa cells and Fig. 3A for BJ1-hTERT cells, regardless of the dose, the mtDNAcn increased as the post-irradiation incubation time increased in both cell types. In HeLa cells, a significant increase in mtDNAcn was observed in 2-Gy-irradiated cells compared with nonirradiated cells 24 h after irradiation. As shown in Fig. 2B for HeLa cells and Fig. 3B for BJ1-hTERT cells, X-ray exposure changed the heteroplasmy of mtDNA. At 6 h after irradiation, the undamaged mtDNA ratio for BJ1-hTERT cells was significantly decreased in the 8-Gy-irradiated cells compared with that for control cells. At 24 h after irradiation, the intact mtDNA ratio for HeLa and BJ1-hTERT cells was significantly decreased in the irradiated cells compared with that for control cells. This trend remained 48 h after irradiation. Thus, X-ray exposure increased mtDNAcn in human cancer and noncancerous cells, regardless of the dose, and decreased the intact copy ratio, resulting in a dynamic shift of heteroplasmy.