Distinct DNA hydroxymethylation landscape and mitochondrial DNA rearrangement signatures induced by single- and multi-fraction alpha particle radiation in lung fibroblasts.

Abstract

Alpha (α)-radiation is a genotoxic and epigenotoxic agent capable of increasing the risk of cancer and other diseases. DNA hydroxymethylation (DNAhm) can modulate gene expression and is considered an under-researched epigenetic event in ionizing radiation studies. Here, the genome-wide DNAhm profile was examined in 64 α-irradiated human embryonic lung fibroblast samples from our 2023 methylome study. These cells were exposed to seven doses (N = 4 per dose) of americium-241 α-particles ranging from 2 to 2200 mGy, using either single-fraction (SF) or multi-fraction (MF) exposure regimens. We report that SF and MF α-irradiation primarily increased DNAhm levels, with a greater number of alterations observed following MF exposure, particularly in gene body regions. Pathway analysis of genes with increased DNAhm levels due to MF exposure suggested disruption of inflammatory responses and other cellular pathways. We also detected DNAhm changes in key genes encoding enzymes involved in DNA methylation (DNAm) and demethylation processes, which support our 2023 DNAm findings. Similar to DNAm, MF α-irradiation induced a greater number of DNAhm changes in aging-associated genes. Compared with equivalent SF doses, MF α-irradiation resulted in more mitochondrial damage. These findings demonstrate that even at comparable doses, SF and MF α-radiation induce radically different effects on the DNAhm and mitochondrial DNA. The DNAhm changes help explain the effects observed in our 2023 methylome study. Altogether, this study supports the idea that environmental radiation exposure regimens are an important consideration when assessing DNAm and DNAhm biomarkers and the potential health effects of α-radiation.